A 25 kW 48 V Mild Hybrid Motor and Inverter

A novel inverter and a corresponding high-powered electric machine (“motor”) were developed for a hybrid vehicle. The inverter is a compact oil cooled silicon MOSFET design rated at 25 kW that drives a frameless 6-phase 8 pole, interior permanent magnet (IPM) motor with oil (Automatic Transmission Fluid, ATF) cooling and novel windings. Both Oil- and water-cooled inverter variants were explored. Both the inverter and the motor were designed, built and tested to A-sample level. A major aim of the design was to make it possible to cool the motor, inverter and gearbox from the same oil supply. The focus of the work presented in this paper is reducing the thermal resistance of the inverter through the use of impingement jet cooling. Cooling of the electrically live tab of MOSFETs is well known to reduce thermal impedance, hence improving performance; this was achieved in the oil-cooled design by exploiting the oil’s electrical insulating property.