Dissertations / Theses on the topic 'Active Phase Converter (APC)'

The dissertation presents a generalized average-current-mode control technique (GACMC), which is an extension of the average-current-mode control (ACMC) for single-phase ac-dc boost converters with power factor correction (PFC). Traditional ACMC is generalized in a sense that it offers improved performance in the form of significant reduction of the current control loop bandwidth requirement for a given line frequency in unidirectional and bidirectional boost PFC converters, and additional functionality in the form of reactive power control capability in bidirectional converters. These features allow using a relatively low switching frequency and slow-switching power devices such as insulated-gate bipolar transistors (IGBTs) in boost PFC converters, including those designed for higher ac line frequencies such as in aircraft power systems (360â 800 Hz). In bidirectional boost PFC converters, including multilevel topologies, the GACMC offers a capability to supply a prescribed amount of reactive power (with leading or lagging current) independently of the dc load power, which allows the converter to be used as a static reactive power compensator in the power system.

A closed-loop dynamic model for the current control loop of the boost PFC converter with the ACMC has been developed. The model explains the structure of the converter input admittance, the current phase lead phenomenon, and lays the groundwork for development of the GACMC. The leading phase admittance cancellation (LPAC) principle has been proposed to completely eliminate the current phase lead phenomenon and, consequently, the zero-crossing distortion in unidirectional converters. The LPAC technique has been adapted for active compensation of the input filter capacitor current in bidirectional boost PFC converters.

The dynamic model of the current control loop for bidirectional boost PFC converters was augmented to include a reactive power controller. The proposed control strategy enables the converter to process reactive power and, thus, be used as a reactive power compensator, independently of the converter operation as an ac-dc converter.

Multiple realizations of the reactive power controller have been identified and examined in a systematic way, along with their merits and limitations, including susceptibility to the ac line noise. Frequency response characteristics of reactive elements emulated by means of these realizations have been described.

Theoretical principles and practical solutions developed in this dissertation have been experimentally verified using unidirectional and bidirectional converter prototypes. Experimental results demonstrated validity of the theory and proposed practical implementations of the GACMC.
Ph. D.

Multi-pulse converters have been widely used for a multi-megawatt scale power generating system to comply with harmonic regulations. Among all types of multi-pulse converters, a 12-pulse converter is the most widely used due to the simple structure, which consists of a delta-delta and a delta-wye phase-shift transformer pair and it effectively mitigates undesirable harmonics from the nonlinear load. In the early 2000s, a shunt type passive front-end for a shipboard power system was proposed. By shunting the two gensets with 30° phase angle difference, a single phase-shift transformer effectively eliminates 5th and 7th harmonics. It achieves a significant size and weight reduction compared to a 12-pulse converter while keep the comparable harmonic cancellation performance. Recently, a hybrid type front-end was proposed. On top of the passive front-end, 3 phase active power filter was added and an additional harmonic cancellation was achieved to further eliminate 11th and 13th harmonics. However, the performance of both the passive and hybrid type front-end are highly dependent on the size of the line reactor in ac mains. A back to back active power filter is proposed in this dissertation to replace the phase-shift transformer in the multi-generator power architecture. The proposed front-end does not include phase-shift transformer and the size and the weight of the overall front-end can be significantly reduced. Due to the active harmonic compensation, the back to back front-end achieves better power quality and the line reactor dependency is improved. The number of required dc-link capacitors is reduced by half by introducing a back to back configuration and the capacitor size is reduced by adjusting the phase angle difference of genset to cancel out the most significant voltage harmonics in the shared dc-link bus. The overview of the existing shunt type front-end is provided and the concept of back to back active power filter is validated by simulation and prototype hardware. The comparison between existing front-end and the proposed front-end is provided to highlight the superior performance of back to back active front-end. The dc-link bus current and voltage ripple analysis is provided to explain the dc-link ripple reduction mechanism.
Doctor of Philosophy
The transportation electrification has gained more and more attention due to its smaller carbon dioxide emission, better fuel efficiency. The recent advances in power devices, microcontrollers, and transducers accelerate the electrification of transportation. This trend is shown in the propulsion system in marine transport as well and the electric propulsion system has been widely used to meet the strict environmental regulations. However, the non-linear circuit components such as capacitor and diode in the electric propulsion system draw non-linear current and significantly deteriorate power quality and lead to critical problems such as reduced life span of circuit components Accordingly, a front-end is required to improve power quality. Also, it is desired to have compact and lightweight front-end for installation flexibility and fuel efficiency improvement. In this dissertation, several front-ends using a phase-shift transformer are reviewed and a detailed analysis is provided to help understand the harmonic cancellation principle of the existing front-end through equivalent circuit analysis, quantitative analysis, and a phasor diagram representation. Based on the analysis of the existing front-ends and shipboard power architecture, lightweight and high-performance front-end is proposed and verified by simulation and prototype hardware. The performance, size comparison between existing front-end and the proposed front-end is provided to show the advantage of the proposed front-end.

The Diploma thesis deals with control of three-phase active rectifier and a three-phase DC/AC converter. It also explains phase-locked loop principle. The theoretical part including first three chapters lists several control approaches to three phase active rectifier and three phase DC/AC converter. Described control approaches to the active rectifier are control in dq frame and control in dq UVW frame. Listed control approaches to the DC/AC converter include cascaded control structure and a full state feedback control. The practical part is divided into last three chapters and includes mathematical description of phase-locked loop principle, model of active rectifier controlled in dq frame and a model of DC/AC converter controlled both by a cascaded control and a full¬ state feedback. The models are created in Matlab Simulink.

Dans une large variété d'applications industrielles, il existe une demande croissante pour améliorer la qualité de l'énergie fournie par les systèmes électriques. En plus de la fiabilité et de la disponibilité d'énergie électrique, la qualité de la puissance fournie devient maintenant une question importante. Parmi les causes de la pauvre qualité de puissance, les harmoniques sont considérés comme la raison qui contribue à la majorité de pannes de courant. Beaucoup d'efforts ont été développés pour résoudre le problème des perturbations harmoniques comme, par exemple, installer des dispositifs spéciaux tels que les filtres actifs. Ce travail de thèse traite le développement d’une commande directe de puissance utilisant l'approche prédictive hybride. La commande hybride considère chaque vecteur de tension du convertisseur comme une entité discrète qui sera appliquée pour commander un système linéaire continu. Un critère pour calculer le vecteur optimal de tension à appliquer sera établi à partir d’un modèle prédictif. Le vecteur optimal de tension à appliquer pour chaque période de commutation, et le correspondant temps d'application seront utilisés pour approcher la valeur réelle des variables d'état du système au point de référence désiré. Deux théories de puissance instantanées seront employées, p-q et p-q-r, pour une application de filtre active parallèle de puissance dans un système triphasé de 4 fils. Ces théories instantanées de puissance ont été développées pour être appliquées aux systèmes non équilibrés utilisant les variables de puissance pour obtenir les courants qui devraient être injectés par le filtre actif. Le filtre actif produira la puissance réactive demandée par la charge et compensera la composante d'ondulation de la puissance active de sorte que la source livre seulement la puissance active constante
In a wide variety of industrial applications, an increasing demand exists to improve the quality of the energy provided by electrical systems. Besides the reliability and availability of electric power, the power quality is now becoming an important issue. Among the causes of the poor power quality, the harmonics are included as the reason which contributes the majority of power failures. Many efforts have been developed to solve the harmonics problem as, for instance, to install special devices such as active filters. This research work deals with the development of direct power control using the hybrid predictive control approach. The hybrid control considers each voltage vector of the converter as a discrete entity which will be applied to control a continuous linear system. One criterion to calculate the optimal voltage vector to apply will be established for the predictive control model. The optimal voltage vector to apply for each switching period, and the corresponding application time will be used to approach the actual value of the state variables of the system to the desired reference point. Two instantaneous power theories will be used, i.e. pq0 and pqr instantaneous power theory for a shunt active power filter application implemented in 3-phase 4-wire system. These instantaneous power theories have been developed to be applied to unbalanced systems using the power variables to obtain the currents that should be injected from active filters. The active filter will produce the required reactive power for the load and compensate the ripple component of active power so that the source only delivers constant active power

Isolated DC-DC converters play a significant role in fast charging and maintaining the variable output voltage for EV applications. This study aims to investigate the different Isolated DC-DC converters for onboard and offboard chargers, then, once the topology is selected, study the control techniques and, finally, achieve a real-time converter model to accomplish Hardware-In-The-Loop (HIL) results. Among the different isolated DC-DC topologies, the Dual Active Bridge (DAB) converter has the advantage of allowing bidirectional power flow, which enables operating in both Grid to Vehicle (G2V) and Vehicle to Grid (V2G) modalities. Recently, DAB has been used in the offboard chargers for high voltage applications due to SiC and GaN MOSFETs; this new technology also allows the utilization of higher switching frequencies. By empowering soft switching techniques to reduce switching losses, higher switching frequency operation is possible in DAB. There are four phase shift control techniques for the DAB converter. They are Single Phase shift, Extended Phase shift, Dual Phase shift, Triple Phase shift controls. This thesis considers two control strategies; Single-Phase, and Dual-Phase shifts, to understand the circulating currents, power losses, and output capacitor size reduction in the DAB. Hardware-In-The-Loop (HIL) experiments are carried out on both controls with high switching frequencies using the PLECS software tool and the RT box supporting the PLECS. Root Mean Square Error is also calculated for steady-state values of output voltage with different sampling frequencies in both the controls to identify the achievable sampling frequency in real-time. DSP implementation is also executed to emulate the optimized DAB converter design, and final real-time simulation results are discussed for both the Single-Phase and Dual-Phase shift controls.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.12 – напiвпровiдниковi перетворювачі електроенергії. − Національний технічний університет "Харківський політехнічний інститут", Харків, 2016. Дисертація присвячена розробці високоефективних та енергозберігаючих напівпровідникових перетворювачів для застосування в нових та перспективних системах електропостачання. Розроблено напівпровідниковий перетворювач з фазовий способом керування для перспективної системи електропостачання FREEDM, який виконує аналогічні функції наявного в цій системі перетворювача і дозволяє отримати кращі енергетичні показники за рахунок зниження комутаційних втрат за допомогою м'якої комутації на основній частоті 50 Гц. Запропонований фазовий спосіб керування заснований на симетричному розладі резонансу і введенні регульованого фазового зсуву між напругами на вході силового напівпровідникового комутатора і мережі змінного струму. У дисертаційній роботі запропонована методика розрахунку основних параметрів перетворювача, проаналізовано якість його роботи, за допомогою комп'ютерного моделювання досліджено однофазна і трифазні схеми перетворювача в різних режимах роботи, а також запропоновані способи захисту від аварійних режимів. Експериментальні дослідження на фізичної моделі підтвердили достовірність теоретичних результатів.
Dissertation on competition degree of candidate of technical sciences of speсiality 05.09.12 – Semiconductor converters of electric energy. – National Technical University "Kharkov Politechnical Institute", Kharkov, 2016. Dissertation is devoted to development of high-performance and energy-saving semiconductor converters for applications in new and perspective power systems. Developed semiconductor converter with phase control method for forwardlooking FREEDM electrical system is presented. It is shown that that converter performs the same functions available in the converter of this system and allows to obtain the best energy performance by reducing switching loss using soft switching at the fundamental frequency 50 Hz. It is demonstrated that the proposed phase control method is based on the symmetric detuning of the resonance and the introduction of a controlled phase shift between the voltages at the input of the power semiconductor switch and the AC mains. In the dissertation a method of calculating the basic converter settings is proposed. The quality of his work is analyzed. With the help of computer simulations single and three phase converter circuit in different operating modes are studied. The methods of protection from emergency modes are proposed. Experimental studies on the physical model confirmed the accuracy of the theoretical results.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.12 – напiвпровiдниковi перетворювачі електроенергії. − Національний технічний університет "Харківський політехнічний інститут", Харків, 2016. Дисертація присвячена розробці високоефективних та енергозберігаючих напівпровідникових перетворювачів для застосування в нових та перспективних системах електропостачання. Розроблено напівпровідниковий перетворювач з фазовий способом керування для перспективної системи електропостачання FREEDM, який виконує аналогічні функції наявного в цій системі перетворювача і дозволяє отримати кращі енергетичні показники за рахунок зниження комутаційних втрат за допомогою м'якої комутації на основній частоті 50 Гц. Запропонований фазовий спосіб керування заснований на симетричному розладі резонансу і введенні регульованого фазового зсуву між напругами на вході силового напівпровідникового комутатора і мережі змінного струму. У дисертаційній роботі запропонована методика розрахунку основних параметрів перетворювача, проаналізовано якість його роботи, за допомогою комп'ютерного моделювання досліджено однофазна і трифазні схеми перетворювача в різних режимах роботи, а також запропоновані способи захисту від аварійних режимів. Експериментальні дослідження на фізичної моделі підтвердили достовірність теоретичних результатів.
Dissertation on competition degree of candidate of technical sciences of speсiality 05.09.12 – Semiconductor converters of electric energy. – National Technical University "Kharkov Politechnical Institute", Kharkov, 2016. Dissertation is devoted to development of high-performance and energy-saving semiconductor converters for applications in new and perspective power systems. Developed semiconductor converter with phase control method for forwardlooking FREEDM electrical system is presented. It is shown that that converter performs the same functions available in the converter of this system and allows to obtain the best energy performance by reducing switching loss using soft switching at the fundamental frequency 50 Hz. It is demonstrated that the proposed phase control method is based on the symmetric detuning of the resonance and the introduction of a controlled phase shift between the voltages at the input of the power semiconductor switch and the AC mains. In the dissertation a method of calculating the basic converter settings is proposed. The quality of his work is analyzed. With the help of computer simulations single and three phase converter circuit in different operating modes are studied. The methods of protection from emergency modes are proposed. Experimental studies on the physical model confirmed the accuracy of the theoretical results.

This work is focused on innovative construction of the industrial radial sealless pump and mainly on construction of the three phase DC/AC converter based on new semiconductor technology SiC. These new semiconductor devices allow move switching frequency up to 100 kHz. For such high switching frequency new non-conventional topology of the output filter was designed. This high frequency is currently unusual in three-phase application with output voltage 400V. High switching frequency reduces size of wound components of the output filter and its presence is accepted in terms of total weight and price of the whole system. Clear sinus waveform of the output converter voltage reduces torque ripple, EMC and extend the lifetime and reliability of mechanical parts and the whole pump drive. Three phase synchronous motor is directly placed into the pump body and is designed as slotless motor. In the inlet area is the classical bearing replaced by active magnetic bearing. It is used due to possibility to pump aggressive liquids or substances where high level of cleanness has to be guaranteed.

Single-phase distribution is a preferred approach for setting up microgrids or supplying power to rural and remote locations due to its lower infrastructure costs when compared to a three-phase grid. On the other hand, three-phase induction machines exhibit smooth torque-speed characteristics, offer better starting torque, have higher power density and are of lower cost compared to their single-phase counterparts. Due to the modernization of the technologies used in agriculture and mechanization of production processes, the demand for electrical energy on single-phase distribution grid has increased considerably in the past decade. However, the sole availability of single-phase power limits the usage of three-phase induction motors in certain applications such as auxiliary services in rail- ways, pumps or mills in the agricultural sector and in small urban and rural industries. Conventionally, power electronics based double-conversion drive systems are available that power three-phase machines with single-phase supply. However, inexpensive and low-efficiency power conversion solutions are often adopted to achieve cost benefits at the expense of performance and power quality. In this context, there is a need for power electronic phase converters that facilitate the use of three-phase induction machines on the single-phase grid while offering high performance at low cost. This work investigates reduced switch-count active phase converters (APC) that serve three-phase loads from a single-phase grid. Specifically, the focus is on topologies that process only a fraction of the load power while still maintaining the quality of power at the grid and load ends. An auxiliary capacitor based active phase converter (AC- APC) topology is shown to have reduced current stress in the switching devices and the dc-link capacitors. At the rated load of 3.3 kVA/0.8 pf, the total VA processed by the semiconductor devices of the conventional topology is 180% of the load VA. Whereas the semiconductor VA of the APC and AC-APC in the experimental prototype are 88% and 40% respectively. Analytical power loss evaluation shows that the device power loss at rated conditions for the APC and AC-APC are 46% and 18% respectively, of that of a conventional double conversion con figuration. Moreover, 50% reduction in the double frequency dc-link ripple is observed in the experimental prototype of AC-APC when compared to that of a standard APC at rated load. The proposed control structure allows asymmetric control of the three legs of the APC. It also facilitates independent selection of optimized components for higher order filters, to meet the independent design requirements at the grid and the load. The control to generate modulation signals for the APC with a shared leg is implemented as two decoupled single-phase converter controllers. A method for soft-starting an induction motor is incorporated in the APC. Moreover, the bidirectional power ow capability of the APC also facilitates injection of power to a single-phase grid. A common-mode filter and its design method are presented for the asymmetric APC, which significantly reduces the effects of common-mode voltage in the system. All the methods proposed in this work are validated on an experimental 5 kVA laboratory converter prototype.

The single phase converters are inherently exposed to the pulsating power. The conventional approach to supply this pulsating power is to use a huge Electrolytic capacitor. However, Electrolytic capacitors with high failure rate brings down the overall system lifetime. The Active Power Decoupling (APD) approaches using a set of switches to control the voltage across the storage capacitor, reduces the capacitance requirement many fold. Thereafter, film capacitors, with higher life time, are used to replace the Electrolytic ones. Among many active solutions proposed in the literature, the AC decoupling topologies, stand out due to their adaptability to high power converter. However, the available solutions lead to excessive voltage and current stress on the switches for the applications involving wide range of power factor (PF). Moreover, when the converter supplies the local non-linear load, the power profile contains even order harmonics other than the double frequency component. Therefore, the converter should now be equipped with the control strategy to supply these harmonic powers as well. The present work aims to address the above mentioned issues. First, an APD scheme is proposed which is suitable for high power application and works seamlessly for any PF without overstressing the switches. The proposed topology achieves upto 57% reduction in average curent stress and 41% reduction in DC bus voltage requirement when compared with the existing solutions available. Second, a robust control structure ensuring a stable operation of the converter is developed. With the proposed control, the fundamental control issue of controlling two states with a single control variable is resolved. Also, the control takes care of practical issues suh as model uncertainty, arising out of the component tolerance, drifts etc.. Finally, a control strategy is developed to compensate selected harmonics from the DC bus in presence of non-linear loads. The generation of reference involves simultaneous solution of a set of non-linear equations. The proposed solution achieves the desired harmonic performance with reduced RMS current in the APD branch. In summary, an APD topology with least switch-stress has been proposed, which works seamlessly for any PF. Also, several robust control mechanisms are devised for the situations like system with more states (uncontrollable), polluted grid and non-linear loads

碩士
國立臺灣海洋大學
電機工程學系
103
Many of power stages work together, there are two kinds method to operating, one of method is in series connection, the other one is parallel connection. If we want to achieve higher output power efficience, we always use the way of paralleling connection, the main of topic in this paper will discuss that use the way of paralleling power stages to increase efficience in the whole of circuit, and complete to the work of power factor correction. Paralleling power stage A method to achieve the desired current sharing is with equalizing resistors, what it means power losses, or connecting converters with high impedance. In this work has been studied that input impedance of active clamp boost converters can work as a lossless equalizing resistor to achieve current sharing and benefits of soft switching can be added to the benefits of parallel association.

碩士
南臺科技大學
電機工程系
106
This thesis proposed a dual phase-shift control method for bidirectional three port full-bridge converter applications. Comparing with the single phase-shift control method, the dual phase-shift strategy is capable of reducing the circulating current, therefore suppressing the reactive power to improve the overall efficiency as well as reducing the current stress of the converter. At first, this thesis adopted the symmetric phase-shift modulation strategy based dual-phase shift control method to the bidirectional dual active bridge (DAB) converter application. Secondly, a three-port isolated full-bridge converter is structured by integrating the DC bus, the battery, and the load. The energy is capable of transferring among these three ports without going through two stages of DC-to-DC conversion processes. In addition, this structure is with the ability of solving the intermittent problem of renewable energy source. Finally, a bidirectional active bridge-to-DC converter and a three-port isolated full-bridge DC-DC converter with power rating of 500W are set to verify the feasibility of the proposed dual-phase shift control method.

碩士
國立中山大學
電機工程學系研究所
102
Recently, the development of electric vehicles (EVs) is valued, and the battery charger is the core of the development of EVs. Therefore, a requirement of the bidirectional power converter is increased. In the thesis, a three-phase dual-active-bridge bidirectional DC converter with a pack of 48V/20AH LiFePO4 batteries is developed to implement a charging/discharging EV battery system. To improve efficiency of the converter, a hybrid modulation is proposed and used to boost efficiency under the light-load condition. A charging/discharging strategy of battery is planned by analysis of the modulation, and validate effectiveness of the strategy was verified from experimeantal results. Finally, the LabVIEW graphical software and CAN-bus protocol are used to produce the current command, which is sent into a digital signal process (DSP) to realize the control of the converter.

碩士
東南科技大學
電機工程研究所
98
This thesis proposes a novel single phase inverter based on the active clamp forward converter technique. First, an active clamp forward converter is used to boost the DC input voltage and to output a sinusoidal full-wave rectifier type voltage. Then the full bridge switches circuit of the inverter changes the polar of the output voltage by controlling the states of the switches to output an AC sinusoidal voltage. The active clamp forward converter has the advantages of simple structure, small size, and low switching los. Moreover, because the switches of the full bridge circuit are used to change the polar of the output voltage, the switching frequency and switching loss are low, so that the output efficiency of the inverter is high. Next, the exactitude of the control circuits was validated by using the simulation. Moreover, an active clamp forward inverter is actually implemented. A Texas Instruments digital signal processor, TMS320F2808, is used to execute the control scheme and control the driving signal. As a result, a fully digital control system is realized to reduce the hardware circuits. Finally, the experimental results can validate the exactitude and the practicability of proposed circuit.

碩士
國立臺灣科技大學
電子工程系
106
The main purpose of this paper is to develop a solid-state transformer using an active dual-bridge converter architecture. Conventional transformers have many problems due to their operation in low-frequency voltages, such as large size and heavy weight. Therefore, new transformers need to be developed to replace them. In this paper, an AC-AC solid-state transformer with an input voltage of 300 Vrms maximum, an output voltage of 300 Vrms and an output power of 5 kW is actually completed. The power circuit mainly includes an active double-bridge converter, and the input voltage value is detected by the phase-locked loop as a reference command for the controller to stabilize the output voltage, and the transformer function is realized by the digital signal processor. Realize digital closed loop control. The experimental results show that the solid-state transformer can effectively stabilize the output voltage equal to the corresponding input voltage under different voltage input conditions, and the efficiency is above 92% under different loads.

碩士
國立臺灣科技大學
電子工程系
105
Full-bridge phase-shift converter has the merit of zero-voltage switching (ZVS) which can reduce the switching loss and the high frequency noise interference. However, there will be voltage spike induced on the secondary side synchronous rectification MOSEFTs. This thesis presents the study upon an active snubber circuit which is designed to reduce the spike. This active snubber is compared with the well-known RC and RCD passive snubbers. The stray energy on the secondary-side is restored to the snubber capacitors, then the snubber transfers the stored energy back to the primary-side. Due to the energy retrieval, the active snubber circuit surpasses the passive counterpart on energy efficiency. Besides, the voltage stress on the synchronous rectification MOSFETs is lowered benefited from the spike reduction; the MOSFET conduction resistance i.e. the conduction loss can also be reduced. That is, the power efficiency is further improved by the application of the active snubber.

碩士
中原大學
電機工程研究所
92
This paper presents the design, experimental results and analysis of an active power factor correction on full bride phase shift inverter, it gives a steady power, low harmonics and high power factor system. And the inverter achieves the Zero-Voltage Switching (ZVS) for reducing power lost. Finally, we could get the power system (include power factor correction) is better than one (include variable transformer) from experimental results, validate the feasibility of the implemented system in high power application.

This thesis presents a novel, fast, and accurate 3 steady-state power-flow analysis (PFA) tool for the real-time operation of the active distribution systems, also known as the active distribution networks (ADN), in the grid-tied and islanded operating modes. Three-phase power-flow models of loads, transformers, and multi-phase power lines and laterals are provided. This thesis also presents novel steady-state, fundamental-frequency, power-flow models of voltage-sourced converter (VSC)-based distributed energy resource (DER) units. The proposed models address a wide array of DER units, i.e., (i) variable-speed wind-driven doubly-fed asynchronous generator-based and (ii) single/three-phase VSC-coupled DER units. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host DER unit within the context of the developed PFA tool. Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed DER models represent (i) the salient VSC control strategies and objectives under balanced and unbalanced power-flow scenarios and (ii) all the operating limits and constraints of the VSC and its host DER unit. Also, the slack bus concept is revisited, associated with the PFA, where a 3 distributed slack bus (DSB) model is proposed for the PFA and operation of islanded ADNs. Distributing the real and reactive slack power among several DER units is essential to provide a realistic power-flow approach for ADNs in the absence of the utility bus. The proposed DSB model is integrated with the developed 3 PFA tool to form a complete ADN PFA package. The new PFA tool, including the proposed DER and DSB models, is tested using several benchmark networks of different sizes, topologies, and parameters. Many case studies, encompassing a wide spectrum of DER control specifications and operating modes, are conducted to demonstrate (i) the numerical accuracy of the proposed models of the DER units and their operating constraints, (ii) the effectiveness of the proposed DSB model for the islanded ADN PFA, and (iii) the computational efficiency of the integrated PFA software tool irrespective of the network topology and parameters.

碩士
國立臺灣科技大學
電子工程系
105
This thesis presents a three-phase wye-delta connected dual active bridge (DAB) DC-DC converter. This topology suits high input voltage and high output current applications very well. The power stage consists of three wye-delta connected transformers, three half-bridge switches in each side of the transformers, and three resonant tanks. Compared to single-phase full-bridge converter, three transformers can share the output power; furthermore, with the feature of wye-delta connection, the turns of high voltage winding and wire gauge of high current winding can be reduced. Thus, the size of transformers can be shrunk. The control signals of primary side and secondary side are 120 phase shifted between each leg of the three phases. And the power of converter is controlled by phase-shift control between primary side and secondary side. In addition, every switch can achieve zero-voltage-switching (ZVS). This thesis will introduce DAB converter first. And then, studies the characteristic of three-phase transformers and operation states of three-phase wye-delta connected DAB DC-DC converter. The power transfer function and soft-switching conditions are included. Finally, a laboratory prototype with 2 kW rated power output is built and tested. The measured efficiency is above 90  under a range of load conditions and all the switches can achieve ZVS.

碩士
國立雲林科技大學
電機工程系碩士班
91
This thesis presents a DSP-based fully digital-controlled single-phase power factor converter (PFC). The proposed PFC controller consists of an inner current-loop controller and an outer voltage-loop controller. The current-loop controller adopts hysteresis current control to achieve power factor correction. The voltage-loop controller employs a PI controller to achieve output voltage regulation. This paper adopts TMS320F240 digital signal processor (DSP) as the controller to achieve high power factor, low steady-state error, output voltage regulation, phase- locked loop and parallel operation. Finally, an experimental test was carried out on a 500 W PFC converter using DSP controller and the experimental results verify the feasibility and superiority of the proposed digital AC/DC converter.

AC-DC converters find application in every day life as a front-end to DC-DC and DC-AC converters. Active three-phase converters shape the three-phase input current to be sinusoidal and to be in-phase with the input voltage, as well as to provide a steady DC output voltage. This thesis investigates various active three-phase rectifier and control topologies and identifies a rectifier and control topology most suitable for use in converting a variable voltage variable frequency generator output to a DC voltage. In this dissertation, design relations are derived for determining the plant transfer response (for the suitable topology/controller), design equations are derived for designing/choosing the filter components, and guidelines are derived that will assist in choosing the right semi-conductor components and to give an estimation of expected system efficiency. The dissertation investigates the implementation of both analogue and digital control and provides implementation methodologies for both controllers. Expected results are verified by simulation and a build-up prototype. It was shown that the VIENNA rectifier is able to convert a generator type input, with variable input voltage amplitude and variable frequency, to a constant DC-bus voltage whilst controlling the input current to be sinusoidal and in phase with the input voltage. The rectifier was able to maintain a constant DC voltage at the output for input voltages as low as half the rated input voltage and for an equivalent output power of half the rated output power. This suggests that the VIENNA rectifier, controlled as a dual-boost rectifier, is suitable for applications that require power factor corrections and simultaneously operate from a wide input voltage range.
Dissertation (MEng (Electrical Engineering))--University of Pretoria, 2007.
Electrical, Electronic and Computer Engineering
MEng
unrestricted

碩士
國立臺灣科技大學
電機工程系
100
The subject of this thesis is to eliminate harmonics of the overall input line current in a 24-pulse converter system. The proposed structure applies two identical side-extended transformers with three-phase input voltage source in reverse order, so that four sets of voltage source with 15 degrees phase-shift are generated, and then sent into 6-pulse converters. The 24-pulse converter system is composed of four 6-pulse converters which connected by inter-phase transformers. While the proposed system works as a 24-pulse converter, all harmonics are eliminated except the 24n±1th, the characteristic harmonic. The two first-stage IPTs add the secondary winding to be an active IPT, and the overall input line conditions is improved by injecting compensation current into the secondary winding with a current-controlled inverter. This thesis proposed a compensation strategy to reduce the 24n±1th harmonic, moreover, the strategy also overcomes the total harmonic distortions caused by unbalance impedance of side-extended transformers, and the unbalanced factor of input line currents can be improved, too. A 6 kW prototype is built for test. Both simulation and experimental results demonstrate the validity of the proposed scheme.

博士
國立臺灣科技大學
電子工程系
107
The operations of the proposed three-phase wye-delta connected dual-active-bridge Series Resonant DC-DC Converter can be under either phase-shift (PS) mode or variable-frequency (VF) mode. For VF mode operation, The primary side Y-connected switch has zero voltage switching (ZVS), and the secondary side is -connected with a low switching loss, thus reducing switching losses and improving conversion efficiency. On the other hand, the PS mode operation with fixed switching frequency in inductive. Improve the problem of no-load distortion of the output voltage of the resonant circuit. Circuit principles and design procedures are presented and verified by the simulations and experimental results. Finally, a laboratory prototype with 2.2 kW rated power output is built and tested. Compare the efficiency of the two modes before light load, The measured efficiency is above 90 .

Dissertação de mestrado em Engenharia Eletrónica Industrial e de Computadores
Hoje em dia, devido à utilização massiva de cargas não lineares pelos consumidores em geral, tem aumentado progressivamente o conteúdo harmónico nas formas de onda das correntes, que, por sua vez, provocam quedas de tensão nas impedâncias das linhas, contribuindo para o aumento do conteúdo harmónico das tensões na rede elétrica. Como resultado, cada vez mais a rede elétrica apresenta baixos índices de qualidade de energia elétrica. O projeto em que esta dissertação está enquadrada consiste no desenvolvimento de um condicionador da qualidade de energia unificado (unified power quality conditioner - UPQC) trifásico com interface, através do barramento cc, a uma fonte de energia renovável e a um sistema de armazenamento de energia. O UPQC desenvolvido consiste na junção de um condicionador ativo série (CAS), um condicionador ativo paralelo (CAP) e um conversor cc-cc com interface com a fonte de energia renovável e o sistema de armazenamento de energia e o barramento cc. Assim, o CAS é responsável por garantir tensões sinusoidais e equilibradas às cargas, o CAP é responsável por garantir correntes sinusoidais e equilibradas na rede elétrica e o conversor cc-cc tem como funcionalidade carregar ou descarregar as baterias e extrair a máxima potência da fonte de energia renovável. Com o desenvolvimento deste UPQC é possível melhorar a qualidade da energia elétrica, beneficiando tanto o utilizador final como o fornecedor de energia e todo o sistema de transporte. Assim, o âmbito desta dissertação é apenas referente ao desenvolvimento do conversor cc-ca para o CAP do UPQC. No âmbito desta dissertação, e de acordo com o enquadramento do projeto, este conversor é responsável por garantir correntes sinusoidais e equilibradas na rede elétrica, manter a tensão do barramento cc regulada e manter um fluxo bidirecional de energia com a rede elétrica de acordo com a operação do conversor cc-cc (fonte de energia renovável e sistema de armazenamento de energia).
Nowadays, due to the massive use of nonlinear loads by consumers in general, it has progressively increased the harmonics content in the waveforms of the currents, causesing voltage drops in the line impedances, contributing for increasing the harmonic content of the voltages in the electrical grid. As a result, each more, the electric grid presents low indices of power quality. The project where this dissertation is framed consists in the development of a three-phase unified power quality conditioner (UPQC) with interface, through the dc-link, to a renewable energy source and to an energy storage system (batteries). The developed UPQC consists is the combination of a series active conditioner (CAS), a parallel active conditioner (CAP) and a dc-dc converter for the interface between the CAS, the CAP, the renewable energy source and energy storage system. Therefore, the CAS is responsible for ensuring sinusoidal and balanced voltages to the loads, the CAP is responsible for ensuring sinusoidal and balanced currents to the electrical grid, and the dc-dc converter has the function of charging or discharging the batteries and extracting the maximum power from the renewable energy source. With the development of this UPQC, it is possible to increase the quality on the electrical grid side, benefiting: the end-user, the electricity supplier and the entire transportation system. Thus, the purpose of this dissertation is only related with the development of the dc-ac converter applied in the CAP of the UPQC. In the context of this work, and according to the project structure, this converter is responsible for ensuring sinusoidal and balanced currents from the electrical grid, maintaining a regulated dc-link voltage, as well as maintaining a bidirectional power flow according to the operation of the dc-dc converter (used to interface the renewable energy source and energy storage system).
FCT – Fundação para a Ciência e Tecnologia pelo suporte financeiro concedido através do Projeto 0302836 NORTE-01-0145-FEDER-030283 e ERDF–COMPETE 2020 Programme, SAICTPAC/0004/2015–POCI–01–0145–FEDER–016434

Dissertação de mestrado integrado em Engenharia Eletrónica Industrial e Computadores
Com o acentuado crescimento tecnológico das últimas décadas, a energia elétrica assume uma posição cada vez mais relevante e imprescindível, sendo que, hoje em dia, muito dificilmente alguém abdicaria dela, principalmente, considerando as necessidades energéticas de bens essenciais como eletrodomésticos e luz elétrica, assim como de sistemas audiovisuais e informáticos. Contudo, normalmente, estes equipamentos comportam-se como cargas não-lineares para a rede elétrica, apresentando elevado conteúdo harmónico, que se traduz em efeitos prejudicais à qualidade da energia elétrica (QEE). Também relevante, é a crescente aposta em veículos elétricos (VEs) recorrendo a baterias como fonte primária ou secundária de energia, convergindo para o novo paradigma de mobilidade elétrica. Porém, com a crescente aposta neste tipo de transportes também podem surgir problemas de QEE provenientes do impacto dos sistemas de carregamento de baterias na rede elétrica que, muitas vezes, apresentam um perfil de carga não-linear. Enquadrada nas vertentes da mobilidade elétrica e da QEE, esta dissertação visa o desenvolvimento de uma nova topologia de conversor CA-CC unificado com características de filtro ativo de potência do tipo paralelo monofásico. Desta forma, assumindo a existência de um conversor CC-CC como elemento intermédio entre o conversor CA-CC proposto e as baterias de VEs, o conversor proposto possibilita dois modos de operação distintos e independentes, mas que também podem ser combinados: operação de carregamento de baterias (CB); operação como filtro ativo paralelo (FAP) do tipo monofásico; e operação simultânea dos modos CB e FAP. Nos três modos de operação, o conversor proposto permite operar com corrente controlada no lado da rede elétrica, controlar o fator de potência e regular a tensão dos barramentos CC. Ao longo da dissertação são apresentados um estudo do estado-da-arte sobre conversores do tipo power factor correction e respetivas estratégias de controlo, o modelo de simulação detalhado do conversor proposto, a implementação laboratorial do protótipo do conversor proposto e, por fim, a validação experimental que permitiu corroborar os resultados de simulação e os objetivos propostos.
With the accentuated technological growth of the last decades, electrical energy assumes an increasingly important and indispensable position, and nowadays it is very difficult for anyone to give up on it, especially considering the energy needs of essential goods such as electric appliances and electric light, as well as audiovisual and computer systems. However, these devices usually behave as non-linear loads for the power grid, presenting high harmonic content, which is manifested in effects that are detrimental to the power quality (PQ). Also relevant is the growing focus on electric vehicles (EVs) using batteries as a primary or secondary source of energy, converging to the new paradigm of electric mobility. However, with the increasing focus on this type of transport, PQ problems can also arise from the impact of battery charging systems on the power grid, which often have a non-linear load profile. Inserted in the aspects of electric mobility and the QEE, this dissertation proposes the development of a new converter topology unified with single-phase shunt active power filter characteristics. Assuming a DC-DC converter as interface between the proposed AC-DC converter and the EV batteries, the proposed converter allows two different and independent operating modes, but they can also be combined: battery charging operation (BC); operation as shunt active power filter (SAPF); and simultaneous operation of BC and SAPF modes. In the three modes, the proposed converter allows the operation with controlled current in the power grid side, controlled the power factor and regulate the DC-link voltage. Throughout the dissertation is presented a study of the state of the art on power factor correction converters and their control strategies, the detailed simulation model of the proposed converter, the laboratory implementation of the prototype of the proposed converter and, finally, the experimental validation that allowed to corroborate the results and the proposed objectives.

Dissertação de mestrado em Engenharia Eletrónica Industrial e de Computadores
Atualmente, a utilização de cargas não-lineares na rede elétrica é uma constante. Este tipo de cargas leva a uma degradação da Qualidade de Energia Elétrica, uma vez que consome harmónicos de corrente, prejudicando o transporte e a distribuição de energia e o funcionamento da maioria dos equipamentos ligados à rede elétrica. Para além disso, em determinados sistemas há cargas que necessitam de ser alimentadas ininterruptamente, tais como controladores de processos industriais, computadores, equipamentos médico e sistemas de comunicação de dados, pelo que estas cargas não podem depender exclusivamente da rede elétrica, uma vez que, sendo esta suscetível a falhas, terá de ser complementada por geradores de emergência ou UPSs (Uninterruptible Power Supplies – fontes de alimentação ininterruptas). Deste modo, torna-se necessário o desenvolvimento e a utilização de equipamentos capazes de mitigar os problemas acima referidos. No Grupo de Eletrónica de Potência e Energia (GEPE) da Universidade do Minho têm sido desenvolvidos Filtros Ativos de Potência para compensar problemas de Qualidade de Energia. Assim sendo, neste trabalho de Mestrado foi proposto o desenvolvimento de um Filtro Ativo Paralelo Monofásico com operação como UPS. Este equipamento é capaz de compensar o fator de potência e os harmónicos de corrente em condições normais de funcionamento da rede elétrica e é também capaz de alimentar, de forma isolada, um conjunto de cargas prioritárias perante eventuais falhas na rede. Para além disso, foi também desenvolvido um conversor CC-CC bidirecional isolado com o intuito de carregar as baterias a partir da rede elétrica, através do barramento CC do Filtro Ativo Paralelo, bem como injetar energia na rede elétrica isolada proveniente das mesmas. Pretendeu-se que o equipamento desenvolvido fosse leve, compacto e com operação silenciosa, de modo a poder ser instalado no quadro elétrico de uma habitação. Deste modo, alguns procedimentos foram tomados aquando do projeto da solução apresentada, tais como a escolha dos semicondutores de potência e dos elementos magnéticos a utilizar. No final, foi efetuado um levantamento de custos da solução obtida de modo a analisar a sua viabilidade comercial.
Nowadays, the use of nonlinear loads connected to the electrical power grid is unceasing. This kind of electrical loads leads to Power Quality declining, since it consumes harmonic currents, worsening power transmission and distribution and the proper operation of a vast amount of power grid connected equipment. Furthermore, there are loads connected to several power systems that need incessant power supplying, such as industrial process controllers, computers, medical equipment and datacenters, whereby these loads cannot depend exclusively upon the power grid, since it is vulnerable to power outages, and therefore must be complemented by emergency generators or UPSs (Uninterruptible Power Supplies). Therefore, the development and use of equipment capable of mitigating these issues is needed. The Group of Energy and Power Electronics (GEPE) of the University of Minho has been developing Active Power Filters to compensate for Power Quality problems. Thus, the development of a Single-Phase Shunt Active Power Filter with UPS operation was proposed in this Master's thesis work. This equipment is capable of compensating for power factor and harmonic currents during normal operation of the power grid, and is also able to supply with isolation a set of priority electrical loads towards eventual power outages. Besides that, a bidirectional isolated DC-DC converter was developed in order to charge the battery pack from the power grid, through the Shunt Active Power Filter DC-link, as well as to provide energy stored in the batteries to the isolated electrical power grid. It was intended for the equipment to be weightless, compact and silent in order to be installed in a domestic electrical switchboard. Consequently, several procedures were taken during the solution’s development, such as the power semiconductors and the magnetic elements selection. In the end, it was performed the costing of the obtained solution with the purpose of evaluating its commercial feasibility.

Η επιβάρυνση του φυσικού περιβάλλοντος από τους συμβατικούς τρόπους ηλεκτροπαραγωγής έστρεψε τα τελευταία χρόνια την παγκόσμια ενεργειακή πολιτική στην ανάπτυξη και βελτίωση μεθόδων ηλεκτροπαραγωγής βασισμένων σε Ανανεώσιμες Πηγές Ενέργειας (ΑΠΕ). Αν και η ενσωμάτωση των ΑΠΕ στο δίκτυο μέσης τάσης δε συνοδεύεται από ιδιαίτερες πρακτικές δυσκολίες, δεν συμβαίνει το ίδιο και με το ηλεκτρικό δίκτυο των αστικών περιοχών, εξαιτίας της δομής των σύγχρονων μεγάλων αστικών κέντρων. Λαμβάνοντας υπόψη ότι οι μεγάλοι καταναλωτές (εργοστάσια και βιομηχανίες) θεωρούνται κατά κοινή πρακτική ως σταθερά φορτία, γίνεται κατανοητό πως ο βαθμός ανάπτυξης των αστικών κέντρων διαδραματίζει πολύ σημαντικό ρόλο τόσο στη ζήτηση ηλεκτρικής ενέργειας όσο και στη διαμόρφωση της αιχμής της καταναλισκόμενης ισχύος. Στο Ελληνικό Σύστημα Ηλεκτρικής Ενέργειας οι μήνες κατά τους οποίους βάλλεται περισσότερο η επάρκεια του ηλεκτρικού συστήματος επικεντρώνονται στη διάρκεια της θερινής περιόδου. Από την άλλη πλευρά, η μέγιστη παραγωγή ηλεκτρικής ενέργειας από την ηλιακή συμπίπτει χρονικά με τις ημερήσιες αιχμές ζήτησης των καλοκαιρινών μηνών. Συνεπώς, η χρήση μικρών ευέλικτων φωτοβολταϊκών (Φ/Β) συστημάτων, που μπορούν να εγκατασταθούν τόσο σε κατοικίες, όσο και σε εμπορικά ή δημοσία κτίρια (Διασυνδεδεμένα κτιριακά Φ/Β συστήματα) μπορεί να συμβάλει τόσο στην εξομάλυνση των αιχμών φορτίου όσο και στη μείωση του συνολικού κόστους ηλεκτροπαραγωγής. Η τελευταία και νεώτερη τεχνολογική τάση στα διασυνδεδεμένα κτιριακά φωτοβολταϊκά συστήματα είναι γνωστή με τον όρο Φωτοβολταϊκά Πλαίσια Εναλλασσομένου Ρεύματος (Φ/Β Πλαίσια Ε.Ρ). Πρόκειται για Φ/Β διατάξεις μικρής ισχύος (έως 300W), οι οποίες δημιουργούνται από την ενσωμάτωση ενός μόνο Φ/Β πλαισίου και ενός μονοφασικού αντιστροφέα σε μια αυτοτελή ηλεκτρονική διάταξη. Σκοπός της παρούσας εργασίας είναι η συμβολή της στον τομέα των Φ/Β μονάδων διεσπαρμένης παραγωγής, με την αναζήτηση μιας διάταξης διασύνδεσης φωτοβολταϊκών γεννητριών μικρής ισχύος με το ηλεκτρικό δίκτυο των αστικών περιοχών. Συγκεκριμένα, διερευνάται η δυνατότητα ανάπτυξης μιας ηλεκτρονικής διάταξης με απομόνωση, η οποία αφ’ ενός μεν θα εξασφαλίζει υψηλό συντελεστή ισχύος και υψηλό βαθμό απόδοσης για ευρύ φάσμα λειτουργίας, αφ’ ετέρου δε θα διέπεται από μικρό βαθμό πολυπλοκότητας στο κύκλωμα ισχύος της προκειμένου να εξασφαλίζεται υψηλή αξιοπιστία. Επιπρόσθετα, ιδιαίτερα χαρακτηριστικά αυτής της διάταξης θα πρέπει να είναι ο μικρός όγκος και το μικρό βάρος, ιδιότητες πολύ σημαντικές εάν αναλογιστούμε τις εφαρμογές για τις οποίες προορίζεται (ενσωμάτωση σε Φ/Β γεννήτριες που θα τοποθετηθούν σε όψεις ή οροφές κτιρίων). Το ενδιαφέρον της εργασίας εστιάσθηκε στον υψίσυχνο αντιστροφέα ρεύματος τοπολογίας Flyback. Για τη διάταξη αυτή διερευνήθηκαν δύο διαφορετικές τεχνικές ελέγχου (οι οποίες οδηγούν σε διαφορετικές καταστάσεις λειτουργίας) και ελέγχθηκε η καταλληλότητα τους για διαφορετικά επίπεδα ισχύος. Για τις δύο αυτές τεχνικές ελέγχου αναπτύχθηκαν μαθηματικά μοντέλα που συνδέουν τη μεταφερόμενη στο δίκτυο ισχύ με τις κατασκευαστικές παραμέτρους του αντιστροφέα και εξήχθησαν κριτήρια για τα ασφαλή όρια λειτουργίας του αντιστροφέα, με γνώμονα την καταπόνηση των ημιαγωγικών στοιχείων ισχύος. Επιπλέον, προτάθηκε η συνδυασμένη εφαρμογή των δύο τεχνικών ελέγχου και παρουσιάστηκε μια στρατηγική σχεδιασμού του αντιστροφέα, ώστε να γίνεται βέλτιστη επιλογή όλων των επιμέρους λειτουργικών του στοιχείων με ταυτόχρονη ελαχιστοποίηση του όγκου του, επίτευξη υψηλού συντελεστή ισχύος καθώς και υψηλού βαθμού απόδοσης, για ευρύ φάσμα της παραγόμενης ισχύος. Τέλος, διερευνήθηκε η δυνατότητα ανάπτυξης ενός ενεργού φίλτρου, για την αποτελεσματική εξομάλυνση της έντονης κυμάτωσης του ρεύματος εισόδου του προτεινόμενου αντιστροφέα. Η κυμάτωση αυτή είναι αποτέλεσμα της τροφοδότηση του μονοφασικού ηλεκτρικού δικτύου Ε.Ρ. από τη συνεχή τάση και το συνεχές ρεύμα που παράγουν οι φωτογεννήτριες και ο περιορισμός της είναι ιδιάζουσας σημασίας προκειμένου να καταστεί δυνατή η αποδοτική λειτουργία της όλης διάταξης. Η λειτουργία του προτεινόμενου ενεργού φίλτρου είναι ανεξάρτητη τόσο των καταστάσεων λειτουργίας του αντιστροφέα τύπου Flyback, όσο και γενικότερα της τοπολογίας του αντιστροφέα, καθιστώντας την έτσι ως μια ελκυστική λύση και για διαφορετικές τοπολογίες μετατροπέων. Η ακρίβεια των μαθηματικών μοντέλων, η ορθότητα της προτεινόμενης στρατηγικής σχεδιασμού και η αποτελεσματικότητα του προτεινόμενου ενεργού φίλτρου επιβεβαιώθηκαν μέσω προσομοίωσης και πειραματικών δοκιμών, ενώ τέλος παρατίθενται τα συμπεράσματα από το σύνολο της εργασίας. Η εργασία αυτή συγχρηματοδοτείται κατά: 80% της Δημόσιας Δαπάνης από την Ευρωπαϊκή Ένωση – Ευρωπαϊκό Κοινωνικό Ταμείο, 20% της Δημόσιας Δαπάνης από το Ελληνικό Δημόσιο – Υπουργείο Ανάπτυξης – Γενική Γραμματεία Έρευνας και Τεχνολογίας και από τον Ιδιωτικό Τομέα, στο πλαίσιο του Μέτρου 8.3 του Ε.Π. Ανταγωνιστικότητα – Γ΄ Κοινοτικό Πλαίσιο Στήριξης.
The aggravation of natural environment from the conventional ways of electricity generation turned during past few years the worldwide energy policy to the development and the improvement of electricity generation methods based on Renewable Energy Sources (RES). Although the interconnection of RES in the medium voltage network is not accompanied by particular practical difficulties, this is not the case for the electric network of urban regions, by reason of the structure of modern big urban centres. Taking into consideration that in common practice the big consumers (factories and industries) are considered as constant loads, it becomes comprehensible that the growth of urban centres plays very important role both in the demand of electrical energy and the formation of peak electricity power consumption. Τhe time period where the sufficiency of the Greek Electric Energy System is threatened is during the aestival period. On the other hand, the peak electricity production from solar energy coincides with the daily peak consumption of summer months. Consequently, the use of small flexible photovoltaic (PV) systems, installed in residences or in commercial and public buildings (BIPV – Building Integrated Photovoltaic’s), can contribute to the normalisation of electrical energy consumption as well as to the reduction of electricity generation total cost. The latest technology on small scale grid-connected residential PV systems is the Alternative Current Photovoltaic Modules (AC-PV Modules) where the power production varies under 0.3kW. An AC-PV Module is the combination of a single PV module and a single-phase power electronic inverter in a single electrical device. The scope of the present work is to contribute in the sector of the Dispersed Power Generation PV systems, with the development of an inverter that will be used for the interconnection of small PV generators with the electric network of urban regions. In more details, the development of an inverter with electrical isolation is investigated, which on the one hand it will ensure high power factor regulation and high efficiency for wide power range and on the other hand it will be characterised by simple power electronic circuit structure in order to ensure high reliability. Moreover, particular characteristics of this inverter should be the small volume and the small weight, attributes very important considering its applications (incorporation in PV generators that will be placed in aspects or roofs of buildings). The interest of present work is focused in the high frequency current source Flyback inverter. For this topology two different control techniques were investigated, leading to different operation modes. Moreover, their suitability is studied for different power levels. For both control techniques mathematic models were developed, connecting the transferred power in the public grid with the inverter operational parameters, as well as criteria for the inverter safe operation area were exported, considering the acceptable peak voltage and current values for the semiconductor switches. Moreover, the combined application of two control techniques is proposed and an optimum inverter design strategy is presented, aiming to the development of an inverter with the smallest possible volume, as well as to the achievement of high power factor regulation and high efficiency for wide power range. Last but not least, a current pulsation smoothing active filter is investigated and developed, which permits the elimination of the low frequency inverter input current. The current pulsation is a result of the power pulsation, due to the single-phase power generation, and its elimination is of great importance in order to exploit the maximum PV generated electricity power. The active filter configuration is independent from the inverter topology and its operation mode and hence it can be applied for various single stage topologies. The precision of the mathematic models, the correctness of the proposed design strategy and the effectiveness of the proposed active filter are validated via simulation and experimental results. Finally, the conclusions of whole study are exhibited. This thesis is part of the 03ED300 research project, implemented within the framework of the “Reinforcement Programme of Human Research Manpower” (PENED) and cofinanced by National and Community Funds (20% from the Greek Ministry of Development-General Secretariat of Research and Technology and 80% from E.U.- European Social Fund).

Dissertação de mestrado em Engenharia Eletrónica e de Computadores
Devido à previsível escassez e às desvantagens inerentes ao uso de combustíveis fósseis na produção de energia elétrica, tem-se vindo a apostar em fontes de energia renovável, nomeadamente a eólica e a solar fotovoltaica. Contudo, estes tipos de fontes apresentam como principais desvantagens a intermitência na produção de energia, bem como a necessidade de um equipamento de interface com a rede elétrica, que tipicamente introduz problemas de qualidade de energia elétrica (QEE). Assim, de forma a possibilitar a integração de fontes de energia renovável na rede elétrica e explorar os incentivos referentes aos períodos de menor procura de energia, surgem novas oportunidades relativamente aos sistemas de armazenamento e gestão de energia, nomeadamente, o conceito de load shifting. Neste sentido, a presente dissertação de mestrado encontra-se inserida no desenvolvimento de um sistema de load-shift com características avançadas. Este dispositivo permite a interface de um sistema de armazenamento de energia com a rede elétrica, simultaneamente com a compensação de problemas de qualidade de energia elétrica relacionados com a corrente, nomeadamente, harmónicos, desequilíbrios e potência reativa. Nesta dissertação é abordado o desenvolvimento do conversor CC-CA trifásico, responsável pela interface com a rede elétrica, absorvendo ou injetando energia elétrica, dependendo do modo de operação do sistema de armazenamento. Além disso, este conversor CC-CA permite a operação como filtro ativo paralelo (FAP) trifásico, sendo esta uma das principais contribuições para a operação do sistema. Ao longo do desenvolvimento desta dissertação, foi possível validar a topologia de conversor CC-CA trifásico com quatro braços a operar em diferentes modos, bem como o seu sistema de controlo. Estes modos envolveram um estudo teórico necessário à execução dos testes de simulação e validação experimental do desempenho do sistema implementado.
Recently, there has been a focus on renewable energy sources, namely wind and solar photovoltaic, due to the predictable scarcity and inherent drawbacks of the use of fossil fuels in the production of electric energy. However, these types of energy sources have their own shortcomings: the intermittence of energy production as well as the need for an electrical network interface device that typically introduces power quality (PQ) problems. Thus, to allow the integration of renewable energy sources in the grid and to explore the incentives for periods of lower energy demand, new opportunities arise regarding energy storage and management systems, namely the load shifting concept. In this context, the present master dissertation is focused on developing a system of load-shift with advanced characteristics. This device allows the interface of a system of energy storage with the electric network, while fixing the electrical power quality problems related to current harmonics, unbalances and reactive power. This investigation discusses the development of three-phase DC-AC converter, which is responsible for interfacing with the grid, absorbing or injecting electrical energy, depending on the mode of operation of the storage system. Additionally, one of the main contributions to the system operation is that the DC-AC converter allows operation as a three-phase shunt active filter (APF). Throughout the development of this dissertation, it was possible to validate the topology of the three-phase DC-AC converter with four legs operating in different modes, as well as its control system. These modes involved a theoretical study, which is necessary to perform the simulation tests and experimental validation of the performance of the implemented system.
Este trabalho de mestrado está enquadrado no projeto de IC&DT “Quality4Power - Enhancing the Power Quality for Industry 4.0 in the era of Microgrids”, financiado pela Fundação para a Ciência e Tecnologia, com a referência PTDC/EEI-EEE/28813/2017.
Este trabalho de mestrado está enquadrado no projeto de IC&DT “newERA4GRIDs – New Generation of Unified Power Conditioner with Advanced Control, Integrating Electric Mobility, Renewables, and Active Filtering Capabilities for the Power Grid Improvement”, financiado pela Fundação para a Ciência e Tecnologia, com a referência POCI-01-0145-FEDER-030283.