Analysis on the Non-minimum Phase Behavior of the Weak Grids Connected VSC

The non-minimum-phase behavior of the weak grids connected VSCs is studied with transfer function-based methods. The model of the the weak grids connected VSC is firstly built with reduced-order multi-input multi-output (MIMO) representation. Then, the single-input single-output (SISO) model is further derived, without changing the structure and parameters of the studied system. The routh criterion is applied on the SISO model to predict the occurrence of the right half plane (RHP) zeros. We find that large equivalent impedance of the power system and large injected active power can result in the non-minimum-phase behavior and that the RHP zeros will not be impacted whether the VSC works in the inverter mode or the rectifier mode. We do simulations under various operating conditions, and simulation results show that the proposed method and the conclusions obtained are correct. Our work contributes to revealing the mechanism of the non-minimum-phase behavior of the weak grids connected VSCs as well as provides useful hints for the control design of compensation.