Flat packaged thyristor assembly for high-voltage application

Applications for high-power thyristors continue to increase at an accelerated pace. The circuit designer (user) and device designer (producer) have attained a high degree of maturity in their respective areas of interest and in the joint effort of mating the device to this application for optimum performance. It is the purpose of this paper to describe and analyze recent developments in the device encapsulation design area which are directed to tailoring thyristors for high-power, multikilovolt service. The use of conventional thyristors in an application requiring, e.g., 100 kilovolts holdoff capability, presents a number of problems. The physical layout alone is quite extensive, considering perhaps 100 devices plus balancing networks, anode reactors, firing circuitry, etc. Also, one must properly cool the aggregate of units which may be dissipating on the order of 25 kilowatts. A thyristor encapsulation and stack module specifically designed to fulfill the requirements of high-power multikilovolt applications are described. Compression bonded encapsulation and integral heat sink design principles are employed. Stack modules for forced air cooling and oil cooling applications are reviewed. Particular note is made of a radar modulator application and, more recently, the projected use in high-voltage dc transmission line converter stations. Mechanical and thermal design features are emphasized in the review. Potential application of the devices in conventional bridge-type arrays is explored.