A Stabilization Strategy Based on Grid Current Feedforward for the Harmonic Oscillation of APF System

In some complex source-load conditions, the active power filter (APF) may lead to harmonic oscillation and deteriorate the power quality. This article built the small signal model to illustrate the interactions among APF, nonlinear load and the grid, with which the reason and characteristic of the harmonic oscillation are investigated. It is found that the harmonic oscillation is prone to occur when the resonant frequency introduced by nonlinear load and grid impedance gets close to the harmonic frequency compensated by the APF. Since the frequency coupling effect employed by nonlinear load is considered, it reveals the interactions between symmetric harmonics, e.g., -5th/7th and -11th/13th, showing their oscillation and suppression together. Then a stabilization strategy based on grid-side current feedforward (GCF) is proposed and compared with the existing stabilizing methods. The proposed method can effectively suppress the harmonic oscillation without affecting the harmonic compensation performance and background perturbation rejection performance. Finally, simulation and experiment validate the theoretical analysis and effectiveness of the proposed method.