Secondary battery system
A secondary battery system capable of acquiring an SOC of a battery with a simple computation without acquiring battery characteristics is to be provided. The secondary battery system according to the present invention is adapted to acquire a momentary SOC (charging SOC) by obtaining an initial value of an SOC from a CCV acquired during a charging period and adding an integrated value of a charge or discharge current to the initial value of the SOC, acquire a momentary SOC (discharging SOC) by obtaining an initial value of an SOC from a CCV acquired during a discharging period and adding an integrated value of a charge or discharge current to the initial value of the SOC, and acquire an SOC close to a true value by averaging the charging SOC and the discharging SOC.
1. A secondary battery system comprising:
a closed circuit voltage (CCV) voltage detection circuit which acquires each of a charging CCV at a predetermined charging point during a charging period of a battery and a discharging CCV at a predetermined discharging point during a discharging period of the battery; and
a battery pack control unit configured to:
calculate a charging state of charge (SOC) based on the charging CCV and a discharging SOC based on the discharging CCV;
calculate, based on the charging SOC and the discharging SOC, a corrected SOC having a reduced gap SOC error that is included in an SOC of the battery and results from a gap with an OCV;
replace, at a predetermined replacement point, the SOC of the battery with the corrected SOC, update the SOC of the battery, and reduce a cumulative SOC error included in the SOC of the battery and resulting from a measurement error of a current value;
acquire m (m is an integer of one or more) number of first SOCs based on the charging SOC and a fluctuation component of the SOC acquired based on a current value integrated from the predetermined charging point;
acquire n (n is an integer of one or more) number of second SOCs based on the discharging SOC and a fluctuation component of the SOC acquired based on a current value integrated from the predetermined discharging point; and
compute an averaged SOC as the corrected SOC by performing averaging processing with use of the m number of the first SOCs and the n number of the second SOCs.
2. A secondary battery system comprising:
a closed circuit voltage (CCV) voltage detection circuit which acquires each of a charging CCV at a predetermined charging point during a charging period of a battery and a discharging CCV at a predetermined discharging point during a discharging period of the battery; and
a battery pack control unit configured to:
calculate a charging state of charge (SOC) based on the charging CCV and a discharging SOC based on the discharging CCV;
calculate, based on the charging SOC and the discharging SOC, a corrected SOC having a reduced gap SOC error that is included in an SOC of the battery and results from a gap with an OCV;
replace, at a predetermined replacement point, the SOC of the battery with the corrected SOC, update the SOC of the battery, and reduce a cumulative SOC error included in the SOC of the battery and resulting from a measurement error of a current value;
acquire m (m is an integer of one or more) number of first SOCs based on an estimated charging SOC calculated by estimating an OCV from the charging CCV and a fluctuation component of the SOC acquired based on a current value integrated from the predetermined charging point;
acquire n (n is an integer of one or more) number of second SOCs based on an estimated discharging SOC calculated by estimating an OCV from the discharging CCV and a fluctuation component of the SOC acquired based on a current value integrated from the predetermined discharging point; and
compute an averaged SOC as the corrected SOC by performing averaging processing with use of the m number of the first SOCs and the n number of the second SOCs.
3. The secondary battery system according to claim 1 , wherein the predetermined charging point is a timing at which a charge current of a predetermined value or lower is detected after a charge current of a predetermined value or higher lasts for a predetermined time or longer, and the predetermined discharging point is a timing at which a discharge current of a predetermined value or lower is detected after a discharge current of a predetermined value or higher lasts for a predetermined time or longer.
4. The secondary battery system according to claim 1 , wherein the predetermined charging point or the predetermined discharging point is a timing at which a charge current or a discharge current of a predetermined value or lower is detected after integrating a charge amount or a discharge amount.
5. The secondary battery system according to claim 1 , wherein the battery pack control unit calculates one or more pairs of one of the first SOCs and one of the second SOCs and performs averaging processing on the first SOC and the second SOC.
6. The secondary battery system according to claim 5 , wherein the battery pack control unit includes: a storage unit which stores a plurality of pairs of one of the first SOCs and one of the second SOCs and discards an oldest pair when a latest pair is stored; and a computation unit which averages the plurality of pairs of the first SOCs and the second SOCs stored in the storage unit.
7. The secondary battery system according to claim 1 , wherein the secondary battery system is mounted in a vehicle system which performs charging control and discharging control of the battery and transmits, to the vehicle system, a command causing the discharging to start when charging lasts for a predetermined time and causing the charging to start when the discharging lasts for a predetermined time.
8. The secondary battery system according to claim 1 , wherein the charging period is a period during which a charger is connected while the discharging period is a period during which the charger is not connected, and
the charging CCV is a CCV acquired by the CCV voltage detection circuit at a point when charging by the charger results in a predetermined charge current value or lower while the discharging CCV is a CCV acquired by the CCV voltage detection circuit at a point when a discharge current value equals a predetermined current value or lower after a vehicle starts traveling upon disconnected from the charger.