A stepless rotation speed precision control method of a magnetic stirrer

Abstract

The application relates to the technical field of motor control, and discloses a stepless rotation speed precision control method of 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 a rotating driving magnetic field is established in an electromagnetic energy conversion unit; a high-frequency orthogonal phase perturbation signal is superimposed in the phase angle of a voltage vector, so that the power angle of the rotating driving magnetic field is induced to produce phase offset fluctuation; a stator current response component is extracted, and a synchronous torque limit value is identified, then a control gain is corrected, and a torque feedforward compensation amount is superimposed; the application realizes online perception of the depth of magnetic coupling by analyzing electromagnetic characteristics, utilizes a dynamic compensation mechanism to offset fluid resistance impact in real time, eliminates the risk of slippage of a stirring sub under a high-viscosity reaction working condition, and improves the synchronous robustness and rotation speed control precision of system operation.

Description

TECHNICAL FIELD

[0001] The application relates to a stepless rotating speed precision control method of a magnetic stirrer and belongs to the technical field of motor control. BACKGROUND

[0002] The current magnetic stirrer generates a rotating magnetic field by using an inverter and drives a stirring sub in a container through a space magnetic coupling mode, so that non-contact stepless speed regulation and mixing of fluid materials are realized. The magnetic coupling interface is jointly formed by the motor rotor magnetic field and the stirring sub permanent magnetic pole, and the physical essence belongs to a variable stiffness elastic coupling system. There is a power angle deviation between the driving magnetic field and the stirring sub magnetic pole, which depends on the load torque. In the steady state, due to the low fluid viscosity 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 biopharmaceuticals or polymer synthesis, the fluid damping characteristics present nonlinear evolution with the chemical reaction process. The dramatic fluctuation of material viscosity causes the shear torque borne by the stirring sub to instantaneously increase, and then the magnetic coupling power angle tends to approach the physical critical point. Current improvements are mostly limited to external environmental physical adaptability, ignoring the prediction of internal dynamics instability by the driving control system. For example, the utility model patent with the authorization publication number CN203002292U discloses a magnetic stirrer, which seals a protective film on the outer wall of the body to eliminate the failure of motor stop due to frosting in an ultra-low temperature environment. However, in the reaction process involving sudden changes in fluid characteristics, such hardware dimension reinforcement does not solve the problem of magnetic slip 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 facing a high-viscosity reaction system load impact, the stirring sub will still uncontrollably jump due to the power angle exceeding the critical point. Because the controller cannot monitor the dynamic evolution of the magnetic coupling margin in real time, the stirring sub is prone to slip and cause synchronization interruption, and finally the stirring sub will jump disorderly in the container, destroying the consistency of material mixing.

[0004] Therefore, how to extract the characteristics of the motor driving current to inverse the instantaneous stiffness of the magnetic coupling system and realize the early prediction and active compensation of the slip state on the premise of using the original processor hardware of the system has become a technical problem to be solved by the application. SUMMARY

[0005] To solve the problems in the background art, the technical scheme of the application is as follows: a stepless rotating speed precision control method 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 instruction, drives the power inverter circuit to output a three-phase current signal to the electromagnetic energy conversion unit, establishes a rotating drive magnetic field corresponding to the speed instruction frequency in the electromagnetic energy conversion unit, and drives the controlled magnetic coupling load arranged in the container to rotate synchronously through the non-rigid magnetic coupling effect;

[0007] Step S2, superimpose a high-frequency orthogonal phase perturbation signal with a preset frequency and amplitude in the phase angle of the voltage vector of the electromagnetic energy conversion unit, so that the power angle of the rotating drive magnetic field produces a controlled phase shift fluctuation near the stable operating point;

[0008] Step S3, the current acquisition circuit is used to monitor the stator current on the output side of the power conversion unit in real time, the digital filter is used to extract the response component in the stator current corresponding to the frequency of the high-frequency orthogonal phase perturbation signal, and the synchronous torque limit value 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, the proportional coefficient and the integral coefficient of the speed control loop are dynamically corrected, the steady-state value of the active component in the stator current is extracted to identify the current fluid load torque, the load torque is fed forward to the torque current instruction, and the electromagnetic torque output by the electromagnetic energy conversion unit is adjusted to offset the resistance impact on the controlled magnetic coupling load due to the change of fluid viscosity.

[0010] Preferably, step S2 comprises: determining the modulation frequency and injection amplitude of the high-frequency orthogonal phase perturbation signal according to the rated speed of the controlled magnetic coupling load and the carrier frequency of the control system; superimposing the high-frequency orthogonal phase perturbation signal into the original phase angle generated by the space vector pulse width modulation algorithm, updating the duty cycle instruction of the power conversion unit, and making the electromagnetic energy conversion unit produce a controlled perturbation response.

[0011] Preferably, in step S3, identifying the synchronous torque limit value of the controlled magnetic coupling load according to the amplitude variation law of the response component comprises 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 in one period of the high-frequency orthogonal phase perturbation signal; step S33, inverting the damping characteristic of the controlled magnetic coupling load under dynamic load through the energy integral value, and outputting the synchronous torque limit value representing the synchronization capability of the controlled magnetic coupling load.

[0012] Preferably, the synchronous torque limit value is determined by the following formula: , wherein, is the synchronous torque limit value, 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 representing the flow coefficient and is preset to be between 0.8 and 1.2.

[0013] Preferably, in step S4, the feedforward compensation on the torque current instruction comprises the following steps: step S41, extracting the real-time electromagnetic torque output by the rotating driving magnetic field according to the active current component in the stator current; step S42, calculating the resistance torque load generated by the fluid in combination with the real-time acceleration and the moment of inertia of the controlled magnetic coupling load; and step S43, converting the resistance torque load into a compensation current value and superimposing the compensation current value on the output end of the torque current regulator in the speed control loop.

[0014] Preferably, step S3 further comprises the following steps: step S51, obtaining temperature data of the stator winding in the electromagnetic energy conversion unit; step S52, calculating the remanence decay ratio of the permanent magnet in the controlled magnetic coupling load according to the temperature data; and step S53, correcting the identified synchronous torque limit value using the remanence decay ratio to output a synchronous torque correction value after temperature rise compensation.

[0015] Preferably, step S3 further comprises the following steps: monitoring the sub-harmonic energy distribution in the torque current feedback value; when the peak value of the sub-harmonic energy distribution in the preset frequency domain interval exceeds a safety threshold, determining that the controlled magnetic coupling load enters a resonance critical state; and adjusting the carrier frequency of the space vector pulse width modulation algorithm to make the system characteristic frequency avoid the mechanical resonance frequency of the controlled magnetic coupling load.

[0016] Preferably, the method further comprises a starting optimization step: during the starting phase of the controlled magnetic coupling load, the rotating driving magnetic field is controlled to operate in a variable frequency and variable voltage mode; the switching point at which the controlled magnetic coupling load transitions from static friction state to dynamic friction state is identified by monitoring the phase lag angle of the stator current; and the integral initial 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 adopts an anti-integral saturation regulator, and the proportional coefficient and the integral coefficient of the regulator are linearly mapped according to the change gradient of the synchronous torque limit value relative to the speed of the controlled magnetic coupling load.

[0018] Preferably, the method further comprises a fault protection step: when the identified synchronous torque limit value is lower than a preset safety lower threshold, the increasing slope of the speed instruction is locked; and at the same time as outputting a warning signal indicating that the controlled magnetic coupling load has a risk of slipping, the rotating driving magnetic field is controlled to reduce to a safe speed interval below 200 r / min in a deceleration mode.

[0019] Compared with the prior art, the present application has the following advantages:

[0020] 1. In the precise control of stepless speed, by superimposing a phase perturbation signal in the control loop of the excitation current component, and monitoring the same frequency response signal generated in the torque current component in real time, the driving system can establish a transient stiffness evaluation mechanism for the non-contact magnetic coupling interface, convert the magnetic coupling margin into quantifiable electrical parameter feedback, enable the motor driving unit to detect the depth of the magnetic potential well, strengthen the magnetic adsorption force in advance before the physical displacement of the stirrer lags, eliminate the jump phenomenon caused by the breakage of magnetic lines of force, and ensure the quasi-synchronous running state in the full-range stepless speed regulation process.

[0021] 2. Using the energy flow conservation relationship between the instantaneous electromagnetic power of the motor and the real-time speed of the stirrer, the system identifies the dynamic damping coefficient of the fluid environment to real-time correct the control gain of the speed regulator, directly maps the nonlinear evolution of fluid shear resistance to the feedforward compensation amount of the torque current loop, makes the driving magnetic field exhibit viscous stress compensation characteristics that match the fluid viscosity characteristics, effectively offsets the load impact generated by non-Newtonian fluid in the polymerization process, and solves the speed overshoot and non-steady-state oscillation problems that frequently occur in the variable damping working condition of the traditional control law.

[0022] 3. Combined with the temperature rise representation parameters obtained by stator winding resistance identification and the cross modulation components extracted by double frequency orthogonal detection signals, a composite regulation system considering thermal demagnetization compensation and dynamic instability prediction is constructed, the excitation compensation gain is dynamically calibrated according to the function relationship that the remanence of permanent magnet decays with temperature, and the information entropy characteristics of cross modulation terms are used to distinguish between stable phase lag and high-risk simple harmonic instability, on the basis of maintaining the magnetic coupling strength, the mechanical swing energy of the stirrer is dissipated by injecting damping components, and the running consistency of the system in high temperature and high dynamic environment is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0023] Fig. 1 The control method flowchart of the orthogonal phase perturbation injection and dynamic torque compensation of the application;

[0024] Fig. 2 The system logic architecture diagram integrating the underlying mechanism, core process and auxiliary protection mechanism of the application. DETAILED DESCRIPTION

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

[0026] The application provides a kind of stepless rotating speed precision control method of magnetic stirrer, power conversion unit is adjusted according to the duty cycle of pulse width modulation signal of rotating speed instruction, driving power inverter circuit outputs three-phase current signal to electromagnetic energy conversion unit, corresponding rotating drive magnetic field of rotating speed instruction frequency is established in electromagnetic energy conversion unit, and the synchronous rotation of controlled magnetic coupling load in container is driven by the non-rigid magnetic coupling effect in space, since the driving magnetic field of magnetic stirrer and controlled magnetic coupling load belong to variable stiffness elastic coupling system, when processing high viscosity or non-newtonian fluid, the torque of load will cause power angle deviation to approach critical point;To cope with the problem that magnetic coupling interface dynamics state is difficult to perceive in real time, the present embodiment superimposes high-frequency orthogonal phase perturbation signal in voltage vector phase angle of electromagnetic energy conversion unit, which has preset frequency and amplitude, induces the phase shift fluctuation of rotating drive magnetic field near stable operating point, current acquisition circuit monitors stator current on the output side of power conversion unit in real time, and the response component corresponding to the frequency of high-frequency orthogonal phase perturbation signal in stator current is extracted by digital filter;High-frequency orthogonal phase perturbation signal superimposes sinusoidal perturbation component Δθ in original phase angle θ generated by space vector pulse width modulation algorithm, and the expression of sinusoidal perturbation component Δθ is , perturbation amplitude Set as 5% to 10% of rated current vector, perturbation frequency Set at 500Hz to 1000Hz, current acquisition circuit obtains three-phase stator current, which is converted into torque current component By coordinate transformation, high-frequency response component is extracted by using center frequency , bandwidth 20Hz digital band-pass filter , the mapping relationship between power angle deviation and magnetic coupling stiffness is established by using Rms value in perturbation period, when fluid viscosity increases and causes magnetic coupling stiffness to drop, Amplitude shows a monotonic increasing trend, and the system dynamically corrects proportional coefficient and integral coefficient according to amplitude change rate, and electromagnetic torque pre-compensation is completed before 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. The anchor is in the physical environment magnetic coupling boundary; based on the evolution of fluid viscosity will cause the adjustment lag, the system based on the identified synchronous torque limit value dynamic correction speed control loop proportional coefficient and integral coefficient, while extracting the steady-state value of the active component in the stator current to identify the current fluid load torque, and perform feedforward compensation on the torque current instruction, including: extracting the real-time electromagnetic torque output by the rotating drive magnetic field according to the active current component in the stator current; combining the real-time acceleration and moment of inertia of the controlled magnetic coupling load to calculate the resistance torque load generated by the fluid; convert the resistance torque load into a compensation current value, and superimpose the compensation current value on the output end of the torque current regulator in the speed control loop, and real-time offset the resistance impact generated by the change of fluid viscosity by adjusting the electromagnetic torque output by the electromagnetic energy conversion unit.

[0029] In response to the magnetic energy product decay caused by ambient temperature and winding temperature rise, the present embodiment adds a temperature rise compensation procedure, obtains the temperature data of the stator winding in the electromagnetic energy conversion unit, and calculates the residual magnetism decay ratio of the permanent magnet in the controlled magnetic coupling load. The engineering calculation model of the residual magnetism decay ratio is: according to the demagnetization characteristic curve of the neodymium-iron-boron permanent magnet in the temperature range of 25-150℃, the control unit establishes a discrete lookup table model with a step of 5℃. When the winding temperature collected by the temperature sensor increases by 10℃, the system automatically retrieves the demagnetization temperature coefficient between 0.008 and 0.015, and performs subtraction compensation on the synchronous torque limit value, to ensure that the control system will not produce slip misjudgment due to the decrease of magnetic energy product under high temperature working condition. The synchronous torque limit value identified is corrected by using the residual magnetism decay ratio, and the synchronous torque correction value after temperature rise compensation is output, so as to correct the control gain; In order to solve the mechanical resonance problem that may occur in the speed regulation cycle, the system monitors the sub-harmonic energy distribution in the torque current feedback value. When the peak value of the sub-harmonic energy distribution in the preset frequency domain interval exceeds the safety threshold, it is determined that the controlled magnetic coupling load enters the resonance critical state. At this time, the system adjusts 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 magnetic coupling load; In order to improve the synchronization robustness of the system, during the starting stage of the controlled magnetic coupling load, the system controls the rotating driving magnetic field to operate in the variable frequency and variable voltage mode. By monitoring the phase lag angle of the stator current, the switching point of the controlled magnetic coupling load from static friction state to dynamic friction state is identified. The bottom processing flow of identifying the switching point is: 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 is greater than 0.8 degrees for 5ms, it is determined that the critical inflection point of the magnetic pole displacement overcoming static friction occurs. At the same time, the comparator determines whether the current torque current component reaches 95% of the starting preset current value. If both conditions are met at the same time, the dynamic friction switching point is locked. The integral initial 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. The proportional coefficient and the integral coefficient are linearly mapped according to the change gradient of the synchronous torque limit value relative to the speed of the controlled magnetic coupling load.

[0030] In the face of extreme disturbance working conditions such as the slip of the stirring rod, the system starts the fault protection procedure. When the identified synchronous torque limit value is lower than the preset safety lower threshold, the increase slope of the speed command is locked. At the same time, the system outputs a warning signal indicating that the controlled magnetic coupling load has a slip risk, and controls the rotating driving magnetic field to reduce to a safe speed range below 200r / min in the deceleration mode. If it is determined that the stirring rod has slipped, that is, 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. : , wherein, is the synchronous torque limit value, 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 flow coefficient and is selected as 1.05 in the embodiment.

[0032] The control unit increases the given value of the excitation current component to strengthen the magnetic flux density of the rotating driving magnetic field and improve the static stiffness of the magnetic coupling, and the control unit extracts the steady-state value of the active component in the torque current component , calculates the fluid resistance torque, and adds it as a feedforward compensation to the output end of the torque current regulator. In the extreme working condition where the viscosity rises to 5000 mPa·s, the instantaneous power angle of the controlled magnetic coupling load is restricted to about 65°, the stirring sub is maintained in a synchronous rotating state at a rotational speed of 300 r / min, and the material mixing process remains consistent in the full viscosity range, solving the problem of synchronous interruption caused by the breaking of magnetic lines in a high-viscosity environment.

[0033] In the test scenario for viscosity gradient fluctuations, the test platform is configured with a drive controller with a current acquisition circuit, an electromagnetic energy conversion unit, and a silicon oil load with non-Newtonian fluid characteristics. The measurement range of the current acquisition circuit is 0 to 10 A, the sampling frequency is set to 10 kHz, and the measurement accuracy is 0.5%. To simulate the industrial electromagnetic environment, the stator current sampling branch is superimposed with a Gaussian white noise with a signal-to-noise ratio of 25 dB, and a power frequency harmonic interference with a frequency of 50 Hz is introduced. The test process involves the frequency of the high-frequency orthogonal phase perturbation signal, which depends on the balance between data acquisition real-time and data processing load. If the frequency is lower than 100 Hz, the identification of the phase difference will be delayed, resulting in compensation lag. If the frequency is higher than 1000 Hz, the switch loss of the power inverter and the rise of the stator iron loss will increase. According to the mechanical time constant of the controlled magnetic coupling load, the frequency is determined to be 500 Hz, 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 pulsation, preventing the response component from being submerged in the background noise. The object of the method of the present application operates in the working conditions where the viscosity gradient is 100 mPa·s, 1000 mPa·s, and 5000 mPa·s. In the initial reference state of 100 mPa·s, the amplitude of the response signal in the torque current component extracted by the system is 0.12 A, and the calculated phase difference is 4.2°, when the viscosity is switched to 1000 mPa·s, the phase lag occurs due to the increase of fluid damping, the response signal of the controlled magnetic coupling load decreases to 0.08 A, the phase difference increases to 15.8°, at this time, the control unit determines the synchronous torque limit value according to the following formula : , wherein, is the synchronous torque limit value, is the instantaneous electromagnetic power of the electromagnetic energy conversion unit, in units of W, ω is the angular velocity of the rotating driving magnetic field, in units of rad / s, and σ is a flow coefficient and is selected as 1.05 in the present test, at this time, the digital filter still accurately locks the 500Hz feature point despite the presence of 25dB noise in the environment, and the current ripple coefficient after processing decreases from 12.5% of the original acquisition value to 2.3%.

[0034] To verify the key parameter boundary, a contrast test is set to have the flow coefficient σ be 0.5, 1.05 and 1.5 respectively, when σ is set to 0.5, the calculated synchronous torque limit value is lower than the actual coupling limit, causing the control unit to trigger limit compensation when the viscosity is 2500 mPa·s, the field current reaches the limiting value, the system generates a 8.5% torque fluctuation and causes the winding to heat up, when σ is set to 1.5, the system overestimates the energy margin, at the inflection point where the viscosity rises to 3800 mPa·s, the phase difference jumps to 85.2° but does not trigger control gain correction, causing the stirrer to lose synchronization within 0.8ms, the sample group of the present application selected as σ being 1.05, when the viscosity rises to 5000 mPa·s, the power angle deviation is constrained to 62.5°, the stirrer maintains stable rotation at 300r / min, and the instantaneous stiffness coefficient is identified by injecting a phase perturbation, which can invert the energy state of the non-contact magnetic coupling interface, limits the flow coefficient σ to between 0.8 and 1.2, so that the identification result of the synchronous torque limit value is in the optimal working window, avoiding control oversaturation while ensuring synchronous stability in high-viscosity conditions, and the synchronous limit torque of the controlled magnetic coupling load is increased to 2.45 times that of the original control method.

[0035] Embodiment Three: The present embodiment combines Figs. 1-2 to explain a stepless speed precise control method of a magnetic stirrer, for example, Fig. 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 Fig. 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. is the excitation current component in A, ω is the angular velocity of the rotating driving magnetic field in rad / s, the calibration parameters are input as the reference of dynamic speed regulation, and the calculation result of the synchronous torque limit value is consistent among different hardware batches.

[0041] In the reaction kettle deployment scenario with a 10mm-thick jacketing layer, the equivalent magnetic reactance of the magnetic coupling interface increases due to the increase in the physical distance, the system faces the risk of protection false triggering caused by the mismatch between the preset torque threshold and the actual slip point, and the control unit executes the field self-adaptive calibration procedure after assembly is completed, drives the rotating driving magnetic field to operate at a speed of 50r / min, and gradually reduces the excitation current component by 0.1A / s until the response component in the stator current has a sudden change in amplitude, the electromagnetic parameters corresponding to the critical point are recorded, and the safe lower threshold in the current physical environment is determined according to the following formula : wherein, is the safe lower threshold in N·m, η is a safety margin coefficient preset to be between 0.85 and 0.95, is the minimum synchronous torque limit value identified at the slip moment.

[0042] When the system is in the synchronous interruption working condition under load impact, the control unit executes the momentum capture procedure based on asymmetric duty cycle modulation, and determines that the system is out of synchronization when the torque current component is lower than the no-load reference for 150ms, the power conversion unit stops the three-phase sinusoidal wave output and switches to the DC bias pulse sequence, which is composed of a d-axis voltage vector with a duration of 20ms and an amplitude of 30% of the rated voltage, and the control unit samples and extracts the induced electromotive force change rate of the three-phase winding during the pulse application, and if the second-order difference value of the induced electromotive force exceeds 50V / s 2 for 3 consecutive sampling periods, the magnetic pole axis position of the controlled magnetic coupling load is determined, and the system immediately re-injects the excitation current with the captured axis phase as the starting angle to establish a magnetic flux locking state, so that the controlled magnetic coupling load transitions from the static state to the synchronous acceleration stage, and the physical obstacle that the magnetic coupling state cannot be closed-loop captured under the thick-wall container working condition is eliminated.

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

[0044] Finally, it should be noted that the above examples are merely intended to illustrate the technical solutions of the present application and not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for stepless control of the rotation speed of a magnetic stirrer, characterized in that The method comprises the following steps: Step S1, the power conversion unit adjusts the duty cycle of the pulse width modulation signal according to the received speed instruction, drives the power inverter circuit to output a three-phase current signal to the electromagnetic energy conversion unit, establishes a rotating drive magnetic field corresponding to the speed instruction frequency in the electromagnetic energy conversion unit, and drives the controlled magnetic coupling load arranged inside the container to rotate synchronously through the non-rigid magnetic coupling effect; Step S2, superimpose a high-frequency orthogonal phase perturbation signal with a preset frequency and amplitude in the phase angle of the voltage vector of the electromagnetic energy conversion unit, so that the power angle of the rotating drive magnetic field produces a controlled phase shift fluctuation near the stable operating point; Step S3, the current acquisition circuit is used to monitor the stator current on the output side of the power conversion unit in real time, the digital filter is used to extract the response component corresponding to the frequency of the high-frequency orthogonal phase perturbation signal in the stator current, and the synchronous torque limit value 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, the proportional coefficient and the integral coefficient of the speed control loop are dynamically corrected, the steady-state value of the active component in the stator current is extracted to identify the current fluid load torque, the torque current instruction is fed forward compensated according to the load torque, and the electromagnetic torque output by the electromagnetic energy conversion unit is adjusted to offset the resistance impact on the controlled magnetic coupling load due to the change of fluid viscosity.

2. The method according to claim 1, wherein, Step S2 comprises: determining the modulation frequency and injection amplitude of the high-frequency orthogonal phase perturbation signal according to the rated speed of the controlled magnetic coupling load and the carrier frequency of the control system; superimposing the high-frequency orthogonal phase perturbation signal into the original phase angle generated by the space vector pulse width modulation algorithm, updating the duty cycle instruction of the power conversion unit, and making the electromagnetic energy conversion unit produce a controlled perturbation response.

3. The method of claim 1, wherein the method comprises: In step S3, identifying the synchronous torque limit value of the controlled magnetic coupling load according to the amplitude variation law of the response component comprises 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 in one period of the high-frequency orthogonal phase perturbation signal; step S33, inverting the damping characteristic of the controlled magnetic coupling load under dynamic load through the energy integral value, and outputting the synchronous torque limit value representing the synchronization capability of the controlled magnetic coupling load.

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

2.

5. The method of claim 1, wherein the method comprises: In step S4, the torque current instruction is fed forward compensated, comprising the following steps: step S41, extracting the real-time electromagnetic torque output by the rotating drive magnetic field according to the active current component in the stator current; step S42, combining the real-time acceleration and moment of inertia of the controlled magnetic coupling load to calculate the resistance torque load generated by the fluid; step S43, converting the resistance torque load into a compensation current value, and superimposing the compensation current value to the output end of the torque current regulator in the speed control loop.

6. The method of claim 1, wherein the method comprises: The step S3 further comprises: a step S51 of acquiring temperature data of the stator winding in the electromagnetic energy conversion unit; a step S52 of calculating a residual magnetism decay ratio of the permanent magnet in the controlled magnetic coupling load according to the temperature data; and a step S53 of correcting the identified synchronous torque limit value by using the residual magnetism decay ratio, and outputting a synchronous torque correction value compensated by temperature rise.

7. The method of claim 1, wherein the method comprises: The step S3 further comprises: monitoring a sub-harmonic energy distribution in the torque current feedback value; determining that the controlled magnetic coupling load enters a resonance critical state when a peak value of the sub-harmonic energy distribution in a preset frequency domain interval exceeds a safety threshold; and adjusting a carrier frequency of the space vector pulse width modulation algorithm so that a system characteristic frequency avoids a mechanical resonance frequency of the controlled magnetic coupling load.

8. The method of claim 1, wherein the method comprises: The method further comprises a starting optimization step: in a starting phase of the controlled magnetic coupling load, the rotating driving magnetic field is controlled to operate in a variable frequency and variable voltage mode; a switching point at which the controlled magnetic coupling load is switched from a static friction state to a dynamic friction state is identified by monitoring a phase lag angle of the stator current; and an integral initial value of a speed control loop is initialized according to a current characteristic value corresponding to the switching point.

9. The method of claim 1, wherein the method comprises: The speed control loop adopts an anti-integral saturation regulator, and a proportional coefficient and an integral coefficient of the regulator are linearly mapped according to a change gradient of the synchronous torque limit value relative to a speed of the controlled magnetic coupling load.

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