CN115932625A - Method for tracking minimum complex impedance amplitude of lithium battery on line - Google Patents
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- CN115932625A CN115932625A CN202310027758.3A CN202310027758A CN115932625A CN 115932625 A CN115932625 A CN 115932625A CN 202310027758 A CN202310027758 A CN 202310027758A CN 115932625 A CN115932625 A CN 115932625A
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Abstract
The invention provides a method for tracking the minimum complex impedance amplitude of a lithium battery on line, which solves the problems of low precision, poor real-time performance, complex circuit and the like when the resistance of the battery is measured by a conventional direct current method or an alternating current injection method, and the main scheme comprises the steps of S1, activating the frequency f in a DC-DC converter s Step disturbance, calculating the lithium ion battery impedance at the odd harmonics of the disturbance, and selecting the minimum value Z in the disturbance min‑o As the initial estimated value of the minimum impedance of the lithium ion battery; s2, correspondingly determining the frequency f of the minimum impedance value in the S1 m Activating frequency f in DC-DC converter m Calculating the impedance of the lithium battery at odd harmonics of the two disturbances according to the disturbances corresponding to the front and rear adjacent frequencies, and selecting a local minimum value Z min‑sm 、Z min‑sn (ii) a S3, comparison Z min‑o 、Z min‑sm And Z min‑sn Selecting the minimum value as the minimum complex resistanceThe reactance magnitude.
Description
Technical Field
The invention relates to the technical field of lithium battery testing, in particular to a method for tracking the minimum complex impedance amplitude of a lithium ion battery on line.
Background
The internal resistance of the battery is a key parameter of chemical power sources. First, lithium batteries are made of a material that acts as a barrier to current flow, as do conventional resistors, and this internal resistance is called the ohmic internal resistance. Secondly, the lithium battery is a system in which electrochemical reaction is generated at every moment, new substances are continuously generated, part of the substances disappear, the electrochemical reaction can also cause the change of ion concentration, and the factors can cause the change of internal resistance, namely the polarization internal resistance, and the lithium battery consists of electrochemical polarization and concentration polarization. The internal resistance of the battery generally includes the above two parts. The minimum impedance is an important parameter for representing the service life of the battery and the running state of the battery, has obvious and strong correlation with the available capacity of the battery, can reflect the health state of the battery, and is also an objective requirement of a battery management system and practical application.
The lithium ion battery impedance measuring method mainly comprises the following steps: open circuit voltage method, transient DC low current electric quantity comparison method, DC discharge method, AC signal injection method, etc.
The open-circuit voltage method estimates the internal resistance of the battery by measuring the terminal voltage of the battery based on the relationship between the internal resistance and the voltage of the battery, and because the relationship has a plurality of influence factors, the uncertainty is large, all measurement accuracies are not high, and even wrong judgment can be given to an operator.
The transient direct-current small-current electric quantity comparison method enables transient small current to flow through a known resistor R and a resistor R in a tested battery, electric quantity consumption of the transient small current on different resistors is synchronously measured, measured values, namely two electric quantity values are respectively in direct proportion to resistance values R of a load resistor R and the load resistor R, the impedance of the tested battery can be obtained through the proportional relation of the two electric quantity values, and online measurement cannot be carried out.
The direct current discharge method is used for discharging a high current of a battery to be detected as the name suggests, and because the special discharge time of the battery has strict limitation, generally, the discharge time is not recommended to exceed 5 seconds, the discharge current is very large, generally, the discharge current can reach 100 amperes, and the current value and the voltage difference value exist, so the internal resistance of the battery can be obtained, and the on-line tracking of the impedance of the lithium ion battery can not be carried out.
The basic idea of the ac signal injection method is to excite the cell with a small ac sinusoidal current/voltage signal of a given frequency and then measure the cell's response to the injected ac current/voltage signal to determine the ac impedance of the cell. Because the detected signals are weak signals, a plurality of amplifying devices and circuits are required to be added, so that the circuit is complex, the interference is high, and errors are easy to occur.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a method for tracking the minimum complex impedance amplitude of a lithium ion battery on line by using the minimum complex impedance of the lithium ion battery controlled by a DC-DC converter based on a disturbance concept.
In order to solve the technical problems, the invention adopts the technical scheme that: a method for tracking the minimum complex impedance amplitude of a lithium battery on line comprises the following steps:
s1, activating frequency f in the DC-DC converter s Step disturbance, calculating the lithium ion battery impedance at the odd harmonics of the disturbance, and selecting the minimum value Z in the disturbance min-o As the initial estimated value of the minimum impedance of the lithium ion battery;
s2, correspondingly determining the frequency f of the minimum impedance value in the S1 m Activating frequency f in DC-DC converter m Calculating the impedance of the lithium battery at odd harmonics of the two disturbances according to the disturbances corresponding to the front and rear adjacent frequencies, and selecting a local minimum value Z min-sm 、Z min-sn ；
S3, comparison Z min-o 、Z min-sm And Z min-sn Selecting the minimum value as the minimum complex impedance amplitude value.
Furthermore, the calculation formula of the impedance of the lithium ion battery in the S1 is as follows,
in the formula, Z s Represents the impedance, V batt-f 、I batt-f 、e jθ-f Denotes V batt 、I batt The result of the FFT analysis of (1).
Further, the odd harmonics in S1 are (2 k-1)f s K ranges from 1 to 10 min-o The frequency of occurrence is expressed as,
f m ＝(2k * -1)f step
correspondingly, the result is that,
further, f in step S2 m The calculation formula of the adjacent frequencies in the front and the back is as follows,
an electronic device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for tracking the minimum complex impedance amplitude of a lithium battery on-line as described above when executing the program.
A non-transitory computer-readable storage medium having stored thereon a computer program, characterized in that: the computer program is used for realizing the steps of the method for tracking the minimum complex impedance amplitude of the lithium battery on line when being executed by a processor.
Compared with the prior art, the invention has the beneficial effects that:
1. the system does not need to be disconnected or interrupted, and the method is very suitable for tracking the minimum impedance in real time;
2. the addition of AC signal injection circuits, response measurement and analysis circuits or devices is not required, reducing cost, design complexity and overall system size.
Drawings
The disclosure of the present invention is illustrated with reference to the accompanying drawings. It is to be understood that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention. In the drawings, like reference numerals are used to refer to like elements throughout. Wherein:
FIG. 1 is a flow chart schematically illustrating minimum complex impedance magnitude on-line tracking according to an embodiment of the present invention;
fig. 2 schematically shows a basic circuit diagram of an on-line EIS measurement proposed according to an embodiment of the present invention.
Detailed Description
It is easily understood that according to the technical solution of the present invention, a person skilled in the art can propose various alternative structures and implementation ways without changing the spirit of the present invention. Therefore, the following detailed description and the accompanying drawings are merely illustrative of the technical aspects of the present invention, and should not be construed as all of the present invention or as limitations or limitations on the technical aspects of the present invention.
An embodiment according to the present invention is shown in conjunction with fig. 1-2.
A method for tracking the minimum complex impedance of a lithium ion battery on line comprises the following steps:
s1: in a DC-DC converter the activation frequency is f s Step perturbation of (2). f. of s The choice of (c) is based on the type of battery and knowledge of the battery. Calculating f s At odd harmonics of (2 k-1) f s And impedance of the lithium ion battery. Due to the attenuation of the higher harmonics, the battery impedance is calculated using only the first 10 harmonics, i.e. k in the range 1 to 10, in order to get an accurate measurement.
Z s ＝(V batt-f /I batt-f )*e jθ-f (1)
Z s Is the impedance, V batt-f 、I batt-f 、e jθ-f Is V batt 、I batt The result of the FFT analysis of (2);
s2: comparing the 10 th harmonic impedance value obtained in step 1, the minimum value Z min-o As a preliminary estimate of the minimum impedance of the battery. Z min-o The frequency of occurrence is denoted f m ＝(2k * -1)f step Then k is * Can be determined according to (2) forCalculating the sine wave disturbance frequency given by the steps (3) and (4);
s3: the range of activation frequencies in a dc-dc converter is (2 k) * -3)f s To (2 k) * -1)f s Multiple sinusoidal perturbations. Calculating the disturbance frequencies according to (3), and then comparing the impedance values Z at these sinusoidal disturbance frequencies sm M =1,2, \ 8230;, 9, obtained at (2 k) * -3)f step ～(2k * -1)f s Local minimum impedance value Z in the range min-sm ；
S4: the activation frequency range in the DC-DC converter is (2 k) * -1)f s To (2 k) * +1)f s Multiple sinusoidal perturbations. And (4) calculating the disturbance frequency according to the step (4). The local minimum impedance value (i.e. Z) in the frequency range is obtained in the same way as in step 3 min-sn )；
S5: comparison of Z min-o 、Z min-sm 、Z min-sn The minimum value is the minimum complex impedance amplitude Z of the battery min 。
In this embodiment, the specific technical solution of the method of the present invention is as follows:
as shown in fig. 2, the present embodiment provides a basic circuit diagram for online EIS measurement.
The battery is a Tenergy ICR 18650-2600 lithium ion battery, and the main specifications of the battery are as follows: maximum voltage 4.2V, nominal voltage 3.7V, nominal capacity 2.6Ah, and initial internal impedance magnitude of 65m Ω at 1kHz, L being inductance of 4.7 μ H, C being capacitance of 120 μ F, S I 、S U Is a MOS transistor.
First, a brand-new battery (battery 1) and an aged battery (battery 2) were selected and subjected to an experiment. Before the experiment, the two batteries were fully charged (4.2V each). The two batteries are then connected to the input terminals of the respective dc converters. In order to reduce the stray impedance value as much as possible, the influence of the stray impedance value on the measurement of the minimum impedance value of all the battery units is uniform, and the layout design of an experimental prototype is symmetrical and uniform. The impedance measurements are taken at the beginning of discharge when each cell is nearly at full charge (i.e., 100% SOC). The frequency of the step disturbance is 200Hz.
According to the impedance tracking method proposed herein, the initial minimum complex impedance magnitude values (Z) of the batteries 1 and 2 min-o ) Respectively at 1.4 and 1.8kHz. For the battery 1, due to Z min-o Occurs at 1.4kHz (i.e. f) m =1.4 kHz), k is calculated from (4) * Has a value of 4. The multi-sine wave perturbation is activated in two frequency ranges, i.e. 1-1.4kHz and 1.4-1.8kHz, the frequency of the multi-sine wave perturbation is calculated according to (5) and (6). The tracking Z of the battery 1 is found by the tracking algorithm proposed above min The value is at 1.56kHz and equal to 64.6 m.OMEGA. For battery 2, due to Z min-o Occurs at 1.8kHz (i.e. f) m =1.8 kHz), according to (4), k * The value of (d) is calculated as 5. The multi-sine wave disturbances are activated in two frequency ranges, i.e. 1.4-1.8kHz and 1.8-2.2kHz, the frequency of the multi-sine wave disturbances being determined according to (5) and (6). The tracking Z of the battery 2 is found by the tracking algorithm proposed in 1.2 min The value is at 1.8kHz, equal to 66.8 m.OMEGA.. It can be seen that Z of the battery 2 min Value ratio Z of battery 1 min The value is large, and the result is in line with the expectation.
The technical scope of the present invention is not limited to the above description, and those skilled in the art can make various changes and modifications to the above-described embodiments without departing from the technical spirit of the present invention, and such changes and modifications should fall within the protective scope of the present invention.
Claims (6)
1. A method for tracking the minimum complex impedance amplitude of a lithium battery on line is characterized by comprising the following steps:
s1, activating frequency f in the DC-DC converter s Step disturbance, calculating the lithium ion battery impedance at the odd harmonics of the disturbance, and selecting the minimum value Z in the disturbance min-o As the initial estimated value of the minimum impedance of the lithium ion battery;
s2, correspondingly determining the frequency f of the minimum impedance value in the S1 m In a DC-DC converter, activating a frequency f m Calculating the impedance of the lithium battery at odd harmonics of the two disturbances according to the disturbances corresponding to the front and rear adjacent frequencies, and selecting a local minimum value Z min-sm 、Z min-sn ；
S3, comparison Z min-o 、Z min-sm And Z min-sn And selecting the minimum value as the minimum complex impedance amplitude.
2. The method of claim 1, wherein the method comprises the steps of: the lithium ion battery impedance calculation formula in S1 is,
Z s ＝(V batt-f /I batt-f )*e jθ-f
in the formula, Z s Represents the impedance, V batt-f 、I batt-f 、e jθ-f Represents V batt 、I batt The result of FFT analysis of (2).
3. The method of claim 1, wherein the method comprises the steps of: the odd harmonic in S1 is (2 k-1) f s K ranges from 1 to 10, Z min-o The frequency of occurrence is indicated as,
f m ＝(2k * -1)f step
correspondingly, the result is that,
4. the on-line tracking lithium battery minimal complexity of claim 1A method of impedance magnitude, characterized by: in said step S2 f m The calculation formula of the adjacent frequencies in the front and the back is as follows,
5. an electronic device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein: the steps of the method for tracking the minimum complex impedance amplitude of the lithium battery on line according to any one of claims 1 to 4 are realized when the processor executes the program.
6. A non-transitory computer-readable storage medium having stored thereon a computer program, characterized in that: the computer program is used for implementing the steps of the method for tracking the minimum complex impedance amplitude of the lithium battery on line according to any one of the claims 1 to 4 when being executed by a processor.
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