Rotor core design method

Abstract

The rotor core for an embedded magnet synchronous motor, which includes a magnet arrangement region and a flux barrier region, can be formed to be smooth overall while having a fine slit shape. [Solution] A rotor core design method for designing the shape of a rotor core comprising a magnet arrangement region and a flux barrier region involves arranging multiple Gaussian bases (52) in the design target region (50), defining a shape function by superimposing Gabor filters at wavelengths individually set for each of the multiple Gaussian bases (52), and using the shape function, determining a core cross-sectional shape that meets pre-set objective conditions using an optimization algorithm.

Description

[Technical Field]

[0001] The present invention relates to a rotor core design method. [Background technology]

[0002] In designing the shape of a rotor core, the core cross-sectional shape is sometimes determined by topology optimization using the finite element method. While various topology optimization techniques exist, the on / off method is particularly suitable because it allows for search independent of initial values.

[0003] An example of topology optimization using the on / off method is disclosed in the paper "Rotor Shape Optimization of Embedded Magnet Synchronous Motor by Topology Optimization Using a Normalized Gaussian Function Network" (Non-Patent Literature 1) by Takahiro Sato et al., published in the Transactions of the Institute of Electrical Engineers of Japan, D. In this Non-Patent Literature 1, the shape function is defined by superimposing spatially smoothly changing normalized Gaussian functions, and by assigning on / off states to each cell according to the positive or negative of its output, it is possible to form a rotor core with a smooth shape. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Takahiro Sato, et al., "Rotor Shape Optimization of Embedded Magnet Synchronous Motor by Topology Optimization Using a Normalized Gaussian Function Network," Transactions on Industry Applications, IEICE, 2015, Vol. 135, No. 3, pp. 291-298. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the method described in Non-Patent Document 1, while forming a smooth shape, had the drawback of resulting in a global shape because the on / off determination was made for a uniform distribution of Gaussian basis functions. For this reason, it was difficult to represent fine shapes, such as slit shapes, and was unsuitable for designing the shape of the rotor core of an embedded magnet synchronous motor that utilizes both magnet torque and reluctance torque.

[0006] Therefore, it is desirable to be able to form a rotor core for an embedded magnet synchronous motor, which has a magnet arrangement region and a flux barrier region, with a fine slit shape while being smooth overall. [Means for solving the problem]

[0007] The rotor core design method relating to this disclosure is: A rotor core design method for designing the shape of a rotor core comprising a magnet arrangement region where permanent magnets are arranged and a flux barrier region that restricts the flow of magnetic flux, In determining the core cross-sectional shape, which is the shape of the cross-section perpendicular to the rotation axis of the rotor core, by topology optimization using the finite element method, Multiple Gaussian bases are placed in the design area, and the shape function is defined by superimposing Gabor filters at wavelengths individually set for each of the multiple Gaussian bases. Using the aforementioned shape function, the core cross-sectional shape that meets the predetermined objective conditions is determined by an optimization algorithm.

[0008] According to this configuration, by defining the shape function using the Gabor filter, it becomes possible to perform on / off determination along the flux flow, and it becomes possible to represent a fine slit shape. At that time, by applying each Gabor filter corresponding to a plurality of Gaussian bases at a wavelength individually set for each Gaussian base, an optimal wavelength can be set for each Gaussian base. As a result, it is possible to achieve both a global shape and a fine shape. Therefore, by designing the shape of the rotor core according to this design method, a rotor core having a magnet arrangement region and a flux barrier region for an embedded magnet synchronous motor can be smoothly formed as a whole while having a fine slit shape.

[0009] Further features and advantages of the technology according to the present disclosure will become clearer from the following description of exemplary and non-limiting embodiments described with reference to the drawings.

Brief Description of the Drawings

[0010] [Figure 1] Schematic diagram of an embedded magnet synchronous motor of an embodiment [Figure 2] Image diagram of a design target area where a plurality of Gaussian bases are arranged [Figure 3] Image diagram showing a state where the wavelength of the Gabor filter is individually set for each Gaussian base [Figure 4] Core cross-sectional shape obtained by the NGnet method [Figure 5] Core cross-sectional shape obtained by the basic Gabor filter method [Figure 6] Core cross-sectional shape obtained by the improved Gabor filter method [Figure 7] Diagram showing the relationship between the wavelength for each Gaussian base and the level of refinement of the core cross-sectional shape [Figure 8] Schematic diagram showing an example of mesh division in the design target area [Figure 9] Schematic diagram showing an example of mesh division smoothed at the material boundary in the design target area

Modes for Carrying Out the Invention

[0011] An embodiment of the rotor core design method will be described with reference to the drawings. The rotor core design method of this embodiment is a method for designing the shape of the rotor core 32 of the rotor 30 that constitutes the embedded magnet synchronous motor 1 as shown in Figure 1.

[0012] As shown in Figure 1, the embedded magnet synchronous motor 1 comprises a stator 20 and a rotor 30 positioned opposite the stator 20. The stator 20 is fixed to a non-rotating member, such as a base or housing. The rotor 30 is positioned radially inward of the stator 20 and is supported so as to be rotatable relative to the stator 20.

[0013] The stator 20 comprises a stator core 22 having a plurality of slots 24, and coils 26 arranged in the slots 24 and wound around the stator core 22. The embedded magnet synchronous motor 1 may be, for example, a three-phase AC motor, in which case the coils 26 include three types of phase coils, such as U-phase coils, V-phase coils, and W-phase coils. The winding method of the coils 26 (each phase coil) is not particularly limited and may be concentric winding or distributed winding, and may be wave winding or overlapping winding. The number of slots 24 is also not particularly limited and is determined according to the number of phases and magnetic poles of the coils 26.

[0014] The rotor 30 comprises a rotor core 32 and permanent magnets 34 fixed within the rotor core 32. In this embodiment, one magnetic pole is formed by a pair of permanent magnets 34 arranged in a V-shape, and pairs of permanent magnets 34 forming the south pole and pairs of permanent magnets 34 forming the north pole are alternately arranged in the circumferential direction. The rotor 30 also includes flux barriers 36 at both ends of the permanent magnets 34 to restrict the flow of magnetic flux. In this embodiment, the flux barriers 36 are composed of voids, but they may also be composed of, for example, resin, varnish, and adhesives filled in the voids.

[0015] In this embodiment, the magnet arrangement region 44 is formed by holes into which the permanent magnets 34 are inserted. The flux barrier region 46 is formed by air gaps that constitute the flux barrier 36. Thus, the rotor core 32 comprises a magnet arrangement region 44 in which the permanent magnets 34 are arranged and a flux barrier region 46 that restricts the flow of magnetic flux.

[0016] In the rotor core design method of this embodiment (hereinafter referred to as "this design method"), the shape of the cross-section of the rotor core 32 perpendicular to the rotation axis X (hereinafter referred to as "core cross-sectional shape") is determined by topology optimization using the finite element method. The "shape" in the core cross-sectional shape mainly refers to the shape of the part that becomes the magnetic path (the part formed of magnetic material), and the bridge portion may also be included in the part that becomes the magnetic path. Below, we will briefly touch upon the outline of the method, and then explain the definition of the shape function, which is its key feature, while comparing it with other examples.

[0017] This design method includes a process for defining the design target area, a mesh generation process, a shape derivation process, and an optimization process.

[0018] In the design target area setting process, the design target area 50 is set to include the magnet arrangement area 44 and the flux barrier area 46 of the rotor core 32. In this embodiment, as shown in Figure 1, the shape of the rotor core 32 is rotationally symmetric (eight-fold symmetry in the illustrated example), and each magnetic pole (a pair of permanent magnets 34 arranged in a V-shape) is plane-symmetric with respect to its respective circumferential center. Taking this symmetry into consideration, in this embodiment, half of the area of ​​each magnetic pole is set as the design target area 50. Furthermore, in this embodiment, of the half of the area of ​​each magnetic pole in the rotor core 32, the area excluding the inner diameter side portion that is fitted to the rotor shaft and the rotor surface facing the stator 20 (in other words, the rotor surface facing the air gap) is set as the design target area 50.

[0019] In the meshing process, the design area 50 is divided into meshes to generate a mesh 54 consisting of a collection of many minute elements (cells 56) (see Figure 8). Figure 8 shows an example of generating a triangular mesh, but the shape of the mesh 54 is not particularly limited, and other shapes of meshes, such as a quadrilateral mesh, may be generated.

[0020] In the shape derivation process, the material distribution of each cell 56 included in the mesh 54 of the design target area 50 is determined, and the overall shape of that area is derived. That is, a material type is assigned to each cell 56, and the overall shape is derived. In this embodiment, for each cell 56, it is determined whether to place a magnetic material (e.g., an iron-based material such as electromagnetic steel or ferrite) or a non-magnetic material (e.g., air) at that position, and the sum of these determines the overall shape of the design target area 50 in the rotor core 32. In the example in Figure 8, the cells 56 in which magnetic material is placed are colored, and the shape of the rotor core 32 is determined by the combination of these cells. The cells 56 that are not colored are cells in which magnetic material is not placed, and the combination of these cells forms the flux barrier area 46.

[0021] The assignment of material types to each cell 56 can be done by defining a shape function that covers the design area 50, and depending on the sign of its output (i.e., the value of the shape function). For example, magnetic materials can be assigned to cells 56 where the value of the shape function is positive or zero, and non-magnetic materials can be assigned to cells 56 where the value of the shape function is negative. Here, the shape of the rotor core 32 is determined based on the material distribution of each cell 56, and the material distribution of each cell 56 is determined based on the output of the shape function. Therefore, how the shape function is defined is very important in order to obtain the desired core cross-sectional shape. The definition of this shape function will be described later.

[0022] In a single shape derivation process, the shape of the rotor core 32 determined based on the material distribution of each cell 56 becomes one candidate for a desirable core cross-sectional shape. The shape derivation process is performed repeatedly, and multiple (many) candidate desirable core cross-sectional shapes are derived.

[0023] In the optimization process, the core cross-sectional shape is optimized in relation to pre-set objective conditions, based on the candidate core cross-sectional shapes derived in the shape derivation process. Here, the objective conditions are conditions that define the desirable characteristics of the embedded magnet synchronous motor 1 equipped with the rotor core 32. The objective conditions include, for example, increasing the output torque, increasing the torque density, reducing torque ripple, and improving the strength against centrifugal force. The objective conditions may be a combination of two or more of these, and if they are a combination, they may be given priority in order of importance.

[0024] Needless to say, "optimization" in this embodiment does not necessarily mean determining the single most suitable core cross-sectional shape. If there is only one objective condition, there is usually only one optimal solution, and finding that solution constitutes optimization. On the other hand, if two or more objective conditions are combined as described above, there are usually multiple Pareto optimal solutions that have a trade-off relationship with each other, so finding the Pareto frontier or selecting a specific Pareto optimal solution from among them is also a form of optimization.

[0025] In the optimization process, an objective function is set according to the target conditions, and the core cross-sectional shape is determined so that the value of that objective function is maximized (or minimized). As described above, when multiple (many) candidate core cross-sectional shapes are derived in the repeatedly executed shape derivation process, the value of the objective function is calculated using each candidate shape as input. Candidate shapes that result in a higher (or lower) value of the objective function are extracted, and the shape function from which they originated is adjusted. That is, the shape function is redefined by fine-tuning the variables included in the shape function, using the shape function from which the candidate shape deemed preferable at that point originated. This is then used in the next shape derivation process and the subsequent optimization process to move in the direction of increasing (or decreasing) the value of the objective function.

[0026] Such optimization processes can be carried out using, for example, genetic algorithms (GA) or covariance matrix adaptation evolution strategies (CMA-ES).

[0027] The optimization process is repeatedly executed until predetermined termination conditions are met. These termination conditions may include, for example, the number of cycles from the shape derivation process to the optimization process reaching a predetermined number, or the change in the value of the objective function remaining below a baseline value for a predetermined number of consecutive times. Through this optimization process, the core cross-sectional shape that meets the predetermined objective conditions is finally determined.

[0028] As mentioned above, in the shape derivation process, how the shape function is defined is extremely important in order to obtain the desired core cross-sectional shape. Therefore, we will explain this point below, but in order to deepen the understanding of this design method, we will first explain an example using a normalized Gaussian network (NGnet), which is a well-known technique, and then proceed to explain this design method.

[0029] In this embodiment, the position and size of the permanent magnet 34 (magnet arrangement area 44) are predetermined and included in the initial conditions.

[0030] In the example using NGnet (hereinafter referred to as the "NGnet method"), first, as shown in Figure 2, multiple Gaussian bases 52 are placed in the design target region 50 so as to densely fill the region. Then, a spatially smoothly changing normalized Gaussian function is assigned to each of the multiple Gaussian bases 52, and the shape function is defined by the superposition of these normalized Gaussian functions. Specifically, the shape function y(x,w) is defined by the following equation.

[0031]

number

[0032] Here, N is the number of Gaussian functions, D is the dimension of the input x, and μ k and Σ k are the center vector and covariance matrix of the Gaussian function k, and w i is the combined weight of the normalized Gaussian function b i (x).

[0033] Using this shape function y(x, w), assign the material type to each cell according to the following.

[0034]

Equation

[0035] Candidate core cross-sectional shapes were derived according to these equations, and then the core cross-sectional shape was optimized by an optimization process. In this embodiment, as an example, optimization was performed with the objective conditions of increasing the outputable torque and reducing the torque ripple. In this example, priority was given to increasing the outputable torque. Specifically, the objective function F(p, θ e ) was defined as follows, and the analysis was advanced to minimize this objective function.

[0036]

Equation

[0037] Here, T ave (p, θ e ) is the average torque of the optimization model, T * ave is the average torque of the reference model, T rip (p, θ e ) is the torque ripple of the optimization model, T * rip is the torque ripple of the reference model. Also, p is a design variable of the topology optimization method, and θ e is a design variable of the initial electrical angle.

[0038] The calculation of the objective function for optimizing the core cross-sectional shape may be performed on the shape of one design area 50, or on the shape of one magnetic pole formed by placing two design areas 50 facing each other. Alternatively, multiple design areas 50 may be connected in the circumferential direction to perform the calculation on the shape of the entire rotor core 32.

[0039] Figure 4 shows the core cross-sectional shape optimized using the NGnet method as a comparative example. Although the NGnet method forms a smooth shape, it can be seen that the shape becomes global because on / off determination is made for a uniform distribution of Gaussian basis functions. For this reason, it is unsuitable for designing the shape of the rotor core 32 of the embedded magnet synchronous motor 1, which utilizes not only the torque due to the magnetic flux of the permanent magnet 34 (hereinafter referred to as "magnet torque") but also the torque due to the current flowing through the coil 26 (hereinafter referred to as "reluctance torque"), as in this embodiment.

[0040] Therefore, the inventors focused on Gabor filters, which are capable of determining on / off states along the flow of magnetic flux, and attempted to effectively utilize reluctance torque by defining a shape function using such a Gabor filter (hereinafter referred to as the "Gabor filter method").

[0041] In the Gabor filter method, similar to the NGnet method described above, first, multiple Gaussian bases 52 are placed in the design target region 50 so as to densely fill the region (see Figure 2). Then, in the Gabor filter method, a Gabor filter is assigned to each of the multiple Gaussian bases 52, and the shape function is defined by the superposition of these Gabor filters. Specifically, the shape function f(x,w,θ) is defined by the following equation.

[0042]

number

[0043] Here, N is the number of Gabor filters, and w i This is a Gabor filter g(x,θi ) are the bond weights. i (x) is a normalized Gaussian function, the same as the one used in the NGnet method described above. λ is the wavelength, and (X i ,Y i )=(xx i ,yy i ) is the position vector of the Gabor filter, and θ i is the rotation angle of the Gabor filter, and (x i ,y i ) are the central coordinates of the Gaussian basis.

[0044] Using this shape function f(x,w,θ), we assign a material type to each cell according to the following:

[0045]

number

[0046] Candidate core cross-sectional shapes were derived according to these equations, and then the core cross-sectional shapes were optimized through an optimization process. The optimization was performed under the same conditions as when using the NGnet method described above.

[0047] Figure 5 shows the core cross-sectional shape optimized using the Gabor filter method. The Gabor filter method yields a fine slit shape along the magnetic flux lines caused by the current flowing through the coil 26, suggesting that reluctance torque can be fully utilized. However, on the other hand, there was concern that the alternating arrangement of cores and air gaps around the permanent magnet 34 would prevent the full utilization of magnet torque, resulting in insufficient improvement in motor characteristics.

[0048] To address the above concerns, the Gabor filter method described in this design is an improved version of the Gabor filter method used in the initial stages of the study (hereinafter referred to as the "basic Gabor filter method" for distinction, and this method is also positioned as a comparative example). Hereafter, this will be referred to as the "improved Gabor filter method."

[0049] In the improved Gabor filter method, as with the NGnet method and the basic Gabor filter method described above, first, multiple Gaussian bases 52 are placed in the design target region 50 so as to densely fill the region. Then, in the improved Gabor filter method, the shape function is defined by superimposing Gabor filters at wavelengths individually set for each of the multiple Gaussian bases 52. Specifically, the shape function f(x,w,θ,λ) is defined by the following equation.

[0050]

number

[0051] Here, N is the number of Gabor filters, and w i This is a Gabor filter g(x,θ i ) are the bond weights. i (x) is a normalized Gaussian function, the same as the one used in the NGnet method described above. λ i is the wavelength, and (X i ,Y i )=(xx i ,yy i ) is the position vector of the Gabor filter, and θ i is the rotation angle of the Gabor filter, and (x i ,y i ) are the central coordinates of the Gaussian basis.

[0052] Furthermore, while λ in the basic Gabor filter method was a fixed wavelength and therefore a constant, in the improved Gabor filter method, λ i It is important to emphasize here that these are individual wavelengths set for each of the 52 Gaussian bases and are therefore variables. In Figure 3, the magnitude of the wavelengths set for each of the 52 Gaussian bases is represented by the intensity of the color assigned to each of the 52 Gaussian bases.

[0053] Using this shape function f(x,w,θ,λ), we assign a material type to each cell according to the following:

[0054]

number

[0055] Candidate core cross-sectional shapes were derived according to these equations, and then the core cross-sectional shapes were optimized through an optimization process. The optimization was performed under the same conditions as when using the NGnet method or the basic Gabor filter method described above.

[0056] Figure 6 shows the core cross-sectional shape optimized using the improved Gabor filter method as an example. It can be seen that the improved Gabor filter method achieves both a global shape similar to that of the NGnet method, the first comparative example, and a fine slit shape similar to that of the basic Gabor filter method, the second comparative example. Since a global shape is formed around the magnetization surface of the permanent magnet 34, it is presumed that the magnet torque can be fully utilized. Furthermore, since fine slit shapes that adjust the flow of magnetic flux due to the current flowing through the coil 26 are formed near the ends of the permanent magnet 34 and at positions away from the permanent magnet 34, it is presumed that the reluctance torque can be fully utilized. Thus, this design method using the improved Gabor filter method makes it possible to form a rotor core 32 of a high-performance embedded magnet synchronous motor 1 that can effectively utilize both magnet torque and reluctance torque.

[0057] Figure 7 shows the optimized core cross-sectional shape and the wavelengths of the Gabor filter for each of the 52 Gaussian bases in the shape function from which it was derived. From this figure, it was confirmed that a global shape is formed in the region where the wavelength of the Gabor filter is long, regardless of whether it is a core or an air gap, and a fine slit shape is formed in the region where the wavelength of the Gabor filter is short. In this design method (improved Gabor filter method), the wavelength of the Gabor filter can be set individually for each of the 52 Gaussian bases, and by optimizing including these wavelengths, it has become possible to suitably design the shape of the rotor core 32 of the embedded magnet synchronous motor 1.

[0058] In this design method using the improved Gabor filter technique, further improvements can be made depending on the target conditions set during the optimization process.

[0059] For example, if the objective condition involves increasing the torque density in addition to increasing the output torque, it is conceivable to evaluate the magnet torque and reluctance torque separately during the optimization process. More specifically, first, current is passed through the coil 26 of the stator 20, and a magnetic field analysis is performed with both the stator 20 and the rotor 30 energized together with the permanent magnet 34. Then, the obtained permeability is fixed, and the analysis is performed with only one of them energized, thereby individually evaluating the influence of each magnetomotive force source (i.e., magnet torque and reluctance torque).

[0060] By determining the magnet torque and reluctance torque separately, it becomes possible to incorporate terms related to them into the objective function. In the example described above, by incorporating a term for reluctance torque alone, in addition to the term for the output torque, it is possible to increase the reluctance torque while simultaneously increasing the total output torque. A larger contribution from reluctance torque makes it possible to miniaturize the rotor 30 while still achieving the same level of total torque output. As a result, the torque density can be increased.

[0061] Furthermore, for example, if the objective condition includes improving the strength against centrifugal force (hereinafter referred to as "centrifugal stress"), it is conceivable to perform the mesh division of the design target area 50, which forms the basis for the shape derivation and optimization processes, based on a shape function. The example shown in Figure 8 is an example of normal mesh division (fixed mesh), in which the core cross-sectional shape (boundary between the core and the void) derived in the shape derivation process is irregular depending on the shape of the mesh 54. Such an irregular shape has many singularities, and there is concern that the accuracy of centrifugal stress calculations in structural analysis will decrease.

[0062] In such cases, when meshing the design target area 50, it is effective to generate the mesh 54 such that at least one of the mesh boundaries aligns with the equilateral plane 60 of the shape function, as shown in Figure 9. In particular, it is preferable to generate the mesh 54 such that at least one of the mesh boundaries aligns with the equilateral plane 60 (zero equilateral plane) where the value of the shape function is zero. Since the zero equilateral plane of the shape function is a reference plane for assigning material types to each cell, generating the mesh 54 so that the mesh boundaries align with it allows for smoothing of the core cross-sectional shape (boundary between the core and the void) derived in the shape derivation process. This allows for accurate calculation of centrifugal stress in structural analysis and enables appropriate improvement of the centrifugal stress of the rotor core 32.

[0063] [Other Embodiments] (1) In the above embodiment, a configuration in which the position and size of the permanent magnet 34 (magnet arrangement area 44) are predetermined was described as an example. However, the configuration is not limited to such a configuration, and the position and size of the permanent magnet 34 may be variable, and the core cross-sectional shape may be designed including the position and size of the magnet arrangement area 44. In this case, the shape function can be defined by a combination of two functions using a Gabor filter, and three material types (core / magnet / air gap) can be assigned based on the combination of positive and negative outputs.

[0064] (2) In this case, it is also possible to change the configuration of the magnetic poles using the permanent magnets 34. For example, one magnetic pole may be composed of two types of permanent magnets 34 whose magnetized surfaces face different directions even when considering symmetry. In such cases, the shape function can be defined by a combination of two functions using a Gabor filter, and the core cross-sectional shape can be designed by assigning four material types (core / magnet 1 / magnet 2 / air gap) based on the combination of positive and negative outputs.

[0065] (3) In the above embodiment, an example was described in which only objective conditions are set in the optimization process and a core cross-sectional shape that conforms to those objective conditions is determined. However, the embodiment is not limited to such an embodiment, and for example, constraint conditions may be set in addition to objective conditions in the optimization process. In this case, processing such as excluding candidate shapes that conform to the constraint conditions may be performed. For example, when designing the core cross-sectional shape including the position and size of the magnet placement area 44, from the viewpoint of practicality, constraint conditions may be imposed on the shape and size of the magnet placement area 44, such as the cross-sectional shape being rectangular or the dimensions being realistic.

[0066] (4) In the above embodiment, a configuration in which one magnetic pole is formed by a pair of permanent magnets 34 arranged in a V-shape was described as an example. However, the configuration is not limited to such a configuration, and the pair of permanent magnets 34 may be arranged vertically or horizontally parallel to each other. Also, one magnetic pole may be composed of one permanent magnet 34 arranged vertically or horizontally, or it may be composed of a combination of three or more permanent magnets 34 in any arrangement.

[0067] (5) The configurations disclosed in each of the above-described embodiments (including the above-described embodiments and other embodiments; the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as this does not cause a conflict. With respect to other configurations, the embodiments disclosed herein are illustrative in all respects and can be modified as appropriate without departing from the spirit of this disclosure.

[0068] [Overview of the Embodiment] In summary, the rotor core design method according to this disclosure preferably comprises the following configurations.

[0069] A rotor core design method for designing the shape of a rotor core (32) comprising a magnet arrangement region (44) where permanent magnets (34) are arranged, and a flux barrier region (46) that restricts the flow of magnetic flux, In determining the core cross-sectional shape, which is the shape of the cross-section perpendicular to the rotation axis (X) of the rotor core (32), by topology optimization using the finite element method, Multiple Gaussian bases (52) are placed in the design target region (50), and the shape function is defined by superimposing Gabor filters at wavelengths individually set for each of the multiple Gaussian bases (52). Using the aforementioned shape function, the core cross-sectional shape that meets the predetermined objective conditions is determined by an optimization algorithm.

[0070] This configuration allows for on / off determination along the flow of magnetic flux by defining the shape function using a Gabor filter, making it possible to represent fine slit shapes. In this case, by applying each Gabor filter corresponding to multiple Gaussian bases (52) at wavelengths individually set for each Gaussian base (52), the optimal wavelength can be set for each Gaussian base (52). As a result, both global and fine shapes can be achieved. Therefore, by designing the shape of the rotor core (32) according to this design method, a rotor core (32) equipped with a magnet arrangement region (44) and a flux barrier region (46) for an embedded magnet synchronous motor can be formed with a fine slit shape while being smooth overall.

[0071] As one aspect, The rotor core (32) is positioned opposite the stator (20) which is equipped with a coil (26). The aforementioned objective condition includes increasing the output torque, In the optimization algorithm described above, it is preferable to evaluate separately the torque due to the magnetic flux of the permanent magnet (34) and the torque due to the current flowing through the coil (26).

[0072] With this configuration, the core cross-sectional shape can be determined so as to prioritize increasing either the torque due to the magnetic flux of the permanent magnet (34) or the torque due to the current flowing through the coil (26), while primarily aiming to increase the total output torque.

[0073] As one aspect, The aforementioned objective condition includes improving the strength against centrifugal force, In the finite element method described above, when dividing the design target region (50) into meshes, it is preferable to generate a plurality of meshes (54) such that any of the mesh boundaries are aligned along the equilateral surfaces (60) of the shape function.

[0074] With this configuration, the boundaries of different materials derived according to the positive or negative output of the shape function are smoothed, allowing the optimization algorithm to accurately calculate the strength against centrifugal force. Therefore, the core cross-sectional shape can be determined more appropriately to improve the strength against centrifugal force.

[0075] The rotor core design method described herein only needs to achieve at least one of the effects described above.

[0076] A rotor core (32) having a core cross-sectional shape determined by any of the rotor core design methods described above is also disclosed herein.

[0077] Furthermore, a rotor core design apparatus for realizing any of the rotor core design methods described above is also disclosed herein. Such a rotor core design apparatus may include a functional unit for performing a design target area setting process, a functional unit for performing a meshing process, a functional unit for performing a shape derivation process, and a functional unit for performing an optimization process. Each of these functional units may be provided in a single information processing device, or they may be distributed among multiple information processing devices that can communicate via a network. [Explanation of Symbols]

[0078] 1: Embedded magnet synchronous motor, 20: Stator, 22: Stator core, 24: Slot, 26: Coil, 30: Rotor, 32: Rotor core, 34: Permanent magnet, 36: Flux barrier, 44: Magnet placement area, 46: Flux barrier area, 50: Design area, 52: Gaussian base, 54: Mesh, 56: Cell, 60: Equilateral surface, X: Rotation axis

Claims

1. A rotor core design method for designing the shape of a rotor core comprising a magnet arrangement region where permanent magnets are arranged and a flux barrier region that restricts the flow of magnetic flux, In determining the core cross-sectional shape, which is the shape of the cross-section perpendicular to the rotation axis of the rotor core, by topology optimization using the finite element method, Multiple Gaussian bases are placed in the design area, and the shape function is defined by superimposing Gabor filters at wavelengths individually set for each of the multiple Gaussian bases. A rotor core design method that uses the shape function described above to determine the core cross-sectional shape that meets pre-set objective conditions using an optimization algorithm.

2. The rotor core is positioned opposite the stator, which is equipped with coils. The aforementioned objective condition includes increasing the output torque, The rotor core design method according to claim 1, wherein the optimization algorithm separately evaluates the torque due to the magnetic flux of the permanent magnet and the torque due to the current flowing through the coil.

3. The aforementioned objective condition includes improving the strength against centrifugal force, The rotor core design method according to claim 1, wherein, in the finite element method, when meshing the design target region, the mesh is generated such that any of the mesh boundaries are aligned along the equilateral planes of the shape function.

4. A rotor core having the core cross-sectional shape determined by the rotor core design method according to any one of claims 1 to 3.

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