电网电压不对称跌落时DFIG的控制策略研究

相比于对称故障，不对称故障时双馈风力发电机(Doubly Fed Induction Generators, DFIG)的电磁暂态过程更为复杂，对DFIG造成的危害也越大。从电网电压不对称跌落时DFIG的电磁暂态过程入手，分析了DFIG各电磁量产生二倍频波动和过电流的直接原因。在此基础上，提出了一种电网电压不对称跌落时转子侧变换器(Rotor Side Converter, RSC)的转子电压补偿控制策略，通过控制RSC交流侧的输出电压，对转子暂态电动势和负序电动势进行补偿。该控制策略可在电网轻度不对称故障时有效消除转子电流二倍频波动；在电网严重不对称故障时最大限度地减小转子电流冲击，增强DFIG的低电压穿越能力。此外，根据转子侧变换器的电压容量，对补偿控制策略的完全补偿范围进行了分析。仿真结果验证了所提出控制策略的有效性。

A control strategy of DFIG under unbalanced voltage dips

Compared with symmetrical voltage fault, the electromagnetic transient process of the doubly fed wind generator (DFIG) under asymmetrical fault is more complex, which causes much harm to the DFIG. The immediate cause of the appearance of pulsation second order component in the rotor current and other variables of the DFIG is analyzed by analyzing the electromagnetic transient process in DFIG during unbalanced grid dips. According to this analysis, a rotor voltage compensation control strategy is proposed to eliminate the rotor current pulsation under slight voltage dip and to reduce the over-current in the rotor circuit under serious voltage dips. Under the proposed control strategy, the AC terminal voltage of the rotor side converter (RSC) is controlled to compensate the DC and negative sequence components of the electromotive force. The complete compensation range is analyzed according to the limited AC terminal voltage of the RSC. Simulation results validate the proposed control strategy.