针对传统锁相方法的锁相精度在电网电压含有负序分量、谐波分量、直流分量等情况下有所降低的问题，本文提出一种基于二阶广义积分器(Second Order Generalized Integrator, SOGI)的改进型三相锁相环设计方案。首先，简要介绍了SOGI可进行信号正交处理的原理；其次，通过频域分析法，直观地指出传统SOGI抗直流偏移干扰能力弱的原因并量化分析了直流分量对基于传统SOGI的不平衡锁相环的影响；然后，为增强SOGI对电压检测信号中直流分量的抗干扰能力，对其进行结构上的改进，提出一种基于改进型SOGI的不平衡锁相环设计方案；最后，通过仿真与实验，验证本文理论研究的正确性。

This paper proposes a PLL based on double second-order generalized integral (DSOGI-PLL) of abstracting grid voltage phase quickly and accurately for low accuracy of traditional PLL in the case of the unbalanced grid voltage in grid-connected PV systems. Firstly, the principle of the SOGI, which can effectively extract the grid voltage positive sequence component, to be used as a quadrature signal generator is analyzed. Secondly, to eliminate the influence of DC offset, an improved structure of SOGI is proposed. So a novel PLL applicable to the case of unbalanced grid which can eliminate the influence of DC offset is shown. Finally, the effectiveness of the proposed PLL is varied by simulation and experiment.