Impedance measurements in battery management circuits

1. A circuit configured to determine a plurality of impedances of a plurality of battery cells, the circuit comprising:

for each of the battery cells, a respective current excitation unit configured to deliver a respective excitation current to a respective one of the plurality of battery cells; and

an analog-to-digital converter (ADC) configured to:

perform one or more first measurements associated with a first battery cell in the presence of a first excitation current, wherein the one or more first measurements associated with the first battery cell comprise one or more current measurements associated with the first battery cell,

perform one or more second measurements associated with the first battery cell in the presence of the first excitation current, wherein the one or more second measurements associated with the first battery cell comprise one or more voltage measurements associated with the first battery cell,

wherein an impedance of the first battery cell is based on the one or more first measurements associated with the first battery cell and the one or more second measurements associated with the first battery cell,

perform one or more first measurements associated with a second battery cell in the presence of a second excitation current, wherein the one or more first measurements associated with the second battery cell comprise one or more current measurements associated with the second battery cell, and

perform one or more second measurements associated with the second battery cell in the presence of the second excitation current, wherein the one or more second measurements associated with the second battery cell comprise one or more voltage measurements associated with the second battery cell,

wherein an impedance of the second battery cell is based on the one or more first measurements associated with the second battery cell and the one or more second measurements associated with the second battery cell.

2. The circuit of claim 1 , further comprising a multiplexer configured to:

select a first set of signals and deliver the first set of signals to the ADC to perform the one or more first measurements associated with the first battery cell in the presence of the first excitation current in a first instance of time, and

select a second set of signals and deliver the second set of signals to the ADC to perform the one or more second measurements associated with the first battery cell in the presence of the first excitation current in a second instance of time.

3. The circuit of claim 2 , wherein the first instance of time and the second instance of time occur after a settling time associated with the excitation current.

4. The circuit of claim 1 , wherein the impedance of the first battery cell comprises a complex impedance and wherein the first excitation current comprises an alternating current (AC) at one or more defined frequencies.

5. The circuit of claim 4 , wherein:

the one or more first measurements associated with the first battery cell comprise two or more first measurements associated with two or more different frequencies of the first excitation current, and

the one or more second measurements associated with the first battery cell comprise two or more second measurements associated with the two or more different frequencies of the first excitation current.

6. The circuit of claim 1 , wherein the ADC comprises an alternating current (AC) sigma-delta ADC that includes capacitors configured to operate as high-pass filters.

7. The circuit of claim 1 , further comprising a multiplexer configured to:

select a first set of signals and deliver the first set of signals to the ADC to perform the one or more first measurements associated with the first battery cell in the presence of the first excitation current;

select a second set of signals and deliver the second set of signals to the ADC to perform the one or more second measurements associated with the first battery cell in the presence of the first excitation current;

select a third set of signals and deliver the third set of signals to the ADC to perform the one or more first measurements associated with the second battery cell in the presence of the second excitation current; and

select a fourth set of signals and deliver the fourth set of signals to the ADC to perform the one or more second measurements associated with the second battery cell in the presence of the second excitation current.

8. The circuit of claim 1 , wherein the circuit is configured to perform one or more battery management functions on the plurality of battery cells, wherein the battery management functions are based on the plurality of determined impedances of the plurality of battery cells.

9. The circuit of claim 8 , wherein one or more battery management functions comprise cell balancing functions.

10. A method of determining a plurality of impedances of a plurality of battery cells, the method comprising:

for each of the battery cells, delivering a respective excitation current to a respective the battery cell;

performing, via an analog-to-digital converter (ADC), one or more first measurements associated with a first the battery cell in the presence of a first excitation current, wherein the one or more first measurements associated with the first battery cell comprise one or more current measurements associated with the first battery cell;

performing, via the ADC, one or more second measurements associated with the first battery cell in the presence of the first excitation current, wherein the one or more second measurements associated with the first battery cell comprise one or more voltage measurements associated with the first battery cell;

determining an impedance of the first battery cell based on the one or more first measurements associated with the first battery cell and the one or more second measurements associated with the first battery cell;

performing, via the ADC, one or more first measurements associated with a second battery cell in the presence of a second excitation current, wherein the one or more first measurements associated with the second battery cell comprise one or more current measurements associated with the second battery cell;

performing, via the ADC, one or more second measurements associated with the second battery cell in the presence of the second excitation current wherein the one or more second measurements associated with the second battery cell comprise one or more voltage measurements associated with the second battery cell; and

determining an impedance of the second battery cell based on the one or more first measurements associated with the second battery cell and the one or more second measurements associated with the second battery cell.

11. The method of claim 10 , further comprising:

selecting, via a multiplexer, a first set of signals and deliver the first set of signals to the ADC to perform the one or more first measurements associated with the first battery cell in the presence of the first excitation current in a first instance of time, and

selecting, via the multiplexer, a second set of signals and deliver the second set of signals to the ADC to perform the one or more second measurements associated with the first battery cell in the presence of the first excitation current in a second instance of time.

12. The method of claim 11 , wherein the first instance of time and the second instance of time occur after a settling time associated with the excitation current.

13. The method of claim 10 , wherein the impedance of the first battery cell comprises a complex impedance and wherein the first excitation current comprises an alternating current (AC) at one or more defined frequencies.

14. The method of claim 13 , wherein:

the one or more first measurements associated with the first battery cell comprise two or more first measurements associated with two or more different frequencies of the first excitation current, and

the one or more second measurements associated with the first battery cell comprise two or more second measurements associated with the two or more different frequencies of the first excitation current.

15. The method of claim 10 , further comprising:

selecting, via a multiplexer, a first set of signals and deliver the first set of signals to the ADC to perform the one or more first measurements associated with the first battery cell in the presence of the first excitation current;

selecting, via the multiplexer, a second set of signals and deliver the second set of signals to the ADC to perform the one or more second measurements associated with the first battery cell in the presence of the first excitation current;

selecting, via the multiplexer, a third set of signals and deliver the third set of signals to the ADC to perform the one or more first measurements associated with the second battery cell in the presence of the second excitation current; and

selecting, via the multiplexer, a fourth set of signals and deliver the fourth set of signals to the ADC to perform the one or more second measurements associated with the second battery cell in the presence of the second excitation current.

16. The method of claim 10 , further comprising:

performing one or more battery management functions on the plurality of battery cells, wherein the battery management functions are based on the plurality of determined impedances of the plurality of battery cells.

17. A battery management system (BMS) configured to monitor a plurality of battery cells arranged in series, the BMS comprising:

a first battery monitoring circuit configured to monitor a first subset of the plurality of battery cells; and

a second battery monitoring circuit configured to monitor a second subset of the plurality of battery cells, wherein the second subset is different than the first subset, wherein the first battery monitoring circuit and the second battery monitoring circuit each comprise:

an impedance measurement circuit configured to determine an impedance of a given battery cell, the impedance measurement circuit comprising:

a current excitation unit configured to deliver an excitation current to the given battery cell; and

an analog-to-digital converter (ADC) configured to:

perform one or more first measurements associated with the given battery cell in the presence of the excitation current, wherein the one or more first measurements comprise one or more current measurements, and

perform one or more second measurements associated with the given battery cell in the presence of the excitation current, wherein the one or more second measurements comprise one or more voltage measurements,

wherein the impedance of the given battery cell is based on the one or more first measurements and the one or more second measurements.

18. The BMS of claim 17 , wherein the impedance measurement circuit associated with each of the first battery monitoring circuit and the second battery monitoring circuit is configured to determine a plurality of impedances associated with a subset of the plurality of battery cells,

wherein for each subset of battery cells, a respective impedance measurement circuit includes a respective current excitation unit configured to deliver a respective excitation current to a respective battery cell,

wherein the ADC is configured to:

perform one or more first measurements associated with a first battery cell in the presence of a first excitation current,

perform one or more second measurements associated with the first battery cell in the presence of the first excitation current,

perform one or more first measurements associated with a second battery cell in the presence of a second excitation current, and

perform one or more second measurements associated with the second battery cell in the presence of the second excitation current.