Method and system for battery management including bypassing battery cells in a battery pack

1. A system comprising:

a battery pack having battery cell sections connected in series, wherein each of the battery cell sections includes:

a first terminal and a second terminal;

a battery cell coupled between the first terminal and the second terminal; and

a bypass switch positioned in parallel with the battery cell, wherein the bypass switch is operable to short circuit the first terminal to the second terminal; and

a control circuit configured to:

determine a capacity of a particular battery cell in a particular battery cell section among the battery cell sections;

determine whether the capacity of the particular battery cell is less than a predefined threshold;

in response to determining that the capacity of the particular battery cell is less than the predefined threshold, execute a bypass sequence for the particular battery cell, wherein the bypass sequence involves:

determining, based on the capacity of the particular battery cell, a bypass period for which to bypass the particular battery cell; and

transmitting a bypass signal to a drive circuit, the drive circuit being configured to receive the bypass signal and responsively operate the bypass switch of the particular battery cell section to bypass the particular battery cell for the bypass period by shorting the first terminal to the second terminal;

determine that the bypass period for the particular battery cell has finished; and

in response to determining that the bypass period for the particular battery cell has finished, execute an activation sequence for the particular battery cell, the activation sequence being configured to allow current flow to the particular battery cell.

2. The system of claim 1 , further comprising a power control switch coupled between the battery pack and a power source for controlling current flow to the battery pack from the power source, wherein the bypass sequence further comprises:

prior to transmitting the bypass signal, transmitting an open signal for opening the power control switch to prevent current flow from the power source to the battery pack during a remainder of the bypass sequence.

3. The system of claim 2 , wherein the open signal is a first open signal, and wherein the bypass sequence comprises:

after transmitting the first open signal, transmitting a second open signal for opening a charging switch of the particular battery cell section to prevent current flow through the particular battery cell, the charging switch being positioned in series with the particular battery cell;

after transmitting the second open signal, transmitting the bypass signal; and

after transmitting the bypass signal, completing the bypass sequence by transmitting a close signal for closing the power control switch to allow current flow from the power source to the battery pack.

4. The system of claim 1 , wherein the bypass period is a portion of a duty cycle for charging the battery pack.

5. The system of claim 1 , wherein the activation sequence comprises:

transmitting a first open signal for opening a power control switch to prevent current flow from a power source to the battery pack during a remainder of the activation sequence;

after transmitting the first open signal, transmitting a second open signal for opening the bypass switch to prevent current from bypassing the particular battery cell;

after transmitting the second open signal, transmitting a first close signal for closing a charging switch of the particular battery cell section to allow current flow through the particular battery cell, the charging switch being positioned in series with the particular battery cell; and

after transmitting the first close signal, completing the activation sequence by transmitting a second close signal for closing the power control switch to allow current flow from the power source to the battery pack.

6. The system of claim 1 , further comprising:

a startup relay configured to draw power from one or more battery cells in the battery pack to activate a boost circuit;

the boost circuit, wherein the boost circuit is configured to generate a drive voltage that is larger than an input voltage to the boost circuit; and

the drive circuit configured to apply the drive voltage generated by the boost circuit to the bypass switch of the particular battery cell to close the bypass switch.

7. The system of claim 1 , further comprising a monitoring circuit configured to measure a voltage across the particular battery cell and transmit a measurement signal indicating the voltage to the control circuit, wherein the control circuit is configured to determine the capacity of the particular battery cell based on the voltage.

8. The system of claim 1 , wherein the control circuit is configured to:

store voltages or charge states associated with the particular battery cell section over multiple charging cycles; and

determine the bypass period based on the stored voltages or charge states.

9. A method comprising:

determining, by a control circuit, a capacity of a particular battery cell in a particular battery cell section of a battery pack, wherein the particular battery cell section includes a bypass switch that is operable to short a first terminal of the particular battery cell section to a second terminal of the particular battery cell section, wherein the particular battery cell is coupled between the first terminal and the second terminal in the particular battery cell section;

determining, by the control circuit, whether the capacity of the particular battery cell is less than a predefined threshold;

in response to determining that the capacity of the particular battery cell is less than the predefined threshold, executing, by the control circuit, a bypass sequence for the particular battery cell, wherein the bypass sequence involves:

determining, based on the capacity of the particular battery cell, a bypass period for which to bypass the particular battery cell; and

transmitting a bypass signal to a drive circuit, the drive circuit being configured to receive the bypass signal and responsively close the bypass switch of the particular battery cell section to bypass the particular battery cell for the bypass period by shorting the first terminal to the second terminal;

determining, by the control circuit, that the bypass period for the particular battery cell has finished; and

in response to determining that the bypass period for the particular battery cell has finished, executing, by the control circuit, an activation sequence for the particular battery cell, the activation sequence being configured to allow current flow to the particular battery cell.

10. The method of claim 9 , wherein the bypass sequence further comprises:

prior to transmitting the bypass signal, transmitting an open signal for opening a power control switch to prevent current flow from a power source to the battery pack during a remainder of the bypass sequence, the power control switch being coupled between the battery pack and the power source.

11. The method of claim 10 , wherein the open signal is a first open signal, and wherein the bypass sequence comprises:

after transmitting the first open signal, transmitting a second open signal for opening a charging switch of the particular battery cell section to prevent current flow through the particular battery cell, the charging switch being positioned in series with the particular battery cell;

after transmitting the second open signal, transmitting the bypass signal; and

after transmitting the bypass signal, completing the bypass sequence by transmitting a close signal for closing the power control switch to allow current flow from the power source to the battery pack.

12. The method of claim 9 , wherein the bypass period is a portion of a duty cycle for charging the battery pack.

13. The method of claim 9 , wherein the activation sequence comprises:

transmitting a first open signal for opening a power control switch to prevent current flow from a power source to the battery pack during a remainder of the activation sequence;

after transmitting the first open signal, transmitting a second open signal for opening the bypass switch to prevent current from bypassing the particular battery cell;

after transmitting the second open signal, transmitting a first close signal for closing a charging switch of the particular battery cell section to allow current flow through the particular battery cell; and

after transmitting the first close signal, completing the activation sequence by transmitting a second close signal for closing the power control switch to allow current flow from the power source to the battery pack.

14. The method of claim 9 , further comprising:

operating a startup relay to draw power from one or more battery cells of the battery pack during a startup phase of the battery pack to activate a boost circuit;

operating the boost circuit to generate a drive voltage that is larger than an input voltage to the boost circuit; and

operating the drive circuit to apply the drive voltage generated by the boost circuit to the bypass switch of the particular battery cell to close the bypass switch.

15. The method of claim 9 , further comprising:

measuring a voltage across the particular battery cell; and

transmitting a measurement signal indicating the voltage to the control circuit, wherein the control circuit is configured to determine the capacity of the particular battery cell based on the voltage.

16. The method of claim 9 , further comprising:

storing voltages or charge states associated with the particular battery cell over multiple charging cycles; and

determining the bypass period based on the stored voltages or charge states.

17. A method comprising:

determining, by a first control circuit associated with a first battery pack, that a battery cell of the first battery pack is to be bypassed for a bypass period based on a capacity of the battery cell; and

in response to determining that the battery cell is to be bypassed for the bypass period:

executing, by the first control circuit, a first bypass sequence configured to bypass the battery cell for the bypass period; and

transmitting, by the first control circuit, a bypass notification to a second control circuit associated with a second battery pack, wherein the second control circuit is configured to:

receive the bypass notification; and

in response to receiving the bypass notification, synchronize a second bypass sequence with the first bypass sequence, the second bypass sequence being configured to bypass another battery cell in the second battery pack.

18. The method of claim 17 , wherein the bypass notification indicates the bypass period, and wherein the second bypass sequence is configured to bypass the another battery cell for the bypass period based on the bypass notification.