Power system

Abstract

To provide an electric power system appropriately combining centralized control and decentralized control.SOLUTION: An electric power system 100 including a plurality of groups each combining a plurality of batteries comprises: a central control unit 102 that determines discharging or charging target electric power for each group; and a decentralized controller C that controls batteries so as to output the determined target electric power to each group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a power system that combines centralized control and distributed control. [Background technology]

[0002] A stationary energy storage system combining multiple types of batteries with different properties, such as lead-acid batteries, lithium-ion batteries, and lithium-ion capacitors, is disclosed, and a technology is disclosed that optimizes the overall system cost by having the lead-acid battery bear the long-period component of the system's power requirements from the power grid and the lithium-ion battery bear the short-period component (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] K.Takeda, C.Takahashi, H.Arita, N.Kusumi, M.Amano, A.Emori, “Design of Hybrid Energy Storage System using Dual Batteries for Renewable Applications”, IEEE PES General Meeting Power & Energy Society (2014) [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In stationary energy storage systems using different types of batteries, it is possible to distribute the system's power requirements according to the characteristics of each battery. However, when multiple batteries suitable for long-period components or multiple batteries suitable for short-period components are provided, it is not specified how the power for the long-period or short-period components should be distributed to each battery. For example, it is not clear whether the power should be simply distributed equally based on the number of batteries.

[0005] Another approach to power distribution involves determining the target power for each battery based on its State of Charge (SOC). Specifically, when the power grid requests discharge, batteries with higher SOCs should have a higher target power (discharge power), while batteries with lower SOCs should have a higher target power (charge power). However, in conventional technology, to apply this method and set the target power, a central control server must constantly monitor the SOC of all batteries and calculate their respective target powers based on that. Consequently, as the number of batteries increases, the computation cost and time of the central control server increase, leading to increased system operating costs. [Means for solving the problem]

[0006] One aspect of the present invention is a power system comprising a group of batteries, each including a central control unit that determines a target power for discharge or charge for each of the groups, and distributed controllers provided in each group that control the batteries to output the determined target power for each of the groups.

[0007] Here, it is preferable for the central control unit to determine the target power for discharge or charge for each of the groups such that the objective function J for the battery characteristics is minimized while satisfying the constraints.

[0008] Furthermore, the objective function J and the constraints are defined as the group i (i=1,2,···N). g Battery B belonging to ) ij (j=1,2,···M i The target power r for the group i is set based on the features of ) and is determined such that the objective function J is minimized while satisfying the constraints. i It is preferable to determine this.

[0009] Furthermore, it is preferable that the distributed controller determines the target power for each of the groups according to the characteristic quantities of the batteries belonging to that group, so as to track the target power for each of the groups.

[0010] Furthermore, it is preferable that the distributed controller determines the target power for the batteries belonging to the group from the central control unit based on the error between the target power for the group and the actual output power of the group, and the State of Charge (SOC) of the batteries belonging to the group.

[0011] Furthermore, in order to determine the target power for each of the groups, it is preferable to use the maximum discharge power, minimum discharge power, maximum charge power, and minimum charge power of the group, as well as the target power for each of the groups in the past.

[0012] Furthermore, in order to determine the target power for each of the groups, it is preferable to use the average SOC of the batteries belonging to the group.

[0013] Furthermore, in order to determine the target power for each of the aforementioned groups, it is preferable to use the average SOC of all batteries belonging to the aforementioned groups. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a power system in which multiple batteries are divided into multiple groups, and which appropriately combines centralized control and distributed control. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows a power system according to an embodiment of the present invention. [Figure 2] This figure shows the definition of physical quantities in embodiments of the present invention. [Figure 3] This figure shows a method for searching for target power according to an embodiment of the present invention. [Figure 4]It is a diagram showing the set values of parameters used in the simulation of power control of the power system in the embodiment of the present invention. [Figure 5] It is a diagram showing the result of the simulation of power control of the power system in the embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0016] As shown in FIG. 1, the power system 100 in the embodiment of the present invention includes a central control unit 102, a monitoring unit 104 (104-1 to 104-N g ), a battery B (B 11 ~B 1M1 , ···, B Ng1 ~B NgMNg ), and a distributed controller C (C 11 ~C 1M1 , ··· C Ng1 ~C NgMNg ).

[0017] The power system 100 can be applied to a stationary power storage system used as a power buffer for a renewable energy system typified by solar power generation or wind power generation, or a vehicle Virtual Power Plant system (vehicle VPP). The power system 100 controls the discharge power supplied from the battery B and the charging power supplied to the battery B (hereinafter, collectively referred to as output power) so as to satisfy the power required from the power grid (system required power).

[0018] In the power system 100, the battery B is grouped so as to belong to any one of a plurality of groups (group 1 to group N g ). In the example of the power system 100 shown in FIG. 1, the battery B 11 ~B 1M1 belongs to group 1. Power y 11 ~B 1M1 is output from each of 11 ~y 1M1 . Power y 11 ~B 1M1 output from each of the batteries B in group 1 11~y 1M1 These are added together and output as the total power y1 for group 1. The same applies to the other groups. Group N g Battery B Ng1 ~B NgMNg It belongs to Battery B. Ng1 ~B NgMNg From each of them, power y Ng1 ~y NgMNg The following is output. Group N g Battery B Ng1 ~B NgMNg Power y output from each of them Ng1 ~y NgMNg These are added together, and group N g Total power y Ng It will be output as follows.

[0019] In the power system 100, battery B belongs to group 1. 11 ~B 1M1 Distributed controller C for each of them 11 ~C 1M1 A similar structure is established for other groups, for example, group N g Battery B belonging to Ng1 ~B NgMNg Distributed controller C for each of them Ng1 ~C NgMNg A system will be established.

[0020] The distributed controller C is installed in each battery B and controls the power y output from the battery B. The distributed controller C sets the target power r to be output from each battery B based on the difference e between the target power r in each group and the total power y of that group. For example, battery B belonging to group 1 11 Corresponding distributed controller C 11 Based on the difference e1 between the target power r1 in group 1 and the total power y1 in group 1, battery B 11 The target power r that should be output from 11 Set the following. Other distributed controllers C are similar, for example, group N g Battery B belonging to Ng1 Corresponding distributed controller C Ng1 is group N g Target power r Ng and the group N g Total power yNg The difference e Ng Based on Battery B Ng1 The target power r that should be output from Ng1 The setting method for the target power r in the distributed controller C will be described later.

[0021] A monitoring unit 104 is provided for each group of batteries B. The monitoring unit 104 monitors and detects the status of the batteries B belonging to each group. The total power y output from the batteries B belonging to each group is input to the monitoring unit 104. The monitoring unit 104 also monitors and detects the State of Charge (SOC), maximum discharge power, minimum discharge power, maximum charge power, and minimum charge power for each battery B belonging to each group. The monitoring unit 104 then outputs the average SOC, maximum discharge power, minimum discharge power, maximum charge power, and minimum charge power for each group to the central control unit 102.

[0022] For example, monitoring unit 104-1 belonging to group 1 is connected to battery B belonging to group 1. 11 ~B 1M1 The total power y1 output from is monitored and detected. In addition, the monitoring unit 104-1 monitors battery B belonging to group 1. 11 ~B 1M1 SOCs for each of these 1j , maximum discharge power u D1j , minimum discharge power l D1j , maximum charging power u C1j , minimum charging power l C1j The monitoring unit 104-1 then monitors and detects (j=1,2···,M1). Based on this information, the monitoring unit 104-1 determines the average SOCs1 and the maximum discharge power U for group 1. D1 , minimum discharge power L D1 , maximum charging power U C1 , minimum charging power L C1 The central control unit 102 receives the result and outputs it. The other monitoring units 104 do the same, for example, group N g Monitoring unit 104-N belonging to this unit g is group N g Battery B belonging to Ng1 ~B NgMNg Total power y output from NgMonitor and detect. Also, the monitoring unit 104-N g is for the group N g for each battery B Ng1 ~B NgMNg about its SOCs Ngj , maximum discharge power u DNgj , minimum discharge power l DNgj , maximum charge power u CNgj , minimum charge power l CNgj monitor and detect (j = 1, 2 ···, M Ng ). Then, the monitoring unit 104-N g is based on this information to obtain for the group N g the average SOCs Ng , maximum discharge power U DNg , minimum discharge power L DNg , maximum charge power U CNg , minimum charge power L CNg and output them to the central control unit 102.

[0023] The maximum discharge power U g , minimum discharge power L Di , maximum charge power U Di , minimum charge power L Ci for each group i (i = 1, 2, ···, N Ci ) can be calculated by the following mathematical formulas (1) to (4).

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[0024] The maximum discharge power for each group can be set as the sum of the maximum discharge powers of the batteries B belonging to that group, as shown in equation (1). However, from the standpoint of battery protection, if it is desirable to avoid operating all batteries B at their maximum discharge power, the maximum discharge power for each group may be set to be less than the sum of the maximum discharge powers of the batteries B belonging to that group. Similarly, the maximum charge power for each group can be set as the sum of the maximum charge powers of the batteries B belonging to that group, as shown in equation (3). However, from the standpoint of battery protection, if it is desirable to avoid operating all batteries B at their maximum charge power, the maximum charge power for each group may be set to be less than the sum of the maximum charge powers of the batteries B belonging to that group.

[0025] Furthermore, the minimum discharge power for each group can be set as the sum of the minimum discharge powers of the batteries B belonging to that group, as shown in equation (2). However, in order to operate the power converter connected to the batteries B in a region of high power conversion efficiency, it is preferable that the target power of each battery B be greater than the minimum discharge power of each battery B. Therefore, the minimum discharge power for each group may be set greater than the sum of the minimum discharge powers of the batteries B belonging to that group. Furthermore, the minimum charge power for each group can be set as the sum of the minimum charge powers of the batteries B belonging to that group, as shown in equation (4). However, in order to operate the power converter connected to the batteries B in a region of high power conversion efficiency, it is preferable that the target power of each battery B be greater than the minimum charge power of each battery B. Therefore, the minimum charge power for each group may be set greater than the sum of the minimum charge powers of the batteries B belonging to that group.

[0026] Alternatively, the monitoring unit 104 may be omitted, and the central control unit 102 may be given the functions of the monitoring unit 104. However, in order to reduce the computation cost and computation time of the central control unit 102, it is preferable to install the monitoring unit 104.

[0027] The central control unit 102 receives the power request r for the system from the power grid to which the power system 100 is connected, and sets target powers r(r1~r) for each group to satisfy the requested power r. Ng The central control unit 102 sets the target power r(r1~r) for each group using the average SOC, maximum discharge power, minimum discharge power, maximum charge power, and minimum charge power received from the monitoring unit 104. Ng Set the target power r(r1~r) for each group in the central control unit 102. Ng The settings for this will be explained later.

[0028] Note that the system power requirement and the target power for each battery B are time-dependent, but in this embodiment, the time-dependent physical quantity A(t) is simply referred to as physical quantity A.

[0029] [Control methods for power systems] The control method in the power system 100 is described below. In the power system 100, the discharge power output from each battery B or the charging power supplied to each battery B is controlled by a combination of centralized control by the central control unit 102 and distributed control by distributed controllers C corresponding to each battery B belonging to each group. Figure 2 summarizes the physical quantities used in the following control method.

[0030] The central control unit 102 receives the system power request r and each group i (i=1,2,···,N) from the monitoring unit 104. g ) Average SOCsi, Maximum discharge power U Di , minimum discharge power L Di , maximum charging power U Ci , minimum charging power L Ci Based on this, we solve the constraint-bound optimization problem (minimization problem) to obtain the target power r for each group i. i Specifically, the central control unit 102 sets the target power r of each group i to minimize the objective function J represented by equation (5). i To decide.

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[0031] Here, we estimate the mean SOC of group i at the next step: s ^ i (t) can be expressed by formula (6).

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[0032] Furthermore, the average SOCs(t) of all batteries B included in the power system 100 can be expressed by formula (7).

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[0033] The constraints for solving equation (5) are the system required power r(t) for power system 100 and the power condition r in group i. i The SOC conditions for (t) and group i are set as equations (8) to (10), respectively.

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[0034] Here, g is included in the objective function J of equation (5). i ,q i (i=1,2,···,N g ) are arbitrary design parameters. The time step T is the time step for updating the target power of each group, and it is preferable to set the time step T to a value such as 30 minutes when entering a market where electricity is traded in 30-minute increments, such as the Japanese wholesale electricity market.

[0035] The terms of the objective function J were set with the following intentions in mind.

[0036] <First term of objective function J> Since battery B tends to degrade in capacity in regions where its State of Charge (SOC) is extremely high or low, it is preferable to equalize the SOCs of all batteries B constituting the power system 100 so that the capacity degradation is as uniform as possible. Therefore, the average SOCs of group i at present i (t) Average SOCs one step ahead ^ i (t) is estimated using equation (6) and matched to the current average SOCs(t) of all batteries B, which is expressed by equation (7).

[0037] Furthermore, the constraints in equation (9) stipulate that if a discharge request is received from the power system (r(t)>0), no charging will be performed for each group (discharge or output power will be set to 0), and if a charge request is received (r(t)<0), no discharging will be performed for each group (charge or output power will be set to 0).

[0038] This allows for control such that when a discharge request is made, the discharge rate is increased for the group with a higher SOC, and when a charge request is made, the charge rate is increased for the group with a lower SOC. As a result, the SOCs of the batteries B included in the power system 100 become uniform.

[0039] <Second term of objective function J> To prevent the total power from becoming oscillating, it is preferable to operate battery B at as constant a power as possible. Therefore, the target power r in each group is i The second term was introduced to reduce the variation of (t).

[0040] The group i(i=1,2,···N) is such that the objective function J is minimized under the constraints of equations (8) to (10) so that the capacity degradation of all batteries B included in the power system 100 is as uniform as possible, and the system operates at a constant power. g ) Target power r i Search for (t).

[0041] Figure 3 shows the target power r that minimizes the objective function J. iWe will show a specific method for searching for (t). The target power r that minimizes the objective function J is shown. i (t)(i=1,2,···N g Once the target power r is determined, i (t) and the output power y of group i i (t) difference e i Based on (t), distributed control is performed by distributed controller C ij Battery B ij Target power r ij Determine (t). Battery B ij The target power r ij (t) Power y ij Charging and discharging are performed by (t).

[0042] Battery B ij Output power y ij (t) is expressed by equations (11) to (13).

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[0043] Battery B ij Target power r ij If (t) is positive, i.e., if discharge is required, then battery B ij Power y output from ij (t) is the target power r ij (t) Minimum discharge power l Dij Maximum discharge power u Dij The following will be controlled. Also, Battery B ij Target power r ij If (t) is negative, i.e., charging is required, then battery B ij Power supplied to y ij (t) is the target power r ij (t) Minimum charging power l Cij Maximum charging power over Cij The following will be controlled. Note that Battery Bij Target power r ij If (t) is 0, Battery B ij The power y of charging and discharging ij (t) is set to 0. Under these constraints, the entire power system 100 is controlled to minimize the objective function J.

[0044] In this way, by setting lower limits on discharge power and charge power, battery B ij This prevents vibrations caused by abrupt switching between charging and discharging. Furthermore, by setting upper limits on the discharge and charging power, battery B ij This can suppress rapid discharge and charging of the battery.

[0045] The validity of power control in the power system 100 in this embodiment will be verified by simulation. The system power requirement for the power system 100 is the target power r that minimizes the objective function J shown in Figure 3. i The same pattern was used as in the example where (t) is searched.

[0046] The power system 100 includes 15 batteries B (#1 to #15), and the initial SOC, maximum discharge power, etc., are set as shown in Figure 4. The number of groups is 3 (N g With a value of 3), batteries #1 to #5 were assigned to group 1, batteries #6 to #10 to group 2, and batteries #11 to #15 to group 3.

[0047] The capacity of each battery B was set to 1.2kWh, and this was the same for all 15 batteries B. That is, the total battery capacity for each group was P1=P2=P3=1.2kWh×5=6kWh. In addition, the maximum discharge power U was set for all groups. Di ,Minimum discharge power L Di These were set to 4kW and 1kW, respectively. That is, the maximum discharge power U of each battery B Dij Assuming 0.8kW, the total maximum discharge power U of the five batteries B included in each group is... Di The power was set to 0.8kW × 5 = 4kW. Also, the minimum discharge power L of each battery B was calculated. DijAssuming 0.1kW, the minimum discharge power L of the five batteries B included in each group. Dij The total is 0.1kW × 5 = 0.5kW, but the minimum discharge power L Di The maximum charging power U was set to a larger value of 1kW. Ci ,Minimum charging power L Ci These values ​​were set to -4kW and -1kW, respectively.

[0048] Furthermore, any design parameter g included in the objective function J i ,q i (i=1,2,3) are each 2×10 11 And set to 1, and the time step T was set to 60 minutes.

[0049] Figure 5 shows the results of a simulation of power control in the power system 100. Figure 5 shows the temporal behavior of the system power requirement for the power system 100 (Figure 5(a)), the target power setting for each group (Figure 5(b)), the power of the batteries B included in each group (Figure 5(c)), and the State of Charge (SOC) (Figure 5(d)).

[0050] As shown in Figure 5(c), the power of each battery B in each group is in the unusable region, i.e., the minimum discharge power L when discharge is required. Dij (=0.1kW) or less, and the minimum charging power L when charging is requested. Cij The discharge or charge power of each battery B was controlled so as not to fall into the range of (=-0.1kW) or higher. In addition, the target power was determined so that the State of Charge (SOC) of each battery B would be as uniform as possible, and some groups would be left idle without being charged or discharged.

[0051] In this embodiment, control was performed to make the average SOC of each group as similar as possible. However, if constraints on SOC are set for each group, and it is permissible to vary the SOC based on those conditions, then it is not necessarily required to control the system to make the average SOC of each group similar.

[0052] As described above, the power system 100 in this embodiment allows the power converter to operate in a region with high power conversion efficiency. In other words, the power loss of the power converter can be reduced. In stationary energy storage systems and vehicle VPPs, the voltage is increased by a power converter to reduce power loss (Joule loss) that occurs when transmitting power from batteries connected to these systems to the power grid, and the power conversion efficiency of the power converter can be increased as the power is greater.

[0053] In other words, in the power system 100 of this embodiment, the target power of a certain group is set to a large value, and the batteries belonging to that group are operated at a relatively large power, while the target power of another group is set to 0, and the batteries belonging to that group are left idle without being charged or discharged. In this way, by leaving some groups of batteries idle, the central control unit determines the target power of each group so that the target power per operating battery does not become small, and thus the power converter can be operated in a region with high power conversion efficiency.

[0054] Furthermore, when attempting to operate batteries and power converters in a region of high power conversion efficiency, the computation cost and time of the central control unit increase as the number of batteries increases. In addition, since information on all batteries is required for calculation, the system becomes vulnerable to delays associated with the exchange of information between the batteries and the central control unit. In other words, if a delay occurs, the central control unit will calculate the target power of each battery based on the delayed information, resulting in a time lag between the system's required power and the target power of each battery, thus degrading responsiveness. In contrast, the power system 100 in this embodiment can reduce the computation cost and time of the central control unit.

[0055] In other words, in the power system 100 of this embodiment, the physical quantity to be calculated is the target power of the battery group, and the number of batteries is equal to the number of groups. Therefore, the calculation cost and calculation time of the central control unit can be reduced compared to simple centralized control.

[0056] Furthermore, the actual total power of all batteries B included in the power system 100 can be made to follow the system power requirements without fluctuating over time. In other words, in the power system 100 of this embodiment, the central control unit determines the target power of each group so that the target power per battery in operation does not decrease, thereby suppressing fluctuations in the total power.

[0057] [Structure of the invention] [Configuration 1] In a power system that includes multiple groups of batteries, A central control unit that determines the target power for discharge or charge for each of the aforementioned groups, A power system comprising: a distributed controller provided in the aforementioned group, which controls the batteries to output the target power determined for each of the aforementioned groups. [Configuration 2] The power system described in Configuration 1, The power system is characterized in that the central control unit determines the target power for discharge or charge for each of the groups so as to minimize the objective function J for the feature quantities of the battery while satisfying the constraints. [Configuration 3] The power system described in Configuration 2, The objective function J and the constraints are defined as the group i(i=1,2,···N) g Battery B belonging to ) ij (j=1,2,···M i The target power r for the group i is set based on the features of ) and is determined such that the objective function J is minimized while satisfying the constraints. i A power system characterized by determining [something]. [Structure 4] The power system described in Configuration 2, The power system is characterized in that the distributed controller determines the target power for each of the batteries belonging to the group according to the characteristic quantities of the batteries in that group, so as to track the target power for each of the groups. [Composition 5] The power system described in configuration 4, The distributed controller is characterized in that it determines the target power for the batteries belonging to the group from the central control unit based on the error between the target power for the group and the actual output power of the group, and the State of Charge (SOC) of the batteries belonging to the group. [Composition 6] A power system described in any one of items 1 to 5, A power system characterized by using the maximum discharge power of the group, the minimum discharge power of the group, the maximum charge power of the group, and the minimum charge power of the group, as well as the past target power for each of the groups, in order to determine the target power for each of the groups. [Composition 7] The power system described in configuration 6, A power system characterized by further using the average SOC of batteries belonging to the group in order to determine the target power for each of the groups. [Structure 8] The power system described in Configuration 7, A power system characterized by further using the average SOC of all batteries belonging to the group in order to determine the target power for each of the group. [Explanation of Symbols]

[0058] 100 Power system, 102 Central control unit, 104 Monitoring unit.

Claims

[Claim 1] In a power system that includes multiple groups of batteries, A central control unit that determines the target power for discharge or charge for each of the aforementioned groups, The group comprises a distributed controller provided in the group, which controls the batteries to output the target power determined for each of the groups, The central control unit, for each battery B ij (j=1,2,...Mi) belonging to the group i (i=1,2,...N g), estimates the average SOC at one step ahead s^i(t), the average SOCs(t) of all batteries B ij, the power condition ri(t), and the time step T, using g i and q i as arbitrary setting parameters. [Math 1] The objective function J defined by, System power requirement r(t) [Math 2] as, [Math 3] [Math 4] A power system characterized by determining the target power r i(t) for the group i such that the objective function J is minimized while satisfying the constraints.

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