Dissertations / Theses on the topic 'Power Quality in DC'

The modern electric power systems are going through significant changes because of continuous increasing demand of electric power. Further, a growing number of renewable energy systems that directly deliver DC power jointly considered with the advance in DC technology allows a more efficient and affordable use of energy. Furthermore, a rising use of DC systems and microgrids in a wide number of applications has motivated the study of Power Quality (PQ). The concept of power quality in DC systems and microgrids brings many challenges and the aim of this thesis is to understand the delivered power quality in DC microgrid systems. In this thesis, the effects of low frequency range (0-2 kHz) conducted emissions on power quality from a microgrid based DC/DC converter under steady state and transient loading conditions represent the main purpose of this work. Indeed, for a DC distribution network there is a lack of standards and guidelines concerning power quality issues and acceptable levels of conducted disturbances in the aforementioned frequency range. Consequently, the objective of this thesis is to quantify adequate power quality indices for DC systems or networks with connected loads such as Low Frequency Sinusoidal Disturbance (% LFSD) and Amplitude Probability Distribution (APD) indices.

Battery storage devices have been widely utilized for different applications. However, for high power applications, battery storage systems come with several challenges, such as the thermal issue, low power density, low life span and high cost. Compared with batteries, supercapacitors have a lower energy density but their power density is very high, and they offer higher cyclic life and efficiency even during fast charge and discharge processes. In this dissertation, new techniques for the control and energy management of the hybrid battery-supercapacitor storage system are developed to improve the performance of the system in terms of efficiency, power quality and reliability. To evaluate the findings of this dissertation, a laboratory-scale DC microgrid system is designed and implemented. The developed microgrid utilizes a hybrid lead-acid battery and supercapacitor energy storage system and is loaded under various grid conditions. The developed microgrid has also real-time monitoring, control and energy management capabilities. A new control scheme and real-time energy management algorithm for an actively controlled hybrid DC microgrid is developed to reduce the adverse impacts of pulsed power loads. The developed control scheme is an adaptive current-voltage controller that is based on the moving average measurement technique and an adaptive proportional compensator. Unlike conventional energy control methods, the developed controller has the advantages of controlling both current and voltage of the system. This development is experimentally tested and verified. The results show significant improvements achieved in terms of enhancing the system efficiency, reducing the AC grid voltage drop and mitigating frequency fluctuation. Moreover, a novel event-based protection scheme for a multi-terminal DC power system has been developed and evaluated. In this technique, fault identification and classifications are performed based on the current derivative method and employing an artificial inductive line impedance. The developed scheme does not require high speed communication and synchronization and it transfers much less data when compared with the traditional method such as the differential protection approach. Moreover, this scheme utilizes less measurement equipment since only the DC bus data is required.

This diploma thesis deals with elektrical power quality in DC grids. Electrical power is commodity and therefore it must be represented not just with quantitative, but also with qualitative parameters. Nowadays, there is an increasing demand for bigger implementation of renewable energy sources and more efficient power systems, which motivates installation of DC grids. However, development of DC grids is decelerated by lack of standardization alson in power quality. The work includes definition of power quality parameters and their measurement methodology.

Cette thèse de doctorat porte sur les fluctuations temporelles du flux lumineux des lampes LED, ce phénomène portant le nom de papilottement (flicker). Le papillotement est habituellement considéré comme une perturbation en raison de son impact négatif sur la santé. Pour les systèmes d'éclairage à base de diodes électroluminescentes (LED), sa définition vient d'être formalisée dans la norme IEEE 1789:2015 et a été décrite pour les appareils alimentés en courant alternatif (CA). Ce papillotement alternatif résulte des interactions entre l'impédance du réseau, l'onde de tension, les courants harmoniques et le convertisseur de courant alternatif en courant continu (CA - CC). L'alimentation en courant continu est généralement obtenue via des convertisseurs à découpage. Par conséquent, les mêmes facteurs perturbateurs sont également présents sur les réseaux à courant continu. Cette thèse résume les diférences entre les propriétés caractéristiques du papillotement sous alimentation en CA et en CC. Il a été montré dans la littérature et aussi dans cette thèse qu'avec les LED, le facteur clé qui affecte le papillotement réside dans la conception du driver de LED - une partie indispensable des systèmes d'éclairage à LED. Cette thèse décrit une méthodologie d'évaluation de la sensibilité au papillotement des lampes LED sous alimentation en CC et analyse la façon dont cette sensibilité se modifie lorsque les drivers de LED sont simplifiés et adaptés à des alimentations CC. La thèse présente un ensemble d'expériences de mesure visant à déterminer la réaction typique du papillotement des lampes LED à la fois sous alimentation CA et CC. D'autres expériences ont été efectuées pour révéler l'impact de l'adaptation du driver à l'alimentation CC (en enlevant le pont redresseur à diodes). On constate que certaines lampes présentent une meilleure résistance au papillotement, tandis que d'autres lampes présentent une moindre résistance. Ces expériences sont accompagnées de simulations de drivers pour les lampes LED visant à reproduire et à expliquer les résultats des mesures. La thèse décrit en outre une expérience de mesure visant à montrer la sévérité typique de la variation de tension dans un réseau CC à basse tension couplé au CA domestique et son impact sur le papillotement. On conclut qu'un tel système est suisamment robuste pour filtrer les perturbations provenant du CA, mais une interaction indésirable entre la lampe et l'alimentation peut se produire
This dissertation thesis is concerned with temporal fluctuations of the luminous flux of LED lamps, a phenomenon referred to as flicker. Flicker is usually regarded as a disturbance due to its negative impact on human health. For lighting systems based on light emitting diodes (LED), its definition has recently been formalised in norm IEEE 1789-2015 and has been documented on devices supplied with AC voltage. AC flicker results from interactions between network impedance, voltage and current harmonics, and the AC to DC converter. DC supplies are generally obtained by switching converters. Consequently, the same perturbing factors are present on DC networks. The thesis summarises the differences between the characteristic properties of flicker under AC and DC supplies. It has been shown in the literature and also in this thesis that the key factor affecting flicker with LEDs is the design of the LED driver-a necessary part of the LED lighting systems. This thesis describes a methodology for the evaluation of the flicker sensitivity of DC supplied LED lamps and analyses how the sensitivity changes when the LED drivers are simplified and accustomed to DC supply. The thesis presents a set of measurement experiments aimed to determine the typical flicker response of LED lamps both under AC and DC supply. Further experiments were performed to reveal the impact of accustomising the driver to the DC supply (removing the diode rectifier). It was found that some lamps show better flicker immunity while other lamps show worse flicker immunity. These experiments are accompanied by LED driver simulations aiming to reproduce and explain the measurement results. The thesis further describes a measurement experiment aimed to show the typical severity of the voltage fluctuation in a low voltage DC network coupled to AC mains and its impact on the flicker. It is concluded that such a system is robust enough to filter out any perturbations coming from the AC supply, but an undesired interaction between the lamp and the supply may occur

The Queensland University of Technology (QUT) allows the presentation of theses for the Degree of Doctor of Philosophy in the format of published or submitted papers, where such papers have been published, accepted or submitted during the period of candidature. This thesis is composed of ten published /submitted papers and book chapters of which nine have been published and one is under review. This project is financially supported by an Australian Research Council (ARC) Discovery Grant with the aim of investigating multilevel topologies for high quality and high power applications, with specific emphasis on renewable energy systems. The rapid evolution of renewable energy within the last several years has resulted in the design of efficient power converters suitable for medium and high-power applications such as wind turbine and photovoltaic (PV) systems. Today, the industrial trend is moving away from heavy and bulky passive components to power converter systems that use more and more semiconductor elements controlled by powerful processor systems. However, it is hard to connect the traditional converters to the high and medium voltage grids, as a single power switch cannot stand at high voltage. For these reasons, a new family of multilevel inverters has appeared as a solution for working with higher voltage levels. Besides this important feature, multilevel converters have the capability to generate stepped waveforms. Consequently, in comparison with conventional two-level inverters, they present lower switching losses, lower voltage stress across loads, lower electromagnetic interference (EMI) and higher quality output waveforms. These properties enable the connection of renewable energy sources directly to the grid without using expensive, bulky, heavy line transformers. Additionally, they minimize the size of the passive filter and increase the durability of electrical devices. However, multilevel converters have only been utilised in very particular applications, mainly due to the structural limitations, high cost and complexity of the multilevel converter system and control. New developments in the fields of power semiconductor switches and processors will favor the multilevel converters for many other fields of application. The main application for the multilevel converter presented in this work is the front-end power converter in renewable energy systems. Diode-clamped and cascade converters are the most common type of multilevel converters widely used in different renewable energy system applications. However, some drawbacks – such as capacitor voltage imbalance, number of components, and complexity of the control system – still exist, and these are investigated in the framework of this thesis. Various simulations using software simulation tools are undertaken and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results. This thesis is divided into two main sections. The first section focuses on solving the capacitor voltage imbalance for a wide range of applications, and on decreasing the complexity of the control strategy on the inverter side. The idea of using sharing switches at the output structure of the DC-DC front-end converters is proposed to balance the series DC link capacitors. A new family of multioutput DC-DC converters is proposed for renewable energy systems connected to the DC link voltage of diode-clamped converters. The main objective of this type of converter is the sharing of the total output voltage into several series voltage levels using sharing switches. This solves the problems associated with capacitor voltage imbalance in diode-clamped multilevel converters. These converters adjust the variable and unregulated DC voltage generated by renewable energy systems (such as PV) to the desirable series multiple voltage levels at the inverter DC side. A multi-output boost (MOB) converter, with one inductor and series output voltage, is presented. This converter is suitable for renewable energy systems based on diode-clamped converters because it boosts the low output voltage and provides the series capacitor at the output side. A simple control strategy using cross voltage control with internal current loop is presented to obtain the desired voltage levels at the output voltage. The proposed topology and control strategy are validated by simulation and hardware results. Using the idea of voltage sharing switches, the circuit structure of different topologies of multi-output DC-DC converters – or multi-output voltage sharing (MOVS) converters – have been proposed. In order to verify the feasibility of this topology and its application, steady state and dynamic analyses have been carried out. Simulation and experiments using the proposed control strategy have verified the mathematical analysis. The second part of this thesis addresses the second problem of multilevel converters: the need to improve their quality with minimum cost and complexity. This is related to utilising asymmetrical multilevel topologies instead of conventional multilevel converters; this can increase the quality of output waveforms with a minimum number of components. It also allows for a reduction in the cost and complexity of systems while maintaining the same output quality, or for an increase in the quality while maintaining the same cost and complexity. Therefore, the asymmetrical configuration for two common types of multilevel converters – diode-clamped and cascade converters – is investigated. Also, as well as addressing the maximisation of the output voltage resolution, some technical issues – such as adjacent switching vectors – should be taken into account in asymmetrical multilevel configurations to keep the total harmonic distortion (THD) and switching losses to a minimum. Thus, the asymmetrical diode-clamped converter is proposed. An appropriate asymmetrical DC link arrangement is presented for four-level diode-clamped converters by keeping adjacent switching vectors. In this way, five-level inverter performance is achieved for the same level of complexity of the four-level inverter. Dealing with the capacitor voltage imbalance problem in asymmetrical diodeclamped converters has inspired the proposal for two different DC-DC topologies with a suitable control strategy. A Triple-Output Boost (TOB) converter and a Boost 3-Output Voltage Sharing (Boost-3OVS) converter connected to the four-level diode-clamped converter are proposed to arrange the proposed asymmetrical DC link for the high modulation indices and unity power factor. Cascade converters have shown their abilities and strengths in medium and high power applications. Using asymmetrical H-bridge inverters, more voltage levels can be generated in output voltage with the same number of components as the symmetrical converters. The concept of cascading multilevel H-bridge cells is used to propose a fifteen-level cascade inverter using a four-level H-bridge symmetrical diode-clamped converter, cascaded with classical two-level Hbridge inverters. A DC voltage ratio of cells is presented to obtain maximum voltage levels on output voltage, with adjacent switching vectors between all possible voltage levels; this can minimize the switching losses. This structure can save five isolated DC sources and twelve switches in comparison to conventional cascade converters with series two-level H bridge inverters. To increase the quality in presented hybrid topology with minimum number of components, a new cascade inverter is verified by cascading an asymmetrical four-level H-bridge diode-clamped inverter. An inverter with nineteen-level performance was achieved. This synthesizes more voltage levels with lower voltage and current THD, rather than using a symmetrical diode-clamped inverter with the same configuration and equivalent number of power components. Two different predictive current control methods for the switching states selection are proposed to minimise either losses or THD of voltage in hybrid converters. High voltage spikes at switching time in experimental results and investigation of a diode-clamped inverter structure raised another problem associated with high-level high voltage multilevel converters. Power switching components with fast switching, combined with hard switched-converters, produce high di/dt during turn off time. Thus, stray inductance of interconnections becomes an important issue and raises overvoltage and EMI issues correlated to the number of components. Planar busbar is a good candidate to reduce interconnection inductance in high power inverters compared with cables. The effect of different transient current loops on busbar physical structure of the high-voltage highlevel diode-clamped converters is highlighted. Design considerations of proper planar busbar are also presented to optimise the overall design of diode-clamped converters.

Orientador: Falcondes Jose Mendes de Seixas
Banca: Carlos Alberto Canesin
Banca: Luiz Carlos Gomes de Freitas
Resumo: Este trabalho propõe um novo conversor CA-CC trifásico de múltiplos pulsos com estágios CC-CC elevadores de tensão controlados pela técnica de histerese constante. Nesta proposta não são empregados indutores de interfase. A finalidade deste conversor é a de possibilitar um barramento CC regulado para aplicações embarcadas, acionamentos elétricos e afins, sempre com preocupações relacionadas aos aspectos de Qualidade de Energia Elétrica. Assim, a proposta deve apresentar elevado fator de potência, baixa distorção harmônica total de corrente drenada da rede elétrica. Ampla revisão bibliográfica, reunindo as propostas mais recentes da literatura para conversores com mesma finalidade, é feita para que sejam estudadas as estruturas de potência, técnicas de controle, versatilidade, possibilidade de isolamento galvânico e robustez. Em seguida, é detalhada a proposta principal deste trabalho por meio da apresentação do equacionamento do autotransformador, dos estágios elevadores de tensão e da técnica de controle. Esta análise permite que sejam feitas simulações com todos os elementos do conversor CA-CC e então, se desenvolva o projeto físico dos elementos magnéticos e se escolham os componentes eletrônicos do protótipo. O número reduzido de componentes de controle e a simplicidade dos circuitos de potência são grandes atrativos da proposta discutida. Todas as informações relevantes são descritas detalhadamente e, sempre que possível, meios alternativos de solucionar problemas são também apresentados, de forma que fiquem claras as possibilidades de melhoria da técnica empregada. A operação conjunta de todos os elementos mais a técnica de controle foi validada, de maneira que se comprovou, por meio de ensaios, todos os princípios de funcionamento da proposta de conversor CA-CC. Pelos resultados experimentais, obteve-se corrente drenada... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work proposes a new AC-DC three-phase multipulse converter with DC-DC boost stages and constant hysteresis control. The objective of this converter is to provide a reliable DC bus for on-board applications, electric motor drives and similars, always considering power quality issues. Thus, the proposal presents high power factor and low harmonic distortions in the currents from the mains. A wide revision is made on other recent proposals found in the scientific literature. Different topologies are compared considering power circuits, control techniques, isolation possibility and robustness. The second chapter presents the details on the main proposal of this work and also the mathematical equations that describe the autotransformer, boost converters and control strategy. Later, simulation results are commented and discussed and the physical design is detailed. The output filter elements, power components and control elements are specified. Experimental results including main waveforms, efficiency, voltage regulation and temperature rise are presented for the autotransformer. The boost stages are also tested and its results are discussed. Finally, the proposed AC-DC converter is tested and the control technique applied to the power stage is validated
Mestre

The installation of wind power plant has significantly increased since several years due to the recent necessity of creating renewable and clean energy sources. Before the accomplishment of a wind power project many pre-studies are required in order to verify the possibility of integrating a wind power plant in the electrical network. The creation of models in different software and their simulation can bring the insurance of a secure operation that meets the numerous requirements imposed by the electrical system. Hence, this Master thesis work consists in the creation of a wind turbine model. This model represents the turbines installed at Lillgrund wind farm, the biggest wind power plant in Sweden. The objectives of this project are to first develop an accurate model of the wind turbines installed at Lillgrund wind farm and further to use it in different kinds of simulations. Those simulations test the wind turbine operating according to different control modes. Also, a power quality analysis is carried out studying in particular two power quality phenomena, namely, the response to voltage sags and the harmonic distortion. The model is created in the software PSCAD that enables the dynamic and static simulations of electromagnetic and electromechanical systems. The model of the wind turbine contains the electrical machine, the power electronics (converters), and the controls of the wind turbine. Especially, three different control modes, e.g., voltage control, reactive power control and power factor control, are implemented, tested and compared. The model is tested according to different cases of voltage sag and the study verifies the fault-ride through capability of the turbine. Moreover, a harmonics analysis is done. Eventually the work concludes about two power quality parameters.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Este trabalho propõe um novo conversor CA-CC trifásico de múltiplos pulsos com estágios CC-CC elevadores de tensão controlados pela técnica de histerese constante. Nesta proposta não são empregados indutores de interfase. A finalidade deste conversor é a de possibilitar um barramento CC regulado para aplicações embarcadas, acionamentos elétricos e afins, sempre com preocupações relacionadas aos aspectos de Qualidade de Energia Elétrica. Assim, a proposta deve apresentar elevado fator de potência, baixa distorção harmônica total de corrente drenada da rede elétrica. Ampla revisão bibliográfica, reunindo as propostas mais recentes da literatura para conversores com mesma finalidade, é feita para que sejam estudadas as estruturas de potência, técnicas de controle, versatilidade, possibilidade de isolamento galvânico e robustez. Em seguida, é detalhada a proposta principal deste trabalho por meio da apresentação do equacionamento do autotransformador, dos estágios elevadores de tensão e da técnica de controle. Esta análise permite que sejam feitas simulações com todos os elementos do conversor CA-CC e então, se desenvolva o projeto físico dos elementos magnéticos e se escolham os componentes eletrônicos do protótipo. O número reduzido de componentes de controle e a simplicidade dos circuitos de potência são grandes atrativos da proposta discutida. Todas as informações relevantes são descritas detalhadamente e, sempre que possível, meios alternativos de solucionar problemas são também apresentados, de forma que fiquem claras as possibilidades de melhoria da técnica empregada. A operação conjunta de todos os elementos mais a técnica de controle foi validada, de maneira que se comprovou, por meio de ensaios, todos os princípios de funcionamento da proposta de conversor CA-CC. Pelos resultados experimentais, obteve-se corrente drenada...
This work proposes a new AC-DC three-phase multipulse converter with DC-DC boost stages and constant hysteresis control. The objective of this converter is to provide a reliable DC bus for on-board applications, electric motor drives and similars, always considering power quality issues. Thus, the proposal presents high power factor and low harmonic distortions in the currents from the mains. A wide revision is made on other recent proposals found in the scientific literature. Different topologies are compared considering power circuits, control techniques, isolation possibility and robustness. The second chapter presents the details on the main proposal of this work and also the mathematical equations that describe the autotransformer, boost converters and control strategy. Later, simulation results are commented and discussed and the physical design is detailed. The output filter elements, power components and control elements are specified. Experimental results including main waveforms, efficiency, voltage regulation and temperature rise are presented for the autotransformer. The boost stages are also tested and its results are discussed. Finally, the proposed AC-DC converter is tested and the control technique applied to the power stage is validated

In this thesis the design, control, stability, input power quality, and motor drive performance of ac motor drives with front end three phase diode rectifiers utilizing low capacitance dc bus capacitor are investigated. Detailed computer simulations of conventional motor drives with diode rectifier front end utilizing high capacitance dc bus capacitor and the drives with low capacitance dc bus capacitor are conducted and the performances are compared. Performance evaluation of various active control methods found in previous studies aiming to provide the dc bus stability of drives with low capacitance dc bus capacitor are done at various load levels and types. Design recommendations are provided for the drives utilizing low capacitance dc bus capacitor.

The ability of a piezoelectric transducer in energy conversion is rapidly expanding in several applications. Some of the industrial applications for which a high power ultrasound transducer can be used are surface cleaning, water treatment, plastic welding and food sterilization. Also, a high power ultrasound transducer plays a great role in biomedical applications such as diagnostic and therapeutic applications. An ultrasound transducer is usually applied to convert electrical energy to mechanical energy and vice versa. In some high power ultrasound system, ultrasound transducers are applied as a transmitter, as a receiver or both. As a transmitter, it converts electrical energy to mechanical energy while a receiver converts mechanical energy to electrical energy as a sensor for control system. Once a piezoelectric transducer is excited by electrical signal, piezoelectric material starts to vibrate and generates ultrasound waves. A portion of the ultrasound waves which passes through the medium will be sensed by the receiver and converted to electrical energy. To drive an ultrasound transducer, an excitation signal should be properly designed otherwise undesired signal (low quality) can deteriorate the performance of the transducer (energy conversion) and increase power consumption in the system. For instance, some portion of generated power may be delivered in unwanted frequency which is not acceptable for some applications especially for biomedical applications. To achieve better performance of the transducer, along with the quality of the excitation signal, the characteristics of the high power ultrasound transducer should be taken into consideration as well. In this regard, several simulation and experimental tests are carried out in this research to model high power ultrasound transducers and systems. During these experiments, high power ultrasound transducers are excited by several excitation signals with different amplitudes and frequencies, using a network analyser, a signal generator, a high power amplifier and a multilevel converter. Also, to analyse the behaviour of the ultrasound system, the voltage ratio of the system is measured in different tests. The voltage across transmitter is measured as an input voltage then divided by the output voltage which is measured across receiver. The results of the transducer characteristics and the ultrasound system behaviour are discussed in chapter 4 and 5 of this thesis. Each piezoelectric transducer has several resonance frequencies in which its impedance has lower magnitude as compared to non-resonance frequencies. Among these resonance frequencies, just at one of those frequencies, the magnitude of the impedance is minimum. This resonance frequency is known as the main resonance frequency of the transducer. To attain higher efficiency and deliver more power to the ultrasound system, the transducer is usually excited at the main resonance frequency. Therefore, it is important to find out this frequency and other resonance frequencies. Hereof, a frequency detection method is proposed in this research which is discussed in chapter 2. An extended electrical model of the ultrasound transducer with multiple resonance frequencies consists of several RLC legs in parallel with a capacitor. Each RLC leg represents one of the resonance frequencies of the ultrasound transducer. At resonance frequency the inductor reactance and capacitor reactance cancel out each other and the resistor of this leg represents power conversion of the system at that frequency. This concept is shown in simulation and test results presented in chapter 4. To excite a high power ultrasound transducer, a high power signal is required. Multilevel converters are usually applied to generate a high power signal but the drawback of this signal is low quality in comparison with a sinusoidal signal. In some applications like ultrasound, it is extensively important to generate a high quality signal. Several control and modulation techniques are introduced in different papers to control the output voltage of the multilevel converters. One of those techniques is harmonic elimination technique. In this technique, switching angles are chosen in such way to reduce harmonic contents in the output side. It is undeniable that increasing the number of the switching angles results in more harmonic reduction. But to have more switching angles, more output voltage levels are required which increase the number of components and cost of the converter. To improve the quality of the output voltage signal with no more components, a new harmonic elimination technique is proposed in this research. Based on this new technique, more variables (DC voltage levels and switching angles) are chosen to eliminate more low order harmonics compared to conventional harmonic elimination techniques. In conventional harmonic elimination method, DC voltage levels are same and only switching angles are calculated to eliminate harmonics. Therefore, the number of eliminated harmonic is limited by the number of switching cycles. In the proposed modulation technique, the switching angles and the DC voltage levels are calculated off-line to eliminate more harmonics. Therefore, the DC voltage levels are not equal and should be regulated. To achieve this aim, a DC/DC converter is applied to adjust the DC link voltages with several capacitors. The effect of the new harmonic elimination technique on the output quality of several single phase multilevel converters is explained in chapter 3 and 6 of this thesis. According to the electrical model of high power ultrasound transducer, this device can be modelled as parallel combinations of RLC legs with a main capacitor. The impedance diagram of the transducer in frequency domain shows it has capacitive characteristics in almost all frequencies. Therefore, using a voltage source converter to drive a high power ultrasound transducer can create significant leakage current through the transducer. It happens due to significant voltage stress (dv/dt) across the transducer. To remedy this problem, LC filters are applied in some applications. For some applications such as ultrasound, using a LC filter can deteriorate the performance of the transducer by changing its characteristics and displacing the resonance frequency of the transducer. For such a case a current source converter could be a suitable choice to overcome this problem. In this regard, a current source converter is implemented and applied to excite the high power ultrasound transducer. To control the output current and voltage, a hysteresis control and unipolar modulation are used respectively. The results of this test are explained in chapter 7.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2007.
Includes bibliographical references (p. 197-204).
THIS THESIS addresses the development of system architectures and circuit topologies for dc-dc power conversion at very high frequencies. The systems architectures that are developed are structured to overcome limitations associated with conventional designs. In particular, the new architectures described here structure the energy processing and control functions of the system in such a manner that high efficiency can be achieved across wide load range while regulating the output. Moreover, these architectures are amenable to circuit designs operating at fixed frequency and duty ratio, considerable easing the circuit design. The thesis also develops new circuit designs that are well suited to these new architectures. As part of this, two new gate drives and control methods are introduced that greatly reduce gating loss at VHF frequencies for fixed frequency, fixed duty ratio operation. One of these gating schemes provides near theoretical minimum loss by resonantly wave shaping the gate voltage to have a trapezoidal drive voltage. This waveshaping approach is then taken a step further, yielding a new class of dc-dc converter that archives a significant reduction in peak switch voltage stress, requires small passive components with low energy storage, and provides the capability for extremely rapid startup and shutdown. This new class of converter is well adapted to the architectures and gate drive methods proposed in the thesis. It is expected that the new architectures and circuit designs introduced here will contribute to the development of power converter having greatly reduced size and improved transient performance.
by Juan Rivas.
Sc.D.

One of the requirements for the next generation of power supplies for distributed power systems (DPSs) is to achieve high power density with high efficiency. In the traditional front-end converter based on the two-stage approach for high-power three-phase DPSs, the DC-link voltage coming from the power factor correction (PFC) stage penalizes the second-stage DC/DC converter. This DC/DC converter not only has to meet the characteristics demanded by the load, but also must process energy with high efficiency, high reliability, high power density and low cost. To meet these requirements, approaches such as the series connection of converters and converters that reduce the voltage stress across the main devices have been proposed. In order to improve the characteristics of these solutions, this dissertation proposes high-efficiency, high-density DC/DC converters for high-power high-voltage applications. In the first part of the dissertation, a DC/DC converter based on a three-level structure and operated with pulse width modulation (PWM) phase-shift control is proposed. This new way to operate the three-level DC/DC converter allows soft-switching operation for the main devices. Zero-voltage switching (ZVS) and zero-voltage and zero-current switching (ZVZCS) soft-switching techniques are studied, analyzed and compared in order to improve the characteristics of the proposed converter. This results in a series of ZVS and ZVZCS three-level DC/DC converters for high-power high-voltage applications. In all cases, results from 6kW prototypes operating at 100 kHz are presented. In addition, with the ultimate goal of improving the power density of the DC/DC converter, a study of several resonant DC/DC converters that can operate at higher switching frequencies is presented. From this study, a three-element ZVS three-level resonant converter for applications with wide input voltage and load variations is proposed. Experimental results at 745 kHz obtained without penalizing the efficiency of the PWM approaches are presented. The second part of the dissertation proposes a quasi-integrated AC/DC three-phase converter that aims to reduce the complexity and cost of the traditional two-stage front-end converter. This converter improves the complexity/low-efficiency tradeoff characteristics evident in the two-stage approach and previous integrated converters. The principle of operation for the converter is analyzed and verified on a 3kW experimental prototype.
Ph. D.

Rozptýlená výroba elektrické energie využívající obnovitelné zdroje, jako je sluneční energie, přispívá ke snížení emisí skleníkových plynů. Z hlediska provozu distribuční soustavy je také výhodné, aby energie byla primárně spotřebována v místě výroby. To je částečně možné přizpůsobením spotřeby, ale především využitím akumulačních systémů. V této práci je představen hybridní systém složený z fotovoltaické elektrárny, akumulátoru elektrické energie a akumulátoru tepelné energie. Výběr a parametry všech částí hybridního systému jsou popsány v práci. Akumulátor elektrické energie je navržen a sestaven z LiNiMnCoO2 článků a řídícího systému zajišťujícího bezpečný provoz. Řídicí systém akumulátoru (BMS) zajistí odpojení baterie, pokud je překročen některý z provozních parametrů baterie. Návrh baterie i sestavy je popsán v práci. Akumulátor tepelné energie sestává z výkonového spínače a nádrže na teplou vodu s topnou patronou pro odporový ohřev vody. Na základě rešerše komerčně používaných zařízení pro regulaci příkonu byly definovány jejich nedostatky a na základě nich bylo navrženo optimální řešení. Řešení spočívá v použití komerčního polovodičového spínacího prvku. Pro tento výkonový spínací prvek byla vytvořena zpětnovazební řídící smyčka s regulátorem výkonu, který byl implementován v prostředí softwaru LabVIEW. V práci je také uveden postup návrhu chladiče spínacího prvku a LCL filtru, který je klíčový pro splnění požadavků elektromagnetické kompatibility. V druhé části práce je popsán návrh nadřazeného řídícího algoritmu, jehož úkolem je řídit výkonové toky v hybridním systému tak, aby byly splněny požadavky definované jak uživatelem, tak i okamžitým stavem akumulátorů. Algoritmus byl implementován v prostředí LabVIEW. Funkčnost celého systému byla ověřena měřením v laboratorních podmínkách. Z výsledků plyne, že nadřazený řídící algoritmus funguje správně. Řídící smyčka tepelného akumulátoru je stabilní a reguluje zátěž na požadovanou hodnotu. Přidanou hodnotou je kratší reakční doba na změnu toku výkonu oproti hybridnímu měniči a díky tomu dochází k minimalizaci přetoků elektrické energie do distribuční sítě. Na práci je možné navázat rozšířením stávajícího algoritmu o možnost řízení/ovládání více typů akumulačních jednotek a generátorů nebo implementováním odlišných strategií řízení.

L'orientation énergétique actuelle vers le développement de systèmes électriques isolés, s'est traduit par l'établissement de nouvelles directives sur les performances et la fiabilité des structures de puissance mises en oeuvre, en particulier ceux à base d'énergies renouvelables. C'est dans ce contexte que s'inscrivent ces travaux de thèse, qui aboutissent à l'élaboration de nouveaux outils destinés à l'amélioration de la qualité d'énergie et de la stabilité d'un micro-réseau autonome. Concernant l'optimisation énergétique des interfaces de conversion pour un réseau autonome, nous avons développé de nouveaux algorithmes de commande basés sur le concept de platitude des systèmes différentiels. L'avantage de cette technique réside dans la possibilité d'implémentation de régulateurs à une boucle. Cela garantit des propriétés dynamiques élevées en asservissement et en régulation. De plus, une prédiction exacte de l'évolution des variables d'états du système est possible. Concernant la stabilité des micro-réseaux autonomes, nous avons proposé des outils pour traiter les phénomènes d'instabilités, causés notamment par la perte d'informations de charges et par le phénomène de résonance des filtres d'interconnexion
The actual electrical energy demand focuses on the development of stand-alone electrical systems which leads to the definition of new directives on performances and reliability of the electrical structures, especially those based on renewable energy. The main objective of this work concerns the development of new tools to improve the power quality and the stability of autonomous micro-grid systems. In this aim, new control algorithms based on the concept of differential flatness have been developed. The main advantage of the proposed technique is the possibility of implementing one loop controllers ensuring high dynamic properties. In the same time, it allows accurate prediction of the evolution of all state variables of the system. Concerning the stability of the autonomous micro-grid systems, we proposed tools to deal with instability phenomena either caused by the loss of load information and the resonance phenomenon of the passive filters

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2003.
Thesis advisor(s): Robert W. Ashton, Todd R. Weatherford. Includes bibliographical references (p. 83-84). Also available online.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.
Includes bibliographical references (p. 75-78).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
A significant factor driving the development of power conversion technology is the need to increase performance while reducing size and improving efficiency. In addition, there is a desire to increase the level of integration of DC-DC converters in order to take advantage of the cost and other benefits of batch fabrication techniques. While advances in the power density and integration of DC-DC converters have been realized through development of better active device technologies, much room for improvement remains in the size and fabrication of passive components. To achieve these improvements, a substantial increase in operating frequency is needed, since intermediate energy storage requirements are inversely proportional to frequency. Unfortunately, traditional power conversion techniques are ill-suited to handle this dramatic escalation of switching frequency. New architectures have been proposed which promise to deliver radical performance improvements while potentially reaching microwave frequencies. These new architectures promise to enable substantial miniaturization of DC-DC converters and to permit much a higher degree of integration. The principal effort of this thesis is the development of design and characterization methods for rectifier topologies amenable to use in the new architectures. A computational design approach allowing fast and accurate circuit analysis and synthesis is developed and applied, along with traditional analysis, to two demonstrative rectifier topologies. In addition, the application of coupled magnetic structures for parasitic mitigation is considered. Experimental implementations are investigated to verify analytic and computational results.
by Riad Samir Wahby.
M.Eng.

Thesis (M.Eng. and S.B.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.
Includes bibliographical references (leaf 125).
by Sauparna Das.
M.Eng.and S.B.

A monolithically integrated smart rectifier has been presented first in this work. The smart rectifier, which integrates a power MOSFET, gate driver and control circuitry, operates in a self-synchronized fashion based on its drain-source voltage, and does not need external control input. The analysis, simulation, and design considerations are described in detail. A 5V, 5-μm CMOS process was used to fabricate the prototype. Experimental results show that the proposed rectifier functions as expected in the design. Since no dead-time control needs to be used to switch the sync-FET and ctrl-FET, it is expected that the body diode losses can be reduced substantially, compared to the conventional synchronous rectifier. The proposed self-synchronized rectifier (SSR) can be operated at high frequencies and maintains high efficiency over a wide load range. As an example of the smart rectifier's application in isolated DC-DC converter, a synchronous flyback converter with SSR is analyzed, designed and tested. Experimental results show that the operating frequency could be as high as 4MHz and the efficiency could be improved by more than 10% compared to that when a hyper fast diode rectifier is used. Based on a new current-source gate driver scheme, an integrated gate driver for buck converter is also developed in this work by using a 0.35μm CMOS process with optional high voltage (50V) power MOSFET. The integrated gate driver consists both the current-source driver for high-side power MOSFET and low-power driver for low-side power iv MOSFET. Compared with the conventional gate driver circuit, the current-source gate driver can recovery some gate charging energy and reduce switching loss. So the current-source driver (CSD) can be used to improve the efficiency performance in high frequency power converters. This work also presents a new implementation of a power supply in package (PSiP) 5MHz buck converter, which is different from all the prior-of-art PSiP solutions by using a high-Q bondwire inductor. The high-Q bondwire inductor can be manufactured by applying ferrite epoxy to the common bondwire during standard IC packaging process, so the new implementation of PSiP is expected to be a cost-effective way of power supply integration.
Ph.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering PhD

Avui en dia la conversió DC-AC té una important aplicació pràctica en el camp dels sistemes de potència ininterrompuda (SPI). Els convertidors commutats bàsics (el buck, lineal, i el boost i el buck-boost, no lineals) presenten una estructura molt simple, i al llarg dels últims quinze anys s'ha estudiat la possibilitat d'usar-los en esquemes de conversió DC-AC.

L'objectiu de la tesi és aconseguir que els convertidors DC-DC de potència bàsics puguin seguir referències alternes mitjançant el voltatge de sortida. També es desenvolupen esquemes robustos per tal d'eliminar l'efecte de possibles pertorbacions en la tasca de seguiment. Els modes de lliscament s'usen com a tècnica de control, i es presenten resultats de simulació.

La tesi s'organitza en capítols. El primer i el segon contenen una introducció i una revisió de la literatura existent. Els continguts i distribució de la resta de capítols segueix a continuació.

El capítol 3 tracta el seguiment exacte i asimptòtic d'una referència variable en el temps per part del voltatge de sortida d'un convertidor reductor, controlat indirectament via el corrent d'entrada. A partir de l'estudi del problema del seguiment en sistemes lineals amb guanys fixos -mitjançant la teoria de mòduls- s'obtenen restriccions sobre els possibles senyals a seguir. A més, es proporciona una estratègia de control lliscant per aconseguir el seguiment, consistent en un procediment per modificar una superfície de lliscament inicialment bona en tasques de regulació i una llei de control. Una adequada elecció de variables d'estat permet que les possibles pertorbacions de la resistència de càrrega satisfacin la condició de superposició.
En el capítol 4 s'usa un procediment basat en inversió per aconseguir el seguiment exacte de referències periòdiques amb la resistència de càrrega dels convertidors no lineals boost i buck-boost. També s'obtenen condicions suficients per a possibles senyals a seguir. Es presenta també un marc general per a un tractament via inversió del problema de seguiment exacte en una certa classe de sistemes bilineals de segon ordre: aquells en els quals el problema d'inversió dóna lloc a una EDO del tipus Abel.

El capítol 5 estudia l'ús del mètode de Galerkin -una generalització del mètode del Balanç Harmònic- en la solució aproximada del problema invers aparegut al capítol anterior, així com l'efecte que té la seva utilització en el control del sistema. Es demostra l'existència d'una successió de solucions aproximades de l'EDO que representa l'esmentat problema invers. També es prova que aquesta successió convergeix uniformement cap a la solució periòdica de l'EDO, i s'obté una cota d'error. La sortida del sistema presenta un comportament periòdic i asimptòticament estable quan es fa anar la successió d'aproximacions de Galerkin en el control del sistema. A l'hora, la successió de sortides periòdiques presenta convergència uniforme cap a la funció desitjada sota una hipòtesi raonable. També s'obtenen en aquest cas cotes d'error.

En el capítol 6 s'aconsegueix seguiment asimptòtic aproximat per a convertidors no lineals bàsics que presenten pertorbacions de càrrega. Això es fa mitjançant un control adaptatiu que estima el paràmetre pertorbat i una aproximació de Galerkin de primer ordre que incorpora l'actualització on-line a una superfície de lliscament apropiada.

El capítol 7 proposa exercir un control directe del voltatge de sortida en convertidors boost i buck-boost bidireccionals, tot aprofitant la robustesa davant pertorbacions externes que ofereix aquest tipus de control. Es segueixen referències periòdiques mentre el voltatge de sortida es regula independentment a un nivell prefixat.
Nowadays, DC-to-AC conversion has an important practical application in the field of uninterruptible power systems (UPS). Basic DC-to-DC switch mode power converters (the buck, which is linear, and the boost and buck-boost, which are nonlinears) possess a very simple structure, and during the last fifteen years the possibility of using them in DC-to-AC conversion schemes has been studied.

The aim of this thesis is to achieve that the output voltage of the DC-to-DC buck, boost and buck-boost power converters can track periodic references. Robust schemes to eliminate disturbance effects in the tracking task are also developed. Sliding modes are used as the control technique, and the obtained results are validated by numeric simulation.

The thesis is organized in chapters. The first and the second one contain an introduction and a review of the existing literature. The contents and contributions of the other chapters follow below.

Chapter 3 deals with the exact and asymptotic tracking of a time varying reference by the load voltage of a step-down converter, indirectly controlled through the input current. Departing from the study of the tracking problem in linear systems with fixed gains with the aid of module theory, conditions over possible reference signals have been obtained. Moreover, a sliding mode strategy to achieve the control target, consisting in a procedure to modify a switching surface initially good for regulation tasks and a control law, is provided. An approppriate choice of state variables allows possible load perturbations to satisfy the matching condition.


In chapter 4, an inversion-based indirect control is used to reach exact tracking of periodic references with the load resistance of nonminimum phase, nonlinear boost and buck-boost converters. Sufficient conditions for candidate references are also obtained. A general frame for an inversion-based treatment of the perfect tracking problem in a certain class of nonminimum phase, second order bilinear systems is proposed: those in which the inversion problem gives raise to an ODE of the Abel type.

Chapter 5 studies the use of the Galerkin method -a generalization of the Harmonic Balance method- in the approximate solution of the inverse problem stated in the former chapter, as well as the effect of its use on the control of the system. The existence of a sequence of approximate solutions for the ODE that represents the quoted inverse problem is proved. This sequence is also proved to converge uniformly to the periodic solution of the ODE, and an error bound has been derived. The system output exhibits a periodic and asymptotically stable behavior when the indirect control using the sequence of Galerkin approximations is performed. In turn, the sequence of periodic outputs is shown to exhibit uniform convergence to the original target function under a reasonable hypothesis. Error bounds have also been obtained.

In chapter 6, approximate asymptotic tracking is achieved for load perturbed, basic, nonlinear power converters. This is done by means of an adaptive control that estimates the perturbation parameter and a first order Galerkin approximation that incorporates the on-line updating into an appropriate sliding surface.

Chapter 7 propounds to exert a direct control of the output voltage in bidirectional boost and buck-boost converters, thus taking advantage of the insensitiveness to external disturbances offered by this type of control. Periodic references are followed, while the unstable inductor current is independently regulated at a prescribed level.

Thesis (Elect. E.)--Massachusetts Institute of Technology, Dept. of Electrical Engieering and Computer Science, 1985.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.
Bibliography: leaves 136-139.
by Andrew Franklin Goldberg.
Elect.E.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
Includes bibliographical references (p. 79-80).
This thesis describes the design, and validation of a maximum power point tracking DC-DC converter capable of following the true global maximum power point in the presence of other local maximum. It does this without the use of costly components such as analog-to-digital converters and microprocessors. It substantially increases the efficiency of solar power conversion by allowing solar cells to operate at their ideal operating point regardless of changes in load, and illumination. The converter switches between a dithering algorithm which tracks the local maximum and a global search algorithm for ensuring that the converter is operating at the true global maximum.
by Joseph Duncan.
M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 321-325).
Power electronics appear in nearly every piece of modern electronic hardware, forming an essential conduit from electrical source to load. Portable electronics, an area where a premium is placed on size, weight, and cost, are driving the development of power systems with greater density and better manufacturability. This motivates a push to higher switching frequencies enabling smaller passive components and better integration. To realize these goals this thesis explores devices, circuits, and passives capable of operating efficiently into the VHF regime (30-300 MHz) and their integration into power electronic systems of high power density. A good integrated power MOSFET presages high-density converters. Previous VHF systems were demonstrated with bulky and expensive RF Lateral, Double-Diffused MOSFETs (LDMOSFET). We show that through a combination of layout optimization and safe operating area (SOA) extension integrated devices can achieve near-parity performance to their purpose-built RF discrete cousins over the desired operating regime. A layout optimization method demonstrating a 2x reduction in device loss is presented alongside experimental demonstration of SOA extension. Together the methods yield a 3x reduction in loss that bolsters the utility of the typical (and relatively inexpensive) LDMOS IC power process for VHF converters. Passive component synthesis is addressed in the context of an isolated VHF converter topology. We present a VHF topology where most of the magnetic energy storage is accomplished in a transformer that forms an essential part of the resonant network. The reduced component count aids in manufacturability and size, but places difficult requirements on the transformer design. An algorithm for synthesizing small and efficient air-core transformers with a fully-constrained inductance matrix is presented. Planar PCB transformers are fabricated and match the the design specifications to within 15%. They are 94% efficient and have a power density greater than 2kW per cubic inch. To take full advantage of good devices and printed passives, we develop an IC for the isolated converter having optimized power devices, and integrated gate driver, controller, and hotel functions. The chip is assembled into a complete converter system using the transformers and circuits described above. Flip-chip mounting is used to overcome bondwire parasitics, and reduce packaging volume. The final system achieves 75% efficiency at 75 MHz at 6W.
by Anthony D. Sagneri.
Ph.D.

There is a steady demand to increase the efficiency and raise the power density of power converters. This trend is desired since it leads to reduced size of the converter. The purpose of this thesis is to investigate materials, topologies, core structure and then build a prototype to demonstrate the result. Two core materials have been compared, Fair-Rite material 68 and Ferroxcube 4F1. The goal was to have 50 V input and 30 V output with 80 % efficiency of the converter. The converter with the Fair-Rite material 68 accomplished a peak efficiency at 11 MHz with 54 % efficiency. The core material Ferroxcube 4F1, reached an efficiency of 52 % at 7 MHz. These results were however with 5 V input and 3 V output. The converter had a low efficiency at 50 V input, which lead to ripple in the circuit. One reason for this behaviour was because the design of the PCB was not optimized for MHz operation. The focus of the PCB was that it should be easy to work with instead of achieving peak performance. Also, from the beginning it was decided that no PCB should be made. The focus was instead on the theory and simulations of the converter so no thoroughly investigation of PCB design was done. The leakage inductance of the transformer core was about 10 % of the primary inductance for both materials. The high leakage inductance is believed to further reduce the efficiency of the converter.

In his thesis, CONDUCTED EMC MODELLING IN MODERN DC-DC POWER CONVERTERS, the conducted electromagnetic effects of high-density high-switching frequency modern power converters are studied. The noise source and noise path were modelled and the results calibrated to accredited noise levels. A VHF frequency model was developed and verified using different analysis packages and compared for accuracy, affordability and ease of use. Noise modes were separated and verified for accuracy. The mechanisms of the noise modes were studied and noise mitigation techniques presented.
Thesis (PhD)--University of Pretoria, 2017.
Electrical, Electronic and Computer Engineering
PhD
Unrestricted

Thesis (M.S.) -- University of Maryland, College Park, 2003.
Thesis research directed by: Dept. of Electrical and Computer Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

n this thesis project, a proposed architecture for the multiple input, single output conversion stage for the DC House was designed, simulated, and tested. This architecture allows for multiple different input sources to be used to create a single higher power output source. The design uses a DC-DC boost converter with a parallelable output which has been demonstrated to allow increased total output power as a function of the number of input sources available. The parallelable output has been shown to distribute load amongst the input sources relatively closely to optimize the system. This approach is also desirable since it allows for flexibility in multiple configurations it can be used in. The design was tested using hardware and data results show the performance met and exceeded the needs of the DC House project. Data was taken for configuration with 1, 2, 3, and 4 input sources providing greater than 600W of total output power at an efficiency of greater than 92%. This architecture demonstrates the possibility of expanding the total available power for a single output in proportion to the number of available input sources.

This thesis presents the concept of the dc power flow controller to address the power flow control issues inside a multiterminal High Voltage Direct Current (HVDC) system. The controller is connected in series on the HVDC transmission line and it is presented as a small appendage of a voltage source converter (VSC) station. The operation and the stability are shown via simulations of a 3-terminal and a 7-terminal HVDC grid. The controller increases the flexibility and the region of operation of the multiterminal HVDC system.The integration of an offshore wind farm into a multiterminal HVDC system is also studied. By using a dc collector network for the aggregation of power produced by the wind turbines, the high civil engineering cost of an offshore platform to support heavy ac transformers required by the converter station for HVDC transmission can be avoided. The challenge is to bridge the two dc voltages without ac transformers.This thesis introduces and analyzes a new dc-dc converter topology which is based on the Marx generator concept. The concept consists of charging capacitors in parallel followed by reconnection in series of the capacitors to create higher dc voltage. The converter with a multi-stage configuration is simulated for proof of concept. Design guidelines are developed and a 5kW prototype has been constructed to verify experimentally the converter topology. The stability of the converter is analyzed using a sampled-data approach and the power ratings of the semiconductor switches and passive components are evaluated.For offshore wind farm application, the Marx dc-dc converter is combined with a step-up converter to form the Marx offshore station which bridges the 10kV dc collector network to the 250kV HVDC transmission line. The Marx offshore station is simulated with an offshore wind farm and an onshore VSC inverter station.The two parts of the thesis, the dc power flow controller and the Marx dc-dc converter, are integrated within a complete multiterminal HVDC system. The simulated system comprises six VSC terminal stations, the Marx offshore station with an offshore wind farm and the dc power flow controller. Both the dc power flow controller and the Marx dc-dc converter enlarge the scope of multiterminal HVDC system.
Cette thèse présente le concept d'un contrôleur de transit de puissance afin de résoudre la problématique de contrôle des mouvements d'énergie dans un réseau multiterminal à courant continu à haute tension (CCHT). Le contrôleur est installé en série sur la ligne de transport CCHT et il est présenté comme un module ajouté à une station convertisseur à CCHT. Le fonctionnement et la stabilité sont démontrés à l'aide de simulations dans des systèmes multiterminaux de 3 et de 7 terminaux. Le contrôleur augmente la flexibilité et l'étendue de l'exploitation d'un système multiterminal CCHT.L'intégration d'un parc éolien installé en mer avec un système multiterminal CCHT est aussi étudiée. En utilisant un réseau à courant continu (cc) pour collecter la puissance produite par les éoliennes, les coûts d'infrastructure associés au support de lourds transformateurs à courant alternatif (ca) requis pour la station du convertisseur servant au transport CCHT peuvent être évités. Le défi consiste à relier les deux tensions cc en omettant l'utilisation de transformateurs ca.Cette thèse introduit et analyse une nouvelle topologie de convertisseurs cc-cc qui est basée sur le concept du générateur Marx. Ce concept consiste à charger des condensateurs en parallèle pour ensuite les connecter en série afin de créer une tension cc plus élevée. Un convertisseur avec une configuration multi-étapes est simulé pour une démonstration de faisabilité. À partir de balises de conceptions, un prototype de 5kW a été conçu, simulé et construit afin de vérifier expérimentalement la topologie du convertisseur. La stabilité de la topologie a été analysée en utilisant une approche de données échantillonnées et des caractéristiques nominales des semiconducteurs de puissance et des composants passifs sont évaluées.Pour l'application dans un parc éolien installé en mer, le convertisseur cc-cc Marx est jumelé avec un hacheur survolteur afin de former une station Marx qui lie le réseau collecteur cc de 10kV au réseau de transport CCHT de 250kV. La station Marx est simulée avec un parc éolien et un convertisseur onduleur.Les deux parties de cette thèse, soit le contrôleur de transit de puissance et le convertisseur cc-cc Marx, sont regroupés dans un même système multiterminal CCHT. Le réseau simulé comprend six stations convertisseurs de type « voltage source converter », la station Marx avec le parc éolien installé en mer et le contrôleur de transit de puissance. Le contrôleur de transit de puissance et le convertisseur cc-cc élargissent la portée du système multiterminal CCHT.

AC or DC has been in the centre of debate since the early days of the electrical system. DC is already proven to be more economical than AC in transmission at elevated power and voltages. Thus, expanding the use of DC to the distribution grids seems promising as most of the distributed generation such as PV generates initial DC voltages and many of the modern loads are using internal DC buses. Still, in order to extend the use of DC to the distribution level a suitable DC distribution grid architecture and a suitable DC/DC converter to serve it should be explored, which is the focus of this Ph.D. A study based on the Libyan grid and loads was carried out to investigate the most suitable DC distribution grid layout. The results showed that DC grid arrangement utilising two port converters have lower total converter losses and smaller converter installed power when compared with arrangements using three ports converter. A multi-cell multi–snubbered three phase dual active bridge (DAB) converter was proposed to serve the chosen DC distribution grid layout. The modular multi-cell multi–snubbered 3 phase DAB converter offered low losses over a wide range of loading profiles. Furthermore, the converter performance can be easily modified to be able to serve a specific DC/DC grid loading profile by altering the snubbers attached to the cells and the power management’s algorithm between the cells while keeping the core cells the same. Extra cells can be added if higher power rating is required, reducing the total cost of expanding the proposed DC distribution system. This thesis is an ambition step on deciding the structure of the futuristic DC grid and the required DC/DC converters to link it is different voltage levels.

The development of a DC-DC converter for use in a proposed range of one to ten kilowatt off-line power supplies is presented. The converter makes good use of established design practices and recent technical advances. The thesis begins with a review of traditional design practices, which are used in the design of a 3kW, 48V output DC-DC converter, as a bench-mark for evaluation of recent technical advances. Advances evaluated include new converter circuits, control techniques, components, and magnetic component designs. Converter circuits using zero voltage switching (ZVS) transitions offer significant advantages for this application. Of the published converters which have ZVS transitions the phase shift controlled full bridge converter is the most suitable, and assessments of variations on this circuit are presented. During the course of the research it was realised that the ZVS range of one leg of the phase shift controlled full bridge converter could be extended by altering the switching pattern, and this new switching pattern is proposed. A detailed analysis of phase shift controlled full bridge converter operation uncovers a number of operational findings which give a better and more complete understanding of converter operation than hitherto published. Converter design equations and guidelines are presented and the effects of the new improvement are investigated by an approximate analysis. Computer simulations using PSPICE2 are carried out to predict converter performance. A prototype converter design, construction details and test results are given. The results obtained compare well to the predicted performance and confirm the advantages of the new switching pattern.

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Bachelors
Engineering
Electrical Engineering

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2000.
Includes bibliographical references.
The imminent introduction of a dual-voltage automotive electrical system has motivated the development of dc/dc converters that are optimized it terms of price, weight, and volume. This thesis investigates the design and optimization of dc/dc converters for dual-voltage automotive electrical system. A prototype dc/dc converter is developed and experimental evaluated, and is used to identify a number of tradeoffs and critical design issues. Based on this information, a CAD optimization tool is developed which allows the design space to be rapidly explored and highly optimized converter design to be developed. The CAD optimization tool is also used to study the effects of variations in system-level specifications on the characteristics of optimized converters.
by Timothy Carl Neugenbauer.
S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 109).
This thesis presents a new topology for a high efficiency dc/dc resonant power converter that utilizes a resistance compression network to provide simultaneous zero voltage switching and near zero current switching across a wide range of input voltage, output voltage and power level. The resistance compression network maintains desired current waveforms over a wide range of voltage operating conditions. The use of on/off control in conjunction with narrowband frequency control enables high efficiency to be maintained across a wide range of power levels. The converter implementation provides galvanic isolation and enables large (greater than 1:10) voltage conversion ratios, making the system suitable for large step-up conversion in applications such as distributed photovoltaic converters. Three 200 W prototypes were designed, built and tested. The first prototype was made as a proof of concept and operated at a switching frequency of 100 kHz. It had an efficiency of 93.5% (at 25 V input and 400 V output). The second prototype was operated at a switching frequency of 500 kHz and had an efficiency of 93% (at 25 V input and 400 V output). The high frequency losses caused by the ringing in voltage and current due to the resonating parasitics of the transformer were removed with the help of a matching network in the third prototype. This final prototype operated at a switching frequency of 500 kHz and showed that over 95% efficiency is maintained across an input voltage range of 25 V - 40 V (at 400 V output) and over 93.7 % efficiency across a wide output voltage range of 250 V - 400 V (at 25 V input). These experimental results demonstrated the effectiveness of the proposed design.
by Wardah Inam.
S.M.

Design and implementation of high power density and high efficiency dc-dc converters has been a primary component for reducing energy cost. Traditionally dc-dc converters are composed with silicon based technology that has limited switching frequency hence, increased volume of passive components and lower efficiency. This research presents a novel type of multilevel modular switched capacitor dc-dc converters with comprehensive design and multiple variant prototypes. Previous versions of traditional multilevel modular switched-capacitor dc-dc converters have a low switching device voltage rating. Additionally, the proposed circuits share all the advantages from the multilevel modular switched capacitor type converters such as soft switching, low voltage device rating, bidirectional operation, high conversion ratio, extremely high or low environment temperature operation, basic control algorithm, and modular structure. The converters in this research are found to be superior due to the simple structure, soft switching, and low conduction loss and, 97% or higher efficiency.

In order to increase the power density, the discontinuous conducting mode (DCM) and small inductance is adopted for high power bidirectional dc-dc converter. The DCM related current ripple is minimized with multiphase interleaved operation. The turn-off loss caused by the DCM induced high peak current is reduced by snubber capacitor. The energy stored in the capacitor needs to be discharged before device is turned on. A complementary gating signal control scheme is employed to turn on the non-active switch helping discharge the capacitor and diverting the current into the anti-paralleled diode of the active switch. This realizes the zero voltage resonant transition (ZVRT) of main switches. This scheme also eliminates the parasitic ringing in inductor current. This work proposes an inductance and snubber capacitor optimization methodology. The inductor volume index and the inductor valley current are suggested as the optimization method for small volume and the realization of ZVRT. The proposed capacitance optimization method is based on a series of experiments for minimum overall switching loss. According to the suggested design optimization, a high power density hardware prototype is constructed and tested. The experimental results are provided, and the proposed design approach is verified. In this dissertation, a general-purposed power stage model is proposed based on complementary gating signal control scheme and derived with space-state averaging method. The model features a third-order system, from which a second-order model with resistive load on one side can be derived and a first-order model with a voltage source on both sides can be derived. This model sets up a basis for the unified controller design and optimization. The Î -type model of coupled inductor is introduced and simplified to provide a more clearly physical meaning for design and dynamic analysis. These models have been validated by the Simplis ac analysis simulation. For power flow control, a unified controller concept is proposed based on the derived general-purposed power stage model. The proposed unified controller enables smooth bidirectional current flow. Controller is implemented with digital signal processing (DSP) for experimental verification. The inductor current is selected as feedback signal in resistive load, and the output current is selected as feedback signal in battery load. Load step and power flow step control tests are conducted for resistive load and battery load separately. The results indicate that the selected sensing signal can produce an accurate and fast enough feedback signal. Experimental results show that the transition between charging and discharging is very smooth, and there is no overshoot or undershoot transient. It presents a seamless transition for bidirectional current flow. The smooth transition should be attributed to the use of the complementary gating signal control scheme and the proposed unified controller. System simulations are made, and the results are provided. The test results have a good agreement with system simulation results, and the unified controller performs as expected.
Ph. D.

A company in Linköping has a project where a solar power home system is designed. The plan is that families that lack grid connection in rural areas of Mali and other countries shall use this system for cooking food and powering every day items. Designing a solar home system for West Africa is more difficult than for other parts of the world, mainly because of the climate, with heat and dust particles in the air, but also because the installation location often is unreachable in short notice. This makes for several specific requirements like high ambient temperature, passive cooling, high efficiency and a long mean time between service needed. On top of this, to get the system modular and easy to install, each physical panel should be independent and smart. The system designed is a push pull dc step-up converter that can be assembled to the back of a solar panel. A base platform for the converter is built and a method of power line communication is proposed. Tests show promising results and further development is ongoing.

This thesis reports on the investigations, simulations and analyses of novel power electronics topologies and control strategies. The research is financed by an Australian Research Council (ARC) Linkage (07-09) grant. Therefore, in addition to developing original research and contributing to the available knowledge of power electronics, it also contributes to the design of a DC-DC converter for specific application to the auxiliary power supply in electric trains. Specifically, in this regard, it contributes to the design of a 7.5 kW DC-DC converter for the industrial partner (Schaffler and Associates Ltd) who supported this project. As the thesis is formatted as a ‘thesis by publication’, the contents are organized around published papers. The research has resulted in eleven papers, including seven peer reviewed and published conference papers, one published journal paper, two journal papers accepted for publication and one submitted journal paper (provisionally accepted subject to few changes). In this research, several novel DC-DC converter topologies are introduced, analysed, and tested. The similarity of all of the topologies devised lies in their ‘current circulating’ switching state, which allows them to store some energy in the inductor, as extra inductor current. The stored energy may be applied to enhance the performance of the converter in the occurrence of load current or input voltage disturbances. In addition, when there is an alternating load current, the ability to store energy allows the converter to perform satisfactorily despite frequently and highly varying load current. In this research, the capability of current storage has been utilised to design topologies for specific applications, and the enhancement of the performance of the considered applications has been illustrated. The simplest DC-DC converter topology, which has a ‘current circulating’ switching state, is the Positive Buck-Boost (PBB) converter (also known as the non-inverting Buck-Boost converter). Usually, the topology of the PBB converter is operating as a Buck or a Boost converter in applications with widely varying input voltage or output reference voltage. For example, in electric railways (the application of our industrial partner), the overhead line voltage alternates from 1000VDC to 500VDC and the required regulated voltage is 600VDC. In the course of this research, our industrial partner (Schaffler and Associates Ltd) industrialized a PBB converter–the ‘Mudo converter’–operating at 7.5 kW. Programming the onboard DSP and testing the PBB converter in experimental and nominal power and voltage was part of this research program. In the earlier stages of this research, the advantages and drawbacks of utilization of the ‘current circulating’ switching state in the positive Buck-Boost converter were investigated. In brief, the advantages were found to be robustness against input voltage and current load disturbances, and the drawback was extra conduction and switching loss. Although the robustness against disturbances is desirable for many applications, the price of energy loss must be minimized to attract attention to the utilization of the PBB converter. In further stages of this research, two novel control strategies for different applications were devised to minimise the extra energy loss while the advantages of the positive Buck-Boost converter were fully utilized. The first strategy is Smart Load Controller (SLC) for applications with pre-knowledge or predictability of input voltage and/or load current disturbances. A convenient example of these applications is electric/hybrid cars where a master controller commands all changes in loads and voltage sources. Therefore, the master controller has a pre-knowledge of the load and input voltage disturbances so it can apply the SLC strategy to utilize robustness of the PBB converter. Another strategy aiming to minimise energy loss and maximise the robustness in the face of disturbance is developed to cover applications with unexpected disturbances. This strategy is named Dynamic Hysteresis Band (DHB), and is used to manipulate the hysteresis band height after occurrence of disturbance to reduce dynamics of the output voltage. When no disturbance has occurred, the PBB converter works with minimum inductor current and minimum energy loss. New topologies based on the PBB converter have been introduced to address input voltage disturbances for different onboard applications. The research shows that the performance of applications of symmetrical/asymmetrical multi-level diode-clamped inverters, DC-networks, and linear-assisted RF amplifiers may be enhanced by the utilization of topologies based on the PBB converter. Multi-level diode-clamped inverters have the problem of DC-link voltage balancing when the power factor of their load closes to unity. This research has shown that this problem may be solved with a suitable multi-output DC-DC converter supplying DClink capacitors. Furthermore, the multi-level diode-clamped inverters supplied with asymmetrical DC-link voltages may improve the quality of load voltage and reduce the level of Electromagnetic Interference (EMI). Mathematical analyses and experiments on supplying symmetrical and asymmetrical multi-level inverters by specifically designed multi-output DC-DC converters have been reported in two journal papers. Another application in which the system performance can be improved by utilization of the ‘current circulating’ switching state is linear-assisted RF amplifiers in communicational receivers. The concept of ‘linear-assisted’ is to divide the signal into two frequency domains: low frequency, which should be amplified by a switching circuit; and the high frequency domain, which should be amplified by a linear amplifier. The objective is to minimize the overall power loss. This research suggests using the current storage capacity of a PBB based converter to increase its bandwidth, and to increase the domain of the switching converter. The PBB converter addresses the industrial demand for a DC-DC converter for the application of auxiliary power supply of a typical electric train. However, after testing the industrial prototype of the PBB converter, there were some voltage and current spikes because of switching. To attenuate this problem without significantly increasing the switching loss, the idea of Active Gate Signalling (AGS) is presented. AGS suggests a smart gate driver that selectively controls the switching process to reduce voltage/current spikes, without unacceptable reduction in the efficiency of switching.

Growing concerns about climate change have led to the world experiencing an unprecedented push towards renewable energy. Economic drivers and government policies mean that small, distributed forms of generation, like solar photovoltaics, will play a large role in our transition to a clean energy future. In this thesis, a novel DC-DC converter known as the Coupled Inductors Combined Cuk-SEPIC' (CI-CCS) converter is explored, which is particularly attractive for these photovoltaic applications. A topological modification is investigated which provides several benefits, including increased power density, efficiency, and operational advantages for solar energy conversion. The converter, which is based on the combination of the Cuk and SEPIC converters, provides a bipolar output (i.e. both positive and negative voltages). This converter also offers both step-up and step-down capabilities with a continuous input current, and uses only a single, ground-referenced switching device. A significant enhancement to this converter is proposed: magnetic coupling of the converter's three inductors. This can substantially reduce the CI-CCS converter's input current ripple - an important benefit for maximum power point tracking (MPPT) in photovoltaic applications. The effect of this coupling is examined theoretically, and optimisations are performed - both analytically and in simulations - to inform the design of a 4 kW prototype CI-CCS converter, switched at a high frequency (100 kHz) with a silicon carbide (SiC) MOSFET. Simulation and experimental results are then presented to demonstrate the CI-CCS converter's operation and highlight the benefits of coupling its inductors. An efficiency analysis is also undertaken and its sources of losses are quantified. The converter is subsequently integrated into a domestic photovoltaic system to provide a practical demonstration of its suitability for such applications. MPPT is integrated into the CI-CCS DC-DC converter, and a combined half bridge/T-type converter is developed and paired with the CI-CCS converter to form an entirely transformerless single-phase solar energy conversion system. The combination of the CI-CCS converter's bipolar DC output with the combined half bridge/T-type converter's bipolar DC input allows grounding at both the photovoltaic panels and the AC grid's neutral point. This eliminates high frequency common mode voltages from the PV array, which in turn prevents leakage currents. The entire system can be operated in grid-connected mode - where the objective is to maximise power extracted from the photovoltaic system, and is demonstrated in stand-alone mode - where the objective is to match solar generation with the load's power demands.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
This work proposes study and implementation of a DC/DC Z-source converter operating in continuous conduction mode (CCM); It is applied to a photovoltaic system connected to a DC microgrid; aiming to inject the electricity supplied from PV array; To this end; the PV array is connected to the input of Z-source converter; which rises from 167V to 400V and injects the output current at the DC bus; using maximum power point tracking techniques (MPPT); The prototype implemented in the laboratory was developed for 1;38 kW output power; with the possibility to be fed either by a DC current source or DC voltage source; which does not happen with traditional converters (Buck; Boost; etc); The average efficiency achieved yield of 94%; As for the electric power processing from renewable sources; two heuristic methods were tested: Perturbe and Observe (P&O) and Conductance Incremental (IC); The average efficiency of the prototype; using the P&O technique in tracking maximum power was 79;9%; while using the second technique (IC) the average efficiency was a 82;5% ;
O presente trabalho propÃe o estudo e a implementaÃÃo de um conversor CC/CC Z-source; operando em modo de conduÃÃo contÃnuo (MCC); O mesmo à aplicado em um sistema fotovoltaico interligado a uma microrede CC; objetivando injetar a energia elÃtrica fornecida a partir de arranjo fotovoltaico;Para tal; o arranjo fotovoltaico à conectado na entrada do conversor Z-source; que a eleva de 167V para 400V e injeta a corrente de saÃda no barramento CC de 400V; utilizando tÃcnicas de rastreamento do ponto de mÃxima potÃncia (MPPT); O protÃtipo implementado em laboratÃrio foi desenvolvido para uma potÃncia nominal de saÃda de 1;38 kW com possibilidade de ser alimentado tanto por uma fonte CC de corrente ou uma fonte CC de tensÃo; diferenciando-se dos conversores tradicionais (Buck; Boost; etc); O mesmo alcanÃou um rendimento mÃdio de 94%; Quanto ao processamento de energia elÃtrica a partir de fontes renovÃveis; foram testados dois mÃtodos heurÃsticos: Pertube e Observe (P&O) e CondutÃncia Incremental (IC); A eficiÃncia mÃdia do protÃtipo usando a tÃcnica P&O no rastreamento da mÃxima potÃncia foi de 79;9%; enquanto usando a segunda tÃcnica alcanÃou-se uma eficiÃncia de 82;5% ;

Loop measurements are very important in evaluating dynamic performance of DC-DC converters. In this thesis, a small loop measurement tool as a low-cost alternative to a network analyzer is proposed. The tool is particularly useful when a network analyzer is not always available for use, for example when engineers are working on-site with customers or when a network analyzer is not affordable due to their relatively high cost. The design, simulation, and hardware implementation of the inexpensive loop measurement tool will be presented in this thesis. Results from computer simulation and hardware prototype demonstrate the ability of the proposed tool to perform phase margin, gain margin, and cross-over frequency measurements of DC-DC converters. These results are then shown to be comparable with those obtained from a network analyzer. The procedure used to perform loop measurements with the proposed tool will be explained. Limitations in the operation as well as further improvements to enhance the performance of the proposed tool will also be discussed.

碩士
國立臺北科技大學
電機工程系碩士班
92
It well known that DC arc furnace requires large capacity rectification equipment and thereby resulting in significant harmonics. Although for the same capacity, the flickers caused by DC arc furnace is only half of that caused by AC one, the resulting impact to power system can’t be neglected due to its large capacity. In this thesis, a case of DC arc furnace with 100 tons is investigated. It was accompanied with filters to cope with the low order odd harmonics, e.g. 3rd, 5th, 7th and 11th harmonics, and no facilities were installed to deal with the even harmonics. Therefore, the associated harmonics may not meet the Tai-power requirement under particular kind of circumstance. Moreover, the flickers caused by the illustrated DC arc furnace may meet the standard of Tai-power using dedicated power line in which the point of common coupling locates at the substation of Tai-power. However, due to the number of user increases and parallel connection to the power line, the point of common coupling is moved to the duty point. Therefore, the flickers caused by the illustrated DC arc furnace can’t meet the standard of Tai-power any more. In this thesis, the harmonics, voltage sags and flickers for the illustrated DC arc furnace are analyzed according to the measured results. The results show that 50 MVR filters for dealing with the even harmonics, e.g. 2nd, 4th, and 6th harmonics, a 90 MVR Thyristor Controlled Reactor (TCR), and other switching equipment are required in order to meet the standards of Tai-power. With this additional Thyristor-controlled Q Compensators (TQC) consisted of LC filters, TCR and switching equipment, the harmonics, voltage sags and flickers issues can be improved. It is expected to measure the system after installation for further analysis to see whether the power quality is improved.

碩士
國立中央大學
電機工程學系
106
A distribution static compensator (DSTATCOM) is proposed to improve power quality, including the grid current harmonic and power factor, resulted from the nonlinear and linear loads. On the other hands, since the instantaneous power following into or out of the DC-link capacitor on the DC side of the DSTATCOM, a sudden load change may cause a serious DC-link voltage fluctuation across the dc capacitor. Hence, the DC-link voltage regulation control of the DSTATCOM is important especially under load variation. In this study, to improve the power quality and keep the DC-link voltage of the DSTATCOM constant under variation of nonlinear and linear loads effectively, the traditional proportional-integral (PI) controller is substituted with a novel online trained compensatory neural fuzzy network with an asymmetric membership function (CFNN-AMF) controller. In the proposed CFNN-AMF, the compensatory parameter to integrate pessimistic and optimistic operations of fuzzy systems is embedded in the CFNN. Moreover, the dimensions of the Gaussian membership functions are directly extended to AMFs for the optimization of the fuzzy rules and the upgrade of learning ability of the networks. Furthermore, the network structure and online learning algorithms of the proposed CFNN-AMF are introduced in detail. Finally, the effectiveness and feasibility of the DSTATCOM using the proposed CFNN-AMF controller for the improvement of power quality and maintaining the constant DC-link voltage under nonlinear and linear load change have been demonstrated by some experimental results.

Nowadays electric propulsion has become a valid alternative to mechanical propulsion for large ships that require high speed. The electric propulsion advantages are well known and widely documented in the literature: higher dynamic performance of the electric propulsion motors; internal combustion engines separation from shafts; increased flexibility in space/zones subdivision; increased efficiency through the modulation of number of running generators; noise and vibration reduction; increasing in automation, with a consequent crew reduction. The use of electric propulsion along with the progressive increase, in number and power, in electrical loads used for ship services, led to the development of the All Electric Ship (AES) concept. Over the last years, the All Electric Ships (AESs) concept has begun to be adopted by the most important Navies, principally by the U.S. Navy, giving a boost to the technological research. An AES is a ship where all onboard electrical loads (including propulsion) are powered by a single electrical system, called Integrated Electrical System (IPS). The IPS requires careful design and management in order to ensure both high Power Quality standard and the continuity of the service. With the technological progress, the shipboard electrical systems have changed considerably, rising from few MW of installed power to values of the order of hundred MW, both in cruises and military ships. Especially in military vessels, considering the number of special devices that are present on board (weapon systems, communication equipment, radar, sonar, and missile guidance systems), a performing and reliable electrical systems is required. Moreover, it is necessary to notice that some of the new electrical pulsed loads specific to military applications (e.g. radar, electromagnetic launchers, etc.) together with electric drives for propulsion engines can cause strong disturbances to the system, thus causing the malfunction of other electric utilities that may endanger the continuity of the service. The penetration of power electronics converters is the main issue for the contribution of harmonic distortion in AC grids, which must be limited not to increase system power losses, and to allow the correct operation of system and user devices. Standards dictate the maximum admissible values of the total voltage harmonic distortion and of the individual harmonics amplitudes, as a function of the rated system voltage. The relatively limited short-circuit power available on board also exposes the IPS to significant voltage sags and flickers caused by switching and/or intermittent loads. In this scenario, DC electrical distribution systems can be very attractive, thanks to their intrinsic immunity to harmonic problems. If DC micro-grids are interfaced to AC networks by means of Front End Converters (FECs), both AC/DC grid decoupling and considerable AC-side harmonic distortion reduction can be achieved. In addition, they simplify the power supply of converter-fed loads and the interfacing of storage systems. The latter can perform several tasks, including ensuring power supply in case of AC grid loss, peak-shaving and levelling pulsating loads further improving both the quality and the continuity of supply to DC islands loads. In the light of the above, it is evident that the electric power system is of primary importance for a modern ship. Moreover, if high-performance is required, careful analysis of the disturbances in the power system is mandatory. In fact, in order to achieve a reliable and performing power system, together with a high-Power Quality, it is necessary to assess this situation and propose guidelines to be observed for the solution of various problems. The definition and evaluation of possible IPS architectures should take into account AC/DC protection devices in order to carry out an integrated analysis of the system. Different MVAC/MVDC electrical distribution layouts coupling with all-electric or hybrid propulsion (electric/diesel/gas turbine) needs to be accurately investigated to show its advantages in terms of reliability, safety and quality of power. The thesis focusses on the Naval Smart Grid (NaSG) research project completed in partnership with the University of Trieste and the Polytechnic University of Milan. The aim of the research is to produce useful results for the design of a new ship, equipped with the following innovative features: modular power system; subsystem flexible integration; efficiency improvement; security improvement; new weapon systems; survivability improvement and high Power Quality standard. The main focus was the study of methodologies/solutions able to improve and define the onboard Power Quality (PQ). The research project reports Power Quality analysis about aspects of continuity of service, harmonic disturbances, pulsed power loads impact on the system, electromechanical transient evaluation and use of power and energy storage systems. An exhaustive investigation was carried out on system architectures in frequency domain to identify resonances and non-linear loads to detect disturbance frequencies. Moreover, the guidelines for the correct coordination of all the elements of the power system design affecting system performance (protections, converters, control systems, energy storage systems, etc.) are reported. A brief abstract for each Chapter is reported. Chapter 1 and 2 - Overview of Electrical Naval Systems and Integrated Power System in Military Ships The chapter reports the complete state of the art on naval electrical system and a brief description of naval classification, showing technological improvements and historical evolution. Details about electric propulsion, electrical generation on board, energy distribution and network layout are carried out. A complete description of the main IPS military ships with their own architecture and features is reported. Chapter 3 - Methodologies for Harmonic Disturbances Analysis and Power Quality (Service Continuity) In the field of Power quality (harmonic content, asymmetries, voltage sags, power factor), methodologies applied for the analysis/detection of harmonic disturbances are reported with an overview of electrical systems dependability in order to evaluate the service continuity of the system. Harmonic distortion could affect equipment on shipboard causing its outages, consequently, in an island system, power distribution network should ensure high re-configurability after faults, damage or untimely switch off. However, the increased interest in system’s safety and resilience generates, in turn, an increase in design burden necessary to analyze the consequences of faults and demonstrate the system’s compliance with the relevant regulations. The chapter presents the models and calculation code used for simulation activities. A Simulink model for time domain analysis and for time varying non-linear load, as well as a Fortran model for harmonic domain are described. Chapter 4 and 5 - Characterization of a military aircraft carrier and Aircraft Cavour – Measurement campaign A measurement campaign onboard the ship Cavour was carried out with the aim to characterize the relevant electric loads on board military vessel and to validate the models of the system’s components to be used. The analysis of data collected, allows to model the behavior of loads in terms of time and frequency domains, thus permitting their use for the required studies. Some specific electrical loads, such as new electrically pulsed loads specific for military applications (e.g. radar, electromagnetic launchers, etc.) with high distorted current absorption were identified. Their characterization was carried out in order to define their contribution to harmonic disturbances and their impact on the network. A model validation based on a measurement campaign is carried out. Chapter 6 - A New layout for an Integrated Power System Naval Unit-All Electric/Hybrid Different IPS architectures are defined: a full MVAC (Medium Voltage Alternate Current) power system, a hybrid MVAC plus MVDC/LVDC islands (Medium/Low Voltage Direct Current) and a MVAC 50-60 Hz, with a hybrid (electric/diesel/gas turbine) propulsion. In the architecture of the latter, the power of the installed engines is much lower than the first two cases. Chapter 7 - Network Equivalents in Harmonic Domain The needs to easily represent a complex network with high accuracy, lead to the development of a methodology based on aggregation of loads, creating a simplified network to carry out harmonic analysis. Different equivalent network models have been proposed that show their accuracy, through network impedances, and compare them with the overall representation of the network. The influence of cables was also studied. The best radial equivalent network was identified. Chapter 8 - Harmonic Analysis In order to propose appropriate solutions designed to improve power quality, the study of system impedance and power systems in frequency domain were studied. This analysis, carried out on the basis of the schematics and data load obtained in cooperation with the IT Navy, revealed some criticalities in the frequency range for both the systems architectures. As to full MVAC (Medium Voltage Alternate Current) power system and hybrid MVAC plus MVDC/LVDC islands, the aim was to evaluate whether or not the inclusion of capacitors (on shore, for power factor correction in shore connections) or filters (onboard, to reduce harmonic disturbances produced by propulsion systems) cause special issues, because of the high power of installed propulsion engines. Moreover, the advantages of DC island on electrical distribution in order to ensure high reliability and quality of service, in addition to the need to increase the efficiency of the ships’ power systems are highlighted. For the MVAC 50-60 Hz layout, the goal is to show how the use of hybrid (electric/diesel/gas turbine) propulsion where the power of engines is significantly reduced as compared to previous cases could solve some issues relating to power quality aspects. Chapter 9 - Reliability Analysis Preliminary studies about dependability, re-configurability and some top-events relevant for the vessel, were evaluated for all electric MVAC/MVAC "hybrid" models. The analysis of electrical disconnection of load areas due to a fault or an untimely tripping of the switches caused by harmonic disturbances was carried out. Chapter 10 - Three-Phase Short Circuit Analysis For MVAC 50-60 Hz Layout Preliminary evaluations were performed by analyzing the system within the perspective of given faults to perform system analysis in both permanent and short-circuit conditions. To highlight possible protection issues, the steady state condition and the three-phase short-circuit faults were studied and simulated under different load conditions for the MVAC architecture plus rotary converters, with hybrid (electric/diesel/gas turbine) propulsion.