Energy storage system, and initial charging method for power storage bank

Abstract

This energy storage system connected to a power grid comprises at least one power storage bank, at least one power conversion unit, and a control device. When the energy storage system is activated, the control device connects the power conversion unit to a power grid after activating the power conversion unit by using the power storage bank prior to initial charging as a power supply, and, after connecting the power conversion unit to the power grid, uses the power conversion unit to perform initial charging of the power storage bank by means of the power of the power grid.

Description

Energy storage system, initial charging method for storage bank

[0001] The present invention relates to a technique for initially charging a storage bank in an energy storage system connected to a power grid.

[0002] In order to achieve efficient energy management, the introduction of energy storage systems is being promoted. When the demand for electricity is lower than the supply, the energy storage system charges a storage battery with surplus electricity, and when the demand for electricity exceeds the supply, the storage battery is discharged to make up for the power shortage. Patent Document 1 discloses a technology related to the energy storage system.

[0003] JP 2023-65595 A

[0004] In order to initially charge the power storage bank 120 when the energy storage system is started up, it is possible to provide the energy storage system with a charging circuit (DC power supply circuit) 200 dedicated to initial charging, as shown in Fig. 10. In Fig. 10, 140 denotes a power conversion unit, and 150 denotes a control device.

[0005] However, installing a charging circuit (DC power supply circuit) 200 dedicated to initial charging is costly, and improvements have been sought. An object of the present invention is to initially charge a power storage bank without using a charging circuit dedicated to initial charging.

[0006] An energy storage system according to one embodiment of the present invention is an energy storage system that is connected to a power grid and includes at least one or more storage banks, at least one or more power conversion units, and a control device.

[0007] When starting up the energy storage system, the control device starts up the power conversion unit using the storage bank before initial charging as a power source, then connects to the power grid, and after connecting to the power grid, uses the power conversion unit to initially charge the storage bank with power from the power grid.

[0008] This technology allows for initial charging of a storage bank without using a dedicated charging circuit for initial charging.

[0009] A perspective view of an energy storage system. A block diagram of an energy storage system. A block diagram of a power conversion unit. A block diagram of a power conversion unit. A flowchart of an initial charging operation. A diagram showing an initial charging path of a power storage bank. A flowchart of an initial charging operation. A diagram showing an initial charging path of a power storage bank. A flowchart of an additional process of a power conversion unit. A block diagram of an energy storage system. A diagram showing a comparative example.

[0010] (Outline of this embodiment) (1) An energy storage system according to one embodiment of the present invention is an energy storage system that is connected to a power grid and includes at least one or more storage banks, at least one or more power conversion units, and a control device.

[0011] When the energy storage system is started up, the control device starts up the power conversion unit using the power storage bank before initial charging as a power source, connects the control device to the power grid, and after connecting to the power grid, initially charges the power storage bank with power from the power grid using the power conversion unit. The initial charging is charging performed on the power storage bank when the energy storage system is started up. In the energy storage system of (1), any configuration other than the above is optional and may be used.

[0012] According to the energy storage system (1), the energy (capacity) of the storage bank before initial charging is used to start the power conversion unit, and the storage bank is initially charged using power from the power grid. This eliminates the need for a dedicated charging circuit for initial charging, simplifying the configuration of the energy storage system. By widely utilizing this technology not only at the initial startup of the energy storage system, but also at startup after maintenance or after an abnormal shutdown, it becomes possible to ensure the capacity of the storage battery panel after system startup. This is expected to contribute to the stable operation of the energy storage system.

[0013] In recent years, the introduction of energy storage systems has progressed in order to achieve carbon neutrality. This requires a large number of storage cells, and the production volume of these cells is on the rise. Against this backdrop, mass-produced inventory is shipped to various locations across the country, and construction schedules are adjusted at each location, resulting in longer storage periods for storage cells. If storage periods are prolonged, the SOC of the storage cells will decrease due to self-discharge, making initial charging necessary when setting up on-site after construction is completed. By applying this technology, initial charging can be performed without installing a dedicated charging circuit, allowing for smooth system setup at the site. This will contribute to efforts toward achieving carbon neutrality.

[0014] (2) In the energy storage system described in (1) above, the control device may determine, at the time of startup of the energy storage system, whether the power conversion unit can be started with the energy that can be output from the power storage bank before initial charging, and if startup is possible, start the power conversion unit using the power storage bank before initial charging as a power source. In the energy storage system of (2), any configuration other than the above is optional and may be any configuration.

[0015] According to the energy storage system (2), if the output energy of the storage bank before initial charging is sufficient to start the power conversion unit, that energy is used to start the power conversion unit, thereby making it possible to effectively utilize the energy of the storage bank before initial charging.

[0016] (3) In the energy storage system described in (1) or (2) above, the power conversion unit may be a plurality of units, and the control device may adjust the number of power conversion units to be activated depending on the state of the power storage bank before initial charging. In the energy storage system of (3), any configuration other than the above is optional and may be any configuration.

[0017] According to the configuration (3), the number of power conversion units to be activated can be adjusted depending on the state of the power storage bank before the initial charge, thereby enabling flexible operation of the energy storage system.

[0018] (4) In the energy storage system described in (3) above, when the energy that can be output from the power storage bank before initial charging is insufficient for the energy required to start up the plurality of power conversion units, the control device may start up some of the power conversion units and start initial charging of the power storage bank. In the energy storage system of (4), any configuration other than the above is optional and may be any configuration.

[0019] According to the configuration (4), even if the energy of the storage bank before the initial charge is insufficient, the initial charge of the storage bank can be started by activating some of the power conversion units. Furthermore, in a single power conversion unit configuration, if the energy of the storage bank before the initial charge is insufficient to start the power conversion unit, it is expected that the power conversion unit cannot be activated and the initial charge of the storage bank cannot be started. However, in a multiple power conversion unit configuration, assuming the overall capacity is the same, the capacity required to start each unit is smaller than in a single unit configuration. For example, in a two-unit configuration, the capacity required to start each unit is only half of the total. Therefore, by using multiple power conversion units and applying this technology, it is expected that the risk of difficulty in starting the initial charge of the storage bank can be reduced and initial charge can be enabled regardless of the state of the storage bank (storage cells).

[0020] (5) In the energy storage system described in (4) above, when the energy shortage of the power storage bank is resolved by starting the initial charging, the control device may start up the remaining power conversion units and increase the number of power conversion units used for the initial charging. In the energy storage system of (5), any configuration other than the above is optional and may be any configuration.

[0021] According to the configuration (5), by increasing the number of power conversion units used for the initial charging, the time required for the initial charging can be shortened.

[0022] (6) In the energy storage system according to any one of (1) to (5), the initial charging of the power storage bank may be performed at the time of initial startup of the energy storage system. In the energy storage system according to (6), any configuration other than the above is optional and may be any configuration.

[0023] According to the configuration (6), when the energy storage system is first started up, the capacity of the storage bank can be restored by initial charging, thereby eliminating capacity shortages. Conversely, before the initial start-up of the energy storage system, such as during storage in a factory, the capacity of the storage bank can be reduced, thereby suppressing cell degradation and enabling storage and transportation at low capacity, which is advantageous in terms of safety and management. When the storage bank uses cells that are prone to chemical reactions, such as lithium-ion secondary batteries, storage and transportation can pose safety issues even at high SOCs. By applying this technology, storage and transportation at low SOCs are possible before installation, eliminating or minimizing safety issues specific to cells. Furthermore, in addition to the above, capacity decline due to natural discharge can also be tolerated.

[0024] <First Embodiment> 1. Description of Energy Storage System 10 Fig. 1 is a perspective view of an energy storage system 10. The energy storage system 10 is a system that is connected to a power grid 1 and adjusts the supply and demand of power. The power grid 1 may be that of a power utility company, or may be an independent power grid that is based on the stand-alone operation output of a large-scale power conditioner.

[0025] 2 is a block diagram of the energy storage system 10. In this embodiment, three energy storage systems 10A to 10C are installed in parallel. Since the energy storage systems 10A to 10C have the same structure, the configuration of the energy storage system 10A will be described as a representative.

[0026] The energy storage system 10A includes a battery panel 20A and a PCS panel 30A. PCS is an abbreviation for Power Conditioning System.

[0027] The battery panel 20A includes a power storage bank 21, a monitoring unit 23, and a housing 25 that houses these components. The power storage bank 21 is composed of a plurality of power storage cells connected in series. Various types of cells can be used as the power storage cells, as long as they are capable of storing electricity (capable of repeated charging and discharging), such as non-aqueous electrolyte secondary battery cells such as lithium-ion secondary batteries, capacitors, NAS battery cells, and redox flow battery cells. The power storage bank 21 may be configured as a single bank or multiple banks. In this embodiment, the power storage bank 21 is configured as two banks.

[0028] The monitoring unit 23 monitors the state of the battery panel 20A. The monitored items include the voltage of the battery panel 20A (total voltage of the power storage bank 21, voltage of each power storage cell), current (total current of the power storage bank 21), temperature, etc. These monitored items can be measured by sensors.

[0029] The battery panel 20A is connected to the PCS panel 30 via a switch SW. In this embodiment, a plurality of (three) battery panels 20A are connected in parallel to one PCS panel 30A.

[0030] The PCS panel 30A includes a power conversion unit 40A, a switch SW, a control device 50A, and a housing 60 that houses these components. The power conversion unit 40A is connected to an interconnection line L1 of the power system 1 via the switch SW.

[0031] As shown in FIG. 3A, the power conversion unit 40A includes a DC / DC converter 41, a link capacitor 42, an inverter 43, a current sensor 44, an LC filter 45, and a switch 46.

[0032] The power conversion unit 40A is a bidirectional power converter capable of reverse conversion (DC to AC) and forward conversion (AC to DC).

[0033] 3A, the power conversion unit 40A performs an inverse conversion operation (DC to AC) to discharge the battery panel 20A and supply AC power to the power grid 1. Also, the power conversion unit 40A performs a forward conversion operation (AC to DC) to charge the battery panel 20A with AC power from the power grid 1, as shown in FIG. 3B.

[0034] In this embodiment, a plurality of power conversion units 40A are provided in parallel to ensure the capacity of the PCS panel 30A.

[0035] The control device 50A includes, for example, a central processing unit (CPU) and a memory for storing various data. The control device 50A controls the power conversion unit 40A in response to commands from a higher-level device 100 such as an EMS (Energy Management System) and adjusts the supply and demand of power.

[0036] Specifically, when the demand for electricity is lower than the supply, the excess electricity is used to charge the battery panel 20A of the energy storage system 10A, and when the demand for electricity exceeds the supply, the power shortage is compensated for by discharging the battery panel 20A of the energy storage system 10A.

[0037] As described above, the energy storage system 10A can improve the efficiency of energy use and contribute to energy conservation by exchanging power with the power grid 1 and adjusting supply and demand.

[0038] As shown in FIGS. 1 and 2, this system includes three energy storage systems 10A to 10C, and control devices 50A to 50C of the energy storage systems 10A to 10C are connected by a communication line L2.

[0039] The three control devices 50A to 50C cooperate by communicating with each other to control the entire energy storage systems 10A to 10C. By adjusting the supply and demand of electricity using the three parallel energy storage systems 10A to 10C, it is possible to adjust three times the amount of energy compared to a single system.

[0040] The control system is not limited to the above, and an integrated control device that integrates the three control devices 50A to 50C may be separately installed. The entire energy storage system 10A to 10C may be controlled via the three control devices 50A to 50C by commands from the integrated control device.

[0041] The control devices 50A to 50C store data (A to D) in memory 51, respectively, in order to initially charge the storage battery panels 20A to 20C. Initial charging is charging that is performed when the energy storage system is started up. Initial charging is not limited to the first start-up after the product is installed, but also includes cases where the storage battery panel 20 is charged when the system is started up after operation has been stopped due to maintenance or a malfunction, or when the system is started up after the storage battery panel 20, etc. has been replaced.

[0042] (A) SOC or capacity of the battery panel before initial charging (B) Voltage of the battery panel (storage cell) before initial charging (C) Lower limit voltage of the battery panel (storage cell) (D) Energy required to start the power conversion unit (power consumption)

[0043] The data (A) may be a measurement value by the monitoring unit 23 or the like, or may be substituted with data at the time of shipment from the factory (during supplementary charging). If a long period of time has passed since shipment from the factory, a decrease in capacity due to self-discharge may be taken into account.

[0044] 2. Initial charging of the battery panels 20 The battery panels 20A to 20C may be supplementally charged before shipping. Supplementary charging is a small amount of charging that prevents the dischargeable capacity from becoming zero, in order to suppress deterioration of the storage cells. Because the amount of energy supplementary charging is not sufficient to adjust the supply and demand of electricity, the battery panels 20A to 20C may be initially charged when the energy storage systems 10A to 10C are started up.

[0045] 4 is a flowchart of the initial charging operation of the battery panels 20A to 20C. The initial charging operation will be described below using the battery panel 20A as an example.

[0046] The initial charging operation of the battery panel 20A is composed of five steps S10 to S50.

[0047] When the initial charging operation starts, the control device 50A first determines in S10 whether the amount of energy that can be output from the storage battery panel 20A before the initial charging is sufficient to start up the power conversion unit 40A. Specifically, when the three power conversion units 40A-1 to 40A-3 are started up using the storage battery panel 20A before the initial charging as a power source, the determination can be made based on whether the storage battery panel 20A can maintain the lower limit voltage required to maintain performance.

[0048] An example of the startup process of the power conversion unit 40A is charging of the components of the power conversion unit 40A, specifically the link capacitor 42 and the LC filter 45.

[0049] <Calculation example> For one surface of a 200 kWh storage battery panel, the amount of energy U1 that can be discharged from the voltage before initial charging to the lower limit voltage for use is: U1 = 200 kWh × (ΔSOC = 0.51%) = 1.020 Wh. The power consumption U2 when the power required for the startup operation of one power conversion unit (charging the link capacitor 42 and LC filter 45) is 1 kW and the operation time required for startup is 1 minute is: U2 = 1 kW × 1 unit × 1 minute = 16.6 Wh.

[0050] For example, as shown in Figure 2, when three power conversion units 40A-1 to 40A-3 are started using three battery panels 20A, U1 x 3 > U2 x 3, so it is possible to start up the three power conversion units 40A using the three battery panels 20A.

[0051] If the power conversion unit 40A can be started by the storage battery panel 20A (S10: YES), the process proceeds to S20.

[0052] When the process proceeds to S20, the control device 50A starts up each of the three power conversion units 40A-1 to 40A-3 on the PCS panel 30A by charging the link capacitor 42 and the LC filter 45 using the battery panel 20A as a power source.

[0053] Thereafter, the control device 50A sends a command to the PCS panel 30A to control each power conversion unit 40A to AC output (reverse conversion operation: discharge in FIG. 3A ) and closes the switch 65. By setting the output to AC output, the output of the power conversion unit 40A can be controlled to a state in which the voltage difference and phase difference with the power grid 1 are small. Therefore, connection to the power grid 1 is possible with a small voltage difference and phase difference.

[0054] Next, in S30, the control device 50A closes the switch SW and connects the activated power conversion unit 40A to the power system 1.

[0055] Thereafter, in S40, the control device 50A sends a command to the PCS panel 30A to switch the power conversion unit 40A to DC output (forward conversion operation in FIG. 3B; charging).

[0056] As a result, as shown in FIG. 5, three power conversion units 40A-1 to 40A-3 of the PCS panel 30A can be used to initially charge three storage battery panels 20A with power from the power system 1.

[0057] The battery panels 20B and 20C can also be initially charged in a similar manner. After the initial charging of the battery panels 20A to 20C is completed, the energy storage system 10 starts operation.

[0058] On the other hand, if it is determined in S10 that the amount of energy in the battery panel 20A is insufficient, the control device 50A issues a charging error warning. When a charging error warning is issued, it is conceivable to start up the power conversion unit 20A using a separate power source and initially charge the battery panel 20A with power from the power grid 1. The separate power source may be, for example, an external portable power source or an internal auxiliary power source. Furthermore, the battery panel 20A may be charged by some other method or route, not limited to the power grid 1.

[0059] 2. Effects According to the energy storage system 10, the energy (capacity) of the battery panel 20 before the initial charge is used to start up the power conversion unit 40, and the battery panel 20 is initially charged with power from the power grid 1. Therefore, there is no need to provide a charging circuit dedicated to the initial charge, and the configuration of the energy storage system 10 can be simplified.

[0060] <Embodiment 2> Fig. 6 is a flowchart of the initial charging operation of battery panels 20A to 20C. The initial charging operation of Fig. 6 differs from the initial charging operation of Fig. 4 in that S25 is added. The differences from the initial charging operation of Fig. 4 will be described below.

[0061] When the initial charging operation starts, the control device 50A first determines the amount of energy that can be output from the storage battery panel 20A in a state before the initial charging in S10.

[0062] If the three power conversion units 40A-1 to 40A-3 can be started with the amount of energy that can be output from the battery panel 20A (S10: YES), as in embodiment 1, the control device 50A starts up the three power conversion units 40A-1 to 40A-3 using the battery panel 20A as a power source.

[0063] Thereafter, the control device 50A connects the three activated power conversion units 40A-1 to 40A-3 to the power system 1, and initially charges the battery panel 20A with power from the power system 1 using the three activated power conversion units 40A-1 to 40A-3 (S20 to S40).

[0064] If the amount of energy that can be output by the storage battery panel 20A is insufficient to start up the three power conversion units 40A-1 to 40A-3 (S10: NO), the process proceeds to S25.

[0065] When the process proceeds to S25, the control device 50A starts up some of the three power conversion units 40A-1 to 40A-3. For example, if two power conversion units can be started up within the output range of the storage battery panel 20A, two of the three power conversion units 40A-1 to 40A-3, namely, 40A-1 and 40A-2, are started up.

[0066] Thereafter, the control device 50A connects the two power conversion units 40A-1 and 40A-2 that have been started to the power grid 1.

[0067] Thereafter, by switching the power conversion unit 40A to charging, the battery panel 20A can be initially charged using the two power conversion units 40A-1 and 40A-2, as shown in FIG. 7 (S20 to S40).

[0068] According to this configuration, even if the amount of energy that can be output from the battery panel 20A is insufficient before the initial charging, the initial charging of the battery panel 20A can be started by activating some of the power conversion units 40A-1, 40A-2.

[0069] 8 is a flowchart of additional processing of the power conversion unit 40A that is executed during initial charging. After the start of initial charging, the SOC of the storage battery panel 20A increases due to charging, and the amount of energy that can be output increases.

[0070] After the start of initial charging, the control device 50A determines whether the energy shortage in the storage battery panel 20A has been resolved (S100). Specifically, the control device 50A determines whether the amount of energy that can be output is sufficient to start up the third power conversion unit 40A-3.

[0071] If the amount of energy is sufficient (S100: YES), the control device 50A temporarily stops the initial charging, starts the power conversion unit 40A-3 using the energy from the storage battery panel 20A, and increases the number of power conversion units 40A used for charging from two to three (S110, S120).

[0072] After the third unit is started, initial charging is resumed, and after resumption, the three power conversion units 40A-1 to 40A-3 are used to initially charge the battery panel 20A with power from the power system 1 (S130).

[0073] According to this configuration, by increasing the number of power conversion units used for initial charging, the time required for initial charging can be shortened.

[0074] <Other Embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0075] (1) In the above embodiment, as shown in Figures 1 and 2, a configuration in which three energy storage systems 10A to 10C are installed side by side is shown. However, the present technology is not limited to this, and can be applied to a single energy storage system 10A as shown in Figure 9. Furthermore, the number of storage battery panels 20A and PCS panels 30A may be one.

[0076] (2) In the above embodiment, the battery panel 20 is initially charged when the energy storage system 10 is first started up. This technology may be applied to initially charge the battery panel 20 not only at the first start up, but also when starting the system after operation has been stopped due to maintenance or an abnormality, or when starting the system after replacing the battery panel 20, etc. Additionally, the technology may be applied to initially charge the battery panel 20 when starting the system after a new battery panel 20 or PCS panel 30 is installed, or when starting the system after the battery panel 20 has discharged below the lower limit voltage (limit) due to operation.

[0077] (3) In the above embodiment, charging of the link capacitor 42 and the LC filter 45 was described as one of the processes for starting up the power conversion unit 40. The start-up process is not limited to charging of the link capacitor 42 and the LC filter 45, and may be any other process that consumes power.

[0078] (4) In the above embodiment, in the flow of the initial charging operation shown in Fig. 4, in S10, it is determined whether the amount of energy in the battery panel 20A before the initial charging is sufficient to start up the power conversion unit 40A. If the energy (capacity) of the battery panel 20A before the initial charging is managed so that it is not insufficient to start up the power conversion unit 40A, S10 may be omitted.

[0079] (5) In the above embodiment, the number of power conversion units 40 to be activated is adjusted depending on the amount of energy that can be output by the storage battery panel 20A. If the storage battery panel 20A is deteriorated before the initial charge due to long-term storage or the like, the number of power conversion units 40 to be activated may be adjusted depending on the degree of deterioration. Specifically, the number of power conversion units 40 to be activated may be reduced as the deterioration progresses. The degree of deterioration may be estimated, for example, from the storage period of the storage cells and the environmental conditions during storage. The data on the storage cells during storage (storage period and environmental conditions) is an example of data for identifying the state of the storage cells before the initial charge. The data may be associated with the storage cells, managed, and stored in advance in the control device 50. Alternatively, the data may be acquired through data communication with the storage facility. In this way, adjusting the number of power conversion units to be activated depending on the state of the storage battery panel 20A before the initial charge, such as the amount of energy that can be output and the degree of deterioration, enables flexible operation and allows initial charging to be performed regardless of the state of the storage battery panel before the initial charge.

[0080] 1 Power system 10A to 10C Energy storage system 20A to 20C Battery panel 30A to 30C PCS panel 40A to 40C Power conversion unit 50A to 50C Control device

Claims

1. An energy storage system interconnected with an electric power grid, comprising: at least one or more storage banks; at least one or more power conversion units; and a control device, wherein, when the energy storage system is started up, the control device starts up the power conversion unit using the storage banks before initial charging as a power source, and then connects the energy storage system to the electric power grid; and after being connected to the electric power grid, the control device initially charges the storage banks using power from the electric power grid using the power conversion unit.

2. An energy storage system as claimed in claim 1, wherein the control device determines, at the time of starting up the energy storage system, whether or not the power conversion unit can be started up with the energy that can be output from the storage bank before initial charging, and if start-up is possible, starts up the power conversion unit using the storage bank before initial charging as a power source.

3. An energy storage system according to claim 1 or claim 2, wherein the power conversion units are multiple, and the control device adjusts the number of power conversion units to be activated depending on the state of the storage bank before initial charging.

4. An energy storage system as described in claim 3, wherein the control device starts up some of the power conversion units and starts initial charging of the storage bank when the energy that can be output from the storage bank before initial charging is insufficient for the energy required to start up multiple power conversion units.

5. An energy storage system according to claim 4, wherein the control device activates the remaining power conversion units and increases the number of power conversion units used for initial charging when the energy shortage in the storage bank is resolved by initial charging.

6. An energy storage system according to claim 1 or 2, wherein the initial charging of the storage bank is performed when the energy storage system is started for the first time.

7. A method for charging a storage bank of an energy storage system connected to a power grid, comprising: at the start-up of the energy storage system, starting up a power conversion unit using the storage bank before initial charging as a power source, and then connecting the energy storage system to the power grid; and after connecting to the power grid, initially charging the storage bank with power from the power grid using the power conversion unit.

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