CN115219900A - State monitoring method and device for lithium ion battery system - Google Patents
State monitoring method and device for lithium ion battery system Download PDFInfo
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- 238000012544 monitoring process Methods 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims abstract description 49
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 34
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 34
- 239000000178 monomer Substances 0.000 claims abstract description 103
- 238000004891 communication Methods 0.000 claims abstract description 12
- 238000010606 normalization Methods 0.000 claims description 42
- 238000012545 processing Methods 0.000 claims description 4
- 230000008447 perception Effects 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 3
- 238000012806 monitoring device Methods 0.000 description 3
- 238000003745 diagnosis Methods 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 230000000284 resting effect Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000013480 data collection Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000000126 substance Substances 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]
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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
- G01R31/387—Determining ampere-hour charge capacity or SoC
- G01R31/388—Determining ampere-hour charge capacity or SoC involving voltage measurements
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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]
- G01R31/389—Measuring internal impedance, internal conductance or related 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]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention discloses a state monitoring method of a lithium ion battery system, which comprises the steps of collecting the voltage and temperature values of each battery monomer, primarily judging the voltage and temperature values of each battery monomer, adjusting the warning values of all the battery monomers to be f times of the original values, normalizing the voltage and temperature values of each battery monomer collected in the step (1), projecting the normalized voltage and temperature values onto a coordinate system, drawing a circle by taking a projection point as the center of a circle and r as the radius, obtaining the number of projection points contained in the circle, adjusting and comparing the warning values and the like; the invention also discloses a state monitoring system of the lithium ion battery system, which comprises an acquisition module, a storage module, an operation module and a communication module. The state monitoring method and the state monitoring system provided by the invention have the advantages of simple logic, scientificity, reasonability, small calculated amount, small storage space and high reliability, and fully consider the temperature consistency of each battery monomer in the battery system and the dynamic change factors thereof.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a state monitoring method and device of a lithium ion battery system.
Background
The lithium ion battery is widely applied to various departments of national economy and the field of resident life, and as a chemical energy storage device with higher energy density and activity, various fault problems inevitably exist in the service process of the lithium ion battery. For the fields of electric automobiles, energy storage and the like, a plurality of lithium ion battery monomers are connected in series and in parallel to form a battery system, the failure rate of the battery system is obviously higher than that of the battery monomers due to the difference of the consistency of the battery monomers, and the damage degree of the battery system after failure is far higher than that of the battery monomers. Therefore, a state monitoring and fault diagnosis technique of the battery system is highly valued. Any condition monitoring and fault diagnosis technique relies on the acquisition of operational data of the monitored object. For lithium ion battery systems, limited to cost and complexity, only the temperature and voltage values of the individual cells making up the system are typically monitored. In the known technical means, the temperature value and the voltage value of each battery cell are generally simply compared with certain upper and lower limit threshold values and judged as a fault if the temperature value and the voltage value of the battery cell exceed the limited ranges. The method does not consider direct damage and potential damage caused by serious reduction of consistency of each battery cell in the battery system, and does not consider dynamic change factors. In fact, if the temperature value or the voltage value of a certain battery cell in the battery system is significantly different from that of other battery cells, the consistency of the battery system is poor, so that the capacity, the power and the safety of the battery system are reduced, and even a thermal runaway accident is caused in a severe case. Therefore, data collection based on the temperature value and the voltage value of the battery is urgently needed, the consistency problem among the single batteries is comprehensively and dynamically considered, and further more effective state monitoring is carried out.
Disclosure of Invention
In order to solve the technical problems, the invention provides the method and the device for monitoring the state of the lithium ion battery, which have the advantages of simple logic, science and reasonability, small calculated amount, small storage space and high reliability.
According to one aspect of the present invention, a state monitoring method for a lithium ion battery system is provided, each battery cell in the battery system is numbered in sequence and is endowed with a warning value, wherein the battery cell with the number i is marked with the warning value W i And the warning values of all the battery monomers are 0 before the battery system leaves the factory; after the battery system leaves the factory, preferably at fixed time intervalsAnd the time interval is between 1 second and 1 minute, and the following steps are sequentially executed for state monitoring:
collecting the voltage value and the temperature value of each battery monomer in the battery system, wherein for the battery monomer with the serial number i in the battery system, the collected voltage value of the battery monomer is recorded as U i A temperature value of T i ；
Step 2, preliminarily judging the voltage and temperature values of each battery monomer, and if any one of the following conditions is met:
(i) At least one battery monomer exists, and the voltage value of the battery monomer is smaller than the lower limit value of the voltage value of the battery monomer or larger than the upper limit value of the voltage value of the battery monomer;
(ii) At least one battery monomer exists, and the temperature value of the battery monomer is greater than the upper limit value of the temperature of the battery monomer;
terminating the execution of all the state monitoring steps, outputting a battery number meeting any one of the conditions (i) and (ii), and judging that the battery system has a fault;
if the condition (i) and the condition (ii) are not met, entering the next step;
step 3, adjusting the warning values of all the battery monomers to be f times of the original values, wherein f is between 0.8 and 0.95;
step 4, normalizing the voltage and temperature values of each battery cell collected in the step 1:
the voltage normalization process for the battery cell with the number i is performed according to the following formula:
in the formula u i Is the normalized voltage value of the battery cell with the number i, U i For the voltage value, U, of the battery cell with the number i acquired in step 1 max Is the maximum value, U, of the voltage values of all the battery cells collected in step 1 min For step 1 CollectionThe minimum value of the voltage values of all the battery cells;
the temperature normalization process for the battery cell with the number i is performed according to the following formula:
in the formula, t i Is the temperature normalized value, T, of the battery cell numbered i i The temperature value T of the battery monomer with the number i acquired in the step 1 max Is the maximum value T of the temperature values of all the battery cells collected in the step 1 min The minimum value of the temperature values of all the single batteries collected in the step 1 is obtained;
and 5, combining the voltage normalization values and the temperature normalization values of all the battery monomers obtained in the step 4 respectively, and projecting the voltage normalization values and the temperature normalization values onto a two-dimensional Cartesian coordinate system with the voltage normalization values as abscissa and the temperature normalization values as ordinate, wherein the projection coordinate of the battery monomer with the number i on the coordinate system is (u) i ,t i )；
Step 6, finding a projection point which is closest to the coordinate (0.5 ) on the coordinate system, drawing a circle by taking the projection point as the center of the circle and r as the radius, obtaining the number of projection points contained in the circle and recording the number as Mc, wherein the radius r is between 0.001 and 0.2;
and 7, processing all the rest projection points except the projection point closest to the coordinates (0.5 ) in the step 6 according to the following method:
for the battery cell with the number i, the coordinates (u) of the projection point of the battery cell are used i ,t i ) Drawing a circle by taking r as a radius as a circle center, obtaining the number of projection points contained in the circle and recording as M i (ii) a If M is i <kMc, then the warning value W i Increasing 1 on the basis of the value of the step 3, otherwise, increasing the warning value W of the step i Keeping the original shape; wherein u is i 、t i Respectively obtaining a voltage normalization value and a temperature normalization value of the battery monomer with the serial number i; r is a radius between 0.001 and 0.2; k is a proportionality coefficient between 0.05 and 0.3A (c) is added; w is a group of i The number of the battery monomer is i;
step 8, comparing the warning values of all the battery monomers with a warning value upper limit Wc respectively, if the warning value of any battery monomer is greater than the warning value upper limit Wc, terminating the execution of all the state monitoring steps, outputting the serial numbers of the battery monomers of which the warning values are greater than the warning value upper limit Wc, and judging that the battery system has faults; otherwise, returning to the step 1; wherein the upper warning limit is between 10 and 100.
In the state monitoring method of the lithium ion battery system, in the step 2, the lower limit value of the voltage of the battery monomer is between 1.8V and 2.5V, and the upper limit value of the voltage of the battery monomer is between 3.7V and 5V.
In the method for monitoring the state of the lithium ion battery system, the upper limit value of the temperature of the battery monomer in the step 2 is between 55 ℃ and 70 ℃.
According to another aspect of the invention. Providing a state monitoring system applying the state monitoring method of the lithium ion battery system, wherein the state monitoring system comprises an acquisition module, a storage module, an operation module and a communication module; wherein:
the acquisition module is used for acquiring voltage values and temperature values of all battery monomers in the battery system and transmitting acquired data to the storage module;
the storage module is used for receiving and storing the acquisition data acquired by the acquisition module and the operation data acquired by the operation module;
the operation module reads data from the storage module, performs operation and judgment according to the state monitoring method of the lithium ion battery system in claims 1-3, and transmits the result to the communication module;
the communication module is used for receiving the operation and judgment results of the operation module and transmitting the operation and judgment results to external equipment for perception of a user.
The invention has the beneficial effects that:
1. the state monitoring method of the lithium ion battery system has the advantages of simple logic, scientific and reasonable structure, small calculated amount, small storage space and high reliability, fully utilizes the voltage and temperature acquisition data of each battery in the service process of the battery system, and focuses on state monitoring and evaluation from the dynamic change angle of consistency. In the process of executing the steps 1 to 8 each time, the warning values of all the battery monomers are reduced to f times of the original values in the step 3, wherein f actually plays a role of a forgetting factor, if the warning value of a certain battery monomer has a certain increasing trend in a certain period in history but does not exceed the upper limit of the warning value, the proportion of the historical increasing part of the warning value in the history to the current warning value is smaller and smaller along with the passage of time, and the recent increasing amount and the current increasing amount of the warning value have larger proportions, so that the historical accidental phenomenon can be eliminated; and if the state of the battery system is improved in the service process, the influence of the problems in the historical stage on the current state can be gradually weakened. And 4, only normalizing the voltage and temperature acquisition values in the monitoring step cycle, so that the pertinence is strong, the voltage and temperature acquisition values are both between 0 and 1, the data are comparable, and whether the battery system is in a charging, discharging or resting state is not considered. In step 6, the projection point closest to the coordinates (0.5 ) on the coordinate system is found, which is actually the point with the most central position, usually the projection points around the position are the most dense, a circle is drawn by taking the projection points as the center of the circle, and the number of projection points contained in the circle is taken as the subsequent comparison reference, which has the advantage of good universality. On the basis, all the projection points draw circles by taking the projection points as circle centers and the number of the projection points contained in the circles is compared with a certain proportion of the reference number of the projection points in the step 6, if the number of the projection points contained in the circles by taking a certain projection point as the circle center is less, the number of the projection points at the position of the projection point is very sparse, and the projection points deviate from the overall voltage and temperature distribution condition and have poor consistency; if the situation occurs continuously for a plurality of times in the subsequent monitoring step circulation of the single battery corresponding to the projection point, the situation that the acquired data of the single battery obviously deviates from other single batteries can be basically determined, the consistency is poor, and the fault can be judged.
2. Although the lithium ion battery state monitoring method carries out calculation and analysis on the voltage and temperature data of all the single batteries acquired each time and fully utilizes all the data, the method does not have complicated calculation with large memory overhead; after each cycle of monitoring steps is completed, except for the fault judgment result, only the serial number of each battery monomer and the warning value thereof are actually transmitted to the next cycle, so that a large amount of memory and storage space are saved, the data communication quantity is very limited, and the state monitoring device of the battery system applying the method also has the advantages of low cost and high reliability.
Drawings
Fig. 1 is a flow field diagram of a state monitoring method for a lithium ion battery system in an embodiment of the present invention.
Fig. 2 is a schematic composition diagram of a lithium ion battery internal short circuit simulation device according to an embodiment of the present invention.
Fig. 3 is a projection diagram of the voltage normalization value and the temperature normalization value corresponding to the battery cells numbered 1 to 20 in the embodiment of the present invention on a two-dimensional coordinate system.
Detailed Description
The invention is further described below with reference to the figures and examples.
As shown in FIG. 1, in a state monitoring method of a lithium ion battery system, each battery cell in the battery system is numbered in sequence and is endowed with a warning value, wherein the warning value of the battery cell with the number i is recorded as W i And the warning values of all the battery monomers are 0 before the battery system leaves a factory; after the battery system leaves a factory, according to a fixed time interval, the following steps are sequentially executed for state monitoring:
collecting the voltage value and the temperature value of each battery monomer in the battery system, wherein for the battery monomer with the serial number i in the battery system, the collected voltage value of the battery monomer is recorded as U i A temperature value of T i ；
Step 2, preliminarily judging the voltage and temperature values of each battery monomer, and if any one of the following conditions is met:
(i) At least one battery monomer exists, and the voltage value of the battery monomer is smaller than the lower limit value of the voltage value of the battery monomer or larger than the upper limit value of the voltage value of the battery monomer;
(ii) At least one single battery exists, and the temperature value of the single battery is greater than the upper limit value of the temperature of the single battery;
terminating the execution of all the state monitoring steps, outputting a battery number meeting any one of the conditions (i) and (ii), and judging that the battery system has a fault;
if the condition (i) and the condition (ii) are not met, entering the next step;
step 3, adjusting the warning values of all the battery monomers to be f times of the original values, wherein f is between 0.8 and 0.95;
step 4, normalizing the voltage and temperature values of each battery monomer collected in the step 1:
the voltage normalization process for the battery cell with the number i is performed according to the following formula:
in the formula u i Is the voltage normalization value of the battery cell with the number i, U i The voltage value, U, of the battery cell with the number i acquired in the step 1 max Is the maximum value, U, of the voltage values of all the battery cells collected in step 1 min The minimum value of the voltage values of all the battery monomers acquired in the step 1 is obtained;
the temperature normalization process for the battery cell with the number i is performed according to the following formula:
in the formula, t i Is the temperature normalization value, T, of the battery cell numbered i i The temperature value T of the battery monomer with the number i acquired in the step 1 max Is the maximum value T of the temperature values of all the battery cells collected in the step 1 min Collected for step 1The minimum value of the temperature values of the single batteries exists;
and 5, combining the voltage normalization values and the temperature normalization values of all the battery monomers obtained in the step 4 respectively, and projecting the voltage normalization values and the temperature normalization values onto a two-dimensional Cartesian coordinate system with the voltage normalization values as abscissa and the temperature normalization values as ordinate, wherein the projection coordinate of the battery monomer with the number i on the coordinate system is (u) i ,t i )；
Step 6, finding a projection point which is closest to the coordinate (0.5 ) on the coordinate system, drawing a circle by taking the projection point as the center of the circle and r as the radius, obtaining the number of projection points contained in the circle and recording the number as Mc, wherein the radius r is between 0.001 and 0.2;
and 7, processing all the rest projection points except the projection point closest to the coordinates (0.5 ) in the step 6 according to the following method:
for the battery cell with the number i, the coordinates (u) of the projection point of the battery cell are used i ,t i ) Drawing a circle by taking r as a radius as a circle center, obtaining the number of projection points contained in the circle and recording as M i (ii) a If M is i <kMc, then the warning value W i Increasing 1 on the basis of the value of the step 3, otherwise, increasing the warning value W of the value i The change is not changed; wherein u is i 、t i The voltage normalization value and the temperature normalization value of the battery cell with the serial number i are respectively; r is a radius between 0.001 and 0.2; k is a proportionality coefficient between 0.05 and 0.3; w i The number of the battery monomer is i;
step 8, comparing the warning values of all the battery monomers with a warning value upper limit Wc respectively, if the warning value of any battery monomer is greater than the warning value upper limit Wc, terminating the execution of all the state monitoring steps, outputting the serial numbers of the battery monomers of which the warning values are greater than the warning value upper limit Wc, and judging that the battery system has faults; otherwise, returning to the step 1; wherein the upper warning limit is between 10 and 100.
In the state monitoring method of the lithium ion battery system, in the step 2, the lower limit value of the voltage of the battery monomer is between 1.8V and 2.5V, and the upper limit value of the voltage of the battery monomer is between 3.7V and 5V.
In the method for monitoring the state of the lithium ion battery system, the upper limit value of the temperature of the battery monomer in the step 2 is between 55 ℃ and 70 ℃.
As shown in fig. 2, the state monitoring system applying the state monitoring method of the lithium ion battery system includes an acquisition module, a storage module, an operation module and a communication module; wherein:
the acquisition module is used for acquiring voltage values and temperature values of all battery monomers in the battery system and transmitting acquired data to the storage module;
the storage module is used for receiving and storing the acquisition data acquired by the acquisition module and the operation data acquired by the operation module;
the operation module reads data from the storage module, performs operation and judgment according to the state monitoring method of the lithium ion battery system in claims 1-3, and transmits the result to the communication module;
the communication module is used for receiving the operation and judgment results of the operation module and transmitting the operation and judgment results to external equipment for perception of a user.
Examples
A lithium ion battery system for an electric automobile comprises 150 lithium iron phosphate prismatic lithium ion batteries which are connected in series, and the serial numbers of the batteries are respectively 1 to 150. Before the battery system leaves a factory, the warning values of all the battery monomers are 0. After shipment, the condition monitoring is cyclically performed at time intervals of 30 seconds. In this embodiment, the lower limit of the single battery voltage is 1.8V, the upper limit of the single battery voltage is 3.8V, and the upper limit of the single battery temperature is 65 ℃.
The following description will be given by taking the condition monitoring and calculation of the first round as an example, the flow chart of the monitoring process is shown in fig. 1, and the composition of the monitoring device is schematically shown in fig. 2.
And 2, preliminarily judging the voltage and temperature values of each battery monomer, and finding that the voltage values of all the battery monomers are in the range from the voltage lower limit value of the battery monomer to the voltage upper limit value of the battery monomer, and the temperature values of all the battery monomers are smaller than the temperature upper limit value of the battery monomer, so that the step 3 is subsequently carried out.
And 3, adjusting the warning values of all the battery monomers to be f times of the original values, wherein the value of f is 0.9, and the warning values of all the battery monomers are 0 before the state monitoring and calculation in the current round, so that the warning values of all the battery monomers continue to be 0 after the calculation and the updating in the step.
Step 4, normalizing the voltage and temperature values of each battery monomer collected in the step 1, and finding the maximum value U in the voltage values of all the battery monomers collected in the step 1 in the processing process max =3.32V, minimum value U of voltage values of all battery cells min =3.28V, maximum value T of temperature values of all battery cells max =26.5 ℃, minimum value T of temperature values of all battery cells min ＝25.8℃。
And 5, combining the voltage normalization values and the temperature normalization values of all the single batteries obtained in the step 4 respectively, and projecting the combined values onto a two-dimensional Cartesian coordinate system taking the voltage normalization values as abscissa and the temperature normalization values as ordinate. For convenience of observation, only the projection of the voltage normalization value and the temperature normalization value corresponding to the battery cells numbered 1 to 20 are given in this embodiment, as shown in fig. 3.
And 6, finding a projection point which is closest to the coordinates (0.5 and 0.5) on the coordinate system, wherein the coordinates of the projection point are (0.534 and 0.478), and the number of the corresponding battery cell is 18. Drawing a circle with (0.534, 0.478) as the center and r =0.1 as the radius, the number of projection points contained in the circle is Mc =22, that is, there are 22 single cells, and the temperature and voltage of the 22 single cells are closer to those of the battery cell numbered 18.
And 7, drawing a circle by taking the position of the residual projection point as the center of the circle and taking r =0.1 as the radius respectively to obtain the number of the projection points contained in the circle. In this embodiment, if the proportionality coefficient k is 0.2, kMc is 4.4, and it is found that the number of projected points contained in the corresponding circles of the three battery cells numbered 35, 68 and 143 is less than or equal to 4, which indicates the temperature and the electricity of the three battery cells and other battery cells in the battery systemIf the voltage comprehensive state difference is large, the alarm values of the three battery cells numbered 35, 68 and 143 are increased by 1 to become W 35 ＝W 68 ＝W 143 =1; while the alert values of the other 147 cells remain at 0.
And 8, comparing the warning values of all the single batteries with the upper warning value limit Wc =20 respectively, and returning to the step 1 to perform the next round of state monitoring and calculation if the warning values of all the single batteries are smaller than the upper warning value limit Wc = 20.
In one year after the electric automobile leaves a factory, although the warning values of certain battery monomers rise frequently, the warning values do not exceed the upper limit of the warning values all the time; and the alarm values of the battery cells are continuously adjusted to be lower as time goes on. And (3) continuously increasing the alarm value of the battery monomer with the number of 107 for a plurality of times until a certain day after one year, breaking through the upper limit of the alarm value at a certain running moment, stopping the execution of all the state monitoring steps, outputting the battery monomer number of 107 to a running computer of the electric automobile, and judging that a battery system has faults. And returning the electric automobile to the factory, and after the single battery is replaced, recovering the battery system to be normal.
It should be noted that, when it is determined that the battery system has a fault and the battery system is maintained, the battery system is put into use again after the warning values of all the battery cells are set to 0.
The state monitoring method of the lithium ion battery system is simple in logic, scientific and reasonable, small in calculated amount, small in storage space and high in reliability, fully utilizes the voltage and temperature acquisition data of each battery in the service process of the battery system, and focuses on state monitoring evaluation from the dynamic change angle of consistency. In the process of executing the steps 1 to 8 each time, the warning values of all the battery monomers are reduced to f times of the original values in the step 3, wherein f actually plays a role of a forgetting factor, if the warning value of a certain battery monomer has a certain degree of increasing trend in a certain period in history but does not exceed the upper limit of the warning value, the proportion of the historical warning value increasing part in the current warning value is smaller and smaller along with the lapse of time, and the proportion of the recent warning value increasing part and the current warning value increasing part is larger, so that the historical accidental phenomenon can be eliminated; and if the state of the battery system is improved in the service process, the influence of the problems in the historical stage on the current state can be gradually weakened. And 4, only normalizing the voltage and temperature acquisition values in the monitoring step cycle, so that the pertinence is strong, the voltage and temperature acquisition values are both between 0 and 1, the data are comparable, and whether the battery system is in a charging, discharging or resting state is not considered. In step 6, the projection point closest to the coordinates (0.5 ) on the coordinate system is found, which is actually the point with the most central position, usually the projection points around the position are the most dense, a circle is drawn by taking the projection points as the center of the circle, and the number of projection points contained in the circle is taken as the subsequent comparison reference, which has the advantage of good universality. On the basis, drawing a circle by taking the projection points as the circle center and comparing the number of the projection points contained in the circle with a certain proportion of the reference number of the projection points in the step 6, wherein if the number of the projection points contained in the circle by taking a certain projection point as the circle center is less, the number of the projection points at the position of the projection point is sparse, and the projection points deviate from the overall voltage and temperature distribution condition and have poor consistency; if the situation occurs continuously for a plurality of times in the subsequent monitoring step circulation of the single battery corresponding to the projection point, the situation that the acquired data of the single battery obviously deviates from other single batteries can be basically determined, the consistency is poor, and the fault can be judged.
Although the lithium ion battery state monitoring method of the embodiment performs calculation and analysis on the voltage and temperature data of all the single batteries acquired each time, and makes full use of all the data, no complex calculation with large memory overhead exists; after each cycle of monitoring steps is completed, except for the fault judgment result, only the serial number of each battery monomer and the warning value thereof are actually transmitted to the next cycle, so that a large amount of memory and storage space are saved, the data communication quantity is very limited, and the state monitoring device of the battery system applying the method also has the advantages of low cost and high reliability.
Claims (4)
1. A state monitoring method of a lithium ion battery system is characterized in that each battery monomer in the battery system is respectively numbered in sequence and is endowed with a warning value, wherein the warning value of the battery monomer with the number i is recorded as W i And the warning values of all the battery monomers are 0 before the battery system leaves the factory; after the battery system leaves a factory, according to a fixed time interval, the following steps are sequentially executed for state monitoring:
step 1, collecting voltage and temperature values of each battery monomer:
acquiring the voltage value and the temperature value of each battery monomer in the battery system, wherein the voltage value of the battery monomer with the serial number of i in the battery system is recorded as U i A temperature value of T i ；
Step 2, preliminarily judging the voltage and temperature values of each battery monomer, and if any one of the following conditions is met:
(i) At least one battery monomer exists, and the voltage value of the battery monomer is smaller than the lower limit value of the voltage of the battery monomer or larger than the upper limit value of the voltage of the battery monomer;
(ii) At least one single battery exists, and the temperature value of the single battery is greater than the upper limit value of the temperature of the single battery;
terminating the execution of all the state monitoring steps, outputting a battery number meeting any one of the conditions (i) and (ii), and judging that the battery system has a fault;
if the condition (i) and the condition (ii) are not met, entering the next step;
step 3, adjusting the warning values of all the battery monomers to be f times of the original values, wherein f is between 0.8 and 0.95;
step 4, normalizing the voltage and temperature values of each battery monomer collected in the step 1:
the voltage normalization process for the battery cell with the number i is performed according to the following formula:
in the formula u i Is the voltage normalization value of the battery cell with the number i, U i The voltage value, U, of the battery cell with the number i acquired in the step 1 max Is the maximum value, U, of the voltage values of all the battery cells collected in step 1 min The minimum value of the voltage values of all the battery monomers acquired in the step 1 is obtained;
the temperature normalization process for the battery cell with the number i is performed according to the following formula:
in the formula, t i Is the temperature normalization value, T, of the battery cell numbered i i The temperature value T of the battery cell with the number i acquired in the step 1 max Is the maximum value T of the temperature values of all the battery cells collected in the step 1 min The minimum value of the temperature values of all the single batteries collected in the step 1 is obtained;
and 5, combining the voltage normalization values and the temperature normalization values of all the battery monomers obtained in the step 4 respectively, and projecting the voltage normalization values and the temperature normalization values onto a two-dimensional Cartesian coordinate system with the voltage normalization values as abscissa and the temperature normalization values as ordinate, wherein the projection coordinate of the battery monomer with the number i on the coordinate system is (u) i ,t i )；
Step 6, finding a projection point which is closest to the coordinate (0.5 ) on the coordinate system, drawing a circle by taking the projection point as the center of the circle and r as the radius, obtaining the number of projection points contained in the circle and recording the number as Mc, wherein the radius r is between 0.001 and 0.2;
and 7, processing all the rest projection points except the projection point closest to the coordinates (0.5 ) in the step 6 according to the following method:
for the battery cell with the number i, projecting point coordinates (u) by the battery cell i ,t i ) Drawing a circle by taking r as a radius as a circle center to obtain a projection point contained in the circleIs numbered as M i (ii) a If M is i <kMc, then making it have the alarm value W i Increasing 1 on the basis of the value of the step 3, otherwise, increasing the warning value W of the value i The change is not changed; wherein u is i 、t i Respectively obtaining a voltage normalization value and a temperature normalization value of the battery monomer with the serial number i; r is a radius between 0.001 and 0.2; k is a proportionality coefficient between 0.05 and 0.3; w i The number of the battery monomer is i;
step 8, comparing the warning values of all the battery monomers with a warning value upper limit Wc respectively, if the warning value of any battery monomer is greater than the warning value upper limit Wc, terminating the execution of all the state monitoring steps, outputting the serial numbers of the battery monomers of which the warning values are greater than the warning value upper limit Wc, and judging that the battery system has faults; otherwise, returning to the step 1; wherein the upper warning limit is between 10 and 100.
2. The method for monitoring the state of a lithium ion battery system according to claim 1, wherein the lower cell voltage limit in step 2 is between 1.8V and 2.5V, and the upper cell voltage limit is between 3.7V and 5V.
3. The method for monitoring the state of a lithium ion battery system according to claim 1, wherein the upper limit of the cell temperature in the step 2 is 55 ℃ to 70 ℃.
4. The state monitoring system applying the state monitoring method of the lithium ion battery system according to any one of claims 1 to 3, which is characterized by comprising an acquisition module, a storage module, an operation module and a communication module; wherein:
the acquisition module is used for acquiring voltage values and temperature values of all battery monomers in the battery system and transmitting acquired data to the storage module;
the storage module is used for receiving and storing the acquisition data acquired by the acquisition module and the operation data acquired by the operation module;
the operation module reads data from the storage module, performs operation and judgment according to the state monitoring method of the lithium ion battery system in claims 1-3, and transmits the result to the communication module;
the communication module is used for receiving the operation and judgment results of the operation module and transmitting the operation and judgment results to external equipment for perception of a user.
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