Electricity storage system

Abstract

An electricity storage system (1) comprises: a plurality of strings (ST1-STm); a solar power generation device (10); and an array system (20) that executes control for causing the voltage, phase, and frequency of a slave string (ST) to match those of a master string (ST). The array system (20) acquires information on the remaining discharge power capacity and the remaining charge power capacity of each of the plurality of strings (ST1 to STm), determines a string having a remaining discharge power capacity equal to or less than a first threshold value and a string having a remaining charge power capacity equal to or less than a second threshold value as low capacity strings (ST), and selects the master string (ST) on the basis of the total value of the remaining discharge power capacity and remaining charge power capacity of each of the strings (ST) being master candidates excluding the determined low capacity strings (ST).

Description

Energy storage system

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

[0002] Conventionally, in order to provide a stable power supply to a load, it has been considered to apply a power storage system including a plurality of power storage devices in addition to grid power such as a commercial power source (see Patent Document 1). In this power storage system, when grid power is no longer available 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.

[0003] Japanese Patent Application Publication No. 2017-184582

[0004] However, the power storage system in Patent Document 1 does not particularly consider the selection of a master power storage device, and the master power storage device may be frequently switched, making control more difficult. To explain in more detail, when grid power is unavailable, the slave power storage device must operate in response to the master power storage device, and the slave power storage device must match the voltage, phase, and frequency of the master power storage device. However, achieving this matching is not easy, and the more frequently the master power storage device is switched, the more difficult the control becomes.

[0005] The present invention has been made to solve these conventional problems, and its purpose is to provide a power storage system that can reduce the number of times the master power storage device is switched.

[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, a separate system device that is 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 transitioning 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 of 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. and a control means for executing the above, wherein the control means comprises: an acquisition means for acquiring information on a remaining discharge power capacity indicating the discharge power capacity up to a discharge end voltage and a remaining charge power capacity indicating the charge power capacity up to a charge end voltage 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 as a low-capacity power storage device, and determining, among the plurality of power storage devices, one 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; and a selection means for selecting the master power storage device based on the sum 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.

[0007] According to the present invention, it is possible to provide a power storage system that can reduce the number of times the master power storage device is switched.

[0008] 1 is a block diagram showing a power storage system according to an embodiment of the present invention. It is a block diagram of the array system shown in FIG. 1. It is a graph showing an example of a remaining discharge power capacity and a remaining charge power capacity when there are nine strings. It is a graph showing an example of a remaining discharge power capacity and a remaining charge power capacity of master candidates obtained by excluding low-capacity strings from the first to ninth strings shown in FIG. 3. It is a flowchart showing a method for selecting a master string according to the present embodiment.

[0009] The present invention will be described below in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below and can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiments shown below, some components are omitted from illustration and description, but it goes without saying that publicly known or well-known technologies are applied as appropriate to the details of the omitted technologies within the scope of the content 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 the power supply from a system power source 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 the array system) 20, and an EMS (Energy Management System) 30.

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

[0012] A plurality of storage batteries B11 to Bmn (n: n is a natural number of 2 or greater) are provided in each of the strings ST1 to STm. The plurality of storage batteries B11 to Bmn are connected in series 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. In this embodiment, the plurality of storage batteries B11 to Bmn are assumed to be, for example, second-hand batteries or batteries made by different manufacturers, and the capacities of the strings ST1 to STm are different.

[0013] The bypass circuits BC11 to BCmn are circuits for bypassing some of the storage batteries B11 to Bmn in each string ST1 to STm so as to remove them from the series connection state. These bypass circuits BC11 to BCmn are capable of switching between a bypass state in which the storage batteries B11 to Bmn are bypassed and a connection state in which the storage batteries B11 to Bmn are not bypassed. Note that the bypass circuits BC11 to BCmn all have the same configuration, so the following description will be given using 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 located closer to the AC / DC converter C1 than the storage battery B11 and is switchable between an on state and an off state by opening and closing the switch. The bypass line BL11 is a conductive line that runs from the AC / DC converter C1 side of the first switch Sa11, bypasses the storage battery B11, and is connected to the side of the storage battery B11 opposite the AC / DC converter C1. The second switch Sb11 is located on the bypass line BL11 and is switchable between an on state and an off state by opening and closing the switch. As shown in FIG. 1 , when the first switch Sa11 is turned on and the second switch Sb11 is turned off, the eleventh bypass circuit BC11 connects the storage battery B11 in series with the other storage batteries B12 to B1n. 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 connection state with the other storage batteries B12 to B1 n 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 connection 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 momentarily 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 to Cm are so-called PCS (Power Conditioning Systems) and are provided at the inlet portions of the strings ST1 to STm, respectively. The AC / DC converters C1 to Cm adjust the voltage (AC / DC conversion) of the storage batteries B11 to Bmn that make up the strings ST1 to STm when charging or discharging.

[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 a plurality of strings ST1 to STm to charge the storage batteries B11 to Bmn in the strings ST1 to STm. Note that while the present embodiment uses the solar power generation device 10 as an example, the present invention is not limited to this, and any device that generates power using natural energy, such as wind power or wave power, or other natural energy, may also be used.

[0017] The MOD systems MB11 to MBmn perform switch control of each bypass circuit BC11 to BCmn and monitor the status of the storage batteries B11 to Bmn. The MOD systems MB11 to MBmn calculate the discharge power capacity up to the discharge end voltage and the charge power capacity up to the charge end voltage for each storage battery B11 to Bmn. The MOD systems MB11 to MBmn use various well-known or publicly known methods to calculate the discharge and charge power capacities. For example, the MOD systems MB11 to MBmn measure the capacity of each storage battery B11 to Bmn in advance, and then sequentially calculate the SOC (State of Charge) and degradation level of each storage battery B11 to Bmn to calculate the discharge and charge power capacities.

[0018] The ST systems SB1 to SBm grasp the status of each string ST1 to STm and control the AC / DC converters C1 to Cm. The ST systems SB1 to SBm aggregate information from multiple MOD systems MB11 to MBmn in the strings ST1 to STm to grasp the status of each string ST1 to STm (at least the remaining charge power capacity and the remaining discharge power capacity). Furthermore, the ST systems SB1 to SBm grasp information on the remaining charge power capacity and the remaining discharge power capacity for multiple patterns when each bypass circuit BC11 to BCmn in the strings ST1 to STm is in a series connection state or a bypass state. Details of this point will be described later in the explanation of the outline of 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 plurality of strings ST1 to STm to the load Lo and charging from the photovoltaic power generation device 10 to the plurality of 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 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 no specific one of the multiple strings ST1 to STm is specified (including a master string, a slave string described later, and a low-capacity string described later) is denoted by the symbol ST) is selected from the multiple strings ST1 to STm when 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 designated as 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). Note that in the first operation mode, the array system 20 performs charge and discharge control in response to instructions from an EMS 30 described later. In addition, the array system 20 determines whether to charge or discharge in the second motion mode based on the voltage and frequency of the 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) 23.

[0022] The acquisition unit 21 acquires information on the remaining discharge power capacity and remaining charge power capacity of each of the plurality of strings ST1 to STm. The acquisition unit 21 receives information on each of the strings ST1 to STm from each of the ST systems SB1 to SBm, thereby acquiring information on the remaining discharge power capacity and remaining charge power capacity of each of the plurality of strings ST1 to STm.

[0023] The determination unit 22 determines, among the plurality of strings ST1 to STm, those for which the remaining discharge power capacity acquired by the acquisition unit 21 is equal to or less than a first threshold as low-capacity strings (low-capacity power storage devices) ST. The determination unit 22 also determines, among the plurality of strings ST1 to STm, those for which the remaining charge power capacity acquired by the acquisition unit 21 is equal to or less than a second threshold as low-capacity strings ST. In other words, the determination unit 22 determines, as low-capacity strings ST, those for which the remaining discharge power capacity is equal to or less than the first threshold and there is no room for discharging, and those for which the remaining charge power capacity is equal to or less than the second threshold and there is 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. In this case, 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 determines whether the grid power cannot be supplied to the load Lo (power outage state) based on a signal from the power receiving device PR that receives the grid power. The EMS 30 also transmits information indicating whether the grid power is in a power outage 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 set, 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, it is possible to select the master string ST so as to reduce the number of times the master string ST is switched. An outline of a method for selecting the master string ST of the energy storage system 1 will be described below.

[0027] FIG. 3 is a graph showing an example of the remaining discharge power capacity and remaining charge power capacity when there are nine strings ST1 to STm. As shown in FIG. 3, the acquisition unit 21 acquires, for example, information from the first ST system SB1 indicating 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, information from the second ST system SB2 indicating 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 remaining charge power capacity of the third to ninth ST systems SB3 to SB9, respectively, of the strings ST3 to ST9.

[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 its 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] 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. 4. As shown in FIG. 4, the selector 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 selector 23 checks the sum of the remaining discharge power capacity and the remaining charge power capacity for the master candidate string ST. 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 60 Wh, 60 Wh, 60 Wh, 60 Wh, and 70 Wh, respectively. Therefore, the selector 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 designates 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. The array system 20 then instructs the ST systems SB1 to SB7, SB9 of the first to seventh and ninth strings ST1 to ST7, ST9, which will become the slave strings ST, to perform tracking control. As a result, the ST systems SB1 to SB7, SB9 execute control to match the voltage, phase, and frequency of the first to seventh and ninth strings ST1 to ST7, ST9 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 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] In this case, the acquisition unit 21 preferably acquires information on the remaining discharge power capacity and remaining charge power capacity for each of the multiple strings ST1 to STm, for example, for all patterns when each of the bypass circuits BC11 to BC1n is in a bypass state. This will be explained using the first string ST1 as an example. For example, if 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 remaining charge power capacity for 15 patterns (2 x 2 x 2 x 2 - 1). The first ST system SB1 then transmits information on the remaining discharge power capacity and remaining charge power capacity for 15 patterns. As a result, the acquisition unit 21 of the array system 20 acquires information on the remaining discharge power capacity and remaining charge power capacity for all patterns. Note that the above "-1" excludes the case where all of the bypass circuits BC11 to BC14 are in a bypass state. The same applies to the second to mth ST systems SB2 to SBm.

[0034] Furthermore, the acquisition unit 21 may acquire information on the remaining discharge power capacity and remaining charge power capacity for some patterns, not all patterns. This will be described using the first string ST1 as an example. For example, the first ST system SB1 determines the remaining discharge current capacity for the storage batteries B11 to B1n of the first string ST1. Next, the first ST system SB1 increases the number of bypass circuits BC11 to BC1n that are in the 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 remaining charge power capacity for the (n-1) pattern. This allows the acquisition unit 21 of the array system 20 to acquire information on the remaining discharge power capacity and remaining charge power capacity for the (n-1) pattern. The same applies to the second to mth ST systems SB2 to SBm. Furthermore, while the information on the remaining discharge power capacity and remaining charge power capacity for the (n-1) pattern is calculated based on the remaining discharge current capacity in the above description, this is not limiting. For example, the remaining charge current capacity may be used as the reference, rather than the remaining discharge current capacity. Furthermore, information on the remaining discharge power capacity and 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 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 for multiple patterns of the bypass circuits BC11 to BCmn as described above, the selection unit 23 identifies 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 process described with reference to FIGS. 3 and 4 in the bypass state with the highest total value of the remaining discharge power capacity and the remaining charge power capacity.

[0036] Furthermore, when the array system 20 receives information about the target SOC from the EMS 30, the selector 23 may determine the master string ST based not only on the sum of the remaining discharge power capacity and the remaining charge power capacity but also on the relationship between the current SOC of the power storage system 1 and the target SOC. For example, if the current SOC is higher than the target SOC, there is a high possibility that discharging will progress in the future. Therefore, the selector 23 may select the string ST with the highest remaining discharge power capacity as the master string ST from among the strings ST whose sum of the remaining discharge power capacity and the remaining charge power capacity is equal to or greater than a third threshold. Similarly, if the current SOC is lower than the target SOC, there is a high possibility that charging will progress in the future. Therefore, the selector 23 may select the string ST with the highest remaining charge power capacity as the master string ST from among the strings ST whose 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 in 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 processing in Fig. 5 is executed, for example, immediately after the EMS 30 determines that a power outage has occurred and the array system 20 starts the second operation mode.

[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 the multiple patterns when switching between the series connection state and the bypass state of the bypass circuits BC11 to BCmn for each of the strings ST1 to STm (S1).

[0039] Next, the array system 20 identifies a pattern that maximizes the sum of the remaining discharge power capacity and the remaining charge power capacity 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 processing 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 (S5) whether information on the target SOC has been acquired from the EMS 30. If information on the target SOC has been acquired (S5: YES), the selector 23 of the array system 20 extracts strings ST whose sum in the pattern identified in step S2 is equal to or greater than a third threshold value (S6).

[0042] Thereafter, the array system 20 determines 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 selector 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 selector 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 selector 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) or if the current SOC is not lower than the target SOC (S9: NO), the selector 23 selects the string ST with the largest 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 low-capacity strings ST with low remaining discharge power capacity and remaining charge power capacity. Therefore, the master string ST is selected from among those strings with ample capacity for both charging and discharging, taking into consideration the usable range (total capacity) of the battery. As a result, a string ST with a certain amount of capacity for both charging from the photovoltaic power generation device 10 and discharging to the load Lo and with a certain amount of overall capacity is selected as the master string ST. Therefore, it is possible to provide an 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 the target SOC has been acquired, it is generally easier to execute control to achieve that target SOC. Therefore, when information on the target SOC is available, the string ST with the largest remaining discharge power capacity or remaining charge power capacity is selected in relation to the current SOC. Therefore, a string ST with a margin for future control is selected as the master string ST, thereby reducing the possibility of switching the master string ST. 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, if 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 and Sb11 to Sbmn to prevent both switches Sa11 to Samn and Sb11 to Sbmn from being momentarily turned ON simultaneously. Therefore, when both switches are OFF, power from the master string ST is temporarily stopped, and the master string ST no longer functions. Therefore, it is important to appropriately bypass the master string ST in advance to maximize its capabilities. Therefore, the energy storage system 1 according to this embodiment selects the master string ST in the state where the combined value of the remaining discharge power capacity and the remaining charge power capacity is highest among multiple patterns in which any of the bypass circuits BC11 to BCmn is in the bypass state. This allows the master string ST to be selected based on a string ST whose capacity has already been drawn out, which further contributes to reducing the number of switching times, and makes it possible to provide a storage system 1 that further contributes to reducing the number of switching times 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 or techniques from the embodiments may be combined within the scope of the present invention. Furthermore, publicly known or well-known techniques may be combined if possible.

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

[0050] In addition, the acquisition unit 21 and the determination unit 22 are mounted on the array system 20, but are not limited to this, and may be configured as distributed functions within each of the ST systems SB1 to SBm. Furthermore, although the energy storage system 1 according to this embodiment includes an EMS 30, it is not necessary to include the EMS 30.

[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 electrical path of UVW. In this case, a master string ST for the U-phase may be selected from the multiple strings ST1 to STm assigned as the U-phase, and a master string ST for the V-phase may be selected from the multiple strings ST1 to STm assigned as the V-phase, and similar processing may be performed for the W-phase.

[0052] 5, the string ST with the largest sum is selected as the master string ST, but it is not limited to the largest, and may be selected randomly from among the 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 a master string ST is selected when transitioning from the first operation mode to the second operation mode has been described. However, this is not particularly limited, and the present invention may be applied to cases in which it is necessary to reselect a master string ST. A case in which it is necessary to reselect a master string ST corresponds to, for example, a case in which, after the master string ST is selected, discharge progresses and the array system 20 determines that the master string ST has no remaining discharge power capacity. Another case in which it is necessary to reselect a master string ST may be a case in which the array system 20 determines that a disconnection has occurred in the master string ST. When reselecting a master string ST, the selector 23 excludes the string ST selected as the master string ST from the multiple strings ST1 to STm and reselects a new master string ST.

[0054] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0055] This application is based on a Japanese patent application (Patent Application No. 2023-128276) filed on August 7, 2023, the contents of which are incorporated herein by reference.

[0056] 1: Power storage system 10: Photovoltaic power generation device (separate system device) 20: Array system (control means) 21: Acquisition unit (acquisition means) 22: Determination unit (determination means) 23: Selection unit (selection means) 30: EMS B11 to Bmn: Storage battery BC11 to BCmn: Bypass circuit C1: AC / DC converter Lo: Load MB11 to MBmn: MOD system PR: Power receiving device SB1 to SBm: ST system ST, ST1 to STm: String (power storage device) ST: Master string (master power storage device) ST: Slave string (slave power storage device) ST: Low-capacity string (low-capacity power storage device)

Claims

1. A power storage system which 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, comprising: a plurality of power storage devices connected in parallel to the load; a separate system device capable of supplying power obtained by utilizing natural energy to the load and the plurality of power storage devices; and a control means which 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 which, 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, selects a master power storage device from the plurality of power storage devices and executes control for matching a voltage, phase and frequency of slave power storage devices among the plurality of power storage devices other than the master power storage device with those of the master power storage device, wherein the control means comprises: an acquisition means for acquiring information on a remaining discharge power capacity indicating a discharge power capacity up to a discharge end voltage and a remaining charge power capacity indicating a charge power capacity up to a charge end voltage for each of the plurality of power storage devices; a determination means for determining, among the plurality of power storage devices, a power storage device whose remaining discharge power capacity acquired by the acquisition means is equal to or less than a first threshold value as a low-capacity power storage device, and determining, among the plurality of power storage devices, a power storage device whose remaining charge power capacity acquired by the acquisition means is equal to or less than a second threshold value as a low-capacity power 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 power storage devices that are master candidates, excluding the low-capacity power storage device determined by the determination means, from the plurality of power storage devices.

2. The energy storage system according to claim 1, characterized in that, when information on target charging rates for the plurality of energy storage devices has been acquired, the selection means selects, among the storage devices that are to be master candidates and whose combined value is equal to or greater than a third threshold, the storage device with the largest remaining discharge power capacity when the current charging rate exceeds the target charging rate, and selects the storage device with the largest remaining charge power capacity when the current charging rate falls below the target charging rate.

3. The energy storage system according to claim 1, wherein each of the plurality of energy storage devices has 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 them, the acquisition means acquires, for each of the plurality of energy storage devices, information on the remaining discharge power capacity and the remaining charge power capacity for a plurality of patterns in which any of the plurality of bypass circuits is bypassed, and the selection means selects, for each of the plurality of energy storage devices, the master energy 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.

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