中文摘要：

提出了直接驱动型永磁同步风力发电系统在电网故障前后的控制策略。采用基于二阶广义积分闭环电网电压跌落检测方法．可精确得出电网电压故障信号、正序分量幅值、相位角。电网电压故障信号送给变桨距执行机构。最大限度地调节桨距角，屏蔽部分输入功率，提高系统低电压穿越能力：探索直驱风电系统在电网电压跌落发生后的控制策略．并实现与正常运行模式的快速平滑切换。故障前，网侧变流器运行在单位功率因数状态。保持直流侧电压恒定：故障后运行在STATCOM模式．依据检测环节所提供的电网电压正序分量幅值和相位角来决定变流器所发无功电流的量值．为电网提供动态无功支持。基于超级电容器的双向DC／DC变换器作为直流侧保护电路．来快速维持直流侧电压稳定．

英文摘要：

The control strategy of direct-drive permanent-magnet synchronous wind power system during grid fault is proposed. The detection method based on the second-order generalized integrator closed-loop is adopted for grid voltage drop to precisely obtain the grid voltage fault signal,positive-sequence component amplitude and phase angle. The grid voltage fault signal is sent to the variable pitch actuator to rapidly adjust the pitch angle and shield part of the input power for improving system LVRT （Low-Voltage Ride-Through） ability. The LVRT control strategies of direct-drive wind power system during grid voltage drop are explored for realizing the quick and smooth transformation of normal operating modes. Before failure,the grid-side converter operates with unity power factor to keep DC-side voltage constant ; after failure, it operates in STATCOM mode, providing the dynamic reactive power support according to the detected magnitude and phase angle of grid-voltage positive-sequence component. The super-capacitor-based hi-directional DC-DC converter is applied in the DC-link protection circuit to quickly maintain the DC-link voltage stable.