CN113805086B - Rapid estimation method for internal resistance of lithium ion battery - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 70
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 18
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 18
- 230000010287 polarization Effects 0.000 claims abstract description 47
- 230000008569 process Effects 0.000 claims abstract description 47
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 18
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 18
- 230000009466 transformation Effects 0.000 claims abstract description 4
- 230000004044 response Effects 0.000 claims description 38
- 230000008859 change Effects 0.000 claims description 28
- 230000001052 transient effect Effects 0.000 claims description 15
- 230000009471 action Effects 0.000 claims description 9
- 239000003990 capacitor Substances 0.000 claims description 7
- 238000002474 experimental method Methods 0.000 claims description 7
- 230000006641 stabilisation Effects 0.000 claims description 3
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- 230000036962 time dependent Effects 0.000 claims description 3
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- 230000000087 stabilizing effect Effects 0.000 abstract description 2
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- 238000006243 chemical reaction Methods 0.000 description 8
- 238000004458 analytical method Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 4
- 238000007599 discharging Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000000157 electrochemical-induced impedance spectroscopy Methods 0.000 description 3
- 238000005259 measurement Methods 0.000 description 2
- 230000000630 rising effect Effects 0.000 description 2
- 230000032683 aging Effects 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 238000007600 charging Methods 0.000 description 1
- 238000010281 constant-current constant-voltage charging Methods 0.000 description 1
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- 230000036541 health Effects 0.000 description 1
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- 230000028161 membrane depolarization Effects 0.000 description 1
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Abstract
The invention discloses a method for estimating internal resistance of a lithium ion battery, which comprises the following steps: performing charge and discharge test on the lithium battery, and collecting and recording a voltage U A of the battery terminal voltage when a discharge loop is disconnected, a voltage stabilizing value U C of the rear end of the discharge loop and a t-U data table of voltage transformation along with time after the discharge loop is disconnected; respectively solving the difference value between the terminal voltage values at the later moment and the previous moment in the t-U data table, taking the previous moment in the two moments corresponding to the difference value as the corresponding voltage UB when the difference value is smaller than the reference threshold voltage, and then calculating the ohmic resistance R0= (UB-UA)/I through a formula; polarization internal resistance r1= (UC-UB)/I; wherein the current I is a discharge current in a discharge process; the invention can rapidly obtain the internal resistance parameter of the lithium battery and ensure the accuracy of the obtained result.
Description
Technical Field
The invention relates to the field of calculation of parameters of lithium batteries, in particular to a method for estimating internal resistance of a lithium ion battery.
Background
With the rapid development of new energy industry, lithium ion batteries have been widely used in various fields due to the characteristics of long cycle life and high energy density, but the nature of high energy density carrier batteries has some unsafe and uncertain factors, so the safety problem of batteries has also attracted a great deal of attention. The internal resistance of the battery is the most important index for measuring the power performance of the battery, and the internal resistance of the lithium ion battery can influence the charge and discharge cut-off voltage of the battery, so that the charge and discharge of the battery are finished too early or too late. Meanwhile, the internal resistance index can characterize the health state of the lithium ion battery, and the internal resistance increase can increase the consumption of the internal energy of the battery, so that the heat production of the battery is increased, and the safe use condition of the battery is influenced. In the prior art, the method for acquiring the battery polarization internal resistance and the polarization capacitance is complex, if the battery polarization internal resistance is to be accurately acquired, an electrochemical workstation is needed to perform an Electrochemical Impedance Spectroscopy (EIS) test, so that requirements on equipment requirements, mastering EIS test processes and principles in actual work are high, a great deal of time is wasted, and the method does not meet the actual requirements. In the practical engineering application process, the inner group of the lithium battery needs to be rapidly measured on the premise of meeting certain precision requirements, and how to rapidly improve the strategy efficiency of the inner group on the premise of ensuring certain precision is very important for the engineering application of the lithium battery.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a rapid estimation method of the internal resistance of a lithium ion battery, which is used for rapidly and ensuring a certain accuracy to realize rapid estimation of the internal resistance parameter of the lithium ion battery.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a rapid estimation method of internal resistance of a lithium ion battery comprises the following steps:
(1) After the discharge is finished, a discharge loop is disconnected, and a voltage U A of the battery terminal voltage when the discharge loop is disconnected, a voltage stabilization value U C of the rear end of the discharge loop and a t-U data table of voltage transformation along with time after the discharge loop is disconnected are acquired and recorded;
(2) In a data table of time-dependent voltage change data t-U in the process of changing from U A to U C, the change process from U A to U C is the change process of voltage under the action of ohmic resistance and polarization resistance of a lithium battery, and voltage U B is arranged between voltage U A and voltage U C, wherein the change process from U A to U B is the change process of voltage under the action of ohmic resistance, and the change process from U B to U C is the change process of voltage under the action of polarization internal resistance; respectively obtaining the difference value between the terminal voltage values at the later moment and the previous moment in the t-U data table, and taking the previous moment in the two moments corresponding to the difference value as the corresponding voltage U B when the difference value is smaller than the reference threshold voltage, wherein the ohmic resistance R0= (U B-UA)/I; wherein the current I is a discharge current in a discharge process; polarization internal resistance r1= (U C-UB)/I;
In the step (2), the reference threshold voltage is calibrated in advance through experiments.
The reference threshold voltage is 0.01V.
The step (2) further includes a solving method of the polarization capacitor C1, where the solving method of the polarization capacitor includes:
a. Establishing a first-order RC model of the lithium ion battery, and simulating the attenuation process of transient response of the lithium ion battery in the process from U B to U C by using a first-order step response curve; wherein the time constant T=R1C1 of the first-order step response, wherein C1 is a polarized capacitor, R1 is a polarized internal resistance, and T is the time constant of the first-order step response;
when t=t, the transient response of the first-order step response system decays by 0.632, with a corresponding voltage of U M; u M＝(UC-UB)*0.632+UB;
According to the obtained time tm of the U M corresponding to the voltage UM and the time tb corresponding to the voltage U B in the T-U data table, obtaining a time constant t=tm-tb according to tm and tb;
The polarization capacitance c1=t/R1 is obtained from t=r1c1.
The invention has the advantages that: the calculation is simple and quick, the cost is low, the speed of calculating the internal resistance is greatly improved while the precision meets the engineering requirement, the rapid use in engineering application is convenient, the calculated amount is small, and the calculation is simple; the experiment verifies that the error is also in the allowable range, and the precision meets the requirement.
Drawings
The contents of the drawings and the marks in the drawings of the present specification are briefly described as follows:
FIG. 1 is a graph of lithium battery discharge voltage versus time;
FIG. 2 is a first order RC model of a lithium battery;
FIG. 3 is a graph of the step response of the first order system of the present invention;
FIG. 4 is a graph showing the comparison of the voltage curves of the present invention and the curves after first order fitting;
FIG. 5 is a table t-U of voltage time curve data after discharge at 1C magnification;
FIG. 6 is a schematic diagram of a time-voltage curve and a first-order fitting curve based on the time-voltage data of FIG. 5.
FIG. 7 is a graph showing the voltage data and time curve after the end of discharge and a first-order and second-order fitting curve.
Detailed Description
The following detailed description of the invention refers to the accompanying drawings, which illustrate preferred embodiments of the invention in further detail.
A rapid estimation method of internal resistance of a lithium ion battery comprises the following steps:
(1) After the discharge is finished, a discharge loop is disconnected, and a voltage U A of the battery terminal voltage when the discharge loop is disconnected, a voltage stabilization value U C of the rear end of the discharge loop and a t-U data table of voltage transformation along with time after the discharge loop is disconnected are acquired and recorded; fig. 1 is a schematic diagram of a voltage change curve after the end of the discharge, and the voltage changes from U A to U C after the end of the discharge, which is caused by the internal resistance of the lithium battery. Wherein U A-UB section is the change caused by the influence of ohmic internal resistance, U B to Uc are the influence of polarized internal resistance, and U B is a demarcation point; FIG. 5 is a table of t-U data showing the statistical voltage variation with time, mainly counting the variation process from the end of discharge U A to Uc;
(2) As shown in fig. 1, in a data table of time-dependent voltage change data t-U in the process of changing from U A to U C, the process of changing from U A to U C is a process of changing voltage under the action of ohmic resistance and polarization resistance of a lithium battery, and voltage U B is set between voltage U A and voltage U C, wherein the process of changing from U A to U B is a process of changing voltage under the action of ohmic resistance, and the process of changing from U B to U C is a process of changing voltage under the action of polarization internal resistance;
Respectively obtaining the difference value between the terminal voltage values at the later moment and the previous moment in a t-U data table, taking the previous moment of the two moments corresponding to the difference value as corresponding voltage U B when the difference value is smaller than the reference threshold voltage, and determining the ohmic resistance R0= (UB-UA)/I after U B is determined; polarization internal resistance r1= (U C-UB)/I; wherein the current I is a discharge current in a discharge process;
The U B is determined by adopting a parameter threshold voltage mode because U B is used as a demarcation point, the change rates of voltages between the front and the back are different, ohm resistance data discrete change is fast, and polarization internal resistance influence change is relatively slow and linear; after the discharge is finished, the voltage between two adjacent points is continuously calculated, when the difference value is larger than the reference threshold voltage, the voltage value is discrete, the voltage is increased faster, which is caused by ohmic resistance, and when the voltage is smaller than the reference threshold voltage, the curve is continuous, the adjacent voltages rise slowly, the part with large discreteness is caused by ohmic internal resistance, the period of the stage is rapid in voltage change, and the succession is good. The specific value of the reference threshold voltage can be verified through repeated experiments, and the difference threshold value corresponding to a certain type of battery can be obtained through conversion after Ub is found through pre-experiment calibration.
In the polarization process, the effect of the internal resistance of polarization and the polarization capacitance are adopted, so that the polarization capacitance C1 is needed to be solved, and the solving method of the polarization capacitance comprises the following steps:
a. Establishing a first-order RC model of the lithium ion battery, and simulating the attenuation process of transient response of the lithium ion battery in the process from U B to U C by using a first-order step response curve; wherein the time constant T=R1C1 of the first-order step response, wherein C1 is a polarized capacitor, R1 is a polarized internal resistance, and T is the time constant of the first-order step response; wherein R1 is obtained in the step (2), and C1 can be confirmed after the time constant T is determined.
As can be seen from analysis of the transient response, when t=t, the transient response of the first-order step response system decays by 0.632, and the corresponding voltage is U M; that is, the voltage in the U B-UC stage decays by 0.632, and the UB-UC is actually rising to UC, so that the voltage in the UB-UC stage decays by 0.632, which is the decaying voltage (UC-U B) by 0.632, and the voltage in the U B stage rises to UC, so that U M is the voltage value of U B plus the decaying voltage, and U M＝(UC-UB)*0.632+UB;
After obtaining U M, finding a time tm corresponding to the voltage U M and a time tb corresponding to the voltage U B in the T-U data table according to the obtained U M, and obtaining a time constant t=tm-tb according to tm and tb; then, the polarization capacitance c1=t/R1 is obtained from t=r1c1, and when T and R1 are both obtained, C1 is also obtained. When the time tm is found in the data table according to U M, if the voltage is not the same as UM, the voltage closest to U M and the time corresponding to the voltage are found as tm.
The application takes 18650 ternary lithium batteries as an example:
(1) Under the condition of room temperature (25 ℃), carrying out 1C-rate constant-current constant-voltage charging on the lithium battery until the cut-off voltage is 4.2V, and stopping charging when the cut-off current is 100 mA;
(2) Placing for 1h;
(3) Constant-current discharging is carried out on the battery for 6min by using the current with the multiplying power of I=1C, and the battery is placed for 1h;
(4) And (3) repeating the step, and stopping the test when the voltage of the battery terminal is reduced to 2.75V.
After the discharge is finished, the discharge loop is disconnected, and a voltage U A of the battery terminal voltage when the discharge loop is disconnected, a voltage stabilizing value U C of the rear end of the discharge loop and a voltage time curve and a data table t-U data table of the voltage change along with time in the process that the terminal voltage is changed from UA to Uc are collected and recorded. As shown in fig. 1, the battery voltage curve after the end of discharging includes AB segments and BC segments at two ends, corresponding to A, B, C points on the curve, and corresponding voltages are UA, UB and UC, respectively, where AB segments are the switching-off loops when the end of discharging, and the voltage rise at one end generated on the battery voltage curve is the occupation voltage of ohmic internal resistance. The BC segment is a segment of gradually rising voltage of the battery end after the loop is disconnected, is a representation of the depolarization process in the battery, is the occupation voltage of the polarized internal resistance, and has different values in different discharging states.
According to the voltage characteristics of the lithium battery, the ohmic internal resistance R 0 and the polarized internal resistance R 1 of the battery can be obtained. Then there are:
However, in the actual test, the position of the point B is fuzzy, and the accurate value of the U B cannot be accurately determined, mainly because the time between the two points AB cannot be accurately found, the machine generally takes seconds as a unit when collecting, and the moment of the point B may be accurately in milliseconds in the actual situation. Therefore, the existing battery internal resistance test method has larger error. In the prior art, the point B and the voltage thereof can be accurately measured through professional equipment instruments, but the test mode can lead to complexity and longer time, and in the engineering application process, generally, only one range of accuracy requirement is required, only the error can be met within an allowable range, and the internal resistance needs to be calculated more quickly, so that in the engineering application field, the time requirement is greater than the accuracy, and the engineering application can be met by estimating the internal resistance parameter as quickly as possible after the accuracy meets a certain requirement. On the condition that the precision requirement is met, the internal resistance parameter can be obtained quickly, and the technical problem to be solved in the engineering field is solved.
Aiming at the technical problem to be solved by the application, in order to quickly determine the point B and the voltage thereof, the calculation of the internal resistance can be realized. The determination of the point B can be performed by calculating the difference between two sets of voltages at adjacent times to determine whether the data obtained by the first-order model is accurate, and when the difference is smaller than or equal to a certain value (when the voltage difference corresponding to fig. 4 is just smaller than or equal to 0.01V, the voltage difference is just the point B and can be obtained by calibration experiment measurement), the continuity of the voltage curve is better, and the voltage curve corresponds to the BC segment in fig. 4. Therefore, the point B in the map is the point at which the difference value is 0.01V or less for the first time. Therefore, the difference processing can be performed through the acquired voltage data table t-U, and the position of the point B and the corresponding voltage thereof can be judged according to the comparison of the difference value and the reference voltage threshold value. Respectively obtaining the difference value between the terminal voltage values at the later moment and the previous moment in a t-U data table, taking the previous moment of the two moments corresponding to the difference value as corresponding voltage U B when the difference value is smaller than the reference threshold voltage, and determining the ohmic resistance R0= (U B-UA)/I after UB; polarization internal resistance r1= (U C-UB)/I; the current I is discharge current in the discharge process, and the 1C-rate charge current is 2A; thereby obtaining ohmic internal resistance and polarization internal resistance. The current I is the constant current discharge current in the discharge process, the constant current discharge current is charged and discharged by 1C multiplying power in the discharge control process, then the constant current is placed after the discharge is finished, the current is 0 at the moment, the current of each section is the difference value between the constant current and the constant current, the absolute value of the difference value is I, and the absolute value is equal to the multiplying power.
In order to obtain the polarization capacitance, as shown in fig. 2, a first-order RC model is established to simulate the phenomenon of the rise of the internal voltage of the lithium battery caused by the planned internal resistance, namely, the BC-section voltage variation curve in fig. 1. The first-order RC model in FIG. 2 includes R0, R1, C1, uocv, R0 represents ohmic internal resistance, R1 represents polarized internal resistance, C1 represents polarized capacitance, and Uocv is a voltage source. The step response curve of the first-order system is shown in fig. 3, and when the inertia link or the integral link (i.e., the part formed by R 1、C1) in the first-order RC model is formed into a unit feedback closed loop system, the first-order system is typical and can be used to simulate the polarization reaction process of the lithium battery.
As can be seen from the graph, the transient response of the first-order system is an exponentially decaying process, which can reflect the voltage variation process of the polarization resistor R 1. The time constant t=r1c 1 of the transient response, R1 is already obtained in step 2, so that the time constant T interface is obtained to obtain C1. Analysis of the transient response proves that when t=t, the transient response of the first-order step response system is attenuated by 0.632, and the corresponding voltage is UM; that is, the UB-UC phase voltage decays by 0.632, and actually UB-UC rises to UC, so that the UB-UC phase voltage decays by 0.632, which is the decaying voltage (UC-U B) by 0.632, and actually U B rises to UC, and UM is the value of UB plus the decaying voltage, and U M＝(UC-UB)*0.632+UB; after obtaining U M, finding a time tm corresponding to the voltage U M and a time tb corresponding to the voltage U B in the T-U data table according to the obtained U M, and obtaining a time constant t=tm-tb according to tm and tb; then, the polarization capacitance c1=t/R1 is obtained from t=r1c1, and when T and R1 are both obtained, C1 is also obtained. When the time tm is found in the data table according to U M, if the same voltage as U M is not found, the voltage closest to U M and the time corresponding to the voltage are found as tm.
The application obtains the ohmic internal resistance and the polarization internal resistance of the battery, and the method can quickly realize the calculation of the internal resistance parameter of the lithium battery and ensure the accuracy of data, and the specific analysis is as follows, as shown in fig. 4, and is the result of the change of the battery voltage after the lithium battery is discharged with the current I and is placed for 1 h. The graph shows that the first half of the curve is AB section, the voltage dispersion of the end of AB section is higher, the growth speed is high, and the first-order fitting of the voltage is started from the B point, so that the B position in the graph can be used as the starting point of the battery polarization reaction, and the ohmic internal resistance of the battery can be obtained through AB section
The change of BC segment is caused by the polarization reaction of the battery, so the polarization internal resistance of the battery can be obtained through BC segmentThe polarization capacitance of the cell needs to be determined from the response curve of fig. 3. As can be seen from fig. 3, the transient response of the first-order system is an exponentially decaying process, and after t=t, the transient response has decayed by 63.2%, and after t=2t, 3T, and 4T, the transient response has decayed to 0.865, 0.95, and 0.982, respectively. And the time constant t=r 1C1. Therefore, to accurately determine the value of C 1, it is important to determine the position of t point, and as can be seen from fig. 4, since the initial phase of the battery voltage changes rapidly when using the first-order fitting, the voltage changes gradually and smoothly with time. The first order response curve also reflects this change, and the degree of fit is higher in the intervals where the change is faster, so the more accurate t is chosen near the segment. The analysis of the battery voltages with different multiplying powers and different aging degrees and the first-order fitting curve thereof shows that when t=t, the battery voltages are the most suitable for practical demands. For example, in fig. 4, if U A＝2.8301V,UB＝3.1023V,UC =3.239V is known, the voltage value U T =3.1023+0.632 (3.239-3.1023) = 3.1886944 at the time T can be obtained according to the first-order response, and it is obvious from fig. 4 that the actual voltage at the time point and the first-order fitting voltage result substantially coincide. Then, the T-U data table of the measured corresponding voltage data is searched through the obtained U T voltage value, and the current time T=67 s can be found. Finally according to/>C 1 was obtained.
Fig. 5 is a table showing voltage-time curve data after discharge is completed at a 1C magnification, and fig. 6 is a schematic diagram showing a time-voltage curve and a first-order fitted curve based on the voltage-time data of fig. 5. Referring to fig. 5 and fig. 6, when the initial point terminal voltage is about 3.17949V during the first-order fitting in fig. 6, and when the difference between the adjacent two points is calculated herein, when the terminal voltage difference between the adjacent two points is smaller than 0.01V, it is considered that the voltage continuity is better at this time, and the terminal voltage value corresponding to the last point when the terminal voltage difference is greater than or equal to 0.01V is determined as the terminal voltage value corresponding to the point B, that is, the polarization reaction initial point. In fig. 6, the value of B point is determined as V B = 3.1780V, which is similar to the voltage 3.17949V at the starting point end in fitting, and the difference between the two values is 0.00149V, and the effect of the difference is very small in the process of obtaining the ohmic internal resistance R 0 or the polarization internal resistance R 1. Since the present sample data is discharged with a 1C rate, i.e. current i=1c=2a, according to ohm's lawThe effect is negligible when calculating the internal resistance at this time. In fig. 5, both U A and Uc are known, after determining U B, R0 and R1 can be obtained, and then the time corresponding to U M is obtained by U M＝UB+(UA-UB by 0.632, i.e. the time constant T, and then C1 is obtained.
Fig. 7 is a schematic diagram of BC-segment voltage data and time curve after discharge and first-order and second-order fitting curves obtained by experiment.
(1) According to the charge and discharge data of the battery under the condition of 1C, a time-voltage relation is made through orign software, and then first-order fitting and second-order fitting are respectively carried out on the time-voltage relation. As shown in fig. 7, a first order fitting equation y1 and a second order fitting equation y2 are derived, respectively.
(2) And (3) by analyzing the fitted result, a conclusion is obtained: the second-order fitting can well reflect the real situation of the battery, and the fitting curve and the actual curve are basically coincident. However, the second order fitting is considered to be high in accuracy, but is complex in calculation, and is not applicable to occasions where the accuracy requirement is not very high and the internal resistance and the polarized capacitance of the battery need to be estimated quickly. Therefore, the method for quickly estimating the internal resistance and the polarization capacitance of the battery is explored while ensuring the precision, and has important practical significance. For this reason, in order to reduce the operations, a reduced order process is conceivable, and a first order fitting is performed on the battery data. It can be seen that the three curves substantially coincide at regions 1 and 2. It is therefore reliable to select the appropriate point in this region to estimate the battery parameters. However, the change in voltage in region 2 over a longer period of time is relatively small and therefore unsuitable for evaluation, so that a suitable point can be selected in region 1.
(3) Based on the steps (1) and (2), the point with the minimum relative error is selected for analysis, and by analysis, we know that the error is the minimum at the intersection point of the three curves. The voltage at the intersection point is shown as a figure, and the point B is a first-order fitting curve starting point, and is a polarization reaction starting point, so that the polarization capacitance of the battery cannot be obtained through the point. And the M point is also the intersection point of the three curves, and the voltage percentage of the M point is calculated to be = (3.31044143-3.14782065)/(3.40531975-3.14782065) =63.15%. (4) From the results, the point location of M is quite specific, approaching the point of T time constant in the first order response curve. At the T time constant, the transient response decays by 63.2%. The polarization capacitance of the battery can be estimated by taking the T point in the first-order response as a special point in the actual curve of the battery. The method not only meets the requirements on precision, but also can realize quick estimation of battery parameters, has good robustness, can realize calculation to quickly obtain the values of ohmic internal resistance, polarized internal resistance and polarized capacitance after the data of charge and discharge measurement due to simple calculation formula, can quickly obtain the internal resistance data, ensures the precision and the accuracy at the same time, finds that the data error obtained according to the method is very small in a fitting curve, and also has the requirement of accurate precision through actual value comparison.
The invention (1) adopts the method of solving the difference value of the voltage between the two points to determine the point B, can improve the solving precision of the ohmic internal resistance, and solves the problem of fuzzy position determination caused by the rapid change of the voltage of the point B in a short time in the actual test process. And the point B and the voltage UB can be rapidly determined only by calibrating the reference voltage threshold value in advance.
(2) The BC segment fits an actual test curve of the battery through first-order response and second-order response, the C point and the M point are accurately positioned through comparing the first-order fitting curve with the second-order fitting curve and combining characteristic analysis of the first-order system response curve, a section of curve with high coincidence degree is used for finding a time constant t through the first-order fitting curve and the second-order fitting curve, and then the polarization capacitance of the battery is solved by combining polarization internal resistance. The method not only can ensure the estimation precision, but also can solve the problem of complex calculation of the polarization reaction resistance and capacitance, can quickly estimate the polarization reaction resistance and capacitance of the battery without a second-order RC model, and has important value in some actual working scenes.
It is obvious that the specific implementation of the present invention is not limited by the above-mentioned modes, and that it is within the scope of protection of the present invention only to adopt various insubstantial modifications made by the method conception and technical scheme of the present invention.
Claims (1)
1. A rapid estimation method of internal resistance of a lithium ion battery is characterized in that: the method comprises the following steps:
(1) After the discharge is finished, a discharge loop is disconnected, and a voltage U A of the battery terminal voltage when the discharge loop is disconnected, a voltage stabilization value U C of the rear end of the discharge loop and a t-U data table of voltage transformation along with time after the discharge loop is disconnected are acquired and recorded;
(2) In a data table of time-dependent voltage change data t-U in the process of changing from U A to U C, the change process from U A to U C is the change process of voltage under the action of ohmic resistance and polarization resistance of a lithium battery, and voltage U B is arranged between voltage U A and voltage U C, wherein the change process from U A to U B is the change process of voltage under the action of ohmic resistance, and the change process from U B to U C is the change process of voltage under the action of polarization internal resistance; respectively solving the difference value between the terminal voltage values at the later moment and the previous moment in the t-U data table, taking the previous moment of the two moments corresponding to the difference value as corresponding voltage U B when the difference value is smaller than the reference threshold voltage, and then solving the ohmic resistance and the polarized internal resistance according to a formula according to the voltage U B:
Ohmic resistance r0= (U B-UA)/I; polarization internal resistance r1= (U C-UB)/I;
wherein the current I is a discharge current in a discharge process;
The reference threshold voltage in the step (2) is calibrated in advance through experiments;
The reference threshold voltage is 0.01V;
The step (2) further includes a solving method of the polarization capacitor C1, where the solving method of the polarization capacitor includes:
a. Establishing a first-order RC model of the lithium ion battery, and simulating the attenuation process of transient response of the lithium ion battery in the process from U B to U C by using a first-order step response curve; wherein the time constant T=R1C1 of the first-order step response, wherein C1 is a polarized capacitor, R1 is a polarized internal resistance, and T is the time constant of the first-order step response;
when t=t, the transient response of the first-order step response system decays by 0.632, with a corresponding voltage of U M; u M＝(UC-UB)*0.632+UB;
According to the obtained U M, the time tm corresponding to the voltage U M and the time tb corresponding to the voltage U B are found in the T-U data table, and according to tm and tb, a time constant T=tm-tb is obtained;
The polarization capacitance c1=t/R1 is obtained from t=r1c1.
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