CN113805067B - System and method for detecting parameters of battery pack - Google Patents
System and method for detecting parameters of battery pack Download PDFInfo
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- CN113805067B CN113805067B CN202111143194.7A CN202111143194A CN113805067B CN 113805067 B CN113805067 B CN 113805067B CN 202111143194 A CN202111143194 A CN 202111143194A CN 113805067 B CN113805067 B CN 113805067B
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- 238000000034 method Methods 0.000 title claims abstract description 28
- 238000001514 detection method Methods 0.000 claims abstract description 161
- 238000012360 testing method Methods 0.000 claims description 80
- 239000003990 capacitor Substances 0.000 claims description 56
- 230000005284 excitation Effects 0.000 claims description 27
- 238000004146 energy storage Methods 0.000 claims description 11
- 238000000157 electrochemical-induced impedance spectroscopy Methods 0.000 description 122
- 210000004027 cell Anatomy 0.000 description 22
- 238000010586 diagram Methods 0.000 description 13
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- 238000001453 impedance spectrum Methods 0.000 description 2
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 1
- 239000011149 active material Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
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- 230000015556 catabolic process 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]
- G01R31/367—Software therefor, e.g. for battery testing using modelling or look-up tables
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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]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
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Abstract
The invention provides a system and a method for detecting parameters of a battery pack, and relates to the technical field of battery detection. The invention relates to a system for detecting parameters of a battery pack, which comprises the battery pack to be detected, an auxiliary unit, EIS detection equipment and a switch unit; the auxiliary unit is suitable for forming a serial system with the battery pack to be tested; the switch unit is used for controlling the current trend; the EIS detection equipment is used for being connected in series with the auxiliary unit and realizing parameter detection of the auxiliary unit, and is also used for being connected in series with the series system and realizing parameter detection of the series system, so that the equivalent circuit parameter of the battery pack to be detected is determined according to the equivalent circuit parameter of the auxiliary unit and the overall circuit parameter of the series system. The technical scheme of the invention can offset the higher open-circuit voltage of the battery pack to be tested, so that the common EIS detection equipment can detect the equivalent circuit and parameters of the high-voltage and high-capacity battery pack.
Description
Technical Field
The invention relates to the technical field of battery detection, in particular to a system and a method for detecting parameters of a battery pack.
Background
The storage battery and the lithium battery are used as relatively mature energy storage devices and are widely applied to the fields of electric energy storage systems, electric automobiles, electric bicycles, consumer electronics and the like. In order to characterize the battery and screen out products with good performance in use, the detection of the performance of the battery cells is important. And eliminating performance degradation or failure products, and carrying out a necessary flow of batch use of the battery cells.
The conventional method mostly realizes the test of the EIS (electrochemical impedance spectroscopy) of the battery through the traditional variable-frequency alternating-current sinusoidal excitation or the excitation of square waves, step waves and the like, so as to evaluate the performance and the state of the battery core. But the method is only applicable to the situations of constant low battery pack voltage such as single battery cell, serial connection of a plurality of battery cells and the like. In addition, in practical tests, since the open circuit voltage of the battery pack is high (more than tens of volts), the ac ripple output characteristics under such dc high voltage conditions are difficult to be satisfied by a common electrochemical workstation or a potentiostat or a galvanostat, and therefore, the method is difficult to be used in the battery pack.
Disclosure of Invention
The invention solves the problem of how to realize the detection of the equivalent circuit and the parameters of the equivalent circuit of the high-voltage and high-capacity battery pack by the common EIS detection equipment.
In order to solve the above problems, the present invention provides a system for detecting parameters of a battery pack, including a battery pack to be tested, an auxiliary unit, an EIS detection device, and a switch unit; the auxiliary unit is suitable for forming a serial system with the battery pack to be tested; the switch unit is used for controlling the current trend so as to realize parameter detection of the auxiliary unit, charging of the auxiliary unit and parameter detection of the serial system; the EIS detection equipment is used for being connected in series with the auxiliary unit and realizing parameter detection of the auxiliary unit, and is also used for being connected in series with the series system and realizing parameter detection of the series system, so that the equivalent circuit parameter of the battery pack to be detected is determined according to the equivalent circuit parameter of the auxiliary unit and the overall circuit parameter of the series system.
According to the system for detecting the parameters of the battery pack, the charged auxiliary unit and the battery pack to be detected are reversely connected in series to offset the higher open-circuit voltage of the battery pack to be detected, so that the requirement of the EIS detection equipment for testing the battery pack to be detected on the voltage is reduced, the parameter requirement of the EIS detection equipment is reduced, and the common EIS detection equipment can detect the equivalent circuit and the parameters of the high-voltage and high-capacity battery pack.
Optionally, the switch unit includes first switch, second switch, third switch and fourth switch, the both ends of first switch respectively with the anodal of battery that awaits measuring reaches the one end of auxiliary unit is connected, the one end of second switch is connected first switch with the junction of auxiliary unit, the other end of second switch is connected the battery that awaits measuring with the junction of EIS check out test set, the both ends of third switch respectively with the other end of auxiliary unit and EIS check out test set are connected, the one end of fourth switch is connected auxiliary unit with the junction of third switch, the other end of fourth switch is connected the junction of battery that awaits measuring with EIS check out test set.
According to the system for detecting the parameters of the battery pack, the switch unit comprises the first switch, the second switch, the third switch and the fourth switch, the equivalent circuit parameters of the auxiliary unit are detected by the EIS detection equipment, the battery pack to be detected charges the auxiliary unit, and the integral circuit parameters of the serial system are detected by the EIS detection equipment through opening and closing of the first switch, the second switch, the third switch and the fourth switch, so that the parameter detection of the battery pack to be detected is realized.
Optionally, the system for detecting the equivalent circuit parameters of the battery pack further comprises a choke unit connected with the fourth switch, wherein the choke unit is used for limiting current when the auxiliary unit is charged and serving as a discharging load when the auxiliary unit is discharged.
According to the system for detecting the parameters of the battery pack, the current limiting of the choke unit is set when the auxiliary unit is charged, and the choke unit is used as a discharging load when the auxiliary unit is discharged, so that the protection of a circuit is realized.
Optionally, the EIS detection device comprises an electrochemical workstation, a FRA combined potentiometer-amperometric combination, or a voltage and current source system capable of achieving EIS test AC output excitation.
According to the system for detecting the parameters of the battery pack, provided by the invention, the requirements of the EIS detection equipment for testing voltage during the battery pack testing to be tested are reduced by setting the specific types of the EIS detection equipment and the circuit setting of the parameter detection system, so that the common EIS detection equipment can detect the equivalent circuit and the parameters of the high-voltage and high-capacity battery pack.
Optionally, the auxiliary unit is an auxiliary capacitor or an auxiliary battery pack, the auxiliary capacitor comprises a passive energy storage capacitor with known parameters, and the auxiliary battery pack comprises an energy storage battery with known parameters and matched with the open-circuit voltage of the battery pack to be tested.
According to the system for detecting the parameters of the battery pack, the charged auxiliary capacitor or the auxiliary battery pack and the battery pack to be detected are reversely connected in series to offset the higher open-circuit voltage of the battery pack to be detected, so that the requirement of the EIS detection equipment for testing the voltage during testing the battery pack to be detected is reduced, the parameter requirement of the EIS detection equipment is reduced, and the common EIS detection equipment can detect the equivalent circuit of the battery pack with high voltage and large capacity and the parameters thereof.
The invention also provides a method for detecting the parameters of the battery pack, which is applied to the system for detecting the parameters of the battery pack and comprises the following steps: after detecting equivalent circuit parameters of an auxiliary unit through EIS detection equipment, connecting the auxiliary unit and a battery pack to be detected in series to form a series system; after the auxiliary unit is charged by the battery pack to be tested, detecting the overall circuit parameters of the serial system by the EIS detection equipment; and determining the equivalent circuit parameters of the battery pack to be tested according to the equivalent circuit parameters of the auxiliary unit and the overall circuit parameters of the serial system.
According to the method for detecting the parameters of the battery pack, the charged auxiliary unit and the battery pack to be detected are reversely connected in series to offset the higher open-circuit voltage of the battery pack to be detected, so that the requirement of the EIS detection equipment for testing the battery pack to be detected on the voltage is reduced, the parameter requirement of the EIS detection equipment is reduced, and the common EIS detection equipment can detect the equivalent circuit and the parameters of the high-voltage and high-capacity battery pack.
Optionally, the switching unit includes a first switch, a second switch, a third switch, and a fourth switch; after the equivalent circuit parameters of the auxiliary unit are detected by the EIS detection equipment, the auxiliary unit and the battery pack to be detected are connected in series to form a series system, which comprises the following steps: opening the first switch and the fourth switch, closing the second switch and the third switch, so that the EIS detection device and the auxiliary unit form a loop to detect equivalent circuit parameters of the auxiliary unit through the EIS detection device; and opening the second switch and the third switch, closing the first switch and the fourth switch, so that the battery pack to be tested and the auxiliary unit form a loop, and charging the auxiliary unit through the battery pack to be tested.
According to the method for detecting the parameters of the battery pack, disclosed by the invention, the equivalent circuit parameters of the auxiliary unit are detected by the EIS detection equipment and the battery pack to be detected is charged to the auxiliary unit through opening and closing the first switch, the second switch, the third switch and the fourth switch, so that the parameter detection of the battery pack to be detected can be realized.
Optionally, after the auxiliary unit is charged by the battery pack to be tested, detecting, by the EIS detection device, an overall circuit parameter of the serial system includes: opening the second switch and the fourth switch, closing the first switch and the third switch, and enabling the EIS detection equipment and the serial system to form a loop so as to complete EIS test of the serial system through the EIS detection equipment; opening the first switch and the third switch, closing the second switch and the fourth switch so that the auxiliary unit and the choke unit form a loop to realize self-discharge of the auxiliary unit; and setting a circuit model of the series system by combining the circuit model of the auxiliary unit, and analyzing and fitting out the overall circuit parameters of the series system.
According to the method for detecting the parameters of the battery pack, the EIS detection equipment detects the parameters of the whole circuit of the serial system through opening and closing the first switch, the second switch, the third switch and the fourth switch, so that the parameter detection of the battery pack to be detected can be realized.
Optionally, the performing, by the EIS detection device, the EIS test of the serial system includes: an alternating current of variable frequency is selected as the excitation current of the EIS detection device.
According to the method for detecting the parameters of the battery pack, the alternating current with variable frequency is selected as the excitation current of the EIS detection equipment, so that high-precision detection of response voltage is facilitated, and the precision of a test result is improved.
Optionally, the determining the equivalent circuit parameter of the battery pack to be tested according to the equivalent circuit parameter of the auxiliary unit and the overall circuit parameter of the serial system includes: and eliminating the equivalent circuit parameters of the auxiliary unit from the overall circuit parameters of the series system to determine the equivalent circuit parameters of the battery pack to be tested.
According to the method for detecting the parameters of the battery pack, the equivalent circuit parameters of the auxiliary unit are removed from the overall circuit parameters of the series system to determine the equivalent circuit parameters of the battery pack to be detected, so that the parameter detection of the battery pack to be detected is realized.
Drawings
FIG. 1 is a schematic diagram of a system for battery parameter detection according to an embodiment of the present invention;
FIG. 2 is an equivalent circuit model of a single cell and a battery pack according to an embodiment of the present invention;
FIG. 3 is a Nyquist diagram of an EIS test of a single battery and a battery pack equivalent circuit according to an embodiment of the present invention;
fig. 4 is a schematic circuit diagram of a battery pack parameter detection circuit according to an embodiment of the present invention;
FIG. 5 is a series connection of a capacitor and a battery in a system for battery parameter detection according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of an EIS test of a system for battery parameter detection according to an embodiment of the invention;
FIG. 7 is a schematic diagram of the overall structure of a system for battery parameter detection according to an embodiment of the present invention;
FIG. 8 is a flowchart of a method for battery parameter detection according to an embodiment of the present invention;
FIG. 9 is a flowchart showing steps for implementing a method for detecting parameters of a battery pack according to an embodiment of the present invention;
Fig. 10 is an equivalent circuit model of the battery pack and auxiliary capacitor after series connection according to the embodiment of the present invention;
FIG. 11 is a schematic diagram showing a voltage waveform at 10Hz current excitation of a battery pack and auxiliary capacitor series system according to an embodiment of the present invention;
Fig. 12 is a schematic diagram of EIS test of a system for battery parameter detection according to an embodiment of the present invention.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
As shown in fig. 1, an embodiment of the present invention provides a system for detecting parameters of a battery pack, including a battery pack to be tested, an auxiliary unit, EIS detection equipment, and a switch unit; the auxiliary unit is suitable for forming a serial system with the battery pack to be tested; the switch unit is used for controlling the current trend so as to realize parameter detection of the auxiliary unit, charging of the auxiliary unit and parameter detection of the serial system; the EIS detection equipment is used for being connected in series with the auxiliary unit and realizing parameter detection of the auxiliary unit, and is also used for being connected in series with the series system and realizing parameter detection of the series system, so that the equivalent circuit parameter of the battery pack to be detected is determined according to the equivalent circuit parameter of the auxiliary unit and the overall circuit parameter of the series system.
Specifically, in the present embodiment, the equivalent circuit principle is described in conjunction with fig. 2 to 7, so as to facilitate a specific description of the present parameter detection scheme.
The battery pack is generally formed by combining a plurality of battery cells in series and parallel, and fig. 2 is an equivalent circuit model of a single battery cell and the battery pack. Wherein V oc is the open circuit voltage of a single cell, R s is the ohmic resistance of the cell, R ct and Q are the charge transfer resistance and capacitance of ions inside the battery at the electrode-electrolyte interface, and W is the Warburg resistance, representing the solid diffusion resistance of ions embedded inside the active material particles. The circuit model can generally characterize the internal electrochemical properties of the battery as it is charged and discharged. In the figure, R line is the wire resistance when the single cells are connected to each other.
In theory, if the consistency of the parameters of each battery cell is completely consistent, the equivalent circuit model of the battery pack is the combination and superposition of the single battery cell models. But due to differences in raw materials and manufacturing processes, the uniformity between the cells may not be completely uniform. Fig. 3 is a Nyquist schematic diagram (Nyquist diagram) of EIS testing of the cell and battery equivalent circuit. In the figure, the EIS test baud chart is converted into a Nyquist chart, and the waveform of the EIS test baud chart can be divided into three parts of ohmic internal resistance (high frequency band), charge transfer (medium frequency band) and ion diffusion (ultra-low frequency band) according to the equivalent circuit of the battery cell. If the consistency of the cells in the battery pack is very good, the EIS-Nyquist diagram of the battery pack is similar to a single cell map. However, when the EIS spectrogram is provided with an additional circular arc, the test result shows that the battery cell body is possibly abnormal; further, similar distortion may occur from EIS-Nyquist of the battery pack of the abnormal cell string. Although the EIS test of the battery pack characterizes the overall characteristics of a standard battery pack, in practical tests, since the open-circuit voltage of the battery pack is high (more than tens of volts), the ac ripple output characteristics under such dc high-voltage conditions are difficult to be satisfied by a common electrochemical workstation or a potentiostat or a galvanostat, and therefore the method is difficult to use in the battery pack. Therefore, the embodiment provides the method for testing the alternating current impedance spectrum of the high-voltage high-capacity battery pack, which has the advantages of low cost, relatively simple structure and strong practicability.
Fig. 4 is a schematic diagram of a system (circuit configuration) for battery parameter detection. The selected auxiliary capacitor is a large-capacity capacitor with equivalent circuit parameters which do not change along with voltage and test frequency (firstly, the auxiliary capacitor bears battery voltage, and secondly, the auxiliary capacitor has stable capacity in a test series system). Firstly, an auxiliary capacitor is connected with a battery pack to be tested in series, and the battery pack charges the auxiliary capacitor after a switch S1 is closed. Since the charge capacity of the auxiliary capacitor is far smaller than that of the battery pack, the port voltage of the auxiliary capacitor can reach the original open-circuit voltage of the battery pack without affecting the capacity state of the battery pack. Thereafter, the connection between the auxiliary capacitor and the battery pack is adjusted as shown in fig. 5.
In fig. 5, the auxiliary capacitor is connected in reverse series with the battery pack, so that the open circuit voltage of the series unit is about 0V. Fig. 6 is an EIS test schematic diagram of an equivalent circuit parameter detection system for a battery. Because the voltage of the serial system terminal is close to 0V, after the EIS detection equipment is connected with the two ends of the tested unit, the EIS test equipment tests that the voltage of the terminal is close to 0V. When the EIS test equipment detects the equivalent circuit parameters of the tested system, two excitation modes are generally included: (1) Detecting an output voltage response by outputting alternating current excitation with variable frequency; (2) The output frequency is variable, the AC voltage is excited, and the output current response is detected. Because the output instantaneous voltage of the test system is close to 0V, the response caused by the alternating current excitation of the subsequent voltage or current is the characteristic effect caused by the auxiliary capacitance and the parameters in the battery, and the response is within the operation parameter interval of the traditional EIS equipment, so that the test of the equivalent circuit characteristic parameters of the series unit can be realized by the traditional EIS equipment. Because the current amplitude that generally causes high capacity battery voltage disturbance is too large, the EIS test system is recommended to be an alternating current excitation test mode. The passive energy storage capacitor after charging with known parameters is connected with the high-capacity battery pack in series, so that the defect of smaller output voltage range of the alternating current impedance test equipment is overcome, and the purpose of representing the characteristics of the high-voltage battery pack by using the alternating current impedance tester is realized.
Fig. 7 is a schematic diagram of the overall structure of a system for detecting parameters of a battery pack according to the present embodiment, wherein S1, S2, S3 and S4 are switching units, C is an auxiliary capacitor without polarity, and R is a choke unit. As shown in connection with fig. 12, the auxiliary capacitor may be replaced with an auxiliary battery pack. According to the circuit shown in fig. 7 or fig. 12, the auxiliary unit is suitable for forming a serial system with the battery pack to be tested, the current trend is controlled by the switch unit to respectively realize the parameter detection of the auxiliary unit, the charging of the auxiliary unit and the parameter detection of the serial system, the EIS detection device is connected with the auxiliary unit in series to realize the parameter detection of the auxiliary unit, and the EIS detection device is connected with the serial system in series to realize the parameter detection of the serial system, so that the equivalent circuit parameter of the battery pack to be tested can be determined according to the equivalent circuit parameter of the auxiliary unit and the overall circuit parameter of the serial system. The auxiliary unit (auxiliary capacitor or auxiliary battery pack) reduces the requirement of the EIS detection equipment for testing voltage when the battery pack to be tested is tested, and reduces the parameter requirement of the EIS detection equipment, so that the common EIS detection equipment can detect the equivalent circuit and the parameters of the high-voltage and high-capacity battery pack.
Because the auxiliary capacitor (or auxiliary battery pack) has lower influence along with frequency and voltage, after the equivalent parameter extraction of a series system is realized, the equivalent parameter of the amplitude capacitor is removed, and then the equivalent circuit of the battery pack and the parameter thereof can be accurately obtained.
In this embodiment, the charged auxiliary unit and the battery pack to be tested are reversely connected in series to offset the higher open circuit voltage of the battery pack to be tested, so that the requirement of the EIS detection device for testing the battery pack to be tested for testing voltage is reduced, the parameter requirement of the EIS detection device is reduced, and the common EIS detection device can detect the equivalent circuit of the high-voltage and high-capacity battery pack and the parameters thereof.
Optionally, the switch unit includes first switch, second switch, third switch and fourth switch, the both ends of first switch respectively with the anodal of battery that awaits measuring reaches the one end of auxiliary unit is connected, the one end of second switch is connected first switch with the junction of auxiliary unit, the other end of second switch is connected the battery that awaits measuring with the junction of EIS check out test set, the both ends of third switch respectively with the other end of auxiliary unit and EIS check out test set are connected, the one end of fourth switch is connected auxiliary unit with the junction of third switch, the other end of fourth switch is connected the junction of battery that awaits measuring with EIS check out test set.
Specifically, in this embodiment, as shown in fig. 7, the switch unit includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4, where two ends of the first switch are connected to the positive electrode of the battery pack to be tested and one end of the auxiliary unit, one end of the second switch is connected to the connection location of the first switch and the auxiliary unit, the other end of the second switch is connected to the connection location of the battery pack to be tested and the EIS detection device, two ends of the third switch are connected to the other end of the auxiliary unit and the EIS detection device, one end of the fourth switch is connected to the connection location of the auxiliary unit and the third switch, and the other end of the fourth switch is connected to the connection location of the battery pack to be tested and the EIS detection device. The equivalent circuit parameters of the auxiliary unit can be detected by the EIS detection equipment, the auxiliary unit is charged by the battery pack to be detected, and the integral circuit parameters of the serial system can be detected by the EIS detection equipment through opening and closing the first switch S1, the second switch S2, the third switch S3 and the fourth switch S4.
In this embodiment, the switch unit includes a first switch, a second switch, a third switch and a fourth switch, and the equivalent circuit parameters of the auxiliary unit, the battery pack to be tested charges the auxiliary unit and the integral circuit parameters of the serial system are detected by the EIS detection device by sequentially opening and closing the first switch, the second switch, the third switch and the fourth switch, so that the parameter detection of the battery pack to be tested is realized.
Optionally, the system for detecting the equivalent circuit parameters of the battery pack further comprises a choke unit connected with the fourth switch, wherein the choke unit is used for limiting current when the auxiliary unit is charged and serving as a discharging load when the auxiliary unit is discharged.
Specifically, in the present embodiment, as shown in connection with fig. 7, the system for battery pack equivalent circuit parameter detection further includes a choke unit connected to the fourth switch, the choke unit for limiting current when the auxiliary unit is charged (S1 and S4 are closed, S2 and S3 are open) and for serving as a discharge load when the auxiliary unit is discharged (S3 and S1 are open, S2 and S4 are closed), thereby protecting the circuit.
Wherein the choke unit may be a charging choke resistor.
The choke unit may be disposed on a side of the fourth switch shown in fig. 7, which is close to a connection between the battery pack to be tested and the EIS detection device, or on a side of the fourth switch, which is close to a connection between the auxiliary unit and the third switch.
In this embodiment, protection of the circuit is achieved by providing a choke unit that limits current when the auxiliary unit is charged and acts as a discharge load when the auxiliary unit is discharged.
Optionally, the EIS detection device comprises an electrochemical workstation, a FRA combined potentiometer-amperometric combination, or a voltage and current source system capable of achieving EIS test AC output excitation.
Specifically, in this embodiment, the EIS detection device includes an electrochemical workstation, a combination device of a FRA (Frequence Response Analysis, frequency response) and a potentiometer-amperometer, or a voltage and current source system capable of implementing EIS test ac output excitation, that is, a test device capable of directly or indirectly performing EIS.
The electrochemical workstation (Electrochemical workstation) is short for an electrochemical measurement system, and is a measurement device commonly used for electrochemical research and teaching. The device is mainly divided into 2 major classes, namely a single-channel workstation and a multi-channel workstation, and is applied to biotechnology, qualitative and quantitative analysis of substances and the like.
In this embodiment, by setting a specific type of the EIS detection device and setting a circuit of the parameter detection system, a requirement of the EIS detection device for testing voltage when the battery pack to be tested is reduced, so that the common EIS detection device can detect an equivalent circuit of the high-voltage and high-capacity battery pack and parameters thereof.
Optionally, the auxiliary unit is an auxiliary capacitor or an auxiliary battery pack, the auxiliary capacitor comprises a passive energy storage capacitor with known parameters, and the auxiliary battery pack comprises an energy storage battery with known parameters and matched with the open-circuit voltage of the battery pack to be tested.
Specifically, in this embodiment, as shown in fig. 6 and 12, the auxiliary unit is an auxiliary capacitor or an auxiliary battery pack, the auxiliary capacitor includes a passive energy storage capacitor with a known parameter, and the auxiliary battery pack includes an energy storage battery with a known parameter and matched with an open circuit voltage of the battery pack to be tested.
In this embodiment, the charged auxiliary capacitor or auxiliary battery pack and the battery pack to be tested are reversely connected in series to offset the higher open-circuit voltage of the battery pack to be tested, so that the requirement of the EIS detection device for testing the battery pack to be tested for testing the voltage is reduced, the parameter requirement of the EIS detection device is reduced, and the common EIS detection device can detect the equivalent circuit of the high-voltage and high-capacity battery pack and the parameters thereof.
Another embodiment of the present invention provides a method for detecting a parameter of a battery pack, which is applied to the system for detecting a parameter of a battery pack, and includes: after detecting equivalent circuit parameters of an auxiliary unit through EIS detection equipment, connecting the auxiliary unit and a battery pack to be detected in series to form a series system; after the auxiliary unit is charged by the battery pack to be tested, detecting the overall circuit parameters of the serial system by the EIS detection equipment; and determining the equivalent circuit parameters of the battery pack to be tested according to the equivalent circuit parameters of the auxiliary unit and the overall circuit parameters of the serial system.
Specifically, in the present embodiment, as shown in fig. 8 and 9, the method for detecting the parameters of the battery pack specifically includes:
(1) An appropriate auxiliary capacitor (or auxiliary battery pack) is selected and built according to the circuit shown in fig. 7. And testing an equivalent circuit of the auxiliary capacitor and parameters thereof by using EIS detection equipment. The high-frequency film capacitor with larger capacitance and limit withstand voltage exceeding the open-circuit voltage of 2 times of the battery pack is recommended, the equivalent parameters of the device are very stable under the conditions of low frequency, medium frequency and high frequency in normal test, and the equivalent parameters of the device are not changed greatly in high and low voltages, so that the test requirement is met.
(2) And S1 and S4 are closed, S2 and S3 are kept to be opened, the battery pack charges the auxiliary capacitor C, and the voltages at the two ends of the capacitor are completely stable. The auxiliary capacitor is connected with the battery pack in reverse series after being charged, so that higher open-circuit voltage of the battery pack is automatically counteracted, and the detection of subsequent EIS test equipment is facilitated. In this step, since the capacity of the capacitor body is much smaller than the battery pack, the charging energy of the capacitor does not substantially affect the capacity of the battery pack in the initial state. Fig. 10 is an equivalent circuit model of the battery pack and auxiliary capacitor after series connection under normal conditions.
(3) And (3) keeping S2 and S4 open, closing S1 and S3, setting the excitation current and the frequency interval of the EIS detection equipment, and completing EIS test of the auxiliary capacitor and battery pack series system. Since the capacity of the entire series unit of the battery pack and the auxiliary capacitor is very large, the current response triggered by the voltage disturbance of the EIS is too large. It is generally recommended to use alternating current disturbances of variable frequency as the excitation type. Fig. 11 is a waveform of output voltage response of the battery pack and auxiliary capacitor series unit under 10Hz current excitation.
The EIS test is to inject excitation with different frequencies into a test system, collect excitation and response signals and extract circuit parameters based on a circuit model. In the test of this step, the injection modes of different frequencies can be generally divided into a mixing mode and a sweep mode, and in principle, two frequency variation modes can be used. It should be noted that, when the sweep mode is selected, since the characteristics of the test system are presented in this patent, the voltage ripple of the EIS test system is related to the magnitude and frequency of the excitation, i.e. the higher the excitation current frequency, the smaller the response voltage. In order to fully meet the requirement of the output voltage of the EIS test system, the excitation current can be properly reduced during the low-frequency test stage, so that the low-frequency output alternating-current voltage is prevented from exceeding the equipment protection threshold.
(4) After the test is completed, S3 and S1 are opened, S2 and S4 are closed, and self-discharge of the capacitor is completed.
(5) And setting a circuit model of the whole series unit by combining the circuit model of the auxiliary capacitor, and fitting out the whole circuit parameter by utilizing analysis software to obtain the equivalent circuit characteristic parameter of the tested battery pack. Because the fitting process of the EIS-Nyquist result of the series integral test and the equivalent circuit model is complex, the circuit model with good or possible abnormal state of the battery pack and the number of the Nyquist arcs are combined, and the order of the time constant (tau=RC) in the equivalent circuit is judged. In the process, a plurality of attempts are needed to properly adjust the circuit model composition, and the possible hidden danger of the battery pack is eliminated according to the abnormal result of the judgment.
The following test results can be selected as the basis for determining the characteristics of the battery pack:
a) When a plurality of circular arcs (more than or equal to 3) appear in the Nyquist spectrum obtained by testing, namely an electric double layer impedance spectrum, the performance of individual cells in the battery pack may be degraded, and the electrochemical side reaction may be aggravated.
B) When the ohm impedance test result in the Nyquist map obtained by the test is larger (the serial-parallel numerical value of the original standard resistance value of the single-cell specification) it can be determined that the individual cells in the battery pack may have the abnormal conditions of tearing of the tab, lower conductivity of the electrode liquid and the like, or the conditions of cold welding of the aluminum row terminal of the cell, loosening of the screw and the like in the battery pack assembling process.
C) When the ultralow frequency region (warburg) in the Nyquist spectrum obtained by the test shows that the slope of the straight line is abnormal (deviates from 45 degrees), the abnormal crystal structure of the positive and negative electrode materials in the respective battery cells may be caused.
In this embodiment, the charged auxiliary unit and the battery pack to be tested are reversely connected in series to offset the higher open circuit voltage of the battery pack to be tested, so that the requirement of the EIS detection device for testing the battery pack to be tested for testing voltage is reduced, the parameter requirement of the EIS detection device is reduced, and the common EIS detection device can detect the equivalent circuit of the high-voltage and high-capacity battery pack and the parameters thereof.
Optionally, the switching unit includes a first switch, a second switch, a third switch, and a fourth switch; after the equivalent circuit parameters of the auxiliary unit are detected by the EIS detection equipment, the auxiliary unit and the battery pack to be detected are connected in series to form a series system, which comprises the following steps: opening the first switch and the fourth switch, closing the second switch and the third switch, so that the EIS detection device and the auxiliary unit form a loop to detect equivalent circuit parameters of the auxiliary unit through the EIS detection device; and opening the second switch and the third switch, closing the first switch and the fourth switch, so that the battery pack to be tested and the auxiliary unit form a loop, and charging the auxiliary unit through the battery pack to be tested.
Specifically, in this embodiment, after detecting the equivalent circuit parameter of the auxiliary unit by the EIS detection device, connecting the auxiliary unit and the battery pack to be tested in series to form a serial system includes: s1 and S4 are opened, S2 and S3 are closed, and an equivalent circuit and parameters of the auxiliary capacitor are tested by using EIS detection equipment; and S1 and S4 are closed, S2 and S3 are kept to be opened, the battery pack charges the auxiliary capacitor C, and the voltages at the two ends of the capacitor are completely stable. The EIS detection equipment can detect the equivalent circuit parameters of the auxiliary unit and the battery pack to be detected can charge the auxiliary unit sequentially through opening and closing the first switch (S1), the second switch (S2), the third switch (S3) and the fourth switch (S4).
In this embodiment, the equivalent circuit parameters of the auxiliary unit are detected by the EIS detection device and the auxiliary unit is charged by the battery pack to be detected by opening and closing the first switch, the second switch, the third switch and the fourth switch, so that the parameter detection of the battery pack to be detected can be realized.
Optionally, after the auxiliary unit is charged by the battery pack to be tested, detecting, by the EIS detection device, an overall circuit parameter of the serial system includes: opening the second switch and the fourth switch, closing the first switch and the third switch, and enabling the EIS detection equipment and the serial system to form a loop so as to complete EIS test of the serial system through the EIS detection equipment; opening the first switch and the third switch, closing the second switch and the fourth switch so that the auxiliary unit and the choke unit form a loop to realize self-discharge of the auxiliary unit; and setting a circuit model of the series system by combining the circuit model of the auxiliary unit, and analyzing and fitting out the overall circuit parameters of the series system.
Specifically, in this embodiment, after the auxiliary unit is charged by the battery pack to be tested, detecting, by the EIS detection device, the overall circuit parameters of the serial system includes: keeping S2 and S4 open, closing S1 and S3, setting the excitation current and frequency interval of the EIS detection equipment, and completing EIS test of the auxiliary capacitor and battery pack series system; after the test is finished, S3 and S1 are disconnected, S2 and S4 are closed, and self-discharge of the capacitor is finished; and setting a circuit model of the whole series unit by combining the circuit model of the auxiliary capacitor, and fitting the whole circuit parameters by using analysis software. The EIS detection device can detect the whole circuit parameters of the series system by opening and closing the first switch S1, the second switch S2, the third switch S3 and the fourth switch S4.
When the auxiliary unit is an auxiliary battery pack, the self-discharging process can be abandoned according to actual requirements, so that the auxiliary battery pack is in an open-circuit state and is not discharged after being cut off from a loop, the voltage of the auxiliary battery pack can be kept unchanged, and the auxiliary battery pack is convenient to continue to use later.
In this embodiment, the EIS detection device detects the overall circuit parameter of the serial system by opening and closing the first switch, the second switch, the third switch and the fourth switch, so that parameter detection of the battery pack to be detected can be achieved.
Optionally, the performing, by the EIS detection device, the EIS test of the serial system includes: an alternating current of variable frequency is selected as the excitation current of the EIS detection device.
Specifically, in the present embodiment, performing the EIS test of the serial system by the EIS detection apparatus includes: an alternating current of variable frequency is selected as the excitation current of the EIS detection device. Since the capacity of the entire series system of the battery pack and the auxiliary capacitor is very large, the current response triggered by the voltage disturbance of the EIS is too large, and it is generally recommended to use an ac current disturbance of a variable frequency as the excitation type.
In this embodiment, by selecting the alternating current with a variable frequency as the excitation current of the EIS detection device, it is beneficial to realize high-precision detection of the response voltage and improve the precision of the test result.
Optionally, the determining the equivalent circuit parameter of the battery pack to be tested according to the equivalent circuit parameter of the auxiliary unit and the overall circuit parameter of the serial system includes: and eliminating the equivalent circuit parameters of the auxiliary unit from the overall circuit parameters of the series system to determine the equivalent circuit parameters of the battery pack to be tested.
Specifically, in the present embodiment, determining the equivalent circuit parameters of the battery pack to be tested according to the equivalent circuit parameters of the auxiliary unit and the overall circuit parameters of the serial system includes: and eliminating the equivalent circuit parameters of the auxiliary unit from the overall circuit parameters of the series system to determine the equivalent circuit parameters of the battery pack to be tested. Because the characteristic parameters of the auxiliary capacitor (or auxiliary battery pack) circuit are known, after the equivalent parameters of the series system are extracted, the equivalent parameters of the amplitude capacitor are removed, and the equivalent circuit of the battery pack and the parameters thereof can be accurately obtained.
In this embodiment, the parameter detection of the battery pack to be tested is realized by removing the equivalent circuit parameters of the auxiliary unit from the overall circuit parameters of the serial system to determine the equivalent circuit parameters of the battery pack to be tested.
Although the present disclosure is disclosed above, the scope of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the disclosure.
Claims (9)
1. A system for detecting parameters of a battery pack, which is characterized by comprising the battery pack to be detected, an auxiliary unit, EIS detection equipment and a switch unit;
the auxiliary unit is suitable for forming a serial system with the battery pack to be tested;
The switch unit is used for controlling the current trend so as to realize parameter detection of the auxiliary unit, charging of the auxiliary unit and parameter detection of the serial system;
the EIS detection equipment is used for being connected with the auxiliary unit in series and realizing parameter detection of the auxiliary unit, and specifically comprises the following steps:
detecting equivalent circuit parameters of the auxiliary unit through the EIS detection equipment;
Charging the auxiliary unit through the battery pack to be tested;
the EIS detection equipment is also used for being connected in series with the series system and realizing parameter detection of the series system, and specifically comprises the following steps:
The EIS test of the serial system is completed through the EIS detection equipment;
realizing self-discharge of the auxiliary unit;
analyzing and fitting out the overall circuit parameters of the serial system;
The EIS detection equipment is also used for determining the equivalent circuit parameters of the battery pack to be detected according to the equivalent circuit parameters of the auxiliary unit and the overall circuit parameters of the serial system, and specifically comprises the following steps: and eliminating the equivalent circuit parameters of the auxiliary unit from the overall circuit parameters of the series system to determine the equivalent circuit parameters of the battery pack to be tested.
2. The system for detecting parameters of a battery pack according to claim 1, wherein the switch unit comprises a first switch, a second switch, a third switch and a fourth switch, two ends of the first switch are respectively connected with a positive electrode of the battery pack to be detected and one end of the auxiliary unit, one end of the second switch is connected with a connection part of the first switch and the auxiliary unit, the other end of the second switch is connected with a connection part of the battery pack to be detected and the EIS detection device, two ends of the third switch are respectively connected with the other end of the auxiliary unit and the EIS detection device, one end of the fourth switch is connected with a connection part of the auxiliary unit and the third switch, and the other end of the fourth switch is connected with a connection part of the battery pack to be detected and the EIS detection device.
3. The system for battery parameter detection according to claim 2, further comprising a choke unit connected with the fourth switch for limiting current when the auxiliary unit is charged and for acting as a discharge load when the auxiliary unit is discharged.
4. The system for battery parameter detection according to claim 1, wherein the EIS detection device comprises an electrochemical workstation, a FRA combined potentiometer-amperometric combination, or a voltage, current source system capable of achieving EIS test ac output excitation.
5. The system for battery parameter detection according to any one of claims 1 to 4, wherein the auxiliary unit is an auxiliary capacitor or an auxiliary battery pack, the auxiliary capacitor comprising a passive energy storage capacitor of known parameters, the auxiliary battery pack comprising an energy storage battery of known parameters and matching the open circuit voltage of the battery pack to be tested.
6. A method for battery parameter detection, applied to the system for battery parameter detection according to any one of claims 1 to 5, characterized by comprising:
After detecting the equivalent circuit parameters of the auxiliary unit through the EIS detection equipment, the auxiliary unit and the battery pack to be detected are connected in series to form a series system, which specifically comprises the following steps:
detecting equivalent circuit parameters of the auxiliary unit through the EIS detection equipment;
Charging the auxiliary unit through the battery pack to be tested;
after the battery pack to be tested charges the auxiliary unit, the EIS detection equipment detects the overall circuit parameters of the serial system, and the method specifically comprises the following steps:
The EIS test of the serial system is completed through the EIS detection equipment;
realizing self-discharge of the auxiliary unit;
analyzing and fitting out the overall circuit parameters of the serial system;
Determining the equivalent circuit parameters of the battery pack to be tested according to the equivalent circuit parameters of the auxiliary unit and the overall circuit parameters of the serial system, wherein the method specifically comprises the following steps: and eliminating the equivalent circuit parameters of the auxiliary unit from the overall circuit parameters of the series system to determine the equivalent circuit parameters of the battery pack to be tested.
7. The method for battery parameter detection according to claim 6, wherein the switching unit includes a first switch, a second switch, a third switch, and a fourth switch; after the equivalent circuit parameters of the auxiliary unit are detected by the EIS detection equipment, the auxiliary unit and the battery pack to be detected are connected in series to form a series system, which comprises the following steps:
Opening the first switch and the fourth switch, closing the second switch and the third switch, so that the EIS detection device and the auxiliary unit form a loop to detect equivalent circuit parameters of the auxiliary unit through the EIS detection device;
And opening the second switch and the third switch, closing the first switch and the fourth switch, so that the battery pack to be tested and the auxiliary unit form a loop, and charging the auxiliary unit through the battery pack to be tested.
8. The method for detecting parameters of a battery pack according to claim 7, wherein detecting the overall circuit parameters of the serial system by the EIS detection device after charging the auxiliary unit by the battery pack to be tested comprises:
Opening the second switch and the fourth switch, closing the first switch and the third switch, and enabling the EIS detection equipment and the serial system to form a loop so as to complete EIS test of the serial system through the EIS detection equipment;
opening the first switch and the third switch, closing the second switch and the fourth switch so that the auxiliary unit and the choke unit form a loop to realize self-discharge of the auxiliary unit;
And setting a circuit model of the series system by combining the circuit model of the auxiliary unit, and analyzing and fitting out the overall circuit parameters of the series system.
9. The method for battery parameter detection according to claim 8, wherein said performing EIS testing of the serial system by the EIS detection device comprises:
An alternating current of variable frequency is selected as the excitation current of the EIS detection device.
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