JPH1070849A - Pull charging detection method and charging controller for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a full charging detection method and a charge controller by monitoring a charge current and a charging time during a constant voltage charging for secondary batteries, by eliminating error in charging time by detecting the full charging state from the amount of change of charging per hour during the relevant constant voltage charging, and enhancing the charging performance and shortening the charging time. SOLUTION: A calculating section (CAL) 12d calculates the change in current value per unit time [Bnow =(I1-I2)/(t2-t1)] from a detection current received from a current detection section (C-DET) 12b and also measuring time received from time counting section (TIM) 12c. The full charging detecting section (FC-DCT) 12e compares the change [Bnow] in the current value to the change in current value [Bstop] per unit time during full charging retained internally and judges whether the secondary batteries (BATT) 10 have become a full charging state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting full charge of a secondary battery such as a lithium ion battery which requires constant voltage charge control, and a charge control device.

[0002]

2. Description of the Related Art Many information processing apparatuses, such as portable personal computers, which are easily carried, incorporate a secondary battery as an operating power source. In charge control of this type of secondary battery, when it reaches full charge,
Since charging is stopped immediately, a full charge detection function is indispensable.

Conventionally, lithium ion batteries have been widely used as secondary batteries in this kind of equipment. In the charge control of this lithium ion battery, it is necessary to perform charge control within a range not exceeding an allowable upper limit voltage due to inherent characteristics of the battery, and therefore, charge control by a constant voltage is required.

With respect to the above-described charge control technique for a lithium ion battery, a first prior art will be described with reference to FIGS. 11 and 12. FIG. FIG. 11 is a diagram showing an example of a charging voltage / current characteristic of a lithium ion battery.

As shown in FIG. 11, in the latter half of charging, the charging current (I) gradually decreases by constant voltage control. Here, the charging current is the full charging detection current [Isto
p], it is determined that the battery is fully charged.

FIG. 12 is a block diagram showing an example of a circuit configuration of a conventional charging circuit for controlling charging of the above-mentioned lithium ion battery. In FIG. 12, a charging circuit (CHG) 121 supplies charging power to a secondary battery (BATT) 120 composed of a lithium ion battery cell. The charge control unit (CHG-CONT) 122 controls the switch 123 to output a charge from the charging circuit (CHG) 121 to the secondary battery (BA).
The power supply to the TT) 120 is turned on / off.

A charge control unit (CHG-CONT) 1
Reference numeral 22 denotes a current detection unit (C-DET) 124 from a charging circuit (CHG) 121 to a secondary battery (BATT) 120.
The charging current [Inow] is monitored sequentially.

At the start of charging, a charge control unit (CHG-CON
T) 122 controls the switch 123 to charge the charging circuit (C
HG) 121 to the secondary battery (BATT) 120.

Charge control unit (CHG-CONT) 122
Stores the current value [Istop] in advance,
Full charge is detected when [Inow ≦ Istop] is reached. When full charge is detected, the charge control unit (CHG-CO
NT) 122 controls the switch 123 to control the charging circuit (C
HG) Stop charging from 121.

However, the above-mentioned prior art has the following problems. Current detector (C-DE
FIG. 14 shows an example of the current value read at T) 124. Here, the actual change in the current value is continuous as shown in the graph (1) in the figure, but the current value read by the current detection unit (C-DET) 124 is converted into a digital value as shown in the graph (2). Current reading unit (C-DET) to read the converted value
Even if the read value of 124 is [I1], the actual current value is between [I1 and I2].

[0011] The maximum of this reading error is [Idigi
t], the time from the start of charging to the end of charging is [ts]
[top], [tstop] is the current error [Id]
igit] will cause a maximum [tdigit] error.

As described above, in the above-described prior art, there is a problem that a relatively large error may occur in the detection of the full charge. In addition, when such an error in the full charge time occurs, the current characteristic near the full charge has a small current change with respect to the time change, so that [tdigit] increases even with a small current error. . Further, in the vicinity of the full charge, the current capacity charged during [tdigit] is very small with respect to the entire charge current capacity, so that time is wasted.

As described above, in the above-mentioned prior art, there is a problem that a large waste of time is likely to be caused in the detection of the full charge at the time of charging. Next, a second related art will be described with reference to FIGS.

FIG. 13 is a block diagram showing a circuit configuration of the second prior art. In FIG. 13, the charging circuit (CH
G) 131 supplies charging power to the secondary battery (BATT) 135. The switch 132 turns on / off charging. The ammeter (C-MET) 133 measures a voltage value [Vnow] according to the charging current.

The comparing unit (COMP) 134 is connected to the [Vno
w] and the internal reference voltage, and the above [Vno
When [w] falls below the reference voltage, the switch 132 is turned off. Here, according to the full charge detection current [Istop],
The full charge detection voltage in the ammeter (C-MET) 133 is [Vstop], and the reference voltage in the comparison unit (COMP) 134 is [Vstop].

At the start of charging, the switch 132 is turned on, and the charging circuit (CHG) 131 supplies the secondary battery (BAT).
T) The power supply to 135 is started. Comparison section (COM
P) 134 compares [Vnow] with [Vstop], turns off the switch 132 when [Vnow ≦ Vstop] is reached, and stops charging from the charging circuit (CHG) 131.

However, the above-mentioned prior art has the following problems. Ammeter (C-MET)
133 has a reading accuracy and a reading value has an error. [Isto] as in the first prior art described above.
Even if p] is set, an error occurs in the time for detecting full charge. Further, even if [Istop] is set in consideration of the error, there is a variation in the error among the ammeters, and when the error is corrected uniformly, a difference in the full charge time occurs between the devices. Further, when the above error is corrected for each device, much time and labor is required for inspection and adjustment, and it is not practically used in consideration of the influence on manufacturing costs and the like.

When such an error in the full charge time occurs, the current characteristic near the full charge has a small current change with respect to the time change, so that even a small current error is [tdigit]. Becomes larger. Further, in the vicinity of the full charge, the current capacity charged during [tdigit] is very small with respect to the entire charge current capacity, so that time is wasted.

As described above, in the above-described prior art, there is a problem that a relatively large time variation occurs in the detection of the full charge and a large amount of time is wasted when charging.

[0020]

As described above, in the charging control of the secondary battery which requires the constant voltage charging control, conventionally, the detection of the full charge has a relatively large variation in time, and the charging is not performed. There has been a problem that a large amount of time is often wasted.

The present invention has been made in view of the above circumstances,
In charge control of a secondary battery that requires constant voltage charge control, it is possible to improve charging performance by eliminating a charge time error due to a current value reading error, and to improve the charge performance of a secondary battery that can reduce the charge time. It is an object to provide a charge detection method and a charge control device.

[0022]

SUMMARY OF THE INVENTION The present invention relates to a method for detecting a full charge of a secondary battery which requires constant voltage charge control, wherein a charge current and a charge time at the time of constant voltage charge of the secondary battery are determined. Monitoring is performed to detect a full charge state from the amount of change in charging current per predetermined time during the constant voltage charging.

As described above, by detecting the full charge based on the change of the charging current per unit time, the variation in the charging end time due to the current detection error can be eliminated, the charging performance can be improved, and the charging time can be shortened.

Further, the present invention provides a charging control apparatus for a secondary battery requiring constant voltage charging control, wherein a means for measuring a charging current and a charging time at the time of constant voltage charging of the secondary battery is provided. Means for detecting the amount of change in charging current per predetermined time based on each of the measured values, comparing the charging current change value with a set value, and when the charging current change value is equal to or less than the set value, Means for determining that the secondary battery has reached a fully charged state.

As described above, by detecting the full charge based on the change in the charging current per unit time, the variation in the charging end time due to the current detection error can be eliminated, and the charging performance can be improved and the charging time can be shortened.

Further, the present invention relates to a method for detecting full charge of a secondary battery which requires constant voltage charge control, wherein a charge current, a charge time, and a temperature (battery temperature or battery ambient temperature) of the secondary battery are provided. Is monitored, and a full charge state is detected from the amount of change in the charging current per predetermined time during constant voltage charging and the temperature of the battery.

As described above, by providing a function of detecting full charge based on a change in charging current per unit time and correcting a full charge detection error in accordance with a change in battery temperature, variations in charging end time due to a current detection error are provided. , The charging performance can be improved, and the charging time can be shortened.

According to another aspect of the present invention, there is provided a charge control device for a secondary battery requiring constant voltage charge control, wherein a means for holding a set current value for detecting a full charge of the secondary battery, Means for measuring the charging current, charging time, and temperature during constant voltage charging of the secondary battery, and means for detecting a change in the charging current per predetermined time based on the measured charging current and charging time. Means for variably controlling the set current value according to the measured battery temperature, comparing the charge current change value with the set current value, and when the charge current change value is equal to or less than the set current value, the secondary battery Means for determining that the battery is fully charged.

As described above, full charge is detected based on a change in charging current per unit time, and a full charge detection error is corrected in accordance with a change in battery temperature. , The charging performance can be improved, and the charging time can be shortened.

The present invention also relates to a method for detecting full charge of a secondary battery which requires constant voltage charge control, wherein when the charge current at the time of constant voltage charge changes by a predetermined value or more, the required change at which the change occurs A time is calculated, and the required time is compared with a set value to detect a fully charged state of the secondary battery.

As described above, by detecting the full charge based on the time change per current, variations in the charge end time due to a current detection error can be eliminated, and the charging performance can be improved and the charging time can be shortened.

Further, according to the present invention, there is provided a charge control device for a secondary battery requiring constant voltage charge control, a means for detecting a charge current as a digital value, a digital counter for counting time, and a digital counter for counting time. A first step of storing a value of the digital counter when a charging current changes by a predetermined value or more;
And a second register that stores the value before the update each time the value of the first register is updated, and calculates a difference between the values stored in the first and second registers. Means for comparing the difference value and the set value, and the result of the comparison,
Means for detecting a full charge state of the secondary battery when the difference between the values stored in the first and second registers is larger than a set value.

As described above, by detecting the full charge based on the time change per current, variation in the charge end time due to a current detection error can be eliminated, and the charging performance can be improved and the charging time can be shortened.

According to the present invention, there is provided a method for detecting a full charge of a secondary battery which requires constant voltage charge control, wherein a charge current, a charge time, and a temperature (battery temperature or battery ambient temperature) of the secondary battery are provided. When the charging current during constant voltage charging changes by a predetermined value or more, the required time at which the change occurs is calculated, and the required time is compared with a set value determined by the temperature of the battery, and the secondary time is calculated. It is characterized by detecting a fully charged state of the battery.

As described above, by providing the function of detecting the full charge by the time change per current and correcting the full charge detection error due to the change of the battery temperature, the variation of the charge end time due to the current detection error can be reduced. Eliminating it can improve the charging performance and shorten the charging time.

Further, according to the present invention, there is provided a charge control device for a secondary battery requiring constant voltage charge control, a means for detecting a charge current as a digital value, a digital counter for counting time, Is changed by one digit or more, a first register for storing the value of the digital counter, and a second register for storing the value before update stored in the first register when updating the first register.
A third register for storing the battery temperature of the secondary battery or the ambient temperature of the battery as a digital value; a means for determining a set value based on the value stored in the third register; A means for calculating a difference between the updated values of the second register and comparing the difference value with the determined set value;
Means for detecting a full charge state of the secondary battery when the difference between the values stored in the registers is larger than the set value.

As described above, full charge is detected based on a time change per current, and a full charge detection error is corrected in accordance with a change in battery temperature. As a result, the charging performance can be improved and the charging time can be shortened.

[0038]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described with reference to FIGS. The first embodiment of the present invention monitors a charging current and a charging time at the time of constant voltage charging of the secondary battery, and determines a full charging based on a change amount of the charging current per predetermined time during the constant voltage charging. The state is detected.

FIG. 1 is a block diagram showing the configuration of the device according to the first embodiment of the present invention. In the figure, reference numeral 10 denotes a secondary battery (BAT) requiring charging at a constant voltage to be charged.
T), 11 are a charging circuit (CHG) for charging the secondary battery (BATT) 10 with a constant current and a constant voltage, and 12 is a secondary battery (BA).
TT) 10 (CHG-CON)
T).

Reference numeral 13 denotes a charge control unit (CHG-CONT) 1 interposed in a charging current path of the secondary battery (BATT) 10.
Reference numeral 14 denotes a charge control switch which is turned on / off by the reference numeral 2, and 14 denotes an ammeter (C-MET) for measuring a charging current.

Reference numerals 12a to 12f each constitute an internal component of the charge control unit (CHG-CONT) 12. Reference numeral 12a denotes an A / D converter for converting an analog measurement current of an ammeter (C-MET) 14 into a digital value. (A /
D).

Reference numeral 12b denotes an A / D converter (A / D) 12.
A current detection unit (C-DET) for detecting the current value digitally converted in a. 12c is a secondary battery (BATT)
Time measuring unit (T
IM).

12d is a current detector (C-DET) 12b
From the detected current of the above and the measurement time of the timer (TIM) 12c,
A calculation unit (CAL) that calculates a change (Bnow) of a current value per unit time.

Reference numeral 12e compares the change [Bnow] of the current value calculated by the calculation unit (CAL) 12d with the change [Bstop] of the current value per unit time at the time of full charge held inside the secondary battery (Bstop). BATT) 10 is a full charge detection unit (FC-DET) for detecting full charge.

12f is a full charge detection unit (FC-DET) 1
A switch control unit (SWC) that controls on / off of a charge control switch 13 interposed in a charging current path between the charging circuit (CHG) 11 and the secondary battery (BATT) 10 under the control of 2e. .

FIG. 2 is a diagram showing the charging current characteristic of the secondary battery (BATT) 10 for explaining the operation in the first embodiment. FIG. 3 is a flowchart for explaining the operation in the first embodiment.

The operation of the first embodiment of the present invention will be described with reference to FIGS. Secondary battery (B
ATT) 10 has an allowable upper limit voltage and requires constant voltage charging for charging. Here, the secondary battery (BATT) 10
When the full charge current of the secondary battery (BATT) 10 is [Istop], the change [Bstop] of the current value per time when the secondary battery (BATT) 10 is fully charged is Bstop = (I3-Istop) as shown in FIG. / (Tstop-t
3).

The charging circuit (CHG) 11 supplies a charging current to the secondary battery (BATT) 10 by constant current / constant voltage control. When the charge control unit (CHG-CONT) 12 detects that the secondary battery (BATT) 10 is fully charged, it turns off the charge control switch 13 to terminate the charging of the secondary battery (BATT) 10.

The operation from the start of charging of the secondary battery (BATT) 10 to the detection of full charge will now be described with reference to the flowchart shown in FIG. When the secondary battery (BATT) 10 to be charged is mounted on a predetermined charging device,
In the charge control unit (CHG-CONT) 12, the switch control unit (SWC) 12f controls the switch-on of the charge control switch 13 to start charging the secondary battery (BATT) 10. At the time of this charging, the charging circuit (CHG) 1
1 supplies a charging current to the secondary battery (BATT) 10 by constant current / constant voltage control as shown in FIG.

At the time of charging the secondary battery (BATT) 10, an ammeter (C-MET) 14 measures a charging current and uses the measured current value as a charging control unit (CHG-CON).
T) 12 to the A / D converter (A / D) 12a (step S1 in FIG. 3).

The timer (TIM) 12c in the charge controller (CHG-CONT) 12 measures the time when the secondary battery (BATT) 10 is charged at a constant voltage, and sends the measured time to the calculator (CAL) 12d. (Step S2 in FIG. 3).

The A / D converter (A / D) 12a converts the current value measured by the ammeter (C-MET) 14 into a digital signal and sends it to the current detector (C-DET) 12b. Further, the current detection unit (C-DET) 12b has an A / D
A current value received from the converter (A / D) 12a is detected and sent to a calculation unit (CAL) 12d.

The calculation unit (CAL) 12d calculates a change in current value per unit time [Bnow] based on the detection current received from the current detection unit (C-DET) 12b and the measurement time received from the timer unit (TIM) 12c. = (I1-I2) / (t
2-t1)], and sends this [Bnow] to the full charge detection unit (FC-DET) 12e (step S in FIG. 3).
3).

The full charge detector (FC-DET) 12e is
Change in current value received from calculation unit (CAL) 12d [Bn
ow] and the change [Bstop] of the current value per unit time at the time of full charge held inside the secondary battery (B).
ATT) 10 is determined to be in a fully charged state (step S4 in FIG. 3).

When the full charge detection section (FC-DET) 12e satisfies [Bnow ≦ Bstop], the secondary battery (B
ATT) 10 when the switch control unit (S)
WC) 12f to send a full charge detection signal (step S5 in FIG. 3).

When the switch control unit (SWC) 12f receives the full charge detection signal from the full charge detection unit (FC-DET) 12e, it turns off the charge control switch 13 and ends the charging of the secondary battery (BATT) 10. I do.

As described above, by detecting the full charge based on the change in the charging current per unit time, the variation in the charging end time due to the current detection error can be eliminated, the charging performance can be improved, and the charging time can be shortened.

Next, a second embodiment of the present invention will be described with reference to FIGS.
An embodiment will be described. The second embodiment of the present invention monitors the charging current, charging time, and temperature (battery temperature or battery ambient temperature) of the secondary battery, and changes the charging current per predetermined time during constant voltage charging. It is characterized by detecting a fully charged state from the amount and the temperature of the battery.

FIG. 4 is a block diagram showing the configuration of the device according to the second embodiment of the present invention. In the figure, reference numeral 20 denotes a secondary battery (BAT) requiring constant voltage charging, which is to be charged.
T) and 21 are a charging circuit (CHG) for charging the secondary battery (BATT) 20 with a constant current and a constant voltage, and 22 is a secondary battery (BA)
Charge control unit (CHG-CON) that controls charging of the TT) 20
T).

Reference numeral 23 denotes a charge control unit (CHG-CONT) 2 interposed in a charging current path of the secondary battery (BATT) 20.
2 is a charge control switch whose on / off control is performed by the switch 2. Reference numeral 24 denotes an ammeter (C-MET) for measuring a charging current interposed in the charging current path.

Reference numeral 25 denotes a temperature sensor (TH) for measuring the battery temperature of the secondary battery (BATT) 20, which transmits the measured temperature data to a temperature detector (T-T) described later in the charge controller (CHG-CONT) 12. DET) 22e.

Reference numerals 22a to 22g each constitute an internal component of the charge control unit (CHG-CONT) 22. Reference numeral 22a denotes an A / D converter for converting an analog current measured by an ammeter (C-MET) 24 into a digital value. (A /
D).

Reference numeral 22b denotes an A / D converter (A / D) 22
A current detection unit (C-DET) for detecting the current value digitally converted in a. 22c is a secondary battery (BATT)
Time measuring unit (T
IM).

Reference numeral 22d denotes a current detector (C-DET) 22b
From the detected current of the above and the measurement time of the timer (TIM) 22c,
A calculation unit (CAL) that calculates a change (Bnow) of a current value per unit time.

Reference numeral 22e denotes a temperature detector (T-DET) for detecting a battery temperature [Tbat] from temperature data obtained from a temperature sensor (TH) 25 provided inside the secondary battery (BATT) 20. Battery temperature [Tbat]
To the full charge detection unit (FC-DET) 22f described later.

Reference numeral 22f denotes a change [Bnow] of the current value calculated by the calculator (CAL) 22d and a temperature detector (T-DE).
T) Receiving the battery temperature [Tbat] detected at 22e, the change [Bnow] of the current value and the current value per unit time at full charge selected on the table according to the battery temperature [Tbat]. A full charge detection unit (FC-DET) that detects the full charge of the secondary battery (BATT) 20 by comparing the change [Bstop] with the change [Bstop].

That is, the full charge detection section (FC-DET) 22
f is a predetermined battery temperature [T1], [T2],
[T3], change in current value per time corresponding to [Tn] [Bstop-1], [Bstop-2], [Bs
top-3],... [Bstop-n] are stored, and the battery temperature [Tba] is stored on this table.
t] and select one [Bstop (-i)] according to
[Bstop] for full charge detection is determined.

22g is a full charge detection section (FC-DET) 2
A switch control unit (SWC) that controls ON / OFF of a charge control switch 23 interposed in a charging current path between the charging circuit (CHG) 21 and the secondary battery (BATT) 20 under the control of 2f. .

FIG. 5 is a diagram showing the charging current characteristics of the secondary battery (BATT) 20 for explaining the operation in the second embodiment. FIG. 6 is a flowchart for explaining the operation in the second embodiment.

The operation of the second embodiment of the present invention will be described with reference to FIGS. Secondary battery (B
ATT) 20 has an allowable upper limit voltage and requires constant voltage charging for charging. This secondary battery (BATT) 20
As shown in FIG. 5, the charging current characteristic of
Then, it changes as shown in graph (1) and at T2 ° C. as shown in graph (2).

The full charge current value at T1 ° C. is [Istop
1], and the full charge current value at T2 ° C. is [Istop
2]. At this time, the change in the current value per time [B
stop] is [Bstop1] = (I3-Istop1) / (tst
op1-t3) [Bstop2] = (I4-Istop2) / (tst
op2-t4).

As described above, the change in the current value per hour of the secondary battery (BATT) 20 changes depending on the battery temperature. The charging circuit (CHG) 11 supplies a charging current to the secondary battery (BATT) 20 by constant current / constant voltage control.
The charge control unit (CHG-CONT) 22 includes a secondary battery (BA
When the full charge of the TT) 20 is detected, the charge control switch 2
3 is turned off, and charging of the secondary battery (BATT) 20 is terminated.

Here, the operation from the start of charging of the secondary battery (BATT) 20 to the detection of full charge will be described with reference to the flowchart shown in FIG. When the secondary battery (BATT) 20 to be charged is mounted on a predetermined charging device,
In the charge control unit (CHG-CONT) 22, the switch control unit (SWC) 22g controls the charge control switch 23 to switch on, and starts charging the secondary battery (BATT) 20. At the time of this charging, the charging circuit (CHG) 2
1 is a secondary battery (BATT) by constant current / constant voltage control
20 is supplied with a charging current.

At the time of charging the secondary battery (BATT) 20, an ammeter (C-MET) 24 measures a charging current and uses the measured current value as a charging control unit (CHG-CON).
T) 22 to the A / D converter (A / D) 22a (step S11 in FIG. 6).

The timer (TIM) 22c in the charge controller (CHG-CONT) 22 measures the time when the secondary battery (BATT) 20 is charged at a constant voltage, and sends the measured time to the calculator (CAL) 22d. (Step S12 in FIG. 6).

The A / D converter (A / D) 22a converts the current value measured by the ammeter (C-MET) 24 into a digital signal, and sends it to the current detector (C-DET) 22b. The current detector (C-DET) 22b detects a current value received from the A / D converter (A / D) 22a and sends it to a calculator (CAL) 22d.

The calculation unit (CAL) 22d calculates a change in current value per unit time [Bnow] based on the detection current received from the current detection unit (C-DET) 22b and the measurement time received from the timer unit (TIM) 22c. = (I1-I2) / (t
2-t1)], and sends this [Bnow] to the full-charge detector (FC-DET) 22f (step S in FIG. 6).
13).

On the other hand, the temperature sensor (TH) 25 provided in the secondary battery (BATT) 20
T) The battery temperature of 20 is measured, and the measured temperature data is used as the temperature detection unit (T) in the charge control unit (CHG-CONT) 22.
-DET) 22e.

The temperature detector (T-DET) 22e detects the battery temperature [T] from temperature data obtained from a temperature sensor (TH) 25 provided inside the secondary battery (BATT) 20.
bat], and sends the detected battery temperature [Tbat] to the full charge detection unit (FC-DET) 22f (step S14 in FIG. 6).

The full charge detector (FC-DET) 22f changes the current value calculated by the calculator (CAL) 22d [Bno].
w] and the battery temperature [Tbat] detected by the temperature detection unit (T-DET) 22e, and the change in the current value [B
current] and a change [Bstop] of a current value per unit time at the time of full charge selected on the table according to the battery temperature [Tbat], and the secondary battery (BATT) 2
A full charge of 0 is detected (steps S15 to S17 in FIG. 6).

That is, the full charge detection section (FC-DET) 22
f is the battery temperature [T1], [T2], [T3],.
Change in current value per time corresponding to [Tn] [Bst
op-1], [Bstop-2], [Bstop-
3],... [Bstop-n] is stored, and one [Bstop (-i)] according to the battery temperature [Tbat] is selected from this table, and [Bstop] for full charge detection is selected. (Step S in FIG. 6)
15).

Further, a full charge detection section (FC-DET) 22
f is [Bstop] determined above and the calculation unit (CAL)
It is determined whether or not [Bnow ≦ Bstop] is obtained by comparing the change of the current value [Bnow] calculated in 22d (step S16 in FIG. 6), and when [Bnow ≦ Bstop] is satisfied, the secondary battery is determined. (BATT) Full charge of the battery 20 is detected (step S17 in FIG. 6).

When the full charge detection unit (FC-DET) 12f detects the full charge of the secondary battery (BATT) 10 at the time when [Bnow ≦ Bstop], the switch control unit (SWC) 22g detects the full charge. Send a signal. The switch control unit (SWC) 22g is a full charge detection unit (FC-D
ET) When the full charge detection signal is received from 22f, the charge control switch 23 is turned off and the secondary battery (BATT) is turned off.
The charging of 20 is ended.

As described above, the function of detecting the full charge based on the change of the charging current per time and correcting the full charge detection error in accordance with the change in the temperature of the battery is provided. Variations can be eliminated, charging performance can be improved, and charging time can be shortened.

Next, referring to FIGS. 7 and 8, the third embodiment of the present invention will be described.
An embodiment will be described. In the third embodiment, when the charging current at the time of constant voltage charging changes by a predetermined value or more, the required time in which the change occurs is calculated, and the required time is compared with a set value to fully charge the secondary battery. The state is detected.

Here, the interval between digital values when the charging current has changed by a predetermined value or more is [Idigit], and the full charge detection point of the secondary battery (BATT) is [Idigit].
It is assumed that there is a time change of [Tstop] or more when the current changes.

FIG. 7 is a block diagram showing the configuration of the device according to the third embodiment of the present invention. In the drawing, reference numeral 30 denotes a secondary battery (BAT) requiring charging at a constant voltage to be charged.
T) and 31 are a charging circuit (CHG) for charging the secondary battery (BATT) 30 with a constant current and a constant voltage, and 32 is a secondary battery (BA)
Charge control unit (CHG-CON) for charging control of the TT) 30
T).

Reference numeral 33 denotes a charge control unit (CHG-CONT) 3 interposed in a charging current path of the secondary battery (BATT) 30.
2 is a charge control switch whose on / off control is performed by the switch 2. Reference numeral 34 denotes an ammeter (C-MET) for measuring the charging current interposed in the charging current path.

Reference numerals 32a to 32g denote internal components of the charge control unit (CHG-CONT) 32. Reference numeral 32a denotes an A / D converter for converting an analog measurement current of an ammeter (C-MET) 34 into a digital value. (A /
D).

Reference numeral 32b denotes a digital counter (COUN) for counting time, the value of which is updated at regular intervals. Reference numeral 32c denotes a digital counter (COUN) 32b each time the current value digitally converted by the A / D converter (A / D) 32a changes by an I digit.
Is a first register (REGA) that stores the count value of the first register (REGA). The value held in the first register (REGA) 32c is T1 here. Reference numeral 32d denotes a second register (REGB) that holds the value before the update when the first register (REGA) 32c is updated, and the value held in the second register (REGA) 32d is T2 here. I do.

32e is an A / D converter (A / D) 32
a is converted to an I digit (Id
Each time a change occurs, the value of the first register (REGA) 32c and the value of the second register (REG) are changed.
B) A comparison unit (COMP) that compares the value with the value of 32d.

Reference numeral 32f compares a comparison result value (T1-T2) of the comparison unit (COMP) 32e with a set value [Tstop] for full charge detection, which is held inside, to obtain a secondary battery (BATT). 30 full charge detection unit (F
C-DET).

32g is a full charge detection section (FC-DET) 3
A switch control unit (SWC) that controls ON / OFF of a charge control switch 33 interposed in a charging current path between the charging circuit (CHG) 31 and the secondary battery (BATT) 30 under the control of 2e. .

FIG. 8 is a flowchart for explaining the operation in the third embodiment. Here, the operation in the third embodiment of the present invention will be described with reference to FIGS.

The secondary battery (BATT) 30 has an allowable upper limit voltage and requires constant voltage charging for charging. Here, the A / D in the charge control unit (CHG-CONT) 32
The interval between digital values when the current converted by the converter (A / D) 32a changes by a predetermined value or more is [Id
digit], and [Ts] in the current change of [Idit].
top] is determined as the time when the secondary battery (BAT)
T) It is a full charge detection point of 30.

A secondary battery (BATT) 30 to be charged
Is attached to a predetermined charging device, the charging control unit (CH
G-CONT) 32, a switch control unit (SW)
C) 32g switches on the charge control switch 33, and starts charging the secondary battery (BATT) 30. At the time of this charging, the charging circuit (CHG) 31 has a constant current
A charging current is supplied to the secondary battery (BATT) 30 by constant voltage control.

At the time of charging the secondary battery (BATT) 30, the digital counter (COUN) 32b updates the value at regular intervals. In addition, ammeter (C-MET)
34 measures the charging current, and uses the measured current value as an A / D converter (A / D) of the charging control unit (CHG-CONT) 32.
D) Send to 32a (step S21 in FIG. 8).

The A / D converter (A / D) 32a converts the current value measured by the ammeter (C-MET) 34 into a digital signal and sends it to the comparator (COMP) 32e (step S22 in FIG. 8). .

Each time the current value digitally converted by the A / D converter (A / D) 32a changes by [Idit], the comparator (COMP) 32e counts the count value of the digital counter (COUN) 32b. 1 (REGA) 32c, and the first
Is stored in the second register (REGA) 32d, and the value (T1) of the first register (REGA) 32c and the value (T2) of the second register (REGB) 32d are stored in the second register (REGA) 32d. ) And the difference (T1-T
2) is calculated, and the comparison result value (T1-T2) is sent to the full charge detection unit (FC-DET) 32f (steps S23 to S26 in FIG. 8).

The full charge detection section (FC-DET) 32f is
Comparison result value (T1-T2) of comparison unit (COMP) 32e
And the set value [Ts held inside for detecting full charge]
top] and [(T1−T2) ≧ Tsto
p], a full charge of the secondary battery (BATT) 30 is detected (steps S27 and S28 in FIG. 8).

When the full charge detection unit (FC-DET) 32f detects the full charge of the secondary battery (BATT) 30 at the time when [(T1-T2) ≧ Tstop], the switch control unit (SWC) 32g A full charge detection signal is sent to
The switch control unit (SWC) 32g is a full charge detection unit (FC
-DET) 32f, when the full charge detection signal is received, the charge control switch 33 is turned off and the secondary battery (BAT) is turned off.
T) Terminate the charging of 30.

In this way, by detecting the full charge by the change of the charging current per time (that is, when the charging current at the time of constant voltage charging changes by a predetermined value or more, the required time in which the change occurs is calculated. By comparing the required time with a set value to detect the fully charged state of the secondary battery), it is possible to improve the charging performance by eliminating the variation of the charging end time due to a current detection error and to shorten the charging time. it can.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. This fourth embodiment monitors the charging current, charging time, and temperature (battery temperature or ambient temperature of the battery) of the secondary battery, and when the charging current at the time of constant voltage charging changes by a predetermined value or more, the change is determined. Is calculated, and the required time is compared with a set value determined by the temperature of the battery to detect a full charge state of the secondary battery.

Here, the interval between the digital values when the charging current has changed by a predetermined value or more is set to [Idigit], and the full charge detection point of the secondary battery (BATT) is set to [Idigit].
It is assumed that there is a time change of [Tstop] or more when the current changes.

FIG. 9 is a block diagram showing the configuration of the device according to the fourth embodiment of the present invention. In the figure, reference numeral 40 denotes a secondary battery (BAT) requiring charging at a constant voltage to be charged.
T) and 41 are a charging circuit (CHG) for charging the secondary battery (BATT) 40 with a constant current and a constant voltage, and 42 is a secondary battery (BA)
(CHG-CON)
T).

Reference numeral 43 denotes a charge control unit (CHG-CONT) 4 interposed in the charge current path of the secondary battery (BATT) 40.
2 is a charge control switch whose on / off control is performed by the switch 2. An ammeter (C-MET) 44 measures the charging current interposed in the charging current path.

Reference numeral 45 denotes a temperature sensor (TH) for measuring the battery temperature of the secondary battery (BATT) 40. The temperature sensor (TH) measures the measured temperature data in the charge control section (CHG-CONT) 42 and is described later. DET) 42f.

Reference numerals 42a to 42h each constitute an internal component of the charge control unit (CHG-CONT) 42. Reference numeral 42a denotes an A / D converter for converting an analog measurement current of an ammeter (C-MET) 44 into a digital value. (A /
D).

Reference numeral 42b denotes a digital counter for counting time (COUN) whose value is updated at regular intervals. Reference numeral 42c denotes a digital counter (COUN) 42b each time the current value digitally converted by the A / D converter (A / D) 42a changes by an I digit.
Is a first register (REGA) that stores the count value of the first register (REGA), and the value held in the first register (REGA) 42c is T1 here. Reference numeral 42d denotes a second register (REGB) that holds a value before updating when the first register (REGA) 42c is updated. Here, the value held in the second register (REGA) 42d is referred to as T2. I do.

42e is an A / D converter (A / D) 42
a is converted to an I digit (Id
Each time a change occurs, the value of the first register (REGA) 42c and the value of the second register (REG
B) A comparison unit (COMP) that compares the value with 42d.

Reference numeral 42f denotes a temperature detector (T-DET) for detecting a battery temperature [Tbat] from temperature data obtained from a temperature sensor (TH) 45 provided inside the secondary battery (BATT) 40. Battery temperature [Tbat]
To the full charge detection unit (FC-DET) 42g described later.

42g is a comparison result value (T1-T2) of the comparison unit (COMP) 42e and a temperature detection unit (T-DET) 2e.
A full-charge detection unit (A) that detects a full charge of the secondary battery (BATT) 30 by comparing a set value [Tstop] for full-charge detection, which is selected according to the battery temperature [Tbat] detected in 2e. FC-DET).

That is, the full charge detection section (FC-DET) 42
g is a predetermined battery temperature [T1], [T2],
[T3],... [Tn] per unit current value (I
change in time (per digit) [Tstop-1],
[Tstop-2], [Tstop-3], ... [Tst
op-n], and one [Tsto] according to the battery temperature [Tbat] is obtained from this table.
p (-i)] and selecting [Tst
op] is determined.

42h is a full charge detection section (FC-DET) 4
A switch control unit (SWC) that controls ON / OFF of a charge control switch 43 interposed in a charging current path between the charging circuit (CHG) 41 and the secondary battery (BATT) 40 under the control of 2g. .

FIG. 10 is a flowchart for explaining the operation in the fourth embodiment. Here, FIG.
The operation in the fourth embodiment of the present invention will be described with reference to FIG.

The secondary battery (BATT) 40 has an allowable upper limit voltage, and requires constant voltage charging for charging. Here, the A / D in the charge control unit (CHG-CONT) 42
The interval between digital values when the current converted by the converter (A / D) 42a changes by a predetermined value or more is [Id
digit], and [Ts] in the current change of [Idit].
top] is determined as the time when the secondary battery (BAT)
T) 40 full charge detection points.

Secondary battery (BATT) 40 to be charged
Is attached to a predetermined charging device, the charging control unit (CH
G-CONT) 42, a switch control unit (SW)
C) 42h switches on the charge control switch 43 to start charging the secondary battery (BATT) 40. At the time of this charging, the charging circuit (CHG) 41 has a constant current
The charging current is supplied to the secondary battery (BATT) 40 by the constant voltage control.

At the time of charging the secondary battery (BATT) 40, the digital counter (COUN) 42b updates the value at regular intervals. In addition, ammeter (C-MET)
44 measures the charging current and converts the measured current value into an A / D converter (A / D) of the charging control unit (CHG-CONT) 42.
D) Send it to 42a (step S31 in FIG. 10).

The A / D converter (A / D) 42a converts the current value measured by the ammeter (C-MET) 44 into a digital signal and sends it to the comparison unit (COMP) 42e (step S32 in FIG. 10). .

When the current value digitally converted by the A / D converter (A / D) 42a changes by [Idigit], the comparison unit (COMP) 42e counts the count value of the digital counter (COUN) 42b every time. 1 (REGA) 42c, and stores the first
Is stored in the second register (REGA) 42d, and the value (T1) of the first register (REGA) 42c and the value (T2) of the second register (REGB) 42d are stored in the second register (REGA) 42d. ) And the difference (T1-T
2) is calculated, and the comparison result value (T1-T2) is sent to the full charge detection unit (FC-DET) 42g (steps S33 to S36 in FIG. 10).

On the other hand, a temperature sensor (TH) 45 provided in a secondary battery (BATT) 40 is connected to a secondary battery (BAT).
T) The battery temperature of 40 is measured, and the measured temperature data is sent to a temperature detection unit (T-DET) 42f described later in the charge control unit (CHG-CONT) 42.

The temperature detector (T-DET) 42f calculates the battery temperature [T] from temperature data obtained from a temperature sensor (TH) 45 provided inside the secondary battery (BATT) 40.
bat], and sends the detected battery temperature [Tbat] to the full-charge detection unit (FC-DET) 42g (FIG. 10).
Step S37).

The full charge detection unit (FC-DET) 42g is
Comparison result value (T1-T2) of comparison unit (COMP) 42e
Is compared with a set value [Tstop] for full charge detection selected on the table according to the battery temperature [Tbat], and when [(T1−T2) ≧ Tstop],
A full charge of the secondary battery (BATT) 40 is detected (FIG. 10).
Steps S38 to S40).

When the full charge detection section (FC-DET) 42g detects the full charge of the secondary battery (BATT) 40 at the time when [(T1-T2) ≧ Tstop], the switch control section (SWC) 42h A full charge detection signal is sent to
The switch control unit (SWC) 42h is a full charge detection unit (FC
-DET) 42g, upon receiving a full charge detection signal, turns off the charge control switch 43 and turns off the secondary battery (BAT).
T) Terminate the charging of 40.

As described above, the function of detecting the full charge based on the time change per current and the function of correcting the full charge detection error due to the change in the battery temperature is provided. , The charging performance can be improved, and the charging time can be shortened.

In the above-described embodiment, the secondary battery (BATT) is provided with means for recording the number of times of charging of the battery, and the number of times of charging is used as a factor for determining the set value of full charge detection. By doing so, more fine-grained charge control can be performed with respect to a characteristic (capacity) change according to the number of times of charging the secondary battery (BATT).

Further, the temperature detection of the secondary battery (BATT) is not limited to the battery temperature measuring means for directly measuring the temperature of the battery cell, but may be an indirect battery for measuring the ambient temperature of the battery such as the temperature inside the battery pack. Temperature measurement means may be used.

[0128]

As described above, according to the present invention, in the charging control of a secondary battery requiring constant voltage charging control, the error in the charging time due to the error in reading the current value is eliminated, and the charging performance is reduced. And a method for detecting a full charge of a secondary battery and a charge control device capable of shortening the charge time.

That is, according to the present invention, in the method for detecting the full charge of a secondary battery that requires constant voltage charge control, the charge current and the charge time during the constant voltage charge of the secondary battery are monitored. By detecting the fully charged state from the change amount of the charging current per predetermined time during the constant voltage charging, eliminating the variation of the charging end time due to the current detection error,
The charging performance can be improved and the charging time can be shortened.

Further, according to the present invention, in a charging control apparatus for a secondary battery requiring constant voltage charging control, a charging current and a charging time during the constant voltage charging of the secondary battery are measured. Means, means for detecting a change amount of the charging current per predetermined time based on each of the measured values, and comparing the change value of the charging current with a set value, wherein the change value of the charging current is equal to or less than the set value. Means for judging that the secondary battery has reached a fully charged state, and detecting a full charge by a change in charging current per unit time. To eliminate
The charging performance can be improved and the charging time can be shortened.

Further, according to the present invention, in a method for detecting full charge of a secondary battery which requires constant voltage charge control, the full charge of the secondary battery is detected by a change in charging current per time.
In addition, by providing a function of correcting a full-charge detection error in accordance with a change in the temperature of the battery, variations in the charge end time due to a current detection error can be eliminated, and the charging performance can be improved and the charging time can be shortened.

According to the present invention, in a charging control apparatus for a secondary battery requiring constant voltage charging control, means for holding a set current value for detecting a full charge of the secondary battery is provided. Means for measuring the charging current, charging time, and temperature during constant voltage charging of the secondary battery, and detecting a change amount of the charging current per predetermined time based on the measured charging current and charging time. Means for variably controlling the set current value according to the measured battery temperature; comparing the charging current change value with the set current value; Means for determining that the next battery has reached a fully charged state, a full charge is detected by a change in charging current per time, and a full charge detection error is corrected in accordance with a change in battery temperature. Error in current detection Eliminating the variations in the charging end time due to, it is possible to improve the charging performance can shorten the charging time.

Further, according to the present invention, in the method of detecting full charge of a secondary battery requiring constant voltage charging control, when the charging current at the time of constant voltage charging changes by a predetermined value or more, the change occurs. By calculating the required time, the required time is compared with a set value to detect the fully charged state of the secondary battery,
Variations in the charging end time due to a current detection error can be eliminated, thereby improving the charging performance and shortening the charging time.

Further, according to the present invention, in a secondary battery charge control device requiring constant voltage charge control, means for detecting a charge current as a digital value, a digital counter for performing time counting, and A first register for storing the value of the digital counter when the detected charging current changes by a predetermined value or more, and a second register for storing a value before the update each time the value of the first register is updated When,
Means for calculating a difference between the values stored in the first and second registers and comparing the difference value with a set value; and, as a result of the comparison, the value of the value stored in the first and second registers. Means for detecting a full charge state of the secondary battery when the difference is greater than a set value, and a configuration in which full charge is detected by a time change per current. , The charging performance can be improved, and the charging time can be shortened.

According to the present invention, in a method of detecting full charge of a secondary battery that requires constant voltage charge control, the charge current, charge time, and temperature of the secondary battery are monitored and the constant voltage is controlled. When the charging current at the time of charging changes by a predetermined value or more, the required time in which the change has occurred is calculated, the required time is compared with a set value determined by the temperature of the battery, and the secondary time is calculated by a time change per current. A function to detect the full charge state of the battery and to correct the full charge detection error in accordance with the change in the temperature of the battery is provided, thereby eliminating the variation in the charge end time due to the current detection error and improving the charging performance. The charging time can be reduced.

According to the present invention, in a charging control apparatus for a secondary battery requiring constant voltage charging control, a means for detecting a charging current by a digital value, a digital counter for counting time, When the charging current changes by one digit or more, a first register for storing the value of the digital counter and a value before updating stored in the first register when updating the first register are stored. A second register, a third register for storing the battery temperature of the secondary battery or the ambient temperature of the battery as a digital value, and means for determining a set value based on the value stored in the third register; Means for calculating a difference between the updated values of the first and second registers, and comparing the difference value with the determined set value;
Means for detecting a full charge state of the secondary battery when the difference between the values stored in the second register is greater than the set value, and detecting a full charge by a time change per current; By correcting the full charge detection error in accordance with the temperature change, the variation in the charging end time due to the current detection error can be eliminated, and the charging performance can be improved and the charging time can be shortened.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a charging current characteristic of a secondary battery for describing an operation in the first embodiment.

FIG. 3 is a flowchart for explaining an operation in the first embodiment.

FIG. 4 is a block diagram showing a configuration of an apparatus according to a second embodiment of the present invention.

FIG. 5 is a view showing a charging current characteristic of a secondary battery for describing an operation in the second embodiment.

FIG. 6 is a flowchart for explaining the operation in the second embodiment.

FIG. 7 is a block diagram showing a configuration of an apparatus according to a third embodiment of the present invention.

FIG. 8 is a flowchart for explaining the operation in the third embodiment.

FIG. 9 is a block diagram showing a configuration of an apparatus according to a fourth embodiment of the present invention.

FIG. 10 is a flowchart for explaining the operation in the fourth embodiment.

FIG. 11 is a diagram showing an example of a charging voltage / current characteristic of a lithium ion battery.

FIG. 12 is a block diagram showing a configuration example of a charge control circuit according to a first conventional technique.

FIG. 13 is a block diagram showing a configuration example of a charge control circuit according to a second conventional technique.

FIG. 14 is a diagram showing an example of a current value for explaining an operation of a charge control circuit according to a conventional technique.

[Explanation of symbols]

10, 20, 30, 40 ... secondary battery (BATT), 11, 21, 31, 41 ... charging circuit (CHG), 12, 22, 32, 42 ... charging control unit (CHG-CON
T), 12a, 22a, 32a, 42a: A / D converter (A / D), 12b, 22b: Current detection unit (C-DET), 12c, 22c: Time measurement unit (TIM), 12d, 22d: Calculation unit (CAL), 12e, 22f, 32f, 42g ... full charge detection unit (FC
-DET), 12f, 22g, 32g, 42h ... switch control unit (S
WC), 13, 23, 33, 43: charge control switch, 14, 24, 34, 44: ammeter (C-MET), 22e, 42f: temperature detector (T-DET), 25, 45: temperature sensor (TH), 32b, 42b ... digital counter (COUN), 32c, 42c ... first register (REGA), 32d, 42d ... second register (REGB), 32e, 42e ... comparison unit (COMP).

Claims (10)

[Claims] In a charge control of a secondary battery requiring constant voltage charge control, a charge current and a charge time during the constant voltage charge of the secondary battery are monitored, and the charge current and the charge time during the constant voltage charge are monitored. A method for detecting a full charge of a secondary battery, comprising detecting a full charge state from a change amount of a charge current per predetermined time. 2. A charging control apparatus for a secondary battery which requires constant voltage charging control, wherein a means for measuring a charging current and a charging time during the constant voltage charging of the secondary battery; Means for detecting a charge current change amount per predetermined time based on the value, comparing the charge current change value with a set value, and when the charge current change value is equal to or less than the set value, the secondary battery is Means for judging that the battery has been fully charged. 3. In the charging control of a secondary battery requiring constant voltage charging control, the charging current, charging time, and temperature of the secondary battery are monitored, and a predetermined A full charge state detection method for a secondary battery, comprising: detecting a full charge state from a change amount of a charging current of the battery and a battery temperature. 4. A charge control device for a secondary battery requiring constant voltage charge control, wherein: a means for holding a set current value for detecting a full charge of the secondary battery; Means for measuring the charging current, charging time, and temperature during constant voltage charging; means for detecting a change in the charging current per predetermined time based on the measured charging current and charging time; and Means for variably controlling the set current value according to the battery temperature; comparing the charge current change value with the set current value, and when the charge current change value is equal to or less than the set current value, the secondary battery is in a fully charged state And a means for judging that the charging has been completed. 5. In charging control of a secondary battery requiring constant voltage charging control, when a charging current at the time of constant voltage charging changes by a predetermined value or more, a required time during which the change occurs is calculated,
A method for detecting a full charge of the secondary battery, comprising detecting the full charge state of the secondary battery by comparing the required time with a set value. 6. A charge control device for a secondary battery requiring constant voltage charge control, means for detecting a charge current as a digital value, a digital counter for performing time counting, and wherein the detected charge current is a predetermined value. A first register that stores the value of the digital counter when the value has changed by more than a value, a second register that stores a value before the value of the first register is updated each time the value of the first register is updated, Means for calculating the difference between the values stored in the second register and comparing the difference value with the set value; and as a result of the comparison, the difference between the values stored in the first and second registers is set value Means for detecting a full charge state of the secondary battery when it is larger than the threshold value. 7. In the charging control of a secondary battery that requires constant voltage charging control, the charging current, charging time, and temperature of the secondary battery are monitored, and the charging current during constant voltage charging is determined to be a predetermined value. When the change is equal to or more than the value, a required time in which the change occurs is calculated, and the required time is compared with a set value determined by the battery temperature to detect a full charge state of the secondary battery. Battery full charge detection method. 8. A charge control device for a secondary battery requiring constant voltage charge control, a means for detecting a charge current as a digital value, a digital counter for counting time, and a charge current of 1 digit or more. A first register for storing the value of the digital counter when the value has changed; a second register for storing a value before update stored in the first register when updating the first register; A third register that stores the battery temperature of the secondary battery or the ambient temperature of the battery as a digital value; a unit that determines a set value based on a value stored in the third register; Means for calculating the difference between the updated values of the registers and comparing the difference value with the determined set value. As a result of the comparison, the value of the value stored in the first and second registers is calculated. Min charging control apparatus characterized by comprising and means for detecting a fully charged state of the secondary battery is greater than the set value. 9. The battery temperature is a battery temperature of a secondary battery charged at a constant voltage or an ambient temperature of the secondary battery.
Or the method for detecting full charge of a secondary battery according to 7. 10. The secondary battery according to claim 3, further comprising means for recording the number of times of charging of the secondary battery, wherein the number of times of charging is used as a factor for determining a set value. Method.