A comprehensive study of neutral-point voltage balancing problem in three-level neutral-point-clamped voltage source PWM inverters

This paper explores the, fundamental limitations of neutral-point voltage b alancing problem for different loading conditions of three-level voltage so urce inverters. A new model in DQ coordinate frame utilizing current switch ing functions is developed as a means to investigate theoretical limitation s and to offer a more intuitive insight into the problem. The low-frequency ripple of the neutral point caused by certain loading conditions is report ed and quantified.