Junction Temperature Elevation as a Result of Thermal Cross Coupling in a Multi-Device Power Electronic Module

Thermal cross coupling effects between various semiconductor elements of a 350A IGBT and cooler are determined from transient thermal impedance measurements from junction to ambient. The dynamic thermal behaviour of the module and cooler is represented in the Laplace transform domain by a matrix-vector formulation in which the temperature elevation of each element is related to the power dissipated in all the active elements. A PSpice representation of the model is developed, in which each term of the trans-impedance matrix is represented by a cascaded R-C network. Results from the simulation of a PWM inverter show that the load power frequency influences the thermal cross-coupling effects within the module. It is clear that thermal cross-coupling is a significant additional source of junction temperature elevation and under some load power conditions can increase the depth of thermal cycles