Vehicle with electrical machine and method for operating the same

1. A vehicle, comprising:

a multi-phase electrical machine, the multi-phase electrical machine comprising a rotor, a first stator system and a second stator system;

a first onboard electrical sub-system having a first nominal DC voltage;

a second onboard electrical sub-system having a second nominal DC voltage;

wherein the first onboard electrical sub-system comprises a first inverter with a first link capacitor, the first stator system being associated with the first inverter;

wherein the second onboard electrical sub-system comprises a second inverter with a second link capacitor, the second stator system being associated with the second inverter;

wherein the first stator system is in a star configuration, the second stator system is in a star or delta configuration, and the first stator system has a higher impedance than the second stator system based on a number of windings in the first stator system and a number of windings in the second stator system, wherein the first stator system is configured to use a lower voltage on average and higher currents on average than the second stator system; and

a transfer circuit electrically coupling a star point of the first stator system in the star configuration to a higher potential of the second onboard electrical sub-system, the transfer circuit being disposed along an electrical path connecting the star point of the first stator system to a higher potential of the second inverter.

2. The vehicle according to claim 1 , wherein:

the transfer circuit comprises a first diode and a second diode, the first diode and the second diode being counter-switched and connected in series.

3. The vehicle according to claim 2 , wherein:

the transfer circuit comprises a first switch connected in parallel with the first diode.

4. The vehicle according to claim 3 , wherein:

the first inverter has three high-side switches and three low-side switches,

the second inverter has three high-side switches and three low-side switches,

the three high-side switches of the first inverter and the three low-side switches of the first inverter are controllable via pulse-width modulation,

the three high-side switches of the second inverter and the three low-side switches of the second inverter are controllable via pulse-width modulation, and

the electrical machine is operable as a motor or a generator when the first switch is open or if the second switch is open, and the electrical machine is operable in a mixed mode via pulse-width modulation control of the high-side switches and the low-side switches of the first and second inverters.

5. The vehicle according to claim 3 , wherein:

the first nominal voltage exceeds the second nominal voltage in a higher nominal voltage direction, and

when the rotor of the electrical machine is stationary, the electrical machine is operable as a DC step-down converter between the first onboard electrical sub-system and the second onboard electrical sub-system.

6. The vehicle according to claim 2 , wherein:

the transfer circuit comprises a second switch connected in parallel with the first diode.

7. The vehicle according to claim 6 , wherein:

the first inverter has three high-side switches and three low-side switches,

the second inverter has three high-side switches and three low-side switches,

the three high-side switches of the first inverter and the three low-side switches of the first inverter are controllable via pulse-width modulation,

the three high-side switches of the second inverter and the three low-side switches of the second inverter are controllable via pulse-width modulation, and

the electrical machine is operable as a motor or a generator when the first switch is open or if the second switch is open, and the electrical machine is operable in a mixed mode via pulse-width modulation control of the high-side switches and the low-side switches of the first and second inverters.

8. The vehicle according to claim 6 , wherein:

the first nominal voltage exceeds the second nominal voltage in a higher nominal voltage direction, and

when the rotor of the electrical machine is stationary, the electrical machine is operable as a DC step-down converter between the first onboard electrical sub-system and the second onboard electrical sub-system.

9. The vehicle according to claim 6 , wherein:

the first nominal voltage exceeds the second nominal voltage in a higher nominal voltage direction, and

when the rotor of the electrical machine is stationary, the electrical machine is operable as a DC step-up converter from the second onboard electrical sub-system to the first onboard electrical sub-system.

10. The vehicle according to claim 2 , wherein:

the transfer circuit comprises a first switch connected in parallel with the first diode, and

the transfer circuit comprises a second switch connected in parallel with the first diode.

11. The vehicle according to claim 10 , wherein:

the first inverter has three high-side switches and three low-side switches,

the second inverter has three high-side switches and three low-side switches,

the three high-side switches of the first inverter and the three low-side switches of the first inverter are controllable via pulse-width modulation,

the three high-side switches of the second inverter and the three low-side switches of the second inverter are controllable via pulse-width modulation, and

the electrical machine is operable as a motor or generator when the first switch is open and if the second switch is open, or the electrical machine is operable in a mixed mode through pulse width-modulated control of the high-side switches and low-side switches of the first and second inverters.

12. The vehicle according to claim 10 , wherein:

the first nominal voltage exceeds the second nominal voltage in a higher nominal voltage direction, and

when the rotor of the electrical machine is stationary, the electrical machine is operable as a DC step-down converter between the first onboard electrical sub-system and the second onboard electrical sub-system.

13. The vehicle according to claim 2 , wherein the transfer circuit comprises only one switch, which is connected in parallel with the first diode.

14. The vehicle according to claim 1 , wherein the second stator system is in the delta configuration and the transfer circuit is connected between the star point of the first stator system and a delta point in the second stator system.

15. A method of operating a vehicle comprising:

a multi-phase electrical machine, the multi-phase electrical machine comprising a rotor, a first stator system and a second stator system;

a first onboard electrical sub-system having a first nominal DC voltage;

a second onboard electrical sub-system having a second nominal DC voltage;

wherein the first onboard electrical sub-system comprises a first inverter with a first link capacitor, the first stator system being associated with the first inverter;

wherein the second onboard electrical sub-system comprises a second inverter with a second link capacitor, the second stator system being associated with the second inverter;

wherein the first stator system is in a star configuration, the second stator system is in a star or delta configuration, and the first stator system has a higher impedance than the second stator system based on a number of windings in the first stator system and a number of windings in the second stator system, wherein the first stator system is configured to use a lower voltage on average and higher currents on average than the second stator system; and

a transfer circuit electrically coupling a star point of the first stator system in the star configuration to a higher potential of the second onboard electrical sub-system, the transfer circuit being disposed along an electrical path connecting the star point of the first stator system to a higher potential of the second inverter, wherein

the transfer circuit comprises a first diode and a second diode, the first diode and the second diode being counter-switched and connected in series,

the transfer circuit comprises a first switch connected in parallel with the first diode,

the first nominal voltage exceeds the second nominal voltage in a higher nominal voltage direction, and

when the rotor of the electrical machine is stationary, the electrical machine is operable as a DC step-down converter between the first onboard electrical sub-system and the second onboard electrical sub-system, the method comprising the acts of:

opening the low-side switches of the second inverter;

opening the high-side switches of the second inverter;

opening the low-side switches of the first inverter;

controlling, via pulse-width modulation, the high-side switches of the first inverter to operate the electrical machine as the DC step-down converter.

16. The method according to claim 15 , further comprising the act of short-circuiting the rotor so that it remains stationary during operation of the electrical machine as the DC step-down converter.

17. A method of operating a vehicle comprising:

a multi-phase electrical machine, the multi-phase electrical machine comprising a rotor, a first stator system and a second stator system;

a first onboard electrical sub-system having a first nominal DC voltage;

a second onboard electrical sub-system having a second nominal DC voltage;

wherein the first onboard electrical sub-system comprises a first inverter with a first link capacitor, the first stator system being associated with the first inverter;

wherein the second onboard electrical sub-system comprises a second inverter with a second link capacitor, the second stator system being associated with the second inverter;

wherein the first stator system is in a star configuration, the second stator system is in a star or delta configuration, and the first stator system has a higher impedance than the second stator system based on a number of windings in the first stator system and a number of windings in the second stator system, wherein the first stator system is configured to use a lower voltage on average and higher currents on average than the second stator system; and

a transfer circuit electrically coupling a star point of the first stator system in the star configuration to a higher potential of the second onboard electrical sub-system, the transfer circuit being disposed along an electrical path connecting the star point of the first stator system to a higher potential of the second inverter, wherein

the transfer circuit comprises a first diode and a second diode, the first diode and the second diode being counter-switched and connected in series,

the transfer circuit comprises a second switch connected in parallel with the first diode,

the first nominal voltage exceeds the second nominal voltage in a higher nominal voltage direction, and

when the rotor of the electrical machine is stationary, the electrical machine is operable as a DC step-up converter from the second onboard electrical sub-system to the first onboard electrical sub-system, the method comprising the acts of:

opening the low-sides switches of the second inverter;

opening the high-sides switches of the second inverter;

opening the low-sides switches of the first inverter;

controlling, via pulse-width modulation, the low-side switches of the first inverter to operate the electrical machine as the DC step-up converter.

18. The method according to claim 17 , further comprising the act of short-circuiting the rotor so that it remains stationary during operation of the electrical machine as the DC step-up converter.