Design and Optimization of A High Power Density Low Voltage DC-DC Converter for Electric Vehicles

This paper presents a high power density LLC converter for Electric Vehicles (EVs) on-board low voltage DC-DC converter. The design specification imposes critical challenges on size and efficiency due to extremely high load current rating and wide input/output voltage range. The proposed design enables high switching frequency by using wide-band-gap (WBG) devices to significantly reduce the size of magnetic components and meet the power density requirement. A two-transformer configuration with series connected primary windings and parallel connected secondary windings is used to reduce the heavy I2R loss on the output side. The structures of parallel resonant inductor and transformers are carefully designed to reduce the fringing loss and AC conduction loss. A single phase 1.3kW LLC prototype with water cooling was built and experiment results verified the design considerations. The prototype achieved 3kW/L of power density and 97% peak efficiency. Full input voltage range from 250V to 430V and output voltage from 9V to 16V operation was verified with 96.5% efficiency achieved at nominal input and full load.