Apparatus and methods for restoring power cell functionality in multi-cell power supplies

1. A method of operating a multi-cell power supply comprising a controller and a plurality of series-connected power cells in each of a plurality of legs, each power cell comprising an inverter and a bypass device to selectively bypass and de-bypass the power cell, wherein after a first power cell faults and is bypassed as a result of a fault, the method comprising through operation of the controller:

temporarily inhibiting operation of the multi-cell power supply by inhibiting gating signals to semiconductor switches of each inverter of each power cell;

reconfiguring a bypass device of the first power cell to de-bypass the first power cell and reconfiguring the plurality of series-connected power cells;

modifying phase angles for reconfigured series-connected power cells; and

resuming the operation of the multi-cell power supply using modified phase angles without halting operation of a load powered by the multi-cell power supply;

wherein de-bypass of the first power cell comprises:

during a time period when the first power cell is bypassed, querying, by the controller, a processor of the first power cell to determine whether the first power cell experienced an overvoltage fault, an over-temperature fault or a line fault:,

reporting, by the processor, operating conditions of the first power cell in response to the querying from the controller; and

de-bypassing the first power cell if the first power cell experienced an overvoltage fault, an over-temperature fault or a line fault and the overvoltage fault, over-temperature fault or line fault no longer exists.

2. The method of claim 1 , further comprising determining if the bypassed power cell is functional prior to de-bypassing the first power cell.

3. The method of claim 1 , wherein each of the legs is connected between a node and a respective line, and the multi-cell power supply comprises line-to-line voltage outputs between pairs of the legs, and wherein the method further comprises:

controlling the plurality of power cells to maximize the line-to-line voltage outputs and

maintaining the line-to-line voltage outputs so as to correspond in magnitude.

4. The method of claim 3 , further comprising balancing a line-to-line phase.

5. The method of claim 3 , wherein maintaining the line-to-line voltage outputs so as to correspond in magnitude comprises adjusting leg-to-leg phase relationships.

6. The method of claim 5 , wherein adjusting comprises calculating leg-to-leg phase angles to produce balanced line-to-line voltages.

7. The method of claim 5 , wherein adjusting comprises using predetermined angles based upon a number of faulted cells in each of the legs.

8. The method of claim 7 , wherein the predetermined angles are obtained from tables of values.

9. The method of claim 1 , wherein, if the first power cell experienced an overvoltage fault, determining, by the controller, if the multi-cell power supply absorbed regenerative power from a load prior to the overvoltage fault of the first power cell.

10. A multi-cell power supply comprising:

a plurality of series-connected power cells in each of a plurality of legs, each power cell comprising an inverter and a bypass device to selectively bypass and de-bypass the power cells; and

a controller, after a first power cell faults and is bypassed as a result of a fault, configured to:

temporarily inhibit operation of the multi-cell power supply by inhibiting gating signals to semiconductor switches of each inverter of each power cell;

reconfigure a bypass device of the first power cell to de-bypass the first power cell and reconfigure the plurality of series-connected power cells;

modify phase angles for reconfigured series-connected power cells; and

resume the operation of the multi-cell power supply using modified phase angles without halting operation of a load powered by the multi-cell power supply;

wherein the controller is further configured to, during a time period when the first power cell is bypassed as a result of a fault:

query a processor of the first power cell to determine whether the first power cell experienced an overvoltage fault, an over-temperature fault or a line fault prior to the first power cell being bypassed, and

de-bypass the first power cell if the first power cell experienced an overvoltage fault, an over-temperature fault or a line fault and the overvoltage fault, over-temperature fault or line fault no longer exists based on reported operating conditions by the processor of the first power cell in response to a query from the controller.

11. The multi-cell power supply of claim 10 , wherein the controller determines if the bypassed power cell is functional prior to de-bypassing the first power cell.

12. The multi-cell power supply of claim 10 , wherein each of the legs is connected between a node and a respective line, and the multi-cell power supply comprises line-to-line voltage outputs between pairs of the legs, and wherein the controller controls the plurality of power cells to maximize the line-to-line voltage outputs and maintain the line-to-line voltage outputs so as to correspond in magnitude.

13. The multi-cell power supply of claim 12 , wherein the controller balances a line-to-line phase.

14. The multi-cell power supply of claim 12 , wherein the controller adjusts leg-to-leg phase relationships to maintain the line-to-line voltage outputs so as to correspond in magnitude.

15. The multi-cell power supply of claim 14 , wherein the controller calculates leg-to-leg phase angles to produce balanced line-to-line voltages.

16. The multi-cell power supply of claim 14 , wherein the controller adjusts leg-to-leg phase relationships by using predetermined angles based upon a number of faulted cells in each of the legs.

17. The multi-cell power supply of claim 16 , wherein the controller obtains the predetermined angles from tables of values.

18. The multi-cell power supply of claim 10 , wherein, if the first power cell experienced an overvoltage fault, the controller is further configured to determine if the multi-cell power supply absorbed regenerative power from a load prior to the overvoltage fault of the first power cell.