Enhanced power recovery strategy in PV-ESS-VSG systems using coordinated virtual impedance and virtual damping control

To address the frequency and power stability issues in the PV-ESS-VSG system after a grid fault, this paper proposes an enhanced power recovery control strategy that integrates coordinated virtual impedance and virtual damping. First, the paper analyzes the cause of impulse current during the power recovery phase from the perspective of reactive power loop bandwidth, and verifies the suppression effect of virtual impedance on impulse current through impedance analysis. However, although increasing virtual impedance reduces impulse current, Nyquist plot analysis reveals that this increase leads to a decrease in the system's damping ratio, causing power and frequency oscillations. To resolve this issue, virtual damping is introduced to enhance the system's power stability. Consequently, an enhanced power recovery control strategy is proposed, coordinating virtual impedance and virtual damping to simultaneously suppress impulse current as well as power and frequency oscillations. Finally, a hardware-in-the-loop experimental platform is employed to verify that the improved VSG control strategy significantly enhances the frequency and power stability of the PV-ESS-VSG system during the power recovery phase.