Energy storage system, initial charging method of battery pack

Abstract

An energy storage system interconnected with a power system includes at least one energy storage unit, at least one power conversion unit, and a control device. When the energy storage system is started, the control device uses the energy storage unit (before initial charging) as a power source to start the power conversion unit. After starting the power conversion unit, the system is interconnected with the power system. After interconnection with the power system, the power conversion unit uses the power from the power system to initially charge the energy storage unit.

Description

Technical Field

[0001] This invention relates to a technique for initial charging of a battery bank in an energy storage system interconnected with a power system. Background Technology

[0002] To achieve efficient energy utilization, the introduction of energy storage systems is being promoted. When electricity demand is lower than supply, the energy storage system charges the battery bank using the surplus electricity; when electricity demand exceeds supply, it compensates for the power shortage by discharging the battery bank. Patent document 1 discloses technology related to energy storage systems.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2023-65595 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] In order to initially charge the energy storage group 120 when the energy storage system starts up, such as Figure 10 As shown, consider setting up a dedicated charging circuit (DC power supply circuit) 200 for initial charging in the energy storage system. Figure 10 140 is the power conversion unit, and 150 is the control device.

[0008] However, setting up a dedicated charging circuit (DC power supply circuit) for initial charging is costly and requires improvement.

[0009] The objective of this invention is to perform initial charging of the battery pack without using a dedicated charging circuit for initial charging.

[0010] Technical solutions to the problem

[0011] One embodiment of the present invention relates to an energy storage system that is interconnected with a power system, which includes at least one energy storage unit, at least one power conversion unit, and a control device.

[0012] When the energy storage system is started, the control device starts the power conversion unit using the battery pack before initial charging as the power source. After starting the power conversion unit, it is interconnected with the power system. After interconnection with the power system, the power conversion unit is used to perform initial charging of the battery pack using the power from the power system.

[0013] Invention Effects

[0014] This technology enables the initial charging of the battery pack without the need for a dedicated initial charging circuit. Attached Figure Description

[0015] Figure 1 This is a three-dimensional diagram of an energy storage system.

[0016] Figure 2 This is a block diagram of an energy storage system.

[0017] Figure 3A This is a block diagram of a power conversion unit.

[0018] Figure 3B This is a block diagram of a power conversion unit.

[0019] Figure 4 This is a flowchart of the initial charging process.

[0020] Figure 5 This is a diagram showing the initial charging path of the battery pack.

[0021] Figure 6 This is a flowchart of the initial charging process.

[0022] Figure 7 This is a diagram showing the initial charging path of the battery pack.

[0023] Figure 8 This is a flowchart of the additional processing for the power conversion unit.

[0024] Figure 9 This is a block diagram of an energy storage system.

[0025] Figure 10 This is a diagram representing a comparative example. Detailed Implementation

[0026] (Summary of this implementation method)

[0027] (1) An energy storage system according to one embodiment of the present invention is an energy storage system interconnected with a power system, comprising at least one energy storage unit, at least one power conversion unit, and a control device.

[0028] The control device starts the power conversion unit using the battery pack before initial charging as the power source when the energy storage system is started. After starting the power conversion unit, it is interconnected with the power system. After interconnection with the power system, the power conversion unit uses the power from the power system to perform initial charging of the battery pack. Initial charging is the charging of the battery pack when the energy storage system is started. In the energy storage system of (1), the structure is arbitrary except for the above-described structure, and can be any structure.

[0029] According to the energy storage system in (1), the power conversion unit is started using the energy (capacity) of the battery pack before initial charging, and the battery pack is initially charged using power from the power system. Therefore, there is no need to set up a dedicated charging circuit for initial charging, which simplifies the structure of the energy storage system. By widely and flexibly utilizing this technology not only during the initial startup of the energy storage system, but also during system startup after maintenance and system startup after abnormal shutdown, the capacity of the battery pack can be ensured after system startup. Therefore, it can be expected to contribute to the stable operation of the energy storage system.

[0030] Furthermore, in recent years, the adoption of energy storage systems is being promoted to achieve carbon neutrality. Therefore, there is a growing demand for energy storage units, leading to an increase in their production volume. Against this backdrop, mass-produced inventory is being distributed across the country, requiring adjustments during project implementation, resulting in longer storage periods for energy storage units. With these extended storage periods, the State of Charge (SOC) of energy storage units decreases due to self-discharge, necessitating initial charging upon commissioning after project completion. This technology eliminates the need for dedicated charging circuits, enabling smooth system commissioning on-site. Therefore, it contributes to measures aimed at achieving carbon neutrality.

[0031] (2) In the energy storage system described in (1) above, the control device can determine whether the power conversion unit can be started using the output energy of the battery pack before initial charging when the energy storage system is started. If it can be started, the power conversion unit is started using the battery pack before initial charging as the power source. In the energy storage system of (2), any structure other than the above-described structure is acceptable.

[0032] According to the energy storage system of (2), if the output energy of the battery pack before initial charging is sufficient to start the power conversion unit, the power conversion unit can be started using this energy. Therefore, the energy of the battery pack before initial charging can be effectively and flexibly utilized.

[0033] (3) In the energy storage system described in (1) or (2) above, there are multiple power conversion units, and the control device can adjust the number of power conversion units activated according to the state of the energy storage group before initial charging. In the energy storage system of (3), any structure other than the above-described structure is acceptable.

[0034] According to the structure of (3), the number of power conversion units to be started can be adjusted according to the state of the energy storage group before initial charging, thus enabling flexible use of the energy storage system.

[0035] (4) In the energy storage system described in (3) above, the control device can start a portion of the power conversion units to begin the initial charging of the energy storage unit if the output energy of the energy storage group before initial charging is insufficient relative to the energy required to start the plurality of power conversion units. In the energy storage system of (4), any structure other than the above-described structure is acceptable.

[0036] According to the structure in (4), even if the energy of the battery bank is insufficient before initial charging, the initial charging of the battery bank can be started by activating a portion of the power conversion units. Furthermore, if the power conversion unit is a single unit, and the energy of the battery bank before initial charging does not meet the capacity required to activate the power conversion unit, it is conceivable that the power conversion unit cannot be activated, and the initial charging of the battery bank cannot begin. However, if the power conversion unit is configured with multiple units, assuming the overall capacity is the same, the capacity required to activate each unit is smaller compared to the case of a single unit. For example, in the case of two units, the capacity required to activate each unit is only half of the overall capacity. Therefore, by configuring the power conversion unit with multiple units and applying this technology, it is expected that the risk of difficulty in initiating the initial charging of the battery bank can be reduced, making initial charging possible regardless of the state of the battery bank (battery unit).

[0037] (5) In the energy storage system described in (4) above, the control device can activate the remaining power conversion units and increase the number of power conversion units used for initial charging after the energy shortage of the battery bank has been eliminated by the start of initial charging. In the energy storage system of (5), any structure other than the above-described structure is acceptable.

[0038] According to the structure of (5), the time required for initial charging can be shortened by increasing the number of power conversion units used for initial charging.

[0039] (6) In any one of the energy storage systems (1) to (5) above, the initial charging of the energy storage group can be performed during the initial startup of the energy storage system. In the energy storage system of (6), any structure other than the above-described structure is acceptable.

[0040] According to the structure of (6), the capacity of the battery pack can be restored by initial charging during the initial startup of the energy storage system, eliminating insufficient capacity. Conversely, during storage in the factory, the capacity of the battery pack can be suppressed before the initial startup of the energy storage system, thus suppressing battery degradation. In addition, since it can be stored and transported at low capacity, it also has advantages in terms of safety and management. In the case of battery packs that are cells that are prone to chemical reactions, such as lithium-ion secondary batteries, there are safety issues in storage and transportation even at high SOC. By applying this technology, storage and transportation at low SOC can be carried out before construction, thus eliminating or suppressing the safety issues specific to the cell. Furthermore, not limited to the above, capacity reduction caused by natural discharge can also be tolerated.

[0041] <Implementation Method 1>

[0042] 1. Description of Energy Storage System 10

[0043] Figure 1 This is a perspective view of the energy storage system 10. The energy storage system 10 is a system interconnected with the power system 1 and performs power supply and demand regulation. The power system 1 can be a power operator's power system or an independent power system consisting of the independent operating output of a large power regulator.

[0044] Figure 2 This is a block diagram of the energy storage system 10. In this embodiment, three energy storage systems, 10A to 10C, are connected in parallel. Since energy storage systems 10A to 10C have the same structure, energy storage system 10A is used as a representative example.

[0045] The energy storage system 10A includes a battery panel 20A and a PCS panel 30A. PCS is an abbreviation for Power Conditioning System.

[0046] The battery pack 20A includes a battery bank 21, a monitoring unit 23, and a housing 25 for storing them. The battery bank 21 is composed of a plurality of battery cells connected in series. Various battery cells are applicable, such as non-aqueous electrolyte secondary battery cells (e.g., lithium-ion secondary batteries), capacitors, NAS battery cells, redox flow battery cells, etc., that can store electricity (can be repeatedly charged and discharged). The battery bank 21 can be a single bank or a plurality of banks. In this embodiment, it is a two-bank structure.

[0047] The monitoring unit 23 monitors the status of the battery pack 20A. The monitored items include the voltage of the battery pack 20A (total voltage of the battery bank 21 and the voltage of each battery cell), the current (total current of the battery bank 21), and the temperature. These monitored items can be measured by sensors.

[0048] Battery panel 20A is connected to PCS panel 30 via switch SW. In this embodiment, multiple (three) battery panels 20A are connected in parallel relative to one PCS panel 30A.

[0049] PCS panel 30A includes a power conversion unit 40A, a switch SW, a control device 50A, and a housing 60 for storing them. The power conversion unit 40A is connected to the interconnection line L1 of the power system 1 via the switch SW.

[0050] like Figure 3A As shown, 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.

[0051] The power conversion unit 40A is capable of performing reverse conversion (DC) operation. AC) and clockwise transformation (AC) A bidirectional power converter (DC).

[0052] Through the inverse conversion operation of the power conversion unit 40A (DC) AC), such as Figure 3A As shown, the battery panel 20A can discharge, supplying AC power to the power system 1. Additionally, the power conversion unit 40A performs forward conversion (AC / AC)... DC), such as Figure 3B As shown, the battery pack 20A can be charged by the AC power of the power system 1.

[0053] In this embodiment, the capacity of the PCS disk 30A is ensured by arranging a plurality of power conversion units 40A in parallel.

[0054] The control device 50A is composed, for example, a CPU (Central Processing Unit) and a memory for storing various data. The control device 50A responds to instructions from a host device 100 such as an EMS (Energy Management System) to control the power conversion unit 40A and adjust the power supply and demand.

[0055] Specifically, when the demand for electricity is lower than the supply, the battery panel 20A of the energy storage system 10A is charged using the surplus electricity. When the demand for electricity exceeds the supply, the power shortage is compensated by discharging the battery panel 20A of the energy storage system 10A.

[0056] As described above, the energy storage system 10A can improve energy utilization efficiency and contribute to energy conservation by interconnecting with the power system 1 and adjusting supply and demand.

[0057] like Figure 1 , 2 As shown, this system is equipped with three energy storage systems 10A~10C, and the control devices 50A~50C of the energy storage systems 10A~10C are connected through communication line L2.

[0058] The three control devices 50A~50C cooperate through mutual communication to control the energy storage system 10A~10C as a whole. By using the three energy storage systems 10A~10C connected in parallel to adjust the power supply and demand, the energy amount can be adjusted three times compared to a single system.

[0059] The control system is not limited to the above; a unified control device consisting of three control devices 50A to 50C can also be set up. Alternatively, the energy storage system 10A to 10C can be controlled as a whole via the three control devices 50A to 50C according to the instructions of the unified control device.

[0060] In order to perform initial charging of the battery packs 20A-20C, control devices 50A-50C store data (A-D) in memory 51 respectively. Initial charging is performed when the energy storage system is started. Initial charging is not limited to the first start after product setup, but also includes charging the battery pack 20 when the system is started after it has stopped operating due to maintenance, abnormality, or other reasons, or when the battery pack 20 is replaced.

[0061] (A) The state of charge (SOC) or capacity of the battery pack before initial charging.

[0062] (B) Voltage of the battery pack (energy storage unit) before initial charging

[0063] (C) Lower limit voltage for use of the energy storage unit (energy storage cell)

[0064] (D) Energy (power consumption) required to start up the power conversion unit

[0065] (A) The data can be the measurement value obtained by the monitoring unit 23, or the data at the time of factory shipment (during recharging). If a long time has passed since the factory shipment, capacity reduction due to self-discharge can also be considered.

[0066] 2. Initial charging of battery pack 20

[0067] The 20A~20C battery packs are sometimes supplemented with a small charge before leaving the factory. This supplementary charge is a small amount of charge to prevent the degradation of the energy storage units and ensure that the discharge capacity is not zero. Since the supplementary charge is not sufficient for power supply and demand adjustment, the 20A~20C battery packs are sometimes initially charged when the energy storage system 10A~10C is started.

[0068] Figure 4 This is a flowchart of the initial charging process for battery packs 20A to 20C. The following explanation uses battery pack 20A as an example to illustrate the initial charging process.

[0069] The initial charging process of the 20A battery pack consists of five steps, S10 to S50.

[0070] Once the initial charging operation begins, the control device 50A first determines in S10 whether the output energy of the battery pack 20A in its pre-initial charging state is sufficient to start the power conversion unit 40A. Specifically, this can be determined by: if the three power conversion units 40A-1 to 40A-3 are started using the battery pack 20A as a power source before the initial charging, whether the battery pack 20A can maintain the lower operating voltage required to maintain performance.

[0071] As an example of the startup process of the power conversion unit 40A, the components of the power conversion unit 40A, specifically, are the charging of the link capacitor 42 and the LC filter 45.

[0072] <Calculation Example>

[0073] For a 200kWh battery pack, the amount of energy U1 that can be discharged from the initial charging voltage to the lower limit voltage is...

[0074] U1=200kWh×(ΔSOC=0.51%)=1.020Wh

[0075] The power required to start up a power conversion unit (charging the link capacitor 42 and LC filter 45) is set to 1kW, and the power consumption U2 is set to the operating time required for startup as one minute.

[0076] U2 = 1kW × 1 unit × 1 minute = 16.6Wh

[0077] For example, such as Figure 2 As shown, when three power conversion units 40A-1 to 40A-3 are started by three battery packs 20A, since U1×3>U2×3, it is possible to start three power conversion units 40A by three battery packs 20A.

[0078] If the power conversion unit 40A can be started via the battery panel 20A (S10: Yes), proceed to S20.

[0079] When transitioning to S20, the control device 50A charges the link capacitor 42 and LC filter 45 using the battery panel 20A as a power source, thereby activating the three power conversion units 40A-1 to 40A-3 of the PCS panel 30A respectively.

[0080] Then, the control device 50A sends a command to the PCS board 30A to control each power conversion unit 40A to AC output ( Figure 3A The reverse conversion operation (discharge) and the switch 65 are turned off. The output of the power conversion unit 40A can be controlled to a state with a small voltage and phase difference with the power system 1 by setting it to AC output mode. Therefore, it can be interconnected with the power system 1 when the voltage and phase differences are small.

[0081] Next, in S30, the control device 50A turns off the switch SW and connects the activated power conversion unit 40A to the power system 1.

[0082] Subsequently, control device 50A sends a command to PCS board 30A in S40 to switch power conversion unit 40A to DC output. Figure 3B (Successive change action; charging).

[0083] Therefore, as Figure 5 As shown, the three power conversion units 40A-1 to 40A-3 of the PCS disk 30A can use the power of the power system 1 to initially charge the three battery disks 20A.

[0084] Battery banks 20B and 20C can also be initially charged using the same method. Then, after the initial charging of battery banks 20A to 20C is completed, the energy storage system 10 begins to operate.

[0085] On the other hand, if the battery pack 20A is determined to have insufficient energy in S10, the control device 50A issues a charging error warning. In the event of a charging error warning, the control device considers using an alternative power source to activate the power conversion unit 20A and initially charge the battery pack 20A using power from the power system 1. Other power sources could be, for example, an external portable power source, a built-in auxiliary power source, etc. Furthermore, the battery pack 20A can be charged using other methods or paths, not limited to the power system 1.

[0086] 2. Effects

[0087] According to the energy storage system 10, the power conversion unit 40 is activated using the energy (capacity) of the battery pack 20 before initial charging, and the battery pack 20 is initially charged using the power from the power system 1. Therefore, there is no need to set up a dedicated charging circuit for initial charging, which simplifies the structure of the energy storage system 10.

[0088] <Implementation Method 2>

[0089] Figure 6 This is a flowchart of the initial charging process of the battery pack (20A~20C). Figure 6 The initial charging action relative to Figure 4 The initial charging process differs from the previous one in that it includes S25. Below is a comparison with... Figure 4 The differences in the initial charging action will be explained.

[0090] Once the initial charging action begins, in S10, before the initial charging begins, the control device 50A determines the amount of energy that the battery pack 20A can output.

[0091] When the three power conversion units 40A-1 to 40A-3 can be started by the output energy of the battery panel 20A (S10: Yes), the control device 50A starts the three power conversion units 40A-1 to 40A-3 by using the battery panel 20A as a power source, just like in Embodiment 1.

[0092] Afterwards, the control device 50A connects the three activated power conversion units 40A-1 to 40A-3 to the power system 1, and uses the activated power conversion units 40A-1 to 40A-3 to perform initial charging of the battery pack 20A through the power of the power system 1 (S20 to S40).

[0093] If the output energy of the battery 20A is insufficient to start the three power conversion units 40A-1 to 40A-3 (S10: No), proceed to S25.

[0094] When transitioning to S25, control device 50A activates some of the three power conversion units 40A-1 to 40A-3. For example, if two power conversion units can be activated within the output range of battery panel 20A, two power conversion units 40A-1 and 40A-2 out of the three 40A-1 to 40A-3 are activated.

[0095] Subsequently, the control device 50A interconnects the two activated power conversion units 40A-1 and 40A-2 with the power system 1.

[0096] Then, by switching the power conversion unit 40A to charging, such as... Figure 7 As shown, two power conversion units 40A-1 and 40A-2 can be used to initially charge the battery pack 20A (S20~S40).

[0097] According to this structure, even if the output energy of the battery pack 20A is insufficient before initial charging, the initial charging of the battery pack 20A can be started by activating some of the power conversion units 40A-1 and 40A-2.

[0098] Figure 8 This is a flowchart of the additional processing performed by the power conversion unit 40A during the initial charging process. After the initial charging begins, the battery bank 20A increases the State of Charge (SOC) by charging, thereby increasing the amount of output energy.

[0099] After the initial charging begins, the control device 50A determines whether the insufficient energy of the battery pack 20A has been eliminated (S100). Specifically, it determines whether the output energy is sufficient to start the third power conversion unit 40A-3.

[0100] When the energy is sufficient (S100: Yes), the control device 50A temporarily stops the initial charging and uses the energy from the battery 20A to start the power conversion unit 40A-3, increasing the number of power conversion units 40A used for charging from two to three (S110, S120).

[0101] Then, after the third unit is started, the initial charging restarts. After restarting, the three power conversion units 40A-1 to 40A-3 are used to perform initial charging of the battery panel 20A through the power of the power system 1 (S130).

[0102] According to this structure, the time required for initial charging can be shortened by increasing the number of power conversion units used for initial charging.

[0103] <Other Implementation Methods>

[0104] The present invention is not limited to the embodiments described above and the accompanying drawings. For example, the following embodiments are also included within the technical scope of the present invention.

[0105] (1) In the above embodiments, such as Figure 1 , 2 The diagram shows a structure where three energy storage systems 10A to 10C are simultaneously installed. However, this is not the only example. Figure 9 As shown, this technology can be applied to a single energy storage system 10A. Additionally, the number of battery panels 20A and PCS panels 30A can also be one.

[0106] (2) In the above embodiment, the battery pack 20 is initially charged during the initial startup of the energy storage system 10. This technology can also be applied to the initial charging of the battery pack 20 during system startup when the system has stopped operating due to maintenance, malfunctions, or other reasons, or when the battery pack 20 has been replaced. Furthermore, this technology can also be applied to the initial charging of the battery pack 20 during system startup when a new battery pack 20 or PCS pack 30 is added, or during system startup when the battery pack 20 is discharged to below the operating lower limit voltage (limit).

[0107] (3) In the above embodiment, as one of the processes for starting the power conversion unit 40, the charging of the link capacitor 42 and the LC filter 45 is shown. The startup process is not limited to the charging of the link capacitor 42 and the LC filter 45; any process that consumes power may be used.

[0108] (4) In the above embodiments, in Figure 4 In the initial charging process shown, step S10 determines whether the energy of the battery pack 20A before initial charging is sufficient to start the power conversion unit 40A. If the energy (capacity) of the battery pack 20A before initial charging is insufficient to start the power conversion unit 40A, step S10 can be omitted.

[0109] (5) In the above embodiment, the number of power conversion units 40 activated is adjusted according to the output energy of the battery pack 20A. If the battery pack 20A deteriorates before initial charging due to long-term storage, the number of power conversion units 40 activated can also be adjusted according to the degree of deterioration. Specifically, the number of power conversion units 40 activated can be reduced as deterioration progresses. The degree of deterioration can be estimated, for example, based on the storage period of the battery pack and the environmental conditions during storage. This storage data (storage period, environmental conditions) is an example of data used to determine the state of the battery pack before initial charging, and can be managed in association with the battery pack and pre-stored in the control device 50. Alternatively, it can be obtained through data communication with the storage facility. Thus, by adjusting the number of power conversion units activated according to the output energy, the degree of deterioration, and other states of the battery pack 20A before initial charging, flexible operation is possible, allowing initial charging to be performed regardless of the state of the battery pack before initial charging.

[0110] 1. Power System

[0111] 10A~10C Energy Storage System

[0112] 20A~20C Battery Panel

[0113] 30A~30C PCS disk

[0114] 40A~40C Power Conversion Unit

[0115] 50A~50C Control Device

Claims

1. An energy storage system interconnected with a power system, wherein, The energy storage system includes at least one energy storage unit, at least one power conversion unit, and a control device. When the energy storage system is started, the control device uses the battery pack (before initial charging) as a power source to start the power conversion unit. After starting the power conversion unit, it is interconnected with the power system. After being interconnected with the power system, the power conversion unit is used to initially charge the energy storage group using power from the power system.

2. The energy storage system according to claim 1, wherein, When the energy storage system is started, the control device determines whether the power conversion unit can be started using the output energy of the battery pack before initial charging. If startup is possible, the power conversion unit is started using the battery pack before initial charging as the power source.

3. The energy storage system according to claim 1 or 2, wherein, The power conversion unit is a plurality of units. The control device adjusts the number of power conversion units activated based on the state of the battery pack before initial charging.

4. The energy storage system according to claim 3, wherein, If the output energy of the energy storage group before initial charging is insufficient relative to the energy required to start the plurality of power conversion units, the control device starts a portion of the power conversion units to begin the initial charging of the energy storage group.

5. The energy storage system according to claim 4, wherein, After the energy shortage of the battery bank is eliminated through initial charging, the control device activates the remaining power conversion units, increasing the number of power conversion units used for initial charging.

6. The energy storage system according to claim 1 or 2, wherein, The initial charging of the energy storage group is performed during the initial startup of the energy storage system.

7. An energy storage system for a battery bank, said energy storage system being interconnected with a power system, wherein in the charging method of the battery bank, When the energy storage system is started, the power conversion unit is activated using the energy storage group before initial charging as the power source. After the power conversion unit is activated, it is interconnected with the power system. After being interconnected with the power system, the power conversion unit is used to initially charge the energy storage group using power from the power system.

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