A new approach to the instantaneous junction temperature evaluation of high power diodes (thyristors) during past current transients

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