A Fast Direct Power Digital Control Strategy for Dual Active Bridge DC-DC Converters

Dual active bridge (DAB) DC-DC converter topologies are attractive in applications requiring galvanic isolation, e.g. electric vehicle chargers and fuel cell systems. Such scenarios benefit from rapid and precise control of the DAB active power, including reverse flow conditions. Rapid and precise control is typically achieved indirectly, using a combination of outer voltage and inner current loops or through feed-forward adaptation of the modulation settings. Furthermore, the control process dynamics are often constrained via low pass filters that eliminate the high-frequency ripple content from AC-side and even DC-side measurements. This paper proposes an alternative digital control formulation that achieves a rapid transient capability and directly controls the DAB power flow. The basis of the approach is a novel variable amplitude dual carrier triple-phase-shift modulator, combined with an ACside current sampling strategy synchronized to DAB converter voltage transitions. This approach allows for rapid computation of the average converter power flow, which can then be combined with a digital proportionalintegral (PI) feedback controller. Feed-forward action is added to the control loop based on a Fourier series approximation of the DAB real power. This approach is validated using detailed time-domain PSIM simulation investigations.