In the normal process of operating, SAPF (shunt active power filter) injects the compensation current into grid to improve the power quality, which may induce the harmonic instability in the whole system. It has been revealed that the instability is induced by the resonance characteristics of grid impedance and loads, which is dominated by the phase characteristics. However, traditional active damper stabilizes the system by increasing the real component of the load’s admittance, which is inefficient when the resonance is severe. Therefore, this paper proposes a novel APF-type active damper to stabilize the system by phase reshaping. The proposed active damper is designed to operate as an APF, which detects the harmonic current as the current reference. And the compensation ratio determines the effect of phase reshaping. Additionally, a PI controller is incorporated to dynamically modify the compensation ratio, which manages to effectively stabilize the system. Compared with traditional active dampers, the APF-type active damper presents an alternative approach of system stabilization with less power loss.  Simulations are conducted to verify the correctness of the analysis and effectiveness of the proposed APF-type active damper.

active damper, harmonic stability, SAPF system, phase reshaping