适用于弱电网的三相并网逆变器锁相环设计

Phase-locked Loop Design of Three-phase Grid-connected Inverter for Weak Grid

弱电网环境下,锁相环会对并网逆变器的稳定性造成威胁,建立考虑锁相环影响的逆变器输出阻抗模型和传统同步参考坐标锁相环的传递函数,基于阻抗分析法分析采用传统锁相环时逆变器的稳定性。随后,研究了一种基于降阶广义积分和二阶广义积分的复合广义积分锁相环,并给出参数设计方法。采用谐波线性化的方法获取复合广义积分锁相环的传递函数,分析弱电网环境下采用新型锁相环时逆变器的稳定性。考虑到系统频率偏移对锁相精度的影响,设计频率自适应结构。理论分析和仿真结果表明,采用复合广义积分锁相环,并网逆变器在高电网阻抗下也能稳定运行,且并网电流质量高。

The stability of a grid-connected inverter will be threatened by phase-locked loop(PLL)under a weak grid environment An output impedance model of inverter considering the influence of PLL and a transfer function of the traditional synchronous reference frame PLL(SRF-PLL)are established,and the stability of the inverter with the traditional PLL is analyzed based on the impedance analysis method.Then,a composite generalized integral PLL(CGI-PLL)based on reduced-order generalized integral and second-order generalized integral is studied,and the corresponding parameter design method is given.The transfer function of CGI-PLL is obtained using the harmonic linearization method,and the stability of the inverter with the novel PLL under the weak grid environment is analyzed.Considering the influence of system frequency ofiset on the phase-locked accuracy,a frequency adaptive structure is designed.The theoretical analysis and simulation results show that the grid-connected inverter with CGI-PLL can operate stably under a large grid impedance,and the quality of grid-connected current is high.