Research On The Thermal Characteristic Of High Voltage Pulse Thyristor

As a high withstand voltage and large through-flow semiconductor, pulse thyristor has been widely used in pulsed power system. This thesis mainly researches the thermal characteristics of pulse thyristor, including calculation of junction temperature based on transient thermal impedance network, analysis of uneven junction temperature distribution on silicon wafer and experimental measurement of junction temperature.In this thesis, the equivalence principle between thermal impedance network model of thyristor and circuit model was derived. The junction temperature response curves under different pulse current were solved based on the thermal impedance parameters of thyristor. At the same time, the junction temperature response curve was calculated while taking the influence of junction temperature on the dissipation power into consideration. The calculation results show that the effect of current peak on junction temperature is more obvious than that of pulse width. The calculation junction temperature while considering the influence of junction temperature on the dissipation power is larger than the junction temperature while not considering the influence of junction temperature on the dissipation power.This thesis analyzes the expansion process of conduction region during the opening of pulse thyristor. The uneven distribution mathematical model of the dissipation power density was established. Combined with the heat transfer finite element model, the uneven temperature distribution of thyristor was solved. Simulation results show that while pulse current flew through thyristor, the heat mainly concentrates near the gate at the beginning and gradually spread to the cathode region around. The transfer velocity of heat depends on the spreading velocity of conduction region. Besides, as the thermal conductivity of silicon and molybdenum are relatively small, the heat mainly concentrates on the silicon wafer of thyristor. There is few heats diffusing to the molybdenum sheet on both sides and the heat diffusing to the copper pedestal is much smaller. The uneven temperature distribution will cause that local temperatures on silicon wafer may reaches hundreds to a thousand degrees. This may reach the melting point of defect lattice on silicon wafer which will melt the silicon wafer and cause the thermal breakdown and damage of thyristor.Based on the basic principle of the thermal sensitive parameter method, this thesis designed an experimental scheme to solve the technical difficulties of measuring the junction temperature of pulse thyristor via thermal sensitive parameter method. A constant current source branch was set in parallel with the thyristor and the thyristor would be triggered in advance. So the voltage on the thyristor would keep between a few volts and tens of volts which could be accurately measured by an ordinary oscilloscope probe. The junction temperature could be calculated through the on-state voltage and thermal sensitive curve. The feasibility of the program was verified by experiments and the thermal sensitive curve of thyristor under 200 A DC was measured. The junction temperature rises are 56.9?, 74.3? and 100.6? while the pulse width of the current is 400?s and the current peaks are respectively 12.48 kA, 26 kA and 39.2kA.