Method for calibrating SOC between series battery modules and SOC estimation method of battery system

Abstract

The invention provides a method for calibrating SOC between series battery modules and an SOC estimation method of a battery system. The method comprises the steps that S1, each BMU estimates the SOC of the battery module where the BMU is located; s2, judging whether the voltage difference of the battery module is abnormal or not, if not, entering the step S3, and if yes, entering the step S6; s3, the BMU marks a first mark; s4, whether the battery module marked with the first flag bit is a reference module or not is judged, if yes, the step S5 is executed, if not, the step S6 is executed, and the reference module is the first battery module which triggers correction and is not calibrated in the battery modules marked with the first flag bit; s5, calculating the calibration amplitude of the reference module, and uploading the calibration amplitude to the BCU; s6, marking the module as a non-reference module, and entering the step S7; s7, the BCU issues the calibration amplitude to all non-reference modules in the battery modules; s8, all the non-reference modules calibrate the SOC of the non-reference modules according to the calibration amplitude.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a method for calibrating the SOC between series-connected battery modules and a method for estimating the SOC of a battery system. Background Art

[0002] In the field of power electronics, battery systems are widely used as energy storage elements in various scenarios, such as electric vehicles and energy storage.

[0003] See also Figure 1 As shown in the typical battery system diagram, the battery system 10 includes multiple battery modules (labeled 111 to 11n) and BCU120 (Battery Control Unit), where multiple battery modules are connected in series. Each battery module includes multiple battery cell strings connected in series and a BMU (Battery Management Unit). The BMU is used to monitor the basic parameters of the battery module in real time, such as voltage, current, and temperature, as well as estimate the state of charge (SOC) and state of health (SOH) of the battery module. It is the core component of the battery management system. Figure 1 As shown, the BCU 120 is used to interact and communicate with the BMU and is responsible for the management and control of the battery system, such as estimating the state of charge (SOC) and state of health (SOH) of the battery system.

[0004] In practical applications, it is very necessary to monitor the state of charge (SOC) of the battery system during use to display the remaining battery capacity to the user. Figure 1 In the battery system shown, the BCU 120 estimates the SOC of the battery system based on the SOC of each battery module.

[0005] In the prior art, the SOC estimation method of the battery module is mainly based on Kalman filtering, ampere-hour integration, etc., and is supplemented by a variety of correction strategies such as charge and discharge end correction, static correction, etc. However, in a high-voltage battery system where battery modules are stacked in series, during actual charging, when one battery module is fully charged, the entire battery system stops charging. During actual discharging, when one battery module is fully discharged, the entire battery system stops discharging, resulting in the battery modules at an intermediate charge level being unable to be fully charged or fully discharged. In addition, in actual applications, when assembling new equipment or replacing battery modules, there is a widespread situation where the battery modules have poor consistency. Under long-term charge and discharge conditions, some battery modules will be charged and discharged in an intermediate charge state for a long time, and cannot be charged or discharged to the end, resulting in the inability to obtain charge and discharge end correction. As a result, the cumulative error in the SOC estimation of these battery modules at an intermediate charge level becomes larger and larger, which in turn causes the SOC estimation error of the battery system to become larger and larger. Summary of the Invention

[0006] According to one embodiment, the present application provides a method for calibrating the SOC between series-connected battery modules, including: S1: each BMU estimates the SOC of the battery module in which it is located; S2: determines whether there is a voltage abnormality in the battery module, if not, enters step S3, if yes, enters step S6; S3: BMU marks the first flag; S4: determines whether the battery module marked with the first flag is a reference module, if so, enters step S5, if not, enters step S6, wherein the reference module is the first battery module in the battery module marked with the first flag that triggers correction and has not been calibrated; S5: calculates the calibration amplitude of the reference module and uploads it to the BCU; S6: marks it as a non-reference module and enters step S7; S7: BCU sends the calibration amplitude to all non-reference modules in the battery module; S8: all non-reference modules calibrate their own SOC with the calibration amplitude.

[0007] Furthermore, step S1 further includes: when the battery module triggers correction, recording the current SOC of the battery module as SOCf, the cumulative charge and discharge capacity difference between this correction and the last correction as QP, and the maximum capacity as Qmax.

[0008] Furthermore, step S2 includes: S21: BMU determines whether its own battery module is in a non-platform area, and if so, proceeds to step S22; S22: BCU obtains the SOC of the battery cell string with the highest voltage and the SOC of the battery cell string with the lowest voltage in the battery module, and calculates the difference ΔSOC between the SOC of the battery cell string with the highest voltage and the SOC of the battery cell string with the lowest voltage in the battery module; S23: determines whether ΔSOC is less than a set value, and if so, proceeds to step S3.

[0009] Furthermore, step S3 further includes: calculating the SOC theoretical value of the battery module marked with the first flag according to the formula SOCh=SOCf+QP / Qmax.

[0010] Furthermore, step S4 also includes: S41: determining whether the battery module marked with the first flag position triggers correction, if so, proceeding to step S42; S42: determining whether the battery module marked with the first flag position that triggers correction has been calibrated, if not, marking it as a reference module, proceeding to step S5.

[0011] Furthermore, step S5 further includes: obtaining the corrected SOC of the reference module, recorded as SOCr, and calculating the cumulative ampere-hour error of the reference module as the calibration amplitude according to the formula ErrorAh=(SOCr-SOCh)*Qmax.

[0012] Furthermore, step S8 also includes: according to the formula SOC_i=SOCf_i+ErrorAh / Qmax_i, where i represents the i-th non-reference module, SOCf_i is the current SOC of the battery module recorded in step S1, and Qmax_i represents the maximum capacity of the i-th non-reference module.

[0013] Furthermore, the process also includes S9: setting the SOC calibration validity flag of all battery modules to 0, and clearing the charge and discharge cumulative capacity difference QP and the maximum capacity Qmax stored in each battery module, and then entering step S1.

[0014] Furthermore, for step S21 and step S23, if no, proceed to step S6.

[0015] Furthermore, for step S41, if no, proceed to step S6; for step S42, if yes, proceed to step S6.

[0016] The present application also provides a method for estimating the SOC of a battery system, including: the above-mentioned method for calibrating the SOC between series-connected battery modules; S10: all BMUs in non-reference modules upload the calibrated SOC of their own battery modules to the BCU, and the BMUs in the reference module upload the corrected SOC of their own battery modules to the BCU; S11: the BCU estimates the SOCs of the battery system.

[0017] Furthermore, step S11 is: the BCU estimates the SOCs of the battery system according to the formula SOCs=Min(SOC_i) / (100%-ΔSOC), where ΔSOC=Max(SOC_i)-Min(SOC_i), where Min(SOC_i) is the minimum SOC value of all battery modules and Max(SOC_i) is the maximum SOC value of all battery modules.

[0018] The features and technical advantages of the present disclosure have been summarized quite broadly above so that the detailed description disclosed below may be better understood. Additional features and advantages of the present disclosure will be described below, which form the subject matter of the claims of the present disclosure. It will be understood by those skilled in the art that the concepts and specific embodiments disclosed herein may be readily used as a basis for modifying or designing other structures or processes for achieving the same purposes of the present disclosure. It will also be appreciated by those skilled in the art that such equivalent structures do not depart from the spirit and scope of the present disclosure as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which: Figure 1 shows a typical battery system schematic; Figure 2 A flow chart of a method for calibrating SOC between series-connected battery modules according to an embodiment of the present application is shown; Figure 3 A flow chart showing a method for calibrating SOC between series-connected battery modules according to another embodiment of the present application is shown; Figure 4 A flow chart of a method for estimating the SOC of a battery system according to an embodiment of the present application is shown.

[0020] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. These figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in this application in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0022] for Figure 1 The battery system shown in the figure, this application proposes a method for calibrating the SOC between series-connected battery modules to improve the accuracy of the SOC of each battery module in the series-connected battery modules. Figure 2 The flowchart of the method for calibrating the SOC between series-connected battery modules according to one embodiment of the present application is shown. The method for calibrating the SOC between series-connected battery modules proposed in the present application includes: S1: Each BMU estimates the SOC of the battery module in which it is located; S2: Determine whether there is a voltage abnormality in the battery module. If not, proceed to step S3. If so, proceed to step S6. S3: BMU marks the first sign; S4: Determine whether the battery module marked with the first flag is a reference module. If so, proceed to step S5; if not, proceed to step S6, where the reference module is the first battery module marked with the first flag that triggers correction and has not been calibrated. S5: Calculate the calibration amplitude of the reference module and upload it to the BCU; S6: Mark as a non-reference module and proceed to step S7; S7: The BCU sends the calibration amplitude to all non-reference modules in the battery module; S8: All non-reference modules calibrate their own SOC using the calibration amplitude.

[0023] Specifically, in step S1, each BMU samples the basic parameters of the battery module, such as open circuit voltage, current, and temperature, and estimates the SOC of the battery module through any applicable SOC estimation method, such as the open circuit voltage method, the ampere-hour accumulation method, and the Kalman filter algorithm. And when the battery module is at rest or at the end of charge and discharge and the correction is triggered, the SOC of the battery module is corrected according to the SOC-OCV parameter table of the battery module to improve the SOC accuracy of the battery module. Specifically, in actual applications, when the battery module leaves the factory, it comes with a calibrated SOC-OCV parameter table at room temperature. Please refer to the example of the SOC-OCV parameter table of a battery module shown in Table 1.

[0024] Table 1

[0025] Where OCV represents the open-circuit voltage of the battery module, and the SOC-OCV parameter table shows the corresponding relationship between OCV and SOC. In actual battery system applications, the open-circuit voltage (OCV) of the battery module is usually monitored in real time. Therefore, the SOC of the battery module can be obtained based on OCV using the SOC-OCV parameter table.

[0026] As can be seen from the aforementioned SOC-OCV parameter table, at the end of discharge (e.g., within 30% SOC), the open-circuit voltage (OCV) varies significantly compared to the range between 30% SOC and 98% SOC, even with the same SOC change. This is typically referred to as the "non-plateau" region, while the range between 30% SOC and 98% SOC is called the "plateau" region. Near full charge, such as between 98% SOC and 100% SOC, the open-circuit voltage also varies significantly, often referred to as the "non-plateau" region, but within a smaller range. To improve SOC estimation accuracy, it's best to select parameters at the end of charge and discharge (i.e., the "non-plateau" region) for estimation. This provides a more accurate SOC and can serve as a standard for correcting SOC.

[0027] Furthermore, step S1 includes: when the battery module triggers correction, recording the current SOC of the battery module as SOCf, the cumulative charge and discharge capacity difference between this correction and the last correction as QP, and the maximum capacity as Qmax.

[0028] Specifically, step S2 includes: S21: BMU determines whether its own battery module is in the non-platform area. If so, proceed to step S22; S22: BCU obtains the SOC of the battery cell string with the highest voltage and the SOC of the battery cell string with the lowest voltage in the battery module, and calculates the difference ΔSOC between the SOC of the battery cell string with the highest voltage and the SOC of the battery cell string with the lowest voltage in the battery module; S23: determines whether ΔSOC is less than the set value. If so, proceed to step S3.

[0029] More specifically, for step S21 and step S23, if no, it is considered that there is a pressure difference abnormality, and the process proceeds to step S6.

[0030] In one embodiment, the preset value may be 5%, but this application does not limit this and may be adjusted according to actual needs.

[0031] As mentioned above, when a battery module is in the non-plateau region, the open-circuit voltage difference varies significantly under the same SOC change. Therefore, by limiting ΔSOC, battery modules with excessively large open-circuit voltage differences are excluded, thus avoiding incorrect corrections caused by excessive voltage differences. Battery modules marked with the first flag become candidate reference modules.

[0032] Furthermore, step S3 includes: calculating the SOC theoretical value of the battery module marked with the first flag according to the formula SOCh=SOCf+QP / Qmax. Since it is a theoretical value, SOCh can be greater than 100% and less than 0%.

[0033] Specifically, step S4 includes: S41: determining whether the battery module marked with the first flag has triggered correction; if so, proceeding to step S42; S42: determining whether the battery module marked with the first flag that has triggered correction has been calibrated; if not, marking it as a reference module and proceeding to step S5. In other words, once a battery module marked with the first flag triggers correction, it is determined whether it has been calibrated. If it has not been calibrated, it is selected as the reference module. In this way, the first battery module that has triggered correction and has not been calibrated among the battery modules with normal pressure differences is found as the reference module, and the remaining modules are marked as non-reference modules. In actual applications, a flag bit can be set in the BMU. When the flag bit is 1, it indicates that it is a reference module, and when the flag bit is 0, it indicates that it is a non-reference module.

[0034] More specifically, for step S41, if no, proceed to step S6; for step S42, if yes, proceed to step S6.

[0035] More specifically, in one embodiment of the present application, when the SOC calibration validity flag of the battery module is assigned a value of 0, it is considered that it has not been calibrated. Of course, when the SOC calibration validity flag of the battery module is assigned a value of 1, it is considered that it has been calibrated.

[0036] Specifically, step S5 includes: obtaining the corrected SOC of the reference module, recorded as SOCr, and calculating the cumulative ampere-hour (Ah) error of the reference module as the calibration amplitude according to the formula ErrorAh=(SOCr-SOCh)*Qmax.

[0037] Specifically, step S8 includes: according to the formula SOC_i=SOCf_i+ErrorAh / Qmax_i, where i represents the i-th non-reference module, SOCf_i is the current SOC of the battery module recorded in step S1, and Qmax_i represents the maximum capacity of the i-th non-reference module.

[0038] In practical applications, the SOC estimation error of a battery module mainly comes from errors caused by current measurement or control, and the cumulative error formed by the integration of ampere-hours during the charging and discharging process. However, in a high-voltage energy storage system with battery modules connected in series, the current should be equal, and the cumulative error ErrorAh in Ah (ampere-hour) in the battery module series system should also be equal. This application will select a reference module for battery modules that trigger corrections and are not mistakenly repaired due to excessive voltage differences. The reference module's cumulative error ErrorAh of Ah will be used to calibrate all other non-reference modules, making the SOC of all battery modules more accurate.

[0039] For further information, see Figure 3 The flowchart of the method for calibrating SOC between series-connected battery modules of another embodiment of the present application is shown. The above-mentioned method for calibrating SOC between series-connected battery modules also includes S9: the SOC calibration validity flag of all battery modules is assigned a value of 0, and the cumulative charge and discharge capacity difference QP and maximum capacity Qmax stored in each battery module are cleared.

[0040] The SOC calibration validity flag of the battery module is set to 0, and the battery modules are waited for the next mutual calibration, that is, the next calibration is continued after the current calibration is completed. Therefore, after step S9 is completed, step S1 is entered.

[0041] The above-described method for calibrating SOC between series-connected battery modules is suitable for batteries whose SOC-OCV curves exhibit plateau characteristics, such as lithium iron phosphate (LFP) batteries. By using the reference module's accumulated Ah error (ErrorAh) to calibrate all other non-reference modules, this method solves the problem of battery modules that remain in the plateau region for extended periods without an opportunity for SOC correction, improving the SOC estimation accuracy of all battery modules. It also addresses the impact of cell inconsistencies on SOC estimation caused by factors such as mixed cell usage in the battery system. Furthermore, by selecting a battery module with no voltage differential anomalies that triggers correction as the reference module, the reference module can provide a more accurate calibration margin.

[0042] Two battery modules are tested and verified. First, the two battery modules are discharged to keep the maximum voltage of the battery cells in the battery modules below 3.25V. The modules are left to stand for 2 hours to correct and judge the voltage difference under static conditions. Then, there is no voltage difference abnormality between the two battery modules. Then, the SOC of the second battery module is artificially modified to 10%, that is, the SOC of the second battery module is artificially lowered, and a condition where the SOC difference between the battery modules is too large is artificially created. Finally, the two battery modules are charged until the battery system is fully charged. Charging will be stopped and full charge correction will be triggered because the first battery module triggers full charge, and there is no voltage difference abnormality between the first battery module and the second battery module. According to the method for calibrating SOC between series-connected battery modules provided in this application, the first battery module is judged to be the reference module, and the calibration amplitude calculated based on the first battery module is sent to the second battery module, which is a non-reference module, through the BCU to calibrate the SOC of the second battery module. The test found that after the first battery module triggered the full charge correction, the second battery module also followed the first battery module and made the correction with the same amplitude.

[0043] Furthermore, this application also provides a method for estimating the SOC of a battery system, see Figure 4 The flowchart of the SOC estimation method of the battery system of one embodiment of the present application is shown. The SOC estimation method of the battery system provided by the present application, based on the above-mentioned method of calibrating the SOC between series battery modules, also includes: S10: the BMUs in all non-reference modules upload the calibrated SOC of their own battery modules to the BCU, and the BMUs in the reference modules upload the corrected SOC of their own battery modules to the BCU; S11: the BCU estimates the SOCs of the battery system.

[0044] Specifically, step S11 is: the BCU estimates the SOCs of the battery system according to the formula SOCs=Min(SOC_i) / (100%-ΔSOC), where ΔSOC=Max(SOC_i)-Min(SOC_i), where Min(SOC_i) is the minimum SOC value of all battery modules, and Max(SOC_i) is the maximum SOC value of all battery modules.

[0045] In this way, the SOC estimation accuracy of the high-voltage energy storage battery system with battery modules connected in series is also improved.

[0046] Although the embodiments of the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.

[0047] Furthermore, the scope of the present application is not intended to be limited to the particular embodiments of the processes, machines, manufacture, compositions of matter, means, methods, and steps described in the specification. As will be readily understood by one of ordinary skill in the art from the disclosure herein, processes, machines, manufacture, compositions of matter, means, methods, or steps that perform substantially the same functions now exist or will later be developed or that achieve substantially the same results as the corresponding embodiments described herein may be utilized in accordance with the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

1. A method for calibrating SOC between series-connected battery modules, characterized in that: include: S1: Each BMU estimates the SOC of the battery module in which it is located; S2: Determine whether there is a voltage abnormality in the battery module. If not, proceed to step S3. If so, proceed to step S6. S3: BMU marks the first sign; S4: Determine whether the battery module marked with the first flag is a reference module. If so, proceed to step S5; if not, proceed to step S6, where the reference module is the first battery module marked with the first flag that triggers correction and has not been calibrated. S5: Calculate the calibration amplitude of the reference module and upload it to the BCU; S6: Mark as a non-reference module and proceed to step S7; S7: The BCU sends the calibration amplitude to all non-reference modules in the battery module; S8: All non-reference modules calibrate their own SOC using the calibration amplitude.

2. The method for calibrating SOC between series-connected battery modules according to claim 1, characterized in that: Step S1 also includes: when the battery module triggers correction, recording the current SOC of the battery module as SOCf, the cumulative charge and discharge capacity difference between the current correction and the last correction as QP, and the maximum capacity as Qmax.

3. The method for calibrating SOC between series-connected battery modules according to claim 2, characterized in that: Step S2 includes: S21: The BMU determines whether its own battery module is in a non-platform area. If so, it proceeds to step S22; S22: The BCU obtains the SOC of the cell string with the highest voltage and the SOC of the cell string with the lowest voltage in the battery module, and calculates the difference ΔSOC between the SOC of the cell string with the highest voltage and the SOC of the cell string with the lowest voltage in the battery module; S23: Determine whether ΔSOC is less than a set value. If so, proceed to step S3.

4. The method for calibrating SOC between series-connected battery modules according to claim 3, characterized in that: Step S3 further includes: calculating the SOC theoretical value of the battery module marked with the first flag according to the formula SOCh=SOCf+QP / Qmax.

5. The method for calibrating SOC between series-connected battery modules according to claim 4, characterized in that: Step S4 further includes: S41: Determine whether the battery module marked with the first flag has triggered correction. If so, proceed to step S42; S42: Determine whether the battery module marked with the first flag that triggers the correction has been calibrated. If not, mark it as a reference module and proceed to step S5.

6. The method for calibrating SOC between series-connected battery modules according to claim 5, characterized in that: Step S5 further includes: obtaining the corrected SOC of the reference module, recorded as SOCr, and calculating the cumulative ampere-hour error of the reference module as the calibration amplitude according to the formula ErrorAh=(SOCr-SOCh)*Qmax.

7. The method for calibrating SOC between series-connected battery modules according to claim 6, characterized in that: Step S8 further includes: according to the formula SOC_i=SOCf_i+ErrorAh / Qmax_i, where i represents the i-th non-reference module, SOCf_i is the current SOC of the battery module recorded in step S1, and Qmax_i represents the maximum capacity of the i-th non-reference module.

8. The method for calibrating SOC between series-connected battery modules according to claim 7, characterized in that: The process also includes S9: setting the SOC calibration validity flag of all battery modules to 0, and clearing the charge and discharge cumulative capacity difference QP and maximum capacity Qmax stored in each battery module, and then entering step S1.

9. The method for calibrating SOC between series-connected battery modules according to claim 3, characterized in that: For step S21 and step S23, if no, proceed to step S6.

10. The method for calibrating SOC between series-connected battery modules according to claim 5, characterized in that: For step S41, if no, proceed to step S6; For step S42, if yes, proceed to step S6.

11. A method for estimating the SOC of a battery system, characterized in that: include: The method for calibrating SOC between series-connected battery modules according to any one of claims 1 to 10; S10: All BMUs in non-reference modules upload the calibrated SOC of their own battery modules to the BCU, and the BMUs in the reference module upload the corrected SOC of their own battery modules to the BCU; S11: BCU estimates the SOCs of the battery system.

12. The SOC estimation method of the battery system according to claim 11, characterized in that: Step S11 is: the BCU estimates the SOCs of the battery system according to the formula SOCs=Min(SOC_i) / (100%-ΔSOC), where ΔSOC=Max(SOC_i)-Min(SOC_i), where Min(SOC_i) is the minimum SOC value of all battery modules and Max(SOC_i) is the maximum SOC value of all battery modules.

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