Importance

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Abstract

A method and apparatus for controlling an AC induction motor, having at least two phases. The motor is controlled in a known manner by two input signals S.sub.1, S.sub.2, which are connected to a resolver (1), the output signals of which are used to generate separate supply signals to the motor phases. A measured signal U, representing the rotational speed of the motor, is fed back to the control system and is used for calculating the oscillator frequency of the oscillator (5), which drives the resolver. A calculating circuit calculates the oscillator frequency as the sum of the first control signal S.sub.1 multiplied by a first constant factor, and the tachometer signal U multiplied by a second constant factor. As a result of this control method the oscillator frequency will increase with increasing control signal S.sub.1 and increasing tachometer signal U, but decrease with increasing motor load, because the motor speed will decrease. This automatic frequency adjustment results in constant amplitude of the stator magnetic field at all motor speeds and at all different loads.

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First Claim