The effect of minimum pulse width limitation on neutral point voltage control and their cooperation in high power three-level NPC converters

It is well known that the minimum pulse width limitation must be considered to ensure the reliable operation of high power three-level neutral point clamped (NPC) converters equipped with GTOs or IGCTs, however the limitation has deleterious influence on neutral point voltage control. Based on the conventional realization of minimum pulse width limitation and its effect on the voltage balancing control (VBC), this paper proposes a novel implementation method of minimum pulse width limitation. The modification of original switching sequence considers both minimum pulse width limitation and voltage balancing control in the same time, and the theoretical analysis of cooperation between them is given in this paper. The performance of the proposed method is verified by simulated and experimental results on a 7.5MVA NPC converter based on IGCTs.