A numerical approach based on transient thermal analysis to estimate the safe operating frequencies of thyristors

The spatio-temporal distribution of temperatures in high-power SCRs used for switching high di/dt current pulses were simulated using the finite element method (FEM). Two types of SCRs, with amplifying gate (unshorted device), and without amplifying gate (shorted device) structures, were analyzed. The details of the numerical simulation, such as the meshing strategy, the heat source model and the boundary conditions are discussed. Based on the analysis, the failure temperature of the unshorted device was computed to be 1100 degrees C. The peak temperature in the shorted device was, however, found to be 335 degrees C. The instantaneous cooling cycles of the devices and their cooling time constants, as obtained from the simulations, are presented. Based on these parameters, the safe operating frequencies of these devices were estimated.>