Power storage system and control method for charge / discharge

Abstract

To provide a power storage system and a control method for charge / discharge.SOLUTION: A power storage system comprises: a plurality of power converters; a plurality of power storage elements charged / discharged via the plurality of power converters; a connection circuit by which a power storage element selected as a maintenance target from among the plurality of power storage elements is connected to one power converter via a first path and the other power storage element is connected to the other power converter via a second path different from the first path; and a control device which executes maintenance via the first path while successively switching the power storage element to be selected as the maintenance target and executes charge / discharge with respect to the other power storage element via the second path.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electricity storage system and a method for controlling charging and discharging. [Background technology]

[0002] 2. Description of the Related Art The use of energy storage elements in large-scale energy storage systems that store electricity generated by renewable energy or existing power generation systems is expanding.

[0003] The operation of energy storage elements requires maintenance work, including periodic inspections for deterioration diagnosis, etc. Patent Document 1 discloses a system in which a maintenance worker goes to the installation site of equipment including energy storage elements and can easily obtain status data of the energy storage elements using a terminal device carried by the maintenance worker.

[0004] In periodic inspections by maintenance workers, status checks, including visual checks, are carried out, and a report is created based on the status data of the storage elements acquired by a terminal device and the status checks at the installation site. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6402925 Summary of the Invention [Problem to be solved by the invention]

[0006] However, large-scale ESS (Energy Storage System) is equipped with a huge number of storage elements, and it is not realistic for maintenance workers to shut down the system for maintenance inspection and maintain and inspect the huge number of storage elements.

[0007] An object of the present invention is to provide an electricity storage system and a method for controlling charging and discharging that can perform maintenance automatically without shutting down the system. [Means for solving the problem]

[0008] An energy storage system according to one embodiment of the present invention includes a plurality of power converters, a plurality of energy storage elements which are charged and discharged via the plurality of power converters, a connection circuit which connects a storage element selected as a maintenance target among the plurality of energy storage elements to one power converter via a first path and connects the other energy storage elements to the other power converter via a second path different from the first path, and a control device which sequentially switches between the storage elements selected as the maintenance target, performs maintenance via the first path, and charges and discharges the other energy storage elements via the second path.

[0009] A charging / discharging control method according to one embodiment of the present invention sequentially selects a storage element to be maintained from a plurality of storage elements that are charged / discharged via a plurality of power converters, connects the selected storage element to one of the plurality of power converters via a first path, and connects the other storage elements to the other power converters via a second path different from the first path, performs maintenance on the selected storage element via the first path, and performs charging / discharging on the other storage elements via the second path. Effect of the Invention

[0010] According to the above aspect, maintenance can be performed automatically without shutting down the system. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic explanatory diagram illustrating an example of installation of a power storage system according to an embodiment. [Diagram 2] FIG. 1 is a circuit diagram showing a configuration example of a power storage system. [Diagram 3] FIG. 13 is a schematic diagram showing a connection state when charging and discharging are performed without maintenance. [Figure 4] FIG. 13 is a schematic diagram showing a connection state when charging and discharging while performing maintenance. [Diagram 5]FIG. 13 is a schematic diagram showing a connection state when charging and discharging while performing maintenance. [Figure 6] FIG. 13 is a schematic diagram showing a connection state when charging and discharging while performing maintenance. [Figure 7] 4 is a flowchart showing a control procedure in the first embodiment. [Figure 8] 10 is a flowchart showing a control procedure in the second embodiment. [Figure 9] 13 is a flowchart showing a control procedure in the third embodiment. [Figure 10] FIG. 13 is a schematic diagram showing an example of installation of a power storage system according to a fourth embodiment. [Figure 11] FIG. 13 is a schematic diagram showing an example of installation of a power storage system according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (1) The energy storage system of the present disclosure includes a plurality of power converters, a plurality of energy storage elements which are charged and discharged via the plurality of power converters, a connection circuit which connects a storage element selected as a maintenance target among the plurality of energy storage elements to one power converter via a first path and connects the other energy storage elements to the other power converters via a second path different from the first path, and a control device which sequentially switches between the energy storage elements selected as the maintenance target, performs maintenance via the first path, and charges and discharges the other energy storage elements via the second path.

[0013] The above-mentioned (1) power storage system is installed in parallel with a power generation facility such as a solar power generation facility or a wind power generation facility, stores power supplied from the power generation facility, and supplies the stored power to a load. The power storage system includes a plurality of power converters and power storage elements. The power converter is, for example, a power conditioner (PCS: Power Conditioning System), and converts DC power supplied from the power generation facility into DC power of a predetermined magnitude and charges the power storage element with the converted DC power. The power converter converts DC power discharged from the power storage element into AC power and supplies the converted AC power to the load. The power storage element includes a secondary battery such as a lead-acid battery or a lithium-ion battery, or a storage cell capable of charging and discharging, such as a capacitor. The power storage element may be a module in which a plurality of power storage elements are connected in series, a bank in which modules are connected in series, a domain in which a plurality of banks are connected in parallel, or the like.

[0014] The energy storage system performs maintenance on a plurality of energy storage elements by sequentially switching between the energy storage elements to be maintained. The energy storage element selected as the maintenance target is connected to one power converter via a first path, and the other energy storage elements are connected to other power converters via a second path. In the energy storage system of (1) above, the path for maintenance (first path) and the path for charging and discharging (second path) can be made different, so that maintenance can be performed on each energy storage element without stopping the original function (charging and discharging function) of the energy storage system.

[0015] Either one or more energy storage devices may be selected as the maintenance target. In the latter case, maintenance is performed simultaneously on the selected energy storage elements, and charging and discharging are performed using the remaining energy storage elements.

[0016] In the energy storage system described in (1) above, maintenance can be automated, eliminating the need for maintenance workers to visit the installation site of the energy storage system. Data showing the state of the energy storage device at the time of maintenance can be acquired remotely and analyzed without visiting the installation site. Maintenance workers do not need to visually check the energy storage elements, reducing human error.

[0017] (2) In the power storage system described above in (1), the plurality of power storage elements may include reused power storage elements.

[0018] It is known that repeated charging and discharging of energy storage elements leads to deterioration. Depending on the cause of deterioration, some energy storage elements may not be suitable for large current applications, but may be suitable for small current applications and may be reused for a different purpose. For example, an energy storage element in which the increase in electrical resistance is the cause of deterioration and the decrease in charge carriers is not progressing is considered to have a storable amount of electricity that has not decreased since its manufacture. Such energy storage elements can be reused to store electricity generated by power generation facilities such as solar power generation facilities and wind power generation facilities. In the energy storage system of (2) above, reused energy storage elements can be incorporated during the manufacture or maintenance of the system, allowing the reused energy storage elements to be effectively utilized.

[0019] (3) In the energy storage system described in (2) above, the control device may control the connection circuit to connect the reused energy storage element to the one power converter via the first path in order to perform maintenance before the reused energy storage element is charged or discharged for the first time in the energy storage system, and perform maintenance via the first path.

[0020] In the energy storage system of (3) above, when a reused energy storage element is incorporated into the energy storage system, maintenance is performed by isolating it from other energy storage elements, and if there are no problems, it is connected to other energy storage elements for charging and discharging, thereby avoiding the risk of malfunctions. Since new energy storage elements are inspected before shipping, advance inspection before incorporation into the energy storage system is generally not required. On the other hand, when a reused energy storage element is incorporated into the energy storage system, advance inspection has traditionally been performed to check the performance of the storage element. In contrast, in the energy storage system of (3) above, the energy storage system itself serves as an inspection device, so advance inspection is not required even if the energy storage element incorporated into the system is a reused product.

[0021] (4) In the energy storage system described in (2) above, the control device may control the connection circuit to connect the reused energy storage element to the one power converter via the first path so as to charge the reused energy storage element before connecting it to other energy storage elements, and may perform charging of the reused energy storage element via the first path.

[0022] In the energy storage system (4) above, when a reused energy storage element is incorporated into the energy storage system, it can be charged separately from the other energy storage elements, so that the voltage can be adjusted before connecting to the other energy storage elements, and it is possible to prevent a large current from flowing into the reused energy storage element. In the energy storage system (4) above, if the voltage of a reused energy storage element is high, the storage element can be separated from the other energy storage elements and discharged. The voltage of a new energy storage element is often known in advance, but the voltage of a reused energy storage element is often unknown. If the voltage of a reused energy storage element is high, it can be separated from the other energy storage elements already incorporated into the energy storage system and discharged to match the voltage of these storage elements.

[0023] (5) In the energy storage system according to any one of (1) to (4) above, the maintenance may include a capacity test on a selected energy storage element.

[0024] In the above-mentioned (5) energy storage system, a capacity test is performed as maintenance for the energy storage system. The capacity test is a test in which the battery is discharged to a voltage defined as zero remaining battery power, and the energy storage element is charged from that state to a voltage defined as fully charged with a constant current to measure the capacity. Since capacity measurement takes time, it is preferable to perform the capacity test automatically using the method disclosed herein. As maintenance for the energy storage system, it is possible to inspect whether a short circuit has occurred in a module or bank including the energy storage element, or to inspect whether an internal short circuit has occurred in the energy storage element itself. Alternatively, as maintenance for the energy storage system, it is possible to inspect whether communication between the energy storage system and the outside is normal.

[0025] (6) The charging and discharging control method disclosed herein sequentially selects a storage element to be maintained from a plurality of storage elements that are charged and discharged via a plurality of power converters, connects the selected storage element to one of the plurality of power converters via a first path, and connects the other storage elements to the other power converters via a second path different from the first path, performs maintenance on the selected storage element via the first path, and performs charging and discharging on the other storage elements via the second path.

[0026] In the charge / discharge control method described above in (6), the maintenance path (first path) and the charge / discharge path (second path) are switched and maintenance is performed automatically, eliminating the need for a maintenance worker to visit the installation site of the energy storage system. Data showing the state of the energy storage device when maintenance is performed can be acquired and analyzed remotely, eliminating the need for a maintenance worker to visually check the energy storage elements, and reducing human error.

[0027] Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof. (Embodiment 1) Fig. 1 is a schematic explanatory diagram illustrating an example of installation of a power storage system 1 according to an embodiment. The power storage system 1 according to the embodiment includes a plurality of power converters 11 and a plurality of power storage elements 12 that are charged and discharged via the plurality of power converters 11 (see Fig. 2). The power converters 11 and the power storage elements 12 included in the power storage system 1 are housed together in, for example, one container. Alternatively, the power storage system 1 may be configured to include a plurality of containers that house the power converters 11 individually, and a plurality of containers that house the power storage elements 12 individually.

[0028] The power storage system 1 is installed alongside a power generation facility such as a solar power generation facility PV or a wind power generation facility WT. The power storage system 1 converts power supplied from the power generation facility into DC power of a predetermined magnitude using a power converter 11, and stores the power by charging the power storage element 12 with the converted DC power. The power storage system 1 converts DC power discharged from the power storage element 12 into AC power using the power converter 11, and supplies the converted AC power to a load PC. The power supply source to the power storage system 1 and the power supply destination of the power storage system 1 may be a power grid PS.

[0029] The power storage system 1 is communicatively connected to a management server 2 and a user server 3 via a communication network NW. The management server 2 is a server operated by an administrator of the power storage system 1, etc. The user server 3 is a server operated by a user, an aggregator, etc. The communication network NW is a general communication network such as the Internet. Alternatively, the communication network NW may be a dedicated line.

[0030] The management server 2 communicates with the user server 3 via the communication network NW to acquire information on power demand. The information on power demand includes, for example, information such as the amount of power to be supplied to the load PC (power request amount for each time period). The management server 2 communicates with the power storage system 1 via the communication network NW to acquire information on the operating state of the power storage system 1. The information on the operating state of the power storage system 1 includes, for example, information such as the current status of the power storage element 12, time transition of SOC (State Of Charge) and SOH (State of Health), charge / discharge execution history, and maintenance execution history. The information acquired by the management server 2 from the power storage system 1 may be notified to the user server 3. The management server 2 may predict the future power supply amount (load) based on the information acquired from the power storage system 1 and the user server 3, and may give the power storage system 1 an instruction to switch between charge and discharge or an instruction to start maintenance.

[0031] 2 is a circuit diagram showing a configuration example of the power storage system 1. The power storage system 1 includes a plurality of power converters 11 and a plurality of power storage elements 12 that are charged and discharged via the plurality of power converters 11. The power converters 11 have a function of converting power supplied from a power generation facility into DC power of a predetermined magnitude and outputting it to the power storage elements 12, and a function of converting the DC power discharged from the power storage elements 12 into AC power and outputting it to the outside (for example, a load PC). The power converters 11 are also called a PCS (Power Conditioning System).

[0032] The storage element 12 is a bank formed by connecting a large number of storage cells in series. The storage cells are, for example, battery cells formed by lithium ion secondary batteries. Alternatively, the storage cells may be battery cells formed by all-solid-state batteries, lead batteries, redox flow batteries, zinc-air batteries, alkaline manganese batteries, lithium-sulfur batteries, sodium-sulfur batteries, silver-zinc oxide batteries, nickel-metal hydride batteries, molten salt thermal batteries, etc., or may be capacitors. Alternatively, the storage element 12 may be a single storage cell, or may be a module formed by connecting a plurality of storage cells in series. The storage element 12 may be a domain formed by connecting a plurality of banks in parallel.

[0033] In the embodiment, a configuration will be described in which the power storage system 1 includes three each of power converters 11 and power storage elements 12. In the following, when the power converters 11 are to be described separately, they will also be referred to as power converters 11A to 11C, and when the power storage elements 12 are to be described separately, they will also be referred to as power storage elements 12A to 12C.

[0034] The power storage system 1 includes, in addition to a power converter 11 and a power storage element 12, a control unit 10, a connection circuit L, and BMUs (Battery Management Units) 13A to 13C.

[0035] The control unit 10 is a control device for controlling the operation of the power storage system 1. The control unit 10 includes, for example, a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). The CPU included in the control unit 10 reads and executes a computer program stored in the ROM, thereby controlling charging and discharging operations and maintenance operations in the power storage system 1. The RAM temporarily stores data generated during the execution of the computer program and data acquired from the outside.

[0036] The control unit 10 may include a communication interface. The communication interface of the control unit 10 includes an internal communication interface for communicating with the power converter 11 and the BMUs 13A-13C and outputting control signals for opening and closing the various switches SW1, SW2, SW1A-SW1C, and SW2A-SW2C. The communication interface of the control unit 10 may include an external communication interface for communicating with the management server 2 and the user server 3 via the communication network NW.

[0037] The control unit 10 may further include a clock that outputs date and time information, a timer that measures elapsed time, a counter that counts numbers, and the like.

[0038] The connection circuit L is a circuit that connects the power converter 11 and the storage element 12. The connection circuit L includes a path L1 (first path) for maintenance and a path L2 (second path) for charging and discharging. The path L1 is provided with a switch SW1 and switches SW1A to SW1C that are controlled to be opened and closed by the control unit 10. The path L2 is provided with a switch SW2 and switches SW2A to SW2C that are controlled to be opened and closed by the control unit 10. These switches SW1, SW2, SW1A to SW1C, and SW2A to SW2C are relay switches, for example. Alternatively, they may be semiconductor switches.

[0039] BMUs 13A to 13C are management devices provided corresponding to each of energy storage elements 12A to 12C. BMUs 13A to 13C monitor the state of each of energy storage elements 12A to 12C, and notify control unit 10 of the obtained data of energy storage elements 12A to 12C.

[0040] In the energy storage system 1 according to the embodiment, a control unit 10 controls the opening and closing of each switch SW1, SW2, SW1A to SW1C, and SW2A to SW2C to switch between a path for charging and discharging without maintenance and a path for charging and discharging while performing maintenance.

[0041] FIG. 3 is a schematic diagram showing a connection state when charging and discharging without maintenance. For simplification, FIG. 3 shows only the connection relationship between the power converter 11 and the storage element 12. When charging and discharging the storage element 12 without maintenance, the control unit 10 opens the switches SW1, SW1A to SW1C on the path L1 and closes the switches SW2, SW2A to SW2C on the path L2. In this connection state, when the storage element 12 is charged, the power supplied from the power generation facility is converted by the power converter 11 into DC power of a predetermined magnitude and output to the storage element 12 via the path L2. The storage element 12 is charged by the DC power supplied via the path L2.

[0042] 3 shows an example of charging the storage element 12, the same applies to discharging from the storage element 12. When discharging from the storage element 12, the DC power output from the storage element 12 is input to the power converter 11 via the path L2, converted to AC power by the power converter 11, and then supplied to the destination load PC.

[0043] 4 to 6 are schematic diagrams showing a connection state when charging and discharging are performed while performing maintenance. For simplification, only the connection relationship between the power converter 11 and the energy storage element 12 is shown in FIG. 4 to FIG. 6. FIG. 4 shows a connection state when the energy storage element 12A is maintained while the energy storage elements 12B and 12C are used for charging and discharging. In this case, the control unit 10 closes the switches SW1 and SW1A in the path L1 and opens the switches SW1B and SW1C. Furthermore, the control unit 10 opens the switches SW2 and SW2A in the path L2 and closes the switches SW2B and SW2C. In this connection state, only the energy storage element 12A is connected to the power converter 11A via the path L1, and the remaining energy storage elements 12B and 12C are connected to the power converters 11B and 11C via a path L2 different from the path L1. The control unit 10 can perform maintenance on the energy storage element 12A via the path L1 while charging and discharging the energy storage elements 12B and 12C via the path L2.

[0044] As maintenance, the control unit 10 performs, for example, a capacity test on the energy storage element 12A. Specifically, the control unit 10 performs a test to measure the capacity by discharging the energy storage element 12A to a voltage defined as zero remaining battery power, and then charging the energy storage element 12A from that state to a voltage defined as fully charged with a constant current. If the ratio of the current full charge capacity (SOH) of the energy storage element 12A to the initial full charge capacity falls below a set value (e.g., 50%), the control unit 10 may output an alert to the management server 2 to urge the replacement of the energy storage element 12A with a new energy storage element.

[0045] FIG. 5 shows a connection state in which the energy storage elements 12A and 12C are used for charging and discharging while performing maintenance on the energy storage element 12B. In this case, the control unit 10 closes the switches SW1 and SW1B in the path L1 and opens the switches SW1A and SW1C. Furthermore, the control unit 10 opens the switches SW2 and SW2B in the path L2 and closes the switches SW2A and SW2C. In this connection state, only the energy storage element 12B is connected to the power converter 11A via the path L1, and the remaining energy storage elements 12A and 12C are connected to the power converters 11B and 11C via a path L2 different from the path L1. The control unit 10 can perform maintenance on the energy storage element 12B using the path L1 while charging and discharging the energy storage elements 12A and 12C using the path L1. Maintenance for the energy storage element 12B is similar to maintenance for the energy storage element 12A.

[0046] FIG. 6 shows a connection state in which the energy storage elements 12A and 12B are used for charging and discharging while performing maintenance on the energy storage element 12C. In this case, the control unit 10 closes the switches SW1 and SW1C on the path L1 and opens the switches SW1A and SW1B. Furthermore, the control unit 10 opens the switches SW2 and SW2C on the path L2 and closes the switches SW2A and SW2B. In this connection state, only the energy storage element 12C is connected to the power converter 11A via the path L1, and the remaining energy storage elements 12A and 12B are connected to the power converters 11B and 11C via a path L2 different from the path L1. The control unit 10 can perform maintenance on the energy storage element 12C using the path L1 while charging and discharging the energy storage elements 12A and 12B using the path L1. Maintenance for the energy storage element 12C is similar to maintenance for the energy storage element 12A.

[0047] 7 is a flowchart showing a control procedure in the first embodiment. The control unit 10 of the power storage system 1 judges whether or not to start maintenance on the power storage element 12 (step S101). For example, the control unit 10 sets in advance a time period during which the amount of power required by the load PC is relatively small (for example, a time period such as nighttime) as a time period during which maintenance is to be performed. The control unit 10 refers to a built-in clock and judges whether the current time is within the time period during which maintenance is to be performed, and judges whether or not to start maintenance. Alternatively, the control unit 10 may judge to start maintenance at regular intervals, or may judge to start maintenance when an instruction is given from the management server 2.

[0048] When the control unit 10 determines not to start maintenance (S101: NO), it waits until the timing to start maintenance. In this case, the connection state between the power converter 11 and the storage element 12 is controlled to the connection state shown in Fig. 3, and charging and discharging are performed via each of the power converters 11A to 11C.

[0049] When it is determined that maintenance should be started (S101: YES), the control unit 10 selects one of the energy storage elements 12 included in the energy storage system 1, for which maintenance has not been completed, as a maintenance target (step S102).

[0050] The control unit 10 controls the opening and closing of switches SW1, SW1A to SW1C on path L1 to connect only the selected storage element 12 to one power converter 11A, and controls the opening and closing of switches SW2, SW2A to SW2C on path L2 to connect the remaining storage elements 12 to the other power converters 11B, 11C (step S103).

[0051] The control unit 10 performs maintenance on the storage elements 12 selected in step S102 via one power converter 11A (step S104), and performs charging and discharging of the remaining storage elements 12 via the other power converters 11B and 11C (step S105).

[0052] After completing the process of step S104, the control unit 10 determines whether or not to end the maintenance (step S106). The control unit 10 determines whether or not to end the maintenance by determining whether or not there is any storage element 12 for which maintenance has not been completed among the storage elements 12 included in the energy storage system 1.

[0053] If there is any energy storage element 12 for which maintenance has not been completed, control unit 10 determines not to end maintenance (S106: NO) and returns the process to step S102. Control unit 10 selects one energy storage element 12 for which maintenance has not been completed, and executes the processes of steps S103 to S106 again.

[0054] If there is no energy storage element 12 for which maintenance has not been completed, the control unit 10 determines that maintenance is to be completed (S106: YES), and ends the process according to this flowchart.

[0055] As described above, in the first embodiment, when performing maintenance on the energy storage elements 12, there is no need to stop the energy storage system 1, and maintenance can be performed on some of the energy storage elements 12 while the remaining energy storage elements 12 are used for charging and discharging.

[0056] Since new energy storage elements are inspected before shipment, advance inspection before incorporation into a system is generally not required. On the other hand, when a reused energy storage element is to be incorporated into a system, advance inspection has conventionally been performed to check the performance of the energy storage element. In contrast, in the energy storage system 1 according to the first embodiment, the energy storage system 1 itself serves as an inspection device, so advance inspection is not required even if the energy storage element to be incorporated into the system is a reused product.

[0057] In the present embodiment, the number of mounted power converters 11 and the number of mounted energy storage elements 12 in the energy storage system 1 are three. Alternatively, the number of mounted power converters 11 may be two or four or more, and the number of mounted energy storage elements 12 may be two or four or more. The numbers of mounted power converters 11 and energy storage elements 12 do not have to be the same.

[0058] In the present embodiment, the configuration is such that maintenance is performed one by one on energy storage elements 12. Alternatively, the configuration may be such that maintenance is performed on a plurality of energy storage elements 12 at a time, and the remaining energy storage elements 12 are charged and discharged.

[0059] In the present embodiment, a capacity test is performed as maintenance for the energy storage element 12. Alternatively, a test may be performed to check whether a short circuit has occurred in the energy storage element 12 itself or in a bank or module including the energy storage element 12, or a test may be performed to check whether communication between the energy storage system 1 and the outside is normal.

[0060] (Embodiment 2) In the second embodiment, a configuration will be described in which, when a reused energy storage element is incorporated into the energy storage system 1, maintenance is performed on the reused energy storage element before charging or discharging it.

[0061] Fig. 8 is a flowchart showing a control procedure in the second embodiment. Reused energy storage elements may be incorporated into the energy storage system 1 at the time of manufacture or after the start of operation. When a reused energy storage element is incorporated into the energy storage system 1, the control unit 10 executes the following process. In the following, the reused energy storage element incorporated into the energy storage system 1 is referred to as energy storage element 12A, and the existing, non-reused energy storage elements are referred to as energy storage elements 12B and 12C. It is assumed that information indicating that the energy storage element 12A is a reused energy storage element is provided to the control unit 10 in advance.

[0062] The control unit 10 selects the reused energy storage element 12A as the energy storage element to be subjected to maintenance (step S201).

[0063] The control unit 10 closes switches SW1 and SW1A on path L1 and opens switches SW1B and SW1C to connect only the selected storage element 12A to one power converter 11A, and opens switches SW2 and SW2A on path L2 and closes switches SW2B and SW2C to connect the remaining storage elements 12B and 12C to the other power converters 11B and 11C (step S202).

[0064] Control unit 10 performs maintenance on reused energy storage element 12A via one power converter 11A (step S203), and performs charging / discharging of the remaining energy storage elements 12B, 12C via the other power converters 11B, 11C (step S204).

[0065] Based on the results of the maintenance, the control unit 10 determines whether or not there is a problem with the reused energy storage element 12A (step S205).

[0066] The control unit 10 performs, for example, a capacity test as maintenance for the reused energy storage element 12A. If the result of the capacity test indicates that there is sufficient full charge capacity, the control unit 10 determines that the incorporated reused energy storage element 12A is problem-free (S205: NO) and ends the processing according to this flowchart. In this case, the reused energy storage element 12A incorporated in the energy storage system 1 is used as one of the energy storage elements 12 that constitute the energy storage system 1.

[0067] If the capacity test results in insufficient full charge capacity, the control unit 10 determines that there is a problem with the incorporated reused storage element 12A (S205: YES) and outputs an alert to the management server 2, prompting the replacement of the storage element 12A with a new storage element (step S206).

[0068] As described above, in the second embodiment, when a reused energy storage element is incorporated in energy storage system 1, maintenance is performed before connecting with other energy storage elements 12, so that the risk of malfunction can be reduced.

[0069] (Embodiment 3) In the third embodiment, a configuration will be described in which, when a reused energy storage element is incorporated into energy storage system 1, the reused energy storage element is charged before being connected to other energy storage elements 12 that are already incorporated.

[0070] Fig. 9 is a flowchart showing a control procedure in the third embodiment. Reused energy storage elements may be incorporated into the energy storage system 1 at the time of manufacture or after the start of operation. When a reused energy storage element is incorporated into the energy storage system 1, the control unit 10 executes the following process. In the following, the reused energy storage element incorporated into the energy storage system 1 is referred to as energy storage element 12A, and the existing, non-reused energy storage elements are referred to as energy storage elements 12B and 12C. It is assumed that information indicating that the energy storage element 12A is a reused energy storage element is given to the control unit 10 in advance.

[0071] The control unit 10 selects the reused energy storage element 12A as the energy storage element to be subjected to maintenance (step S301).

[0072] The control unit 10 closes switches SW1 and SW1A on path L1 and opens switches SW1B and SW1C to connect only the selected storage element 12A to one power converter 11A, and opens switches SW2 and SW2A on path L2 and closes switches SW2B and SW2C to connect the remaining storage elements 12B and 12C to the other power converters 11B and 11C (step S302).

[0073] The control unit 10 charges the reused energy storage element 12A via one of the power converters 11A (step S303). The process after charging is the same as in the first embodiment, and when the timing for starting maintenance arrives, charging and discharging are performed while sequentially performing maintenance on the elements including the reused energy storage element 12A.

[0074] As described above, in the third embodiment, when a reused energy storage element is incorporated in energy storage system 1, the reused energy storage element is charged before being connected to other energy storage elements 12, thereby preventing a large current from flowing into the reused energy storage element.

[0075] Alternatively, when a reused energy storage element is incorporated in the energy storage system 1, the reused energy storage element may be discharged before being connected to the other energy storage elements 12. The voltage of a new energy storage element is often known in advance, but the voltage of a reused energy storage element is often unknown. When the voltage of a reused energy storage element is high, it can be separated from the other energy storage elements 12 already incorporated in the energy storage system 1 and discharged to match the voltage of these energy storage elements 12.

[0076] (Embodiment 4) 10 is a schematic diagram showing an installation example of the power storage system 1 in the fourth embodiment. The power storage system 1 in the fourth embodiment is connected between a power system PS and a load PC, for example. The internal configuration and operation of the power storage system 1 are similar to those in the first to third embodiments, and therefore description thereof will be omitted.

[0077] The power storage system 1 in the fourth embodiment functions as, for example, a UPS (Uninterruptible Power Supply). The power storage system 1 stores power supplied from a power system PS during normal operation, and supplies the stored power to a load PC during a power outage or the like.

[0078] (Embodiment 5) 11 is a schematic diagram showing an installation example of the power storage system 1 according to the fifth embodiment. The power storage system 1 according to the fifth embodiment is connected to, for example, a power system PS. The internal configuration and operation of the power storage system 1 are similar to those of the first to third embodiments, and therefore description thereof will be omitted.

[0079] The power storage system 1 in the fifth embodiment is a system used for adjusting the supply and demand of power. The power storage system 1 stores surplus power in the power system PS, and when the power to be supplied from the power system PS is insufficient, supplies the stored power to the power system PS to make up for the power shortage in the power system PS.

[0080] The disclosed embodiments are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0081] 1. Energy storage system 10. Control Unit 11 Power Converter 12 Energy storage element 13 BMU L1, L2 route SW1, SW2, SW1A to SW1C, SW2A to SW2C switches

Claims

1. A plurality of power converters; A plurality of storage elements that are charged and discharged via the plurality of power converters; a connection circuit that connects a storage element selected as a maintenance target among the plurality of storage elements to one power converter via a first path and connects other storage elements to the other power converter via a second path different from the first path; a control device that performs maintenance via the first path while sequentially switching between the storage elements selected as maintenance targets, and that performs charging and discharging of the other storage elements via the second path; A power storage system comprising:

2. The plurality of storage elements include reused storage elements. The power storage system according to claim 1 .

3. The control device controls the connection circuit to connect the reused energy storage element to the one power converter via the first path, in order to perform maintenance on the reused energy storage element before the reused energy storage element is charged or discharged for the first time in the energy storage system, and performs maintenance on the reused energy storage element via the first path. The power storage system according to claim 2 .

4. The control device controls the connection circuit to connect the reused energy storage element to the one power converter via the first path so as to charge the reused energy storage element before connecting it to another energy storage element, and charges the reused energy storage element via the first path. The power storage system according to claim 2 .

5. The maintenance includes capacity testing of selected storage elements. The power storage system according to any one of claims 1 to 4.

6. Sequentially selecting a storage element to be maintained from a plurality of storage elements that are charged and discharged via a plurality of power converters; connecting a selected storage element to one of the plurality of power converters via a first path, and connecting another storage element to the other power converter via a second path different from the first path; performing maintenance on the selected energy storage element via the first path; Charging and discharging the other storage element via the second path Method of controlling charging and discharging.

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