Inter-module battery balancing using voltages to select battery sub-modules to power loads

1. A system, comprising:

a plurality of battery sub-modules, wherein:

the plurality of battery sub-modules are electrically connected in series in order to provide power to a primary load;

each battery sub-module includes a plurality of cells electrically connected in series; and

a controller that is configured to:

select one or more battery sub-modules from the plurality of battery sub-modules, including by:

obtaining at least one voltage from each battery sub-module; and

selecting one or more battery sub-modules based at least in part on the obtained voltages,

wherein the plurality of battery sub-modules include at least one unselected battery sub-module;

wherein each selected battery sub-module is coupled to a secondary load;

configure those secondary loads in the one or more selected battery sub-modules to draw power from the at least one unselected battery sub-module so that the secondary loads coupled to the selected battery sub-modules do not consume power at least temporarily from the plurality of cells in the selected battery sub-modules while (1) the plurality of battery sub-modules is not providing power to the primary load, or (2) the plurality of battery sub-modules is not being charged.

2. The system of claim 1 , wherein each secondary load is powered using a lower voltage than the primary load.

3. The system of claim 1 , wherein at least one secondary load coupled to a battery sub-module includes a battery management system that monitors the plurality of cells in that battery sub-module.

4. The system of claim 1 , wherein selecting the one or more battery_sub-modules is based at least in part on a plurality of minimum cell voltages which includes a minimum cell voltage from each battery sub-module in the plurality of battery sub-modules.

5. The system of claim 1 , wherein selecting the one or more battery sub-modules is based at least in part on a plurality of maximum cell voltages which includes a maximum cell voltage from each battery sub-module in the plurality of battery sub-modules.

6. The system of claim 1 , wherein selecting the one or more battery sub-modules includes:

comparing, for each battery sub-module in the plurality of battery sub-modules, a minimum cell voltage against a voltage threshold in order to identify any battery sub-modules with a minimum cell voltage that does not exceed the voltage threshold; and

selecting one or more of those battery sub-modules with a minimum cell voltage that does not exceed the voltage threshold.

7. The system of claim 1 , wherein the controller is further configured to:

determine an imbalance metric associated with a degree of imbalance between battery sub-modules in the plurality of battery sub-modules;

determine whether the imbalance metric exceeds an imbalance threshold;

in response to determining that the imbalance metric exceeds the imbalance threshold, perform pre-charging balancing; and

after performing pre-charging balancing, charge the plurality of battery sub-modules.

8. The system of claim 7 , wherein pre-charging balancing comprises configuring those second loads in the one or more selected battery sub-modules to draw power from the at least one unselected battery sub-module so that the secondary loads coupled to the selected battery sub-modules do not consume power at least temporarily from the plurality of cells in the selected battery sub-modules while (1) the plurality of battery sub-modules is not providing power to the primary load, or (2) the plurality of battery sub-modules is not being charged.

9. The system of claim 1 , further comprising:

an electric aircraft including one or more lift fans, wherein the electric aircraft is powered by the plurality of battery sub-modules, wherein the primary load includes the one or more lift fans.

10. The system of claim 1 , wherein each secondary loads includes one or more of an electronic device, a motor, or a solenoid.

11. The system of claim 1 , wherein the controller is configured to balance voltage levels of the plurality of battery sub-modules.

12. A method, comprising:

selecting one or more battery sub-modules from a plurality of battery sub-modules, including by:

obtaining at least one voltage from each battery sub-module; and

selecting one or more battery sub-modules based at least in part on the obtained voltages, wherein:

the plurality of battery sub-modules are electrically connected in series in order to provide power to a primary load;

each battery sub-module includes a plurality of cells electrically connected in series;

wherein the plurality of battery sub-modules include at least one unselected battery sub-module;

wherein each selected battery sub-module is coupled to a secondary load; and

configuring those secondary loads in the one or more selected battery sub-modules to draw power from the at least one unselected battery sub-module so that the secondary loads coupled to the selected battery sub-modules do not consume power at least temporarily from the plurality of cells in the selected battery sub-modules while (1) the plurality of battery sub-modules is not providing power to the primary load, or (2) the plurality of battery sub-modules is not being charged.

13. The method of claim 12 , wherein each secondary load is powered using a lower voltage than the primary load.

14. The method of claim 12 , wherein at least one secondary load coupled to a battery sub-module includes a battery management system that monitors the plurality of cells in that battery sub-module.

15. The method of claim 12 , wherein selecting the one or more battery_sub-modules is based at least in part on a plurality of minimum cell voltages which includes a minimum cell voltage from each battery sub-module in the plurality of battery sub-modules.

16. The method of claim 12 , wherein selecting the one or more battery sub-modules is based at least in part on a plurality of maximum cell voltages which includes a maximum cell voltage from each battery sub-module in the plurality of battery sub-modules.

17. The method of claim 12 , wherein selecting the one or more battery sub-modules includes:

comparing, for each battery sub-module in the plurality of battery sub-modules, a minimum cell voltage against a voltage threshold in order to identify any battery sub-modules with a minimum cell voltage that does not exceed the voltage threshold; and

selecting one or more of those battery sub-modules with a minimum cell voltage that does not exceed the voltage threshold.

18. The method of claim 12 , further comprising:

determining an imbalance metric associated with a degree of imbalance between battery sub-modules in the plurality of battery sub-modules;

determining whether the imbalance metric exceeds an imbalance threshold;

in response to determining that the imbalance metric exceeds the imbalance threshold, performing pre-charging balancing; and

after performing pre-charging balancing, charging the plurality of battery sub-modules.

19. The method of claim 12 , wherein pre-charging balancing comprises configuring those second loads in the one or more selected battery sub-modules to draw power from the at least one unselected battery sub-module so that the secondary loads coupled to the selected battery sub-modules do not consume power at least temporarily from the plurality of cells in the selected battery sub-modules while (1) the plurality of battery sub-modules is not providing power to the primary load, or (2) the plurality of battery sub-modules is not being charged.

20. The method of claim 12 , wherein each secondary load includes one or more of an electronic device, a motor, or a solenoid.