Excitation circuit and control method for flux switching motor

• US 6,943,510 B2
• Filed: 02/07/2003
• Issued: 09/13/2005
• Est. Priority Date: 08/06/2001
• Status: Expired due to Fees

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Gorti, Bhanu
• Primary Examiner(s): Fletcher, Marlon T.
• Assistant Examiner(s): SMITH, TYRONE W
• Application Number:
  US10/360,968
• Publication Number:
  US 20030117095A1
• Time in Patent Office: 949 Days
• Field of Search: 318/268, 318/275, 318/800, 318/801, 318430-434, 318/445, 318/798
• US Class Current: 318/275
• CPC Class Codes: H02P 25/0925 wherein the converter comprises only one switch per phase
• CPC Class Codes: H02P 6/085 in a bridge configuration
• CPC Class Codes: H02P 6/15 Controlling commutation time
• CPC Class Codes: H02P 6/20 Arrangements for starting H02P6/08 takes precedence

Abstract

An excitation circuit for a flux switching motor. The circuit includes a low-value film capacitor across the DC side of a bridge rectifier. A plurality of electronic switches are arranged in an H-bridge configuration for switching current flow through an armature winding of the motor in accordance with a PWM control scheme and single-pulse control scheme controlled by a microcontroller. A start-up diode is placed across the field winding of the motor and is electronically switched out of the circuit after a startup phase of the motor has completed. The circuit implements armature energy recirculation through the field winding during startup to promote more uniform and quicker startup of the motor. The use of a film capacitor improves the power factor of the circuit, helps to eliminate the introduction of harmonics into the AC voltage source, and helps in mitigating EMI. Reverse commutation is used to bring the motor to a quick stop when it is powered off.

Claims

1. An excitation circuit for a flux switching motor having a field winding and an armature winding, comprising:

a rectifier circuit for converting an AC input signal into a rectified AC signal;

an H-bridge switching circuit responsive to said rectified AC output and being coupled across said armature winding, said H-bridge switching circuit including a plurality of switches, at least a designated pair of said switches each having a bypass element;

an armature energy recovery capacitor coupled across an output of said switching circuit;

said bypass elements of said designated pair of switches of said H-bridge switching circuit permitting recirculation of armature current through said armature winding during a start-up phase of operation of said motor regardless of a direction of current flow through said armature winding; and

a controller for controlling on and off switching of each of said switches of said H-bridge circuit.

2. The excitation circuit of claim 1, further comprising:

a semiconductor coupled across said field winding for energy recirculation; and

a switch element controlled by said controller for switching said semiconductor across said field winding during said start-up phase of operation of said motor.

3. The excitation circuit of claim 2, wherein said switch element comprises a relay for recirculating field energy.

4. The excitation circuit of claim 1, wherein said bypass elements comprise free wheeling diodes.

5. The excitation circuit of claim 1, wherein said controller provides a pulse width modulation (PWM) switching signal to selected ones of said switches during said start-up phase of operation.

6. The excitation circuit of claim 1, wherein said controller controls said H-bridge switching circuit to effect a braking action when said motor is turned off.

7. The excitation circuit of claim 1, further comprising a capacitor of 10 ufd-15 ufd coupled across an output of said rectifier circuit.

8. The excitation circuit of claim 1, further comprising:

an on/off switch for controlling the application of said AC input signal to said excitation circuit; and

a detection circuit for detecting if said AC input signal has been applied to said excitation circuit while said on/off switch is being held by a user in an on position, and for preventing said AC input signal from starting said motor.

9. The excitation circuit of claim 8, wherein said detection circuit enables said AC input signal to be applied to said excitation circuit to start said motor only after said user has released said on/off switch from said on position into an off position.

10. The excitation circuit of claim 8, wherein said detection circuit comprises:

a rectifier circuit;

a comparator responsive to an output of said rectifier circuit; and

a latch circuit responsive to engagement of said on/off switch and an output of said comparator for generating a signal for controlling said excitation circuit to control turning on of said motor in response to a position of said on/off switch.

11. The excitation circuit of claim 10, further comprising:

a voltage divider circuit operably coupled to said rectifier circuit; and

a capacitor coupled to an input of said comparator and to said voltage divider circuit, for providing a time delay to an input signal applied to said comparator, to thereby provide a time period during which portions of said excitation circuit may be powered on so that said position of said on/off switch can be detected.

12. An excitation circuit for a flux switching motor having a field winding and an armature winding, comprising:

a rectifier circuit for converting an AC input signal into a rectified AC signal;

an H-bridge switching circuit responsive to said rectified AC output and being coupled across said armature winding;

an armature energy recovery capacitor coupled across an output of said switching circuit;

a controller for controlling an on and off switching of each of said switch components of said H-bridge circuit; and

an on/off switch operably associated with said controller and engageable by a user between an on position and an off position, for signaling said controller when a user is powering on and off said excitation circuit; and

a detection circuit responsive to said position of said on/off switch and to an application of said AC input signal to said excitation circuit for preventing immediate turn on of said excitation circuit if said AC input signal is first applied to said excitation circuit while a user is holding said on/off switch in an on position.

13. The excitation circuit of claim 12, wherein said detection circuit comprises a latching circuit responsive to the application of said AC input signal to said excitation circuit and to a position of said on/off switch;

and

said latching circuit generating a signal for preventing commutation of said flux switching motor if said user is holding said on/off switch in said on position when said AC input signal if initially applied to said excitation circuit.

14. The excitation circuit of claim 12, said H-bridge switching circuit comprising:

a plurality of bypass elements for permitting recirculation of armature current through selected switch components of said H-bridge circuit and through said armature winding during a start-up phase of operation of said motor.

15. An excitation circuit for a flux switching motor having a field winding and an armature winding, said excitation circuit comprising a rectifier circuit for receiving an AC input signal and generating a rectified AC signal over a pair of DC bus lines;

an H-bridge switching circuit coupled across said DC bus lines, said armature winding being coupled between selected ones of a plurality of switch components of said H-bridge switching circuit, at least a designated pair of said switch components each having a bypass elements associated therewith an armature recovery capacitor coupled across said DC bus lines and across said switching circuit said bypass elements of said H-bridge switching circuit permitting recirculation of armature current flowing through said armature winding during a stand-up phase of operation of said motors regardless of a direction of current flow through said armature winding; and

a controller for generating a switching signal for controlling said H-bridge switching circuit, said controller producing a pulse width modulated (PWM) switching signal for controlling said switch components.

16. The excitation circuit of claim 15, further comprising a capacitor coupled across said DC bus lines.

17. The excitation circuit of claim 15, further comprising a current bypass element coupled across said field winding during a start-up phase of operation of said motor.

18. The excitation circuit of claim 17, wherein said current bypass element comprises a diode;

and

wherein said diode is selectively switched across said field winding to provide a current path during said start-up phase.

19. The excitation circuit of claim 18, further comprising a relay responsive to said controller for selectively switching said diode across said field winding.

20. The excitation circuit of claim 15, wherein said controller controls said H-bridge circuit to implement a regenerative braking action when said motor is turned off.

21. A method for exciting a flux switching motor having a field winding and an armature winding, said method comprising providing an AC input signal from an AC power source using a rectifier to receive said AC input signal and generate a rectified AC signal on a pair of DC bus lines using an H-bridge switching circuit having a plurality of independent controllable switching elements with a designated pair of said switching elements each having a bypass elements and with said H-bridge switching circuit being operable coupled across said armature winding to selectively direct an armature current flow through said armature winding;

using said bypass elements to permit recirculation of said current flow through said armature winding via said designated pair of switching elements and said bypass elements during start-up phase of operation of said motor;

using a controller to control said H-bridge to operate said motor and to effect bi-directional recirculation of said armature current through said armature winding; and

using an armature energy recovery capacitor coupled across said H-bridge switching circuit to store armature energy during operation of said motor.

22. A method for exciting a flux switching motor having a field winding and an armature winding, said method comprising providing an AC input signal from an AC power source rectifying said AC input signal to generate a rectified AC signal;

applying said rectified AC signal to a switching circuit associated with said armature winding to alternately switch a direction of armature current flowing through said armature winding;

an H-bridge switching circuit using a plurality of bypass elements with said switching circuit to permit recirculation of said armature current flowing through said armature winding when switching the direction of said flow of said armature current through said armature winding;

using a controller to control operation of said switching circuit;

and using an energy recovery capacitor to store armature energy during operation of said switching circuit.

23. A method for controlling a flux switching motor, comprising:

defining a first start-up speed range;

defining a second start-up speed range subsequent to said first start-up speed range;

defining a first time envelope during which a pulse width modulated (PWM) switching signal having a predetermined duty cycle is to be applied to said flux switching motor;

applying said PWM switching signal, in accordance with said first time envelope, to said flux switching motor to commutate said flux switching motor during said first start-up speed range;

modifying said first time envelope to produce a second time envelope;

at a beginning of said second start-up speed range, applying said PWM switching signal in accordance with said second time envelope to continue commutating said flux switching motor.

24. The method of claim 23, wherein said first and second time envelopes are defined in relation to a pulse speed signal indicative of a motor speed of said flux switching motor.

25. The method of claim 24, wherein said second time envelope has a shorter time period than said first time envelope.

26. The method of claim 24, wherein said predetermined duty cycle of said PWM switching signal is modified during said second start-up speed range.

27. A method for commutating a flux switching motor, said method comprising:

defining a first speed range for said flux switching motor;

defining a second speed range for said flux switching motor;

applying a plurality of turn-on electrical commutation pulses to said flux switching motor during said first speed range, each of said turn on electrical commutating pulses comprising a pulse width modulated (PWM) commutating signal having a predetermined duty cycle;

said PWM commutating signal being further applied in accordance with a first predefined time envelope such that an overall time period of each of said turn-on electrical commutation pulses is controlled; and

modifying said first predefined time envelope to produce a second predefined time envelope such that said overall time period of each of said turn-on electrical commutating pulses is modified.

28. The method of claim 27, wherein said first and second predefined time envelopes are generated in relation to a motor speed signal indicative of a speed of said flux switching motor.

29. The method of claim 27, wherein said second predefined time envelope has a shorter duration than said first predefined time envelope.

30. The method of claim 27, wherein said predetermined duty cycle of said PWM commutating signal is modified during said second speed range.

31. A method for commutating a flux switching motor, comprising:

sensing a motor speed of said flux switching motor;

generating a commutating signal including a plurality of turn-on commutating pulses that are applied to said flux switching motor to commutate said motor, each said turn-on commutating pulse being comprised of a pulse width modulated (PWM) signal; and

modifying a time envelope during which each said turn-on pulse is applied to said flux switching motor in accordance with said sensed motor speed to further control the power applied to said motor as said motor increases in speed from a non-rotating condition to a condition wherein said motor is operating at a rated motor speed.

32. The method of claim 31, wherein said time envelope is reduced as said motor speed of said flux switching motor increases.

33. The method of claim 31, wherein a duty cycle of said PWM signal is modified as said motor speed of said flux switching motor increases.

34. The method of claim 31, where said PWM signal is ceased and a single turn-on pulse is applied, in accordance with said time envelope, when said flux switching motor reaches a predetermined motor speed.

35. A method for commutating an electric motor from a non-rotating condition up to a predetermined operating speed, comprising:

sensing a motor speed of said motor;

applying a pulsed, turn-on electrical commutation signal comprised of a plurality of turn-on pulses, each said turn-on pulse including a pulse width modulated (PWM) signal having a predetermined duty cycle, to said motor to commutate said motor;

further controlling said turn-on pulses by modifying a time envelope of each said turn-on pulse as said motor speed increases such that an amount of power delivered to said motor is varied as said motor speed increases.

36. The method of claim 35, further comprising modifying said predetermined duty cycle in accordance with said sensed motor speed such that said predetermined duty cycle increases in percentage as said motor speed increases.

37. The method of claim 35, further comprising ceasing generation of said PWM signal at a predetermined sensed motor speed and using a plurality of single pulses each having a period in accordance with said time envelope.

38. A power tool comprising:

an on/off switch engageable by a user for turning on and off said power a flux switching motor having a field winding and an armature winding;

an excitation circuit including;

a rectifier circuit for receiving an AC input signal and generating a rectified AC signal over a pair of DC bus lines;

an H-bridge switching circuit coupled across said DC bus lines said armature winding being coupled between selected ones of a plurality of switch components of said H-bridge switching circuit;

an armature recovery capacitor coupled across said DC bus lines and across said switching circuit said H-bridge switching circuit including a plurality of bypass elements for permitting recirculation of armature current flowing through said armature winding during a startup phase of operation of said motor; and

a controller responsive to said operation of said on/off switch for generating a pulse width modulated switching signal for controlling said H-bridge switching circuit to control on and off switching of selected ones of said switch components to commutate said motor.

39. The power tool of claim 38, further comprising a detection circuit for detecting if said on/off switch is being held by said user in an on position when an AC signal is first applied to said power tool, to prevent said flux switching motor from being turned on.

40. The power tool of claim 39, wherein said detection circuit comprises a latch circuit, said latch circuit detecting when said on/off switch has been released after said AC signal has initially been applied to said power tool, to thereafter enable said power tool to be turned on.

41. The power tool of claim 39, wherein said H-bridge switching circuit further comprises a driver circuit:

and

wherein said latch circuit applies an output signal to said driver circuit to control said H-bridge switching circuit independently of operation of said controller.

42. A power tool comprising:

an on/off switch engageable by a user for placing said tool in an on condition and an off condition;

a flux switching motor having a field winding and an armature winding, said excitation circuit comprising;

a rectifier circuit for receiving an AC input signal and generating a rectified AC signal over a pair of DC bus lines;

an H-bridge switching circuit coupled across said DC bus lines, said armature winding being coupled between selected ones of a plurality of switch components of said H-bridge switching circuit;

an armature recovery capacitor coupled across said DC bus lines and across said switching circuit; and

a controller for generating a switching signal for controlling said H-bridge switching circuit, said controller producing a pulse width modulated (PWM) switching signal for controlling selected ones of said switch components;

said power tool further including a detection circuit responsive to a position of said on/off switch for preventing powering on of said power tool if said AC input signal is initially applied to said power tool while said user is holding said on/off switch in an on position.

43. The power tool of claim 42, wherein said detection circuit includes a latching circuit responsive to said on/off switch for enabling said H-bridge switching circuit for operation independently of said controller.

44. The apparatus of claim 42, said H-bridge switching circuit further comprising:

a plurality of bypass elements for permitting recirculation of armature current flowing through said armature winding during a start-up phase of operation of said motor.