Implementation of the AC/AC converter based on neutral-point switch-clamped topology

A single-phase AC/AC converter based on neutral-point switch-clamped topology is proposed. The adopted AC/DC converter is controlled to have a stable constant DC bus voltage and draw a sinusoidal line current with unity input power factor. The AC side voltage of the AC/DC converter is controlled to generate a unipolar PWM waveform using the conventional half-bridge PWM rectifier and one AC power switch with voltage stress v_dc/2. A carrier-based current control scheme is used in the inner control loop to track the line current command. A proportional-integral (PI) control is adopted in the outer control loop to maintain the constant DC bus voltage. On the inverter side, a sinusoidal output voltage is generated to provide a stable and clean source voltage to the critical load. A fixed-frequency current controller is adopted to generate the proper PWM waveform. A conventional half-bridge PWM inverter with one AC power switch is used in the DC/AC converter to generate the unipolar PWM voltage waveform on the AC side. The system model and control algorithm are described and analysed. To verify the effectiveness of the proposed operation scheme, experimental results based on a laboratory prototype were performed.