Method and system for estimating state of charge of lithium iron phosphate battery

Abstract

The application provides a lithium iron phosphate battery state of charge estimation method and system, comprising the following steps: step S1: in the series lithium iron phosphate battery branch of the battery system, using a replacement module with a larger capacity than the main loop battery to replace the original battery connected with the main loop battery, and obtaining the estimated state of charge of the replacement module; step S2: obtaining the estimated state of charge of the main loop battery through the estimated state of charge of the replacement module. The application uses a replacement module with a larger capacity than the main loop battery to replace the original battery, and uses the estimated state of charge of the replacement module to obtain the state of charge of the main battery loop, which is beneficial to improve the state of charge estimation accuracy of the lithium iron phosphate battery, expand the state of charge estimation interval of the lithium iron phosphate battery, and improve the stability of the battery system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium iron phosphate battery state of charge estimation, in particular to a lithium iron phosphate battery state of charge estimation method and system. BACKGROUND

[0002] At present, secondary batteries are widely used in the field of new energy, and the most promising subsequent development among them is lithium ion batteries, sodium ion batteries and other new energy batteries. Among such batteries, lithium iron phosphate batteries have the characteristics of high safety, low cost, high temperature stability, etc. However, due to the relative relationship between voltage and state of charge (SOC) is not sensitive at some state of charge, the voltage changes little with the state of charge, so it is difficult to judge the state of charge according to the voltage. In the prior art, the means for judging the state of charge is to use the method of current integration for cumulative calculation.

[0003] The Chinese patent document with publication number CN113109717A discloses a lithium battery state of charge estimation method based on characteristic curve optimization, which includes the following: every 10% battery state of charge SOC is a sampling point, the discrete OCV-SOC characteristic curve L1 is obtained, and the continuous OCV-SOC characteristic curve L2 is obtained; based on the differential evolution DE method, the obtained characteristic curve L1 and characteristic curve L2 are fused; finally, based on the extended Kalman EKF, the weight term factor of the historical SOC estimation result error is introduced to establish a W-EKF estimation model, the second-order RC battery equivalent circuit model is combined, the real-time collected lithium battery measured voltage, current and temperature data under different working conditions are input, and the SOC value at the current time is accurately estimated.

[0004] For the related technology in the above, it is more dependent on the sampling accuracy and calculation accuracy of the battery management system, and often the state of charge accuracy is low due to error accumulation, which affects the normal use of the battery system. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide a lithium iron phosphate battery state of charge estimation method and system.

[0006] According to the lithium iron phosphate battery state of charge estimation method provided by the present application, the following steps are included:

[0007] Step S1: In the series lithium iron phosphate battery branch of the battery system, a replacement module with larger capacity than the main loop battery is used to replace the original battery connected to the main loop battery;

[0008] Step S2: Obtain the estimated state of charge of the replacement module, and obtain the estimated state of charge of the main loop battery through the estimated state of charge of the replacement module.

[0009] By adopting the technical scheme, the original battery is replaced by a replacement module with a larger capacity than the main loop battery, and the state of charge of the main battery loop is obtained by using the estimated state of charge of the replacement module, which is beneficial to improve the estimation accuracy of the state of charge of the lithium iron phosphate battery and expand the estimation interval of the state of charge of the lithium iron phosphate battery, and improve the stability of the battery system.

[0010] In a possible implementation, the capacity of the replacement module is A, the capacity of the main loop battery is B, and the estimated state of charge of the replacement module is X;

[0011] The estimated state of charge of the main loop battery is X*A / B.

[0012] By adopting the technical scheme, the state of charge of the main loop battery is calculated by using the determination method of X*A / B, which is beneficial to improve the convenience and accuracy of the state of charge estimation of the lithium iron phosphate battery.

[0013] In a possible implementation, the replacement module is a replacement battery.

[0014] The capacity of the replacement module is the capacity of the replacement battery.

[0015] The estimated state of charge of the replacement module is the estimated state of charge of the replacement battery.

[0016] By adopting the technical scheme, the replacement battery is used to estimate the state of charge of the main loop battery, which further improves the convenience of the state of charge estimation of the lithium iron phosphate battery.

[0017] In a possible implementation, the replacement module is a plurality of connected replacement batteries.

[0018] By adopting the technical scheme, when the capacity of the replacement battery is insufficient, a plurality of connected replacement batteries can be used, which is beneficial to expand the application range of the main loop battery, and further improve the adaptability of the method. In addition, the larger the capacity difference between the replacement battery and the main loop battery, the wider the interval of the state of charge estimation of the main loop battery, and the more accurate the estimation, which further improves the estimation accuracy of the state of charge of the lithium iron phosphate battery and expands the estimation interval of the state of charge of the lithium iron phosphate battery.

[0019] In a possible implementation, the plurality of replacement batteries are the same, and the connection mode of the plurality of replacement batteries is parallel connection.

[0020] The estimated state of charge of the replacement module includes the estimated state of charge of a single replacement battery.

[0021] The estimated state of charge of the main loop battery is the product of the number of the replacement batteries and the estimated state of charge of a single replacement battery.

[0022] By using the above technical solution, the estimated state of charge of the main loop battery is calculated by the product of the number of the replacement batteries and the estimated state of charge of a single replacement battery, which further improves the convenience of the state of charge estimation of the lithium iron phosphate battery and expands the estimation interval of the state of charge of the lithium iron phosphate battery.

[0023] In a possible implementation, the replacement module is provided in multiple.

[0024] By using the above technical solution, the replacement module is provided in multiple, which is conducive to reducing the inaccurate estimation caused by individual failure of the replacement battery and other problems, and improving the accuracy of the state of charge estimation of the lithium iron phosphate battery.

[0025] In a possible implementation, the replacement module uses a lithium iron phosphate battery.

[0026] By using the above technical solution, the lithium iron phosphate battery is used, which is conducive to improving the estimation accuracy of the state of charge of the lithium iron phosphate battery.

[0027] According to the present application, a system for estimating the state of charge of a lithium iron phosphate battery is provided, which comprises the following modules:

[0028] Module M1: for using a replacement module with a larger capacity than the main loop battery in a series lithium iron phosphate battery branch of a battery system, replacing the original battery connected with the main loop battery, and obtaining the estimated state of charge of the replacement module;

[0029] Module M2: for obtaining the estimated state of charge of the replacement module, and obtaining the estimated state of charge of the main loop battery by the estimated state of charge of the replacement module.

[0030] By using the above technical solution, the original battery is replaced by the replacement module with a larger capacity than the main loop battery, and the state of charge of the main battery loop is obtained by the estimated state of charge of the replacement module, which is conducive to improving the estimation accuracy of the state of charge of the lithium iron phosphate battery, expanding the estimation interval of the state of charge of the lithium iron phosphate battery, and improving the stability of the battery system.

[0031] In a possible implementation, the capacity of the replacement module is A, the capacity of the main loop battery is B, and the estimated state of charge of the replacement module is X.

[0032] The estimated state of charge of the main loop battery is X*A / B.

[0033] By adopting the technical scheme, the state of charge of the main loop battery is calculated by using the X*A / B determination mode, which is beneficial to improving the convenience and accuracy of the state of charge estimation of the lithium iron phosphate battery.

[0034] In a possible implementation, the replacement module is a replacement battery.

[0035] The capacity of the replacement module is the capacity of the replacement battery.

[0036] The estimated state of charge of the replacement module is the estimated state of charge of the replacement battery.

[0037] By adopting the technical scheme, the state of charge of the main loop battery is calculated by using the X*A / B determination mode, which is beneficial to improving the convenience and accuracy of the state of charge estimation of the lithium iron phosphate battery.

[0038] Compared with the prior art, the present application has the following beneficial effects:

[0039] 1. The present application uses a replacement module with a larger capacity than the main loop battery to replace the original battery, and uses the estimated state of charge of the replacement module to obtain the state of charge of the main battery loop, which is beneficial to improving the estimation accuracy of the state of charge of the lithium iron phosphate battery and expanding the estimation interval of the state of charge of the lithium iron phosphate battery, thereby improving the stability of the battery system.

[0040] 2. When the capacity of the replacement battery is insufficient, multiple connected replacement batteries can be used, which is beneficial to expanding the application range of the main loop battery, thereby improving the adaptability of the method, and in addition, the larger the capacity difference between the replacement battery and the main loop battery, the wider the interval of the estimated state of charge of the main loop battery and the more accurate the estimation, thereby further improving the estimation accuracy of the state of charge of the lithium iron phosphate battery and expanding the estimation interval of the state of charge of the lithium iron phosphate battery.

[0041] 3. The estimated state of charge of the main loop battery is calculated by multiplying the number of replacement batteries and the estimated state of charge of a single replacement battery, which further improves the convenience of the state of charge estimation of the lithium iron phosphate battery and expands the estimation interval of the state of charge of the lithium iron phosphate battery. BRIEF DESCRIPTION OF DRAWINGS

[0042] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, with reference to the accompanying drawings:

[0043] Figure 1 The circuit schematic diagram of the first embodiment of the present application;

[0044] Figure 2 The "SOC-voltage" curve of the lithium iron phosphate battery of the present application;

[0045] Figure 3 Circuit schematic diagram of the embodiment three of the present application;

[0046] Figure 4 Circuit schematic diagram of the embodiment four of the present application. DETAILED DESCRIPTION

[0047] The present application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present application. These are within the scope of protection of the present application.

[0048] The embodiment one of the present application discloses a method for estimating the state of charge of a lithium iron phosphate battery, as shown in Figure 1 and Figure 2 The method comprises the following steps: step S1: in the series lithium iron phosphate battery branch of the battery system, a replacement module with a larger capacity than the main loop battery is used to replace the original battery connected to the main loop battery. Step S2: obtain the estimated state of charge of the replacement module, and obtain the estimated state of charge of the main loop battery through the estimated state of charge of the replacement module. The main loop battery (ordinary battery in the figure) and the original battery are the same, and the main loop battery is the battery in the series lithium iron phosphate branch except the original battery. The original battery and the main loop battery are connected in series on the lithium iron phosphate battery branch.

[0049] In a possible implementation, the replacement module is a replacement battery, and the replacement battery is a lithium iron phosphate battery or a lithium battery. The capacity of the replacement module is A, the capacity of the main loop battery is B, and the estimated state of charge of the replacement module is X. The capacity of the replacement module is the capacity of the replacement battery. The estimated state of charge of the replacement module is the estimated state of charge of the replacement battery. The estimated state of charge of the main loop battery is X*A / B.

[0050] For example, the embodiment one can use a lithium iron phosphate battery with a larger difference from the original battery capacity and higher than the original battery capacity as a replacement battery. The estimated SOC of the replacement battery is converted to the estimated SOC of the main loop battery using proportional conversion. Specifically, the estimated state of charge of the replacement battery is converted to the state of charge of the main loop battery using proportional conversion. Wherein, the greater the capacity difference between the replacement battery and the main loop battery, the wider the interval of the accurate state of charge estimation. The greater the capacity difference between the replacement battery and the main loop battery, the more accurate the estimation, but if the difference is too large, it will cause cost waste, leading to the inability to be practically applied.

[0051] As shown in Figure 2As shown, lithium iron phosphate batteries have a voltage plateau segment, and the state of charge (SOC) can be estimated by voltage. The correspondence between voltage and SOC is a unique attribute of the battery. The state of charge (SOC) of the battery is related to the voltage, and the state of charge of the battery is obtained by looking up data based on the battery's own attributes.

[0052] Embodiment 1 of the present invention also discloses a system for estimating the state of charge of a lithium iron phosphate battery, such as... Figure 1 As shown, the system includes the following modules: Module M1: Used to replace the primary battery connected to the main circuit battery with a replacement module having a larger capacity than the main circuit battery in the series lithium iron phosphate battery branch of the battery system. Module M2: Used to obtain the estimated state of charge of the replacement module, and obtain the estimated state of charge of the main circuit battery through the estimated state of charge of the replacement module.

[0053] In one possible implementation, the capacity of the replacement module is A, the capacity of the main circuit battery is B, and the estimated state of charge (SOC) of the replacement module is X; the estimated SOC of the main circuit battery is X*A / B. The replacement module is the replacement battery; the capacity of the replacement module is the capacity of the replacement battery; and the estimated SOC of the replacement module is the estimated SOC of the replacement battery.

[0054] Embodiment 2 of the present invention also provides a method for estimating the state of charge of a lithium iron phosphate battery. The difference from Embodiment 1 is that the replacement module consists of multiple connected replacement batteries. These replacement batteries can be identical, different, or partially identical. Specifically, the replacement batteries can also be multiple identical or different batteries connected in series. Alternatively, the replacement module can use multiple different replacement batteries connected in parallel.

[0055] Embodiment 3 of the present invention also discloses a method for estimating the state of charge of a lithium iron phosphate battery, such as... Figure 3 As shown, the difference from Embodiment 2 is that when multiple replacement batteries are identical and connected in parallel, the estimated state of charge (SOC) of the replacement module includes the estimated SOC of a single replacement battery; the estimated SOC of the main circuit battery is the product of the number of replacement batteries and the estimated SOC of a single replacement battery. The SOC of the parallel-connected replacement batteries is consistent with that of the main circuit battery at a predetermined SOC value. The predetermined value is preferably 0%. The parallel-connected replacement batteries are set to be n identical batteries, where n ≥ 2. When the estimated SOC of the replacement battery is X, and X is within a predetermined SOC range, the estimated SOC of the main circuit battery is nX.

[0056] For example, the embodiment of the present application takes n=2, replaces the battery with a lithium iron phosphate battery, and takes the predetermined value as 0%, and the predetermined range SOC as 0%~30% SOC, which is not limited thereto. In terms of electrical principles, in each series lithium iron phosphate battery branch, at least one battery position is selected, two same lithium iron phosphate batteries are connected in parallel to replace the battery, and the state of charge of the two batteries is consistent with that of the other main loop batteries at the 0% SOC position. Since the current flowing through each battery of the replacement battery is about half of that of the main loop, when the state of charge of the main loop battery changes between 0%~100%, the state of charge of each replacement battery is exactly half of the state of charge of the main loop battery, i.e. 0%~50%.

[0057] In the more accurate interval of the SOC of the replacement battery (the interval in which the voltage of the replacement battery in the interval segment battery changes more obviously with the state of charge, which can be used for the estimation of the state of charge), for example, the 0%~30% SOC interval of the lithium iron phosphate battery, the estimated SOC of the main loop battery is obtained by the estimated SOC of the replacement battery, and the SOC of the two replacement batteries (0%~60% SOC); the estimated SOC of the main loop battery is still used in other intervals (for example, the 90%~100% SOC of the lithium iron phosphate battery).

[0058] For example, the embodiment of the present application takes n=2, replaces the battery with a lithium iron phosphate battery, and takes the predetermined value as 0%, and the predetermined range SOC as 0%~30% SOC, which is not limited thereto. In terms of electrical principles, in each series lithium iron phosphate battery branch, at least one battery position is selected, two same lithium iron phosphate batteries are connected in parallel to replace the battery, and the state of charge of the two batteries is consistent with that of the other main loop batteries at the 0% SOC position. Since the current flowing through each battery of the replacement battery is about half of that of the main loop, when the state of charge of the main loop battery changes between 0%~100%, the state of charge of each replacement battery is exactly half of the state of charge of the main loop battery, i.e. 0%~50%. Figure 3As shown, since the voltage of the lithium iron phosphate battery generally changes obviously with the state of charge in the interval of about 0% to 30% SOC and 90% to 100% SOC, the state of charge can be used for estimation, so when the estimated state of charge X of the replacement battery is in the interval of 0% to 30% SOC, the state of charge of the main circuit battery is (2*X), and is more accurate, the state of charge of the main circuit battery in the interval of 0% to 60% SOC can be accurately estimated, and the voltage of the main circuit battery is still used for estimation in the interval of 90% to 100% SOC, so the accurate interval of the state of charge estimated according to the voltage is expanded from 0% to 30% SOC and 90% to 100% SOC to 0% to 60% SOC and 90% to 100% SOC. The voltage value corresponding to 0% SOC is 2.5V, and the voltage value corresponding to 30% SOC is 3.228V, but the actual value of 3.228V of the battery of different brands, systems and materials will have a little deviation. The voltage corresponding to the battery is collected through the voltage sampling circuit of the battery management system (BMS). Since the battery voltage and the SOC have a corresponding relationship, when the voltage of the main circuit battery is in the preset value, the SOC is determined to be in the interval of 90% to 100%. The preset value includes 3.331V to 3.65V, 90% corresponds to 3.331V, and 100% corresponds to 3.65V, but the actual value of 3.331V of the battery of different brands, systems and materials will have a little deviation. The values of 30%, 60%, 90% in the third embodiment (except 0% and 100%) are assumed values for convenience of description, and are not limited thereto.

[0059] The fourth embodiment of the present application also discloses a method for estimating the state of charge of a lithium iron phosphate battery, as shown in Figure 4 The difference between the third embodiment and the fourth embodiment is that the replacement module is provided in multiple. In a possible implementation manner, the replacement module is provided in multiple on the series lithium iron phosphate battery branch. Generally, in order to reduce the inaccuracy caused by the failure or problem of the replacement battery, at least two same replacement modules can be arranged in the same series battery branch. The replacement modules calibrate each other when estimating the main circuit battery; or, single (when there are more than 3 replacement batteries) or multiple (when there are more than 2 replacement batteries) measurements can be performed, the value greatly different from the remaining results is discarded, and then the average value of the remaining results is taken.

[0060] The present application improves the estimation accuracy of the state of charge (SOC) of the lithium iron phosphate battery and expands the interval in which the state of charge (SOC) of the lithium iron phosphate battery is more accurate.

[0061] In the description of the present application, it needs to be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0062] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the above specific embodiments, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be arbitrarily combined with each other without conflict.

Claims

1. A method of estimating the state of charge of a lithium iron phosphate battery, characterized in that, The method comprises the following steps: Step S1: in a series lithium iron phosphate battery branch of a battery system, using a replacement module with a capacity larger than that of a main loop battery to replace an original battery connected with the main loop battery, the replacement module being a lithium iron phosphate battery; Step S2: obtaining an estimated state of charge of the replacement module, in a state of charge interval in which the voltage of the replacement module changes more obviously with the state of charge, obtaining an estimated state of charge of the main loop battery through the estimated state of charge of the replacement module according to a proportional relationship between the capacity of the replacement module and the capacity of the main loop battery; in a state of charge interval in which the voltage of the main loop battery changes more obviously with the state of charge, directly using the estimated state of charge of the main loop battery.

2. The method of estimating state of charge of a lithium iron phosphate battery of claim 1, wherein, If the capacity of the replacement module is A, the capacity of the main loop battery is B, and the estimated state of charge of the replacement module is X; The estimated state of charge of the main loop battery is X*A / B.

3. The method of estimating state of charge of a lithium iron phosphate battery of claim 1, wherein, The replacement module is a replacement battery; The capacity of the replacement module is the capacity of the replacement battery; The estimated state of charge of the replacement module is the estimated state of charge of the replacement battery.

4. The method of claim 1, wherein the method further comprises: The replacement module is a plurality of connected replacement batteries.

5. The method of estimating state of charge of a lithium iron phosphate battery of claim 4, wherein, The plurality of replacement batteries are the same, and the plurality of replacement batteries are connected in parallel; The estimated state of charge of the replacement module comprises an estimated state of charge of a single replacement battery; The estimated state of charge of the main loop battery is the product of the number of the replacement batteries and the estimated state of charge of a single replacement battery.

6. The method of estimating state of charge of a lithium iron phosphate battery of claim 1, wherein, The replacement module is provided in a plurality of ways.

7. The method of estimating state of charge of a lithium iron phosphate battery of claim 1, wherein, The replacement module adopts a lithium iron phosphate battery.

8. A system for estimating the state of charge of a lithium iron phosphate battery, characterized in that it comprises: The method comprises the following modules: Module M1: for using a replacement module with a capacity larger than that of a main loop battery to replace an original battery connected with the main loop battery in a series lithium iron phosphate battery branch of a battery system, the replacement module being a lithium iron phosphate battery; Module M2: for obtaining an estimated state of charge of the replacement module, in a state of charge interval in which the voltage of the replacement module changes more obviously with the state of charge, obtaining an estimated state of charge of the main loop battery through the estimated state of charge of the replacement module according to a proportional relationship between the capacity of the replacement module and the capacity of the main loop battery; in a state of charge interval in which the voltage of the main loop battery changes more obviously with the state of charge, directly using the estimated state of charge of the main loop battery.

9. The system for estimating state of charge of a lithium iron phosphate battery of claim 8, wherein, The capacity of the replacement module is A, the capacity of the main loop battery is B, and the estimated state of charge of the replacement module is X; The estimated state of charge of the main loop battery is X*A / B.

10. The system for estimating state of charge of a lithium iron phosphate battery of claim 8, wherein, The replacement module is a replacement battery; The capacity of the replacement module is the capacity of the replacement battery; The estimated state of charge of the replacement module is the estimated state of charge of the replacement battery.

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