CN115219933A - Method for evaluating health state of liquid-cooled battery pack - Google Patents
Method for evaluating health state of liquid-cooled battery pack Download PDFInfo
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- CN115219933A CN115219933A CN202210728384.3A CN202210728384A CN115219933A CN 115219933 A CN115219933 A CN 115219933A CN 202210728384 A CN202210728384 A CN 202210728384A CN 115219933 A CN115219933 A CN 115219933A
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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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L3/00—Electric devices on electrically-propelled vehicles for safety purposes; Monitoring operating variables, e.g. speed, deceleration or energy consumption
- B60L3/12—Recording operating variables ; Monitoring of operating variables
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- B60L58/00—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles
- B60L58/10—Methods or circuit arrangements for monitoring or controlling batteries or fuel cells, specially adapted for electric vehicles for monitoring or controlling batteries
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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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- Y02E60/10—Energy storage using batteries
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Abstract
The invention discloses a health state assessment method for a liquid-cooled battery pack, which comprises the steps of testing and calibrating a battery pack sample in advance to respectively obtain the environmental temperatures of the battery pack sample at a service life starting point and a service life ending point and a data table formed by the heat absorption rates corresponding to the environmental temperatures; in the use process of the battery pack product after leaving the factory, for each charging process, recording the average value of the ambient temperature of the current charging process, counting and calculating the heat absorption rate of the battery pack, inquiring a data table to respectively obtain the heat absorption rate values of the battery pack at the service life starting point and the service life ending point under the average value of the ambient temperature of the current charging process, calculating and storing the health state of the battery pack in the current charging process, and outputting the health state of the final battery pack to a user according to the stored data. The method reflects the health state of the battery pack according to the change condition of the ratio of the heat absorption capacity of the liquid cooling plate to the charging capacity of the battery pack in the charging process, and has the advantages of simplicity and convenience in implementation, good universality and high accuracy and reliability.
Description
Technical Field
The invention relates to the field of batteries, in particular to a method for evaluating the health state of a liquid-cooled battery pack.
Background
As a chemical energy storage power source, the battery is usually provided with electric energy to the outside in a form of a battery pack formed by a plurality of single cells and a cooling system, wherein the liquid cooling system is widely used for cooling the battery pack due to the advantages of strong cooling capacity, good environmental adaptability, high temperature consistency and the like. Performance degradation inevitably occurs during the operation of the battery pack due to various internal and external factors, so people need to accurately grasp the health status of the battery pack during the operation. The State of health of the battery is expressed in english and is called SOH for short. The SOH of the battery represents the capacity of the current battery to store and release electric energy relative to the new battery, and represents the state of the battery from the beginning to the end of the life in percentage form, and is used for quantitatively describing the performance state of the current battery. The performance indexes of the battery are more, various SOH definitions are provided at home and abroad, the definition of the SOH is lack of unification in concept, and the current SOH definitions are mainly embodied in the aspects of capacity, electric quantity, internal resistance, cycle frequency, peak power and the like. For example, when defined in terms of capacity, SOH is the ratio of the current capacity of the battery to the rated capacity of the battery.
In the actual use process of a user, the accurate test on the SOH of the battery has great technical difficulty: from the aspects of capacity and electric quantity, the battery needs to be completely charged and discharged, but a user rarely carries out complete charging and discharging on the battery in the using process; from the perspective of internal resistance, the internal resistance of the battery can be accurately measured only by using a special precise instrument and a testing method, and the condition obviously does not exist in the using process of a common user; from the viewpoint of cycle number, the battery rarely undergoes charge-discharge cycles between a fixed initial charge state and a fixed final charge state during actual use; from the perspective of peak power, it is necessary to charge and discharge the battery according to a fixed charging and discharging current and a fixed charging and discharging time length in the using process, and a charging and discharging current value reaching a limit is necessary to obtain the peak power, which not only interferes with the normal use of a user, but also causes an adverse effect on the service life of the battery due to frequent large-current charging and discharging. Therefore, there is a need to propose a new method for estimating the health status of a battery pack without interfering with the normal use of a user, requiring special instruments and testing methods, and causing no damage to the battery itself.
Disclosure of Invention
In order to solve the technical problems, the invention provides the method for evaluating the health state of the liquid-cooled battery pack, which is simple and convenient to implement, good in universality and high in accuracy and reliability.
The technical scheme for solving the problems is as follows: a health state assessment method for a liquid-cooled battery pack is characterized in that the battery pack dissipates heat through a liquid cooling plate attached to the battery pack, cooling liquid flows through the liquid cooling plate, a battery pack manufacturer performs test calibration on heat absorption rates of a plurality of battery pack samples at a service life starting point and a service life ending point at different environmental temperatures in advance, total heat absorption capacity Q of the battery pack from a complete discharge state to a full charge state in the whole process of the battery pack at different environmental temperatures and charging capacity W of the battery pack are obtained, and the ratio of the total heat absorption capacity Q to the charging capacity W of the battery pack is calculated to obtain a heat absorption rate k:
k＝Q/W (1)
wherein Q is the total heat absorption capacity of the liquid cooling plate in the whole process of charging the battery pack from the complete discharge state to the full state at a certain specified ambient temperature, W is the charge capacity of the battery pack in the whole process of charging the battery pack from the complete discharge state to the full state at the certain specified ambient temperature, and k is the heat absorption rate at the certain specified ambient temperature;
through the test calibration, a plurality of environment temperatures of the battery pack sample at the service life starting point and the heat absorption rate k value corresponding to one of the environment temperatures are obtained, and a first data table is formed accordingly;
in the use process of the battery pack product after leaving factory, for each charging process, the SOH of the battery pack is calculated according to the following steps i ：
SOH i ＝100％×(k e -k i )/(k e -k b ) (2)
in the formula, SOH i The health state of the battery pack corresponding to the current charging process, k e Endothermic rate, k, at ambient temperature average of the present charging process for the end-of-life package sample obtained in step B3 b Heat absorption rate, k, at the average value of the ambient temperature of the current charging process for the life start point battery pack sample obtained in step B2 i The heat absorption rate of the battery pack for the current charging process obtained in the step B1;
as a further improvement of the technical scheme of the invention, the SOH calculated in step 4 i The calculation result of the formula (2) is corrected and stored because the actual application occasion does not exclude the occurrence of special conditions and measurement errors: if calculated SOH i If the content is less than 0%, correcting the content to be 0%; if calculated SOH i If it is greater than 100%, it is corrected to 100%.
For any certain moment when the battery pack product is used after leaving factory, if the stored SOH i If the calculation result record is more than or equal to N times, calculating the latest N times of SOH i Calculating the average value of the results and outputting the average value as the final health state to the user; if the SOH stored i If the calculation result records are less than N times, all the stored SOH are calculated i And calculating an average value of the results and outputting the average value as a final health state to a user, wherein N is a positive integer.
In the method for evaluating the health status of the liquid-cooled battery pack, the heat absorption rates of the battery pack samples at the start point and the end point of the service life are respectively tested and calibrated at different environmental temperatures, wherein the different environmental temperature values are an arithmetic difference series which takes the lowest allowable charging environmental temperature of the battery pack as a first term and takes the highest allowable charging environmental temperature of the battery pack as a last term, and the number of terms is greater than 5.
In the method for evaluating the health status of the liquid-cooled battery pack, the value of the positive integer N is between 5 and 50.
In the method for evaluating the health status of the liquid-cooled battery pack, the total heat absorption capacity of the liquid-cooled plate during the charging process is the product of the average flow rate of the cooling liquid flowing through the liquid-cooled plate during the charging process, the average temperature difference of the cooling liquid flowing through the liquid-cooled plate, the charging process duration and the specific heat capacity of the cooling liquid, wherein the average temperature difference of the cooling liquid flowing through the liquid-cooled plate is the difference between the average temperature value of the cooling liquid flowing out of the liquid-cooled plate and the average temperature value of the cooling liquid flowing into the liquid-cooled plate.
In the method for estimating the state of health of the liquid-cooled battery pack, the charging amount of the battery pack is the total electric energy provided by the charging device to the battery pack during the charging process, and the value of the total electric energy can be obtained by the charging device of the battery pack.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack sample at the service life starting point in the test and calibration process of the heat absorption rate of the battery pack manufacturer is the battery pack in the factory state.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack manufacturer samples the end-of-life point in the process of testing and calibrating the heat absorption rate are obtained by performing an accelerated life test on the battery pack samples to enable the battery pack samples to reach the end-of-life state specified by the battery pack manufacturer.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack manufacturer can obtain the battery pack in a completely discharged state at different environmental temperatures in the test calibration process of the heat absorption rate, the battery pack is firstly placed at room temperature for more than 1 hour and is subjected to constant current discharge at a rate of 0.01C to 0.5C until the discharge cut-off voltage of the battery pack is reached, and then the battery pack is transferred to the test specified environmental temperature and is placed for more than 1 hour.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack is charged from a complete discharge state to a full state in the test calibration process of the heat absorption rate by a battery pack manufacturer, and the battery pack is charged from the complete discharge state to the charge cut-off voltage of the battery pack at a constant current of 0.01C-1C multiplying power at the test specified environmental temperature.
In the method for evaluating the health status of the liquid-cooled battery pack, the average flow rate of the cooling liquid flowing through the liquid-cooled plate in the charging process is an average value of flow rate values of the cooling liquid flowing through the liquid-cooled plate at each moment in the charging process, wherein the flow rate value of the cooling liquid flowing through the liquid-cooled plate at each moment is obtained by: if the flow value flowing through the liquid cooling plate is constant all the time in the charging process, the flow value is obtained by looking up the design data of the battery pack; if the flow value flowing through the liquid cooling plate in the charging process is not constant, the flow value at each moment is obtained in any one of the following three ways:
(i) Measuring a flow value by installing a flowmeter in a cooling liquid delivery pipeline communicated with the liquid cooling plate;
(ii) The flow value is obtained by measuring the pressure difference delta P between the inlet and the outlet of the liquid cooling plate and calculating:
in the formula, q is a flow value of cooling liquid passing through the liquid cooling plate, delta P is a pressure difference between an inlet and an outlet of the liquid cooling plate obtained through measurement, and xi is a resistance coefficient of a flow passage in the liquid cooling plate;
(iii) The flow value is obtained by measuring the rotational speed of the centrifugal pump powering the coolant flow and looking up a table: testing and calibrating a liquid cooling pipeline comprising a liquid cooling plate in advance, measuring flow values of cooling liquid passing through the liquid cooling plate corresponding to different centrifugal pump rotating speed values and forming a data table; and measuring the current rotating speed value of the centrifugal pump, searching two rotating speed values closest to the measured rotating speed value and flow values corresponding to the rotating speed values from a data table, and obtaining the current flow value in a linear interpolation mode.
The invention has the beneficial effects that:
1. the invention refers to the existing current practice of taking the internal resistance change of the battery as the quantitative evaluation index of the health state, utilizes the principle that the heat production quantity is increased and the charging efficiency is reduced when the internal resistance of the battery is increased, approximately equates the heat absorption quantity of the liquid cooling plate to the heat production quantity of the battery, uses the ratio of the total heat absorption quantity of the liquid cooling plate in the whole charging process and the charging quantity of the battery pack on the basis to obtain the heat absorption rate index, and measures the health state by analyzing the change condition of the heat absorption quantity in the using process of the battery. The method is scientific and reasonable, and essentially also evaluates the internal resistance change condition of the battery in the using process; in practical application, however, only the temperature sensors at the inlet and the outlet of the liquid cooling plate and the ambient temperature sensor are needed to be added on the basis of the original battery pack, and the temperature difference of the cooling liquid at the inlet and the outlet is counted, so that a precise internal resistance measuring instrument or a special measuring means is not needed, the normal use of the battery pack is not interfered, and any negative influence is not brought to the battery pack, so that the method is simple and convenient to implement and has good universality.
2. Considering that the charging quantity of the battery pack is different every time, the environmental temperature can also influence the internal resistance of the battery pack during charging, and further the heat generation quantity of the charging process under different environmental temperatures is different, the ratio of the total heat absorption quantity of the liquid cooling plate in the whole charging process under different environmental temperatures to the charging quantity of the battery pack is used to obtain the heat absorption rate index, and the heat absorption rate value is a relative value related to the temperature. Recording the average value of the ambient temperature in the current charging process and the corresponding current heat absorption rate value during each charging, and obtaining the heat absorption capacity value of the battery pack at the service life starting point and the service life ending point corresponding to the average value of the ambient temperature in the current charging process through table look-up estimation for calculating the health state; finally, errors and deviations are eliminated through a health state correction and statistical correction method, so that the health state assessment has high accuracy and reliability.
Drawings
Fig. 1 is a flowchart illustrating a method for evaluating a state of health of a liquid-cooled battery pack according to an embodiment of the invention.
Fig. 2 is a schematic structural diagram of a liquid-cooled battery pack and a liquid-cooled pipeline system thereof in an embodiment of the present invention, in which fig. 1 is a centrifugal pump, 2 is a constant-speed motor, 3 is an expansion tank, 4 is a first heat exchanger, 5 is a battery pack, 6 is a second heat exchanger, 7 is a first temperature sensor, 8 is a second temperature sensor, 9 is a third temperature sensor, 10 is an information processing module, and 11 is a vehicle computer.
Detailed Description
The invention is further described below with reference to the drawings and examples.
As shown in fig. 1, a method for evaluating the health status of a liquid-cooled battery pack, where the battery pack dissipates heat through a liquid-cooled plate attached to the battery pack, and a cooling liquid flows through the liquid-cooled plate, a manufacturer of the battery pack performs test calibration of heat absorption rates at different environmental temperatures on battery pack samples at a life start point and a life end point in advance, to obtain the total heat absorption Q of the liquid-cooled plate and the charge W of the battery pack in the whole process of charging the battery pack from a fully discharged state to a fully charged state at different environmental temperatures, and calculates the ratio of the total heat absorption Q to the charge W of the battery pack to obtain the heat absorption rate k:
k＝Q/W (1)
wherein Q is the total heat absorption capacity of the liquid cooling plate in the whole process of charging the battery pack from the complete discharge state to the full charge state at a certain specified ambient temperature, W is the charge capacity of the battery pack in the whole process of charging the battery pack from the complete discharge state to the full charge state at the certain specified ambient temperature, and k is the heat absorption rate at the certain specified ambient temperature;
through the test calibration, a plurality of environment temperatures of the battery pack sample at the service life starting point and the heat absorption rate k value corresponding to one of the environment temperatures are obtained, and a first data table is formed accordingly;
in the use process of the battery pack product after leaving factory, for each charging process, the SOH of the battery pack is calculated according to the following steps i ：
SOH i ＝100％×(k e -k i )/(k e -k b ) (2)
in the formula, SOH i The state of health of the battery pack corresponding to the current charging process, k e Endothermic rate, k, at ambient temperature average of the present charging process for the end-of-life package sample obtained in step B3 b Endothermic rate, k, at ambient temperature average of present charge process for life start point battery pack sample obtained in step B2 i The heat absorption rate of the battery pack for the current charging process obtained in the step B1;
as a further improvement of the technical scheme of the invention, the SOH calculated in step 4 i The calculation result of the formula (2) is corrected and then stored, because the actual application occasion does not exclude the occurrence of special situations and measurement errors: if calculated SOH i If the content is less than 0%, correcting the content to be 0%; if calculated SOH i If it is greater than 100%, it is corrected to 100%.
For any certain moment when the battery pack product is used after leaving factory, if the stored SOH i If the calculation result record is greater than or equal to N times, calculating the latest N times of SOH i Calculating an average value of the results and outputting the average value as a final health state to the user; if the SOH stored i If the calculation result records are less than N times, calculating all the stored SOH i The result of the calculationAnd outputting the average value of the data to the user as the final health state, wherein N is a positive integer.
In the method for evaluating the health status of the liquid-cooled battery pack, the heat absorption rates of the battery pack samples at the start point and the end point of the service life are respectively tested and calibrated at different environmental temperatures, wherein the different environmental temperature values are an arithmetic difference series which takes the lowest allowable charging environmental temperature of the battery pack as a first term and takes the highest allowable charging environmental temperature of the battery pack as a last term, and the number of terms is greater than 5.
In the method for evaluating the health status of the liquid-cooled battery pack, the value of the positive integer N is between 5 and 50.
In the method for evaluating the health status of the liquid-cooled battery pack, the total heat absorption capacity of the liquid-cooled plate during the charging process is the product of the average flow rate of the cooling liquid flowing through the liquid-cooled plate during the charging process, the average temperature difference of the cooling liquid flowing through the liquid-cooled plate, the charging process duration and the specific heat capacity of the cooling liquid, wherein the average temperature difference of the cooling liquid flowing through the liquid-cooled plate is the difference between the average temperature value of the cooling liquid flowing out of the liquid-cooled plate and the average temperature value of the cooling liquid flowing into the liquid-cooled plate.
In the above method for evaluating the state of health of the liquid-cooled battery pack, the charging amount of the battery pack is the total electric energy provided by the charging device to the battery pack during the charging process, and the value of the total electric energy can be obtained by the charging device of the battery pack.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack sample at the service life starting point in the test and calibration process of the heat absorption rate of the battery pack manufacturer is the battery pack in the factory state.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack manufacturer samples the end-of-life point in the process of testing and calibrating the heat absorption rate are obtained by performing an accelerated life test on the battery pack samples to enable the battery pack samples to reach the end-of-life state specified by the battery pack manufacturer.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack manufacturer can obtain the battery pack in a completely discharged state at different environmental temperatures in the test calibration process of the heat absorption rate, the battery pack is firstly placed at room temperature for more than 1 hour and is subjected to constant current discharge at a rate of 0.01C to 0.5C until the discharge cut-off voltage of the battery pack is reached, and then the battery pack is transferred to the test specified environmental temperature and is placed for more than 1 hour.
According to the method for evaluating the health state of the liquid-cooled battery pack, the battery pack is charged from a complete discharge state to a full state in the test calibration process of the heat absorption rate by a battery pack manufacturer, and the battery pack is charged from the complete discharge state to the charge cut-off voltage of the battery pack at a constant current of 0.01C-1C multiplying power at the test specified environmental temperature.
In the above method for evaluating the health status of the liquid-cooled battery pack, the average flow rate of the cooling liquid flowing through the liquid-cooled plate in the charging process is an average value of flow rate values of the cooling liquid flowing through the liquid-cooled plate at each moment in the charging process, where the flow rate value of the cooling liquid flowing through the liquid-cooled plate at each moment is obtained as follows: if the flow value flowing through the liquid cooling plate is constant all the time in the charging process, the flow value is obtained by looking up the design data of the battery pack; if the flow value flowing through the liquid cooling plate in the charging process is not constant, the flow value at each moment is obtained in any one of the following three ways:
(i) Measuring a flow value by installing a flowmeter in a cooling liquid delivery pipeline communicated with the liquid cooling plate;
(ii) The flow value is obtained by measuring the pressure difference delta P between the inlet and the outlet of the liquid cooling plate and calculating:
in the formula, q is a flow value of the cooling liquid passing through the liquid cooling plate, delta P is a pressure difference between an inlet and an outlet of the liquid cooling plate obtained by measurement, and xi is a resistance coefficient of a flow passage in the liquid cooling plate;
(iii) The flow value is obtained by measuring the rotational speed of the centrifugal pump powering the coolant flow and looking up a table: testing and calibrating a liquid cooling pipeline comprising a liquid cooling plate in advance, measuring flow values of cooling liquid passing through the liquid cooling plate corresponding to different centrifugal pump rotating speed values and forming a data table; and measuring the current rotating speed value of the centrifugal pump, searching two rotating speed values closest to the measured rotating speed value and flow values corresponding to the rotating speed values from the data table, and obtaining the current flow value in a linear interpolation mode.
Examples
The battery of a battery pack of a pure electric vehicle is a lithium ion power battery which is formed by 1 parallel 94 strings, the rated capacity of the battery pack is 150Ah, the rated voltage is 300V, the charging and discharging cut-off voltages are 345V and 235V respectively, the battery pack is thermally managed in a liquid cooling mode, the cooling liquid is an ethylene glycol aqueous solution with the specific heat capacity of 3.8kJ/kg DEG C, and a liquid cooling pipeline system can be seen in figure 2.
As shown in fig. 2, the battery pack liquid cooling system comprises a centrifugal pump 1, a constant speed motor 2 mechanically connected with the centrifugal pump 1 and used for driving the centrifugal pump 1 to operate, an expansion water tank 3, a first heat exchanger 4 and a second heat exchanger 6, wherein the centrifugal pump 1, the expansion water tank 3, the first heat exchanger 4 and the second heat exchanger 6 are sequentially connected through a pipeline, the second heat exchanger 6 is connected with the centrifugal pump 1 through a pipeline, the first heat exchanger 4 is tightly attached to a battery pack 5 and cools the battery pack 5 by means of cooling liquid flowing through the first heat exchanger 4, and the second heat exchanger 6 is used for cooling the cooling liquid; in order to realize the health state evaluation of the battery pack, a first temperature sensor 7 arranged at the inlet of the first heat exchanger 4, a second temperature sensor 8 arranged at the outlet of the first heat exchanger 4, a third temperature sensor 9 used for acquiring the external environment temperature of the electric automobile, and an information processing module 10 electrically connected with the first temperature sensor 7, the second temperature sensor 8 and the third temperature sensor 9 are additionally arranged; the first temperature sensor 7 is used for collecting the temperature of the cooling liquid flowing into the first heat exchanger 4, the second temperature sensor 8 is used for collecting the temperature of the cooling liquid flowing out of the first heat exchanger 4, and the information processing module 10 is further electrically connected with the traveling computer 11. The statistical analysis and calculation of the relevant data are performed by the information processing module.
Because the rotating speed of the centrifugal pump 1 is unchanged, the flow of the cooling liquid in the working process is unchanged, and the mass flow of the cooling liquid passing through the first heat exchanger 4 is constant and is 0.3kg/s.
And randomly selecting two intact battery pack samples in a factory state for heat absorption rate test calibration.
Firstly, one of the battery packs is used as a life starting point sample, and the other sample is subjected to an accelerated life test, the sample is placed in a high-temperature environment at 55 ℃ to continuously perform a cycle of charging at a constant current of 1C to a charge cut-off voltage, standing for 0.5 hour, discharging at a constant current of 1C to a discharge cut-off voltage, standing for 0.5 hour, and the sample is transferred to a room-temperature environment after 100 times of circulation to test the capacity of the sample, and when the capacity of the room-temperature environment is attenuated to be below 80% of the rated capacity, the sample of the battery pack is considered to reach a life end state.
Then, testing and calibrating the heat absorption rate of the battery pack sample at the service life starting point and the service life ending point at a plurality of different environmental temperatures respectively, wherein the selected environmental temperatures are-5 ℃, 15 ℃, 25 ℃, 35 ℃ and 45 ℃, and a plurality of environmental temperatures of the battery pack sample at the service life starting point and the heat absorption rate k value corresponding to one of the environmental temperatures are obtained to form a first data table, which is shown in table 1; a plurality of ambient temperatures and endothermic k values corresponding to one of the ambient temperatures and the end-of-life cell pack samples were obtained and a second data table was constructed therefrom, see table 2.
TABLE 1 first data Table
| Ambient temperature | -5℃ | 5℃ | 15℃ | 25℃ | 35℃ | 45℃ |
| Rate of heat absorption k | 0.082 | 0.078 | 0.063 | 0.052 | 0.043 | 0.039 |
TABLE 2 second data Table
| Ambient temperature | 5℃ | 5℃ | 15℃ | 25℃ | 35℃ | 45℃ |
| Rate of heat absorption k | 0.15 | 0.12 | 0.11 | 0.093 | 0.088 | 0.079 |
In the using process of the battery pack product after leaving factory, taking a charging process which takes 1 hour for a certain time as an example, the SOH of the battery pack is calculated according to the following steps i ：
In this embodiment, the positive integer N is 30. After the charging is completed, the SOH stored in the information processing module 10 i If the calculated result record is more than 30, calculating the latest 30 times of SOH i The average value of the calculation results is 78%, and the health state of the battery pack, which is finally output to the travel computer 11 and displayed to the user, is 78%.
The method for evaluating the health status of a liquid-cooled battery pack provided by this embodiment refers to the existing current practice that the internal resistance change of a battery is used as the quantitative evaluation index of the health status, utilizes the principle that the heat generation amount increases and the charging efficiency decreases when the internal resistance of the battery increases, and approximately equates the heat absorption amount of a liquid-cooled plate as the heat generation amount of the battery, on the basis, uses the ratio of the total heat absorption amount of the liquid-cooled plate in the whole charging process and the charging amount of the battery pack to obtain the heat absorption rate index, and measures the health status by analyzing the change condition of the heat absorption amount in the battery using process. The method is scientific and reasonable, and essentially evaluates the internal resistance change condition of the battery in the using process; in practical application, however, only the temperature sensors at the inlet and the outlet of the liquid cooling plate and the environmental temperature sensor are needed to be added on the basis of the original battery pack, and the temperature difference of the cooling liquid at the inlet and the outlet is counted, so that a precise internal resistance measuring instrument or a special measuring means is not needed, the normal use of the battery pack is not interfered, and any negative influence is not brought to the battery pack, therefore, the method is simple and convenient to implement and has good universality.
Considering that the charging amount of the battery pack is different each time, the ambient temperature also affects the internal resistance of the battery pack during charging, and further, the heat generation amount in the charging process at different ambient temperatures is different, in this embodiment, the ratio of the total heat absorption amount of the liquid cooling plate in the whole charging process at different ambient temperatures to the charging amount of the battery pack is used to obtain the heat absorption rate index, and the heat absorption rate value is a relative value related to the temperature. Recording the average value of the ambient temperature in the current charging process and the corresponding current heat absorption rate value during each charging, and obtaining the heat absorption capacity value of the battery pack at the service life starting point and the service life ending point corresponding to the average value of the ambient temperature in the current charging process through table look-up estimation for calculating the health state; finally, errors and deviations are eliminated through a health state correction and statistical correction method, so that the health state assessment has high accuracy and reliability.
Claims (10)
1. The utility model provides a liquid cooling type battery package health assessment method, the battery package is through the liquid cooling board heat dissipation that hugs closely with it and the interior flow of liquid cooling board has the coolant liquid, its characterized in that, battery package manufacturer carries out the test calibration of heat absorption rate under a plurality of different ambient temperatures to the battery package sample of life-span initial point and life-span termination point respectively in advance, obtains the total heat absorption Q of battery package from the complete discharge state to full electric charge overall process liquid cooling board and the charge volume W of battery package under the different ambient temperatures and calculates the ratio of the two in order to obtain the heat absorption rate k:
k＝Q/W (1)
wherein Q is the total heat absorption capacity of the liquid cooling plate in the whole process of charging the battery pack from the complete discharge state to the full state at a certain specified ambient temperature, W is the charge capacity of the battery pack in the whole process of charging the battery pack from the complete discharge state to the full state at the certain specified ambient temperature, and k is the heat absorption rate at the certain specified ambient temperature;
through the test calibration, a plurality of environment temperatures of the battery pack sample at the service life starting point and the heat absorption rate k value corresponding to one of the environment temperatures are obtained, and a first data table is formed accordingly;
in the use process of the battery pack product after leaving factory, for each charging process, the SOH of the battery pack is calculated according to the following steps i ：
Step 1, recording an average value of the ambient temperature of the current charging process, counting the total heat absorption amount of the liquid cooling plate and the charging amount of the battery pack in the current charging process, and dividing the total heat absorption amount by the charging amount to obtain the heat absorption rate k of the battery pack i ；
Step 2, two environment temperature values which are closest to the environment average temperature in the current charging process and corresponding to the two environment temperature values are inquired from the first data tableThe heat absorption rate value is obtained by linear interpolation, and the heat absorption rate k of the life initial point battery pack sample under the average value of the ambient temperature in the current charging process b ；
Step 3, two environment temperature values which are closest to the environment average temperature in the current charging process and heat absorption rate values corresponding to the two environment temperature values are inquired from a second data table, and the heat absorption rate k of the battery pack sample at the end point of the service life under the environment temperature average value in the current charging process is obtained in a linear interpolation mode e ；
Step 4, calculating the SOH of the battery pack according to the data obtained in the current charging process i And storing:
SOH i ＝100％×(k e -k i )/(k e -k b ) (2)
in the formula, SOH i The state of health of the battery pack corresponding to the current charging process, k e Endothermic rate, k, at ambient temperature average of the present charging process for the end-of-life package sample obtained in step B3 b Endothermic rate, k, at ambient temperature average of present charge process for life start point battery pack sample obtained in step B2 i The heat absorption rate of the battery pack for the current charging process obtained in the step B1;
if the stored SOH is available at any time after the battery pack product leaves the factory i If the calculation result record is more than or equal to N times, calculating the latest N times of SOH i Calculating the average value of the results and outputting the average value as the final health state to the user; if the SOH stored i If the calculation result records are less than N times, calculating all the stored SOH i And calculating an average value of the results and outputting the average value as a final health state to a user, wherein N is a positive integer.
2. The method for assessing the health status of a liquid-cooled battery pack according to claim 1, wherein the test calibration of the heat absorption rate at several different environmental temperatures is performed on the battery pack samples at the beginning point of life and the end point of life, respectively, wherein the several different environmental temperature values are an arithmetic sequence with the lowest allowable charging environmental temperature of the battery pack as a first term, the highest allowable charging environmental temperature of the battery pack as a last term, and the number of terms is greater than 5.
3. The liquid-cooled battery pack state of health assessment method of claim 1, wherein the positive integer N takes on a value between 5 and 50.
4. The method of claim 1, wherein the total heat absorption of the liquid-cooled battery pack during charging is a product of an average flow rate of the coolant flowing through the liquid-cooled plate during charging, an average temperature difference of the coolant flowing through the liquid-cooled plate, a duration of the charging, and a specific heat capacity of the coolant, wherein the average temperature difference of the coolant flowing through the liquid-cooled plate is a difference between an average coolant temperature flowing out of the liquid-cooled plate and an average coolant temperature flowing into the liquid-cooled plate.
5. The method of claim 1, wherein the amount of charge of the battery pack is the total power provided by a charging process charging device to the battery pack and is obtained by the charging device of the battery pack.
6. The method for assessing the state of health of a liquid-cooled battery pack according to claim 1, wherein the sample of the battery pack at the beginning of life of the manufacturer of the battery pack during calibration of the endothermic rate test is the battery pack at the time of factory shipment.
7. The method of claim 1, wherein the end-of-life sample of the battery pack manufacturer during calibration of endothermic heat absorption rate is obtained by performing an accelerated life test on the battery pack sample to achieve the end-of-life condition specified by the battery pack manufacturer.
8. The method for assessing the state of health of a liquid-cooled battery pack according to claim 1, wherein the battery pack manufacturer is configured to obtain a completely discharged state of the battery pack at different environmental temperatures during calibration of the heat absorption rate test by first allowing the battery pack to stand at room temperature for more than 1 hour and discharging the battery pack at a constant current of 0.01C to 0.5C rate to a discharge cut-off voltage of the battery pack, and then allowing the battery pack to stand at a test-specified environmental temperature for more than 1 hour.
9. The method for evaluating the health status of a liquid-cooled battery pack according to claim 1, wherein the battery pack manufacturer charges the battery pack from a fully discharged state to a fully charged state during calibration of the heat absorption rate test, and charges the battery pack from the fully discharged state to a charge cut-off voltage of the battery pack at a constant current of 0.01C to 1C rate at a specified test environmental temperature.
10. The method for health assessment of liquid-cooled battery packs according to claim 4, wherein the average flow rate of the cooling fluid flowing through the liquid-cooled plates during the charging process is an average of the flow rate values of the cooling fluid flowing through the liquid-cooled plates at each time of the charging process, wherein the flow rate values of the cooling fluid flowing through the liquid-cooled plates at each time are obtained by: if the flow value flowing through the liquid cooling plate is always constant in the charging process, the flow value is obtained by looking up the design data of the battery pack; if the flow value flowing through the liquid cooling plate in the charging process is not constant, the flow value at each moment is obtained in any one of the following three ways:
(i) Measuring a flow value by installing a flowmeter in a cooling liquid delivery pipeline communicated with the liquid cooling plate;
(ii) The flow value is obtained by measuring the pressure difference delta P between the inlet and the outlet of the liquid cooling plate and calculating:
in the formula, q is a flow value of cooling liquid passing through the liquid cooling plate, delta P is a pressure difference between an inlet and an outlet of the liquid cooling plate obtained through measurement, and xi is a resistance coefficient of a flow passage in the liquid cooling plate;
(iii) The flow value is obtained by measuring the rotational speed of the centrifugal pump powering the coolant flow and looking up a table: testing and calibrating a liquid cooling pipeline comprising a liquid cooling plate in advance, measuring flow values of cooling liquid passing through the liquid cooling plate corresponding to different centrifugal pump rotating speed values and forming a data table; and measuring the current rotating speed value of the centrifugal pump, searching two rotating speed values closest to the measured rotating speed value and flow values corresponding to the rotating speed values from a data table, and obtaining the current flow value in a linear interpolation mode.
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