Charging control method and system for electric vehicle

1. A charging control method for an electric vehicle, comprising:

monitoring, by a controller, a state of an auxiliary battery including a state of charge (SOC) and temperature of the auxiliary battery;

determining, by the controller, a charging mode of the electric vehicle based on the monitored state of the auxiliary battery;

setting, by the controller, a charging voltage of the auxiliary battery based on the monitored SOC and temperature of the auxiliary battery; and

charging, by the controller, the auxiliary battery with the set charging voltage,

wherein the charging mode includes a charging-oriented mode for charging the auxiliary battery and a low-voltage charging mode for maintaining a voltage of the auxiliary battery, and

wherein the determination of the charging mode includes:

when the monitored SOC of the auxiliary battery is greater than a preset first SOC criterion for a preset first minimum holding time, determining, by the controller, the low-voltage charging mode of the vehicle as the charging mode; and

when the monitored SOC of the auxiliary battery is less than or equal to the preset first SOC criterion, determining, by the controller, the charging-oriented mode of the electric vehicle as the charging mode wherein the first minimum holding time is changed based on a value of the monitored SOC of the auxiliary battery.

2. The charging control method of claim 1 , further comprising:

after charging the auxiliary battery, changing, by the controller, the charging mode of the electric vehicle based on the monitored state of the auxiliary battery.

3. The charging control method of claim 2 , wherein the changing of the charging mode includes:

when a holding time of the charging-oriented mode is greater than a maximum time, changing, by the controller, the charging mode of the electric vehicle to the low-voltage charging mode.

4. The charging control method of claim 3 , wherein the maximum time is changed based on a value of the monitored SOC of the auxiliary battery.

5. The charging control method of claim 2 , further comprising:

monitoring, by the controller, the state of the auxiliary battery including the state of charge (SOC), the temperature, and charging current of the auxiliary battery,

wherein the changing of the charging mode comprises:

when the monitored SOC of the auxiliary battery is less than or equal to the first SOC criterion and is greater than a second SOC criterion, which is preset to a value less than that of the first SOC criterion, for a preset second minimum holding time, and when an average charging current of the auxiliary battery at the charging is greater than a charging current criterion, changing, by the controller, the charging mode of the electric vehicle to the low-voltage charging mode.

6. The charging control method of claim 5 , wherein the second minimum holding time is changed based on the value of the monitored SOC of the auxiliary battery.

7. The charging control method of claim 1 , wherein the setting of the charging voltage includes setting, by the controller, the charging voltage using map data in which the temperature and the SOC of the auxiliary battery based on the determined charging mode are used as inputs and the charging voltage is an output.

8. A charging control system for an electric vehicle, comprising:

a memory configured to store program instructions; and

a processor configured to execute the program instructions, the program instructions when executed configured to:

monitor a state of an auxiliary battery including a state of charge (SOC) and temperature of the auxiliary battery;

determine a charging mode of the electric vehicle based on the monitored state of the auxiliary battery;

set a charging voltage of the auxiliary battery based on the monitored SOC and temperature of the auxiliary battery; and

charge the auxiliary battery with the set charging voltage,

wherein the charging mode includes a charging-oriented mode for charging the auxiliary battery and a low-voltage charging mode for maintaining a voltage of the auxiliary battery, and

wherein the program instructions when executed are further configured to:

determine the low-voltage charging mode of the vehicle as the charging mode when the monitored SOC of the auxiliary battery is greater than a preset first SOC criterion for a preset first minimum holding time; and

determine the charging-oriented mode of the electric vehicle as the charging mode when the monitored SOC of the auxiliary battery is less than or equal to the preset first SOC criterion wherein the first minimum holding time is changed based on a value of the monitored SOC of the auxiliary battery.

9. The charging control system of claim 8 , wherein the program instructions when executed are further configured to:

change the charging mode of the electric vehicle based on the monitored state of the auxiliary battery after charging the auxiliary battery.

10. The charging control system of claim 9 , wherein the program instructions when executed are further configured to:

change the charging mode of the electric vehicle to the low-voltage charging mode when a holding time of the charging-oriented mode is greater than a maximum time.

11. The charging control system of claim 10 , wherein the maximum time is changed based on a value of the monitored SOC of the auxiliary battery.

12. The charging control system of claim 9 , wherein the program instructions when executed are further configured to:

change the charging mode of the electric vehicle to the low-voltage charging mode when the monitored SOC of the auxiliary battery is less than or equal to the first SOC criterion and is greater than a second SOC criterion, which is preset to a value less than that of the first SOC criterion, for a preset second minimum holding time, and when an average charging current of the auxiliary battery at the charging is greater than a charging current criterion.