Determining battery DC impedance

1. A battery charging system for a propulsion battery providing an operational current to an electric propulsion motor of an electric vehicle, the battery charging system comprising:

a charger coupled to the propulsion battery;

a battery data acquisition and monitoring subsystem; and

a battery management system configured to:

(a) measure a DC impedance of the propulsion battery after a recharging sequence of the propulsion battery that includes an intermediate depolarizing relaxation period in which a charging current of the propulsion battery is set to zero amperes for a predetermined length of time and establishes a relaxed parameter for the propulsion battery;

(b) determine a ratio of said measured DC impedance and a reference DC impedance for the propulsion battery to establish an impedance degradation factor;

(c) obtain, during use of the propulsion battery providing the operational current to the electric propulsion motor after a lapse of a sustained peak power period of provision of the operational current to the electric propulsion motor and responsive to a set of operational attributes of the propulsion battery acquired by said battery data acquisition and monitoring subsystem during provision of the operational current to the electric propulsion motor, an operational reference impedance for the propulsion battery; and

(d) apply said impedance degradation factor to said operational reference impedance to obtain a real-time effective impedance for the propulsion battery during provision of the operational current to the electric propulsion motor and wherein the propulsion battery includes lithium-ion energy storage elements; and

(e) providing a feed-forward parameter based on the real-time effective impedance, the feed-forward parameter controlling a level of sustained peak power.

2. The battery charging system of claim 1 , wherein the battery management system is further configured to control a charging current to the propulsion battery according to a profile.

3. The battery charging system of claim 2 , wherein the battery management system performs subtraction of a target voltage and a maximum cell voltage and uses the subtraction in producing the charging current.

4. The battery charging system of claim 1 , wherein the data acquisition and monitoring subsystem acquires at least voltage, state-of-charge and temperature.

5. The battery charging system of claim 1 , wherein the data acquisition and monitoring subsystem is part of the battery management system.

6. The battery charging system of claim 5 , wherein the battery management system including the data acquisition and monitoring subsystem is part of the charger.

7. The battery charging system of claim 1 , wherein obtaining the operational reference impedance includes using a low pass filter.

8. The battery charging system of claim 7 , wherein the battery management system performs a subtraction of the operational reference impedance obtained using the low pass filter and an impedance obtained by dividing a change in voltage by a change in current, and wherein the subtraction is provided to the low pass filter.

9. The battery charging system of claim 1 , wherein the relaxed parameter comprises a relaxed voltage of the propulsion battery.

10. The battery charging system of claim 1 , wherein obtaining the operational reference impedance comprises using a lookup table that is responsive to state-of-charge and battery temperature.

11. The battery charging system of claim 1 , wherein obtaining the real-time effective impedance comprises multiplying the impedance degradation factor and the operational reference impedance.

12. The battery charging system of claim 1 , wherein the battery management system is further configured to calculate available current or available power using the real-time effective impedance.

13. The battery charging system of claim 12 , wherein the battery management system is further configured to use the calculated available current or available power to represent a state-of-health of the propulsion battery.

14. The battery charging system of claim 1 , wherein the battery management system is further configured to use the calculated available current or available power to provide the feed-forward parameter.

15. The battery charging system of claim 14 , wherein the feed-forward parameter is used to indicate a level of sustained peak power.