Three-level inverter based active power filter for the three-phase, four-wire system

In this paper, the three-phase four-wire active power filter based on a three-level neutral-point-clamped inverter is presented. The proposed active power filter and controller eliminate harmonics in all three phases as well as the neutral current. The existing neutral-point-clamped inverter for a three-phase three-wire system is used for the three-phase four-wire system since the split DC capacitors provide a neutral connection. To regulate and balance the split DC-capacitor voltages, the new control using the sign cubical hysteresis controller is proposed. The control method discerns the harmonic currents by Fast Fourier Transform choosing switching states from a switching table based on the hysteresis control. The simulation and experimental results verify the feasibility of the three-phase four- wire active power filter.