Neutral current ripple minimization in a three-level rectifier

This paper proposes a novel neutral-point voltage regulator for a three-level diode clamped rectifier that uses a fast space vector modulator in conjunction with a sharing function controller for neutral-point regulation. Redundant state choices are controlled via a continuous sharing function, and small signal models are developed for closed-loop regulators with this sharing function as the control variable. A significant improvement is seen in the voltage distortion at the neutral point when the regulator is used, and this leads to a definitive reduction in the required dc bus capacitance.