Rotor structure and application of asynchronous starting permanent magnet synchronous motor

Abstract

The present application discloses the rotor structure and application of an asynchronous start permanent magnet synchronous motor. The conductive bars are distributed unevenly and asymmetrically as a whole. The conductive bars and permanent magnets together form a multi-layer rotor structure with a magnetic flux barrier function. The conductive bars are tilted in the direction of the motor's main magnetic flux, which significantly increases the d-axis magnetic resistance, reduces the d-axis magnetizing inductance, increases the motor's salient pole ratio, increases the magnetic resistance torque, increases the acceleration torque during the pull-in synchronization process, and strengthens the pull-in synchronization capability. When the number of conductive bars is the same as in the related art, the conductive bar cross-sectional area in the back-electromotive force direction is larger, the overall conductive bar resistance is reduced, the slip rate near the critical synchronous speed is reduced, and the pull-in synchronization capability is improved. In addition, the conductive bars in the direction of the motor's main magnetic flux have a certain spatial tilt angle, which causes significant changes in the d- and q-axis currents, reduces the d-axis inductance, increases the d-axis current, and reduces the q-axis current, resulting in a smaller composite current, a larger internal power factor angle, and a smaller power factor angle, thereby improving both the power factor and efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of motors, and in particular to the rotor structure and application of asynchronous start permanent magnet synchronous motors. Background Art

[0002] Asynchronous-start permanent magnet synchronous motors (ASMs) offer not only self-starting capability but also high efficiency, a high power factor, and strong overload capacity. They are a new type of permanent magnet motor with promising development prospects. Replacing or partially replacing industrial asynchronous motors with ASMs can achieve significant energy savings. However, in practical applications, traditional ASMs must not only demonstrate excellent steady-state performance but also meet the requirements for reliable transient operation, especially in specialized applications such as the textile and chemical fiber industries and fans and pumps with long annual operating times. The starting process of an ASM consists of an asynchronous starting phase and a pull-in phase. The pull-in phase often involves a large system moment of inertia, requiring more energy to accelerate to the synchronous speed. This places stringent requirements on pull-in performance, especially in specialized applications. Poor or impossible pull-in synchronization can significantly impact the motor's steady-state operation. Furthermore, prolonged, high starting currents increase the motor's impact on the power supply and negatively impact the permanent magnet's ability to resist demagnetization.

[0003] In view of the drawbacks of the two-pole asynchronous start permanent magnet synchronous motor in the above related technologies when applied in certain special occasions, it is necessary to propose a new rotor structure of the two-pole asynchronous start permanent magnet synchronous motor. Summary of the Invention

[0004] In view of this, the present application provides a rotor structure and application of an asynchronous start permanent magnet synchronous motor, which can improve the motor's pull-in synchronization capability while meeting the technical requirements of asynchronous motors of corresponding power levels.

[0005] The present application provides a rotor structure, comprising:

[0006] It includes conductive bars distributed in an annular manner on the inner surface of the rotor body, characterized in that the conductive bars in the main magnetic flux direction are asymmetrically distributed along the d-axis direction and arranged at uniform intervals, and the conductive bars in the back electromotive force direction are symmetrically distributed along the q-axis direction and arranged at non-uniform intervals.

[0007] Optionally, the extension direction of the conductive bars in the main magnetic flux direction is inclined relative to the radial direction of the rotor body.

[0008] Optionally, the inclination direction of the end portion of the guide bar close to the axis is opposite to the rotation direction of the rotor body.

[0009] Optionally, the conductive bars can form a magnetic flux barrier structure with the built-in permanent magnets of the rotor body in the back electromotive force direction.

[0010] Optionally, the cross-sectional area of ​​the conductive bars in the back electromotive force direction is not less than the cross-sectional area of ​​the conductive bars in the main magnetic flux direction.

[0011] In a second aspect, the present application provides an asynchronous start permanent magnet synchronous motor, comprising the rotor structure as described above.

[0012] In a third aspect, the present application provides an application of the asynchronous starting permanent magnet synchronous motor as described above, which is applied to a motor device for achieving unidirectional rotation.

[0013] In this technical solution, the rotor structure features an overall uneven and asymmetrical distribution of conductive bars. Together, the bars and permanent magnets form a multi-layered rotor structure that acts as a flux barrier. The bars are tilted in the direction of the motor's main magnetic flux, significantly increasing the d-axis reluctance and reducing the d-axis magnetizing inductance. This increases the motor's saliency ratio, boosting reluctance torque, and increasing the acceleration torque during pull-in synchronization, while reducing the required energy and enhancing pull-in synchronization capability. While maintaining the same number of conductive bars as a conventional two-pole asynchronous start permanent magnet synchronous motor, the bar cross-section in the direction of the motor's back EMF is larger, reducing the overall resistance of the rotor bars. This reduces the motor's slip near the critical synchronous speed and improves pull-in synchronization capability.

[0014] Furthermore, the bars in the direction of the motor's main magnetic flux have a certain spatial tilt angle, which significantly changes the d-axis and q-axis currents. This reduces the d-axis inductance, increases the d-axis current, and reduces the q-axis current. This results in a smaller resultant current, a larger internal power factor angle, and a smaller power factor angle, improving both the power factor and efficiency. The bars in the direction of the motor's main magnetic flux have a certain spatial tilt angle, creating a more pronounced flux barrier in the d-axis direction, which, to a certain extent, reduces the risk of permanent magnet demagnetization. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings will make the technical solutions and other beneficial effects of the present application apparent.

[0016] Figure 1 Schematic diagram of the overall structure of the rotor structure in the related art;

[0017] Figure 2 Provide an overall structural diagram of the rotor structure for the application embodiment;

[0018] Figure 3 Provide a magnetic field line distribution diagram of the rotor structure in steady-state operation for the application embodiment;

[0019] Figure 4 A speed diagram of a rotor structure in related art under different load torque multiples;

[0020] Figure 5 Provide a rotational speed diagram of the rotor structure under different load torque multiples for the application embodiment;

[0021] Figure 6 A speed diagram of a rotor structure in related art at different multiples of the moment of inertia;

[0022] Figure 7 Provide a rotational speed diagram of the rotor structure at different multiples of the moment of inertia for the application embodiment;

[0023] Figure 8 The critical pull-in characteristic curves of the related art rotor structure and the rotor structure of the present application;

[0024] Figure 9 The waveform diagram of eddy current loss on the guide bar when the rotor structure of the related art and the rotor structure of the present application are in steady state operation;

[0025] Figure 10 The A-phase current waveform diagram of the rotor structure in the related art and the rotor structure in the present application;

[0026] Figure 11 The time-space vector diagrams of the rotor structure of the related art and the rotor structure of the present application;

[0027] Figure 12 This is a demagnetization area diagram of a rotor structure in the related art;

[0028] Figure 13 This is a demagnetization area diagram of the rotor structure provided in this application;

[0029] Figure 14 Rated torque diagrams of the rotor structure in related art and the rotor structure in this application;

[0030] The components in the figure are identified as follows:

[0031] 1,2,3,4,5-conducting bars; 6-air slot; 7-permanent magnet. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0033] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the described features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0034] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections, electrical connections, or mutual communication; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to internal communication between two components or the interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0035] The disclosure below provides many different embodiments or examples for realizing different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present application. In addition, the present application may repeat reference numbers and / or reference letters in different examples, and such repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present application provides examples of various specific processes and materials, but those of ordinary skill in the art will appreciate the application of other processes and / or the use of other materials.

[0036] refer to Figure 2The rotor structure provided in the embodiment of the present application includes 20 non-uniform and asymmetric guide bars 1, 2, 3, 4, 5, 2 guide bars 1, 2, 3, 4, 5, 4 guide bars 1, 2, 3, 4, 5, and 4 guide bars 1, 2, 3, 4, 5, which are annularly distributed on the rotor surface. The guide bars 1, 2, 3, 4, 5 are uniformly and asymmetric distributed along the d-axis direction. The cross-sectional areas of the guide bars 1, 2, 3, 4, 5 and the guide bars 1, 2, 3, 4, 5 are equal to the cross-sectional areas of the guide bars 1, 2, 3, 4, 5 in the rotor structure in the related art. Conductive bars 1, 2, 3, 4, 5 and 1, 2, 3, 4, 5 are symmetrically and unevenly distributed along the q-axis. The cross-sectional area of ​​conductive bars 1, 2, 3, 4, 5 is larger than that of conductive bars 1, 2, 3, 4, 5, and the cross-sectional area of ​​conductive bars 1, 2, 3, 4, 5 is larger than that of conductive bars 1, 2, 3, 4, 5. The sum of the number of conductive bars 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, and 1, 2, 3, 4, 5 is the same as the number of conductive bars 1, 2, 3, 4, 5. Considering the stress direction, the distance between rotor air slot 6 and conductive bars 1, 2, 3, 4, 5 and 1, 2, 3, 4, 5 is no less than 1 mm. Conductive bars 1, 2, 3, 4, 5 and 1, 2, 3, 4, 5, together with the permanent magnets 7 in the rotor air slot 6, form a two-layer flux barrier structure. All guide bars are cast aluminum.

[0037] The approximate expression of the steady-state electromagnetic torque of a permanent magnet synchronous motor is:

[0038]

[0039] Where m is the number of phases, p is the number of pole pairs, U is the motor terminal voltage, E0 is the motor back EMF, X d is the direct-axis reactance, X q is the quadrature-axis reactance, θ is the power angle, ω s is the synchronous electrical angular velocity of the motor.

[0040] During the motor starting process, the asynchronous starting permanent magnet synchronous motor satisfies the mechanical motion equation

[0041]

[0042] Arrange the right side of the above formula, and we get

[0043]

[0044] Substitution

[0045]

[0046] Where, T L is the load torque, s is the slip rate, and J is the moment of inertia of the system (including the motor and the load).

[0047] From the above analysis, it can be seen that when the system's rotational inertia is constant, the factors affecting the motor's ability to pull in synchronization are mainly the permanent magnet pulsating torque and the critical speed when starting to pull in synchronization.

[0048] Pulsating torque is the electromagnetic torque at the end of the motor's synchronization process, when it is close to the synchronous speed. It includes pulsating torque with single slip frequency and pulsating torque with double slip frequency. The former is generated by the permanent magnet magnetic field, while the latter is generated by the asymmetry of the rotor magnetic circuit and is a kind of reluctance torque. Therefore, the greater the motor's back electromotive force, the greater the pulsating torque during synchronization, causing the motor to accelerate, increasing the motor's synchronization ability and facilitating synchronization. At the same time, increasing the ratio of the quadrature-axis armature reaction reactance to the direct-axis armature reaction reactance (X) q / X d The reluctance torque can be increased, and the reluctance torque plays an enhancing role in the process of pulling in synchronization, which is also beneficial to improving the pulling in performance.

[0049] The critical speed depends on the motor's torque-speed curve, or the stiffness of its mechanical characteristic curve. The stiffer the mechanical characteristic curve, or the steeper it is, the higher the motor's critical speed, the smaller the increase in rotor kinetic energy required to achieve synchronization, and the better the motor's ability to achieve synchronization. Conversely, the softer the mechanical characteristic curve, the lower the critical speed and the more difficult it is to achieve synchronization.

[0050] The hardness of the mechanical characteristic curve refers to the slip rate being less than the corresponding maximum asynchronous torque T cmax Slip rate s m The slope of the curve is then used to calculate the asynchronous torque T c Taking the first-order derivative of the slip rate s, we get

[0051]

[0052] Where R1 is the stator resistance, R2 is the rotor resistance, X1 is the stator leakage reactance, X2 is the rotor leakage reactance, and c is the correction coefficient.

[0053] It can be seen that the slope of the curve is related to the stator and rotor resistance and the stator and rotor leakage reactance.

[0054] The novel structure in the present invention mainly analyzes the influence of rotor resistance and rotor leakage reactance.

[0055] make Get the critical slip rate s m for

[0056]

[0057] It can be seen that the smaller the rotor resistance, the smaller the critical slip rate, the higher the slope of the motor mechanical characteristic curve, the higher the critical speed of the motor, and the stronger the motor's ability to pull in synchronization.

[0058] Taking the rotor leakage reactance X2 as the independent variable, the slope of the torque-slip curve is derived to obtain

[0059]

[0060] It can be seen that the derivative of the slope of the torque-slip curve with respect to the rotor leakage reactance is negative. When the rotor leakage reactance is used as the independent variable, reducing the rotor leakage reactance will increase the slope of the curve, that is, the motor's pull-in synchronization capability is enhanced.

[0061] During the motor's pull-in synchronization process, the magnetic path of the air gap synthetic magnetic field mainly flows from the terminal voltage direction ( Figure 3 The inclination direction of the teardrop-shaped guide bar is the same as the magnetic circuit flow direction, which can reduce the eddy current loss on the guide bar. Figure 1 The conductor bars 1, 2, 3, 4, and 5 in the middle motor are denser in order to increase the core saturation of the leakage magnetic circuit, reduce the leakage magnetic permeance, thereby increasing the rotor leakage reactance and improving the pulling-in synchronization capability.

[0062] exist Figure 1 Motor and Figure 2 While the number of all the conductor bars of the motor remains unchanged, the cross-sectional areas of the conductor bars 1, 2, 3, 4, 5 and the conductor bars 1, 2, 3, 4, 5 are increased, the rotor resistance is reduced, and the pulling-in synchronization capability is enhanced.

[0063] The bars 1, 2, 3, 4, 5 and the permanent magnets 7 together form a multi-layer rotor structure with a flux barrier effect. The bars 1, 2, 3, 4, 5 have a certain tilt angle in space, so Figure 2 The motor's direct-axis magnetic resistance increases, the direct-axis magnetizing inductance decreases, and the ratio of the motor's quadrature-axis armature reaction reactance to the direct-axis armature reaction reactance is X. q / X d The larger the torque, the greater the reluctance torque, the larger the acceleration torque during the synchronization process, the less energy required, and the stronger the synchronization capability.

[0064] For asynchronous starting permanent magnet synchronous motors, the pull-in capability refers to the maximum value of the moment of inertia that can be pulled into synchronization when the motor starts with a fixed load torque. The maximum moment of inertia that the motor can drag under a series of different load torques is obtained and plotted into a curve. This curve is called the critical pull-in synchronization JT. L The curve is used to characterize the motor's ability to pull into synchronization.

[0065] When the system moment of inertia is constant, Figure 1 Motor and Figure 2 The motors drive different load torques respectively. Figure 1 The maximum load torque that the motor can pull into synchronization is as follows: Figure 4 As shown in the figure, the three curves represent the speed diagrams under different load torque multiples. It can be seen that when the load torque is 2.3 times the rated load, the motor cannot be pulled into synchronization. When the load torque is 2.2 times the rated load, the motor is barely pulled into synchronization, indicating that the motor's ability to pull into synchronization has reached its limit. Figure 1 The pull-in torque of the motor, that is, the maximum load torque it can drag, is 2.2 times the rated load.

[0066] Figure 2 The maximum load torque that the motor can pull into synchronization is as follows: Figure 5 As shown in the figure, the three curves represent the speed diagrams under different load torque multiples. It can be seen that when the load torque is 2.7 times the rated load, the motor cannot be pulled into synchronization. When the load torque is 2.6 times the rated load, the motor can barely be pulled into synchronization, indicating that the motor's ability to pull into synchronization has reached its limit. Figure 1 The pull-in torque of the motor, that is, the maximum load torque it can drag, is 2.8 times the rated load.

[0067] When the load size does not reach the rated load, Figure 1 Motor and Figure 2 The motor operates under different times of the rated load corresponding to the moment of inertia. Figure 6 As can be seen from the figure, as the moment of inertia increases, Figure 1 The time it takes for the motor to be pulled into synchronization becomes longer. When the moment of inertia multiple is 5.1 times, the motor gradually pulls into synchronization after several cycles of speed oscillation. When the moment of inertia multiple continues to increase to 5.2 times, the motor cannot obtain enough energy during the synchronization process to enable the electromagnetic torque to overcome the load torque and achieve smooth synchronization. The motor continues to oscillate around the synchronous speed. Therefore, Figure 1 The maximum moment of inertia that the motor can pull into synchronization under rated load is 5.1 times.

[0068] from Figure 7 As can be seen from the figure, as the moment of inertia increases, Figure 2 The time it takes for the motor to be pulled into synchronization becomes longer. When the moment of inertia multiple is 6.7 times, the motor gradually pulls into synchronization after several cycles of speed oscillation. When the moment of inertia multiple continues to increase to 6.8 times, the motor cannot obtain enough energy during the synchronization process to allow the electromagnetic torque to overcome the load torque and achieve smooth synchronization. The motor continues to oscillate around the synchronous speed. Therefore, Figure 2 The maximum moment of inertia that the motor can pull into synchronization under rated load is 6.7 times.

[0069] The critical pull-in characteristic curves of the two motors are as follows: Figure 8As shown. The horizontal axis represents different load torques, and the vertical axis represents the maximum system moment of inertia corresponding to different load torques. The coordinate axis values ​​represent the rated load torque multiple and moment of inertia multiple of the corresponding motor. It can be clearly seen that Figure 2 The motor's moment of inertia under different load torque multiples is higher than Figure 1 motor. Therefore, Figure 2 The motor's ability to pull in synchronization is significantly stronger than Figure 1 Motor.

[0070] Figure 9 The waveform diagram of eddy current loss on the conductor bar of the two motors when they are running in steady state shows that Figure 2 The eddy current loss of the motor is compared Figure 1 The motor has been reduced by approximately 25%.

[0071] The bars in the direction of the main magnetic flux of the motor have a certain tilt angle in space, which causes a large change in the dq axis current, a decrease in the d axis inductance, an increase in the d axis current, and a decrease in the q axis current, resulting in a smaller composite current, a larger internal power factor angle, and a smaller power factor angle. Figure 10 As you can see, Figure 2 The effective value of the motor phase current is lower than Figure 1 motor, so Figure 2 The efficiency of the motor is higher than Figure 1 Motor. Figure 11 The time-space vector diagram shows that Figure 2 The power factor angle θ2 of the motor is less than Figure 1 The power factor angle of the motor is θ1, so Figure 2 The power factor of the motor is higher than Figure 1 Motor.

[0072] Under rated operating conditions, both motors do not experience demagnetization. When the number of winding turns is reduced and the output current is increased to a certain value, both motors experience demagnetization. Figure 12 and Figure 13 It can be seen that the black area is the demagnetization area. The demagnetization areas of the two motors are mainly concentrated on the outer permanent magnets close to the air gap. Under the same working conditions, Figure 2 The demagnetization area of ​​the motor is smaller than Figure 1 Motor, Description Figure 2 The new rotor structure of the motor makes the permanent magnet more resistant to demagnetization than Figure 1 Motor.

[0073] from Figure 13 It can be seen that due to the inclination of the rotor bars, the magnetic circuit flow is smoother. In the torque pulsation diagram obtained by simulation, Figure 2 The torque ripple of the motor is significantly smaller than Figure 1 Motor.

[0074] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A rotor structure of an asynchronous start permanent magnet synchronous motor, characterized in that: It includes conductive bars distributed in an annular manner on the inner surface of the rotor body, and is characterized in that: the conductive bars in the main magnetic flux direction are asymmetrically distributed along the d-axis direction and are arranged at uniform intervals, the conductive bars in the main magnetic flux direction are teardrop-shaped conductive bars, the extension direction of the conductive bars in the main magnetic flux direction is inclined relative to the radial direction of the rotor body, the inclination direction of the end of the conductive bar close to the axis is opposite to the rotation direction of the rotor body, and the conductive bars in the back electromotive force direction are symmetrically distributed along the q-axis direction and are arranged at uneven intervals.

2. The rotor structure according to claim 1, characterized in that: The conductive bars can form a magnetic flux barrier structure with the built-in permanent magnets of the rotor body in the back electromotive force direction.

3. The rotor structure according to claim 1, characterized in that: The cross-sectional area of ​​the conductive bar in the back electromotive force direction is no less than the cross-sectional area of ​​the conductive bar in the main magnetic flux direction.

4. An asynchronous starting permanent magnet synchronous motor, characterized in that: The invention comprises a rotor structure according to any one of claims 1 to 3.

5. An application of the asynchronous start permanent magnet synchronous motor according to claim 4, characterized in that: Applied to motor devices for achieving unidirectional rotation.

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