State-Space Modeling Based Low-Frequency Small-Signal Stability Analysis of VSC Connected to Weak Grids

To reveal the influence of multiple control loops on the stability of low-frequency small disturbances in voltage source converters (VSCs) connected to weak grids, this paper proposes a state space modeling and analysis method. Taking into account the influences of factors such as external loop control and phase-locked loop, a state space model of the DC voltage control unit connected to the weak network is established. The influence laws of multiple control links such as DC voltage control, AC voltage control, and phase-locked loop control on the stability of low-frequency small disturbances in the system are studied through the variation of eigenvalues. The participation factor analysis reveals the dominant stabilityinfluencing parameters in the system. Meanwhile, the influence degree of system parameters on stability is quantitatively evaluated by using dynamic characteristic indicators such as damping coefficient and damping oscillation frequency. Finally, based on the simulation model of the DC system connected to the weak power grid built in PSCAD/EMTDC for analysis, the effectiveness of the method was verified.