Six-Degree-of-Freedom Modulation Technique for Dual Active Bridge DC-DC Converter

Existing multi-degree-of-freedom (M-DoF) modulation techniques for dual active bridge (DAB) converters have not reached their upper limits. In this article, a six-degree-of-freedom (6-DoF) modulation technique is proposed for the DAB converter to further improve the efficiency. Compared with the conventional 5-DoF modulation scheme, the switching frequency is the sixth degree of freedom added to optimization. A power loss model is established based on the frequency domain method. The deadtime of the gate driver signal is also included in the power loss model, resulting in a more accurate loss model. In addition, the situations of asymmetric inductor current are also considered during modeling, resulting in a more accurate MOSFET conduction loss expression and DC bus capacitor conduction loss expression. The minimum power loss of the DAB converter is determined using the particle swarm optimization (PSO) algorithm. A comparison with the existing state-of-the-art 5-DoF modulation approach is implemented through a 1kW laboratory prototype, which shows the advantages of the proposed 6-DoF modulation strategy.