Storage battery system and method for controlling charging and discharging of storage battery system

Abstract

A storage battery system (100) is provided with a charging / discharging control device (101) to which a plurality of sets of storage battery modules (102) and converters (103) are connected and which controls charging / discharging of the storage battery modules (102). The charging / discharging control device (101) comprises: a converter efficiency estimation unit (203) for obtaining information including the currents, voltages and temperatures of the storage battery modules (102) and the currents and voltages of the converters (103) to estimate the conversion efficiencies of the converters (103); a storage battery performance estimation unit (204) for estimating a storage battery performance including a rating capacity; and an output lower-limit value determination unit (205) for separating the sets into groups (111, 112) comprising sets having the same converter characteristics and for determining an output lower-limit value on the basis of the rating capacities of the storage battery modules within the groups.

Description

[Technical field]

[0001] The present application relates to a storage battery system and a method for controlling charging and discharging of a storage battery system. [Background technology]

[0002] With the increase in electric vehicles and hybrid vehicles, methods of reusing deteriorated batteries and batteries with different characteristics depending on the vehicle model, such as modular batteries with different voltages and capacities, or batteries made of different materials, are being considered. In addition, methods of reusing batteries that can no longer be used in high-output electric vehicles for low-output stationary applications are being considered.

[0003] Methods of reuse that are being considered include disassembling batteries down to the smallest unit, the battery cells, and reconstructing them into batteries with the same degree of deterioration, and disassembling them down to the battery modules and using them as is. Because disassembling them down to the smallest unit, the battery cells, and reconstructing them is costly, attention is being paid to the method of disassembling them down to the battery modules and reusing them for stationary purposes. At present, this is limited to batteries with similar characteristics, such as batteries with the same degree of deterioration or batteries of the same type.

[0004] On the other hand, when used in large-scale storage battery systems such as large-capacity storage battery systems for grids, a control technology is needed that efficiently uses storage battery modules with different characteristics such as capacity and deterioration state. Large-capacity storage battery systems are composed of multiple storage battery modules, and the efficiency of the storage battery system is improved by controlling the output of each storage battery module. In addition, the converters connected to each storage battery module and converting the output power of each storage battery module are less efficient in the range where the output of the storage battery module is low, so the development of a control method especially in the low output range is a challenge in order to improve efficiency.

[0005] In response to this, a control method for a battery system in which multiple sets of storage batteries and converters are connected in parallel to a power system has been disclosed, which includes a power distribution determination unit that distributes the total charging / discharging power of the multiple storage battery / converter sets to the multiple storage battery / converter sets, and the power distribution determination unit compares the limit output when the conversion efficiency of the converter is equal to or higher than a reference efficiency with the total charging / discharging power, and when the total charging / discharging power is equal to or higher than the limit output, determines the number of operating units so that the output of all operating storage battery / converter sets is equal to or higher than the limit output (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-162917 A Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Document 1 further discloses that for all pairs of storage batteries and converters that have been decided to operate, output allocation is determined according to the margin of upper and lower limits of the charge amount, and that the pair to be operated is selected from the viewpoint of remaining life management of each pair. However, although the variation in the capacity of storage batteries is taken into consideration, it does not take into consideration the combination of storage battery modules with different characteristics, such as used batteries, or the case where the efficiency of converters is different.

[0008] The present application discloses technology for solving the above-mentioned problems, and aims to provide a storage battery system and a method for controlling charging and discharging of a storage battery system that can be operated efficiently even if the storage battery system is equipped with storage battery modules with different characteristics and converters with different characteristics. [Means for solving the problem]

[0009] The storage battery system disclosed in the present application comprises: A storage battery system including a plurality of sets of storage battery modules and converters connected to each other and a charge / discharge control device that controls charging and discharging of the storage battery modules, The charge / discharge control device includes: obtaining information including a current, a voltage, and a temperature of the battery module and a current and a voltage of the converter; a converter efficiency estimating unit that estimates a conversion efficiency of the converter based on the acquired information; a battery performance estimation unit that estimates battery performance including at least a rated capacity of the battery module based on the acquired information; an output lower limit value determination unit that classifies the plurality of sets into one or a plurality of groups based on the conversion efficiency of the converter estimated by the converter efficiency estimation unit, and determines an output lower limit value of the storage battery module so as to exceed a target conversion efficiency set for each of the classified groups, The output lower limit value determination unit determines an output lower limit value of the storage battery module for each of the separated groups based on a rated capacity of the storage battery module. Effect of the Invention

[0010] According to the storage battery system and the charge / discharge control method for the storage battery system disclosed in the present application, even if the system is equipped with storage battery modules with different characteristics and converters with different characteristics, it is possible to operate the system efficiently even in a low output range where the conversion efficiency is low. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a configuration of a storage battery system according to a first embodiment. [Diagram 2] 1 is a functional block diagram showing a configuration of a charge / discharge control device according to a first embodiment. [Diagram 3] 2 is a diagram for explaining power conversion in a storage battery unit included in the storage battery system according to embodiment 1. FIG. [Figure 4] 2 is a configuration diagram showing an example of a converter of a storage battery unit included in the storage battery system according to embodiment 1. FIG. [Diagram 5] FIG. 5A is a diagram illustrating a method for determining the lower output limit of a battery module, and shows the configuration and conversion efficiency curve of an example using n battery units with the same characteristics. FIG. 5B is a diagram illustrating the configuration and conversion efficiency curve of an example using n-2 battery units with the same characteristics. [Figure 6] FIG. 13 is a diagram for explaining a method for determining an output lower limit value by an output lower limit value determination unit of the charge / discharge control device in accordance with embodiment 1, and is a diagram showing a configuration diagram and a conversion efficiency curve in a case where storage battery modules having different characteristics are used in part. [Figure 7] 7 is a diagram showing the rated capacity, coefficient (rated capacity ratio), and output lower limit value of each storage battery module in the first unit group shown in FIG. 6. FIG. [Figure 8] 7 is a diagram showing the rated capacity, coefficient (rated capacity ratio), and output lower limit value of each storage battery module in the second unit group shown in FIG. 6. FIG. [Figure 9] 7 is a diagram illustrating a specific example of a storage battery module of the first unit group shown in FIG. 6. FIG. [Figure 10] 10A and 10B are diagrams for explaining a method of calculating an output lower limit value of the storage battery module shown in FIG. 9 and a diagram showing the calculation result. [Figure 11] 7 is a diagram illustrating a specific example of a storage battery module of the second unit group 112 shown in FIG. 6. FIG. [Figure 12] 12A to 12C are diagrams for explaining a method of calculating an output lower limit value of the storage battery module shown in FIG. 11 and diagrams showing calculation results. [Figure 13] 5 is a flowchart showing a procedure for determining an output lower limit value of each storage battery module in the charge / discharge control device according to the first embodiment. [Figure 14] FIG. 14A is a diagram for explaining the effect of control by the charge / discharge control device of embodiment 1, where FIG. 14A is a comparative example in which the output lower limit value is fixed, and FIG. 14B is a diagram in which the output lower limit value is determined by the charge / discharge control device of embodiment 1. [Figure 15] 10A and 10B are diagrams for explaining the deterioration progression of a storage battery module in a comparative example in which the output lower limit value is fixed. [Figure 16]4 is a diagram for explaining the progression of deterioration of a storage battery module when an output lower limit value is determined by the charge / discharge control device according to the first embodiment. FIG. [Figure 17] 11 is a diagram for explaining the replacement frequency and maintenance cost of a storage battery module in a comparative example in which the output lower limit value is fixed. FIG. [Figure 18] 10 is a diagram for explaining the replacement frequency and maintenance cost of a storage battery module when an output lower limit value is determined by the charge / discharge control device according to the first embodiment. FIG. [Figure 19] FIG. 2 is a hardware configuration diagram of the charge / discharge control device according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the present embodiment will be described with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

[0013] Embodiment 1 The battery system according to the first embodiment will be described below with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of a storage battery system according to embodiment 1. In Fig. 1, a storage battery system 100 includes a plurality of storage battery units 110 and a charge / discharge control device 101. Each storage battery unit 110 includes a storage battery module 102 and a converter 103, and is connected to the other storage battery units 110 and a load or a power source via a connection unit 106. The storage battery module 102 has a plurality of battery cells 104, which are the minimum units, connected in series or in parallel, and has a battery management unit (hereinafter referred to as BMU) 105 that monitors and controls the battery cells.

[0014] In the battery system 100, if a plurality of battery units 110 are connected in series as shown in FIG. 1, the voltages V1, . . . , V n If multiple storage battery units 110 are connected in parallel, the currents I1, . . . , I nBy controlling the current I of each storage battery module 102 indirectly, b1 , ,I bn Or voltage V b1 , , ,V bn It becomes possible to control the following. The charge / discharge control device 101 is a device that acquires information on each storage battery module 102 and distributes required output or input to a load or power source to each storage battery unit 110 .

[0015] The converter 103 may be, for example, an AC / DC converter that converts the direct current of the storage battery module 102 into an alternating current, or a DC / DC converter that converts the voltage of the storage battery module 102 into an arbitrary voltage, as will be described later.

[0016] The battery cells 104 of each storage battery module 102 are rechargeable secondary batteries, such as lithium ion batteries, nickel metal hydride batteries, and lead storage batteries. The BMU 105 has upper and lower voltage limits, maximum charge / discharge current, and maximum cell temperature set for the purpose of preventing overcharging, over-discharging, overvoltage, overcurrent, temperature abnormalities, etc. of the battery cells 104, and has protection functions as well as functions for monitoring the status of the battery cells 104, such as voltage measurement, current measurement, power measurement, temperature measurement, full charge management, and remaining capacity management.

[0017] The connection unit 106 connects the storage battery module 102 and the converter 103, and connects the converter 103 to another converter 103, a load, or a power source. Note that the storage battery unit 110 is assumed to be configured such that the converter 103 and the battery cells 104 excluding the BMU 105 of the storage battery module 102 or only the battery cells 104 can be replaced via the connection unit 106.

[0018] Fig. 2 is a functional block diagram showing the configuration of the charge / discharge control device 101 according to the first embodiment. In Fig. 2, the charge / discharge control device 101 includes a current acquisition unit 200, a voltage acquisition unit 201, a temperature acquisition unit 202, a converter efficiency estimation unit 203, a storage battery performance estimation unit 204, and an output lower limit value determination unit 205. Note that the figure shows one of the multiple storage battery units 110 as an example to explain the flow of information with the charge / discharge control device 101.

[0019] The current acquiring unit 200, the voltage acquiring unit 201, and the temperature acquiring unit 202 respectively acquire the current, voltage, and temperature of the storage battery module 102 via the converter 103. Using the acquired current and voltage values, the converter efficiency estimating unit 203 calculates the conversion efficiency of the converter 103. Note that, although a detailed configuration of the converter 103 will be described later, it is preferable that the converter 103 is configured to be able to measure the current and voltage of the storage battery module 102.

[0020] Here, the output P of the storage battery module 102 is calculated using FIG. b1 In the storage battery unit 110 having the converter 103 and the storage battery module 102 shown in FIG. b1 is expressed by using the conversion efficiency Ce of the converter 103, P b1 =Ce P1 (1) Here, the voltage of the battery module is V b1 , current I b1 If the converted voltage is V1 and the converted current is I1, then equation (1) becomes: V b1 I b1 = Ce V1 I1 (2) It becomes.

[0021] From equation (2), the current I b1 is expressed as the following equation (3).

number

[0022] As described above, it is understood that the current of the storage battery module 102 can be indirectly controlled by controlling the voltage and current of the converter 103. In this embodiment, the converter 103 has a function of measuring voltage and current, but measurements may be performed within the storage battery module 102 and acquired by the BMU 105. Even in this case, it is sufficient that the charge / discharge control device 101 can acquire such information from the BMU 105 or from the BMU 105 via the converter 103.

[0023] Next, the battery performance estimation unit 204 of the charge / discharge control device 101 will be described. The storage battery performance estimation unit 204 has a function of estimating deterioration and rated capacity as the storage battery performance of the storage battery module 102. The deterioration of the storage battery module 102 can be estimated by a general method, and in this embodiment, a method of calculating resistance using Ohm's law will be described. The resistance value R of the storage battery module bn is correlated with the deterioration of the battery module, and by tracking the resistance over time, the deterioration of the battery can be determined. bn and current I bn Get R bn =V bn / I bn It is possible to calculate it from: The time for calculating the resistance may be arbitrary, but since the resistance value changes depending on the state of charge and temperature, if the state of charge and temperature are constant, there will be less error and the deterioration state can be detected accurately.

[0024] In addition, the rated capacity refers to the amount of electricity that can be stored in the storage battery module, and is the sum of the currents when charging within the control range of the storage battery module (for example, the cell voltage range from 2.5V to 4.2V).

[0025] In the case of a storage battery system 100 including storage battery modules 102 with different characteristics as assumed in this embodiment, there are cases where storage battery modules 102 with a smaller rated capacity due to the progress of deterioration and storage battery modules 102 with different rated capacities are connected in the storage battery system 100. For this reason, the rated capacity is estimated for each storage battery module 102 and used for control. As described above, the estimation method may be the sum of the currents when charging within the specified range of the storage battery module 102 (for example, a cell voltage range of 2.5 V to 4.2 V), but the rated capacity sent from the BMU 105 of each storage battery module 102 may also be used.

[0026] Here, the configuration of converter 103 will be described with reference to FIG. 4 is a configuration diagram showing an example of the converter 103 provided in the storage battery unit 110. The converter 103 converts the voltage V b 4 shows an example of an isolated converter having a full bridge circuit composed of switching elements SW1 to SW4 on the storage battery module side across a transformer, and a full bridge circuit composed of switching elements SW11 to SW14 on the load and power supply side. The converter 103 is not limited to this circuit configuration, and may have other circuit configurations and may be either an isolated or non-isolated configuration.

[0027] The converter 103 converts the voltage V b In order to increase or decrease the voltage of the battery module 102, the converter 103 transmits a control command for turning on and off each switching element. bn , current I bn The converter 103 further includes an ammeter 304 and a voltmeter 305, and the current I n , voltage V nThis information is also transmitted to the controller 303. The information collected in the controller 303 is transmitted to the charge / discharge control device 101 as battery information.

[0028] In addition, as a feature of the storage battery system 100, when the storage battery units 110 are connected in series, the sum of the voltages of the storage battery units 110 must be the voltage V required for the power source and the load. V1+V2+···+V n =V When the storage battery units 110 are connected in parallel, the sum of the currents of the storage battery units 110 must be the current I required by the power source and the load. I1+I2+···+I n =I holds true.

[0029] The converter 103 has a function of measuring voltage and current. bn , current I bn Alternatively, the BMU 105 may measure the voltage and current and transmit the measured voltage and current to the charge / discharge control device 101. Even in the case of transmitting the measured voltage and current, there is no problem as long as the charge / discharge control device 101 can acquire the voltage and current information.

[0030] In this way, the battery performance estimation unit 204 of the charge / discharge control device 101 estimates the voltage V bn and current I bn The deterioration state of each storage battery module can be estimated by Ohm's law described above. In addition, the rated capacity can also be calculated by calculating the voltage V bn and current I bn In addition, if the rated capacity of the storage battery module is known in advance, it can be obtained from the BMU 105, and it is not necessary to obtain it from the converter 103. In addition, the battery module voltage V bn , current I bn and the temperature may be transmitted to the controller 303 of the transducer 103 .

[0031] Next, the output lower limit value determination unit 205 of the charge / discharge control device 101 will be described. The output lower limit value determination unit 205 calculates and determines an output limit value in the low load region of the storage battery module 102 using the conversion efficiency of the converter estimated by the converter efficiency estimation unit 203, and the deterioration of the storage battery module 102 and the rated capacity of the storage battery module 102 estimated by the storage battery performance estimation unit 204. A method of calculating the output lower limit value, which is the output limit value, will be described below.

[0032] Fig. 5 is a diagram for explaining a method for determining the output lower limit value of a storage battery module, Fig. 5A is an example using n storage battery units 110 with the same characteristics, and Fig. 5B is an example using n-2 storage battery units 110 with the same characteristics. Here, "same characteristics" means that the converters 103 of each storage battery unit 110 all have the same converter characteristics, i.e., the same conversion efficiency characteristics, and the deterioration state and rated capacity of the storage battery modules 102 are also approximately equal.

[0033] 5A, for a required output P of the storage battery system 100, n storage battery units (n is a natural number of 3 or more) equally distribute the required output P to each storage battery unit, resulting in an output P / n [W]. A conversion efficiency curve of the converter is shown, but when the required output P is low, due to the conversion efficiency characteristics, the efficiency at the distributed output P / n is small, and there is a risk that the conversion efficiency of the converter will deteriorate. Here, the output lower limit value equal to or greater than the conversion efficiency Z is defined as Pth, and the output borne by each storage battery module is set to be equal to or greater than this Pth, thereby improving the conversion efficiency.

[0034] 5B shows an example in which the number of storage battery units 110 having the same characteristics as in FIG. 5A is reduced by two from n to n-2. An output P / (n-2) [W], which is an equal distribution of the required output P, ​​is distributed to each storage battery unit, but the output P / (n-2) exceeds the output lower limit Pth on the conversion efficiency curve, and the conversion efficiency becomes Z or higher.

[0035] Thus, the method of adjusting the number of battery units has no problem when the characteristics of the converter and the battery modules are the same. However, when using battery modules with different characteristics or converters with different conversion efficiency characteristics, it is necessary to determine the lower limit value of the output considering the different characteristics.

[0036] Next, the case including battery modules with different characteristics will be described. FIG. 6 shows a configuration example including a first unit group 111 having m (m is a natural number of 2 or more and m < n) battery units 110 with the same characteristics shown in FIG. 5A in the battery system 100, and a second unit group 112 having n - m battery units 110 with the same characteristics within the unit but different characteristics from the first unit group 111, and a conversion efficiency curve of the converter. There are n battery units 110 in the battery system 100, and the battery modules 102 of the battery units 110 in the second unit group 112 are, for example, recycled products. group In FIG. 6, since the first unit group 111 and the second unit group 112 have different battery module characteristics and conversion efficiency characteristics, different lower limit values of the output are set for the different conversion efficiency curves. Here, it is assumed that each group has a conversion efficiency curve with equal characteristics, that is, the conversion characteristics are equal within each group. For the conversion efficiency Z, the lower limit value of the output of the battery modules in the first unit group 111 is

[0037] and for the conversion efficiency Z, the lower limit value of the output of the battery modules in the second unit group 112 is Pth _a Hereinafter, the method for determining the lower limit value of the output of each battery module in each group will be described. Pth _b Hereinafter, the method for determining the lower limit value of the output of each battery module in each group will be described.

[0038] FIG. 7 shows the rated capacity, coefficient (rated capacity ratio), and lower limit value of the output of each battery module in the first unit group 111. First, the rated capacities are defined as Q1, Q2, . . ., Qa, . . ., Qm-1, and Qm for the storage battery modules 1 to m of the first unit group 111. The output lower limit value at the conversion efficiency Z of the converter of the storage battery module of the first unit group 111 Pth _a The output lower limit value Pth of each battery module is distributed according to the rated capacity of the battery module. _1 ,···,Pth _m is expressed as the following equation (4).

[0039]

number

number

[0040] Qa indicates the rated capacity that is closest to the average among the rated capacities of the storage battery modules of the first unit group 111. Using equation (5), the output lower limit Pth of each battery module _1 ,···,Pth _m is expressed as the following equation (6).

number

[0041] At this time, the conversion efficiency corresponding to the lower limit of the output of each battery module is Z1, Z2, . . ., Z m Then, the average efficiency Z of the first unit group 111 is α_ave is calculated as follows:

number

[0042] Similar calculations are performed for the storage battery modules of the second unit group 112. FIG. 8 shows the rated capacity, coefficient (rated capacity ratio), and output lower limit value of each storage battery module of the second unit group 112. The rated capacities are defined as Qm+1, Qm+2, . . ., Qb. . ., Qn-1, and Qn for the storage battery modules m+1 to n of the second unit group 112. The lower limit of the output at the efficiency Z of the converter of the storage battery modules of the second unit group 112 Pth _b The output lower limit value Pth of each battery module is distributed according to the rated capacity of the battery module. _m+1 ,···,Pth _n is expressed as the following equation (7).

[0043]

number

number

[0044] Qb indicates the rated capacity that is closest to the average among the rated capacities of the storage battery modules of the second unit group 112. Using equation (8), the output lower limit Pth of each battery module is _m+1 ,···,Pth _n is expressed as the following equation (9).

number

[0045] At this time, the efficiency of each battery module is Z m+1 ,Z m+2 ,···,Z n Then, the average efficiency Z of the second unit group 112 is β_ave is calculated as follows:

number

[0046] As described above, even in a storage battery system including storage battery modules with different characteristics such as the first unit group 111 and the second unit group 112, the output lower limit value of each storage battery module in each group can be calculated so that each group exceeds the target conversion efficiency Z, and therefore, the storage battery system can perform charge / discharge control that exceeds the target conversion efficiency Z. In other words, a storage battery system that can be operated efficiently can be realized.

[0047] A more specific example will be described below. Assume a storage battery system equipped with 10 storage battery units 110. The storage battery modules of the storage battery units 110 are referred to as storage battery modules 1, 2, ..., 10. A first unit group is equipped with storage battery modules 1 to 5, and a second unit group is equipped with storage battery modules 6 to 10. It is assumed that converter characteristics are equivalent within each group, and the rated capacity of the storage battery modules is different within each group. Here, although there are storage battery modules with different rated capacities, if the storage batteries have the same initial characteristics, the difference in rated capacity indicates deterioration of the storage batteries.

[0048] FIG. 9 shows the rated capacity of the storage battery modules of the first unit group and the coefficient (rated capacity ratio) calculated therefrom, and FIG. 11 shows the rated capacity of the storage battery modules of the second unit group and the coefficient (rated capacity ratio) calculated therefrom. First, the storage battery modules 1 to 5 of the first unit group will be described. FIG. 10 shows the conversion efficiency curve, which is the converter characteristic of the first unit group, and the output lower limit value of each storage battery module calculated using the curve. Here, the target conversion efficiency is set to 90%. The output that satisfies the target conversion efficiency of 90% is 88 [kW]. From FIG. 9, the storage battery module that is closest to the average rated capacity is storage battery module 3, and the output lower limit value of each storage battery module is calculated based on this. That is, the output lower limit value Pth of storage battery module 3 _3 is 88 [kW], and each storage battery module is calculated by multiplying the coefficient from storage battery module 3. The results are shown in Figure 10.

[0049] Furthermore, when this result is plotted on a conversion efficiency curve, it can be seen that, with respect to storage battery module 3, which has the closest average rated capacity, the output lower limit values ​​of storage battery modules 4 and 5, which have larger rated capacities, are controlled to be larger, and the output lower limit values ​​of storage battery modules 1 and 2, which have smaller rated capacities, are controlled to be smaller. When controlled at or above this output lower limit, the average conversion efficiency of this first group of units can exceed 90% of the target conversion efficiency.

[0050] Next, the storage battery modules 6 to 10 of the second unit group will be described. FIG. 12 shows the conversion efficiency curve, which is the converter characteristic of the second unit group, and the output lower limit value of each storage battery module calculated using the curve. Here, the target conversion efficiency is set to 90%. The output that satisfies the target conversion efficiency of 90% is 18 [kW]. From FIG. 11, the storage battery module that is closest to the average rated capacity is storage battery module 8, and the output lower limit value of each storage battery module is calculated based on this. That is, 8 Output lower limit Pth _8 is 18 [kW], and each storage battery module is calculated by multiplying it by a coefficient from storage battery module 8. The results are shown in FIG.

[0051] Furthermore, when this result is plotted on a conversion efficiency curve, it can be seen that, with respect to the storage battery module 8 that is closest to the average rated capacity, the output lower limit values ​​of the storage battery modules 6 and 7 with larger rated capacities are controlled to be larger, and the output lower limit values ​​of the storage battery modules 9 and 10 with smaller rated capacities are controlled to be smaller. When controlled at or above this output lower limit value, the average conversion efficiency of this second unit group can exceed 90% of the target conversion efficiency.

[0052] In addition, the average output of the battery modules classified into the two groups was 88 kW and 18 kW, respectively, resulting in a conversion efficiency of 90% for the entire battery system. In this embodiment and the examples, the conversion efficiency curve of the converter is approximated as a linear function to determine the output lower limit, but there are no restrictions on the approximation curve, and any approximation formula may be used as long as it can adequately explain the conversion efficiency curve of the converter. However, an approximation curve that can accurately explain the conversion efficiency curve is preferable. This is because if the error is large, there is a risk of an error occurring between the target conversion efficiency of the control and the average conversion efficiency.

[0053] In the above example, the converters are pre-sorted into groups with equal converter characteristics. The steps of the method for determining the output lower limit of the battery module will be described below with reference to the flowchart, including the concept of sorting. FIG. 13 is a flowchart showing the operation procedure of the charge / discharge control device 101. When the charge / discharge control is started, first, in step S1, the charge / discharge control device 101 receives the voltage V of the storage battery module 102 from the converter 103 or the BMU 105. bn , current I bn , the voltage V of the converter 103 n , current I n In addition, the temperature of the storage battery module 102 is acquired from the BMU 105.

[0054] In step S2, the converter efficiency estimation unit 203 estimates the voltage V bn , current I bn and the voltage V of the converter 103n , current I n The conversion efficiency and converter characteristics of the converter 103 are estimated using the above. The conversion efficiency is calculated by using the input (voltage V bn ×Current I bn ), and the input of the converter 103 (voltage V n ×Current I n ) and during discharging, the output of the storage battery module 102 (voltage V bn ×Current I bn ), and the output of the converter 103 (voltage V n ×Current I n The conversion efficiency characteristic can be obtained by plotting the conversion efficiency on the horizontal axis against the input or output of the converter.

[0055] In step S3, the multiple storage battery modules 102 are classified into groups of storage battery modules having the same or equivalent converter characteristics based on the estimated conversion efficiency characteristics of each converter. Here, a group having the same or equivalent converter characteristics refers to those whose converter characteristics can be expressed by a single approximated conversion efficiency curve. Also, when multiple storage battery modules 102 have the same or equivalent converter characteristics, there is one group.

[0056] Next, in step S4, the storage battery performance estimation unit 204 calculates the voltage V bn , current I bn and the temperature of the battery module 102 are used to estimate the performance of each battery module 102. The estimated performance includes the rated capacity of the battery module.

[0057] In step S5, the output lower limit value determination unit 205 obtains a rated capacity ratio (coefficient) within each group from the estimated rated capacity of each storage battery module. Meanwhile, it calculates an output lower limit value for each group from the conversion efficiency curve and target conversion efficiency of the converter. It allocates the output lower limit value of the group to each storage battery module within the group in accordance with the rated capacity ratio, and determines the output lower limit value of each storage battery module. The output lower limit value set by this procedure is input to the BMU 105 of each storage battery module 102, and the BMU 105 controls each storage battery module 102 so that the output is equal to or higher than the output lower limit value.

[0058] In this way, even if the storage battery system 100 is equipped with storage battery modules 102 with different performance, the storage battery modules are separated into groups based on equivalent converter characteristics, and the lower output limit value of each storage battery module is determined so as to achieve the target conversion efficiency of the group, thereby enabling the storage battery system 100 to operate with high efficiency.

[0059] In this embodiment, the output lower limit value is determined based on the rated capacity ratio of the storage battery modules. However, regardless of the rated capacity ratio, i.e., even if the output is not allocated precisely in accordance with the rated capacity ratio, it is desirable to set a high output lower limit value for storage battery modules with large rated capacities and a low output lower limit value for storage battery modules with small rated capacities.

[0060] The effects of this embodiment will be described below in comparison with a comparative example. 14A and 14B are diagrams for explaining a method for determining an output lower limit value when a plurality of storage battery modules included in a storage battery system have, for example, two types of converter characteristics. In the comparative example of FIG. 14A, multiple conversion efficiency curves A and B are not assumed, so for example, the output lower limit value is determined based on one of the conversion efficiency curves for the target conversion efficiency Z. Here, the output lower limit value Pn is determined based on the conversion efficiency curve A. And the output lower limit value Pn is set for all storage battery modules. In this case, the efficiency of the storage battery module having the conversion efficiency curve B becomes poor at the output Pn. In the present embodiment of FIG. 14B, the output lower limit values ​​Pn, P1 corresponding to the target efficiency Z are determined for each of the multiple conversion efficiency curves A, B, so that each storage battery module is efficiently controlled.

[0061] In this way, by determining the output lower limit value according to the converter characteristics and the storage battery module characteristics, it is possible to expect high efficiency of each storage battery module, and as a result, it is possible to expect improved efficiency in the low load range of the storage battery system.

[0062] Fig. 15 is a diagram for explaining a method for determining the output lower limit value of a storage battery module and a diagram showing a life curve for a storage battery system having a plurality of storage battery modules as a comparative example. Here, the output lower limit value Pth determined based on the target conversion efficiency on one conversion efficiency curve as shown in Fig. 14A is set for all storage battery modules. _a was set as the output lower limit for all storage battery modules. Therefore, because the output lower limit is not set according to the state of each storage battery module, as the use of the storage battery system progresses, the capacity maintenance rate of the rated capacity, which is an index of the lifespan, decreases, and the rate of decrease differs depending on the storage battery module, resulting in greater variation in deterioration.

[0063] Fig. 16 is a diagram for explaining a method for determining the output lower limit value of a storage battery module and a diagram showing a life curve for a storage battery system according to this embodiment having a plurality of storage battery modules. As described above, in this embodiment, the storage battery modules are not only classified according to converter characteristics, but also the output lower limit value corresponding to the target conversion efficiency Z is allocated according to the rated capacity, which is an index of the deterioration degree of the storage battery module, so that the average conversion efficiency within the classified group becomes the target conversion efficiency Z. That is, when there are m storage battery modules in this group as shown in the upper diagram of Fig. 16, the output lower limit value is Pth _1 From Pth _m In other words, the battery module with a large rated capacity is allocated up to the output lower limit Pth _a The lower output limit value Pth is set to a larger value, and the battery module with a smaller rated capacity has a lower output limit Pth _a With this setting, as the battery storage system is used, the capacity maintenance rate, which is an indicator of the battery life, decreases, but the difference in the rate of deterioration of the battery modules decreases, indicating that the variation in deterioration is small.

[0064] In this way, by determining the output lower limit value based on the deterioration (rated capacity), the output of the storage battery module with greater deterioration can be suppressed and the output of the storage battery module with less deterioration can be increased, thereby equalizing the deterioration and expecting to extend the life of the storage battery system itself and suppress the variation in deterioration.

[0065] Fig. 17 is a diagram for explaining the maintenance cost for a storage battery system having a plurality of storage battery modules as a comparative example, when the storage battery system has the life curve shown in Fig. 15. When the storage battery module is replaced each time the life is reached, the cost of the battery to be replaced and various expenses are incurred for each replacement. The various expenses include the cost of the workers who perform the replacement and the cost of stopping the storage battery system for the replacement.

[0066] On the other hand, Fig. 18 shows a diagram for explaining the maintenance cost when the storage battery system according to this embodiment having a plurality of storage battery modules has the life curve shown in Fig. 16. In this embodiment, the variation in life is suppressed, so that the frequency of replacement is reduced, and it is possible to reduce various expenses. Therefore, it is possible to reduce the maintenance cost of the storage battery system.

[0067] The charge / discharge control device 101 of the present embodiment is configured with a processor 1001 and a storage device 1002, as shown in FIG. 19, which is an example of hardware. Although the storage device is not shown, it includes a volatile storage device such as a random access memory and a non-volatile auxiliary storage device such as a flash memory. Also, instead of the flash memory, a hard disk auxiliary storage device may be included. The processor 1001 executes a program input from the storage device 1002. In this case, the program is input from the auxiliary storage device to the processor 1001 via the volatile storage device. Also, the processor 1001 may output data such as a calculation result to the volatile storage device of the storage device 1002, or may store the data in the auxiliary storage device via the volatile storage device. Moreover, the controller 303 included in the converter 103 also has a hardware configuration as shown in FIG. 19, for example, and controls the operation of each switching element.

[0068] In the present embodiment, the charge / discharge control device 101 is incorporated in the storage battery system 100 as an example. However, the charge / discharge control device 101 does not have to be incorporated in the storage battery system 100.

[0069] Although exemplary embodiments are described in this application, the various features, aspects, and functions described in the embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless variations not illustrated are expected within the scope of the technology disclosed in the present specification, including, for example, modifying, adding, or omitting at least one component. [Explanation of symbols]

[0070] 100: Battery system, 101: Charge / discharge control device, 102: Battery module, 103: Converter, 104: Battery cell, 105: BMU, 106: Connection unit, 110: Battery unit, 111: First unit group, 112: Second unit group, 200: Current acquisition unit, 201: Voltage acquisition unit, 202: Temperature acquisition unit, 203: Converter efficiency estimation unit, 204: Battery performance estimation unit, 205: Output lower limit value determination unit, 301: Voltmeter, 302: Ammeter, 303: Controller, 304: Ammeter, 305: Voltmeter, 1001: Processor, 1002: Storage device

Claims

1. A storage battery system including a plurality of sets of storage battery modules and converters connected to each other and a charge / discharge control device that controls charging and discharging of the storage battery modules, The charge / discharge control device includes: obtaining information including a current, a voltage, and a temperature of the battery module and a current and a voltage of the converter; a converter efficiency estimating unit that estimates a conversion efficiency of the converter based on the acquired information; a battery performance estimation unit that estimates battery performance including at least a rated capacity of the battery module based on the acquired information; an output lower limit value determination unit that classifies the plurality of sets into one or a plurality of groups based on the conversion efficiency of the converter estimated by the converter efficiency estimation unit, and determines an output lower limit value of the storage battery module so as to exceed a target conversion efficiency set for each of the classified groups, The output lower limit value determination unit determines an output lower limit value of the storage battery module for each of the separated groups based on a rated capacity of the storage battery module.

2. The storage battery system according to claim 1 , wherein the plurality of storage battery modules include those having different storage battery performances.

3. The storage battery system according to claim 1 or 2, wherein the plurality of converters include converters having different converter characteristics.

4. The storage battery system according to claim 1 , wherein the output lower limit value determination unit increases the output lower limit value as the rated capacity of the storage battery module in the group increases.

5. A method for controlling charging and discharging a battery system in which a plurality of sets of a battery module and a converter are connected, comprising: obtaining information including a current, a voltage, and a temperature of the battery module and a current and a voltage of the converter; estimating a conversion efficiency of the converter based on the acquired information; classifying the plurality of storage battery modules into groups of storage battery modules according to converter characteristics based on the estimated conversion efficiency of the converter; a storage battery performance estimation step of estimating storage battery performance including a rated capacity of the storage battery module based on the acquired information; a step of allocating an output lower limit value of a group corresponding to a set target conversion efficiency of the group among the groups classified in the classifying step according to performance of the storage battery module, and determining an output lower limit value of the storage battery module; A method for controlling charging and discharging a battery system comprising the above-mentioned.

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