改进的DFIG与VSC-HVDC协调控制改善风电场低电压穿越能力

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)。

Improvement of low voltage ride through capability of wind farm using coordinated control of the improved DFIG and VSC-HVDC

The real-time transient stability detection and emergency control technology based on wide area response has become a hot research area in power system stability studies. Several different technologies have been proposed, but lots of problems remain to be solved before they can be applied in practice. A wide area measurement system (WAMS) based test platform is developed for transient stability detection and control. The design as well as main function modules of the platform are introduced. In addition, three generator power angle prediction methods and six response based transient instability detection technologies are given. Results of engineering application demonstrate that the developed test platform can provide a real-time operation environment, which can effectively compare and analyze the validity and practicability of these transient stability detection technologies. Based on the measured perturbed trajectories from actual power systems or the Real-Time Digital Simulators (RTDS), the platform can realize the assessment and visual result presentation of various responses from different transient instability detection technologies. The test platform can be applied to different power systems and it is convenient to embed new transient instability detection modules. Meanwhile some deficiencies and shortcomings in engineering application are pointed out and corresponding suggestions are given. In conclusion, the hardware and software structure, function modulus and engineering applications are presented. The application in actual power systems shows that it has a good application perspective.