Capacity estimation device and capacity estimation method

Abstract

The present invention provides a capacity estimation device and a capacity estimation method that can improve the accuracy of estimating the full charge capacity of an energy storage element. [Solution] The capacity estimation device includes a control unit, which selects one or more banks from among multiple banks of an energy storage facility in which multiple banks are connected in parallel, each bank having multiple series-connected energy storage elements and a current control unit that controls the current flowing through the multiple series-connected energy storage elements. The control unit discharges and / or charges the energy storage elements of the selected specific bank to a predetermined charge level, and while the energy storage elements of the specific bank are being discharged and / or charged, it acquires the voltage and current of the energy storage elements of the specific bank, and estimates the capacity of the energy storage elements of the specific bank based on the acquired voltage and current.

Description

Technical Field

[0001] The present invention relates to a capacity estimation device and a capacity estimation method.

Background Art

[0002] In recent years, the introduction of renewable energy such as solar power generation and wind power generation has been rapidly progressing. The power supply amount of such renewable energy fluctuates depending on the weather and time zone. Therefore, an energy storage system (ESS) is being utilized. In addition, the ESS is increasingly being used for power trading.

[0003] Patent Document 1 discloses an ESS composed of a module in which a plurality of power storage elements are connected in series and a bank in which a plurality of modules are connected in series.

[0004] Since the ESS is operated over a long period (for example, about 20 years), the deterioration diagnosis of the power storage element is important. Particularly for power trading, it is important to estimate how much power can be discharged, that is, the full charge capacity (FCC) of the power storage element.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] There are power storage elements in which deterioration is promoted in regions where the state of charge (SOC) is high and low. Therefore, conventionally, the ESS has been mainly operated in the intermediate SOC region between the high SOC region and the low SOC region, and the estimation accuracy of the full charge capacity of the power storage element cannot be improved.

[0007] The present invention aims to provide a capacity estimation device and a capacity estimation method that can improve the accuracy of estimating the full charge capacity of an energy storage element. [Means for solving the problem]

[0008] A capacity estimation device according to one aspect of the present invention includes a control unit, which selects one or more banks from among a plurality of banks of an energy storage facility in which a plurality of banks are connected in parallel, each bank having a plurality of series-connected energy storage elements and a current control unit that controls the current flowing through the plurality of series-connected energy storage elements, discharges and / or charges the energy storage elements of the selected specific bank to a predetermined charge level, acquires the voltage and current of the energy storage elements of the specific bank while the energy storage elements of the specific bank are being discharged and / or charged, and estimates the capacity of the energy storage elements of the specific bank based on the acquired voltage and current. [Effects of the Invention]

[0009] According to the capacity estimation device of the above embodiment, the accuracy of estimating the full charge capacity of the energy storage element can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows an overview of the remote monitoring system. [Figure 2] This is a block diagram showing the internal configuration of the equipment included in the remote monitoring system. [Figure 3] This is a block diagram showing an example configuration of an energy storage system. [Figure 4] This figure shows an example of the domain configuration of the first embodiment. [Figure 5] This figure shows an example of the first stage of control of banks within a domain by a server device. [Figure 6] This figure shows an example of the second stage of control of banks within a domain by a server device. [Figure 7] This figure shows an example of the third stage of control of banks within a domain by a server device. [Figure 8]This figure shows an example of the relationship between the number of banks to be shut off and the state of charge (SOC) at the end of discharge of the energy storage element. [Figure 9] This figure shows another example of a server device controlling banks within a domain. [Figure 10] This diagram shows the timing of the bank's circuit breaker closing (turning on). [Figure 11] This figure shows an example of the domain configuration in the second embodiment. [Figure 12] This figure shows a first example of controlling banks within a domain using a server device. [Figure 13] This figure shows a second example of controlling banks within a domain using a server device. [Figure 14] This figure shows an example of capacity estimation using the ΔSOC method. [Figure 15] This figure shows an example of a partial charge / discharge profile for an energy storage element. [Figure 16] This figure shows an example of capacity estimation based on overall discharge characteristics. [Modes for carrying out the invention]

[0011] (1) The capacity estimation device includes a control unit, which selects one or more banks from among a plurality of banks of an energy storage facility in which a plurality of banks are connected in parallel, each bank having a plurality of series-connected energy storage elements and a current control unit that controls the current flowing through the plurality of series-connected energy storage elements, discharges and / or charges the energy storage elements of the selected specific bank to a predetermined charge level, acquires the voltage and current of the energy storage elements of the specific bank while the energy storage elements of the specific bank are being discharged and / or charged, and estimates the capacity of the energy storage elements of the specific bank based on the acquired voltage and current.

[0012] The energy storage device includes banks connected in parallel. Each bank includes, for example, modules connected in series, and each module includes energy storage elements connected in series. In a module, some of the energy storage elements may be connected in parallel. The current control unit controls the current (discharge current and charge current) flowing through the plurality of energy storage elements included in the bank. The current control unit includes, for example, a circuit breaker. The circuit breaker can turn on and off the discharge current flowing from the bank and the charge current flowing into the bank. The current control unit may be a power supply device (for example, a DC / DC converter) that can control the direction of the current flowing into the bank (that is, whether it is a charge current or a discharge current).

[0013] The energy storage device is connected to the power grid via a PCS (Power Conditioning System), and the energy storage elements of each bank are discharged to supply a predetermined amount of power to the power grid as determined by a contract or the like. Also, the energy storage device charges the energy storage elements of each bank to receive a predetermined amount of power from the power grid as determined by a contract or the like. The discharge and charge of the energy storage elements are performed, for example, once to several times a day. When discharging the energy storage elements of all banks of the energy storage device to supply a specified amount of power to the power grid, the charge rate of the energy storage elements of the bank becomes, for example, 30% to 50%. By setting the lower limit of the charge rate of the energy storage elements during discharge to such an intermediate value, deterioration of the energy storage elements can be suppressed.

[0014] The deterioration state of the energy storage element can be determined by estimating the full charge capacity. For estimating the full charge capacity, for example, a method of estimating the charge rate based on the OCV (Open Circuit Voltage) when the energy storage element is charged and discharged is used. At that time, the greater the variation range of the charge rate of the energy storage element from the start to the end of each of charging and discharging, the higher the estimation accuracy of the full charge capacity.

[0015] The control unit selects a specific bank from among the banks in the energy storage system, discharges and / or charges the energy storage elements of the selected bank to a predetermined charge level, and estimates the capacity of the energy storage elements based on the voltage and current of the energy storage elements during discharge and / or charging. The capacity estimation of a specific bank is performed, for example, once a year. Although discharge and / or charging are performed at a high rate during capacity estimation, degradation of the energy storage elements does not progress significantly if the frequency is low. The capacity estimation of the energy storage elements of a specific bank can be performed while the energy storage system is in operation.

[0016] Compared to discharging (or charging) all storage elements in all banks, the amount of energy discharged (or charged) by only the storage elements in a specific bank increases, allowing for a lower charge level at the end of discharge (or a higher charge level at the end of charging). This increases the range of variation in the charge level of the storage elements from the start to the end of discharge, improving the accuracy of estimating the full charge capacity. Furthermore, it allows for periodic diagnosis and verification that the system can actually discharge down to a low charge level.

[0017] (2) In the capacity estimation device described in (1) above, the current control unit may include a circuit breaker, and the control unit may interrupt the current flowing to the energy storage elements of banks other than the specific bank with the circuit breaker, thereby discharging and / or charging the energy storage elements of the specific bank to a predetermined charge level.

[0018] By interrupting the current flowing to energy storage elements in banks other than a specific bank using a circuit breaker, the amount of energy discharged and / or charged by the energy storage elements in that specific bank can be increased, thereby increasing the range of variation in the charge level of the energy storage elements in that specific bank. Circuit breakers are components that are normally provided in the banks of energy storage systems, and there is no additional cost. Applying such a new control method to circuit breakers can improve the accuracy of estimating the full charge capacity.

[0019] (3) In the capacity estimation device described in (1) or (2) above, the control unit may gradually decrease the number of banks selected for discharge and / or gradually increase the number of banks selected for charge.

[0020] In operations where a specified amount of electricity is supplied from a storage facility to the power grid periodically (for example, once to several times a day) based on a contract, the number of banks selected for discharge can be gradually reduced. This prevents abnormalities such as the voltage of a particular bank's storage element dropping below expectations, while gradually increasing the range of fluctuation in the charge level of the storage element from the start to the end of discharge. In the case of charging, this also prevents abnormalities such as the voltage of the storage element rising above expectations.

[0021] (4) The current control unit may include a DC / DC converter.

[0022] (5) The capacity estimation method involves selecting one or more banks from among a plurality of banks of an energy storage system, each of which is connected in parallel, and each bank comprises a plurality of series-connected energy storage elements and a current control unit that controls the current flowing through the plurality of series-connected energy storage elements. The energy storage elements of the selected specific bank are discharged and / or charged to a predetermined charge level. While the energy storage elements of the specific bank are being discharged and / or charged, the voltage and current of the energy storage elements of the specific bank are acquired, and the capacity of the energy storage elements of the specific bank is estimated based on the acquired voltage and current.

[0023] The present invention will be specifically described with reference to the drawings illustrating its embodiments.

[0024] Figure 1 shows an overview of the remote monitoring system 100. The remote monitoring system 100 enables remote access to information regarding energy storage elements and power supply-related devices included in the mega solar power generation system S, thermal power generation system F, and wind power generation system W. Rectifiers (DC power supply devices or AC power supply devices) D installed in uninterruptible power supply (UPS) U, stabilized power supply systems for railways, etc., may also be remotely monitored.

[0025] A power conditioner (PCS) P and an energy storage system 101 are installed side-by-side in the mega solar power generation system S, the thermal power generation system F, and the wind power generation system W. The energy storage system 101 may be composed of multiple containers C containing groups of energy storage modules L, installed side-by-side. Alternatively, the groups of energy storage modules L and the power conditioner P may be located inside a building (energy storage room). The groups of energy storage modules L include multiple energy storage elements. The energy storage elements are preferably rechargeable, such as secondary batteries like lead-acid batteries and lithium-ion batteries, or capacitors. Some of the energy storage elements may be non-rechargeable primary batteries.

[0026] In the remote monitoring system 100, a communication device 1 (see Figure 2) is installed / connected to each of the energy storage systems 101 or devices (P, U, D and the management device M described later) in the systems S, F, and W that are to be monitored. The remote monitoring system 100 includes the communication device 1, a server device 2 which is an information processing device that collects information from the communication device 1, a client device 3 for viewing the collected information, and a network N which is a communication medium between the devices.

[0027] The communication device 1 may be a terminal device (measurement monitor) that communicates with a battery management unit (BMU) provided in the energy storage element to receive information about the energy storage element, or it may be an ECHONET® / ECHONETLite® compatible controller. The communication device 1 may be an independent device, or it may be a network card type device that can be mounted on a power conditioner P or a group of energy storage modules L. One communication device 1 is provided for each group of energy storage modules in the energy storage system 101 in order to acquire information about the group of energy storage modules L. Multiple power conditioners P are connected to each other so as to enable serial communication, and the communication device 1 is connected to the control unit of one of the representative power conditioner P.

[0028] The server device 2 shown in Figure 1 includes a web server function and presents information obtained from the communication device 1 installed / connected to each monitored device in response to access from the client device 3.

[0029] Network N includes a public communication network N1, which is the so-called internet, and a carrier network N2 that implements wireless communication according to a predetermined mobile communication standard. The public communication network N1 includes a general optical line, and Network N includes a dedicated line to which the server device 2 is connected. Network N may also include an ECHONET / ECHONET Lite compatible network. The carrier network N2 includes a base station BS, and the client device 3 can communicate with the server device 2 via Network N from the base station BS. Access points AP are connected to the public communication network N1, and the client device 3 can send and receive information between the server device 2 and the access point AP via Network N.

[0030] In this manner, the remote monitoring system 100 utilizes communication devices 1 installed on or connected to each monitored device, and the server device 2 collects information such as the state of charge (SOC), state of health (SOH), and other conditions of the energy storage elements in the energy storage system 101, as well as any abnormalities detected by each device. The collected information is presented collectively via the server device 2.

[0031] Figure 2 is a block diagram showing the internal configuration of the device included in the remote monitoring system 100. As shown in Figure 2, the communication device 1 comprises a control unit 10, a storage unit 11, a first communication unit 12, and a second communication unit 13. The control unit 10 is a processor using a CPU (Central Processing Unit), and it uses built-in memory such as ROM (Read Only Memory) and RAM (Random Access Memory) to control each component and execute processing.

[0032] The storage unit 11 uses non-volatile memory such as flash memory. The storage unit 11 stores a device program 1P that the control unit 10 reads and executes. The device program 1P includes a communication program compliant with SSH (Secure Shell), SNMP (Simple Network Management Protocol), etc. The storage unit 11 also stores information collected by the processing of the control unit 10, event logs, and other information. The information stored in the storage unit 11 can also be read via a communication interface such as USB, whose terminals are exposed on the housing of the communication device 1. The device program 1P stored in the storage unit 11 may be a copy of the device program 4P stored in the recording medium 4, read and stored in the storage unit 11.

[0033] The first communication unit 12 is a communication interface that enables communication between the communication device 1 and the monitored device to which it is connected. The first communication unit 12 uses a serial communication interface such as RS-232C or RS-485. For example, the power conditioner P is equipped with a control unit that has a serial communication function compliant with RS-485, and the first communication unit 12 communicates with that control unit. When the control boards provided in the energy storage module group L are connected by a CAN (Controller Area Network) bus and communication between the control boards is realized by CAN communication, the first communication unit 12 is a communication interface based on the CAN protocol. The first communication unit 12 may also be a communication interface that complies with the ECHONET / ECHONETLite standard.

[0034] The second communication unit 13 is an interface that enables communication via the network N, and uses a communication interface such as Ethernet® or a wireless communication antenna. The control unit 10 can communicate with the server device 2 via the second communication unit 13. The second communication unit 13 may also be a communication interface that conforms to the ECHONET / ECHONETLite standard.

[0035] In the communication device 1 configured in this way, the control unit 10 acquires measurement data for the energy storage element obtained from the device to which the communication device 1 is connected via the first communication unit 12. The control unit 10 may also function as an SNMP agent by reading and executing an SNMP program and respond to information requests from the server device 2.

[0036] Server device 2 uses a server computer and includes a control unit 20, a storage unit 21, and a communication unit 22. In this embodiment, server device 2 is described as a single server computer, but processing may be distributed among multiple server computers.

[0037] The control unit 20 is a processor using a CPU or GPU (Graphics Processing Unit), and it uses built-in memory such as ROM and RAM to control each component and execute processing. The control unit 20 performs communication and information processing based on the server program 21P stored in the storage unit 21. The server program 21P includes a web server program, and the control unit 20 functions as a web server that provides web pages to the client device 3. Based on the server program 21P, the control unit 20 collects information from the communication device 1 as an SNMP server.

[0038] The storage unit 21 uses non-volatile memory such as a hard disk or flash memory. The storage unit 21 stores the server program 21P and the data processing program 22P described above. The server program 21P and data processing program 22P stored in the storage unit 21 may be copies of the server program 51P and data processing program 52P stored in the recording medium 5, read out and stored in the storage unit 21.

[0039] The storage unit 21 stores measurement data of the power conditioner P and energy storage module group L of the energy storage system 101 that are to be monitored, collected by the processing of the control unit 20. The measurement data is associated with identification information (number) that identifies the energy storage system 101 or the power conditioner P. The measurement data of the energy storage module group L is stored according to a hierarchical structure of domain, bank, module, or cell.

[0040] The storage unit 21 stores multiple images for displaying the status of the monitored energy storage module group L or devices P, U, and D. These multiple images are stored in the storage unit 21 in association with identification information that identifies the monitored energy storage module group L or devices P, U, and D. The multiple images include images representing the energy storage module group L or devices P, U, and D.

[0041] The communication unit 22 is a communication device that enables communication connection and transmission / reception of information via the network N. Specifically, the communication unit 22 is a network card compatible with the network N.

[0042] Client device 3 is a computer used by operators such as administrators or maintenance personnel of the energy storage systems 101 of the power generation systems S, F, and W. Client device 3 may be a desktop or laptop personal computer, or a so-called smartphone or tablet type communication terminal. Client device 3 comprises a control unit 30, a storage unit 31, a communication unit 32, a display unit 33, and an operation unit 34.

[0043] The control unit 30 is a processor using a CPU. Based on the client program 3P stored in the memory unit 31, the control unit 30 displays the web page provided by the server device 2 on the display unit 33. The client program 3P is embedded in the web page provided by the web server function of the server device 2 and includes a script and a web browser program that are temporarily stored in the client device 3, and is a program for displaying a web-based screen based on the operation of the server device 2.

[0044] The storage unit 31 uses non-volatile memory such as a hard disk or flash memory. Various programs, including the client program 3P, are stored in the storage unit 31. The client program 3P may be a copy of the client program 6P stored in the recording medium 6, read out and stored in the storage unit 11.

[0045] The communication unit 32 uses a communication device such as a network card for wired communication, a wireless communication device for mobile communication connected to a base station BS (see Figure 1), or a wireless communication device that supports connection to an access point AP. The control unit 30 can communicate with the server device 2 or send and receive information via the network N through the communication unit 32.

[0046] The display unit 33 uses a display such as a liquid crystal display or an organic EL (Electro-Luminescence) display. The display unit 33 displays an image of a web page provided by the server device 2 through processing based on the client program 3P of the control unit 30. The display unit 33 is preferably a touch panel type display, but it may also be a non-touch panel type display.

[0047] The operation unit 34 is a user interface such as a keyboard and pointing device or an audio input unit that can input and output to and from the control unit 30. The operation unit 34 may use the touch panel of the display unit 33 or physical buttons provided on the housing. The operation unit 34 notifies the control unit 30 of the user's operation information.

[0048] In the remote monitoring system 100 configured in this way, the server device 2 periodically acquires various information from the communication device 1, including the status of the power conditioner P, the energy storage module group L (management device M), the uninterruptible power supply U, and the rectifier D, based on the data processing program 22P, and stores it in the storage unit 21. The communication device 1 transmits status information for each energy storage module group L, with parent-child relationships linked according to the hierarchical structure. Based on the information acquired from the energy storage elements or each power supply-related device using the communication device 1, the server device 2 creates screen information (display information) that visually represents the status of the monitored system or device according to the hierarchical structure of the energy storage cells, and transmits it to the client device 3.

[0049] Figure 3 is a block diagram showing an example configuration of the energy storage system 101. The energy storage module group L may have a hierarchical structure consisting of energy storage modules (also called "modules") which are made up of multiple energy storage elements (also called "energy storage cells" or "cells") connected in series, banks which are made up of multiple modules connected in series, and domains which are energy storage facilities made up of multiple banks connected in parallel. In Figure 3, only one domain is shown for convenience. The energy storage system 101 is a large-scale ESS that includes multiple domains.

[0050] The energy storage system 101 includes a power conditioner (PCS) P. The power conditioner P supplies electricity generated by a power generation system such as a solar system to the energy storage system 101, and also supplies the electricity stored in the energy storage system 101 to other power consuming equipment (loads) or the power grid. The power conditioner P is connected to multiple parallel banks #1-#N by power lines 42. A switch 43 is provided between the branching point of the power lines 42 to the multiple banks and the power conditioner P. The switching of the switch 43 switches the power supply from the power conditioner P to the entire domain on and off. The switch 43 may be provided inside the power conditioner P.

[0051] Each bank is provided with a circuit breaker 41 as a current control unit. The circuit breaker 41 switches the power supply from the branching point of the power line 42 to the group of energy storage modules L on and off. The circuit breaker 41 switches between an ON state, where the power line 42 and the group of energy storage modules L are connected, and an OFF state, where they are not connected. With the group of energy storage modules L of each bank connected to the power line 42, charging or discharging, i.e., power supply, is performed to each group of energy storage modules L through the power conditioner P, switch 43, power line 42, and circuit breaker 41. In Figure 3, a circuit breaker 41 is provided for each bank, but multiple banks may be divided into groups, and one circuit breaker 41 may be provided for each group.

[0052] In the example shown in Figure 3, management devices (BMUs) M are provided for each bank and each domain. When explaining the management devices M provided for each bank and the management devices M provided for each domain separately, they are denoted in parentheses as B for banks and D for domains for ease of explanation. The management devices (B) M for banks communicate via serial communication with control boards (CMUs: Cell Monitoring Units) with communication functions that are built into each energy storage module. The management devices M operate by receiving power from the power conditioner P or from the group of energy storage modules L via the power line 42.

[0053] Control device (B)M is connected to circuit breaker 41, and control device (D)M is connected to switch 43. Circuit breaker 41 and switch 43 are controlled by control device M, respectively.

[0054] Communication device 1 is connected to the group of energy storage modules L to be monitored via management device M. As described above, communication device 1 is connected to management device M via a serial communication cable by the first communication unit 12. Communication device 1 may be configured integrally with management device M. Communication device 1 operates on power supplied via a separate path from the power line 42. These multiple communication devices 1 are connected to each other to send and receive information. In the example shown in Figure 3, they are connected by a communication bus. The communication bus is, for example, a LAN cable. Alternatively, the communication bus may be a CAN bus, a LAN cable, or an ECHONET Lite compatible communication medium. Management device (D)M of a domain and management device (D)M of other domains in the same system may be connected by a different communication bus, such as a CAN bus, and may be able to communicate with each other. Management device M can control the circuit breaker 41 and the switch 43, respectively, based on instructions from communication device 1.

[0055] The communication device 1 connected to the management device (B)M of each bank, upon receiving instructions via the second communication unit 13, has the function of causing the battery module group L to perform a predetermined charge or discharge, and estimating the full charge capacity from the voltage and current measurements taken during that time.

[0056] A domain (energy storage facility) is connected to the power grid (generation grid, loads, etc.) via a power conditioner (PCS) P, and the energy storage elements in each bank are discharged to supply a predetermined amount of energy to the power grid as stipulated in the contract. Conversely, the energy storage elements in each bank of the domain are charged to receive a predetermined amount of energy from the power grid as stipulated in the contract. Discharging and charging of the energy storage elements is performed, for example, once to several times a day. When all the energy storage elements in the domain's banks are discharged to supply the predetermined amount of energy to the power grid, the State of Charge (SOC) of the energy storage elements in each bank will be, for example, 30% to 50%.

[0057] Next, the method for controlling banks within the domain of the energy storage system 101 by the server device 2 will be described. The server device 2 also functions as a capacity estimation device.

[0058] (First Embodiment) Figure 4 shows an example of the configuration of a domain in the first embodiment. Multiple energy storage elements 8 are connected in series to form one bank. In the example in Figure 4, N1 energy storage elements 8 are connected in series to form a bank. Note that a bank can also be viewed as a configuration in which multiple modules are connected in series. A domain has a configuration in which multiple banks are connected in parallel. In the example in Figure 4, N2 banks are connected in parallel. A circuit breaker 41 is connected to each bank, and the on / off state of the circuit breaker 41 is controlled by the control device (B)M. The current and voltage of the energy storage elements 8 are also acquired by the control device (B)M.

[0059] The power conditioner (PCS) P is equipped with a bidirectional DC / DC converter and a bidirectional DC / AC converter and is connected to the power grid. When a predetermined amount of power is supplied from the domain to the power grid as stipulated in the contract, the energy storage elements 8 in the domain are discharged, and the power conditioner (PCS) P boosts the voltage in the bank to the required DC voltage using the DC / DC converter, converts the boosted DC voltage to AC voltage using the DC / AC converter, and supplies it to the power grid. Also, when a predetermined amount of power is received from the power grid from the domain as stipulated in the contract, the energy storage elements 8 in the domain are charged. In this case, the power conditioner (PCS) P converts the AC voltage of the power grid to DC voltage using the DC / AC converter, steps down the converted DC voltage using the DC / DC converter, and supplies the stepped-down DC voltage to the bank.

[0060] When a specified amount of power is supplied to the power grid (sold) by discharging all the energy storage elements 8 in a domain bank, the State of Charge (SOC) of the energy storage elements in the bank will be, for example, 30% to 50%. By setting the lower limit of the SOC of the energy storage elements during discharge to such an intermediate value, the degradation of the energy storage elements can be suppressed. On the other hand, to estimate the full charge capacity of the energy storage elements 8, methods such as estimating the SOC based on the OCV (Open circuit voltage) when the energy storage elements 8 are charged and discharged are used. In this case, for example, if the fluctuation of the SOC from the start to the end of discharge is, for example, from 100% to 30%, the fluctuation range of the SOC (100% to 30%) is narrow, and more specifically, the SOC at the end of discharge is not low, so accurate capacity estimation is not possible. The following describes a method for controlling the banks within a domain to perform accurate capacity estimation.

[0061] Figure 5 shows an example of the first stage of control of banks within a domain by the server device 2. When supplying the contracted amount of power (e.g., 750 kWh) to the power grid (during power sales), the circuit breaker 41 is opened (off) for one of the N2 banks, preventing the energy storage elements of that bank from discharging. At the start of discharge, it is assumed that the energy storage elements 8 of the N2 banks are fully charged using the contracted amount of power. The server device 2 selects specific (N2-1) banks within the domain and discharges the energy storage elements 8 of the selected banks. In this case, since the number of banks to be discharged is reduced from N2 to (N2-1), the energy storage elements 8 of the specific bank can be discharged to a lower SOC. The bank control shown in Figure 5 can be performed during actual domain operation, so there is no need to stop the operation of the energy storage system 101.

[0062] In the example shown in Figure 5, the State of Charge (SOC) based on the Open Circuit Voltage (OCV) of the energy storage element at the end of discharge is, for example, around 25%, which is not a sufficiently low SOC. In this case, the second stage of control, illustrated in Figure 6 below, is implemented.

[0063] Figure 6 shows an example of the second stage of control of banks within a domain by the server device 2. When supplying the contracted amount of power (e.g., 750 kWh) to the power grid (during power sales), the circuit breakers 41 are opened (off) for two of the N2 banks, preventing the energy storage elements in those banks from discharging. At the start of discharge, it is assumed that the energy storage elements 8 in the N2 banks are fully charged using the contracted amount of power. The server device 2 selects specific (N2-2) banks within the domain and discharges the energy storage elements 8 in the selected banks. In this case, the number of banks to be discharged is reduced from N2 to (N2-2), allowing the energy storage elements 8 in the specific banks to be discharged to a lower SOC. The bank control shown in Figure 6 can be performed during actual domain operation, so there is no need to stop the operation of the energy storage system 101.

[0064] In the example shown in Figure 6, the State of Charge (SOC) based on the Open Circuit Voltage (OCV) of the energy storage element at the end of discharge is, for example, around 18%, which is not a sufficiently low SOC. In this case, the third stage of control, illustrated in Figure 7 below, is implemented.

[0065] Figure 7 shows an example of the third stage of control of banks within a domain by the server device 2. In the third stage, after the first and second stages described above, the number of specific banks is reduced by increasing the number of times the circuit breaker 41 is opened (turned off) when the daily contracted amount of power is supplied (when selling power), and specific (N2-n) banks are selected within the domain. The server device 2 selects specific (N2-n) banks within the domain and discharges the energy storage elements 8 of the selected banks. In this case, since the number of banks to be discharged is reduced from N2 to (N2-n), the energy storage elements 8 of specific banks can be discharged to a lower SOC. The bank control shown in Figure 7 can be performed during actual operation of the domain, so there is no need to stop the operation of the energy storage system 101.

[0066] In the example shown in Figure 7, the State of Charge (SOC) of the energy storage element based on its Open Circuit Voltage (OCV) at the end of discharge is, for example, about 4%, which is a sufficiently low SOC. Because the SOC of the energy storage element 8 is low, the server device 2 can estimate the capacity of the energy storage element 8 in a specific bank. Details of the capacity estimation method will be described later.

[0067] As described above, the control unit 20 selects one or more banks from among multiple banks of an energy storage system, each of which is connected in parallel and each bank is equipped with multiple series-connected energy storage elements and a circuit breaker 41 (current control unit) that controls the current flowing through the multiple series-connected energy storage elements. The control unit discharges the energy storage elements of the selected bank to a predetermined state of charge (SOC), and while the energy storage elements of the selected bank are being discharged, it acquires the voltage and current of the energy storage elements of the selected bank. Based on the acquired voltage and current, the control unit 20 can estimate the capacity of the energy storage elements of the selected bank.

[0068] The power grid needs to be supplied with the contracted amount of power (a predetermined amount of power as stipulated in the contract, etc.). By discharging the energy storage elements 8 of a specific bank, the number of banks used for discharge is reduced, the amount of power discharged by the energy storage elements 8 of that specific bank increases, and the State of Charge (SOC) at the end of discharge can be lowered. This increases the range of fluctuation in the SOC of the energy storage elements 8 from the start to the end of discharge, that is, lowers the SOC at the end of discharge, and improves the accuracy of estimating the full charge capacity.

[0069] The predetermined SOC may be a value lower than the median value, for example, 0% or more and less than 30%. More preferably, the predetermined SOC may be 0% or more and 20% or less. This is because a lower SOC value allows for a larger fluctuation range of SOC during charging and discharging.

[0070] The current control unit includes a circuit breaker 41, and the control unit 20 may use the circuit breaker 41 to interrupt the current flowing to the energy storage elements of banks other than the specific bank, thereby discharging the energy storage elements 8 of the specific bank to a predetermined state of charge (SOC).

[0071] By interrupting the current flowing to the energy storage elements 8 in banks other than the specific bank using the circuit breaker 41, the amount of power discharged by the energy storage elements 8 in the specific bank can be increased. This allows for a larger fluctuation range of the State of Charge (SOC) of the energy storage elements 8 in the specific bank. Furthermore, since the elements discharge down to a low SOC, it is possible to periodically diagnose and verify that the energy storage elements 8 can actually discharge down to a low SOC, thereby diagnosing the health of the energy storage elements 8.

[0072] The control unit 20 may gradually reduce the number of banks selected for discharge. Conversely, during charging, the control unit 20 may gradually increase the number of banks selected for charging.

[0073] In operations where a specified amount of electricity is supplied periodically (for example, once to several times a day) from a domain (energy storage facility) to the power grid based on a contract, the number of banks selected for discharge can be gradually reduced. This prevents abnormalities such as the voltage of the energy storage elements 8 in a particular bank dropping below expectations, while gradually increasing the fluctuation range of the state of charge (SOC) of the energy storage elements from the start to the end of discharge. In the case of charging, this also prevents abnormalities such as the voltage of the energy storage elements rising above expectations.

[0074] Figure 8 shows an example of the relationship between the number of banks to be shut off and the State of Charge (SOC) of the energy storage element 8 at the end of discharge. In Figure 8, the vertical axis represents the number of banks to be shut off within the domain, and the horizontal axis represents the SOC of the energy storage element 8 in a specific bank that has not been shut off at the end of discharge. The chart shown in Figure 8 is a schematic representation and may not actually be a straight line. Also, the example shown in Figure 8 may vary depending on the number of banks within the domain.

[0075] As shown in Figure 8, if the circuit breaker 41 of one bank in the domain is tripped and the energy storage elements of the remaining specific bank are discharged, we assume that the SOC of the energy storage elements at the end of discharge was 25%. Next, if we increase the number of banks to trip, tripping the circuit breakers 41 of two banks and discharging the energy storage elements of the remaining specific bank, we assume that the SOC of the energy storage elements at the end of discharge was 20%. Furthermore, if we increase the number of banks to trip, tripping the circuit breakers 41 of three banks and discharging the energy storage elements of the remaining specific bank, we assume that the SOC of the energy storage elements at the end of discharge was 16%. Extend the straight line represented by the solid line in Figure 8 and draw a dashed line. On the dashed line, we can estimate what the SOC of the energy storage elements 8 will be depending on how many banks are tripped. In the example shown in Figure 8, it can be estimated that if the circuit breakers 41 for six banks are tripped, the SOC at the end of discharge for the energy storage element 8 in a particular bank will be around 5%, and if the circuit breakers 41 for seven banks are tripped, the SOC at the end of discharge for the energy storage element 8 in a particular bank will be around 2-3%.

[0076] As described above, when the energy storage elements 8 of a particular bank are discharged, the control unit 20 may calculate the State of Charge (SOC) at the end of the discharge of the energy storage elements 8 of a particular bank in relation to the number of banks, and determine the lower limit of the number of banks to be selected based on the calculated SOC.

[0077] By associating the number of banks of a particular type with the State of Charge (SOC) of the energy storage element at the end of discharge, it is possible to estimate how much the SOC of the energy storage element 8 at the end of discharge can be reduced depending on the number of banks of that particular type. When selecting banks of a particular type, it is possible to determine the lower limit of the number of banks of that particular type so that the voltage of the energy storage element 8 does not reach the discharge termination voltage. The discharge termination voltage is the voltage at which the voltage of the energy storage element 8 should not be discharged any further.

[0078] Figure 9 shows another example of control of banks within a domain by the server device 2. In the example in Figure 9, the order in which the banks are tripped by the circuit breaker 41 is reversed compared to the examples in Figures 5 to 7. That is, when the control unit 20 selects a specific bank, it may prioritize selecting banks that have not yet been selected.

[0079] By prioritizing banks that have not yet been selected, all banks in the domain can be selected, and therefore the capacity of the energy storage elements 8 in all banks can be estimated.

[0080] Although not shown in the figures, the control unit 20 may, when it has finished discharging a particular bank, charge the energy storage element 8 of that particular bank until its State of Charge (SOC) reaches a predetermined value (e.g., 100%), and while the energy storage element 8 of that particular bank is being charged, acquire the voltage and current of the energy storage element 8 of that particular bank, and estimate the capacity (full charge capacity) of the energy storage element 8 of that particular bank based on the acquired voltage and current.

[0081] When charging the energy storage elements 8 of a specific bank, a predetermined amount of energy is received from the power grid, so the capacity estimation of the energy storage elements 8 can be performed during actual domain operation. Furthermore, the accuracy of capacity (full charge capacity) estimation can be improved by increasing the fluctuation range of the state of charge (SOC) of the energy storage elements 8 from the start to the end of charging.

[0082] As described above, server device 2 controls the opening (turning off) of circuit breakers 41 in banks other than the specific bank within the domain. The opened circuit breakers 41 then need to be closed (turned on) at the required timing. When connecting banks that have been interrupted by circuit breakers 41, if there is a voltage difference between the voltage of the interrupted bank and the voltage of the uninterrupted bank, an overcurrent may flow from the bank with the higher voltage to the bank with the lower voltage. The following describes how to prevent overcurrent.

[0083] Figure 10 shows the timing of the Close (On) state of the bank's circuit breaker 41. The upper chart shows the timing of charging and discharging. 750kWh of discharge occurs between time t1 and t2, and 750kWh of charging occurs between time t3 and t4. The timing of discharge can increase revenue by, for example, performing it when electricity rates are high, and the timing of charging can suppress revenue expenditure by, for example, performing it when electricity rates are low. Similarly, 750kWh of discharge occurs between time t5 and t6, 750kWh of charging occurs between time t7 and t8, 750kWh of discharge occurs between time t9 and t10, and 750kWh of charging occurs between time t11 and t12.

[0084] The middle chart shows the State of Charge (SOC) of the energy storage elements 8 in each bank (indicated as B in the diagram). At time t1, the SOC of the energy storage elements 8 in banks 1-20 is 100%. At time t2, when the discharge is complete, the SOC of the energy storage elements 8 in banks 1-20 is 40%. Between time t4 and t5, the circuit breakers 41 for banks 1-3 are opened as required. During the discharge period from time t5 to t6, banks 1-3 are not discharged because they are tripped. Therefore, the SOC of the energy storage elements 8 in banks 1-3 is maintained at 100%. On the other hand, the energy storage elements 8 in banks 4-20 are discharged. In this case, the number of banks supplying 750kWh of electricity decreases from 20 to 17, so the energy storage elements in banks 4-20 are discharged to a lower SOC, and the SOC at time t6 is 30%.

[0085] After charging is complete at point t8, as shown in the lower bank voltage chart, the charge and discharge kWh are the same, so the voltages of banks 1 to 20 are all the same. Closing the circuit breakers 41 for banks 1 to 3 at this time prevents overcurrent. After closing the circuit breakers 41 for banks 1 to 3, the circuit breakers 41 for banks 1 to 6 are opened. During the discharge period from point t9 to t10, banks 1 to 6 are shut off and therefore do not discharge. As a result, the SOC of the energy storage elements 8 in banks 1 to 6 is maintained at 100%. On the other hand, the energy storage elements 8 in banks 7 to 20 are discharged. In this case, the number of banks supplying 750 kWh of power decreases from 20 to 14, so the energy storage elements in banks 7 to 20 are discharged to an even lower SOC, and the SOC at point t10 is 5%.

[0086] After charging is complete at point t12, as shown in the lower bank voltage chart, the charge and discharge kWh are the same, so the voltages of banks 1 to 20 are all the same. By closing the circuit breakers 41 for banks 1 to 6 at this timing, overcurrent can be prevented.

[0087] (Second Embodiment) In the first embodiment described above, a circuit breaker 41 was provided as the current control unit, but in the second embodiment, a DC / DC converter 44 is provided instead of the circuit breaker 41. As in the first embodiment, the mainstream lithium-ion secondary battery used as the energy storage element 8 is a lithium-ion secondary battery called a ternary (NMC) system, which uses nickel (Ni), manganese (Mn), and cobalt (Co) as the positive electrode material. On the other hand, an LFP (lithium iron phosphate battery) is a lithium-ion secondary battery whose positive electrode material is composed of lithium (Li), iron (Fe), and phosphorus (P), and does not use rare metals such as cobalt and nickel used in ternary batteries, but instead uses iron phosphate, making it inexpensive to manufacture. Because LFPs have little voltage change during charging and discharging, if the energy storage elements 8 in each bank are LFPs, the current will be divided between banks due to variations in the internal resistance of the LFPs. To suppress this current division, a DC / DC converter 44 is used instead of a circuit breaker 41.

[0088] Figure 11 shows an example of the configuration of a domain in the second embodiment. Multiple energy storage elements 8 are connected in series to form one bank. In the example in Figure 11, M1 energy storage elements 8 are connected in series to form a bank. The energy storage elements 8 are LFPs. The domain has a configuration in which multiple banks are connected in parallel. In the example in Figure 11, M2 banks are connected in parallel. A DC / DC converter 44 is connected to each bank, and the operation of the DC / DC converter 44 is controlled by the management device (B)M. The current and voltage of the energy storage elements 8 are also detected by the management device (B)M.

[0089] The power conditioner (PCS) P is equipped with a bidirectional DC / AC converter and is connected to the power grid. When supplying a predetermined amount of energy from the domain to the power grid as stipulated in the contract, the energy storage elements 8 in the domain are discharged, the voltage in the bank is boosted to the required DC voltage by the DC / DC converter 44, and the boosted DC voltage is converted to AC voltage by the DC / AC converter of the power conditioner (PCS) P and supplied to the power grid. Also, when receiving a predetermined amount of energy from the power grid as stipulated in the contract, the energy storage elements 8 in the domain are charged. In this case, the power conditioner (PCS) P converts the AC voltage of the power grid to DC voltage with the DC / AC converter, steps down the converted DC voltage with the DC / DC converter 44, and supplies the stepped-down DC voltage to the bank.

[0090] When a specified amount of power is supplied to the power grid (sold) by discharging all the energy storage elements 8 in a domain bank, the State of Charge (SOC) of the energy storage elements in the bank will be, for example, 30% to 50%. By setting the lower limit of the SOC of the energy storage elements during discharge to such an intermediate value, the degradation of the energy storage elements can be suppressed. On the other hand, to estimate the full charge capacity of the energy storage elements 8, methods such as estimating the SOC based on the OCV (Open circuit voltage) when the energy storage elements 8 are charged and discharged are used. In this case, for example, if the fluctuation of the SOC from the start to the end of discharge is, for example, from 100% to 30%, the fluctuation range of the SOC (100% to 30%) is narrow, and more specifically, the SOC at the end of discharge is not low, so accurate capacity estimation is not possible. The following describes a method for controlling the banks within a domain to perform accurate capacity estimation.

[0091] Figure 12 shows a first example of control of banks within a domain by the server device 2. In Figure 12, multiple energy storage elements within a bank are grouped together and shown as a single bank. As shown in Figure 12, it is assumed that the domain has 10 banks. It is also assumed that we want to estimate the capacity of the energy storage elements in bank 1. When receiving the contracted amount of power from the power grid, the DC / DC converters 44 of banks 1 to 10 are controlled to discharge the energy storage elements in bank 1 and charge the energy storage elements in banks 2 to 10. By controlling the DC / DC converter 44 of bank 1, the SOC of the energy storage elements in bank 1 can be set to 0% at the end of discharge. Also, by controlling the DC / DC converters 44 of banks 2 to 10, the SOC of the energy storage elements in banks 2 to 10 can be set to approximately 55% at the end of charging. By setting the SOC to approximately 55%, the degradation of the energy storage elements can be suppressed. The bank control shown in Figure 12 can be performed during the actual operation of the domain, so it is not necessary to stop the operation of the energy storage system 101.

[0092] As described above, the current control unit includes a DC / DC converter 44, and when the control unit 20 charges the energy storage elements of a domain, it may charge the energy storage elements of other banks (bank 1 in the example of Figure 12) and discharge the energy storage elements of the selected specific bank to a predetermined SOC.

[0093] When discharging the energy storage elements in a specific bank, the discharge current is used to charge the energy storage elements in other banks. This allows the energy storage elements in a specific bank to be discharged until they reach a low state of charge (SOC), thereby increasing the fluctuation range of the SOC of the energy storage elements from the start to the end of discharge, and thus lowering the SOC of the energy storage elements and improving the accuracy of estimating the full charge capacity.

[0094] Figure 13 shows a second example of control of banks within a domain by the server device 2. When supplying the contracted amount of power to the power grid, the DC / DC converters 44 of banks 1 to 10 are controlled to charge the energy storage elements in bank 1 and discharge the energy storage elements in banks 2 to 10. By controlling the DC / DC converter 44 of bank 1, the SOC of the energy storage elements in bank 1 can be set to 100% at the end of charging. Also, by controlling the DC / DC converters 44 of banks 2 to 10, the SOC of the energy storage elements in banks 2 to 10 can be set to approximately 45% at the end of discharge. By setting the SOC to approximately 45%, the degradation of the energy storage elements can be suppressed. The bank control shown in Figure 13 can be performed during actual domain operation, so there is no need to stop the operation of the energy storage system 101.

[0095] As described above, when the control unit 20 discharges the energy storage elements of a domain, it may discharge the energy storage elements of other banks (excluding bank 1 in the example in Figure 13) to charge the energy storage elements of the selected specific bank.

[0096] When charging the energy storage elements in a specific bank, the charging current is generated using the discharge current of the energy storage elements in other banks. The energy storage elements in a specific bank may be charged until their State of Charge (SOC) reaches 100%. This increases the range of fluctuation in the SOC of the energy storage elements from the start to the end of charging, thereby improving the accuracy of estimating the full charge capacity.

[0097] Next, we will explain the method for estimating the capacity of the energy storage element.

[0098] Figure 14 shows an example of capacity estimation using the ΔSOC method. As shown in Figure 14A, it is assumed that the energy storage element (cell) discharges at a constant current I for a discharge time t. The stable voltage of the energy storage element immediately before discharge is defined as OCVa (open-circuit voltage), and the voltage of the energy storage element after discharge has stabilized is defined as OCVb (open-circuit voltage). The current and voltage during discharge of the energy storage element can be taken from data obtained during the actual operation of the energy storage system 101.

[0099] As shown in Figure 14B, based on the SOC-OCV characteristics of the energy storage element, SOCa corresponding to OCVa and SOCb corresponding to OCVb can be identified. The SOC-OCV characteristics can be stored, for example, in the memory unit 21.

[0100] As shown in Figure 14C, the estimated capacity (Ah) of an energy storage element can be calculated using the formula: Estimated Capacity (Ah) = {(Current I × Discharge Time t) / (SOCa - SOCb)}. The estimated capacity is the full charge capacity of the energy storage element. The State of Health (SOH) of the energy storage element can be calculated from the ratio of the estimated full charge capacity to the initial full charge capacity of the energy storage element. For example, if the initial full charge capacity of the energy storage element is 50 Ah and the estimated full charge capacity of the energy storage element is 40 Ah, then the SOH of the energy storage element will be {(40 / 50) × 100} = 80%.

[0101] Figure 15 shows an example of a partial charge / discharge profile of an energy storage element. In Figure 15, the horizontal axis represents the amount of charge (Ah), and the vertical axis represents the voltage (V). The amount of charge can be obtained, for example, by current integration. For example, the amount of charge Q(t) can be calculated using the formula {Q(t) = ΣI(t) × Δt}. A partial charge / discharge profile can be drawn by plotting the amount of charge and the voltage at the time when that amount of charge was obtained (the voltage corresponding to that amount of charge). The charging and discharging current and voltage of the energy storage element can be taken from data obtained during the actual operation of the energy storage system 101.

[0102] Figure 16 shows an example of capacity estimation based on overall discharge characteristics. In Figure 16, the horizontal axis represents integrated capacity (Ah), and the vertical axis represents voltage (V). In Figure 16, the overall charge-discharge characteristics (reproduced overall discharge curve) estimated based on the partial charge-discharge profile are shown. The overall charge-discharge characteristics reproduce continuous charging and discharging from the upper limit voltage to the lower limit voltage set for the energy storage element. The fully charged capacity of the energy storage element (estimated capacity Q) can be calculated by subtracting the integrated capacity corresponding to the upper limit voltage from the integrated capacity corresponding to the lower limit voltage of the overall discharge curve.

[0103] Furthermore, the method for estimating the overall discharge characteristics based on the partial charge-discharge profile can be the method described in Japanese Patent Application Publication No. 2023-010325.

[0104] There are several methods for estimating the capacity of energy storage elements, including the 0% detection method, the 3% detection method, and the 7% detection method (cell voltage drop detection method). For example, the 3% detection method estimates the capacity of the energy storage element by calculating the cumulative discharge amount from 100% to 3% voltage during discharge. Similarly, it estimates the capacity of the energy storage element by calculating the cumulative charge amount from 3% to 100% voltage during charging. The State of Health (SOH) can be estimated by determining how much the estimated capacity has decreased compared to the initial capacity. The other methods, the 0% detection method and the 7% detection method, work in a similar manner.

[0105] The aforementioned capacity estimation methods—the ΔSOC method, the overall discharge characteristics-based capacity estimation, and the cell voltage drop detection method—improve in accuracy as the State of Charge (SOC) of the energy storage element becomes lower.

[0106] According to the embodiments described above, since the energy storage element is discharged to a predetermined state of charge (SOC), the accuracy of estimating the full charge capacity of the energy storage element can be improved, regardless of whether it is ternary or iron-based. Furthermore, since the frequency of discharging the energy storage element to a predetermined SOC is low (for example, only a few times a year), the energy storage element does not deteriorate.

[0107] The matters described in each embodiment can be combined with each other. Furthermore, the independent and dependent claims described in the claims can be combined with each other in any combination, regardless of the form of reference. Moreover, although the claims use a multi-claim format in which claims refer to two or more other claims (multi-claim format), it is not limited to this. A multi-claim format in which at least one multi-claim is referenced (multi-multi-claim) may also be used. For example, the capacity estimation method may be performed by a communication device or a management device instead of being performed by the server device 2. [Explanation of Symbols]

[0108] 1. Communication device 10 Control Unit 11 Storage section 12. First Communications Department 13. Second Communications Department 1P Device Program 2 Server devices 20 Control Unit 22P Data Processing Program 2P Automatic Monitor 3. Client devices 33 Display section

Claims

1. Equipped with a control unit, The control unit, Select one or more banks from among a plurality of banks of an energy storage system, each of which is connected in parallel, and each bank comprises a plurality of energy storage elements connected in series and a current control unit that controls the current flowing through the plurality of energy storage elements connected in series. The selected energy storage elements in a specific bank are discharged and / or charged to a predetermined charge level. While the energy storage elements of the specified bank are being discharged and / or charged, the voltage and current of the energy storage elements of the specified bank are acquired. Based on the acquired voltage and current, the capacity of the energy storage elements in the specific bank is estimated. Capacity estimation device.

2. The current control unit includes a circuit breaker, The control unit, The circuit breaker interrupts the current flowing to the energy storage elements in banks other than the specified bank, thereby allowing the energy storage elements in the specified bank to discharge and / or charge to a predetermined charge level. The capacity estimation device according to claim 1.

3. The control unit, Gradually reduce the number of banks selected for discharge and / or gradually increase the number of banks selected for charge. A capacity estimation device according to claim 1 or claim 2.

4. The current control unit includes a DC / DC converter. The capacity estimation device according to claim 1.

5. Select one or more banks from among a plurality of banks of an energy storage system, each of which is connected in parallel, and each bank comprises a plurality of energy storage elements connected in series and a current control unit that controls the current flowing through the plurality of energy storage elements connected in series. The selected energy storage elements in a specific bank are discharged and / or charged to a predetermined charge level. While the energy storage elements of the specified bank are being discharged and / or charged, the voltage and current of the energy storage elements of the specified bank are acquired. Based on the acquired voltage and current, the capacity of the energy storage elements in the specific bank is estimated. Capacity estimation method.

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