A Novel DC-link Voltage and Current Control Algorithm for Neutral-Point-Clamped Converters

A novel DC-link voltage and current control algorithm for Three-Level Neutral-Point-Clamped converters (NPCs) is proposed in this paper. It is developed with the aim of sharing the overall DC-link voltage among DC-link capacitors as needed, without impairing NPC load performances. The proposed algorithm consists of an external DC-link voltage control loop, which synthesizes an appropriate reference DC-link current profile on the basis of the reference DC-link voltages. Such a current profile is then tracked by means of an inner DC-link current control system. This last synthesizes the most suitable PWM pattern for DC-link voltage regulation, prioritizing NPC load requirements at the same time. The effectiveness of the proposed DC-link voltage and current control algorithm is verified through extensive simulations, which refer to the case study of a three-phase NPC that feeds a Surface-Mounted Permanent Magnet Synchronous Machine.