Secondary battery control device and SOC detection method

A control system of a secondary battery comprising:

• an electrode using positive electrode active material that shows a difference between an open circuit voltage curve charge and an open circuit voltage curve during discharge;
• and
• a voltmeter for detecting a terminal voltage of the secondary battery;
• an ammeter for detecting a current value of the secondary battery;
• a controller configured to detect the discharge of the secondary battery, the controller comprising:
• a storing unit configured to store discharge open circuit voltage information, the discharge open circuit voltage information being a relationship between an SOC in a discharge process and an open circuit voltage for each changeover SOC, wherein a changeover SOC being defined as an SOC when changing a state of the secondary battery from charging to discharging;
• an SOC calculating unit configured to calculate the SOC of the secondary battery in the discharge process, by:
• in response to determining that a charge of the secondary battery is finished:
• obtaining the terminal voltage form the voltmeter;
• obtaining the current value from the ammeter;
• determining an open circuit voltage based on the terminal voltage and the current value;
• determining a changeover SOC, wherein the changeover SOC corresponds to the open circuit voltage on the open circuit voltage curve during charge;
• obtaining, from the storing unit, a relationship based on the changeover SOC, wherein the relationship differs from the open circuit voltage curve during discharge;
• and
• in response to determining a discharge of the secondary battery is started, using the relationship to determine the SOC of the secondary battery;
• and
• discharging the secondary battery according to the relationship instead of according to the open circuit voltage curve during discharge.