On-line simulation of the junction temperature for the thermal protection of high power gate turn-off thyristors used in pulsed duty invertorsFunded under: FP3-FUSION 11C
A new high power (25 MW) amplifier system based on gate turn-off thyristors (GTOs) is to be used as a power amplifier in the control system of the vertical position of the plasma in the JET experiment. The new amplifier is characterised by a nominal duty cycle of 30 s every 600 s. The power dissipation in each GTO can reach peaks of almost 8.1 kW for short periods. The switching frequency of each GTO and the current during the execution of a JET pulse are somewhat unpredictable. It was therefore felt necessary to provide the power devices with thermal protection, which has to be reasonably accurate in order not to limit the performances of the amplifier. At the same time it should be reasonably simple and cost effective. An on-line simulation/calculation of the junction temperature was therefore adopted: the conduction losses, the turn-on and turn-off losses are taken into account; the direction of the output current together with the knowledge of which GTOs are in the ON status determine if the current is flowing in the GTOs or in the freewheeling diodes. A detailed description is given of the model used and of the hardware realisation of the simulation.
Bibliographic Reference: Report: JET-P(93)45 EN (1993) 6 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199311382 / Last updated on: 1994-11-28
Original language: en
Available languages: en