A low-cost, low-interruption-cycle high-precision identification method for the radial displacement of the rotor of a bearingless permanent magnet thin-film motor
By employing a six-tooth pole pair structure and three Hall sensors combined with negative sequence demodulation in a bearingless thin-film motor, the algorithm process is simplified, hardware costs and interrupt cycles are reduced, and computational efficiency and accuracy are improved. This solves the problems of high sensor cost and algorithm complexity, and achieves high-precision identification of rotor radial displacement.
Patent Information
- Application Number
- CN202210216980.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-03-07
- Publication Date
- 2025-12-02
- Estimated Expiration
- 2042-03-07
AI Technical Summary
Existing bearingless sheet motors suffer from high sensor costs, complex algorithms, and large errors when identifying rotor radial displacement, making them unable to meet the stable levitation performance requirements of ultra-clean medical fields such as heart pumps.
A six-tooth, one-pole motor structure is adopted, using three Hall sensors and a negative-sequence demodulation method to simplify the algorithm process, reduce hardware costs and improve computational efficiency. Radial displacement is directly calculated through the negative-sequence decoupling method.
It reduces hardware costs, improves algorithm efficiency and accuracy, reduces interruption cycles, and meets the stable levitation performance requirements of bearingless thin-plate motors in the ultra-clean medical field.
Smart Images
Figure CN114614721B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of bearingless motor control technology, and mainly to a low-cost, low-interruption-cycle high-precision identification method for the radial displacement of the rotor of a bearingless permanent magnet thin-film motor. Background Technology
[0002] Bearingless thin-plate motors, lacking a shaft and with separate stator and rotor, have a short axial length, making them easy to achieve five-degree-of-freedom levitation and uniquely suited for applications in ultra-clean medical fields such as cardiac pumps. Traditional bearingless control requires displacement sensors to sample displacement signals for closed-loop operation. However, commonly used displacement sensors, such as eddy current sensors, are bulky, expensive, and highly susceptible to environmental influences, failing to meet the requirements of small size and stable levitation performance in cardiac pumps. Therefore, a displacement-free algorithm is needed to replace displacement sensors.
[0003] Among existing identification methods, the flux linkage identification method cannot identify flux linkages at zero speed and thus displacement; the high-frequency injection method has too low a signal-to-noise ratio and a large impact on the fundamental frequency, failing to meet the requirements of displacement identification algorithms; the Hall sensor-based displacement-free algorithm has a high signal-to-noise ratio, accurate displacement calculation, and excellent dynamic performance, and can effectively replace displacement sensors to achieve displacement closed-loop. However, the demodulation method used in the related algorithms proposed in existing patents is the positive-sequence demodulation method. Because its phase sequence is inconsistent with the Hall signal, it must undergo rotation transformation after demodulation to obtain the radial displacement, making the program cumbersome and redundant, increasing algorithm error and calculation time. At the same time, the large number of Hall sensors increases hardware costs. Summary of the Invention
[0004] Purpose of the invention: To address the problems existing in the above-mentioned background technology, the present invention provides a low-cost, low-interruption-cycle high-precision identification method for the radial displacement of the rotor of a bearingless permanent magnet thin-film motor. On the one hand, it proposes a negative sequence demodulation method, which simplifies the core algorithm, reduces the interruption cycle, and improves the efficiency and accuracy of the algorithm. On the other hand, it uses three Hall sensors to identify the displacement, which effectively reduces the hardware cost compared with the existing technology.
[0005] Technical solution: To achieve the above objectives, the technical solution adopted by this invention is as follows:
[0006] A low-cost, low-interruption-cycle high-precision identification method for the radial displacement of a bearingless permanent magnet thin-film motor rotor is disclosed. The bearingless permanent magnet thin-film motor employs a six-tooth, one-pole motor structure, comprising six L-shaped stators. Each L-shaped stator includes an axial stator yoke and radial stator teeth, surrounding the thin-film rotor. The radial stator teeth are flush with the rotor. Each axial stator yoke is wound with a levitation winding and a torque winding, respectively. The torque winding has one pole, and the levitation winding has two poles, simultaneously achieving levitation control and rotation control. The bottom of the L-shaped stators is connected by a core magnetic ring. A pair of permanent magnets is attached to the outer side of the thin-film rotor. The magnetic field of the permanent magnets is sinusoidally distributed in space. Three programmable Hall sensors (Hall1-Hall3) are sequentially installed in the radial stator slots, with a 120-degree interval between adjacent Hall sensors. The displacement is calculated based on the output signals of Hall1-Hall3. Specifically...
[0007] The rotor is mechanically fixed at the center position, and the rotor is rotated to obtain the output signals Hall1-Hall3. At this time, the output signals are independent of the displacement change. The average value of the three Hall signal amplitudes is taken, which is the permanent magnet flux linkage coefficient k4. The basic permanent magnet flux linkage is subtracted from the three Hall signals respectively to obtain Hall signals that are only related to the displacement change. Then, the effective components of the three Hall signals are obtained by simplification. The simplified Hall signals are multiplied by a cosine negative sequence component that is a harmonic of the rotor frequency, and the sum is obtained to obtain the rotor radial displacement x. The simplified Hall signals are multiplied by a sine negative sequence component that is a harmonic of the rotor frequency, the sum is taken, and the opposite number is obtained to obtain the rotor radial displacement y.
[0008] Furthermore, in step S1, several layers of insulating tape are uniformly wrapped around the outside of the rotor to fix it in the central position. For the Hall sensor Hall1, the output signal is related to the rotor's displacement along and perpendicular to Hall1, the rotor angle, and the permanent magnet flux linkage. The thin-film rotor does not have silicon steel sheets, and the armature leakage magnetic reluctance is relatively large, so the leakage magnetic reluctance is ignored. The output signal is expressed as follows:
[0009] Hall1=k1*l*cos(θ l -θ0)cos(ωt-θ0)+
[0010] k2*l*sin(θ l -θ0)sin(ωt-θ0)+k4*cos(ωt-θ0)
[0011] Where θ l ωt represents the eccentric angle, l represents the eccentric length, ωt represents the rotor angle, θ0 represents the mechanical angle where Hall1 is located; k1 is the displacement coefficient along the Hall1 direction, k2 is the displacement coefficient perpendicular to the Hall1 direction, and k4 is the permanent magnet flux linkage coefficient when there is no eccentricity.
[0012] Starting from the location of Hall1, and taking θ0 = 0, substitute the measured k4 into the expression and subtract this term. Then, the component of Hall1 that is only related to displacement is Hall. 1_eff The expression is as follows:
[0013] Hall 1_eff =k1*l*cos(θ) l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)
[0014] Since the angle between adjacent Hall sensors is 120 degrees, substituting θ0+2pi / 3 and θ0-2pi / 3 into θ0 respectively, we obtain the Hall... 2_eff and Hall 3_eff :
[0015] Hall 2_eff =k1*l*cos(θ) l -θ0-2pi / 3)cos(ωt-θ0-2pi / 3)+
[0016] k2*l*sin(θ l -θ0-2pi / 3)sin(ωt-θ0-2pi / 3)
[0017]
[0018] Furthermore, the three displacement-related components are simplified as follows:
[0019]
[0020]
[0021]
[0022] Furthermore, the simplified Hall signal is multiplied by a cosine negative-sequence component that is one harmonic of the rotor frequency, and then summed to obtain the rotor radial displacement x, as follows:
[0023]
[0024] The simplified Hall signal is multiplied by a sinusoidal negative-sequence component that is one harmonic of the rotor frequency, summed, and the opposite number is taken to obtain the rotor radial displacement y, which is proportional to x, as follows:
[0025]
[0026] Beneficial effects:
[0027] (1) This invention employs a negative-order decoupling method, which simplifies the algorithm and significantly improves efficiency. By studying the expressions of various Hall signals, it was found that the displacement-related signal form in the Hall signal is the projection of the displacement in the Hall direction (or perpendicular) multiplied by a cosine quantity related to the rotor angle. Specifically, taking the Hall... 1_eff For example, l*cos(θ) l -θ0) is the projection of the displacement in the Hall direction, l*sin(θ) l -θ0) is the projection of the displacement in the direction perpendicular to the Hall. cos(ωt-θ0) and sin(ωt-θ0) are sine and cosine quantities related to the rotor.
[0028] This invention simplifies the three Hall signals to obtain three-phase cosines with in-phase angles and negative-sequence angles. Existing technologies use a three-phase positive-sequence multiplication signal, which is inconsistent with the simplified Hall signal, requiring further rotational transformation after demodulation to obtain the radial displacement. This invention proposes a negative-sequence decoupling method, setting the multiplication signal used for demodulation to a unified three-phase negative-sequence component form, canceling out the rotor angle and initial Hall angle present in the Hall signal itself, retaining only the required rotor eccentricity angle, thus directly obtaining the radial displacements x and y. The proposed technique requires only two lines of code for algorithm implementation, eliminating the need for additional rotational transformations, significantly reducing algorithm length and improving efficiency. Simultaneously, this invention reduces the error of the original algorithm and improves computational accuracy.
[0029] (2) This invention uses three Hall sensors in its hardware, reducing costs. Hall sensors need to achieve both displacement and angle identification. The angle can be obtained from three Hall sensors through a 3x2 transformation followed by an arctangent, which is the optimal number for accurate angle calculation. Based on this consideration, this invention proposes a three-Hall displacement calculation method. Existing six-Hall displacement calculation algorithms require the summation of two mechanically opposite Hall sensors to offset the influence of the base permanent magnet flux linkage. This invention proposes an offline rotor center measurement algorithm to obtain the amplitude of the base permanent magnet flux linkage, and calculates the component of the base permanent magnet flux linkage in real time based on the theoretically derived functional relationship. This decouples the base permanent magnet flux linkage from the Hall signal, thus reducing the number of Hall sensors by half in hardware. Attached Figure Description
[0030] Figure 1 This is a block diagram of the motor rotor radial displacement identification method provided by the present invention;
[0031] Figure 2 This is a schematic diagram of the mechanical position of the bearingless permanent magnet thin-film motor Hall sensor used in this invention;
[0032] Figure 3 This is an axial cross-sectional view of the six-tooth, one-pole, bearingless permanent magnet thin-film motor provided by the present invention;
[0033] Figure 4 This is a schematic diagram of the rotor eccentricity of the bearingless permanent magnet thin-film motor provided by the present invention;
[0034] Figure 5 This is a flowchart of an existing algorithm for identifying the radial displacement of a motor rotor.
[0035] Figure 6 This is a comparison chart of the displacement identification results of the present invention and the prior art;
[0036] Figure 7 This is an overall block diagram of a bearingless permanent magnet thin-film motor system using a displacement-free algorithm. Detailed Implementation
[0037] 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.
[0038] The bearingless permanent magnet thin-film motor structure used in this invention is as follows: Figure 3 As shown, a six-tooth, one-pole motor structure is adopted, including six L-shaped stators 2. Each L-shaped stator includes an axial stator yoke and radial stator teeth, which surround a thin-plate rotor. The radial stator teeth are flush with the rotor. Each axial stator yoke is wound with a suspension winding 4 and a torque winding 5. The torque winding has one pair of poles, and the suspension winding has two pairs of poles, realizing both suspension control and rotation control. The bottom of the L-shaped stators is connected by an iron core magnetic ring 3. A pair of permanent magnets is attached to the outside of the thin-plate rotor 1, and the magnetic field of the permanent magnets is sinusoidally distributed in space.
[0039] This embodiment employs three programmable Hall sensors (Hall1-Hall3) sequentially installed in the radial stator slots, with a 120-degree interval between adjacent Hall sensors; the displacement is calculated based on the output signals of Hall1-Hall3. Specific settings are as follows... Figure 2 As shown. Since the Hall element needs to identify both displacement and angle, the angle can be obtained by transforming three Hall elements into their arctangents. This is the optimal number of elements for accurate angle calculation.
[0040] The following provides a specific method for identifying the radial displacement of the motor rotor, with the following algorithm framework: Figure 1 As shown.
[0041] First, the signal of the Hall sensor when the rotor rotates at the center position is calculated experimentally. This signal is independent of displacement changes. The specific calculation method is as follows: wrap several layers of insulating tape evenly around the outside of the rotor until the rotor can be mechanically fixed at the center position. Rotate the rotor and observe the output of the three Hall sensors. The average value of the three Hall signal amplitudes is the permanent magnet flux linkage coefficient k4.
[0042] For Hall sensor Hall1, the output signal is related to the rotor displacement along and perpendicular to Hall1, the rotor angle, and the permanent magnet flux linkage. Since the thin-film rotor does not have silicon steel sheets, the armature leakage magnetic reluctance is relatively large, so the leakage magnetic reluctance is ignored. The output signal is expressed as follows:
[0043] Hall1=k1*l*cos(θ l -θ0)cos(ωt-θ0)+
[0044] k2*l*sin(θ l -θ0)sin(ωt-θ0)+k4*cos(ωt-θ0)
[0045] Among them, such as Figure 4 As shown, θ l ωt represents the eccentric angle, l represents the eccentric length, ωt represents the rotor angle, θ0 represents the mechanical angle where Hall1 is located; k1 is the displacement coefficient along the Hall1 direction, k2 is the displacement coefficient perpendicular to the Hall1 direction, and k4 is the permanent magnet flux linkage coefficient when there is no eccentricity.
[0046] Starting from the location of Hall1, and taking θ0 = 0, substitute the measured k4 into the expression and subtract this term. Then, the component of Hall1 that is only related to displacement is Hall. 1_eff The expression is as follows:
[0047] Hall 1_eff =k1*l*cos(θ) l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)
[0048] Since the angle between adjacent Hall sensors is 120 degrees, substituting θ0+2pi / 3 and θ0-2pi / 3 into θ0 respectively, we obtain the Hall... 2_eff and Hall 3_eff :
[0049] Hall 2_eff =k1*l*cos(θ) l -θ0-2pi / 3)cos(ωt-θ0-2pi / 3)+
[0050] k2*l*sin(θ l -θ0-2pi / 3)sin(ωt-θ0-2pi / 3)
[0051]
[0052] The three displacement-related components are simplified and processed using the product-to-sum formula, with the following results:
[0053]
[0054]
[0055]
[0056] The simplified Hall signal is multiplied by a cosine negative-sequence component that is one harmonic of the rotor frequency, and then summed to obtain the rotor radial displacement x, as follows:
[0057]
[0058] The simplified Hall signal is multiplied by a sinusoidal negative-sequence component that is one harmonic of the rotor frequency, summed, and the opposite number is taken to obtain the rotor radial displacement y, which is proportional to x, as follows:
[0059]
[0060] The block diagram of the displacement identification algorithm based on the positive sequence demodulation method in the prior art is as follows: Figure 5 As shown, with Figure 1 In comparison, three more Hall sensors were used in the first half, while the demodulation process in the second half involves an αβ-dq rotation change. The specific procedure is as follows:
[0061] x=l1*cos(2ωt-3θ0)+l2*sin(2ωt-3θ0)
[0062] y=-l1*sin(2ωt-3θ0)+l2*cos(2ωt-3θ0)
[0063] Since the computationally intensive parts of the above program are the four trigonometric functions, each occupying approximately 40 clock cycles, and assuming a controller frequency of 100MHz, the total time required is nearly 2ns. From an error perspective, the rotor angle error will be doubled in the calculation result.
[0064] Therefore, the identification method provided by this invention reduces the number of Hall sensors and lowers hardware costs by eliminating the need for front and rear parts, while improving the efficiency and accuracy of the algorithm and reducing the interrupt cycle.
[0065] Furthermore, MATLAB simulations were used to obtain displacement identification effect diagrams of existing displacement identification methods and the method provided by this invention, such as... Figure 6 As shown, the displacements identified by both methods highly coincide with the given displacement, verifying the effectiveness of both methods. However, from the magnified local image, the improved method fits the given displacement even better than the original method, i.e., it is more accurate, verifying the correctness of the above theoretical analysis.
[0066] Figure 7 This is a block diagram of a bearingless permanent magnet thin-film motor system employing a displacement-free algorithm. The torque control section uses vector control, with an outer speed loop (using Hall effect sensors to calculate the speed as feedback) and an inner current loop. The displacement control section has an outer displacement loop (using Hall effect sensors to calculate the displacement using a displacement-free algorithm) and an inner current loop.
[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A low-cost, low-interruption-cycle, high-precision identification method for the radial displacement of a bearingless permanent magnet thin-film motor rotor, wherein the bearingless permanent magnet thin-film motor adopts a six-tooth, one-pole motor structure, including six L-shaped stators; each L-shaped stator includes an axial stator yoke and radial stator teeth, surrounding a thin-film rotor, the radial stator teeth being flush with the rotor, each axial stator yoke having a levitation winding and a torque winding respectively, the torque winding having one pole and the levitation winding having two poles, simultaneously achieving levitation control and rotation control; the bottom of the L-shaped stators is connected by an iron core magnetic ring; a pair of permanent magnets are attached to the outer side of the thin-film rotor; the magnetic field of the permanent magnets is sinusoidally distributed in space; characterized in that... Three programmable Hall sensors, Hall1 to Hall3, are sequentially installed in the radial stator slots, with a 120-degree interval between adjacent Hall sensors. Displacement is calculated based on the output signals of Hall1 to Hall3. Specifically, The rotor is mechanically fixed at the center position, and the rotor is rotated to obtain the output signals Hall1-Hall3. At this time, the output signals are independent of displacement changes. The average value of the three Hall signal amplitudes is taken, which is the permanent magnet flux linkage coefficient k4. The basic permanent magnet flux linkage is subtracted from the three Hall signals to obtain Hall signals that are only related to displacement changes. Then, the effective components of the three Hall signals are obtained by simplification. The three simplified Hall signals are multiplied by a cosine negative sequence component that is a harmonic of the rotor frequency, and the sum is obtained to obtain the rotor radial displacement x. The three simplified Hall signals are multiplied by a sine negative sequence component that is a harmonic of the rotor frequency, the sum is taken, and the opposite number is obtained to obtain the rotor radial displacement y. Several layers of insulating tape are evenly wrapped around the outside of the rotor to fix it in the center position. For Hall sensor Hall1, the output signal is related to the rotor's displacement along and perpendicular to Hall1, the rotor angle, and the permanent magnet flux linkage. The output signal is expressed as follows: Hall1=k1*l*cos(θ l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0)+k4*cos(ωt-θ0) Where θ l ωt represents the eccentric angle, l represents the eccentric length, ωt represents the rotor angle, θ0 represents the mechanical angle where Hall1 is located; k1 is the displacement coefficient along the Hall1 direction, k2 is the displacement coefficient perpendicular to the Hall1 direction, and k4 is the permanent magnet flux linkage coefficient when there is no eccentricity. Starting from the location of Hall1, and taking θ0 = 0, substitute the measured k4 into the expression and subtract this term. Then, the component of Hall1 that is only related to displacement is Hall. 1_eff The expression is as follows: Hall 1_eff =k1*l*cos(θ l -θ0)cos(ωt-θ0)+k2*l*sin(θ l -θ0)sin(ωt-θ0) Since the angle between adjacent Hall sensors is 120 degrees, substituting θ0+2pi / 3 and θ0-2pi / 3 into θ0 respectively, we obtain the Hall... 2_eff and Hall 3_eff : Hall 2_eff =k1*l*cos(θ l -θ0-2pi / 3)cos(ωt-θ0-2pi / 3)+k2*l*sin(θ l -θ0-2pi / 3)sin(ωt-θ0-2pi / 3) 2. The low-cost, low-interruption-cycle high-precision identification method for the radial displacement of a bearingless permanent magnet thin-film motor rotor according to claim 1, characterized in that, The three displacement-related components are simplified as follows:
3. The low-cost, low-interruption-cycle high-precision identification method for the radial displacement of a bearingless permanent magnet thin-film motor rotor according to claim 2, characterized in that, The simplified three Hall signals are multiplied by the negative sequence cosine of the rotor frequency (one harmonic of the rotor frequency), and then summed to obtain the rotor radial displacement x, as follows: The simplified three Hall signals are multiplied by a sinusoidal negative-sequence component that is one harmonic of the rotor frequency, summed, and the opposite number is taken to obtain the rotor radial displacement y, which is proportional to x, as follows: