Sampling method and system for three-phase current of motor

Abstract

The invention provides a motor three-phase current sampling method and system, and the method comprises the steps: carrying out the N times of sampling of the motor three-phase current in a control period, and calculating an arithmetic mean value, so as to obtain an initial average current, thereby effectively smoothing the random noise, and improving the signal-to-noise ratio of a signal. And furthermore, aiming at systematic amplitude attenuation which is introduced by a zero-order retainer in the system and is related to frequency, a compensation coefficient is determined based on amplitude-frequency characteristics of the systematic amplitude attenuation, the coefficient is utilized to compensate the initial average current so as to offset an inherent error, and finally a final sampling result capable of accurately restoring the real amplitude of the current is obtained. According to the method, multi-sampling and zero-order maintenance compensation are combined, so that the inherent deviation of a sampling system is corrected from the source, the current sampling precision is remarkably improved, and a solid foundation is laid for high-performance vector control of the motor.

Description

Technical Field

[0001] This invention relates to the field of new energy vehicles, and in particular to a method and system for sampling three-phase current of an electric motor. Background Technology

[0002] The current sampling stage plays a crucial role in the high-performance vector control system of permanent magnet synchronous motors. It provides the most basic current feedback signal for coordinate transformation and closed-loop regulation, which is a prerequisite for achieving precise torque and field control.

[0003] However, in practical digital control systems, the sampled current value is not the actual current at the current moment. It is affected by a series of delay factors such as sensor response, filter phase lag, analog-to-digital conversion, and digital processing. These inherent delays not only directly reduce the sampling accuracy of the current but also cause a series of deteriorations in control performance, specifically manifested as a significant increase in torque ripple, poor system stability, slow dynamic response speed, and insufficient current loop phase margin, ultimately limiting the stability and performance ceiling of the entire drive system.

[0004] Therefore, effectively suppressing or compensating for the negative impact of current sampling delay has become one of the key technical challenges in improving the dynamic performance and operating accuracy of permanent magnet synchronous electric drive systems. Summary of the Invention

[0005] In order to overcome the above-mentioned technical defects, the purpose of this invention is to provide a method and system for sampling three-phase current of a motor.

[0006] This invention discloses a method for sampling three-phase current of a motor, characterized by comprising the following steps: Within one control cycle, the three-phase current of the motor is sampled N times, where N≥3, to obtain N sampled values ​​of the current for each phase. Calculate the arithmetic mean of N sampled values ​​of the current in each phase, and use it as the initial average current of that phase; Based on the amplitude-frequency characteristics of the zero-order hold, the compensation coefficients used to compensate for the initial average current are determined. The initial average current is compensated using a compensation coefficient to obtain the final sampling result of the current in each phase.

[0007] Preferably, the control period is one complete control cycle of the PWM signal.

[0008] Preferably, all N samples are taken at the peaks or troughs of the waveform of the three-phase current.

[0009] Preferably, the amplitude-frequency characteristic of the zero-order hold is as follows: .

[0010] Preferably, the compensation coefficient is: .

[0011] Preferably, the initial average current is multiplied by the compensation coefficient to obtain the final sampling result.

[0012] A second aspect of the present invention also provides a sampling system for three-phase current of a motor, including a current sampling module and a calculation module for sampling the current; the calculation module is used to execute the sampling method as described in any of the preceding claims.

[0013] Preferably, the computing module is an MCU.

[0014] Compared with existing technologies, the above technical solution has the following advantages: 1. The motor three-phase current sampling method and system provided by this invention effectively smooths random noise and improves the signal-to-noise ratio of the current signal by performing multiple samplings and calculating the average value within a control cycle. Furthermore, based on the problem that the zero-order hold in the system causes inherent, frequency-dependent systematic amplitude attenuation of the current signal, the sampled current value is compensated to offset this error, ensuring that the final sampling result accurately reproduces the true amplitude of the current. 2. Furthermore, the sampling method provided in this application, by defining the control period as the PWM signal period, ensures strict synchronization between current sampling and the control system pulse width, effectively avoiding additional phase errors introduced by timing mismatch. Sampling at key points such as the peaks or troughs of the current waveform maximizes the capture of current amplitude information, providing a high-quality data foundation for subsequent compensation. Accurate modeling of the zero-order hold amplitude-frequency characteristics, implemented through simple multiplication operations, enables high-precision error correction to operate stably in various general-purpose microcontrollers (MCUs) with extremely low computational burden. Finally, this series of methods is integrated into a complete sampling system, transforming this sampling method into a tangible product that can be directly applied to complete vehicles. Attached Figure Description

[0015] Figure 1 A schematic diagram of the actual current and sampled current data in the motor three-phase current sampling method provided in this application; Figure 2 A flowchart illustrating the method for sampling the three-phase current of a motor provided in this application; Figure 3 The flowchart illustrates the algorithm for the sampling method of the three-phase current of the motor provided in this application. Detailed Implementation

[0016] The advantages of the present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments.

[0017] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0018] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0019] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0020] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0022] In the following description, suffixes such as "module," "part," or "unit" used to denote elements are used only for the convenience of the description of the invention and have no specific meaning in themselves. Therefore, "module" and "part" can be used interchangeably.

[0023] Please see Figures 1-3 , Figure 1 A schematic diagram of the actual current and sampled current data in the motor three-phase current sampling method provided in this application; Figure 2 A flowchart illustrating the method for sampling the three-phase current of a motor provided in this application; Figure 3 The flowchart illustrates the algorithm for the sampling method of the three-phase current of the motor provided in this application.

[0024] like Figures 1-3 As shown, this invention discloses a method for sampling the three-phase current of a motor, characterized by comprising the following steps: Within one control cycle, the three-phase current of the motor is sampled N times, where N≥3, to obtain N sampled values ​​of the current for each phase. Calculate the arithmetic mean of N sampled values ​​of the current in each phase, and use it as the initial average current of that phase; Based on the amplitude-frequency characteristics of the zero-order hold, the compensation coefficients used to compensate for the initial average current are determined. The initial average current is compensated using a compensation coefficient to obtain the final sampling result of the current in each phase.

[0025] The principle needs to be explained here: such as Figure 1 As shown, in a digital control system, the discrete points sampled by the current sensor need to be reconstructed into a continuous stepped signal using a zero-order hold for the controller to use. The essence of a zero-order hold is to "hold" the value of a sampled point until the next sampled point arrives.

[0026] This "holding" behavior is a rectangular wave in the time domain and equivalent to a low-pass filter in the frequency domain. Its amplitude-frequency response curve (i.e., the system's gain for signals of different frequencies) is not a flat straight line, but a "Sinc function" shape that gradually decays as the frequency increases.

[0027] This leads to critical sampling errors: firstly, attenuation of the fundamental current: the fundamental component of the motor current is not zero in frequency. Therefore, even for the fundamental current, the zero-order hold will cause some amplitude measurement attenuation. Secondly, severe attenuation and distortion of harmonic currents: the harmonic components contained in the current have higher frequencies. According to the above principle, the higher the frequency, the more severe the attenuation. This results in the harmonic amplitude of the current sampled by the control system being much lower than the true value, significantly reducing the effectiveness of control strategies such as harmonic suppression.

[0028] Therefore, this application effectively smooths random noise and improves the signal-to-noise ratio of the current signal by performing multiple samplings and calculating the average value within a control cycle. Furthermore, based on the problem that the zero-order hold in the system causes an inherent, frequency-dependent systematic amplitude attenuation of the current signal, the sampled current value is compensated to offset this error, thereby ensuring that the final sampling result accurately reproduces the true amplitude of the current.

[0029] The above is an explanation of the basic concept of the sampling method provided in this application. The specific implementation of the method will be described in detail below.

[0030] First, it should be noted that there are no restrictions on the specific sampling period and time.

[0031] In one possible implementation, the control period is one complete control cycle of the PWM signal.

[0032] By explicitly defining the control cycle as a complete cycle of the PWM signal, this scheme ensures that the current sampling process remains strictly synchronized with the core modulation rhythm of the motor control system. This synchronization mechanism effectively avoids additional phase delays or errors introduced by mismatches between the sampling timing and the control cycle, allowing the sampled current data to more accurately reflect the motor state under the current control action. This enhances the accuracy of current harmonic component analysis, providing a reliable guarantee for achieving smoother torque output and faster dynamic response.

[0033] In one possible implementation, the N samples are all located at the peaks or troughs of the waveform of the three-phase current.

[0034] By precisely positioning sampling points at the peaks or troughs of the current waveform, targeted capture of key current characteristic points is achieved. Since these points contain the most critical information about the current amplitude and typically have a high signal-to-noise ratio, this sampling strategy maximizes the extraction of effective current signal energy. This helps to more accurately reconstruct the actual current amplitude in complex electromagnetic environments, and is particularly beneficial for suppressing potential interference at non-characteristic points, thus providing higher-quality raw data for further precise compensation and control.

[0035] Once relatively accurate sampling data is obtained, the sampling data can be compensated: like Figures 2-3 As shown, in one possible implementation, the amplitude-frequency characteristic of the zero-order hold is: .

[0036] in, The amplitude gain of the zero-order hold. Let ω be the sampling period of the system and ω be the angular frequency of the input signal. By modeling this characteristic, the system can clearly understand the gain changes experienced by the signal at different frequencies, laying a solid theoretical foundation for achieving targeted and accurate amplitude compensation.

[0037] Transforming the above equation, we can further obtain the compensation coefficient as follows: .

[0038] Furthermore, the initial average current is multiplied by the compensation coefficient to obtain the final sampling result.

[0039] In summary, this compensation coefficient directly corrects for the amplitude attenuation caused by sample-and-hold operations, effectively restoring the true amplitude of the current signal at its fundamental and key harmonic frequencies. This precise mathematical compensation overcomes the inherent distortion problem in traditional sampling methods, significantly reducing the amplitude error of current measurement. This allows the control system to make decisions based on more realistic current feedback, thereby effectively reducing torque ripple and improving the smoothness of motor operation. This linear compensation method requires no complex iteration or transformation process, has a low computational burden, and low processor requirements, enabling the high-precision current sampling compensation algorithm to run in real time on common microcontrollers. It ensures the speed and reliability of the compensation process, making it ideal for motor control applications with extremely high real-time requirements.

[0040] The above is a complete description of one embodiment of a method for sampling three-phase current of a motor provided in this application.

[0041] A second aspect of the present invention also provides a sampling system for three-phase current of a motor, including a current sampling module and a calculation module for sampling the current; the calculation module is used to execute the sampling method as described in any of the foregoing embodiments.

[0042] Furthermore, the computing module is an MCU.

[0043] As mentioned above, the sampling method provided in this application has a low computational burden, and therefore can run stably on various general-purpose microcontrollers (MCUs). This allows the method to be transformed into a tangible product that can be directly applied to a vehicle, thereby enhancing the vehicle's driving performance.

[0044] It should be noted that the embodiments of the present invention have better implementability and are not intended to limit the present invention in any way. Any person skilled in the art may use the above-disclosed technical content to change or modify it into equivalent effective embodiments. However, any modifications or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method of sampling three-phase currents of an electric machine, characterized in that, The method comprises the following steps: In a control period, N times of sampling are performed on three-phase currents of the motor, N≥3, to obtain N sampling values of each phase current; An arithmetic mean value of the N sampling values of each phase current is calculated as an initial average current of the phase; A compensation coefficient for compensating the initial average current is determined based on the amplitude-frequency characteristic of a zero-order holder; The initial average current is compensated by using the compensation coefficient to obtain a final sampling result of each phase current.

2. The sampling method of claim 1, wherein, The control period is one complete control period of a PWM signal.

3. The sampling method of claim 1, wherein, The N times of sampling are all located at a peak or a trough of a waveform of the three-phase currents.

4. The sampling method of claim 1, wherein, The amplitude-frequency characteristic of the zero-order hold is: .

5. The sampling method of claim 4, wherein, The compensation coefficient is: .

6. The sampling method of claim 5, wherein, The initial average current is multiplied by the compensation coefficient to obtain the final sampling result.

7. A system for sampling three-phase currents of an electric machine, characterized in that The sampling system comprises a current sampling module for sampling the current and a calculation module; the calculation module is configured to perform the sampling method according to any one of claims 1-6.

8. The sampling system of claim 7, wherein, The calculation module is an MCU.

Images