ENHANCED OPERATION OF GATE-TURN-OFF THYRISTORS WITH A LIQUIDNITROGEN COOLING PHASE FOR 20-10 KV POTENTIAL POWER CON- DITIONING

THE PHASE I PROJECT CONSISTS OF A FEASIBILITY DEMONSTRATION FOR LOW TEMPERATURE OPERATION OF HIGH POWER GATE-TURN-OFF (GTO) THYRISTORS THAT USE THE MATRIX MULTIPLIER GATE PATTERN, AND FOR CONTINUOUS OPERATION OF THE DEVICES AT LIQUID NITROGEN TEMPERATURES. THE GTO WILL BE AN 80 MM DEVICE WITH A BLOCKING CAPABILITY OF 4.5 KV AND A SURGE CURRENT RATING OF 44,000 A. THE OBJECTIVE OF THIS PROJECT IS THE ENHANCEMENT OF REVERSE RECOVERY CHARGE, BLOCKING, AND SURGE CURRENT CHARACTERISTICS IN THE TEMPERATURE RANGE 77 K TO 150 K. PRELIMINARY ANALYSIS INDICATES A 70% REDUCTION IN TURN-OFF TIME BY USING HIGH RESISTIVITY FLOAT-ZONE SILICON WITH A (1-1-1)/1 DEGREES ORIENTATION. THE EXPERIMENTAL R&D PROGRAM IN PHASE I HAS SIX 80 MM DIAMETER WAFER GTO THYRISTORS FABRICATED WITH THE GATE LAYOUT AND STACKED IN SERIES FOR AN OPERATING POTENTIAL OF 22-25 KV AT 1.0-3.0 KA. EACH GTO STACK MODULE PROVIDES A MAXIMUM CONTINUOUS OUTPUT POWER HANDLING OF 75 MW AND SURGE POWER CAPABILITY OF 1.1 GW AT THE LIQUID NITROGEN TEMPERATURE AFFORDED BY A TURN-OFF TIME OF 30 MICROSECONDS.