Frequency Coupling of Asymmetrical VSC-dominated Power Systems in Small-signal Dynamic Analysis

The frequency coupling has brought great challenges to the small-signal dynamic analysis of the VSC-dominated power systems. However, few have cognized the essence of the frequency coupling, especially its inner relationship with the asymmetry of the system. Thus, this paper will emphatically study the frequency coupling of the asymmetrical VSC-dominated power systems in the small-signal dynamic analysis. First, this paper will summarize the asymmetrical factors of VSC and the power network. Then, the effects of the system’s asymmetry on the frequency coupling will be analyzed. The results indicate that the asymmetry of VSC and the power network can induce the frequency coupling of the linearized VSC-dominated power systems. Moreover, the utilized coordinate for system modeling and analysis have great effects on the frequency coupling. Therefore, by choosing the appropriate coordinate according to the asymmetries of VSC and the power network, this system can also be modeled and analyzed with the linear time invariant (LTI) methods, rather than the complicated linear time periodic (LTP) methods. Eventually, the time domain simulations will verify the correctness of the analysis.