双馈风力发电系统的低压穿越运行与控制

根据紧急电网规程要求，风电场须具备外部电压故障下不间断运行能力，即电网故障时风电机组应能保持与电网连接并向系统不间断供电。由于双馈感应发电机（DFIG）励磁变换器容量有限，电网故障时会产生转子过电流和变换器直流环节过电压，须实行保护和控制。讨论了外部电压骤降下DFIG风电系统的低压穿越控制策略和保护方案，并对一台1．5Mw商用DFIG风电系统进行了仿真研究。结果表明快速短接保护装置（Crowbar）的切除时刻和所用串联电阻大小对故障电网恢复和变换器保护有较大影响。配合Crowbar而采用串联电阻及改进网侧变换器控制策略的方式，可以实现DFIG成功穿越定子剩余电压为15％的电网骤降故障，且无需吸收大量无功功率，有利于电网的恢复。

Low Voltage Ride Through Operation and Control of Doubly Fed Induction Generator Wind Turbines

Grid codes require wind farms to stay connected and continue generation in the main system low voltage emergency conditions.Due to the limited capacity of converters,DFIG wind turbines may suffer from over rotor currents or over voltages in the DC-links.As a result,appropriate control and protection schemes must be applied.This paper discusses a control and protection scheme for the low voltage ride through(LVRT)operation of DFIG wind turbines.Simulations on a 1.5 MW commercial DFIG wind turbine demonstrate that the timing of deactivating crowbar and the value of the series resistor have critical effects on the converter safety and the system recovery.By use of a rotor crowbar connected with a series resistor and a modified control strategy on the grid-side converter,the DFIG wind turbine is capable of riding through voltage dips up to 15% without absorbing a lot of reactive power,which greatly contributes to the main system voltage recovery.