Importance

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Abstract

An apparatus for controlling the supply of power to a variable-speed induction motor converts an AC power source voltage to a motor supply voltage at a designated frequency, with the amplitude of the motor supply voltage being controlled in accordance with the motor load such that the degree of slip conforms to a predetermined optimum slip charactistic, whereby high efficiency and stability are maintained over a wide range of load values. The motor supply voltage amplitude is detected to provide an indication of the motor load, an optimum value of an operating parameter of the motor which varies in accordance with degree of slip is derived based on the designated frequency and the detected voltage amplitude, using a predetermined function corresponding to that frequency, and the motor supply voltage amplitude is controlled such as to reduce an amount of difference between the optimum value of the operating parameter and a detected value of that parameter.

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First Claim