非理想电网条件下并网逆变器多频耦合抑制及稳定性分析

非理想电网中的负序分量和直流偏置会导致并网逆变器产生多频耦合现象，增加并网电流谐波含量，降低系统稳定裕度。采用二阶复数滤波器结构锁相环(SCF-PLL)控制策略，有效削弱电网负序分量和直流偏置产生的倍频谐波在并网系统中的传输，抑制多频耦合；建立非理想电网下具有SCF-PLL控制策略的并网逆变器降阶导纳模型，并通过广义奈奎斯特判据对并网系统进行稳定性分析。通过RT-LAB硬件在环实验验证了理论分析的正确性以及SCF-PLL对非理想电网条件良好的适应性。

Multi-frequency coupling suppression and stability analysis of grid-connected inverter under non-ideal grid condition

The negative sequence component and DC bias in non-ideal grid will lead to the multi-frequency coupling phenomenon of grid-connected inverter, increase the harmonic component of grid-connected current and reduce the system stability margin. The SCF-PLL(Second-order Complex Filter Phase Locked Loop) control strategy is adopted to effectively reduce the transmission of double-frequency harmonics generated by the negative sequence component and DC bias in the power grid and suppress the multi-frequency coupling. A reduced-order admittance model of grid-connected inverter with SCF-PLL control strategy under non-ideal grid is established, and the stability of the grid-connected system is analyzed by the generalized Nyquist criterion. RT-LAB hardware-in-the-loop experiments verify the correctness of theoretical analysis and the good adaptability of SCF-PLL to non-ideal grid condition.