Inductive energy storage systems require opening switches which are technically much more difficult to realize than closing switches. Most advanced state-of-the-art semiconductor devices, namely, integrated gate-commutated thyristors, are capable of breaking currents on the order of 4 kA. However, the ISL has developed a high-power opening switch based on standard high-power thyristors and using our so-called Inverse Current Commutation with Semiconductor devices (ICCOS) countercurrent commutation principle. These ICCOS opening switches, capable of interrupting pulse currents up to 28 kA, exploit the general property of thyristors, according to which falling short of the holding current puts the device into its blocking state. For this, a well-dimensioned countercurrent pulse is injected, via an elaborate circuit, into the thyristor which is in its conducting state. A 50-mu F capacitor is used as the countercurrent pulse source, as well as a fast current-rise thyristor and a fast-recovery diode for the countercurrent subcircuit. The countercurrent energy stored in the dedicated capacitor is not lost in the switching process but fed into the load, in addition to the main-circuit energy. The achieved ICCOS switch-off time is about 30 mu s.
