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 a power storage system.

Background Art

[0002] Conventionally, in order to stably supply power to a load, in addition to grid power such as commercial power, it has been considered to apply a power storage system including a plurality of power storage devices (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, any 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. Further, the master power storage device can become a slave power storage device by switching, and any one of the slave power storage devices can become the master power storage device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems 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 has not been particularly considered, and the switching of the master power storage device can occur frequently. When the switching of the master power storage device occurs, control becomes more difficult. Specifically, when grid power cannot be obtained, it is necessary to make the slave power storage device operate following the master power storage device. 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 number of times of switching the master power storage device increases, the control becomes even more difficult.

[0005] The present invention has been made to solve such conventional problems, and an object thereof is to provide a power storage system capable of reducing the number of switching operations of the master power storage device.

Means for Solving the Problems

[0006] A power storage system according to the present invention is 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, including: a plurality of power storage devices connected in parallel to the load; a separate power system device capable of supplying power obtained by using natural energy to the load and the plurality of power storage devices; control means for controlling discharge from the plurality of power storage devices to the load and charging from the separate power system device to the plurality of power storage devices, and when shifting from the first operation mode to the second operation mode or when it is necessary to reselect a master power storage device, selecting a master power storage device from the plurality of power storage devices and performing control to match the voltage, phase, and frequency of the master power storage device with those of slave power storage devices excluding the master power storage device among the plurality of power storage devices; the control means including: acquisition means for acquiring information on the remaining discharge power capacity indicating the discharge power capacity until reaching the discharge cut-off voltage and the remaining charge power capacity indicating the charge power capacity until reaching the charge cut-off voltage for each of the plurality of power storage devices; determination means for determining, among the plurality of power storage devices, those with the remaining discharge power capacity acquired by the acquisition means being less than or equal to a first threshold value as low-capacity power storage devices and those with the remaining charge power capacity acquired by the acquisition means being less than or equal to a second threshold value as the low-capacity power storage devices; and selection means for selecting the master power storage device based on the sum 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 candidates for the master excluding the low-capacity power storage devices determined by the determination means from the plurality of power storage devices.

Effects of the Invention

[0007] According to the present invention, it is possible to provide a power storage system capable of reducing the number of switching operations of the master power storage device.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and can be appropriately changed without departing from the gist of the present invention. Also, in the embodiments shown below, there are some places where the illustration and description of some configurations are omitted. However, it goes without saying that well-known or well-understood technologies are appropriately applied within the range where there is no contradiction with the content described below regarding the details of the omitted technologies.

[0010] FIG. 1 is a block diagram showing an energy storage system according to an embodiment of the present invention. As shown in FIG. 1, the energy storage system 1 is provided to stabilize the power supply from the grid power such as commercial power to the load Lo, and includes a plurality of strings (energy storage devices) ST1 to STm, a photovoltaic power generation device (off-grid device) 10, each module battery management system (hereinafter referred to as MOD system) MB11 to MBmn, a plurality of string battery management systems (hereinafter referred to as ST system) 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] The plurality (m: m is a natural number of 2 or more) of strings ST1 to STm are connected in parallel to the 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] The plurality of storage batteries B11 to Bmn are provided in plural (n: n is a natural number of 2 or more) for each of the strings ST1 to STm. In each of the strings ST1 to STm, n are connected in series. Each of the storage batteries B11 to Bmn is formed, for example, as a module composed of a plurality of unit cells, but is not particularly limited thereto and may be composed of a single cell. In the present embodiment, it is assumed that the plurality of storage batteries B11 to Bmn are composed of, for example, used batteries or batteries of different manufacturers, and the capacities are different between the strings ST1 to STm.

[0013] The bypass circuits BC11 to BCmn are circuits for bypassing some of the batteries B11 to Bmn in each string ST1 to STm to remove them from the series connection state. These bypass circuits BC11 to BCmn can transition between a bypass state in which the batteries B11 to Bmn are bypassed and a connection state in which the batteries B11 to Bmn are not bypassed. Since all of the bypass circuits BC11 to BCmn have the same configuration, the 11th bypass circuit BC11 will be described as an example below.

[0014] The 11th 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 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 battery B11 from the AC / DC converter C1 side of the first switch Sa11 and is connected to the opposite side of the AC / DC converter C1 of the 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, in this 11th bypass circuit BC11, when the first switch Sa11 is in the on state and the second switch Sb11 is in the off state, the battery B11 is connected in series with the other batteries B12 to B1n. On the other hand, in the 11th bypass circuit BC11, when the first switch Sa11 is in the off state and the second switch Sb11 is in the on state, the battery B11 is bypassed and enters a bypass state in which it is removed from the series connection state with the other batteries B12 to B1n. Note that when switching between the series connection state and the bypass state, the 11th bypass circuit BC11 has a configuration that prevents both the first switch Sa11 and the second switch Sb11 from being simultaneously on instantaneously by intervening a period in which both are in the off state.

[0015] The AC / DC converters C1 to Cm are what is called a so-called PCS (Power Conditioning System), and each is provided at a site that serves as the inlet of the strings ST1 to STm. The AC / DC converters C1 to Cm perform voltage adjustment (AC-DC conversion) during charging and discharging of the plurality of storage batteries B11 to Bmn that make up the strings ST1 to STm.

[0016] The photovoltaic power generation device 10 generates electricity by receiving sunlight. This photovoltaic power generation device 10 can supply the generated electric power to the load Lo. Furthermore, the photovoltaic power generation device 10 can also supply the generated electric power to each of the plurality of strings ST1 to STm to charge each storage battery B11 to Bmn in the strings ST1 to STm. In the present embodiment, the photovoltaic power generation device 10 is taken as an example, but it is not particularly limited thereto, and as long as it generates electricity using natural energy, it may generate electricity using wind power, wave power, etc., or may generate electricity using other natural energy.

[0017] The MOD systems MB11 to MBmn perform switch control of the respective bypass circuits BC11 to BCmn, monitor the states of the storage batteries B11 to Bmn, and the like. By this MOD system MB11 to MBmn, for each of the storage batteries B11 to Bmn, the discharge power capacity until reaching the discharge cut-off voltage and the charge power capacity until reaching the charge cut-off voltage are calculated. Note that various known or well-known methods are adopted for calculating the discharge and charge power capacities by the MOD systems MB11 to MBmn. For example, the MOD systems MB11 to MBmn measure the capacity of each of the storage batteries B11 to Bmn in advance, and then sequentially calculate the SOC (state of charge) and the degree of deterioration of the storage batteries B11 to Bmn to calculate the discharge and charge power capacities.

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

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

[0020] When discharging to the load Lo, this array system 20 executes a first operation mode and a second operation mode. The first operation mode is an operation mode in which when grid power is supplied to the load Lo, a plurality of strings ST1 to STm are made to follow the grid power (that is, the voltage, phase, and frequency are made to match). The second operation mode is an operation mode in which when grid power is not supplied to the load Lo, a master string (master energy storage device) ST (a string (including the master string, the slave string described later, and the low-capacity string described later) when any one of the plurality of strings ST1 to STm is not specified) is selected from the plurality of strings ST1 to STm. Further, the second operation mode is an operation mode in which the strings ST other than the master string ST are used as slave strings (slave energy storage devices) ST, and the slave strings ST are made to follow the master string ST (that is, the voltage, phase, and frequency are made to match). Note that the array system 20 performs charge and discharge control in response to an instruction from the EMS 30 described later in the first operation mode. Also, the array system 20 determines charge and discharge based on the voltage and frequency of a power line (not shown) connected to the power receiving point in the second operation mode.

[0021] Such an array system 20 includes an acquisition unit (acquisition means) 21, a determination unit (determination means) 22, and a selection unit (selection means) 23.

[0022] The acquisition unit 21 acquires information on the remaining discharge power capacity and the remaining charge power capacity of each of the plurality of strings ST1 to STm. This acquisition unit 21 acquires information on the remaining discharge power capacity and the remaining charge power capacity of each of the plurality of 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 plurality of strings ST1 to STm, the string ST with a remaining discharge power capacity acquired by the acquisition unit 21 that is equal to or less than the first threshold value as a low-capacity string (low-capacity power storage device) ST. Further, the determination unit 22 also determines, among the plurality of strings ST1 to STm, the string ST with a remaining charge power capacity acquired by the acquisition unit 21 that is equal to or less than the second threshold value as the low-capacity string ST. That is, the determination unit 22 determines, as the low-capacity string ST, those with a remaining discharge power capacity equal to or less than the first threshold value and having no margin for discharge, and those with a remaining charge power capacity equal to or less than the second threshold value and having no margin for charge.

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

[0025] Referring to FIG. 1 again. 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. Further, the EMS 30 transmits information on whether it 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 the target SOC of the power storage system 1 (the entire plurality of strings ST1 to STm) is determined, the EMS 30 transmits this information to the array system 20. Also, when the power storage system 1 is fully charged, the EMS 30 also transmits a signal instructing the photovoltaic power generation device 10 to suppress the power generation amount.

[0026] In the power storage system 1 as described above, when shifting from the first operation mode to the second operation mode, the master string ST can be selected so that the number of switching times of the master string ST is reduced. Hereinafter, an outline of the method for selecting the master string ST of the power 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 there are nine strings ST1 to STm. As shown in FIG. 3, the acquisition unit 21 acquires information that, for example, the remaining discharge power capacity of the first string ST1 from the first ST system SB1 is 30 Wh and the remaining charge power capacity is 30 Wh. Further, the acquisition unit 21 acquires information that, for example, the remaining discharge power capacity of the second string ST2 from the second ST system SB2 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 the respective strings ST3 to ST9 of the third to ninth ST systems SB3 to SB9.

[0028] For example, assume that the first threshold value is 10 Wh and the second threshold value 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 value. 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 the remaining charge power capacity of the master candidates excluding the low-capacity strings 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 excluding the low-capacity strings ST from the first to ninth strings ST1 to ST9. 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 total value of the remaining discharge power capacity and the remaining charge power capacity for the string ST that is a master candidate. Here, in the example shown in FIG. 4, the total values 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 in order. Therefore, the selection unit 23 determines the eighth string ST8 with the maximum total value 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 issues an instruction to perform follow-up control on the ST systems SB1 to SB7, SB9 of the first to seventh, and ninth strings ST1 to ST7, ST9 that are slave strings ST. 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 that 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 a plurality of patterns when any one of the plurality of bypass circuits BC11 to BCmn is in a bypass state for each of the plurality of strings ST1 to STm.

[0033] At this time, the acquisition unit 21 preferably 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 the bypass state, for example, for each of the plurality of strings ST1 to STm. Taking the first string ST1 as an example for explanation. For example, when the number of storage batteries B11 to B1n in the first ST system SB1 is four (when n = 4), information on the remaining discharge power capacity and the remaining charge power capacity is acquired 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 in 15 patterns. 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 all patterns. Note that the above "-1" is for excluding the case where all the bypass circuits BC11 to BC14 are in the bypass state. The same applies to the second to m-th ST systems SB2 to SBm.

[0034] Further, the acquisition unit 21 may acquire information on the remaining discharge power capacity and the remaining charge power capacity not only for all patterns but also for some patterns. Taking the first string ST1 as an example for explanation. For example, the first ST system SB1 grasps the remaining discharge current capacity of 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 become bypass states 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 (n - 1) patterns. 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 (n - 1) patterns. Note that the same applies to the second to m-th ST systems SB2 to SBm. Also, in the above, information on the remaining discharge power capacity and the remaining charge power capacity is calculated for (n - 1) patterns based on the remaining discharge current capacity, but it is not limited to this. For example, not only the remaining discharge current capacity but also the remaining charge current capacity may be used as a reference. Furthermore, information on the remaining discharge power capacity and the remaining charge power capacity may be calculated for both the remaining discharge current capacity and the remaining charge current capacity patterns ((n - 1)×2 patterns), or information on the remaining discharge power capacity and the remaining charge power capacity may be calculated based on completely different criteria.

[0035] As described above, 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, 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. Then, the selection unit 23 executes the processes 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 on the target SOC from the EMS 30, the selection unit 23 may determine the master string ST not only based on the sum value of the remaining discharge power capacity and the remaining charge power capacity, but also based on 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, discharge is likely to proceed in the future. Therefore, the selection unit 23 may select, as the master string ST, the string ST with the highest remaining discharge power capacity from among the strings ST for which the sum value of the remaining discharge power capacity and the remaining charge power capacity is equal to or greater than the third threshold value. Similarly, when the current SOC is lower than the target SOC, charging is likely to proceed in the future. Therefore, the selection unit 23 may select, as the master string ST, the string ST with the highest remaining charge power capacity from among the strings ST for which the sum value of the remaining discharge power capacity and the remaining charge power capacity is equal to or greater than the third threshold value.

[0037] Next, with reference to FIG. 5, a method for selecting the master string ST of the power storage system 1 according to the present embodiment will be described. FIG. 5 is a flowchart showing the method for selecting the master string ST according to the present embodiment. The process of FIG. 5 is executed, for example, immediately after the array system 20 starts the second operation mode when it is determined in the EMS 30 that a power failure has occurred.

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

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

[0040] After that, the determination unit 22 of the array system 20 determines that the string ST with the remaining discharge power capacity in the pattern specified in step S2 being equal to or less than the first threshold value is a low-capacity string ST (S3). Next, the determination unit 22 determines that the string ST with the remaining charge power capacity in the pattern specified in step S2 being equal to or less than the second threshold value is a low-capacity string ST (S4). After the process of step S4, the 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 is acquired from the EMS 30 (S5). When information on the target SOC has been acquired (S5: YES), the selection unit 23 of the array system 20 extracts the string ST with the total value in the pattern specified in step S2 being equal to or greater than the third threshold value (S6).

[0042] After that, the array system 20 determines whether the current SOC of the power storage system 1 is higher than the target SOC (S7). When the current SOC is higher than the target SOC (S7: YES), the selection unit 23 selects, as the master string ST, the string ST with the maximum remaining discharge power capacity among the strings ST extracted in step S6 (S8). After that, the process shown in FIG. 5 ends.

[0043] On the other hand, when 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). When the current SOC is lower than the target SOC (S9: YES), the selection unit 23 selects, as the master string ST, the string ST with the maximum remaining charge power capacity among the strings ST extracted in step S6 (S10). After that, the process shown in FIG. 5 ends.

[0044] Also, when information on the target SOC has not been acquired (S5: NO), and when the current SOC is not lower than the target SOC (S9: NO), the selection unit 23 selects, as the master string ST, the string ST with the maximum total value in the pattern specified in step S2 (S11). After that, the process shown in FIG. 5 ends.

[0045] In this way, according to the power storage system 1 according to this embodiment, the array system 20 controls the discharge to the load Lo and the charging from the solar power generation device 10, and except for the low-capacity string ST with a low remaining discharge power capacity and a low remaining charge power capacity, selects the master string ST based on the sum value of the remaining discharge power capacity and the remaining charge power capacity. For this reason, the master string ST is selected from those having a margin in both charging and discharging, taking into account the usable range (total capacity) as a battery. As a result, there is a certain degree of margin in both the case where charging is performed from the solar power generation device 10 and the case where discharging to the load Lo is performed, and a string ST with a certain degree of large total capacity is selected as the master string ST. Therefore, it is possible to provide the power storage system 1 capable of reducing the possibility of switching the master string ST and reducing the number of switching times of the master string ST.

[0046] Further, when the information on the target SOC is acquired, basically, control to achieve the target SOC becomes easier to execute. Therefore, when there is information on the target SOC, the string ST with the largest remaining discharge power capacity or remaining charge power capacity is selected based on the relationship with the current SOC. For this reason, a string ST with a margin according to 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 the power storage system 1 capable of reducing the number of switching times of the master string ST.

[0047] Here, when a plurality of strings ST1 to STm have bypass circuits BC11 to BCmn, the bypass circuits BC11 to BCmn cannot be switched when the master string ST is being charged or discharged. The bypass circuits BC11 to BCmn are switched through the off states of both switches Sa11 to Samn and Sb11 to Sbmn in order to prevent both switches Sa11 to Samn and Sb11 to Sbmn from being instantaneously turned on simultaneously. For this reason, when both are off, the power from the master string ST temporarily stops, and thus it no longer functions as the master string ST. Therefore, it is important to perform bypass appropriately in advance to draw out the capabilities of the master string ST. Thus, the power storage system 1 according to the present embodiment 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 the highest among a plurality of patterns in which any one of the bypass circuits BC11 to BCmn is in a bypass state. As a result, the master string ST is selected based on the string ST in a state where its capabilities have been drawn out in advance, which can contribute to reducing the number of switching operations, and further contribute to reducing the number of switching operations of the master string ST, thereby providing the power storage system 1.

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

[0049] For example, in the above embodiment, the power outage state in which grid power cannot be obtained is determined by the EMS 30, but it is not limited to this, and it may be determined by the array system 20. Also, for the EMS 30 and each of the systems MB11 to MBmn, SB1 to SBm, and 20, when it is not a power outage state in which grid power can be obtained, they may operate by grid power or may operate by other than grid power. Furthermore, these may be provided with an internal power source or may be configured to receive power from the string ST of the power storage system 1.

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

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

[0052] Also, in step S11 shown in FIG. 5, the string ST with the maximum total value is selected as the master string ST. However, in particular, it is not limited to the maximum, and it may be randomly selected from the strings ST whose total value is equal to or greater than a predetermined threshold value. Furthermore, in the above embodiment, the first threshold value and the second threshold value are assumed to be the same value, but the present invention is not particularly limited to this, and they may be different values.

[0053] Furthermore, in the above embodiment, an example of selecting the master string ST when shifting from the first operation mode to the second operation mode has been described. However, the present invention is not particularly limited to this, and it may be applied when it is necessary to reselect the master string ST. When it is necessary to reselect the master string ST, for example, it corresponds to a case where, after selecting the master string ST, discharge progresses and the array system 20 determines that the remaining discharge power capacity of the master string ST has run out. Also, when reselection is necessary, it may be a case where the array system 20 determines that a disconnection has occurred in the master string ST. When the selection unit 23 reselects the master string ST, it excludes the string ST that was selected as the master string ST from the plurality of strings ST1 to STm and reselects.

Explanation of Reference Numerals

[0054] 1: Energy 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~Bmn: 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~STm: String (energy storage device) ST: Master string (master energy storage device) ST: Slave string (slave energy storage device) ST: Low-capacity string (low-capacity energy storage device)

Claims

1. A power storage system that operates in a first operation mode when system power is supplied to a load and operates in a second operation mode when the system power cannot be supplied to the load, comprising: a plurality of power storage devices connected in parallel to the load; a separate power system device capable of supplying power obtained by using natural energy to the load and the plurality of power storage devices; controlling discharge from the plurality of power storage devices to the load and charging from the separate power system device to the plurality of power storage devices, and when shifting from the first operation mode to the second operation mode, or when it is necessary to reselect a master power storage device, selecting a master power storage device from the plurality of power storage devices, and performing control to match the voltage, phase, and frequency of the master power storage device with those of slave power storage devices excluding the master power storage device among the plurality of power storage devices; control means; wherein the control means: acquisition means for acquiring information on the remaining discharge power capacity indicating the discharge power capacity until reaching the discharge cut-off voltage and the remaining charge power capacity indicating the charge power capacity until reaching the charge cut-off voltage for each of the plurality of power storage devices; determination means for determining, among the plurality of power storage devices, those with the remaining discharge power capacity acquired by the acquisition means being less than or equal to a first threshold as low-capacity power storage devices, and those with the remaining charge power capacity acquired by the acquisition means being less than or equal to a second threshold as the low-capacity power storage devices; selection means for selecting the master power storage device based on the sum 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 devices determined by the determination means from the plurality of power storage devices; A power storage system characterized by comprising the above.

2. When information on a target charge rate is acquired for the plurality of power storage devices, the selection means, among the power storage devices that are master candidates, for those power storage devices with the sum value being greater than or equal to a third threshold, when the current charge rate exceeds the target charge rate, selects the power storage device with the largest remaining discharge power capacity, and when the current charge rate is lower than the target charge rate, selects the power storage device with the largest remaining charge power capacity. The power storage system according to claim 1, characterized by the above.

3. The plurality of power storage devices each include a plurality of storage batteries connected in series and a plurality of bypass circuits for disconnecting each storage battery from the series connection state and bypassing it. The acquisition means acquires information on the remaining discharge power capacity and the remaining charge power capacity for a plurality of patterns when 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 total 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, characterized in that.

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