ZVS Boundary Assessment for T-type-based Dual Active Bridge Series Resonant Converters using State-Plane Analysis

This paper investigates the soft-switching range of a three-level T-type primary bridge-based dual active bridge series resonant converter, employing a leading-edge modulation technique. A closed-form solution for the zero voltage switching (ZVS) boundary is derived for all switches, utilizing the fundamental harmonic approximation (FHA) and state-plane method. Comparative analysis reveals the superior accuracy of the state-plane method over FHA, especially at different frequency ratios (F). Variation of ZVS boundary with converter gain and F is highlighted, offering valuable insights for achieving wide gain operation of the series resonant converter. The solutions are validated through PLECS simulations. Furthermore, considering non-ideal conditions like output capacitance of MOSFET and circuit dead time, ZVS boundaries are modified in the analysis and also validated via simulations. Finally, the ZVS boundaries are validated using an 18 kW hardware prototype of a T-type primary bridge-based dc-dc converter designed for battery charging applications.