Harmonics compensation for grid-connected inverter caused by local nonlinear load

This paper proposes a controller design of a distributed power source inverter to be useful both under the stand alone mode and the grid-connected mode to compensate the current harmonics from the local nonlinear load. The PR based multi-loop controller is used to improve the system dynamic performance and to compensate the output voltage or grid current harmonics depending on the operation modes, respectively. The multi-loop controller consists of an outer current controller and an inner voltage controller which also has an inner current controller. The stability of each controller is verified by the Root locus and Bode plot of the transfer function. In this paper, in spite of the current harmonics caused by the local nonlinear load, the controller is designed to regulate the inverter output voltage to be sinusoidal with constant voltage and constant frequency in the stand alone mode and to control the grid current to be sinusoidal in the grid-connected mode, respectively. The validity of the proposed control algorithm and the controller design results have been verified through the PSiM simulation and experimental results.