Device and method for calculating electrochemical impedance spectrum of battery pack

Abstract

An apparatus, method and apparatus for calculating an electrochemical impedance spectrum of a battery pack comprising n battery cells connected in series wherein the apparatus comprises: n current generating circuits, the k battery unit in the n battery units and the k current generation circuit in the n current generation circuits form a k series loop and are configured to generate k excitation current in the k series loop, the k excitation current has a first frequency, and k is smaller than or equal to n; a voltage detection circuit configured to detect a voltage of each of the n battery cells; and an electrochemical impedance spectroscopy control and calculator configured to calculate an impedance of a kth battery cell for the kth excitation current based on the kth excitation current and the detected voltage of the kth battery cell, the impedance including a real part and an imaginary part.

Description

Technical Field

[0001] The present invention relates to the technical field of battery management, and in particular to a device and method for calculating an electrochemical impedance spectrum of a battery pack. Background Art

[0002] Lithium-ion batteries have become the mainstream energy conversion devices widely used in new energy vehicles, energy storage systems, consumer electronics, industry and other fields. However, in recent years, frequent fires and explosions caused by thermal runaway of batteries have continued to increase. How to accurately calculate the SOX state (state of charge SOC, state of health SOH, etc.) of lithium-ion batteries, monitor their safety, and predict the remaining life have become the key to the safe and low-cost application of lithium-ion batteries.

[0003] As a highly time-varying nonlinear electrochemical system, lithium-ion batteries have great limitations in accurately monitoring SOX and safety over their entire life cycle based on existing measurable physical signals such as current, voltage, and temperature. Therefore, a technical means is urgently needed to test and obtain physical information inside the battery to monitor its reaction process.

[0004] Electrochemical impedance spectra (EIS) can obtain the impedance information inside the battery cell (or battery unit) through frequency domain technology to track the impact of various reaction processes inside the battery cell on the impedance (such as ohmic impedance in the high frequency band, dual capacitance characteristics and charge transfer impedance in the medium frequency band, and Warburg impedance of Li+ diffusion inside the solid active material in the low frequency band). EIS can provide the fourth dimension of battery physical quantity information in addition to current, voltage, and temperature. It can be used to calculate the aging state of the battery, predict the remaining life RUL of the battery, and provide early warning of internal short circuits or even thermal runaway risks through internal lithium analysis and charging behavior analysis.

[0005] However, the existing battery EIS data is usually tested offline in the laboratory using expensive impedance analyzers, which has the disadvantages of high detection cost and inability to monitor the EIS of each string of cells in the battery pack installed in the application system in real time. Therefore, a low-cost, simple and effective device and method is needed to detect and calculate the EIS impedance information of a single cell or battery pack in the application system online. The present application solves this demand. Summary of the invention

[0006] Preferred embodiments of the present disclosure generally solve or circumvent these and other problems, and generally achieve technical advantages, by providing an apparatus and method for easily and accurately calculating the electrochemical impedance spectrum of a battery pack.

[0007] According to one embodiment of the present application, a device for calculating the electrochemical impedance spectrum (EIS) of a battery pack is provided, wherein the battery pack includes n battery cells connected in series, and the device includes: n current generating circuits, wherein the kth battery cell among the n battery cells and the kth current generating circuit among the n current generating circuits form a kth series loop, and are configured to generate a kth excitation current in the kth series loop, wherein the kth excitation current has a first frequency, wherein k is less than or equal to n; a voltage detection circuit, configured to detect the voltage of each of the n battery cells; and an electrochemical impedance spectrum control and calculator, configured to calculate the impedance of the kth battery cell for the kth excitation current based on the kth excitation current and the detected voltage of the kth battery cell, wherein the impedance includes a real part and an imaginary part.

[0008] According to one embodiment of the present application, a method for calculating an electrochemical impedance spectrum of a battery pack is provided, wherein the battery pack includes n battery cells connected in series, and the method includes: S1: generating n excitation currents and continuing for a first period of time, wherein a kth excitation current among the n excitation currents flows through a kth battery cell among the n battery cells, and the kth excitation current has a first frequency, wherein k is less than or equal to n; S2: obtaining a voltage condition of a kth battery cell among the n battery cells within the first period of time; S3: calculating an impedance of a kth battery cell for a kth excitation current having a first frequency based on the kth excitation current and the voltage of the kth battery cell, wherein the impedance includes a real part and an imaginary part, thereby obtaining an impedance of the n battery cells; and S4: changing the frequencies of the n excitation currents, and repeating S1-S3, thereby obtaining the impedance of the n battery cells at different frequencies.

[0009] According to one embodiment of the present application, an electronic device is provided, comprising the above-mentioned device for calculating the electrochemical impedance spectrum of a battery pack.

[0010] The above is a fairly broad overview of the features and technical advantages of the present application, so that the following detailed description of the present application can be better understood. The additional features and advantages of the present application will be described below, and they form the subject matter of the claims of the present application. It will be appreciated by those skilled in the art that the disclosed concepts and specific embodiments can be easily utilized as the basis for modifying or designing other structures or processes for realizing the same purpose of the present application. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present application as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more fully understand the present application and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0012] Figure 1 An equivalent circuit model diagram of a battery cell provided by an embodiment of the present application is shown;

[0013] Figure 2 A high-level block diagram of a device for calculating electrochemical impedance spectroscopy (EIS) of a battery pack provided by an embodiment of the present application is shown;

[0014] Figure 3 A high-level block diagram of an EIS control and calculator provided by an embodiment of the present application is shown;

[0015] Figure 4 A high-level block diagram of an apparatus for calculating the EIS of a battery pack provided by another embodiment of the present application is shown;

[0016] Figure 5 A high-level block diagram of an EIS control and calculator provided by another embodiment of the present application is shown;

[0017] Figure 6 A high-level block diagram of an apparatus for calculating the EIS of a battery pack provided by another embodiment of the present application is shown;

[0018] Figure 7 A flow chart of a method for calculating the EIS of a battery pack provided by an embodiment of the present application is shown;

[0019] Figure 8 A flow chart of a method for calculating the EIS of a battery pack provided by another embodiment of the present application is shown; and

[0020] Fig. 9 A graph showing the EIS of a battery cell provided in an embodiment of the present application is shown.

[0021] Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated.The figures are drawn to clearly illustrate the relevant aspects of the various embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0022] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0023] In the field of electric vehicles, industry or energy storage applications, the batteries used for power supply are usually composed of the following components to form different levels of systems: battery cells, battery modules, battery packs, battery clusters, and battery packs. As the smallest basic component, the battery cell has a voltage of about 2.0V-4.5V, depending on the chemical properties of the battery and the current state of charge. Multiple battery cells are connected in parallel and in series to form a battery module. The parallel connection is to increase the capacity, and the series connection is to increase the voltage; then multiple battery modules are connected in series to form a battery pack, and its voltage range can be 40V-800V depending on the application. Battery packs can generally meet small industrial applications and electric vehicle power battery applications, but for large energy storage systems, multiple battery packs can be connected in series to increase the voltage platform to 1500V to form a battery cluster, and the battery cluster is finally connected in parallel to form a large battery pack. Regardless of the topology structure, each string of battery cells (composed of a single cell or in parallel) is the most basic monitored unit for battery management. Understanding the electrical characteristics of the smallest battery cell can give us a comprehensive understanding of the electrical characteristics of the entire battery pack, and thus accurately estimate the battery pack's state of charge (SoC), state of health (SoH), safety, etc.

[0024] Figure 1 An equivalent circuit model diagram of a battery cell provided by an embodiment of the present application is shown. The equivalent circuit model includes a voltage source representing the open circuit voltage OCV of the battery cell. The equivalent circuit model also includes an equivalent series resistance Rohmic, which reflects the transient resistance characteristics of the battery. The equivalent circuit model also includes n RCL parallel networks, which reflect the charge transfer reaction and charge diffusion characteristics of the battery. The number n of RCL networks can be 1 to 3, or even more. Figure 1 The components of the battery model (OCV, Rohmic, RCL network) depend on multiple parameters, such as temperature, SOC, load, aging degree, etc., and the relationship between these parameters is nonlinear; the relationship between each resistance value and SOC in the model is nonlinear and temperature-dependent.

[0025] Typically, the way to obtain information about these impedances (including resistance, capacitance and inductance) is to measure the voltage and current of the battery cell simultaneously and repeatedly at certain intervals. The results of the measurements are then used to fit the model to obtain the impedance value. The model can also output the SoC and SoH that reflect the battery state. This way of working means that all impedances and parameters of the battery cell, including multiple RCL networks, are directly measured. By improving the accuracy of the model's estimation of its impedances and parameters, the accuracy of the SoC and SoH indications can be improved.

[0026] One way to directly measure the impedance of a battery is to use electrochemical impedance spectroscopy. This method is a technique for determining the impedance of a battery cell at different frequencies. Typically, the impedance measurement results are represented in a Nyquist plot: the real and imaginary parts of the impedance are represented on the X-axis and Y-axis, respectively. Then, the measurement is repeated at different frequencies, and finally a curve of impedance variation with frequency is represented in the Nyquist plot. The curve can show three parts: a high-frequency (kHz level) part indicating the inductive impedance, a medium-frequency (Hz level) part indicating the "kinetic" impedance, and a low-frequency (mHz level) part indicating the "diffusion" impedance.

[0027] Please refer to Figure 2 , Figure 2 A high-level block diagram of an apparatus for calculating electrochemical impedance spectroscopy (EIS) of a battery pack provided by an embodiment of the present application is shown.

[0028] The device 10 for calculating the electrochemical impedance spectrum of a battery pack can obtain data reflecting the state of the battery pack to detect and calculate the impedance of the battery pack. Figure 2 As shown, the battery pack includes n battery cells Cell1-Celln, wherein the n battery cells are connected in series. The negative electrode of the first battery cell Cell1 is connected to the first input end of the device 10, the positive and negative electrodes of the two adjacent battery cells are connected to the corresponding input ends of the device 10, and the positive electrode of the nth battery cell Celln is connected to the n+1th input end of the device 10. The input end of the device 10 performs signal detection or sampling on each battery cell, and the battery cell signal can also be detected through a series resistor and a parallel capacitor. In one embodiment, the battery pack includes 18 battery cells connected in series.

[0029] The device 10 for calculating the electrochemical impedance spectrum of a battery pack includes n current generating circuits for generating an excitation current flowing through the plurality of battery cells. Each current generating circuit includes an excitation current source 1011-101n. Figure 2 As shown, the first end of the first excitation current source 1011 is connected to the negative electrode of the first battery cell Cell1 through the first input end of the device 10, and the second end is connected to the positive electrode of the first battery cell Cell1 through the second input end of the device 10. In this way, the first excitation current source 1011 and the first battery cell Cell1 form a first series loop. The first excitation current source 1011 generates a first excitation current I having a first frequency. ex,1 Inject into the first series loop.

[0030] The first end of the second excitation current source 1012 is connected to the negative electrode of the second battery cell Cell2 through the second input end of the device 10, and the second end is connected to the positive electrode of the second battery cell Cell2 through the third input end of the device 10. In this way, the second excitation current source 1012 and the second battery cell Cell2 form a second series loop. The second excitation current source 1012 generates a second excitation current I having a first frequency. ex,2 Injected into the second series loop. Similarly, the first end of the nth excitation current source 101n is connected to the negative electrode of the nth battery cell Cell through the nth input end of the device 10, and the second end is connected to the positive electrode of the nth battery cell Celln through the n+1th input end of the device 10. In this way, the nth excitation current source 101n and the nth battery cell Celln form an nth series loop. The nth excitation current source 101n injects the nth excitation current I having the first frequency into the nth series loop. ex,n Inject into the nth series loop.

[0031] The excitation current sources 1011-101n can also change the frequency and inject excitation currents with other frequencies into the kth series loop. The excitation current source receives a control signal Ctrln from the EIS control and calculator 103. The amplitude and frequency of the excitation current are default values ​​or configured by the user through the EIS control and calculator 103. In one embodiment, the excitation current sources 1011-101n are constant current sources. In one embodiment, the excitation current sources 1011-101n generate sine wave currents, such as sinusoidal currents. In another embodiment, the excitation current sources 1011-101n generate square wave currents. Square wave currents have the following advantages: 1. Square wave currents are easy to generate, and the cost and accuracy of the circuits used are easy to control. 2. The square wave current and the amplitude of the disturbance voltage of the battery cell generated by the excitation are relatively stable and easy to detect, which is conducive to reducing the requirements for voltage detection and better reducing the deviation of the impedance amplitude and phase (or the real and imaginary parts of the impedance) introduced by the sampling error of the low amplitude signal. 3. When the current and voltage amplitudes are large, after discrete Fourier transform calculation, in addition to the fundamental frequency, the higher harmonics still have considerable energy density, which can be used for higher frequency EIS information and expand the EIS frequency detection and calculation range of the device.

[0032] The device 10 also includes a voltage detection circuit 102, which is configured to detect the voltage of each battery cell in the n battery cells Cell1-Celln, and the detected voltage includes the voltage change on each battery cell caused by the excitation current. The voltage detection circuit 102 includes n voltage analog-to-digital converters VADC1-VADCn. Among them, the two input ends of the first voltage analog-to-digital converter VADC1 are connected to the first input end and the second input end of the device 10. The two input ends of the second voltage analog-to-digital converter VADC2 are connected to the second input end and the third input end of the device 10. By analogy, the two input ends of the nth voltage analog-to-digital converter VADCn are connected to the nth input end and the n+1th input end of the device 10. In this way, the kth voltage analog-to-digital converter among the n voltage analog-to-digital converters VADC1-VADCn is connected to the kth battery cell among the n battery cells Cell1-Celln, so that when the kth excitation current flows through the kth battery cell, the voltage of the kth battery cell is synchronously detected, where k is a positive real number less than or equal to n. In this way, one excitation can detect and calculate the EIS information of all battery cells connected in series, saving detection time.

[0033] The device 10 also includes an electrochemical impedance spectroscopy control and calculator 103. The control and calculator 103 is configured to receive the voltage of the battery cell detected by each voltage analog-to-digital converter VADC1-VADCn, and each excitation current (having a first frequency) generated by each excitation current source. The control and calculator 103 calculates the impedance of each battery cell under each excitation current having the first frequency based on the voltage and excitation current, the impedance including a real part and an imaginary part, and outputs the real part value Z of the impedance Re and the imaginary value Z Im The control and calculator 103 is further configured to control each excitation current source 1011-101n to generate each excitation current having a second frequency, and calculate the impedance of each battery cell based on these excitation currents and the impedance of each battery cell detected under the action of the second excitation current. By repeating the above operations, the control and calculator 103 can obtain the electrochemical impedance spectrum of each battery cell in different frequency bands.

[0034] In one embodiment, the positive and negative electrodes of each battery cell are connected to the input terminal of the device 10 through a battery resistor. Figure 2 As shown, taking battery cell Cell1 as an example, the positive electrode of battery cell Cell1 passes through resistor R Bal1 The negative electrode of the battery cell Cell2 is connected to the second input terminal of the device 10 through the resistor R Bal0 Connected to the first input terminal of the device 10.

[0035] Please refer to Figure 3 , Figure 3FIG. 2 shows a high-level block diagram of an electrochemical impedance spectroscopy control and calculator provided by an embodiment of the present application. Figure 3 As shown, the electrochemical impedance spectroscopy control and calculator 50 includes a memory 501 , a discrete Fourier transform (DFT) calculator 502 , and a controller 503 .

[0036] The electrochemical impedance spectroscopy control and calculator 50 receives the voltage of the battery cell detected by each voltage analog-to-digital converter VADC1-VADCn and the current value I of the excitation current generated by each excitation current source 1011-101n. Ex Specifically, the controller 503 controls each excitation current source to generate an excitation current flowing through each battery cell, and the current has a first frequency and lasts for a period of time, such as 2-3 pulse cycles. During this period of time, the n voltage analog converters sample the voltage values ​​ΔV of the n battery cells multiple times. cell，m , and multiple sampled voltage values ​​ΔV cell，m Input control and calculator 50. Taking the first battery cell Cell1 as an example, within the pulse period, the voltage analog converter VADC1 samples the voltage value ΔV of the first battery cell Cell1 multiple times (for example, 128 times). cell，1 The control and calculator 50 stores these voltage values ​​in the memory. In addition, the control and calculator 50 also stores the current value I of the excitation current flowing through the first battery cell Cell1 during this period. Ex The DFT calculator 502 calculates the current value I of the first battery cell Cell1 based on the current value I Ex and multiple voltage values ​​ΔV cell，1 , the voltage or current representation in the frequency domain is calculated by the discrete Fourier transform rule. It should be noted that the DFT calculator 502 can perform calculations synchronously during the current and voltage sampling process, that is, the process of storing, calculating and refreshing at the same time. These voltage or current representations are then filtered out by the filter 504 to remove unnecessary high-order harmonic components, and the impedance of the battery cell Cell1 at the first frequency is obtained, which includes the real part Z Re and the imaginary part Z Im By using the above method, the impedances of the other battery cells Cell2-Celln at the first frequency can be calculated.

[0037] Then, the controller 303 controls the n excitation current sources to generate n excitation currents of different frequencies (second frequencies) to be injected into the n battery cells respectively. Repeating the above method, the electrochemical impedance spectrum control and calculator 30 calculates the impedance of each battery cell Cell1-Celln at the second frequency. By changing the frequency of the excitation current source, the electrochemical impedance spectrum of the entire battery pack can be obtained.

[0038] In one embodiment, the electrochemical impedance spectroscopy control and calculator 30 further includes a filter 505 connected to the memory 501 for receiving the voltage value ΔV output by the voltage analog converter. cell，m The filter 505 outputs the filtered voltage value VEIS to the memory 501 to remove the voltage value ΔV output by the voltage analog converter. cell The DFT calculator 502 calculates the impedance of each battery cell based on the filtered voltage value VEIS.

[0039] The discrete Fourier transform calculator 502 performs discrete Fourier transform according to formula (1):

[0040]

[0041] Wherein, N is the total number of samples of the voltage analog-to-digital converter, n is the sampling time of the analog-to-digital converter, x[n] is the signal value at time n, such as a voltage value or a current value, k is the frequency in question, and X[k] is the DFT value at frequency k, such as a voltage DFT value and a current DFT value.

[0042] The battery cell impedance value at frequency k is obtained by dividing the voltage DFT value by the current DFT value at frequency k.

[0043] Figure 4 1 shows a high-level block diagram of an apparatus for calculating the electrochemical impedance spectrum of a battery pack provided by another embodiment of the present application. In this embodiment, the apparatus 30 for calculating the electrochemical impedance spectrum of a battery pack includes an excitation current source 3011-301n, a voltage detection circuit 302, and an electrochemical impedance spectrum control and calculator 303, which functions similarly to Figure 2 The device 30 also includes a plurality of multiplexers, wherein a first end of the multiplexer is connected to a plurality of battery cells, and a second end of the multiplexer is connected to a voltage analog-to-digital converter. Figure 4 As shown, in this embodiment, the device 30 includes three multiplexers MUX1, MUX2, and MUX3. On the one hand, each of the three multiplexers can be connected to multiple battery cells through the input end of the device 30; on the other hand, the three multiplexers are connected to three voltage analog-to-digital converters respectively. The multiplexer is used to switch the channels connected to the battery cells in a patrol manner, so that the voltage analog-to-digital converter can detect the voltage of each battery cell connected to the multiplexer. It should be noted that this application does not limit the number of multiplexers and the number of connected battery cells.

[0044] The device 30 for calculating the electrochemical impedance spectrum of a battery pack further includes an excitation current detector, which includes n reference resistors and a current analog-to-digital converter 304. Figure 4 As shown, the first reference resistor Rref1 The first series circuit is formed with the first battery cell Cell1 and the first excitation current source; the second reference resistor R ref2 The second series circuit is formed with the second battery cell Cell2 and the second excitation current source; and by analogy, the nth reference resistor R refn The nth series loop is formed with the nth battery cell Celln and the nth excitation current source. The current analog-to-digital converter 304 detects the reference current flowing through the n reference resistors through the multiplexer MUX patrol switching, and outputs the detected reference current values ​​to the electrochemical impedance spectroscopy control and calculator 303. The multiplexer MUX is connected to both ends of each reference resistor and has 2n connection ports E0-E 2n-1 .

[0045] The current value fed back by the excitation current sources 3011-301n to the control and calculator 303 may not be the actual current value in the loop. By setting an excitation current detector and feeding back the actually measured loop current to the control and calculator 303, the current information in the loop can be obtained more accurately, thereby accurately calculating the impedance value of the battery cell.

[0046] Figure 5 FIG. 6 shows a high-level block diagram of an electrochemical impedance spectroscopy control and calculator provided by another embodiment of the present application. In addition to a memory 601, a DFT calculator 602, a controller 603, a filter 604, and a filter 605, the electrochemical impedance spectroscopy control and calculator 60 also includes a weighter 607, which receives a reference current I detected by an excitation current detector 610. ref , and the excitation current value I generated by the excitation current source Excitation , and output the electrochemical impedance spectroscopy current IEIS value to the memory based on the set weight value a, that is, I EIS =aI ref +(1-a)I Excitation The weight factor a depends on the accuracy of the excitation current detector 610. For example, when the detection accuracy of the excitation current detector 610 is high, due to I ref The accuracy is higher, so the weight value a can be selected with a larger value. ref To obtain a more accurate I EIS Otherwise, a smaller weight value should be selected. In one embodiment, the weighter 607 can be implemented by a current filter.

[0047] The memory 601 stores the weighted I EIS And the battery cell voltage V detected by the voltage detection circuit EIS The DFT calculator 602 is based on the current value I EIS and multiple voltage values ​​V EIS, the voltage or current representation in the frequency domain is calculated by the discrete Fourier transform rule. These voltage or current representations are then passed through the filter 604 to obtain the impedance of the battery cell at a specific frequency, which includes the real part Z Re and the imaginary part Z Im By using the above method, the impedance of all battery cells at multiple frequencies can be calculated, thereby obtaining the electrochemical impedance spectrum of the entire battery pack.

[0048] In one embodiment, the electrochemical impedance spectroscopy control and calculator 60 further includes a filter 606, which is connected to a weighter 607 and is used to receive the current value output by the excitation current detector. The filter 606 outputs the filtered current value to the weighter 607 to remove high-frequency clutter in the current output by the current detector and improve the current detection accuracy.

[0049] Figure 6 20 is a high-level block diagram of an apparatus for calculating the electrochemical impedance spectrum of a battery pack according to another embodiment of the present application. The apparatus 20 for calculating the electrochemical impedance spectrum of a battery pack includes a voltage detection circuit 202, an electrochemical impedance spectrum control and calculator 203, and its functions are similar to those of Figure 2 or Figure 4 The device 20 is similar to that in the device shown. In the device 20, the n current generating circuits include n switch tubes 2011-201n. Taking the first switch tube 2011 as an example, the first end of the first switch tube 2011 is connected to the positive electrode of the first battery cell Cell1, and the second end of the switch tube 2011 is connected to the negative electrode of the battery cell Cell1. The control end of the switch tube 2011 is connected to the EIS control and calculator 203, and is configured to receive an excitation current control signal from the EIS control and calculator 203 to generate an excitation current in the series circuit formed by the switch tube 2011 and the battery cell Cell1. The control signal controls the conduction and disconnection of the switch device 2011, thereby generating a square wave excitation current in the series circuit.

[0050] The switch tube can be formed by any controllable device, such as a metal oxide semiconductor field effect transistor (MOSFET) device, a bipolar junction transistor (BJT) device, a super junction transistor (SJT) device, an insulated gate bipolar transistor (IGBT) device, a gallium nitride (GaN)-based power device and / or the like.

[0051] The functions of the voltage detection circuit 202 and the electrochemical impedance spectroscopy control and calculator 203 are similar to Figure 2 or Figure 4 The similarities among the devices shown are not repeated here.

[0052] In another embodiment, if Figure 6As shown, the device 20 for calculating the electrochemical impedance spectrum of a battery pack further includes an excitation current detector, which includes n reference resistors and a current analog-to-digital converter 204. Figure 6 As shown, the first reference resistor R ref1 The first series circuit is formed with the first battery cell Cell1 and the first switch tube; the second reference resistor R ref2 The second series circuit is formed with the second battery cell Cell2 and the second switch tube; and by analogy, the nth reference resistor R refn The nth series loop is formed with the nth battery cell Celln and the nth switch tube. The current analog-to-digital converter 204 detects the reference current flowing through the n reference resistors through the multiplexer MUX patrol switching, and outputs the detected reference current values ​​to the electrochemical impedance spectroscopy control and calculator 203. The multiplexer MUX is connected to both ends of each reference resistor and has 2n connection ports E0-E 2n-1 .

[0053] The current value of the excitation current obtained by controlling the switch tubes 2011-201n may not be the actual current value in the loop. By setting an excitation current detector and feeding back the actually measured loop current to the control and calculator 203, the current information in the loop can be obtained more accurately, thereby accurately calculating the impedance value of the battery cell.

[0054] Figure 7 A flow chart of a method for calculating the electrochemical impedance spectrum of a battery pack provided in one embodiment of the present application is shown. Figure 7 The flowchart shown is only an example, which should not unduly limit the scope of the claims. Those skilled in the art will recognize many variations, substitutions, and modifications. For example, Figure 7 The various steps shown in the drawings may be added, removed, substituted, rearranged, and repeated.

[0055] Return to reference Figure 2 The computing device shown and Figure 3 The electrochemical impedance spectroscopy control and calculator shown. Figure 7 As shown, the method for calculating the electrochemical impedance spectrum of a battery pack includes the following steps:

[0056] In step 702, a current generating circuit in a device for calculating an electrochemical impedance spectrum of a battery pack generates n excitation currents for a first period of time. The kth excitation current of the n excitation currents flows through the kth battery cell of the n battery cells, and the kth excitation current has a first frequency, where k is less than or equal to n. In one embodiment, the excitation current is a sine wave current or a square wave current.

[0057] In step 704, a voltage detection circuit in a device for calculating an electrochemical impedance spectrum of a battery pack obtains a voltage condition of a kth battery cell among the n battery cells within a first time period.

[0058] In one embodiment, the voltage detection circuit includes n voltage analog-to-digital converters. The voltage conditions of the n battery cells are obtained through the n voltage analog-to-digital converters, wherein the kth voltage analog-to-digital converter among the n voltage analog-to-digital converters is connected to the kth battery cell among the n battery cells.

[0059] In step 706, the control and calculator in the device for calculating the electrochemical impedance spectrum of the battery pack calculates the impedance of the kth battery cell for the kth excitation current with the first frequency based on the kth excitation current and the voltage of the kth battery cell, wherein the impedance includes a real part and an imaginary part, thereby obtaining the impedance of the n battery cells.

[0060] In step 708 , the device for calculating the electrochemical impedance spectrum changes the frequency of the excitation current and repeats steps 702 to 706 , thereby obtaining the impedances of the n battery cells at different frequencies.

[0061] Return to reference Figure 4 or Figure 6 The computing device shown and Figure 5 In one embodiment, in step 704, during a first period of time, a multiplexer in a device for calculating the electrochemical impedance spectrum of a battery pack is used to switch channels connected to the battery cells in a patrol manner, so that a voltage analog-to-digital converter obtains the voltage of the battery cells connected to the multiplexer, wherein a first end of the multiplexer is connected to a plurality of battery cells, and a second end is connected to a voltage analog-to-digital converter.

[0062] In one embodiment, in step 706, a control and a calculator in a device for calculating an electrochemical impedance spectrum calculate the impedance of the kth battery cell for the kth excitation current having a first frequency based on the kth excitation current, the kth reference current and the voltage of the kth battery cell, wherein the kth reference current is a current flowing through a kth reference resistor, and the kth reference resistor and the kth battery cell form a kth series circuit.

[0063] In one embodiment, the electrochemical impedance spectroscopy control and calculator assigns a set weight value to the kth excitation current and the kth reference current to generate the kth electrochemical impedance current and output it to the memory.

[0064] In one embodiment, the method further includes charging or discharging the battery pack at a current lower than a threshold current or resting the battery pack for a specific time before step 702, so that the battery pack reaches a steady state. For example, the threshold current is 1 ampere, and the specific time is 30 minutes.

[0065] Figure 8 A flow chart of a method for calculating the electrochemical impedance spectrum of a battery pack provided by another embodiment of the present application is shown. Figure 8 The flowchart shown is only an example, which should not unduly limit the scope of the claims. Those skilled in the art will recognize many variations, substitutions, and modifications. For example, Figure 8 The various steps shown in the drawings may be added, removed, substituted, rearranged, and repeated.

[0066] In step 800 , the battery management system BMS monitors the working state of the battery pack, and the device for calculating the electrochemical impedance spectrum is in a standby state.

[0067] In step 802, the device for calculating the electrochemical impedance spectrum determines whether the EIS test is allowed. The judgment is based on whether the battery pack is in a steady state, for example, the battery is charged and discharged with a charging current or a discharging current less than a threshold for a period of time, or the relay is disconnected and left to stand for a period of time. If the judgment result is no, return to step 800, if the judgment result is yes, proceed to step 804.

[0068] In step 804, the device for calculating the electrochemical impedance spectrum determines whether the EIS test of all frequency bands is completed, for example, the frequency is in the range of 5kHz to 0.01mHz. If the judgment result is yes, return to step 800, if the judgment result is no, proceed to step 806.

[0069] In step 806, the device for calculating the electrochemical impedance spectrum determines whether the EIS test of all cells is completed when the excitation signal is at the frequency fn. If the judgment result is yes, the process proceeds to step 8062, and the EIS control and calculator in the device for calculating the electrochemical impedance spectrum control the current generating circuit (such as a controllable constant current source) to generate a new sinusoidal or square excitation current of a specific frequency fn (for example, fn = 794Hz). If the judgment result is no, the process proceeds to step 8064, and the EIS control and calculator control the current generating circuit (such as a controllable constant current source) to continue to generate the sinusoidal or square excitation current of the previous specific frequency fn (for example, fn = 1kHz).

[0070] In step 808, the EIS control and calculator in the device for calculating the electrochemical impedance spectrum controls all VADCs to obtain the influence of the excitation current on the voltage of the battery cell under test according to the control algorithm. In one embodiment, the EIS control and calculator controls all VADCs to perform synchronous voltage sampling on all battery cell channels. In another embodiment, the EIS control and calculator controls all VADCs to control the multiplexer MUX to switch the battery cell channels in a round-robin manner to obtain voltage sampling.

[0071] In step 810, the device for calculating electrochemical impedance spectroscopy receives data of excitation current and response voltage, and the EIS control and calculator calculates battery cell impedance information.

[0072] In step 812 , the EIS control and calculator outputs the real impedance Re and the imaginary impedance Im of the battery cell at the frequency fn, and returns to step 802 .

[0073] Fig. 9 The figure shows a curve diagram of the electrochemical impedance spectrum of a battery cell provided by an embodiment of the present application. The curve is measured by the above-mentioned device and method, and the curve diagram shows the relationship between the frequency and impedance of the battery cell. Fig. 9 In the graph, the horizontal axis represents the real part of the impedance, the vertical axis represents the imaginary part of the impedance, and the unit of impedance is milliohm. The triangle represents the electrochemical impedance of the battery cell at a temperature of 40 degrees Celsius and a state of charge of 10%. Among them, the leftmost triangle represents the impedance of the battery cell at a frequency of 1500Hz, and the rightmost triangle represents the impedance of the battery cell at a frequency of 0.1Hz. The square represents the electrochemical impedance of the battery cell at a temperature of 20 degrees Celsius and a state of charge of 25%. The circle represents the electrochemical impedance of the battery cell at a temperature of 20 degrees Celsius and a state of charge of 90%. The star represents the electrochemical impedance of the battery cell at a temperature of 20 degrees Celsius and a state of charge of 50%. The frequency range of the above impedance curves is 1500Hz to 0.1Hz.

[0074] Although the embodiments of the present application and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

[0075] In addition, the scope of the present application is not limited to the specific embodiments of the processes, machines, manufactures, material compositions, modes, methods, and steps described in this specification. Those skilled in the art will readily understand from the disclosure of the present application that, according to the present application, currently existing or later to be developed processes, machines, manufactures, material compositions, modes, methods, or steps that perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein may be utilized. Therefore, it is intended that the appended claims include such processes, machines, manufactures, material compositions, modes, methods, or steps within their scope.

Claims

1. A device for calculating an electrochemical impedance spectrum (EIS) of a battery pack, the battery pack comprising n battery cells connected in series, the device comprising: n current generating circuits, wherein a kth battery cell among the n battery cells and a kth current generating circuit among the n current generating circuits form a kth series loop, and are configured to generate a kth excitation current in the kth series loop, the kth excitation current having a first frequency, wherein k is less than or equal to n; a voltage detection circuit configured to detect a voltage of each of the n battery cells; and The electrochemical impedance spectroscopy control and calculator is configured to calculate the impedance of the kth battery cell for the kth excitation current based on the kth excitation current and the detected voltage of the kth battery cell, wherein the impedance includes a real part and an imaginary part.

2. The device according to claim 1, characterized in that The n current generating circuits include n excitation current sources, and a kth excitation current source among the n excitation current sources is configured to inject the kth excitation current into the kth series loop.

3. The device according to claim 1, characterized in that The n current generating circuits include n switching tubes, the kth switching tube among the n switching tubes and the kth battery cell form a kth series loop, and the kth switching tube receives a control signal from the electrochemical impedance spectroscopy control and calculator to generate the kth excitation current in the kth series loop.

4. The device according to claim 1, characterized in that The excitation current is a sine wave current or a square wave current, and the amplitude and frequency of the excitation current are default values ​​or configurable through the electrochemical impedance spectroscopy control and calculator.

5. The device according to any one of claims 1 to 4, characterized in that The voltage detection circuit includes a plurality of voltage analog-to-digital converters for converting analog signals representing voltage measurement values ​​into digital signals.

6. The device according to claim 5, characterized in that The voltage detection circuit includes n voltage analog-to-digital converters, wherein the kth voltage analog-to-digital converter among the n voltage analog-to-digital converters is connected to the kth battery cell and is used to detect the voltage of the kth battery cell.

7. The device according to claim 5, characterized in that The device further comprises a multiplexer, wherein a first end of the multiplexer is connected to a plurality of battery cells, and a second end of the multiplexer is connected to a voltage analog-to-digital converter.

8. The device according to any one of claims 1 to 4, characterized in that The electrochemical impedance spectroscopy control and calculator includes: A memory, used to store the voltage of the kth battery cell and the kth excitation current measured for the kth excitation current; a discrete Fourier transform (DFT) calculator that receives the measured voltage of the kth battery cell and the kth excitation current stored in the memory and calculates the impedance of the kth battery cell including a real part and an imaginary part; and The controller is used to control the current generating circuit to generate a kth excitation current.

9. The device according to any one of claims 1 to 4, characterized in that The device also includes an excitation current detector, which includes n reference resistors and a current analog-to-digital converter. The kth reference resistor among the n reference resistors forms the kth series loop with the kth battery cell and the kth current generating circuit; the current analog-to-digital converter is used to detect the n reference currents flowing through the n reference resistors, and feed the n reference currents into the electrochemical impedance spectroscopy control and calculator.

10. The device according to claim 9, characterized in that The electrochemical impedance spectroscopy control and calculator includes: A weighter, for receiving a kth excitation current from a kth current generating circuit and a kth reference current from an excitation current detector, and generating a kth electrochemical impedance spectroscopy current based on a set weight value; A memory, for storing the voltage of the kth battery cell and the kth electrochemical impedance spectroscopy current measured for the kth excitation current; a discrete Fourier transform (DFT) calculator that receives the measured voltage of the kth battery cell and the kth electrochemical impedance spectroscopy current stored in the memory and calculates the impedance of the kth battery cell including a real part and an imaginary part; and The controller is used to control the current generating circuit to generate a kth excitation current.

11. A method for calculating an electrochemical impedance spectrum of a battery pack, the battery pack comprising n battery cells connected in series, the method comprising: S1: generating n excitation currents for a first period of time, wherein a k-th excitation current among the n excitation currents flows through a k-th battery cell among the n battery cells, and the k-th excitation current has a first frequency, wherein k is less than or equal to n; S2: obtaining a voltage condition of a kth battery cell among the n battery cells within a first time period; S3: calculating the impedance of the kth battery cell for the kth excitation current having the first frequency based on the kth excitation current and the voltage of the kth battery cell, wherein the impedance includes a real part and an imaginary part, thereby obtaining the impedance of the n battery cells, and S4: Change the frequencies of the n excitation currents and repeat S1-S3 to obtain the impedances of the n battery cells at different frequencies.

12. The method according to claim 11, characterized in that The excitation current is a sine wave current or a square wave current.

13. The method according to claim 11 or 12, characterized in that: S2 includes: in a first time period, obtaining voltage conditions of the n battery cells through n voltage analog-to-digital converters, wherein the kth voltage analog-to-digital converter among the n voltage analog-to-digital converters is connected to the kth battery cell among the n battery cells.

14. The method according to claim 11 or 12, characterized in that: S2 includes: in a first time period, switching channels connected to battery cells in a patrol manner through a multiplexer so that a voltage analog-to-digital converter obtains the voltage condition of the battery cells connected to the multiplexer, wherein a first end of the multiplexer is connected to a plurality of battery cells, and a second end is connected to a voltage analog-to-digital converter.

15. The method according to claim 11 or 12, characterized in that: S3 also includes: calculating the impedance of the kth battery cell for the kth excitation current having a first frequency based on the kth excitation current, the kth reference current and the voltage of the kth battery cell, wherein the kth reference current is a current flowing through a kth reference resistor, and the kth reference resistor and the kth battery cell form a kth series circuit.

16. The method according to claim 15, characterized in that The set weight value is allocated to the kth excitation current and the kth reference current to generate a kth electrochemical impedance current.

17. The method according to claim 11 or 12, characterized in that: Prior to S1, this also included: S0: The battery pack is charged or discharged or left at rest with a current lower than a threshold current for a specific period of time so that the battery pack reaches a steady state.

18. An electronic device comprising the device according to any one of claims 1 to 10.

Images