Method for acquiring electrochemical impedance spectrum of battery, vehicle and storage medium

Abstract

This application relates to the field of vehicles, and more specifically, to a method for obtaining an electrochemical impedance spectroscopy (EIS) of a battery, a vehicle capable of implementing the method, and a computer storage medium. The method is applied to an electric drive system of a vehicle, the electric drive system being connected to a battery of the vehicle and including a motor and motor control circuitry for controlling energy transfer from the battery to the motor. The method includes: step 202: determining a target excitation current based on a frequency sweep requirement of the EIS; step 204: adjusting the actual excitation current flowing through the electric drive system via the motor control circuitry, based on the target excitation current, such that the actual excitation current is close to the target excitation current; step 206: calculating the battery impedance at the current frequency of the target excitation current based on the voltage across the battery and the actual excitation current; and step 208: changing the frequency of the target excitation current, and repeating steps 204 and 206 until all frequencies of the frequency sweep requirement are covered.

Description

Technical Field

[0001] This application relates to the field of vehicles, and more specifically, to a method for obtaining an electrochemical impedance spectroscopy of a battery, a vehicle capable of implementing the method, and a computer storage medium. Background Technology

[0002] Electrochemical impedance spectroscopy (EIS) is commonly used to identify the state of charge (SOC) and state of health (SOH) of a battery, and also for fault detection and analysis in battery packs. A battery's EIS is obtained by applying AC voltage or current perturbations at different frequencies to the battery terminals to measure the change in battery impedance as a function of frequency. Generally, EIS needs to be calibrated offline in a laboratory environment; however, this requires significant testing resources and is also difficult to cover parameter variations caused by complex operating conditions in real-time applications.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] This application provides a method for obtaining the electrochemical impedance spectroscopy (EIS) of a battery, a vehicle capable of implementing the method, and a computer storage medium. The method enables real-time online measurement of the EIS of a vehicle's power battery using the vehicle's electric drive system, saving offline calibration resources, better adapting to real-world environments, and eliminating the need for additional hardware and costs.

[0005] According to a first aspect of this application, a method for obtaining the electrochemical impedance spectroscopy of a battery is provided, applied to an electric drive system of a vehicle, the electric drive system being connected to a battery of the vehicle and including a motor and a motor control circuit for controlling energy transfer from the battery to the motor, the method comprising: step 202: determining a target excitation current based on a frequency sweep requirement of the electrochemical impedance spectroscopy; step 204: adjusting the actual excitation current flowing through the electric drive system via the motor control circuit based on the target excitation current, such that the actual excitation current is close to the target excitation current; step 206: calculating the impedance of the battery at the current frequency of the target excitation current based on the voltage across the battery and the actual excitation current; and step 208: changing the frequency of the target excitation current, and repeating steps 204 and 206 until all frequencies of the frequency sweep requirement are covered.

[0006] As an alternative or supplement to the above solutions, in a method according to an embodiment of this application, the target excitation current is the target direct-axis current of the motor, the actual excitation current is the actual direct-axis current of the motor, and wherein the target direct-axis current includes a DC component and an AC component.

[0007] As an alternative or supplement to the above solution, the method according to an embodiment of this application further includes: maintaining the quadrature-axis current of the motor at zero through a motor control circuit.

[0008] As an alternative or supplement to the above solutions, in a method according to an embodiment of this application, the electric drive system further includes a first capacitor and a second capacitor, wherein the first capacitor is located between the DC positive bus and the DC negative bus of the motor control circuit, and the second capacitor is located between the neutral point of the motor and the DC negative bus.

[0009] As an alternative or supplement to the above solutions, in a method according to an embodiment of this application, the target excitation current is the common-mode current of the motor winding, and wherein the common-mode current includes an AC component.

[0010] As an alternative or supplement to the above solution, in a method according to an embodiment of this application, step 206 includes: performing fast Fourier transform on the voltage across the battery and the actual excitation current respectively; determining the voltage across the battery at the current frequency of the target excitation current and the current of the actual excitation current at the current frequency; and dividing the voltage by the current to obtain the impedance of the battery at the current frequency.

[0011] According to a second aspect of this application, a vehicle is provided, including a battery and an electric drive system connected to the battery. The electric drive system includes: a motor including a plurality of windings; a motor control circuit configured to control energy transfer from the battery to the motor, and including a plurality of bridge arms connected in parallel between a DC positive bus and a DC negative bus, the midpoint of each of the plurality of bridge arms being connected to a corresponding winding of an electrode; and a controller configured to perform the following steps: step 202: determining a target excitation current based on a frequency sweep requirement of an electrochemical impedance spectroscopy; step 204: adjusting the actual excitation current flowing through the electric drive system via the motor control circuit based on the target excitation current, such that the actual excitation current is close to the target excitation current; step 206: calculating the impedance of the battery at the current frequency of the target excitation current based on the voltage across the battery and the actual excitation current; and step 208: changing the frequency of the target excitation current, and repeating steps 204 and 206 until all frequencies in the frequency sweep requirement are covered.

[0012] As an alternative or supplement to the above solutions, in a vehicle according to an embodiment of this application, a first capacitor and a second capacitor are further included. The first capacitor is located between the DC positive bus and the DC negative bus of the motor control circuit, and the second capacitor is located between the neutral point of the motor and the DC negative bus.

[0013] As an alternative or supplement to the above solutions, in a vehicle according to an embodiment of this application, the target excitation current is the common-mode current of the motor winding, and wherein the common-mode current includes an AC component.

[0014] According to a third aspect of this application, a computer storage medium is provided, the computer storage medium including instructions that, when executed, perform the method according to a first aspect of this application. Attached Figure Description

[0015] The above and / or other aspects and advantages of this application will become clearer and more readily understood from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are denoted by the same reference numerals. In the drawings: Figure 1 These are circuit diagrams of a battery and electric drive system in a vehicle according to some embodiments of this application; Figure 2 This is a flowchart of a method 200 for obtaining an electrochemical impedance spectrum of a battery according to some embodiments of this application; Figure 3 This is based on some embodiments of the present application. Figure 1 Circuit diagram execution Figure 2 Control block diagram for step 204; Figure 4 The illustrated diagrams are circuit diagrams of the battery and electric drive system in a vehicle according to other embodiments of this application; and Figure 5 This is based on some embodiments of the present application. Figure 4 Circuit diagram execution Figure 2 The control block diagram for step 204 in the process. Detailed Implementation

[0016] The following detailed description is merely exemplary in nature and is not intended to limit the disclosed technology or its application and use. Furthermore, it is not intended to be bound by any express or implied theory presented in the foregoing technical fields, background art, or the following detailed description.

[0017] In the following detailed description of the embodiments, numerous specific details are set forth in order to provide a more thorough understanding of the disclosed technology. However, it will be apparent to those skilled in the art that the disclosed technology can be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0018] Terms such as "possessing" and "comprising" indicate that, in addition to the units (modules) and steps directly and explicitly stated in the specification and claims, the technical solution of this application does not exclude the presence of other units (modules) and steps not directly or explicitly stated. Terms such as "first" and "second" do not indicate the order of the units in terms of time, space, size, etc., but are merely used to distinguish the units. Furthermore, the steps in this document are not limited to being performed in the order they are written; a step written later may be performed simultaneously with or before a step written earlier.

[0019] To perform real-time online EIS measurements in an in-vehicle environment, an additional sweep frequency circuit module is typically required, which may negatively impact vehicle cost and size optimization. Since the vehicle's electric drive system inherently contains switching devices and inductive windings (part of the motor), AC disturbances can be applied to the battery via the multiplexed electric drive system (without adding any hardware). The battery impedance Z (e.g., Z = R + jX, where R is resistance, X is reactance, and j is the imaginary unit) can then be calculated based on the measured results after the disturbance, allowing for the online acquisition of the battery's real-time EIS.

[0020] The embodiments of this application will now be described in detail with reference to the accompanying drawings. Figure 1 , Figure 1 These are illustrated circuit diagrams of a battery and electric drive system in a vehicle according to some embodiments of this application. Specifically, the electric drive system is connected to the positive and negative terminals of the battery and includes a motor and a motor control circuit for controlling the energy transfer from the battery to the motor. As an example, the motor may be a three-phase motor and includes three windings LA, LB, and LC. Accordingly, the motor control circuit includes three arms corresponding to the three-phase windings, each arm including a set of controllable switches (e.g., Q1 / Q2, Q3 / Q4, or Q5 / Q6), and the midpoint of each arm is connected to the corresponding motor winding.

[0021] also, Figure 1 The diagram also illustrates capacitor C1 located between the DC positive bus and the DC negative bus of the motor control circuit. The current ib flowing through the electric drive system can be adjusted by controlling the on and off states of the controllable switch in the motor control circuit. Figure 1As illustrated in the diagram, the current ib can originate from the positive terminal of the battery, pass sequentially through the upper bridge arm, the motor windings, and the lower bridge arm, and return to the negative terminal of the battery, thus forming a loop. It should be understood that at some times, this loop can be formed by turning on both upper bridge arms (e.g., Q1 and Q3) and the remaining phase of the lower bridge arm (e.g., Q6). At other times, the loop can be formed by turning on one upper bridge arm (e.g., Q1) and the other two phases of the lower bridge arms (e.g., Q4 and Q6). Thus, the current flowing through the motor can be regulated by the motor control circuitry. This current also flows through the battery and can therefore be used as the excitation current for electrochemical impedance spectroscopy measurements.

[0022] Next reference Figure 2 , Figure 2 This is a flowchart of a method 200 for obtaining an electrochemical impedance spectroscopy spectrum of a battery according to some embodiments of this application. Figure 2 As illustrated in the diagram, in step 202, the target excitation current ib* is determined based on the frequency sweep requirement of the electrochemical impedance spectroscopy. Specifically, the electrochemical impedance spectroscopy is used to indicate the impedance characteristics of the battery at different frequencies, and the frequency sweep requirement indicates at which frequency points what excitation current should be applied.

[0023] In some embodiments, Figure 2 Method 200 can be performed by a controller in the vehicle's electric drive system. It should be understood that, in other embodiments, it can also be performed by other controllers in the vehicle that are communicatively coupled to the controller of the electric drive system, such as the controller of the battery management system (BMS), a controller dedicated to EIS measurements, etc.

[0024] In some embodiments, the target excitation current ib* can be the target direct-axis current id* of the motor, and the target direct-axis current id* includes a DC component and an AC component. For example, id* = A + B*cos(ω1*t), where A is the DC component, B*cos(ω1*t) is the AC component, B is the amplitude of the AC component, ω1 is the frequency of the AC component, and t is time. By setting the DC component A, a bias can be provided for the actual direct-axis current id, making it easier to detect. In some embodiments, the DC component A can be set to be equal to or slightly larger than the amplitude B of the AC component to ensure that the direct-axis current is positive.

[0025] In step 204, based on the target excitation current, the actual excitation current flowing through the electric drive system is adjusted by the motor control circuit so that the actual excitation current ib approaches the target excitation current ib*. In an embodiment where the target excitation current ib* is the target direct-axis current id*, the actual excitation current ib is correspondingly the actual direct-axis current id of the motor. While adjusting the direct-axis current id of the motor, the quadrature-axis current iq of the motor can be kept at zero by the motor control circuit, thereby eliminating motor torque and avoiding noise, vibration, and harshness (NVH) problems caused by low-order pulsating torque or safety issues caused by unexpected torque.

[0026] In some embodiments, step 204 can be accomplished through closed-loop control. (See reference...) Figure 3 , Figure 3 This is based on some embodiments of the present application. Figure 1 Circuit diagram execution Figure 2 The control block diagram for step 204 in the process.

[0027] Specifically, in the embodiment where the target excitation current ib* is the target direct-axis current id*, the target quadrature-axis current iq* is set to 0. By subtracting the target direct-axis current id* and the target quadrature-axis current iq* from the direct-axis current id_fb and quadrature-axis current iq_fb fed back by the motor's three-phase current sampling unit, respectively, the corresponding direct-axis current error signals and quadrature-axis current error signals can be obtained. These signals can then be provided to the corresponding quasi-proportional resonant (QPR) controller to generate a voltage command. This voltage command is further provided to a sinusoidal pulse width modulation (SPWM) module to generate a control signal for controlling the controllable switches in the motor control circuit, for example, for controlling the on / off states of Q1-Q6. Thus, an actual excitation current ib, close to the target excitation current ib*, is also applied to the battery.

[0028] return Figure 2In step 206, based on the voltage Vb across the battery and the actual excitation current ib, the impedance of the battery at the current frequency of the target excitation current ib* is calculated. In some embodiments, step 206 includes: performing a Fast Fourier Transform (FFT) on the voltage Vb across the battery and the actual excitation current ib, respectively; determining the voltage Vb across the battery at the current frequency (e.g., ω1) of the target excitation current and the current of the actual excitation current ib at the current frequency; and dividing the voltage by the current to obtain the impedance of the battery at the current frequency. Specifically, the FFT transforms the voltage Vb across the battery and the actual excitation current ib from the time domain to the frequency domain. Then, the amplitude and phase of the voltage Vb at a specific frequency (e.g., ω1), and the amplitude and phase of the excitation current ib at that specific frequency can be determined. Through division, the amplitude and phase of the battery impedance at that specific frequency can be obtained and stored in a storage device as values ​​on the electrochemical impedance spectrum corresponding to that specific frequency.

[0029] In step 207, it is determined whether the impedance at all frequencies in the frequency sweep requirement has been calculated. That is, it is determined whether all frequency points in the frequency sweep requirement have been traversed.

[0030] In response to the fact that not all frequency points in the frequency sweep requirement have been traversed, proceed to step 208, change the frequency of the target excitation current (e.g., change ω1 to the next frequency point ω2), and repeat steps 204 and 206 until all frequencies in the frequency sweep requirement are covered.

[0031] If the impedance at all frequencies required for the frequency sweep has been calculated, the electrochemical impedance spectrum of the battery (corresponding to the frequency sweep requirement) can be generated based on the impedance at all frequencies, thus concluding this online EIS measurement.

[0032] Next reference Figure 4 , Figure 4 The illustrated diagrams are circuit diagrams of the battery and electric drive system in a vehicle according to other embodiments of this application. Figure 4 The circuit diagram in the diagram is suitable for vehicles with higher voltage platforms (e.g., a 900V platform), and capacitor C2 is used for boost charging (e.g., from a 750V charging station). Specifically, in addition to the battery, motor control circuit, and motor windings in the vehicle, Figure 4The diagram also illustrates capacitor C1 located between the DC positive bus and the DC negative bus of the motor control circuit, and capacitor C2 located between the neutral point of the motor (e.g., the neutral point of the three-phase winding) and the DC negative bus. In this configuration, current ib can start from the positive terminal of the battery, pass sequentially through the upper bridge arm, the motor winding, switch K1, and capacitor C2, and return to the negative terminal of the battery, thus forming a loop.

[0033] Figure 2 Method 200 can also be applied to Figure 4 The circuit diagram is shown. The steps in method 200 are consistent with those described above and will not be repeated here. However, it should be noted that... Figure 4 In the case of , the target excitation current ib* is the target common-mode current i0* of the motor winding, and the target common-mode current i0* includes an AC component. For example, i0*=B*cos(ω1*t), where B is the amplitude of the AC component, ω1 is the frequency of the AC component, and t is time.

[0034] exist Figure 4 In the circuit diagram, since the components of the excitation current i0 flowing through the motor windings LA, LB, and LC are equal (e.g., all i0 / 3), it will not cause unintended rotation of the motor. Compared to keeping the motor's quadrature-axis current iq zero throughout the circuit, this may be easier to implement in terms of control and has lower requirements for sampling accuracy and control loop. The following will refer to... Figure 5 This describes the corresponding adjustments made to the control process.

[0035] Figure 5 This is based on some embodiments of the present application. Figure 4 Circuit diagram execution Figure 2 The control block diagram for step 204 is shown below. Specifically, in the embodiment where the target excitation current ib* is the target common-mode current i0*, the corresponding common-mode current error signal can be obtained by subtracting the target common-mode current i0* from the common-mode current i0_fb fed back by the motor common-mode current sampling unit. This common-mode current error signal can then be provided to the QPR controller to generate a voltage command. The voltage command is further provided to the SPWM module to generate a control signal for controlling the controllable switches in the motor control circuit, for example, for controlling the on / off state of Q1-Q6. Thus, an actual excitation current ib, close to the target excitation current ib*, is applied to the battery.

[0036] return Figure 4 It should be understood that Figure 4 The circuit diagram in the diagram also does not add any additional components for real-time online EIS measurement of the battery. Figure 4The capacitor C2 and switch K1 are actually set up for performing boost charging for the vehicle (e.g., a vehicle on a 900V platform). For example, during boost charging, the DC positive and DC negative terminals of the charging pile (not shown in the figure) can be connected to the two ends of capacitor C2 respectively, and the vehicle's battery is charged after the vehicle maintains the voltage across C2 below the maximum voltage of the charging pile (e.g., 750V) through motor closed-loop control.

[0037] Furthermore, as described above, this application can also be implemented as a computer storage medium storing instructions that, when executed, perform a program describing the method described in any of the above embodiments. Here, various types of computer storage media can be used, such as disks (e.g., magnetic disks, optical disks, etc.), cards (e.g., memory cards, optical cards, etc.), semiconductor memory (e.g., ROM, non-volatile memory, etc.), and tapes (e.g., magnetic tape, cassette tape, etc.).

[0038] Where applicable, the various embodiments provided in this application may be implemented using hardware, software, or a combination of hardware and software. Furthermore, where applicable, without departing from the scope of this application, the various hardware and / or software described herein may be combined into composite components comprising software, hardware, and / or both. Where applicable and within the scope of this application, the various hardware and / or software components described herein may be divided into sub-components comprising software, hardware, or both. Additionally, where applicable, it is contemplated that software components may be implemented as hardware components, and vice versa.

[0039] The software (such as program code and / or data) according to this application can be stored on one or more computer storage media. It is also contemplated that the software identified herein can be implemented using one or more networked and / or otherwise general-purpose or special-purpose computers and / or computer systems. Where applicable, the order of the various steps described herein can be changed, combined into compound steps, and / or divided into sub-steps to provide the features described herein.

[0040] The embodiments and examples presented herein are provided to best illustrate embodiments of this application and its particular applications, thereby enabling those skilled in the art to implement and use this application. However, those skilled in the art will understand that the above description and examples are provided for ease of illustration and example only. The descriptions presented are not intended to cover all aspects of this application or to limit this application to the precise forms disclosed.

Claims

1. A method for obtaining an electrochemical impedance spectroscopy (EIS) of a battery, applied to an electric drive system of a vehicle, the EIS being connected to a battery of the vehicle and including a motor and a motor control circuit for controlling energy transfer from the battery to the motor, the method comprising: Step 202: Determine the target excitation current based on the frequency sweep requirements of the electrochemical impedance spectroscopy; Step 204: Based on the target excitation current, adjust the actual excitation current flowing through the electric drive system through the motor control circuit so that the actual excitation current is close to the target excitation current. Step 206: Based on the voltage across the battery and the actual excitation current, calculate the battery impedance at the current frequency of the target excitation current; as well as Step 208: Change the frequency of the target excitation current, and repeat steps 204 and 206 until all frequencies required for the frequency sweep are covered.

2. The method as described in claim 1, wherein, The target excitation current is the target direct-axis current of the motor, and the actual excitation current is the actual direct-axis current of the motor. The target direct-axis current includes a DC component and an AC component.

3. The method of claim 2, further comprising: The quadrature-axis current of the motor is kept at zero by means of a motor control circuit.

4. The method of claim 1, wherein, The electric drive system also includes a first capacitor and a second capacitor. The first capacitor is located between the DC positive bus and the DC negative bus of the motor control circuit, and the second capacitor is located between the neutral point of the motor and the DC negative bus.

5. The method of claim 4, wherein, The target excitation current is the target common-mode current of the motor winding, and the target common-mode current includes an AC component.

6. The method of claim 1, wherein, Step 206 includes: Perform fast Fourier transform on the voltage across the battery and the actual excitation current respectively. Determine the voltage across the battery at the current frequency of the target excitation current and the actual excitation current at that current frequency; and Divide the voltage by the current to obtain the battery impedance at the current frequency.

7. A vehicle comprising a battery and an electric drive system connected to the battery, the electric drive system comprising: An electric motor, which includes multiple windings; A motor control circuit configured to control energy transfer from a battery to a motor, and comprising multiple bridge arms connected in parallel between a DC positive bus and a DC negative bus, wherein the midpoint of each of the multiple bridge arms is connected to a corresponding winding of an electrode. as well as The controller is configured to perform the following steps: Step 202: Determine the target excitation current based on the frequency sweep requirements of the electrochemical impedance spectroscopy; Step 204: Based on the target excitation current, adjust the actual excitation current flowing through the electric drive system through the motor control circuit so that the actual excitation current is close to the target excitation current. Step 206: Based on the voltage across the battery and the actual excitation current, calculate the battery impedance at the current frequency of the target excitation current; as well as Step 208: Change the frequency of the target excitation current, and repeat steps 204 and 206 until all frequencies required for the frequency sweep are covered.

8. The vehicle as claimed in claim 7 further includes a first capacitor and a second capacitor, wherein the first capacitor is located between the DC positive bus and the DC negative bus of the motor control circuit, and the second capacitor is located between the neutral point of the motor and the DC negative bus.

9. The vehicle as claimed in claim 8, wherein, The target excitation current is the target common-mode current of the motor winding, and the target common-mode current includes an AC component.

10. A computer storage medium comprising instructions that, when executed, perform the method as described in any one of claims 1-6.

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