CN113917335A - Power battery RC equivalent circuit parameter solving method - Google Patents

Power battery RC equivalent circuit parameter solving method Download PDF

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Publication number
CN113917335A
CN113917335A CN202111162907.4A CN202111162907A CN113917335A CN 113917335 A CN113917335 A CN 113917335A CN 202111162907 A CN202111162907 A CN 202111162907A CN 113917335 A CN113917335 A CN 113917335A
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time
voltage
polarization
under different
internal resistance
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王涛
张秋豪
邓星
喻成
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Chongqing Changan New Energy Automobile Technology Co Ltd
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Chongqing Changan New Energy Automobile Technology Co Ltd
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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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
    • G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery

Abstract

The invention provides a method for solving parameters of an RC (resistor-capacitor) equivalent circuit of a power battery, which comprises the following steps: carrying out HPPC test on a power battery in advance to obtain a pulse discharge current time-varying curve and a pulse discharge voltage time-varying curve of a battery monomer of the power battery under different SOC conditions; building a first-order RC equivalent circuit of the battery monomer; obtaining terminal voltage U at two ends of the polarized capacitor based on a state equation of a first-order RC equivalent circuitpA functional expression that varies with time t; determining the resistance value R of the ohmic internal resistance under different SOC conditions based on the pulse discharge current time-varying curve and the pulse discharge voltage time-varying curve of a single battery of the power battery under different SOC conditions0(ii) a Bringing multiple groups of data under the same SOC condition into terminal voltages U at two ends of the polarization capacitorpIn the function expression changing along with the time t, the corresponding C value and the corresponding C value under different SOC conditions are solved by utilizing an optimization algorithm,Capacitance value C of polarization capacitorpAnd resistance value R of the polarization resistorp。

Description

Power battery RC equivalent circuit parameter solving method
Technical Field
The invention belongs to the field of power batteries, and particularly relates to a method for solving various electrical parameter problems in power battery RC equivalent circuits of pure electric vehicles, hybrid electric vehicles, large-scale electromechanical equipment and energy storage equipment.
Background
With the increasing strengthening of the environmental protection requirement, the use scenes of the power battery are more and more, so that whether the indexes such as the charge and discharge performance, the SOC and the SOH of the power battery can be rapidly and accurately predicted is more and more important, and the prediction of the performance and the indexes is closely related to each parameter in the equivalent circuit model.
At present, common battery models mainly include equivalent circuit models, empirical models, electrochemical models and the like, wherein the equivalent circuit models are circuits which are formed by adopting RC circuits as basic constituent elements and can simulate voltage changes in the discharging process of lithium ion batteries. The direct current internal resistance of the battery is generally completed by an HPPC (hybrid Pulse Power Characteristic) test method. The method for solving the open-circuit voltage Uoc, the ohmic internal resistance R0, the electrochemical polarization capacitance Cp and the electrochemical polarization internal resistance Rp in the RC equivalent circuit by aiming at the test method is complex and occupies computing resources.
In order to effectively solve the defects of complex operation mode, inaccurate calculation result and excessive resource occupation in calculation, the method is derived theoretically, and a simple algorithm tool is used for rapidly solving various parameters in the RC equivalent circuit.
Disclosure of Invention
The invention aims to solve the defects of complicated operation mode, inaccurate parameter calculation result, excessive resource occupation in calculation and the like caused by using an RC equivalent circuit model at the present stage, and provides a method for solving parameters of an RC equivalent circuit of a power battery.
The technical scheme of the invention is as follows:
the invention provides a method for solving parameters of an RC (resistor-capacitor) equivalent circuit of a power battery, which comprises the following steps:
carrying out HPPC test on a power battery in advance to obtain a pulse discharge current time-varying curve and a pulse discharge voltage time-varying curve of a battery monomer of the power battery under different SOC conditions;
building a first-order RC equivalent circuit of the battery monomer; the first order RC equivalent circuit comprises: the device comprises a voltage source for representing the open-circuit voltage of the power battery, and an electrochemical polarization simulation circuit connected with the negative electrode of the voltage source, wherein the electrochemical polarization simulation circuit is also electrically connected with the negative electrode of a voltage output end; the ohmic internal resistance is connected with the positive electrode of the voltage source and is also electrically connected with the positive electrode of the voltage output end; the electrochemical polarization simulation circuit comprises a polarization capacitor and a polarization resistor which are connected in parallel;
obtaining terminal voltage U at two ends of the polarized capacitor based on a state equation of a first-order RC equivalent circuitpA function expression varying with time t, a terminal voltage U across the polarization capacitorpThe function expression varying with time t is Up=Uoc-IL*Ro-IL*Rp+C*e-1/Cp*RpWherein, CpIs the capacitance value of the polarization capacitor, RpIs the resistance value of the polarization resistor, ILFor the current flowing through the ohmic internal resistance, UocIs the open circuit voltage of the voltage source, C is a constant;
determining the resistance value R of the ohmic internal resistance under different SOC conditions based on the pulse discharge current time-varying curve and the pulse discharge voltage time-varying curve of a single battery of the power battery under different SOC conditions0；
Bringing multiple sets of data under the same SOC condition into terminal voltages QUOTE at two ends of the polarization capacitor
Figure DEST_PATH_IMAGE002
Figure DEST_PATH_IMAGE002A
In the function expression changing along with the time t, the optimization algorithm is utilized to solve the corresponding QUOTE under different SOC conditions
Figure DEST_PATH_IMAGE004
Figure DEST_PATH_IMAGE004A
Capacitance C of value, polarization capacitancepAnd resistance value R of the polarization resistorpFurther obtaining the terminal voltage at two ends of the polarization capacitor under different SOC conditionsUpA functional expression that varies with time t; a set of data under the same SOC condition includes: open circuit voltage U of the voltage sourceocTerminal voltage U at two ends of the ohm internal resistanceocResistance value R of the ohmic internal resistance corresponding to one pulse discharge moment0A current value I corresponding to a pulse discharge moment and flowing through the ohm internal resistanceL；
Based on terminal voltages U at two ends of the polarization capacitor under different SOC conditionspFitting a function expression which changes along with the time t to form terminal voltage U at two ends of the polarization capacitorpCurve over time t.
Preferably, the method further comprises:
based on terminal voltages U at two ends of the polarization capacitor under different SOC conditionspObtaining terminal voltage U at two ends of the ohmic internal resistance under different SCO conditions by a function expression changing along with time tLA functional expression that varies with time t;
based on terminal voltage U at two ends of ohmic internal resistance under different SCO conditionsLAnd fitting a curve of the discharge voltage of the battery monomer of the power battery along with the change of the time t by the function expression along with the change of the time t.
Preferably, under different SOC conditions, the terminal voltage U at two ends of the ohmic internal resistanceLAnd the terminal voltage U between the two ends of the polarization capacitorpAll satisfy:
UL=Uoc-IL*R0-Up
Uocis the open circuit voltage of the voltage source, ILThe current passing through the ohmic internal resistance is determined based on a time variation curve of pulse discharge current of a battery cell of the power battery.
The invention has the beneficial effects that:
by adopting HPPC test data of single batteries of power batteries of practical mass-production vehicles, combining with the theory of RC equivalent circuit models of the single batteries and solving unknown parameters in an equivalent circuit model state equation through an optimization algorithm, the method can quickly and accurately solve the result by the equation with a small amount of calculation resources.
Drawings
FIG. 1 is a graph of current I and voltage U in HPPC test data screened in an embodiment of the present invention;
FIG. 2 is a model schematic of a first order RC equivalent circuit in an embodiment of the present invention;
FIG. 3a is a graph of pulse discharge voltage of a battery cell in an embodiment of the present invention;
FIG. 3b is a graph of pulse discharge current for a cell in an embodiment of the present invention;
fig. 4 is a schematic diagram of the terminal voltage Up values and the corresponding fitting curves corresponding to different times determined based on the solved functional relation between the terminal voltage Up and the time t in the embodiment of the present invention.
Detailed Description
Specific embodiments of the present invention are described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention. To better explain the technical content of the present invention, the theory applied by the present invention will be explained first.
According to the method, all values of discharge current I and discharge voltage U of the power battery changing along with time t in the whole testing process under different SOC conditions need to be screened out based on actual values obtained by carrying out HPPC testing on the power battery, then the data are expressed by curves, the change rule is carefully checked, and obviously abnormal data and burr data are removed. Finally, curves of the discharge current I and the discharge voltage U of the power battery under a certain SOC condition are obtained according to the curve shown in FIG. 1, and the corresponding data are considered as available data.
After the curve determination of the discharge current I and the discharge voltage U of the power battery under all SOC conditions is completed, further, the curves of the pulse discharge current and the pulse discharge voltage of each battery cell under different SOC conditions with the time t need to be determined based on these data. As shown in fig. 3a and 3 b.
As shown in fig. 3a and 3b, for a certain battery cell, in the time-varying curve of the pulse discharge current of the certain battery cell, the current I of the certain battery cell during pulse discharge can be determinedLSimilarly, in the pulse discharge voltage-time change curve, the voltage U1 of the battery cell before pulse discharge and the voltage U2 after discharge, the minimum voltage U4 of the voltage of the battery cell after discharge stop before the action of an external power supply, the voltage U4 after the external power supply stop and the voltage U5 after one pulse discharge cycle is completed and tends to be stable can be determined.
After the data screening is completed, the RC equivalent circuit model of the battery cell is selected, as shown in fig. 2, in this embodiment, the first-order RC equivalent circuit model is selected as the equivalent circuit of the battery cell. The first order RC equivalent circuit comprises: the device comprises a voltage source for representing the open-circuit voltage of the power battery, and an electrochemical polarization simulation circuit connected with the negative electrode of the voltage source, wherein the electrochemical polarization simulation circuit is also electrically connected with the negative electrode of a voltage output end; the ohmic internal resistance is connected with the positive electrode of the voltage source and is also electrically connected with the positive electrode of the voltage output end; the electrochemical polarization simulation circuit comprises a polarization capacitor and a polarization resistor which are connected in parallel. Based on the first-order RC equivalent circuit, the state equation corresponding to the circuit schematic diagram can be listed:
UL=Uoc-IL*R0-Up
Rp*Cp*dUp/dt+Up=IL*Rp
wherein: u shapeLRepresenting the actual measured end-of-line voltage; u shapeocRepresents the open circuit voltage of a voltage source in the circuit; i isLIndicating the passing ohmic internal resistance R in the circuit0The current of (a); r0Indicating ohmic internal resistance in the circuit; rpIndicating the polarization internal resistance; cpRepresents the polarization capacitance; u shapepRepresenting the terminal voltage across the polarization capacitor; t represents time.
Solving the parameters by the following steps:
taking discharge as an example, for a battery core under a certain SOC condition, theThe variations of the discharge voltage and discharge current shown in fig. 3a and 3b solve the ohmic internal resistance R under the SOC condition0Namely: r0=U2-U1/ILOr R0=U3-U4/IL. In the time-varying curve of the discharge current of the battery core, the discharge currents corresponding to the periods U1 and U2 are the same, and the discharge current at this time is determined as IL in the present embodiment (e.g., in fig. 3a, I is the same)LNamely 30A). Through the formula, the ohmic internal resistance R corresponding to the battery core body during the 10 th pulse discharge can be calculated0. Similarly, the ohmic internal resistance R corresponding to each pulse discharge of the battery core body under each specific SOC condition of the power battery can be calculated0。
For open circuit voltage U in the formulaocAnd terminal voltage U at two ends of ohmic internal resistanceLIt can be detected.
2. Solving a differential equation Rp*Cp*dUp/dt+Up=IL*RpGeneral solution U ofp=IL*Rp-C*e-1/Cp*RpPolarizing the terminal voltage U at both ends of the capacitorpSubstituting the equation into equation UL=Uoc-IL*R0-UpTo obtain the terminal voltage U at both ends of the polarized capacitorpEquation U for sum time tp=Uoc-IL*Ro-IL*Rp+C*e-1/Cp*Rp。
3. Bringing multiple sets of data under the same SOC condition into terminal voltages QUOTE at two ends of the polarization capacitor
Figure DEST_PATH_IMAGE005
Figure DEST_PATH_IMAGE005A
Solving the corresponding QUOTE under different SOC conditions based on an optimization algorithm in a function expression changing along with the time t
Figure DEST_PATH_IMAGE004AA
Figure DEST_PATH_IMAGE004AAA
Capacitance C of value, polarization capacitancepAnd resistance value R of the polarization resistorpFurther obtaining the terminal voltage U at two ends of the polarization capacitor under different SOC conditionspA functional expression that varies with time t; a set of data under the same SOC condition includes: open circuit voltage U of the voltage sourceocTerminal voltage U at two ends of the ohm internal resistanceocResistance value R of the ohmic internal resistance corresponding to one pulse discharge moment0A current value I corresponding to a pulse discharge moment and flowing through the ohm internal resistanceL。
Specifically, under each SOC condition, the ohmic internal resistance R corresponding to the battery core body at different pulse discharge time can be obtained0And a current I flowing through the ohmic internal resistanceL. Thus, under a SOC condition, a plurality of sets of data can be obtained, wherein a set of data comprises: open circuit voltage U of the voltage sourceocTerminal voltage U at two ends of the ohm internal resistanceocResistance value R of the ohmic internal resistance corresponding to one pulse discharge moment0A current value I corresponding to a pulse discharge moment and flowing through the ohm internal resistanceL。
At the same time, the formula U is utilizedL=Uoc-IL*R0-UpCan determine the corresponding U at different pulse discharge momentsp。
Further, a plurality of sets of data under each SOC condition are substituted into the above-mentioned functional expression Up=Uoc-IL*Ro-IL*Rp+C*e-1/Cp*RpThe unknown parameters C, C in the function expression are solved by using the existing optimization algorithmpAnd Rp。
Under different SOC conditions, the discharge current and the discharge voltage of the battery core body corresponding to different pulse discharge moments are not completely the same, so that the calculated ohmic internal resistance R corresponding to different pulse discharge moments0Nor will they be identical. Further, the function expressions under different SOC conditions are calculatedParameter C, CpAnd RpNor will they be identical.
Determining terminal voltages U at two ends of corresponding polarization capacitors under different SOC conditionspAfter the function expression changing along with the time t, the terminal voltage U at two ends of the polarization capacitor corresponding to different time points can be calculatedpThe specific numerical value of (1). Further, a terminal voltage U can be fitted to both ends of the polarization capacitorpCurve over time t.
4. As shown in FIG. 4, the terminal voltages U at two ends of the polarized capacitor corresponding to different times t are respectively plottedpAnd the fitted terminal voltage U at both ends of the polarization capacitorpIf the degree of engagement is high, the fitted terminal voltage U at two ends of the polarization capacitor can be determined according to the curve changing along with the time tpThe accuracy of the curve over time t is high.
And all parameters of the RC equivalent circuit of the power battery to be solved based on the HPPC test data are solved.
Further, in this embodiment, the terminal voltages U at the two ends of the ohmic internal resistance under different SCO conditions may be obtained based on a function expression of the terminal voltages Up at the two ends of the polarization capacitor changing with time t under different SOC conditionsLA functional expression that varies with time t; based on terminal voltage U at two ends of ohmic internal resistance under different SCO conditionsLAnd fitting a curve of the discharge voltage of the battery monomer of the power battery along with the change of the time t by the function expression along with the change of the time t.
The fitted curve of the discharge voltage of the battery monomer of the power battery changing along with the time t can be used as a curve of the discharge voltage of the battery monomer changing along with the time t under the specific SOC condition in the practical application.
While the foregoing has described illustrative embodiments of the invention in order to facilitate the understanding of the invention by those skilled in the art, it is to be understood that the invention is not limited to the precise embodiments disclosed, and that various changes may be apparent to those skilled in the art without departing from the spirit and scope of the invention as defined and limited only by the appended claims.

Claims (3)

1. A method for solving parameters of an RC equivalent circuit of a power battery is characterized by comprising the following steps:
carrying out HPPC test on a power battery in advance to obtain a pulse discharge current time-varying curve and a pulse discharge voltage time-varying curve of a battery monomer of the power battery under different SOC conditions;
building a first-order RC equivalent circuit of the battery monomer; the first order RC equivalent circuit comprises: the device comprises a voltage source for representing the open-circuit voltage of the power battery, and an electrochemical polarization simulation circuit connected with the negative electrode of the voltage source, wherein the electrochemical polarization simulation circuit is also electrically connected with the negative electrode of a voltage output end; the ohmic internal resistance is connected with the positive electrode of the voltage source and is also electrically connected with the positive electrode of the voltage output end; the electrochemical polarization simulation circuit comprises a polarization capacitor and a polarization resistor which are connected in parallel;
obtaining terminal voltage U at two ends of the polarized capacitor based on a state equation of a first-order RC equivalent circuitpA function expression varying with time t, a terminal voltage U across the polarization capacitorpThe function expression varying with time t is Up=Uoc-IL*Ro-IL*Rp+C*e-1/Cp*RpWherein, CpIs the capacitance value of the polarization capacitor, RpIs the resistance value of the polarization resistor, ILFor the current flowing through the ohmic internal resistance, UocIs the open circuit voltage of the voltage source, C is a constant;
determining the resistance value R of the ohmic internal resistance under different SOC conditions based on the pulse discharge current time-varying curve and the pulse discharge voltage time-varying curve of a single battery of the power battery under different SOC conditions0；
Bringing multiple groups of data under the same SOC condition into terminal voltages U at two ends of the polarization capacitorpIn the function expression changing along with the time t, the optimization algorithm is utilized to solve the electricity of the corresponding C value and polarization capacitance under different SOC conditionsCapacity value CpAnd resistance value R of the polarization resistorpFurther obtaining the terminal voltage U at two ends of the polarization capacitor under different SOC conditionspA functional expression that varies with time t; a set of data under the same SOC condition includes: open circuit voltage U of the voltage sourceocTerminal voltage U at two ends of the ohm internal resistanceocResistance value R of the ohmic internal resistance corresponding to one pulse discharge moment0A current value I corresponding to a pulse discharge moment and flowing through the ohm internal resistanceL；
Based on terminal voltages U at two ends of the polarization capacitor under different SOC conditionspFitting a function expression which changes along with the time t to form terminal voltage U at two ends of the polarization capacitorpCurve over time t.
2. The method of claim 1, further comprising:
based on terminal voltages U at two ends of the polarization capacitor under different SOC conditionspObtaining terminal voltage U at two ends of the ohmic internal resistance under different SCO conditions by a function expression changing along with time tLA functional expression that varies with time t;
based on terminal voltage U at two ends of ohmic internal resistance under different SCO conditionsLAnd fitting a curve of the discharge voltage of the battery monomer of the power battery along with the change of the time t by the function expression along with the change of the time t.
3. The method of claim 2, wherein terminal voltage U across said ohmic internal resistance is at different SOC conditionsLAnd the terminal voltage U between the two ends of the polarization capacitorpAll satisfy:
UL=Uoc-IL*R0-Up
Uocis the open circuit voltage of the voltage source, ILThe current passing through the ohmic internal resistance is determined based on a time variation curve of pulse discharge current of a battery cell of the power battery.
CN202111162907.4A 2021-09-30 2021-09-30 Power battery RC equivalent circuit parameter solving method Pending CN113917335A (en)

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106908732A (en) * 2017-02-09 2017-06-30 北京长城华冠汽车科技股份有限公司 A kind of lithium ion battery equivalent circuit model parameter discrimination method and device

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106908732A (en) * 2017-02-09 2017-06-30 北京长城华冠汽车科技股份有限公司 A kind of lithium ion battery equivalent circuit model parameter discrimination method and device

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