Rotor structure, motor and design method

Abstract

The invention provides a rotor structure, a motor and a design method, the rotor structure comprises a rotor core, the outer wall of the rotor core is provided with a plurality of projections, the plurality of projections are arranged at intervals along the circumferential direction of the rotor core, a first magnetic steel and a second magnetic steel are arranged between two adjacent projections, and the first magnetic steel and the second magnetic steel are arranged at intervals along the circumferential direction of the rotor core. The first magnetic steel is neodymium iron boron magnetic steel, and the second magnetic steel is neodymium iron boron magnetic steel. According to the surface-mounted synchronous motor, the technical problem that the cost is high due to the fact that a rare earth permanent magnet is adopted by the surface-mounted synchronous motor in the prior art can be solved.

Description

Technical Field

[0001] This invention belongs to the field of motor technology, specifically relating to a rotor structure, a motor, and a design method. Background Technology

[0002] Surface-mounted rare-earth permanent magnet synchronous motors offer a range of advantages, including high power density, high torque density, and good speed regulation performance. However, the electromagnetic torque of a surface-mounted rare-earth permanent magnet synchronous motor consists only of the permanent magnet torque, limiting its performance to that of the rare-earth permanent magnet, which is also quite expensive.

[0003] Two common ways to increase the maximum output torque are to increase the amount of permanent magnets or to increase the size of the motor. However, in some cases, such as robot joint motors, increasing the size or the amount of permanent magnets is not advisable.

[0004] In surface-mounted permanent magnet synchronous motors with salient poles, the torque component consists of two parts: permanent magnet torque and reluctance torque, due to the unequal inductances along the d and q axes. This improves the utilization rate of permanent magnet materials. However, the reluctance torque and permanent magnet torque have a phase difference, preventing them from forming the maximum electromagnetic torque at the same current angle, resulting in some performance waste.

[0005] Due to the high cost and other technical problems associated with surface-mounted synchronous motors using rare-earth permanent magnets in existing technologies, this invention researches and designs a rotor structure, motor, and design method. Summary of the Invention

[0006] Therefore, the present invention provides a rotor structure, motor, and design method that can solve the technical problem of high cost in the prior art of surface-mounted synchronous motors using rare earth permanent magnets.

[0007] To address the aforementioned problems, the present invention provides a rotor structure comprising: a rotor core, wherein the outer wall of the rotor core is provided with a plurality of protrusions, the plurality of protrusions being arranged at intervals along the circumference of the rotor core, and a first magnet and a second magnet being disposed between two adjacent protrusions, wherein the first magnet is a neodymium iron boron magnet or a ferrite magnet, and the second magnet is a neodymium iron boron magnet.

[0008] In some embodiments, the thickness of the first magnet is greater than the thickness of the second magnet along the radial direction of the rotor core.

[0009] In some embodiments, the first magnet and the second magnet are arranged sequentially along the circumference of the rotor core; with the cross-section of the rotor core as the projection plane, the outer peripheral walls of the first magnet and the second magnet coincide with the circle formed by the protruding outer peripheral wall.

[0010] In some embodiments, the rotor core is provided with slots located on the d-axis.

[0011] The present invention also provides an electric motor comprising the aforementioned rotor structure.

[0012] The present invention also provides a design method for the aforementioned rotor structure, which is specifically implemented according to the following steps:

[0013] Step 1: The fundamental component of the magnetic flux density in the air gap above the rotor core is B. Calculate the relationship between the fundamental component of the magnetic flux density B and the angle parameter of the permanent magnet.

[0014] Step 2: Obtain the magnetic flux density B and the structural parameters and performance parameters of the permanent magnet;

[0015] Step 3: Combining the relationships from Step 1 and Step 2, we can obtain the constraint expression that satisfies the requirement that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle.

[0016] In some implementations, step 1 specifically involves calculating the fundamental expression of the air gap magnetic flux density using Fourier transform. Since the magnetic flux density is neither odd nor even, the fundamental wave consists of a sine component and a cosine component. Can be written When the Fourier fundamental coefficient At that time, the fundamental component can be further written as , It is the current angle.

[0017] In some embodiments, step 1 further includes establishing a coordinate system with the center of the rotor core as the origin, the Y-axis passing through the center of one of the protrusions along the axial direction of the rotor core, and the angle between the Y-axis and one side of the protrusion being... 1. The angle between the d-axis and the Y-axis is 2. The angle between the side of the second magnet facing away from the Y-axis and the Y-axis is . 3;

[0018] Depend on The relationship between B and the angle parameters of the permanent magnet can then be obtained.

[0019]

[0020] In the formula, p is the number of pole pairs; B1 and B2 are the air gap magnetic flux density under ideal conditions.

[0021] available:

[0022] ;

[0023] Further, we can obtain:

[0024] .

[0025] In some implementations, step 2 specifically involves obtaining the magnetic flux density B and the structural and performance parameters of the permanent magnet through a magnetic circuit model.

[0026] In some implementations, step 2 specifically involves combining the relationships from step 1 and step 2, eliminating B, to obtain the constraint expression that satisfies the requirement that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle.

[0027] The rotor structure, motor, and design method provided by this invention have the following beneficial effects:

[0028] By combining NdFeB magnets to form a magnetic steel structure, or combining ferrite and NdFeB magnets to form a magnetic steel structure, the amount of rare earth permanent magnets used can be reduced while ensuring that the performance does not degrade, thus significantly reducing the cost of the magnetic steel. Furthermore, by setting reasonable parameters, the effect of NdFeB leakage magnetism on ferrite demagnetization can be avoided. Attached Figure Description

[0029] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the rotor structure of the present invention;

[0031] Figure 2 This is a partially enlarged view of the rotor structure of the present invention;

[0032] Figure 3 This is an assembly drawing of the rotor structure of the present invention;

[0033] Figure 4 This is a schematic diagram of the rotor structure of the present invention;

[0034] Figure 5 This is a schematic diagram of the magnetic circuit established by the magnets in the rotor structure of the present invention.

[0035] The attached figures are labeled as follows:

[0036] 1. Protrusion; 2. First magnet; 3. Second magnet; 4. Groove. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0039] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0040] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0041] See also Figure 1-5As shown, according to an embodiment of the present invention, a rotor structure is provided, comprising: a rotor core, wherein a plurality of protrusions 1 are provided on the outer wall of the rotor core, the plurality of protrusions 1 are arranged at intervals along the circumference of the rotor core, and a first magnet 2 and a second magnet 3 are provided between two adjacent protrusions 1, wherein the first magnet 2 is a neodymium iron boron magnet or a ferrite magnet, and the second magnet 3 is a neodymium iron boron magnet.

[0042] In this technical solution, a magnetic steel structure is formed by combining NdFeB magnets with NdFeB magnets, or by combining ferrite and NdFeB magnets. This ensures that performance does not degrade while reducing the amount of rare-earth permanent magnets used, significantly lowering the cost of the magnetic steel. Furthermore, by setting appropriate parameters, the impact of NdFeB magnet leakage on ferrite demagnetization is avoided. Of course, the second magnet 3 can also be made of ferrite.

[0043] In some embodiments, the thickness of the first magnet 2 is greater than the thickness of the second magnet 3 along the radial direction of the rotor core.

[0044] In this technical solution, ferrite magnets and neodymium iron boron magnets are installed on the rotor core. The thickness of the ferrite magnet must be greater than that of the neodymium iron boron magnet to ensure that the ferrite magnet is not demagnetized by the leakage magnetism of the neodymium iron boron magnet, which would affect its performance.

[0045] In some embodiments, the first magnet 2 and the second magnet 3 are arranged sequentially along the circumference of the rotor core; with the cross-section of the rotor core as the projection plane, the outer peripheral walls of the first magnet 2 and the second magnet 3 coincide with the circle formed by the outer peripheral wall of the protrusion 1.

[0046] In this technical solution, since the thickness of the first magnet 2 is greater than the thickness of the second magnet 3, a groove can be opened on the outer peripheral wall of the rotor core, and part of the first magnet 2 can be inserted into the groove so that the outer peripheral wall of the first magnet 2, the second magnet 3, and the protrusion 1 are located on the same circle, ensuring the gap between the rotor and the stator, thereby ensuring the magnet strength of the rotor core and improving the motor performance.

[0047] In some embodiments, the rotor core is provided with a slot 4, which is located on the d-axis.

[0048] In this technical solution, slot 4 is located on the d-axis, and along the radial direction of the rotor core, slot 4 is located in the middle of the rotor core. It should be noted that, in conjunction with reference to Figure 2, the first magnet 2 is at least partially located on the d-axis of the rotor core. The hole in the d-axis increases its saliency ratio, thereby increasing the proportion of reluctance torque. The shape of the hole in the d-axis can be arbitrarily selected, and the hole should be located at the actual d-axis position.

[0049] In some embodiments, between two adjacent protrusions 1, the first magnet 2 is arranged closer to one protrusion 1 than the second magnet 3, with gaps between the first magnet 2 and one protrusion 1, and between the second magnet 3 and the other protrusion 1. Along the circumference of the rotor core 2, the first magnet 2 and the second magnet 3 have the same length. The minimum distance between the first magnet 2 and one protrusion 1 is not greater than the length of the first magnet 2, and the minimum distance between the second magnet 3 and the other protrusion 1 is greater than the length of the first magnet 2. This effectively prevents magnetic leakage. (See also...) Figure 3 As shown, for two adjacent stator teeth, the first magnet 2 is arranged opposite to one stator tooth, the second magnet 3 is partially opposite to one stator tooth, and the remaining part of the second magnet 3 is arranged opposite to the other stator tooth. This results in an asymmetrical magnetic field distribution, making it easier to calculate the parameters of the magnetic field offset. While limiting the cost of permanent magnets, parameters such as the percentage of permanent magnet thickness are calculated when the magnetic flux density amplitude is maximized, thus maximizing the utilization rate of the permanent magnets.

[0050] The present invention also provides an electric motor, including the rotor structure described above.

[0051] The present invention also provides a design method for the above-mentioned rotor structure, which is specifically implemented according to the following steps:

[0052] Step 1: The fundamental component of the magnetic flux density in the air gap above the rotor core is B. Calculate the relationship between the fundamental component of the magnetic flux density B and the angle parameter of the permanent magnet.

[0053] Step 2: Obtain the magnetic flux density B and the structural parameters and performance parameters of the permanent magnet;

[0054] Step 3: Combining the relationships from Step 1 and Step 2, we can obtain the constraint expression that satisfies the requirement that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle.

[0055] The motor of this invention, due to the introduction of salient poles, is a surface-mounted permanent magnet synchronous reluctance motor containing reluctance torque. This is because the introduction of salient poles and the d-axis perforation increases the reluctance torque component. p is the extreme logarithm; It is a permanent magnet flux linkage; These are the d-axis current and the q-axis current, respectively. These are the d-axis inductance and the q-axis inductance, respectively. They are determined by the magnetic torque. As can be seen from the expression, For permanent magnet torque, The reluctance torque is 45° out of phase and has different current angles at its amplitude. Therefore, it is impossible to synthesize the maximum electromagnetic torque at the amplitude. For example, the current angle is 45° when the permanent magnet torque is at its maximum, while the current angle is 90° when the reluctance torque is at its maximum. Since the amplitudes are not together, the maximum electromagnetic torque cannot be superimposed. It is the maximum values ​​of the two sine waves that are obtained at the same time.

[0056] The air gap on the rotor core under no-load conditions refers to the physical gap between the main pole shoes and the armature when the motor is in no-load condition.

[0057] Traditional design methods cannot accurately determine the condition of a 45° magnetic field offset. They can only obtain the design for maximum torque through a scanning method. This traditional scanning method involves continuously changing parameters, performing finite element calculations on each set of parameters, and finding the set of parameters that maximizes torque, which is time-consuming. The rotor structure design method of this invention, through salient pole configuration and permanent magnet parameter design, utilizes the axis-shifting effect to modulate the magnetic field, allowing both torque components to reach their amplitudes at the same current angle. The specific method is as follows:

[0058] In some implementations, due to the asymmetry between ferrite and NdFeB permanent magnets, the ideal unloaded air gap magnetic flux density is a non-odd and non-even function. The magnitude and phase of the permanent magnet torque are mainly determined by the fundamental magnetic flux density; therefore, shifting the fundamental magnetic flux density by 45° is sufficient. Specifically, step 1 involves calculating the expression for the fundamental air gap magnetic flux density using a Fourier transform. Since the magnetic flux density is neither odd nor even, the fundamental wave consists of sine and cosine components. Can be written When the Fourier fundamental coefficient At that time, the fundamental component can be further written as , It is the current angle.

[0059] In some embodiments, step 1 further includes establishing a coordinate system with the center of the rotor core as the origin, the Y-axis passing through the center of one of the protrusions (1) along the axial direction of the rotor core, and the angle between the Y-axis and one side of the protrusion (1) being . 1. The angle between the d-axis and the Y-axis is 2. The angle between the side of the second magnet facing away from the Y-axis and the Y-axis is . 3;

[0060] Depend on The relationship between B and the angle parameters of the permanent magnet can then be obtained.

[0061]

[0062] In the formula, p is the number of pole pairs; B1 and B2 are the air gap magnetic flux density under ideal conditions.

[0063] available:

[0064] ;

[0065] Further, we can obtain:

[0066] .

[0067] In some implementations, step 2 specifically involves obtaining the magnetic flux density B and the structural and performance parameters of the permanent magnet through a magnetic circuit model.

[0068] See magnetic circuit establishment and connection. Figure 5 As shown, the magnet is equivalent to a series connection of magnetomotive force and reluctance FPM.RPM; the air gap reluctance is Rg; where FPM3 and RPM3 are the equivalent magnetomotive force sources of the saturated magnet. The flux linkage Φ can be calculated from this, and the flux linkage divided by the area through which it passes gives the magnetic flux density B. From this, the expressions for the magnetic flux density B and the permanent magnet parameters can be obtained.

[0069] To obtain the magnetic flux density B and the structural and performance parameters of the permanent magnet, a magnetic circuit model is established. The magnetic circuit model provides the expressions for the magnetic flux density B and the structural and performance parameters of the permanent magnet. When establishing the magnetic circuit model, the influence of salient pole oversaturation on the accuracy of the magnetic circuit model must be considered due to the introduction of salient poles.

[0070] When the salient pole is oversaturated, its BH curve saturation region can be approximated as a permanent magnet subjected to reverse demagnetization.

[0071] According to Thevenin's theorem:

[0072]

[0073] In the formula, FPMi is the magnetomotive force; RPMi is the permanent magnet reluctance; Rgi is the air gap reluctance; its magnitude is affected by the parameters of the permanent magnet and the structural parameters of the motor.

[0074] This refers to the magnetic flux of a permanent magnet corresponding to the breath.

[0075] From Cramer's rule, we can obtain:

[0076]

[0077] Furthermore, we can obtain:

[0078]

[0079] In the formula, Si is the area through which the magnetic flux passes, from which we can obtain:

[0080]

[0081] In some implementations, step 2 specifically involves combining the relationships from step 1 and step 2, eliminating B, to obtain the constraint expression that satisfies the requirement that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle.

[0082] The present invention discloses a rotor structure design method. Step 1 involves calculating the magnetic flux density, deriving the relationship between the magnetic flux density and the angle parameter. Step 2 involves establishing a magnetic circuit model, another method for calculating the magnetic flux density, which yields the relationship between the magnetic flux density and the permanent magnet parameter. Solving both models simultaneously and eliminating B results in a constraint relationship that satisfies the 45° offset condition. As long as the parameters satisfy this constraint relationship, the magnetic field will be offset by 45°, and both the reluctance torque and the permanent magnet torque will reach their peak values ​​at the same current angle.

[0083] The present invention discloses a rotor structure design method, which calculates the actual d-axis position based on the permanent magnet parameters. The d-axis defines the direction of maximum magnetic flux. The permanent magnet is installed offset from the original physical d-axis. The motor structure parameters that satisfy the offset of 45° are calculated so that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle, thereby increasing the maximum electromagnetic torque.

[0084] This invention discloses a rotor structure design method for a surface-mounted permanent magnet synchronous motor. This method increases the salient pole ratio and reluctance torque content, reduces the phase difference between the reluctance torque and the permanent magnet torque, allowing them to reach their peak values ​​at the same current angle, thus increasing the maximum electromagnetic torque. The permanent magnets are selected as a combination of low-performance ferrite and high-performance neodymium iron boron (NdFeB) magnets. This ensures no performance degradation while reducing the amount of rare-earth permanent magnets used, significantly lowering magnet costs. Furthermore, through reasonable parameter settings, the demagnetization effect of NdFeB leakage magnetism on the ferrite is avoided. Holes are drilled in the rotor core to increase its salient pole ratio, further increasing the reluctance torque content and improving the utilization rate of the magnet performance. The magnets are installed off-axis (d-axis offset) to achieve a shaft shifting effect. Specific motor parameters are calculated to reduce the phase difference between the permanent magnet torque and the reluctance torque, allowing them to reach their peak values ​​at the same current angle, thereby increasing the maximum output torque. The magnets employ a ferrite-NdFeB combination structure, requiring the ferrite thickness to be greater than the NdFeB thickness to reduce the impact of NdFeB on ferrite demagnetization. This results in an asymmetrical magnetic field distribution, making it easier to calculate the parameters of the magnetic field offset. While limiting the cost of permanent magnets, parameters such as the percentage of permanent magnet thickness when the magnetic flux density fundamental wave amplitude is maximized are calculated to achieve the highest utilization rate of the permanent magnet. It will be readily understood by those skilled in the art that the advantageous technical features of the above methods can be freely combined and superimposed without conflict.

[0085] 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 protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A rotor structure, characterized in that: include: The rotor core has multiple protrusions (1) on its outer wall. The multiple protrusions (1) are arranged at intervals along the circumference of the rotor core. A first magnet (2) and a second magnet (3) are arranged between two adjacent protrusions (1). The first magnet (2) is a neodymium iron boron magnet or a ferrite magnet, and the second magnet (3) is a neodymium iron boron magnet.

2. The rotor structure according to claim 1, characterized in that: Along the radial direction of the rotor core, the thickness of the first magnet (2) is greater than the thickness of the second magnet (3).

3. The rotor structure according to claim 1, characterized in that: Along the circumference of the rotor core, the first magnet (2) and the second magnet (3) are arranged in sequence; with the cross-section of the rotor core as the projection plane, the outer peripheral walls of the first magnet (2) and the second magnet (3) coincide with the circle formed by the outer peripheral wall of the protrusion (1).

4. The rotor structure according to claim 1, characterized in that: The rotor core is provided with a slot (4), which is located on the d-axis.

5. An electric motor, characterized in that, The rotor structure includes any one of claims 1 to 4.

6. The design method of the rotor structure according to any one of claims 1 to 4, characterized in that, The specific steps are as follows: Step 1: The fundamental component of the magnetic flux density in the air gap above the rotor core is B. Calculate the relationship between the fundamental component of the magnetic flux density B and the angle parameter of the permanent magnet. Step 2: Obtain the magnetic flux density B and the structural parameters and performance parameters of the permanent magnet; Step 3: Combining the relationships from Step 1 and Step 2, we can obtain the constraint expression that satisfies the requirement that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle.

7. The design method of the rotor structure according to claim 6, characterized in that, Step 1 specifically involves calculating the fundamental expression of the air gap magnetic flux density using Fourier transform. Since the magnetic flux density is neither odd nor even, the fundamental wave consists of a sine component and a cosine component. Can be written When the Fourier fundamental coefficient At that time, the fundamental component can be further written as , It is the current angle.

8. The design method of the rotor structure according to claim 7, characterized in that, Step 1 further includes establishing a coordinate system with the center of the rotor core as the origin, the Y-axis passing through the center of one of the protrusions (1) along the axial direction of the rotor core, and the angle between the Y-axis and one side of the protrusion (1) being .

1. The angle between the d-axis and the Y-axis is 2. The angle between the side of the second magnet facing away from the Y-axis and the Y-axis is . 3; Depend on The relationship between B and the angular parameters of the permanent magnet can then be obtained. ； ； In the formula, p is the pole logarithm; B1 and B2 are the air gap magnetic flux density under ideal conditions. available: ； Further, we can obtain: 。 9. The design method of the rotor structure according to claim 6, characterized in that, Step 2 specifically involves obtaining the magnetic flux density B and the structural and performance parameters of the permanent magnet through a magnetic circuit model.

10. The design method of the rotor structure according to claim 6, characterized in that, Specifically, step 2 involves combining the relationships from step 1 and step 2, eliminating B, to obtain the constraint expression that satisfies the requirement that the permanent magnet torque and the reluctance torque reach their peak values ​​at the same current angle.

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