GRID INTEGRATION OF SOLAR PV SYSTEM

Abstract

The project aims at design and analysis of a grid connected Solar Photovoltaic (SPV) system which maintains its DC link voltage at appropriate level and deliver the electrical power into grid at unity power factor. A 50kW PV array is designed and connected to the grid through a dc-dc boost converter and voltage source inverter (VSI). The operation of this PV system is demonstrated at varying solar irradiance. When the irradiance is varied, the output power of the PV array also varies and hence a dc to dc boost converter is needed to maintain its output voltage and current conditions in order to obtain the maximum power from PV array at any point of time. This is achieved using maximum power point tracking (MPPT) method. The Perturb and Observe (P&O) algorithm of MPPT is used in the present analysis which helps to maintain the output of the PV array at its maximum operating conditions. This MPPT algorithm is also implemented using XILINX SYSTEM GENERATOR which makes use of the Xilinx library block set in the MATLAB/simulink environment. It allows design using existing Xilinx blocks or code in verilog or VHDL using black box. It is also possible to write a MATLAB code in m-code block if the input and output and the desired function are known. The MPPT control is implemented in a dc to dc boost converter that increases the output voltage of the PV array to a higher level. The switching of the MOSFET switch in the Boost converter is controlled by the MPPT algorithm. A VSI is being used to convert DC output power of boost converter into three phase AC power which is delivered to the grid. The VSI Maintain the DC link voltage at 800V and also deliver three phase AC power at unity power factor to the utility or the grid. Two control schemes are used in the VSI: 1) A simple PI controller to regulate DC link voltage using the reference current waveform generated using grid voltage. The reference current is compared with actual grid current to generate PWM control signals for switches in VSI. 2) Power balance theory: This technique of inverter control involves generation of reference current waveform using the grid voltage, load current and the DC link voltage. The grid

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current is then compared with this generated reference waveform and the PWM signals are generated, which are given to the VSI as the gate pulses. A complete model of grid tied solar PV system for 50kWp power is developed in MATLAB/Simulink and performance of the system is analyzed under varying solar irradiance level.