In view of weak harmonic compensation result of active power filter due to traditional control proposal under grid distortion

a kind of improved proposal is proposed

which consists of improved synchronous phase-locked loop（SRF-PLL）

improved harmonic detection method and adaptive resonant currentcontroller. The improved synchronous phase-locked loop（SRF-PLL）uses the moving average filter to ex-tract accurately the positive sequence component of the fundamental wave of distortion grid voltage toachieve tracking grid phase of SRF-PLL with no static difference and high accuracy. The improved harmon-ic detection method adopts moving average filter instead of low pass filter for DC extraction

which overcomes such defects of traditional detection method as weak real time dynamic due to low pass filter. The PI+VPI（vector proportional integral）current control scheme is used to achieve excellent current control per-formance of the active power filter under the condition of grid distortion. One 5kVA three-phase active power filter experimental platform is set up to verify the superiority of the proposed control strategy.