Alternating current excitation method, vehicle-mounted power battery EIS online measurement method, equipment and medium

Abstract

The invention relates to an alternating-current excitation method, a vehicle-mounted power battery EIS online measurement method, equipment and a medium, and the method comprises the steps: enabling a built-in bidirectional DC-DC converter in a starting power supply to be connected to a to-be-measured vehicle-mounted power battery, and injecting an alternating-current excitation signal into the to-be-measured vehicle-mounted power battery through the bidirectional DC-DC converter in an EIS alternating-current excitation period, and EIS online alternating current excitation is realized. Compared with the prior art, the EIS AC excitation function is realized by directly utilizing the starting power supply, so that the EIS online measurement of the power battery is realized, the efficient utilization of an internal power supply system of an electric vehicle is formed, the repeated design of an AC-DC conversion technology in a vehicle-mounted charger is avoided, and the redundancy and complexity of the power supply system are reduced.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical measurement, and in particular to an alternating current excitation method, an on-vehicle power battery EIS online measurement method, equipment and medium. Background Art

[0002] With the continuous development of the electric vehicle industry, the health, safety, and life of lithium-ion power batteries have attracted more and more attention. Among them, how to accurately measure the internal state of the power battery and reflect information such as safety and life has become one of the key issues. A more accurate method is to use electrochemical impedance spectroscopy (EIS) testing to reflect the internal state information of the power battery. Its advantage is that the EIS test can reflect a variety of complex electrochemical properties such as material transfer, rate constants, diffusion coefficients, etc.; and EIS measurement is a non-destructive measurement and does not damage the battery.

[0003] EIS measurement includes three key links: AC excitation, signal measurement and impedance calculation. Among them, EIS AC excitation requires the power battery to realize charging and discharging within the periodic excitation signal. In each excitation signal cycle, the battery will switch between the charging and discharging states, that is, an AC signal is injected into the battery. In vehicle-mounted applications, a specially designed device is required to generate an AC signal, and make it as low-cost, small-sized, and without increasing the complexity of the system as possible. However, on-vehicle power battery EIS measurement and online diagnosis of power battery status have not yet been applied to actual vehicles. The reason is that under vehicle-mounted conditions, expensive and bulky electrochemical workstations cannot be used, and traditional on-vehicle chargers can only provide one-way power input.

[0004] The existing on-board EIS AC excitation device is implemented using the existing on-board charger. Since the on-board charger has devices such as AC-DC conversion and DC-DC conversion that convert AC mains power into DC power, it has the basis for realizing EIS AC excitation. However, the traditional on-board charger is a unidirectional charger and can only realize unidirectional power transmission from the on-board charger to the power battery. If EIS AC excitation is to be realized, the unidirectional AC-DC and DC-DC conversions must be changed to bidirectional AC-DC and DC-DC conversions, and key components and circuits such as energy storage inductors, transformers, and low-voltage control circuits must be redesigned according to the working characteristics of EIS AC excitation, which increases the complexity of the system.

[0005] Therefore, it is necessary to develop an EIS online measurement solution that is accurate, reliable, low-cost, small in size, and does not increase the complexity of the system. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide an AC excitation method, an on-board power battery EIS online measurement method, equipment and medium.

[0007] The purpose of the present invention can be achieved by 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, wherein a bidirectional DC-DC converter built into a starting power supply is connected to the on-board power battery to be tested, and during an EIS AC excitation cycle, an AC excitation signal is injected into the on-board power battery to be tested through the bidirectional DC-DC converter to achieve EIS online AC excitation.

[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 switch tubes Q1 to Q4, a secondary side active full-bridge converter composed of switch tubes Q5 to Q8, an inductor element Ls connected in series with the transformer for instantaneous energy storage, a current stabilizing inductor L connected in series with the output side, and capacitors C1 and C2 that play a role of voltage stabilization and filtering at the input side and the output side respectively;

[0011] By controlling the phase lag and leading output power between the driving 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 EIS online AC excitation.

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

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

[0014] According to a second aspect of the present invention, there is provided a vehicle-mounted power battery EIS online measurement method, comprising:

[0015] Using the above method, an AC excitation signal is input to the vehicle power battery to be tested;

[0016] Measure the excitation response signal generated by the vehicle power battery to be tested;

[0017] According to the measured excitation response signal, a digital lock-in amplifier is used to calculate the impedance and obtain the EIS data of the vehicle power battery.

[0018] Preferably, the excitation response signal generated by the vehicle-mounted power battery to be tested is measured, specifically: using a bus-based distributed battery management system, performing voltage measurement through a low-speed electronic control unit LECU, and performing current measurement through a central electronic control unit CECU.

[0019] Preferably, the impedance calculation is performed using a digital lock-in amplifier according to the measured excitation response signal to obtain the EIS data of the vehicle power battery, specifically:

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

[0021] According to a third aspect of the present invention, there is provided an electronic device, comprising a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the program, any one of the methods described above is implemented.

[0022] According to a fourth aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, wherein when the program is executed by a processor, any one of the methods described above is implemented.

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

[0024] (1) The present invention only connects the bidirectional DC-DC converter connecting the starting power supply to the power grid to the power battery. On the one hand, the power battery can be powered by the starting power supply through the bidirectional DC-DC converter in the starting power supply, that is, the power battery can be charged within the periodic excitation signal. On the other hand, the starting power supply can be charged by the power battery, that is, the power battery can be discharged externally within the periodic excitation signal. Through the above process, the EIS AC excitation of the power battery can be realized by utilizing the two-phase power conversion function in the existing starting power supply, thereby realizing the online measurement of the EIS of the power battery, forming an efficient utilization of the internal power system of the electric vehicle, avoiding the repeated design of the AC-DC conversion technology in the on-board charger, reducing the redundancy and complexity of the power system, and realizing the low-cost, small-volume, and non-redundant structure on-board power battery EIS online measurement.

[0025] (2) The present invention applies a dual-active full-bridge converter to the starting power supply. By controlling the phase lag and lead output power between the driving signals of the H-bridge switch tubes on both sides, that is, adjusting the amplitude and direction of the AC excitation, the transmission energy direction can be changed more continuously and smoothly, meeting the requirement of periodic bidirectional AC excitation for online EIS measurement.

[0026] (3) The current loop closed-loop control strategy is applied to the dual active full-bridge converter. The selection and switching of the output current reference value are adjusted according to whether the output is AC or DC, which improves the overall control reliability.

[0027] (4) The digital lock-in amplifier uses the cross-correlation operation between the signal to be measured and the reference signal to filter the signal to be measured, improve the signal-to-noise ratio, and ensure signal accuracy and measurement flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the EIS measurement principle;

[0029] Figure 2 Schematic diagram of EIS measurement and charging function using the starting power supply;

[0030] Figure 3 To communicate motivational flow chart;

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

[0032] Figure 5 It is a schematic diagram of the AC excitation control strategy;

[0033] Figure 6 This is a schematic diagram of signal measurement using a battery management system;

[0034] Figure 7 Schematic diagram of impedance calculation using a digital lock-in amplifier. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0036] Example

[0037] like Figure 1 As shown, the power battery EIS measurement generally uses current excitation to avoid using voltage excitation to cause equipment overcurrent. After inputting the AC excitation current signal to the power battery, the corresponding excitation response signal will be obtained, and then the power battery impedance can be calculated. The impedance calculation expression in the frequency domain is obtained:

[0038]

[0039] The impedance can also be calculated using complex form:

[0040] z=Z′+jZ″ (2)

[0041] Among them, Z′ is the real part and Z″ is the imaginary part. Then, the electrochemical process information of the power battery is observed through the Nyquist diagram or the Bode diagram, reflecting the law of change of physical information such as material transfer, rate constant, diffusion coefficient, etc. with frequency.

[0042] Power battery EIS 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] Power battery EIS measurement includes three key links: AC excitation, signal measurement and impedance measurement.

[0044] This embodiment makes an innovative design for the AC excitation link, and provides an AC excitation method for online EIS measurement of an on-board power battery. The bidirectional DC-DC converter built into the starting power supply is connected to the on-board power battery to be tested. During the EIS AC excitation cycle, the AC excitation signal is injected into the on-board power battery to be tested through the bidirectional DC-DC converter, thereby realizing EIS online AC excitation.

[0045] Next, the method of this embodiment is introduced in detail.

[0046] Since the starting power supply needs to receive power grid charging and convert it into DC power to supply the on-board computer, lights, horns, remote locks, etc., the starting power supply has built-in AC-DC converter and DC-DC converter. Now the DC-DC converter is connected to the power battery, and combined with the needs of power battery impedance measurement, the starting power supply parameter design is fine-tuned to achieve power battery EIS AC excitation.

[0047] The starting power supply parameter design is combined with the power battery impedance measurement requirements to obtain the specific performance parameters of this AC excitation device. Here, a 48V starting power supply is taken as an example. In the starting function, the input voltage of the DC-DC converter of the starting power supply is 400V, the output rated voltage is 48V, and the voltage range is 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, in order to achieve smooth switching of the current transmission direction, the bidirectional DC-DC converter in this embodiment uses a dual active full bridge (Dual Active Bridge, DAB) converter, and the DAB converter is connected to the power battery to be tested. When selecting the starting function and the AC excitation function, the current loop closed-loop control strategy is used to select and switch the output current reference value. When the starting power supply is switched to the starting function, a stable direct current will be applied to the on-board computer, lights, horns, remote control locks, etc. to achieve the starting function. When the starting power supply is switched to the AC excitation function, charging and discharging excitation signals will be periodically applied to the power battery, that is, the AC excitation function is achieved.

[0049] like Figure 4 As shown, the two active full-bridge converters are respectively a primary-side active full-bridge converter composed of Q1 to Q4 and a secondary-side active full-bridge converter composed of Q5 to Q8. s is an inductor element for instantaneous energy storage, which is connected in series with the transformer; L is a current-stabilizing inductor, which is connected in series with the output side; V1 is the DC bus voltage output by the previous AC-DC converter; V2 is the voltage on the output filter capacitor; V out The output voltage is measured; C1 and C2 are capacitors that play the role of voltage stabilization and filtering on the input and output sides respectively. Both H-bridges of the dual active full-bridge topology have switch tube drive signals with a duty cycle of 50%. By controlling the phase lag and lead between the drive signals of the switch tubes of the H-bridges on both sides, the magnitude and direction of the output power can be adjusted, that is, the amplitude and direction of the AC excitation can be adjusted.

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

[0051] According to the AC excitation device parameter requirements, the topology DC bus voltage V1 = 400V, the output voltage V out =48V, maximum phase shift duty ratio D max =0.5. It is determined according to the maximum range of soft switching of the DAB converter, so that the topology boost ratio is 1 under rated working conditions, and the primary and secondary turns ratio of the transformer is as follows:

[0052]

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

[0054]

[0055] Taking into account the efficiency loss, the actual L s =2mH. At this time, the current peak value of the series inductor on the primary side of the transformer reaches its maximum value. Combining the input and output voltages and the series inductor value, the maximum value of the inductor current is obtained as follows:

[0056]

[0057] After determining the inductance value, peak current and maximum current effective value, 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, according to whether the starting power supply performs the starting function or the AC excitation function, this embodiment provides a control strategy for the starting power supply AC excitation device. 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 starting motors, on-board computers, car lights, horns, remote control locks, etc., and must be able to generate AC for measuring the impedance of the battery. 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 tube drive signal on the primary side remains unchanged, and the output current is adjusted by changing the phase difference between the MOSFET switch tube drive signal on the secondary side and the primary side signal. Provides size and orientation control.

[0059] This embodiment also provides an on-vehicle power battery EIS online measurement method, including:

[0060] Using the above method, an AC excitation signal is input to the vehicle power battery to be tested;

[0061] Measure the excitation response signal generated by the vehicle power battery to be tested: For a bus-based distributed battery management system, the voltage is measured through the low-speed electronic control unit LECU, and the current is measured through the central electronic control unit CECU;

[0062] According to the measured excitation response signal, a digital lock-in amplifier is used to filter the excitation response signal using the cross-correlation operation between the excitation response signal and the reference signal to obtain the amplitude of the current and voltage signals and the phase difference relative to the reference signal. Then, the impedance calculation formula is used to calculate the amplitude and phase of the impedance to obtain the EIS data of the on-board power battery.

[0063] like Figure 6The figure shows a schematic diagram of using a battery management system to measure voltage and current signals. Since the power battery module of an actual electric vehicle is 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 battery pack to achieve voltage and current measurement of each battery cell. Since the impedance frequency range of the on-board power battery is generally 0.1 to 500 Hz, and is generally calculated with 20 times oversampling, the frequency requirement is about 10 kHz. For a general bus-based distributed battery management system, voltage measurement is performed in the LECU and current measurement is performed in the CECU.

[0064] like Figure 7 The figure shows a schematic diagram of impedance calculation using a digital lock-in amplifier. The digital lock-in amplifier can use the cross-correlation operation between the measured signal and the reference signal to filter the measured signal, improve the signal-to-noise ratio, and ensure signal accuracy and measurement flexibility. The digital lock-in amplifier can be used to obtain the amplitude of the current and voltage signals and the phase difference relative to the reference signal, and then the impedance calculation formula can be used to calculate the amplitude and phase of the impedance.

[0065] Through the above technical solution, the design method of the present invention for realizing EIS calculation function by using starting power supply can be applied on real vehicles, and realizes EIS calculation and vehicle-mounted online diagnosis with low cost, small volume and no redundant structure, laying a foundation for the application of electrochemical impedance measurement in battery health state estimation, aging mode quantitative identification, life prediction and temperature estimation.

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

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

[0068] The processing unit performs the various methods and processes described above. For example, in some embodiments, the method can be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program can be loaded and / or installed on the device via a 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 method described above can be performed. Alternatively, in other embodiments, the CPU can be configured as an executor by any other appropriate means (e.g., by means of firmware).

[0069] The functions described above herein may be performed at least in part by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chip systems (SOCs), load programmable logic devices (CPLDs), and the like.

[0070] The program code for implementing the method of the present invention can be written in any combination of one or more programming languages. These program codes can be provided to a processor or controller of a general-purpose computer, a special-purpose computer or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code can be executed entirely on the machine, partially on the machine, partially on the machine as a stand-alone software package and partially on a remote machine, or entirely on a remote machine or server.

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

[0072] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An AC excitation method for online EIS measurement of vehicle power batteries, characterized in that: The bidirectional DC-DC converter built in the starting power supply is connected to the vehicle-mounted power battery to be tested. During the EIS AC excitation cycle, the AC excitation signal is injected into the vehicle-mounted power battery to be tested through the bidirectional DC-DC converter to realize EIS online AC excitation.

2. The method according to claim 1, characterized in that: The bidirectional DC-DC converter is a dual active full-bridge converter.

3. The method according to claim 2, characterized in that The control circuit of the dual active full-bridge converter includes a primary side active full-bridge converter composed of switch tubes Q1-Q4, a secondary side active full-bridge converter composed of switch tubes Q5-Q8, an inductor element Ls connected in series with the transformer for instantaneous energy storage, a current stabilizing inductor L connected in series with the output side, and capacitors C1 and C2 that play the role of voltage stabilization and filtering at the input side and the output side respectively; By controlling the phase lag and leading output power between the driving 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 EIS online AC excitation.

4. The method according to claim 3, characterized in that The output current control of the dual active full-bridge converter adopts a closed-loop control strategy of a current loop, and selects and switches the output current reference value according to whether the output current is direct current or alternating current.

5. The method according to claim 4, characterized in that During the output current control process of the dual active full-bridge converter, the phase of the primary switch tube drive signal is maintained, and the output current is controlled by changing the phase difference between the secondary switch tube drive signal and the primary switch tube drive signal.

6. A vehicle-mounted power battery EIS online measurement method, characterized in that: include: Adopting the method described in any one of claims 1 to 5 to input an AC excitation signal to the vehicle-mounted power battery to be tested; Measure the excitation response signal generated by the vehicle power battery to be tested; According to the measured excitation response signal, a digital lock-in amplifier is used to calculate the impedance and obtain the EIS data of the vehicle power battery.

7. The method according to claim 6, characterized in that The excitation response signal generated by the vehicle power battery to be tested is measured, specifically: using a bus-based distributed battery management system, performing voltage measurement through a low-speed electronic control unit LECU, and performing current measurement through a central electronic control unit CECU.

8. The method according to claim 6, characterized in that According to the measured excitation response signal, a digital lock-in amplifier is used to perform impedance calculation to obtain the EIS data of the vehicle power battery, specifically: According to the measured excitation response signal, a digital lock-in amplifier is used to filter the excitation response signal using the cross-correlation operation between the excitation response signal and the reference signal to obtain the amplitude of the current and voltage signals and the phase difference relative to the reference signal. Then, the impedance calculation formula is used to calculate the amplitude and phase of the impedance to obtain the EIS data of the vehicle power battery.

9. An electronic device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor executes the program, the method according to any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the method according to any one of claims 1 to 8 is implemented.

Images