A method, device and system for detecting rotor displacement of a bearingless motor

Abstract

This invention discloses a method, device, and system for detecting rotor displacement in a bearingless motor, belonging to the field of bearingless motor technology. The method includes: setting three detection coils (a first detection coil, a second detection coil, and a third detection coil) in the stator slots of the bearingless motor; the spatial positions of the slot vectors corresponding to the three detection coils are aligned with the axes of the A, B, and C phase windings of the bearingless motor, respectively; the three detection coils are connected in series; one end of the third detection coil is grounded; and the other end of the first detection coil forms the detection end; the induced electromotive force (EMF) V at the detection end is measured; the rotor eccentricity is calculated based on its fundamental amplitude |V|; and the phase difference between the phase of the fundamental component of the induced EMF V and the axis of the A-phase winding is calculated as the rotor eccentricity direction. The rotor eccentricity and the rotor eccentricity direction together constitute the rotor displacement detection result. This invention can improve the integration and reliability of rotor displacement detection in bearingless motors while reducing detection costs.

Description

Technical Field

[0001] This invention belongs to the field of bearingless motor technology, and more specifically, relates to a method, device and system for detecting rotor displacement of a bearingless motor. Background Technology

[0002] Bearingless motors, due to their frictionless advantage, have become a research hotspot in the field of high-speed motors. Because the mechanical bearings are eliminated, the rotor of a bearingless motor inevitably shifts from its equilibrium position. Therefore, bearingless motor systems require rotor displacement detection equipment, currently mostly using eddy current sensors. However, as the rotor's degrees of freedom increase, the number of eddy current sensors required for bearingless motor systems also increases, leading to increased design costs. Furthermore, under high-speed and high-temperature conditions, eddy current sensors are at risk of damage, potentially causing the bearingless motor to malfunction.

[0003] A detection coil is a detection solution integrated inside a motor. By measuring the parameters of the inductance and induced electromotive force of the detection coil, the condition of the motor can be identified. Furthermore, since the detection coil can be embedded in the motor windings, the risk of damage is low.

[0004] Currently, detection schemes based on probe coils are common in bearing motors and are frequently used to detect rotor eccentricity faults. For example, patent application publication number "CN114200303A" discloses a fault detection system based on a group of probe coils. This scheme can detect faults such as rotor dynamic eccentricity and rotor static eccentricity based on the voltage signals of each probe coil and the rotor position. In this scheme, the acquisition of rotor position information actually relies on an additional rotor position sensor. Therefore, it is not suitable for detecting rotor position in bearingless motors.

[0005] The patent application with publication number "CN113251910A" discloses a displacement detection method using a weak coupling between a detection coil and a magnetic bearing. This method involves winding the detection coil around the teeth of the stator core of the magnetic bearing, making the magnetic flux through the detection coil from the magnetic bearing approach zero. Two adjacent detection coils are connected in series to form an inductor, and the rotor displacement is detected by monitoring changes in the inductance value. However, this method requires a large number of detection coils, and the inductance measurement is quite complex. Summary of the Invention

[0006] In view of the shortcomings of the existing technology and the need for improvement, the present invention provides a method, device and system for detecting rotor displacement of bearingless motors. The purpose is to improve the integration and reliability of rotor displacement detection of bearingless motors, while reducing the detection cost.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for detecting rotor displacement of a bearingless motor using a detection coil is provided, comprising:

[0008] Three detection coils are installed in the stator slots of the bearingless motor, namely the first detection coil, the second detection coil, and the third detection coil. The spatial positions of the slot vectors corresponding to the first detection coil, the second detection coil, and the third detection coil are respectively aligned with the axes of the A, B, and C phase windings of the bearingless motor. The two ends of the second detection coil are connected to the first end of the first detection coil and the first end of the third detection coil, respectively. The second end of the third detection coil is grounded, and the second end of the first detection coil constitutes the detection end.

[0009] The induced electromotive force V at the detection end is measured. The rotor eccentricity ε is calculated based on the fundamental amplitude |V| of the induced electromotive force V. The phase difference between the phase of the fundamental component of the induced electromotive force V and the axis of the A-phase winding is calculated as the eccentricity direction of the rotor. The rotor eccentricity ε and the rotor eccentricity direction together constitute the rotor displacement detection result.

[0010] Furthermore, the pitch τ of each detection coil c for:

[0011]

[0012] Where, τ t This refers to the torque winding pitch of a bearingless motor.

[0013] Furthermore, the number of turns of each detection coil is the maximum number of turns allowed in the stator slot space.

[0014] Furthermore,

[0015] ε=|V| / (3ω e k′)

[0016] Where, ω e denoted as ω, and k' is the combined constant coefficient.

[0017] According to another aspect of the present invention, a bearingless motor rotor displacement detection device is provided, comprising: a coil group, an induced electromotive force measurement module, and a signal processing module;

[0018] The coil group includes three coils, namely the first detection coil, the second detection coil, and the third detection coil. The three coils are arranged in the stator slots of the bearingless motor. The spatial positions of the slot vectors corresponding to the first detection coil, the second detection coil, and the third detection coil are respectively aligned with the axes of the A, B, and C phase windings of the bearingless motor. The two ends of the second detection coil are connected to the first end of the first detection coil and the first end of the third detection coil, respectively. The second end of the third detection coil is grounded, and the second end of the first detection coil constitutes the detection end.

[0019] The induced potential measurement module is connected to the probe end and is used to measure the induced potential V at the probe end.

[0020] The signal processing module, connected to the induced electromotive force measurement module, is used to calculate the rotor eccentricity ε based on the fundamental amplitude |V| of the induced electromotive force V, and to calculate the phase difference between the phase of the fundamental component of the induced electromotive force V and the axis of the A-phase winding, which serves as the eccentricity direction of the rotor. The rotor eccentricity ε and the rotor eccentricity direction together constitute the rotor displacement detection result.

[0021] Furthermore, the pitch τ of each detection coil c for:

[0022]

[0023] Where, τ t This refers to the torque winding pitch of a bearingless motor.

[0024] Furthermore, the number of turns of each detection coil is the maximum number of turns allowed in the stator slot space.

[0025] Furthermore,

[0026] ε=|V| / (3ω e k′)

[0027] Where, ω e denoted as ω, and k' is the combined constant coefficient.

[0028] According to another aspect of the present invention, a bearingless motor system is provided, comprising: a bearingless motor, and a bearingless motor rotor displacement detection device provided by the present invention.

[0029] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0030] (1) This invention sets up three detection coils and makes the spatial position of these three detection coils consistent with the axis of the three-phase winding. As a result, the fundamental amplitude and phase of the induced electromotive force of the three detection coils are the same, and they can be directly algebraically accumulated. Therefore, after measuring the induced electromotive force at the detection end, the rotor eccentricity and rotor eccentricity scheme can be calculated based on the fundamental amplitude and phase of the induced electromotive force, and the rotor displacement detection can be accurately completed. Since only three detection coils need to be set up and the three detection coils are set in the stator slots, the detection method has high integration and low cost. In addition, the risk of damage to the detection coils is low and the detection method has high reliability.

[0031] (2) In a preferred embodiment of the present invention, the pitch τ of the detection coil is set. c Torque winding pitch τ of a bearingless motor tsatisfy It can simultaneously ensure that the amplitude of rotor displacement is significant and harmonic interference is small.

[0032] (3) In a preferred embodiment of the present invention, the number of turns of each detection coil is the maximum number of turns allowed in the stator slot space, thereby maximizing the magnitude of the induced electromotive force when the rotor is displaced. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the vector distribution and structure of the first detection coil proposed in this invention; wherein, (a) is a schematic diagram of the vector distribution of the detection coil, and (b) is a schematic diagram of the structure of the detection coil;

[0034] Figure 2 This is a schematic diagram of the second type of probe coil vector distribution and structure proposed in this invention; wherein, (a) is a schematic diagram of the probe coil vector distribution, and (b) is a schematic diagram of the probe coil structure;

[0035] Figure 3 This is a schematic diagram showing the distribution of the detection coils in one embodiment of the present invention;

[0036] Figure 4 This is a finite element simulation waveform of the induced electromotive force of the detection coil under no-load conditions in one embodiment of the present invention.

[0037] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0038] I, II, III, and IV are the four coils in the first detection coil arrangement scheme;

[0039] 1-First detection coil, 2-Second detection coil, 3-Third detection coil. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0041] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0042] To improve the integration and reliability of rotor displacement detection in bearingless motors while reducing detection costs, this invention provides a method, device, and system for rotor displacement detection in bearingless motors. The overall idea is to reasonably arrange the position of the detection coil in the bearingless motor and derive the relationship between the induced electromotive force in the detection coil and the rotor position under this arrangement, so that the rotor position can be detected by detecting the induced electromotive force in the detection coil.

[0043] How to set up the detection coil is the key to realizing the above technical concept. Figure 1 As shown, this is a common arrangement for detecting certain physical quantities using probe coils in a motor. It includes four probe coils: I, II, III, and IV. Each probe coil corresponds to a slot vector with a spatial position differing by 90°. Figure 1 As shown in (a), two pairs of detector coils with opposite phases are connected in series in opposite phase to form two detector coil groups, as follows. Figure 1 As shown in (b) of the diagram.

[0044] The measured signal in this scheme is the induced electromotive force V of two sets of probe coils. 13 and V 24 Mathematical analytical models were established for two operating conditions: no-load operation and operation with levitation current. (No-load operation refers to the motor rotating at its rated speed with no current flowing through the windings; levitation operation refers to the motor not rotating with rated levitation current flowing through the windings.) According to Faraday's law of electromagnetic induction, solving for the induced electromotive force requires first determining the magnetic flux linkages of each set of detection coils. The composition of the magnetic flux linkages differs depending on the number of pole pairs. Since the harmonic components are minimal, in practical applications, only the fundamental frequency component can be considered. Therefore, the mathematical analytical model for the induced electromotive force of this scheme can be summarized as follows:

[0045] 1) No-load condition

[0046]

[0047] In the formula, ω e ε is the electrical angular frequency; ε is the rotor eccentricity. I is the initial phase angle; p is the number of rotor pole pairs; I pm is the equivalent excitation current of the permanent magnet; k is a constant coefficient related to the motor design parameters, specifically:

[0048]

[0049] In the formula, N is the number of turns of the detection coil; h PM g is the thickness of the permanent magnet; g0 is the air gap length; B r For remanence of permanent magnets; a PM1 R is the fundamental coefficient of the Fourier decomposition of the permanent magnet magnetomotive force; l is the outer radius of the rotor; and l is the stack length of the iron core.

[0050] V 24 Then with V 13 The amplitudes are the same, but the phase leads by p*π / 2.

[0051] 2) Suspension Condition

[0052]

[0053] In the formula, I s For floating current; k s To combine the constant coefficients, which are related to the parameters of the levitation winding, specifically:

[0054]

[0055] In the formula, N s a is the number of turns in series per phase of the levitation winding; s1 The Fourier decomposition fundamental coefficient of the suspension winding is given by .

[0056] Due to the inherent characteristics of bearingless motors, the number of pole pairs p of the floating windings... s It differs from the rotor pole pair number p by one.

[0057] Comparing the mathematical models of induced electromotive force (EMF) under no-load and levitation conditions, it can be found that when the number of pole pairs is fixed, the induced EMF under one condition is only proportional to the rotor eccentricity, while the induced EMF under the other condition is only proportional to the current. Specifically, under the premise that the number of rotor pole pairs p = 2n, the induced EMF under levitation condition is proportional to the levitation current and independent of the rotor eccentricity, and its amplitude will be much larger than that under no-load condition, causing strong interference to rotor displacement detection. However, under the premise that p = 2n-1, the induced EMF under no-load condition will cause strong interference to the levitation condition.

[0058] Therefore, the commonly used detection coil arrangement scheme in motors cannot be applied to rotor position detection in bearingless motors.

[0059] Based on this, the present invention proposes a new detection coil arrangement scheme, such as... Figure 2 As shown. It includes three detection coils, each with its corresponding slot vector spatially aligned with the axis of its respective phase winding. The axes of each detection coil differ by a mechanical angle of 120°. Figure 2 As shown in (a), the three coils are connected in series end to end to form a coil group, as follows: Figure 2 As shown in (b) of the diagram.

[0060] exist Figure 2 With the probe coil arrangement shown, the measured signal is only the induced electromotive force V. This is because, under normal circumstances, the number of rotor pole pairs in a bearingless motor satisfies the following specific condition:

[0061] p = 3n ± 1, n = 1, 2, 3...

[0062] Therefore, the mathematical analytical model of the induced electromotive force in the detection coil group under different operating conditions of the motor can be summarized as follows:

[0063] 1) No-load condition

[0064]

[0065] In the formula, k′ is the constant coefficient of merging; it should be noted that since the spatial positions of the three detection coils are consistent with the axes of the three-phase windings, the fundamental amplitude and phase of the induced electromotive force of the three detection coils are the same, so they can be directly algebraically accumulated.

[0066] 2) Suspension Condition

[0067]

[0068] In the formula, k s ′ represents the constant coefficient for merging under this scheme;

[0069] k′ and k s The calculation method for ′ is related to the motor's own parameters. For details, please refer to the calculation method in the first coil arrangement scheme.

[0070] The comparison shows that the second detection coil arrangement has the advantages of simple calculation and weak coupling, which can effectively detect the rotor position of a bearingless motor, and also has high integration, low cost, and high reliability. Based on this, the detection coil in this invention adopts such an arrangement.

[0071] The rotor position detection method and apparatus provided by this invention are applicable to any bearingless motor with a rotor pole pair number satisfying p = 3n ± 1, n = 1, 2, 3... For ease of description and without loss of generality, the following embodiments will use a 36-slot / 4-pole bearingless permanent magnet motor as an example.

[0072] The following is an example.

[0073] Example 1:

[0074] A method for detecting rotor displacement of a bearingless motor using a detection coil includes:

[0075] like Figure 3As shown, three detection coils are set in the stator slots of the bearingless motor, namely the first detection coil 1, the second detection coil 2, and the third detection coil 3. The spatial positions U, V, and W of the slot vectors corresponding to the first detection coil 1, the second detection coil 2, and the third detection coil 3 are respectively aligned with the axes of the A, B, and C phase windings of the bearingless motor. The two ends of the second detection coil 2 are connected to the first end of the first detection coil 1 and the first end of the third detection coil 3, respectively. The second end of the third detection coil 3 is grounded, and the second end of the first detection coil 1 constitutes the detection end.

[0076] Based on the analysis above, it can be seen that, through Figure 3 After setting up the coils as shown, the rotor coil displacement can be detected based on the induced electromotive force measured at the detection end. Considering that the number of turns and pitch of the detection coils have a significant impact on the amplitude and harmonic content of the induced electromotive force, analysis shows that, in order to simultaneously ensure a significant amplitude and low harmonic interference when the rotor displacement occurs, the pitch τ of each detection coil is set as shown in this embodiment. c It should meet the following requirements:

[0077]

[0078] Where, τ t The torque winding pitch is the torque winding pitch of the bearingless motor. Optionally, in this embodiment, the torque winding pitch τ t =7, the probe coil pitch is set to 6.

[0079] Meanwhile, in this embodiment, the number of turns of the detection coil is set to the maximum value allowed by the slot space, specifically 70 turns.

[0080] Rotor displacement detection includes two aspects: eccentricity detection and eccentricity direction detection. Based on the above-mentioned detection coil setup, this embodiment further includes:

[0081] The induced electromotive force V at the probe end is measured, and the rotor eccentricity ε is calculated based on the fundamental amplitude of the induced electromotive force V, |V|.

[0082] The phase difference between the phase of the fundamental component of the induced electromotive force V and the axis of the A-phase winding is calculated and used as the eccentric direction of the rotor. The rotor displacement detection result is composed of the rotor eccentricity ε and the rotor eccentricity direction.

[0083] Based on the above expressions relating induced electromotive force and rotor eccentricity under no-load and suspended conditions, the rotor eccentricity under different conditions can be calculated after measuring the induced electromotive force at the probe end. By adding the two together, the final rotor eccentricity can be calculated.

[0084] Because the spatial position of each detection coil is consistent with the axis of each phase winding, the direction of rotor eccentricity depends on the angle of offset between the phase of the induced electromotive force of the coil group and the axis of the A-phase winding.

[0085] Considering the combined constant coefficient k of the same bearingless motor under levitation conditions s Since ε' is much smaller than k' under no-load conditions, in order to effectively reduce the computational load and improve the detection efficiency without affecting the detection accuracy, this embodiment ignores the induced electromotive force component corresponding to the suspension condition when calculating the rotor eccentricity. Accordingly, in this embodiment, the mathematical analytical model for calculating the rotor eccentricity is: ε=|V| / (3ω e k′).

[0086] The following explains the validity of the mathematical analytical model for rotor eccentricity:

[0087] Once the motor design parameters are determined, the magnetomotive force under different operating conditions can be calculated, thus obtaining the spatiotemporal expression for the air gap magnetic flux density. Taking the first detection coil 1 as an example, the expression for the infinitesimal flux linkage element it hinges can be written, integrated with respect to spatial angular position, and then differentiated with respect to time to obtain the expression for the induced electromotive force of the coil. After setting the eccentricity of the rotor along the X and Y directions, the fundamental amplitude of the induced electromotive force can be calculated.

[0088] Simultaneously, a corresponding finite element simulation model was established. Given the same rotor displacement conditions, the simulated waveform of the induced electromotive force under no-load conditions is shown in the attached figure. Figure 4 As shown, Figure 4 The results shown demonstrate that the detection coil arrangement scheme adopted in this embodiment can effectively sense the displacement changes of the rotor, and... Figure 4 The waveform shown contains a large third harmonic component, so it is necessary to perform Fourier decomposition on it in actual analysis to extract the fundamental amplitude and compare it with the theoretical calculation results. The results are shown in Table 1.

[0089] Table 1 Comparison between mathematical analytical model and simulation results

[0090]

[0091] As shown in Table 1, the mathematical analytical model of rotor eccentricity used in this embodiment has high calculation accuracy and can be used to realize rotor displacement detection.

[0092] In summary, this embodiment uses three detection coils positioned with their spatial locations aligned with the axes of the three-phase windings. This ensures that the fundamental amplitude and phase of the induced electromotive force (EMF) in the three coils are identical, allowing for direct algebraic summation. Therefore, after measuring the induced EMF at the detection end, the rotor eccentricity and eccentricity scheme can be calculated based on the fundamental amplitude and phase of the induced EMF, accurately detecting rotor displacement. Since only three detection coils are required and are located within the stator slots, the detection method boasts high integration, low cost, low risk of coil damage, and high reliability.

[0093] It should be noted that, since the naming of the three phases A, B, and C of the motor can be interchanged in practical applications, the correspondence between the three detection coils and the three-phase windings in this embodiment can also be flexibly adjusted. It should be noted that when determining the rotor eccentricity direction, the phase corresponding to the detection coil of the detection end should be selected.

[0094] Example 2:

[0095] A bearingless motor rotor displacement detection device includes: a coil group, an induced electromotive force measurement module, and a signal processing module;

[0096] The coil group includes three coils, namely the first detection coil, the second detection coil, and the third detection coil. The three coils are arranged in the stator slots of the bearingless motor. The spatial positions of the slot vectors corresponding to the first detection coil, the second detection coil, and the third detection coil are respectively aligned with the axes of the A, B, and C phase windings of the bearingless motor. The two ends of the second detection coil are connected to the first end of the first detection coil and the first end of the third detection coil, respectively. The second end of the third detection coil is grounded, and the second end of the first detection coil constitutes the detection end.

[0097] The induced potential measurement module is connected to the probe end and is used to measure the induced potential V at the probe end.

[0098] The signal processing module, connected to the induced electromotive force measurement module, is used to calculate the rotor eccentricity ε based on the fundamental amplitude |V| of the induced electromotive force V, and to calculate the phase difference between the phase of the fundamental component of the induced electromotive force V and the axis of the A-phase winding, which serves as the eccentricity direction of the rotor. The rotor eccentricity ε and the rotor eccentricity direction together constitute the rotor displacement detection result.

[0099] In this embodiment, the pitch τ of each detection coil c 6:

[0100] The number of turns for each detection coil is the maximum number of turns allowed in the stator slot space, specifically 70;

[0101] The mathematical analytical model used to calculate rotor eccentricity can be found in the description in Example 1 above, specifically as follows:

[0102] ε=|V| / (3ω e k′)

[0103] Where, ω e denoted as ω, and k' is the combined constant coefficient.

[0104] In this embodiment, the basis for setting the pitch and number of turns of the detection coil, as well as the basis for the mathematical analytical model of the rotor eccentricity, can be referred to the description in Embodiment 1 above.

[0105] Example 3:

[0106] A bearingless motor system includes: a bearingless motor, and the bearingless motor rotor displacement detection device provided in Embodiment 2 above.

[0107] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for detecting rotor displacement of a bearingless motor using a detection coil, characterized in that, include: Three detection coils are installed in the stator slot of the bearingless motor, namely the first detection coil, the second detection coil and the third detection coil; The spatial positions of the slot vectors corresponding to the first, second, and third detection coils are respectively aligned with the axes of the A, B, and C three-phase windings of the bearingless motor. The two ends of the second detection coil are respectively connected to the first end of the first detection coil and the first end of the third detection coil. The second end of the third detection coil is grounded, and the second end of the first detection coil constitutes the detection end. Measure the induced potential at the probe end V According to the induced electromotive force V Fundamental amplitude | V | Calculate rotor eccentricity ε And calculate the induced electromotive force. V The phase difference between the phase of the fundamental component and the axis of phase A winding is used as the eccentricity direction of the rotor, determined by the rotor eccentricity. ε Together with the rotor eccentricity direction, they constitute the displacement detection result of the rotor; The number of rotor pole pairs in a bearingless motor satisfies the following condition: Furthermore, rotor eccentricity ε for: Where, ω e It is the electric angular frequency. k' This is for merging constant coefficients.

2. The method for detecting rotor displacement of a bearingless motor using a detection coil as described in claim 1, characterized in that, Pitch of each probe coil τ c for: in, τ t The torque winding pitch of the bearingless motor is given.

3. The method for detecting rotor displacement of a bearingless motor using a detection coil as described in claim 1, characterized in that, The number of turns for each detection coil is the maximum number of turns allowed in the stator slot space.

4. A bearingless motor rotor displacement detection device, characterized in that, include: Coil assembly, induced electromotive force measurement module, and signal processing module; The coil group includes three coils: a first detection coil, a second detection coil, and a third detection coil. The three coils are disposed in the stator slots of the bearingless motor. The spatial positions of the slot vectors corresponding to the first, second, and third detection coils are respectively aligned with the axes of the A, B, and C phase windings of the bearingless motor. The two ends of the second detection coil are respectively connected to the first end of the first detection coil and the first end of the third detection coil. The second end of the third detection coil is grounded, and the second end of the first detection coil constitutes a detection end. The induced potential measurement module is connected to the detection end and is used to measure the induced potential of the detection end. V ; The signal processing module is connected to the induced electromotive force measurement module and is used to process the induced electromotive force. V Fundamental amplitude | V | Calculate rotor eccentricity ε And calculate the induced electromotive force. V The phase difference between the phase of the fundamental component and the axis of phase A winding is used as the eccentricity direction of the rotor, determined by the rotor eccentricity. ε Together with the rotor eccentricity direction, they constitute the displacement detection result of the rotor; The number of rotor pole pairs in a bearingless motor satisfies the following condition: Furthermore, rotor eccentricity ε for: Where, ω e It is the electric angular frequency. k' This is for merging constant coefficients.

5. The bearingless motor rotor displacement detection device as described in claim 4, characterized in that, Pitch of each probe coil τ c for: in, τ t The torque winding pitch of the bearingless motor is given.

6. The bearingless motor rotor displacement detection device as described in claim 4, characterized in that, The number of turns for each detection coil is the maximum number of turns allowed in the stator slot space.

7. A bearingless motor system, characterized in that, include: A bearingless motor, and the rotor displacement detection device for a bearingless motor as described in any one of claims 4 to 6.

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