中文摘要：

针对相位、幅值和频率是光伏并网逆变系统的关键信息，鉴于传统的锁相环方法难以适应低电压穿越的性能要求，本文提出一种新的i相锁相环方法，其主要由三部分组成：①线电压幅值和相位的测量；②正交信号发生器的选择（OSG）；③线电压和相电压之间的转换。研究结果表明，当电网电压发生偏移和跌落时，该三相锁相环的方法可以准确地检测出故障信号。因此，该方法可为光伏并网逆变系统实现低电压穿越提供技术支持。

英文摘要：

Phase, amplitude and frequency of the utility voltage are critical information for the operation of the photovoltaic grid-connected inverter systems. Considering that the traditional phase-locked loop （PLL） methods are difficult to adapt the performance requirements of low voltage ride through （LVRT） in three- phase three-wire photovoltaic grid systems, a new three-phase PLL approach was presented in this paper. Three fundamental functional parts make up the proposed method： 1 measurement of line voltage amplitude and line voltage phase; 2 choice of orthogonal signal generator （OSG） ; 3 transformation between line voltage and phase voltage. Research results show that when grid voltage offsets and dips, this three-phase PLL method can detect the fault signal accurately. It provides a technical support for low voltage ride through of the photovoltaic grid-connected inverter systems.