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A power conversion apparatus includes an interfacing circuit that enables a current source inverter to operate from a voltage energy storage device (voltage source), such as a battery, ultracapacitor or fuel cell. The interfacing circuit, also referred to as a voltage-to-current converter, transform

A power conversion apparatus includes an interfacing circuit that enables a current source inverter to operate from a voltage energy storage device (voltage source), such as a battery, ultracapacitor or fuel cell. The interfacing circuit, also referred to as a voltage-to-current converter, transforms the voltage source into a current source that feeds a DC current to a current source inverter. The voltage-to-current converter also provides means for controlling and maintaining a constant DC bus current that supplies the current source inverter. The voltage-to-current converter also enables the current source inverter to charge the voltage energy storage device, such as during dynamic braking of a hybrid electric vehicle, without the need of reversing the direction of the DC bus current.

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1. A power conversion apparatus configured to operate in one of a plurality of operational modes, the power conversion apparatus comprising: a first electric machine operable as a motor or as a generator as determined by the operational mode in which the power conversion apparatus is operating;a sec

1. A power conversion apparatus configured to operate in one of a plurality of operational modes, the power conversion apparatus comprising: a first electric machine operable as a motor or as a generator as determined by the operational mode in which the power conversion apparatus is operating;a second electric machine operable as a motor or as a generator as determined by the operational mode in which the power conversion apparatus is operating;a first current source inverter electrically connected to the first electric machine;a second current source inverter electrically connected to the second electric machine;a voltage-to-current source converter electrically connected to the first current source inverter and the second current source inverter;an energy storage device electrically connected to the voltage-to-current source converter; anda controller for determining the operational mode of the apparatus by controlling operation of the first current source inverter, the second current source inverter, and the voltage-to-current source converter. 2. The power conversion apparatus of claim 1 wherein the controller generates control signals to determine the operational mode selected from the plurality of operational modes which include: at least one operational mode in which power from the second current source inverter and the energy storage device is provided to the first current source inverter to drive the first electric machine;at least one operational mode in which power from the second current source inverter is provided to the first current source inverter to drive the first electric machine, and the energy storage device is bypassed;at least one operational mode in which power from the second current source inverter charges the energy storage device and is provided to the first current source inverter to drive the first electric machine;at least one operational mode in which power from the first current source inverter and the second current source inverter charges the energy storage device: andat least one operational mode in which power from the energy storage device is provided to the first current source inverter to drive the first electric machine and to the second current source inverter to drive the second electric machine. 3. The power conversion apparatus of claim 1 wherein the controller generates control signals to control the voltage-to-current source converter to direct flow of an electric current between the first current source inverter, the second current source inverter and the energy storage device, and wherein in a first operational mode, the electric current flows from the second current source inverter, through the energy storage device in a forward-biased direction, and into the first current source inverter,in second and third operational modes, the electric current flows from the second current source inverter into the first current source inverter, while bypassing the energy storage device, andin a fourth operational mode, the electric current flows from the second current source inverter, through the energy storage device in a reverse-biased direction to charge the energy storage device, and into the first current source inverter. 4. The power conversion apparatus of claim 3 wherein the voltage-to-current source converter comprises a pair of diodes (Da, Db) and a pair of semiconductor switches (Sa, Sb) connected in a bridge configuration, and wherein in the first operational mode, the diodes (Da, Db) are reverse-biased and the switches (Sa, Sb) are closed, and the electric current flows from the second current source inverter, through the switch (Sb), through the energy storage device, through the switch (Sa), and into the first current source inverter,in the second operational mode, the diode (Db) is reverse-biased, the diode (Da) is forward-biased, the switch (Sa) is open, the switch (Sb) is closed, and the electric current flows from the second current source inverter, through the switch (Sb), through the diode (Da), and into the first current source inverter,in the third operational mode, the diode (Db) is forward-biased, the diode (Da) is reverse-biased, the switch (Sa) is closed, the switch (Sb) is open, and the electric current flows from the second current source inverter, through the diode (Db), through the switch (Sa), and into the first current source inverter, andin the fourth operational mode, the diodes (Da, Db) are forward-biased and the switches (Sa, Sb) are open, and the electric current flows from the second current source inverter, through the diode (Db), through the energy storage device, through the diode (Da), and into the first current source inverter. 5. The power conversion apparatus of claim 1 wherein the energy storage device comprises a battery or an ultracapacitor bank. 6. The power conversion apparatus of claim 1 for providing power to an electrically powered vehicle, wherein at least one of the operational modes provides for charging the energy storage device during dynamic braking of the vehicle. 7. The power conversion apparatus of claim 1 operable with no requirement for a DC bus capacitor bank. 8. The power conversion apparatus of claim 1 wherein the first current source inverter includes six semiconductor switches controlled by the controller according to a pulse width modulation scheme to generate a sinusoidally-modulated pulse train in each of three phase currents which drive the first electric machine, andthe second current source inverter includes six semiconductor switches controlled by the controller according to a pulse width modulation scheme to generate a sinusoidally-modulated pulse train in each of three phase currents which drive the second electric machine. 9. A power conversion apparatus configured to operate in one of a plurality of operational modes, the power conversion apparatus comprising: an electric machine operable as a motor or as a generator as determined by the operational mode in which the power conversion apparatus is operating;a current source inverter electrically connected to the electric machine;a voltage-to-current source converter electrically connected to the current source inverter;an ultracapacitor bank electrically connected to the voltage-to-current source converter;a fuel cell stack electrically connected to the voltage-to-current source converter; andone or more controllers for determining the operational mode of the apparatus by controlling operation of the current source inverter, the voltage-to-current source converter, and the fuel cell stack. 10. The power conversion apparatus of claim 9 wherein the one or more controllers generate control signals to determine the operational mode selected from the plurality of operational modes which include: at least one operational mode in which power from the fuel cell stack and the ultracapacitor bank is provided to the current source inverter to drive the electric machine;at least one operational mode in which power from the fuel cell stack is provided to the current source inverter to drive the electric machine, and the ultracapacitor bank is bypassed;at least one operational mode in which power from the fuel cell stack charges the ultracapacitor bank and is provided to the current source inverter to drive the electric machine; andat least one operational mode in which power from the current source inverter and the fuel cell stack charges the ultracapacitor bank. 11. The power conversion apparatus of claim 9 wherein the one or more controllers generate control signals to determine the operational mode selected from the plurality of operational modes which include: at least one operational mode in which the fuel cell stack and the ultracapacitor bank are connected in parallel to provide power to the current source inverter to drive the electric machine;at least one operational mode in which the ultracapacitor bank alone provides power to the current source inverter to drive the electric machine;at least one operational mode in which the fuel cell stack alone provides power to the current source inverter to drive the electric machine; andat least one operational mode in which power from the current source inverter charges the ultracapacitor bank. 12. The power conversion apparatus of claim 9 wherein the fuel cell stack is electrically connected in parallel to the ultracapacitor bank through a diode. 13. The power conversion apparatus of claim 9 wherein the fuel cell stack is electrically connected in parallel to the ultracapacitor bank through a buck converter. 14. A power conversion apparatus configured to operate in one of a plurality of operational modes, the power conversion apparatus comprising: an electric machine operable as a motor or as a generator as determined by the operational mode in which the power conversion apparatus is operating;a current source inverter electrically connected to the electric machine;a voltage-to-current source converter electrically connected to the current source inverter;a fuel cell stack electrically connected to the voltage-to-current source converter; andone or more controllers for determining the operational mode of the apparatus by controlling operation of the current source inverter, the voltage-to-current source converter, and the fuel cell stack. 15. The power conversion apparatus of claim 14 wherein the one or more controllers generate control signals to determine the operational mode selected from the plurality of operational modes which include: at least one operational mode in which power from the fuel cell stack is provided to the current source inverter to drive the electric machine; andat least one operational mode in which power from the fuel cell stack is not provided to the current source inverter to drive the electric machine.