MODEL PREDICTIVE CONTROL STRATEGY FOR LEAKAGE CURRENT REDUCTION IN PHOTOVOLTAIC SYSTEMS: A STUDY ON PUC AND CSC INVERTER TOPOLOGIES

Abstract

Solar energy is one of the most commonly used sources of renewable energy. It is a clean and noiseless energy source that does not emit greenhouse gases. This thesis focuses on studying a double-stage transformerless photovoltaic (PV) microinverter grid-connected system. The main concern when using a transformerless PV setup is the need to take safety measures, as this configuration can result in PV panel leakage current issues. This thesis studies this issue in two inverter topologies: the packed U-cell (PUC) and the crossover switches cell (CSC) inverters. A Finite-Control-Set model Predictive Control is proposed to mitigate the PV panel leakage current. The proposed controller was simulated using Matlab/Simulink, and the results show that the controller effectively mitigates the leakage current. In the case of a PUC inverter, the RMS leakage current decreases from 336 mA to 155 mA. In the case of a CSC inverter, it decreases from 360 mA to 140 mA, which is below 300 mA as per the DIN VDE 0126-1-1 standard. These results were achieved while maintaining a gird current total harmonic distortion (THD) of less than 5% and maintaining the voltage across the inverter capacitors constant with less than 0.5% variation. Furthermore, a hardware-in-the-loop implementation was utilized to test and validate a proposed control algorithm for the PUC inverter. Through this testing, it was found that the PV panel leakage current has been successfully mitigated from 1.1 A to 0.5 A while maintaining the PUC capacitor fixed with minor variations and the THD remaining below 5.6%.