直流换相失败故障下DFIG暂态特性分析与过电压抑制

DFIG Transient Overvoltage Characteristics Analysis and Overvoltage Suppression Under DC Commutation Failure

在大规模风电基地通过电网换相高压直流输电(LCCHVDC)远距离送出的背景下,直流系统换相失败故障会在送端产生暂态电压扰动。已有研究缺乏对风电机组呈现出的电压“先低后高”连续变化且磁链不断累积特性的探讨,亟须从磁链累积的角度分析风电机组在换相失败期间的电压特性,提出一种具有暂态电压抑制作用的风机故障穿越(fault ride through,FRT)策略。首先,采用曲线拟合的方法,推导了双馈风电机组(doubly fed induction generator,DFIG)在直流系统换相失败期间的电压与磁链方程,分析了直流系统定电流环节(constant current amplifier,CCA)控制对暂态过电压的影响;其次,提出一种基于灭磁控制的故障穿越策略,通过全定子磁链观测并引入灭磁系数,在转子侧变流器(rotor side converter,RSC)有功、无功电流参考值中分别计及灭磁电流,拓宽了RSC无功输出的能力。最后,MATLAB/Simulink平台验证了所提策略在实现DFIG故障穿越的基础上还能够进一步抑制暂态过电压,提高了系统稳定性与安全性。

Transmitting large-scale wind power through a line-commutated converter-based high-voltage direct current(LCC-HVDC)system has become a common scheme in China.Under this condition,commutation failure faults will generate transient voltage disturbances at the sending end.Recent studies lack discussion on the continuous change of voltage and continuous accumulation of flux links presented by wind turbines,and it is urgent to analyze the voltage characteristics of wind turbines during commutation failure from the perspective of flux accumulation and propose a fault ride through(FRT)control strategy for active voltage suppression of wind turbine.Firstly,the curve fitting method is used to derive the voltage and flux linkage equations of doubly fed induction generator(DFIG)during commutation failure,and the influence of constant current amplifier(CCA)control of LCC-HVDC system on transient overvoltage is analyzed.Secondly,an FRT strategy based on demagnetization control is proposed,which compensates the demagnetization current in the active and reactive current reference value of the rotor side converter(RSC)respectively by observing the full stator flux linkage,and introduces demagnetization coefficient,broadens the ability of RSC reactive power output.Finally,the MATLAB/Simulink simulation platform verifies that the proposed strategy can not only achieve fault ride-through of DFIG but also suppress the transient overvoltage,which improves the system's stability and safety.