Minimum Backflow power and ZVS condition for a dual active bridge DC/DC converter with extended phase shift modulation based on KKT conditions

This paper provides a method to obtain the optimal extended phase shift (EPS) modulation for a dual active bridge (DAB) DC/DC converter to achieve minimum backflow power and ensure zero-voltage switching (ZVS) conditions. Firstly, the formulation of the transmission power and backflow power equations for the DAB converter under EPS modulation is established. The backflow power, which significantly impacts the converter's efficiency, is analyzed and minimized by adjusting the phase shift parameters. Subsequently, by defining the backflow power as the objective function, the Karush-Kuhn-Tucker (KKT) conditions are employed to derive optimal modulation parameters that minimize power losses and enhance efficiency. The main contribution of this work is the establishment of a set of conditions that not only minimize backflow power but also guarantee ZVS across a wide operating range. This dual optimization approach ensures that the converter operates efficiently and reliably, reducing power losses and improving overall performance. Finally, simulation results validate the theoretical findings, demonstrating significant reductions in backflow power and confirming the ZVS condition over various load and input voltage conditions. Comparisons with traditional phase shift modulation methods show the superiority of the proposed approach in achieving lower power losses and enhanced converter performance.