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A multi-energy storage device system includes an electric drive coupled to a load, a DC link coupled to the electric drive, and a bi-directional voltage converter having an output channel coupled to the DC link and an input channel. A first energy storage device (ESD) is coupled to the input channel

A multi-energy storage device system includes an electric drive coupled to a load, a DC link coupled to the electric drive, and a bi-directional voltage converter having an output channel coupled to the DC link and an input channel. A first energy storage device (ESD) is coupled to the input channel, and a switch is coupled to the DC link and to a second ESD. A system controller causes the switch to couple the second ESD to the DC link for delivering energy stored in the second ESD to the electric drive. The system controller also causes the voltage converter to convert a voltage of the first ESD to a higher voltage and to deliver the higher voltage to the DC link, wherein the higher voltage is greater than the voltage of the second ESD and causes the switch to decouple the second ESD from the DC link.

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1. A multi-energy storage device system comprising: an electric drive coupled to a load;a direct current (DC) link coupled to the electric drive;a bi-directional voltage converter comprising an output channel coupled to the DC link and comprising an input channel;a first energy storage device couple

1. A multi-energy storage device system comprising: an electric drive coupled to a load;a direct current (DC) link coupled to the electric drive;a bi-directional voltage converter comprising an output channel coupled to the DC link and comprising an input channel;a first energy storage device coupled to the input channel of the bi-directional voltage converter;a switch coupled to the DC link;a second energy storage device coupled to the switch; anda system controller configured to: send a signal to the switch to couple the second energy storage device to the DC link such that energy stored in the second energy storage device is delivered to the electric drive and such that a voltage of the second energy storage device is reduced as the energy stored therein is delivered to the electric drive; andcause the bi-directional voltage converter to convert a voltage of the first energy storage device to a higher voltage and to deliver the higher voltage to the DC link, wherein the higher voltage is greater than the voltage of the second energy storage device and causes the switch to decouple the second energy storage device from the DC link. 2. The system of claim 1 wherein the system controller is further configured to: cause the switch to couple the second energy storage device to the DC link such that energy generated in the electric drive is delivered to the second energy storage device and such that a voltage of the second energy storage device is increased as the energy is delivered thereto from the electric drive; andcause the bi-directional voltage converter to lower a current flowing through the switch to cause the switch to decouple the second energy storage device from the DC link. 3. The system of claim 1 wherein the system controller is further configured to: cause the switch to couple the second energy storage device to the DC link such that energy generated in the electric drive is delivered to the second energy storage device and such that a voltage of the second energy storage device is increased as the energy is delivered thereto from the electric drive; andcause the inverter to lower a voltage on the DC link to a voltage lower than a voltage of the second energy storage device to cause the switch to decouple the second energy storage device from the DC link. 4. The system of claim 1 further comprising a dynamic retarder coupled to the DC link; and wherein the system controller is further configured to: cause the switch to couple the second energy storage device to the DC link such that energy generated in the electric drive is delivered to the second energy storage device and such that a voltage of the second energy storage device is increased as the energy is delivered thereto from the electric drive; andcause the dynamic retarder to lower a current flowing through the switch to cause the switch to decouple the second energy storage device from the DC link. 5. The system of claim 4 wherein the dynamic retarder comprises: a resistor; anda switching device. 6. The system of claim 1 wherein the switch comprises a pair of silicon controlled rectifiers coupled together and arranged in an anti-parallel configuration. 7. The system of claim 1 further comprising a charge circuit coupled to the second energy storage device; and wherein the system controller is further configured to cause the charge circuit to increase the voltage of the second energy storage device if the second energy storage device is decoupled from the DC link. 8. The system of claim 7 wherein the charge circuit is further coupled to the DC link and configured to convert a voltage of the DC link to a charging voltage and to supply the charging voltage to the second energy storage device to increase the voltage thereof. 9. The system of claim 7 wherein the charge circuit is further coupled to the first energy storage system and configured to convert a voltage of the first energy storage system to a charging voltage and to supply the charging voltage to the second energy storage device to increase the voltage thereof. 10. The system of claim 1 wherein the system controller is further configured to cause the bi-directional voltage converter to boost a voltage from the first energy storage device and to supply the boosted voltage to the DC link prior to causing the switch to couple the second energy storage device to the DC link, wherein the boosted voltage is substantially equal to a voltage of the second energy storage device. 11. The system of claim 1 wherein the first energy storage device comprises a battery; and wherein the second energy storage device comprises an ultracapacitor comprising a plurality of series- and parallel-connected capacitor cells, each capacitor cell having a capacitance greater than 100 Farads. 12. A method of assembling a propulsion energy system, the method comprising: coupling an output channel of a bi-directional voltage converter assembly to a direct current (DC) link, the bi-directional voltage converter assembly comprising a first bi-directional voltage converter;coupling a first energy storage device to a first input channel of the bi-directional voltage converter assembly;coupling a switch to the DC link;coupling second energy storage device to the switch;coupling a load to the DC link, the load configured to receive energy from one of the first energy storage device and the second energy storage device via the DC link;coupling a controller to the bi-directional voltage converter assembly and to the switch; andconfiguring the controller to: send a signal to the switch to couple the second energy storage device to the DC link such that energy stored in the second energy storage device is delivered to the load and such that a voltage of the second energy storage device is reduced as the energy stored therein is delivered to the load; andcause the bi-directional voltage converter to convert a voltage of the first energy storage device to a higher voltage and to deliver the higher voltage to the DC link, wherein the higher voltage is greater than the voltage of the second energy storage device and causes the switch to decouple the second energy storage device from the DC link. 13. The method of claim 12 further comprising configuring the controller to set a voltage of the DC link via boost control of the voltage of the first energy storage device. 14. The method of claim 12 wherein the first energy storage device comprises a battery; and wherein the second energy storage device comprises an ultracapacitor. 15. The method of claim 14 wherein the ultracapacitor is configured to provide a higher power than the battery. 16. The method of claim 12 further comprising: coupling a dynamic retarder to the DC link; andconfiguring the controller to: cause the load to operate in a regenerative braking mode and to supply a regenerative braking voltage to the DC link;cause the switch to couple the second energy storage device to the DC link such that the regenerative braking voltage is delivered to the second energy storage device and such that a voltage of the second energy storage device is increased as the regenerative braking voltage is delivered thereto; andcause the dynamic retarder to lower a current flowing through the switch to cause the switch to decouple the second energy storage device from the DC link. 17. The method of claim 12 wherein coupling the switch to the DC link comprises coupling a pair of silicon controlled rectifiers arranged in an anti-parallel configuration to the DC link. 18. The method of claim 12 further comprising coupling a charge circuit the second energy storage device; and configuring the controller to cause the charge circuit to increase the voltage of the second energy storage device if the second energy storage device is decoupled from the DC link. 19. A non-transitory computer readable storage medium having a computer program stored thereon and representing a set of instructions that when executed by a computer causes the computer to: send a signal to a first switch to transfer a voltage stored in a second energy storage device to a direct current (DC) link coupled to a load such that the voltage stored in the second energy storage device is delivered to the load as a voltage of the second energy storage device is reduced; andcontrol a bi-directional voltage converter to convert a first voltage of a first energy storage device to a second voltage and to deliver the second voltage to the DC link, wherein the second voltage is greater than the voltage of the second energy storage device and causes the first switch to deactivate. 20. The computer readable storage medium of claim 19 wherein the set of instructions further causes the computer to: activate the first switch to transfer a voltage on the DC link generated by the load to the second energy storage device such that the voltage of the second energy storage device is increased; andactivate a dynamic retarder switch in a dynamic retarder coupled to the DC link to reduce a current flowing through the switch to a level less than a holding current of the first to deactivate the first switch. 21. The computer readable storage medium of claim 20 wherein the set of instructions further causes the computer to activate a charge circuit coupled to the second energy storage device when the second energy storage device is decoupled from the DC link to cause the charge circuit to increase the voltage of the second energy storage device.