1. Field of the Invention
Aspects of the present invention relate to a battery management system. More particularly, aspects of the present invention relate to a state of charge (SOC) reset method usable in a vehicle using electrical energy, and a battery management system using the same.
2. Description of the Related Art
Many vehicles have an internal combustion engine that uses gasoline or heavy oil as a main fuel. Such vehicles have a serious influence on the generation of environmental pollution. Examples of such pollution include air pollution. In recent years, much effort has been made to develop an electric vehicle or a hybrid vehicle to reduce the generation of environmental pollution.
An electric vehicle refers to a vehicle using a battery engine that operates on electrical energy output from a battery. As a main power source, the electric vehicle uses a battery in which a plurality of rechargeable secondary cells is provided as one pack. Accordingly, the electric vehicle is advantageous in that no discharge gas is produced, and noise that is produced is very small.
A hybrid vehicle refers to an intermediary vehicle between the vehicle using an internal combustion engine and the electric vehicle using an electric motor as an engine. The hybrid vehicle uses two or more power sources, which include an internal combustion engine and the electric motor. Currently, a type of the hybrid vehicle that uses an internal combustion engine and a fuel cell is being developed. The fuel cell directly obtains electrical energy from an induced chemical reaction of a continuously supplied hydrogen and oxygen. Another type of the hybrid vehicle uses a battery and a fuel cell.
In the electric or the hybrid vehicle that uses the electrical energy, performance of the battery has a direct influence on the performance of the vehicle. Thus, not only should each battery cell have excellent performance, but each battery cell should also have a battery management system (BMS) to measure a voltage of each battery cell, and a voltage and a current of a whole battery. Accordingly, a way to effectively manage charge and discharge of each battery cell is seriously required.
Particularly, when an initial state of charge (SOC) is to be reset in estimating a state of charge (SOC) of the battery, an open circuit voltage (OCV) is measured upon a key-on state, and the initial SOC is reset using a relation table of the SOC relative to the OCV.
To reset the SOC, the battery must not have been charging and discharging for a predetermined time so that the OCV could be measured. The SOC associated with the measured OCV is then calculated, to thereby reset the initial SOC. When the battery has not been charged and discharged for a predetermined time, the OCV is reset once the chemical reaction in the battery is stabilized and the voltage does not change. Once the OCV is reset, the SOC associated with a reset value of the OCV is calculated, and the estimated SOC is obtained using the calculated SOC.
However, in a related art, a waiting time necessary to reset the OCV, which is a time when the battery is not charged and discharged, is set irrespective of a state of the battery. In some cases, the OCV cannot be reset because the charge and discharge may begin before the waiting time expires. Accordingly, the SOC also cannot be reset, and causes problems in exactly calculating the SOC.