A ZVS Bidirectional 48V/12V Converter with Magnetic Integration for 48V Mild Hybrid Vehicles

This paper presents a ZVS-bidirectional converter for 48V MHVs. The proposed converter boasts attractive features, including enhanced voltage gain, minimized voltage stresses, a shared electrical ground for input and output, positive output voltage polarity, and continuous low-ripple current on both sides facilitated by the presence of inductors. Additionally, the proposed converter benefits from a single-magnetic core integrating three-winding coupled inductors. In this arrangement, the currents in the second and third windings, which correspond to the currents of the converter’s 12V and 48V sides, are ripple-free, while the first winding experiences a sufficient current swing (i.e., TCM operation) to achieve ZVS. Consequently, both ZVS and current-ripple-cancellation are achieved using this magnetic integration. Mathematical and physical models, as well as magnetic system simulation, are used to elucidate the current-ripple-cancellation and to design the magnetic system. Variable-frequency control is applied to optimize the current ripple according to the output power, improving efficiency. Finally, we present the experimental results of an 800W Si-based prototype that operates under variable-frequency control within a switching frequency range of 250-500 kHz. The converter achieves a peak efficiency of 96.5%, with efficiencies of 96.1% and 96% in boost and buck modes at full-load conditions, respectively. Moreover, the converter retains above 94% power efficiency at above 25% of full load.