Energy Storage System

Abstract

To provide a power storage system capable of accurately grasping a full charge capacity of a battery pack.SOLUTION: A power storage system that performs charging and discharging with an external system includes a power converter, a plurality of battery packs connected in parallel with each other to the power converter, and a control device that controls an operation of the power converter. The control device operates the power converter to supply power from a designated first battery pack of the plurality of battery packs to a designated at least one second battery pack of the plurality of battery packs to completely discharge the first battery pack. The control device operates the power converter so as to supply power from the at least one second battery pack to the first battery pack to fully charge the first battery pack. The control device calculates a full charge capacity of the first battery pack based on a transition from a fully discharged state to a fully charged state.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an electricity storage system. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2014-103804 (Patent Document 1) discloses a battery system in which a plurality of assembled batteries are connected in parallel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-103804 A [Patent Document 2] JP 2013-169051 A [Patent Document 3] JP 2012-85487 A [Patent Document 4] JP 2011-188700 A [Patent Document 5] JP 2010-142040 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a system such as that disclosed in Patent Document 1, it is desirable to accurately grasp the full charge capacity of the battery pack in order to prevent overcharging and over-discharging of the battery pack.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to accurately grasp the full charge capacity of a battery pack. [Means for solving the problem]

[0006] According to an aspect of the present disclosure, a power storage system that charges and discharges with an external system includes a power conversion device, a plurality of assembled batteries connected in parallel to the power conversion device, and a control device that controls operation of the power conversion device. The control device operates the power conversion device to supply power from a specified first assembled battery among the plurality of assembled batteries to at least one specified second assembled battery among the plurality of assembled batteries, thereby fully discharging the first assembled battery. The control device operates the power conversion device to supply power from the at least one second assembled battery to the first assembled battery, thereby fully charging the first assembled battery. The control device calculates a full charge capacity of the first assembled battery based on a transition from a fully discharged state to a fully charged state.

[0007] According to the above configuration, the full charge capacity of the first assembled battery is calculated by transitioning the first assembled battery from a fully discharged state to a fully charged state, so that the full charge capacity of the first assembled battery can be accurately grasped.

[0008] Preferably, the control device stores information specifying a length of wiring between the first assembled battery and a plurality of remaining assembled batteries excluding the first assembled battery from the plurality of assembled batteries, and designates, based on the information, a battery among the remaining assembled batteries that has the shortest length of wiring between the battery and the first assembled battery as one of the at least one second assembled battery.

[0009] According to the above configuration, the length of the wiring used when charging and discharging the first assembled battery can be shortened, and therefore the amount of power loss when measuring the full charge capacity of the first assembled battery can be reduced compared to when a battery other than the specified second assembled battery is used as the discharge destination and charge source.

[0010] Preferably, the power storage system further includes a sensor device for measuring a temperature of each of the plurality of assembled batteries. The control device designates a battery having the highest temperature among the remaining plurality of assembled batteries, excluding the first assembled battery, as one of the at least one second assembled battery.

[0011] According to the above configuration, the electrical resistance during charge and discharge of the first battery pack can be reduced. Therefore, compared with the case of using a battery pack other than the second battery pack specified as the target of the discharge destination and the charge source, the amount of power loss when measuring the full charge capacity of the first battery pack can be reduced.

Advantages of the Invention

[0012] According to the above disclosure, the full charge capacity of the battery pack can be accurately grasped.

Brief Description of the Drawings

[0013] [Figure 1] It is a diagram for explaining the configuration of the power storage system and the external system. [Diagram 2] It is a diagram for explaining the process when measuring the full charge capacity of the battery pack. [Diagram 3] It is a flowchart for explaining the flow of the process when measuring the full charge capacity of three battery packs. [Figure 4] It is a diagram for explaining other processes when measuring the full charge capacity of the battery pack. [Diagram 5] It is a diagram showing the configuration of the ECU. [Figure 6] It is a diagram for explaining still other processes when measuring the full charge capacity of the battery pack.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same members are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0015] <A. Overall Configuration> Fig. 1 is a diagram for explaining the configuration of a power storage system and an external system. As shown in Fig. 1, a power storage system 1 is connected to an external system 900 via a power line. The power storage system 1 can be supplied with power from the external system 900 and can be discharged to the external system 900.

[0016] The power storage system 1 includes a plurality of battery units 10A, 10B, ... and a host controller 20. In the following, any one of the plurality of battery units 10A, 10B, ... will also be referred to as a "battery unit 10".

[0017] The battery unit 10A includes a power control unit (PCU) 11, a battery pack 12A, a battery pack 12B, a battery pack 12C, and an electronic control unit (ECU) 13.

[0018] The PCU 11 is a power conversion device including an inverter, a DC / DC converter, etc. In the battery unit 10A, three assembled batteries 12A, 12B, and 12C are connected in parallel to the PCU 11. More specifically, the battery unit 10A has three terminals 111, 112, and 113 for external connection of the PCU 11. The assembled battery 12A is connected to the terminal 111 of the three terminals. The assembled battery 12B is connected to the terminal 112. The assembled battery 12C is connected to the terminal 113.

[0019] The assembled batteries 12A, 12B, and 12C are each a pack of multiple cells (also referred to as "battery cells") of the same type. The assembled batteries 12A, 12B, and 12C are also referred to as "battery packs." Each of the assembled batteries 12A, 12B, and 12C is, for example, a ternary lithium-ion battery (hereinafter referred to as a "ternary battery") or an iron phosphate lithium-ion battery (hereinafter referred to as an "LFP battery").

[0020] Like the battery unit 10A, the battery unit 10B includes a PCU 11, battery packs 12A, 12B, and 12C, and an ECU 13. Note that in the battery unit 10B, the type of battery pack connected to the PCU 11 may be different from that in the battery unit 10A. For example, the battery unit 10A may include two ternary batteries and one LFP battery as the battery packs 12A, 12B, and 12C, and the battery unit 10B may include one ternary battery and two LFP batteries as the battery packs 12A, 12B, and 12C. The combination of the battery packs included in each battery unit 10 is not particularly limited.

[0021] In the following description, any one of the multiple battery packs 12A, 12B, and 12C will also be referred to as "battery pack 12."

[0022] In this example, a PCU and an ECU that were installed in a vehicle are repurposed as the PCU 11 and the ECU 13, respectively. Similarly, assembled batteries that were installed in a vehicle are repurposed as the assembled batteries 12A, 12B, and 12C. In this manner, the energy storage system 1 is constructed using unnecessary vehicle parts. In detail, the three-phase AC motor connected to the PCU of the vehicle is removed, and three assembled batteries (one each for the U layer, V layer, and W layer) are connected. Note that terminals 111, 112, and 113 are terminals for the U layer, the V layer, and the W layer, respectively.

[0023] The external system 900 includes a PCS (Power Conditioning System) 910, a solar power generation device 920, a load 930, and a power system 940. The battery units 10 (more specifically, the PCUs 11) are connected to the PCS 910 in parallel with each other.

[0024] PCS910 is a power conversion device capable of both AC / DC conversion (conversion from alternating current to direct current) and DC / AC conversion (conversion from direct current to alternating current). PCS910 receives DC power from, for example, a solar power generation device 920. PCS910 supplies AC power to a load 930. Note that the load 930 includes electrical products used at home (such as air conditioners and lighting fixtures, etc.). PCS910 exchanges AC power with the power grid 940.

[0025] Each ECU13 includes a processor and a memory and controls the battery unit 10. Each ECU13 is communicably connected to the upper controller 20.

[0026] The upper controller 20 includes a processor and a memory (both not shown) and sends commands to each ECU13. The upper controller 20 is communicably connected to a server (not shown) via the network NW.

[0027] In the power storage system 1, each battery unit 10 is charged by the external system 900 at least during the late-night time zone and discharges to the external system 900 at least during the daytime time zone. Specifically, for each of the three battery packs 12 of each battery unit 10, power is supplied from the external system 900 at least during the late-night time zone and discharged to the external system 900 at least during the daytime time zone.

[0028] <B. Outline of Processing> FIG. 2 is a diagram for explaining the processing when measuring the full charge capacity of the battery pack 12A. As shown in state (A) of FIG. 2, the ECU13 operates the PCU11 to supply power from the battery pack 12A to the battery packs 12B and 12C to fully discharge the battery pack 12A. The ECU13 typically determines whether the battery pack 12A is fully discharged (SOC (State Of Charge) = 0%) based on the voltage of the battery pack 12A.

[0029] After that, as shown in state (B), the ECU 13 operates the PCU 11 to supply power from the battery packs 12B and 12C to the battery pack 12A, and fully charges the battery pack 12A. The ECU 13 typically determines whether the battery pack 12A has reached a fully charged state (SOC (State Of Charge) = 100%) based on the voltage of the battery pack 12A.

[0030] The ECU 13 calculates (identifies) the full charge capacity (FCC (Full Charge Capacity)) of the battery pack 12A based on the transition from the fully discharged state to the fully charged state. The ECU 13 can typically calculate the full charge capacity using a current measurement method (Coulomb counter method, current integration method). Specifically, the ECU 13 can calculate the full charge capacity by determining the amount of charge that has flowed into the battery pack 12A from the fully discharged state to the fully charged state (specifically, integrating the current value over time).

[0031] When measuring the full charge capacity of the battery packs 12B and 12C, the same processing as that for the battery pack 12A is performed.

[0032] <C. Control Structure> FIG. 3 is a flowchart for explaining the processing flow when measuring the full charge capacity of the three battery packs 12A, 12B, and 12C. Steps S10, S20, and S30 are steps for measuring the full charge capacity of the battery packs 12A, 12B, and 12C, respectively. As shown in FIG. 3, step S10 includes steps S11 to S15. Step S20 includes steps S21 to S25. Step S30 includes steps S31 to S35.

[0033] In step S1, the ECU 13 determines whether a predetermined timing has been reached. Examples of the predetermined timing include any time within a time period when charging and discharging are not performed with the external system 900.

[0034] In step S11, the ECU 13 discharges the battery pack 12A and charges the battery packs 12B and 12C. In step S12, the ECU 13 determines whether the battery pack 12A is completely discharged. If the ECU 13 determines that the battery pack 12A is completely discharged (YES in step S12), then in step S13, the ECU 13 discharges the battery packs 12B and 12C and charges the battery pack 12A. If the ECU 13 determines that the battery pack 12A is not completely discharged (NO in step S12), then the ECU 13 continues to discharge the battery pack 12A until the battery pack 12A is completely discharged.

[0035] In step S14, the ECU 13 determines whether the battery pack 12A is fully charged. If the ECU 13 determines that the battery pack 12A is fully charged (YES in step S14), the ECU 13 identifies the full charge capacity of the battery pack 12A in step S15. If the ECU 13 determines that the battery pack 12A is not fully charged (NO in step S14), the ECU 13 continues charging the battery pack 12A until the battery pack 12A is fully charged.

[0036] This completes the measurement of the full charge capacity of the battery pack 12A. Next, the ECU 13 executes steps S21 to S25 included in step S20.

[0037] In step S21, the ECU 13 discharges the battery pack 12B and charges the battery packs 12A and 12C. In step S22, the ECU 13 determines whether the battery pack 12B is completely discharged. If the ECU 13 determines that the battery pack 12B is completely discharged (YES in step S22), then in step S23, the ECU 13 discharges the battery packs 12A and 12C and charges the battery pack 12B. If the ECU 13 determines that the battery pack 12B is not completely discharged (NO in step S22), then the ECU 13 continues to discharge the battery pack 12B until the battery pack 12B is completely discharged.

[0038] In step S24, the ECU 13 determines whether the battery pack 12B is fully charged. If the ECU 13 determines that the battery pack 12B is fully charged (YES in step S24), the ECU 13 identifies the full charge capacity of the battery pack 12B in step S25. If the ECU 13 determines that the battery pack 12B is not fully charged (NO in step S24), the ECU 13 continues charging the battery pack 12B until the battery pack 12B is fully charged.

[0039] This completes the measurement of the full charge capacity of the battery pack 12B. Next, the ECU 13 executes steps S31 to S35 included in step S30.

[0040] In step S31, the ECU 13 discharges the battery pack 12C and charges the battery packs 12A and 12B. In step S12, the ECU 13 determines whether the battery pack 12C is completely discharged. If the ECU 13 determines that the battery pack 12C is completely discharged (YES in step S32), then in step S33, the ECU 13 discharges the battery packs 12A and 12B and charges the battery pack 12C. If the ECU 13 determines that the battery pack 12C is not completely discharged (NO in step S32), then the ECU 13 continues to discharge the battery pack 12C until the battery pack 12C is completely discharged.

[0041] In step S34, the ECU 13 determines whether the battery pack 12C is fully charged. If the ECU 13 determines that the battery pack 12C is fully charged (YES in step S34), the ECU 13 identifies the full charge capacity of the battery pack 12C in step S35. If the ECU 13 determines that the battery pack 12C is not fully charged (NO in step S34), the ECU 13 continues charging the battery pack 12C until the battery pack 12C is fully charged. This ends the measurement of the full charge capacity of the battery pack 12C.

[0042] Note that in the above description, the processing of step S10, step S20, and step S30 is described by taking the configuration of continuous processing as an example, but it is not limited thereto. Also, the order of step S10, step S20, and step S30 is not limited to the above.

[0043] The timings for executing step S10, step S20, and step S30 may be set individually. The ECU 13 may be configured such that step S10 is executed at timing Ta, step S20 is executed at timing Tb, and step S30 is executed at timing Tc.

[0044] <D. Parentheses> When the power storage system 1 is enclosed in parentheses, it is as follows. As described above, the power storage system 1 performs charge and discharge with the external system 900. The power storage system 1 includes a PCU 11, a plurality of battery packs 12 (in this example, three battery packs 12A, 12B, and 12C) that are connected in parallel to the PCU 11, and an ECU 13 that controls the operation of the PCU 11.

[0045] The ECU 13 operates the PCU 11 to supply power from a designated first battery pack (for example, battery pack 12A in the example of FIG. 1) among the plurality of battery packs to at least one designated second battery pack (for example, the remaining battery packs 12B and 12C in the example of FIG. 1) among the plurality of battery packs, thereby fully discharging the first battery pack.

[0046] The ECU 13 operates the PCU 11 to supply power from the at least one second battery pack to the first battery pack, thereby fully charging the first battery pack. The ECU 13 calculates (identifies) the full charge capacity of the first battery pack based on the transition from the fully discharged state to the fully charged state.

[0047] According to such a configuration, since the full charge capacity of the first battery pack is calculated by transitioning the first battery pack from the fully discharged state to the fully charged state, the full charge capacity of the first battery pack can be accurately grasped.

[0048] <E. Modification Example> <e1. First Modification Example> In the above, for example, when measuring the full charge capacity of the battery pack 12A, the remaining two battery packs 12B and 12C in the battery unit 10 were used. However, it is not limited to this.

[0049] For example, when the full charge capacity of the battery pack 12B is larger than that of the battery pack 12A and the current battery capacity of the battery pack 12B is small, it is also possible to measure the full charge capacity of the battery pack 12A using only the battery pack 12B among the two battery packs 12B and 12C. Such a modification example can also be applied to the modification examples described later.

[0050] <e2. Second Modification Example> In the above, the configuration in which three battery packs 12 are connected to the PCU11 has been described. Hereinafter, the measurement of the full charge capacity in a configuration in which more battery packs 12 are connected to the PCU will be described. In particular, a configuration using the wiring length information will be described.

[0051] FIG. 4 is a diagram for explaining the process when measuring the full charge capacity of the battery pack 12C. As shown in FIG. 4, the battery unit 110 includes a PCU11A, six battery packs 12 (12A to 12F), and an ECU13A. The PCU11A has the same function as the PCU11, except that the number of connectable battery packs 12 is different from that of the PCU11.

[0052] FIG. 5 is a diagram showing the configuration of the ECU13A. As shown in FIG. 5, the ECU13 includes a processor 131 and a memory 132. A data table DT is stored in the memory 132. The data table DT stores information on the wiring lengths between two of the six battery packs 12.

[0053] In this example, six battery packs 12 are connected to the PCU 11A, and therefore 15 pieces of length information (L1 to L15) are stored in the data table DT. In the following, the wiring lengths between the battery pack 12C and the remaining five battery packs 12A, 12B, 12D, 12E, and 12F are respectively designated as L2, L6, L10, L11, and L12. For convenience of explanation, L6 <L10<L2<L11<L12とする。

[0054] When measuring the full charge capacity of the battery pack 12C, the ECU 13A uses, in this example, two battery packs 12 as targets for discharging and charging. Specifically, from among the remaining five battery packs 12, the ECU 13A selects the battery pack 12B having the shortest wiring length to the battery pack 12C and the battery pack 12D having the second shortest wiring length.

[0055] Therefore, when measuring the full charge capacity of the battery pack 12C, the ECU 13A operates the PCU 11A to supply power from the battery pack 12C to the battery packs 12B and 12D, thereby fully discharging the battery pack 12C, as shown in state (A) of Fig. 4. Thereafter, as shown in state (B), the ECU 13A operates the PCU 11A to supply power from the battery packs 12B and 12D to the battery pack 12C, thereby fully charging the battery pack 12C. The ECU 13A calculates the full charge capacity of the battery pack 12C based on the transition from the fully discharged state to the fully charged state.

[0056] From the above, when focusing on the measurement of the full charge capacity of the battery pack 12C, it can be said that the ECU 13A has the following configuration. The ECU 13A stores information specifying the lengths of wiring between the battery pack 12C and the remaining battery packs 12A, 12B, 12D, 12E, and 12F. Based on the information, the ECU 13A specifies (designates) the battery pack 12B, which has the shortest length of wiring between the battery pack 12C and the battery pack 12D, which has the second shortest length, as targets for the discharge destination and the charge source.

[0057] According to such a configuration, the length of the wiring used during charging and discharging of the assembled battery 12C can be shortened. Therefore, compared with the case of using two assembled batteries 12 other than the assembled batteries 12B and 12D as the discharge destination and the charge source, the amount of power loss when measuring the full charge capacity of the assembled battery 12C can be reduced.

[0058] In the above description, for the sake of convenience of explanation, the process during the measurement of the full charge capacity of the assembled battery 12C has been described as an example, but it is not limited thereto. The above-described selection process of the discharge destination and the charge source can also be applied when measuring the full charge capacity of the other assembled batteries 12A, 12B, 12D, 12E, and 12F.

[0059] Also, in the above description, when measuring the full charge capacity of the assembled battery 12, two assembled batteries 12 are used as the discharge destination and the charge source, but it is not limited thereto. When measuring the full charge capacity of the assembled battery 12, three or more assembled batteries 12 may be used as the discharge destination and the charge source.

[0060] <e3. Third Modification Example> FIG. 6 is a diagram for explaining the process when measuring the full charge capacity of the assembled battery 12A. As shown in FIG. 6, the battery unit 210 includes a PCU 11A, six assembled batteries 12 (12A to 12F), and an ECU 13B.

[0061] Specifically, the battery unit 210 includes a sensor device 14 that measures the temperature of each of the six assembled batteries 12. Each assembled battery 12 has a temperature sensor 129. The sensor device 14 is composed of six temperature sensors 129. Hereinafter, a configuration using the detection results of each temperature sensor 129 will be described.

[0062] Each temperature sensor 129 measures the temperature of the assembled battery 12. Each temperature sensor 129 periodically notifies the measurement result to the ECU 13B.

[0063] When measuring the full charge capacity of the battery pack 12A, the ECU 13B uses two battery packs 12 in this example as targets for discharging destination and charging source. In detail, the ECU 13B selects the battery pack with the highest temperature and the battery pack with the second highest temperature from among the battery packs 12B to 12F excluding the battery pack 12A based on temperature information acquired from each temperature sensor 129. For example, when the temperature of the battery pack 12D is the highest and the temperature of the battery pack 12F is the second highest, the ECU 13B selects the two battery packs 12D and 12F.

[0064] Therefore, when measuring the full charge capacity of the battery pack 12A, the ECU 13B operates the PCU 11A to supply power from the battery pack 12A to the battery packs 12D and 12F, thereby fully discharging the battery pack 12A, as shown in state (A) of Fig. 6. Thereafter, as shown in state (B), the ECU 13B operates the PCU 11A to supply power from the battery packs 12D and 12F to the battery pack 12A, thereby fully charging the battery pack 12A. The ECU 13B calculates the full charge capacity of the battery pack 12A based on the transition from the fully discharged state to the fully charged state.

[0065] From the above, the ECU 13B selects the battery pack 12D with the highest temperature and the battery pack 12F with the second highest temperature among the remaining battery packs 12B to 12F excluding the battery pack 12A from the battery packs 12. This configuration can reduce the electrical resistance during charging and discharging of the battery pack 12A. Therefore, the amount of power loss during measuring the full charge capacity of the battery pack 12A can be reduced compared to when two battery packs 12 other than the batteries 12D and 12F are used as the discharge destination and charge source.

[0066] In the above, for convenience of explanation, the process of measuring the full charge capacity of the assembled battery 12A has been described as an example, but the present invention is not limited to this. The above-mentioned selection process of the targets of the discharge destination and the charge source can also be applied to measuring the full charge capacities of the other assembled batteries 12B to 12F.

[0067] Also, in the above, when measuring the full charge capacity of the assembled battery 12, two assembled batteries 12 were used as the discharge destination and the charge source, but the present invention is not limited thereto. When measuring the full charge capacity of the assembled battery 12, three or more assembled batteries 12 may be used as the discharge destination and the charge source.

[0068] <F. Appendix> (1) A control method in a power storage system that performs charge and discharge with an external system, comprising: a step of operating the power conversion device so that the control device supplies power from a designated first assembled battery among a plurality of assembled batteries connected in parallel to each other to at least one designated second assembled battery among the plurality of assembled batteries, thereby fully discharging the first assembled battery; a step of operating the power conversion device so that the control device supplies power from the at least one second assembled battery to the first assembled battery, thereby fully charging the first assembled battery; a step of calculating the full charge capacity of the first assembled battery based on the transition from the fully discharged state to the fully charged state by the control device.

[0069] (2) A program that causes one or more processors (for example, the processor 131 of the ECU 13) to execute each step of the control method.

[0070] (3) A non-transitory computer-readable storage medium storing the program. It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present disclosure is shown by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Description of Reference Numerals

[0071] 1 Energy storage system, 10A, 10B, 110, 210 Battery unit, 12A, 12B, 12C, 12D, 12E, 12F Battery pack, 14 Sensor device, 20 Upper controller, 111, 112, 113 Terminal, 129 Temperature sensor, 131 Processor, 132 Memory, 900 External system, 920 Photovoltaic power generation device, 930 Load, 940 Power system, DT data table, NW network.

Claims

1. A power storage system that charges and discharges between an external system, A power conversion device; A plurality of assembled batteries connected in parallel to the power conversion device; A control device for controlling an operation of the power conversion device, The control device includes: operating the power conversion device to supply power from a designated first assembled battery among the plurality of assembled batteries to at least one designated second assembled battery among the plurality of assembled batteries, thereby completely discharging the first assembled battery; operating the power conversion device to supply power from the at least one second assembled battery to the first assembled battery, thereby fully charging the first assembled battery; calculating a full charge capacity of the first assembled battery based on the transition from the fully discharged state to the fully charged state; storing information for specifying a length of wiring between the first assembled battery and a plurality of assembled batteries remaining from the plurality of assembled batteries excluding the first assembled battery; and designating, based on the information, one of the remaining plurality of assembled batteries that has the shortest length of wiring between itself and the first assembled battery, as one of the at least one second assembled battery.

2. A power storage system that charges and discharges between an external system, A power conversion device; A plurality of assembled batteries connected in parallel to the power conversion device; a sensor device for measuring a temperature of each of the plurality of assembled batteries; A control device for controlling an operation of the power conversion device, The control device includes: operating the power conversion device to supply power from a designated first assembled battery among the plurality of assembled batteries to at least one designated second assembled battery among the plurality of assembled batteries, thereby completely discharging the first assembled battery; operating the power conversion device to supply power from the at least one second assembled battery to the first assembled battery, thereby fully charging the first assembled battery; calculating a full charge capacity of the first assembled battery based on the transition from the fully discharged state to the fully charged state; the battery pack having the highest temperature among the remaining battery packs excluding the first battery pack from the plurality of battery packs is designated as one of the at least one second battery pack.

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