INDUCTION MOTOR SPEED CONTROL

• Main Authors: KONRAD C, CHAUSSE B
• Format: Patent
• Language: English
• Published: 25.10.1972
• Subjects: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORSOR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER; ELECTRICITY; GENERATION

A control circuit for regulating the speed of a polyphase induction motor by changing the frequency and voltage level of the supply source supplying power to the motor. The difference between a speed reference signal and an output signal from a closed loop feedback circuit is converted to a sine wave alternating current signal having a frequency which varies with the time integral of the difference. A circuit for amplifying this alternating current signal provides power to the induction motor. A pair of diodes connected in the feedback circuit limits the rate of change of the frequency of the alternating current signal to a value determined by the design of the motor. The voltage amplitude of the alternating current supplied to the motor is adjusted as a function of the frequency and is further adjusted as a function of slip of the motor. Additional adjustment of the volts/cycle/second value of the alternating current supplied to the motor allows for overexcitation of the motor even beyond the design limits of the motor in order to provide the greatest possible torque to maximize the rate of change in speed and direction of the motor.