Lithium battery SOC (State of Charge) estimation method and calibration device based on dynamic voltage

Abstract

The invention relates to the field of battery SOC estimation, and discloses a lithium battery SOC estimation method based on dynamic voltage, which is applied to low-end SOC estimation, and comprises the following steps of: calculating a dynamic voltage value according to polarization voltage change generated along with temperature change and current change of a lithium battery calibrated by a discharge OCV curve to obtain a dynamic discharge voltage-SOC curve table; therefore, SOC estimation is carried out according to the currently acquired cell voltage value. The invention also discloses a lithium battery SOC calibration device which comprises a cell monitoring and signal acquisition part for monitoring the voltage, current and temperature of the cell and a processor, and when the SOC is lower than a certain threshold value, the processor adopts the lithium battery SOC estimation method based on the dynamic voltage to correct and calibrate the low-end SOC estimated value of the lithium battery. When iteration continuous judgment is corrected, errors can be effectively avoided, SOC correction is more accurate and reliable, and a guarantee is provided for safe and stable operation of the battery cell.

Description

Technical Field

[0001] The present invention relates to the field of battery SOC estimation, and in particular to a lithium battery SOC estimation method and calibration device based on dynamic voltage. Background Art

[0002] Lithium batteries have been widely used in electric vehicles and energy storage industries due to their relatively stable charge and discharge characteristics and low self-discharge rate. In battery management systems, accurate estimation of battery SOC (State of Charge) is crucial to improving the efficiency and safety of battery management systems. Accurate SOC estimation can prevent overcharging or over-discharging of batteries, extend battery life, and thus improve customer experience.

[0003] Generally, there are several methods for estimating SOC (battery health state):

[0004] 1. Full charge estimation: when certain temperature conditions are met, if the battery voltage is greater than a certain threshold and the current is less than a certain threshold for a certain period of time, the SOC is calibrated to 100% or other calibration values.

[0005] 2. Use the voltage rebound characteristic to quickly calibrate SOC. When the battery cell is charged and discharged at a certain rate, the current steady-state voltage value of the battery cell is quickly calculated through the standing time after the charge and discharge voltage and the rebound voltage value, and then the steady-state voltage value is obtained through the OCV-SOC relationship.

[0006] 3. Small slope estimation: when the battery cell is in a small current constant current charging condition, the dV / dQ value is calculated in real time, the peak point of dV / dQ is captured, and the SOC is corrected to the calibrated value.

[0007] 4. Low-end SOC estimation: When the battery cell is in a static state, the SOC value is obtained by looking up the OCV-SOC voltage table through the current voltage. If the SOC is lower than a certain threshold, it is considered that the SOC obtained by looking up the table is more accurate, and the SOC is corrected to the table SOC value.

[0008] For low-end SOC estimation, it is usually considered that the absolute value of the current is less than a certain threshold (0.05C) and lasts for a period of time (two hours). At this time, the battery cell is considered to be in a static state and the voltage conforms to the OCV-SOC curve distribution. However, since the OCV-SOC curve of the lithium iron phosphate battery has a long voltage platform area, the voltage change in the voltage platform area is small. Therefore, if the table is directly corrected, there will be a large SOC error.

[0009] The current low-end SOC estimation regards the working condition where the current is less than a certain threshold and lasts for a long time as the static working condition of the battery cell. At this time, the correction method generally uses the OCV table to look up the current battery cell sample voltage value to obtain the current SOC value and determine whether its SOC is lower than a certain threshold. However, if the lithium iron phosphate battery cell is used for a low-voltage power supply. In the actual application scenario of the low-voltage power supply, there is often a period of long-term discharge with a small current (generally the current value is 0.05C and below). During this process, the battery cell has a certain concentration polarization voltage, which will gradually accumulate over time, and eventually cause the actual discharge voltage of the battery cell to deviate from the OCV-SOC curve. At this time, if the OCV-SOC curve table is directly checked, there will be a large SOC correction error. If the SOC correction is inaccurate, it will cause the battery management system to incorrectly estimate the current state of charge of the battery cell. In severe cases, it may cause an over-discharge accident of the battery cell, posing a certain threat to the safe operation of the battery cell. Summary of the invention

[0010] The technical problem to be solved by the present invention is to provide a lithium battery SOC estimation method and calibration device based on dynamic voltage, so as to solve the current technical problem of inaccurate low-end SOC estimation.

[0011] Technical Solution

[0012] The lithium battery SOC estimation method based on dynamic voltage is characterized in that it is applied to low-end SOC estimation, and the polarization voltage changes of the lithium battery calibrated by the discharge OCV curve caused by the temperature change and the current change are calculated to calculate the dynamic voltage factor and obtain the dynamic discharge voltage-SOC curve table, so as to perform SOC estimation according to the currently collected battery cell voltage value.

[0013] The specific steps include:

[0014] Step 1, calculating the dynamic capacity factor at different temperatures, different current values ​​and different SOC intervals, and calibrating the dynamic capacity factor table according to different voltage intervals measured by experiments; the dynamic capacity factor is the polarization voltage change caused by the temperature change and current size change in different SOC intervals;

[0015] Step 2: The battery cell continuously monitors and determines the current and voltage during operation. When it is determined that a low-current discharge process has begun, the current temperature value is collected, and the cumulative capacity difference of different SOC intervals based on a certain time interval is calculated according to the dynamic capacity factor of different SOC intervals, and the total cumulative capacity value is calculated by continuous iteration and update;

[0016] Step 3, using the ratio of the dynamically updated cumulative capacity value of different SOC intervals to the set discharge capacity constant value to calculate the dynamic voltage factor of different SOC intervals, after calculating the dynamic voltage factor of different SOC intervals, the dynamic voltage value of different SOC intervals can be calculated to obtain a dynamic discharge voltage-SOC curve table;

[0017] Step 4: Correct the SOC estimate based on the currently collected cell voltage value.

[0018] In step 1, the calculation of the dynamic capacity factor adopts the following method steps:

[0019] 1) Calibration of discharge OCV curves at different temperatures, drawing discharge OCV curves at different temperature points within the temperature range;

[0020] 2) Calibration of discharge voltage curves at different temperatures and currents. By selecting different constant small currents to discharge from SOC 100 to 0, a discharge voltage curve table at different temperatures and different constant small currents is obtained and recorded. A discharge voltage point is recorded for each 1% SOC change, and a complete discharge voltage curve under different conditions is drawn;

[0021] 3) Set the upper limit threshold of the low-end SOC, and divide the SOC less than or equal to the upper limit threshold into multiple intervals, and calculate the dynamic capacity factor α of different temperatures, different current values ​​and different SOC intervals according to the previous calibration data cap .

[0022] The different temperatures are selected from a plurality of different temperatures between 15° C. and 45° C., and the different currents are selected from a plurality of different constant small currents.

[0023] The temperatures are selected as 15° C., 25° C., and 45° C., respectively, and the currents are selected as 100 mA, 300 mA, and 500 mA.

[0024] The different SOC intervals are divided into three SOC intervals ([0, 10], (10, 20), (20, 30]) to calibrate and calculate the value of the dynamic capacity factor respectively.

[0025] In step 2, the cumulative capacity difference is calculated using the following formula:

[0026] Delta cap(m-n) = Deltat*I*α cap(T1℃-I-m-n) ,

[0027] Among them, Deltat is the interval time, mn is the SOC interval, m is the interval low value, n is the interval high value, T1 is the current temperature, I is the current value, α cap(T1℃-I-m-n ) is the dynamic capacity factor when the temperature is T1, the current is I, and the SOC range is mn.

[0028] The cumulative capacity value is the discharge capacity value at the last moment plus the cumulative capacity difference.

[0029] In step 3, the calculation formula of the dynamic voltage factor is as follows:

[0030]

[0031] Among them, the numerator is the cumulative capacity value calculated when the SOC is in the [m, n] interval, which is continuously updated during the discharge process. The denominator is the discharge capacity value calculated by discharging at 25℃-500mA for 2 hours, which is a constant of 1Ah. The dynamic voltage factor range is [0, 1], which is characterized by that when the duration of 500mA low current discharge exceeds 2h, its discharge voltage tends to be stable, and the influence of concentration polarization gradually decreases with time and is considered to be negligible. Therefore, if the calculated cumulative capacity value is greater than or equal to the discharge capacity value calculated by discharging at 25℃-500mA for 2h, its dynamic voltage factor no longer changes, and the upper limit is constant at 1.

[0032] In step 3, the calculation formula of the dynamic voltage value is as follows, when the current temperature is T2°C and the SOC is in the interval [m, n]:

[0033] V T2-m-n =α vol(m-n) *V dischar-T2-500m4-m-n +(1-α volt(m-n) )*OCV T2-m-n ,

[0034] Among them, V T2-m-n is the dynamic voltage curve calculated for T2℃, α vol(m-n) is the discharge voltage factor when SOC is mn, V dischar-T2-500mA-m-n It represents the discharge curve at T2℃, 500mA constant small current and SOC mn, OCV T2-m-n It is the discharge OCV curve when the SOC is mn at T2℃.

[0035] In the step four, the currently collected battery cell voltage value adopts: real-time collection of the battery cell voltage value at the current temperature, collection of the battery cell voltage sampling values ​​of the first x points, taking the maximum and minimum values ​​of the x battery cell voltage sampling points, and judging that the deviation between the maximum and minimum values ​​does not exceed the set threshold value, confirming that the current battery cell voltage sampling is relatively stable, and taking the average value of the first x battery cell voltage sampling points as the battery cell voltage value at the current moment.

[0036] A lithium battery SOC calibration device, characterized in that it includes a battery cell monitoring and signal acquisition component to monitor the battery cell voltage, current and temperature, and a processor, wherein the processor uses the method as claimed in claim 1 to correct and calibrate the low-end SOC estimation of the lithium battery.

[0037] Beneficial Effects

[0038] First, the present invention proposes an innovative estimation and calibration method, abandoning the original static voltage table correction strategy and adopting an adaptive dynamic voltage calculation strategy for SOC correction and calibration. This method has higher accuracy and can cover a wider range of actual discharge conditions.

[0039] Secondly, the present invention proposes a dynamic capacity factor or a dynamic voltage factor, which greatly saves the storage space of the chip through preliminary experimental calibration and averaging within a certain range. It does not use complex algorithms such as neural networks and is more suitable for embedded algorithm application scenarios.

[0040] Moreover, the algorithm proposed in the present invention is based on the extended design of electrochemical theories such as concentration polarization of lithium iron phosphate batteries, and has certain generalizability and can be applied to other types of batteries such as ternary batteries.

[0041] The method for correcting the error of low-end SOC based on the dynamic capacity factor calibrated based on the discharge OCV curve proposed in the present invention can effectively avoid corrections with larger errors during continuous judgment of correction iterations, making the SOC correction more accurate and reliable, thereby providing guarantee for the safe and stable operation of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the discharge OCV at a specific temperature and the discharge voltage curve under different discharge currents;

[0043] Figure 2 A schematic diagram of a multi-interval dynamic discharge voltage-SOC curve table architecture at T°C;

[0044] Figure 3 The figure is a flow chart for SOC correction and calibration at low-end SOC. When the current is less than or equal to 500mA for two hours, the first trigger condition is met, and the cumulative capacity values ​​of different SOC intervals are recorded, the dynamic voltage is calculated, and the SOC correction is performed. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with specific embodiments and drawings.

[0046] In order to solve the technical problem of inaccurate low-end SOC estimation, the present invention proposes a lithium battery SOC estimation method based on dynamic voltage, which is applied to low-end SOC estimation. The polarization voltage changes of the lithium battery calibrated by the discharge OCV curve with temperature changes and current changes are used to calculate the dynamic voltage value and obtain a dynamic discharge voltage curve table, so as to perform SOC estimation based on the currently collected battery cell voltage value.

[0047] The specific steps include:

[0048] Step 1, calculating the dynamic capacity factor at different temperatures, different current values ​​and different SOC intervals, and calibrating the dynamic capacity factor table according to different voltage intervals measured by experiments; the dynamic capacity factor is the polarization voltage change caused by the temperature change and current size change in different SOC intervals;

[0049] Step 2: The battery cell continuously monitors and determines the current and voltage during operation. When it is determined that a low-current discharge process has begun, the current temperature value is collected, and the cumulative capacity difference of different SOC intervals based on a certain time interval is calculated according to the dynamic capacity factor of different SOC intervals, and the total cumulative capacity value is calculated by continuous iteration and update;

[0050] Step 3, using the ratio of the dynamically updated cumulative capacity value of different SOC intervals to the set discharge capacity constant value to calculate the dynamic voltage factor of different SOC intervals, after calculating the dynamic voltage factor of different SOC intervals, the dynamic voltage value of different SOC intervals can be calculated to obtain a dynamic discharge voltage curve table;

[0051] Step 4: Correct the SOC estimate based on the currently collected cell voltage value.

[0052] According to the actual scenario analysis, when the battery cell is in the low-end discharge state, it usually undergoes a long period of high-current discharge process, so OCV only considers the discharge OCV curve at this time (the charging OCV curve is not taken into consideration). If the discharge process is completed, it enters the pre-charge state. Generally, the charging current value is greater than 4A, and the low-end discharge correction judgment will be exited at this time. Therefore, if the SOC is lower than the set threshold (usually the SOC lower limit value of the voltage platform area), the method of the present invention is used to correct the SOC.

[0053] 1. The dynamic capacity factor needs to be calculated. The calculation of the dynamic capacity factor adopts the following method and steps, taking the temperature of 15°C-45°C, the current of 100mA-500mA, and the SOC taking the lower limit value of 30 in the voltage platform area as an example.

[0054] First, calibrate the discharge OCV curve at different temperatures (15℃-45℃):

[0055] The cell temperature was adjusted to 25°C, and after charging to 3.65V at 1C constant current, the 3.65V constant voltage was reduced to 0.05C and left to stand for 1 hour, at which time the SOC was considered to have reached 100. The cell was then adjusted to different temperatures (15°C, 25°C, 45°C), left to stand for three hours, and after the temperature inside and outside the cell was evenly distributed, the discharge OCV at the current voltage point of 100SOC was recorded, and then 1C was discharged to 5% SOC, left to stand for three hours, and the discharge OCV at the current voltage point of 95SOC was recorded. By analogy, the discharge OCV values ​​of a total of 21 points from 0-100SOC were calibrated, and the discharge OCV curves of the three temperature points were drawn using the same method.

[0056] Then the discharge voltage curves at different temperatures (15℃-45℃) and different currents (100mA, 300mA, 500mA) are calibrated:

[0057] The cell temperature was adjusted to 25°C, and after charging to 3.65V at 1C constant current, the 3.65V constant voltage was used to drop the current to 0.05C and let it stand for 1 hour. At this time, the SOC was considered to reach 100. The cell was then adjusted to different temperatures (15°C, 25°C, 45°C), left to stand for three hours, and discharged to 0SOC at different constant small currents (100mA, 300mA, 500mA). The discharge voltage curves of different temperatures and different constant small currents were obtained and recorded. A discharge voltage point was recorded for every 1% change in SOC, and a complete discharge voltage curve under different conditions was drawn.

[0058] Finally, the dynamic capacity factor is calibrated and calculated:

[0059] The upper limit threshold of the corrected SOC is set to 30SOC (if the current voltage is less than or equal to 30 when the dynamic voltage table is checked), it is considered that if the SOC is greater than 30, the current battery cell is in the voltage platform area. If the SOC table is used, the correction error is large. At the same time, 30SOC is subdivided into three intervals [0,10], (10,20), (20,30). The dynamic capacity factor α at different temperatures (15℃, 25℃, 45℃) and different constant small currents (100mA, 300mA, 500mA) is calibrated. cap .

[0060] Taking the 15℃ 100mA constant low current discharge curve as an example, it is divided into three SOC intervals ([0,10], (10,20), (20,30]) and calibrated α respectively. cap value.

[0061] If the SOC is in the range of [0-10], then

[0062]

[0063] If the SOC is in the range of (10-20), then

[0064]

[0065] If the SOC is in the range of (20-30], then

[0066]

[0067] Among them, α cap(15℃-100mA-0-10) It indicates the value of the dynamic capacity factor when the temperature is 15°C, the current is 100mA, and the SOC is in the range of [0-10]. Indicates that the temperature is 15°C, the current is 100mA, and different SOC values ​​(each SOC i The discharge voltage at Indicates the temperature is 25℃, different SOC values ​​(each SOC i The open circuit voltage OCV value when the value is 0, and the other values ​​are expressed by analogy.

[0068] The above calculation is to obtain the dynamic capacity factor at 15 degrees and 100mA, and SOC in different SOC ranges ([0,10], (10,20), (20,30]) by taking the average value. The discharge curves of other temperatures and different small currents are calculated in the same way as above. Here, the average value of the dynamic capacity factor is used for calibration in different SOC ranges, because the difference in the dynamic capacity factor within a certain SOC range is relatively small and can be approximated as an average value, which can reduce a certain storage space of the processor (MCU).

[0069] The 500mA 25 degree discharge voltage and the 25 degree 0CV discharge voltage are both reference values, that is, the discharge voltage curves at different temperatures and currents are converted to the discharge voltage curve values ​​of 25 degrees 500mA and 25 degrees 0CV.

[0070] By analogy, the dynamic capacity factor of different temperatures, different current values ​​and different SOC ranges can be obtained, and the dynamic capacity factor table can be calibrated according to the different voltage ranges measured experimentally.

[0071] 2. Cumulative capacity calibration

[0072] During operation, the battery cell continuously monitors the current and voltage. When the temperature is in the range of [15°C-45°C] and the discharge current I is less than or equal to 500mA, it is considered that the low-current discharge process begins. The current temperature value T1°C is collected and the cumulative capacity difference of different SOC intervals ([0, 10], (10, 20), (20, 30]) of this program scheduling interval (Delta-t) is converted according to the following conversion formula. When the temperature is T1°C and the current value is IA, when the SOC is in the range of [0, 10],

[0073] Deltacap(0-10) = Deltat*I*α cap(T1℃-I-0-10) ;

[0074] When SOC is in the interval (10, 20),

[0075] Delta cap(10-20) = Deltat*I*α cap(T1℃-I-10-20) ;

[0076] When SOC is in the (20, 30] interval,

[0077] Delta cap(20-30) = Deltat*I*α cap(T1℃-I-20-30) .

[0078] Among them, Delta cap(10-20) is the cumulative capacity difference when the SOC is in the (10, 20) interval.

[0079] After calculating the cumulative capacity difference of this scheduling interval, the total cumulative capacity value is calculated by continuous iteration and updating. When the SOC is in the interval [0, 10], as shown in the following formula:

[0080] Cap vpdate(0-10) =Cap LastTime(0-10) +Delta cap(0-10) ;

[0081] Among them, Cap update(0-10) Cap is the cumulative capacity value of continuous iteration (SOC range is 0-10), LastTime(0-10) is the cumulative capacity value at the previous moment, Delta cap(0-10) is the cumulative capacity difference when the SOC is in the (0, 10) interval.

[0082] Taking this as an example, the cumulative capacity values ​​of different SOC intervals ([0, 10], (10, 20), (20, 30]) are continuously updated. When the current is less than or equal to 500mA for two hours, the first trigger condition is met, and the cumulative capacity values ​​of different SOC intervals are recorded at the same time. If the discharge current is greater than 500mA or the temperature exceeds the range of [15°C, 45°C] or there is a charging current greater than 4A for 1 minute (at this time, the battery cell is considered to be in a charging state and there is no small current discharge scenario), it is considered that the current scenario does not meet the small current discharge correction condition, then the small current discharge correction judgment is exited, and the cumulative capacity values ​​of different SOC intervals are cleared.

[0083] 3. Dynamic Voltage Factor Calculation

[0084] When the first trigger condition is met, the dynamic voltage factor of different SOC intervals is calculated using the cumulative capacity values ​​of different SOC intervals. Taking the SOC in the [0, 10] interval as an example, the dynamic factor calculation formula is:

[0085]

[0086] The numerator is the cumulative capacity value calculated when the SOC is in the [0, 10] interval, which is continuously updated during the discharge process. The denominator is the discharge capacity value calculated when the discharge is 25°C and 500mA for 2h, which is a constant value of 1Ah. The dynamic voltage factor range is [0, 1], which indicates that when the 500mA low current discharge lasts for more than 2h, its discharge voltage tends to be stable, and the influence of concentration polarization gradually decreases with time and is considered to be negligible. Therefore, if the calculated cumulative capacity value is greater than or equal to the discharge capacity value calculated when the discharge is 25°C and 500mA for 2h, its dynamic voltage factor will no longer change, and the upper limit will be constant at 1.

[0087] After calculating the dynamic voltage factors of different SOC intervals ([0, 10], (10, 20), (20, 30]), we can calculate the dynamic voltage values ​​of different SOC intervals. Assuming that the current temperature is T2°C, when the SOC is in the [0, 10] interval,

[0088] V T2-0-10 =α vol(0-10) *V dischar-T2-500mA-0-10 +(1-α volt0-10) )*OCV T2-0-10 ;

[0089] Where V T2-0-10 is the dynamic voltage curve calculated for T2℃, α volt(0-10) Expressed as the discharge voltage factor for SOC 0-10. V dischar-T2-500mA-0-10 It means the discharge curve of 500mA constant current at SOC 0-10 at T2℃, OCV T2-0-10 It shows the discharge OCV curve when SOC is 0-10 at T2℃.

[0090] Similarly, when SOC is in the interval (10, 20),

[0091] V T2-10-20 =α volt(10-20) *V dischar-T2-500mA-10-20 +(1-α volt(10-20) )*OCV T2-10-20 ;

[0092] When SOC is in the (20, 30] interval,

[0093] V T2-20-30 =α volt20-30) *Vdischar-T2-500mA-20-30 +(1-α volt(20-30 )*OCV T2-20-30 .

[0094] When the first trigger condition is met, the dynamic discharge voltage curve table under the current state is calculated. Since correction is only made when the SOC is less than or equal to 30, only the discharge voltage curve below 30 is recorded to save memory space. After calculating the discharge voltage curve, the corresponding SOC correction is made according to the currently collected battery cell voltage value.

[0095] 4. SOC correction determination

[0096] Collect the cell voltage value at the current temperature T2℃ in real time to avoid abnormal fluctuations in hardware sampling, which may cause inaccurate cell voltage sampling and large correction value errors. Collect the cell voltage sampling values ​​of the first 10 points, take the maximum and minimum values ​​of the ten cell voltage sampling points, if the deviation between the maximum and minimum values ​​exceeds 10mV, it is considered that the hardware cell sampling has abnormal fluctuations at this time, and the current cell voltage lookup value is not used. If the deviation between the maximum and minimum values ​​of the ten cell sampling points is less than 10mV, it is considered that the current cell voltage sampling is relatively stable. Take the average value of the first ten cell voltage sampling points as the cell voltage value at the current moment.

[0097] Compare the filtered cell voltage value with the currently calculated dynamic discharge voltage-SOC curve. Since the dynamic voltage factors in different SOC ([0,10], (10,20), (20,30]) intervals are different, the final calculated dynamic discharge voltage table is not continuous and needs to be considered in segments. Figure 2 Schematic diagram of the dynamic discharge voltage-SOC curve table architecture for multiple intervals (three intervals) at T℃.

[0098] If the current filtered cell voltage is less than V T2-0-10 If the lower limit is reached, the SOC is corrected to 0;

[0099] If the current filtered cell voltage is greater than or equal to V T2-0-10 The lower limit value is less than or equal to V T2-0-10 If the upper limit value is reached, the SOC is corrected to the corresponding value of the cell voltage after filtering.

[0100] If the current filtered cell voltage is greater than V T2-0-10 The upper limit value is also less than V T2-10-20 If the lower limit is reached, the SOC is corrected to 10.

[0101] If the current filtered cell voltage is greater than or equal to V T2-10-20 The lower limit value is less than or equal to V T2-10-20 If the upper limit value is reached, the SOC is corrected to the corresponding value of the cell voltage after filtering.

[0102] If the current filtered cell voltage is greater than V T2-10-20 The upper limit value is also less than V T2-20-30 If the lower limit is reached, the SOC is corrected to 20.

[0103] If the current filtered cell voltage is greater than or equal to V T2-20-30 The lower limit value is less than or equal to V T2-20-30 If the upper limit value is reached, the SOC is corrected to the corresponding value of the cell voltage after filtering.

[0104] If the current filtered cell voltage is greater than V T2-20-30 If the upper limit value is reached, it is considered that the current SOC is in the lithium iron phosphate voltage platform area and no SOC correction is performed.

[0105] If the corrected SOC interval is between [0 10), the current correction error is recorded as Error1;

[0106] If the corrected SOC interval is between [10 15], the current correction error is Error2;

[0107] If the corrected SOC interval is between (15 30], the current correction error is Error3;

[0108] If correction has been made, record the current correction error value.

[0109] Among them, Error2>Error3>Error1.

[0110] The error is determined based on the slope of the discharge curve. If the discharge curve changes greatly with SOC, it is considered that the SOC correction is more accurate. If the discharge curve changes less with SOC, it is considered that the SOC correction value has a larger error.

[0111] This process triggers a correction every two hours. The first correction is made without considering the correction error. The subsequent corrections take into account the current correction error. If the current correction error is less than the correction error recorded last time, this correction is adopted. If the current correction error is greater than or equal to the correction error recorded last time, this correction is not adopted and the next two-hour SOC correction judgment is made.

[0112] If the discharge current is not less than or equal to 500mA or the temperature is [15℃-45℃] during the low-current continuous discharge, it is considered that the current conditions exceed the low-end discharge SOC correction range, the correction error accuracy is reduced, and the low-end discharge correction strategy is not adopted. At this time, the discharge capacity and discharge voltage factors are reset to zero, and the two-hour discharge judgment is repeated. See the attached for the specific process. Figure 3 Indicates.

[0113] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A lithium battery SOC estimation method based on dynamic voltage, characterized in that: Applied to low-end SOC estimation, the polarization voltage changes of lithium batteries caused by temperature and current changes calibrated by the discharge OCV curve are used to calculate the dynamic voltage factor and obtain the dynamic discharge voltage-SOC curve table, so as to estimate the SOC based on the currently collected battery cell voltage value.

2. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 1, characterized in that: The specific steps include: Step 1: Calculate the dynamic capacity factor at different temperatures, different current values ​​and different SOC intervals, and calibrate the dynamic capacity factor table according to different voltage intervals measured experimentally; The dynamic capacity factor is the change in polarization voltage caused by the change in temperature and current magnitude in different SOC intervals; Step 2: The battery cell continuously monitors and determines the current and voltage during operation. When it is determined that a low-current discharge process has begun, the current temperature value is collected, and the cumulative capacity difference of different SOC intervals based on a certain time interval is calculated according to the dynamic capacity factor of different SOC intervals, and the total cumulative capacity value is calculated by continuous iteration and update; Step 3, using the ratio of the dynamically updated cumulative capacity value of different SOC intervals to the set discharge capacity constant value to calculate the dynamic voltage factor of different SOC intervals, after calculating the dynamic voltage factor of different SOC intervals, the dynamic voltage value of different SOC intervals can be calculated to obtain a dynamic discharge voltage-SOC curve table; Step 4: Correct the SOC estimate based on the currently collected cell voltage value.

3. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 2, characterized in that: In step 1, the calculation and calibration of the dynamic capacity factor adopts the following method steps: 1) Calibration of discharge OCV curves at different temperatures, drawing discharge OCV curves at different temperature points within the temperature range; 2) Calibration of discharge voltage curves at different temperatures and currents. By selecting different constant small currents to discharge from SOC 100 to 0, a discharge voltage curve table at different temperatures and different constant small currents is obtained and recorded. A discharge voltage point is recorded for each 1% SOC change, and a complete discharge voltage curve under different conditions is drawn; 3) Set the upper limit threshold of the low-end SOC, and divide the SOC less than or equal to the upper limit threshold into multiple intervals, and calculate the dynamic capacity factor α of different temperatures, different current values ​​and different SOC intervals according to the previous calibration data cap .

4. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 3, characterized in that: The different temperatures are selected from a plurality of different temperatures between 15° C. and 45° C., and the different currents are selected from a plurality of different constant small currents.

5. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 4, characterized in that: The temperatures are selected as 15° C., 25° C., and 45° C., respectively, and the currents are selected as 100 mA, 300 mA, and 500 mA.

6. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 3, characterized in that: The different SOC intervals are divided into three SOC intervals ([0, 10], (10, 20), (20, 30]) to calibrate and calculate the value of the dynamic capacity factor respectively.

7. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 2, characterized in that: In step 2, the cumulative capacity difference is calculated using the following formula: Participate cap(m-n) =Delta*I*α cap(T1℃-l-m-n) , Among them, Deltat is the interval time, mn is the SOC interval, m is the interval low value, n is the interval high value, T1 is the current temperature, I is the current value, α cap(T1℃-l-m-n) It is the dynamic capacity factor when the temperature is T1, the current is I, and the SOC range is mn.

8. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 7, characterized in that: The cumulative capacity value is the discharge capacity value at the last moment plus the cumulative capacity difference.

9. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 2, characterized in that: In step 3, the calculation formula of the dynamic voltage factor is as follows: Among them, the numerator is the cumulative capacity value calculated when the SOC is in the [m,n] interval, which is continuously updated during the discharge process. The denominator is the discharge capacity value calculated by discharging at 25℃-500mA for 2 hours, which is a constant of 1Ah. The dynamic voltage factor range is [0,1], which is characterized by that when the duration of 500mA low current discharge exceeds 2h, its discharge voltage tends to be stable, and the influence of concentration polarization gradually decreases with time and is considered to be negligible. Therefore, if the calculated cumulative capacity value is greater than or equal to the discharge capacity value calculated by discharging at 25℃-500mA for 2h, its dynamic voltage factor no longer changes, and the upper limit is constant at 1.

10. The method for estimating lithium battery SOC based on dynamic voltage according to claim 9, characterized in that: In step 3, the calculation formula of the dynamic voltage value is as follows, when the current temperature is T2°C and the SOC is in the interval [m,n]: V T2-m-n = αvolt(m-n) *V dischar-T2-500mA-m-n +(1-α volt(m-n) )*OCV T2-m-n , Among them, V T2-m-n is the dynamic voltage curve calculated for T2℃, α volt(m-n) is the discharge voltage factor in the SOC range of mn, V dischar-T2-500mA-m-n It represents the discharge curve of 500mA constant small current in the SOC range of mn at T2℃, COV T2-m-n It is the discharge OCV curve when the SOC is in the mn range at T2℃.

11. The method for estimating SOC of a lithium battery based on dynamic voltage according to claim 2, characterized in that: In the step four, the currently collected battery cell voltage value adopts: real-time collection of the battery cell voltage value at the current temperature, collection of the battery cell voltage sampling values ​​of the first x points, taking the maximum and minimum values ​​of the x battery cell voltage sampling points, and judging that the deviation between the maximum and minimum values ​​does not exceed the set threshold value, confirming that the current battery cell voltage sampling is relatively stable, and taking the average value of the first x battery cell voltage sampling points as the battery cell voltage value at the current moment.

12. A lithium battery SOC calibration device, characterized in that: The invention comprises a cell monitoring and signal acquisition component for monitoring the cell voltage, current and temperature, and a processor, wherein the processor adopts the method as claimed in claim 1 to correct and calibrate the low-end SOC estimation of the lithium battery.

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