Battery's state-of-charge balancing control method for hybrid vehicle

A battery's state-of-charge (SOC) balancing control method for a hybrid vehicle is provided, in which the outside air temperature at a traveling destination is reflected to perform the control.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2009-0110676 filed Nov. 17, 2009, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates to a battery's state-of-charge (SOC) balancing control method for a hybrid vehicle, in which the outside air temperature at a traveling destination is considered in determining an SOC strategy value.

(b) Background Art

Hybrid vehicles employ an electric motor as an auxiliary power source as well as an internal combustion engine to reduce exhaust gas and improvement fuel efficiency. The electric motor is driven by charge and discharge of a battery to increase the efficiency of a hybrid system (load leveling). Moreover, the battery is charged by regenerative braking during deceleration, in which the kinetic energy, which would be otherwise dissipated as frictional heat by a brake system, is converted into electrical energy by the power generation of the motor, thereby improving the fuel efficiency.

Various factors affect the fuel efficiency and driving performance of hybrid vehicles. One of the factors is the state-of-charge (SOC) of the battery.

The battery is an energy source for operating the motor of the hybrid vehicle and a DC/DC converter, and a battery controller monitors the voltage, current, and temperature of the battery and controls the overall SOC (%) of the battery. The operating point of the battery should be controlled such that the battery's SOC is maintained in a normal range and, if the battery's SOC is out of the normal range, it should be controlled to be restored to the normal range.

In an SOC band control of a high voltage battery, when the battery's SOC is lower than a preset value, the engine should be operated at an operating point higher than a desired power level to control the battery's SOC to charge orientation. On the contrary, when the battery's SOC is higher, the battery's SOC should be controlled to discharge orientation by increasing the amount of energy discharged from the electric motor.

A conventional SOC band control method of a high voltage battery is described with reference toFIGS. 3 and 4.

As shown inFIG. 4, the conventional SOC band control method includes a step of monitoring the current SOC value, a step of determining the orientation of the SOC value with a predetermined hysteresis, a step of determining an SOC strategy value based on the current SOC value, and a step of controlling the operating point of the vehicle based on the SOC strategy value.

For example, as shown inFIG. 3, the SOC strategy values are divided into critical low range 0 (SOC 0 to 25), low range 1 (SOC 25 to 40), normal range 2 (SOC 40 to 70), high range 3 (SOC 70 to 80), and critical high range 4 (SOC 80 to 100).

The SOC strategy value is determined based on the SOC value transmitted from a battery controller (BMS), and a hysteresis is determined such that the SOC strategy value is not suddenly changed by the current SOC value. That is, the hysteresis is predetermined such that the SOC strategy value is not suddenly changed by the current SOC value, and the orientation of the SOC value is determined by the predetermined hysteresis.

However, when the SOC strategy value is determined based on only the current SOC value, it is difficult to maintain the SOC strategy value in the normal range 2 in the event of a sudden change in the outside air temperature at a particular destination where it is expected to use an substantial amount of electricity by an auxiliary electrical load such as an air conditioner.

SUMMARY OF THE DISCLOSURE

In one aspect, the present invention provides a battery's state-of-charge (SOC) balancing control method for a hybrid vehicle, the method including: monitoring a current SOC value; recognizing an outside air temperature at a traveling destination; calculating an SOC compensation value based on the outside air temperature at the traveling destination; determining an SOC strategy value in accordance with the calculated SOC compensation value; and controlling the operating point of the vehicle based on the determined SOC strategy value.

Preferably, orientation of the SOC value is determined based on a predetermined hysteresis.

Preferably, the determined SOC strategy value has a value obtained by subtracting from the current SOC value an SOC comparison value corresponding to an estimated amount of power consumed by an air conditioner at the traveling destination such that the determined SOC strategy value falls within a low range thereby enabling the battery to be charged.

Suitably, the outside air temperature at a particular destination may be automatically recognized when the destination is input into a navigation system.

DETAILED DESCRIPTION

For a better understanding of the present invention, it is described how an SOC strategy value is determined in a conventional SOC balancing control method with reference toFIG. 3. According to the conventional SOC balancing control method, for example, in a state where the current SOC value is 42, the current outside air temperature is 25° C., and the outside air temperature at a particular traveling destination is 35° C., the SOC strategy value is determined by considering the current SOC value transmitted from a battery controller (BMS) without considering the outside air temperature at a particular traveling destination. As a result, the SOC strategy value 42 is determined to fall within the normal range 2 (SOC 40 to 70).

That is, according to the conventional method, in a state where the current SOC strategy value is 42 but the amount of electrical energy to be used to operate an air conditioner, an auxiliary electrical load, at or toward the traveling destination is increased, it is determined that the battery does not need to be charged at present.

As a result, when the vehicle reaches the destination and the air conditioner is turned on in a state where the current SOC value falls within the normal range 2 (SOC 40 to 70), the hybrid vehicle operates in a discharge operating point, and thereby the battery's SOC may be reduced to a point below the normal range.

According to the present invention, on the other hand, the SOC strategy value is determined by considering the outside air temperature at a particular destination besides the current SOC value.

A method for determining an SOC strategy value in an SOC balancing control of a high voltage battery in accordance with an exemplary embodiment of the present invention will be described below with reference toFIGS. 1 and 2.

First, the battery controller monitors the current SOC value and recognizes the outside air temperature at a particular destination. Preferably, the outside air temperature at a particular destination may be input directly by a driver or automatically recognized when the driver inputs the destination into a navigation system.

The SOC strategy value is determined in accordance with a final SOC compensation value calculated based on the outside air temperature at the destination such that the SOC value, obtained by subtracting the SOC compensation value from the current SOC value considering the outside air temperature at the destination, falls within the range of 0 to 100. For example, when the current SOC value is 42, the current outside air temperature is 25° C., and the outside air temperature at the destination is recognized as 35° C., a strategy control (feed-forward control), in which the battery is charged in advance in the expectation that the use of the air conditioner is increased when the vehicle reaches the destination, is performed. That is, if the estimated amount of power to be consumed by the air conditioner at the temperature of the destination (i.e., an SOC comparison value SOC_Comp) is 5, the strategy determination input value for determining the SOC strategy value is 37, a value in the low range 1, which is obtained by subtracting the SOC comparison value SOC_Comp 5, from the current SOC value 42.

In the case where the SOC strategy value is above the normal range 2 (SOC 40 to 70), the hybrid vehicle operates in a discharge operating point. Whereas, when the SOC strategy value is below the normal range, the hybrid vehicle operates in a charge operating point.

Therefore, as the thus determined SOC strategy value falls within the low range 1 (SOC 25 to 40), the hybrid vehicle operates in the charge operating point, and the battery's SOC is charge-oriented controlled based on the determined SOC strategy value, thereby charging the battery. As a result, the SOC value can be controlled to maintain in the normal range.

According to the present invention, since the SOC strategy value is determined by considering the outside air temperature at a particular destination besides the current SOC value, it is possible to provide an efficient SOC balancing control. That is, since the SOC strategy value is determined in the expectation of an increase in the auxiliary electrical load, it is possible to maintain the SOC strategy value in the normal range, thereby providing an efficient SOC balancing control.