Abstract: In order to measure the rotation speed of an induction machine whose stator is connected via a controllable AC controller to a single-phase or polyphase AC power supply system, the stator is disconnected from the AC power supply system for at least a predetermined time period (&Dgr;t). This is preferably achieved by opening active devices in the AC controller, with at least one stator voltage, which is induced in the stator by the rotary movement of the rotor, being measured in this time period (&Dgr;t). The measured values are used to determine the frequency of the stator voltage and to derive the rotation speed of the induction machine.

Abstract: A method of smoothly stopping pump drives without pressure surges is provided. To accomplish this, the phase control angle between the motor current and the motor voltage is increased according to a linear ramp starting from 0.degree. with the help of an a.c. power controller, where the phase angle decreases and reaches a turning point. If the turning point is detected by observing the phase angle, the phase control is based on this by means of a controller with a predefined linear phase angle reference curve as a function of time. Then the motor rpm does not change abruptly because a rapid change in phase angle is prevented.

Abstract: In the open-loop control of A.C. power controllers through the phase-angle control of semiconductor valves (4), the chronological sequence of the firing signals (Z) for the semiconductor valves (4) is determined by reference signals (X). When the reference signals (X) fail for one or more periods, this chronological sequence is disturbed and damage to the load (2) to be controlled can result. Therefore, according to the invention, a method is provided whereby a safety firing signal (ZS) is always derived from the preceding firing signals (Z) when the expected reference signal (X) fails. In addition, a device for implementing the method is specified.

Abstract: In the control of a.c. power controllers by the phase-angle control of semiconductor valves that are used to automatically control the power factor, it is necessary to determine the phase-angle between the current I and the voltage U by measuring the time difference between the current zero crossing and the voltage zero crossing. However, disturbances superimposed on the line voltage produce considerable statistical fluctuations, particularly in the measurement of the times for the voltage zero crossings. These fluctuations are propagated to the phase-angle and may lead to an unstable control response. Therefore, to determine the time difference, a reference time, which is calculated from the measured actual times of the preceding voltage zero crossings, is used for the voltage zero crossing.

Abstract: A method and apparatus for controlling single or polyphase a.c. power controllers when controlling a.c. power controllers by means of phase angle control of semiconductor switches, the firing signals on the one hand must be long enough to guarantee a reliable firing and, on the other hand, be short enough to prevent an overloading of ignition amplifiers. According to the invention, therefore the use of firing signals with variable temporal lengths is provided, which end at least approximately at the reestablishment of the current flowing in the phase that has been fired. Moreover, devices for implementing the method are specified.