CN104678309A - Method for measuring dynamic external characteristics of power battery - Google Patents

Abstract

The invention relates to a method for measuring dynamic external characteristics of a power battery, and belongs to the technical field of a battery. The method is characterized in that the dynamic external characteristics of the power battery near different working currents can be obtained through a method of stacking dynamic excitation on the different working currents, time-varying characteristics which are mixedly stacked in the dynamic external characteristics of the power battery can be approximately removed based on a constant-current characteristic curve of the power battery and a curve differencing method, and the accurate measuring on the dynamic external characteristics of the power battery can be finally realized. According to the method disclosed by the invention, different dynamic characteristic information in the power battery under different working current conditions can be more fully revealed, and thus high modeling accuracy can be obtained; the method not only can be offline used by a power battery manufacturer to test basic parameters of the power battery, but also can be used for online testing the power battery.

Description

A kind of method measuring the dynamic external characteristics of electrokinetic cell

Technical field

The present invention relates to a kind of method measuring the dynamic external characteristics of electrokinetic cell, particularly relate to the method for testing of electrokinetic cell and relevant data processing method, belong to cell art.

Background technology

Along with the progress of novel renewable energy technology, microgrid and electric vehicle engineering, battery energy storage system is applied in the middle of commercial production and daily life by increasingly extensive.In order to ensure safety, the Effec-tive Function of battery energy storage system, system is all equipped with the state of battery management system to battery energy storage system medium power battery and monitors, and predicts electrokinetic cell external characteristics.Wherein, carrying out Accurate Determining to the external characteristics of electrokinetic cell is that battery management system carries out the key of effectively management to battery, and this work determines operational efficiency and the security of whole battery energy storage system.

It is the Modeling Research of electrokinetic cell that the external characteristics of current driving force battery measures research major embodiment.Common electrokinetic cell model mainly comprises electrochemical model and equivalent-circuit model two class.Electrochemical model can reflect the physical and chemical process of electrokinetic cell inside comparatively imperfectly, contributes to studying meticulously the change occurred inner in the electrokinetic cell course of work; But this kind of model structure is complicated, and relate to the physical-chemical parameters being difficult in a large number obtain, therefore electrochemical model is generally applied to the performance evaluation of electrokinetic cell to relevant theoretical research.Equivalent-circuit model uses the known circuit devcie of certain physical characteristics to describe the electric external characteristics of electrokinetic cell; This kind of model structure is simple, easy to understand, and model parameter has clear and definite physical chemical mechanism explanation, is therefore most widely used in electrokinetic cell Modeling Research.

At present more existing equivalent-circuit model research work about electrokinetic cell, exemplary operation such as:

Massimo C.New dynamical models of lead–acid batteries[J].IEEE Transactions On Power Systems,vol.15,No.4,pp.1184-1190,November 2000。

The document gives the general structure of electrokinetic cell equivalent-circuit model and the external characteristics assay method of electrokinetic cell, and establishes three rank equivalent-circuit models of lead-acid power accumulator.This model uses the open-circuit voltage of variable voltage source-representation electrokinetic cell, two variable resistors are used to represent ohmic internal resistance and the activation polarize internal resistance of electrokinetic cell respectively, use a resistance capacitance parallel branch to represent concentration polarization and the dynamic process thereof of electrokinetic cell, use a controlled current source branch road to represent the self-discharge processes of electrokinetic cell.The document carrys out the terminal voltage external characteristics of direct matching electrokinetic cell under different operating mode by regulating model parameter.Although the modeling result in document is unsatisfactory, cause electrokinetic cell external characteristics to measure and there is relatively large deviation, the electrokinetic cell equivalent-circuit model general structure that the document provides and electrokinetic cell external characteristics assay method are the bases of follow-up numerous research.

Because electrokinetic cell has comparatively strong nonlinearity characteristic and time-varying characteristics, its dynamic external characteristics is the acting in conjunction result of inner Different Dynamic process, and the time-varying characteristics of some of them dynamic process and electrokinetic cell exist aliasing.In order to carry out Accurate Measurement to electrokinetic cell external characteristics, necessary data processing must be carried out to eliminate the time-varying characteristics component in determination data, and to the modeling respectively of the Different Dynamic process of electrokinetic cell inside in modeling process.But, existing electrokinetic cell modeling work does not carry out systematic study to the Different Dynamic process of electrokinetic cell, this causes the dynamic perfromance understanding of electrokinetic cell unclear, and the model of foundation lacks mechanism explain, and finally have impact on electrokinetic cell external characteristics estimating precision.In order to address this problem, some researchs introduce the external characteristics mensuration that a large amount of empirical parameter carrys out auxiliary power battery, the accidentalia chosen in the subjective factor and electrokinetic cell condition often including researcher individual of these empirical parameters, electrokinetic cell characteristic can not be reflected objectively, finally cause these electrokinetic cell external characteristics mensuration work repeatabilities poor.

Summary of the invention

The object of the invention is to propose a kind of method measuring the dynamic external characteristics of electrokinetic cell, the dynamic external characteristics of electrokinetic cell near different operating electric current is obtained by the method superposing dynamic exciting on different operating electric current, ask poor method to be similar to the time-varying characteristics eliminating aliasing in the dynamic external characteristics of electrokinetic cell based on the constant current characteristic of electrokinetic cell and curve, final draft realizes the Accurate Measurement to the dynamic external characteristics of electrokinetic cell.

The method of the dynamic external characteristics of the mensuration electrokinetic cell that the present invention proposes, comprises the following steps:

(1) according to electrokinetic cell standard discharge current, the cut-off voltage corresponding with standard discharge current, standard charging current, standard charge voltage and the cut-off current corresponding with standard charge voltage that electrokinetic cell product manual specifies, the operation of standard charge and discharge cycles is carried out repeatedly to electrokinetic cell, finally carry out standard charging, electrokinetic cell is completely filled or completely puts;

(2) from the electrokinetic cell range of safety operation that power battery product handbook specifies, obtain N number of working current of electrokinetic cell, be designated as i ₁, i ₂..., i _n, and obtain the cut-off voltage corresponding with each working current according to electrokinetic cell product manual;

(3) respectively step (1) completely to be filled with each working current of step (2) or the electrokinetic cell completely put carries out constant-current charge or discharge operation, the cut-off voltage making each constant-current charge under a working current or discharge operation is the cut-off voltage that the electrokinetic cell product manual in step (2) specifies, in each constant-current charge or discharge operation process, the time dependent curve of terminal voltage of electrokinetic cell under record different operating electric current, be designated as constant current characteristic, record the working time T that electrokinetic cell continues under different operating electric current simultaneously; Again one or many is carried out as the standard charging of step (1) or discharge operation to electrokinetic cell, make electrokinetic cell finally be in expiring of defined in electrokinetic cell product manual and fill or completely put state;

(4) from N number of working current of step (2), any two different working current i are chosen _jand i _k, with working current i _jcarrying out the duration to electrokinetic cell is t ₁constant current operation, subsequently with working current i _kcarrying out the duration to electrokinetic cell is t ₂constant current operation, until the terminal voltage of electrokinetic cell reaches the working current i with defined in electrokinetic cell product manual _kcorresponding cut-off voltage, and the time dependent curve of working current recording twice constant current operation process medium power battery, be designated as working current curve, and the time dependent curve of electrokinetic cell terminal voltage, is designated as dynamic characteristic; Finally one or many is carried out as the standard charging of step (1) or discharge operation to electrokinetic cell, make electrokinetic cell finally be in expiring of defined in electrokinetic cell product manual and fill or completely put state;

(5) working current value of each point ordinate of the working current curve of step (4) is deducted i _j, delete the horizontal ordinate t of working current curve ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, the initial value obtaining ordinate is 0, stop value is i _k-i _jworking current curve;

(6) working current of step (3) is made to be i _kconstant current characteristic align from the end of curvilinear abscissa with the dynamic characteristic of step (4), delete the horizontal ordinate t in two curves ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, calculates the difference of the ordinate in two segment of curve, obtains residual error curve;

(7) adopt the thevenin equivalent circuit model containing second order resistance-capacitance network as the basic model of electrokinetic cell, obtain math equation as follows:

$\left\{\begin{array}{c}{C}_1\frac{d{U}_{C1}}{\mathrm{dt}}+\frac{U_{C1}}{R_1}=i\\ C_2\frac{d{U}_{C2}}{\mathrm{dt}}+\frac{U_{C2}}{R_2}=i\\ \mathrm{OCV}+U_{C1}+U_{C2}+i\·R_0=U_t\end{array}\right.$

Wherein, i represents the working current of electrokinetic cell, U _trepresent the terminal voltage of electrokinetic cell, OCV represents the open-circuit voltage of electrokinetic cell, R ₀for the ohmic internal resistance value of electrokinetic cell, R ₁for the concentration polarization resistance value of electrokinetic cell, R ₂represent that internal temperature of power battery changes the internal resistance change component caused, C ₁for the capacitance of the first electric capacity in thevenin equivalent circuit model, C ₂for the capacitance of the second electric capacity in thevenin equivalent circuit model, C ₁r ₁for the time constant of electrokinetic cell mass transfer dynamic process, C ₂r ₂for the time constant of internal temperature of power battery change tread process, U _c1with U _c2be respectively the voltage at the first electric capacity and the second electric capacity two ends in electrokinetic cell thevenin equivalent circuit model;

According to superposition principle, the open-circuit voltage OCV of electrokinetic cell is set to 0, obtains the terminal voltage U of electrokinetic cell _tand the transport function between electrokinetic cell working current i:

$\begin{array}{c}G\left(s\right)=R_0+\frac{R_1}{R_1{C}_{1}s+1}+\frac{R_2}{R_2{C}_{2}s+1}\\ =R_0+\frac{(R_1{R}_2{C}_1+R_1{R}_2{C}_2)s+R_1+R_1}{R_1{C}_1{R}_2{C}_2{s}^2+(R_1{C}_1+R_2{C}_2)s+1}\end{array};$

(8) using the working current curve of step (5) as the input data of model, the dynamic response curve obtained using step (6) is as the output data of thevenin equivalent circuit model, adopt the transport function of least square method solution procedure (7), obtain each capacitance-resistance parameter R ₀, R ₁, C ₁, R ₂and C ₂, detailed process is as follows:

(8-1) transport function of a following form is set up:

$G\left(s\right)=k+\frac{b_{1}s+b_0}{s^2+a_{1}s+a_0}$

Wherein, k, a ₀, a ₁, b ₀and b ₁for undetermined coefficient, adopt least square method, use the input data of thevenin equivalent circuit model and export this transport function of data direct solution, obtaining k, a ₀, a ₁, b ₀and b ₁;

(8-2) above-mentioned k, a is utilized ₀, a ₁, b ₀and b ₁, by following computing formula, calculate each capacitance-resistance parameter R in the math equation of step (7) ₀, R ₁, C ₁, R ₂and C ₂:

$\left\{\begin{array}{c}{R}_0=k\\ R_1=\frac{b_1}{\sqrt{a_1^2\text{-4}{a}_0}}-\frac{2b_0}{a_1\sqrt{a_1^2-4a_0}+a_1^2-{4a}_0}\\ R_2=\frac{b_0}{a_0}-R_1\\ C_1=\frac{2}{a_1+\sqrt{a_1^2-{4a}_0}}/R_1\\ C_2=\frac{2}{a_1-\sqrt{a_1^2-{4a}_0}}/R_2\end{array}\right.$

(9) from the working current curve and dynamic characteristic of step (4) electrokinetic cell, read and horizontal ordinate t respectively ₁the working current numerical value i of corresponding ordinate _t1with terminal voltage numerical value U _t1, according to thevenin equivalent circuit model, U _c1with U _c2be respectively:

U _C1＝i _t1·R ₁

U _C2＝i _t1·R ₂

According to the math equation of step (7), open-circuit voltage parameter OCV is:

OCV＝U _t1-i _t1·(R ₀+R ₁+R ₂)；

(10) repeat step (4) to step (9), travel through all two different working current i _jand i _k, travel through with working current i _jelectrokinetic cell is carried out to the duration t of constant current operation ₁, complete the discharge and recharge operation of the electrokinetic cell under all different conditions, measure the dynamic external characteristics of electrokinetic cell.

The method of the dynamic external characteristics of the mensuration electrokinetic cell that the present invention proposes, its advantage is:

1, the method for the dynamic external characteristics of the mensuration electrokinetic cell of the present invention's proposition, can be similar to and eliminate the time dependent characteristic of electrokinetic cell external characteristics, therefore, it is possible to use a simple Linear Time Invariant resistance-capacitance network and direct voltage source to describe dynamic external characteristics near electrokinetic cell working current in mensuration process, thus simplify mensuration process and improve estimating precision, final operational efficiency and the control accuracy improving battery management system.

2, the method for the dynamic external characteristics of the mensuration electrokinetic cell of the present invention's proposition, the Changing Pattern of electrokinetic cell thevenin equivalent circuit model parameter with working current can be obtained, thus the estimating precision to the dynamic external characteristics of electrokinetic cell under different operating current condition can be improved, make battery management system under the different operating current condition of electrokinetic cell, the parameters of electrokinetic cell can be obtained more exactly, and control more accurately.

3, the assay method of the present invention's proposition, only needs by means of simple electrokinetic cell charging/discharging apparatus and data acquisition unit, do not need the instrumentation of additional expensive, and data processing can be carried out online, is therefore conducive to engineering construction.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of the dynamic external characteristics method of the mensuration electrokinetic cell that the present invention proposes.

Fig. 2 is in the inventive method, working current curve processing embodiment, wherein, the electrokinetic cell working current curve of Fig. 2 (a) for measuring by experiment, Fig. 2 (b) is that Fig. 2 (c) is working current segment of curve remaining after Delete superfluous data along the electrokinetic cell working current curve after the translation of ordinate direction;

Fig. 3 is method in the present invention, dynamic characteristic Processing Example, wherein, Fig. 3 (a) is the electrokinetic cell constant current characteristic and dynamic characteristic that measure by experiment, Fig. 3 (b) is constant current characteristic section remaining after Delete superfluous data and dynamic characteristic section, and Fig. 3 (c) carries out curve for constant current characteristic section and dynamic characteristic section and asks the residual error curve that obtains after difference;

Fig. 4 is the thevenin equivalent circuit model schematic of the electrokinetic cell that the inventive method relates to.

Fig. 5 is a measurement result schematic diagram of the dynamic external characteristics method of the mensuration electrokinetic cell that the present invention proposes.

Fig. 6 is the thevenin equivalent circuit model capacitance-resistance parameter identification result that the inventive method obtains under different operating current conditions, and wherein Fig. 6 (a) is R ₀, Fig. 6 (b) is R ₁, Fig. 6 (c) is C ₁, Fig. 6 (d) is R ₂, Fig. 6 (e) is C ₂.

Embodiment

The method of the dynamic external characteristics of the mensuration electrokinetic cell that the present invention proposes, its FB(flow block) as shown in Figure 1, comprises the following steps:

(1) according to electrokinetic cell standard discharge current, the cut-off voltage corresponding with standard discharge current, standard charging current, standard charge voltage and the cut-off current corresponding with standard charge voltage that electrokinetic cell product manual specifies, the operation of standard charge and discharge cycles is carried out repeatedly to electrokinetic cell, finally carry out standard charging, electrokinetic cell is completely filled or completely puts;

(2) from the electrokinetic cell range of safety operation that power battery product handbook specifies, obtain N number of working current of electrokinetic cell, be designated as i ₁, i ₂..., i _n, and obtain the cut-off voltage corresponding with each working current according to electrokinetic cell product manual;

(3) respectively step (1) completely to be filled with each working current of step (2) or the electrokinetic cell completely put carries out constant-current charge or discharge operation, the cut-off voltage making each constant-current charge under a working current or discharge operation is the cut-off voltage that the electrokinetic cell product manual in step (2) specifies, in each constant-current charge or discharge operation process, the time dependent curve of terminal voltage of electrokinetic cell under record different operating electric current, be designated as constant current characteristic, record the working time T that electrokinetic cell continues under different operating electric current simultaneously; Again one or many is carried out as the standard charging of step (1) or discharge operation to electrokinetic cell, make electrokinetic cell finally be in expiring of defined in electrokinetic cell product manual and fill or completely put state;

(4) from N number of working current of step (2), any two different working current i are chosen _jand i _k, with working current i _jcarrying out the duration to electrokinetic cell is t ₁constant current operation, subsequently with working current i _kcarrying out the duration to electrokinetic cell is t ₂constant current operation, until the terminal voltage of electrokinetic cell reaches the working current i with defined in electrokinetic cell product manual _kcorresponding cut-off voltage, and the time dependent curve of working current recording twice constant current operation process medium power battery, be designated as working current curve, and the time dependent curve of electrokinetic cell terminal voltage, is designated as dynamic characteristic; Finally one or many is carried out as the standard charging of step (1) or discharge operation to electrokinetic cell, make electrokinetic cell finally be in expiring of defined in electrokinetic cell product manual and fill or completely put state;

(5) working current value of each point ordinate of the working current curve of step (4) is deducted i _j, delete the horizontal ordinate t of working current curve ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, the initial value obtaining ordinate is 0, stop value is i _k-i _jworking current curve; Figure 2 shows that an embodiment of the inventive method, there is shown i _j=-3.9A, i _k=-19.5A, t ₁=1155s, t2=879s, T _kworking current curve acquisition process under=1110s condition, the working current curve of Fig. 2 (a) for obtaining in step (4), deducts i by the working current value of each point ordinate of working current curve _jafter just can obtain the curve shown in Fig. 2 (b), based on this, delete the horizontal ordinate t on curve ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, just can obtain the working current segment of curve shown in Fig. 2 (c).

(6) working current of step (3) is made to be i _kconstant current characteristic align from the end of curvilinear abscissa with the dynamic characteristic of step (4), delete the horizontal ordinate t in two curves ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, calculates the difference of the ordinate in two segment of curve, obtains residual error curve; Figure 3 shows that an embodiment of the inventive method, there is shown i _j=-3.9A, i _k=-19.5A, t ₁=1155s, t ₂=879s, T _kresidual error curve acquisition process under=1110s condition, the dynamic characteristic of Fig. 3 (a) for obtaining in the constant current characteristic that obtains in step (3) and step (4), and two the end alignment of curvilinear abscissa, deletes the horizontal ordinate t in two curves ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards just can obtain the segment of curve shown in Fig. 3 (b), based on this, calculates the difference of the ordinate in two segment of curve, just can obtain the residual error curve shown in Fig. 3 (c).

Particularly, the object of curve alignment herein ensures that constant current characteristic and dynamic characteristic are at horizontal ordinate t ₂the state-of-charge that segment of curve is afterwards corresponding identical, curve asks poor object to be eliminate in the dynamic external characteristics of electrokinetic cell to change caused change component by state-of-charge.The residual error curve finally obtained is only by working current curve and the t of step (5) ₁the parameter of the thevenin equivalent circuit model in moment determined, namely eliminates the time dependent characteristic of thevenin equivalent circuit model parameter in electrokinetic cell dynamic external characteristics mensuration process.

(7) adopt the thevenin equivalent circuit model containing second order resistance-capacitance network as the basic model of electrokinetic cell, thevenin equivalent circuit model as shown in Figure 4, obtains math equation as follows:

$\left\{\begin{array}{c}{C}_1\frac{d{U}_{C1}}{\mathrm{dt}}+\frac{U_{C1}}{R_1}=i\\ C_2\frac{d{U}_{C2}}{\mathrm{dt}}+\frac{U_{C2}}{R_2}=i\\ \mathrm{OCV}+U_{C1}+U_{C2}+i\·R_0=U_t\end{array}\right.$

Wherein, i represents the working current of electrokinetic cell, U _trepresent the terminal voltage of electrokinetic cell, these two amounts directly can record in electrokinetic cell experimentation; OCV represents the open-circuit voltage of electrokinetic cell, and the electromotive force of approximate representation electrokinetic cell, R ₀for the ohmic internal resistance value of electrokinetic cell, R ₁for the concentration polarization resistance value of electrokinetic cell, R ₂represent that internal temperature of power battery changes the internal resistance change component caused, C ₁for the capacitance of the first electric capacity in thevenin equivalent circuit model, C ₂for the capacitance of the second electric capacity in thevenin equivalent circuit model, C ₁r ₁for the time constant of electrokinetic cell mass transfer dynamic process, C ₂r ₂for the time constant of internal temperature of power battery change tread process, these six amounts are thevenin equivalent circuit model parameters.U _c1with U _c2be respectively the voltage at the first electric capacity and the second electric capacity two ends in electrokinetic cell thevenin equivalent circuit model; These two amounts are state variables of model, are jointly determined by the working current of electrokinetic cell and model parameter.

Dynamic perfromance represented by thevenin equivalent circuit model capacitance-resistance part is the core of whole model, therefore according to superposition principle, the open-circuit voltage OCV of electrokinetic cell is set to 0, obtains the terminal voltage U of electrokinetic cell _tand the transport function between electrokinetic cell working current i:

$\begin{array}{c}G\left(s\right)=R_0+\frac{R_1}{R_1{C}_{1}s+1}+\frac{R_2}{R_2{C}_{2}s+1}\\ =R_0+\frac{(R_1{R}_2{C}_1+R_1{R}_2{C}_2)s+R_1+R_1}{R_1{C}_1{R}_2{C}_2{s}^2+(R_1{C}_1+R_2{C}_2)s+1}\end{array};$

(8) using the working current curve of step (5) as the input data of model, the dynamic response curve obtained using step (6) is as the output data of thevenin equivalent circuit model, adopt the transport function of least square method solution procedure (7), obtain each capacitance-resistance parameter R ₀, R ₁, C ₁, R ₂and C ₂, detailed process is as follows:

(8-1) transport function of a following form is set up:

$G\left(s\right)=k+\frac{b_{1}s+b_0}{s^2+a_{1}s+a_0}$

Wherein, k, a ₀, a ₁, b ₀and b ₁for undetermined coefficient, adopt least square method, use the input data of thevenin equivalent circuit model and export this transport function of data direct solution, obtaining k, a ₀, a ₁, b ₀and b ₁;

(8-2) above-mentioned k, a is utilized ₀, a ₁, b ₀and b ₁, by following computing formula, calculate each capacitance-resistance parameter R in the math equation of step (7) ₀, R ₁, C ₁, R ₂and C ₂:

$\left\{\begin{array}{c}{R}_0=k\\ R_1=\frac{b_1}{\sqrt{a_1^2\text{-4}{a}_0}}-\frac{2b_0}{a_1\sqrt{a_1^2-4a_0}+a_1^2-{4a}_0}\\ R_2=\frac{b_0}{a_0}-R_1\\ C_1=\frac{2}{a_1+\sqrt{a_1^2-{4a}_0}}/R_1\\ C_2=\frac{2}{a_1-\sqrt{a_1^2-{4a}_0}}/R_2\end{array}\right.$

(9) from the working current curve and dynamic characteristic of step (4) electrokinetic cell, read and horizontal ordinate t respectively ₁the working current numerical value i of corresponding ordinate _t1with terminal voltage numerical value U _t1, according to thevenin equivalent circuit model, U _c1with U _c2be respectively:

U _C1＝i _t1·R ₁

U _C2＝i _t1·R ₂

According to the math equation of step (7), open-circuit voltage parameter OCV is:

OCV＝U _t1-i _t1·(R ₀+R ₁+R ₂)；

Due in step (6), the residual error curve obtained is only by working current curve and the t of step (5) ₁the parameter of the thevenin equivalent circuit model in moment determined, therefore use the math equation of the working current curve of step (5) and the residual error curve solution procedure (7) of step (6), what obtain is that electrokinetic cell is with working current i _jcarrying out the duration is t ₁constant current operation after corresponding thevenin equivalent circuit model parameter.In order to obtain the capacitance-resistance parameter of the thevenin equivalent circuit model in other situations, must more operate electrokinetic cell at different conditions.

(10) repeat step (4) to step (9), travel through all two different working current i _jand i _k, travel through with working current i _jelectrokinetic cell is carried out to the duration t of constant current operation ₁, complete the discharge and recharge operation of the electrokinetic cell under all different conditions, measure the dynamic external characteristics of electrokinetic cell.

A kind of method measuring the dynamic external characteristics of electrokinetic cell that the present invention proposes, can be divided into experimental implementation and data processing from principle.Experimental implementation refers to carries out required permanent working current experiment to electrokinetic cell and exchanges work as Current experiments to obtain the necessary data needed for modeling, this part content comprises the step (1) of the modeling method that the present invention proposes to step (4), and step (10); Data processing refers to carries out necessary data processing to experimental result, and to obtain the process of electrokinetic cell thevenin equivalent circuit model parameter, this part content comprises the step (5) of the modeling method that the present invention proposes to step (9).

The method of dynamic external characteristics of the mensuration electrokinetic cell that the present invention proposes obtains the dynamic external characteristics of electrokinetic cell near different operating electric current by superposing dynamic exciting on different operating electric current, and asks poor method be similar to the time-varying characteristics of aliasing in the dynamic external characteristics of elimination electrokinetic cell based on the constant current characteristic of electrokinetic cell and curve.Be compared to traditional modeling method, the method that the present invention proposes can disclose the dynamic characteristic information that electrokinetic cell is inner different under different operating current condition more fully, therefore has higher modeling accuracy.Specific embodiment party face, the inventive method not only can make, for the basic parameter of test electrokinetic cell, also to can be used for the on-line determination of electrokinetic cell for electrokinetic cell manufacturer off-line.

Below an embodiment of the inventive method:

This instance data derives from the experiment carried out current widely used a lithium iron phosphate dynamic battery, without loss of generality, provides the measurement result of electrokinetic cell under discharging condition here.Electrokinetic cell parameter and experiment condition as follows:

Table 1

Electrokinetic cell model	BAK 36800MP-Fe
		Electrokinetic cell product batch number	2VF10L0606877
Electrokinetic cell rated capacity (ampere-hour)	6.5
		Electrokinetic cell rated current (C leads)	0.2
Electrokinetic cell operating temperature ratings (K)	298
		Environment temperature (K)	298
The working current (C leads) chosen	0.2,0.6,1.0,1.4,1.8,2.2,2.6,3.0
		The switching point position (%) chosen	10,20,30,40,50,60,70,80,90,100
Working current transient process	Step, transient process is less than 0.5 sampling period

Adopt the modeling method that the present invention proposes, as follows to the modeling result of above-mentioned lithium iron phosphate dynamic battery:

Fig. 2, Fig. 3 and Fig. 5 give i _j=-3.9A, i _k=-19.5A, t ₁=1155s, t2=879s, T _kone group of experimental result of electrokinetic cell and model prediction result under=1110s condition.Wherein, Fig. 3 (a) gives the electrokinetic cell constant current characteristic and dynamic characteristic that record in experimentation, and two curves align according to the requirement of the method for the invention step (6).As can be seen from Figure, there is notable difference in the discharge curve of electrokinetic cell under dynamic operation condition and constant current operating mode, this species diversity reduced gradually along with the time, and the dynamic process that this species diversity reduces obviously is longer than the concentration polarization dynamic process embodied in terminal voltage dynamic characteristic.According to relevant galvanochemistry data, the dynamic process that between constant current characteristic and dynamic characteristic, difference reduces gradually caused by the temperature variation dynamic process of electrokinetic cell inside, and the residual error curve of constant current characteristic and dynamic characteristic therefore can be used to represent the temperature variation dynamic process of electrokinetic cell inside.Fig. 2 (c), Fig. 3 (c) sets forth the working current curve and residual error curve that obtain after electrokinetic cell working current curve and dynamic characteristic process respectively through the method for the invention step (5) and step (6), in the parameter identification process of step (9), these two curves are respectively as input data and the output data of thevenin equivalent circuit model.As can be seen from the figure, under step excitation, residual error curve has obviously embodied second order dynamic process: Mutational part is caused jointly by the ohmic internal resistance of electrokinetic cell inside and activation polarize internal resistance, utilizes this part data can obtain R in thevenin equivalent circuit model ₀parameter; The small time constant dynamic process identical with Mutational part direction represents the material diffusion process of electrokinetic cell inside, utilizes this part data can obtain R in thevenin equivalent circuit model ₁with C ₁parameter; The large time constant dynamic process contrary with Mutational part direction represents the temperature changing process of electrokinetic cell inside, utilizes this part data can obtain R in thevenin equivalent circuit model ₂with C ₂parameter.Because the capacitance-resistance parameter of electrokinetic cell inside has negative temperature coefficient, therefore for representing the R of internal temperature of power battery change procedure ₂with C ₂parameter is negative value.Based on this, each capacitance-resistance parameter in thevenin equivalent circuit model just can be obtained by identification.Fig. 5 gives the measurement result of the dynamic external characteristics of electrokinetic cell.As can be seen from the figure, the electrokinetic cell dynamic response curve that thevenin equivalent circuit model provides and actual experiment result maximum error are less than 1 ‰, and this error has reached the limit of accuracy of the dynamic external characteristics determination experiment of electrokinetic cell under laboratory environment.Measurement result illustrates, the modeling method that the present invention proposes can set up electrokinetic cell external characteristics model accurately, and the key parameter of Obtaining Accurate electrokinetic cell inside accordingly.(a), (b), (c) of Fig. 6, (d), (e) sets forth R in thevenin equivalent circuit model ₀, R ₁, C ₁, R ₂and C ₂corresponding relation between parameter and working current.Owing to being merely able to utilize the dynamic characteristic of electrokinetic cell to obtain in these capacitance-resistance parameters, therefore do not comprise i in figure _jwith i _kmodel parameter data under equal condition.As can be seen from Figure, approximate between model each capacitance-resistance parameter and working current exist simple linear relationship, therefore for other dynamic duty electric current operating modes, more adequately can obtain model parameter by the method for interpolation, and then the dynamic external characteristics of electrokinetic cell is estimated.If electrokinetic cell manufacturer can measure electrokinetic cell according to the proposed method, and provide experimental result as shown in the figure in electrokinetic cell handbook, so the design of battery management system will be simplified.

Claims (1)

1. measure a method for the dynamic external characteristics of electrokinetic cell, it is characterized in that the method comprises the following steps:

(1) according to electrokinetic cell standard discharge current, the cut-off voltage corresponding with standard discharge current, standard charging current, standard charge voltage and the cut-off current corresponding with standard charge voltage that electrokinetic cell product manual specifies, the operation of standard charge and discharge cycles is carried out repeatedly to electrokinetic cell, finally carry out standard charging, electrokinetic cell is completely filled or completely puts;

(2) from the electrokinetic cell range of safety operation that power battery product handbook specifies, obtain N number of working current of electrokinetic cell, be designated as i ₁, i ₂..., i _n, and obtain the cut-off voltage corresponding with each working current according to electrokinetic cell product manual;

(3) respectively step (1) completely to be filled with each working current of step (2) or the electrokinetic cell completely put carries out constant-current charge or discharge operation, the cut-off voltage making each constant-current charge under a working current or discharge operation is the cut-off voltage that the electrokinetic cell product manual in step (2) specifies, in each constant-current charge or discharge operation process, the time dependent curve of terminal voltage of electrokinetic cell under record different operating electric current, be designated as constant current characteristic, record the working time T that electrokinetic cell continues under different operating electric current simultaneously; Again one or many is carried out as the standard charging of step (1) or discharge operation to electrokinetic cell, make electrokinetic cell finally be in expiring of defined in electrokinetic cell product manual and fill or completely put state;

(4) from N number of working current of step (2), any two different working current i are chosen _jand i _k, with working current i _jcarrying out the duration to electrokinetic cell is t ₁constant current operation, subsequently with working current i _kcarrying out the duration to electrokinetic cell is t ₂constant current operation, until the terminal voltage of electrokinetic cell reaches the working current i with defined in electrokinetic cell product manual _kcorresponding cut-off voltage, and the time dependent curve of working current recording twice constant current operation process medium power battery, be designated as working current curve, and the time dependent curve of electrokinetic cell terminal voltage, is designated as dynamic characteristic; Finally one or many is carried out as the standard charging of step (1) or discharge operation to electrokinetic cell, make electrokinetic cell finally be in expiring of defined in electrokinetic cell product manual and fill or completely put state;

(5) working current value of each point ordinate of the working current curve of step (4) is deducted i _j, delete the horizontal ordinate t of working current curve ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, the initial value obtaining ordinate is 0, stop value is i _k-i _jworking current curve;

(6) working current of step (3) is made to be i _kconstant current characteristic align from the end of curvilinear abscissa with the dynamic characteristic of step (4), delete the horizontal ordinate t in two curves ₁segment of curve before and horizontal ordinate t ₁+ t ₂-10% × T _ksegment of curve afterwards, calculates the difference of the ordinate in two segment of curve, obtains residual error curve;

(7) adopt the thevenin equivalent circuit model containing second order resistance-capacitance network as the basic model of electrokinetic cell, obtain math equation as follows:

$\left\{\begin{array}{c}{C}_1\frac{d{U}_{C1}}{\mathrm{dt}}+\frac{U_{C1}}{R_1}=i\\ C_2\frac{d{U}_{C2}}{\mathrm{dt}}+\frac{U_{C2}}{R_2}=i\\ \mathrm{OCV}+U_{C1}+U_{C2}+i\·R_0=U_t\end{array}\right.$

Wherein, i represents the working current of electrokinetic cell, U _trepresent the terminal voltage of electrokinetic cell, OCV represents the open-circuit voltage of electrokinetic cell, R ₀for the ohmic internal resistance value of electrokinetic cell, R ₁for the concentration polarization resistance value of electrokinetic cell, R ₂represent that internal temperature of power battery changes the internal resistance change component caused, C ₁for the capacitance of the first electric capacity in thevenin equivalent circuit model, C ₂for the capacitance of the second electric capacity in thevenin equivalent circuit model, C ₁r ₁for the time constant of electrokinetic cell mass transfer dynamic process, C ₂r ₂for the time constant of internal temperature of power battery change tread process, U _c1with U _c2be respectively the voltage at the first electric capacity and the second electric capacity two ends in electrokinetic cell thevenin equivalent circuit model;

According to superposition principle, the open-circuit voltage OCV of electrokinetic cell is set to 0, obtains the terminal voltage U of electrokinetic cell _tand the transport function between electrokinetic cell working current i:

$\begin{array}{c}G\left(s\right)=R_0+\frac{R_1}{R_1{C}_{1}s+1}+\frac{R_2}{R_2{C}_{2}s+1}\\ =R_0+\frac{(R_1{R}_2{C}_1+R_1{R}_2{C}_2)s+R_1+R_1}{R_1{C}_1{R}_2{C}_2{s}^2+(R_1{C}_1+R_2{C}_2)s+1}\end{array};$

(8) using the working current curve of step (5) as the input data of model, the dynamic response curve obtained using step (6) is as the output data of thevenin equivalent circuit model, adopt the transport function of least square method solution procedure (7), obtain each capacitance-resistance parameter R ₀, R ₁, C ₁, R ₂and C ₂, detailed process is as follows:

(8-1) transport function of a following form is set up:

$G\left(s\right)=k+\frac{b_{1}s+b_0}{s^2+a_{1}s+a_0}$

Wherein, k, a ₀, a ₁, b ₀and b ₁for undetermined coefficient, adopt least square method, use the input data of thevenin equivalent circuit model and export this transport function of data direct solution, obtaining k, a ₀, a ₁, b ₀and b ₁;

(8-2) above-mentioned k, a is utilized ₀, a ₁, b ₀and b ₁, by following computing formula, calculate each capacitance-resistance parameter R in the math equation of step (7) ₀, R ₁, C ₁, R ₂and C ₂:

$\left\{\begin{array}{c}{R}_0=k\\ R_1=\frac{b_1}{\sqrt{a_1^2-4a_0}}-\frac{2b_0}{a_1\sqrt{a_1^2-4a_0}+a_1^2-4a_0}\\ R_2=\frac{b_0}{a_0}-R_1\\ C_1=\frac{2}{a_1+\sqrt{a_1^2-4a_0}}/R_1\\ C_2=\frac{2}{a_1-\sqrt{a_1^2-4a_0}}/R_2\end{array}\right.$

(9) from the working current curve and dynamic characteristic of step (4) electrokinetic cell, read and horizontal ordinate t respectively ₁the working current numerical value i of corresponding ordinate _t1with terminal voltage numerical value U _t1, according to thevenin equivalent circuit model, U _c1with U _c2be respectively:

U _C1＝i _t1·R ₁

U _C2＝i _t1·R ₂

According to the math equation of step (7), open-circuit voltage parameter OCV is:

OCV＝U _t1-i _t1·(R ₀+R ₁+R ₂)；

(10) repeat step (4) to step (9), travel through all two different working current i _jand i _k, travel through with working current i _jelectrokinetic cell is carried out to the duration t of constant current operation ₁, complete the discharge and recharge operation of the electrokinetic cell under all different conditions, measure the dynamic external characteristics of electrokinetic cell.