An on-line measurement method and device of lithium ion battery electrochemical impedance spectrum based on correlation detection principle

Abstract

The application discloses a kind of lithium ion battery electrochemical impedance spectrum online measurement method and device based on correlation detection principle, using digital-analog converter generates sinusoidal reference signal one aspect is controlled by voltage decision device to open and close the excitation branch of lithium ion battery excitation, for battery to send in rectangular wave excitation signal;Another aspect is after delay to ensure that the dry line current of battery is same frequency and in phase, as the detection signal of correlation detection.In the battery two ends, battery open-circuit voltage and dry line current sensor are arranged, correlation detection is carried out using the open-circuit voltage, dry line current of lithium ion battery and sinusoidal reference signal, then the real part and imaginary part of electrochemical impedance of the frequency are solved using the detection result after digital analysis, to carry out frequency point scanning with every ten times frequency 10-20 frequency points, and draw lithium ion battery electrochemical impedance spectrum.The application can well inhibit noise signal and load signal in lithium ion battery online acquisition, and the circuit structure is relatively simple, measurement precision is high and cost is relatively low.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of on-line measurement of electrochemical impedance spectroscopy of lithium ion batteries, and more particularly relates to an on-line measurement method and device of electrochemical impedance spectroscopy of lithium ion batteries based on correlation detection principle. BACKGROUND

[0002] With the increasing depletion of fossil energy and the increasingly serious environmental problems, more and more attention is paid to the development and use of new energy. As a crucial part of new energy, the lithium ion battery which can be repeatedly charged and used has attracted great attention. Lithium ion batteries have many advantages such as high power density and energy density, long cycle life, low self-discharge rate, moderate price, etc., and are therefore favored by consumers and widely used in many scenes.

[0003] At present, sudden fire and explosion accidents of lithium ion batteries occur from time to time, which has caused people's doubts about the safety of lithium ion batteries. Obtaining the internal condition of the battery can help us prevent accidents, but how to accurately evaluate the internal electrochemical information of the lithium ion battery has become an urgent need for the development of lithium ion batteries. The existing battery measurement system generally measures the voltage, current and temperature signals of the battery in time domain, and cannot accurately reveal the complex electrochemical characteristics of the battery. Electrochemical impedance spectroscopy (EIS) measurement can well solve this problem. EIS measurement is a non-destructive measurement method, which can well reveal the electrochemical behavior inside the battery and reflect the health status of the battery, and is an effective means to solve the measurement difficulty of the internal information of the battery.

[0004] However, the measurement method of electrochemical impedance spectroscopy mainly focuses on the frequency domain measurement method, which needs to design an electrochemical workstation to perform 10-20 frequency point frequency scanning every ten times for an offline single battery to obtain the impedance information of each frequency point. This method is costly, difficult to promote, and requires high voltage and current noise and load signal, which cannot be applied to on-line measurement.

[0005] Therefore, it is an urgent need to design an electrochemical impedance spectroscopy measurement method and device with strong anti-noise performance and low cost to meet the on-line measurement scene of lithium ion batteries, and at the same time ensure the measurement accuracy under high noise and disturbance. SUMMARY

[0006] (I) Technical problems to be solved

[0007] Based on the defects mentioned in the above background art, the present application discloses a lithium ion battery electrochemical impedance spectrum online measurement method and device based on correlation detection principle, which includes the combination of software and hardware, so that the method has high noise resistance, and aims to solve the technical problems of high cost of electrochemical impedance spectrum online measurement, great influence of noise and load signal, and inability to perform real-time online measurement.

[0008] (II) Technical scheme

[0009] The present application discloses a lithium ion battery electrochemical impedance spectrum online measurement method based on correlation detection principle, comprising the following steps:

[0010] Step S100: data preparation, in the use process of lithium ion battery in energy storage system, the voltage between the two ends of the battery is measured by a voltage sensor, and the current of the battery is measured by a current sensor;

[0011] Step S200: excitation injection, a excitation resistor controlled by an electronic switch is connected between the lithium ion battery and the load as an excitation circuit, and the electronic switch is controlled by a voltage decision device to open and close the electronic switch;

[0012] Step S300: correlation operation, the sine signal is delayed to ensure that the sine signal and the fundamental wave signal of the main circuit current are the same frequency and phase, the battery open circuit voltage and the main circuit current signal affected by the excited signal are analyzed and correlated to obtain the voltage signal V c obtained after the correlation detection of the main circuit current signal and the reference sine signal, the open circuit voltage signal is also correlated with the sine signal and the sine signal delayed by 90° to obtain the voltage signals V a and V b obtained after the correlation detection of the open circuit voltage signal and the reference sine signal and the sine signal delayed by 90° respectively;

[0013] Step S400: impedance solving, three groups of voltage signals V a , V b and V c obtained by correlation operation are collected, and the collected results are digitally processed to calculate the real part and the imaginary part of the lithium ion battery electrochemical impedance at this frequency point; wherein the real part R and the imaginary part X are calculated by the following formula respectively:

[0014]

[0015] Step S500: frequency spectrum drawing, the electrochemical impedance at each frequency point is calculated at a speed of 10-20 frequency points per decade, and the results are drawn into an electrochemical impedance spectrum with the real part of the impedance as the x-axis and the negative imaginary part as the y-axis.

[0016] Preferably, the method further comprises a step S600 of result verification, in which the prepared electrochemical impedance spectrum is compared with the electrochemical impedance spectrum measured by the electrochemical workstation offline to verify the measurement result.

[0017] Preferably, the step S200 specifically comprises:

[0018] Step S210: determining the specific frequency of the excitation signal, gradually increasing the excitation signal from low frequency to high frequency, the lowest excitation signal frequency being 0.1 HZ, and the frequency change being realized by the step S500;

[0019] Step S220: generating a corresponding sinusoidal signal according to the selected signal frequency;

[0020] The generated sinusoidal excitation signal is U f (t), the amplitude of the sinusoidal excitation signal is set as A, the frequency is set as f, and the angular frequency is set as ω, and the expression of the sinusoidal excitation signal is shown in formula (1);

[0021] U f (t) = Asinωt = Asin2πft (1)

[0022] Step S230: generating a zero-crossing detection rectangular wave excitation signal according to the generated sinusoidal signal;

[0023] The specific expression of the rectangular wave excitation signal is shown in formula (2):

[0024]

[0025] wherein B is the amplitude of the excitation signal of the battery, and T = 1 / f represents the period of the sinusoidal signal;

[0026] Step S240: obtaining the current excitation signal of the battery;

[0027] The excitation circuit as a branch is connected in series with a fixed value excitation resistor to be connected in parallel across the battery, according to Ohm's law, the current excitation signal x f (t) of the battery is calculated, and the specific expression is shown in formula (3).

[0028]

[0029] wherein x is the rectangular wave excitation signal, R f is the excitation resistor.

[0030] Preferably, the step S300 specifically comprises:

[0031] Step S310: signal analysis of the open circuit voltage and the dry circuit current of the battery excited by the rectangular wave current excitation signal; according to Ohm's law, Kirchhoff's voltage and Kirchhoff's current law and considering the noise existing in the circuit measurement, the voltage and current formula of the circuit is given as shown in formula (4)-(8).

[0032] x0(t) = x(t) + μ(t) (4)

[0033] x(t) = x f (t) + x L (t) (5)

[0034] y(t) = V SOC +y z (t) (6)

[0035] y z (t) = x(t) · Z = [x L (t) + x f (t) + μ(t)] · Z (7)

[0036] y0(t) = y(t) + ν(t) (8)

[0037] Wherein, x0(t) is the measurement value of the dry circuit current acquisition device, y0(t) is the measurement value of the battery voltage acquisition device, x L (t) is the current flowing through the battery load, x f (t) is the current generated by the battery excitation signal, x(t) is the normal dry circuit current of the battery, y(t) is the normal open circuit voltage of the battery, V SOC is the voltage of the lithium ion battery, y z (t) is the response signal of the battery impedance to the dry circuit current signal, Z is the battery impedance, due to the existence of some noise signals in the circuit, μ(t) is the noise signal of the battery dry circuit current, and ν(t) is the noise signal of the battery open circuit voltage.

[0038] Preferably, step S300 further comprises:

[0039] Step S320: correlation detection of the dry circuit current signal and the same frequency and same phase sinusoidal reference signal to obtain V c ;

[0040] The dry circuit current signal and the same frequency and same phase sinusoidal reference signal are correlated and detected, the dry circuit current signal x0(t) and the sinusoidal reference signal U f (t) are input into the multiplication circuit and the integration circuit to obtain the key measurement result V c (t), and formula (13) is obtained.

[0041]

[0042] wherein the sinusoidal excitation signal U f (t) is also used as a sinusoidal reference signal, V c (t) represents the measurement result of the correlation detection between the line current signal and the sinusoidal reference signal, represents the correlation result between the measurement value x0(t) of the line current acquisition device and the sinusoidal reference signal U f (t).

[0043] Substituting the formula (4) and the formula (5) into the formula (13), the measurement value of the line current signal is decomposed into the sum of the load current, the excitation current and the noise current, and the formula (14) is obtained;

[0044]

[0045] The respective operation is performed on each part, and the formula (15)-(17) is obtained;

[0046]

[0047] wherein, represents the correlation detection result between the load current signal and the sinusoidal reference signal, represents the correlation detection result between the excitation current signal and the sinusoidal reference signal, represents the correlation detection result between the noise current signal and the sinusoidal reference signal, and T represents the period of the sinusoidal reference signal;

[0048] Substituting the formula (15)-(17) back into the formula (14), the alternative expression (18) of the formula (14) is obtained;

[0049]

[0050] Since the load current signal x L (t) of the battery and the line current noise μ(t) do not have the correlation relationship with the sinusoidal reference signal U f (t), the integral of them with the sinusoidal reference signal in the period is about 0, and the formula (19) and the formula (20) are obtained

[0051]

[0052] Substituting the formula (19) and the formula (20) back into the formula (18), the more simplified correlation detection result between the line current measurement value and the sinusoidal reference signal is obtained, and the expression is shown in the formula (21);

[0053]

[0054] Fourier series expansion of expression (3) of rectangular wave current excitation signal yields multi-frequency synthesis form of rectangular wave current excitation signal, as shown in equations (22) and (23);

[0055]

[0056] Among them, I ω This represents the amplitude of the DC component. These are the fundamental component and all odd harmonic components;

[0057] Substituting equation (22) into equation (21), we obtain expression (24);

[0058]

[0059] For a sine function, its integral over one period is 0, and the integral of an odd-order sine signal that is an integer multiple of it and has a different frequency is also 0, so we get equations (25) and (26).

[0060]

[0061] Substituting equations (25) and (26) into equation (24), only the correlation response of the first harmonic component of the sinusoidal reference signal and the excitation signal is retained, resulting in equation (27).

[0062]

[0063] Where A is the amplitude of the sinusoidal excitation signal, f is the frequency of the sinusoidal excitation signal, and ω is the angular frequency of the sinusoidal excitation signal.

[0064] Preferably, step S300 further includes:

[0065] The open-circuit voltage signal is correlated with a sinusoidal reference signal of the same frequency and phase and a sinusoidal reference signal of the same frequency but with a phase 90° behind, respectively. The open-circuit voltage signal y0(t) is correlated with the sinusoidal reference signal U. f (t) The key measurement result V is obtained by feeding it into the two ends of the multiplication circuit and the integrator circuit. a The open-circuit voltage signal y0(t) is compared with a sinusoidal reference signal U delayed by 90°. f (t-90°) is fed into the two ends of the multiplication and integration circuits to obtain the key measurement result V. b The correlation detection results of the open-circuit voltage signal with the sinusoidal reference signal with the same frequency and phase and the sinusoidal reference signal with the same frequency and phase lagging by 90° are shown in Equations (42) and (43), respectively.

[0066]

[0067] Among them, I ωis the amplitude of the direct current component, R is the real part of the internal impedance of the lithium ion battery, X is the imaginary part of the internal impedance of the lithium ion battery, both are values to be solved.

[0068] Preferably, step S500 further comprises the following steps:

[0069] Spectrum mapping, the electrochemical impedance of each frequency point is calculated at the speed of 10-20 frequency points per decade, and the results are made into an electrochemical impedance spectrum with the real part of impedance as the x-axis and the negative imaginary part as the y-axis; the frequency point calculation expression is shown as formula (46);

[0070]

[0071] Wherein, f is the frequency of the selected sinusoidal excitation signal, and n is the number of frequency points.

[0072] In addition, the application also discloses a lithium ion battery electrochemical impedance spectrum online measurement device based on correlation detection principle, comprising:

[0073] At least one processor; and at least one memory connected in communication with the processor, wherein:

[0074] The memory stores program instructions executable by the processor, and the processor calling the program instructions can execute the lithium ion battery electrochemical impedance spectrum online measurement method based on the correlation detection principle according to any one of the above.

[0075] (Three) beneficial effects

[0076] The application designs a lithium ion battery electrochemical impedance spectrum measurement method and device based on correlation detection principle, which includes the combination of software and hardware improvement, on the basis of adding a controllable switch in the excitation branch, through data preparation, the voltage between the two ends of the lithium ion battery is measured by the voltage sensor and the current of the battery is measured by the current sensor during the use of the lithium ion battery; a fixed resistor controlled by an electronic switch is connected between the lithium ion battery and the load, and the electronic switch is controlled by a sinusoidal signal to generate a rectangular wave excitation signal by opening and closing the electronic switch through a voltage decision device. The sinusoidal signal which is also the reference signal is delayed to ensure that the sinusoidal signal and the fundamental signal of the main circuit current are the same frequency and in phase, the open circuit voltage of the battery affected by the excitation signal and the main circuit current signal are analyzed and correlated, and the open circuit voltage signal is also correlated with the excitation signal and the excitation signal delayed by 90 degrees. Then, three groups of voltage signals V a ~V cThe collection is carried out, and the collection results of three voltage signals are digitally processed to calculate the real part and the imaginary part of the lithium ion battery electrochemical impedance of the frequency point. Finally, the electrochemical impedance Z of each frequency point is calculated at the speed of 10-20 frequency points per ten times, and the results are plotted into the electrochemical impedance spectrum with the impedance real part as the x-axis and the negative imaginary part as the y-axis. By comparing with the offline measurement results of the battery in the static state of the electrochemical workstation, it is proved that the designed device has relatively accurate impedance spectrum measurement effect and high anti-noise performance, has practical online measurement application value, and has low cost. BRIEF DESCRIPTION OF DRAWINGS

[0077] In order to more clearly illustrate the technical solutions in the present application or prior art, the drawings required to be used in the embodiments will be briefly introduced as follows:

[0078] Figure 1 The flowchart of the online measurement of the lithium ion battery electrochemical impedance spectrum based on the correlation detection provided by the present application is shown in the figure.

[0079] Figure 2 The principle diagram of the online measurement of the lithium ion battery electrochemical impedance spectrum based on the correlation detection in the present application is shown in the figure.

[0080] Figure 3 The functional block diagram of the online measurement of the lithium ion battery electrochemical impedance spectrum based on the correlation detection provided by the present application is shown in the figure.

[0081] Figure 4 The physical object diagram of the online measurement of the lithium ion battery electrochemical impedance spectrum based on the correlation detection in the present application is shown in the figure.

[0082] Explanation of reference numerals:

[0083] 10, measurement module; 20, excitation generation module; 30, first correlation detection module; 40, second correlation detection module; 50, third correlation detection module; 60, calculation module. DETAILED DESCRIPTION

[0084] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0085] In order to solve the technical problems that the electrochemical impedance spectrum measurement is high in cost, greatly affected by noise and load signals, and cannot be measured online, such as Figure 1As shown, the present application designs a lithium ion battery electrochemical impedance spectrum measurement method and device based on correlation detection principle, and the specific measurement principle of the lithium ion battery electrochemical impedance spectrum measurement method based on correlation detection principle includes the following steps:

[0086] Step S100, data preparation, in the use process of lithium ion battery in energy storage system, the voltage between the two ends of the battery is measured by voltage sensor, and the current of the battery is measured by current sensor.

[0087] In another embodiment, the hybrid power pulse characteristic (HPPC) test is carried out on a certain 18650 nickel-cobalt-aluminum type lithium ion battery, the terminal voltage between the two ends of the battery is measured by voltage sensor, and the current of the battery is measured by current sensor.

[0088] Step S200: excitation injection, a excitation resistance controlled by an electronic switch is connected between the lithium ion battery and the load as an excitation circuit, and the electronic switch is controlled by a sine signal through a voltage decision device to control the opening and closing of the electronic switch.

[0089] In another embodiment, step S200 in the specific excitation generation process includes the following steps:

[0090] Step S210: determine the specific frequency of the excitation signal.

[0091] In one embodiment, the present application gradually increases the excitation signal from low frequency to high frequency, the lowest excitation signal frequency is 0.1HZ, and the frequency change is realized by step S500.

[0092] Step S220: generate the corresponding sine signal according to the selected signal frequency.

[0093] The generated sine excitation signal is U f (t), the amplitude of the sine excitation signal is set as A, the frequency is set as f, and the angular frequency is set as ω, then the expression of the sine excitation signal is shown in formula (1).

[0094] U f (t)=Asinωt=Asin2πft (1)

[0095] Step S230: generate a zero-crossing detection rectangular wave excitation signal according to the generated sine signal.

[0096] The measurement of electrochemical impedance spectroscopy generally requires three conditions: causality, linearity and stability. The AC impedance Z of lithium battery is generally very small, ranging from a few milliohms to tens of milliohms. One of the prerequisites for ensuring the effectiveness of impedance measurement is to make the excitation signal in the approximate linear region of the electrode system, that is, under the condition of ensuring the accuracy and signal-to-noise ratio of the signal measurement, the excitation signal amplitude applied to the battery should be as small as possible. In this example, the generated sinusoidal signal is converted into a rectangular wave signal with a duty cycle of 50% through a zero-crossing detector, and the opening and closing of the electronic switch in the excitation circuit is controlled according to the positive and negative of the rectangular wave signal, generating a rectangular wave excitation signal in the circuit The specific expression is shown in equation (2).

[0097]

[0098] Where B is the amplitude of the excitation signal of the battery, T = 1 / f represents the period of the sinusoidal signal, and according to the Bulter-Volmer equation and the linear condition requirements of the measurement, the amplitude B of the voltage signal is generally not more than 10 mV.

[0099] Step S240: Obtain the current excitation signal of the battery.

[0100] The excitation circuit as a branch is connected in series with a fixed value excitation resistor in parallel across the battery, and according to Ohm's law, the current excitation signal x f (t) of the battery is calculated.

[0101]

[0102] Where, is the rectangular wave excitation signal, R f is the excitation resistance.

[0103] Step S300: correlation operation, delay processing of the sinusoidal signal, ensure that the sinusoidal signal and the fundamental wave signal of the main circuit current are the same frequency and in phase, and the open circuit voltage of the battery affected by the excitation signal and the main circuit current signal are analyzed and correlated to obtain the voltage signal V c representing the correlation detection of the main circuit current signal and the sinusoidal signal as a reference; the open circuit voltage signal is also correlated with the sinusoidal signal and the sinusoidal signal delayed by 90° to obtain the voltage signals V a and V b representing the correlation detection of the open circuit voltage of the battery and the sinusoidal signal and the sinusoidal signal delayed by 90° as a reference.

[0104] In another embodiment, step S300 specifically includes the following steps:

[0105] Step S310: signal analysis is performed on the open circuit voltage and the dry circuit current of the battery subjected to the rectangular wave current excitation signal.

[0106] According to Ohm's law, Kirchhoff's voltage and current law and considering the noise existing in the circuit measurement, the voltage and current formula of the circuit is given as shown in formula (4)-(8).

[0107] x0(t)=x(t)+μ(t) (4)

[0108] x(t)=x f (t)+x L (t) (5)

[0109] y(t)=V SOC +y z (t) (6)

[0110] y z (t)=x(t)·Z=[x L (t)+x f (t)+μ(t)]·Z (7)

[0111] y0(t)=y(t)+ν(t) (8)

[0112] As Figure 2 shown, wherein x0(t) is the measurement value of the dry circuit current acquisition device, y0(t) is the measurement value of the battery voltage acquisition device, x L (t) is the current flowing through the battery load, x f (t) is the current generated by the battery excitation signal, x(t) is the normal dry circuit current of the battery, y(t) is the normal open circuit voltage of the battery, V SOC is the voltage of the lithium ion battery, y z (t) is the response signal of the battery impedance to the dry circuit current signal, Z is the battery impedance, due to the existence of some noise signals in the circuit, μ(t) is the noise signal of the battery dry circuit current, ν(t) is the noise signal of the battery open circuit voltage, and PSD is the power spectral density calculation function.

[0113] Step S320: the dry circuit current signal is correlated with the same frequency and same phase sine reference signal to obtain V c .

[0114] In the field of signal processing, cross-correlation detection means is an effective means to characterize the similarity of two signals, and its essence is to perform inner product operation on two signals to obtain the inner product projection of one vector on another vector. The smaller the angle between the two signal vectors, the larger the inner product, and the higher the signal similarity.

[0115] The cross-correlation calculation formula of different two groups of time domain signals f(t) and g(t) is shown in formula (9).

[0116]

[0117] The discrete expression form is shown in formula (10).

[0118]

[0119] Wherein, f(t) and g(t) are two different groups of time domain signals, Representing convolution operation.

[0120] The autocorrelation calculation formula of the time domain signal f(t) is shown in formula (11).

[0121]

[0122] The discrete expression form is shown in formula (12).

[0123]

[0124] In the application, the correlation detection principle is used to effectively identify and extract the response of different frequency excitation signals from the battery terminal voltage signal containing multiple frequency information, and then realize the calculation of the impedance of each frequency point.

[0125] The main current signal is correlated with the sinusoidal reference signal of the same frequency and phase, the main current signal x0(t) and the sinusoidal reference signal U f (t) are input into the multiplication circuit and the integration circuit to obtain the key measurement result V c (t) The specific expression is shown in formula (13).

[0126]

[0127] Wherein, the sinusoidal excitation signal U f (t) is also used as a sinusoidal reference signal at this time, that is, the two are the same sinusoidal signal, V c (t) represents the measurement result after the main current signal and the sinusoidal reference signal are correlated, represents the correlation result of the measurement value x0(t) of the main current acquisition device and the sinusoidal reference signal U f (t).

[0128] Substitute formula (4) and formula (5) into formula (13), decompose the measurement value of the main current signal into the sum of the load current, the excitation current and the noise current, and obtain formula (14).

[0129]

[0130] The respective operation is performed for each part to obtain equations (15) to (17).

[0131]

[0132] wherein, represents the correlation detection result of the load current signal and the sinusoidal reference signal, represents the correlation detection result of the excitation current signal and the sinusoidal reference signal, represents the correlation detection result of the noise current signal and the sinusoidal reference signal, and T represents the period of the sinusoidal reference signal.

[0133] Substituting equations (15) to (17) into equation (14) obtains the alternative expression (18) of equation (14).

[0134]

[0135] Since the load current signal x L (t) and the noise current μ(t) do not have the correlation relationship with the sinusoidal reference signal U f (t), their integrals with the sinusoidal reference signal in the period are about 0, and equations (19) and (20) are obtained.

[0136]

[0137] Substituting equations (19) and (20) into equation (18) obtains the more simplified correlation detection result of the line current measurement value and the sinusoidal reference signal, and the expression is shown in equation (21).

[0138]

[0139] The Fourier series expansion is performed on the expression (3) of the rectangular wave current excitation signal to obtain the multi-frequency synthesis form of the rectangular wave current excitation signal, and the expressions are shown in equations (22) and (23).

[0140]

[0141] wherein, I ω is the amplitude of the direct current component, is the fundamental wave component and each odd harmonic component.

[0142] Substituting equation (22) into equation (21) obtains expression (24).

[0143]

[0144] For a sinusoidal function, the integral of it in a period is 0, and the integral of odd order sinusoidal signals with integer multiples of its frequency and different frequency is also 0, so formula (25) and formula (26) are obtained.

[0145]

[0146] Substitute formula (25) and formula (26) into formula (24), only the correlation response of the first harmonic component of the sinusoidal reference signal and the excitation signal is retained, and formula (27) is obtained.

[0147]

[0148] Step S330: Correlation detection of the open circuit voltage signal with the sinusoidal reference signal of the same frequency and the same phase and the sinusoidal reference signal of the same frequency and the phase lagging 90°, respectively, to obtain V a and V b .

[0149] Let the open circuit voltage signal be correlation detected with the sinusoidal reference signal of the same frequency and the same phase, and the open circuit voltage signal y0(t) and the sinusoidal reference signal U f (t) are input into the multiplication circuit and the integration circuit to obtain the key measurement result V a (t), as shown in expression (28).

[0150]

[0151] Substitute formula (7) and formula (8) into formula (28), and decompose the measurement value of the open circuit voltage into the sum form of multiple groups of voltage signals, and the expression is shown in formula (29).

[0152]

[0153] Each part is calculated respectively to obtain formula (30).

[0154]

[0155] wherein, is the correlation detection result of the voltage measurement noise signal and the sinusoidal reference signal. Since the voltage measurement noise signal and the sinusoidal reference signal also have no correlation, the integral of them with the sinusoidal reference signal in a period is also 0, and expression (31) is obtained.

[0156]

[0157] Substitute formula (19), formula (20) and formula (31) into expression (30) to obtain the simplified expression (32) of the correlation detection of the open circuit voltage and the sinusoidal reference signal.

[0158]

[0159] Based on the characteristics of the battery's internal impedance, we can divide the impedance into the real part and the imaginary part, and obtain the expression for the impedance Z (33).

[0160] Z = R + jX (33)

[0161] Where R is the real impedance of the battery and X is the imaginary impedance of the battery.

[0162] Substituting equation (33) into equation (32), we can divide the correlation detection results of the open-circuit voltage and the sinusoidal reference signal into two parts: one related to the real part of the battery and the other related to the imaginary part of the battery, and obtain the specific expression as shown in equation (34).

[0163]

[0164] For V a By defining the two parts of (t) separately, we obtain equations (35) and (36).

[0165]

[0166] Substituting equations (21) and (27) into equation (35), we obtain the simplified result of equation (35) as shown in equation (37).

[0167]

[0168] Expand equation (36) and apply the imaginary part to the sinusoidal reference signal, treating it as 90° lagging, to obtain expression (38).

[0169]

[0170] For a cosine function, its integral over one period is 0, and the integral of an odd-order sine signal that is an integer multiple of it is also 0, so we get equations (39) and (40).

[0171]

[0172] Substituting equations (39) and (40) into equation (38), we obtain equation (41).

[0173] V a,X =0 (41)

[0174] Substituting equations (37) and (41) into equation (34), the final result of the correlation detection between the battery open-circuit voltage and the sinusoidal reference signal is shown in equation (42).

[0175]

[0176] Similarly, the open circuit voltage of the battery is correlated with the sine reference signal delayed by 90°, and the open circuit voltage signal y0(t) is correlated with the sine reference signal delayed by 90° U f (t-90°) into the multiplication circuit and the integral circuit to obtain the key measurement result V b (t). b As shown in equation (43).

[0177]

[0178] Step S400: impedance solving, three groups of voltage signals V a , V b and V c obtained by correlation operation are collected, and the collected results are digitally processed to calculate the real part R and the imaginary part X of the electrochemical impedance of the lithium ion battery at this frequency point.

[0179] In step S400, V a , V b and V c are important data for solving the electrochemical impedance spectrum of the lithium ion battery, as shown in equations (27), (42) and (43), the value of V a is exactly equal to the product of the value of V c and the real part impedance of the battery, and the value of V b is exactly equal to the product of the value of V c and the imaginary part impedance of the battery. Therefore, by dividing the correlation detection result V a of the sine reference signal and the open circuit voltage signal by the correlation detection result V c of the sine reference signal and the DC current signal, the real part impedance measurement result of the lithium ion battery can be obtained, and the expression is shown in equation (44).

[0180]

[0181] By dividing the correlation detection result V b of the sine reference signal delayed by 90° and the open circuit voltage signal by the correlation detection result V c of the sine reference signal and the DC current signal, the imaginary part impedance measurement result of the lithium ion battery can be obtained, and the expression is shown in equation (45).

[0182]

[0183] Step S500: frequency spectrum drawing, the electrochemical impedance at each frequency point is calculated at a speed of 10-20 frequency points per decade, and the results are plotted into an electrochemical impedance spectrum with the real part impedance as the x-axis and the negative imaginary part as the y-axis.

[0184] In another embodiment, step S500 further comprises specifically:

[0185] After collecting the battery impedance data of a frequency point, the frequency of the battery excitation signal is changed to obtain the battery impedance data of the next frequency point. In this example, 51 impedance collections are performed at 10 collection points per 10 times of frequency, and then the impedance collection of the lithium ion battery online electrochemical impedance spectrum at 0.1-10000HZ is completed. The impedance data of each frequency point is plotted into an electrochemical impedance spectrum with the impedance real part as the x-axis and the negative imaginary part as the y-axis. The frequency point calculation expression in this example is shown in formula (46).

[0186]

[0187] Step S600: result verification, comparing the prepared electrochemical impedance spectrum with the electrochemical impedance spectrum measured by the offline electrochemical workstation to verify the measurement result.

[0188] The electrochemical workstation is an offline measurement instrument with high measurement accuracy and confidence, so the measurement result of the electrochemical workstation is taken as the true value, and the impedance spectrum measurement of the same battery is completed at the same collection frequency points. By comparing the two sets of measurement results, the performance of the design is verified to be effective.

[0189] Figure 3 The example function block diagram of the lithium ion battery electrochemical impedance spectrum online detection device based on the correlation detection principle provided by the present application. In this embodiment, the lithium ion battery electrochemical impedance spectrum online detection device based on the correlation detection principle provided by the present application comprises a measurement module 10, an excitation generation module 20, a first correlation detection module 30, a second correlation detection module 40, a third correlation detection module 50, and a calculation module 60. Among them, the measurement module 10 is used for data preparation, and the voltage between the lithium ion battery is measured by a voltage sensor during the use of the lithium ion battery, and the current of the battery is measured by a current sensor; the excitation generation module 20 is used for generating rectangular wave excitation signals and sinusoidal reference signals of different frequencies; the first correlation detection module 30 is used for completing the correlation detection of the battery dry circuit current signal and the sinusoidal reference signal; the second correlation detection module 40 is used for completing the correlation detection of the battery open circuit voltage signal and the sinusoidal reference signal; the third correlation detection module 50 is used for completing the correlation detection of the battery open circuit voltage signal and the sinusoidal reference signal delayed by 90°; the calculation module 60 is used for processing the correlation detection results of the first, second and third correlation detection modules, and calculating the impedance data of the lithium ion battery at different frequency points.

[0190] The methods contained in the measurement module 10 (corresponding to step S100), the excitation generation module 20 (corresponding to step S200), the first correlation detection module 30, the second correlation detection module 40, the third correlation detection module 50 (the three detection modules 30-50 all correspond to step S300) and the calculation module 60 (corresponding to steps S400-S500) have been introduced above, and will not be repeated here. The circuit design physical diagram of each module is shown in Figure 4

[0191] The online measurement device for electrochemical impedance spectroscopy of lithium ion batteries based on the correlation detection principle disclosed in the embodiment is applied to real-time measurement of electrochemical impedance spectroscopy in lithium ion battery energy storage and vehicle-mounted systems. Measuring the response signal of a weak excitation signal to calculate the battery impedance spectrum is still the most mainstream electrochemical impedance spectroscopy measurement method. However, due to the extremely weak injected excitation signal, it is extremely susceptible to noise interference and load signals in the measurement device, and therefore can only be applied to offline measurement, which is insufficient to meet the real-time requirements of battery energy storage systems and vehicle-mounted systems. In view of this problem, the present application ingeniously proposes an online electrochemical impedance spectroscopy measurement method with simple structure based on the correlation detection principle and the elimination characteristics of non-correlation signals, solves the drawbacks of high cost and inability to meet the requirements of online measurement of traditional measurement devices, and verifies the effect of the method on online electrochemical impedance spectroscopy measurement on test data. By comparing with the offline electrochemical impedance spectroscopy measurement results of the electrochemical workstation, the actual effect of the device on online electrochemical impedance spectroscopy measurement is verified, and the device has application value in real-time measurement of electrochemical impedance spectroscopy in energy storage and vehicle-mounted systems.

[0192] In the above examples provided by the present application, the online measurement method of the present application can also be realized in the form of a software program, which can be stored in a computer readable storage medium. The above software functional units are stored in a storage medium, including a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor to execute part of the steps of the method described in each example of the present application. The aforementioned storage medium includes: a U disk, a mobile hard disk, a read-only memory (Read-Only Memory, ROM), a random access memory (Random Access Memory, RAM), a magnetic disk or an optical disk, and various program code storage media.

[0193] ​Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features therein can be replaced by equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for on-line measurement of electrochemical impedance spectrum of lithium ion battery based on correlation detection principle, characterized in that, The method comprises the following steps: Step S100: data preparation, during the use of the lithium ion battery in the energy storage system, the voltage across the battery is measured by a voltage sensor, and the current of the battery is measured by a current sensor; Step S200: excitation injection, an excitation resistor controlled by an electronic switch is connected across the lithium ion battery and the load to serve as an excitation circuit, and the opening and closing of the electronic switch are controlled by a voltage decision device and a sine signal; Step S300: correlation operation, delay processing is performed on the sinusoidal signal, ensuring that the sinusoidal signal is the same frequency and in phase with the fundamental current signal, and the battery open circuit voltage affected by the excited signal and the current signal are analyzed and correlated to obtain the voltage signal V c representing the correlation detection of the current signal and the sinusoidal signal as a reference; the open circuit voltage signal is also correlated with the sinusoidal signal and the sinusoidal signal delayed by 90° to obtain the voltage signals V a and V b representing the correlation detection of the battery open circuit voltage and the sinusoidal signal and the sinusoidal signal delayed by 90° as a reference, respectively. Step S400: impedance solving, collecting three groups of voltage signals V a , b and V c obtained by correlation operation, and performing digital processing on the collection results to calculate the real part and the imaginary part of the lithium ion battery electrochemical impedance at the frequency point; wherein the real part R and the imaginary part X are calculated by the following formulas respectively: Step S500: spectrum plotting, the electrochemical impedance at each frequency point is calculated at a speed of 10-20 frequency points per decade, and the electrochemical impedance spectrum is plotted with the real part of the impedance as the x-axis and the negative imaginary part as the y-axis.

2. The on-line measurement method of electrochemical impedance spectroscopy of lithium ion battery based on correlation detection principle according to claim 1, characterized in that, The method further comprises the following step S600: result verification, the electrochemical impedance spectrum is compared with the electrochemical impedance spectrum measured by the electrochemical workstation offline, and the measurement result is verified.

3. The on-line measurement method of electrochemical impedance spectroscopy of lithium ion battery based on correlation detection principle according to claim 1, characterized in that, Step S200 specifically comprises the following steps: Step S210: determining the specific frequency of the excitation signal, the excitation signal is gradually increased from low frequency to high frequency, and the lowest excitation signal frequency is 0.1 HZ, and the frequency change is realized by step S500; Step S220: generating a corresponding sine signal according to the selected signal frequency; The generated sinusoidal excitation signal is U f (t), set the amplitude of the sinusoidal excitation signal as A, the frequency as f, and the angular frequency as ω, then the expression of the sinusoidal excitation signal is shown as formula (1); U f (t) = Asinωt = Asin2πft (1) Step S230: generating a zero-crossing detection rectangular wave excitation signal according to the generated sine signal; Rectangular wave excitation signal The specific expression is shown in equation (2): Wherein, B is the amplitude of the excitation signal of the battery, and T=1 / f represents the period of the sine signal; Step S240: obtaining the current excitation signal of the battery; The excitation circuit as a branch is connected in series with a fixed value excitation resistance to be connected in parallel across the battery. According to Ohm's law, the current excitation signal x of the battery is calculated f (t), which is specifically expressed as formula (3); wherein R is a rectangular wave excitation signal, f R is an excitation resistance.

4. The on-line measurement method of electrochemical impedance spectroscopy of lithium ion battery based on correlation detection principle according to claim 1, characterized in that, Step S300 specifically comprises the following steps: Step S310: signal analysis on the open circuit voltage and the main circuit current of the battery subjected to the rectangular wave current excitation signal; according to Ohm's law, Kirchhoff's voltage and Kirchhoff's current law, and considering the noise existing in the circuit measurement, the voltage and current formulas of the circuit are given as shown in formulas (4)-(8); x0(t)=x(t)+μ(t) (4) x(t) = x f (t) + x L (t) (5) y(t) = V SOC + y z (t) (6) y z (t) = x(t) · Z = [x L (t) + x f (t) + μ(t)] · Z (7) y0(t)=y(t)+ν(t) (8) Wherein, x0(t) is the measured value of the dry way current collection device, y0(t) is the measured value of the battery voltage collection device, x L (t) is the current flowing through the battery load, x f (t) is the current generated by the battery excitation signal, x(t) is the normal dry way current of the battery, y(t) is the normal open circuit voltage of the battery, V SOC is the voltage of the lithium ion battery, y z (t) is the response signal of the battery impedance to the dry way current signal, Z is the battery impedance, due to the existence of some noise signals in the circuit, μ(t) is the noise signal of the battery dry way current, ν(t) is the noise signal of the battery open circuit voltage.

5. The on-line measurement method of electrochemical impedance spectroscopy of lithium ion battery based on correlation detection principle according to claim 4, characterized in that, Step S300 further comprises the following steps: Step S320: Correlation detection is performed on the dry route current signal and the sinusoidal reference signal of the same frequency and phase to obtain V c ; The dry route current signal is correlated with a sinusoidal reference signal of the same frequency and phase, and the dry route current signal x0(t) and the sinusoidal reference signal U f (t) are input into a multiplication circuit and an integration circuit to obtain a key measurement result V c (t), to obtain formula (13); wherein the sinusoidal excitation signal U f (t) is also used as a sinusoidal reference signal, V c (t) represents the measurement result of the correlation detection between the line current signal and the sinusoidal reference signal, represents the correlation result between the measurement value x0(t) of the line current acquisition device and the sinusoidal reference signal U f (t). Substitute formulas (4) and (5) into formula (13), decompose the measured value of the main circuit current signal into the sum of the load current, the excitation current and the noise current, and obtain formula (14); Each part is operated respectively to obtain formulas (15)-(17); wherein represents a correlation detection result of the load current signal and the sinusoidal reference signal, represents a correlation detection result of the exciting current signal and the sinusoidal reference signal, represents a correlation detection result of the noise current signal and the sinusoidal reference signal, and T represents a period of the sinusoidal reference signal. Substitute formulas (15)-(17) back into formula (14) to obtain the alternative expression (18) of formula (14); The load current signal x of the battery L (t) and the mains current noise μ(t) have no correlation with the sinusoidal reference signal U f (t), their integrals over a period with the sinusoidal reference signal are approximately zero, resulting in equations (19) and (20) Substitute formulas (19) and (20) back into formula (18) to obtain a more simplified correlation detection result of the main circuit current measured value and the sine reference signal, and the expression is shown in formula (21); The Fourier series expansion of the expression (3) of the rectangular wave current excitation signal is carried out to obtain the multi-frequency synthesis form of the rectangular wave current excitation signal, and the expressions are shown in formulas (22) and (23); wherein I ω is the amplitude of the direct current component, is the fundamental component and each odd harmonic component; Substitute formula (22) into formula (21) to obtain expression (24); For a sine function, the integral in one period is 0, and the integral of an odd multiple of a sine signal of a different frequency is also 0, so formulas (25) and (26) are obtained; Substitute formula (25) and formula (26) into formula (24), only the correlation response of the first harmonic component of the sine reference signal and the excitation signal is reserved, formula (27) is obtained; Wherein, A is the amplitude of the sine excitation signal, f is the frequency of the sine excitation signal, and ω is the angular frequency of the sine excitation signal.

6. The on-line measurement method of electrochemical impedance spectroscopy of lithium ion battery based on correlation detection principle according to claim 5, characterized in that, Step S300 further includes: The open circuit voltage signal is respectively correlated with the same frequency and same phase sinusoidal reference signal and the same frequency and 90° phase lag sinusoidal reference signal, and the open circuit voltage signal y0(t) is sent into the multiplication circuit and the integral circuit to obtain the key measurement result V f (t) at both ends. a The open circuit voltage signal y0(t) is sent into the multiplication circuit and the integral circuit to obtain the key measurement result V f (t-90°) at both ends. b The correlation detection results of the open circuit voltage signal with the same frequency and same phase sinusoidal reference signal and the same frequency and 90° phase lag sinusoidal reference signal are shown in formula (42) and formula (43). where I ω is the amplitude of the DC component, R is the real part of the internal impedance of the lithium-ion battery, and X is the imaginary part of the internal impedance of the lithium-ion battery, both of which are values to be solved.

7. The on-line measurement method of electrochemical impedance spectroscopy of lithium ion battery based on correlation detection principle according to claim 1, characterized in that, Step S500 specifically further includes: Spectrum mapping, the electrochemical impedance of each frequency point is calculated at the speed of 10-20 frequency points per ten times frequency, and the result is made into an electrochemical impedance spectrum with the impedance real part as the x-axis and the negative imaginary part as the y-axis; The frequency point calculation expression is shown as formula (46); Wherein, f is the selected sine excitation signal frequency, and n is the frequency point number.

8. A lithium ion battery electrochemical impedance spectroscopy on-line measuring device based on the correlation detection principle, characterized in that, Comprise: At least one processor; And at least one memory connected with the processor in communication, wherein: The memory has program instructions that can be executed by the processor, and the processor calling the program instructions can execute the lithium ion battery electrochemical impedance spectrum online measurement method based on the correlation detection principle as claimed in any one of claims 1 to 7.

Images