Analysis and Stabilization of APF Systems Considering Dynamic of Nonlinear Loads

The active power filter (APF) is effective for harmonic suppression. But it may cause harmonic oscillation under certain source-load conditions. This article analyzes the harmonic oscillation and its stabilization. The dynamics of theAPF's current control and the nonlinear load's frequency coupling effect are considered, which are normally ignored in existing research. It is found that the frequency coupling effect makes symmetric harmonics (-5th/7th, -11th/13th, for example) share their harmonic dynamics and oscillate or converge together. And the APF's current controller can provide harmonic damping. Then two regular harmonic stabilizing methods, harmonic suppressing ratio reducing (SRR) and harmonic virtual admittance (HVA) control, are reassessed considering the nonlinear load. Analyzing results show that frequency coupling caused by the nonlinear load has different impacts on the SRR and HVA, which provides theoretical guidance for choosing or designing stabilizing strategies. Models in this article are verified by frequency-sweeping simulation, and analyzing conclusions about the oscillation features and stabilizingmethods are verified by both simulations and experiments.