Battery impedance identification method, system and electric vehicle

Abstract

This invention discloses a battery impedance identification method, system, and electric vehicle. The method includes: identifying the target angular frequency set {2ω1, 2ω2, ..., 2ω...}. n ,ω2-ω1,...,ω n -ω n‑1 ,ω1+ω2,...,ω n‑1 +ω n |ω1<ω2<...<ω n The current signal is determined to acquire the current of each phase of the drive motor load and the rotor position information. After coordinate transformation, the zero-axis current i0 of the load in the synchronous rotating coordinate system is obtained. The current signal and the zero-axis current command value are acquired and input into the zero-axis current regulator. The output of the zero-axis current regulator controls the drive inverter to make the zero-axis current i0 follow the current signal. After the current signal is injected and a steady state is reached, the voltage u across the power battery to be tested is acquired. bat With current i bat By using frequency domain analysis to obtain the voltage and current phasors at the target angular frequency, the battery impedance at that frequency is calculated. By injecting an excitation signal with controllable amplitude and frequency into the battery through the zero-axis control degree of the drive inverter, online or offline battery impedance identification can be achieved without affecting load operation.

Description

Technical Field

[0001] This invention belongs to the field of battery impedance detection technology, and more specifically, relates to a battery impedance identification method, system, and electric vehicle based on the zero-axis control degree of freedom of the drive inverter. Background Technology

[0002] High-voltage battery packs typically consist of dozens or even hundreds of cells connected in series and parallel. However, during operation, if even one cell experiences thermal runaway, the fault will propagate rapidly, causing the entire battery system to catch fire, explode, and release toxic gases within a very short time. Causes of battery thermal runaway include potential defects, mechanical abuse, electrical abuse, thermal abuse, and electrochemical abuse; over 90% of thermal runaways are accompanied by internal short circuits within the battery. Battery management based on online impedance monitoring can effectively identify short-circuit possibilities at an early stage, thereby preventing battery thermal runaway and showing broad application prospects.

[0003] Currently, battery impedance identification methods are mainly divided into two categories.

[0004] One type requires additional hardware circuitry to provide a separate excitation signal. For example, patent CN115267584A achieves the measurement of the impedance spectrum of each individual cell within the battery system by bypassing a parallel current disturbance generation circuit in the battery system and installing a cell impedance spectrum time-division multiplexing measurement circuit in each battery pack. Patent CN213457292U discloses a measurement device for the electrochemical impedance spectrum of an embedded battery for electric vehicles, the device including a central signal processor, a transceiver controller, and multiple analog signal front-ends. Considering the application scenarios of high-voltage batteries, adding additional hardware devices is costly and difficult to meet electromagnetic compatibility requirements.

[0005] Another type is based on generating an excitation signal for impedance identification using existing hardware. For example, patent CN115047366A uses a charging power supply to realize online detection of battery AC impedance, which does not require additional hardware, saves costs, and has little impact on the battery system. However, this method still has the following limitations: (1) The application scenario is limited to when connected to a charging power supply, and it cannot be used when discharging; (2) The excitation signal comes from a PWM carrier, which can only obtain impedance at the kHz frequency and cannot obtain a complete impedance spectrum including the mid and low frequencies; (3) The amplitude of the excitation signal depends on the carrier frequency and the charger hardware design, and is not arbitrarily adjustable. When the battery impedance is low, the response signal is difficult to meet the signal-to-noise ratio requirements; (4) Harmonic pollution is inevitably generated on the load side, affecting the normal operation of the load. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a battery impedance identification method, system, and electric vehicle based on the zero-axis control degree of freedom of the drive inverter. The purpose is to inject an excitation signal with controllable amplitude and frequency into the battery through the zero-axis control degree of freedom of the drive inverter, thereby achieving online or offline battery impedance identification without affecting load operation.

[0007] To achieve the above objectives, according to one aspect of the present invention, a battery impedance identification method based on the zero-axis control degree of freedom of a drive inverter is provided, comprising:

[0008] Based on the target angular frequency set {2ω1, 2ω2, ..., 2ω} n ,ω2-ω1,...,ω n -ω n-1 ,ω1+ω2,..…,ω n-1 +ω n |ω1<ω2<...<ω n Determine the current signal to be injected. Among them, amplitude A k The values ​​are chosen to ensure that the battery cells are in a quasi-linear state and that the voltage response at at least some target angular frequencies meets the signal-to-noise ratio requirements, phase It can be any value;

[0009] The load current of each phase and rotor position information of the drive motor are obtained, and the zero-axis current i0 of the load in the synchronous rotating coordinate system is obtained by coordinate transformation.

[0010] Acquire current signal and zero-axis current command value The zero-axis current regulator is input, and the output of the zero-axis current regulator controls the inverter to make the zero-axis current i0 follow the input.

[0011] When the current current signal is injected After reaching a steady state, the voltage u across the power battery under test is acquired. bat With current i bat The voltage phasor at the angular frequency of the target to be identified is obtained through frequency domain analysis. Current phasor Based on voltage phasors Current phasor Calculate the battery impedance at the angular frequency of the target to be identified.

[0012] In one embodiment, the acquisition of the current signal and zero-axis current command value The zero-axis current regulator is input, and the output of the zero-axis current regulator controls the inverter to make the zero-axis current i0 follow the input. include:

[0013] Method 1: Input to the zero-axis current regulator, and control the inverter through the output of the zero-axis current regulator to make the zero-axis current i0 follow the input.

[0014] or,

[0015] Method 2: Set the zero-axis current command value The first regulating branch of the input zero-axis current regulator will input the current signal. The second regulating branch of the input zero-axis current regulator controls the inverter through the total output of the two regulating branches of the zero-axis current regulator. Follow the zero-axis current command value make Follow current signal

[0016] In one embodiment, method 2 includes:

[0017] Method 2-1: The first regulating branch of the zero-axis current regulator is a proportional-integral controller, and the second regulating branch is a proportional-resonant controller;

[0018] or,

[0019] Method 2-2: The first regulating branch of the zero-axis current regulator is a proportional-integral controller, and the second regulating branch is a proportional-multiresonant controller.

[0020] In one embodiment, when the current signal When the signal is a single frequency and the injection frequency ω1 does not exceed 10Hz, select mode 1; where the zero-axis current regulator in mode 1 is a proportional-integral controller.

[0021] In one embodiment,

[0022] When current signal When the signal is a single frequency and the injection frequency exceeds 10Hz, select mode 2-1;

[0023] When current signal For multi-frequency signals, select mode 2-2.

[0024] In one embodiment,

[0025] When the zero-axis current i0 of the load in the synchronous rotating coordinate system is obtained through coordinate transformation, the current components in other axes in the synchronous rotating coordinate system are also obtained.

[0026] When the battery discharges, the current signal While performing control, the current command values ​​of other axes in the synchronous rotating coordinate system are also input to the corresponding axial current regulators. The output of the other axial current regulators controls the drive inverter to complete the closed-loop control of the load current.

[0027] In one embodiment, when the current current signal is completed The voltage u across the power battery to be tested during injection bat With current i bat After sampling, update the target angular frequency set to be identified and update the current signal. Reinject a new current signal After reaching a steady state, the voltage u across the power battery under test is acquired. bat With current i bat Repeat the process to obtain the battery impedance at multiple target angular frequencies to be identified.

[0028] According to a second aspect of the present invention, a battery impedance identification system based on the zero-axis control degree of freedom of a drive inverter is provided, comprising:

[0029] The current signal construction unit is used to construct the target signal based on the set of angular frequencies to be identified {2ω1, 2ω2, ..., 2ω}. n ,ω2-ω1,...,ω n -ω n-1 ,ω1+ω2,...,ω n-1 +ω n |ω1<ω2<...<ω n Determine the current signal to be injected. Among them, amplitude A k This ensures that the battery cells are in a quasi-linear state and that the voltage response at at least some target angular frequencies meets the signal-to-noise ratio requirements, phase... It can be any value;

[0030] The calculation unit is used to obtain the current of each phase of the drive motor load and the rotor position information, and obtain the zero-axis current i0 of the load in the synchronous rotating coordinate system through coordinate transformation.

[0031] Zero-axis current regulator, used to acquire current signal and zero-axis current command value The inverter is driven by output control to make the zero-axis current i0 follow the output.

[0032] Impedance analysis unit, when the current current signal is injected After reaching a steady state, the voltage u across the power battery under test is acquired. bat With current i bat The voltage phasor at the angular frequency of the target to be identified is obtained through frequency domain analysis. Current phasor Based on voltage phasors Current phasor Calculate the battery impedance at the angular frequency of the target to be identified.

[0033] In one embodiment, the zero-axis current regulator is used to obtain The inverter is driven by output control to make the zero-axis current i0 follow the output. Alternatively, the zero-axis current regulator has a first adjustment branch and a second adjustment branch, wherein the first adjustment branch is used to obtain the zero-axis current command value. The second adjustment branch is used to acquire the current signal. The total output of the two regulating branches controls the drive inverter to enable... Follow the zero-axis current command value make Follow current signal

[0034] According to a third aspect of the invention, an electric vehicle is provided, including a drive motor, a drive inverter, a power battery, and a controller, wherein the controller includes the battery impedance identification system based on the zero-axis control degree of freedom of the drive inverter as described above.

[0035] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0036] (1) When performing battery impedance identification, the present invention can set the injected current signal according to the target angular frequency of the excitation signal to be identified. Different injected current signals will result in different excitation signals applied to the battery. Therefore, when performing impedance identification, the amplitude and frequency of the excitation signal can be controlled, and an arbitrary waveform excitation signal can be designed to match the impedance identification requirements.

[0037] (2) When performing impedance identification, the present invention utilizes a drive inverter with zero-axis control degree of freedom. The current signal is injected through the zero-axis control degree of freedom of the drive inverter to generate an excitation signal. No additional hardware device is required to generate the excitation signal. It has good electromagnetic compatibility performance, low cost, and high reliability.

[0038] (3) When performing impedance identification, the frequency range that can be identified by the present invention can be kHz and below, which can meet the impedance identification needs of most batteries.

[0039] (4) The present invention does not affect the torque of the drive motor load when performing impedance identification.

[0040] (5) The present invention can identify battery impedance during the operation of the drive motor, for monitoring the battery safety status and working status, and provide data reference for improving battery operating efficiency and safety;

[0041] (6) The present invention can inject an AC excitation signal of any frequency at any time during the operation of the drive motor, which is flexible and fast.

[0042] (7) This invention is applicable to battery-powered resistive-inductive load power systems and is not limited by the number of load phases. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of an online impedance detection system for vehicle-mounted power batteries according to one embodiment;

[0044] Figure 2 This is a circuit diagram of an embodiment of an on-board power battery, drive inverter, and drive motor.

[0045] Figure 3 This is a flowchart illustrating the steps of a battery impedance identification method based on the zero-axis control degree of freedom of a drive inverter, according to one embodiment.

[0046] Figure 4(a) is a schematic diagram of load current control using a PI controller that is shared by the injected current and the zero-axis reference current during motor operation in one embodiment.

[0047] Figure 4(b) is a schematic diagram of load current control using a PR controller for the injected current during motor operation in one embodiment;

[0048] Figure 4(c) is a schematic diagram of load current control using a PI-MRS controller for the injected current during motor operation in one embodiment.

[0049] Figure 5 A schematic diagram of the current vector of a surface-mount permanent magnet synchronous motor when an injected current signal is applied, according to one embodiment.

[0050] Figure 6 A schematic diagram of the current vector of a built-in permanent magnet synchronous motor when an injected current signal is received, according to one embodiment.

[0051] Figure 7 A time-domain waveform diagram of battery current for online identification of 1Hz-1kHz impedance spectrum of vehicle power battery in one embodiment;

[0052] Figure 8 The figure shows the time-domain waveform of the battery voltage flow (most DC components are filtered out) for online identification of the impedance spectrum of an on-board power battery in the range of 1Hz to 1kHz, as an example of one embodiment.

[0053] Figure 9 The comparison results of online identification amplitude-frequency characteristics of impedance spectrum of vehicle power battery in 1Hz to 1kHz are presented in one embodiment.

[0054] Figure 10 The results show the comparison of phase frequency characteristics of online impedance spectrum identification of vehicle power battery in the 1Hz-1kHz range, as an example. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0056] To facilitate understanding of this invention, the system architecture for battery impedance identification will first be introduced using an electric vehicle as an example.

[0057] The drive motor, drive inverter, and power battery are the three most crucial components of an electric vehicle's power system. For example... Figure 1 In China, power batteries typically consist of dozens or hundreds of lithium-ion battery cells connected in series and parallel. The drive inverter employs a series winding topology with zero-axis current control capability, and its structure is as follows: Figure 2 As shown. The drive motor is typically a permanent magnet synchronous motor, which has advantages such as high energy density, high power factor, and high efficiency. The controller is responsible for data acquisition and calculation, and the implementation of control algorithms. The power battery converts the stored chemical energy into electrical energy, which is output to the drive inverter, converting direct current into alternating current, and then into the mechanical energy of the motor to drive its operation. However, during the energy release process of the power battery, non-ideal reactions may occur inside the battery, leading to battery aging or even thermal runaway and fire accidents. Changes in battery impedance can sensitively monitor abnormalities in the internal physicochemical structure of the battery, react to the occurrence of the above situations, provide timely warnings of accidents, and prevent the escalation of faults and serious losses.

[0058] This invention is based on inverters with zero-axis control freedom (including but not limited to series winding, open winding, asymmetrical half-bridge, asymmetrical full-bridge, etc. topologies) and resistive-inductive loads (including but not limited to motors, magnetic bearings, etc.). By injecting an excitation signal with controllable amplitude and frequency into the battery through the inverter's zero-axis control freedom, it achieves online or offline battery impedance identification. Figure 2 As shown.

[0059] like Figure 3 The diagram shows the steps of a battery impedance identification method based on the zero-axis control degree of freedom of a drive inverter. It mainly includes the following steps. It should be noted that the order of these steps is only one possible implementation and is not limited to any particular order.

[0060] Step S100: Based on the target angular frequency set {2ω1, 2ω2, ..., 2ω...} n ,ω2-ω1,…..,ω n -ω n-1 ,ω1+ω2,...,ω n-1 +ω n |ω1<ω2<...<ω n Determine the current signal to be injected.

[0061] Where n≥1, amplitude A k The selected values ​​ensure that the battery cells are in a quasi-linear state and that the voltage response meets the signal-to-noise ratio (SNR) requirement at at least some target angular frequencies. If there are too many target angular frequencies, it may be impossible for the battery's voltage response to meet the SNR requirement at every single target angular frequency. In this case, it is sufficient to ensure that the condition is met at some angular frequencies, and subsequent impedance analysis will only focus on the impedance at the target angular frequencies that meet this condition. The phase value is used to determine the phase. This can be any value. Once the application device is determined, the voltage response signal-to-noise ratio requirement is also determined.

[0062] When n=1, it means that the target angular frequency set to be identified has only one element, namely {2ω1}, where 2ω1 is the angular frequency of the excitation signal applied to the battery after the injected current signal. After applying the excitation signal, the battery impedance at angular frequency 2ω1 can be obtained by measurement and calculation. At this time, the injected current signal... This refers to a single-frequency injected signal.

[0063] When n>1, it indicates that the target angular frequency set to be identified has multiple elements. In this case, the injected current signal is... This refers to a multi-frequency injection signal. After the current signal is injected, the number of angular frequencies of the excitation signal applied to the battery is 3n-2, which are the various angular frequencies in the target angular frequency set. As long as the target angular frequency to be identified is within the target angular frequency set, the current signal can be used.

[0064] The lower limit of the identifiable target frequency depends on the battery system's operating conditions (battery charge / discharge rate). The choice between single-frequency and multi-frequency signal injection can be made based on the identification time. Specifically, if the battery is offline or operating online with very low charge / discharge current (i.e., the battery state is approximately quasi-steady), impedance identification at a lower frequency (below 1Hz) can be performed. To save identification time, multiple frequency current signals can be injected simultaneously to generate multiple low-frequency excitation signals. If the battery is operating online with high current charge / discharge, low-frequency impedance identification takes too much time and cannot guarantee that the battery system is in a quasi-steady state during this period; therefore, spending a long time on low target frequency impedance identification is not recommended.

[0065] Step S200: Obtain the current of each phase of the drive motor load and the rotor position information, and obtain the zero-axis current i0 of the load in the synchronous rotating coordinate system through coordinate transformation.

[0066] Specifically, sampling can be performed using Hall current sensors, sampling resistors, etc., to measure the current of each phase of the drive motor load, or the data to be measured can be read directly through a data acquisition board.

[0067] Taking three-phase current as an example, obtain the three-phase current i of the drive motor load. a i b i c And the rotor electrical angle θ, through Park coordinate transformation, yields the load direct-axis current i. d Cross-axis current i q And the zero-axis current i0. The rotor electrical angle θ is measured by sensors such as rotary transformers or optical encoders.

[0068] Step S300: Acquire current signal and zero-axis current command value The zero-axis current regulator is input, and the output of the zero-axis current regulator controls the inverter to make the zero-axis current i0 follow the input.

[0069] Specifically, it can be divided into the following methods:

[0070] Method 1, as shown in Figure 4(a), for the current signal and zero-axis current command value After summing, Using the zero-axis current i0 as the input and the zero-axis current i0 as the feedback, the output of the zero-axis current regulator controls the inverter, causing the zero-axis current i0 to follow... Specifically, the zero-axis current regulator is a proportional-integral (PI) controller.

[0071] Method 2: Using current signals respectively and zero-axis current command value As input, the zero-axis current command value The first regulating branch of the input zero-axis current regulator will input the current signal. The second regulating branch of the input zero-axis current regulator controls the inverter through the total output of the two regulating branches of the zero-axis current regulator. Follow the zero-axis current command value make Follow current signal

[0072] The first and second adjustment branches can have different structures, but both essentially achieve zero-axis current i0 following. For example, you can choose from the following two settings:

[0073] Method 2-1: As shown in Figure 4(b), the first regulating branch of the zero-axis current regulator is a proportional-integral controller (PI controller), and the second regulating branch is a proportional-resonant controller (PR controller). The zero-axis current command value is used... For the input of the proportional-integral controller, with For feedback; using current signal As the input of the proportional resonant controller, with For feedback, the sum of the outputs of the proportional-integral controller and the proportional-resonant controller serves as the output of the zero-axis current regulator. The output of the zero-axis current regulator controls the inverter to ensure that each feedback quantity follows its corresponding input quantity. Follow the zero-axis current command value make Follow current signal

[0074] Method 2-2: As shown in Figure 4(c), the first regulating branch of the zero-axis current regulator is a proportional-integral controller (PI controller), and the second regulating branch is a proportional-multiresonant controller (PI-MRS controller). The zero-axis current command value is... For the input of the proportional-integral controller, with For feedback; using current signal For the input of the proportional-multiresonant controller, with For feedback, the sum of the outputs of the proportional-integral controller and the proportional-multiresonant controller serves as the output of the zero-axis current regulator. The output of the zero-axis current regulator controls the inverter to ensure that each feedback quantity follows its corresponding input quantity. Follow the zero-axis current command value make Follow current signal

[0075] In one embodiment, different methods can be selected depending on the situation. When the current signal is a single-frequency signal or the injection frequency does not exceed 10Hz, method 1 is selected. When the current signal is a single-frequency signal or the injection frequency exceeds 10Hz, method 2-1 is selected; when the current signal is a multi-frequency signal, method 2-2 is selected. Matching different methods to different situations can improve the processing effect of different signals.

[0076] Understandably, when the battery is offline or charging, there is no need to control the current components along the axes other than the zero axis in the synchronous rotating coordinate system; only the injection along the zero axis needs to be controlled as described above. When the battery is discharging, the injected current signal... Simultaneously, current command values ​​for other axes in the synchronous rotating coordinate system are input to the corresponding axial current regulators. The output of these other axial current regulators controls the inverter to complete closed-loop control of the load current. For example, for a three-phase load, the DC current command value will also be... The input DC current regulator controls the inverter through its output to ensure the direct-axis current i... d Follow DC current command value And, the quadrature axis current command value The input AC current regulator controls the inverter through its output to make the quadrature axis current i q Follow the quadrature axis current command value For example, the output u of the DC current regulator d The output quantity u of the AC current regulator q The output u0 of the zero-axis current regulator is input to the space vector modulator. Through the space vector modulation algorithm, the duty cycle of each phase bridge arm of the drive inverter is calculated to obtain the drive signal for controlling the drive inverter. Pulse width modulation is then performed to control the load current.

[0077] During normal load operation, the system control chip (controller) directly receives the switch signal or calculates and generates the drive current command I from the sensor signal. d * I q * I0 * .

[0078] The following analysis examines the impact of the injected current signal on the entire system.

[0079] Analyzing the injected current signal using the above method Then, an AC excitation can be applied to the battery:

[0080]

[0081] Among them, U bat I bat These are the DC components of the battery voltage and current, respectively. These are the AC components of the battery voltage and current, respectively, P. cap The power supplied by the supporting capacitor connected in parallel with the battery, R and L are the resistance and inductance of each phase load, respectively, and P loss This refers to inverter losses.

[0082] ia i b i c For the three-phase load current, the expression is as follows:

[0083]

[0084] Where A is the fundamental amplitude, which is the AC current of each phase when the drive motor is running stably. ω is the fundamental frequency.

[0085] Because the battery has extremely low internal resistance, neglect That is to say:

[0086]

[0087] If the injected current signal For a single-frequency signal, i.e., n=1, combining formulas (1) to (3), we can obtain:

[0088]

[0089] As can be seen from equation (4), the battery is injected with AC excitation current. The excitation current contains a component with an angular frequency of 2ω1; therefore, the impedance at this angular frequency can be obtained during subsequent impedance analysis. Meanwhile, although... The existence will introduce and Coupling terms between when When it is a constant, The frequency is ω1. Because P loss The existence of There exist a small number of harmonics with an angular frequency of ω, the amplitude of which is related to P. loss The amplitude is positively correlated and has no effect on impedance identification.

[0090] If the injected current signal For a multi-frequency signal, i.e., n>1, it can be similarly deduced that the AC excitation current contains 2ω1, 2ω2, ..., 2ω n ,ω2-ω1,...,ω n -ω n-1 ,ω1+ω2,...,ω n-1 +ω n These frequency components allow for the acquisition of impedance at various angular frequencies during subsequent impedance analysis, enabling impedance identification at multiple frequencies through a single injection.

[0091] Step S400: When the current current signal is injected After reaching a steady state, the voltage u across the power battery under test is acquired. batWith current i bat The voltage phasor at the angular frequency of the target to be identified is obtained through frequency domain analysis. Current phasor Based on voltage phasors Current phasor Calculate the battery impedance at the angular frequency of the target to be identified.

[0092] Specifically, the current current signal can be injected. After reaching a steady state, continue injection for at least two more cycles and acquire the voltage u across the power battery under test. bat With current i bat End the signal injection. Specifically, anti-aliasing filtering can be applied to the voltage and current of the battery (system, module, or individual cell) under test, with a filter cutoff frequency of f. c Then measure the voltage u across the filtered battery. bat With current i bat Hall voltage and Hall current sensors can be used for sampling respectively, with a sampling frequency f. s Satisfy f s >2.56f c .

[0093] After obtaining the voltage u at both ends of the power battery to be tested bat With current i bat After the current current signal injection ends, the target angular frequency set to be identified can be updated and steps S100 to S400 can be re-executed. This process is repeated to obtain the battery voltage u at a large number of target angular frequencies. bat With current i bat This allows for the calculation of impedance at a large number of target angular frequencies, forming an impedance spectrum.

[0094] For the voltage u that reaches steady state bat With current i bat Frequency domain analysis (such as Fourier decomposition) is performed to obtain the voltage and current phasors at the target angular frequency. and The battery impedance at the target angular frequency is

[0095] Accordingly, the present invention also relates to a battery impedance identification system based on the zero-axis control degree of freedom of a drive inverter, comprising:

[0096] The current signal construction unit is used to construct the target signal based on the set of angular frequencies to be identified {2ω1, 2ω2, ..., 2ω...} n ,ω2-ω1,………,ω n -ω n-1 ,ω1+ω2,………,ω n-1 +ωn |ω1<

[0097] ω2<………<ω n Determine the current signal to be injected. Among them, amplitude A k This ensures that the battery cells are in a quasi-linear state and that the voltage response at at least some target angular frequencies meets the signal-to-noise ratio requirements, phase... It can be any value;

[0098] The calculation unit is used to obtain the current of each phase of the drive motor load and the rotor position information, and obtain the zero-axis current i0 of the load in the synchronous rotating coordinate system through coordinate transformation.

[0099] Zero-axis current regulator, used to acquire current signal and zero-axis current command value The inverter is driven by output control to make the zero-axis current i0 follow the output.

[0100] Impedance analysis unit, when the current current signal is injected After reaching a steady state, the voltage u across the power battery under test is acquired. bat With current i bat The voltage phasor at the angular frequency of the target to be identified is obtained through frequency domain analysis. Current phasor Based on voltage phasors Current phasor Calculate the battery impedance at the angular frequency of the target to be identified.

[0101] Furthermore, the zero-axis current regulator is used to obtain The inverter is driven by output control to make the zero-axis current i0 follow the output. Alternatively, the zero-axis current regulator has a first regulating branch and a second regulating branch, the first regulating branch being used to obtain the zero-axis current command value. The second adjustment branch is used to acquire the current signal. The total output of the two regulating branches controls the drive inverter to enable... Follow the zero-axis current command value make Follow current signal

[0102] Understandably, this identification system can perform the identification process described above, and its various functional modules can perform corresponding steps, as described above, and will not be repeated here.

[0103] Accordingly, the present invention also relates to an electric vehicle, as described above, comprising a drive motor, a drive inverter, a power battery, and a controller, wherein the controller comprises the aforementioned battery impedance identification system based on the zero-axis control degree of freedom of the drive inverter.

[0104] The following is a specific embodiment illustrating the process of performing online impedance testing during motor operation.

[0105] When the motor is running, sample the three-phase current i of the motor. a i b i c , and the motor rotor position information θ.

[0106] The controller calculates the direct-axis, quadrature-axis, and zero-axis currents i based on the three-phase currents and the motor rotor position information. d i q 、i0.

[0107] When the motor is running stably, it has stable direct-axis, quadrature-axis, and zero-axis currents. d =I d * i q =I q * i0 = I0 * , Figures 4(a) to 4(c) The control block diagram shown only operates the PI controllers on the d, q, and zero axes to ensure that the current follows the command current I without steady-state error. d * I q * I0 * The zero-axis PR controller or PI-MRS controller is not working at this time.

[0108] The controller receives a battery impedance identification command, with an identification angular frequency of 2ω1 and an identification frequency of 2f1 = ω1 / π. The injected quadrature-axis current amplitude is A1. The selection of A1 should be as small as possible while ensuring that the battery's voltage response meets the signal-to-noise ratio requirements, in order to avoid the battery failing to meet the test conditions.

[0109] A sinusoidal current command is first generated in the PR controller on the zero axis. Set the resonant angular frequency of the PR controller to ω1, and determine other parameters according to the relevant parameters of the motor. Enable PR control and execute 4-8 injection cycles.

[0110] The direct-axis and quadrature-axis PI controllers output voltages u, respectively. d u q The zero-axis PI and PR controller outputs are summed to obtain voltage u0. Motor vector control is then performed, generating a PWM signal, which is sent to the inverter to control the switching transistors to achieve current control.

[0111] The torque expression for a surface-mounted permanent magnet synchronous motor is T = 1.5p. n ψ f i q The torque expression for a built-in permanent magnet synchronous motor is T. e =1.5P n [ψ f i q +(L d -L q )i d i q ], where p n Let ψ be the extreme logarithm. f For permanent magnet flux linkage, i q i d These represent the q-axis current and d-axis current, respectively, while the motor torque is independent of the zero-axis current i0. Through the above control, an AC excitation signal can be injected while maintaining constant motor torque. The vector diagrams for the surface-mounted permanent magnet synchronous motor and the built-in permanent magnet synchronous motor are shown below. Figure 5 , Figure 6 As shown, the current vector i oscillates on the constant torque surface, which can generate AC excitation on the power battery.

[0112] The voltage and current signals of the battery pack during impedance identification are subjected to anti-aliasing filtering and sampled. A reasonable injection duration is adopted to ensure that the excitation and response signals reach a steady state. The time-domain waveforms of the current and voltage signals of the battery under test (after filtering out most of the DC component) during impedance identification are shown below. Figure 7 , Figure 8 As shown.

[0113] Perform Fourier decomposition on the sampled signals that have reached steady state (i.e., the voltage and current signals mentioned above), and calculate the components of voltage and current at angular frequency 2ω1. Thus, the overall impedance of the battery pack at this frequency is obtained as follows:

[0114] After completing the impedance identification at frequency 2f1, repeat the above steps until the battery impedance identification for all frequencies to be measured is completed. The comparison results of the amplitude-frequency and phase-frequency characteristics of the impedance spectrum identification of on-board power batteries in the frequency range of 1Hz to 1kHz are as follows: Figure 9 , Figure 10 As shown in the figure, it can be seen that the ground impedance amplitude identified by the above method is basically matched with the true value.

[0115] Those skilled in the art will readily understand that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A battery impedance identification method based on the zero-axis control degree of freedom of a drive inverter, characterized in that, include: Based on the target angular frequency set to be identified Determine the current signal to be injected , Among them, amplitude The values ​​are chosen to ensure that the battery cells are in a quasi-linear state and that the voltage response at at least some target angular frequencies meets the signal-to-noise ratio requirements, phase It can be any value; The current of each phase of the drive motor load and the rotor position information are obtained, and the zero-axis current of the load in the synchronous rotating coordinate system is obtained through coordinate transformation. ; Acquire current signal and zero-axis current command value And input to the zero-axis current regulator, the output of the zero-axis current regulator controls the drive inverter to make the zero-axis current... follow ; When the current current signal is injected After reaching a steady state, the voltage across the power battery under test is acquired. With current The voltage phasor at the angular frequency of the target to be identified is obtained through frequency domain analysis. Current phasor Based on voltage phasors Current phasor Calculate the battery impedance at the angular frequency of the target to be identified.

2. The battery impedance identification method based on the zero-axis control degree of freedom of the drive inverter as described in claim 1, characterized in that, The acquisition of current signal and zero-axis current command value And input to the zero-axis current regulator, the output of the zero-axis current regulator controls the drive inverter to make the zero-axis current... follow ,include: Method 1: Input to the zero-axis current regulator, and control the inverter through the output of the zero-axis current regulator to ensure zero-axis current... follow ; or, Method 2: Set the zero-axis current command value The first regulating branch of the input zero-axis current regulator will input the current signal. The second regulating branch of the input zero-axis current regulator controls the inverter through the total output of the two regulating branches of the zero-axis current regulator. Follow the zero-axis current command value ,make Follow current signal .

3. The battery impedance identification method for the zero-axis control degree of freedom of the drive inverter as described in claim 2, characterized in that, Method 2 includes: Method 2-1: The first regulating branch of the zero-axis current regulator is a proportional-integral controller, and the second regulating branch is a proportional-resonant controller; or, Method 2-2: The first regulating branch of the zero-axis current regulator is a proportional-integral controller, and the second regulating branch is a proportional-multiresonant controller.

4. The battery impedance identification method based on the zero-axis control degree of freedom of the drive inverter as described in claim 2, characterized in that, When current signal A single-frequency signal and injected frequency When the frequency is no more than 10Hz, select mode 1; in mode 1, the zero-axis current regulator is a proportional-integral controller.

5. The battery impedance identification method for the zero-axis control degree of freedom of the drive inverter as described in claim 3, characterized in that, When current signal When the signal is a single frequency and the injection frequency exceeds 10Hz, select mode 2-1; When current signal For multi-frequency signals, select mode 2-2.

6. The battery impedance identification method for the zero-axis control degree of freedom of the drive inverter as described in claim 1, characterized in that, The zero-axis current of the load in the synchronous rotating coordinate system is obtained through coordinate transformation. At the same time, the current components of other axes in the synchronous rotating coordinate system are also obtained; When the battery discharges, the current signal While performing control, the current command values ​​of other axes in the synchronous rotating coordinate system are also input to the corresponding axial current regulators. The output of the other axial current regulators controls the drive inverter to complete the closed-loop control of the load current.

7. The battery impedance identification method for the zero-axis control degree of freedom of the drive inverter as described in claim 1, characterized in that, When the current current signal is completed Voltage at both ends of the power battery to be tested during injection With current After sampling, update the target angular frequency set to be identified and update the current signal. Reinject a new current signal After reaching a steady state, the voltage across the power battery under test is acquired. With current Repeat the process to obtain the battery impedance at multiple target angular frequencies to be identified.

8. A battery impedance identification system based on the zero-axis control degree of freedom of a drive inverter, characterized in that, include: Current signal construction unit, used to construct the target signal based on the set of angular frequencies to be identified. Determine the current signal to be injected , Among them, amplitude Ensure that the battery cells are in a quasi-linear state and that the voltage response at at least some target angular frequencies meets the signal-to-noise ratio requirements, phase It can be any value; The calculation unit is used to obtain the current of each phase of the drive motor load and the rotor position information, and obtain the zero-axis current of the load in the synchronous rotating coordinate system through coordinate transformation. ; Zero-axis current regulator, used to acquire current signal and zero-axis current command value And by controlling the output quantity to drive the inverter to achieve zero-axis current. follow ; Impedance analysis unit, when the current current signal is injected After reaching a steady state, the voltage across the power battery under test is acquired. With current The voltage phasor at the angular frequency of the target to be identified is obtained through frequency domain analysis. Current phasor Based on voltage phasors Current phasor Calculate the battery impedance at the angular frequency of the target to be identified.

9. The battery impedance identification system based on the zero-axis control degree of freedom of the drive inverter as described in claim 8, characterized in that, The zero-axis current regulator is used to obtain And by controlling the output quantity to drive the inverter to achieve zero-axis current. follow ; Alternatively, the zero-axis current regulator has a first adjustment branch and a second adjustment branch, wherein the first adjustment branch is used to obtain the zero-axis current command value. The second adjustment branch is used to acquire the current signal. The total output of the two regulating branches controls the drive inverter to make it so that... Follow the zero-axis current command value ,make Follow current signal .

10. An electric vehicle, comprising a drive motor, a drive inverter, a power battery, and a controller, characterized in that, The controller includes the battery impedance identification system based on the zero-axis control degree of freedom of the drive inverter as described in claim 8 or 9.

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