Shunt active filter based on three-level inverter for three-phase four-wire systems

The three-phase four-wire active power filter (APF) based on a three-level neutral-point-clamped (NPC) inverter is presented. The proposed APF and controller eliminate harmonics in all three phases as well as the neutral current. The existing NPC 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 APF.