Load demand and power generation balancing in direct series electric drive system

• US 20100066277A1
• Filed: 09/15/2008
• Published: 03/18/2010
• Est. Priority Date: 09/15/2008
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Bailey, Bradley
• Granted Patent: US 8,253,357 B2
• Time in Patent Office: Days
• US Class Current: 318/143
• CPC Class Codes: B60L 50/61 by batteries charged by engine-driven generators, e.g. series hybrid electric vehicles
• CPC Class Codes: Y02T 10/62 Hybrid vehicles
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• 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

Abstract

An electric drive system includes a prime mover connected to a generator (204), which is controlled in part by an excitation current. The generator (204) makes electrical power available on a dc link (312). A method of load demand and power generation balancing within the electric drive system includes determining a voltage of the dc link (312) and determining a torque command by an operator of the system. A speed for each of one or more drive motors (210) receiving power from the dc link (312) is determined and normalized to derive an average motor speed (712). A mechanical power (718) being commanded is derived based on the average motor speed (712) and the torque command. A predicted excitation current (730) that is required to achieve the derived mechanical power (718) is determined and an actual excitation current (734) is determined based on the predicted excitation current (730). The actual excitation current (734) is then applied to the generator (204).

Claims

1. A method of load demand and power generation balancing within an electric drive system, the electric drive system including a fuel-driven prime mover for driving an electrical power generator controlled at least in part by an excitation current, the electrical power generator making electrical power available on a DC link having a voltage characteristic and a current characteristic, the method comprising:

determining a voltage of the DC link;

determining a torque command by an operator of the electric drive system;

determining a speed for each of one or more drive motors receiving power from the DC link;

normalizing the determined speed to derive an average motor speed;

deriving a mechanical power that is being commanded based on the average motor speed and the torque command;

determining a predicted excitation current that is required to achieve the derived mechanical power;

determining an actual excitation current based on the predicted excitation current; and

applying the actual excitation current to the electrical power generator.

2. The method of load demand and power generation balancing according to claim 1, wherein determining the predicted excitation current that is required to achieve the derived mechanical power further comprises approximating a transient performance of the electrical power generator as the excitation current changes.

3. The method of load demand and power generation balancing according to claim 2, wherein approximating the transient performance of the electrical power generator as the excitation current changes includes applying a computational representation of the electrical power generator.

4. The method of load demand and power generation balancing according to claim 2, wherein approximating the transient performance of the electrical power generator as the excitation current changes includes applying a model-based algorithm.

5. The method of load demand and power generation balancing according to claim 2, wherein deriving the mechanical power that is being commanded based on the average motor speed and the torque command includes applying an efficiency function.

6. The method of load demand and power generation balancing according to claim 5, wherein the efficiency function determines an efficiency of each motor at the average motor speed to convert electrical power to mechanical power.

7. The method of load demand and power generation balancing according to claim 1, wherein deriving the mechanical power that is being commanded includes multiplying the average motor speed by the torque command.

8. The method of load demand and power generation balancing according to claim 1, further including using a power predictor function to determine a power available to the electric drive system based on the actual excitation current and the voltage in the DC link.

9. A controller for balancing a load demand and power generation within an electric drive system, the electric drive system including a fuel-driven prime mover for driving an electrical power generator controlled at least in part by an excitation current, the electrical power generator making electrical power available on a DC link having a voltage characteristic and a current characteristic, the controller including computer-executable instructions on a computer-readable medium, the computer-executable instructions comprising:

instructions for determining a voltage of the DC link;

instructions for determining a torque command by an operator of the electric drive system;

instructions for determining a speed for each of one or more drive motors receiving power from the DC link;

instructions for normalizing the determined speed to derive an average motor speed;

instructions for deriving a mechanical power that is being commanded based on the average motor speed and the torque command;

instructions for determining a predicted excitation current that is required to achieve the derived mechanical power;

instructions for determining an actual excitation current based on the predicted excitation current; and

instructions for applying the actual excitation current to the electrical power generator.

10. The controller for balancing the load demand and power generation according to claim 9, wherein the instructions for determining the predicted excitation current that is required to achieve the derived mechanical power further comprise instructions for approximating a transient performance of the electrical power generator as the excitation current changes.

11. The controller for balancing the load demand and power generation according to claim 10, wherein the instructions for approximating the transient performance of the electrical power generator as the excitation current changes include instructions for applying a computational representation of the electrical power generator.

12. The controller for balancing the load demand and power generation according to claim 10, wherein the instructions for approximating the transient performance of the electrical power generator as the excitation current changes include instructions for applying a model-based algorithm.

13. The controller for balancing the load demand and power generation according to claim 10, wherein the instructions for deriving the mechanical power that is being commanded based on the average motor speed and the torque command include instructions for applying an efficiency function.

14. The controller for balancing the load demand and power generation according to claim 13, wherein the efficiency function determines an efficiency of each motor at the average motor speed to convert electrical power to mechanical power.

15. The controller for balancing the load demand and power generation according to claim 9, wherein the instructions for deriving the mechanical power that is being commanded include instructions for multiplying the average motor speed by the torque command.

16. The controller for balancing the load demand and power generation according to claim 9, wherein the computer-executable instructions further include instructions for using a power predictor function to determine a power available to the electric drive system based on the actual excitation current and the voltage in the DC link.

17. A computer-readable medium having thereon computer-executable instructions for balancing a load demand and power generation within an electric drive system, the electric drive system including a fuel-driven prime mover for driving an electrical power generator controlled at least in part by an excitation current, the electrical power generator making electrical power available on a DC link having a voltage characteristic and current a characteristic, a controller including the computer-executable instructions on the computer-readable medium, the computer-executable instructions comprising:

instructions for determining a voltage of the DC link;

instructions for determining a torque command by an operator of the electric drive system;

instructions for determining a speed for each of one or more drive motors receiving power from the DC link;

instructions for normalizing the determined speed to derive an average motor speed;

instructions for deriving a mechanical power that is being commanded based on the average motor speed and the torque command;

instructions for determining a predicted excitation current that is required to achieve the derived mechanical power;

instructions for determining an actual excitation current based on the predicted excitation current; and

instructions for applying the actual excitation current to the electrical power generator.

18. The computer-readable medium according to claim 17, wherein the instructions for determining the predicted excitation current that is required to achieve the derived mechanical power further comprise instructions for approximating a transient performance of the electrical power generator as the excitation current changes by applying one of a computational representation of the electrical power generator and a model-based algorithm.

19. The computer-readable medium according to claim 17, wherein the instructions for deriving the mechanical power that is being commanded based on the average motor speed and the torque command include instructions for applying an efficiency function.

20. The computer-readable medium according to claim 17, wherein the instructions for deriving a mechanical power that is being commanded include instructions for multiplying the average motor speed by the torque command.