CN113378379B - Lithium battery thermal management design method, system and terminal based on critical heat exchange coefficient - Google Patents
Lithium battery thermal management design method, system and terminal based on critical heat exchange coefficient Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 49
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 41
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 41
- 238000013461 design Methods 0.000 title claims abstract description 27
- 238000000556 factor analysis Methods 0.000 claims abstract description 8
- 230000017525 heat dissipation Effects 0.000 claims description 31
- 230000006870 function Effects 0.000 claims description 26
- 230000008859 change Effects 0.000 claims description 13
- 230000008569 process Effects 0.000 claims description 13
- 238000004088 simulation Methods 0.000 claims description 12
- 238000013459 approach Methods 0.000 claims description 9
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 7
- 229910001416 lithium ion Inorganic materials 0.000 claims description 7
- 238000004364 calculation method Methods 0.000 claims description 6
- 238000007599 discharging Methods 0.000 claims description 6
- 238000004590 computer program Methods 0.000 claims description 4
- 230000001351 cycling effect Effects 0.000 claims description 3
- 238000012545 processing Methods 0.000 claims description 3
- 238000013486 operation strategy Methods 0.000 abstract description 2
- 238000005457 optimization Methods 0.000 abstract 1
- 230000020169 heat generation Effects 0.000 description 12
- 238000012360 testing method Methods 0.000 description 4
- 230000008878 coupling Effects 0.000 description 3
- 238000010168 coupling process Methods 0.000 description 3
- 238000005859 coupling reaction Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 230000005855 radiation Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 239000012782 phase change material Substances 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000013021 overheating Methods 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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Abstract
The invention belongs to the technical field of lithium battery thermal management, and discloses a lithium battery thermal management design method, a system and a terminal based on a critical heat exchange coefficient, which comprise the steps of defining the critical heat exchange coefficient h cr; establishing a set of numerical solution method for determining critical heat exchange coefficients; based on the influence factor analysis, a fitting formula of h cr is obtained. The invention provides and quantitatively solves a design concept based on the critical heat exchange coefficient to design a heat management system of the lithium battery, and analyzes the quantitative influence of various working condition factors on the critical heat exchange coefficient. Based on the design concept, an operation strategy based on intervention time is provided, and the battery temperature is effectively controlled in a safety range; the invention innovatively provides the critical heat exchange coefficient h cr, and develops a set of numerical solution method for determining the critical heat exchange coefficient, the critical heat exchange coefficient h cr can effectively guide the thermal safety operation of the system, and has good guiding significance for the parameter selection and the optimization design of the thermal management system.
Description
Technical Field
The invention belongs to the technical field of lithium battery thermal management, and particularly relates to a lithium battery thermal management design method, system and terminal based on a critical heat exchange coefficient.
Background
At present, lithium batteries are the most widely used power batteries at present due to the advantages of large capacity, high energy density, small self-discharge and the like. When the battery temperature is too high, the battery discharge will accelerate, causing a series of dangers such as overheating, ignition, explosion, etc., so a more advanced and more reasonable thermal management system needs to be designed to keep the battery temperature in the ideal operating temperature range.
In order to solve the problem of rapid heat generation of batteries under extreme working conditions, a common method is to adopt a heat dissipation system with high conduction capacity to improve heat dissipation capacity, such as heat pipes, phase change materials, heat pipe-phase change material coupling and the like, and the like (Nanchang university. A cylindrical lithium battery module for vehicles based on heat pipe and liquid cooling coupling heat dissipation: CN202011502669.2[ P ].2021-02-12 ]) an invention of a heat pipe and liquid cooling coupling heat dissipation heat management system. But with the consequent increase in system complexity and energy consumption. When designing a thermal management system, researchers generally perform a series of tests such as multiplying power test, test in a high-temperature environment and the like on the system, and then perform optimal design, so that the test period is long and the resource consumption is large. Battery thermal management under extreme conditions is therefore challenging.
By the nature of thermal management, ensuring that the heat dissipation system removes the generated heat in a timely manner avoids the rapid rise .Semenov(SEMENOV N.N..Some Problems in Chemical Kinetics and Reactivity,Volume 2[M].Princeton University Press:2017-03-14.) in battery temperature suggests a tool to represent the interaction between heat generation and heat dissipation that compares the rate of heat generation and heat dissipation as a function of battery temperature. The SEMENOV chart can be used to analyze the impact of changes in the convective heat transfer coefficient on the thermal runaway process, predicting the safe area of the thermal design space. The concept of SEMENOV drawing, i.e. matching of battery heat generation and dissipation, can be extended to battery thermal management, but related studies in the past have been qualitative analyses only, lacking quantitative studies.
Through the above analysis, the problems and defects existing in the prior art are as follows:
The design concept of the lithium battery thermal management system under the extreme working condition lacks a clear theoretical guidance, which can cause the system to be too redundant and reduce the reliability and the economy of the system. In addition, the heat dissipation performance of the designed thermal management system is insufficient, which also causes the safety performance of the battery to be reduced.
The difficulty of solving the problems and the defects is as follows:
Proper quantitative analysis methods are lacking to investigate the relationship between the actual heat dissipation requirement and the actual working condition. The invention provides a heat management system design method based on a critical heat exchange coefficient by applying the heat generation and heat dissipation balance principle. H cr is a function depending on actual operation condition parameters, and the balance condition of heat generation and heat dissipation of the battery can be rapidly judged by combining the actual parameters.
The meaning of solving the problems and the defects is as follows:
According to the actual operation condition parameters, the critical heat exchange coefficient is calculated, and a design basis is provided for the design of the heat dissipation performance of the thermal management system. On the basis of judging the temperature rise risk based on the critical heat exchange coefficient, the invention can guide the battery system to take auxiliary intervention measures.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a lithium battery thermal management design method, a system and a terminal based on a critical heat exchange coefficient.
The invention is realized in such a way that the lithium battery thermal management design method based on the critical heat exchange coefficient comprises the following steps:
Step one, defining a critical heat exchange coefficient h cr; establishing a set of numerical solution method for determining critical heat exchange coefficients;
Step two, based on influence factor analysis, obtaining a fitting function formula of h cr about actual operation condition parameters;
Step three, based on h cr, carrying out unexpected temperature rise risk pre-judgment on the battery; taking intervention measures on the battery during the intervention time.
In the first step, the critical heat exchange coefficient h cr is a heat exchange coefficient minimum threshold value for ensuring that the temperature of the lithium battery is in an ideal working range, and under the extreme working condition of high-rate discharge, the heat generating process and the heat dissipating process of the battery are comprehensively considered, and the change of the highest temperature of the battery along with time mainly comprises four conditions of case 1, case 2, case 3 and case 4:
In case 1, the heat dissipation capacity of the lithium ion battery heat dissipation system is far greater than the self-heat generation capacity of the battery, and the highest temperature of the lithium ion battery can be well controlled within a threshold range;
In case 2, the highest temperature of the lithium battery is just controlled at T cr and is in a critical state;
When case 3 is adopted, the equivalent heat dissipation coefficient of the system is lower than case 2, the highest temperature can exceed T cr, but the temperature rise can be controlled slowly;
In case 4, the thermal management system cannot timely remove the self-generated heat band, the battery temperature can be rapidly and continuously increased in an uncontrolled manner, and at a certain time, T max＝Tcr, the time is defined as intervention time tau intv;
For a given cell, given T cr, the h corresponding to case 2 is determined to be h cr.
Further, in the first step, the establishing a set of numerical solution methods for determining the critical heat exchange coefficient specifically includes:
The first step: selecting working condition data parameters: battery initial temperature T 0, heat exchange ambient temperature T ab, discharge rate C rate;
And a second step of: designing an equivalent heat exchange coefficient of the thermal management system as h, and obtaining the change of the battery temperature along with time by using a temperature acquisition device or numerical simulation;
and a third step of: determining a maximum safety temperature T cr according to actual conditions and engineering requirements, detecting whether the temperature condition of the battery in the discharging process is always within the battery safety temperature T cr, if not, increasing h by a self-defined small amount dh, and returning to the second step;
Fourth step: and detecting whether the temperature condition of the battery in the discharging process is satisfied and the self-defined micro-quantity dT approaches the battery safety temperature T cr, if not, properly reducing h by the self-defined micro-quantity dh, returning to the second step, gradually cycling to enable T max to approach T cr, and when T max approaches T cr infinitely, outputting h as h cr.
Further, in the second step, the obtaining a fitting function formula of h cr with respect to the actual operating condition parameter based on the influence factor analysis includes:
(1) And the heat exchange environment temperature T ab and the discharge multiplying power C rate are sensitive factors of h cr, h cr when T ab is a certain value is taken as a reference h crf, the discharge multiplying power is changed, and the critical heat exchange coefficients under different multiplying powers are obtained through calculation. Fitting to obtain a functional relation formula showing the critical heat exchange coefficient and the discharge multiplying power: h crf＝g1(Crate).
(2) Changing T ab, calculating to obtain h cr when T ab is different, and defining dimensionlessSimulation results in/>And (3) fitting the average trend curve with T ab, wherein the function form is as follows: /(I)
Further, the relation between the actual operation condition parameter and h cr includes:
Combining the g 1 function and the g 2 function yields a functional relationship indicating the relationship of h cr to T ab、Crate: h cr＝f(Tab,Crate).
Further, in the third step, the predicting the risk of unexpected temperature rise of the battery based on h cr includes:
Comparing the magnitude relation between the equivalent heat exchange coefficient h of the heat radiation system and the corresponding h cr of the actual working condition; when the actual heat dissipation condition h of the system is smaller than the critical heat exchange coefficient h cr under the actual working condition, judging that the battery has the risk of unexpected temperature rise; when the actual heat dissipation condition h of the system is larger than or equal to the critical heat exchange coefficient h cr under the actual working condition, judging that the battery is free from the risk of unexpected temperature rise.
Further, in the third step, the taking the intervention measure on the battery within the intervention time includes:
(1) And determining the working condition data parameters at the moment, obtaining the change of the battery temperature along with time by using a temperature acquisition device or numerical simulation, and recording the discharge time at the moment when the maximum battery temperature T max is equal to or infinitely close to T cr, wherein the time period is intervention time tau intv.
(2) The battery is controlled to run in a rate-reducing mode through the thermal management system, namely, the charge-discharge rate C rate is reduced in the intervention time; selecting a value of the reduced discharge multiplying power C rate, calculating h cr under the working condition according to a fitting function h cr＝f(Tab,Crate of h cr), and continuously reducing the value of the multiplying power when the reduced multiplying power is still larger than the equivalent heat exchange coefficient h of the battery thermal management system until h > h cr.
Another object of the present invention is to provide a lithium battery thermal management system based on critical heat exchange coefficient for implementing the method for designing lithium battery thermal management based on critical heat exchange coefficient.
The invention further aims to provide a lithium battery related to the lithium battery thermal management design method based on the critical heat exchange coefficient.
It is another object of the present invention to provide a computer readable storage medium storing a computer program, which when executed by a processor, causes the processor to perform the method for designing thermal management of a lithium battery based on a critical heat exchange coefficient.
Another object of the present invention is to provide an information data processing terminal including a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to execute the steps of:
Step one, defining a critical heat exchange coefficient h cr; establishing a set of numerical solution method for determining critical heat exchange coefficients;
Step two, based on influence factor analysis, obtaining a fitting function formula of h cr about actual operation condition parameters;
Step three, based on h cr, carrying out unexpected temperature rise risk pre-judgment on the battery; taking intervention measures on the battery during the intervention time.
By combining all the technical schemes, the invention has the advantages and positive effects that:
the invention creatively provides a design concept of a thermal management system based on a critical heat exchange coefficient h cr. h cr is a minimum threshold of heat exchange coefficient capable of ensuring that the temperature of the lithium battery is in an ideal working range. h cr can be used to quickly determine the balance of heat generation and heat dissipation of the battery. When h > h cr, the system can ensure the safe operation of the battery; when h < h cr, the battery temperature exceeds the ideal working range, and the risk of rapid temperature rise exists.
The invention provides a method for establishing a h cr calculation model based on an experiment or numerical simulation method, wherein the established h cr model is a function of actual operation condition parameters. The model has the advantages that the maximum rated working condition parameters of the power battery can be converted into the heat exchange coefficient requirements of the heat management and radiation system, and the design of the heat management system is quantitatively guided.
The model of the critical heat exchange coefficient h cr can also be used for judging the risk of the over-rated working condition, guiding the thermal management system to implement auxiliary intervention means in effective time aiming at unexpected temperature rise risk, and ensuring safe operation of the battery.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of matching of heat generation rate and heat dissipation rate of a lithium battery according to an embodiment of the present invention.
Fig. 2 is a flowchart of the calculation of the determination h cr according to an embodiment of the present invention.
Fig. 3 is a graph of the maximum temperature of the battery over time for the same C rate、Tab、T0 provided by an embodiment of the present invention.
Fig. 4 is a schematic diagram of a change of h cr along with a discharge rate and a heat exchange environment temperature according to an embodiment of the present invention.
FIG. 5 shows the various magnification factors provided by the embodiment of the inventionSchematic of the relationship with T ab.
Fig. 6 is a graph of temperature change of a battery operated with reduced magnification intervention, provided by an embodiment of the invention.
Fig. 7 is a graph of temperature profile for a battery intervention operating strategy provided by an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Aiming at the problems existing in the prior art, the invention provides a lithium battery thermal management design method based on a critical heat exchange coefficient, and the invention is described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the lithium battery thermal management design method based on the critical heat exchange coefficient provided by the embodiment of the invention includes:
S101, defining a critical heat exchange coefficient h cr; establishing a set of numerical solution method for determining critical heat exchange coefficients;
S102, based on influence factor analysis, obtaining a fitting function formula of h cr with respect to actual operation condition parameters;
S103, based on h cr, predicting the unexpected temperature rise risk of the battery; taking intervention measures on the battery during the intervention time.
In step S101 in the embodiment of the present invention, under the extreme working condition of high-rate discharge, the heat generating process and the heat dissipating process of the battery are comprehensively considered, and the change of the highest temperature of the battery along with time mainly has four conditions, as shown in fig. 2. In fig. 2, T 0 represents the battery initial temperature; t cr is the maximum safe temperature (which can be selected according to the actual situation); case 1, case 2, case 3, and case 4 represent four different heat generation and heat dissipation relationships.
In case 1, the heat dissipation capacity of the lithium ion battery heat dissipation system is far greater than the self-heat generation capacity of the battery, and the highest temperature of the lithium ion battery can be well controlled within a threshold range;
In case 2, the highest temperature of the lithium battery is just controlled at T cr and is in a critical state;
When case 3 is adopted, the equivalent heat dissipation coefficient of the system is lower than case 2, the highest temperature can exceed T cr, but the temperature rise can be controlled slowly;
In case 4, the thermal management system cannot timely remove the self-generated heat band, the battery temperature can be rapidly and continuously increased in an uncontrolled manner, and at a certain time, T max＝Tcr, the time is defined as intervention time tau intv;
For a given battery, given T cr, the meaning of h corresponding to case 2 being determined as h cr.hcr is that the minimum threshold of the heat exchange coefficient can ensure that the temperature of the lithium battery is in the ideal working range.
In step S101 in the embodiment of the present invention, the critical heat exchange coefficient is not a constant value, and it is known from the heat generation and heat dissipation models that h cr is related to T ab (heat exchange ambient temperature), T 0 (initial temperature of battery) and C rate (discharge rate), and the numerical solution flow is shown in fig. 3, where dT and dh are self-defined tiny amounts. The description of fig. 3 is as follows:
The first step: selecting working condition data parameters: battery initial temperature T 0, heat exchange ambient temperature T ab, discharge rate C rate;
And a second step of: designing an equivalent heat exchange coefficient of the thermal management system as h, and obtaining the change of the battery temperature along with time by using a temperature acquisition device or numerical simulation;
and a third step of: determining a maximum safety temperature T cr according to actual conditions and engineering requirements, detecting whether the temperature condition of the battery in the discharging process is always within the battery safety temperature T cr, if not, increasing h by a self-defined small amount dh, and returning to the second step;
Fourth step: and detecting whether the temperature condition of the battery in the discharging process is satisfied and the self-defined micro-quantity dT approaches the battery safety temperature T cr, if not, properly reducing h by the self-defined micro-quantity dh, returning to the second step, gradually cycling to enable T max to approach T cr, and when T max approaches T cr infinitely, outputting h as h cr.
In step S102 of the embodiment of the invention, based on influence factor analysis, a fitting function formula of h cr about actual operation condition parameters is obtained
The method specifically comprises the following steps:
a. And the heat exchange environment temperature T ab and the discharge multiplying power C rate are sensitive factors of h cr, h cr when T ab is a certain value is taken as a reference h crf, the discharge multiplying power is changed, and the critical heat exchange coefficients under different multiplying powers are obtained through calculation. Fitting to obtain a functional relation formula showing the critical heat exchange coefficient and the discharge multiplying power: h crf＝g1(Crate).
B. Changing T ab, calculating to obtain h cr when T ab is different, and defining dimensionlessSimulation results in/>And (3) fitting the average trend curve with T ab, wherein the function form is as follows: /(I)
C. combining the g 1 function and the g 2 function yields a functional relationship indicating the relationship of h cr to T ab、Crate: h cr＝f(Tab,Crate).
In step S103 in the embodiment of the present invention, based on h cr, the battery is subjected to unexpected temperature rise risk prediction
The method specifically comprises the following steps:
Comparing the magnitude relation between the equivalent heat exchange coefficient h of the heat radiation system and the corresponding h cr of the actual working condition; when the actual heat dissipation condition h of the system is smaller than the critical heat exchange coefficient h cr under the actual working condition, judging that the battery has the risk of unexpected temperature rise; when the actual heat dissipation condition h of the system is larger than or equal to the critical heat exchange coefficient h cr under the actual working condition, judging that the battery is free from the risk of unexpected temperature rise.
In step S103 of the embodiment of the present invention, an intervention measure is taken on the battery during the intervention time
The method specifically comprises the following steps:
(1) And determining the working condition data parameters at the moment, obtaining the change of the battery temperature along with time by using a temperature acquisition device or numerical simulation, and recording the discharge time at the moment as intervention time tau intv when the maximum battery temperature T max is equal to or infinitely close to T cr.
(2) The battery is controlled to run in a rate-reducing mode through the thermal management system, namely, the charge-discharge rate C rate is reduced in the intervention time; selecting a value of the reduced discharge multiplying power C rate, calculating h cr under the working condition according to a fitting function h cr＝f(Tab,Crate of h cr), and continuously reducing the value of the multiplying power when the reduced multiplying power is still larger than the equivalent heat exchange coefficient h of the battery thermal management system until h > h cr.
The technical scheme of the invention is further described below with reference to the specific embodiments.
1) The numerical solution method of the critical equivalent heat exchange coefficient h cr comprises the following steps:
The following relevant parameters need to be measured or directly given: certain 18650 lithium batteries have a size of l×r and an equivalent radial thermal conductivity of k T,x; the axial heat conductivity coefficient is k T,y; the density is rho cell; the specific heat capacity is c cell. The initial temperature is set to 303.15K, the maximum safety temperature T cr =313.15K (which can be changed according to the actual situation), the initial SOC value SOC (0) =1, and the discharge is stopped when the SOC falls to 0.2.
The discharge rate is set to 7C, and the heat exchange environment temperature T ab is set to 300K, T 0 to 303.15K. And changing different h values to obtain a change curve of the highest temperature of the plurality of batteries along with time. The battery temperature may be collected by a temperature collection device or a numerical value. The invention establishes a battery model, and the balance of heat generation and heat dissipation of the lithium battery meets the following formula:
Wherein T is the temperature of the battery, K; t w is the temperature of the outer wall of the battery, K; k w is the thermal conductivity of the outer wall, W.m -1·K-1; l and R represent the length and radius of the cell, respectively; h is the equivalent heat exchange coefficient of the lithium ion battery and the outside, W.m -2·K-1; q is the rate of heat generation per unit volume of the lithium battery, W.m -3, which is obtained by simulation and actual measurement.
The maximum safe temperature T cr is determined to be 313.15K. Finding out the heat exchange coefficient which ensures that the temperature of the battery under the working condition is within T cr according to a numerical solution flow chart shown in figure 3, namely h cr＝39W·m-2·K-1, wherein the maximum temperature of the battery is changed along with time when h is smaller than h cr as shown in figure 4, and the maximum temperature is very easy to exceed T cr;
Setting a plurality of working conditions of different heat exchange environment temperatures, discharge multiplying powers and initial temperatures, solving a critical equivalent heat exchange coefficient h cr corresponding to the working conditions, wherein the critical equivalent heat exchange coefficient h cr is shown in the figure 5 and is used for the different environment temperatures and discharge multiplying powers, and the calculation result shows that the discharge multiplying powers and the heat exchange environment temperatures are sensitive factors of the critical heat exchange coefficients;
2) Obtaining a fitting function formula of h cr with respect to actual operation condition parameters:
H cr at T ab =293.15K was chosen as reference h crf. And establishing a functional relation h crf＝g1(Crate between h crf and discharge multiplying power by using a curve fitting method;
Setting working conditions of different T ab, calculating h cr when different T ab are obtained, and defining dimensionless Simulation results in/>The average trend curve with T ab is shown in FIG. 6 as the average trend curve at different discharge rates,/>Similar to T ab, the scatter points are distributed on and under a curve. Method for establishing/>, by using curve fittingFunctional relation to the average trend curve of T ab: /(I)
Combining the g 1 function and the g 2 function yields a functional relationship indicating the relationship of h cr to T ab、Crate:
In the formula, each coefficient value is shown in the attached table 1.
Table 1h cr fitting equation coefficient values
3) Predicting unexpected temperature rise risk:
The heat exchange ambient temperature T ab is set to 300K, and the discharge multiplying power is set to 7C. The heat management system h is designed to be 39 W.m -2·K-1, the h cr is calculated to be 68 W.m -2·K-1 according to the fitting function relation of h cr＝f(Tab,Crate), and the battery temperature rising risk is predicted based on the critical heat exchange coefficient h cr, namely h is judged to be smaller than h cr, and h is judged to be smaller than h cr under the working condition.
4) And (3) intervention operation:
After the risk that the battery does exceed the ideal working temperature range is predicted, the intervention time can be calculated according to the actual use condition and engineering requirements, and intervention measures such as reducing the discharge rate can be implemented on the battery operation within the intervention time.
Setting the discharge rate to 7C, setting the heat exchange environment temperature T ab to 300K, T 0 to 303.15K, calculating to obtain a change curve of the battery temperature along with time through a numerical model, observing that when the highest temperature T max of the lithium battery reaches the set temperature T cr, recording the discharge time as intervention time, and when T ab =300K, setting the intervention time of the lithium battery to 216s;
The intervention operation scheme is implemented in detail: the discharge rate of the battery is controlled. H cr when 5C, T ab =300K was calculated to be 31w·m -2·K-1, at which time h > h cr. At the intervention time point, the discharge multiplying power is reduced to 5C, the data are substituted into the model, the change of the battery temperature under the intervention scheme is solved, a temperature curve under the battery intervention operation strategy is given in the figure 7, and the highest temperature of the lithium battery is reduced by about 3K.
In the description of the present invention, unless otherwise indicated, the meaning of "a plurality" is two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front," "rear," "head," "tail," and the like are used as an orientation or positional relationship based on that shown in the drawings, merely to facilitate description of the invention and to simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.
Claims (6)
1. The lithium battery thermal management design method based on the critical heat exchange coefficient is characterized by comprising the following steps of:
Step one, defining a critical heat exchange coefficient h cr; establishing a set of numerical solution method for determining critical heat exchange coefficients;
step two, based on influence factor analysis, obtaining a fitting function formula of h cr about actual operation condition data parameters;
step three, based on h cr, carrying out unexpected temperature rise risk pre-judgment on the battery; taking intervention measures on the battery in the intervention time;
In the first step, the critical heat exchange coefficient h cr is a heat exchange coefficient minimum threshold value for ensuring that the temperature of the lithium battery is in an ideal working range, and under the extreme working condition of high-rate discharge, the heat generating process and the heat dissipating process of the battery are comprehensively considered, and the change of the highest temperature of the battery along with time mainly comprises four conditions of case 1, case 2, case 3 and case 4:
In case 1, the heat dissipation capacity of the lithium ion battery heat dissipation system is far greater than the self-heat generation capacity of the battery, and the highest temperature of the lithium ion battery can be well controlled within a threshold range;
In case 2, the highest temperature of the lithium battery is just controlled at T cr and is in a critical state;
When case 3 is adopted, the equivalent heat dissipation coefficient of the system is lower than case 2, the highest temperature can exceed T cr, but the temperature rise can be controlled slowly;
In case 4, the thermal management system cannot timely remove the self-generated heat band, the battery temperature can be rapidly and continuously increased in an uncontrolled manner, and at a certain time, T max＝Tcr, the time is defined as intervention time tau intv;
For a determined battery, given T cr, h corresponding to case 2 is determined as h cr;
in the first step, the establishing a set of numerical solution method for determining the critical heat exchange coefficient specifically includes:
The first step: selecting working condition data parameters: battery initial temperature T 0, heat exchange ambient temperature T ab, discharge rate C rate;
And a second step of: designing an equivalent heat exchange coefficient of the thermal management system as h, and obtaining the change of the battery temperature along with time by using a temperature acquisition device or numerical simulation;
And a third step of: determining a maximum safe temperature T cr according to actual conditions and engineering requirements, detecting whether the temperature condition of the battery in the discharging process is always within the maximum safe temperature T cr of the battery, if not, increasing h by a self-defined tiny amount dh, and returning to the second step;
Fourth step: detecting whether the temperature condition of the battery in the discharging process is satisfied with the self-defined tiny amount dT to approach the safe temperature T cr of the battery, if not, properly reducing h by the self-defined tiny amount dh, returning to the second step, gradually cycling to enable T max to approach T cr, and when T max approaches T cr infinitely, outputting h as h cr;
in the second step, the obtaining the fitting function formula of h cr based on the influence factor analysis includes:
(1) The heat exchange environment temperature T ab and the discharge multiplying power C rate are sensitive factors of h cr, h cr when T ab is a certain value is taken as a reference h crf, the discharge multiplying power is changed, and critical heat exchange coefficients under different multiplying powers are obtained through calculation; fitting to obtain a functional relation formula showing the critical heat exchange coefficient and the discharge multiplying power: h crf＝g1(Crate);
(2) Changing T ab, calculating to obtain h cr when T ab is different, and defining dimensionless Simulation results in/>And (3) fitting the average trend curve with T ab, wherein the function form is as follows: /(I)
(3) Combining the g 1 function and the g 2 function yields a functional relationship indicating the relationship of h cr to T ab、Crate: h cr＝f(Tab,Crate).
2. The critical heat exchange coefficient-based lithium battery thermal management design method as claimed in claim 1, wherein the quantitative solution isThe relationship with T ab includes:
Simulation to obtain the ratio of each And (3) fitting the average trend curve with T ab, wherein the function form is as follows: /(I)
3. A lithium battery thermal management system based on critical heat exchange coefficient implementing the critical heat exchange coefficient-based lithium battery thermal management design method of any one of claims 1-2.
4. A lithium battery related to a lithium battery thermal management design method based on critical heat exchange coefficient according to any one of claims 1-2.
5. A computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to execute the critical heat exchange coefficient-based lithium battery thermal management design method according to any one of claims 1 to 2.
6. An information data processing terminal, characterized in that the information data processing terminal comprises a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to execute the steps of the lithium battery thermal management design method based on the critical heat exchange coefficient as claimed in any one of claims 1 to 2.
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