Analysis and implementation of shunt active power filter with three-level PWM scheme

A three-phase four-wire voltage source inverter for power quality compensator under the balanced and unbalanced conditions is proposed to provide balanced three-phase source currents and improve input power factor. The proposed inverter is based on the conventional three-phase voltage source inverter with three additional ac power switches to perform three-level pulsewidth modulation. The voltage stress of three ac power switches is clamped to half dc-link voltage. The balanced reference line currents are estimated using the dc bus voltage and load currents. A voltage controller is used in the outer loop control to compensate the switching losses of the voltage source inverter. To perform the integrated power quality compensation, hysteresis current control scheme is adopted to track the balanced line current commands in phase with mains voltages. Three voltage levels are generated on the ac terminal of the proposed inverter. Simulation results were provided to verify the effectiveness of the proposed control scheme.