Suppression Method of Modulation Switching for the Inverter Oscillation caused by Harmonic Control

There exists the risk that harmonic disturbances in the grid force the inverters to output harmonic current due to their non-linear port impedance. Compared with traditional harmonic suppression methods, the proposed vector resonance controller is not affected by phase disturbances from PLL and needs small calculations. By analyzing the loop gain of the harmonic suppression methods, resonance risk common to the methods is pointed out, and damping method is constructed to improve the stability margin. To make up for the harmonic suppression accuracy lost while improving the stability margin and to suppress the resonance, a switching method to hysteresis current control (HCC) is proposed. This method is based on the robustness and rapidity of HCC. A frequency loop with feedforward is designed to fix the switching frequency of HCC. A smooth switching scheme and switching condition are given. The simulation results validates the effectiveness of the proposed method.