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 DC 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 DC 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 a three-level PWM scheme instead of a two-level PWM scheme are that the blocking voltage of each power switch is clamped to half of DC bus voltage, and voltage harmonics on the AC side of a rectifier are reduced. The effectiveness of the proposed control algorithm is verified by software simulations and experimental results from a laboratory prototype.
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