Method and device for estimating charging time constant of lithium battery in real time

Abstract

The invention discloses a lithium battery charging time constant real-time estimation method and device, and the method comprises the steps: a first unit delay module outputs a stored lithium battery charging current sampling value I [n-1] at a previous moment to a current predictor, and obtains and stores a lithium battery charging current sampling value I [n] at a current moment; and the second unit delay module outputs the stored charging time constant tau [n-1] of the lithium battery at the previous moment to the current predictor, and obtains and stores the estimated value tau [n] of the charging time constant of the lithium battery obtained at the current moment. According to the method, a charging current sampling value of a lithium battery in a constant-voltage charging stage is taken as a target value of a feedback system, a charging current predicted value calculated according to a charging time constant estimated value is taken as a feedback value, and tracking of the feedback system by the feedback system is realized through a PI estimator; and the requirements on rapidness and accuracy of estimation of the charging time constant of the lithium battery are met, so that the performance of a lithium battery management system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery management, and particularly relates to a method and device for real-time estimation of lithium battery charging time constant. BACKGROUND

[0002] With the increasing application of lithium batteries in consumer electronics, transportation tools, unmanned aerial vehicles, portable power tools, energy storage devices and other fields, lithium battery management technology is increasingly valued, and lithium battery management systems are continuously developing towards high safety, high precision and high reliability. During the charging phase of the lithium battery, the management system needs to estimate the lithium battery charging time constant in real time in order to predict the full charge capacity (FCC) and average time to full (ATTF) of the lithium battery (see ZL202010316849.5 - a method and device for estimating the full charge capacity of a lithium battery), and to provide accurate information about the state of the battery for devices using lithium batteries.

[0003] The charging process of a lithium battery can generally be divided into two stages: constant current (CC) and constant voltage (CV). During the CV stage, the charging current of the lithium battery approximately decreases exponentially (as shown in FIG. 1), at which time the lithium battery can be equivalent to a resistor-capacitor (RC) circuit under constant voltage power supply. Figure 1 The charging time constant of a lithium battery refers to the time constant τ of the equivalent RC circuit of the lithium battery under constant voltage charging. The size of τ reflects the speed of the change in the charging current. The greater τ is, the slower the charging current decreases, and the longer the charging time. Conversely, the smaller τ is, the faster the charging current decreases, and the shorter the charging time. There are two existing methods for estimating the charging time constant τ of a lithium battery: (1) point current method. Let 、 be the sampling values of the charging current at time 0 and time t, respectively (see FIG. 2), and let be the sampling interval, then τ can be directly calculated as Figure 1 . (2) Current integration method. This method obtains τ according to the current integration formula of the RC circuit , where I(t) is the battery charging current from t0 to t, and Q is the total charging amount during the period from t0 to t, i.e. .

[0004] ​​​​For ideal RC circuit, the accurate charging time constant can be obtained by using point current method and current integration method. However, as a complex electrochemical system, the parameters of the equivalent circuit of lithium battery often have time-varying property. Generally, the charging time constant of lithium battery changes with the aging degree of the battery and the temperature of the battery body. Even in a charging process, the charging time constant changes slowly, generally smaller in the initial stage of charging and increasing in the end of charging. In addition, the current fluctuation and measurement error (collectively referred to as current noise) in the charging process will cause the change of the estimated value of the charging time constant. Due to the above reasons, the point current method and the current integration method are not suitable for real-time estimation of the charging time constant. The former can quickly track the change of the charging time constant, but cannot resist the interference of current noise, so the error is large; the latter can effectively eliminate the influence of current noise by means of integration effect, but cannot track the real change of the charging time constant in time. Both methods cannot fully meet the requirements of real-time and accuracy of the battery management system for the estimation of the charging time constant. SUMMARY

[0005] Therefore, it is necessary to provide a method and device for real-time estimation of the charging time constant of lithium battery, to solve the problem that the existing method for estimating the charging time constant of lithium battery cannot meet the requirements of real-time and accuracy of the battery management system.

[0006] To achieve the above purpose, the present application provides a method for real-time estimation of the charging time constant of lithium battery, comprising the following steps:

[0007] The first unit delay module outputs the stored last time lithium battery charging current sample value I[n-1] to the current predictor, and simultaneously acquires and stores the current time lithium battery charging current sample value I[n], n being the sample serial number;

[0008] The second unit delay module outputs the stored last time lithium battery charging time constant estimation value τ[n-1] to the current predictor, and simultaneously acquires and stores the current time lithium battery charging time constant estimation value τ[n], n being the sample serial number;

[0009] The current predictor calculates the current predicted value I[n] according to the last time lithium battery charging current sample value I[n-1] and the last time lithium battery charging time constant estimation value τ[n-1];

[0010] The difference d[n] between I[n] and I[n] is calculated;

[0011] The d[n] is input into the PI estimator, and the PI estimator calculates the current time lithium battery charging time constant estimation value τ[n];

[0012] ​​The above process is repeated as n increases from 1 until the end of charging, and τ[0] is preset as an initial value at the starting moment.

[0013] Further, the calculation formula of the current predictor for calculating the current prediction value at the current moment is:

[0014]

[0015] where T is a current sampling period, is a natural constant.

[0016] Further, the calculation formula of the PI estimator is:

[0017] ;

[0018] K P is a proportional coefficient, and K I is an integral coefficient.

[0019] Further, K P = 20, and K I = 8.

[0020] Further, τ[0] = 1000 seconds.

[0021] The present application provides a device for real-time estimation of a lithium battery charging time constant, comprising a first unit delay module, a second unit delay module, a difference calculator, a current predictor, and a PI estimator.

[0022] The first unit delay module is used to output the stored last moment lithium battery charging current sample value I[n-1] to the current predictor, and simultaneously acquire and store the current moment lithium battery charging current sample value I[n], where n is a sampling serial number.

[0023] The second unit delay module is used to output the stored last moment lithium battery charging time constant estimation value τ[n-1] to the current predictor, and simultaneously acquire and store the current moment obtained lithium battery charging time constant estimation value τ[n], where n is a sampling serial number.

[0024] The current predictor is used to calculate the current prediction value ;

[0025] The difference calculator is used to calculate the difference d[n] between I[n] and , and input d[n] into the PI estimator.

[0026] The PI estimator is used to calculate the current moment lithium battery charging time constant estimation value τ[n].

[0027] From n =1, the above process is repeated as n increases until the end of charging, at the starting time, τ[0] is preset to the initial value.

[0028] Further, the current predictor calculates the calculation formula of the current prediction value at the current time:

[0029]

[0030] Where T is the current sampling period, is a natural constant.

[0031] Further, the calculation formula of the PI estimator is:

[0032] ;

[0033] K P is a proportional coefficient, K I is an integral coefficient.

[0034] Further, K P =20, K I =8.

[0035] Further, the τ[0]=1000 seconds.

[0036] Unlike the prior art, the above technical solution takes the lithium battery constant voltage charging stage current sampling value as the target value of the feedback system, and takes the charging current prediction value calculated according to the charging time constant estimation value as the feedback value. The PI estimator realizes the tracking of the latter to the former, meets the requirements of the charging time constant estimation speed and accuracy of the lithium battery, and helps to improve the performance of the lithium battery management system. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The current curve of the lithium battery in the constant voltage charging stage is the background technology;

[0038] Figure 2 The principle diagram of the lithium battery charging time constant real-time estimation system of the application;

[0039] Figure 3 The principle diagram of the PI estimator of the application;

[0040] Figure 4 The current sampling data of a section of lithium battery in the constant voltage charging stage;

[0041] Figure 5 The lithium battery charging time constant curve real-time estimation curve of the application;

[0042] Figure 6 This is the error curve for real-time estimation of the lithium battery charging time constant curve of the present invention. Detailed Implementation

[0043] To explain in detail the technical content, structural features, objectives, and effects of the technical solution, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0044] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0045] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0046] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0047] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0048] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0049] The same as the understanding in the "Patent Examination Guidelines", in the present application, "greater than", "less than", "exceed" and the like are understood as not including the number; "above", "below", "within" and the like are understood as including the number. In addition, in the description of the embodiments of the present application, the meaning of "multiple" is two or more (including two), and similar expressions related to "multiple" are also understood in this way, for example, "multiple groups", "multiple times" and the like, unless otherwise explicitly and specifically limited.

[0050] In the description of the embodiments of the present application, the spatially related expressions used, such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like, indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or the drawings, and are only for the convenience of describing the specific embodiments of the present application or for the reader to understand, and do not indicate or imply that the indicated device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0051] Unless otherwise explicitly specified or limited, in the description of the embodiments of the present application, the terms "mount", "connect", "connect", "fix", "set" and the like should be understood broadly. For example, the "connection" can be fixed connection, or detachable connection, or integral setting; it can be mechanical connection, or electrical connection, or communication connection; it can be directly connected, or indirectly connected through an intermediate medium; it can be the communication or interaction relationship between two elements. For those skilled in the art to which the present application belongs, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0052] Please refer to Figures 1 to 6 The present application provides a method for real-time estimation of lithium battery charging time constant, comprising the following steps: a first unit delay module outputs a lithium battery charging current sample value I[n-1] at the last moment to a current predictor, while acquiring and storing a lithium battery charging current sample value I[n] at the current moment, n being a sample sequence number; a second unit delay module outputs a stored lithium battery charging time constant estimation value τ[n-1] at the last moment to the current predictor, and acquires and stores a lithium battery charging time constant estimation value τ[n] obtained at the current moment, n being a sample sequence number; the current predictor calculates a current prediction value at the current moment according to the lithium battery charging current sample value I[n-1] at the last moment and the lithium battery charging time constant estimation value τ[n-1] at the last moment; calculates the difference between I[n] and The difference d[n] is input into the PI estimator, which calculates the estimated value of the lithium battery charging time constant τ[n] at the current moment. The above process repeats until the charging is finished. At the beginning moment, τ[0] is preset to the initial value.

[0053] This invention proposes a method and corresponding implementation device for real-time estimation of the charging time constant of a lithium battery during constant-voltage charging. For computational convenience, the method and device are implemented as a discrete-time system, the principle of which is as follows: Figure 2 As shown. For ease of description, this device will be referred to as the lithium battery charging time constant τ estimation system. This system applies the closed-loop control principle to the real-time estimation of the lithium battery charging time constant. Its input is the current lithium battery charging current sample value I[n], and its output is the current estimated value of τ τ[n]. Figure 2 middle The module is a unit delay module, whose function is to store the input data and output it after a one-sampling-period delay. During system operation, the current predictor first predicts the current value at the current moment based on the previous current sample value I[n-1] and the estimated value τ[n-1] of τ at the previous moment. The calculation formula is: Where T is the current sampling period, I[n] is a natural constant; then the system calculates I[n] and The difference d[n] is then calculated, and finally, d[n] is input into the PI estimator to obtain the estimated value of τ at the current time. Starting from n = 1, the above process repeats continuously as n increases until the charging ends.

[0054] This invention uses the sampled charging current value of the lithium battery during the constant voltage charging stage as the target value of the feedback system, and the predicted charging current value calculated based on the estimated charging time constant as the feedback value. The PI estimator enables the latter to track the former, achieving the requirements of speed and accuracy in estimating the lithium battery charging time constant, thereby helping to improve the performance of the lithium battery management system.

[0055] The PI estimator consists of a proportional (P) element and an integral (I) element connected in parallel, such as... Figure 3 As shown. Where K P K is the proportionality coefficient. I The proportional element amplifies the current difference, enabling a rapid response to changes in τ. The integral element, by integrating the current difference, filters out current noise when τ is stable. The PI estimator, formed by combining the proportional and integral elements, can quickly track changes in τ and output a high-precision τ value. The input-output relationship of the PI estimator is as follows:

[0056] .

[0057] At the starting time of the τ estimation system, τ[0] can take an empirical value, which can generally be taken as τ[0]=1000 seconds. The values of K P and K I can be conveniently determined by trial and error, and the criterion for judging the values is the absolute value of d[n]. If the absolute value of d[n] sequence is small, it can be considered that the values of K P and K I are appropriate. For example, Figure 4 is a current sampling data of a lithium battery in the constant voltage charging stage, where I[0]=2400mA. Figure 5 is a charging time constant curve real-time estimation curve obtained by using the method disclosed in the present patent, and τ[0]=1000 seconds is taken in calculation. Figure 6 is an error curve obtained in the above charging time constant curve real-time estimation. In this example, K P =20 and K I =8 are obtained by trial and error. From the error curve shown in Figure 6 , it can be seen that the estimation error of the charging time constant is small. This indicates that the accuracy of the charging time constant estimation value is high.

[0058] The present application provides a device for real-time estimation of the charging time constant of a lithium battery, which comprises a first unit delay module, a second unit delay module, a difference calculator, a current predictor and a PI estimator. The first unit delay module is used to output the stored last-time lithium battery charging current sampling value I[n-1] to the current predictor, and at the same time, to obtain and store the current-time lithium battery charging current sampling value I[n], where n is the sampling sequence number. The second unit delay module is used to output the stored last-time lithium battery charging time constant τ[n-1] to the current predictor, and at the same time, to obtain and store the current-time lithium battery charging time constant estimation value τ[n], where n is the sampling sequence number. The current predictor is used to calculate the current prediction value I based on the last-time lithium battery charging current sampling value I[n-1] and the last-time lithium battery charging time constant estimation value τ[n-1]. The difference calculator is used to calculate the difference d[n] between I[n] and I , and input d[n] into the PI estimator. The PI estimator is used to calculate the current-time lithium battery charging time constant estimation value τ[n]. From n=1, the above process is repeated as n continuously increases until the charging is completed. At the starting time, τ[0] is preset as an initial value. The device of the present application meets the requirements of the estimation speed and accuracy of the lithium battery charging time constant, thereby helping to improve the performance of the lithium battery management system.

[0059] Further, the current predictor calculates the calculation formula of the current prediction value at the current time as follows:

[0060]

[0061] wherein T is a current sampling period, is a natural constant.

[0062] Further, the calculation formula of the PI estimator is as follows:

[0063] ;

[0064] K P is a proportional coefficient, K I is an integral coefficient.

[0065] In a preferred embodiment, K P = 20, K I = 8. In a preferred embodiment, the τ[0] = 1000 seconds.

[0066] It should be noted that although the above embodiments have been described herein, the patent protection scope of the present application is not limited thereby. Therefore, based on the innovative idea of the present application, the changes and modifications of the embodiments described herein, or the equivalent structure or equivalent process transformation using the content of the present application specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included in the patent protection scope of the present application.

Claims

1. A method for real-time estimation of the charging time constant of a lithium battery, characterized in that, Includes the following steps: The first unit delay module outputs the stored lithium battery charging current sample value I[n-1] from the previous moment to the current predictor, and at the same time acquires and stores the lithium battery charging current sample value I[n] from the current moment, where n is the sampling sequence number; The second unit delay module outputs the stored lithium battery charging time constant estimate τ[n-1] from the previous moment to the current predictor, and acquires and stores the lithium battery charging time constant estimate τ[n] obtained at the current moment, where n is the sampling sequence number; The current predictor calculates the predicted current value at the current moment based on the sampled lithium battery charging current value I[n-1] and the estimated lithium battery charging time constant τ[n-1] from the previous moment. ; Calculate I[n] and The difference d[n]; Input d[n] into the PI estimator, and the PI estimator calculates the estimated value of the lithium battery charging time constant τ[n] at the current moment; Starting from n = 1, as n increases, the above process repeats until the charging ends. At the beginning, τ[0] is preset to the initial value.

2. The method for real-time estimation of lithium battery charging time constant according to claim 1, characterized in that, The formula for calculating the predicted current value at the current moment by the current predictor is as follows: Where T is the current sampling period. It is a natural constant.

3. The method for real-time estimation of lithium battery charging time constant according to claim 1, characterized in that, The calculation formula for the PI estimator is as follows: ； K P K is the proportionality coefficient. I is the integral coefficient.

4. The method for real-time estimation of lithium battery charging time constant according to claim 3, characterized in that: K P =20,K I =8。 5. The method for real-time estimation of lithium battery charging time constant according to claim 1, characterized in that: The τ[0] = 1000 seconds.

6. A device for real-time estimation of the charging time constant of a lithium battery, characterized in that, Includes a first unit delay module, a second unit delay module, a difference calculator, a current predictor, and a PI estimator; The first unit delay module is used to output the stored lithium battery charging current sample value I[n-1] from the previous moment to the current predictor, and at the same time acquire and store the lithium battery charging current sample value I[n] from the current moment, where n is the sampling sequence number; The second unit delay module is used to output the stored lithium battery charging time constant estimate τ[n-1] from the previous moment to the current predictor, and to acquire and store the lithium battery charging time constant estimate τ[n] obtained at the current moment, where n is the sampling sequence number; The current predictor is used to calculate the predicted current value at the current moment based on the sampled lithium battery charging current value I[n-1] at the previous moment and the estimated lithium battery charging time constant value τ[n-1] at the previous moment. ; The difference calculator is used to calculate I[n] and The difference d[n] is calculated and then input into the PI estimator; The PI estimator is used to calculate the estimated value τ[n] of the lithium battery charging time constant at the current moment; Starting from n = 1, as n increases, the above process repeats until the charging ends. At the beginning, τ[0] is preset to the initial value.

7. The apparatus for real-time estimation of lithium battery charging time constant according to claim 6, characterized in that, The formula for calculating the predicted current value at the current moment by the current predictor is as follows: Where T is the current sampling period. It is a natural constant.

8. The apparatus for real-time estimation of lithium battery charging time constant according to claim 6, characterized in that, The calculation formula for the PI estimator is as follows: ； K P K is the proportionality coefficient. I is the integral coefficient.

9. The apparatus for real-time estimation of lithium battery charging time constant according to claim 8, characterized in that: K P =20,K I =8。 10. The apparatus for real-time estimation of lithium battery charging time constant according to claim 6, characterized in that: The τ[0] = 1000 seconds.

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