A Quasi-Harmonic Voltage Compensation Control of PV Grid-Connected Converter for Suppressing Sub/Super-Synchronous Oscillation in Weak Grid

In photovoltaic (PV) generation systems, the grid-connected converter is prone to interact with weak grids, which can cause sub/super-synchronous oscillations (SSOs) and seriously threaten power system safety. First, the mechanism and characteristics of the SSO in the PV grid-connected system are analyzed based on the eigenvalues. As the grid stiffness declines, a pair of eigenvalues of the PV grid-connected system tends to exhibit negative damping, which will trigger system oscillation. To address this problem, a quasi-harmonic voltage compensation method is proposed, which can actively suppress the SSO without using any harmonic extraction filters. Under the proposed control, the eigenvalues of the PV grid-connected system shift to the positive damping direction, which can effectively improve the system stability. Meanwhile, the parameter design method of the proposed controller is given while considering the system stability. Finally, the validity of the proposed control algorithm and the above theoretical analysis is confirmed by simulation and experiment.