Battery management system and battery management method

Abstract

The present invention provides a battery management system and a battery management method. A battery well (2) includes: a storage unit (21) that stores a plurality of used batteries; a power conversion device (AC / DC converter (22) and DC / DC converter (23)) that is electrically connected between the plurality of used batteries stored in the storage unit (21) and a power system; and a server (20) that controls the operation of the power conversion device according to a demand response request from the power system (5) to charge and discharge the plurality of used batteries. When the server (20) selects a part of the used batteries whose degree of deterioration reaches a reference value among the plurality of used batteries as the batteries to be replaced, in addition to the part of the used batteries, the server (20) also selects the used batteries whose degree of deterioration does not reach the reference value but is presumed to reach the reference value within a predetermined period as the used batteries to be replaced.

Description

Technical Field

[0001] The present disclosure relates to a battery management system and a battery management method. Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2018-205873 discloses prompting a user of an electric vehicle having a storage battery suitable for a power storage system to replace the storage battery. Summary of the Invention

[0003] In recent years, the popularization of vehicles equipped with drive batteries has been rapidly developing. Therefore, the number of used batteries (Japanese: chukodenchi) recovered due to replacement, disassembly, etc. of these vehicles has increased. From the viewpoint of promoting sustainable development goals (SDGs: Sustainable Development Goals), it is required to reuse used batteries by manufacturing new battery packs using the recovered used batteries. The inventors have focused on the case where the following problems may occur when reusing used batteries.

[0004] Batteries are stored at a logistics base or the like during the period of waiting for use. Costs are incurred to properly store the batteries. In addition, it may take a certain amount of time (storage period) from the storage of the recovered batteries to their shipment for the next use. Therefore, it is preferable to effectively utilize the storage period of the batteries.

[0005] Therefore, it is conceivable to store and manage a plurality of batteries in a storage facility and charge and discharge the plurality of batteries in response to demand response requirements from the power system. Thereby, the manager of the batteries can receive payment of compensation from the manager of the power system (typically, an electric power company).

[0006] The performance of new batteries is managed substantially uniformly, whereas the deviation of the performance (degree of deterioration) of batteries is large. In addition, if the batteries are charged and discharged as described above, the deterioration of the batteries is accelerated. Therefore, it is required to replace the deteriorated first battery among the plurality of batteries stored in the storage facility with another battery that is not more deteriorated. However, replacing the batteries requires effort and cost.

[0007] The present disclosure has been made to solve the above problems, and an object of the present disclosure is to reduce the effort and cost of replacing batteries in a battery management system and a battery management method.

[0008] (1) A battery management system according to an aspect of the present disclosure includes: a storage, which stores a plurality of batteries; a power conversion device, which is electrically connected between the plurality of batteries stored in the storage and a power system; and a server, which controls the operation of the power conversion device according to a demand response request from the power system, so as to charge and discharge the plurality of batteries. When the server replaces the first battery whose degree of deterioration reaches a reference value among the plurality of batteries, in addition to the first battery, it also selects a second battery that, although its degree of deterioration has not reached the reference value, is presumed to reach the reference value within a predetermined period as the battery to be replaced.

[0009] (2) The above-mentioned first battery includes a battery whose full charge capacity is lower than the reference capacity. When the server replaces the first battery, in addition to the first battery, it also selects a second battery that, although its full charge capacity exceeds the reference capacity at that time point, is presumed to be lower than the reference capacity within a predetermined period as the battery to be replaced.

[0010] In the structures of the above (1) and (2), a battery that, although its degree of deterioration has not reached the reference value at that time point, is presumed to reach the reference value within a predetermined period is also selected as the battery to be replaced. That is, when replacing the first battery whose degree of deterioration reaches the reference value, the second battery that needs to be replaced in the near future is also replaced. Thereby, the number of battery replacements can be reduced. Therefore, the effort and cost of replacing the battery can be reduced.

[0011] (3) When the number of second batteries is more than a predetermined amount, the server preferentially selects a second battery with a smaller full charge capacity as the battery to be replaced compared to a second battery with a larger full charge capacity.

[0012] (4) When the number of second batteries is more than a predetermined amount, the server sequentially selects from the second batteries with a smaller full charge capacity as the battery to be replaced.

[0013] In the structures of the above (3) and (4), the second battery with a smaller full charge capacity is preferentially replaced. Thereby, the recovery amount of the full charge capacity before and after replacement becomes larger, so that the reward obtained from the power system manager accompanying the charge and discharge of the battery can be increased.

[0014] (5) The battery management method for other aspects of the present disclosure is a battery management method using a server. This management method includes a first step and a second step. The first step is a step in which the server charges and discharges a plurality of batteries stored in a storage vault according to a demand response requirement from a power system. The second step is a step in which the server selects a first battery whose degree of deterioration has reached a reference value among the plurality of batteries as the battery to be replaced. The selection step (the second step) includes the following steps: The server selects, in addition to the above-mentioned first battery, a second battery that, although its degree of deterioration has not reached the reference value, is presumed to reach the reference value within a predetermined period as the battery to be replaced.

[0015] According to the method in the above (5), similarly to the structure in the above (1), it is possible to reduce the effort and cost of battery replacement.

[0016] The above and other objects, features, aspects, and advantages of the present invention will become apparent from the following detailed description of the present invention understood in association with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a diagram showing one form of the logistics of the battery pack in the present embodiment.

[0018] Figure 2 It is a diagram showing an example of a case where used batteries are stored in a storage unit.

[0019] Figure 3 It is a flowchart showing an outline of the operation process for reusing used batteries.

[0020] Figure 4 It is a system configuration diagram showing the electrical structure of a battery cellar.

[0021] Figure 5 It is a diagram showing an example of the data structure of battery data.

[0022] Figure 6 It is a diagram for explaining the replacement method of used batteries in the comparative example.

[0023] Figure 7 It is a diagram for explaining the replacement method of used batteries in the present embodiment.

[0024] Figure 8 It is a flowchart showing a first example of the processing steps related to the replacement of used batteries in the present embodiment.

[0025] Figure 9 It is a flowchart showing a second example of the processing steps related to the replacement of used batteries in the present embodiment.

[0026] Figure 10 It is a functional block diagram of a server related to the deterioration evaluation of used batteries.

[0027] Figure 11 It is a functional block diagram of a server related to power adjustment between a battery well and a power system. Detailed implementation manners

[0028] In the present disclosure and embodiments, the charging and discharging of a battery refers to at least one of battery charging and discharging. That is, the charging and discharging of a battery is not limited to both battery charging and discharging, and may be only battery charging or only battery discharging.

[0029] In the present disclosure and embodiments, a battery pack includes a plurality of modules (also referred to as blocks, stacks). The plurality of modules may be connected in series or may be connected in parallel with each other. Each of the plurality of modules includes a plurality of unit cells (single cells).

[0030] Generally, the "reuse" of a battery pack is roughly divided into reuse, reassembly, and material recycling. In the case of reuse, the recovered battery pack undergoes necessary shipping inspections and is directly shipped as a reused product. In the case of reassembly, the recovered battery pack is temporarily disassembled into modules. Then, the usable modules (which may also be modules that can be used after performance recovery) among the disassembled modules are combined to manufacture a new battery pack. The newly manufactured battery pack undergoes shipping inspections and is shipped as a reassembled product. In contrast, in material recycling, renewable materials (resources) are taken out from each unit cell. The recovered battery pack is not used as another battery pack.

[0031] In the embodiments described below, the battery pack recovered from a vehicle is temporarily disassembled into modules. Then, various processes are performed in units of modules. That is, hereinafter, a reusable used battery refers to a module that can be reassembled. However, the disassembly of the module is not necessary. Depending on the structure of the battery pack or the degree of deterioration of the battery pack, it may also be reused without being disassembled into modules.

[0032] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In addition, the same or corresponding parts in the drawings are denoted by the same reference numerals, and their descriptions will not be repeated.

[0033] [Embodiments]

[0034] <Battery logistics model>

[0035] Figure 1 It is a diagram showing one form of the logistics of the battery pack in the present embodiment. Hereinafter, Figure 1The form of the logistics shown is called the "battery logistics model". The battery logistics model 100 includes a recycler 1, a battery well 2, a customer (sales target) 3, a recycling factory 4, a power system 5, and a distributed energy resource (DER) 6.

[0036] The recycler 1 recovers used battery packs (second - hand batteries 9) from multiple vehicles. The recycler 1 can be a vehicle sales store (dealer) or a vehicle dismantler. In addition, in this example, identification information (battery ID) is assigned to each second - hand battery 9 (refer to Figure 5 ). Therefore, in the battery logistics model 100, the second - hand battery 9 can be identified using the battery ID, and data related to the second - hand battery 9 (such as the battery data described later) can be managed or the circulation path of the second - hand battery 9 can be traced.

[0037] The battery well 2 is a facility for appropriately managing the second - hand batteries 9 recovered by the recycler 1, similar to a wine cellar that stores wine bottles under temperature and humidity control. The battery well 2 is set at a logistics base near a port in the Figure 1 example shown. The battery well 2 includes a server 20 for managing data related to the second - hand batteries 9 and multiple storage units 21. In addition, the battery well 2 corresponds to the "battery management system" of the present disclosure. The storage unit 21 corresponds to the "storage vault" of the present disclosure. The batteries stored in the battery well 2 are not limited to second - hand batteries and can also include new batteries.

[0038] Figure 2 is a diagram showing an example of the situation where the second - hand battery 9 is stored in the storage unit 21. As Figure 2 shown, multiple storage units 21 are arranged inside the building of the battery well 2. Each of the multiple storage units 21 is configured to store a large number of second - hand batteries 9. In the present embodiment, the battery well 2 conducts a degradation evaluation test on each second - hand battery 9 stored in the storage unit 21, and the details will be described later. Then, the battery well 2 determines whether each second - hand battery 9 is reusable or not (suitable for reuse or not suitable for reuse) based on the results of the degradation evaluation test.

[0039] Returning to Figure 1 , the customer 3 sells the second - hand batteries 9 determined by the battery well 2 to be reusable. The customer 3 can include a sales store 31 that sells the second - hand batteries 9 for use in vehicles and a user 32 that uses them for fixed use in factories, buildings, etc. In addition, the customer 3 can also include a sales store 33 that sells the second - hand batteries 9 as supplies (replacement parts for maintenance and repair).

[0040] Recycling factory 4 performs material recycling for recycling used batteries 9 determined to be non-recyclable by battery pit 2 as raw materials for other products.

[0041] Power system 5 is a power grid constructed by power generation stations, power transmission and distribution equipment, etc. In this embodiment, the power company serves as both a power generation operator and a power transmission and distribution operator. The power company is equivalent to an ordinary power transmission and distribution operator and is also equivalent to the manager of power system 5, maintaining and managing power system 5. An operator server 50 is provided in power system 5. The operator server 50 belongs to the power company and manages the power supply and demand of power system 5. Server 20 and operator server 50 are configured to be able to communicate bidirectionally.

[0042] DER 6 is a relatively small-scale power device provided at the logistics base (or its surrounding area) where battery pit 2 is provided and capable of exchanging power with battery pit 2. DER 6 includes, for example, a power generation type DER and a power storage type DER.

[0043] The power generation type DER may include a natural variable power source and a generator. The natural variable power source is a power generation device whose power generation output varies according to meteorological conditions. Figure 1 A solar power generation device (solar panel) is illustrated as an example, but the natural variable power source may also replace the solar power generation device or include a wind power generation device in addition to it. On the other hand, a generator is a power generation device that does not depend on meteorological conditions. The generator may include a steam turbine generator, a gas turbine generator, a diesel engine generator, a gas engine generator, a biomass generator, a stationary fuel cell, etc. The generator may also include a cogeneration system that utilizes the heat generated during power generation.

[0044] The power storage type DER may include a power storage system and a heat storage system. The power storage system is a stationary power storage device that stores the power generated by power generation such as a natural variable power source. The power storage system may also be a power-to-gas device that uses power to produce gaseous fuels (hydrogen, methane, etc.). The heat storage system includes a heat storage tank provided between a heat source and a load and is configured to temporarily store the liquid medium in the heat storage tank in a heat-insulated state. By using the heat storage system, the generation and consumption of heat can be staggered in time. Therefore, for example, the heat generated by operating a heat source machine by consuming power at night can be stored in the heat storage tank, and the heat can be consumed during the day for air conditioning.

[0045] In this way, the used batteries 9 recovered by the recycler 1 are stored in the battery well 2 while waiting for shipment to the customers 3 or the recycling factory 4. However, in order to properly store the used batteries 9 in the battery well 2, maintenance costs (operating costs) are also incurred. Moreover, a certain amount of time may be required from the storage of the recovered used batteries 9 to their shipment to the customers 3 or the recycling factory 4. Therefore, it is preferable to effectively utilize the storage period of the used batteries 9 in the battery well 2.

[0046] In the present embodiment, in addition to functioning as a storage place for the used batteries 9, the battery well 2 also functions as a virtual power plant (VPP: Virtual Power Plant). As a result, the opportunity for the used batteries 9 to be charged and discharged serves both as the degradation evaluation of the used batteries 9 that determines the reuse method of the used batteries 9 and as the adjustment of the power supply and demand balance of the power system 5 that utilizes the power of the used batteries 9. As a result, in the battery well 2, the storage of the used batteries 9, the degradation evaluation of the used batteries 9, and the adjustment of the power supply and demand balance based on the used batteries 9 are carried out "in a trinity".

[0047] <Reuse process of used batteries>

[0048] Figure 3 It is a flowchart showing an outline of the operation process for reusing the used batteries 9. First, the used batteries 9 recovered by the recycler 1 are delivered to the battery well 2 (S1).

[0049] In the present embodiment, the server 20 performs a degradation evaluation test (performance inspection) on each used battery 9 while it is stored in the storage unit 21 (S2). The server 20 evaluates the degree of degradation of each used battery 9 based on electrical characteristics such as the full charge capacity and the internal impedance (e.g., AC impedance). Then, the server 20 determines whether each used battery 9 is reusable or non-reusable based on the results of the degradation evaluation test (S3).

[0050] In the present embodiment, the used batteries 9 are classified according to the results of the degradation evaluation test (more specifically, the measurement results of the full charge capacity). For example, as Figure 2 shown, for the used batteries 9 that can be reassembled, they are classified into 4 grades of S grade, A grade, B grade, and C grade in descending order of full charge capacity. As a result, the selling price of the used batteries 9 can be set in association with the grade, and the quality of the used batteries 9 can be guaranteed according to the grade. Therefore, the used batteries 9 passing through the battery well 2 can be smoothly circulated in the market. In addition, for the used batteries 9 with a full charge capacity lower than the specified value, they are classified as lower than the C grade (recorded as Re) and used for material recycling.

[0051] In the case where it is determined that reuse is possible (Yes in S3), the operation process proceeds to the performance recovery process (S4). In the performance recovery process, a process for recovering the performance of the used battery 9 (performance recovery process) is implemented. For example, by overcharging the used battery 9, the full charge capacity of the used battery 9 can be recovered. However, the performance recovery process may be omitted. Alternatively, according to the results of the degradation evaluation test, the performance recovery process may be implemented for the used battery 9 with a large degree of degradation (substantial reduction in performance), while the performance recovery process may not be implemented for the used battery 9 with a small degree of degradation (little reduction in performance).

[0052] Next, a new battery pack is manufactured (reassembled) using the used battery 9 whose performance has been recovered through the performance recovery process (S5). The used battery 9 for reassembling the battery pack is basically the used battery 9 whose performance has been recovered through the performance recovery process, but may also include the used battery 9 for which the performance recovery process has been omitted, and may also include new batteries (new modules). Thereafter, the battery pack is sold and shipped to the customer 3 (S6).

[0053] According to the results of the degradation evaluation test, in the case where it is determined that reuse is not possible (No in S3), the used battery 9 is transported to the recycling factory 4 (S7). In the recycling factory 4, the used battery 9 is disassembled and recycled.

[0054] In this way, during the period from when the used battery 9 is recovered by the recycler 1 until it is delivered to the customer 3 or the recycling factory 4, the used battery 9 is stored in the battery well 2, and the degradation evaluation test is implemented during this period. When measuring electrical characteristics such as the full charge capacity of the used battery 9 in the degradation evaluation test, the used battery 9 is charged and discharged. In the present embodiment, the power received and transmitted between the battery well 2 (and DER6) and the power system 5 is used for this charging and discharging. Thereby, the battery well 2 functions as a VPP (and one of the DERs) and contributes to the load balancing of the power system 5. More specifically, in the time period when there is a surplus of supply over demand in the power system 5, the battery well 2 absorbs the power surplus by charging the used battery 9 with the surplus amount of power. On the other hand, in the case where there is a shortage of supply over demand in the power system 5, the battery well 2 alleviates the power shortage by discharging an amount of power corresponding to the shortage from the used battery 9.

[0055] However, the battery well 2 may not contribute to both the absorption of power surplus and the mitigation of power shortage in the power system 5. The battery well 2 may also be configured to contribute to only one of the absorption of power surplus and the mitigation of power shortage. For example, the battery well 2 may be configured to charge the used battery 9 with the surplus power in the power system 5. On the other hand, the discharge destination of the discharged power from the used battery 9 does not include the power system 5. The discharge destination of the discharged power from the used battery 9 may be only the DER 6, for example.

[0056] <System Structure of Battery Well>

[0057] Figure 4 It is a system structure diagram showing the electrical structure of the battery well 2. The battery well 2 includes, for example, a storage unit 21, an AC / DC converter 22, a DC / DC converter 23, and a server 20. In addition, in Figure 4 order to facilitate the illustration on the drawing, only one storage unit 21 is shown, but as Figure 2 shown, a typical battery well 2 includes a plurality of storage units 21.

[0058] The storage unit 21 houses a plurality of used batteries 9. In Figure 4 the plurality of used batteries 9 are connected in parallel to each other, but this is only an example, and the connection method of the plurality of used batteries 9 is not particularly limited. The plurality of used batteries 9 may be connected in series, or may be combined with series connection and parallel connection. The storage unit 21 includes a voltage sensor 211, a current sensor 212, and a relay 213.

[0059] The voltage sensor 211 detects the voltage VB of the used battery 9 and outputs its detected value to the server 20. The current sensor 212 detects the current IB charged and discharged in the used battery and outputs its detected value to the server 20. In addition, when the temperature is used in the degradation evaluation of the used battery 9, the storage unit 21 may also include a temperature sensor (not shown). In addition, each sensor may also be a sensor provided on the used battery 9.

[0060] The relay 213 includes, for example, a first relay electrically connected to the positive electrode side of the used battery 9 and a second relay electrically connected to the negative electrode side of the used battery 9. The relay 213 is configured to be able to switch the electrical connection and disconnection between the used battery 9 and the power system 5. Thus, any used battery 9 can be electrically disconnected during the charging and discharging of other used batteries 9, and the used battery 9 can be taken out from the storage unit 21.

[0061] The AC / DC converter 22 is electrically connected between the power system 5 and the DC / DC converter 23. The AC / DC converter 22 is configured to be able to perform a bidirectional power conversion operation for charging and discharging the used battery 9 stored in the storage unit according to a control instruction (charge / discharge instruction) from the server 20. More specifically, the AC / DC converter 22 converts the AC power supplied from the power system 5 into DC power for charging the used battery 9. In addition, the AC / DC converter 22 converts the DC power discharged from the used battery 9 into AC power for supplying to the power system 5.

[0062] The DC / DC converter 23 is electrically connected between the AC / DC converter 22 and the storage unit 21, and is also electrically connected between the DER 6 and the storage unit 21. The DC / DC converter 23 is also configured to be able to perform a bidirectional power conversion operation according to a control instruction (charge / discharge instruction) from the server 20, similarly to the AC / DC converter 22. The DC / DC converter 23 can charge the used battery 9 with DC power from the AC / DC converter 22 and / or the DER 6, or discharge the DC power stored in the used battery 9 to the AC / DC converter 22 and / or the DER 6. In addition, the AC / DC converter 22 and the DC / DC converter 23 correspond to the "power conversion device" of the present disclosure.

[0063] The server 20 includes a processor such as a CPU (Central Processing Unit), memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and input / output ports for inputting / outputting various signals (not shown). The server 20 executes various controls based on the signals received from each sensor, the programs stored in the memories, and the maps. The server 20 includes a battery data storage unit 201, a degradation evaluation unit 202, a power adjustment unit 203, a timing adjustment unit 204, and a display unit 205.

[0064] The battery data storage unit 201 stores the battery data for managing the used battery 9 in the battery well 2.

[0065] Figure 5FIG. is an example of a data structure showing battery data. The battery data is stored in a mapping format, for example. The battery data includes, for example, identification information (battery ID) for identifying the used battery 9, the model number of the used battery 9, the manufacturing date, the current SOC (State Of Charge), the full charge capacity, the internal impedance, the grade, the deterioration evaluation date and time (the latest date and time when the deterioration evaluation test was performed), the storage location (identification information of the storage unit in which the used battery 9 is stored), and whether replacement is required (presence or absence of the selection of a battery that needs to be replaced) as parameters. In addition, the battery data may include parameters other than the above (such as the index ΣD indicating the deviation of the salt concentration distribution in the electrolyte of the used battery 9).

[0066] Referring again to Figure 4 , the deterioration evaluation unit 202 performs a deterioration evaluation test on the used battery 9 based on the voltage VB and current IB detected by the voltage sensor 211 and current sensor 212, respectively, during the charge and discharge of the used battery 9. An example of this evaluation method is described in Figure 10 . The deterioration evaluation unit 202 classifies the used battery 9 based on the results of the deterioration evaluation test.

[0067] The power adjustment unit 203 performs power adjustment between the battery well 2 (and DER6) and the power system 5. More specifically, the server 20 selects the used battery 9 that performs charge and discharge in response to a demand response (DR: Demand Response) request from the operator server 50 (refer to Figure 1 ). The power adjustment unit 203 outputs commands to the relay 213, the AC / DC converter 22, and the DC / DC converter 23 in such a way that the selected used battery 9 performs charge and discharge. An example of this control method is described in Figure 11 .

[0068] The timing adjustment unit 204 adjusts the timing of the deterioration evaluation test of the used battery 9 performed by the deterioration evaluation unit 202 and the timing of the power adjustment between the battery well 2 and the power system 5 performed by the power adjustment unit 203. More specifically, the timing adjustment unit 204 performs timing adjustment in such a way that the deterioration evaluation test of the used battery 9 is performed in accordance with the timing of the DR of the battery well 2 in response to a DR request from the operator server 50. In addition, operations performed in accordance with the DR of the battery well 2 are not limited to the deterioration evaluation test of the used battery 9, and performance recovery processing (refer to Figure 3 S4) may also be performed in addition to the deterioration evaluation test.

[0069] The display unit 205 displays battery data according to the operation of the manager of the battery well 2 (which may also be an operator working in the battery well 2) (refer to Figure 5)。In addition, the display unit 205 displays the progress and results of the degradation evaluation test performed by the degradation evaluation unit 202. Thereby, the manager can grasp the status of the degradation evaluation test. Moreover, the display unit 205 displays the state of the used battery 9 selected by the power adjustment unit 203 and being charged and discharged. Thereby, the manager can grasp the status of the power adjustment between the battery well 2 and the power system 5.

[0070] <Replacement of Used Batteries>

[0071] The performance of new batteries is managed approximately uniformly. In contrast, the degree of degradation of the used battery 9 has a large deviation. In addition, if the battery well 2 functions as a VPP, the degradation of the used battery is accelerated along with the charge and discharge of the used battery 9. Therefore, it is preferable to replace a part of the used batteries 9 that have deteriorated (for example, the used batteries 9 that have deteriorated to the extent for material recycling) among the multiple used batteries stored in the storage unit 21 of the battery well 2 with other used batteries that are not more deteriorated. However, the replacement of the used battery 9 takes time and cost.

[0072] Therefore, in the present embodiment, the following structure is adopted: taking the opportunity of replacing a part of the deteriorated used batteries 9, the used batteries that are not overly deteriorated at this time point but are presumed to have accelerated degradation in the near future are also replaced. To make it easier to understand the replacement method of the used batteries adopted in the present embodiment, first, the replacement method of the used batteries in the comparative example will be described.

[0073] Figure 6 is a diagram for explaining the replacement method of the used battery 9 in the comparative example. In Figure 6 and Figure 7 , the horizontal axis represents the elapsed time. The vertical axis represents the full charge capacity of each used battery 9. In this example, for simplicity of explanation, an example in which the number of used batteries 9 stored in the battery well 2 is three will be described. These used batteries 9 are recorded as "First Battery" to "Third Battery". In the order of the First Battery, the Second Battery, and the Third Battery, the degree of degradation is from small to large (the full charge capacity is from large to small).

[0074] In this example, the degradation evaluation tests of the First Battery to the Third Battery are periodically performed. Regarding the full charge capacity of the First Battery to the Third Battery, a reference amount CX is set. The used battery 9 whose full charge capacity is lower than the reference amount CX among the First Battery to the Third Battery is determined as the used battery that needs to be replaced. Hereinafter, these batteries will also be recorded as "batteries to be replaced". The batteries to be replaced correspond to the "used batteries to be replaced" in the present disclosure.

[0075] As Figure 6As shown, let N be a natural number. In the Nth degradation evaluation test, the full charge capacities of the first to third batteries all exceed the reference amount CX. Therefore, it is determined that there is no need to replace the battery. In the subsequent (N + 1)th degradation evaluation test, the full charge capacities of the first and second batteries exceed the reference amount CX. On the other hand, the full charge capacity of the third battery is lower than the reference amount CX. Therefore, the third battery is determined to need replacement. In the (N + 2)th degradation evaluation test, the full charge capacity of the first battery exceeds the reference amount CX. On the other hand, the full charge capacity of the second battery is lower than the reference amount CX. Therefore, the second battery is determined to need replacement. Thus, in the comparative example, the third battery is replaced after the (N + 1)th degradation evaluation test, and the second battery is replaced after the (N + 2)th degradation evaluation test. That is, the replacement of the used battery 9 is performed twice.

[0076] Figure 7 FIG. is a diagram for explaining the replacement method of the used battery 9 in the present embodiment. In the present embodiment, regarding the full charge capacities of the first to third batteries, in addition to the reference amount CX, a reference amount CY larger than the reference amount CX is also set. The reference amount CY can be set, for example, to be higher than the reference amount CX by the amount of decrease in the full charge capacity generated during the implementation interval of the degradation evaluation test. In this way, as a result of performing the degradation evaluation test at a certain point in time, when the full charge capacity is in the range between the reference amount CX and the reference amount CY, it can be presumed that the full charge capacity will be lower than the reference amount CX when the next degradation evaluation test is performed.

[0077] As Figure 7 shown, in the Nth degradation evaluation test, the full charge capacities of the first and second batteries both exceed the reference amount CY. The full charge capacity of the third battery exceeds the reference amount CX but is lower than the reference amount CY. Thus, when there is no used battery with a full charge capacity lower than the reference amount CX, it is determined that there is no need to replace the battery.

[0078] In the (N + 1)th degradation evaluation test, the full charge capacity of the first battery exceeds the reference amount CY. The full charge capacity of the second battery exceeds the reference amount CX but is lower than the reference amount CY. The full charge capacity of the third battery is lower than the reference amount CX. In this case, the third battery is determined to need replacement in the same way as in the comparative example. In addition, in the present embodiment, it is also determined that the second battery needs replacement. This is because the full charge capacity of the second battery exceeds the reference amount CX but is lower than the reference amount CY, so it is presumed that it will be lower than the reference amount CX in the near future (for example, when the next degradation evaluation test is performed).

[0079] In the (N + 2)-th degradation evaluation test, the full charge capacity of the first battery exceeds the reference amount CX (and also exceeds the reference amount CY in this example). Therefore, it is determined that there is no need to replace the battery.

[0080] As described above, in the comparative example, the replacement of the third battery and the replacement of the second battery are performed separately, so a total of 2 replacements of the used battery 9 are made. In contrast, in the present embodiment, the second battery is also replaced (replaced in advance) together with the opportunity to replace the third battery. Thus, only 1 replacement of the used battery 9 is required, and compared with the comparative example, the number of replacements of the used battery 9 can be reduced. Therefore, the effort and cost of replacing the used battery can be reduced.

[0081] <Replacement process of used battery>

[0082] Figure 8 It is a flowchart showing the first example of the processing steps related to the replacement of the used battery 9 in the present embodiment. This flowchart (and other flowcharts described later) is called and executed from the main routine (not shown) when a predetermined condition is satisfied. Each step is implemented by software processing of the server 20, but can also be implemented by hardware (circuit) configured in the server 20. Hereinafter, the steps will be abbreviated as S.

[0083] In S11, the server 20 determines whether the pre-determined replacement research period of the used battery 9 has arrived. The frequency of researching the replacement of the used battery 9 can be, for example, once a day, once a week, or once a month. When the replacement research period of the used battery 9 has not arrived (in S11, "No"), the subsequent processing is skipped and the processing returns to the main routine.

[0084] When the replacement research period of the used battery 9 has arrived (in S11, "Yes"), the server 20 obtains the results (full charge capacity C) of the degradation evaluation tests implemented through other processes for each of the multiple used batteries 9 stored in the battery well 2 (S12). Specifically, the server 20 can read the full charge capacity C from the battery data stored in the battery data storage unit 201.

[0085] In S13, the server 20 determines whether there is a used battery 9 among the multiple used batteries 9 stored in the battery well 2 whose full charge capacity C is less than the reference amount CX. When there is no used battery 9 whose full charge capacity C is less than the reference amount CX (in S13, "No"), the server 20 determines that there is no need to replace the battery (S17).

[0086] In the case where the full charge capacity C of the used battery 9 is less than the reference amount CX (Yes in S13), the server 20 further determines whether there is a used battery 9 whose full charge capacity C is less than the reference amount CY in addition to the used battery 9 whose full charge capacity C is less than the reference amount CX (S14). In the case where there is no used battery 9 whose full charge capacity C is less than the reference amount CY in addition to the used battery 9 whose full charge capacity C is less than the reference amount CX (No in S14), the server 20 selects only the used battery 9 whose full charge capacity C is less than the reference amount CX as the battery to be replaced (S16).

[0087] On the other hand, in the case where there is a used battery 9 whose full charge capacity C is less than the reference amount CY (Yes in S14), that is, in the case where there are both a used battery 9 whose full charge capacity C is less than the reference amount CX and a used battery 9 whose full charge capacity C is equal to or greater than the reference amount CX and less than the reference amount CY, the server 20 selects both of these used batteries 9 as the batteries to be replaced (S15). When the processing of S15 to S17 ends, the server 20 returns the processing to the main routine.

[0088] In addition, in Figures 6 - 8 an example of evaluating the degree of deterioration of the used battery 9 based on the full charge capacity has been described. However, the degree of deterioration of the used battery 9 can also be evaluated based on other indicators such as the internal impedance.

[0089] In the actual operation of the battery well 2, there is an upper limit to the number of used batteries 9 that can be replaced in one replacement opportunity. This upper limit can be determined, for example, according to the number of operators replacing the used battery 9 or the length of the operation time. In the case where the number of used batteries 9 to be replaced exceeds the upper limit, it is required to decide which used battery 9 to select as the battery to be replaced.

[0090] Figure 9 is a flowchart showing a second example of the processing steps related to the replacement of the used battery 9 in the present embodiment. The processing of S21 to S24 is the same as the processing of S11 to S14 in the Figure 8 shown flowchart. In addition, the processing in the case where the determination in S23 is No and the processing in the case where the determination in S24 is No are the same as the processing of S17 and S16 in the above flowchart, respectively. Therefore, detailed descriptions are not repeated.

[0091] In the case where there are both a used battery 9 whose full charge capacity C is less than the reference amount CX and a used battery 9 whose full charge capacity C is equal to or greater than the reference amount CX and less than the reference amount CY (Yes in S24), the server 20 proceeds to S25.

[0092] In S25, the server 20 determines whether the total number of used batteries 9 that satisfy the conditions determined to be "Yes" in S23 and S24, that is, the total number of used batteries 9 with a full charge capacity C less than the reference amount CX and the total number of used batteries 9 with a full charge capacity C equal to or greater than the reference amount CX and less than the reference amount CY, exceeds the upper limit. When the total number is equal to or less than the upper limit (in S25, "No"), the server 20 selects all used batteries 9 with a full charge capacity C less than the reference amount CX and all used batteries 9 with a full charge capacity C equal to or greater than the reference amount CX and less than the reference amount CY as the batteries that need to be replaced (S27).

[0093] In contrast, when the total number exceeds the upper limit (in S25, "Yes"), the server 20 selects all used batteries 9 with a full charge capacity C less than the reference amount CX as the batteries that need to be replaced, and also selects used batteries 9 with a full charge capacity C equal to or greater than the reference amount CX and less than the reference amount CY as the batteries that need to be replaced within the range where the number of replaced used batteries does not exceed the upper limit (S26). More specifically, the smaller the full charge capacity of the used battery 9, the higher the priority order for the server 20 to select it as the battery that needs to be replaced. For example, the server 20 can select a number of used batteries 9 not exceeding the upper limit from the used batteries 9 arranged in ascending order of full charge capacity.

[0094] By preferentially replacing the used battery 9 with a small full charge capacity in this way, the recovery amount of the full charge capacity of the replaced used battery (the difference between the full charge capacity after replacement and the full charge capacity before replacement) becomes larger. In this way, when the battery well 2 functions as a VPP, the amount of power that the battery well 2 can charge and discharge becomes larger, so the remuneration obtained from the power company can be increased. Therefore, the operating profit of the battery well 2 can be increased.

[0095] <Deterioration evaluation>

[0096] Figure 10 It is a functional block diagram of the server 20 (deterioration evaluation unit 202) related to the deterioration evaluation of the used battery 9. Hereinafter, for the sake of simplicity of explanation, one used battery 9 will be focused on for explanation. However, in fact, when there are multiple used batteries 9 for which deterioration evaluation has not been performed, the same processing can be performed on these used batteries 9 simultaneously. The deterioration evaluation unit 202 includes a current integration unit 71, an OCV (Open Circuit Voltage) calculation unit 72, an SOC change amount calculation unit 73, a full charge capacity calculation unit 74, and a classification unit 75.

[0097] The current integration unit 71 calculates the integrated value (current integration amount) ΔAh (unit: Ah) of the current charged and discharged in the used battery 9 during the period from when the start condition for current integration is satisfied to when the end condition is satisfied, based on the current IB detected by the current sensor 212. In the present embodiment, as described above, charging and discharging of the used battery 9 are performed according to the DR request from the operator server 50, and the current flowing during this DR is integrated. More specifically, in the case of performing an increased DR (request for an increase in power demand), the used battery 9 is charged to increase the power demand of the battery well 2, and the charging current at this time is integrated. On the other hand, in the case of performing a decreased DR, the used battery 9 is discharged to reduce the power demand of the battery well 2, and the discharge current at this time is integrated. The current integration unit 71 outputs the calculated current integration amount ΔAh to the full charge capacity calculation unit 74.

[0098] The OCV calculation unit 72 calculates the OCV of the used battery 9 at the start of current integration and the OCV of the used battery 9 at the end of current integration. The OCV can be calculated, for example, according to the following formula (1).

[0099] OCV = VB - ΔVp - IB × R…(1)

[0100] In formula (1), the internal impedance of the used battery 9 is denoted as R, and the polarization voltage is denoted as Vp. At the start of current integration (just before starting charging and discharging), the current IB = 0. In addition, when the used battery 9 is placed without being charged or discharged before the start of current integration, it can be approximated that the polarization voltage Vp ≈ 0. Therefore, the OCV at the start of current integration can be calculated based on the voltage VB detected by the voltage sensor 211. On the other hand, regarding the internal impedance R, it can be determined according to the relationship (Ohm's law) between the voltage VB and the current IB. In addition, when the charging and discharging of the used battery 9 are performed at a constant current, by previously measuring the relationship between the current and the polarization voltage Vp, the polarization voltage Vp can also be determined according to the current IB detected by the current sensor 212. Therefore, the OCV of the used battery 9 at the end of current integration can also be calculated based on the voltage VB and the current IB. The OCV calculation unit 72 outputs the two calculated OCVs to the SOC change amount calculation unit 73.

[0101] The SOC change amount calculation unit 73 calculates the SOC change amount ΔSOC of the used battery 9 during the period from the start of current integration to the end of current integration based on two types of OCVs. The SOC change amount calculation unit 73 previously has a characteristic curve (OCV-SOC curve) indicating the SOC dependency of the OCV. Therefore, the SOC change amount calculation unit 73 can read the SOC corresponding to the OCV at the start of current integration and the SOC corresponding to the OCV at the end of current integration by referring to the OCV-SOC curve, and calculate the difference between these SOCs as ΔSOC. The SOC change amount calculation unit 73 outputs the calculated ΔSOC to the full charge capacity calculation unit 74.

[0102] The full charge capacity calculation unit 74 calculates the full charge capacity C of the used battery 9 based on ΔAh from the current integration unit 71 and ΔSOC from the SOC change amount calculation unit 73. Specifically, the full charge capacity C of the used battery 9 can be calculated according to the following formula (2) in which the ratio of ΔAh to ΔSOC is set equal to the ratio of the full charge capacity C to ΔSOC = 100%. In addition, since the full charge capacity C0 in the initial state is known from the specifications of the used battery 9, the full charge capacity calculation unit 74 can further calculate the capacity retention rate Q (Q = C / C0) based on the full charge capacity C. The full charge capacity calculation unit 74 outputs the calculated full charge capacity C to the grading unit 75.

[0103] C = ΔAh / ΔSOC × 100…(2)

[0104] The grading unit 75 grades the used battery 9 based on the full charge capacity C. The grading unit 75 can record the date and time of grading as the deterioration evaluation date and time in the battery data (refer to Figure 5 ).

[0105] The grade of the used battery 9 is displayed on the display unit 205 together with the battery ID, storage location, etc. of the used battery 9. Thus, when a request to purchase the used battery 9 is received from the customer 3, the operator working in the battery well 2 can take out the used battery 9 of the grade that meets the requirements of the customer 3 from the storage location. By appropriately taking out the used batteries for sale from the storage unit 21, the situation where there is no vacancy in the storage unit 21 can be suppressed.

[0106] In addition, the method for calculating the full charge capacity C described above is merely an example. In calculating the full charge capacity C, any method can be adopted as long as it uses the voltage VB and current IB detected during the charge and discharge of the used battery 9. Additionally, instead of or in addition to the full charge capacity C, the grade of the used battery 9 can be determined based on other characteristics (such as the internal impedance of the used battery 9, an index ΣD representing the deviation of the electrolyte concentration in the lithium-ion battery, etc.). Further, the grading unit 75 can also determine the grade of the used battery 9 according to the length of time the used battery 9 is charged and discharged and / or the number of times the used battery 9 is charged and discharged. Although the accuracy may slightly decrease, the grading unit 75 can also determine the grade of the used battery 9 according to the elapsed time since the manufacture of the used battery 9. The grading unit 75 can also combine the above-mentioned various elements (full charge capacity C, internal impedance R, index ΣD, charge and discharge time, number of charge and discharge cycles, elapsed time since manufacture, etc.) to determine the grade of the used battery 9.

[0107] <Power adjustment>

[0108] Figure 11 It is a functional block diagram of the server 20 (power adjustment unit 203) related to the power adjustment between the battery well 2 and the power system 5. In this example, for ease of understanding, it is assumed that the DER 6 is a power generation type DER (especially a natural variable power source such as a solar power generation device) for explanation. The power adjustment unit 203 includes an overall adjustment amount calculation unit 81, a DER adjustment amount calculation unit 82, a battery well adjustment amount calculation unit 83, a used battery selection unit 84, a conversion operation unit 85, and an instruction generation unit 86.

[0109] The overall adjustment amount calculation unit 81 receives a DR request from the operator server 50 and calculates the total amount of electric power that needs to be adjusted using the battery well 2 and the DER 6 within a predetermined period (for example, 30 minutes). Hereinafter, this amount of electric power is referred to as the overall adjustment amount and is also denoted as kWh(total). The overall adjustment amount calculation unit 81 outputs the calculated kWh(total) to the battery well adjustment amount calculation unit 83.

[0110] The DER adjustment amount calculation unit 82 obtains the operating state of each DER 6 (more specifically, the expected amount of electric power generated by each DER 6 during the predetermined period) through communication with the DER 6. Hereinafter, this amount of electric power is referred to as the DER adjustment amount and is also denoted as kWh(DER). The DER adjustment amount calculation unit 82 outputs the obtained kWh(DER) to the battery well adjustment amount calculation unit 83.

[0111] The battery well adjustment amount calculation unit 83 calculates the amount of power that needs to be adjusted using the battery well 2 based on kWh(total) from the overall adjustment amount calculation unit 81 and kWh(DER) from the DER adjustment amount calculation unit 82. Hereinafter, this amount of power will be referred to as the battery well adjustment amount, and is also denoted as kWh(bat). The battery well adjustment amount calculation unit 83 can, for example, calculate the battery well adjustment amount kWh(bat) as the difference between the above two amounts of power, i.e., ΔkWh = kWh(total) - kWh(DER). The battery well adjustment amount calculation unit 83 outputs the calculated kWh(bat) to the used battery selection unit 84.

[0112] The used battery selection unit 84 grasps the charge-dischargeable amount of power for each of the multiple used batteries 9 stored in the multiple storage units 21 (refer to Figure 5 the battery data). The used battery selection unit 84 selects the used batteries to be used in power adjustment from the multiple used batteries 9 based on kWh(bat) from the battery well adjustment amount calculation unit 83. When kWh(bat) > 0, the power shortage of the power system 5 is supplemented by discharging from the battery well 2. Therefore, the used battery selection unit 84 selects the number of used batteries 9 that can discharge a power amount of kWh(bat) or more. On the other hand, when kWh(bat) < 0, the power surplus of the power system 5 is absorbed by charging the battery well 2. Therefore, the used battery selection unit 84 selects the number of used batteries 9 that can charge a power amount of kWh(bat) (absolute value) or more. When selecting the used batteries 9, priority is given to charging and discharging the used batteries 9 of the grade with low demand. On the other hand, charging and discharging of the used batteries 9 of the grade with high demand are avoided as much as possible. The details of this processing content are described in Figures 8 - 10 and will not be repeated here. The used battery selection unit 84 outputs the selected used batteries 9 and the amount of power assigned to each of the selected used batteries 9 (the amount of power adjusted by each used battery 9) to the conversion calculation unit 85.

[0113] The conversion calculation unit 85 calculates the power to be charged and discharged in each of the used batteries 9 selected by the used battery selection unit 84. More specifically, the conversion calculation unit 85 converts the amount of power (unit: kWh) adjusted by each used battery 9 into power (unit: kW) using the remaining time of power adjustment for each used battery 9. As an example, when the power adjustment amount assigned to a certain used battery 9 is 10 kWh and the remaining time of power adjustment is 15 minutes, it can be calculated as 10 kWh × (60 minutes / 15 minutes) = 40 kW. The conversion calculation unit 85 outputs the power to be charged and discharged in each used battery 9 to the command generation unit 86.

[0114] The instruction generation unit 86 generates charge / discharge instructions for the AC / DC converter 22 and the DC / DC converter 23 based on the operation result of the conversion operation unit 85, and also generates opening / closing instructions for the relay 213. More specifically, in addition, the instruction generation unit 86 generates the opening / closing instructions in such a manner that the selected used battery 9 is electrically connected to the DC / DC converter 23, while the unselected used battery 9 is electrically disconnected from the DC / DC converter 23. The instruction generation unit 86 generates the charge / discharge instructions in such a manner that charging and discharging are performed with the total of the power allocated to the selected used battery 9.

[0115] In addition, it is noted that Figure 11 The power adjustment method shown is merely an example. In this example, a situation is assumed where the DER 6 is a power generation type DER, particularly a natural power source whose power generation amount cannot be controlled. Therefore, the battery well adjustment amount calculation unit 83 calculates the battery well adjustment amount kWh(bat) based on the difference kWh(total) - kWh(DER) obtained by subtracting the DER adjustment amount kWh(DER) from the overall adjustment amount kWh(total). That is, in this example, after determining the DER adjustment amount kWh(DER), the battery well adjustment amount kWh(bat) is used for the final power adjustment. However, for example, when the DER 6 includes a power storage type DER, the battery well adjustment amount calculation unit 83 may also allocate the overall adjustment amount kWh(total) to the DER adjustment amount kWh(DER) and the battery well adjustment amount kWh(bat), and use both the DER adjustment amount kWh(DER) and the battery well adjustment amount kWh(bat) for power adjustment.

[0116] As described above, in the present embodiment, the degree of deterioration of each used battery 9 is evaluated while being stored in the storage unit 21. Thereby, the storage period of the used battery 9 can be effectively utilized in terms of time. Moreover, the charging and discharging of the used battery 9 for evaluating the degree of deterioration of the used battery 9 are basically performed according to the DR request from the operator server 50. In addition, when the number of used batteries 9 is large, a large amount of power is charged and discharged, and this large amount of power is transferred between the battery well 2 and the power system 5 according to the DR request from the operator server 50. As a result, the operating company of the battery well 2 can receive payment (rewards) from the power company, and thus can use this reward as the operating cost of the battery well 2. Or, the operating company of the battery well 2 can recover a part of the initial investment (initial cost) of the battery well 2. Thereby, the storage period of the used battery 9 can also be effectively utilized financially.

[0117] In addition, in the present embodiment, together with the opportunity to replace a part of the used battery 9 with increased deterioration, the used battery 9 that is presumed to deteriorate in the near future is replaced in advance. Thus, compared with the case where no advance replacement is performed, the number of replacements of the used battery 9 can be reduced. Therefore, the labor and cost of replacing the used battery 9 can be reduced.

[0118] Moreover, in the present embodiment, with respect to the used battery 9 that is presumed to deteriorate in the near future, the used battery 9 is preferentially replaced in ascending order of full charge capacity. In this way, with the replacement, the full charge capacity of the used battery 9 is greatly restored. Therefore, when the battery well 2 functions as a VPP, the amount of power that the battery well 2 can charge and discharge becomes larger. Therefore, the remuneration from the power company can be increased.

[0119] The embodiments of the present invention have been described, but it should be considered that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A battery management system, wherein, Comprising: A storage vault that stores a plurality of batteries; A power conversion device electrically connected between the plurality of batteries stored in the storage vault and a power system; And A server that controls the operation of the power conversion device according to a demand response request from the power system, thereby charging and discharging the plurality of batteries, The server: Determines whether there is a first battery among the plurality of batteries stored in the storage vault whose degree of deterioration reaches a reference value; Determines whether there is a second battery among the plurality of batteries stored in the storage vault that is not considered to have reached the reference value but is presumed to reach the reference value within a predetermined period as a battery to be replaced; Determines whether the total number of the first battery and the second battery exceeds the upper limit of the number of batteries that can be replaced in one replacement opportunity, and the upper limit is determined according to the number of operators for replacing batteries or the length of the operation time; When the total number is below the upper limit, selects all of the first battery and all of the second battery as batteries that need to be replaced; And When the total number exceeds the upper limit, selects all of the first battery and a part of the second battery within the range where the number of batteries to be replaced does not exceed the upper limit as batteries that need to be replaced, The first battery includes a battery whose full charge capacity is lower than the reference capacity, When the server replaces the first battery, in addition to the first battery, it also selects a second battery that, although its full charge capacity exceeds the reference capacity at that time point, is presumed to have a full charge capacity lower than the reference capacity within the predetermined period as the battery to be replaced; When the number of the second batteries is more than a predetermined amount, the server preferentially selects a second battery with a smaller full charge capacity as the battery to be replaced compared to a second battery with a larger full charge capacity.

2. The battery management system according to claim 1, wherein When the number of the second batteries is more than the predetermined amount, the server sequentially selects from the second batteries with a smaller full charge capacity as the batteries to be replaced.

3. A battery management method, which is a battery management method using a server, wherein, The battery management method includes: The server charges and discharges a plurality of batteries stored in a storage vault according to a demand response request from a power system; The server determines whether there is a first battery among the plurality of batteries stored in the storage vault whose degree of deterioration reaches a reference value; The server determines whether there is a second battery among the plurality of batteries stored in the storage vault that is not considered to have reached the reference value but is presumed to reach the reference value within a predetermined period as a battery to be replaced; The server determines whether the total number of the first battery and the second battery exceeds the upper limit of the number of batteries that can be replaced in one replacement opportunity, and the upper limit is determined according to the number of operators for replacing batteries or the length of the operation time; When the total number is below the upper limit, the server selects all of the first battery and all of the second battery as batteries that need to be replaced; and In the case where the total quantity exceeds the upper limit, the server selects all of the first batteries and a part of the second batteries within the range where the replaced batteries do not exceed the upper limit as the batteries that need to be replaced. The first battery includes a battery with a full charge capacity lower than the reference capacity. When the server replaces the first battery, in addition to the first battery, the server also selects the second battery that, although the full charge capacity exceeds the reference capacity at this time point, is presumed to have a full charge capacity lower than the reference capacity within the predetermined period as the battery to be replaced. When the number of the second batteries is more than the predetermined quantity, the server preferentially selects a second battery with a smaller full charge capacity as the battery to be replaced compared to a second battery with a larger full charge capacity.

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