Instantaneous junction temperature evaluation of high-power diodes (thyristors) during current transients

In this paper, an approach to the instantaneous junction temperature evaluation of high-power diodes (thyristors) is presented. The model allows obtaining the instantaneous junction temperature waveform starting from the expressions of the device transient thermal impedance and forward voltage drop. The linearity properties of resistors and capacitors (RCs) networks are used to obtain the thermal system transfer function from the transient thermal impedance curve. Thus, an expression that relates the forward voltage drop to the forward current and the junction temperature is used to "feedback" the influence of the temperature variation on the device forward characteristic. The model is also validated by comparing the results obtained from simulation against the one obtained from surge tests performed on one sample device.