Mitigation of Sub synchronous Resonance for Grid-Connected Inverters in Series-Compensated Weak Power Grids Through Observed Q-Axis Grid Voltage Feedback

In this paper, to mitigate the impact of the PLL and obtain the stable operation of the power system, a q-axis voltage feedback method has been proposed in literature to damp the harmonic oscillations in the weak power grid where, however, the series compensation is not considered. Because the real q-axis voltage cannot be obtained, the q-axis voltage output from the PLL is used as the feedback variable in literature. However, due to the dynamic response of the PLL, the q-axis voltage output from the PLL is different from the real q-axis voltage, and the direct use of it for the damping of the SSR in the power grid with series compensations is invalid, which is investigated in this article. Besides, an observed q-axis voltage feedback method is proposed in this article to damp the SSR in the series-compensated power grid with GCIs being connected.

Index Terms—Grid-connected inverter (GCI), series compensation, stability, sub synchronous resonance (SSR).