提高DFIG低电压穿越能力的改进控制策略

双馈感应发电机(doubly fed induction generator, DFIG)并网处发生短路故障时，基于传统crowbar技术的DFIG低电压穿越能力较低，须从电网吸收大量的无功功率，机端电压难以恢复。针对这一技术弊端，提出一种改进的综合控制策略:首先在原有crowbar技术的基础上引入直流卸荷电路(DC-chopper)，在故障时能够抑制直流母线过电压和转子侧过电流；其次在转子侧变换器引入一个定子励磁电流的微分补偿项控制，以提升机组系统轴系机械应力。当电网发生严重故障时，改进的网侧变换器控制策略可将正常运行模式切换到无功支撑模式，从而补偿系统所需无功并为电网提供部分的无功功率。在PSCAD/EMTDC平台搭建DFIG并网的仿真模型，其仿真结果表明，在不同电压跌落程度下，提出的控制策略均能提高DFIG的低电压穿越能力。

Improved Control Strategy of Enhancing Low Voltage Ride Through Capability for DFIG

When a short circuit fault occurs in the grid side connected the DFIG, the LVRT ability of DFIG based on the traditional crowbar technology is poor, and the DFIG need to absorb a mass of reactive power from the grid. Therefore, the terminal voltage is difficult to be recovered. In reaction to this technical disadvantage, an improved integrated control strategy is proposed. Firstly, through using DC-chopper in the basis of the crowbar technology, the DC bus overvoltage and the overcurrent of the rotor side can be limited during the fault stage. Secondly, a differential compensation term control of stator exciting current is introduced to the rotor side to enhance the mechanical stress of the system unit shaft. When a serious fault occurs in the grid, the improved GSC control strategy can be switched from normal operation mode to supporting mode of the reactive power, which compensates to the needed reactive power of the system and provides a part of reactive power to grid. A simulation model of grid-connected DFIG is built in the PSCAD/EMTDC platform. The experimental results show that, in different voltage dip, the proposed control strategy can improve the capability of low voltage ride through of DFIG.