The design and research of the Hybrid Active Power Filters

In this paper, a double closed loop current controller is proposed for Parallel Hybrid Active Power Filter (PHAPF) characterized by series connection of a three-phase single-tuned series resonance LC filter for the seventh harmonic frequency and a low voltage rating three-phase voltage source PWM inverter. The proposed controller is composed by a grid current feedback control and a 5th harmonic of grid current feedback control aiming at enhancing filtering characteristics at 5th harmonic frequency. The dc-voltage control loop is also designed based on system model with PI regulator. Simulation and experimental results obtained from a 20kVA/380V laboratory system verify that the proposed control strategy could not only improve the effect of passive filters but also acquire good filtering performance at both steady and transient state.