A Voltage Self-Stability Control of STATCOM for Damping Subsynchronous Oscillation in Photovoltaic Power Station Under Weak Grid

Under weak grid, the photovoltaic (PV) power station is easy to occur subsynchronous oscillations (SSO) owing to the impedance interaction. First, with and without considering the static synchronous compensator (STATCOM), the SSO mechanism and characteristics of the PV power station under weak grid are analyzed and compared based on impedance method. The stability of the PV power station declines as the grid stiffness decrease, which can cause SSO. To address this problem, a voltage self-stability control of STATCOM is proposed by compensating for the distorted current based on the distorted voltage in d-axis. Under the proposed control, the parallel impedance of improved STATCOM and grid is attenuated significantly, which equivalently enhances the grid stiffness from the point-of-view of impedance. Without using any harmonic extraction filters, the proposed control of STATCOM can effectively improve the stability of PV power station, which is simpler. Finally, the proposed control and theoretical analysis are validated by simulation and experimental results.