Estimation of transient thermal impedance for constant current of a power thyristor using temperature field calculation

Transient thermal impedance for constant current is calculated by dividing the overtemperature of a given spot within a silicon pellet by power losses. The calculation of the temperature field in the silicon pellet is based on the assumption that losses are produced in the silicon pellet only. Calculated results for one power thyristor are compared to its catalog values. The best agreement was obtained in the case of uniform loss distribution throughout the silicon pellet volume, with the temperature at the r/2 spot in the central silicon pellet plane being taken as virtual junction temperature. Understandably, the best agreement obtained was for a temperature at the r/2 spot in silicon pellet's central plane, since the catalog curve is based on the measurement of forward voltage drop which is dependent on total temperature field in a silicon pellet. The difference between calculated transient thermal impedance curve for constant current and its catalog curve in the entire time area is, in this case, for cooling from the anode side, from the cathode side, and from both sides, 11.4, 10.3, and 3.6%, respectively.<
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