JP6171897B2 - Approximation function creation program, approximation function creation method, approximation function creation device, and charging rate estimation program - Google Patents

Description

  The present invention relates to an approximation function creation program, an approximation function creation method, an approximation function creation device, and a charging rate estimation program.

  Conventionally, a secondary battery that can be repeatedly used by charging is known. Examples of the secondary battery include a lithium ion secondary battery. In order to know how much of the remaining electric power is stored in the secondary battery, it is important for operation to accurately calculate the state of charge (SoC). Thus, for example, a technique for estimating the charging rate of the secondary battery from the terminal voltage of the secondary battery using a Kalman filter is known.

JP 2009-234557 A JP 2012-139025 A

  By the way, in the secondary battery, there is a correlation between the voltage of the terminal in a state where no load is applied, so-called open circuit voltage (OCV) and the charging rate. The correlation between the OCV and the charging rate can be expressed by a characteristic curve. By accurately functionalizing this characteristic curve, the estimation accuracy of the charging rate of the secondary battery is improved.

  On the other hand, when the Kalman filter handles a nonlinear function, the amount of calculation greatly increases. For this reason, when estimating the charging rate of a secondary battery using a Kalman filter, if a non-linear function is used as a characteristic curve, the calculation load increases. For this reason, for example, an engineer obtains an approximate function in which a characteristic curve is approximated by a broken line by trial and error.

  However, the characteristic curve may not be approximated accurately by trial and error by an engineer. Further, the characteristic curve of the secondary battery changes depending on the type. For this reason, it is difficult for an engineer to create an approximate function of each characteristic curve by trial and error.

  In one aspect, an object of the present invention is to provide an approximation function creation program, an approximation function creation method, an approximation function creation device, and a charging rate estimation program capable of accurately approximating a characteristic curve.

  The approximate function creation program according to one aspect causes a computer to execute a process of acquiring characteristic curve data indicating a correlation between an open circuit voltage of a secondary battery and a charging rate of the secondary battery. Further, the approximate function creation program causes the computer to move the intermediate point while moving the intermediate point within a range where the change rate of the open circuit voltage with respect to the charging rate of the characteristic curve indicated by the acquired data is equal to or less than a predetermined threshold. For each position, a process for calculating the similarity is executed. The approximate function creation program uses a computer to approximate the approximate line obtained by approximating the characteristic curve data of each divided range obtained by dividing the range with the intermediate point as the boundary, and the characteristic curve data used for approximating the approximate line. Let the degree be calculated. Further, the approximate function creation program causes the computer to execute a process of generating an approximate function that approximates the characteristic curve using the approximate straight line of each divided range with the calculated intermediate point as the boundary.

  The characteristic curve can be approximated with high accuracy.

FIG. 1 is a diagram schematically illustrating an example of a flow in which a lithium ion battery is used. FIG. 2 is a diagram showing the overall configuration of the approximate function creation device. FIG. 3 is a diagram illustrating an example of a characteristic curve. FIG. 4 is a diagram schematically illustrating an example of an approximate line for each division range. FIG. 5 is a diagram schematically illustrating an example of an approximate line of the low charge rate portion. FIG. 6 is a diagram schematically illustrating an example of an approximate line of the high charge rate portion. FIG. 7 is a diagram schematically illustrating an example of the switching point. FIG. 8 is a diagram illustrating an example of the generated approximate function. FIG. 9 is a diagram illustrating an example of an approximate function for discharging and an approximate function for charging. FIG. 10 is a flowchart showing the procedure of the approximate function creation process. FIG. 11 is a diagram illustrating an example of a computer that executes an approximate function creation program.

  Hereinafter, an approximate function creating program, an approximate function creating method, an approximate function creating device, and a charge rate estimating program according to the present application will be described with reference to the accompanying drawings. Note that this embodiment does not limit the disclosed technology. Each embodiment can be appropriately combined within a range in which processing contents are not contradictory.

[Secondary battery]
First, the secondary battery will be briefly described. Examples of the secondary battery include a lithium ion secondary battery. Hereinafter, a lithium ion secondary battery will be described as an example of the secondary battery. Hereinafter, the lithium ion secondary battery is also referred to as a lithium ion battery.

  Lithium ion batteries are used in various devices such as personal computers, mobile phones, electric cars, and electric motorcycles. For example, in an electric vehicle, an electric motorcycle, or the like, it is known to replace a secondary battery such as a lithium ion battery together with a module so as to eliminate a loss of usage time due to charging time. As described above, since lithium ion batteries are used in various devices, it is important to obtain a charging rate with high accuracy.

  FIG. 1 is a diagram schematically illustrating an example of a flow in which a lithium ion battery is used. In the example of FIG. 1, a schematic configuration of the lithium ion battery 10 is shown. The lithium ion battery 10 includes a cell 11 and a control chip 12. The cell 11 is a component capable of storing and discharging electric power by a chemical change. The control chip 12 is a control IC (Integrated Circuit) that controls the lithium ion battery 10. The control chip 12 includes a storage unit 12A such as a nonvolatile memory. The storage unit 12A stores various programs and various information used for controlling the lithium ion battery 10. For example, the storage unit 12A stores a charging rate estimation program for estimating the charging rate. Further, for example, various kinds of information used for estimating the charging rate is stored in the storage unit 12A. As an example, the storage unit 12A stores information on an approximate function that approximates a characteristic curve. The approximate function information is created by the approximate function creating device 20 based on, for example, measurement data obtained by measuring the electrical characteristics of the cell 11 through experiments or the like. The characteristics of the lithium ion battery 10 are different for each type such as a model number. Further, the lithium ion battery 10 may have different characteristics for each manufactured unit or individual. The approximate function information may be created by obtaining measurement data for each type of lithium ion battery 10 or may be created by obtaining measurement data for each unit or individual. The lithium ion battery 10 is mounted and used in various devices 21. The control chip 12 functions as a processing unit that performs various controls by operating various programs. For example, the control chip 12 has an estimation unit 12B as a processing unit by operating a charging rate estimation program. The control chip 12 estimates the charging rate based on various information such as the terminal voltage of the lithium ion battery 10 and information on the approximate function stored in the storage unit 12A. For example, the control chip 12 estimates the charging rate using a Kalman filter. The control chip 12 performs various controls. For example, when the charge rate of the cell 11 is estimated and the cell 11 is overcharged or overdischarged, the control chip 12 performs control to cut off the current from the terminal used for charging and discharging power.

  Note that characteristics of the secondary battery such as the lithium ion battery 10 may change over time. For this reason, the information stored in the storage unit 12A may be updatable. For example, the storage unit 12A of the control chip 12 stores a program that can generate information on the approximate function, the control chip 12 measures the characteristic curve of the cell 11, and generates information on the approximate function based on the measured measurement data. May be. In this case, the control chip 12 or the lithium ion battery 10 functions as the approximate function creation device 20. Further, the approximate function information may be updated via the network 23. For example, the device 21 transmits measurement data obtained by measuring the characteristic curve of the cell 11 to the approximate function creation device 20 via the network 23. The approximate function creation device 20 may return information on the approximate function created based on the measurement data via the network 23 to update the information stored in the storage unit 12A.

  Next, the approximate function creation device 20 according to the first embodiment will be described. FIG. 2 is a diagram showing the overall configuration of the approximate function creation device. As shown in FIG. 2, the approximate function creating apparatus 20 includes an external I / F (interface) unit 30, a display unit 31, an input unit 32, a storage unit 33, and a control unit 34. Note that the approximate function creation device 20 may have various functional units included in a known computer in addition to the functional units illustrated in FIG.

  The external I / F unit 30 is an interface that inputs and outputs information with other devices. For example, the external I / F unit 30 is an interface that performs communication control with other devices. As an aspect of the external I / F unit 30, a network interface card such as a LAN card can be employed. For example, the external I / F unit 30 receives measurement data 40 indicating the electrical characteristics of the cell 11 measured by an experiment or the like from another device. The external I / F unit 30 may be an interface such as a USB (Universal Serial Bus) port.

  The display unit 31 is a display device that displays various types of information. Examples of the display unit 31 include display devices such as an LCD (Liquid Crystal Display) and a CRT (Cathode Ray Tube). The display unit 31 displays various information.

  The input unit 32 is an input device that inputs various types of information. For example, examples of the input unit 32 include input devices such as a mouse and a keyboard. The input unit 32 receives an operation input from an administrator or the like, and inputs operation information indicating the received operation content to the control unit 34.

  The storage unit 33 is a storage device that stores various data. For example, the storage unit 33 is a storage device such as a hard disk, an SSD (Solid State Drive), or an optical disk. Note that the storage unit 33 may be a semiconductor memory that can rewrite data, such as a random access memory (RAM), a flash memory, and a non-volatile static random access memory (NVSRAM).

  The storage unit 33 stores an OS (Operating System) executed by the control unit 34 and various programs. For example, the storage unit 33 stores various programs used for creating the approximate function. Furthermore, the storage unit 33 stores various data used in the program executed by the control unit 34. For example, the storage unit 33 stores the measurement data 40. The storage unit 33 can also store other electronic data in addition to the information exemplified above.

  The measurement data 40 is data obtained by measuring the electrical characteristics of the cell 11 through experiments or the like. In the present embodiment, as the measurement data 40, voltage change data 41 obtained by measuring the voltage change of the terminal when the current flowing through the terminal used for charging / discharging the power of the lithium ion battery 10 is prepared. For example, voltage change data 41 is prepared by measuring changes in the voltage of the terminal of the lithium ion battery 10 when the value of the current flowing through the terminal of the lithium ion battery 10 is changed without changing the sign. In addition, voltage change data 41 is prepared by measuring changes in the voltage of the terminal of the lithium ion battery 10 when the sign of the current flowing through the terminal of the lithium ion battery 10 is changed. For example, voltage change data 41 is prepared by measuring the voltage change when the current flowing through the terminal of the lithium ion battery 10 is switched from 5A to 10A and when the current is switched from -10A to 10A. In this embodiment, when the sign of current is positive, it is in a charged state in which current flows to the lithium ion battery 10, and when the sign of current is negative, it is in a discharged state in which current flows from the lithium ion battery 10. To do.

  Further, in this embodiment, as the measurement data 40, the characteristic data 42 of the characteristic curve showing the correlation between the OCV and the charging rate when the charging rate of the lithium ion battery 10 is charged from 0% to 100% with a constant current is used. prepare. In the present embodiment, as the measurement data 40, characteristic data 42 of a characteristic curve showing the correlation between the OCV and the charging rate when the charging rate of the lithium ion battery 10 is discharged from 100% to 0% at a constant current is used. prepare.

  FIG. 3 is a diagram illustrating an example of a characteristic curve. The example of FIG. 3 shows a characteristic curve indicating the correlation between the OCV of the lithium ion battery 10 and the charging rate stored in the characteristic data 42. As shown in FIG. 3, there is a correlation between the OCV and the charging rate of the lithium ion battery 10. The lithium ion battery 10 has hysteresis during charging and discharging, and the correlation between the OCV and the charging rate may be different between charging and discharging. In the example of FIG. 3, a characteristic curve 60 at the time of charging and a characteristic curve 61 at the time of discharging are shown. In the characteristic curves 60 and 61, the change in the OCV with respect to the change in the charge rate is large in the range where the charge rate is high and the range where the charge rate is low.

  The control unit 34 has an internal memory for storing programs defining various processing procedures and control data, and executes various processes using these. As shown in FIG. 2, the control unit 34 includes an acquisition unit 50, a first calculation unit 51, a second calculation unit 52, a third calculation unit 53, a generation unit 54, and an output unit 55.

  The acquisition unit 50 is a processing unit that acquires various types of information. For example, the acquisition unit 50 acquires characteristic curve data. For example, the acquiring unit 50 acquires characteristic curve data by reading the characteristic data 42 stored in the storage unit 33. In the present embodiment, since the characteristic data 42 is stored in the storage unit 33, the acquisition unit 50 acquires the characteristic data 42 from the storage unit 33. However, the present invention is not limited to this. When the characteristic data 42 is stored in another device, the acquisition unit 50 may acquire the characteristic data 42 from the other device via the network 23.

The first calculation unit 51 is a processing unit that performs various calculations. For example, the first calculator 51 calculates an error due to hysteresis from the voltage change data 41 from the characteristic curve during charging and the characteristic curve during discharging. For example, the first calculation unit 51 obtains the amount of change in current and the amount of change in voltage when the current flowing from the lithium ion battery 10 is switched from the voltage change data 41. For example, when the current is switched from 5A to 10A, the amount of change in the current is 5A. The amount of change in voltage when this current is switched from 5 A to 10 A is defined as V ₁ . Further, when the current is switched from −10 A to 10 A, the amount of change in the current is 20 A. The amount of change in voltage when this current is switched from −10 A to 10 A is V ₂ . When the resistance generated with respect to the current change is R ₀ and the error due to the hysteresis due to the switching of the sign of the flowing current is H, the following relations (1) and (2) are established.

5 × R ₀ = V ₁ (1)
20 × R ₀ + H = V ₂ (2)

The coefficient “5” multiplied by R ₀ in this equation (1) is the amount of change in current when the current is switched from 5A to 10A. The coefficient “20” multiplied by R ₀ in equation (2) is the amount of change in current when the current is switched from −10 A to 10 A.

  From the equations (1) and (2), the following equation (3) is obtained. That is, when the current flowing through the terminal of the lithium ion battery 10 is changed by changing the sign, the current change amount and the voltage change amount, and when the current flowing through the terminal is changed without changing the sign, The error H due to hysteresis can be calculated from the amount of change and the amount of change in voltage.

H = V ₂ -4 × V ₁ (3)

  The first calculation unit 51 changes the amount of change in current and voltage when the current flowing through the terminal of the lithium ion battery 10 is changed by changing the sign, and the amount of change in current without changing the sign. The error H is calculated from the amount of change in current and the amount of change in voltage. In this embodiment, the error H due to hysteresis is calculated from the amount of change in current and the amount of change in voltage when the current flowing through the terminal is changed, but the error H due to hysteresis may be obtained from the characteristic data 42. For example, the first calculation unit 51 may set the difference in voltage between the characteristic curve during charging and the characteristic curve during discharging shown in FIG.

  Here, as shown in FIG. 3, the characteristic curve shows a large change in the OCV with respect to the change in the charge rate in the high charge rate portion where the charge rate is high and the low charge rate portion where the charge rate is low, and the change in the charge rate in the center portion The change in OCV with respect to is small. When linearly approximating such a characteristic curve, linear approximation is performed by dividing a high charge rate portion, a central portion, and a low charge rate portion.

  The second calculation unit 52 is a processing unit that performs linear approximation of the central portion of the characteristic curve. First, the 2nd calculation part 52 specifies the boundary of a high charge rate part and a center part, and a center part and a low charge rate part. For example, the second calculation unit 52 specifies a range in which the change rate of the open circuit voltage with respect to the charging rate of the characteristic curve is equal to or less than a predetermined threshold as the central portion. This threshold is determined by an administrator or the like to a value that can be regarded as a stable range of change in the open circuit voltage with respect to the charging rate, and is set to 500, for example. For example, the second calculation unit 52 obtains the change rate of the open circuit voltage with respect to the charge rate in order from the charge rate of 50%, which is the center of the characteristic curve, to the high charge rate side, and the charge rate at which the change rate exceeded the threshold first. Is the boundary on the high charge rate side. Further, the second calculation unit 52 obtains the change rate of the open circuit voltage with respect to the charge rate in order from the charge rate of 50% to the low charge rate side, and first calculates the charge rate at which the change rate exceeded the threshold value on the low charge rate side. Boundary. The characteristic curve used for determining the boundary may be a characteristic curve at the time of charging or a characteristic curve at the time of discharging, and a characteristic curve obtained by averaging the characteristic curve at the time of charging and the characteristic curve at the time of charging. There may be. In addition, the second calculation unit 52 may use a charge rate at which the rate of change exceeds a threshold value in either one of the characteristic curve at the time of charging or the characteristic curve at the time of discharge as a boundary. The rate may be the boundary. A central portion is between the boundary on the high charge rate side and the boundary on the low charge rate side.

  The second calculation unit 52 corrects the characteristic curve at the time of charging and the characteristic curve at the time of discharging according to the error H due to hysteresis. For example, the second calculation unit 52 subtracts H / 2 from the voltage of each charging rate of the characteristic curve at the time of charging, adds H / 2 to the voltage of each charging rate of the characteristic curve at the time of discharging, The error H is corrected by half. The second calculation unit 52 may correct only one of the characteristic curve during charging and the characteristic curve during discharging. For example, the 2nd calculation part 52 may perform correction | amendment which subtracts H from the voltage of each charge rate of the characteristic curve at the time of charge.

  The second calculator 52 calculates data of an average characteristic curve from the corrected characteristic curve during charging and the characteristic curve during discharging. For example, the second calculation unit 52, for each predetermined step width from the boundary on the low charge rate side, in the characteristic curve at the time of charging and the characteristic curve at the time of discharging, the latest charging rate larger than the charging rate of the step size, The voltage at the latest charging rate is specified. Then, the second calculating unit 52 calculates the average characteristic curve data by averaging the specified charging rate and voltage for each step size. For example, when the charge rate at the low charge rate side boundary is 0.1 and the step size is 0.05, the most recent charge rate greater than 0.15 in the characteristic curve at the time of charge is a, and the voltage , C, the latest charge rate greater than 0.15 in the characteristic curve during discharge is b, and the voltage is d. In this case, the second calculation unit 52 calculates average characteristic curve data by setting the charging rate to (a + b) / 2 and the voltage to (c + d) / 2.

  The second calculation unit 52 moves the intermediate point within the range of the central portion. Then, the second calculation unit 52 divides the range of the central portion for each intermediate point position with the intermediate point as a boundary, and approximate straight lines approximating the average characteristic curve data of each divided range, The degree of similarity with the data of the average characteristic curve used for approximation of the approximate line is calculated. For example, the second calculation unit 52 moves the intermediate point with a predetermined step size from the boundary on the low charge rate side. Each time the intermediate point moves, the second calculator 52 divides the range of the central portion with the intermediate point as a boundary. Then, for each divided range, the second calculation unit 52 obtains an approximate line that approximates the data of the average characteristic curve in the divided range.

  FIG. 4 is a diagram schematically illustrating an example of an approximate line for each division range. In the example of FIG. 4, a boundary C1 on the low charging rate side and a boundary C2 on the high charging rate side are shown. In the example of FIG. 4, the range of the central portion between the boundary C1 and the boundary C2 is divided into two divided ranges by an intermediate point, and an approximate straight line L1 that approximates the characteristic curve data of the divided ranges for each divided range. , L2 is shown.

The second calculator 52 obtains the similarity between the approximate straight line and the average characteristic curve for each divided range. For example, the second calculation unit 52 obtains the determination coefficient R ² as the similarity between the approximate line and the average characteristic curve. The index used as the degree of similarity is not limited to the determination coefficient R ² , and may be any as long as it shows the degree of similarity between the approximate line and the average.

The second calculation unit 52 identifies the approximate straight line of each divided range with the middle point having the highest similarity as the boundary as the approximate straight line of the central portion range. For example, the second calculation unit 52 identifies an approximate straight line in each divided range with an intermediate point having the highest determination coefficient R ^{2 as} an approximate straight line in the range of the central portion.

  In the present embodiment, as shown in FIG. 4, an example is described in which the middle portion is one and the range of the central portion is divided into two divided ranges by the middle point, but a plurality of middle points may be provided. The range of the central portion may be divided into three or more divided ranges. For example, the second calculation unit 52 moves the plurality of intermediate points within the range of the central portion, and divides the range of the central portion with the plurality of intermediate points as boundaries. Then, the second calculation unit 52 approximates the average characteristic curve data of each divided range for each of the plurality of intermediate points, and the average characteristic curve data used to approximate the approximate line. The degree of similarity may be calculated. For example, when two intermediate points are provided, the first intermediate point and the second intermediate point, the second calculation unit 52 moves the first intermediate point from the low charging rate side boundary to the high charging rate side boundary. Let Then, every time the second calculation unit 52 moves the first intermediate point, the second calculation unit 52 moves the second intermediate point from the position of the first intermediate point to the boundary on the high charge rate side, thereby reducing the range of the central portion. The first intermediate point and the second intermediate point are used as a boundary to divide into three divided ranges. Then, the second calculator 52 uses, for each of the positions of the first intermediate point and the second intermediate point, an approximate straight line approximating the data of the average characteristic curve of each divided range, and an approximation of the approximate straight line. The similarity with the average characteristic curve data may be calculated.

  The third calculation unit 53 is a processing unit that performs linear approximation of the high charge rate portion and the low charge rate portion. For example, the third calculation unit 53 calculates an approximate straight line approximating data in a range where the charging rate is equal to or higher than the boundary on the high charging rate side, and an approximate straight line approximating data in the range where the charging rate is equal to or lower than the boundary on the low charging rate side. Ask.

  Here, the characteristic curve at the time of charging may include the influence of the transient characteristic due to the current change when charging is started in the low charging rate portion. In addition, the characteristic curve at the time of discharge may include the influence of the transient characteristic due to the current change when the discharge is started in the high charge rate portion.

  Therefore, the third calculation unit 53 calculates an approximate straight line that approximates the data of the characteristic curve at the time of discharging for the low charge rate portion. In addition, the third calculation unit 53 calculates an approximate straight line that approximates the characteristic curve data at the time of charging for the high charge rate portion.

  FIG. 5 is a diagram schematically illustrating an example of an approximate line of the low charge rate portion. In the example of FIG. 5, an approximate straight line L3 that approximates the data of the characteristic curve at the time of discharge is shown. FIG. 6 is a diagram schematically illustrating an example of an approximate line of the high charge rate portion. In the example of FIG. 6, an approximate straight line L4 that approximates the characteristic curve data during charging is shown.

  The generation unit 54 is a processing unit that generates an approximate function approximating the characteristic curve. For example, the generation unit 54 generates a characteristic curve using the approximate straight line specified by the second calculation unit 52 and the approximate straight line of the low charge rate portion and the approximate straight line of the high charge rate portion calculated by the third calculation unit 53. Generate an approximate function. At this time, the generation unit 54 generates an approximate function using an intersection of approximate lines with adjacent ranges as a switching point of the approximate lines.

  FIG. 7 is a diagram schematically illustrating an example of the switching point. In the example of FIG. 7, an intersection point between the approximate line L1 and the approximate line L2 is set as a switch point of the approximate line.

  FIG. 8 is a diagram illustrating an example of the generated approximate function. In the example of FIG. 8, a line L5 by an approximate function generated from the characteristic curve at the time of discharging and the characteristic curve at the time of charging is shown.

  The generating unit 54 changes the generated approximate function according to the error H to approximate an approximate function for discharging and approximates a characteristic curve for discharging, and an approximate function for charging that approximates the characteristic curve for charging. Generate. For example, the generation unit 54 generates an approximate function for discharging by subtracting H / 2 from the voltage of each charging rate of the approximate function. Further, the generation unit 54 adds H / 2 to the voltage of each charging rate of the approximate function to generate an approximate function for charging. The change corresponding to the error H is preferably changed at a rate corresponding to the correction of the error H by the second calculation unit 52. For example, when the second calculating unit 52 performs correction by subtracting H / 2 from the generated characteristic curve and adding H / 2 to the characteristic curve during discharge, the generating unit 54 sets the approximate function to H / 2. The subtracting change is performed to generate an approximate function for discharging, and the subtracting function is added to H / 2 to generate an approximate function for charging.

  FIG. 9 is a diagram illustrating an example of an approximate function for discharging and an approximate function for charging. In the example of FIG. 9, a line L6 of the approximate function for discharge obtained by subtracting H / 2 from the line L5 by the approximate function is shown. In the example of FIG. 9, an approximate function line L7 for charging obtained by adding H / 2 to the line L5 by the approximate function is shown.

  The output unit 55 is a processing unit that performs various outputs. For example, the output unit 55 outputs information on the approximate function generated by the generation unit 54. The output by the output unit 55 may store information on the approximate function in the storage unit 33. Further, the output by the output unit 55 may display information on the display unit 31. The output by the output unit 55 may output information to an external device via the external I / F unit 30.

  Information on the output approximate function is stored in the storage unit 12 </ b> A of the control chip 12 of the lithium ion battery 10. The estimation unit 12B of the control chip 12 acquires the information of the approximate function from the storage unit 12A. And the estimation part 12B estimates the charging rate of the lithium ion battery 10 using the information of the acquired approximate function. For example, the estimation unit 12B measures the current and terminal voltage of the lithium ion battery 10. This terminal voltage includes noise and the like. Accordingly, the estimation unit 12B estimates the charging rate by the Kalman filter using the information of the approximate function from the terminal voltage. For this reason, the control chip 12 can estimate the charging rate with high accuracy using the information of the approximate function.

  Note that various integrated circuits and electronic circuits can be employed for the control unit 34. Further, a part of the functional unit included in the control unit 34 may be another integrated circuit or an electronic circuit. For example, an ASIC (Application Specific Integrated Circuit) is an example of the integrated circuit. Examples of the electronic circuit include a central processing unit (CPU) and a micro processing unit (MPU).

[Process flow]
Subsequently, a flow of an approximate function creation process in which the approximate function creation device 20 according to the present embodiment creates an approximate function will be described. FIG. 10 is a flowchart showing the procedure of the approximate function creation process. The approximate function creation process is started at a predetermined timing, for example, at a timing when the creation of an approximate function is instructed from another device via the input unit 32 or the external I / F unit 30.

  As shown in FIG. 10, the acquisition unit 50 acquires characteristic curve data by reading the characteristic data 42 stored in the storage unit 33 (S10). The first calculator 51 calculates an error H due to hysteresis between the characteristic curve at the time of charging and the characteristic curve at the time of discharging (S11). The 2nd calculation part 52 specifies the boundary of a high charge rate part, a center part, and a center part and a low charge rate part (S12). The second calculator 52 corrects the characteristic curve at the time of charging and the characteristic curve at the time of discharging according to the error H due to hysteresis, and calculates an average characteristic curve (S13).

  The second calculation unit 52 approximates each of the characteristic curves of the divided ranges obtained by dividing the range with the intermediate point as a boundary for each position of the intermediate point while moving the intermediate point within the range of the central portion. Then, the similarity with the data used for the approximation of the approximate straight line is calculated (S14). And the 2nd calculation part 52 specifies the approximate straight line of each division | segmentation range on the boundary of the intermediate point with the highest similarity (S15). The 3rd calculation part 53 calculates | requires the approximate straight line which approximated the data of the low charge rate part, and the approximate straight line which approximated the data of the high charge rate part (S16).

  The generation unit 54 generates an approximate function that approximates the characteristic curve using the approximate straight line in the central portion, the approximate straight line in the high charge rate portion, and the approximate straight line in the low charge rate portion (S17). The generating unit 54 changes the generated approximate function according to the error H to generate an approximate function for discharging that approximates a characteristic curve at the time of discharge and an approximate function for charging that approximates the characteristic curve at the time of charging. (S18), and the process ends.

[Effect of Example 1]
As described above, the approximate function creation device 20 acquires characteristic curve data indicating the correlation between the open circuit voltage of the secondary battery and the charging rate of the secondary battery. The approximate function creation device 20 moves the intermediate point within a range where the change rate of the open circuit voltage with respect to the charging rate of the characteristic curve indicated by the acquired characteristic curve data is equal to or less than a predetermined threshold. Then, the approximate function creation device 20 uses the approximate line obtained by approximating the characteristic curve data of each divided range obtained by dividing the range at the intermediate point for each position of the intermediate point, and used to approximate the approximate line. The similarity with the characteristic curve data is calculated. The approximate function creation device 20 generates an approximate function that approximates the characteristic curve using an approximate line in each divided range with the calculated intermediate point as the boundary. Thereby, the approximate function creating apparatus 20 can accurately approximate the characteristic curve.

  In addition, the approximate function creation device 20 generates an approximate function using an intersection of approximate lines with adjacent division ranges as a switching point of the approximate line. Thereby, the approximate function creation apparatus 20 according to the present embodiment can generate an approximate function that can smoothly switch the approximate line.

  Further, the approximate function creation device 20 calculates an error due to hysteresis between the characteristic curve at the time of charging the secondary battery and the characteristic curve at the time of discharging. The approximate function creation device 20 uses the data obtained by correcting the characteristic curve data at the time of charging and the data of the characteristic curve at the time of discharging after performing correction according to the error, and the approximate straight line and the approximate straight line. The similarity with the data used for the approximation is calculated. The approximate function creation device 20 changes the approximate function according to the error to generate an approximate function that approximates the characteristic curve during discharging and an approximate function that approximates the characteristic curve during charging. Thereby, the approximate function creating apparatus 20 can generate an approximate function for discharging that approximates a characteristic curve at the time of discharging and an approximate function for charging that approximates the characteristic curve at the time of charging.

  Further, the approximate function creation device 20 calculates an approximate straight line that approximates the characteristic curve data during charging for a high charge rate range in which the charge rate is higher than the range of the characteristic curve. The approximate function creation device 20 calculates an approximate straight line that approximates the data of the characteristic curve at the time of discharge for the low charge rate range where the charge rate is lower than the range of the characteristic curve. The approximate function creation device 20 further generates an approximate function by further using the approximate straight lines of the calculated high charge rate range and low charge rate range. The approximate function creation device 20 intersects the approximate straight line of the high charge rate range with the approximate straight line of the divided range on the highest charge rate range side, and the approximate straight line of the low charge rate range and the closest charge rate range side. Approximate functions are generated with the intersection of the divided range with the approximate line as the switching point of the approximate line. Thereby, the approximate function creating apparatus 20 according to the present embodiment can accurately generate an approximate function including the high charge rate range and the low charge rate range.

  Although the embodiments related to the disclosed apparatus have been described above, the present invention may be implemented in various different forms other than the above-described embodiments. Therefore, another embodiment included in the present invention will be described below.

  For example, in the above-described embodiment, the case where a lithium ion battery is used as the secondary battery has been described, but the disclosed apparatus is not limited thereto. The secondary battery may be a lithium ion polymer secondary battery, a calcium ion secondary battery, a nanowire battery, a nickel metal hydride secondary battery, or a lead storage battery. Moreover, as a lithium ion battery, it is applicable also to a lithium cobalt ion battery, a lithium iron phosphate battery, etc. Thereby, the charge rate of various batteries can be measured.

[Distribution and integration]
In addition, each component of each illustrated apparatus does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to that shown in the figure, and all or a part thereof may be functionally or physically distributed or arbitrarily distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. For example, the acquisition unit 50, the first calculation unit 51, the second calculation unit 52, the third calculation unit 53, the generation unit 54, and the output unit 55 of the above embodiment are connected as an external device of the approximate function creation device 20 via a network. You may do it. Further, the acquisition unit 50, the first calculation unit 51, the second calculation unit 52, the third calculation unit 53, the generation unit 54, and the output unit 55 of the above-described embodiment are respectively provided by different devices, and are connected via a network to cooperate. Thus, the function of the above approximate function creation device 20 may be realized.

[Approximate function creation program]
The various processes described in the above embodiments can be realized by executing a prepared program on a computer such as a personal computer or a workstation. In the following, an example of a computer that executes an approximate function creation program having the same function as that of the above-described embodiment will be described with reference to FIG. FIG. 11 is a diagram illustrating an example of a computer that executes an approximate function creation program.

  As shown in FIG. 11, the computer 300 includes a central processing unit (CPU) 310, a read only memory (ROM) 320, a hard disk drive (HDD) 330, and a random access memory (RAM) 340. These units 310 to 340 are connected via a bus 400.

  The ROM 320 stores in advance an approximate function creation program 320a that exhibits the same function as each processing unit of the above embodiment. For example, the approximate function creation program 320a that performs the same functions as the acquisition unit 50, the first calculation unit 51, the second calculation unit 52, the third calculation unit 53, the generation unit 54, and the output unit 55 of the above embodiment is stored. . Note that the approximate function creation program 320a may be separated as appropriate.

  Then, the CPU 310 reads the approximate function creation program 320a from the ROM 320 and executes it, thereby executing the same operation as in the above embodiment. That is, the approximate function creation program 320a performs the same operations as the acquisition unit 50, the first calculation unit 51, the second calculation unit 52, the third calculation unit 53, the generation unit 54, and the output unit 55 of the above embodiment.

  The approximate function creation program 320a described above does not necessarily need to be stored in the ROM 320 from the beginning. The approximate function creation program 320 a may be stored in the HDD 330.

  The ROM 320 may store a charging rate estimation program for estimating the charging rate. In this case, a charging rate estimation program that exhibits the same function as the estimation unit 12B of the above embodiment is stored. Note that the charging rate estimation program may be appropriately separated.

  In this case, the CPU 310 reads the charge rate estimation program from the ROM 320 and executes it, thereby executing the same operation as in the above embodiment. That is, the charging rate estimation program performs the same operation as that of the estimation unit 12B.

  Note that the above-described charging rate estimation program is not necessarily stored in the ROM 320 from the beginning. The charging rate estimation program may be stored in the HDD 330.

  Further, for example, the program is stored in a “portable physical medium” such as a flexible disk (FD), a CD-ROM, a DVD disk, a magneto-optical disk, an IC card or the like inserted into the computer 300. Then, the computer 300 may read and execute the program from these.

  Further, for example, the program is stored in a “portable physical medium” such as a flexible disk (FD), a CD-ROM, a DVD disk, a magneto-optical disk, an IC card or the like inserted into the computer 300. Then, the computer 300 may read and execute the program from these.

  Furthermore, the program is stored in “another computer (or server)” connected to the computer 300 via a public line, the Internet, a LAN, a WAN, or the like. Then, the computer 300 may read and execute the program from these.

DESCRIPTION OF SYMBOLS 10 Lithium ion battery 20 Approximate function creation apparatus 33 Memory | storage part 34 Control part 40 Measurement data 41 Voltage change data 42 Characteristic data 50 Acquisition part 51 1st calculation part 52 2nd calculation part 53 3rd calculation part 54 Generation part 55 Output part

Claims (7)

The computer obtains the characteristic curve data showing the correlation between the open circuit voltage of the secondary battery and the charging rate of the secondary battery,
Within the range where the change rate of the open circuit voltage with respect to the charging rate of the characteristic curve indicated by the acquired characteristic curve data is below a predetermined threshold, the intermediate point is delimited at each intermediate point position while moving the intermediate point. And calculating the similarity between the approximate line obtained by approximating the characteristic curve data of each divided range obtained by dividing the range and the characteristic curve data used for approximation of the approximate line,
An approximate function creation program that executes processing for generating an approximate function that approximates a characteristic curve using an approximate straight line of each divided range with an intermediate point having the highest similarity as a boundary. The approximation function creating program according to claim 1, wherein the generating process generates an approximate function using an intersection of approximate lines with adjacent division ranges as a switching point of the approximate line. The data of the characteristic curve includes data of a characteristic curve at the time of charging the secondary battery and data of a characteristic curve at the time of discharging,
On the computer,
Further executing a process of calculating an error due to hysteresis between the characteristic curve at the time of charging the secondary battery and the characteristic curve at the time of discharging,
In the process of calculating the similarity, the similarity is calculated using data obtained by correcting the characteristic curve data during charging and the characteristic curve data during discharging after performing correction according to the error. And
The generating process includes generating an approximate function approximating a characteristic curve at the time of discharging and an approximate function approximating a characteristic curve at the time of charging by changing the approximate function according to the error. Item 3. An approximation function creation program according to item 1 or 2. On the computer,
For the high charging rate range where the charging rate is higher than the range of the characteristic curve, calculate an approximate straight line approximating the characteristic curve data during charging, and for the low charging rate range where the charging rate is lower than the range during discharging To further execute a process of calculating an approximate straight line that approximates the characteristic curve data of
The processing to be generated further uses the approximate straight lines of the calculated high charge rate range and low charge rate range, and the intersection of the approximate straight line of the high charge rate range and the approximate straight line of the divided range on the highest charge rate range side And generating an approximate function with the intersection of the approximate straight line in the low charge rate range and the approximate straight line in the divided range on the lowest charge rate range side as the switching point of the approximate straight line, respectively. The approximate function creation program described. The computer obtains characteristic curve data showing the correlation between the open circuit voltage of the secondary battery and the charging rate of the secondary battery,
Within the range where the change rate of the open circuit voltage with respect to the charging rate of the characteristic curve indicated by the acquired characteristic curve data is below a predetermined threshold, the intermediate point is delimited at each intermediate point position while moving the intermediate point. As an approximation straight line approximating the characteristic curve data of each divided range obtained by dividing the range, and the similarity between the characteristic curve data used for approximating the approximate straight line is calculated,
An approximation function creating method characterized by executing a process of generating an approximation function approximating a characteristic curve using an approximation straight line in each divided range with a calculated intermediate point as the boundary. An acquisition unit for acquiring data of a characteristic curve indicating a correlation between an open circuit voltage of the secondary battery and a charging rate of the secondary battery;
Within the range where the change rate of the open circuit voltage with respect to the charging rate of the characteristic curve indicated by the characteristic curve data acquired by the acquisition unit is equal to or less than a predetermined threshold, for each position of the intermediate point while moving the intermediate point, A calculation unit that calculates the similarity between the approximate line obtained by approximating the characteristic curve data of each divided range obtained by dividing the range with the intermediate point as a boundary, and the characteristic curve data used for approximation of the approximate line;
A generation unit that generates an approximate function that approximates a characteristic curve using an approximate straight line of each divided range with a middle point having the highest similarity calculated by the calculation unit;
An approximate function creation device characterized by comprising: The rate of change of the open circuit voltage with respect to the charging rate of the characteristic curve indicated by the characteristic curve data indicating the correlation between the open circuit voltage of the secondary battery and the charging rate of the secondary battery is less than a predetermined threshold. For each position of the intermediate point while moving the intermediate point within the range, an approximate straight line approximating the characteristic curve data of each divided range obtained by dividing the range with the intermediate point as a boundary, and for approximating the approximate straight line The degree of similarity with the characteristic curve data was calculated, and information on the approximation function that approximated the characteristic curve generated using the approximate straight line of each divided range with the highest calculated similarity as the boundary is obtained. And
A charge rate estimation program for executing a process of estimating a charge rate of the secondary battery using information of the obtained approximate function.

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