Electric Vehicle with Transient Current Management for DC-DC Converter

• US 20130187446A1
• Filed: 01/23/2012
• Published: 07/25/2013
• Est. Priority Date: 01/23/2012
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Ferrel, Mark J., DeDona, Matthew Roger
• Granted Patent: US 9,340,114 B2
• Time in Patent Office: Days
• US Class Current: 307/9.1
• CPC Class Codes: B60L 2210/12 Buck converters
• CPC Class Codes: B60L 2240/525 Temperature of converter or components thereof
• CPC Class Codes: B60L 50/16 with provision for separate direct mechanical propulsion
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility

Abstract

An electric or hybrid electric vehicle includes a battery coupled to a traction motor and a DC-DC power converter for managing transient current demands of vehicle accessories such as an electrical power assisted steering (EPAS) motor or antilock braking system (ABS) with a controller coupled to the power converter that generates a first duty cycle signal to supply current at a first level for a first time period to accommodate transient current for an EPAS, ABS, or other short duration event, and a second duty cycle signal that limits the current to a second level lower than the first level for a second time period upon expiry of the first time period to manage temperature of the converter. The controller may also generate a duty cycle signal based on measured or estimated transistor temperature of the DC-DC converter to lower the current limit when transistor temperature exceeds a threshold.

Claims

1. A vehicle comprising:

a battery coupled to a traction motor and a power converter; and

a controller coupled to the power converter that generates a first duty cycle signal to supply current at a first level for a first time period, and a second duty cycle signal that limits the current to a second level lower than the first level for a second time period upon expiry of the first time period.

2. The vehicle of claim 1 wherein the power converter comprises a DC-DC buck converter.

3. The vehicle of claim 1 further comprising:

an electric power assisted steering (EPAS) motor coupled to the power converter, wherein the first time period accommodates operation of the EPAS motor during a steering maneuver.

4. The vehicle of claim 1 further comprising:

an antilock braking system (ABS) coupled to the power converter, wherein the first time period accommodates operation of the ABS during a braking event.

5. The vehicle of claim 1 wherein the first and second time periods are based on thermal characteristics of the power converter.

6. The vehicle of claim 1 wherein the power converter includes at least one transistor and wherein the first and second time periods are determined based on temperature of the at least one transistor.

7. The vehicle of claim 6 wherein the second time period is about one-hundred times longer than the first time period.

8. The vehicle of claim 7 wherein the controller generates a zero duty cycle signal when the temperature of the at least one transistor exceeds a first threshold.

9. The vehicle of claim 8 wherein the controller generates a duty cycle signal to limit the current to a third level lower than the second level while the temperature of the at least one transistor is between the first threshold and a second threshold lower than the first threshold.

10. The vehicle of claim 9 wherein the controller maintains the duty cycle signal to limit the current to the third level until the temperature of the at least one transistor is less than a third threshold.

11. A method for controlling a vehicle having a battery powered traction motor and a power converter coupled to the battery, comprising:

generating a duty cycle control signal for the power converter to supply current at a first level for a first time period; and

generating a duty cycle control signal that limits the current to a second level lower than the first level for a second time period upon expiry of the first time period.

12. The method of claim 11 wherein the converter comprises a DC-DC buck converter.

13. The method of claim 11 further comprising:

generating a duty cycle control signal that limits the current to a third level lower than the second level while converter temperature is between a first threshold and a second threshold.

14. The method of claim 11 wherein the second time period is on the order of one-hundred times longer than the first time period.

15. The method of claim 11 further comprising performing an antilock braking system (ABS) during the first time period.

16. The method of claim 11 further comprising performing an electrical power assisted steering (EPAS) maneuver during the first time period.

17. The method of claim 11 wherein the converter includes at least one transistor, the method further comprising generating a duty cycle control signal for the power converter based on temperature of the at least one transistor.

18. The method of claim 17 wherein the temperature is estimated based on duration and level of current supplied by the power converter.

19. A method for controlling a vehicle having a battery selectively coupled to a traction motor and a DC-DC converter having an output current limited to a maximum current, comprising:

controlling a duty cycle of the DC-DC converter to limit output current to a first level below the maximum current for a first period of time when temperature of the DC-DC converter is below a first threshold and the output current exceeds a second level for a second period of time;

controlling the duty cycle of the DC-DC converter to limit output current to a second level lower than the first level when the temperature of the DC-DC converter is between the first threshold and a second threshold higher than the first threshold until the temperature of the DC-DC converter is below a third threshold; and

controlling the duty cycle of the DC-DC converter to provide substantially zero output current when the temperature of the DC-DC converter exceeds the second threshold until the temperature of the DC-DC converter is below a fourth threshold.

20. The method of claim 19 further comprising supplying current to an electric power assisted steering system during the second period of time.