Abstract: In a method of operating and controlling hysteresis motors energized by a three-phase power supply and individually monitored by an operating monitoring system, whereby the effective power output of the individual motors is determined and the three-phase voltage is changed if the effective power output deviates from a predetermined range, the hysteresis motors are first energized at an intermediate range voltage until they reach nominal speed and are then running at synchronous speed, the supply voltage is then increased to an upper range, where the remanent magnet pole strength is impressed on the armature and then reduced to a lower range for continuous operation of the motors, the power output of the individual motors is monitored and, if it drops below a threshold indicating a switch to asynchronous operation, the operating voltage is again increased to the intermediate range for renewed synchronization.

Abstract: A method for optimizing the power input to a plurality of parallel connected hysteresis motors wherein a three phase alternating voltage source jointly supplies the motors with an adjustable operating voltage. The method includes measuring, during the operation of each motor, the phase angle difference between motor voltage and motor current and determining the power factor therefrom for each motor. The effective current value of each motor is measured during operation and is combined with the power factor to obtain the active current for each motor. An active current limit value at which each motor transitions from synchronous to asynchronous operation is measured once and stored for each motor prior to commencement of continuous synchronous operation.

Abstract: A circuit arrangement for the automatic de-excitation of a hysteresis motor whose reactive power intake is compensated by capacitors and whose stator windings, which are fed from a three phase mains via a frequency converter, magnetize the rotor with their rotating field and thus produce a permanently magnetic excitation which continues in the rotor in the form of residual magnetic poles even after disconnection of the motor from the three phase mains. A voltage monitor monitors the mains side input to the frequency converter and responds upon interruption of the mains voltage due to malfunction or end of operation. Upon interruption of the mains voltage a capacitor of a buffer circuit in the d.c. intermediate circuit of the frequency converter transfers its stored energy, with decaying voltage, to the stator of the motor via an inverter which forms the output of the frequency converter, and upon response of the voltage monitor, the output frequency f.sub.