双馈风机定子侧串阻抗的阻值优化

Optimization of the string impedance on the stator side of the DFIG

当电网受到大扰动导致电压骤降时,双馈风机需配合硬件改造措施以实现机组的低电压穿越。针对双馈风机采用定子侧串联阻抗的低电压穿越策略中存在的阻值整定问题,首先推导了双馈风机的转子暂态电流和开路电动势表达式,再以故障期间换流器的运行限制分析其有功无功耦合特性,最后结合上述分析提出了一种基于无功最优定子侧串阻抗的阻值优化方法。通过转子暂态电流约束和转子开路电动势约束确定阻抗选取范围,以暂态期间最大无功出力为目标,优选串联的阻抗值。仿真结果表明,所提方法优选出的阻抗值不仅能够有效抑制双馈风机所受到的暂态冲击,还能保证机组在故障期间提供无功功率,为电网电压提供支撑,提升机组故障运行能力。

When there is a large disturbance in the power grid and the voltage drops,the doubly-fed wind induction generator(DFIG)needs to cooperate with hardware modification measures to achieve low voltage ride-through(LVRT).To solve the problem of resistance value setting in the LVRT strategy of a DFIG using stator side series impedance,this paper first derives the expression of rotor transient current and open-circuit electromotive force of a doubly-fed fan,then analyzes the active and reactive power coupling characteristics of the inverter with the operating limit of the inverter during the fault period.Finally,combined with the analysis above,it proposes a resistance optimization method based on the optimal reactive power stator side string impedance.The impedance selection range is determined by the transient current constraint and the open-circuit electromotive force constraint of the rotor,and the impedance value of series connection is optimized with the maximum reactive power output during the transient period as the goal.The simulation results show that the impedance value optimized by the proposed method can not only effectively suppress the transient shock to the DFIG,but also ensures that the unit can provide reactive power during the fault period,support the grid voltage,and improve fault operation ability.