Thermal Simulations and Experimental Verification of Power Modules Designed for Double Sided Cooling

Cooling power modules on both sides of the active switching devices reduces the operational junction temperature compared to conventional single sided cooling. In this work, thermal simulations of power modules based on single sided cooling concepts are compared with double sided cooling counterparts. Expected junction temperatures, maximum temperatures and maximum current capability is analyzed. In addition, experimental verification in the form of comparisons with thermal characterization tests for both single-and double sided power modules based on SiC bipolar junction transistors is presented. Results from simulations show that cooling of both sides of the active switching devices can reduce the thermal resistance by more than 40 percent. This number depends on the heat transfer coefficient. From one example, simulating a worst case stall condition of the electric machine, the use of double sided cooling reduces the maximum junction temperature from 167 °C to 106 °C at a load current of 300 A using a heat transfer coefficient of 4 kW/m2K and 4 kHz switching frequency. Furthermore, the temperature decreases to 97 °C if AlN-based DBC substrates are used instead of alumina DBCs. Results from the experimental comparison between double-and single sided cooling showed that the maximum temperature for a load current range of 15 A to 50 A was reduced by 18 percent to 55 percent by using double sided cooling. At a device temperature of 60 °C, the increased thermal capability of the double sided version allowed for a 20 A higher load current, which corresponded to operation under 50 percent higher power losses. Double sided cooling also increased the maximum current capability through a single SiC BJT by more than 20 percent beyond the maximum current capability through the single sided cooling version.