Axial flux permanent magnet motor rotor design method and motor

Abstract

The application relates to the motor technical field and discloses an axial flux permanent magnet motor rotor design method and a motor. The axial flux permanent magnet motor rotor design method comprises the following steps: a surface-embedded permanent magnet rotor topological structure model is established, wherein permanent magnets are arranged along a circumferential direction of a rotor core, the permanent magnets in each magnetic pole range contain a first magnet segment and second magnet segments arranged on two sides of the first magnet segment along the circumferential direction, and the axial thickness of the first magnet segment is greater than that of the second magnet segment; the width parameter and the thickness parameter of the first magnet segment and the second magnet segment are adjusted under the constraint condition that the total volume of the permanent magnets is unchanged and the optimization target that the air gap magnetic flux density fundamental wave amplitude is maximum, and target size parameters of the permanent magnets are obtained. The application can effectively improve the air gap magnetic flux density fundamental wave amplitude and improve the magnetic flux density waveform quality without increasing the permanent magnet consumption.

Description

Technical Field

[0001] This application relates to the field of motor technology, specifically to a rotor design method and motor for an axial flux permanent magnet motor. Background Technology

[0002] Axial flux permanent magnet motors, due to their flat structure, have a compressed rotor core dimension in the axial direction, and the permanent magnets are typically surface-mounted to the rotor core surface. In existing designs, the cross-sectional thickness of the surface-mounted permanent magnets is uniform along the circumference within each pole region, resulting in poor sinusoidal distribution of air gap magnetic flux density, high harmonic content, and insufficient fundamental component, thus affecting the overall electromagnetic performance of the motor. Current rotor design methods for axial flux permanent magnet motors lack systematic optimization design methods for selecting permanent magnet structural parameters, especially the multi-parameter collaborative optimization design method aimed at maximizing the fundamental amplitude of air gap magnetic flux density under the constraint of keeping the total permanent magnet volume constant.

[0003] Therefore, there is an urgent need for a rotor design method for axial flux permanent magnet motors to solve the problems of poor air gap magnetic flux density waveform quality and lack of systematic magnet parameter optimization design methods in related technologies. Summary of the Invention

[0004] This application provides a rotor design method and motor for an axial flux permanent magnet motor to solve the problems of poor air gap magnetic flux density waveform quality and lack of systematic magnet parameter optimization design methods in related technologies.

[0005] In a first aspect, this application provides a rotor design method for an axial flux permanent magnet motor, the method comprising: A topological model of a surface-embedded permanent magnet rotor is established. In the topological model, permanent magnets are arranged in the rotor core along the circumferential direction. The permanent magnets in each magnetic pole range include a first magnet segment and a second magnet segment located on both sides of the first magnet segment along the circumferential direction. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment. Under the constraint of keeping the total volume of the permanent magnet constant, with the goal of maximizing the amplitude of the air gap magnetic flux density fundamental wave, the width and thickness parameters of the first and second magnet segments are adjusted to obtain the target size parameters of the permanent magnet.

[0006] In one optional implementation, adjusting the width and thickness parameters of the first and second magnet segments includes: Based on the axial thickness distribution of the first and second magnet segments along the circumferential direction, and the air gap length distribution along the circumferential direction, the distribution relationship of the air gap magnetic flux density along the circumferential direction is established. The amplitude of the fundamental component of the air gap magnetic flux density is calculated based on the distribution relationship, and used as the target quantity for evaluating the width and thickness parameters.

[0007] In one optional implementation, adjusting the width and thickness parameters of the first and second magnet segments further includes: Within the range of width and thickness parameters, multiple sets of sample parameter combinations are selected, and the air gap magnetic flux density base wave amplitude corresponding to each sample parameter combination is calculated through the distribution relationship. Based on the combination of parameters for each sample and the corresponding air gap magnetic flux density base wave amplitude, fit an approximate functional relationship between the width parameter and the thickness parameter and the air gap magnetic flux density base wave amplitude. The parameter combination that maximizes the fundamental wave amplitude of the air gap magnetic flux density is determined based on the approximate functional relationship and used as the target size parameter.

[0008] In one alternative implementation, in the topological model, the first magnet segment and the second magnet segment are made of the same permanent magnet material.

[0009] In one alternative implementation, the method further includes: When establishing the topological model, the circumferential width of the first magnet segment increases proportionally with the increase of the radial position. The ratio of the circumferential width of the first magnet segment at each radial position to the radial distance at that radial position is kept constant, so that the polar arc coefficient of the first magnet segment is the same at each radial position.

[0010] In one alternative implementation, the thickness parameter satisfies the following condition: The axial thickness of the second magnet segment is not less than one-third of the axial thickness of the first magnet segment, and not greater than two-thirds of the axial thickness of the first magnet segment.

[0011] In one optional implementation, in the topological model, the rotor core surface is provided with a groove corresponding to the position of the first magnet segment, the portion of the first magnet segment that exceeds the axial thickness of the second magnet segment is embedded in the groove, and the surfaces of the first magnet segment and the second magnet segment facing the air gap are flush.

[0012] In one alternative implementation, in the topological model, the two second magnet segments located on both sides of the first magnet segment have equal axial thickness and equal circumferential width, and the two second magnet segments are symmetrically arranged about the first magnet segment.

[0013] In one alternative implementation, the method further includes: The first magnet segment and / or the second magnet segment are divided into multiple sub-units along the radial direction.

[0014] Secondly, this application provides an axial flux permanent magnet motor, including a stator and a surface-embedded permanent magnet rotor, with an air gap formed between the stator and the surface-embedded permanent magnet rotor; The surface-embedded permanent magnet rotor includes a rotor core, and permanent magnets are arranged along the circumferential direction of the rotor core; The permanent magnet includes a first magnet segment and a second magnet segment located on both sides of the first magnet segment along the circumferential direction within each magnetic pole range. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment.

[0015] The axial flux permanent magnet motor rotor design method of this application establishes a surface-embedded permanent magnet rotor topology model including a first magnet segment and second magnet segments located on both sides of it. The axial thickness of the first magnet segment is greater than that of the second magnet segment, so that the thickness of the permanent magnet exhibits spatial variation in the circumferential direction, providing a structural basis for the active modulation of the air gap magnetic flux density distribution. On this basis, with the total volume of the permanent magnet remaining unchanged as a constraint and the fundamental amplitude of the air gap magnetic flux density being maximized as the objective, the width and thickness parameters of the first and second magnet segments are systematically adjusted. This allows the target size parameters of the permanent magnet that optimize the fundamental component of the air gap magnetic flux density to be determined without increasing the amount of permanent magnet used. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of the first method for designing the rotor of an axial flux permanent magnet motor according to an embodiment of this application; Figure 2 This is a second flowchart illustrating the rotor design method for an axial flux permanent magnet motor according to an embodiment of this application; Figure 3 This is a schematic diagram of the magnetic pole cross-section at the average radius of the surface-embedded T-shaped permanent magnet rotor according to an embodiment of this application; Figure 4 This is a schematic diagram of a surface-embedded T-type permanent magnet rotor model according to an embodiment of this application; Figure 5 This is a schematic diagram of the air gap magnetic flux path according to an embodiment of this application; Figure 6 This is a schematic diagram of the thickness function of the permanent magnet according to an embodiment of this application; Figure 7 This is a schematic diagram of the equivalent magnetic circuit of a motor according to an embodiment of this application; Figure 8 This is a schematic diagram comparing the permanent magnets before and after optimization according to an embodiment of this application; Figure 9This is a schematic diagram comparing the air gap magnetic flux density harmonic distribution before and after optimization according to an embodiment of this application; Figure 10 This is a schematic diagram illustrating the process of equivalently modeling an AFPM motor at the average radius into a two-dimensional LSPM motor model according to an embodiment of this application. Figure 11 These are schematic diagrams of two-dimensional equivalent models of AFPM motors with two rotor configurations according to embodiments of this application; Figure 12 This is a schematic diagram of the air gap magnetic flux density and harmonic distribution of a conventional surface-mounted AFPM motor and a surface-embedded T-type permanent magnet rotor AFPM motor under no-load conditions, according to embodiments of this application. Figure 13 This is a schematic diagram of the no-load flux linkage waveform and its harmonics for two rotor configurations according to embodiments of this application at the same rotational speed; Figure 14 This is a schematic diagram of the no-load back EMF waveform and its harmonics for two rotor configurations according to embodiments of this application at the same speed; Figure 15 This is a schematic diagram of the electromagnetic torque waveform and its harmonics of two rotor configurations under load conditions for one electrical cycle according to embodiments of this application. Figure 16 This is a structural block diagram of an axial flux permanent magnet motor rotor design device according to an embodiment of this application; Figure 17 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained.

[0020] AFPM (Axial Flux Permanent Magnet): refers to a type of motor structure in which the direction of the magnetic field in the air gap is parallel to the rotation axis of the motor. Due to its flat structure, it is often used in space-constrained applications.

[0021] Topology: In mechanical or electromagnetic structural design, it refers to the physical arrangement, connection method, and cross-sectional configuration of the various components in space.

[0022] Air gap magnetic density: refers to the magnetic flux density in the air gap region between the stator and rotor of a motor. Its waveform and amplitude directly determine the output performance of the motor.

[0023] Harmonics: In periodic non-sinusoidal electromagnetic signals, sinusoidal wave components with frequencies that are integer multiples of the fundamental frequency. Harmonics typically lead to increased heating, vibration, and losses in motors.

[0024] Eddy current loss refers to the resistive heat loss caused by the induction of a circular current (eddy current) inside a conductor (such as a permanent magnet or iron core) by an alternating magnetic field.

[0025] Back Electromotive Force (Back EMF): When a motor is running, the rotor magnetic field cuts the stator windings, and the electromotive force is generated in the opposite direction to the applied voltage.

[0026] Torque ripple: The periodic fluctuation phenomenon that occurs when a motor outputs mechanical torque, affecting the smoothness of motor operation.

[0027] LSPM (Linear Synchronous Permanent Magnet): refers to a type of linear motor. In theoretical analysis, the circular structure of a rotary motor is often expanded radially into a linear form (i.e., LSPM) to simplify two-dimensional electromagnetic field analysis.

[0028] As an optional application scenario of this application, the axial flux permanent magnet motor rotor design method provided in this application can be executed through a terminal device equipped with motor design software. Exemplarily, the motor design software can be any engineering design software capable of providing motor parameter modeling and optimization functions. If the motor design software is running, the terminal device can display the software's user interface, which may include a topology configuration page, a parameter input page, and an optimization result output page. In some embodiments, the terminal device communicates with a server to utilize the computing resources provided by the server to complete relatively complex parameter optimization calculation tasks; the terminal device can be a workstation, desktop computer, laptop computer, etc., and the server can be various types of computing systems capable of providing computing power, including but not limited to cloud servers or high-performance computing clusters.

[0029] It should be noted that the above optional application scenarios are merely examples of one application scenario and do not limit the scope of protection of this application.

[0030] In related technologies, axial flux permanent magnet motors are constrained by their flat disc structure. The rotor permanent magnets are usually mounted using a surface-mount method with a uniform cross-sectional thickness along the circumference, resulting in high harmonic content and poor waveform quality in the air gap magnetic flux density. Furthermore, existing rotor parameter design methods lack the means to systematically optimize the various dimensional parameters of the magnets while keeping the total volume of the permanent magnets constant. To address the above technical problems, this application provides a rotor design method for axial flux permanent magnet motors to determine the optimal target dimensional parameters of the permanent magnets without increasing the amount of permanent magnets used.

[0031] According to an embodiment of this application, an embodiment of an axial flux permanent magnet motor rotor design method is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0032] This embodiment provides a rotor design method for an axial flux permanent magnet motor, which can be used in the aforementioned terminal devices, such as workstations and desktop computers. Figure 1 This is a flowchart of the axial flux permanent magnet motor rotor design method according to an embodiment of this application, such as... Figure 1 As shown, the process includes the following steps: Step S101: Establish the topological structure model of the surface-embedded permanent magnet rotor.

[0033] A topological model is a structural model that mathematically describes the geometry and spatial relationships of the components of a surface-embedded permanent magnet rotor (i.e., a rotor configuration in which the rotor core surface has grooves and the permanent magnets are partially embedded in the grooves and partially mounted on the rotor core surface). Its purpose is to clarify the definition and constraint relationships of each geometric variable, and to provide a quantifiable structural basis for subsequent parameter optimization.

[0034] In the topological model, the rotor core is provided with permanent magnets along the circumferential direction. The permanent magnets in each magnetic pole range include a first magnet segment and a second magnet segment located on both sides of the first magnet segment along the circumferential direction.

[0035] The first magnet segment refers to the magnet part in the middle region of each magnetic pole, and the second magnet segment refers to the magnet parts located on both sides of the first magnet segment. The axial thickness of the first magnet segment is greater than that of the second magnet segment. That is, along the rotor axial direction, the size of the first magnet segment in the middle region is larger, and the size of the second magnet segments on both sides is smaller. The entire magnetic pole forms a stepped profile that is thick in the middle and thin on both sides in the axial cross section.

[0036] When establishing the topology model, it is necessary to clearly determine the circumferential arrangement of each magnetic pole on the rotor core, the relative positional relationship between the first and second magnetic segments, and the thickness constraint relationship between the two in the axial direction. The width and thickness parameters of the first and second magnetic segments should be included in the adjustable variable set of the model as the objects for subsequent optimization and adjustment.

[0037] Step S102: Under the constraint of keeping the total volume of the permanent magnet constant, with the goal of maximizing the amplitude of the air gap magnetic flux density fundamental wave, adjust the width and thickness parameters of the first and second magnet segments to obtain the target size parameters of the permanent magnet.

[0038] The constant total volume of the permanent magnet means that throughout the entire process of adjusting the size parameters of each magnet segment, the total volume of the permanent magnet formed by the first magnet segment and the second magnet segments on both sides remains constant and does not increase or decrease due to parameter adjustments. This constraint condition eliminates the magnetic field enhancement effect caused by changes in the amount of permanent magnet material, so that the optimization results can truly reflect the influence of the topological structure and parameter ratio on the electromagnetic performance.

[0039] The fundamental amplitude of the air gap magnetic flux density refers to the peak value of the fundamental component of the magnetic flux density distribution in the air gap. Its magnitude directly determines the magnetic flux amplitude, back EMF amplitude, and output torque capability of the motor. It is a core basic parameter for measuring the electromagnetic performance of permanent magnet motors. Maximizing it as the optimization goal helps to strengthen the main magnetic field of the air gap of the motor as much as possible with the same amount of permanent magnets.

[0040] The width parameter refers to the circumferential dimension of the first or second magnet segment, while the thickness parameter refers to its axial dimension.

[0041] When performing this step, based on the topological model established in step S101, under the constraint that the total volume of the permanent magnet remains unchanged, the width and thickness parameters of the first and second magnet segments are systematically adjusted within the feasible parameter space. The corresponding air gap magnetic flux density fundamental wave amplitude is calculated and evaluated for different parameter combinations. Finally, the parameter combination that maximizes the air gap magnetic flux density fundamental wave amplitude is determined as the target size parameter output for the permanent magnet.

[0042] It is important to note that there is a mutually restrictive relationship between the width parameters of the first and second magnet segments: for example, if the width parameter of the first magnet segment is too large, a strong leakage flux path is easily formed between the magnetic poles, resulting in a reduction in the effective magnetic flux entering the air gap; if the width parameter of the second magnet segment is too large, it may cause an increase in the local magnetic saturation of the rotor core, which in turn weakens the fundamental frequency content of the air gap magnetic flux density. Therefore, under the premise of keeping the total volume of the permanent magnet constant, reasonably determining the ratio of the width and thickness parameters of the first and second magnet segments is the core of this step.

[0043] In summary, the axial flux permanent magnet motor rotor design method provided in this application establishes a topological structure model including a first magnet segment and second magnet segments located on both sides of it, clarifies the geometric relationship and adjustable parameter set of each magnet segment, and, under the constraint of keeping the total volume of the permanent magnet constant, takes the maximization of the fundamental wave amplitude of the air gap magnetic flux density as the optimization objective, systematically adjusts the width and thickness parameters of the first and second magnet segments, thereby obtaining the target size parameters of the permanent magnet that optimize the air gap main magnetic field without increasing the amount of permanent magnet material used.

[0044] This embodiment provides a rotor design method for an axial flux permanent magnet motor, which can be used in the aforementioned terminal devices, such as workstations and desktop computers. Figure 2 This is a flowchart of the axial flux permanent magnet motor rotor design method according to an embodiment of this application, such as... Figure 2 As shown, the process includes the following steps: Step S201: Establish the topological structure model of the surface-embedded permanent magnet rotor.

[0045] A topological model is a structural model that mathematically describes the geometry and spatial relationships of the components of a surface-embedded permanent magnet rotor, providing a quantifiable structural basis for subsequent parameter optimization.

[0046] In the topological model, permanent magnets are arranged along the circumference of the rotor core. Within each magnetic pole region, the permanent magnets include a first magnet segment and second magnet segments located on both sides of the first magnet segment. The first magnet segment refers to the magnet portion in the middle region of each magnetic pole, and the second magnet segments refer to the magnet portions located on both sides of the first magnet segment. The axial thickness of the first magnet segment is greater than that of the second magnet segment. That is, along the rotor axial direction, the first magnet segment in the middle region is larger in size, while the second magnet segments on both sides are smaller in size. The entire magnetic pole forms a stepped profile with a thicker middle and thinner sides in the axial cross section.

[0047] When establishing the topology model, it is necessary to clearly determine the circumferential arrangement of each magnetic pole on the rotor core, the relative positional relationship between the first and second magnetic segments, and the thickness constraint relationship between the two in the axial direction. The width and thickness parameters of the first and second magnetic segments should be included in the adjustable variable set of the model as the objects for subsequent optimization and adjustment.

[0048] To further clarify the material properties in the topological model, in one optional implementation, the first magnet segment and the second magnet segment can be made of the same permanent magnet material.

[0049] Permanent magnet materials refer to magnetic materials with strong coercivity and remanent magnetic induction. Common permanent magnet materials include neodymium iron boron, ferrite, samarium cobalt, etc. Remanent magnetic induction refers to the magnetic induction intensity that the material can still maintain after the external magnetic field is removed, while relative permeability describes the material's magnetic permeability as a multiple of the vacuum permeability.

[0050] Using the same permanent magnet material for the first and second magnet segments means that they have the same remanent magnetic induction and relative permeability. When establishing the air gap magnetic flux density distribution relationship, it is not necessary to define the material parameters of the two types of magnet segments separately, which helps to simplify the analytical modeling process and reduce the parameter dimensionality of the model. At the same time, the constraint of the same material also allows the performance differences between different parameter combinations to be purely attributed to the ratio of geometric structural parameters, eliminating the interference of material differences on the comparison results and making the optimization conclusions more objective.

[0051] Furthermore, considering that the rotor of the axial flux permanent magnet motor has a certain span in the radial direction, in order to ensure the geometric rationality of the topology model in the radial direction, when establishing the topology model, the circumferential width of the first magnet segment can be increased proportionally with the increase of the radial position, so that the ratio of the circumferential width of the first magnet segment at each radial position to the radial distance at that position remains constant, so that the polar arc coefficient of the first magnet segment at each radial position is the same.

[0052] The pole arc coefficient is the ratio of the circumferential arc length covered by the magnetic pole at a certain radial position to the pole pitch at that position. It is a dimensionless parameter describing the coverage range of the magnetic pole. In an axial flux permanent magnet motor, the pole pitch increases linearly with the increase of the radial position. If the circumferential width of the first magnet segment does not change proportionally with the radial position, the pole arc coefficient at different radial positions will be different, resulting in inconsistent modulation of the air gap flux by the magnetic pole in the radial direction.

[0053] Maintaining a constant pole arc coefficient at each radial position ensures that the first magnet segment covers the air gap magnetic flux distribution in a consistent proportion across the entire radial span, resulting in uniformity of the air gap magnetic flux density distribution in the radial direction. This provides a geometric constraint condition universally applicable in the radial direction for subsequent analytical modeling. In practice, the circumferential width of the first magnet segment at its average radius can be used as a reference value, and the corresponding circumferential widths at each radial position from the inner diameter to the outer diameter can be determined sequentially according to a proportional relationship.

[0054] Regarding the assembly relationship between the rotor core and the permanent magnet, in one optional embodiment, the topological model can be configured such that: a groove is provided on the surface of the rotor core corresponding to the position of the first magnet segment, the portion of the first magnet segment that exceeds the axial thickness of the second magnet segment is embedded in the groove, and the surfaces of the first magnet segment and the second magnet segment facing the air gap are flush.

[0055] The groove refers to a slot-shaped structure pre-machined on the surface of the rotor core at the installation position corresponding to the first magnet segment. Its axial depth is equal to the difference between the axial thickness of the first magnet segment and the second magnet segment, and its circumferential width corresponds to the circumferential width of the first magnet segment.

[0056] Embedding refers to inserting the portion of the first magnet segment that protrudes from the second magnet segment in the axial direction into the groove, so that the first magnet segment and the groove wall form mechanical contact in the radial direction. The groove wall can provide radial positioning constraints for the first magnet segment, effectively preventing radial displacement of the first magnet segment under high-speed rotation conditions and improving the mechanical reliability of the rotor structure.

[0057] The surfaces of the first and second magnet segments facing the air gap are flush, meaning their end faces facing the air gap are in the same axial plane. This ensures the overall surface of the permanent magnet facing the air gap remains flat, which helps maintain a stable and uniform air gap length along the circumference and provides regular geometric boundary conditions for subsequent air gap magnetic flux density modeling. In actual manufacturing, structural adhesive can be used to fix the first magnet segment in the groove and bond the second magnet segment to the rotor core surface to assist in achieving reliable assembly and fixation.

[0058] Furthermore, in the topological model, the geometric symmetry of the two second magnet segments can be further constrained: the two second magnet segments located on both sides of the first magnet segment have equal axial thickness and equal circumferential width, and the two second magnet segments are symmetrically arranged about the first magnet segment.

[0059] Symmetrical arrangement means that the two second magnet segments are mirror images of the center line of the first magnet segment in the circumferential direction. The two segments are equidistant from the center line of the first magnet segment in the circumferential direction, have equal circumferential widths in the outward direction, and equal axial thicknesses, and are completely identical in geometry and size.

[0060] This symmetrical constraint ensures the structural symmetry of the magnetic poles in the circumferential direction, so that the air gap magnetic flux density distribution in each magnetic pole range remains symmetrical about the center line of the magnetic pole. This helps to reduce the even harmonic components caused by structural asymmetry, improve the symmetry of the magnetic flux density waveform, and also helps to simplify the processing technology and reduce the complexity of rotor assembly.

[0061] Step S202: Under the constraint of keeping the total volume of the permanent magnet constant, with the goal of maximizing the amplitude of the air gap magnetic flux density fundamental wave, adjust the width and thickness parameters of the first and second magnet segments to obtain the target size parameters of the permanent magnet.

[0062] In this step, the constant total volume of the permanent magnet is a constraint condition that runs through the entire process. This means that during the process of arbitrarily adjusting the width and thickness parameters of the first and second magnet segments, the total volume of the permanent magnet formed by the two segments remains constant and does not increase or decrease with the change of parameters.

[0063] The significance of this constraint lies in eliminating the magnetic field enhancement effect caused by the increase in the amount of permanent magnet material, ensuring that the performance improvement obtained by optimization comes entirely from the change in the ratio of magnet geometric structure parameters, so that the optimization conclusion has objective evaluation significance for the topological structure performance, and also meets the actual needs of controlling the cost and amount of permanent magnet material in engineering design.

[0064] The fundamental amplitude of the air gap magnetic flux density is the peak value of the fundamental component in the Fourier expansion of the air gap magnetic flux density along the circumferential direction. It is a core fundamental parameter for evaluating the electromagnetic performance of a permanent magnet motor, and its magnitude directly affects the motor's flux linkage amplitude, back EMF amplitude, and output torque under rated operating conditions. Maximizing its value aims to increase the effective main magnetic flux entering the air gap by adjusting the ratio of magnet geometric parameters. The target size parameters refer to the specific combinations of the width and thickness parameters of the first magnet segment and the second magnet segment, determined after systematic parameter adjustment, that maximize the fundamental amplitude of the air gap magnetic flux density under the aforementioned constraints.

[0065] When setting the thickness parameters, the axial thickness of the second magnet segment can be no less than one-third of the axial thickness of the first magnet segment and no more than two-thirds of the axial thickness of the first magnet segment.

[0066] The range is set based on the following considerations: When the axial thickness of the second magnet segment is less than one-third of the axial thickness of the first magnet segment, the thickness difference between the second magnet segment and the first magnet segment on both sides is too large, and the contribution of the magnet segments on both sides to the air gap magnetic flux is greatly reduced, thus limiting the overall magnetic field modulation effect; when the axial thickness of the second magnet segment exceeds two-thirds of the axial thickness of the first magnet segment, the thicknesses of the two tend to be close, the stepped shape of the magnetic pole cross section gradually degenerates, and the modulation effect of the spatial variation of the magnet thickness in the circumferential direction on the air gap magnetic flux waveform is weakened, making it difficult to reflect the structural advantages of the stepped cross section in terms of magnetic field distribution optimization.

[0067] By constraining the axial thickness of the second magnet segment within the aforementioned range, it is possible to ensure that the magnetic pole cross-section has significant stepped characteristics while taking into account the effective contribution of the magnet segments on both sides to the air gap flux, so that the overall structure's magnetic flux density modulation effect is within a reasonable and effective range.

[0068] To provide a quantitative and systematic evaluation of the width and thickness parameters, in one optional implementation, the distribution relationship of the air gap magnetic flux density along the circumferential direction can be established based on the axial thickness distribution of the first and second magnet segments along the circumferential direction and the distribution of the air gap length along the circumferential direction. The amplitude of the fundamental component of the air gap magnetic flux density can then be calculated based on this distribution relationship as a target quantity for evaluating the width and thickness parameters.

[0069] The axial thickness distribution along the circumferential direction refers to expressing the axial thickness of the first magnet segment and the second magnet segment as a function of circumferential angular coordinates: this function takes a larger value within the circumferential angle range corresponding to the first magnet segment and a smaller value within the circumferential angle range corresponding to the second magnet segment, forming a thickness function that changes periodically in a stepped manner along the circumferential direction.

[0070] The distribution of air gap length along the circumferential direction refers to the relationship between the actual magnetic circuit length at each circumferential position of the air gap and the circumferential angle: Since the stator has a toothed structure, the equivalent magnetic circuit length of the air gap changes periodically along the circumferential direction. The air gap magnetic circuit length is smaller at the stator tooth tip and larger at the center of the slot. It can be described as a function of the circumferential angle coordinates.

[0071] Substituting the two functions above into the air gap magnetic flux density expression derived based on the equivalent magnetic circuit principle, we can obtain the analytical distribution relationship of the air gap magnetic flux density as a function of the circumferential angle. Performing a Fourier expansion on this distribution relationship and extracting the amplitude of the fundamental component, we can use this amplitude as a quantitative target quantity to evaluate the merits of the current parameter combination. This analytical evaluation method transforms the complex magnetic field problem into a parameterized mathematical expression, allowing for rapid calculation of the target quantity under different parameter combinations without repeatedly calling finite element simulations, thus providing an efficient evaluation basis for multivariate parameter optimization.

[0072] After establishing the above evaluation target quantities, the width and thickness parameters can be systematically adjusted in the following three steps to obtain the target size parameters.

[0073] The first step is to select multiple sets of sample parameter combinations within the range of width and thickness parameters, and calculate the air gap magnetic flux density base wave amplitude corresponding to each sample parameter combination through the distribution relationship.

[0074] The range of values ​​refers to the upper and lower limits of each width and thickness parameter predetermined based on the topological rationality constraints (such as the width parameter of the first magnet segment should be greater than that of the second magnet segment to maintain the stepped shape, and the axial thickness of the second magnet segment should meet the aforementioned proportional constraints) and the requirements of engineering feasibility.

[0075] A sample parameter combination refers to a set of several sets of parameter values ​​selected according to certain rules within the above-mentioned range. Methods such as uniform design, central composite design, and Latin hypercube design can be used to distribute the sample points in the parameter space to ensure that the sample points have good coverage and representativeness of the entire parameter space. For example, several sets of sample parameter combinations can be uniformly selected in the parameter space.

[0076] For each set of sample parameters, substitute the aforementioned analytical distribution relationship of air gap magnetic flux density and perform Fourier expansion to calculate the corresponding fundamental amplitude of air gap magnetic flux density, thereby constructing a sample dataset consisting of each set of sample parameters and its corresponding fundamental amplitude of air gap magnetic flux density.

[0077] The second step is to fit an approximate functional relationship between the width and thickness parameters and the amplitude of the air gap magnetic flux density base wave, based on the combination of parameters for each sample and the corresponding amplitude of the air gap magnetic flux density base wave.

[0078] Fitting refers to establishing an approximate function with an explicit expression between the width parameter, thickness parameter (design variable) and the amplitude of the air gap magnetic flux density base wave (target quantity) based on the sample dataset established in the previous step. It is also called a surrogate model or response surface model.

[0079] For example, a quadratic polynomial can be used to describe this approximate functional relationship. This involves fitting the fundamental wave amplitude of the air gap magnetic flux density to a linear combination of the first-order and second-order terms of each design variable, as well as the pairwise interactions between variables. Based on the sample dataset, the coefficients of each polynomial are determined using regression methods such as least squares, resulting in a surrogate model capable of rapidly predicting the fundamental wave amplitude of the air gap magnetic flux density across the entire parameter space. Besides the quadratic polynomial, other surrogate model forms such as radial basis function networks, Kriging models, and support vector regression can be flexibly selected based on the parameter space dimension and the number of samples.

[0080] By establishing approximate functional relationships, the target quantity, which originally required calling the analytical distribution relationship to calculate in each evaluation, is transformed into an explicit expression that can be calculated directly and quickly, significantly reducing the computational cost in the subsequent optimization stage.

[0081] The third step is to determine the parameter combination that maximizes the amplitude of the air gap magnetic flux density fundamental wave based on the approximate functional relationship, and use it as the target size parameter.

[0082] In the parameter space described by the approximate functional relationship, numerical optimization methods can be used to find the optimal value. Numerical optimization methods include, but are not limited to, gradient-based algorithms (such as sequential quadratic programming) and heuristic algorithms (such as genetic algorithms and particle swarm optimization algorithms). Under the conditions of satisfying the constraint of the total volume of the permanent magnet remaining unchanged and the constraint of the range of values ​​of each parameter, the combination of design variable values ​​that makes the output value of the approximate function reach a larger value is searched, and this combination is used as the target size parameter output.

[0083] For example, if a quadratic polynomial response surface is used as a surrogate model, its analytical differentiability allows for direct numerical optimization to solve for extrema, resulting in high computational efficiency. If necessary, the obtained target size parameters can be further substituted back into the analytical distribution relationship of the air gap magnetic flux density or the finite element simulation model for verification, confirming that the fundamental amplitude of the air gap magnetic flux density meets expectations. Through these three steps, multi-parameter systematic optimization can be completed with fewer analytical model calculations, efficiently obtaining the target size parameters.

[0084] Step S203: Divide the first magnet segment and / or the second magnet segment into multiple sub-units along the radial direction.

[0085] This step can be performed at any stage after the topology model is established in step S201, or it can be implemented as a further processing step for the geometric configuration of the permanent magnet after the target size parameters are obtained in step S202.

[0086] Radial division refers to dividing a magnetic segment that was originally a whole in the radial direction into multiple magnetic segments with a certain size in the radial direction, arranged sequentially in the radial direction; sub-units refer to the smaller magnetic segments obtained after division. Each sub-unit is independent of each other in the radial direction, and there may be a certain gap between them, or they may be arranged close to each other, depending on the engineering requirements.

[0087] The division can target the first magnet segment, the second magnet segment, or both simultaneously in a radial division. The specific choice can be flexibly determined based on the induced eddy current level and loss control requirements of each magnet segment under operating conditions. The number of sub-units can be flexibly determined based on the rotor operating speed, motor power supply frequency, and eddy current loss control requirements: the more sub-units there are, the smaller the radial dimension of each sub-unit, the smaller the cross-sectional area of ​​the eddy current circulation within a single sub-unit, and the more significant the eddy current loss suppression effect. However, the requirements for machining and assembly precision will also increase accordingly, requiring a trade-off based on the actual engineering situation.

[0088] Under the combined action of high-speed operation and alternating magnetic field of axial flux permanent magnet motor, eddy currents will be induced in the permanent magnet. The amplitude of the eddy current is closely related to the size of the magnet in the cross section perpendicular to the eddy current flow direction. By dividing the magnet segment into multiple sub-units in the radial direction, the circulation cross-sectional area of ​​the eddy current inside each sub-unit is greatly reduced, thereby reducing the eddy current amplitude, suppressing eddy current loss, and improving the thermal management characteristics of the motor under high-speed operation conditions.

[0089] In summary, the axial flux permanent magnet motor rotor design method provided in this application establishes a topological model with a first magnet segment and two second magnet segments on both sides. Under the constraint of keeping the total volume of the permanent magnet constant, and with the goal of maximizing the fundamental wave amplitude of the air gap magnetic flux density, the width and thickness parameters of each magnet segment are systematically adjusted. Without increasing the amount of permanent magnet material, the target size parameters that make the air gap main magnetic field tend to be better are determined. Furthermore, through radial segmentation, the eddy current loss of the permanent magnet can be suppressed while maintaining the above-mentioned electromagnetic performance optimization results, thereby achieving a synergistic improvement in electromagnetic performance and loss characteristics.

[0090] This embodiment provides an axial flux permanent magnet motor, which includes a stator and a surface-embedded permanent magnet rotor, with an air gap formed between the stator and the surface-embedded permanent magnet rotor. The surface-embedded permanent magnet rotor includes a rotor core, with permanent magnets arranged along the circumferential direction on the rotor core. Each permanent magnet includes a first magnet segment and a second magnet segment located on both sides of the first magnet segment within each magnetic pole range along the circumferential direction. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment.

[0091] The stator is the stationary magnetic circuit and winding support component in an axial flux permanent magnet motor, typically consisting of a stator core and stator windings embedded within it. The stator core is generally made of laminated magnetically conductive materials, providing a low-resistivity conduction path for the air gap flux. The stator core has teeth and slots spaced circumferentially. The stator windings are embedded in these slots, and when energized, they interact with the air gap magnetic field to generate an electromagnetic torque that drives the rotor, or induce an electromotive force when the rotor rotates. The openings formed between the teeth and slots constitute the stator slot openings, and their width and distribution modulate the circumferential distribution of the air gap magnetic flux.

[0092] The air gap between the stator and the surface-embedded permanent magnet rotor refers to the distance between their axially opposite surfaces, and is the core path for magnetic field transmission within the motor. In axial flux permanent magnet motors, the air gap exists axially between the stator end face and the rotor end face. The distribution characteristics of the air gap magnetic flux density directly determine the motor's flux linkage amplitude, back electromotive force amplitude, and output torque. Due to the stator's slotted structure, the equivalent magnetic path length of the air gap varies periodically along the circumference. The effective magnetic path length is smaller at the stator tooth tips and larger at the slot openings. This periodic variation modulates the circumferential distribution of the air gap magnetic flux density.

[0093] A surface-embedded permanent magnet rotor is a rotating component in an axial flux permanent magnet motor that generates an excitation magnetic field and transmits electromagnetic torque. Its key feature is that the rotor core surface has grooves corresponding to the magnet mounting positions. A portion of the permanent magnet is embedded in these grooves, while the remainder is mounted on the rotor core surface. The rotor core comprises the rotor core and the permanent magnets fixed thereon. The rotor core serves as the mechanical support foundation for the surface-embedded permanent magnet rotor. It is typically made of magnetically conductive material, is disc-shaped, and has a relatively small axial dimension, conforming to the flat structure characteristic of axial flux motors. Multiple magnetic poles are spaced apart along the circumference of the rotor core. Each pole is provided with a magnetic field by a corresponding permanent magnet, and the polarities of adjacent poles alternate along the circumference.

[0094] The permanent magnet comprises a first magnet segment and second magnet segments located on either side of the first magnet segment within each magnetic pole region along the circumferential direction. Within each magnetic pole region, the second magnet segments are positioned on either side of the first magnet segment with the first magnet segment as the center. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment. That is, along the axial direction of the motor, the extension dimension of the first magnet segment located in the middle is greater than the extension dimension of the second magnet segments on both sides. The entire magnetic pole exhibits a stepped profile that is thicker in the middle and thinner on both sides in the axial cross-section.

[0095] Because the first and second magnet segments differ in axial thickness, the permanent magnet thickness varies at different positions along the circumference, resulting in variations in the permanent magnet driving magnetomotive force (PMMF). At the corresponding positions in the first magnet segment, the permanent magnet thickness is greater, leading to a higher equivalent driving PMMF and a correspondingly higher air gap magnetic flux density. Conversely, at the corresponding positions in the second magnet segment, the permanent magnet thickness is smaller, resulting in a relatively lower equivalent driving PMMF and a relatively lower air gap magnetic flux density. By rationally designing the width and thickness parameters of the first and second magnet segments, the distribution of the air gap magnetic flux density along the circumference can be made to approximate a sinusoidal waveform, reducing the harmonic content in the air gap magnetic flux density. This increases the fundamental amplitude of the air gap magnetic flux density without changing the amount of permanent magnet material used, thereby improving the electromagnetic performance of the motor under both no-load and load conditions.

[0096] In summary, the axial flux permanent magnet motor provided in this application provides a first magnet segment with a larger axial thickness and a second magnet segment with a smaller axial thickness located on both sides of each magnetic pole within the range of the surface-embedded permanent magnet rotor. This creates a stepped spatial variation in the thickness of the permanent magnet in the circumferential direction. Without changing the properties of the permanent magnet material or increasing the amount of permanent magnet used, it achieves active modulation of the air gap flux density distribution. This helps to reduce the harmonic content of the air gap flux density and increase the fundamental amplitude, thereby improving the motor's flux linkage, back EMF, and output torque characteristics.

[0097] To better illustrate the axial flux permanent magnet motor rotor design method of this application, a preferred embodiment will be provided below. This embodiment is intended to detail the implementation process of this application, but is not intended to limit the scope of protection of this application.

[0098] This embodiment comprehensively describes the structural scheme of a surface-embedded T-type permanent magnet rotor and the overall scheme of an axial flux permanent magnet motor (AFPM motor) using this rotor, combining specific motor structural parameters, modeling process, and simulation verification results. The structural parameters, optimization process, and simulation results of the following motor prototype are used as the subject of this embodiment because the prototype has specific values ​​and calculation results in the design, modeling, optimization, and verification stages, facilitating a relatively complete and verifiable presentation of the implementation process and technical effects of the technical solution. It should be understood that the technical solution of this application is not limited to the specific dimensions, pole slot combinations, and parameter values ​​corresponding to the following motor prototype; AFPM motors of other specifications and pole slot combinations can also be designed using the following approach.

[0099] AFPM motors, due to their flat structure and compact axial dimensions, have certain application value in new energy vehicle drives and wind power generation. The rotor structure is one of the factors affecting the electromagnetic performance and operational reliability of AFPM motors. The topology of the permanent magnet has a certain impact on the air gap magnetic field distribution, motor back EMF, output torque, torque ripple, and loss level. Traditional radial flux motors typically use two types of permanent magnet mounting methods: surface-mounted and embedded. The embedded method embeds the permanent magnet inside the rotor core, which can generate both permanent magnet torque and reluctance torque simultaneously through the rotor's salient pole effect, offering relatively greater design freedom. However, the axial space of the AFPM motor rotor is relatively limited, restricting the applicability of the embedded method. For the surface-mounted method, when the permanent magnet cross-section is a uniform rectangle, the air gap magnetic flux density waveform deviates from a sinusoidal waveform, resulting in relatively high harmonic content. Existing technologies also include processing the permanent magnet into trapezoidal, stepped, or segmented sinusoidal structures to improve the waveform, but these methods are relatively difficult and costly to manufacture.

[0100] In view of this, the present embodiment focuses on the optimal design of the AFPM motor rotor, and mainly includes the following aspects: First, a T-type permanent magnet rotor topology is proposed, and an analytical model of air gap magnetic flux density is established; second, based on this analytical model, the influence law of permanent magnet structural parameters on electromagnetic performance is analyzed, and the structural parameter optimization is completed; third, combined with the formation mechanism of eddy current loss in permanent magnets, the eddy current loss is suppressed to a certain extent by segmenting the permanent magnets in the radial direction; fourth, the performance of the two configurations of the traditional surface-mounted rotor and the T-type permanent magnet rotor is simulated and compared, to verify the effects of the T-type permanent magnet rotor in improving magnetic flux density distribution, increasing electromagnetic torque and suppressing harmonics.

[0101] Figure 3 is a schematic cross-sectional view of the magnetic pole of the T-type permanent magnet rotor in this embodiment at the average radius. As shown in Figure 3 , the permanent magnet at this magnetic pole is composed of a plurality of magnets with the same material but different thicknesses and widths: the part with a width of w 1 and a thickness of h m1 has a relatively small thickness, the part with a width of w 2 and a thickness of h m2 has a relatively large thickness, h m2 is greater than h m1 , so that the permanent magnet at this magnetic pole presents a T-shaped profile that is thick in the middle and thin on both sides along the circumferential direction.

[0102] It should be noted that in this embodiment, h m2 represents the axial thickness of the first magnet segment (i.e., the thicker magnet segment located at the middle position of each magnetic pole), and h m1 represents the axial thickness of the second magnet segment (i.e., the thinner magnet segments respectively located on both sides of the first magnet segment), satisfying h m2 > h m1 , which is consistent with the limitation that the axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment in the above embodiment. It should be noted that the subscript numbers in the above parameter symbols are only parameter numbers, and there is no direct numerical correspondence with the sequence numbers of "first" and "second" in the above embodiments.

[0103] In the T-type permanent magnet rotor, the rotor slot width at the average radius is w 2, the slot width is extended to any radius with the same pole arc coefficient, and the slot width w(r) at any radius r can be expressed as: ; In the formula, r is the radial distance at the calculated location. R av This represents the average radius of the rotor. R av It can be determined by the inner radius. R i and outer radius R o Represented as: ; In the formula, R i The inner radius of the rotor. R o denoted as the outer radius of the rotor.

[0104] The slot depth of the rotor is h m2 and h m1 The difference, that is h m2 - h m1 . Figure 3 The length of the thicker section of the permanent magnet embedded in the rotor is... h m2 - h m1 This part can be fixed in the groove with glue to prevent radial displacement during high-speed rotation; the thinner permanent magnets on both sides can be fixed to the rotor surface with glue. Figure 3 After the middle part of the permanent magnets on both sides is embedded into the rotor core, the resulting motor rotor is as follows: Figure 4 As shown. Figure 4 This is a schematic diagram of the T-type permanent magnet rotor model in this embodiment. Figure 4 The image shows both a 3D model and a 2D model of a T-shaped permanent magnet rotor; [The image is composed of...] Figure 4 As can be seen, the permanent magnet rotor has multiple magnetic poles arranged along the circumference, and the polarities of adjacent permanent magnets are opposite.

[0105] In the structural parameters of a T-type permanent magnet rotor, when the structural parameters h m2 as well as w When the value of 2 is relatively large, the local magnetic flux density in the rotor core will increase, the rotor saturation degree will increase accordingly, and the fundamental frequency content of the air gap magnetic flux density may decrease accordingly; when wWhen the value of 1 is relatively large, leakage flux paths are easily formed, reducing the magnetic energy utilization rate of the permanent magnet and affecting the effective establishment of the air gap main magnetic field. It is evident that the structural parameters of the T-shaped permanent magnet rotor have a certain impact on the air gap magnetic field distribution; improper parameter selection may lead to attenuation of the fundamental magnetic flux density and increased leakage flux. Therefore, this embodiment optimizes the structural parameters of the T-shaped permanent magnet rotor by establishing an analytical model of the air gap magnetic flux density at the average radius, as detailed below.

[0106] Before establishing the analytical model of the air gap magnetic flux density of the AFPM motor corresponding to the T-type permanent magnet rotor, this embodiment makes the following two simplifications: First, the difference in magnetic permeability between the stator and rotor core materials in different directions is ignored, and the local saturation that may occur in ferromagnetic materials under high magnetic flux density is not considered. Furthermore, it is assumed that both the stator and rotor cores have infinite magnetic permeability, and the magnetic potential decrease is mainly concentrated in the air gap and non-ferromagnetic regions to simplify the magnetic circuit solution process. It should be noted that, in order to reduce the complexity of the analysis, the influence of core saturation is not considered in the structural parameter optimization analysis.

[0107] Secondly, ignoring the actual slot shape of the stator, we analyze it as an equivalent rectangular slot with a width equal to the actual slot opening width and an infinite depth.

[0108] To simplify the modeling process while considering the influence of the tooth structure on the air gap magnetic flux density, this embodiment models the air gap magnetic flux density based on the equivalent magnetic circuit method, transforming the magnetic field distribution problem into a problem of calculating magnetic circuit parameters. Figure 5 This is a schematic diagram of the air gap magnetic flux path in this embodiment. Figure 5 middle b 0 represents the slot width. g This is the air gap length.

[0109] At the air gap location where the T-shaped permanent magnet is embedded in the rotor, the air gap magnetic flux density is relatively enhanced; the magnetic flux is approximated as a set of parallel lines. Approximating the magnetic circuit at the tooth slots, it can be considered equivalent to a set of concentric quarter-circle arcs. Figure 5 It is evident that the path length traversed by the magnetic flux is not constant, but rather a function δ(α) that varies with the central angle, i.e., the distribution function of the air gap length along the circumference. This function reaches its maximum value at the center of the slot and its minimum value at the inter-tooth position, and can be expressed as: ; In the formula, δ(α) is the distribution function of the air gap length along the circumference, α is the central angle, and g is the air gap length. b 0 represents the width of the stator slot.

[0110] Similar to the air gap length, the thickness of the permanent magnet is also a function of its position in the circumferential direction, such as... Figure 6 As shown. Figure 6This is a schematic diagram of the permanent magnet thickness function in this embodiment. The horizontal axis α represents the angular position corresponding to the circumferential direction, and the vertical axis... h m The thickness of the permanent magnet; by Figure 6 It can be seen that the thickness of the permanent magnet is along the circumferential direction. h m1 and h m2 The two values ​​show a step-like change, which corresponds to the structural characteristics of the aforementioned T-shaped permanent magnet, which is thick in the middle and thin on both sides.

[0111] Since it is assumed that the permeability of the stator and rotor cores is infinite, the magnetic reluctance in the equivalent magnetic circuit consists only of the air gap reluctance and the permanent magnet reluctance. Based on this, we can obtain the following... Figure 7 The equivalent magnetic circuit of the motor is shown. Figure 7 This is a schematic diagram of the equivalent magnetic circuit of the motor in this embodiment. Figure 7 middle, R m , R g ( α () are permanent magnet reluctance and air gap reluctance. r ( α ( ) represents the permanent magnet flux, and the three can be represented as follows: ; In the formula, μ 0 represents the free permeability, which is 4 × 10⁻⁶. 7 Wb / (A m); μ r The relative permeability of a permanent magnet; h m The thickness of the permanent magnet; A g , A m These represent the air gap area and the permanent magnet area, respectively.

[0112] Based on the magnetic reluctance and permanent magnet flux in the magnetic circuit, the air gap magnetic flux density can be expressed as: ; When Δ α As the magnetic flux density approaches infinity, the area of ​​the permanent magnet equals the area of ​​the reluctance magnet, and the above expression for the air gap magnetic flux density can be simplified to: ; The above formula is the analytical model of the air gap magnetic flux density at the average radius in this embodiment. This model uses the permanent magnet thickness function to reflect the influence of the T-shaped permanent magnet structure on the air gap magnetic flux density distribution, and reflects the cogging effect in the air gap length function. This reduces the modeling difficulty and provides an analytical basis for subsequent structural parameter optimization.

[0113] A well-designed T-type permanent magnet parameter structure is essential to realizing the advantages of this structure. This embodiment, based on the aforementioned air gap magnetic flux density analytical model and using the motor shown in Table 1 as a prototype, optimizes the structural parameters of the T-type permanent magnet rotor.

[0114] Table 1; ; In the optimization process of T-type permanent magnet parameters, to ensure comparability between different structural schemes, this embodiment uses maintaining the total volume of the permanent magnet as a basic constraint and maximizing the fundamental wave amplitude of the air gap magnetic flux density as the optimization objective. Adopting the constraint of maintaining the constant permanent magnet volume eliminates the magnetic field enhancement effect caused by increasing the amount of permanent magnet material, allowing the optimization results to more accurately reflect the influence of rotor topology and parameter allocation on electromagnetic performance. It also meets the practical need in motor engineering design to limit the cost and quantity of permanent magnet materials. Under this constraint, the optimization of the T-type permanent magnet rotor is not simply about increasing the size of the permanent magnet, but rather about increasing the effective main magnetic flux entering the air gap by reasonably adjusting key structural parameters such as the width of the top transverse magnet, the width of the longitudinal magnet, and its height. The optimization objective and constraint can be expressed as: ; Where X is the structural parameter vector of the T-type rotor permanent magnet; V pm This represents the total volume of the permanent magnet; V 0 represents the volume of the reference permanent magnet.

[0115] In the selection of key parameters, to ensure the rationality of the T-shaped permanent magnet rotor topology, the value range of each optimization variable needs to be constrained. Firstly, to avoid limiting the width of the top permanent magnet... w 1 less than w 2. This causes the rotor structure to evolve into an inverted T-shaped permanent magnet, weakening the expected magnetic field modulation effect. This paper will... w 2 represents w Multiples of 1, that is: ; To avoid rotor saturation due to excessively large hm2, its thickness is set at 0.75% of the rotor thickness, fixed at 7.5 mm. The structural optimization parameters and their ranges for the T-type permanent magnet are selected as follows: ; Regarding the above value range, the following explanations apply: When the k value exceeds 0.85, the cross-section of the permanent magnet is approximately rectangular, similar to traditional surface-mount magnets, and it loses its magnetic field modulation effect. When the k value is less than 0.15, its volume is too small, and its magnetic field modulation effect is low. h m1 The optimization range should be appropriately selected, within h m2The optimal range for the pole arc coefficient of surface-mount permanent magnets is 0.7-0.8, selected within one-third to two-thirds of the range. w The range of values ​​corresponds to the upper and lower limits of the optimal interval for the polar arc coefficient.

[0116] Because the T-type permanent magnet rotor has multiple optimization parameters, and these parameters interact with each other, using traditional single-factor scanning methods not only involves a large computational workload but also makes it difficult to find a satisfactory solution. Therefore, this embodiment employs the response surface methodology (RSM) to optimize the parameters of the T-type permanent magnet rotor. The RSM establishes an approximate functional relationship between design variables and the target response by selecting representative sample points within the design space, enabling multivariate optimization analysis with relatively few computations.

[0117] Based on the aforementioned optimization range, this embodiment uniformly selects 100 sets of sample points within the design space. For each set of parameters, the corresponding magnetic flux density waveform is calculated using the aforementioned air gap magnetic flux density analytical model, and the fundamental amplitude value of the air gap magnetic flux density corresponding to each set of parameters is obtained through Fourier decomposition. Subsequently, a response surface model is established using a quadratic polynomial: ; The quadratic response surface model was optimized using the numerical optimization function in the response surface methodology. The optimal parameter combination obtained was: w1 = 20.97 mm. h m1 =4.36mm; k =0.23mm, corresponding to w2=4.82mm. The rotor structure meets the requirements of unchanged total permanent magnet volume, reasonable topology, and engineering feasibility. Comparison of permanent magnets before and after optimization: Figure 8 As shown, by Figure 8 It is evident that, compared to the original permanent magnet structure, the optimized permanent magnet structure has adjusted the size distribution of each part while maintaining the same volume.

[0118] Figure 9 This is a schematic diagram comparing the harmonic distribution of the air gap magnetic flux density before and after optimization in this embodiment. Figure 9 It can be seen that the fundamental amplitude of the air gap magnetic flux density before optimization was 0.98T, while the fundamental amplitude of the air gap magnetic flux density after optimization reached 1.026T, an increase of about 4.7%. This result shows that, under the premise of unchanged permanent magnet content, the T-type permanent magnet rotor can increase the fundamental component of the air gap magnetic flux density and enhance the main magnetic field of the motor air gap.

[0119] After optimizing the structural parameters of the T-type permanent magnet rotor and analyzing the suppression effect of radial segmentation of the permanent magnet in conjunction with the eddy current loss formation mechanism, this embodiment selects a traditional surface-mounted AFPM motor and an AFPM motor using a T-type permanent magnet rotor as comparison objects to further verify the advantages of the T-type permanent magnet rotor in electromagnetic performance. The stator structures of the two motor configurations are the same, with differences only on the rotor side. The T-type permanent magnet rotor adopts the aforementioned optimized structural parameters. To reduce the performance difference caused by the difference in permanent magnet volume, the permanent magnet volume in the traditional surface-mounted scheme is the same as that in the T-type permanent magnet, so that the magnetic energy product of the two schemes remains consistent.

[0120] This embodiment uses the two-dimensional finite element method to simulate and verify AFPM motors with two rotor configurations. The two motors use the same mesh density and simulation conditions to ensure that the results are comparable.

[0121] In terms of air gap structure and magnetic flux path, the AFPM motor has similar characteristics to the Linear Synchronous Permanent Magnet Motor (LSPM motor). Based on this similarity, the AFPM motor can be equivalent to the LSPM motor, and its electromagnetic performance can be analyzed and calculated using the two-dimensional finite element method. Figure 10 This is a schematic diagram illustrating the process of equivalently modeling the AFPM motor into a two-dimensional LSPM motor model at the average radius in this embodiment. Figure 10 As shown, by selecting a cross section at the average radius of the AFPM motor and cutting and unfolding it along the generatrix of the cross section, a simplified two-dimensional LSPM motor model can be obtained. Figure 11 This is a schematic diagram of the two-dimensional equivalent model of the AFPM motor with two rotor configurations in this embodiment. Figure 11 The paper presents a two-dimensional equivalent model of a T-type permanent magnet rotor AFPM motor and a two-dimensional equivalent model of a traditional surface-mounted AFPM motor.

[0122] This embodiment mainly compares and analyzes the key electromagnetic performance indicators of the two rotor configurations from three aspects: air gap magnetic flux density distribution and back EMF characteristics under no-load conditions, and electromagnetic torque output capability under load conditions.

[0123] The air gap magnetic flux density distribution is a crucial fundamental parameter that determines the electromagnetic performance of a permanent magnet motor. Its waveform quality and fundamental amplitude directly affect the motor's flux linkage, back EMF, and torque output capability. Figure 12 This is a schematic diagram showing the air gap magnetic flux density and harmonic distribution of a conventional surface-mounted AFPM motor and a T-type permanent magnet rotor AFPM motor under no-load conditions, as described in this embodiment. Figure 12It can be observed that after adopting the T-type permanent magnet rotor, the amplitude of the air gap magnetic flux density is improved and the waveform is closer to a sine wave. This indicates that the T-type permanent magnet improves the transmission path of magnetic flux inside the rotor and in the air gap by redistributing the spatial layout of the permanent magnet, so that more magnetic flux can be effectively coupled into the air gap to form the main magnetic field.

[0124] Back EMF and flux linkage are important indicators for evaluating the no-load performance of permanent magnet motors. Their amplitudes are closely related to the main magnetic flux in the air gap, while their waveform quality is directly related to the distribution characteristics of the magnetic flux density in the air gap. Figure 13 This is a schematic diagram of the no-load flux linkage waveform and its harmonics for the two rotor configurations in this embodiment at the same speed. Figure 14 Table 2 shows the no-load back EMF waveform and its harmonics for the two rotor configurations in this embodiment at the same speed. Table 2 compares the no-load electromagnetic performance of AFPM motors with different rotor configurations.

[0125] Table 2; ; Table 2 shows that, while maintaining the same amount of permanent magnets, the adoption of T-type magnetic poles improves the no-load electromagnetic performance of the motor: the fundamental amplitude of the air gap magnetic flux density increases from 1.01T to 1.06T, an increase of approximately 4.95%, and the total harmonic distortion rate of the magnetic flux density decreases by 3.79%; the fundamental amplitudes of the flux linkage and back EMF increase by 6.67% and 6.66%, respectively, with corresponding decreases in the total harmonic distortion rate of 2.67% and 0.93%, respectively. These results indicate that T-type magnetic poles not only enhance the main air gap magnetic field and increase the effective fundamental component, but also play a positive role in improving the waveform quality of the air gap magnetic flux density. This improvement is directly reflected in the corresponding indicators of flux linkage and back EMF.

[0126] The above results demonstrate that, under the same permanent magnet quantity, T-shaped magnetic poles can enhance the effective main magnetic flux entering the air gap by optimizing the spatial distribution of permanent magnets, thereby strengthening the fundamental components of flux linkage and back EMF. For permanent magnet motors, higher air gap magnetic flux density, larger flux linkage amplitude, and higher back EMF fundamental value generally mean that the motor has a stronger electromagnetic torque output capability under the same current excitation, which is beneficial to improving the motor's torque density. In addition, T-shaped magnetic poles also exhibit a certain suppression effect on harmonic components, which helps to reduce torque ripple, improve motor operation smoothness, and also helps to reduce additional losses caused by higher harmonics, especially permanent magnet eddy current losses.

[0127] Further analysis of the data in Table 2 reveals that the total harmonic distortion rate of the flux linkage is significantly lower than that of the air gap magnetic flux density, indicating that the three-phase symmetrical winding structure has a certain suppressive effect on the third harmonic component in the flux linkage.

[0128] The improvement in air gap magnetic flux density amplitude and waveform quality brought about by the T-type permanent magnet rotor will ultimately be reflected in the torque output capability. To compare the load performance of the two rotor configurations, this embodiment conducted load electromagnetic torque simulation analysis on the surface-mounted AFPM motor and the T-type permanent magnet rotor AFPM motor under the same 50A rated current excitation.

[0129] Figure 15 This is a schematic diagram of the electromagnetic torque waveform and its harmonics for one electrical cycle under load conditions for the two rotor configurations in this embodiment. Table 3 lists the average torque and torque pulsation data for the two rotor configurations.

[0130] Table 3; ; Depend on Figure 15 As shown in Table 3, the T-type permanent magnet rotor AFPM motor can output a higher average electromagnetic torque when under load, which is related to its relatively high air gap magnetic flux density fundamental amplitude under no-load conditions; at the same time, since the total distortion rate of magnetic flux density harmonics of the T-type permanent magnet rotor AFPM motor is relatively low, its load torque pulsation is also relatively lower.

[0131] In summary, the T-shaped permanent magnet rotor structure proposed in this embodiment, by changing the cross-section of the surface-mounted permanent magnet from a uniform rectangle to a T-shape with a thicker middle and thinner sides, actively modulates the spatial distribution of the air gap magnetic flux density without increasing the amount of permanent magnets used. This makes the air gap magnetic flux density waveform closer to a sinusoidal distribution, achieving both harmonic suppression and fundamental frequency enhancement. Furthermore, the increase in the fundamental frequency amplitude of the air gap magnetic flux density can further drive the increase in the fundamental frequency amplitudes of the flux linkage and back EMF. The reduction in the harmonic content of the air gap magnetic flux density also helps to reduce the total harmonic distortion rate of the flux linkage and back EMF. This allows the motor to achieve higher electromagnetic torque output and lower torque ripple under the same current excitation, and helps to suppress additional losses caused by higher harmonics, especially permanent magnet eddy current losses. Overall, this contributes to improving the comprehensive electromagnetic performance and torque density of the AFPM motor.

[0132] This embodiment also provides an axial flux permanent magnet motor rotor design device, which is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0133] This embodiment provides a rotor design device for an axial flux permanent magnet motor, such as... Figure 16 As shown, it includes: Module 1601 is used to build a topological model of a permanent magnet rotor. In the topological model, permanent magnets are arranged in the rotor core along the circumferential direction. The permanent magnets include a first magnet segment and a second magnet segment located on both sides of the first magnet segment within each magnetic pole range along the circumferential direction. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment. The adjustment module 1602 is used to adjust the width and thickness parameters of the first and second magnet segments to obtain the target size parameters of the permanent magnet, with the goal of maximizing the fundamental wave amplitude of the air gap magnetic flux density, while keeping the total volume of the permanent magnet constant.

[0134] In one alternative implementation, the adjustment module 1602 is used to: Based on the axial thickness distribution of the first and second magnet segments along the circumferential direction, and the air gap length distribution along the circumferential direction, the distribution relationship of the air gap magnetic flux density along the circumferential direction is established. The amplitude of the fundamental component of the air gap magnetic flux density is calculated based on the distribution relationship, and used as the target quantity for evaluating the width and thickness parameters.

[0135] In one alternative implementation, the adjustment module 1602 is used to: Within the range of width and thickness parameters, multiple sets of sample parameter combinations are selected, and the air gap magnetic flux density base wave amplitude corresponding to each sample parameter combination is calculated through the distribution relationship. Based on the combination of parameters for each sample and the corresponding air gap magnetic flux density base wave amplitude, fit an approximate functional relationship between the width parameter and the thickness parameter and the air gap magnetic flux density base wave amplitude. The parameter combination that maximizes the fundamental wave amplitude of the air gap magnetic flux density is determined based on the approximate functional relationship and used as the target size parameter.

[0136] In one alternative implementation, in the topological model, the first magnet segment and the second magnet segment are made of the same permanent magnet material.

[0137] In an alternative implementation, the construction module 1601 is further configured to: When establishing the topological model, the circumferential width of the first magnet segment increases proportionally with the increase of the radial position. The ratio of the circumferential width of the first magnet segment at each radial position to the radial distance at that radial position is kept constant, so that the polar arc coefficient of the first magnet segment is the same at each radial position.

[0138] In one alternative implementation, the thickness parameter satisfies the following condition: The axial thickness of the second magnet segment is not less than one-third of the axial thickness of the first magnet segment, and not greater than two-thirds of the axial thickness of the first magnet segment.

[0139] In one optional implementation, in the topological model, the rotor core surface is provided with a groove corresponding to the position of the first magnet segment, the portion of the first magnet segment that exceeds the axial thickness of the second magnet segment is embedded in the groove, and the surfaces of the first magnet segment and the second magnet segment facing the air gap are flush.

[0140] In one alternative implementation, in the topological model, the two second magnet segments located on both sides of the first magnet segment have equal axial thickness and equal circumferential width, and the two second magnet segments are symmetrically arranged about the first magnet segment.

[0141] In one alternative embodiment, the device further includes: The partitioning module 1603 is used to divide the first magnet segment and / or the second magnet segment into multiple sub-units along the radial direction.

[0142] The axial flux permanent magnet motor rotor design device provided in this application embodiment can execute the axial flux permanent magnet motor rotor design method provided in any embodiment of this application, and has the corresponding functional modules and beneficial effects of the method. Further functional descriptions of the above modules and units are the same as those in the corresponding embodiments above, and will not be repeated here.

[0143] Figure 17 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0144] The following is a detailed reference. Figure 17 The diagram illustrates a structural schematic suitable for implementing the electronic device described in the embodiments of this application. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 1701, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 1702 or a program loaded from memory 1708 into random access memory (RAM) 1703. The RAM 1703 also stores various programs and data required for the operation of the electronic device. The processor 1701, ROM 1702, and RAM 1703 are interconnected via a bus 1704. An input / output (I / O) interface 1705 is also connected to the bus 1704.

[0145] Typically, the following devices can be connected to I / O interface 1705: input devices 1706 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 1707 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 1708 including, for example, magnetic tapes, hard disks, etc.; and communication devices 1709. Communication device 1709 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 17Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0146] Specifically, according to embodiments of this application, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this application include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via communication device 1709, or installed from memory 1708, or installed from ROM 1702. When the computer program is executed by processor 1701, it performs the functions defined in the axial flux permanent magnet motor rotor design method of embodiments of this application.

[0147] Figure 17 The electronic device shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of this application.

[0148] This application also provides a computer-readable storage medium. The methods described in this application can be implemented in hardware or firmware, or implemented as recordable on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the axial flux permanent magnet motor rotor design method shown in the above embodiments is implemented.

[0149] A portion of this application can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to this application through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0150] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and all such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A rotor design method for an axial flux permanent magnet motor, characterized in that, The method includes: A topological model of a surface-embedded permanent magnet rotor is established. In the topological model, a permanent magnet is arranged in the rotor core along the circumferential direction. The permanent magnet includes a first magnet segment and a second magnet segment located on both sides of the first magnet segment in each magnetic pole range along the circumferential direction. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment. Under the constraint of keeping the total volume of the permanent magnet constant, with the goal of maximizing the amplitude of the air gap magnetic flux density fundamental wave, the width and thickness parameters of the first and second magnet segments are adjusted to obtain the target size parameters of the permanent magnet.

2. The method according to claim 1, characterized in that, The adjustment of the width and thickness parameters of the first magnet segment and the second magnet segment includes: Based on the axial thickness distribution of the first magnet segment and the second magnet segment along the circumferential direction, and the air gap length distribution along the circumferential direction, the distribution relationship of the air gap magnetic flux density along the circumferential direction is established, and the amplitude of the fundamental component of the air gap magnetic flux density is calculated based on the distribution relationship, so as to serve as the target quantity for evaluating the width parameter and the thickness parameter.

3. The method according to claim 2, characterized in that, The adjustment of the width and thickness parameters of the first magnet segment and the second magnet segment further includes: Within the range of the width and thickness parameters, multiple sets of sample parameter combinations are selected, and the air gap magnetic flux density fundamental wave amplitude value corresponding to each sample parameter combination is calculated through the distribution relationship. Based on the combination of parameters for each sample and the corresponding air gap magnetic flux density base wave amplitude value for each combination of parameters, fit an approximate functional relationship between the width parameter and the thickness parameter and the air gap magnetic flux density base wave amplitude value. The parameter combination that maximizes the fundamental wave amplitude of the air gap magnetic flux density is determined based on the approximate functional relationship and used as the target size parameter.

4. The method according to claim 1, characterized in that, In the topological structure model, the first magnet segment and the second magnet segment are made of the same permanent magnet material.

5. The method according to claim 1, characterized in that, The method further includes: When establishing the topological model, the circumferential width of the first magnet segment increases proportionally with the increase of the radial position, and the ratio of the circumferential width of the first magnet segment at each radial position to the radial distance at that radial position is kept constant, so that the polar arc coefficient of the first magnet segment at each radial position is the same.

6. The method according to claim 1, characterized in that, The thickness parameter satisfies the following condition: The axial thickness of the second magnet segment is not less than one-third of the axial thickness of the first magnet segment, and not greater than two-thirds of the axial thickness of the first magnet segment.

7. The method according to claim 1, characterized in that, In the topological model, the rotor core surface has a groove corresponding to the position of the first magnet segment. The portion of the first magnet segment that exceeds the axial thickness of the second magnet segment is embedded in the groove. The surfaces of the first magnet segment and the second magnet segment facing the air gap are flush.

8. The method according to claim 1, characterized in that, In the topological model, the two second magnet segments located on both sides of the first magnet segment have equal axial thickness and equal circumferential width, and the two second magnet segments are symmetrically arranged about the first magnet segment.

9. The method according to claim 1, characterized in that, The method further includes: The first magnet segment and / or the second magnet segment are divided into multiple sub-units along the radial direction.

10. An axial flux permanent magnet motor, characterized in that, It includes a stator and a surface-embedded permanent magnet rotor, with an air gap formed between the stator and the surface-embedded permanent magnet rotor; The surface-embedded permanent magnet rotor includes a rotor core, and the rotor core is provided with permanent magnets along the circumferential direction; The permanent magnet includes a first magnet segment and a second magnet segment located on both sides of the first magnet segment in the circumferential direction within each magnetic pole range. The axial thickness of the first magnet segment is greater than the axial thickness of the second magnet segment.

Images