A quasi-resonant bi-directional tri-mode DC-DC converter with limited valley current

This work targets non-isolated, bi-directional dc-dc converters for hybrid energy-storage systems in light electric vehicles. Three operating modes are used to achieve high-efficiency over the full load range based on the inductor current constraints. The highest switching frequency is used near the rated current in order to limit the peak inductor current and avoid saturation. Soft-switching ZVS turn-on is achieved on both transistors in the mid-load range, where the frequency is automatically controlled to maintain a fixed dead-time and near-constant negative inductor valley-current. Pulse-frequency-modulation is used at light-load conditions for improved efficiency. A 2 kW two-phase bi-directional dc-dc converter prototype was implemented to demonstrate the tri-mode operation. The converter operates with an input voltage of 50 V and an output voltage of 100 V. Using the proposed tri-mode control scheme, a peak efficiency of 97.5% is achieved while a minimum efficiency of 88% is maintained over the full load range.