中文摘要：

经VSC-HVDC并网风电系统在风电场侧故障时,风电机组出口母线电压过低,极易引起风力机脱网。而双馈风力发电机（DFIG）传统的Crowbar技术在故障时将转子侧变流器（RSC）短接,使发电机定子侧失去了为电网提供无功的能力,风力机的低电压穿越能力较低。提出一种改进的DFIG模型,加入了主动式DC-Chopper,与传统的Crowbar相配合,降低Crowbar动作的概率,使得DFIG转子侧变流器可以控制定子侧在故障时期继续提供无功功率。并利用此改进的DFIG与VSC-HVDC协调控制,改善风电场侧母线电压水平。通过算例仿真表明,在严重故障时采用改进式DFIG的Crowbar仍未动作。从而大大降低Crowbar动作的概率,双馈风电机组RSC故障期间可以继续投入运行并为电网提供无功支持。完成故障期间DFIG两侧变流器与VSC-HVDC风电场侧变流器（WFVSC）之间的无功协调,使风电场具有更好的低电压穿越能力（Low Voltage Ride Though,LVRT）。

英文摘要：

When failures occurred in the wind farm side of the VSC-HVDC system, the grid voltage of wind farm was too low, leading to the typical tripping events of wind turbines. However, traditional DFIG uses Crowbar technology, the rotor side converter（RSC） is short circuited and the stator side of wide turbine loses its ability of providing reactive power for grid during the failures, the low voltage ride through ability of DFIG is low. This paper presents a new improved model of DFIG using active DC-Chopper to match the Crowbar. The RSC is controlled to make the stator side of wide turbine provide part of reactive power in a failure. Reactive power coordinated control strategy of the improved DFIG and VSC-HVDC is adopted, which improves voltage stability of system. The simulation results demonstrate that when the failure is serious, the improved type of DFIG Crowbar does still not act, so as to reduce the probability of the Crowbar action, and RSC can still provide reactive power support to grid. Reactive power coordinated control strategy of the two sides＇ converters and wind farm side of VSC-HVDC（WFVSC） makes the wind farm have a better ability of low voltage ride through.