DESIGN, CONTROL AND ANALYSIS OF GRID CONNECTED PV SYSTEM

Abstract

Solar photovoltaic (PV) generating system is gaining lot of importance theses days. Out of all the renewable energy sources solar PV is most promising because of clean and inexhaustible supply, less maintenance requirement, lower mechanical components involved and can be installed in modular from small-scale to large-scale generating system. The modern distributed grid is connected with different power electronic loads and other types of linear (lagging or leading) loads. These loads may results in poor power factor and produces harmonics to the grid. In this thesis work, design, control and analysis of grid connected PV system has been presented. It enables the active and reactive compensation to the distribution, load balancing in three-phase and power quality improvement. The proposed system is implemented in both the single-phase and three-phase distribution network. Maximum Power Point Tracking (MPPT) technique has been implemented to extract maximum power from the PV in both single-stage and double-stage grid-connected PV system. Parameters of the proposed system has been estimated and the prototype of singlephase and three-phase Shunt Active Power Filter (SAPF) have been configured. The proper functioning of the grid-connected PV system require a suitable control algorithm. Conventionally, control algorithms require synchronization technique, fundamental component estimation technique, DC-link voltage controller and the feed-forward term. For the purpose of estimation grid synchronization signal different conventional techniques have been presented and novel advanced techniques have been proposed for both the single-phase and three-phase grid-connected PV system. Phase Locked Loops (PLLs) are widely employed to estimate synchronizing iv signal and also have the capability of phase, frequency and the magnitude of the grid voltage signal. These techniques have been tested under different grid voltage conditions such as voltage sag/swell, harmonics, frequency change, phase change and noisy grid. For the single-phase system the conventional algorithms presented are Synchronous Reference Frame Phase Locked Loop (SRF-PLL) , Enhanced Phase Locked Loop (EPLL), Second-Order Generalized Integrator-PLL (SOGI-PLL) have been employed. Further new and advanced technique such combined SOGI-FLL and Reduced Order Generalized Integrator (ROGI) has been proposed which shows the improved performance during the harmonic grid. A fast and robust technique based on adaptive zero-crossing detection has been proposed which shows the precise frequency estimation and faster dynamic response. For the three-phase system, the simplest unit-template method has been used to generate synchronizing but it works good when the grid voltage has no abnormalities. The conventional three-phase SRF-PLL has been also presented and its poor performance during the harmonic grid and dynamic condition. Further advanced technique have been proposed to improve the performance of PLLs. Improved Adaline PLL has been proposed which has adaptive in nature and improves it dynamic response without compromising the steady-state performance. An adaptive spline based PLL has been proposed for smooth estimation of grid parameters and distortion free synchronizing signals. Some conventional and advanced techniques have been employed for estimation of fundamental component of the non-linear load current. Further the synchronization techniques and the fundamental estimation technique have been employed in single-phase and three-phase system feeding linear/non-linear load under normal and distorted grid conditions for SAPF system. The PV has been connected in both single-stage and double-stage mode to the DC-link of the Voltage Source Converter (VSC). dSpace 1104 has been used for single-phase grid-connected PV system and dSpace 1202 has been used for three-phase grid-connected PV system for processing the grid parameter signals and to estimate switching pulses for Insulated-Gate v Bipolar Transistor (IGBT) switches of VSC and DC-DC converter. The proposed system and algorithms have been simulated and analysed in MATLAB/Simulink environment. The experimental results validate and fulfils the objectives of the thesis work.