一种转子串联可变电阻与卸荷电路配合的低电压穿越方法

针对双馈感应发电机(DFIG)转子串联固定电阻在低电压穿越(LVRT)时,应对故障时的灵活性较低,且低穿效果过于依赖制动电阻的问题,文章提出了转子串联可变电阻与直流侧卸荷电路配合的改进方案。该方案根据转子故障电流的时域表达式对串联阻值进行整定并形成策略表。基于PSCAD/EMTDC仿真不同电压跌落情况下,改进方案的低电压穿越特性。结果表明,文章所提出的方案改善了风电机组的暂态稳定性,有效降低无功损耗,总体上低电压穿越效果较好。

An improved low voltage ride-through scheme of combination of rotor series variable resistance and DC-chopper circuit

In the case of power grid fault,the low voltage ride-through(LVRT)scheme of the double-fed induction generator rotor series fixed resistor lacks of flexibility during disturbances,and the LVRT effect relies too much on the value of the braking resistor.Aim at this shortage,an improved low voltage ride-through scheme of combination of rotor series variable resistance and DC-chopper circuit is proposed.Firstly,the principle of the scheme and the control strategy of the protection circuit are introduced.Then the series resistance is set according to the time domain expression of the rotor fault current and forms a strategy table.Finally,the low voltage ride-through characteristics of the improved scheme under different voltage drops are simulated based on PSCAD/EMTDC.The results show that new scheme is suitable for different degrees of faults,improves the transient stability of DFIG and reduces the reactive power loss.Overall,the improved scheme has Better LVRT characteristics.