Method for predicting temperature state of lithium battery of energy storage power station

Abstract

The invention provides a method for predicting the temperature state of a lithium battery of an energy storage power station. The method comprises the following steps: establishing a second-order equivalent circuit model of the lithium battery according to internal electrochemical characteristics of the lithium battery during charging and discharging; establishing a thermal circuit model of the lithium battery according to the heat transfer relationship among the parts when the lithium battery works and the heat transfer relationship between the lithium battery and external air; establishing a thermoelectric coupling model according to the coupling relationship among the lithium battery end voltage, heat and temperature; and finally, estimating the temperature state of the lithium battery by using the thermoelectric coupling model, and comparing the temperature state with the actual battery temperature. According to the method, the number of nodes needing to be calculated is greatly reduced, the calculation time is shortened, and the requirement for timeliness in engineering is met on the premise that the precision is guaranteed to a certain degree.

Description

Technical Field

[0001] The present invention relates to the field of energy storage batteries, and in particular to a method for predicting the temperature state of lithium batteries in energy storage power stations. Background Art

[0002] Under the background of the global consensus on "dual carbon" and the reform of the world energy system, the scale of energy storage systems is growing rapidly, and the energy storage industry is developing in full swing, among which the electrochemical energy storage industry is developing the fastest. There are many electrochemical energy storage technology routes, including lithium-ion batteries, sodium-based batteries, flow batteries, lead-acid batteries, etc. Lithium-ion batteries have been widely used in energy storage power stations due to their excellent performance such as high energy density, short response time, low maintenance cost and flexibility. However, fires and explosions in lithium-ion battery energy storage power stations are common. There are many reasons for the safety accidents of energy storage power stations. One of the important reasons is that lithium-ion batteries release a lot of heat during operation, which threatens the safe operation of energy storage power stations and causes fires in severe cases. This is the thermal runaway characteristic of lithium-ion batteries. If we can predict the process of lithium battery temperature rise, we can avoid thermal runaway of lithium batteries, thereby avoiding the occurrence of energy storage power station accidents.

[0003] Lithium battery temperature state estimation mainly uses a model-based approach to predict the temperature state changes of lithium batteries by establishing a high-fidelity model. The most commonly used model is the finite element model. The finite element model can predict the spatial distribution of the temperature inside the battery. The temperature results simulated using the finite element method are very accurate and can simulate the temperature of lithium batteries in several areas, but this method takes a lot of time. In addition, during the iteration process, for example, optimization of size, architecture, or control will also lead to longer calculation time.

[0004] How to establish a general model with fast speed and high accuracy so that the temperature prediction results can remain accurate over time is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to solve the problem of lithium battery temperature state estimation and propose a method for predicting the temperature state of lithium batteries in energy storage power stations. The method constructs a thermoelectric coupling model of lithium batteries by establishing a second-order equivalent circuit model and a thermal circuit model. The model can accurately describe the electrochemical and thermal characteristics of lithium batteries during the charging and discharging process, and realizes the bidirectional coupling of the circuit model and the thermal circuit model.

[0006] The technical solution of the present invention is:

[0007] The present invention provides a method for predicting the temperature state of a lithium battery in an energy storage power station, comprising:

[0008] S1. Establish a second-order equivalent circuit model of lithium battery according to the internal electrochemical characteristics of lithium battery during charging and discharging;

[0009] S2. Establish a thermal circuit model of the lithium battery based on the heat transfer relationship between various parts of the lithium battery when it is working and the heat transfer relationship between the lithium battery and the external air;

[0010] S3. Establish a thermoelectric coupling model based on the coupling relationship between the lithium battery terminal voltage, heat and temperature;

[0011] S4. Estimate the temperature state of the lithium battery using the thermoelectric coupling model and compare it with the actual battery temperature.

[0012] Furthermore, the second-order equivalent circuit model of the lithium battery is established according to the internal electrochemical characteristics of the lithium battery during charging and discharging as described in S1, including:

[0013] S11, establishing a second-order equivalent circuit model of a lithium battery, wherein the second-order equivalent circuit model includes an ideal voltage source, an ohmic internal resistance, and two RC parallel branches connected in series in sequence, wherein the RC parallel branch is composed of a polarization resistor and a polarization capacitor connected in series;

[0014] S12. Using Kirchhoff's law, write the system equation and observation equation of the second-order equivalent circuit model.

[0015] Furthermore, the system equation is:

[0016]

[0017] Among them, R1 and R2 are polarization resistors, C1 and C2 are polarization capacitors, U0 represents the terminal voltage of the battery, and I represents the current;

[0018] The observation equation is:

[0019] U0=U oc -R0I-U C1 -U C2 (2)

[0020] Where U oc represents an ideal voltage source, which has a nonlinear relationship with SOC; R0 represents the ohmic internal resistance; U C1 and U C2 Represents the polarization capacitor voltage.

[0021] Furthermore, the ohmic internal resistance and polarization internal resistance are obtained by fitting the voltage and current data during the battery charging and discharging process using a least squares algorithm corresponding to each temperature state of the battery.

[0022] Furthermore, the heat circuit model of the lithium battery is established according to the heat transfer relationship between the various parts of the lithium battery when it is working and the heat transfer relationship between the lithium battery and the external air as described in S2, including:

[0023] S21, equating the thermal circuit model to a circuit model, equating the heat source to a constant current source, equating the ambient temperature to a constant voltage source, equating the battery temperature to a voltage, and equating the thermal resistance and thermal capacitance to a resistor and a capacitor;

[0024] S22. Assuming that the battery density and heat generation are uniform, and the thermal circuit model structure is bilaterally symmetrical, write the KCL equation based on Kirchhoff's current law.

[0025] Furthermore, the KCL equation is:

[0026] T2(k+2)=AT2(k+1)+BT2(k)+CP c (k) (11)

[0027] Among them, A, B, and C are constants, which are obtained by fitting the voltage and current data during the battery charging and discharging process using the least squares algorithm. c is the heat generation power of the battery; T1 = T1′-T a , T2=T2′-T a ; T1′ is the center temperature of the battery body, T a is the external environment temperature, T2′ is the battery surface temperature.

[0028] Furthermore, the step of establishing a thermoelectric coupling model according to the coupling relationship between the lithium battery terminal voltage, heat and temperature in S3 includes:

[0029] The circuit model is used to calculate the heat generation power based on the total internal resistance and current of the battery;

[0030] The thermal circuit model is used to calculate the battery temperature based on the heat generation power, and the temperature is fed back to the circuit model.

[0031] Furthermore, S3 specifically includes:

[0032] First, the circuit model calculates the heat generation power P based on the total internal resistance of the battery, i.e. the ohmic internal resistance, the sum of R1 and R2, and the current. c ;

[0033] P c =I 2 R=I 2 (R0+R1+R2)

[0034] Among them, R is the total internal resistance of the battery, R1 and R2 are polarization resistances, and R0 represents the ohmic internal resistance;

[0035] Secondly, the thermal circuit model calculates the battery temperature T2 at the next moment based on the heat generation power;

[0036] T2(k+2)=AT2(k+1)+BT2(k)+CP c (k)

[0037] Among them, k represents the current moment, A, B, and C are constants;

[0038] Based on the battery temperature T2, the ohmic internal resistance and polarization internal resistance at the corresponding temperature are obtained and substituted into the circuit model. The heat generation power P of the battery at the next moment is calculated according to the total internal resistance R of the battery corresponding to the temperature. c , cycle in sequence to couple the electrical circuit and the thermal circuit.

[0039] Furthermore, S4 specifically includes inputting the charging and discharging current of the lithium battery into the thermoelectric coupling model, predicting the temperature change curve of the lithium battery when the initial temperature is known; and comparing the predicted temperature change curve of the lithium battery with the measured temperature.

[0040] Beneficial effects of the present invention:

[0041] The present invention uses a thermoelectric coupling model to predict the temperature of a lithium battery. The heat transfer relationship between the battery and the outside world is represented by thermal resistance. Compared with the finite element model, the number of nodes that need to be calculated is greatly reduced, which shortens the calculation time. Under the premise of ensuring a certain degree of accuracy, the engineering requirements for timeliness are met.

[0042] The present invention uses a circuit model to calculate the heat generation power, uses a thermal circuit model to calculate the temperature of the battery at the next moment according to the heat generation power, searches for the internal resistance according to the calculated temperature, and then brings it into the circuit model, calculates the heat generation power of the battery at the next moment according to the total internal resistance of the battery corresponding to the temperature, and completes the coupling of the circuit and the thermal circuit in this cycle. This method can not only accurately predict the temperature change of lithium batteries, but also provides a theoretical basis for the thermal management and safety control of lithium batteries, which is of great significance to improving the service life and safety of lithium batteries.

[0043] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0045] Figure 1 A flow chart of the implementation process of the present invention is shown.

[0046] Figure 2 A schematic diagram of a second-order equivalent circuit model of a lithium battery in the present invention is shown.

[0047] Figure 3 A schematic diagram of the temperature points of the lithium battery in the present invention is shown.

[0048] Figure 4 A schematic diagram of a thermal circuit model of a lithium battery in the present invention is shown.

[0049] Figure 5 A schematic diagram of the thermoelectric coupling model of a lithium battery in the present invention is shown.

[0050] Figure 6 A schematic diagram showing the comparison results of the predicted temperature and the actual temperature in the present invention is shown.

[0051] Figure 7 A schematic diagram of the difference between the predicted temperature and the actual temperature in the present invention is shown. DETAILED DESCRIPTION

[0052] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0053] Figure 1 A flow chart of the implementation process of the present invention is shown.

[0054] like Figure 1 As shown, this embodiment provides a method for predicting the temperature state of a lithium battery in an energy storage power station, comprising the following steps:

[0055] First, the second-order equivalent circuit model and thermal circuit model of the lithium battery are established. Then, the thermoelectric coupling model is established based on the relationship between the terminal voltage, heat and temperature of the lithium battery. Finally, the temperature is predicted based on the thermoelectric coupling model and the input of the model: current and initial temperature.

[0056] S1. A second-order equivalent circuit model of a lithium battery is established based on the internal electrochemical characteristics of the lithium battery during charging and discharging.

[0057] S11. Establish a second-order equivalent circuit model of lithium battery, such as Figure 2 shown.

[0058] In the figure, U oc It represents an ideal voltage source and has a nonlinear relationship with SOC; R0 represents the ohmic internal resistance, R1 and R2 are polarization resistors, C1 and C2 are polarization capacitors, and U0 represents the terminal voltage of the battery.

[0059] S12. Write down the system equations and observation equations of the second-order equivalent circuit model of lithium batteries.

[0060] According to Kirchhoff's Current Law (KCL), the system equation and observation equation can be obtained as follows, defining the direction of the discharge current as positive and the charging current as negative.

[0061] System equations:

[0062]

[0063] In the formula, R1 and R2 are polarization resistors, C1 and C2 are polarization capacitors, U0 represents the terminal voltage of the battery, and I represents the current.

[0064] Observation equation:

[0065] U0=U oc -R0I-U C1 -U C2 (2)

[0066] Where U oc represents an ideal voltage source, which has a nonlinear relationship with SOC; R0 represents the ohmic internal resistance; U C1 and U C2 Represents the polarization capacitor voltage.

[0067] S2. A thermal circuit model of the lithium battery is established based on the heat transfer relationship between the various parts of the lithium battery when it is working and the heat transfer relationship between the lithium battery and the external air.

[0068] S21. Equivalent the thermal circuit model to the circuit model, the heat source (heat generating power) to the constant current source; the ambient temperature to the constant voltage source; the battery temperature to the voltage; the thermal resistance and heat capacity to the resistance and capacitance; the same thickness temperature is the same and the heat is only transferred along the thickness direction and the battery heat source is located in the center of the battery body. The battery temperature point is as follows: Figure 3 shown.

[0069] In the figure, T1 is the center temperature of the battery body; T2 is the surface temperature of the battery; T a is the ambient temperature.

[0070] Thermal circuit model Figure 4 As shown, R th1 is the thermal resistance, R tha is the convection thermal resistance, C th1 and C th2 is the heat capacity, P c is the heat generation power of the battery.

[0071] S22. Assuming that the battery density and heat generation are uniform, and the above model structure is symmetrical on both sides, the parameters of the battery on both sides of the model with the constant current source as the center are equal, and only one side of the thermal circuit model needs to be modeled.

[0072] Write the KCL equation based on Kirchhoff's current law.

[0073]

[0074] In the formula, R th1 is the thermal resistance, R tha is the convection thermal resistance, C th1 and C th2 is the heat capacity, P c is the heat generation power of the battery.

[0075] Let T1 = T1' - T a , T2=T2'-T a

[0076]

[0077] Discretize the above formula

[0078]

[0079] Let sampling time ΔT = 1s

[0080]

[0081] make

[0082]

[0083] Transform equation (6) into

[0084]

[0085] Further simplifying the above equation, we can get the difference equation about T2:

[0086]

[0087] make

[0088]

[0089] Get the difference equation about T2

[0090] T2(k+2)=AT2(k+1)+BT2(k)+CP c (k) (11)

[0091] The heat generation power is

[0092]

[0093] The above formula consists of two parts: irreversible heat and reversible heat. The reversible heat in one cycle is almost zero and can be ignored. Then the heat generation power is;

[0094] P c =I(U oc -U0) (13)

[0095] S3. Establish a thermoelectric coupling model based on the coupling relationship between electricity and heat, such as Figure 5 As shown;

[0096] First, the circuit model calculates the heat generation power based on the battery internal resistance and current. The thermal circuit model can calculate the battery temperature at the next moment based on the heat generation power. The calculated temperature is brought into the circuit model, and the heat generation power of the battery at the next moment is calculated based on the total internal resistance of the battery corresponding to the temperature. The coupling of the circuit and the thermal circuit is completed, and a thermoelectric coupling model is established.

[0097] S4. Estimate the temperature state of the lithium battery using a thermoelectric coupling model and compare it with the actual battery temperature.

[0098] First, calculate the heat generation power P of the battery through the circuit c

[0099] P c =I(U oc -U0)=I 2 R (14)

[0100] Where R is the total internal resistance of the battery.

[0101] The total internal resistance of the battery is the sum of the ohmic internal resistance and the polarization internal resistance

[0102] R=R0+R1+R2 (15)

[0103] The ohmic internal resistance and polarization internal resistance can be identified by using the least squares method with the help of battery experimental data. The parameter identification results are shown in Table 1.

[0104] Table 1 Battery internal resistance identification results

[0105] parameter Value <![CDATA[R0]]> <![CDATA[2.50×10 -5 ]]> <![CDATA[R1]]> <![CDATA[8.06×10 -5 ]]> <![CDATA[R2]]> <![CDATA[3.84×10 -4 ]]> R <![CDATA[4.95×10 -4 ]]>

[0106] Secondly, the battery temperature is calculated by the thermal circuit model

[0107] T2(k+2)=AT2(k+1)+BT2(k)+CP c (k) (16)

[0108] The values ​​of A, B and C can be identified through battery experimental data, as shown in Table 2:

[0109] Table 2 Difference equation coefficient identification results

[0110] parameter Value A <![CDATA[9.01×10 -1 ]]> B <![CDATA[8.98×10 -2 ]]> C <![CDATA[9.00×10 -2 ]]>

[0111] The comparison between the predicted temperature and the actual temperature is shown in the figure below. Figure 6As shown, the predicted temperature is subtracted from the actual temperature, and the result is as follows Figure 7 shown.

[0112] Analysis of the above simulation results shows that the accuracy of temperature prediction using this method is relatively high, which proves the effectiveness of the present invention.

[0113] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for predicting the temperature state of a lithium battery in an energy storage power station, characterized in that: include: S1. Establish a second-order equivalent circuit model of lithium battery according to the internal electrochemical characteristics of lithium battery during charging and discharging; S2. Establish a thermal circuit model of the lithium battery based on the heat transfer relationship between various parts of the lithium battery when it is working and the heat transfer relationship between the lithium battery and the external air; S3. Establish a thermoelectric coupling model based on the coupling relationship between the lithium battery terminal voltage, heat and temperature; S4. Estimate the temperature state of the lithium battery using the thermoelectric coupling model and compare it with the actual battery temperature.

2. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 1, characterized in that In S1, the second-order equivalent circuit model of the lithium battery is established according to the internal electrochemical characteristics of the lithium battery during charging and discharging, including: S11, establishing a second-order equivalent circuit model of a lithium battery, wherein the second-order equivalent circuit model includes an ideal voltage source, an ohmic internal resistance, and two RC parallel branches connected in series in sequence, wherein the RC parallel branch is composed of a polarization resistor and a polarization capacitor connected in series; S12. Using Kirchhoff's law, write the system equation and observation equation of the second-order equivalent circuit model.

3. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 2, characterized in that: The system equation is: Among them, R1 and R2 are polarization resistors, C1 and C2 are polarization capacitors, U0 represents the terminal voltage of the battery, and I represents the current; The observation equation is: U0=U oc -R0I-U C1 -U C2 (2) Where U oc represents an ideal voltage source, which has a nonlinear relationship with SOC; R0 represents the ohmic internal resistance; U C1 and U C2 Represents the polarization capacitor voltage.

4. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 3, characterized in that: The ohmic internal resistance and polarization internal resistance are obtained by fitting the voltage and current data during the battery charging and discharging process using a least squares algorithm corresponding to each temperature state of the battery.

5. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 1, characterized in that In S2, the heat circuit model of the lithium battery is established according to the heat transfer relationship between the various parts of the lithium battery when it is working and the heat transfer relationship between the lithium battery and the external air, including: S21, equating the thermal circuit model to a circuit model, equating the heat source to a constant current source, equating the ambient temperature to a constant voltage source, equating the battery temperature to a voltage, and equating the thermal resistance and thermal capacitance to a resistor and a capacitor; S22. Assuming that the battery density and heat generation are uniform, and the thermal circuit model structure is bilaterally symmetrical, write the KCL equation based on Kirchhoff's current law.

6. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 5, characterized in that: The KCL equation is: T2(k+2)=AT2(k+1)+BT2(k)+CP c (k) (11) Among them, A, B, and C are constants, which are obtained by fitting the voltage and current data during the battery charging and discharging process using the least squares algorithm. c is the heat generation power of the battery; T1=T1'-T a , T2=T2'-T a ; T1' is the center temperature of the battery body, T a is the external environment temperature, T2' is the battery surface temperature.

7. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 1, characterized in that In S3, establishing a thermoelectric coupling model according to the coupling relationship between the lithium battery terminal voltage, heat and temperature includes: The circuit model is used to calculate the heat generation power based on the total internal resistance and current of the battery; The thermal circuit model is used to calculate the battery temperature based on the heat generation power, and the temperature is fed back to the circuit model.

8. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 7, characterized in that S3 specifically includes: First, the circuit model calculates the heat generation power P based on the total internal resistance of the battery, i.e. the ohmic internal resistance, the sum of R1 and R2, and the current. c ; P c =I 2 R=I 2 (R0+R1+R2) Among them, R is the total internal resistance of the battery, R1 and R2 are polarization resistances, and R0 represents the ohmic internal resistance; Secondly, the thermal circuit model calculates the battery temperature T2 at the next moment based on the heat generation power; T2(k+2)=AT2(k+1)+BT2(k)+CP c (k) Among them, k represents the current moment, A, B, and C are constants; Based on the battery temperature T2, the ohmic internal resistance and polarization internal resistance at the corresponding temperature are obtained and substituted into the circuit model. The heat generation power P of the battery at the next moment is calculated according to the total internal resistance R of the battery corresponding to the temperature. c , cycle in sequence to couple the electrical circuit and the thermal circuit.

9. The method for predicting the temperature state of a lithium battery in an energy storage power station according to claim 1, characterized in that S4 specifically includes: inputting the charging and discharging current of the lithium battery into the thermoelectric coupling model, and predicting the temperature change curve of the lithium battery when the initial temperature is known; and comparing the predicted temperature change curve of the lithium battery with the measured temperature.

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