Abstract：Active power filters（APF）are widely used for dynamic compensation of power system harmonic.

However，under weak grid conditions，the interaction between APF，nonlinear loads and grid impedance can easily lead to the stability issue of harmonic oscillation around the compensation frequency，resulting in the fault of

harmonic compensation and further deterioration of the system's power quality. Through small-signal modelling of

the loop，the harmonic oscillation mechanism in APF system under weak grid conditions was revealed，and an

active damping scheme based on inductor current feedback was proposed to suppress harmonic oscillation

according to the conclusion of stability analysis，which ensures the stable harmonic compensation capability of APF

under weak grid conditions. The effectiveness of the proposed scheme was verified by PLECS time-domain

simulations and hardware platform experiments.

      Key words：active power filter（APF）；weak grid；small-signal modeling；stability analysis；active damping