Induction motor control system

• US 3,882,364 A
• Filed: 04/08/1974
• Issued: 05/06/1975
• Est. Priority Date: 08/18/1972
• Status: Expired due to Term

• Current Assignee: David M. Erdman, Floyd H. Wright
• Original Assignee: David M. Erdman, Floyd H. Wright
• Inventors: Wright, Floyd H., Erdman, David M.
• Primary Examiner(s): Rubinson, G. Z.
• Application Number:
  US05/458,996
• Time in Patent Office: 393 Days
• Field of Search: 318/221R,221E,227,224,230
• US Class Current: 318/786
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor

Abstract

A TRIAC, connected in series with the start winding of an induction motor, is fired in response to an average signal proportional to the speed of the rotor. The average signal is developed from a filtered control signal produced by a pick-up coil wound around one of the poles of the motor so as to sense flux variations, or slot ripple, resulting from the moving rotor teeth.

Claims

1. A control system for an induction motor with at least a pair of poles and a multi-toothed rotor and having a first winding and a second winding, comprising:

means for energizing said first winding from an alternatingcurrent source;

a bidirectional switch for connecting the source to the second winding in response to a firing signal;

means for sensing an operating characteristic of said motor and developing a control signal in response to flux variations effected by the teeth in said rotor, the control signal including a ripple frequency corresponding to movement of slots between said teeth past one of said poles;

filter means for removing from said control signal components having frequencies of the alternating current;

regulating means responsive to the filtered control signal for developing an average signal that is proportional to said ripple frequency and that is also proportional to the speed of said rotor, said regulating means including a comparator responsive To said filtered control signal for developing a control voltage representative of the ripple frequency;

said trigger means for applying said firing signal to said switch and responsive to said average signal for terminating the application of said firing signal when said speed reaches a predetermined value.

2. Apparatus as defined in claim 1 in which said comparator includes an opertional amplifier coupled between said filter means and said trigger means and exhibiting a high-pass frequency characteristic.

3. Apparatus as defined in claim 1 in which said comparator includes a logic gate coupled between said filter means and said trigger means and exhibiting a squaring function to said control signal.

4. A control system for an induction motor with at least a pair of poles and a multi-toothed rotor and having a first winding and a second winding, comprising:

means for energizing said first winding from an alternating-current source;

a bidirectional switch for connecting the source to said second winding in response to a firing signal;

means for sensing an operating characteristic of said motor and developing a control signal in response to flux variations effected by the teeth in said rotor, the control signal including a ripple frequency corresponding to movement of slots between said teeth past one of said poles;

filter means for removing from said control signal components having frequencies of the alternating current;

regulating means responsive to the filtered control signal for developing an average signal proportional to the speed of said rotor and said average signal being proportional to the frequency of said control pulses, said regulating means including means responsive to the filtered control signal for developing a square wave representative of the ripple frequency and means for differentiating said square wave to develop control pulses; and

trigger means for applying said firing signal to said switch and responsive to said average signal for terminating the application of said firing signal when said speed reaches a predetermined value.

5. Apparatus as defined in claim 4 in which said regulating means further includes a one-shot multi-vibrator responsive to said control pulses and from the output of which said average signal is developed.

6. Apparatus as defined in claim 5 in which said multi-vibrator includes an operational amplifier that exhibits a squaring function.

7. Apparatus as defined in claim 5 in which said multi-vibrator includes a pair of interacting logic gates.

8. Apparatus as defined in claim 1 in which said regulating means includes an integrator responsive to said control signal for developing said average signal.

9. Apparatus as defined in claim 8 in which said trigger means includes a comparator responsive to said average signal for developing said firing signal.

10. Apparatus as defined in claim 9 in which said comparator includes an operational amplifier coupled between said integrator and said switch and exhibiting a low-pass frequency characteristic.

11. Apparatus as defined in claim 9 in which said comparator includes a logic gate coupled between said integrator and said switch.

12. Apparatus as defined in claim 9 in which said comparator includes a zero-voltage switch responsive to said average signal and said alternating current for developing said firing signal in timed relation to zero crossings of the alternating-current power.

13. Apparatus as defined in claim 9 in which said comparator exhibits hysteresis, becoming effectively non-conductive when said speed reaches said predetermined level and again becoming effectively conductive only when said speed decreases to a significantly lower level.

14. A control system for an induction motor with at least a pair of poles and a multi-toothed rotor and having a first winding and a second winding, comprising:

means for energizing said first winding from an alternating-current source;

a bidirectional switch for connecting the source to said second winding in response to a firing signal;

means for sensing an operating characteristic of said motor to develop a control signal in response to flux variations effected by the teeth in said rotor;

filter means for removing from said control signal components having frequencies of the alternating current;

regulating means responsive to the filtered control signal for developing an average signal proportional to the speed of said rotor; and

trigger means for applying said firing signal to said switch and responsive to said average signal for terminating the application of said firing signal when said speed reaches a predetermined value; and

wherein said regulating and trigger means include logic gates intercoupled as a clocked multivibrator to develop said firing signal in response to an average of said control signal.

15. Apparatus as defined in claim 1 in which said regulating means includes a phase sensitive loop responsive to said control signal for developing said average signal.

16. A control system for an induction motor with at least a pair of poles and a multi-toothed rotor and having a first winding and a second winding, comprising:

means for energizing said first winding from an alternating-current source;

a bidirectional switch for connecting the source to said second winding in response to a firing signal;

means for sensing an operating characteristic of said motor to develop a control signal in response to flux variations effected by the teeth in said rotor;

filter means for removing from said control signal components having frequencies of the alternating current;

regulating means responsive to the filtered control signal for developing an average signal proportional to the speed of said rotor, said regulating means including a phase sensitive loop responsive to said control signal for developing said average signal, said loop includes a phase detector responsive to said control signal for developing a ripple signal, a low-pass filter responsive to said ripple signal for developing said average signal, and an oscillator responsive to said average signal for shifting the phase of said detector into lock with the phase of said control signal; and

trigger means for applying said firing signal to said switch and responsive to said average signal for terminating the application of said firing signal when said speed reaches a predetermined value.

17. Apparatus as defined in claim 16 in which said oscillator is operable only at frequencies greater than significant harmonics of the frequency of said alternating current.

18. Apparatus as defined in claim 16 in which said trigger means includes a Schmitt trigger circuit responsive to a value of said average signal only within a selected range for developing said firing signal.