New Analytical Model for Real-Time Junction Temperature Estimation of Multichip Power Module Used in a Motor Drive

A new analytical electro-thermal model of a multichip power module is described in this paper. The proposed model is intended to be used during in-service conditions inside a motor drive for remaining useful lifetime calculation, in combination with a thermal cycle counting algorithm. The model allows fast calculations of the chips temperature, based on simple analytical expressions of averaged total power losses, and mathematical formulations of thermal impedances using the Foster network representation. The proposed model is computationally efficient, since it does not require the switching instants information, but only the used pulse width modulation (PWM) technique, which is advantageous for embedding in terms of reducing computation resources and time. Finally, a comparison between the proposed model results and experimental measurements is conducted at different operating points of the motor drive, and under two different switching modes; the third harmonic injection PWM for output frequencies below 20 Hz and the discontinuous PWM for frequencies above 20 Hz. The results obtained are very satisfactory in terms of mean temperature levels and temperature swings for frequencies from 1 to 50 Hz.