CN113009361B - A battery state-of-charge estimation method based on open-circuit voltage calibration - Google Patents

Abstract

The invention relates to a battery state-of-charge estimation method based on open-circuit voltage calibration, which takes the difference value of the terminal voltage of a battery equivalent circuit model and the actual battery terminal voltage as the input of a feedback correction controller, regulates and controls the working state of the battery equivalent circuit model through the current value output by the feedback correction controller, and ensures that the terminal voltage of the battery equivalent circuit model changes along with the actual battery terminal voltage in real time, thereby continuously calibrating the open-circuit voltage of the battery equivalent circuit model and acquiring the actual battery state-of-charge estimation value. The method has the advantages of high estimation precision, simplicity, feasibility and easy realization.

Description

A battery state-of-charge estimation method based on open-circuit voltage calibration

technical field

The invention belongs to the field of electric vehicle battery management systems, and in particular relates to a battery state of charge estimation method based on open-circuit voltage calibration.

Background technique

The battery pack is an important part of a pure electric vehicle, usually consisting of hundreds or thousands of single cells. However, during the operation of an electric vehicle, the difference in the state-of-charge (SOC) of the battery greatly reduces the life and capacity of the battery pack, which makes the cost and performance of the electric vehicle unable to meet the needs of use. In addition, the battery SOC estimation is the decision basis for the battery management system (Battery-Management-System, BMS) to implement management and formulate control commands, which directly reflects the remaining mileage of the electric vehicle. Therefore, accurate and efficient estimation of battery SOC is of great significance for improving battery system performance and ensuring the safe and reliable operation of pure electric vehicles.

The battery SOC is the ratio of the current available capacity of the battery to the rated capacity and cannot be measured directly by sensors. In addition, the driving conditions of electric vehicles are complex, and the repeated acceleration and deceleration cause great difficulty in estimating the battery SOC. At present, the commonly used methods include open-circuit voltage method, ampere-hour integration method, estimation method based on Equivalent-Circuit-Model (ECM) and data-driven estimation method. Among them, researchers mainly study SOC estimation methods based on equivalent circuit model and data-driven, mainly including extended Kalman, open circuit voltage recursion, joint estimation, neural network and support vector machine and other methods. However, the above-mentioned method is extremely complicated, and its high control cost is not conducive to direct application in the industrial field. In addition, the accuracy of the ampere-hour integration method is limited by the measurement accuracy of the sensor, and accumulated errors will occur during use, resulting in a gradual decrease in the accuracy of SOC estimation and the inability to accurately obtain the battery SOC.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a battery state-of-charge estimation method based on open-circuit voltage calibration, which not only has high estimation accuracy, but also is simple, feasible and easy to implement.

In order to achieve the above object, the technical solution adopted in the present invention is: a method for estimating the battery state of charge based on open circuit voltage calibration, the difference between the terminal voltage of the battery ECM and the actual battery terminal voltage is used as the input of the feedback correction controller, and The working state of the battery ECM is regulated by the current value output by the feedback correction controller, so that the terminal voltage of the battery ECM follows the actual battery terminal voltage change in real time, so as to continuously calibrate the open circuit voltage of the battery ECM and obtain the estimated value of the actual battery state of charge.

Further, the method for estimating battery state of charge based on open circuit voltage calibration includes the following steps:

Establish a battery equivalent circuit model ECM;

Design a feedback correction controller for terminal voltage calibration, so that the terminal voltage of the battery ECM always follows the actual battery terminal voltage change, thereby simulating the actual battery working state;

Use the battery charge and discharge tester to obtain the actual battery terminal voltage, and input the difference between the battery ECM terminal voltage and the actual battery terminal voltage into the feedback correction controller;

Input the current value output by the feedback correction controller into the battery ECM to correct the terminal voltage output by the battery ECM;

Through continuous feedback correction, the terminal voltage of the battery ECM is made to approach the actual battery terminal voltage, even if the difference between the two is smaller than the set threshold, so as to simulate the actual battery working state and obtain the battery state of charge estimation value.

Further, according to the actual battery terminal voltage data, the input current of the battery ECM is continuously feedback adjusted, so that the difference between the battery ECM terminal voltage and the actual battery terminal voltage is less than the set threshold, so as to continuously calibrate the battery ECM's open circuit voltage. In this process, since the step response of the battery ECM is similar to that of the actual battery, the operating state of the battery ECM, including the working current, working voltage and SOC, is approximately equal to the actual battery, and then the estimated value of the actual battery SOC is obtained.

Further, the battery ECM adopts a second-order RC battery ECM. First, the battery OCV-SOC curve is obtained by fitting the obtained pulse discharge curve, and the calculation formula is as follows:

(1)

(1)

(2)

(2)

Among them, V _OCV is the open circuit voltage of the battery ECM, V _m is the terminal voltage of the second-order RC battery ECM, V _R0 is the voltage of R ₀ in the second-order RC battery ECM, V ₁ and V ₂ are the voltages of the first and second-order RC links, respectively. voltage, and the RC parameters in the battery ECM can be obtained by interpolation. The calculation formula is as follows:

(3)。

(3).

Further, the model accuracy of the established battery ECM was tested. During the test, the actual battery and the battery ECM were tested under the condition of 1/3 C pulse charge and discharge, and the terminal voltage responses of the two were compared.

Further, a proportional-integral (PI) feedback controller and a Sliding-mode-Control (SMC) feedback controller are respectively used as feedback correction controllers to adjust the input current of the battery ECM. , respectively as follows:

(4)

(4)

(5)

(5)

Among them, K _p is the proportional coefficient, K _i is the integral coefficient, Va is the actual battery terminal voltage, V _m is the terminal voltage _of the battery ECM, and I _Bat is the input current of the battery ECM.

Further, build a battery SOC estimation accuracy test platform, and load the obtained battery current and terminal voltage data into the battery SOC estimation accuracy test platform to obtain battery SOC estimation results, including feedback control based on PI and feedback control based on SMC. The estimation results of the controller are used to analyze the battery SOC estimation accuracy of different feedback correction controllers under different operating conditions.

Further, the battery SOC estimation accuracy test platform uses the battery charge and discharge tester to obtain the data obtained from the U.S. Urban Dynamometer Driving Schedule (UDDS) and the New European Driving Cycle (NEDC) respectively. The single battery is charged and discharged under electrical conditions, and the battery SOC estimation accuracy of different feedback correction controllers under different operating conditions is analyzed: Compared with the SOC estimation accuracy based on PI feedback controller, the SOC estimation accuracy based on SMC feedback controller higher; comparing the SOC estimation accuracy under different operating conditions, the maximum estimation error of the battery operating under the NEDC electrical condition is larger, while the maximum estimation error under the UDDS operating condition is smaller.

Compared with the prior art, the present invention has the following beneficial effects: the method mainly realizes the battery state of charge estimation through the battery ECM and the feedback correction controller, which takes the difference between the terminal voltage of the battery ECM and the actual battery terminal voltage as the feedback Correct the input of the control, and output the current value as the input of the battery ECM to calibrate the working state of the battery ECM, so that the terminal voltage of the battery ECM is close to the actual battery terminal voltage, so as to obtain the estimated value of the battery state of charge. This method can make the terminal voltage output by the battery ECM follow the actual battery terminal voltage in real time, so as to continuously calibrate the open circuit voltage of the battery ECM and obtain the actual SOC of the battery. . In addition, the method has low requirements on the complexity of the control circuit, is simple, feasible, easy to implement, and can run efficiently and stably in embedded systems, and can be used in energy storage power supplies, electric vehicle power batteries, consumer electronics power supplies, and other fields.

Description of drawings

FIG. 1 is a working principle diagram of an embodiment of the present invention.

FIG. 2 is an equivalent circuit model of an n-order RC battery in an embodiment of the present invention.

FIG. 3 is a dynamic response curve diagram of a battery model in an embodiment of the present invention.

FIG. 4 is a graph showing the change of the battery terminal voltage based on the PI feedback controller under the UDDS current condition in the embodiment of the present invention.

FIG. 5 is a graph of battery SOC estimation based on a PI feedback controller under a UDDS current condition in an embodiment of the present invention.

FIG. 6 is a graph showing the change of the battery terminal voltage based on the PI feedback controller under the NEDC current condition in the embodiment of the present invention.

FIG. 7 is a graph of battery SOC estimation based on a PI feedback controller under the NEDC current condition according to an embodiment of the present invention.

FIG. 8 is a graph showing a voltage change curve of a battery terminal based on an SMC feedback controller under a UDDS current working condition in an embodiment of the present invention.

FIG. 9 is a graph of battery SOC estimation based on an SMC feedback controller under a UDDS current condition in an embodiment of the present invention.

FIG. 10 is a graph showing the change of the battery terminal voltage based on the SMC feedback controller under the NEDC current condition in the embodiment of the present invention.

FIG. 11 is a graph of battery SOC estimation based on the SMC feedback controller under the NEDC current condition in the embodiment of the present invention.

In the picture: 1- battery charge and discharge tester (BTS 5V12A), 2- 18650 ternary lithium battery, 3- battery equivalent circuit model, 4- feedback correction controller, 11- self-discharge resistance, 12- battery capacitance, 13-battery internal resistance, 14-battery first-order RC, 15-battery nth-order RC.

Detailed ways

In order to show the content and features of the present invention more clearly, the following will describe the specific implementation process of the battery state of charge estimation method based on open circuit voltage calibration with reference to the accompanying drawings and technical solutions. The present invention can be implemented in different forms, and should not be limited to the described implementation cases.

A method for estimating battery state of charge based on open-circuit voltage calibration proposed in this embodiment, its implementation principle is shown in Figure 1, wherein the test system is composed of a battery charge and discharge tester, a battery ECM and a feedback correction controller. Specific working process: first initialize the initial value of the battery SOC, then the feedback correction controller adjusts the input current of the battery ECM in real time according to the difference between the terminal voltage output by the battery ECM and the measured actual battery terminal voltage, and makes the output current of the battery ECM The terminal voltage always changes with the actual battery terminal voltage, and then the open circuit voltage of the battery ECM after calibration is obtained, and finally the battery SOC value in the battery ECM is obtained, which is considered to be the actual battery SOC estimated value.

The specific implementation process of the method includes the following steps:

(a), analyze the working principle of the battery SOC estimation method based on open circuit voltage calibration according to FIG. 1;

(b), taking the 18650 ternary lithium battery as the experimental object, to establish the battery second-order RC battery ECM;

(c) Use a battery charge-discharge tester to conduct a charge-discharge test on the 18650 ternary lithium battery, and obtain the experimental data under the electrical conditions of UDDS and NEDC respectively;

(d), respectively applying the experimental data obtained in step (c) to test the performance of the proposed method for estimating the battery state of charge based on open-circuit voltage calibration;

In this embodiment, step (a) includes the following process:

a. Referring to Figure 1, the battery charge and discharge tester conducts charge and discharge tests on the 18650 ternary lithium battery to simulate the normal working state of the battery, and the battery SOC estimation method based on open circuit voltage calibration will be based on the actual battery terminal voltage data. The input current of the battery ECM makes the terminal voltage of the battery ECM approximately equal to the actual battery terminal voltage, and then the calibrated open circuit voltage is obtained to obtain the actual battery SOC. In this process, since the step response of the battery ECM is similar to that of the actual battery, the operating state of the battery ECM, including the working current, working voltage and SOC, will be similar to that of the actual battery, and then the actual battery SOC value will be obtained.

In this embodiment, step (b) establishes a battery ECM according to FIG. 2 , and takes the second-order RC battery ECM as an example to implement the proposed battery SOC estimation method. The battery ECM establishment includes the following processes:

b1. First carry out the parameter design of the RC equivalent circuit in the ECM: design a pulse discharge test to discharge the battery at a fixed capacity percentage, and let the battery open-circuit voltage stabilize at the end of the discharge, and cycle until the battery is empty . Secondly, the above tests were carried out at different temperatures to obtain the pulse discharge curves of the battery at different temperatures.

b2. First, fit the battery OCV-SOC curve according to the obtained pulse discharge curve, and finally obtain the following formula:

(1)

(1)

(2)

(2)

Among them, V _OCV is the open circuit voltage of the battery ECM, V _m is the terminal voltage of the second-order RC battery ECM, V _R0 is the voltage of R ₀ in the second-order RC battery ECM, V ₁ and V ₂ are the voltages of the first and second-order RC links, respectively. voltage, and the RC parameters in the ECM can be obtained by interpolation, and then the formula (3) can be determined:

(3)

(3)

b3. Test the model accuracy of the established battery ECM, that is, test the actual battery and ECM under the condition of 1/3 C pulse charge and discharge, respectively, and compare their terminal voltage responses. The results are shown in Figure 3.

In this embodiment, step (c) uses a battery charge-discharge tester to charge and discharge the 18650-type ternary lithium battery, and obtain experimental data under the electrical conditions of UDDS and NEDC, respectively. Among them, the electrical conditions of UDDS and NEDC are obtained by using Advisor based on the simulation of actual electric vehicle parameters, and the experimental steps for obtaining the operating state data of the battery working process are as follows: First, use a battery charge and discharge tester to charge the 18650 at 1C at 25°C , when it reaches the charging cut-off voltage of 4.2V, it will stand for 1h. Then, the UDDS and NEDC conditions were respectively loaded to both ends of the battery to continuously charge and discharge the battery. When the discharge reached the cut-off voltage, the experiment was terminated after standing for a period of time. The terminal voltage responses of the 18650 ternary lithium battery under the two working conditions are shown in Figure 4, Figure 8 and Figure 6, Figure 10, respectively.

In this embodiment, step (d) respectively applies the experimental data obtained in step (c) to test the performance of the proposed battery state of charge estimation method, and the specific process is as follows:

d1. Design a feedback correction controller for terminal voltage calibration, so that the output terminal voltage of the battery ECM always follows the actual battery terminal voltage change, so as to simulate the actual battery working state and obtain the battery SOC. The present invention adopts the PI controller and the SMC controller to feedback and adjust the input current of the battery ECM, respectively, as follows:

(4)

(4)

(5)

(5)

Among them, K _p is the proportional coefficient, K _i is the integral coefficient, Va is the actual battery terminal voltage, V _m is the terminal voltage _of the battery ECM, and I _Bat is the input current of the battery ECM.

d2. Build the proposed battery SOC estimation accuracy test platform as shown in Figure 1, and load the obtained battery current and terminal voltage data into the battery state-of-charge estimation simulation platform based on open-circuit voltage calibration to obtain the battery SOC estimation result, The test results based on the PI feedback controller are shown in Figure 4, Figure 5, Figure 6, and Figure 7, respectively, while the test results based on the SMC feedback controller are shown in Figure 8, Figure 9, Figure 10, and Figure 11, respectively.

d3. Analyze the battery SOC estimation accuracy of different feedback correction controllers under different working conditions: from the estimation results in Figure 5, Figure 7, Figure 9 and Figure 11, the SOC estimation accuracy based on the SMC feedback controller is higher, and the maximum It exceeds 4.8%, while the SOC estimation accuracy based on the PI feedback controller is slightly worse, and the maximum is not more than 8.8%. Comparing the SOC estimation accuracy under different operating conditions, the results show that the maximum estimation error of the battery operating under the NEDC electrical condition is relatively large. , while the maximum estimation error under UDDS conditions is smaller.

The battery state-of-charge estimation method based on open-circuit voltage calibration proposed by the invention reduces the estimation difficulty while ensuring the battery SOC estimation accuracy, thereby reducing the cost of the control system and the complexity of battery state-of-charge estimation.

Obviously, various modifications can be made to this invention by those skilled in the art without departing from the scope of the invention. Therefore, if the modifications of the present invention fall within the scope of the claims of the present invention and technical equivalents thereof, the present invention also includes these modifications.

Claims (6)

1. A battery state-of-charge estimation method based on open-circuit voltage calibration, characterized in that the difference between the terminal voltage of the battery equivalent circuit model and the actual battery terminal voltage is used as the input of the feedback correction controller, and the feedback correction control is performed. The current value output by the controller regulates the working state of the battery equivalent circuit model, so that the terminal voltage of the battery equivalent circuit model follows the actual battery terminal voltage in real time, so as to continuously calibrate the open circuit voltage of the battery equivalent circuit model and obtain the actual battery state of charge Estimated value; it includes the following steps: Establish a battery equivalent circuit model ECM; Design a feedback correction controller for terminal voltage calibration, so that the terminal voltage of the battery ECM always follows the actual battery terminal voltage change, thereby simulating the actual battery working state; Use the battery charge and discharge tester to obtain the actual battery terminal voltage, and input the difference between the battery ECM terminal voltage and the actual battery terminal voltage into the feedback correction controller; Input the current value output by the feedback correction controller into the battery ECM to correct the terminal voltage output by the battery ECM; Through continuous feedback correction, the terminal voltage of the battery ECM is made to approach the actual battery terminal voltage, even if the difference between the two is less than the set threshold, so as to simulate the actual battery working state and obtain the battery state of charge estimate value; The battery ECM adopts the second-order RC battery ECM. First, the battery OCV-SOC curve is obtained by fitting the obtained pulse discharge curve. The calculation formula is as follows:

(1)

(2) Among them, V _OCV is the open circuit voltage of the battery ECM, V _m is the terminal voltage of the second-order RC battery ECM, V _R0 is the voltage of R ₀ in the second-order RC battery ECM, V ₁ and V ₂ are the voltages of the first and second-order RC links, respectively. voltage, and the RC parameters in the battery ECM can be obtained by interpolation. The calculation formula is as follows:

(3). 2 . The battery state-of-charge estimation method based on open-circuit voltage calibration according to claim 1 , wherein the input current of the battery ECM is continuously feedback adjusted according to the actual battery terminal voltage data, so that the The difference between the terminal voltage and the actual battery terminal voltage is less than the set threshold, so as to obtain the battery open circuit voltage of the calibrated battery ECM; in this process, since the step response of the battery ECM and the actual battery is similar, the operation of the battery ECM is The state, including the working current, working voltage and SOC, is approximately equal to the actual battery, and then the actual battery SOC estimation value is obtained. 3. A method for estimating battery state of charge based on open circuit voltage calibration according to claim 1, wherein the model accuracy of the established battery ECM is tested, and during the test, the actual battery and the battery ECM are respectively measured in amplitude The test is carried out under the condition of 1/3 C pulse charge and discharge, and the terminal voltage responses of the two are compared. 4. a kind of battery state-of-charge estimation method based on open-circuit voltage calibration according to claim 1, is characterized in that, adopts PI feedback controller and SMC feedback controller as feedback correction controller respectively to the input current of battery ECM. The feedback adjustment is as follows:

(4)

(5) Among them, K _p is the proportional coefficient, K _i is the integral coefficient, Va is the actual battery terminal voltage, V _m is the terminal voltage _of the battery ECM, and I _Bat is the input current of the battery ECM. 5 . The battery state-of-charge estimation method based on open-circuit voltage calibration according to claim 4 , wherein a battery SOC estimation accuracy test platform is built, and the obtained battery current and terminal voltage data are loaded into the battery SOC. 6 . In the estimation accuracy test platform, the battery SOC estimation results are obtained, including the estimation results based on the PI feedback controller and the SMC feedback controller, respectively, and the battery SOC estimation accuracy of different feedback correction controllers under different operating conditions is analyzed. 6. The method for estimating battery state of charge based on open-circuit voltage calibration according to claim 5, wherein the battery SOC estimation accuracy test platform adopts a battery charging and discharging tester to measure the UDDS and NEDC working conditions of automobiles respectively. The obtained electrical conditions are used to charge and discharge the single battery; the battery SOC estimation accuracy of different feedback correction controllers under different operating conditions is analyzed. Compared with the SOC estimation accuracy based on the PI feedback controller, the SOC based on the SMC feedback controller The estimation accuracy is higher; comparing the SOC estimation accuracy under different operating conditions, the maximum estimation error of the battery operating under the NEDC electrical condition is larger, while the maximum estimation error under the UDDS operating condition is smaller.

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