Single-phase neutral point diode clamped rectifier with high input power factor

A new control scheme for the single-phase neutral point diode clamped rectifier is proposed to achieve a unity power factor, balanced neutral point voltage and constant do bus voltage. Four power switches are used in the proposed rectifier to generate a three-level PWM waveform on the rectifier terminal voltage. The line current command is derived from a do link voltage regulator and an output power estimator. The hysteresis current controller is used to track the line current command. To balance the neutral point voltage, a capacitor voltage compensator is employed. The main advantages of using three-level PWM scheme instead of two-level PWM scheme are that the blocking voltage of each power switch is clamping to half of do bus voltage, and voltage harmonic on the ac side of rectifier is reduced. The effectiveness of the proposed control algorithm is verified by software simulations and experimental results from a laboratory prototype.