Robust Current Control Method for LCL-Type Shunt Active Power Filters with Inverter-Side Current Feedback Active Damping

This paper has presented a current control method for LCL-type shunt active power filters (APF), which has good robustness against grid impedance variation. In the current control method, the grid current is measured to implement grid harmonic closed-loop regulation, and the inverter-side current feedback active damping (AD) is adopted to attenuate the LCL-filter resonance. For the inverter-side current feedback AD, a repetitive control link is introduced to replace the common proportional feedback link, which can extend the valid damping region for LCL resonance frequency up to one-fourth of the sampling frequency (f_s/4) and improve the system robustness to grid impedance. Then, the optimal damping coefficient of the repetitive link is obtained by the root locus of AD inner loop. Meanwhile, considering that the control plant exists the obvious phase delay at the higher harmonic orders, the resonant controller with phase angle compensation is introduced to constitute the current controller and avoid the harmonic amplification. Finally, experimental results on a 30kVA APF prototype have validated the robustness of the proposed current control method.