AC excitation methods, online EIS measurement methods for vehicle-mounted power batteries, equipment and media

Abstract

This invention relates to an AC excitation method, an online EIS measurement method for vehicle-mounted power batteries, equipment, and a medium. The method includes: connecting a bidirectional DC-DC converter built into a starting power supply to the vehicle-mounted power battery under test; and injecting an AC excitation signal into the vehicle-mounted power battery under test through the bidirectional DC-DC converter during the EIS AC excitation cycle, thereby achieving online EIS AC excitation. Compared with existing technologies, this invention directly utilizes the starting power supply to achieve the EIS AC excitation function, thus realizing online EIS measurement of the power battery. This results in efficient utilization of the internal power system of the electric vehicle, avoids the redundant design of AC / DC conversion technology in the on-board charger, and reduces power system redundancy and complexity.

Description

Technical Field

[0001] This invention relates to the field of electrochemical measurement, and in particular to an AC excitation method, an online EIS measurement method, equipment, and medium for vehicle-mounted power batteries. Background Technology

[0002] With the continuous development of the electric vehicle industry, the health, safety, and lifespan of lithium-ion power batteries have attracted increasing attention. Among these, accurately measuring the internal state of power batteries to reflect information such as safety and lifespan has become a key issue. One relatively accurate method is to use electrochemical impedance spectroscopy (EIS) to reflect the internal state information of power batteries. Its advantages include the ability to reflect various complex electrochemical properties such as mass transfer, rate constants, and diffusion coefficients; and the fact that EIS measurement is non-destructive, causing no damage to the battery.

[0003] EIS measurement comprises three key stages: AC excitation, signal measurement, and impedance calculation. EIS AC excitation requires the battery to undergo cyclic charging and discharging within a given excitation signal cycle. During each excitation signal cycle, the battery switches between charging and discharging states, injecting an AC signal into the battery. In automotive applications, a specially designed device is needed to generate the AC signal, while maintaining low cost, small size, and minimal increase in system complexity. However, on-board EIS measurement and online battery status diagnostics for automotive power batteries have not yet been implemented in real-world vehicles because expensive and bulky electrochemical workstations cannot be used under automotive conditions, and traditional on-board chargers can only provide unidirectional power input.

[0004] Current on-board EIS AC excitation devices utilize existing on-board chargers. Since on-board chargers contain AC-DC and DC-DC converters to convert AC mains power to DC power, they have the foundation for implementing EIS AC excitation. However, traditional on-board chargers are unidirectional, only enabling unidirectional energy transfer from the charger to the battery. To implement EIS AC excitation, the unidirectional AC-DC and DC-DC converters need to be changed to bidirectional AC-DC and DC-DC converters. Furthermore, key components and circuits such as the energy storage inductor, transformer, and low-voltage control circuit need to be redesigned according to the operating characteristics of EIS AC excitation, increasing system complexity.

[0005] Therefore, there is a need to develop an accurate, reliable, low-cost, compact EIS online measurement solution that does not increase system complexity. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by providing an AC excitation method, an online EIS measurement method, equipment, and medium for vehicle power batteries.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] According to a first aspect of the present invention, an AC excitation method for online EIS measurement of an on-board power battery is provided. A bidirectional DC-DC converter built into a starting power supply is connected to the on-board power battery under test. During the EIS AC excitation cycle, an AC excitation signal is injected into the on-board power battery under test through the bidirectional DC-DC converter to realize online AC excitation of EIS.

[0009] Preferably, the bidirectional DC-DC converter is a dual active full-bridge converter.

[0010] Preferably, the control circuit of the dual active full-bridge converter includes a primary-side active full-bridge converter composed of switching transistors Q1 to Q4, a secondary-side active full-bridge converter composed of switching transistors Q5 to Q8, an inductor Ls connected in series with the transformer for instantaneous energy storage, a current-regulating inductor L connected in series with the output side, and capacitors C1 and C2 that respectively serve as voltage regulators and filters on the input and output sides.

[0011] By controlling the magnitude and direction of the phase lag and lead output power between the drive signals of the H-bridge switches on both sides of the dual active full-bridge converter, the amplitude and direction of the AC excitation are adjusted, thereby realizing online AC excitation of EIS.

[0012] Preferably, the output current control of the dual active full-bridge converter adopts a closed-loop control strategy of the current loop, and the output current reference value is selected and switched according to whether the output current is DC or AC.

[0013] Preferably, during the output current control process of the dual active full-bridge converter, the phase of the primary-side switch drive signal is maintained, and the output current is controlled by changing the phase difference between the secondary-side switch drive signal and the primary-side switch drive signal.

[0014] According to a second aspect of the present invention, an online EIS measurement method for an on-board power battery is provided, comprising:

[0015] The above method is used to input an AC excitation signal to the on-board power battery under test;

[0016] The excitation response signal generated by the on-board power battery under test is measured.

[0017] Based on the measured excitation response signal, impedance calculation is performed using a digital lock-in amplifier to obtain the EIS data of the vehicle power battery.

[0018] Preferably, the measurement of the excitation response signal generated by the on-board power battery under test specifically involves: using a bus-based distributed battery management system, measuring the voltage through the low-speed electronic control unit (LECU) and measuring the current through the central electronic control unit (CECU).

[0019] Preferably, the step of using a digital lock-in amplifier to calculate impedance based on the measured excitation response signal to obtain the EIS data of the vehicle power battery specifically involves:

[0020] Based on the measured excitation response signal, a digital lock-in amplifier is used to filter the excitation response signal by performing cross-correlation calculation between the excitation response signal and the reference signal, thereby obtaining the amplitude of the current and voltage signals and the phase difference relative to the reference signal. Then, the amplitude and phase of the impedance are calculated using the impedance calculation formula to obtain the EIS data of the vehicle power battery.

[0021] According to a third aspect of the present invention, an electronic device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the program to implement any of the methods described above.

[0022] According to a fourth aspect of the invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements any of the methods described herein.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) This invention connects only the bidirectional DC-DC converter, which is connected to the power grid, to the power battery. On the one hand, the power battery can receive power from the power supply through the bidirectional DC-DC converter in the power supply, thus enabling charging of the power battery within the periodic excitation signal. On the other hand, the power supply can be charged by the power battery, thus enabling the power battery to discharge to the outside within the periodic excitation signal. Through the above process, the AC excitation of the power battery EIS can be realized using the two-phase power conversion function in the existing power supply, thereby realizing online measurement of the power battery EIS. This forms an efficient utilization of the internal power system of the electric vehicle, avoids the repeated design of AC-DC conversion technology in the on-board charger, reduces the redundancy and complexity of the power system, and realizes low-cost, small-size, and non-redundant on-board power battery EIS online measurement.

[0025] (2) This invention applies a dual active full-bridge converter to a startup power supply. By controlling the magnitude and direction of the phase lag and lead output power between the drive signals of the H-bridge switching transistors on both sides, i.e. adjusting the amplitude and direction of the AC excitation, the direction of the transmitted energy can be changed more continuously and smoothly, meeting the requirement of periodic bidirectional AC excitation for online EIS measurement.

[0026] (3) Applying the current loop closed-loop control strategy to the dual active full-bridge converter, the selection and switching of the output current reference value are adjusted according to whether the start-up output is AC or DC, resulting in higher overall control reliability.

[0027] (4) The digital lock-in amplifier uses the cross-correlation operation between the signal under test and the reference signal to filter the signal under test, improve the signal-to-noise ratio, and ensure signal accuracy and measurement flexibility. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the EIS measurement principle;

[0029] Figure 2 A schematic diagram illustrating the EIS measurement and charging functions using the startup power supply;

[0030] Figure 3 A flowchart for communication and incentive processes;

[0031] Figure 4 This is a schematic diagram of a dual active full-bridge converter;

[0032] Figure 5 A schematic diagram of the incentive control strategy for communication;

[0033] Figure 6 A schematic diagram illustrating signal measurement using a battery management system;

[0034] Figure 7 This is a schematic diagram for impedance calculation using a digital lock-in amplifier. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0036] Example

[0037] like Figure 1 As shown, current excitation is generally used for EIS measurement of power batteries to avoid overcurrent caused by voltage excitation. After inputting an AC excitation current signal to the power battery, a corresponding excitation response signal is obtained, which can then be used to calculate the power battery impedance. The impedance calculation expression in the frequency domain is obtained as follows:

[0038]

[0039] Impedance can also be calculated using complex form:

[0040] z=Z′+jZ″ (2)

[0041] Here, Z′ is the real part and Z″ is the imaginary part. Furthermore, Nyquist or Bode plots can be used to observe the electrochemical process information of the power battery, reflecting the changes in physical information such as mass transfer, rate constant, and diffusion coefficient with frequency.

[0042] The Electro-Insulation (EIS) of a power battery is generally divided into three parts: high-frequency, medium-frequency, and low-frequency. The high-frequency part reflects the ohmic resistance, the medium-frequency part reflects the charge transfer process involving electrons and lithium ions, and the low-frequency part reflects the diffusion of lithium ions in the active material.

[0043] EIS measurement of power batteries includes three key steps: AC excitation, signal measurement, and impedance measurement.

[0044] This embodiment features an innovative design for the AC excitation stage, providing an AC excitation method for online EIS measurement of vehicle-mounted power batteries. The bidirectional DC-DC converter built into the starting power supply is connected to the vehicle-mounted power battery under test. During the EIS AC excitation cycle, the bidirectional DC-DC converter injects the AC excitation signal into the vehicle-mounted power battery under test, achieving online EIS AC excitation.

[0045] Next, the method of this embodiment will be described in detail.

[0046] Since the starting power supply needs to receive charging from the grid and convert it into DC power to supply the vehicle's computer, lights, horn, remote locks, etc., it has a built-in AC-DC converter and a DC-DC converter. This DC-DC converter is now connected to the power battery. By fine-tuning the starting power supply parameters to meet the requirements of power battery impedance measurement, AC excitation of the power battery's EIS (Electronic Information System) can be achieved.

[0047] By combining the design of the starting power supply parameters with the requirements of power battery impedance measurement, the specific performance parameters of this AC excitation device can be obtained. Here, a 48V starting power supply is taken as an example. In the starting function, the DC-DC converter of the starting power supply has an input voltage of 400V and an output rated voltage of 48V, with a voltage range of 36V to 52V. In the AC excitation function, the AC output frequency is 0.1 to 500Hz, and the AC output amplitude is 2A.

[0048] like Figure 3As shown, in this embodiment, to achieve smooth switching of current transmission direction, a dual active bridge (DAB) converter is selected as the bidirectional DC-DC converter, and the DAB converter is connected to the power battery under test. When selecting the start-up function and the AC excitation function, a current loop closed-loop control strategy is used to select and switch the output current reference value. When the start-up power supply is switched to the start-up function, a stable DC current is applied to the on-board computer, headlights, horn, remote lock, etc., to achieve the start-up function. When the start-up power supply is switched to the AC excitation function, charging and discharging excitation signals are periodically applied to the power battery, thus achieving the AC excitation function.

[0049] like Figure 4 As shown, the two active full-bridge converters are the primary-side active full-bridge converter composed of Q1 to Q4 and the secondary-side active full-bridge converter composed of Q5 to Q8, respectively. s The inductor is a momentary energy storage element connected in series with the transformer; L is a constant current inductor connected in series with the output side; V1 is the DC bus voltage output from the preceding AC-DC converter; V2 is the voltage across the output filter capacitor; V out The output voltage is measured; C1 and C2 are capacitors that serve as voltage regulators and filters on the input and output sides, respectively. Both H-bridges in the dual active full-bridge topology have switching transistor drive signals with a duty cycle of 50%. By controlling the phase lag and lead between the switching transistor drive signals of the two H-bridges, the magnitude and direction of the output power are adjusted, i.e., the amplitude and direction of the AC excitation.

[0050] The design of the DAB converter includes detailed design of the energy storage inductor and transformer.

[0051] Based on the parameter requirements of the AC excitation device, the topology DC bus voltage V1 = 400V, and the output voltage V... out =48V, maximum phase shift duty cycle D max =0.5. Based on the maximum range for soft switching in the DAB converter, to ensure a topology step-up ratio of 1 under rated operating conditions, the number of turns on the primary and secondary sides of the transformer is as follows:

[0052]

[0053] With a fixed transformer turns ratio and switching frequency, the maximum output power of the topology is determined by the instantaneous energy storage inductance value. When the output voltage is at its minimum V2 = 36V and the input voltage V1 = 400V, the output power should reach a maximum of 0.072kW. At a switching frequency f = 100kHz, the inductance values ​​that achieve a maximum power of 0.072kW are as follows:

[0054]

[0055] Considering efficiency losses, the actual value is L. s = 2mH. At this point, the peak current in the series inductor on the primary side of the transformer reaches its maximum value. Combining the input and output voltages with the series inductance value, the maximum inductor current is obtained as follows:

[0056]

[0057] After determining the inductance value, peak current, and maximum effective current, the area product method (AP method) is used to design the inductor and transformer, and the power MOSFET is selected accordingly.

[0058] like Figure 5 As shown, this embodiment presents a control strategy for the AC excitation device of the starting power supply, depending on whether the starting function or AC excitation function is performed. A current loop closed-loop control strategy is adopted to adjust the selection and switching of the output current reference value. The designed DC-DC converter must be able to generate DC power for starting motors, vehicle computers, headlights, horns, remote locks, etc., and also generate AC power for measuring battery impedance. The output current control of the DAB converter adopts a current loop closed-loop control strategy, and selects and switches the output current reference value according to whether the output is AC or DC. During the control process, the phase of the MOSFET switch drive signal on the primary side remains unchanged, and the output current is controlled by changing the phase difference between the MOSFET switch drive signal on the secondary side and the primary side signal. Perform size and orientation control.

[0059] This embodiment also provides a method for online measurement of EIS of vehicle power batteries, including:

[0060] The above method is used to input an AC excitation signal to the on-board power battery under test;

[0061] The excitation response signal generated by the on-board power battery under test is measured: For a bus-based distributed battery management system, voltage is measured through the low-speed electronic control unit (LECU) and current is measured through the central electronic control unit (CECU).

[0062] Based on the measured excitation response signal, a digital lock-in amplifier is used to filter the excitation response signal by performing cross-correlation calculation between the excitation response signal and the reference signal, thereby obtaining the amplitude of the current and voltage signals and the phase difference relative to the reference signal. Then, the amplitude and phase of the impedance are calculated using the impedance calculation formula to obtain the EIS data of the vehicle power battery.

[0063] like Figure 6The diagram illustrates voltage and current signal measurements using a battery management system. Since the power battery modules of actual electric vehicles are often composed of multiple battery cells connected in series, it is necessary to measure the voltage of each battery cell and the total current of the series-connected battery pack to achieve voltage and current measurement for each individual battery cell. Because the impedance frequency range of on-board power batteries is generally 0.1–500Hz, and is typically calculated with 20x oversampling, the required sampling frequency is around 10kHz. For a typical bus-based distributed battery management system, voltage measurement is performed in the LECU (Leveled Electronic Control Unit), and current measurement is performed in the CECU (Centered Battery Control Unit).

[0064] like Figure 7 The diagram illustrates impedance calculation using a digital lock-in amplifier (LLP). The LLP utilizes the cross-correlation between the measured signal and a reference signal to filter the measured signal, improving the signal-to-noise ratio and ensuring signal accuracy and measurement flexibility. The amplitude and phase difference relative to the reference signal of the current and voltage signals can be obtained using the LLP, and then the impedance amplitude and phase can be calculated using the impedance calculation formula.

[0065] Through the above technical solution, the design method of realizing EIS calculation function using a starting power supply, as designed in this invention, can be applied in actual vehicles, achieving low-cost, small-size, and non-redundant EIS calculation and on-board online diagnostics. This lays the foundation for the application of electrochemical impedance spectroscopy in battery health estimation, aging mode quantitative identification, lifespan prediction, and temperature estimation.

[0066] The electronic device of this invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). The RAM may also store various programs and data required for device operation. The CPU, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.

[0067] Multiple components in the device are connected to the I / O interface, including: input units such as keyboards and mice; output units such as various types of displays and speakers; storage units such as disks and optical discs; and communication units such as network interface cards (NICs), modems, and wireless transceivers. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0068] The processing unit performs the various methods and processes described above. For example, in some embodiments, the methods may be implemented as computer software programs tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the methods described above may be performed. Alternatively, in other embodiments, the CPU may be configured as the executor by any other suitable means (e.g., by means of firmware).

[0069] The functions described above in this document can be performed at least in part by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SoCs), payload programmable logic devices (CPLDs), and so on.

[0070] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0071] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0072] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An AC excitation method for online EIS measurement of vehicle-mounted power batteries, characterized in that, The bidirectional DC-DC converter built into the starting power supply is connected to the vehicle power battery under test. During the EIS AC excitation cycle, the AC excitation signal is injected into the vehicle power battery under test through the bidirectional DC-DC converter to realize EIS online AC excitation. The bidirectional DC-DC converter is a dual active full-bridge converter; The control circuit of the dual active full-bridge converter includes a primary-side active full-bridge converter composed of switching transistors Q1~Q4, a secondary-side active full-bridge converter composed of switching transistors Q5~Q8, an inductor Ls connected in series with the transformer for instantaneous energy storage, a current-regulating inductor L connected in series with the output side, and capacitors C1 and C2 that play a role in voltage regulation and filtering on the input and output sides, respectively. By controlling the magnitude and direction of the phase lag and lead output power between the drive signals of the H-bridge switches on both sides of the dual active full-bridge converter, the amplitude and direction of the AC excitation are adjusted to achieve online AC excitation of EIS. The output current control of the dual active full-bridge converter adopts a closed-loop control strategy of the current loop, and selects and switches the output current reference value according to whether the output current is DC or AC.

2. The method according to claim 1, characterized in that, During the output current control process of the dual active full-bridge converter, the phase of the primary-side switch drive signal is maintained, and the output current is controlled by changing the phase difference between the secondary-side switch drive signal and the primary-side switch drive signal.

3. A method for online measurement of EIS in vehicle-mounted power batteries, characterized in that, include: The method described in any one of claims 1 to 2 is used to input an AC excitation signal to the on-board power battery under test; The excitation response signal generated by the on-board power battery under test is measured. Based on the measured excitation response signal, impedance calculation is performed using a digital lock-in amplifier to obtain the EIS data of the vehicle power battery.

4. The method according to claim 3, characterized in that, The measurement of the excitation response signal generated by the on-board power battery under test is specifically carried out by using a bus-based distributed battery management system, measuring the voltage through the low-speed electronic control unit (LECU), and measuring the current through the central electronic control unit (CECU).

5. The method according to claim 3, characterized in that, The process involves using a digital lock-in amplifier to calculate impedance based on the measured excitation response signal, thereby obtaining the EIS data of the vehicle-mounted power battery. Specifically: Based on the measured excitation response signal, a digital lock-in amplifier is used to filter the excitation response signal by performing cross-correlation calculation between the excitation response signal and the reference signal, thereby obtaining the amplitude of the current and voltage signals and the phase difference relative to the reference signal. Then, the amplitude and phase of the impedance are calculated using the impedance calculation formula to obtain the EIS data of the vehicle power battery.

6. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the program, it implements the method as described in any one of claims 1 to 5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 5.

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