Battery pack charge cell balancing
Systems and methods are described for managing charging and discharging of battery packs. In one or more aspects, a system and method are provided to minimize overcharging of battery cells of specific battery chemistries while still enabling fast charging cycles. In other aspects, a buck converter may be used to reduce a voltage of power used to charge the cells. In further aspects, a fast overcurrent protection circuit is described to address situations involving internal short circuits of a battery cell or battery pack. In yet further aspects, a bypass circuit is provided in series-connected battery packs to improve the charging of undercharged battery packs while also increasing the efficiency of the overall charging process. In other aspects, a circuit is provided that permits a controller to determine a configuration of battery packs. In yet further aspects, a system may determine a discharge current for a collection of battery packs based on each battery pack's state of health (SOH) and forward that determination to an external device.
1. A device comprising:
a plurality of series-connected battery cells of a battery chemistry;
a first pathway between a power source and the plurality of series-connected battery cells, wherein the first pathway is configured to supply the plurality of series-connected battery cells with current at a first voltage;
a second pathway between the power source and the plurality of series-connected battery cells, wherein the second pathway is configured to supply the plurality of series-connected battery cells with current at a second voltage, wherein the second voltage is lower than the first voltage; and
a pathway control circuit configured to select, based on states of charge (SOC) of battery cells of the plurality of series-connected battery cells, between the first pathway and the second pathway,
wherein, based on the battery chemistry, a first voltage across a first battery cell having a higher SOC increases faster than a second voltage across a second battery cell having a lower SOC than the first battery cell.
2. The device of claim 1 ,
wherein the battery chemistry of the series-connected battery cells is selected from the group of:
lithium iron phosphate (LFP);
lithium nickel manganese cobalt oxide (NMC); and
lithium nickel cobalt aluminum oxides (NCA).
3. The device of claim 1 ,
wherein the second pathway comprises a buck converter configured to receive the first voltage and output the second voltage.
4. The device of claim 1 , further comprising:
a voltage detector configured to detect a voltage across each cell of the plurality of series-connected battery cells, wherein the voltage detector is configured to determine whether a cell voltage of at least one cell of the plurality of series-connected battery cells satisfies a cell threshold voltage,
wherein the pathway control circuit comprises a pathway switch configured to receive a power supply voltage and output the first voltage to the first pathway, and
wherein the pathway switch is controlled to connect, based on a determination by the voltage detector that at least one cell of the plurality of series-connected battery cells is greater than or equal to the cell threshold voltage, the power supply voltage to the second pathway.
5. The device of claim 4 , further comprising:
a second pathway switch configured to selectively connect one of the first pathway or the second pathway to the plurality of series-connected battery cells,
wherein the second pathway switch is controlled based on the determination by the voltage detector that at least one cell of the plurality of series-connected battery cells greater than or equal to the cell threshold voltage.
6. The device of claim 4 ,
wherein the voltage detector further comprises one or more comparators configured to compare a voltage across an individual battery cell with a reference voltage, and
wherein the pathway control circuit further comprises a comparator-controlled switch configured to, based on a comparison by one or more comparators that the voltage of the individual battery cell is greater than or equal to the reference voltage, control the operation of the pathway switch.
7. The device of claim 4 , wherein the voltage detector comprises:
a plurality of individual voltage detectors, wherein each individual voltage detector is configured to detect a voltage across an individual battery cell of the plurality of series-connected battery cells.
8. The device of claim 7 , wherein each individual voltage detector comprises:
a comparator configured to compare a reference voltage and the voltage across the individual battery cell of the plurality of series-connected battery cells.
9. The device of claim 4 , further comprising:
one or more selectable connectors configured to selectively connect the one or more voltage detectors to individual battery cells; and
a controller configured to control the one or more selectable connectors to selectively connect to the individual battery cells.
10. A method comprising:
providing, via a first pathway, power at a first voltage level to series-connected battery cells;
detecting, across each battery cell of the series-connected battery cells, a cell voltage;
comparing each cell voltage with a reference voltage;
determining, based on the comparison, that at least one cell voltage is greater than or equal to the threshold voltage;
disconnecting, based on a determination that at least one cell voltage is greater than or equal to the threshold voltage and via at least a first switch, the first pathway from the series-connected battery cells;
providing, via at least a second switch and via a second pathway, power at a second voltage level to the series-connected battery cells,
wherein the second voltage level is lower than the first voltage level.
11. The method of claim 10 , wherein providing the power at the second voltage level comprises:
reducing, via a buck converter, the first voltage level to the second voltage level.
12. The method of claim 10 ,
wherein determining the voltage across each cell is performed simultaneously for each battery cell of the series-connected battery cells.
13. The method of claim 10 ,
wherein determining the voltage across each cell is performed sequentially across the series-connected battery cells.
14. The method of claim 10 , further comprising:
determining, based on the based on the comparison, that all cell voltages are higher than a second threshold voltage;
providing, based on the determination that all cell voltages are higher than the second threshold voltage, power at a third voltage level to the series-connected battery cells.
15. The method of claim 14 , wherein providing power at the third voltage level comprises providing a trickle charge to the series-connected battery cells.
16. The method of claim 10 , further comprising:
determining, based on the based on the comparison, that all cell voltages are higher than a second threshold voltage;
providing, based on the determination that all cell voltages are higher than the second threshold voltage, an indication that the battery cells are charged.
17. The method of claim 10 , wherein the determining that the at least one cell voltage is greater than or equal to the threshold voltage further comprises:
determining that other series-connected cells are below a second threshold voltage.
18. The method of claim 10 , wherein determining that at least one cell voltage is greater than or equal to the threshold voltage further comprises:
determining that the at least one cell's voltage level is increasing faster than the voltage level of other cells.
19. The method of claim 10 ,
wherein a determination that that at least one cell voltage is greater than or equal to the threshold voltage indicates that the at least one cell's voltage level is increasing faster than the voltage level of other cells.
20. The method of claim 10 ,
wherein providing power via the second pathway at the second voltage level permits balancing of the series-connected battery cells.