A Suitable PWM for DC-link Voltage Equalization of Three-Level Neutral-Point Clamped Converters

A novel DC-link voltage equalization algorithm for Three-Level Neutral-Point-Clamped Converters (NPCs) is presented in this paper. It mainly consists of appropriate pulse width modulation patterns, which are alternatively employed in order to exploit the DC-link capacitors differently, for a given reference voltage space vector. Thus, the most suitable PWM pattern is chosen in each sampling time interval in accordance with DC-link voltage equalization needs, without affecting NPC performances in terms of output voltage and current waveforms. The worth and effectiveness of the proposed equalization algorithm are verified through a simulation study, which refers to the case of a Surface-Mounted Permanent Magnet Synchronous Machine (SPM) fed by a three-phase NPC.