Performance analysis method for topological structure of multi-topology axial flux permanent magnet motor based on electromagnetic-thermal coupling

Abstract

The invention discloses a performance analysis method for a topological structure of a multi-topology axial flux permanent magnet motor based on electromagnetic-thermal coupling, and the method comprises the steps: firstly building three-dimensional electromagnetic finite element models of four typical axial flux permanent magnet motors, and calculating electromagnetic loss including iron core loss, copper loss and permanent magnet eddy current loss; importing the loss data into a three-dimensional fluid-thermal coupling model, and simulating the temperature rise of the motor under a natural cooling condition; the performance of the motor is subjected to double constraints of winding insulation and irreversible demagnetization temperature of a permanent magnet, so that the maximum current density of safe steady-state operation of the motor is determined and identified by adopting an iterative electromagnetic-thermal coupling analysis method, and the maximum torque density of each topological structure is evaluated under thermal constraints. The electromagnetic performance and the thermal constraint can be coupled, so that the optimal performance achieved by different axial magnetic flux permanent magnet motor topological structures can be compared, and the problem of inaccurate performance evaluation caused by neglect of the thermal constraint in the existing motor design is solved.

Description

Technical Field

[0001] This invention relates to motor design and performance evaluation technology, specifically to a performance analysis method for a multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling. Background Technology

[0002] Axial flux permanent magnet motors (ACMs) offer advantages such as high torque density and compact structure, and have shown potential for application in electric propulsion aircraft in recent years. Both the stator and rotor of an ACM are disc-shaped, hence the name disc-type permanent magnet motor. Energy conversion occurs through an axial air gap magnetic field. Depending on the number of stators and rotors, ACMs can be configured in various topologies, commonly including single-stator single-rotor, single-stator dual-rotor, dual-stator single-rotor, and yokeless segmented armature motors.

[0003] Currently, research and comparisons on different axial motor topologies mostly focus on electromagnetic performance. A common approach is to compare electromagnetic parameters such as output torque, torque ripple, and efficiency using finite element analysis under pre-set electromagnetic load conditions such as current density, outer diameter, and slot fill factor. However, this method has significant limitations: it ignores the fundamental limitation imposed by thermal constraints on the motor's continuous output capability.

[0004] In actual operation, the continuous output capacity of an electric motor is mainly constrained by two conditions: (1) the maximum allowable operating temperature of the winding insulation. If this temperature is exceeded, the insulation layer will age faster or even break down, leading to motor failure. (2) the temperature at which the permanent magnet undergoes irreversible demagnetization. When the local temperature of the permanent magnet exceeds the demagnetization inflection point, irreversible demagnetization will occur, causing a permanent decline in motor performance.

[0005] If only electromagnetic performance is considered during the design phase, a topology with superior electromagnetic performance under ideal cooling conditions may be selected. However, under actual thermal boundary conditions, this topology may fail to achieve the goal of long-term safe operation due to poor heat dissipation paths and excessively high hotspot temperatures. Conversely, a topology whose electromagnetic performance appears inferior at the same current density may be able to withstand higher current densities before reaching its thermal limit due to its superior thermal management characteristics (such as more efficient heat dissipation area and lower thermal resistance paths). This allows it to achieve higher continuous torque output in practical applications, thus achieving high torque density and high power density performance.

[0006] Therefore, comparing purely electromagnetic performance without considering thermal constraints is incomplete and may lead to biased design decisions, failing to truly uncover the optimal motor topology under given space and heat dissipation conditions. Currently, there is a lack of a systematic, fair, and precise universal method that can couple electromagnetic performance with thermal constraints to compare and optimize the optimal performance achievable by different axial flux permanent magnet motor topologies. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a performance analysis method for multi-topology axial flux permanent magnet motors based on electromagnetic-thermal coupling, which can couple electromagnetic performance with thermal constraints, thereby comparing the optimal performance that can be achieved by different axial flux permanent magnet motor topologies.

[0008] Technical solution: The present invention provides a performance analysis method for a multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling, comprising:

[0009] Establish a unified comparison benchmark: Establish a multi-topology axial flux permanent magnet motor topology; set the same parameters for all axial flux permanent magnet motor topologies, and determine the equivalent thermal conductivity, thermal safety boundary, ambient temperature, and design criteria for the same cooling method and heat dissipation structure for each component of the axial flux permanent magnet motor topology.

[0010] Initial electromagnetic analysis: A three-dimensional electromagnetic finite element model of the topology of the multi-topology axial flux permanent magnet motor is established in electromagnetic simulation software; initial current density and speed conditions are applied to the three-dimensional electromagnetic finite element model, and three-dimensional electromagnetic simulation analysis is performed to calculate the losses of each component of the motor;

[0011] Initial thermal analysis: In ANSYS Fluent software, a three-dimensional thermal simulation model containing the motor solid domain and the external cooling fluid domain is established for each axial flux permanent magnet motor topology in the multi-topology axial flux permanent magnet motor topology; the simulation boundary and parameters of the three-dimensional thermal simulation model are set; the losses of each component of the motor are used as volume heat sources and applied to each component in the motor solid domain within the three-dimensional thermal simulation model; according to the design criteria, thermal simulation is performed on the multi-topology axial flux permanent magnet motor topology to obtain the steady-state temperature field distribution of each axial flux permanent magnet motor topology under the initial current density;

[0012] Two-way electromagnetic-thermal coupling iterative analysis: Utilizing the steady-state temperature field distribution of each axial flux permanent magnet motor topology, the material parameters within each axial flux permanent magnet motor are updated. Using the updated material parameters, a three-dimensional electromagnetic simulation analysis is performed again on each axial flux permanent magnet motor topology to obtain the updated heat source distribution. This updated heat source distribution is then input into the three-dimensional thermal simulation model of each axial flux permanent magnet motor topology. After multiple iterations, the accurate temperature distribution of each part of the motor corresponding to different current densities is obtained. Combining the temperature distribution of each part of the motor, a fitting numerical method is used to determine the current density for safe and stable motor operation under the dual thermal constraints of winding insulation limitations and irreversible demagnetization of the permanent magnet. Based on the current density, the motor torque density is calculated, thus obtaining the motor torque density of each axial flux permanent magnet motor topology. The motor torque density reflects the optimal performance that the motor can achieve under actual operating conditions.

[0013] Comparing motor torque density: The motor torque density of all axial flux permanent magnet motor topologies is compared, and the axial flux permanent magnet motor topology with the highest motor torque density is selected.

[0014] Furthermore, setting the same parameters for all axial flux permanent magnet motor topologies includes:

[0015] Set the same dimensional constraints, current density, slot fill factor, material, and speed conditions for all axial flux permanent magnet motor topologies.

[0016] Furthermore, the multi-topology axial flux permanent magnet motor topology includes single stator single rotor, single stator dual rotor, dual stator single rotor, and yokeless segmented armature structure.

[0017] Furthermore, the losses of the various components of the motor include stator core losses, rotor core losses, winding copper losses, and permanent magnet eddy current losses.

[0018] Furthermore, the calculation formula for the stator and rotor core losses is as follows:

[0019] ;

[0020] In the formula, For stator and rotor core losses; This is hysteresis loss; This is eddy current loss; This is for additional losses.

[0021] Furthermore, the hysteresis loss The calculation formula is as follows:

[0022] ;

[0023] The eddy current loss The calculation formula is as follows:

[0024] ;

[0025] The additional losses The calculation formula is as follows:

[0026] ;

[0027] in, This is the hysteresis loss coefficient; This is the eddy current loss coefficient; This is the additional loss factor; The frequency of the alternating magnetic field, This represents the magnetic flux density amplitude.

[0028] Furthermore, the formula for calculating the copper loss of the winding is as follows:

[0029] ;

[0030] In the formula, For winding copper losses; The number of phases of the winding; This represents the effective value of the phase current passing through the winding; Let be the winding resistance; the calculation process for the winding resistance is as follows:

[0031] ;

[0032] In the formula, α is the resistance value at 0℃; α is the temperature coefficient of resistance at room temperature. Operating temperature; The initial ambient temperature; where temperature resistance value at time It can be calculated using the following formula:

[0033] ;

[0034] In the formula, The resistivity of copper wire; The length of each phase coil; This refers to the cross-sectional area of ​​the winding.

[0035] Combining the above formulas, the formula for calculating the copper losses in the motor windings when considering temperature changes is as follows:

[0036] .

[0037] Furthermore, the setting of the simulation boundaries and parameters of the three-dimensional thermal simulation model includes:

[0038] Pressure inlet and pressure outlet are set in the three-dimensional thermal simulation model to simulate the self-ventilation cooling effect of the motor; the equivalent thermal conductivity of the materials of each component of the motor is applied to the three-dimensional thermal simulation model.

[0039] Furthermore, by combining the temperature distribution of various parts of the motor and employing a fitting numerical method, the current density for safe and stable operation of the motor is determined under the dual thermal constraints of winding insulation limitations and irreversible demagnetization of the permanent magnet, including:

[0040] By using the precise temperature distribution of each part of the motor corresponding to different current densities obtained through multiple iterations, the current density-temperature sample points of each component of the motor are obtained. After obtaining the current density-temperature sample points of each component of the motor, a quadratic curve of winding hot spot temperature and current density is fitted by numerical method. The quadratic curve will intersect with the horizontal line of winding insulation temperature limit at one point. The current density corresponding to this intersection point is the limit current density that satisfies the thermal constraint.

[0041] By utilizing the linear relationship between the demagnetization rate and current density after irreversible demagnetization of a permanent magnet, two non-zero demagnetization rate sample points of the permanent magnet and the corresponding current densities are selected to fit a linear curve. The linear curve is then extended in reverse to the position where the demagnetization rate approaches zero by using the linear extrapolation method, thereby accurately estimating the critical current density threshold when the permanent magnet is about to undergo irreversible demagnetization.

[0042] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows:

[0043] (1) The design method is more accurate and forward-looking: the two-way electromagnetic-thermal coupling iterative analysis can more accurately predict the actual performance of the motor. Thermal bottlenecks can be identified in advance during the design stage, and the heat dissipation path or electromagnetic design can be optimized or the electromagnetic design can be adjusted to avoid repeated modifications due to overheating problems in the later stage.

[0044] (2) The evaluation system is more comprehensive and closer to engineering practice: This invention breaks through the traditional comparison framework based solely on electromagnetic performance and creatively introduces dual thermal constraints as the termination condition for performance evaluation. The evaluation index has been changed from "torque density under a given current" to "the maximum torque density that the motor can operate safely and stably under the dual thermal constraints of winding insulation limitation and irreversible demagnetization of permanent magnets". This index directly reflects the motor's continuous output capability under actual working conditions and has direct guiding value for engineering design and application.

[0045] (3) Strong versatility and wide range of applications: This method is not only applicable to the comparison between various topologies of axial flux permanent magnet motors, but its core ideas and processes can also be extended to the topology selection, cooling scheme optimization and extreme performance evaluation of other types of motors, providing a general framework for the systematic design of high power density motors. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the process of the present invention;

[0047] Figure 2 These are three-dimensional schematic diagrams of four AFPM topologies in embodiments of the present invention;

[0048] Figure 3 This is a schematic diagram of the localized cooling method for the YASA motor in an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the topology and heat dissipation structure of the YASA motor in an embodiment of the present invention;

[0050] Figure 5 This is a schematic diagram of a 1 / 4 three-dimensional model of the YASA motor described in this invention;

[0051] Figure 6 This is a stator and rotor magnetic flux density cloud diagram of the YASA motor under load in an embodiment of the present invention;

[0052] Figure 7 This is a schematic diagram of a three-dimensional thermal simulation model in an embodiment of the present invention.

[0053] Figure 8 This is a cloud map showing the steady-state temperature distribution of various components of the YASA motor obtained through thermal analysis in an embodiment of the present invention.

[0054] Figure 9 This is an overall flowchart of the electromagnetic-thermal coupling iterative analysis and performance optimization method in this embodiment of the invention. Detailed Implementation

[0055] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0056] like Figure 1 As shown, the performance analysis method for a multi-topology axial flux permanent magnet motor based on electromagnetic-thermal coupling of the present invention includes the following steps:

[0057] S1. Establish a unified comparison benchmark: Establish a multi-topology axial flux permanent magnet motor topology; set the same parameters for all axial flux permanent magnet motor topologies, and determine the equivalent thermal conductivity, thermal safety boundary, ambient temperature, and design criteria for the same cooling method and heat dissipation structure of each component material in the axial flux permanent magnet motor topology.

[0058] Multi-topology axial flux permanent magnet motor topologies include single-stator single-rotor, single-stator dual-rotor, dual-stator single-rotor, and yokeless segmented armature structures, such as... Figure 2 As shown, Figure 2 Figure (a) in the figure is a schematic diagram of a single stator and single rotor structure; Figure 2 Figure (b) is a schematic diagram of a dual-stator single-rotor structure; Figure 2 Figure (c) is a schematic diagram of a single-stator dual-rotor structure; Figure 2 Figure (d) in the diagram is a schematic diagram of a segmented armature structure without a yoke.

[0059] Specifically, all axial flux permanent magnet motor topologies are given the same parameters, namely: the same external dimension constraints, current density, and slot fill factor.

[0060] In this embodiment, the following are the design criteria for all axial flux permanent magnet motor topologies, including dimensional constraints, current density, slot fill factor, materials, speed conditions, equivalent thermal conductivity of motor components, thermal safety boundaries, ambient temperature, and the same cooling method and heat dissipation structure:

[0061] (1) Dimensional constraints: The outer diameter is uniformly 320mm, the inner diameter is 226mm, and the total axial installation space is constrained to 70mm. Each topology is adjusted and laid out within this space.

[0062] (2) Electromagnetic load reference: The initial current density is designed to be The slot fill rate remains consistent.

[0063] (3) Materials: The stator and rotor cores are made of 35WW250 silicon steel sheets; the permanent magnets are made of N42UH; and the windings are made of copper wire.

[0064] (4) Speed ​​conditions: The speed of the permanent magnet motor topology with each axial flux is set to be .

[0065] (5) Thermal safety boundary: The insulation class is H, and the maximum allowable operating temperature is A 10% safety margin is uniformly reserved, and the target for limiting the winding hot spot temperature is set as follows: The safe threshold for the temperature at which permanent magnets undergo irreversible demagnetization is determined based on the material properties of N42UH.

[0066] (6) Cooling conditions: Natural air cooling is used uniformly. It is assumed that the motor is placed in still air and relies on the rotor rotation for self-ventilation and heat dissipation. The housing design of all topologies follows the same heat dissipation criteria to ensure consistent baseline heat dissipation capacity.

[0067] (7) Ambient temperature: uniformly set to .

[0068] (8) The cooling method of YASA motor is as follows: Figure 3 As shown, Figure 3 In the process, based on the inherent centrifugal fan characteristics of the axial flux permanent magnet motor, when it rotates, it drives natural air to enter from the air inlet of the front and rear end covers, flows through the contact side between the permanent magnet and the air gap, and the contact side between the stator core and the air gap, and exchanges heat with each component inside the motor and transfers the heat generated by the motor due to losses. The heated natural air is finally discharged from the air outlet in the circumferential direction of the casing.

[0069] (9) The heat dissipation structure of the YASA motor is as follows Figure 4 As shown, Figure 4 The YASA motor mainly consists of a single stator and dual rotors, concentrated windings, stator support, epoxy resin potting, and an outer casing. Specifically, the YASA motor's heat dissipation structure includes end covers 1, casing 2, epoxy resin potting 3, windings 4, rotor core 5, first permanent magnet 6, stator support 7, stator core 8, and second permanent magnet 9. Since the stator core 8 has no yoke, each stator tooth is independent. The windings 4 are wound on segmented stators, which are placed in slots formed by the stator support 7 and further fixed together with the windings by the epoxy resin potting 3. The first permanent magnet 6 is attached to the rotor core 5. The first permanent magnet 6 and the rotor core 5 are embedded together in the end covers of the casing 2 on both sides, forming a whole with the casing 2. This means that the rotation of the rotor will drive the casing to rotate, drawing natural air from outside the casing 2 into the motor, forming a self-heating structure. The end caps 1 on both sides are connected as a whole by the housing 2 containing holes around the motor. The cooling air that enters the motor axially will eventually be discharged from the air outlet around the housing 2.

[0070] (10) Equivalent thermal conductivity of motor components: Apply the equivalent thermal conductivity of each part of the motor in Table 3 to the... Figure 4 On the corresponding parts of the motor.

[0071] S2. Initial Electromagnetic Analysis: Establish a three-dimensional electromagnetic finite element model of the multi-topology axial flux permanent magnet motor topology in electromagnetic simulation software; apply initial current density and speed conditions to the three-dimensional electromagnetic finite element model, perform three-dimensional electromagnetic simulation analysis, and calculate the losses of each component of the motor.

[0072] The initial current density and rotation speed conditions have been set in step S1.

[0073] The losses of various components in a motor include stator and rotor core losses, winding copper losses, and permanent magnet eddy current losses. Among these, winding copper losses are calculated based on DC resistance, while iron losses and eddy current losses are directly calculated using finite element software. The specific calculation methods for the losses of each motor component are as follows:

[0074] (1) Stator and rotor core losses:

[0075] Currently, the core loss separation model proposed by Bertotti et al. is widely used in engineering. The specific Bertotti core loss calculation formula is as follows:

[0076] ;

[0077] In the formula, For stator and rotor core losses; This is hysteresis loss; This is eddy current loss; This is an additional loss. Among them, hysteresis loss... The energy loss caused by hysteresis during the magnetization process of permanent magnet materials is calculated by the following formula:

[0078] ;

[0079] Eddy current loss The energy loss is caused by eddy currents generated in the iron core in a changing magnetic field. The flow of these eddy currents in the conductor creates a Joule heating effect. This energy loss is calculated by the following formula:

[0080] ;

[0081] Additional losses The calculation formula is:

[0082] ;

[0083] in, This is the hysteresis loss coefficient; This is the eddy current loss coefficient; This is the additional loss factor; The frequency of the alternating magnetic field, This represents the magnetic flux density amplitude.

[0084] (2) The calculation process for winding copper loss is as follows:

[0085] ;

[0086] In the formula, For winding copper losses; The number of phases of the winding; This is the effective value of the phase current through the winding, in amperes (A). The winding resistance is expressed in units of . .

[0087] winding resistance It is related to temperature, and its calculation formula is as follows:

[0088] ;

[0089] In the formula, For temperature The resistance value at room temperature; α is the temperature coefficient of resistance at room temperature; Operating temperature; This is the initial ambient temperature.

[0090] Wherein, temperature is resistance value at time It can be calculated using the following formula:

[0091] ;

[0092] In the formula, The resistivity of copper wire; The length of each phase coil; This represents the cross-sectional area of ​​the winding.

[0093] Combining the above formulas, the formula for calculating the copper losses in the motor windings when considering temperature changes is as follows:

[0094] .

[0095] (3) Eddy current loss of permanent magnet:

[0096] The eddy current loss of permanent magnets can be calculated using the following formula:

[0097] ;

[0098] in, This represents the eddy current loss of the magnet, measured in W. Eddy current density, in A / mm 2 ; The conductivity of the permanent magnet is expressed in S / m.

[0099] In this embodiment, taking the YASA topology as an example, a three-dimensional electromagnetic finite element model is constructed and initial electromagnetic analysis is performed. To improve computational efficiency, a 1 / 4-dimensional electromagnetic finite element model is adopted based on the symmetry of the motor structure. A 1 / 4-dimensional electromagnetic finite element model of the YASA motor is established in ANSYS Maxwell, as follows: Figure 5 As shown.

[0100] Apply rated speed and initial current density The sinusoidal excitation, while the material parameters of the motor are... Under the given conditions, after electromagnetic simulation, the output torque was found to be approximately 500 Nm. The heat source distribution of each part of the motor was calculated using the following formula:

[0101] The heat source refers to the heat generated per unit volume by motor losses during steady-state operation, and its expression is:

[0102]

[0103] In the formula, As a heat source; For the losses of various components of the motor; This refers to the volume of each component of the motor.

[0104] The calculation results of the heat source distribution of each part of the motor are shown in Table 1:

[0105] Table 1. Heat source distribution of various parts of the motor

[0106]

[0107] S3. Initial Thermal Analysis: In ANSYS Fluent software, a three-dimensional thermal simulation model containing the motor solid domain and the external cooling fluid domain is established for each axial flux permanent magnet motor topology in the multi-topology axial flux permanent magnet motor topology. The simulation boundary and parameters of the three-dimensional thermal simulation model are set. The losses of each component of the motor calculated in step 2 are used as volume heat sources and applied to each component in the motor solid domain in the three-dimensional thermal simulation model. According to the design criteria determined in step 1, thermal simulation is performed on the multi-topology axial flux permanent magnet motor topology to obtain the steady-state temperature field distribution of each axial flux permanent magnet motor topology under the initial current density.

[0108] In this embodiment, taking the YASA topology as an example, a three-dimensional thermal simulation model is constructed and an initial thermal analysis is performed using the three-dimensional thermal simulation model.

[0109] In this embodiment, the simulation boundaries and parameters of the three-dimensional thermal simulation model are set, including:

[0110] In the three-dimensional thermal simulation model, pressure inlet and pressure outlet are set to simulate the self-ventilation cooling effect of the motor; the equivalent thermal conductivity of the materials of each component of the motor in step S1 is applied to the three-dimensional thermal simulation model.

[0111] A 3D model including a YASA motor model and an external air domain was created in ANSYS Fluent. To reduce computational costs, the motor thermal model was a 1 / 4 scale model, and its fluid domain settings were as follows. Figure 7 As shown: the left and right ends of the air domain are designated as pressure inlets, and the cylindrical surface as a pressure outlet, simulating self-ventilation. In the figure, gray area I represents the external cooling fluid domain of the motor, and area II represents the solid domain of the motor.

[0112] The loss values ​​in Table 1 are converted into heat generation rates by volume and applied to the corresponding areas. Table 2 shows the heat generation rates of various parts of the YASA motor.

[0113] Table 1. Losses and heat generation rate of various parts of the motor

[0114]

[0115] The thermal conductivity of the motor material is set as shown in Table 3.

[0116] Table 3 Material parameters of various parts of the motor

[0117]

[0118] Perform fluid-structure interaction temperature field calculations to obtain the steady-state temperature field as follows: Figure 8 As shown, Figure 8 Figure (a) in the figure is a schematic diagram of the temperature distribution of the motor windings; Figure 8 Figure (b) in the diagram is a schematic diagram of the temperature distribution of the motor stator; Figure 8 Figure (c) in the diagram is a schematic diagram of the temperature distribution of the motor rotor; Figure 8 Figure (d) shows a schematic diagram of the temperature distribution in the permanent magnet of the motor. The results show that... Under current density, the highest winding temperature reaches The temperature far exceeds the winding insulation limit, and the highest stator temperature is... The highest temperature of permanent magnets is .

[0119] S4. Two-way electromagnetic-thermal coupling iterative analysis: Utilizing the steady-state temperature field distribution of each axial flux permanent magnet motor topology, the material parameters within each axial flux permanent magnet motor are updated. Using the updated material parameters, a three-dimensional electromagnetic simulation analysis is performed again on each axial flux permanent magnet motor topology to obtain the updated heat source distribution of each axial flux permanent magnet motor topology. The updated heat source distribution is then input into the three-dimensional thermal simulation model of each axial flux permanent magnet motor topology. After multiple iterations, the accurate temperature distribution of each part of the motor corresponding to different current densities is obtained. Combining the temperature distribution of each part of the motor, a fitting numerical method is used to determine the current density for safe and stable operation of the motor under the dual thermal constraints of winding insulation limitation and irreversible demagnetization of the permanent magnet. Based on the current density, the motor torque density can be calculated, thus obtaining the motor torque density of each axial flux permanent magnet motor topology. The motor torque density reflects the optimal performance that the motor can achieve under actual operating conditions.

[0120] Among these methods, considering the temperature distribution of various parts of the motor, a numerical fitting method is used to determine the current density for safe and stable operation of the motor under the dual thermal constraints of winding insulation limitations and irreversible demagnetization of the permanent magnet. This includes:

[0121] By using the precise temperature distribution of various parts of the motor corresponding to different current densities obtained through multiple iterations, sample points of current density versus temperature of each motor component are obtained. After obtaining these sample points, the relationship between the winding hot spot temperature and the current density can be fitted into a precise quadratic curve. Based on the characteristics of this quadratic curve, this study uses a numerical method to fit the aforementioned quadratic curve of winding hot spot temperature versus current density. This quadratic curve intersects the horizontal line limiting the winding insulation temperature at a single point. The current density corresponding to this intersection point is the limiting current density that satisfies the thermal constraint.

[0122] Because the demagnetization rate of a permanent magnet after irreversible demagnetization exhibits a good linear relationship with the current density, this linear relationship is utilized. Two non-zero demagnetization rate sample points of the permanent magnet and the corresponding current densities are selected to fit a linear curve. Then, the linear curve is extended backward to the position where the demagnetization rate approaches zero by linear extrapolation, thereby accurately estimating the critical current density threshold when the permanent magnet is about to undergo irreversible demagnetization.

[0123] The above process constitutes the complete process of determining the current density of the motor under dual thermal constraints.

[0124] In this embodiment, the formula for calculating the motor torque density is as follows:

[0125]

[0126] In the formula, The torque density of the motor, This represents the torque of the motor. This refers to the weight of the motor.

[0127] Step S4 enables the motor to operate safely and stably under the two thermal constraints mentioned above, and achieve optimal performance.

[0128] Perform electromagnetic-thermal coupling iterative analysis: Initiate as follows Figure 9 The iterative process is shown. At the start of the analysis, it is assumed that the initial temperature of all motor components is... The process then proceeds in an iterative loop: each iteration first updates the material parameters based on the current component temperature, then performs ANSYS Maxwell 3D electromagnetic finite element analysis to evaluate the motor's electromagnetic performance. The resulting loss data is input into ANSYS Fluent 3D thermal finite element analysis to obtain a new temperature field. Afterward, it checks whether the temperature field meets the convergence criteria. If it does not, the parameters are updated and the process is repeated until the convergence condition is met, at which point the loop terminates, and finally, accurate motor performance results are output. This process, through the mutual feedback between temperature and electromagnetic parameters, achieves accurate simulation of the motor's performance under thermal equilibrium conditions.

[0129] The torque density of the permanent magnet motor topology with each axial flux under dual thermal constraints was calculated and compared as follows:

[0130] Based on the aforementioned electromagnetic-thermal coupling iterative process, the maximum safe and stable operating current density of the YASA axial permanent magnet motor topology is determined and identified, and the current density value under dual thermal constraints is obtained. The calculated output torque for continuous safe and stable operation is as follows: .

[0131] The same process was applied to other topologies of axial flux permanent magnet motors. Under a unified benchmark and thermal constraints, their respective maximum safe current density and corresponding limiting torque density were obtained through iterative optimization.

[0132] S5. Compare motor torque density: Compare the motor torque density of all axial flux permanent magnet motor topologies obtained in step S4, and select the axial flux permanent magnet motor topology with the highest motor torque density.

[0133] For each topology, the maximum safe steady-state current density determined in section 4 is substituted into the electromagnetic model. Simultaneously, material parameters for the temperature of various parts of the motor under this current density are set, and the continuous output torque that the motor can generate under this safe operating condition is calculated. Combining the total mass of the motor (including all active materials and structural components), the torque density of its maximum safe and stable operation under dual thermal constraints is calculated and compared with the torque density values ​​of axial motors for all topologies.

[0134] Based on the comparison results, the topology with the highest torque density under a given unified benchmark was selected as the optimal solution. This solution represents a design that can achieve the highest continuous output capability while meeting actual thermal safety operating requirements.

[0135] In the future, in fields where high torque density of axial flux permanent magnet motors is required, such as aerospace electric propulsion applications, the axial flux permanent magnet motor topology with the highest torque density selected using the method in this case can serve as a selection criterion.

[0136] This invention compares the performance of axial flux permanent magnet motors with different topologies, aiming to address the problem of inaccurate performance evaluations caused by neglecting thermal constraints in existing motor designs. The method first establishes three-dimensional electromagnetic finite element models of four typical axial flux permanent magnet motors (single-stator single-rotor, single-stator dual-rotor, dual-stator single-rotor, and yokeless segmented armature structure), calculating electromagnetic losses including core losses, copper losses, and permanent magnet eddy current losses. Subsequently, the loss data is imported into a three-dimensional fluid-thermal coupling model to simulate the motor's temperature rise under natural cooling conditions. Since motor performance is constrained by both winding insulation and the irreversible demagnetization temperature of the permanent magnets, an iterative electromagnetic-thermal coupling analysis method is used to determine and identify the maximum safe steady-state current density of the motor, thereby evaluating the maximum torque density of each topology under thermal constraints. This method provides a unified framework for accurately analyzing the performance of axial motors with different topologies and offers a more practical evaluation system for topology selection of high-power-density motors.

[0137] This invention establishes a bidirectional coupled electromagnetic-thermal analysis process to systematically explore and compare the maximum safe steady-state current density and torque density achievable by different topologies under unified heat dissipation conditions and thermal safety boundaries. This provides a scientific and accurate basis for topology selection and extreme design of high-power-density motors. This invention overcomes the deficiency of existing axial motor topology comparisons, which only focus on electromagnetic performance while neglecting thermal constraints.

[0138] This invention establishes a rigorous and unified electromagnetic-thermal coupling comparative analysis process, using the dual thermal constraints of winding insulation limitations and irreversible demagnetization of permanent magnets as the final benchmark for performance evaluation. This achieves a precise and fair comparison of the ultimate performance of axial flux permanent magnet motors with different topologies. Examples demonstrate that evaluating performance solely from an electromagnetic perspective may yield different conclusions than considering thermal constraints, highlighting the engineering practical value of this method. This method can effectively guide R&D personnel in topology selection and parameter optimization during the early stages of motor design, thereby developing advanced motor products that truly meet the requirements of high power density and high reliability. This invention is applicable to the selection and ultimate performance evaluation of high power density motors in fields such as electric vehicles and aerospace.

Claims

1. A performance analysis method for a multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling, characterized in that, include: Establish a unified comparison benchmark: Establish a multi-topology axial flux permanent magnet motor topology; set the same parameters for all axial flux permanent magnet motor topologies, and determine the equivalent thermal conductivity, thermal safety boundary, ambient temperature, and design criteria for the same cooling method and heat dissipation structure for each component of the axial flux permanent magnet motor topology. Initial electromagnetic analysis: A three-dimensional electromagnetic finite element model of the topology of the multi-topology axial flux permanent magnet motor is established in electromagnetic simulation software; initial current density and speed conditions are applied to the three-dimensional electromagnetic finite element model, and three-dimensional electromagnetic simulation analysis is performed to calculate the losses of each component of the motor; Initial thermal analysis: In ANSYS Fluent software, a three-dimensional thermal simulation model containing the motor solid domain and the external cooling fluid domain is established for each axial flux permanent magnet motor topology in the multi-topology axial flux permanent magnet motor topology; the simulation boundary and parameters of the three-dimensional thermal simulation model are set; the losses of each component of the motor are used as volume heat sources and applied to each component in the motor solid domain within the three-dimensional thermal simulation model; according to the design criteria, thermal simulation is performed on the multi-topology axial flux permanent magnet motor topology to obtain the steady-state temperature field distribution of each axial flux permanent magnet motor topology under the initial current density; Two-way electromagnetic-thermal coupling iterative analysis: Utilizing the steady-state temperature field distribution of each axial flux permanent magnet motor topology, the material parameters within each axial flux permanent magnet motor are updated. Using the updated material parameters, a three-dimensional electromagnetic simulation analysis is performed again on each axial flux permanent magnet motor topology to obtain the updated heat source distribution. This updated heat source distribution is then input into the three-dimensional thermal simulation model of each axial flux permanent magnet motor topology. After multiple iterations, the accurate temperature distribution of each part of the motor corresponding to different current densities is obtained. Combining the temperature distribution of each part of the motor, a fitting numerical method is used to determine the current density for safe and stable motor operation under the dual thermal constraints of winding insulation limitations and irreversible demagnetization of the permanent magnet. Based on the current density, the motor torque density is calculated, thus obtaining the motor torque density of each axial flux permanent magnet motor topology. The motor torque density reflects the optimal performance that the motor can achieve under actual operating conditions. Comparing motor torque density: The motor torque density of all axial flux permanent magnet motor topologies is compared, and the axial flux permanent magnet motor topology with the highest motor torque density is selected.

2. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 1, characterized in that: The method of setting the same parameters for all axial flux permanent magnet motor topologies includes: Set the same dimensional constraints, current density, slot fill factor, material, and speed conditions for all axial flux permanent magnet motor topologies.

3. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 1, characterized in that: The multi-topology axial flux permanent magnet motor topologies include single stator single rotor, single stator dual rotor, dual stator single rotor, and yokeless segmented armature structure.

4. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 1, characterized in that: The losses of the motor components include stator and rotor core losses, winding copper losses, and permanent magnet eddy current losses.

5. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 4, characterized in that: The formula for calculating the stator and rotor core losses is as follows: ； In the formula, For stator and rotor core losses; This is hysteresis loss; This is eddy current loss; This is for additional losses.

6. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 5, characterized in that: The hysteresis loss The calculation formula is as follows: ； The eddy current loss The calculation formula is as follows: ； The additional losses The calculation formula is as follows: ； in, This is the hysteresis loss coefficient; The eddy current loss coefficient is used. This is the additional loss factor; The frequency of the alternating magnetic field, This represents the magnetic flux density amplitude.

7. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 4, characterized in that: The calculation process for the winding copper loss is as follows: ； In the formula, For winding copper losses; The number of phases of the winding; This represents the effective value of the phase current passing through the winding; Let be the winding resistance; wherein, the formula for calculating the winding resistance is as follows: ； In the formula, α is the resistance value at 0℃; α is the temperature coefficient of resistance at room temperature. Operating temperature; The initial ambient temperature; where temperature resistance value at time It can be calculated using the following formula: ； In the formula, The resistivity of copper wire; The length of each phase coil; This refers to the cross-sectional area of ​​the winding. Combining the above formulas, the formula for calculating the copper losses in the motor windings when considering temperature changes is as follows: 。 8. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 4, characterized in that: The formula for calculating the eddy current loss of the permanent magnet is as follows: ； in, This refers to the eddy current loss of the magnet; The density is the eddy current density. The conductivity of the permanent magnet.

9. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 1, characterized in that, The setting of simulation boundaries and parameters for the three-dimensional thermal simulation model includes: Pressure inlet and pressure outlet are set in the three-dimensional thermal simulation model to simulate the self-ventilation cooling effect of the motor; the equivalent thermal conductivity of the materials of each component of the motor is applied to the three-dimensional thermal simulation model.

10. The performance analysis method for the multi-topology axial flux permanent magnet motor topology based on electromagnetic-thermal coupling according to claim 1, characterized in that, The method, combining the temperature distribution of various parts of the motor, uses a numerical fitting approach to determine the current density for safe and stable operation of the motor under the dual thermal constraints of winding insulation limitations and irreversible demagnetization of the permanent magnet. This includes: By using the precise temperature distribution of each part of the motor corresponding to different current densities obtained through multiple iterations, the current density-temperature sample points of each component of the motor are obtained. After obtaining the current density-temperature sample points of each component of the motor, a quadratic curve of winding hot spot temperature and current density is fitted by numerical method. The quadratic curve will intersect with the horizontal line of winding insulation temperature limit at one point. The current density corresponding to this intersection point is the limit current density that satisfies the thermal constraint. By utilizing the linear relationship between the demagnetization rate and current density after irreversible demagnetization of a permanent magnet, two non-zero demagnetization rate sample points of the permanent magnet and the corresponding current densities are selected to fit a linear curve. The linear curve is then extended in reverse to the position where the demagnetization rate approaches zero by using the linear extrapolation method, thereby accurately estimating the critical current density threshold when the permanent magnet is about to undergo irreversible demagnetization.

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