Rozprawy doktorskie na temat „PV BASED MICRO GRID”

Photovoltaic (PV) generator generates clean energy but also brings active power fluctuation to the network. The thesis investigates the frequency stability issue of a MW level stand-alone hybrid micro grid which contains PV generator, diesel generator, storage unit and loads. The PV generator can only generate as much power as the sun provides. The resulting power mismatch between PV generation and load demand needs to be compensated. The slow responding diesel generator is designed to compensate for the steady state power mismatch. The battery, as the fast responding storage unit, is set to reject the power transients. A battery control method based on the micro grid frequency feedback and PV output feed-forward is presented to satisfy the requirement of active power compensation in transients. It will be shown that the method keeps the stand - alone micro grid frequency within a specified region and provides the diesel generators more margin of time to adjust their output for better diesel efficiency.

Renewable energy source plays an important role in the energy cogeneration and distribution. Traditional solar-based inverter system is two stages in cascaded, which has a simpler controller but low efficiency. A new solar-based single-stage grid-connected inverter system can achieve higher efficiency by reducing the power semiconductor switching loss and output stable and synchronized sinusoid current into the utility grid. Controlled by the digital signal processor, the inverter can also draw maximum power from the solar array, thereby maximizing the utilization of the solar array. In Chapter 1, a comparison between the traditional two-stage inverter and the single-stage inverter is made. To increase the ability of power processing and enhance the efficiency further, a full-bridge topology is chosen, which applies the phase-shift technique to achieve zero-voltage transition. In Chapter 2, average-mode and switch-mode Pspice simulations are applied. All the features of the inverter system are verified, such as stability, zero voltage transition and feed-forward compensation, etc. All these simulation results provide useful design tips for prototyping. In Chapter 3, a phase-shift controller is designed based on UCC3895. Also, a detailed design procedure is given, including key components selection, transformer and inductor design and driver circuits design. In Chapter 4, experimental results of a prototype DC/DC converter are presented and analyzed. By optimization of the circuit, the problems of the prototype are solved and the prototype is working stably. The thesis' conclusion is given in Chapter 5.
M.S.E.E.
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering

With the increasing trend of utilizing renewable energy generators such as photovoltaic (PV) cells and wind turbines, power systems are transforming from a centralized power grid structure to a cluster of smart micro-grids with more autonomous power sharing capabilities. Even though the decentralized control of power systems is a reliable and cost effective solution, due to the inherent heterogeneous nature of micro-grids, optimal and efficient power sharing among distributed generators (DG’s) is a major issue which calls for advanced control techniques for voltage stabilization of the entire micro-grid cluster. The proposed consensus based algorithm in this thesis is a solution to overcome these control challenges, which only requires each DG to exchange information with its directly connected neighboring DG’s, in order to maintain the power balance and voltage stability of the entire micro-grid cluster. The proposed method in this thesis is simulated in PSCAD and its effectiveness is demonstrated using several realistic and practical cases including micro-grid topology changes, communication delays, and load changes.

Nearly one fifth of the global population lacks access to electricity and electricity access is essential for economic growth and human well-being. SHSs and micro-grids both have the possibility of increasing the electricity access in developing countries. The decision to choose either SHSs or micro-grids for rural electrification is a complex task that must consider both the technological factors that separate these two systems and the non-technological factors. Separate times of peak load between households (inter-class diversity) has shown to be one major advantage for the use of micro-grids. Studies have shown that the diversity factor present in micro-grids can scale down the necessary capacity of PV modules and energy storage of up to 80%, in comparison to stand-alone systems (e.g. SHSs). These reductions are nevertheless based on assumed diversity factors, not using real load profiles and the necessary capacities are calculated using intuitive methods (known to be inexact). From interviews in a rural community of Nicaragua, the author generated load profiles and determined the diversity factor of the community. The load profiles were generated with a specially designed software to formulate realistic load profiles for off-grid consumers in rural areas. These load profiles were later used in the software HOMER where the diversity’s influence on required capacity and NPC were determined by comparing SHSs to a PV based micro-grid. The study showed that the required capacity and NPC of the inverter and charge controller are clearly decreased as an influence of inter-class diversity. The required PV and battery capacity are also decreased when a micro-grid is utilized, but these reductions are most likely a result from the limited nominal power per component considered in HOMER.
Nästan en femtedel av världens befolkning saknar tillgång till elektricitet. Nicaragua är ett av de länder där en stor del av befolkningen saknar eltillgång och det gäller speciellt hushållen på landsbygden. Utbyggnader av elnätet till dessa områden är ofta låg-prioriterade på grund av höga kostnader för att tillgodose ett många gånger lågt energi och effektbehov. En alternativ lösning för att ge dessa hushåll tillgång till elektricitet är att använda off-grid system, system frikopplade från det nationella elnätet. Två vanligt förekommande off-grid system är solar home systems (SHSs) och micro-grids. Det faktum att flera hushåll ofta använder sin toppeffekt vid olika tillfällen (sammanlagring av effekt) har visat sig vara till stor fördel för micro-grids. Tidigare studier har visat att sammanlagringsfaktorn i ett micro-grid kan reducera nödvändig kapacitet av solceller och energilager upp till 80%, i jämförelse med enskilda system (t.ex. SHSs). Dessa studier bygger dock på antagna sammanlagringsfaktorer, overkliga lastprofiler och nödvändig kapacitet beräknas med intuitiva metoder. Med data från intervjuer i ett landsbygdssamhälle i Nicaragua skapas lastprofiler och en sammanlagringsfaktor beräknas för samhället. Lastprofilerna skapas i en programvara utvecklad för att formulera realistiska lastprofiler för off-grid konsumenter i landsbygdsområden. Lastprofilerna används senare i programvaran HOMER där sammanlagringens påverkan på nödvändig kapacitet och kostnad undersöks genom en jämförelse mellan SHSs och ett solcellsdrivet micro-grid. Studien visar att nödvändig kapacitet och nuvärdeskostnad för växelriktare och laddningsregulator tydligt minskar till följd av sammanlagring. Nödvändig kapacitet på solceller och batterier minskar också när ett micro-grid används. Dock beror detta med stor sannolikhet inte på sammanlagring utan är ett resultat från de begränsade märkeffekter på komponenter som användes i HOMER.

Les travaux de thèse s’inscrivent dans les problématiques des travaux de recherche de l’équipe thématique : Maitrise des Energies Renouvelables et systèmes de Stockage (MERS) du laboratoire GREAH-EA3220. Ils englobent le dimensionnement des éléments constitutifs du système et la gestion optimale de l’énergie électrique pour un système hybride (Diesel à vitesse variable, Eolien, PV et Batteries) dédié aux sites isolés. Les sources de production d'énergie alimentent des charges par le biais de convertisseurs multi-niveaux d’électronique de puissance. Le groupe électrogène comportant un moteur diesel à vitesse variable est considéré comme la principale source d’énergie utilisée pour contrôler la tension continue du point de couplage. Ce type de groupe électrogène est choisi pour optimiser la consommation du carburant. Il est sollicité pour délivrer une puissance électrique compatible avec le régime du moteur qui supporte mal les variations fréquentes et rapides. Les sources d’énergie renouvelables dont on cherche à augmenter la part d’énergie pour satisfaire la demande sont pilotées de manière à extraire instantanément le maximum de puissances disponible par les ressources (ensoleillement, vent). Celles-ci imposent ainsi leurs dynamiques et leurs intermittences au point de couplage. Le pack des batteries sert à compenser les fluctuations rapides de l’énergie provenant des sources d’énergie renouvelables par rapport à une évolution plus lente prise en charge par le groupe électrogène. La gestion des interactions au sein du système électrique hybride résultant est assurée au moyen de convertisseurs statiques multi-niveaux (AC / DC, DC / DC et DC / AC). Une approche de gestion d’énergie électrique fondée sur la répartition fréquentielle des perturbations induites au point de couplage par les sources renouvelables. Une plateforme expérimentale à échelle réduite (1/22) a été développée pour valider expérimentalement les approches théoriques et les simulations. Les résultats de simulations obtenus dans l’environnement logiciel Matlab/Simulink/SimPowerSystems et ceux issus du dispositif expérimental réalisé et piloté par dSPACE-1104 prouvent l’adéquation des méthodes de contrôle proposées
The thesis works are part of the research work of the thematic team: Mastery of Renewable Energies and Storage Systems (MERS) of the GREAH-EA3220 laboratory. They include the dimensioning of the constituent elements of the system and the optimal management of electrical energy for a hybrid system (Variable speed Diesel, Wind, PV and Batteries) dedicated to isolated sites. Power sources supply loads through multi-level converters of power electronics. The generator set with a variable speed diesel engine is considered to be the main source of energy used to control the DC voltage at the coupling point. This type of generator is chosen to optimize fuel consumption. It is used to deliver an electrical power compatible with the engine speed which does not tolerate frequent and rapid variations. Renewable energy sources whose share of energy is sought to meet demand are managed so as to instantly extract the maximum power available from resources (sunshine, wind). These thus impose their dynamics and their intermittences at the coupling point. The battery pack is used to compensate for rapid fluctuations in energy from renewable energy sources compared to a slower evolution supported by the generator. Interactions within the resulting hybrid electrical system are managed by means of multi-level static converters (AC / DC, DC / DC and DC / AC). An electrical energy management approach based on the frequency distribution of disturbances induced at the coupling point by renewable sources. An experimental platform on a reduced scale (1/22) has been developed to experimentally validate theoretical approaches and simulations. The results of simulations obtained in the Matlab / Simulink / SimPowerSystems software environment and those from the experimental device produced and piloted by dSPACE-1104 prove the adequacy of the proposed control methods

In this thesis, an evaluation of a stand-alone hybrid micro grid for the Wawashang Complex is presented. A solution for a new electricity supply and distribution system for the complex is proposed with a focus on optimal configuration of the system. A field trip to Wawashang was conducted in April 2014 in order to collect data regarding biomass potential for electricity production and information for a possible distribution system design. The demand to be covered is divided into two systems; the micro grid, which denotes all buildings excluding the carpentry workshop and is the system for which the distribution system is designed, and the carpentry workshop. A single-phase/three-wire (split-phase) solution is suggested for the distribution system configuration, presenting the advantage of considerably smaller conductor size requirements than single-phase/two-wire systems for the same voltage drop and power loss. The total power loss of the distribution system is 896 kWh/year or 2.4 % of the demand. The production system for the micro grid consists of a PV array and a battery bank, and for the carpentry workshop a diesel generator. Additionally, a biomass based generator is available for both systems according to a defined schedule. The simulation software HOMER is used to run simulations for the two systems simultaneously, with the intention of obtaining optimal operation of the biomass generator. Two cases are evaluated on both technical and economical aspects. In Case I, the high frequency AC power output from the biomass generator is rectified to DC power and then connected to the single-phase AC bus of the micro grid through a DC-AC converter and similarly to the three-phase AC loads of the carpentry workshop. In Case II, the output from the biomass generator is connected to the DC bus of the micro grid after rectification. The simulation results shows that the optimal solution in both cases is to operate the biomass generator as much as possible in the carpentry workshop with the diesel generator available to cover peak loads. In Case I, the biomass generator is operated with a load following strategy, while in Case II a cycle charging strategy is applied, resulting in a higher exploitation of the available biomass resource in the latter. Both cases present advantages and disadvantages and are similar in reliability and cost. Case II is evaluated as the optimal solution for the Wawashang Complex, as it is the overall least expensive, most reliable and least unbalanced system when it comes to seasonal variations. The system consists of a 9 kW converter, a PV array with a global power of 30 kWp, producing a total of 37 254 kWh/year and a battery bank with a nominal capacity of 294 kWh (for the micro grid), a 15 kW biomass generator producing a total of 38 477 kWh/year divided between the micro grid (19.4 %) and the carpentry workshop (80.6 %) and a 15 kW diesel generator producing 5 400 kWh/year for the carpentry workshop. Total excess electricity is 6.3 % and unmet load is 0.21 %. Total NPC is US$ 311 224 and levelized COE is US$ 0.285/kWh.

Universal access to electricity stands high on the global agenda and is regarded as essential for positive development in sectors such as health care, education, poverty reduction, food production and climate change. Decentralized, off-grid electrification is deemed an important complement to centralized grid extension. By utilizing a renewable energy source, solar technology for the generation of electricity, photovoltaics (PV) is being considered as a way forward to minimize the environmental problems related to energy use. This thesis aims to contribute to improving the technical and social feasibility of PV and PV-diesel hybrid micro-grids for the purpose of providing access to electricity to people in rural areas of countries with low level access to electricity. In line with these general aims, the focus has been to address three questions related to challenges in three phases of rural electrification. The work has a multi-disciplinary approach, addressing mainly technical and social aspects of long-term sustainability of micro-grids, in a local context, and the changes these are intended to generate. One specific micro-grid in Tanzania has been used as a major case study. The thesis is developed through three papers, all presenting methodologies or aspects for investigation in rural electrification projects and studies in general, and for PV-diesel hybrid micro-grids in particular. Paper I puts forward a methodology to facilitate non-social scientific researchers to take social aspects increasingly into consideration. Paper II is a guideline to support system users to increasingly apply an evaluation based system operation. Paper III specifically highlights the importance to consider blackouts when investigating how an existing off-grid PV-diesel hybrid system shall be utilized when a national grid becomes available.

Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid, the active and reactive power control and consequently voltage regulation is one of the main requirements. Therefore, the capability of the single-stage boost-inverter in controlling the active power and providing the reactive power is investigated. It is demonstrated that the injected active and reactive power can be independently controlled through two modulation indices introduced in the proposed switching algorithm. The system is capable of injecting a desirable level of reactive power, while the maximum power point tracking (MPPT) dictates the desirable active power. The developed switching pattern is experimentally verified through a laboratory scaled three-phase 200W boost-inverter for both grid-connected and stand-alone cases and the results are presented.

L’intégration de panneaux photovoltaïques dans un système électrique réduit la consommation des sources fossiles et apporte des avantages environnementaux. Toutefois, l'intermittence et les fluctuations de puissance détériorent la qualité d’alimentation électrique. La solution proposée est d’ajouter des éléments de stockage, coordonnés par un contrôleur local qui gère les flux de puissance entre toutes les sources et la disponibilité énergétique. Ce générateur actif PV peut générer des références de puissance et fournir des services « système » au réseau électrique. Puis les concepts liés au micro réseau sont transposés pour concevoir un système central de gestion de l'énergie d'un réseau électrique résidentiel, qui est alimenté par des générateurs actifs PV et une micro turbine à gaz. Un réseau de communication est utilisé pour échanger des données et des références de puissance. Un système de gestion de l'énergie est développé avec différentes fonctions de contrôle sur des échelles de temps différentes afin de maximiser l'utilisation de l'énergie PV. Une planification opérationnelle quotidienne est conçue par un algorithme déterministe, qui utilise la prédiction d'énergie PV et de la charge. Puis ces références de puissance sont actualisées chaque demi-heure en tenant compte de la disponibilité de l’énergie PV et l’état des unités de stockage. Les erreurs de prévision et les incertitudes sont compensées par le réglage primaire de fréquence. Les résultats de simulation et les tests valident la conception de la commande du générateur actif photovoltaïque ainsi que le système central de gestion de l'énergie du réseau résidentiel étudié
The integration of PV power generation in a power system reduces fuel consumption and brings environmental benefits. However, the PV power intermittency and fluctuations deteriorate the power supply quality. A solution is proposed by adding energy storages, which are coordinated by a local controller that controls the power flow among all sources and implements an inner energy management. This PV based active generator can generate power references and can provide ancillary services in an electric network. Then micro grid concepts are derived to design a central energy management system of a residential network, which is powered by PV based active generators and a gas micro turbine. A communication network is used to exchange data and power references. An energy management system is developed with different time-scale functions to maximize the use of PV power. An operational daily planning is designed by a determinist algorithm, which uses 24 hour-ahead PV power prediction and load forecasting. Then power references are refreshed each half of an hour by considering the PV power availability and the states of energy storage units. Prediction errors and uncertainties are compensated by primary frequency controllers. Simulation and testing results validate the design of the PV active generator local controller and the central energy management system of the studied residential network

Creative ways of utilising renewable energy sources in electricity generation especially in remote areas and particularly in countries depending on imported energy, while increasing energy security and reducing cost of such isolated off-grid systems, is becoming an urgently needed necessity for the effective strategic planning of Energy Systems. The aim of this research project was to design and implement a new decision support framework for the optimal design of hybrid micro grids considering different types of different technologies, where the design objective is to minimize the total cost of the hybrid micro grid while at the same time satisfying the required electric demand. Results of a comprehensive literature review, of existing analytical, decision support tools and literature on HPS, has identified the gaps and the necessary conceptual parts of an analytical decision support framework. As a result this research proposes and reports an Iterative Analytical Design Framework (IADF) and its implementation for the optimal design of an Off-grid renewable energy based hybrid smart micro-grid (OGREH-SμG) with intra and inter-grid (μG2μG & μG2G) synchronization capabilities and a novel storage technique. The modelling design and simulations were based on simulations conducted using HOMER Energy and MatLab/SIMULINK, Energy Planning and Design software platforms. The design, experimental proof of concept, verification and simulation of a new storage concept incorporating Hydrogen Peroxide (H2O2) fuel cell is also reported. The implementation of the smart components consisting Raspberry Pi that is devised and programmed for the semi-smart energy management framework (a novel control strategy, including synchronization capabilities) of the OGREH-SμG are also detailed and reported. The hybrid μG was designed and implemented as a case study for the Bayir/Jordan area. This research has provided an alternative decision support tool to solve Renewable Energy Integration for the optimal number, type and size of components to configure the hybrid μG. In addition this research has formulated and reported a linear cost function to mathematically verify computer based simulations and fine tune the solutions in the iterative framework and concluded that such solutions converge to a correct optimal approximation when considering the properties of the problem. As a result of this investigation it has been demonstrated that, the implemented and reported OGREH-SμG design incorporates wind and sun powered generation complemented with batteries, two fuel cell units and a diesel generator is a unique approach to Utilizing indigenous renewable energy with a capability of being able to synchronize with other μ-grids is the most effective and optimal way of electrifying developing countries with fewer resources in a sustainable way, with minimum impact on the environment while also achieving reductions in GHG. The dissertation concludes with suggested extensions to this work in the future.

The utilization of renewable energy systems and battery storage is a promising solution for remote area electrification. In particular, the integration of renewable energy systems and battery storage units are commonly used to establish discrete electricity generation and stand-alone micro-grids, due to their commercial availability and well-studied electrical behaviour. However, being a highly feasible solution for micro-grid planning, the underlying challenging to find the optimal balance between economics and amenity is often overlooked. The work presented in this thesis aims to use real-world projects to explore the challenges of optimal micro-grid component sizing, by providing an understanding of the key challenges in the process – the techno-economic balance. Potential solutions are provided after identifying the problem, including the utilization of existing infrastructural hardware, incorporation of novel demand management strategies, the establishment of poly-generation to improve generation and storage diversity and reduce the problem of intermittency. It is modeled and shown in this study that the demand management approach of non-critical load deferring could substantially improve network availability in a stand-alone micro-grid, with its effectiveness comparable to loss of electricity – a conventional demand management approach that is significantly more disruptive. A real-world case study project in Bruny Island, Australia is constructed as a mixed integer linear programming model to validate research concepts and provide sensitivity analysis simulations to proposed micro-grid system configurations. Up-to-date utility tariffs and micro-grid component pricings are adopted to reflect both the infrastructural and social environment of the studied area, followed by a series of scenarios configured to map out the potential infrastructural transition of Bruny Island. Furthermore, after the Bruny Island base scenario is established in the model, desalination, electric vehicles and vehicle-to-grid are introduced into the model as methods of increasing generation and demand diversity. It is shown in the modeling results, although each technology intervention contributes in improving the economics of the micro-grid, their impacts may differ due to the local climate conditions and social mix. From the analysis on the model results, this study quantifies the importance of a comprehensive model that utilizes complete cycle, fine-resolution input data, instead of the over-generalized approach. Additionally, this study attempts to provide a novel design mindset for micro-grid infrastructural transitions, to maximize the benefits of existing hardware, reduce interruption and minimize system cost.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
PROSUP - Programa de Suporte à Pós-Gradução de Instituições de Ensino Particulares
Este trabalho trata do desenvolvimento e do comissionamento de uma microrrede fotovoltaica de 1680 W pico conectada/isolada com estocagem para gerenciamento e controle de uma carga considerada crítica. Esta microrrede, empregando duas tecnologias de módulos, foi instalada no Laboratório de Energias Renováveis da Unisinos. A microrrede é composta de dois painéis de módulos, um de 1080 W de silício multicristalino, e um de 600 W de silício monocristalino. O primeiro é do sistema conectado à rede e o segundo é do sistema isolado, respectivamente. O sistema de gerenciamento e controle, chamado de supervisório, monitora e controla as duas redes através do sistema de aquisição de dados, que possui como tarefa o armazenamento dos dados em um cartão de memória além de mostrar em tempo real as variáveis envolvidas no processo através de um display de cristal líquido. São feitas análises dos valores de correntes e tensões, tanto alternada quanto contínua, para determinação das potências de entrada e de saída dos equipamentos envolvidos no processo, como também variáveis como temperatura ambiente e do painel FV e irradiância. A proposta deste estudo é demonstrar a disponibilidade do sistema para satisfazer uma carga que pode ser considerada como um processo crítico, a fim de entregar uma potência constante para a carga. Para isto, é necessário que a carga seja comutada entre os sistemas conectado à rede e isolado de acordo com as variáveis analisadas pelo sistema de aquisição de dados. As análises dos dados são divididas em duas partes: sistema FV conectado à rede e sistema isolado. Para cada sistema, foi analisado o comportamento da tensão, corrente e potência dos painéis fotovoltaicos, assim como o comportamento dos inversores e banco de estocagem de energia, considerando dias com céu claro e céu nublado. Para o dia de céu claro analisado, foi injetado na rede da concessionária 5,8 kWh de energia. A eficiência global, ηs deste sistema conectado ficou na ordem de 9 %. O sistema de aquisição de dados e controle da microrrede mostrou-se adequado com o propósito de alimentar a carga em permanência. Sempre que a rede da concessionária é desligada, a carga é automaticamente direcionada para o sistema isolado. Quando o banco de estocagem atinge 50 % de sua capacidade, a carga volta a ser alimentada pelo sistema conectado em paralelo com a rede da concessionária.
This work deals with the development and commissioning of a photovoltaic micro-grid 1680 W connected/alone with storage for management and control of a load considered critical. This micro-grid, employing two PV modules technologies, was installed on Renewable Energy Laboratory at Unisinos. The micro-grid panels is composed of two modules, a 1080 W multicrystalline silicon, and a 600 W of monocrystalline silicon. The first is a grid-connected system and the second is a stand-alone system, respectively. The management and control system, called supervisory, monitors and controls the two systems via data acquisition, which has the task of storing the data on a memory card in addition to showing real-time variables involved in the process through a liquid crystal display. Are made analysis of current values and voltages, AC and DC, to determine the input and output power of the equipment involved in the process, as well as variables such as ambient temperatures and PV module and irradiance. The purpose of this study is to prove availability of the system to meet a load that can be considered as a critical process, in order to maintain a constant power to the load. For this, it is necessary that the load is switched between systems connected to the grid and alone, according to the variables analyzed by the data acquisition system. The analyzes of the data are divided into two parts: PV grid-connected and alone system. For each system, the behavior of tension was analyzed, current and power of the PV panels, as well as the behavior of inverters and power storage bank, considering days with clear skies and overcast sky. For clear sky days analyzed, it was injected into the mains 5.8 kWh of energy. The overall efficiency of this system connected, ηs is 9 %. The data acquisition and control system micro-grid was adequate for the purpose of feeding a remaining charging. Whenever, the mains is switched off, the load is automatically directed to the alone system. When the storage capacity of the database reaches 50%, the load is once again powered by the connected system in parallel with the utility grid.

Fossil fuels and non-renewable resources are being replaced with, as modern day society has coined the term, green energy. This movement towards green energy creates a demand for renewable energy resources, such as solar photovoltaic (PV) systems. This study used Geographic Information Systems (GIS) in conjunction with Remote Sensing (RS) practices and two weighting systems the Analytical Hierarchy Process (AHP) and Rank-Order methods for PV site selection. Six multi-criteria models were developed using spatial factors and constraining images to locate potential photovoltaic power plant sites for three settings of fixed axis PV arrays. This analysis was performed at a macro regional scale and further analysis is encouraged for micro site selection.

This thesis describes the current situation of the electrical grid on a general level and contemporary support policies for residents who feed renewably produced electricity into the grid within a Swedish context. It shows which issues currently exists and suggests a new way to value overproduced renewable electricity which is not self-consumed. This way is called a dynamic price function (DPF), and this thesis models, simulates and analyzes the DPF in order to create an economic incentive to support the balance of the electrical grid – one of its most important parameters. The suggested DPF could potentially work with any renewable source in any area, but the focus in this thesis has been on solar power-systems for households in local areas. While the currently support policies, which uses static models to value overproduced renewable electricity, have created important incentives for the initial penetration of solar power among local residents they do not scale well as the share of renewable production on a local level increase. This might cause negative impacts on the electrical grid. The thesis’ results show that by designing the DPF in certain ways it is possible to create an economic incentive for different behaviors. The most promising design incorporates three different incentives at the same time and they are: 1) to incentivize the initial penetration of solar power in local areas which do not have any production, 2) to incentivize a higher share of solar power, but not too high, and 3) to procure storage possibilities for overproduced electricity. These incentives do not only encourage a more even geographical distribution of solar power, but also allow for a higher share of solar power in the energy system without risking the balance of the grid.

Dans le contexte des Sciences de l'Information et de la Technologie, un des challenges est de créer des systèmes de plus en plus petits embarquant de plus en plus d'intelligence au niveau matériel et logiciel avec des architectures communicantes de plus en plus complexes. Ceci nécessite des méthodologies robustes de conception afin de réduire le cycle de développement et la phase de prototypage. Ainsi, la conception et l'optimisation de la couche physique de communication est primordiale. La complexité de ces systèmes rend difficile leur optimisation notamment à cause de l'explosion du nombre des paramètres inconnus. Les méthodes et outils développés ces dernières années seront à terme inadéquats pour traiter les problèmes qui nous attendent. Par exemple, la propagation des ondes dans une cabine d'avion à partir des capteurs ou même d'une antenne, vers le poste de pilotage est grandement affectée par la présence de la structure métallique des sièges à l'intérieur de la cabine, voir les passagers. Il faut, donc, absolument prendre en compte cette perturbation pour prédire correctement le bilan de puissance entre l'antenne et un possible récepteur. Ces travaux de recherche portent sur les aspects théoriques et de mise en oeuvre pratique afin de proposer des outils informatiques pour le calcul rigoureux de la réflexion des champs électromagnétiques à l'intérieur de très grandes structures . Ce calcul implique la solution numérique de très grands systèmes inaccessibles par des ressources traditionnelles. La solution sera basée sur une grille de calcul et un supercalculateur. La modélisation électromagnétique des structures surdimensionnées par plusieurs méthodes numériques utilisant des nouvelles ressources informatiques, hardware et software, pour dérouler des calculs performants, représente le but de ce travail. La modélisation numérique est basée sur une approche hybride qui combine la méthode Transmission-Line Matrix (TLM) et l'approche modale. La TLM est appliquée aux volumes homogènes, tandis que l'approche modale est utilisée pour décrire les structures planaires complexes. Afin d'accélérer la simulation, une implémentation parallèle de l'algorithme TLM dans le contexte du paradigme de calcul distribué est proposé. Le sous-domaine de la structure qui est discrétisé avec la TLM est divisé en plusieurs parties appelées tâches, chacune étant calculée en parallèle par des processeurs différents. Pour accomplir le travail, les tâches communiquent entre elles au cours de la simulation par une librairie d'échange de messages. Une extension de l'approche modale avec plusieurs modes différents a été développée par l'augmentation de la complexité des structures planaires. Les résultats démontrent les avantages de la grille de calcul combinée avec l'approche hybride pour résoudre des grandes structures électriques, en faisant correspondre la taille du problème avec le nombre de ressources de calcul utilisées. L'étude met en évidence le rôle du schéma de parallélisation, cluster versus grille, par rapport à la taille du problème et à sa répartition. En outre, un modèle de prédiction a été développé pour déterminer les performances du calcul sur la grille, basé sur une approche hybride qui combine une prédiction issue d'un historique d'expériences avec une prédiction dérivée du profil de l'application. Les valeurs prédites sont en bon accord avec les valeurs mesurées. L'analyse des performances de simulation a permis d'extraire des règles pratiques pour l'estimation des ressources nécessaires pour un problème donné. En utilisant tous ces outils, la propagation du champ électromagnétique à l'intérieur d'une structure surdimensionnée complexe, telle qu'une cabine d'avion, a été effectuée sur la grille et également sur le supercalculateur. Les avantages et les inconvénients des deux environnements sont discutés.

Le développement rapide des véhicules électriques (EVs) augmente la demande de puissance, ce qui provoque une charge supplémentaire sur le réseau public et augmente les fluctuations de la charge. Par conséquent, la forte pénétration des EVs est freinée. Un algorithme simulé en temps réel et basé sur des règles est élaboré pour les bornes de recharge des EVs alimentées par un micro-réseau DC afin de faire face aux incertitudes du comportement des utilisateurs des EVs. L'algorithme prend en considération les choix arbitraires et aléatoires proposés via l'interface homme-machine. Les résultats de simulation sont obtenus sous MATLAB / Simulink et vérifient la faisabilité de la stratégie de gestion proposée. Cette stratégie présente de bonnes performances en garantissant un contrôle précis. Par ailleurs, les algorithmes d'optimisation de délestage et de la restauration des EVs (SROA) pour la recharge de la puissance de la batterie peuvent être utilisés pour répondre aux besoins des utilisateurs. Aussi les algorithmes SROA maintiennent l'équilibre de la puissance de la station de recharge des EVs. Les algorithmes SROA prennent en compte l'intermittence de la source photovoltaïque (PV), la limitation de capacité du stockage et la limitation de puissance du réseau public. En comparant les résultats de la simulation aux algorithmes basés sur les règles, les algorithmes SROA proposés respectent le choix de l'utilisateur, réduisent le temps de charge total, augmentent le plein débit et maximisent l'utilisation de la puissance disponible. Les résultats de la simulation montrent la faisabilité et l'efficacité des algorithmes SROA. En outre, une station de charge basée sur le PV pour les EVs peut participer à la résolution de certains problèmes liés au pic de puissance. D'autre part, la technologie de véhicule à réseau (V2G) est conçue et appliquée pour fournir des services auxiliaires au réseau pendant les périodes de pointe, et V2G considère la dualité de la batterie des EVs « charge et source ». Ainsi, un algorithme de recherche dynamique des pics et de vallées est proposé pour une station de recharge des EVs afin d'atténuer l'impact sur le réseau public. Cet algorithme réduit ainsi le coût énergétique du réseau public. Les résultats de la simulation démontrent bien l'efficacité de l'algorithme de recherche des pics et des vallées. L'algorithme peut garantir l'équilibre du réseau public, satisfaire la demande de charge des utilisateurs des EVs et, surtout, réduire le coût énergétique du réseau public
The rapid development of electric vehicles (EVs) increases the power demand, which causes an extra burden on the public grid increasing the load fluctuations, therefore, hindering the high penetration of EVs. A real-time rule-based algorithm for electric vehicle (EV) charging stations empowered by a DC microgrid is proposed to deal with the uncertainties of EV users’ behaviour considering its arbitrary and random choices through the human-machine interface, meanwhile considering most of the users’ choices. The simulation results obtained under MATLAB/Simulink verify the feasibility of the proposed management strategy that presents a good performance in terms of precise control. In addition, EV shedding and restoration optimization algorithms (SROA) for battery charging power can be used to meet user needs while maintaining EV charging station power balance, taking into consideration the intermittency of the photovoltaic (PV) source, the capacity limitation of the storage, and the power limitation of the public grid. The simulation results show that compared with rule-based algorithm, the proposed SROA respect the user's choice while reducing total charging time, increasing the full rate, and maximizing the available power utilization, which shows the feasibility and effectiveness of SROA. Furthermore, a PV based charging station for EVs can participate to solve some peak power problems. On the other hand, vehicle to grid (V2G) technology is designed and applied to provide ancillary services grid during the peak periods, considering the duality of EV battery “load-source”. So, a dynamic searching peak and valley algorithm, based on energy management, is proposed for an EV charging station to mitigate the impact on the public grid, while reducing the energy cost of the public grid. Simulation results demonstrate the proposed searching peak and valley algorithm effectiveness, which can guarantee the balance of the public grid, meanwhile satisfy the charging demand of EV users, and most importantly, reduce the public grid energy cost

This thesis presents the development of a new multiscale stochastic fracture mechanics modelling framework informed by in-situ X-ray Computed Tomography (X-ray CT) tests, which can be used to enhance the quality of new designs and prognosis practices for fibre reinforced composites. To reduce the empiricism and conservatism of existing methods, this PhD research systematically has tackled several challenging tasks including: (i) extension of the cohesive interface crack model to multi-phase composites in both 2D and 3D, (ii) development of a new in-house loading rig to support in-situ X-ray CT tests, (iii) reconstruction of low phase-contrast X-ray CT datasets of carbon fibre composites, (iv) integration of X-ray CT image-based models into detailed crack propagation FE modelling and (v) validation of a partially informed multiscale stochastic modelling method by direct comparison with in-situ X-ray CT tensile test results.

Small wind turbines, and especially urban-mounted turbines which require no dedicated pole, have garnered great public enthusiasm in recent years. This enthusiasm has fueled widespread growth among energy conservationists, and estimates predict that the power produced nationally by small wind will increase thirty-fold by 2013. Unfortunately, most of the wind resources currently available have been designed for larger, rural-mounted turbines; thus, they are not well suited for this nascent market. A consequence of this is that many potential urban small wind turbine owners over-predict their local wind resource, which is both costly and inefficient. According to a recent study published by Encraft Ltd., small wind turbines mounted to buildings far underperformed their rural pole mounted counterparts. As a proposed solution to this problem, this project introduces the concept of a Web-based Wind Assessment System (WWAS). This system combines all the necessary resources for potential urban small wind turbine customers into a single web-based tool. The system also presents the concept of a modular wind measurement system, which couples with the WWAS to provide real-time wind data measurements. The benefits of the system include its ease of use, flexibility of installation, data accessibility from any web browser, and expert advice. The WWAS prevents potential clients from investing in a system that may not be viable for their location. In addition, a small wind turbine is designed in this project, which has a unique modular mounting system, allowing the same baseline wind turbine to attach to various structures using interchangeable mounting hardware. This includes such accessible urban structures as street lights, building corners, flag poles, and building walls, among others. This design also utilizes concepts that address some of the challenges associated with mounting small wind turbines to existing urban structures. These concepts include: swept tip blades and lower RPM to reduce noise; vibration suppression using rubber shims; a netted duct to protect wildlife; and a direct-drive permanent magnet generator to ensure low starting torque. Finally, the cost of this system is calculated using off-the-shelf components, which minimize testing and certification expense. This small wind turbine system is designed to be grid-connected, has a 6 foot diameter rotor, and is rated at 1 kW. This design features a unique modular interchangeable mounting system. The cost for this complete system is estimated to be $2,050. If a users' site has an average wind speed of 14 mph (6.5 m/s), this system will generate a return on investment in 8.5 years, leaving over 10 years of profit. The profit for this system, at this sample average wind speed, yields over $4,000 during its 20-year design life, which is a two-fold return on investment. This project has implications for various stakeholders in the small wind turbine market, including designers, engineers, manufacturers, and potential customers. Equally important is its potential role in guiding our future national--even global--energy agenda.

In recent years, with the exhaustion of fossil fuels and increasing public awareness about the use of green energy, the renewable energy has gained popularity and is emerging as an important source of energy. Also, the electrical power grid is on the threshold of a paradigm shift from centralized power generation, transmission and massive electric grids to distributed generation (DG). DG basically uses small-scale generators, like photovoltaic (PV) panels, wind turbine, fuel cells, small and micro hydropower, diesel generator set, etc., and is confined to small distribution networks to produce power close to the end users. Renewable energy sources (RES) are the important constituents of DG and provide electricity with higher reliability and security and have fewer harmful environmental consequences than traditional power generators. With increased penetration of DGs into the traditional grid system, it is required to resolve the technical and operational problems viz. power quality, voltage instability, fault identification and clearing, etc. brought by the DG deployment. PV based microgrid may be one of the solutions to meet these challenges. A microgrid is a group of interconnected loads and distributed generators within clearly defined electrical boundaries that acts as a single controllable entity with respect to the grid. It can be connected and disconnected from the grid to enable it to operate either in grid-tied or standalone mode. Grid-tied PV based microgrid can be either single-stage or two-stage depending on the technical requirements. In single stage configuration, PV array is directly connected to a DC/AC converter whereas in two-stage configuration an additional DC/DC converter with maximum power point tracking (MPPT) capability is connected in between the PV array and DC/AC converter and provides the desired DC voltage to the inverter. This research work aims at modelling, design and development of a two-stage threephase grid-tied PV based microgrid. In order to predict the behaviour of the designed system under steady state as well as in the dynamic state, modelling of the overall system has been carried out. Steady state response of the PV based microgrid is studied from its mathematical model comprising of the governing equations of the designed vii system. Characterization studies viz. sensitivity and reliability analysis are the performance indicators of any system. Accordingly, the sensitivity analysis of the designed system has been performed and the sensitivity functions of the major components, i.e. solar cell and converter have been developed. Also, component and system level reliability analysis have been performed for the system under consideration. In the present work, the two stages of power conversion consist of boost converter and grid interfacing inverter. The DC-DC converter is used to boost the output voltage of the PV array to the required DC link voltage level along with the functionality of tracking the maximum power obtained from PV array under varying irradiation and temperature. The PV inverter is used to convert the generated DC voltage to AC of required voltage and frequency and to maintain the power balance between DG, load and grid. The interfacing control algorithms are used to control the inverter for its efficient utilization and grid synchronization. Conventional control algorithms use feedback controller like proportional integral (PI) controller for DC-link voltage control. These controllers are not best suited for nonlinear systems like PV based microgrid as the overshoots and long settling time in their response are inevitable. In order to overcome the drawbacks of the conventional algorithms, an intelligent asymmetrical fuzzy logic (AFL) based interfacing control algorithm and feedforwardfeedback adaptive interfacing control algorithm are proposed and developed for the PV inverter. The proposed algorithms also improves the utilization of the proposed system by incorporating additional features of active power filter (APF), VAR generation, and load balancing in the inverter. Grid interconnection of PV based microgrid has the advantage of efficient utilization of generated power. But the technical requirements from the utility grid side need to be satisfied to ensure the safety of the operators and the reliability of the utility grid. According to IEEE Std 1547-2003, one such technical requirement of the grid interconnection is the response of the microgrid to islanding. This research work proposes a novel islanding detection algorithm based on the estimation and analysis of negative sequence components of the voltage (Vneg) at the point of common coupling (PCC). Wavelet packet transform (WPT) is used for the features extraction from Vneg viii components. The binary tree classifier is used to discriminate between other disturbances and islanding condition. The proposed algorithm is capable of detecting islanding events even under the worst-case scenario, where the inverter output power is nearly equal to the local load consumption. Also, the proposed method is faster than the existing passive detection methods. A standalone PV system can be used efficiently and economically to feed household loads, the majority of which works on DC power, such as LED (Light Emitting Diodes) lights, BLDC (Brushless DC) drives, mobile phones, computers, televisions, etc. Standalone PV system feeding DC power directly to loads can be an attractive solution to locally utilize DC electricity with minimum distribution and conversion losses. This concept has recently resulted in a novel grid system known as DC nanogrid. A DC nanogrid supplies the residential and commercial loads which may operate on AC or DC voltage of different utilization levels. Interfacing such variety of loads and controlling power flow between these loads presents an interesting challenge. Multiple dedicated converters can serve the purpose, but they exhibit the problems of power flow coordination, low efficiency, higher component count, and the increased size of the system. The last objective of this research is to develop innovative multi-terminal voltage converters for renewable-energy applications. A PV based multi-terminal DC nanogrid is developed using dual-input single-output (DISO) and single-input dualoutput (SIDO) converter configurations with improved reliability and efficiency. The characterization studies of these converters such as sensitivity analysis and reliability analysis have been carried out. Also, the performance of the developed converter configurations are investigated using MATLAB along with Simulink toolbox. The SIDO converter configurations are experimentally validated using a 100W prototype, built and tested in the laboratory of DTU for practical applications. The research work presented in the thesis is expected to provide good exposure to design, development and control of the grid-tied PV based microgrid and DC nanogrid

Indiana University-Purdue University Indianapolis (IUPUI)
This thesis presents a converter topology for photovoltaic panels. This topology minimizes the number of switching devices used, thereby reducing power losses that arise from high frequency switching operations. The control strategy is implemented using a simple micro-controller that implements the proportional plus integral control. All the control loops are closed feedback loops hence minimizing error instantaneously and adjusting efficiently to system variations. The energy management between three components, namely, the photovoltaic panel, a battery and a DC link for a microgrid, is shown distributed over three modes. These modes are dependent on the irradiance from the sunlight. All three modes are simulated. The maximum power point tracking of the system plays a crucial role in this configuration, as it is one of the main challenges tackled by the control system. Various methods of MPPT are discussed, and the Perturb and Observe method is employed and is described in detail. Experimental results are shown for the maximum power point tracking of this system with a scaled down version of the panel's actual capability.

碩士
國立臺灣大學
機械工程學研究所
103
A networking technique for solar PV power co-sharing in a micro-grid composed of several hybrid solar PV systems (HyPVs) with limited battery storage, called “HyPV-net”, was developed. A power switching control was used to distribute the solar PV power between individual HyPVs. Excess solar PV power in an individual HyPV at low load power consumption will be transmitted to its neighbor HyPV through a central control unit (CCU) via ac power line. This will increase the PV power generation of the grid and improve the economy of the system. A long-term system performance simulation of HyPV-net for system design was carried out. A HyPV-net with two HyPVs was built and tested to measure its performance and verify the simulation results.

This thesis presents a novel Zero Voltage Switching (ZVS) approach in a grid connected single-stage flyback inverter without using any additional auxiliary circuits. The soft-switching of the primary switch is achieved by allowing negative current from the grid-side through bidirectional switches placed on the secondary side of the transformer. Basically, the negative current discharges the MOSFET’s output capacitor thereby allowing turn-on of the primary switch under zero voltage. In order to optimize the amount of reactive current required to achieve ZVS a variable frequency control scheme is implemented over the line cycle. In addition, the bi-directional switches on the secondary side of the transformer have ZVS during the turn-on times. Therefore, the switching losses of the bi-directional switches are negligible. A 250W prototype has been implemented in order to validate the proposed scheme. Experimental results confirm the feasibility and superior performance of the converter compared to the conventional flyback inverter.
Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2012-07-06 16:24:13.385

碩士
國立清華大學
電機工程學系所
105
This thesis develops a switched-reluctance generator (SRG) based DC microgrid with hybrid storage, energy harvesting and grid-connected capability. The microgrid DC bus voltage is established by the wind SRG via an interleaved boost DC/DC converter. The hybrid energy storage system consists of a SRM driven flywheel, a lead-acid battery bank and a super-capacitor. While the super-capacitor bank is directly connected across the SRG output, the battery and the flywheel are respectively interfaced to the common DC bus via its bidirectional DC/DC converter. Satisfactory energy support discharging and charging characteristics are preserved by proper controls. In addition, a chopped dump load is equipped for avoiding bus over-voltage in the occurrence of energy surplus. The isolated grid-connection of the established microgrid to utility grid is achieved by a bidirectional LLC resonant converter and a bidirectional single-phase three-wire (1P3W) inverter. The schematics and control schemes of these two power stages are all properly designed and implemented. Good inverter output waveforms are obtained via the designed proportional plus resonant control scheme. And the microgrid-to-grid (M2G) and the grid-to-microgrid (G2M) bidirectional operations can be smoothly conducted. To further enhance the power supplying quality of the established microgrid, a three-phase Vienna SMR based energy support scheme (ESS) is developed. As wind and stored energies are deficient, the possible harvested AC and DC sources can be plugged into the ESS to provide energy support for the microgrid. The control schemes of all the established power converters are realized digitally and evaluated experimentally.

碩士
中原大學
電機工程研究所
101
Abstract In the thesis, we use digital signal processor (DSP) as the control core and build the protection feature of international regulations and grid-connected regulations to design a grid-connected 3000 watt photovoltaic (PV) inverter. First, we introduce the grid-connected photovoltaic (PV) inverter block diagram and explain all functions on the digital signal processor (DSP) TSM320F2808 control system to achieve a system configuration and interface. Secondly, we introduce a photovoltaic (PV) inverter power stage structure, and combine zero crossing detection with AC synchronization in the hardware design. In addition, the functional safety functionality is implemented according to the requirements of VDE-AR-N 4105, such as relay defect detection, insulation resistance (RISO) measurement and residual current monitoring unit detection (RCMU). Third, design the digital signal processor (DSP) software control algorithm of this system; we introduce each function of close loop system control, voltage monitoring, frequency monitoring, insulation detection, residual current monitoring unit detection, improved maximum power point tracking (MPPT) algorithm and anti-islanding protection algorithm. Finally, we complete a prototype of 3000watt photovoltaic (PV) inverter and implement to assess the predictions. The experimental results are in feasibility close to the estimation. The contributions of our research are as follows: (1) Import an IEC62109 and VDE-AR-N 4105 specifications requirements that has system security. (2) Improve perturbation and observation (P&O) control to reach the maximum power point quick tracking. (3) Invent a new detect unit with relay, provide more security protection of this mechanism and simplify some circuits on inverter system. Thereby, optimize about cost and reliability.

Mestrado de dupla diplomação com a Ecóle Supérieur en Sciences Apliquées
Photovoltaic (PV) energy is becoming an important alternative energy source, since it is abundant in nature, non-polluting and requires low maintenance. However, it suffers from low energy conversion efficiency, which can be even lower if the photovoltaic generator does not operate around a so-called Maximum Power Point (MPP). Tracking this point, which changes its location depending on weather conditions, is a very important step in the design of a photovoltaic system. Several techniques have been investigated in the literature in the MPP context. However, some techniques such as the Kalman filter are steel unknown with a lack of information in real test conditions, since their evaluation is limited only in simulation and literature review. This work presents an experimental evaluation of the Kalman filter based on a comparison with two well-known maximum power point tracking (MPPT) algorithms, which are the Perturbation and observation (among the simplest techniques) and the Particle Swarm Optimization (among the most complex techniques). The experimental tests were carried out under real atmospheric conditions, using Matlab/Simulink and the 1103 dSPACE real-time controller board. The results show that the Kalman filter has a higher aptitude to operate closer to the MPP, with a low oscillation in steady-state compared to the other MPPT evaluated in this work. However, the technique’s flaw lies in the shadow situation where it can not differentiate between the local and global optimums, unlike the particle swarm optimization.
A energia fotovoltaica (PV) está a tornar-se uma importante fonte de energia alternativa, uma vez que é abundante na natureza, não poluente, e requer pouca manutenção. No entanto, sofre de uma baixa eficiência de conversão energética, que pode ser ainda mais baixa se o gerador PV não operar em torno do chamado Ponto de Potência Máxima (MPP). O rastreio deste ponto, que muda a sua localização dependendo das condições meteorológicas, é um passo muito importante na concepção de um sistema PV. Várias técnicas têm sido investigadas na literatura no contexto do MPP. No entanto, o desempenho de algumas técnicas, como o filtro Kalman, em condições reais de teste, ainda desconhecido, ou existe pouca informação, uma vez que a sua avaliação é limitada apenas na simulação e revisão da literatura. Este trabalho apresenta uma avaliação experimental do filtro de Kalman com base numa comparação com dois seguidores de ponto de potência máxima (MPPT) bem conhecidos, que são a Perturbação e observação e a Optimização do Enxame de Partículas. Os testes experimentais foram realizados em condições atmosféricas reais, utilizando o Matlab/Simulink e a carta de controlo em tempo real dSPACE. Os resultados mostram que o filtro de Kalman tem uma maior aptidão para operar mais perto do MPP, com uma baixa oscilação em regime permenente, comparativemente com os outros algoritmos MPPT avaliados neste trabalho. No entanto, a desvantagem ocorre aquando da ocorãncia de sombra, onde a técnica não consegue diferenciar entre os óptimos locais e global, ao contrário da optimização do enxame de partículas. Palavras-chave: Fotovoltaico (PV), Seguimento do Ponto de Potência Máxima (MPPT), Perturbação e Observação (PO), Optimização de enxame de partículas (PSO), Filtro de Kalman (KF), Sistema PV ligado à Rede, dSPACE 1103.

This project consists of two parts in first part detail about modified perturb & observe & input voltage sensor (IVS) algorithms,second part is about two stage grid integration of PV panel using damped second order generalised integrator (SOGI) algorithm.Conventional perturb & observe MPPT algorithm use PV panel voltage and current to vary duty ratio dc-dc converter such that maximum power is extracted from PV panel.IVS based algorithm PV panel voltage alone to track maximum power point of PV panel.These two algorithms are simulated using MATLAB/Simulink for rating of PV panel in laboratory. SEPIC converter is used for interfacing PV panel and dc load.Experimental setup of two algorithms are implemented & experimental results are compared with simulated results. A detailed comparison is made between two algorithms. In grid integration of PV module using damped SOGI algorithms, maximum power is extracted from PV module by varying duty ratio of dc-dc chopper by using IVS based algorithm. A three phase Voltage source converter is used for synchronisation. Along with supplying power to grid this control algorithm also improve power quality by injecting current to grid at unity power factor. Triggering pulses for VSC are given by comparing estimated grid current with actual grid current using hysteresis control.PV array grid integration by damped SOGI algorithm is simulated using MATLAB/Simulink.

碩士
國立中央大學
電機工程學系
105
In this paper, the converter is used to simulate the synchronous generators. In island mode, converter can meet load requirements and provide stable voltage and frequency support .In grid-connected mode, converter can output request active power or reactive power. The control strategy of the virtual synchronous generators (VSG) is making distributed power supply operate safely and stably. The virtual synchronous generators are need to realize seamless transform between the island mode and grid-connected mode .This paper use a pre-synchronous method of VSG based on virtual power and secondary frequency and voltage regulation is put forward to achieve seamless transform. In island mode, multiple VSGs connected to work as a unit, each VSG should according to the capacity to sharing power which required by load . This paper simulates the operation of the virtual synchronous generator in Matlab/Simulink, and verifies the effectiveness of the proposed control algorithm.

Current Source Inverter (CSI) topology is gaining acceptance as a competitive alternative for grid interface of renewable energy systems due to its unique and advantageous features. Merits of CSI over the more popular Voltage Source Inverter (VSI) topology have been elaborated on by a number of researchers. However, there is a dearth of quality work in modeling and control of CSI topology interfacing renewable energy resources to the grid. To enrich the study focussing on application of CSI for renewable energy interface, this thesis develops a multilevel structure based on CSI for three-phase grid-connected Photovoltaic (PV) application. In the first part of research, a single-stage CSI interfacing to PV array is developed. The CSI-based PV system is equipped with Maximum Power Point Tracker (MPPT), DC-link current controller, and AC-side current controller. To eliminate the nonlinearity introduced by the PV array, a feed-forward control is introduced in the DC-link current controller. The AC-side current controller is responsible for maintaining unity power factor at the Point of Common Coupling (PCC). To verify the performance of the developed CSI-based PV system, a number of simulation studies are carried out in PSCAD/EMTDC environment. To illustrate the performance of the CSI-based PV system during transients on the grid side, simulation studies are carried out for four kinds of faults. Results obtained from fault studies are highly in favor of CSI topology and provide illustrative evidence for short-circuit current protection capability of the CSI. On the other hand, the VSI-based PV system performs poorly when subjected to similar grid transients. To extend the research on CSI-based PV system further, a multilevel structure based on CSI is developed. The multilevel structure is a parallel combination of $n$ CSI units and capable of producing $2n+1$ levels of current at the terminal of the inverter. Each unit in the multilevel structure has its own MPPT, DC-link current controller. However, on the AC-side a combined current controller is proposed. The design results in a high power rating with reduced number of filters, sensors and controllers. The developed multilevel structure can operate with PV arrays exposed to equal and unequal insolation level. However, when the PV arrays are operating under unequal insolation level, low order harmonics are generated in the sinusoidal current that is injected into the grid. Elimination of these harmonics is performed by implementing a modified control strategy in stationary reference frame that corresponds to the harmonic component that needs to be minimized. The modified control strategy operates in coordination with the existing DC-side and AC-side current controllers, and MPPTs. Therefore, real-time suppression of current harmonics can be ensured. Performance of the multilevel structure is verified by different transient studies.

In the present day, owing to the increasing number of electronic loads such as computer power supplies, Compact fluorescent lamps (CFL) and the increasing number of sources such as solar photovoltaics, fuel cells (DC sources), DC Micro-grids provide a more efficient solution compared to the AC counterpart in terms of the number of stages involved in conversion. Also, the ability to be readily buffered to storage elements is an advantage in a DC system. Apart from this, there are no issues of frequency stability, reactive power transfer and ac power losses. A DC micro-grid is effectively a multi-port dc-dc converter. The ports refer to the various sources and loads that are part of the micro-grid. Sources could be unidirectional (as in the case of PV, load) or bidirectional (as in the case of batteries). Interfacing a variety of ports and controlling power flow between these ports presents an interesting challenge. Commonly used topologies interface the various ports at the DC bus capacitor thereby making the DC bus capacitor bulky. Apart from this, the DC bus coupled topologies route power from one port to another via the central capacitor. This increases the number of stages in transferring power from one port to another. An alternative topology is to use the active bridge type converters where dynamic power flow equations are required to control inter-port power flow. But, as the number of stages increase, the computations get tedious.In this thesis, a novel topology is proposed that uses a UU type transformer core to interface all the power ports. This alleviates the problems faced in the DC bus coupled topologies. A PWM scheme to control simultaneous power flow from each of the ports is also proposed in this thesis. The PWM scheme enables the usage of simple constant frequency average current mode control to dynamically control power sharing ratio between the various ports delivering to loads. By means of the proposed PWM scheme and the control scheme, the drawbacks of the active bridge topologies are alleviated. Using the proposed topology and the PWM scheme, a prototype micro-grid system is developed for a system comprising of the utility grid, batteries, solar PVs and resistive loads. Yet another aspect of the thesis explores the concept of connecting multiple micro-grids in order to create a 'local power network'. A potential application for this could be in interconnecting residential buildings and routing power from one house to another in order to balance demand and supply among these houses. This is against the growing trend of using the utility grid to also sink power and subsequently route it to other houses connected to the grid. Unfortunately not all areas have access to the utility grid. Additionally, turning the grid bidirectional requires that a number of standards be met and policies be created. But, the standard for using a local network that only involves a unidirectional grid is fixed by the community that owns such a network. In a crude sense, this scenario can be compared to the existence of a local area network to transfer information among users of the network. In this thesis, a prototype local power network interconnecting two micro-grids has been implemented.

In the present day, owing to the increasing number of electronic loads such as computer power supplies, Compact fluorescent lamps (CFL) and the increasing number of sources such as solar photovoltaics, fuel cells (DC sources), DC Micro-grids provide a more efficient solution compared to the AC counterpart in terms of the number of stages involved in conversion. Also, the ability to be readily buffered to storage elements is an advantage in a DC system. Apart from this, there are no issues of frequency stability, reactive power transfer and ac power losses. A DC micro-grid is effectively a multi-port dc-dc converter. The ports refer to the various sources and loads that are part of the micro-grid. Sources could be unidirectional (as in the case of PV, load) or bidirectional (as in the case of batteries). Interfacing a variety of ports and controlling power flow between these ports presents an interesting challenge. Commonly used topologies interface the various ports at the DC bus capacitor thereby making the DC bus capacitor bulky. Apart from this, the DC bus coupled topologies route power from one port to another via the central capacitor. This increases the number of stages in transferring power from one port to another. An alternative topology is to use the active bridge type converters where dynamic power flow equations are required to control inter-port power flow. But, as the number of stages increase, the computations get tedious.In this thesis, a novel topology is proposed that uses a UU type transformer core to interface all the power ports. This alleviates the problems faced in the DC bus coupled topologies. A PWM scheme to control simultaneous power flow from each of the ports is also proposed in this thesis. The PWM scheme enables the usage of simple constant frequency average current mode control to dynamically control power sharing ratio between the various ports delivering to loads. By means of the proposed PWM scheme and the control scheme, the drawbacks of the active bridge topologies are alleviated. Using the proposed topology and the PWM scheme, a prototype micro-grid system is developed for a system comprising of the utility grid, batteries, solar PVs and resistive loads. Yet another aspect of the thesis explores the concept of connecting multiple micro-grids in order to create a 'local power network'. A potential application for this could be in interconnecting residential buildings and routing power from one house to another in order to balance demand and supply among these houses. This is against the growing trend of using the utility grid to also sink power and subsequently route it to other houses connected to the grid. Unfortunately not all areas have access to the utility grid. Additionally, turning the grid bidirectional requires that a number of standards be met and policies be created. But, the standard for using a local network that only involves a unidirectional grid is fixed by the community that owns such a network. In a crude sense, this scenario can be compared to the existence of a local area network to transfer information among users of the network. In this thesis, a prototype local power network interconnecting two micro-grids has been implemented.

The need for power supply from the main grid is rising drastically as the investment in economic activities and population grow rapidly, as does the improvement of comfort level and power consumption required by contemporary home appliances. Global warming and greenhouse gas (GHG) emissions have negative impacts due to the use of fossil fuel power plants. These are the main challenges which have given pressure in using sustainable and renewable energy resources (SRES) for power generation. Moreover, the world's energy sector is confronted with growing issues as a result of increased energy demand, efficiency, supply fluctuations and energy demand dynamics, and a shortage of analyses essential for appropriate energy management. Incorporation of artificial intelligent solutions into power systems, possess the high potential to enhance power efficiency, cost savings, and user comfort. As a result, it is imperative to create intelligent optimization-based algorithms for use in various renewable energy systems. In this study energy systems are mainly hybrid solar- based micro-grid systems. In particular, this study investigates the potential of hybrid biogas fuelled systems for generating electricity for commercial use in Tanzanian environment and potential of non-perennial tributary for electricity generation particularly in areas with a long standing period of time and extensive high rainfall for expanding the potential of hydro energy resource. This research work presents the techno-economic feasibility analysis of a standalone solar photovoltaic (SPV) system coupled with a battery bank that is expected to offer power to a typical rural residence at Simboya village using hybrid optimization multiple energy renewables (HOMER) and particle swarm optimization (PSO) platforms. HOMER is used to carry out techno-economic viability analysis of small wind turbine electric system (SWTES) for electrical water and power supply for peasant‘s residence at Simboya village, it describes the techno-economic feasibility assessment of a hybrid SPV/biogas generator/battery system optimized by HOMER pro and the grey wolf optimization (GWO) platforms to supply power to Simboya village, also it covers the techno-economic evaluation of the SPV-hydro-biogas battery bank system which is expected to deliver power to same village, it presents the techno-economic study of the SPV/Small hydro/Battery energy system configuration predicted to supply electricity to Ikukwa village utilizing HOMER, PSO , GWO, and GWO PSO hybrid platforms. The key findings of this research work are summarized as follows: Findings by HOMER platform, daily electricity consumption and peak power output of the XXVI residential house for the proposed rural site is 0.16kWh/day and 0.18kW, respectively. Total net present cost (NPC) of standalone SPV system (first scenario) and diesel generator (DG) set (second scenario) are $ 2089 and $ 19 488, respectively. Optimization results by HOMER software and the PSO technique for the aforesaid configurations (scenarios) are also compared. Optimization results of scenario 1 (SPV system) indicate the reduction of total NPC in the PSO technique equivalent to 69.33% while results of scenario 2 (DG) show the decline in total NPC in the PSO technique equals to 69.31%. Scaled peak power and energy consumption during rainy season are 1.48 KW and 11.26 kWh / day respectively. Total NPC for SWTES is $ 106 273. 80 and levelized cost of energy (LCOE) is estimated to be $ 1.58/ kWh. The cost for batteries is $ 77 892. 96 (73.3%) being higher than the cost for wind turbine (WT) which is 18 369. 80 (17.3%). The cost for converter is $ 6713.11(6.3%). In optimization by HOMER, the optimal configuration of SPV/biogas generator/battery system components are 40 kW SPV, 25 kW biogas generator, 144 Generic 1kWh Li-ion batteries, four in series with 36 strings of system bus voltage 24V and 40 kW converter with a dispatch strategy of cycle charging. Total NPC, investment cost, LCOE for the off-grid hybrid renewable energy supply system (HRESS) is $106,383.50, $ 78500 and $ 0.1109/kWh respectively. The analysis of the optimized system by GWO method has shown that over-all NPC and LCOE are $ 85, 106 A and $ 0.0887/kWh respectively. The use of AI optimization (GWO) technique has further reduced the financial metrics of power generation up to around 20 % when compared with HOMER. Moreover, techno-economic analysis is carried out for off-grid hybrid SPV-hydro- biogas-battery bank system for delivering power supply to Simboya village. HOMER platform is used for simulation purposes. The penetration levels for hydro and SPV energy sources are 470 % and 90.1 %, respectively. The efficiency of biogas generator is estimated to be 31.0 %. The optimal design of off grid hybrid system consists of 10 kW of biogas, 30 kW of SPV, 85.1 kW of hydro, 48 batteries and 20 kW of converter. Total NPC and LCOE for hybrid solar PV-hydro- biogas-battery bank system & DG are $ 77861.88. Optimal results of SPV/Hydro/battery hybrid micro grid system based on the lowest NPC via HOMER , PSO, GWO, and GWO-PSO hybrid technique platforms are $ 141, 397.76, $ 95,167.21, $ 92,472.82, and $ 91, 854.10, respectively. Optimization results of same configuration in terms of LCOE via HOMER, PSO, GWO, and GWO-PSO hybrid technique platforms are $ 0.1818/ kWh, $ 0.1185 kWh, $ 0.1182/ kWh, and $ 0.1181/ kWh, respectively. Conclusively, renewable energy based systems are cost effective, sustainable and ecologically friendly. Optimization using AI algorithms yield significant results in minimal generation costs.

Implementing a smarter grid for improved management and use of power is extremely important for the future and development of South Africa. Even more important is nding the best way to implement these grids in South Africa. A number of evolutions are expected, but ultimately the eventual solution will need to satisfy the requirements of the grid, while adhering to the relevant standards to result in a suitable solution for South Africa. It can therefore not be assumed that a solution which works successfully in another country will have the same results in South Africa. The economy, nancial strength and technological maturity of South Africa are among the factors which are unique and will require an implementation tailored to t South Africa and these factors. The architecture of the grid gives it structure. This report considers the architecture for implementing the grid in South Africa, employing a view which places more importance on the consumers. An existing architecture, the OPEN meter architecture, is identi ed and localised based on a South African context, and then validated using existing international frameworks which de ne characteristics that every grid architecture must have.

碩士
國立勤益科技大學
電機工程系
99
Under the circumstances of petroleum resources in dwindling and the trend of consciousness of environmental protection rising up, clean, non-contaminated and inexhaustible energy source is in urgent need. Thus, the development and application of the renewable energy become one of the most important studies that every country is engaging in as well as putting it the primary energy policy in consideration in recently years. The integration of renewable energy into an independent power system shall be populated in the near future. For this, the main purpose of the thesis is to develop a dispatch and monitoring-control system of the hybrid renewable energy based micro grid, which includes a wind turbine and solar cell; in the mean time, a highly mobilized and widely applicable micro turbine was adopted as well. Further, an operation strategy for the purpose of back-up power supply is derived. The renewable energies are optimally dispatched in the normal condition. In case the utility is in abnormal or interrupted, the overall hybrid power system is ensured to keep the power loading in demand, so the operation can be run steadily. The constructed dispatch and monitoring-control system of the integrated hybrid power system is able to operate in grid-connected mode or independent operation mode. In grid-connected mode, the renewable energy is adapted as primary power supply of loading. When the power generated by renewable energy is larger than the demand, it can be feedback to the power company. If the loading demand increases or external environmental factor results in insufficient output power, the micro turbines shall be adopted for the backup in power supply for the balance management of power system. It can be a useful reference for the overall design and operation in planning and integrating the hybrid power system derived from renewable energy.

Ever-increasing fossil fuels consumption in recent decades has emitted tremendous amounts of greenhouse gases, a big part of which cannot be absorbed by natural processes happening in nature. These gases have increased earth temperature by absorbing extra radiations from sunlight and turning them into heat. Global warming has had terrible effects for all creatures around the world and can threat life on Earth in future. Utilization of green or renewable energies during the recent years is getting more popular and can be a solution to this serious problem. A big source of these pollutants is transportation sector. Electrification of transportation can noticeably reduce greenhouse gasses if the electricity is obtained using renewable energy sources. Otherwise, it will just shift the problem from streets to fossil fuel power plants. Electric vehicles (EVs) were introduced around one century ago; however, they were replaced by internal combustion engine cars over time. Nevertheless, recently they are getting more interest because of their superior performance and clean operation. Solar electricity which can be obtained using photovoltaic panels is one of the easiest ways as long as sun is available. They can be easily mounted on the roofs of buildings or roof tops of parking slots generating electric power to charge the battery pack of the EVs while providing shade for the cars. Since solar energy is intermittent and variable, power grid should be involved to ensure enough power is available. Conventional solar chargers inject power to the grid and use grid as the main source because of its reliability and being infinite. Hence, they use grid as a kind of energy storage system. This approach can lead to problems for grid stability if solar panels are utilized in large scales and comparable to the grid. In this work, a solar powered grid-tied EV/PHEV charger is introduced which uses all the available power from PV panels as the main energy source and drains only the remaining required power from the grid. The proposed configuration provides great flexibility and supports all the possible power flows. To design an efficient system the load should be known well enough first. A comprehensive study has been done about behavior, characteristics and different models of different chemistries of batteries. Specific phenomena happening in battery packs are outlined. A novel maximum power point tracking (MPPT) technique has been proposed specifically for battery charging applications. A specific configuration involving DC link coupling technique has been proposed to connect different parts of the system. Different possible topologies for different parts of the proposed configuration have been considered and the suitable ones have been selected. Dual active bridge topology is the heart of this configuration which acts as the bidirectional charger. A detailed state space modeling process has been followed for the power converters and various small signal transfer functions have been derived. Controllers have been designed for different power converters using SISO design tool of Matlab/Simulink. Different modes of operation for the charger including constant current mode (CCM) and constant voltage mode (CVM) have been analyzed and appropriate cascade controllers have been designed based on required time domain and frequency domain characteristics. Finally, simulation tests have been conducted and test results have been graphed and analyzed for different modes of operation, all possible power flows and various voltage and current set points.

碩士
國立清華大學
電機工程學系
104
This thesis develops the plug-in energy support systems for a wind switched- reluctance generator (SRG) based DC micro-grid. The auxiliary energy support from the accessible AC or DC sources can be achieved as the energy deficiencies of wind source and storage devices occur. First, an available wind SRG based micro-grid is redesigned and employed as the studied platform. It is equipped with a hybrid energy storage system consisting of a flywheel, a lead-acid battery bank and a super-capacitor bank. The common DC bus voltage of micro-grid is established by the SRG via an interleaved boost DC/DC converter. Thanks to the interleaving approach, the well-regulated DC bus voltage with lower ripple and fault-tolerance is preserved. For performing experimental test, a three-phase load inverter is established. The balanced three-phase voltages with good waveform and dynamic response characteristics are obtained by applying the designed space-vector PWM switching and dynamic control schemes. In the hybrid energy storage system, while the super-capacitor bank is directly connected across the SRG output, the battery and the switched-reluctance motor (SRM) driven flywheel are respectively interfaced to the common DC bus via a bilateral buck/boost-buck/boost DC/DC converter and an one-leg bilateral buck-boost DC/DC converter. In the developed single-phase AC source plug-in energy support systems (ESSs), two schematics are proposed: (i) Single-phase SMR based ESS: an external SMR is added to excite the 400V micro-grid bus from the mains; and (ii) Single-phase buck and buck-boost SMR based ESSs: only a full-bridge diode rectifier and an AC-side low-pass filter are externally added. A buck SMR or a buck-boost SMR is formed using the embedded power devices to dedicatedly charge the flywheel and battery bank. As to the three-phase AC source plug-in ESS, an extra three-phase Vienna SMR is equipped. Through proper arrangement and control, the micro-grid can be supported auxiliary energy from three-phase AC, single-phase AC or DC source.

碩士
國立清華大學
電機工程學系
102
In this thesis, a switched-reluctance generator (SRG) based DC micro-grid is established. It is equipped with a hybrid energy storage system composed of a flywheel and a lead-acid battery bank. The plug-in energy support through SRG power circuit from the utility grid is also implemented. The developed SRG is interfaced to the micro-grid common DC bus via an interleaved boost DC/DC converter. Well regulated DC bus voltage is obtained under varying shaft driving speeds and load conditions by properly treating the related key issues, such as power circuit design, robust voltage control, voltage command setting and commutation shift, etc. Also, lower input current ripples and higher reliability are preserved since the interleaving technique. To evaluate the established DC micro-grid experimentally, a three-phase load inverter with proper control is established. Good AC voltage waveform and dynamic response characteristics are achieved under linear and nonlinear load. In the developed hybrid energy storage system, the battery bank is interfaced to the common DC bus through a bilateral buck/boost DC/DC converter. Good charging and discharging characteristics are achieved through properly designing the power circuit and controllers. As to the switched-reluctance motor driven flywheel, the proposed bilateral boost/boost DC/DC converter is employed as its interface. Several discharging performance improvement approaches are proposed and comparatively evaluated. In the developed plug-in energy support mechanism, a single phase interleaved boost switched-mode rectifier is formed using the original SRG system components. The energy support from the mains to the micro-grid with good line drawn power quality is achieved.

碩士
國立清華大學
電機工程學系
99
This thesis presents the development of an experimental common DC-bus micro-grid system with a wind-driven switched-reluctance generator (SRG) as distributed generation source. In the establishment of SRG system, its power circuit and control scheme are first properly designed considering the alleviation of DC-link voltage ripples effects caused by commutation and switching. Moreover, the simple robust control is applied to yield improved DC output voltage regulation characteristics under varying prime mover driving speed. Then the operating performance is further enhanced via commutation shift approach. Having established the well-regulated SRG system, its output voltage (48VDC) is boosted by an isolated current-fed push-pull (CFPP) interface DC/DC to establish the common DC bus (400VDC). Similarly, the well-regulated DC bus voltage is achieved by the properly designed schematic and control scheme. As to the test load of micro-grid, a three-phase three-wire load inverter is established. Good AC output waveforms and regulation performance are obtained by applying the developed simple robust control approach. To provide the energy support for the micro-grid under generating fluctuation, a lead-acid battery energy storage system with bidirectional CFPP isolated interface DC/DC converter is developed. Good charging and discharging control performances are evaluated experimentally. In addition, a CFPP based switch-mode rectifier (SMR) is established and employed as an auxiliary charger. It can let the battery be charged from utility grid as the SRG fault is occurred. This SMR is formed using the embedded components of the SRG interfaced boost CFPP DC/DC converter, only an external diode bridge is needed. Through the proposed proper control, good charging characteristics and line drawn power quality are achieved.

碩士
國立清華大學
電機工程學系
100
This thesis develops a wind switched-reluctance generator (SRG) based DC micro-grid with battery energy storage buffer and three-phase load inverter. In the developed SRG, its power circuit is properly designed, and the hysteresis current-controlled PWM switching is applied to enhance the winding current control robustness against the adverse effects of back electromotive force. Then good generating performance under varying wind speed and load is achieved via proper voltage command setting, robust control and commutation shift. The SRG generated speed-dependent voltage is boosted and controlled by a current-fed push-pull interface converter to establish voltage well-regulated common DC bus. An active clamp circuit is equipped for increasing the operation reliability and efficiency of this DC/DC converter. The proposed micro-grid is supported by an energy storage system consisting of a flywheel and a lead-acid battery bank. The switched- reluctance motor (SRM) driven flywheel system is interfaced to the common DC bus through a bidirectional DC/DC converter. Good charging and discharging operation characteristics are obtained by properly designing the schematics and control schemes for the SRM drive and its followed interfaced converter. Similar to those of SRG, the voltage command of the SRM-driven flywheel in generating mode is also automatically adapted to the decreasing rotor speed and the voltage tracking error during the stored energy discharging. As to the battery energy storage system a bilateral buck/boost DC/DC converter is employed as an interface converter. Through proper circuit and controller designs, good common-bus DC voltage regulation in discharging mode and better charging performance are preserved. For making the performance experimental assessment, a three-phase load inverter is designed and implemented. The per-phase based control scheme is adopted, and the simple robust control is applied to yield good output voltage waveforms under linear and nonlinear loads. The control algorithms of all constituted power stages are realized fully digitally using digital signal processor (DSP). Normal operations and control performance of the established micro-grid are demonstrated experimentally.

碩士
國立清華大學
電機工程學系
101
his thesis develops a wind switched-reluctance generator (SRG) based DC micro-grid, it is equipped with a three-phase load inverter and a hybrid energy storage system consisting of a lead-acid battery and a flywheel. The established SRG is interfaced to micro-grid common DC bus via an interleaving current-fed push-pull (CFPP) DC/DC converter formed using two cells. Well regulated DC bus voltage is obtained under varying shaft driving speeds and load levels through properly treating the key issues, such as power circuit design, robust voltage and current controls, voltage command setting and commutation shift, etc. Meanwhile, lower ripples and higher reliability are possessed thanks to the interleaving operation. To make experimental evaluation for micro-grid, a three-phase load inverter is designed and implemented. The current control scheme in d-q domain with zero sequence control signal injection is adopted. Good AC output voltage waveforms and dynamic regulation characteristics under unknown and nonlinear loads are obtained. A hybrid energy storage system consisting of a flywheel and a lead-acid battery bank is established to provide energy storage support for the proposed DC micro-grid. Each storage device is interfaced to the micro-grid DC bus via a bilateral buck/boost DC/DC converter. For enhancing the SRM flywheel discharging performance, automatically adapting the voltage command, proper commutation instant setting and controller tuning are also made under generating mode. As to the battery energy storage system, good common-bus DC voltage regulation in discharging mode and good charging performance are obtained by the proper designs of its circuit and controller. Digital signal processor (DSP) is used to realize the digital controls of all constituted power stages in the developed micro-grid. The operation characteristics and control performances of the whole micro-grid are evaluated experimentally.

Electric power has become a basic necessity of human life. The major share of electric power comes from fossil fuel which results in global warming and pollution. A share of generated power comes from nuclear power which is equally dangerous. Big hydro projects take away lots of fertile land. The continuous usage of fossil fuel also poses a threat of petroleum and coal getting over in the near future. The only way out of this energy scarcity is to depend more and more on renewable sources like solar, wind and micro-hydro. At present, instead of having preference over any particular source of renewable energy, effort should be made to extract power from every possible energy source available in whatever form it is and use it in an optimal way. Like any renewable energy sources, the wind power contains large potential for harnessing energy that has been well understood hundreds of years ago. The importance of wind power generation has come to focus recently both at installation and research level and lot of activities are being carried out for efficient use of wind energy. There are different types of wind turbine designs available in the literature. But the most commercially used model is the two or three blade horizontal axis propeller type wind turbine. Research has shown that variable speed operation of this type of turbine is advantageous over fixed speed operation in terms of total energy synthesis. The most commonly used machines for wind power conversion are synchronous machine, squirrel cage induction machine and slip ring induction machine (SRIM). Variable speed operation using synchronous machine or squirrel cage induction machine requires large ratings of the power converters. However, SRIM based variable speed wind generator is advantageous over other schemes due to its inherent advantages like lower power rating for the converters, higher energy capture and the flexibility of sharing reactive power between the stator and the rotor. SRIM is used for both grid connected and stand alone applications and have been reported in the literature. The grid connected applications have received major attention in the literature whereas there are only a very few instances of its stand alone counterparts. There are many places both within and outside India where utility grid has not yet reached or the available grid is very weak. Moreover, in many of the places, the transmission line is so long that the losses in the system are extremely high. Isolated wind power generation can be of great advantage in such places where the available wind power is harnessed and utilized locally. This has been the motivation to go for proposing an isolated wind power generation scheme in this thesis. The proposed scheme is designed to supply power to the load even when very low or no wind power is available. Therefore, a battery bank is also a part of the system. The power converter assembly of the proposed scheme has three major components. One is the rotor side converter which is connected to the rotor terminals of the SRIM. The second one is the stator side converter with output LC filter which is connected to the stator side. These two converters share a common DC link which is interfaced to the battery bank through a multi phase bi-directional fly-back DC-DC converter. Fig. 1. Overall block diagram of the proposed stand alone wind power generator Functionally, this thesis proposes a system as shown in Fig. 1, which has primarily two components with multiple energy ports viz. (i) the SRIM is one triple energy port component and (ii) the proposed power conditioner is another triple energy port component. The SRIM device consists of (i) a mechanical energy port that is interfaced with the windmill shaft (ii) an AC port through the stator windings that is interfaced with the micro-grid/load and (iii) a third port which is also an AC port through the rotor windings of the SRIM that interfaces with an AC port of the proposed power conditioner. The proposed power conditioner is another triple energy port device which consists of (i) a DC energy port that interfaces with a battery/accumulator, (ii) an AC port that interfaces with the rotor windings of the SRIM and (iii) another AC port that generates the micro-grid that is connected to the load and the stator port of the SRIM. The proposed power conditioner provides the frame work for managing the energy flow from the mechanical port of the SRIM to the rotor and accumulator as well as from the mechanical port to the stator/load and accumulator. Further, energy interaction can also take place between the stator and the rotor externally through the power conditioner. The power interfaces on all three energy ports of the proposed power conditioner poses several challenges that have been discussed in this thesis. This thesis focuses on developing schemes to solve these challenges as explained below. Speed sensorless control is a natural choice for slip ring induction machine because of the flexibility of sensing both stator and rotor currents. There are different methods proposed in the literature which deal with the speed sensorless control of slip ring induction machine. However, the elimination of the measurement noise in the flux position estimation is not sufficiently addressed. It is important to address this issue as this would lead to deterioration in rotor side control of SRIM if the measurement noise is not eliminated. Primarily, the schemes which use algebraic relation between the estimated rotor current in stator reference frame and the sensed rotor current, are prone to measurement noise. On the other hand, the schemes, which use rotor back-emf integration, are affected by DC drift problems, though they are not much affected by measurement noise. The proposed stator flux position estimation scheme incorporates the benefits obtained from both the above schemes while eliminating the disadvantages inherent to them. The rotor flux position is estimated by integrating the rotor back-electromotive force. The stator flux is then obtained from the rotor flux estimate. This integration mechanism leads to several problems like dc drift and lack of error decaying mechanism. This estimation scheme solves the above problems including reduction in the propagation of noise in the sensed current to the estimated rotor side unit vectors. On the implementation front, this scheme also eliminates the need for differentiating the unit vectors for estimating slip frequency. This makes the proposed flux estimator very robust. The proposed scheme is simulated and experimentally verified. There is an internal DC bus within the proposed power conditioner that manages the energy flow through the three energy ports. The internal DC bus is interfaced to an external accumulator or battery through a power interface called the multi phase bi-directional dc-dc converter. It is generally advantageous to have the motor rated for higher voltages in order to achieve better efficiencies for a given power rating as compared to low voltage motors. This implies higher DC bus voltage. On the other hand, it is advantageous to have the battery bank rated for low voltage in order to improve the volumetric efficiency which is better at lower battery bank voltages. Both these are contradictory requirements. The above problem is solved in this thesis by proposing a multi power port topology using a bidirectional fly-back converter that is capable of handling multiple power sources and still maintain simplicity and features like high gain, wide load variations and lower output current ripple. As a spin-off, the scheme can handle parallel energy transfer from even a eutectic combination of batteries without any additional control circuitry for parallel operation. Further, the scheme also incorporates a novel transformer winding technique which significantly reduces the leakage inductance of the coupled inductor. The proposed multi-port bidirectional converter is analyzed by including non-idealities like leakage inductance. The DC bus voltage regulation requirement is not very stringent because it is not directly fed to any load. Therefore, hysteresis voltage regulation with small proportional correction is used for DC bus voltage control. The proposed converter is built and experimentally verified in the proposed system as well as in a hybrid-electric vehicle prototype. The third port of the proposed power conditioner interfaces with the stator of the SRIM and the load. The stator/load needs to be connected to a stiff micro-grid. The control requirement of the micro-grid is very stringent because, even for a sudden variation in the wind speed or the load, the grid voltage magnitude and frequency should not change. The dynamic response of the grid voltage controller has to be very fast. Moreover, the grid voltage must be balanced in presence of unbalanced loading. This thesis proposes a converter called the stator side converter along with three phase L-C filter at its output to form the micro-grid. A generalized control scheme is proposed wherein the negative sequence components and the harmonics can be eliminated at the micro-grid by means of feed-forward compensators included in the fundamental positive synchronous reference frame alone. The theoretical foundation for this scheme is developed and discussed in the thesis. In isolated locations linear loads constitute a significant percentage of the total load. Therefore, on the implementation front, only the compensation of fundamental negative sequence is demonstrated. One more necessity for compensating the fundamental negative sequence is that, the SRIM offers only leakage impedance to the fundamental negative sequence components resulting in high fundamental negative sequence current even for a small fundamental negative sequence voltage present at the micro-grid. The proposed scheme ensures balanced three phase currents at the SRIM windings and the full unbalanced current is provided from the stator side converter. This scheme is validated both by simulation and experimentation. The proposed power conditioner is integrated and used in the implementation of the entire wind power generation scheme that is proposed in the thesis. The maximum power point tracking of the wind power unit is also incorporated in the proposed system. The simulation and experimental results are also presented. Finally, the engineering issues involved in the implementation of the proposed scheme are discussed in detail highlighting the hardware configuration and the equipments used. The wind turbine is emulated using a chopper controlled DC motor. The shaft torque of the DC motor is controlled to give the Cp−λ characteristic of a typical windmill. The control issues of the DC machine to behave as a wind turbine are also explained. Finally the thesis is concluded by a statement of potentials and possibilities for future work in this research area.

Electric power has become a basic necessity of human life. The major share of electric power comes from fossil fuel which results in global warming and pollution. A share of generated power comes from nuclear power which is equally dangerous. Big hydro projects take away lots of fertile land. The continuous usage of fossil fuel also poses a threat of petroleum and coal getting over in the near future. The only way out of this energy scarcity is to depend more and more on renewable sources like solar, wind and micro-hydro. At present, instead of having preference over any particular source of renewable energy, effort should be made to extract power from every possible energy source available in whatever form it is and use it in an optimal way. Like any renewable energy sources, the wind power contains large potential for harnessing energy that has been well understood hundreds of years ago. The importance of wind power generation has come to focus recently both at installation and research level and lot of activities are being carried out for efficient use of wind energy. There are different types of wind turbine designs available in the literature. But the most commercially used model is the two or three blade horizontal axis propeller type wind turbine. Research has shown that variable speed operation of this type of turbine is advantageous over fixed speed operation in terms of total energy synthesis. The most commonly used machines for wind power conversion are synchronous machine, squirrel cage induction machine and slip ring induction machine (SRIM). Variable speed operation using synchronous machine or squirrel cage induction machine requires large ratings of the power converters. However, SRIM based variable speed wind generator is advantageous over other schemes due to its inherent advantages like lower power rating for the converters, higher energy capture and the flexibility of sharing reactive power between the stator and the rotor. SRIM is used for both grid connected and stand alone applications and have been reported in the literature. The grid connected applications have received major attention in the literature whereas there are only a very few instances of its stand alone counterparts. There are many places both within and outside India where utility grid has not yet reached or the available grid is very weak. Moreover, in many of the places, the transmission line is so long that the losses in the system are extremely high. Isolated wind power generation can be of great advantage in such places where the available wind power is harnessed and utilized locally. This has been the motivation to go for proposing an isolated wind power generation scheme in this thesis. The proposed scheme is designed to supply power to the load even when very low or no wind power is available. Therefore, a battery bank is also a part of the system. The power converter assembly of the proposed scheme has three major components. One is the rotor side converter which is connected to the rotor terminals of the SRIM. The second one is the stator side converter with output LC filter which is connected to the stator side. These two converters share a common DC link which is interfaced to the battery bank through a multi phase bi-directional fly-back DC-DC converter. Fig. 1. Overall block diagram of the proposed stand alone wind power generator Functionally, this thesis proposes a system as shown in Fig. 1, which has primarily two components with multiple energy ports viz. (i) the SRIM is one triple energy port component and (ii) the proposed power conditioner is another triple energy port component. The SRIM device consists of (i) a mechanical energy port that is interfaced with the windmill shaft (ii) an AC port through the stator windings that is interfaced with the micro-grid/load and (iii) a third port which is also an AC port through the rotor windings of the SRIM that interfaces with an AC port of the proposed power conditioner. The proposed power conditioner is another triple energy port device which consists of (i) a DC energy port that interfaces with a battery/accumulator, (ii) an AC port that interfaces with the rotor windings of the SRIM and (iii) another AC port that generates the micro-grid that is connected to the load and the stator port of the SRIM. The proposed power conditioner provides the frame work for managing the energy flow from the mechanical port of the SRIM to the rotor and accumulator as well as from the mechanical port to the stator/load and accumulator. Further, energy interaction can also take place between the stator and the rotor externally through the power conditioner. The power interfaces on all three energy ports of the proposed power conditioner poses several challenges that have been discussed in this thesis. This thesis focuses on developing schemes to solve these challenges as explained below. Speed sensorless control is a natural choice for slip ring induction machine because of the flexibility of sensing both stator and rotor currents. There are different methods proposed in the literature which deal with the speed sensorless control of slip ring induction machine. However, the elimination of the measurement noise in the flux position estimation is not sufficiently addressed. It is important to address this issue as this would lead to deterioration in rotor side control of SRIM if the measurement noise is not eliminated. Primarily, the schemes which use algebraic relation between the estimated rotor current in stator reference frame and the sensed rotor current, are prone to measurement noise. On the other hand, the schemes, which use rotor back-emf integration, are affected by DC drift problems, though they are not much affected by measurement noise. The proposed stator flux position estimation scheme incorporates the benefits obtained from both the above schemes while eliminating the disadvantages inherent to them. The rotor flux position is estimated by integrating the rotor back-electromotive force. The stator flux is then obtained from the rotor flux estimate. This integration mechanism leads to several problems like dc drift and lack of error decaying mechanism. This estimation scheme solves the above problems including reduction in the propagation of noise in the sensed current to the estimated rotor side unit vectors. On the implementation front, this scheme also eliminates the need for differentiating the unit vectors for estimating slip frequency. This makes the proposed flux estimator very robust. The proposed scheme is simulated and experimentally verified. There is an internal DC bus within the proposed power conditioner that manages the energy flow through the three energy ports. The internal DC bus is interfaced to an external accumulator or battery through a power interface called the multi phase bi-directional dc-dc converter. It is generally advantageous to have the motor rated for higher voltages in order to achieve better efficiencies for a given power rating as compared to low voltage motors. This implies higher DC bus voltage. On the other hand, it is advantageous to have the battery bank rated for low voltage in order to improve the volumetric efficiency which is better at lower battery bank voltages. Both these are contradictory requirements. The above problem is solved in this thesis by proposing a multi power port topology using a bidirectional fly-back converter that is capable of handling multiple power sources and still maintain simplicity and features like high gain, wide load variations and lower output current ripple. As a spin-off, the scheme can handle parallel energy transfer from even a eutectic combination of batteries without any additional control circuitry for parallel operation. Further, the scheme also incorporates a novel transformer winding technique which significantly reduces the leakage inductance of the coupled inductor. The proposed multi-port bidirectional converter is analyzed by including non-idealities like leakage inductance. The DC bus voltage regulation requirement is not very stringent because it is not directly fed to any load. Therefore, hysteresis voltage regulation with small proportional correction is used for DC bus voltage control. The proposed converter is built and experimentally verified in the proposed system as well as in a hybrid-electric vehicle prototype. The third port of the proposed power conditioner interfaces with the stator of the SRIM and the load. The stator/load needs to be connected to a stiff micro-grid. The control requirement of the micro-grid is very stringent because, even for a sudden variation in the wind speed or the load, the grid voltage magnitude and frequency should not change. The dynamic response of the grid voltage controller has to be very fast. Moreover, the grid voltage must be balanced in presence of unbalanced loading. This thesis proposes a converter called the stator side converter along with three phase L-C filter at its output to form the micro-grid. A generalized control scheme is proposed wherein the negative sequence components and the harmonics can be eliminated at the micro-grid by means of feed-forward compensators included in the fundamental positive synchronous reference frame alone. The theoretical foundation for this scheme is developed and discussed in the thesis. In isolated locations linear loads constitute a significant percentage of the total load. Therefore, on the implementation front, only the compensation of fundamental negative sequence is demonstrated. One more necessity for compensating the fundamental negative sequence is that, the SRIM offers only leakage impedance to the fundamental negative sequence components resulting in high fundamental negative sequence current even for a small fundamental negative sequence voltage present at the micro-grid. The proposed scheme ensures balanced three phase currents at the SRIM windings and the full unbalanced current is provided from the stator side converter. This scheme is validated both by simulation and experimentation. The proposed power conditioner is integrated and used in the implementation of the entire wind power generation scheme that is proposed in the thesis. The maximum power point tracking of the wind power unit is also incorporated in the proposed system. The simulation and experimental results are also presented. Finally, the engineering issues involved in the implementation of the proposed scheme are discussed in detail highlighting the hardware configuration and the equipments used. The wind turbine is emulated using a chopper controlled DC motor. The shaft torque of the DC motor is controlled to give the Cp−λ characteristic of a typical windmill. The control issues of the DC machine to behave as a wind turbine are also explained. Finally the thesis is concluded by a statement of potentials and possibilities for future work in this research area.

博士
國立清華大學
電機工程學系
103
This dissertation is aimed at the development and operation controls of a DC micro-grid powered by wind permanent-magnet synchronous generator (PMSG) and DC source with hybrid energy storage devices. The DC sources are interfaced to the common DC bus via an interleaved DC/DC boost converter. As to the wind PMSG, after exploring the derated characteristics of PMSG systems with various AC/DC converters, a three-phase Vienna switch-mode rectifier (SMR) is developed as its interface to establish the common DC bus voltage of DC micro-grid. Its developed power is improved by proper commutation tuning and robust controls. The possible harvested DC or AC sources can be interfaced to the DC micro-grid via the embedded circuit components of Vienna SMR. Since the generating powers from various sources in a micro-grid are unpredictable and fluctuated, energy storage buffer is required to improve its power supplying quality. In the developed micro-grid, the battery/flywheel/super-capacitor hybrid energy storage system with bidirectional DC/DC interface converters is developed. And the droop control approach with adaptive predictive current control is proposed to yield good energy storage support control characteristics. Moreover, a chopped resistive dump load is equipped to regulate the energy balance when system energy surplus occurs. In test load arrangement, a single-phase three-wire (1P3W) inverter is established to yield 60Hz 220V/110V AC voltages for powering the home appliances. Good sinusoidal output voltage waveforms and dynamic responses due to load and DC-bus voltage changes are obtained by the proposed robust control schemes. When the renewable energy is surplus or insufficient, the microgrid-to-grid (M2G)/grid-to-microgrid (G2M) bidirectional operations can be also conducted by the established 1P3W inverter. Moreover, the bidirectional inter-connected operations between the developed micro-grid and the electric vehicle (M2V/V2M) can also be applicable. In addition, various motor drives, lighting devices and DC converter fed loads can be directly powered from the DC bus of the established micro-grid.

碩士
東吳大學
資訊管理學系
104
In recent years, researchers have indicated that using Mindtools as mobile learning strategies is effective for improving students’ learning achievement. Researchers have further identified that learning in an authentic environment with quality knowledge constructional supports can engage students in thorough observations and knowledge construction. Grid-based knowledge constructional tools such as repertory grid enables students to compare the characteristics and its value of learning targets in Natural Science course. Although researchers have identified the effectiveness of Mindtools, many students may not aware the whole knowledge structure when they are creating grid-based Mindtools. To cope with the problem, this study integrated the concept map-based global view and knowledge grid-based micro view into a ubiquitous peer-assessment model, which allows students to reinforce the overall understanding of attributed features of learning contents. From the experimental results, it was found that the proposed ubiquitous peer-assessment model not only significantly promoted the students’ learning motivation, self-efficacy, and collaborative learning ability, but also improved their learning achievement. Moreover, the quality of experimental students’ knowledge grid is significantly better than those in the control group.