An Improved DC-Link Voltage Equalization for Three-Level Neutral-Point Clamped Converters

A DC-link voltage equalization algorithm (DCL-E) for Three-Level Neutral-Point Clamped converters (NPCs) is proposed in this paper. It consists of appropriately regulating DC-link currents with the aim of equalizing DC-link voltages as fast as possible, minimizing capacitor voltage and current ripple and prioritizing NPC load requirements at the same time. This goal is achieved by means of suitable PWM patterns, which also guarantee an appropriate DC-link capacitor exploitation over both transient and steady state operation. The effectiveness of the proposed DCL-E is verified through a simulation study, which refers to the case of a three-phase NPC that feeds a Surface-Mounted Permanent Magnet Synchronous Machine.