A DC-link voltage balancing algorithm for 3-level converter using the zero sequence current

Abstract

The voltage unbalance between the upper and lower capacitors is an important problem in the three-level PWM converter system, and it is known that the voltage unbalance is directly related to the zero sequence. In this paper, we provide a zero sequence current path by connecting the neutral point of the source transformer to the midpoint of the DC link capacitors. Further, we control the unbalanced voltage with the zero sequence current. The zero sequence current is controlled by the zero sequence voltage made from sinusoidal PWM. The effectiveness of the proposed scheme is verified by computer simulations and experiment.