Brushless electrical machine

1. A bridge converter for a multi-phase electrical machine having a plurality of stator windings, the bridge converter being supplied with a DC voltage, V DC , comprising:

a number, N, of bridge cells coupled in series, each bridge cell having a multi-phase inverter coupled to a subset of the stator windings and operative to supply power to the subset at a voltage V DC /N each bridge cell having a local ground at a different potential than other local grounds corresponding to other bridge cells, wherein the multi-phase inverter is coupled to the local ground for the bridge cell; and

each bridge cell further having a controller coupled to the local ground and to the multi-phase inverter, and constructed to provide control signals for operating the multi-phase inverter.

2. The bridge converter of claim 1 , further comprising a voltage divider having N segments, each segment corresponding to one of the N bridge cells, the potential difference across each segment being V DC /N, each segment having a local ground reference coupled to the controller of the corresponding one of the N bridge cells.

3. The bridge converter of claim 2 , wherein the controller is constructed to detect a bridge cell voltage imbalance based on comparing an actual voltage at the local ground of the corresponding one of the N bridge cells with a reference voltage at the local ground reference for the corresponding one of the N bridge cells.

4. The bridge converter of claim 2 , wherein the controller is constructed to selectively increase or decrease a power output of the corresponding one of the N bridge cells based on a comparison of an actual voltage at the local ground for the corresponding one of the N bridge cells with a reference voltage at the local ground reference for the corresponding one of the N bridge cells.

5. The bridge converter of claim 1 , further comprising an isolation device in communication with each controller and operative to isolate and supply a same demand signal to each controller.

6. The bridge converter of claim 1 , wherein each bridge cell includes switching devices; and wherein the controller of each of the corresponding one of the N bridge cells is constructed to provide gate drive signals to the switching devices.

7. The bridge converter of claim 6 , wherein the controller is not isolated from the multi-stage inverter.

8. The bridge converter of claim 1 , wherein the electrical machine includes a sensor operative to provide a commutation signal; wherein the controller is coupled to the sensor and operative to receive the commutation signal and provide the control signals based on the commutation signal; and wherein the sensor is not isolated from the controller.

9. A multi-phase electrical machine powered by a DC voltage, V DC , comprising:

a plurality of stator windings;

a bridge converter having a number, N, of bridge cells coupled in series, each bridge cell having a multi-phase inverter coupled to a subset of the stator windings and operative to supply power to the subset at a voltage V DC /N, each bridge cell having a local ground at a different potential than other local grounds corresponding to other bridge cells, wherein the multi-phase inverter is coupled to the local ground for the bridge cell;

each bridge cell further having a controller coupled to the local ground and to the multi-phase inverter, and constructed to provide control signals for operating the multi-phase inverter; and

a sensor operative to provide a commutation signal to at least one of the controllers.

10. The electrical machine of claim 9 , further comprising a voltage divider having N segments, each segment corresponding to one of the N bridge cells, the potential difference across each segment being V DC /N, each segment having a local ground reference coupled to the controller of the corresponding one of the N bridge cells.

11. The electrical machine of claim 10 , wherein each controller is constructed to detect a bridge cell voltage imbalance based on comparing an actual voltage at the local ground of the corresponding one of the N bridge cells with a reference voltage at the local ground reference for the corresponding one of the N bridge cells.

12. The electrical machine of claim 10 , wherein each controller is constructed to selectively increase or decrease a power output of the corresponding one of the N bridge cells based on a comparison of an actual voltage at the local ground for the corresponding one of the N bridge cells with a reference voltage at the local ground reference for the corresponding one of the N bridge cells.

13. The electrical machine of claim 9 , further comprising an optocoupler in communication with each controller and operative to optically isolate and supply a same demand signal to each controller.

14. The electrical machine of claim 9 , wherein each bridge cell includes switching devices; and wherein the controller of each of the corresponding one of the N bridge cells is constructed to provide gate drive signals to the switching devices.

15. The electrical machine of claim 14 , wherein the controller is not optically isolated from the multi-phase inverter.

16. The electrical machine of claim 9 , wherein the sensor is not isolated from the controller.

17. An electrical machine, comprising:

a plurality of stator windings of the electrical machine;

a plurality of bridge cells of the electrical machine, the plurality of bridge cells coupled in series, each bridge cell having a multi-phase inverter coupled to a subset of the stator windings of the electrical machine and operative to supply power to the subset; and

means for controlling the multi-phase inverters, wherein the means or controlling the multi-phase inverters is not isolated from the multi-phase inverters.

18. The electrical machine of claim 17 , further comprising means for balancing a power output of at least one of the bridge cells.

19. The electrical machine of claim 17 , further comprising a sensor operative to provide a commutation signal to the means for controlling.

20. The electrical machine of claim 19 , wherein the sensor is not isolated from the means for controlling.