System and method for detecting motor coil-to-coil faults

• US 20060055419A1
• Filed: 09/16/2004
• Published: 03/16/2006
• Est. Priority Date: 09/16/2004
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Deere & Company
• Inventors: Hopman, Jeffrey Gerald, Boeshans, Brian Frederick, Shaw, Robert Boyd, Paulson, John David
• Granted Patent: US 7,126,368 B2
• Time in Patent Office: Days
• US Class Current: 324/765.10
• CPC Class Codes: G01R 31/343 in operation
• CPC Class Codes: H02H 11/005 in case of too low isolation resistance, too high load, short-circuit; earth fault
• CPC Class Codes: H02H 7/0833 for electric motors with control arrangements

Abstract

A system and method detects coil-to-coil faults in an electric motor having a plurality of coils. The method includes applying a square wave signal to a first coil of the motor, connecting a capacitor and a resistor between ground potential and a second coil of the motor, applying the coil output voltage to an amplifying and peak detecting circuit, applying an output of the amplifying and peak detecting circuit to the input of the control unit and, after a delay period, generating a motor fault signal if the coil output voltage is below a predetermined threshold. The square wave signal is amplified by a circuit which prevents transmission of voltage signals from the coils to the output of the control unit during normal operation of the motor.

Claims

1. A fault detection system for detecting coil-to-coil faults in an electric motor having a plurality of phase coils, the fault detection system comprising:

a driver circuit connected to a first one of the coils and applying a periodic current having a certain frequency to the coil;

a first normally open switch having a first terminal connected to a second one of the coils and having a second terminal;

a capacitor and a resistor connected between ground potential and the second terminal of the first switch;

a second normally open switch having a first terminal connected to a third one of the coils and having a second terminal connected to a ground potential; and

a control unit having a first output connected to the first switch, a second output connected to the second switch, a third output connected to the driver circuit, and an input receiving an output signal from the second one of the coils, the control unit closing the switches and causing the driver circuit to apply the periodic current to the first coil, the control unit generating a motor fault signal and preventing normal operation of the motor when the output signal is below a predetermined threshold.

2. The fault detection system of claim 1, wherein:

the control unit delays receiving the output signal from the detector/amplifier circuit until a steady-state condition exists.

3. The fault detection system of claim 1, wherein:

the driver circuit includes components which prevent transmission of voltage signals from the coils to the output of the control unit during normal operation of the motor.

4. The fault detection system of claim 1, further comprising:

an amplifier and peak detection circuit connected between the second one of the coils and the input of the control unit.

5. A fault detection system for detecting coil-to-coil faults in an electric motor having a plurality of phase coils, the fault detection system comprising:

a driver circuit connected to a first one of the coils and applying a square wave signal to the coil;

a capacitor and a resistor connected between ground potential and a second one of the coils by a first switch;

a second switch connected between ground potential and a third one of the coils;

an amplifier and peak detection circuit connected between the second one of the coils and the input of the control unit; and

a control unit having a first output coupled to the driver circuit, a second output controlling the first switch, a third output controlling the second switch, and an input receiving an output signal from the amplifier and peak detection circuit, the control unit closing both switches and causing the driver circuit to apply a periodic signal to the first one of the motor coils, the control unit generating a motor fault signal and preventing normal operation of the motor when the output signal is below a predetermined threshold.

6. The fault detection system of claim 5, wherein:

the control unit delays receiving the output signal from the detector/amplifier circuit until a steady-state condition exists.

7. The fault detection system of claim 5, wherein:

the driver circuit includes components which prevent transmission of voltage signals from the coils to the output of the control unit during normal operation of the motor.

8. The fault detection system of claim 5, wherein:

the switches comprise normally open switches.

9. A method for detecting coil-to-coil faults in an electric motor having a plurality of coils, the fault detection method comprising:

connecting a capacitor and a resistor between ground potential and a second coil of the motor;

connecting a third coil of the motor to ground potential;

applying a time-varying current having a certain frequency to a first coil of the motor;

monitoring a coil output voltage at the second coil; and

generating a motor fault signal if the coil output voltage is below a predetermined threshold.

10. The method of claim 9, further comprising:

delaying receiving the output signal from the detector/amplifier circuit until a steady-state condition exists.

11. The method of claim 9, further comprising:

preventing transmission of voltage signals from the coils to the output of the control unit during normal operation of the motor.

12. The method of claim 9, further comprising:

applying the coil output voltage to an amplifying and peak detecting circuit; and

applying an output of the amplifying and peak detecting circuit to the input of the control unit.

13. A method for detecting coil-to-coil faults in an electric motor having a plurality of coils, the fault detection method comprising:

applying a time-varying current having a certain frequency to a first coil of the motor;

connecting a capacitor and a resistor between ground potential and a second coil of the motor;

applying the coil output voltage to an amplifying and peak detecting circuit; and

applying an output of the amplifying and peak detecting circuit to the input of the control unit and

generating a motor fault signal if the coil output voltage is below a predetermined threshold.

14. The method of claim 13, further comprising:

delaying receiving the output signal from the detector/amplifier circuit until a steady-state condition exists.

15. The method of claim 13, further comprising:

preventing transmission of voltage signals from the coils to the output of the control unit during normal operation of the motor.

16. The method of claim 13, further comprising:

disconnecting the capacitor and the resistor between the ground potential and the second coil of the motor.