A combination of high prices of fossil fuels and the increased awareness of their negative environmental impact has influenced the development of new cleaner energy sources. Among various viable technologies, fuel cells have emerged as one of the most promising sources for both portable and stationary applications. Fuel cell stacks produce DC voltage with a 2:1 variation in output voltage from no load to full load conditions. Hence, to increase the utilization efficiency and system stability, a power conditioner consisting of DC-DC and DC-AC converters is required for load interface. The design of power conditioners is driven by the application. This dissertation presents several different solutions for applications ranging from low-power portable sources for small electronics and laptop computers to megawatt-power applications for fuel cell power plants. The design and analysis for each power conditioner is presented in detail and the performance is verified using simulations and prototypes. Special consideration is given to the role of supercapacitors who act as the additional energy storage elements. It is shown that the supercapacitor connected at the terminals of a fuel cell can contribute to increased steady state stability when powering constant power loads, improved transient stability against load transients, and increased fuel efficiency (i.e. reduced hydrogen consumption).

Este trabalho apresenta o estudo, análise e a implementação de três topologias de condicionadores ativos de energia elétrica, utilizados para a melhoria da qualidade da energia em sistemas elétricos trifásicos a quatro fios. Estes condicionadores de qualidade de energia podem trabalhar tanto como um condicionador unificado de qualidade de energia (UPQC), bem como uma fonte de alimentação ininterrupta (UPS), permitindo: (i) a supressão das correntes harmônicas da carga; (ii) a compensação de energia reativa da carga; (iii) compensação dos desequilíbrios das correntes de carga; (iv) a compensação de desequilíbrios de tensão da rede; (v) supressão das tensões harmônicas da rede elétrica; (vi) a regulação das tensões de saída (tensões de carga); e (vii) fornecimento de energia ininterrupta para as cargas críticas (sistema UPS). Dentre as três topologias de UPQC/UPS estudadas, uma delas é proposta neste trabalho com o intuito de reduzir a tensão no barramento CC. Além disso, todas as topologias em estudo são constituídas por dois conversores PWM, nos quais é adotada uma estratégia de controle dual. Desse modo, o conversor colocado em paralelo com a carga, funciona como uma fonte de tensão senoidal, enquanto que o conversor colocado em série entre a rede elétrica e a carga, é controlado para operar como uma fonte de corrente senoidal. Tanto os controladores de tensão, quanto os de corrente são implementados no referencial síncrono dq0. Além disso, a técnica de modulação vetorial espacial tridimensional (3-D-SVM) é empregada nos conversores. Testes experimentais são apresentados para validar o desenvolvimento teórico e verificar o bom desempenho estático e dinâmico dos condicionadores ativos de energia elétrica, operando como UPQC, bem como sistema UPS. / This work presents the study, analysis and implementation of three topologies of active power conditioners, which are used to improve the power quality in three-phase four-wire systems. These power quality conditioner can work as unified power quality conditioner (UPQC), as well as an uninterruptible power supply (UPS) system allowing: (i) suppression of load harmonic currents; (ii) compensation of load reactive power; (iii) load unbalances compensation; (iv) utility voltage unbalances compensation; (v) utility voltage harmonics suppression; (vi) regulation of the output voltages (load voltages); and (vii) uninterruptible power for critical loads when working as UPS system. Among the three topologies of UPQC/UPS studied, one of them is proposed in this work in order to reduce the DC-bus voltage. Besides, all the topologies are comprised of two PWM converters, where a dual control strategy is adopted. The first converter, which is placed in parallel with the load, operates as a sinusoidal voltage source, while the second, which is placed in series between the utility grid and the load, is controlled to operate as a sinusoidal current source. Both the voltage and current controllers are implemented into the synchronous rotating reference frame (dq0-axes). In addition, the series and parallel converters use the three-dimensional space vector modulation (3-D-SVM) technique. The experimental tests are presented to validate the theoretical development and to verify the effective static and dynamic performance of the proposed active power conditioners, operating as UPQC and UPS.

Present day electrical equipment is rapidly becoming more and more sensitive to power quality problems, especially voltage sags. Various voltage sag correction devices are avaliable. This thesis analyzes a two-switch, single-phase electronic voltage regulator for correcting voltage sags. The theory of this voltage regulator has been investigated. An analytical method for sizing the energy storage capacitors has been established. The voltage regulator has been modeled and its steady-state and dynamic behavior has been studied by means of detailed computer simulations. A 220-V, 50-Hz, 1-kW rated regulator has been designed, simulated, and built. The results on the performance of voltage regulator and conclusions are also given.

Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-03-01T13:53:52Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) tese Marcio Evaristo.pdf: 8889950 bytes, checksum: 03f74b7936d018faa7c9615f9a22abe9 (MD5) / Made available in DSpace on 2016-03-01T13:53:52Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) tese Marcio Evaristo.pdf: 8889950 bytes, checksum: 03f74b7936d018faa7c9615f9a22abe9 (MD5) Previous issue date: 2015-08-04 / Apesar da grande quantidade de propostas publicadas de dispositivos para compensação de energia reativa em sistemas de distribuição, há uma carência de soluções em topologias para a compensação de reativo com ênfase na redução de custos, volume, peso e perdas. Foram estas as motivações que levaram às novas contribuições desta tese. Este trabalho apresenta um conjunto de dispositivos para compensação de energia reativa e controle da tensão em sistemas de distribuição. Os dispositivos propostos possuem várias características interessantes, tais como a ausência de harmônicos durante a operação em regime permanente, redução das perdas por chaveamento, dispensa do uso de grandes capacitores, não utilização de etapa em corrente contínua e não exigem um controle sofisticado. Adicionalmente, os dispositivos propostos podem ser dimensionados de acordo com as exigências do projeto onde serão utilizados, proporcionando uma adequação entre os recursos utilizados e os requisitos de custo e desempenho exigidos pela aplicação. Durante o desenvolvimento deste trabalho, os dispositivos propostos foram modelados digitalmente utilizando-se o software MATLAB/Simulink, para avaliação de desempenho em relação aos dispositivos tradicionais. O desempenho dos dispositivos propostos, observados nas simulações, foi bastante satisfatório, atendendo o objetivo de redução de perdas técnicas em sistemas de distribuição. / Despite the large number of proposals for reactive power compensation in distribution systems, there is a lack of solutions with emphasis on cost reduction, volume, weight and losses. These were the reasons which led to new contributions of this thesis proposal. This work presents a set of devices for reactive power compensation and voltage control in distribution systems. The proposed devices have several interesting features such as the absence of harmonics during steady-state operation, reducing switching losses, eliminating large capacitors and direct current stage and does not require a sophisticated control. In addition, the proposed devices can be sized according to the design requirements which will be used, providing coupling between the resources and the cost and performance requirements of the application. During the development of this work, the proposed devices have been digitally modeled using MATLAB / Simulink software for performance evaluation compared to traditional devices. The performance of the proposed devices was quite satisfactory, achieving the goal of reducing technical losses in distribution systems.

Este trabalho apresenta o estudo, análise e a implementação de três topologias de condicionadores ativos de energia elétrica, utilizados para a melhoria da qualidade da energia em sistemas elétricos trifásicos a quatro fios. Estes condicionadores de qualidade de energia podem trabalhar tanto como um condicionador unificado de qualidade de energia (UPQC), bem como uma fonte de alimentação ininterrupta (UPS), permitindo: (i) a supressão das correntes harmônicas da carga; (ii) a compensação de energia reativa da carga; (iii) compensação dos desequilíbrios das correntes de carga; (iv) a compensação de desequilíbrios de tensão da rede; (v) supressão das tensões harmônicas da rede elétrica; (vi) a regulação das tensões de saída (tensões de carga); e (vii) fornecimento de energia ininterrupta para as cargas críticas (sistema UPS). Dentre as três topologias de UPQC/UPS estudadas, uma delas é proposta neste trabalho com o intuito de reduzir a tensão no barramento CC. Além disso, todas as topologias em estudo são constituídas por dois conversores PWM, nos quais é adotada uma estratégia de controle dual. Desse modo, o conversor colocado em paralelo com a carga, funciona como uma fonte de tensão senoidal, enquanto que o conversor colocado em série entre a rede elétrica e a carga, é controlado para operar como uma fonte de corrente senoidal. Tanto os controladores de tensão, quanto os de corrente são implementados no referencial síncrono dq0. Além disso, a técnica de modulação vetorial espacial tridimensional (3-D-SVM) é empregada nos conversores. Testes experimentais são apresentados para validar o desenvolvimento teórico e verificar o bom desempenho estático e dinâmico dos condicionadores ativos de energia elétrica, operando como UPQC, bem como sistema UPS. / This work presents the study, analysis and implementation of three topologies of active power conditioners, which are used to improve the power quality in three-phase four-wire systems. These power quality conditioner can work as unified power quality conditioner (UPQC), as well as an uninterruptible power supply (UPS) system allowing: (i) suppression of load harmonic currents; (ii) compensation of load reactive power; (iii) load unbalances compensation; (iv) utility voltage unbalances compensation; (v) utility voltage harmonics suppression; (vi) regulation of the output voltages (load voltages); and (vii) uninterruptible power for critical loads when working as UPS system. Among the three topologies of UPQC/UPS studied, one of them is proposed in this work in order to reduce the DC-bus voltage. Besides, all the topologies are comprised of two PWM converters, where a dual control strategy is adopted. The first converter, which is placed in parallel with the load, operates as a sinusoidal voltage source, while the second, which is placed in series between the utility grid and the load, is controlled to operate as a sinusoidal current source. Both the voltage and current controllers are implemented into the synchronous rotating reference frame (dq0-axes). In addition, the series and parallel converters use the three-dimensional space vector modulation (3-D-SVM) technique. The experimental tests are presented to validate the theoretical development and to verify the effective static and dynamic performance of the proposed active power conditioners, operating as UPQC and UPS.

This dissertation aims to present a detailed analysis of the grid voltage disturbance in frequency domain for the current control design in the grid-tie inverter applications and to propose current control techniques in order to minimize its impact and maximize feasibility of the power conditioning system in distributed generations. Because the grid voltage is constantly changing, the inverter must be able to response to it. If the inverter is unable to respond properly, then the grid voltage power comes back to the system and damages the fuel cell power conditioning systems. A closed-loop dynamic model for the current control loop of the grid-tie inverter has been developed. The model explains the structure of the inverter admittance terms. The disturbance of the grid voltages has been analyzed in frequency domain. The admittance compensator has been proposed to prevent the grid voltage effect. The proposed lead-lag current control with admittance compensator transfers current properly without system failure. In order to get rid of the steady-state error of the feedback current, a proportional-resonant controller (PR) has been adopted. A PR control with admittance compensation provides great performance from zero power to full power operation. In addition, active and reactive power flow controller has been proposed based on the PR controller with admittance compensation. The proposed active and reactive power flow control scheme shows a wide range power flow control from pure leading power to pure lagging power. Finally, the proposed controller scheme has been verified its feasibility in three phase grid-tie inverter applications. First of all, a half-bridge grid-tie inverter has been designed with PR controller and admittance compensation. Then three individual grid-tie inverters has been combined and produced three phase current to the three phase grid in either balanced condition or unbalanced condition. The proposed control scheme can be applied not only single phase grid-tie inverter application, but also three phase grid-tie inverter application. This research can be applicable to the photovoltaic PCS as well. This technology makes renewable energy source more plausible for distributed generations. / Ph. D.

The demand for increased renewable energy production has led to increased photovoltaic (PV) installations worldwide. As this demand continues to grow, it is important that the costs of PV installations decrease while the power output capability increases. One of the components in PV installations that has lots of room for improvement is the power conditioning system. The power conditioning system is responsible for converting the power output of PV modules into power useable by the utility grid while insuring the PV array is outputting the maximum available power. Modular power conditioning systems, where each PV module has its own power converter, have been proven to yield higher output power due to their superior maximum power point tracking capabilities. However, this comes with the disadvantages of higher costs and lower power conversion efficiencies due to the increased number of power electronics converters. The primary objective of this dissertation is to develop a high-efficiency, low cost microconverter in an effort to increase the output power capability and decrease the cost of modular power conditioning systems. First, existing isolated dc-dc converter topologies are explored and a new topology is proposed based on the highly-efficient series resonant converter operating near the series resonant frequency. Two different hybrid modes of operation are introduced in order to add wide input-voltage regulation capability to the series resonant converter while achieving high efficiency through low circulating currents, zero-current switching (ZCS) of the output diodes, zero-voltage switching (ZVS) and/or ZCS of the primary side active switches, and direct power transfer from the source to the load for the majority of the switching cycle. Each operating mode is analyzed in detail using state-plane trajectory plots. A systematic design approach that is unique to the newly proposed converter is presented along with a detailed loss analysis and loss model. A 300-W microconverter prototype is designed to experimentally validate the analysis and loss model. The converter featured a 97.7% weighted California Energy Commission (CEC) efficiency with a nominal input voltage of 30 V. This is higher than any other reported CEC efficiency for PV microconverters in literature to date. Each operating mode of the proposed converter can be controlled using simple fixed-frequency pulse-width modulation (PWM) based techniques, which makes implementation of control straightforward. Simplified models of each operating mode are derived as well as control-to-input voltage transfer functions. A smooth transition method is then introduced using a two-carrier PWM modulator, which allows the converter to transition between operating modes quickly and smoothly. The performance of the voltage controllers and transition method were verified experimentally. To ensure the proposed converter is compatible with different types of modular power conditioning system architectures, system-level interaction issues associated with different modular applications are explored. The first issue is soft start, which is necessary when the converter is beginning operation with a large capacitive load. A novel soft start method is introduced that allows the converter to start up safely and quickly, even with a short-circuited output. Maximum power point tracking and double line frequency ripple rejection are also explored, both of which are very important to ensuring the PV module is outputting the maximum amount of available power. Lastly, this work deals with efficiency optimization of the proposed converter. It is possible to use magnetic integration so that the resonant inductor can be incorporated into the isolation transformer by way of the transformer leakage inductance in order to reduce parts count and associated costs. This chapter, however, analyzes the disadvantages to this technique, which are increased proximity effect losses resulting in higher conduction losses. A new prototype is designed and tested that utilizes an external resonant inductor and the CEC efficiency was increased from 97.7% to 98.0% with a marginal 1.8% total cost increase. Additionally, a variable frequency efficiency optimization algorithm is proposed which increases the system efficiency under the high-line and low-line input voltage conditions. This algorithm is used for efficiency optimization only and not control, so the previously presented simple fixed-frequency modeling and control techniques can still be utilized. / Ph. D.

Submitted by Morgana Silva (morgana_linhares@yahoo.com.br) on 2016-07-27T17:45:52Z No. of bitstreams: 1 arquivototal.pdf: 2648831 bytes, checksum: 9541497365622df815ae71c695bd6f89 (MD5) / Made available in DSpace on 2016-07-27T17:45:52Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2648831 bytes, checksum: 9541497365622df815ae71c695bd6f89 (MD5) Previous issue date: 2015-02-24 / In recent decades, the growing demand for miniaturized, portable and autonomous electronics has intensified the search for new and appropriate energy sources. Following this context, the purpose of this work is to develop an energy-autonomous electronic system, powered by magnetic energy harvesting. Being the energy harvesting system composed of an electromagnetic transducer, to capture and convert stray magnetic field around power lines, and an electronic circuit to condition the energy generated by the transducer and provide adequate power for a resistive load of low consumption. An experimental methodology was employed to select the appropriate material for the core of the transducer therefore been conducted many laboratory tests to analyze and compare the performance of the transducers with respect to power and power density provided by the transducers two ferromagnetic materials distinct, the Ferrite and Nanocrystalline Alloy (FeSiB). After analyzing the data, it is concluded that for this application the Nanocrystalline Alloy showed the best results in terms of power density, and therefore, was selected as the material of the toroidal core of the transducer. However, in the output of the secondary coil was observed high voltage peaks, so that could cause damage to electronic devices connected to the coil circuit. Therefore, it chose to divide the secondary coil into two coils, both connected in parallel to reduce the inductance, at end It is found the effectiveness of the solution, because, reduced voltage spikes and kept the magnitude of the effective tension. However, the showed transducer high inductive reactance, due to its physical parameters, in particular, the high permeability, to compensate were used capacitances connected in series with the coil, in order to define the ideal situation for the system provide maximum power for the load. The power conditioning circuit has been designed to power the wireless sensor node nRF24LE1 the Nordic semiconductors, therefore, have been designed a full-wave rectifier, a filter to the capacitor and a voltage regulator. Finally, it can be concluded that an electronic system with energetic autonomy could be implemented, using as power supply the energy harvesting by magnetic induction, and it can be installed in environments in which there is a magnetic field available for "exploited". / Nas últimas décadas, a crescente demanda por circuitos eletrônicos miniaturizados, portáteis e autônomos, vem intensificando a busca por novas e adequadas fontes energéticas. Seguindo este contexto, o propósito desta dissertação é desenvolver um sistema eletrônico energeticamente autônomo, alimentado por colheita de energia magnética. Sendo o sistema de colheita composto por um transdutor eletromagnético, para captar e converter o campo magnético disperso em torno de linhas de potência, e um circuito eletrônico para condicionar a energia gerada pelo transdutor e fornecer a potência adequada para uma carga resistiva de baixo consumo. Uma metodologia experimental foi empregada para selecionar o material adequado para o núcleo do transdutor, por isso, foram realizados diversos testes em laboratório para analisar e comparar o desempenho dos transdutores em relação à potência e a densidade de potência, fornecidas pelos transdutores de dois materiais ferromagnéticos distintos, a Ferrita e a liga Nanocristalina (FeSiB). Após a análise dos dados, concluiu-se que para esta aplicação a liga Nanocristalina apresentou os melhores resultados quanto à densidade de potência, e por isso, foi selecionada como o material do núcleo toroidal do transdutor. Porém, na saída da bobina secundária se observou altos picos de tensão, de modo que poderia ocasionar danos aos dispositivos eletrônicos do circuito conectado a bobina. Portanto, optou-se por fazer a divisão da bobina secundária em dois enrolamentos, ambos ligados em paralelo, para reduzir a indutância, ao final constatou-se a eficácia da solução, pois, reduziu os picos de tensão e manteve a magnitude da tensão eficaz. Contudo, o transdutor apresentou alta reatância indutiva, devido os seus parâmetros físicos, em particular, a alta permeabilidade, para compensá-la foram utilizadas capacitâncias ligadas em série com a bobina, a fim de definir a situação ideal para o sistema fornecer a máxima potência à carga. O circuito de condicionamento de energia foi projetado para alimentar o nó sensor sem fio nRF24LE1 da Nordic semiconductors, para tanto, foram projetados um retificador de onda completa, um filtro à capacitor e um regulador de tensão. Por fim, pode-se concluir que um sistema eletrônico com autonomia energética pode ser implementado, utilizando-se como fonte de alimentação a colheita de energia por indução magnética, e o mesmo pode ser instalado em ambientes nos quais existam um campo magnético disponível para ser “aproveitado”.

本論文では，電力利用率向上と需給バランス調整に寄与する蓄電池付太陽光PCSの新たな制御法について検討を行い，その有効性を確認している。受電点の潮流に応じてPCSの力率を制御することで，逆潮流時には系統電圧の上昇を抑制しつつ，順潮流時には負荷への電力利用率を向上する手法を提案し，フィールド試験により有効性を定量評価した。また，受電電力の制御目標値を可変とする制御を用い目標値を最適化することで，新たな機器を付加する必要なく上げ下げのDRに対応し需給バランスを調整する制御手法を提案し，その有効性をシミュレーションおよび実機により検証した。 / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

Ultra low power wireless sensors and sensor systems are of increasing interest in a variety of applications ranging from structural health monitoring to industrial process control. Electrochemical batteries have thus far remained the primary energy sources for such systems despite the finite associated lifetimes imposed due to limitations associated with energy density. However, certain applications (such as implantable biomedical electronic devices and tire pressure sensors) require the operation of sensors and sensor systems over significant periods of time, where battery usage may be impractical and add cost due to the requirement for periodic re-charging and/or replacement. In order to address this challenge and extend the operational lifetime of wireless sensors, there has been an emerging research interest on harvesting ambient vibration energy. Vibration energy harvesting is a technology that generates electrical energy from ambient kinetic energy. Despite numerous research publications in this field over the past decade, low power density and variable ambient conditions remain as the key limitations of vibration energy harvesting. In terms of the piezoelectric transducers, the open-circuit voltage is usually low, which limits its power while extracted by a full-bridge rectifier. In terms of the interface circuits, most reported circuits are limited by the power efficiency, suitability to real-world vibration conditions and system volume due to large off-chip components required. The research reported in this thesis is focused on increasing power output of piezoelectric transducers and power extraction efficiency of interface circuits. There are five main chapters describing two new design topologies of piezoelectric transducers and three novel active interface circuits implemented with CMOS technology. In order to improve the power output of a piezoelectric transducer, a series connection configuration scheme is proposed, which splits the electrode of a harvester into multiple equal regions connected in series to inherently increase the open-circuit voltage generated by the harvester. This topology passively increases the rectified power while using a full-bridge rectifier. While most of piezoelectric transducers are designed with piezoelectric layers fully covered by electrodes, this thesis proposes a new electrode design topology, which maximizes the raw AC output power of a piezoelectric harvester by finding an optimal electrode coverage. In order to extract power from a piezoelectric harvester, three active interface circuits are proposed in this thesis. The first one improves the conventional SSHI (synchronized switch harvesting on inductor) by employing a startup circuitry to enable the system to start operating under much lower vibration excitation levels. The second one dynamically configures the connection of the two regions of a piezoelectric transducer to increase the operational range and output power under a variety of excitation levels. The third one is a novel SSH architecture which employs capacitors instead of inductors to perform synchronous voltage flip. This new architecture is named as SSHC (synchronized switch harvesting on capacitors) to distinguish from SSHI rectifiers and indicate its inductorless architecture.