Suppressing High-Frequency Oscillations in Dual Active Bridge Converters With Active-Clamped Series-Connected Power Devices

This article proposes a novel approach to suppress high-frequency oscillations and the resultant voltage overshoots in the transformer of dual active bridge converters that utilize active-clamped series-connected power devices. The series connection of power devices with active clamping modules allows these converters to support high voltages and achieve high power density. However, the high dv/dt associated with two-level operation, particularly when using wide bandgap power devices, can induce significant high-frequency oscillations in the transformer voltage, which can degrade the overall performance of the converter. This study presents a comprehensive analysis of the switching mechanisms of auxiliary switches in active clamping modules. Each switching event of the auxiliary switch triggers a step-like voltage excitation that leads to an oscillation. Leveraging the principle of mutual cancellation, the paper outlines an optimal switching timing for the auxiliary switches to minimize these voltage spikes. Experimental results from a 1kV, 4.6kW dual active bridge converter prototype with six series-connected power devices demonstrate that this method reduces the spike amplitude by approximately 97%, while also maintaining voltage balance among the power devices. Importantly, no additional power loss is introduced, and optimal suppression can be consistently achieved regardless of the converter's working conditions.