Low Torque Ripple Rotor and Synchronous Reluctance Motor

Abstract

The present invention provides a low torque ripple rotor and a synchronous reluctance motor, wherein a plurality of groups of air barriers are arranged on the rotor in a circumferential distribution, and a notch with a concave arc cross-section extending along the axial direction of the rotor is formed on the outer wall of the rotor, and the number of the notches is matched with the number of groups of the air barriers; the rotor is applied to the synchronous reluctance motor, which can effectively reduce the torque ripple of the motor.

Description

Technical Field

[0001] The present invention belongs to the technical field of motors, and particularly relates to a low torque ripple rotor and a synchronous reluctance motor. Background Art

[0002] In the rotor structure of a synchronous reluctance motor, there are no squirrel-cage bars and permanent magnets. Compared with induction motors and permanent magnet synchronous motors, the synchronous reluctance motor does not need to consider the risks of high-temperature fracture of squirrel-cage bars and high-temperature demagnetization of permanent magnets, and has the advantages of simple structure, low failure rate and reliable operation.

[0003] The synchronous reluctance motor follows the basic principle that magnetic lines of force close along the path with the least magnetic resistance, and uses the difference in magnetic resistance between the direct-axis and quadrature-axis magnetic circuits of the rotor to generate magnetic resistance torque to drive the motor to operate. Generally speaking, in the prior art, multiple layers of magnetic barriers are arranged on the rotor of the synchronous reluctance motor to increase the saliency ratio of the motor, and several open slots are arranged on the stator cooperating with the rotor, which will cause uneven air-gap permeance and complex magnetic circuits inside the motor, and will generate large torque ripple while increasing the magnetic resistance torque. On the one hand, torque ripple will cause periodic oscillation of the rotational speed during low-speed operation of the motor, seriously affecting the control performance of the synchronous reluctance motor; on the other hand, large torque ripple will also increase the vibration and noise of the motor.

[0004] In the prior art application scenarios, the synchronous reluctance motor has large torque ripple, and suppressing torque ripple is of great significance for improving the electromagnetic performance of the motor and expanding the application occasions of the motor. Summary of the Invention

[0005] To solve the above technical problems, the present application proposes a low torque ripple rotor and a synchronous reluctance motor, and the specific technical solutions are as follows:

[0006] In a first aspect, the present application provides a low torque ripple rotor, on which several groups of air magnetic barriers are arranged along the circumferential direction, and a notch with a concave arc cross-section extending along the axial direction of the rotor is provided on the outer wall of the rotor, and the number of notches matches the number of groups of air magnetic barriers.

[0007] In a preferred solution, the outer contour of the cross-section of the rotor is a non-circular closed curve, and the non-circular closed curve satisfies Equation (1):

[0008]

[0009] In Equation (1):

[0010] r(θ) is the distance from the outer contour of the cross-section of the rotor to the center of the circle;

[0011] D i is the inner diameter of the stator corresponding to the rotor;

[0012] is the independent variable of the curve equation, i.e., the spatial position angle;

[0013] is the initial position angle of the curve equation;

[0014] a, b, and k are parameters for changing the curvature and shape of the non-circular closed curve. a is the parameter for adjusting the maximum air-gap thickness; b is the parameter for adjusting the minimum air-gap thickness; k is the parameter for controlling the number of notches on the non-circular closed curve.

[0015] In the preferred solution, the arc bottom of the notch coincides with the q-axis of the rotor, The initial value of is 0.

[0016] In the preferred solution, the air magnetic barrier is an air slot formed by the first slot wing, the one-word slot, and the second slot wing connected in sequence. The center of the one-word slot coincides with the q-axis of the rotor. The first slot wing and the second slot wing are symmetric about the q-axis. The included angle α between the first slot wing and the one-word slot is 110~145°.

[0017] In the preferred solution, the total thickness of the air slot along the radial direction of the rotor in each group of air magnetic barriers is h, and the rotor thickness is H. The value of h / H is 0.25~0.5.

[0018] In the second aspect, the present application provides a synchronous reluctance motor, and the motor includes the low torque ripple rotor described in any one of the above.

[0019] In the preferred solution, the outside of the rotor is a stator. The inner wall of the stator has pear-shaped slots and armature windings embedded in the pear-shaped slots. The armature windings are of a double-layer short-pitch distributed structure.

[0020] In the preferred solution, the minimum value range of the length of the non-uniform air gap formed between the inner diameter of the stator and the outer diameter of the rotor is 0.25~2 mm.

[0021] The beneficial effects of the present invention are:

[0022] (1) A concave arc-shaped notch is provided on the outer wall of the rotor, making the outer contour of the rotor structure a non-circular closed curve, resulting in uneven radial length of the air gap between the inner diameter of the motor stator and the outer diameter of the rotor, which can optimize the sinusoidality of the air-gap magnetic density; the number of concave arcs of the closed curve is the same as the number of air slot groups, and the air gap length is the largest at the center line of the air slot, that is, the air gap length in the quadrature magnetic circuit is increased without changing the air gap length in the direct-axis magnetic circuit, ensuring the salient pole ratio and output torque of the motor; the closed curve satisfies the above specific polar coordinate equation, and by adjusting parameters a and b, the curvature of the non-circular closed curve is changed, so that this type of rotor is applicable to synchronous reluctance motors with different powers and structures, improving the versatility of this structure; the rotor of the motor adopts a multi-layer magnetic barrier structure, and the magnetic resistance of the magnetic circuit varies greatly. By reasonably utilizing the unevenness of the radial length of the air gap, the torque ripple generated by the difference in magnetic resistance of the magnetic circuit of the motor is weakened.

[0023] (2) In the structure setting of the air slot, the value range of the angle between the two-wing slot and the bottom one-word slot is controlled, so that there is no air magnetic barrier in the direct-axis magnetic circuit, ensuring that the magnetic resistance of the direct-axis magnetic circuit is small. This rotor structure increases the difference between the quadrature-axis and direct-axis magnetic resistances, effectively improving the salient pole ratio and output average torque of the synchronous reluctance motor. Brief Description of the Drawings

[0024] Figure 1 The figure shows a schematic structural diagram of the rotor;

[0025] Figure 2 The figure shows a schematic structural diagram of the motor in Embodiment 1;

[0026] Figure 3 The figure shows a schematic structural diagram of the motor in Comparative Example 1;

[0027] Figure 4 The figure shows a torque comparison diagram of Embodiment 1 and Comparative Example 1 during light-load operation by finite element simulation;

[0028] Figure 5 The figure shows a torque comparison diagram of Embodiment 1 and Comparative Example 1 during heavy-load operation by finite element simulation. Detailed Description of the Embodiments

[0029] In the following description, certain specific details are set forth in order to provide a thorough understanding of the various embodiments. However, those skilled in the art will understand that the present invention may be practiced without these details. In other instances, well-known structures have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments. Unless the context otherwise requires, throughout the specification and the appended claims, the word "comprising" shall be interpreted in an open, inclusive sense, i.e., as "including but not limited to".

[0030] The low-torque ripple rotor structure described in this application refers to Figure 1As shown, a shaft hole 7 is provided on the rotor body 6 for connecting a rotating shaft. An air groove is also provided on the rotor body 6 to form a magnetic flux barrier. The air groove includes a first groove wing 3, a straight groove 4, and a second groove wing 5 that are connected in sequence. The first groove wing 3 and the second groove wing 5 are symmetrically arranged about the center of the straight groove 4. At the same time, the center of the straight groove 4 coincides with the q-axis of the rotor body 6. This air groove is a closed groove, that is, the ends of the first groove wing 3 and the second groove wing 5 do not extend to the outer wall of the rotor body 6 to form an opening. Generally, the ends of the first groove wing 3 and the second groove wing 5 should be set at a certain distance from the outer wall of the rotor body 6, such as 2 mm, 2.3 mm, 2.6 mm, and generally not less than 2 mm.

[0031] See Figure 1 , several groups of air grooves are evenly distributed along the circumferential direction of the rotor body 6 on the rotor body 6. Each group is provided with several air grooves. Define the thickness of the rotor body 6 as H, define the total thickness of all air grooves in the radial direction of the rotor body 6 as h, and define the value of h / H as the rotor magnetic barrier occupancy rate. The larger this value, the greater the magnetic resistance of the cross-axis magnetic circuit of the motor, and the greater the difference in magnetic resistance between the cross-axis and direct-axis of the motor. However, if the rotor magnetic barrier occupancy rate is further increased, on the one hand, it will reduce the mechanical strength of the rotor and the operating stability of the motor, and on the other hand, it will reduce the effective area of the rotor core, resulting in an enhanced saturation effect in the physical domain of the rotor, which will further reduce the magnetic resistance difference between the cross-axis and direct-axis magnetic circuits and weaken the average torque of the motor. Therefore, the reasonable range of the value of h / H should be 0.25 - 0.5.

[0032] See Figure 1 , in the structure of each air groove, the included angle α formed by the first groove wing 3 and the straight groove 4, and the second groove wing 5 and the straight groove 4 should be limited to 110 - 145°. The size of this included angle α directly affects the magnetic resistance of the magnetic circuit. Increasing the included angle can increase the magnetic resistance of the cross-axis magnetic circuit, thereby increasing the difference in magnetic resistance between the cross-axis and direct-axis, and improving the saliency ratio and reluctance torque of the motor. The larger this included angle, the greater the reluctance torque, but the increase in this included angle will cause the magnetic flux distribution in the physical domain of the rotor to be uneven, thereby increasing the torque ripple of the motor.

[0033] Combined with Figure 1 , a notch 8 is also provided on the circumferential outer wall of the rotor body 6. The notch 8 is formed by the inward depression of the outer wall of the rotor body 6, so that the outer cross-sectional contour of the rotor body 6 enclosed by the notch 8 and other parts of the notch 8 is a non-circular closed curve. When setting in this application such as Figure 1When there is a concave arc-shaped notch 8 as shown, the number of notches 8 should be the same as the number of groups of air grooves, and at the same time, it is ensured that the air gap length formed between the inner diameter of the stator and the outer diameter of the rotor at the notch 8 on the q-axis is the largest, so as to increase the air gap length in the quadrature-axis magnetic circuit without changing the air gap length in the direct-axis magnetic circuit, ensuring the saliency ratio and output torque of the motor. In addition, the notch 8 makes the air gap length uniformly decrease along the outer circumference of the rotor from the quadrature axis to the direct axis, improving the uniformity of the magnetic resistance distribution from the quadrature-axis magnetic circuit to the direct-axis magnetic circuit of the motor, and further reducing the torque ripple of the synchronous reluctance motor.

[0034] Based on the non-circular closed curve setting of the external cross-sectional contour of the rotor body 6, in the motor using this rotor, the characteristic that the air gap between the inner diameter of the stator and the outer diameter of the rotor is constant and uniform in the radial direction of the motor is changed. This non-uniform air gap formed between the inner diameter of the stator and the outer diameter of the rotor can optimize the sinusoidality of the air gap magnetic density.

[0035] At the same time, affected by the motor processing technology and motor efficiency, the minimum value range of the length of the non-uniform air gap formed between the inner diameter of the stator and the outer diameter of the rotor is 0.25 - 2 mm.

[0036] In addition, this curve simultaneously satisfies the following equation:

[0037]

[0038] In the above formula:

[0039] Di is the inner diameter of the stator corresponding to the rotor body 6;

[0040] is the independent variable of this curve equation, that is, the spatial position angle;

[0041] is the initial position angle of the curve equation;

[0042] a, b, and k are parameters that change the curvature and shape of the non-circular closed curve. Specifically, k is a parameter that controls the number of concave arc-shaped notches 8 of the non-circular closed curve. Generally, the value of k is the number of pole pairs p of the motor; parameter a is a parameter that adjusts the maximum air gap length, that is, the depression depth of the non-circular closed curve at the q-axis; parameter b is a parameter that adjusts the minimum air gap length; by adjusting the values of parameters a and b, the constraint conditions of the maximum air gap length and the minimum air gap length in the design of the synchronous reluctance motor can be satisfied; generally speaking, first adjust parameter a to meet the constraint of the maximum air gap length, and then continuously adjust parameter b to meet the known condition of the minimum air gap length.

[0043] The closed curve satisfies the above specific polar coordinate equation, aiming to change the curvature of the non-circular closed curve by adjusting parameters a and b during the motor parameter setting process, so that this rotor type is applicable to synchronous reluctance motors with different powers and structures, and the versatility of this structure is improved.

[0044] Combined with the foregoing description, the rotor of the motor adopts a multi-layer magnetic barrier structure, and the magnetic resistance of the magnetic circuit varies greatly. By reasonably utilizing the non-uniformity of the radial length of the air gap, the torque ripple generated by the difference in the magnetic resistance of the magnetic circuit of the motor is weakened.

[0045] Based on Figure 1 the rotor structure shown in, the present application also applies it to a synchronous reluctance motor, which cooperates with the stator 1 to form a synchronous reluctance motor reference Figure 2 as shown. Figure 2 In, the inner wall of the stator 1 has a pear-shaped groove and an armature winding 2 embedded in the pear-shaped groove. Each pear-shaped groove is embedded with a three-phase armature winding 2, and the armature winding 2 is a double-layer short-pitch distributed structure, and the coil pitch is eight. This stator structure generates a highly sinusoidal stator magnetomotive force by adopting a double-layer distributed winding structure, with less harmonic content. According to the slot-pole combination of the motor, a short-pitch winding is selected to reduce the content of high-order harmonics, effectively improve the waveform of the armature magnetomotive force, and reduce torque ripple.

[0046] Embodiment 1

[0047] This embodiment discloses a synchronous reluctance motor with low torque ripple. The main parameters of the motor are shown in Table 1, and the structure is shown in Figure 2 as shown.

[0048]

[0049] At the same time, in this embodiment, the parameters in Equation (1) are set as follows: the inner diameter of the stator Di is 170 mm, the initial position angle φ is 0, the parameter k is 2, and a and b are parameters that satisfy the minimum air gap length of 0.75 mm and the maximum air gap length of 8.25 mm. Specifically, a is 1.65 and b is 1.2.

[0050] Comparative Example 1

[0051] This comparative example discloses a synchronous reluctance motor with low torque ripple. The main parameters of the motor are shown in Table 2, and the structure is shown in Figure 3 as shown.

[0052]

[0053] According to the motor parameters described in Embodiment 1 and Comparative Example 1, the torque comparison during light load operation and heavy load operation is carried out by finite element simulation, and the results are shown in Figure 4 and Figure 5 .

[0054] As Figure 4 shown, it is a torque comparison diagram during light load operation of finite element simulation. As shown in the figure, for the structure of a conventional synchronous reluctance motor, the average torque output during light load is 7.67 Nm, and the torque ripple is 49.5%. While for the synchronous reluctance motor structure proposed by the present invention, the average torque output during light load is 6.56 Nm, and the torque ripple is 19.8%. By comparison, it can be seen that for the synchronous reluctance motor proposed by the present invention, the average torque during light load operation is reduced by 14.4% compared with that of the conventional synchronous reluctance motor, but the torque ripple is reduced by 29.7%. This shows that the synchronous reluctance motor proposed by the present invention can greatly reduce the torque ripple of the motor while ensuring that the output torque drops within a reasonable range.

[0055] As Figure 5 shown, it is a torque comparison diagram during heavy load operation of finite element simulation. As shown in the figure, for the structure of a conventional synchronous reluctance motor, the average torque output during heavy load is 26.9 Nm, and the torque ripple is 48.73%. While for the synchronous reluctance motor structure proposed by the present invention, the average torque output during heavy load is 26.52 Nm, and the torque ripple is 36.82%. By comparison, it can be seen that for the synchronous reluctance motor proposed by the present invention, the average torque during heavy load operation is reduced by 1.4% compared with that of the conventional synchronous reluctance motor, but the torque ripple is reduced by 11.91%. This shows that for the synchronous reluctance motor proposed by the present invention, the output torque hardly drops during heavy load operation, but the torque ripple drops significantly.

[0056] Examples 2 - 7

[0057] On the basis of Example 1, Examples 2 - 7 ensure that the minimum air gap length is 0.75 mm, and the minimum distance from the end of the air slot to the outer wall of the rotor is 2.6 mm. The difference from Example 1 is that different maximum air gap lengths are obtained by changing the parameters a and b in Equation (1), as shown in Table 3 specifically.

[0058]

[0059] Similarly, according to the motor parameters recorded in Examples 2 - 7, finite element simulation of torque comparison during light load operation is carried out, and the results are shown in Table 3.

[0060] Combined with Table 3, it is found that with the increase of the maximum air gap length, the output torque of the synchronous reluctance motor proposed by the present invention hardly changes, but the torque ripple monotonically decreases. On the basis of ensuring the mechanical strength and operation stability of the rotor, adjusting the parameters a and b can ensure that the output torque remains unchanged while the torque ripple decreases, making this rotor structure applicable to synchronous reluctance motors with different powers and structures, verifying that the low - torque - ripple synchronous reluctance motor proposed by the present invention has strong applicability.

[0061] In addition, according to the motor parameters described in Embodiment 1 and Comparative Example 1, the armature current of the motor determines the output torque and output power. Different armature current conditions are set, and a finite element simulation is carried out to compare the load-carrying running torques. The results are shown in Table 4.

[0062]

[0063] Combined with Table 4, it can be seen that as the armature current increases, the average torques of the motors in Comparative Example 1 and Embodiment 1 both increase monotonically. However, the torque ripple in Comparative Example 1 is close to 50%, while that in Embodiment 1 is significantly reduced compared with Comparative Example 1, and the suppression effect on torque ripple is more obvious under the light load condition of the motor. Further combined with the foregoing Embodiments 2 to 7, under the same working conditions, Equation (1) can also be further combined to adjust its parameters to optimize the non-circular closed curve, thereby obtaining a better suppression effect on torque ripple.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them.

Claims

1. Low-torque-ripple rotor, on which several groups of air magnetic barriers distributed circumferentially are arranged, characterized in that, The outer wall of the rotor has notches extending along the axial direction of the rotor and having a concave arc-shaped cross section, and the number of the notches matches the number of air magnetic barrier groups; The outer contour of the cross section of the rotor is a non-circular closed curve, and the non-circular closed curve satisfies Equation (1): （1）； In Equation (1): r(θ) is the distance from the outer contour of the cross section of the rotor to the center of the circle; D i is the inner diameter of the stator corresponding to the rotor; θ is the independent variable of the curve equation, that is, the spatial position angle; is the initial position angle of the curve equation; a is a parameter for adjusting the maximum thickness of the air gap; b is a parameter for adjusting the minimum thickness of the air gap; k is a parameter for controlling the number of notches on the non-circular closed curve.

2. The low-torque ripple rotor according to claim 1, wherein, The arc bottom of the notch coincides with the q-axis of the rotor, and its initial value is 0.

3. The low torque ripple rotor according to claim 1, wherein The air magnetic barrier is an air groove in which a first groove wing, a one-word groove, and a second groove wing are connected in sequence. The center of the one-word groove coincides with the q-axis of the rotor. The first groove wing and the second groove wing are symmetric about the q-axis. The included angle α between the first groove wing and the one-word groove is 110° to 145°.

4. The low torque ripple rotor according to claim 1, wherein, The total thickness of the air grooves in each group of air magnetic barriers along the radial direction of the rotor is h, the thickness of the rotor is H, and the value of h / H is 0.25 to 0.

5.

5. Synchronous reluctance motor, characterized in that, The motor includes the low torque ripple rotor according to any one of claims 1 to 4.

6. The synchronous reluctance motor according to claim 5, characterized in that, The outside of the rotor is a stator. The inner wall of the stator has pear-shaped grooves and armature windings embedded in the pear-shaped grooves. The armature windings are of a double-layer short-pitch distributed structure.

7. The synchronous reluctance motor according to claim 6, characterized in that, The minimum value range of the length of the non-uniform air gap formed between the inner diameter of the stator and the outer diameter of the rotor is 0.25 to 2 mm.

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