Frequency Response Characteristic Analysis of SSCI for DFIG-based Wind Farms Considering Rotor Speed Control Based on Complex Torque Coefficients method

摘要

The sub-synchronous control interaction (SSCI) in the doubly-fed induction generator (DFIG) based wind farm is mainly caused by the interaction among the multiple dynamic controllers of the wind turbine and fixed series capacitor in the transmission line. In this paper, starting from the rotor voltage equation of DFIG, the transfer function of the electromagnetic torque to the rotor speed is derived based on the rotor speed control and the rotor side converter (RSC). Then, the electrical damping coefficient expression for evaluating the SSCI stability of DFIG based wind farm grid-connected to system with the series compensated transmission line is further proposed based on the complex torque coefficient method. Based on the electrical damping coefficient expression of the electromagnetic torque, the effects of the wind speed, the compensation level, the parameters of the rotor speed control and RSC control on SSCI stability are analysed. The analysis results shows that the instability of SSCI may appear caused by reducing wind speed, increasing serial compensation level, increasing the proportion and the integral parameters of the RSC controller. Finally, the correctness and effectiveness of analysing the SSCI stability characteristic based on the proposed electrical damping characteristic is validated by the time-domain simulations in PSCAD/EMTDC.