CN117092530A - Method for estimating SOH capacity of lithium iron phosphate battery and readable storage medium - Google Patents
Method for estimating SOH capacity of lithium iron phosphate battery and readable storage medium Download PDFInfo
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- CN117092530A CN117092530A CN202310894445.8A CN202310894445A CN117092530A CN 117092530 A CN117092530 A CN 117092530A CN 202310894445 A CN202310894445 A CN 202310894445A CN 117092530 A CN117092530 A CN 117092530A
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 171
- 238000000034 method Methods 0.000 title claims abstract description 57
- 238000003860 storage Methods 0.000 title claims abstract description 20
- 230000008569 process Effects 0.000 claims abstract description 14
- 230000007613 environmental effect Effects 0.000 claims description 3
- 238000004140 cleaning Methods 0.000 claims description 2
- 230000005611 electricity Effects 0.000 abstract description 2
- 238000007599 discharging Methods 0.000 abstract 1
- 238000004590 computer program Methods 0.000 description 7
- 230000008859 change Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 238000005070 sampling Methods 0.000 description 5
- 230000006870 function Effects 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical group [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- QSNQXZYQEIKDPU-UHFFFAOYSA-N [Li].[Fe] Chemical compound [Li].[Fe] QSNQXZYQEIKDPU-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000013480 data collection Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/378—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC] specially adapted for the type of battery or accumulator
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
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Abstract
The embodiment of the application provides a method for estimating SOH capacity of a lithium iron phosphate battery and a readable storage medium, belonging to the field of SOH estimation of lithium iron phosphate batteries. The estimation method comprises the steps of judging whether the lithium iron phosphate battery is in a constant-current slow charge state or not; according to the method, the SOH capacity value of the lithium iron phosphate battery is estimated according to the inflection point and the charging end point, so that the estimation of the SOH capacity value of the lithium iron phosphate battery in the charging process can be realized, namely the estimation of the SOH capacity value of the lithium iron phosphate battery on the whole vehicle is realized without discharging electricity, and the reliability and the applicable environment of the estimation of the SOH capacity value of the lithium iron phosphate battery are improved.
Description
Technical Field
The application relates to the technical field of SOH estimation of lithium iron phosphate batteries, in particular to an estimation method of SOH capacity of a lithium iron phosphate battery and a readable storage medium.
Background
A lithium iron phosphate battery is a lithium ion battery using lithium iron phosphate (LiFePO 4) as a positive electrode material and carbon as a negative electrode material. The SOH capacity of the lithium iron phosphate battery is the battery health of the battery, and is also the percentage of the current capacity and the delivery capacity of the battery.
In the prior art, the SOH capacity of a lithium iron phosphate battery is generally estimated by a discharge experiment method, and the battery needs to be discharged until the voltage is close to a cut-off voltage, so that the percentage of the ratio of the electric quantity discharged by the battery to the rated capacity of the battery is the SOH capacity of the battery. However, the method needs to continuously discharge to a cut-off voltage, is difficult to realize on the whole vehicle, and cannot reliably measure the SOH capacity of the lithium iron phosphate battery.
The inventor discovers that the solution in the prior art has the defect that the SOH capacity of the lithium iron phosphate battery cannot be reliably measured on the whole vehicle in the process of realizing the application.
Disclosure of Invention
The embodiment of the application aims to provide a method for estimating the SOH capacity of a lithium iron phosphate battery and a readable storage medium, and the method for estimating the SOH capacity of the lithium iron phosphate battery and the readable storage medium can reliably measure the SOH capacity of the lithium iron phosphate battery on a whole vehicle.
In order to achieve the above objective, an embodiment of the present application provides a method for estimating SOH capacity of a lithium iron phosphate battery, including:
judging whether the lithium iron phosphate battery is in a constant-current slow charge state or not;
acquiring the ambient temperature of the lithium iron phosphate battery under the condition that the lithium iron phosphate battery is in a constant-current slow charge state;
judging whether the ambient temperature is within a preset range;
acquiring multiple groups of data of the lithium iron phosphate battery under the condition that the environmental temperature is judged to be in a preset range, wherein the data comprise an SOC value and a voltage;
determining a middle stage of the lithium iron phosphate battery according to a plurality of groups of data, and determining an inflection point on the middle stage;
and acquiring the SOH capacity value of the lithium iron phosphate battery according to the inflection point in the charging process and the end point when the charging is completed.
Optionally, determining a middle period of the lithium iron phosphate battery according to the plurality of sets of data, and determining an inflection point on the middle period includes:
initializing the first continuous times and the second continuous times to be 0;
taking three groups of continuous data as a data set;
calculating a first derivative of voltage with time in the data set according to formula (1),
wherein k is i For the first derivative of voltage with time, U, in the ith data set 1i For the voltage of the first group of the ith data set, U 3i And (3) for the voltage of the third group of the ith data set, T is the preset time interval, and i is an integer number.
Optionally, determining a middle period of the lithium iron phosphate battery according to the plurality of sets of data, and determining an inflection point on the middle period further includes:
judging whether the first derivative of the voltage and time in the data set is smaller than or equal to a preset threshold value;
under the condition that the first derivative of the voltage and time in the data set is less than or equal to a preset threshold value, updating the first continuous times according to a formula (2),
n 1 * ＝n 1 +1， (2)
wherein n is 1 * For the current first continuous times, n 1 For the last of said first consecutive times;
judging whether the first continuous times is larger than or equal to a first continuous times threshold value;
under the condition that the first continuous times are larger than or equal to a first continuous times threshold value, judging that the lithium iron phosphate battery is in a charging platform period;
under the condition that the first continuous times are smaller than a first continuous times threshold value, resetting the second continuous times, and acquiring a next data set;
returning to the step of calculating the first derivative of voltage with time in the data set according to equation (1).
Optionally, determining a middle period of the lithium iron phosphate battery according to the plurality of sets of data, and determining an inflection point on the middle period further includes:
in case it is determined that the first derivative of voltage with time in the data set is greater than a preset threshold, updating the second consecutive number of times according to formula (3),
n 2 * ＝n 2 +1， (3)
wherein n is 2 * For the current second continuous times, n 2 For the last said second consecutive number;
judging whether the second continuous times is larger than or equal to a second continuous times threshold value;
under the condition that the second continuous times are larger than or equal to a second continuous times threshold value, judging that the lithium iron phosphate battery is in a middle stage of charging;
under the condition that the second continuous times are smaller than a second continuous times threshold value, cleaning the first continuous times, and acquiring a next data set;
returning to the step of calculating the first derivative of voltage with time in the data set according to equation (1).
Optionally, determining a middle period of the lithium iron phosphate battery according to the plurality of sets of data, and determining an inflection point on the middle period further includes:
acquiring a plurality of data sets in the middle period;
respectively calculating first derivatives of voltage and time in a plurality of data sets according to a formula (1), and forming a derivative set;
obtaining a maximum value in the derivative set;
and determining the corresponding charging time according to the maximum value in the derivative set.
Optionally, according to the inflection point in the charging process and the end point when the charging is completed, obtaining the SOH capacity value of the lithium iron phosphate battery includes:
acquiring the completion time of the charging terminal point of the lithium iron phosphate battery;
calculating the charge time length of the lithium iron phosphate battery from the inflection point to the end point according to the formula (4),
ΔT＝T 2 -T 1 ， (4)
wherein DeltaT is the charging time length from the inflection point to the end point of the lithium iron phosphate battery, T 2 For the completion time, T 1 The charging time is the charging time;
calculating the charge amount of the lithium iron phosphate battery from the inflection point to the end point according to formula (5),
C 0 ＝ΔT·I， (5)
wherein C is 0 And I is the current of the lithium iron phosphate battery when the constant current is slowly charged.
Optionally, according to the inflection point in the charging process and the end point when the charging is completed, obtaining the SOH capacity value of the lithium iron phosphate battery further includes:
acquiring the coefficient of the lithium iron phosphate battery according to the temperature;
calculating the SOH capacity value of the lithium iron phosphate battery according to a formula (6),
wherein SOH is the SOH capacity value of the lithium iron phosphate battery, k is the coefficient, and C * Is the rated capacity of the lithium iron phosphate battery.
In another aspect, the present application also provides a computer-readable storage medium storing instructions for being read by a machine to cause the machine to perform the estimation method as described in any one of the above.
According to the technical scheme, the method for estimating the SOH capacity of the lithium iron phosphate battery and the readable storage medium are used for selecting the state of constant current slow charge and the temperature of the lithium iron phosphate battery, acquiring a plurality of groups of data during charging of the lithium iron phosphate battery, determining the middle period of charging of the lithium iron phosphate battery and the inflection point on the middle period of charging of the lithium iron phosphate battery according to the data, and estimating the SOH capacity value of the lithium iron phosphate battery according to the inflection point and the charging end point.
Additional features and advantages of embodiments of the application will be set forth in the detailed description which follows.
Drawings
The accompanying drawings are included to provide a further understanding of embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain, without limitation, the embodiments of the application. In the drawings:
fig. 1 is a flowchart of a method of estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application;
fig. 2 is a flowchart of acquiring a plurality of sets of data in a method for estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application;
FIG. 3 is a flowchart of finding a middle period in a method for estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application;
fig. 4 is a flowchart for obtaining an inflection point in a method for estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application;
fig. 5 is a flowchart for calculating a battery SOH capacity value in a method for estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application;
fig. 6 is a graph showing a relationship between voltage and SOC in a method for estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application.
Detailed Description
The following describes the detailed implementation of the embodiments of the present application with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating and illustrating the application, are not intended to limit the application.
Fig. 1 is a flowchart of a method of estimating SOH capacity of a lithium iron phosphate battery according to an embodiment of the present application, and in fig. 1, the estimation method may include:
in step S10, it is determined whether the lithium iron phosphate battery is in a constant current slow charge state.
In step S11, in the case where it is determined that the lithium iron phosphate battery is in the constant current slow charge state, the ambient temperature of the lithium iron phosphate battery is obtained. In the constant-current slow charge state of the lithium iron phosphate battery, the relationship between the voltage and the SOC value is affected by temperature, so that the ambient temperature of the lithium iron phosphate battery needs to be measured.
In step S12, it is determined whether the ambient temperature is within a preset range.
In step S13, under the condition that the environmental temperature is determined to be within the preset range, a plurality of sets of data of the lithium iron phosphate battery are obtained, wherein the data comprise an SOC value and a voltage. If the ambient temperature is within the preset range, it is indicated that there is a certain relationship between the voltage and the SOC value of the lithium iron phosphate battery, and specifically, fig. 6 may be used. If the ambient temperature is not within the preset range, stopping the estimation. Specifically, the temperature prediction range includes (25-T, 25+T), where T is the fluctuating temperature. Specifically, to further improve the accuracy of SOH capacity value estimation for lithium iron phosphate batteries, the range of data collection may include SOC values between 40% -80%. Specifically, as shown in fig. 6, the SOC value is between 40% and 80% and includes two plateau phases and one middle phase, and the middle phase is located between the two plateau phases, and the slope is higher, i.e., the jitter is greater.
In step S14, a middle stage of the lithium iron phosphate battery is determined according to the plurality of sets of data, and an inflection point on the middle stage is determined. As is clear from the relationship between the voltage and the SOC value of the lithium iron phosphate battery shown in fig. 6, when the SOC value of the lithium iron phosphate battery is around 65%, that is, there is a constant inflection point in the middle period where the slope is large, and therefore the inflection point can be regarded as a calibration point.
In step S15, the SOH capacity value of the lithium iron phosphate battery is obtained according to the inflection point in the charging process and the end point when the charging is completed. The end point when the charging is completed is also a fixed point, so that the SOH capacity value of the lithium iron phosphate battery can be calculated under the limitation of the inflection point and the position of the end point.
In step S10 to step S15, the state of the lithium iron phosphate battery is firstly determined to determine that the lithium iron phosphate battery is in a constant current slow charge state, and then the ambient temperature of the lithium iron phosphate battery is obtained, and under the condition that the ambient temperature is in a preset range, the SOC value and the voltage of the lithium iron phosphate battery are collected. And determining the middle stage of the lithium iron phosphate battery and inflection points on the middle stage according to the collected multiple groups of data, and combining with the end point of the charged lithium iron phosphate battery, so that the SOH capacity value of the lithium iron phosphate battery can be calculated.
The conventional estimation of the SOH capacity value of the lithium iron phosphate battery is generally estimated by using a discharge experiment method, but the method is difficult to realize on the whole vehicle, has larger limitation, and further affects the reliability of the SOH capacity value of the lithium iron phosphate battery. In the embodiment of the application, the sampling inflection point and the tail end point are combined with a mode of calculating the SOH capacity value of the lithium iron phosphate battery, so that the SOH capacity value of the lithium iron phosphate battery can be estimated in the charging process, namely, the SOH capacity value of the lithium iron phosphate battery is estimated on the whole vehicle, the electricity is not required to be discharged, and the reliability and the applicable environment of the SOH capacity value estimation of the lithium iron phosphate battery are improved.
In this embodiment of the present application, in order to obtain a voltage corresponding to the SOC value of the lithium iron phosphate battery between 40% and 80%, the SOC value of the lithium iron phosphate battery needs to be selected, and specifically, the selecting step may be as shown in fig. 2. Specifically, in fig. 2, the estimation method may include:
in step S20, the SOC value of the current lithium iron phosphate battery is obtained.
In step S21, it is determined whether the SOC value of the current lithium iron phosphate battery is greater than 40%.
In step S22, if it is determined that the SOC value of the current lithium iron phosphate battery is greater than 40%, it is again determined whether the SOC value of the current lithium iron phosphate battery is less than 80%.
In step S23, if it is determined that the SOC value of the current lithium iron phosphate battery is less than 80%, the SOC value and the voltage of the current lithium iron phosphate battery are obtained. If the value of the SOC value of the lithium iron phosphate battery is greater than 40% and less than 80%, it is indicated that the stage includes two stage periods and a middle stage period, and the SOC value and voltage in the range are obtained, so that the subsequent searching of the middle stage period can be facilitated.
In step S24, the SOC value of the next lithium iron phosphate battery is obtained at a preset time interval, and the SOC value of the next lithium iron phosphate battery is used as the SOC value of the current lithium iron phosphate battery. The SOC value of the next lithium iron phosphate battery is taken as the SOC value of the current lithium iron phosphate battery, that is, the SOC value representing the determination of the SOC value is real-time, and when the SOC value reaches the SOC value of the next lithium iron phosphate battery obtained according to the time interval, the SOC value of the next lithium iron phosphate battery is the SOC value of the lithium iron phosphate battery corresponding to the current moment at this time, that is, the SOC value of the lithium iron phosphate battery is obtained again after the preset time interval.
In step S25, a step of determining whether or not the SOC value of the current lithium iron phosphate battery is greater than 40% is returned. The SOC value of the next lithium iron battery still needs to be determined in the range where the SOC value is located, so as to ensure the reliability of subsequent estimation.
In step S26, if it is determined that the SOC value of the current lithium iron phosphate battery is 40% or less, the process returns to the step of acquiring the SOC value of the current lithium iron phosphate battery. If the SOC value of the lithium iron phosphate battery is less than or equal to 40%, it is indicated that the SOC value is not within the preferred sampling range at this time, and therefore, it is necessary to continuously monitor the SOC value of the lithium iron phosphate battery.
In step S27, if it is determined that the SOC value of the current lithium iron phosphate battery is 80% or more, the process returns to the step of acquiring the SOC value of the current lithium iron phosphate battery. In the same way, if the current SOC value of the lithium iron phosphate battery is greater than or equal to 80%, it is indicated that the SOC value is not within the preferred sampling range at this time, and therefore, it is necessary to continuously monitor the SOC value of the lithium iron phosphate battery.
In step S20 to step S27, the SOC value of the current lithium iron phosphate battery is first obtained, then it is determined whether the SOC value of the current lithium iron phosphate battery is between 40% and 80%, if so, the SOC value and the voltage at the current time are collected, otherwise, the SOC value of the lithium iron phosphate battery needs to be continuously monitored. The sampling limits the sampling range of the SOC value, so that the searching range and difficulty in the middle period are further reduced.
In this embodiment of the present application, in order to determine the inflection point on the middle stage of the lithium iron phosphate battery, it is necessary to determine the range of the middle stage first, and specifically the determination step may be as shown in fig. 3 and 4. Specifically, in fig. 3 and 4, the estimation method may further include:
in step S30, the first continuous number and the second continuous number are initialized to 0.
In step S31, three consecutive sets of data are taken as one data set.
In step S32, the first derivative of voltage with time in the data set is calculated according to equation (1),
wherein k is i For the first derivative of voltage with time, U, in the ith data set 1i For the voltage of the first group of the ith data set, U 3i For the voltage of the third group of the ith data set, T is a preset time interval, and i is an integer number. Wherein the change of the first derivative of voltage and time and the slope of the voltage and SOC valueThe change is the same, and the change rate of the available voltage and the first derivative of time reaction voltage is further the same.
In step S33, it is determined whether the first derivative of the voltage and time in the data set is less than or equal to a preset threshold. The preset threshold value is an intermediate value of the voltage change rate in the platform period and the change rate in the middle period.
In step S34, in case it is determined that the first derivative of the voltage with time in the data set is less than or equal to the preset threshold, the first continuous number is updated according to formula (2),
n 1 * ＝n 1 +1， (2)
wherein n is 1 * For the current first number of consecutive times, n 1 Is the last first consecutive number. Specifically, if the first derivative of voltage and time is less than or equal to the preset threshold, it is indicated that the lithium iron phosphate battery may be in the plateau phase at this time.
In step S35, it is determined whether the first number of consecutive times is greater than or equal to a first consecutive time threshold.
In step S36, in the case where it is determined that the first continuous number is greater than or equal to the first continuous number threshold, it is determined that the lithium iron phosphate battery is in the plateau phase of charging. If the first continuous times is greater than or equal to the first continuous times threshold, the continuous times that the voltage and the first derivative of time of the lithium iron phosphate battery are both smaller than or equal to the preset threshold satisfy the requirement of the plateau, and the lithium iron phosphate battery can be determined to be in the charged plateau.
In step S37, if the first number of consecutive times is determined to be smaller than the first number of consecutive times threshold, the second number of consecutive times is cleared, and the next data set is acquired. If the first continuous times is smaller than the first continuous times threshold, it is indicated that the continuous times of which the voltage and the first derivative of time of the lithium iron phosphate battery are smaller than or equal to the preset threshold do not meet the requirement of the plateau, and whether the lithium iron phosphate battery is in the charged plateau cannot be determined temporarily. In addition, if the first continuous times is smaller than the first continuous times threshold value, the lithium iron phosphate battery is not in the middle period, and the second continuous times are cleared.
In step S38, the first derivative step of the voltage with time in the data set is calculated according to formula (1) is returned. And when the first continuous times are smaller than the first continuous times threshold value, continuing to calculate the next data set.
In step S39, in case it is determined that the first derivative of voltage with time in the data set is greater than the preset threshold, the second consecutive number of times is updated according to formula (3),
n 2 * ＝n 2 +1， (3)
wherein n is 2 * For the current second consecutive number, n 2 For the last second consecutive number. Specifically, if the first derivative of voltage and time is greater than the preset threshold, it indicates that the lithium iron phosphate battery may be in a middle stage at this time.
In step S40, it is determined whether the second consecutive times is greater than or equal to a second consecutive times threshold.
In step S41, in the case where it is determined that the second continuous number is greater than or equal to the second continuous number threshold, it is determined that the lithium iron phosphate battery is in the middle stage of charging. If the second continuous times is greater than or equal to the second continuous times threshold, the continuous times that the voltage and the first derivative of time of the lithium iron phosphate battery are both greater than the preset threshold meet the requirement of the platform period, and the lithium iron phosphate battery can be determined to be in the middle period of charging.
In step S42, if the second continuous frequency is determined to be smaller than the second continuous frequency threshold, the first continuous frequency is cleared, and the next data set is acquired. If the second continuous times is smaller than the second continuous times threshold, it is indicated that the continuous times of which the voltage and the first derivative of time of the lithium iron phosphate battery are smaller than or equal to the preset threshold do not meet the requirement of the plateau, and whether the lithium iron phosphate battery is in the charged plateau cannot be determined temporarily. In addition, if the second continuous times is smaller than the second continuous times threshold value, the lithium iron phosphate battery is not in the platform phase, and the first continuous times are cleared.
In step S43, the first derivative step of the voltage with time in the data set is calculated according to formula (1) is returned. And when the second continuous times are smaller than the second continuous times threshold value, continuing to calculate the next data set.
In step S44, a plurality of data sets in the middle period are acquired. After the middle period is determined, multiple groups of data in the middle period are acquired.
In step S45, first derivatives of voltages and time in the plurality of data sets are calculated according to formula (1), respectively, and derivative sets are formed.
In step S46, the maximum value in the derivative set is acquired. The value with the largest slope in the middle stage is the inflection point.
In step S47, the corresponding charging moment is determined from the maximum value in the derivative set. Wherein, the charging moment is determined according to the inflection point.
In steps S30 to S47, the data set of the lithium iron phosphate battery is calculated to obtain a first derivative of voltage and time, and the first derivative is compared with a preset threshold value and recorded for a plurality of times. If the continuous times of the first derivative smaller than or equal to the preset threshold value is larger than or equal to the first continuous times threshold value, the continuous times of the first derivative smaller than or equal to the preset threshold value are indicated to meet the requirement of the plateau, the plateau is considered, and otherwise, the plateau is the middle-stage. After the middle period is identified, calculating the data in the middle period again, and searching a value with the maximum first derivative of the voltage and time, wherein the value is a value corresponding to the inflection point. The method can accurately and reliably find the inflection point position on the middle stage and the corresponding charging time.
In this embodiment of the present application, after the charge time of the inflection point is obtained, it is also necessary to estimate the SOH capacity value of the lithium iron phosphate battery, and specifically the estimation step may be as shown in fig. 5. Specifically, in fig. 5, the estimation method may further include:
in step S50, the completion time of the charging end point of the lithium iron phosphate battery is obtained. The charging end point is the point corresponding to 100% of the SOC value, and the moment value at the moment is obtained, namely the completion moment.
In step S51, the charge duration of the lithium iron phosphate battery from the inflection point to the end point is calculated according to formula (4),
ΔT＝T 2 -T 1 ， (4)
wherein DeltaT is the charging time from the inflection point to the end point of the lithium iron phosphate battery, T 2 To complete the moment, T 1 Is the charging time.
In step S52, the charge amount of the lithium iron phosphate battery from the inflection point to the end point is calculated according to formula (5),
C 0 ＝ΔT·I， (5)
wherein C is 0 And I is the current of the lithium iron phosphate battery when the constant current is slowly charged. Specifically, since the lithium iron phosphate battery is charged slowly with constant current, I is a constant value.
In step S53, the coefficient of the lithium iron phosphate battery is obtained according to the temperature. Wherein the coefficient varies with temperature.
In step S54, the SOH capacity value of the lithium iron phosphate battery is calculated according to formula (6),
wherein SOH is SOH capacity value of lithium iron phosphate battery, k is coefficient, C * Is the rated capacity of the lithium iron phosphate battery.
In steps S50 to S54, a charge amount is calculated according to the time values of the inflection point and the end point and the charge current, and the SOH capacity value of the lithium iron phosphate battery is calculated according to the charge amount, and is accurate and reliable.
In another aspect, the present application also provides a computer-readable storage medium, in particular, the computer-readable storage medium storing instructions for being read by a machine to cause the machine to perform the estimation method as any one of the above.
According to the technical scheme, the method for estimating the SOH capacity of the lithium iron phosphate battery and the readable storage medium are used for selecting the state of constant current slow charge and the temperature of the lithium iron phosphate battery, acquiring a plurality of groups of data during charging of the lithium iron phosphate battery, determining the middle period of charging of the lithium iron phosphate battery and the inflection point on the middle period of charging of the lithium iron phosphate battery according to the data, and estimating the SOH capacity value of the lithium iron phosphate battery according to the inflection point and the charging end point.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
In one typical configuration, a computing device includes one or more processors (CPUs), input/output interfaces, network interfaces, and memory.
The memory may include volatile memory in a computer-readable medium, random Access Memory (RAM) and/or nonvolatile memory, etc., such as Read Only Memory (ROM) or flash RAM. Memory is an example of a computer-readable medium.
Computer readable media, including both non-transitory and non-transitory, removable and non-removable media, may implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of storage media for a computer include, but are not limited to, phase change memory (PRAM), static Random Access Memory (SRAM), dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium, which can be used to store information that can be accessed by a computing device. Computer-readable media, as defined herein, does not include transitory computer-readable media (transmission media), such as modulated data signals and carrier waves.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises an element.
The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and variations of the present application will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the application are to be included in the scope of the claims of the present application.
Claims (8)
1. The method for estimating the SOH capacity of the lithium iron phosphate battery is characterized by comprising the following steps of:
judging whether the lithium iron phosphate battery is in a constant-current slow charge state or not;
acquiring the ambient temperature of the lithium iron phosphate battery under the condition that the lithium iron phosphate battery is in a constant-current slow charge state;
judging whether the ambient temperature is within a preset range;
acquiring multiple groups of data of the lithium iron phosphate battery under the condition that the environmental temperature is judged to be in a preset range, wherein the data comprise an SOC value and a voltage;
determining a middle stage of the lithium iron phosphate battery according to a plurality of groups of data, and determining an inflection point on the middle stage;
and acquiring the SOH capacity value of the lithium iron phosphate battery according to the inflection point in the charging process and the end point when the charging is completed.
2. The method of estimating according to claim 1, wherein determining a mid-period of the lithium iron phosphate battery from the plurality of sets of the data, and determining an inflection point on the mid-period comprises:
initializing the first continuous times and the second continuous times to be 0;
taking three groups of continuous data as a data set;
calculating a first derivative of voltage with time in the data set according to formula (1),
wherein k is i For the first derivative of voltage with time, U, in the ith data set 1i For the voltage of the first group of the ith data set, U 3i And (3) for the voltage of the third group of the ith data set, T is the preset time interval, and i is an integer number.
3. The method of estimating according to claim 2, wherein determining a mid-period of the lithium iron phosphate battery from the plurality of sets of the data, and determining an inflection point on the mid-period further comprises:
judging whether the first derivative of the voltage and time in the data set is smaller than or equal to a preset threshold value;
under the condition that the first derivative of the voltage and time in the data set is less than or equal to a preset threshold value, updating the first continuous times according to a formula (2),
n 1 * ＝n 1 +1， (2)
wherein n is 1 * For the current first continuous times, n 1 For the last of said first consecutive times;
judging whether the first continuous times is larger than or equal to a first continuous times threshold value;
under the condition that the first continuous times are larger than or equal to a first continuous times threshold value, judging that the lithium iron phosphate battery is in a charging platform period;
under the condition that the first continuous times are smaller than a first continuous times threshold value, resetting the second continuous times, and acquiring a next data set;
returning to the step of calculating the first derivative of voltage with time in the data set according to equation (1).
4. The method of estimating according to claim 3 wherein determining a mid-period of the lithium iron phosphate battery based on the plurality of sets of data and determining an inflection point on the mid-period further comprises:
in case it is determined that the first derivative of voltage with time in the data set is greater than a preset threshold, updating the second consecutive number of times according to formula (3),
n 2 * ＝n 2 +1， (3)
wherein n is 2 * For the current second continuous times, n 2 For the last said second consecutive number;
judging whether the second continuous times is larger than or equal to a second continuous times threshold value;
under the condition that the second continuous times are larger than or equal to a second continuous times threshold value, judging that the lithium iron phosphate battery is in a middle stage of charging;
under the condition that the second continuous times are smaller than a second continuous times threshold value, cleaning the first continuous times, and acquiring a next data set;
returning to the step of calculating the first derivative of voltage with time in the data set according to equation (1).
5. The method of estimating according to claim 4 wherein determining a mid-period of the lithium iron phosphate battery based on the plurality of sets of data and determining an inflection point on the mid-period further comprises:
acquiring a plurality of data sets in the middle period;
respectively calculating first derivatives of voltage and time in a plurality of data sets according to a formula (1), and forming a derivative set;
obtaining a maximum value in the derivative set;
and determining the corresponding charging time according to the maximum value in the derivative set.
6. The method of estimating according to claim 5, wherein obtaining the SOH capacity value of the lithium iron phosphate battery according to the inflection point during the charging and the end point at the completion of the charging comprises:
acquiring the completion time of the charging terminal point of the lithium iron phosphate battery;
calculating the charge time length of the lithium iron phosphate battery from the inflection point to the end point according to the formula (4),
ΔT＝T 2 -T 1 ， (4)
wherein DeltaT is the charging time length from the inflection point to the end point of the lithium iron phosphate battery, T 2 For the completion time, T 1 The charging time is the charging time;
calculating the charge amount of the lithium iron phosphate battery from the inflection point to the end point according to formula (5),
C 0 ＝ΔT·I， (5)
wherein C is 0 And I is the current of the lithium iron phosphate battery when the constant current is slowly charged.
7. The method of estimating according to claim 6, wherein obtaining the SOH capacity value of the lithium iron phosphate battery according to the inflection point during the charging and the end point at the completion of the charging further comprises:
acquiring the coefficient of the lithium iron phosphate battery according to the temperature;
calculating the SOH capacity value of the lithium iron phosphate battery according to a formula (6),
wherein SOH is the SOH capacity value of the lithium iron phosphate battery, k is the coefficient, and C * Rated for the lithium iron phosphate batteryCapacity.
8. A computer readable storage medium storing instructions for being read by a machine to cause the machine to perform the estimation method according to any one of claims 1 to 7.
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