Harmonic Stability Analysis of Load-Current-Detected Shunt APF Considering the Place of Reactive Power Compensating Capacitor

Due to the special application scenarios of APF, APF operates interacting with nonlinear loads and the grid impedance, which may cause the harmonic oscillation issues. When the passive filter is installed near APF and operates together with APF to improve the power quality, the reactive power compensating capacitor increases the possibility of oscillation. This paper analyzes the harmonic stability mechanism of APF system when the capacitor is at the load side. By building the small signal model of the systeme, the loop gain formula is developed. Bode plots show that load-side capacitor is likely to cause the harmonic oscillation with the capacitance changing. To improve the stability, the existing strategy of harmonic virtual admittance is introduced and a strategy based on feeding grid current forward is proposed. The proposed stabilization method can not only restrain the harmonic oscillation problem but also reject the background harmonic perturbation effectively. Finally, the mechanism analysis and the proposed stabilization method are verified by simulation results.