New Surface Mount SiC MOSFETs Enable High Efficiency High Power Density Bi-directional On-Board Charger with Flexible DC-link Voltage

On-board chargers (OBCs) in Electric Vehicles (EVs) have been one of the first applications to drive adoption of SiC MOSFETs. Typically, OBC system designers utilize a TO247 package because of its power dissipation capability, but that comes with certain risks. The assembly process for TO247 package system is very labor intensive and human error can reduce reliability by placing stress on the solder joint and bending leads. Surface mount (SMT) devices are produced by an automated process, which increases their reliability, but the thermal design is of big concern. This paper investigates a 6.6kW bi-directional on-board charger utilizing a SiC MOSFET in an SMT TO263-7L package and Printed Circuit Board (PCB) with AlN inlay. A prototype with switching frequency of 67kHz for a totem pole PFC converter and 200kHz for a CLLC resonant converter is demonstrated with 36W/in3 power density and above 97% system peak efficiency for both charging and discharging mode. All SiC MOSFETs in the TO263-7L surface mount package meet thermal requirement on a 65°C cooling plate.