CN115267333A - Lithium battery broadband impedance spectrum testing method based on pseudorandom sequence - Google Patents

Abstract

The invention discloses a method for testing lithium battery broadband impedance spectrum based on pseudo-random sequence, and belongs to the technical field of power lithium battery application. The lithium battery broadband impedance spectrum testing method includes the following steps: designing a pseudo-random sequence for broadband impedance measurement; injecting the pseudo-random sequence into the lithium battery through the battery management system, collecting the terminal voltage and current of the lithium battery during the injection process, and calculating the lithium battery The measured impedance of the battery at different frequencies; the measured impedance is filtered through an adaptive bilateral filter in the frequency domain to obtain a broadband impedance. By injecting a pseudo-random sequence into the lithium battery, the impedance measurement results are filtered through a bilateral filtering algorithm to reduce noise interference, thereby improving the accuracy and stability of broadband impedance measurement of power lithium batteries.

Description

A testing method of lithium battery broadband impedance spectroscopy based on pseudo-random sequence

technical field

The invention belongs to the technical field of power lithium battery application, and in particular relates to a lithium battery broadband impedance spectrum testing method based on a pseudo-random sequence.

Background technique

Lithium-ion batteries have the advantages of high power density, long cycle life, no memory effect and low self-discharge rate, and have received a lot of attention in power systems, new energy vehicles and various portable electronic devices. In order to ensure that the lithium-ion battery can work in a safe and reliable environment, it is often necessary to monitor the state of the battery in real time through the battery management system. Among them, the battery impedance is closely related to the state of charge, aging state, and temperature of the battery. Electrochemical impedance spectroscopy can be used to estimate the state of the battery and diagnose faults in real time, but it is necessary to quickly and accurately measure the battery impedance at different frequencies. Measurement.

The common impedance spectrum test method is the frequency response analysis method, which measures the broadband impedance by sweeping the sinusoidal signal, which can provide sufficiently accurate and reliable measurement results, but the premise is that it takes a long time. By superimposing sinusoidal signals, the impedance spectrum test time can be greatly shortened, but the wave generation of sinusoidal superposition signals requires complex hardware design, which greatly limits the practical use of this method. Using square wave signal to measure impedance spectrum is relatively easy to implement, but the frequency domain information contained in square wave signal is extremely insufficient, so it is difficult to obtain complete impedance spectrum information. In contrast, the pseudo-random binary sequence contains sufficient harmonics in the frequency domain, and the signal has limited signal amplitude, which can effectively simplify the hardware design, so it is especially suitable for the measurement of broadband impedance.

Pseudo-random sequence frequency domain signals have low power content and are easily interfered by measurement noise. The interference of noise to the signal can be filtered out to a certain extent by designing the impedance filter. Although the traditional moving average filter is simple, its performance is insufficient for filtering out noise with large variance. As the signal power and signal-to-noise ratio decrease, the results of impedance filtering are very prone to deviation. Due to limited frequency resolution, the availability of data in the low frequency range is extremely scarce, which further limits the accuracy of impedance measurements. At present, there is still a lack of effective and reliable means for online measurement of battery broadband impedance. The performance of the traditional pseudo-random sequence needs to be further improved, and the accuracy and reliability of battery impedance measurement need to be strengthened.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a lithium battery broadband impedance spectrum testing method based on a pseudo-random sequence. By injecting a pseudo-random sequence into the lithium battery, the impedance measurement result is filtered by a bilateral filtering algorithm, reducing the Noise interference, thereby improving the accuracy and stability of broadband impedance measurement of power lithium batteries.

In order to achieve the above object, the present invention adopts the following technical scheme: a lithium battery broadband impedance spectrum testing method based on a pseudo-random sequence, specifically comprising the following steps:

Step 1. Design a pseudo-random sequence for broadband impedance measurement;

Step 2. Inject a pseudo-random sequence into the lithium battery through the battery management system, collect the terminal voltage and current of the lithium battery during the injection process, and calculate the measured impedance of the lithium battery at different frequencies;

Step 3. Filtering the measured impedance through an adaptive bilateral filter in the frequency domain to obtain broadband impedance.

Further, the pseudo-random sequence is a double pseudo-random sequence or a mixed pseudo-random sequence.

Further, the mixed pseudo-random sequence SH is formed by superimposing the first subsequence S _A and the second subsequence S _B : S _H =0.5( _SA +S _B ), wherein the length of the first subsequence _{S A} is N ₁ , the injection frequency is f ₁ , the length of the second subsequence S _B is N ₂ , and the injection frequency is f ₂ , satisfying:

Further, the double pseudo-random sequence is composed of a third subsequence and a fourth subsequence, the injection frequency of the third subsequence is f ₃ and the injection frequency f ₄ of the fourth subsequence satisfies: f ₃ =1.5f ₄ .

为：Further, the measured impedance of the lithium battery at different frequencies

for:

Among them, V(f) is the voltage harmonic amplitude at impedance frequency f, and I(f) is the current harmonic amplitude at impedance frequency f.

为：Further, the broadband impedance

for:

为锂电池在阻抗频率f下的阻抗，g₁(f)为关于阻抗频率的核函数，

为关于量测阻抗的核函数。Among them, f is the impedance frequency, f _i-1 is the lower bound of the filtering window, and f _i+1 is the upper bound of the filtering window,

is the impedance of the lithium battery at the impedance frequency f, g ₁ (f) is the kernel function about the impedance frequency,

is the kernel function about the measured impedance.

分别为：Further, the kernel function g ₁ (f) about the impedance frequency, the kernel function about the measured impedance

They are:

关于实部阻抗的标准差，

w_f为加权系数；

为关于虚部阻抗的标准差，

为关于实部阻抗的均值，

为锂电池在阻抗频率f下的阻抗的实部，

为锂电池在阻抗频率f下的阻抗的虚部，

为关于虚部阻抗的均值。Wherein, σ _f is the standard deviation about frequency, μ _f is the mean value about frequency, μ _f =f', and f' is the midpoint of the filtering window;

With respect to the standard deviation of the real impedance,

w _f is the weighting coefficient;

is the standard deviation about the imaginary part impedance,

is the mean value with respect to the real impedance,

is the real part of the impedance of the lithium battery at the impedance frequency f,

is the imaginary part of the impedance of the lithium battery at the impedance frequency f,

is the mean value with respect to the imaginary part impedance.

Further, the weighting coefficient w _f is obtained by the current harmonic amplitude I(f):

Further, when the pseudo-random sequence is a double pseudo-random sequence, σ _f =(f _i+1 -f _i-1 )/6.

Further, when the pseudo-random sequence is a mixed pseudo-random sequence,

Compared with the prior art, the present invention has the following beneficial effects: the lithium battery broadband impedance spectrum testing method based on the pseudo-random sequence of the present invention injects a mixed pseudo-random sequence or double pseudo-random sequence, and uses an adaptive bilateral filter to measure The result is filtered, so as to realize the fast measurement of the broadband impedance of the lithium battery. In addition, the mixed pseudo-random sequence or double pseudo-random sequence proposed by the present invention can enhance the signal-to-noise ratio of the signal in the low-frequency range, and has sufficiently high robustness. Compared with the traditional impedance measurement scheme, the lithium battery broadband impedance spectrum of the present invention The test method can quickly and accurately measure the impedance of lithium batteries, and the impedance measurement results are accurate and stable, which is suitable for various application scenarios of lithium batteries.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used together with the specific implementation to explain the present invention, but do not constitute a limitation to the present invention.

Fig. 1 is the flow chart of the lithium battery broadband impedance spectrum test method based on the pseudo-random sequence of the present invention;

Fig. 2 is the broadband impedance measurement figure under the environment temperature 25 ℃, state of charge of embodiment 1 is 80%;

Fig. 3 is a broadband impedance measurement diagram of embodiment 1 at an ambient temperature of 25°C and a state of charge of 20%;

Fig. 4 is a broadband impedance measurement diagram of embodiment 1 at an ambient temperature of 35°C and a state of charge of 50%;

Fig. 5 is a broadband impedance measurement diagram of Example 1 at an ambient temperature of 15°C and a state of charge of 50%;

Fig. 6 is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 25°C and a state of charge of 80%;

Fig. 7 is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 25°C and a state of charge of 20%;

Fig. 8 is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 35°C and a state of charge of 50%;

FIG. 9 is a measurement diagram of broadband impedance of Example 2 at an ambient temperature of 15° C. and a state of charge of 50%.

Detailed ways

The technical solutions of the present invention will be described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific implementation manners described here are only used to illustrate and explain the embodiments of the present invention, and are not intended to limit the embodiments of the present invention.

Figure 1 is a flow chart of the lithium battery broadband impedance spectrum testing method based on a pseudo-random sequence in the present invention, the lithium battery broadband impedance spectrum testing method specifically includes the following steps:

Step 1. Design a pseudo-random sequence for broadband impedance measurement; the pseudo-random sequence in the present invention is a double pseudo-random sequence or a mixed pseudo-random sequence.

The mixed pseudo-random sequence can improve the low-frequency harmonic power content in the frequency domain, so that the low-frequency impedance of the battery can be better measured; the mixed pseudo-random sequence _SH is formed by superimposing the first subsequence S _A and the second subsequence S _B : S _H =0.5( _{SA +S B )} , wherein the length of the first subsequence S _A is N ₁ , the injection frequency is f ₁ , the length of the second subsequence S _B is N ₂ , and the injection frequency is f ₂ , Satisfy:

The double pseudo-random sequence can improve the high-frequency harmonic power content in the frequency domain, so that the high-frequency impedance of the battery can be better measured; the double pseudo-random sequence is composed of the third subsequence and the fourth subsequence, and the length of the third subsequence is N ₃ , the injection frequency is f ₃ and the length of the fourth subsequence is N ₄ , the injection frequency f ₄ satisfies: f ₃ =1.5f ₄ , N ₃ >N ₄ .

Step 2. Inject a pseudo-random sequence into the lithium battery through the battery management system, collect the terminal voltage and current of the lithium battery during the injection process, and calculate the measured impedance of the lithium battery at different frequencies

Among them, V(f) is the voltage harmonic amplitude at impedance frequency f, and I(f) is the current harmonic amplitude at impedance frequency f.

具有计算量小且滤波精度高的特点。Step 3. In order to reduce the impact of measurement noise and other external disturbances on impedance measurement, the measured impedance is filtered through an adaptive bilateral filter in the frequency domain to obtain broadband impedance

It has the characteristics of small calculation amount and high filtering precision.

为锂电池在阻抗频率f下的阻抗，g₁(f)为关于阻抗频率的核函数，

为关于量测阻抗的核函数。Among them, f is the impedance frequency, f _i-1 is the lower bound of the filtering window, and f _i+1 is the upper bound of the filtering window,

is the impedance of the lithium battery at the impedance frequency f, g ₁ (f) is the kernel function about the impedance frequency,

is the kernel function about the measured impedance.

In the present invention:

μ_f为关于频率的均值，μ_f＝f'，f'为滤波窗口的中点；

关于实部阻抗的标准差，

w_f为加权系数，加权系数w_f通过电流谐波幅值I(f)求得

为关于虚部阻抗的标准差，

为关于实部阻抗的均值，

为锂电池在阻抗频率f下的阻抗的实部，

为锂电池在阻抗频率f下的阻抗的虚部，

为关于虚部阻抗的均值。Among them, σ _f is the standard deviation about the frequency, when the pseudo-random sequence is a double pseudo-random sequence, σ _f =(f _i+1 -f _i-1 )/6; when the pseudo-random sequence is a mixed pseudo-random sequence,

μ _f is the mean value about the frequency, μ _f =f', f' is the midpoint of the filter window;

With respect to the standard deviation of the real impedance,

w _f is the weighting coefficient, and the weighting coefficient w _f is obtained by the current harmonic amplitude I(f)

is the standard deviation about the imaginary part impedance,

is the mean value with respect to the real impedance,

is the real part of the impedance of the lithium battery at the impedance frequency f,

is the imaginary part of the impedance of the lithium battery at the impedance frequency f,

is the mean value with respect to the imaginary part impedance.

Example 1

In this embodiment, taking a 18650 cylindrical lithium iron phosphate battery with a rated capacity of 1.5Ah and a rated voltage of 3.6V as an example, the broadband impedance is obtained based on the mixed pseudo-random sequence lithium battery broadband impedance spectrum test method:

Step 1: Design a mixed pseudo-random sequence for broadband impedance measurement. In this embodiment, the length N1 of the _first subsequence S _A is 8191 bits, the injection frequency f1 is 7000 Hz, and the category _of the pseudo-random sequence is the maximum length sequence; The length N ₂ of the second sequence S _B is 63 bits, the injection frequency f ₂ is 53.8 Hz, and the category of the pseudo-random sequence is a maximum-length sequence.

Step 2: Inject the mixed pseudo-random sequence designed in step 1 into the 18650 cylindrical lithium iron phosphate battery through the battery management system, collect the terminal voltage and current at both ends of the battery during the signal injection, and calculate the lithium battery at different frequencies Measure impedance. In this embodiment, the signal sampling frequency is 70kHz.

Step 3. Filtering the measured impedance through an adaptive bilateral filter in the frequency domain to obtain broadband impedance.

As shown in Figure 2, the ambient temperature is 25°C and the state of charge is 80% of the broadband impedance measurement diagram, it can be seen that the measured impedance can be accurately fitted with the real value, indicating that the method used in Example 1 is at an ambient temperature of It has a high impedance measurement accuracy at 25°C and a state of charge of 80%. Figure 3 is a broadband impedance measurement diagram at an ambient temperature of 25°C and a state of charge of 20%. It can be seen that the measured impedance can be accurately measured. Fitting with the real value shows that the method adopted in Example 1 has a relatively high impedance measurement accuracy at an ambient temperature of 25° C. and a state of charge of 20%. Therefore, the method adopted in Embodiment 1 is applicable to the measurement of battery impedance in different states of charge. As shown in Figure 4, the ambient temperature is 35 ° C, the state of charge is 50% of the broadband impedance measurement diagram, it can be seen that the measured impedance can be accurately fitted with the real value, indicating that the method used in Example 1 is at an ambient temperature of It has high impedance measurement accuracy at 35°C and 50% state of charge; as shown in Figure 5, the broadband impedance measurement diagram at an ambient temperature of 15°C and a state of charge of 50% shows that the measured impedance can be accurately measured Fitting with the real value shows that the method adopted in embodiment 1 has higher impedance measurement accuracy at ambient temperature of 15°C and state of charge of 50%; as can be seen from the combination of Fig. 4 and 5: embodiment 1 The adopted method is suitable for battery impedance measurements at different ambient temperatures.

Example 2

In this embodiment, taking a 18650 cylindrical lithium iron phosphate battery with a rated capacity of 1.5Ah and a rated voltage of 3.6V as an example, the broadband impedance is obtained based on the double pseudo-random sequence lithium battery broadband impedance spectrum test method:

Step 1: Design a double pseudo-random sequence for broadband impedance measurement. In this embodiment, the length of the third subsequence is 8191 bits, the injection frequency _f3 is 7000 Hz, the length of the fourth subsequence is 1023 bits, and the injection frequency f ₄ is 4667Hz.

Step 2: Inject the double pseudo-random sequence designed in step 1 into the 18650 cylindrical lithium iron phosphate battery through the battery management system, collect the terminal voltage and current at both ends of the battery during the signal injection, and calculate the lithium battery at different frequencies Measure impedance. In this embodiment, the signal sampling frequency is 70kHz.

Step 3. Filtering the measured impedance through an adaptive bilateral filter in the frequency domain to obtain broadband impedance.

As shown in Figure 6, the ambient temperature is 25°C and the state of charge is 80% of the broadband impedance measurement diagram, it can be seen that the measured impedance can be accurately fitted with the real value, indicating that the method used in Example 2 is used when the ambient temperature is It has high impedance measurement accuracy at 25°C and a state of charge of 80%. Figure 7 is a broadband impedance measurement diagram at an ambient temperature of 25°C and a state of charge of 20%. It can be seen that the measured impedance can be accurately measured. Fitting with the real value shows that the method adopted in Example 2 has a relatively high impedance measurement accuracy at an ambient temperature of 25° C. and a state of charge of 20%. Combining Fig. 6 and Fig. 7, it can be seen that the method adopted in Embodiment 2 is applicable to the measurement of battery impedance in different states of charge. As shown in Figure 8, the ambient temperature is 35°C and the state of charge is 50% of the broadband impedance measurement diagram, it can be seen that the measured impedance can be accurately fitted with the real value, indicating that the method used in Example 2 is at an ambient temperature of It has high impedance measurement accuracy at 35°C and 50% state of charge; as shown in Figure 9, it is a broadband impedance measurement diagram at an ambient temperature of 15°C and a state of charge of 50%. It can be seen that the measured impedance can be accurately measured Fitting with the real value shows that the method adopted in Example 2 has a relatively high impedance measurement accuracy at an ambient temperature of 15° C. and a state of charge of 50%. Combining FIG. 8 and FIG. 9 , it is illustrated that the method adopted in Embodiment 2 is applicable to battery impedance measurement at different ambient temperatures.

The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (10)

1. A method for testing a broadband impedance spectrum of a lithium battery based on a pseudorandom sequence is characterized by comprising the following steps:

step 1, designing a section of pseudo-random sequence for broadband impedance measurement;

step 2, injecting a pseudorandom sequence into the lithium battery through a battery management system, collecting the terminal voltage and current of the lithium battery in the injection process, and calculating the measurement impedance of the lithium battery under different frequencies;

and 3, filtering the measured impedance through a self-adaptive bilateral filter in a frequency domain to obtain the broadband impedance.

2. The method for testing the broadband impedance spectrum of the lithium battery based on the pseudorandom sequence as claimed in claim 1, wherein the pseudorandom sequence is a dual pseudorandom sequence or a mixed pseudorandom sequence.

3. The method as claimed in claim 2, wherein the pseudo-random sequence S is a mixed pseudo-random sequence S_HFrom a first subsequence S_AAnd a second subsequence S_BAnd (3) stacking: s_H＝0.5(S_A+S_B) Wherein the first subsequence S_AHas a length of N₁Injection frequency of f₁A second subsequence S_BIs of length N₂Injection frequency of f₂And satisfies the following conditions:

4. the method as claimed in claim 2, wherein the dual pseudo-random sequence comprises a third subsequence and a fourth subsequence, and the injection frequency of the third subsequence is f₃And injection frequency f of the fourth subsequence₄Satisfies the following conditions: f. of₃＝1.5f₄。

5. The method as claimed in claim 1, wherein the measured impedance of the lithium battery at different frequencies is measured by the pseudo-random sequence-based method for testing the broadband impedance spectrum of the lithium battery

Comprises the following steps:

where V (f) is the voltage harmonic amplitude at the impedance frequency f and I (f) is the current harmonic amplitude at the impedance frequency f.

6. The method as claimed in claim 1, wherein the method for testing the broadband impedance spectrum of the lithium battery based on the pseudorandom sequence comprises

Comprises the following steps:

wherein f is the impedance frequency, f_i-1To the lower bound of the filter window, f_i+1In order to be the upper bound of the filtering window,

is the impedance, g, of the lithium battery at an impedance frequency, f₁(f) Is a kernel function with respect to the frequency of the impedance,

is a kernel function with respect to the measured impedance.

7. The method as claimed in claim 6, wherein the pseudo-random sequence-based test method for broadband impedance spectrum of lithium battery is characterized in thatKernel function g of impedance frequency₁(f) Kernel function for measuring impedance

Respectively as follows:

wherein σ_fAs standard deviation with respect to frequency, μ_fIs a mean value with respect to frequency, mu_f= f ', f' is the midpoint of the filtering window;

with respect to the standard deviation of the real part impedance,

w_fis a weighting coefficient;

as regards the standard deviation of the imaginary impedance,

as an average value with respect to the real part impedance,

is the real part of the impedance of the lithium battery at the impedance frequency f,

being the imaginary part of the impedance of the lithium battery at the impedance frequency f,

as a mean value with respect to the imaginary impedance.

8. The method as claimed in claim 7, wherein the weighting factor w is a function of the impedance spectrum of the lithium battery_fThe current harmonic amplitude I (f) is used to obtain:

9. the method as claimed in claim 7, wherein when the pseudo-random sequence is a dual pseudo-random sequence, σ is determined by the pseudo-random sequence_f＝(f_i+1-f_i-1)/6。

10. The method as claimed in claim 7, wherein, when the pseudo-random sequence is a mixed pseudo-random sequence,

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