A New Redistributed Dwell Time Method for Neutral Point Voltage Control of Multilevel Converters

Balancing the capacitor voltage for the Three Level Neutral Point Clamped Converters (3L-NPC) is a chronic issue especially when one capacitor is defected. This could lead to have unequal dc-link voltage distribution and the neutral point will be drifted. Several algorithms had been proposed depending on the implemented modulation method. The Space Vector Modulation (SVM) method is widely used as it offers the simplest way to balance the capacitors by intensively using the small redundant vectors which leads to having excessive switching for the semiconductors, therefore, the switching losses increase. In this paper, an effective technique to balance the voltage of the capacitor is introduced for SVM modulator. The proposed technique redistributes the SVM pattern's dwell time as a result, the switching frequency while keeping the SVM switching time intact. The proposed technique uses simple dwell time distribution factor to control the balancing regulation rate. The effectiveness of the introduced technique is verified with defected dc-link capacitors and shows a remarkable performance.