Output current control for grid interfacing VSI under low switching frequency and distorted grid

The increase of grid-tied distributed generators (DGs) and nonlinear loads may generate harmful low order harmonics, polluting the grid and deteriorating the operation of other power electronics based loads and DGs. In order to improve the output current of the voltage source inverter (VSI) in grid-tied DG system, two methods are proposed in this paper to compensate the output harmonic under distorted voltage in a weak grid. The proposed methods do not rely on the close-loop feedback control of harmonic current and therefore are very suitable for VSI with low switching frequency, whose close loop control feedback bandwidth may be limited for harmonic regulation. The principle and stability analysis of the proposed two strategies are presented, and their effectiveness is verified by experiment results.