A GaN-Based Three-Level Dual Active Half Bridge Converter With Active Cancellation of the Steady-State DC Offset Current

The dual active bridge (DAB) is a widely used isolated DC-DC converter topology, particularly in automotive on-board charger (OBC) applications due to its high power density, inherent bidirectional power flow and reliability. Besides, the implementation of multilevel switching cells helps reduce the voltage stress in all devices, allowing the converter to be used in high voltage battery systems (600 V and higher). Due to circuit non-idealities, a steady-state DC offset current occurs at the transformer which leads to increased power losses, loss of zero-voltage switching and possibly magnetic core saturation. This paper discusses the physical implementation of an active cancellation method of the steady-state DC offset current, applied to a GaN-based three-level dual active half bridge (DAHB). The proposed method uses a duty cycle modulation in the primary half-bridge to compensate the non-ideal behavior of the devices. Experimental validation is done on a 1.5 kW three-level dual active half bridge converter based on 650 V GaN transistors.