4-DoF Control and Efficiency Oriented Co-Optimization of a 15-kW Multilevel Series Resonant DAB (ML-SRDAB) Converter

This paper proposes a co-optimization framework of key design parameters and four-degree-of-freedom (4-DoF) control for a 15-kW Multilevel Series Resonant Dual Active Bridge (ML-SRDAB) converter. The proposed DC/DC converter is suitable to meet the requirements of an SAE J3068-compliant on-board charger (OBC) in an electric vehicle (EV) with a 1.25 kV powertrain. A generalized harmonic approximation (GHA) based model that estimates the high-frequency link voltages and current in a 4-DoF controlled ML-SRDAB is developed. A framework to design the resonant tank component set for variation in turns-ratio, based on the first-harmonic approximation (FHA), is proposed. The resonant tank selection framework and steady-state model under 4-DoF control are used to arrive to an optimal value of the inductor, capacitors, and turns ratio for maximizing the time weighted average efficiency (TWAE) over the DC/DC converter's operating range. The co-optimization achieves a 98.05% TWAE for the proposed OBC.