SINGLE STAGE GRID-CONNECTED MICRO-INVERTER FOR PHOTOVOLTAIC SYSTEMS by Nikhil Sukesh-Department of Electrical and Computer Engineering--Queen’s University Kingston, Ontario, Canada-

 

SINGLE STAGE GRID-CONNECTED MICRO-INVERTER FOR PHOTOVOLTAIC SYSTEMS by Nikhil Sukesh 

 A thesis submitted to the Department of Electrical and Computer Engineering In conformity with the requirements for the degree of Master of Applied Sciences Queen’s University Kingston, Ontario, Canada 

 Abstract This thesis concentrates on the design and control of a single stage inverter for photovoltaic (PV) micro-inverters. The PV micro-inverters have become an attractive solution for distributed power generation systems due to their modular approach and independent Maximum Power Point Tracking (MPPT). Since each micro-inverter has an individual inverter section, it is essential to have small-sized power conversion units. Moreover, these inverters should provide large voltage amplification in order to connect to the utility grid because of the low voltages of the PV panels. In order to operate these inverters at high frequencies, the soft-switching of the power MOSFETs is an important criterion to minimize the switching losses during the power transfer. A novel Zero Voltage Switching (ZVS) scheme to improve the efficiency of a single stage grid-connected flyback inverter is proposed in this thesis. The proposed scheme eliminates the need for auxiliary circuits to achieve soft-switching for the primary switch. ZVS is realized by allowing the current from the grid-side to flow in a direction opposite to the actual power transfer with the help of bi-directional switches placed on the secondary side of the transformer. The negative current discharges the output capacitor of the primary MOSFETs thereby allowing turn-on of the switch under zero voltage. In order to optimize the amount of reactive current required to achieve ZVS a variable frequency control scheme is implemented over the line cycle. Thus the amount of negative current in each switching cycle is dependent on the line cycle. Since the proposed topology operates with variable frequency, the conventional methods of modeling would not provide accurate small signal models for the inverter. A modified state-space approach taking into account the constraints associated with variable switching frequency as well as the negative current is used to obtain an accurate small signal model. Based on the linearized inverter model, a stable closed loop control scheme with peak current mode control is implemented for a wide range of operation. The system incorporates the controllers for both the positive as well as negative peak of inductor current. Simulation and the experimental results presented in the thesis confirm the viability of the proposed topology.

LINK: https://qspace.library.queensu.ca/bitstream/handle/1974/7317/Sukesh_Nikhil_201207_MASC.pdf?sequence=1&isAllowed=y

MICROINVERSOR FOTOVOLTAICO NÃO ISOLADO DE DOIS ESTÁGIOS-Gustavo Carlos Knabben-Programa de Pós-Graduação em Engenharia Elétrica da Universidade Federal de Santa Catarina

 

MICROINVERSOR FOTOVOLTAICO NÃO ISOLADO DE DOIS ESTÁGIOS 

AUTOR Gustavo Carlos Knabben  Dissertação submetida ao Programa de Pós-Graduação em Engenharia Elétrica da Universidade Federal de Santa Catarina para obtenção do Grau de Mestre em Engenharia Elétrica. 

Orientador: Prof. Denizar Cruz Martins, Dr.

 Co-orientador: Prof. Roberto Francisco Coelho, Dr. 

Florianópolis 2017

 RESUMO Esta dissertação de mestrado apresenta o procedimento utilizado no projeto e construção de um protótipo de microinversor fotovoltaico, capaz de processar energia de um módulo fotovoltaico de silício cristalino de até 250 W de potência e injetá-la na rede elétrica com 220 V de valor eficaz de tensão e 60 Hz de frequência. O trabalho compreende revisão bibliográfica em microinversores comerciais, normas para conexão à rede elétrica, caracterização de geradores fotovoltaicos, topologias aplicadas a microinversores e influência das correntes de modo comum na operação desses equipamentos. Optou-se por processar a energia em dois estágios de conversão. O primeiro, cccc, é composto por um conversor Boost com célula de ganho. O segundo, cc-ca, principal foco desta dissertação, é o conversor em ponte completa com modulação dois níveis. A estratégia de controle é baseada em compensação da corrente injetada na rede elétrica, com imposição, por PLL, de uma forma de onda senoidal em fase com a tensão; regulação do barramento cc principal; técnica de MPPT; método de antiilhamento; partida suave de todo o sistema; algoritmos de proteção; e desacoplamento dos estágios cc-cc e cc-ca por filtragem ativa. A experimentação do sistema projetado e construído contou com resultados satisfatórios e de acordo com teoria e simulação. 

Palavras-chave: Microinversor. Fotovoltaico. Rede Elétrica. Controle. Ponte Completa.

LINK:https://repositorio.ufsc.br/handle/123456789/178588

High-Performance Voltage Controller Design Based on Capacitor Current Control Model for Stand-alone Inverters Byeng-Joo Byen, Jung-Muk Choe and Gyu-Ha Choe--Dept. of Electrical Engineering, Konkuk University, Korea.

High-Performance Voltage Controller Design Based on Capacitor Current Control Model for Stand-alone Inverters Byeng-Joo Byen*, Jung-Muk Choe** and Gyu-Ha Choe†

 † Corresponding Author: Dept. of Electrical Engineering, Konkuk University, Korea. (ghchoe@konkuk.ac.kr) * Dept. of Electrical Engineering, konkuk University, Korea. (cooks321@konkuk.ac.kr) ** Dept. of Electrical Computer Engineering, Virginia Polytechnic Institute and State University, USA. (jmchoe@vt.edu) 

 Abstract – This study proposes high-performance voltage controller design that employs a capacitor current control model for single-phase stand-alone inverters. The single-phase stand-alone inverter is analyzed via modeling, which is then used to design the controller. A design methodology is proposed to maximize the bandwidth of the feedback controller. Subsequently, to compensate for the problems caused by the bandwidth limitations of the controller, an error transfer function that includes the feedback controller is derived, and the stability of the repetitive control scheme is evaluated using the error transfer function. The digital repetitive controller is then implemented. The simulation and experimental results show that the performance of the proposed controller is high in a 1.5 kW singlephase stand-alone inverter prototype. 

Keywords: AC-DC converter, Digital control, Repetitive control, Capacitor current control model

LINK: http://koreascience.or.kr/article/JAKO201525961704096.pdf

Estudo comparativo de estratégias de controle para inversores de fontes ininterruptas de energia-Dissertação de Mestrado-Autor Rodrigues, Álvaro Jorge -ESCOLA POLITÉCNICA DA UNIVERSIDADE DE SÃO PAULO

 Orientador Komatsu, Wilson (Catálogo USP) 

Banca examinadoraKomatsu, Wilson (Presidente) Kaiser, Walter Marafão, Fernando Pinhabel 

Resumo Em português

Este trabalho tem como objetivo reunir, registrar, estudar e comparar as estratégias de controle utilizadas em inversores para fontes ininterruptas de energia, efetuado através de levantamento bibliográfico, englobando estratégias antigas (implementadas muitas vezes na forma analógica) e recentes (com implementação digital). É realizada comparação dos desempenhos, determinados analiticamente por modelamento e/ou por simulação computacional, entre algumas estratégias de controle. É apresentado um método para a implementação digital de um inversor monofásico para fontes ininterruptas de energia com transformador na saída. O método utilizado consiste de: Análise e modelagem dos controladores e planta, adotando-se critérios para o ajuste dos respectivos parâmetros; Simulação no modo de tempo contínuo; Roteiro da discretização para possibilitar implementação digital; Simulação em tempo discreto; Implementação em protótipo experimental. O controle é realizado com uma estratégia de múltiplas malhas, usando três malhas: uma malha interna de corrente usando controlador proporcional com compensação feedforward da perturbação da tensão de saída no controle da corrente e uma malha externa de tensão com um controlador proporcional + ressonante. Uma terceira malha de controle externa a malha de tensão é adicionada para prevenir a saturação do núcleo do transformador. O inversor é implementado através de um arranjo físico de baixa potência, possibilitando comparação dos resultados de simulação e experimentais.

Título em inglês A comparative study of control strategies in inverters for uninterruptible power supplies.

Palavras-chave em inglêsPower electronics Protection of electrical devices Switch mode power supplies

LINK:https://teses.usp.br/teses/disponiveis/3/3143/tde-20012011-102638/pt-br.php

Single Phase Transformer Based Inverter For Nonlinear Load Application Using PI Controller R. Ramesh, A. John Dhanaseely, P. Pughazendiran

Single Phase Transformer Based Inverter For Nonlinear Load Application Using PI Controller R. Ramesh1, A. John Dhanaseely2, P. Pughazendiran3 PG Student1, Associate professors,  IFET College of Engineering, Villupuram.

 Abstract

 The paper presents a single phase transformer based inverter for nonlinear load application using PI controller. A capacitive full bridge circuit is used to provide instant current under nonlinear load conditions and thereby reducing the harmonics. A new proportional plus integral controller for inverter control is proposed to eliminate the dc current component, and steady state error under heavy load applications. The proposed controllers consist of PI controller act as voltage controller and DC offset canceller. The experimental result derived by using the MATLAB software. I. INTRODUCTION Single phase inverter is widely used in various application such as UPS, Renewable energy conversion, power source etc. The single phase inverter can be divided into half bridge, full bridge, and three level structures. The main function of the inverter is to provide an AC output voltage with less voltage distortion under both linear and nonlinear load applications. The inverter can be divided into transformer based and transformer less types. Although transformer less inverter without line frequency transformer is placed in front of load for isolation purpose, and to provide the compact size, lowest cost, less voltage distortion from the line frequency transformer and to provide fast response, but there is no galvanic isolation between power source and load.

The transformer based inverter has the important characteristics is to provide the galvanic isolation between power source and the load, with the line frequency transformer between inverter and the load. For safety application such as medical installation , data center UPS system require isolation between the output neutral and power source , the transformer based inverter are heavy in demand.

The transformer based inverter has the capable to block the DC voltage, and filter out the high frequency noise generated by the inverter and to increasing the output voltage range. Nonlinear load, such as rectifier is very popular during this year. Blocking the DC voltage is also very important for the load contained magnetic component such as inductor, and transformer.

DC voltage component exist in the output of AC inverter which may cause saturation and increase the power loss of line frequency transformer. The voltage feedback signal is taking from the transformer at the inverter output and uses low pass filter to separate the DC voltage, and thereby reducing the control method.

LINK:  https://www.researchgate.net/profile/Pugazhendiran_P/publication/266327044_Single_Phase_Transformer_Based_Inverter_For_Nonlinear_Load_Application_Using_PI_Controller/links/59cc7c9caca272bb050ce2e1/Single-Phase-Transformer-Based-Inverter-For-Nonlinear-Load-Application-Using-PI-Controller.pdf