Reference electrode-based battery imbalance diagnosis

1 . A method comprising:

determining a state of health of a cell group (SOH CG ), the cell group including a plurality of cells and the plurality of cells including a first set of cells and a second set of cells, wherein each cell in the first set of cells includes a reference electrode and each cell in the second set of cells lacks the reference electrode;

determining a state of health of a cell of the cell group in the second set of cells by multiplying the SOH CG by the number of cells of the cell group, subtracting the state of health of cells with reference electrodes, and dividing a remainder by a number of cells in the second set of cells;

determining a cell imbalance of the cell group based on a comparison of the state of health of the cell group and the state of health of the cell, wherein the cell imbalance of the cell group is a condition where the state of health of the cell group is not equal to the state of health of the cell of the cell group; and

generating an alert signal or a control signal based on the cell imbalance;

transmitting the alert to a controller configured to control the cell group, wherein the alert causes the controller to perform one of powering down a device including the cell group and disconnecting individual cells of the cell group such that the cell group may be used without contribution from a cell including the imbalance.

2 . The method of claim 1 , wherein determining the state of health of the cell group includes:

measuring a first set of voltages across cathodes and anodes of multiple cells of the cell group; and

comparing changes in the first set of voltages to changes in states of charge of the cell group.

3 . The method of claim 1 , wherein determining the state of health of the cell includes:

discharging the cell group to a target state of charge range based on an expected cause of failure of the cell group;

upon determining that a first diagnostic condition is met, measuring, at the target state of charge range, a second set of voltages of the cell of the cell group;

determining metrics of the second set of voltages; and

determining the state of health of the cell based on the metrics.

4 . The method of claim 3 , wherein the initial a first diagnostic condition includes: (i) a change in a voltage of the cell group that is below a voltage threshold, or (ii) a current of the cell group that is below a current threshold value.

5 . The method of claim 3 , wherein the second set of voltages includes a potential difference across the cell group, a potential difference across a reference electrode and a cathode of the cell, or a potential difference across the reference electrode and an anode of the cell.

6 . The method of claim 3 , wherein the metrics include statistical variances and averages of voltages corresponding to state of health data points for various cell cycles.

7 . The method of claim 3 , wherein determining the state of health of the cell involves using the metrics as indexes of a predetermined state of health table, and wherein the state of health table includes mappings between the metrics, cell cycles, and state of health values.

8 . A vehicle power control system, comprising:

a cell group (SOH CG ), the cell group including a plurality of cells and the plurality of cells including a first set of cells and a second set of cells, wherein each cell in the first set of cells includes a reference electrode and each cell in the second set of cells lacks the reference electrode;

a processor; and

memory or storage comprising an algorithm or computer instructions, which when executed by the processor, performs an operation comprising:

determining a state of health of the cell group;

determining a state of health of a cell in the second set of cells by multiplying the SOH CG by the number of cells of the cell group, subtracting the state of health of cells with reference electrodes, and dividing a remainder by a number of cells in the second set of cells;

determining a cell imbalance of the cell group based on a comparison of the state of health of the cell group and the state of health of the cell, wherein the cell imbalance of the cell group is a condition where the state of health of the cell group is not equal to the state of health of the cell of the cell group;

generating an alert signal or a control signal based on the cell imbalance;

transmitting the alert to a controller configured to control the cell group, wherein the alert causes the controller to perform one of powering down a device including the cell group and disconnecting individual cells of the cell group such that the cell group may be used without contribution from a cell including the imbalance.

9 . The vehicle power control system of claim 8 , wherein determining the state of health of the cell group includes:

measuring a first set of voltages across cathodes and anodes of multiple cells of the cell group; and

comparing changes in the first set of voltages to changes in states of charge of the cell group.

10 . The vehicle power control system of claim 8 , wherein determining the state of health of the cell includes:

discharging the cell group to a target state of charge range based on an expected cause of failure of the cell group;

upon determining that a first diagnostic condition is met, measuring, at the target state of charge range, a second set of voltages of the cell of the cell group, wherein the cell imbalance of the cell group is a condition where the state of health of the cell group is not equal to the state of health of the cell of the cell group;

determining metrics of the second set of voltages;

determining the state of health of the cell based on the metrics; and

transmitting the alert to a controller configured to control the cell group, wherein the alert causes the controller to perform one of powering down a device including the cell group and disconnecting individual cells of the cell group such that the cell group may be used without contribution from a cell including the imbalance.

11 . The vehicle power control system of claim 10 , wherein the first diagnostic condition includes: (i) a change in a voltage of the cell group that is below a voltage threshold, or (ii) a current of the cell group that is below a current threshold value.

12 . The vehicle power control system of claim 10 , wherein the second set of voltages includes a potential difference across the cell group, a potential difference across a reference electrode and a cathode of the cell, or a potential difference across the reference electrode and an anode of the cell.

13 . The vehicle power control system of claim 10 , wherein the metrics include statistical variances and averages of voltages corresponding to state of health data points for various cell cycles.

14 . The vehicle power control system of claim 10 , wherein determining the state of health of the cell involves using the metrics as indexes of a predetermined state of health table, and wherein the state of health table includes mappings between the metrics, cell cycles, and state of health values.

15 . A non-transitory computer-readable storage medium having a non-transitory computer-readable program code embodied therewith, the computer-readable program code executable by one or more computer processors to perform an operation comprising:

determining a state of health of a cell group (SOH CG ), the cell group including a plurality of cells and the plurality of cells including a first set of cells and a second set of cells, wherein each cell in the first set of cells includes a reference electrode and each cell in the second set of cells lacks the reference electrode;

determining a state of health of a cell of the cell in the second set of cells by multiplying the SOH CG by the number of cells of the cell group, subtracting the state of health of cells with reference electrodes, and dividing a remainder by a number of cells in the second set of cells;

determining a cell imbalance of the cell group based on a comparison of the state of health of the cell group and the state of health of the cell; and

generating an alert signal or a control signal based on the cell imbalance.

16 . The computer-readable storage medium of claim 15 , wherein determining the state of health of the cell group includes:

measuring a first set of voltages across cathodes and anodes of multiple cells of the cell group; and

comparing changes in the first set of voltages to changes in states of charge of the cell group.

17 . The computer-readable storage medium of claim 15 , wherein determining the state of health of the cell includes:

discharging the cell group to a target state of charge range based on an expected cause of failure of the cell group;

upon determining that a first diagnostic condition is met, measuring, at the target state of charge range, a second set of voltages of the cell of the cell group;

determining metrics of the second set of voltages; and

determining the state of health of the cell based on the metrics.

18 . The computer-readable storage medium of claim 17 , wherein the first diagnostic condition includes: (i) a change in a voltage of the cell group that is below a voltage threshold, or (ii) a current of the cell group that is below a current threshold value.

19 . The computer-readable storage medium of claim 17 , wherein the second set of voltages includes a potential difference across the cell group, a potential difference across a reference electrode and a cathode of the cell, or a potential difference across the reference electrode and an anode of the cell.

20 . The computer-readable storage medium of claim 17 , wherein the metrics include statistical variances and averages of voltages corresponding to state of health data points for various cell cycles, wherein determining the state of health of the cell involves using the metrics as indexes of a predetermined state of health table, and wherein the state of health table includes mappings between the metrics, cell cycles, and state of health values.