An improved method for harmonic mitigation and stability improvement of the grid-connected inverters under local load variation and weak grid condition

摘要

Variable voltage and current harmonics appear to be critical challenges for grid-connected inverters at the point of common coupling (PCC). The nonlinear local load and grid impedance variations contribute a lot to the problem. In this paper, a novel control strategy is proposed using the variable virtual admittance (VVA) and series active filter concepts capable of improving harmonic mitigation and stability in grid-connected inverters. The magnitude and phase angle of the VVA are adaptively determined according to the local load variation. Moreover, the series active filter injects a series voltage to reduce the grid impedance effect. The proposed control method can be simply implemented, where sinusoidal grid-injected current and sinusoidal local load voltage can also be achieved under local load variation and weak grid condition. The theoretical approach is verified using several simulation case studies in Matlab/Simulink software.