Stepless rotating speed accurate control method of magnetic stirrer

Abstract

The invention relates to the technical field of motor control, and discloses a stepless rotation speed precise control method for a magnetic stirrer, which comprises the following steps: a power conversion unit outputs a three-phase current signal according to a rotation speed instruction, and establishes a rotation driving magnetic field in an electromagnetic energy conversion unit; superposing a high-frequency quadrature phase perturbation signal in a phase angle of the voltage vector to induce a power angle of a rotary driving magnetic field to generate phase deviation fluctuation; according to the method, online sensing of the magnetic coupling depth is achieved by analyzing the electromagnetic characteristics, fluid resistance impact is counteracted in real time through a dynamic compensation mechanism, the slippage risk of the stirrer under the working condition of high-viscosity reaction is eliminated, and the reliability of the stirrer is improved. And the synchronous robustness and the rotating speed control precision of system operation are improved.

Description

Technical Field

[0001] This invention relates to a method for precise stepless speed control of a magnetic stirrer, belonging to the field of electric motor control technology. Background Technology

[0002] Current magnetic stirrers utilize inverters to generate rotating magnetic fields and drive stirrers within containers via spatial magnetic coupling, thereby achieving non-contact stepless speed regulation and mixing of fluid materials. The magnetic coupling interface is jointly formed by the motor rotor magnetic field and the permanent magnet poles of the stirrer. Its physical essence belongs to a variable stiffness elastic coupling system. There is a power angle deviation between the driving magnetic field and the stirrer magnetic poles that depends on the load torque. Under steady-state conditions, due to the low viscosity of the fluid and constant damping, the control unit maintains synchronous rotation by adjusting the output frequency of the inverter circuit.

[0003] In specific working conditions such as biopharmaceutical or polymer synthesis, the fluid damping characteristics exhibit nonlinear evolution with the progress of chemical reactions. Drastic fluctuations in material viscosity lead to a sudden increase in the shear torque borne by the stirrer, causing the magnetic coupling angle to approach the physical critical point. Current improvements are mostly limited to external environmental physical adaptability, neglecting the drive control system's ability to anticipate internal dynamic instability. For example, the utility model patent with authorization announcement number CN203002292U discloses a magnetic stirrer that eliminates the motor's failure due to frost in ultra-low temperature environments by sealing a protective film on the outer wall of the stirrer. However, when it comes to fluid characteristics... During the reaction process of sex mutation, such hardware reinforcement has not solved the problem of magnetic slippage of the stir bar caused by the lag of the control strategy. The equipment regards the magnetic coupling interface as a static or quasi-static transmission link and lacks closed-loop perception of the magnetic potential well depth and the instantaneous stiffness coefficient of the magnetic field. The motor operates normally in a specific environment, but when faced with the load impact of the high viscosity reaction system, the stir bar will still jump uncontrollably because the power angle exceeds the critical point. Because the controller has difficulty monitoring the dynamic evolution of the magnetic coupling margin in real time, the stir bar is prone to slippage and synchronization interruption. Ultimately, the stir bar jumps randomly in the container, which destroys the consistency of material mixing.

[0004] Therefore, the technical problem to be solved by this invention is how to invert the instantaneous stiffness of a magnetically coupled system by extracting the features of the motor drive current, and how to achieve early prediction and active compensation of the slip state while utilizing the existing processor hardware of the system. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for precise stepless speed control of a magnetic stirrer, comprising the following steps:

[0006] Step S1: The power conversion unit adjusts the duty cycle of the pulse width modulation signal according to the received speed command, drives the power inverter circuit to output a three-phase current signal to the electromagnetic energy conversion unit, and establishes a rotating drive magnetic field corresponding to the speed command frequency in the electromagnetic energy conversion unit, so as to drive the controlled magnetic coupling load set inside the container to rotate synchronously through non-rigid magnetic coupling.

[0007] Step S2: A high-frequency orthogonal phase perturbation signal with a preset frequency and amplitude is superimposed on the phase angle of the voltage vector of the electromagnetic energy conversion unit, so that the power angle of the rotating driving magnetic field generates controlled phase shift fluctuations near the stable operating point.

[0008] Step S3: The stator current on the output side of the power conversion unit is monitored in real time using the current acquisition circuit. The response component corresponding to the frequency of the high-frequency orthogonal phase perturbation signal in the stator current is extracted by the digital filter. The synchronous torque limit between the rotating drive magnetic field and the controlled magnetic coupling load is identified according to the amplitude variation law of the response component.

[0009] Step S4: Based on the identified synchronous torque limit value, dynamically correct the proportional coefficient and integral coefficient of the speed control loop, extract the steady-state value of the active component in the stator current to identify the current fluid load torque, perform feedforward compensation on the torque current command according to the load torque, and adjust the electromagnetic torque output by the electromagnetic energy conversion unit to counteract the resistance impact on the controlled magnetic coupling load caused by the change in fluid viscosity.

[0010] Preferably, step S2 includes: determining the modulation frequency and injection amplitude of the high-frequency orthogonal phase perturbation signal based on the rated speed of the controlled magnetically coupled load and the carrier frequency of the control system; superimposing the high-frequency orthogonal phase perturbation signal onto the original phase angle generated by the space vector pulse width modulation algorithm; updating the duty cycle command of the power conversion unit; and causing the electromagnetic energy conversion unit to generate a controlled perturbation response.

[0011] Preferably, in step S3, identifying the synchronous torque limit value of the controlled magnetically coupled load based on the amplitude variation law of the response component includes the following steps: Step S31, converting the extracted response component into a current vector in the torque direction through coordinate transformation; Step S32, calculating the energy integral value of the current vector within one cycle of the high-frequency orthogonal phase perturbation signal; Step S33, inverting the damping characteristics of the controlled magnetically coupled load under dynamic load through the energy integral value, and outputting the synchronous torque limit value characterizing the synchronization capability of the controlled magnetically coupled load.

[0012] Preferably, the synchronous torque limit value is determined by the following formula: ,in, This is the limit value of synchronous torque. ω is the instantaneous electromagnetic power of the electromagnetic energy conversion unit, ω is the angular velocity of the rotating driving magnetic field, and σ is a dimensionless constant characterizing the fluid coefficient and preset between 0.8 and 1.2.

[0013] Preferably, in step S4, performing feedforward compensation on the torque current command includes the following steps: Step S41, extracting the real-time electromagnetic torque output by the rotating drive magnetic field based on the active current component in the stator current; Step S42, calculating the resistance torque load generated by the fluid by combining the real-time acceleration and moment of inertia of the controlled magnetically coupled load; Step S43, converting the resistance torque load into a compensation current value, and superimposing the compensation current value onto the output of the torque current regulator in the speed control loop.

[0014] Preferably, step S3 further includes: step S51, obtaining temperature data of the stator winding in the electromagnetic energy conversion unit; step S52, calculating the residual magnetism attenuation ratio of the permanent magnet in the controlled magnetic coupling load based on the temperature data; step S53, using the residual magnetism attenuation ratio to correct the identified synchronous torque limit value, and outputting the synchronous torque correction value after temperature rise compensation.

[0015] Preferably, step S3 further includes: monitoring the subharmonic energy distribution in the torque current feedback value; when the peak value of the subharmonic energy distribution in the preset frequency domain exceeds the safety threshold, determining that the controlled magnetically coupled load has entered the resonance critical state; adjusting the carrier frequency of the space vector pulse width modulation algorithm so that the system characteristic frequency avoids the mechanical resonance frequency of the controlled magnetically coupled load.

[0016] Preferably, the method further includes a startup optimization step: during the startup phase of the controlled magnetically coupled load, the rotating drive magnetic field is controlled to operate in a variable frequency and variable voltage mode; by monitoring the phase lag angle of the stator current, the switching point where the controlled magnetically coupled load changes from a static friction state to a dynamic friction state is identified; and the initial integral value of the speed control loop is initialized according to the current characteristic value corresponding to the switching point.

[0017] Preferably, the speed control loop employs an anti-integral saturation regulator, and the proportional coefficient and integral coefficient of the regulator are linearly mapped according to the gradient of the change in synchronous torque limit value relative to the speed of the controlled magnetically coupled load.

[0018] Preferably, the method further includes a fault protection step: step S81, when the identified synchronous torque limit value is lower than the preset safety lower limit threshold, the increase slope of the speed command is locked; step S82, while outputting a warning signal indicating that the controlled magnetically coupled load has a risk of slippage, the rotating drive magnetic field is controlled to reduce to a safe speed range below 200 r / min in deceleration mode.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. In stepless speed control, by superimposing a phase perturbation signal in the control loop of the excitation current component and monitoring the synchronous response signal generated in the torque current component in real time, the drive system can establish an instantaneous stiffness evaluation mechanism for the non-contact magnetic coupling interface, convert the magnetic field coupling margin into a quantifiable electrical parameter feedback, enabling the motor drive unit to detect the depth of the magnetomotive force well, strengthen the magnetic field adsorption force in advance before the stir bar undergoes physical displacement lag, eliminate the skipping phenomenon caused by the breakage of magnetic lines of force, and ensure the quasi-synchronous operation state in the full-range stepless speed regulation process.

[0021] 2. By utilizing the energy flow conservation relationship between the instantaneous electromagnetic power of the motor and the real-time rotational speed of the stirrer, the system identifies the dynamic damping coefficient of the fluid environment to correct the control gain of the speed regulator in real time. The nonlinear evolution of the fluid shear resistance is directly mapped to the feedforward compensation of the torque current loop, so that the driving magnetic field exhibits viscous stress compensation characteristics that match the viscous properties of the fluid. This effectively offsets the load impact generated by the non-Newtonian fluid during the polymerization reaction and solves the problem of frequent speed overshoot and unsteady oscillation in traditional control laws under variable damping conditions.

[0022] 3. Combining the temperature rise characterization parameters obtained from stator winding resistance identification and the cross-modulation components extracted from dual-frequency orthogonal detection signals, a composite adjustment system that takes into account both thermal demagnetization compensation and dynamic instability prediction was constructed. The excitation compensation gain was dynamically calibrated based on the functional relationship of permanent magnet remanence decay with temperature, and the information entropy characteristics of the cross-modulation term were used to distinguish between stable phase lag and high-risk harmonic instability. While maintaining the magnetic coupling strength, the mechanical oscillation energy of the stirrer was dissipated by injecting damping components, ensuring the consistency of system operation under high temperature and high dynamic environment. Attached Figure Description

[0023] Figure 1 This is a flowchart of the control method for orthogonal phase perturbation injection and dynamic torque compensation of the present invention;

[0024] Figure 2 This is a system logic architecture diagram that integrates the underlying mechanism, core process, and auxiliary protection mechanism of this invention. Detailed Implementation

[0025] The present invention will be described in detail below through specific embodiments, so as to enable those skilled in the art to more clearly understand the technical solutions claimed by the present invention. The following embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0026] This invention provides a method for precise stepless speed control of a magnetic stirrer. A power conversion unit adjusts the duty cycle of a pulse width modulation signal according to the speed command, driving a power inverter circuit to output a three-phase current signal to an electromagnetic energy conversion unit. A rotating driving magnetic field corresponding to the speed command frequency is established in the electromagnetic energy conversion unit. The non-rigid magnetic coupling within the space drives a controlled magnetically coupled load inside the container to rotate synchronously. Since the driving magnetic field of the magnetic stirrer and the controlled magnetically coupled load are a variable stiffness elastic coupling system, when handling high-viscosity or non-Newtonian fluids, drastic fluctuations in load torque can cause the power angle deviation to approach a critical point. To address this... To address the challenge of real-time sensing of the dynamic state of the magnetic coupling interface, this implementation superimposes a high-frequency orthogonal phase perturbation signal with a preset frequency and amplitude onto the voltage vector phase angle of the electromagnetic energy conversion unit. This induces controlled phase shift fluctuations in the power angle of the rotating driving magnetic field near the stable operating point. The current acquisition circuit monitors the stator current at the output of the power conversion unit in real time and extracts the response component corresponding to the frequency of the high-frequency orthogonal phase perturbation signal from the stator current using a digital filter. A sinusoidal perturbation component Δθ is superimposed onto the original phase angle θ generated by the space vector pulse width modulation algorithm. The expression for the sinusoidal perturbation component Δθ is as follows: perturbation amplitude Set to 5% to 10% of the rated current vector, perturbation frequency The frequency range is set between 500Hz and 1000Hz. The current acquisition circuit obtains the three-phase stator current and converts it into torque current components through coordinate transformation. Using center frequency Extracting high-frequency response components using a 20Hz bandwidth digital bandpass filter. ,use A mapping relationship between the power angle offset and magnetic coupling stiffness is established based on the root mean square value within the perturbation period. When the fluid viscosity increases, leading to a decrease in magnetic coupling stiffness... The amplitude shows a monotonically increasing trend. The system dynamically corrects the proportional coefficient and integral coefficient according to the amplitude change rate, and completes electromagnetic torque pre-compensation before the physical displacement lag occurs.

[0027] To transform the aforementioned response components into quantifiable synchronization capability indicators, the system executes the following path: The extracted response components are transformed into current vectors in the torque direction through coordinate transformation; their energy integral value within the period of the high-frequency orthogonal phase perturbation signal is calculated; the damping characteristics of the controlled magnetically coupled load under dynamic load are inverted using this value, and the synchronization torque limit value characterizing the synchronization capability of the controlled magnetically coupled load is output. Specifically, the physical logic for establishing the mapping from energy integral value to synchronization capability inversion is as follows: The control unit internally stores a stiffness mapping table based on 256 discrete sampling points. This table uses electrical... The magnetic energy conversion unit uses the integral of the no-load reference current energy in the range of 0 r / min to 1000 r / min as the denominator and the real-time calculated energy integral value as the numerator to calculate its amplitude increment ratio. When this increment ratio exceeds 15% for three consecutive samples within 10 ms, it is determined that the magnetic coupling stiffness has weakened. The processor then uses a linear interpolation algorithm to map the increment ratio to an attenuation gain between 0.85 and 0.95 to correct the synchronous torque limit value, ensuring that the inversion process has a physical measurement basis. Specifically, the calculation formula for the synchronous torque limit value is as follows: ,in, This is the limit value of synchronous torque. ω is the instantaneous electromagnetic power of the electromagnetic energy conversion unit, ω is the angular velocity of the rotating driving magnetic field, and σ is a dimensionless constant characterizing the fluid coefficient and preset between 0.8 and 1.2.

[0028] Synchronous torque limit The identification process involves characterizing the fluid coefficient σ during calibration, and in the system initialization phase, the driving electromagnetic energy conversion unit generates a locking magnetic field to bring the controlled magnetically coupled load to rest. An external loading device applies an increasing tangential load to the controlled magnetically coupled load, and the stator current phase abrupt change is monitored to identify magnetic pole slippage. The instantaneous electromagnetic power of the slippage is recorded. With the synchronous angular velocity ω, according to the formula Determine the σ calibration value. To accurately measure the pull-out torque, the actual operating conditions considered the magnetic circuit loss caused by the thickness of the container bottom plate and the thermal demagnetization effect of the permanent magnet. The dimensionless constant σ was linearly corrected within the range of 0.8 to 1.2. The experimental calibration steps for this correction process were as follows: Under gradient operating conditions with material viscosities of 100 mPa·s, 1000 mPa·s, and 5000 mPa·s, the critical electromagnetic power at the moment of slippage was recorded. The system calculated the average active current every 200 ms and looked up the corresponding correction step in the preset third-order viscosity mapping table based on the current value. When the load current fluctuation exceeded 50 mA, the constant σ was adjusted incrementally or decrementally in steps of 0.02, thereby transforming the static formula into an adaptive algorithm dynamically coupled with fluid viscosity. The system periodically collected the stator winding temperature and calculated the remanent magnetization attenuation ratio, which was then superimposed on the σ calculation loop as a correction factor to identify the output. Anchored to the magnetic coupling boundary of the physical environment; based on the fact that fluid viscosity evolution will cause regulation lag, the system dynamically corrects the proportional coefficient and integral coefficient of the speed control loop based on the identified synchronous torque limit value. At the same time, it extracts the steady-state value of the active component in the stator current to identify the current fluid load torque, and performs feedforward compensation on the torque current command, including: extracting the real-time electromagnetic torque output by the rotating drive magnetic field based on the active current component in the stator current; calculating the resistance torque load generated by the fluid by combining the real-time acceleration and moment of inertia of the controlled magnetically coupled load; converting the resistance torque load into a compensation current value, and superimposing the compensation current value onto the output of the torque current regulator in the speed control loop. By adjusting the electromagnetic torque output by the electromagnetic energy conversion unit, the resistance impact caused by the change in fluid viscosity is offset in real time.

[0029] To address the magnetic energy product decay caused by ambient temperature and winding temperature rise, this implementation incorporates a temperature rise compensation procedure. It acquires the temperature data of the stator winding in the electromagnetic energy conversion unit and calculates the residual magnetism decay ratio of the permanent magnet within the controlled magnetic coupling load. The engineering calculation model for the residual magnetism decay ratio is as follows: the control unit establishes a discrete lookup table model with 5°C steps based on the demagnetization characteristic curve of the neodymium iron boron permanent magnet in the range of 25°C to 150°C. For every 10°C increase in winding temperature collected by the temperature sensor, the system automatically retrieves the corresponding demagnetization temperature between 0.008 and 0.015. The system calculates a coefficient and performs subtraction compensation on the synchronous torque limit to ensure that the control system will not make slippage errors due to the decrease in magnetic energy product under high-temperature conditions. This residual magnetism attenuation ratio is used to correct the identified synchronous torque limit, outputting a temperature-compensated synchronous torque correction value to adjust the control gain. To address potential mechanical resonance issues during speed regulation cycles, the system monitors the subharmonic energy distribution in the torque current feedback value. When the peak value of the subharmonic energy distribution in the preset frequency range exceeds a safety threshold, the controlled magnetically coupled load is determined to have entered a resonance critical state. At this point, the system adjusts... The carrier frequency of the space vector pulse width modulation algorithm ensures that the system's characteristic frequency avoids the mechanical resonance frequency of the controlled magnetically coupled load. To improve the system's synchronous robustness, during the startup phase of the controlled magnetically coupled load, the system controls the rotating drive magnetic field to operate in a variable frequency and variable voltage mode. By monitoring the phase lag angle of the stator current, the switching point of the controlled magnetically coupled load from static friction to dynamic friction is identified. The underlying processing flow for identifying this switching point is as follows: The processor establishes a first-in-first-out buffer with a depth of 20 sampling points and collects the phase lag angle value at a frequency of 1000Hz. When the absolute value of the second-order difference of the data in the buffer exceeds 0.8 degrees for 5 consecutive ms, it is determined to be the critical inflection point where the magnetic pole overcomes static friction and displacement occurs. At the same time, the comparator determines whether the current torque current component reaches 95% of the preset startup current value. If both conditions are met simultaneously, the dynamic friction switching point is locked. The initial integral value of the speed control loop is initialized according to the current characteristic value corresponding to the switching point. The speed control loop adopts an anti-integral saturation regulator, whose proportional coefficient and integral coefficient are linearly mapped according to the gradient of the synchronous torque limit value relative to the speed of the controlled magnetically coupled load.

[0030] When faced with extreme disturbance conditions such as stirrer slippage, the system activates its fault protection procedure. When the identified synchronous torque limit value falls below the preset safety lower limit threshold, the increase slope of the speed command is locked. Simultaneously, a warning signal indicating a risk of slippage in the controlled magnetically coupled load is output, and the rotating drive magnetic field is controlled to reduce to a safe speed range below 200 r / min in deceleration mode. If it is determined that stirrer slippage has occurred, i.e., the torque current component... When the characteristic disappears, the system switches the output voltage vector of the drive motor to an asymmetric pulse sequence to detect the magnetic pole position of the stirrer. The specific execution logic of this asymmetric pulse sequence is as follows: the power conversion unit stops the orthogonal vector output and instead injects a DC bias voltage vector with a duration of 20ms and an amplitude of 30% of the rated DC bus voltage into the three-phase stator windings. During the injection, the rate of change of the induced current is obtained through the sampling resistor. When the second-order differential peak of the feedback current of a certain phase changes abruptly within 50 microseconds and exceeds 1.2 amperes, the system determines the electrical angle corresponding to the peak point as the physical position of the magnetic pole axis of the controlled magnetic coupling load. By obtaining the induced current of the controlled magnetic coupling load... The generated current feedback signal adjusts the initial phase of the driving magnetic field, enabling the drive motor and the controlled magnetically coupled load to re-establish magnetic coupling synchronization. Through real-time acquisition and closed-loop logic calculation of the above physical parameters, this implementation converts the energy margin of the non-contact magnetic coupling interface into controllable electrical parameter feedback. The system no longer relies on static magnetic coupling design, but eliminates the risk of synchronization interruption under high viscosity reaction conditions through dynamic magnetomotive force well depth sensing and torque feedforward compensation, achieving precise speed control during stepless speed regulation. All measurement data and physical parameters use standard units, such as frequency in Hz and speed in r / min, to ensure consistency in engineering implementation.

[0031] Example 1: In the industrial reactor conditions for polymer synthesis, the viscosity of the material increases from an initial 10 mPa·s to 5000 mPa·s as the polymerization reaction progresses, causing the material to exhibit non-Newtonian fluid characteristics. Its load torque fluctuates nonlinearly with the stirring speed. When the fluid resistance torque approaches the magnetic coupling limit, the work angle between the controlled magnetically coupled load and the rotating driving magnetic field increases. Once the critical point of 90° is exceeded, slippage and loss of synchronization occur, leading to disordered jumping of the stir bar at the bottom of the container and localized temperature rise. To maintain the dynamic stability of the magnetic coupling interface, the control unit injects frequency into the electromagnetic energy conversion unit. A high-frequency orthogonal phase perturbation signal with a constant amplitude A at 500 Hz is used to extract the torque current component from the stator current in real time using a digital filter. Same frequency response signal By calculating the phase difference of the response signal relative to the perturbation input. To determine the instantaneous stiffness coefficient of the magnetic potential well. When the viscosity of the material in the reactor reaches 3500 mPa·s, the phase difference is monitored. Determine the instantaneous stiffness coefficient by shifting the steady-state operating point from 5° to 42°. Calculating down to the preset instability threshold, for the above operating conditions, the system initiates compensation logic, utilizing the identified instantaneous stiffness coefficient. Correct the proportional and integral coefficients of the speed control loop, and determine the synchronous torque limit value according to the following formula. : ,in, This is the limit value of synchronous torque. ω is the instantaneous electromagnetic power of the electromagnetic energy conversion unit, ω is the angular velocity of the rotating driving magnetic field, and σ is the fluid coefficient, which is selected as 1.05 in this embodiment.

[0032] Based on the above calculation results, the control unit increases the excitation current component. The given value is used to enhance the magnetic flux density of the rotating drive magnetic field, improve the static stiffness of the magnetic coupling, and at the same time, the control unit extracts the torque current component. The steady-state value of the active component is used to calculate the fluid resistance torque and add it to the output of the torque current regulator as a feedforward compensation. Under the extreme condition where the viscosity rises to 5000 mPa·s, the instantaneous power angle of the controlled magnetically coupled load is constrained to around 65°, and the stir bar is kept in a synchronous rotation state at a speed of 300 r / min. The material mixing process remains consistent throughout the entire viscosity range, solving the problem of synchronous interruption caused by the breakage of magnetic lines of force in high viscosity environments.

[0033] Example 2: In the test scenario targeting viscosity gradient fluctuations, the test platform is configured with a drive controller equipped with a current acquisition circuit, an electromagnetic energy conversion unit, and a silicone oil load with non-Newtonian fluid characteristics. The current acquisition circuit has a measurement range of 0 to 10 A, a sampling frequency of 10 kHz, and a measurement accuracy of 0.5%. To simulate an industrial electromagnetic environment, Gaussian white noise with a signal-to-noise ratio of 25 dB is superimposed on the stator current sampling branch, and power frequency harmonic interference of 50 Hz is introduced. The test process involves high-frequency orthogonal phase perturbation signals. The value depends on the balance between the real-time nature of data acquisition and the data processing load. If the frequency is below 100Hz, the phase difference will be significant due to the rapid evolution of fluid viscosity. The recognition delay causes compensation lag. If the frequency is higher than 1000Hz, the switching losses and stator iron losses of the power inverter increase. Based on the mechanical time constant of the controlled magnetically coupled load, this experiment determines the frequency. The frequency is set to 500Hz, and the amplitude A of the perturbation signal is set to 10% of the rated current value to balance the signal-to-noise ratio and torque ripple, and to prevent response components. Submerged in background noise, the method of this invention operates under viscosity gradients of 100 mPa·s, 1000 mPa·s, and 5000 mPa·s. Under the initial reference state of 100 mPa·s, the torque current component extracted by the system... Response signal in With an amplitude of 0.12A, the calculated phase difference The phase hysteresis is 4.2°. When the viscosity changes to 1000 mPa·s, the controlled magnetically coupled load experiences phase hysteresis due to increased fluid damping, resulting in a response signal... Reduced to 0.08A, phase difference When the angle is increased to 15.8°, the control unit determines the synchronous torque limit value according to the following formula. : ,in, This is the limit value of synchronous torque. ω is the instantaneous electromagnetic power of the electromagnetic energy conversion unit, in W; ω is the angular velocity of the rotating driving magnetic field, in rad / s; σ is the fluid coefficient, which is selected as 1.05 in this experiment. At this time, even though there is 25dB of noise in the environment, the digital filter still accurately locks the 500Hz feature point, and the processed current ripple coefficient decreases from 12.5% ​​of the original acquired value to 2.3%.

[0034] To verify the boundaries of key parameters, comparative tests were set up to characterize the fluid coefficient σ with values ​​of 0.5, 1.05, and 1.5. When σ was set to 0.5, the calculated limit value of the synchronous torque was... The current was below the actual coupling limit, causing the control unit to trigger limit compensation at a viscosity of 2500 mPa·s, resulting in an increase in excitation current. Upon reaching the limit value, the system experiences an 8.5% torque ripple and causes winding temperature rise. When σ is set to 1.5, the system's estimated energy margin is too large. At the inflection point where the viscosity rises to 3800 mPa·s, the phase difference... The jump to 85.2° failed to trigger control gain correction, causing the stir bar to lose synchronization within 0.8ms. Using the sample group of this invention with σ=1.05, when the viscosity increased to 5000 mPa·s, the work angle deviation was constrained to 62.5°, and the stir bar maintained a stable rotation of 300 r / min. The instantaneous stiffness coefficient was identified by injecting phase perturbations. It can invert the energy state of the non-contact magnetic coupling interface, limiting the characterizing fluid coefficient σ to between 0.8 and 1.2, thus limiting the synchronous torque limit. The identification results are in the optimal working window, which ensures synchronous stability under high viscosity conditions while avoiding oversaturation of the control. The synchronous limit torque of the controlled magnetic coupling load is increased to 2.45 times that of the original control method.

[0035] Example 3: This example combines Figures 1 to 2 This document describes a method for precise stepless speed control of a magnetic stirrer, as follows: Figure 1As shown, in step S1, the power conversion unit adjusts the duty cycle of the pulse width modulation signal according to the speed command, driving the power inverter circuit to output a three-phase current signal to the electromagnetic energy conversion unit to establish a rotating drive magnetic field corresponding to the speed command frequency. Through non-rigid magnetic coupling, the controlled magnetically coupled load is driven to rotate synchronously. In step S2, a high-frequency orthogonal phase perturbation signal with a preset frequency and amplitude is superimposed on the voltage vector phase angle of the electromagnetic energy conversion unit, inducing the power angle of the rotating drive magnetic field to generate controlled phase offset fluctuations near the stable operating point. Then, in step S3, the stator current is monitored in real time using the current acquisition circuit, and the response component corresponding to the frequency of the high-frequency orthogonal phase perturbation signal is extracted through a digital filter. The synchronous torque limit value between the rotating drive magnetic field and the controlled magnetically coupled load is identified according to the amplitude change law of the response component. Finally, in step S4, the proportional and integral coefficients of the speed control loop are dynamically corrected based on the synchronous torque limit value, the steady-state value of the active component of the stator current is extracted to identify the fluid load torque, and feedforward compensation is performed on the torque current command to adjust the output electromagnetic torque to counteract the resistance impact caused by the change in fluid viscosity.

[0036] like Figure 2 As shown, the architecture centers on the precise stepless speed control of the magnetic stirrer, radiating outwards to form four main branches. The underlying core mechanism branch includes four technical elements: orthogonal phase perturbation induction, online sensing of magnetic coupling depth, extraction of stator current response components, and analysis of power angle phase shift fluctuations. The core control process branch covers four execution stages: establishing a rotating drive magnetic field, superimposing high-frequency perturbation signals, dynamic correction and feedforward compensation, and identifying the synchronous torque limit value. The auxiliary optimization and protection branch integrates three guarantee mechanisms: temperature rise remanent magnetization attenuation compensation, mechanical resonance suppression, and fault slip capture protection. The technical achievements and pain point solutions branch are reflected in three target effects: eliminating the risk of high viscosity slippage, offsetting fluid resistance impact, and improving synchronous robustness.

[0037] Example 4: In a process involving the synthesis of precision pharmaceutical intermediates, the permanent magnet of the controlled magnetically coupled load has a magnetic energy product of 35 MGOe, and the physical partition thickness at the bottom of the container is 5 mm. Before operation, the system performs an offline calibration procedure. The power conversion unit drives the electromagnetic energy conversion unit to generate a static locking magnetic field. A tangential force is applied to the controlled magnetically coupled load through an external force gauge, and the load is gradually increased until physical displacement occurs. The excitation current component output by the power conversion unit is recorded. and its corresponding pull-out torque The initial calibration value characterizing the fluid coefficient σ is determined by the following formula: Where σ is the fluid coefficient, The pull-out torque is expressed in N·m, and ω is the calibrated reference angular velocity, which is taken as 1 rad / s in this case. This refers to the electromagnetic power of the electromagnetic energy conversion unit, measured in W.

[0038] To correct the phase lag deviation at the magnetic coupling interface, the control unit monitors the instantaneous rate of change of the active current component in the stator current, i.e., the torque current component. The first derivative with respect to time t characterizes the dynamic response hysteresis of the controlled magnetically coupled load. When the rotational speed switches between 100 r / min and 800 r / min and the absolute value of the first derivative exceeds 2.5 A / s, the system is determined to have entered the nonlinear hysteresis region. The control unit calculates the hysteresis angle compensation component Δθ according to the following formula: Where Δθ is the hysteresis angle compensation component, The quadrature-axis inductance of the electromagnetic energy conversion unit, measured in ohms (H). This refers to the torque current component, expressed in amperes (A). The equivalent flux linkage of the controlled magnetically coupled load is expressed in Wb. The control unit superimposes the calculated hysteresis compensation component Δθ into the coordinate transformation angle of the rotating drive magnetic field. By generating a magnetic field lead to offset the mechanical hysteresis, the speed deviation of the controlled magnetically coupled load during dynamic speed regulation is constrained to within 0.5%. When the characterizing fluid coefficient σ is set to 1.02, the synchronous torque limit value is... The identification error rate is less than 1.2%, and the response bandwidth of the controlled magnetically coupled load under viscosity change conditions is improved by 35%.

[0039] Example 5: In an industrial production line scenario involving the large-scale deployment of various types of magnetic stirrers, the physical specifications of the controlled magnetically coupled load and the thickness of the container partition have processing tolerances. This results in a fluctuation of 0.1mm to 0.5mm in the physical air gap between the rotating drive magnetic field and the controlled magnetically coupled load. This hardware-level difference affects the preset synchronous torque limit. Identification discrepancies can arise between different individual devices, and the system faces control stability risks due to inconsistent coupling characteristic benchmarks.

[0040] To address the aforementioned operating conditions, the control unit initiates a magnetic field coupling characteristic calibration process before formal operation. This involves controlling the power conversion unit to drive the electromagnetic energy conversion unit to perform an unloaded frequency sweep within the range of 10Hz to 100Hz, recording the excitation current components at each frequency point. In response, a coupled mapping model for the current hardware is constructed using the extracted current amplitude features, and the calibration characterization fluid coefficient is determined by a formula. : ,in, To calibrate and characterize the fluid coefficients, The intrinsic electromagnetic constant of the electromagnetic energy conversion unit is expressed in N·m / A. Here, ω represents the excitation current component (in amperes), and ω represents the angular velocity of the rotating drive magnetic field (in rad / s). The calibration parameters are used as the reference input for dynamic speed regulation to ensure the synchronous torque limit value is reached. The calculation results remain consistent across different hardware batches.

[0041] Example 6: In a reactor deployment scenario with a 10mm thick jacketed partition, the equivalent magnetic reactance at the magnetic coupling interface increases due to the increased physical distance. The system faces the risk of false triggering of protection due to the mismatch between the preset torque threshold and the actual slip point. After assembly, the control unit executes the field adaptive calibration procedure, driving the rotating drive magnetic field to operate at a speed of 50r / min, and gradually reducing the excitation current component at a gradient of 0.1A / s. Until the response component in the stator current When a sudden change in amplitude occurs, record the electromagnetic parameters corresponding to the critical point, and determine the lower safety threshold under the current physical environment according to the following formula. : ,in, The lower safety threshold is expressed in N·m, and η is a safety margin coefficient preset between 0.85 and 0.95. This is the minimum synchronous torque limit value identified at the moment of slippage.

[0042] When the system experiences a synchronization interruption under load impact, the control unit executes a momentum capture procedure based on asymmetric duty cycle modulation, when the torque current component... If the average value is lower than the no-load reference for 150ms, it is determined to be out of sync. The power conversion unit stops the three-phase sinusoidal wave output and switches to a DC bias pulse sequence, which consists of a d-axis voltage vector with a duration of 20ms and an amplitude of 30% of the rated voltage. The control unit samples and extracts the rate of change of the induced electromotive force of the three-phase windings during the pulse application period. If the second-order difference value of the induced electromotive force exceeds 50V / s for three consecutive sampling cycles... 2 The position of the magnetic pole axis of the controlled magnetically coupled load is determined, and the system then re-injects excitation current with the captured axis phase as the starting angle. Establishing a magnetic flux locking state allows the controlled magnetically coupled load to transition from a static state to a synchronous acceleration phase, eliminating the physical obstacle that prevents the closed-loop capture of the magnetic coupling state under thick-walled container conditions.

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0044] 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 it. 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 spirit and scope of the technical solutions of the present invention.

Claims

1. A method for precise stepless speed control of a magnetic stirrer, characterized in that, Includes the following steps: Step S1: The power conversion unit adjusts the duty cycle of the pulse width modulation signal according to the received speed command, drives the power inverter circuit to output a three-phase current signal to the electromagnetic energy conversion unit, and establishes a rotating drive magnetic field corresponding to the speed command frequency in the electromagnetic energy conversion unit, so as to drive the controlled magnetic coupling load set inside the container to rotate synchronously through non-rigid magnetic coupling. Step S2: A high-frequency orthogonal phase perturbation signal with a preset frequency and amplitude is superimposed on the phase angle of the voltage vector of the electromagnetic energy conversion unit, so that the power angle of the rotating driving magnetic field generates controlled phase shift fluctuations near the stable operating point. Step S3: The stator current on the output side of the power conversion unit is monitored in real time using the current acquisition circuit. The response component corresponding to the frequency of the high-frequency orthogonal phase perturbation signal in the stator current is extracted by the digital filter. The synchronous torque limit between the rotating drive magnetic field and the controlled magnetic coupling load is identified according to the amplitude variation law of the response component. Step S4: Based on the identified synchronous torque limit value, dynamically correct the proportional coefficient and integral coefficient of the speed control loop, extract the steady-state value of the active component in the stator current to identify the current fluid load torque, perform feedforward compensation on the torque current command according to the load torque, and adjust the electromagnetic torque output by the electromagnetic energy conversion unit to counteract the resistance impact on the controlled magnetic coupling load caused by the change in fluid viscosity.

2. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, Step S2 includes: determining the modulation frequency and injection amplitude of the high-frequency orthogonal phase perturbation signal based on the rated speed of the controlled magnetically coupled load and the carrier frequency of the control system; superimposing the high-frequency orthogonal phase perturbation signal onto the original phase angle generated by the space vector pulse width modulation algorithm; updating the duty cycle command of the power conversion unit; and enabling the electromagnetic energy conversion unit to generate a controlled perturbation response.

3. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, In step S3, identifying the synchronous torque limit value of the controlled magnetically coupled load based on the amplitude variation law of the response component includes the following steps: Step S31, converting the extracted response component into a current vector in the torque direction through coordinate transformation; Step S32, calculating the energy integral value of the current vector within one cycle of the high-frequency orthogonal phase perturbation signal; Step S33, inverting the damping characteristics of the controlled magnetically coupled load under dynamic load through the energy integral value, and outputting the synchronous torque limit value characterizing the synchronization capability of the controlled magnetically coupled load.

4. The method for precise stepless speed control of a magnetic stirrer according to claim 3, characterized in that, The limit value of synchronous torque is determined by the following formula: ,in, This is the limit value of synchronous torque. ω is the instantaneous electromagnetic power of the electromagnetic energy conversion unit, ω is the angular velocity of the rotating driving magnetic field, and σ is a dimensionless constant characterizing the fluid coefficient and preset between 0.8 and 1.

2.

5. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, In step S4, the feedforward compensation for the torque current command includes the following steps: Step S41, extract the real-time electromagnetic torque output by the rotating drive magnetic field based on the active current component in the stator current; Step S42, calculate the resistance torque load generated by the fluid by combining the real-time acceleration and moment of inertia of the controlled magnetically coupled load; Step S43, convert the resistance torque load into a compensation current value and superimpose the compensation current value onto the output of the torque current regulator in the speed control loop.

6. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, Step S3 further includes: step S51, obtaining temperature data of the stator winding in the electromagnetic energy conversion unit; step S52, calculating the residual magnetism attenuation ratio of the permanent magnet in the controlled magnetic coupling load based on the temperature data; step S53, using the residual magnetism attenuation ratio to correct the identified synchronous torque limit value, and outputting the synchronous torque correction value after temperature rise compensation.

7. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, Step S3 further includes: monitoring the subharmonic energy distribution in the torque current feedback value; when the peak value of the subharmonic energy distribution in the preset frequency domain exceeds the safety threshold, determining that the controlled magnetically coupled load has entered the resonance critical state; adjusting the carrier frequency of the space vector pulse width modulation algorithm so that the system characteristic frequency avoids the mechanical resonance frequency of the controlled magnetically coupled load.

8. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, The method also includes a startup optimization step: during the startup phase of the controlled magnetically coupled load, the rotating drive magnetic field is controlled to operate in a variable frequency and variable voltage mode; by monitoring the phase lag angle of the stator current, the switching point of the controlled magnetically coupled load from static friction state to dynamic friction state is identified; and the initial integral value of the speed control loop is initialized according to the current characteristic value corresponding to the switching point.

9. The method for precise stepless speed control of a magnetic stirrer according to claim 1, characterized in that, The speed control loop uses an anti-integral saturation regulator. The proportional coefficient and integral coefficient of the regulator are linearly mapped according to the gradient of the change in synchronous torque limit value relative to the speed of the controlled magnetically coupled load.

Images