Power limit value setting program, power limit value setting method, and power limit value setting device

Abstract

Conventional methods have the problem of not being able to properly control the charge and discharge current when the internal parameters of a secondary battery change. [Solution] The power limit value setting program of the present invention causes a computer to perform the following: a battery measurement process (S1) to acquire measured values ​​of the charge / discharge current and battery temperature of a secondary battery; a lithium concentration estimation process (S2) to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode by applying the charge / discharge current and battery temperature to a solid-phase diffusion model in a physical battery model used for estimating the state of the secondary battery; a diffusion approximation value calculation process (S3) to calculate the diffusion approximation lithium concentration by applying the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a pre-set approximation function; and a power limit calculation process (S4) to calculate a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit map in which the relationship between the diffusion approximation lithium concentration and the power limit value is mapped.

Description

[Technical Field]

[0001] The present invention relates, for example, to a power limit value setting program, a power limit value setting method, and a power limit value setting device for setting a power limit value, which is a limit value for the charging and discharging current of a secondary battery. [Background technology]

[0002] In the use of secondary batteries, control is sometimes implemented to limit the maximum charge and discharge current to prevent lithium from depositing on the negative electrode side. One example of such a technique for limiting the maximum charge and discharge current in secondary batteries is disclosed in Patent Document 1.

[0003] The battery charge / discharge control device described in Patent Document 1 has an input permission power adjustment means that adjusts the input permission power to the battery so that the negative electrode potential of the lithium-ion secondary battery does not fall to the lithium reference potential based on the charging history during charging and discharging. The input permission power adjustment means determines the input permission power based on the allowable charging current set as the maximum current at which metallic lithium does not deposit on the negative electrode, and changes it so as to decrease the allowable charging current according to the charging duration and increase the allowable charging current according to the discharging duration. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5223920 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the technology described in Patent Document 1 uses test data obtained by conducting tests on the secondary battery in advance. Therefore, if the internal parameters of the secondary battery change due to continued use, it has the problem that it is not possible to control the charge and discharge current appropriately.

[0006] This invention has been made in view of the above circumstances, and aims to control the charge and discharge current that suppresses lithium deposition regardless of changes in the internal parameters of a secondary battery. [Means for solving the problem]

[0007] One embodiment of the power limit value setting program according to the present invention causes a computer to execute the following: a battery measurement process to acquire measured values ​​of the charge / discharge current and battery temperature of a secondary battery; a lithium concentration estimation process to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode by applying the charge / discharge current and the battery temperature to a solid-phase diffusion model in a physical battery model used for estimating the state of the secondary battery; a diffusion approximation value calculation process to calculate the diffusion approximation lithium concentration by applying the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a preset approximation function; and a power limit calculation process to calculate a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit map in which the relationship between the diffusion approximation lithium concentration and the power limit value is mapped.

[0008] One embodiment of the power limit value setting method according to the present invention involves causing a computer to execute the following: a battery measurement process to acquire measured values ​​of the charge / discharge current and battery temperature of a secondary battery; a lithium concentration estimation process to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode by applying the charge / discharge current and the battery temperature to a solid-phase diffusion model in a physical battery model used for estimating the state of the secondary battery; a diffusion approximation value calculation process to calculate the diffusion approximation lithium concentration by applying the negative electrode surface lithium concentration and the average lithium concentration on the negative electrode to a preset approximation function; and a power limit calculation process to calculate a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit map in which the relationship between the diffusion approximation lithium concentration and the power limit value is mapped.

[0009] One aspect of the power limit value setting device according to the present invention acquires measurement values of the charge / discharge current and the battery temperature of a secondary battery, and applies the charge / discharge current and the battery temperature to a solid-phase diffusion model in a physical battery model used for estimating the state of the secondary battery to estimate the lithium concentration on the negative electrode surface and the average lithium concentration in the negative electrode. A lithium concentration estimation unit, a diffusion approximation value calculation unit that calculates a diffusion approximation lithium concentration by applying the lithium concentration on the negative electrode surface and the average lithium concentration in the negative electrode to a preset approximation function, and the diffusion approximation lithium concentration and the power limit value And a power limit calculation unit that calculates a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit map in which the relationship is mapped.

Advantages of the Invention

[0010] According to the power limit value setting program, the power limit value setting method, and the power limit value setting device of the present invention, it is possible to control the charge / discharge current that suppresses lithium precipitation regardless of changes in the internal parameters of the secondary battery.

Brief Description of the Drawings

[0011] [Figure 1] It is a diagram for explaining lithium precipitation in a secondary battery. [Figure 2] It is a block diagram of a secondary battery system to which the power limit value setting program according to Embodiment 1 is applied. [Figure 3] It is a flowchart for explaining the flow of the power limit value setting method according to Embodiment 1. [Figure 4] It is a block diagram of the power limit value setting device according to Embodiment 1. [Figure 5] It is a diagram for explaining the diffusion approximation lithium concentration. [Figure 6] It is a graph for explaining a concentration difference profile showing the time change of the lithium concentration difference. [Figure 7] It is a diagram for explaining an example of a power limit map. [Figure 8] It is a flowchart for explaining the procedure for creating a power limit map. [Modes for carrying out the invention]

[0012] For clarity of explanation, the following descriptions and drawings have been omitted and simplified as appropriate. Furthermore, each element shown in the drawings as a functional block performing various processes can be composed of a CPU (Central Processing Unit), memory, and other circuits in hardware terms, and implemented in software terms by programs loaded into memory. Therefore, it will be understood by those skilled in the art that these functional blocks can be implemented in various ways using hardware alone, software alone, or a combination thereof, and are not limited to any one of these. In each drawing, the same elements are denoted by the same reference numeral, and redundant explanations have been omitted where necessary.

[0013] Furthermore, the program described above includes, when loaded into a computer, a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored in a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray® disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically, or otherwise propagating signals.

[0014] Embodiment 1 The power limit value setting program according to Embodiment 1 calculates a power limit value, which is a limit on the charge and discharge power to prevent lithium deposition on the negative electrode side of the secondary battery. Therefore, lithium deposition in secondary batteries will be explained.

[0015] Figure 1 shows a diagram illustrating lithium deposition in a secondary battery. As shown in Figure 1, in a secondary battery, electrodes are arranged so that a positive electrode active material layer formed on the surface of the positive electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector face each other via a separator (not shown). Lithium ions are intercalated between these positive and negative electrode active material layers. In addition, an SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode active material layer. In a secondary battery, charging and discharging occur through the exchange of lithium ions (Li+) between the positive electrode active material layer and the negative electrode active material layer. Figure 1 shows the direction of lithium ion movement during charging.

[0016] In the negative electrode active material layer of a secondary battery, lithium ions can accumulate on the surface of the negative electrode active material layer when the lithium ion mobility is low and the charge / discharge current is large. The phenomenon in which these accumulated lithium ions become metal and precipitate is called lithium deposition. To suppress this lithium deposition, it is necessary to control the charge / discharge current so that lithium ions do not accumulate on the surface of the negative electrode active material layer. More specifically, lithium deposition is greatly influenced by two parameters: the solid-phase lithium concentration and the effect of diffusion within the negative electrode active material layer. It is believed that this can be suppressed by controlling the secondary battery with a charge / discharge current that allows sufficient diffusion of lithium ions within the negative electrode active material layer. Therefore, in the secondary battery system 1 according to Embodiment 1, a power limit value to suppress lithium deposition is calculated using a power limit value setting program. The power limit value setting program, the power limit value setting method, and the power limit value setting device will be described in detail below.

[0017] Figure 2 shows a block diagram of a secondary battery system to which the power limit value setting program according to Embodiment 1 is applied. As shown in Figure 2, the secondary battery system 1 according to Embodiment 1 includes a secondary battery 10, a power limit value setting device 11, a current sensor 12, a temperature sensor 13, and a voltage sensor 14. The secondary battery 10 is, for example, a battery pack in which multiple secondary batteries are connected in series to function as a single battery. Instead of a battery pack, a single battery can also be used as the secondary battery 10. The secondary battery 10 is a secondary battery capable of supplying power to a power supply destination and receiving power from a power supply destination.

[0018] The power limit value setting device 11 is implemented using some functions of the state estimation processing device that estimates the state of the secondary battery 10. Figure 2 shows only the function for calculating the power limit value. The state estimation processing device, although not shown in Figure 2, has a function to output state estimation values ​​other than the power limit value, for example, it outputs an estimated value of the State of Charge (SOC) of the secondary battery 10. The power limit value setting device 11 also uses the physical battery model of the secondary battery used in the state estimation device in its calculations.

[0019] The current sensor 12 measures the charge and discharge current of the secondary battery 10 and transmits the measured value as the charge and discharge current Icd to the power limit value setting device 11. The temperature sensor 13 measures the temperature of the secondary battery 10 and transmits the measured value as the battery temperature T to the power limit value setting device 11. The voltage sensor 14 measures the voltage difference between the positive and negative electrodes of the secondary battery 10 and transmits the measured value as the battery voltage Vb to the power limit value setting device 11. The power limit value setting device 11 calculates the power limit value of the secondary battery 10 using the values ​​transmitted from the various sensors. Details of the power limit value calculation process in the power limit value setting device 11 will be described later.

[0020] Furthermore, the power limit value setting device 11 can be implemented, for example, by an MCU (Micro Controller Unit) equipped with a program-executable arithmetic unit 20. This power limit value setting device 11 includes not only the arithmetic unit 20, but also analog-to-digital converters 21-23, a communication interface 24, and a memory 25.

[0021] The analog-to-digital converters 21-23 convert the analog value of the input signal into a digital value and transmit it to the calculation unit 20. Analog-to-digital converter 21 is used to acquire the charge / discharge current Icd, analog-to-digital converter 22 is used to acquire the battery temperature T, and analog-to-digital converter 23 is used to acquire the battery voltage Vb. In other words, analog-to-digital converters 21-23 function as a battery measurement parameter acquisition unit that acquires the charge / discharge current, battery temperature, and battery voltage, which are measured values ​​of the secondary battery.

[0022] The communication interface 24 transmits the power limit value calculated by the arithmetic unit 20 to a higher-level system that controls the power supply circuit. The memory 25 stores and inputs / outputs information such as programs executed in the arithmetic unit 20 and intermediate data generated by calculations performed by the arithmetic unit 20.

[0023] Here, the secondary battery system 1 according to Embodiment 1 has a distinctive feature in the method of setting the power limit value performed by the calculation unit 20. This power limit value setting method can be implemented by executing a power limit value setting program in the calculation unit 20, or by configuring the calculation unit 20 as dedicated hardware capable of implementing the power limit value setting method. The following description will explain an example in which the calculation unit 20 implements the power limit value setting program. When the calculation unit 20 is configured as dedicated hardware, the hardware should be configured to enable the functions of the processing units described below.

[0024] Next, we will briefly explain the power limit value setting method according to Embodiment 1. Figure 3 shows a flowchart illustrating the flow of the power limit value setting method according to Embodiment 1.

[0025] As shown in Figure 3, in the power limit value setting method according to Embodiment 1, first, a battery measurement process is performed to obtain measured values ​​of the charge / discharge current Icd and the battery temperature T (Step S1). Next, a lithium concentration estimation process is performed to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode by applying the charge / discharge current Icd and the battery temperature T to the solid-phase diffusion model in the physical battery model used for estimating the state of the secondary battery (Step S2). After that, a diffusion approximation value calculation process is performed to calculate the diffusion approximation lithium concentration by applying the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a preset approximation function (Step S3).

[0026] There are various methods for calculating the diffusion-approximate lithium concentration, but Figure 3 shows an example of a diffusion-approximate value calculation process that includes a difference calculation process (step S31), a decay-time concentration difference calculation process (step S32), a ratio calculation process (step S33), and a diffusion-approximate lithium concentration calculation process (step S34).

[0027] In the difference calculation process, the difference between the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode is calculated as the concentration difference (step S31). In the decay concentration difference calculation process, the concentration difference on the concentration difference profile after a predetermined power limit time is calculated as the decay concentration difference by referring to a concentration difference profile that shows the decay characteristics of the concentration difference using a predetermined function (step S32). In the ratio calculation process, a ratio value indicating the ratio between the concentration difference and the decay concentration difference is calculated (step S33). In the diffusion approximate lithium concentration calculation process, the diffusion approximate lithium concentration is calculated by applying the ratio value, the lithium concentration on the negative electrode surface, and the average lithium concentration on the negative electrode to a predetermined approximation function (step S34).

[0028] In the power limit value setting method according to Embodiment 1, a power limit calculation process is performed to calculate a power limit value corresponding to the diffusion approximate lithium concentration based on a power limit map that maps the relationship between the diffusion approximate lithium concentration and the power limit value (step S4). The power limit map is prepared in advance and remains fixed during the period in which the secondary battery system 1 is in operation unless there is an external update process.

[0029] Next, the power limit value setting device 11, which is realized by executing a power limit value setting program in the calculation unit 20, will be described. Figure 4 shows a block diagram of the power limit value setting device 11 according to Embodiment 1. As shown in Figure 4, the power limit value setting device 11 has a lithium concentration estimation unit 31, a diffusion approximation value calculation unit 32, and a power limit calculation unit 33. The diffusion approximation value calculation unit 32 also has a difference calculation unit 41, a decay concentration difference calculation unit 42, a ratio calculation unit 43, and a diffusion approximation lithium concentration calculation unit 44.

[0030] The lithium concentration estimation unit 31 acquires the measured values ​​of the secondary battery's charge / discharge current Icd and battery temperature T, and applies the charge / discharge current Icd and battery temperature T to the solid-phase diffusion model in the physical battery model used for estimating the state of the secondary battery to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode. In the example shown in Figure 4, in addition to the charge / discharge current Icd and battery temperature T, the lithium concentration estimation unit 31 receives a negative electrode lithium concentration correction value NLi_ofs. This negative electrode lithium concentration correction value NLi_ofs is a value calculated in other processes in the physical battery model and improves calculation accuracy. The negative electrode lithium concentration on the surface and the average lithium concentration on the negative electrode can be calculated even without using the negative electrode lithium concentration correction value NLi_ofs.

[0031] The solid-phase diffusion model is a state-space model derived by approximating the diffusion equation for the solid phase. Using this solid-phase diffusion model, it is possible to calculate estimated values ​​of internal parameters such as the lithium concentration at the negative electrode surface, the average lithium concentration at the negative electrode, the lithium concentration difference, and the open-circuit voltage (OCV) due to lithium concentration. This section will explain this solid-phase diffusion model in detail.

[0032] The solid-phase diffusion model calculates the state of diffusion of a solid-phase object into space over time, and can numerically represent the change in lithium ion concentration. The solid-phase diffusion model uses equations (1) to (4) to calculate the lithium concentration C at the negative electrode surface. surf and the average lithium concentration C of the negative electrode ave Derive the following.

[0033] Specifically, a s Let be the area ratio, A be the reaction area of ​​the electrode, and L be the area ratio. n If we let J be the electrode thickness and F be the Faraday constant, then the ion flow area J is the ion flow velocity. Li This is expressed by equation (1).

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[0034] Negative electrode surface lithium concentration C surf and the negative electrode average lithium concentration C ave The values are different due to the influence of diffusion inside the active material. The lower the diffusion, the more difficult it is for lithium ions to diffuse inside the active material, so lithium ions tend to accumulate on the surface. On the other hand, the higher the diffusion, the easier it is for lithium ions to diffuse, so lithium precipitation is less likely to occur.

[0035] The diffusion approximation value calculation unit (32) applies the negative electrode surface lithium concentration C surf and the negative electrode average lithium concentration C ave to a preset approximation function to calculate a diffusion approximation lithium concentration. Here, the diffusion approximation lithium concentration will be described. FIG. 5 shows a diagram for explaining the diffusion approximation lithium concentration. The diffusion approximation lithium concentration is calculated using the concentration difference between the negative electrode surface lithium concentration C surf and the negative electrode average lithium concentration C ave [ The diffusion approximation lithium concentration is the equivalent steady-state value of the active material having a lithium ion concentration difference (steady state: no lithium concentration difference, the negative electrode surface lithium concentration C surf and the negative electrode average lithium concentration C ave are the same). In FIG. 5, when there is a concentration difference between the negative electrode surface lithium concentration C surf and the negative electrode average lithium concentration C ave , the gradient of the lithium ion concentration in the active material is shown by a dashed line, and the lithium ion concentration equivalent to the steady state where the concentration difference between the negative electrode surface lithium concentration C surf [[ID=2 / 8]]and the negative electrode average lithium concentration C ave disappears is shown by a diffusion approximation lithium concentration straight line. In the diffusion approximation value calculation unit (32), this diffusion approximation lithium concentration is calculated using the negative electrode surface lithium concentration C surf and the negative electrode average lithium concentration C ave before reaching the steady state.

[0036] In the specific example shown in FIG. 4, the diffusion approximation value calculation unit (32) includes a difference calculation unit (41), a concentration difference calculation unit during attenuation (42), a ratio calculation unit (43), and a diffusion approximation lithium concentration calculation unit (44). The difference calculation unit (41) is the negative electrode surface lithium concentration C surfFrom the average lithium concentration C of the negative electrode ave The concentration difference obtained by subtracting C diff (=C surf -C ave Calculate ).

[0037] The decay-time concentration difference calculation unit 42 refers to a concentration difference profile that shows the decay characteristics of the concentration difference using a predetermined function, and calculates the concentration difference on the concentration difference profile after a predetermined power limit time has elapsed from the present time as the decay-time concentration difference. The concentration difference profile will now be explained. Figure 6 shows a graph illustrating the concentration difference profile that shows the change in lithium concentration difference over time.

[0038] There is a difference between the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode within the active material. The concentration difference profile is calculated assuming the battery remains stationary until the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode become equal. As an example of this concentration difference profile, as shown in Figure 6, it can be modeled as an exponential relationship with time as a variable. In the example shown in Figure 6, the function of the concentration difference line is y(t)=y(0)e at Then, if the initial concentration difference, which is the concentration difference at the present time (t=0), is denoted as y(0), then the concentration difference after the power limit specified time tp has elapsed (t=tp) is y(t)=y(0)e atp This is the result.

[0039] The ratio calculation unit 43 calculates a ratio value r that represents the ratio of the concentration difference to the concentration difference at decay. More specifically, the ratio calculation unit 43 defines the ratio value r as the proportion of the concentration difference at decay y(tp) to the initial concentration difference y(0). In other words, the ratio value r is expressed by equation (5).

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[0040] The diffusion approximation lithium concentration calculation unit 44 calculates the ratio value r and the lithium concentration C on the negative electrode surface. surf and the average lithium concentration C of the negative electrode ave Applying this to a pre-defined approximation function, the diffusion approximate lithium concentration Capprox This calculates the following. Various approximation functions can be considered depending on the specifications, but one example of an approximation function is expressed by equation (6).

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[0041] Next, the power limit calculation unit 33 will be explained. The power limit calculation unit 33 calculates a power limit value corresponding to the diffusion approximate lithium concentration based on a power limit map that maps the relationship between the diffusion approximate lithium concentration and the power limit value. Now, let's explain the power limit map. Figure 7 shows an example of a power limit map.

[0042] The example power limit map shown in Figure 7 has the diffusion-approximate lithium concentration on the horizontal axis and the power limit value on the vertical axis. In the power limit map, a curve for the power limit value against the diffusion-approximate lithium concentration is defined for each temperature. The power limit value curve is defined for each temperature, and in Figure 7, four power limit value curves are shown for -15°C, -20°C, -25°C, and -30°C. Furthermore, in Figure 7, the power limit value curve is defined so that the power limit value increases in the negative direction as the temperature increases. In other words, if the diffusion-approximate lithium concentration is the same, the absolute value of the power limit value increases as the temperature increases. The larger the absolute value of this power limit value, the greater the power that can be allowed to charge the secondary battery 10. In other words, the larger the absolute value of this power limit value, the greater the charging current that can be allowed to charge the secondary battery 10.

[0043] The power limit map is pre-generated and, for example, stored in the memory 25 of the power limit value setting device 11. Therefore, the method for generating the power limit map will now be explained. The power limit map is created by a numerical calculation process that provides a temperature variable corresponding to the battery temperature, a negative electrode average lithium concentration variable corresponding to the negative electrode average lithium concentration, and a power limit variable corresponding to the power limit value to the potential map and reaction overvoltage model in the physical battery model. Specifically, the negative electrode lithium temperature variable, which corresponds to the negative electrode average lithium concentration, is provided to the potential map to calculate the negative electrode open-circuit voltage for each power limit variable corresponding to the power limit value. Furthermore, the temperature variable corresponding to the battery temperature T and the negative electrode average lithium concentration variable are provided to the reaction overvoltage model to calculate the negative electrode reaction overvoltage for each power limit variable. Then, the negative electrode potential is calculated from the negative electrode open-circuit voltage and the negative electrode reaction overvoltage, and the values ​​corresponding to the negative electrode average lithium concentration variable and power limit variable when the negative electrode potential becomes 0V are set as the values ​​on the power limit map. By repeatedly performing this calculation process, the power limit map shown in Figure 7 can be created.

[0044] The process described above will be explained using a flowchart. Figure 8 shows a flowchart illustrating the procedure for creating a power limit map. In the flowchart shown in Figure 8, there are multiple candidate values ​​for the temperature variable T, the negative electrode average lithium concentration variable Cave, and the power limit variable PL, and the numbers of these candidate values ​​are denoted as l, n, and m, respectively. In Figure 8, the maximum values ​​of l, n, and m are denoted as L, N, and M, respectively.

[0045] The flowchart shown in Figure 8 illustrates, for example, the processing steps of a power limit map creation program when executed on a computer. In other words, the power limit map can be created through computer calculations. Furthermore, the potential map and reaction overvoltage model can utilize models determined during the design phase of the secondary battery 10.

[0046] As shown in Figure 8, the power limit map creation program first initializes the variable l to 1 and reads the first temperature variable T[l] (steps S11, S12). Next, it initializes the variable n to 1 and reads the first negative electrode average lithium concentration variable Cave[n] (steps S13, S14). Next, it initializes the variable m to 1 and reads the first power limit variable PL[m] (steps S15, S16).

[0047] Then, based on the variables read in steps S12, S14, and S16, the calculation processes in steps S17 to S20 are executed. In step S17, the negative electrode open circuit voltage "n" at the power limit variable PL[m] is calculated from the potential map using the negative electrode average lithium concentration variable Cave[n] as the key. In step S18, the negative electrode average lithium concentration variable Cave[n] and the temperature variable T[l] are input to the reaction overvoltage model to calculate the negative electrode reaction overvoltage[n] at the power limit variable PL[m]. In step S19, the negative electrode potential[n] is calculated from the negative electrode open circuit voltage[n] and the negative electrode reaction overvoltage[n]. Then, in step S20, it is determined whether or not the negative electrode potential[n] is 0V. Note that in step S20, the negative electrode potential[n] does not necessarily have to be exactly 0V; for example, it may be considered 0V if it is within a certain range, such as 0.1V to -0.1V.

[0048] In step S20, if it is determined that the negative electrode potential [0] is not 0V, the flowchart in Figure 8 updates the power limit variable PL[m] to the next candidate value and repeats the process in steps S16 to S20 (the NO branch in step S20). On the other hand, if it is determined in step S20 that the negative electrode potential [0] is not 0V, the flowchart in Figure 8 maps the power limit value PL[m] used in the calculation at that point to the power limit map as the power limit value corresponding to the temperature variable T[l] and the negative electrode average lithium concentration variable Cave[n] (step S22).

[0049] In the flowchart shown in Figure 8, first, the temperature variable [l] and the negative electrode average lithium concentration Cave[n] are determined, and the power limit variable is changed to determine the power limit value at which the negative electrode potential [n] becomes 0V (step S22). Then, while maintaining the temperature variable [l], the negative electrode average lithium concentration Cave[n] is shifted to the next candidate (step S23), and the power limit variable is changed again to determine the power limit value at which the negative electrode potential [n] becomes 0V (step S22). After that, the temperature variable [l] is shifted to the next candidate (step S24), and the negative electrode average lithium concentration variable Cave[n] and the power limit variable are changed again to determine the power limit value at which the negative electrode potential [n] becomes 0V (step S22). By performing this process, it becomes possible to generate a power limit map like the one shown in Figure 7.

[0050] As described above, according to the power limit value setting program, method and apparatus of Embodiment 1, the negative electrode average lithium concentration variable C is generated in the state estimation process using a physical battery model, which is performed in real time as a management process for the secondary battery 10. ave and the lithium concentration C on the negative electrode surface surf The diffusion approximate lithium concentration C is calculated using simple calculations (basic arithmetic operations) approx The power limit value is calculated from a pre-generated power limit map using the key. In this process, the power limit value setting program, method, and apparatus according to Embodiment 1 do not require convergence calculations to converge the numerical values, thus enabling faster power limit value setting. In other words, the power limit value setting program, method, and apparatus according to Embodiment 1 can easily update the power limit value in real time while the secondary battery 10 is in operation.

[0051] Furthermore, in the power limit value setting program, method, and apparatus according to Embodiment 1, even when the internal parameters change due to the use of the secondary battery 10, the lithium concentration estimation process (step S2) performed by the lithium concentration estimation unit 31 determines the negative electrode average lithium concentration variable C corresponding to the changed internal parameters. ave and the lithium concentration C on the negative electrode surface surf This is calculated. Therefore, the power limit value setting program, method and apparatus according to Embodiment 1 does not require prior testing to acquire the internal parameters of the secondary battery 10. In other words, the power limit value setting program, method and apparatus according to Embodiment 1 makes it possible to set a power limit value corresponding to changes in the internal parameters of the secondary battery 10 without performing prior testing to acquire the internal parameters of the secondary battery 10.

[0052] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of Symbols]

[0053] 1. Secondary battery system 10 Secondary battery 11 Power limit value setting device 12 Current Sensor 13 Temperature sensor 14 Voltage Sensor 20 Arithmetic section 21 Analog-to-Digital Converter 22 Analog-to-Digital Converters 23 Analog-to-Digital Converter 24 Communication Interfaces 25 memory 31 Lithium concentration estimation unit 32 Diffusion Approximation Calculation Unit 33 Power Limit Calculation Unit 41 Difference calculation part 42. Concentration difference calculation unit during decay 43 Ratio Calculation Unit 44 Diffusion Approximate Lithium Concentration Calculation Unit

Claims

1. A battery measurement process that acquires measured values ​​of the charge / discharge current and battery temperature of a secondary battery, A lithium concentration estimation process that applies the charge / discharge current and the battery temperature to the solid-phase diffusion model in the physical battery model used for estimating the state of the secondary battery to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode, A diffusion approximation calculation process that calculates the diffusion approximation lithium concentration by applying the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a predetermined approximation function, A power limit calculation process that calculates a power limit value corresponding to the diffusion approximate lithium concentration based on a power limit map that maps the relationship between the diffusion approximate lithium concentration and the power limit value, A power limit setting program that instructs a computer to perform this action.

2. In the diffusion approximation calculation process, A difference calculation process that calculates the difference between the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode as the concentration difference, A concentration difference calculation process at decay time is performed by referring to a concentration difference profile that shows the decay characteristics of the concentration difference using a predetermined function, and calculating the concentration difference on the concentration difference profile after a predetermined power limit time has elapsed from the present time as the concentration difference at decay time. A ratio calculation process that calculates a ratio value representing the ratio between the aforementioned concentration difference and the aforementioned concentration difference during decay, A diffusion approximate lithium concentration calculation process that calculates the diffusion approximate lithium concentration by applying the ratio value, the negative electrode surface lithium concentration, and the negative electrode average lithium concentration to the pre-set approximation function, A power limit value setting program according to claim 1, which causes a computer to execute the following.

3. The power limit map is created by a numerical calculation process that assigns a temperature variable corresponding to the battery temperature, a negative electrode average lithium concentration variable corresponding to the negative electrode average lithium concentration, and a power limit variable corresponding to the power limit value to the potential map and reaction overvoltage model in the physical battery model. The power limit value setting program according to claim 1, wherein the power limit calculation process refers to the power limit map stored in memory.

4. A battery measurement process that acquires measured values ​​of the charge / discharge current and battery temperature of a secondary battery, A lithium concentration estimation process that applies the charge / discharge current and the battery temperature to the solid-phase diffusion model in the physical battery model used for estimating the state of the secondary battery to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode, A diffusion approximation calculation process that calculates the diffusion approximation lithium concentration by applying the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a predetermined approximation function, A power limit calculation process that calculates a power limit value corresponding to the diffusion approximate lithium concentration based on a power limit map that maps the relationship between the diffusion approximate lithium concentration and the power limit value, A method for setting power limit values ​​to instruct a computer to perform a specific action.

5. A lithium concentration estimation unit that obtains measured values ​​of the charge / discharge current and battery temperature of a secondary battery, and applies the charge / discharge current and battery temperature to a solid-phase diffusion model in a physical battery model used for estimating the state of the secondary battery to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode, A diffusion approximation value calculation unit calculates the diffusion approximation lithium concentration by applying the lithium concentration on the surface of the negative electrode and the average lithium concentration of the negative electrode to a preset approximation function, A power limit calculation unit calculates a power limit value corresponding to the diffusion approximate lithium concentration based on a power limit map that maps the relationship between the diffusion approximate lithium concentration and the power limit value. A power limit value setting device having [a specific feature].

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