Design and Four-Degree-of-Freedom Modulation Method of Dual Active Bridge Converter

This article presents a design and modulation method of a fifth-order resonant dual active bridge (DAB) converter achieving consistent high efficiency over wide output voltage variations. A fifth-order resonant network is designed through a newly proposed two-frequency resonant network design method. Four-degree-of-freedom (4DOF) in control of DAB converters, duty ratios on the primary and secondary sides, a voltage phase shift angle, and switching frequency, are utilized to reduce conduction losses while achieving zero-voltage switching (ZVS) across the entire load voltage range. Accurate steady-state resonant currents on each side are derived by harmonic decomposition. The derived currents are utilized to obtain optimal 4DOF modulation parameters numerically. The merits of the proposed design in terms of rms currents and frequency range are highlighted by a comparison with series-resonant (SR) DAB converters, which use the same 4DOF modulation. The effectiveness of the proposed design and modulation method is verified through simulations and experiments with a 5.0-kW DAB converter prototype. The prototype covers a load voltage range from 400 to 800 V and a fixed input voltage of 400 V at a switching frequency from 140 to 200 kHz, achieving a peak efficiency of 98.9%.