Traction Motor Retarding Flux Reference

• US 20150028782A1
• Filed: 10/16/2014
• Published: 01/29/2015
• Est. Priority Date: 10/18/2012
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Crosman, Alexander Cameron III, Williams, Joshua M.
• Granted Patent: US 9,344,028 B2
• Time in Patent Office: Days
• US Class Current: 318/400.15
• CPC Class Codes: B60L 3/10 Indicating wheel slip ; Correction of wheel slip
• CPC Class Codes: H02P 21/141 Flux estimation
• CPC Class Codes: H02P 21/16 Estimation of constants, e.g. the rotor time constant
• CPC Class Codes: H02P 2205/03 Power loop, i.e. comparison of the motor power with a power reference
• CPC Class Codes: H02P 2205/05 Torque loop, i.e. comparison of the motor torque with a torque reference
• CPC Class Codes: H02P 23/0077 Characterised by the use of a particular software algorithm
• CPC Class Codes: H02P 23/14 Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility

Abstract

A traction motor system calculates motor flux by generating a real time effective resistance of a resistance grid calculated from motor torque and measured voltage on a DC link. Calculating effective resistance avoids solely relying on DC link voltage, which can be influenced by conditions such as wheel slip and drop out of one or more resistance grids. The effective resistance calculation is based on nominal motor values using known power levels and conditions. From these nominal values and the effective resistance, various scaling factors based on actual motor power can be generated and used to adjust a nominal flux reference to more accurately reflect actual motor flux. The scaling factors include power and torque scaling factors and a resistance scaling factor that is active during conditions such as wheel slip.

Claims

1. A method of adjusting electrical power application in a motor control system using an AC motor driven by an inverter bank that is coupled to a resistive grid during retard operation, the method comprising:

developing a nominal flux estimate corresponding to a DC link voltage;

adjusting the nominal flux estimate with a scale factor; and

setting inverter operation to adjust motor torque based on the adjusted flux estimate.

2. The method of claim 1, wherein the scale factor is a resistance scale factor calculated as a ratio of measured grid resistance and a base grid resistance.

3. The method of claim 2, wherein the resistance scale factor is calculated as

4. The method of claim 1, wherein adjusting the nominal flux estimate further comprises adjusting the nominal flux estimate using a power scale factor when the AC motor is operating in a constant power region.

5. The method of claim 4, wherein the power scale factor is a function of a torque times mechanical frequency vs. a characteristic torque times a corner point mechanical frequency.

6. The method of claim 1, wherein adjusting the nominal flux estimate further comprises adjusting the nominal flux estimate using a torque scale factor when the AC motor is operating in a constant torque region.

7. The method of claim 6, wherein the torque scale factor is a function of a torque vs. a characteristic torque.

8. A method of operating an AC motor driven by an inverter, the method comprising:

determining that operation of the AC motor is in a constant power region;

multiplying a DC link voltage and a power scale factor to generate an adjusted flux estimate, wherein the power scale factor is a function of a torque times mechanical frequency vs. a characteristic torque times a corner point mechanical frequency; and

setting the inverter operation to adjust motor torque based on the adjusted flux estimate.

9. The method of claim 8, further comprising:

determining that operation of the AC motor is in a constant torque region;

multiplying the DC link voltage and a torque scale factor to generate the adjusted flux estimate, wherein the torque scale factor is a function of a torque vs. a characteristic torque.

10. The method of claim 9, further comprising multiplying the DC link voltage and one of the torque scale factor or the power scale factor by a braking factor to generate the adjusted flux estimate.

11. The method of claim 10, wherein the braking factor is calculated as

12. The method of claim 9, further comprising multiplying the DC link voltage and one of the power scale factor or the torque scale factor by a resistance scale factor to generate the adjusted flux estimate.

13. The method of claim 12, wherein the resistance scale factor is calculated as

14. An alternating current (AC) motor system adapted to adjust motor flux, the system comprising:

an AC generator;

a rectifier that converts an output of the AC generator to DC power;

a DC link coupled to the rectifier;

a resistive grid selectively coupled to the DC link;

a plurality of AC motors;

a plurality of inverters, each of the plurality of inverters electrically coupling the DC link to a respective one AC motor of the plurality of AC motors;

a controller coupled to the DC link, the resistive grid, and each of the plurality of inverters, the controller including;

a processor; and

a memory storing instructions that when executed on the processor cause the controller to;

calculate an estimated flux at each inverter of the plurality of inverters; and

adjust a setting based on the estimated flux for each inverter of the plurality of inverters that controls a torque of the AC motor associated with each inverter.

15. The AC motor system of claim 14, wherein to calculate the estimated flux, the memory stores further instructions that when executed on the processor cause the controller to calculate a resistance scale factor based on an effective resistance at each inverter of the plurality of inverters, the resistance scale factor used in a calculation of the estimated flux.

16. The AC motor system of claim 15, wherein the resistance scale factor is less than one when one inverter is cut out and the remaining inverters are producing approximately equal power.

17. The AC motor system of claim 15, wherein the resistance scale factor is greater than one when all inverters are online and are producing unequal power caused by wheel slip.

18. The AC motor system of claim 14, wherein to calculate the estimated flux, the memory stores further instructions that when executed on the processor cause the controller to calculate a power scale factor based on a torque of an AC motor of the plurality of AC motors, the power scale factor used in a calculation of the estimated flux when the AC motor is operating in a constant power region.

19. The AC motor system of claim 14, wherein to calculate the estimated flux, the memory stores further instructions that when executed on the processor cause the controller to calculate a torque scale factor based on a torque of an AC motor of the plurality of AC motors, the torque scale factor used in a calculation of the estimated flux when the AC motor is operating in a constant torque region.

20. The AC motor system of claim 14, wherein to calculate the estimated flux, the memory stores further instructions that when executed on the processor cause the controller to calculate a brake factor based on a DC link voltage in propel mode at throttle level 8 and a DC link voltage in brake mode at throttle level 8, the brake factor used to calculate the estimated flux.