Neutral Point Voltage Fluctuation Suppression for Electrolytic Capacitorless Vienna Rectifiers Based on Optimal Duty Cycle Model Predictive Control

To enhance the lifespan of Vienna rectifiers, the electrolytic capacitors in the dc link can be substituted with slim-film capacitors. However, the decrease in capacitance leads to an increase in neutral point (NP) voltage fluctuation and input current harmonics. To solve this issue, a model predictive control strategy based on three-vector duty cycle optimization is proposed. The negative influence of reduced capacitance and high modulation index on the NP fluctuation and the input current harmonics is analyzed. In order to suppress the NP fluctuation and eliminate weighting factors, the subsectors division and the NP voltage hysteresis are introduced to select effective voltage vectors, reducing 27 candidate voltage vectors to three sets of switch sequences. Then the Karush–Kuhn–Tucker condition is used to derive the duty cycle of the convex quadratic optimization issue within the boundary and constraint interval. With the proposed strategy, both the NP voltage fluctuation and the input current harmonics can be reduced simultaneously. The effectiveness is verified on an electrolytic capacitorless Vienna rectifier platform.