Determining battery DC impedance

1. A controller for use in a battery charging system, the controller including processing circuitry configured to:

during a charging operation:

initiate a relaxation period in response to a state of charge (S.O.C.) of a propulsion battery reaching a predetermined level during the charging operation;

receive a D.C. impedance of the propulsion battery from a battery data acquisition and monitoring subsystem, the D.C. impedance determined by the battery data acquisition and monitoring subsystem during the charging operation;

obtain a reference D.C. impedance, the reference D.C. impedance indicating an impedance associated with a new battery;

determine an impedance degradation factor of the propulsion battery using the D.C. impedance and the reference D.C. impedance;

during operational use of the propulsion battery:

obtain an operational reference impedance of the propulsion battery;

determine a real-time effective impedance for the propulsion battery based on the impedance degradation factor and the operational reference impedance; and

generate a feed-forward parameter based on the real-time effective impedance.

2. The controller of claim 1 , wherein:

the propulsion battery includes a plurality of cells forming a multi-cell battery pack; and

the processing circuitry is further configured to determine the impedance degradation factor for individual cells included in the multi-cell battery pack.

3. The controller of claim 1 , wherein the processing circuitry is further configured to:

determine that the propulsion battery is at a predetermined temperature prior to initiating the charging operation.

4. The controller of claim 1 , wherein:

the D.C. impedance of the propulsion battery corresponds to a measurement made after the relaxation period.

5. The controller of claim 4 , wherein the processing circuitry is further configured to:

instruct a battery charger to provide a charging current to the propulsion battery until the S.O.C. the propulsion battery reaches the predetermined level.

6. The controller of claim 5 , wherein the processing circuitry is further configured to:

set the charging current provided to the propulsion battery to zero amperes for a duration of the relaxation period.

7. The controller of claim 5 , wherein the processing circuitry is further configured to:

obtain a first voltage of the propulsion battery upon conclusion of the relaxation period;

instruct the battery charger to resume providing a charging current to the propulsion battery;

obtain a second voltage of the propulsion battery after the battery charger has resumed providing the charging current to the propulsion battery; and

determine the D.C. impedance of the propulsion battery based, at least in part on a difference between the first voltage of the propulsion battery and the second voltage of the propulsion battery.

8. A method for use in a battery charging system controller, the method comprising:

during a charging operation:

initiating a relaxation period in response to a state of charge (S.O.C.) of a propulsion battery reaching a predetermined level during the charging operation;

receiving at the battery charging system controller, a D.C. impedance of the propulsion battery from a battery data acquisition and monitoring subsystem, the D.C. impedance determined by the battery data acquisition and

monitoring subsystem during the charging operation;

obtaining a reference D.C. impedance, the reference D.C. impedance indicating an impedance associated with a new battery;

determining an impedance degradation factor of the propulsion battery using the D.C. impedance and the reference D.C. impedance; during operational use of the propulsion battery:

obtaining an operational reference impedance of the propulsion battery;

determining a real-time effective impedance for the propulsion battery based on the impedance degradation factor and the operational reference impedance; and

generate a feed-forward parameter based on the real-time effective impedance.

9. The method of claim 8 , wherein the propulsion battery includes a plurality of cells forming a multi-cell battery pack, the method further including:

determining the impedance degradation factor for individual cells included in the multi-cell battery pack.

10. The method of claim 8 , further comprising:

determining that the propulsion battery is at a predetermined temperature prior to initiating the charging operation.

11. The method of claim 8 , wherein the D.C. impedance of the propulsion battery corresponds to a measurement made after a relaxation period.

12. The method of claim 11 , further including:

instructing a battery charger to provide a charging current to the propulsion battery until the S.O.C. of the propulsion battery reaches a predetermined level.

13. The method of claim 12 , further including:

setting the charging current provided to the propulsion battery to zero amperes for a duration of the relaxation period.

14. The method of claim 12 , further including:

obtaining a first voltage of the propulsion battery upon conclusion of the relaxation period;

instructing the battery charger to resume providing a charging current to the propulsion battery;

obtaining a second voltage of the propulsion battery after the battery charger has resumed providing the charging current to the propulsion battery; and

determining the D.C. impedance of the propulsion battery based, at least in part on a difference between the first voltage of the propulsion battery and the second voltage of the propulsion battery.

15. A battery charging system comprising:

a battery data acquisition and monitoring subsystem;

a battery charger;

a controller coupled to the battery data acquisition and monitoring subsystem and the battery charger, the controller configured to:

during a charging operation:

initiate a relaxation period in response to a state of charge (S.O.C.) of a propulsion battery reaching a predetermined level during the charging operation;

receive a D.C. impedance of a propulsion battery from the battery data acquisition and monitoring subsystem;

obtain a reference D.C. impedance, the reference D.C. impedance indicating an impedance associated with a new battery;

determine an impedance degradation factor of the propulsion battery using the D.C. impedance and the reference D.C. impedance;

during operational use of the propulsion battery:

obtain an operational reference impedance of the propulsion battery;

determine a real-time effective impedance for the propulsion battery based on the impedance degradation factor and the operational reference impedance; and

generate a feed-forward parameter based on the real-time effective impedance.

16. The battery charging system of claim 15 , wherein the controller is further configured to:

determine that the propulsion battery is at a predetermined temperature prior to initiating the charging operation.

17. The battery charging system of claim 15 ,

wherein the D.C. impedance of the propulsion battery corresponds to a measurement made by the battery data acquisition and monitoring subsystem after the relaxation period.

18. The battery charging system of claim 17 , wherein the controller is further configured to:

instruct the battery charger to provide a charging current to the propulsion battery until the S.O.C. of the propulsion battery reaches a predetermined level.

19. The battery charging system of claim 17 , wherein the controller is further configured to:

set the charging current provided to the propulsion battery to zero amperes for a duration of the relaxation period.

20. The controller of claim 17 , wherein the controller is further configured to:

obtain a first voltage of the propulsion battery, from the battery data acquisition and monitoring subsystem, upon conclusion of the relaxation period;

instruct the battery charger to resume providing a charging current to the propulsion battery;

obtain a second voltage of the propulsion battery, the battery data acquisition and monitoring subsystem, after the battery charger has resumed providing the charging current to the propulsion battery; and

determine the D.C. impedance of the propulsion battery based, at least in part on a difference between the first voltage of the propulsion battery and the second voltage of the propulsion battery.