Neutral Point Voltage Balancing Control Based on Adjusting Application Times of Redundant Vectors for Three-Level NPC Inverter

Three-level neutral-point-clamped (NPC) inverter is used in many industrial applications due to its attractive advantages in terms of harmonics content, achieved power level, and electromagnetic interference reduction. However, the main concern in this topology is the imbalance of the neutral point (NP) voltage in the dc side of the inverter. Indeed, the NP voltage distorts the output voltage of the inverter and increases voltage stress on its switching devices. In this article, a new NP voltage balancing control based on modified three-level space vector pulse width modulation (SVPWM) is proposed. The core idea of this method consists in adjusting the application times of redundant vectors in such a way that the NP voltage is kept balanced. In this method, the appropriate adjustment direction is determined by measuring only the capacitor voltages and the output currents of the inverter. The performances of the proposed method are validated and compared through various experimental tests, and the obtained results show an excellent NP voltage balancing regardless of the modulation index values.

I. Introduction

Multilevel inverters have been receiving more and more attention for medium- and high-voltage applications due to their several advantages over the conventional two-level inverter including higher voltage capability, lower dv/dt, less harmonic distortion, and reduced switching devices blocking voltages.