Abstract 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.
A speed control for use with an induction motor, comprising a. means for producing a reference signal proportional to motor speed desired; b. means for producing a feedback signal proportional to actual motor speed; c. means responsive to said reference signal and said feedback signal for producing an output signal proportional to the time integral of the algebraic sum of said reference and feedback signals; d. means responsive to said output signal for developing a control signal the frequency of which is proportional to the magnitude of said output signal; e. means for adjusting the amplitude of said control signal in response to said output signal in a manner such that the volts per cycle per second of said control signal is substantially constant; f. means for measuring the level of slip of the motor, and for producing a limit signal when the slip has reached a predetermined value, said limit signal acting to modify the value of said output signal; and g. means for applying a signal proportional to said control signal to said motor for controlling the speed thereof.
Claim 2
Dependent Claim
181 words
A speed control for use with an induction motor, comprising a. means for producing a reference signal proportional to motor speed desired; b. means for producing a feedback signal proportional to actual motor speed; c. means responsive to said reference signal and said feedback signal for producing an output signal proportional to the time integral of the algebraic sum of said reference and feedback signals; d. means responsive to said output signal for developing a control signal the frequency of which is proportional to the magnitude of said output signal; e. means for adjusting the amplitude of said control signal in response to said output signal in a manner such that the volts per cycle per second of said control signal is substantially constant; f. means for measuring the level of slip of the motor, and for producing a limit signal when the slip has reached a predetermined value, said limit signal acting to modify the value of said output signal; and g. means for applying a signal proportional to said control signal to said motor for controlling the speed thereof.
Claim 3
Dependent Claim
22 words
The invention claimed in claim 1 further including means for limiting the rate of change of the frequency of said control signal.
Claim 4
Dependent Claim
63 words
The invention claimed in claim 1 wherein said means for measuring the slip of the motor and for producing said limit signal comprises a. means for producing a slip signal proportional to the difference between said output signal and said feedback signal; and b. means for determining when said slip signal exceeds a predetermined value representing the maximum allowable slip of the motor.
Claim 5
Dependent Claim
28 words
The invention claimed in claim 3 further including means for further adjusting the amplitude of the control signal as a function of the magnitude of said slip signal.
Claim 6
Dependent Claim
28 words
The invention claimed in claim 1 further including means for reversing the direction of rotation of the motor as a function of the polarity of said output signal.
Claim 7
Dependent Claim
18 words
The invention claimed in claim 1 wherein the last recited means includes means to amplify said control signal.