Parallel Resonance Detection and Selective Compensation Control for SAPF With Square-Wave Current Active Injection

Due to capacitor elements and inductive line impedance in power system, parallel resonance could be triggered in the presence of harmonic currents from nonlinear load, whose frequency may shift resulting from intermittent switching of the capacitor devices. So it is difficult for shunt active power filter (SAPF) to damp parallel resonance. This paper investigates parallel resonance detection with square-wave current active injection and selective compensation control with closed-loop regulation of point of common coupling (PCC) voltage for SAPF. The principles of parallel resonance and its frequency detection are analyzed by means of equivalent circuit. Through injecting given square-wave current lasting for 0.5 s, SAPF could fast detect parallel resonance with the help of spectrum analysis of resonance power index. In order to improve power quality of both PCC voltage and grid current, SAPF is controlled to suppress specified harmonic currents from nonlinear load and selectively damp parallel resonance at the same time. In addition, ordinary proportional-integral plus advanced repetitive controller in parallel is used to improve current tracking performance. Experiment test results are provided to verify the validity of proposed detection and control methods.