Method for obtaining optimal frequency of pulse current based on three-dimensional response surface

Abstract

The present invention specifically relates to a method for obtaining the optimal frequency of a pulse current based on a three-dimensional response surface, including: obtaining the battery impedance corresponding to each state of charge at different temperatures during an electrochemical impedance spectrum test; for a certain state of charge at a certain temperature: obtaining the frequency corresponding to each battery impedance through an impedance spectrum; then fitting all battery impedances and frequencies, and determining the optimal battery impedance; finally obtaining the frequency corresponding to the optimal battery impedance as the optimal frequency through an impedance spectrum; fitting the optimal frequencies of each state of charge at different temperatures to obtain the corresponding optimal frequency-temperature-state of charge three-dimensional response surface; when the battery is charged, combining the optimal frequency-temperature-state of charge three-dimensional response surface to obtain the optimal frequency as the operating frequency of the battery pulse current. The present invention can establish a three-dimensional response surface of optimal frequency-temperature-state of charge, thereby ensuring that the pulse current of the battery has an optimal frequency in the entire charging interval.

Description

Technical Field

[0001] The present invention relates to the technical field of power battery management, and in particular to a method for obtaining an optimal frequency of a pulse current based on a three-dimensional response surface. Background Art

[0002] As environmental pollution and energy crisis become increasingly serious, electric vehicles, as green and economical means of transportation, have gradually won the market and are widely used. As an important energy storage component of electric vehicles, the performance of power batteries is closely related to the normal operation and good work of the vehicle. Unlike fuel vehicles, the power batteries in electric vehicles need to undergo continuous charging and discharging processes during use. Different charging and discharging strategies have a certain impact on the performance and life of the battery.

[0003] At present, power batteries still face safety issues such as slow charging speed, short driving range, and easy thermal runaway and fire. Some power battery charging strategies include multi-stage constant current charging, pulse charging, methods based on equivalent circuit models, and methods based on electrochemical models. Among them, the pulse current used in the pulse charging method has the advantages of eliminating or reducing the polarization voltage of the battery and improving the charging performance of the battery in the next charging cycle. This advantage is particularly prominent in low temperature environments, so it has received widespread attention.

[0004] However, most of the existing pulse charging strategies do not directly consider the influence of temperature and state of charge during use, but control the pulse current from the lithium deposition or overpotential detection inside the battery in the laboratory. There is a lack of a simple and easy-to-promote method for selecting the optimal frequency of the pulse charging current to achieve adaptive changes in the charging frequency during the charging process, ensuring that the pulse current has the optimal frequency throughout the battery charging range, thereby improving the battery charging effect. Therefore, how to design a simple and feasible strategy that can ensure that the pulse current of the battery has the optimal frequency throughout the charging range is a technical problem that needs to be solved urgently. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is: how to provide a method for obtaining the optimal frequency of pulse current based on a three-dimensional response surface, establish a three-dimensional response surface of optimal frequency-temperature-state of charge, and then ensure that the pulse current of the battery has an optimal frequency in the entire charging range, thereby improving the charging effect of the battery pulse charging and providing a simple and easy charging strategy for the power battery.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The method for obtaining the optimal frequency of pulse current based on three-dimensional response surface includes:

[0008] S1: Perform an electrochemical impedance spectroscopy test on the battery to obtain an impedance spectrum reflecting the corresponding relationship between battery impedance and frequency;

[0009] S2: During the electrochemical impedance spectroscopy test, the battery impedance corresponding to each state of charge at different temperatures is obtained;

[0010] S3: For a certain state of charge at a certain temperature: obtain the frequency corresponding to each battery impedance through the impedance spectrum; then fit all battery impedances and frequencies, and determine the optimal battery impedance; finally, obtain the frequency corresponding to the optimal battery impedance through the impedance spectrum as the optimal frequency of the corresponding state of charge at the corresponding temperature;

[0011] S4: fitting the optimal frequencies of various charge states at different temperatures to obtain the corresponding optimal frequency-temperature-charge state three-dimensional response surface;

[0012] S5: When the battery is charging, the corresponding optimal frequency is obtained as the operating frequency of the battery pulse current according to the real-time temperature and charge state of the battery combined with the optimal frequency-temperature-charge state three-dimensional response surface.

[0013] Preferably, in step S1, an electrochemical impedance spectroscopy test is performed on an electrochemical workstation: first, a small-amplitude sinusoidal current signal is used as a disturbance within a certain frequency range to cause the battery's electrode system to produce an approximately correlated voltage signal response; then the corresponding voltage signal response is measured by the electrochemical workstation; finally, the impedance information inside the battery at the corresponding frequency is calculated based on the ratio of the corresponding voltage signal to the current signal, so as to obtain an impedance spectrum reflecting the corresponding relationship between the battery impedance and the frequency within the corresponding frequency range.

[0014] Preferably, in step S3, the battery impedance and frequency are fitted by the following formula to obtain a corresponding impedance-frequency fitting curve; and then the optimal battery impedance is determined by the impedance-frequency fitting curve;

[0015] |Z|=a1·f re 5 +b1·f re 4 +c1·f re 3 +d1·f re 2 +f1·f re +g1;

[0016] Where: |Z| represents the battery impedance after fitting; a1, b1, c1, d1, e1, f1, g1 all represent coefficients; f re Indicates frequency.

[0017] Preferably, in step S3, the optimal battery impedance refers to the minimum battery impedance.

[0018] Preferably, the relationship between the optimal battery impedance and the optimal frequency is analyzed by an AC impedance model that does not consider the influence of temperature and state of charge, and it is determined that the minimum battery impedance corresponds to an optimal frequency, that is, the optimal battery impedance is the minimum battery impedance.

[0019] Preferably, the AC impedance model is represented by the following formula:

[0020]

[0021] ω s =2πf s ;

[0022] Where: Z battery represents the battery impedance; f s Indicates the battery charging frequency; R ct represents the charge transfer resistance; C d represents double layer capacitance; R o Indicates ohmic resistance; L d represents the anode inductance; ω s represents circular frequency; j represents imaginary number.

[0023] Preferably, the optimal frequency corresponding to the minimum battery impedance is determined by the following steps:

[0024] 1) Assume:

[0025] The AC impedance model is rewritten as Z battery =X+jY;

[0026] 2) For the AC impedance model Z battery Taking the derivative, we get:

[0027]

[0028] in:

[0029] 3) Order Get the extreme value, that is, the frequency corresponding to the minimum battery impedance:

[0030]

[0031] Where K is:

[0032]

[0033] 3) f Zmin Bringing back the AC impedance model, we get the expression for the minimum battery impedance:

[0034]

[0035] The optimal frequency corresponding to the minimum battery impedance is determined by the expression of the minimum battery impedance.

[0036] Preferably, in step S4, an array of temperature, state of charge and optimal frequency corresponding to each other is constructed; then the array is transferred into a three-dimensional coordinate system, with the state of charge as the x-axis, the temperature as the y-axis, and the optimal frequency as the z-axis; finally, the optimal frequency-temperature-state of charge three-dimensional response surface is obtained by fitting the following polynomial;

[0037] f optimal =a+b·SOC+c·SOC 2 +d·SOC 3 +e·SOC 4 +f·T+g·T 2 +h·T 3 +i·T 4 ;

[0038] Where: a, b, c, d, e, f, g, h, i all represent coefficients; f optimal represents the optimal frequency; SOC represents the state of charge; T represents the temperature.

[0039] Preferably, the optimal frequency-temperature-state of charge three-dimensional response surface refers to a graphical expression of a fitting polynomial.

[0040] Preferably, the temperature, state of charge and optimal frequency are fitted by the Curve Fitting toolbox of Matlab software to obtain the optimal frequency-temperature-state of charge three-dimensional response surface.

[0041] The method for obtaining the optimal frequency of pulse current based on the three-dimensional response surface in the present invention has the following beneficial effects:

[0042] The present invention obtains the frequency corresponding to the battery impedance of different charge states at various temperatures through an impedance spectrum, and performs fitting calculation on the corresponding battery impedance and frequency to obtain the corresponding optimal battery impedance, and then obtains the frequency corresponding to the optimal battery impedance through the impedance spectrum as the optimal frequency of the corresponding charge state at various temperatures, so that the optimal frequency of the corresponding charge state at various temperatures can be fitted to obtain the optimal frequency-temperature-charge state three-dimensional response surface, and then the optimal frequency-temperature-charge state three-dimensional response surface can be established with the help of the electrochemical impedance spectrum of the battery. At the same time, when the battery is charged, the optimal frequency is obtained according to the real-time temperature and charge state of the battery combined with the optimal frequency-temperature-charge state three-dimensional response surface as the operating frequency of the battery pulse current, so that it can be ensured that the pulse current of the battery has the optimal frequency in the entire charging interval, thereby improving the charging effect of the battery pulse charging, and providing a simple and easy charging strategy for the power battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to make the purpose, technical solution and advantages of the invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0044] Figure 1 It is a logic block diagram of the method for obtaining the optimal frequency of pulse current based on three-dimensional response surface;

[0045] Figure 2 It is a flow chart of the method for obtaining the optimal frequency of pulse current based on three-dimensional response surface;

[0046] Figure 3 The impedance-frequency fitting curve is at 25°C and the state of charge is 100%;

[0047] Figure 4 This is the circuit diagram of the battery AC impedance model;

[0048] Figure 5 The optimal frequency-temperature-state of charge response surface established;

[0049] Figure 6 The simulation results of pulse variable frequency charging are shown in Figure 2 to obtain the optimal frequency using the established three-dimensional response surface. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but only represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0051] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] The following is a further detailed description through specific implementation methods:

[0053] Example:

[0054] This embodiment discloses a method for obtaining the optimal frequency of a pulse current based on a three-dimensional response surface.

[0055] like Figure 1 and Figure 2 As shown, the method for obtaining the optimal frequency of pulse current based on the three-dimensional response surface includes:

[0056] S1: Perform an electrochemical impedance spectroscopy test on the battery to obtain an impedance spectrum reflecting the corresponding relationship between battery impedance and frequency;

[0057] S2: During the electrochemical impedance spectroscopy test, the battery impedance corresponding to each state of charge at different temperatures is obtained;

[0058] In this embodiment, the state of charge (SOC) represents the ratio of the remaining power in the power battery to its rated capacity, which can clearly and accurately represent the current state of the power battery.

[0059] Specifically, the temperature intervals are set to -20°C, 10°C, 0°C, 10°C, 25°C, and the state of charge intervals are set to 100%, 95%, 90%, 80%, 70% ..., 30%, 25%, 20%, 15%, 10%, 5% and 0. Of course, the temperature intervals and state of charge intervals can be larger or smaller.

[0060] S3: For a certain state of charge at a certain temperature: obtain the frequency corresponding to each battery impedance through the impedance spectrum; then fit all battery impedances and frequencies, and determine the optimal battery impedance; finally, obtain the frequency corresponding to the optimal battery impedance through the impedance spectrum as the optimal frequency of the corresponding state of charge at the corresponding temperature;

[0061] S4: fitting the optimal frequencies of various charge states at different temperatures to obtain the corresponding optimal frequency-temperature-charge state three-dimensional response surface;

[0062] S5: When the battery is charging, the corresponding optimal frequency is obtained as the operating frequency of the battery pulse current according to the real-time temperature and charge state of the battery combined with the optimal frequency-temperature-charge state three-dimensional response surface.

[0063] The present invention obtains the frequency corresponding to the battery impedance of different charge states at various temperatures through an impedance spectrum, and performs fitting calculation on the corresponding battery impedance and frequency to obtain the corresponding optimal battery impedance, and then obtains the frequency corresponding to the optimal battery impedance through the impedance spectrum as the optimal frequency of the corresponding charge state at various temperatures, so that the optimal frequency of the corresponding charge state at various temperatures can be fitted to obtain the optimal frequency-temperature-charge state three-dimensional response surface, and then the optimal frequency-temperature-charge state three-dimensional response surface can be established with the help of the electrochemical impedance spectrum of the battery. At the same time, when the battery is charged, the optimal frequency is obtained according to the real-time temperature and charge state of the battery combined with the optimal frequency-temperature-charge state three-dimensional response surface as the operating frequency of the battery pulse current, so that it can be ensured that the pulse current of the battery has the optimal frequency in the entire charging interval, thereby improving the charging effect of the battery pulse charging, and providing a simple and easy charging strategy for the power battery.

[0064] During the specific implementation process, an electrochemical impedance spectroscopy test is carried out on an electrochemical workstation: first, a small-amplitude sinusoidal current signal is used as a disturbance within a certain frequency range to cause the battery's electrode system to produce an approximately correlated voltage signal response; then the corresponding voltage signal response is measured by the electrochemical workstation; finally, the impedance information inside the battery at the corresponding frequency is calculated based on the ratio of the corresponding voltage signal to the current signal, so as to obtain an impedance spectrum that reflects the correspondence between the battery impedance and frequency within the corresponding frequency range.

[0065] In this embodiment, the sweep frequency range of the used data is 0.1mHz-6000Hz.

[0066] In the specific implementation process, the battery impedance and frequency are fitted by the following formula to obtain the corresponding impedance-frequency fitting curve; and then the optimal battery impedance is determined by the impedance-frequency fitting curve;

[0067] |Z|=a1·f re 5 +b1·f re 4 +c1·f re 3 +d1·f re 2 +f1·f re +g1;

[0068] Where: |Z| represents the battery impedance after fitting; a1, b1, c1, d1, e1, f1, g1 all represent coefficients; f re Indicates frequency.

[0069] Taking 25℃ and 100% state of charge as an example, the impedance-frequency fitting curve is as follows: Figure 3 shown.

[0070] Among them, a1=-5.5839e-18; b1=9.8376e-14; c1=-6.7835e-10; d1=2.4221; e1=-06; f1=-0.0042053; g1=23.3415, R2 is 0.99959, the residual norm is 0.043042, and the fitting effect is good.

[0071] In this embodiment, in order to narrow the data range, only impedance data and frequency data of 450 Hz-6000 Hz are selected for fitting, and all fitting equations are quintic polynomials.

[0072] During specific implementation, the optimal battery impedance refers to the minimum battery impedance.

[0073] The relationship between the optimal battery impedance and the optimal frequency is analyzed by using an AC impedance model that does not consider the effects of temperature and state of charge, and it is determined that the minimum battery impedance corresponds to an optimal frequency, that is, the optimal battery impedance is the minimum battery impedance.

[0074] The AC impedance model is Figure 4 As shown, R ct is the charge transfer resistance; C d is the double layer capacitance; R o is the ohmic resistance; L d is the anode inductance; OCV is the open circuit voltage; U t is the terminal voltage.

[0075] The AC impedance model is expressed by the following formula:

[0076]

[0077] ω s =2πf s ;

[0078] Where: Z battery represents the battery impedance; f s Indicates the battery charging frequency; R ct represents the charge transfer resistance; C d represents double layer capacitance; R o Indicates ohmic resistance; L d represents the anode inductance; ω s represents circular frequency; j represents imaginary number.

[0079] Determine the optimal frequency for minimum battery impedance by following these steps:

[0080] 1) Assume:

[0081] The AC impedance model is rewritten as Z battery =X+jY;

[0082] 2) For the AC impedance model Z battery Taking the derivative, we get:

[0083]

[0084] in:

[0085] 3) Order Get the extreme value, that is, the frequency corresponding to the minimum battery impedance:

[0086]

[0087] Where K is:

[0088]

[0089] 3) f Zmin Bringing back the AC impedance model, we get the expression for the minimum battery impedance:

[0090]

[0091] The optimal frequency corresponding to the minimum battery impedance is determined by the expression of the minimum battery impedance.

[0092] From the expression of minimum battery impedance, we can know that the value of minimum battery impedance is related to the resistance and reactance (capacitive reactance, inductive reactance) in the AC impedance model, and the resistance and reactance are related to the temperature and charge state during the charging process.

[0093] Therefore, during the charging process, the internal resistance of the battery will change with the changes in temperature and state of charge. In order to reduce the battery energy loss during the charging process, an optimal charging frequency f can be sought. optimal To reduce the battery impedance Z battery , so that the electrical energy converted into chemical energy is minimized. In summary, considering the effects of temperature and state of charge on impedance, the relationship between the optimal frequency, temperature and state of charge can be fitted using electrochemical impedance spectroscopy test data, thereby establishing the optimal frequency-temperature-state of charge three-dimensional response surface.

[0094] The present invention analyzes the relationship between the optimal battery impedance and the optimal frequency by constructing an AC impedance model that does not consider temperature and state of charge, and obtains the optimal frequency corresponding to the minimum battery impedance, so that the three-dimensional response surface of the optimal frequency-temperature-state of charge can be effectively established with the help of the electrochemical impedance spectrum of the battery, which can ensure that the pulse current of the battery in the entire charging range has the optimal frequency, thereby further improving the charging effect of the battery pulse charging.

[0095] In the specific implementation process, the extreme value of the fitting polynomial of impedance and frequency at each temperature and the state of charge value of 20%-80% is obtained to obtain the optimal frequency value at each temperature and each state of charge.

[0096] Construct an array with one-to-one correspondence between temperature, state of charge and optimal frequency; then convert the array into a three-dimensional coordinate system, with the state of charge as the x-axis, temperature as the y-axis, and optimal frequency as the z-axis; finally, the following fitting polynomial is used to obtain Figure 5 The optimal frequency-temperature-state of charge three-dimensional response surface shown;

[0097] f optimal =a+b·SOC+c·SOC 2 +d·SOC 3 +e·SOC 4 +f·T+g·T 2 +h·T 3 +i·T 4 ;

[0098] Where: a, b, c, d, e, f, g, h, i all represent coefficients; f optimal represents the optimal frequency; SOC represents the state of charge; T represents the temperature.

[0099] like Figure 5As shown, the optimal frequency-temperature-state of charge three-dimensional response surface refers to the graphical expression of the fitting polynomial.

[0100] In this embodiment, the temperature, state of charge and optimal frequency are fitted by the Curve Fitting toolbox of Matlab software to obtain the optimal frequency-temperature-state of charge three-dimensional response surface.

[0101] In order to better illustrate the advantages of the technical solution of the present invention, the following experiments are disclosed in this embodiment.

[0102] In this experiment, an equivalent circuit charging simulation model of a battery is established, the optimal frequency of the optimal frequency-temperature-state of charge three-dimensional response surface is loaded with current with positive and negative pulses, and a pulse current charging simulation with the optimal frequency is implemented to verify the results of the present invention.

[0103] The equivalent circuit models established can adopt: Rint model, Thevenin model and DP model, etc.

[0104] In this embodiment, the equivalent circuit model is the Thevenin model, and the specific circuit equation is:

[0105]

[0106] The discretized expression is:

[0107]

[0108] Where: U t is the terminal voltage of the power battery system; U D is the voltage drop of the RC parallel link of the power battery system; U oc is the ideal voltage source of the power battery system; R i is the ohmic internal resistance of the power battery system; R D is the polarization resistance of the power battery system; C D The polarization capacitance of the power battery system; i L is the current flowing through the power battery system.

[0109] Figure 5 The optimal frequency-temperature-state of charge three-dimensional response surface established in the example of the present invention and applied to the charging simulation from 20% state of charge to 80% state of charge is shown. It can be seen that the optimal frequency is seriously affected by temperature. As the temperature decreases, the optimal frequency shows an upward trend. The influence of the state of charge on the frequency is not large compared to the temperature, but the optimal frequency of the battery also changes significantly with the change of the state of charge.

[0110] Figure 6The comparison chart is a graph of the battery charging simulation results of obtaining the optimal frequency using the frequency-temperature-state of charge three-dimensional response surface under three low temperature environments and the constant current charging results with the same theoretical current value. Figure 6 (a) is the charging simulation result at -20℃. Figure 6 (b) is the charging simulation result at -10℃. Figure 6 (c) is the charging simulation result at 0°C. It can be seen that the pulse current charging time with the optimal frequency is shorter than the constant current charging time, which proves that the pulse current with the optimal frequency has the effect of improving the charging speed in a low temperature environment, and also verifies that the optimal frequency based on the three-dimensional response surface does have certain effects.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A method for obtaining the optimal frequency of pulse current based on a three-dimensional response surface, characterized in that: include: S1: Perform an electrochemical impedance spectroscopy test on the battery to obtain an impedance spectrum reflecting the corresponding relationship between battery impedance and frequency; S2: During the electrochemical impedance spectroscopy test, the battery impedance corresponding to each state of charge at different temperatures is obtained; S3: For a certain state of charge at a certain temperature: obtain the frequency corresponding to each battery impedance through the impedance spectrum; then fit all battery impedances and frequencies, and determine the optimal battery impedance; finally, obtain the frequency corresponding to the optimal battery impedance through the impedance spectrum as the optimal frequency of the corresponding state of charge at the corresponding temperature; In step S3, the battery impedance and frequency are fitted by the following formula to obtain a corresponding impedance-frequency fitting curve; and then the optimal battery impedance is determined by the impedance-frequency fitting curve; |Z|=a1·f re 5 +b1·f re 4 +c1·f re 3 +d1·f re 2 +f1·f re +g1; Where: |Z| represents the battery impedance after fitting; a1, b1, c1, d1, e1, f1, g1 all represent coefficients; f re Indicates frequency; The relationship between the optimal battery impedance and the optimal frequency is analyzed by using an AC impedance model that does not consider the effects of temperature and state of charge, and it is determined that the minimum battery impedance corresponds to an optimal frequency, that is, the optimal battery impedance is the minimum battery impedance; The AC impedance model is expressed by the following formula: oh s =2πf s ; Where: Z battery represents the battery impedance; f s Indicates the battery charging frequency; R ct represents the charge transfer resistance; C d represents double layer capacitance; R o Indicates ohmic resistance; L d represents anode inductance; ω s represents circular frequency; j represents imaginary number; S4: fitting the optimal frequencies of various charge states at different temperatures to obtain the corresponding optimal frequency-temperature-charge state three-dimensional response surface; S5: When the battery is charging, the corresponding optimal frequency is obtained as the operating frequency of the battery pulse current according to the real-time temperature and charge state of the battery combined with the optimal frequency-temperature-charge state three-dimensional response surface.

2. The method for obtaining the optimal frequency of pulse current based on three-dimensional response surface according to claim 1, characterized in that: In step S1, an electrochemical impedance spectroscopy test is performed on an electrochemical workstation: first, a small-amplitude sinusoidal current signal is used as a disturbance within a certain frequency range to cause the battery's electrode system to produce an approximately related voltage signal response; then the corresponding voltage signal response is measured by the electrochemical workstation; finally, the impedance information inside the battery at the corresponding frequency is calculated based on the ratio of the corresponding voltage signal to the current signal, so as to obtain an impedance spectrum reflecting the corresponding relationship between the battery impedance and the frequency within the corresponding frequency range.

3. The method for obtaining the optimal frequency of pulse current based on three-dimensional response surface according to claim 1, characterized in that: Determine the optimal frequency for minimum battery impedance by following these steps: 1) Assume: The AC impedance model is rewritten as Z battery =X+jY; 2) For the AC impedance model Z battery Taking the derivative, we get: in: γ=R ct 2 C d ; 3) Order Get the extreme value, that is, the frequency corresponding to the minimum battery impedance: Where K is: 3) f Zmin Bringing back the AC impedance model, we get the expression for the minimum battery impedance: The optimal frequency corresponding to the minimum battery impedance is determined by the expression of the minimum battery impedance.

4. The method for obtaining the optimal frequency of pulse current based on three-dimensional response surface according to claim 1, characterized in that: In step S4, an array of temperature, state of charge and optimal frequency corresponding to each other is constructed; then the array is transferred into a three-dimensional coordinate system, with the state of charge as the x-axis, the temperature as the y-axis, and the optimal frequency as the z-axis; finally, the optimal frequency-temperature-state of charge three-dimensional response surface is obtained by fitting the following polynomial; f optimal =a+b·SOC+c·SOC 2 +d·SOC 3 +e·SOC 4 +f·T+g·T 2 +h·T 3 +i·T 4 ; Where: a, b, c, d, e, f, g, h, i all represent coefficients; f optimal represents the optimal frequency; SOC represents the state of charge; T represents the temperature.

5. The method for obtaining the optimal frequency of pulse current based on three-dimensional response surface according to claim 4, characterized in that: The optimal frequency-temperature-state of charge three-dimensional response surface refers to the graphical expression of the fitting polynomial.

6. The method for obtaining the optimal frequency of pulse current based on three-dimensional response surface according to claim 4, characterized in that: The temperature, state of charge and optimal frequency were fitted by the Curve Fitting toolbox of Matlab software to obtain the optimal frequency-temperature-state of charge three-dimensional response surface.

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