A method for calculating soc of lithium iron phosphate battery

Abstract

The application discloses a SOC calculation method of a lithium iron phosphate battery, and comprises the following steps: determining a plurality of SOC threshold points according to an SOC-OCV curve of the battery, and determining a plurality of calibration intervals based on the plurality of SOC threshold points, wherein adjacent SOC threshold points correspond to minimum values and maximum values of the calibration intervals respectively; obtaining an initial SOC T0 of the battery, calculating an SOC T1 by using ampere-hour integration based on the SOC T0, and determining a corresponding delta SOC ah of the ampere-hour integration; obtaining a dynamic voltage of the battery, and determining a corresponding SOC dyn of the dynamic voltage according to the dynamic voltage; obtaining an open circuit voltage of the battery, and determining a corresponding SOC ocv of the open circuit voltage according to the open circuit voltage; and calibrating the SOC T1 by using the delta SOC ah, the SOC dyn and the SOC ocv according to a calibration interval in which the SOC T1 is located to obtain an SOC T1'.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power calculation of lithium iron phosphate battery, in particular to a SOC calculation method of lithium iron phosphate battery. BACKGROUND

[0002] With the explosive growth of new energy electric vehicle market, the dependence on the sinking market is increasing, accompanied by the increase of demand for low-cost electric vehicles. The ternary lithium battery has high dependence on nickel, cobalt and manganese, and the cost compression space is relatively low; while the lithium iron phosphate battery has lower raw material cost and is more competitive in the sinking market. In addition, the stability of the electrochemical properties of the lithium iron phosphate battery can greatly reduce the safety hazard. In recent years, the market share of lithium iron phosphate battery has been gradually increasing.

[0003] Compared with ternary lithium battery, the development of battery management system of lithium iron phosphate battery is more difficult. For ternary lithium battery, SOC calibration can be realized by single open circuit voltage, and high-precision SOC calculation can be realized by auxiliary ampere-hour integration and independent calculation of dynamic voltage. However, the open circuit voltage of lithium iron phosphate battery cannot correspond to SOC, and even the single voltage corresponding to SOC in 10mV will exceed 25%. Considering the ampere-hour integration and dynamic voltage calibration error caused by unstable current in dynamic driving process, only single calibration cannot meet the demand of high-precision SOC. SUMMARY

[0004] To solve at least one aspect of the above problem, the present application provides a SOC calculation method of lithium iron phosphate battery, comprising: determining a plurality of SOC threshold points according to the SOC-OCV curve of the battery, and determining a plurality of calibration intervals based on the plurality of SOC threshold points, wherein adjacent SOC threshold points correspond to the minimum and maximum values of the calibration intervals respectively; obtaining the initial SOC T0 of the battery, calculating the SOC T1 by ampere-hour integration based on the SOC T0, and determining the corresponding SOC T1. SOCah of ampere-hour integration; obtaining the dynamic voltage of the battery, and determining the corresponding SOCdyn according to the dynamic voltage; obtaining the open circuit voltage of the battery, and determining the corresponding SOCocv according to the open circuit voltage; according to the calibration interval where the SOC T1 is located, the SOC T1 is calibrated by using the SOC T1. SOCah, SOCdyn and SOCocv, and the expression of the calibrated SOC T1` is: SOC T1` = SOC T0 + SOC, SOC = aSOCdyn + bSOCocv + cSOCah, wherein a + b + c = 1, and the values of a, b and c are determined based on the calibration interval where the SOC T1 is located.

[0005] Preferably, the plurality of SOC threshold points further comprises a battery minimum available SOC low determined according to battery characteristics, and an over-discharge alarm is issued when the SOCT0 is less than or equal to the SOC low.

[0006] Preferably, the plurality of SOC threshold points further comprises a battery maximum available SOChigh determined according to battery characteristics, and an over-charge alarm is issued when the SOCT0 is greater than or equal to the SOChigh.

[0007] Preferably, the step of determining the values of a, b and c based on the calibration interval in which the SOCT1 is located further comprises: determining whether the SOCT0 is reliable; if not, a is greater than or equal to c, and c is greater than or equal to b; if yes, when the battery is in a charging state and the current is less than or equal to a set current threshold, b is greater than or equal to a, and a is greater than or equal to c; when the battery is in a charging state and the current is greater than the set current threshold, b is greater than or equal to c, and c is greater than or equal to a; and when the battery is in a discharging state, b is greater than or equal to c, and c is greater than or equal to a.

[0008] Preferably, the step of obtaining a dynamic voltage of the battery and determining a corresponding SOCdyn based on the dynamic voltage comprises: determining the dynamic voltage according to the battery temperature, current and resistance, and determining the SOCdyn based on the dynamic voltage.

[0009] Preferably, the step of obtaining an open-circuit voltage of the battery after it is at rest and determining a corresponding SOCocv based on the open-circuit voltage comprises: obtaining the open-circuit voltage after the battery has been at rest for more than a first preset time, and determining the SOCocv corresponding to the open-circuit voltage according to a SOC-OCV curve.

[0010] Preferably, the step of correcting the SOCT1 to obtain SOCT1` using the △SOCah, SOCdyn and SOCocv according to the calibration interval in which the SOCT1 is located further comprises: determining the current state of the battery, obtaining the open-circuit voltage when the battery has been at rest for more than a second preset time, and calibrating the SOCT1` based on the open-circuit voltage, and the second preset time is greater than the first preset time.

[0011] Preferably, the method further comprises using Kalman filtering to follow the calibrated SOCT1`, and determining that the SOCT1` is unreliable when the SOCT1` exceeds a set error threshold.

[0012] The SOC calculation method for the lithium iron phosphate battery has the following beneficial effects: the SOC is calibrated according to different states of the battery through the open-circuit voltage, ampere-hour integration and dynamic voltage, so as to improve the accuracy of the SOC calculation result of the battery; and the SOC is calibrated through the open-circuit voltage obtained in the resting state of the battery, so as to further improve the accuracy of the SOC. BRIEF DESCRIPTION OF DRAWINGS

[0013] For a better understanding of the above-described and other objects, features, and advantages of the present application, reference should be made to the following implementation, which is illustrative only and does not limit the scope of the application. The same reference numerals in different drawings denote the same or similar components. It is to be understood that the drawings are schematically illustrating the preferred embodiments of the present application and, therefore, are not limiting of the scope of the application, and each component is not necessarily drawn to scale.

[0014] Figure 1 A flow chart of the SOC calculation method of the lithium iron phosphate battery according to an embodiment of the present application in the battery charging state is shown;

[0015] Figure 2 A flow chart of the SOC calculation method of the lithium iron phosphate battery according to an embodiment of the present application in the battery discharging state is shown. DETAILED DESCRIPTION

[0016] Exemplary embodiments of the present disclosure are described herein with reference to the accompanying drawings, which are shown by way of illustration. The drawings and description are not intended to limit the scope of the present disclosure. The various details of the embodiments of the present disclosure can be combined to create yet other embodiments of the present disclosure. Thus, the following description and drawings are to be regarded as illustrative in nature and non-limiting.

[0017] As used herein, the terms "comprises," "comprising," "includes," "including" and the like mean, and are used herein to mean, "including and not limiting to." The term "or" means "and / or" unless clearly indicated otherwise. The term "based on" means "based, at least in part, on." The terms "one example embodiment" and "an example embodiment" mean "at least one example embodiment." The term "another embodiment" means "at least one additional embodiment." The terms "a first," "a second," etc. do not require a strict numbering of their objects but are used merely as labels to identify individual claimed objects. Other definitions can be found in the following description.

[0018] To at least partially solve one or more of the above problems and other potential problems, one embodiment of the present disclosure proposes a method for calculating the SOC of a lithium iron phosphate battery, comprising: determining a plurality of SOC threshold points according to the SOC-OCV curve of the battery, and determining a plurality of calibration intervals based on the plurality of SOC threshold points, wherein adjacent SOC threshold points correspond to the minimum and maximum values of the calibration intervals, respectively; obtaining the initial SOC T0 of the battery, calculating the SOC T1 using ampere-hour integration based on the SOC T0, and determining the SOC ah corresponding to the ampere-hour integration; obtaining the dynamic voltage of the battery, and determining the SOC dyn corresponding to the dynamic voltage; obtaining the open circuit voltage of the battery, and determining the SOC ocv corresponding to the open circuit voltage; and according to the calibration interval in which the SOC T1 is located, calibrating the SOC T1 using the SOC dyn, the SOC ocv, and the SOC ah to obtain the expression of the calibrated SOC T1` as follows: SOC T1` = SOC T0 + SOC, SOC = aSOC dyn + bSOC ocv + cSOC ah, wherein a + b + c = 1, and the values of a, b, and c are determined based on the calibration interval in which the SOC T1 is located.

[0019] Specifically, as shown in Figure 1 and Figure 2 , a plurality of SOC threshold points SOC1, SOC2, SOC3, and SOC4 are selected according to the SOC-OCV curve of the lithium iron phosphate battery, and calibration intervals [0, SOC1), [SOC1, SOC2), [SOC2, SOC3), [SOC3, SOC4), and [SOC4, 100%] are determined according to the selected plurality of SOC threshold points. Those skilled in the art can understand that in other embodiments, the number of selected SOC threshold points is three, five, or more, depending on different models of lithium iron phosphate batteries and different SOC-OCV curves, and the calibration intervals established based on the SOC threshold points vary with the number of SOC threshold points, for example, [0, SOC1), [SOC1, SOC2), [SOC2, SOC3), [SOC3, 100%]; or [0, SOC1), [SOC1, SOC2), [SOC2, SOC3), [SOC3, SOC4), [SOC4, SOC5), [SOC5, 100%].

[0020] In some embodiments, the plurality of SOC threshold points further includes a minimum available SOC low of the battery determined according to the battery characteristics, and when the SOC T1 is less than or equal to the SOC low, an over-discharge warning is issued.

[0021] Specifically, SOClow is less than SOC1, and the minimum available SOC value of the lithium iron phosphate battery is determined by the battery characteristics of the lithium iron phosphate battery, which is SOClow, and it should be noted that the minimum available SOC value of different batteries is different. By determining SOClow, the SOC of the battery is less than or equal to the value, and an over-discharge alarm is issued to avoid damage to the battery electrode active material and shorten the battery life.

[0022] In some embodiments, the plurality of SOC threshold points further include a highest available SOChigh of the battery determined according to the battery characteristics, and when SOCT1 is greater than or equal to SOChigh, an overcharge alarm is issued.

[0023] Specifically, SOChigh is less than or equal to 100%, and the maximum available SOC value of the lithium iron phosphate battery is determined by the battery characteristics of the lithium iron phosphate battery, which is SOChigh, and it should be noted that the maximum available SOC value of different batteries is different. By determining SOChigh, the SOC of the battery is greater than or equal to the value, and an overcharge alarm is issued to avoid the battery from continuing to charge after reaching the full state, causing the battery to deform or leak, and to avoid the battery performance to be reduced or damaged.

[0024] When calculating the SOC of the lithium iron phosphate battery, taking the battery discharge state as an example, the value of the SOC of the battery at the previous time is obtained as the initial time SOCT0, and the SOCT1 at the current time T1 is calculated by ampere-hour integration, and the SOCah corresponding to the ampere-hour integration process is obtained, and the dynamic voltage corresponding to the SOCdyn is determined by obtaining the dynamic voltage in the discharge process of the battery. In some embodiments, the step of obtaining the dynamic voltage of the battery and determining the SOCdyn corresponding to the dynamic voltage comprises: determining the dynamic voltage according to the battery temperature, current and resistance, and determining the SOCdyn based on the dynamic voltage. The open circuit voltage of the battery is obtained after the battery is at rest for a time Tocv to determine the SOCocv corresponding to the open circuit voltage. In some embodiments, the step of obtaining the open circuit voltage of the battery after the battery is at rest and determining the SOCocv corresponding to the open circuit voltage comprises: obtaining the open circuit voltage after the battery is maintained in a static state for more than a first predetermined time, i.e. obtaining the open circuit voltage of the lithium iron phosphate battery after the vehicle is static for a certain time Tocv, wherein Tocv is determined by the battery current being lower than a certain value Imin, and the SOCocv corresponding to the open circuit voltage is determined according to the SOC-OCV curve. According to the calibration interval to which SOCT1 belongs, a, b, and c are assigned values to calibrate SOCT1. In some embodiments, a calibrated SOCT1` is obtained by calibrating SOCT1, and SOCT1` is used as the initial time SOC for calculating the battery SOC at the next time.

[0025] In some embodiments, the step of determining the values of a, b and c based on the calibration interval in which the SOCT1 is located further comprises: determining whether the SOCT0 is reliable; if not, a is greater than or equal to c, and c is greater than or equal to b; if reliable, when the battery is in a charging state and the current is less than or equal to a set current threshold, b is greater than or equal to a, and a is greater than or equal to c; when the battery is in a charging state and the current is greater than the set current threshold, b is greater than or equal to c, and c is greater than or equal to a; and when the battery is in a discharging state, b is greater than or equal to c, and c is greater than or equal to a.

[0026] Specifically, the SOCT1` is followed by Kalman filtering to improve the accuracy of the calculation, and the Kalman filtering of the SOCT1` is used to issue an unreliable alarm when the error of the SOCT1` is greater than a preset error threshold, so that the battery management system adjusts the calibration coefficient or adjusts the charging current of the battery to realize the smooth processing of the battery SOC calculation and reduce the calculation error.

[0027] In some embodiments, the step of determining the values of a, b and c based on the calibration interval in which the SOCT1 is located further comprises: determining whether the SOCT0 is reliable; if not, a is greater than or equal to c, and c is greater than or equal to b; if reliable, when the battery is in a charging state and the current is less than or equal to a set current threshold, b is greater than or equal to a, and a is greater than or equal to c; when the battery is in a charging state and the current is greater than the set current threshold, b is greater than or equal to c, and c is greater than or equal to a; and when the battery is in a discharging state, b is greater than or equal to c, and c is greater than or equal to a.

[0028] Specifically, taking the SOC at the T2 time of the battery discharging state as an example, the SOCT2 is calculated by ampere-hour integration with the SOCT1` as the initial value, and the SOCT2 is further calibrated, i.e. SOCT2` = SOCT1` + △SOC, △SOC = aSOCdyn + bSOCocv + c△SOCah, whether the SOCT1` is reliable is determined by Kalman filtering method, if not, a is greater than or equal to c, and c is greater than or equal to b; if reliable, b is greater than or equal to c, and c is greater than or equal to a.

[0029] In some embodiments, after the step of correcting the SOCT1 by using △SOCah, SOCdyn and SOCocv to obtain SOCT1` according to the calibration interval in which the SOCT1 is located, further comprises: determining the current state of the battery, obtaining the open circuit voltage when the battery is static for more than a second preset time, and calibrating the SOCT1` by the open circuit voltage, and the second preset time is greater than the first preset time.

[0030] Specifically, the second preset time is greater than Tocv, when the vehicle is static for more than the second preset time, the battery reaches a stable state, the open circuit voltage obtained is a stable value, and the SOCT1` is further calibrated by the obtained open circuit voltage to obtain SOCT1`` to improve the calculation accuracy.

[0031] In some embodiments, the step of determining the values of a, b and c based on the calibration interval in which the SOCT1 is located further comprises: determining whether the SOCT0 is reliable; if not, a is greater than or equal to c, and c is greater than or equal to b; if reliable, when the battery is in a charging state and the current is less than or equal to a set current threshold, b is greater than or equal to a, and a is greater than or equal to c; when the battery is in a charging state and the current is greater than the set current threshold, b is greater than or equal to c, and c is greater than or equal to a; and when the battery is in a discharging state, b is greater than or equal to c, and c is greater than or equal to a.

[0032] In particular, the error threshold is set to 10%, and SOCT1` is determined to be untrustworthy when the calibrated SOCT1` is followed by Kalman filtering to determine that it is untrustworthy. In other embodiments, the error threshold can be 5% or 15%, and in other embodiments, the error threshold can be determined based on the characteristics of the lithium iron phosphate battery.

[0033] As Figure 1The SOC calculation method of the lithium iron phosphate battery is shown in a flow chart of a battery charging state. In this embodiment, the SOC1, SOC2, SOC3 and SOC4 threshold points are determined according to the SOC-OCV curve of the lithium iron phosphate battery, and the minimum available SOClow and the highest available SOChigh of the battery are determined, and the calibration interval is determined to include [0, SOClow), [SOClow, SOC1), [SOC1, SOC2), [SOC2, SOC3), [SOC3, SOC4), [SOC4, SOChigh), [SOChigh, 100%]. The SOC calculation steps at the T1 moment in the charging process of the battery are as follows: SOCT1 is calculated by ampere-hour integration based on the SOC at the initial moment; it is judged whether SOCT1 belongs to the calibration interval, if SOCT1 is less than SOClow, SOCT0 is credible, the value relationship of a, b and c is that b is greater than or equal to c, and c is greater than or equal to a, that is, the weight of the SOCocv corresponding to the open circuit voltage is greater than or equal to the weight of the SOCdyn corresponding to the dynamic voltage, and the weight of the SOCdyn is greater than or equal to the weight of the ampere-hour integration △SOCah; if SOCT1 is greater than or equal to SOClow, it is judged whether SOCT1 belongs to the calibration interval [SOClow, SOC1), if yes, SOCT0 is credible, the value relationship of a, b and c is that b is greater than or equal to c, and c is greater than or equal to a, if not, it is judged whether SOCT1 belongs to the calibration interval [SOC1, SOC2); if SOCT1 belongs to the calibration interval [SOC1, SOC2), SOCT0 is not credible, the value relationship of a, b and c is that a is greater than or equal to c, and c is greater than or equal to b, if not, it is judged whether SOCT1 belongs to the calibration interval [SOC2, SOC3); if SOCT1 belongs to the calibration interval [SOC2, SOC3), SOCT0 is credible, the value relationship of a, b and c is that b is greater than or equal to c, and c is greater than or equal to a, if not, it is judged whether SOCT1 belongs to the calibration interval [SOC3, SOC4); if SOCT1 belongs to the calibration interval [SOC3, SOC4), SOCT0 is not credible, the value relationship of a, b and c is that a is greater than or equal to c, and c is greater than or equal to b, if not, it is judged whether SOCT1 belongs to the calibration interval [SOC4, SOChigh); if SOCT1 belongs to the calibration interval [SOC4, SOChigh), SOCT0 is credible, it is judged whether the battery current is less than or equal to the set current threshold, if lower than the set current threshold, the value relationship of a, b and c is that b is greater than or equal to a, and a is greater than or equal to c, if not, it is judged whether SOCT1 belongs to the calibration interval [SOChigh, 100%); if yes, a no-charging alarm is issued.If the battery enters a static state after the T1 moment, and the static time is greater than the second preset time, the SOCT1` is further calibrated by the open circuit voltage to obtain SOCT1``.

[0034] As Figure 2The SOC calculation method of the lithium iron phosphate battery is shown in the flow chart of the battery discharge state. In this embodiment, the SOC1, SOC2, SOC3 and SOC4 threshold points are determined according to the SOC-OCV curve of the lithium iron phosphate battery, and the minimum available SOClow and the highest available SOChigh of the battery are determined. The calibration interval determined includes [0, SOClow), [SOClow, SOC1), [SOC1, SOC2), [SOC2, SOC3), [SOC3, SOC4), [SOC4, SOChigh), [SOChigh, 100%). The SOC calculation steps at T1 time in the discharge process of the battery are as follows: SOCT1 is calculated by using ampere-hour integration based on the initial SOC at the initial time; it is judged whether SOCT1 belongs to the calibration interval [SOChigh, 100%); if yes, an overcharge warning is issued to avoid damage to the battery due to overcharge, and it is judged whether SOCT0 is reliable; the value relationship of a, b and c is that b is greater than or equal to c, and c is greater than or equal to a, that is, the weight of the SOCocv corresponding to the open circuit voltage is greater than or equal to the weight of the SOCdyn corresponding to the dynamic voltage, and the weight of the SOCdyn is greater than or equal to the weight of the ampere-hour integration △SOCah; if not, it is judged whether SOCT1 belongs to the calibration interval [SOC4, SOChigh); if SOCT1 belongs to the calibration interval [SOC4, SOChigh), SOCT0 is reliable, and the value relationship of a, b and c is that b is greater than or equal to c, and c is greater than or equal to a; if not, it is judged whether SOCT1 belongs to the calibration interval [SOC3, SOC4); if SOCT1 belongs to the calibration interval [SOC3, SOC4), SOCT0 is not reliable, and the value relationship of a, b and c is that a is greater than or equal to c, and c is greater than or equal to b; if not, it is judged whether SOCT1 belongs to the calibration interval [SOC2, SOC3); if SOCT1 belongs to the calibration interval [SOC2, SOC3), SOCT0 is reliable, and the value relationship of a, b and c is that b is greater than or equal to c, and c is greater than or equal to a; if not, it is judged whether SOCT1 belongs to the calibration interval [SOC1, SOC2); if SOCT1 belongs to the calibration interval [SOC1, SOC2), SOCT0 is not reliable, and the value relationship of a, b and c is that a is greater than or equal to c, and c is greater than or equal to b; if not, it is judged whether SOCT1 belongs to the calibration interval [SOClow, SOC1); if SOCT1 belongs to the calibration interval [SOClow, SOC1), SOCT0 is reliable, and the value relationship of a, b and c is that b is greater than or equal to a, and a is greater than or equal to c; if not, it is judged whether SOCT1 belongs to the calibration interval [0, SOChigh), and if yes, a discharge prohibition warning is issued.If the battery enters a static state after T1, and the static time is greater than the second preset time, the SOCT1` is further calibrated by the open circuit voltage to obtain SOCT1``.

[0035] The SOC weighted calculation defines the weight of the open circuit voltage, dynamic voltage, and ampere-hour integral in both discharge and charge directions. According to the different intervals (SOClow, SOC1 to SOC4, SOChigh) passed by SOCT0 and SOCT1, the current size is implemented to distribute the weight, and the SOC is estimated. The different SOC intervals are described as follows: SOClow corresponds to the minimum available SOC. SOC1 is the upper limit of the [SOClow, SOC1) interval. In this interval, the SOC can be calibrated by increasing the weight of the open circuit voltage, the dynamic voltage, and the ampere-hour integral according to the current and charge-discharge quantity. SOC2 is the upper limit of the [SOC1, SOC2) interval. In this interval, the SOC can be calibrated by increasing the weight of the ampere-hour integral and dynamic voltage. Since the open circuit voltage is smooth in this interval, the weight of the open circuit voltage is the lowest. SOC3 is the upper limit of the [SOC2, SOC3) interval. In this interval, the SOC can be calibrated by increasing the weight of the open circuit voltage, the dynamic voltage, and the ampere-hour integral according to the current and charge-discharge quantity. SOC4 is the upper limit of the [SOC3, SOC4) interval. In this interval, the SOC can be calibrated by increasing the weight of the ampere-hour integral and dynamic voltage. Since the open circuit voltage is smooth in this interval, the weight of the open circuit voltage is the lowest. In the [SOC4, SOChigh) interval, the SOC can be calibrated by increasing the weight of the open circuit voltage, the dynamic voltage, and the ampere-hour integral according to the current and charge-discharge quantity. SOChigh corresponds to the maximum available SOC of the battery.

[0036] The SOC calculation method of the lithium iron phosphate battery of the present application is based on the real-time changes of voltage and current and the change of ampere-hour integral statistics, and the weights of open-circuit voltage, dynamic voltage and ampere-hour integral are defined in different SOC intervals to calibrate SOC. Different weights exist in different SOC intervals, so the battery SOC calculation can be converted into optimal SOC estimation in a three-dimensional environment, and the calculation accuracy of the SOC of the lithium iron phosphate battery is improved. After the vehicle is stationary (i.e. the current is lower than a certain value Imin) for a certain time Tocv, the open-circuit voltage of the lithium iron phosphate battery is obtained, and the corresponding SOCocv is obtained; during the charging / discharging process of the vehicle, the initial SOC SOCT0 is recorded, the SOC corresponding to the dynamic voltage (affected by temperature, current and resistance) is recorded, i.e. SOCdyn, the SOC change ΔSOCah obtained by ampere-hour integration is recorded, and the stop SOC SOCT1 is recorded, such as the vehicle stationary time exceeding Tocv to obtain SOCocv. In different SOC calibration intervals, combined with SOCocv, SOCdyn and ΔSOCah, the SOC calibration result SOCT1` is obtained according to the three-dimensional SOC weight in the span (including the intermediate span) from SOCT0 to SOCT1. SOCT1` is used as a new round of SOCT0 for estimation. Different weighting coefficients are used in the two directions of charging and discharging to complete SOC calibration.

[0037] The SOC weighted calculation method based on the lithium iron phosphate power battery improves the single-dimensional SOC calculation to SOC calibration in a three-dimensional environment. SOC calibration is completed through the accuracy advantage and internal connection of the three SOC corresponding relationships in different SOC intervals. The weight distribution between the three SOC corresponding relationships can be completed by calibration, and the requirement for controller computing power is not high, and it can be realized in a real vehicle.

[0038] The above has described various embodiments of the present disclosure, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The choice of terms used herein is intended to best explain the principles, practical applications or technical improvements in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the present document.

Claims

1. A method for calculating the State of Charge (SOC) of a lithium iron phosphate battery, characterized in that, include: Multiple SOC threshold points are determined based on the SOC-OCV curve of the battery, and multiple calibration intervals are determined based on the multiple SOC threshold points. Adjacent SOC threshold points correspond to the minimum and maximum values ​​of the calibration interval, respectively. Obtain the initial battery time SOCT0, calculate SOCT1 based on SOCT0 using ampere-hour integration, and determine the ΔSOCah corresponding to the ampere-hour integration; Obtain the dynamic voltage of the battery and determine its corresponding SOCdyn based on the dynamic voltage; Obtain the open-circuit voltage of the battery and determine its corresponding SOCocv based on the open-circuit voltage; Based on the calibration interval where SOCT1 is located, SOCT1 is calibrated using ΔSOCah, SOCdyn, and SOCocv to obtain the expression for SOCT1': SOCT1` = SOCT0 + △SOC, △SOC=aSOCdyn+bSOCocv+c△SOCah, Where a+b+c=1, the values ​​of a, b, and c are determined based on the calibration interval where SOCT1 is located, including: determining whether SOCT0 is reliable using a Kalman filter algorithm; if not reliable, then a is greater than or equal to c, and c is greater than or equal to b; if reliable, when the battery is in a charging state and the current is less than or equal to the set current threshold, then b is greater than or equal to a, and a is greater than or equal to c; when the battery is in a charging state and the current is greater than the set current threshold, then b is greater than or equal to c, and c is greater than or equal to a; when the battery is in a discharging state, then b is greater than or equal to c, and c is greater than or equal to a.

2. The method according to claim 1, characterized in that, Multiple SOC threshold points also include determining the minimum usable SOClow of the battery based on battery characteristics. When SOCT1 is less than or equal to SOClow, an over-discharge alarm is issued.

3. The method according to claim 2, characterized in that, Multiple SOC threshold points also include determining the battery's highest usable SOChigh based on battery characteristics. When SOCT1 is greater than or equal to SOChigh, an overcharge alarm is issued.

4. The method according to claim 3, characterized in that, The steps of obtaining the dynamic voltage of the battery and determining its corresponding SOCdyn based on the dynamic voltage include: determining the dynamic voltage based on the battery temperature, current and resistance, and determining the SOCdyn based on the dynamic voltage.

5. The method according to claim 4, characterized in that, The steps of obtaining the open-circuit voltage of the battery after it has been left to stand still, and determining the corresponding SOCocv based on the open-circuit voltage, include: obtaining the open-circuit voltage after the battery has been left to stand still for more than a first preset time, and determining the SOCocv corresponding to the open-circuit voltage based on the SOC-OCV curve.

6. The method according to claim 5, characterized in that, The step of correcting SOCT1 using ΔSOCah, SOCdyn, and SOCocv based on the calibration interval where SOCT1 is located to obtain SOCT1' also includes: determining the current state of the battery, obtaining the open-circuit voltage when the battery is left idle for more than a second preset time, and calibrating SOCT1' using the open-circuit voltage, wherein the second preset time is greater than the first preset time.

7. The method according to claim 1, characterized in that, It also includes using Kalman filtering to track the calibrated SOCT1' and determining that SOCT1' is unreliable when SOCT1' exceeds a set error threshold.

Images