针对电网三相不平衡时常用锁相环方法存在电压测量偏移降低检测准确度和抗低次谐波干扰能力弱的问题,本文提出一种基于改进型二阶广义积分器(Second Order Generalized Integrator, SOGI)的三相锁相环设计方案。首先,分析了SOGI可提取出电压正序基波分量的原理;然后,通过对SOGI进行频域特性分析,找到传统SOGI抗直流分量和低次谐波干扰能力弱的原因。据此,提出一种能消除直流分量影响的改进型SOGI结构,并以此改进型SOGI为基础通过多个并联来达到消除低次谐波干扰的目的;最后,利用PSCAD软件对基于传统型SOGI的锁相环、基于单个改进型SOGI的锁相环、基于多个改进型SOGI并联的锁相环,这三种锁相环进行多项对比仿真,仿真结果证明了本文所提锁相方案的有效性。
英文摘要:
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. Further more, the low-order harmonic can be filtered through a structure of parallel SOGIs. So a novel PLL applicable to the case of unbalanced grid which can eliminate both the influence of DC offset and low-order harmonic is shown. Finally, the PSCAD model is established and feasibility of the novel PLL is verified.