A Hybrid Power Synchronization Scheme for Stability Enhancement of Virtual Synchronous Generator Control

Sub-synchronous oscillation (SSO) is a commonly observed issue in series-compensated transmission systems (SCTSs) with the virtual synchronous generator (VSG) control. Prior-art research has revealed that such SSOs are attributed to the impedance resonance between the capacitive series-compensated line and the inductive VSG in the sub-synchronous frequency range. To address the SSO issue, in this letter, a hybrid power synchronization control is proposed to improve the stability of the VSG in the SCTS. With the proposed control, the low-frequency impedance of the VSG is optimized to be of resistive-inductive characteristics, effectively reducing the SSO risk due to impedance mismatching. In addition, the proposed method is not limited to inner-loop implementations, meaning that it can be applied to power-synchronous grid-forming converters even when inner loops are simplified or omitted. The effectiveness of the proposed control has been verified through experimental tests.