JP4811349B2 - Battery pack and control method - Google Patents

Description

  The present invention relates to a control method for controlling the balance between the capacity of a battery pack and battery cells of a secondary battery.

  As a battery pack of a secondary battery using a lithium ion secondary battery or the like, a battery pack in which a plurality of battery cells are connected in series and / or in parallel is widely used. In such a battery pack, the capacity balance between the battery cells (hereinafter referred to as cell balance as appropriate) may be lost due to repeated charging / discharging or being left in a high temperature environment. If charging / discharging is performed in a state in which the cell balance is lost, any of the plurality of battery cells may be in an overcharged state or an overdischarged state, which promotes deterioration of the battery cell.

  Therefore, conventionally, as a method of matching the cell balance, a battery cell having a high voltage among a plurality of battery cells is detected, and the detected battery cell is discharged by a discharge circuit provided in the battery pack, so that other batteries There is a method of matching the cell balance with the cell.

  For example, in the case of a battery pack using an assembled battery in which a plurality of battery cells are connected in series, the process of matching the cell balance is performed as shown in the flowchart of FIG. Measured. In step S102, the battery cell having the maximum voltage is detected based on the voltage of each battery cell measured in step S101, and the detected battery cell is discharged by the discharge circuit.

  By doing so, the voltage of each battery cell becomes substantially equal, so that overcharge and overdischarge of a specific battery cell can be prevented, and the promotion of deterioration of the battery pack can be prevented.

  In this way, the voltage of a plurality of battery cells connected in series is detected, and when any of the battery cells becomes a predetermined voltage or higher, the discharge circuit is used to discharge the cell to another battery cell. A technique for matching the balance is described in Patent Document 1 below.

JP 2002-58170 A

  By the way, there are mainly two factors that cause the cell balance to collapse. First, for example, it is conceivable that the cell balance is lost due to the self-discharge amount of each battery cell being different. For example, when the battery pack is left for a long time, the characteristics of the battery cells may vary, and the self-discharge amount may change. In this way, a difference occurs in the self-discharge amount of each battery cell, and the cell balance is lost.

  FIG. 6 shows the charge / discharge voltage characteristics of two battery cells connected in series when the self-discharge amount of each battery cell is different. A graph indicated by a solid line shows the charge / discharge voltage characteristics of a battery cell with a small amount of self-discharge. The graph indicated by the dotted line shows the charge / discharge voltage characteristics of the battery cell having a larger amount of self-discharge than the battery cell indicated by the solid line graph.

  As shown in FIG. 6, a battery cell with a large amount of self-discharge has a lower cell voltage at the start of charging than a battery cell with a small amount of self-discharge. In addition, the slope of the charge / discharge characteristics is substantially equal between the battery cell having a large self-discharge amount and the battery cell having a small self-discharge amount.

  Usually, in such a battery pack, in order to prevent being overcharged or overdischarged, when any battery cell is fully charged, charging is stopped and when any battery cell is fully discharged. When charging, battery cells with a small amount of self-discharge are fully charged first, and battery cells with a large amount of self-discharge are charged before they are fully charged. Is stopped. In addition, when discharging, battery cells with a large amount of self-discharge are fully discharged first, and battery cells with a small amount of self-discharge are stopped before reaching a complete discharge state.

  That is, when the cell balance is lost due to the difference in the self-discharge amount, it is considered that the voltage of the battery cell having a small self-discharge amount is always increased.

  Next, as another factor that the cell balance is lost, for example, the battery capacity of each battery cell may be different. In the battery pack, for example, the battery cell deteriorates due to repeated charge and discharge, and the internal impedance of the battery cell increases, so that the voltage drop at the time of discharge increases and the battery capacity may decrease. In this way, a difference occurs in the battery capacity of each battery cell, and the cell balance is lost.

  FIG. 7 shows the charge / discharge characteristics of two battery cells connected in series when the battery capacity of each battery cell is different. A graph indicated by a solid line shows the charge / discharge characteristics of a battery cell having a large battery capacity. The graph shown by a dotted line shows the charge / discharge voltage characteristics of a battery cell having a smaller battery capacity than the battery cell shown by the solid line.

  As shown in FIG. 7, a battery cell with a small battery capacity has a lower cell voltage at the start of charging than a battery cell with a large battery capacity. Further, the slope of the charge / discharge characteristics is different between a battery cell having a small battery capacity and a cell having a large battery capacity.

  A battery cell with a low battery capacity has a low cell voltage at the start of charging, but because of a low battery capacity, the battery cell is fully charged earlier than a battery cell with a large battery capacity. Charging is stopped before charging. In addition, a battery cell with a small battery capacity has a high cell voltage at the start of discharge, but a battery cell with a large battery capacity is in a fully discharged state before a battery cell with a large battery capacity is in a fully discharged state. Discharging is stopped.

  That is, when cell balance is lost due to different battery capacities, the voltage of a battery cell with a small battery capacity increases in a fully charged state, and the voltage of a battery cell with a small battery capacity in a fully discharged state. It is thought to be lower. The fully charged state is a state in which the Battery Association of Japan has charged up to the upper limit charging voltage (for example, 4.2 V) shown in the “Guide for Safe Use of Lithium Ion Secondary Batteries in Notebook PCs”. The discharge state refers to a state where the battery is discharged to a lower limit discharge voltage (for example, 2.5 V).

  Here, consider a case where the cell balance is matched using the method described in Patent Document 1 described above. When the cell balance is lost due to the difference in the self-discharge amount of the battery cell, as shown in FIG. 6, the battery cell with a small self-discharge amount always has a higher cell voltage than the battery cell with a large self-discharge amount. By discharging a battery cell with a small amount of self-discharge and lowering the cell voltage, the cell balance with a battery cell with a large amount of self-discharge can be matched.

  However, when the cell balance is lost due to different battery capacities of the battery cells, as shown in FIG. 7, the battery cell with a small battery capacity has a lower cell voltage than the battery cell with a large battery capacity at the start of charging. However, in the vicinity of the fully charged state, a battery cell with a smaller battery capacity has a higher cell voltage than a battery cell with a larger battery capacity. Therefore, for example, when a battery cell with a high cell voltage is discharged near the start of charging, a battery cell with a large battery capacity is discharged, but a battery cell with a high cell voltage is discharged near a full charge. As a result, a battery cell having a small battery capacity is discharged.

  That is, depending on the discharge timing, a battery cell having a small battery capacity is discharged, and there is a problem that the cell balance may be further lost. If the cell balance is further disrupted, a battery cell with a small battery capacity may be in an overcharged state during charging and an overdischarged state during discharging, which may further promote deterioration of the battery cell.

  Conventionally, since the cell balance state is simply determined based on the cell voltage difference of each battery cell at a certain point in time, the cause of the cell balance breakdown is that the self-discharge amount of each battery cell is different. There is a problem that it cannot be determined whether there is a difference in battery capacity based on an increase in internal impedance or the like.

  Therefore, an object of the present invention is to provide a battery pack and a control method that can determine a factor that breaks the cell balance between battery cells and can match the cell balance.

To solve the problems described above, the first invention is a battery pack for a secondary battery having a plurality of battery cell Le, during the charge and discharge control to measure the voltages of the battery cells, respectively First cell position information indicating the position of the battery cell having the maximum voltage during charging, and second cell position information indicating the position of the battery cell having the maximum voltage during discharging based on the measurement result And a discharge circuit for discharging a predetermined battery cell among the plurality of battery cells based on control by the control unit, the control unit includes first cell position information and second cell position information. When the first cell position information and the second cell position information match, the self-discharge amount of the plurality of battery cells is different and the cell balance of the plurality of battery cells is lost. The first cell location information and the first Causing the battery cells corresponding to the cell position information discharged by controlling the discharge circuit that a battery pack characterized by.

The second invention is a control method of a battery pack for a secondary battery having a plurality of battery cell Le, during the charge and discharge, the voltages of the battery cells measured respectively, based on the measurement result Storing in the storage unit first cell position information indicating the position of the battery cell having the maximum voltage during charging, and second cell position information indicating the position of the battery cell having the maximum voltage during discharging; When the first cell position information and the second cell position information are compared, and the first cell position information and the second cell position information match, the self-discharge amounts of the plurality of battery cells are different. The control method is characterized in that the battery balance is determined to be broken by the discharge circuit, and the battery cells corresponding to the first cell position information and the second cell position information are discharged by the discharge circuit.

As described above, in the first and second inventions, the voltage of a plurality of battery cells is measured during charging and discharging, and the position of the battery cell that becomes the maximum voltage during charging is determined based on the measurement result. The first cell position information to be displayed and the second cell position information to indicate the position of the battery cell having the maximum voltage at the time of discharging are stored in the storage unit, and the first cell position information and the second cell position information are If the first cell position information and the second cell position information match, it is determined that the cell balance is lost due to the difference in the self-discharge amount of the plurality of battery cells, Since the battery cells corresponding to the cell position information and the second cell position information are discharged by the discharge circuit, the cell balance of the plurality of battery cells can be matched.

  The present invention is based on the first cell position information indicating the position of the battery cell having the maximum voltage during charging and the second cell position information indicating the position of the battery cell having the maximum voltage during discharging. Since the factor that the cell balance of the battery cell is lost is determined and the battery cell having a high voltage is discharged according to the determination result, there is an effect that the cell balance of the plurality of battery cells can be matched.

  In addition, since the present invention makes it possible to match the cell balance of the plurality of battery cells by discharging the battery cells having a high voltage, it is possible to prevent the battery cells from being overdischarged and to deteriorate the battery pack. There is an effect that the promotion of can be prevented. Furthermore, the present invention can be realized only by changing software processing by the control unit, and a circuit configuration similar to that of a conventional battery pack can be applied. Therefore, no new cost is generated.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a battery pack 1 according to an embodiment of the present invention includes an assembled battery 2, an MPU (Micro Processing Unit) 3 as a control unit, discharge circuits 4 a and 4 b (hereinafter, it is not necessary to distinguish between them). In this case, it is simply referred to as a discharge circuit 4), a switch circuit 5 and a current detection resistor 6, and a positive terminal 7 and a negative terminal 8 are respectively connected to a positive terminal and a negative terminal of an external electronic device or charger, Charging / discharging the assembled battery 2 is performed.

  The assembled battery 2 is a secondary battery such as a lithium ion secondary battery, and is an assembled battery in which a plurality of battery cells are connected in series and / or in parallel. In this example, a case will be described in which two battery cells 11a and 11b (hereinafter simply referred to as a battery cell 11 as appropriate unless otherwise distinguished) are connected in series.

  The MPU 3 controls each unit using a RAM (Random Access Memory) (not shown) as a work memory according to a program stored in advance in a ROM (Read Only Memory) (not shown). The MPU 3 measures the voltage of the battery cells 11a and 11b every predetermined time, and measures the magnitude and direction of the current flowing through the current detection resistor 6 every predetermined time.

  Then, the MPU 3 controls the switch circuit 5 based on the measured voltage value and current value. When the voltage of any battery cell becomes the overcharge detection voltage, or when the voltage of any battery cell falls below the overdischarge detection voltage, the switch circuit 5 is turned off to overcharge or overdischarge. To prevent. Here, in the case of a lithium ion battery, the overcharge detection voltage per battery cell is determined to be, for example, 4.2 V ± 0.05 V, and the overdischarge detection voltage is determined to be 2.5 V ± 0.1 V. Details of the switch circuit 5 will be described later.

  Further, the MPU 3 includes a memory 16 such as a nonvolatile memory EEPROM (Electrically Erasable and Programmable Read Only Memory) as a storage unit therein, and the voltage of each battery cell 11 at the time of charging and discharging at a predetermined time. Information indicating the cell position of the battery cell having the maximum voltage at the time of measurement (hereinafter referred to as cell position information as appropriate) is stored in the memory 16. Note that the cell position information of the maximum voltage at the time of charging is preferably near full charge where the voltage of the battery cell is stable, for example, and the cell position information of the maximum voltage at the time of discharging is, for example, the remaining battery Near the complete discharge where the capacity is determined is preferable.

  The MPU 3 adjusts the voltage of each battery cell 11 based on the cell position information of the maximum voltage at the time of charging and discharging stored in the memory 16 and performs a balancing process for matching the cell balance between the battery cells 11. Do. When the voltage difference between the battery cells 11 exceeds a predetermined amount, the MPU 3 controls the discharge circuit 4 corresponding to the battery cell to be discharged based on the cell position information, and discharges the desired battery cell 11. Reduce voltage. For example, when the voltage difference between the battery cells 11 is about 100 mV, the battery cell having a high cell voltage is discharged with a discharge current of about several mA to several tens mA. Then, when the voltage difference between the battery cells 11 is about 0 mV to 50 mV, or when the voltages of the battery cells 11 match, the cell balance can be matched by ending the balance process. Details of the balance process will be described later.

  The cell position information is information indicating which of the plurality of battery cells 11 is the battery cell. As the cell position information, for example, a number assigned in advance for each battery cell is used in order from the battery cell at the foremost stage or the last stage.

  The switch circuit 5 includes a charge control FET (Field Effect Transistor) 14a, a discharge control FET 14b, and parasitic diodes 15a and 15b, and is controlled by the MPU 3. The charge control FET 14a is turned off when the battery voltage becomes the overcharge detection voltage, and is controlled by the MPU 3 so that the charge current does not flow in the current path of the assembled battery 2. Note that after the charge control FET 14a is turned off, only discharge is possible via the parasitic diode 15a. The discharge control FET 14 b is turned off when the battery voltage becomes the overdischarge detection voltage, and is controlled by the MPU 3 so that the discharge current does not flow in the current path of the assembled battery 2. Note that after the discharge control FET 14b is turned OFF, only charging is possible via the parasitic diode 15b.

  The discharge circuit 4 is provided corresponding to each battery cell 11 of the battery pack 1, and in this example, the discharge circuits 4a and 4b are provided corresponding to the two battery cells 11a and 11b, respectively. . The discharge circuit 4a includes a discharge load 12a and a switch element 13a. The switch element 13a is turned on based on the control of the MPU 3, and the battery cell 11a is discharged by the discharge load 12a to reduce the voltage. Similarly to the discharge circuit 4a, the discharge circuit 4b includes a discharge load 12b and a switch element 13b. The switch element 13b is turned on based on the control of the MPU 3, and the discharge load 12b discharges the battery cell 11b to generate a voltage. Reduce. In the following description, when there is no need to indicate specific discharge loads and switch elements, they are simply referred to as discharge loads 12 and switch elements 13 as appropriate.

  The balance process according to the embodiment of the present invention will be described with reference to the flowchart shown in FIG. Processing is started by charging / discharging of the battery pack 1, and in step S11, the voltage of each battery cell 11 at the time of charging is measured every predetermined time. Whether the state of the battery pack 1 is being charged or discharged is determined by the direction of the current flowing through the current detection resistor 6.

  In step S12, cell position information of the battery cell having the maximum voltage among the battery cells 11 at the time of charging measured in step S11 is stored in the memory 16. Note that the cell position information of the maximum voltage at the time of charging is preferably stored near full charge where the voltage of the battery cell is stable, for example.

  Next, in step S13, the voltage of each battery cell 11 at the time of discharging is measured every predetermined time. In step S14, cell position information of the battery cell having the maximum voltage among the battery cells 11 at the time of discharge measured in step S13 is stored in the memory 16. The cell position information of the maximum voltage at the time of discharge is preferably stored, for example, near the complete discharge where the remaining capacity of the battery is determined.

  In step S15, the cell position information of the maximum voltage during charging stored in the memory 16 is compared with the cell position information of the maximum voltage during discharging. When the cell position information of the maximum voltage at the time of charging and the cell position information of the maximum voltage at the time of discharging coincide with each other, it is determined that the cell balance is lost due to the difference in self-discharge amount, and the process proceeds to step S16.

  In step S16, when the voltage difference between the battery cells 11 exceeds a predetermined amount such as about 100 mV, the switch element 13 of the corresponding discharge circuit 4 is turned on based on the cell position information of the maximum voltage, and the discharge load 12 discharges the battery cell having a high cell voltage. For example, when the voltage difference between the battery cells 11 reaches a predetermined amount such as about 0 mV to 50 mV, or when the voltages of the battery cells 11 match, the discharge is completed, and the series of processes ends.

  On the other hand, if the cell position information of the maximum voltage at the time of charging and the cell position information of the maximum voltage at the time of discharging do not match in step S15, the series of processing ends without discharging by the discharging circuit 4.

  As described above, in the embodiment of the present invention, the cell position of the maximum voltage at the time of charging is compared with the cell position of the maximum voltage at the time of discharging, and the self-discharge amount is different if the cell positions match. Therefore, it is determined that the cell balance has been lost, and the battery cell having a high cell voltage is discharged. By doing so, the voltage of the battery cell with a small amount of self-discharge can be lowered to the voltage of the battery cell with a large amount of self-discharge, and the cell balance of each battery cell can be matched. In addition, since the voltage of the battery cell having a high cell voltage is discharged, overcharging can be prevented during charging, and cell deterioration can be prevented from being accelerated.

  Next, a first modification of the embodiment of the present invention will be described. In the first modification of this embodiment, in addition to comparing the cell position information of the maximum voltage during charging and discharging, by comparing the cell position information of the minimum voltage during charging and discharging, The cell balance status can be judged more accurately.

  The battery pack according to the first modification of the embodiment of the present invention can be realized with the same configuration except for the operation of the MPU 3 in the battery pack 1 according to the above-described embodiment shown in FIG. Therefore, the same parts as those in this embodiment are denoted by the same reference numerals, and the description other than the processing operation by the MPU 3 is omitted.

  The MPU 3 stores in the memory 16 the cell position information that becomes the maximum voltage and the cell position information that becomes the minimum voltage when the voltage of each battery cell 11 at the time of charging is measured every predetermined time. Further, the MPU 3 stores in the memory 16 the cell position information that becomes the maximum voltage and the cell position information that becomes the minimum voltage when the voltage of each battery cell 11 at the time of discharging is measured every predetermined time. Note that the cell position information of the maximum voltage and the cell position information of the minimum voltage at the time of charging are preferably stored near full charge where the voltage of the battery cell is stable, for example. The maximum voltage cell position information and the minimum voltage cell position information at the time of discharge are preferably stored in the vicinity of complete discharge where the remaining capacity of the battery is determined.

  Then, the MPU 3 adjusts the voltage of each battery cell 11 based on the cell position information stored in the memory 16 and performs a balance process for matching the cell balance between the battery cells 11. When the voltage difference between the battery cells 11 exceeds a predetermined amount, the MPU 3 controls the discharge circuit 4 corresponding to the battery cell to be discharged based on the cell position information, and discharges the desired battery cell 11. Reduce voltage.

  The balance process according to the first modification of the embodiment of the present invention will be described with reference to the flowchart shown in FIG. Processing is started by charging / discharging of the battery pack 1, and in step S21, the voltage of each battery cell 11 at the time of charging is measured every predetermined time. Whether the state of the battery pack 1 is being charged or discharged is determined by the direction of the current flowing through the current detection resistor 6.

  In step S22, cell position information of the battery cell having the maximum voltage and the minimum voltage among the battery cells 11 at the time of charging measured in step S21 is stored in the memory 16, respectively. Note that the cell position information of the maximum voltage and the cell position information of the minimum voltage at the time of charging are preferably stored near full charge where the voltage of the battery cell is stable, for example.

  Next, in step S23, the voltage of each battery cell 11 at the time of discharging is measured every predetermined time. In step S24, cell position information of the battery cell having the maximum voltage and the minimum voltage among the battery cells 11 at the time of discharge measured in step S23 is stored in the memory 16, respectively. The maximum voltage cell position information and the minimum voltage cell position information at the time of discharge are preferably stored in the vicinity of complete discharge where the remaining capacity of the battery is determined, for example.

  In step S25, the cell position information of the maximum voltage during charging and the cell position information of the maximum voltage during discharging stored in the memory 16 are compared. If it is determined that the cell position information of the maximum voltage at the time of charging and the cell position information of the maximum voltage at the time of discharging match, the process proceeds to step S26.

  In step S26, the cell position information of the minimum voltage during charging and the cell position information of the minimum voltage during discharging stored in the memory 16 are compared. If the cell position information of the minimum voltage at the time of charging and the cell position information of the minimum voltage at the time of discharging coincide with each other, it is determined that the cell balance is lost due to the difference in self-discharge amount, and the process proceeds to step S27.

  In step S27, when the voltage difference between the battery cells 11 is a predetermined amount or more, such as about 100 mV, the switch element 13 of the corresponding discharge circuit 4 is turned on based on the cell position information of the maximum voltage, and the discharge load 12 discharges the battery cell having a high cell voltage. Then, for example, the discharge is completed when the voltage difference between the battery cells 11 reaches a predetermined amount such as about 0 mV to 50 mV, or when the voltages of the battery cells 11 match, and the series of processes ends. .

  On the other hand, if the cell position information of the maximum voltage at the time of charging does not match the cell position information of the maximum voltage at the time of discharging in step S25, and the cell position information of the minimum voltage at the time of charging and the cell position information at the time of discharging in step S26. If the cell position information of the minimum voltage does not match, the series of processing ends without discharging by the discharge circuit 4.

  Thus, in the first modification of the embodiment of the present invention, the cell position of the maximum voltage during charging is compared with the cell position of the maximum voltage during discharging and the cell position of the minimum voltage during charging. Is compared with the cell position of the minimum voltage at the time of discharge, and if the cell positions match, it is determined that the cell balance has been lost due to the difference in self-discharge, and the battery cell with a high cell voltage is discharged. Like to do. By doing so, it is possible to more reliably detect the factor that has lost the cell balance, reduce false detection, and more appropriately match the cell balance.

  Next, a second modification of the embodiment of the present invention will be described. As described in the background art section, when cell balance is lost due to different battery capacities of battery cells, the cell voltage of a battery cell with a small battery capacity is low at the start of charging and is high near full charge. In addition, it is high at the start of discharge and low in the vicinity of complete discharge.

  Therefore, in the second modification of the embodiment of the present invention, the cell balance state is determined based on the cell position information of the maximum voltage during charging and the cell position information of the minimum voltage during discharging, and the determination result Based on the above, a battery cell having a high cell voltage is discharged only during charging.

  The battery pack according to the second modification of the embodiment of the present invention is other than the operation of the MPU 3 in the battery pack 1 according to the above-described embodiment shown in FIG. 1 and the first modification of this embodiment. Can be realized with the same configuration. Therefore, here, the same reference numerals are given to the same parts as those of this embodiment and the first modification of this embodiment, and the description is omitted except for the processing operation by the MPU 3.

  The MPU 3 has cell position information that is the maximum voltage when the voltage of each battery cell 11 during charging is measured every predetermined time, and the minimum voltage when the voltage of each battery cell 11 during discharge is measured every predetermined time. Is stored in the memory 16. Note that storing the cell position information of the maximum voltage at the time of charging is preferably near full charge where the voltage of the battery cell is stable, for example, and storing the cell position information of the minimum voltage at the time of discharging is, for example, the remaining battery Near the complete discharge where the capacity is determined is preferable.

  Then, the MPU 3 adjusts the voltage of each battery cell 11 based on the cell position information stored in the memory 16 and performs a balance process for matching the cell balance between the battery cells 11. When the voltage difference between the battery cells 11 exceeds a predetermined amount, the MPU 3 controls the discharge circuit 4 corresponding to the battery cell to be discharged based on the cell position information, and discharges the desired battery cell 11. Reduce voltage.

  The balance process according to the second modification of the embodiment of the present invention will be described with reference to the flowchart shown in FIG. Processing is started by charging / discharging the battery pack 1, and in step S31, the voltage of each battery cell 11 at the time of charging is measured every predetermined time. Whether the state of the battery pack 1 is being charged or discharged is determined by the direction of the current flowing through the current detection resistor 6.

  In step S <b> 32, cell position information of the battery cell having the maximum voltage among the battery cells 11 at the time of charging measured in step S <b> 31 is stored in the memory 16. Note that the cell position information of the maximum voltage at the time of charging is preferably stored near full charge where the voltage of the battery cell is stable, for example.

  Next, in step S33, the voltage of each battery cell 11 at the time of discharging is measured every predetermined time. In step S <b> 34, cell position information of the battery cell having the minimum voltage among the battery cells 11 at the time of discharging measured in step S <b> 33 is stored in the memory 16. Note that the cell position information of the minimum voltage at the time of discharging is preferably stored, for example, near the complete discharge where the remaining capacity of the battery is determined.

  In step S35, the cell position information of the maximum voltage during charging and the cell position information of the minimum voltage during discharging stored in the memory 16 are compared. If it is determined that the cell position information of the maximum voltage during charging matches the cell position information of the minimum voltage during discharging, the process proceeds to step S36.

  In step S36, it is determined whether or not the battery pack 1 is being charged. Whether the battery is being charged is determined by the direction of the current flowing through the current detection resistor 6. If it is determined that charging is in progress, the process proceeds to step S37.

  In step S37, when the voltage difference between the battery cells 11 exceeds a predetermined amount such as about 100 mV, the switch element 13 of the corresponding discharge circuit 4 is turned on based on the cell position information of the maximum voltage, and the discharge load 12 discharges the battery cell having a high cell voltage. For example, when the voltage difference between the battery cells 11 reaches a predetermined amount such as about 0 mV to 50 mV, or when the voltages of the battery cells 11 match, the discharge is completed, and the series of processes ends.

  On the other hand, if it is determined in step S35 that the cell position information of the maximum voltage during charging does not match the cell position information of the minimum voltage during discharging, and if it is determined in step S36 that charging is not in progress, the discharging circuit A series of processes are completed without performing the discharge by 4.

  Thus, in the second modification of the embodiment of the present invention, the cell position of the maximum voltage at the time of charging is compared with the cell position of the minimum voltage at the time of discharging. It is determined that the cell balance has been lost due to different battery capacities, and the battery cell having a high cell voltage is discharged during charging. By doing so, it is possible to prevent the voltage of the battery cell having a small battery capacity from rising to the overcharge voltage and to prevent the deterioration of the battery cell.

  In addition, since the battery cells are not discharged at the time of leaving and discharging, it is possible to prevent the battery cells having a small battery capacity from being accidentally discharged and to maximize the discharge time of the battery pack.

  The embodiment of the present invention, the first modification of the embodiment, and the second modification have been described above. However, the present invention is an embodiment of the above-described embodiment of the present invention. The present invention is not limited to the first modification and the second modification, and various modifications and applications can be made without departing from the gist of the present invention. For example, the memory 16 provided in the MPU 3 may be provided outside the MPU 3. Further, for example, the cell position information may be stored in a volatile memory such as a RAM.

It is a block diagram which shows the structure of an example of the battery pack by one Embodiment of this invention. It is a flowchart which shows the flow of the process which matches the cell balance in the battery pack by one Embodiment of this invention. It is a flowchart which shows the flow of the process which makes a cell balance correspond in the battery pack by the 1st modification of one Embodiment of this invention. It is a flowchart which shows the flow of the process which makes a cell balance correspond in the battery pack by the 2nd modification of one Embodiment of this invention. It is a flowchart which shows the flow of the process which matches the cell balance by the conventional battery pack. It is a basic diagram which shows the charging / discharging voltage characteristic in case the amount of self discharges of each battery cell differs. It is a basic diagram which shows the charging / discharging voltage characteristic when the battery capacity of each battery cell differs.

Explanation of symbols

1 battery pack 2 assembled battery 3 MPU
4a, 4b Discharge circuit 5 Switch circuit 6 Current detection resistor 11a, 11b Battery cell 12a, 12b Discharge load 13a, 13b Switch element 16 Memory

Claims (5)

A battery pack for a secondary battery having a plurality of battery cell Le,
A controller that measures the voltages of the plurality of battery cells during charging and discharging;
Based on the measurement result, the first cell position information indicating the position of the battery cell having the maximum voltage during charging and the second cell position information indicating the position of the battery cell having the maximum voltage during discharging are stored. A storage unit to
A discharge circuit for discharging a predetermined battery cell among the plurality of battery cells based on the control by the control unit;
The control unit
The first cell position information and the second cell position information are compared, and if the first cell position information and the second cell position information match, the plurality of battery cells Judging that the cell balance of the plurality of battery cells is broken due to different discharge amounts,
A battery pack that discharges battery cells corresponding to the first cell position information and the second cell position information by controlling the discharge circuit. The battery pack according to claim 1,
The storage unit
The first cell position information based on the voltages of the plurality of battery cells measured near the fully charged state, and the second cell position information based on the voltages of the plurality of battery cells measured near the fully discharged state. And a battery pack. The battery pack according to claim 1,
The storage unit
Based on the measurement result by the control unit, the third cell position information indicating the position of the battery cell having the minimum voltage at the time of charging, and the fourth cell position indicating the position of the battery cell having the minimum voltage at the time of discharging. Remember more information,
The control unit
When the first cell position information and the second cell position information are compared with each other, and the first cell position information and the second cell position information match, the third cell position information And the fourth cell position information are further compared, and when the third cell position information and the fourth cell position information match, the self-discharge amounts of the plurality of battery cells are different. Judging that the cell balance of the plurality of battery cells is broken,
A battery pack that discharges battery cells corresponding to the first cell position information and the second cell position information by controlling the discharge circuit. The battery pack according to claim 1,
The storage unit
Based on the measurement result by the control unit, further stores the fourth cell position information indicating the position of the battery cell that becomes the minimum voltage during discharge,
The control unit
When the first cell position information and the fourth cell position information are compared, and the first cell position information and the fourth cell position information match, the batteries of the plurality of battery cells It is determined that the cell balance of the plurality of battery cells has been lost due to different capacities,
A battery pack that discharges battery cells corresponding to the first cell position information by controlling the discharge circuit during charging. A control method of a battery pack for a secondary battery having a plurality of battery cell Le,
Measure the voltage of each of the plurality of battery cells during charging and discharging,
Based on the measurement result, the first cell position information indicating the position of the battery cell having the maximum voltage during charging and the second cell position information indicating the position of the battery cell having the maximum voltage during discharging are stored. Remember in the department,
The first cell position information and the second cell position information are compared, and if the first cell position information and the second cell position information match, the plurality of battery cells Judge that the cell balance is broken due to different discharge amount,
A control method comprising discharging a battery cell corresponding to the first cell position information and the second cell position information by a discharge circuit.

Images