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Inversor CS Boost monofásico em aplicações com fontes renováveis

De Brito, Moacyr A.G.; Sampaio, Leonardo P.; Luigi, G.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
POR
Relevância na Pesquisa
56.43%
This paper presents a new methodology for the operation and control of a single-phase current-source (CS) Boost Inverter, considering that the conventional current-source inverter (CSI) has a right-half-plane (RHP) zero in its control-to-output transfer function, and this RHP zero causes the known non-minimum-phase effects. In this context, a special design with low boost inductance and a multi-loop control is developed in order to assure stable and very fast dynamics. Furthermore, the Inverter presents output voltage with very low total harmonic distortion (THD), reduced components and high power density. Therefore, this paper presents the inverter operation, the proposed control technique, and main simulation and experimental results in order to demonstrate the feasibility of the proposal. © 2010 IEEE.

Single stage converters for low power stand-alone and grid-connected PV systems

Junior, Luigi G.; De Brito, Moacyr A.G.; Sampaio, Leonardo P.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 1112-1117
ENG
Relevância na Pesquisa
56.16%
This work presents the evaluation of different power electronic integrated converters suitable for photovoltaic applications, in order to reduce complexity and improve reliability. The rated voltages available in Photovoltaic (PV) modules have usually low values for applications such as regulated output voltages in stand-alone or grid-connected configurations. In these cases, a boost stage or a transformer will be necessary. Transformers have low efficiencies, heavy weights and have been used only when galvanic isolation is mandatory. Furthermore, high-frequency transformers increase the converter complexity. Therefore, the most usual topologies use a boost stage and one inverter stage cascaded. However, the complexity, size, weight, cost and lifetime might be improved considering the integration of both stages. In this context, some integrated converters are analyzed and compared in this paper in order to support future evaluations and trends for low power single-phase inverters for PV systems. Power decoupling, MPPT and Tri-State modulations are also considered. Finally, simulation and experimental results are presented and compared for the analyzed topologies. © 2011 IEEE.

Single-phase current-source-boost inverter for renewable energy sources

Sampaio, Leonardo P.; De Brito, Moacyr A.G.; Junior, Luigi G.; De A. E Melo, Guilherme; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 1118-1123
ENG
Relevância na Pesquisa
56.42%
This paper presents a new methodology for the operation and control of a single-phase current-source (CS) Boost Inverter, considering that the conventional CS boost inverter has a right-half-plane (RHP) zero in its control-to-output transfer function, and this RHP zero causes the known non-minimum-phase effects. In this context, a special design with low boost inductance and a multi-loop control is developed in order to assure stable and very fast dynamics. Furthermore, the proposed inverter presents output voltage with very low total harmonic distortion (THD), reduced components and high power density. Therefore, this paper presents the inverter operation, the proposed control technique, the main simulation results and a prototype in order to demonstrate the feasibility of the proposal. © 2011 IEEE.

Evaluation of integrated inverter topologies for low power PV systems

Junior, Luigi G.; De Brito, Moacyr A. G.; Sampaio, Leonardo P.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 35-39
ENG
Relevância na Pesquisa
56.3%
This work presents the stage integration in power electronics converters as a suitable solution for solar photovoltaic inverters. The rated voltages available in Photovoltaic (PV) modules have usually low values for applications such as regulated output voltages in stand-alone or grid-connected configurations. In these cases, a boost stage or a transformer will be necessary. Transformers have low efficiencies, heavy weights and have been used only when galvanic isolation is mandatory. Furthermore, high-frequency transformers increase the converter complexity. Therefore, the most usual topologies use a boost stage and one inverter stage cascaded. However, the complexity, size, weight, cost and lifetime might be improved considering the integration of both stages. These are the expected features to turn attractive this kind of integrated structures. Therefore, some integrated converters are analyzed and compared in this paper in order to support future evaluations and trends for low power single-phase inverters for PV systems. © 2011 IEEE.

A comparative study of MPPT strategies and a novel singlephase integrated buck-boost inverter for small wind energy conversion systems

Peña, José C.U.; De Brito, Moacyr A.G.; E Melo, Guilherme de A.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 458-465
ENG
Relevância na Pesquisa
66.4%
This paper presents the analysis of some usual MPPT (Maximum Power Point Tracking) strategies intended for small wind energy conversion (up to 1kW) based on permanent magnet synchronous generators (PMSG), considering the stand-alone application for a novel buck-boost integrated inverter. Each MPPT method is analytically introduced and then it is simulated using MatLab/Simulink considering standard conditions of wind and also commercially available turbines and generators. The extracted power in each case is compared with the maximum available power, so the tracking factor is calculated for each method. Thus, the focus is on the application to improve the efficiency of stand-alone wind energy conversion systems (WECS) with battery chargers and AC load supplied by inverter. Therefore, for this purpose a novel single phase buck-boost integrated inverter is introduced. Finally, the main experimental results for the introduced inverter are presented. © 2011 IEEE.

Tri-state single-phase integrated inverters with input to output power decoupling control

De Brito, Moacyr A.G; Junior, Luigi G.; Sampaio, Leonardo P.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 293-297
ENG
Relevância na Pesquisa
66.27%
Researches on control for power electronics have looked for original solutions in order to advance renewable resources feasibility, specially the photovoltaic (PV). In this context, for PV renewable energy source the usage of compact, high efficiency, low cost and reliable converters are very attractive. In this context, two improved simplified converters, namely Tri-state Boost and Tri-state Buck-Boost integrated single-phase inverters, are achieved with the presented Tri-state modulation and control schemes, which guarantees the input to output power decoupling control. This feature enhances the field of single-phase PV inverters once the energy storage is mainly inductive. The main features of the proposal are confirmed with some simulations and experimental results. © 2012 IEEE.

A single-phase single-stage buck-boost inverter intended for low power alternative energy conversion systems: Analysis, design and experimentation

Pena, Jose C. U.; E Melo, Guilherme de A.; De Brito, Moacyr A. G.; Canesin, Carlos A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
66.44%
This paper presents the operational analysis of the single-phase integrated buck-boost inverter. This topology is able to convert the DC input voltage into AC voltage with a high static gain, low harmonic content and acceptable efficiency, all in one single-stage. Main functionality aspects are explained, design procedure, system modeling and control, and also component requirements are detailed. Main simulation results are included, and two prototypes were implemented and experimentally tested, where its results are compared with those corresponding to similar topologies available in literature. © 2012 IEEE.

Mini-inversores para aproveitamento de energia fotovoltaica, com técnicas de MPPT, sincronismo e conexão com a rede de CA em BT, proteção de ilhamento, gerenciamento da energia e da operação

Alves, Marcos Gutierrez
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 169 f. : il.
POR
Relevância na Pesquisa
26%
Pós-graduação em Engenharia Elétrica - FEIS; Considerando-se as políticas mundiais e nacionais com relação às mudanças climáticas decorrentes da ação humana, no contexto da produção e consumo de energia elétrica, novas fontes renováveis e alternativas para a produção de energia elétrica, com menores impactos ambientais e elevadas eficiências têm sido exploradas na literatura científica. Dentro deste contexto é desenvolvido neste trabalho um sistema de geração de energia elétrica de pequeno porte baseado na associação em série de poucos painéis solares fotovoltaicos. São apresentadas análises e simulações de diversas estruturas monofásicas não isoladas que contemplam o estado da arte e integram parte das estruturas mais utilizadas pela indústria. O sistema proposto para operar como Geração Distribuída (GD) é um sistema a duplo estágio, composto pelo conversor elevador Boost entrelaçado e em cascata com o inversor monofásico em ponte completa. O sistema de GD proposto possui um algoritmo tipo P&O (Perturband Observe) para a extração da máxima potência (MPPT – Maximum Power Point Tracking), mesclando o algoritmo P&O para o rastreamento do MPP, com o potencial do algoritmo Vcte (Tensão constante) para o processo de inicialização do sistema...

Uma nova metodologia de projeto e controle para o inversor Boost (CSI) monofásico, para o aproveitamento de fontes alternativas e renováveis de energia elétrica

Sampaio, Leonardo Poltronieri
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 110 f. : il.
POR
Relevância na Pesquisa
76.46%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Engenharia Elétrica - FEIS; Este trabalho propõe uma nova abordagem na metodologia de operação para o inversor Boost monofásico, como estrutura base para o aproveitamento de fontes alternativas e renováveis de energia elétrica. Considerando-se que equipamentos eletro/eletrônicos convencionais em CA (corrente alternada) necessitam, normalmente, de níveis e formato de tensão diferentes daqueles fornecidos por essas fontes de energia, o inversor proposto é uma estrutura integrada que tem a capacidade de operar como conversor elevador de tensão e inversor, apresentando um número reduzido de componentes e rendimento maior, quando comparado às formas tradicionais de se associar em cascata o conversor elevador com o inversor. O projeto convencional do inversor fonte de corrente (CSI) exige uma indutância elevada de entrada, além disso, o modelo a pequeno sinais do CSI é semelhante ao do conversor Boost no modo de condução contínua, apresentando um zero no semi-plano direito na função de transferência para o controle da tensão de saída, sendo que este zero causa o conhecido efeito de fase não-mínima. Desta forma, uma metodologia especial de projeto é apresentada resultando numa indutância Boost reduzida e numa técnica de controle utilizando um sistema multi-malhas...

Inversor Buck-Boost integrado para aplicações com micro-geradores eólicos

Ugaz Peña, José Carlos
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 127 f. : il.
POR
Relevância na Pesquisa
36.36%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Engenharia Elétrica - FEIS; O presente estudo propõe a utilização do conversor integrado Buck-Boost monofásico no aproveitamento da energia proveniente de pequenos geradores eólicos, considerando-se o atual crescimento da utilização em pequena escala de potência das fontes de energia alternativas, o que motiva o desenvolvimento de novas e eficientes tecnologias para os sistemas de conversão. Tipicamente, os sistemas de conversão de energia eólica, em baixas potências, disponibilizam tensões contínuas de saída na faixa de 12 V até 48 V (valores médios), por outro lado, a grande maioria das cargas de uso domiciliar necessitam de tensão alternada com valores eficazes entre 110 V a 240 V. Isto leva à necessidade da utilização de conversores CC-CA, denominados de inversores. As estruturas inversoras tradicionais fornecem tensões alternadas cujo valor de pico está limitado ao valor máximo da tensão de entrada, o que leva à necessidade de incluir um estágio elevador adicional ao sistema de conversão de energia eólica, antes de realizar a conversão CC-CA, resultando em redução do rendimento, aumento de peso e volume. O inversor integrado apresentado neste trabalho realiza...

Um novo sistema de refrigeração com controle de temperatura, compressor aberto, máquina de indução trifásica com velocidade variável e correção ativa do fator de potência do estágio de entrada

Leandro, Eduardo
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 166 f. : il.
POR
Relevância na Pesquisa
36.18%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Pós-graduação em Engenharia Elétrica - FEIS; Este trabalho apresenta uma nova proposta para sistema de refrigeração com controle dinâmico de temperatura, operando com estrutura de compressor aberto, acionado por motor de indução trifásico com velocidade variável, e estágio de entrada retificador com correção ativa do fator de potência. O estágio de entrada é composto por um retificador Boost monofásico com elevado fator de potência, com duas células entrelaçadas, operando no modo de condução crítica, empregando técnica de comutação não dissipativa e controlado por dispositivo FPGA, associado a um estágio de saída inversor de dois níveis convencional trifásico à IGBT, o qual é controlado por um Processador Digital de Sinais (DSP - Digital Signal Processor). A técnica de comutação não dissipativa para o estágio de entrada é baseada em células ZCS (Zero-current-switching). As principais características do retificador incluem a redução da ondulação da corrente de entrada, redução da ondulação da tensão de saída retificada, utilização de componentes com reduzidos esforços...

Simulation results of a 1 kW photovoltaic system with MPPT function in the inverter

Gonçalves, Henrique; Hlaili, Manel; Amira, Haddouk; Mechergui, Hafidh; Afonso, João L.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 11/07/2012 ENG
Relevância na Pesquisa
46.04%
Photovoltaic pumping systems are commonly used in remote regions, where the access to electrical energy is difficult or very expensive. This paper presents simulation results of a 1 kW photovoltaic system proposed in a cascade topology, consisting of a DC-DC boost converter followed by a single-phase inverter. The Maximum Power Point Tracking (MPPT) function is performed by the inverter, instead of by the DC-DC converter, as usually is done. The MPPT function uses an Incremental Conductance algorithm. This paper presents simulation results, in steady state and transient conditions, for the proposed photovoltaic system operating in different circumstances, which in real facilities can be caused by solar radiation variations.; FEDER Funds - Operational Program for Competitiveness Factors (COMPETE), FCOMP-01-0124-FEDER-022674 and the project PTDC/EEA-EEL/104569/2008.; Fundação para a Ciência e a Tecnologia (FCT) - FCOMP-01-0124-FEDER-022674, PTDC/EEA-EEL/104569/2008.

Projecto, montagem e teste de uma unidade modular de detecção de radiação Geiger-Muller

Cavaleiro, António Pedro Marques Pita
Fonte: Instituto Politécnico de Lisboa Publicador: Instituto Politécnico de Lisboa
Tipo: Dissertação de Mestrado
Publicado em /09/2013 POR
Relevância na Pesquisa
46.25%
Esta dissertação apresenta o estudo e o projecto de uma fonte de alimentação para um detector de radiação Geiger-Muller. A fonte de alimentação tanto pode funcionar com a tensão da rede como pode ser integrada em sistemas de electrónica modular NIM de modo a ser facilmente integrada em qualquer tipo de laboratório. A fonte de alimentação inclui os seguintes módulos: 1) rectificador controlado; 2) conversor boost; 3) inversor de tensão; 4) transformador de impulsos; 5) ponte rectificadora de díodos e 6) separador de Alta Tensão – Sinal. Os resultados obtidos experimentalmente estão de acordo com resultados obtidos por simulações usando o Matlab/Simulink ou o OrCAD. Estes resultados permitem demonstrar a fiabilidade e a validade da fonte de alimentação proposta para alimentar o detector Geiger-Muller. A fonte de alimentação foi testada em condições reais de funcionamento com fontes de isótopos radioactivos escolhidos.; This MSc thesis presents the research and project of a power supply for a Geiger-Muller radiation detector. The power supply may work with mains voltage or may be integrated in a NIM module so that can be easily integrated in any kind of laboratory. The power supply includes the following modules: 1) single-phase full wave controlled rectifier; 2) Boost converter; 3) Voltage inverter; 4) pulse transformer; 5) single-phase bridge rectifier and 6) separador de Alta Tensão – Sinal. The results obtained experimentally match the results obtained by simulations using Matlab/Simulink or OrCAD. This results allow to demonstrate the fiability and validate the proposed power supply to connect to the Geiger-Muller detector. The power supply was tested in real conditions of functioning with chosen sources of radioactive isotopes.

PV inverters for module level applications

Barbosa, José Nilton Tavares
Fonte: FCT-UNL Publicador: FCT-UNL
Tipo: Dissertação de Mestrado
Publicado em /09/2011 ENG
Relevância na Pesquisa
26.27%
Dissertação para obtenção do Grau de Mestre em Energias Renováveis – Conversão Eléctrica e Utilização Sustentáveis; Nowadays, the photovoltaic (PV) energy is presented as one of the most promising source of clean energy, and so a good way for greenhouse gas emissions mitigation and reduce the fossil fuel dependence. Within it, the photovoltaic energy has caused a huge interest in the electronic converters, and the need to improve their efficiency and reducing their cost. With this work I present a solution for a module scale grid-connected single-phase inverter. The solution consists in a two-stage inverter insolated with a grid line transformer. The two-stage inverter is composed by a DC-DC converter and a DC-AC converter connected through a DC-link capacitor. The DC-DC converter in case is a boost converter used to elevate the voltage from the PV module to a higher level. For the DC-AC converter it is used a full-bridge inverter, and both the DC-DC and the DC-AC converters use the IGBTs form an integrated module with its respective drivers. To the boost control it is implemented a Maximum Power Point Tracking algorithm that can optimize the power extraction from the PV source and for the inverter it is used a sliding mode hysteretic control. Once this inverter is conceived to work connected to the grid...

Switching Patterns and Steady-State Analysis of Grid-Connected and Stand-Alone Single-Stage Boost-Inverters for PV Applications

Saghaleini, Mahdi
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
76.46%
Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. In a micro-grid...

Switching patterns and steady-state analysis of grid-connected and stand-alone single-stage boost-inverters for PV applications

Saghaleini, Mahdi
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
56.29%
Renewable or sustainable energy (SE) sources have attracted the attention of many countries because the power generated is environmentally friendly, and the sources are not subject to the instability of price and availability. This dissertation presents new trends in the DC-AC converters (inverters) used in renewable energy sources, particularly for photovoltaic (PV) energy systems. A review of the existing technologies is performed for both single-phase and three-phase systems, and the pros and cons of the best candidates are investigated. ^ In many modern energy conversion systems, a DC voltage, which is provided from a SE source or energy storage device, must be boosted and converted to an AC voltage with a fixed amplitude and frequency. A novel switching pattern based on the concept of the conventional space-vector pulse-width-modulated (SVPWM) technique is developed for single-stage, boost-inverters using the topology of current source inverters (CSI). The six main switching states, and two zeros, with three switches conducting at any given instant in conventional SVPWM techniques are modified herein into three charging states and six discharging states with only two switches conducting at any given instant. The charging states are necessary in order to boost the DC input voltage. It is demonstrated that the CSI topology in conjunction with the developed switching pattern is capable of providing the required residential AC voltage from a low DC voltage of one PV panel at its rated power for both linear and nonlinear loads. ^ In a micro-grid...

Implementation and performance evaluation of a low-cost current-source grid-connected inverter for PV applications

Ertasgin, G.; Whaley, D.; Ertugrul, N.; Soong, W.
Fonte: IEEE; CD Publicador: IEEE; CD
Tipo: Conference paper
Publicado em //2008 EN
Relevância na Pesquisa
36.25%
This paper investigates the performance of a 150 W single-phase current-source grid-connected inverter for PV cells. The constant-current source is realised using a DC link inductor and the inverter is implemented using a single boost switch, a H-bridge inverter and an LC output filter. Although the DC link inductor causes the inverter to be less efficient than an equivalent voltage-source inverter, it offers lower cost due to the zero-current switching and lower number of components. In addition, the output current is easily controlled using the boost switch and simple open-loop control. The inverter input is simulated using the dark I-V configuration of two PV cells. The advantage of this arrangement is the ability to conveniently simulate the PV cell over a wide range of irradiances. The entire system is implemented to verify the simulation results. Furthermore, the paper also examines the proposed inverterpsilas ability to deliver sinusoidal current to the grid whilst meeting the appropriate standards, i.e. total harmonic distortion and power factor requirements. Additionally, the inverterpsilas ability to maximise the PV cell and inverter output power is shown.; Ertasgin, G.; Whaley, D.M.; Ertugrul, N. and Soong, W.L.

Low-cost current-source 1-ph photovoltaic grid-connected inverter.

Ertasgin, Gurhan
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2010
Relevância na Pesquisa
56.26%
This research investigates a complete analysis and investigation of a single-phase currentsource (CSI) grid-connected inverter topology that is based on a photovoltaic array as a supply and a DC link inductor acting as a constant-current source. The proposed low-cost system is implemented using an open-loop control to prove the concept. Then a well-known feedforward compensation control is implemented to achieve acceptable total harmonic distortion of the inverter output current. A single boost switch (based on a switched-mode rectifier) has a duty-cycle that is modulated sinusoidally at the mains (grid) frequency such that it produces an output current that appears a full-wave rectified sinewave that is synchronised to the grid voltage. Additionally, a H-bridge inverter circuit and a capacitive-inductive low-pass grid filter is used to unfold, filter and feed the sinusoidal output current into the grid. A number of detailed PV array models are studied and used in the simulations. The relationship between the PV array output ripple and the DC link energy storage (element) for single-phase grid-connected inverters is analysed. The “balanced" ripple definition is introduced to estimate the PV array output power reduction due to ripple. The proposed grid-connected CSI topology is idealised which ignores : component losses...

Analysis and design of single-phase current-source grid-connected PV inverter

Ertasgin, G.; Soong, W.; Ertugrul, N.
Fonte: IEEE; Online Publicador: IEEE; Online
Tipo: Conference paper
Publicado em //2013 EN
Relevância na Pesquisa
66.37%
This paper investigates the performance of a 150 W single-phase current-source grid-connected inverter for photovoltaic (PV) applications. The constant-current source is realized using a large DC link inductor and the inverter is implemented using a single boost switch, a H-bridge inverter and a CL output filter. Although the DC link inductor causes the inverter to be less efficient than an equivalent voltage-source inverter, it offers lower cost due to the zero-current switching and lower number of components. In addition, the output current is easily controlled using the boost switch and offers simple open-loop and feed-forward control. The paper compares the simulated and measured inverter performance with regards to output power, total harmonic distortion and power factor. Additionally the scaling of the concept to a higher power (1.2 kW) inverter was also investigated using simulations.; G. Ertasgin, W.L. Soong and N. Ertugrul