22kW High-Power-Density Bidirectional DC/DC Converter with Top-Side-Cooled SiC MOSFETs for OBCs

Abstract:
This paper presents the design and analysis of a 22 kW SiC MOSFET-based bidirectional DC-DC converter for on-board chargers (OBC) used in Electric Vehicles (EVs). Top-side-cooled (TSC) SiC MOSFETs (E3M0032120U2, 32 mOmega / 1200V from Wolfspeed) are used in the design. When compared to through-hole devices, the top-side-cooled power device offers lower parasitic inductances and facilitates automated assembly while delivering superior thermal performance. A digitally controlled prototype with a switching frequency of 135 kHz - 250 kHz for a CLLC resonant converter was built and tested. Detailed thermal designs are provided and compared with different thermal interface materials (TIM), namely Aluminum Nitride (AlN) and Aluminum Oxide (Al2O3) substrates. The experimental results show that the design has achieved a power density of 9.4 kW/L and a peak efficiency of 98.6% for a wide battery voltage range from 200 V to 800 V. Moreover, the thermal test results demonstrate that the use of an AlN substrate with a soft gap pad (SF1000) as TIM has around 10 °C lower case temperature than the use of an Al2O3 substrate with the same gap pad.