A method and device for automatically fitting parameters of a second-order RC equivalent circuit model

Abstract

The present invention provides a method and device for automatically fitting parameters of a second-order RC equivalent circuit model. The automatic fitting process of the second-order RC equivalent circuit model comprises first acquiring HPPC test data and obtaining a data set of calibration points based on the HPPC test data; then automatically fitting the HPPC test data to obtain initial parameter values ​​of the second-order RC equivalent circuit model at the calibration points; and finally, obtaining the RC parameters of the second-order RC equivalent circuit model based on the data set of calibration points and the initial interval parameter values ​​of the calibration points. The automatic fitting method of the present invention can improve the efficiency and accuracy of parameter fitting in a second-order RC equivalent circuit model.

Description

Technical Field

[0001] The present invention relates to data processing technology, and in particular to an automatic fitting method and device for second-order RC equivalent circuit model parameters. Background Art

[0002] In battery management systems, the second-order RC equivalent circuit model of lithium batteries is widely used. However, the parameters in the second-order RC equivalent circuit model require a large number of HPPC (Hybrid Pulse Power Characteristic) tests and are obtained through fitting methods.

[0003] Currently, parameter fitting is primarily performed using the cftool fitting tool provided by MATLAB. In battery management systems, pulse voltage curves vary significantly across different SOC (State of Charge) ranges, and parameters also vary somewhat across different pulse rates. Therefore, manual fitting is required to fit the parameters of the second-order RC equivalent circuit model across different pulse rates and SOC ranges. However, manual fitting is labor-intensive and prone to errors, resulting in poor efficiency and accuracy. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a method and device for automatically fitting the parameters of a second-order RC equivalent circuit model, so as to solve the problems of poor efficiency and low accuracy in manual fitting in the prior art.

[0005] To achieve the above and other related objectives, the present invention provides a method for automatically fitting parameters of a second-order RC equivalent circuit model, comprising at least the following steps:

[0006] Acquire HPPC test data, and obtain a data set of calibration points based on the HPPC test data;

[0007] Automatically fitting the HPPC test data to obtain initial parameter values ​​of a second-order RC equivalent circuit model at calibration points;

[0008] The RC parameters of the second-order RC equivalent circuit model are obtained according to the data set of the calibration points and the initial values ​​of the interval parameters of the calibration points.

[0009] Preferably, the data set of calibration points obtained according to the HPPC test data includes:

[0010] Determining the breakpoints of each calibration point in the HPPC test data according to the pulse current change;

[0011] The corresponding data set is obtained according to the voltage data corresponding to the breakpoints of each calibration point.

[0012] Preferably, the breakpoints of each calibration point of the HPPC test data within the full range of SOC are determined according to the change of the pulse current;

[0013] The calibration points include pulse points and rest points; correspondingly, the breakpoints of the pulse points are the pulse start point and the pulse end point, and the breakpoints of the rest point are the rest start point and the rest end point.

[0014] Preferably, the method of determining the breakpoints of each calibration point in the HPPC test data according to the change of the pulse current is:

[0015] If the current value at the k-1th moment satisfies -N<I k-1 <N, and the current value at time k+1 satisfies M<I k-1 <H, where M is much larger than N, then time k is the pulse starting point, and time k+Δt1 is the pulse end point; time k+Δt1+1 is the hold starting point, and time k+Δt1+Δt2 is the hold end point, where Δt1 is the pulse time and Δt2 is the hold time.

[0016] Preferably, the automatic fitting process for the HPPC test data to obtain the initial parameter values ​​of the second-order RC equivalent circuit model at the calibration point includes:

[0017] Determine the second-order RC equivalent circuit model;

[0018] Converting the second-order RC equivalent circuit model to obtain a fitting model;

[0019] Automatic fitting processing is performed on the HPPC test data to obtain initial values ​​of interval parameters of the fitting model at calibration points.

[0020] Preferably, the automatic fitting process adopts the nonlinear least square method of the LM algorithm.

[0021] Preferably, the process of automatically fitting the HPPC test data to obtain the initial values ​​of the interval parameters of the fitting model at the calibration points includes:

[0022] Divide the entire SOC interval into n SOC intervals;

[0023] Extract a section of pulse voltage data in each SOC interval from the data set of the calibration point to obtain the regional pulse voltage data of the calibration point in each SOC interval;

[0024] The pulse voltage data of each SOC interval is processed to obtain the initial value of the interval parameter.

[0025] Preferably, the process of obtaining the RC parameters of the second-order RC equivalent circuit model according to the data set of the calibration points and the initial values ​​of the interval parameters of the calibration points includes:

[0026] Obtaining a pulse voltage fitting result of the calibration point in each interval according to the interval parameter initial value of the calibration point and the zone pulse voltage data of the corresponding interval in the data set of the calibration point;

[0027] The pulse voltage fitting results of all intervals of the calibration points are fitted to obtain the parameter values ​​of the fitting model;

[0028] The RC parameters of the second-order RC equivalent circuit model are obtained according to the parameter values ​​of the fitting model.

[0029] To achieve the above-mentioned objectives and other related objectives, the present invention also provides an automatic fitting device for second-order RC equivalent circuit model parameters, comprising a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, the steps of the above-mentioned method for automatic fitting of second-order RC equivalent circuit model parameters are implemented.

[0030] As described above, the method and device for automatically fitting the parameters of the second-order RC equivalent circuit model of the present invention have the following beneficial effects:

[0031] The automatic fitting process for the parameters of a second-order RC equivalent circuit model proposed in the present invention first obtains HPPC test data and, based on the HPPC test data, generates a dataset of calibration points. Automatic fitting is then performed on the HPPC test data to obtain initial parameter values ​​for the second-order RC equivalent circuit model at the calibration points. Finally, the RC parameters of the second-order RC equivalent circuit model are obtained based on the dataset of calibration points and the initial interval parameter values ​​at the calibration points. This automatic fitting method improves the efficiency and accuracy of parameter fitting in a second-order RC equivalent circuit model. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Shown is a flow chart of the automatic fitting method for the second-order RC equivalent circuit model parameters of the present invention.

[0033] Figure 2 Shown is a schematic diagram of HPPC test data of an embodiment of the present invention.

[0034] Figure 3 Shown is a schematic diagram of the results of the automatic fitting device for the second-order RC equivalent circuit model parameters of the present invention. DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] See also Figure 1-3 It should be noted that the diagrams provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Therefore, the diagrams only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0037] The present invention divides the HPPC test intervals into segments based on the SOC intervals, automatically fitting the HPPC test data for each segmented SOC interval, and then automatically fitting all intervals as a whole, thereby efficiently and accurately achieving rapid fitting of the parameters of the second-order RC equivalent circuit model. Based on this technical concept, the present invention proposes a method and device for automatically fitting the parameters of the second-order RC equivalent circuit model.

[0038] Method Example:

[0039] like Figure 1 The flow chart of the automatic fitting method of the second-order RC equivalent circuit model parameters of the present invention is shown below. Figure 1 The automatic fitting method of the second-order RC equivalent circuit model parameters of the present invention is introduced in detail.

[0040] S1, obtaining HPPC test data, and obtaining a data set of calibration points based on the HPPC test data; the calibration points include pulse points and rest points;

[0041] In the present invention, during the HPPC test, the battery is charged with a set pulse current, then paused for a certain period of time before being charged again with a constant pulse current. Therefore, the calibration points in the HPPC test data include the pulse point and the pause point; the HPPC test data includes pulse voltage data and pulse current data.

[0042] S11, determining the breakpoints of each calibration point in the HPPC test data according to the change of the pulse current;

[0043] The calibration points of the present invention include pulse points and rest points. The breakpoints of the pulse points are the pulse starting point and the pulse end point, and the breakpoints of the rest point are the rest starting point and the rest end point.

[0044] Specifically, the breakpoints of each calibration point of the HPPC test data within the full range of SOC are determined according to the change of the pulse current;

[0045] SOC (State of Charge) is a physical quantity that reflects the remaining condition of the battery and is defined as the ratio of the remaining battery capacity to the battery capacity.

[0046] In view of the small fluctuations in current in actual testing, if the pulse current change meets the set conditions, the pulse start point, pulse end point, shelving start point and shelving end point are determined according to the time corresponding to the pulse current change.

[0047] Specifically, if the current value at the k-1th moment satisfies -N<I k-1 <N, and the current value at time k+1 satisfies M<I k-1 <H, where M is much larger than N, then time k is the pulse starting point, and time k+Δt1 is the pulse end point; time k+Δt1+1 is the hold starting point, and time k+Δt1+Δt2 is the hold end point, where Δt1 is the pulse time and Δt2 is the hold time.

[0048] In the embodiment of the present invention, a 45A charging HPPC is used as an example to perform a test and obtain HPPC test data. Figure 2 As shown, according to the change of pulse current, if the current value at the k-1 moment satisfies -0.5 k-1 <0.5, and the current value at k+1 satisfies 44.5 k-1 <45.5, then k is the pulse starting point, k+Δt1 is the pulse end point; k+Δt1+1 is the hold starting point, k+Δt1+Δt2 is the hold end point, where Δt1 is the pulse time and Δt2 is the hold time.

[0049] Traverse the full range of SOC in the HPPC test data and obtain the breakpoints of all calibration points.

[0050] S12, obtaining a corresponding data set according to the voltage data corresponding to the breakpoints of each calibration point;

[0051] The data set of the pulse point includes a pulse start voltage data set and a pulse end voltage data set, and the data set of the rest point includes a rest start voltage data set and a rest end voltage data set;

[0052] Specifically, the voltage data corresponding to all pulse starting points at the calibration points within the SOC range are collected and recorded as a pulse starting point voltage data set bp1, the voltage data corresponding to all pulse end points are collected and recorded as a pulse end point voltage data set bp2, the voltage data corresponding to all shelving starting points are collected and recorded as a shelving starting point voltage data set bp3, and the voltage data corresponding to all shelving end points are collected and recorded as a shelving end point voltage data set bp4.​​

[0053] S2, performing automatic fitting processing on the HPPC test data to obtain initial parameter values ​​of the second-order RC equivalent circuit model at the calibration point;

[0054] S21, determine the second-order RC equivalent circuit model;

[0055] In the embodiment of the present invention, the HPPC test process involves a pulse phase and a rest phase after the pulse, wherein the pulse phase is a zero-state response and the rest phase after the pulse is a zero-input response; therefore:

[0056] The zero-state response of the second-order RC equivalent circuit model is:

[0057]

[0058] The zero input state of the second-order RC equivalent circuit model is:

[0059]

[0060] S22, converting the second-order RC equivalent circuit model to obtain a fitting model; the fitting model includes a pulse fitting model and a shelf fitting model;

[0061] Pulse phase:

[0062] The pulse fitting model obtained by converting the zero-state response of the second-order RC equivalent circuit model is:

[0063]

[0064] Shelf phase after pulse:

[0065] The shelved fitting model obtained by converting the zero input state of the second-order RC equivalent circuit model is:

[0066]

[0067] S23, performing automatic fitting processing on the HPPC test data to obtain initial values ​​of interval parameters of the fitting model at calibration points;

[0068] The present invention adopts the nonlinear least square method of the LM (Levenberg-Marquardt) algorithm to perform automatic fitting processing.

[0069] The present invention processes the pulse fitting model and the shelving fitting model respectively to obtain the initial value of the parameter of the pulse point and the initial value of the parameter of the shelving point;

[0070] In the embodiment of the present invention, the zero-state response of a second-order RC equivalent circuit model is taken as an example to illustrate the nonlinear least squares fitting process.

[0071]

[0072] Where A is the parameter set a0, a1, a2, a3, a4 to be optimized and estimated, and t is the pulse time.

[0073] Since different initial values ​​A0 have a great influence on the number of iterations and parameter solution of the LM algorithm, the present invention performs the following iterative fitting process according to the characteristics of RC parameter fitting:

[0074] S231, dividing the entire SOC interval into n SOC intervals;

[0075] In the present invention, the entire SOC range (0%-100%) is divided into n intervals according to percentages, where n>2. The proportions of each interval can be equal or unequal. For example, if n is 5 and the SOC is divided equally, then the first interval is 0%-20%, the second interval is 21%-40%, the third interval is 41%-60%, the fourth interval is 61%-80%, and the fifth interval is 81%-100%.

[0076] In the embodiment of the present invention, the full SOC interval is divided into n intervals. Correspondingly, the data set of the calibration point can also be understood as having n. Each data in the data set is represented as bp1ij, bp2ij, bp3ij, and bp4ij, where i represents the ordinal number of the interval and j represents the ordinal number of the pulse voltage in the interval. Therefore, bp1ij means the jth pulse voltage of the i-th interval in the pulse starting point voltage data set, and bp2ij means the jth pulse voltage of the i-th interval in the pulse ending point voltage data set. Similarly, bp3ij means the jth pulse voltage of the i-th interval in the shelving starting point voltage data set, and bp4ij means the jth pulse voltage of the i-th interval in the shelving ending point voltage data set.

[0077] Specifically, the data set of the pulse points is divided into n data groups, and each data group contains a number of pulse voltage data, that is, one pulse voltage data or more than two pulse voltage data.

[0078] More specifically, the pulse starting point voltage data bp1 = {(bp111,…,bp11t1), (bp121,…,bp12t2),…, (bp1n1,…,bp1ntm)}; the pulse end point voltage data bp2 = {(bp211,…,bp21t1), (bp221,…,bp22t2),…, (bp2n1,…,bp2ntm)}; the shelving starting point voltage data bp3 = {(bp311,…,bp11t1), (bp321,…,bp32t2),…, (bp3n1,…,bp3ntk)}; the pulse end point voltage data bp4 = {(bp411,…,bp41t1), (bp421,…,bp42t2),…, (bp4n1,…,bp4ntk)}.

[0079] S232, extracting a section of pulse voltage data in each SOC interval from the data set of the calibration point to obtain the pulse voltage data of the calibration point in each SOC interval;

[0080] In this invention, the pulse point dataset includes the pulse start voltage dataset and the pulse end voltage dataset, and the rest point dataset includes the rest start voltage dataset and the rest end voltage dataset. Furthermore, the full SOC interval is divided into n intervals, and correspondingly, the calibration point dataset can also be understood as being divided into n intervals. Therefore, a segment of pulse voltage data is extracted in each SOC interval as the basis for obtaining the initial parameter values.

[0081] In an embodiment of the present invention, the pulse starting point voltage in the data set of the pulse point is taken as an example for explanation: the pulse starting point voltage data bp1 = {(bp111,…,bp11t1), (bp121,…,bp12t2),…, (bp1n1,…,bp1ntm)}; then the n SOC intervals into which the pulse electrical data is divided are (bp111,…,bp11t1), (bp121,…,bp12t2),…, (bp1n1,…,bp1ntm) in sequence; further, a section of pulse voltage data is extracted in the first SOC interval (bp111,…,bp11t1) to form the first zone pulse voltage data,…, a section of pulse voltage data is extracted in the nth SOC interval (bp1n1,…,bp1ntm) to form the nth zone pulse voltage data.

[0082] S233, processing the pulse voltage data of each SOC interval to obtain an initial value of an interval parameter;

[0083] In the present invention, the LM algorithm is used to perform nonlinear least squares fitting processing on the zone pulse voltage data of each SOC interval, and the initial values ​​of the interval parameters that meet the set requirements are recorded; wherein the set requirements are minimum RMSE and maximum R-Square.

[0084] Specifically, the pulse voltage data of each SOC interval in the pulse phase are fitted using the nonlinear least squares method of the LM algorithm, and the initial value of the interval parameter is obtained when the RMSE is minimized and the R-Square is maximized within the set number of iterations.

[0085] Pulse phase:

[0086] The LM algorithm is used to perform nonlinear least square fitting on the pulse voltage data of the first zone. During the iteration process, when the RMSE is minimum and the R-Square is maximum, it is recorded as the initial value of the interval parameter A0. 1 Similarly, the initial values ​​of the interval parameters of the remaining n-1 pulse voltage data are A0 2 ,…,A0 n .

[0087] Therefore, the initial values ​​of the interval parameters of the n intervals of the zero-state response of the second-order RC equivalent circuit model are A0 and A1 respectively. 1 , A0 2 ,…,A0 n .

[0088] Shelf phase after pulse:

[0089] The fitting process is the same as that in the pulse stage. The initial values ​​of the interval parameters of the n intervals of the zero input response of the second-order RC equivalent circuit model are B0 and B1 respectively. 1 , B0 2 ,…,B0 n .

[0090] S3, obtaining RC parameters of the second-order RC equivalent circuit model according to the data set of the calibration points and the initial values ​​of the interval parameters of the calibration points.

[0091] The purpose of this step is to first fit the pulse voltage data of all SOC intervals of the same calibration point to obtain the pulse voltage fitting results, and then process the pulse voltage fitting results of different stages to obtain the RC parameters of the second-order RC equivalent circuit model, and also to obtain the RC parameters of each calibration point.

[0092] S31, obtaining a pulse voltage fitting result of the calibration point in each interval according to the initial value of the interval parameter of the calibration point and the zone pulse voltage data of the corresponding interval in the data set of the calibration point;

[0093] In this step, the nonlinear least squares method of the LM algorithm is still used for fitting, and the pulse voltage fitting results of the calibration points in each interval are obtained with the minimum RMSE and the maximum R-Square as the criteria;

[0094] Specifically, the initial values ​​of the interval parameters of the calibration points obtained in step S2 are used as the optimal initial values ​​for fitting, and the pulse voltage data of the corresponding intervals in the data set of the calibration points are used as the data points to be fitted. The nonlinear least squares method of the LM algorithm is used for fitting, and the pulse voltage fitting results of the calibration points in each interval are obtained when the RMSE is minimized and the R-Square is maximized in the set number of iterations.

[0095] More specifically, in the pulse stage: the pulse voltage fitting results of the pulse point in each interval are obtained based on the pulse starting point voltage data set and the initial values ​​of the interval parameters of the pulse point; in the shelving stage after the pulse: the pulse voltage fitting results of the shelving point in each interval are obtained based on the shelving starting point voltage data set and the initial values ​​of the interval parameters of the shelving point.

[0096] S32, performing fitting processing on the pulse voltage fitting results of all intervals of the calibration point to obtain parameter values ​​of the fitting model;

[0097] The purpose of this step is to call the nonlinear least squares method based on the LM algorithm again to fit the pulse voltage fitting results of all intervals, thereby improving the fitting efficiency while ensuring that the parameters are the global optimal solution.

[0098] In the embodiment of the present invention, the pulse voltage fitting results of all intervals in the pulse phase are refitted to obtain the parameter values ​​a0, a1, a2, a3, and a4 of the fitting model corresponding to the zero response state in the pulse phase;

[0099] In an embodiment of the present invention, the pulse voltage fitting results of all intervals in the rest phase after the pulse are refitted to obtain the parameter values ​​b0, b1, b2, b3, and b4 of the simulation model corresponding to the zero input state in the rest phase.

[0100] S33: Obtain RC parameters of a second-order RC equivalent circuit model according to the parameter values ​​of the fitting model.

[0101] In the embodiment of the present invention, the RC model parameter values ​​at each SOC calibration point can be calculated according to R1=a1 / I, R2=a3 / I, τ1=a2, τ2=a4, τ'1=b2, τ'2=b4.

[0102] Device Example:

[0103] The present invention also provides an automatic fitting device for second-order RC equivalent circuit model parameters. Figure 3 As shown, it includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, the steps of the above-mentioned method for automatically fitting the parameters of the second-order RC equivalent circuit model are implemented.

[0104] The detailed process of the steps of the method for automatically fitting the parameters of the second-order RC equivalent circuit model has been described in detail in the method embodiment and will not be repeated here.

[0105] In summary, the present invention divides the SOC into zones and selects a section of voltage data to be fitted within the zone. After multiple fittings, initial values ​​for the interval parameters are obtained, achieving optimization of the interval parameter initial values. Each interval parameter initial value is then used as the initial value for voltage fitting at the SOC calibration point within the corresponding zone, improving parameter fitting efficiency and preventing the fitting from falling into a local optimum. This improves the efficiency and accuracy of parameter fitting in the second-order RC equivalent circuit model. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0106] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for automatically fitting parameters of a second-order RC equivalent circuit model, characterized in that: At least the following steps are included: S1: Acquire HPPC test data, and obtain a data set of calibration points based on the HPPC test data; the calibration points include pulse points and rest points; S2: Automatically fitting the HPPC test data to obtain initial parameter values ​​of the second-order RC equivalent circuit model at calibration points; S3: Obtaining RC parameters of the second-order RC equivalent circuit model based on the data set of the calibration point and the initial values ​​of the interval parameters of the calibration point; In step S3, obtaining the pulse voltage fitting results of the calibration point in each interval based on the initial values ​​of the interval parameters of the calibration point and the zone pulse voltage data of the corresponding interval in the data set of the calibration point; The pulse voltage fitting results of all intervals of the calibration points are fitted to obtain parameter values ​​of the fitting model; and the RC parameters of the second-order RC equivalent circuit model are obtained according to the parameter values ​​of the fitting model.

2. The automatic fitting method for second-order RC equivalent circuit model parameters according to claim 1, characterized in that: The data set of calibration points obtained according to the HPPC test data includes: Determining the breakpoints of each calibration point in the HPPC test data according to the pulse current change; The corresponding data set is obtained according to the voltage data corresponding to the breakpoints of each calibration point.

3. The automatic fitting method for second-order RC equivalent circuit model parameters according to claim 2, characterized in that: Determining the breakpoints of each calibration point of the HPPC test data within the full range of SOC according to the change of the pulse current; The calibration points include pulse points and rest points; correspondingly, the breakpoints of the pulse points are the pulse start point and the pulse end point, and the breakpoints of the rest point are the rest start point and the rest end point.

4. The automatic fitting method for second-order RC equivalent circuit model parameters according to claim 3, characterized in that: The method for determining the breakpoints of each calibration point in the HPPC test data according to the change of pulse current is as follows: If the current value at the k-1th moment satisfies -N<I k-1 <N, and the current value at time k+1 satisfies M<I k-1 <H, where M is greater than N, then time k is the pulse starting point, and time k+Δt1 is the pulse end point; time k+Δt1+1 is the hold starting point, and time k+Δt1+Δt2 is the hold end point, where Δt1 is the pulse time and Δt2 is the hold time.

5. The automatic fitting method for second-order RC equivalent circuit model parameters according to claim 1, characterized in that: Automatic fitting processing is performed on the HPPC test data to obtain the initial parameter values ​​of the second-order RC equivalent circuit model at the calibration point, including: Determine the second-order RC equivalent circuit model; Converting the second-order RC equivalent circuit model to obtain a fitting model; Automatic fitting processing is performed on the HPPC test data to obtain initial values ​​of interval parameters of the fitting model at calibration points.

6. The automatic fitting method for second-order RC equivalent circuit model parameters according to claim 5, characterized in that: The automatic fitting process adopts the nonlinear least square method of the LM algorithm.

7. The automatic fitting method for second-order RC equivalent circuit model parameters according to claim 6, characterized in that: The process of automatically fitting the HPPC test data to obtain the initial values ​​of the interval parameters of the fitting model at the calibration points includes: Divide the entire SOC interval into n SOC intervals; Extract a section of pulse voltage data in each SOC interval from the data set of the calibration point to obtain the regional pulse voltage data of the calibration point in each SOC interval; The pulse voltage data of each SOC interval is processed to obtain the initial value of the interval parameter.

8. An automatic fitting device for second-order RC equivalent circuit model parameters, characterized in that: The invention comprises a memory, a processor and a program stored in the memory and executable on the processor. When the processor executes the program, the steps of the method for automatically fitting the parameters of the second-order RC equivalent circuit model according to any one of claims 1 to 7 are implemented.

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