Otimização meta heurística e controle baseado no modelo interno aplicados em sistemas de geração fotovoltaica conectados à rede elétrica monofásica

This paper presents the study, development and application of new control techniques for photovoltaic power generation systems, connected to single-phase power grid in order to improve the efficiency of these systems in relation to control methods typically used. The work is divided into two main parts, which are related to tracking the maximum power point (Maximum Power Point Tracking - MPPT) and then the internal controller of boost quadratic converters - side of the photovoltaic panels - as well as the controllers the voltage inverter, the side of the single-phase mains. The first part of the work is the development of a heuristic goal algorithm for MPPT, which is based on the method of simulated annealing (Simulated Annealing - SA) and aims at determining the overall maximum point, seeking out solutions in a close vicinity, so as to prevent the docking local maxima in the curve of power output of the photovoltaic array, thereby improving the utilization of energy in partial shading situations. The second part presents the design of controllers based on internal model (Internal Model Control - IMC) with 1 degree of freedom (1 Degree of Freedom - 1 DOF) applied, first, the DC-DC Boost Quadratic converter, used for MPPT, and thereafter, a voltage inverter with LCL filter connected to the single phase power supply operating in current injection mode. A mathematical modeling of both converters and analyzed the compensation of internal feedback to the voltage inverter system corresponding to the disconnection of the mains voltage through the power strategy a head (feedforward). A basis of comparison for the performance analysis of IMC-1DOF converter is aiming at, is also applied to the current injection system, Proportional-Resonant Controller (P + Res). They are presented computer simulation and experimental results of both controllers, which allow you to check the system performance in low and non-linear local load network situation.Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorTese (Doutorado)Este trabalho apresenta o estudo, desenvolvimento e aplicação de novas técnicas de controle aos sistemas de geração de energia fotovoltaica, conectados à rede elétrica monofásica, visando a melhoria da eficiência destes sistemas em relação aos métodos de controle tipicamente utilizados. O trabalho é dividido em duas partes principais, as quais estão relacionadas ao rastreamento do ponto de máxima potência (Maximum Power Point Tracking – MPPT) e, depois, ao controlador interno dos conversores boost-quadrático – lado dos painéis fotovoltaicos – assim como aos controladores do inversor de tensão, no lado da rede elétrica monofásica. A primeira parte do trabalho consiste no desenvolvimento de um algoritmo de meta heurística para o MPPT, o qual é baseado no método do recozimento simulado (Simulated Annealing - SA) e tem como objetivo a determinação do ponto de máximo global, buscando soluções fora de uma vizinhança próxima, de modo a evitar o atracamento em máximos locais da curva de potência de saída do arranjo de painéis fotovoltaicos, melhorando, assim, o aproveitamento da energia em situações de sombreamento parcial. A segunda parte do trabalho apresenta o projeto de controladores baseados no modelo interno (Internal Model Control – IMC) com 1 grau de liberdade (1 Degree of Freedom – 1 DOF) aplicados, primeiramente, ao conversor CC-CC Boost Quadrático, utilizado para o MPPT, e, posteriormente, a um inversor de tensão com filtro LCL, conectado à rede elétrica monofásica, operando no modo de injeção de corrente. É apresentada a modelagem matemática de ambos os conversores e analisada a compensação da realimentação interna ao sistema do inversor de tensão, correspondente ao desacoplamento da tensão da rede, através da estratégia de alimentação à frente (Feedforward). Visando-se uma base de comparação, para a análise de desempenho do conversor IMC – 1DOF, também é aplicado ao sistema de injeção de corrente, o controlador Proporcional-Ressonante (P+Res). São apresentados resultados de simulação computacional e experimentais de ambos os 8 controladores, os quais permitem verificar o desempenho do sistema em situação de rede fraca e carga local não-linear

Discrete time current regulation of grid connected converters with LCL filters

Two important components of a grid connected power electronic converter are the line filter and the closed loop current regulator. Together they are largely responsible for system stability, power flow and power quality into the grid. The LCL filter is a smaller and cheaper line filter alternative because of its third order filtering capability. However the LCL filter has a resonance that must be appropriately damped using either passive or active techniques, generating more losses or adding complexity to the controller respectively. It is now generally accepted that the PWM transport delay due to discrete/digital implementations is the main limiting factor for controller bandwidth in L filtered systems. However, despite the large body of literature for the LCL filter, there is still only limited consensus regarding the implications of PWM transport delay on the current regulator and active damping controller for this type of filter. This thesis applies discrete time models to these systems to overcome these perceived limitations and hence develop the optimal controllers. This knowledge is then used to enhance the current regulator to overcome further practical problems. The first part of this thesis focuses on the development of discrete time current regulation for a grid connected inverter. The benefits of discrete time modelling and control for current regulation are demonstrated by using a discrete state feedback controller for an L filter system. A precise discrete time model of the LCL filter system is then developed to exactly identify the frequency region where active damping is mandatory, and the high frequency region where active damping is not required. The critical frequency, which separates these two regions, is identified as a fraction of the sampling frequency, demonstrating the controller's dependence on PWM transport delay. Controllers and gain selection methods are developed and verified for each region. A generalised approach for analysis of the LCL filtered system is then developed so that all forms can be evaluated on a precisely comparable basis. Using this generalised approach the particular advantages and disadvantages of each control method are readily identified. The second part of this thesis looks at the impact of two practical issues for current regulation of LCL filtered grid connected converters. It firstly identifies that practical converters generally do not match their ideal output current quality expectations. The reasons for this distortion are explained and harmonic compensators are then proposed as an effective solution to overcome it. Secondly the implications of a virtual neutral common mode EMI filter on the current regulator are investigated. A virtual neutral filter design is proposed that utilises the primary LCL filter components. The active damping current regulator is then enhanced to avoid interference from the additional current path and to actively damp the common mode resonance. All theoretical work is validated by extensive simulation and experimental results