An Analog-based, Duty Cycle Modulation Method to Remove the DC Bias in the Transformer for a Dual Active Bridge Converter

The transformer in a dual active bridge (DAB) converter can have DC magnetic flux bias due to asymmetries in circuit parameters and the non-ideal behavior of semiconductor switches. This DC bias will increase the conduction losses of the transformer and power devices, lead to loss of ZVS, and even saturate the magnetic cores of the transformer and inductor, leading to the converter failure in the end. To prevent this risk, this paper proposes a duty cycle modulation method to compensate the DC bias by regulating the duty cycle of square voltages generated by the primary and secondary side H-bridges. The conditions to achieve zero DC bias in the transformer and the small-signal model to regulate the DC bias current are derived. Tunnel magnetoresistance (TMR) is employed to sense the currents, and an analog integration and sampling method is proposed to detect DC bias. The proposed method is verified through experimental results on an 800W DAB prototype.