METHOD FOR DETECTING DETERIORATION OF PERMANENT MAGNET IN ELECTRIC MOTOR AND SYSTEM FOR THE METHOD

• US 20120187878A1
• Filed: 01/19/2012
• Published: 07/26/2012
• Est. Priority Date: 01/20/2011
• Status: Abandoned Application

• Current Assignee: Kabushiki Kaisha Toyota Jidoshokki (Toyota Motor Corporation)
• Original Assignee: Kabushiki Kaisha Toyota Jidoshokki (Toyota Motor Corporation)
• Inventors: FUKASAKU, Hiroshi, NAJIMA, Kazuki
• Application Number:
  US13/353,706
• Publication Number:
  US 20120187878A1
• Time in Patent Office: Days
• US Class Current: 318/400.21
• CPC Class Codes: G01R 33/007 Environmental aspects, e.g. temperature variations, radiation, stray fields G01R33/025 takes precedence
• CPC Class Codes: G01R 33/10 Plotting field distribution ; Measuring field distribution
• CPC Class Codes: G01R 33/1207 Testing individual magnetic storage devices, e.g. records carriers or digital storage elements functional testing G06F11/00, G06F11/28

Abstract

A method for detecting deterioration of a permanent magnet in an electric motor is characterized by peak current measuring steps and a determination step. In the first peak current measuring step, when the electric motor is started, a first pulsed voltage is applied to the multi-phase coils so as to generate magnetic flux directed in the same direction as generated by the permanent magnet and a first peak current is measured. In a second peak current measuring step, a second pulsed voltage is applied to the multi-phase coils so as to generate magnetic flux directed in the direction opposite to the direction in which magnetic flux is generated by the permanent magnet and a second peak current is measured. In a determination step, it is determined whether or not the permanent magnet is deteriorated based on the difference of the absolute value between the first and the second peak currents.

Claims

1. A method for detecting deterioration of a permanent magnet in an electric motor, the electric motor having multi-phase coils and a rotor that incorporates the permanent magnet, the method comprising:

a first peak current measuring step of applying a first pulsed voltage to the multi-phase coils so as to generate magnetic flux directed in the same direction as the magnetic flux generated by the permanent magnet and measuring a first peak current when the electric motor is started;

a second peak current measuring step of applying a second pulsed voltage to the multi-phase coils so as to generate magnetic flux directed in the direction opposite to the direction in which magnetic flux is generated by the permanent magnet and measuring a second peak current when the electric motor is started; and

a determination step of determining whether or not the permanent magnet is deteriorated based on the difference of the absolute value between the first peak current and the second peak current.

2. The method according to claim 1, wherein the method further includes, before the first peak current measuring step, a first pulse width determining step of measuring a first voltage of a power source and determining based on the first voltage a first pulse width of the first pulsed voltage to be applied to the multi-phase coils in the first peak current measuring step, and

the method further includes, before the second peak current measuring step, a second pulse width determining step of measuring a second voltage of the power source and determining based on the second voltage a second pulse width of the second pulsed voltage to be applied to the multi-phase coils in the second peak current measuring step.

3. The method according to claim 1, wherein the method further includes a rotor positioning step of flowing current through the multi-phase coils to position the rotor at a predetermined initial angular position just after the electric motor is instructed to start.

4. The method according to claim 1, wherein the method further includes a rotor initial position detecting step of detecting an angular position of the rotor just after the electric motor is instructed to start.

5. The method according to claim 1, wherein the electric motor is incorporated in a motor compressor for a vehicle air conditioner.

6. A system for detecting deterioration of a permanent magnet in an electric motor comprising:

an electric motor that has a stator core around which multi-phase coils are wound and a rotor incorporating a permanent magnet;

an inverter circuit that has a plurality of switching elements converting a direct current power from a power source into an alternating current power to be supplied to the multi-phase coils;

a current sensor that measures a current flowing through each coil or a current from the power source; and

a controller that controls ON/OFF operation of a plurality of switching elements, the controller is configured to perform the method according to claim 1.

7. The system according to claim 6, wherein the method further includes, before the first peak current measuring step, a first pulse width determining step of measuring a first voltage of a power source and determining based on the first voltage a first pulse width of the first pulsed voltage to be applied to the multi-phase coils in the first peak current measuring step, and

the method further includes, before the second peak current measuring step, a second pulse width determining step of measuring a second voltage of the power source and determining based on the second voltage a second pulse width of the second pulsed voltage to be applied to the multi-phase coils in the second peak current measuring step.

8. The system according to claim 6, wherein the method further includes a rotor positioning step of flowing current through the multi-phase coils to position the rotor at a predetermined initial angular position just after the electric motor is instructed to start.

9. The system according to claim 6, wherein the method further includes a rotor initial position detecting step of detecting an angular position of the rotor just after the electric motor is instructed to start.

10. The system according to claim 6, wherein the electric motor is incorporated in a motor compressor for a vehicle air conditioner.