CN110031772B - Real-time estimation method for equivalent internal resistance of lithium ion battery - Google Patents
Real-time estimation method for equivalent internal resistance of lithium ion battery Download PDFInfo
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 54
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 54
- 238000000034 method Methods 0.000 title claims abstract description 51
- 238000012937 correction Methods 0.000 claims abstract description 24
- 238000012360 testing method Methods 0.000 claims description 34
- 238000001228 spectrum Methods 0.000 claims description 26
- 238000007599 discharging Methods 0.000 claims description 21
- 238000009825 accumulation Methods 0.000 claims description 3
- 238000012544 monitoring process Methods 0.000 abstract description 4
- 230000020169 heat generation Effects 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 4
- 230000009286 beneficial 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
- 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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Abstract
The invention discloses a real-time estimation method for equivalent internal resistance of a lithium ion battery, which comprises the steps of monitoring the ambient temperature, the discharge current and the discharge duration of the battery on line, calculating the charge state of the battery, selecting a corresponding correction coefficient according to the monitoring value, determining the pilot internal resistance of the battery according to the charge state, and finally estimating the real-time equivalent internal resistance of the battery.
Description
Technical Field
The application relates to the field of electric vehicle battery thermal management, in particular to a real-time estimation method for equivalent internal resistance of a lithium ion battery.
Background
The power battery pack is a main energy storage component of the electric automobile. The lithium ion battery is widely applied to power battery packs of a plurality of electric passenger vehicles due to the advantages of high energy density, no memory effect, long cycle life and the like.
The Equivalent Internal Resistance (EIR) of the lithium ion battery is an important index which is required to be referred to for calculating the heat generation rate of the battery.
At present, the equivalent internal resistance of a lithium ion battery is mainly obtained by measuring the battery in an off-line state by a constant current intermittent discharge method. Meanwhile, a large amount of experimental data prove that the equivalent internal resistance of the lithium ion battery is influenced by the ambient temperature, the discharge rate, the discharge duration and the State of Charge (SoC) of the battery and changes constantly in the discharge process of the lithium ion battery. In addition, the working state of the electric automobile is complex and changeable, and in the process, the output power of the vehicle-mounted lithium ion battery pack changes constantly, so that the heat generation rate of the battery also changes in real time. In order to calculate the real-time heat generation rate of the lithium ion battery and make a decision in time by a battery management system, the method for testing the equivalent internal resistance of the battery off line is not applicable.
Disclosure of Invention
The invention provides a real-time estimation method for equivalent internal resistance of a lithium ion battery, aiming at the inconvenience of offline testing the equivalent internal resistance of the battery in calculating the real-time heat generation rate of the battery. The method comprises the steps of calculating the charge state of the battery by monitoring the ambient temperature, the discharge current and the discharge time of the battery on line, selecting a corresponding correction coefficient according to a monitoring value, determining the pilot internal resistance of the battery according to the charge state, and finally estimating the real-time equivalent internal resistance of the battery.
The present invention achieves the above object by:
a real-time estimation method for equivalent internal resistance of a lithium ion battery comprises the following steps:
a. extracting a certain number of lithium ion batteries as samples, testing the available capacity C of the sample batteries by a constant current discharge method, and fitting the available capacity and the temperature T of the batteries by using a formula (1) by taking test data as a data base:
wherein, y0A and k are the three fitting parameters of the first order attenuation equation.
The constant current discharge test experiment performed on the sample lithium ion battery in the step a specifically comprises the following steps:
a1. and (3) carrying out pretreatment operation on the sample lithium ion battery, setting the temperature of the incubator to be 40 ℃, and keeping the temperature of the battery consistent with the ambient temperature. The sample cell was subjected to a total of 6 full charge cycles (primary cell full charge and primary cell full discharge were regarded as one cycle) in order to obtain a stable cell capacity.
a2. Fully charging the battery, setting a discharge cut-off voltage, enabling the battery to perform constant current discharge at a certain multiplying power, stopping discharging when the voltage is lower than the discharge cut-off voltage, and taking the total discharge capacity as the available capacity C of the battery.
a3. Before testing, the cells were allowed to stand in an incubator for 10 minutes in order to keep the cell temperature consistent with the ambient temperature.
a4. The test was carried out by setting 1 temperature variable at intervals of 10 ℃ from-20 ℃ to 50 ℃.
a5. Each test is repeatedly executed three times, and the average value of the available capacities of the batteries obtained by the three tests is used as the final result of the test.
b. Reading a temperature value T (t) and a current value I (t) of the battery in the discharging process, calculating the available capacity C (t) at each moment in the discharging process according to the formula (1), and reading the state of charge SoC (t) before discharging0) Calculating the state of charge (SoC) (t) of the battery at the current moment by using a charge accumulation method:
c. and establishing a parameter database of the lithium ion battery, wherein the parameter database comprises the pilot internal resistance and the correction coefficient.
c1. A lithium ion battery sample is tested by using a constant current intermittent discharge method, the temperature of an incubator is set to be 40 ℃, the battery is discharged for 10 minutes at a rate of 0.3 ℃, about 5% of electric quantity is discharged, and then the battery is kept stand for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, so that a discharge-standing cycle is taken as one time. And starting from the SoC =100%, repeating the circulation until the battery voltage is lower than the cut-off voltage, and recording the equivalent internal resistance of the battery under different SoC states to obtain an EIR-SoC spectrum. According to the state of charge SoC (t) obtained in the step b, searching the corresponding equivalent internal resistance of the battery from the EIR-SoC spectrum, and taking the equivalent internal resistance as the pilot internal resistance R (t) required to be referred to for determining the equivalent internal resistance R (t) of the battery at the current momentp(SoC)。
c2. A lithium ion battery sample is tested by using a constant current intermittent discharge method, different temperature boxes are respectively set, the battery is discharged for 10 minutes at a rate of 0.3C (about 5% of electric quantity is discharged), and then the battery is kept stand for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, so that a discharge-standing cycle is taken as one time. Starting from SoC =100%, the above cycle is repeated until the battery voltage is lower thanAnd cutting off the voltage, and recording the battery EIR at different charge states of the SoC under the temperature of each temperature box group to obtain an EIR-SoC-ambient temperature spectrum. Corresponding pilot internal resistance R under different charge states SoCp(SoC) is taken as a reference, then the state of charge SoC is fixed and unchanged, and the equivalent internal resistance EIR of the battery corresponding to different battery temperatures T is takenTDefining a temperature correction coefficient KT：
c3. And (3) testing a lithium ion battery sample by using a constant current intermittent discharge method, setting the temperature of a temperature box to be 40 ℃, aligning the state of charge (SoC) of the battery with each state of charge (SoC) in the step (c), charging the battery for 10 minutes at different multiplying powers, standing the battery for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, discharging for 10 minutes, and standing according to the method. And recording the EIR of the battery under different SoCs to obtain an EIR-SoC-discharge rate spectrum. Corresponding pilot internal resistance R under different charge states SoCp(SoC) is taken as a reference, then the SOC is fixed and is not changed, and the equivalent internal resistance EIR of the battery corresponding to different discharge multiplying power r is takenrDefining the discharge rate correction coefficient Kr：
c4. And (3) testing a lithium ion battery sample by using a constant current intermittent discharge method, setting the temperature of a temperature box to be 40 ℃, aligning the state of charge SoC of the battery with each state of charge SoC in the step (C), charging the battery for different time lengths t at 0.3C multiplying power, standing the battery for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, discharging for t seconds, and standing according to the method. And recording the equivalent internal resistance EIR of the battery under different charge states SoC to obtain an EIR-SoC-discharge duration spectrum. Corresponding pilot internal resistance R under different charge states SoCp(SoC) is taken as a reference, then the fixed state of charge SoC is unchanged, and corresponding different discharge time lengths t are takenEquivalent internal resistance EIR of batterytDefining a discharge duration correction factor Kt：
c5. Thus, a spectrum k including an "EIR-SoC" spectrum was obtainedT、Kr、KtThe parameter database of the selected type lithium ion battery can search relevant data according to the discharge working condition of the battery so as to calculate the real-time equivalent internal resistance EIR (t) of the lithium ion battery.
d. The constant current voltage discharge method for testing the EIR of the battery described in the steps c1 to c4 is to record the voltage E (t) at the beginning of discharge in each discharge time period t0) Voltage E (t) of the battery at the end of discharge1) And the discharge current I (t), the equivalent internal resistance EIR (t) of the battery in the time t can be calculated by the following formula (6):
e. a method for calculating the real-time equivalent internal resistance EIR (t) of the lithium ion battery is provided:
f. for reference values (for example, temperature correction coefficients corresponding to an ambient temperature of 25 ℃) which are not recorded in the database, interpolation calculation can be performed on adjacent reference values (temperature correction coefficients corresponding to 20 ℃ and 30 ℃) to obtain the required reference values.
The invention has the beneficial effects that: the real-time equivalent internal resistance of the lithium ion battery is estimated on line by collecting the ambient temperature, the discharge current and the discharge duration of the lithium ion battery on line, so that the purpose of calculating the real-time heat generation rate of the lithium ions is achieved. The invention is established in that a large number of test experiments are carried out on the selected lithium ion battery, the result is reliable, the experimental method is mature, and the operability is strong.
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The invention is further illustrated with reference to the following figures and examples:
FIG. 1 is a flow chart for building a database of lithium ion battery parameters;
FIG. 2 is a database diagram of a sample lithium ion battery;
FIG. 3 is a flow chart of one embodiment of the method of the present invention.
Detailed Description
The invention provides a real-time estimation method of equivalent internal resistance EIR of a lithium ion battery, which comprises the steps of establishing a parameter database of the lithium ion battery, wherein the flow of the parameter database is shown in figure 1; the equivalent internal resistance EIR of the lithium ion battery is estimated in real time, and the flow is shown in FIG. 3.
Firstly, extracting a certain number of lithium ion batteries as samples, testing the available capacity C of the sample batteries by a constant current discharge method, and fitting the available capacity and the battery temperature T by using a formula (1) by taking test data as a data base:
wherein, y0A and k are the three fitting parameters of the first order attenuation equation.
The constant current discharge test experiment performed on the sample lithium ion battery comprises the following specific steps:
a. and (3) carrying out pretreatment operation on the sample lithium ion battery, setting the temperature of the incubator to be 40 ℃, and keeping the temperature of the battery consistent with the ambient temperature. The sample cell was subjected to a total of 6 full charge cycles (primary cell full charge and primary cell full discharge were regarded as one cycle) in order to obtain a stable cell capacity.
b. The battery was fully charged to a state of charge SoC =100%, the discharge cutoff voltage was set to 2.5V, and discharged at a rate of 0.5C, followed by discharge at a rate of 0.1C, and the discharge was stopped when the voltage was lower than the discharge cutoff voltage, and the total discharge capacity was regarded as the available capacity C of the battery.
c. Before testing, the cells were allowed to stand in an incubator for 10 minutes in order to keep the cell temperature consistent with the ambient temperature.
d. The test was carried out by setting 1 temperature variable at intervals of 10 ℃ from-20 ℃ to 50 ℃.
e. Each test is repeatedly executed three times, and the average value of the available capacities of the batteries obtained by the three tests is used as the final result of the test.
At the moment, reading the temperature value T (t) and the current value I (t) of the battery in the discharging process, calculating the available capacity C (t) at each moment in the discharging process according to the formula (1), and reading the state of charge SoC (t) before discharging0) Calculating the state of charge (SoC) (t) of the battery at the current moment by using a charge accumulation method:
secondly, testing the equivalent internal resistance EIR of the lithium ion battery under various discharging conditions by using a constant current intermittent discharge method, and establishing a parameter database of the lithium ion battery, wherein the parameter database comprises the pilot internal resistance and the correction coefficient. The method comprises the following specific steps:
a. a lithium ion battery sample is tested by using a constant current intermittent discharge method, the temperature of an incubator is set to be 40 ℃, the battery is discharged for 10 minutes at a rate of 0.3 ℃, about 5% of electric quantity is discharged, and then the battery is kept stand for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, so that a discharge-standing cycle is taken as one time. Starting from the state of charge SoC =100%, the above cycle is repeated until the battery voltage is lower than the cut-off voltage, and the battery EIR under different states of charge SoC is recorded, so as to obtain an "EIR-SoC" spectrum, as shown in the upper left-hand line spectrum of fig. 2. According to the state of charge SoC (t) obtained in the step b, searching the corresponding equivalent internal resistance EIR of the battery from the EIR-SoC spectrum, and taking the equivalent internal resistance EIR as the pilot internal resistance R which is required to be referred to for determining the equivalent internal resistance R (t) of the battery at the current momentp(SoC)。
b. Testing a lithium ion battery sample by using a constant current intermittent discharge method, and respectively setting the temperature of a temperature box at-20 ℃, 10 ℃, 0 ℃, 10 ℃, 20 ℃, 30 ℃, 40 ℃ and 50 ℃, and discharging the battery at a rate of 0.3 DEG CAfter 10 minutes (about 5% of the charge was discharged), the cell was allowed to stand for 2 hours until the cell voltage change rate was less than 0.1mV/min, which served as a "discharge-stand" cycle. Starting from the state of charge SoC =100%, the above cycle is repeated until the battery voltage is lower than the cut-off voltage, and the equivalent internal resistance EIR of the battery at different states of charge SoC at the temperature of each temperature box group is recorded, so as to obtain an "EIR-SoC-ambient temperature" spectrum, as shown in the upper right-hand line spectrum of fig. 2. Corresponding pilot internal resistance R under different charge states SoCp(SoC) is taken as a reference, then the state of charge SoC is fixed and unchanged, and the equivalent internal resistance EIR of the battery corresponding to different battery temperatures T is takenTDefining a temperature correction coefficient KT：
c. And (3) testing a lithium ion battery sample by using a constant current intermittent discharge method, setting the temperature of a temperature box to be 40 ℃, aligning the state of charge SoC of the battery with each state of charge SoC in the step C, charging the battery for 10 minutes at different multiplying powers (0.1C, 0.3C, 0.5C, 0.7C, 1.0C, 1.2C, 1.4C, 1.6C, 1.8C and 2.0C), standing the battery for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, discharging for 10 minutes, and standing according to the method. The battery EIR under different socs is recorded to obtain an "EIR-SoC-discharge rate" spectrum, as shown in the lower left corner spectrum of fig. 2. Corresponding pilot internal resistance R under different charge states SoCp(SoC) is taken as a reference, then the SOC is fixed and is not changed, and the equivalent internal resistance EIR of the battery corresponding to different discharge multiplying power r is takenrDefining the discharge rate correction coefficient Kr：
d. Testing a lithium ion battery sample by using a constant current intermittent discharge method, setting the temperature of a temperature box to be 40 ℃, aligning the state of charge (SoC) of the battery with each state of charge (SoC) in the step C, and charging the battery at 0.3C multiplying powerElectricity for t seconds (t is 30, 60, 120, 240, 360, 480, 600), then the battery is kept still for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, then the battery is discharged for t seconds, and then the battery is kept still according to the method. The battery EIR under different states of charge SoC is recorded to obtain an "EIR-SoC-discharge duration" spectrum, as shown in the lower right-hand corner spectrum of fig. 2. Corresponding pilot internal resistance R under different charge states SoCp(SoC) is taken as a reference, then the SOC is fixed and is not changed, and the equivalent internal resistance EIR of the battery corresponding to different discharge time lengths t is takentDefining a discharge duration correction factor Kt ：
The method for testing the equivalent internal resistance EIR of the battery by the constant current voltage discharge method in the steps a to d is to record the voltage E (t) when the discharge is started in each section of discharge time t0) Voltage E (t) of the battery at the end of discharge1) And the discharge current I (t), the equivalent internal resistance EIR (t) of the battery in the time t can be calculated by the following formula (6):
thus, a spectrum k including an "EIR-SoC" spectrum was obtainedT、Kr、KtThe parameter database of the selected type lithium ion battery can search relevant data according to the discharge working condition of the battery so as to calculate the real-time equivalent internal resistance EIR (t) of the lithium ion battery.
Finally, calculating the real-time equivalent internal resistance EIR (t) of the lithium ion battery according to the formula (7):
thus, at any time t in the discharging process, the temperature correction coefficient K of the internal resistance of the battery is determined according to the temperature T (t) of the batteryT(ii) a Determining the battery based on the battery discharge current I (t)Discharge multiplying power r (t) and further determining a battery internal resistance discharge multiplying power correction coefficient Kr(ii) a Determining the discharge duration correction coefficient K of the battery internal resistance according to the continuous discharge duration of the batteryt(ii) a Determining the available capacity C (t) of the battery according to the ambient temperature T (t) of the battery, further determining the current state of charge SoC (t) of the battery, and then searching the corresponding pilot internal resistance R according to the state of charge SoC (t)p(SoC)。
For reference values (for example, temperature correction coefficients corresponding to an ambient temperature of 25 ℃) which are not recorded in the database, interpolation calculation can be performed on adjacent reference values (temperature correction coefficients corresponding to 20 ℃ and 30 ℃) to obtain the required reference values.
Claims (3)
1. A real-time estimation method for equivalent internal resistance of a lithium ion battery is characterized by comprising the following steps:
a. extracting a certain number of lithium ion batteries as samples, testing the available capacity C of the sample batteries by a constant current discharge method, and fitting the available capacity and the temperature T of the batteries by using a formula (1) by taking test data as a data base:
wherein, y0A and k are three fitting parameters;
b. reading a temperature value T (t) of the battery in the discharging process, and calculating the available capacity C (t) of each moment in the discharging process according to the formula (1); at the same time, the state of charge SoC (t) before discharge is read0) And a current value I (t) in the discharging process, wherein the charge state SoC (t) of the battery at the current moment is calculated by using a charge accumulation method:
c. establishing a parameter database of the lithium ion battery by using a constant current intermittent discharge method, wherein the parameter database comprises a pilot internal resistance Rp(SoC) and correction factor KT、KrAnd KtWherein, K isTAs a temperature correction coefficient, Kr As discharge rate correction factor, KtA discharge duration correction factor;
d. the real-time equivalent internal resistance of the lithium ion battery can be obtained by the formula (7):
e. and for the reference values which are not recorded in the database, carrying out interpolation calculation on the adjacent reference values to obtain the required reference values.
2. The real-time estimation method of the equivalent internal resistance of the lithium ion battery according to claim 1, characterized in that: the specific steps of performing constant current discharge test on the lithium ion battery of the sample in the step a comprise:
a1. carrying out pretreatment operation on a lithium ion battery, setting a certain incubator temperature, keeping the temperature of the battery consistent with the ambient temperature, and carrying out multiple 'filling-emptying' cycles on a sample battery;
a2. fully charging the battery, discharging the battery at a certain multiplying power, stopping discharging when the voltage is lower than a discharge cut-off voltage, and taking the total discharge capacity as the available capacity C of the battery, wherein before testing, the battery is kept in a temperature box for a period of time in order to keep the temperature of the battery consistent with the ambient temperature;
a3. setting different incubator temperatures, and repeating a 2;
a4. each test is repeatedly executed three times, and the average value of the available capacities of the batteries obtained by the three tests is used as the final result of the test.
3. The real-time estimation method of the equivalent internal resistance of the lithium ion battery according to claim 2, characterized in that: the specific steps of the constant current intermittent discharge method for the lithium ion battery of the sample in the step c comprise:
c1. setting the temperature of the incubator at 40 ℃ from the state of chargeStarting SoC =100%, repeatedly carrying out 'discharging-standing' circulation on the battery until the voltage of the battery is lower than a cut-off voltage, recording the equivalent internal resistance EIR of the battery under different charge states SoC, and obtaining an EIR-SoC spectrum, wherein the 'discharging-standing' circulation is to discharge the battery for 10 minutes at a multiplying power of 0.3C, then standing the battery for 2 hours until the voltage change rate of the battery is lower than 0.1mV/min, and then searching the corresponding equivalent resistance of the battery from the EIR-SoC spectrum according to the charge state SoC (t) of the battery obtained by executing the step b, and taking the equivalent resistance as the pilot internal resistance R (t) required to be referred for determining the equivalent internal resistance R (t) of the battery at the current momentp(SoC)；
c2. Respectively setting different temperature boxes, starting from the state of charge SoC =100%, repeatedly carrying out the discharge-standing circulation on the battery until the voltage of the battery is lower than a cut-off voltage, recording the equivalent internal resistance EIR of the battery with different states of charge SoC under the temperature of each temperature box group to obtain an EIR-SoC-environmental temperature spectrum, and then carrying out corresponding pilot internal resistance R under different states of charge SoCp(SoC) is taken as a reference, the SOC is fixed and is not changed, and the equivalent internal resistance EIR of the battery corresponding to different battery temperatures T is taken according to the EIR-SoC-environmental temperature spectrumTDefining a temperature correction coefficient KT:
c3. Setting the temperature of a temperature box to be 40 ℃, aligning the battery charge state SoC with each charge state SoC in the step c1, charging the battery for 10 minutes at different rates, standing the battery for 2 hours until the battery voltage change rate is lower than 0.1mV/min, discharging for 10 minutes, standing the battery for 2 hours until the battery voltage change rate is lower than 0.1mV/min, recording the equivalent internal resistance EIR of the battery under different charge state SoCs to obtain an EIR-SoC-discharge rate spectrum, and then, aligning the corresponding pilot internal resistance R under different charge state SoCsp(SoC) is taken as a reference, the fixed state of charge SoC is not changed, and the equivalent internal resistance EIR of the battery corresponding to different discharge multiplying factors r is taken according to the EIR-SoC-discharge multiplying factor spectrumrDefining discharge rate correction systemNumber Kr：
c4. Setting the temperature of a temperature box to be 40 ℃, aligning the battery SOC with each SOC in the step C1, charging the battery for different time lengths t at 0.3C multiplying power, standing the battery for 2 hours until the battery voltage change rate is lower than 0.1mV/min, discharging for t seconds, standing the battery for 2 hours until the battery voltage change rate is lower than 0.1mV/min, recording the equivalent internal resistance EIRs of the battery under different SoCs to obtain an EIR-SoC-discharging time length spectrum, and then, aligning the corresponding pilot internal resistance R under different SoCsp(SoC) is taken as a reference, the fixed state of charge SoC is not changed, and the equivalent internal resistance EIR of the battery corresponding to different discharge time lengths t is taken according to the EIR-SoC-discharge time length spectrumtDefining a discharge duration correction factor Kt：
The method for obtaining the equivalent internal resistance EIR of the battery under different charge states SoC in the steps c1 to c4 comprises the step of recording the voltage E (t) at the beginning of discharge in each section of discharge time t0) Voltage E (t) of the battery at the end of discharge1) And the discharge current I (t), the equivalent internal resistance EIR (t) of the battery in the time t can be calculated by the formula (6):
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