Steady-State and Transient DC Magnetic Flux Bias Suppression Methods for a Dual Active Bridge Converter

This article presents dc magnetic flux bias suppression methods for a dual active bridge (DAB) converter in both steady state and transient process. The steady-state dc offset is caused by asymmetries of the circuit and power switches in practice, while the transient offset is caused by the sudden update of phase shift ratio. This dc bias will increase the conduction losses, lead to loss of zero voltage switching (ZVS), and even saturate the magnetic components. To prevent this risk, this article proposes methods to suppress the dc bias both in steady state and transient process. For steady-state dc bias suppression, the duty cycles of square voltages generated by the primary and secondary side H-bridges are regulated according to the dc bias current. The conditions to achieve zero dc bias and the small-signal model to regulate the dc bias current are derived. For transient dc bias suppression, the phase shift ratio variation is limited to ensure the peak inductor current within the safe operating range. Tunnel magnetoresistance (TMR) is employed to sense the currents, and an analog integration and sampling method is proposed to detect dc bias. Finally, the proposed method is verified through experimental results on a 3200-W DAB prototype.