When voltage sags and frequency fluctuation occurred in the condition of grid side three-phase imbalance, to maintain converter normal work and realize wind turbine low voltage ride through, this paper uses second-order generalized integral based method to detect the positive sequence voltage and phase of the above two power grid unbalanced faults quickly and accurately. It has three basic function compositions: 1) quadrature-signals generator (QSG); 2) positive-sequence calculator module; 3) phase locked loop (PLL). This paper's innovation lies in using double second-order generalized integral baesd method to set up QSG module, therefore, the power grid synchronous detection system is called SOGI-PLL. The PLL based on this method is verified through establishing simulation model in PSIM, and the results show that for the positive sequence voltage component and phase of two power imbalance fault conditions, the system can quickly detect positive sequence component and phase information and make fault response time control in the millisecond time level; and can achieve a frequency adaptive detection with tracking error of less than 2?. rnThis work is supported by National Natural Science Foundation of China (No. 50907067 and No. 51067009) and Natural Science Foundation of Xinjiang (No. 2011211A017).%在电网侧三相不平衡条件下发生电压跌落和频率波动时,为保持控制系统中变流器正常工作和实现风机的低电压穿越,现使用基于二阶广义积分的方法对上述两种电网不平衡故障条件下的正序电压和相位进行快速精确的检测.此电网同步检测系统主要由三个基本功能块组成:1)正交信号发生器(QSG);2)正序分量计算模块;3)锁相环( PLL).利用基于双二阶广义积分的方法搭建了QSG模块,为此,这个电网同步检测系统命名为SOGI-PLL.通过在PSIM软件中搭建仿真模型对基于该方法的PLL进行了验证,结果表明:对于两种电网不平衡故障条件下的正序电压分量及相位,系统能较快地检测出正序分量和相位信息,故障响应时间控制在毫秒级别；且实现了频率自适应检测,跟踪误差小于2％.
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