Importance

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Abstract

The invention relates to a method of preventing the stalling of an asynchronous machine controlled by a controller (6) affecting the slip and having a response time less than a rotor time constant (.tau..sub.r) of the machine. To minimize the safety margin between the allowable maximum torque and the stalling torque, the method comprises the steps of measuring rotational vectors (i.sub.s, u.sub.s) for the stator current and stator voltage of the machine; determining, on the basis of the measured rotational vectors (i.sub.s, u.sub.s) of the stator current and stator voltage and a short-circuit inductance (.sigma.L.sub.s) of the machine, two vectors one of which (.phi..sub.s) is parallel to the direction of the stator flux (.psi..sub.s) and the other (.phi..sub.r) to the rotor flux (.psi..sub.r); determining an angle (.gamma.) between said vectors parallel to the stator and rotor fluxes or a value (.mu.) proportional to it; and preventing the controller from performing operations tending to increase the torque of the asynchronous machine when said angle (.gamma.) or the value (.mu.) proportional to it corresponds to a predetermined angle between the stator and rotor flux vectors.

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First Claim