A method for correcting an SOC of a power battery

Abstract

The application belongs to the technical field of batteries, and relates to a power battery SOC estimation correction method; the method comprises 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; powering on the model, and obtaining a reference SOC value; detecting parameters of the model, and if the detection fails, performing power-off processing on the model, otherwise obtaining a model output voltage value V BATT and a corresponding SOC value of the model; calculating a feedback factor of the model, updating values of V BATT and according to the feedback factor; performing current integration according to the updated values; correcting charging / discharging end period data according to a current integration result; the application updates V BATT by introducing a feedback factor, effectively simplifies the SOC estimation complexity of the power battery, improves the estimation accuracy, can further calibrate an initial SOC value, and offsets an open-loop estimation error caused by an open-circuit voltage.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power batteries, and particularly relates to a power battery SOC estimation correction method. BACKGROUND

[0002] With the development of society, as an indispensable energy storage device in modern society, the performance demand of power batteries is increasing. Accurate estimation of the SOC (State-of-Charge) of the power battery is one of the important prerequisites for ensuring the safe and stable operation of the battery management system, which can help solve the safety problem caused by overcharging. Since the battery charge cannot be directly measured, the SOC of the battery is usually obtained by using an estimation method, and the unit is usually percentage.

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

[0004] The above SOC estimation methods have the following problems: the ampere-hour integration method lacks feedback correction ability, has large error at high temperature and severe current fluctuation, and accumulates error due to inaccurate current test; the open-circuit voltage method takes a long time to test and cannot obtain dynamic data, and the precision is difficult to guarantee due to internal impedance, battery aging and other reasons; the data-driven method usually has good effect, but the implementation principle is complex, the calculation complexity is high in actual application, a large amount of training is needed, and timely updating is needed as the battery ages. Therefore, there is an urgent need for a battery SOC estimation method with high precision and low complexity. SUMMARY

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

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

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

[0008] S3, obtain the parameters of the battery second-order RC equivalent model, detect the parameters of the battery second-order RC equivalent model, if the detection is passed, execute step S4, otherwise, perform power-off processing on 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 a 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, update the V BATT value according to the current V BATT and the K factor value, and return to step S5;

[0012] S7, obtain the current value, update the SOC value according to the current 初始 value, and perform current integration on the updated SOC 初始 value;

[0013] S8, correct the charging / discharging end data of the battery according to the current integration result;

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

[0015] The present application introduces a factor K, compares K with a set threshold K1, further calibrates the SOC 初始 , so as to provide a more accurate SOC initial value for current integration, improve the estimation accuracy; the present application introduces a correction mechanism for charging / discharging end correction, which makes up for the open-loop estimation error caused by open circuit voltage; compared with the conventional SOC estimation method, the estimation method provided by the present application has the advantages of easy implementation and maintenance, higher calculation accuracy, and wide application scene range. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 The present application is a calculation method flowchart;

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

[0018] The calculation method in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the mentioned embodiments are only a part of the embodiments of the present application, but not all the embodiments. All other embodiments obtained by a person of ordinary skill in the art without creative work should belong to the scope of protection of the present application.

[0019] The battery second-order RC equivalent model mentioned in the embodiments is shown in Figure 2 The battery second-order RC equivalent circuit model is used to approximately describe the behavior of the actual circuit, and the model is composed of two RC networks and an internal resistance R series ; specifically, OCV represents the open-circuit voltage of the battery; V BATT represents the output voltage of the equivalent model, and V BATT is defined as follows:

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

[0021] wherein V series represents the voltage across the internal resistance R series ; R transient_S and C transient_S represent the electrochemical polarization resistance and capacitance, respectively; V transient_S represents the voltage across the electrochemical polarization resistance; R transient_L and C transient_L represent the concentration polarization resistance and capacitance of the battery, respectively; and V transient_L represents the voltage across the concentration polarization resistance of the battery.

[0022] The specific operation of the embodiments includes the following steps:

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

[0024] S2. Powering on the battery second-order RC equivalent model, and obtaining a reference SOC value SOC 初始 .

[0025] Specifically, obtaining the reference SOC value SOC 初始 includes: obtaining the value of the open-circuit voltage OCV after powering on, and obtaining the corresponding SOC value of the OCV value through the SOC-OCV curve; obtaining the recorded SOC value at the end of the last battery use; checking the standing time after the last battery use, and if the time is greater than the voltage stable standing time of the battery of this type, selecting the SOC value calibrated according to the OCV value as SOC 初始, if not, the SOC value recorded at the end of the last battery use is selected as the SOC 初始 .

[0026] S3, parameters of the battery second-order RC equivalent model are acquired, the parameters of the battery second-order RC equivalent model are detected, if the detection is passed, step S4 is executed, otherwise the model is powered off;

[0027] Specifically, the detection is used to determine whether the circuit is in a safe state, if each parameter is safe, the detection is passed.

[0028] S4, the output voltage value V BATT .

[0029] S5, the output voltage value V BATT is acquired according to the SOC-OCV curve

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

[0031] S6, a threshold K1 is set; according to and the reference SOC value SOC 初始 , the K factor value of the model is calculated; the K factor value is compared with the set threshold K1, if the K factor value is less than the threshold, step S7 is executed, otherwise, the V BATT is updated according to the current V BATT and the K factor value, and returns to step S5;

[0032] Specifically, when the battery is discharged, V BATT is less than OCV, so When the battery is charged, 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] Further, 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] Wherein, SOC 真实 is the real SOC initial value, and SOC 测量SOC is the measured value of SOC, here SOC 测量 SOC is the measured value of SOC, here SOC 初始 K1 is a constant, and K1 is usually less than 1%, and K1 is usually set to 1% in the embodiment of the application; 真实 K1 is a constant, and K1 is usually less than 1%, and K1 is usually set to 1% in the embodiment of the application;

[0037] V is the current value of V BATT V is the current value of V BATT The formula used is:

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

[0039] V BATT，new is the value of V BATT after updating.

[0040] S7, obtaining the current value of SOC , updating the value of SOC 初始 according to the current value of SOC 初始 , and integrating the current of the updated value of SOC .

[0041] Specifically, the value of SOC is obtained, the value of SOC 初始 is updated to the value, denoted as SOC 初始，更新 , and the formula used for current integration is:

[0042]

[0043] Wherein, η is the integral error; Q 满 is the amount of electricity when the battery is fully charged last time; i(t) is the current at time t; the current is defined as positive during discharging and negative during charging; further, the integral error η is mainly determined by the accuracy of the integral method, and since the sampling time and offset error of different experimental equipment are different, the calculation method and value of η are also different in specific application; in this embodiment, the rectangular integral method is taken as an example to illustrate η: in the rectangular integral method, the current on each integral minimum time unit is assumed to be constant, while the actual current is usually variable, and the error generated thereby is related to the current variation rate, and at this time, η can be represented as:

[0044] η = ξ i / C batt

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

[0046]

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

[0048] S8, correct the end-of-charge / discharge data of the battery according to the current integration result;

[0049] Specifically, the SOC, temperature, current time, and SOC change amount are obtained and recorded; since the SOC is not sensitive to the OCV change in the end-of-charge / discharge stage, multiple (3-10) corrections in the end-of-charge / discharge stage will not cause significant deviation of the SOC data; the SOC value in the current integration result is used to update the data point of the end-of-charge / discharge in the SOC-OCV image.

[0050] Further, the SOC estimation variance ξ S 2 is calculated to evaluate the effect of the current correction. 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 to the battery capacity, η c and η d are the charging and discharging efficiencies, n c and n d are the sample numbers of charging and discharging, and C batt is the battery capacity; in the result of multiple corrections of the end-of-charge / discharge data, ξ S 2 a smaller value indicates better correction effect.

[0053] The application combines the ampere-hour integration method and the open circuit voltage method, and introduces a feedback factor to iteratively correct the initial SOC value, so that the result of current integration is more accurate, and the defect of static measurement of the open circuit voltage method is avoided; through the introduction of the correction mechanism of the end of charging / discharging correction, the open loop estimation error caused by the open circuit voltage is compensated, so that the accuracy of the correction of the data at the end of the charging / discharging of the power battery is improved.

[0054] The above describes only one embodiment of the application, and those skilled in the art can think of various changes, modifications, replacements and deformations of the embodiments without departing from the principles and spirits of the application. The protection scope of the application is defined by the appended claims and their equivalents, and the above behaviors should be covered in the protection scope of the application.

Claims

1. A method for correcting the SOC estimation of a power battery, characterized in that, Comprise: S1, according to the characteristics of the battery, the battery second order RC equivalent model is constructed, the SOC-OCV curve of the battery second order RC equivalent model is obtained; S2, power on the second-order RC equivalent model of the battery, obtain the reference SOC value SOC 初始 ; S3, the parameters of the battery second order RC equivalent model are obtained, the parameters of the battery second order RC equivalent model are detected, if the detection is passed, step S4 is executed, otherwise the model is powered off; S4, obtaining the output voltage value V of the second-order RC equivalent model of the battery BATT ; S5, obtaining the output voltage value V from the SOC-OCV curve BATT corresponding SOC value S6, set threshold K1; according to and the reference SOC value SOC 初始 K factor value of the calculation 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 and the K factor value update the V BATT value, and return to step S5; S7, obtaining a current value, updating the SOC 初始 value according to the current value, and integrating the current with the updated SOC 初始 value; S8, the charging / discharging end data of the battery is corrected according to the current integral result.

2. The power battery SOC estimation and correction method as described in claim 1, characterized in that, The acquiring the reference SOC value comprises: acquiring the SOC value recorded at the end of the last test and the SOC value calibrated by the open circuit voltage; comparing the battery resting time with the stable battery resting time, and selecting the reference SOC value SOC 初始 .

3. The method of claim 1, wherein The K factor value of the calculation model is: wherein k is the value of the factor K, SOC 初始 is the reference SOC value.

4. The K-factor threshold K1 of claim 1, wherein, The relationship between threshold K1 and battery SOC is: K1 = | SOC 真实 - SOC 测量 | / SOC 真实 * 100% where SOC 真实 is the true SOC initial value, SOC 测量 is the measured value of SOC.

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

01.

6. The power battery SOC estimation and correction method as described in claim 1, characterized in that, To V BATT The value is updated to: V BATT，new = f(k, V BATT ) = V BATT *(1+ k) where f is a function of k and V BATT and k is the value of the factor K.

7. The power battery SOC estimation and correction method as described in claim 1, characterized in that, updating the SOC 初始 value includes setting a current value as an updated SOC 初始 value, and noting the updated updated SOC 初始 as the SOC 初始，更新 .

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

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