CN110161421A - A kind of method of battery impedance within the scope of on-line reorganization setpoint frequency - Google Patents

A kind of method of battery impedance within the scope of on-line reorganization setpoint frequency Download PDF

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Publication number
CN110161421A
CN110161421A CN201910428872.0A CN201910428872A CN110161421A CN 110161421 A CN110161421 A CN 110161421A CN 201910428872 A CN201910428872 A CN 201910428872A CN 110161421 A CN110161421 A CN 110161421A
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China
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voltage
impedance
frequency
scope
method
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CN201910428872.0A
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Chinese (zh)
Inventor
戴海峰
魏学哲
高倩
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同济大学
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/367Software therefor, e.g. for battery testing using modelling or look-up tables
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/385Arrangements for measuring battery or accumulator variables
    • G01R31/387Determining ampere-hour charge capacity or SoC
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/389Measuring internal impedance, internal conductance or related variables

Abstract

The present invention relates to a kind of methods of battery impedance within the scope of on-line reorganization setpoint frequency, comprising the following steps: 1) obtains the voltage data and current data and setpoint frequency range in time domain online;2) adding window correction and Fast Fourier Transform (FFT) are carried out to voltage and current data, obtains the voltage and current value in frequency domain, and choose target frequency section;3) available voltage and current data are selected using filter criteria;4) available voltage and current data are fitted to obtain the expression formula of voltage, electric current using least square method, and obtain impedance accordingly.Compared with prior art, the present invention has many advantages, such as that on-line measurement, detection are accurate.

Description

A kind of method of battery impedance within the scope of on-line reorganization setpoint frequency

Technical field

The present invention relates to battery impedance testing fields, hinder more particularly, to battery within the scope of a kind of on-line reorganization setpoint frequency Anti- method.

Background technique

Currently, lithium ion battery is big with its capacity density, have extended cycle life, the advantages that charging rate is fast obtained it is extensive Using.But although lithium ion battery possesses plurality of advantages, due to itself belonging to very complicated electro-chemical systems, Reaction is made of many complicated electrode processes, this brings great difficulty to its characteristic of research and application.

Electrochemical impedance spectroscopy (Electrochemical Impedance Spectroscopy, EIS) has broadband model The abundant impedance information enclosed can reflect each electrode process of battery, can also characterize temperature, the state-of-charge (State of battery Of Charge, SOC) and the characteristics such as health status (State of Health, SOH), therefore Applied Electrochemistry impedance spectrum is to electricity Pond characteristic, which carries out research, becomes hot spot.

The measuring principle of electrochemical impedance spectroscopy is to work as battery to be under equilibrium state, applies small size simple alternating current excitation letter Number, the impedance under current frequency is calculated by calculating ac-excited response under same frequency and simple alternating current excitation.Due to EIS Measuring instrument is costly, and in practical applications without ac-excited source, thus traditional EIS measurement usually laboratory into Row.In order to solve this problem, many online researchs for obtaining electrochemical impedance are dedicated to the electrochemistry that design has alternating current source Impedance measurement car-mounted device, but this method not only will increase cost, but also will increase battery management system design complexities.This There are some scholars outside using time-frequency convert method, using the voltage and current data computing impedance in battery time domain, but this side Method can be only applied to specific criteria operating condition, however the operating condition of battery is in dynamic change on real vehicle, and institute is in this way There is also certain limitations.

Just because of current impedance On-line Measuring Method, there are many limitations, and there is an urgent need to propose that a kind of improvement project is come It is online to obtain battery impedance.

Summary of the invention

It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art and provide a kind of on-line reorganizations to set The method of battery impedance in frequency range.

The purpose of the present invention can be achieved through the following technical solutions:

A kind of method of battery impedance within the scope of on-line reorganization setpoint frequency, to measure the resistance of vehicle-mounted lithium ion battery It is anti-, comprising the following steps:

1) voltage data and current data and setpoint frequency range in time domain are obtained online;

2) adding window correction and Fast Fourier Transform (FFT) are carried out to voltage and current data, obtains the voltage and current in frequency domain Value, and choose target frequency section;

3) available voltage and current data are selected using filter criteria;

4) available voltage and current data are fitted to obtain the expression formula of voltage, electric current using least square method, And impedance is obtained accordingly.

The frequency range is set as 0.01-6Hz.

It is power function variation relation between voltage and current and frequency within the scope of setpoint frequency in the step 4).

The objective function that the voltage and current uses least square method to be fitted are as follows:

Log | U |=a1·logf+b1

Log | I |=a2·logf+b2

Wherein, | U | it is voltage magnitude, | I | it is current amplitude, f is frequency, a1, a2, b1, b2For fitting constant.

Expression formula in the step 4), between impedance and frequency are as follows:

In the step 2), by adding Hanning window to be corrected.

In the step 2), the target frequency segment limit of selection is 0-50Hz.

In the step 3), available voltage and electricity are chosen by the fit equation index of standard deviation and impedance magnitude Flow data is then determined as available voltage when standard deviation is less than the fit equation index of given threshold and impedance magnitude less than 0 And current data.

Compared with prior art, the invention has the following advantages that

1) Fast Fourier Transform (FFT) method is utilized, realization obtains battery impedance in the dynamic case, overcomes traditional resistance Anti- spectrum can only measure the shortcomings that battery impedance under the off-line state of laboratory.

2) present invention carries out windowing process to the voltage and current data of acquisition to reduce spectral leakage, improves impedance width It is worth computational accuracy.

3) the invention proposes screening index, ensure that measurement data availability in computing impedance.

4) least square method approximating method is used, calculating process is simple, and easy to accomplish, calculating speed is fast.

Detailed description of the invention

Fig. 1 is the schematic diagram of 0.01Hz-6Hz impedance magnitude under different SOC.

Fig. 2A is the voltage data measured under time domain;Fig. 2 B is the current data measured under time domain.

Fig. 3 A is the voltage amplitude-frequency characteristic schematic diagram in 0-50Hz frequency range after Fast Fourier Transform (FFT);Fig. 3 B is electricity Press phase-frequency characteristic schematic diagram;Fig. 3 C is the electric current amplitude-frequency characteristic signal in 0-50Hz frequency range after Fast Fourier Transform (FFT) Figure;Fig. 3 D is voltage phase-frequency characteristic schematic diagram.

Fig. 4 A is voltage magnitude characteristic and the linear fit result schematic diagram based on least square method;Fig. 4 B is electric current width It is worth characteristic and the linear fit result schematic diagram based on least square method.

Fig. 5 is the method for the present invention flow chart.

Specific embodiment

The present invention is described in detail with specific embodiment below in conjunction with the accompanying drawings.

Embodiment

In order to make the object, technical scheme and advantages of the embodiment of the invention clearer, below in conjunction with the embodiment of the present invention In attached drawing, technical scheme in the embodiment of the invention is clearly and completely described.Obviously, described embodiment is A part of the embodiment of the present invention, instead of all the embodiments.Based on the embodiments of the present invention, those of ordinary skill in the art Every other embodiment obtained without creative efforts, shall fall within the protection scope of the present invention.

Firstly, it is necessary to first analyze the impedance magnitude changing rule in target frequency section.Fig. 1 is that impedance magnitude exists Variation tendency in 0.01Hz-6Hz frequency range.It can be seen from the figure that impedance magnitude is about within the scope of 0.01Hz-6Hz As the raising of frequency quickly reduces in 0.5Hz, after 1Hz-6Hz with frequency increase and reduced trend gradually tends to be flat It is slow.From the direct observation of figure it is found that in 0.01Hz-6Hz frequency range, power function variation rule are presented in impedance magnitude and frequency Rule.

For sampling thheorem and the indoor equipment sampling precision problem of experiment, the present invention is to standard work each in battery time domain The sampling period of voltage and current data is set as 0.01s under condition, i.e. sample frequency is 100Hz, through fast Fourier (Fast Fourier Transformation, FFT) transformation after the available valuable spectrum information in 50Hz.

Selection for battery floor data in time domain, the present invention choose an example and are illustrated.Fig. 2A and Fig. 2 B institute Be shown as the unified Light-duty Vehicle test procedure in the whole world (Worldwide-harmonized Light Vehicles Test Cycle, WLTC) the voltage signal and current signal under operating condition.After selected characteristic frequency band, need to the voltage and current data in time domain Carry out Fast Fourier Transform (FFT).Fourier transformation is a kind of important method of digital processing field, can be by signal from original Beginning time domain is converted to the representation of frequency domain.Any signal continuously measured can be decomposed into the sine wave letter of different frequency Number, to obtain amplitude and the phase angle of sine wave signal, i.e. spectrum information in a frequency domain.Actually should during, be used for Expression and the discrete Fourier transform (Discrete Fourier Transform, DFT) of analysis discrete time signal are more often With.DFT's is defined as:

Wherein, X (k) indicates the data after DFT transform, and x (n) is the analog signal of sampling.

Fast Fourier Transform (FFT) can more rapidly process digital signal, be more widely applied.FFT method is to DFT The improvement of method, this method can greatly reduce multiplication number, improve calculating speed.Based on FFT method, voltage and electricity are obtained The amplitude-frequency characteristic and phase-frequency characteristic of stream are as shown in Fig. 3 A- Fig. 3 D.Wherein, Fig. 3 A is voltage amplitude-frequency characteristic;Fig. 3 B is voltage phase frequency Characteristic;Fig. 3 C is electric current amplitude-frequency characteristic;Fig. 3 D is electric current phase-frequency characteristic.

As can be seen that amplitude with the variation of frequency meets Bending influence from Fig. 3 A, Fig. 3 C, this conclusion with The impedance magnitude that experiment measures in 0.01Hz-6Hz frequency range is consistent with the variation relation of frequency.The present invention uses Function Fitting Method impedance magnitude on-line calculation method is designed.

The relationship of voltage, electric current and frequency is respectively as shown in formula (2) and formula (3):

Wherein, | U | it is voltage magnitude, | I | it is current amplitude, f indicates frequency, a1, a2,For constant.

In order to simplify fit equation (2) and formula (3), consider to carry out under log-log coordinate using linear least square method Linear fit.When using linear least square fitting method, the objective function of voltage and current fitting is respectively as follows:

Log | U |=a1·logf+b1#(4)

Log | I |=a2·logf+b2#(5)

Above-mentioned equation difference is as shown in Figure 4 A and 4 B shown in FIG..Wherein, Fig. 4 A is the fitting of voltage magnitude logarithm and frequency logarithm As a result, Fig. 4 B is the fitting result of current amplitude logarithm and frequency logarithm.Oblique line in figure is fitting a straight line, and scatterplot is FFT change Data point after changing.

Fig. 5 is finally established battery impedance amplitude on-line calculation method flow chart.In step 501, the electricity in time domain Pressure and current data can directly obtain in practical applications.In step 503, in order to reduce the influence of spectrum leakage, to adopting Collect data-signal adding window.The premise of FFT assumes that time signal is that the period is unlimited, but one section can only be intercepted in actual operation Signal, which results in spectrum leakages.Therefore to solve this problem it is necessary to carry out windowing process to data.Following Step 505 in, FFT transform is carried out to the signal after adding window, the voltage and current value in available frequency domain.

It, can since the direct current component being superimposed in voltage in time domain, current data can be separated by FFT transform It is rejected with the influence by removal DC component by bias direct current to impedance magnitude, as illustrated at step 507.

According to Shannon's sampling theorem, sample frequency is at least twice of signal highest frequency, otherwise will lead to the height of script Frequency signal is sampled low frequency signal, the aliasing of frequency spectrum occurs.Generally in practical applications, the sample frequency of BMS can be with Reach 100Hz, so range of target frequencies is 0-50Hz, as indicated at 509.

Found in actual moving process, not all floor data after FFT transform and least square fitting, The impedance magnitude being calculated all meets required precision, i.e. error is maintained within the scope of certain error.Two are primarily present to ask Topic, first is that the impedance magnitude numerical problem calculated, second is that impedance magnitude changing rule Trend Problem.Therefore, the invention proposes Screening conditions, to remove not available data in advance.

For first problem, selection criteria difference is as Rule of judgment.By analysis, not available voltage and current data Have the characteristics that distribution diverging and the order of magnitude is too small.In statistics, standard deviation is a kind of for quantifying the change of one group of data value The measure of change amount.The smaller expression data point of standard deviation tends to the mean value close to set, and standard deviation is larger, indicates data Point is distributed in bigger value range, be easy to cause the inaccuracy of fitting result.It can be with by the comparison of different data index It was found that the standard deviation of voltage and current should limit in a certain range, so as to reject unavailable data.Step 511 embodies This process.

After having selected available data, logarithm can be taken simultaneously to voltage magnitude and current amplitude.In step 515, Function Fitting is carried out using least square method, obtains the functional relation expression between voltage and frequency and electric current and frequency Formula.In step 517, result is obtained to fitting and carries out antilogarithm operation.May finally obtain voltage magnitude | U | with frequency f it Between relationship and current amplitude | I | the relationship between frequency.Based on both sides relation, in step 519, can be calculated Relationship between impedance and frequency:

For Second Problem, according to the available index of Fig. 1 less than zero, therefore second screening conditions can be proposed, That is parameter (a1-a2) less than zero.If (a1-a2) it is greater than zero, illustrate that the trend of matched curve is incorrect, therefore such Data point needs are removed.Detailed process is as shown in step 521.In conclusion the invention proposes two main filter criterias: 1. the standard deviation of voltage data and current data;2. the index of the fit equation of impedance magnitude.

In addition, systematic error must be taken into consideration in measurement process.In actual measurement, impedance magnitude due to systematic error all Greater than offline measured value, but curve can preferably concentrate in certain section, therefore according to this feature by calculated width Value curve translates downwards a distance, corrects the error.

Claims (8)

1. a kind of method of battery impedance within the scope of on-line reorganization setpoint frequency, to measure the impedance of vehicle-mounted lithium ion battery, Characterized by comprising the following steps:
1) voltage data and current data and setpoint frequency range in time domain are obtained online;
2) adding window correction and Fast Fourier Transform (FFT) are carried out to voltage and current data, obtain the voltage and current value in frequency domain, And choose target frequency section;
3) available voltage and current data are selected using filter criteria;
4) it is fitted to obtain the expression formula of voltage, electric current using least square method to available voltage and current data, and according to This obtains impedance.
2. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 1, which is characterized in that The frequency range is set as 0.01-6Hz.
3. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 2, which is characterized in that It is power function variation relation between voltage and current and frequency within the scope of setpoint frequency in the step 4).
4. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 3, which is characterized in that The objective function that the voltage and current uses least square method to be fitted are as follows:
Log | U |=a1·logf+b1
Log | I |=a2·logf+b2
Wherein, | U | it is voltage magnitude, | I | it is current amplitude, f is frequency, a1,a2,b1,b2For fitting constant.
5. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 4, which is characterized in that Expression formula in the step 4), between impedance and frequency are as follows:
6. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 1, which is characterized in that In the step 2), by adding Hanning window to be corrected.
7. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 1, which is characterized in that In the step 2), the target frequency segment limit of selection is 0-50Hz.
8. the method for battery impedance within the scope of a kind of on-line reorganization setpoint frequency according to claim 5, which is characterized in that In the step 3), available voltage and current data are chosen by the fit equation index of standard deviation and impedance magnitude, When standard deviation is less than the fit equation index of given threshold and impedance magnitude less than 0, then it is determined as available voltage and current Data.
CN201910428872.0A 2019-05-22 2019-05-22 A kind of method of battery impedance within the scope of on-line reorganization setpoint frequency CN110161421A (en)

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