JP2003333762A - Voltage level equalization device for battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To equalize the voltage levels of the electric cells constituting a battery pack while reducing the loss of energy in the battery pack to the utmost. <P>SOLUTION: A voltage level equalization device is provided with a equalization circuit 1 that equalizes the voltage levels of the electric cells SB that are electrically connected in series in the battery pack CB constituted by combining a plurality of electric cells SB in a state that the electric cells SB, SB are electrically connected in series at least at one place. The device is also provided with: an equalizer circuit control means BC that stops the operation of the equalizer circuit 1 to equalize the voltage levels when a variation in voltage level between the electric cells SB that constitute the battery pack CB becomes less than prescribed; and a residual capacity detection means RS that detects the residual capacity of the electric cell SB or a physical quantity having a fixed relation with the residual capacity of the electric cell SB. The equalization circuit control means BC is configured so as to set and change the prescribed value based on the detected information of the residual capacity detection means RS. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery pack formed by combining a plurality of cells in a state in which the cells are electrically connected in series at least at one location. The present invention relates to a voltage level equalizing device for an assembled battery, which is provided with an equalizing circuit that equalizes the voltage levels of the unit cells.

[0002]

2. Description of the Related Art A battery pack is a battery in which unit cells are combined in series or in parallel to form a single battery, and is used in various devices such as portable personal computers and electric vehicles. In the assembled battery configured in this way, it is inevitable that the state of charge of each unit cell will fluctuate due to the capacity of each unit cell, the voltage at the time of assembly, the change over time (deterioration), the difference in self-discharge, and the variation in internal impedance. . But,
The same discharge current flows in the cells connected in series, and variations in the charging / discharging state appear as variations in the terminal voltage, which may lead to overcharging or overdischarging of some of the cells. In such a case, it is possible to equalize the charging / discharging states of the cells by using the voltage level equalizing device for the assembled battery. Conventionally, the operation mode of the voltage level equalization device has been to use it together with a charging device for charging the assembled battery so that the equalization circuit is always operated while the assembled battery is being charged or discharged, or the assembled battery is charged. It was common to activate the equalization circuit before starting the discharge operation.

[0003]

Therefore, in the above-mentioned conventional configuration, the equalization circuit is operated without considering the state of each unit cell constituting the assembled battery, and therefore it is not always necessary to operate the equalization circuit. There is a case where the equalization circuit is operated until there is no such situation, and there is a disadvantage that the energy of the battery pack is unnecessarily reduced due to energy loss due to the operation of the equalization circuit. The present invention has been made in view of the above circumstances, and an object thereof is to make it possible to equalize the voltage levels of the unit cells constituting the battery pack while suppressing the energy loss of the battery pack as much as possible. There is a point to.

[0004]

By providing the structure according to claim 1, a plurality of cells are combined in a state where the cells are electrically connected in series at at least one location. In a voltage level equalizing device for an assembled battery, which is provided with an equalization circuit for equalizing the voltage levels of the cells that are electrically connected in series in the assembled battery, a voltage level between the cells constituting the assembled battery. The equalizing circuit control means for stopping the voltage level equalizing operation of the equalizing circuit when the variation becomes smaller than a set value, and the remaining capacity of the unit cell or a constant relationship with the remaining capacity of the unit cell. Remaining capacity detecting means for detecting a physical quantity that is provided, and the equalizing circuit control means is configured to change the setting of the set value based on the detection information of the remaining capacity detecting means. It has been.

That is, when the variation in the voltage level among the cells forming the assembled battery becomes large, the equalizing circuit is operated, and the variation in the voltage level becomes smaller than the set value, and the variation between the cells becomes small. The equalization circuit is deactivated when the voltage levels are sufficiently equalized, and the set value for determining whether or not to deactivate the equalization circuit is the detection information of the remaining capacity detection means. The setting is changed by. This is based on the fact that the remaining capacity and the open cell voltage are not in a linear relationship as shown in FIG. 6 which shows the relationship between the remaining capacity of the single cell and the open cell voltage of the single cell. Although FIG. 6 shows several kinds of data with different specifications and discharge conditions, in general, there is a large tangent slope on the low residual capacity side, and there is also a characteristic with a wavy characteristic on the high residual capacity side. The relationship between the remaining capacity and the open cell voltage is shown in FIG.
In such a non-linear relationship as shown in FIG. 6, in the region where the tangent slope of the characteristic shown in FIG. 6 (ratio of change in open cell voltage with respect to change in remaining capacity) is large, the opening when the remaining capacity varies between the single cells In the region where the tangent slope is small, on the contrary, the variation in the cell voltage becomes large, and conversely, the variation in the open cell voltage when the remaining capacity varies between the unit cells becomes relatively small. Therefore, in the region where the tangent slope is large, even if there is a large variation in the voltage level between the unit cells, the actual residual capacity dispersion is not so large, and conversely, in the region where the tangent slope is small, This means that even if the variation in the voltage level among the single cells is small, the variation in the actual remaining capacity is large.

Therefore, as described above, the operation of the equalizing circuit is stopped based on the detection information of the remaining capacity of the unit cell or the remaining capacity detecting means for detecting the physical quantity having a fixed relationship with the remaining capacity of the unit cell. By changing the set value for determining whether or not to change according to the remaining capacity ratio or the like, it is possible to operate the equalization circuit accurately according to the actual state of the variation between the unit cells. How to specifically change the set value depends on what the remaining capacity detecting means directly detects, but basically, the ratio of the change in the open cell voltage to the change in the remaining capacity. Is set so that the set value in the region where is large is larger than the set value in the region where the change in the open cell voltage with respect to the change in the remaining capacity is small. As a result, it has become possible to equalize the voltage levels of the cells constituting the battery pack while suppressing the energy loss of the battery pack as much as possible.

Further, by providing the configuration according to claim 2, the equalization circuit control means is configured to: when the assembled battery is not charging or discharging, or when the charging / discharging current of the assembled battery is small. The remaining capacity detecting means is configured to operate the equalization circuit, and the remaining capacity detecting means is constituted by voltage measuring means for measuring the output voltage of the unit cell. That is,
When the battery pack is not being charged / discharged or when the charge / discharge current of the battery pack is small, the voltage of each battery cell is stable, so that the voltage levels of the battery cells can be equalized stably. Moreover, in such a state, the measured value of the output voltage of the unit cell becomes a value extremely close to the open cell voltage, and by utilizing the correspondence relationship between the open cell voltage and the remaining capacity,
It is possible to simply substitute the measured value of the output voltage of the unit cell as a physical quantity having a fixed relationship with the remaining capacity. As a result, the voltage level among the unit cells can be equalized with good stability while having a simple device configuration.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a voltage level equalizing device for an assembled battery of the present invention will be described below with reference to the drawings. <First Embodiment> As shown in FIG. 1, the voltage level equalizing device VL of the first embodiment is intended for a battery pack CB configured by combining battery cells SB, and is independent from other devices. In addition to being configured as a device, the battery pack CB may be incorporated in a device in which the battery pack CB is used, a charging device for the battery pack CB, or the like. In the first embodiment, the charging circuit C
A case where the assembled battery CB is incorporated together with G into a device in which it is used will be exemplified.

[Structure of assembled battery CB] This assembled battery CB has a structure in which at least one unit cell SB and unit cell S are arranged.
A plurality of unit cells SB with B electrically connected in series
It is configured by combining, and more specifically,
The assembled battery CB is composed of single cells SB of the same type, and all these single cells SB are electrically connected in series and housed in one package. The first embodiment exemplifies an assembled battery CB configured by connecting four lithium ion batteries, each of which is a single battery SB, in series.

[Configuration of Voltage Level Equalizing Device VL] The voltage level equalizing device VL includes a power transfer circuit 1a for converting a DC voltage input by a switching element or a coil into a different DC voltage and a pulse for switching operation. Equalization circuit 1 mainly composed of oscillator circuit 1b
And an equalization control unit 2 that controls the equalization circuit 1 to equalize the voltage levels of the individual cells SB, and an equalization operation management unit that manages at what timing the voltage levels are equalized. 3, and a voltage detector 5 for measuring the output voltage of each unit cell SB and a current detector 4 for detecting the charging / discharging current to the assembled battery.

The power transfer circuit 1a includes four unit cells SB.
Is provided with a transformer 6 having four secondary side coils 6b corresponding to the respective transformers, and a switching element 7 for switching a DC voltage input to the primary side coil 6a of the transformer 6, and Secondary coil 6b
A secondary circuit including a rectifying diode 8 and a smoothing capacitor 9 is provided corresponding to each of the above, and constitutes a so-called flyback converter circuit which is an example of a switching power supply circuit configuration. The switching element 7 has F
ET and a rectifying diode 8 is a Schottky barrier diode. The DC voltage generated by the secondary coil 6b, the rectifying diode 8 and the smoothing capacitor 9 is output to each unit cell SB via the switch 10 and the diode 11 which are configured by FETs.

In the voltage level equalizer VL shown in FIG. 1, the voltage across the battery pack CB is used as the DC voltage applied to the primary side of the transformer 6 of the power transfer circuit 1a.
The switch 1 of the four secondary circuits of the transformer 6
The output voltage of the secondary side circuit in which 0 is in the “ON” state is supplied to the corresponding single battery SB. Switch 10 ON
When instructed to execute the voltage level equalization operation, the equalization control unit 2 that controls ON / OFF controls the lowest output voltage among the output voltages of the four unit cells SB obtained from the voltage detection circuit 5. By outputting a signal to turn on the switch 10 corresponding to the unit cell SB and turning on the switching element 7 by the output pulse of the pulse oscillation circuit 1b, the voltage is the lowest depending on the voltage of the entire assembled battery CB. The voltage level is equalized by charging the unit cell SB of the voltage. In the first embodiment, each unit cell SB is a lithium-ion battery having the same specification, and the voltage between the terminals corresponding to each unit cell SB is equalized to substantially the same voltage.

[Control by Equalization Operation Management Unit 3] Next,
The control of the voltage level equalization by the equalization operation management unit 3 will be described based on the flowcharts of FIGS. 2 and 3 executed by the equalization operation management unit 3. The equalization operation management unit 3 that determines whether or not to perform the voltage level equalization operation (hereinafter, may be simply referred to as “balance operation”) between the unit cells SB, when the balance operation is not performed, The process 2 is repeatedly executed at high speed to monitor the timing at which the balance operation can be started. That is, the equalizing operation management unit 3 is when the battery pack CB is not being charged or discharged, or when the charge / discharge current of the battery pack CB is sufficiently small, and
When the remaining capacity of each unit cell is larger than the set capacity, the start of the balance operation is instructed. Specifically, the equalization operation management unit 3 does not charge or discharge the assembled battery CB when the charge / discharge current value detected by the current detector 4 is smaller than the set current value set to a very small value. Alternatively, it is determined that the charging / discharging current is sufficiently small (step # 1), and if the battery pack CB is not charging / discharging, or the charging / discharging current is sufficiently small, the battery SB When all the voltages are higher than the set voltage, it is determined that the remaining capacity of each unit cell SB is larger than the set capacity (step # 2).

As an example of specific numerical values in each judgment process, in the judgment of step # 1, the charge / discharge rate is 0.0.
It may be set so that the balance operation is executed when the value is 1 CA or less. This is, for example, when the unit cell SB is 5
If the battery is 0 Ah, it means that the balance operation is executed at 0.5 A or less. Further, in the determination of step # 2, the set capacity can be arbitrarily set from the viewpoint of avoiding the energy loss of the assembled battery CB by performing the balance operation in the state where the remaining capacity is low. However, it is also desirable to set the set capacity in relation to a device equipped with the assembled battery CB, that is, depending on what kind of circuit the load circuit of the assembled battery CB is. For example, in the case where the assembled battery CB is incorporated in a device such as a hybrid vehicle in which charging / discharging of the assembled battery CB is controlled so that the remaining capacity of each single battery SB is maintained within a set range, the remaining capacity is temporarily assumed. If the control range of 30% to 70% is set, the set capacity is set to “30
By setting “%”, it is possible to prevent the balance operation from interfering with the control of the remaining capacity and exerting a bad influence.

When the charging / discharging current is sufficiently small and the remaining capacity of each unit cell SB is larger than the set capacity, the equalization control unit 2 is instructed to start the balancing operation (step # 3) and the balancing operation is performed. The built-in timer for measuring the execution time of the operation starts counting (step # 4).
In response to the balance operation start command from the equalization operation management unit 3, the equalization control unit 2 operates the equalization circuit 1 to start the balance operation as described above, and the equalization operation management unit 3 performs the balance operation. The equalization circuit 1 is maintained in the operating state until the stop command is received. In addition, as described above, the remaining capacity of each unit cell SB is determined by the voltage detection circuit 5.
The measured value of the output voltage of B can be used as a substitute, when the assembled battery CB is not charging or discharging, or when the charging / discharging current is sufficiently small, the output voltage of each battery SB by the voltage detection circuit 5 is almost opened. This is because the cell voltage matches the cell voltage, and the open cell voltage and the remaining capacity have a fixed relationship shown in FIG. Therefore, the voltage detection circuit 5, which is the voltage measuring means VM for measuring the output voltage of the unit cell SB, outputs the output voltage of the unit cell SB corresponding to the open cell voltage which is a physical quantity having a fixed relationship with the remaining capacity of the unit cell SB. It functions as a remaining capacity detecting means RS for detecting

On the other hand, after the balancing operation is started by the processing of FIG. 2, the equalization operation management section 3 repeatedly executes the processing shown in FIG. 3 at high speed to monitor the timing at which the balancing operation should be stopped. That is, step # in FIG.
Similar to the process of 1 and step # 2, it is determined whether the charge / discharge current value detected by the current detector 4 is smaller than the set current value set to a very small value (step # 1
1) Also, depending on whether the output voltage of each unit cell SB is higher than the set voltage, it is determined whether the remaining capacity of each unit cell SB is larger than the set capacity (step # 12). The specific setting for each determination process may be the same as in step # 1 and step # 2.

Thereafter, it is further determined whether or not the time measured by the built-in timer, which has started the time measurement at the start of the balance operation, is longer than the set time (step # 13).
It is desirable to set this set time according to the capacity of the unit cell SB and the magnitude of the current (electric power) generated by the transformer specifications of the equalization circuit 1. For example, it can be set in the range of 30 minutes to 12 hours, and generally, it is practical to set it for about 2 hours. Next, it is determined whether or not the voltage level variations among the unit cells SB are sufficiently equalized by the balance operation (steps # 14, # 15). To determine if this voltage level variation is sufficiently equalized,
The variation of the voltage level is obtained from the measured value of the voltage of each cell SB by the voltage detection circuit 5, and the variation of the voltage level is determined based on the magnitude relation with the set value for the determination. The value is changed according to the remaining capacity of the single battery SB.

Therefore, first, the remaining capacity of the unit cell SB is obtained and the corresponding set value for discrimination is determined. However, as described above, when the assembled battery CB is not being charged / discharged or the charging / discharging current is sufficiently small, the output voltage of each unit cell SB by the voltage detection circuit 5 functioning as the remaining capacity detection means RS is Since the measured value can be used as the remaining capacity of each unit cell SB, for example, the average value of the output voltage of each unit cell SB is used as the remaining capacity to determine the set value for the determination. To this end, the equalization operation management unit 3 stores a data table showing the relationship between the open cell voltage and the set value for the determination, and the data table is used to calculate the output voltage of each unit cell SB from the measured value. The set value for determination is set (step # 14), and it is determined whether or not the balance operation is completed depending on whether the variation in voltage level is smaller than the set value for determination (step # 15).

More specifically, each unit cell SB will be described.
The voltage level variation is due to the difference (Vdave) between the average voltage of each cell SB and the highest voltage or the lowest voltage of the output voltage of each cell SB, and the maximum of the output voltage of each cell SB. Difference between voltage and minimum voltage (Vdmax)
As for “Vdave”, the set value for determination is changed in the range of 25 to 50 mV according to the open cell voltage (that is, the remaining capacity), and “Vdmax” is obtained.
With respect to the above, the setting value for determination is changed in the range of 50 to 100 mV according to the open cell voltage, and any variation becomes a balance operation when the setting value for determination is set within the above range. Is judged to have been completed.
Of course, it may be determined that the balance operation has been completed when only one of the variations becomes equal to or less than the determination setting value, or the setting range of the determination setting value may be appropriately changed. .

Steps # 11, # 12, # 13, #
In each determination process of 15, when the charging / discharging current detected by the current detector 4 is larger than the set current value, each unit cell SB
Is less than the set capacity, the elapsed time from the start of the balance operation is longer than the set time, or the variation in the voltage level of each unit cell SB is the set value for determination. If any one of the cases below is satisfied, the balancing operation is immediately stopped (step # 16). The management unit 3 executes the balance operation when all of the following four conditions are satisfied. That is, the first condition is that the battery pack CB is not being charged or discharged, or the charge / discharge current of the battery pack CB is sufficiently small, and the second condition is that the remaining capacity of each unit cell SB is set. It is larger than the capacity, the third condition is that the elapsed time from the start of the balance operation is shorter than the set time, and the fourth condition is that the variation in the voltage level of each unit cell SB is determined as described above. Is larger than the set value for. Therefore, the equalization operation management unit 3 stops the voltage level equalization operation of the equalization circuit 1 when the variation in the voltage level among the unit cells SB included in the assembled battery CB becomes smaller than the set value. It functions as the circuit control means BC.

<Second Embodiment> Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment only in the specific configuration of the equalization circuit 1 and the control operation of the equalization control unit 2, and the operation of the equalization operation management unit 3 is common to the first embodiment. is there. Therefore, only the configuration of the equalization circuit 1 and the control operation of the equalization control unit 2 will be described. As shown in FIG. 4, the equalizing circuit 1 according to the second embodiment mainly includes a power transfer circuit 21a and a pulse oscillating circuit 21b for switching operation, which constitute a flyback converter circuit, as in the first embodiment. However, the relation between the primary side coil 22a and the secondary side coil 22b in the transformer 22 is opposite to that in the first embodiment. That is, four primary coils 22a are provided for each of the four unit cells SB, and one secondary coil 22b is provided. Each of the four primary side circuits connected to the four primary side coils 22a is provided with a switching element 23 formed of an FET, and the secondary side circuit connected to the secondary side coil 22b is provided for rectification. Diode 24 and smoothing capacitor 2
And 5 are provided.

In the voltage level equalizer VL shown in FIG. 4, the voltage across each cell SB is used as the DC voltage applied to the primary side of the transformer 22 of the power transfer circuit 21a, and the four primary sides are used. A pulse signal is input to any one of the switching elements 23 in the circuit, and the voltage generated in the secondary circuit accordingly is supplied to both ends of the assembled battery CB to charge the entire assembled battery CB. Equalization control unit 2
Are instructed to execute the voltage level equalization operation, the four unit cells S obtained from the voltage detection circuit 5
The output switching circuit 26 is controlled so that the output pulse of the pulse oscillation circuit 1b is supplied to the switching element 23 corresponding to the cell SB having the highest voltage of B. Therefore, in the second embodiment, the voltage level is equalized by charging the entire assembled battery CB with the output voltage of the unit cell SB having the highest output voltage.

<Third Embodiment> Next, a third embodiment of the present invention will be described. Also in the third embodiment, only the specific configuration of the equalization circuit 1 and the control operation of the equalization control unit 2 are different from the first embodiment, and the operation of the equalization operation management unit 3 is common to the first embodiment. is there. Therefore, only the configuration of the equalization circuit 1 and the control operation of the equalization control unit 2 will be described. As shown in FIG. 5, the equalization circuit 1 according to the third exemplary embodiment includes an electric resistance 31 and an FE corresponding to each unit cell SB.
And a switch 32 composed of T. When the equalization control unit 2 is instructed to execute the voltage level equalization operation, the unit cells SB other than the lowest unit cell SB among the four unit cells SB obtained from the voltage detection circuit 5 are detected. A control signal is sent so that the switches 32 corresponding to the respective switches are turned on, and the switches 3
By discharging the electric resistance 31 so that the voltage of each unit cell SB whose 2 is in the “ON” state approaches the voltage of the unit cell SB having the lowest voltage, the voltage levels are equalized. Alternatively, four unit cells SB obtained from the voltage detection circuit 5
Switch 3 corresponding to the highest voltage unit cell SB
The voltage level may be equalized by sending a control signal so that 2 is in the “ON” state and discharging the cell SB having the highest voltage by the electric resistance 31.

<Other Embodiments> Other embodiments will be listed below. (1) In the above-described embodiment, the voltage detection circuit 5 which is the voltage measuring means VM for measuring the output voltage of each single battery SB is used as the remaining capacity detecting means RS for detecting the remaining capacity of each single battery SB.
However, the remaining capacity detecting means RS may be configured so as to directly obtain the remaining capacity by a calculation process from the detection information of the voltage detection circuit 5 and the detection information of the current detector 4. good. (2) In the above embodiment, the voltage level equalizer VL
Although the assembled battery CB in which four unit cells SB are connected in series is illustrated as an object of the balance operation of 1., the number of used unit cells SB and the connection method can be variously changed, and the assembled battery CB of various configurations can be changed. The present invention can be applied for the balance operation. For example, even in the case of an assembled battery including a portion in which unit cells are connected in parallel, there is no problem in the balance operation of the voltage level equalization device VL.

(3) In the above embodiment, each unit cell SB is
As a condition for executing the balancing operation of the battery pack C
B is not charging / discharging, or the charging / discharging current of the assembled battery CB is sufficiently small, the remaining capacity of each unit cell SB is larger than the set capacity, and the elapsed time from the start of the balance operation. It is illustrated that the case is executed only when all of the four conditions of being shorter than the set time and having a variation in the voltage level of each cell SB larger than the set value for the determination are set. It is most preferable to satisfy all the conditions, but it is necessary as a condition for performing the balance operation that at least the variation in the voltage level of each unit cell SB is larger than the set value for the determination, and All or any of the conditions may be omitted.

[0026]

According to the structure of the above-mentioned claim 1, since the relationship between the remaining capacity of the unit cell and the open cell voltage is non-linear, the remaining capacity of the unit cell or the remaining capacity of the unit cell is constant. Based on the detection information of the remaining capacity detection means for detecting the physical quantity having the relationship of the above, by changing the setting value for determining whether to stop the operation of the equalization circuit, the variation between the unit cells. It is possible to operate the equalization circuit appropriately according to the actual condition of. As a result, it has become possible to equalize the voltage levels of the cells constituting the battery pack while suppressing the energy loss of the battery pack as much as possible.

Further, according to the above-mentioned structure, the output voltage of each unit cell is stable when the assembled battery is not being charged or discharged or when the assembled battery has a small charging / discharging current. Not only can the voltage levels of the batteries be equalized in a stable manner, but in such a condition, the measured output voltage of the cells will be very close to the open cell voltage, and the open cell voltage and the remaining By utilizing the correspondence relationship with the capacity, the measured value of the output voltage of the unit cell can be easily substituted as the physical quantity having a constant relationship with the remaining capacity. As a result, the voltage level among the unit cells can be equalized with good stability while having a simple device configuration.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a voltage level equalizing device according to a first embodiment of the present invention.

FIG. 2 is a flowchart in the embodiment of the present invention.

FIG. 3 is a flowchart in the embodiment of the present invention.

FIG. 4 is a circuit configuration diagram of a voltage level equalizing device according to a second embodiment of the present invention.

FIG. 5 is a circuit configuration diagram of a voltage level equalizing device according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between an open cell voltage of a battery and a remaining capacity.

[Explanation of symbols]

1 Equalization circuit BC equalization circuit control means CB battery pack RS Remaining capacity detection means SB single battery VM voltage measuring means

Claims (2)

[Claims] 1. A voltage level of the unit cells electrically connected in series in an assembled battery formed by combining a plurality of unit cells in a state where the unit cells and the unit cells are electrically connected in series at at least one location. A voltage level equalizing device for an assembled battery provided with an equalizing circuit for equalizing the battery pack, wherein the equalization is performed when the variation in the voltage level among the cells forming the assembled battery is smaller than a set value. An equalization circuit control means for stopping the voltage level equalization operation of the equalization circuit, and a remaining capacity detection means for detecting a remaining capacity of the unit cell or a physical quantity having a constant relationship with the remaining capacity of the unit cell are provided. The equalization circuit control means is an assembled battery voltage level equalization device configured to change the setting of the set value based on the detection information of the remaining capacity detection means. 2. The equalization circuit control means is configured to operate the equalization circuit when the battery pack is not being charged or discharged, or when the charge / discharge current of the battery pack is small. The voltage level equalizing device for an assembled battery according to claim 1, wherein the remaining capacity detecting means is constituted by voltage measuring means for measuring an output voltage of the unit cell.