Oil-cooled type magnetic flux switching permanent magnet traction motor thermal analysis method and device

Abstract

The application provides an oil-cooled magnetic flux switching permanent magnet traction motor thermal analysis method and device, relates to the motor design technical field, and includes the following steps: determining the geometric parameters and material parameters of each component in the motor to be analyzed; abstracting and dividing each component in physics into at least one lumped thermodynamic node; determining the connection mode of each lumped thermodynamic node based on the heat transfer characteristics of each component, and establishing a parameter matrix; determining the key heat transfer parameters of the motor to be analyzed; and constructing a lumped parameter thermal network model based on the lumped thermodynamic nodes and the parameter matrix and the key heat transfer parameters. The method and device provided by the application convert the complex continuous heat transfer problem into a discrete problem for solving, have fast calculation, greatly improve the calculation efficiency, can be reanalyzed only by modifying the corresponding parameters, provide convenience for fast thermal analysis and optimization of the motor in the early design stage, and improve the thermal analysis efficiency and accuracy.

Description

Technical Field

[0001] This application relates to the field of motor design technology, and in particular to a thermal analysis method and apparatus for an oil-cooled flux-switching permanent magnet traction motor. Background Technology

[0002] In-wheel motors, as an advanced distributed drive solution, have received considerable attention in recent years. They provide core support for chassis architecture innovation in the new energy vehicle sector and demonstrate significant potential in cutting-edge technologies such as independent wheel drive in rail transit. In-wheel motors place the motor directly within the wheel hub, driving the wheel directly, offering advantages such as small size and high efficiency. However, due to the harsh environment and poor heat dissipation of the motor within the hub, excessively high motor temperatures accelerate the aging of insulation materials and cause irreversible demagnetization of permanent magnets, significantly shortening their lifespan. Therefore, solving the technical challenge of heat dissipation is crucial for in-wheel motors. For in-wheel motor selection, permanent magnet motors are a better choice, offering reliable and flexible operation, eliminating the need for excitation windings on the rotor, reducing size and weight, and improving efficiency. Among them, the flux-switching permanent magnet motor is a type of stator permanent magnet motor. Its stator is mainly assembled from flux switchers, which consist of a set of electromagnets and a set of magnetic conductors. When the electromagnets are energized, the flux switcher transfers the magnetic flux from one magnetic conductor to another, changing the path of the magnetic flux and thus converting electrical energy into mechanical energy. The rotor of an external rotor flux-switching permanent magnet motor is typically a salient-pole structure, and it rotates along with the casing during operation. If cooling oil is added directly into the motor cavity, the motor's own agitation can achieve direct cooling without an external circulation system, greatly improving efficiency.

[0003] In the field of motor thermal analysis, the finite element method (FEM) is currently the mainstream approach. Based on a precise geometric model of the motor, the FEM can achieve fluid-thermal coupling, automatically calculate complex flow and heat transfer phenomena, and boasts high computational accuracy. However, the FEM requires high-quality discretized meshes, involves a massive computational load, and is very slow. Furthermore, it requires reprocessing for motor models of different sizes, lacks flexibility, and is difficult to integrate with electromagnetic analysis of the motor to achieve electromagnetic-thermal coupling optimization.

[0004] Therefore, how to provide a thermal analysis method for permanent magnet traction motors of various sizes that is fast and accurate has become a technical problem that the industry urgently needs to solve. Summary of the Invention

[0005] This application provides a thermal analysis method and apparatus for oil-cooled flux-switching permanent magnet traction motors, which can be used to perform rapid and accurate thermal analysis on oil-cooled flux-switching permanent magnet traction motors of various sizes.

[0006] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor, including: Determine the geometric and material parameters of each component in the motor to be analyzed; The components are physically abstracted and divided into at least one lumped thermodynamic node; The connection method of each lumped thermodynamic node is determined based on the heat transfer characteristics of each component, and a parameter matrix including lumped thermal resistance, lumped thermal conductivity and lumped heat capacity is established. Determine the key heat transfer parameters of the motor to be analyzed; the key heat transfer parameters include the equivalent thermal conductivity of the winding, contact thermal resistance, and convective heat transfer resistance. Based on the lumped thermodynamic nodes, the parameter matrix, and the key heat transfer parameters, a lumped parameter thermal network model of the motor to be analyzed is constructed.

[0007] In some embodiments, determining the geometric and material parameters of each component in the motor to be analyzed includes: Considering the geometric features of each component that affect heat transfer, determine the axial, radial, and angular parameters of each component in cylindrical coordinates, or determine the parameters of each component's coordinate axes in Cartesian coordinates. Thermal conductivity, specific heat capacity, and density are defined as the material parameters.

[0008] In some embodiments, physically abstracting and dividing the various components into at least one lumped thermodynamic node includes: Based on the physical characteristics of each component, each component is divided into at least one lumped thermodynamic node; the number of lumped thermodynamic nodes is determined based on the heat generation and / or temperature calculation accuracy of each component.

[0009] In some embodiments, the equivalent thermal conductivity of the winding is determined based on the following steps: The tangential radial equivalent thermal conductivity of the winding is determined based on the thermal conductivity of each component in the stator winding slot and the total area of ​​each component in the stator winding slot. The axial equivalent thermal conductivity of the winding is determined based on the thermal conductivity of copper in each component and the motor slot fill factor.

[0010] In some embodiments, the contact thermal resistance is determined based on the following steps: The contact thermal resistance between the two components is determined based on the equivalent air gap thickness and contact area between the two contacting components, as well as the thermal conductivity of air.

[0011] In some embodiments, the motor to be analyzed is an oil-cooled flux-switching permanent magnet traction motor.

[0012] In some embodiments, the convective heat transfer resistance is determined based on the following steps: For oil-cooled flux-switching permanent magnet traction motors, the forced convection heat transfer coefficient of the cooling medium generated by the motor's rotation agitating the internal cooling oil is calibrated using particle method simulation or experimental data. And the environmental natural convection heat transfer coefficient between the motor casing and the external ambient air is calculated using empirical formulas.

[0013] This application provides a thermal analysis device for an oil-cooled flux-switching permanent magnet traction motor, comprising: The determination module is used to determine the geometric and material parameters of each component in the motor to be analyzed; The partitioning module is used to physically abstract and divide each component into at least one lumped thermodynamic node; A module is established to determine the connection method of each lumped thermodynamic node based on the heat transfer characteristics of each component, and to establish a parameter matrix including lumped thermal resistance, lumped thermal conductivity and lumped heat capacity. The calculation module is used to determine the key heat transfer parameters of the motor to be analyzed; the key heat transfer parameters include the equivalent thermal conductivity of the winding, the contact thermal resistance, and the convective heat transfer resistance. A construction module is used to construct a lumped parameter thermal network model of the motor to be analyzed based on the lumped thermodynamic nodes, the parameter matrix, and the key heat transfer parameters.

[0014] This application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the traction motor thermal analysis method.

[0015] This application provides a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the aforementioned thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor.

[0016] This application provides a thermal analysis method and apparatus for an oil-cooled flux-switching permanent magnet traction motor. By transforming the complex continuum heat transfer problem into a discrete problem similar to a circuit network, it avoids the complex mesh discretization and massive partial differential equation solving process of the traditional finite element method. It only requires focusing on the top-level settings of the motor thermal model, such as geometric parameters, heat transfer methods between components, and cooling methods. The parameter matrix is ​​then constructed and the results are obtained through simple matrix operations. It features fast calculation and ease of implementation, thus greatly improving computational efficiency. At the same time, the model is based on parameterization. When the motor size, operating conditions, or materials change, only the corresponding parameters need to be modified for re-analysis, which has high flexibility. This provides convenience for rapid thermal analysis and optimization of permanent magnet traction motors in the early design stage, improving the efficiency and accuracy of thermal analysis. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the 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 based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of an oil-cooled flux-switching permanent magnet traction motor example provided in this application.

[0020] Figure 2 This is a flowchart illustrating the thermal analysis method for permanent magnet traction motors provided in this application.

[0021] Figure 3 This is a schematic diagram of the lumped thermodynamic node provided in this application.

[0022] Figure 4 This is a schematic diagram of the equivalent method for motor windings provided in this application.

[0023] Figure 5 This is a schematic diagram of the particle method simulation results at different rotational speeds provided in this application.

[0024] Figure 6 This is a schematic diagram comparing the predicted steady-state temperature rise of the motor winding under rated operating conditions with experimental data provided in this application.

[0025] Figure 7 This is a schematic diagram comparing the predicted steady-state temperature rise of the permanent magnet under rated operating conditions of the motor provided in this application with the experimental data.

[0026] Figure 8 This is a schematic diagram comparing the predicted results of transient temperature rise of the motor winding under peak operating conditions provided in this application with experimental data.

[0027] Figure 9 This is a schematic diagram comparing the predicted results of transient temperature rise of permanent magnet under peak operating conditions of the motor provided in this application with experimental data.

[0028] Figure 10 This is a schematic diagram of the thermal analysis device for permanent magnet traction motors provided in this application.

[0029] Figure 11 This is a schematic diagram of the structure of the electronic device provided in this application.

[0030] Figure label: 1: Shaft; 2: Bushing; 3: Permanent magnet; 4: Winding; 5: Stator core; 6: Rotor; 7: Housing; 8: Copper conductor; 9: Enamel film; 10: Groove insulation paper; 11: Encapsulation and air; 12: Equivalent solid; 14: Rotor yoke node; 15: Rotor tooth node; 16: Air gap; 17: In-slot winding node; 18: End winding node; 19: Stator tooth node; 20: Stator yoke node; 21: Upper permanent magnet node; 22: Lower permanent magnet node; 23: Cooling oil; 1010: Define module; 1020: Divide module; 1030: Create module; 1040: Calculate module; 1050: Construct module; 1110: Processor; 1120: Communication interface; 1130: Memory; 1140: Communication bus. Detailed Implementation

[0031] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0032] It should be noted that the terms "first," "second," etc., used in this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that comprises a series of steps, units, or modules is not necessarily limited to those explicitly listed, but may include other steps, units, or modules not explicitly listed or inherent to such processes, methods, products, or devices.

[0033] Hub motors are a type of traction motor used in distributed drives. Figure 1 This is a schematic diagram of an oil-cooled flux-switching permanent magnet traction motor example provided in this application, such as... Figure 1 As shown, the components of the motor may include a rotating shaft 1, a bushing 2, a permanent magnet 3, a winding 4, a stator core 5, a rotor 6, and a housing 7.

[0034] The motor has a salient-pole rotor with an air gap between the stator and rotor. The stator is composed of alternating U-shaped modular stator cores and permanent magnets. The windings are three-phase symmetrical AC windings using round copper wire. The motor described in this application uses an oil-cooling method, where cooling oil is directly added to the motor cavity, and the rotation and agitation of the salient-pole rotor and the casing directly cool the various components of the motor.

[0035] Figure 2 This is a flowchart illustrating the thermal analysis method for permanent magnet traction motors provided in this application, as shown below. Figure 2 As shown, the method includes steps 210, 220, 230, 240 and 250.

[0036] Step 210: Determine the geometric and material parameters of each component in the motor to be analyzed.

[0037] Specifically, the entity executing the thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor provided in this application is an oil-cooled flux-switching permanent magnet traction motor thermal analysis device or system. This device can be implemented through software, such as an oil-cooled flux-switching permanent magnet traction motor thermal analysis program; it can also be a device executing the oil-cooled flux-switching permanent magnet traction motor thermal analysis method, such as a mobile terminal, tablet computer, desktop computer, or server.

[0038] The motor to be analyzed can be a permanent magnet traction motor cooled by methods such as oil cooling, forced air cooling, and water cooling. The method provided in this application will be described below using an oil-cooled flux-switching permanent magnet traction motor as an example. As mentioned above, the motor components may include a shaft, bushing, permanent magnet, windings, stator core, rotor, and housing.

[0039] Geometric parameters refer to the data used to describe the dimensions, shape, and relative positions of these components. For the convenience of subsequent calculations, the geometric model of the motor can be appropriately simplified, for example, ignoring minor features such as chamfers and mounting holes that have little impact on overall heat transfer, retaining only the main geometric contours. Geometric parameters can be defined in various ways. For example, they can be described using coordinate parameters of the three axes in a three-dimensional Cartesian coordinate system, or, based on the rotational symmetry characteristics of the motor, using axial, radial, and angular parameters in a cylindrical coordinate system.

[0040] Material parameters refer to the physical properties of the materials used in various components. These properties directly determine the heat transfer and storage capacity within and between components. For thermal analysis, the most crucial material parameters typically include: thermal conductivity (unit: W / (m·K), which characterizes the material's ability to conduct heat; specific heat capacity (unit: J / (kg·K), which characterizes the amount of heat absorbed by a unit mass of material when its temperature increases by 1 K (Kelvin); and density (unit: kg / m³). 3 (kg per cubic meter). These parameters form the basis for subsequent calculations of lumped thermal resistance, lumped thermal conductivity, and lumped heat capacity.

[0041] Step 220: Physically abstract each component and divide it into at least one lumped thermodynamic node.

[0042] Specifically, a lumped thermodynamic node can be understood as a virtual point or region in space that is lumped together and has a uniform temperature. Each node represents the average thermodynamic state of its corresponding physical region and is considered to have a concentrated heat capacity.

[0043] A physical component can be abstracted and divided into one or more lumped thermodynamic nodes. The granularity of the division can be adjusted according to actual needs. For example, for components with simple shapes and small internal temperature differences (such as shafts), the entire component can be divided into a single node. However, for critical components with large heat generation and drastic temperature gradient changes (such as windings that generate major copper losses), or components whose temperature distribution needs to be closely monitored (such as temperature-sensitive permanent magnets), it is necessary to divide them into multiple nodes to obtain more accurate temperature distribution information. For example, it can be divided into multiple sub-regions along the axial, radial, and / or circumferential directions, with each sub-region corresponding to a node. Increasing the number of nodes can improve the accuracy of the model's description of the temperature distribution.

[0044] Step 230: Determine the connection method of each lumped thermodynamic node based on the heat transfer characteristics of each component, and establish a parameter matrix including lumped thermal resistance, lumped thermal conductivity and lumped heat capacity.

[0045] Specifically, the connection method defines the heat transfer path between nodes. If there is a direct heat conduction or convection path between the physical regions represented by two nodes, then these two nodes are connected in the thermal network. Heat always flows from nodes with higher temperatures to nodes with lower temperatures. Heat sources and heat capacity are added directly to the nodes; heat capacity can be ignored in steady-state temperature rise calculations, and nodes are connected by thermal resistance.

[0046] After determining the connection method, a parameter matrix describing the entire thermal network needs to be established. This parameter matrix is ​​the basis for mathematically solving the model, and it typically records the parameter values ​​of all components in the network. These parameters mainly include lumped thermal resistance, lumped thermal conductance, and lumped heat capacity.

[0047] Lumped thermal resistance describes the degree to which heat flow is impeded between nodes, corresponding to conductive and convective thermal resistance. Lumped thermal conductance, the reciprocal of lumped thermal resistance, describes the ability to conduct heat between nodes. Lumped heat capacity describes the ability of each node to store thermal energy, determined by the mass and specific heat capacity of its corresponding physical region. Lumped heat capacity can be ignored in steady-state temperature rise calculations; however, it is an essential parameter for transient temperature rise analysis.

[0048] In addition, a connection matrix can be established to describe the network topology and record the connection relationships between nodes.

[0049] Step 240: Determine the key heat transfer parameters of the motor to be analyzed; key heat transfer parameters include the equivalent thermal conductivity of the windings, contact thermal resistance, and convective heat transfer resistance.

[0050] Specifically, in the thermal network model, some heat transfer parameters cannot be easily found in material handbooks due to the complexity of their physical processes, but they are crucial to the accuracy of the model. In this embodiment, these parameters are defined as key heat transfer parameters. These parameters include the equivalent thermal conductivity of the windings, contact thermal resistance, and convective heat transfer resistance.

[0051] Actual motor windings are complex composite structures comprising copper wires, varnish, slot insulation, and filling air or potting compound. Directly modeling these microstructures is impractical. Therefore, it is necessary to treat the winding as an equivalent entity with uniform properties and determine its equivalent thermal conductivity. This parameter comprehensively reflects the macroscopic thermal conductivity under the combined effects of multiple materials.

[0052] Due to limitations in machining precision and assembly processes, the contact surfaces between internal components of a motor (such as the mating surface between the stator core and the housing) are not in perfect contact. Their surfaces have microscopic roughness and unevenness, resulting in tiny gaps filled with air or other media between the contact surfaces. These gaps significantly impede heat transfer; this additional thermal resistance is known as contact thermal resistance.

[0053] Convective thermal resistance describes the heat transfer capacity between a solid surface and a fluid (such as internal cooling oil or external ambient air). In the oil-cooled motor described in this application, the internal cooling oil undergoes complex forced convection due to the rotation of the rotor, and its heat transfer capacity directly affects the motor's heat dissipation performance. Simultaneously, natural or forced convection heat dissipation also occurs between the motor casing and the ambient air. The heat transfer capacity of these convection processes is characterized by convective thermal resistance.

[0054] These key heat transfer parameters can be determined through various methods, such as theoretical analysis, numerical simulation, or experimental measurement.

[0055] Step 250: Based on the lumped thermodynamic nodes and parameter matrix, as well as the key heat transfer parameters, construct the lumped parameter thermal network model of the motor to be analyzed.

[0056] Specifically, the key heat transfer parameters (equivalent thermal conductivity, contact thermal resistance, convective heat transfer resistance, etc.) determined in the previous step are calculated and integrated into the established parameter matrix, thus completing the assignment of values ​​to all parameters such as thermal resistance and heat capacity.

[0057] At this point, a complete lumped-parameter thermal network model (referred to as the thermal network model) has been constructed. Mathematically, this model can be expressed as a system of algebraic equations. By taking the heat sources generated during motor operation (such as copper losses in the windings and iron losses in the core) as input (equivalent to current sources in a circuit), and solving this system of equations, the temperature value of each lumped thermodynamic node (equivalent to the voltage value in a circuit) can be quickly obtained, thereby enabling the analysis and prediction of the entire motor temperature field.

[0058] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor. By transforming the complex continuum heat transfer problem into a discrete problem similar to a circuit network, it avoids the complex mesh discretization and massive partial differential equation solving process of the traditional finite element method. It only requires focusing on the top-level settings of the motor thermal model, such as geometric parameters, heat transfer methods between components, and cooling methods. The parameter matrix is ​​then constructed and simple matrix operations are performed to obtain the results. This method is characterized by fast calculation and ease of implementation, thereby greatly improving computational efficiency. At the same time, the model is based on parameterization. When the motor size, operating conditions, or materials change, only the corresponding parameters need to be modified for re-analysis, which has high flexibility. This provides convenience for rapid thermal analysis and optimization of permanent magnet traction motors in the early design stage, improving the efficiency and accuracy of thermal analysis.

[0059] It should be noted that each implementation method of this application can be freely combined, rearranged, or executed individually, and does not need to rely on or depend on a fixed execution order.

[0060] In some embodiments, determining the geometric and material parameters of each component in the motor to be analyzed includes: Considering the geometric features of each component that affect heat transfer, determine the axial, radial, and angular parameters of each component in cylindrical coordinates, or determine the parameters of each component's coordinate axes in Cartesian coordinates. Thermal conductivity, specific heat capacity, and density are defined as material parameters.

[0061] Specifically, determining the geometric parameters hinges on effectively mathematically describing the physical structure of the motor while simultaneously considering both simplicity and accuracy in modeling. To this end, embodiments of this application include consideration of geometric features in each component that influence heat transfer. This means that the geometric model of the motor can be reasonably simplified during the parameterization process. For example, geometric details on motor components that have minimal impact on the overall heat transfer path (such as assembly screw holes, slight chamfers, nameplates, etc.) can be ignored. In this way, only the essential geometric contours crucial for thermal analysis are retained, such as the inner and outer diameters, tooth height, and tooth width of the stator core, the cross-sectional area of ​​the windings, and the dimensions of the permanent magnets, thereby significantly simplifying the parameterization process and reducing modeling complexity.

[0062] After identifying the key geometric features that need to be described, a suitable coordinate system can be selected to define its parameters.

[0063] One alternative approach is to determine the axial, radial, and angular parameters of each component in a cylindrical coordinate system. Given that motors, especially their stator and rotor sections, typically have rotationally symmetric cylindrical structures, using a cylindrical coordinate system is a very natural and efficient method. Axial parameters generally refer to dimensions along the motor's axis of rotation, such as the stacked length of the stator core and the axial thickness of the permanent magnets; radial parameters refer to dimensions along the radius, such as the inner and outer diameters of the stator core and the thickness of the housing; and angular parameters refer to dimensions along the circumferential direction, such as the angular range occupied by a single stator tooth or slot.

[0064] Another option is to determine the parameters of each component's coordinate axes in a Cartesian coordinate system. For some regularly shaped rectangular components, or when certain components can be approximated as cubes on a macroscopic scale, using a Cartesian coordinate system (i.e., a rectangular coordinate system composed of the x, y, and z axes) to define their length, width, and height parameters may be more intuitive and convenient.

[0065] Because the motors under analysis typically exhibit high periodic symmetry (e.g., composed of multiple identical stator slots and permanent magnets arranged circumferentially), it is unnecessary to describe the entire 360-degree motor when defining geometric parameters. Instead, the geometric parameters can usually be defined within a representative minimum symmetry unit (e.g., a single slot tooth structure, or even half a slot). Later, when constructing the complete model, it can be expanded by arraying or multiplying by the number of cycles, which can further significantly reduce the workload of parameter definition.

[0066] Regarding the determination of material parameters, the embodiments of this application define thermal conductivity, specific heat capacity, and density as the material parameters.

[0067] Thermal conductivity is the core basis for calculating the internal thermal resistance of motor components. Different components of a motor are made of different materials; for example, the windings are usually made of copper, the stator and rotor cores are made of silicon steel sheets, and the casing may be made of aluminum alloy. The thermal conductivity of these materials varies greatly, and accurately defining the thermal conductivity of each component is fundamental to ensuring the accuracy of the model calculations.

[0068] Specific heat capacity and density are key to calculating the lumped heat capacity of nodes. The lumped heat capacity (calculated as: specific heat capacity × density × volume) characterizes the ability of a node to absorb or release heat when the node temperature changes. This is essential for transient thermal analysis (such as simulating the process of a motor going from a cold start to thermal equilibrium, or the temperature rise process when running at peak power).

[0069] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor, which clearly, efficiently, and specifically defines the motor's geometric and material parameters. This parameterized simplification and the clear definition of core material properties lay a solid data foundation for the subsequent rapid and accurate construction of a lumped parameter thermal network model, making the entire modeling process more standardized and easier to implement, and improving the efficiency and accuracy of thermal analysis.

[0070] In some embodiments, the various components are physically abstracted and divided into at least one lumped thermodynamic node, including: Based on the physical properties of each component, each component is divided into at least one lumped thermodynamic node; the number of lumped thermodynamic nodes is determined based on the heat generation and / or temperature calculation accuracy of each component.

[0071] Specifically, the physical characteristics in the embodiments of this application can be understood from multiple dimensions. For example, one dimension is the function and structural integrity of the component. Generally, a component with a clear physical boundary and a single function (such as a shaft or a single permanent magnet) can be considered as a basic dividing unit. Another dimension is the material homogeneity of the component. If a component is made of a single homogeneous material, it can be considered as a whole; if it is composed of multiple materials (such as windings), its internal structure needs to be specially considered when dividing it.

[0072] Based on the physical properties of each component, each component is divided into one or more lumped thermodynamic nodes. The number of lumped thermodynamic nodes is determined based on the heat generation and / or temperature calculation accuracy of each component.

[0073] In one specific embodiment, the number of lumped thermodynamic nodes is determined based on the amount of heat generated. The heat generation of different components within the motor varies significantly. For example, windings generate substantial copper losses due to current flow, and the stator core generates iron losses due to the alternating magnetic field; these are the main heat sources. For these high-heat-generating components, their internal temperature gradients are typically large. To accurately capture their highest temperature points and temperature distribution, more refined division is needed, i.e., dividing them into more lumped thermodynamic nodes. For example, windings can be divided into multiple nodes radially (from near the slot bottom to near the slot opening) and axially (inside the slot and at the ends). In contrast, components such as shafts and bushings, which generate almost no heat or very little heat, have small internal temperature differences and can usually be divided into one or a few nodes.

[0074] In another specific embodiment, the number of lumped thermodynamic nodes is determined based on the accuracy of temperature calculations. Some components, while generating relatively little heat themselves, are extremely sensitive to temperature, thus requiring precise temperature monitoring. The most typical example is permanent magnets. Permanent magnets (especially rare-earth permanent magnets such as neodymium iron boron) suffer irreversible demagnetization failure at excessively high temperatures, directly affecting motor performance and lifespan. Therefore, although permanent magnets themselves do not generate heat (only a small amount of eddy current loss), relatively fine node division is still necessary to accurately assess whether their operating temperature is within a safe range.

[0075] In actual division, to ensure the accuracy of temperature calculation in different spatial dimensions, the division fineness in different spatial dimensions is given.

[0076] Figure 3 This is a schematic diagram of the lumped thermodynamic nodes provided in this application, such as... Figure 3 As shown, the lumped thermodynamic nodes in a certain motor can be specifically divided into rotor yoke node 14; rotor tooth node 15; slot winding node 17; end winding node 18; stator tooth node 19; stator yoke node 20; upper permanent magnet node 21; and lower permanent magnet node 22. The motor also includes an air gap 16 and cooling oil 23.

[0077] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor. The granularity of the partitioning is dynamically determined based on the importance of each component in the thermal analysis (i.e., the amount of heat generated and its temperature sensitivity). By finely partitioning key components (such as windings and permanent magnets) while coarsely partitioning non-critical components, the total number of nodes in the entire model can be effectively controlled while ensuring the calculation accuracy of critical areas, thus ensuring the high efficiency of the thermal analysis method.

[0078] In some embodiments, the equivalent thermal conductivity of the winding is determined based on the following steps: The equivalent thermal conductivity of the winding is determined based on the thermal conductivity of each component in the stator winding slot and the total area of ​​each component in the stator winding slot. The axial equivalent thermal conductivity of the winding is determined based on the thermal conductivity of copper in each component and the motor slot fill factor.

[0079] Specifically, Figure 4 This is a schematic diagram of the equivalent method for motor windings provided in this application, such as... Figure 4As shown, the motor winding slots are not composed of a single homogeneous material, but rather a complex microstructure composed of multiple materials, including copper wires 8, varnish film 9 on the wire surface, slot insulation paper 10 on the slot walls, and potting compound and air 11 filling the spaces between them. These components exhibit vastly different thermal conductivityes (for example, copper's thermal conductivity is much higher than that of air and insulating materials), resulting in significant anisotropic thermal conductivity of the winding as a whole, meaning that its thermal conductivity varies in different directions. Directly and accurately modeling this microstructure in the model would make the calculations extremely complex. Therefore, this application proposes a method for calculating the equivalent thermal conductivity of the winding, treating it macroscopically as an equivalent entity 12.

[0080] The tangential radial direction generally refers to the direction of heat conduction in a plane perpendicular to the conductor axis, that is, the direction in which heat is transferred from the center of the winding to the slot wall (radially) or along the circumference (tangentially). In this direction, heat needs to pass through multiple layers of different materials in sequence, which can be considered as a series connection in the heat transfer path. The path for heat transfer from the center of the slot to the slot wall includes the copper conductor, enamel film, sealant, slot insulation paper, etc. The thermal resistance of these components is superimposed layer by layer. Therefore, the equivalent thermal conductivity of the tangential radial direction can be derived based on the calculation principle of series thermal resistance.

[0081] Assuming the space inside the slot is uniformly filled with copper wire, enamel film, slot insulation, potting compound, and air, and that the internal thermal conductivity of the same material is the same, the space inside the slot can be considered as a single solid. Therefore, the equivalent radial thermal conductivity of the winding is: In the formula, The equivalent radial thermal conductivity of the winding; , , , , These are the thermal conductivity of copper, the thermal conductivity of varnish film, the thermal conductivity of slotted insulating paper, the thermal conductivity of potting, and the thermal conductivity of air, all in W / (m·K). , , , , These are the total area of ​​copper in a single tank, the total area of ​​the varnish film, the total area of ​​the tank insulation paper, the total area of ​​the potting, and the total area of ​​air. This represents the total area within a single slot.

[0082] Axial direction refers to the direction parallel to the conductor (i.e., the axis of rotation of the motor). In this direction, heat is mainly transferred along the copper conductor, which has extremely high thermal conductivity, while other components such as insulating materials and air are distributed parallel to the copper conductor. Therefore, these different materials can be considered as being in parallel along the heat transfer path. In the parallel heat conduction model, the total thermal conductivity is mainly determined by the part with the strongest thermal conductivity, namely the copper conductor. Other materials (such as insulating varnish, air, etc.) occupy a relatively small cross-sectional area, and their thermal conductivity is much lower than that of copper; therefore, their contribution to the total axial thermal conductivity can be simplified or ignored.

[0083] The slot fill factor (usually denoted by k) of a motor is defined as the ratio of the total cross-sectional area of ​​all copper conductors in the slots to the total cross-sectional area of ​​the stator slots. It directly reflects the proportion of the main heat conduction channels (copper) on the axial direction.

[0084] The axial equivalent thermal conductivity of the winding is: In the formula, denoted as axial equivalent thermal conductivity of the winding; k is the motor slot fill factor (%).

[0085] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor. This method can scientifically and rationally determine the equivalent thermal conductivity of the winding in different directions, accurately characterizing its anisotropic thermal conductivity. Applying this precisely calculated equivalent parameter to a lumped-parameter thermal network model can greatly improve the accuracy of the model's temperature prediction for the winding, a key heat-generating component, while avoiding the complexity of modeling microscopic details, thus improving the efficiency and accuracy of thermal analysis.

[0086] In some embodiments, the contact thermal resistance is determined based on the following steps: The contact thermal resistance between the two components is determined based on the equivalent air gap thickness and contact area between the two contacting components, as well as the thermal conductivity of air.

[0087] Specifically, contact thermal resistance is caused by the roughness of the surfaces of two contacting objects and the gap between the contact surfaces. It is related to factors such as the type of contact surface material and the contact pressure.

[0088] In this application embodiment, the microscopically complex imperfect contact interface is equivalent to a virtual thin layer filled with air of uniform thickness, i.e., an equivalent air gap. The contact thermal resistance can be calculated using the equivalent air gap thickness, as shown in the formula: In the formula, The contact thermal resistance between the two components; It is the equivalent air gap thickness between the two components. It refers to the contact area between two components. The greatest contact thermal resistance of a motor mainly exists on the contact surface between silicon steel and aluminum alloy.

[0089] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor, which can quantify the complex physical phenomenon of contact thermal resistance in a simple and effective way. By incorporating the accurately calculated contact thermal resistance into the lumped-parameter thermal network model, the model can more realistically reflect the actual obstacles encountered by heat transfer between components, thereby significantly improving the calculation accuracy of the entire thermal analysis model.

[0090] In some embodiments, the motor to be analyzed is an oil-cooled flux-switching permanent magnet traction motor.

[0091] Specifically, the cooling method of the oil-cooled flux-switching permanent magnet traction motor is as follows: cooling oil is added into the motor cavity, and the various components are directly cooled by the rotation and agitation of the rotor and the housing.

[0092] In some embodiments, for an oil-cooled flux-switched permanent magnet traction motor, the convective heat transfer resistance is determined based on the following steps: The forced convection heat transfer coefficient of the cooling medium caused by the agitation of the internal cooling oil due to the rotation of the motor is calibrated using particle method simulation or experimental data. And the environmental natural convection heat transfer coefficient between the motor casing and the external ambient air is calculated using empirical formulas.

[0093] Specifically, convective heat transfer is one of the two main ways in which motors dissipate heat (the other being heat conduction). It describes the heat exchange process between a solid surface and the fluid in contact with it. Its heat transfer capacity is usually characterized by the convective heat transfer coefficient, while the convective heat transfer resistance is the reciprocal of the convective heat transfer coefficient.

[0094] In the oil-cooled external rotor motor described in this application, the convective heat transfer process is particularly complex, involving two distinctly different environments: the inside of the motor and the outside. Specifically, the convective heat transfer coefficient can include the forced convection heat transfer coefficient of the cooling medium and the natural convection heat transfer coefficient of the environment.

[0095] The oil-cooled flux-switching permanent magnet traction motor addressed in this application has a unique cooling method: cooling oil is directly filled into the motor cavity, and the outer rotor structure of the motor rotates along with it during operation. This rotation strongly agitates the internal cooling oil, forming complex turbulent and two-phase (oil-gas mixture) flows, thereby forcibly cooling the surfaces of various heat-generating components inside the motor through convection. This internal flow field state is related to various factors such as motor speed, cooling oil viscosity, filling volume, and internal structure, and is difficult to accurately describe using traditional theoretical formulas. Therefore, this application proposes to use particle method simulation or experimental data to calibrate the forced convection heat transfer coefficient of the cooling medium generated by the agitation of the internal cooling oil due to motor rotation.

[0096] The particle method is an advanced meshless computational fluid dynamics approach. Its principle is to discretize a continuous fluid domain into a large swarm of particles, and characterize the fluid motion by solving the equations for each particle. This method does not require mesh generation or solving complex partial differential equations, and it performs well in simulating two-phase free flow.

[0097] Figure 5 This is a schematic diagram of the particle method simulation results at different rotational speeds provided in this application, as shown below. Figure 5 As shown, the particle method can clearly simulate the flow and distribution of cooling oil inside the motor at different speeds (e.g., 60 rpm in part (a) and 120 rpm in part (b), where rpm stands for revolutions per minute). Through this simulation, the average convective heat transfer coefficient between the surfaces of various components inside the motor and the cooling oil can be directly calculated. It can be seen that the oil flow state differs significantly at different speeds, with the convective thermal resistance at 60 rpm being much lower than that at 120 rpm.

[0098] Another approach is to build an experimental platform, place temperature sensors at key locations inside a real motor prototype, and run the motor under different operating conditions (such as different speeds and different loads) to measure the steady-state temperature of each component. Then, by reverse calculation, the convective heat transfer coefficient value that best matches the measured temperature can be derived.

[0099] By using one of the two methods mentioned above, the complex forced convection heat transfer coefficient inside the motor can be obtained, which is the core element to ensure the accuracy of the model.

[0100] The motor casing serves as the final heat dissipation surface, and its heat needs to be dissipated through convection with the external ambient air. This process is relatively simpler than the internal oil churning flow and can generally be divided into two cases: natural convection and forced convection, for which there are already many mature engineering calculation models.

[0101] Therefore, this application proposes to use an empirical formula to calculate the ambient natural convection heat transfer coefficient between the motor housing and the external ambient air.

[0102] In the formula, The convective heat transfer coefficient is the outer surface of the casing. The convective heat transfer coefficient of the outer surface of the end cap; The wind speed at the surface of the casing (m / s); Re is the Reynolds number of the air at the end face; R is the outer radius of the end cover; n is the rotational speed (rad / s, radians per second); air viscosity (kg / s·m, kilograms per second per meter); The thermal conductivity of air.

[0103] This application provides a thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor. This method utilizes advanced numerical simulation technology to solve the problem of accurately modeling complex internal flows, while also leveraging mature empirical formulas to efficiently handle the relatively simple external heat dissipation environment. This combined strategy accurately captures the main heat dissipation paths and heat transfer characteristics of the motor during actual operation. By substituting the calculated convective heat transfer coefficient into the lumped-parameter thermal network model, the efficiency and accuracy of the thermal analysis are improved.

[0104] In some embodiments, for water-cooled flux-switching permanent magnet traction motors, a method combining computational fluid dynamics simulation and experimentation is used to calibrate the forced convection heat transfer coefficient of the cooling medium flowing through the cooling water jacket inside the motor housing or stator core.

[0105] In some embodiments, for a forced air-cooled flux-switching permanent magnet traction motor, fluid dynamics simulation and experimental data are used to calibrate the forced convection heat transfer coefficient of the cooling airflow driven by an independent fan or the rotor rotation itself, flowing through the winding ends, air gap and heat dissipation fins of the motor.

[0106] In some embodiments, the lumped parameter thermal network model established in this application can be conveniently coupled with the motor electromagnetic model to achieve electromagnetic-thermal coupling design optimization of the motor, providing convenience for the initial stage of motor design.

[0107] The lumped-parameter thermal network model built in this application was compared with experimental data under various operating conditions, such as... Figure 6 As shown in 7, 8 and 9. Figure 6 This is a schematic diagram comparing the predicted steady-state temperature rise of the motor winding under rated operating conditions with experimental data provided in this application. Figure 7 This is a schematic diagram comparing the predicted steady-state temperature rise of the permanent magnet under rated operating conditions of the motor provided in this application with experimental data. Figure 8 This is a schematic diagram comparing the predicted results of transient temperature rise of the motor winding under peak operating conditions provided in this application with experimental data. Figure 9This is a schematic diagram comparing the predicted results of transient temperature rise of permanent magnet under peak operating conditions of the motor provided in this application with experimental data.

[0108] It should be noted that "NC120", "OC60", and "OC120" in the figure represent three operating conditions: natural cooling at 120 rpm, oil cooling at 60 rpm, and oil cooling at 120 rpm, respectively. The steady-state test was performed with a given current of 9 A (Amperes), and the transient test was performed with a given current of 18 A. The comparative results show that the lumped-parameter thermal network model built in this application example has high accuracy in both steady-state and transient temperature rise prediction.

[0109] The apparatus provided in the embodiments of this application is described below. The apparatus described below can be referred to in correspondence with the method described above.

[0110] Figure 10 This is a schematic diagram of the thermal analysis device for permanent magnet traction motors provided in this application, as shown below. Figure 10 As shown, the device includes: The determination module 1010 is used to determine the geometric and material parameters of each component in the motor to be analyzed; The partitioning module 1020 is used to physically abstract and partition each component into at least one lumped thermodynamic node; Module 1030 is established to determine the connection method of each lumped thermodynamic node based on the heat transfer characteristics of each component, and to establish a parameter matrix including lumped thermal resistance, lumped thermal conductance and lumped heat capacity. Calculation module 1040 is used to determine the key heat transfer parameters of the motor to be analyzed; the key heat transfer parameters include the equivalent thermal conductivity of the windings, contact thermal resistance and convective heat transfer resistance. Module 1050 is used to construct a lumped parameter thermal network model of the motor to be analyzed based on lumped thermodynamic nodes and parameter matrices, as well as key heat transfer parameters.

[0111] This application provides a thermal analysis device for an oil-cooled flux-switching permanent magnet traction motor. By transforming the complex continuous heat transfer problem into a discrete problem similar to a circuit network, it avoids the complex mesh discretization and massive partial differential equation solving process of traditional finite element methods. It only requires focusing on the top-level settings of the motor thermal model, such as geometric parameters, heat transfer methods between components, and cooling methods. The parameter matrix is ​​then constructed and simple matrix operations are performed to obtain the results. It features fast calculation and ease of implementation, thereby greatly improving computational efficiency. At the same time, the model is based on parameterization. When the motor size, operating conditions, or materials change, only the corresponding parameters need to be modified for re-analysis, which has high flexibility. This provides convenience for rapid thermal analysis and optimization of permanent magnet traction motors in the early design stage, improving the efficiency and accuracy of thermal analysis.

[0112] Figure 11 This is a schematic diagram of the structure of the electronic device provided in this application, such as... Figure 11 As shown, the electronic device may include: a processor 1110, a communications interface 1120, a memory 1130, and a communications bus 1140, wherein the processor 1110, the communications interface 1120, and the memory 1130 communicate with each other via the communications bus 1140. The processor 1110 can call logical commands in the memory 1130 to execute the methods described in the above embodiments, for example: The geometric and material parameters of each component in the motor to be analyzed are determined; each component is physically abstracted and divided into at least one lumped thermodynamic node; the connection method of each lumped thermodynamic node is determined based on the heat transfer characteristics of each component, and a parameter matrix including lumped thermal resistance, lumped thermal conductivity, and lumped heat capacity is established; the key heat transfer parameters of the motor to be analyzed are determined; the key heat transfer parameters include the equivalent thermal conductivity of the winding, contact thermal resistance, and convective heat transfer thermal resistance; based on the lumped thermodynamic nodes, the parameter matrix, and the key heat transfer parameters, a lumped parameter thermal network model of the motor to be analyzed is constructed.

[0113] Furthermore, the logical commands in the aforementioned memory can be implemented as software functional units and sold or used as independent products, and can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several commands to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0114] The processor in the electronic device provided in this application embodiment can call logical instructions in the memory to implement the above method. Its specific implementation method is the same as the aforementioned method implementation method and can achieve the same beneficial effect, which will not be repeated here.

[0115] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to perform the methods provided in the above embodiments.

[0116] The specific implementation method is the same as the aforementioned method implementation method and can achieve the same beneficial effects, so it will not be repeated here.

[0117] This application provides a computer program product, including a computer program that, when executed by a processor, implements the method described above.

[0118] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0119] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor, characterized in that, include: Determine the geometric and material parameters of each component in the motor to be analyzed; The components are physically abstracted and divided into at least one lumped thermodynamic node; The connection method of each lumped thermodynamic node is determined based on the heat transfer characteristics of each component, and a parameter matrix including lumped thermal resistance, lumped thermal conductivity and lumped heat capacity is established. Determine the key heat transfer parameters of the motor to be analyzed; the key heat transfer parameters include the equivalent thermal conductivity of the winding, contact thermal resistance, and convective heat transfer resistance. Based on the lumped thermodynamic nodes, the parameter matrix, and the key heat transfer parameters, a lumped parameter thermal network model of the motor to be analyzed is constructed.

2. The thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor according to claim 1, characterized in that, The determination of the geometric and material parameters of each component in the motor to be analyzed includes: Considering the geometric features of each component that affect heat transfer, determine the axial, radial, and angular parameters of each component in cylindrical coordinates, or determine the parameters of each component's coordinate axes in Cartesian coordinates. Thermal conductivity, specific heat capacity, and density are defined as the material parameters.

3. The thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor according to claim 1, characterized in that, The process of physically abstracting and dividing each component into at least one lumped thermodynamic node includes: Based on the physical characteristics of each component, each component is divided into at least one lumped thermodynamic node; the number of lumped thermodynamic nodes is determined based on the heat generation and / or temperature calculation accuracy of each component.

4. The thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor according to claim 1, characterized in that, The equivalent thermal conductivity of the winding is determined based on the following steps: The tangential radial equivalent thermal conductivity of the winding is determined based on the thermal conductivity of each component in the stator winding slot and the total area of ​​each component in the stator winding slot. The axial equivalent thermal conductivity of the winding is determined based on the thermal conductivity of copper in each component and the motor slot fill factor.

5. The thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor according to claim 1, characterized in that, The contact thermal resistance is determined based on the following steps: The contact thermal resistance between the two components is determined based on the equivalent air gap thickness and contact area between the two contacting components, as well as the thermal conductivity of air.

6. A thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor according to any one of claims 1 to 5, characterized in that, The motor to be analyzed is an oil-cooled flux-switched permanent magnet traction motor.

7. The thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor according to claim 6, characterized in that, The convective heat transfer resistance is determined based on the following steps: The forced convection heat transfer coefficient of the cooling medium caused by the agitation of the internal cooling oil due to the rotation of the motor is calibrated using particle method simulation or experimental data. And the environmental natural convection heat transfer coefficient between the motor casing and the external ambient air is calculated using empirical formulas.

8. A thermal analysis device for an oil-cooled flux-switching permanent magnet traction motor, characterized in that, include: The determination module is used to determine the geometric and material parameters of each component in the motor to be analyzed; The partitioning module is used to physically abstract and divide each component into at least one lumped thermodynamic node; A module is established to determine the connection method of each lumped thermodynamic node based on the heat transfer characteristics of each component, and to establish a parameter matrix including lumped thermal resistance, lumped thermal conductivity and lumped heat capacity. The calculation module is used to determine the key heat transfer parameters of the motor to be analyzed; the key heat transfer parameters include the equivalent thermal conductivity of the winding, the contact thermal resistance, and the convective heat transfer resistance. A construction module is used to construct a lumped parameter thermal network model of the motor to be analyzed based on the lumped thermodynamic nodes, the parameter matrix, and the key heat transfer parameters.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor as described in any one of claims 1 to 7.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the thermal analysis method for an oil-cooled flux-switching permanent magnet traction motor as described in any one of claims 1 to 7.

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