Power systems are at risk of sub-synchronous oscillation (SSO) when connecting doubly-fed induction generator (DFIG)-based wind turbines to transmission lines with series compensation. This paper focuses on the mechanism and mitigation strategy of SSO. Firstly, the mechanism of SSO is studied from two aspects: induction generator effect (IGE) and sub-synchronous control interaction (SSCI). An equivalent circuit is developed to illustrate the negative resistance effect. Based on the result of the analysis, the SSO mitigation strategy using notch filter and virtual resistance control is proposed. In order to verify the result of analysis and the effectiveness of mitigation strategy, time-domain simulations are carried out based on PowerFactory DIgSILENT.
Photovoltaic (PV) station generally adopts single-stage grid-connection inverter considering the cost and efficiency, and the controller parameters have great influence on the grid-connected performance of PV system. The PV array, maximum power point tracking (MPPT), the inverter and its control system models are built in PSASP/UD. The PI parameters of invert controller are tuned by adaptive genetic algorithm (AGA) and genetic algorithm (GA) respectively in single-machine infinite bus system (SMIBS) based on Simulink. Finally, single-machine infinite bus system (FMTAS) with PV based on PSASP/UD is used to verify the feasibility and effectiveness of models and validity of controller parameters.
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