JP2001309570A - How to adjust battery capacity - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method of adjusting the capacity of a battery pack that reduces the voltage variation of the cells constituting the battery pack and reduces the capacity difference. SOLUTION: The voltage of each lithium ion battery is measured while the switch is turned off at regular time intervals (S106).
The time interval during which the switch is turned on is determined by the voltage difference between the voltage between both ends of each lithium ion battery and the average voltage between both ends of the lithium ion battery constituting the battery pack 1, or the voltage between both ends of each lithium ion battery and the battery pack 1. One or both of the voltage difference between the terminal voltage of the smallest lithium ion battery among the lithium ion batteries is calculated as a control parameter of the proportional control and the integral control (S108), and the switch is turned on during the time width (S112). , S116). The variation in voltage of the lithium ion battery constituting the assembled battery is smaller than in the case where the on / off control is simply performed, and the capacity adjustment accuracy is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting the capacity of a battery pack, and more particularly to a method for adjusting the capacity of a battery pack in which a plurality of cells are connected in series, and a voltage measurement circuit for measuring the voltage of the cells and a switch. The present invention relates to a capacity adjusting method for a battery pack in which a capacity adjusting resistor for adjusting the capacity of a cell is connected in parallel.

[0002]

2. Description of the Related Art In general, in an assembled battery in which a plurality of cells are connected in series, if the charge level of the cells deviates from the average value for some reason during charging and discharging, the cells deviated from the average value are overcharged. Alternatively, overdischarge may occur, causing problems inherent to the assembled battery, such as a decrease in the discharge performance of the assembled battery and a shortened life due to the overdischarge.

In order to prevent these problems, each cell constituting the assembled battery is provided with a cell voltage measurement (detection) circuit for measuring (detecting) the cell voltage of the cell, and a cell via a switch. And a capacity adjusting resistor for adjusting the capacity of the capacitor are connected in parallel. Then, after measuring the battery voltage of the single battery by the single battery voltage measurement circuit, by turning on a switch connected to the single battery having a high battery voltage, the current of the single battery having the high battery voltage is supplied to the capacity adjusting resistor. To discharge,
2. Description of the Related Art A capacity adjustment method for reducing a voltage difference between cells constituting an assembled battery is used. Since this capacity adjustment method can prevent the above-described problem inherent in the assembled battery,
Conventionally, it has been generally used as a method of adjusting the capacity of a battery pack.

[0004] Further, in a battery pack using lithium ion batteries using amorphous carbon as the negative electrode active material, which has a high correlation between the open circuit voltage and the charge level, as a unit cell, the battery voltage of each lithium ion battery is reduced by the battery voltage. Is controlled so as to approach the average battery voltage of the lithium ion battery constituting the above. That is,
The capacity of each lithium-ion battery is increased by turning on the lithium-ion batteries that are higher than the average battery voltage of the lithium-ion batteries constituting the assembled battery for a certain period of time and turning off the lithium-ion batteries that are lower than the average battery voltage. A capacity adjustment method for adjusting is used.

Further, in a battery pack using a lithium-ion battery as a unit cell, the unit cell enters a battery abnormal state such as abnormal heat generation due to overcharging. Overcharge detection function is additionally provided.

[0006]

However, according to the conventional capacity adjusting method of turning on and off the switch so that the voltage of the unit cell approaches the average unit cell voltage of the assembled battery, the voltage variation of the unit cell is still large. Has issues.

In a battery pack using lithium ion batteries as unit cells, when the charge level of any of the lithium ion batteries deviates from the average value, it is determined that the battery is in an abnormal state, and the safety of the battery is ensured. In some cases, the overcharge detection function was activated early and stopped charging the lithium ion battery before full charge.

The present invention has been made in view of the above circumstances, and has as its object to provide a method of adjusting the capacity of a battery pack that can reduce the voltage variation of the cells constituting the battery pack and reduce the capacity difference.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a method in which a plurality of cells are connected in series, and a voltage measuring circuit and a switch for measuring the voltage of the cells are connected to the cells. A method of adjusting the capacity of an assembled battery in which a capacity adjusting resistor for adjusting the capacity of the cell is connected in parallel with each other, wherein the voltage measuring circuit is in a state where all the switches are turned off at predetermined time intervals. And the at least one of a voltage difference between the cell voltage and the average cell voltage of the battery pack and a voltage difference between the cell voltage and the minimum battery voltage of the battery pack are proportionally controlled. And calculating a time width of an on-time for turning on each of the switches as a control parameter of the integral control, during the calculated time width,
Turning on the switch to discharge the cell to the capacity adjusting resistor to adjust the capacity.

According to the present invention, the voltage of the cell is measured by a voltage measuring circuit in a state where all the switches are turned off at predetermined time intervals, and the switch is turned on to discharge the cell to the capacity adjusting resistor. The proportional control and the integral control are performed using at least one of the voltage difference between the cell voltage and the average cell voltage of the battery pack and the voltage difference between the cell voltage and the minimum battery voltage of the battery pack as a control parameter. Compared to the capacity adjustment method in which the switch is simply turned on and off so that the voltage of the battery pack approaches the average cell voltage of the battery pack, the variation in the voltage of each battery cell constituting the battery pack can be reduced, and the capacity of the battery cell can be reduced. Adjustment accuracy can be improved.

The time width of the ON time can be obtained by any one of the following arithmetic expressions (1) to (4).

[0012]

(Equation 2)

At this time, when the value of the calculated time width is negative, the value of the calculated time width is corrected to 0, and the value of the calculated time width is set in advance and the value of the set time shorter than the predetermined time is set. If the value is corrected to the value of the set time when the value is larger than the set time, it is possible to obtain a time width of the ON time in which the capacity can be actually adjusted.

[0014]

Embodiments of a battery pack to which the present invention can be applied will be described below with reference to the drawings.

(Structure) As shown in FIG. 1, a battery pack 10 according to the present embodiment includes an assembled battery 1 in which a plurality of lithium ion batteries 11, 12,... I have.

One end of a switch SW is connected to the positive side of the lithium ion battery 11, and one end of a capacity adjusting resistor R for adjusting the capacity of the lithium ion battery 11 is connected to the other end of the switch SW. ing. The other end of the capacity adjusting resistor R is connected to the negative side of the lithium ion battery 11. Therefore, the capacity adjusting resistor R is connected in parallel to the lithium ion battery 11 via the switch SW.

The switch SW is a resistor and an FET (not shown)
(Field effect transistor). That is, when a weak binary high-level signal is input to the gate of the FET, a current flows from the drain side to the source side of the FET.
Is turned on, and when a binary low-level signal is input to the gate of the FET, no current flows from the drain side to the source side, so that the switch SW is turned off.

The lithium ion battery 11 detects the voltage across the lithium ion battery 11 (cell voltage).
A voltage detection circuit 31 to be measured is connected in parallel with the lithium ion battery 11. The voltage detection circuit 31 includes a detection circuit for detecting a voltage between both ends of the lithium ion battery 11 and an AD conversion unit for converting an analog value of the voltage between both ends detected by the detection circuit into a digital value. The detection circuit section is composed of an operational amplifier and a resistor, and is a differential amplifier circuit having an amplification factor of 1. The AD converter is a comparator, D /
A circuit comprising A and control logic, samples and holds the voltage of the lithium ion battery 11 output from the detection circuit unit, and executes quantization and encoding.

The lithium ion batteries 12... 1
m, like the lithium-ion battery 11, the switch S
A resistor R for capacitance adjustment and a voltage detection circuit 32 via W
3m are connected in parallel. The switch SW and the voltage detection circuit 32... 3 m connected in parallel to each lithium ion battery 12... 1 m have the same circuit configuration as the switch SW and the voltage detection circuit 31 connected in parallel to the lithium ion battery 11. The nominal resistance characteristic including the resistance value of the capacitance adjusting resistor R connected in series to each of the switches SW is the same as that of the capacitance adjusting resistor R connected in series to the switch SW of the lithium ion battery 11.

The battery pack 10 includes a microcomputer (hereinafter referred to as a microcomputer) 4 for controlling the battery pack 10. The microcomputer 4 includes a CPU for performing arithmetic processing, a ROM for storing programs executed by the CPU and various setting values, a RAM serving as a work area for the CPU, an input / output interface serving as a port for input / output signals with the outside, and the like. It is composed of

The above-described voltage detection circuits 31, 32,.
m is connected to the AD conversion input port of the microcomputer 4. Therefore, the voltage detecting circuits 31, 32,... 3m are connected in parallel to the lithium ion batteries 11, 12,.
, And A / D-converted and output to the microcomputer 4. For this reason, the microcomputer 4 is configured to be able to take in each voltage value of each lithium ion battery constituting the battery pack. Each switch SW is connected to an output port of the microcomputer 4. Therefore, the switch S to which the binary high level signal of the weak current is output from the microcomputer 4
W is turned on, and the switch SW to which the binary low level signal is output is turned off.

The battery pack 10 is inserted between the plus side of the lithium-ion battery 11 and the plus terminal of the battery pack 1 to detect the charge, discharge and rest states of the battery pack 1 to detect the state of the battery pack 1. Is output to the microcomputer 4. The charge / discharge determination unit 2 is connected to the microcomputer 4 and detects the direction of current flowing through the battery pack 1 by a shunt (shunt) resistance, and determines whether the battery pack 1 is in a charge, discharge, or rest state. 4 is output. The negative side of the unit cell 1m is the battery pack 1
0 is connected to the minus terminal of the battery pack 1
The plus and minus terminals of 0 are connected to a charger or load.

(Operation) Next, the operation of the battery pack 10 of the present embodiment will be described with reference to a flowchart, assuming that the battery pack 1 is in a charged state. In addition,
When power is supplied to the microcomputer 4 in the initial state, R
The various set values stored in the OM are transferred to the RAM and become ready for routine processing. When the battery pack 1 output from the charge / discharge determination unit 2 is in a charged state, the following charge control routine is executed. You.

As shown in FIG. 2, in the charge control routine, first, in step 102, the output levels of the binary signals output from the output port of the microcomputer 4 are all set to the low level. Thereby, the lithium ion batteries 11, 12
... All the switches SW connected to 1 m are turned off (the state shown in FIG. 1).

In the next step 104, an OFF setting time for turning off all the switches SW (for example, all switches S
.. (One second after W is turned off), and in step 106, the voltage detection circuits 31, 32,.
The voltage value output from the 3 m
12... 1 m. As a result, it is possible to detect a correct voltage of each lithium ion battery while eliminating a transient phenomenon caused by the switch SW. The off set time can be measured by an internal clock (not shown) in the microcomputer 4.

Next, at step 108, the time width of the ON time of all the switches SW is calculated by one of the following arithmetic expressions (1) to (4) and stored in the RAM. That is, for example, when using the arithmetic expression (2), the time width of the ON time of all the switches SW is calculated by the arithmetic expression (2) and stored in the RAM.

[0027]

(Equation 3)

These arithmetic expressions are based on the time width of the ON time of the switch SW, the voltage difference between the terminal voltage of each lithium ion battery and the average terminal voltage of the lithium ion battery constituting the battery pack 1, or the lithium ion battery. The on-time of the switch SW is set as one or both of the voltage difference between the voltage between both ends of the battery and the voltage between both ends of the smallest lithium ion battery among the lithium ion batteries constituting the assembled battery 1 as control parameters of proportional control and integral control. It is to calculate. In these arithmetic expressions (1) to (4), the constant 1 and the constant 2 are the battery capacity, the battery characteristics, the interval of the voltage detection time, and the resistance value of the capacity adjusting resistor R of the lithium ion batteries 11, 12,. , The optimum value changes, so that the optimum value may be selected according to these conditions.

In step 110, since the calculated on-time may take a negative value, when the negative value is used, the capacity adjustment of the lithium ion battery cannot be realized. When the on-time has a negative value, the on-time is corrected to 0.

In the next step 112, a switch SW whose ON time takes a positive value (hereinafter referred to as a target switch).
In order to adjust the capacity of the lithium-ion battery connected to the target switch by setting the switch to the ON state during the ON time, a binary high-level signal is output from the output port connected to the target switch. Next, in step 114, it is determined whether or not an on-set time (for example, 9 seconds after the target switch SW is turned on) has elapsed. If a negative determination is made, the on-time has elapsed in the next step 116. It is determined whether or not this is the case. If a negative determination is made, the process returns to step 112.
On the other hand, when an affirmative determination is made in step 116, the capacity adjustment of the lithium ion battery to be adjusted has been completed, and in the next step 118, the target switch SW is turned off and the process returns to step 102.

Thus, for example, in the lithium ion battery 11, the switch SW is turned on, so that a closed circuit is formed between the lithium ion battery 11, the switch SW, and the capacity adjusting resistor R. Therefore, the lithium ion battery 11
Is consumed by the capacity adjusting resistor R during the on-time,
The capacity of the lithium ion battery 11 is adjusted. In the case of other lithium-ion batteries requiring capacity adjustment, similarly, a binary high-level signal is output from the output port to the switch SW during the on-time to adjust the capacity.

On the other hand, when an affirmative determination is made in step 114, the process returns to step 102. In steps 114 and 102, when the on-time according to the above-mentioned arithmetic expression exceeds the on-set time, the on-time is limited to the on-set time.

Therefore, in the charge control routine shown in FIG. 2, each of the lithium ion batteries 11, 12,...
The voltage is measured every second), and the capacitance is adjusted almost uniformly by the capacitance adjusting resistor R.

[0034]

Next, a battery pack 10 according to an embodiment manufactured in accordance with the above embodiment will be described in detail. Note that a battery pack of a comparative example manufactured to confirm the effect of the example is also described.

(Embodiment) In this embodiment, according to the above-described embodiment, the battery pack 1 is made up of eight lithium ion batteries in series.
And the resistance value of the capacitance adjustment resistor R was 39Ω.
These lithium-ion batteries intentionally have 1228 mA
h to 1477 mAh. Further, the OFF setting time is set to 1 second, the ON setting time is set to 9 seconds, and the constant 1 is set to 0.48 (sec) by using the above-described equation (2).
/ mV) and constant 2 was set to 1 (sec / mV).

(Comparative Example) In this comparative example, the configuration was the same as that of the embodiment, including the variation of the lithium ion battery. However, the operation is the same as that of the embodiment in that the control interval is performed every 10 seconds and the voltage is measured one second after the switches of all lithium ion batteries are turned off. The battery voltage of the average lithium ion battery is calculated, and if the voltage of the lithium ion battery is higher than the average voltage, the switch is turned on for 4 seconds, and if the voltage of the lithium ion battery is lower than the average voltage, the switch is turned off. This embodiment is different from the embodiment in that the conventional control is performed.

(Test) Next, the voltage of each lithium ion battery when the assembled batteries of the example and the comparative example were charged while adjusting the capacity was measured. The measurement results are shown in FIGS.
Shown in

As shown in FIG. 4, in each lithium ion battery of the comparative example, the voltage difference at the end of charging is small, but the voltage of the maximum lithium ion battery 11 and the voltage of the minimum lithium ion battery 14 are about the same. A voltage difference of 70 mV has occurred. This value corresponds to a capacity difference of 18% in terms of capacity.
On the other hand, in the embodiment, as shown in FIG. 3, there is only a voltage difference of about 10 mV between the maximum voltage of the lithium ion battery 17 and the minimum voltage of the lithium ion battery 14 at the end of charging. This value is only about 2.8% difference in capacity,
It can be seen that the variation is extremely small as compared with the comparative example.

As described above, the only difference between the embodiment and the comparative example is the method of calculating the ON time of the switch SW. Or one or both of the voltage difference between the voltage across the lithium ion battery and the voltage difference between the voltage across the lithium ion batteries and the voltage across the smallest lithium ion battery among the lithium ion batteries constituting the battery pack 1. It can be seen that if the calculation is performed as the control parameters of the proportional control and the integral control, the variation in the voltage between both ends of each lithium ion battery can be extremely reduced, and the accuracy of the capacity adjustment of each lithium ion battery can be improved. Therefore, since the overcharge detection function does not operate erroneously during charging and the charging is stopped early, the lithium ion batteries can be charged almost uniformly and until they are fully charged.

In the above embodiment, the case where the operation formula (2) is used has been described. However, the constant 1 and the constant 2 are set to 0.48 (sec / mV) and 1 in the same manner as in the case of the operation formula (2).
Even if the calculation formulas (1), (3) and (4) are used as (sec / mV), as shown in FIG. 5, the change in the standard deviation of the voltage of each lithium ion battery is different, but the calculation formula (2) As in the case of using (1), the voltage variation at the end of charging and the capacity difference upon completion of charging can be extremely reduced.

In the above embodiment, when the on-time exceeds the on-set time in step 114, the process returns to step 102 to limit the on-time to the on-set time.
If it is determined in step 110 whether the on-time exceeds the on-set time, and if it is determined that the on-time exceeds the on-set time, the on-time is set as the on-set time, the determination in step 114 can be omitted.

Further, in this embodiment, the charge control routine in the case where the battery pack 1 is in the charged state has been described for the sake of simplicity.
Since there is variation in the internal resistance of 2... 1 m, the voltage of each lithium ion battery is measured at predetermined time intervals during discharging and at rest, similarly to the flowchart shown in FIG. It is preferable to adjust the capacity of each lithium ion battery by calculating the on-time in any one of the above) to (4). In this case, the voltage difference between the voltages across the lithium ion batteries is extremely small in both the discharging and resting states, so that a specific lithium ion battery does not become a load on other lithium ion batteries. Since the rated voltage of the battery can be reliably output and each lithium ion battery maintains a substantially uniform voltage, it is preferable from the viewpoint of the life of the entire assembled battery 1.

In this embodiment, an example in which the AD converter is arranged in the voltage detection circuits 31, 32,..., 3m has been described, but the AD converter may be arranged in the microcomputer 4. Further, in the battery pack 10 of the present embodiment, the voltage detection circuits 31, 32,.
Although an example is shown in which the same number as 1, 12,... 1 m is provided, these voltage detection circuits may be combined into one voltage detection circuit.

[0044]

As described above, according to the present invention,
The cell voltage is measured by the voltage measurement circuit with all the switches turned off at predetermined time intervals, and the time width of the on-time during which the switch is turned on and the cell is discharged to the capacity adjusting resistor is combined with the cell voltage. Since proportional control and integral control are performed using at least one of the voltage difference between the average cell voltage of the battery and the voltage difference between the cell voltage and the minimum cell voltage of the battery pack as a control parameter, the voltage of the battery cell is controlled by the unit cell voltage of the battery pack. Compared to the capacity adjustment method in which the switch is simply turned on and off so as to approach the battery average voltage, it is possible to reduce the variation in the voltage of each cell constituting the assembled battery and to improve the capacity adjustment accuracy of the cell. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a battery pack according to an embodiment to which the present invention can be applied.

FIG. 2 is a flowchart illustrating a charge control routine of the battery pack according to the embodiment.

FIG. 3 is a characteristic diagram showing charging characteristics of each lithium ion battery of the example when time is plotted on the horizontal axis and voltage is plotted on the vertical axis.

FIG. 4 is a characteristic diagram showing charging characteristics of each lithium ion battery of a comparative example when time is plotted on the horizontal axis and voltage is plotted on the vertical axis.

FIG. 5 is a characteristic diagram showing a change in voltage variation of each lithium ion battery when the arithmetic expressions (1) to (4) are used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Assembled battery 11,12 ... 1m Lithium ion battery (assembled battery) 31,32 ... 3m Voltage detection circuit (voltage measurement circuit) 4 Microcomputer R resistance SW switch

Claims (3)

[Claims] A plurality of cells are connected in series, a voltage measuring circuit for measuring the voltage of the cells and a capacity adjusting resistor for adjusting the capacity of the cells via a switch. Is a method of adjusting the capacity of the battery packs connected in parallel, wherein the voltage measurement circuit measures the cell voltage with the switches turned off at predetermined time intervals, and the cell voltage and the cell voltage are measured. Turning on each of the switches as at least one of a voltage difference between an average cell voltage of the assembled battery and a voltage difference between the unit cell voltage and a minimum cell voltage of the assembled battery as a control parameter of proportional control and integral control; Calculating a time width of time, and adjusting the capacity by discharging the unit cell to the capacity adjusting resistor by turning on the switch during the calculated time width. Capacity adjustment method of a battery. 2. The battery pack according to claim 1, wherein an arithmetic expression for calculating the time width of the on-time is one of the following arithmetic expressions (1) to (4). Capacity adjustment method. (Equation 1) 3. When the calculated time width has a negative value, the value of the calculated time width is corrected to 0, and the calculated time width value is set in advance and is shorter than the predetermined time. 3. The method according to claim 2, further comprising a correction step of correcting the value of the set time when the value is larger than the value.