CN110646741A - Parameter obtaining method for lithium ion battery equivalent circuit model - Google Patents
Parameter obtaining method for lithium ion battery equivalent circuit model Download PDFInfo
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- CN110646741A CN110646741A CN201910892347.4A CN201910892347A CN110646741A CN 110646741 A CN110646741 A CN 110646741A CN 201910892347 A CN201910892347 A CN 201910892347A CN 110646741 A CN110646741 A CN 110646741A
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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]
- G01R31/382—Arrangements for monitoring battery or accumulator variables, e.g. SoC
- G01R31/3842—Arrangements for monitoring battery or accumulator variables, e.g. SoC combining voltage and current measurements
Abstract
The invention discloses a parameter acquisition method of an equivalent circuit model of a lithium ion battery, which adopts an improved HPPC method to acquire parameters of the equivalent circuit, can acquire all the parameters under one test, can adjust the test time according to objective conditions, adjust the complexity of the model according to the computing power of a simulation platform and select different parameter application methods according to the application scene of a battery cell: such as a data table or a functional expression. The parameter acquisition method of the lithium ion battery equivalent circuit model has the advantages of high test speed, accurate test result, customizability and the like, can be applied to the aspects of simulation, battery management and the like of electric vehicles, micro-grids and energy storage systems, and has wide application prospect.
Description
Technical Field
The invention relates to a lithium ion battery parameter acquisition method, in particular to a parameter acquisition method of a lithium ion battery equivalent circuit model, and belongs to the technical field of lithium ion batteries.
Background
Lithium ion batteries are widely used in a plurality of fields such as mobile electronic devices, electric vehicles, energy storage devices and the like as the current electric energy storage technical means with the highest energy density. The vigorous development and increasing demand of the application market also put higher requirements on a plurality of technical indexes of the lithium ion battery, such as energy density, capacity density, power density and the like.
The modeling work of the lithium ion battery plays a crucial role in the simulation of the lithium battery, and the lithium ion battery is widely applied to the research process of electric vehicles, micro-grids and light storage systems. The accurate battery model is also the basis of methods such as battery state of charge estimation, state of health estimation and residual life estimation.
Common lithium ion battery models include electrochemical models and equivalent circuit models. The equivalent circuit model simulates the state of the battery by using circuit elements such as a resistor, a capacitor and the like, expresses the internal change of the battery through the characteristics of external elements, and has the advantages of intuition, visibility, less parameters, convenience in simulation and the like. In order to obtain various parameters in the equivalent circuit model, a series of test analysis and data processing are required to be carried out on the battery. For this reason, various equivalent circuit parameter acquisition methods have been devised. For example, chinese patent application No. 2017113765734 entitled "equivalent circuit-based lithium ion battery SOC estimation algorithm" discloses an equivalent circuit-based method for estimating the state of charge (SOC) of a power battery of a lithium ion battery, but this method can estimate only one parameter of the battery, and thus the application range is limited. Therefore, it is necessary to invent a parameter obtaining method for obtaining as much parameter information as possible in one test.
Disclosure of Invention
In order to solve the technical problem, the invention provides a parameter acquisition method of an equivalent circuit model of a lithium ion battery, which can acquire a plurality of parameters of the battery in a one-time test process.
Therefore, the invention adopts the following technical scheme:
a parameter obtaining method for an equivalent circuit model of a lithium ion battery comprises the following steps:
s1: connecting the single battery cell into a battery cell test cabinet, and setting a plurality of test temperatures;
s2: performing constant current charge/discharge circulation N times under the standard working condition of the battery core to obtain a battery core charge/discharge curve, and analyzing the change rate of the battery voltage of each SOC section, wherein N is an integer more than or equal to 2;
s3: carrying out an improved HPPC test, specifically: carrying out SOC segmentation according to the charging/discharging curve in the step S2, and adjusting the pulse charging/discharging frequency in each segment, wherein, at the stage of fast battery voltage change, pulses are carried out every 1.5-2.5% of SOC; at the stage of slow change of the battery voltage, carrying out pulse every 3-5% of SOC; standing for 1-3min after each pulse charging/discharging;
s4: adjusting the state of charge: according to the pulse charging/discharging condition in the step S3, performing constant current charging/discharging to adjust the state of charge, wherein the amplitude is 1.5-5% SOC, and standing for a short time, such as 1-3min, after the charging/discharging time is cut off to obtain the open-circuit voltage corresponding to the state of charge;
s5: processing the charging/discharging data to obtain equivalent circuit parameters: acquiring open-circuit voltage data in the step S4, and resistance and capacitance data acquired in the step S3; establishing an equivalent circuit model, wherein the equivalent circuit is composed of an ideal controlled voltage source and an ohmic resistor R0The battery simulation circuit is formed by connecting a plurality of RC units in series and is used for simulating a battery; each RC unit consists of a polarization resistor and a polarization capacitor which are connected in parallel; as shown in fig. 1;
s6: and performing piecewise fitting on the charge/discharge curve, wherein the function relation of the change of the battery terminal voltage along with time in the charge/discharge process is as follows:
after the charging/discharging is finished, the function relation of the change of the battery terminal voltage along with the time is as follows:
wherein: u is the battery terminal voltage, UocIs an open circuit voltage, R0Is ohmic resistance, RiIs a polarization resistance, CiIs a polarization capacitance, tauiIs a time constant (i ═ 1,2, 3);
s7: and selecting corresponding equivalent circuit parameters according to different temperatures and charge states to perform simulation applying the equivalent circuit model, and adopting a data set or fitting an SOC-X curve function according to different operation platforms.
Further, in step S5, the equivalent circuit model includes a first-order Thevenin model, a second-order RC model, and a third-order RC model.
Further, in step S7, the curve fitting method uses a least squares method.
Further, in step S5, the ideal controlled voltage source in the equivalent circuit model represents the open-circuit voltage, and each parameter varies with the change of the battery state of charge and the state of charge/discharge.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts an improved HPPC method to obtain parameters of an equivalent circuit, can obtain all parameters under one test, can adjust test time according to objective conditions, can adjust the complexity of a model according to the computing capacity of a simulation platform, and can select different parameter application methods according to an electric core application scene: such as a data table or a functional expression. The parameter acquisition method of the lithium ion battery equivalent circuit model has the advantages of high test speed, accurate test result, customizability and the like, can be applied to the aspects of simulation, battery management and the like of electric vehicles, micro-grids and energy storage systems, and has very wide application prospect.
Drawings
Fig. 1 is a circuit configuration of an equivalent circuit in the present invention.
Detailed Description
The invention provides a parameter acquisition method of an equivalent circuit model of a lithium ion battery, which comprises the following steps:
s1: connecting the single battery cell into a battery cell test cabinet, setting a plurality of test temperatures, such as-10 ℃, 0 ℃, 10 ℃, 25 ℃, 30 ℃, 40 ℃, 45 ℃ and the like in the embodiment, and respectively testing at different set temperatures;
s2: performing constant current charging-discharging under the standard working condition of the battery core, circulating for 3 times, obtaining a battery core charging/discharging curve, and analyzing the change rate of the battery voltage of each SOC section;
s3: carrying out an improved HPPC test, specifically: carrying out SOC segmentation according to the charging/discharging curve in the step S2, and adjusting the pulse charging/discharging frequency in each segment, wherein, at the stage of fast battery voltage change, pulses are carried out every 1.5-2.5% of SOC; at the stage of slow change of the battery voltage, carrying out pulse every 3-5% of SOC; standing for a short time after each pulse charge/discharge, such as standing for 1-3 min;
s4: adjusting the state of charge: according to the pulse charging/discharging condition in the step S3, performing constant current charging/discharging to adjust the state of charge, wherein the amplitude is 1.5-5% SOC, and after the charging/discharging time is cut off, similarly performing short-time standing, such as standing for 1-3min, so as to obtain the open-circuit voltage corresponding to the state of charge;
s5: processing the charging/discharging data to obtain equivalent circuit parameters: acquiring open-circuit voltage data after standing in the step S4, and acquiring resistance and capacitance data during each pulse process by fitting an acquired time-voltage curve after pulse-standing in the step S3 and respectively acquiring constant term values of the obtained functional expression; establishing an equivalent circuit model, wherein the equivalent circuit comprises an ideal controlled voltage source and an ohmic resistor R which are connected in series0And a plurality of RC units, each RC unit is composed of a polarization resistor and a polarization capacitor which are connected in parallel; as shown in fig. 1; the equivalent circuit model mainly comprises a first-order Thevenin model, a second-order RC model, a third-order RC model and the like; in the equivalent circuit model, an ideal controlled voltage source represents an open-circuit voltage, and each parameter changes along with the change of the charge state and the charge/discharge state of the battery.
S6: the function fitting of the "time-voltage" curve obtained from the charge/discharge test is a piecewise fitting, i.e. fitting for each pulse-rest phase separately. During charging/discharging, the function relation of the terminal voltage of the battery along with the change of time is as follows:
after the charging/discharging is finished, the function relation of the change of the battery terminal voltage along with the time is as follows:
wherein: u is the battery terminal voltage, UocIs an open circuit voltage, R0Is ohmic resistance, RiIs a polarization resistance, CiIs a polarization capacitance, taui＝RiCiIs a time constant (i ═ 1,2, 3); the "time-voltage" curve is a curve with an independent variable t and a dependent variable U.
S7: the battery property, that is, the parameters of the equivalent circuit, are constantly changed with the battery temperature and the battery state of charge, and in the application process of the equivalent circuit model, corresponding equivalent circuit parameters are selected according to different temperatures and states of charge to perform model simulation. Meanwhile, according to different operation platforms, aiming at the calculation capacity, data storage capacity and the like of the platforms, the application of the model after the mathematic processing is carried out by selecting a data set or an SOC-X curve function formula obtained by fitting; the curve fitting method uses a least square method, and most curve functions obtained by fitting are polynomial functions.
Claims (4)
1. A parameter acquisition method for an equivalent circuit model of a lithium ion battery is characterized by comprising the following steps: the method comprises the following steps:
s1: connecting the single battery cell into a battery cell test cabinet, and setting a plurality of test temperatures;
s2: performing constant current charge/discharge circulation N times under the standard working condition of the battery core to obtain a battery core charge/discharge curve, and analyzing the change rate of the battery voltage of each SOC section, wherein N is an integer more than or equal to 2;
s3: carrying out an improved HPPC test, specifically: carrying out SOC segmentation according to the charging/discharging curve in the step S2, and adjusting the pulse charging/discharging frequency in each segment, wherein, at the stage of fast battery voltage change, pulses are carried out every 1.5-2.5% of SOC; at the stage of slow change of the battery voltage, carrying out pulse every 3-5% of SOC; standing for 1-3min after each pulse charging/discharging;
s4: adjusting the state of charge: according to the pulse charging/discharging condition in the step S3, performing constant current charging/discharging to adjust the state of charge, wherein the amplitude is 1.5-5% of SOC, and standing after the charging/discharging time is cut off to obtain an open-circuit voltage corresponding to the state of charge;
s5: processing the charging/discharging data to obtain equivalent circuit parameters: acquiring open-circuit voltage data in the step S4, and resistance and capacitance data acquired in the step S3; establishing an equivalent circuit model, wherein the equivalent circuit comprises ohmic resistors R connected in series0Each RC unit consists of a polarization resistor and a polarization capacitor which are connected in parallel; as shown in fig. 1;
s6: and performing piecewise fitting on the charge/discharge curve, wherein the function relation of the change of the battery terminal voltage along with time in the charge/discharge process is as follows:
after the charging/discharging is finished, the function relation of the change of the battery terminal voltage along with the time is as follows:
wherein: u is the battery terminal voltage, UocIs an open circuit voltage, R0Is ohmic resistance, RiIs a polarization resistance, CiIs a polarization capacitance, tauiIs a time constant (i ═ 1,2, 3);
s7: and selecting corresponding equivalent circuit parameters according to different temperatures and charge states to perform simulation applying the equivalent circuit model, and adopting a data set or fitting an SOC-X curve function according to different operation platforms.
2. The method for obtaining parameters of an equivalent circuit model of a lithium ion battery according to claim 1, characterized in that: in step S5, the equivalent circuit model includes a first-order Thevenin model, a second-order RC model, and a third-order RC model.
3. The method for obtaining parameters of an equivalent circuit model of a lithium ion battery according to claim 1, characterized in that: in step S7, the curve fitting method uses a least squares method.
4. The method for obtaining parameters of an equivalent circuit model of a lithium ion battery according to claim 1, characterized in that: in step S5, the ideal controlled voltage source represents the open-circuit voltage in the equivalent circuit model, and each parameter varies with the change of the battery state of charge and the state of charge/discharge.
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