Energy storage system, method of deploying energy storage bank

Abstract

To suppress cross current of a bank in deployment to a main line in a power storage system with a plurality of parallely connected energy storage banks.SOLUTION: A power storage system S1 comprises: a plurality of energy storage banks B which are parallelly connected with a main line L; and a system controller 100. The system controller 100 executes processing of alleviating cross current generated among the energy storage banks B to alleviate the cross current in accordance with deployment of the energy storage banks B to the main line L when the maximum voltage difference ΔVm among the energy storage banks B is a first threshold V1 or more, and deploys the energy storage banks B to the main line L without restriction of the processing of alleviating the cross current when the maximum voltage difference ΔVm among the energy storage banks B is less than the first threshold before deployment of the energy storage banks B to the main line L.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a technology for suppressing cross currents when connecting power storage modules to a main line in a power storage system composed of a plurality of power storage modules.

Background Art

[0002] In recent years, power storage systems for residential use, industrial use and energy management have become widely popular to achieve energy conservation. The power storage unit of a power storage system is composed of a plurality of power storage banks connected in parallel. Patent Document 1 is a literature that discloses this type of technology.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] There is a voltage difference between different power storage banks due to factors such as variations in initial SOC. When there is a voltage difference between power storage banks, after the installation work of the power storage system, cross current flows between the power storage banks when connecting each power storage bank to the main line. If the cross current exceeds the limit value, problems such as failure of the power storage banks and protection devices may occur, so it has been required to suppress the cross current to below the limit value.

[0005] An object of the present invention is to suppress cross current generated between power storage banks when connecting the power storage banks to the main line in a power storage system provided with a plurality of power storage banks connected in parallel.

Means for Solving the Problem

[0006] The power storage system comprises: a plurality of power storage banks connected in parallel to a main line; and a system control device.

[0007] Before connecting the energy storage bank to the main line, the system control device performs a process to mitigate the crosscurrents occurring between the energy storage banks if the maximum voltage difference between the energy storage banks is greater than or equal to a first threshold, thereby mitigating the crosscurrents associated with connecting the energy storage bank to the main line. If the maximum voltage difference between the energy storage banks is less than the first threshold, the system control device connects the energy storage bank to the main line without any restrictions on the crosscurrent mitigation process. [Effects of the Invention]

[0008] This technology can suppress lateral currents that occur between energy storage banks when power is supplied to the main line in an energy storage system equipped with multiple energy storage banks connected in parallel. [Brief explanation of the drawing]

[0009] [Figure 1A] Schematic diagram of energy storage bank input [Figure 1B] Its equivalent circuit [Figure 2] Table showing the applicable voltage difference [Figure 3] Equivalent circuit of a battery storage bank [Figure 4] Equivalent circuit of a battery storage bank [Figure 5] Diagram showing the order in which the energy storage banks are used. [Figure 6] Diagram showing the order in which the energy storage banks are used. [Figure 7] Diagram showing the order in which the energy storage banks are used. [Figure 8] Block diagram showing the system configuration of the energy storage system [Figure 9] Block diagram of the energy storage module [Figure 10] Diagram showing the energy storage module and sensor unit. [Figure 11] Energy storage bank loading sequence [Figure 12A] Simulation results (showing voltage changes on the main line) [Figure 12B] Simulation results (showing the voltage change in the bank) [Figure 12C] Simulation results (showing the current change in the bank) [Figure 13A] Simulation result (showing voltage change of main line) [Figure 13B] Simulation result (showing voltage change of banks) [Figure 13C] Simulation result (showing current change of banks) [Figure 14] Diagram showing the connection order of storage battery banks [Figure 15] Connection sequence of storage battery banks [Figure 16] Flowchart of pre-warning processing for on-bank [Figure 17] Diagram summarizing subsequent responses for cases with and without an on-bank before executing cross-current mitigation processing

Mode for Carrying Out the Invention

[0010] (1) A power storage system according to an embodiment of the present invention includes a plurality of power storage banks connected in parallel to a main line, and a system control device. Before connecting the power storage banks to the main line, if the maximum voltage difference between the power storage banks is equal to or greater than a first threshold, the system control device executes processing for mitigating cross current generated between the power storage banks to mitigate cross current accompanying connection of the power storage banks to the main line; and if the maximum voltage difference between the power storage banks is less than the first threshold, the system control device connects the power storage banks to the main line without restrictions on said processing for mitigating cross current.

[0011] According to the power storage system according to an embodiment of the present invention, the following effects can be achieved. When the maximum voltage difference between the power storage banks is higher than the first threshold, cross current may occur in the power storage banks during connection to the main line, which may exceed a limit value. According to this power storage system, in the aforementioned case, the cross current generated between the power storage banks can be suppressed to below the limit value by the cross current mitigation processing. Therefore, occurrence of malfunctions in the power storage banks, protection devices thereof and the like can be suppressed. Furthermore, when the maximum voltage difference between the power storage banks is less than the first threshold, the power storage banks are connected to the main line without restrictions on the cross current mitigation processing, so the work of connecting the power storage banks can be completed in a short time.

[0012] (2) In the energy storage system described in (1) above, if the maximum voltage difference between energy storage banks is greater than or equal to a second threshold higher than the first threshold, the system control device may use the energy storage bank with the lowest voltage or the energy storage bank with the highest voltage as the reference bank, calculate the voltage difference of each energy storage bank with respect to the reference bank, exclude energy storage banks whose calculated voltage difference is greater than or equal to the second threshold, and determine the order in which the energy storage banks are connected to the main line.

[0013] According to the energy storage system described in (2) above, in the initial stages of the power supply operation, such as when only one energy storage bank is supplied to the main line, energy storage banks that cannot be expected to mitigate lateral flow can be excluded, and the power supply operation to the main line can proceed with the other energy storage banks while suppressing lateral flow.

[0014] (3) In the energy storage system described in (2) above, the system control device may calculate the number of energy storage banks to be excluded from determining the order of operation for cases where the energy storage bank with the lowest voltage is used as the reference bank and for cases where the energy storage bank with the highest voltage is used as the reference bank, and select the energy storage bank with the fewer number of excluded energy storage banks as the reference bank.

[0015] According to the energy storage system described in (3) above, the number of energy storage banks excluded from determining the order of input can be reduced, and more energy storage banks can be included in the process of mitigating cross-flow.

[0016] (4) A power storage system according to any one of the above items (1) to (3), wherein the process for mitigating the crosscurrent may be a process in which the crosscurrent of the power storage bank is estimated at predetermined intervals based on the measured values ​​of the current and voltage of the power storage bank, and the power storage bank is connected to the main line after the estimated value of the crosscurrent falls below a limit value.

[0017] According to the energy storage system described in (4) above, the energy storage bank can be connected to the main line at the time when the crosscurrent falls below the limit value.

[0018] (5) In the energy storage system described in (4) above, the system control device may discontinue the process for mitigating crosscurrent if, after executing the process for mitigating crosscurrent, the estimated value of the crosscurrent is greater than or equal to a limit value, but the current measurement value of the energy storage bank is less than a predetermined value.

[0019] According to the energy storage system described in (5) above, it is possible to suppress the repeated process of estimating crossflow even when the estimated value of crossflow is unlikely to fall below the limit value.

[0020] The following describes the process for mitigating the crossflow I in energy storage bank B. 1. Calculation of the applicable voltage difference Figure 1 shows a schematic diagram of the energy storage system S and its equivalent circuit. The energy storage system S consists of M energy storage banks B-1, B-2, ..., BM connected in parallel. Hereafter, energy storage bank B will be simply referred to as bank B.

[0021] Each bank B is connected to the main line L via a switch SW. Closing the switch SW connects it to the main line L, and opening the switch SW disconnects it from the main line L.

[0022] Let bank B, which is already connected to the main line L, be called on-bank B, and bank B, which will be connected to the main line L, be called on-bank B. The relationship between the voltage difference Von between the on-bank B group and the on-bank B group and the cross-current I can be calculated using Equation 1. The cross-current I is the current generated between banks due to the voltage difference between banks when the banks are connected (the current flowing between the on-bank and the on-bank).

[0023]

number

[0024] Rbank represents the resistance of bank B (number of cells in series × internal resistance of cells), the contact resistance of switch SW, and the wiring resistance. Non is the number of on-banks before switching on. I is the cross-current (current flowing between banks). Note that the first term on the right-hand side of equation 1 is the combined resistance of on-bank B group, and it decreases as the number of on-banks increases.

[0025] 2. Determination of the applicable voltage range Based on the following conditions, the voltage difference Von between the unconnected bank B and the on-bank B that allows the unconnected bank B to be connected can be calculated using Equation 1. Isys(MAX) is the rated current of the energy storage system S1. "Ready to operate" means that the crosscurrent I does not exceed the rated current Isys(MAX). The rated current Isys(MAX) corresponds to the "limit value" in this invention.

[0026] Conditions (1200V system) Von: Voltage difference between the unconnected bank B and the on-bank B group before connection. Rbank: 210mΩ Non: 1~57 Isys(MAX) = 50A

[0027] As shown in Figure 2, the voltage difference Von that can be switched on varies depending on the number of on-banks, with the value decreasing as the number of on-banks increases. Also, in the case of a 1200V system, if the voltage difference Von between bank B and on-bank group B is less than 10.5[V], the crosscurrent I will be less than the rated current regardless of the number of on-banks before switching on, and switching on will be possible.

[0028] When the voltage difference Von is 10.5[V] or more, the crosscurrent I may exceed the rated current depending on the number of on-banks. Also, calculations show that when the number of on-banks = 1, if the voltage difference between on-bank B and unconnected bank B is 21[V] or more, the crosscurrent I cannot be kept below the rated current. Therefore, when the number of on-banks = 1, the upper limit voltage difference that allows bank B to be connected to the main line L is 21[V].

[0029] Hereinafter, the first threshold V1 is the voltage difference between the on-bank B group and the un-connected bank B, which allows the unconnected bank B to be connected to the main line L, regardless of the number of on-banks before connection. In this embodiment, the first threshold V1 = 10.5 [V]. V1 = 10.5V is just an example, and other values ​​may be used.

[0030] The second threshold V2 is the upper limit voltage difference between on-bank B and un-connected bank B, which allows unconnected bank B to be connected to the main line L when the number of on-banks before connection = 1. In this embodiment, the second threshold V2 = 21[V]. V2 = 21V is just an example, and other values ​​may be used. However, V2 > V1.

[0031] 3. Regarding mitigation of crossflow Using a 1200V system as an example, we will explain the crossflow mitigation process that reduces the crossflow I in bank B when power is supplied to the main line L.

[0032] As described above, if the voltage difference V between the on-bank B and the unconnected bank B is 10.5[V] or more, the crosscurrent I may exceed the rated current of 50[A]. Therefore, the crosscurrent I at the time of connection is estimated by calculation, and based on the estimation result, it is determined whether the unconnected bank B can be connected to the main line L.

[0033] Figure 3 shows the equivalent circuit of Bank B when the second bank, Bank B-2, is switched on after the first bank, Bank B-1, has been switched on (only one bank is on). When the second bank, Bank B-2, is switched on, the voltage difference VH-VL1 between the banks that keeps the crosscurrent I below the rated current of 50[A] is as follows: VH is the voltage of Bank B-1, which has a higher voltage, and VL1 is the voltage of Bank B-2, which has a lower voltage.

[0034]

number

[0035]

number

[0036] Figure 4 shows the equivalent circuit of bank B when the third bank B-3 is switched on (on-banks B-1 and B-2). The lateral current Ion flowing through on-banks B-1 and B-2 after the third bank B-3 is switched on, and the lateral current Iin flowing through the switched-on third bank B-3, are as follows. Note that Ire is the lateral current between on-banks B-1 and B-2 before switching. Vdelta is the measured voltage difference between the average voltage of on-banks B-1 and B-2 (average of VH and VL1) and the voltage VL2 of the unswitched bank B-3.

[0037]

number

number

[0038] In this configured system, the crosscurrent Ion of on-banks B-1 and B-2, and the crosscurrent Iin of bank B-3 that connects to the main line L (hereinafter referred to as the connection bank) must be kept below the rated current of 50[A].

[0039] The transverse flow mitigation process disclosed herein involves engaging bank B in accordance with (1) to (5) below.

[0040] (1) As shown in Figure 5, banks B-1 to B-20 are numbered in descending order of total voltage. (2) As shown in Figure 6, the bank B-20 with the highest voltage is turned on first. (3) As shown in Figure 6, the lowest voltage bank B-1 is switched on second. (4) Of the banks that have not yet been switched on, the crosscurrents Ion and Iin when bank B, which has a lower voltage, is switched on are estimated using equations 6 and 7 shown below, and bank B is switched on to the main line L after the estimated values ​​of the crosscurrents Ion and Iin become less than the rated current Isys. (5) Repeat (4).

[0041]

number

number

[0042] Equation 6 is the estimation formula for the crossflow Ion in on-bank group B, and Equation 7 is the estimation formula for the crossflow Iin in connected bank B. By substituting the measured voltage difference Vdelta between on-bank group B and unconnected bank B, and the measured crossflow Ire before connection, into Equations 6 and 7, the crossflows Ion and Iin can be estimated.

[0043] Isys(max) = 50[A], and Rbank uses the measured values ​​of the resistance of bank B (number of series connections × internal cell resistance), the contact resistance of switch SW, and the wiring resistance. Also, S is the safety margin (S < 1).

[0044] <Embodiment 1> Figure 8 is a block diagram of the energy storage system S1. The energy storage system S1 is connected to the grid G ​​via a power conditioner 10. The grid G ​​has grid power sources 1 and distributed power sources 3 such as solar power generation panels 2 and wind turbines, and supplies AC power to the energy storage system S1 and demand facilities (not shown) at commercial frequency.

[0045] The power conditioner 10 is a bidirectional power converter that can convert AC power from the grid G ​​into DC power to charge the energy storage system S1. It can also convert the DC power supplied from the energy storage system S1 into AC power and output it to the grid G.

[0046] The S1 energy storage system can be used for a variety of applications, including residential, industrial, and energy management. By storing surplus electricity from the grid G ​​and discharging it according to the balance of electricity supply and demand, the S1 energy storage system can contribute to the efficient use of energy.

[0047] The energy storage system S1 consists of multiple banks, comprising banks B-1 to BM, bank management devices 50-1 to 50-M, and a system management device 100.

[0048] Each bank B-1 through BM is connected in parallel to the power conditioner 10 via the main line L. Each bank B-1 through BM is equipped with switches SW-1 through SW-M, such as relays.

[0049] By closing each switch SW, bank B can be connected to the main line L. Conversely, by opening each switch SW, bank B can be disconnected from the main line L. Banks B-1 through BM have the same configuration.

[0050] As shown in Figure 9, Bank B consists of multiple energy storage modules 30-1, 30-2, and 30-M, multiple sensor units 35-1, 35-2, and 35-M, a switch SW, and a current sensor 40, all connected in series.

[0051] As shown in Figure 10, one energy storage module 30 is composed of multiple energy storage cells 31 connected in series. The energy storage cells 31 can be lithium-ion secondary battery cells or the like.

[0052] Each sensor unit 35 is provided for each energy storage module 30. The sensor unit 35 detects the cell voltage Vc of each energy storage cell 31. The sensor unit 35 also has a temperature sensor 36 and detects the battery temperature T of the energy storage module 30.

[0053] As shown in Figure 9, the sensor unit 35 is connected to adjacent sensor units 35 in a communicative manner. In response to instructions from the bank management device 50, the sensor unit 35 transmits data sequentially from higher to lower sensor units 35, thereby aggregating the measurement results of each sensor unit 35 into the lowest sensor unit 35M and transmitting it to the bank management device 50.

[0054] Bank management devices 50-1 to 50-M are provided for each bank B-1 to BM. Each bank management device 50-1 to 50-M comprises an arithmetic unit 51 such as a CPU and a storage unit 53.

[0055] The bank management devices 50-1 to 50-M monitor the total voltage V of bank B (the total voltage of all energy storage modules 30-1 to 30-M), the bank current I, the cell voltage Vc of each energy storage cell 31, and the battery temperature T, based on various data transmitted from the sensor unit 35 and the current sensor 40. They also control the opening and closing of the switch SW to connect or disconnect bank B from the main line L.

[0056] The bank management devices 50-1 to 50-M are connected to the system management device 100. The system management device 100 includes an arithmetic unit 101 such as a CPU and a storage unit 103.

[0057] The system management device 100 monitors the overall system status based on monitoring data for banks B-1 to BM (data on the total voltage V of bank B, bank current I, and battery temperature T) transmitted from the bank management devices 50-1 to 50-M.

[0058] 2. Transverse flow mitigation treatment Figure 11 shows the connection sequence of bank B to the main line L. The activation sequence for Bank B is executed when the energy storage system S1 is brought to the site and installed, that is, after the installation of the energy storage system S1, when each Bank B-1 to BM is connected to the main line L. At this time, the power conditioner 10 is stopped in its pre-operation state, and each Bank B1 to BM is not in a state to charge or discharge between the grid G ​​and the load via the main line L and the power conditioner 10.

[0059] The activation sequence for Bank B consists of 12 steps, from S1 to S110. Hereafter, the number of parallel connections for Bank B will be assumed to be 20 (M=20). First, in S1, each bank management device 50-1 to 50-20 detects the total voltage V of each Bank B-1 to B-20 (all banks are not activated at this point). Specifically, the sensor unit 35 measures the cell voltage Vc of each energy storage cell 31 and detects the total voltage V of each Bank B-1 to B-20 from the measurement results. Once each bank management device 50-1 to 50-20 detects the total voltage V of each Bank B-1 to B-20, it transmits the detection result of the total voltage V to the system management device 100. When the system management device 100 receives the data of the total voltage V of each Bank B-1 to B-20 from each bank management device 50-1 to 50-20, it compares the total voltage V of each Bank B-1 to B-20 and calculates the maximum voltage difference ΔVm between Bank B. The maximum voltage difference ΔVm is the voltage difference between the highest voltage bank B and the lowest voltage bank B.

[0060] Subsequently, the process moves to S10, where the system management device 100 compares the maximum voltage difference ΔVm with the first threshold V1 and determines whether the maximum voltage difference ΔVm is greater than or equal to the first threshold V1. The first threshold V1 is a threshold used to determine whether or not the crosscurrent mitigation process can be performed, and in this example, V1 = 10.5V.

[0061] If the maximum voltage difference ΔVm between banks B is less than the first threshold V1 (S10: NO), the crosscurrent I will not exceed the rated current regardless of the order and timing in which banks B-1 to B-20 are switched on. Therefore, the system proceeds to S20, and the system management device 100 switches all banks B-1 to B-20 to the main line L without being restricted by the crosscurrent mitigation process. In this embodiment, the system management device 100 sends commands to each bank management device 50-1 to 50-20 to close switches SW-1 to SW-20 in sequence, thereby switching each bank B-1 to B-20 to the main line L in sequence and completing the switching operation for banks B-1 to B-20.

[0062] If the maximum voltage difference ΔVm between banks B is greater than or equal to the first threshold V1 (S10: YES), the system proceeds to S30. Upon proceeding to S30, the system management device 100 compares the maximum voltage difference ΔVm between banks B obtained in S10 with the second threshold V2 and determines whether the maximum voltage difference ΔVm is less than the second threshold V2.

[0063] The second threshold V2 is the upper limit of the voltage difference ΔV between banks B at which the crosscurrent I can be kept below the rated current by the crosscurrent mitigation process when the number of on-banks = 1. In this example, V2 = 21[V].

[0064] If the maximum voltage difference ΔVm between banks B is less than the second threshold V2 (S30: YES), the system management device 100 performs cross-current mitigation processing (S40~S100) for all banks B.

[0065] Specifically, first, in S40, the system management device 100 sends a command to the bank management device 50 to connect bank B (in this example, B-20), which has the highest voltage among the unconnected banks B-1 to B-20, to the main line L. Then, in S50, it connects bank B (in this example, bank B-1), which has the lowest voltage among the unconnected banks B-1 to B-20, to the main line L (see Figure 6). Since there is a voltage difference ΔV between the two banks B-20 and B-1, after the second bank B-1 is connected, a crosscurrent I flows between the two banks B-20 and B-1.

[0066] Next, the process moves to S60, where the system management device 100 selects bank B-2, which has the lowest voltage among the unactivated banks B-2 to B-19. After that, the process moves to S70.

[0067] When the system transitions to S70, the system management device 100 determines whether the following closing conditions are met for the bank B selected in S60, based on the measured values ​​of the bank current I and total voltage V for each bank B.

[0068] <Input conditions> (A) After the selected bank is filled, the crossflow Ion of on-bank B satisfies equation 6. (B) After the selected bank is fed in, the crossflow Iin of the feeding bank B satisfies equation 7.

[0069] If the above activation conditions are met (S70:YES), the system management device 100 proceeds to S90 and activates bank B, which was selected in S60, to the main line L.

[0070] On the other hand, if the above input conditions are not met (S70:NO), the process proceeds to S80 and waits for a predetermined time. After that, the process proceeds to S70 to re-evaluate whether the input conditions are met. By waiting for the predetermined time to elapse, the lateral flow Ion generated between the first and second on-bank B gradually decreases and becomes smaller. When the input conditions change from not met to met due to the decrease in lateral flow Ion, the process proceeds to S90.

[0071] When the system management device 100 transitions to S90, it connects bank B, which was selected in S60, to the main line L.

[0072] Subsequently, the process moves to S100, where the system management device 100 determines whether or not there are any unfilled bank B units. If there are unfilled bank B units, the process moves to S60 and the above steps are repeated. When there are no more unfilled bank B units, the system determines NO in S100, and the series of processes ends.

[0073] Furthermore, if the maximum voltage difference ΔVm between banks B calculated in S10 is greater than or equal to the second threshold V2 (S30: NO), the system management device 100 proceeds to S110, sets the bank B with the lowest voltage as the reference bank, and calculates the voltage difference ΔV of each bank B relative to the reference bank B. Then, it excludes any bank B whose voltage difference ΔV exceeds the second threshold V2 and determines the order in which the banks B are turned on.

[0074] In the example in Figure 7, bank B-1 has the lowest voltage, so banks B-19 and B-20, whose voltage difference ΔV with bank B-1 exceeds the second threshold V2, are excluded, and the switching order is determined from banks B-1 to B-18, whose voltage difference ΔV with bank B-1 is less than the second threshold V2.

[0075] The order of switching on the batteries is determined by starting with Bank B, which has the highest voltage, followed by Bank B with the lowest voltages. In this example, the order is determined to be B-18, B-1, B-2, ..., B-16, B-17.

[0076] Once the input order is determined in S110, the first bank B-18 is then connected to the main line in S40, and the second bank B-1 is connected to the main line L in S50. Subsequently, the processes from S60 to S100 are carried out according to the input order determined in S110 until there are no unconnected banks B. When there are no unconnected banks B, a NO determination is made in S100, and the series of processes ends.

[0077] Furthermore, the two banks B-19 and B-20, which were excluded from determining the order of input in S110, may be excluded from the crossflow mitigation process itself, or the crossflow mitigation process may be performed again after the input work for the main line L of banks B1 to B18, which were not excluded, has been completed, and an attempt may be made to input them to the main line L.

[0078] The reason for attempting to activate the two banks B-19 and B-20, which were excluded from determining the activation order, is that even if the voltage difference ΔV is large in the initial stages of the activation process for bank B and does not meet the activation conditions for S70, as the activation process progresses, the voltage of the on-bank B group increases, reducing the voltage difference ΔV with the on-bank B group and potentially meeting the activation conditions for S70. The voltage difference is the voltage difference between the excluded banks B-19 and B-20 and the on-bank B group.

[0079] Figures 12A to 12C show the results of Simulation 1 of the transverse flow mitigation treatment. The conditions for Simulation 1 are as follows:

[0080] <Simulation 1> Number of banks: 5 15 units in series System rated current: 50A Bank 1 voltage: 743.3V Bank 2 voltage: 728.9V Bank 3 voltage: 730.1V Bank 4 voltage: 730.8V Bank 5 voltage: 731.6V Safety margin 10% Maximum voltage difference between banks: 14.4V First threshold: 7.2V Second threshold: 14.4V

[0081] In Simulation 1, as shown in Figure 12A, after Bank 1, which had the highest voltage, was switched on, Bank 2, which had the lowest voltage, was switched on after 1 minute had elapsed. After Bank 2 was switched on, a crosscurrent occurred between Banks 1 and 2 due to the voltage difference ΔV between Bank 1 and Bank 2. Immediately after Bank 2 was switched on, the crosscurrent Ion was large, and in this state, the conditions for switching on the next Bank 3 were not met. However, the crosscurrent Ion decreased over time, and eventually the conditions for switching on the next Bank 3 were met, and the next Bank B3 was switched on. Similarly, Banks 4 and 5 were switched on after waiting for the conditions to be met. As shown in Figure 12C, in Simulation 1, the current I of each Bank 1 to 5 was kept below the system rated current (50A), confirming the effectiveness of the simulation.

[0082] Figures 13A to 13C show the results of Simulation 2 for the transverse flow mitigation process. The conditions for Simulation 2 are as follows:

[0083] <Simulation 2> Number of banks: 5 15 units in series System rating 50A Bank 1 voltage: 743.3V Bank 2 voltage: 728.9V Bank 3 voltage: 735.6V Bank 4 voltage: 740.7V Bank 5 voltage: 745.7V Safety margin 10% Maximum voltage difference between banks: 16.8V First threshold: 7.2V Second threshold: 14.4V

[0084] In Simulation 2, in the state before the start of the cross-current relaxation process, the voltage difference ΔV between Bank 5 and Bank 2 is not less than the second threshold 14.4 [V], and Bank 5 was outside the target scope of the cross-current relaxation process. However, as shown in FIGS. 13B and 13C, after turning on Banks 1 to 4, the voltage difference ΔV between the on-banks 1 to 4 and Bank 5 becomes less than the second threshold 14.4, the closing condition for Bank 5 is satisfied, and finally Bank 5 can be connected to the main line L.

[0085] Initially, even for a Bank B that is outside the target scope of the cross-current relaxation process, the voltage of the on-bank group B changes due to the connection of Bank B (increases as the number of connected banks increases in this embodiment), therefore, after the start of the connection operation of Bank B, as the number of connected Bank B increases, the connection condition is satisfied, and there are cases where Bank B that was initially outside the target scope can be connected to the main line L.

[0086] 3. Effects According to the power storage system S1 disclosed in the present specification, when the maximum voltage difference ΔVm between Banks B is higher than the first threshold V1, and there is a possibility that the cross-current I generated between Banks B when connected to the main line L exceeds the limit value (rated current) (S10: YES), the relaxation process (S40 to S100) for relaxing the cross-current I is executed. Therefore, it is possible to suppress the cross-current I exceeding the limit value from flowing between the banks.

[0087] Therefore, when connecting Bank B to the main line L, it is possible to suppress the occurrence of malfunctions in Bank B and its protection devices, etc. Furthermore, when the maximum voltage difference ΔVm between banks is within a predetermined range (V1≦ΔVm<V2), Bank B can be automatically connected to the main line L, so there is no need to monitor the connection status of Bank B during the connection operation, which has the advantage of reducing the monitoring burden on operators. Furthermore, when the maximum voltage difference ΔVm between Banks B is less than the first threshold V1 (S10: NO), all Banks B are connected to the main line L without being restricted by the relaxation process for relaxing cross-current I, so the connection operation of Bank B can be completed in a short time.

[0088] <Embodiment 2> In Embodiment 1, in the switching-on sequence for bank B shown in Figure 11, if the maximum voltage difference ΔVm between banks calculated in S1 is greater than or equal to the second threshold V2 (S30: NO), the system management device 100 uses the bank B with the lowest voltage as a reference (B-1 in the example of Figure 7), excludes bank B whose voltage difference ΔV from the reference bank B-1 exceeds the second threshold V2 (excluding B-19 and B-20 in the example of Figure 7), and targets bank B whose voltage difference ΔV from the reference bank B-1 is less than the second threshold V2 (B-1 to B-18 in the example of Figure 7) to determine the switching-on order of bank B for the main line L.

[0089] In Embodiment 2, in the switching-on sequence for bank B shown in Figure 11, if the maximum voltage difference ΔVm between banks calculated in S1 is greater than or equal to the second threshold V2 (S30: NO), the system management device 100 selects bank B with the highest voltage as the reference bank (bank B-20 in the example of Figure 14), excludes banks B whose voltage difference ΔV from reference bank B-20 exceeds the second threshold V2 (excluding banks B-1 and B-2 in the example of Figure 14), and selects banks B whose voltage difference ΔV from reference bank B-20 is less than the second threshold V2 (B-3 to B20 in the example of Figure 14) to determine the switching-on order of banks B for the main line L.

[0090] Furthermore, the choice of which bank to select as the reference bank—the lowest voltage bank B-1 or the highest voltage bank B-20—may be determined by the following method: Calculate the number of banks B to be excluded from determining the switching order for both the case where the lowest voltage bank B-1 is the reference bank and the case where the highest voltage bank B-20 is the reference bank, and select the bank B with the fewer excluded banks as the reference bank.

[0091] This reduces the number of Bank B banks excluded from determining the input order, making it possible to include more Bank B banks in the crossflow mitigation process.

[0092] <Embodiment 3> Figure 15 shows the engagement sequence for bank B to main line L. The engagement sequence in Figure 15 adds step S75 to the engagement sequence shown in Figure 7. Step S75 is executed if the result in S70 is NO.

[0093] When the system transitions to S75, the system management device 100 compares the current I of each on-bank B with a predetermined value and determines whether the current I of on-bank B is less than or equal to the predetermined value. The predetermined value is, for example, 2[A].

[0094] The system management device 100 determines that if the current I of on-bank B is greater than a predetermined value (S75:NO), the voltage difference ΔV between banks will decrease over time, and the on-up condition may be met, and proceeds to S80. After proceeding to S80, it waits for a predetermined time, then proceeds to S70 to re-determine whether the on-up condition has been met.

[0095] The system management device 100 determines that if the current I in on-bank B is below a predetermined value (S75: YES), a decrease in the voltage difference ΔV between banks due to the passage of time cannot be expected, and therefore the on-up condition is unlikely to be met. In this case, the system management device 100 terminates the on-up sequence for bank B.

[0096] By adding S75, it is possible to suppress the repetition of S70, S75, and S80 even when the conditions for S70 are unlikely to be met. One possible case in which S75 results in a YES judgment is when S70 is performed on bank B, which was excluded in S110.

[0097] <Embodiment 4> Figure 16 is a flowchart of the on-bank pre-warning process. The on-bank pre-warning process is performed before the execution of the input sequence shown in Figures 11 and 15, and consists of steps S210 to S230.

[0098] In S210, the system management device 100 determines whether there is an on-bank B that has been switched on to the main line L. The presence or absence of on-bank B can be determined from the status of switches SW-1 to SW-20 of each bank B-1 to B-20.

[0099] If there is no on-bank B (S210:YES), the system management device 100 starts the input sequence shown in Figures 11 and 15.

[0100] If on-bank B is present (S210: YES), the system management device 100 displays a guidance message on the display unit provided in the energy storage system S1 requesting the disconnection of on-bank B.

[0101] Following the display of the guidance message, when the system management device 100 confirms that Onbank B has been disconnected from the main line L by the operator and that Onbank B no longer exists, the system management device 100 then starts the connection sequence shown in Figures 11 and 15.

[0102] This configuration prevents the input sequence from starting while bank B is already in existence.

[0103] <Embodiment 5> Figure 17 is a chart summarizing the subsequent actions taken when on-bank services are available and when they are not, before the implementation of the cross-flow mitigation process.

[0104] If the maximum voltage difference between banks B is less than the first threshold (ΔVm <V1) The system control device 100 connects all banks B to the main line L if there are no on-bank B. If there are on-bank B, it connects all banks B to the main line L if the current of on-bank B is less than a predetermined value (for example, less than 2[A]). If the current I of on-bank B is greater than or equal to the predetermined value, it stops connecting banks B.

[0105] If the current I in on-bank B exceeds a predetermined value, there is a possibility that current is flowing between it and other energy storage systems S or the power grid. In such a situation, if bank B is connected to the main line L, the crosscurrent I generated between banks B may exceed the rated current.

[0106] If the maximum voltage difference between banks B is greater than or equal to the first threshold and less than the second threshold (V1 ≤ ΔVm <V2) The system control device 100 performs crossflow mitigation processing if there is no on-bank B. If there is an on-bank B, it displays a guidance message to disconnect on-bank B from the main line L.

[0107] If the maximum voltage difference between banks B is greater than or equal to the second threshold (V2 ≤ ΔVm) If there is no on-bank B, the system control device 100 performs a crossflow mitigation process and handles the bank B that could not be connected to the main line L individually. If there is an on-bank B, it displays a guidance message to disconnect on-bank B from the main line L.

[0108] <Other Embodiments> The present invention is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of the present invention.

[0109] (1) In the above embodiment, the bank with the highest voltage was switched on first to the main line L, and then the banks B with the lowest voltage were switched on in order. The order in which banks B are switched on may be reversed. That is, the bank B with the lowest voltage may be switched on first to the main line L, and then the banks B with the highest voltage were switched on to the main line L in order.

[0110] (2) The energy storage cell is not limited to lithium-ion secondary batteries; other non-aqueous electrolyte secondary batteries or lead-acid batteries may also be used. Capacitors can also be used instead of energy storage cells. [Explanation of Symbols]

[0111] 30 Energy Storage Modules 35 Module Sensor Unit 40 Current Sensor 50 Bank Management Device 100 System Management Devices B. Energy Storage Bank S1 Energy Storage System

Claims

1. It is an energy storage system, Multiple energy storage banks connected in parallel to the main line, Includes a system control unit, The system control device, before connecting the energy bank to the main line, if the maximum voltage difference between the energy banks is greater than or equal to a first threshold, performs a process to mitigate the crosscurrent that occurs between the energy banks, thereby mitigating the crosscurrent that occurs when the energy bank is connected to the main line. In the process for mitigating crossflow, the crossflow is estimated based on the voltage difference between the energy storage banks and the resistance of the energy storage banks, and the connection of the energy storage banks to the main line is controlled based on the estimated crossflow. A power storage system that, when the maximum voltage difference between power storage banks is less than a first threshold, connects the power storage banks to the main line without any restrictions on the processing to mitigate crosscurrents.

2. An energy storage system, Multiple energy storage banks connected in parallel to the main line, Includes a system control unit, The system control device, before connecting the energy bank to the main line, if the maximum voltage difference between the energy banks is greater than or equal to a first threshold, performs a process to mitigate the crosscurrent that occurs between the energy banks, thereby mitigating the crosscurrent that occurs when the energy bank is connected to the main line. If the maximum voltage difference between energy storage banks is less than the first threshold, the energy storage bank is connected to the main line without any restrictions on the processing to mitigate crosscurrents. The system control device, when the maximum voltage difference between energy storage banks is greater than or equal to a second threshold higher than the first threshold, uses the energy storage bank with the lowest voltage or the energy storage bank with the highest voltage as the reference bank, calculates the voltage difference of each energy storage bank relative to the reference bank, excludes energy storage banks whose calculated voltage difference is greater than or equal to the second threshold, and determines the order in which the energy storage banks are connected to the main line.

3. The energy storage system according to claim 2, The aforementioned system control device calculates the number of energy storage banks to be excluded from determining the order of operation, for cases where the energy storage bank with the lowest voltage is used as the reference bank and for cases where the energy storage bank with the highest voltage is used as the reference bank, and selects the energy storage bank with the fewer number of excluded banks as the reference bank.

4. A power storage system according to claim 1 or claim 2, The energy storage system comprises the process of mitigating crosscurrent by estimating the crosscurrent of the energy storage bank at predetermined intervals based on measured values ​​of the current and voltage of the energy storage bank, and then connecting the energy storage bank to the main line after the estimated value of the crosscurrent falls below a limit value.

5. The energy storage system according to claim 4, The system control device discontinues the process for mitigating crosscurrent if, after executing the process for mitigating crosscurrent, the estimated value of the crosscurrent is greater than or equal to a limit value, but the current measurement value of the energy storage bank is less than a predetermined value.

6. The method of loading into the energy storage bank, Before the power bank is connected to the main line, if the maximum voltage difference between the power banks is greater than or equal to a first threshold, a process is performed to mitigate the crosscurrents that occur between the power banks, thereby mitigating the crosscurrents that occur when the power bank is connected to the main line. In the process for mitigating crossflow, the crossflow is estimated based on the voltage difference between the energy storage banks and the resistance of the energy storage banks, and the connection of the energy storage banks to the main line is controlled based on the estimated crossflow. A method for connecting an energy storage bank, wherein, when the maximum voltage difference between energy storage banks is less than a first threshold, the energy storage bank is connected to the main line without any restrictions on the processing to mitigate crosscurrents.

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