Selective Harmonic and DC Offset Elimination in Grid Connected Single Phase Inverter by Using Optimal Controller and Modified EPLL

Abstract

This paper proposed a modified Enhancement Phase Lock Loop (EPLL) and an optimal controller to efficiently operate grid-connected inverter for distributed renewable energy application. Conventionally, a basic EPLL structure is used to generate the inverter reference signal and a proportional (P) or proportional integral (PI) controller is used to meet the system specifications. In the presence of small dc offset or lower order harmonics in the grid, this EPLL cannot generate a pure sinusoidal reference signal. Furthermore, P or PI controller is not robust enough to eliminate the disturbance due to the inverter or system uncertainties. In this paper, 1) an optimal controller is designed by using linear quadratic regulation (LQR) technique based on state space approach to remove the effect of the inverter and system uncertainties; and 2) it also presents a systematic design approach of a modified EPLL to eliminate the unwanted dc offset and selective lower order harmonics from the grid. A MATLAB simulation model is developed for the proposed system to investigate the performance of the optimal controller with the modified EPLL. The proposed control system shows better performance compare to the conventional control model in the presence of various system uncertainties and lower order harmonics in the grid.