JPH11150877A - Voltage correction circuit of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the voltage correction circuit of a secondary battery for correcting the voltage difference due to the variations of discharge amount of a plurality of secondary batteries which are connected in series and the scattered in the discharge amount. SOLUTION: Discharge circuits 2, 3, and 4 that can be turned on or off are connected to each both terminals of secondary batteries B1, B2, and B3, each terminal voltage of the batteries B1, B2, and B3, is measured by a microcontroller 7 via a switching circuit 5 and a differential amplifier 6, and the variations degree of the terminal voltage of the batteries B1, B2, and B3 and the variations degree of the capacities are discriminated based on the measurement result. When the variations degree of the terminal voltage is large, a discharge circuit connected to the secondary battery in which the terminal voltage indicates a maximum value from among the batteries B1, B2, and B3 is kept on until the terminal voltage decreases to a set value. When the variations degree of the capacity is large, the discharge circuit is maintained to be off, regardless of the degree of dispersion of the terminal voltage, and voltage correction for prohibition is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage correction circuit for a secondary battery, and more particularly to a voltage correction circuit for correcting variations in terminal voltages of a plurality of secondary batteries connected in series.

[0002]

2. Description of the Related Art A non-aqueous solvent secondary battery such as a lithium secondary battery and a lead storage battery have a problem in that if the terminal voltage becomes too low due to discharging or leaving, or if the terminal voltage becomes too high during charging, the battery will not be charged. Performance may be degraded and safety may be impaired. For this reason, in these secondary batteries, it is necessary to monitor the terminal voltage and control the charging and discharging so that the terminal voltage is within a predetermined range before use.

In particular, in the case of a lithium secondary battery, for example, when the terminal voltage becomes 2 V or less, the current collector copper used for the negative electrode begins to dissolve in the electrolytic solution, and the battery performance deteriorates.
When the terminal voltage exceeds 4.5 V, gas is generated due to decomposition of the electrolytic solution, and as a result, the pressure inside the battery rises, the safety valve operates, and liquid leakage may occur. Therefore, when a lithium secondary battery is used, the discharge current is cut off when the terminal voltage decreases and reaches a preset discharge prohibition voltage, and the charge is cut off when the terminal voltage rises and reaches the charge prohibition voltage. Generally, charging and discharging are performed via a protection circuit having a function. The discharge prohibition voltage is set to a voltage slightly higher than the voltage 2V at which the negative electrode copper begins to dissolve (eg, 2.3 V), and the charge prohibition voltage is set to a voltage slightly lower than the voltage at which the decomposition of the electrolytic solution starts (eg, 4.35 V). Is set.

In a conventional secondary battery protection circuit, when a plurality of secondary batteries are used in series, a similar protection operation is performed by detecting individual terminal voltages. That is, when a plurality of secondary batteries are connected in series and used, the terminal voltage is detected for each battery, and when the terminal voltage of any of the batteries reaches the discharge prohibition voltage or lower, discharging is prohibited, and When the terminal voltage of the battery reaches a charging prohibition voltage or higher, charging is prohibited, thereby protecting the secondary battery.

[0005]

However, in the above-described conventional protection circuit, when a plurality of secondary batteries are connected in series and used, the amount of charge, the amount of self-discharge, and the capacity of each secondary battery are reduced. If they are different, the terminal voltage of the secondary battery varies.

For this reason, at the time of discharging, the terminal voltage of a battery with a small charge drops earlier than the terminal voltage of another battery and reaches the discharge prohibition voltage. May stop. Also, when charging, on the contrary, a battery with a large amount of charge reaches the charge prohibition voltage quickly, so it can not be charged until full charge,
Use time will be shortened. Further, in order to avoid such inconveniences, there is a trouble that each battery must be used after being connected in series after adjusting their terminal voltages.

On the other hand, like a personal computer, R
In devices with a built-in volatile storage device such as AM, when the terminal voltage of the secondary battery used for the power supply drops, the data in the volatile storage device is transferred to a non-volatile storage device such as a hard disk to transfer the data. We try to prevent loss. However, when a conventional protection circuit is used in such a device, if the terminal voltage of some secondary batteries having a small amount of charge or a large amount of self-discharge decreases and reaches the discharge prohibition voltage, However, at that time, even if the terminal voltage of the secondary battery is sufficiently high on average, the discharge may be suddenly interrupted, resulting in a problem that data in the volatile storage device is lost.

The present invention provides a voltage correction circuit for a secondary battery which can correct the variation in the amount of charge and the amount of discharge of a plurality of secondary batteries connected in series to avoid the above-mentioned inconveniences during discharge and charge. The purpose is to provide.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is to determine a terminal voltage variation of a plurality of secondary batteries connected in series and discharge the secondary battery so as to correct the variation. The main point is what we did.

That is, the voltage correction circuit for a secondary battery according to the present invention comprises: a discharge means which can be turned on / off connected to both ends of a plurality of secondary batteries connected in series; First determining means for determining the degree of variation in the terminal voltage of the battery by comparing it with the first set value; and determining whether the degree of variation in the capacity of the plurality of secondary batteries is compared with the second set value. And a control unit that controls the discharging unit based on the determination results of the first and second determination units.

The control means (a) determines that the degree of variation of the terminal voltage exceeds the first set value by the first determination means, and determines the degree of variation of the capacitance to the second set value by the second determination means. When it is determined that the terminal voltage is equal to or less than the predetermined value, the discharging unit connected to the secondary battery having the maximum terminal voltage among the plurality of secondary batteries is turned on. Means is turned off to correct the voltage of the secondary battery exhibiting the maximum value, and (b) when the second determining means determines that the degree of variation in capacity exceeds the second set value, the first The voltage correction is prohibited by maintaining the discharging means in the off state irrespective of the determination result of the determining means.

In the voltage correction circuit for a secondary battery according to the present invention, the terminal voltages of a plurality of series-connected secondary batteries vary for some reason. By discharging the secondary battery whose voltage indicates the maximum value and reducing the terminal voltage thereof to, for example, substantially the same voltage as the terminal voltage of another secondary battery, and performing voltage correction, the terminal voltage variation is reduced. be able to. That is, variations in the terminal voltage of the secondary battery due to differences in the amount of charge and the amount of self-discharge are corrected.

Further, in this voltage correction circuit, even when the terminal voltage varies widely, when the capacity varies greatly, the secondary battery is not discharged and the voltage correction is prohibited. By doing so, the discharge is not interrupted even when the terminal voltage is high on average during the discharge.

That is, when the variation in the capacity of the secondary battery becomes large, the secondary battery having a small capacity tends to be overcharged when charging and overdischarged when discharging, as compared with a secondary battery having a large capacity. When the voltage correction works, the secondary battery having a small capacity is discharged, and the battery is further overdischarged at the time of discharging. As a result, if the above-described voltage correction is simply performed, the discharge is interrupted even if the terminal voltage is high on average during the discharge, which may have an adverse effect. Thus, in the present invention, such a problem is prevented by prohibiting the voltage correction when the variation in capacitance is large.

Therefore, a volatile storage device such as a personal computer is built in, and when the terminal voltage of the secondary battery drops, the data in the volatile storage device is transferred to the nonvolatile storage device to prevent data loss. When a secondary battery is used as the power supply for the device, the terminal voltage of some of the secondary batteries drops quickly and reaches the discharge prohibition voltage, so that the discharge is not suddenly interrupted, and the volatile storage device is used. Data is securely stored.

On the other hand, at the time of charging, since all the secondary batteries are charged evenly, the charging is reliably performed until the battery is fully charged, and the use time is prolonged. In addition, there is no need for the troublesome work of connecting the series voltages after adjusting the terminal voltages of a plurality of secondary batteries as in the related art.

In the present invention, the discharging means is constituted by, for example, a switching element and a resistance element connected in series to both ends of each of the plurality of secondary batteries. The state is turned on / off.

Further, the first judging means in the present invention comprises:
Specifically, for example, (a) the voltage difference between the maximum value and the minimum value of the terminal voltage of a plurality of secondary batteries, and (b) the voltage difference between the maximum value and the average value of the terminal voltages of a plurality of secondary batteries. (C) any one of the voltage difference between the maximum value of the terminal voltages of the plurality of secondary batteries and the average value of the terminal voltages of the other secondary batteries excluding the secondary battery having the maximum terminal voltage; By comparing with the setting value of
The degree of variation in terminal voltage is determined.

Further, the second judging means in the present invention comprises:
Specifically, for example, the voltage difference between the maximum value and the minimum value of the terminal voltage at the end of discharging of the plurality of secondary batteries is set to Vc, and when the voltage correction is performed when charging the plurality of secondary batteries and not performed. When the values of Vc at this time are Vc1 and Vc2, respectively, the degree of variation in capacitance is determined by comparing the value of Vc1−Vc2 with the second set value.

Further, the control means according to the present invention is arranged such that the terminal voltage of the secondary battery connected to the discharge means in the ON state is reduced.
(a) when the voltage has dropped to the minimum value of the terminal voltages of the other secondary batteries, (b) when the voltage has dropped to the average value of the terminal voltages of the other secondary batteries, (c) a plurality of At any point in time when the terminal voltage of the secondary battery has dropped to the average value, the discharging means is turned off.

However, when the voltage between both ends of the plurality of secondary batteries connected in series is equal to or less than a predetermined value, or when the maximum value of the terminal voltages of the plurality of secondary batteries is equal to or less than a predetermined value, the discharging means is turned on. It is desirable not to be in a state.

[0022]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a voltage correction circuit for a secondary battery according to one embodiment of the present invention. In the figure, there are a plurality of secondary battery groups 1 (3 in this example).
) Of secondary batteries B1, B2, and B3 are connected in series. The + terminal of the secondary battery B1 is connected to the external connection terminal a,
The minus terminal of the secondary battery B1 and the plus terminal of the secondary battery B2 are connected to the external connection terminal b, and the minus terminal of the secondary battery B2 and the plus terminal of the secondary battery B3.
The terminal is connected to the external connection terminal c, and the negative terminal of the secondary battery B3 is connected to the external connection terminal d.

SW1, SW2, SW3 are switch elements,
R1, R2 and R3 are discharge resistors, and the switching element S
A first discharge circuit 2 is formed by W1 and the resistor R1, a second discharge circuit 3 is formed by the switch element SW2 and the resistor R2, and a third discharge circuit 4 is formed by the switch element SW3 and the resistor R3. doing. Both ends of the first discharge circuit 2 are connected to the external connection terminals a and b of the secondary battery group 1, and both ends of the second discharge circuit 3 are connected to the external connection terminals b and c of the secondary battery group 1. Both ends of the circuit 4 are connected to external connection terminals c and d of the secondary battery group 1, respectively.

The switching circuit 5 comprises a first switch SW4 comprising switching contacts e, f, g and a common contact k, and a second switching switch S4 comprising switching contacts h, i, j and a common contact l.
W5, and the switches SW4 and SW5 are linked. That is, when the common contact k is switched to the switching contact e, the common contact l is switched to the switching contact h,
When the common contact k is switched to the switching contact f, the common contact l is switched to the switching contact i, and when the common contact k is switched to the switching contact g, the common contact l is switched to the switching contact j. The switching contacts e, f, and g of the first switching switch SW4 of the switching circuit 5 are connected to the terminals a, b, and c of the secondary battery group 1, respectively, and the second switching switch S
The switching contacts h, i, j of W5 are terminals b,
are connected to c and d, respectively.

The common terminals k, l of the first and second switches SW4, SW5 of the switching circuit 5 are connected to the input terminals m, n of the differential amplifier 6, respectively. The differential amplifier 6 includes an operational amplifier A and a plurality of resistors, and has input terminals m and n.
A voltage corresponding to the voltage difference between the two is generated at the output terminal O. By the switching circuit 5 and the differential amplifier 6, the secondary battery group 1
Of the secondary batteries B1, B2, and B3 are configured.

The output terminal O of the differential amplifier 6 is connected to the input terminal P of the microcontroller 7. The microcontroller 7 has a built-in A / D converter.
The output voltage of the differential amplifier 6 input to the input terminal P is converted into a digital value by the / D converter. This A /
From the digital value obtained by the D converter, the switching circuit 5, the differential amplifier 6, and the A
Batteries B1, B2, B3 measured by the / D converter
The first determination is made by comparing the degree of variation of the terminal voltage of the secondary battery with the first set value, and the degree of variation of the capacity of the secondary batteries B1, B2, and B3 is determined by comparing with the second set value. A second determination is made.

The microcontroller 7 outputs a control signal for selecting a changeover contact of the changeover switch 5 from an output terminal Q. By the control signal from the output terminal Q,
The common terminals k and l are sequentially switched to switching contacts e and h, switching contacts f and i, and switching contacts g and j.

Further, the microcontroller 7 makes the discharge circuits 2, 3, 4 based on the first and second judgment results.
ON / OFF control of the switches SW1, SW2, SW3. That is, the microcontroller 7 further includes three output terminals R, S, and T, and turns on / off the switch element SW1 of the discharge circuit 2 via the output terminal R.
The control circuit controls ON / OFF of the switch element SW2 of the discharge circuit 3 via the output terminal S, and ON / OFF controls the switch element SW3 of the discharge circuit 4 via the output terminal T.

Next, the operation of the thus configured secondary battery voltage correction circuit of FIG. 1 will be described with reference to the flowchart of FIG. When charging starts, the secondary battery B
, B2, and B3 are detected (step S1).
0). In this case, the switches SW4 and SW5 of the switching circuit 5 are controlled by the
1 and the differential amplifier 6 generates a voltage corresponding to the terminal voltage of the secondary battery B1. The output voltage of the differential amplifier 6 is input to the input terminal P of the microcontroller 7,
After being converted into a digital value by the A / D converter, it is stored in the memory. Hereinafter, similarly, the switches SW4 and SW5 of the switching circuit 5 sequentially select the secondary batteries B2 and B3,
The output voltage of the differential amplifier 6 at that time is input to the microcontroller 7, converted into a digital value, and stored in the memory.

When the terminal voltages of the secondary batteries B1, B2, and B3 are all stored in the memory as digital values, the first determination, that is, the determination of the degree of variation in the terminal voltages of B1, B2, and B3 is performed. (Step S1
1). That is, in step S11, the maximum value Vmax and the minimum value Vmin of the terminal voltages of the secondary batteries B1, B2, and B3 stored in the memory are obtained, and the difference between the two, that is, the degree of variation of the terminal voltage is determined by the first setting. The value Va is compared with the value Va. Here, normally, there is almost no difference between the terminal voltages of the secondary batteries B1, B2, and B3, and Vmax−Vmin ≦ Va (NO in step S11). Therefore, the process returns to step S10 and the detection of the terminal voltage is continued. .

On the other hand, if a large variation occurs in the terminal voltages of the secondary batteries B1, B2, and B3 due to any cause, for example, a difference in the amount of charge or the amount of self-discharge, Vmax−Vmin> V
a (YES in step S11), and in this case, the process proceeds to step S12 to perform the second determination, that is, B1, B2, B
The determination of the degree of variation of the capacitance of No. 3 is performed. That is, in step S12, the difference between Vc1 and Vc2 previously stored and held in the memory is compared with the second set value Vb. Here, Vc: a value of Vmax−Vmin at the end of discharging Vc1: a value of Vc when voltage correction is performed during charging Vc2: a value of Vc when voltage correction is not performed during charging, Vc1 -Vc2 represents the degree of variation in the capacity of the secondary batteries B1, B2, B3.

Here, normally, the secondary batteries B1, B2, B3
Are substantially the same, the charge amounts of B1, B2, and B3 are adjusted if the voltage correction described below is performed.
Since the variation in terminal voltage at the time of discharge is smaller than that when no voltage correction is performed, even if the terminal voltages of B1, B2, and B3 are high on average, the discharge is not interrupted at the time of discharge.

On the other hand, when the variation in the capacity of the secondary batteries B1, B2, and B3 becomes large, the secondary battery having a small capacity is overcharged at the time of charging compared to the secondary battery having a large capacity.
Since the battery tends to be over-discharged at the time of discharge, if the voltage correction is performed, the secondary battery having a small capacity is discharged, and the discharge is further over-discharged. As a result,
When the voltage is corrected, the secondary batteries B1, B2, B3
Even if the terminal voltage is high on average, the discharge is interrupted, and the voltage correction operation may have an adverse effect.

Therefore, when the variation in the capacity of the secondary batteries B1, B2, and B3 is small and Vc1−Vc2 ≦ Vb (NO in step S12), the process proceeds to step S13 to perform the voltage correction. Is large and Vc1-Vc2> Vb
In the case of (YES in step S12), voltage correction is not performed, and the process returns to step S10 to continue the detection of the terminal voltage. In this way, it is possible to avoid the above-described adverse effects caused by performing the voltage correction when the variation in capacitance is large.

In the voltage correction in step S13, the switch of the discharge circuit connected to the battery whose terminal voltage is the maximum value among the secondary batteries B1, B2, and B3 is turned on to start discharging the secondary battery. When the terminal voltage drops to the minimum value among the terminal voltages of the secondary batteries B1, B2, and B3, the switch is turned off and the discharge is terminated.

As described above, according to the present invention, even if the terminal voltages of the plurality of secondary batteries B1, B2, and B3 connected in series fluctuate for some reason, the secondary battery showing the maximum terminal voltage is discharged to discharge the terminal. By performing the voltage correction by lowering the voltage, the variation in the terminal voltage can be reduced.

In the present invention, the secondary batteries B1, B
In the case where there is a large variation in the capacitances of the capacitors B2 and B3, even if the variation in the terminal voltage is large, the voltage correction is prohibited, so that the adverse effect of the voltage correction in such a case can be avoided.

The present invention is not limited to the above embodiment, but can be implemented with various modifications as follows. (1) In the above embodiment, an example in which three secondary batteries are connected in series has been described. However, the voltage correction circuit of the present invention can be applied to a case where two or four or more secondary batteries are connected in series. Can be.

(2) In the above embodiment, the voltage difference between the maximum value and the minimum value is determined as the degree of variation in the terminal voltage of the plurality of secondary batteries B1, B2, B3, and this is compared with the first set value. However, a voltage difference between the maximum value and the average value or a voltage difference between the maximum value and the average value of the other terminal voltages excluding the maximum value is obtained as the degree of variation of the terminal voltage and compared with the first set value. Is also good.

(3) In the above embodiment, the secondary battery whose terminal voltage has the maximum value is discharged until the terminal voltage reaches the terminal voltage of the battery whose terminal voltage has the minimum value at the time of voltage correction. Discharge is performed when the average value of the terminal voltage of the battery or the average value of the terminal voltage of the rechargeable batteries excluding the rechargeable battery with the maximum value of the terminal voltage (that is, the rechargeable battery without voltage correction) is reduced. You may make it stop.

(4) In the above embodiment, only the terminal voltage during charging is monitored. However, immediately after the start of charging, the terminal voltage may not be stable. May be prohibited.

(5) In the above embodiment, the case where the voltage correction is performed at the time of charging has been described. However, the present invention can be applied to the case where the voltage correction is performed at the time of discharging or at rest. In addition, the present invention can be variously modified and implemented without departing from the gist.

[0043]

As described above, according to the present invention, when the terminal voltages of a plurality of secondary batteries connected in series vary for some reason, the secondary battery showing the maximum terminal voltage is discharged. Then, by performing the voltage correction by reducing the voltage to substantially the same as the terminal voltage of the other secondary batteries, the variation in the terminal voltage can be reduced. That is,
Even if there are variations in the amount of charge and the amount of self-discharge, they can be automatically corrected.

Further, when the variation in the capacity of the plurality of secondary batteries is large, the voltage correction is not performed even if the variation in the terminal voltage is large, so that the secondary battery having a small capacity is discharged by the voltage correction. This prevents over-discharge from occurring and does not increase the variation in terminal voltage during charging by voltage correction.This ensures that even if the terminal voltage is high on average, discharge is interrupted and voltage correction has the opposite effect. Adverse effects can be avoided.

Therefore, the discharge is not interrupted when the terminal voltage of the secondary battery is high on average during the discharge. Therefore, when the terminal voltage of the secondary battery which is the power source is lowered as in a personal computer, the discharge becomes volatile. In the case of devices that transfer data from a storage device to a non-volatile storage device to prevent data loss, the terminal voltage of some rechargeable batteries drops quickly and reaches the discharge prohibition voltage, causing sudden discharge. It is possible to avoid loss of data in the volatile storage device due to the interruption.

On the other hand, at the time of charging a plurality of secondary batteries, all the secondary batteries are charged evenly, so that charging can be reliably performed until the secondary battery is fully charged. The length of the battery can be lengthened, and the troublesome work of connecting the terminal voltages of a plurality of secondary batteries and connecting them in series as in the related art is not required.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a voltage correction circuit of a secondary battery according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Secondary battery group B1, B2, B3 ... Secondary battery 2,3,4 ... Discharge circuit 5 ... Switching circuit 6 ... Differential amplifier 7 ... Microcontroller

Claims (5)

[Claims] An on / off discharging means connected to both ends of a plurality of secondary batteries connected in series, and a first setting of a degree of variation in terminal voltages of the plurality of secondary batteries. A first determination unit that determines by comparing the first and second values with each other; a second determination unit that determines a degree of variation in the capacity of the plurality of secondary batteries by comparing with a second set value; Control means for controlling the discharging means based on the determination result of the second determination means, the control means comprising: (a) the first determination means determines the degree of variation of the terminal voltage to a first set value; When it is determined that the voltage has exceeded the threshold value and when the degree of variation in the capacity is determined to be equal to or less than a second set value by the second determination unit, the secondary battery whose terminal voltage has the maximum value among the plurality of secondary batteries Turn on the discharging means connected to the When the terminal voltage decreases to a predetermined value, the discharging means is turned off to perform voltage correction of the secondary battery indicating the maximum value, and (b) the degree of variation in the capacity is determined by the second determining means to be a second degree. When it is determined that the voltage exceeds the set value, the voltage correction is prohibited by maintaining the discharging unit in an off state regardless of the determination result of the first determining unit. circuit. 2. The voltage correction of a secondary battery according to claim 1, wherein said discharging means comprises a switch element and a resistance element connected in series to both ends of each of said plurality of secondary batteries. circuit. 3. The first determination means includes: (a) a voltage difference between a maximum value and a minimum value of terminal voltages of the plurality of secondary batteries, and (b) a terminal voltage of the plurality of secondary batteries. (C) the maximum value of the terminal voltages of the plurality of secondary batteries and the terminal voltage of the other secondary batteries excluding the secondary battery whose terminal voltage indicates the maximum value. 2. The voltage correction circuit for a secondary battery according to claim 1, wherein a degree of variation of the terminal voltage is determined by comparing any one of a voltage difference from an average value and a first set value. 4. The method according to claim 1, wherein the second determining means sets a voltage difference between a maximum value and a minimum value of the terminal voltage at the end of discharging of the plurality of secondary batteries to Vc, and charges the plurality of secondary batteries. In this case, when the values of Vc when the voltage correction is performed and when they are not performed are Vc1 and Vc2, respectively, the value of Vc1−Vc2 is compared with a second set value to determine the degree of variation of the capacitance. The voltage correction circuit for a secondary battery according to claim 1, wherein: 5. The control unit according to claim 1, wherein the terminal voltage of the secondary battery connected to the discharging unit in the on state is reduced to (a) the minimum voltage among the terminal voltages of the other secondary batteries. ,
(b) at the time when the voltage has decreased to the average value of the terminal voltages of the other secondary batteries, and (c) at the time when the voltage has decreased to the average value of the terminal voltages of the plurality of secondary batteries. 2. The voltage correction circuit for a secondary battery according to claim 1, wherein the voltage is turned off.