Device-Sensor Assembly FEA Modeling to Support Kalman-Filter-Based Junction Temperature Monitoring

Junction temperature monitoring for power devices is an essential requirement for high-reliability applications. Temperature sensitive electrical parameters (TSEPs) are powerful tools in this process, but to achieve sufficient accuracy they require complex characterization procedures for each part, that can hardly be implemented in mass-produced converters. This paper proposes a combination of interdisciplinary approaches to ultimately solve this problem for power MOSFETs by an automated procedure that can occur in-place, with devices mounted and without any specific user intervention nor additional heating components. The TSEP exploited in this paper is the ON-state drain-source voltage of the power MOSFET. A wide-bandwidth ON-state voltage sensing circuit and a low-cost thermistor conditioning circuit to sense the case temperature of the device are presented and modeled. A lumped parameters thermal model of the system is given, and finite-element method (FEM) simulations are employed to obtain first-guess values for the unknown thermal network parameters, integrating information from the device datasheet. Finally, an observer based on the Kalman filter applied to the data collected from these sources is presented and evaluated experimentally. Performance is assessed with the use of thermal imaging techniques.