SWITCHING CIRCUIT FOR MOTOR START WINDING

• US 3,761,792 A
• Filed: 02/07/1972
• Issued: 09/25/1973
• Est. Priority Date: 02/07/1972
• Status: Expired due to Term

• Current Assignee: John A. Whitney, Richard E. Woods, William H. Hohman
• Original Assignee: John A. Whitney, Richard E. Woods, William H. Hohman
• Inventors: Whitney, John A., Woods, Richard E., Hohman, William H.
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/223,865
• Time in Patent Office: 596 Days
• Field of Search: 318/221E,221R,227
• US Class Current: 318/788
• CPC Class Codes: H02P 1/44 by phase-splitting with a capacitor

Abstract

In an AC motor having a main winding and a start winding, a thyristor in series with the start winding uncouples the start winding from an AC power source when the motor reaches a preselected cut-out speed, and recouples the start winding to the AC power source when the motor speed is reduced to a preselected cut-in speed. Various electrical characteristics are utilized to control start winding power removal and reapplication. One embodiment utilizes the change with motor speed of the phase difference of the current through the start winding relative to the applied voltage. Another embodiment utilizes the change with motor speed of the phase difference between the voltage of the start winding or start capacitor versus applied voltage. Finally, an embodiment utilizes the change with motor speed of the magnitude of the voltage induced across the start winding relative to the magnitude of applied voltage.

Claims

1. In an electric motor having a main winding and a start winding each connecTable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding to said AC source;

switch means connected between said start winding and said AC source and gatable to couple current to said start winding; and

control means for gating said switch means to cause current flow through said start winding, the phase of said current through said start winding relative to the phase of said voltage varying with motor speed, said control means including reference means for developing a reference signal related to the phase of the voltage from said AC source, and network means responsive to a predetermined change in the relative phase between said reference signal and the phase of current through said start winding for terminating the gating of said switch means.

2. The control circuit of claim 1 wherein said control means develops a monitor signal having a phase which varies with motor speed upon termination of the gating of said switch means, and cut-in means for gating said switch means to reapply power to said start winding in response to a preselected change in the relative phase between said monitor signal and said reference signal, which preselected change indicates that said motor has assumed a preselected cut-in speed.

3. The control circuit of claim 2 wherein said cut-in means is coupled to a junction between said switch means and said start winding, said junction having a voltage sum of applied voltage and voltage induced across the start winding to thereby cause said voltage sum to correspond to said monitor signal.

4. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding to said AC source;

thyristor means connected between said start winding and said AC source and gatable by a trigger signal to a conduction state to pass current to said start winding;

control means for gating said thyristor means to cause current flow through said start winding, the phase of said current through said start winding relative to the phase of said voltage varying with motor speed, said control means including reference means for developing a reference signal related to the phase of the voltage from said AC source, and network means responsive to a predetermined change in the relative phase between said reference signal and the phase of current through said start winding for terminating the gating of said thyristor means, including trigger means for generating said trigger signal in response to said reference signal having a first phase angle and for terminating said trigger signal when said reference signal has a second phase angle, coupling means for coupling said network means to said thyristor means, said predetermined change in the relative phase corresponding to a current crossover through said thyristor means which occurs at a third phase angle spaced from said first and second phase angles and not located therebetween.

5. The control circuit of claim 4 wherein said trigger means comprises continuous trigger pulse generating means enabled at said first phase angle and disabled at said second phase angle.

6. The control circuit of claim 4 wherein said trigger means comprises oscillator means for generating a pulse burst comprising a plurality of pulses, the first pulse of said burst occurring at said first phase angle and the last pulse of said burst occurring at said second phase angle.

7. The control circuit of claim 4 wherein said network means includes temporary disabling means for temporarily disabling said trigger means in response to said reference signal assuming said second phase angle, including a switching device which assumes a low impedance state to shunt said trIgger means in response to said reference signal reaching a magnitude corresponding to said second phase angle.

8. The control circuit of claim 7 wherein said reference means includes first electrical path means in parallel with said AC source for developing a first reference signal having a phase corresponding to said first phase angle, and second electrical path means in parallel with said AC source and having a different time constant than said first electrical path means for developing a second reference signal having a phase corresponding to said second phase angle, said first electrical path means being coupled to said trigger means to initiate generation of said trigger signal, said temporarily disabling means includes a thyristor means having power terminals exhibiting conductive and nonconductive states therebetween and coupled across said trigger means, said thyristor means further having a gate terminal for controlling the state of said thyristor means, said second electrical path means being coupled to said gate terminal to thereby effectively terminate said trigger signal.

9. The control circuit of claim 1 wherein a start capacitor is serially connected in circuit with said start winding and said switch means, and said reference means includes phase shift means for introducing a phase shift in said reference signal to compensate for the current phase shift introduced by said start capacitor.

10. The control circuit of claim 9 wherein said phase shift means comprises a capacitor.

11. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding in parallel with said AC source;

thyristor means having a pair of power terminals exhibiting conductive and nonconductive states therebetween under control of a gate terminal, said thyristor means reverting to the nonconductive state when a current between the pair of power terminals decreases below a minimum holding value;

start winding circuit means for connecting one of the power terminals directly to one side of said AC source and for connecting said start winding and the other of power terminals in series with the other side of said AC source to cause the phase of current through the thyristor means to be directly proportional to the phase of current through the start winding; and

control means for said thyristor means including electrical path means in parallel with said AC source for developing with reference to said one side of said AC source a reference signal having a phase fixed with respect to the phase of voltage from said AC source, and network means connected with said electrical path means and said gate terminal for controlling the state of said thyristor means in response to the relative phase difference between the phase of said start winding current and the phase of said reference signal.

12. The control circuit of claim 11 wherein said electrical path means includes first branch means having a plurality of electrical elements in series across said AC source and second branch means connected between said network means and a junction between adjacent elements in said first branch means, one of said branch means including phase shift means for causing said reference signal to have a fixed phase offset with respect to the phase of voltage from said AC source.

13. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding in parallel with said AC source;

thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate terminal, said thyristor means reverting to The nonconductive state when a current between the power terminals decreases below a minimum holding value;

start winding circuit means for connecting said start winding and said power terminals in series across said AC source to cause the phase of current through the thyristor means to be directly proportional to the phase of current through the start winding; and

control means for said thyristor means including electrical path means in parallel with said AC source for developing a reference signal having a phase fixed with respect to the phase of voltage from said AC source, network means connected with said electrical path means and said gate terminal for controlling the state of said thyristor means in response to the relative phase difference between the phase of said start winding current and the phase of said reference signal, said electrical path means includes first branch means having a plurality of electrical elements in series across said AC source and second branch means connected between said network means and a junction between adjacent elements in said first branch means, one of said branch means including phase shift means comprising a voltage breakdown device which conducts when the voltage thereacross exceeds a predetermined level, and said one branch means connects said voltage breakdown device in a series circuit to cause the reference signal to have a fixed phase lag with respect to the phase of voltage from said AC source.

14. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding in parallel with said AC source;

thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate terminal, said thyristor means reverting to the nonconductive state when a current between the power terminals decreases below a minimum holding value;

start winding circuit means for connecting said start winding and said power terminals in series across said AC source to cause the phase of current through the thyristor means to be directly proportional to the phase of current through the start winding; and

control means for said thyristor means including electrical path means in parallel with said AC source for developing a reference signal having a phase fixed with respect to the phase of voltage from said AC source, network means connected with said electrical path means and said gate terminal for controlling the state of said thyristor means in response to the relative phase difference between the phase of said start winding current and the phase of said reference signal, temperature coefficient impedance means and safety means for preventing said thyristor means from being gated into said conductive state when the impedance of said temperature coefficient impedance means changes to a predetermined value which indicates a motor overload.

15. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding in parallel with said AC source;

thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate terminal, said thyristor means reverting to the nonconductive state when a current between the power terminals decreases below a minimum holding value;

start winding circuit means for connecting said start winding and said power terminals in series across said AC source to cause the phase of current through the thyristor means to be directly proportional to the phase of current through the start winding, including a junction located between said start winding and said powEr terminals, the voltage at said junction being unclamped when said thyristor means reverts to said nonconductive state; and

control means for said thyristor means including electrical path means in parallel with said AC source for developing a reference signal having a phase fixed with respect to the phase of voltage from said AC source, and network means responsive to the relative phase difference between the phase of said start winding current and the phase of said reference signal, including a first trigger circuit connected between said electrical path means and said gate terminal for controlling the state of said thyristor means and a second trigger circuit connected between said first trigger circuit and said junction to modify control of the state of said thyristor means in response to the phase of voltage at said junction.

16. The control circuit of claim 15 wherein said second trigger circuit gates said thyristor means into said conductive state when the speed of said motor falls below a preselected cut-in speed as determined by the phase of the unclamped voltage at said junction.

17. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

main winding circuit means connecting said main winding to said AC source, switch means connected between said start winding and said AC source and gatable from a nonconductive state during which a sum voltage is developed to a conductive state which passes power to said start winding, reference means for developing a reference signal related to the phase of voltage from said AC source, and control means for controlling the state of said switch means in response to the relative phase between said sum voltage and said reference signal.

18. The control circuit of claim 17 including a start capacitor, series means connecting said start capacitor in a series path with said switch means and start winding to cause said sum voltage to lag current through said series path when said switch means is gated to said conductive state, said switch means includes a gate terminal for controlling the state of said switch means, and said control means includes impedance means coupled between a junction in said series path and said gate terminal for passing said sum voltage to said gate terminal.

19. The control circuit of claim 18 wherein said reference means comprises a series of electrical elements in series across said AC source, a voltage breakdown device which conducts when the voltage thereacross exceeds a predetermined level, and means connecting said voltage breakdown device between a junction in the series of electrical elements and said impedance means whereby said reference signal has a fixed phase lag with respect to the phase of voltage from said AC source.

20. The control circuit of claim 19 wherein said impedance means includes capacitor means charged by said sum voltage, and said reference means includes thyristor means in shunt with said capacitor means and having a gate terminal coupled to said voltage breakdown device to control the state of said thyristor means in response to the fixed phase lag reference signal.

21. The control circuit of claim 17 wherein said control means includes initial means for gating said switch means for at least a first time period, sampling means for disabling the gating of said switch means for a second time period substantially less than said first time period, and network means for terminating the gating of said switch means in response to a predetermined change in the relative phase between said reference signal and said sum voltage developed while said sampling means maintains said switch means in its nonconductive state.

22. The control circuit of claim 21 wherein said reference means includes phase shift means for causing the phase of said reference signal to lag by a fixed offset said voltage from said AC source, start winding circuit means connecting said switch means and said start winding in a series path, said control means includes monitor means coupled to a junction in said series path for developing said sum voltage when said switch means is disabled by said sampling means, and said network means comprises comparison means having a first input coupled to said reference means and a second input coupled to said monitor means for controlling the state of said switch means in response to the lag or lead of said reference signal with respect to said sum voltage.

23. The control circuit of claim 17 wherein said electric motor includes a sensor winding mutually coupled to said start winding to develop a sensor voltage having a phase following the phase of said sum voltage, and said control means comprises network means coupled to said reference means and said sensor winding for controlling the state of said switch means in response to the relative phase difference between said reference signal and said sensor voltage.

24. The control circuit of claim 23 wherein said reference means comprises first electrical path means in parallel with said AC source and second electrical path means coupled between said first electrical path means and said switch means for passing a trigger signal to gate said switch means to said conductive state, one of said path means including capacitor means, said network means includes thyristor means coupled across said capacitor means and thyristor trigger means coupled between said sensor winding and said thyristor means for gating the thyristor means to shunt said capacitor means in response to the phase of said sensor winding.

25. The control circuit of claim 17 wherein said control means includes initial means for maintaining said switch means gated to said conductive state until the motor speed exceeds a cut-out value, and cut-in means responsive to a predetermined relative phase between said reference signal and said sum voltage for gating said switch means to said conductive state to reapply power to said start winding.

26. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electrical power to the start winding, comprising:

switch means having a reference side directly connected with one side of said AC source and an opposite side connected in a series circuit with said start winding and another side of said AC source, said switch means having an on state to apply power to said start winding and produce an increase in motor speed and an off state to remove power from said start winding and develop at said opposite side a voltage sum of the applied voltage and a voltage induced across the start winding, control means for maintaining the on state of said switch means until the motor speed exceeds a cut-out value, including cut-in means coupled to the series circuit and responsive to a predetermined relative phase between said applied voltage and said voltage sum for turning on said switch means to reapply power to said start winding, said relative phase between said voltages varying with motor speed and occurring with reference to said reference side of said switch means.

27. The control circuit of claim 26 wherein said switch means comprises thyristor means having power terminals connected between said start winding and said AC source and exhibiting conductive and nonconductive states therebetween under control of a gate terminal, said control means includes reference means coupled to said AC source for developing a reference signal related to the phase of voltage from said AC source, and network means coupled between said reference means and said gate terminal for terminating the gating of said switch means in response to a predetermined change in the relative phase between said reference signal and the phase of current through the start winding, said predetermined change corresponding to said cut-out valve of motor speed.

28. The motor control circuit of claim 26 wherein said switch means comprises thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate terminal, said control means includes reference means in parallel with said AC source for developing a reference signal related to the phase of voltage from said AC source, and network means coupled to said reference means and to said series circuit for terminating a trigger signal to said gate electrode in response to a predetermined change in the relative phase between said reference signal and said voltage sum.

29. The control circuit of claim 26 wherein said switch means turns on in response to a trigger signal and turns off during a current cross-over through the switch means, said control means includes trigger means responsive to the phase of the applied voltage for generating said trigger signal with reference to said reference side of said switch means, means for effectively disabling said trigger means to maintain said switch means in an off state in response to said voltage sum being developed, and said cut-in means includes means for effectively enabling said trigger means to turn on said switch means in response to the relative phase assuming said predetermined relative phase which corresponds to said cut-in value.

30. The control circuit of claim 29 wherein said trigger means includes capacitor means connected in a charging path with reference to said reference side for generating said trigger signal when said capacitor means has a predetermined charge, said effectively disabling means comprises a semiconductor switch having on and off states and coupled in shunt with said capacitor means to disable said trigger means in response to said semiconductor switch being turned on and to enable said trigger means in response to said semiconductor switch being turned off, said effectively enabling means includes means for turning off said semiconductor switch in response to said relative phase assuming said cut-in value.

31. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

switch means connected between said start winding and said AC source and gatable to apply power to said start winding, control means for repetitively gating said switch means while said motor is below a cut-out speed to pass selected phase angles, sampling means for periodically disabling the gating of said switch means during said selected phase angles, including monitor means effective while said switch means is disabled by said sampling means for developing a signal representative of the speed of said motor, and said control means includes termination means coupled to said monitor means for terminating the gating of said switch means when said signal indicates the motor has exceeded said cut-out speed.

32. The control circuit of claim 31 wherein said sampling means includes means effective only after a plurality of cycles of voltage have been gated for disabling said switch means for a sampling interval substantially less than the interval of the gated plurality of cycles of voltage.

33. The control circuit of claim 31 wherein said control means includes start winding circuit means for connecting said start winding and said switch means in series across said AC source, reference means in parallel with said AC source for developing a reference signal related to the phase of voltage from said AC source, said monitor means being connected to a junction in said start winding circuit means for developing a voltage sum signal corresponding to the sum of applied voltage and voltage induced in said start winding, said termination means being responsive to a predetermined change in the relative phase between said reference signal and said voltage sum signal for terminating the gating of said switch means.

34. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

thyristor means having first and second power terminals with a conductive state therebetween under control of a gate signal between a gate terminal and said second power terminal;

winding circuit means connecting said AC source to said main winding and to said start winding through said power terminals including a common line directly connecting said second power terminal to one side of said AC source, first rectification means for rectifying a first alternating signal to develop with respect to said common line a first DC signal having a scalar magnitude proportional to a first characteristic, second rectification means for rectifying a second alternating signal different than said first alternating signal to develop with respect to said common line a second DC signal having a scalar magnitude proportional to a second characteristic, and scalar means coupled between said gate terminal and said first rectification means and said second rectification means for effectively generating said gate signal between said gate terminal and said one side of said AC source in response to an arithmetic sum or difference of the scalar magnitudes of said first and second DC signals.

35. The control circuit of claim 34 wherein said first rectification means is coupled across said AC source to develop a first DC voltage corresponding to the voltage of said AC source.

36. The control circuit of claim 35 wherein said winding circuit means develops at a junction an alternating voltage proportional to a speed varying voltage induced in the start winding and to the absolute magnitude of the voltage of said AC source, said second rectification means includes diode means coupled between said junction and said scalar means for rectifying the alternating voltage to develop a second DC voltage proportional to the scalar magnitude thereof, and said scalar means being responsive to the arithmetic difference of the scalar magnitudes of said first and second DC voltages.

37. The control circuit of claim 35 wherein said winding circuit means includes a start capacitor, series means including said common line for connecting said start winding, said start capacitor, and said power terminals in series across said AC source, said second rectification means includes diode means coupled between said series means and said scalar means for rectifying a voltage across said start capacitor to develop a second DC voltage, and said scalar means being responsive to the arithmetic difference of the scalar magnitudes of said first and second DC voltages.

38. The control circuit of claim 40 wherein said first rectification means includes first diode means coupled to first filtering capacitor means for developing across said first filtering capacitor means a first DC voltage corresponding to said first DC signal, said second rectification means includes second diode means coupled to second filtering capacitor means for developing across said second filtering capacitor means a second DC voltage corresponding to said second DC signal, said first and second impedance means being respectively coupled to said first and second filtering capacitor means to cause the scalar filtering capacitor means to be responsive to the voltage difference of the DC voltages across said first and second filtering capacitor means.

39. The control circuit of claim 34 wherein said winding circuit means includes resistor means serially coupling the start winding with the AC source, said start winding having a resistance distributed therethrough, which is large with respect to the resistor means, and said second rectification means includes a filteRing capacitor means connected to a junction in the first rectification means which is at a potential different than the voltage from said AC source.

40. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

switch means actuable to pass power;

winding circuit means connecting to said AC source said main winding and said start winding through said switch means, including first rectification means for rectifying a first alternating signal to develop a first DC signal having a scalar magnitude proportional to a first characteristic, second rectification means for rectifying a second alternating signal different than said first alternating signal to develop a second DC signal having a scalar magnitude proportional to a second characteristic, and scalar means for controlling actuation of said switch means in response to an arithmetic sum or difference of the scalar magnitudes of said first and second DC signals, including scalar filtering capacitor means, first impedance means coupling said first rectification means to said scalar filtering capacitor means, and second impedance means coupling said second rectification means to said scalar filtering capacitor means.

41. The control circuit of claim 38 wherein said first and second diode means are oppositely poled to charge said first and second filtering capacitor means to opposite polarities, and each of said impedance means comprise resistive means whereby said polarities are subtracted at said scalar filtering capacitor means.

42. The control circuit of claim 40 wherein said switch means comprises thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate terminal, series means connecting said start winding and said power terminals in series across said AC source to cause the phase of current through the thyristor means to be directly proportional to the phase of current through the start winding, and said scalar means includes a voltage breakdown device which conducts when the voltage thereacross exceeds a predetermined level and means connecting said voltage breakdown device in series between said gate terminal and said scalar filtering capacitor means.

43. The control circuit of claim 42 wherein said scalar means includes third diode means coupled between said series means and said second rectification means and poled to gate said thyristor means to said conductive state when the speed of said motor falls below a predetermined cut-in speed.

44. In an electric motor having a main winding and a start winding each connectable with an AC source of voltage, a control circuit for controlling the application of electric power to the start winding, comprising:

switch means actuable to pass power;

winding circuit means connecting to said AC source said main winding and said start winding through said switch means, including a start capacitor, and series means connecting said start capacitor in series with said start winding and said switch means, first diode means coupled to first filtering capacitor means for developing across said first filtering capacitor means a first DC voltage having a scalar magnitude proportional to a first alternating signal, said first diode means being connected to one side of said start capacitor, second diode means coupled to second filtering capacitor means for developing across said second filtering capacitor means a second DC voltage having a scalar magnitude proportional to a second alternating signal different than said first alternating signal, said second diode means being connected to the opposite side of said start capacitor, and scalar means coupled to said first capacitor means and said second capacitor means for controlling actuation of said switch means in response to an arithmetic sum or diffeRence of the scalar magnitudes of said first and second DC voltages.

45. The control circuit of claim 44 wherein said winding circuit means includes resistor means shunting said sides of said start capacitor to which said first and second diode means are connected in said series means.