Methods of and/or apparatus for braking an electronically commutated motor and/or laundry machines incorporating the same

• US 5,247,231 A
• Filed: 12/19/1991
• Issued: 09/21/1993
• Est. Priority Date: 12/19/1990
• Status: Expired due to Term

• Current Assignee: Fisher & Paykel Limited
• Original Assignee: Fisher & Paykel Limited
• Inventors: Glucina, Anthony P.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/810,397
• Time in Patent Office: 642 Days
• Field of Search: 318/138, 318/254, 318/375, 318/376, 318/377, 318/378, 318/379, 318/380, 318/439
• US Class Current: 318/380
• CPC Class Codes: H02P 6/24 Arrangements for stopping

Abstract

A method of braking an electronically commutated motor (ECM) by connecting a braking resistor across the motor supply rails and controlling the commutation sequences of the motor. The commutation switching devices are controlled to commutate power generated in said windings by rotation of the motor rotor to the power supply ratio. The power commutated to the supply rails is dissipated in the braking resistance to brake the motor.

Claims

1. A method of braking an electronically commutated motor (ECM) having a rotor and a stator including energisable windings, and using a power supply having an upper and a lower voltage rail, commutating circuitry to supply commutating EMF'"'"'s to said motor, commutation control means controlling at least one switching device for each said winding to selectively connect said windings between said rails, and braking switch for connecting a braking resistance between said rails, when braking is desired, said method comprising the steps of continuing to maintain voltage on said voltage rails and to supply commutating EMF'"'"'s to said motor connecting said braking resistance between said rails and controlling the commutation sequences of said motor by controlling connection of the windings of the motor to said rails by said at least one switching device for each winding in a commutation sequence so that currents flowing in said braking resistance due to back EMF'"'"'s generated in said windings and due to kinetic energy in the rotating rotor are augmented by controlling the phase relationship between the generated back EMF'"'"'s and the commutating EMF'"'"'s applied by said commutating circuitry.

2. A method as claimed in claim 1 wherein said phase relationship comprises an angular displacement of 180°

to 360°

electrical between the principal axis of the magnetic field of one of said windings connected between said rails by said at least one switching device and the principal axis of the magnetic field of said rotor.

3. A method as claimed in claim 1 which includes the step of controlling said phase relationship between said commutating EMF'"'"'s and said back EMF'"'"'s in said windings so that currents passed to said braking resistance by said back EMF'"'"'s generated are increased or decreased by controlling said commutation sequences to control said phase relationship.

4. A method as claimed in claim 1 and further includes the step of using the braking resistance having a value of resistance which is to give an acceptable compromise on braking over the speed range of the motor in use.

5. A method as claimed in any one of the claim 1 and further includes the step of using a speed dependent braking resistor as said braking resistance.

6. A method as claimed in any one of claim 1 and further includes the step of using a negative temperature coefficient resistor as said braking resistance.

7. A method as claimed in any one of the claim 1 and further includes the steps of using a plurality of individual braking resistors each connectable between said upper and lower voltage rails, sensing the speed of rotation of said motor with motor speed sensing means, and changing the value of said braking resistance by connecting said individual braking resistors between said rails individually or in combination.

8. A method as claimed in claim 1 and further includes the step of controlling said switching devices using pulse width modulation (PWM) methods such that each said switching device is switched "on" for a predetermined "on" time period and switched "off" for a predetermined "off" time period, said "on" period and said "off" period together defining a modulation time period of a predetermined duration.

9. A method as claimed in claim 8 and further includes the steps of initiating braking by connecting said braking resistance between said rails, controlling said commutating circuitry so that all said switching devices are turned "off" and using a free wheel diode associated with each switching device to pass current to said braking resistance and then, after a period of time, commencing commutation of said switching devices to cause said phase relationship between said commutating EMF'"'"'s and said back EMF'"'"'s.

10. A method as claimed in claim 9 and further includes the step of controlling said switching devices after commencement of commutation of said switching devices to increase braking by increasing the duration of said "on" time period relative to said "off" time period in said modulation time period.

11. A method as claimed in claim 8 and further includes the step of controlling the current levels flowing in said windings so that a predetermined current limit is not exceeded.

12. A method as claimed in claim 11 and further includes the steps of controlling said current levels by sensing, by use of current sensing means, the currents flowing in at least one of said upper or lower voltage rails and on the currents reaching or exceeding said predetermined current limit, passing a signal from said current sensing means to said commutating circuitry to cause said switching devices which are "on" to be switched "off" until the commencement of the next modulation period.

13. A method as claimed in claim 12 wherein said lower voltage rail is at a lower voltage than said upper voltage rail and said method includes the step of sensing currents flowing in said lower voltage rail.

14. A method as claimed in claim 12 and further includes the step of controlling currents flowing in said windings by controlling the duration of said "on" period relative to the duration of said "off" period in each said modulation period.

15. A method as claimed in claim 1 and further includes the steps of causing said commutating circuitry and said commutation control means to be supplied with power supplied by the electrical energy generated in said windings during braking of said motor.

16. A method as claimed in claim 1, said method is used for braking a spin tub and agitator assembly of a laundry machine driven by said motor, said spin tub and said agitator assembly being fixed to said rotor, at least while in spin mode.

17. A braking apparatus for braking an electronically commutated motor (ECM) having energisable windings and a rotor, said apparatus comprising a power supply means for supplying power to an upper and a lower voltage rail, commutation circuitry to supply commutating EMF'"'"'s to said motor, commutation control means, at least one switching device for each winding of said motor, said at least one switching device being controlled by said commutation control means and said commutation circuitry for selectively connecting said windings between said upper and lower rails, a braking switch, a braking resistance switchable by said braking switch to be connected between said voltage rails, said commutation control means controlling the commutation of said motor by controlling connection of the windings of the motor to said rails through appropriate said at least one switching device for each winding so that voltage is maintained on said rails and commuting EMF'"'"'s are being supplied to said motor and said braking resistance is connected between said rails, said commutation control means controls the commutation sequences of said motor by controlling connection of the windings of the motor to said rails by said at least one switching device for each winding in a commutation sequence so that currents flowing in said braking resistance due to back EMF'"'"'s generated in said windings and due to kinetic energy in the rotating rotor are augmented by controlling the phase relationship between the generated back EMF'"'"'s and the commutating EMF'"'"'s applied by said commutation circuitry.

18. Apparatus as claimed in claim 17 wherein said phase relationship comprises an angular displacement of 180°

to 360°

between the principal axis of the magnetic field of one of said windings connected between said rails by said at least one switching device and the principal axis of the magnetic field of said rotor.

19. Apparatus as claimed in claim 17 wherein said commutation control means controls said phase relationship between said commutating EMF'"'"'s and said back EMF'"'"'s in said windings so that currents passed through said braking resistance are increased or decreased by controlling said commutation sequences to control said phase relationship.

20. Apparatus as claimed in claim 19 wherein the value of said braking resistance is selected to give an acceptable compromise on braking over the speed range of the motor in use.

21. Apparatus as claimed in claim 19 wherein said braking resistance comprises a speed dependent braking resistance.

22. Apparatus as claimed in claim 19 wherein said braking resistance comprises a negative temperature coefficient resistor.

23. Apparatus as claimed in claim 19 wherein said braking resistance comprises a plurality of individual braking resistors each connectable between said upper and lower voltage rails such that said individual braking resistors are connected between said rails individually or in combination dependent on the speed of rotation of said motor to change the value of said braking resistance.

24. Apparatus as claimed in claim 19 wherein said commutation control means includes a pulse width modulation (PWM) control means to control said switching devices using PWM methods such that each said switching device is switched "on" for a predetermined "on" time period and switched "off" for a predetermined "off" time period, said "on" period and said "off" period together defining a modulation time period of a predetermined duration.

25. Apparatus as claimed in claim 24 wherein initial braking means are provided including at least one free wheel diode associated with each said switching device such that braking of said motor is initiated by controlling said commutation circuitry so that all said switching devices are turned "off" and using said free wheel diodes associated with each said switching device to pass current to said braking resistance and, after a period of time, commencing commutation of said switching devices to cause said phase relationship between said commutating EMF'"'"'s and said back EMF'"'"'s in said windings.

26. Apparatus as claimed in claim 25 wherein said PWM control means includes duty cycle control means such that after commencement of commutation of said switching devices, increased braking is effected by increasing the duration of said "on" time period relative to said "off" time period in said modulation period.

27. Apparatus as claimed in claim 24 wherein said commutation control means includes current control means to control the currents flowing in said windings so that a predetermined current limit is not exceded.

28. Apparatus as claimed in claim 27 wherein said current control means include current sensing means to sense the currents flowing in at least one of said upper or lower voltage rails such that when the currents reach or exceed said predetermined limit, said current sensing means passes a signal to said commutation circuitry to cause said switching devices which are "on" to be switched "off" until the commencement of the next modulation period.

29. Apparatus as claimed in claim 28 wherein said lower voltage rail is at a lower voltage than said upper voltage rail and said current sensing means sense currents flowing in said lower voltage rail only.

30. Apparatus as claimed in claim 28 wherein said current control means control currents flowing in said windings by controlling the duration of said "on" period relative to the duration of said "off" period in each said modulation period.

31. Apparatus as claimed in claim 19 wherein said commutation circuitry and said commutation control means are supplied with power supplied by the electrical energy generated in said windings during braking of said motor.

32. Apparatus as claimed in claim 19 which is used in a laundry machine having a cabinet, a water container within said cabinet, a spin tub within said container, an agitator within said spin tub and connected so as to be rotated back and forth by said motor and to be rotated with said spin tub when driven continuously in one direction, said agitator and said spin tub being fixed, at least during a spin cycle, to said rotor.