Radial displacement sensor detection deviation correction method for bearingless permanent magnet sheet motor

Abstract

The application discloses a bearingless permanent-magnet thin-slice motor radial displacement sensor detection deviation correction method capable of accurately calculating eccentric direction and distance and quickly correcting through suspension current, and comprises the following steps: based on Maxwell stress tensor method and virtual displacement method, mathematical models of controllable suspension force of the bearingless permanent-magnet thin-slice motor and unbalanced magnetic pull caused by eccentricity in a rotor coordinate system are derived respectively; the suspension current is divided into two types of anti-eccentricity and anti-disturbance, and decoupling between eccentric distance and corresponding suspension current components is realized; with the aim of eliminating anti-eccentricity current, the eccentric direction and size are judged by extracting m-axis and n-axis suspension current components to determine a compensation point, and a cycle algorithm of step tracking minimum current is introduced near the compensation point. The application can correct the rotor static eccentricity phenomenon caused by the radial displacement sensor, effectively improve system efficiency and reduce temperature rise speed, and has the characteristics of short time consumption, low cost and high accuracy compared with existing methods.

Description

Technical Field

[0001] This invention relates to the field of optimization of bearingless motor control systems, and specifically to a method for correcting the detection deviation of a radial displacement sensor in a bearingless permanent magnet thin-film motor. Background Technology

[0002] Bearingless permanent magnet thin-film motors can achieve five-degree-of-freedom full levitation of the rotor using electromagnetic force. Compared to traditional motors, their bearingless design allows for easy sealing of the rotor, thus isolating it from external contaminants. These motors have found widespread application in applications requiring high purity, such as ventricular assist devices and semiconductor cleaning pumps.

[0003] The rotor axial length of a bearingless permanent magnet thin-film motor is relatively small compared to its outer diameter. Therefore, active control is not required in one axial and two torsional degrees of freedom; stable levitation can be achieved solely through magnetic reluctance. However, displacement closed-loop control is necessary in the two radial degrees of freedom to ensure the rotor levitates at the geometric center of the air gap. In the displacement closed-loop control system, eddy current sensors and linear Hall effect sensors are commonly used to detect rotor position. However, the output of displacement sensors is susceptible to changes caused by temperature, electromagnetic interference, etc. Furthermore, the use of multiple sensors makes complete output calibration difficult and prone to problems such as assembly asymmetry, introducing displacement detection deviations. This results in the rotor being eccentrically positioned, not at the geometric center of the stator, during stable levitation. This eccentricity leads to uneven magnetic flux density distribution, generating an unbalanced magnetic pull pointing towards the minimum air gap. To balance this, the displacement closed-loop control system introduces redundant levitation current components, resulting in reduced motor power density, increased noise, and increased heat generation. Actual experiments have shown that a 0.1mm eccentricity in a single direction can increase the system input power by 96% compared to a non-eccentric configuration, thus necessitating correction.

[0004] However, existing related research is still limited and has various shortcomings. For example, the paper "Eccentricitycompensation for bearingless motor based on the tracking of the minimum antieccentric levitation current" compensates for detection deviation by iteratively searching for the minimum levitation current. However, this method can only determine the quadrant in which the rotor is located, but cannot identify the specific direction and magnitude of rotor eccentricity. Furthermore, the iterative algorithm used is complex, has a long correction time, and consumes a lot of resources. Summary of the Invention

[0005] Objective: To address the problems existing in the background technology, this invention proposes a method for correcting the deviation detected by a radial displacement sensor in a bearingless permanent magnet thin-film motor, which can accurately calculate and quickly correct the eccentricity direction and distance using the levitation current. First, based on Maxwell's stress tensor method and virtual displacement method in the rotor coordinate system, a mathematical model of the motor is derived, establishing the functional relationship between the levitation current, controllable levitation force, eccentricity distance, and unbalanced magnetic pull. Then, the levitation current is divided into two categories: anti-eccentricity and anti-disturbance, achieving decoupling between the eccentricity distance and the corresponding levitation current component. Next, with the goal of eliminating anti-eccentricity current, the eccentricity direction and magnitude are quickly and directly determined by extracting the m-axis and n-axis levitation current components to identify the compensation point. The minimum levitation current is then tracked cyclically near the compensation point to determine the compensation value. The compensation value is fed back to the displacement closed-loop control system, thereby correcting the deviation. This invention can accurately determine and quickly correct the direction and magnitude of rotor static eccentricity caused by the radial displacement sensor, effectively improving system efficiency and reducing the temperature rise rate. Compared with existing methods, it has the advantages of shorter processing time, lower cost, and higher accuracy.

[0006] Technical conditions: To achieve the above objectives, the technical solution of this invention is: a method for correcting the detection deviation of a radial displacement sensor in a bearingless permanent magnet thin-film motor, comprising:

[0007] Define the coordinate system when the rotor is located at the geometric center of the air gap, i.e., without eccentricity, as the stator coordinate system xOy. According to Maxwell's stress tensor method, the x-axis and y-axis components of the controllable levitation force F acting on the rotor can be obtained by integrating along the circumference of the air gap Γ:

[0008]

[0009]

[0010] In the formula, r is the rotor radius; l is the axial length of the rotor; μ0 is the vacuum permeability; B is the air gap magnetic flux density; and θ is the air gap circumference angle.

[0011] During normal operation of the motor, both torque and suspension magnetic fields exist simultaneously in the air gap. Therefore, B can be further expressed as:

[0012] B(θ,t)=B PM,T cos(p T θ-ω T t+λ)+B S cos(p S θ-ω S t+μ)

[0013] In the formula, B PM,T B is the amplitude of the combined air gap magnetic flux density of the permanent magnet and the torque magnetic field; S p is the amplitude of the air gap magnetic flux density of the levitation magnetic field; TThe number of pole pairs in the torque winding should be equal to the number of pole pairs in the permanent magnet; p S For the number of pole pairs of the levitation winding, p should satisfy... S =p T ±1;ω S With ω T λ and μ are the electric angular velocities of the torque magnetic field and the levitation magnetic field, respectively; λ and μ are the initial phase angles.

[0014] Combining the two equations above, we can obtain F. x With F y The expression is:

[0015] F x =F M cos(μ-λ)

[0016] F y =F M sin(μ-λ)

[0017] In the formula, F M This represents the amplitude of Maxwell's force.

[0018] As can be seen from the above equation, the radial levitation force in the stator coordinate system is related to the rotor position, which is inconvenient for application. To further decouple, let's define a rotor coordinate system mO'n, then transforming the above equation yields:

[0019] F x =k(i Sm ψ f +i Sn ψ Tn )

[0020] F y =-k(i Sn ψ f -i Sm ψ Tn )

[0021] In the formula, L S Mutual inductance of the torque windings; N T With N S These are the number of turns for the torque winding and the suspension winding, respectively; i Sm with i Sn Ψ represents the m-axis and n-axis components of the levitation current. f For permanent magnet flux linkage; Ψ Tn This represents the n-axis component of the torque winding flux linkage.

[0022] When the radial displacement sensor produces a detection deviation, the permanent magnet rotor of the motor will no longer be suspended at the geometric center of the stator, but will be located at the detection center. This eccentricity will cause an increase in the self-inductance of the torque winding, which can be expressed as:

[0023]

[0024] In the formula, L Tm,n x represents the self-inductance components of the torque winding along the m-axis and n-axis; e With y e The rotor eccentricity in the stator coordinate system; k e C is a constant.

[0025] According to the principle of virtual displacement, the unbalanced magnetic pull on the rotor is the partial derivative of the inductance energy stored in the torque winding with the radial displacement, and its result is zero only when the rotor is located at the geometric center of the stator. Since the torque control section uses i... Tm =0 control, therefore the expression for the unbalanced magnetic pull is:

[0026]

[0027] In the formula, W m Energy is stored in the torque winding inductance; I f i is the equivalent excitation current of the permanent magnet; Tn This represents the n-axis component of the torque winding current.

[0028] According to the above formula, the unbalanced magnetic pull on the rotor depends only on the n-axis component of the torque winding current and the magnitude of eccentricity, and is independent of the levitation current. Taking the x-axis as an example, when the torque winding is not current-carrying, the unbalanced magnetic pull F on the rotor can be obtained through finite element simulation. ex Mean and eccentricity x e The relationship is linear, therefore the corresponding m-axis component of the levitation current i Sm The current increases proportionally. However, during actual motor operation, random external disturbances also act on the rotor, causing fluctuations in the m-axis and n-axis components of the levitation current. To accurately identify displacement detection deviations, the levitation current needs to be classified. The levitation current resisting unbalanced magnetic pull is defined as the anti-eccentric current i. e When the rotor is in a static eccentric state, the anti-eccentric current is a constant DC component, which is easy to extract; the current resisting external disturbances is the anti-disturbance current i. r Since the external disturbance force is random, the anti-disturbance current that counteracts it is a fluctuating quantity, which needs to be eliminated by low-pass filtering.

[0029] Meanwhile, since bearingless motors generally have smaller rotors and lighter loads, their torque current n-axis component i Tn Much smaller than the equivalent excitation current I of the permanent magnet f To simplify the analysis, i is ignored. Tn The influence of the eccentricity can be investigated by low-pass filtering the m-axis and n-axis components of the detected levitation current, extracting the DC component to obtain the anti-eccentricity current, and combining it with the above theoretical analysis and simulation results to calculate the specific direction and magnitude of the rotor eccentricity.

[0030] The smaller the eccentricity distance, the smaller the corresponding anti-eccentricity current. When the rotor is located at the geometric center of the stator, i.e., without eccentricity, the anti-eccentricity current is zero, and the system reaches its optimal operating state. A hysteresis comparator is introduced into the algorithm for eliminating the anti-eccentricity current. h This is an error limit value, applied only when the absolute value of the anti-eccentric current is greater than i. h The subsequent algorithm continues to execute; j and j h These are the number of fluctuations and the limit value for the number of fluctuations, respectively. The fluctuation only occurs when the anti-eccentric current exceeds the limit value i. h The number of times is more than j h Then continue executing the subsequent algorithm. Set i h With j h The purpose of this is to prevent the system from fluctuating repeatedly in order to eliminate the anti-eccentric current. The complete correction algorithm is only executed when both the absolute value of the anti-eccentric current and the number of fluctuations exceed the limit value. The new displacement detection deviation is calculated and compensated. Otherwise, the output result of the previous cycle remains unchanged.

[0031] The displacement detection deviation correction algorithm proposed in this invention is based on the above theoretical derivation and simulation. While it is relatively accurate in identifying the eccentricity direction, its calculation of the eccentricity magnitude depends on model parameters, which may result in the rotor center not being located at the stator geometric center after compensation. To address this issue, a cyclic algorithm for tracking the minimum anti-eccentricity current in a step-by-step manner is added near the compensation point. d With y d The outer range is defined by h; the number of iterations is h; and x is x. h With y h This represents the displacement step size incremented in each iteration. The implementation of this iterative algorithm does not directly use the displacement compensation value x calculated in the previous stage. e With y e Instead of feeding back into the displacement setting, x is used as the input. e ±x d With y e ±y d Feedback is sent back (incrementing when eccentricity is in the positive direction and subtracting when it is in the opposite direction), and the loop count h is set to zero. After this displacement feedback, the previous judgment part is skipped in the next loop cycle, and the loop algorithm is entered directly. The loop count h is incremented by 1, and the anti-eccentricity current of this cycle is sampled. If the sampled result is less than the current value of the previous loop cycle, the loop continues. At this time, the displacement feedback value is... and The cycle continues until the anti-eccentric current in a certain cycle is greater than the current in the previous cycle, at which point the cycle ends and the compensation value is determined.

[0032] Compared with the algorithm in the literature "Eccentricity compensation for bearingless motor based on the tracking of the minimum antieccentric levitation current", the radial displacement sensor detection deviation correction method for bearingless permanent magnet thin-film motor proposed in this invention, after quickly determining the specific direction and magnitude of the eccentricity through the levitation current offset, only adds a step tracking loop algorithm near the compensation point. Therefore, it can accurately levitate the rotor to the geometric center of the stator through compensation while ensuring speed, so that the motor operates in the optimal state. At this time, the unbalanced magnetic pull is 0, the levitation current is minimal, and the system efficiency is the highest.

[0033] This invention also provides a hardware system for radial displacement sensor detection deviation correction of a bearingless permanent magnet thin-film motor, comprising: a power module, a control module, and a bearingless permanent magnet thin-film motor; the power module consists of a sampling circuit and two sets of three-phase full-bridge inverters; the sampling circuit has six current sampling channels, responsible for sampling the current of the three-phase floating winding and the current of the three-phase torque winding; the two sets of three-phase full-bridge inverters respectively control the floating winding and the torque winding; the control module includes a DSP main control chip and its peripheral circuits, a conditioning circuit, and an external AD circuit; the conditioning circuit converts the level output of the current sensor to within 0-3V for safe input to the DSP's internal ADC module; the external AD circuit uses a 12-bit ADC chip to achieve high-precision sampling of the Hall sensor output and transmits the result to the DSP; the DSP, as the main control chip, collects all external data and uses algorithms to calculate and generate six sets of PWM waves to control the two sets of inverters.

[0034] The present invention also provides a bearingless permanent magnet thin-film motor, which uses the above-mentioned radial displacement sensor detection deviation correction method for a bearingless permanent magnet thin-film motor to correct the radial displacement sensor detection deviation.

[0035] Beneficial effects: This invention proposes a method for correcting the detection deviation of a radial displacement sensor applicable to bearingless permanent magnet thin-film motors. The proposed method can effectively correct the rotor static eccentricity caused by the radial displacement sensor, effectively improving system efficiency and reducing the rate of temperature rise. Compared with existing methods, it features shorter processing time, lower cost, and higher accuracy. Attached Figure Description

[0036] Figure 1 This is a flowchart of the radial displacement sensor detection deviation correction method for bearingless permanent magnet thin-film motors proposed in this invention;

[0037] Figure 2 This is a schematic diagram of the coordinate system definition;

[0038] Figure 3 This is a graph showing the relationship between the unbalanced magnetic pull force, the eccentric distance, and the corresponding anti-eccentric current obtained from finite element simulation.

[0039] Figure 4 This is a schematic diagram of the forces acting on the rotor of the motor during normal operation;

[0040] Figure 5 This is a block diagram of a bearingless permanent magnet thin-film motor suspension control system that incorporates displacement detection deviation identification and correction algorithms;

[0041] Figure 6 It is a displacement simulation waveform diagram;

[0042] Figure 7 This is a simulation waveform of the anti-eccentric current;

[0043] Figure 8 This is a diagram of the experimental platform;

[0044] Figure 9 This is the waveform of the static suspension displacement before correction;

[0045] Figure 10 This is the waveform of the static levitation current before correction;

[0046] Figure 11 This is the corrected static levitation displacement waveform;

[0047] Figure 12 This is the corrected static levitation current waveform;

[0048] Figure 13 This is a waveform diagram of the suspension displacement at 3000 rpm;

[0049] Figure 14 It is the floating current waveform at 3000 rpm;

[0050] Figure 15 This is a comparison chart of algorithm execution time. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0052] This invention proposes a method for correcting the detection deviation of a radial displacement sensor applicable to bearingless permanent magnet thin-film motors. Figure 1 This is a flowchart of the method.

[0053] Example 1

[0054] This embodiment adopts the following bearingless permanent magnet thin-film motor structure: six stator teeth, one pair of permanent magnets on the rotor, two pairs of suspended windings, and the winding structure is centralized.

[0055] The coordinate system defined when the rotor is located at the geometric center of the air gap, i.e., without eccentricity, is the stator coordinate system xOy, as follows: Figure 2 As shown. According to Maxwell's stress tensor method, the x-axis and y-axis components of the controllable levitation force F on the rotor can be obtained by integrating along the air gap circumference Γ:

[0056]

[0057]

[0058] In the formula, r is the rotor radius; l is the axial length of the rotor; μ0 is the vacuum permeability; B is the air gap magnetic flux density; and θ is the air gap circumference angle.

[0059] During normal operation of the motor, both torque and suspension magnetic fields exist simultaneously in the air gap. Therefore, B can be further expressed as:

[0060] B(θ,t)=B PM,T cos(p T θ-ω T t+λ)+B S cos(p S θ-ω S t+μ)

[0061] In the formula, B PM,T B is the amplitude of the combined air gap magnetic flux density of the permanent magnet and the torque magnetic field; S p is the amplitude of the air gap magnetic flux density of the levitation magnetic field; T The number of pole pairs in the torque winding should be equal to the number of pole pairs in the permanent magnet; p S For the number of pole pairs of the levitation winding, p should satisfy... S =p T ±1;ω S With ω T λ and μ are the electric angular velocities of the torque magnetic field and the levitation magnetic field, respectively; λ and μ are the initial phase angles.

[0062] Substituting equation (2) into equation (1) yields F x With F y The expression is:

[0063] F x =F M cos(μ-λ)

[0064] F y =F M sin(μ-λ)

[0065] In the formula, F MThis represents the amplitude of Maxwell's force.

[0066] As can be seen from the above equation, the radial levitation force in the stator coordinate system is related to the rotor position, which is inconvenient for application. To further decouple, a rotor coordinate system mO'n is defined as follows: Figure 2 Then, transforming the above equation, we get:

[0067] F x =k(i Sm ψ f +i Sn ψ Tn )

[0068] F y =-k(i Sn ψ f -i Sm ψ Tn )

[0069] In the formula, L S Mutual inductance of the torque windings; N T With N S These are the number of turns for the torque winding and the suspension winding, respectively; i Sm with i Sn Ψ represents the m-axis and n-axis components of the levitation current. f For permanent magnet flux linkage; Ψ Tn This represents the n-axis component of the torque winding flux linkage.

[0070] When the radial displacement sensor produces a detection deviation, the permanent magnet rotor of the motor will no longer be suspended at the stator geometric center O, but will be located at the detection center O'. This eccentricity will cause an increase in the self-inductance of the torque winding, which can be expressed as:

[0071]

[0072] In the formula, L Tm,n x represents the self-inductance components of the torque winding along the m-axis and n-axis; e With y e The rotor eccentricity in the stator coordinate system; k e C is a constant.

[0073] According to the principle of virtual displacement, the unbalanced magnetic pull on the rotor is the partial derivative of the inductance energy stored in the torque winding with the radial displacement, and its result is zero only when the rotor is located at the geometric center of the stator. Since the torque control section uses i... Tm =0 control, therefore the expression for the unbalanced magnetic pull is:

[0074]

[0075] In the formula, W m Energy is stored in the torque winding inductance; If i is the equivalent excitation current of the permanent magnet; Tn This represents the n-axis component of the torque winding current.

[0076] According to the above formula, the unbalanced magnetic pull on the rotor is only related to the n-axis component of the torque winding current and the magnitude of eccentricity, and is independent of the levitation current. A finite element simulation model is built using a 6-slot, 2-pole bearingless permanent magnet thin-film motor as an example, and its parameters are shown in Table 1.

[0077] Table 1 Motor Parameters

[0078]

[0079] Taking the x-axis as an example, when the torque winding is not energized, the simulation results show the relationship between the unbalanced magnetic pull on the rotor and the eccentricity and corresponding anti-eccentricity current, as follows: Figure 3 As shown. It can be seen that F ex Mean and eccentricity x e The relationship is linear, therefore the corresponding m-axis component of the levitation current i Sm The current increases proportionally. However, during actual operation of the motor, random external disturbances also act on the rotor, causing fluctuations in the m-axis and n-axis components of the suspending current. A schematic diagram of the rotor forces is shown below. Figure 4 As shown. To accurately identify displacement detection deviations, the levitation current needs to be classified. The levitation current resisting unbalanced magnetic pull is defined as the anti-eccentric current i. e When the rotor is in a static eccentric state, the anti-eccentric current is a constant DC component, which is easy to extract; the current resisting external disturbances is the anti-disturbance current i. r Since the external disturbance force is random, the anti-disturbance current that counteracts it is a fluctuating quantity, which needs to be eliminated by low-pass filtering.

[0080] Meanwhile, since bearingless motors generally have smaller rotors and lighter loads, their torque current n-axis component i Tn Much smaller than the equivalent excitation current I of the permanent magnet f To simplify the analysis, i is ignored. Tn The influence of the eccentricity can be investigated by low-pass filtering the m-axis and n-axis components of the detected levitation current, extracting the DC component to obtain the anti-eccentricity current, and combining it with the above theoretical analysis and simulation results to calculate the specific direction and magnitude of the rotor eccentricity.

[0081] according to Figure 3 The smaller the eccentricity, the smaller the corresponding anti-eccentricity current. When the rotor is located at the geometric center of the stator (i.e., without eccentricity), the anti-eccentricity current is zero, and the system reaches its optimal operating state. The block diagram of the bearingless permanent magnet thin-plate motor suspension control system, which incorporates displacement detection, deviation identification, and correction algorithms, is shown below. Figure 5As shown. Here, LPF represents a low-pass filter; a hysteresis comparator is introduced in the algorithm for eliminating the anti-eccentric current, i h This is an error limit value, applied only when the absolute value of the anti-eccentric current is greater than i. h The subsequent algorithm continues to execute; j and j h These are the number of fluctuations and the limit value for the number of fluctuations, respectively. The fluctuation only occurs when the anti-eccentric current exceeds the limit value i. h The number of times is more than j h The subsequent algorithm continues to execute. Set i h With j h The purpose of this is to prevent the system from fluctuating repeatedly in order to eliminate the anti-eccentric current. The complete correction algorithm is only executed when both the absolute value of the anti-eccentric current and the number of fluctuations exceed the limit value. The new displacement detection deviation is calculated and compensated. Otherwise, the output result of the previous cycle remains unchanged.

[0082] The displacement detection deviation correction algorithm proposed in this invention is based on the above theoretical derivation and simulation. While it is relatively accurate in identifying the eccentricity direction, its calculation of the eccentricity magnitude depends on model parameters, which may result in the rotor center not being located at the stator geometric center after compensation. To address this issue, a cyclic algorithm for step-tracking the minimum anti-eccentricity current is added near the compensation point. Figure 5 The lower right part of the diagram. Where x d With y d The outer range is defined by h; the number of iterations is defined by x. h With y h This represents the displacement step size incremented in each iteration. The implementation of this iterative algorithm does not directly use the displacement compensation value x calculated in the previous stage. e With y e Instead of feeding it back into the displacement setting, x is used as the input. e ±x d With y e ±y d Feedback is sent back (incrementing when eccentricity is in the positive direction and subtracting when it is in the opposite direction), and the loop count h is set to zero. After this displacement feedback, the previous judgment part is skipped in the next loop cycle, and the loop algorithm is entered directly. The loop count h is incremented by 1, and the anti-eccentricity current of this cycle is sampled. If the sampled result is less than the current value of the previous loop cycle, the loop continues. At this time, the displacement feedback value is... and The cycle continues until the anti-eccentric current in a certain cycle is greater than the current in the previous cycle, at which point the cycle ends and the compensation value is determined.

[0083] Compared with the algorithm in the literature "Eccentricity compensation for bearingless motor based on the tracking of the minimum antieccentric levitation current", the radial displacement sensor detection deviation identification and correction method for bearingless permanent magnet thin-film motor proposed in this invention directly and quickly determines the specific direction and magnitude of the eccentricity using the levitation current offset, and only adds a step tracking loop algorithm near the compensation point. Therefore, it can accurately levitate the rotor to the geometric center of the stator through compensation while ensuring speed, so that the motor operates in the optimal state. At this time, the unbalanced magnetic pull is 0, the levitation current is minimal, and the system efficiency is the highest.

[0084] A simulation model of a bearingless permanent magnet thin-film motor control system was built using Simulink to verify the speed and effectiveness of the proposed displacement detection deviation identification and correction algorithm. The rotor eccentricity error caused by the displacement sensor causes the rotor to be located at the detection center, not the geometric center of the stator, during stable operation. To simulate this deviation, an offset was added to the radial displacement feedback loop, with an x-axis offset of -0.2 mm and a y-axis offset of 0.1 mm, thus positioning the rotor at (0.2 mm, -0.1 mm). Simultaneously, a random disturbance was added to the displacement calculation module to simulate external disturbances. Figure 6 The figure shows the displacement waveform. The error limit value i for the correction algorithm in the simulation is... h Take 0.02A, and set the fluctuation number limit j. h Take 10, and expand the range to x. d With y d Take 0.1 mm, and increase the displacement by step size x. h With y h The deviation is set to 0.01 mm, and the cycle time is set to 0.1 s. It can be seen that before the displacement detection deviation occurs, the rotor runs stably at the zero point of the stator geometric center. When the deviation occurs at 0.7 s, the rotor then runs stably at the position (0.2 mm, -0.1 mm), at which point the anti-eccentric current increases. The correction algorithm starts at 1.5 s, and detects that the anti-eccentric current exceeds the limit value i within 10 consecutive control cycles. h The direction and magnitude of the eccentricity are then determined, and an expansion range of 0.1 mm is added, meaning that the x-axis and y-axis compensation values ​​at that moment are -0.1 mm and 0 mm, respectively. A loop algorithm is then started, decreasing the x-axis displacement compensation value by 0.01 mm and increasing the y-axis displacement compensation value by 0.01 mm in each loop cycle, while also detecting the magnitude of the anti-eccentricity current, until it reaches the allowable error range of the hysteresis comparator.

[0085] The waveforms of the anti-eccentric current m-axis and n-axis components after the correction algorithm is started are as follows: Figure 7As shown in the figure, it can be seen that both the x-axis and y-axis reach the minimum anti-eccentricity current point after approximately 10 cycles, and the floating current gradually decreases in each cycle. This is because the eccentricity distance of the y-axis set in the simulation is exactly equal to the outer expansion range y. d Therefore, the compensation value for the first cycle is 0mm, i.e., no compensation. In the next cycle, the compensation value is given as 0.01mm and i is monitored. en The fluctuation in the anti-eccentric current component is due to the low-pass filter's inability to completely filter out pulsations, causing some anti-disturbance current to mix into the anti-eccentric current. However, this can be mitigated by appropriately setting the limit value i. h If the fluctuation is kept within the error range allowed by the hysteresis comparator, the correction algorithm will not be triggered, thus maintaining the stability of the system.

[0086] based on Figure 8 The experimental platform shown verifies the proposed displacement detection deviation identification and correction algorithm. The specific parameters of the experimental prototype have been given above. With the correction algorithm inactive and the rotational speed set to 0 rpm (i.e., stationary suspension), the rotor displacement waveform and related suspension current waveforms are as follows: Figure 9 and Figure 10 As shown in the figure, it can be seen that the rotor's x-axis and y-axis displacements can be stabilized near the detection zero point. However, from the levitation current waveform, it can be obtained that the m-axis component i of the anti-eccentric current at this time... em With n-axis component i en The magnitudes are -0.36A and -0.13A respectively; taking phase A of the floating winding as an example, its current i SA The average value is approximately -0.37A, meaning the rotor is actually in a static eccentric state, introducing redundant current components into the levitation control system. As mentioned earlier, this phenomenon may be caused by assembly errors, incomplete calibration of Hall outputs, or exposure to temperature or electromagnetic interference. After adding the correction algorithm proposed in this invention to the program, the rotor displacement waveform and related levitation current waveform during stable levitation are as follows: Figure 11 and Figure 12 As shown, after the correction algorithm is applied, the rotor is not suspended at the detection zero point, but the average value of the suspended A-phase current is reduced by 0.37A compared with before the correction, the anti-eccentric current is about 0A, and the rotor is located at the true stator geometric center.

[0087] The static levitation experiments described above have essentially determined the displacement detection deviations caused by assembly errors and incomplete output calibration of the Hall sensor, which are 0.168 mm eccentricity towards the x-axis and -0.061 mm eccentricity towards the y-axis. Theoretically, these corrections can stabilize the rotor at the stator's geometric center. However, the Hall sensor output is still susceptible to external interference. To simulate this, offsets of +0.2 mm and -0.2 mm were applied to the x-axis and y-axis displacement detection feedback loops, respectively. At a given speed of 3000 rpm, the rotor displacement waveform and related levitation current waveforms after the correction algorithm was activated at a certain moment are shown below. Figure 13 and Figure 14 As shown in the figure. It can be seen that the algorithm proposed in this invention can detect anti-eccentric current i greater than the limit value. em with i en The algorithm can effectively determine the direction and magnitude of the eccentricity, and performs a step-by-step operation near the compensation point every 0.1s cycle, gradually reducing the anti-eccentric current to approximately 0A and decreasing the peak-to-peak value of the suspended A-phase current by 1A. In the experiment, the total time for the identification and correction algorithm was approximately 2s, which is 90% faster than the cyclic algorithm in the literature "Eccentricity compensation for bearingless motor based on the tracking of the minimum antieccentric levitation current". Figure 15 As shown, the algorithm is more convenient and easier to implement, verifying its speed and effectiveness.

[0088] This invention also provides a hardware system for radial displacement sensor detection deviation correction of a bearingless permanent magnet thin-film motor, comprising: a power module, a control module, and a bearingless permanent magnet thin-film motor; the power module consists of a sampling circuit and two sets of three-phase full-bridge inverters; the sampling circuit has six current sampling channels, responsible for sampling the current of the three-phase floating winding and the current of the three-phase torque winding; the two sets of three-phase full-bridge inverters respectively control the floating winding and the torque winding; the control module includes a DSP main control chip and its peripheral circuits, a conditioning circuit, and an external AD circuit; the conditioning circuit converts the level output of the current sensor to within 0-3V for safe input to the DSP's internal ADC module; the external AD circuit uses a 12-bit ADC chip to achieve high-precision sampling of the Hall sensor output and transmits the result to the DSP; the DSP, as the main control chip, collects all external data and uses algorithms to calculate and generate six sets of PWM waves to control the two sets of inverters.

[0089] The present invention also provides a bearingless permanent magnet thin-film motor, which uses the above-mentioned radial displacement sensor detection deviation correction method for a bearingless permanent magnet thin-film motor to correct the radial displacement sensor detection deviation.

[0090] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. It should be noted that any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for correcting the detection deviation of a radial displacement sensor in a bearingless permanent magnet thin-film motor, characterized in that, Includes the following steps: Based on Maxwell's stress tensor method and virtual displacement method, mathematical models of the controllable levitation force and the unbalanced magnetic pull caused by eccentricity of the bearingless permanent magnet thin-film motor in rotor coordinate system are derived respectively, thereby establishing the functional relationship between levitation current and controllable levitation force, as well as between eccentricity distance and unbalanced magnetic pull. The floating current is divided into two categories: anti-eccentricity and anti-disturbance, so as to achieve decoupling between the eccentricity distance and the corresponding floating current component. With the goal of eliminating anti-eccentric current, by extracting m shaft and n The axial suspension current component is used to determine the direction and magnitude of eccentricity and thus the compensation point. The minimum floating current is tracked stepwise near the compensation point to determine the compensation value. Specifically, this includes introducing a cyclic algorithm to track the minimum current stepwise near the calculated compensation point to determine the optimal compensation value. The cyclic algorithm is implemented by not directly feeding the displacement compensation value calculated in the previous stage back to the displacement setpoint, but by adding or subtracting an extended range from the calculated value and feeding it back. When the eccentricity is positive, the value is added; otherwise, it is subtracted. At this time, the number of cycles is set to zero. After the displacement feedback, the previous stage calculation is skipped in the next cycle, and the cyclic algorithm is entered directly. The number of cycles is incremented by 1, and the anti-eccentricity current of this cycle is sampled. If the sampled result is less than the current value of the previous cycle, the cycle continues. At this time, the displacement feedback value is the value of the previous cycle minus or plus the number of cycles multiplied by the step size, until the anti-eccentricity current of a certain cycle is greater than the current of the previous cycle, then the cycle is exited and the compensation value is determined. The compensation value is fed back to the displacement closed-loop control system to correct the deviation.

2. The radial displacement sensor detection deviation correction method for a bearingless permanent magnet thin-film motor according to claim 1, characterized in that, The process of deriving the expression for the controllable radial levitation force of a bearingless permanent magnet sheet motor in the rotor coordinate system based on Maxwell's stress tensor method includes: obtaining the controllable levitation force on the rotor by integrating along the air gap circumference based on Maxwell's stress tensor method. x shaft and y Shaft component expression; determine the magnetic field existing in the air gap during normal motor operation; derive the stator coordinate system by simultaneously solving the above two equations. x O y The expression for the controllable radial levitation force; the rotor coordinate system is defined based on the position of the center of the circle when the rotor is statically eccentric. m O' n The expression for the controllable radial levitation force in the rotor coordinate system is derived through coordinate transformation.

3. The radial displacement sensor detection deviation correction method for a bearingless permanent magnet thin-film motor according to claim 1, characterized in that, The process of deriving the expression for the unbalanced magnetic pull force on the rotor of a bearingless permanent magnet thin-plate motor under static eccentric operation in the rotor coordinate system based on the virtual displacement method includes: determining the relationship between the eccentricity distance and the self-inductance of the motor torque winding; deriving the expression for the energy storage of the torque winding inductance; and deriving the expression for the unbalanced magnetic pull force by obtaining the partial derivative between the energy storage of the torque winding inductance and the radial displacement based on the virtual displacement method.

4. The radial displacement sensor detection deviation correction method for a bearingless permanent magnet thin-film motor according to claim 1, characterized in that, The process of classifying the levitation current into two categories, anti-eccentricity and anti-disturbance, and decoupling the eccentricity distance from the corresponding levitation current component includes: defining the levitation current resisting unbalanced magnetic pull as the anti-eccentricity current, which is a constant DC component when the rotor is in a static eccentricity state; the current resisting external disturbances is the anti-disturbance current, which is a fluctuating quantity and is eliminated using a low-pass filter; and decoupling the eccentricity distance from the corresponding levitation current component by recognizing that the magnitude of the anti-eccentricity current resisting unbalanced magnetic pull is proportional to the eccentricity distance.

5. The radial displacement sensor detection deviation correction method for a bearingless permanent magnet thin-film motor according to claim 1, characterized in that, The goal is to eliminate the reverse eccentric current by extracting... m shaft and n The process of determining the eccentricity direction and magnitude and establishing the compensation point based on the axial levitation current components includes: transforming the detected three-phase levitation current of the motor into levitation current in a two-phase rotating coordinate system based on coordinate transformation; and performing low-pass filtering on the current to extract the eccentricity. m shaft and n The anti-eccentric current component of the shaft; the correspondence between controllable radial force and levitation current obtained based on finite element simulation; the correspondence between unbalanced magnetic pull force and eccentric distance obtained based on finite element simulation; the two correspondences obtained from finite element simulation are compared with the detected anti-eccentric current. m shaft and n By combining the shaft components, the rotor direction can be calculated. x shaft and y The magnitude of the axial eccentricity determines the compensation point.

6. A hardware system for correcting radial displacement sensor detection deviation of a bearingless permanent magnet thin-film motor based on the method described in any one of claims 1-5, characterized in that, include: The system comprises a power module, a control module, and a bearingless permanent magnet thin-film motor. The power module consists of a sampling circuit and two sets of three-phase full-bridge inverters. The sampling circuit has six current sampling channels, responsible for sampling the current of the three-phase floating winding and the current of the three-phase torque winding. The two sets of three-phase full-bridge inverters respectively control the floating winding and the torque winding. The control module includes a DSP main control chip and its peripheral circuits, a conditioning circuit, and an external AD circuit. The conditioning circuit converts the output level of the current sensor to within 0-3V for safe input to the DSP's internal ADC module. The external AD circuit uses a 12-bit ADC chip to achieve high-precision sampling of the Hall sensor output and transmits the results to the DSP. The DSP, as the main control chip, collects all external data and uses algorithms to generate six sets of PWM waves to control two inverters.

7. A bearingless permanent magnet thin-film motor, characterized in that, It uses the method described in any one of claims 1-5 to correct the detection deviation of the radial displacement sensor.

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