Research on the Active Power Control Stability of the Renewable Energy Connected to Weak Grids

This paper proposes a novel method to analyze the stability of grids-connected VSC based on its single-input single-output (SISO) open-loop transfer function model. Unlike the traditional eigenvalue analysis, impedance analysis or complex torque analysis, the transfer function based analysis is applied. And the multi-input multi-output (MIMO) model of grids-connected VSC is derived firstly and simplifies to a SISO model, which yields the open-loop transfer function. Then, the Bode plot and Nyquist curve based stability criterion can be applied to analyze the stability of the weak grids-connected VSC. Impact of the interaction between phase-locked loop and outer loop on system stability is studied by analyzing the phase stability margin of the open-loop transfer function. Finally, the time-domain simulations matches well with the results obtained from the analysis based on Nyquist curve and Bode plot.