Static and Dynamic Voltage Balancing for an IGCT-Based Resonant DC Transformer

This paper focuses on the operational characteristics of a medium voltage resonant DC transformer based on a split capacitor IGCT 3L-NPC leg. The study delves into both the dynamic and static balancing aspects of the 3L-NPC when operating in a two-level, 50% duty cycle mode. This particular operating condition, which skips the zero-level state and involves extra low turn-off current due to the resonant operation, presents challenges in ensuring reliable medium-frequency operation of the DC transformer. Thus, this work evaluates the behavior across various turn-off current conditions, an assessment of the dynamic balancing incorporating a low-value capacitive snubber, and the performance of the NPC symmetrizing resistor for the static voltage balancing. To validate the effectiveness of the designed snubber configurations, practical experiments are conducted using the MV prototype.