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Because of its short turn-off time, the silicon-controlled rectifier (SCR) can be turned off by means of capacitor discharge pulses and, therefore, it can be used not only to switch on heavy currents, but also to switch them off. This holds true for high operating frequencies as well as for an almost unlimited number of switching duties. As a result, the possibility arises of a pulse technique with new methods of both contactless and continuous speed control of d-c and a-c motors; this technique, in turn, presents new possibilities for the inverter-type speed control of 3-phase motors.
Klemens Heumann (Wed,) studied this question.