Computer program product including power limit value setting program, power limit value setting method, and power limit value setting device

Abstract

In a conventional method, when the internal parameters of a secondary battery change, there has been a problem that it is impossible to appropriately control the charge / discharge current. A power limit value setting program according to the present invention causes a computer to execute: a battery measurement process for acquiring measured values of a charge / discharge current and a battery temperature of a secondary battery; a lithium concentration estimation process for applying the charge / discharge current and the battery temperature to a solid phase diffusion model in a physical battery model for state estimation of the secondary battery, and estimating a negative electrode surface lithium concentration and a negative electrode average lithium concentration; a diffusion approximation value calculation process for calculating a diffusion approximation lithium concentration by applying the negative electrode surface lithium concentration and the negative electrode average lithium concentration to a preset approximation function; and a power limit calculation process that calculates a power limit value corresponding to the diffusion approximation lithium concentration on the basis of a power limit map that maps a relationship between the diffusion approximation lithium concentration and the power limit value.

Description

Technical Field

[0001] The present invention relates to a power limit setting procedure, a power limit setting method, and a power limit setting device for setting, for example, a limit value for the charging and discharging current of a secondary battery, i.e., a power limit value. Background Technology

[0002] In the use of secondary batteries, sometimes the maximum charge and discharge current is limited to prevent lithium from depositing on the negative electrode side. An example of such a technique for limiting the maximum charge and discharge current in a secondary battery is disclosed in Japanese Patent No. 5223920.

[0003] The battery charge / discharge control device described in Japanese Patent No. 5223920 includes an input allowable power adjustment unit. This input allowable power adjustment unit adjusts the input allowable power to the battery based on the charging history during charging and discharging to prevent the negative electrode potential of the battery, which is composed of a lithium-ion secondary battery, from dropping to the lithium reference potential. The input allowable power adjustment unit determines the input allowable power based on the allowable charging current and changes it in a manner that the allowable charging current is reduced according to the charging duration and increased according to the discharging duration. The allowable charging current is set as the maximum current that will prevent metallic lithium from being deposited at the negative electrode. Summary of the Invention

[0004] However, in the technology described in Japanese Patent No. 5223920, since test data obtained by conducting tests on secondary batteries in advance is used, there is a problem that the internal parameters of the secondary battery cannot be properly controlled when the secondary battery continues to be used and changes occur.

[0005] The present invention was made in view of the above circumstances, and its object is to control the charge and discharge current to suppress lithium deposition regardless of how the internal parameters of the secondary battery change.

[0006] Regarding one aspect of the computer program product containing a power limit setting procedure according to the present invention, the power limit setting procedure causes a computer to perform battery measurement processing, lithium concentration estimation processing, diffusion approximation calculation processing, and power limit calculation processing. The battery measurement processing acquires measured values ​​of the charge / discharge current and battery temperature of the secondary battery. The lithium concentration estimation processing applies the charge / discharge current and battery temperature to a solid-phase diffusion model in a physical battery model to estimate the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode. The physical battery model is used for state estimation of the secondary battery. The diffusion approximation calculation processing applies the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode to a pre-set approximation function to calculate the diffusion approximation lithium concentration. The power limit calculation processing calculates a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit mapping, wherein the power limit mapping maps the relationship between the diffusion approximation lithium concentration and the power limit value.

[0007] In one aspect of the power limit setting method of the present invention, a computer performs battery measurement processing, lithium concentration estimation processing, diffusion approximation calculation processing, and power limit calculation processing. The battery measurement processing acquires measured values ​​of the charge / discharge current and battery temperature of the secondary battery. The lithium concentration estimation processing applies the charge / discharge current and battery temperature to a solid-phase diffusion model in a physical battery model to estimate the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode. The physical battery model is used for state estimation of the secondary battery. The diffusion approximation calculation processing applies the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode to a pre-set approximation function to calculate the diffusion approximation lithium concentration. The power limit calculation processing calculates a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit mapping, wherein the power limit mapping maps the relationship between the diffusion approximation lithium concentration and the power limit value.

[0008] One aspect of the power limit setting device according to the present invention includes: a lithium concentration estimation unit that acquires measured values ​​of the charge / discharge current and battery temperature of a secondary battery, applies the charge / discharge current and battery temperature to a solid-phase diffusion model in a physical battery model, and estimates the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode, the physical battery model being used for state estimation of the secondary battery; a diffusion approximation calculation unit that applies the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode to a pre-set approximation function to calculate a diffusion approximation lithium concentration; and a power limit calculation unit that calculates a power limit value corresponding to the diffusion approximation lithium concentration based on a power limit mapping, the power limit mapping mapping being a mapping of the relationship between the diffusion approximation lithium concentration and the power limit value.

[0009] According to the power limit setting program, power limit setting method and power limit setting device of the present invention, the charging and discharging current for suppressing lithium deposition can be controlled regardless of how the internal parameters of the secondary battery change. Attached Figure Description

[0010] The above and other objects, features and advantages of this disclosure will be more fully understood from the following detailed description and accompanying drawings.

[0011] Figure 1 This diagram illustrates lithium deposition in a secondary battery.

[0012] Figure 2 This is a block diagram of a secondary battery system that applies the power limit setting procedure described in Implementation Method 1.

[0013] Figure 3 This is a flowchart illustrating the power limit value setting method involved in Implementation Method 1.

[0014] Figure 4 This is a block diagram of the power limit setting device according to Embodiment 1.

[0015] Figure 5 This is a graph illustrating the approximate lithium concentration during diffusion.

[0016] Figure 6 This is a graph illustrating the concentration difference curve showing the change in lithium concentration over time.

[0017] Figure 7 This is a diagram illustrating an example of power limit mapping.

[0018] Figure 8 This is a flowchart illustrating the process of creating a power limit mapping. Detailed Implementation

[0019] For clarity, appropriate omissions and simplifications have been made to the following descriptions and figures. Furthermore, the elements depicted in the figures as functional blocks performing various processes can be implemented in hardware as a central processing unit (CPU), memory, and other circuitry, or in software as a program loaded into memory. Therefore, those skilled in the art should understand that these functional blocks can be implemented in various forms, including but not limited to, hardware alone, software alone, or combinations thereof. It should be noted that the same reference numerals are used for the same elements in the figures, and repeated descriptions are omitted as necessary.

[0020] Furthermore, the aforementioned program includes a set of instructions (or software code) that, when read by a computer, causes the computer to perform one or more of the functions described in the embodiments. The program may be stored on a non-transitory computer-readable medium or a physical recording medium. By way of example, and not limitation, computer-readable media or physical storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD), Blu-ray disc or other optical disc storage, magnetic cartridges, magnetic tape, disk storage, or other magnetic storage devices. The program may be transmitted on a temporary computer-readable medium or a communication medium. By way of example, and not limitation, temporary computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagation signals.

[0021] Implementation Method 1

[0022] In the power limit setting procedure described in Embodiment 1, a power limit value is calculated. This power limit value is a limit on the charging and discharging power used to prevent lithium deposition on the negative electrode side of the secondary battery. Therefore, lithium deposition in the secondary battery will be explained.

[0023] Figure 1 A diagram illustrating lithium deposition in a secondary battery is shown. (See diagram for example.) Figure 1 As shown, in a secondary battery, the electrodes are configured such that a positive active material layer formed on the surface of the current collector on the positive electrode side and a negative active material layer formed on the surface of the current collector on the negative electrode side are facing each other across a separator (not shown). Lithium ions are embedded in these positive and negative active material layers. Additionally, a solid electrolyte interphase (SEI) film is formed on the surface of the negative active material layer. In the secondary battery, charging and discharging are performed by the acceptance and donation of lithium ions (Li+) between the positive and negative active material layers. Figure 1 The diagram shows the direction of lithium ion movement during charging.

[0024] In the negative electrode active material layer of a secondary battery, when the lithium-ion mobility is low and the charge / discharge current is high, lithium ions may sometimes accumulate on the surface of the negative electrode active material layer. Furthermore, the phenomenon where lithium ions accumulated on the surface of the negative electrode active material layer turn into metal and are deposited is called lithium deposition. To suppress this lithium deposition, it is necessary to control the charge / discharge current to avoid lithium ion accumulation on the surface of the negative electrode active material layer. More specifically, lithium deposition is considered to be largely influenced by two parameters: the concentration of solid-phase lithium in the negative electrode active material layer and the diffusion effect. The secondary battery can be controlled by allowing sufficient lithium-ion diffusion within the negative electrode active material layer to be achieved with a charge / discharge current, thereby suppressing lithium deposition. Therefore, in the secondary battery system 1 according to Embodiment 1, a power limit setting program is used to calculate a power limit value to suppress lithium deposition. The power limit setting program, power limit setting method, and power limit setting device will be described in detail below.

[0025] Figure 2 A block diagram of a secondary battery system using the power limit setting procedure described in Implementation Method 1 is shown. Figure 2 As shown, the secondary battery system 1 according to Embodiment 1 includes a secondary battery 10, a power limit 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. Alternatively, a single battery may be used instead of a battery pack. The secondary battery 10 is capable of supplying power to and from a power source.

[0026] The power limit setting device 11 is a device that utilizes part of the function of a state estimation processing device that estimates the state of the secondary battery 10. Figure 2 The diagram only shows the function for calculating power limit values. The state estimation processing unit, although... Figure 2 The diagram is omitted, but it has the function of providing state estimation values ​​other than output power limits, such as an estimate of the State of Charge (SOC) of the secondary battery 10. Furthermore, the power limit setting device 11 utilizes the physical battery model of the secondary battery used in the state estimation device in its calculations.

[0027] The current sensor 12 sends the measured value of the charging and discharging current of the secondary battery 10, Icd, to the power limit setting device 11. The temperature sensor 13 sends the measured value of the temperature of the secondary battery 10, T, to the power limit setting device 11. The voltage sensor 14 sends the measured value of the voltage difference between the positive and negative terminals of the secondary battery 10, Vb, to the power limit setting device 11. The power limit setting device 11 uses the values ​​sent from the various sensors to calculate the power limit value of the secondary battery 10. Details regarding the calculation and processing of the power limit value in the power limit setting device 11 will be described later.

[0028] Alternatively, the power limit setting device 11 can be implemented, for example, by a microcontroller unit (MCU) having an arithmetic unit 20 capable of executing programs. This power limit setting device 11 includes not only the arithmetic unit 20, but also analog-to-digital converters 21 to 23, a communication interface 24, and a memory 25.

[0029] Analog-to-digital converters 21 to 23 convert the analog values ​​of the input signals into digital values ​​and transmit them to the arithmetic unit 20. Analog-to-digital converter 21 is used to acquire the charging / discharging 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 to 23 function as battery measurement parameter acquisition units, acquiring the measured values ​​of the secondary battery, namely the charging / discharging current, battery temperature, and battery voltage.

[0030] The communication interface 24 sends the power limit value calculated by the arithmetic unit 20 to the host system of the circuit controlling the power supply target. The memory 25 stores information such as the program executed in the arithmetic unit 20 and intermediate data generated during the calculation in the arithmetic unit 20, and performs input / output.

[0031] In the secondary battery system 1 according to Embodiment 1, the power limit setting method performed in the arithmetic unit 20 has one characteristic. This power limit setting method can be implemented by the arithmetic unit 20 executing a power limit setting program, or it can be implemented by configuring the arithmetic unit 20 as dedicated hardware capable of implementing the power limit setting method. In the following description, an example of implementing a power limit setting program in the arithmetic unit 20 will be explained. It should be noted that when the arithmetic unit 20 is configured with dedicated hardware, it is sufficient to configure the hardware to perform the functions of the processing unit described below.

[0032] Next, the power limit setting method according to Embodiment 1 will be briefly described. Figure 3 A flowchart illustrating the power limit value setting method according to Embodiment 1 is shown.

[0033] like Figure 3 As shown, in the power limit setting method according to Embodiment 1, firstly, a battery measurement process is performed to obtain the measured values ​​of the charge / discharge current Icd and the battery temperature T (step S1). Next, a lithium concentration estimation process is performed, which applies the charge / discharge current Icd and the battery temperature T to a solid-phase diffusion model in a physical battery model to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode. This physical battery model is used for state estimation of the secondary battery (step S2). Afterward, a diffusion approximation calculation process is performed, which applies the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a pre-set approximation function to calculate the diffusion approximation lithium concentration (step S3).

[0034] Although various methods can be considered to calculate the diffusion approximation of lithium concentration, in Figure 3 As an example of diffusion approximation calculation processing, examples of differential calculation processing (step S31), concentration difference calculation processing during decay (step S32), ratio calculation processing (step S33), and diffusion approximation lithium concentration calculation processing (step S34) are shown.

[0035] In the differential calculation process, the difference between the lithium concentration on the negative electrode surface and the average lithium concentration of the negative electrode is used as the concentration difference for calculation (step S31). In the concentration difference calculation process during decay, the concentration difference on the concentration difference curve after a predetermined power limit time is used as the concentration difference during decay, referring to the concentration difference curve obtained by representing the decay characteristics of the concentration difference with a predetermined function (step S32). In the ratio calculation process, a ratio value representing the ratio between the concentration difference and the concentration difference during decay is calculated (step S33). In the diffusion approximate lithium concentration calculation process, the ratio value, the lithium concentration on the negative electrode surface, and the average lithium concentration of the negative electrode are applied to a predetermined approximate function to calculate the diffusion approximate lithium concentration (step S34).

[0036] Then, in the power limit value setting method according to Embodiment 1, a power limit calculation process is performed. This power limit calculation process is based on a power limit mapping to calculate a power limit value corresponding to the diffusion approximate lithium concentration. This power limit mapping maps the relationship between the diffusion approximate lithium concentration and the power limit value (step S4). It should be noted that the power limit mapping is a pre-prepared mapping, which has fixed content as long as there is no external update processing during the use of the secondary battery system 1.

[0037] Next, the power limit setting device 11, which is implemented by executing a power limit setting program in the arithmetic unit 20, will be described. Figure 4 A block diagram of the power limit setting device 11 according to Embodiment 1 is shown. Figure 4 As shown, the power limit setting device 11 includes a lithium concentration estimation unit 31, a diffusion approximation calculation unit 32, and a power limit calculation unit 33. Furthermore, the diffusion approximation calculation unit 32 includes a difference calculation unit 41, a concentration difference calculation unit 42 during decay, a ratio calculation unit 43, and a diffusion approximation lithium concentration calculation unit 44.

[0038] The lithium concentration estimation unit 31 acquires the measured values ​​of the charge / discharge current Icd and the battery temperature T of the secondary battery, and applies the charge / discharge current Icd and the battery temperature T to the solid-phase diffusion model in the physical battery model to estimate the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode. This physical battery model is used for state estimation of the secondary battery. Figure 4 In the example shown, in addition to the charge / discharge current Icd and the battery temperature T, the negative electrode lithium concentration correction value NLi_ofs is also input to the lithium concentration estimation unit 31. This negative electrode lithium concentration correction value NLi_ofs is a value calculated in other processes in the physical battery model, and is a value that improves the calculation accuracy. Even without using the negative electrode lithium concentration correction value NLi_ofs, it is possible to calculate the lithium concentration on the negative electrode surface and the average lithium concentration of the negative electrode.

[0039] The solid-state diffusion model is a state-space model that approximates and derives the solid-state diffusion equation. Using this model, estimates 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) based on lithium concentration can be calculated. This solid-state diffusion model is described in detail here.

[0040] The solid-phase diffusion model is a model for calculating the diffusion of a solid phase into space over time, and can numerically represent the change in lithium ion concentration. The solid-phase diffusion model derives the lithium concentration C at the negative electrode surface using formulas (1) to (4). surf and the average lithium concentration C of the negative electrode ave .

[0041] Specifically, in the case of a s The area ratio is given by A as the electrode and L as the reaction area. n Given the electrode heat and F as the Faraday constant, the ion flow rate area J Li This is expressed by formula (1).

[0042] [Calculation Formula 1]

[0043]

[0044] Furthermore, in R n Given the radius of the negative electrode active material, the average lithium concentration C within the negative electrode active material is... ave This is expressed by formula (2).

[0045] [Calculation Formula 2]

[0046]

[0047] Furthermore, when the lithium diffusion coefficient in the solid phase is set as D... s In the case of [condition], the volume-average concentration flow rate q is expressed by formula (3). It should be noted that since the lithium diffusion coefficient depends on temperature, the lithium diffusion coefficient is a function of the battery temperature T.

[0048] [Calculation Formula 3]

[0049]

[0050] Moreover, the surface lithium concentration C within the negative electrode active material surf This is expressed by formula (4).

[0051] [Calculation Formula 4]

[0052]

[0053] Lithium concentration C on the negative electrode surface surf and the average lithium concentration C of the negative electrode ave The difference in values ​​is due to the influence of diffusion within the active material. Lower diffusion values ​​make it more difficult for lithium ions to diffuse within the active material, thus causing them to accumulate on the surface. Conversely, higher diffusion values ​​make it easier for lithium ions to diffuse, thus reducing the likelihood of lithium deposition.

[0054] The diffusion approximation calculation unit 32 calculates the lithium concentration C on the negative electrode surface by... surf and the average lithium concentration C of the negative electrode ave The approximate lithium concentration for diffusion is calculated using a predefined approximation function. The approximate lithium concentration for diffusion is explained here. Figure 5 A graph illustrating the approximate lithium concentration at the diffusion surface is shown. The lithium concentration C at the negative electrode surface is used. surf and the average lithium concentration C of the negative electrode ave The diffusion approximate lithium concentration is calculated using the concentration difference. The diffusion approximate lithium concentration is the equivalent steady-state value of an active material with a lithium-ion concentration difference (steady-state: no lithium concentration difference, lithium concentration C at the negative electrode surface). surf and the average lithium concentration C of the negative electrode ave Same). In Figure 5 In the figure, the lithium concentration C on the negative electrode surface is shown by a dashed line. surf With the average lithium concentration of the negative electrode C aveThe lithium-ion concentration gradient within the active material in the presence of a concentration difference is represented by a linear approximation of the lithium concentration at the negative electrode surface, showing the relationship with the lithium concentration C. surf and the average lithium concentration C of the negative electrode ave The equivalent lithium-ion concentration in a stable state without a concentration difference. In the diffusion approximation calculation unit 32, the lithium concentration C at the negative electrode surface before reaching the stable state is used. surf and the average lithium concentration C of the negative electrode ave To calculate the approximate lithium concentration for this diffusion.

[0055] exist Figure 4 In the specific example shown, the diffusion approximation calculation unit 32 includes a difference calculation unit 41, a concentration difference calculation unit 42 during decay, a ratio calculation unit 43, and a diffusion approximation lithium concentration calculation unit 44. The difference calculation unit 41 calculates the lithium concentration C from the negative electrode surface. surf Subtract the average lithium concentration C of the negative electrode ave The resulting concentration difference C diff (=C surf -C ave ).

[0056] The concentration difference calculation unit 42 calculates the concentration difference during decay by referring to the concentration difference curve obtained by expressing the decay characteristics of the concentration difference as a predetermined function, and taking the concentration difference on the concentration difference curve after a predetermined power limit time from the current time point as the concentration difference during decay. Therefore, the concentration difference curve will be explained. Figure 6 A graph illustrating the change in lithium concentration over time is shown.

[0057] There is a difference between the lithium concentration at the negative electrode surface and the average lithium concentration inside the active material. The concentration difference curve is calculated assuming the battery is at rest until the lithium concentration at the negative electrode surface equals the average lithium concentration at the negative electrode. As an example of this concentration difference curve, such as... Figure 6 As shown, it can be modeled using an exponential function with time as the variable. In Figure 6 In the example shown, the function of the concentration difference line in the concentration difference curve is y(t) = y(0)e at Furthermore, if the concentration difference at the current time point (t=0), i.e., the initial concentration difference, is set as y(0), the concentration difference after the power-limited time tp (t=tp) is y(t) = y(0)e atp .

[0058] The ratio calculation unit 43 calculates a ratio value r that represents the ratio between the concentration difference and the concentration difference at decay. More specifically, the ratio calculation unit 43 uses the degree to which the concentration difference y(tp) at decay is proportional to the initial concentration difference y(0) as the ratio value r. That is, the ratio value r is expressed by formula (5).

[0059] [Calculation Formula 5]

[0060]

[0061] The diffusion approximate 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 The approximate lithium concentration C is calculated by applying a predefined approximation function. approx Approximation functions can be considered in various ways depending on the specifications. An example of an approximation function is represented by formula (6).

[0062] [Calculation Formula 6]

[0063]

[0064] Next, the power limitation calculation unit 33 will be explained. The power limitation calculation unit 33 calculates a power limitation value corresponding to the diffusion approximate lithium concentration based on a power limitation mapping, which maps the relationship between the diffusion approximate lithium concentration and the power limitation value. Here, the power limitation mapping will be explained. Figure 7 A diagram illustrating an example of power limit mapping is shown.

[0065] exist Figure 7 In the example of the power limitation mapping shown, the horizontal axis is set to the diffusion approximate lithium concentration, and the vertical axis is set to the power limitation value. In the power limitation mapping, a curve of the power limitation value versus the diffusion approximate lithium concentration is specified for each temperature. Furthermore, the curve of the power limitation value is specified for each temperature. Figure 7 The diagram shows curves for four power limit values: -15℃, -20℃, -25℃, and -30℃. Additionally, in... Figure 7 The power limit value is defined by a curve where the higher the temperature, the larger the negative power limit value. That is, if the diffusion is approximately the same for the same lithium concentration, the higher the temperature, the larger the absolute value of the power limit. The larger the absolute value of this power limit, the greater the permissible charging power for the secondary battery 10. In other words, the larger the absolute value of this power limit, the greater the permissible charging current for the secondary battery 10.

[0066] The power limitation map is pre-generated, for example, stored in the memory 25 of the power limitation value setting device 11. Therefore, the method for generating the power limitation map will be described. The power limitation map is generated through numerical computation processing, which 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 limitation variable corresponding to the power limitation value to the potential mapping and reaction overvoltage model in the physical battery model. Specifically, the variable corresponding to the negative electrode average lithium concentration, i.e., the negative electrode lithium temperature variable, is provided to the potential mapping, and the negative electrode open-circuit voltage corresponding to each power limitation variable is calculated. In addition, the temperature variable corresponding to the battery temperature T and the negative electrode average lithium concentration variable are provided to the reaction overvoltage model, and the negative electrode reaction overvoltage for each power limitation variable is calculated. Moreover, the negative electrode potential is calculated based on the negative electrode open-circuit voltage and the negative electrode reaction overvoltage, and the value corresponding to the negative electrode average lithium concentration variable and the power limitation variable when the negative electrode potential is 0V is used as the value on the power limitation map. Furthermore, by repeatedly performing such computation processing, it is possible to generate... Figure 7 The power limit mapping is shown.

[0067] The above process is illustrated using a flowchart. Therefore, Figure 8 A flowchart illustrating the process of creating a power limit map is shown. Figure 8 In the flowchart shown, the temperature variable T, the average lithium concentration variable Cave (anode), and the power limitation variable PL each have multiple candidate values, which are numbered l, n, and m, respectively. Additionally, in Figure 8 In the above, the maximum values ​​of l, n, and m are set as L, N, and M, respectively.

[0068] Figure 8 The flowchart shown illustrates the processing steps of a power limit mapping creation program, for example, when executed on a computer. That is, the power limit mapping can be created through computer computation. Furthermore, the potential mapping and reactive overvoltage model can utilize models determined during the design phase of the secondary battery 10.

[0069] like Figure 8 As shown, in the power limit mapping process, variable 1 is first initialized with 1, and the first temperature variable T[l] is read (steps S11, S12). Next, variable n is initialized with 1, and the first negative electrode average lithium concentration variable Cave[n] is read (steps S13, S14). Next, variable m is initialized with 1, and the first power limit variable PL[m] is read (steps S15, S16).

[0070] Then, based on the variables read in steps S12, S14, and S16, the calculation processes in steps S17 to S20 are performed. In step S17, the negative electrode average lithium concentration variable Cave[n] is used as a key, and the negative electrode open-circuit voltage "n" when the power limit variable PL[m] is calculated according to the potential mapping. In step S18, the negative electrode average lithium concentration variable Cave[n] and the temperature variable T[l] are input into the reaction overvoltage model, and the negative electrode reaction overvoltage [n] when the power limit variable PL[m] is calculated. In step S19, the negative electrode potential [n] is calculated based on the negative electrode open-circuit voltage [n] and the negative electrode reaction overvoltage [n]. Then, in step S20, it is determined whether the negative electrode potential [n] is 0V. It should be noted that in step S20, the negative electrode potential [n] may not be completely 0V; it may be considered as 0V as long as it is within a certain range, such as 0.1V to -0.1V.

[0071] In step S20, if it is determined that the negative electrode potential [0] is not 0V, then... Figure 8 In the flowchart, the power limit variable PL[m] is updated to the next candidate value, and the processing of steps S16 to S20 is performed again (the "No" branch of step S20). On the other hand, in step S20, if it is determined that the negative electrode potential [0] is not 0V, Figure 8 In the flowchart, the power limit value PL[m] used to calculate at this time point is used as the power limit value corresponding to the temperature variable T[l] and the negative electrode average lithium concentration variable Cave[n], and is mapped in the power limit mapping (step S22).

[0072] exist Figure 8 In the flowchart shown, firstly, the temperature variable [l] and the average lithium concentration Cave[n] at the negative electrode are determined, and the power limit variable is changed, while simultaneously determining the power limit value when the negative electrode potential [n] is 0V (step S22). Then, while maintaining the temperature variable [l], the average lithium concentration Cave[n] at the negative electrode is moved to the next candidate (step S23), and the power limit variable is changed again, while simultaneously determining the power limit value when the negative electrode potential [n] is 0V (step S22). Then, the temperature variable [l] is moved to the next candidate (step S24), and the average lithium concentration variable Cave[n] and the power limit variable are changed again, while simultaneously determining the power limit value when the negative electrode potential [n] is 0V (step S22). By performing this process, a process can be generated. Figure 7 The power limit mapping is shown.

[0073] Based on the above explanation, according to the power limit setting procedure, method, and apparatus involved in Embodiment 1, the negative electrode average lithium concentration variable C generated in the state estimation process will be used. ave and lithium concentration C on the negative electrode surfacesurf The approximate lithium concentration C obtained through diffusion is calculated using simple arithmetic operations (the basic level of arithmetic). approx The power limit value is calculated based on a pre-generated power limit mapping, and this state estimation process is performed in real time as a management process for the secondary battery 10, using a physical battery model. In this process, the power limit value setting procedure, method, and apparatus according to Embodiment 1 do not require convergence calculations to achieve numerical convergence, thus enabling high-speed power limit value setting. That is, in the power limit value setting procedure, method, and apparatus according to Embodiment 1, the power limit value can be easily updated in real time during the operation of the secondary battery 10.

[0074] Furthermore, in the power limit setting procedure, method, and apparatus described in Embodiment 1, even when the internal parameters change due to the use of the secondary battery 10, the negative electrode average lithium concentration variable C corresponding to the changed internal parameters can be calculated through the lithium concentration estimation process (step S2) performed by the lithium concentration estimation unit 31. ave and lithium concentration C on the negative electrode surface surf Therefore, in the power limit setting procedure, method, and apparatus according to Embodiment 1, prior testing for obtaining the internal parameters of the secondary battery 10 is not required. That is, in the power limit setting procedure, method, and apparatus according to Embodiment 1, the power limit value corresponding to the change of the internal parameters of the secondary battery 10 can be set without performing prior testing for obtaining the internal parameters of the secondary battery 10.

[0075] It should be noted that the present invention is not limited to the above embodiments, and appropriate modifications can be made without departing from the spirit of the invention.

Claims

1. A computer program product including a power limit value setting procedure, wherein, The power limit setting program enables the computer to perform battery measurement processing, lithium concentration estimation processing, diffusion approximation calculation processing, and power limit calculation processing. The battery measurement process obtains the measured values ​​of the charging and discharging current and battery temperature of the secondary battery. The lithium concentration estimation process applies the charge / discharge current and the battery temperature to the solid-phase diffusion model in the physical battery model to estimate the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode. This physical battery model is used for state estimation of the secondary battery. The diffusion approximation calculation process applies the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a pre-defined approximation function to calculate the diffusion approximation lithium concentration. The power limitation calculation process is based on a power limitation mapping, which calculates the power limitation value corresponding to the diffusion approximate lithium concentration. The power limitation mapping maps the relationship between the diffusion approximate lithium concentration and the power limitation value.

2. The computer program product including a power limit value setting program according to claim 1, wherein, In the diffusion approximation calculation process, the computer performs differential calculation, concentration difference calculation during decay, ratio calculation, and diffusion approximation lithium concentration calculation. The differential calculation process uses the difference between the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode as the concentration difference for calculation. The concentration difference calculation during decay is performed by referring to the concentration difference curve obtained by representing the decay characteristics of the concentration difference with a specified function. The concentration difference on the concentration difference curve after a predetermined power limit time has elapsed from the current time point is used as the concentration difference during decay. The ratio calculation process calculates a ratio value representing the ratio between the concentration difference and the concentration difference at decay. The diffusion approximate lithium concentration calculation process applies the ratio value, the negative electrode surface lithium concentration, and the negative electrode average lithium concentration to a pre-defined approximation function to calculate the diffusion approximate lithium concentration.

3. The computer program product including a power limit value setting program according to claim 1, wherein, The power limitation mapping is created through numerical computation, which provides the potential mapping and reaction overvoltage model in the physical battery model with 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 limitation variable corresponding to the power limitation value. In the power limitation calculation process, the power limitation mapping stored in memory is referenced.

4. A method for setting a power limit value, wherein, The power limit setting method enables the computer to perform battery measurement processing, lithium concentration estimation processing, diffusion approximation calculation processing, and power limit calculation processing. The battery measurement process obtains the measured values ​​of the charging and discharging current and battery temperature of the secondary battery. The lithium concentration estimation process applies the charge / discharge current and the battery temperature to the solid-phase diffusion model in the physical battery model to estimate the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode. This physical battery model is used for state estimation of the secondary battery. The diffusion approximation calculation process applies the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode to a pre-defined approximation function to calculate the diffusion approximation lithium concentration. The power limitation calculation process is based on a power limitation mapping, which calculates the power limitation value corresponding to the diffusion approximate lithium concentration. The power limitation mapping maps the relationship between the diffusion approximate lithium concentration and the power limitation value.

5. A power limit setting device, wherein, The power limit setting device has: The lithium concentration estimation unit acquires the measured values ​​of the charge / discharge current and battery temperature of the secondary battery, applies the charge / discharge current and battery temperature to the solid-phase diffusion model in the physical battery model, and estimates the lithium concentration on the negative electrode surface and the average lithium concentration on the negative electrode. The physical battery model is used for state estimation of the secondary battery. A diffusion approximation calculation unit applies the lithium concentration at the negative electrode surface and the average lithium concentration at the negative electrode to a pre-set approximation function to calculate the diffusion approximation lithium concentration; and The power limitation calculation unit calculates a power limitation value corresponding to the diffusion approximate lithium concentration based on a power limitation mapping, wherein the power limitation mapping maps the relationship between the diffusion approximate lithium concentration and the power limitation value.

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