Robust control method for LCL‐type shunt active power filter under weak grid condition

Abstract

This study presents an improved double closed-loop current (fundamental and harmonics current) control method for inductive-capacitive-inductive (LCL) type shunt active power filter (SAPF), which is designed to enhance the robustness of the SAPF system to adapt weak grid application condition. Due to the variation of weak grid impedance, fundamental current control loop based on grid current feedback control method may become unstable, a robust parameters design method in discrete z-domain according to amplitude-frequency and phase-frequency characteristics is proposed to fit the grid impedance variation. The harmonics current of non-linear load exists in a wide frequency range, normal resonant controller will cause the system unstable due to the negative −180° cross of phase at high-frequency range, a digital phase-lead resonant controller (PL-RC) is proposed to extend the bandwidth of the harmonics current control, then the quantities of the PL-RCs used to suppress harmonics can be increased considerably compared with normal resonant controller. Experimental results are presented to verify the effectiveness of the robust parameters design method and the proposed PL-RC.