Submitted by ALESSANDRO LUCINDO DA LUZ null (aledaluz@hotmail.com) on 2018-01-10T01:24:32Z No. of bitstreams: 1 Operacao flexivel conversores_ALuz.pdf: 10997918 bytes, checksum: 18fe1f6d3eba73d11bf63fab8cf0a0be (MD5) / Approved for entry into archive by Maria Marlene Zaniboni null (zaniboni@bauru.unesp.br) on 2018-01-10T11:41:48Z (GMT) No. of bitstreams: 1 luz_al_me_bauru.pdf: 10997918 bytes, checksum: 18fe1f6d3eba73d11bf63fab8cf0a0be (MD5) / Made available in DSpace on 2018-01-10T11:41:48Z (GMT). No. of bitstreams: 1 luz_al_me_bauru.pdf: 10997918 bytes, checksum: 18fe1f6d3eba73d11bf63fab8cf0a0be (MD5) Previous issue date: 2017-11-13 / Este trabalho de mestrado descreve uma estratégia de operação multifuncional e flexível aplicado a conversores trifásicos CC-CA (inversores) conectados à rede de distribuição de energia elétrica. A estratégia proposta é capaz de injetar potência ativa na rede e compensar correntes de distúrbios (reativos, desbalanço e harmônicos) simultaneamente. O maior objetivo desta operação flexível é de melhorar a Qualidade de Energia Elétrica em um ponto de acoplamento comum (PAC) permitindo a compensação total ou parcial destes distúrbios ou fatores que degradam a Qualidade de Energia Elétrica. O fator de potência é o principal fator de qualidade a ser observado e ele é calculado através da Teoria da Potência Conservativa – CPT. Entretanto, com base no fator de potência medido pelo lado da rede de distribuição e o fator de potência desejado, um coeficiente de compensação – k é calculado para o ajuste das correntes de compensação dos distúrbios que geram a potência não ativa. / This paper depicts a multifunctional and flexible control strategy applied in three-phase inverters, which are connected to the distribution network. The proposed strategy is able to inject active power into the electrical grid and compensate current disturbances (reactive, harmonics and unbalance) simultaneously. The main goal of this flexible strategy is to improve the Power Quality at the point of common coupling (PCC) allowing full or partial compensation of disturbances. Power factor is the main quality index observed and it is calculated according to Conservative Power Theory - CPT. Therefore, based on the power factor measured in the grid side and the desired value for the power factor, a compensation coefficient - k is calculated continuously adjusting the amplitude of the compensation current.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-05-08T00:11:48Z No. of bitstreams: 1 NAYARA BRANDÃO DE FREITAS – DISSERTAÇÃO (PPGEE) 2016.pdf: 3718233 bytes, checksum: f4f88b8a316139fc246558ded5f688d9 (MD5) / Made available in DSpace on 2018-05-08T00:11:48Z (GMT). No. of bitstreams: 1 NAYARA BRANDÃO DE FREITAS – DISSERTAÇÃO (PPGEE) 2016.pdf: 3718233 bytes, checksum: f4f88b8a316139fc246558ded5f688d9 (MD5) Previous issue date: 2016-06-23 / O tema desenvolvido consiste no estudo, caracterização e análise de conversores multiníveis CA/CC/CA monofásicos/monofásicos, monofásicos/bifásicos e monofásicos/trifásicos aplicados a sistemas de conversão e compensação de energia, empregando IGBTs (Transistor Bipolar de Porta isolada) como dispositivos semicondutores. No decorrer do trabalho, diversas topologias são analisadas e comparadas utilizados critérios como quantidade de barramentos CC, valores das tensões dos barramentos CC, WTHD (Distorção Harmônica Total Ponderada) das tensões chaveadas, frequências de chaveamentos dos IGBTs e perdas por condução e chaveamento. Os sistemas de controle das variáveis dos conversores estudados são apresentados e o controle individual dos barramentos CC é abordado com destaque. Implementações experimentais foram utilizadas para comprovar a teoria apresentada e mostrar a viabilidade dos sistemas. / This work consists in the study, characterization, anda analysis of AC/DC/AC multilevel converters are applied to conversion and compensation systems and employ and IGBTs (Insulated Gate Bipolar Transistor) as power semiconductor device. Many topologies are analyzed and compared considering the number of DC-links, DC-links voltages values, WTHDs (Weighted Total Harmonic Distortion) of the generated voltages, and semiconductors conduction and switching losses. The control systems of the studied converters are presented and the individual control of the DC-links voltages in highlighted. Experimental results are provided in order to prove the theoretical results and the viability of the systems.

High frequency link power converters for DC – 3Φ AC applications are investigated. Low cost, reduced size, galvanic isolation and efficient large boosting of voltage level are the key motivations behind the selection of such topologies. This thesis proposes high frequency link 3Φ inverters for three wire and four wire systems. The proposed topologies have the simplest power circuit configuration and commutation requirements among all high frequency link topologies reported in the literature. A full load efficiency greater than 90% is achieved with a passive snubber. The effect of various circuit non-idealities are common and important for desirable performances of these topologies. A few such issues are highlighted. Firstly, the special commutation requirement of the power circuit causes a non-linear distortion in the output voltages and thus makes the gain of the power converter time varying. A simple compensation technique is adopted to mitigate the problem. Secondly, the high frequency transformer should operate with only switching frequency component. However, in the practical situations a significant amount of low frequency component gets injected into the transformer and results in peaky transformer magnetizing current unless it is over designed. A suitable measure is incorporated in the proposed topologies to achieve a magnetic protection. The power circuit topology is used as stand-by AC power supply. These are of interest for Uninterruptible Power Supply (UPS) and Micro-grid applications. One of the main objectives of such supplies is to provide a high quality and highly reliable power to the connected loads. A voltage regulation loop based on proportional + multiresonant controller is proposed to achieve excellent quality of the output voltage with unbalanced and nonlinear loadings. The factors influencing regulation and stability of the voltage waveform are identified and necessary modifications are carried out to improve the performance. The potential of this voltage regulation loop along with P/Q droop technique and a simple resistive virtual output impedance loop is exploited to achieve decentralized paralleling of inverters. A trade off between the output voltage power quality and the sharing accuracy is examined. The total harmonic distortion and degree of unbalance in the output voltage waveform are experimentally measured well below the specified limit for stand alone AC supplies with an excellent sharing accuracy. Some of the grid interactive modes are addressed for the completeness of the work. A shunt compensator system and a double conversion system based on the same high frequency link converter are experimentally evaluated. These systems can find their application in UPS systems. A few important observations on the power circuit performances are indicated.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-07-11T12:39:13Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação Mestrado M276 - Gilberto.pdf: 3559945 bytes, checksum: e0e92cec09c72c5a7b8b98260c3b9a8e (MD5) / Made available in DSpace on 2017-07-11T12:39:13Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertação Mestrado M276 - Gilberto.pdf: 3559945 bytes, checksum: e0e92cec09c72c5a7b8b98260c3b9a8e (MD5) Previous issue date: 2016-03-22 / Este trabalho apresenta um estudo comparativo de conversores monofásicos aplicados a sistemas fotovoltaicos sem transformador. Topologias de inversores sem transformador têm menores custos, tamanho e peso. Contudo, a não utilização do transformador pode ser responsável por consideráveis valores de correntes de fuga. A associação em série de vários módulos fotovoltaicos se faz necessária para alcançar o nível de tensão desejado no barramento c.c.. Com o intuito de reduzir o número de módulos fotovoltaicos em série, topologias com característica de elevação de tensão (boost) podem ser utilizadas. Portanto, topologias que possuem estas características e que possam apresentar baixos valores de correntes de fuga devem ser escolhidas para o estudo. As topologias presentes neste trabalho são: o conversor de dois estágios, o inversor fonte Z monofásico com diodo adicional, e o inversor fonte Z de três estados. / This work presents a comparative study of single-phase converters applied to transformerless photovoltaic systems. Topologies of transformerless inverters have lower costs, size and weight. However, not using it may cause considerable amounts of leakage currents. The association in series of several PV modules is needed to achieve the voltage level desired in d.c. bus. In order to reduce the number of photovoltaic modules in series, topologies with voltage boost characteristic can be used. Therefore, topologies that have voltage boost characteristic and can have low leakage current values are chosen for the study. Topologies present in this work are: the two stages single-phase converter, the single-phase Z-source inverter with additional diode, and the single-phase three switch three state Z-source inverter.

Enhancing performance of power electronics converters has always been an interesting topic in the power electronics community. Over the years, researchers and engineers are developing new high performance component, novel converter topologies, smart control methods and optimal design procedures to improve the efficiency, power density, reliability and reducing the cost. Besides pursuing high performance, researchers and engineers are striving to modularize the power electronics converters, which provides redundancy, flexibility and standardization to the end users. The trend of modularization has been seen in photovoltaic inverters, telecommunication power supplies, and recently, HVDC applications. A systematic optimal design approach for modular power converters is developed in this dissertation. The converters are developed for aerospace applications where there are stringent requirement on converter form factor, loss dissipation, thermal management and electromagnetic interference (EMI) performance. This work proposed an optimal design approach to maximize the nominal power of the power converters considering all the constraints, which fully reveals the power processing potential. Specifically, this work studied three-phase active front-end converter, three-phase isolated ac/dc converter and inverter. The key models (with special attention paid to semiconductor switching loss model), detailed design procedures and key design considerations are elaborated. With the proposed design framework, influence of key design variables, e.g. converter topology, switching frequency, etc. is thoroughly studied. Besides optimal design procedure, control issues in paralleling modular converters are discussed. A master-slave control architecture is used. The slave controllers not only follow the command broadcasted by the master controller, but also synchronize the high frequency clock to the master controller. The control architecture eliminates the communication between the slave controllers but keeps paralleled modules well synchronized, enabling a fully modularized design. Furthermore, the implementation issues of modularity are discussed. Although modularizing converters under form factor constraints adds flexibility to the system, it limits the design space by forbidding oversized components. This work studies the influence of the form factor by exploring the maximal nominal power of a double-sized converter module and comparing it with that of two paralleled modules. The tradeoff between modularity and performance is revealed by this study. Another implementation issue is related to EMI. Scaling up system capacity by paralleling converter modules induces EMI issues in both signal level and system level. This work investigates the mechanisms and provides solutions to the EMI problems. / Ph. D. / As penetration of power electronics technologies in electric power delivery keeps increasing, performance of power electronics converters becomes a key factor in energy delivery efficacy and sustainability. Enhancing performance of power electronics converters reduces footprint, energy waste and delivery cost, and ultimately, promoting a sustainable energy use. Over the years, researchers and engineers are developing new technologies, including high performance component, novel converter topologies, smart control methods and optimal design procedures to improve the efficiency, power density, reliability and reducing the cost of power electronics converters. Besides pursuing high performance, researchers and engineers are striving to modularize the power electronics converters, enabling power electronics converters to be used in a “plug-and-play” fashion. Modularization provides redundancy, flexibility and standardization to the end users. The trend of modularization has been seen in applications that process electric power from several Watts to Megawatts. This dissertation discusses the design framework for incorporating modularization into existing converter design procedure, synergically achieving performance optimization and modularity. A systematic optimal design approach for modular power converters is developed in this dissertation. The converters are developed for aerospace applications where there is stringent v requirement on converter dimensions, loss dissipation, and thermal management. Besides, to ensure stable operation of the onboard power system, filters comprising of inductors and capacitors are necessary to reduce the electromagnetic interference (EMI). Owning to the considerable weight and size of the inductors and capacitors, filter design is one of the key component in converter design. This work proposed an optimal design approach that synergically optimizes performance and promotes modularity while complying with the entire aerospace requirement. Specifically, this work studied three-phase active front-end converter, three-phase isolated ac/dc converter and three-phase inverter. The key models, detailed design procedures and key design considerations are elaborated. Experimental results validate the design framework and key models, and demonstrates cutting-edge converter performance. To enable a fully modularized design, control of modular converters, with focus on synchronizing the modular converters, is discussed. This work proposed a communication structure that minimizes communication resources and achieves seamless synchronization among multiple modular converters that operate in parallel. The communication scheme is demonstrated by experiments. Besides, the implementation issues of modularity are discussed. Although modularizing converters under form factor constraints adds flexibility to the system, it limits the design space by forbidding oversized components. This work studies the impact of modularity by comparing performance of a double-sized converter module with two paralleled modules. The tradeoff between modularity and performance is revealed by this study.

No description available.

As fossil fuel sources continue to diminish, oil prices continue to increase, and global warming and CO2 emissions keep impacting the environment, it has been necessary to shift energy consumption and generation to a different path. Solar energy has proven to be one of the most promising sources of renewable energy because it is environmentally friendly, available anywhere in the world, and cost competitive. For photovoltaic (PV) system engineers, designing a PV system is not an easy task. Research demonstrates that different PV technologies behave differently under certain conditions; therefore energy production varies not only with capacity of the system but also with the type of module. For years, researchers have also studied how these different technologies perform for long periods of time, when exposed out in the field. In this study, data collected by the Florida Solar Energy Center for periods of over four years was analyzed using two techniques, widely accepted by researchers and industry, to evaluate the long‐term performance of five systems. The performance ratio analysis normalizes system capacity and enables the comparison of performance between multiple systems. In PVUSA Regression analysis, regression coefficients are calculated which correspond to the effect of irradiance, wind speed, and ambient temperature, and these coefficients are then used to calculate power at a predetermined set of conditions. This study allows manufacturers to address the difficulties found on system lifetime when their modules are installed out on the field. Also allows for the further development and improvement of the different PV technologies already commercially available.

Indiana University-Purdue University Indianapolis (IUPUI) / The substantial increase demand for electrical energy requires high efficient apparatus dealing with energy conversion. Several technologies have been suggested to implement power supplies with higher efficiency, such as multilevel and interleaved converters. This thesis proposes an energy conversion unit with an optimized number of output voltage levels per number of switches nL=nS. The proposed five-level four-switch per phase converter has nL=nS=5/4 which is by far the best relationship among the converters presented in technical literature. A comprehensive literature review on existing five-level converter topologies is done to compare the proposed topology with conventional multilevel converters. The most important characteristics of the proposed configuration are: (i) reduced number of semiconductor devices, while keeping a high number of levels at the output converter side, (ii) only one DC source without any need to balance capacitor voltages, (iii) high efficiency, (iv) there is no dead-time requirement for the converters operation, (v) leg isolation procedure with lower stress for the DC-link capacitor. Single-phase and three-phase version of the proposed converter is presented in this thesis. Details regarding the operation of the configuration and modulation strategy are presented, as well as the comparison between the proposed converter and the conventional ones. Simulated results are presented to validate the theoretical expectations. In addition a fault tolerant converter based on proposed topology for micro-grid systems is presented. A hybrid pulse-width-modulation for the pre-fault operation and transition from the pre-fault to post-fault operation will be discussed. Selected steady-state and transient results are demonstrated to validate the theoretical modeling.