JP3398304B2 - Voltage measurement circuit for secondary battery and protection circuit using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage measuring circuit for measuring a battery voltage particularly suitable for protection of a secondary battery and a protection circuit using the voltage measuring circuit, and more particularly to a plurality of secondary batteries connected in series. Voltage measuring circuit and protection circuit for

[0002]

2. Description of the Related Art A non-aqueous solvent type secondary battery such as a lithium secondary battery or a lead storage battery is a battery if the terminal voltage becomes too low due to discharging or leaving, or if the terminal voltage becomes too high during charging. Performance may deteriorate and safety may be impaired. Therefore, in these secondary batteries, it is necessary to monitor the terminal voltage and control the charging and discharging so that the terminal voltage falls within a predetermined range before use.

Particularly, in the case of a lithium secondary battery, for example, when the terminal voltage exceeds 4.5 V, gas is generated due to decomposition of the electrolytic solution, and as a result, the internal pressure of the battery rises and the safety valve operates, causing leakage. May liquify. The terminal voltage is 2
When the voltage becomes V or less, the copper of the current collector used for the negative electrode begins to dissolve in the electrolytic solution and the battery performance deteriorates. Therefore, when a lithium secondary battery is used, the charging current is interrupted when the terminal voltage rises to reach the charging prohibition voltage Vov during charging, and the terminal voltage decreases when discharging to reach a preset discharging prohibition voltage Vuv. It is common to perform charging / discharging via a protection circuit having a function of interrupting the discharge current when reaching.

The charge inhibition voltage Vov is set to a voltage slightly lower than the voltage at which the decomposition of the electrolytic solution starts (eg, 4.35V), and the discharge inhibition voltage Vuv is slightly higher than the voltage at which the negative electrode copper starts to dissolve (eg, the voltage). 2 to 2.5 V). When using multiple secondary batteries connected in series,
The terminal voltage of each battery is measured, and these are compared with the charge inhibition voltage Vov and the discharge inhibition voltage Vuv, and whether each terminal voltage has risen to the charge inhibition voltage Vov and whether it has dropped to the discharge inhibition voltage Vuv. Whether or not is determined, and charging / discharging is controlled according to the determination result.

By the way, in recent years, an electronic circuit has been built in a battery pack, and by this electronic circuit, data indicating the state of the battery such as the terminal voltage of the secondary battery, the battery temperature, and the charge amount is stored in the battery pack which is a charger or a load. However, regarding the terminal voltage of the secondary battery, a value corresponding to the sum of the terminal voltages of all the batteries connected in series is output. When operating the protection circuit described above, an average value is obtained from the sum of the terminal voltages of the plurality of secondary batteries connected in series, and the average value is compared with the charge inhibition voltage Vov or the discharge inhibition voltage Vuv.

[0006]

However, when the plurality of secondary batteries connected in series have different capacities or different amounts of charge, the terminal voltage of each battery varies. In the secondary battery voltage measuring method described above, even when the terminal voltage varies for each such battery, the average value is obtained from the sum of the terminal voltages,
The protection operation is performed in comparison with the charge prohibition voltage and discharge prohibition voltage.

Therefore, even if the terminal voltage of the battery having the minimum capacity or the battery having the maximum charge amount reaches the charge inhibition voltage earlier than the other batteries during charging, if the terminal voltage of the secondary battery is high on average, Since the average value does not reach the charge prohibition voltage, charging cannot be stopped, which causes overcharge. On the contrary, during discharging, even if the terminal voltage of the battery with the smallest capacity or the battery with the smallest amount of charge reaches the discharge inhibition voltage earlier than other batteries, the discharge is stopped if the terminal voltage of the battery is high on average. However, there is an inconvenience that over-discharge occurs.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to perform a reliable protection operation without being affected by variations in terminal voltages of a plurality of secondary batteries connected in series. An object of the present invention is to provide a secondary battery voltage measuring circuit and a protection circuit using the same.

[0009]

In order to solve the above problems, the present invention normally uses the average value of the terminal voltages of a plurality of secondary batteries connected in series as the measured value of the battery voltage. When the maximum value of each terminal voltage is higher than a certain value or the minimum value thereof is lower than a certain value, the maximum value or the minimum value thereof is used as the measured value of the battery voltage.

That is, the voltage measuring circuit for the first secondary battery according to the present invention comprises maximum value detecting means for detecting the maximum value of the terminal voltages of the plurality of secondary batteries connected in series. The average value detecting means for detecting the average value of the terminal voltage of each of the plurality of secondary batteries is compared with the maximum value and the first set value lower than the charge inhibition voltage, and the maximum value is equal to or more than the first set value. In this case, the maximum value is the measured value of the battery voltage, and when the maximum value is lower than the first set value, the average value is the measured value of the battery voltage.

A second secondary battery voltage measuring circuit according to the present invention comprises a minimum value detecting means for detecting a minimum value of terminal voltages of a plurality of secondary batteries connected in series, and a plurality of minimum value detecting means. If the average value detecting means for detecting the average value of the respective terminal voltages of the secondary battery and the second setting value higher than the minimum value and the discharge inhibition voltage are compared, and the minimum value is equal to or less than the second setting value Has a minimum value as the measured value of the battery voltage, and when the minimum value is higher than the second set value, a measuring means for making the average value the measured value of the battery voltage.

The voltage measuring circuit for the third secondary battery according to the present invention has the functions of the above-mentioned first and second voltage measuring circuits, and is used for a plurality of secondary batteries connected in series. Maximum value detection means for detecting the maximum value of each terminal voltage, minimum value detection means for detecting the minimum value of each terminal voltage of the plurality of secondary batteries, and a plurality of secondary batteries The average value detecting means for detecting the average value of each terminal voltage is compared with the maximum value and the first set value lower than the charge prohibition voltage, and is lower than the minimum value and the first set value and higher than the discharge prohibition voltage. When the maximum value is greater than or equal to the first set value, the maximum value is the measured value of the battery voltage, and when the minimum value is less than or equal to the second set value, the minimum value is the battery voltage. Measured value, maximum value is lower than the first set value and minimum value is the second If higher value is characterized by comprising a measuring means for the measurement of the battery voltage average value.

Further, the first secondary battery protection circuit according to the present invention compares the measured value obtained by the above-mentioned first or third voltage measurement circuit with the charge inhibition voltage, and the measured value shows the charge inhibition. It is characterized by comprising means for inhibiting charging of the secondary battery when the voltage rises.

The second secondary battery protection circuit according to the present invention compares the measured value obtained by the above-mentioned second or third voltage measuring circuit with the discharge inhibition voltage, and the measured value is the discharge inhibition voltage. It is characterized in that it is provided with a means for inhibiting the discharge of the secondary battery when the battery voltage drops to 0.

The third secondary battery protection circuit according to the present invention compares the measured value obtained by the above-mentioned third voltage measurement circuit with the charge inhibition voltage and the discharge inhibition voltage, and the measured value is the charge inhibition voltage. It is characterized in that it is provided with a means for prohibiting the charging of the secondary battery when the temperature rises up to, and prohibiting the discharging of the secondary battery when the measured value falls to the discharge inhibition voltage.

As described above, according to the present invention, in a normal case, that is, when the maximum value of the terminal voltage of each of the plurality of secondary batteries connected in series is lower than the first set value, or when the minimum value is the second value. If the value is higher than the set value, the average value is output as the measured value of the battery voltage. If the maximum value is the first set value or more, the maximum value is output, and if the minimum value is the second set value or less, the minimum value is output. Each value is output as a measured value of the battery voltage.

Therefore, for example, when the terminal voltage of the secondary battery varies and the terminal voltage of the battery having the minimum capacity or the battery having the maximum charge amount reaches the charge inhibition voltage earlier than other batteries, or when the battery is discharged. When the terminal voltage of the battery with the smallest capacity or the battery with the smallest amount of charge reaches the discharge inhibition voltage earlier than other batteries, they are immediately detected from the measured value of the battery voltage to protect against the stop of charging and the stop of discharge. The operation can be performed, and it is possible to reliably prevent overcharge and overdischarge.

Further, since the average value of the terminal voltage of a plurality of secondary batteries is usually output as the measured value of the battery voltage, the charging state and discharging state of the secondary battery when the protective operation is not performed are monitored. be able to.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a voltage measuring circuit of a secondary battery according to an embodiment of the present invention. In the figure, a plurality of secondary battery groups 1 (three in this example)
The secondary batteries B1, B2 and B3 are connected in series. The secondary batteries B1, B2, B3 are, for example, non-aqueous solvent secondary batteries such as lithium ion secondary batteries, or lead storage batteries. The positive terminal of the secondary battery B1 is terminal a, the negative terminal of the secondary battery B1 and the positive terminal of the secondary battery B2 are terminal b, the negative terminal of the secondary battery B2 and the positive terminal of the secondary battery B3 are terminal c. The negative terminal of the secondary battery B3 is connected to the terminal d.

The switching circuit 2 includes a first switching switch SW1 including switching contacts e, f and g and a common contact k, and a second switching switch S including switching contacts h, i and j and a common contact l.
The switch SW1 and the switch SW2 are interlocked with each other. That is, when the common contact k is switched to the switching contact e, the common contact 1 is switched to the switching contact h, and when the common contact k is switched to the switching contact f, the common contact 1 is switched to the switching contact i, When the common contact k is switched to the switching contact g, the common contact 1 is switched to the switching contact j. The changeover contacts e, f, g of the first changeover switch SW1 of the changeover circuit 2 are respectively connected to the terminals a, b, c of the secondary battery group 1, and the second changeover switch S1.
The switching contacts h, i, j of W2 are the terminals b of the secondary battery group 1,
c and d, respectively.

The common terminals k and l of the first and second changeover switches SW1 and SW2 of the changeover circuit 2 are connected to the input terminals m and n of the differential amplifier 3, respectively. The differential amplifier 3 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 them is generated at the output terminal P. By the switching circuit 5 and the differential amplifier 3, the secondary battery group 1
The voltage measuring circuit for measuring the terminal voltage of each of the secondary batteries B1, B2, B3 in FIG.

The output terminal P of the differential amplifier 3 is connected to the input terminal AN of the microcontroller 4. The microcontroller 4 has a built-in A / D converter, and this A / D converter converts the output voltage of the differential amplifier 3 input to the input terminal AN into a digital value. This A / D
From the digital value obtained by the converter, by software processing by an internal program in the microcontroller 4, the switching circuit 2, the differential amplifier 3, and the A / D
Detects the maximum value of the terminal voltages of the secondary batteries B1, B2, B3 measured by the converter, and detects the minimum value of the terminal voltages of the secondary batteries B1, B2, B3. Minimum value detection and secondary batteries B1, B
The average value detection for detecting the average value of the terminal voltages of 2 and B3 and the battery voltage measurement based on these are performed.

At this time, the microcontroller 4 determines the changeover switch S of the changeover circuit 2 based on the value N of the internal counter.
A control signal for selecting the switching contact of W1 and SW2 is output from the output terminal Q. The control signal from the output terminal Q causes the common terminals k and l to have an internal counter value of N = 1.
, The contacts are switched to the switching contacts e and h respectively, and N =
When it is 2, it is switched to the switching contacts f and i, respectively, and N
= 3, the contacts are switched to the switching contacts g and j, respectively.

Next, the operation of the voltage measuring circuit for the secondary battery of FIG. 1 thus constructed will be described with reference to the flowchart of FIG. When the circuit starts operating, N = 1 is set as the initial state (step S1). In this case, the switches SW1 and SW2 of the switching circuit 2 select the secondary battery B1 (step S2), and the differential amplifier 3 generates a voltage corresponding to the terminal voltage of the secondary battery B1. The output voltage of the differential amplifier 3 is input to the input terminal AN of the microcontroller 4. In the microcontroller 4, the output voltage of the differential amplifier 3 is converted into a digital value V (A
After being converted into N), it is stored as a memory value D (1) (step S3). Here, in step S4, N + 1
→ When N is executed, N = 2, so that the process returns to step S2 via step S5 for determining whether N = 4.

Next, from N = 2, the switch S of the switching circuit 2
W1 and SW2 select the secondary battery B2 this time (step S2), and the output of the differential amplifier 3 generates a voltage corresponding to the terminal voltage of the secondary battery B2. The output voltage of the differential amplifier 3 is input to the input terminal AN of the microcontroller 4. In the microcontroller 4, as in the case of N = 1, the output voltage of the differential amplifier 3 is converted into the digital value V (AN) by the A / D converter and then stored as the memory value D (2) (step S3). . Here, step S4
By executing N + 1 → N, N = 3, so N =
4 through step S5 to determine whether or not
Return to.

Next, from N = 3, the switch S of the switching circuit 2
Select the secondary battery B3 for W1 and SW2 (step S
2), the differential amplifier 3 generates a voltage corresponding to the terminal voltage of the secondary battery B3. The output voltage of the differential amplifier 3 is input to the input terminal AN of the microcontroller 3. In the microcontroller 3, as in the case of N = 1 and N = 2, the output voltage of the differential amplifier 3 is converted into a digital value V (AN) by the A / D converter, and then the memory value D
It is stored as (3) (step S3). Here, when N + 1 → N is executed in step S4, N = 4,
Since YES is determined in step S5, step S6 is performed this time.
Proceed to.

In step S6, the memory value D (N) (N
= 1, 2, 3), the minimum value is the memory value D (min)
The maximum value is stored as the memory value D (max), and the average value of the memory values D (N) (N = 1, 2, 3) is stored as the memory value D (mean).

Next, in step S7, the maximum value D (max)
And a first set value V1 preset to an appropriate value (eg 4V) lower than the charging inhibition voltage Vov (eg 4.5V).
And D (max) ≧ V1 (step S7
YES), D as the measured value of the battery voltage D (out)
(Max) is output (steps S8 and S12).

If D (max) <V1 in step S7 (No in step S7), the process proceeds to step S9 to set the minimum value D (min) and the discharge inhibit voltage Vuv (for example, 2 to 2).
The predetermined second set value V2 is compared with an appropriate value (for example, 3.6 V) higher than 2.5 V, and D (min) ≦
In the case of V2 (Yes in step S9), D (min) is output as the measured value D (out) of the battery voltage (steps S10 and S12). If D (min)> V2 (NO in step S9), the average value D (mean) is output as D (out) (steps S11, S1).
2).

In step S12, the measured value of battery voltage D (o
ut) is output, the process returns to step S1 and the above processing is repeated. Next, a secondary battery protection circuit using the voltage measurement circuit of the present embodiment will be described with reference to FIG.
In FIG. 3, field effect transistors (FETs) 5 and 6 which are switching elements are added to the configuration shown in FIG.

That is, in this embodiment, the secondary battery B1,
In the secondary battery group 1 in which B2 and B3 are connected in series, the positive terminal of the battery B1 is connected to the + side external connection terminal 7, the negative terminal of the battery B3 is connected to the source of the first FET5, and the drain of the FET5. Is connected to the drain of the second FET 6, and the source of the FET 6 is connected to the-side external connection terminal 8. The parasitic diode D1 is connected in parallel to the first FET 5 so as to be in the forward direction during charging, and is connected in parallel to the second FET 6 so as to be in the forward direction during discharging.

A charger is connected between the external connection terminals 7 and 8 during charging, and a device used by the battery pack, which is a load, is connected during discharging. Also, the first and second FETs
The gates of 5 and 6 are connected to the control terminals R and S of the microcontroller 4, respectively.

In this embodiment, the microcontroller 4
Performs the overcharge prevention operation by comparing the measured value D (out) obtained by measuring the battery voltage as described above with the charge inhibition voltage Vov during charging. That is, when the measured value D (out) of the battery voltage rises to the charge inhibition voltage Vov,
When the control terminal S of the microcontroller 4 becomes low level and the second FET 6 becomes non-conducting, charging is stopped and overcharge of the secondary battery group 1 is prevented.

Furthermore, the microcontroller 4 discharges the measured value D (out) of the battery voltage and the discharge inhibition voltage Vu during discharge.
Compared with v, the over-discharge prevention operation is performed. That is, when the measured value D (out) of the battery voltage drops to the discharge inhibition voltage Vuv, the control terminal R of the microcontroller 4 becomes low level, the first FET 5 becomes non-conductive, and the discharge is stopped. Over-discharge of the secondary battery group 1 is prevented.

As described above, in this embodiment, as the measured value D (out) of the battery voltage, the maximum value D (max) is output when D (max) ≧ V1 and the maximum value D (max) ≧ V2 is output when D (min) ≦ V2. The minimum value D (min) is output. Therefore, by using this measured value D (out), the secondary batteries B1, B
The protection operation can be surely performed without being affected by the variations in the terminal voltages of B2 and B3.

That is, the terminal voltages of the secondary batteries B1, B2, B3 have variations, and the terminal voltage of the battery having the minimum capacity or the battery having the maximum charge amount reaches the charge inhibition voltage earlier than other batteries during charging. When the terminal voltage of the battery with the minimum capacity or the battery with the minimum charge amount reaches the discharge inhibition voltage earlier than other batteries when discharging, those are immediately detected from the measured value of the battery voltage to stop charging or discharge. The stop protection operation can be performed, and it becomes possible to reliably prevent overcharge and overdischarge.

In the normal case, that is, D (max) <
When V1 and D (min)> V2, the average value D (m
ean) is output as the measured value D (out) of the battery voltage, so that the progress of charging and discharge of the secondary batteries B1, B2, B3 when the protection operation against the above-mentioned overcharge and overdischarge is not performed. It is possible to monitor the progress.

That is, as described above, D (max) ≧ V
In case of 1, D (max) is output and D (min) ≦ V2
In the method of outputting D (min) in the case of
When x) ≧ V1 or D (min) ≦ V2, neither the charging state nor the discharging state of the secondary battery can be known by the charger or the device used, but D (max) <V1 and D (mi
By outputting the average value D (mean) when n)> V2, it is possible to grasp how much the charging states and discharging states of the secondary batteries B1, B2, B3 are advanced overall. .

Further, according to the above embodiment, the microcontroller 4 detects all the maximum, minimum and average values of the terminal voltages of the secondary batteries B1, B2, B3 from the voltage of the output terminal P of the differential amplifier 3. Since the switching circuit 2 and the differential amplifier 3 are on the battery pack side together with the secondary battery group 1 and the microcontroller 4 is on the external device side such as a charger or a used device, the battery pack and the external device are The number of connecting lines between them can be minimized.

The present invention is not limited to the above embodiment, but can be carried out in various modifications as follows. (1) In the above embodiment, an example in which three secondary batteries are connected in series has been described, but when two or four or more secondary batteries are connected in series, or a cell in which a plurality of secondary batteries are connected in parallel is used. Even when a plurality of blocks are connected in series, the voltage measuring circuit and the protection circuit of the present invention can be applied.

(2) In the above embodiment, the first set value V
Measured value of battery voltage D (out) with 1 and second set value V2
However, it is also possible to perform the smoothing process so that D (out) continuously changes near V1 or V2 or both.

(3) In the above embodiment, D (max) ≧
D (max) in the case of V1 is the measured value of battery voltage D (ou
t), and D (min) when D (min) ≦ V2 is the measured value D (out) of the battery voltage.
And V1 or D (min) and V2 may be omitted. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0043]

As described above, according to the present invention, when the maximum value of the terminal voltage of each of a plurality of secondary batteries connected in series is greater than or equal to the first set value, the maximum value of the battery voltage is By outputting the measured value as the measured value, and when the minimum value is less than or equal to the second set value, the minimum value is output as the measured value of the battery voltage. Battery or the battery with the maximum charge reaches the charge inhibit voltage earlier than other batteries, or the battery with the minimum capacity or the battery with the minimum charge has a faster terminal voltage than other batteries when discharging. When the discharge inhibit voltage is reached, it can be detected immediately from the measured value of the battery voltage to perform the protection operation of the charge stop and the discharge stop, and the overcharge and the overdischarge can be surely prevented.

In a normal state in which the maximum value is lower than the first set value or the minimum value is higher than the second set value, the average value of the terminal voltages of the plurality of secondary batteries is calculated as the battery voltage. Since it is output as the measured value of, the charging state and the discharging state when the protection operation of the secondary battery is not performed can be monitored.

[Brief description of drawings]

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

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

FIG. 3 is a block diagram showing a configuration of a secondary battery protection circuit according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Secondary battery group B1, B2, B3 ... Secondary battery 2 ... Switching circuit 3 ... Differential amplifier 4 ... Micro controller

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-117072 (JP, A) JP-A-8-140206 (JP, A) JP-A-51-85437 (JP, A) JP-A-7- 105986 (JP, A) JP-A-57-105975 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02J ⁷ /00-7/36 G01R 19/165 G01R 31/36

Claims (6)

(57) [Claims] 1. A maximum value detecting means for detecting a maximum value among terminal voltages of a plurality of secondary batteries connected in series, and an average value of terminal voltages of the plurality of secondary batteries. The average value detecting means for detecting is compared with the maximum value and a first set value lower than the charge inhibition voltage, and when the maximum value is equal to or higher than the first set value, the maximum value is taken as the measured value of the battery voltage, and the maximum A voltage measuring circuit for a secondary battery, comprising: a measuring unit that uses the average value as a measured value of the battery voltage when the value is lower than the first set value. 2. A minimum value detecting means for detecting a minimum value among terminal voltages of a plurality of secondary batteries connected in series, and an average value of terminal voltages of the plurality of secondary batteries. The average value detection means for detecting is compared with the second set value higher than the minimum value and the discharge inhibition voltage, and when the minimum value is equal to or lower than the second set value, the minimum value is set as the measured value of the battery voltage, and the minimum value is set. A voltage measuring circuit for a secondary battery, comprising: a measuring unit that uses the average value as a measured value of the battery voltage when the value is higher than the second set value. 3. A maximum value detecting means for detecting a maximum value among the terminal voltages of a plurality of secondary batteries connected in series, and a minimum value among the terminal voltages of the plurality of secondary batteries. A minimum value detecting means for detecting a value, an average value detecting means for detecting an average value of terminal voltages of the plurality of secondary batteries, and a first set value lower than the maximum value and the charge inhibition voltage. In addition to the comparison, the minimum value is compared with a second set value that is lower than the first set value and higher than the discharge prohibition voltage. If the maximum value is equal to or larger than the first set value, the maximum value is the measured value of the battery voltage. When the minimum value is less than or equal to the second set value, the minimum value is the measured value of the battery voltage, and when the maximum value is lower than the first set value and the minimum value is higher than the second set value, the average value is And a measuring means for measuring the battery voltage. Voltage measuring circuit of the battery. 4. Comparing the measured value obtained by the voltage measuring circuit according to claim 1 with the charging prohibition voltage, and prohibiting charging of the secondary battery when the measured value rises to the charging prohibition voltage. A protection circuit for a secondary battery, characterized by comprising: 5. The measured value obtained by the voltage measuring circuit according to claim 2 or 3 is compared with the discharge inhibition voltage, and when the measured value drops to the discharge inhibition voltage, the discharge of the secondary battery is inhibited. A protection circuit for a secondary battery, characterized by comprising: 6. The measured value obtained by the voltage measuring circuit according to claim 3 is compared with the charge inhibition voltage and the discharge inhibition voltage, and when the measured value rises to the charge inhibition voltage, the secondary battery A protection circuit for a secondary battery, comprising means for inhibiting charging and for inhibiting discharge of the secondary battery when a measured value drops to a discharge inhibition voltage.