Electric drive system having DC bus voltage control

• US 7,298,102 B2
• Filed: 10/29/2004
• Issued: 11/20/2007
• Est. Priority Date: 05/25/2004
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Guven, Mustafa, Sopko, Tom, Kuras, Brian
• Primary Examiner(s): IP, SHIK LUEN PAUL
• Application Number:
  US10/977,293
• Publication Number:
  US 20050263331A1
• Time in Patent Office: 1,117 Days
• Field of Search: 318140-149, 318/139, 318/439, 320/104, 320/149, 320/150, 123/179.3, 180/65.1
• US Class Current: 318/139
• CPC Class Codes: B60K 6/46 Series type
• CPC Class Codes: B60L 2200/40 Working vehicles
• CPC Class Codes: B60L 2220/18 Reluctance machines
• CPC Class Codes: B60L 50/61 by batteries charged by engine-driven generators, e.g. series hybrid electric vehicles
• CPC Class Codes: B60W 10/08 including control of electric propulsion units, e.g. motors or generators
• CPC Class Codes: B60W 10/26 for electrical energy, e.g. batteries or capacitors
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60W 20/10 Controlling the power contribution of each of the prime movers to meet required power demand
• CPC Class Codes: B60W 2300/17 Construction vehicles, e.g. graders, excavators
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02T 10/62 Hybrid vehicles
• 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 90/16 Information or communication technologies improving the operation of electric vehicles

Abstract

An electric drive system has a power source and a generator operatively connected to the power source. The electric drive system also has at least one energy storage device such as a capacitor configured to store a supply of power. The electric drive system further has a common bus configured to direct the power output to the capacitor. The electric drive system also has at least one motor configured to receive power from the common bus. A controller for the electric drive system is provided, having an article therewith having a computer readable medium with a control algorithm recorded thereon. The control algorithm includes means for compensating for a change in power demand on a DC bus of the electric drive system.

Claims

1. A controller for an electric drive system in a work machine comprising an article that includes a computer readable medium having a control algorithm recorded thereon;

said controller being configured via said control algorithm to compensate for a change in requested power demand on a DC bus of the electric drive system having an electric motor and a generator separate from the electric motor connected therewith, wherein said controller includes;

means for determining a change in requested power demand on said DC bus; and

means for compensating for the change in requested power demand via at least one of the generator and an energy storage device, including means for commanding a current change at a DC to DC converter coupling the energy storage device with said DC bus and means for commanding a power output change of said generator;

said means for compensating further including means for compensating for the change in power demand primarily via the energy storage device rather than the generator, if a stored energy of said energy storage device is within a predetermined middle range.

2. The controller of claim 1 wherein said controller further comprises means for determining whether a stored energy of said energy storage device is within said predetermined middle range, an upper range or a lower range, and wherein said means for compensating includes means for compensating for a change in motor loading on said DC bus via commanding a current change at said DC to DC converter where the stored energy is within said middle, upper or lower range.

3. The controller of claim 2 wherein said means for compensating includes means for commanding a change in power output of said generator to said DC bus such that the change in power demand is compensated for at least partially by said generator, if the stored energy of said energy storage device is outside of said predetermined middle range.

4. The controller of claim 3 wherein said means for compensating includes means for commanding a change in power output of said generator to said DC bus such that the change in power demand is compensated for in part by said generator and in part by said energy storage device, if the stored energy of said energy storage device is outside of said predetermined middle range but within the predetermined upper or lower ranges.

5. The controller of claim 4 wherein said energy storage device comprises a capacitor, and wherein said means for commanding further includes means for sending commands for at least one of said capacitor and said generator simultaneous with determining a change in requested power demand on said DC bus based on the change in motor loading.

6. The controller of claim 5 wherein said means for compensating includes means for commanding increasing a power output of said generator to said DC bus, if the stored energy of said energy storage device is within or below said predetermined lower range.

7. The controller of claim 6 wherein said means for compensating includes means for commanding decreasing a power output of said generator to said DC bus, if the stored energy of said energy storage device is within or above said predetermined upper range.

8. The controller of claim 4 wherein said energy storage device comprises a capacitor, and wherein said controller further includes means for returning the stored energy of said energy storage device toward a target quantity of stored energy via at least one of the motor and the generator, if the stored energy of said energy storage device is outside the predetermined middle range, at least in part via commanding a current change at said DC to DC converter.

9. The controller of claim 8 wherein said means for returning includes means for commanding a generator output change and a current change at said DC to DC converter to drive the stored energy of the energy storage device toward said predetermined middle range.

10. The controller of claim 9 wherein said means for returning includes means for commanding a current change at said DC to DC converter to lower a quantity of stored energy of said energy storage device, if the stored energy of said energy storage device is above said predetermined middle range.

11. The controller of claim 9 wherein said means for returning includes means for selectively commanding a decrease in power output of said generator to offset in said DC bus at least a portion of stored energy discharged to said DC bus by said energy storage device.

12. An electric drive system for a work machine comprising:

a DC bus;

an energy storage device configured to supply power to and absorb power from said DC bus;

a generator configured to supply power to and absorb power from said DC bus;

a motor separate from said generator and configured to supply power to and absorb power from said DC bus;

a DC to DC converter coupling said energy storage device with said DC bus;

an electronic control module operable to control a voltage of said DC bus, said electronic control module including means for determining a quantity of stored energy of said energy storage device, means for determining a requested change in power demand on the DC bus, and means for compensating for the change in requested power demand on said DC bus, said means for compensating including means for commanding a current at said DC to DC converter, and means for commanding a power output of said generator;

said electronic control module further being operable via said means for compensating to partition a power flow among said generator, said motor and said energy storage device, at least in part via current commands to said DC to DC converter to control current flow into and out of said DC bus which are based at least in part on the determined quantity of stored energy of said energy storage device.

13. A method of controlling a power supply to a DC bus in an electric drive system having a generator and a motor separate from the generator coupled with the DC bus, said method comprising the step of:

determining a quantity of stored energy of an energy storage device coupled with the DC bus;

determining a requested change in power demand on the DC bus based on a change in motor loading on the DC bus; and

compensating for the requested change in power demand on the DC bus at least in part with the energy storage device by commanding a current flow at a DC to DC converter coupling the energy storage device with the DC bus, if a stored energy of the energy storage device is within a predetermined middle range.

14. The method of claim 13 wherein the step of compensating for the change in power demand on the DC bus comprises:

compensating for the change in power demand at least in part with the generator, including commanding a power output of the generator based on the determined quantity of stored energy of the energy storage device.

15. The method of claim 13 wherein:

the step of determining a quantity of stored energy of the energy storage device further comprises determining whether the quantity of stored energy is within the predetermined middle ranges, a predetermined upper range, or a predetermined lower range;

the step of compensating for the change in power demand on the DC bus further comprises;

compensating for the change in power demand on the DC bus primarily with the energy storage device, if the quantity of stored energy is within the predetermined middle range, and compensating for the change in power demand on the DC bus at least in part with the generator, if the stored energy of the energy storage device is outside of the predetermined middle range.

16. The method of claim 13 wherein the step of compensating for the change in power demand on the DC bus further comprises:

compensating for the change in power demand on the DC bus in part with the generator and in part with the energy storage device, if the stored energy of the energy storage device is outside of the predetermined middle range but within one of a predetermined upper or lower range.

17. The method of claim 16 wherein the step of compensating for the change in power demand on the DC bus further comprises:

compensating for the change in power demand solely with the generator, if the stored energy of the energy storage device is outside of the predetermined middle, upper and lower ranges.

18. The method of claim 17 wherein the energy storage device comprises a capacitor, the method further comprising the step of:

returning the stored energy of the energy storage device toward a target quantity of stored energy at least in part by commanding a current flow at the DC to DC converter, if the stored energy of the energy storage device is outside the predetermined middle range.

19. The method of claim 18 wherein the step of returning the stored energy of the energy storage device toward a target quantity comprises adjusting the power output or rate of change in the power output of the generator, if the stored energy of the energy storage device is outside the predetermined middle range.