双馈风电机组在不对称电网故障下的稳定性控制研究

为避免电网电压不对称跌落导致双馈风电机组(DFIG)脱网运行,分析了电网不对称故障时双馈风力发电机组直流母线电压波动机理,直流侧过电压这一现象主要由定子侧直流分量和电网电压负序分量引起.通过参考系坐标变换导出在正负序坐标系中双馈感应发电机的电压和电流方程,建立了正、负序坐标系下DFIG数学模型,利用机、网变流器协调控制方法,在不对称电网故障期间,机侧变流器转子电流的负序分量控制为零,网侧变流器采用双闭环正、负序电流控制抑制网侧负序分量,结合功率计算模块,有效抑制了机组电磁转矩与电流的2倍频波动,以及直流母线电压与电流负序分量的波动,改善了DFIG在不对称电网故障下的动态性能.仿真结果表明了该控制策略的可行性.

Research on Stability Control of Doubly-fed Induction Generater under Asymmetric Power Grid Faults

In order to avoid the asymmetric drop of grid voltage leading to the disconnection of doubly-fed Induction Generater (DFIG), the mechanism of DC bus voltage fluctuation of DFIG under asymmetric grid fault is analyzed. The phenomenon of DC side overvoltage is mainly caused by DC component of stator side and negative sequence component of grid voltage. The voltage and current equations of doubly fed induction generator in positive and negative sequence coordinate system are derived by coordinate transformation of reference frame. The mathematical model of DFIG in positive and negative sequence coordinate system is established. Using coordinated control method of machine and network converter, the negative sequence component of rotor current of machine side converter is controlled to zero during asymmetric grid fault, The converter adopts double closed-loop positive and negative sequence current control to suppress the negative sequence component on the grid side, and combines with power tracking control module to effectively suppress the double frequency fluctuation of electromagnetic torque and current, as well as the fluctuation of DC bus voltage and the negative sequence component of current, thus improving the dynamic performance of DFIG under asymmetric grid fault. The simulation results show the reliability of the control strategy.