CN115494415A - Battery cell internal resistance estimation method - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 41
- 238000001816 cooling Methods 0.000 claims abstract description 68
- 239000000110 cooling liquid Substances 0.000 claims abstract description 66
- 239000007788 liquid Substances 0.000 claims abstract description 48
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 21
- 239000010959 steel Substances 0.000 claims abstract description 21
- 230000008569 process Effects 0.000 claims abstract description 19
- 238000007599 discharging Methods 0.000 claims abstract description 17
- 239000002826 coolant Substances 0.000 claims description 10
- 230000008859 change Effects 0.000 description 10
- 238000012360 testing method Methods 0.000 description 5
- 238000001514 detection method Methods 0.000 description 4
- 230000014759 maintenance of location Effects 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical group [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000012809 cooling fluid Substances 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- 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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- 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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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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- Y02E60/10—Energy storage using batteries
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Abstract
The invention relates to the technical field of secondary batteries, and provides a battery cell internal resistance estimation method, which specifically comprises the following steps: s1, measuring the temperature difference delta t of cooling liquid in an outlet and an inlet of a liquid cooling plate in a battery in the charging and discharging process of the battery; s2, measuring the volume V of the cooling liquid discharged from the liquid cooling plate in unit time Cold (ii) a S3, passing the temperature difference Deltat and the volume V Cooling by cooling Calculating the heat Q absorbed by the cooling liquid discharged from the liquid cooling plate Suction device (ii) a S4, passing the heat Q Suction device Calculating the heat loss Q in the charging and discharging process of the battery Decrease in the thickness of the steel (ii) a S5, loss of Q by said heat Decrease in the thickness of the steel Calculating the internal resistance R of the battery General assembly (ii) a S6, passing the internal resistance R General assembly Calculating the resistance R of a single cell in the battery Inner part . Method for estimating internal resistance of battery cellThe actual heat loss of the battery is indirectly calculated by taking away heat by the cooling liquid, and the total resistance of the battery is calculated, so that the high estimation accuracy of the internal resistance is ensured when the battery is used at different degrees.
Description
Technical Field
The invention relates to the technical field of secondary batteries, in particular to a method for estimating the internal resistance of a battery cell.
Background
The internal resistance of the battery can change in the long-term use process of the lithium battery, the existing monitoring mode is mainly to monitor through voltage drop change, the voltage drop change can reflect the change of the resistance, but only when the resistance change is large, the change of the resistance can be judged through voltage drop, the internal resistance of the battery is proved to have changed greatly, the change of the internal resistance can influence the heat generated by the battery, if the risk of fire disaster can not be judged and detected in advance, the internal resistance of the battery is monitored, and therefore the internal resistance of the battery is also one of means for monitoring the health of the battery.
In the prior art, the publication No. CN112180277A, "method for estimating dc resistance of power battery", discloses that a battery is cyclically aged by a constant current, a discharge capacity retention rate and a dc resistance retention rate are measured, and a battery resistance to be measured is estimated by an obtained curve equation.
Because the constant current is used for carrying out charge and discharge test, errors exist in actual detection data in different working conditions of the battery, and meanwhile, although the battery capacity and the resistance are closely related, other factors influencing the battery capacity still exist, so that the difference of the corresponding resistance value of a curve equation obtained through the discharge capacity retention rate is larger than the actual resistance value.
Disclosure of Invention
In view of this, the present invention provides a method for estimating internal resistance of a battery cell, which directly estimates the resistance of a battery through heat loss generated during the use of the battery, and avoids errors and environmental influences existing during the test process, thereby improving the accuracy of estimating the internal resistance of the battery.
The technical scheme of the invention is realized as follows: the invention provides a method for estimating the internal resistance of a battery cell, which comprises the following steps:
s1, measuring the temperature difference delta t of cooling liquid in an outlet and an inlet of a liquid cooling plate in a battery in the charging and discharging process of the battery;
s2, measuring the volume V of the cooling liquid discharged out of the liquid cooling plate in unit time Cold ；
S3, passing the temperature difference Deltat and the volume V Cold Calculating the heat Q absorbed by the cooling liquid discharged from the liquid cooling plate Suction device ；
S4, passing the heat Q Suction device Calculating the heat loss Q in the charging and discharging process of the battery Decrease in the thickness of the steel ；
S5, loss of Q by said heat Decrease in the thickness of the steel Calculating the internal resistance R of the battery General (1) ；
S6, passing the internal resistance R General (1) Calculating the resistance R of a single cell in the battery Inner part 。
Based on the above technical solution, preferably, in step S1, the calculation formula of the temperature difference Δ t is: Δ t = t Go out -t Into Wherein t is Go out For the temperature of the cooling liquid at the outlet of the liquid-cooled plate, t Into For the temperature of the cooling liquid at the inlet of said liquid-cooled plate, t Go out And t Into The units of (A) are all.
Further preferably, the temperature of the coolant at the outlet and the temperature of the coolant at the inlet of the liquid cooling plate are measured by temperature sensors installed at the outlet and the inlet of the liquid cooling plate.
On the basis of the above technical solution, preferably, in step S2, the volume V Cold The calculation formula of (2) is as follows: v Cold =q Cooling by cooling * t, wherein q Cooling by cooling The unit of the flow rate of the cooling liquid is L/min, and t is unit time min.
Further preferably, the coolant flow rate q is set to be lower than the coolant flow rate q Cold And the flow meter is arranged at the outlet of the liquid cooling plate or the inlet of the liquid cooling plate.
Based on the above technical solution, preferably, in step S3, the heat quantity Q Suction device The calculation formula of (c) is: q Suction device =C Cooling by cooling *ρ Cold *V Cold * Δ t, wherein C Cold The specific heat capacity of the cooling liquid is expressed in units of KJ/(kg), rho DEG C Cold The density of the cooling liquid is expressed in kg/L.
Based on the above technical solution, preferably, in step S4, the heat loss Q is Damage to The calculation formula of (2) is as follows: q Damage to =Q Suction device * k, wherein k represents the heat loss coefficient and the value of k is greater than 1.
Further preferably, the heat loss coefficient k is measured by simulating that the battery is charged and discharged under different environments.
Based on the above technical solution, preferably, in step S5, the internal resistance R is General (1) The calculation formula of (2) is as follows: r General assembly =Q Decrease in the thickness of the steel /（I 2 * t), wherein I is the circuit current in the charging and discharging process of the battery, the unit is A, and t is the unit time min.
In addition to the above technical solution, preferably, in step S6, the resistor R Inner part =（R General assembly -circuit fixed resistance)/number of cells.
Compared with the prior art, the method for estimating the internal resistance of the battery cell has the following beneficial effects:
(1) The actual heat loss of the battery is indirectly calculated by taking away heat by the cooling liquid, and the total resistance of the battery is calculated, so that the phenomenon that the charging and discharging times and the accuracy are in inverse proportion due to error superposition of a curve equation obtained in a test stage can be avoided, and the high estimation accuracy on the internal resistance is ensured when the battery is used at different degrees;
(2) The resistance of a single battery cell is calculated according to the obtained total resistance of the battery, the service life of the battery can be judged according to the change condition of the resistance of the battery cell, or an alarm is given when the resistance is abnormally changed, and the like, so that the risk of fire caused by the battery is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a flowchart of a battery cell internal resistance estimation method according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As shown in fig. 1, the method for estimating internal resistance of a battery cell according to the embodiment of the present invention includes steps S1 to S6.
Step S1: and measuring the temperature difference delta t of cooling liquid in an outlet and an inlet of a liquid cooling plate in the battery in the charging and discharging process of the battery.
The battery is a lithium ion battery, a lead-acid battery and the like in a battery system with a liquid cooling circulation system, and is generally a power battery or an energy storage container and the like, the liquid cooling plate is a component in the liquid cooling circulation system and is provided with a cooling liquid outlet and a cooling liquid inlet, the liquid cooling plate is in contact with a battery cell in the battery, and the cooling liquid is injected into the liquid cooling plate for circulation, so that the temperature of the battery is reduced.
In the actual detection process, the temperature t of the cooling liquid at the inlet of the liquid cooling plate is detected Into Temperature t of cooling liquid at outlet of liquid cooling plate Go out The calculation formula of the temperature difference delta t of the cooling liquid in the outlet and the inlet is as follows: Δ t = t Go out -t Into I.e. the temperature t of the cooling liquid from the outlet of the liquid-cooled plate Go out Minus the temperature t of the cooling liquid at the inlet of the liquid-cooled plate Into So as to obtain the temperature difference delta t, t of the cooling liquid in the outlet and the inlet of the liquid cooling plate Go out And t Into The units of (d) are all in degrees Celsius, and the calculated Δ t is also in degrees Celsius.
Specifically, the temperature sensors are respectively arranged at the outlet and the inlet of the liquid cooling plate, or the temperature sensors are arranged on a pipeline connected with the outlet and the inlet of the liquid cooling plate, so that the temperature of the cooling liquid at the outlet of the liquid cooling plate can be respectively measured through the two temperature sensorst Go out Temperature t of cooling liquid at inlet of liquid cooling plate Into 。
Step S2: measuring the volume V of the cooling liquid discharged from the liquid-cooled plate in unit time Cold 。
The unit time can be defined as a unit interval from a certain moment to another moment when the battery works continuously, and in the unit time, the volume of the cooling liquid discharged out of the liquid-cooled plate is equal to the volume of the cooling liquid entering the liquid-cooled plate, so that the volume of the cooling liquid discharged out of the liquid-cooled plate can be directly measured, and the volume of the cooling liquid discharged out of the liquid-cooled plate can also be indirectly obtained by measuring the volume of the cooling liquid entering the liquid-cooled plate.
Specifically, the coolant flow rate q is first detected Cold Volume V of the liquid-cooled plate from which the cooling liquid is discharged Cold Equal to unit time and coolant flow q Cold The volume V of the liquid coolant exiting the liquid-cooled plate Cold The calculation formula of (2) is as follows: v Cold =q Cooling by cooling * t, wherein q Cold The unit of (a) is L/min, t is unit time min, and in the actual use process of the battery, q is Cold The temperature of the battery is automatically controlled by detecting the temperature of the battery directly through the liquid cooling circulation system.
Further, the flow rate q of the cooling liquid Cold The flowmeter can be directly arranged at the outlet of the liquid cooling plate, the inlet of the liquid cooling plate or a pipeline connecting the outlet of the liquid cooling plate and the inlet of the liquid cooling plate for measurement, one or more flowmeters can be arranged, and the average value of each flowmeter can be used as the actual flow q of the cooling liquid for installing more than one flow meter Cold Thereby improving the accuracy of the detection, it is noted that the flow rate q of the cooling liquid does not have to be measured by a flow meter Cold The flow q of the cooling liquid can also be indirectly obtained directly by detecting the rotating speed of a liquid pump for transmitting the cooling liquid Cold The numerical value of (c).
And step S3: by said temperature difference Δ t and said volume V Cold Calculating the heat Q absorbed by the cooling liquid discharged from the liquid cooling plate Suction device 。
Heat Q absorbed by liquid cooling plate cooling liquid Suction device The temperature difference Deltat obtained in step S1 is multiplied by the specific heat capacity C of the cooling liquid Cold And a cooling liquidDensity of rho Cold And multiplying the volume V of the cooling fluid discharged from the liquid cooling plate per unit time obtained in the step S2 by the volume V Cold 。
Heat quantity Q absorbed by specific cooling liquid Suction device The calculation formula of (2) is as follows: q Suction device =C Cold *ρ Cold *V Cold * Δ t, wherein C Cold The specific heat capacity of the cooling liquid is expressed in KJ/(kg ℃), rho Cooling by cooling The density of the internal cooling liquid is expressed in kg/L, the specific heat capacity and the density of the cooling liquid are related to the solution adopted by the cooling liquid, and the specific heat capacity and the density are different according to different solutions.
And step S4: by the heat quantity Q Suction device Calculating the heat loss Q in the charging and discharging process of the battery Damage to 。
Heat quantity Q absorbed by cooling liquid in charging and discharging process of battery Suction device The heat Q absorbed by the cooling liquid is not the heat generated by the internal resistance of the battery, but has a fixed proportionality coefficient under different environments Suction device Multiplying by this factor to obtain the heat loss Q Decrease in the thickness of the steel 。
Specifically, the heat Q absorbed by the cooling liquid Suction device And heat loss Q Decrease in the thickness of the steel The fixed proportionality coefficient under different environments is defined as the heat loss coefficient k, then the heat loss Q Decrease in the thickness of the steel The calculation formula of (2) is as follows: q Damage to =Q Suction device * k, wherein the value of k is more than 1, otherwise, before the battery leaves the factory, the environment test is carried out by simulating different temperatures and different cooling liquid flows, and the heat loss Q is directly measured by the Joule law Damage to And measuring the value of k in different environments, and calling the value of k in the corresponding temperature environment and flow rate in the actual estimation process to obtain the heat Q absorbed by the cooling liquid Suction device To obtain heat loss Q Decrease in the thickness of the steel 。
Step S5: by said heat loss Q Damage to Calculating the internal resistance R of the battery General assembly 。
In obtaining heat loss Q Decrease in the thickness of the steel Then, Q can be known from Joule's law Damage to =I 2 R General assembly t, the internal resistance R can be converted General assembly The calculation formula of (2) is as follows: r General assembly =Q Decrease in the thickness of the steel /（I 2 *t），Wherein I is the circuit current in the charging and discharging process of the battery, the unit is A, and t is the volume V in the step S2 Cold The unit time for discharging the cooling liquid out of the liquid cooling plate, the current I, the unit time and the heat loss Q Damage to Substituting into a formula to obtain the internal resistance R General (1) The circuit current I can be measured directly by the battery system.
Step S6: by the internal resistance R General (1) Calculating the resistance R of a single cell in the battery Inner part 。
The number of cells in a battery is known, and in a battery with cells in series, the resistance R Inner part The following formula can be obtained by adding the fixed resistance of the circuit to the sum of all the cell resistances: resistance R Inner part =（R General (1) Circuit fixed resistance)/number of cells, wherein the fixed resistance of the circuit is associated with the fastening mode and the production process, is not easy to change and can be measured in the factory process.
Knowing the resistance R of a single cell Inner part Is in direct proportion to parameters such as charging and discharging times of the battery, vehicle mileage and the like, namely the resistance R of a single electric core Inner part Determining the service life of the battery, or at the resistance R Inner part And when abnormal change occurs, alarming and the like are carried out, so that the risk of fire caused by the battery is reduced.
In one particular embodiment: taking a certain power battery as an example, 128 cells are connected in series, wherein the current is 168.4A, and the cooling liquid in the liquid cooling plate is water and glycol 1:1 mixing at room temperature, C Cold =3.2KJ/（kg*℃），ρ Cooling by cooling =1.071kg/L, coolant flow q Cold The relationship between the temperature difference delta t and the temperature difference of the cooling liquid in the outlet and the inlet of the liquid cooling plate is shown in the following table.
| Flow rate q Cold （L/min） | Temperature difference Δ t (. Degree. C.) |
| 4 | 24.3 |
| 6 | 16.2 |
| 8 | 12.1 |
| 10 | 9.7 |
| 12 | 8.1 |
| 14 | 6.9 |
| 16 | 6.1 |
The method for estimating the internal resistance of the battery cell of the embodiment is as follows.
1) During the charging and discharging process of the battery, the temperature difference delta t between the cooling liquid at the outlet of the liquid cooling plate and the cooling liquid at the inlet of the liquid cooling plate is measured to be 9.8 ℃.
2) Measuring the volume V of the cooling liquid discharged from the liquid cooling plate in unit time Cold As can be seen from the above table, the flow rate q at a temperature of 9.7 ℃ is Δ t Cold The volume V of the liquid-cooled plate is 10L/min, the unit time is directly 1min, and the volume V of the liquid-cooled plate discharged when the temperature difference delta t =9.8 ℃ can be obtained Cooling by cooling =q Cold *t=10L。
3) Calculating the heat Q absorbed by the cooling liquid discharged from the liquid cooling plate Suction device Volume V of the liquid-cooled plate Cold =10L, temperature difference Δ t =9.7 ℃, Q Suction device =C Cold *ρ Cold *V Cold *△t=3.2*1.071*10*9.7（KJ）=332.48KJ。
4) Heat absorbed by cooling fluidQuantity Q Suction device =332.48KJ, equation Q Damage to =Q Suction device * k, at the same temperature difference Deltat and the same flow rate q Cold The following tests were carried out several times, as shown in the following table.
| Current (A) | Heat loss Q Decrease in the thickness of the steel （KJ） | Heat quantity Q Suction device （KJ) | Coefficient of heat loss k |
| 168.4 | 376.7 | 332.48 | 1.133 |
| 168.4 | 368.72 | 332.48 | 1.109 |
| 168.4 | 375.37 | 332.48 | 1.129 |
Thus giving a k-average at this ambient condition of: 1.124.
substituting the k value under the environment to obtain Q Decrease in the thickness of the steel =332.48 × 1.124 (KJ) =373.71KJ, and it is known that the calculated heat loss Q is Decrease in the thickness of the steel And the actual detection processHeat loss Q obtained in Decrease in the thickness of the steel The error is within 2%.
5) Measuring Q Decrease in the thickness of the steel After =373.71KJ, the value is substituted into the formula: r General assembly =Q Decrease in the thickness of the steel /（I 2 *t）=373.71/（168.4 2 *60 ) =0.21963 Ω, i.e. R General assembly =219.63 milliohm, due to R General (1) And Q Damage to Proportional, calculated R General assembly The error will also be within 2%.
6) At R General assembly =219.63 milliohm, resistance R Inner part =（R General (1) -circuit fixed resistance)/number of cells, where the circuit fixed resistance is 115.96 milliohms, substituted into the formula: resistance R Inner part = 219.63-115.96/128 milliohm =0.81 milliohm, i.e. the individual cell resistance R Inner part =0.81 milliohms.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to cover any modifications, equivalents, improvements, etc. within the spirit and scope of the present invention.
Claims (10)
1. A method for estimating the internal resistance of a battery cell is characterized by comprising the following steps:
s1, measuring the temperature difference delta t of cooling liquid in an outlet and an inlet of a liquid cooling plate in a battery in the charging and discharging process of the battery;
s2, measuring the volume V of the cooling liquid discharged from the liquid cooling plate in unit time Cooling by cooling ；
S3, passing the temperature difference delta t and the volume V Cold Calculating the heat Q absorbed by the cooling liquid discharged from the liquid cooling plate Suction device ；
S4, passing the heat Q Suction device Calculating the heat loss Q in the charging and discharging process of the battery Decrease in the thickness of the steel ；
S5, loss of Q by said heat Damage to Calculating the internal resistance R of the battery General (1) ；
S6, passing the internal resistance R General (1) Calculating the resistance R of a single cell in the battery Inner part 。
2. The method for estimating internal resistance of battery cell according to claim 1, wherein in step S1, the calculation formula of the temperature difference Δ t is: Δ t = t Go out -t Into Wherein t is Go out For the temperature of the cooling liquid at the outlet of the liquid cooling plate, t Into For the temperature of the cooling liquid at the inlet of said liquid-cooled plate, t Go out And t Into The units of (A) are all.
3. The method for estimating the internal resistance of the battery cell according to claim 2, wherein the temperature of the coolant at the outlet and the temperature of the coolant at the inlet of the liquid cooling plate are measured by temperature sensors installed at the outlet and the inlet of the liquid cooling plate.
4. The method of claim 1, wherein in step S2, the volume V is calculated Cooling by cooling The calculation formula of (2) is as follows: v Cold =q Cold * t, wherein q Cooling by cooling The unit of the flow rate of the cooling liquid is L/min, and t is unit time min.
5. The method for estimating internal resistance of battery cell according to claim 4, wherein the flow rate q of the cooling liquid is Cold And the flow meter is arranged at the outlet of the liquid cooling plate or the inlet of the liquid cooling plate.
6. The method for estimating internal resistance of battery cell of claim 1, wherein in step S3, the heat Q is Suction device The calculation formula of (2) is as follows: q Suction device =C Cold *ρ Cold *V Cold * Δ t, wherein C Cold The specific heat capacity of the cooling liquid is expressed in KJ/(kg ℃), rho Cold The density of the cooling liquid is expressed in kg/L.
7. The method for estimating internal resistance of battery cell according to claim 1, wherein in step S4, the heat loss Q is Decrease in the thickness of the steel The calculation formula of (c) is: q Decrease in the thickness of the steel =Q Suction device * k, where k represents heat lossCoefficient and k is greater than 1.
8. The method for estimating internal resistance of a battery cell according to claim 7, wherein the heat loss coefficient k is measured by charging and discharging a simulated battery under different environments.
9. The method for estimating internal resistance of battery cell of claim 1, wherein in step S5, the internal resistance R is General assembly The calculation formula of (2) is as follows: r General assembly =Q Decrease in the thickness of the steel /（I 2 * t), wherein I is the circuit current in the charging and discharging process of the battery, the unit is A, and t is the unit time min.
10. The method for estimating internal resistance of battery cell according to claim 1, wherein in step S6, the resistance R is Inner part =（R General (1) -circuit fixed resistance)/number of cells.
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