WO2019069971A1 - Assembled battery - Google Patents

Abstract

A rechargeable battery pack (1) is provided. The assembled battery includes a plurality of battery cells (11 to 14), a detection unit (31), a plurality of discharge resistors (33), and a control unit (32). The plurality of battery cells are connected in series with one another. The detection unit detects cell voltages (Vc1 to Vc4) between both ends of each battery cell. The plurality of discharge resistors are connected in parallel with the respective battery cells, and can short-circuit and discharge the respective battery cells. The control unit controls the discharge of each battery cell based on the cell voltage detected by the detection unit. The control unit changes the resistance value by one or more discharge resistors for discharging the battery cell in which the cell voltage is detected, according to the magnitude of the detected cell voltage.

Description

Assembled battery

The present invention relates to a battery assembly including a plurality of rechargeable battery cells.

There is known a technology for equalizing the voltage of each battery cell when charging an assembled battery including a plurality of battery cells (for example, Patent Document 1).

Patent Document 1 discloses a power storage device that aims to complete charging of a power storage unit formed of battery cells in a short time. The power storage device of Patent Document 1 includes a plurality of power storage units connected in series, a cell balance unit connected in parallel to each of the power storage units via a switch, and a control unit that controls charging current for charging the power storage unit. Have. The control unit is communicably connected to a control device that performs charge management of the power storage device, and performs control to switch the charge current to a second constant current value smaller than the first constant current value.

JP, 2015-61335, A

An object of the present invention is to provide an assembled battery capable of rapidly equalizing the voltages of the battery cells in the assembled battery at the time of full charge.

An assembled battery according to the present invention is a rechargeable assembled battery. The assembled battery includes a plurality of battery cells, a detection unit, a plurality of discharge resistors, and a control unit. The plurality of battery cells are connected in series with one another. The detection unit detects the cell voltage between both ends of each battery cell. The plurality of discharge resistors are connected in parallel with the respective battery cells, and can short-circuit and discharge the respective battery cells. The control unit controls the discharge of each battery cell based on the cell voltage detected by the detection unit. The control unit changes the resistance value of one or more discharge resistors for discharging the battery cell in which the cell voltage is detected, in accordance with the magnitude of the detected cell voltage.

According to the battery pack of the present invention, the battery cell is discharged while changing the resistance value of the discharge resistor in accordance with the magnitude of the cell voltage. Thereby, the voltage of the battery cell can be rapidly equalized in the rechargeable battery pack.

The figure for demonstrating the usage example of the assembled battery which concerns on Embodiment 1. A circuit diagram showing a configuration of a battery assembly according to Embodiment 1. Diagram for explaining the task of balancing operation of the assembled battery The figure for demonstrating the balance operation of the assembled battery which concerns on Embodiment 1. Timing chart for explaining the balance operation of the battery pack The figure for demonstrating simulation of balance operation of an assembled battery concerning Embodiment 1. The circuit diagram which shows the structure of the assembled battery which concerns on Embodiment 2. The figure for demonstrating the operation example of the assembled battery which concerns on Embodiment 2.

Hereinafter, an embodiment of a battery assembly according to the present invention will be described with reference to the attached drawings.

It goes without saying that each embodiment is an example, and partial replacement or combination of the configurations shown in different embodiments is possible. In the second and subsequent embodiments, the description of items common to the first embodiment will be omitted, and only different points will be described. In particular, the same operation and effect by the same configuration will not be sequentially referred to in each embodiment.

(Embodiment 1)
In the first embodiment, in a battery assembly including a plurality of chargeable battery cells, a battery assembly performing a balance operation for achieving a balance state at the time of charging will be described. The balanced state refers to a state in which the voltages of the battery cells connected in series in the assembled battery are equalized. In addition, the balance operation refers to an operation of discharging a certain battery cell using a discharge resistance or the like connected in parallel to each battery cell in the assembled battery.

In general, it is preferable that the balance operation be completed as early as possible for safety (overcharge prevention) of the assembled battery and suppression of deterioration promotion. Conventionally, there has been means for setting the resistance value of the discharge resistor small, but in that case, the bypass current flowing through the discharge resistor becomes large. For this reason, in the assembled battery, it is easy to determine a malfunction by underestimating the voltage of the battery cell by the overvoltage during the balance operation, and the smoothness of the voltage between the series cells tends to be poor. As described above, the inventor of the present application focused on the problem that the accuracy of the balance operation is reduced by the above setting alone.

The battery assembly according to the present embodiment can quickly equalize the voltages of the battery cells in the battery assembly when fully charged while preventing the above-described malfunction determination. Hereinafter, the configuration and operation of the battery assembly according to the present embodiment will be described with reference to FIGS. 1 to 6.

1. Configuration The configuration of the battery assembly according to the first embodiment will be described with reference to FIGS. FIG. 1 is a view for explaining a usage example of the battery assembly 1 according to the present embodiment.

The battery assembly 1 according to the present embodiment constitutes a power storage device that stores power that can be supplied to various electronic devices (for example, on-vehicle devices and mobile devices). In the usage example of FIG. 1, the battery assembly 1 is connected to the load 2 and the charging circuit 20 via the positive electrode terminal 1 p and the negative electrode terminal 1 m. The assembled battery 1 supplies the assembled battery voltage Va between the positive electrode terminal 1 p and the negative electrode terminal 1 m to various loads 2. Further, the battery assembly 1 according to the present embodiment is a secondary battery, and can be charged by a charging circuit 20 connected between both terminals 1 p and 1 m.

The charging circuit 20 includes, for example, a generator and a converter, and controls a voltage for charging the battery pack 1. The charging circuit 20 also includes a detection circuit that detects the battery pack voltage Va. The charging circuit 20 executes a charging operation for charging the battery pack 1 when the battery pack voltage Va detected by the detection circuit is less than a predetermined value, and when the battery pack voltage Va detected is equal to or higher than a predetermined value The charging operation of the battery 1 is stopped. The predetermined value is, for example, a voltage value indicating a fully charged state of the battery pack 1 (for example, 14.2 V).

As shown in FIG. 1, the assembled battery 1 includes a plurality of battery cells 11 to 14, a battery protection circuit unit 10, and a balance circuit unit 3. In the present embodiment, an example in which four battery cells 11, 12, 13, 14 are connected in series in the assembled battery 1 will be described.

The first to fourth battery cells 11 to 14 are formed of lithium ion batteries, and for example, the material of the positive electrode includes lithium iron phosphate (LFP) and the material of the negative electrode includes graphite (Gr) (hereinafter referred to as “LFP- Sometimes called "gr cell". Each of the battery cells 11 to 14 may be configured by one storage element, or may include a plurality of storage elements. The plurality of storage elements may be connected in parallel, for example. The plurality of storage elements may be combined appropriately to constitute one battery cell.

The battery protection circuit unit 10 is incorporated inside the battery pack 1, and forcibly ends charging of the battery pack 1 when any of the first to fourth battery cells 11 to 14 is in an abnormal charging state. To realize the battery protection function. The battery protection circuit unit 10 detects the cell voltages Vc1 to Vc4, which are the voltages across the terminals of the battery cells 11 to 14, and when any cell voltage exceeds a predetermined threshold (for example, 4 V), The switch 10a and the like are controlled to cut off the power supply to the battery cells 11-14.

The balance circuit unit 3 has a balance function of discharging the battery cells 11 to 14 so as to equalize the cell voltages Vc1 to Vc4 in the vicinity of the fully charged state of each of the battery cells 11 to 14 when charging the assembled battery 1 or the like. To realize. In the battery assembly 1 according to the present embodiment, the balance circuit unit 3 incorporated inside adjusts the discharge of each of the battery cells 11 to 14 in stages according to the magnitude of the cell voltages Vc1 to Vc4. Hereinafter, the detail of a structure of the assembled battery 1 which concerns on this embodiment is demonstrated using FIG.

FIG. 2 is a circuit diagram showing the configuration of the battery assembly 1 according to the first embodiment. In FIG. 2, illustration of the battery protection circuit unit 10 (FIG. 1) and the like is omitted. As shown in FIG. 2, the battery assembly 1 according to the present embodiment includes a plurality of stages of balance circuits 3-1 to 3-3. Hereinafter, an example in which three stages of balance circuits 3-1, 3-2 and 3-3 are provided in the battery assembly 1 will be described.

The balance circuits 3-1 to 3-3 in each stage include four discharge circuits 30 for discharging the first to fourth battery cells 11 to 14, a detection unit 31, and a control unit 32. The detection unit 31 and the control unit 32 of each of the balance circuits 3-1 to 3-3 are mounted on, for example, the same IC or the like.

In the balance circuits 3-1 to 3-3 of each stage, the four discharge circuits 30 are connected in parallel to one of the first to fourth battery cells 11 to 14, respectively. In the present embodiment, each discharge circuit 30 is configured by a series circuit of the discharge resistor 33 and the switch 34. Each discharge resistor 33 has, for example, a common resistance value R (for example, 100 Ω). The switch 34 is configured of, for example, an FET, an IGBT or the like.

When the switch 34 is turned on, the discharge circuit 30 for each of the battery cells 11 to 14 shorts the corresponding battery cell with the discharge resistor 33 to discharge the battery cell. In the battery assembly 1 according to the present embodiment, multistages using discharge circuits 30 for three stages parallel to one another for each of the battery cells 11 to 14 by the three stages of balance circuits 3-1 to 3-3. Discharge operation (balance operation) is performed.

The detection unit 31 includes a voltage measurement circuit and the like, and detects cell voltages Vc1 to Vc4 of the four battery cells 11 to 14, respectively. The detection unit 31 in each of the balance circuits 3-1 to 3-3 in each stage outputs a detection value indicating the detection result of the cell voltages Vc1 to Vc4 to the control unit 32 in the same stage.

Control unit 32 includes a logic circuit and the like. The control unit 32 of each stage controls the discharge in the balance operation of the corresponding battery cells 11 to 14 based on the detection values of the cell voltages Vc1 to Vc4. Each control unit 32 performs comparison determination with a predetermined threshold value on the detection value of each of the cell voltages Vc1 to Vc4, and performs on / off control of each switch 34 according to the determination result.

First to third different threshold values Vth1, Vth2, and Vth3 are set in the control unit 32 of the first to third stages of balance circuits 3-1 to 3-3 (hereinafter, Vth1 <Vth2 <Vth3). And). For example, the first threshold value Vth1 is set to a value equal to or higher than a voltage obtained by dividing the charging voltage of the battery pack 1 by the number of series cells.

For example, when the control unit 32 of the first stage balance circuit 3-1 determines that the detected value of the cell voltage Vc1 of the first battery cell 11 is larger than the first threshold value Vth1, the first battery cell is determined. A control signal S11 is generated so as to turn on the switch 34 of the discharge circuit 30 for 11. Further, when the control unit 32 determines that the detected value of the cell voltage Vc1 is less than or equal to the first threshold value Vth1, the control unit 32 generates a control signal S11 so as to turn off the switch 34.

Similarly to the above, in the first stage balance circuit 3-1, the second to fourth battery cells 12 to 12 are compared based on the comparison results of the detected values of the cell voltages Vc2 to Vc4 and the first threshold value Vth1. Control signals S12 to S14 for on / off controlling the switches 34 of the discharge circuit 30 for 14 are generated. Further, in the second and third stages of balance circuits 3-2 and 3-3, each switch is compared based on the comparison result of the detected value of each cell voltage Vc1 to Vc4 with the second and third threshold values Vth2 and Vth3. 34 control signals S21 to S24 and S31 to S34 are generated.

2. Operation The operation of the battery assembly 1 configured as described above will be described below.

In the battery assembly 1 according to the present embodiment, when charged from the charging circuit 20 (FIG. 1) or the like, a battery cell having a voltage higher than a specified voltage among the plurality of battery cells 11 to 14 in the balance circuit unit 3. Perform a balance operation to discharge the According to the balance operation, during charging by the charging circuit 20 or in the charging operation stop state, the discharge resistance 33 is turned on (shorted) according to the cell voltages Vc1 to Vc4 of the plurality of battery cells 11 to 14 inside the assembled battery 1 to discharge By doing this, the cell voltages Vc1 to Vc4 are equalized.

2-1. About a subject The subject of the balance operation | movement in an assembled battery is demonstrated using FIG. 3 (a), (b). FIG. 3A is a graph illustrating charge voltage characteristics of a battery cell. FIG. 3 (b) is an enlarged view of the vicinity of the fully charged state in FIG. 3 (a). The vertical axis of FIG. 3 indicates the cell voltage [V], and the horizontal axis indicates the charge amount, that is, the charged capacity [Ah].

FIG. 3A exemplifies a characteristic curve 61 in the case of using an LFP-Gr cell (hereinafter sometimes abbreviated as “cell”) having a fully charged capacity 2 Ah as a battery cell. A characteristic curve 61 shows the relationship between the charge amount of the cell at the time of cell charging and the cell voltage. In the LFP-Gr cell, as shown in FIG. 3A, the cell voltage rises sharply near the fully charged state (near 2 Ah).

When a battery pack is configured using a plurality of cells as in the battery pack 1 according to the present embodiment, ideally, the characteristic curves of all the cells overlap, that is, there is no SOC (State Of Charge) shift. In the state. However, there may be a deviation in the characteristic curve due to deterioration variation among battery cells in the assembled battery or a micro short circuit inside the cells. The characteristic curve 61 of FIG. 3A shows the charge voltage characteristic of a normal battery cell (hereinafter sometimes referred to as the “normal characteristic curve 61”).

FIG. 3B shows the characteristic curves 61 and 62 of two cells in the vicinity of the fully charged state. Specifically, a normal characteristic curve 61 and a characteristic curve 62 of the battery cell shifted from the normal characteristic curve 61 are shown. For example, when a battery pack composed of two cells with different SOCs as shown in the characteristic curves 61 and 62 is charged to a certain capacity (for example, 2.015 Ah), one cell becomes 3.8 V as shown in FIG. 3 (b) , And the other cell is at 3.55V. A state where the voltage of a specific cell generated due to SOC deviation is high causes accelerated deterioration of the cell, an unsafe state, and a decrease in the effective capacity of the battery pack, so charging as shown in FIGS. 3 (a) and 3 (b). In a battery pack having voltage characteristics, it is necessary to perform a balance operation at the end of charging.

In the conventional balance operation, when it is determined that the detected value of the cell voltage is larger than the threshold value (FIG. 3 (b)) near the fully charged state, the battery with the discharge resistance of the preset resistance value. The cells were shorted and the battery cells were discharged until they were below the threshold. Here, if the set resistance value is large, the discharge period for discharging the battery cell becomes long, and it takes a long time until the capacity of the assembled battery is optimized. Furthermore, during the above discharge period, the battery cell to be discharged is in an abnormal state beyond full charge, and there is a concern that the deterioration of the battery cell may be promoted.

On the other hand, when a small resistance value is set to the discharge resistance in the conventional balance operation, the voltage drop (overvoltage) due to the internal resistance of the battery cell and the bypass current becomes large, and the detected value of the cell voltage falls from the actual cell voltage. In the conventional balance operation, it is difficult to balance the voltages of the individual cells in the assembled battery quickly and with high precision.

Therefore, in the battery assembly 1 according to the present embodiment, the resistance value (synthetic resistance) at the time of discharging the battery cell is changed in stages using the balance circuits 3-1 to 3-3 in a plurality of stages. As a result, it is possible to accurately balance the state of charge in the battery assembly 1 by suppressing the prolongation or interruption of the balance operation. Hereinafter, the details of the operation of the battery assembly 1 according to the present embodiment will be described.

2-2. Balance Operation The balance operation in the battery assembly 1 according to the present embodiment will be described with reference to FIGS. FIG. 4 is a view for explaining the balance operation of the battery assembly 1 according to the present embodiment. FIG. 5 is a timing chart for explaining the balance operation of the battery pack 1.

In FIG. 4, the characteristic curves 61 are used to illustrate the first to third threshold values Vth1 to Vth3 set in the balance circuits 3-1 to 3-3 of each stage. In the example of FIG. 4, the first threshold value Vth1 in the first stage balance circuit 3-1 is set to 3.55 V (the voltage obtained by dividing the charging voltage of the assembled battery 1 by the number of serial cells). The first threshold value Vth1 is set to be equal to or higher than the charging voltage / the number of serial cells in the battery assembly 1 in which a plurality of battery cells are connected in series. The number of series cells is the number of battery cells connected in series with each other in the assembled battery 1. Further, the second threshold value Vth2 = 3.6 V is set in the second stage balance circuit 3-2, and the third threshold value Vth1 = 3.65 V is set in the third stage balance circuit 3-3. It is done.

Below, the balance operation with respect to the 1st battery cell 11 is demonstrated as an example. According to the characteristic curve 61, the same battery cell 11 is charged, from the state of the point P1 where the cell voltage Vc1 is smaller than the first threshold value Vth1, a third threshold value along the steep rise of the characteristic curve 61. It is assumed that the state of the point P2 is larger than Vth3. An operation example of the assembled battery 1 in such a case is shown in FIGS. 5 (a) to 5 (d).

FIG. 5A shows the control timing of the control signal S11 of the discharge circuit 30 for the first battery cell 11 in the first stage balance circuit 3-1 (FIG. 2). FIGS. 5B and 5C show control timings of control signals S21 and S31 for discharging the battery cell 11 in the second and third stages of the balance circuits 3-2 and 3-3, respectively. FIG. 5 (d) shows the change timing of the resistance value for discharging the battery cell 11.

FIGS. 5A to 5D show an operation example in the case where the cell voltage Vc1 of the first battery cell 11 reaches the point P1 at time t1 and reaches the point P2 at time t2 thereafter (see FIG. See Figure 4). At time t11, t12 and t13 between time t1 and time t2, the balance circuits 3-1 to 3-3 (FIG. 2) of each stage start the balance operation.

First, at time t11, the control unit 32 (FIG. 2) of the first stage balance circuit 3-1 determines that the detected value of the cell voltage Vc1 is larger than the first threshold value Vth1, and As shown in a), a control signal S11 is generated. Thereby, in the first stage balance circuit 3-1, the switch 34 of the discharge circuit 30 for the first battery cell 11 is turned on, and the discharge resistor 33 shorts the battery cell 11. At this time, the battery cell 11 is discharged based on the resistance value “R” of one discharge resistor 33 (FIG. 5 (d)).

Next, at time t12, the control unit 32 of the second stage balance circuit 3-2 determines that the detected value of the cell voltage Vc1 becomes larger than the second threshold value Vth2, and the control signal S21 causes the switch 34 to be switched. Is turned on (FIG. 5 (b)). At this time, the two discharge resistors 33 are short-circuited in parallel to the first battery cell 11, and the resistance value for discharging the battery cell 11 is set to the combined resistance value “R / 2” of the two discharge resistors 33. (FIG. 5 (d)).

Next, at time t13, the control unit 32 of the third stage balance circuit 3-3 determines that the detected value of the cell voltage Vc1 becomes larger than the third threshold value Vth3, and the control signal S31 causes the switch 34 to be switched. Is turned on (FIG. 5 (c)). At this time, the number of discharge resistors 33 shorting the first battery cell 11 is three, and the resistance value for discharging the battery cell 11 is “R / 3” (FIG. 5 (d)).

Also, after time t2, when the control unit 32 of the third stage balance circuit 3-3 determines that the detected value of the cell voltage Vc1 has become equal to or less than the third threshold value Vth3, as shown in FIG. As described above, the switch 34 of the discharge circuit 30 is turned off by the control signal S31. At this time, the discharge of the first battery cell 11 by the third stage balance circuit 3-3 is stopped, and the resistance value for discharging the battery cell 11 returns from “R / 3” to “R / 2”. (FIG. 5 (d)).

Thereafter, when control unit 32 of second stage balance circuit 3-2 determines that the detected value of cell voltage Vc1 has become equal to or less than second threshold value Vth2, the control signal S21 (FIG. 5 (b)) causes The discharge of the battery cell 11 of 1 is stopped. Also in the first stage balance circuit 3-1, when the control unit 32 determines that the detected value of the cell voltage Vc1 has become equal to or less than the first threshold value Vth1, the control signal S11 (FIG. 5A) is used. The discharge of the battery cell 11 is stopped.

By stopping the discharge by the first stage balance circuit 3-1, the balance operation of the example of FIGS. 5 (a) to 5 (d) ends.

According to the above-described operation, in accordance with the magnitude of the cell voltage Vc1 of the first battery cell 11, the resistance value for discharging the battery cell 11 is changed stepwise as shown in FIG. 5 (d). Ru. Such balance operation is similarly performed for the other battery cells 12-14. As a result, the voltage of each of the battery cells 11 to 14 in the assembled battery 1 can be made uniform quickly.

2-3. About simulation About the above balance operation, this inventor performed simulation for confirming an effect. A simulation performed by the inventor of the present application will be described using FIGS. 6 (a) and 6 (b).

FIG. 6A is a graph showing a simulation result of the balance operation of the battery assembly 1 according to the present embodiment. FIG. 6B is a graph showing the simulation result of the balance operation of the comparative example. The horizontal axes of the graphs in FIGS. 6A and 6B indicate time [seconds]. The vertical axis on the left side in FIGS. 6A and 6B indicates voltage [V], and the vertical axis on the right side indicates current [mA].

In the simulation of FIG. 6A, it is simulated that the first battery cell 11 is discharged after time t2 in the operation example of FIGS. 5A to 5D. In this simulation, the cell voltage Vc1 of the first battery cell 11 is set to 3.8 V as an initial condition, and the cell voltages Vc2 = Vc3 = Vc4 = 3.55 V of the remaining battery cells 12 to 14 are set. Further, the resistance value per one discharge resistor 33 was set to R = 100Ω.

In the above setting, the bypass currents Ib1, Ib2, Ib3 flowing in the discharge resistance 33 for the first battery cell 11 in each of the first, second and third balance circuits 3-1 to 3-3, and the batteries The total bypass current Ib (= Ib1 + Ib2 + Ib3) for discharging the cell 11 was numerically calculated (see FIG. 2). Furthermore, the cell voltage Vc1 of the same battery cell 11 being discharged by the bypass current Ib was numerically calculated. Thereby, the simulation result as shown to Fig.6 (a) was obtained.

Further, in the same setting as above, the battery cell is discharged by the balance operation with one threshold of 3.55 V (see FIG. 3B) and one resistor as a comparative example to the simulation of FIG. Simulation was also performed. The simulation result is shown in FIG. According to the simulation result of FIG. 6B, the operation period of the balance operation from the initial state same as FIG. 6A to when the cell voltage reaches the threshold of 3.55 V or less was about 1200 seconds.

On the other hand, in the simulation of the present embodiment (FIG. 6A), in the initial state, the balance of the first to third stages with respect to the cell voltage Vc1 larger than the third threshold value Vth3 (= 3.65 V). Each of the circuits 3-1 to 3-3 passes bypass currents Ib1, Ib2 and Ib3. As a result, the bypass current Ib is increased and the cell voltage Vc1 is rapidly reduced. According to the simulation result of FIG. 6A, the operation period of the balance operation until the cell voltage Vc1 reaches the first threshold value Vth1 (= 3.55 V) is approximately 700 seconds by such balance operation. Was shortened to

As described above, according to the balance operation of the battery assembly 1 according to the present embodiment (FIG. 6A), the effect that the operation period of the balance operation can be shortened more remarkably than in the comparative example of FIG. We were able to.

Further, according to the balance operation according to the present embodiment, as shown in FIG. 6A, the bypass current Ib1, Ib2, Ib3 of each stage is one by one according to the decrease of (the detected value of) the cell voltage Vc1. It becomes “0”, and the bypass current Ib is reduced stepwise. As a result, by reducing the overvoltage due to the bypass current as the cell voltage becomes lower as the state is closer to the ideal state (3.55 V), the situation where the balance operation is erroneously interrupted due to the overvoltage is avoided, and each The charge states of the battery cells 11 to 14 can be balanced.

3. As described above, the battery pack 1 according to the present embodiment is a rechargeable battery pack. The battery assembly 1 includes a plurality of battery cells 11 to 14, a detection unit 31, a plurality of discharge resistors 33, and a control unit 32. The plurality of battery cells 11 to 14 are connected in series to one another. Detection unit 31 detects cell voltages Vc1 to Vc4 across the battery cells 11 to 14, respectively. The plurality of discharge resistors 33 are connected in parallel with the battery cells 11 to 14, and can discharge the battery cells 11 to 14 by shorting them. The control unit 32 controls the discharge of each of the battery cells 11 to 14 based on the cell voltages Vc1 to Vc4 detected by the detection unit 31. Control unit 32 changes the resistance value by one or more discharge resistors 33 for discharging battery cells 11 to 14 in which the cell voltage is detected, according to the magnitudes of detected cell voltages Vc1 to Vc4. Do.

According to the assembled battery 1 described above, the bypass current Ib is increased or decreased according to the magnitude of the cell voltages Vc1 to Vc4 detected during the discharge of each of the battery cells 11 to 14. The voltage can be equalized.

That is, in the assembled battery 1, the state of ΔV> overvoltage with respect to the difference (referred to as “ΔV”) between “the value to which the cell voltage should be converged by the balance operation (for example, Vth1)” and “the current cell voltage value” It can be made easy to realize. That is, the assembled battery 1 allows the overvoltage by increasing the bypass current as ΔV is larger. Moreover, the overvoltage is minimized by reducing the bypass current as ΔV is smaller. By performing such an operation, it is possible to shorten the time until reaching the balance state while preventing the malfunction determination in the battery assembly 1.

In the present embodiment, the control unit 32 reduces the above-described resistance value as the cell voltages Vc1 to Vc4 detected by the detection unit 31 when the battery cells 11 to 14 are discharged are larger (see FIG. 5D). As a result, the bypass current Ib can be increased as the cell voltages Vc1 to Vc4 increase, and the charge states of the battery cells 11 to 14 can be efficiently balanced.

Further, in the present embodiment, the control unit 32 changes the above-described resistance value stepwise based on a plurality of predetermined threshold values Vth1 to Vth3. As a result, the state of charge of the battery cells 11 to 14 can be precisely balanced with simple control.

Further, in the present embodiment, the minimum threshold value Vth1 among the plurality of threshold values Vth1 to Vth3 is equal to or more than the voltage obtained by dividing the charging voltage of the assembled battery 1 by the number of serial cells. The said charge voltage is prescribed | regulated, for example as assembled battery voltage Va (FIG. 1) of the state of a full charge. The number of series cells is the number of battery cells connected in series in the assembled battery 1. This makes it possible to reduce the balance operation when the battery cells 11 to 14 normally reach the fully charged state. When the charging voltage fluctuates, the voltage is set equal to or higher than the lower limit voltage of the assumed charging voltage divided by the number of series cells.

Further, the battery assembly 1 in the present embodiment further includes a plurality of switches 34 provided between the discharge resistors 33 and the battery cells. A plurality of discharge circuits 30 configured by a series circuit of the discharge resistor 33 and the switch 34 are provided in parallel to one battery cell. With such a simple circuit configuration, it is possible to accurately balance the charge states of the battery cells 11-14.

Further, in the present embodiment, the number of the plurality of battery cells 11 to 14 is four. The number of battery cells in the assembled battery 1 is not limited to four, and may be five or more, or two or three. Each battery cell in assembled battery 1 may be connected in series with each other, or may include a set connected in parallel.

Further, in the present embodiment, the battery cells 11 to 14 are lithium ion batteries including a positive electrode including LFP and a negative electrode including Gr. The charge state can be accurately balanced with respect to such charge voltage characteristics of the LFP-Gr cell (FIGS. 3A and 3B).

In the first embodiment described above, an example in which three stages of balance circuits 3-1 to 3-3 are provided in the assembled battery 1 has been described, but the number of stages of balance circuits provided in the assembled battery 1 is two. It may be four stages or more.

Second Embodiment
In the first embodiment, the resistance value of the combined resistance between the multistage balance circuits 3-1 to 3-3 is changed. In the second embodiment, an assembled battery using a variable resistor will be described.

The assembled battery according to the second embodiment will be described with reference to FIGS.

FIG. 7 is a circuit diagram showing a configuration of the battery assembly 1A according to the second embodiment. The battery assembly 1A according to the present embodiment has the same configuration as that of the battery assembly 1 (FIG. 2) of the first embodiment, except for the multistage balance circuits 3-1 to 3-3 as shown in FIG. A stage balance circuit 3A is provided.

The balance circuit 3A of the present embodiment includes a discharge resistor 33A configured of a variable resistor, instead of each discharge resistor 33 of the first embodiment. Further, the control unit 32A of the balance circuit 3A of the present embodiment is configured by, for example, a microcomputer. The control unit 32A controls the switches 34 based on the detection values of the cell voltages Vc1 to Vc4 by the detection unit 31, and changes the resistance value of the discharge resistor 33A. FIG. 8 shows an example of the operation of the battery assembly 1A according to the second embodiment.

FIG. 8 shows an operation example in the case where the control unit 32A of the balance circuit 3A of the second embodiment controls the discharge resistor 34A to realize the same balance operation as that of the first embodiment (FIG. 6 (a)). reference).

In the present operation example, first to third threshold values Vth1 to Vth3 are set in advance in the control unit 32A (see FIG. 4). Control unit 32A turns on / off corresponding switch 34 based on whether any of the detection values of cell voltages Vc1 to Vc4 is larger than first threshold value Vth1. Further, the control unit 32A compares and determines the detected values of the cell voltages Vc1 to Vc4 with the second and third threshold values Vth2 and Vth3, and the resistance value of the corresponding discharge resistor 33A is determined, for example, according to the determination result. Select from three setting values R, R / 2, R / 3.

By the operation as described above, it is possible to change the bypass current Ib stepwise as shown in FIG. 8 and to obtain the same effect as the simulation result of the first embodiment.

In the above operation example, the control unit 32A changes the resistance value of the discharge resistor 33A stepwise by the plurality of threshold determinations. Not limited to this, for example, the control unit 32A may change the resistance value of the discharge resistor 33A continuously and stepwise (or sufficiently subdivided).

As described above, in the battery assembly 1A according to the present embodiment, the discharge resistor 33A is configured of a variable resistor. This makes it possible to balance the charge states of the battery cells 11 to 14 with high accuracy.

(Other embodiments)
Although the above-mentioned each embodiment explained the example which battery cells 11-14 are LFP-Gr cells, the battery cell of an assembled battery is not limited to LFP-Gr cells, for example, various lithium of olivine type and non-olivine type. It may be configured by an ion battery.

Moreover, although each above-mentioned embodiment demonstrated the assembled battery 1 provided with a battery protection circuit part, an assembled battery may be provided separately from a battery protection circuit part.

The above-described embodiment is an exemplification, and the present invention is not limited to the above-described embodiment. The scope of the present invention is indicated not by the above description but by the claims, and various changes, substitutions, additions, omissions, etc. can be made within the scope of the claims or the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 assembled battery 11-14 battery cell 3-1-3-3, 3 A balance circuit 30 discharge circuit 31 detection part 32.32A control part 33.33A discharge resistance 34 switch

Claims (8)

A rechargeable battery pack,
A plurality of battery cells connected in series with one another;
A detection unit that detects a cell voltage between both ends of each battery cell;
A plurality of discharge resistances connected in parallel with each battery cell and capable of short circuiting the respective battery cells, and discharging
A control unit that controls discharge of each battery cell based on the cell voltage detected by the detection unit;
The assembled battery which changes the resistance value by one or more discharge resistances for discharging the battery cell in which the said cell voltage was detected according to the magnitude | size of the detected cell voltage in the said control part. The assembled battery according to claim 1, wherein the control unit decreases the resistance value as the cell voltage detected by the detection unit when the battery cell is discharged is larger. The assembled battery according to claim 1, wherein the control unit changes the resistance value stepwise based on a plurality of predetermined threshold values. The minimum threshold value among the plurality of threshold values is equal to or higher than a voltage obtained by dividing the charge voltage of the assembled battery by the number of series cells, and the number of series cells is a battery cell connected in series in the assembled battery The assembled battery according to any one of claims 1 to 3, which is the number of batteries. And a plurality of switches provided between each discharge resistor and each battery cell,
5. The assembled battery according to any one of claims 1 to 4, wherein a plurality of series circuits of the discharge resistor and the switch are provided in parallel with one battery cell. The assembled battery according to any one of claims 1 to 4, wherein the discharge resistor comprises a variable resistor. The assembled battery according to any one of claims 1 to 6, wherein the number of the plurality of battery cells is four or more. The assembled battery according to any one of claims 1 to 7, wherein the battery cell is a lithium ion battery including a positive electrode containing lithium iron phosphate and a negative electrode containing graphite.

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