Smooth switching method of high frequency injection to flux linkage observer of permanent magnet synchronous motor

Abstract

The present application belongs to the field of motor position sensorless control, and particularly relates to a smooth switching method of high-frequency injection to flux observer of permanent magnet synchronous motor. The method steps are as follows: injecting a rotating high-frequency voltage vector with a ramp-up amplitude when the rotor is stationary; collecting three-phase current, transforming and extracting high-frequency current negative sequence component, and solving the rotor electric angle; after the angle convergence is determined, applying positive and negative voltage pulses to eliminate 180-degree polarity ambiguity; keeping high-frequency injection, and initializing the flux observer in the background; after the speed and angle difference value conditions are met, using a fading factor to linearly transition the phase-locked loop reference angle, synchronously reducing the high-frequency injection voltage amplitude, and closing the high-frequency injection when the fading factor is 1, and completing the switching to the flux observer mode. The present application sets the cross-fading object as the phase-locked loop reference, guarantees the continuous and smooth speed in the switching process, and avoids angle mutation and transient impact.

Description

Technical Field

[0001] This invention belongs to the field of sensorless motor control, specifically relating to a smooth switching method for high-frequency injection of a permanent magnet synchronous motor into a flux linkage observer. Background Technology

[0002] In the full operating condition coverage of motors, rotor position estimation during the stationary and zero-speed phases is a technical challenge. Under these conditions, the motor's back electromotive force (EMF) signal is extremely weak, approaching zero. This renders traditional flux linkage observers based on the back EMF principle ineffective, failing to accurately capture rotor position information and consequently affecting control accuracy and system stability. To address this issue, the industry commonly employs the high-frequency signal injection method. By injecting a specific high-frequency signal into the motor windings, the high-frequency response generated by the motor's salient pole characteristics is utilized to indirectly estimate the rotor position. This method has become the mainstream solution for position estimation under stationary and zero-speed conditions.

[0003] However, when the motor speed increases to the range where the flux linkage observer can operate normally, a mode switch from high-frequency signal injection to flux linkage observer control is required. Currently, this switching process faces a key technical bottleneck: if the timing of the switch is not accurately determined, or if the switching method is poorly designed, it can easily lead to problems such as sudden changes in rotor angle and transient impacts in the speed control loop. In severe cases, it can even cause the motor to lose synchronism, disrupting the continuity and stability of the system operation. Summary of the Invention

[0004] The smooth switching method for high-frequency injection of permanent magnet synchronous motor into the flux observer provided by the present invention can effectively solve the problems existing in the background art.

[0005] This invention provides a smooth switching method for high-frequency injection of a permanent magnet synchronous motor into a flux linkage observer, comprising the following steps:

[0006] S1. When the rotor is stationary, inject a rotating high-frequency voltage vector with an increasing amplitude ramp into the stator αβ stationary coordinate system.

[0007] S2. Collect the three-phase current and obtain the α and β axis currents through Clark transformation. Use Q parallel interleaved Goertzel windows to perform single-frequency discrete Fourier transform on the α and β axis currents respectively. Extract the negative sequence component of the high-frequency current at the injection frequency, calculate the rotor position double angle, divide by two and superimpose phase offset compensation to obtain the rotor electrical angle estimate.

[0008] S3. Perform consistency judgment on the rotor electrical angle estimation values ​​obtained by solving multiple consecutive windows. When the consecutive consistency reaches a preset number, the angle is judged to converge.

[0009] S4. After the angle convergence, apply positive and negative voltage pulses along the currently estimated d-axis. Use the magnetic circuit saturation effect to compare the amplitude of the d-axis current response corresponding to the positive and negative pulses, eliminate the 180° polarity ambiguity, and obtain the true rotor electrical angle.

[0010] S5. Maintain the high-frequency injected rotating high-frequency voltage vector, and use the obtained real rotor electrical angle as the current loop commutation reference. At the same time, run the flux observer in the background and initialize the flux of the observer with the real rotor electrical angle.

[0011] S6. Continuously monitor the motor operating status and the observer's working status. When both of the following conditions are met simultaneously and the preset number of de-jitter judgments is reached consecutively, it is determined that the crossfade switching condition is met, and proceed to the next step:

[0012] 1) The electric angular velocity of the motor exceeds the preset first threshold;

[0013] 2) Estimated observation angle output by the magnetic flux observer With high-frequency injection solution angle estimation value The difference is less than the preset second threshold;

[0014] S7. Set the de-emphasis factor k, which increases linearly from 0 to 1. The reference angle of the phase-locked loop is calculated using the following formula:

[0015]

[0016] in, This is the estimated high-frequency injection angle after filtering.

[0017] While the dilution factor k increases linearly, the target amplitude of the high-frequency injection voltage is simultaneously reduced to zero by a ramp of (1−k).

[0018] When the fade factor k reaches 1, the high-frequency injection voltage amplitude drops to zero, the high-frequency injection module is turned off, the motor is completely switched to the pure flux observer operation mode, and the entire static start-up and smooth switching process is completed.

[0019] As a further optimization of the present invention, the voltage amplitude amp injected in step S1 is implemented with an exponential approximation method to achieve soft start, and the phase step is subjected to spread spectrum jitter according to the following formula:

[0020]

[0021] in, The phase step size for each control cycle, where Δ is the jitter coefficient. The angle of the current rotating high-frequency vector in the αβ plane. This refers to the jitter frequency.

[0022] As a further optimization of the present invention, the phase offset compensation amount in step S2 is dynamically adjusted according to the rotor electric angular velocity, and linear interpolation is performed between the stationary phase offset value and the rotating phase offset value to compensate for the negative sequence component phase offset caused by the saturation of the driving current and the back electromotive force when the speed increases.

[0023] As a further optimization of the present invention, in step S2, the startup delay of the Q parallel interleaved Goertzel windows satisfies , where N is the number of sampling points in a single window, and q is the window number.

[0024] As a further optimization of the present invention, after step S4 is completed, zero voltage is output and a preset control period is maintained to discharge the residual current in the motor winding. The discharge time is not less than 3 times the electrical time constant of the motor.

[0025] As a further optimization of the present invention, in step S6, the first threshold is 60 rad / s and the second threshold is 1.0 rad.

[0026] As a further optimization of the present invention, in step S6, the current high-frequency injection solution angle estimate is continuously compared with the previous one. If the angle jumps between the two times exceed π / 2, then π is added to the current angle estimate.

[0027] This invention provides a smooth switching method for high-frequency injection into a flux linkage observer in a permanent magnet synchronous motor. By setting the crossfading object as the phase-locked loop (PLL) reference rather than the output angle, the PLL output speed remains continuous during the switching process, resulting in a smooth and reasonable switching that avoids problems such as sudden rotor angle changes and transient impacts in the speed control loop. Simultaneously, this invention also considers angle update rate and signal-to-noise ratio, eliminates the inherent 180° polarity ambiguity of the high-frequency injection method, and solves the problems of sudden voltage changes at startup and audible noise caused by concentrated energy at a single frequency. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the method flow in this embodiment;

[0029] Figure 2 This is a schematic diagram of the timing relationship of Q parallel interleaved Goertzel windows (Q=4, N=120).

[0030] Figure 3 This is a two-level transition diagram of the motor-level state machine and the high-frequency injection internal state machine;

[0031] Figure 4 This is a schematic diagram showing the changes in the phase-locked loop reference angle and the injection voltage amplitude during the high-frequency injection to the observer crossfading switching process. Detailed Implementation

[0032] like Figure 1-4 As shown, this embodiment establishes a control framework based on the αβ stationary coordinate system and the dq rotating coordinate system of the permanent magnet synchronous motor. The control loop execution frequency is adapted to the PWM carrier frequency. Through multi-level coordination of high-frequency voltage injection, signal processing, polarity discrimination, observer initialization, and crossfading switching, sensorless static start-up and smooth operation switching are achieved. The entire implementation process includes five core stages: static angle identification, polarity elimination, transition preparation, switching determination, and bumpless switching. Each stage achieves orderly transition through a state machine, ensuring the stability of the start-up process and the continuity of the switching process.

[0033] This embodiment specifically includes the following steps:

[0034] S1. When the rotor is stationary, start the high-frequency voltage injection process.

[0035] In the αβ stationary coordinate system, a rotating high-frequency voltage vector is generated in each control cycle, and its expression is as follows:

[0036]

[0037]

[0038]

[0039] in, This represents the high-frequency voltage component along the α-axis. This represents the high-frequency voltage component along the β axis. The angle of the current rotating high-frequency vector in the αβ plane. For the first One control cycle, The phase step size for each control cycle is determined by the ratio of the injection frequency to the control loop execution frequency, i.e. , For injection frequency, To control the execution frequency of the loop.

[0040] To avoid audible noise caused by sudden voltage spikes during startup, the injected voltage amplitude (amp) is soft-started using an exponential approximation method. By gradually approaching the target amplitude, the impact of voltage spikes is reduced. Simultaneously, to further disperse energy concentration at a single frequency, spread-spectrum jitter can be optionally applied to the phase step, specifically expressed as:

[0041]

[0042] Where Δ is the jitter coefficient. The jitter frequency is set to disperse the energy of the injected frequency into a narrow band range, effectively suppressing audible noise.

[0043] S2. After sampling the three-phase stator current of the motor, the α-axis current is obtained through Clark transformation. With β-axis current .against and Q parallel interleaved Goertzel windows are set up, and each window is used to perform a single-frequency discrete Fourier transform on the corresponding axis current.

[0044] The start-up delay of each Goertzel window is allocated according to the window number, so that the phases of the Q windows are parallel and interleaved, ensuring that at any given time, one window has completed full sampling accumulation, thereby increasing the angle update rate by a factor of Q while maintaining the single-window signal-to-noise ratio. Specifically, the start-up delay of the Q parallel and interleaved Goertzel windows satisfies , where N is the number of sampling points in a single window, and q is the window number.

[0045] Signal processing for each window follows a second-order recursive formula:

[0046]

[0047]

[0048]

[0049] Where x is the current value at the current sampling point ( or ), where coeff is a pre-calculated coefficient, and its expression is: m is the DFT frequency point corresponding to the injection frequency, which is determined by the injection frequency, the number of sampling points in a single window, and the execution frequency of the control loop. N is the number of sampling points in a single window.

[0050] After a window has accumulated N sampling points, the complex DFT value of that window at the injection frequency is calculated, as shown in the following expression:

[0051]

[0052]

[0053] in, for The pre-calculated value, for The pre-calculated value is obtained. The complex DFT real part of the α-axis current is obtained using the above formulas. virtual part and the complex DFT real part of the β-axis current virtual part .

[0054] The negative sequence component of the high-frequency current is extracted based on the complex DFT results. The extraction formula is as follows:

[0055]

[0056]

[0057] The rotor position double angle is calculated using the negative sequence component, then divided by two and superimposed with phase offset compensation to obtain the estimated rotor electrical angle value. The specific formula is as follows:

[0058]

[0059]

[0060] in, This is the phase offset compensation amount, used to compensate for the inherent phase lag of the Goertzel DFT, as well as the systematic phase deviation caused by the motor resistance, d / q axis inductance, and injection frequency, ensuring the accuracy of angle estimation.

[0061] Specifically, phase offset compensation amount Dynamic adjustments are made based on the rotor's electrical angular velocity. Linear interpolation is performed between the stationary phase offset value and the rotating phase offset value to compensate for the negative sequence component phase offset caused by drive current saturation and back electromotive force when the speed increases, ensuring the accuracy of angle estimation at different speeds.

[0062] S3. To ensure the reliability of the rotor electrical angle estimate, an angle convergence determination mechanism is set up. The rotor electrical angle estimate obtained from each window is stored in a ring buffer, the length of which is the preset number of consecutive determinations. Consistency checks are performed on multiple consecutive angle estimates in the buffer. If the difference between any two angle values ​​is less than the preset angle tolerance, the angle is determined to be converged; if the consistency requirement is not met, the buffer is cleared and re-accumulated until the convergence condition is met.

[0063] During the angle locking phase, if the angle convergence condition is not met after the preset timeout period, the system will be forced to enter the next phase to prevent the motor from stalling during startup and improve the robustness of the method.

[0064] S4. After angle convergence, the polarity resolution stage begins, utilizing the magnetic circuit saturation effect to eliminate 180° polarity ambiguity. The specific implementation process is as follows:

[0065] Positive pulse application: Apply a positive voltage pulse of preset amplitude along the currently estimated d-axis direction for a preset number of sampling periods, collect the d-axis current during this period, calculate its average amplitude, and denot it as . ;

[0066] Negative pulse application: Apply a negative voltage pulse with the same amplitude as the positive pulse along the opposite direction of the currently estimated d-axis (i.e., the θ+π direction), for the same number of sampling periods, acquire the corresponding d-axis current, calculate the average amplitude, and denot it as... ;

[0067] Polarity determination: comparison and The size, if Greater than This indicates that the current estimated angle differs from the actual rotor angle by 180°, so the estimated angle value should be adjusted to θ + π; if Greater than or equal to If the current angle estimate remains unchanged, it will be the true rotor electrical angle.

[0068] Judgment principle: When the d-axis magnetic circuit is in the positive direction, it is affected by magnetic saturation, resulting in smaller inductance and greater current response. This characteristic is used to distinguish between the N pole and the S pole.

[0069] After polarity identification is completed, a zero-voltage signal is output and a preset control cycle is continued to discharge the residual current in the motor winding. The discharge time is not less than 3 times the electrical time constant of the motor, and the discharge rate is >95%, ensuring that the residual current discharge rate meets the subsequent switching requirements and avoiding current surges during switching transients.

[0070] S5. After polarity resolution is completed, the transition phase begins. During this phase, high-frequency injection operation is maintained, using the actual rotor electrical angle as the reference for current loop commutation to ensure stable motor operation under zero-speed conditions. Simultaneously, the flux linkage observer is activated in the background, and the flux linkage of the observer is initialized using the actual rotor electrical angle. The initialization formula is:

[0071]

[0072]

[0073] Where λ is the permanent magnet flux linkage of the permanent magnet synchronous motor, and θ is the actual rotor electrical angle. This initialization setting enables the flux linkage observer to have an accurate observation basis from the initial stage, thus accelerating the convergence speed of the observer.

[0074] S6. During the transition phase, continuously monitor the motor operating status and the observer's working status. When both of the following conditions are met simultaneously and the preset number of de-jitter judgments is reached consecutively, it is determined that the switching conditions are met:

[0075] 1) The electric angular velocity of the motor exceeds the preset first threshold, which is the lowest angular velocity at which the back electromotive force can be effectively observed, ensuring that the flux linkage observer can achieve accurate angle estimation based on the back electromotive force. Specifically, the first threshold can be set to 60 rad / s.

[0076] 2) Estimated observation angle output by the magnetic flux observer With high-frequency injection solution angle estimation value If the difference is less than a preset second threshold, it indicates that the observer has converged and its angle estimate is reliable. Specifically, the second threshold can be set to 1.0 rad, i.e. .

[0077] Furthermore, this embodiment also provides a method for online 180° ambiguity elimination, that is, during the transition phase, the current and previous high-frequency injection solution angle estimates are continuously compared. If the angle jumps between the two times exceed π / 2, then π is added to the current angle estimate to eliminate angle ambiguities that may occur during continuous operation.

[0078] S7. Once the switching conditions are met, the cross-fading switching process is initiated. The core of this process is to achieve a seamless transition by using a hybrid phase-locked loop reference angle. The specific implementation method is as follows:

[0079] Set the de-emphasis factor k, which increases linearly from 0 to 1. The reference angle of the phase-locked loop is calculated using the following formula:

[0080]

[0081] in, The high-frequency injection angle estimate is obtained after filtering. The high-frequency injection angle estimate is then subjected to low-pass filtering. The filtering process considers the shortest path around ±π to avoid filter spikes at the ±π switching point and eliminates the angle step effect, making the angle output smoother.

[0082] While the de-emphasis factor k increases linearly, the target amplitude of the high-frequency injection voltage is simultaneously reduced to zero by a ramp of (1−k), achieving a smooth shutdown of the high-frequency injection. Throughout the de-emphasis switching process, a phase-locked loop tracks... It outputs continuous phase and speed signals to ensure that there are no transient shocks in motor speed and no jumps in angle during the switching process.

[0083] When the fade factor k reaches 1, the high-frequency injection voltage amplitude drops to zero, the high-frequency injection module is turned off, the motor is completely switched to the pure flux observer operation mode, and the entire static start-up and smooth switching process is completed.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for smoothly switching high-frequency injection from a permanent magnet synchronous motor into a flux linkage observer, characterized in that, Includes the following steps: S1. When the rotor is stationary, inject a rotating high-frequency voltage vector with an increasing amplitude ramp into the stator αβ stationary coordinate system. S2. Collect the three-phase current and obtain the α and β axis currents through Clark transformation. Use Q parallel interleaved Goertzel windows to perform single-frequency discrete Fourier transform on the α and β axis currents respectively. Extract the negative sequence component of the high-frequency current at the injection frequency, calculate the rotor position double angle, divide by two and superimpose phase offset compensation to obtain the rotor electrical angle estimate. S3. Perform consistency judgment on the rotor electrical angle estimation values ​​obtained by solving multiple consecutive windows. When the consecutive consistency reaches a preset number, the angle is judged to converge. S4. After the angle convergence, apply positive and negative voltage pulses along the currently estimated d-axis. Use the magnetic circuit saturation effect to compare the amplitude of the d-axis current response corresponding to the positive and negative pulses, eliminate the 180° polarity ambiguity, and obtain the true rotor electrical angle. S5. Maintain the high-frequency injected rotating high-frequency voltage vector, and use the obtained real rotor electrical angle as the current loop commutation reference. At the same time, run the flux observer in the background and initialize the flux of the observer with the real rotor electrical angle. S6. Continuously monitor the motor operating status and the observer's working status. When both of the following conditions are met simultaneously and the preset number of de-jitter judgments is reached consecutively, it is determined that the crossfade switching condition is met, and proceed to the next step: 1) The electric angular velocity of the motor exceeds the preset first threshold; 2) Estimated observation angle output by the magnetic flux observer With high-frequency injection solution angle estimation value The difference is less than the preset second threshold; S7. Set the de-emphasis factor k, which increases linearly from 0 to 1. The reference angle of the phase-locked loop is calculated using the following formula: in, This is the estimated high-frequency injection angle after filtering. While the dilution factor k increases linearly, the target amplitude of the high-frequency injection voltage is simultaneously reduced to zero by a ramp of (1−k). When the fade factor k reaches 1, the high-frequency injection voltage amplitude drops to zero, the high-frequency injection module is turned off, the motor is completely switched to the pure flux observer operation mode, and the entire static start-up and smooth switching process is completed.

2. The smooth switching method for high-frequency injection of permanent magnet synchronous motor into the flux linkage observer according to claim 1, characterized in that, The voltage amplitude amp injected in step S1 is used to achieve soft start using an exponential approximation method, and spread spectrum jitter is applied to the phase step according to the following formula: in, The phase step size for each control cycle, where Δ is the jitter coefficient. The angle of the current rotating high-frequency vector in the αβ plane. This refers to the jitter frequency.

3. The smooth switching method for high-frequency injection of permanent magnet synchronous motor into the flux linkage observer according to claim 1, characterized in that, The phase offset compensation amount in step S2 is dynamically adjusted according to the rotor electric angular velocity. It is linearly interpolated between the stationary phase offset value and the rotating phase offset value to compensate for the negative sequence component phase offset caused by the saturation of the drive current and the back electromotive force when the speed increases.

4. The smooth switching method for high-frequency injection of permanent magnet synchronous motor into the flux linkage observer according to claim 1, characterized in that, In step S2, the startup delay of the Q parallel interleaved Goertzel windows satisfies , where N is the number of sampling points in a single window, and q is the window number.

5. The smooth switching method for high-frequency injection of permanent magnet synchronous motor into the flux observer according to claim 1, characterized in that, After step S4 is completed, zero voltage is output and the preset control cycle is continued to discharge the residual current in the motor winding. The discharge time is not less than 3 times the electrical time constant of the motor.

6. The smooth switching method for high-frequency injection of a permanent magnet synchronous motor into a flux linkage observer according to claim 1, characterized in that, In step S6, the first threshold is 60 rad / s and the second threshold is 1.0 rad.

7. The smooth switching method for high-frequency injection of a permanent magnet synchronous motor into a flux linkage observer according to claim 1, characterized in that, In step S6, the angle estimate value calculated by the current high-frequency injection is continuously compared with that of the previous high-frequency injection. If the angle jumps by more than π / 2, the current angle estimate value is supplemented with π.

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