Power storage system

Abstract

To provide a power storage system that can reduce the number of times of switching a master power storage device.SOLUTION: A power storage system 1 comprises: a plurality of strings ST1-STm; a photovoltaic power generation device 10; and an array system 20 that matches the voltage, phase, and frequency of the master string ST with those of the slave strings ST. The array system 20 acquires information on the remaining discharge power capacities and the remaining charge power capacities of the plurality of strings ST1-STm, determines ones with a remaining discharge power capacity equal to or less than a first threshold and ones with a remaining charge power capacity equal to or less than a second threshold as low capacity strings ST, and selects a master string ST on the basis of the total value of the remaining discharge power capacities and the remaining charge power capacities of the strings ST to be master candidates which are determined by excluding the determined low capacity strings ST from the plurality of strings.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electricity storage system. [Background technology]

[0002] Conventionally, in order to provide a stable power supply to a load, the application of a power storage system including a plurality of power storage devices in addition to grid power such as a commercial power source has been considered (see, for example, Patent Document 1). In this power storage system, when grid power cannot be obtained due to a power outage or the like, one of the plurality of power storage devices becomes a master power storage device, and the others become slave power storage devices that operate following the master power storage device. In addition, the master power storage device can be switched to become a slave power storage device, and any one of the slave power storage devices can also become the master power storage device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-184582 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the power storage system of Patent Document 1, the selection of the master power storage device is not particularly considered, and the master power storage device may be frequently switched, and when the master power storage device is switched, control becomes more difficult. In more detail, when grid power is not available, it is necessary to make the slave power storage device follow the master power storage device, and the slave power storage device needs to match the voltage, phase, and frequency of the master power storage device. However, this matching control is not easy, and when the master power storage device is switched frequently, control becomes even more difficult.

[0005] The present invention has been made to solve such conventional problems, and has an object to provide a power storage system that can reduce the number of times the master power storage device is switched. [Means for solving the problem]

[0006] The power storage system according to the present invention is a power storage system that operates in a first operation mode when grid power is being supplied to a load, and operates in a second operation mode when the grid power cannot be supplied to the load, and includes a plurality of power storage devices connected in parallel to the load, and a separate system device capable of supplying power obtained by utilizing natural energy to the load and the plurality of power storage devices, and controls discharging from the plurality of power storage devices to the load and charging from the separate system device to the plurality of power storage devices, and when the system transitions from the first operation mode to the second operation mode or when it is necessary to reselect a master power storage device, selects a master power storage device from the plurality of power storage devices, and controls slave power storage devices among the plurality of power storage devices other than the master power storage device to match the voltage, phase, and frequency of the master power storage device. the control means includes an acquisition means for acquiring information on a remaining discharge power capacity indicating a discharge power capacity until a discharge end voltage is reached and a remaining charge power capacity indicating a charge power capacity until a charge end voltage is reached for each of the plurality of power storage devices; a determination means for determining, among the plurality of power storage devices, one whose remaining discharge power capacity acquired by the acquisition means is equal to or less than a first threshold value as a low-capacity storage device, and determining one whose remaining charge power capacity acquired by the acquisition means is equal to or less than a second threshold value as the low-capacity storage device; and a selection means for selecting the master power storage device based on a combined value of the remaining discharge power capacity and the remaining charge power capacity acquired by the acquisition means for each of the storage devices to be master candidates, excluding the low-capacity storage device determined by the determination means, from the plurality of power storage devices. Effect of the Invention

[0007] According to the present invention, it is possible to provide a power storage system that is capable of reducing the number of times the master power storage device is switched. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing an electricity storage system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram of the array system shown in FIG. [Diagram 3] 13 is a graph showing an example of remaining discharge power capacity and remaining charge power capacity in a case where the number of strings is nine. [Figure 4] 4 is a graph showing an example of remaining discharge power capacities and remaining charge power capacities of master candidates excluding low-capacity strings from the first to ninth strings shown in FIG. [Diagram 5] 10 is a flowchart showing a method for selecting a master string according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described below along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be modified as appropriate within the scope of the present invention. In addition, in the embodiments shown below, some configurations are omitted from illustration and description, but it goes without saying that publicly known or well-known technologies are appropriately applied to the details of the omitted technologies within the scope of the contents described below.

[0010] Fig. 1 is a block diagram showing a power storage system according to an embodiment of the present invention. As shown in Fig. 1, the power storage system 1 is provided to stabilize power supply from a system power such as a commercial power source to a load Lo, and includes a plurality of strings (power storage devices) ST1 to STm, a photovoltaic power generation device (separate system device) 10, module battery management systems (hereinafter referred to as MOD systems) MB11 to MBmn, a plurality of string battery management systems (hereinafter referred to as ST systems) SB1 to SBm, an array battery management system (control means: hereinafter referred to as array system) 20, and an EMS (Energy Management System) 30.

[0011] A plurality of (m: m is a natural number of 2 or more) strings ST1 to STm are connected in parallel to a load Lo, and each includes a plurality of storage batteries B11 to Bmn, a plurality of bypass circuits BC11 to BCmn, and AC / DC converters C1 to Cm.

[0012] A plurality of storage batteries B11 to Bmn (n batteries: n is a natural number of 2 or more) are provided in each of the strings ST1 to STm. The plurality of storage batteries B11 to Bmn are connected in series in a number of n batteries in each of the strings ST1 to STm. Each of the storage batteries B11 to Bmn is formed as a module made up of a plurality of unit cells, for example, but is not limited to this and may be made up of a single cell. Note that in this embodiment, it is assumed that the storage batteries B11 to Bmn are made up of, for example, second-hand batteries or batteries made by different manufacturers, and the capacity differs between the strings ST1 to STm.

[0013] The bypass circuits BC11-BCmn are circuits for bypassing some of the batteries B11-Bmn in each of the strings ST1-STm so as to remove them from the series connection state. These bypass circuits BC11-BCmn are capable of switching between a bypass state in which the batteries B11-Bmn are bypassed and a connection state in which the batteries B11-Bmn are not bypassed. Note that the bypass circuits BC11-BCmn all have the same configuration, so the following description will be given taking the eleventh bypass circuit BC11 as an example.

[0014] The eleventh bypass circuit BC11 includes a first switch Sa11, a bypass line BL11, and a second switch Sb11. The first switch Sa11 is provided on the AC / DC converter C1 side of the storage battery B11 and can be switched between an on state and an off state by opening and closing. The bypass line BL11 is a conductive line that bypasses the storage battery B11 from the AC / DC converter C1 side of the first switch Sa11 to the side opposite the AC / DC converter C1 of the storage battery B11. The second switch Sb11 is provided on the bypass line BL11 and can be switched between an on state and an off state by opening and closing. As shown in FIG. 1, the eleventh bypass circuit BC11 is in a state in which the storage battery B11 is connected in series with the other storage batteries B12 to B1n by the first switch Sa11 being in an on state and the second switch Sb11 being in an off state. On the other hand, the eleventh bypass circuit BC11 is in a bypass state in which the storage battery B11 is bypassed and removed from the series-connected state with the other storage batteries B12-B1n by turning the first switch Sa11 to the off state and the second switch Sb11 to the on state. Note that, when switching between the series-connected state and the bypass state, the eleventh bypass circuit BC11 is configured to prevent both the first switch Sa11 and the second switch Sb11 from being instantaneously turned on at the same time by inserting a period during which both the first switch Sa11 and the second switch Sb11 are in the off state.

[0015] The AC / DC converters C1-Cm are so-called PCS (Power Conditioning Systems) and are provided at the inlet portions of the strings ST1-STm, respectively. The AC / DC converters C1-Cm adjust the voltage (AC / DC conversion) when charging and discharging the multiple storage batteries B11-Bmn that make up the strings ST1-STm.

[0016] The solar power generation device 10 receives sunlight and generates power. The solar power generation device 10 is capable of supplying the generated power to a load Lo. Furthermore, the solar power generation device 10 can supply the generated power to each of the multiple strings ST1 to STm to charge the storage batteries B11 to Bmn in the strings ST1 to STm. Note that, although the solar power generation device 10 is taken as an example in this embodiment, the present invention is not limited to this, and as long as the device generates power using natural energy, the device may generate power using wind power, wave power, or other natural energy.

[0017] The MOD systems MB11-MBmn perform switch control of each of the bypass circuits BC11-BCmn and monitor the state of the storage batteries B11-Bmn. The MOD systems MB11-MBmn calculate the discharge power capacity until the discharge end voltage and the charge power capacity until the charge end voltage for each of the storage batteries B11-Bmn. Note that the MOD systems MB11-MBmn use various publicly known or well-known methods for calculating the discharge and charge power capacities. For example, the MOD systems MB11-MBmn measure the capacity of each of the storage batteries B11-Bmn in advance, and then sequentially calculate the SOC (State of charge) and deterioration degree of each of the storage batteries B11-Bmn to calculate the discharge and charge power capacities.

[0018] The ST systems SB1-SBm grasp the state of each of the strings ST1-STm and control the AC / DC converters C1-Cm. The ST systems SB1-SBm grasp the state (at least the remaining charge power capacity and the remaining discharge power capacity) of each of the strings ST1-STm by aggregating information from a plurality of MOD systems MB11-MBmn in the strings ST1-STm. Furthermore, the ST systems SB1-SBm grasp information on the remaining charge power capacity and the remaining discharge power capacity for a plurality of patterns when each of the bypass circuits BC11-BCmn in the strings ST1-STm is in a series connection state and when it is in a bypass state. Details of this point will be described later in the explanation of the outline of the operation.

[0019] Fig. 2 is a block diagram of the array system 20 shown in Fig. 1. As shown in Fig. 2, the array system 20 executes overall control of the power storage system 1, and controls discharging from the multiple strings ST1 to STm to the load Lo and charging from the solar power generation device 10 to the multiple strings ST1 to STm.

[0020] The array system 20 executes a first operation mode and a second operation mode when discharging to the load Lo. The first operation mode is an operation mode in which the multiple strings ST1 to STm follow the grid power (i.e., match the voltage, phase, and frequency) when the grid power is supplied to the load Lo. The second operation mode is an operation mode in which a master string (master power storage device) ST (a string when any of the multiple strings ST1 to STm is not specified (including a master string, a slave string described later, and a low-capacity string described later) is indicated by the symbol ST) is selected from the multiple strings ST1 to STm when the grid power is not supplied to the load Lo. Furthermore, the second operation mode is an operation mode in which the strings ST other than the master string ST are slave strings (slave power storage devices) ST, and the slave string ST follows the master string ST (i.e., match the voltage, phase, and frequency). In the first operation mode, the array system 20 performs charge and discharge control upon receiving an instruction from an EMS 30 described later. In addition, in the second motion mode, the array system 20 determines whether to charge or discharge based on the voltage and frequency of a power line (not shown) connected to the power receiving point.

[0021] Such an array system 20 includes an acquisition section (acquisition means) 21, a determination section (decision means) 22, and a selection section (selection means) .

[0022] The acquisition unit 21 acquires information on 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 information on the remaining discharge power capacity and the remaining charge power capacity of each of the multiple strings ST1 to STm by receiving information on each of the strings ST1 to STm from each of the ST systems SB1 to SBm.

[0023] The determination unit 22 determines, among the multiple strings ST1 to STm, a string whose remaining discharge power capacity acquired by the acquisition unit 21 is equal to or less than a first threshold as a low-capacity string (low-capacity power storage device) ST. The determination unit 22 also determines, among the multiple strings ST1 to STm, a string whose remaining charge power capacity acquired by the acquisition unit 21 is equal to or less than a second threshold as a low-capacity string ST. That is, the determination unit 22 determines, as a low-capacity string ST, a string whose remaining discharge power capacity is equal to or less than the first threshold and has no room for discharging, and a string whose remaining charge power capacity is equal to or less than the second threshold and has no room for charging.

[0024] The selection unit 23 selects a master string ST from among the strings ST1 to STm that are master candidates excluding the low-capacity string ST determined by the determination unit 22. At this time, the selection unit 23 selects the master string ST based on the sum of the remaining discharge power capacity and the remaining charge power capacity acquired by the acquisition unit 21. In this embodiment, the selection unit 23 determines the string ST with the largest sum as the master string ST.

[0025] Referring again to FIG. 1, the EMS 30 judges whether the grid power cannot be supplied to the load Lo (power failure state) based on a signal from the power receiving device PR that receives the grid power. The EMS 30 also transmits information on whether the grid power is in a power failure state to the array system 20. The array system 20 determines whether to execute the first operation mode or the second operation mode based on this information. Furthermore, when a target SOC of the power storage system 1 (all of the multiple strings ST1 to STm) is determined, the EMS 30 transmits this information to the array system 20. Furthermore, when the power storage system 1 is sufficiently charged, the EMS 30 also transmits a signal to the photovoltaic power generation device 10 to suppress the amount of power generation.

[0026] In the energy storage system 1 as described above, when transitioning from the first operation mode to the second operation mode, the master string ST can be selected so as to reduce the number of times the master string ST is switched. Hereinafter, an overview of a method for selecting the master string ST of the energy storage system 1 will be described.

[0027] Fig. 3 is a graph showing an example of the remaining discharge power capacity and the remaining charge power capacity when the number of strings ST1 to STm is nine. As shown in Fig. 3, the acquisition unit 21 acquires, for example, from the first ST system SB1, information that the remaining discharge power capacity of the first string ST1 is 30 Wh and the remaining charge power capacity is 30 Wh. The acquisition unit 21 also acquires, for example, from the second ST system SB2, information that the remaining discharge power capacity of the second string ST2 is 10 Wh and the remaining charge power capacity is 30 Wh. Similarly, the acquisition unit 21 acquires information on the remaining discharge power capacity and the remaining charge power capacity of each of the third to ninth ST systems SB3 to SB9.

[0028] For example, assume that 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 a low-capacity string ST because the remaining discharge power capacity is equal to or less than the first threshold. Similarly, the determination unit 22 determines that the fifth, sixth, and ninth strings ST5, ST6, and ST9 are low-capacity strings ST.

[0029] Fig. 4 is a graph showing an example of the remaining discharge power capacity and remaining charge power capacity of master candidates excluding the low-capacity string ST from the first to ninth strings ST1 to ST9 shown in Fig. 3. As shown in Fig. 4, the selection unit 23 extracts the first, third, fourth, seventh, and eighth strings ST1, ST3, ST4, ST7, and ST8 from the first to ninth strings ST1 to ST9 excluding the low-capacity string ST. The extracted first, third, fourth, seventh, and eighth strings ST1, ST3, ST4, ST7, and ST8 become master candidates.

[0030] Next, the selection unit 23 checks the sum of the remaining discharge power capacity and the remaining charge power capacity for the string ST that is a master candidate. In the example shown in Fig. 4, the sums of the first, third, fourth, seventh, and eighth strings ST1, ST3, ST4, ST7, and ST8 are 60Wh, 60Wh, 60Wh, 60Wh, and 70Wh, respectively. Therefore, the selection unit 23 determines the eighth string ST8, which has the largest sum, as the master string ST.

[0031] After the master string ST is determined as described above, the array system 20 sets the eighth string ST8 as the master string ST and the first to seventh and ninth strings ST1 to ST7, ST9 as slave strings ST. Then, the array system 20 instructs the ST systems SB1 to SB7, SB9 of the first to seventh and ninth strings ST1 to ST7, ST9 that are to become the slave strings ST to perform tracking control. As a result, the ST systems SB1 to SB7, SB9 execute control to make the voltages, phases and frequencies of the first to seventh and ninth strings ST1 to ST7, ST9 coincide with those of the eighth string ST8, which is the master string ST.

[0032] Here, it is preferable that the acquisition unit 21 acquires information on the remaining discharge power capacity and the remaining charge power capacity for each of the multiple strings ST1 to STm for multiple patterns in which any of the multiple bypass circuits BC11 to BCmn is in a bypass state.

[0033] At this time, it is preferable that the acquisition unit 21 acquires 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 a bypass state for each of the multiple strings ST1 to STm. The first string ST1 will be taken as an example. For example, when the number of storage batteries B11 to B1n in the first string ST1 is four (n=4), the first ST system SB1 acquires information on the remaining discharge power capacity and the remaining charge power capacity in 15 patterns of 2×2×2×2-1. Then, the first ST system SB1 transmits information on the remaining discharge power capacity and the remaining charge power capacity of the 15 patterns. As a result, the acquisition unit 21 of the array system 20 acquires information on the remaining discharge power capacity and the remaining charge power capacity for all patterns. Note that the above "-1" is for excluding the case where all the bypass circuits BC11 to BC14 are in a bypass state. The same is true for the second to m-th ST systems SB2 to SBm.

[0034] The acquisition unit 21 may acquire information on the remaining discharge power capacity and the remaining charge power capacity for some patterns, not all patterns. The first string ST1 will be taken as an example. For example, the first ST system SB1 grasps the remaining discharge current capacity for the storage batteries B11-B1n of the first string ST1. Next, the first ST system SB1 increases the number of bypass circuits BC11-BC1n that are in a bypass state in order from the one with the smallest remaining discharge current capacity, and calculates and transmits information on the remaining discharge power capacity and the remaining charge power capacity for the (n-1) pattern. Thereby, the acquisition unit 21 of the array system 20 acquires information on the remaining discharge power capacity and the remaining charge power capacity for the (n-1) pattern. The same applies to the second to m-th ST systems SB2-SBm. In the above, the information on the remaining discharge power capacity and the remaining charge power capacity for the (n-1) pattern is calculated based on the remaining discharge current capacity, but this is not limited to the above. For example, the remaining charge current capacity may be used as the reference, not limited to the remaining discharge current capacity. Furthermore, information on the remaining discharge power capacity and the remaining charge power capacity may be calculated for both patterns of the remaining discharge current capacity and the remaining charge current capacity ((n-1) x 2 patterns), or information on the remaining discharge power capacity and the remaining charge power capacity may be calculated using completely different criteria.

[0035] When the acquisition unit 21 acquires information on the remaining discharge power capacity and the remaining charge power capacity in a plurality of patterns of the bypass circuits BC11 to BCmn in the above manner, the selection unit 23 identifies the bypass state in which the total value of the remaining discharge power capacity and the remaining charge power capacity is the highest. Then, the selection unit 23 executes the process described with reference to Figs. 3 and 4 in the bypass state in which the total value of the remaining discharge power capacity and the remaining charge power capacity is the highest.

[0036] Furthermore, when the array system 20 receives information on the target SOC from the EMS 30, the selection unit 23 may determine the master string ST not only from the sum of the remaining discharge power capacity and the remaining charge power capacity but also from the relationship between the current SOC of the power storage system 1 and the target SOC. For example, when the current SOC is higher than the target SOC, there is a high possibility that discharging will proceed in the future. Therefore, the selection unit 23 may select the string ST with the highest remaining discharge power capacity as the master string ST from among the strings ST in which the sum of the remaining discharge power capacity and the remaining charge power capacity is equal to or greater than a third threshold. Similarly, when the current SOC is lower than the target SOC, there is a high possibility that charging will proceed in the future. Therefore, the selection unit 23 may select the string ST with the highest remaining charge power capacity as the master string ST from among the strings ST in which the sum of the remaining discharge power capacity and the remaining charge power capacity is equal to or greater than a third threshold.

[0037] Next, a method for selecting a master string ST of the power storage system 1 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the method for selecting a master string ST according to this embodiment. Note that the process of Fig. 5 is executed immediately after it is determined that the EMS 30 is in a power outage state and the array system 20 starts the second operation mode, for example.

[0038] As shown in FIG. 5, first, the acquisition unit 21 of the array system 20 acquires information on the remaining discharge power capacity and remaining charge power capacity for each of multiple patterns when the bypass circuits BC11 to BCmn are switched between the series connection state and the bypass state for each of the strings ST1 to STm (S1).

[0039] Next, the array system 20 identifies a pattern in which the sum of the remaining discharge power capacity and the remaining charge power capacity is maximized for each of the strings ST1 to STm, and identifies each capacity in that pattern (S2).

[0040] Thereafter, the determination unit 22 of the array system 20 determines a string ST whose remaining discharge power capacity in the pattern identified in step S2 is equal to or less than a first threshold as a low-capacity string ST (S3). Next, the determination unit 22 determines a string ST whose remaining charge power capacity in the pattern identified in step S2 is equal to or less than a second threshold as a low-capacity string ST (S4). After the process of step S4, a string ST that has not been determined as a low-capacity string ST becomes a master candidate.

[0041] Next, it is determined whether information on the target SOC has been acquired from the EMS 30 (S5). If the information on the target SOC has been acquired (S5: YES), the selection unit 23 of the array system 20 extracts strings ST whose sum values ​​in the pattern identified in step S2 are equal to or greater than a third threshold value (S6).

[0042] After that, the array system 20 judges whether the current SOC of the power 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). Then, the process shown in FIG. 5 ends.

[0043] On the other hand, if the current SOC is not higher than the target SOC (S7: NO), the selection unit 23 determines whether the current SOC of the power storage system 1 is lower than the target SOC (S9). If the current SOC is lower than the target SOC (S9: YES), the selection unit 23 selects the string ST with the largest remaining charge power capacity from among the strings ST extracted in step S6 as the master string ST (S10). Then, the process shown in FIG. 5 ends.

[0044] If the target SOC information has not been acquired (S5: NO) and if the current SOC is not lower than the target SOC (S9: NO), the selector 23 selects the string ST with the maximum sum in the pattern identified in step S2 as the master string ST (S11). Then, the process shown in FIG. 5 ends.

[0045] In this way, according to the energy storage system 1 of this embodiment, the array system 20 controls discharging to the load Lo and charging from the photovoltaic power generation device 10, and selects the master string ST based on the sum of the remaining discharge power capacity and the remaining charge power capacity, excluding the low-capacity string ST with low remaining discharge power capacity and remaining charge power capacity. For this reason, the master string ST is selected from among those having margins in both charging and discharging, taking into consideration the range of use (total capacity) that can be used as a battery. As a result, a string ST having a certain margin or more in both the case where charging is performed from the photovoltaic power generation device 10 and the case where discharging is performed to the load Lo, and having a certain large total capacity, is selected as the master string ST. Therefore, it is possible to provide the energy storage system 1 that can reduce the possibility of switching the master string ST and reduce the number of times the master string ST is switched.

[0046] Furthermore, when information on a target SOC has been acquired, control that achieves the target SOC is generally more likely to be executed, so that when information on the target SOC is available, the string ST with the largest remaining discharge power capacity or the largest remaining charge power capacity is selected in relation to the current SOC. As a result, a string ST with a margin for future control is selected as the master string ST, and the possibility of switching the master string ST can be reduced. Therefore, it is possible to provide a power storage system 1 that can reduce the number of times the master string ST is switched.

[0047] Here, when multiple strings ST1 to STm have bypass circuits BC11 to BCmn, the bypass circuits BC11 to BCmn cannot be switched while the master string ST is being charged or discharged. The bypass circuits BC11 to BCmn are switched via the off state of both switches Sa11 to Samn, Sb11 to Sbmn to prevent both switches Sa11 to Samn, Sb11 to Sbmn from being instantaneously turned on at the same time. Therefore, when both switches are off, the power from the master string ST is temporarily stopped, and the master string ST does not function. Therefore, it is essential to draw out the capacity of the master string ST by performing an appropriate bypass in advance. Therefore, the power storage system 1 according to this embodiment selects the master string ST in a state where the sum of the remaining discharge power capacity and the remaining charge power capacity is the highest among multiple patterns in which any of the bypass circuits BC11 to BCmn is in the bypass state. As a result, the master string ST is selected based on the string ST whose capacity has already been brought out, which contributes to a further reduction in the number of switching operations, and it is possible to provide a storage system 1 which contributes to further reducing the number of switching operations of the master string ST.

[0048] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and modifications may be made without departing from the spirit of the present invention, and techniques of the embodiments may be combined. Furthermore, known or well-known techniques may be combined if possible.

[0049] For example, in the above embodiment, the power outage state where the grid power is not available is determined by the EMS 30, but this is not limiting and the determination may be made by the array system 20. Furthermore, the EMS 30 and each of the systems MB11-MBmn, SB1-SBm, and 20 may operate using the grid power when the grid power is not available, or may operate using power other than the grid power. Furthermore, these may be provided with an internal power supply, or may be configured to receive power from the string ST of the power storage system 1.

[0050] In addition, the acquiring unit 21 and the deciding unit 22 are mounted on the array system 20, but are not limited thereto, and may be configured as a part of functions in each of the ST systems SB1 to SBm. Furthermore, although the power storage system 1 according to the present embodiment includes an EMS 30, the EMS 30 may not be included.

[0051] 1 may be applied to a configuration in which power is supplied from each of the strings ST1 to STm to a load Lo via a three-phase electric circuit of UVW. In this case, a master string ST for the U phase is selected from the multiple strings ST1 to STm assigned as the U phase, and a master string ST for the V phase is selected from the multiple strings ST1 to STm assigned as the V phase, and similar processing is performed for the W phase.

[0052] 5, the string ST with the maximum sum is selected as the master string ST, but it is not limited to the maximum, and may be selected randomly from strings ST with a sum equal to or greater than a predetermined threshold. Furthermore, in the above embodiment, the first threshold and the second threshold are assumed to be the same value, but they are not limited to this and may be different values.

[0053] Furthermore, in the above embodiment, an example in which the master string ST is selected when the operation mode is shifted from the first operation mode to the second operation mode has been described, but the present invention is not limited to this, and may be applied to a case in which the master string ST needs to be reselected. A case in which the master string ST needs to be reselected corresponds to a case in which, for example, after the master string ST is selected, discharging progresses and the array system 20 determines that the remaining discharge power capacity of the master string ST has run out. Another case in which the selection needs to be reselected may be a case in which the array system 20 determines that a disconnection has occurred in the master string ST. When reselecting the master string ST, the selector 23 selects the master string ST by excluding the string ST selected as the master string ST from the multiple strings ST1 to STm. [Explanation of symbols]

[0054] 1: Energy storage system 10: Solar power generation equipment (separate system equipment) 20: Array system (control means) 21: Acquisition part (acquisition means) 22: Determination unit (determination means) 23: Selection unit (selection means) 30: EMS B11~Bmn:Storage battery BC11~BCmn: Bypass circuit C1: AC / DC converter Lo:Load MB11~MBmn: MOD system PR: Power receiving device SB1~SBm: ST system ST, ST1 to STm: Strings (energy storage devices) ST: Master string (master power storage device) ST: Slave string (slave power storage device) ST: Low-capacity string (low-capacity storage device)

Claims

1. A power storage system that operates in a first operation mode when grid power is supplied to a load, and operates in a second operation mode when the grid power cannot be supplied to the load, A plurality of power storage devices connected in parallel to the load; a separate system device capable of supplying electric power obtained by utilizing natural energy to the load and the plurality of power storage devices; a control means for controlling discharging from the multiple power storage devices to the load and charging from the separate system device to the multiple power storage devices, and for selecting a master power storage device from the multiple power storage devices when the operation mode is shifted from the first operation mode to the second operation mode or when it is necessary to reselect a master power storage device, and for executing control for slave power storage devices among the multiple power storage devices other than the master power storage device to match a voltage, a phase, and a frequency with the master power storage device, The control means an acquisition means for acquiring information on a remaining discharge power capacity indicating a discharge power capacity until a discharge end voltage is reached and a remaining charge power capacity indicating a charge power capacity until a charge end voltage is reached for each of the plurality of power storage devices; a determination means for determining, among the plurality of power storage devices, a device whose remaining discharge power capacity acquired by the acquisition means is equal to or less than a first threshold as a low-capacity power storage device, and determining, among the plurality of power storage devices, a device whose remaining charge power capacity acquired by the acquisition means is equal to or less than a second threshold as the low-capacity power storage device; a selection means for selecting the master power storage device based on a combined value of the remaining discharge power capacity and the remaining charge power capacity acquired by the acquisition means for each of the power storage devices to be master candidates, excluding the low-capacity power storage device determined by the determination means, from the plurality of power storage devices; A power storage system comprising:

2. When information on target charging rates for the plurality of power storage devices is acquired, the selection means selects, among the power storage devices to be the master candidates, the power storage device having the largest remaining discharge power capacity when the current charging rate exceeds the target charging rate, and selects the power storage device having the largest remaining charge power capacity when the current charging rate falls below the target charging rate, for the power storage devices having the summed value equal to or greater than a third threshold value. The power storage system according to claim 1 .

3. Each of the plurality of power storage devices includes a plurality of storage batteries connected in series and a plurality of bypass circuits for removing each of the storage batteries from a series-connected state and bypassing the storage batteries, the acquiring means acquires information on the remaining discharge power capacity and the remaining charge power capacity for a plurality of patterns in which any one of the plurality of bypass circuits is bypassed for each of the plurality of power storage devices; The selection means selects the master power storage device in a bypass state in which the combined value of the remaining discharge power capacity and the remaining charge power capacity is the highest among the plurality of patterns for each of the plurality of power storage devices. The power storage system according to claim 1 .

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