Stability Analysis of SAPF by Viewing DFT as Cluster of BPF for Selective Harmonic Suppression and Resonance Damping

This paper addresses the stability analysis of a shunt active power filter (SAPF) with capacitive load for selective harmonic suppression and resonance damping. If the capacitive load current is measured as part of harmonic suppression current reference, the SAPF with conventional selective harmonic suppression would amplify the corresponding harmonic beyond the resonance frequency. Previous studies could not clearly explain this harmonic amplification phenomenon without the selective harmonic extraction model in stability analysis. By viewing the discrete Fourier transform (DFT) as a cluster of band-pass filter (BPF), the modeling process is taken into consideration and is well simplified. The stability condition for suppressing and damping each selected harmonic can be easily estimated with the help of Nyquist stability criterion or root locus method in different SAPF control scenarios. To avoid the instability and compensate the harmonic current, a novel combined control strategy of the SAPF is carried out to simultaneously suppress the harmonics whose frequencies are lower than the resonance frequency and mitigate the rest of the harmonics by a resonance damping method. Experiments have been performed to verify the effectiveness of the proposed strategy.