Origin Analysis and Mitigation Method of Voltage Oscillation Occurred Inside the Winding of Medium-Voltage Medium-Frequency Transformer

The medium-voltage medium-frequency transformer is a critical component of high-power dc converters. However, the ultrafast switching speed of wide bandgap semiconductors can induce voltage oscillations in the medium-frequency transformer, increasing the risk of primary-insulation partial discharge and leading to permanent breakdown. Existing research has focused on voltage oscillations occurring at ports, but there is insufficient knowledge about those happening within the winding. This article presents a model for calculating internal voltage oscillations. Compared to conventional models, it is simple and considers the core electrical energy for the first time. Accordingly, the physically-based analytical formulas are derived to calculate voltage oscillations. Based on the model, the relationship between voltage oscillations, port voltage, and transformer structure is analyzed. The oscillation mitigation method is presented and validated by experiment.