Method of controlling speed of at least one induction motor and device therefor

A method of controlling the speed of an induction motor comprises the steps of feeding a supply voltage to the winding of a motor stator and obtaining a signal proportional to the motor speed by varying the voltage across the winding of a motor rotor before activating switch thyristors in the rotor circuit. When the obtained signal exceeds a predetermined value, a signal enabling the switch thyristors will be shaped using the same signal. After one of the thyristors is activated, the level of the voltage measured across the rotor winding is reduced to zero or to a value below a predetermined value, thereby causing the signal to cease. Then the entire process is repeated for each of the subsequent thyristors. The speed of several motors may be controlled. A device for accomplishing the hereinproposed method comprises a unit for effecting sampled-data control of a motor speed, said unit being connected through a pulse distributor to the control input of a thyristor switch which is, in turn, connected to the winding of the motor rotor. The unit for effecting sampled-data control of the speed of the motor rotor contains an element having an adjustable operating threshold and a pulse shaper connected to the pulse distributor, said element and said pulse distributor being placed in series. The input of the element having an adjustable operating threshold is electrically coupled to the output of the thyristor switch.