实现转子转速保护的双馈异步发电机有功输出速降新方案

A novel fast active power output reduction scheme of a DFIG for rotor speed security

当电网发生输电阻塞、直流闭锁、短路故障等异常状况时,迅速降低风电机组有功输出可有效减小系统发生安全稳定事故的风险。风电机组的变流器能够快速准确地控制有功输出,然而,由于桨距角动作缓慢,风力机捕获的机械功率难以及时调整以匹配速降后的有功输出,所累积的盈余能量易造成转子过转速,损害风力机机械系统。为此,提出一种通过协调控制直流卸荷电路与风力机桨距角实现转子转速保护的双馈异步发电机(Doubly-Fed Induction Generator,DFIG)有功输出速降方案。在通过转子侧变流器将有功输出迅速降至指令值后,即投入卸荷电阻消耗不平衡能量来及时抑制过转速,同时尽快调整桨距角从根本上消除盈余能量,切出卸荷电阻,在更长时间尺度下维持初始转速。分别在执行上级有功速降指令与低电压穿越两种场景下,通过与现有仅依赖桨距角或能量装置的两种典型DFIG功率控制方案和常用撬棒保护方案的仿真对比,验证了该方案的多方面优越性。

Fast active Power output Reduction(FPR)of Wind Turbine Generators(WTGs)is an effective way to minimize risks of stability and security accidents of a connected power grid under abnormal conditions such as transmission congestion,DC blocking and short-circuit faults.An accurate FPR can be readily achieved by WTG power electronic drives.However,because of slowly-responsive pitch control,WTG mechanical input cannot be adjusted in a timely manner to match the reduced electrical output.The accumulated surplus energy may lead to rotor over-speed,posing the threat of damage to the WTG mechanical system.Therefore,this paper proposes an FPR scheme of a doubly-fed induction generator-based WTG in effort to avoid rotor over-speed by DC chopper and pitch control coordination.After the FPR command is executed by the rotor-side converter control,the rotor over-speed is first restrained earlier by triggering the DC chopper to dissipate the excessive energy.The pitch angle is controlled at maximal rate to eliminate excessive power,switch off the DC chopper and maintain the rotor speed at the original level over a longer period.The various advantages of the proposed FPR scheme over two typical ones are verified through comparative simulation studies,under scenarios of higher-level power command execution and low voltage ride-through.