Performance analysis of PLL based DSGCP (Double Stage Grid Connected Photovoltaic) system with non-linear load under normal and various grid fault conditions

The demand for non-conventional energy sources is growing by days and solar energy is one of the leading among these. In order to synchronize Photovoltaic (PV) system with the grid, a few major aspects such as controlling the DC link voltage (Vdc) at the output of DC-DC boost converter and controlling of generation of reference current and pulses for the voltage source inverter (VSI) are to be taken care of. In present work, we have connected a PV plant to the grid by means of DC-DC boost converter and VSI following extraction of maximum power using conventional Perturb & Observe (P&O) method. A non-linear R-L load having total harmonic distortion (THD) of 22.24% has been tied with the same grid and a proportional-integral (PI) controller has been used to control the DC link voltage. Automatic gain control enabled phase locked loop (PLL) is used here for generating gate pulses to the VSI. The entire system has been simulated in Matlab-Simulink environment under normal and different grid fault situations. Harmonics analysis of different system parameters such as inverter current, load current and grid current have been illustrated at pre-fault, during fault and post-fault conditions. It is observed that all the parameters are well within the permissible limit under all situations and capacitor voltage profile also remains almost stable throughout; although, minor and non-similar variations in DC link voltage is noticed during the different grid faults.