Stability Analysis and Subsynchronous Oscillation of Grid-Tied VSC Under Different Grid Strengths

Recently, with the development of renewable energy, the proportion of power electronic equipment in the power system has gradually increased, which makes the stability and subsynchronous oscillation (SSO) of power system more complicated. In this paper, based on the sixth-order state space model of the grid-tied voltage source converter (VSC) in the time domain, we discuss the stability domain of the system when the parameters of different controllers change under different power grid intensities. These stable regions can provide guidance for the adjustment of controller parameters. Then we further research the dynamic process of the eigenvalues when the system leaves the stable region, and verify that the situation where a single eigenvalue crosses the virtual axis only occurs when the controller parameter is negative. Finally, in the area where the system is unstable, we find that the main factor causing SSO is phase-locked loop (PLL) by comparing the bandwidth of the controller. The results are also consistent with the time domain simulation in Matlab / Simulink.