Battery Surface Temperature Monitoring System and Method Based on Double-Helix Optical Fiber Sensor

Abstract

The present invention relates to the technical field of battery temperature detection, and specifically discloses a battery surface temperature monitoring system and method based on a double-helical optical fiber sensor. The system includes: a double-helical distributed optical fiber, which includes a first helical structure and a second helical structure with opposite winding directions; the double-helical distributed optical fiber is laid flat on the battery surface; the battery is divided into left and right parts with the battery center point O, and the centers of the two parts are A and B respectively; the starting end of the double-helical distributed optical fiber uses point A as the helical starting point, spirally winds outward in a first direction for a set number of turns to form a first helical structure; the end of the first helical structure passes through point O for transition, and then spirally winds inward in a second direction for a set number of turns to reach the terminal of the distributed optical fiber, and the terminal uses point B as the helical end point to form a second helical structure. The present invention can comprehensively and accurately monitor the temperature change of the battery from both sides of the electrode tab to the center.

Description

Technical Field

[0001] The present invention relates to the technical field of battery temperature detection, and particularly to a battery surface temperature monitoring system and method based on a double-helical fiber optic sensor. Background Art

[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries (LIBs) have the advantages of high energy density, wide operating temperature range, long cycle life, etc., and are indispensable in electric vehicles (EVs) and energy storage systems (ESSs), and also play a key role in reducing carbon dioxide emissions.

[0004] Lithium-ion batteries usually need to be tested under various current loads and environmental conditions to quantify key parameters such as impedance and temperature. These parameters are not only the basis for laboratory experiments but also necessary conditions for accurately evaluating the performance and safety of batteries in actual applications. Therefore, real-time temperature measurement of lithium-ion batteries is essential for maximizing performance, extending life, and reducing the risk of thermal runaway.

[0005] Traditional surface temperature measurement usually uses devices such as thermocouples and thermistors to achieve. They are often fixed at preset positions and rely to a large extent on point-based methods, unable to achieve full-range temperature measurement; Fiber Bragg Grating (FBG) sensors are a kind of quasi-distributed fiber grating sensors, which are made by engraving Bragg gratings at specific positions on the optical fiber and have been preliminarily used to measure parameters such as battery temperature and strain. The prior art discloses the use of FBG sensors to monitor battery temperature and has achieved certain results in state estimation, fault diagnosis, thermal runaway warning, etc.; however, it also faces a series of technical problems, such as:

[0006] The prior art discloses a fiber optic sensor monitoring device and system, which realizes temperature / strain monitoring at multiple positions by cascading multiple sensing units composed of fiber gratings and Fabry-Perot cavities. However, this method has a relatively complex operation process, can only achieve multi-point measurement, cannot achieve full-range temperature measurement, and has high requirements for the interval setting of sensors.

[0007] The prior art discloses a battery monitoring method and system based on fiber optic sensors. A single optical fiber is sequentially passed through the positive and negative electrode tabs of each battery, so that multiple batteries are connected in series. The optical fiber between the positive and negative electrode tabs of each battery is coated with a thermosensitive material or a piezoelectric material, and the rest is not coated; the temperature change of the battery to be measured can be obtained through the frequency shift of the uncoated part; this scheme can realize synchronous measurement of multiple batteries, but for a single battery, it cannot achieve full-range temperature measurement.

[0008] The prior art discloses a method for arranging a fiber optic sensor in a loop and disk shape. This method winds a single fiber optic to form a loop and disk structure, which is attached to the surface of the battery to monitor the temperature. However, this solution is arranged in a single helix (disk shape) and uses a fiber Bragg grating (FBG) sensor. Although it covers the entire surface, due to the limitations of the number of Bragg gratings and manufacturing conditions, it is impossible to accurately measure the temperature at any position. At the same time, the operation and use of the FBG sensor are relatively troublesome, and it is necessary to ensure that the grating area is not damaged. The rectangular disk arrangement of the fiber optic may cause the bending degree at the four vertices to be too large, and the radius exceeds the maximum allowable bending radius of the fiber optic, resulting in fiber optic damage or excessive loss, affecting the monitoring effect. In addition, due to the limitations of temperature information and irregular arrangement, the spacing calculation and temperature mapping rules are not given, and it is impossible to accurately reconstruct the distribution of the battery temperature field, which has certain limitations.

[0009] In addition, the resolution of the fiber Bragg grating sensor has certain limitations. The resolution refers to the spatial resolution measured by the fiber optic sensor, that is, the minimum distance that the sensor can distinguish between two adjacent measurement points. When using a fiber Bragg grating sensor, each measurement point is a grating area. The length of the grating area and the distance between adjacent grating areas usually need to be greater than certain specific thresholds L1 and L2. An overly short grating area will reduce the number of fiber optic cycles, resulting in insufficient Bragg reflection conditions, broadening of the reflection peak, and a decrease in resolution. Moreover, the reflection intensity is related to the length of the grating area and the depth of refractive index adjustment. An overly short grating area leads to insufficient reflectivity and a poor signal-to-noise ratio. The typical grating area length is 5 - 10 mm. An overly short grating area will also increase the manufacturing difficulty and reduce the performance of the sensor. At the same time, the number of gratings cannot be too many. Each grating has a specific reflection wavelength. When there are multiple gratings, the wavelength interval needs to be large enough to avoid overlap. When light propagates in the fiber optic, it loses part of its energy every time it passes through a grating. Too many gratings will cause the signal at the far end to be too weak. Interference between multiple gratings may cause crosstalk and affect the measurement accuracy.

[0010] In summary, the above method is inherently limited to discrete or single-point measurements, or only realizes continuous measurements at multiple points in a local area. Since the resolution of the FBG sensor cannot reach a relatively high level, it may cause the temperature information between adjacent measurement points to be unobtainable, that is, features are lost. When these features are missing, the measured temperature information is incomplete, which will lead to inaccurate analysis of the temperature change across the entire surface of the battery. When further reconstructing the battery temperature field, it will also cause the reconstruction result to be inaccurate. This greatly hinders the comprehensive analysis of the thermal, mechanical, and other characteristics of the battery and affects the effectiveness of the battery management system (BMS) in managing battery performance and safety. Summary of the Invention

[0011] To solve the above problems, the present invention proposes a battery surface temperature monitoring system and method based on a double - helix optical fiber sensor. A double - helix sensor structure is designed, and the two double - helices are respectively arranged near the positive and negative electrodes of the battery to achieve full - range measurement of the battery surface temperature.

[0012] In some embodiments, the following technical solutions are adopted:

[0013] A battery surface temperature monitoring system based on a double - helix optical fiber sensor, comprising: a double - helix distributed optical fiber, the double - helix distributed optical fiber including a first helix structure and a second helix structure with opposite winding directions; the double - helix distributed optical fiber is laid flat on the battery surface; the battery is divided into left and right parts with the center point O of the battery, and the centers of the two parts are A and B respectively; the starting end of the double - helix distributed optical fiber takes point A as the helix starting point, spirally winds outward in the first direction for a set number of turns to form a first helix structure; the end of the first helix structure passes through point O and then spirally winds inward in the second direction for a set number of turns to reach the terminal of the distributed optical fiber, and the terminal takes point B as the helix end point to form a second helix structure.

[0014] Wherein, the first helix structure covers the positive - electrode region on the battery surface, and the second helix structure covers the negative - electrode region on the battery surface.

[0015] As a further solution, the helix pitch of the first helix structure or the second helix structure is specifically:

[0016] ;

[0017] Wherein, W is the battery width, n is the number of turns of the helix, g is the minimum pitch, α is the exponential coefficient, controlling the non - linear relationship between the helix pitch S and the battery width W , usually 0 < α ≤1; k is the adjustment factor.

[0018] The functional relationships between the exponential coefficient α and the adjustment factor k and the battery width W are respectively established, specifically:

[0019] α = A / (1 + B W );

[0020] k = C· W D ;

[0021] Among them, A and C are proportionality coefficients; B is an adjustment factor used to control α the rate of decline; D is an exponential factor.

[0022] As a further solution, the parametric equation of the first helical structure is:

[0023] x1 = r × cos(t);

[0024] y1 = r × sin(t);

[0025] The parametric equation of the second helical structure is:

[0026] x2 = -r × cos(t);

[0027] y2 = -r × sin(t);

[0028] To ensure that the starting point of the second helical structure is connected to the ending point of the first helical structure, the coordinates of the second helical structure are translated:

[0029] x2’ = x2 + x 1end +L;

[0030] y2’ = y2 + y 1end ;

[0031] Among them, (x1, y1) represents the Cartesian coordinates of each measurement point on the first helical structure, (x2, y2) represents the Cartesian coordinates of each measurement point on the second helical structure, and (x2’, y2’) represents the Cartesian coordinates of each measurement point on the translated second helical structure; t is the angle, and its value range is [0, 2πn], where n is the number of turns of the helix; r is the radius of the helix, and the radius of the helix r and the angle t have the following relationship: r = a + b × t ; a is the initial radius of the helix, b is the rate at which the radius increases with the angle; L is the translation amount, x 1end is the x coordinate of the ending point of the first helical structure, and y 1end is the y coordinate of the ending point of the first helical structure.

[0032] In some other embodiments, the following technical solution is adopted:

[0033] A method for monitoring the surface temperature of a battery based on a double - helix optical fiber sensor, including:

[0034] Determine the center O of the battery, and divide the battery into left and right parts with the center point O of the battery. The centers of the two parts are A and B respectively;

[0035] The starting end of the distributed optical fiber takes point A as the spiral starting point, spirally winds outward along the first direction for a set number of turns, and forms a first spiral structure; the end of the first spiral structure passes through point O for transition, and then spirally winds inward along the second direction for a set number of turns. Finally, the terminal of the distributed optical fiber takes point B as the spiral end point to form a second spiral structure;

[0036] Place the battery with the double - spiral distributed optical fiber in a temperature control device to provide a set temperature environment for the battery;

[0037] Charge and discharge the battery through a battery detection device, use the OFDR system to interrogate the double - spiral distributed optical fiber at regular intervals, detect the interference optical signal and transmit it to the upper computer, and the upper computer analyzes the interference signal to obtain the temperature information of each data point of the double - spiral distributed optical fiber.

[0038] As a further solution, it also includes: mapping the temperature data obtained by the double - spiral distributed optical fiber to the battery surface, so as to obtain the full - range temperature change information on the battery surface; specifically:

[0039] Take the center point O of the battery as the origin to establish a plane coordinate system on the battery surface; convert the Cartesian coordinates of the data points on the double - spiral distributed optical fiber to the plane coordinate system on the battery surface;

[0040] Calculate the arc length of the circular arc segment between two adjacent data points on the double - spiral distributed optical fiber, and determine the circular arc segment between two adjacent data points in the plane coordinate system; use the interpolation algorithm to evenly distribute the optical fiber measurement point data within the circular arc segment, so as to obtain the full - range temperature data distribution on the battery surface.

[0041] As a further solution, calculate the arc length of the circular arc segment between two adjacent data points on the double - spiral distributed optical fiber, specifically:

[0042] ;

[0043] where a is the initial radius of the spiral, and b is the rate of increase of the radius with the increase of the angle; t from 0 to 2π n evenly divide m into t 0, t 1,..., t i …, t m 。

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] (1) The present invention designs a double - helix tape - type distributed optical fiber sensor structure, which can optimize the layout of the distributed optical fiber sensor on the battery surface. The temperature measurement is not limited by the number of measurement points, and can obtain the battery surface temperature data in real - time, comprehensively and continuously, eliminating the single - point measurement error caused by high - rate charge and discharge, realizing the leap from point - to - surface acquisition of temperature change information, and having strong adaptability.

[0046] For lithium - ion soft - pack or square batteries with tabs at both ends, the temperature generally shows a gradually decreasing gradient distribution from the tabs to the center of the battery. This distribution may be uneven, especially during high - rate discharge or charge, and the temperature gradient on the side close to the tab is steeper. In the single - helix structure disclosed in the prior art, it is difficult to achieve comprehensive and continuous measurement of the temperature in the areas of the two tab positions. Through the double - helix structure of the present invention, the battery is divided into left and right parts, and each part is arranged with spiral optical fibers to monitor the heat generation changes in the two parts; the left and right spirals are connected at the mid - point to monitor the temperature change at the center of the battery, and the temperature monitoring points can be reasonably arranged according to the heat distribution of the battery to comprehensively and accurately monitor the temperature change of the battery from both sides of the tabs to the center.

[0047] (2) By reasonably designing the spiral pitch and the coordinates of each point on the spiral, the present invention accurately obtains the double - helix structure, maps the optical fiber data to the battery surface, and reconstructs the battery surface temperature distribution, which can ensure that the temperature at most positions on the surface can be monitored by the sensor as much as possible, realize the all - around monitoring of the battery surface, discover potential temperature abnormal points early, and can optimize the battery design according to the temperature distribution.

[0048] (3) In the prior art, FBG sensors are used for battery surface temperature measurement. Due to the limitations of the number and spacing of measurement points, the spatial resolution cannot reach a high level, which limits the ability of the sensor to obtain information. This may result in the inability to obtain the temperature information between adjacent measurement points, that is, the loss of features, and further lead to incomplete temperature information measurement. The present invention uses a distributed optical fiber sensor to achieve high spatial resolution. It uses continuous back - scattering signals and broadband laser sweep frequency, rather than discrete - point measurement; through interference, the signals of each scattering point can be analyzed to provide continuous spatial information.

[0049] (4) The double - helix tape - type distributed optical fiber sensor structure of the present invention is high - temperature resistant and not easily corroded, has high precision and fast response, and is expected to be implanted into the battery to monitor the uneven temperature distribution and evolution, providing corresponding support for exploring the safe use boundary.

[0050] Other features and additional advantages of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of this aspect. Description of the Drawings

[0051] Figure 1 Schematic diagram of the layout structure of the double - helix distributed optical fiber on the battery surface in the embodiment of the present invention;

[0052] Figure 2 Comsol simulation result of the temperature change during the charge - discharge process of the soft - pack battery in the embodiment of the present invention;

[0053] Figure 3 Evolution of the battery surface temperature corresponding to the first spiral structure under 0.5C current in the embodiment of the present invention;

[0054] Figure 4 Evolution of the battery surface temperature corresponding to the second spiral structure under 0.5C current in the embodiment of the present invention;

[0055] Figure 5 Evolution of the battery surface temperature corresponding to the first spiral structure under 1.0C current in the embodiment of the present invention;

[0056] Figure 6 Evolution of the battery surface temperature corresponding to the second spiral structure under 1.0C current in the embodiment of the present invention. Detailed implementation manners

[0057] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0058] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or their combinations.

[0059] Embodiment 1

[0060] In one or more embodiments, a battery surface temperature monitoring system based on a double - helix optical fiber sensor is disclosed. Combined with Figure 1 , it includes: a double - helix distributed optical fiber, which includes a first spiral structure and a second spiral structure with opposite winding directions; the double - helix distributed optical fiber is laid flat on the battery surface, and the specific laying method is as follows:

[0061] The battery is divided into left and right parts with the center point O of the battery as the dividing point, and the centers of the two parts are A and B respectively; the starting end of the double - helix distributed optical fiber takes point A as the spiral starting point, spirally winds outward along the first direction for a set number of turns to form a first spiral structure; the end of the first spiral structure passes through point O for transition, then spirally winds inward along the second direction for a set number of turns to reach the terminal of the distributed optical fiber, and the terminal takes point B as the spiral ending point to form a second spiral structure.

[0062] As a specific example, in this embodiment, a distributed optical fiber sensor based on Rayleigh scattering is selected. An optical fiber with a core diameter of 9μm and a cladding diameter of 125μm is selected. The surface of the optical fiber is coated with polyimide, and the coating method can adopt dip - coating, spraying or spin - coating processes to ensure that the coating is uniform and of moderate thickness (usually from a few micrometers to dozens of micrometers); after coating, the polyimide coating is hardened by high - temperature curing (usually 200°C - 300°C) to form a protective layer. Then the optical fiber is fixed in a soluble polytetrafluoroethylene (PFA) or polyimide (PI) sleeve, and through physical design, the external mechanical stress is reduced or completely blocked from being transmitted to the optical fiber core, so that the change of the Rayleigh scattering signal mainly reflects the temperature effect rather than the strain effect, in order to isolate the influence of strain on temperature.

[0063] The sleeve is usually a flexible or rigid protective layer (such as a polymer sleeve, a stainless - steel tube or a slack structure) that wraps the sensing optical fiber. The optical fiber maintains a certain degree of freedom inside the sleeve and is not directly and tightly coupled with the external structure; the sleeve absorbs or disperses the tensile, compressive or bending stresses applied from the outside, preventing these forces from directly acting on the optical fiber. Under this design, when the external environment undergoes mechanical deformation (such as being stretched or compressed), the sleeve will bear these stresses first, and since the optical fiber is in a slack state, it will not be stretched or compressed, so its length and strain state basically remain unchanged, making the signal change only caused by temperature and ensuring the accuracy of the temperature measurement result.

[0064] The first spiral structure is arranged near the positive electrode of the battery, covering the positive - electrode area on the battery surface, and spiraling in the counter - clockwise direction; the second spiral structure is arranged near the negative electrode of the battery, covering the negative - electrode area on the battery surface, and spiraling in the clockwise direction.

[0065] The first spiral structure and the second spiral structure can completely cover all areas of the battery surface to achieve full - range temperature measurement of the battery surface.

[0066] For lithium - ion soft - pack or square batteries with positive and negative electrode tabs at both ends, during the charging and discharging process, the temperature - field distribution is a complex problem of heat conduction and heat generation, affected by multiple factors, including the charging and discharging rate of the battery, the material and design of the electrode tabs, the environmental temperature, and the heat - conduction characteristics of the internal structure of the battery. Figure 2 The comsol simulation results of the temperature change of the soft - pack battery are given.

[0067] After investigation and further research, it is found that:

[0068] (1) As the conductive connection points of the positive and negative electrodes of the battery, the tabs will generate joule heat (i.e., resistive heat) due to the passage of current during charge and discharge. The tabs are usually made of metal (such as aluminum for the positive electrode and nickel or nickel-plated copper for the negative electrode). Although their resistance is relatively low, during high-rate charge and discharge, the current density is large, and obvious heat accumulation occurs. Therefore, the tabs and the nearby areas are often local high-temperature areas on the surface and inside of the battery.

[0069] (2) When the tabs are located at both ends of the battery, the heat mainly transfers from the tabs at both ends to the center of the battery. Since a layered structure (such as winding or stacking) is usually adopted, the heat transfer along the axial direction of the tabs and the direction perpendicular to the tabs will show differences: the temperature is the highest in the area close to the tabs because the heat source is concentrated here, and there may be additional contact resistance when the tabs are connected to the external circuit, further exacerbating the heat generation. The temperature in the middle of the battery is relatively low because the heat needs to transfer through the materials inside the battery cell (such as electrodes, separators, and electrolytes), and the thermal conductivity of these materials is usually low, resulting in low heat transfer efficiency. Generally, a gradient distribution of gradually decreasing temperature is presented from the tabs to the center of the battery. This distribution may be uneven, especially during high-rate discharge or charge, and the temperature gradient on the side close to the tabs is steeper.

[0070] For the above reasons, the double-helix structure shown in Figure 1 is adopted in this embodiment, aiming to comprehensively and accurately monitor the temperature change of the battery from both sides of the tabs to the center. The battery is divided into left and right parts, and each part is arranged with spiral optical fibers to monitor the heat generation change. The left and right spirals are connected at the midpoint to monitor the temperature change at the center of the battery.

[0071] Specifically, the specific layout methods of the first spiral structure and the second spiral structure are as follows:

[0072] (1) Calculate the spiral pitch of the first spiral structure or the second spiral structure, specifically:

[0073] ;

[0074] Among them, W is the width of the battery, n is the number of turns of the spiral line, g is the minimum pitch, α is the exponential coefficient, controlling the non-linear relationship between the spiral pitch S and the battery width W , usually 0 < α ≤1; k is the adjustment factor.

[0075] Among the above parameters, set the minimum pitchg The purpose is to ensure that the spiral pitch S does not tend to 0, especially when the battery width W is very large; if g = 0, there is no lower limit, S and it may approach 0, resulting in too many turns. g > 0 can ensure the visibility of the spiral or meet the actual application requirements. The minimum pitch g in this embodiment ranges from [0.1 to 1], specifically depending on the size of the battery width W and the specific application scenario. As a specific example, the width of the soft-pack battery used W is 9.9 cm, and the minimum pitch g is set to 0.3 cm to ensure that the pitch is meaningful in practice.

[0076] Exponential coefficient α is used to control the rate at which the spiral pitch S changes with the battery width W. α When = 0, the requirements are not met; α when = 1, it shows a strict inverse ratio, S and it decreases rapidly; 0 < α < 1, showing a moderate inverse relationship, S and it decreases more gently.

[0077] Adjustment factor k is used to control the absolute size of the spiral pitch S , k the larger it is, S the larger the spiral pitch is, and the number of turns of the spiral n is smaller (the number of turns decreases). If the battery width W is between 1 and 100, α = 0.5, then k = 5 to 20 is a reasonable starting point, k = 10 is a compromise value, which can generate a larger W at small S and maintain a reasonable W at large S .

[0078] In this embodiment, it is desired that α and k can be adaptively adjusted according to the battery width W , rather than being fixed values, so as to obtain a reasonable spiral pitch S and the number of turns N at different widths. Therefore, a dynamic adjustment mechanism is introduced to make α and k become W functions of

[0079] α = A / (1 + B W );

[0080] k = C · W D ;

[0081] Among them, A is the proportionality coefficient and also the maximum α value. The value range of A is 0.5 < A < 1.5; when A < 0.5, α is too small and S does not decrease significantly enough; when A > 1.5, α is too large and S decreases too fast, and the number of turns n may be too small; in this embodiment, A = 1 is selected, which is simple and effective, and α gradually decreases from 1.

[0082] B is the adjustment factor used to control the α decrease rate. The larger B is, the faster α decreases. The smaller B is, the slower α decreases. When W = 0, α = A, and when W is very large, α → 0. The reasonable range of B should be between [0.01, 0.2]. When B < 0.01, α hardly changes with W and loses adaptability. When B > 0.2, α decreases too fast and S is too small at high W. In this embodiment, the value of B is in [0.05, 0.1], with a moderate rate and suitable for a medium-width range.

[0083] C is the proportionality coefficient, which determines the absolute magnitude of k and directly affects the value of S. The larger C is, the larger S is and the smaller the number of turns n is. The reasonable range of C should be between 2 and 10. When C < 2, S is relatively small and the number of turns n may be too large. When C > 10, S is relatively large and N may be less than 1. In this embodiment, the value of C is in [3, 7] to balance S and the number of turns n.

[0084] D is the exponent, 0 < D < 1, which makes k increase slowly with W and avoids S from decreasing too fast. The reasonable range of D should be between 0.3 and 0.7. It is recommended that D take 0.5, which is simple and has a smooth effect.

[0085] (2) Calculate the parametric equations of the first helical structure and the second helical structure.

[0086] The parametric equation of the first helical structure is:

[0087] x1 = r × cos(t);

[0088] y1 = r × sin(t);

[0089] The parametric equation of the second helical structure is:

[0090] x2 = -r × cos(t);

[0091] y2 = -r × sin(t);

[0092] To ensure that the starting point of the second helical structure continues from the ending point of the first helical structure, translate the coordinates of the second helical structure:

[0093] x2’ = x2 + x 1end +L;

[0094] y2’ = y2 + y 1end ;

[0095] Where, (x1, y1) represents the Cartesian coordinates of each measurement point on the first helical structure, (x2, y2) represents the Cartesian coordinates of each measurement point on the second helical structure, and (x2’, y2’) represents the Cartesian coordinates of each measurement point on the translated second helical structure; t is the angle, and its value range is [0, 2πn]. The t values of different position points are different, and n is the number of turns of the helix; for example, if you want the number of turns of the helix to be 4, then n is set to 4, that is, it winds four turns.

[0096] r is the radius of the helix. The relationship between the radius r of the helix and the angle t is: r = a + b × t; a is the initial radius of the helix, and b is the rate at which the radius increases with the increase of the angle; x 1end is the x coordinate of the ending point of the first helical structure, y 1end is the y coordinate of the ending point of the first helical structure; L is the translation amount, which is actually the radius value of the first helix at the parameter t = 2π× n That is:

[0097] ;

[0098] Suppose when a =1, b =0.5, then r =1+0.5 t . When n takes 4 (that is, it winds 4 turns), then

[0099] L = 1 + 4π ≈ 13.5664;

[0100] The translation amount L can be used to ensure that after the second helix is translated, its end exactly aligns with the ending point of the first helix, thus forming a continuous double - helix curve.

[0101] As the angle t increases linearly, the helix gradually expands outwards, thus obtaining the first helical curve starting from the origin with a gradually increasing radius. When t = 0, r = 1, and at this time (x1, y1) = (1, 0), and the starting point is on the positive x - axis. As t increases, r becomes larger, and at the same time, cos(t) and sin(t) make the point move along the circumference, forming an expanding helix.

[0102] The second helical structure is a helix symmetric to the first helical structure, forming a mirror image effect by taking the inverse on the x-axis; that is, the shape of the second helical structure is the same as that of the first helical structure, but the direction is opposite.

[0103] By the above method, the coordinates of points at different positions on the first helical structure and the second helical structure can be obtained. Combining with the helical pitch, the specific layout methods of the first helical structure and the second helical structure can be determined.

[0104] After the layout methods of the first helical structure and the second helical structure are determined, further, the temperature data obtained by the double-helical distributed optical fiber can be mapped to the battery surface through a spatial mapping algorithm, so as to obtain the full-range temperature change information on the battery surface; the specific process is as follows:

[0105] Taking the center point O of the battery as the origin, a plane coordinate system of the battery surface is established; the Cartesian coordinates of the data points on the double-helical distributed optical fiber are converted into the plane coordinate system of the battery surface;

[0106] Calculate the arc length of the circular arc segment between two adjacent data points on the double-helical distributed optical fiber, and determine the circular arc segment between two adjacent data points in the plane coordinate system; use the interpolation algorithm to evenly distribute the optical fiber measurement point data within the circular arc segment, so as to accurately map each data point and the corresponding circular arc segment between every two data points in the double-helical structure to the battery surface, obtain the distribution of the double-helical structure on the battery surface; and then obtain the full-range temperature data distribution on the battery surface.

[0107] Specifically, calculating the arc length of the circular arc segment between two adjacent data points on the double-helical distributed optical fiber is specifically:

[0108] ;

[0109] where a is the initial radius of the helix, and b is the rate at which the radius increases with the angle; in matlab, the linspace function can be used to t evenly divide from 0 to 2π n into m data points, and the corresponding angle values of each data point are respectively t 0, t 1,..., t i …, t m 。

[0110] Assume t is evenly distributed (the linspace function in matlab can make the points evenly distributed), then

[0111] ;

[0112] Then the difference between adjacent points is

[0113] ;

[0114] The t value pairs of adjacent points are ( t i , t i+1 ), such as ( t 1, t 2), ( t 2, t 3),..., ( t 1999 , t 2000 ).

[0115] The arc length of each pair of adjacent points can be calculated using the formula L . For example: when a = 1, b = 0.5, the arc length between each pair of points can be calculated as L i . Such as t 1 = 0, t 2 = 8π / 1999, and the arc length between these two points is calculated as 0.013. Since t is uniformly distributed, the Δ t between adjacent points is fixed. However, since r ( t ) = a + b t is linear, the arc length element [( a + b t) 2 + b 2 1 / 2 will increase as t increases, so the arc length between adjacent points will gradually increase.

[0116] In actual situations, it can be calculated at intervals of specific values such as π / 4 or π / 2, which can reduce the amount of calculation.

[0117] Based on the distribution of the double - helix structure on the battery surface, lay the distributed optical fiber flat on the battery surface. The operation process needs to be cautious to avoid damage to the sensor.

[0118] In some embodiments, since there is a PFA or PI sleeve outside the optical fiber, for convenient operation, it can be directly pasted on the battery surface using epoxy resin glue. After pasting, use PI tape for secondary fixation to prevent the sensor from falling off or being damaged due to other uncertain factors.

[0119] ​In some other embodiments, according to the battery size, a flexible thin-film substrate is designed, and grooves adapted to the double-helix distributed optical fiber are formed on the substrate by laser cutting. The double-helix distributed optical fiber is embedded in the grooves and fixed with ultraviolet curing glue, then laid flat on the battery surface and fixed with PI tape.

[0120] Through any one of the above two embodiments, the double-helix distributed optical fiber sensor can be fixed on the battery surface to form a double-helix tape-type temperature sensor arrangement.

[0121] After the sensor is arranged, the battery surface is wiped and cleaned with anhydrous ethanol. A refrigerant is used to locate the starting and ending points of the sensor. The optical fiber terminal generally needs to be knotted to reduce the reflection loss. In this embodiment, the spatial resolution of the sensor is set to 1.28 mm, that is, a measurement point is located every 1.28 mm to obtain temperature change information.

[0122] As a further embodiment, the battery surface temperature monitoring system based on the double-helix optical fiber sensor further includes: a temperature control device, a battery detection device, an OFDR (Optical Frequency Domain Reflectometry) system, and a host computer;

[0123] The battery with the double-helix tape-type temperature sensor arranged is placed in the temperature control device, and the temperature control device can provide a stable temperature environment required for the battery.

[0124] In this embodiment, the temperature control device is an incubator that can maintain a certain temperature constantly; the battery detection device is a charge and discharge tester, which is connected to the host computer and can charge and discharge the battery according to the control configuration file of the host computer, and collect relevant electrical signal data at the same time; the OFDR system is connected to the host computer. The OFDR system periodically interrogates the double-helix distributed optical fiber, detects the interference optical signal, extracts the distributed temperature information and transmits it to the host computer, so as to obtain the temperature change information of the entire range of the battery surface.

[0125] Specifically, the battery to be tested is placed in the incubator, and the positive and negative electrodes of the battery are connected to the signal line and the test line of the charge and discharge tester. The charge and discharge operation of the battery is performed through the test software in the host computer. When the battery is charging and discharging, the surface temperature changes. The optical fiber sensor is affected by the temperature, resulting in a frequency shift of the interference optical signal. The frequency shift is detected by the photodetector PD, and then analyzed and processed in the data processing unit DPU to extract the distributed temperature information.

[0126] In this embodiment, the OFDR system generally includes: a tunable laser source (TLS), an optical coupler (OC), an interferometer, a photodetector (PD), and a data processing unit (DPU); the tunable laser source emits an optical signal with linearly tuned frequency, and the optical coupler divides the optical signal into two paths: one path is injected into the fiber under test, and the other path serves as a reference optical path. When the optical signal propagates in the fiber under test, due to effects such as Rayleigh scattering and Fresnel reflection, a reflected signal is generated; the reflected signal and the reference optical path signal interfere in the interferometer, thereby generating an interference signal.

[0127] When the temperature applied to the fiber changes, the effective refractive index and effective length of the fiber also change, thereby causing a shift in the Rayleigh scattering wavelength inside the fiber. This relationship can be expressed as:

[0128] ;

[0129] where, K T = α + ζ , K ε = 1 - p e are the temperature sensitivity coefficient and the strain sensitivity coefficient respectively; α is the thermal expansion coefficient, ζ is the thermo-optic coefficient, p e is the photoelastic coefficient.

[0130] Δ λ generally refers to the offset of the spectral frequency of the backscattered light relative to the reference state. λ 0 refers to the nominal operating wavelength of the laser source, usually 1550 nm, corresponding to a frequency of about 193.5 THz, which is the most commonly used low-loss wavelength window in optical signal communication and fiber optic sensing. In the OFDR system, the laser will perform a linear frequency sweep around this central wavelength, and the sweep range may be from dozens of GHz to several THz. For example, if the central wavelength of the laser is 1550 nm, the sweep range may be from 1549 nm to 1551 nm, corresponding to a frequency change of ±193.5 GHz.

[0131] Indicates the strain change. The position information is reflected by the measurement principle of optical frequency domain reflectometry (OFDR). OFDR uses a linearly tunable laser to emit an optical signal. The Rayleigh scattering signal in the optical fiber is reflected back and interferes with the reference light. By analyzing the frequency of the interference signal, the position of the scattering point can be determined. In OFDR, the frequency of the laser light source changes linearly at a certain rate (sweep rate, unit: Hz / s). The optical signals reflected from the scattering points at different positions in the optical fiber will have different time delays (τ), which correspond to different interference frequencies (f).

[0132] The relationship formula between the interference frequency and the position is:

[0133] f = (2n / c) * sweep_rate * z;

[0134] where f is the frequency of the interference signal (unit: Hz), n is the refractive index of the optical fiber, c is the speed of light (about 3×10 8 m / s), sweep_rate is the laser frequency sweep rate (unit: Hz / s), and z is the position in the optical fiber (unit: m).

[0135] By performing a Fourier transform on the interference signal, the frequency f can be mapped to the position z, so that the temperature change information corresponding to different positions of the optical fiber can be obtained.

[0136] This embodiment uses a distributed optical fiber sensor to achieve high spatial resolution. It utilizes continuous backscattering signals and broadband laser sweeping, rather than discrete point measurements. The spatial resolution formula is as follows:

[0137] Δ z = c / 2· n eff ·Δ F ;

[0138] where c is the speed of light, n eff is the refractive index of the optical fiber, Δ F is the laser sweep range. The larger Δ F , the higher the resolution. Rayleigh scattering is generated by natural refractive index fluctuations in the optical fiber and is continuously distributed along the optical fiber. OFDR provides continuous spatial information by analyzing the signals of each scattering point through interference.

[0139] Different from FBG which relies on discrete grating regions, distributed sensing does not require a prefabricated structure, and theoretically the resolution can have no fixed point limit.

[0140] This example uses a soft pack battery produced by a company to verify the feasibility and effectiveness of the method of this example. The rated capacity of the NCM battery is 80.7Ah, the voltage range is 2.8~4.25V, and the maximum charge / discharge current is 193.7A (2.4C) / 161A (2C). The battery parameter specifications are shown in Table 1.

[0141] Table 1

[0142]

[0143] The above-mentioned soft-pack battery is arranged with the double-helix distributed optical fiber of this embodiment, and the battery surface temperature monitoring system based on the double-helix optical fiber sensor of this embodiment is used for temperature testing; all experiments are carried out in a constant temperature environment of 25°C. Before the current loading begins, the battery initially rests for 180 minutes to reach thermal equilibrium. The battery is charged using a constant current-constant voltage (CC-CV) protocol. The charging rates are 0.5C and 1C, respectively. In the CC stage, the battery is charged to a cut-off voltage of 4.2V. Next, the charging mode is switched to constant voltage (CV) until the current drops to C / 20. The battery cell is then allowed to stand for 180 minutes. In each discharge stage, the current rate remains constant and consistent with the charging stage. The discharge ends when the voltage drops to 2.8V. The battery still needs to rest for 180 minutes before starting the next charge and discharge cycle at a higher rate.

[0144] Figures 3 - 6 The results of the battery surface temperature evolution at current rates of 0.5C and 1C are given respectively, and each rate includes the temperature changes of the first spiral structure and the second spiral structure. x The axis represents the fiber length, y The axis is the charge and discharge time, z The axis is the surface temperature. As can be seen from the figure, the method proposed in this embodiment can realize the full range temperature monitoring of the battery surface, and the temperature of each point on the battery surface shows strong inconsistency and anisotropy. Compared with other positions, the temperature changes more dramatically at the positions close to the center of the battery and the positive and negative electrodes during the charging and discharging process.

[0145] The temperature optical fiber sensor used in this embodiment is coated with polyimide coating on the surface and encapsulated in a loose sheath tube made of PFA material. The allowable operating temperature is -60℃~300℃, and the monitoring temperature range is full; the double helix layout structure can ensure that the temperature monitoring radiates outward from different center points of the battery. Figure 3 and Figure 4 For example, the horizontal axis is the charge and discharge time, and the vertical axis is the length of the optical fiber along the battery surface. It can be seen that temperature changes can be monitored at any position along the entire optical fiber, and all-round monitoring can be achieved.

[0146] In this embodiment, a distributed fiber optic sensor is adopted to monitor temperature changes, which can achieve temperature measurement at any position along a single optical fiber and has a high spatial resolution. Compared with traditional fiber Bragg grating sensors, the number of measurement points has an exponential span. While ensuring accuracy, more temperature change information on the battery surface can be obtained, without being limited by the number of gratings. In addition, this method can obtain sufficient temperature information, which helps to reconstruct the distribution of the battery surface temperature field subsequently and further supports battery thermal management.

[0147] Although the specific implementation mode of the present invention has been described above in conjunction with the drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative labor are still within the protection scope of the present invention.

Claims

1. A battery surface temperature monitoring system based on a double - helix optical fiber sensor, characterized in that, Comprising: A double - helix distributed optical fiber, the double - helix distributed optical fiber including a first helical structure and a second helical structure with opposite winding directions; the double - helix distributed optical fiber is laid flat on the surface of the battery; taking the center point O of the battery to divide the battery into two left and right parts, the centers of the two parts are A and B respectively; the starting end of the double - helix distributed optical fiber uses point A as the helical starting point, spirally winds outward in the first direction for a set number of turns to form a first helical structure; the end of the first helical structure passes through point O for transition, and then spirally winds inward in the second direction for a set number of turns to reach the terminal of the distributed optical fiber, and the terminal uses point B as the helical end point to form a second helical structure; The helical pitch of the first helical structure or the second helical structure is specifically: ； Among them, W is the battery width, n is the number of turns of the spiral, g is the minimum spacing, α is the exponential coefficient that controls the spiral spacing S and the non-linear relationship with the battery width W where 0 < α ≤ 1; k is the adjustment factor; The parametric equation of the first helical structure is: x1 = r × cos(t); y1 = r × sin(t); The parametric equation of the second helical structure is: x2 = -r × cos(t); y2 = -r × sin(t); In order to ensure that the starting point of the second helical structure continues the end point of the first helical structure, translate the coordinates of the second helical structure: x2’ = x2 + x 1end +L; y2’ = y2 + y 1end ; Among them, (x1, y1) represents the Cartesian coordinates of each measurement point on the first helical structure, (x2, y2) represents the Cartesian coordinates of each measurement point on the second helical structure, and (x2’, y2’) represents the Cartesian coordinates of each measurement point on the second helical structure after translation; t is the angle, and its value range is [0, 2πn], r is the radius of the helix, and the radius of the helix r and the angle t are related as follows: r = a + b × t ; a is the initial radius of the helix, b is the rate at which the radius increases with the angle; L is the translation amount, x 1end is the x coordinate of the end point of the first helical structure, and y 1end is the y coordinate of the end point of the first helical structure.

2. The battery surface temperature monitoring system based on a double - helix optical fiber sensor according to claim 1, wherein, The surface of the double - helix distributed optical fiber is coated with polyimide, and the distributed optical fiber coated with polyimide is fixed in a soluble polytetrafluoroethylene or polyimide sleeve.

3. A battery surface temperature monitoring system based on a double - helix optical fiber sensor according to claim 1, characterized in that, The first helical structure covers the positive - electrode region on the surface of the battery, and the second helical structure covers the negative - electrode region on the surface of the battery.

4. A battery surface temperature monitoring system based on a double - helix optical fiber sensor as claimed in claim 1, wherein, Also comprising: A temperature control device, a battery detection device, an OFDR system and a host computer; the battery provided with the double - helix optical fiber sensor is arranged in the temperature control device, the battery is charged and discharged through the battery detection device, the OFDR system interrogates the double - helix distributed optical fiber at regular intervals, detects the interference optical signal and analyzes it to obtain the temperature change information at different positions, and transmits it to the host computer, so as to extract the temperature change information of the entire surface of the battery.

5. The battery surface temperature monitoring system based on a double-helix optical fiber sensor according to claim 1, characterized in that Establish the exponential coefficient and the adjustment factor respectively α and the adjustment factor k and the function relationship with the battery width W is specifically as follows: α =A / (1 + B W ) k =C· W D ； where A and C are proportionality coefficients; B is a regulating factor used to control α the rate of decline; and D is an exponential factor.

6. A method for monitoring the surface temperature of a battery in a battery surface temperature monitoring system based on a double - helix optical fiber sensor as claimed in claim 1, characterized in that, Comprising: Determine the center O of the battery, take the center point O of the battery to divide the battery into two left and right parts, the centers of the two parts are A and B respectively; The starting end of the distributed optical fiber uses point A as the helical starting point, spirally winds outward in the first direction for a set number of turns to form a first helical structure; the end of the first helical structure passes through point O for transition, and then spirally winds inward in the second direction for a set number of turns, and finally the terminal of the distributed optical fiber uses point B as the helical end point to form a second helical structure; Arrange the battery provided with the double - helix distributed optical fiber in the temperature control device to provide a set temperature environment for the battery; Charge and discharge the battery through the battery detection device, use the OFDR system to interrogate the double - helix distributed optical fiber at regular intervals, detect the interference optical signal and transmit it to the host computer, and the host computer analyzes the interference signal to obtain the temperature information of each data point of the double - helix distributed optical fiber.

7. The battery surface temperature monitoring method according to claim 6, wherein, Also comprising: Map the temperature data obtained by the double - helix distributed optical fiber to the surface of the battery, so as to obtain the temperature change information of the entire surface of the battery; Specifically: Taking the center point O of the battery as the origin, establish a plane coordinate system on the surface of the battery; convert the Cartesian coordinates of the data points on the double - helix distributed optical fiber to the plane coordinate system on the surface of the battery; Calculate the arc length of the circular arc segment between two adjacent data points on the double-helix distributed optical fiber, and determine the circular arc segment between two adjacent data points in the plane coordinate system; use the interpolation algorithm to evenly distribute the optical fiber measurement point data within the circular arc segment, so as to obtain the full-range temperature data distribution on the battery surface.

8. The battery surface temperature monitoring method according to claim 7, wherein, Calculate the arc length of the circular arc segment between two adjacent data points on the double-helix distributed optical fiber, specifically: ； where a is the initial radius of the helix and b is the rate at which the radius increases with the angle; t from 0 to 2π n divide evenly m into t 0, t 1,..., t i …, t m .

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