CN101013765A - Method for real-time evaluating internal-external temperature difference of nickel-hydrogen electrokinetic cell - Google Patents

Abstract

The invention relates to battery set thermal management technique, which is characterized by the following: getting nickel and hydrogen battery even thermal proportion based on experiment, thermal speed and battery balance motion temperature parameters; in computer, establishing battery thermal module to use software Fluent to get inside temperature field distribution; then using natural wind temperature difference and even current as input to establish one temperature difference module to reflect current, work time and surface transmission parameters.

Description

A kind of method of real-time evaluating internal-external temperature difference of nickel-hydrogen electrokinetic cell

Technical field

A kind of method of real-time evaluating internal-external temperature difference of nickel-hydrogen electrokinetic cell relates to battery for electric automobile group thermal management technology field.

Background technology

New-energy automobile is the inevitable choice of auto industry reply world environments and energy problem.Electric automobile is the focus of present world car science and technology as the new-energy automobile most important component.According to the difference of power source, can be divided into pure battery electric automobile (BEV), hybrid vehicle (HEV) and fuel cell car (FCV) three major types to electric automobile.BEV and HEV all adopt electrokinetic cell as power source, and electrokinetic cell all has decisive influence to dynamic property, fail safe and the economy of car load.

The electrokinetic cell of BEV and HEV the most normal use at present is Ni-MH battery and lithium ion battery.Because Ni-MH battery and lithium ion battery all have optimum operating temperature range, they in use all need thermal management technology.The optimum operating temperature range of Ni-MH battery is 25 ℃～40 ℃, and comparatively speaking, Ni-MH battery opposite heat tube reason technology requirement is more urgent.The direct purpose of using thermal management technology will make battery work in the Optimal Temperature scope exactly.If Ni-MH battery and lithium ion battery are not worked in the Optimal Temperature scope, their operating efficiency and useful life all can reduce.If there is not heat management, then may make battery be in superheat state, overheated meeting causes the thermal runaway of battery, causes and burns vehicle so that threaten the accident of passenger's personal safety.

All be furnished with the battery pack heat management system on the electric automobile and realize control the power battery pack working temperature.The battery pack heat management system can adopt air-cooled and liquid cooling dual mode, and adopting maximum at present is air cooling system.The control unit of heat management system is according to the battery pack Current Temperatures of battery pack temperature sensor acquisition, control the operating state of heat management system fan or pump (oil pump or water pump) based on predefined thermal management policy, thereby realize control the battery pack operating temperature range.

Because be subjected to the restriction of battery production technology, the used temperature sensor of current battery group heat management system all is arranged in the surface of battery, temperature sensor measurement be the surface temperature of battery cell in the battery pack, be not the maximum temperature of inside battery.For the battery pack heat management system, use the maximum temperature of battery pack inside obviously more reliable, safer as input than using the battery cell surface temperature as input.

Not making temperature sensor go deep into wanting to grasp the maximum temperature of inside battery under the situation of inside battery, must know the Changing Pattern of internal temperature of battery field.Ni-MH battery and lithium ion battery constitute by multiple material, inside has liquid to exist, their living hot and state-of-charge (SOC), operating currents in the course of the work are closely related, their heat dissipating state also is subjected to the influence of heat management system specific heat load and battery case structure, so want to grasp the Changing Pattern not a duck soup of electrokinetic cell internal temperature field on the electric automobile.Domestic and international existing research work at present is not also about the introduction of the open source literature of counting cell internal temperature field in real time on electric automobile.

From the administrative skill of electric automobile power battery, be necessary to propose a kind of can the change under the situation that has the battery temperature sensor arrangement now, in real time the method for the inner maximum temperature of estimating battery.

In the domestic and international research work, have the temperature field of utilization battery thermal model calculated off-line inside battery, and then optimize the research method of battery pack heat management system design with temperature field result of calculation.This method will be for the invention provides the research basis.

Summary of the invention

The invention provides a kind of under the situation that does not change current battery temperature sensor position, measure the simple and easy method of inside battery maximum temperature, this method can be easy to use in existing thermal management system of electric automobile control unit, realizes on the electric automobile the real-time measurement to the power battery pack maximum temperature.

It is the research basis that the present invention gives birth to thermal characteristics with battery, with the battery thermal model is theoretical foundation, the temperature field of adopting the method for numerical computations to obtain inside battery, analysis temperature field obtain the rule that influences that the temperature difference between inside battery maximum temperature point and the surface temperature measurement point is subjected to battery operated electric current, battery working time, outside batteries radiating condition, battery thermal physical property parameter (specifically referring to density, specific heat and conductive coefficient).Obtain the maximum temperature of inside battery with this temperature difference and the addition of measured battery surface temperature.Research thinking of the present invention and applying step are applicable to the Ni-MH battery electrokinetic cell of various models.

As shown in Figure 1, application process of the present invention is divided into five steps, below five steps is elaborated.

The first step is carried out battery testing.

The battery testing content of the first step comprises the living thermal characteristics test of battery, battery thermal physical property parameter experiment with measuring and the test of battery equilibrium electromotive force temperature effect coefficient.It is to grasp battery (battery surface thermal transmission coefficient difference) under different radiating conditions, the living enthusiasm condition when each typical electrical flow valuve constant current charge and constant-current discharge that battery is given birth to the thermal characteristics test; The purpose of battery thermal physical property parameter experiment with measuring is to obtain the density of battery, specific heat and conductive coefficient; The influence coefficient of battery equilibrium electromotive force temperature effect coefficient experimental measurement is used to describe the degree of battery equilibrium electromotive force temperature influence.Test data that above-mentioned battery testing measures or parameter are to carry out the basis that battery cell internal temperature Flow Field Numerical is calculated, and the difference variation rule of the inner maximum temperature of battery cell surface temperature and battery cell will serve as according to analyzing with internal temperature of battery field result of calculation.

In second step, set up the battery thermal model.

The battery thermal model is the theoretical foundation of counting cell monomer internal temperature field.The present invention uses the three-dimensional batteries thermal model shown in the formula (1) to come counting cell monomer temperature inside field.Find the solution the heat conduction differential equation shown in the formula (1) and need solve three key issues: 1. thermal physical property parameter, i.e. density p, specific heat C _pλ (comprises λ with conductive coefficient _x, λ _yAnd λ _z) accurately obtain; 2. give birth to hot speed

Accurate expression; 3. definite condition (initial condition and boundary condition) accurately determines.

$\mathrm{\ρ}{C}_p\frac{\∂T}{\∂t}={\mathrm{\λ}}_x\frac{{\∂}^{2}T}{{\∂x}^2}+{\mathrm{\λ}}_y\frac{{\∂}^{2}T}{{\∂y}^2}+{\mathrm{\λ}}_z\frac{{\∂}^{2}T}{{\∂z}^2}+\stackrel{\·}{q}---\left(1\right)$

In the first step of invention, solved the problem of obtaining of thermal physical property parameter.

Give birth to hot speed

The hot speed of life shown in the employing formula (2) is calculated.I in the formula (2) _LBe operating current; U _LBe operating voltage; E ₀For the battery equilibrium electromotive force, because of E ₀With open circuit voltage U _OcNumerically very approaching, use open circuit voltage U during calculating _OcReplace; T is a battery temperature;

Temperature effect coefficient for the battery equilibrium electromotive force; V _BBe the battery volume.First on formula (2) right side

The living heat that causes owing to the internal resistance of cell and other irreversible effects is described, second

Be because the living heat that the inside battery electrochemical reaction causes.

$\stackrel{\&CenterDot;}{q}=\frac{I_L}{V_B}\&CenterDot;(E_0-U_L)-\frac{I_L}{V_B}\&CenterDot;T\&CenterDot;\frac{{\mathrm{<figure-callout\; id="0"\; label="dE"\; filenames="A20071006306100191.png,A20071006306100201.png"\; state="\{\{state\}\}">dE</figure-callout>}}_0}{\mathrm{dT}}---\left(2\right)$

Initial condition defines with temperature in the definite condition.Boundary condition is described with formula (3), and wherein h is thermal transmission coefficient, the T between battery surface and surrounding fluid (air, oil or water) _∞Be the temperature of battery surrounding fluid, T is the battery surface temperature, and λ is the conductive coefficient of battery material, and n is the direction vertical with battery surface, is x, y, three coordinate directions of z in rectangular coordinate system.When determining definite condition, the present invention calculates h by Fluid Mechanics Computation method (Computational fluid dynamics is called for short CFD).It is a kind of universal method in the numerical heat transfer that the CFD method is asked for h, for the different air velocity of battery surface, can the CFD method calculate corresponding h.

$-\mathrm{\&lambda;}$ $\left(\frac{\&PartialD;T}{\&PartialD;n}\right)=h(T-T_{\&infin;})---\left(3\right)$

The 3rd step, counting cell internal temperature field.

Owing to can't measure the temperature of inside battery each point in real time, the present invention is based on battery and give birth to thermal characteristics test data (test of the invention first step obtains), the methods analyst internal temperature of battery field of employing numerical computations is subjected to the rule that influences of battery operated electric current, battery working time, outside batteries radiating condition (battery surface thermal transmission coefficient) and battery thermal physical property parameter, and this rule will be used to set up battery temperature difference model.The grid model of battery need be set up in counting cell temperature inside field, and computational process uses Fluent software to finish.

In the 4th step, set up battery temperature difference model.

Temperature difference T between the inner maximum temperature of battery cell surface temperature and battery cell is battery operated electric current I, battery working time t, battery heat dissipation environment and battery thermal physical property parameter coupling action result.Wherein battery surface thermal transmission coefficient h describes the heat dissipation environment of battery, and the battery thermal physical property parameter comprises density, specific heat and conductive coefficient.Though under same operating current, the hot speed of life of Ni-MH battery is slightly different during difference SOC, but because the hot speed of life at Ni-MH battery different SOC place in SOC working range commonly used is equal substantially, so the present invention ignores the influence of SOC to the battery cell internal-external temperature difference.For the battery of determining, the hot parameter of its material is determined, when using battery thermal model counting cell monomer internal temperature field, considered the influence of battery thermal physical property parameter, so the present invention proposes battery cell internal-external temperature difference estimation model as the formula (4), this model has been considered the influence of operating current I, operating time t and battery surface thermal transmission coefficient h, and has realized the lotus root of separating of influencing factor is analyzed.Temperature difference estimation model is benchmark, wherein f with the temperature difference of (h=5) under the Natural Heat Convection condition ₁(I t) is described under the Natural Heat Convection condition different electric currents and operating time to the coupling influence of battery cell internal-external temperature difference, f ₂(h) be influence coefficient (the during h=5 f of battery radiating condition to the battery internal-external temperature difference ₂(h)=1).f ₁(I, t) and f ₂(h) computing formula is respectively suc as formula shown in (5) and the formula (6).According to temperature difference model shown in the formula (4), the battery outside wall temperature of on electric automobile, measuring, the historical information of battery pack work and battery pack heat management system outlet wind speed or flow rate of liquid, the maximum temperature of counting cell group inside in real time according to the battery pack heat management system.

ΔT＝f ₁(I，t)·f ₂(h) (4)

$f_1(I,t)\mathrm{\&Delta;}{T}_{h=5}=k\left(I\right)\&CenterDot;t^m=(a_1{\left(\frac{I}{C_N}\right)}^3+a_2{\left(\frac{I}{C_N}\right)}^2+a_3\left(\frac{I}{C_N}\right))\&CenterDot;t^m---\left(5\right)$

$f_2\left(h\right)=\mathrm{\&beta;}\&CenterDot;h^{\frac{1}{n}}---\left(6\right)$

At f shown in the formula (5) ₁(I, k in computing formula t) (I) describe the influence of different electric currents to the battery temperature difference, t ^mDescribe the influence of operating time to the battery temperature difference, m is a positive number.Asking for f ₁(I in the time of t), at first based on internal temperature of battery field result of calculation, obtains when different electric current constant current charges or constant-current discharge (under the natural air cooled radiating condition), and the time dependent curve of the battery temperature difference, this curve are sets of curves of corresponding different electric currents.Because every curve all has the characteristics of power function, determine that based on many difference curve features the suitable span of m is 0.5～0.8, choose suitable m with the method for exhaustion and draw the power function of each bar difference curve of match in this scope, the foundation of determining the concrete numerical value of m is parameter m and makes 1C by the k (I) that m further calculates _NError minimum between the calculated curve of charging process battery internal-external temperature difference and the power function fitting curve.After determining m, adopt the principle of calculated curve and matched curve error minimum, determine the coefficient (being k (I) value) of each bar matched curve.After the expression formula of each current fitting curve all provided, the k during according to different electric current (I) value provided the general expression formula of k (I), C in the formula (5) with cubic polynomial _NIt is the rated capacity of battery.

Also find f by big quantity research ₂(h) the most suitablely come match with power function.At f shown in the formula (6) ₂(h) in the computing formula, n is a positive integer, and β is for guaranteeing f ₂(h) coefficient of curve fit precision.When specifically asking for n and β, at first to calculate 1C _NThe battery temperature difference of different surfaces thermal transmission coefficient correspondence when charging finishes under the charging current, thus the difference curve of different surfaces thermal transmission coefficient correspondence obtained.Be benchmark (f during h=5 with the temperature difference under the free convection condition then ₂(h)=1), difference curve is carried out the equal proportion conversion, thereby obtain f ₂(h), according to f ₂(h) curvilinear characteristic is determined the value of Integer n and factor beta.The detailed process of determining n and β is as follows: comprehensive f ₂(h) curvilinear characteristic and n are that the requirement of integer determines that n should choose in 2,3,4,5 four positive integers, use the method for exhaustion to determine that n and β get concrete numerical value, promptly according to the principle of calculated curve and matched curve error minimum, try to achieve n and be taken as 2,3,4 and the β value of 5 o'clock correspondences, thereby obtain four groups of (n, β), these four groups (n, β) in a group of selected error minimum be final parameter.

Because the electric automobile power battery group is usually operated under the state that time-dependent current charges and discharge, and the living heat of charging there are differences with the living heat of discharge, so will be on electric automobile monomer internal-external temperature difference in the estimating battery group in real time, also need to solve the problem of time-dependent current to the constant current equivalence.In order to solve the practical problems of battery temperature difference model on electric automobile, the present invention is the time-dependent current discharge process with the time-dependent current charge and discharge process equivalence of battery pack at first, uses the average current of time-dependent current discharge process electric current I then

Input as temperature difference estimation model.In the course of the work, along with the variation of heat management system fan or pump work state, battery surface thermal transmission coefficient h can change, and uses the time average of h here

Input as temperature difference estimation model.

Computing formula as the formula (7), Computing formula as the formula (8).

$\stackrel{\&OverBar;}{I}=\frac{\underset{t=t_j}{\mathrm{\&Sigma;}}(I_d\&CenterDot;t)+\underset{t=t_k}{\mathrm{\&Sigma;}}(\mathrm{\&alpha;}\&CenterDot;|I_c|\&CenterDot;t)}{\underset{t=t_i}{\mathrm{\&Sigma;}}t}---\left(7\right)$

$\stackrel{\&OverBar;}{h}=\frac{\underset{t=t_i}{\mathrm{\&Sigma;}}(h_i\&CenterDot;t)}{\underset{t=t_i}{\mathrm{\&Sigma;}}t}---\left(8\right)$

Thus, can obtain complete battery temperature difference model as the formula (9) according to formula (4)～formula (8), the m in the m formula (5) in the formula (9) is identical, and the n in n in the formula (9) and the formula (6) is identical.

$\mathrm{\&Delta;T}=f_1(\stackrel{\&OverBar;}{I},t)\&CenterDot;f_2\left(\stackrel{\&OverBar;}{h}\right)=\mathrm{\&beta;}\&CenterDot;k\left(\stackrel{\&OverBar;}{I}\right)\&CenterDot;t^m\&CenterDot;{\stackrel{\&OverBar;}{h}}^{\frac{1}{n}}---\left(9\right)$

In the 5th step, use battery temperature difference model measurement inside battery maximum temperature.

According to what test data and the identification of internal temperature of battery Flow Field Numerical result of calculation obtained battery temperature difference model related parameter such as β, m, n, α etc. are arranged, through optimizing, just can be applied to carry out the real-time measurement of battery pack maximum temperature in the Thermal Management System for EV Battery Packs.

Description of drawings

Fig. 1 applying step of the present invention

Fig. 2 is by the 320 monomer series-connected 80Ah Ni-MH battery groups that constitute

Fig. 3 Ni-MH battery module and battery cell

Fig. 4 obtains the process of the inner maximum temperature of battery cell

Fig. 5 Ni-MH battery monomer is given birth to thermal characteristics test schematic diagram:

The 1-temperature sensor; The 2-data acquisition module.

Fig. 6 monomer is given birth to thermal characteristics test point for measuring temperature

Thermal characteristics test temperature change curve is given birth in Fig. 7 Ni-MH battery monomer 40A constant current:

-■-1,2_ fill-▲-5,6_ fills-◆-1,2_ puts--5,6_ are put

-●-3,4_ fills--7,8_ fill--3,4_ is put-●-7,8_ puts

Thermal characteristics test temperature change curve is given birth in Fig. 8 Ni-MH battery monomer 80A constant current:

-■-1,2_ fill-▲-5,6_ fills-◆-1,2_ puts--5,6_ are put

-●-3,4_ fills--7,8_ fill--3,4_ is put-●-7,8_ puts

Fig. 9 Ni-MH battery monomer avergae specific heat test schematic diagram:

The 3-charger; The 4-battery module; The 5-galvanometer; The adiabatic bucket of 6-; The 7-thermometer.

Figure 10 Ni-MH battery balance electric gesture temperature effect coefficient test schematic diagram:

A) battery temperature; B) ambient temperature.

Figure 11 Ni-MH battery single part schematic diagram:

The 8-battery cell; The 9-shell; The 10-kernel; The 11-air gap; The 12-collector; The 13-casing cover; The 14-nut.

The open circuit voltage of Figure 121 0 monomer Ni-MH battery module

Monomer heat-dissipating space structural representation in Figure 13 battery case

Typical air gap cross section between Figure 14 battery cell

Figure 15 Ni-MH battery simplex mesh model

Figure 161 C _NDischarge monomer each point variations in temperature

C) 9 accounting temperatures; D) 1 accounting temperature; E) 8 test temperatures; F) 1 test temperature.

Figure 171 C _NThe temperature of face 1-5-2-6 when charging finishes

Figure 181 C _NThe Temperature Distribution of each line in monomer when charging finishes

--line 5-6---line 1-2---line 9-10

The internal-external temperature difference of battery cell during different electric current under Figure 19 free convection condition

Figure 20 constant current charge or the 1 hour internal-external temperature difference of battery cell constantly that discharges:

The temperature difference when g) charging, fitting formula is k=1.372x ³-0.882x ₂+ 2.724x;

The temperature difference when h) charging, fitting formula is k=2.7333x ³-3.184x ₂+ 2.1387x.

Figure 21 thermal transmission coefficient h is to the influence coefficient of the inside and outside temperature difference:

I) result of curve fit; J) structure of numerical computations.

Current value during the identical internal-external temperature difference of Figure 22:

Curve when k) discharging; Situation when l) charging.

Figure 23 Ni-MH battery group working condition tests i-v curve:

Figure is the change curve of battery voltage in the working condition tests a); Figure b) change curve of battery pack current in the working condition tests.

Battery cell internal-external temperature difference estimation model effect under Figure 24 working condition tests

M) temperature difference model results estimated; N) thermal model result calculated.

Embodiment

With one by 320 monomer series-connected forming, rated capacity is that the Ni-MH battery group of 80Ah is an example, introduces the implementation process of estimating electric automobile power battery internal-external temperature difference method in real time below.Figure 2 shows that the Ni-MH battery group, Figure 3 shows that battery module and battery cell in the battery pack, rightmost side battery cell has been peelled off shell among the figure.Fig. 4 has provided the process of utilizing the present invention to obtain the inner maximum temperature of battery cell

The first step: carry out battery testing.

(1) Ni-MH battery is given birth to the thermal characteristics test

Battery is given birth to the thermal characteristics test and is used for grasping the temperature variation curve of battery at the charge and discharge process battery surface, and this curve is the basic foundation of checking battery thermal model.Battery is given birth to constant current charge and the discharge heat test that the thermal characteristics content of the test is a battery cell under the natural air cooled condition, and selecting electric current for use is 40A (C _N/ 2) and 80A (1C _N).All heat tests all carry out in room temperature (about 25 ℃).Figure 5 shows that the Ni-MH battery monomer gives birth to thermal characteristics test schematic diagram, Fig. 6 mid point 1～8 are the temperature survey point.Figure 7 shows that the temperature variation curve of Ni-MH battery monomer 40A constant current charge and each point for measuring temperature of discharge, Figure 8 shows that the temperature variation curve of Ni-MH battery monomer 80A constant current charge and each point for measuring temperature of discharge.In the two figure explanation, the mean value of " point 1,2 fills " expression charging test mid point 1 and point 2 temperature, other points are also identical therewith.

(2) battery thermal physical property parameter experiment with measuring

The battery thermal physical property parameter comprises density, specific heat and conductive coefficient.

The present invention uses cooling method to measure the avergae specific heat of battery, Figure 9 shows that the test schematic diagram.Among Fig. 9, fill the electric insulation vegetable oil that specific heat is 1.876 kJ/ (kgK) in the adiabatic bucket, tested battery cell is placed in the adiabatic bucket, and vegetable oil is just with the complete submergence of battery cell; The transducer of thermometer is fully immersed in the vegetable oil.Making battery cell before the test is 0 ℃.At first quality is poured in the adiabatic bucket for the 3.205kg vegetable oil is heated to 35.62 ℃ in the test, rapidly 0 ℃ of battery cell is put into adiabatic bucket then and made it to carry out heat exchange with vegetable oil, the temperature of battery and vegetable oil is 28.25 ℃ when reaching heat balance.According to the conservation of energy, can calculate the avergae specific heat G of battery cell by formula (10) _pBe 1.028kJ/ (kgK).M wherein _Oil, C _{P, oil}, Δ T _OilBe respectively quality, specific heat and the variations in temperature of oil, M and Δ T _CellBe respectively the quality and the variations in temperature of battery cell.

$C_p=\frac{m_{\mathrm{oil}}\&CenterDot;C_{p,\mathrm{oil}}\&CenterDot;\mathrm{\&Delta;}{T}_{\mathrm{oil}}}{M\&CenterDot;\mathrm{\&Delta;}{T}_{\mathrm{cell}}}=\frac{3.205\&times;1.876\&times;(35.62-28.25)}{1.526\&times;(28.25-0)}=1.028\mathrm{kJ}/(\mathrm{kg}\&CenterDot;K)---\left(10\right)$

(3) battery equilibrium electromotive force temperature effect coefficient test

The temperature effect coefficient d E of the battery equilibrium electromotive force in the thermal source item of battery thermal model (being that battery is given birth to hot speed) ₀/ dT need pass through experimental measurement.Present embodiment design process of the test is as shown in figure 10 measured this influence coefficient.In the experiment three SOC are respectively 0.25,0.5 and 0.75 10 monomer Ni-MH battery modules and put into insulating box, the temperature in the control insulating box changes according to temperatur-timel curve shown in dotted lines in Figure 10.According to the module open circuit voltage that test records, use linear regression method to calculate the Ni-MH battery balance electric gesture temperature effect coefficient of ordering at three SOC, it is final for 0.000167V/ ℃ to average

In second step, set up the battery thermal model.

Present embodiment is by determining the battery thermal physical property parameter, giving birth to hot speed, three thermal models that will usually set up Ni-MH battery of definite condition.Before determining three elements, at first analyze the physical structure of Ni-MH battery monomer.Figure 11 shows that the part schematic diagram of Ni-MH battery monomer, complete battery cell is made of part 9～part 14.Wherein, shell 9 and the complete shell of casing cover 13 common formation monomers, material is reinforced nylon 66 (a kind of engineering plastics); Kernel 10 is thermal source parts of battery cell, and it alternately is overrided to form by pole piece and barrier film, in the present embodiment it is considered as the commaterial of homogeneous media; Collector 12 (comprising pole) is identical with the material of nut 14, is brass; 11 is the air gap between battery kernel and the shell.

(1) obtains the battery thermal physical property parameter

Table 1 is depicted as each part quality that constitutes the Ni-MH battery monomer, and table 2 is depicted as the thermal physical property parameter of each material of Ni-MH battery monomer in room temperature.Except that the battery specific heat that Fig. 9 measures, other parameters all can obtain by the thermal physical property parameter handbook of searching typical material.Wherein consider the characteristics that air gap gas is kept in motion, the air gap gas conduction coefficient of choosing is through repeatedly calculating preferred equivalent conductive coefficient.

The weight of each part of table 1 Ni-MH battery monomer

Title	Material	Volume (mm 3)	Total weight (kg)	Density (kg/m 3)
					Battery cell	Multiple material	557937	1.5260	2735
Shell	Nylon 66	144422	0.1964	1360
					Collector	Brass	4567	0.0779	8530
Nut	Brass	1088	0.0371	8530
					Air gap	Air gap gas	43032	0.00005	1.165
Kernel	Inner nuclear material	357000	1.2141	3401

The thermal physical property parameter of each material of table 2 Ni-MH battery monomer

Material	Density	Specific heat	Conductive coefficient
				kg/m 3	kJ/(kg·K)	W/(m·K)
	Nylon 66	1360	1.500				0.35
7/3 brass				8530	0.396	121
	Air gap gas	1.225	1.006				242
Inner nuclear material				3401	1.012	0.82，0.9，0.9

(2) Ni-MH battery is given birth to determining of hot Rate Models

Present embodiment calculates with the hot rate equation of life shown in the formula (2).I wherein _L, U _L, T is the data of test data sheet, E ₀Be 1/10th of 10 monomer Ni-MH battery module open circuit voltage numerical value shown in Figure 12, the temperature effect coefficient d E of balance electric gesture ₀/ dT is 0.000167 V/ ℃, V _BBe the 557937mm in the table 1 ³

(3) definite condition determines

Initial condition in the definite condition is determined with temperature, all is taken as 25 ℃ of room temperatures.Battery surface thermal transmission coefficient in the boundary condition adopts numerical computation method to try to achieve.Ni-MH battery case shown in Figure 2 has heat-dissipating space structure shown in Figure 13, because this heat-dissipating space structure has symmetry, asks the battery surface thermal transmission coefficient so computer memory shown in Figure 14 is got in the cross section.Survey the outlet wind speed of Ni-MH battery case shown in Figure 2 after fan is opened, as the important indicator of battery surface thermal transmission coefficient calculating.By the battery surface thermal transmission coefficient that calculates under the fan work condition is 8.95W/ (m ²K).

The 3rd step, counting cell internal temperature field.

Behind the grid model of having set up the Ni-MH battery monomer, the Ni-MH battery thermal model that uses the present invention to set up in second step calculates the Ni-MH battery monomer temperature inside field under different service conditions.Figure 15 shows that present embodiment carries out Ni-MH battery monomer internal temperature Flow Field Numerical and calculates used grid model, grid model adopts the hybrid grid scheme.Collector and the area of space geometry more complicated of closing on thereof are used the positive tetrahedron grid; Other area of space geometries are fairly simple, use the regular hexahedron grid.The regular hexahedron grid is a structured grid, the positive tetrahedron grid is a unstructured grid, internal point all in the net region of structured grid all have identical adjacent cells, and the internal point in the net region of unstructured grid does not have identical adjacent cells.

At the software that carries out using when calculate battery cell internal temperature field is Fluent.Shown in Figure 16 is Ni-MH battery monomer 1C under the natural air cooled condition _NIn the discharge process, test value and calculated value that battery temperature changes, calculated value is wherein set up battery thermal model result calculated with present embodiment exactly.In giving birth to the thermal characteristics test, 1C _NBe 2700s discharge time.Provided 1C among Figure 16 _NConstant-current discharge battery cell point 1, point 9 accounting temperature and put 1, the test temperature of point 8.From 1C _NThe numerical result that constant-current discharge and other are given birth to the thermal characteristics processs of the test and test data relatively, in off-test constantly, the Ni-MH battery thermal model numerical result of present embodiment foundation and the error of test data all are no more than 1.5 ℃.

Figure 17 is Ni-MH battery monomer 1C _NThe Temperature Distribution of inner each face of the constant current charge battery cell finish time, temperature unit is K among the figure.Shown in Figure 17 corresponding diagram 6 perpendicular to the face 1-5-2-6 of z axle.Figure 18 is Ni-MH battery monomer 1C _NThe Temperature Distribution of each line of the constant current charge inside battery finish time, the position of line is defined by Fig. 6.On electric automobile, can't measure Figure 17, Temperature Distribution shown in Figure 180, can grasp the temperature difference of battery surface and maximum temperature point by this Temperature Distribution that calculates.

Adopt identical method, the Ni-MH battery thermal model that uses present embodiment to set up can calculate battery cell temperature inside field in other constant currents and the time-dependent current process of the test, thereby grasps the temperature difference information of inside battery maximum temperature and battery surface temperature.

In the 4th step, set up battery temperature difference model.

Set up the Ni-MH battery temperature difference model of present embodiment research and need ask for f respectively ₁(I, t) and f ₂And solve time-dependent current and discharge and recharge temperature difference application of model problem under the working condition tests condition (h).

Carry out numerical computations based on (h=5) battery cell constant current charge, discharge test data under the Natural Heat Convection condition, can obtain battery cell internal-external temperature difference curve shown in Figure 19.The difference curve that the numerical result that shows among the figure is to use the Ni-MH battery thermal model to calculate, concrete numerical value are the difference of point 1 shown in Figure 6 and point 9 temperature.Compare with the experimental measurement temperature, the numerical computations temperature that is used to calculate the temperature difference can guarantee the error less than 1 ℃.

Because f ₂(5)=1, use power function that each numerical result among Figure 19 is carried out match, can obtain the f shown in the formula (11) ₁(optimal value of m is taken as 0.65 for I, expression formula t).

f ₁(I，t)＝ΔT _h＝5＝k(I)·t ^m＝k(I)·t ^0.65 (11)

The value of coefficient k (I) was carried out match with cubic polynomial to k (I) when table 3 was depicted as different electric current, obtained the expression formula of the k (I) shown in the formula (12).As shown in figure 20, k (I) the expression constant current charge or the 1 hour internal-external temperature difference of battery cell constantly that discharges, the abscissa current ratio is current value and battery rated capacity C among the figure _NRatio.

K (I) value during the different electric current of table 3

Current ratio	0C N	0.5C N	1C N	1.5C N
					K (I), charging	0	1.313	3.214	6.732
K (I), discharge	0	0.615	1.688	5.269

$k\left(I\right)=\left\{\begin{array}{cc}1.732{\left(\frac{\left|I\right|}{C_N}\right)}^3-0.882{\left(\frac{\left|I\right|}{C_N}\right)}^2+2.724\left(\frac{\left|I\right|}{C_N}\right),& (I<0)\\ 2.7333{\left(\frac{I}{C_N}\right)}^3-3.184{\left(\frac{I}{C_N}\right)}^2+2.1387\left(\frac{I}{C_N}\right),& (I\&GreaterEqual;0)\end{array}\right.---\left(12\right)$

Utilization Ni-MH battery thermal model carries out battery cell internal temperature field and calculates, and uses result of calculation can ask for f ₂(h), the calculated data of using here remains 1C _NThe constant current charge test data.When power taking pool surface thermal transmission coefficient h is respectively different values such as 5,8.95,25,50, carry out 1C _NBattery cell internal-external temperature difference under the constant current charge condition calculates, and can obtain difference curve Δ T (h).Because f ₂(5)=1, carry out the equal proportion adjustment, can obtain f according to Δ T (h) curve ₂(h) be respectively 1,8.95,25 and 50 o'clock numerical value at h, concrete numerical value is shown in the each point of Figure 21 mark.With power function fitting curve f ₂(h), obtain formula shown in the formula (13), the suitable value of n is 3, has provided f among Figure 21 ₂(h) matched curve.

$f_2\left(h\right)=\mathrm{\&beta;}\&CenterDot;h^{\frac{1}{n}}=0.6733{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="A20071006306100191.png"\; state="\{\{state\}\}">h</figure-callout>}}^{\frac{1}{3}}---\left(13\right)$

Present embodiment is still set up the electric current equivalent relation of charge and discharge with the internal-external temperature difference of constant current charge or 1 hour moment battery cell that discharges.Abscissa and the ordinate of conversion Figure 20 are drawn again, obtain the charge and discharge current value of battery cell internal-external temperature difference correspondence shown in Figure 22.The discharging current of each temperature difference correspondence among Figure 22 and the ratio of charging current are averaged, promptly obtain obtaining the average proportions factor alpha between required discharging current of same battery monomer internal-external temperature difference and the charging current.For the Ni-MH battery monomer of present embodiment research, α is taken as 1.695.

Derivation above comprehensive can obtain the Ni-MH battery monomer internal-external temperature difference estimation model shown in the formula (14).I wherein _dBe discharging current, corresponding is t constantly _j, I _cBe charging current (negative value) that corresponding is t constantly _k

In the 5th step, use battery temperature difference model measurement inside battery maximum temperature.

Present embodiment is estimated temperature difference application of model effect with the operating mode test data.Because the maximum temperature of battery cell inside is used the precision based on the battery thermal model result of calculation Indirect evaluation battery cell internal-external temperature difference estimation model of test data here in can't the experiment with measuring process.

$\left\{\begin{array}{c}\mathrm{\&Delta;T}=f_1(\stackrel{\&OverBar;}{I},t)\&CenterDot;f_2\left(\stackrel{\&OverBar;}{h}\right)=\mathrm{\&beta;}\&CenterDot;k\left(\stackrel{\&OverBar;}{I}\right)\&CenterDot;t^m\&CenterDot;{\stackrel{\&OverBar;}{h}}^n\\ =(1.8403{\left(\frac{\stackrel{\&OverBar;}{I}}{C_N}\right)}^3-2.1438{\left(\frac{\stackrel{\&OverBar;}{I}}{C_N}\right)}^2+1.44\left(\frac{\stackrel{\&OverBar;}{I}}{C_N}\right))\&CenterDot;t^{0.65}{\stackrel{\&OverBar;}{h}}^{\frac{1}{3}}\\ \stackrel{\&OverBar;}{I}=\frac{\underset{t=t_j}{\mathrm{\&Sigma;}}(I_d\&CenterDot;t)+\underset{t=t_k}{\mathrm{\&Sigma;}}(\mathrm{\&alpha;}\&CenterDot;|I_c|\&CenterDot;t)}{\underset{t=t_i}{\mathrm{\&Sigma;}}t}\\ \stackrel{\&OverBar;}{h}=\frac{\underset{t=t_i}{\mathrm{\&Sigma;}}(h_i\&CenterDot;t)}{\underset{t=t_i}{\mathrm{\&Sigma;}}t}\end{array}\right.---\left(14\right)$

Shown in Figure 23 is Ni-MH battery group working condition tests process schematic diagram, and test lasts 6000s, maximum discharge current 190.88A in the test, maximum charging current 91.24A, average current 49.78A.The initial SOC of test is 0.734, and stopping SOC is 0.245, and the battery pack mean temperature is 24.51 ℃ during on-test, and the battery pack mean temperature was 26.17 ℃ when test was finished.Because battery pack fan standard-sized sheet in the process of the test is so power taking pool surface thermal transmission coefficient is 8.95W/ (m ²K).

Use battery thermal model and temperature difference model to calculate respectively based on working condition tests data shown in Figure 23, obtain the result of calculation of battery thermal model shown in Figure 24 and the estimated result of temperature difference estimation model.With thermal model result of calculation is benchmark, calculates to such an extent that the mean error of temperature difference estimation model is 0.17 ℃, and worst error is 0.37 ℃.Here thermal model result of calculation can guarantee 1 ℃ with interior error, and in general, battery cell internal-external temperature difference estimation model has satisfactory accuracy.

By embodiment as seen, the temperature difference model that the present invention proposes is simplified the Ni-MH battery thermal model of complexity and is practiced on electric automobile, has tentatively solved the real-time measurement problem of battery pack maximum temperature on electric automobile.

Claims (1)

1, a kind of method of implementing evaluating internal-external temperature difference of nickel-hydrogen electrokinetic cell is characterized in that, contains following steps successively:

Step (1) is carried out Ni-MH battery and is given birth to thermal characteristics test, battery thermal physical property parameter experiment with measuring and the test of battery equilibrium electromotive force temperature effect coefficient, wherein:

Battery is given birth to the thermal characteristics test, be the constant current charge and the discharge heat test of battery cell under natural air cooled condition, to grasp battery under different radiating conditions, living enthusiasm condition when the typical electrical flow valuve constant current charge of each setting and constant-current discharge obtains the temperature variation curve of battery surface in the charge and discharge process;

Battery thermal physical property parameter experiment with measuring is the avergae specific heat C that measures battery with cooling method _p:

$C_p=\frac{m_{\mathrm{oil}}{C}_{p,\mathrm{oil}}\&CenterDot;{\mathrm{\&Delta;T}}_{\mathrm{oil}}}{M\&CenterDot;{\mathrm{\&Delta;T}}_{\mathrm{cell}}}$

M wherein _Oil, C _{P, oil}, Δ T _OilBe respectively quality, specific heat and the variations in temperature of electric insulation vegetable oil, test records, M and Δ T _CellBe respectively the quality and the variations in temperature of battery cell,

Obtain other thermal physical property parameters, density and conductive coefficient by handbook;

This influence coefficient is measured in the test of battery equilibrium electromotive force temperature effect coefficient

The degree of temperature influence, T is the temperature of battery surface, E ₀Be battery equilibrium electromotive force usefulness, use the open circuit voltage U of battery in the test _OcReplace U _OcBy given battery charge state and U _OcCurve draw;

Step (2) in the battery thermal management system based on computer, is calculated and is set up Ni-MH battery and give birth to hot Rate Models: give birth to hot speed $\stackrel{\&CenterDot;}{q}=\frac{I_L}{V_B}\&CenterDot;(E_0-U_L)-\frac{I_L}{V_B}\&CenterDot;T\&CenterDot;\frac{{\mathrm{dE}}_0}{\mathrm{dT}},$

I wherein _LBe battery operated electric current, U _LBe battery operated voltage, V _BBe the battery volume,

The living heat that causes owing to the internal resistance of cell and other irreversible effects is described,

Be the living heat that causes owing to the inside battery electrochemical reaction,

Initial condition is a room temperature,

Boundary condition is: $-\mathrm{\&lambda;}\left(\frac{\&PartialD;T}{\&PartialD;n}\right)=h(T-T_{\&infin;}),$

T wherein _∞Be the temperature of battery surrounding fluid, h is the thermal transmission coefficient between battery surface and surrounding fluid, is given value, and the direction that the n representative is vertical with battery surface is x, y, three coordinate directions of z in rectangular coordinate system,

Step (3), described system-computed internal temperature of battery field, contain following steps successively:

Step (3.1), the scheme that adopts regular hexahedron grid and positive tetrahedron grid to combine is set up the grid model of Ni-MH battery monomer: in the Ni-MH battery simplex mesh model, collector and the area of space geometry more complicated of closing on thereof are used the positive tetrahedron grid; Other area of space geometries are fairly simple, use the regular hexahedron grid; The regular hexahedron grid is a structured grid, the positive tetrahedron grid is a unstructured grid, internal point all in the net region of structured grid all have identical adjacent cells, and the internal point in the net region of unstructured grid does not have identical adjacent cells;

Step (3.2), adopt the Fluent computed in software under natural air cooled condition the Ni-MH battery monomer at different charge and discharge electric currents, temperature inside field under battery working time, battery surface thermal transmission coefficient and the battery thermal physical property parameter;

Step (4), described system is being ignored under the condition of Ni-MH battery state-of-charge SOC to the influence of battery cell internal-external temperature difference, with the temperature difference under the Natural Heat Convection condition is benchmark, and the thermal transmission coefficient h=5 between this moment battery surface and surrounding fluid is calculated as follows temperature difference T:

$\mathrm{\&Delta;T}=\mathrm{\&beta;}\&CenterDot;k\left(\stackrel{\&OverBar;}{I}\right)\&CenterDot;t^m\&CenterDot;{\stackrel{\&OverBar;}{h}}^{\frac{1}{n}}$

Wherein:

Be the average current of electric current I in the time-dependent current discharge process,

$\stackrel{\&OverBar;}{I}=\frac{\underset{t=t_j}{\mathrm{\&Sigma;}}(I_d\&CenterDot;t)+\underset{t=t_k}{\mathrm{\&Sigma;}}(\mathrm{\&alpha;}\&CenterDot;|I_c|\&CenterDot;t)}{\underset{t=t_i}{\mathrm{\&Sigma;}}t},$

T is the operating time, and i is the sequence number of t,

α is required discharging current of identical Ni-MH battery monomer internal-external temperature difference and the average proportions coefficient between the charging current, is taken as 1.695,

I _dBe discharging current, corresponding is t constantly _j,

I _cBe charging current, corresponding is t constantly _k,

t _i＝t _i+t _k，

$\stackrel{\&OverBar;}{h}=\frac{\underset{t=t_i}{\mathrm{\&Sigma;}}(h_i\&CenterDot;t)}{\underset{t=t_i}{\mathrm{\&Sigma;}}t},$

For at the thermal transmission coefficient mean value of t in the time,

Different under the Natural Heat Convection condition

With the coupling influence of operating time, wherein to the battery cell internal-external temperature difference:

t ^mDescribe the influence of operating time, be positive number the battery temperature difference, The influence of different electric currents to the battery temperature difference described, t ^mWith

Obtain according to following steps:

At first, when different electric current constant current charge under natural air cooled radiating condition that obtains according to step (3) or constant-current discharge, the time dependent curve of each bar battery temperature difference, all have this common ground of power function feature and determine the power function exponent m: determine that based on many difference curve features the suitable span of m is 0.5～0.8, choose suitable m to determine the power function of each bar difference curve of match with the method for exhaustion in this scope, the foundation of determining the concrete numerical value of m is parameter m and is further calculated by m

Make 1C _NError minimum between the calculated curve of charging process battery internal-external temperature difference and the power function fitting curve;

Secondly, adopt the principle of the power function curve error minimum of temperature difference calculated curve and institute's match to determine each bar matched curve

Coefficient a ₁, a ₂, a ₃

Obtain: $k\left(\stackrel{\&OverBar;}{I}\right)=a_1{\left(\frac{\stackrel{\&OverBar;}{I}}{C_N}\right)}^3+a_2{\left(\frac{\stackrel{\&OverBar;}{I}}{C_N}\right)}^2+a_3\left(\frac{\stackrel{\&OverBar;}{I}}{C_N}\right)$ , C wherein _NBe the rated capacity of battery,

For being benchmark with the temperature difference under the Natural Heat Convection condition, the influence coefficient of the battery internal-external temperature difference of battery radiating condition is described, described β, n obtain according to the following steps:

At first, calculate 1C _NThe battery temperature difference of different surfaces thermal transmission coefficient correspondence when charging finishes under the charging current, thus the difference curve of different surfaces thermal transmission coefficient correspondence obtained,

Secondly, be benchmark with the temperature difference under the free convection condition, described difference curve is carried out the conversion of equal proportion, obtain 1C _NThe time different surfaces thermal transmission coefficient to the influence curve of the temperature difference, and the value of definite Integer n and factor beta: the feature of combined influence curve and n are that the requirement of integer determines that n should choose in 2,3,4,5 four positive integers, use the method for exhaustion to determine n and the concrete numerical value of β, promptly according to the principle of calculated curve and matched curve error minimum, try to achieve n and be taken as 2,3,4 and the β value of 5 o'clock correspondences, thus obtain four groups (n, β), these four groups (n, β) in selected error minimum be final parameter;

Step (5), computer application battery temperature difference model, obtain the temperature difference between inside battery maximum temperature point and each point for measuring temperature of surface,, obtain the maximum temperature of inside battery with respect to external environment condition this each point temperature difference and corresponding each battery surface differential temperature survey value addition.

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