Residual capacity measurement system for battery

Details Residual capacity measurement system for battery Residual capacity measurement system for battery

2000-06-26

2001-10-30

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

With charging

Reexamination Certificate

active

06310462

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for performing analysis, calculation, computation, determination, detection, estimation, measurement and/or prediction (hereinafter collectively referred to as “detection”) of the state of charge (hereinafter sometimes abbreviated as “SOC”) of a battery, in terms of a residual capacity, by using a saturation or full-charge voltage of the battery.
2. Description of the Related Art
The accurate estimation of the residual capacity is an important capability in an electrical vehicle which runs on battery power.
For example, in a battery residual capacity detection system disclosed in Japanese Patent Application Laid-Open Publication No.8-278351, making use of ease of calculation, a battery controller determines the residual capacity (SOC) of a battery immediately after an ignition switch is turned on, using the following expression (1), and displays this value.
SOC
=[(
Vn
2
−Ve
2
)]/(
Vs
2
−Ve
2
)]×100%  (1),
where Vn is an estimation voltage of the battery, Ve is a discharge-end voltage of the battery, and Vs is a full-charge voltage of the battery.
Generally, in the electrical vehicle, the battery is fully charged after a travel or trip, such as when in a guarage.
During operation of an electrical vehicle, the battery has its terminal voltage and discharge current providing their time-dependent values, of which prescribed numbers are collected on associated axes of a voltage vs. current coordinate system, where they are averaged to provide a set of corresponding component data. When a prescribed number of such sets of data have been accumulated, a correlation between their component data is calculated to determine its coefficient r, and an associated regressoin line is defined as an expression for linear approximation, such that Y=aX+b, where Y and X are values on the axes of the coordinate system, and “a” and “b” are constants. As the coefficient r indicates a significant negative correlation, the regression line is determined by applying the method of least squares to calculation of the constants “a” and “b”. A current value of the battery voltage Vn is estimated by subsituting a reference current Io into the expression of linear approximation.
Then, the estimation voltage Vn is substituted into the expression (1) to determine the residual capacity of the battery in terms of a current SOC during vehicle operation.
As shown in
FIG. 11
for relatively high ambient temperatures, the residual capacity is calculated to be displayed as a 100% at the startup of operation (switching of ignition to on and start of driving) after a full charge. As the vehicle is driven, the residual capacity gradually decreases along a given characteristic curve.
At relatively low temperatures, however, the battery capacity becomes smaller than in a high-temperature range.
Thus, as shown in
FIG. 12
, in contrast to the residual capacity characteristic in the high temperature range (for example, on a summer day), it so happens in a low temperature range (for example, during the winter) that, even though the battery is fully charged, the battery voltage remains short, with a failure to display a matured residual capacity.
Under this condition, because the battery is apparently not fully charged, charging tends to be kept continued. Further, there will not be displayed an initial 100% residual capacity, and the charging might be kept long, resulting in possible deterioration of the battery.
Even if a correction is made for calculation to display an initially 100% residual capacity after a full charge in a low temperature range, a full-charge voltage Vs to be used therefor upon completion of an associated full charge is to be used as a constant in the expression (1). Thus, at low temperatures in the range, calculated values of the residual capacity describe another tendency than a gradual drop from the 100%, as illustrated by a residual capacity characteristic A in FIG.
13
.
For example, with a full charge at a low temperature, the characteristic A would indicate a gradual decrease from a 80% residual capacity, when driving. Initially after the full charge, however, there would be a sudden decrease (a) from a 100% to lower than the 80% (for example, to a 70%), before entering the gradual decrease.
At low temperatures in the ragne, therefore, even if the battery has a full charge, the displayed residual capacity will be lower, so that the driver will think that the drivable distance is shorter than it actually is.
Further, even while driving, the residual capacity at part of the characteristic curve A subsequent from the sudden decrease (a) might be by calculation based on the constant voltage Vn, thus having wrong values displayed.
SUMMARY OF THE INVENTION
The present invention has been made with such points in view. It therefore is an object of the present invention to provide a residual capacity detection system for a battery enabling a residual battery capacity of 100% to be detected immediately after a full charge, irrespective of ambient temperatures to be high or low. It is preferable if like detection can be maintained as well during subsequent operation.
An aspect of the present invention to achieve the object is a battery residual capacity detection system having a calculator for estimating the battery voltage from a linear approximation representing a relationship between a terminal voltage of the battery, detected by a voltage detector and a current flowing in a load from the battery, detected by a current sensor, and a reference current, and determining the residual capacity of the battery from this estimation voltage, a full-charge voltage, and a discharge-end voltage, the calculator having a full-charge voltage corrector that, immediately after a change in the load, reads the obtained estimation voltage, changes the full-charge voltage to the estimation voltage, determines the residual capacity.
By adopting this configuration, the full-charge voltage is the estimation voltage of the battery immediately after a change in the load, the subsequent residual capacity being calculated in accordance with this full-charge voltage (battery voltage estimated immediately after a change in the load). Thus, even under residual capacity variation related to the temperature, the residual capacity is determined using the full-charge voltage at the time of the change, resulting in a determination of the residual capacity that takes into consideration the influence of temperature.
The present invention also has a full-charge voltage estimator. Immediately after a change occurs in the load, the full-charge voltage estimator deletes the current full-charge voltage setting, then reads the estimation voltage obtained immediately after the change and the maximum set maximum residual capacity, and using the maximum residual capacity, the estimation voltage obtained immediately after the change in the load, and the discharge-end voltage to estimate and set the new full-charge voltage.
For this reason, after charging is ended midway, the estimated battery voltage immediately after the electrical vehicle motor is driven and the load changes is used to estimate the full-charge voltage corresponding to that estimation voltage, this estimated full-charge voltage being used to determine the residual capacity.


REFERENCES:
patent: 5539318 (1996-07-01), Sasaki
patent: 5872453 (1999-02-01), Shimoyama et al.
patent: 5898292 (1999-04-01), Takemoto et al.
patent: 8-62310 (1996-03-01), None
patent: 8-240647 (1996-09-01), None
patent: 8-278351 (1996-10-01), None
patent: 9-318717 (1997-12-01), None
patent: 10-24670 (1998-09-01), None

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