Abstract: An induction generator/motor system has an induction machine connected at its secondary side to a cyclo-converter. An induced voltage develops when the cyclo-converter pauses during a transient phenomenon occurring in the system. When the induced voltage exceeds a predetermined voltage range which covers the maximum output voltage derivable from the cyclo-converter, the polarity of thyristor converters of the cyclo-converter is switched such that the induced voltage is applied to a thyristor converter to be rendered conductive next in forward relationship therewith, thereby preventing occurrence of an overvoltage.

Abstract: In a pumping-up generator/motor system comprising an induction generator/motor, at least one cyclo-converter connected to the secondary winding of the induction generator motor for controlling the rotational speed of the generator/motor in the motor mode and for maintaining the output frequency thereof in the generator mode at a constant level, the center of the speed range of the generator/motor in the generator mode is set near the synchronous speed thereof and a plurality of converter units constituting each cyclo-converter are connected in parallel in the generator mode, and in series in the motor mode thereby allowing the capacity of the cyclo-converter to be made smaller.

Abstract: An applied voltage detecting device for an electric power convertor is disclosed which detects a forward voltage and a backward voltage applied to a power convertor consisting of a semiconductor power control rectification element.The forward and backward voltages are detected by a detecting circuit while a relative potential difference is being provided to these voltages. The voltages detected by the detecting circuit are converted to optical signals and are picked up by a single optical transmission circuit. The optical signal is again converted to the electric signal by a discrimination circuit, which discriminates whether the signal is the forward detection voltage or the backward detection voltage from the potential difference between them.The present invention can simplify the detecting device because both forward and backward voltages can be detected by the single optical transmission circuit.