Control systems and power systems

Abstract

This system achieves highly efficient operation as a whole while suppressing concentrated degradation of specific energy storage devices. [Solution] The control system 30 is a control system for controlling a plurality of energy storage units, each containing an energy storage device, and comprises a command acquisition unit 51 that acquires a power command value P, and a command distribution unit 52 that sets individual command values ​​Pm for one or more of the plurality of energy storage units according to the power command value P, and the command distribution unit 52 sets individual command values ​​Pm for each of the plurality of energy storage units such that the objective function obtained by summing a degradation index that includes the product of a weighted value corresponding to the total number of cycles Cn of the energy storage devices and the degradation rate of the energy storage devices with the individual command values ​​of the energy storage units as variables is minimized for the plurality of energy storage units.

Description

Technical Field

[0001] The present disclosure relates to a technique for controlling a plurality of power storage devices.

Background Art

[0002] Techniques for controlling a plurality of power storage devices according to a command value of power to be exchanged with a power system have been conventionally proposed. For example, Patent Document 1 discloses a configuration in which, using the results of detecting the deterioration states of a first power storage device and a second power storage device, the power distribution of each power storage device is set so that the life periods of the first power storage device and the second power storage device are the same.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in practice, it is not easy to suppress, for example, the concentration of power distribution to a specific power storage device among a plurality of power storage devices. Therefore, there is room for further improvement from the viewpoint of realizing highly efficient operation of the entire power storage system by suppressing the concentrated deterioration of a specific power storage device.

Means for Solving the Problems

[0005] To solve the above problems, a control system according to one aspect of the present disclosure is a control system for controlling a plurality of energy storage units, each containing an energy storage device, comprising: a command acquisition unit for acquiring a power command value; and a command distribution unit for setting individual command values ​​for one or more of the plurality of energy storage units according to the power command value, wherein the command distribution unit sets individual command values ​​for each of the plurality of energy storage units such that an objective function obtained by summing a degradation index that includes the product of a weighted value corresponding to the total number of cycles of the energy storage device and the degradation rate of the energy storage device with the individual command value of the energy storage unit as a variable is minimized.

[0006] A power system according to one aspect of the present disclosure is a power system comprising a plurality of energy storage units and a control system, wherein the control system comprises a command acquisition unit that acquires a power command value and a command distribution unit that sets individual command values ​​for one or more of the plurality of energy storage units according to the power command value, and the command distribution unit sets individual command values ​​for each of the plurality of energy storage units such that an objective function obtained by summing a degradation index that includes the product of a weighted value corresponding to the total number of cycles of the energy storage device and the degradation rate of the energy storage device with the individual command value of the energy storage unit as a variable is minimized for each of the plurality of energy storage units. [Brief explanation of the drawing]

[0007] [Figure 1] This is a block diagram illustrating the configuration of a power system according to the first embodiment. [Figure 2] This is a block diagram illustrating the configuration of an energy storage unit. [Figure 3] This graph shows the degradation of the electrical characteristics of energy storage devices. [Figure 4] This is a graph showing the degradation characteristics of an energy storage device. [Figure 5] This is a block diagram illustrating the configuration of a control system. [Figure 6] This is a block diagram illustrating the functional configuration of a control system. [Figure 7]This is a flowchart of the power distribution process. [Figure 8] This graph shows the relationship between the total number of cycles and the degree of degradation in an energy storage device. [Figure 9] This is a block diagram illustrating the configuration of a power system in a modified example. [Figure 10] This is a block diagram illustrating the configuration of a power system in a modified example. [Modes for carrying out the invention]

[0008] The embodiments for implementing this disclosure will be described with reference to the drawings. The embodiments described below are exemplary embodiments that may be envisioned when implementing this disclosure. Therefore, the scope of this disclosure is not limited to the embodiments described below.

[0009] A: Embodiment Figure 1 is a block diagram illustrating the configuration of a power system 100 according to one embodiment of the present disclosure. The power system 100 is a system that exchanges power (AC power) with a power grid 10. The power grid 10 is a distribution or transmission system for supplying power generated by power generation facilities (not shown), such as a thermal power plant or a nuclear power plant, to business facilities or consumers such as ordinary households.

[0010] As illustrated in Figure 1, the power system 100 comprises a power storage system 20 and a control system 30. The power storage system 20 is a power facility composed of a plurality (N) of power storage units 21 (where N is a natural number greater than or equal to 2). The control system 30 can communicate with each of the plurality of power storage units 21 via a communication network (not shown), such as a dedicated line.

[0011] Each of the N energy storage units 21 is a power device capable of charging and discharging electricity. Specifically, each energy storage unit 21 is a grid battery capable of discharging electricity to the power system 10 and charging electricity supplied from external devices such as the power system 10. The control system 30 is a computer system that controls the operation of each energy storage unit 21. Specifically, the control system 30 commands each energy storage unit 21 to charge or discharge the amount of electricity it should charge or discharge.

[0012] Figure 2 is a block diagram illustrating the configuration of each energy storage unit 21. As illustrated in Figure 2, each of the N energy storage units 21 comprises an energy storage device 211 and a control device 212. The energy storage device 211 is a battery capable of charging and discharging power. For example, the energy storage device 211 is composed of a plurality of battery cells connected in series or parallel to each other. Each battery cell is, for example, a lithium-ion battery in which the positive electrode active material is formed of a metal oxide containing lithium and the negative electrode active material is mainly formed of a carbon-based material.

[0013] The control device 212 is a Power Conditioning System (PCS) that controls the discharge and charging of the energy storage device 211. Specifically, the control device 212 controls the charging and discharging of the energy storage device 211 according to the command values ​​(individual command values ​​Pm, described later) supplied from the control system 30 to each energy storage unit 21. The control device 212 also functions as a power converter that converts DC / AC power between the energy storage device 211 and the power grid 10. That is, the control device 212 converts AC power supplied from the power grid 10 into DC power and outputs it to the energy storage device 211, and converts DC power supplied from the energy storage device 211 into AC power and outputs it to the power grid 10.

[0014] The electrical characteristics such as the capacity of the power storage device 211 deteriorate over time due to the continuous operation (charging or discharging) of the power storage device 211. FIG. 3 is a graph regarding the deterioration of the electrical characteristics of the power storage device 211. In FIG. 3, the number of charge-discharge cycles by the power storage device 211 is taken as the horizontal axis, and the temporal change in the discharge capacity of the power storage device 211 is illustrated. The discharge capacity shown on the vertical axis is a value normalized with the initial discharge capacity as 100%.

[0015] FIG. 3 also shows the temporal change in the discharge capacity for each of a plurality of cases where the C-rate during the operation of the power storage device 211 is different. Specifically, the discharge capacity is shown for the case where the C-rate is 0.1C (low C-rate), the case where the C-rate is 0.3C, and the case where the C-rate is 0.5C (high C-rate). The C-rate is the speed of charging and discharging, and is expressed by, for example, a current value or a power value. Note that 0.5C, which is exemplified as the high C-rate in the present embodiment, is the rated C-rate of the power storage device 211.

[0016] As can be understood from FIG. 3, when the power storage device 211 is operated at a low C-rate (0.1C) or a high C-rate (0.5C), there is a tendency that the deterioration of the power storage device 211 over time is promoted as compared with the case where it is operated at an intermediate C-rate (0.3C).

[0017] FIG. 4 is a graph of the relationship between the C-rate of the power storage device 211 and the deterioration rate (hereinafter referred to as "deterioration characteristic D"). The C-rate is shown on the horizontal axis by the power value (individual command value Pm) instructed to the power storage device 211. The deterioration rate on the vertical axis is the rate at which the power storage device 211 deteriorates. Specifically, the ratio at which the discharge capacity of the power storage device 211 decreases for each charge-discharge cycle over a predetermined number is exemplified as the deterioration rate.

[0018] FIG. 4 shows a power value corresponding to a specific C-rate (hereinafter referred to as “reference C-rate Popt”). The reference C-rate Popt is, for example, 0.3C. In the following description, a specific C-rate below the reference C-rate Popt is referred to as a “low C-rate”, and a specific C-rate above the reference C-rate Popt is referred to as a “high C-rate”. The low C-rate is, for example, 0.1C, and the high C-rate is, for example, 0.5C.

[0019] The tendency of deterioration of the power storage device 211 described above with reference to FIG. 3 can also be confirmed from FIG. 4. Specifically, as understood from FIG. 4, the deterioration rate during operation at a low C-rate exceeds the deterioration rate during operation at the reference C-rate Popt. Similarly, the deterioration rate during operation at a high C-rate exceeds the deterioration rate during operation at the reference C-rate Popt.

[0020] As described above, each power storage device 211 in the present embodiment exhibits a deterioration characteristic D in which the deterioration rate during operation at a low C-rate and the deterioration rate during operation at a high C-rate exceed the deterioration rate during operation at the reference C-rate Popt. That is, the reference C-rate Popt is a C-rate at which the deterioration rate is minimized within the range between the low C-rate and the high C-rate under the deterioration characteristic D.

[0021] FIG. 5 is a block diagram illustrating the configuration of the control system 30. As illustrated in FIG. 5, the control system 30 includes a control device 31, a storage device 32, and a communication device 33. The control system 30 can be realized by a single device or by a plurality of devices separately configured from each other.

[0022] The control device 31 consists of one or more processors that control each element of the control system 30. Specifically, the control device 31 is composed of one or more types of processors, such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), or ASIC (Application Specific Integrated Circuit).

[0023] The storage device 32 is one or more memories that store programs executed by the control device 31 and data used by the control device 31. The storage device 32 is composed of known recording media, such as magnetic recording media or semiconductor recording media. The storage device 32 may be composed of a combination of multiple types of recording media. A portable recording media that can be attached to and detached from the control system 30 may be used as the storage device 32.

[0024] The communication device 33 communicates with external devices by wire or wireless connection. Specifically, the communication device 33 communicates with each energy storage unit 21 (specifically, the control device 212). For example, the communication device 33 transmits an individual command value Pm to each energy storage unit 21. The communication device 33 also receives the total number of cycles Cn from each energy storage unit 21.

[0025] The total number of cycles Cn is the total number of cycles in the past operation of the nth energy storage unit 21 out of N energy storage units 21. The total number of cycles Cn is the number of times the charge and discharge pair has been repeated (number of cycles). Specifically, the total number of cycles Cn is the equivalent number of cycles. The equivalent number of cycles is the equivalent or virtual number of charge and discharge (charge depth) in a portion of the interval from the minimum value (0%) to the maximum value (100%) of the charge rate, calculated by considering the charge from the minimum value to the maximum value and the discharge from the maximum value to the minimum value as one cycle. The total number of cycles Cn for each energy storage unit 21 may be stored in the memory device 32 and updated as needed.

[0026] Furthermore, the communication device 33 of this embodiment communicates with the management systems 41 and 42 shown in Figure 1. The management systems 41 and 42 are computer systems for managing electricity transactions with the power system 100. The management system 41 manages electricity transactions in the wholesale electricity market. On the other hand, the management system 42 manages electricity (adjustment capacity) transactions in the supply and demand adjustment market. As described above, the power system 100 of this embodiment is capable of handling electricity transactions in multiple different electricity markets. The communication device 33 receives commands for electricity transactions in the wholesale electricity market from the management system 41 and commands for electricity transactions in the supply and demand adjustment market from the management system 42.

[0027] The wholesale electricity market managed by management system 41 is an electricity market aimed at relatively long-term power operation, so the fluctuations in the electricity traded are long-period. On the other hand, the supply and demand adjustment market managed by management system 42 is an electricity market that targets adjustment capacity to respond to short-term or sudden events such as actual electricity demand, the amount of electricity generated from renewable energy, and sudden power shortages due to power source failures, so the fluctuations in the electricity traded are short-period compared to the wholesale electricity market.

[0028] Generally, energy storage devices 211 are designed with a large capacity sufficient to adequately handle long-period operations such as those in the wholesale electricity market. However, energy storage devices 211 designed and installed under conditions suitable for long-period operations are not necessarily suitable for short-period operations such as those in the supply and demand adjustment market. For example, in the supply and demand adjustment market, a power level significantly lower than the rated power of the energy storage device 211 may be required. As illustrated above, in a power system 100 that handles electricity trading in multiple different electricity markets, it is conceivable that operation of the energy storage device 211 at a low C-rate may be required. However, as mentioned above, operation at a low C-rate may accelerate the deterioration of the energy storage device 211.

[0029] Taking the above circumstances into consideration, the control system 30 of this embodiment controls each energy storage device 211 using the degradation characteristics D of each energy storage device 211 so as to suppress the degradation of each energy storage device 211 caused by operation at a low C rate.

[0030] Figure 6 is a block diagram illustrating the functional configuration of the control system 30. The control device 31 implements multiple functions (command acquisition unit 51, command distribution unit 52) ​​for controlling each energy storage unit 21 by executing a program stored in the memory device 32.

[0031] The command acquisition unit 51 acquires a power command value P. The power command value P is the total power to be charged or discharged by the entire energy storage system 20 (i.e., N energy storage units 21). Charging / discharging is distinguished, for example, by the sign of the power command value P.

[0032] Specifically, the command acquisition unit 51 sets the power command value P in accordance with the commands received by the communication device 33 from the management systems 41 and 42. That is, the power command value P is the total value of the power that the power system 100 should send and receive based on transactions in multiple power markets such as the wholesale power market and the supply and demand adjustment market.

[0033] In the above explanation, the command acquisition unit 51 sets the power command value P in response to a command from an external device such as the management system 41 or management system 42. However, the command acquisition unit 51 may also receive the power command value P set by the external device via the communication device 33. In other words, "acquisition" of the power command value P includes both receiving and setting (e.g., generating or calculating) the power command value P.

[0034] The command distribution unit 52 sets individual command values ​​Pm (m=1~M) for M (0≦M≦N) of the N energy storage units 21, according to the power command value P acquired by the command acquisition unit 51. In other words, the command distribution unit 52 distributes the power command value P to the M energy storage units 21. The number of energy storage units 21 M is the total number of energy storage units 21 that should actually be operated out of the N energy storage units 21 (hereinafter referred to as "number of operating units"). Specifically, the command distribution unit 52 determines the M energy storage units 21 that should share the power command value P out of the N energy storage units 21, and the power distribution by each of the M energy storage units 21 (i.e., the individual command value Pm). In other words, the individual command value Pm corresponds to the allocation of the power command value P to one energy storage unit 21.

[0035] In this embodiment, the command distribution unit 52 uses the degradation characteristics D of each energy storage unit 21 to set individual command values ​​Pm for each energy storage unit 21 according to the power command value P. Specifically, the command distribution unit 52 sets individual command values ​​Pm for each energy storage unit 21 using the objective function G expressed by the following formula (1).

number

[0036] In equation (1), the symbol Xn is a variable (hereinafter referred to as the "operation variable") that represents the operation / stop of the nth energy storage unit 21 out of the N energy storage units 21. Specifically, the operation variable Xn is a flag that is set to either the numerical value 1, which represents operation, or the numerical value 0, which represents stopping operation.

[0037] In equation (1), the symbol Fn(Pn) is a function that represents the degradation characteristic D of the energy storage device 211 in the nth energy storage unit 21 out of N energy storage units 21. Specifically, the function Fn(Pn) is the degradation rate of the energy storage device 211 expressed with the individual command value Pn(C rate) as the variable. That is, when the energy storage unit 21 is operated with the individual command value Pn as the C rate, the degradation of the energy storage device 211 progresses according to the degradation rate Fn(Pn).

[0038] The degradation rate Fn(Pn) is set individually for each of the N energy storage units 21. Therefore, the degradation rate Fn(Pn) may differ for each energy storage unit 21. However, the degradation rate Fn(Pn) may be common to two or more of the N energy storage units 21.

[0039] In equation (1), the symbol √Cn is a weighted value for the degradation rate Fn(Pn). That is, in this embodiment, the weighted value √Cn is the total number of cycles Cn raised to the power of 1 / 2. Therefore, as the total number of cycles Cn of the energy storage device 211 increases, the weighted value √Cn of the energy storage device 211 increases.

[0040] As explained above, the objective function G is the sum of degradation indices for N energy storage units 21, which include the product of a weighted value √Cn corresponding to the total number of cycles Cn of the energy storage unit 211, the degradation rate Fn(Pn) of the energy storage unit 211 with the individual command value Pn of the energy storage unit 21 as a variable, and an operating variable Xn representing the operation / stop of the energy storage unit 21. The objective function G can also be expressed as the weighted sum of degradation rates Fn(Pn) to which the weighted value √Cn is applied.

[0041] The command distribution unit 52 sets individual command values ​​Pn and operating variables Xn for each of the N energy storage units 21 so as to minimize the objective function G described above. Of the N energy storage units 21, the individual command values ​​Pn of M energy storage units 21 whose operating variables Xn indicate operation are instructed to each energy storage unit 21 as individual command values ​​Pm.

[0042] Furthermore, to minimize the objective function G, any known optimization algorithm suitable for optimization problems such as linear programming (LP), integer programming (IP), mixed-integer programming (MIP), or mixed-integer linear programming (MILP) can be arbitrarily employed.

[0043] Specifically, the command distribution unit 52 minimizes the objective function G under the constraints expressed by the following equations (2a) and (2b).

number

[0044] The constraint in equation (2a) is that the sum of the individual command values ​​Pn in the N energy storage units 21 matches the power command value P. Also, the symbol Rn in equation (2b) is the rated output of the energy storage device 211 in the nth energy storage unit 21. That is, the constraint in equation (2b) is that the individual command value Pn is set with the rated output Rn as the upper limit.

[0045] As described above, in this embodiment, the operating variable Xn and individual command value Pn for each energy storage unit 21 are determined so as to minimize the objective function G, which is the sum of degradation indices including the product of the weighted value √Cn, the degradation rate Fn(Pn), and the operating variable Xn, for multiple energy storage units 21. Therefore, the operation / stop settings for each energy storage unit 21 can be configured so as to suppress the concentration of power distribution to a particular energy storage unit 21.

[0046] Figure 7 is a flowchart of the processes executed by the control device 31 (hereinafter referred to as "power control processing"). For example, command distribution processing is initiated by an interrupt signal that occurs at a predetermined interval.

[0047] When power control processing begins, the control device 31 (command acquisition unit 51) acquires the power command value P (S1). The control device 31 (command distribution unit 52) ​​also acquires the total number of cycles Cn for each energy storage unit 21 (S2).

[0048] The control device 31 (command distribution unit 52) ​​sets individual command values ​​Pm for each of the M energy storage units 21 out of the N energy storage units 21 according to the power command value P (S3). Specifically, the control device 31 sets the individual command values ​​Pm and operating variable Xn for each energy storage unit 21 so as to minimize the objective function G, which includes a weighted value √Cn corresponding to the total number of cycles Cn for each energy storage unit 21, the degradation rate Fn(Pn) of the energy storage device 211 with the individual command value Pn of each energy storage unit 21 as a variable, and an operating variable Xn representing the operation / stop of the energy storage unit 21. The control device 31 (command distribution unit 52) ​​then instructs each of the M energy storage units 21 out of the N energy storage units 21 whose operating variable Xn indicates operation to set the individual command value Pm for that energy storage unit 21 (S4). Specifically, the control device 31 transmits the individual command value Pm to each energy storage unit 21 via the communication device 33.

[0049] Figure 8 is a graph showing the relationship between the total number of cycles Cn of the energy storage device 211 and the degree of degradation E of the energy storage device 211. The degradation of the energy storage device 211 consists of cycle degradation caused by repeated discharge and charging, and storage degradation that progresses over time due to the continuous charge state. The degree of degradation E exemplified in Figure 8 represents the degree of cycle degradation in the energy storage device 211.

[0050] As illustrated in Figure 8, the degree of degradation E increases as the total number of cycles Cn increases. Specifically, the degree of degradation E of the energy storage device 211 tends to be proportional to the square root of the total number of cycles Cn. Therefore, the degradation rate of the energy storage device 211 is proportional to the -1 / 2 power of the total number of cycles Cn (i.e., 1 / √Cn). In other words, the more the total number of cycles Cn of the energy storage device 211 increases, the lower the degradation rate of the energy storage device 211 becomes.

[0051] Here, we assume a configuration in which the individual command values ​​Pn and operating variables Xn for each energy storage unit 21 are set by minimizing the objective function G, which does not include the total number of cycles Cn, as shown in equation (3) below (hereinafter referred to as "proportionality"). In proportionality, the sum of the degradation rates Fn(Pn) in each energy storage unit 21 is minimized.

number

[0052] However, as mentioned above, the more the total number of cycles Cn of the energy storage device 211 increases, the lower the rate of degradation of the energy storage device 211 becomes. Therefore, proportionally, power is preferentially allocated to energy storage units 21 whose energy storage devices 211 have already deteriorated due to past operation. Consequently, degradation progresses intensively in the energy storage device 211 of a specific energy storage unit 21 out of the N energy storage units 21, resulting in a problem where the overall operational efficiency of the power system 100 decreases.

[0053] In contrast to proportionality, in this embodiment, the individual command value Pm for each energy storage unit 21 is set so as to minimize the objective function G, which is the sum of degradation indices for multiple energy storage units 21 that include the product of a weighted value √Cn corresponding to the total number of cycles Cn of the energy storage unit 211 and the degradation rate Fn(Pn) of the energy storage unit 211. That is, the individual command value Pn for each energy storage unit 21 is set taking into account not only the degradation rate Fn(Pn) of the energy storage unit 211 but also the total number of cycles Cn. Specifically, as a result of multiplying the degradation rate Fn(Pn) by the weighted value √Cn, the effect of the degradation rate Fn(Pn) decreasing as the total number of cycles Cn increases is mitigated. Therefore, the concentration of power distribution to a specific energy storage unit 21 can be suppressed. As a result of suppressing the concentration of power distribution to a specific energy storage unit 211, the decrease in the overall operational efficiency of the power system 100 can be suppressed.

[0054] In actual operation of the power system 100, deteriorated energy storage devices 211 are replaced as needed. In the proportional system described above, specific energy storage units 21 deteriorate intensively, requiring frequent replacement of the energy storage devices 211 at short intervals. Since the energy storage units 211 cannot be operated during the period in which replacement work is carried out, a decrease in the operating revenue of the power system 100 becomes a problem in the proportional system. In contrast to the proportional system, according to this embodiment, as described above, concentrated deterioration of specific energy storage devices 211 is suppressed, so the replacement interval of the energy storage devices 211 is longer than in the proportional system. Therefore, the decrease in operating revenue can be suppressed.

[0055] Incidentally, the degradation represented by the degradation rate Fn(Pn) includes degradation caused by the degree of degradation in each energy storage unit 21 (hereinafter referred to as "degree of degradation"). The proportional approach minimizes the overall degradation, including the degradation caused by the degree of degradation. However, when considering the long-term operation of the energy storage system 20, all energy storage units 21 are usually used until the degradation of each unit 21 has progressed sufficiently. Therefore, even if degradation caused by the degree of degradation is avoided in the short term with the proportional approach, it does not contribute to minimizing long-term degradation.

[0056] In contrast to proportionality, in this embodiment, as can be understood from the above-mentioned formula (1), the degradation caused by the degree of degradation (degradation rate Fn(Pn)) among the degradation occurring in each energy storage unit 21 is selectively minimized as a result of offsetting by the total number of cycles Cn raised to the power of -1 / 2. Therefore, according to this embodiment, compared to proportionality, the overall degradation of the energy storage system 20 is minimized from a long-term perspective.

[0057] In this embodiment, the weighted value √Cn increases as the total number of cycles Cn of the energy storage device 211 increases. Therefore, compared to a proportional approach where the individual command value Pn of each energy storage unit 21 is set solely from the perspective of minimizing the degradation rate Fn(Pn) of the energy storage device 211, the concentration of power distribution to a specific energy storage unit 21 can be effectively suppressed. Specifically, since the weighted value √Cn is set to the power of 1 / 2 of the total number of cycles Cn, in a configuration using an energy storage device 211 that exhibits the trend shown in Figure 8 where the degradation rate of the energy storage device 211 is proportional to the power of -1 / 2 of the total number of cycles Cn, the concentration of power distribution to a specific energy storage unit 21 can be suppressed with high accuracy.

[0058] Furthermore, in this embodiment, the relationship between the individual command value Pn and the degradation rate Fn(Pn) is set individually for each energy storage unit 21. Therefore, even if the relationship between the individual command value Pn and the degradation rate Fn(Pn) differs for each energy storage unit 21, the concentration of power distribution to a specific energy storage unit 21 can be suppressed with high accuracy.

[0059] In this embodiment, in the process of allocating a power command value P to individual command values ​​Pm for one or more energy storage units 21, the individual command value Pm for each energy storage unit 21 is set by utilizing degradation characteristics in which the degradation rate during operation at low C-rate and high C-rate exceeds the degradation rate during operation at a standard C-rate. Therefore, multiple energy storage units 21 can be operated efficiently while suppressing the degradation of the energy storage device 211 caused by operation (charging or discharging) at a low C-rate.

[0060] B: Modification The following are examples of specific modifications that may be added to each of the embodiments exemplified above. Two or more embodiments may be arbitrarily selected from the following examples and merged as appropriate, provided they do not contradict each other.

[0061] (1) In the above-described embodiment, examples were given of energy storage devices 211 having degradation characteristics D in which the degradation rate during operation at a low C rate and a high C rate exceeds the degradation rate during operation at a reference C rate. However, the degradation characteristics D of each energy storage device 211 can be arbitrarily changed. For example, the degradation characteristics D of the energy storage device 211 may be such that the degradation rate F increases monotonically with respect to the C rate.

[0062] (2) In the embodiments described above, the degradation rate Fn(Pn) was exemplified as a function with the individual command value Pm as a variable, but the degradation rate Fn may also be expressed as a function that depends on factors other than power (individual command value Pm). For example, the degradation rate Fn may be expressed as a function that includes the state of charge (SOC) or temperature of the energy storage device 211 as variables in addition to the individual command value Pm. For example, a form in which the degradation rate Fn is a larger value as the charge level increases, or a form in which the degradation rate Fn is a larger value as the temperature increases, can be envisioned.

[0063] (3) In the embodiments described above, the objective function G is shown to include a weighted value √Cn, but the weighted value of the degradation rate Fn(Pn) in the objective function G is not limited to the square root of the total number of cycles Cn. For example, assuming that the degradation rate Fn(Pn) of the energy storage device 211 tends to decrease as the total number of cycles Cn of the energy storage device 211 increases, a value that increases monotonically with respect to the total number of cycles Cn is suitable as the weighted value of the degradation rate Fn(Pn).

[0064] Furthermore, the form of the weighted value of the degradation rate Fn(Pn) in the objective function G may change over time. For example, the total number of cycles Cn raised to the power of α (Cn α If we assume that ) is a weighted value for the degradation rate Fn(Pn), then we can assume a form in which the exponent α changes depending on variables such as the degradation rate Fn(Pn) or the total number of cycles Cn.

[0065] (4) In the embodiments described above, the objective function G was shown to include an operating variable Xn. However, under the condition that all (N) energy storage units 21 of the energy storage system 20 are to be operated, for example, it is not necessary to decide whether to operate or stop each energy storage unit 21. Therefore, the operating variable Xn may be omitted.

[0066] (5) In the embodiments described above, an example was given in which the degradation rate Fn(Pn) is set individually for each energy storage unit 21. However, the relationship between the individual command value Pn and the degradation rate Fn(Pn) may be common to all energy storage units 21 of the energy storage system 20. The relationship between the individual command value Pn and the degradation rate Fn(Pn) may change over time.

[0067] (6) In the embodiments described above, the energy storage device 211 of each energy storage unit 21 is composed of a plurality of battery cells. The degradation characteristics D of the energy storage unit 21 may be set according to the degradation characteristics of each of the plurality of battery cells. For example, the degradation rate Fn(Pn) of the energy storage unit 21 is expressed by the following formula (4).

number

[0068] In equation (4), the symbol Kn represents the number of battery cells constituting the energy storage device 211 of the nth energy storage unit 21. Therefore, the symbol Pn / Kn in equation (4) corresponds to the amount allocated per battery cell when the individual command value Pn of the energy storage unit 21 is evenly distributed among the Kn battery cells. Note that the number of battery cells Kn may differ for each energy storage unit 21.

[0069] Furthermore, the function f() in equation (4) is a degradation function that represents the degradation characteristics of a single battery cell. Therefore, the symbol f(Pn / Kn) in equation (4) represents the degradation rate of a single battery cell when operated with a power value Pn / Kn as the C rate. As can be understood from equation (4), the degradation rate Fn(Pn) of the energy storage unit 21 corresponds to the sum of the degradation rates f(Pn / Kn) of the Kn battery cells.

[0070] (7) As illustrated in Figure 9, the power system 100 may include power generation equipment 60. Power generation equipment 60 is, for example, a distributed power source that generates electricity using renewable energy. For example, any type of power generation system that utilizes renewable energy can be used as power generation equipment 60, such as a solar power generation system that converts solar energy into electricity, a wind power generation system that converts wind energy into electricity, a geothermal power generation system that converts geothermal energy into electricity, a hydroelectric power generation system that converts hydroelectric energy into electricity, or a biomass power generation system that converts biomass energy into electricity. Although one power generation equipment 60 is shown for convenience in Figure 12, multiple power generation equipment 60 of the same or different types may be installed in the power system 100. Furthermore, although power generation equipment 60 has been described as an element of the power system 100 in the above explanation, power generation equipment 60 may also be understood as an external element of the power system 100.

[0071] The control system 30 (command acquisition unit 51) sets a power command value P for the energy storage system 20 in accordance with commands from external devices such as the management systems 41 and 42, and the power generated by the power generation equipment 60. For example, the power command value P is set according to the difference between the target value corresponding to the command from the management system 41 or management system 42 and the amount of power generated by the power generation equipment 60. Alternatively, the control system 30 (command acquisition unit 51) may set the power command value P so that the prediction error of the amount of power generated by the power generation equipment 60 is absorbed by the energy storage system 20.

[0072] (8) In the above-described embodiment, a configuration was shown in which the control device 212 of each energy storage unit 21 converts the power from DC to AC. In this configuration, AC power is exchanged between the power system 10 and the energy storage system 20 (each energy storage unit 21). On the other hand, as illustrated in Figure 10, a power converter 24 may be installed between the power system 10 and the energy storage system 20.

[0073] The power conversion device 24 in Fig. 10 is a PCS that converts DC / AC power between the power grid 10 and the energy storage system 20. That is, the power conversion device 24 converts the AC power supplied from the power grid 10 into DC power and outputs it to each energy storage unit 21, and converts the DC power supplied from each energy storage unit 21 into AC power and outputs it to the power grid 10.

[0074] Therefore, in the configuration of Fig. 10, the control device 212 of each energy storage unit 21 is a DC / DC converter that converts DC power into DC power of another voltage value. That is, the control device 212 converts the DC power supplied from the power conversion device 24 into DC power of another voltage value and outputs it to the energy storage device 211, and converts the DC power supplied from the energy storage device 211 into DC power of another voltage value and outputs it to the power conversion device 24. As can be understood from the above description, each energy storage unit 21 and the power conversion device 24 are connected by a DC bus 25.

[0075] (9) In the above-described embodiment, as illustrated in Fig. 4, a form in which the deterioration rate monotonically decreases toward the reference C rate Popt within the range of a low C rate (Pm < Popt) was exemplified. However, the deterioration characteristic D of the energy storage device 211 is not limited to the above example. For example, a form in which the deterioration rate decreases to a value lower than the deterioration rate corresponding to the reference C rate Popt at a C rate even lower than the ranges illustrated in Figs. 4 and 10 is also assumed. As described above, the reference C rate Popt may not be the C rate at which the deterioration rate is minimized in the deterioration characteristic D. Also, the reference C rate Popt may not be the only extreme point in the deterioration characteristic D.

[0076] (10) In the above-described embodiment, as illustrated in Fig. 4, 0.5C, which is the rated C rate of the energy storage device 211, was exemplified as the high C rate. However, the high C rate is not limited to the above example. For example, the high C rate may be a C rate higher than the rated C rate (0.5C).

[0077] (11) The functions of the control system 30 in the above-described form are realized through the cooperation of one or more processors constituting the control device 31 and the program stored in the storage device 32, as described above. The programs exemplified above can be provided in a form stored on a computer-readable recording medium and installed on a computer. The recording medium is, for example, a non-transitory recording medium, such as an optical recording medium (optical disc) like a CD-ROM, but also includes any known form of recording medium such as a semiconductor recording medium or a magnetic recording medium. Note that a non-transitory recording medium includes any recording medium except for transient propagation signals (transitory, propagating signals), and volatile recording media are not excluded. Furthermore, in a configuration in which a distribution device distributes a program via a communication network, the recording medium in which the distribution device stores the program corresponds to the non-transitory recording medium described above.

[0078] (12) The notation "the nth" (where n is a natural number) in this application is used solely as a formal and convenient label to distinguish each element in notation, and has no substantive meaning whatsoever. Therefore, there is no room for restrictive interpretation of the position or order of each element based on the notation "the nth".

[0079] C: Note From the forms exemplified above, the following configuration can be understood, for example.

[0080] A control system according to one aspect of the present disclosure (Aspect 1) is a control system for controlling a plurality of energy storage units, each containing an energy storage device, comprising: a command acquisition unit for acquiring a power command value; and a command distribution unit for setting individual command values ​​for one or more of the plurality of energy storage units according to the power command value, wherein the command distribution unit sets individual command values ​​for each of the plurality of energy storage units such that an objective function obtained by summing a degradation index that includes the product of a weighted value corresponding to the total number of cycles of the energy storage device and the degradation rate of the energy storage device with the individual command value of the energy storage unit as a variable is minimized.

[0081] There is a tendency for the rate of degradation of an energy storage device to decrease as its degradation progresses. Therefore, in a configuration where individual command values ​​for each energy storage unit are set solely from the perspective of minimizing the rate of degradation of the energy storage device, power is preferentially allocated to energy storage devices that have already deteriorated due to past operation. In other words, degradation progresses concentratedly in the energy storage devices of specific energy storage units among multiple energy storage units, resulting in a problem where the overall operational efficiency of the power system decreases. In Embodiment 1, the individual command values ​​for each energy storage unit are set so as to minimize the objective function obtained by summing the degradation index, which includes the product of a weighted value corresponding to the total number of cycles of the energy storage device and the degradation rate of the energy storage device, for multiple energy storage units. In other words, the individual command values ​​for each energy storage unit are set taking into account not only the degradation rate of the energy storage device but also the total number of cycles. Therefore, the concentration of power allocation to specific energy storage units can be suppressed. As a result of suppressing concentrated degradation of specific energy storage devices, the decrease in the overall operational efficiency of the power system can be suppressed.

[0082] In the specific example of Embodiment 1 (Embodiment 2), the more the total number of cycles of the energy storage device increases, the lower the rate of degradation of the energy storage device, and the more the total number of cycles of the energy storage device increases, the higher the weight value of the energy storage device. In the above embodiment, the weight value increases as the total number of cycles of the energy storage device increases. Therefore, compared to an embodiment in which individual command values ​​for each energy storage unit are set solely from the viewpoint of minimizing the rate of degradation of the energy storage device, it is possible to effectively suppress the concentration of power distribution to a specific energy storage unit.

[0083] In a specific example of Embodiment 1 or Embodiment 2 (Embodiment 3), the degradation rate of the energy storage device is proportional to the -1 / 2 power of the total number of cycles, and the weighting value is the 1 / 2 power of the total number of cycles. There is a tendency for the degradation rate of the energy storage device to be proportional to the -1 / 2 power of the total number of cycles. According to Embodiment 3, since the 1 / 2 power of the total number of cycles is set as the weighting value, in an embodiment using an energy storage device exhibiting the above tendency, the concentration of power distribution to a specific energy storage unit can be suppressed with high accuracy.

[0084] In any specific example of Embodiments 1 to 3 (Embodiment 4), the degradation index for each energy storage unit includes the product of a weighted value corresponding to the total number of cycles of the energy storage device, the degradation rate of the energy storage device with the individual command value of the energy storage unit as a variable, and an operating variable representing the operation / stop of the energy storage unit. The command distribution unit sets the individual command value and the operating variable for each of the plurality of energy storage units so as to minimize the objective function. In the above embodiment, the operating variable and individual command value for each energy storage unit are determined so as to minimize the objective function obtained by summing the degradation index, which includes the product of the weighted value, the degradation rate, and the operating variable, for the plurality of energy storage units. Therefore, the operation / stop of each energy storage unit can be set so as to suppress the concentration of power distribution to a particular energy storage unit.

[0085] In any specific example of Embodiments 1 to 4 (Embodiment 5), the relationship between the individual command value and the degradation rate is set individually for each of the multiple energy storage units. According to the above embodiments, even if the relationship between the individual command value and the degradation rate (degradation characteristics) differs for each energy storage unit, the concentration of power distribution to a specific energy storage unit can be suppressed with high accuracy.

[0086] A power system according to one aspect of the present disclosure (Aspect 6) is a power system comprising a plurality of energy storage units, each containing an energy storage device, and a control system, wherein the control system comprises a command acquisition unit for acquiring a power command value and a command distribution unit for setting individual command values ​​for one or more of the plurality of energy storage units according to the power command value, and the command distribution unit sets individual command values ​​for each of the plurality of energy storage units such that an objective function obtained by summing a degradation index that includes the product of a weighted value corresponding to the total number of cycles of the energy storage device and the degradation rate of the energy storage device with the individual command value of the energy storage unit as a variable is minimized.

[0087] In a specific example of Embodiment 6 (Embodiment 7), the degradation rate corresponds to degradation characteristics in which the degradation rate during operation at a low C rate below the standard C rate and the degradation rate during operation at a high C rate above the standard C rate exceed the degradation rate during operation at the standard C rate. In the above embodiment, in the process of allocating power command values ​​to individual command values ​​for one or more energy storage units, the degradation characteristics in which the degradation rate during operation at low C rates and high C rates exceeds the degradation rate during operation at the standard C rate are utilized to set the individual command values ​​for each energy storage unit. Therefore, multiple energy storage units can be operated efficiently while suppressing the degradation of the energy storage device caused by operation at a low C rate (charging or discharging). [Explanation of Symbols]

[0088] 100...Power system, 10...Power grid, 20...Energy storage system, 21...Energy storage unit, 211...Energy storage device, 212...Control device, 30...Control system, 31...Control device, 32...Memory device, 33...Communication device, 41,42...Management system, 51...Command acquisition unit, 52...Command distribution unit, 60...Power generation equipment.

Claims

1. A control system for controlling multiple energy storage units, each containing an energy storage device, A command acquisition unit that acquires power command values, The system comprises a command distribution unit that sets individual command values ​​for one or more of the plurality of energy storage units according to the power command value, The command distribution unit, For each of the multiple energy storage units, the individual command values ​​are set such that the objective function obtained by summing the degradation index, which includes the product of a weighted value corresponding to the total number of cycles of the energy storage unit and the degradation rate of the energy storage unit with the individual command value of the energy storage unit as a variable, is minimized. Control system.

2. As the total number of cycles of the energy storage device increases, the rate of degradation of the energy storage device decreases. As the total number of cycles of the energy storage device increases, the weighting value of the energy storage device increases. The control system according to claim 1.

3. The degradation rate of the aforementioned energy storage device is proportional to the -1 / 2 power of the total number of cycles. The aforementioned weighted value is the square root of the total number of cycles. The control system of claim 2.

4. The degradation index for each of the aforementioned energy storage units includes the product of a weighted value corresponding to the total number of cycles of the energy storage device, the degradation rate of the energy storage device with the individual command value of the energy storage unit as a variable, and an operating variable representing the operation / stop of the energy storage unit. The command distribution unit sets the individual command values ​​and operating variables for each of the plurality of energy storage units so that the objective function is minimized. The control system according to claim 1.

5. The relationship between the individual command value and the degradation rate is set individually for each of the multiple energy storage units. The control system according to claim 1.

6. A power system comprising multiple energy storage units, each containing an energy storage device, and a control system, The control system is A command acquisition unit that acquires power command values, The system comprises a command distribution unit that sets individual command values ​​for one or more of the plurality of energy storage units according to the power command value, The command distribution unit, For each of the multiple energy storage units, the individual command values ​​are set such that the objective function obtained by summing the degradation index, which includes the product of a weighted value corresponding to the total number of cycles of the energy storage unit and the degradation rate of the energy storage unit with the individual command value of the energy storage unit as a variable, is minimized. Power system.

7. The aforementioned degradation rate corresponds to a degradation characteristic in which the degradation rate during operation with a low C-rate below the standard C-rate and the degradation rate during operation with a high C-rate above the standard C-rate exceed the degradation rate during operation with the standard C-rate. The power system according to claim 6.

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