Procedure and apparatus for braking a synchronous motor

• US 5,847,533 A
• Filed: 09/28/1995
• Issued: 12/08/1998
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Kone Oyj
• Original Assignee: Kone Oyj
• Inventors: Mustalahti, Jorma, Aulanko, Esko, Hakala, Harri
• Primary Examiner(s): Ip, Paul
• Application Number:
  US08/535,515
• Time in Patent Office: 1,167 Days
• Field of Search: 318/138, 318/254, 318/245, 318/699-836
• US Class Current: 318/798
• CPC Class Codes: H02P 3/06 for stopping or slowing an individual dynamo-electric motor or dynamo-electric converter
• CPC Class Codes: H02P 6/24 Arrangements for stopping

Abstract

The invention relates to a method and an apparatus for braking a synchronous motor (2) magnetized with permanent magnets. According to the invention, there is connected to the input connectors (38,40,42) of the synchronous motor a non-linear braking resistor (60) by means of which the stator windings of the synchronous motor (2) are closed.

Claims

1. A method for braking a synchronous motor having input connectors for the supply of a voltage into its stator windings, comprising the steps of:

(a) determining whether braking is needed; and

(b) if braking is needed, then connecting at least one braking resistor having a non-linear resistance characteristic to the input connectors of the synchronous motor, thereby closing the stator windings of the synchronous motor through the at least one braking resistor,

wherein the non-linear resistance characteristic is such that a resistance value of said braking resistor increases as the voltage across the braking resistor increases.

2. The method as defined in claim 1, wherein the synchronous motor is fed by a frequency converter having an intermediate circuit, and further wherein said step (b) connects the braking resistor to the intermediate circuit of the frequency converter.

3. The method as defined in claim 1, further comprising the step of (c) shortcircuiting the stator windings when the speed of the motor is substantially zero.

4. The method as defined in claim 3, wherein the motor is magnetized with permanent magnets, and further wherein said step (b) connects the braking resistor by closing a switch controlled by the electromotive force of the motor.

5. The method as defined in claim 3, wherein the short-circuiting of said step (c) causes the braking resistor to no longer be connected to the input connectors of the synchronous motor.

6. The method as defined in claim 1, wherein said step (b) connects the at least one braking resistor by closing at least one switch.

7. The method as defined in claim 1, wherein the non-linear resistance characteristic is such that a resistance value of the braking resistor increases with increased temperature.

8. The method as defined in claim 1, wherein the motor is an elevator motor, and said step (b) slows an elevator car controlled by the elevator motor.

9. An apparatus for braking a synchronous motor provided with input connectors for the supply of a voltage into the motor'"'"'s stator windings, said apparatus comprising:

at least one braking resistor having a non-linear resistance characteristic, said at least one braking resistor being selectively connected to the input connectors of the synchronous motor; and

at least one switch for selectively connecting said at least one braking resistor to the input connectors such that the stator windings of the synchronous motor can be closed, wherein the non-linear resistance characteristic is such that a resistance value of said braking resistor increases as the voltage across said braking resistor increases.

10. The apparatus as defined in claim 9, further comprising a frequency converter provided with an intermediate circuit having d.c. conductors, said at least one braking resistor and said switch being mounted between the d.c. conductors of said intermediate circuit.

11. The apparatus as defined in claim 10, further comprising a second switch connected in parallel with said at least one braking resistor for selectively short-circuiting the stator windings of the motor.

12. The apparatus as defined in claim 10, wherein the non-linear resistance characteristic is such that a resistance value of said braking resistor increases with increased temperature.

13. The apparatus as defined in claim 9, wherein the synchronous motor is magnetized with permanent magnets, and said switch is controlled by the electromotive force of the motor.

14. The apparatus as defined in claim 9, wherein said motor is an elevator motor and said switch selectively connects said braking resistor in order to slow an elevator car controlled by the elevator motor.

15. The apparatus as defined in claim 9, wherein the non-linear resistance characteristic is such that a resistance value of said braking resistor increases with increased temperature.

16. The apparatus as defined in claim 9, further comprising:

a second braking resistor connected in series with said braking resistor and in parallel with said switch; and

a second switch for selectively connecting said second braking resistor to the input connectors of the motor.

17. The apparatus as defined in claim 16, wherein said second switch is a transistor.

18. A method for braking a synchronous motor having input connectors for the supply of a voltage into its stator windings, comprising the steps of:

(a) determining whether braking is needed; and

(b) if braking is needed, then connecting at least one braking resistor having a non-linear resistance characteristic to the input connectors of the synchronous motor, thereby closing the stator windings of the synchronous motor through the at least one braking resistor,

wherein said step (b) connects the at least one braking resistor by closing at least one switch, and

wherein there are a plurality of the braking resistors equal in number to the number of input connectors of the motor, the plurality of braking resistors being arranged in a star configuration, and further wherein said step (b) connects a respective one of the three braking resistors to a respective pair of the input connectors.

19. The method as defined in claim 18, wherein there are exactly three of the braking resistors and exactly three of the switches, and said step (b) controls the three switches such that they open and close together.

20. An apparatus for braking a synchronous motor provided with input connectors for the supply of a voltage into the motor'"'"'s stator windings, said apparatus comprising:

at least one braking resistor having a non-linear resistance characteristic, said at least one braking resistor being selectively connected to the input connectors of the synchronous motor; and

at least one switch for selectively connecting said at least one braking resistor to the input connectors such that the stator windings of the synchronous motor can be closed,

wherein there are a plurality of said braking resistors equal in number to the number of input connectors of the motor, said plurality of braking resistors being arranged in a star configuration such that a respective one of said braking resistors is selectively connected between a respective pair of the input connectors.

21. The apparatus as defined in claim 20, wherein there are exactly three of said braking resistors and exactly three of said switches.

22. The apparatus as defined in claim 21, wherein said three switches are controlled such that they open and close together.

23. A method for braking a motor having stator windings, the method comprising the steps of:

(a) supplying power to the motor in order to drive the motor;

(b) determining when braking of the motor is needed;

(c) connecting, when said step (b) determines that braking is needed, at least one braking resistor across the stator windings, the braking resistor having a resistance characteristic such that a rise in voltage across the braking resistor increases the resistance of the braking resistor.

24. The method as defined in claim 23, wherein said step (b) determines that braking is needed in response to a break in the power supplied to the motor in step (a).

25. The method as defined in claim 23, wherein the motor is an elevator motor mechanically linked to an elevator car, and said step (b) includes detecting an overspeed condition of the elevator car and determining that braking is needed when the overspeed condition of the elevator car is detected.

26. The method as defined in claim 23, wherein the resistance characteristic is a non-linear voltage-current characteristic.

27. The method as defined in claim 23, wherein the resistance characteristic is non-linear and is such that a rise in temperature increases the resistance of the braking resistance.

28. The method as defined in claim 23, wherein a plurality of the braking resistors are connected in series, and said step (c) selectively connects or short-circuits the braking resistors individually as the speed of the elevator car changes.

29. The method as defined in claim 23, wherein the motor is a synchronous motor.

30. The method as defined in claim 29, wherein the synchronous motor is mechanically liked to an elevator car such that said step (a) moves the elevator car up/down.

31. A method for minimizing sink speed of an elevator car driven by a synchronous motor, said method comprising:

(a) connecting a first braking resistance across stators of the synchronous motor when the elevator car is being braked from a first speed; and

(b) connecting a second braking resistance across the stators when the elevator car is being braked from a second speed, the second speed being slower than the first speed,

wherein the second braking resistance is lower than the first braking resistance.

32. The method as defined in claim 31, wherein the same resistor is used for the first and second braking resistances, and a voltage across the resistor is higher at the first speed than the voltages across the resistor at the second speed.

33. The method as defined in claim 31, wherein said step (b) is performed when the elevator car is released from a stopped state and no power is being supplied to the synchronous motor.

34. A method for braking an elevator car mechanically linked to an elevator motor having stator windings, the method comprising the steps of:

(a) moving the elevator car by supplying power to the motor;

(b) determining when braking of the moving elevator car is needed;

(c) connecting, when said step (b) determines that braking is needed, a braking resistance across the stator windings, the braking resistance having a non-linear resistance characteristic, wherein the braking resistance includes a plurality of series-connected resistors, and the non-linear characteristic is accomplished by selectively connecting or short-circuiting the individual resistors as the speed of the elevator car changes.