Battery capacity detection system with temperature correction

Details Battery capacity detection system with temperature correction Battery capacity detection system with temperature correction

2000-07-03

2001-08-14

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

With charging

C320S150000

Reexamination Certificate

active

06275008

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a battery capacity detection system and, more particularly, to a battery capacity detection system with a chargeable capacity calculating function using a temperature sensor, for correcting a voltage in a full charge state by using an actually detected temperature and obtaining a chargeable capacity at the time point.
In recent years, an accurate prediction of a state of charge (SOC, also called dischargeable capacity) of a battery as a power source mounted on an electric vehicle has been being attempted.
Japanese Patent Application Laid-Open Publication No. 8-278351 discloses a battery SOC measuring apparatus.
In the battery SOC measuring apparatus, since calculation is easy, a battery controller calculates the SOC of a battery immediately after turning on an ignition by the following equation and displays the result.
SOC=
(
Vn
2
−Ve
2
)/(
Vs
2
−Ve
2
)×100(%)
where, Vn denotes an estimated voltage of the battery, Ve denotes a discharge end voltage (a fixed value) and Vs is a voltage of the battery in a fully charged state.
The voltage Vs in the fully charged state is a voltage when the battery is fully charged (substantially 100%) at the temperature of, for example, 20° C. in an initial state where degradation of the battery is not progressed yet. That is, the voltage Vs is a fixed value.
The estimated voltage Vn of the battery is obtained as follows. First, a predetermined number of values of each of a discharge current from the battery and a terminal voltage are collected and averaged. When a predetermined number of the averaged data is collected, a correlation coefficient (r) of the data is obtained. When the correlation coefficient (r) shows a strong negative correlation, a regression line (also called approximation line) is obtained by the method of least squares. From the approximation line Y (Y=aX+b) and a reference current Io, the present battery estimated voltage Vn is calculated.
The present SOC during driving is derived by the equation by using the estimated voltage Vn and the like and is properly displayed.
That is, in the battery SOC measuring apparatus, the SOC can be known without measuring the temperature.
In what is called a hybrid vehicle as well, the battery SOC measuring apparatus is used. Some battery SOC measuring apparatuses each for use in a hybrid vehicle obtain a regenerative energy to charge the battery. There is a case such that the SOC of the battery during driving is calculated, a chargeable capacity is obtained from the difference between the SOC and the SOC in the full charge state and, if it is chargeable, the battery is charged.
SUMMARY OF THE INVENTION
The inventors of the present invention have, however, examined and found that, even if the battery is in a fully charged state, the capacity tends to be calculated and displayed lower than the actual capacity when the temperature is low.
Specifically, as shown in
FIG. 6
, although the battery is in a fully charged state, when the temperature is low (for example, in winter), the voltage of the battery drops and the SOC characteristic is calculated and displayed lower than that at the time of high temperature (for example, in summer). Even when the electric vehicle is driven and a drive distance D becomes longer, such a state occurs.
For example, when the temperature is 20 (° C.) and the SOC is calculated as 90 (%), a chargeable state is determined and the battery is charged. When the temperature is 0 (° C.) and the SOC is 90 (%), there is a case such that the battery is already in a fully charged state.
Consequently, when it is calculated that the battery is not fully charged or the like, the battery is re-charged. At the time of low temperature, however, there is a case that the SOC is not calculated as 100 (%). In such a case, unnecessary charging is continuously performed and even a case such that it degrades the battery can be assumed.
The invention has been achieved on the basis of the above examinations and its object is to provide a battery capacity measurement apparatus with a chargeable capacity calculating function using a temperature sensor, which actually detects the temperature and can accurately calculate the chargeable capacity of the battery by using the detected temperature.
A battery capacity detection system according to the present invention comprises: a temperature sensor sensing a temperature of a battery; a full-charge voltage calculation processing section for calculating a voltage of the battery in a fully charged state by using the temperature of the battery sensed by the temperature sensor; and an SOC calculation section for calculating an SOC of the battery by using the voltage of the battery in the full-charge state calculated by using the temperature by the full-charge voltage calculation section.


REFERENCES:
patent: 5592094 (1997-01-01), Ichikawa
patent: 5650712 (1997-07-01), Kawai et al.
patent: 5767659 (1998-06-01), Farley
patent: 5-161215 (1993-06-01), None
patent: 8-278351 (1996-10-01), None
patent: 9-154202 (1997-06-01), None
patent: 10-293164 (1998-11-01), None

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