High Efficiency Bidirectional LLC+C Resonant Converter With Parallel Transformers for Solar-Charged Electric Vehicles

Recent interest in electric vehicles with onboard solar generation presents a new opportunity for using solar electric vehicles (SEVs) for distributed generation when the traction battery is fully charged. This concept presents a new power electronic challenge: the onboard charger should have high efficiency in the grid-to-vehicle (G2V) direction for normal charging power levels (i.e., 6.6 kW) and also high efficiency in the vehicle-to-grid (V2G) direction for much lower solar power levels (i.e., < 800 W). However, typical onboard charger topologies have low efficiency at light loads. This article proposes a novel bidirectional LLC+C converter to address this challenge. It operates as a full-bridge LLC converter in the G2V direction and a half-bridge LLCC converter with a smaller transformer in the V2G direction. Simulation results show a maximum efficiency gain of 5.1% in the V2G direction compared to the standard full-bridge LLC converter. To experimentally validate the topology and operation, a 6.6-kW prototype with 450–700-V input is designed, built, and tested. The experimental results show that the proposed converter achieves high efficiency in the V2G direction at 700 W (95.7%).