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

Abstract

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

Description

Technical Field

[0001] The present invention belongs to the technical field of power lithium battery applications, and in particular, relates to a lithium battery broadband impedance spectrum testing method based on a pseudo-random sequence. Background Art

[0002] 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 lithium-ion batteries can work in a safe and reliable environment, it is often necessary to monitor the battery status in real time through a battery management system. Among them, battery impedance is closely related to the battery's state of charge, aging state and temperature. Electrochemical impedance spectroscopy can be used to estimate the battery status and diagnose faults in real time, but it is necessary to quickly and accurately measure the battery impedance at different frequencies.

[0003] The most common impedance spectrum test method is the frequency response analysis method. This method measures broadband impedance by sweeping a sinusoidal signal, which can provide sufficiently accurate and reliable measurement results, but it takes a long time. The impedance spectrum test time can be greatly shortened by superimposing sinusoidal signals, but the generation of the sinusoidal superposition signal requires complex hardware design, which greatly limits the practical use of this method. It is relatively easy to implement the impedance spectrum using a square wave signal, but the frequency domain information contained in the 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 frequency domain harmonics. The signal contains a limited signal amplitude, which can effectively simplify the hardware design, so it is particularly suitable for broadband impedance measurement.

[0004] The power content of the frequency domain signal of the pseudo-random sequence is low and is easily interfered by measurement noise. By designing an impedance filter, the interference of noise on the signal can be filtered out to a certain extent. Although the traditional sliding mean filter is simple, it is not good enough to filter out noise with large variance. As the signal power and signal-to-noise ratio decrease, the impedance filtering results are very prone to deviations. Due to the limitation of frequency resolution, the available data in the low-frequency range is extremely scarce, which further limits the accuracy of impedance measurement. At present, there is still a lack of effective and reliable means to conduct online measurement of battery broadband impedance. The performance of traditional pseudo-random sequences needs to be further improved, and the accuracy and reliability of battery impedance measurement need to be strengthened. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a lithium battery broadband impedance spectrum testing method based on a pseudo-random sequence. A pseudo-random sequence is injected into the lithium battery, and the impedance measurement results are filtered using a bilateral filtering algorithm to reduce noise interference, thereby improving the accuracy and stability of broadband impedance measurement of power lithium batteries.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: a lithium battery broadband impedance spectrum testing method based on pseudo-random sequence, specifically comprising the following steps:

[0007] Step 1, design a pseudo-random sequence for broadband impedance measurement;

[0008] Step 2: inject a pseudo-random sequence into the lithium battery through the battery management system, collect the voltage and current of the lithium battery terminal during the injection process, and calculate the measured impedance of the lithium battery at different frequencies;

[0009] Step 3: Filter the measured impedance in the frequency domain using an adaptive bilateral filter to obtain a broadband impedance.

[0010] Furthermore, the pseudo-random sequence is a double pseudo-random sequence or a mixed pseudo-random sequence.

[0011] Furthermore, the mixed pseudo-random sequence S H From the first subsequence S A and the second subsequence S B Superposition: S H =0.5(S A +S B ), where the first subsequence S A The length of the second subsequence is N1, the injection frequency is f1, and the B The length is N2, the injection frequency is f2, and it satisfies:

[0012] Furthermore, the double pseudo-random sequence consists of a third subsequence and a fourth subsequence, and the injection frequency of the third subsequence is f3 and the injection frequency of the fourth subsequence is f4, which satisfies: f3=1.5f4.

[0013] Furthermore, the measured impedance of the lithium battery at different frequencies for:

[0014]

[0015] 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.

[0016] Furthermore, the broadband impedance for:

[0017]

[0018] Where f is the impedance frequency, f i-1 is the lower bound of the filter window, f i+1is the upper bound of the filter window, is the impedance of the lithium battery at impedance frequency f, g1(f) is the kernel function of impedance frequency, is the kernel function of the measured impedance.

[0019] Furthermore, the kernel function g1(f) about impedance frequency and the kernel function about measured impedance They are:

[0020]

[0021]

[0022] Among them, σ f is the standard deviation with respect to frequency, μ f is the mean with respect to frequency, μ f =f', f' is the midpoint of the filter window; Regarding the standard deviation of the real impedance, w f is the weighting coefficient; is the standard deviation of the imaginary impedance, is the mean value of 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 of the imaginary impedance.

[0023] Furthermore, the weighting coefficient w f The current harmonic amplitude I(f) is obtained:

[0024]

[0025] Furthermore, when the pseudo-random sequence is a double pseudo-random sequence, σ f =(f i+1 -f i-1 ) / 6.

[0026] Furthermore, when the pseudo-random sequence is a mixed pseudo-random sequence,

[0027] Compared with the prior art, the present invention has the following beneficial effects: the wide-band impedance spectrum testing method for lithium batteries based on pseudo-random sequences of the present invention injects a mixed pseudo-random sequence or a double pseudo-random sequence, and uses an adaptive bilateral filter to filter the measurement results, thereby realizing rapid measurement of the wide-band impedance of lithium batteries. 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 signals in the low-frequency range, and has sufficiently high robustness. Compared with traditional impedance measurement schemes, the wide-band impedance spectrum testing method for lithium batteries of the present invention can quickly and accurately measure the impedance of lithium batteries, and the impedance measurement results are accurate and stable, and are suitable for various application scenarios of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the specific embodiments, but do not constitute a limitation of the present invention.

[0029] Figure 1 It is a flow chart of the lithium battery broadband impedance spectrum testing method based on pseudo-random sequence of the present invention;

[0030] Figure 2 This is a broadband impedance measurement diagram of Example 1 at an ambient temperature of 25° C. and a state of charge of 80%;

[0031] Figure 3 This is a broadband impedance measurement diagram of Example 1 at an ambient temperature of 25° C. and a state of charge of 20%;

[0032] Figure 4 This is a broadband impedance measurement diagram of Example 1 at an ambient temperature of 35° C. and a state of charge of 50%;

[0033] Figure 5 This is a broadband impedance measurement diagram of Example 1 at an ambient temperature of 15° C. and a state of charge of 50%;

[0034] Figure 6 This is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 25° C. and a state of charge of 80%;

[0035] Figure 7 This is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 25° C. and a state of charge of 20%;

[0036] Figure 8 This is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 35° C. and a state of charge of 50%;

[0037] Fig. 9 This is a broadband impedance measurement diagram of Example 2 at an ambient temperature of 15° C. and a state of charge of 50%. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific implementation methods described herein are only used to illustrate and explain the embodiments of the present invention, and are not used to limit the embodiments of the present invention.

[0039] like Figure 1 The flowchart of the lithium battery broadband impedance spectrum testing method based on pseudo-random sequence of the present invention is as follows:

[0040] Step 1, designing 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.

[0041] The mixed pseudo-random sequence can increase the low-frequency harmonic power content in the frequency domain, so as to better measure the low-frequency impedance of the battery; the mixed pseudo-random sequence S H From the first subsequence S A and the second subsequence S B Superposition: S H =0.5(S A +S B ), where the first subsequence S A The length of the second subsequence is N1, the injection frequency is f1, and the B The length is N2, the injection frequency is f2, and it satisfies:

[0042] The double pseudo-random sequence can increase the high-frequency harmonic power content in the frequency domain, so as to better measure the high-frequency impedance of the battery; the double pseudo-random sequence is composed of a third subsequence and a fourth subsequence, the length of the third subsequence is N3, the injection frequency is f3 and the length of the fourth subsequence is N4, and the injection frequency f4 satisfies: f3=1.5f4, N3>N4.

[0043] Step 2: Inject a pseudo-random sequence into the lithium battery through the battery management system, collect the voltage and current of the lithium battery during the injection process, and calculate the measured impedance of the lithium battery at different frequencies

[0044]

[0045] 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.

[0046] Step 3: In order to reduce the influence of measurement noise and other external interference on impedance measurement, the measured impedance is filtered in the frequency domain through an adaptive bilateral filter to obtain a broadband impedance. It has the characteristics of small calculation amount and high filtering accuracy.

[0047]

[0048] Where f is the impedance frequency, f i-1 is the lower bound of the filter window, f i+1 is the upper bound of the filter window, is the impedance of the lithium battery at impedance frequency f, g1(f) is the kernel function of impedance frequency, is the kernel function of the measured impedance.

[0049] In the present invention:

[0050]

[0051] 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 with respect to frequency, μ f =f', f' is the midpoint of the filter window; Regarding the standard deviation of the real impedance, w f is the weighting coefficient, weighting coefficient w f The current harmonic amplitude I(f) is obtained is the standard deviation of the imaginary impedance, is the mean value of 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 of the imaginary impedance.

[0052] Example 1

[0053] 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, a lithium battery broadband impedance spectrum test method based on a mixed pseudo-random sequence is used to obtain broadband impedance:

[0054] Step 1: Design a mixed pseudo-random sequence for broadband impedance measurement. In this embodiment, the first subsequence S A The length N1 is 8191 bits, the injection frequency f1 is 7000 Hz, and the pseudo-random sequence type is the maximum length sequence; the second sequence S BThe length N2 is 63 bits, the injection frequency f2 is 53.8 Hz, and the pseudo-random sequence type is the maximum length sequence.

[0055] 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 process, and calculate the measured impedance of the lithium battery at different frequencies. In this embodiment, the signal sampling frequency is 70kHz.

[0056] Step 3: Filter the measured impedance in the frequency domain using an adaptive bilateral filter to obtain a broadband impedance.

[0057] like Figure 2 2 is a broadband impedance measurement diagram at an ambient temperature of 25°C and a state of charge of 80%. It can be seen that the measured impedance can accurately fit the true value, indicating that the method adopted in Example 1 has a high impedance measurement accuracy at an ambient temperature of 25°C and a state of charge of 80%. Figure 3 This 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 accurately fit the true value, indicating that the method used in Example 1 has a high impedance measurement accuracy at an ambient temperature of 25°C and a state of charge of 20%. Therefore, the method used in Example 1 is suitable for measuring battery impedance at different states of charge. Figure 4 This is a broadband impedance measurement diagram at an ambient temperature of 35°C and a state of charge of 50%. It can be seen that the measured impedance can accurately fit the true value, indicating that the method used in Example 1 has a higher impedance measurement accuracy at an ambient temperature of 35°C and a state of charge of 50%. Figure 5 1 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 accurately fit the true value, indicating that the method adopted in Example 1 has a high impedance measurement accuracy at an ambient temperature of 15°C and a state of charge of 50%. Figure 4 and 5 It can be seen from the combination that the method adopted in Example 1 is suitable for measuring battery impedance at different ambient temperatures.

[0058] Example 2

[0059] 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, a lithium battery broadband impedance spectrum test method based on a double pseudo-random sequence is used to obtain broadband impedance:

[0060] 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 f4 is 4667 Hz.

[0061] Step 2: Inject the dual 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 process, and calculate the measured impedance of the lithium battery at different frequencies. In this embodiment, the signal sampling frequency is 70kHz.

[0062] Step 3: Filter the measured impedance in the frequency domain using an adaptive bilateral filter to obtain a broadband impedance.

[0063] like Figure 6 2 is a broadband impedance measurement diagram at an ambient temperature of 25°C and a state of charge of 80%. It can be seen that the measured impedance can accurately fit the true value, indicating that the method used in Example 2 has a higher impedance measurement accuracy at an ambient temperature of 25°C and a state of charge of 80%. Figure 7 This 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 accurately fit the true value, indicating that the method used in Example 2 has a high impedance measurement accuracy at an ambient temperature of 25°C and a state of charge of 20%. Figure 6 and Figure 7 It can be seen from the above that the method used in Example 2 is suitable for measuring the impedance of batteries with different charge states. Figure 8 3 is a broadband impedance measurement diagram at an ambient temperature of 35°C and a state of charge of 50%. It can be seen that the measured impedance can accurately fit the true value, indicating that the method used in Example 2 has a higher impedance measurement accuracy at an ambient temperature of 35°C and a state of charge of 50%. Fig. 9 The figure 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 accurately fit the true value, indicating that the method used in Example 2 has a high impedance measurement accuracy at an ambient temperature of 15°C and a state of charge of 50%. Figure 8 and Fig. 9 This shows that the method adopted in Example 2 is suitable for measuring battery impedance at different ambient temperatures.

[0064] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, 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

1. A lithium battery broadband impedance spectrum testing method based on pseudo-random sequence, characterized in that: The specific steps include: 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 voltage and current of the lithium battery terminal during the injection process, and calculate the measured impedance of the lithium battery at different frequencies; Step 3: Filter the measured impedance in the frequency domain through an adaptive bilateral filter to obtain a broadband impedance; The broadband impedance for: Where f is the impedance frequency, f i-1 is the lower bound of the filter window, f i+1 is the upper bound of the filter window, is the impedance of the lithium battery at impedance frequency f, g1(f) is the kernel function of impedance frequency, is the kernel function of the measured impedance; The kernel function g1(f) about impedance frequency and the kernel function about measured impedance They are: Among them, σ f is the standard deviation with respect to frequency, μ f is the mean with respect to frequency, μ f =f', f' is the midpoint of the filter window; Regarding the standard deviation of the real impedance, w f is the weighting coefficient; is the standard deviation of the imaginary impedance, is the mean value of 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 of the imaginary impedance.

2. A lithium battery broadband impedance spectrum testing method based on pseudo-random sequence according to claim 1, characterized in that: The pseudo-random sequence is a double pseudo-random sequence or a mixed pseudo-random sequence.

3. A lithium battery broadband impedance spectrum testing method based on pseudo-random sequence according to claim 2, characterized in that: The mixed pseudo-random sequence S H From the first subsequence S A and the second subsequence S B Superposition: S H =0.5(S A +S B ), where the first subsequence S A The length of the second subsequence is N1, the injection frequency is f1, and the B The length is N2, the injection frequency is f2, and it satisfies:

4. A lithium battery broadband impedance spectrum testing method based on pseudo-random sequence according to claim 2, characterized in that: The double pseudo-random sequence is composed of a third subsequence and a fourth subsequence, and the injection frequency of the third subsequence is f3 and the injection frequency of the fourth subsequence is f4, which satisfies: f3=1.5f4.

5. The method for testing wide-band impedance spectrum of lithium battery based on pseudo-random sequence according to claim 1, characterized in that: The measured impedance of the lithium battery at different frequencies for: 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 for testing wide-band impedance spectrum of lithium battery based on pseudo-random sequence according to claim 1, characterized in that: The weighting coefficient w f The current harmonic amplitude I(f) is obtained:

7. A method for testing wide-band impedance spectrum of lithium batteries based on pseudo-random sequences according to claim 1, characterized in that: When the pseudo-random sequence is a double pseudo-random sequence, σ f =(f i+1 -f i-1 ) / 6.

8. A method for testing wide-band impedance spectrum of lithium battery based on pseudo-random sequence according to claim 1, wherein when the pseudo-random sequence is a mixed pseudo-random sequence,

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