Power battery SOC estimation correction method

Abstract

The invention belongs to the technical field of batteries, and relates to a power battery SOC estimation correction method. Comprising the following steps: constructing a battery second-order RC equivalent model according to power battery characteristics, and obtaining an SOC-OCV curve of the model; electrifying the model, and obtaining a reference SOC value; detecting parameters of the model, if the detection fails, performing power failure processing on the model, and otherwise, obtaining a model output voltage value VBATT and a corresponding SOC value; calculating a feedback factor of the model, and updating values of VBATT and # imgabs0 # according to the feedback factor; performing current integration according to the updated # imgabs 1 # value; correcting the charging / discharging end-stage data according to the current integration result; according to the method, the feedback factor is introduced to update the VBATT, the SOC estimation complexity of the power battery is effectively simplified, the estimation precision is improved, the SOC initial value can be further calibrated, and open-loop estimation errors caused by open-circuit voltage can be made up.

Description

Technical Field

[0001] The present invention belongs to the technical field of power batteries, and in particular relates to a method for estimating and correcting the SOC of a power battery. Background Art

[0002] With the development of society, power batteries, as indispensable energy storage devices in modern society, have increasing performance requirements. Accurately estimating the power battery SOC (State-of-Charge) is one of the important prerequisites for ensuring the safe and stable operation of the battery management system. For example, it can help solve safety problems caused by battery overcharging. Since the battery charge cannot be measured directly, the battery SOC is usually estimated, and its unit is usually a percentage.

[0003] At present, the common estimation methods include the ampere-hour integration method, the open circuit voltage method and the data-driven estimation method. The ampere-hour integration method is a simple and widely used SOC estimation method. This method integrates the current in the time dimension during the charging and discharging process to obtain the battery SOC; the open circuit voltage method is used for static measurement, and the SOC is estimated based on the relationship between the battery open circuit voltage and SOC SOC = f (OCV), where OCV is the battery open circuit voltage, and f is a specific function that reflects the mathematical relationship between the battery open circuit voltage and SOC; the data-driven estimation method evaluates the battery SOC based on data collection, analysis and interpretation. Common methods include fuzzy logic, support vector machines, neural networks, etc., which usually require the use of mathematical models and computer algorithms.

[0004] The above SOC estimation methods have the following problems: the ampere-hour integration method lacks feedback correction capability, has large errors at high temperatures and when current fluctuates violently, and will cause cumulative errors due to inaccurate current testing; the open circuit voltage method has a long test time, cannot obtain dynamic data, and its accuracy is difficult to guarantee due to internal impedance, battery aging, etc.; the data-driven method usually works better, but the implementation principle is complex, the calculation complexity is high in actual application, a lot of training is required, and it needs to be updated in time as the battery ages. Therefore, a battery SOC estimation method with high accuracy and low complexity is urgently needed. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a power battery SOC estimation and correction method, which combines the ampere-hour integration method and the open circuit voltage method, introduces a feedback mechanism, and can accurately estimate the battery SOC value on the basis of easy implementation and has a wide range of applications. The method proposed by the present invention includes:

[0006] S1. Construct a second-order RC equivalent model of the battery according to the characteristics of the power battery, and obtain the SOC-OCV curve of the second-order RC equivalent model of the battery;

[0007] S2. Power on the battery second-order RC equivalent model and obtain the reference SOC value SOC 初始 ;

[0008] S3, obtaining parameters of the second-order RC equivalent model of the battery, and testing the parameters of the second-order RC equivalent model of the battery. If the test passes, execute step S4, otherwise, power off the model;

[0009] S4. Obtain the output voltage value V of the battery second-order RC equivalent model BATT ;

[0010] S5. Obtain the output voltage value V according to the SOC-OCV curve BATT Corresponding SOC value

[0011] S6, set threshold K1; according to and the reference SOC value SOC 初始 Calculate the K factor value of the model; compare the K factor value with the set threshold K1. If the K factor value is less than the threshold, execute step S7; otherwise, according to the current V BATT V vs. K factor value BATT The value is updated and returns to step S5;

[0012] S7. Get current value, according to the current Value for SOC 初始 The value is updated and the updated SOC 初始 The value is used to integrate the current;

[0013] S8, correcting the battery charge / discharge final data according to the current integration result;

[0014] The beneficial effects of the present invention are:

[0015] The present invention introduces factor K and compares K with the set threshold K1 to further calibrate SOC 初始 , thereby achieving the effect of quickly providing a more accurate SOC initial value for current integration and improving estimation accuracy; the present invention introduces a correction mechanism for charge / discharge terminal correction to compensate for the open-loop estimation error caused by open-circuit voltage; compared with conventional SOC estimation methods, the estimation method provided by the present invention has the advantages of easy implementation and maintenance, higher calculation accuracy, and a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the calculation method of the present invention;

[0017] Figure 2 Battery second-order RC equivalent circuit model. DETAILED DESCRIPTION

[0018] The following will be combined with the accompanying drawings of the embodiments of the present invention to clearly and completely describe the calculation method in the embodiments of the present invention. Obviously, the embodiments mentioned are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0019] The second-order RC equivalent model of the battery mentioned in this embodiment is as follows Figure 2 As shown in the figure, the second-order RC equivalent circuit model of the battery is used to approximately describe the behavior of the actual circuit. The model consists of two RC networks and an internal resistor R series Specifically, OCV represents the open circuit voltage of the battery; V BATT Represents the equivalent model output voltage, and defines V BATT as follows:

[0020] V BATT =OCV-V series -V transient_S -V transient_L ;

[0021] Among them, V series Indicates internal resistance R series Voltage across the terminals; R transient_S and C transient_S Respectively represent electrochemical polarization resistance and capacitance; V transient_S Represents the voltage across the electrochemical polarization resistor; R transient_L and C transient_L Respectively represent the concentration polarization resistance and capacitance of the battery; V transient_L Represents the voltage across the concentration polarization resistor of the battery.

[0022] The specific operations of this embodiment include the following steps:

[0023] S1. Construct a second-order RC equivalent model of the battery according to the characteristics of the power battery, and obtain the SOC-OCV curve of the second-order RC equivalent model of the battery.

[0024] S2. Power on the battery second-order RC equivalent model and obtain the reference SOC value SOC 初始 ;

[0025] Specifically, the reference SOC value SOC is obtained. 初始 , including: obtaining the open circuit voltage OCV value after power-on, and obtaining the SOC value corresponding to the OCV value through the SOC-OCV curve; obtaining the SOC value recorded at the end of the last battery use; checking the static time after the last use of the battery, if the time is greater than the voltage stable static time of this type of battery, select the SOC value calibrated according to the OCV value as the SOC 初始If not, the SOC value recorded at the end of the last battery use is used as the SOC 初始 .

[0026] S3, obtaining parameters of the second-order RC equivalent model of the battery, and testing the parameters of the second-order RC equivalent model of the battery. If the test passes, execute step S4, otherwise, power off the model;

[0027] Specifically, the detection is used to determine whether the circuit is in a safe state. If all parameters are safe, the detection passes.

[0028] S4. Obtain the output voltage value V of the battery second-order RC equivalent model BATT .

[0029] S5. Obtain the output voltage value V according to the SOC-OCV curve BATT Corresponding SOC value

[0030] Specifically, when the open circuit voltage is V BATT , the SOC value corresponding to its horizontal axis in the SOC-OCV curve.

[0031] S6, set threshold K1; according to and the reference SOC value SOC 初始 Calculate the K factor value of the model; compare the K factor value with the set threshold K1. If the K factor value is less than the threshold, execute step S7; otherwise, according to the current V BATT V vs. K factor value BATT The value is updated and returns to step S5;

[0032] Specifically, when the battery is discharged, due to V BATT is less than OCV, so When the battery is charging, V BATT is greater than OCV, so Preferably, κ is the value of factor K, and the formula used to calculate the K factor is:

[0033]

[0034] Furthermore, the size of K1 is determined by the calculation accuracy, and the relationship between K1 and SOC is:

[0035] K1=|SOC 真实 -SOC 测量 | / SOC 真实 *100%

[0036] Among them, SOC 真实 is the actual initial SOC value, SOC 测量is the measured value of SOC, where SOC 测量 SOC 初始 ; Due to SOC 真实 It cannot be obtained, so the value of K1 can only be proposed. Usually, K1 < 1%, so the value of K1 is generally selected as 1%;

[0037] Preferably, according to the current V BATT Update V with K factor value BATT The formula used is:

[0038] V BATT，new =f(κ,V BATT )=V BATT *(1+κ)

[0039] Among them, V BATT，new After updating V BATT The value of .

[0040] S7. Get current value, according to the current Value for SOC 初始 The value is updated and the updated SOC 初始 The value is used to integrate the current;

[0041] Specifically, get the current The value of SOC 初始 The value of is updated to this value, recorded as SOC 初始，更新 , the formula used for current integration is:

[0042]

[0043] Where η is the integral error; Q 满 is the amount of electricity that the battery was fully charged the last time; i(t) is the current at time t; when the current is integrated, the discharge process is positive and the charging process is negative; further, the integral error η is mainly determined by the accuracy of the integral method. Due to the different sampling times and offset errors of different experimental equipment, the calculation method and value of η in specific applications are also different; this embodiment uses the rectangular integral method as an example to illustrate η: in the rectangular integral method, the current on each integral minimum time unit is assumed to be a constant, while the actual current is usually variable, and the resulting error is related to the current change rate. At this time, η can be expressed as:

[0044] η=ξ i / C batt

[0045] Among them, ξ i is the standard deviation of the current; C batt is the battery capacity; the standard deviation of the current ξ i It can be calculated by the following formula:

[0046]

[0047] Where N is the number of measurements, I n is the current value measured at the nth time, is the average value of all measured currents.

[0048] S8, correcting the battery charge / discharge final data according to the current integration result;

[0049] Specifically, the SOC, temperature, current time, and SOC change are obtained and recorded; since SOC is not as sensitive to changes in OCV as in the middle of charge / discharge in the final stage of charge / discharge, multiple (3 to 10 times) corrections in the final stage will not cause a significant shift in the SOC data; the SOC value in the current integration result is used to update the data points at the end of charge / discharge in the SOC-OCV image.

[0050] Furthermore, by calculating the SOC estimation variance ξ S 2 Evaluate the effect of this correction and calculate the SOC estimation variance ξ S 2 To the formula:

[0051] ξ S 2 =η*Δ*ρ I *(η c *n c +η d *n d )*C batt 2 / 3600 2

[0052] Where Δ is the current sampling interval, ρ I is the ratio of the integral error coefficient to the standard deviation of the load current and the battery capacity, η c With η d are the efficiency of charge and discharge, n c With n d are the number of samples for charging and discharging, respectively, C batt is the battery capacity; in the results of multiple corrections to the final charge / discharge data, ξ S 2 A smaller value indicates that the correction is more effective.

[0053] The present invention combines the ampere-hour integration method with the open-circuit voltage method, introduces a feedback factor, and iteratively corrects the initial SOC value, so that the result of current integration is more accurate and avoids the static measurement defects of the open-circuit voltage method; by introducing a correction mechanism for charge / discharge terminal correction, the open-loop estimation error caused by the open-circuit voltage is compensated, thereby improving the accuracy of the correction of the power battery charge / discharge terminal data.

[0054] The above only describes one embodiment of the present invention. Those skilled in the art can conceive of various changes, modifications, substitutions and deformations of these embodiments without departing from the principle and spirit of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents, and the above-mentioned actions should be covered within the scope of protection of the present invention.

Claims

1. A power battery SOC estimation and correction method, characterized in that: include: S1. Construct a second-order RC equivalent model of the battery according to the characteristics of the power battery, and obtain the SOC-OCV curve of the second-order RC equivalent model of the battery; S2. Power on the battery second-order RC equivalent model to obtain the reference SOC value SOC 初始 ; S3, obtaining parameters of the second-order RC equivalent model of the battery, and testing the parameters of the second-order RC equivalent model of the battery. If the test passes, execute step S4, otherwise, power off the model; S4. Obtain the output voltage value V of the battery second-order RC equivalent model BATT ; S5. Obtain the output voltage value V according to the SOC-OCV curve BATT Corresponding SOC value S6, set threshold K1; according to and the reference SOC value SOC 初始 Calculate the K factor value of the model; compare the K factor value with the set threshold K1. If the K factor value is less than the threshold, execute step S7; otherwise, according to the current V BATT K factor value vs. V BATT The value is updated and returns to step S5; S7. Get current value, according to the current Value for SOC 初始 The value is updated and the updated SOC 初始 The value is used to integrate the current; S8. Correct the battery charging / discharging final data according to the current integration result.

2. A power battery SOC estimation and correction method according to claim 1, characterized in that: Obtaining the benchmark SOC value includes: obtaining the SOC value recorded at the end of the last test and the SOC value calibrated by the open circuit voltage; comparing the battery rest time with the battery stable rest time, and selecting the benchmark SOC value SOC 初始 .

3. A power battery SOC estimation and correction method as claimed in claim 1, characterized in that The K factor value of the calculation model is: Among them, κ is the value of factor K, SOC 初始 is the benchmark SOC value.

4. The K factor threshold value K1 according to claim 1, characterized in that: The relationship between threshold K1 and battery SOC is: K1=|SOC 真实 -SOC 测量 | / SOC 真实 *100% Among them, SOC 真实 is the actual initial SOC value, SOC 测量 is the measured value of SOC.

5. A power battery SOC estimation and correction method as claimed in claim 4, characterized in that: The optimal value of the K factor threshold K1 is 0.

01.

6. A power battery SOC estimation and correction method as claimed in claim 1, characterized in that: V BATT The value is updated to: V BATT，new =f(κ,V BATT )=V BATT *(1+k) Where f is the value of the relationship between κ and V BATT function, κ is the value of factor K.

7. A power battery SOC estimation and correction method according to claim 1, characterized in that: About SOC 初始 The value is updated by: The value is used as the updated SOC 初始 value, and record the updated SOC after the update 初始 For SOC 初始，更新 .

8. A power battery SOC estimation and correction method as claimed in claim 1, characterized in that: The formula for current integration is: Among them, SOC 初始，更新 For the updated SOC 初始 The value of Q 满 is the amount of electricity the battery was fully charged last time, η is the integral error, and i(t) is the current at time t.

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