Three-dimensional thermal network magnetic-thermal coupling simulation method for permanent magnet motor based on double-oil cooling

Abstract

The application discloses a kind of based on double oil path cooling permanent magnet motor three-dimensional thermal network magnetic heat coupling simulation method, belong to motor thermal analysis and temperature field simulation technical field, for solving the problem that existing existing thermal network modeling method cannot consider simulation accuracy and efficiency simultaneously. Including: establishing permanent magnet motor three-dimensional thermal network temperature node system;Establish each node loss model, introduce the dynamic correction relationship of material parameter with temperature change;For in-slot winding, anisotropic equivalent heat conduction model is established;For motor solid components, three-dimensional conduction thermal network is established;According to the flow path of in-slot cooling oil path and air gap cooling oil path, oil flow network is established, and flow thermal resistance and convective heat transfer thermal resistance are calculated;Based on the above model, magnetic heat bidirectional coupling iterative solution is carried out, and motor steady-state temperature field is obtained.The application can quickly and accurately evaluate the temperature distribution of double-oil-cooled permanent magnet motor, and is suitable for application scenarios such as electro-hydraulic actuators with high requirements for power density and thermal management.

Description

Technical Field

[0001] This invention relates to the field of motor thermal analysis and temperature field simulation technology, specifically to a three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling. It is applicable to rapid temperature field analysis and thermal evaluation of immersion oil-cooled permanent magnet motors with dual oil circuit cooling structures in the slot and air gap, and is especially suitable for application scenarios with high power density and thermal management requirements, such as electro-hydraulic actuators (EHA). Background Technology

[0002] High-speed permanent magnet motors, with their high power density and excellent dynamic response, are widely used in aerospace, CNC machine tools, electric vehicles, and other fields. Temperature control is crucial for maintaining motor performance, efficiency, and reliability. Therefore, accurate and rapid analysis and evaluation of the motor's temperature field are of great significance. The main method for calculating motor temperature rise includes the lumped parameter thermal network (LPTN) method. LPTN discretizes the motor into a finite number of nodes, which are connected by thermal resistance and thermal capacitance, transforming the heat transfer problem into a circuit problem for solution. This method can quickly establish a temperature rise calculation model based on motor design parameters, requires relatively few computational resources, and can rapidly achieve the thermal performance evaluation of the motor.

[0003] Although the lumped parameter thermal network method has made significant progress in the thermal analysis of motors, existing thermal network modeling methods still have the following shortcomings for permanent magnet motors with dual oil-cooled structures:

[0004] First, there is insufficient detailed modeling of the in-slot cooling structure. Existing models often treat the in-slot windings as isotropic homogeneous entities or simply perform lumped processing when establishing the thermal network of the in-slot windings. However, the in-slot windings are composed of various materials such as copper conductors, enameling layers, impregnating resin, and residual air, and their thermal conductivity differs significantly along the conductor direction (axial) and perpendicular to the conductor direction (radial / circumferential). Adopting the isotropic assumption will distort the heat conduction path of the in-slot windings, affecting the accuracy of the winding temperature rise calculation.

[0005] Second, there is a lack of systematic three-dimensional network description of the oil heat transfer path in dual-oil-circuit cooling structures. Most existing LPTN models for oil-cooled motors are designed for a single oil circuit, or treat the cooling oil temperature as uniform or only make simplifications. For dual-oil-circuit structures with both in-slot and air-gap cooling oil circuits, the flow paths of the two oil circuits, the heat exchange methods with solid components, and the cooling effects on different regions are all different. Existing models fail to perform fine axial discretization of the two oil circuits along the oil flow direction, and cannot accurately describe the impact of the oil friction temperature rise effect on the cooling effect.

[0006] Therefore, how to provide a three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling that can balance computational efficiency and simulation accuracy is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] In view of the above problems, this invention is proposed to provide a three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling, which overcomes or at least partially solves the above problems, thereby meeting the needs of rapid analysis and thermal evaluation of motor temperature field in engineering practice.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a three-dimensional thermal network magnetothermal coupling simulation method for a permanent magnet motor based on dual-oil-path cooling. The permanent magnet motor has an in-slot cooling oil path and an air gap cooling oil path. The method includes the following steps: S1: Based on the structural characteristics of the permanent magnet motor, the motor as a whole is spatially discretized in three dimensions: axial, radial and circumferential, and a temperature node system of a three-dimensional thermal network is established. S2: Based on the dynamic relationship between the structural material parameters of the permanent magnet motor and temperature, a loss model of each node in the temperature node system is established to obtain the thermal power data of each node at different temperatures. S3: For the slot winding region, establish equivalent thermal conductivity models along the conductor direction and radial direction of the slot winding region to obtain the equivalent thermal conductivity of the slot winding in the axial, radial and circumferential directions. S4: Based on the temperature node system, a three-dimensional thermal network including conductive thermal resistance is established based on the equivalent thermal conductivity of the slot winding and other solid components of the motor, in order to obtain the temperature field solution data of the solid part of the motor. S5: Based on the actual flow paths of the cooling oil circuit in the tank and the air gap cooling oil circuit, establish an oil flow network, discretize the oil along the flow direction into multiple oil nodes, and establish an oil circuit thermal resistance model to obtain the flow thermal resistance between adjacent oil nodes and the convective thermal resistance between oil nodes and adjacent solid nodes. S6: Based on the thermal power data, the temperature field solution data of the solid part of the motor, and the flow thermal resistance and convection thermal resistance, perform a global thermal network magnetothermal bidirectional coupling iterative solution until the temperature converges to obtain the steady-state temperature field of the permanent magnet motor.

[0009] Preferably, in step S1, the motor is divided into five adjacent regions along the motor axis: front cover region, front cavity region, effective section region of stator and rotor core, rear cavity region and rear cover region. The front cover region and the rear cover region are located at opposite ends of the motor axial direction, the front cavity region is located between the front cover region and the effective section region of the stator and rotor core, and the rear cavity region is located between the effective section region of the stator and rotor core and the rear cover region. Both the in-slot cooling oil passage and the air gap cooling oil passage penetrate the front cavity region, the effective section region of the stator and rotor core, and the rear cavity region.

[0010] Preferably, in step S1, the spatial discretization further includes: The front cover area and the rear cover area are each treated as a whole temperature node; The front cavity region and the rear cavity region are each treated as a whole temperature node; The effective section region of the stator and rotor core is discretized into multiple sub-segments along the axial direction, with each sub-segment serving as an axial temperature node. The motor is divided into multiple concentric ring layers radially from the center outwards. Along the circumferential direction, a single stator tooth and its adjacent stator slot are considered as a basic heat transfer unit, and the number of units is equal to the number of motor slots.

[0011] Preferably, in step S2, the loss model includes a winding copper loss model, a stator and rotor iron loss model, a permanent magnet eddy current loss model, and a rotor oil churning loss model. The winding copper loss model dynamically updates the winding material property parameters according to the node temperature and calculates the copper loss heat power in real time. The stator and rotor iron loss model dynamically updates the hysteresis loss coefficient and eddy current loss coefficient according to the node temperature, and calculates the stator and rotor iron loss heat power in real time. The permanent magnet eddy current loss model dynamically updates the conductivity temperature coefficient and remanence temperature coefficient according to the node temperature, and calculates the permanent magnet eddy current loss heat power in real time based on the finite element electromagnetic field model and maps it to the temperature node system. The rotor churning loss model dynamically updates the circumferential Reynolds number of the air gap based on the node temperature, and calculates the rotor churning loss heat power in real time.

[0012] Preferably, in step S3, the equivalent thermal conductivity model of the in-slot winding includes: A parallel thermal conductivity model is used to calculate the corresponding thermal conductivity based on the volume fill rate of the copper conductor and the insulating matrix material to obtain the axial equivalent thermal conductivity of the winding in the slot. A series thermal conductivity model is used to calculate the corresponding thermal conductivity based on the volume fill rate of the copper conductor and the insulating matrix material, and the radial equivalent thermal conductivity and circumferential equivalent thermal conductivity of the winding in the slot are obtained by summing them in series.

[0013] Preferably, in step S4, in the temperature node system, a single stator tooth and an adjacent stator slot are used as a basic heat transfer unit to construct the corresponding in-slot winding node along the circumferential direction; for the first i The first axial segment and the first k The slot winding nodes in each circumferential slot unit adopt a thermal network model that includes radial thermal resistance, axial thermal resistance, and circumferential thermal resistance; wherein, the radial thermal resistance, axial thermal resistance, and circumferential thermal resistance are calculated based on the equivalent thermal conductivity of the slot winding in the axial, radial, and circumferential directions obtained in step S3.

[0014] Preferably, in step S4, the other solid components of the motor include end caps, shafts, housings, sheaths, stator yokes, stator teeth, and permanent magnets; For the end cap, shaft, housing, and sheath, a thermal network model that only includes radial and axial thermal resistance is used. For the stator yoke, stator teeth, and permanent magnet, which have a tile-like structure after circumferential discretization, a thermal network model including radial thermal resistance, axial thermal resistance, and circumferential thermal resistance is adopted.

[0015] Preferably, in step S5, the method for establishing the oil circuit thermal resistance model includes: Along the oil flow direction, the cooling oil passage in the tank and the air gap cooling oil passage are respectively discretized into multiple oil nodes along the motor axis. Adjacent oil nodes are connected by flow thermal resistance, which is calculated based on the oil mass flow rate and constant pressure specific heat capacity. The oil circuit thermal resistance model includes: a convective heat transfer model between the oil node in the slot and the adjacent winding node, and a convective heat transfer model between the oil node in the air gap and the adjacent rotor sleeve node.

[0016] Preferably, the convective thermal resistance between the oil node in the tank and the adjacent winding node is calculated based on the flow state parameters of the cooling oil, the thermal property parameters of the oil, and the geometric parameters of the flow channel in the tank, wherein the flow state parameters are determined based on the oil flow velocity and the hydraulic diameter. The convective thermal resistance between the air gap oil node and the adjacent rotor sleeve node is calculated based on the rotational flow state parameters of the cooling oil, the thermal properties of the oil, and the geometric parameters of the air gap, wherein the rotational flow state parameters are determined based on the rotor speed and the air gap width.

[0017] Preferably, in step S6, the magnetocaloric bidirectional coupling iterative solution includes the following sub-steps: S10: Obtain the current temperature of each node; S20: Based on the current temperature of each node, call the loss model in step S2 to calculate the thermal power data of each node, and call the oil circuit thermal resistance model in step S5 to calculate the convective thermal resistance between each oil node and its adjacent solid node. S30: Load the thermal power data calculated in step S20 onto the corresponding permanent magnet motor structural nodes of the three-dimensional thermal network established in step S4, and load the convective thermal resistance calculated in step S20 and the flow thermal resistance between adjacent oil nodes established in step S5 into the global thermal network to solve for the new temperature of each node. S40: Update the corresponding material properties in step S2 based on the temperature of each structural node of the permanent magnet motor obtained from the solution; S50: Return to step S20 using the updated material properties, and repeat steps S20 to S40 until the temperature change at each node meets the preset convergence condition.

[0018] The specific beneficial effects of the above-mentioned technical solutions provided in the embodiments of the present invention include at least the following: This invention spatially discretizes the motor in three dimensions: axial, radial, and circumferential, and establishes a three-dimensional thermal network temperature node system. This system can capture the temperature distribution characteristics in the three-dimensional space inside the motor, overcoming the problem that traditional two-dimensional or one-dimensional thermal network models cannot reflect local temperature rise hotspots. While maintaining the advantages of the lumped parameter thermal network method in fast solution, it significantly improves the spatial resolution of temperature field calculation.

[0019] This invention establishes an equivalent heat conduction model for the in-slot winding region, which is axially parallel and radial / circumferentially series-connected. It accurately distinguishes the difference in heat transfer capacity along the conductor direction and perpendicular to the conductor direction, and overcomes the problem of heat conduction path distortion caused by the traditional model treating the in-slot winding as an isotropic uniform entity. This improves the calculation accuracy of temperature distribution in the winding region.

[0020] Based on the actual flow path of the dual oil circuits, this invention performs axial discretization of the in-slot cooling oil circuit and the air gap cooling oil circuit along the flow direction, and connects adjacent oil nodes through flow thermal resistance. This can capture the influence of the cooling oil temperature rise effect along the flow path on the heat dissipation capacity, and overcome the calculation deviation caused by treating the oil temperature as uniform or only simplifying it in the existing model. This provides a more accurate evaluation of the cooling effect for motors with complex dual oil circuit cooling structures.

[0021] This invention employs differentiated modeling methods, using a four-thermal-resistance network model and a six-thermal-resistance network model, for continuous structural components such as end caps, shafts, housings, and sheaths, and for components with tile-like structures after circumferential discretization, such as stator yokes, stator teeth, and permanent magnets. Without excessively increasing the computational burden, it precisely depicts the conduction paths in three-dimensional space, thereby improving the calculation accuracy of temperature gradients at complex geometric structures of stators and rotors.

[0022] This invention introduces dynamic correction relationships of key parameters such as copper resistance, iron loss coefficient, permanent magnet conductivity and remanence, and oil viscosity with temperature into the loss model at each node. It achieves real-time linkage updates between loss and temperature through iterative solution via magnetocaloric bidirectional coupling. Simultaneously, the oil viscosity is updated synchronously during the iteration process to correct the convective heat transfer coefficient, so that both the heat source input and heat dissipation boundary conditions change dynamically with temperature, thereby improving the reliability of temperature field calculation results across the entire operating range. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 A flowchart illustrating the three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual-oil-path cooling, provided in an embodiment of the present invention. Figure 2 A schematic diagram of a dual-oil-path cooling structure and axial partitioning for simultaneous oil cooling in the air gap and slot, provided in an embodiment of the present invention. Figure 3 A schematic diagram of the radial model of a specific example motor provided in this embodiment of the invention; Figure 4 A schematic diagram of the axial model of a specific example motor provided in this embodiment of the invention; Figure 5 This is an equivalent reconstruction diagram of a single-tooth single-slot unit structure containing an in-slot cooling channel provided in an embodiment of the present invention. Figure 6 A schematic diagram of the thermal network model for the radial and axial thermal resistances of the solid structure of the motor part provided in an embodiment of the present invention; Figure 7 A schematic diagram of the thermal network model of the radial thermal resistance, axial thermal resistance and circumferential thermal resistance of the solid structure of the motor part provided in the embodiment of the present invention.

[0025] In the diagram, 1 is the housing, 2 is the stator, 3 is the stator winding, 4 is the sheath, 5 is the permanent magnet, 6 is the rotor core, 7 is the shaft, 8 is the end cover, 9 is the bearing, 10 is the in-slot cooling oil passage, 11 is the air gap cooling oil passage, 12 is the end oil area, 21 is the stator yoke, 22 is the stator tooth, 200 is the equivalent stator tooth, and 300 is the equivalent winding. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The permanent magnet motor is a surface-mounted internal rotor permanent magnet synchronous motor. Taking a permanent magnet motor with a rated power of 11kW and a rated speed of 9000rpm used in an electro-hydraulic actuator (EHA) as an example, the motor structure of the embodiment is as follows: Figures 2-4 As shown.

[0028] The motor has 9 stator slots and 6 rotor poles. Both the stator core and rotor core 6 are made of laminated silicon steel sheets. The motor adopts an internal rotor structure, with the following components arranged from the center outwards: shaft 7, rotor core 6, permanent magnet 5, sheath 4, air gap, stator 2, and housing 1. End covers 8 are provided at both ends of the motor, including a front cover and a rear cover. The shaft 7 is supported on the end covers 8 by bearings 9. Specifically: The stator 2 includes a stator core and stator windings 3. The stator core is annular, with nine stator slots evenly spaced along its inner circumference, forming stator teeth 22 between the slots. The stator windings 3 are embedded in the stator slots and are distributed windings made of round copper wire with an enameled insulation layer on the surface of the conductors. The space between the stator windings 3 and the stator slot walls is filled with impregnated resin. Each stator slot contains two layers of winding conductors, an upper winding and a lower winding.

[0029] The rotor core 6 is fixedly mounted on the rotating shaft 7, and permanent magnets 5 are uniformly attached to the outer surface of the rotor core 6 along the circumference. A protective sleeve 4 is provided on the outer periphery of the permanent magnets 5. The protective sleeve 4 is a cylindrical structure that fits around the permanent magnets 5 and is used to fix and protect the permanent magnets 5 during high-speed rotation. An air gap is formed between the outer surface of the protective sleeve 4 and the inner surface of the stator 2.

[0030] The motor has two independent cooling oil flow paths: the in-slot cooling oil path 10 and the air gap cooling oil path 11. The cooling oil uses the hydraulic oil of the electro-hydraulic actuator system itself as the cooling medium. It enters the motor from the oil inlet at the front end of the motor, flows through the two oil paths after being partially diverted at the front end of the motor, and finally flows out from the oil outlet at the rear end of the motor. The motor end has an end oil area 12, including a front end oil chamber and a rear end oil chamber.

[0031] Cooling oil passage 10 in the tank: such as Figure 3As shown, each stator slot is provided with two in-slot cooling oil passages 10, which are arranged radially at intervals along the slot. The radial centerline between the two in-slot cooling oil passages 10 serves as the boundary. The winding located on the side closer to the slot opening on the radial centerline is the upper winding, and the winding closer to the slot bottom is the lower winding. The cross-sectional shape of the in-slot cooling oil passage 10 is square, and it runs through the entire stator slot along the motor axis. After the cooling oil flows in from the front oil inlet, it is distributed into the in-slot cooling oil passages 10 of each stator slot through the front end oil cavity. It flows axially through the entire effective section of the stator and rotor core, cooling the stator windings 3 and the stator core in the slot. After flowing out of the stator slot, it collects in the rear end oil cavity and flows out from the rear end oil outlet.

[0032] Air gap cooling oil circuit 11: After the cooling oil flows in from the front oil inlet, it enters the air gap through the front end oil chamber, flows axially through the entire air gap area, cools the sheath 4, permanent magnet 5 and rotor core 6, and flows out of the air gap and collects in the rear end oil chamber, and flows out from the rear end oil outlet.

[0033] The two oil paths flow independently after splitting at the front end, and each flows through a solid component through a convective heat exchange. They then merge at the rear end and flow out of the motor together.

[0034] This invention specifically discloses a three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual-oil-circuit cooling, combined with, for example... Figure 1 The flowchart shown is shown.

[0035] The steps of the method according to the embodiments of the present invention are described below: S1: Based on the structural characteristics of the permanent magnet motor, the motor as a whole is spatially discretized in three dimensions: axial, radial and circumferential, and a temperature node system of a three-dimensional thermal network is established.

[0036] In one embodiment, the motor structure is divided into regions in three dimensions—axial, radial, and circumferential—based on the structural characteristics of each part of the permanent magnet motor.

[0037] In this embodiment, step S1, spatial discretization includes: The motor can be divided into multiple concentric ring layers radially from the center outwards, which can be up to seven concentric ring layers. Along the circumferential direction, a single stator tooth 22 and an adjacent stator slot are used as a basic heat transfer unit, and the number of units is equal to the number of motor slots Z.

[0038] In this embodiment, step S1, spatial discretization includes: The motor is divided into five adjacent regions along its axial direction: front cover region, front cavity region, effective section region of stator and rotor core, rear cavity region, and rear cover region. The front cover area and the rear cover area are located at the two ends of the motor axis, respectively. The front cavity area is located between the front cover area and the effective section area of ​​the stator and rotor core, and the rear cavity area is located between the effective section area of ​​the stator and rotor core and the rear cover area. The in-slot cooling oil passage 10 and the air gap cooling oil passage 11 both penetrate the front cavity region, the effective section region of the stator and rotor cores, and the rear cavity region.

[0039] Furthermore, the front cover area and the rear cover area are each treated as a single temperature node; Treat the front cavity region and the rear cavity region as a single temperature node; The effective segment region of the stator and rotor cores is discretized along the axial direction as follows: There are 10 sub-segments, each serving as an axial temperature node, for a total of 10 axial nodes. .

[0040] Therefore, in this embodiment, the motor is divided into Each node.

[0041] Furthermore, the motor is divided into five regions along its axial direction: The first region is the front end cover region, extending from the outer end face to the inner end face of the end cover, including the front end cover housing, the front end cover bearing, and the shaft extension section. The second region is the front end cavity region, extending from the inner end face of the front end cover to the front end face of the stator core, including the front winding and the front end cavity oil. The third region is the effective section of the stator and rotor core, extending from the front end face of the stator core to the rear end face of the stator core. The fourth region is the rear end cavity region, extending from the rear end face of the stator core to the inner end face of the rear end cover, including the rear winding and the rear end cavity oil. The fifth region is the rear end cover region, extending from the inner end face of the rear end cover to the outer end face of the rear end cover, including the rear end cover housing, the rear end cover bearing, and the shaft extension section. The concentric ring layers divided along the radial direction of the motor include the layer containing the housing 1, the composite layer of the stator 2 and the stator winding 3, the oil circuit layer, the layer containing the sheath 4, the layer containing the permanent magnet 5, the layer containing the rotor core 6, and the layer containing the shaft 7.

[0042] In this embodiment, a unified node numbering system is established: Axial index: ,common A axial region; in this specific implementation example, preferably .

[0043] Radial index: This corresponds to 7 radial layers; Circumferential Index: This corresponds to 9 toothed units.

[0044] Any node Representing the i The first axial region, the first jThe radial layer, the first k The average temperature at each circumferential position. Because the first The internal structure of each axial region is relatively simple, so radial and circumferential divisions are no longer required for these axial regions.

[0045] S2: Based on the dynamic relationship between the structural material parameters of the permanent magnet motor and temperature, the losses in each region of the motor are calculated independently, and a loss model of each node in the temperature node system is established to obtain the thermal power data of each node at different temperatures, so as to realize the dynamic update of losses with node temperature.

[0046] In one embodiment, in step S2, the loss model includes a winding copper loss model, a stator and rotor iron loss model, a permanent magnet eddy current loss model, and a rotor oil churning loss model; the total heat source of the motor is expressed as:

[0047] in, This indicates the temperature of each node in the motor, i.e. ; A model representing the total heat source at each node temperature of the motor; A model representing the winding copper loss at various node temperatures of the motor; A stator and rotor iron loss model representing the temperature at each node of the motor; The permanent magnet eddy current loss model represents the temperature at each node of the motor. This represents the rotor oil churning loss model at various node temperatures of the motor.

[0048] The winding copper loss model dynamically updates the winding material property parameters based on the node temperature, and calculates the copper loss heat power in real time. :

[0049]

[0050]

[0051] in, The AC copper loss of the windings at various node temperatures of the motor. The winding DC copper loss at various node temperatures of the motor. This represents the number of winding phases. This is the effective value of the phase current. Initial temperature Lower node winding resistance, The temperature coefficient of resistance of copper. The magnetic flux density angular frequency, The magnitude of the magnetic flux density. This is the length of the conductor segment. The diameter of the copper wire used for winding. Initial temperature Resistivity of the lower node winding.

[0052] The stator and rotor iron loss model dynamically updates the hysteresis loss coefficient and eddy current loss coefficient based on the node temperature, and calculates the stator and rotor iron loss heat power in real time. : 。

[0053] Considering the effect of temperature on the iron loss coefficient:

[0054]

[0055] in, The operating frequency of the motor. The magnitude of the magnetic flux density. Here is the hysteresis loss coefficient at each node temperature of the motor. Initial temperature Hysteresis loss coefficient Here is the eddy current loss coefficient at each node temperature of the motor. Initial temperature Lower eddy current loss coefficient, For additional loss coefficient, , The temperature correction factor can be obtained from the silicon steel loss data provided by the manufacturer. The Steinmetz coefficient, whose value depends on the magnetization properties and magnetic flux density amplitude of the ferromagnetic material. It is usually between 1.6 and 2.5, and can be obtained from the material loss data provided by the manufacturer.

[0056] The permanent magnet eddy current loss model dynamically updates the conductivity temperature coefficient and remanence temperature coefficient based on the node temperature, and calculates the permanent magnet eddy current loss heat power in real time based on the finite element electromagnetic field model. And mapped to the temperature node system:

[0057] in, Let be the conductivity of permanent magnet 5 at each node temperature of the motor. The initial temperature of permanent magnet 5 Lower conductivity, The temperature coefficient of electrical conductivity The remanence of the permanent magnets at various node temperatures of the motor. The initial temperature of permanent magnet 5 Residual magnetism, is the temperature coefficient of remanence.

[0058] In the finite element method (FEM) calculation of eddy current loss of permanent magnets, firstly, the conductivity and remanence density of each element of the permanent magnet are updated based on the temperature feedback from the thermal network nodes; then, the updated conductivity and remanence are assigned to each element of the permanent magnet finite element model, and the eddy current density of each element is obtained by solving the finite element model, and the eddy current loss volume density of each element is calculated according to Joule's law; finally, based on the axial and radial region division of permanent magnet 5, the eddy current loss power of the elements covered by each region is accumulated to obtain the equivalent thermal power carried by each temperature node.

[0059] The rotor churning loss model dynamically updates the circumferential Reynolds number of the air gap based on the node temperature, and calculates the rotor churning loss heat power in real time. :

[0060] in, The coefficient of surface friction, For the density of the oil, The rotor's mechanical angular velocity, The radius of the rotor surface. The segment length is the length of the two oil passages that are axially discretely segmented along the direction of oil flow.

[0061]

[0062] in, The width of the air gap. For the air gap circumferential Reynolds number:

[0063] in, This is the dynamic viscosity coefficient of the oil. This is a viscosity-temperature characteristic parameter of oil, used to describe the sensitivity of viscosity to temperature changes, and is an empirical constant.

[0064] S3: For the slot winding region, establish equivalent thermal conductivity models along the conductor direction and radial direction of the slot winding region to obtain the equivalent thermal conductivity of the slot winding with anisotropy in the axial, radial and circumferential directions.

[0065] In one embodiment, in step S3, such as Figure 5 As shown, the slot winding and stator teeth 22 are treated equivalently to obtain equivalent stator teeth 200 and equivalent windings 300, which facilitates the establishment of a thermal network without sacrificing accuracy. The equivalent heat conduction model of the slot winding includes: A parallel thermal conductivity model is used to calculate the corresponding thermal conductivity based on the volume fill rate of the copper conductor and the insulating matrix material to obtain the axial equivalent thermal conductivity of the winding in the slot. A series thermal conductivity model is used to calculate the corresponding thermal conductivity based on the volume fill rate of the copper conductor and the insulating matrix material, and the radial equivalent thermal conductivity and circumferential equivalent thermal conductivity of the winding in the slot are obtained by summing them in series.

[0066] In this embodiment, in the slot winding, each conductor is basically arranged parallel to the motor axis. When the heat flow propagates along the direction of the conductor, the copper conductor and the insulating substrate simultaneously bear the heat flow. Its heat conduction process can be approximated as a parallel heat conduction model.

[0067] Let the cross-sectional area of ​​the winding be The area of ​​the copper conductor is The area of ​​the insulating substrate is Then we have: .

[0068] According to Fourier's law of heat conduction, the heat flows of each part are as follows:

[0069] in, For heat flow in copper conductors; For the heat flow of the insulating substrate; The thermal conductivity of copper conductors; The equivalent thermal conductivity of the insulating matrix is ​​given by the equivalent value calculated based on the volume ratio of each component. The insulating matrix includes the enameled layer, impregnating resin, and residual air. This represents the temperature difference between the current temperature and the temperature at the previous time step.

[0070] The total heat flow can be expressed as: .

[0071] On the other hand, if the entire winding is considered as a uniform medium, its axial heat flow can be expressed as:

[0072] in, The equivalent thermal conductivity of the winding, This represents the equivalent area of ​​the winding. Equalizing the two equations, we get: 。

[0073] Define axial copper fill rate : 。

[0074] The axial equivalent thermal conductivity of the winding in the slot is: .

[0075] In this embodiment, when the heat flow propagates radially, the heat flow needs to pass continuously through the copper conductor, the enameled layer and the impregnating resin. Therefore, the heat conduction process can be approximated as a series heat conduction model.

[0076] According to Fourier's law, the thermal resistance of a copper conductor... Thermal resistance of insulating substrate They are respectively:

[0077] Total thermal resistance for:

[0078] Let the total length be for:

[0079] in, This is the total radial length of the copper conductor. This is the total radial length of the insulating body; Then the equivalent thermal resistance It can be represented as:

[0080] Combined with radial copper fill rate :

[0081] The radial equivalent thermal conductivity of the winding in the slot can be obtained. for: .

[0082] The radial direction of the in-slot winding relative to the motor includes both circumferential and radial directions. Therefore, when establishing the thermal network for the in-slot winding, both radial and circumferential heat transfer can be used. Perform the calculation.

[0083] Because copper has a much higher thermal conductivity than insulating materials, it typically has the following properties: ; This indicates that the windings inside the slot exhibit significant thermal anisotropy.

[0084] S4: Based on the temperature node system, a three-dimensional thermal network including conductive thermal resistance is established based on the equivalent thermal conductivity of the in-slot windings and other solid components of the motor, which is used to obtain the temperature field solution data of the solid parts of the motor.

[0085] In one embodiment, in step S4, other solid components of the motor include end cap 8, shaft 7, housing 1, sheath 4, stator yoke 21, stator teeth 22, and permanent magnet 5. For end cap 8, shaft 7, housing 1 and sheath 4, a thermal network model that only includes radial thermal resistance and axial thermal resistance is adopted; For the stator yoke 21, stator teeth 22 and permanent magnet 5, which have a tile-like structure after circumferential discretization, a thermal network model including radial thermal resistance, axial thermal resistance and circumferential thermal resistance is adopted.

[0086] In this embodiment, for the end cover 8, housing 1, rotating shaft 7 and sheath 4, since their circumferential structure is continuous and symmetrical, the heat source distribution is relatively uniform, and the circumferential temperature gradient is small, only the heat transfer process in the radial and axial directions is considered, and the influence of circumferential thermal resistance on the temperature field calculation results is ignored.

[0087] The thermal network of end cap 8 and rotating shaft 7 was calculated using a solid cylindrical model, and the thermal network includes outer surface nodes. Left end face node Right end face node and average temperature nodes : from to The radial thermal resistance is:

[0088] from to and The axial thermal resistance is:

[0089] in, For the radial thermal resistance of end cap 8 / rotating shaft 7, , End cap 8 / pivot 7 to , to Axial thermal resistance, The radius of end cap 8 / rotating shaft 7, Thermal conductivity of end cap 8 / rotating shaft 7 This refers to the axial length of the end cap 8 / rotating shaft 7.

[0090] In this embodiment, the thermal network of the housing 1 and the sheath 4 is modeled using an equivalent thermal path topology structure model of a hollow cylinder cross, which models the heat flow paths in both the axial and radial directions. Specifically, after equating the housing 1 and the sheath 4 to hollow cylinders, the calculation formulas for the four thermal resistances in this cross-shaped equivalent thermal path topology are derived: Radial thermal resistance simplified to:

[0091] The axial thermal resistance is:

[0092] in, For the heat of the casing 1 / sheath 4 from the average radius Flowing outward radius The thermal resistance encountered during conduction; For the heat of the casing 1 / sheath 4 from the average radius Flowing towards the inner radius The thermal resistance encountered at the location; , The heat from the average temperature node is respectively transferred from the casing 1 / sheath 4. Flowing to the left end face node Average temperature nodes Flowing to the right end face node The thermal resistance encountered at the location; ; The axial length of housing 1 / shroud 4; Let be the thermal conductivity of the material of the casing 1 / sheath 4. The thermal network structure is as follows: Figure 6 As shown, it consists of four thermal resistors.

[0093] In this embodiment, the rotor core 6, permanent magnet 5, and stator yoke 21 are partitioned to form a tile-like structure. Considering the silicon steel sheet stacked structure, the radial thermal conductivity of the rotor core 6 and stator yoke 21 is... With axial thermal conductivity The radial thermal conductivity is different for rotor core 6 and stator yoke 21. With axial thermal conductivity The calculation formula is as follows, and the radial thermal conductivity is used instead of the circumferential thermal conductivity:

[0094]

[0095] in, It is the stacking coefficient of rotor core 6 / permanent magnet 5 / stator yoke 21. For the thermal conductivity of the silicon steel sheet body, The thermal conductivity between silicon steel sheets.

[0096] The formula for calculating radial thermal resistance is:

[0097] in, The heat generated by the rotor core 6 / permanent magnet 5 / stator yoke 21 from the average radius Flowing outward radius The thermal resistance encountered during conduction, The heat generated by the rotor core 6 / permanent magnet 5 / stator yoke 21 from the average radius Flowing towards the inner radius The thermal resistance encountered at the location, For circumferential angle, It is the axial length of rotor core 6 / permanent magnet 5 / stator yoke 21.

[0098] Axial thermal resistance (connection) to and The formula for calculating ) is:

[0099] Circumferential thermal resistance (from the average temperature node) (To both circumferential end faces) is:

[0100] in, , The heat from the rotor core 6, permanent magnet 5, and stator yoke 21 is respectively transferred from the average temperature node. Flowing to the left end face node Average temperature nodes Flowing to the right end face node The thermal resistance encountered at the location; , The heat from the rotor core 6, permanent magnet 5, and stator yoke 21 is respectively transferred from the average temperature node. The thermal resistance encountered at both circumferential end faces. A thermal network, such as... Figure 7 As shown, it consists of six thermal resistors.

[0101] In one embodiment, in step S4, the temperature node system constructs a corresponding in-slot winding node along the circumferential direction using a single stator tooth 22 and an adjacent stator slot as a basic heat transfer unit; for the first i The first axial segment and the first k The slot winding nodes in each circumferential slot unit adopt a thermal network model that includes radial thermal resistance, axial thermal resistance and circumferential thermal resistance; wherein, the radial thermal resistance, axial thermal resistance and circumferential thermal resistance are calculated based on the equivalent thermal conductivity of the slot winding in the axial, radial and circumferential directions obtained in step S3.

[0102] In this embodiment, for the three-dimensional thermal network of a single circumferential stator tooth stator slot unit... The first axial segment, the first One circumferential groove element, defining temperature nodes: stator yoke nodes. stator tooth node Upper winding node lower winding node Upper oil passage node Lower oil passage node .

[0103] Radial thermal resistance of stator yoke 21 Axial thermal resistance Circumferential thermal resistance :

[0104]

[0105]

[0106] in, For the circumferential angle of a single stator single-slot unit structure, The outer radius of stator yoke 21, The inner radius of stator yoke 21, For the first Each axial segment length, The radial thermal conductivity of the stator yoke 21 material is given. The axial thermal conductivity of the stator yoke 21 material is given. The circumferential thermal conductivity is the circumferential thermal conductivity of the stator yoke 21 material.

[0107] radial thermal resistance of stator tooth 22 region Axial thermal resistance Circumferential thermal resistance :

[0108]

[0109]

[0110] in, The width of stator tooth 22, The height of stator tooth 22, The axial length of stator tooth 22, The radial average radius of stator tooth 22.

[0111] Radial thermal resistance of the upper winding Axial thermal resistance Axial thermal resistance radial thermal resistance of the lower winding Axial thermal resistance Axial thermal resistance :

[0112]

[0113]

[0114] in This refers to the height of the upper winding. This refers to the height of the lower winding. This is the average circumferential length of the upper winding. This represents the average length of the lower winding. , , These are the effective thermal conductivity cross-sectional areas of the upper winding, namely the radial, axial, and circumferential areas. , , These represent the effective thermal conductivity cross-sectional areas in the radial, axial, and circumferential directions of the lower winding, respectively.

[0115] S5: Based on the actual flow paths of the cooling oil passage 10 in the tank and the air gap cooling oil passage 11, establish an oil flow network, discretize the oil along the flow direction into multiple oil nodes, and establish an oil passage thermal resistance model to obtain the flow thermal resistance between adjacent oil nodes and the convective thermal resistance between oil nodes and adjacent solid nodes.

[0116] In one embodiment, step S5, the method for establishing the oil circuit thermal resistance model includes: Along the oil flow direction, the in-tank cooling oil passage 10 and the air gap cooling oil passage 11 are discretized into multiple oil nodes along the motor axis. Adjacent oil nodes are connected by flow thermal resistance, which is calculated based on the oil mass flow rate and constant pressure specific heat capacity. Specifically, according to the law of conservation of energy, the first... The oil flow node and the first The flow thermal conductivity between oil nodes is defined as:

[0117] in, Indicates the first Segmental flow thermal conductivity, It is the oil mass flow rate. It is the constant pressure specific heat capacity of hydraulic oil.

[0118] To unify the thermal network configuration, the axial energy transport term of the oil is equivalent to the flow thermal resistance. Its numerical value is defined as:

[0119] This thermal resistance is only used for solving thermal networks and does not represent the actual thermal resistance.

[0120] The oil circuit thermal resistance model includes: a convective heat transfer model between the oil node in the slot and the adjacent winding node, and a convective heat transfer model between the oil node in the air gap and the adjacent rotor sleeve node. The convective thermal resistance between the oil and solid components is also considered. Represented as:

[0121] in, The convective heat transfer coefficient at the interface. Let be the area of ​​the interface.

[0122] The convective thermal resistance between the oil node in the coolant tank and the adjacent winding node is calculated based on the flow state parameters, thermal properties of the cooling oil, and geometric parameters of the flow channel within the coolant tank. The flow state parameters are determined based on the oil velocity and hydraulic diameter. Specifically, the convective heat transfer coefficient between the oil node in the coolant tank and the winding within the coolant tank is expressed as:

[0123]

[0124]

[0125]

[0126] in, The convective heat transfer coefficient between the oil node in the slot and the winding in the slot is given. For Nusselt numbers, For Prandtl numbers, The Reynolds number is... For the density of the oil, For oil flow rate, The hydraulic diameter of the oil is... The thermal conductivity of the oil is... This refers to the dynamic viscosity of the oil.

[0127] The convective thermal resistance between the air gap oil node and the adjacent rotor sleeve node is calculated based on the rotational flow state parameters, oil thermal properties, and air gap geometric parameters of the cooling oil. The rotational flow state parameters are determined based on the rotor speed and air gap width. Specifically, the convective heat transfer coefficient between the air gap oil node and the rotor sleeve is expressed as:

[0128]

[0129] in, The convective heat transfer coefficient between the air gap oil node and the rotor sleeve is given. The average radius of the air gap is 1. The width of the air gap. ω is the rotor mechanical angular velocity.

[0130] S6: Based on thermal power data, temperature field solution data of the solid part of the motor, and flow thermal resistance and convection thermal resistance, the three-dimensional thermal network is coupled and assembled with the oil flow network into a global thermal network, and a magnetothermal bidirectional coupling iterative solution is performed until the temperature converges to obtain the steady-state temperature field of the permanent magnet motor.

[0131] In one embodiment, step S6, the magnetothermal bidirectional coupling iterative solution includes the following sub-steps: S10: Obtain the current temperature of each node; S20: Based on the current temperature of each node, call the loss model in step S2 to calculate the thermal power data of each node, and call the oil circuit thermal resistance model in step S5 to calculate the convective thermal resistance between each oil node and its adjacent solid node. S30: Load the thermal power data calculated in step S20 onto the corresponding permanent magnet motor structural nodes of the three-dimensional thermal network established in step S4, and load the convective thermal resistance calculated in step S20 and the flow thermal resistance between adjacent oil nodes established in step S5 into the global thermal network to solve for the new temperature of each node. S40: Update the corresponding material properties in step S2 based on the temperature of each structural node of the permanent magnet motor obtained from the solution; S50: Return to step S20 using the updated material properties, and repeat steps S20 to S40 until the temperature change at each node meets the preset convergence condition.

[0132] Table 1 shows a consistency comparison between the results of temperature field simulation using existing finite element thermal simulation software and the results of the three-dimensional thermal network magnetothermal coupling method of the present invention.

[0133] Table 1. Calculation error results of the method of the present invention and existing finite element thermal simulation software.

[0134] The specific embodiment focuses on a high-speed permanent magnet synchronous motor for electro-hydraulic actuators, and simulation calculations are performed under typical operating conditions of 90 degrees Celsius. This condition represents a typical high-temperature and harsh operating environment. Under such conditions, the motor's material properties are highly sensitive to ambient temperature, making accurate calculation of the temperature field a significant challenge. Against this backdrop, the lumped-parameter thermal network model constructed in this invention, while significantly reducing the order and simplifying the computational scale, maintains a maximum deviation of 8.77% and an average deviation of 6.29% in computational accuracy at 90°C, verifying the engineering feasibility and computational reliability of this invention under high-temperature operating conditions.

[0135] In terms of computational efficiency, the method of this invention shows significant advantages. On the same computer hardware platform (Intel Core i5-13400, RAM 16GB), the 3D thermal steady-state solution of the motor is performed using the finite element simulation software Ansys Fluent, and the solution time for a single iteration reaches 5 hours. When the iterative solution of magnetothermal coupling is added, at least 5 iterations are required to reach a convergent solution. However, the simulation model of this invention is built in MATLAB, and the calculation time for a single iteration is 3.2 seconds, which greatly reduces the amount of computation and significantly improves the computational efficiency, thus meeting the requirements of real-time thermal management.

[0136] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0137] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for magnetic-thermal coupling simulation of a three-dimensional thermal network of a permanent magnet motor based on dual-oil cooling, characterized in that, The permanent magnet motor has in-slot cooling oil passages and air gap cooling oil passages. The method includes the following steps: S1: Based on the structural characteristics of the permanent magnet motor, the motor as a whole is spatially discretized in three dimensions: axial, radial and circumferential, and a temperature node system of a three-dimensional thermal network is established. S2: Based on the dynamic relationship between the structural material parameters of the permanent magnet motor and temperature, a loss model of each node in the temperature node system is established to obtain the thermal power data of each node at different temperatures. S3: For the slot winding region, establish equivalent thermal conductivity models along the conductor direction and radial direction of the slot winding region to obtain the equivalent thermal conductivity of the slot winding in the axial, radial and circumferential directions. S4: Based on the temperature node system, a three-dimensional thermal network including conductive thermal resistance is established based on the equivalent thermal conductivity of the in-slot windings and other solid components of the motor, which is used to obtain the temperature field solution data of the solid parts of the motor. S5: Based on the actual flow paths of the cooling oil circuits in the tank and the air gap cooling oil circuits, an oil flow network is established. The oil is discretized into multiple oil nodes along the flow direction, and an oil circuit thermal resistance model is established to obtain the flow thermal resistance between adjacent oil nodes and the convective thermal resistance between oil nodes and adjacent solid nodes. The method for establishing the oil circuit thermal resistance model includes: Along the direction of oil flow, the cooling oil passage in the tank and the air gap cooling oil passage are discretized into multiple oil nodes along the motor axis. Adjacent oil nodes are connected by flow thermal resistance, which is calculated based on the oil mass flow rate and constant pressure specific heat capacity. The oil circuit thermal resistance model includes: the convective heat transfer model between the oil node in the slot and the adjacent winding node, and the convective heat transfer model between the oil node in the air gap and the adjacent rotor sleeve node. S6: Based on the thermal power data, the temperature field solution data of the solid part of the motor, the flow thermal resistance and the convection thermal resistance, perform a global thermal network magnetothermal bidirectional coupling iterative solution until the temperature converges to obtain the steady-state temperature field of the permanent magnet motor.

2. The simulation method for three-dimensional thermal network magnetothermal coupling of permanent magnet motor based on dual oil circuit cooling as described in claim 1, characterized in that, In step S1, the motor is divided into five adjacent regions along the motor axis: front cover region, front cavity region, effective section region of stator and rotor core, rear cavity region, and rear cover region. The front cover area and the rear cover area are located at the two ends of the motor axis, respectively. The front cavity area is located between the front cover area and the effective section area of ​​the stator and rotor core, and the rear cavity area is located between the effective section area of ​​the stator and rotor core and the rear cover area. The cooling oil passages in the tank and the air gap cooling oil passages both run through the front cavity region, the effective section region of the stator and rotor cores, and the rear cavity region.

3. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 2, characterized in that, In step S1, spatial discretization also includes: Treat the front cover area and the rear cover area as a single temperature node; Treat the front cavity region and the rear cavity region as a single temperature node; The effective section of the stator and rotor core is discretized into multiple sub-segments along the axial direction, with each sub-segment serving as an axial temperature node. The motor is divided into multiple concentric ring layers radially from the center outwards. Along the circumferential direction, a single stator tooth and its adjacent stator slot are considered as a basic heat transfer unit, and the number of units is equal to the number of motor slots.

4. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 1, characterized in that, In step S2, the loss model includes the winding copper loss model, the stator and rotor iron loss model, the permanent magnet eddy current loss model, and the rotor oil churning loss model. The winding copper loss model dynamically updates the winding material property parameters based on the node temperature and calculates the copper loss heat power in real time. The stator and rotor iron loss model dynamically updates the hysteresis loss coefficient and eddy current loss coefficient based on the node temperature, and calculates the stator and rotor iron loss heat power in real time. The permanent magnet eddy current loss model dynamically updates the conductivity temperature coefficient and remanence temperature coefficient according to the node temperature. Based on the finite element electromagnetic field model, the permanent magnet eddy current loss heat power is calculated in real time and mapped to the temperature node system. The rotor oil churning loss model dynamically updates the circumferential Reynolds number of the air gap based on the node temperature, and calculates the rotor oil churning loss heat power in real time.

5. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 1, characterized in that, In step S3, the equivalent heat conduction model of the in-slot winding includes: A parallel thermal conductivity model is used to calculate the corresponding thermal conductivity based on the volume fill rate of the copper conductor and the insulating matrix material to obtain the axial equivalent thermal conductivity of the winding in the slot. A series thermal conductivity model is used to calculate the corresponding thermal conductivity based on the volume fill rate of the copper conductor and the insulating matrix material, and the radial equivalent thermal conductivity and circumferential equivalent thermal conductivity of the winding in the slot are obtained by summing them in series.

6. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 1, characterized in that, In step S4, in the temperature node system, a single stator tooth and its adjacent stator slot are used as a basic heat transfer unit to construct the corresponding in-slot winding node along the circumferential direction; for the first i The first axial segment and the first k The slot winding nodes in each circumferential slot unit adopt a thermal network model that includes radial thermal resistance, axial thermal resistance and circumferential thermal resistance; wherein, the radial thermal resistance, axial thermal resistance and circumferential thermal resistance are calculated based on the equivalent thermal conductivity of the slot winding in the axial, radial and circumferential directions obtained in step S3.

7. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 1, characterized in that, In step S4, other solid components of the motor include end caps, shafts, housings, sheaths, stator yokes, stator teeth, and permanent magnets; For end caps, shafts, housings, and sheaths, a thermal network model that only includes radial and axial thermal resistance is used. For the stator yoke, stator teeth, and permanent magnet, which have a tile-like structure after circumferential discretization, a thermal network model including radial thermal resistance, axial thermal resistance, and circumferential thermal resistance is adopted.

8. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 1, characterized in that, The convective thermal resistance between the oil node in the tank and the adjacent winding node is calculated based on the flow state parameters of the cooling oil, the thermal property parameters of the oil, and the geometric parameters of the flow channel in the tank. The flow state parameters are determined based on the oil flow velocity and hydraulic diameter. The convective thermal resistance between the air gap oil node and the adjacent rotor sleeve node is calculated based on the rotational flow state parameters of the cooling oil, the thermal properties of the oil, and the geometric parameters of the air gap. The rotational flow state parameters are determined based on the rotor speed and the air gap width.

9. The three-dimensional thermal network magnetothermal coupling simulation method for permanent magnet motors based on dual oil circuit cooling as described in claim 1, characterized in that, In step S6, the magnetothermal bidirectional coupling iterative solution includes the following sub-steps: S10: Obtain the current temperature of each node; S20: Based on the current temperature of each node, call the loss model in step S2 to calculate the thermal power data of each node, and call the oil circuit thermal resistance model in step S5 to calculate the convective thermal resistance between each oil node and its adjacent solid node. S30: Load the thermal power data calculated in step S20 onto the corresponding permanent magnet motor structural nodes of the three-dimensional thermal network established in step S4, and load the convective thermal resistance calculated in step S20 and the flow thermal resistance between adjacent oil nodes established in step S5 into the global thermal network to solve for the new temperature of each node. S40: Update the corresponding material properties in step S2 based on the temperature of each structural node of the permanent magnet motor obtained from the solution; S50: Return to step S20 using the updated material properties, and repeat steps S20 to S40 until the temperature change at each node meets the preset convergence condition.

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