Method and system for controlling an electric vehicle while charging

1. A vehicle comprising:

a traction battery having a plurality of cells, the traction battery having a first pack exposed to a cabin temperature and a second pack spaced apart from the first pack and exposed to an external environmental temperature;

a thermal circuit connected to the traction battery, and having a thermal source, a thermal sink, and a valve system; and

a controller connected to the traction battery and the thermal circuit, the controller configured to: (i) charge the traction battery using a maximum charging current based on a lowest temperature cell while the traction battery is connected to a charger and external power source, (ii) heat the traction battery if the lowest temperature cell is below a predetermined temperature while the traction battery is charging, and (iii) control the valve system to bias heating to the pack having the lowest cell temperature.

2. The vehicle of claim 1 wherein the controller is configured to receive a maximum available current from the charger and external power source.

3. The vehicle of claim 2 wherein the maximum charging current is less than the maximum current from the charger and external power source.

4. The vehicle of claim 3 wherein the controller is configured to heat the traction battery using a current equal to the difference between the maximum available current and the maximum charging current.

5. The vehicle of claim 1 wherein the thermal source of the thermal circuit comprises an electric heater.

6. A method of controlling an electric vehicle comprising:

detecting if a traction battery is connected to a charger and external power source;

measuring cell temperatures in the traction battery to determine a lowest temperature cell;

charging the traction battery using a maximum charging current associated with the lowest temperature cell while the traction battery is connected to the charger and external power source; and

heating the traction battery using a current equal to the difference between a maximum available current from the charger and the maximum charging current if the lowest temperature cell is below a predetermined temperature while the traction battery is charging

wherein the maximum charging current associated with the lowest temperature cell is a percentage of the available current from the charger;

wherein the lowest cell temperature is within one of a series of temperature ranges, the series of temperature ranges being defined by a series of temperature thresholds, each temperature range having an associated percentage; and

wherein the percentage is a constant predetermined value within each temperature range, and decreases as the temperature range decreases.

7. The method of claim 6 wherein the maximum charging current associated with the lowest temperature cell is the minimum of one of a maximum current for the lowest temperature cell and a percentage of the available current from the charger.

8. The method of claim 6 wherein the maximum charging current is less than the maximum available current from the charger and external power source if the lowest temperature is below the predetermined temperature.

9. The method of claim 6 wherein charging the traction battery and heating the traction battery are conducted simultaneously.

10. The method of claim 6 further comprising adjusting the maximum charging current as the traction battery is heated and the temperature of the lowest temperature cell increases.

11. The method of claim 6 wherein the percentage is based on cell temperature.

12. A method for controlling an electric vehicle while connected to a charger, comprising, in response to a low cell temperature in a traction battery, charging the battery using a first portion of power from the charger while heating the battery using a second portion of power from the charger, the first and second portions a function of a series of predetermined percentages of power from the charger defined by a series of low temperature thresholds.

13. The method of claim 12 further comprising measuring a temperature for each cell in the battery to determine the low cell temperature.

14. The method of claim 12 further comprising estimating a temperature for each cell in the battery to determine the low cell temperature.

15. The method of claim 12 wherein the series of low temperature thresholds provides a series of temperature ranges, each temperature range having an associated percentage in the series of predetermined percentages of power.

16. The method of claim 15 wherein the percentage within each temperature range in the series of temperature ranges is a constant predetermined value.

17. The method of claim 15 wherein each percentage in the series of predetermined percentages of power decreases as the low temperature thresholds decrease in value thereby providing a decreasing first portion of power with decreasing temperature.

18. The method of claim 12 further comprising biasing heating to a pack in the traction battery with the low cell temperature, the traction battery having at least two packs.