Battery soc estimation method based on battery cell voltage

Abstract

The application discloses a power battery SOC estimation method based on battery monomer voltage, and the main design concept of the application is that the characteristics of end pressure difference amplification of a battery pack with poor monomer consistency are utilized, the actual SOC maximum and minimum values are estimated based on the maximum and minimum values of the monomer voltage and the rated capacity, and the actual power value in the actual charging and discharging process is estimated by using the weighted summation of the two. Meanwhile, in the process of continuously obtaining the actual power value, the pre-calibrated monomer voltage OCV table is inquired according to the set power interval and the charging and discharging current threshold, so that the actual SOC maximum and minimum values participating in the estimation are corrected in real time, that is, the actual power estimation value is continuously corrected based on the calibrated monomer voltage value in the charging and discharging process, so that the actual SOC of the battery pack can be accurately calculated when the monomers of the battery pack have large differences, and the charging and discharging capacity of the battery pack can be accurately reflected.

Description

Technical Field

[0001] This invention relates to the field of new energy vehicles, and in particular to a method for estimating the state of charge (SOC) of a power battery based on the voltage of a single battery cell. Background Technology

[0002] As a key component of new energy vehicles, the consistency of individual battery cells within a battery pack significantly impacts its actual charge / discharge capacity and safety performance. In practical applications, due to differences between battery packs or potential self-discharge issues in individual cells, the voltage of a particular cell in the battery pack may be significantly lower at the end of discharge or significantly higher at the end of charging. This affects the actual discharge capacity of the battery pack, leading to a large deviation in SOC estimation. Consequently, the battery pack may prematurely activate self-protection mechanisms or reach its charging protection voltage prematurely, severely impacting the charge / discharge capacity of the battery pack and the user experience. Summary of the Invention

[0003] In view of the above, the present invention aims to provide a method for estimating the state of charge (SOC) of a power battery based on the voltage of a single battery cell, thereby solving the aforementioned technical problems.

[0004] The technical solution adopted in this invention is as follows:

[0005] This invention provides a method for estimating the state of charge (SOC) of a power battery based on the voltage of a single battery cell, including:

[0006] Based on simulated charge and discharge, the initial minimum SOC and initial maximum SOC values ​​corresponding to the minimum and maximum voltages of the individual cells are obtained in advance.

[0007] Based on the rated capacity of the battery pack, the initial minimum SOC value, and the initial maximum SOC value, the first rated capacity value and the second rated capacity value corresponding to the minimum SOC value and the maximum SOC value are respectively obtained.

[0008] In actual charging and discharging processes, based on the first rated capacity value and the second rated capacity value, the actual minimum SOC and the actual maximum SOC of a single battery cell are estimated by ampere-hour integration.

[0009] Based on preset weight values, the weighted sum of the actual minimum SOC and the actual maximum SOC is used as the estimated actual power capacity of the power battery.

[0010] When the estimated actual power consumption reaches the set range and the charging / discharging current is less than the preset current threshold, the pre-calibrated individual cell voltage OCV table is consulted to correct the minimum and maximum actual SOC values ​​in real time; wherein, the individual cell voltage OCV table is calibrated within the preset current and power consumption range.

[0011] In at least one possible implementation, the method further includes: adjusting the weight value in real time using the corrected actual minimum SOC value and the actual maximum SOC value, and dynamically estimating the actual power consumption estimate based on the adjusted weight value.

[0012] In at least one possible implementation, the step of obtaining the initial minimum SOC and initial maximum SOC values ​​corresponding to the minimum and maximum voltages of the individual cells based on simulated charge and discharge includes:

[0013] Discharge the battery pack to the protection voltage, obtain the minimum and maximum voltage of each individual cell, and estimate the initial minimum and maximum SOC values ​​under this condition using an OCV lookup table; and,

[0014] After the battery pack is fully charged, the initial minimum and maximum SOC values ​​under that state are estimated by ampere-hour integration.

[0015] In at least one possible implementation, the step of using the weighted sum of the actual minimum SOC and the actual maximum SOC as the estimated actual battery capacity based on a preset weight value includes:

[0016] A first weight N and a second weight M are preset; where N+M=1, and during the charging process, N gradually increases while M gradually decreases, and during the discharging process, N gradually decreases while M gradually increases.

[0017] The estimated actual power SOC is SOC = N × SOCmax + M × SOCmin, and SOC = SOCmax at the end of charging and SOC = SOCmin during discharge protection, where SOCmax is the maximum actual SOC and SOCmin is the minimum actual SOC.

[0018] In at least one possible implementation, the method further includes:

[0019] During actual discharge, the displayed battery level is recorded at the moment when a single battery cell malfunction occurs.

[0020] The error power value is calculated in real time based on the displayed power value and the estimated actual power value at the current moment.

[0021] Based on the error power value, the rate of change of the displayed power value is adjusted to make it closer to the actual power estimate.

[0022] In at least one of the possible implementations, adjusting the rate of change of the displayed battery value includes reducing it by a preset offset value each time the displayed battery value is acquired.

[0023] In at least one of the possible implementations, the step of reducing the displayed battery value by a preset offset value each time it is acquired specifically includes: during the process of correcting the displayed battery value to the target displayed battery value, the displayed battery value is reduced by a preset offset value each time the actual battery estimated value decreases by a preset battery gradient, until the erroneous battery value is eliminated.

[0024] The main design concept of this invention lies in utilizing the characteristic of voltage difference amplification at the end of a battery pack with poor individual cell consistency. Based on the maximum and minimum values ​​of the individual cell voltages and the rated capacity, the maximum and minimum values ​​of the actual SOC are estimated. The actual charge value during the actual charging and discharging process is estimated by using a weighted sum of the two values. Simultaneously, while continuously acquiring this actual charge value, a pre-calibrated individual cell voltage OCV table is consulted according to the set charge range and charging and discharging current threshold. This allows for real-time correction of the estimated maximum and minimum values ​​of the actual SOC. In other words, the estimated actual charge value is continuously corrected based on the calibrated individual cell voltage values ​​during the charging and discharging process. This enables accurate calculation of the actual SOC of the current battery pack when there are large differences between individual cells, accurately reflecting its charging and discharging capabilities.

[0025] Furthermore, in some embodiments, linear correction can be performed during battery discharge based on the error between the actual SOC and the displayed SOC to avoid phenomena such as SOC jumps or premature discharge protection when the SOC is high. For example, when the actual SOC suddenly decreases due to faults such as self-discharge or leakage of a single battery cell, the rate of decrease / increase of the displayed battery level can be automatically adjusted to ensure that the battery level displayed to the user shows a linear trend and that there are no sudden changes in the battery level value. Attached Figure Description

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to the accompanying drawings, wherein:

[0027] Figure 1 A flowchart illustrating the SOC estimation method for power batteries based on individual cell voltage provided in this embodiment of the invention;

[0028] Figure 2 The graphs showing the relationship between actual charge, maximum actual charge, minimum actual charge, and time during the actual charging and discharging process provided in this embodiment of the invention. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0030] Before detailing the specific solution of this invention, the derivation process of this invention will be explained as follows: Analysis shows that when a single cell in a battery pack has severe self-discharge or a cell problem, its voltage difference with other cells at the end rapidly increases. At low voltage levels, this leads to premature discharge protection of the battery pack; at high voltage levels, it causes the battery pack to reach the charging end voltage prematurely, resulting in insufficient actual charging capacity. Currently, a common solution is to use OCV correction to calibrate the SOC error of the power battery. This method typically estimates the current actual SOC based on the minimum single-cell voltage Vmin of the battery pack through table lookup interpolation. To ensure the accuracy of the SOC, it is usually necessary to let the battery rest for more than 30 minutes after charging and discharging to allow the single-cell voltage to stabilize before performing OCV estimation. This is not only time-consuming, but also, when the battery pack experiences single-cell self-discharge or cell problems, Vmin is severely low. If the aforementioned resting condition of more than 30 minutes is not met for a long time, OCV correction cannot be performed, which may result in the power battery reaching discharge protection when the SOC value is high. On the other hand, if the resting condition is met to trigger OCV correction, the estimated value based on Vmin may also be low. Similarly, intuitively, users will still see the SOC jump, causing concerns and troubles such as battery pack power loss.

[0031] Therefore, based on the traditional OCV modification, this invention proposes an embodiment of a power battery SOC estimation method based on the cell voltage. Specifically, as follows: Figure 1 As shown, it includes:

[0032] Step S1: Based on simulated charging and discharging, the initial minimum SOC value (SOCmi = B%) and the initial maximum SOC value (SOCma = A%) corresponding to the minimum voltage (Vmin) and maximum voltage (Vmax) of the single cell are obtained in advance. It can be understood that when the cell is fully charged, SOCma = 100%, and when the discharge protection is reached, SOCmi is 0%.

[0033] Furthermore, the step of obtaining the initial minimum SOC and initial maximum SOC values ​​corresponding to the minimum and maximum voltages of the individual cells based on simulated charge and discharge includes:

[0034] Discharge the battery pack to the protection voltage, obtain the minimum and maximum voltage of each cell, and perform OCV lookup (this OCV table is pre-calibrated based on the traditional OCV correction method, which is different from the cell voltage OCV table mentioned below) to estimate the initial minimum and maximum SOC values ​​under this state; and after the battery pack is fully charged, estimate the initial minimum and maximum SOC values ​​under this state through ampere-hour integration.

[0035] Step S2: Combining the rated capacity (C) of the battery pack, the initial minimum SOC value, and the initial maximum SOC value, calculate the first rated capacity value (B% × C) and the second rated capacity value ((100% - A%) × C) corresponding to the minimum SOC value and the maximum SOC value, respectively.

[0036] Step S3: During actual charging and discharging, based on the first rated capacity value and the second rated capacity value, estimate the actual minimum SOC and the actual maximum SOC of the battery cell using ampere-hour integration.

[0037] Step S4: Based on the preset weight values, the weighted sum of the actual minimum SOC and the actual maximum SOC is used as the estimated actual power capacity of the battery pack.

[0038] Further, the step of using the weighted sum of the actual minimum SOC and the actual maximum SOC as the estimated actual battery capacity based on preset weight values ​​includes:

[0039] A first weight N and a second weight M are preset; where N+M=1, and during the charging process, N gradually increases while M gradually decreases, and during the discharging process, N gradually decreases while M gradually increases.

[0040] The estimated actual power capacity SOC is given by SOC = N × SOCmax + M × SOCmin, where SOC = SOCmax at the end of charging and SOC = SOCmin during discharge protection. SOCmax is the maximum actual SOC value, and SOCmin is the minimum actual SOC value. For the specific relationship between SOC, SOCmax, and SOCmin in this step, please refer to [reference needed]. Figure 2 Indication.

[0041] Step S5: When the estimated actual power consumption reaches the set range and the charging / discharging (i.e., charging or discharging) current is less than the preset low current threshold, the pre-calibrated individual cell voltage OCV table is consulted to correct the actual minimum SOC and the actual maximum SOC in real time. The individual cell voltage OCV table is calibrated under the preset low current and power consumption range (for example, in actual operation, the OCV table can be calibrated under 5A and 10A charging / discharging currents and the ranges of SOC < 20% and SOC > 90%, respectively, because the voltage difference of the problematic individual cell is usually amplified at the end).

[0042] This step is to ensure the accuracy of SOCmax and SOCmin. It addresses the problem of being unable to estimate OCV when the resting conditions are not met. It is a correction method proposed based on the characteristic that small current charging and discharging has little impact on the voltage stability of individual battery cells. For example, when the aforementioned estimated actual charge is below 20% and the discharge current is ≤10A, the aforementioned actual minimum and maximum SOC values ​​can be corrected in real time by querying the specific OCV table.

[0043] Therefore, by using the corrected actual minimum SOC value (lookup table value) and actual maximum SOC value (lookup table value), the aforementioned weight values ​​N and M can be adjusted in real time.

[0044] Furthermore, if a battery malfunction during discharge causes an abnormal drop or rise in the voltage of a single cell, which could lead to abnormal fluctuations in the estimated actual battery capacity, the following steps can be taken: Record the displayed battery capacity value as SOC_hmi at the moment of the battery cell malfunction, and calculate the error value △SOC between the displayed battery capacity value and the estimated actual battery capacity value SOC.

[0045] △SOC=SOC_hmi-SOC

[0046] Because the voltage fluctuation of a single battery cell is large when it fails, the error charge value △SOC is not a stable value during the battery pack discharge process. Therefore, real-time iterative calculation is required in the estimation algorithm. To ensure that the displayed charge value SOC_hmi is linearly corrected to 0% at the end of the process from battery discharge to the failure battery cell reaching the protection voltage, the error charge value △SOC calculated in real-time needs to be adjusted during the discharge process by changing the rate of change of the displayed charge value SOC_hmi to make it approach the actual charge estimate value SOC. That is, each time the displayed charge value SOC_hmi is calculated, it is reduced by a preset offset value so that before reaching the final target displayed charge value SOCtarget (which can be understood as the actual charge estimate value SOC estimated by the aforementioned embodiment after a correction period), the aforementioned error is eliminated (i.e., △SOC is corrected to 0). The specific calculation relationship can be referred to as follows: For every preset charge gradient (e.g., 1%) decrease in the actual charge estimate value SOC, the offset value SOCcal of the displayed charge value SOC_hmi is:

[0047] SOCcal=1%+ΔSOC / (SOC_hmi-SOCtarget)

[0048] As the actual estimated battery level SOC decreases from SOC_hmi to SOCtarget, SOC_hmi is further reduced by ΔSOC (accumulated by SOCcal). This means that once the displayed battery level reaches the expected target, the error battery level is completely corrected. This effectively avoids the problem of premature power interruption caused by a large error between the displayed battery level SOC_hmi and the actual estimated battery level SOC.

[0049] In summary, the main design concept of this invention lies in utilizing the characteristic of voltage difference amplification at the end of a battery pack with poor individual cell consistency. Based on the maximum and minimum values ​​of the individual cell voltages and the rated capacity, the maximum and minimum values ​​of the actual SOC are estimated. The actual charge value during the actual charging and discharging process is estimated by using a weighted sum of the two values. Simultaneously, while continuously acquiring this actual charge value, a pre-calibrated individual cell voltage OCV table is consulted according to the set charge range and charging and discharging current threshold. This allows for real-time correction of the estimated maximum and minimum values ​​of the actual SOC. In other words, the estimated actual charge value is continuously corrected based on the calibrated individual cell voltage values ​​during the charging and discharging process. This enables accurate calculation of the actual SOC of the current battery pack when there are large differences between individual cells, accurately reflecting its charging and discharging capabilities.

[0050] In this embodiment of the invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0051] The above description of the structure, features, and effects of the present invention is based on the embodiments shown in the figures. However, the above are only preferred embodiments of the present invention. It should be noted that the technical features involved in the above embodiments and their preferred methods can be reasonably combined and matched by those skilled in the art to form a variety of equivalent solutions without departing from or changing the design concept and technical effects of the present invention. Therefore, the present invention is not limited to the scope of implementation shown in the figures. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments, that do not exceed the spirit covered by the specification and figures, should be within the protection scope of the present invention.

Claims

1. A method for estimating the state of charge (SOC) of a power battery based on the voltage of a single battery cell, characterized in that, include: Based on simulated charge and discharge, the initial minimum SOC and initial maximum SOC values ​​corresponding to the minimum and maximum voltages of the individual cells are obtained in advance. Based on the rated capacity of the battery pack, the initial minimum SOC value, and the initial maximum SOC value, the first rated capacity value and the second rated capacity value corresponding to the minimum SOC value and the maximum SOC value are respectively obtained. In actual charging and discharging processes, based on the first rated capacity value and the second rated capacity value, the actual minimum SOC and the actual maximum SOC of a single battery cell are estimated by ampere-hour integration. Based on preset weight values, the weighted sum of the actual minimum SOC and the actual maximum SOC is used as the estimated actual power capacity of the power battery. To ensure the accuracy of the actual minimum and maximum SOC values, and addressing the issue of OCV estimation being impossible under conditions of inactivity, the following correction method is proposed, taking into account the characteristic that low-current charging and discharging has minimal impact on the voltage stability of individual battery cells: When the estimated actual power capacity reaches the set range and the charging / discharging current is less than the preset current threshold, the pre-calibrated single-cell voltage OCV table is consulted to correct the minimum and maximum actual SOC values ​​in real time. The single-cell voltage OCV table is calibrated within the preset current and power range by utilizing the characteristic of voltage difference amplification at the end of the battery pack with poor single-cell consistency. By real-time correction of the actual minimum and maximum SOC values ​​used in the estimation, the actual energy estimate can be continuously corrected based on the calibrated cell voltage value during the charging and discharging process.

2. The power battery SOC estimation method based on single-cell voltage according to claim 1, characterized in that, The method further includes: adjusting the weight value in real time using the corrected actual minimum SOC value and the actual maximum SOC value, and dynamically estimating the actual power consumption estimate based on the adjusted weight value.

3. The power battery SOC estimation method based on single-cell voltage according to claim 1, characterized in that, The initial minimum and maximum SOC values, respectively corresponding to the minimum and maximum voltages of the individual cells, obtained in advance based on simulated charge and discharge include: The battery pack is discharged to the protection voltage, and the minimum and maximum voltages of individual cells are obtained. Then, the initial minimum and maximum SOC values ​​of the battery pack under the protection voltage state are estimated using an OCV lookup table. After the battery pack is fully charged, the minimum and maximum initial SOC values ​​of the battery pack at the end of the full charge state are estimated by ampere-hour integration.

4. The power battery SOC estimation method based on single cell voltage according to claim 1, characterized in that, The step of using the weighted sum of the actual minimum SOC and the actual maximum SOC as the estimated actual battery capacity based on a preset weight value includes: A first weight N and a second weight M are preset; where N + M = 1, and during the charging process, N gradually increases while M gradually decreases, and during the discharging process, N gradually decreases while M gradually increases; The actual power estimation value SOC = N × SOCmax + M × SOCmin, and SOC = SOCmax at the end of charging and SOC = SOCmin during discharge protection, where SOCmax is the maximum actual SOC and SOCmin is the minimum actual SOC.

5. The method for estimating the state of charge (SOC) of a power battery based on the voltage of a single battery cell according to any one of claims 1 to 4, characterized in that, The method further includes: During actual discharge, the displayed battery level is recorded at the moment when a single battery cell malfunction occurs. The error power value is calculated in real time based on the displayed power value and the estimated actual power value at the current moment. Based on the error power value, the rate of change of the displayed power value is adjusted to make it closer to the actual power estimate.

6. The power battery SOC estimation method based on single cell voltage according to claim 5, characterized in that, The adjustment of the rate of change of the displayed battery value includes: reducing the displayed battery value by a preset offset value each time it is acquired.

7. The power battery SOC estimation method based on single cell voltage according to claim 6, characterized in that, The step of reducing the displayed battery value by a preset offset value each time it is obtained specifically includes: when the displayed battery value is corrected to the target displayed battery value, the displayed battery value is reduced by a preset offset value each time the actual battery estimated value decreases by a preset battery gradient, until the erroneous battery value is eliminated.

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