基于复转矩系数法的双馈风机次同步控制相互作用阻尼特性研究

Study on Sub-synchronous Control Interaction Damping Characteristics of Doubly-fed Induction Generator Based on Complex Torque Coefficient Method

双馈风电场中的次同步控制相互作用(subsynchronous control interaction,SSCI)主要由双馈感应电机的多动态控制与传输线路中的固定串联电容之间的相互作用引起。从双馈风机转子电压方程出发,基于转速控制、转子侧变流器(rotor side control,RSC)的功率外环和电流内环控制,推导了电磁转矩对转速的传递函数,进而基于复转矩系数法提出了用于分析双馈风电机场经串补线路并网系统SSCI稳定性的电气阻尼系数表达式。在此基础上,利用电磁转矩的电气阻尼系数表达式分析了风速、串补度、转速和RSC不同控制参数对SSCI稳定特性的影响。分析结果表明:降低风速、增大串补度、增大转速和RSC控制的比例参数和减小RSC控制的积分参数都会导致系统SSCI不稳定。最后利用PSCAD/EMTDC时域仿真,验证了利用所提电气阻尼特性分析系统SSCI稳定性的正确性和有效性。

Sub-synchronous control interaction(SSCI) in doubly-fed induction generator(DFIG) based wind farm is mainly caused by the interaction among multiple dynamic controllers of DFIG-based wind turbines and the fixed series capacitor in transmission line. In this paper, starting from the rotor voltage equation of DFIG, the transfer function of electromagnetic torque to rotor speed was derived based on rotor speed control, power and current control loops of rotor side converter(RSC). Then, an electrical damping coefficient expression for analyzing SSCI stability characteristics of the DFIG-based wind turbine connected to power grid through series compensated transmission line was proposed based on complex torque coefficient method. Based on the electrical damping coefficient expression of electromagnetic torque, the effects of wind speed, compensation level, the parameters of the rotor speed control and the parameters of RSC control on SSCI stability were analyzed. The analysis results show that instability of SSCI may appear due to reducing wind speed, increasing serial compensation level, increasing the proportion parameters of RSC control and rotor speed control, or decreasing the integral parameters of the RSC control. Finally, correctness and effectiveness of analyzing SSCI stability characteristics based on the proposed electrical damping characteristics were validated with time-domain simulations in PSCAD/EMTDC.