DESIGN AND DEVELOPMENT OF NEW CONTROLLERS FOR GRID TIED PV SYSTEMS

Abstract

Modern power distribution systems face twin challenges of increased use of power electronic based loads and integration of renewable energy systems. These power electronic devices cause current based power quality problems in distribution systems. Prominent power quality problems include poor power factor, load unbalancing, harmonics in supply current, voltage regulation etc. The Shunt Active Power Filter (SAPF) is employed to mitigate current based power quality problems. Several controllers are designed to achieve this task. The synchronizing signals are sinusoidal in shape in case of normal grid and can be extracted with the help of unit in phase template method. But under weak grid conditions there are problems of voltage sag, swell, distortion and DC offset. Thus, there is a need of effective Phase Locked Loop (PLL) methods employed for estimation of synchronizing template signals under distorted grid conditions. Several controllers are designed to achieve the task of mitigation of power quality problems. The SAPF can be configured for single phase as well as three phase systems. Two-Leg Voltage Source Converter (VSC) configurations have been used in single-phase system. These are H-bridge for single phase system and three-phase three leg configuration for three-phase system. SAPF working is based on the fundamental load current for generation of reference signals. The fundamental component of load current is extracted with the help of several algorithms. Various type of control algorithms has been proposed in this work. Time domain conventional techniques along with adaptive and Functional Link Neural Network and Fractional Delay algorithms are proposed. 2 The entire thesis work has been split in to six chapters. The first two chapters deal with the introduction and literature review related to problems and mitigation techniques of shunt compensation, PLL and battery energy storage systems. The third chapter deals with the design and analysis of PV integrated grid connected systems. The configuration of SAPF in single-phase and three-phase PV integrated grid connected and battery energy storage systems are discussed. The fourth chapter discusses the shunt compensation in single-phase grid connected systems. The control algorithms considered for compensation are Synchronous Reference Frame Theory (SRFT), Second Order Generalized Integrator (SOGI), Trigonometric Functional Link Neural Network (TFLNN) and Legendre Functional Neural Network (LFNN). These algorithms are studied under varying load conditions i.e., linear, non-linear and mixed loading conditions using Matlab Simulink models. The algorithms have also been tested in the Simulink environment as well as hardware developed in the laboratory with and without PV interfaced systems. The fifth chapter deals with the shunt compensation in three-phase grid connected systems. It studies some conventional and few algorithms such as Synchronous Reference Frame Theory (SRFT), Second Order Generalized Integrator (SOGI), Adaptive Volterra Second Order Filter (AVSF) and Cubic Bezier Functional Expansion Based Adaptive Filter (CB-FEBAF) under varying load conditions such as linear, non linear and mixed loading conditions. Their efficiency has been tested in the Simulink as well as on the hardware developed in the laboratory with and without PV interfaced systems. The sixth chapter studies the voltage-based power quality problems that arises in weak grid conditions such as voltage sag, swell, distortion, phase change and frequency change. PLL has been used to generate the synchronizing template for 3 reference waveform generation. Some conventional PLLs have been studied such as Synchronous Reference Frame Theory (SRFT), Second Order Generalised Integrator (SOGI) and some new PLLs such as Quadratic Bernstein Functional Blending Neural Network (QB-FBNN) and Fractional Delay Newton Structure for (FD-NSLI) Lagrangian Interpolation method have been proposed. Extensive Simulation and experimental results have been taken for PLL testing. Chapter 7 studies the battery integrated system where the voltage control mode and current control mode both are studied. This system considers a battery integrated PV systems under grid connected and islanding mode. Control algorithms such as Synchronous Reference Frame Theory (SRFT) and Grid Sequence Separator (GSS) based control have been developed and tested using MATLAB Based models.