A sensorless axial magnetic field permanent magnet synchronous motor system with low moment of inertia

Abstract

The present invention discloses a low moment of inertia, position sensorless axial magnetic field permanent magnet synchronous motor system, comprising an axial magnetic field permanent magnet synchronous motor and a position sensorless control system. The axial magnetic field permanent magnet synchronous motor comprises a stationary rotor yoke, a stator, and a rotor. The rotor is arranged on the motor shaft, located between the stationary rotor yoke and the stator, and an air gap is provided between the stationary rotor yoke and the stator. The rotor comprises a plurality of magnets, magnetic patches, and a rotor core. The magnetic patches are attached to the surface of the magnets, the contact surface between the magnetic patches and the magnets is arc-shaped, and the magnetic patches are concave in the middle. The magnets are evenly spaced or embedded in the surface of the rotor core. The position sensorless control system is used to realize the drive control of the axial magnetic field permanent magnet synchronous motor. The present invention attaches high-permeability patches to the surface of the rotor permanent magnet, significantly improving the salient pole effect of the motor by enhancing the magnetic conductivity of the magnetic circuit, thereby optimizing the accuracy of rotor position estimation.

Description

Technical Field

[0001] The present invention relates to the technical field of permanent magnet synchronous motors, and in particular to a position sensorless axial magnetic field permanent magnet synchronous motor system with low moment of inertia. Background Art

[0002] Axial-field permanent magnet synchronous motors (PMSMs) are widely used in new energy vehicles, industrial drives, and other fields due to their high efficiency, high power density, and reliability. Traditional PMSM control relies on mechanical position sensors (such as encoders or resolvers) to obtain rotor position information. However, these sensors increase system cost, complexity, and maintenance requirements, and their reliability is particularly reduced in harsh environments such as high temperature, high humidity, or strong magnetic fields. Therefore, sensorless control technology has become a hot research topic. When the motor is running at high speed, control methods based on back-EMF (back-EMF) calculate rotor position information, but these methods fail at zero or low speeds due to the weak back-EMF signal. High-frequency signal injection, which injects a high-frequency signal into the motor windings and exploits the saliency effect, has become an effective solution for zero or low speed operation. Due to the symmetry of the magnetic circuit design of typical axial-field permanent magnet synchronous motors, such as uniform magnet distribution, consistent air gap thickness, and symmetrical rotor core structure, the magnetic circuit characteristics of the direct and quadrature axes are nearly identical, resulting in equal direct and quadrature inductances and a lack of saliency. Especially when the motor is running at zero speed or low speed, this equal inductance characteristic makes it difficult for the motor to generate a sufficiently strong high-frequency current response when applying the position sensorless control technology of the high-frequency signal injection method. The signal amplitude is weak, the signal-to-noise ratio is low, and it is easily affected by noise interference. The accuracy and robustness of the rotor position estimation will be significantly reduced. Therefore, it is not suitable to directly apply the position sensorless technology. Summary of the Invention

[0003] The purpose of the present invention is to provide a low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system, which utilizes thinned magnetic steel and attached high permeability core to enhance the salient pole effect. When the motor operates at zero speed or low speed, a high-frequency voltage signal is injected into the direct axis of the orthogonal and direct axis coordinate system to form a pulsating voltage signal in the stationary coordinate system. Combined with a position tracking observer, high-precision rotor position estimation is achieved during zero speed or low speed operation. At high speed, the speed and position information is solved by back electromotive force, thereby reducing system complexity and noise impact.

[0004] The technical solution of the present invention is: a low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system, including an axial magnetic field permanent magnet synchronous motor and a position sensorless control system, the axial magnetic field permanent magnet synchronous motor includes a stationary rotor yoke, a stator and a rotor, the rotor is arranged on the motor shaft, located between the stationary rotor yoke and the stator, and an air gap is provided between the stationary rotor yoke and the stator, the rotor includes a plurality of magnets and magnetic patches and a rotor core, the magnetic patches are attached to the surface of the magnets, the contact surface between the magnetic patches and the magnets is arc-shaped, and the magnetic patches are concave in the middle, the magnets are equidistantly mounted or embedded in the surface of the rotor core, and the position sensorless control system is used to realize the drive control of the axial magnetic field permanent magnet synchronous motor.

[0005] Compared with the prior art, the present invention has the following significant advantages:

[0006] (1) The present invention enhances the salient pole effect of the axial magnetic field motor by thinning the magnetic steel and attaching high-permeability magnetic patches, thus overcoming the limitation of equal inductance of the d-axis and q-axis.

[0007] (2) The high-conductivity magnetic patch of the present invention is flexible in design, and its thickness and shape can be adjusted to adapt to various working conditions, thereby improving versatility;

[0008] (3) The present invention improves the signal-to-noise ratio of the high-frequency signal injection method when the motor is running at low speed or zero speed, thereby improving the accuracy and robustness of rotor position estimation;

[0009] (4) The present invention combines a phase-locked loop and back-electromotive force method to achieve full-speed rotor position tracking, ensuring stability and reliability at different speeds;

[0010] (5) The present invention does not require a mechanical position sensor, reducing system complexity and cost while maintaining high efficiency and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a block diagram of a low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system of the present invention;

[0012] Figure 2 It is an exploded schematic diagram of the axial magnetic field permanent magnet synchronous motor of the present invention.

[0013] Figure 3 This is a block diagram of the implementation principle of the rotor position estimation based on the injection of the pulsating high-frequency voltage signal of the position tracking observer when the motor in the present invention runs at zero speed or low speed.

[0014] Figure 4 It is the simulation result of the rotor position estimation based on the injection of the pulsating high-frequency voltage signal of the position tracking observer when the motor in the present invention runs at zero speed or low speed.

[0015] Figure 5 This is a block diagram of the implementation principle of the rotor position estimation of the sliding film observer based on the phase-locked loop when the motor in the present invention runs at high speed.

[0016] Figure 6 This is the simulation result of the rotor position estimation of the sliding film observer based on the phase-locked loop when the motor in the present invention runs at high speed. DETAILED DESCRIPTION

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] A low-moment-of-inertia, position-sensorless, axial-field permanent-magnet synchronous motor system and its control method are described. By thinning the magnetic steel and attaching a high-permeability core to the surface, the salient polarity is enhanced, enabling high-precision rotor position estimation in all-speed operating scenarios. The contact surface between the magnetic patch and the magnetic steel is curved, with the patch recessed in the middle. This increases the magnetic resistance of the direct axis, reducing the inductance of the direct axis and enhancing the saliency of the quadrature and direct-axis inductances. This improves the magnetic field response to high-frequency signal injection at zero or low speeds, enabling the motor to generate stronger position-related signals, making it suitable for position-sensorless control. Furthermore, even at high speeds, the generated back-electromotive force can still be used to estimate rotor position information.

[0019] like Figure 1 As shown in FIG, a low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system includes an axial magnetic field permanent magnet synchronous motor and a position sensorless control system. Figure 2 As shown, the axial magnetic field permanent magnet synchronous motor includes a stationary rotor yoke 11, a stator 12, a rotor 13, and an air gap 14. The rotor 13 is arranged on the motor shaft, located between the stationary rotor yoke 11 and the stator 12, and an air gap 14 is provided between the rotor 13 and the stationary rotor yoke 11 and the stator 12. The rotor 13 includes a plurality of magnetic steels 131 and magnetic conductive patches 133, and a rotor core 132. The magnetic steels 131 and magnetic conductive patches 133 are evenly spaced and mounted or embedded on the surface of the rotor core 132. The stationary rotor yoke 11 includes a magnetic yoke 111 and a magnetic yoke core 112. The stator 12 includes a stator core 121 and a plurality of stator windings 122. The magnetic steel 131 is thinned, and a magnetic patch 133 with stronger magnetic conductivity is attached to its surface. The contact surface between the magnetic patch 133 and the magnetic steel 131 is arc-shaped, and the magnetic patch is concave in the middle to increase the magnetic resistance of the direct axis, thereby reducing the inductance of the direct axis and enhancing the salient pole effect of the direct-axis inductance to improve the magnetic field response when a high-frequency signal is injected.

[0020] The sensorless control system is used to calculate the motor rotor position information and drive an axial magnetic field permanent magnet synchronous motor. Specific functions include: when the axial magnetic field permanent magnet synchronous motor is operating at zero speed or low speed, injecting a high-frequency voltage signal into the d-axis of the axial magnetic field permanent magnet synchronous motor and extracting the q-axis current of the axial magnetic field permanent magnet synchronous motor to obtain the rotor position information of the axial magnetic field permanent magnet synchronous motor through calculation, and simultaneously feeding the rotor position information back to the axial magnetic field permanent magnet synchronous motor as feedback to form a closed control loop; when the axial magnetic field permanent magnet synchronous motor is operating at high speed, extracting the back electromotive force generated by the axial magnetic field permanent magnet synchronous motor during operation, and then calculating the rotor position information of the axial magnetic field permanent magnet synchronous motor and simultaneously feeding the rotor position information back to the axial magnetic field permanent magnet synchronous motor as feedback to form a closed control loop.

[0021] In a further embodiment, by thinning the thickness of the magnetic steel 131 and attaching a high-permeability patch 133, the thickness of the magnetic steel 131 is 60% to 80% of the original thickness of the original magnetic steel (10 mm), and the thickness of the magnetic patch 133 is 1.0 mm to 3.0 mm. The magnetic steel 131 is cut into a convex center, while the magnetic patch 133 is concave in the center and tightly attached to the magnetic steel 131. Because the magnetic permeability of the magnetic steel 131 is lower than that of the high-permeability patch 133, the direct-axis magnetic resistance is larger than the quadrature-axis magnetic resistance, and the direct-axis inductance is smaller than the quadrature-axis inductance L. d < L q , enhancing the salient pole effect of the AC and DC axis inductance to improve the magnetic field response when high-frequency signals are injected, enabling the motor to generate stronger position-related signals.

[0022] In a further embodiment, the magnet steel 131 and the magnetic conductive patch 133 have the same magnetizing direction and alternate in positive and negative directions along the axial direction.

[0023] In a further embodiment, the magnetic conductive patch 133 is made of soft magnetic alloy.

[0024] In a further embodiment, the rotor core 132 includes two rings connected by rotor spokes.

[0025] In a further embodiment, the rotor 13 is of yoke-free type, and a plurality of magnets 131 and magnetic patches 133 are embedded in the spokes of the rotor core 132, and the total thickness of the magnets 131 and the attached magnetic patches 133 is equal to the thickness of the spokes.

[0026] In a further embodiment, the system has two working modes, namely: when the motor is running at zero speed or low speed, the rotor position is estimated based on the injection of a pulsating high-frequency voltage signal of a position tracking observer, including injecting a high-frequency voltage signal into the d-axis of the stator winding 122, collecting the q-axis current in the stator winding 122, and using the position tracker to estimate the rotor position information; when the motor is running at high speed, the rotor position is estimated based on the back electromotive force generated by the speed-related electrical signal in the three-phase permanent magnet synchronous motor based on the fundamental wave mathematical model, collecting the back electromotive force in the stator winding 122, and using a phase-locked loop-based sliding film observer to estimate the rotor position information.

[0027] In a further embodiment, when the motor is running at zero speed or low speed, a high-frequency voltage signal is injected into the d-axis of the axial magnetic field permanent magnet synchronous motor, and the q-axis current of the axial magnetic field permanent magnet synchronous motor is extracted. A rotor synchronous rotating coordinate system is established, The axis is the estimated rotor synchronous rotation coordinate system, and the quadrature and direct axes are the actual rotor synchronous rotation coordinate system. is a two-phase stationary coordinate system, is the estimated rotor position angle, is the actual rotor position angle, and the rotor estimated error angle is calculated for:

[0028]

[0029] like Figure 3 As shown in the figure, the voltage equation of the permanent magnet synchronous motor can be expressed in the quadrature and direct axis synchronous rotating coordinate system as follows:

[0030]

[0031] Where: 、 are the quadrature and direct axis components of the stator voltage respectively; 、 are the quadrature and direct axis components of the stator current respectively; R is the stator resistance; 、 are the quadrature and direct axis components of the stator flux respectively; is the electrical angular velocity; 、 They are the quadrature and direct axis inductance components respectively; is the permanent magnet flux linkage.

[0032] The frequency of the high-frequency injection signal is generally much higher than the fundamental frequency of the motor , since the resistance is much smaller than the reactance at high frequencies, it can be ignored. At this point, the voltage equation of the three-phase permanent magnet synchronous motor under high frequency excitation can be simplified to:

[0033]

[0034] Then, in the estimated rotor synchronous rotating coordinate system, the relationship between the high-frequency voltage and current is:

[0035]

[0036] Where, 、 ,as well as 、 In the estimated rotor synchronous rotating coordinate system, middle Axis and High-frequency components of shaft voltage and current. is the average inductance, is a semi-differential inductor.

[0037] In a further embodiment, a high-frequency voltage signal is injected into the d-axis of the stator winding 122 based on an estimated rotor synchronous rotating coordinate system:

[0038]

[0039] Where, is the amplitude of the high-frequency voltage signal, is the frequency of the high-frequency voltage signal.

[0040] In a further embodiment, the q-axis current in the stator winding 122 is collected. After the above derivation, the high-frequency voltage signal injected into the d-axis is substituted into the high-frequency voltage and current equations in the synchronously rotating rotor coordinate system. After integration, the following equations can be obtained:

[0041]

[0042] when When , in the estimated rotor synchronous rotating coordinate system, The amplitude of the shaft high-frequency current component and the rotor position estimation error angle Related. Figure 2 As shown, thinning the magnetic steel 131 and attaching the high-permeability patch 133 can significantly increase the direct-axis inductance. and quadrature-axis inductance The difference between the two makes it easier to extract high-frequency current signals.

[0043] In a further embodiment, a position tracker is used to estimate the rotor position information:

[0044] (1) A bandpass filter (BPF) is used to extract the high-frequency current signal containing the rotor position information and filter out the fundamental current and high-frequency carrier current in the motor current signal;

[0045] (2) The high-frequency current signal containing the rotor position information is passed through a low-pass filter (LPF) to obtain the rotor position error signal, and the error signal is linearized, that is:

[0046]

[0047] Where, is the error signal coefficient.

[0048] (3) Adjust the PI parameter gain in the position tracking observer so that As approaches zero, the rotor position angle estimation error also approaches zero, and the estimated value of the rotor position converges to the actual value of the rotor position.

[0049] (4) Estimated rotor speed obtained through position tracking observation , (using phase-locked loop structure), the speed calculation formula is:

[0050]

[0051] Where k p , k i are the proportional and integral gain coefficients of the PI regulator in the position tracking observer, and t is the integral time variable.

[0052] Integrate the estimated rotor speed to get the estimated rotor position The obtained rotor position information is fed back to the servo control system of the axial permanent magnet synchronous motor to form a control closed loop.

[0053] In a further embodiment, the present invention builds a proposed pulse high-frequency voltage signal injection model based on position tracking observer in simulation software. Figure 4 The actual and estimated rotor positions are displayed. Due to the lag between the simulated system and the actual system, there is a sudden change in position during the position cycle switching, but the error remains within a very small range throughout the stable operation. This demonstrates that the improved axial permanent magnet synchronous motor, due to its increased saliency, can be applied to position sensorless control technology based on high-frequency signal injection at zero or low speeds.

[0054] In a further embodiment, Figure 5 As shown, when the motor is running at high speed, according to the equivalent control principle of sliding mode control, the back electromotive force in the voltage of the stator winding (122) is separated and extracted to keep it on the sliding film surface. The voltage equation of the permanent magnet synchronous motor in the stationary coordinate system is:

[0055]

[0056] Where, 、 is the stator voltage; 、 is the stator current; To expand the back electromotive force, and satisfy:

[0057]

[0058] The extended back EMF contains all the information about the motor rotor position and speed. The extended back EMF is observed using a sliding film observer. The general design of a sliding film observer is as follows:

[0059]

[0060] Where, is the observed value of the stator current, is the control input of the observer.

[0061] Rewriting the voltage equation in the stationary coordinate system into the state equation of the current and subtracting it from the above equation can obtain the stator current error equation:

[0062]

[0063] Where: is the current observation error. The sliding mode control law is designed as:

[0064]

[0065] Where:

[0066] When the state variable of the observer reaches the sliding surface After that, the observer state will always remain on the sliding surface.

[0067] In a further embodiment, the separated back electromotive force is processed by sliding mode and then passed through a low-pass filter to obtain a back electromotive force signal containing rotor position information. According to the equivalent control principle of sliding mode control, the control quantity at this time can be regarded as an equivalent control quantity, and it can be obtained:

[0068]

[0069] Since the actual control quantity is a discontinuous high-frequency switching signal, a low-pass filter is required to extract the continuous back-EMF estimate:

[0070]

[0071] Where, 、 is the actual discontinuous back electromotive force control quantity, 、 The continuous back electromotive force signal is obtained after the discontinuous back electromotive force control quantity after the synovial film processing passes through the low-pass filter. is the time constant of the low-pass filter.

[0072] In a further embodiment, after the output angle generated by the phase-locked loop is fed back, it is compared with the back electromotive force signal including the input angle to obtain the rotor position error angle, and the signal including the rotor position error angle information is linearized.

[0073] Assumptions ,when When, think If established, then:

[0074]

[0075] Where, 、 The back electromotive force control quantity after the synovial film processing is passed through a low-pass filter to obtain a back electromotive force signal containing the rotor position information.

[0076] In a further embodiment, the PI parameter gain in the phase-locked loop is adjusted so that the error signal after linearization is smaller than the error value. As the input of the phase-locked loop PI regulator, the PI parameter gain in the phase-locked loop is adjusted so that Approaches zero, making the estimated rotor position Converge to the actual rotor position At the same time, the error signal is passed through the proportional-integral link to obtain the estimated rotor speed , integrate the estimated rotor speed to get the estimated rotor position The obtained rotor position information is fed back to the servo control system of the axial permanent magnet synchronous motor to form a control closed loop.

[0077] In a further embodiment, the error signal is passed through a proportional-integral link in a phase-locked loop to obtain an estimated rotor speed. :

[0078]

[0079] Where k p , k i are the proportional and integral gain coefficients of the PI regulator in the phase-locked loop, and t is the integral time variable. This invention identifies the rotor position based on the electrical model of the motor during operation, thereby achieving sensorless control. At zero or low speeds, high-frequency signal injection is required to track the rotor salient poles caused by the difference in quadrature and direct axis inductances, thereby calculating the rotor salient pole position. At high speeds, high-frequency signal injection is no longer required because the motor's back EMF has already been established.

[0080] In a further embodiment, the present invention builds the proposed phase-locked loop-based synovial observer model in simulation software. Figure 6 The actual and estimated rotor positions are displayed. Due to the lag between the simulation system and the actual system, there is a sudden change in position during the position cycle switching, but the error remains within a very small range throughout the stable operation. This demonstrates the feasibility of using the speed-related electrical signal (generated back EMF) of a three-phase permanent magnet synchronous motor based on a fundamental wave mathematical model to estimate rotor position at high speeds.

[0081] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention.

Claims

1. A low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system, characterized in that: The invention comprises an axial magnetic field permanent magnet synchronous motor and a position sensor-free control system, wherein the axial magnetic field permanent magnet synchronous motor comprises a stationary rotor yoke (11), a stator (12) and a rotor (13), wherein the rotor (13) is arranged on the motor shaft and is located between the stationary rotor yoke (11) and the stator (12), and an air gap (14) is provided between the stationary rotor yoke (11) and the stator (12), and the rotor (13) comprises a plurality of magnetic steels (131) and magnetic conductive patches (133) and a rotor core ( 132), the magnetic patch (133) is attached to the surface of the magnetic steel (131), the contact surface between the magnetic patch (133) and the magnetic steel (131) is arc-shaped, the magnetic patch (133) is concave in the middle, the magnetic steel (131) is mounted or embedded on the surface of the rotor core (132) at equal intervals, and the position sensorless control system is used to realize the drive control of the axial magnetic field permanent magnet synchronous motor; the specific method of realizing the drive control of the axial magnetic field permanent magnet synchronous motor by the position sensorless control system is: When the operating speed of the axial magnetic field permanent magnet synchronous motor is lower than the set threshold, a high-frequency voltage signal is injected into the d-axis of the axial magnetic field permanent magnet synchronous motor, and the q-axis current of the axial magnetic field permanent magnet synchronous motor is extracted. The rotor position information of the axial magnetic field permanent magnet synchronous motor is obtained through calculation, and the rotor position information is fed back to the axial magnetic field permanent magnet synchronous motor to form a control closed loop. When the operating speed of the axial magnetic field permanent magnet synchronous motor is not lower than the set threshold, the back electromotive force generated during the operation of the axial magnetic field permanent magnet synchronous motor is extracted, and the rotor position information of the axial magnetic field permanent magnet synchronous motor is obtained through calculation. At the same time, the rotor position information is fed back to the axial magnetic field permanent magnet synchronous motor to form a control closed loop; When the operating speed of the axial magnetic field permanent magnet synchronous motor is lower than the set threshold, the q-axis current of the axial magnetic field permanent magnet synchronous motor is extracted, and the specific method for obtaining the rotor position information of the axial magnetic field permanent magnet synchronous motor through calculation is as follows: A bandpass filter is used to extract the high-frequency current signal containing the rotor position information and to filter out the fundamental current and high-frequency carrier current in the motor current signal; The high-frequency current signal containing the rotor position information is passed through a low-pass filter to obtain the rotor position error signal, and the error signal is linearized; Adjust the PI parameter gain in the position tracking observer so that the error signal after linearization is less than the error threshold; After the position tracking observer, the estimated rotor speed is obtained , the specific formula is: ； Where k p , k i are the proportional and integral gain coefficients of the PI regulator in the position tracking observer, is the rotor position estimation error angle, is the error signal coefficient, t is the integration time variable; Integrate the estimated rotor speed to get the estimated rotor position .

2. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 1, characterized in that: The error signal after linearization is specifically: ； Where, In the estimated rotor synchronous rotating coordinate system The high-frequency component of the shaft current, is the frequency of the high-frequency voltage signal, is the amplitude of the high-frequency voltage signal, 、 are the quadrature and direct axis inductance components respectively.

3. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 1, characterized in that: When the operating speed of the axial magnetic field permanent magnet synchronous motor is not lower than the set threshold, the back electromotive force generated during the operation of the axial magnetic field permanent magnet synchronous motor is extracted, and the specific method for calculating the rotor position information of the axial magnetic field permanent magnet synchronous motor is as follows: According to the equivalent control principle of sliding mode control, the back electromotive force in the collected voltage of the stator winding (122) is separated and extracted so that the back electromotive force is maintained on the sliding film surface; The separated back electromotive force is processed by sliding film and then passed through a low-pass filter to obtain a back electromotive force signal containing rotor position information; The output angle feedback generated by the phase-locked loop is compared with the back electromotive force signal to obtain a signal containing rotor position error information, and the signal containing the rotor position error information is linearized; Adjust the PI parameter gain in the phase-locked loop so that the error signal after linearization is less than the error threshold; After the phase-locked loop, the estimated rotor speed is obtained , the specific formula is: ； Where k p , k i is the proportional and integral gain coefficient of the PI regulator in the phase-locked loop, is the rotor position angle, is the estimated rotor position angle, t is the integration time variable, and k is the error signal coefficient; Integrate the estimated rotor speed to get the estimated rotor position .

4. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 3, characterized in that: The error signal after linearization is specifically: ； Where, 、 The back electromotive force signal is obtained after the back electromotive force control quantity after the sliding film processing passes through the low-pass filter.

5. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 1, characterized in that: The thickness of the magnetic steel (131) is 6 mm to 8 mm, and the thickness of the magnetic conductive patch (133) is 1.0 mm to 3.0 mm.

6. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 1, characterized in that: The magnetizing directions of the magnetic steel (131) and the magnetic conductive patch (133) are the same, and are alternately positive and negative along the axial direction.

7. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 1, characterized in that: The magnetic conductive patch (133) is made of a soft magnetic alloy.

8. The low moment of inertia position sensorless axial magnetic field permanent magnet synchronous motor system according to claim 1, characterized in that: The rotor core (132) comprises two circular rings, which are connected via rotor spokes.

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