Mechanism analysis and mitigation strategies for oscillatory instability of synchronous generators affected by voltage source converters

Abstract

The electric power systems are experiencing a transformation to be characterized by power electronic devices, for example, voltage source converters (VSCs). However, the large-capacity VSC will interact with the synchronous generators (SGs) and could lead to low-frequency oscillation (LFO). It becomes a hurdle for the secure and stable operation of modern electric power systems. Therefore, this paper analyses the oscillatory instability mechanism of the SG with the penetration of grid-forming (GFM) and grid-following (GFL) VSC. The distinctive transfer function model of the SG-VSC system is first developed. Then, through parameter sensitivity and transfer function analysis, the impact of three types of VSC is investigated, encompassing GFM-VSC and GFL-VSCs with two conventional reactive control schemes. It proves that the voltage control of the VSC can be detrimental to the damping torque of the SG. According to the theoretical analysis, a supplementary compensator is proposed to suppress the LFO induced by the VSC. Finally, case studies in a two-area test system validate the analytical results and robustness of the proposed enhancement method.