KR20110047497A - Method for generating state-of-charge standard information of secondary battery and method for estimating state-of-charge of secondary battery using state-of-charge standard information - Google Patents

Abstract

PURPOSE: A method for generating state-of-charge standard information of a secondary battery and a method for estimating state-of-charge of the secondary battery using state-of-charge standard information are provided to generate the charges state information of a battery by extracting parameters of an equivalent circuit to the secondary battery. CONSTITUTION: A method for generating state-of-charge standard information of a secondary battery and a method for estimating state-of-charge of the secondary battery using state-of-charge standard information are comprised of steps: receiving first impedance; generating first parameters of the equivalent circuit to the secondary battery; and generating approximated second parameters of the charged secondary cell by using the first parameter.

Description

METHODO FOR GENERATING STATE-OF-CHARGE STANDARD INFORMATION OF SECONDARY BATTERY AND METHOD FOR ESTIMATING STATE-OF-CHARGE OF SECONDARY BATTERY USING STATE-OF-CHARGE STANDARD INFORMATION}

The present invention relates to a method of generating charge state reference information of a secondary battery and a method of measuring a state of charge of a secondary battery using the state of charge reference information.

Recently, with the diversification of mobile device functions and the trend of digital convergence, secondary batteries such as lithium ion battery and lithium polymer battery, which are eco-friendly, ultra-light and high-performance energy, are widely used. High capacity batteries are expected to be in high demand for electric vehicles.

When such a secondary battery is used in an electronic device, it is necessary to calculate the usable time, and when the secondary battery supplies power to an important facility or a computer network, it is necessary to prevent sudden shutdown due to the discharge of the secondary battery. There is. In addition, a large-capacity lithium polymer battery used for an electric vehicle needs not to be discharged to such an extent that cranking is impossible, and a running distance through the lithium polymer battery needs to be accurately calculated to ensure reliability.

Since the state of charge of a secondary battery cannot be measured directly, it is mainly measured by an indirect method using a terminal voltage or a current. However, due to nonlinearity of the secondary battery, it is difficult to accurately measure the state of charge of the secondary battery using only the terminal voltage. In particular, in the case of a lithium polymer battery, there are not many established methods for measuring the state of charge. Representative methods used to measure the state of charge of the secondary battery include Coulomb Counting, Kalman Filter, Fuzzy Logic, and Neural Network.

The coulomb counting method calculates the discharge charge of the secondary battery, and if the accurate current sensor is used, very accurate and reliable state of charge information can be obtained.However, a system where the charge / discharge current crosses for a very short time accumulates errors. It can be difficult to apply. Kalman Filter is difficult to use because the algorithm itself has to be complicated and accurate system modeling is required, and many state variables are required for accurate estimation. Fuzzy Logic and Neural Network's methods are rarely used because they have many empirical factors, which make accurate measurements impossible, many calculations, and reliability problems.

The present invention has been proposed in order to solve the above problems, and the charging state of the secondary battery using the charging state reference information generation method and the charging state reference information of the secondary battery for measuring the state of charge of the secondary battery more quickly and easily The purpose is to provide a measurement method.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

The present invention for achieving the above object comprises the steps of receiving the first impedance information in each of the preset state of charge state of the secondary battery; Generating a parameter of the equivalent circuit according to each of the states of charge by using an equivalent circuit for the secondary battery and the first impedance information; And generating an approximated parameter according to the state of charge of the secondary battery using the parameter.

In addition, the present invention for achieving the above object is a step of receiving charge state reference information for measuring the state of charge of the secondary battery and the first parameter of the equivalent circuit for the secondary battery; And comparing the state of charge reference information with the first parameter to measure the state of charge of the secondary battery, wherein the state of charge reference information includes impedance at each of the preset state of charge states of the secondary battery. A method of measuring a state of charge of a secondary battery using information and charging state reference information which is an approximated parameter of the equivalent circuit according to the state of charge of the secondary battery, generated through the equivalent circuit of the secondary battery, is provided.

According to the present invention, the parameters of the equivalent circuit of the secondary battery is extracted using the impedance information of the secondary battery, and the state of charge of the secondary battery is quickly and easily generated by generating the charging state reference information using the extracted parameters. Reference information may be generated, and the state of charge of the secondary battery may be measured using the state of charge reference information.

First, a concept of a method of generating charge state reference information of a secondary battery according to the present invention will be described.

The impedance information of the secondary battery indicates the internal state of the secondary battery. In other words, the impedance information of the secondary battery varies according to the state of charge of the secondary battery. The present invention generates charge state reference information for measuring the state of charge of the secondary battery by using impedance information that varies according to the state of charge of the secondary battery, and charges the secondary battery by using the generated state of charge reference information. The condition can be measured. At this time, the charging state reference information generation method of the secondary battery according to the present invention by generating the charging state reference information according to the state of charge of the secondary battery using the impedance information in each of the preset state of charge state of the secondary battery In addition, it is possible to generate the charging state reference information more quickly and easily without having to measure the impedance according to all the charging states of the secondary battery.

More specifically, according to the present invention, the parameters of the equivalent circuit are calculated using the impedance information in each of the preset state of charge states of the secondary battery and the equivalent circuit for the secondary battery. For example, the state of charge of the secondary battery may be a stage obtained by dividing the state of charge of the secondary battery from 0% to 100% by 20%, and the impedance information in each of the preset state of charge may be 20% or 40%. , Impedance information at 60%, 80%, and 100% state of charge. According to the present invention, the parameters of each state of charge state are approximated to extract the parameters according to the secondary battery state of charge, that is, 0% to 100% state of charge.

The parameter may be a resistance value or a time constant value of the equivalent circuit, and as described above, since the impedance information varies depending on the state of charge of the secondary battery, the parameter also varies. Here, the charging state reference information becomes a parameter.

DETAILED DESCRIPTION Hereinafter, the most preferred embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. The above objects, features, and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, and in describing the present invention, a detailed description of well-known technology related to the present invention may unnecessarily obscure the subject matter of the present invention. If it is determined that the detailed description thereof will be omitted.

1 is a flowchart illustrating a method of generating charge state reference information of a secondary battery according to an embodiment of the present invention.

As shown in FIG. 1, the method of generating charge state reference information of a secondary battery according to the present invention starts from step S101.

In operation S101, the apparatus for generating charge state reference information receives, that is, receives first impedance information in each of the preset state of charge states of the secondary battery.

As described above, the preset state of charge may be a step of dividing the state of charge from 0% to 100% by 20% as an embodiment. The first impedance information may be impedance information within a preset frequency range generated by electrochemical impedance spectroscopy, or may be impedance information for two or more frequencies in the preset frequency range.

In operation S103, the apparatus for generating charge state reference information generates a parameter of an equivalent circuit according to each state of charge state, using the equivalent circuit and the first impedance information for the secondary battery. In general, an equivalent circuit for a secondary battery is represented by a resistor and a capacitor. Since the impedance includes a capacitance value according to a resistance value and a frequency, a parameter of the equivalent circuit can be obtained using the first impedance information. The apparatus for generating charging state reference information may generate, for example, a parameter of an equivalent circuit according to each of the charging state steps by performing curve fitting. The parameter of the equivalent circuit may be a resistance value, capacitance value or time constant value of the equivalent circuit.

In operation S105, the apparatus for generating charge state reference information generates an approximated parameter according to the state of charge of the secondary battery, using the parameters of the equivalent circuit according to each state of charge state. That is, the apparatus for generating charging state reference information does not approximate the parameter according to each of the preset stages of charging state, but the approximated parameter according to the state of charge from 0% to 100%, that is, the charge state reference information for measuring the state of charge of the secondary battery. Create

The apparatus for generating charging state reference information may generate an approximated parameter by approximating, for example, a parameter of an equivalent circuit according to each state of charge state in the form of a cubic equation. The approximated parameter may be more accurate as the preset state of charge divided by a percentage less than 20%.

In general, since impedance information is measured in a preset frequency range, for example, in a range of 10 mHz to 1 kHz, it takes considerable time to measure impedance. According to the present invention, by using a parameter measured in each of the preset state of charge stages, 0 Since the parameter according to the state of charge from% to 100% can be generated, the time for generating the reference information can be reduced. The state of charge of the secondary battery of which the state of charge is unknown may be measured by comparing the parameters of the secondary battery of which the state of charge is unknown and the state of charge reference information.

When the secondary battery is used in an electric vehicle or the like, the charging state reference information generating method according to the present invention is used in the electric vehicle, so that the charging state reference information can be generated quickly and easily. The state of charge of the battery can be easily measured.

2 to 4 are diagrams for describing a method of generating charge state reference information according to a first embodiment of the present invention. In FIGS. 2 to 4, a secondary battery is a lithium polymer battery. do.

FIG. 2 is a diagram illustrating first impedance information for each preset state of charge state of a commercial lithium polymer battery produced by each of BNK, Aenergy, and SONY, and is a Nyquist impedance plot showing an impedance spectrum. The battery capacity of each of BNK, Aenergy, and SONY is 1600mAh, 1800mAh, and 1350mAh.

The state of charge of the secondary battery may be set through a charge / discharge experiment. In an embodiment of the present invention, the secondary battery is charged with a constant current of 1 C. When the secondary battery is charged at a maximum voltage of 4.2 V, the secondary battery is charged to CC-CV (constant current— Constant voltage) charging method may be used. The secondary battery is discharged with a current of 0.2C according to the IEC 61960 standard, and the rated capacity can be calculated by adding the current amount up to the discharge termination voltage of 3.0V.

The charged state stage of the secondary battery may be set according to the amount of charge from the calculated rated capacity, and the first impedance information through electrochemical impedance spectroscopy may be generated according to the charged stage. In the frequency range of 10 mHz to 1 kHz through electrochemical impedance spectroscopy, the result of measuring the impedance in each state of charge divided by 100% state of charge by 20% is shown in FIG. 2.

According to the present invention, the parameters of the equivalent circuit of FIG. 3 can be obtained by using the first impedance information shown in FIG. 2 and the equivalent circuit shown in FIG. 3. More specifically, the parameters of the equivalent circuit may be extracted by curve fitting the first impedance information through the electrochemical impedance spectroscopy to the equivalent circuit of FIG. 3. The extracted parameters may be approximated to generate parameters according to the 0% to 100% state of charge of the secondary battery, and the approximated parameters, that is, the charge state reference information, are shown in FIG. 4.

4 is a diagram illustrating charging state reference information according to the present invention. In FIG. 4, squares and triangles represent time constant values and resistance values in respective preset state states of charge, and (a), (b) and ( c) Each of the drawings shows charging state reference information of each of BNK, Aenergy, and SONY. That is, FIG. 4 illustrates a parameter according to the state of charge of 0% to 100% of the secondary battery using the time constant value and the resistance value of each preset state of charge state.

According to the present invention, when the parameters of the secondary battery as the state of charge measurement, for example, time constant value or resistance value, are known, the state of charge of the secondary battery as the state of charge measurement can be measured using the state of charge reference information. have. However, as shown in FIG. 4, there may be the same state of charge for any time constant value or resistance value, which will be described in more detail with reference to FIG. 8.

Meanwhile, although the lithium polymer batteries of BNK, Aenergy, and SONY have been described as examples in FIGS. 2 to 4, the other secondary batteries also exhibit similar impedance characteristics as those of the lithium polymer batteries. Can be applied.

5 and 6 are diagrams for describing a method of generating charge state reference information according to a second specific embodiment of the present invention. As shown in FIGS. 2 to 4, a secondary battery is a lithium polymer battery. It is explained.

5 and 6 are views for explaining step S103 of FIG. 1 in more detail.

In operation S103, the apparatus for generating charging state reference information may generate a parameter of an equivalent circuit according to each stage of charging state by using the semicircle characteristic and the first impedance information of the impedance spectrum of the secondary battery. Here, the first impedance information may be impedance information for two or more frequencies in a preset frequency range.

Looking at the impedance spectrum shown in Figure 2, the impedance information of the secondary battery has a characteristic that is represented by a large semi-circle in the low frequency region. By using the impedance characteristics of the secondary battery, it is possible to generate by approximating the parameters of the equivalent circuit according to each state of charge stage. More specifically, the impedance characteristic represented by a large semicircle in the low frequency region is an impedance characteristic according to a randle's circuit of the secondary battery illustrated in FIG. 5, and an approximated parameter may be generated using a circle equation. .

Here, the impedance characteristics according to the equivalent circuit of FIG. 3 and the ladle circuit of FIG. 5 will be described.

As described above, FIG. 3 is a diagram showing a general equivalent circuit for the secondary battery. R _Ω represents the total resistance connecting the electrodes of the secondary battery, such as the electrolyte, the electrode, and the resistance of the terminal block, to the inside, and is a point where the real axis and the graph intersect in FIG. 3. R _f and Q _f (Constant Phase Element, CPE) represent the components of a passivation film formed on the surface of the cathode, and in FIG. _Rct (Charge Transfer Resistance) and C _dl (Double Layer Capacitance) represent the electron transfer reaction between the electrode (anode and cathode) of the secondary battery and the interface between the electrolyte, Figure 3 Represents a large semicircle of the low frequency region. Z _W (Warburg Impedance) is a property in which mass transport prevents charge transfer due to diffusion.

Therefore, impedance characteristics represented by large semicircles in the low frequency region are R _Ω , in the equivalent circuit shown in FIG. 3. It can be approximated by the characteristics of R _ct and C _dl , and R _Ω , in FIG. 3. R _ct and C _dl correspond to R _s , R _p and C _p of the ladle circuit of FIG. 5.

Since the impedance characteristic appears as a semicircle, an approximated parameter can be generated using the equation of the circle. Since the original equation is used, an approximated parameter of the preset frequency range may be generated by using first impedance information, which is impedance information for two or more frequencies in the preset frequency range. That is, according to the present invention, for example, a parameter may be generated by selecting only two or more frequencies in a frequency range of 10 mHz to 1 kHz. In this case, the frequency to be selected is preferably selected in the frequency domain where the impedance characteristic appears as a semicircle.

Due to the characteristics of low frequency, the measurement of impedance in the low frequency region requires a considerable time, but according to the present invention, since the parameter can be generated using only the impedance information of the preset frequency range without measuring the impedance over the preset frequency range more quickly. The charging state reference information may be generated.

As illustrated in FIG. 6, the impedance characteristics of the secondary battery in the low frequency region are semicircular, and in FIG. 6, the case where impedance information for two frequencies is used is described as an embodiment.

In FIG. 6, the case where 1.48 Hz and 0.32 Hz located to the left and right from the cut-off frequency of the Nyquist impedance plot is used as the sample frequency will be described as a temporary example. In FIG. 6, 1.474 Hz to 24.54 Hz and 0.126 Hz to 0.325 Hz are frequency ranges for selecting a sample frequency in which semicircle characteristics are commonly maintained in FIGS. 3A, 3B, and 3C. The selected 1.48 Hz, 0.32 Hz is included in the frequency range. In FIG. 6, although the sample frequency is selected in the frequency range in which the semicircle characteristics are commonly maintained in FIGS. 3A, 3B, and 3C, the sample frequency is shown in the frequency range in which the semicircle characteristics appear for each lithium polymer battery. Can be selected.

When the two impedance information measured at the sample frequency, that is, the first impedance information are represented by (ReZ ₁ , ImZ ₁ ) and (ReZ ₂ , ImZ ₂ ), the first impedance information is expressed in Equation 1, which is a circle equation. By substituting, the equivalent circuit parameters can be obtained.

[Equation 1] is an equation of a circle having a midpoint of (x ₁ , 0) and a radius of r, and the value of x ₁ and r obtained from [Equation 1] is substituted into [Equation 2], and the R _{The s} and R _p parameters can be obtained.

The impedance of the ladle circuit can be expressed as shown in [Equation 3], by substituting R _s , R _p and the frequency and impedance values obtained from [Equation 1] and [Equation 2] into [Equation 3]. The value of _p can be calculated. The product of the obtained R _p and C _p represents the time constant value of the circuit. Here, the frequency substituted in [Equation 3] may be one of the sample frequencies, and the impedance substituted in [Equation 3] may be an impedance with respect to the frequency substituted in [Equation 3].

FIG. 7 is a diagram illustrating a result of comparing time constant values obtained using impedances within a preset frequency range with time constant values according to the methods described with reference to FIGS. 5 and 6.

In FIG. 7, the parameters of each of the preset charging state steps are displayed. As a result of the analysis using the least-square method, the accuracy of BNK 98.8%, Aenergy 99.01%, and Sony 93.6% can be obtained. That is, according to the present invention, since the parameters can be obtained without measuring all the impedances within the preset frequency range, the charging state reference information can be generated quickly and easily, and the accuracy is also excellent.

8 is a flowchart illustrating a method of measuring a state of charge of a secondary battery using state of charge reference information according to an embodiment of the present invention.

As shown in FIG. 8, the method for measuring the state of charge of the secondary battery according to the present invention starts from step S801.

In operation S801, the charging state measuring apparatus receives, that is, receives the charging state reference information for measuring the state of charge of the secondary battery and the first parameter of the equivalent circuit for the secondary battery. The charging state measuring device may receive the charging state reference information from the above-described reference information generating device. That is, the charging state reference information is information generated by the above-described reference information generating device, and is generated through an equivalent circuit for the secondary battery and impedance information in each of the preset charging state steps of the secondary battery. This is an approximated second parameter of the equivalent circuit according to the state of charge. The first parameter may be generated by electrochemical impedance spectroscopy and input to the state of charge measuring device, and the parameter may be a time constant value or a resistance value of an equivalent circuit.

In operation S803, the charging state measuring apparatus compares the charging state reference information and the first parameter to measure the state of charge of the secondary battery. That is, since the charge state reference information is information indicating a parameter according to the state of charge of the secondary battery, the state of charge of the secondary battery can be measured by comparing the parameters of the secondary battery to be measured with the state of charge reference information. have.

On the other hand, as described above, there may be the same state of charge for any time constant value or resistance value in FIG. For example, in FIG. 4A, the parameters of the state of charge 60% and the state of charge 80% of the state of charge 80% are symmetrical with the parameters between the state of charge 80% and 100%. In this case, the same state of charge may appear for the same time constant value or resistance value.

In this case, in operation S803, the state of charge measurement device may measure the state of charge of the secondary battery by determining one of the same state of charge using the state of charge with the additional measurement result. For example, in FIG. 4, when the first measurement result is 0.12 and the state of charge is measured at 70% and 90%, and after a further measurement, the first parameter is 0.15, the secondary battery is in use. If so, the amount of charge in the secondary battery is reduced, so the first measurement shows that the state of charge is 70% instead of 90%. That is, in FIG. 4, the charging state may be accurately measured by calculating the increase and decrease of the currently measured state of charge and the previously measured state of charge, and by using the state of charge and the slope of the first parameter.

Although the present invention has been described by a process point of view, each step of configuring a method of generating reference information for measuring the state of charge of the secondary battery according to the present invention and a method of measuring the state of charge of the secondary battery using the state of charge reference information Can be easily understood from an apparatus point of view. Therefore, each step included in the method of generating reference information for measuring the state of charge of the secondary battery and the method of measuring the state of charge of the secondary battery using the state of charge reference information according to the present invention is reference information for measuring the state of charge of the secondary battery. It can be understood as a component included in the apparatus for measuring the state of charge of the secondary battery using the generating device and the state of charge reference information.

Meanwhile, the method of generating reference information for measuring the state of charge of the secondary battery as described above and the method of measuring the state of charge of the secondary battery using the state of charge reference information can be prepared by a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. And the recording medium includes all types of recording media (intangible medium such as a carrier wave as well as tangible media such as CD and DVD) readable by a computer.

Although the present invention has been described by means of limited embodiments and drawings, the present invention is not limited thereto and is intended to be equivalent to the technical idea and claims of the present invention by those skilled in the art to which the present invention pertains. Of course, various modifications and variations are possible.

1 is a flowchart illustrating a method of generating reference information for measuring a state of charge of a secondary battery according to an embodiment of the present invention;

2 to 4 are views for explaining a method of generating reference information for measuring the state of charge of the reference secondary battery according to a specific embodiment of the present invention;

5 and 6 are views for explaining step S103 of FIG. 1 in more detail;

7 is a view showing a result of comparing a time constant value obtained by using an impedance within a preset frequency range and a time constant value according to the method described in FIGS. 5 and 6;

8 is a flowchart illustrating a method of measuring a state of charge of a secondary battery using state of charge reference information according to an embodiment of the present invention.

Claims (9)

Receiving first impedance information in each of the preset state of charge states of the secondary battery; Generating a first parameter of the equivalent circuit according to each of the state of charge using the equivalent circuit and the first impedance information for the secondary battery; And Generating an approximated second parameter according to the state of charge of the secondary battery using the first parameter Charging state reference information generation method of a secondary battery comprising a. The method of claim 1, The first impedance information is Generated by electrochemical impedance spectroscopy, impedance information within a predetermined frequency range Method of generating charge state information of a secondary battery. The method of claim 1, The first impedance information is Impedance information for two or more frequencies in the preset frequency range. Generating the first parameter of the equivalent circuit The first parameter is generated by using the semicircle characteristic of the impedance spectrum of the secondary battery and the first impedance information. Method of generating charge state information of a secondary battery. The method of claim 3, The equivalent circuit is A ladle circuit for the secondary battery, Generating the second impedance information To generate the first parameter using a circle equation Method of generating charge state information of a secondary battery. The method of claim 2 or 3, The first and second parameters are Time constant value or resistance value Method of generating charge state information of a secondary battery. The method of claim 1, The secondary battery Lithium polymer battery Method of generating charge state information of a secondary battery. Receiving charge state reference information for measuring a state of charge of a secondary battery and a first parameter of an equivalent circuit for the secondary battery; And Measuring the state of charge of the secondary battery by comparing the state of charge reference information and the first parameter; Including; The charging state reference information The second parameter generated through the impedance information and the equivalent circuit for the secondary battery in each of the preset state of charge state of the secondary battery, and is an approximated second parameter of the equivalent circuit according to the state of charge of the secondary battery. Method of measuring the state of charge of the secondary battery using the state of charge reference information. The method of claim 7, wherein Measuring the state of charge of the secondary battery When the same state of charge is measured as a result of the comparison between the state of charge reference information and the first parameter, determining one of the same state of charge by using the state of charge with the additional measurement result Method of measuring the state of charge of the secondary battery using the state of charge reference information. The method according to claim 7 or 8, The first and second parameters are Time constant value or resistance value Method of measuring the state of charge of the secondary battery using the state of charge reference information.

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