A simplified thermal analysis approach for power transistor rating in PWM-controlled DC/AC converters

A simplified dynamic thermal analysis approach is proposed for the estimation of the peak junction temperature in power IGBT transistors operating in pulse-width modulation (PWM) controlled DC/AC converters. This approach can be used for the rating of electron devices or heatsink systems in power circuit design, as it provides a direct analytical link, in terms of electrical and thermal device parameters and converter operating conditions between the case and the peak junction temperatures. In this way, by imposing a given upper limit on the junction temperature, indirect constraints on device size or load current or heatsink efficiency can easily be obtained. The approach is based on mild, pessimistic approximations on both the spectrum of dissipated power and on the dynamic thermal behavior of the device. The validity of such approximations has been verified by comparison with the results of accurate numerical simulations carried out by using measurement-based loss models. Possible ways of using this approach in a converter rating context are outlined in the paper, by considering different design scenarios.