A Quasi-Harmonic Voltage Feedforward Control for Improving Power Quality in VSG-Based Islanded Microgrid

The voltage harmonics caused by nonlinear load seriously affect the safe and stable operation of the islanded microgrid based on a virtual synchronous generator (VSG). First, the voltage distortion mechanism and characteristics of the VSG-based islanded microgrid are revealed based on the impedance method. Due to the large impedance of VSG, a significant distorted voltage will be caused by the harmonic current induced by nonlinear load, which can degrade the power quality of the islanded microgrid. Second, to address this issue, a quasi-harmonic voltage feedforward control of VSG is proposed based on the rated voltage and sampling voltage. The proposed control can significantly reduce the impedance of VSG, which makes the improved VSG more like an ideal voltage source and thus enhances the voltage robustness. Compared to the traditional harmonic suppression method, the proposed control does not need a harmonic extraction filter and can mitigate wideband harmonics without knowing the harmonic frequency in advance. Finally, the proposed control and theoretical analysis are validated by simulation and experimental results.