Battery surface temperature monitoring system and method based on double-spiral optical fiber sensor

Abstract

The invention relates to the technical field of battery temperature detection, and particularly discloses a battery surface temperature monitoring system and method based on a double-spiral optical fiber sensor, and the system comprises a double-spiral distributed optical fiber which comprises a first spiral structure and a second spiral structure which are opposite in winding direction; the double-helix distributed optical fiber is laid on the surface of the battery; the battery is divided into a left part and a right part by a battery center point O, and the centers of the two parts are A and B respectively; the starting end of the double-helix distributed optical fiber spirally and outwards surrounds a set number of turns along a first direction by taking a point A as a spiral starting point to form a first spiral structure; and the tail end of the first spiral structure passes through point O transition, spirally and inwards surrounds a set number of turns along a second direction and then reaches the terminal of the distributed optical fiber, and the terminal takes a point B as a spiral end point to form a second spiral structure. The temperature change of the battery from the two sides of the tab to the center can be comprehensively and accurately monitored.

Description

Technical Field

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

[0002] The statements in this section merely provide background 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, and long cycle life. They are indispensable in electric vehicles (EVs) and energy storage systems (ESSs), and also play a key role in reducing CO2 emissions.

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

[0005] Traditional surface temperature measurement is usually achieved using devices such as thermocouples and thermistors, which are often fixed at pre-set positions and rely heavily on point-based methods, and cannot achieve full-range temperature measurement; Fiber Bragg Grating (FBG) sensor is a quasi-distributed fiber Bragg grating sensor, which is made by burning Bragg gratings at specific positions on optical fibers, and has been initially used to measure battery temperature, strain and other parameters. 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: The prior art discloses a fiber optic sensor monitoring device and system, which realizes temperature / strain monitoring at multiple locations by cascading multiple sensing units composed of fiber gratings and Fabry-Perot cavities. However, the operation process of this method is relatively complicated, and it can only realize multi-point measurement, but cannot realize full-range temperature measurement, and has high requirements for the interval setting of sensors.

[0006] The prior art discloses a battery monitoring method and system based on an optical fiber sensor, in which a single optical fiber is passed through the positive and negative pole tabs of each battery in turn, thereby connecting multiple batteries in series, and the optical fiber located between the positive and negative pole tabs of each battery is coated with a thermosensitive material or a piezoelectric material, while the remaining portion is not coated; the temperature change of the battery to be tested itself can be obtained through the frequency offset of the uncoated portion; this scheme can realize the synchronous measurement of multiple batteries, but for a single battery, full-range temperature measurement cannot be achieved.

[0007] The prior art discloses a method for laying out optical fiber sensors in a ring-disk structure, which winds a single optical fiber to form a ring-disk structure and attaches it to the surface of a battery to monitor the temperature. However, this scheme is a single spiral (disk-shaped) layout, and uses a fiber Bragg grating (FBG) sensor. Although it covers the entire surface, it is limited by the number of Bragg gratings and manufacturing conditions, and cannot achieve accurate measurement of the temperature at any position. At the same time, the operation and use of FBG sensors are relatively troublesome, and it is necessary to ensure that the grating area is not damaged. The rectangular disk-shaped arrangement of optical fibers may cause the four vertices to bend too much, and the radius exceeds the maximum allowable bending radius of the optical fiber, resulting in damage or excessive loss of the optical fiber, affecting the monitoring effect. In addition, due to the limitation of temperature information and the irregular layout, no spacing calculation and temperature mapping rules are given, and the distribution of the battery temperature field cannot be accurately reconstructed, which has certain limitations.

[0008] In addition, the resolution of the fiber Bragg grating sensor will have certain limitations. Resolution refers to the spatial resolution of the fiber sensor measurement, 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 are usually greater than a certain threshold value L1 and L2. A grating area that is too short will reduce the number of fiber cycles, resulting in insufficient Bragg reflection conditions, a wider reflection peak, and a decrease in resolution. The reflection intensity is related to the grating area length and the refractive index adjustment depth. A grating area that is too short will result in insufficient reflectivity and a poor signal-to-noise ratio. The typical grating area length is 5-10mm. A grating area that is too short will also increase the difficulty of manufacturing 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 must be large enough to avoid overlap. When light propagates in the optical fiber, it loses some energy each time it passes through a grating. Too many gratings will cause the far-end signal to be too weak. Interference between multiple gratings may cause crosstalk and affect measurement accuracy.

[0009] In summary, the above methods are inherently limited to discrete or single-point measurements, or only achieve continuous measurements of multiple points in local areas. Since the resolution of the FBG sensor cannot reach a high level, the temperature information between adjacent measurement points may not be obtained, that is, the features are lost. When these features are missing, the measured temperature information is incomplete, which will lead to inaccurate analysis of the temperature changes on the entire surface of the battery. When the battery temperature field needs to be further reconstructed, the reconstruction results will also 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

[0010] In order 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, designs a double-helix sensor structure, and the double helix is ​​arranged near the positive and negative poles of the battery respectively, so as to realize full-range measurement of the battery surface temperature.

[0011] In some embodiments, the following technical solutions are adopted: A battery surface temperature monitoring system based on a double-helix optical fiber sensor comprises: a double-helix distributed optical fiber, the double-helix distributed optical fiber comprises 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 two parts, left and right, 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 spiral starting point, spirally winds outwards in a first direction for a set number of turns, to form a first spiral structure; the tail end of the first spiral structure transitions through point O, spirally winds inwards in a second direction for a set number of turns, and reaches the terminal of the distributed optical fiber, and the terminal takes point B as the spiral end point to form a second spiral structure.

[0012] The first spiral structure covers the positive electrode area on the surface of the battery, and the second spiral structure covers the negative electrode area on the surface of the battery.

[0013] As a further solution, the helical pitch of the first helical structure or the second helical structure is specifically: ; in, W is the battery width, n is the number of turns of the helix, g is the minimum spacing, α is the exponential coefficient, controlling the spiral pitch S With battery width W Nonlinear relationship, usually 0< α ≤1; k is the regulating factor.

[0014] Establish exponential coefficients respectively α and regulatory factors k With battery width W The functional relationship between them is as follows: α =A / (1+B W ); k =C W D ; Among them, A and C are proportional coefficients; B is the adjustment factor used to control α The rate of decline; D is the exponential factor.

[0015] As a further solution, 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); To ensure that the starting point of the second spiral structure continues the end point of the first spiral structure, the coordinates of the second spiral structure are translated: x2' = x2 + x 1end +L; y2' = y2 + y 1end ; Wherein, (x1, y1) represents the Cartesian coordinates of each measuring point on the first spiral structure, (x2, y2) represents the Cartesian coordinates of each measuring point on the second spiral structure, and (x2', y2') represents the Cartesian coordinates of each measuring point on the second spiral structure after translation; t is the angle, ranging from [0, 2πn], where n is the number of turns of the helix; r is the radius of the helix, the radius of the helix r With Angle t The relationship is: 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, x 1end is the x coordinate of the end point of the first helical structure, y 1end is the y coordinate of the end point of the first helix. In other embodiments, the following technical solutions are adopted: A battery surface temperature monitoring method based on a double-helix optical fiber sensor, comprising: Determine the battery center O, and divide the battery into two parts, the left and right parts, with the centers of the two parts A and B respectively; The beginning of the distributed optical fiber takes point A as the spiral starting point, and spirals outward along the first direction for a set number of turns to form a first spiral structure; the tail end of the first spiral structure transitions through point O, and spirals inward along the second direction for a set number of turns, and finally the terminal of the distributed optical fiber takes point B as the spiral end point to form a second spiral structure; The battery provided with the double-helix distributed optical fiber is placed in a temperature control device to provide a set temperature environment for the battery; The battery is charged and discharged through the battery detection device, and the OFDR system is used to regularly query the double-helix distributed optical fiber, detect the interference light signal and transmit it to the host computer. The host computer analyzes the interference signal to obtain the temperature information of each data point of the double-helix distributed optical fiber. As a further solution, the temperature data acquired by the double-helix distributed optical fiber is mapped to the battery surface, thereby obtaining the temperature change information of the battery surface in the whole range; specifically: 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-helix distributed optical fiber are converted into the plane coordinate system of the battery surface; The arc length of the arc segment between two adjacent data points on the double-helix distributed optical fiber is calculated to determine the arc segment between two adjacent data points in the plane coordinate system; the optical fiber measurement point data within the arc segment is evenly distributed using an interpolation algorithm to obtain the full range temperature data distribution of the battery surface.

[0016] As a further solution, the arc length of the arc segment between two adjacent data points on the double-helix distributed optical fiber is calculated as follows: ; 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 Evenly divide m data points, the angle values ​​corresponding to each data point are t 0, t 1,..., t i …, t m . Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention designs a double-helix magnetic 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 measuring 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, and realizing the leap from point to surface acquisition of temperature change information, with strong adaptability.

[0017] For lithium-ion soft-pack or square batteries with tabs at both ends, the temperature usually decreases gradually from the tabs to the center of the battery. This distribution may be uneven, especially when discharging or charging at high rates, the temperature gradient near the tab is steeper. The single helix structure disclosed in the prior art makes it difficult to achieve comprehensive and continuous measurement of the temperature in the area where the tabs are located at both ends; the present invention divides the battery into two parts, left and right, through a double helix structure, and each part is arranged with a spiral optical fiber to monitor the heat generation changes of the two parts; the left and right helices are connected at the middle point to monitor the temperature changes in the center of the battery, and the temperature monitoring points can be reasonably arranged according to the heat distribution of the battery, and the temperature changes of the battery from the two sides of the tabs to the center can be comprehensively and accurately monitored.

[0018] (2) The present invention accurately obtains the double helix structure by reasonably designing the helical pitch and the coordinates of each point on the helix line, maps the optical fiber data to the battery surface, and reconstructs the temperature distribution on the battery surface. This can ensure that the temperature at most locations on the surface can be monitored by the sensor, thereby achieving all-round monitoring of the battery surface, discovering potential temperature anomalies as early as possible, and optimizing the battery design based on the temperature distribution.

[0019] (3) The prior art uses FBG sensors to measure the surface temperature of batteries. Due to the number and spacing of measurement points, the spatial resolution cannot reach a high level, which limits the sensor's ability to obtain information. This may result in the failure to obtain temperature information between adjacent measurement points, i.e., loss of features, which in turn leads to incomplete measured temperature information. The present invention uses distributed optical fiber sensors to achieve high spatial resolution. It uses continuous backscattered signals and wide-band laser scanning instead of discrete point measurements; the signal of each scattering point can be analyzed through interference to provide continuous spatial information.

[0020] (4) The double-helix magnetic tape-type distributed optical fiber sensor structure of the present invention is resistant to high temperatures and is not susceptible to corrosion. It has high accuracy and fast response. It is expected to be implanted inside the battery to monitor uneven temperature distribution and evolution, providing corresponding support for exploring the boundaries of safe use.

[0021] Other features and advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the layout structure of the double-helix distributed optical fiber on the surface of the battery in an embodiment of the present invention; Figure 2 The comsol simulation result of the temperature change of the soft-pack battery during the charging and discharging process in the embodiment of the present invention; Figure 3The battery surface temperature evolution corresponding to the first spiral structure at 0.5C current in the embodiment of the present invention; Figure 4 The battery surface temperature evolution corresponding to the second spiral structure at 0.5C current in the embodiment of the present invention; Figure 5 is the battery surface temperature evolution corresponding to the first spiral structure at 1.0C current in an embodiment of the present invention; Figure 6 Graph 1 is the battery surface temperature evolution corresponding to the second spiral structure at a current of 1.0C in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0024] It should be noted that the terms used herein are only for describing specific embodiments 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, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0025] Embodiment 1 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 , including: a double-helix distributed optical fiber, the double-helix distributed optical fiber includes a first helix structure and a second helix structure in opposite directions; the double-helix distributed optical fiber is laid flat on the surface of the battery, and the specific layout is as follows: The battery is divided into two parts, left and right, 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 spiral starting point, and spirals outward along the first direction for a set number of turns to form a first spiral structure; the tail end of the first spiral structure transitions through point O, spirals inward along the second direction for a set number of turns, and reaches the terminal of the distributed optical fiber, and the terminal takes point B as the spiral end point to form a second spiral structure.

[0026] As a specific example, this embodiment selects a distributed optical fiber sensor based on Rayleigh scattering, selects an optical fiber with a core diameter of 9μm and a cladding diameter of 125μm, and coats the surface of the optical fiber with polyimide. The coating method can be dip coating, spray coating or spin coating process to ensure that the coating is uniform and the thickness is moderate (usually a few microns to tens of microns); 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 the external mechanical stress is reduced or completely blocked from being transmitted to the optical fiber core through physical design, so that the change of the Rayleigh scattering signal mainly reflects the temperature effect, rather than the strain effect, to isolate the influence of strain on temperature.

[0027] The sheath is usually a flexible or rigid protective layer (such as a polymer sheath, stainless steel tube or a relaxed structure) that wraps the sensing optical fiber. The optical fiber maintains a certain degree of freedom inside the sheath and is not directly coupled to the external structure; the sheath absorbs or disperses the tensile, compressive or bending stresses applied by the outside world to prevent these forces from acting directly on the optical fiber. Under this design, when the external environment undergoes mechanical deformation (such as stretching or compression), the sheath will first bear these stresses, and the optical fiber will not be stretched or compressed because it is in a relaxed state, so its length and strain state remain basically unchanged, so that the signal change is only caused by temperature, ensuring the accuracy of the temperature measurement results.

[0028] The first spiral structure is arranged near the positive electrode of the battery, covers the positive electrode area on the surface of the battery, and spirals in a counterclockwise direction; the second spiral structure is arranged near the negative electrode of the battery, covers the negative electrode area on the surface of the battery, and spirals in a clockwise direction.

[0029] The first spiral structure and the second spiral structure can completely cover various areas of the battery surface to achieve full-range measurement of the battery surface temperature.

[0030] For lithium-ion soft-pack or square batteries with positive and negative tabs at both ends, the temperature field distribution during the charge and discharge process is a complex heat conduction and heat generation problem, which is affected by many factors, including the battery's charge and discharge rate, tab material and design, ambient temperature, and the thermal conductivity characteristics of the battery's internal structure. Figure 2 The Comsol simulation results of the temperature variation of the soft-pack battery are given.

[0031] After investigation and further research, we found that: (1) The tabs are the conductive connection points between the positive and negative electrodes of the battery. During the charge and discharge process, Joule heat (i.e., resistance heat) will be generated due to the passage of current. 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 low, the current density is high during high-rate charge and discharge, and heat accumulation is obvious. Therefore, the tabs and the surrounding areas are often local high-temperature areas on the surface and inside of the battery.

[0032] (2) When the tabs are located at both ends of the battery, heat is mainly transferred from the tabs at both ends to the center of the battery. Since a layered structure (such as winding or lamination) is usually used, the heat transfer along the axial direction of the tab and perpendicular to the tab will show differences: the temperature is highest in the area close to the tab because the heat source is concentrated here, and there may be additional contact resistance when the tab is connected to the external circuit, further aggravating the heat generation. The temperature in the middle of the battery is relatively low because the heat needs to be transferred through the materials inside the battery cell (such as electrodes, diaphragms and electrolytes), and the thermal conductivity of these materials is usually low, resulting in low heat transfer efficiency. From the tab to the center of the battery, there is usually a gradient distribution with a gradually decreasing temperature. This distribution may be uneven, especially during high-rate discharge or charge, when the temperature gradient close to the tab is steeper.

[0033] Based on the above reasons, this embodiment adopts Figure 1 The double helix structure shown is designed to comprehensively and accurately monitor the temperature changes of the battery from both sides of the lug to the center. The battery is divided into two parts, left and right, and each part is arranged with spiral optical fiber to monitor the heat generation changes. The left and right spirals are connected at the middle point to monitor the temperature changes in the center of the battery.

[0034] Specifically, the specific layout method of the first spiral structure and the second spiral structure is as follows: (1) Calculate the helical pitch of the first helical structure or the second helical structure, specifically: ; in, W is the battery width, n is the number of turns of the helix, g is the minimum spacing, α is the exponential coefficient, controlling the spiral pitch S With battery width W Nonlinear relationship, usually 0< α ≤1; k is the regulating factor.

[0035] In the above parameters, set the minimum spacing g The purpose is to ensure the spiral pitch S Does not approach 0, especially in the battery width W In very large cases; if g =0 means no lower limit, SIt may approach 0, resulting in too many circles. g >0 can ensure the visibility of the spiral or meet the actual application requirements. g The value range is [0.1~1], depending on the battery width W As a specific example, the width of the soft pack battery used is W The minimum spacing is 9.9 cm. g Set to 0.3cm to ensure that the spacing is meaningful.

[0036] Exponential coefficient α To control the pitch of the spiral S The rate of change with the battery width W. α =0, the demand is not met; α =1, it is strictly inversely proportional. S Decline quickly; 0< α <1, showing a mild inverse relationship, S The decline is relatively gentle.

[0037] Modulating Factor k To control the pitch of the spiral S The absolute size of k The bigger, S The larger the number of turns of the spiral n The smaller (the number of turns decreases). If the battery width W Between 1 and 100, α =0.5, then k =5~20 is a reasonable starting point. k =10 is a compromise value, which can be used in small W When a larger S , in the big W Keep reasonable S .

[0038] In this embodiment, it is hoped that α and k Can be adjusted according to battery width W Adaptive adjustment, rather than fixed value, to get reasonable spiral pitch at different widths S and the number of turns N. Therefore, a dynamic adjustment mechanism is introduced to make α and k become W The function is: α =A / (1+B W ); k =C W D ; Among them, A is the proportional coefficient, which is 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 drop significantly enough. When A>1.5, α is too large, S drops 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.

[0039] B is a regulating factor used to control the rate of α decrease. 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 [0.05, 0.1], with a moderate rate, suitable for a medium width range.

[0040] C is the proportionality coefficient, which determines the absolute value 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 is less than 2, S is too small and the number of turns n may be too many. When C is greater than 10, S is too large and N may be less than 1. In this embodiment, the value of C is between [3, 7] to balance S and the number of turns n.

[0041] D is an exponent, 0<D<1, which makes k increase slowly with W to avoid S decreasing too quickly. The reasonable range of D should be between 0.3 and 0.7. It is recommended that D be 0.5, which is simple and has a smooth effect.

[0042] (2) Calculate the parametric equations of the first helical structure and the second helical structure.

[0043] 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); To ensure that the starting point of the second spiral structure continues the end point of the first spiral structure, the coordinates of the second spiral structure are translated: x2' = x2 + x 1end +L; y2' = y2 + y 1end ; Wherein, (x1, y1) represents the Cartesian coordinates of each measuring point on the first spiral structure, (x2, y2) represents the Cartesian coordinates of each measuring point on the second spiral structure, and (x2', y2') represents the Cartesian coordinates of each measuring point on the second spiral structure after translation. t is the angle, ranging from [0, 2πn], with different t values ​​at different positions. n is the number of turns of the spiral. For example, if you want the number of turns of the spiral to be 4, then n is set to 4, i.e., four turns.

[0044] r is the radius of the spiral. The relationship between the radius r of the spiral and the angle t is: r = a + b × t; a is the initial radius of the spiral, b is the rate at which the radius increases with the angle; x 1end is the x coordinate of the end point of the first helical structure, y 1end is the y coordinate of the end point of the first spiral structure; L is the translation, which is actually the first spiral at parameter t = 2π× n The radius value at is: ; Assume that a =1, b =0.5, then r =1+0.5 t . When n is 4 (i.e. 4 turns), then L = 1 + 4π ≈ 13.5664; Translation L It can be used to ensure that the end of the second helix is ​​aligned with the end of the first helix after translation, thus forming a continuous double helix curve.

[0045] As the angle t increases linearly, the spiral gradually expands outward, thus obtaining the first spiral curve starting from the origin with a gradually increasing radius. When t = 0, r = 1, at this time (x1, y1) = (1, 0), the starting point is in the positive direction of the 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 a spiral that expands outward.

[0046] The second helical structure is a helix symmetrical to the first helical structure, and a mirror image effect is formed by inverting it 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.

[0047] The coordinates of points at different positions on the first spiral structure and the second spiral structure can be obtained in the above manner. Combined with the spiral pitch, the specific layout of the first spiral structure and the second spiral structure can be determined.

[0048] After the layout of the first helical structure and the second helical structure is determined, the temperature data obtained by the double-helix distributed optical fiber can be further mapped to the battery surface through a spatial mapping algorithm, thereby obtaining the temperature change information of the battery surface over the entire range; the specific process is as follows: 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-helix distributed optical fiber are converted into the plane coordinate system of the battery surface; The arc length of the arc segment between two adjacent data points on the double-helix distributed optical fiber is calculated to determine the arc segment between two adjacent data points in the plane coordinate system; the optical fiber measurement point data within the arc segment is evenly distributed using an interpolation algorithm, so that each data point in the double-helix structure and the arc segment corresponding to each two data points are accurately mapped to the battery surface, and the distribution of the double-helix structure on the battery surface is obtained; and the full-range temperature data distribution on the battery surface is then obtained.

[0049] Specifically, the arc length of the arc segment between two adjacent data points on the double-helix distributed optical fiber is calculated as follows: ; Where a is the initial radius of the spiral, and b is the rate at which the radius increases with the angle. In MATLAB, the linspace function can be used to convert t From 0 to 2π n Evenly divide m data points, the angle values ​​corresponding to each data point are t 0, t 1,..., t i …, t m .

[0050] Assumptions t is uniformly distributed (the linspace function in Matlab can make the points uniformly distributed), then ; Then the difference between adjacent points is ; Adjacent points t The value pair is ( t i , t i+1 ),like( t 1, t 2), ( t 2, t 3), ..., ( t 1999 , t 2000 ).

[0051] The arc length of each pair of adjacent points can be calculated using the formula L Calculation. For example: a =1, b =0.5, the arc length between each pair of points can be calculated L i .like t 1=0, t 2=8π / 1999, the arc length between these two points is calculated to be 0.013. t is evenly distributed, and the Δ between adjacent points t is fixed. But due to r ( t )= a + b t is linear, the arc length is infinitesimal [( a + b t) 2 +b 2 ] 1 / 2 Will follow t As it increases, the arc lengths of adjacent points gradually become larger.

[0052] In actual situations, the calculation can be performed at intervals of specific values ​​such as π / 4 or π / 2, which can reduce the amount of calculation.

[0053] Based on the distribution of the double helix structure on the battery surface, the distributed optical fiber is laid flat on the battery surface. The operation process needs to be cautious to avoid damage to the sensor.

[0054] In some embodiments, since the optical fiber is provided with a PFA or PI sleeve, for ease of operation, it can be directly attached to the battery surface using epoxy resin glue. After attachment, PI tape is used for secondary fixation to prevent other uncertain factors from causing the sensor to fall off or be damaged.

[0055] In other embodiments, a flexible film substrate is designed according to the battery size, and a groove compatible with the double-helix distributed optical fiber is formed on the substrate by laser cutting. The double-helix distributed optical fiber is embedded in the groove and fixed with UV-curing adhesive, and then laid flat on the battery surface and fixed with PI tape.

[0056] Through any of the above two implementations, it is possible to fix the double-helix distributed optical fiber sensor on the surface of the battery to form a double-helix magnetic tape type temperature sensor arrangement.

[0057] After the sensor is laid out, use anhydrous ethanol to wipe and clean the battery surface. Use refrigerant to locate the start and end points of the sensor. The optical fiber terminal generally needs to be knotted to reduce reflection loss. In this embodiment, the spatial resolution of the sensor is set to 1.28 mm, that is, a measuring point is located every 1.28 mm to obtain temperature change information.

[0058] As a further implementation, 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; The battery provided with the double-helix magnetic tape temperature sensor is arranged in a temperature control device, and the temperature control device can provide the battery with the required stable temperature environment.

[0059] In this embodiment, the temperature control device is a temperature box 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 execute the control configuration file of the host computer to charge and discharge the battery, and collect relevant electrical signal data at the same time; the OFDR system is connected to the host computer, and the OFDR system periodically queries the double-helix distributed optical fiber, detects the interference light signal, extracts the distributed temperature information and transmits it to the host computer, thereby obtaining the full range of temperature change information on the battery surface.

[0060] Specifically, the battery to be tested is placed in a temperature box, and the positive and negative electrodes of the battery are connected to the signal lines and test lines of the charge and discharge tester. The battery is charged and discharged through the test software in the host computer. When the battery is charged and discharged, the surface temperature changes. The fiber optic sensor is affected by temperature, causing the interference light signal to shift in frequency. The frequency shift is detected by the photodetector PD, and then analyzed and processed in the data processing unit DPU to extract distributed temperature information.

[0061] 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 a frequency-linearly tuned optical signal, and the optical coupler divides the optical signal into two paths: one path is injected into the optical fiber to be tested, and the other path is used as a reference optical path. When the optical signal propagates in the optical fiber to be tested, a reflection signal is generated due to effects such as Rayleigh scattering and Fresnel reflection; the reflection signal interferes with the reference optical path signal in the interferometer, thereby generating an interference signal.

[0062] When the temperature applied to the optical fiber changes, the effective refractive index and effective length of the optical fiber will also change, causing the Rayleigh scattering wavelength inside the optical fiber to shift. This relationship can be expressed as: ; in, KT = α + ζ , K ε =1- p e are the temperature sensitivity coefficient and the strain sensitivity coefficient respectively; α is the coefficient of thermal expansion, ζ is the thermo-optical coefficient, p e is the photoelastic coefficient.

[0063] Δ λ Usually refers to the shift in the spectral frequency of the backscattered light relative to a reference state. λ 0 refers to the nominal operating wavelength of the laser source, which is usually 1550nm, corresponding to a frequency of about 193.5THz, which is the most commonly used low-loss wavelength window in optical signal communications 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 tens of GHz to several THz. For example, if the central wavelength of the laser is 1550nm, the sweep range may be 1549nm to 1551nm, corresponding to a frequency change of ±193.5 GHz.

[0064] Indicates strain changes. Position information is reflected through the measurement principle of optical frequency domain reflectometry (OFDR). OFDR uses a linearly tuned laser to emit a light signal, and the Rayleigh scattered 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 light signals reflected back from scattering points at different positions in the optical fiber will have different time delays (τ), which corresponds to different interference frequencies (f).

[0065] The relationship between interference frequency and position is: f = (2n / c) * sweep_rate * z; Where f is the frequency of the interference signal (unit: Hz), n is the refractive index of the optical fiber, and 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 fiber (unit: m).

[0066] By performing 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.

[0067] This embodiment uses a distributed optical fiber sensor to achieve high spatial resolution, which uses continuous backscattered signals and broadband laser sweeps instead of discrete point measurements. The spatial resolution formula is as follows: Δ z = c / 2· n eff Δ F ; Where c is the speed of light, n eff is the refractive index of the optical fiber, Δ F is the laser sweep range. F The larger the value, the higher the resolution. Rayleigh scattering is caused by the natural refractive index fluctuations in the optical fiber and is continuously distributed along the optical fiber. OFDR provides continuous spatial information by interferometrically analyzing the signal at each scattering point.

[0068] Unlike FBG, which relies on discrete gate regions, distributed sensing does not require prefabricated structures and theoretically has no fixed point restrictions on resolution.

[0069] 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.

[0070] Table 1

[0071] The above-mentioned soft-pack battery is arranged with the double-helix distributed optical fiber of this embodiment, and the temperature test is carried out using the battery surface temperature monitoring system based on the double-helix optical fiber sensor of this embodiment; 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.

[0072] Figure 3-Figure 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, yThe 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. 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.

[0073] This embodiment uses a distributed fiber optic sensor to monitor temperature changes, which can achieve temperature measurement at any position along an optical fiber with high spatial resolution. Compared with traditional fiber Bragg grating sensors, the number of measurement points is exponentially cross-domain. While ensuring accuracy, more temperature change information on the battery surface is obtained, and it is no longer limited by the number of gratings. In addition, this method obtains sufficient temperature information, which is helpful for the subsequent reconstruction of the distribution of the battery surface temperature field, and further supports battery thermal management.

[0074] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A battery surface temperature monitoring system based on a double-helix optical fiber sensor, characterized in that: include: A double-helix distributed optical fiber, the double-helix distributed optical fiber comprises 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 a battery; the battery is divided into two parts, left and right, 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 spiral starting point, and spirally winds outward along a first direction for a set number of turns to form a first helical structure; the tail end of the first helical structure transitions through point O, and spirally winds inward along a 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 end point to form a second helical structure.

2. A battery surface temperature monitoring system based on a double-helix optical fiber sensor as claimed in claim 1, characterized in that: 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 as claimed in claim 1, characterized in that: The first spiral structure covers the positive electrode area on the battery surface, and the second spiral structure covers the negative electrode area on the battery surface.

4. A battery surface temperature monitoring system based on a double-helix optical fiber sensor as claimed in claim 1, characterized in that: Also includes: Temperature control device, battery detection device, OFDR system and host computer; the battery equipped with a double-helix optical fiber sensor is set in the temperature control device, and the battery is charged and discharged through the battery detection device. The OFDR system periodically queries the double-helix distributed optical fiber, detects and analyzes the interference light signal, obtains the temperature change information at different positions, and transmits it to the host computer, thereby extracting the temperature change information of the whole range of the battery surface.

5. A battery surface temperature monitoring system based on a double-helix optical fiber sensor as claimed in claim 1, characterized in that: The helical pitch of the first helical structure or the second helical structure is specifically: ； in, W is the battery width, n is the number of turns of the helix, g is the minimum spacing, α is the exponential coefficient, controlling the spiral pitch S With battery width W Nonlinear relationship, 0< α ≤1; k is the regulating factor.

6. A battery surface temperature monitoring system based on a double-helix optical fiber sensor as claimed in claim 5, characterized in that: Establish exponential coefficients respectively α and regulatory factors k With battery width W The functional relationship between them is as follows: α =A / (1+B W ); k =C· W D ； Among them, A and C are proportional coefficients; B is the adjustment factor used to control α The rate of decline; D is the exponential factor.

7. A battery surface temperature monitoring system based on a double-helix optical fiber sensor as claimed in claim 1, characterized in that: 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); To ensure that the starting point of the second spiral structure continues the end point of the first spiral structure, the coordinates of the second spiral structure are translated: x2’ = x2 + x 1end +L; y2' = y2 + y 1end ; Wherein, (x1, y1) represents the Cartesian coordinates of each measuring point on the first spiral structure, (x2, y2) represents the Cartesian coordinates of each measuring point on the second spiral structure, and (x2', y2') represents the Cartesian coordinates of each measuring point on the second spiral structure after translation; t is the angle, ranging from [0, 2πn], where n is the number of turns of the helix; r is the radius of the helix, the radius of the helix r With Angle t The relationship is: 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, x 1end is the x coordinate of the end point of the first helical structure, y 1end is the y coordinate of the end point of the first helix.

8. A battery surface temperature monitoring method based on a double-helix optical fiber sensor, characterized in that: include: Determine the battery center O, and divide the battery into two parts, the left and right parts, with the centers of the two parts A and B respectively; The beginning of the distributed optical fiber takes point A as the spiral starting point, and spirals outward along the first direction for a set number of turns to form a first spiral structure; the tail end of the first spiral structure transitions through point O, and spirals inward along the second direction for a set number of turns, and finally the terminal of the distributed optical fiber takes point B as the spiral end point to form a second spiral structure; The battery provided with the double-helix distributed optical fiber is arranged in a temperature control device to provide a set temperature environment for the battery; The battery is charged and discharged through the battery detection device, and the OFDR system is used to regularly query the double-helix distributed optical fiber, detect the interference light signal and transmit it to the host computer. The host computer analyzes the interference signal to obtain the temperature information of each data point of the double-helix distributed optical fiber.

9. A battery surface temperature monitoring method based on a double-helix optical fiber sensor as claimed in claim 8, characterized in that: Also includes: The temperature data obtained by the double-helix distributed optical fiber is mapped to the battery surface to obtain the temperature change information of the entire range of the battery surface; Specifically: 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-helix distributed optical fiber are converted into the plane coordinate system of the battery surface; The arc length of the arc segment between two adjacent data points on the double-helix distributed optical fiber is calculated to determine the arc segment between two adjacent data points in the plane coordinate system; the optical fiber measurement point data within the arc segment is evenly distributed using an interpolation algorithm to obtain the full range temperature data distribution of the battery surface.

10. A battery surface temperature monitoring method based on a double-helix optical fiber sensor as claimed in claim 9, characterized in that: Calculate the arc length 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 Evenly divide m data points, the angle values ​​corresponding to each data point are t 0, t 1,..., t i …, t m .

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