Electrical machine drive method and system

• US 6,683,435 B1
• Filed: 06/21/2002
• Issued: 01/27/2004
• Est. Priority Date: 06/21/2002
• Status: Active Grant

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Motor Company
• Inventors: Liang, Feng, Huang, Henry Heping, Degner, Michael W.
• Primary Examiner(s): Leykin, Rita
• Application Number:
  US10/064,218
• Time in Patent Office: 585 Days
• Field of Search: 318/254, 318/138, 318/439, 318/801, 318/563, 318/434, 318/727
• US Class Current: 318/727
• CPC Class Codes: B60L 3/0023 Detecting, eliminating, remedying or compensating for drive train abnormalities, e.g. failures within the drive train

Abstract

An electrical machine drive system (100) includes a DC power source (102), an inverter (104) and a three-phase electrical machine (106). In response to a fault condition, power switches (122, 124) in the inverter are opened. Any short circuits are then determined by examining the phase currents of the three-phase electrical machine. If short circuits are found in the inverter, then the inverter is made balanced by shorting all upper braches (122, 126) or all lower branches (124, 128), depending on the location of the short circuit. Torque ripples are avoided by balancing the circuit during the fault mode, thereby providing comfort to a user of an electric or hybrid electric vehicle employing the electrical machine drive system.

Claims

1. A method of operating an electrical machine drive system that includes a three-phase electrical machine, and an inverter coupled to the three-phase electrical machine, the inverter including a first stage, a second stage, and a third stage, wherein the first stage is coupled to a first phase of the three-phase electrical machine, the second stage is coupled to a second phase of the three-phase electrical machine, and the third stage is coupled to a third phase of the three-phase electrical machine;

and wherein each of the first stage, the second stage and the third stage includes an upper power switch and a lower power switch and the upper power switch has an upper diode coupled across the upper power switch and the lower power switch has a lower diode coupled across the lower power switch;

the method comprising the steps of;

opening the upper power switch and the lower power switch of each of the first stage, the second stage and the third stage of the inverter; and

determining whether a diode or a power switch in the inverter is shorted.

2. The method of claim 1 further comprising the step of:

if an upper diode or an upper power switch in one of the first stage, the second stage, and the third stage is shorted, then ensuring the upper diode or the upper power switch of each of the first stage, the second stage and the third stage is shorted.

3. The method of claim 1 further comprising the step of:

if a lower diode or a lower power switch in one of the first stage, the second stage, and the third stage is shorted, then ensuring the lower diode or the lower power switch of each of the first stage, the second stage, and the third stage is shorted.

4. The method of claim 1 wherein the step of determining whether a diode or a power switch in the inverter is shorted includes the step of determining a phase current for each of the first phase, the second phase, and the third phase of the three-phase electrical machine.

5. The method of claim 4 wherein the step of determining whether a diode or a power switch in the inverter is shorted includes the step of determining whether an average phase current for each of the first phase, the second phase, and the third phase of the three-phase electrical machine is equal to, greater than, or less than zero.

6. The method of claim 5 further comprising the step of determining that a lower diode or a lower power switch of one of the first stage, the second stage and the third stage is shorted by determining that two average phase currents for two of the first phase, the second phase, and the third phase of the three-phase electrical machine are greater than or equal to zero and another average phase current of the first phase, the second phase and the third phase of the three-phase electrical machine is less than zero.

7. The method of claim 5 further comprising the step of determining that an upper diode or an upper power switch of one of the first stage, the second stage and the third stage is shorted by determining that two average phase currents for two of the first phase, the second phase, and the third phase of the three-phase electrical machine are less than or equal to zero and another average phase current of the first phase, the second phase and the third phase of the three-phase electrical machine is greater than zero.

8. The method of claim 2 wherein the step of ensuring that an upper diode or an upper power switch of each of the first stage, the second stage and the third stage is shorted includes the step of turning on the upper power switch of each of the first stage, the second stage and the third stage.

9. The method of claim 3 wherein the step of ensuring a lower diode or a lower power switch of each of the first stage, the second stage and the third stage is shorted includes the step of turning on the lower power switch of each of the first stage, the second stage and the third stage.

10. An electrical machine drive system comprising:

a three-phase electrical machine;

an inverter coupled to the three-phase electrical machine, the inverter including a first stage, a second stage, and a third stage, wherein the first stage is coupled to a first phase of the three-phase electrical machine, the second stage is coupled to a second phase of the three-phase electrical machine, and the third stage is coupled to a third phase of the three-phase electrical machine;

and wherein each of the first stage, the second stage and the third stage includes an upper power switch and a lower power switch and the upper power switch has an upper diode coupled across the upper power switch to form an upper branch and the lower power switch has a lower diode coupled across the lower power switch to form a lower branch;

a first current sensor coupled to sense a phase current of the first phase of the three-phase electrical machine;

a second current sensor coupled to sense a phase current of the second phase of the three-phase electrical machine;

a third current sensor coupled to sense a phase current of the third phase of the three-phase electrical machine; and

a control circuit coupled to control the first stage, the second stage, and the third stage of the inverter and coupled to the first current sensor, the second current sensor and the third current sensor, wherein the control circuit, in response to a fault condition;

opens the upper power switch and the lower power switch of each of the first stage, the second stage and the third stage of the inverter; and

determines whether a diode or a power switch in the inverter is shorted.

11. The system of claim 10 wherein if the upper branch in one of the first stage, the second stage, and the third stage is shorted, then the control circuit ensures the upper branch of each of the first stage, the second stage and the third stage is shorted.

12. The system of claim 10 wherein if the lower branch in one of the first stage, the second stage, and the third stage is shorted, then the control circuit ensures the lower branch of each of the first stage, the second stage, and the third stage is shorted.

13. The system of claim 10 wherein the fault condition is one of an over current condition and an over voltage condition.

14. The system of claim 10 wherein the control circuit determines whether a diode or a power switch is shorted based upon the phase current of the first phase, the phase current of the second phase and the phase current of the third phase.

15. The system of claim 12 wherein the control circuit determines that the lower branch of one of the first stage, the second stage and the third stage is shorted by determining that two average phase currents for two of the first phase, the second phase, and the third phase of the three-phase electrical machine are greater than or equal to zero and another average phase current of the first phase, the second phase and the third phase of the three-phase electrical machine is less than zero.

16. The system of claim 11 wherein the control circuit determines that the upper branch of one of the first stage, the second stage and the third stage is shorted by determining that two average phase currents for two of the first phase, the second phase, and the third phase of the three-phase electrical machine are less than or equal to zero and another average phase current of the first phase, the second phase and the third phase of the three-phase electrical machine is greater than zero.

17. The system of claim 10 wherein the control circuit comprises one of a microprocessor, a micro-controller, and a digital signal processor.

18. A method of operating an electrical machine drive system that includes a three-phase electrical machine, and an inverter coupled to the three-phase electrical machine, the inverter including a first stage, a second stage, and a third stage, wherein the first stage is coupled to a first phase of the three-phase electrical machine, the second stage is coupled to a second phase of the three-phase electrical machine, and the third stage is coupled to a third phase of the three-phase electrical machine;

and wherein each of the first stage, the second stage and the third stage includes an upper power switch and a lower power switch and the upper power switch has an upper diode coupled across the upper power switch to form an upper branch and the lower power switch has a lower diode coupled across the lower power switch to form a lower branch;

the method comprising the steps of;

opening the upper power switch and the lower power switch of each of the first stage, the second stage and the third stage of the inverter in response to a fault condition;

determining whether a diode or a power switch in the inverter is shorted; and

if the upper branch or the lower branch in one of the first stage, the second stage, and the third stage is shorted, then ensuring some other branches are shorted such that each phase current of the first phase, the second phase and the third phase is balanced.

19. The method of claim 18 wherein the upper power switch and the lower power switch of each of the first phase, the second phase and the third phase are chosen from the group consisting of bipolar transistors, MOS transistors, and field-effect transistors.

20. The method of claim 18 wherein the step of determining whether a diode or a power switch in the inverter is shorted includes the step of determining whether an average phase current for each of the first phase, the second phase, and the third phase of the three-phase electrical machine is equal to, greater than, or less than zero.