Single-phase ac/ac converter based on half-bridge NPC topology

A novel single-phase ac/ac converter is proposed to draw a sinusoidal line current with nearly unity power factor and to provide a stable ac voltage to the critical loads. The proposed ac/ac converter is based on the half-bridge neutral-point diode-clamped topology. The rectifier part is controlled to generate a unipolar PWM waveform on the ac terminal using the power switches with voltage stress of half the DC link. The current control scheme with fixed switching frequency is employed in the inner control loop to track the line current command. To regulate the dc bus voltage, a proportional-integral (PI) control is adopted in the outer control loop. The inverter part with half-bridge neutral point clamped scheme is employed to generate a stable and clean sinusoidal output voltage to the critical load. The experimental results based on a laboratory prototype were implemented to verify the effectiveness of the proposed control scheme.