Energy storage system

Abstract

The present invention provides an energy storage system that can increase or decrease output power while suppressing the progression of degradation of the first and second batteries as a whole. [Solution] The energy storage system is an energy storage system that is provided with a changeable target output power and a specific power threshold. The energy storage system comprises a first battery and a second battery having different rated outputs and cycle lives from each other, and an output distribution determination unit that determines the output distribution between the first battery and the second battery based on the target output power and power threshold.

Description

[[Technical Field]]

[0001] The present invention relates to a power storage system. [[Background Art]]

[0002] An energy system including a battery (e.g., a lithium ion battery) and solar power generation is known in the related art (see, for example, Patent Document 1). [[Prior Art Literature]] [[Patent Literature]]

[0003] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2023-124292 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0004] In recent years, as an alternative to a single battery such as the above-described battery, a power storage system including two batteries (a first battery and a second battery) having different characteristics from each other has also been proposed. Incidentally, a power generator that generates power using renewable energy such as solar power generation is prone to fluctuations in the amount of generated power (generated power) due to its characteristics. Therefore, in order to compensate for the above-described fluctuations, it is desired for the power storage system to increase or decrease the output power (promptly). In addition, in order to suppress the life cycle cost of the power storage system as much as possible, it is desired for the power storage system to suppress the progress of deterioration of the first battery and the second battery as a whole.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide a power storage system that can increase or decrease output power while suppressing the progress of deterioration of the first battery and the second battery as a whole. [[Means for Solving the Problem]]

[0006] An energy storage system according to one aspect of the present invention is an energy storage system provided with a changeable target output power and a specific power threshold, comprising a first battery and a second battery having different rated outputs and cycle lives, and an output distribution determination unit that determines the output distribution between the first battery and the second battery based on the target output power and the power threshold. [Effects of the Invention]

[0007] With the above configuration, it is possible to increase or decrease the output power while suppressing the progression of degradation of the first and second batteries as a whole. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic block diagram showing the general configuration of an energy storage system according to one embodiment of the present invention. [Figure 2A] This is a bar graph comparing the rated capacities of the first and second batteries of the energy storage system described above. [Figure 2B] This is a bar graph comparing the rated outputs of the first battery and the second battery described above. [Figure 2C] This is a bar graph comparing the cycle lifespans of the first battery and the second battery described above. [Figure 3] This figure shows the configuration of the DC-DC converter section of the above energy storage system. [Figure 4A] This is an explanatory diagram illustrating the flow of direct current through the bidirectional chopper circuit of the DC-DC converter section under specific conditions during charging of the first battery. [Figure 4B] This is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit under other specific conditions during the charging of the first battery described above. [Figure 5A] This is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit under specific conditions when the first battery is discharged. [Figure 5B]This is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit under other specific conditions during the discharge of the first battery described above. [Figure 6] This flowchart shows the process for calculating the target output power of the above energy storage system. [Figure 7] This is an explanatory diagram illustrating the distribution mode related to the output distribution between the first battery and the second battery described above. [Figure 8] This is a flowchart showing the specific flow of the power threshold set in the above energy storage system. [Figure 9A] This flowchart shows part of the process of selecting one of the above distribution modes. [Figure 9B] This flowchart shows the remaining steps in selecting one of the above distribution modes. [Figure 10] This is a block diagram schematically showing the configuration of a modified version of the above energy storage system. [Figure 11A] This diagram illustrates the management of the charge level of the second battery mentioned above. [Figure 11B] This diagram illustrates the management of the charge level of the second battery mentioned above. [Figure 12] This flowchart shows the flow of adjusting the charge and discharge ranges of the first battery and the second battery 112 described above. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings.

[0010] [1. Outline configuration of the energy storage system] FIG. 1 is a block diagram schematically illustrating a schematic configuration of a power storage system 1 according to an embodiment of the present invention. The power storage system 1 constitutes an energy system ES. The energy system ES is grid-connected to an electric power grid EG. The electric power grid EG (also referred to as a commercial power grid) supplies commercial power generated by a commercial power source (not shown). In addition to the power storage system 1, the energy system ES includes a photovoltaic power generation device 2, an engine generator 3, and a load 4. However, the energy system ES may be configured excluding the engine generator 3.

[0011] The photovoltaic power generation device 2 is a device that generates power using sunlight. More specifically, the photovoltaic power generation device 2 includes a solar panel (not shown) that generates power from sunlight, and a power conditioner (not shown) that converts DC power output from the solar panel into AC power. The photovoltaic power generation device 2 is an example of a renewable energy power generation device 200 that generates power using renewable energy. In the photovoltaic power generation device 2 as the renewable energy power generation device 200, sunlight is used as the renewable energy. Other examples of the renewable energy power generation device 200 include a wind power generator that generates power using wind force, a hydroelectric power generator that generates power using hydraulic power, and the like.

[0012] The engine generator 3 includes an engine (not shown) and a generator (not shown) coupled to the engine. The engine described above is configured as a gas engine, but may be configured as, for example, a hydrogen engine, a gasoline engine, a diesel engine, or the like. The generator described above generates power using motive power output from the engine. Electric power generated by the generator is supplied to the load 4 or supplied to the power storage system 1. Note that the engine generator 3 may constitute a cogeneration device capable of recovering waste heat from the engine. That is, the energy system ES may be configured to include the cogeneration device described above.

[0013] Load 4 is electrically connected to the energy storage system 1, the solar power generation device 2, the engine generator 3, and the power grid EG. Load 4 is supplied with power from at least one of the energy storage system 1, the solar power generation device 2, the engine generator 3, and the power grid EG. Load 4 consumes the supplied power. That is, the power demand (power consumption) of Load 4 is covered by at least one of the actual power (output power) of the energy storage system 1, the power generated by the solar power generation device 2, the power generated by the engine generator 3, and the grid power supplied from the power grid EG. Load 4 includes, for example, household electrical appliances, industrial (industrial, facility) electrical equipment, etc. Specifically, motors, pumps, etc. installed in these devices consume power.

[0014] The energy storage system 1 comprises multiple batteries 11, a control device 12, and multiple DC-DC converters 13. Each battery 11 stores power. Each battery 11 also supplies the stored power to a load 4. Power supply from each battery 11 to the load 4 is performed based on output commands output from the control device 12. The power output from each battery 11 constitutes the actual power of the energy storage system 1.

[0015] In this embodiment, two batteries 11 are provided. However, the number of batteries 11 is not limited to two; for example, there may be one or three or more. In this embodiment, one battery 11 is referred to as the first battery 111, and the other battery 11 is referred to as the second battery 112. That is, the energy storage system 1 comprises the first battery 111 and the second battery 112.

[0016] The first battery 111 and the second battery 112 are each composed of rechargeable storage batteries, such as lithium-ion batteries. The first battery 111 and the second battery 112 may be composed of multiple cells unitized together, or they may be composed of a single cell. In this embodiment, the first battery 111 is composed of a lithium iron phosphate battery, and the second battery 112 is composed of a ternary lithium-ion battery containing lithium titanate in the negative electrode. However, the configurations of the first battery 111 and the second battery 112 are not limited to those described above and may be modified as appropriate.

[0017] The first battery 111 and the second battery 112 have different characteristics. More details are as follows: Figure 2A is a bar graph comparing the rated capacities of the first battery 111 and the second battery 112. Figure 2B is a bar graph comparing the rated outputs of the first battery 111 and the second battery 112. Figure 2C is a bar graph comparing the cycle lives of the first battery 111 and the second battery 112.

[0018] As shown in Figures 2A to 2C, the first battery 111 and the second battery 112 have different rated capacities, rated outputs, and cycle lives. In detail, as shown in Figure 2A, the rated capacity of the first battery 111 is greater than that of the second battery 112. In other words, the first battery 111 is a high-capacity battery compared to the second battery 112.

[0019] As shown in Figure 2B, the rated output of the second battery 112 is greater than the rated output of the first battery 111. In other words, the second battery 112 is a higher-output battery compared to the first battery 111.

[0020] As shown in Figure 2C, the cycle life of the second battery 112 is longer than that of the first battery 111. In other words, the degradation of the second battery 112 progresses more slowly than that of the first battery 111. Put another way, the second battery 112 degrades less easily than the first battery 111.

[0021] As shown in Figure 1 (returning), the control device 12 controls each part of the energy storage system 1. More specifically, the control device 12 is a computer device comprising an arithmetic unit 121 and a memory unit 122. The control device 12 may consist of a single piece of hardware, or it may consist of multiple pieces of hardware that can communicate with each other.

[0022] The arithmetic unit 121 is, for example, a processor or a microprocessor. In Figure 1, as an example, one arithmetic unit 121 is shown in the control device 12, but there may be two or more arithmetic units 121.

[0023] The memory unit 122 is a main memory device such as ROM (Read Only Memory) or RAM (Random Access Memory). The memory unit 122 may further include an auxiliary storage device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive). Programs, data, etc., are stored in the memory unit 122. The arithmetic unit 121 reads, for example, a program from the memory unit 122 and performs arithmetic processing according to the program.

[0024] Through the cooperation of the aforementioned hardware and software, the control device 12 can be operated as a target output power calculation unit 123, a power threshold identification unit 124, and an output distribution determination unit 125. In other words, the energy storage system 1 comprises a target output power calculation unit 123, a power threshold identification unit 124, and an output distribution determination unit 125. The target output power calculation unit 123, the power threshold identification unit 124, and the output distribution determination unit 125 will be described later.

[0025] The functional units 123 to 125 of the control device 12 may be implemented by software, that is, by causing the arithmetic unit 121 to perform arithmetic processing according to the program, as described above, but they may also be implemented by other methods. At least one of the functional units 123 to 125 may be implemented using, for example, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), etc. That is, at least one of the functional units 123 to 125 may be implemented in hardware using a dedicated IC, etc. Also, at least one of the functional units 123 to 125 may be implemented using a combination of software and hardware. Furthermore, each functional unit 123 to 125 is a conceptual configuration. Therefore, the function performed by one component may be distributed among multiple components, or the functions of multiple components may be integrated into one component.

[0026] In this embodiment, two DC-DC converters 13 are provided. However, the number of DC-DC converters 13 is not limited to two; there may be one or three or more.

[0027] One DC-DC converter 13 is connected in series with the first battery 111, and the other DC-DC converter 13 is connected in series with the second battery 112. More specifically, one DC-DC converter 13 and the first battery 111 form one pair, and the other DC-DC converter 13 and the second battery 112 form another pair. These pairs are then connected in parallel.

[0028] One DC-DC converter 13 electrically connects the first battery 111 to the power system EG. Specifically, the first battery 111 is grid-connected to the power system EG via one DC-DC converter 13. The other DC-DC converter 13 electrically connects the second battery 112 to the power system EG. Specifically, the second battery 112 is grid-connected to the power system EG via the other DC-DC converter 13. In other words, both the first battery 111 and the second battery 112 are grid-connected to the power system EG.

[0029] One DC-DC converter 13 also electrically connects the first battery 111 to the solar power generation device 2, the engine generator 3, and the load 4. The other DC-DC converter 13 also electrically connects the second battery 112 to the solar power generation device 2, the engine generator 3, and the load 4. In other words, the first battery 111 and the second battery 112 are connected to a renewable energy power generation device 200 (in this embodiment, the solar power generation device 2) that generates electricity using renewable energy.

[0030] It is desirable to suppress the emission of greenhouse gases such as carbon dioxide emitted when generating electricity supplied to the first battery 111 and the second battery 112. From this viewpoint, it is desirable that the first battery 111 and the second battery 112 be connected to a renewable energy power generation device 200 that generates electricity using renewable energy, as in this embodiment.

[0031] Each DC-DC converter 13 constitutes a DC-DC converter unit 14. That is, the energy storage system 1 includes a DC-DC converter unit 14 connected to the first battery 111 and the second battery 112. The configuration of the DC-DC converter unit 14 will be described below.

[0032] [2. Configuration of the DC-DC converter section] Figure 3 shows the configuration of the DC-DC converter unit 14. The two DC-DC converters 13 constituting the DC-DC converter unit 14 have identical configurations. However, the two DC-DC converters 13 may have different configurations. In Figure 3, as an example, one of the two DC-DC converters 13 is shown that is connected to the first battery 111. Note that Figure 3 shows the components necessary to explain the features of this embodiment, and descriptions of general components are omitted.

[0033] The DC-DC converter section 14 has a bidirectional chopper circuit 141. Specifically, one bidirectional chopper circuit 141 is provided for each DC-DC converter 13. Each bidirectional chopper circuit 141 includes a coil 141a, two switching elements 141b, two diodes 141c, two capacitors 141d, and a current sensing unit 141e.

[0034] Coil 141a is connected in series with battery 11 (first battery 111 in Figure 3). In particular, coil 141a is located at a higher potential than battery 11. Coil 141a is also connected in series with each switching element 141b.

[0035] The two switching elements 141b are connected in series with each other. In the following, the switching element 141b located on the high-potential side may be referred to as the first switching element 141b1, and the switching element 141b located on the low-potential side may be referred to as the second switching element 141b2.

[0036] A diode 141c is connected in parallel to each switching element 141b. Each switching element 141b is, for example, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). However, each switching element 141b only needs to be able to perform the function of switching between electrical connection and disconnection, and may also be, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0037] One capacitor 141d is connected in parallel to the battery 11, and the other capacitor 141d is connected in parallel to two switching elements 141b that are connected in series with each other. Hereafter, the capacitor 141d connected in parallel to the battery 11 will be called the first capacitor 141d1, and the capacitor 141d connected in parallel to the two switching elements 141b will be called the second capacitor 141d2.

[0038] The current detection unit 141e is connected in series with the battery 11. The current detection unit 141e detects the magnitude and direction of the DC current flowing into or out of the battery 11, and outputs information regarding the detected DC current to the control device 12.

[0039] The bidirectional chopper circuit 141 functions as a step-down chopper circuit when the battery 11 is being charged, and as a step-up chopper circuit when the battery 11 is being discharged. More details are as follows: Figure 4A is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit 141 when the first switching element 141b1 is ON during battery 11 charging. Figure 4B is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit 141 when the first switching element 141b1 is OFF during battery 11 charging. Figure 5A is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit 141 when the second switching element 141b2 is ON during battery 11 discharge. Figure 5B is an explanatory diagram illustrating the flow of DC current through the bidirectional chopper circuit 141 when the second switching element 141b2 is OFF during battery 11 discharge. In Figures 4A, 4B, 5A, and 5, the flow of DC current is shown by solid arrows.

[0040] As shown in Figure 4A, when the battery 11 is being charged, the first switching element 141b1 is switched (at high speed) between the ON state (connected state) and the OFF state (disconnected state), and the second switching element 141b2 is always kept in the OFF state.

[0041] When the second switching element 141b2 is in the off state and the first switching element 141b1 is in the on state, a DC current flows into the battery 11 and the first capacitor 141d1 via the first switching element 141b1 and the coil 141a. At this time, the DC current flowing into the battery 11 via the coil 141a gradually increases over time. The first capacitor 141d1 stores the supplied power.

[0042] As shown in Figure 4B, when the first switching element 141b1 switches from the ON state to the OFF state, a DC current flows into the battery 11 due to the coil 141a continuing to supply DC current (for a while) and the first capacitor 141d1 discharging. At this time, the DC current flowing into the battery 11 gradually decreases over time.

[0043] Therefore, when the battery 11 is being charged, the bidirectional chopper circuit 141 steps down the input voltage 141Vi to the output voltage 141Vo (i.e., the input voltage of the battery 11) by discretizing and smoothing the input voltage 141Vi.

[0044] As shown in Figure 5A, when the battery 11 is discharged, the first switching element 141b1 is always in the off state, and the second switching element 141b2 is switched (at high speed) between the on state and the off state.

[0045] When the first switching element 141b1 is in the off state and the second switching element 141b2 is in the on state, the DC current flowing from the battery 11 circulates through a series circuit consisting of the battery 11, the coil 141a, and the second switching element 141b2. More specifically, the DC current flowing from the battery 11 flows into the first capacitor 141d1 while circulating through the series circuit. At this time, the DC current circulating through the series circuit is gradually reduced over time by the coil 141a. The first capacitor 141d1 stores the supplied power. On the other hand, as the second capacitor 141d2 discharges, a DC current flows outside the bidirectional chopper circuit 141.

[0046] As shown in Figure 5B, the second switching element 141b2 is switched from the ON state to the OFF state. Then, the DC current flowing from the battery 11, coil 141a, and first capacitor 141d1 flows to the outside of the bidirectional chopper circuit 141 and to the second capacitor 141d2 via the diode 141c connected in parallel with the first switching element 141b1. At this time, the DC current flowing from coil 141a gradually decreases over time. The second capacitor 141d2 stores the supplied power. In other words, the second capacitor 141d2 smooths the power output from the bidirectional chopper circuit 141.

[0047] Therefore, when the battery 11 is discharged, the bidirectional chopper circuit 141 steps down the input voltage 141Vi (i.e., the output voltage of the battery 11) to the output voltage 141Vo by discretizing and smoothing the input voltage 141Vi.

[0048] The switching between the on and off states of each switching element 141b is performed based on an on / off instruction output from the control device 12 (see Figure 1). In detail, the control device 12 performs control (e.g., feedback control) using the magnitude of the DC current that flowed into the battery 11 immediately before that point, as detected by the current detection unit 141e, and the magnitude of the current instruction value based on the power instruction value described later. This calculates the on / off instruction. Specifically, the control device 12 calculates the on / off instruction so that the magnitude of the DC current flowing into the battery 11 matches the magnitude of the target output current. However, the calculation of the on / off instruction by the control device 12 is not limited to the above method and may be modified as appropriate.

[0049] As described above, the bidirectional chopper circuit 141 of this embodiment steps down the voltage when the battery 11 is being charged and steps up the voltage when the battery 11 is being discharged. Specifically, the bidirectional chopper circuit 141 provided in one DC-DC converter 13 connected to the first battery 111 steps down the voltage when the first battery 111 is being charged and steps up the voltage when the first battery 111 is being discharged. The bidirectional chopper circuit 141 provided in the other DC-DC converter 13 connected to the second battery 112 steps down the voltage when the second battery 112 is being charged and steps up the voltage when the second battery 112 is being discharged. However, the bidirectional chopper circuit 141 may, for example, step up the voltage when the battery 11 is being charged and step down the voltage when the battery 11 is being discharged, depending on the relationship between the rated voltage of the battery 11 and the voltage of the device to which the battery 11 is connected. In other words, the bidirectional chopper circuit 141 performs either step up or step down (step down in this embodiment) when charging at least one of the first battery 111 and the second battery 112. Furthermore, the bidirectional chopper circuit 141 performs the other of voltage boosting and voltage bucking (in this embodiment, voltage boosting) when at least one of the first battery 111 and the second battery 112 is discharged.

[0050] The rated voltage of the first battery 111 and the second battery 112 is determined according to their configuration, etc. That is, various values ​​can be used as the rated voltage of the first battery 111 and the second battery 112. From the viewpoint of matching the rated voltage of the first battery 111 and the second battery 112 with the voltage of the destination to which the first battery 111 and the second battery 112 are connected, and facilitating the connection of the first battery 111 and the second battery 112, the following configuration is desirable. That is, as shown in Figures 1 and 3, etc., it is desirable that the energy storage system 1 includes a DC-DC converter unit 14 connected to the first battery 111 and the second battery 112.

[0051] From the viewpoint of achieving a simple (with fewer components) and reliable configuration that matches the rated voltage of the first battery 111 and the second battery 112 with the voltage of the destination to which the first battery 111 and the second battery 112 are connected, the following configuration is desirable. That is, as in this embodiment, it is desirable that the DC-DC converter section 14 has a bidirectional chopper circuit 141. Furthermore, it is desirable that this bidirectional chopper circuit 141 performs either voltage boosting or voltage bucking (in this embodiment, voltage bucking) when charging at least one of the first battery 111 and the second battery 112. Also, it is desirable that this bidirectional chopper circuit 141 performs the other of voltage boosting or voltage bucking (in this embodiment, voltage boosting) when discharging at least one of the first battery 111 and the second battery 112.

[0052] [3. Calculation of the target output power of the energy storage system] The process for calculating the target output power of energy storage system 1 will be explained based on Figure 6. Figure 6 is a flowchart showing the process for calculating the target output power of energy storage system 1. The flowchart shown in Figure 6 starts, for example, when the operation of energy system ES (see Figure 1) begins.

[0053] In step S1, the target output power calculation unit 123 (see Figure 1) determines whether the energy system ES is in operation or not. If the energy system ES is in operation (Yes in step S1), the process proceeds to step S2. If the energy system ES is not in operation (No in step S1), this flowchart ends.

[0054] In step S2, the target output power calculation unit 123 calculates the power difference between the power generated by the photovoltaic power generation device 2 (see Figure 1) and the power demanded by the load 4 (see Figure 1). In this embodiment, this calculation is achieved by subtracting the power generated by the photovoltaic power generation device 2 from the power demanded by the load 4. The power generated by the photovoltaic power generation device 2 and the power demanded by the load 4 are detected by a power detection unit (not shown) appropriately provided in the energy system ES. The power detection unit outputs the detected power generated by the photovoltaic power generation device 2 and the power demanded by the load 4 to the control device 12 (see Figure 1). The energy system ES may have one or more power detection units.

[0055] As described above, the power demand of load 4 is covered by the actual power of the energy storage system 1, the power generated by the solar power generation device 2, the power generated by the engine generator 3 (see Figure 1), and the grid power supplied from the power grid EG (see Figure 1). Therefore, for example, when the engine generator 3 is stopped, the power difference between the power generated by the solar power generation device 2 and the power demand of load 4 corresponds to the sum of the actual power of the energy storage system 1 and the grid power from the power grid EG. Once the power difference between the power generated by the solar power generation device 2 and the power demand of load 4 is calculated, the process proceeds to the next step S3.

[0056] In step S3, the target output power calculation unit 123 separates the power difference calculated in step S2 into low-frequency components and high-frequency components. In this embodiment, this separation is achieved by a high-pass filter. However, this separation may be achieved by a low-pass filter instead of, or in addition to, a high-pass filter, or by filters other than high-pass and low-pass filters.

[0057] In detail, the photovoltaic power generation device 2 generates electricity according to the degree of sunlight irradiating the solar panels. Therefore, the power generated by the photovoltaic power generation device 2 gradually increases or decreases in response to the sun's diurnal motion, and also rapidly increases or decreases in a short period of time (e.g., 1 minute) due to factors such as the solar panels being shaded. In other words, the power generated by the photovoltaic power generation device 2 includes both low-frequency and high-frequency components.

[0058] The power demand of Load 4 fluctuates according to its usage. Specifically, since the usage of Load 4 corresponds to power consumption activity, the power demand of Load 4 gradually increases as power consumption activity gradually intensifies and gradually decreases as power consumption activity gradually subsides. Furthermore, because the usage of Load 4 changes moment by moment, the power demand of Load 4 also increases and decreases even in short periods of time. In other words, similar to the power generated by the solar power generation device 2, the power demand of Load 4 also includes both low-frequency and high-frequency components. However, the degree of increase and decrease in the power demand of Load 4 in short periods of time is smaller than the degree of increase and decrease in the power generated by the solar power generation device 2 in short periods of time.

[0059] Therefore, the power difference between the power generated by the solar power generation device 2 and the power demanded by the load 4 also includes both low-frequency and high-frequency components. In other words, the separation of the power difference by the target output power calculation unit 123 means separating the power difference, which includes both low-frequency and high-frequency components, into the power difference of the low-frequency component and the power difference of the high-frequency component. Once the power difference is separated into low-frequency and high-frequency components, the process proceeds to the next step S4.

[0060] In step S4, the target output power calculation unit 123 determines the high-frequency component (power difference) of the power difference separated in step S3 as the target output power of the energy storage system 1. In this embodiment, when the energy storage system 1 as a whole is charged, in order to make the charging direction of the target output power of the energy storage system 1 a positive value, the positive and negative values ​​of the above high-frequency component are reversed and the result is determined as the target output power of the energy storage system 1.

[0061] Furthermore, the target output power calculation unit 123 determines the low-frequency component (power difference) of the power difference separated in step S3 to be the generated power of the engine generator 3 and the grid power from the power grid EG. That is, for example, if the engine generator 3 is stopped, the low-frequency component (power difference) is determined to be the grid power from the power grid EG. Based on the target output power of the energy storage system 1 calculated by the target output power calculation unit 123, the energy storage system 1 outputs power. That is, the actual power of the energy storage system 1 is output based on the target output power.

[0062] In this embodiment, when purchasing grid power from the power grid EG, the price of grid power is discounted if fluctuations in grid power are kept within a predetermined range. Therefore, the calculation of the target output power of the energy storage system 1 by the target output power calculation unit 123 in this embodiment is configured so that the discount is applied by keeping fluctuations in grid power within the predetermined range. That is, the target output power calculation unit 123 calculates the target output power of the energy storage system 1 based on conditions related to the grid power supplied from the power grid EG. However, the above conditions are not limited to the conditions related to the discount on the price of grid power as described above, but may be any appropriate conditions.

[0063] In other words, the energy storage system 1 is provided with a target output power, and this target output power is configured to be changeable. Alternatively, the energy storage system 1 may be configured such that the target output power is output to the energy storage system 1 from an external source.

[0064] In this embodiment, the processes in steps S3 and S4 are collectively referred to as the filtering process 123F. That is, the target output power calculation unit 123 performs the filtering process 123F. This filtering process 123F separates the power equivalent to the sum of the actual power of the energy storage system 1 and the grid power from the power grid EG (in this embodiment, the power difference between the power generated by the solar power generation device 2 and the demand power of the load 4) into low-frequency components and high-frequency components. The filtering process 123F then calculates one of the separated low-frequency components and high-frequency components (in this embodiment, the high-frequency component) as the target output power of the energy storage system 1.

[0065] For example, in order to suppress the price of grid electricity purchased from the power grid EG, the following configuration is desirable from the standpoint of meeting (or avoiding) conditions related to grid electricity. That is, as in this embodiment, it is desirable that the energy storage system 1 is equipped with a target output power calculation unit 123 that calculates the target output power of the energy storage system 1 based on conditions related to grid electricity supplied from the power grid EG.

[0066] From the viewpoint of simply realizing a suitable configuration when the conditions related to grid power supplied from the power grid EG are conditions related to fluctuations in grid power, the following configuration is desirable. That is, as in this embodiment, it is desirable that the filter process 123F separates the power equivalent to the sum of the actual power output based on the target output power of the energy storage system 1 and the grid power supplied from the power grid EG into low-frequency components and high-frequency components. It is also desirable that the filter process 123F calculates one of the separated low-frequency components and high-frequency components (the high-frequency component in this embodiment) as the target output power of the energy storage system 1. And it is desirable that the target output power calculation unit 123 performs such a filter process 123F.

[0067] The actual power of the energy storage system 1 consists of power output from the first battery 111 and power output from the second battery 112. Specifically, the energy storage system 1 determines the output distribution between the first battery 111 and the second battery 112, and outputs power from the first battery 111 and the second battery 112 based on the determined output distribution. The determination of the output distribution between the first battery 111 and the second battery 112 will be explained below.

[0068] [4. Determination of output distribution between the first and second batteries] First, the distribution mode DM related to the output distribution between the first battery 111 and the second battery 112 will be explained based on Figure 7. Figure 7 is an explanatory diagram illustrating the distribution mode DM related to the output distribution between the first battery 111 and the second battery 112. The energy storage system 1 has a first distribution mode DM1, a second distribution mode DM2, a third distribution mode DM3, a fourth distribution mode DM4, a fifth distribution mode DM5, and a sixth distribution mode DM6 as distribution modes DM. In other words, the energy storage system 1 is equipped with multiple distribution modes DM.

[0069] Each distribution mode DM has a setting for the output distribution between the first battery 111 and the second battery 112. More specifically, the first distribution mode DM1 is a mode in which both the first battery 111 and the second battery 112 stop outputting. For example, in the first distribution mode DM1, the power instruction value for the first battery 111 and the power instruction value for the second battery 112 are set to zero. Based on this power instruction value for the first battery 111, each switching element 141b (see Figure 3, etc.) included in one of the DC-DC converters 13 (see Figure 1) connected in series with the first battery 111 is controlled. As a result, the first battery 111 stops outputting. Similarly, based on this power instruction value for the second battery 112, each switching element 141b included in the other DC-DC converter 13 (see Figure 1) connected in series with the second battery 112 is controlled. As a result, the second battery 112 stops outputting.

[0070] The second distribution mode DM2 is a mode in which the first battery 111 is stopped and the second battery 112 outputs power corresponding to the difference between the load 4 and the solar power generation device 2 (see Figure 1). For example, in the second distribution mode DM2, the power instruction value for the first battery 111 is set to zero, and the absolute value of the target output power of the energy storage system 1 is set as the power instruction value for the second battery 112. Based on this power instruction value for the first battery 111, each switching element 141b included in one DC-DC converter 13 is controlled, causing the first battery 111 to stop outputting power. Also, based on this power instruction value for the second battery 112, each switching element 141b included in the other DC-DC converter 13 is controlled, causing the second battery 112 to output power of the same magnitude as the target output power of the energy storage system 1.

[0071] The third distribution mode DM3 is a mode in which the first battery 111 outputs power corresponding to the difference between the load 4 and the solar power generation device 2, and the second battery 112 stops outputting power. For example, in the third distribution mode DM3, the rated output of the first battery 111 is set as the power instruction value for the first battery 111, and the power instruction value for the second battery 112 is set to zero. Based on this power instruction value for the first battery 111, each switching element 141b included in one DC-DC converter 13 is controlled so that the first battery 111 outputs power equal to its rated output. Also, based on this power instruction value for the second battery 112, each switching element 141b included in the other DC-DC converter 13 is controlled so that the second battery 112 stops outputting power.

[0072] The fourth distribution mode DM4 is a mode in which both the first battery 111 and the second battery 112 output power corresponding to the difference between the load 4 and the solar power generation device 2. For example, in the fourth distribution mode DM4, a specific power threshold is set as the power instruction value for the first battery 111, and the value obtained by subtracting the specific power threshold from the absolute value of the target output power of the energy storage system 1 is set as the power instruction value for the second battery 112. Based on this power instruction value for the first battery 111, each switching element 141b included in one DC-DC converter 13 is controlled so that the first battery 111 outputs power of the same magnitude as the specific power threshold. Also, based on this power instruction value for the second battery 112, each switching element 141b included in the other DC-DC converter 13 is controlled. As a result, the second battery 112 outputs power of the same magnitude as the power obtained by subtracting the specific power threshold from the absolute value of the target output power of the energy storage system 1.

[0073] The fifth distribution mode, DM5, is a mode in which the first battery 111 outputs to the second battery 112 to charge the second battery 112, or the second battery 112 outputs to the first battery 111 to charge the first battery 111. For example, in the fifth distribution mode, DM5, the rated output of the first battery 111 is set as the power instruction value for the first battery 111. Based on this power instruction value for the first battery 111, each switching element 141b included in one of the DC-DC converters 13 is controlled. As a result, when the second battery 112 is being charged, the first battery 111 discharges power equal to its rated output, and when the first battery 111 is being charged, power equal to its rated output is supplied to the first battery 111. When the first battery 111 is being charged, power equal to the target output power of the energy storage system 1 is supplied to the energy storage system 1.

[0074] Furthermore, the value obtained by subtracting the absolute value of the target output power of the energy storage system 1 from the rated output of the first battery 111 is set as the power instruction value for the second battery 112. Based on this power instruction value for the second battery 112, each switching element 141b included in the other DC-DC converter 13 is controlled. As a result, when the second battery 112 is being charged, the second battery 112 is supplied with power equal to the value obtained by subtracting the absolute value of the target output power of the energy storage system 1 from the rated output of the first battery 111. Consequently, the load 4 is supplied with power equal to the value obtained by subtracting the target output power of the energy storage system 1. Also, when the first battery 111 is being charged, the second battery 112 outputs power equal to the value obtained by subtracting the absolute value of the target output power of the energy storage system 1 from the rated output of the first battery 111.

[0075] The sixth distribution mode, DM6, is a mode in which the first battery 111 outputs power corresponding to the difference between the load 4 and the solar power generation device 2, and the second battery 112 stops outputting power. For example, in the sixth distribution mode, the absolute value of the target output power of the energy storage system 1 is set as the power instruction value for the first battery 111, and the power instruction value for the second battery 112 is set to zero. Based on this power instruction value for the first battery 111, each switching element 141b included in one of the DC-DC converters 13 is controlled so that the first battery 111 outputs power of the same magnitude as the target output power of the energy storage system 1. Also, based on this power instruction value for the second battery 112, each switching element 141b included in the other DC-DC converter 13 is controlled so that the second battery 112 stops outputting power.

[0076] From the standpoint of simplifying the determination of the output distribution between the first battery 111 and the second battery 112, it is desirable that the energy storage system 1, as in this embodiment, includes a plurality of distribution modes DM in which the output distribution between the first battery 111 and the second battery 112 is set.

[0077] A specific power threshold is identified by the power threshold identification unit 124 (see Figure 1). More specifically, the following applies: Figure 8 is a flowchart showing the power threshold identification process. The flowchart shown in Figure 8 starts, for example, just before the date changes. In this embodiment, the power threshold is identified daily. However, the timing at which the flowchart shown in Figure 8 starts may be changed as appropriate. For example, this flowchart may start multiple times per day. In this case, the power threshold is identified multiple times per day.

[0078] In step S11, the power threshold identification unit 124 substitutes the rated output of the first battery 111 into the candidate value. Once the rated output of the first battery 111 is substituted into the candidate value, the process proceeds to the next step S12.

[0079] In step S12, the power threshold identification unit 124 reduces the candidate value by a predetermined amount (for example, 0.1 kW). Once the candidate value has been reduced by the predetermined amount, the process proceeds to the next step S13.

[0080] In step S13, the power threshold identification unit 124 determines whether the difference obtained by subtracting a candidate value from the maximum value of the estimated power of the energy storage system 1 is smaller than the rated output of the second battery 112. In this embodiment, the estimated power of the energy storage system 1 means, for example, the estimated power to be used the day after the time this determination is made. However, the estimated power of the energy storage system 1 is not limited to the above. For example, the estimated power of the energy storage system 1 may be the estimated power to be used two days after the time this determination is made, or it may be the estimated power to be used the following week.

[0081] If the above difference is smaller than the rated output of the second battery 112 (Yes in step S13), the process proceeds to step S14. If the above difference is not smaller than the rated output of the second battery 112 (No in step S13), the power threshold identification unit 124 increases the candidate value by the above predetermined amount (step S16) and identifies the increased candidate value as the power threshold (step S17).

[0082] In step S14, the power threshold identification unit 124 determines whether the estimated daily power of the second battery 112 is less than the rated capacity of the second battery 112. In this embodiment, the estimated daily power of the second battery 112 means the amount of power obtained by adding up the estimated power of the second battery 112 for a predetermined time interval over a day. Here, the estimated power of the second battery 112 is calculated (estimated) by estimating the output distribution between the first battery 111 and the second battery 112, which will be described later, based on the estimated power of the energy storage system 1 described above and a candidate value (provisional power threshold) at this point in time.

[0083] If the estimated daily power consumption of the second battery 112 is less than the rated capacity of the second battery 112 (Yes in step S14), the process proceeds to step S15. If the estimated daily power consumption of the second battery 112 is not less than the rated capacity of the second battery 112 (No in step S14), the power threshold identification unit 124 increases the candidate value by the predetermined amount (step S16). The power threshold identification unit 124 then identifies the increased candidate value as the power threshold (step S17).

[0084] In step S15, the power threshold determination unit 124 determines whether the remaining lifespan of the second battery 112 is less than the remaining lifespan of the first battery 111. The remaining lifespan (also called remaining lifespan) of the battery 11 (in this embodiment, the first battery 111 and the second battery 112) is calculated by an appropriate method. For example, the remaining lifespan of the battery 11 is calculated by dividing the difference obtained by subtracting the number of charge / discharge cycles performed on the battery 11 up to that point from the cycle lifespan of the battery 11 by the cycle lifespan of the battery 11. That is, in this calculation method, the remaining lifespan of the battery 11 is 1 before the start of use (when unused) and becomes 0 when the number of cycles of the battery 11 reaches its cycle lifespan.

[0085] If the remaining lifespan of the second battery 112 is less than that of the first battery 111 (Yes in step S15), the power threshold determination unit 124 determines the candidate value at that time as the power threshold (without increasing it by the predetermined amount mentioned above) (step S17). If the remaining lifespan of the second battery 112 is not less than that of the first battery 111 (No in step S15), the process returns to step S12.

[0086] Thus, the power threshold determination unit 124 determines the power threshold by repeating the process from step S12 to step S15 until any one of the three specific conditions shown in steps S13, S14, and S15 is met. However, the power threshold determination unit 124 may determine the power threshold by repeating the process from step S12 to step S15 until any two of the three conditions are met, or until all three conditions are met. In other words, the power threshold determination unit 124 determines a specific power threshold based on at least one of the remaining lifespan of the first battery 111 and the second battery, the rated output of the second battery 112, and the rated capacity of the second battery 112. Therefore, the energy storage system 1 is provided with a specific power threshold.

[0087] From the perspective of achieving the identification of a specific power threshold with a simple configuration, it is desirable that the energy storage system 1 includes a power threshold identification unit 124 that identifies a specific power threshold, as in this embodiment. Furthermore, from the perspective of preventing the second battery 112 from degrading faster than the first battery 111, preventing the second battery 112 from outputting more than its rated output, and maximizing the charging capacity of the second battery 112, the following configuration is desirable. That is, as in this embodiment, it is desirable that the power threshold identification unit 124 identifies a specific power threshold based on at least one of the remaining lifespan of the first battery 111 and the second battery, the rated output of the second battery 112, and the rated capacity of the second battery 112.

[0088] Next, as an example of a method for selecting one distribution mode DM from multiple distribution modes DM, the process of selecting one distribution mode DM from multiple distribution modes DM will be explained based on Figures 9A and 9B. Figures 9A and 9B are flowcharts illustrating the process of selecting one distribution mode DM from multiple distribution modes DM. The flowcharts shown in Figure 9A and Figure 9B are connected by a connector A. The flowchart shown in Figure 9A, like the flowchart shown in Figure 6, is initiated, for example, when the operation of the energy system ES begins. Note that the method for selecting one distribution mode DM from multiple distribution modes DM may be any method appropriate to the situation.

[0089] In particular, as shown in Figure 9A, in step S21, the output distribution determination unit 125 (see Figure 1) determines whether the target output power of the energy storage system 1 calculated by the target output power calculation unit 123 is a charging output (whether it is a positive value indicating the charging direction). If the target output power of the energy storage system 1 is a charging output (Yes in step S21), the process proceeds to step S22. If the target output power of the energy storage system 1 is not a charging output (i.e., the target output power of the energy storage system 1 is a discharge output) (No in step S21), the process proceeds to step S35 via connector A.

[0090] In step S22, the output distribution determination unit 125 determines whether the charge rate of the first battery 111 is less than the first threshold for the first battery. Here, the charge rate of the battery 11 (in this embodiment, the first battery 111 and the second battery 112) means the ratio of the remaining charge capacity (at that time) to the charge capacity when fully charged. The charge rate of the battery 11 is calculated by the control device 12 based on information about the battery 11 (e.g., voltage, current, temperature, etc.) detected by various sensors (not shown) provided on the battery 11. The first threshold for the first battery is set in advance and stored in the storage unit 122.

[0091] If the charge level of the first battery 111 is less than the first threshold for the first battery (Yes in step S22), the process proceeds to step S26. If the charge level of the first battery 111 is not less than the first threshold for the first battery (No in step S22), the process proceeds to step S23.

[0092] In step S23, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is less than the first threshold for the second battery. The first threshold for the second battery is preset and stored in the storage unit 122. If the charge level of the second battery 112 is less than the first threshold for the second battery (Yes in step S23), the output distribution determination unit 125 selects the second distribution mode DM2 as the distribution mode DM (step S24). Therefore, the first battery 111 stops outputting, and the second battery 112 outputs power to the load 4 equal to the target output power of the energy storage system 1.

[0093] If the charge level of the second battery 112 is not less than the first threshold for the second battery (No in step S23), the output distribution determination unit 125 selects the first distribution mode DM1 as the distribution mode DM (step S25). Therefore, both the first battery 111 and the second battery 112 stop outputting.

[0094] In step S26, the output distribution determination unit 125 determines whether the target output power of the energy storage system 1 (calculated by the target output power calculation unit 123) is greater than a specific power threshold. The power threshold is determined by the power threshold determination unit 124 (see Figure 1), as shown in Figure 8. If the target output power of the energy storage system 1 is greater than the specific power threshold (Yes in step S26), the process proceeds to step S27. If the target output power of the energy storage system 1 is not greater than the specific power threshold (No in step S26), the process proceeds to step S30.

[0095] In step S27, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is less than the first threshold for the second battery. If the charge level of the second battery 112 is less than the first threshold for the second battery (Yes in step S27), the output distribution determination unit 125 selects the fourth distribution mode DM4 as the distribution mode DM (step S28). Therefore, the first battery 111 outputs power equal to the magnitude of a specific power threshold, and the second battery 112 outputs power equal to the magnitude of the power obtained by subtracting the specific power threshold from the absolute value of the target output power of the energy storage system 1.

[0096] If the charge level of the second battery 112 is not less than the first threshold for the second battery (No in step S27), the output distribution determination unit 125 selects the third distribution mode DM3 as the distribution mode DM (step S29). Therefore, the first battery 111 outputs power equal to its rated output to the load 4, and the second battery 112 stops outputting.

[0097] In step S30, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is less than the second threshold for the second battery and greater than the third threshold for the second battery. The second threshold for the second battery and the third threshold for the second battery are set in advance and stored in the storage unit 122. The second threshold for the second battery is set to be greater than the third threshold for the second battery and less than the first threshold for the second battery.

[0098] If the charge level of the second battery 112 is less than the second threshold for the second battery and greater than the third threshold for the second battery (Yes in step S30), the output distribution determination unit 125 selects the sixth distribution mode DM6 as the distribution mode DM (step S31). Therefore, the first battery 111 outputs power equal to the target output power of the energy storage system 1 to the load 4, and the second battery 112 stops outputting. If the charge level of the second battery 112 is greater than the second threshold for the second battery, or less than the third threshold for the second battery (No in step S30), the process proceeds to step S32.

[0099] In step S32, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is less than the third threshold for the second battery. If the charge level of the second battery 112 is less than the third threshold for the second battery (Yes in step S32), the output distribution determination unit 125 selects the second distribution mode DM2 as the distribution mode DM (step S33). Therefore, the first battery 111 stops outputting, and the second battery 112 outputs power to the load 4 equal to the target output power of the energy storage system 1.

[0100] If the charge level of the second battery 112 is not less than the third threshold for the second battery (No in step S32), the output distribution determination unit 125 selects the fifth distribution mode DM5 as the distribution mode DM (step S34). At this time, since the charge level of the second battery 112 is relatively high, the first battery 111 is charged by the discharge of the second battery 112. That is, the first battery 111 is charged at its rated output, and the second battery 112 discharges power obtained by subtracting the absolute value of the target output power of the energy storage system 1 from the rated output of the first battery 111.

[0101] In particular, as shown in Figure 9B, in step S35, the output distribution determination unit 125 determines whether the charge level of the first battery 111 is greater than the second threshold for the first battery. The above-mentioned second threshold for the first battery is set in advance and stored in the storage unit 122. If the charge level of the first battery 111 is greater than the second threshold for the first battery (Yes in step S35), the process proceeds to step S39. If the charge level of the first battery 111 is not greater than the second threshold for the first battery (No in step S35), the process proceeds to step S36.

[0102] In step S36, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is greater than the fourth threshold for the second battery. The fourth threshold for the second battery is preset and stored in the storage unit 122. If the charge level of the second battery 112 is greater than the fourth threshold for the second battery (Yes in step S36), the output distribution determination unit 125 selects the second distribution mode DM2 as the distribution mode DM (step S37). Therefore, the first battery 111 stops outputting, and the second battery 112 outputs power equal to the target output power of the energy storage system 1 to the load 4. If the charge level of the second battery 112 is not greater than the fourth threshold for the second battery (No in step S36), the output distribution determination unit 125 selects the first distribution mode DM1 as the distribution mode DM (step S38). Therefore, both the first battery 111 and the second battery 112 stop outputting.

[0103] In step S39, the output distribution determination unit 125 determines whether the absolute value of the target output power of the energy storage system 1 (calculated by the target output power calculation unit 123) is greater than a specific power threshold. The power threshold is determined by the power threshold determination unit 124, as shown in Figure 8. If the absolute value of the target output power of the energy storage system 1 is greater than the specific power threshold (Yes in step S39), the process proceeds to step S40. If the absolute value of the target output power of the energy storage system 1 is not greater than the specific power threshold (No in step S39), the process proceeds to step S43.

[0104] In step S40, the output distribution determination unit 125 determines whether the charge level of the first battery 111 is greater than the third threshold for the first battery. If the charge level of the first battery 111 is greater than the third threshold for the first battery (Yes in step S40), the output distribution determination unit 125 selects the fourth distribution mode DM4 as the distribution mode DM (step S41). Therefore, the first battery 111 outputs power equal to the magnitude of a specific power threshold, and the second battery 112 outputs power equal to the magnitude of the power obtained by subtracting the specific power threshold from the absolute value of the target output power of the energy storage system 1.

[0105] If the charge level of the first battery 111 is not greater than the third threshold for the first battery (No in step S40), the output distribution determination unit 125 selects the third distribution mode DM3 as the distribution mode DM (step S42). Therefore, the first battery 111 outputs power equal to its rated output to the load 4, and the second battery 112 stops outputting.

[0106] In step S43, similar to step S30, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is less than the second threshold for the second battery and greater than the third threshold for the second battery. If the charge level of the second battery 112 is less than the second threshold for the second battery and greater than the third threshold for the second battery (Yes in step S43), the output distribution determination unit 125 selects the sixth distribution mode DM6 as the distribution mode DM (step S44). Therefore, the first battery 111 outputs power to the load 4 equal to the target output power of the energy storage system 1, and the second battery 112 stops outputting. If the charge level of the second battery 112 is greater than the second threshold for the second battery, or less than the third threshold for the second battery (No in step S43), the process proceeds to step S45.

[0107] In step S45, the output distribution determination unit 125 determines whether the charge level of the second battery 112 is greater than the second threshold for the second battery. If the charge level of the second battery 112 is greater than the second threshold for the second battery (Yes in step S45), the output distribution determination unit 125 selects the second distribution mode DM2 as the distribution mode DM (step S46). Therefore, the first battery 111 stops outputting, and the second battery 112 outputs power to the load 4 equal to the target output power of the energy storage system 1.

[0108] If the charge level of the second battery 112 is not greater than the second threshold for the second battery (No in step S45), the output distribution determination unit 125 selects the fifth distribution mode DM5 as the distribution mode DM (step S47). At this time, because the charge level of the second battery 112 is relatively low, the second battery 112 is charged by discharging the first battery 111. That is, the first battery 111 is discharged at its rated output, and the second battery 112 is charged with power obtained by subtracting the absolute value of the target output power of the energy storage system 1 from the rated output of the first battery 111.

[0109] In this way, the output distribution determination unit 125 determines the output distribution between the first battery 111 and the second battery 112 by selecting one of a plurality of distribution modes DM based on at least the charge rate of the first battery 111. In particular, when the distribution mode DM is the fourth distribution mode DM4, the output distribution between the first battery 111 and the second battery 112 is determined based on the target output power of the energy storage system 1 and a specific power threshold. In other words, the output distribution determination unit 125 determines the output distribution between the first battery 111 and the second battery 112 based on the target output power of the energy storage system 1 and a specific power threshold.

[0110] With the above configuration, the output distribution between the first battery 111 and the second battery 112 can be adjusted according to the target output power of the energy storage system 1 at that time, thereby (quickly) increasing or decreasing the output power of the energy storage system 1. This allows for compensation of fluctuations in the power generated by, for example, the renewable energy power generation device 200 (in this embodiment, the photovoltaic power generation device 2) connected to the energy storage system 1. Furthermore, the output level of the lower-output type of the first battery 111 and the second battery 112, which deteriorates quickly (in this embodiment, the first battery 111), can be adjusted based on a specific power threshold. In other words, the output level of the higher-output type of the first battery 111 and the second battery 112, which deteriorates slowly (in this embodiment, the second battery 112), can be adjusted. Therefore, the output of the first battery 111 and the second battery 112 can be controlled while taking into account the overall deterioration of the first battery 111 and the second battery 112. This allows for suppressing the overall degradation of the first battery 111 and the second battery 112 compared to a case where the output distribution between the first battery 111 and the second battery 112 is always biased towards one or the other. As a result, the life cycle cost of the energy storage system 1 can be reduced. Thus, the output power can be increased or decreased while suppressing the overall degradation of the first battery 111 and the second battery 112.

[0111] From the perspective of easily realizing a configuration in which the second battery 112 is higher output type and degrades more slowly (less prone to degradation) than the first battery 111, the following configuration is desirable. That is, as shown in Figures 2B and 2C, it is desirable that the rated output of the second battery 112 is greater than the rated output of the first battery 111, and that the cycle life of the second battery 112 is longer than the cycle life of the first battery 111.

[0112] Even if the first battery 111 is a lower-output type and degrades faster than the second battery 112, if the output distribution between the first battery 111 and the second battery is determined by the method described above, the following may occur. That is, the amount of power output per day from the first battery 111 may be greater than the amount of power output per day from the second battery 112. In this case, we compare the case where the rated capacity of the first battery 111 is greater than that of the rated capacity of the second battery 112 and the case where it is less. When the rated capacity of the first battery 111 is greater than that of the rated capacity of the second battery 112, the effective charging capacity of the energy storage system 1 is greater. Also, in a configuration where the first battery 111 is a lower-output type and degrades faster than the second battery 112, the first battery 111 is often cheaper than the second battery 112 when comparing them at the same charging capacity. Therefore, from the perspective of making it easier to effectively increase the capacity of the energy storage system 1 at a low cost, it is desirable that the rated capacity of the first battery 111 be greater than the rated capacity of the second battery 112, as shown in Figure 2A.

[0113] Since both the first battery 111 and the second battery 112 are composed of lithium-ion batteries, they are more susceptible to degradation when overcharged or over-discharged. The overcharged state refers to a state in which the charge level of battery 11 is higher than a predetermined charge level threshold (e.g., 80%). The over-discharged state refers to a state in which the charge level of battery 11 is lower than a predetermined other charge level threshold (e.g., 20%) that is lower than the predetermined charge level threshold. As described above, in this embodiment, the first battery 111 degrades faster (is more susceptible to degradation) than the second battery 112. In such a case, in order to efficiently suppress the progression of degradation of both the first battery 111 and the second battery 112 as a whole, it is desirable to prioritize suppressing the degradation of the first battery 111. From this perspective, as shown in Figures 9A and 9B, it is desirable that the output distribution determination unit 125 selects one of a plurality of distribution modes DM based on at least the charge level of the first battery 111.

[0114] [5. Variations] Figure 10 is a schematic block diagram showing the configuration of a modified example of the energy storage system 1. The energy storage system 1 shown in Figure 10 has the same configuration as the energy storage system 1 shown in Figure 1, except that the control device 12 operates as a charge rate management unit 126 and a charge / discharge range adjustment unit 127. That is, the energy storage system 1 shown in Figure 10 includes a charge rate management unit 126 and a charge / discharge range adjustment unit 127.

[0115] The charge rate management unit 126 is a functional unit that manages the charge rate of the second battery 112 during charging and discharging. More details are as follows: Figures 11A and 11B are diagrams illustrating the management of the charge rate of the second battery 112 by the charge rate management unit 126. Figure 11A schematically shows the change in the charge rate of the second battery 112 during charging, and Figure 11B schematically shows the change in the charge rate of the second battery 112 during discharging.

[0116] The charge level of the second battery 112 can normally fluctuate between 100% (indicating a fully charged state) and 0% (indicating a completely discharged state). However, in this modified example, the charge level management unit 126 keeps it within a specific charge / discharge range R1. The specific charge / discharge range R1 refers to the range obtained by subtracting the adjustment range R3 from the charge / discharge range R2. In other words, the specific charge / discharge range R1 is set within the charge / discharge range R2. The charge / discharge range R2 is generally the range within which the battery's charge level can be controlled, that is, the range within which the battery's charge level fluctuates. For example, if the charge / discharge range of the second battery 112 is 60%, the charge / discharge range R2 is set to any 60% within the practical range R4 (e.g., the range from 10% to 90%), where the load on the second battery 112 is relatively small and the degradation progresses relatively slowly. Note that the charge / discharge range R2 is not limited to the practical range R4, but may be set to any range from 0% to 100%.

[0117] The adjustment range R3 is a range set in accordance with the charge / discharge rates for power supply and demand adjustment, recovery of surplus power generated by the solar power generation device 2 (see Figure 10) (hereinafter referred to as surplus power recovery), and peak cutting of the power demand of load 4 (see Figure 10) (hereinafter simply referred to as peak cutting). In detail, the adjustment range R3 includes a charge-side adjustment range R31 set in accordance with the charge rate for power supply and demand adjustment and surplus power recovery, and a discharge-side adjustment range R32 set in accordance with the discharge rate for power supply and demand adjustment and peak cutting. For example, if the charge rate for power supply and demand adjustment and surplus power recovery is 10%, the charge-side adjustment range R31 is set to 10%. Also, if the discharge rate for power supply and demand adjustment and peak cutting is 10%, the discharge-side adjustment range R32 is set to 10%. As a method for calculating the charge rate and discharge rate for power supply and demand adjustment, etc., for example, a method can be adopted that uses known assumed fluctuations of adjustment capacity for power supply and demand adjustment traded in the power supply and demand adjustment market. This method calculates the maximum charge amount per charge cycle and the maximum discharge amount per discharge cycle based on the assumed fluctuations of known adjustment capacity. Then, the maximum charge amount per charge cycle is converted to a charge rate and used as the charge rate for power supply and demand adjustment, etc., and the maximum discharge amount per discharge cycle is converted to a charge rate and used as the discharge rate for power supply and demand adjustment, etc.

[0118] When the second battery 112 is being charged for purposes other than adjusting power supply and demand (i.e., while its charge level is increasing), if the charge level of the second battery 112 reaches the upper limit of the specific charge / discharge range R1, the charge level management unit 126 stops charging the second battery 112 (see Figure 11A). This stops the increase in the charge level of the second battery 112. At this time, the charge level management unit 126 stops charging the second battery 112 and starts charging the first battery 111. As a result, even if charging of the second battery 112 is stopped, the energy storage system 1 can still charge the amount of energy that needs to be charged.

[0119] On the other hand, when the second battery 112 is being discharged for reasons other than power supply and demand adjustment (i.e., while its charge level is decreasing), if the charge level of the second battery 112 reaches the lower limit of the specified charge / discharge range R1, the charge level management unit 126 stops discharging the second battery 112 (see Figure 11B). This stops the decrease in the charge level of the second battery 112. At this time, the charge level management unit 126 stops discharging the second battery 112 and starts discharging the first battery 111. As a result, even if the discharge of the second battery 112 is stopped, the energy storage system 1 can still discharge the amount of power that needs to be discharged. In this way, the charge level management unit 126 keeps the charge level of the second battery 112 within the specified charge / discharge range R1.

[0120] In a configuration where the charge level of the second battery 112 is kept within the charge / discharge range R2 (not the specific charge / discharge range R1) when power supply and demand adjustment is not requested, problems may arise when power supply and demand adjustment is requested. For example, if the upper limit of the charge / discharge range R2 is set to 100% or close to it, charging for power supply and demand adjustment may cause the charge level of the second battery 112 to reach the upper limit of the charge / discharge range R2, resulting in the inconvenience of not being able to fully charge the amount of energy that needs to be charged for power supply and demand adjustment. Also, if the lower limit of the charge / discharge range R2 is set to 0% or close to it, discharging for power supply and demand adjustment may cause the charge level of the second battery 112 to reach the lower limit of the charge / discharge range R2, resulting in the inconvenience of not being able to fully discharge the amount of energy that needs to be discharged for power supply and demand adjustment. In other words, in a configuration where the charge level of the second battery 112 is kept within the charge / discharge range R2 when power supply and demand adjustment is not requested, the adjustment capacity for power supply and demand adjustment may be insufficient, and it may not be possible to respond to requests for power supply and demand adjustment. In this respect, the configuration in which the charge rate of the second battery 112 is kept within a specific charge / discharge range R1 set within the charge / discharge range R2 when power supply and demand adjustment is not requested is advantageous over the above configuration in terms of securing adjustment capacity for power supply and demand adjustment, because a buffer (adjustment range R3 in the modified example) is secured outside the specific charge / discharge range R1. Therefore, from the viewpoint of securing adjustment capacity for power supply and demand adjustment and realizing a power storage system 1 that can respond to power supply and demand adjustment, it is desirable that the power storage system 1 includes a charge rate management unit 126 that keeps the charge rate of the second battery 112 within a specific charge / discharge range R1, as in the modified example.

[0121] The charge / discharge range adjustment unit 127 is a functional unit that adjusts at least one of the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112. Below, as an example, we will describe the case in which the charge / discharge range adjustment unit 127 adjusts both the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112. Figure 12 is a flowchart showing the flow of adjustment of the respective charge / discharge range R2 of the first battery 111 and the second battery 112 by the charge / discharge range adjustment unit 127. The adjustment of the respective charge / discharge range R2 of the first battery 111 and the second battery 112 is performed by executing a charge / discharge range adjustment loop. The charge / discharge range adjustment loop is executed periodically (for example, once a day).

[0122] In step S51, the charge / discharge range adjustment unit 127 predicts the difference between the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112 for each candidate value of the charge / discharge range R2 of the second battery 112. Candidate values ​​for the charge / discharge range R2 of the second battery 112 include, for example, values ​​that are changed in 10% increments from 0% to 80%. However, this is an example, and the candidate values ​​for the charge / discharge range R2 of the second battery 112 may be set appropriately considering the cost of calculation processing, etc. Any method can be used for the above prediction. In a modified example, the prediction is performed by simulating the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112 using each candidate value of the charge / discharge range R2 of the second battery 112. This simulation has at least one of the following parameters: season (e.g., spring, summer, autumn, and winter) and weather (e.g., sunny, cloudy, rainy). In other words, the parameters used for adjustment by the charge / discharge range adjustment unit 127 include at least one of the season and weather.

[0123] In step S52, the charge / discharge range adjustment unit 127 extracts the battery with the smallest difference after a predetermined period from the difference between the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112 predicted in step S51. In a modified example, the predetermined period is one day. However, this is an example, and the predetermined period may be less than one day or two days or more.

[0124] In step S53, the charge / discharge range adjustment unit 127 identifies candidate values ​​for the charge / discharge range R2 of the second battery 112 that correspond to the predicted difference between the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112, which was extracted in step S52, as the charge / discharge range R2 of the second battery 112. As a result, within the adjustment range of the modified example, the difference between the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112 is minimized.

[0125] In step S54, the charge / discharge range adjustment unit 127 calculates the charge / discharge range R2 of the first battery 111. In the modified example, this calculation is performed by subtracting the charge / discharge range R2 of the second battery 112, which was identified in step S53, from the total charge capacity required for the entire energy storage system 1, and converting the difference into a charge / discharge range. As the total charge capacity required for the entire energy storage system 1, for example, the total amount of surplus power generated by the solar power generation device 2 per day on a sunny autumn day can be used. From this, it can be said that the charge / discharge range adjustment unit 127 adjusts the charge / discharge range R2 of the first battery 111 based on the charge / discharge range R2 of the second battery 112. Note that any method other than the above method may be used for the above calculation. Once the charge / discharge range R2 of the first battery 111 is calculated, the process returns to the beginning of the charge / discharge range adjustment loop, and after a predetermined period (for example, 1 day), the process from step S51 onwards is performed again.

[0126] In this way, the charge / discharge range adjustment unit 127 adjusts the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112. In particular, the charge / discharge range adjustment unit 127 makes the above adjustment so that the difference between the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112 becomes small. The charge / discharge range adjustment unit 127 also makes the above adjustment at predetermined intervals. For example, if the process in step S54 is deleted, the charge / discharge range R2 of only the second battery 112 will be adjusted. Also, if the process in step S54 is deleted and the processes in steps S51 to S53 are changed so that the charge / discharge range R2 of the first battery 111 is specified, the charge / discharge range R2 of only the first battery 111 will be adjusted.

[0127] If the energy storage system 1 is used for purposes such as adjusting power supply and demand without regulating the respective charge / discharge ranges R2 of the first battery 111 and the second battery 112, the progression of their degradation may vary, potentially leading to the deterioration of the energy storage system 1 as a whole accelerating beyond expectations. This is because the discharge depth corresponding to the charge / discharge range R2 is correlated with the rate of degradation caused by repeated charging and discharging (cycle degradation). To suppress such problems, it is effective to regulate the charge / discharge range R2 of at least one of the first battery 111 and the second battery 112. In other words, regulating the charge / discharge range R2 of at least one of the first battery 111 and the second battery 112 is an effective measure to suppress the above-mentioned problems, and it is desirable to take such a measure. From this perspective, as shown in the modified example, it is desirable that the energy storage system 1 includes a charge / discharge range adjustment unit 127 that adjusts at least one of the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112.

[0128] From the standpoint of reliably suppressing variations in the progression of degradation of the first battery 111 and the second battery 112, it is desirable that the charge / discharge range adjustment unit 127 makes the above adjustment, as shown in the modified example, so that the difference between the remaining lifespan of the first battery 111 and the remaining lifespan of the second battery 112 becomes small.

[0129] To avoid the inconvenience of insufficient charging capacity for the entire energy storage system 1 due to adjusting the charge / discharge range R2 of the second battery 112 in order to suppress variations in the progression of degradation of the first battery 111 and the second battery 112, the following configuration is desirable. That is, as in the modified example, it is desirable that the charge / discharge range adjustment unit 127 adjusts the charge / discharge range R2 of the first battery 111 based on the charge / discharge range R2 of the second battery 112.

[0130] From the viewpoint of continuously obtaining the effects of adjusting the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112, the following configuration is desirable. That is, as in the modified example, it is desirable that the charge / discharge range adjustment unit 127 adjusts at least one of the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112 at predetermined intervals.

[0131] When seasons or weather changes (or even within the same season if the weather changes, or even within the same weather if the season changes), the amount of sunshine, the characteristics of the power demand of load 4 (peak value, total amount per day), etc., change, and therefore the frequency of requests for power supply and demand adjustments changes. It is desirable to adjust at least one of the charge / discharge range R2 of the first battery 111 and the charge / discharge range R2 of the second battery 112, taking into account such changes (increases or decreases) in the frequency of requests for power supply and demand adjustments due to seasonal or weather changes. From this perspective, as shown in the modified example, it is desirable that the parameters used for such adjustments include at least one of season and weather.

[0132] [6. Addendum] The energy storage system 1 described in this embodiment can also be described as the energy storage system shown in the following appendix.

[0133] The energy storage system described in Appendix (1) is A storage system having a changeable target output power and a specific power threshold, The first and second batteries have different rated outputs and cycle lives, The system includes an output distribution determination unit that determines the output distribution between the first battery and the second battery based on the target output power and the power threshold.

[0134] The energy storage system in Appendix (2) is the same as the energy storage system described in Appendix (1), The rated output of the second battery is greater than the rated output of the first battery. The cycle life of the second battery is longer than that of the first battery.

[0135] The energy storage system in Appendix (3) is the same as the energy storage system described in Appendix (2), The rated capacity of the first battery is greater than the rated capacity of the second battery.

[0136] The energy storage system in Appendix (4) is the same as the energy storage system described in Appendix (2) or (3), The system includes a charge rate management unit that keeps the charge rate of the second battery within a specific charge / discharge range set within the charge / discharge range of the second battery.

[0137] The energy storage system in Appendix (5) is an energy storage system described in any of Appendix (2) to (4), The system includes a charge / discharge range adjustment unit that adjusts at least one of the charge / discharge ranges of the first battery and the charge / discharge range of the second battery.

[0138] The energy storage system in Appendix (6) is the same as the energy storage system described in Appendix (5), The charge / discharge range adjustment unit performs the adjustment so that the difference between the remaining lifespan of the first battery and the remaining lifespan of the second battery becomes small.

[0139] The energy storage system in Appendix (7) is the same as the energy storage system described in Appendix (5) or (6), The charge / discharge range adjustment unit performs the adjustment at predetermined intervals.

[0140] The energy storage system in Appendix (8) is an energy storage system described in any of Appendix (5) to (7), The parameters used in the aforementioned adjustment include at least one of the season and weather.

[0141] The energy storage system in Appendix (9) is an energy storage system described in any of Appendix (5) to (8), The charge / discharge range adjustment unit adjusts the charge / discharge range of the first battery based on the charge / discharge range of the second battery.

[0142] The energy storage system in Appendix (10) is an energy storage system described in any of Appendix (1) to (9), The system includes a power threshold determination unit that determines the power threshold based on at least one of the remaining lifespan of the first battery and the second battery, the rated output of the second battery, and the rated capacity of the second battery.

[0143] The energy storage system in Appendix (11) is an energy storage system described in any of Appendix (1) to (10), The system includes a target output power calculation unit that calculates the target output power based on conditions related to grid power supplied from the power grid to which the first battery and the second battery are connected.

[0144] The energy storage system in Appendix (12) is the same as the energy storage system described in Appendix (11), The target output power calculation unit separates the power equivalent to the sum of the actual power output based on the target output power and the grid power into low-frequency components and high-frequency components, and performs a filtering process to calculate one of the low-frequency components or the high-frequency component as the target output power.

[0145] The energy storage system in Appendix (13) is an energy storage system described in any of Appendix (1) to (12), The system includes a DC-DC converter unit connected to the first battery and the second battery.

[0146] The energy storage system in Appendix (14) is the same as the energy storage system described in Appendix (13), The DC-DC converter section has a bidirectional chopper circuit that performs either a voltage boost or a voltage drop when charging at least one of the first battery and the second battery, and performs the other voltage boost or voltage drop when discharging at least one of the first battery and the second battery.

[0147] The energy storage system in Appendix (15) is an energy storage system described in any of Appendix (1) to (14), The system includes multiple distribution modes in which the output distribution between the first battery and the second battery is set.

[0148] The energy storage system in Appendix (16) is the same as the energy storage system described in Appendix (15), The output distribution determination unit selects one of the plurality of distribution modes based at least on the charge rate of the first battery.

[0149] The energy storage system in Appendix (17) is an energy storage system described in any of Appendix (1) to (16), The first battery and the second battery are connected to a renewable energy power generation device that generates electricity using renewable energy.

[0150] Although embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and it can be expanded or modified without departing from the spirit of the invention. [Industrial applicability]

[0151] This invention can be used, for example, in energy storage systems for industrial and residential use. [Explanation of Symbols]

[0152] 1. Energy storage system 14. DC-DC Converter Section 111 First Battery 112 Second Battery 123 Target Output Power Calculation Unit 123F Filtering 124 Power threshold identification unit 125 Output distribution determination unit 126 Charging rate management department 127 Charge / Discharge Range Adjustment Section 141 Bidirectional Chopper Circuit 200 Renewable Energy Power Generation Devices DM distribution mode EG power system R1 Specific charge / discharge range R2 Charge / Discharge Range

Claims

1. A storage system having a changeable target output power and a specific power threshold, The first and second batteries have different rated outputs and cycle lives, A power storage system comprising: an output distribution determination unit that determines the output distribution between the first battery and the second battery based on the target output power and the power threshold.

2. The rated output of the second battery is greater than the rated output of the first battery. The energy storage system according to claim 1, wherein the cycle life of the second battery is longer than the cycle life of the first battery.

3. The energy storage system according to claim 2, wherein the rated capacity of the first battery is greater than the rated capacity of the second battery.

4. The energy storage system according to claim 2, further comprising a charge rate management unit that keeps the charge rate of the second battery within a specific charge / discharge range set within the charge / discharge range of the second battery.

5. The energy storage system according to claim 2, further comprising a charge / discharge range adjustment unit for adjusting at least one of the charge / discharge range of the first battery and the charge / discharge range of the second battery.

6. The energy storage system according to claim 5, wherein the charge / discharge range adjustment unit performs the adjustment so that the difference between the remaining lifespan of the first battery and the remaining lifespan of the second battery becomes small.

7. The energy storage system according to claim 5, wherein the charge / discharge range adjustment unit performs the adjustment at predetermined intervals.

8. The energy storage system according to claim 5, wherein the parameters used for the adjustment include at least one of season and weather.

9. The energy storage system according to claim 5, wherein the charge / discharge range adjustment unit adjusts the charge / discharge range of the first battery based on the charge / discharge range of the second battery.

10. The energy storage system according to claim 1, further comprising a power threshold determination unit that determines the power threshold based on at least one of the remaining lifespan of the first battery and the remaining lifespan of the second battery, the rated output of the second battery, and the rated capacity of the second battery.

11. The energy storage system according to claim 1, further comprising a target output power calculation unit that calculates the target output power based on conditions relating to grid power supplied from a power grid to which the first battery and the second battery are connected.

12. The energy storage system according to claim 11, wherein the target output power calculation unit separates the power equivalent to the sum of the actual power output based on the target output power and the grid power into low-frequency components and high-frequency components, and performs a filtering process to calculate one of the low-frequency components and the high-frequency components as the target output power.

13. The energy storage system according to claim 1, comprising a DC-DC converter unit connected to the first battery and the second battery.

14. The energy storage system according to claim 13, wherein the DC-DC converter section has a bidirectional chopper circuit that performs either a voltage boost or a voltage drop when charging at least one of the first battery and the second battery, and performs the other voltage boost or voltage drop when discharging at least one of the first battery and the second battery.

15. The energy storage system according to claim 1, comprising a plurality of distribution modes in which the output distribution between the first battery and the second battery is set.

16. The energy storage system according to claim 15, wherein the output distribution determination unit selects one of the plurality of distribution modes based at least on the charge rate of the first battery.

17. The energy storage system according to any one of claims 1 to 16, wherein the first battery and the second battery are connected to a renewable energy power generation device that generates electricity from renewable energy.

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