Thermal Simulation of Paralleled SiC PiN Diodes in a Module Designed for 6.5 kV/1 kA

Abstract

This work shows thermal simulations of a package of 48/96 high-voltage (6.5 kV/1 kA) PiN diodes. A temperature dependent heat generation for a forward voltage of 3.6 V with a realistic heat generating volume in the diode of (2.7x2.7x0.01) mm3 was used. The thermal coupling of two diodes was determined to be less than 1 % for a distance between the diodes of 10 mm. The temperature distribution for the entire module has been studied for two different ceramic insulating materials, AlN and Al2O3, as well as for two numbers of diodes, 48 and 96. This led to a maximum temperature of 106 °C/118 °C (AlN, 48/96 diodes) and 123 °C/144 °C (Al2O3, 48/96 diodes). Assuming a constant applied voltage, a variance of ±0.5 V of the characteristic curve (forward voltage versus current) due to variations in the production process was considered fork single diodes. For a shift of +0.5 V for a single diode, the maximum temperature difference to the cooler temperature becomes approximately twice the original difference. Additionally, the operation under constant current (7.1 A, 10.2 A, 14.2 A) was studied including single diode failure. For single diode failure, the resulting change of the maximum temperature would be less than 3 %.