POWER STORAGE SYSTEM

Abstract

An energy storage system 1 comprises a plurality of strings ST1 to STm, a solar power generation device 10, and an array system 20 that controls the matching of the voltage, phase, and frequency of a slave string ST to that of a master string ST. The array system 20 acquires information about the remaining discharge power capacity and the remaining charge power capacity of each of the multiple strings ST1 to STm, identifies a string with a remaining discharge power capacity equal to or less than a first threshold and a string with a remaining charge power capacity equal to or less than a second threshold as the low-capacity string ST, and selects the master string ST based on the sum of the remaining discharge power capacity and the remaining charge power capacity of each of the candidate master strings ST, except for the identified low-capacity string ST.

Description

TECHNICAL AREA

[0001] The present invention relates to an electricity storage system. STATE OF THE ART

[0002] Previous technology considered an energy storage system with multiple energy storage devices to provide a stable power supply for a load in addition to the grid power supply, such as a commercial power supply (see patent reference 1). In the energy storage system, if grid power is unavailable due to a power outage or similar event, one of the multiple energy storage devices becomes the master energy storage device, and the other energy storage devices become slave energy storage devices, operating in sync with the master energy storage device. The master energy storage device can be switched to become a slave energy storage device, and each of the slave energy storage devices can be switched to become the master energy storage device. QUOTE LIST PATENT LITERATURE

[0003] Patent Literature 1: JP 2017-184582 A SUMMARY OF THE INVENTIONAL PROBLEM

[0004] In the energy storage system described in patent literature 1, however, the selection of the master energy storage device is not given particular consideration. The master energy storage device can be switched frequently, and control becomes more difficult with each switch. More precisely, when no grid power is available, the slave energy storage devices must operate in such a way as to follow the master energy storage device, and the slave energy storage devices must match the voltage, phase, and frequency of the master energy storage device. This matching control, however, is not simple and becomes increasingly difficult the more frequently the master energy storage device is changed.

[0005] The present invention was developed to solve such a problem in the prior art, and its aim is to provide an energy storage system that can reduce the number of switching operations of a master energy storage device. SOLUTION TO THE PROBLEM

[0006] An energy storage system according to the present invention is an energy storage system that operates in a first operating mode when mains power is supplied to a load, and in a second operating mode when no mains power is supplied to the load, wherein the energy storage system comprises: a large number of energy storage devices connected in parallel to the load; a separate system device configured to supply the energy derived from natural energy to the load and the multiple energy storage devices; and a control unit configured to control the discharge from the plurality of energy storage devices to the load and the charge from the separate system device to the plurality of energy storage devices, and which performs a control to select a master energy storage device from the plurality of energy storage devices when an operating mode is switched from the first operating mode to the second operating mode or when it is necessary to reselect a master energy storage device, and adjusts the voltage, phase and frequency between the master energy storage device and a slave energy storage device, which is not a master energy storage device, from the plurality of energy storage devices, wherein The control unit includes: a collection unit configured to collect information about a remaining discharge power capacity, indicating a discharge power capacity until reaching a discharge end voltage, and a remaining charge power capacity, indicating a charge power capacity until reaching a charge end voltage, for each of the multitude of energy storage devices; a determination unit configured to identify, from among the multitude of energy storage devices, an energy storage device whose remaining discharge power detected by the detection unit is equal to or less than a first threshold, as a low-capacity energy storage device, and an energy storage device whose remaining charge power detected by the detection unit is equal to or less than a second threshold, as a low-capacity energy storage device; and a selection unit configured to select the master energy storage device based on a total value of the remaining discharge power capacity and the remaining charge power capacity detected by the detection unit of each energy storage device that is a master candidate, except for the low-capacity energy storage device selected by the determination unit from the multitude of energy storage devices. ADVANTAGES OF THE INVENTION

[0007] According to the present invention, it is possible to provide a power storage system that can reduce the number of switching operations of a master power storage device. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a block diagram showing an energy storage system according to an embodiment of the present invention. Fig. 2 is a block diagram of a Fig. 1 array system shown. Fig. Figure 3 is a graph showing an example of the remaining discharge power capacities and the remaining charge power capacities when there are nine strings. Fig. Figure 4 is a graph showing an example of the remaining discharge power capacities and the remaining charge power capacities of master candidates, with low-capacity strings removed from the ones shown. Fig. The first to ninth strands shown in the 3 are excluded. Fig. Figure 5 is a flowchart showing a master strand selection procedure according to the present embodiment. DESCRIPTION OF THE EXECUTION FORMS

[0008] The present invention is described below with reference to a preferred embodiment. The present invention is not limited to the embodiment described below and can be modified appropriately without departing from the essential nature of the present invention. In the embodiment described below, there may be sections in which the illustration and description of part of a configuration is omitted, and it is understood that a publicly known or generally known technique may be appropriately applied to details of an omitted technique in an area where no contradiction arises with the content described below.

[0009] Fig. Figure 1 is a block diagram showing an energy storage system according to an embodiment of the present invention. As shown in Fig. As shown in Figure 1, an energy storage system 1 is provided to stabilize the supply of grid power, such as commercial electricity, to a load Lo, and includes a variety of strings (energy storage devices) ST1 to STm, a solar power generation device (separate system device) 10, module battery management systems (hereinafter referred to as MOD systems) MB11 to MBmn, multiple string battery management systems (hereinafter referred to as ST systems) SB1 to SBm, an array battery management system (control unit: hereinafter referred to as array system) 20 and an energy management system (EMS) 30.

[0010] The multitude (m: m is a natural number of 2 or more) of strands ST1 to STm are connected in parallel to the load Lo and each includes a multitude of storage batteries B11 to Bmn, a multitude of bypass circuits BC11 to BCmn and AC / DC converters C1 to Cm.

[0011] The plurality of storage batteries B11 to Bmn (n: n is a natural number of 2 or more) are provided in the respective strings ST1 to STm. In the strings ST1 to STm, n storage batteries B11 to Bmn are connected in series. Each of the storage batteries B11 to Bmn is, for example, designed as a module with several unit cells, but is not specifically limited to this and can also consist of a single cell. In the present embodiment, it is assumed that the plurality of storage batteries B11 to Bmn are, for example, used batteries or batteries from different manufacturers and that the strings ST1 to STm have different capacities.

[0012] Bypass circuits BC11 to BCmn are used to bypass a portion of the storage batteries B11 to Bmn in strings ST1 to STm, thus isolating them from a series connection. These circuits can be switched between a bypass state, in which storage batteries B11 to Bmn are bypassed, and a connected state, in which they are not bypassed. All bypass circuits BC11 to BCmn have the same configuration. Therefore, bypass circuit BC11 is described below as an example.

[0013] The 11th bypass circuit BC11 comprises a first switch Sa11, a bypass line BL11, and a second switch Sb11. The first switch Sa11 is located closer to the AC / DC converter C1 than the storage battery B11 and can be switched between an ON state and an OFF state by opening and closing it. The bypass line BL11 is a conductive line that bypasses the storage battery B11 from one side of the first switch Sa11 connected to the AC / DC converter C1 and is connected to the other side of the storage battery B11 opposite the AC / DC converter C1. The second switch Sb11 is located on the bypass line BL11 and can be switched between the ON state and the OFF state by opening and closing it. As shown in Fig. As shown in Figure 1, the 11th bypass circuit BC11 connects the storage battery B11 in series with the other storage batteries B12 to B1n when the first switch Sa11 is on and the second switch Sb11 is off. However, when the first switch Sa11 is off and the second switch Sb11 is on, the 11th bypass circuit BC11 bypasses the storage battery B11 and enters the bypass state, in which it is not connected in series with the other storage batteries B12 to B1n. The 11th bypass circuit BC11 prevents both the first switch Sa11 and the second switch Sb11 from being switched on simultaneously by inserting a time interval during the switchover between the series and bypass states, during which both the first switch Sa11 and the second switch Sb11 are off.

[0014] The AC / DC converters C1 to Cm are so-called power conditioning systems (PCS) and are located at the inputs of strings ST1 to STm. During the charging and discharging of the multiple storage batteries B11 to Bmn, which form strings ST1 to STm, the AC / DC converters C1 to Cm perform voltage adaptation (AC / DC conversion).

[0015] The solar power generating device 10 generates electricity by receiving sunlight. The solar power generating device 10 can supply the generated electricity to the load Lo. The solar power generating device 10 can further supply the generated electricity to each of the multiple strings ST1 to STm in order to charge the storage batteries B11 to Bmn in the strings ST1 to STm. Although the solar power generating device 10 is used as an example in the present embodiment, the present invention is not specifically limited to it, and a corresponding device can generate electricity using wind power, wave power, and other natural energy sources, as long as the device generates electricity using natural energy sources.

[0016] The MOD systems MB11 to MBmn perform switching control of the bypass circuits BC11 to BCmn, monitor the states of the storage batteries B11 to Bmn, and similar functions. The MOD systems MB11 to MBmn calculate discharge capacities up to the point of reaching discharge end voltages and charge capacities up to the point of reaching charge end voltages for the respective storage batteries B11 to Bmn. Various publicly known or generally accepted methods are used by the MOD systems MB11 to MBmn to calculate these discharge and charge capacities. For example, the MOD systems MB11 to MBmn first measure the capacities of the storage batteries B11 to Bmn and then sequentially calculate the states of charge (SOC) and wear levels of the storage batteries B11 to Bmn to determine the discharge and charge capacities.

[0017] The ST systems SB1 to SBm monitor the states of strings ST1 to STm, control the AC / DC converters C1 to Cm, and so on. The ST systems SB1 to SBm monitor the states (at least the remaining charging and discharging capacities) of strings ST1 to STm by collecting information from the multiple MOD systems MB11 to MBmn in strings ST1 to STm. Furthermore, the ST systems SB1 to SBm monitor the remaining charging and discharging capacities for multiple patterns when the bypass circuits BC11 to BCmn in strings ST1 to STm are in series-connected and bypass states. This will be described in detail later in an overview of operations.

[0018] Fig. 2 is a block diagram of the in Fig. 1. Array system 20 shown. As in Fig. As shown in Figure 2, the array system 20 performs the overall control of the energy storage system 1 and controls the discharge from the plurality of strings ST1 to STm to the load Lo and the charging from the solar power generation device 10 into the plurality of strings ST1 to STm.

[0019] During discharge to load Lo, the array system 20 operates in two modes: a first and a second. The first mode is one in which the multiple strings ST1 to STm follow the mains current (i.e., voltage, phase, and frequency are matched) when mains current is supplied to load Lo. The second mode is one in which, when mains current is not supplied to load Lo, a master string (master power storage device) ST (a string (including a master string, a slave string to be described later, and a low-capacity string to be described later), where none of the multiple strings ST1 to STm are specified, is indicated by the reference symbol ST) is selected from the multiple strings ST1 to STm.The second operating mode is furthermore an operating mode in which the strings ST, except for the master string ST, are slave strings (slave energy storage) ST, and the slave strings ST follow the master string ST (i.e., voltage, phase, and frequency are adjusted). The array system 20 performs charge and discharge control in response to an instruction from the EMS 30, which is described later in the first operating mode. In addition, the array system 20 determines the charge and discharge based on a voltage and frequency of a power line (not shown) connected to a power receiving point in the second operating mode.

[0020] The array system 20 contains a detection unit 21, a determination unit 22 and a selection unit 23.

[0021] The acquisition unit 21 acquires information about the remaining discharge power capacity and the remaining charge power capacity of each of the multiple strings ST1 to STm. The acquisition unit 21 acquires the information about the remaining discharge power capacity and the remaining charge power capacity of each of the multiple strings ST1 to STm by receiving information about each of the strings ST1 to STm from one of the respective ST systems SB1 to SBm.

[0022] The determination unit 22 designates as a low-capacity string (low-capacity energy storage device) ST a string whose remaining discharge power, as detected by the detection unit 21, is equal to or less than a first threshold value among the plurality of strings ST1 to STm. Furthermore, the determination unit 22 designates as a low-capacity string ST a string whose remaining charge capacity, as detected by the detection unit 21, is equal to or less than a second threshold value among the plurality of strings ST1 to STm. That is to say, the determination unit 22 designates as a low-capacity string ST a string whose remaining discharge power is equal to or less than the first threshold value and which has no capacity for discharge, as well as a string whose remaining charge capacity is equal to or less than the second threshold value and which has no capacity for charging.

[0023] The selection unit 23 selects the master strand ST from the master candidate strands ST, excluding the strand ST with low capacity identified by the determination unit 22 from the plurality of strands ST1 to STm. At this point, the selection unit 23 selects the master strand ST based on a total value of the remaining discharge power capacity and the remaining charge power capacity, as detected by the detection unit 21. In the present embodiment, the selection unit 23 designates the strand ST with the highest total value as the master strand ST.

[0024] It will be revisited Fig. 1. Reference is made to the EMS 30. Based on a signal from a power receiving device PR, which receives the grid power, the EMS 30 determines whether the grid power is in a state (power outage state) in which it cannot be delivered to the load Lo. The EMS 30 transmits information about whether the grid power supply is in a power outage state to the array system 20. Based on this information, the array system 20 determines whether to execute the first or second operating mode. Once a target state of charge (SOC) of the energy storage system 1 (all strings ST1 to STm) has been determined, the EMS 30 transmits this information to the array system 20. If the energy storage system 1 is sufficiently charged, the EMS 30 then transmits a signal to the solar power generation device 10 to limit the amount of power generated.

[0025] In the energy storage system 1 described above, when switching from the first to the second operating mode, the master string ST can be selected to reduce the number of switching operations. The following is an overview of a procedure for selecting the master string ST of energy storage system 1.

[0026] Fig. Figure 3 is a diagram showing an example of the remaining discharge power capacities and the remaining charge power capacities when there are nine strings ST1 to STm. As in Fig. As shown in Figure 3, the acquisition unit 21, for example, acquires information indicating that the remaining discharge power capacity of the first string ST1 is 30 Wh and the remaining charge power capacity is 30 Wh from the first ST system SB1. The acquisition unit 21 further acquires information indicating that the remaining discharge power capacity of the second string ST2 is 10 Wh and the remaining charge power capacity is 30 Wh from the second ST system SB2. Similarly, the acquisition unit 21 acquires information about the remaining discharge power capacity and the remaining charge power capacity of each of the strings ST3 to ST9 from the third to ninth ST systems SB3 to SB9.

[0027] For example, the first threshold is 10 Wh and the second threshold is also 10 Wh. In this case, the determination unit 22 determines that the second string ST2 is the low-capacity string ST, since the remaining discharge power capacity is equal to or less than the first threshold. Similarly, the determination unit 22 determines the fifth, sixth, and ninth strings ST5, ST6, and ST9 as low-capacity strings ST.

[0028] Fig. Figure 4 is a diagram showing an example of the remaining discharge power capacities and the remaining charge power capacities of master candidates, with the low-capacity strings ST being those from the first to ninth strings ST1 to ST9, which are shown in Fig. 3 are shown, are excluded. As in Fig. As shown in Figure 4, selection unit 23 extracts the first, third, fourth, seventh, and eighth strands ST1, ST3, ST4, ST7, and ST8, excluding the low-capacity strands ST from the first to ninth strands ST1 to ST9. The extracted first, third, fourth, seventh, and eighth strands ST1, ST3, ST4, ST7, and ST8 are master candidates.

[0029] Next, selection unit 23 checks the total value of the remaining discharge power capacity and the remaining charge power capacity for each of the master candidate strings ST. Here, in which Fig. In the example shown, the total values ​​of the first, third, fourth, seventh, and eighth strands ST1, ST3, ST4, ST7, and ST8 are 60 Wh, 60 Wh, 60 Wh, 60 Wh, and 70 Wh, respectively. Therefore, selection unit 23 designates the eighth strand ST8, with the highest total value, as the master strand ST.

[0030] After the master strand ST has been determined as described above, array system 20 sets the eighth strand ST8 as the master strand ST and sets the first through seventh and ninth strands ST1 through ST7 and ST9 as slave strands ST. Array system 20 then instructs the ST systems SB1 through SB7 and SB9 of the first through seventh and ninth strands ST1 through ST7 and ST9, which are the slave strands ST, to perform follow-up control. Consequently, the ST systems SB1 through SB7 and SB9 perform control to align the voltages, phases, and frequencies of the first through seventh and ninth strands ST1 through ST7 and ST9 with those of the eighth strand ST8, which is the master strand ST.

[0031] Here, the acquisition unit 21 preferably records information for each of the plurality of strands ST1 to STm about the remaining discharge power capacity and the remaining charge power capacity for multiple patterns when one of the multiple bypass circuits BC11 to BCmn is in the bypass state.

[0032] At this point, the acquisition unit 21 preferably acquires, for example, for each of the multiple strings ST1 to STm, information on the remaining discharge power capacity and the remaining charge power capacity for all patterns when each of the bypass circuits BC11 to BC1n is in the bypass state. The first string ST1 is described as an example. If, for example, the number of storage batteries B11 to B1n of the first string ST1 is four (n = 4), the first ST system SB1 acquires the information on the remaining discharge power capacity and the remaining charge power capacity for 15 patterns of 2 × 2 × 2 × 2 - 1. Subsequently, the first ST system SB1 transmits the information on the remaining discharge power and the remaining charge power of 15 patterns.Accordingly, the acquisition unit 21 of the array system 20 records the information about the remaining discharge power capacity and the remaining charge power capacity for all patterns. The aforementioned "-1" serves to exclude a case in which all bypass circuits BC11 to BC14 are in the bypass state. The same applies to the second to mST systems SB2 to SBm.

[0033] Furthermore, the acquisition unit 21 can acquire information about the remaining discharge current capacity and the remaining charge current capacity not only for all patterns but also for a subset of the patterns. As an example, the first string ST1 is described. For instance, the first ST system SB1 acquires a remaining discharge current capacity for the storage batteries B11 to B1n of the first string ST1. Subsequently, the first ST system SB1 increases the number of bypass circuits BC11 to BC1n that are in the bypass state, in ascending order of the remaining discharge current capacity, and calculates and transmits the information about the remaining discharge current capacity and the remaining charge current capacity for (n-1) patterns. Accordingly, the acquisition unit 21 of the array system 20 acquires the information about the remaining discharge current capacity and the remaining charge current capacity for (n-1) patterns.The same applies to the second to mST systems SB2 to SBm. In the description above, the information on the remaining discharge power capacity and the remaining charge power capacity for (n-1) samples is calculated with reference to the remaining discharge current capacity, but the present invention is not limited to this. For example, not only the remaining discharge current capacity but also a remaining charge current capacity can be used as a reference. Furthermore, the information on the remaining discharge power capacity and the remaining charge power capacity for samples ((n-1)×2 samples) can be calculated from both the remaining discharge current capacity and the remaining charge current capacity, or the information on the remaining discharge power capacity and the remaining charge power capacity can be calculated based on completely different criteria.

[0034] As described above, when the acquisition unit 21 acquires the information on the remaining discharge power capacity and the remaining charge power capacity for the multitude of bypass circuit patterns BC11 to BCmn, the selection unit 23 specifies the bypass state with the highest total value of the remaining discharge power capacity and the remaining charge power capacity. The selection unit 23 then executes the following with reference to the Fig. 3 and Fig. 4 described processing in the bypass state with the largest total value of the remaining discharge power capacity and the remaining charge power capacity.

[0035] When the array system 20 receives the target SOC information from the EMS 30, the selection unit 23 can determine the master string ST not only based on the total value of the remaining discharge power capacity and the remaining charge power capacity, but also based on a relationship between the current SOC of the energy storage system 1 and the target SOC. For example, if the current SOC is higher than the target SOC, there is a high probability that a discharge will occur afterward. Therefore, the selection unit 23 can select the string ST with the largest remaining discharge power capacity as the master string ST from among the strings ST that each have a total value of remaining discharge power capacity and remaining charge power capacity equal to or greater than a third threshold. If the current SOC is lower than the target SOC, it is also very likely that a charge will occur afterward.Therefore, the selection unit 23 can select the string ST with the largest remaining charging capacity as the master string ST from the strings ST that each have a total value of remaining discharge capacity and remaining charging capacity that is equal to or greater than the third threshold.

[0036] Then, with reference to Fig. 5 a method for selecting the master string ST of the power storage system 1 according to the present embodiment is described. Fig. Figure 5 is a flowchart showing a procedure for selecting the master strand ST according to the present embodiment. The processing of Fig. For example, step 5 is executed immediately after the EMS 30 has determined the power failure state and the array system 20 has started the second operating mode.

[0037] As in Fig. As shown in Figure 5, the acquisition unit 21 of the array system 20 first acquires information about the remaining discharge power capacity and the remaining charge power capacity for each of a multitude of patterns for strings ST1 to STm when the bypass circuits BC11 to BCmn switch between the series state and the bypass state (S1).

[0038] Then, the array system 20 establishes a pattern with the largest total value of the remaining discharge power capacity and the remaining charge power capacity for each of the strings ST1 to STm and sets each capacity in the pattern (S2).

[0039] The selection unit 22 of the array system 20 then designates the string ST whose remaining discharge power capacity in the pattern defined in step S2 is equal to or less than the first threshold as the low-capacity string ST (S3). The selection unit 22 then designates the string ST whose remaining charge power capacity in the pattern defined in step S2 is equal to or less than the second threshold as the low-capacity string ST (S4). Through the processing of step S4, the string ST that was not designated as the low-capacity string ST becomes the master candidate.

[0040] Next, it is determined whether the information about the target SOC is captured by EMS 30 (S5). If the information about the target SOC is captured (S5: YES), the selection unit 23 of the array system 20 extracts the string ST whose total value in the pattern specified in step S2 is equal to or greater than the third threshold (S6).

[0041] The array system 20 then determines whether the current state of charge (SOC) of the energy storage system 1 is higher than the target SOC (S7). If the current SOC is higher than the target SOC (S7: YES), the selection unit 23 selects the string ST with the largest remaining discharge power capacity from among the strings ST extracted in step S6 as the master string ST (S8). After that, the Fig. Processing shown in step 5 has been completed.

[0042] If, however, the current SOC is not higher than the target SOC (S7: NO), selection unit 23 determines whether the current SOC of energy storage system 1 is lower than the target SOC (S9). If the current SOC is lower than the target SOC (S9: YES), selection unit 23 selects the string ST with the highest remaining charge power as the master string ST from among the strings ST extracted in step S6 (S10). The process then ends in Fig. 5 shown processing methods.

[0043] If the information about the target SOC is not captured (S5: NO) and the current SOC is not lower than the target SOC (S9: NO), selection unit 23 selects the strand ST with the largest total value in the pattern defined in step S2 as the master strand ST (S11). After that, the process ends in Fig. 5 shown processing methods.

[0044] As described above, in the present embodiment, the array system 20, according to the energy storage system 1, controls the discharge to the load Lo and the charging from the solar power generation device 10 and selects the master string ST based on the total value of the remaining discharge power capacity and the remaining charge power capacity, excluding the string ST with low capacity, which has a low remaining discharge power capacity and a low remaining charge power capacity. Therefore, the master string ST is selected from master candidates, taking into account a battery-usable range (total capacity), which has a reserve for both charging and discharging.Accordingly, the string ST, which has a certain margin or more both when charging from the solar power generation device 10 and when discharging to the load Lo, and has a certain large total capacity, is selected as the master string ST. Therefore, it is possible to provide the power storage system 1, which can reduce the probability of switching the master string ST and reduce the number of switching operations.

[0045] Furthermore, once the information about the target state of charge (SOC) is acquired, it is fundamentally simple to implement a control system to achieve the target SOC. Accordingly, when the target SOC information is available, the ST string with the largest remaining discharge or charge capacity is selected based on its relationship to the current SOC. Therefore, the ST string with sufficient capacity for future control is chosen as the master ST string, and the probability of switching the master ST string can be reduced. Consequently, it is possible to deploy energy storage system 1, which can reduce the number of switching operations of the master ST string.

[0046] If the multiple strands ST1 to STm contain bypass circuits BC11 to BCmn, these bypass circuits cannot be switched when the master strand ST is being charged and discharged. The bypass circuits BC11 to BCmn are switched by turning off both switches Sa11 to Samn and switches Sb11 to Sbmn to prevent them from being turned on simultaneously. Therefore, the power supply from the master strand ST is temporarily interrupted when both switches Sa11 to Samn and Sb11 to Sbmn are off, rendering the master strand ST inoperable. Consequently, it is necessary to implement a suitable bypass in advance to utilize the capabilities of the master strand ST.Therefore, according to the present embodiment, the energy storage system 1 selects the master string ST in a state where the total value of the remaining discharge power capacity and the remaining charge power capacity is greatest among a variety of patterns when one of the bypass circuits BC11 to BCmn is in the bypass state. Accordingly, the master string ST is selected based on the string ST in a state where the power is extracted in advance, and thus it is possible to provide the energy storage system 1, which can help to further reduce the number of switching operations of the master string ST.

[0047] Although the present invention is described with reference to the embodiment described above, the present invention is not limited to the embodiment described above, and modifications may be made without departing from the essential nature of the present invention, and techniques from embodiments may be combined. Furthermore, publicly known or generally known techniques may be combined where possible.

[0048] For example, in the embodiment described above, the power failure state, in which no mains power can be drawn, is determined by the EMS 30, but the present invention is not limited to this, and the power failure state can be determined by the array system 20. Furthermore, each system of the EMS 30, the MOD systems MB11 to MBmn, the ST systems SB1 to SBm, and the array system 20 can be powered by the mains power supply or, in a non-power failure state in which mains power can be drawn, by a power source other than the mains power supply. In addition, these can include an internal power supply or receive power from the ST strings of the energy storage system 1.

[0049] Furthermore, the detection unit 21 and the determination unit 22 are mounted on the array system 20, but the present invention is not limited thereto, and the detection unit 21 and the determination unit 22 can be distributed as specific functions in the ST systems SB1 to SBm. Moreover, according to the present embodiment, the energy storage system 1 includes the EMS 30, but need not necessarily include the EMS 30.

[0050] Furthermore, this can be in Fig. The example shown is applied to a configuration where the power from each of the strands ST1 to STm is delivered to the load Lo via a three-phase circuit from UVW. In this case, the master strand ST for the U phase can be selected from the multitude of strands ST1 to STm assigned as the U phase, the master strand ST for the V phase can be selected from the multitude of strands ST1 to STm assigned as the V phase, and the W phase can undergo the same processing.

[0051] Furthermore, in step S11, which is in Fig.As shown in Figure 5, the string ST with the largest total value is selected as the master string ST, wherein the total value is not specifically limited to the largest value and can be randomly selected from the strings ST whose total value is equal to or greater than a predetermined threshold. Furthermore, in the above embodiment, it is assumed that the first threshold and the second threshold have the same value, but the present invention is not specifically limited to this, and the first threshold and the second threshold may have different values.

[0052] The embodiment described above illustrates an example where the master string ST is selected when the operating mode switches from the first to the second operating mode, but the present invention is not specifically limited to this and can be applied to a case where the master string ST needs to be reselected. The case where the master string ST needs to be reselected corresponds, for example, to a situation where discharge continues after the master string ST has been selected and the array system 20 detects that the remaining discharge power capacity of the master string ST is exhausted. When it is necessary to reselect the master string ST, the array system 20 can detect a break in the master string ST.When reselecting the master strand ST, the selection unit 23 excludes the strand ST selected as master strand ST from the multitude of strands ST1 to STm and reselects the master strand ST.

[0053] Although various embodiments are described above, it is understood that the present invention is not limited to these examples. It is obvious that those skilled in the art can make various modifications or corrections within the scope of the claims, and it is understood that these modifications or corrections naturally fall within the technical scope of the present invention. Furthermore, the components described in the embodiments above can be freely combined without departing from the spirit of the invention. LIST OF REFERENCE MARKS 1. Energy storage system 10 Solar power generation device (separate system device) 20 Array system (control unit) 21 recording units 22 Unit of determination 23 Selection Unit 30 EMS B11 to Bmn: Storage battery BC11 to BCmn: Bypass circuit C1 AC / DC converter Lo Last MB11 to MBmn: MOD system PR power receiving device SB1 to SBm ST system ST, ST1 to STm strand (energy storage device) ST Master String (Master Energy Storage Device) ST Slave string (Slave power storage device) ST string with low capacity (low capacity energy storage device) QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2017-184582 A

[0003]

Claims

[1] An electricity storage system which operates in a first operating mode when grid power is supplied to a load and in a second operating mode when grid power is not supplied to the load, wherein the electricity storage system comprises: a large number of energy storage devices connected in parallel to the load; a separate system device configured to supply the load and the multitude of energy storage devices with electricity derived from natural energy; and a control unit configured to control the discharge from the plurality of energy storage devices to the load and the charge from the separate system device to the plurality of energy storage devices, and to perform control to select a master energy storage device from the plurality of energy storage devices when switching from the first operating mode to the second operating mode or when it is necessary to reselect a master energy storage device, and to match the voltage, phase, and frequency between the master energy storage device and a slave energy storage device, which is not the master energy storage device, from the plurality of energy storage devices, wherein The control unit includes: a collection unit configured to collect information about a remaining discharge power capacity, indicating a discharge power capacity until reaching a discharge end voltage, and a remaining charge power capacity, indicating a charge power capacity until reaching a charge end voltage, for each of the multitude of energy storage devices; a determination unit configured to identify, from among the multitude of energy storage devices, an energy storage device whose remaining discharge power detected by the detection unit is equal to or less than a first threshold, as a low-capacity energy storage device, and an energy storage device whose remaining charge power detected by the detection unit is equal to or less than a second threshold, as a low-capacity energy storage device; and a selection unit configured to select the master energy storage device based on a total value of the remaining discharge power capacity and the remaining charge power capacity detected by the detection unit of each energy storage device that is a master candidate, except for the low-capacity energy storage device selected by the determination unit from the multitude of energy storage devices. [2] Energy storage system according to claim 1, wherein when information about a target state of charge, which is a setpoint, is acquired for the multiple energy storage devices, for an energy storage device whose total value is equal to or greater than a third threshold among the energy storage devices that are master candidates, the selection unit selects an energy storage device with the largest remaining discharge power when an actual state of charge exceeds the target state of charge, and selects an energy storage device with the largest remaining charging power when the actual state of charge is below the target state of charge. [3] Energy storage system according to claim 1, wherein Each of the multitude of energy storage devices contains a multitude of series-connected storage batteries and a multitude of bypass circuits configured to bypass the respective storage batteries by disconnecting the storage batteries from a series-connected state. The acquisition unit for each of the multitude of energy storage devices acquires information about the remaining discharge power capacity and the remaining charge power capacity for a multitude of patterns when one of the multitude of bypass circuits is bypassed, and The selection unit for each of the multitude of power storage devices selects the master storage device in a bypass state that has the greatest total value of remaining discharge power capacity and remaining charge power capacity among the multitude of patterns.

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