Role of Parasitics in a Dual Active Bridge DC-DC Converter with Gallium Nitride devices

Owing to the large di/dt and dv/dt introduced by Gallium Nitride (GaN) switching devices, optimization of parasitic elements in a converter becomes very critical. This paper evaluates the impact of the parasitics of an high-frequency isolation transformer and printed circuit board (PCB) on the performance of a GaN based Dual Active Bridge isolated DC-DC converter. An iterative optimization tool is built to optimize the isolation transformer in terms of its weight and efficiency. Initial testing of the prototype revealed that parasitic elements of the PCB have adverse affects on the converter and it did not work beyond 35 VDC. Hence, based on practical results, PCB parasitic elements were optimized. With optimized layout design, converter did operate as it was intended to. However, due to excessive ringing in the switching voltages, converter efficiency was below the target efficiency (η > 90%). To eliminate this high-frequency ringing, inter-winding capacitance of the transformer was reduced by changing the winding configuration. This successfully reduced the ringing and aided the converter to reach its target efficiency.