Modeling and Terminal Characteristics of Grid-Connected Inverter With Faulty Control Strategies

In this paper, considering the influence of decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL), the small-signal sequence impedance model is proposed for a typical fault control structure in wind energy applications. Based on the established sequence impedance model, the frequency characteristics of double-sequence control strategy and single-sequence control strategy are compared and analyzed. Using the generalized Nyquist criterion, the influences of grid impedance on the stability of grid-connected systems with different control strategies are analyzed. The developed models and the theoretical analysis are verified by simulation results.