Electric motor, compressor, and method for controlling electric motor or compressor

Patent metadata

Field	Value
Publication number	US-10090793-B2
Application number	US-201414580979-A
Country	US
Kind code	B2
Filing date	Dec 23, 2014
Priority date	Dec 30, 2013
Publication date	Oct 2, 2018
Grant date	Oct 2, 2018

Abstract

An electric motor, a compressor including the electric motor and a method for controlling the electric motor or the compressor are provided. The electric motor includes: a stator; single-phase or multiphase windings disposed on the stator; and a rotor, where the rotor includes a permanent magnet, and at least part of the permanent magnet is ferrite. By using a permanent magnet synchronous motor in a variable-speed compressor, costs of the variable-speed compressor are significantly reduced, and the performance thereof is basically the same as that of a variable-speed compressor using a rare-earth permanent magnet synchronous motor. By controlling the electric motor or the compressor, costs of the electric motor or the compressor are reduced, and moreover, and the ferrite in the electric motor can be protected from irreversible demagnetization at a low temperature, thereby improving the reliability of the compressor.

First claim

What is claimed is:

1. An electric motor, comprising:
a stator;
single-phase or multiphase windings disposed on the stator; and
a rotor, wherein the rotor comprises a rotor core made up of rotor laminations, a permanent magnet slot formed in the rotor core, and a permanent magnet disposed in the permanent magnet slot, and wherein at least part of the permanent magnet is ferrite;
a heating element located in the permanent magnet slot and disposed on a surface of or close to the ferrite of the rotor and operable for heating the ferrite.

2. The electric motor according to claim 1 , wherein the electric motor is a built-in permanent magnet motor.

3. The electric motor according to claim 1 , wherein the heating element is made of an electric conductive material.

4. The electric motor according to claim 3 , wherein the heating element comprises at least one of a silicon steel sheet, a magnetic iron sheet and a magnetic iron block.

5. The electric motor according to claim 1 , wherein the windings of the stator in the electric motor are operable for generating an alternating magnetic field to enable the heating element to generate heat, and the heat generated by the heating element is operable for heating the ferrite.

6. The electric motor according to claim 5 , wherein
the electric motor is connected to a drive; and
the drive is operable for applying a pulse current or a sine current to the windings of the stator to enable the windings of the stator to generate the alternating magnetic field, wherein the alternating magnetic field enables the heating element to generate an eddy current and to generate the heat.

7. The electric motor according to claim 5 , wherein
the electric motor is connected to a drive;
before the electric motor is started, the windings of the stator are operable for generating a pulsating magnetic field under the effect of a pulse current applied by the drive, wherein the pulsating magnetic field generates an eddy current in the heating element so as to generate the heat; and/or,
when the electric motor is started or is running, the windings of the stator are operable for generating a pulsating magnetic field or a high-frequency rotating magnetic field under the effect of a pulse current component or high-frequency sine current component applied by the drive, wherein the pulsating magnetic field or the high-frequency rotating magnetic field generates an eddy current in the heating element so as to generate the heat.

8. The electric motor according to claim 7 , wherein the pulse current or the pulse current component or the high-frequency sine current component applied to the windings of the stator makes a magnetic axis of the magnetic field generated by the windings of the stator substantially coincide with a magnetic axis of the rotor.

9. The electric motor according to claim 1 , wherein the ferrite has an average thickness greater than or equal to 4 mm, and less than or equal to 6 mm.

10. The electric motor according to claim 1 , wherein in an axial direction of the rotor, a rotor core formed by rotor laminations has a same length as a stator core formed by stator laminations, or the rotor core formed by the rotor laminations is longer than the stator core formed by the stator laminations.

11. The electric motor according to claim 10 , wherein in the axial direction of the rotor, a rotor core formed by rotor laminations is 6 mm to 16 mm longer than a stator core formed by stator laminations.

12. The electric motor according to claim 1 , wherein
the stator comprises: a stator core; multiple stator teeth extending inward along a radial direction of the stator; and stator slots distributed between the stator teeth;
the windings are wound on the stator teeth and operable for generating a rotating magnetic field; and
the rotor is rotatably disposed in the stator and is at a distance from the stator, the permanent magnet is disposed on the rotor to form a rotor pole.

13. The electric motor according to claim 1 , wherein the heating element is operable for generating an eddy current under affection of a heating current applied to the windings of the stator in the electric motor, and is operable for generating the heat for heating the ferrite.

14. A compressor, comprising:
a shell;
a high-pressure chamber and a low-pressure chamber within the shell; and
an electric motor according to claim 1 disposed in the low-pressure chamber.

15. A method for controlling an electric motor according to claim 1 or a compressor comprising the electric motor according to claim 1 , comprising:
obtaining a temperature of the electric motor;
searching for a maximum allowable working current of the electric motor corresponding to the temperature of the electric motor according to a relationship table between maximum allowable working currents and temperatures of the electric motor; and
controlling the electric motor or the compressor according to the maximum allowable working current of the electric motor.

16. The method according to claim 15 , wherein the controlling the electric motor or the compressor comprises:
when a working current of the electric motor is lower than a specified threshold, keeping the electric motor running normally;
when the working current of the electric motor is greater than the specified threshold and lower than the maximum allowable working current, generating an alarm but keeping the electric motor running normally; and
when the working current of the electric motor is greater than the maximum allowable working current, stopping the electric motor.

17. The method according to claim 16 , wherein the specified threshold is 90% of the maximum allowable working current.

18. The method according to claim 15 , wherein the temperature of the electric motor is determined according to at least one of a winding temperature, a rotor temperature and an ambient temperature of the electric motor.

19. The method according to claim 15 , further comprising: heating the ferrite of the rotor by the heating element.

20. The electric motor according to claim 1 , further comprising a second heating element disposed on the surface of or close to the ferrite of the rotor and operable for heating the ferrite.

21. The electric motor according to claim 1 , wherein the heating element is disposed on an upper surface of the ferrite of the rotor or a lower surface of the ferrite of the rotor.

22. The electric motor according to claim 20 , wherein the heating element and the second heating element are respectively disposed on an upper surface of the ferrite of the rotor and a lower surface of the ferrite of the rotor, or the heating element and the second heating element are respectively disposed on two side surfaces of the ferrite of the rotor.

Assignees

• Danfoss Tianjin Ltd

Inventors

• Liu Wanzhen
• Yao Li
• Lin Yan
• Wang Zhenyu

Classifications

• H02K15/125

  Heating or drying of machines in operational state, e.g. standstill heating · CPC title

• H02H7/0844

  Fail safe control, e.g. by comparing control signal and controlled current, isolating motor on commutation error · CPC title

• H02K2213/03

  Machines characterised by numerical values, ranges, mathematical expressions or similar information · CPC title

• H02K11/0094

  Structural association with other electrical or electronic devices · CPC title

• H02P29/62 Primary

  for raising the temperature of the motor · CPC title