中文说明：
论述了风力发电并网的PLL技术，基于传统PI-PLL技术基础上，以双同步旋转坐标系建立电网电压不平衡的数学模型。
English Description：
The PLL technology of wind power grid connection is discussed. Based on the traditional pi-pll technology, the mathematical model of power grid voltage imbalance is established in the double synchronous rotating coordinate system