Electric powertrain system having bidirectional DC generator

1. An electric powertrain for use with an engine and a traction device, comprising:

a DC motor/generator operable to:

receive at least a portion of a first mechanical output from the engine and produce a DC power output; and

receive DC power and produce a second mechanical output;

a drivetrain operable to:

receive the DC power output and use the DC power output to drive the traction device; and

generate DC power when the traction device is operated in a dynamic braking mode;

an AC alternator operable to receive a portion of the first mechanical output and produce an AC power output; and

a rectifier coupled with the AC alternator, the rectifier being operable to convert the AC power output to a DC power output combinable with the DC power output of the DC motor/generator, wherein:

the engine is rated to produce a first amount of mechanical power and to receive a second amount of mechanical power, the second amount of mechanical power being less than the first amount of mechanical power;

the DC motor/generator is sized based on the second amount of mechanical power; and

the AC alternator is sized based on a difference between the first and second amounts of mechanical power.

2. The electric powertrain of claim 1 , further including a braking grid operable to dissipate as heat a portion of the DC power generated by the drivetrain.

3. The electric powertrain of claim 2 , further including a chopper operable to control an amount of DC power dissipated by the braking grid.

4. The electric powertrain of claim 1 , wherein the drivetrain includes at least one DC traction motor operable to act as a DC motor and a DC generator.

5. The electric powertrain of claim 1 , wherein the drivetrain includes:

at least one AC traction motor operable to act as an AC motor and an AC generator; and

a bidirectional power converter coupled with the at least one AC traction motor, the bidirectional power converter being operable to act as an inverter and a rectifier.

6. The electric powertrain of claim 1 , further including a controller operable to:

set the DC motor/generator to act as a DC motor;

set the DC motor/generator to act as a DC generator; and

block a current from flowing from the rectifier to the AC alternator.

7. The electric powertrain of claim 1 , wherein the AC alternator is further sized based on a frequency of the portion of the first mechanical output delivered to the AC alternator.

8. The electric powertrain of claim 1 , wherein:

the engine is rated to produce a maximum amount of mechanical power; and

the DC motor/generator is sized based on the maximum amount of mechanical power.

9. The electric powertrain of claim 1 , further including a controller operable to:

set the DC motor/generator to act as a DC motor; and

set the DC motor/generator to act as a DC generator.

10. The electric powertrain of claim 1 , further including a connection to an off-board DC power source, the connection operable to receive DC power from the off-board DC power source to supplement the generated DC power.

11. The electric powertrain of claim 10 , wherein the DC motor/generator is further operable to convert at least a portion of the DC power received from the off-board DC power source to at least a portion of the second mechanical power output.

12. An electric powertrain for use with an engine and a traction device, comprising:

a motor/generator configured to:

receive at least a portion of a first mechanical output from the engine and produce a power output; and

receive power and produce a second mechanical output;

a drivetrain configured to:

receive the power output and use the power output to drive the traction devices; and

generate power when the traction device is operated in a dynamic braking mode;

an alternator configured to receive a portion of the first mechanical output and produce an AC power output; and

a rectifier connected to the alternator, the rectifier being configured to convert the AC power output to a DC power output combinable with the power output of the motor/generator, wherein:

the engine is rated to produce a first amount of mechanical power and to receive a second amount of mechanical power, the second amount of mechanical power being less than the first amount of mechanical power;

the motor/generator has a capacity corresponding to the second amount of mechanical power; and

the alternator has a capacity corresponding to a difference between the first and second amounts of mechanical power.

13. The electric powertrain of claim 12 , wherein the capacity of the alternator further corresponds to a frequency of the portion of the first mechanical output delivered to the alternator.

14. An electric powertrain for use with an engine and a traction device, comprising:

a DC motor/generator configured to receive at least a portion of a first mechanical output from the engine and produce a DC power output, and to receive DC power and produce a second mechanical output;

at least one AC traction motor operable to act as an AC motor and an AC generator;

a bidirectional power converter coupled between the DC motor/generator and the at least one AC traction motor, the bidirectional power converter being operable to act as an inverter and a rectifier to receive the DC power output from the DC motor/generator and use the DC power output to drive the at least one traction motor, and to generate DC power directed to the DC motor/generator when the at least one AC traction motor is operated in a dynamic braking mode; and

an AC alternator operable to receive a portion of the first mechanical output and produce an AC power output, wherein:

the engine is rated to produce a first amount of mechanical power and to receive a second amount of mechanical power, the second amount of mechanical power being less than the first amount of mechanical power;

the DC motor/generator has a capacity corresponding to the second amount of mechanical power; and

the alternator has a capacity corresponding to a difference between the first and second amounts of mechanical power.

15. The electric powertrain of claim 14 , further including a braking grid operable to dissipate as heat a portion of the DC power generated by the bidirectional power converter.

16. The electric powertrain of claim 15 , further including a chopper operable to control an amount of DC power dissipated by the braking grid.

17. The electric powertrain of claim 14 , further including:

a rectifier coupled with the AC alternator, the rectifier being operable to convert the AC power output to a DC power output combinable with the DC power output of the DC motor/generator.

18. The electric powertrain of claim 14 , further including a connection to an off-board DC power source, the connection operable to receive DC power from the off-board DC power source to supplement the generated DC power.