Excitation circuit and control method for flux switching motor

• US 20030042859A1
• Filed: 08/06/2002
• Published: 03/06/2003
• Est. Priority Date: 08/06/2001
• Status: Abandoned Application

• Current Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Original Assignee: Black & Decker Incorporated (Stanley Black & Decker, Inc.)
• Inventors: Hilsher, William F., Walter, Richard T., Gorti, Bhanuprasad V.
• Application Number:
  US10/213,777
• Publication Number:
  US 20030042859A1
• Time in Patent Office: Days
• US Class Current: 318/275
• CPC Class Codes: H02P 6/085 in a bridge configuration
• 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;

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

said H-bridge switching circuit including 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; and

a controller for controlling an on and off switching of each of said switch components 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 switch components 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 film capacitor having a capacitance of between about 10 μ

fd-15 μ

fd coupled across an output of said rectifier circuit.

8. 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;

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 components for permitting recirculation of armature current flowing through said armature winding during a start-up phase of operation of said motor; 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.

9. The excitation circuit of claim 8, further comprising a film capacitor coupled across said DC bus lines.

10. The excitation circuit of claim 8, further comprising a current bypass element coupled across said field winding during a start-up phase of operation of said motor.

11. The excitation circuit of claim 10, 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.

12. The excitation circuit of claim 11, further comprising a relay responsive to said controller for selectively switching said diode across said field winding.

13. The excitation circuit of claim 8, wherein said controller controls said H-bridge circuit to implement a regenerative braking action when said motor is turned off.

14. 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 operably coupled across said armature winding to selectively direct current flow of said rectified AC signal through said armature winding;

using a plurality of bypass components associated with said H-bridge circuit to permit recirculation of said current flow through said armature winding during a start-up phase of operation of said motor;

using a controller to control said H-bridge to operate said motor; and

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

15. 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;

using a plurality of bypass components 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.

16. 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.

17. The method of claim 16, 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.

18. The method of claim 17, wherein said second time envelope has a shorter time period than said first time envelope.

19. The method of claim 17, wherein said predetermined duty cycle of said PWM switching signal is modified during said second start-up speed range.

20. 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.

21. The method of claim 20, 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.

22. The method of claim 20, wherein said second predefined time envelope has a shorter duration than said first predefined time envelope.

23. The method of claim 20, wherein said predetermined duty cycle of said PWM commutating signal is modified during said second speed range.

24. 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.

25. The method of claim 24, wherein said time envelope is reduced as said motor speed of said flux switching motor increases.

26. The method of claim 24, wherein a duty cycle of said PWM signal is modified as said motor speed of said flux switching motor increases.

27. The method of claim 24, 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.

28. 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.

29. The method of claim 28, 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.

30. The method of claim 28, 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.