Design method of stator oil circuit structure for high-speed oil-cooled flat wire motor

Abstract

The present invention provides a method for designing the stator oil circuit structure of a high-speed oil-cooled flat wire motor. Based on the ideas of the thermal network method and the finite element method, the method sequentially establishes a structural model, a loss model, and a thermal analysis model of the high-speed flat wire motor. Then, through step-by-step simulation calculations, the temperature rise of various important positions inside the motor when different spray ring structures and iron core oil circuit layouts are selected is determined to determine the optimal design scheme for the motor oil cooling system. Finally, a test motor entity is built for the optimal design scheme determined by simulation, and bench tests are carried out to verify the rationality of the scheme. In this way, a set of accurate and efficient oil cooling system design theories suitable for flat wire winding permanent magnet drive motors is formed.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor manufacturing for new energy vehicles, and particularly relates to a method for designing a stator oil circuit structure of a high-speed oil-cooled flat wire motor. Background Art

[0002] Currently, flat-wire permanent magnet synchronous motors (PMSMs) are increasingly being adopted in new energy vehicles due to their advantages, including high slot fill rate, high power density and efficiency, and excellent heat dissipation. However, at high speeds, the large cross-sectional area of ​​the flat wire leads to an enhanced skin effect and increased AC losses under the action of high-frequency currents. Core losses also increase with increasing speed, placing higher demands on the motor's heat dissipation system. Existing heat dissipation systems for flat-wire motors primarily employ water cooling or oil-water hybrid systems, both of which have drawbacks. For example, water cooling is only suitable for medium- and low-speed motors and cannot meet the heat dissipation requirements of high-speed motors. Oil-water hybrid systems utilize water channels to cool the stator core and reduce the water temperature through heat exchange between the casing oil circuit and the water channels. This results in poor heat dissipation for the end windings, often requiring oil injection through spray pipes or spray rings. This not only increases the complexity of the cooling system but also makes uneven oil spraying difficult to avoid. Some recent existing technologies use spray cooling and pure oil cooling. Although they can improve the heat dissipation effect to a certain extent, they have many adverse effects on motor performance, losses, etc. It can be seen that there is still a lot of room for improvement in the overall design and oil circuit layout of these new motor heat dissipation systems. At this stage, this field also urgently needs a set of effective design theories. Summary of the Invention

[0003] In view of this, and in response to the technical problems existing in this field, the present invention provides a method for designing a stator oil circuit structure of a high-speed oil-cooled flat wire motor, which specifically includes the following steps:

[0004] Step 1: Use finite element simulation software to establish a high-speed flat wire permanent magnet drive motor model, including a two-dimensional magnetic field model and a three-dimensional structural model of the motor;

[0005] Step 2: Select the appropriate stator end spray ring type and oil circuit layout, and design the overall structure of the oil cooling system;

[0006] Step 3: Consider the motor's winding loss, core loss, and permanent magnet eddy current loss to establish a motor electromagnetic loss model;

[0007] Step 4: Using the motor electromagnetic loss model established in step 3, combined with the motor's speed-torque mechanical characteristics, calculate the loss distribution cloud diagrams under rated and peak operating conditions, and select multiple typical operating conditions corresponding to the rated and peak operating conditions to calculate the motor electromagnetic loss and temperature rise respectively;

[0008] Step 5: Perform finite element simulation based on the three-dimensional structural model to extract the fluid domain model of the motor and establish a three-dimensional thermal analysis model of the motor for finite element simulation of the motor temperature rise under rated and peak operating conditions; set the simulation boundary conditions and the cooling oil inlet flow rate and inlet temperature;

[0009] Step 6: Design different combinations of the number, diameter, and shape of the spray ring spray holes, and use the fluid domain 3D thermal analysis model to simulate the winding temperature and stator core temperature cloud map to determine the optimal spray ring specifications;

[0010] Step 7: When the steady-state average temperature of the winding with the optimal spray ring specification obtained by simulation in step 6 exceeds the corresponding threshold, the stator core oil circuits set at the end windings on both sides are simulated and optimized, including: selecting different stator core oil circuit layouts, performing finite element simulation to calculate the stator temperature field corresponding to each oil circuit layout, and using fluid domain model extraction and three-dimensional thermal analysis model to obtain winding temperature and core temperature cloud maps, thereby determining the optimal stator core oil circuit layout and then determining the optimal oil cooling system structure;

[0011] Step 8: Based on the determined optimal oil cooling system structure, a three-dimensional thermal analysis model is used to simulate the stator temperature distribution cloud under different typical operating conditions, and the distribution areas corresponding to the maximum temperatures of the windings and stator core are determined, which will serve as the basis for subsequent motor cooling system optimization;

[0012] Step 9. Build a high-speed flat-wire permanent magnet drive test motor entity based on the optimal oil cooling system structure, and construct a motor temperature rise test platform based on the test motor entity; use the test platform to drive the test motor entity to operate under rated and peak conditions, and measure the temperature rise of the end winding and stator core at the same time, so as to verify the effect of the designed optimal oil cooling system structure.

[0013] Furthermore, in step one, a two-dimensional electromagnetic field model of the motor is established using Motor CAD software, and a three-dimensional structural model of the motor is established using Solid Works software.

[0014] Furthermore, in step 2, an oil circuit layout consisting of an oil inlet pipeline, two spray rings, a stator core oil circuit and an oil outlet pipeline is specifically designed; wherein, the spray rings are arranged at both ends of the casing, and the stator core is located between the two spray rings; after the cooling oil flows from the outside of the casing into the inside through the oil pipeline, part of the cooling oil is distributed to a spray ring, and under the action of oil pressure, it is sprayed from the spray holes distributed circumferentially on the spray ring to cool the end winding on one side close to it; the other part of the cooling oil flows through the stator core oil circuit to the other spray ring, and the stator core and the end winding on the other side are cooled during the flow process; the cooling oil after cooling is discharged from the casing through the oil outlet pipeline and enters the next cooling cycle.

[0015] Furthermore, the motor electromagnetic loss model established in step 3 specifically includes:

[0016] Winding loss model:

[0017] P Cu =P DC +P AC

[0018] Where, P Cu is the total winding loss, P DC is the DC loss of the winding; P AC is the winding AC loss;

[0019] Among them, the DC loss P DC Calculated using the following formula:

[0020] P DC =mI 2 R DC

[0021] Where m is the number of motor phases, I is the effective value of the motor phase current, and R DC is the DC resistance of the winding, which is specifically expressed as:

[0022]

[0023] Where, l Cu is the average half-turn length of the winding, N Φ is the number of series turns per phase, σ Cu is the electrical conductivity of copper, N is the number of parallel branches, and S is the cross-sectional area of ​​the winding;

[0024] AC loss P AC Calculated using the following formula:

[0025]

[0026] Where k s is the AC loss coefficient, B is the magnetic flux density, ω is the electrical angular frequency, d is the conductor thickness, W is the flat wire width, and l is the conductor length;

[0027] Core loss model:

[0028]

[0029] Where, P ir is the core loss, P h is the hysteresis loss, P e is the eddy current loss, P ex is the additional loss, K h and ɑ is the hysteresis loss coefficient, K eis the eddy current loss coefficient, K ex is the additional loss coefficient, B m is the peak value of magnetic flux density, f is the repetitive magnetization frequency;

[0030] Permanent magnet eddy current loss model:

[0031]

[0032] Where, P PM is the eddy current loss of the permanent magnet, L a is the axial length of the permanent magnet, L b is the average width of the permanent magnet, V is the volume of the permanent magnet, ρ pm is the resistivity of the permanent magnet, K pm is the eddy current loss coefficient of the permanent magnet, f pm is the magnetic field alternating frequency, B pm is the maximum magnetic flux density of the permanent magnet.

[0033] Furthermore, in step five, the motor fluid domain model is extracted using Ansys Space Claim software, and a three-dimensional thermal analysis model is established using Ansys Fluent software.

[0034] Furthermore, in step six simulation, the maximum temperature of 180°C allowed by the motor insulation grade H is used as the threshold of the steady-state average temperature of the winding, and when the determined optimal injection ring specification exceeds this threshold, the core oil circuit simulation optimization of step seven is performed.

[0035] Furthermore, the core oil circuit layout selected in step seven includes: a layout form in which multiple axially extending straight oil circuits are evenly arranged outside the stator core, and various staggered oil circuit layout forms including straight oil circuits, and setting the cross-sectional shape and size specifications at each position of the oil circuit.

[0036] Furthermore, in step nine, a motor temperature rise test platform is specifically constructed, which consists of a test motor entity, a dynamometer, a controller, a thermometer, a power analyzer, and a constant temperature oil tank; wherein, the controller is used to drive and control the operation of the test motor entity; the test motor entity is connected to the dynamometer through a coupling, and various motor operating conditions are loaded through the dynamometer; thermocouples connected to the thermometer are provided at the end windings and stator core slots of the test motor entity to measure the temperature rise at the corresponding positions; the power analyzer is used to measure the motor power and speed under various working conditions; the constant temperature oil tank is connected to the oil cooling system in the test motor entity and provides cooling oil circulation for it.

[0037] The above-mentioned method for designing the stator oil circuit structure of a high-speed oil-cooled flat wire motor provided by the present invention is based on the ideas of the thermal network method and the finite element method. The structural model, loss model and thermal analysis model of the high-speed flat wire motor are established in sequence. Then, through step-by-step simulation calculations, the temperature rise of each important position inside the motor when different spray ring structures and iron core oil circuit layouts are selected is determined to determine the optimal design scheme of the motor oil cooling system. Finally, a test motor entity is built for the optimal design scheme determined by simulation and bench tests are carried out to verify the rationality of the scheme. In this way, a set of accurate and efficient oil cooling system design theories suitable for flat wire winding permanent magnet drive motors are formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the structure of a high-speed flat wire winding motor to which the method provided by the present invention is applicable;

[0039] Figure 2 A schematic diagram of an optional oil cooling system structure for executing the method of the present invention;

[0040] Figure 3 A schematic diagram of a spray ring structure that can be selected when performing the method of the present invention;

[0041] Figure 4 The diagram is a schematic diagram of optional stator core oil circuit layouts when executing the method of the present invention. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0043] The method provided by the present invention specifically comprises the following steps:

[0044] Step 1: Use finite element simulation software to establish a high-speed flat wire permanent magnet drive motor model, including a two-dimensional magnetic field model and a three-dimensional structural model of the motor;

[0045] Step 2: Select the appropriate stator end spray ring type and oil circuit layout, and design Figure 2 The overall structure of the oil cooling system shown;

[0046] Step 3: Consider the motor's winding loss, core loss, and permanent magnet eddy current loss to establish a motor electromagnetic loss model;

[0047] Step 4: Using the motor electromagnetic loss model established in step 3, combined with the motor's speed-torque mechanical characteristics, calculate the loss distribution cloud diagrams under rated and peak operating conditions, and select multiple typical operating conditions corresponding to the rated and peak operating conditions to calculate the motor electromagnetic loss and temperature rise respectively;

[0048] Step 5: Perform finite element simulation based on the three-dimensional structural model to extract the fluid domain model of the motor and establish a three-dimensional thermal analysis model of the motor for finite element simulation of the motor temperature rise under rated and peak operating conditions; set the simulation boundary conditions and the cooling oil inlet flow rate and inlet temperature;

[0049] Step 6: Design different combinations of the number, diameter, and shape of the spray ring spray holes, and use the fluid domain 3D thermal analysis model to simulate the winding temperature and stator core temperature cloud map to determine the optimal spray ring specifications;

[0050] Step 7: When the steady-state average temperature of the winding with the optimal spray ring specification obtained by simulation in step 6 exceeds the corresponding threshold, the stator core oil circuits set at the end windings on both sides are simulated and optimized, including: selecting different stator core oil circuit layouts, performing finite element simulation to calculate the stator temperature field corresponding to each oil circuit layout, and using fluid domain model extraction and three-dimensional thermal analysis models to obtain winding temperature and core temperature cloud maps, thereby determining the optimal stator core oil circuit layout and then obtaining the optimal oil cooling system structure;

[0051] Step 8: Based on the determined optimal oil cooling system structure, a three-dimensional thermal analysis model is used to simulate the stator temperature distribution cloud under different typical operating conditions, and the distribution areas corresponding to the maximum temperatures of the windings and stator core are determined, which will serve as the basis for subsequent motor cooling system optimization;

[0052] Step 9. Build a high-speed flat-wire permanent magnet drive test motor entity based on the determined optimal oil cooling system structure, and construct a motor temperature rise test platform based on the test motor entity; drive the test motor entity to operate under rated and peak conditions through the test platform, and measure the temperature rise of the end winding and stator core at the same time, so as to verify the effect of the designed optimal oil cooling system structure.

[0053] In a preferred embodiment of the present invention, first in step 1, a two-dimensional electromagnetic field model of the motor is established using Motor CAD software, and a three-dimensional structural model of the motor is established using SolidWorks software. Figure 1 The specific motor structure is shown, and its parameters are shown in Table 1 below

[0054] Table 1 Key parameters of motor

[0055]

[0056] In order to improve the motor slot fill rate and power density, the flat wire motor winding design uses a 7-layer distributed winding with a pitch of 5.

[0057] In step 2, the oil circuit layout consisting of the oil inlet pipeline, two spray rings, stator core oil circuit and oil outlet pipeline is specifically designed, such as Figure 2 As shown, spray rings are located at both ends of the housing, with the stator core located between them. Cooling oil flows from the outside of the housing into the interior through an oil pipeline, where it is partially distributed to one spray ring. Under the action of oil pressure, it is sprayed from spray holes distributed circumferentially around the spray ring, cooling the end windings near it. The remaining cooling oil flows through the stator core oil circuit to the other spray ring, cooling both the stator core and the end windings on the other side. After cooling, the cooling oil flows out of the housing through the oil outlet pipeline and enters the next cooling cycle.

[0058] In step three, a motor electromagnetic loss model is established, and in step four, each loss under rated and peak operating conditions is simulated and calculated to obtain the corresponding loss distribution cloud map. As the speed increases, the motor's winding loss, core loss, and permanent magnet eddy current loss further increase. Winding loss is the main component of the motor's electromagnetic loss, and permanent magnet eddy current loss is very small. The winding loss at rated operating peak speed is 1.75 times that at rated speed. The winding loss at peak operating peak speed is 1.59 times that at rated speed.

[0059] Considering that electric vehicles draw high current, generate significant losses, and generate more heat in their drive motors during starting, accelerating, and climbing, we calculated the motor's electromagnetic losses and temperature rise at four typical operating points where the motor is prone to heat generation, as shown in Table 2.

[0060] Table 2 Motor electromagnetic losses under typical working conditions

[0061]

[0062] In step five, the motor fluid domain model was extracted using Ansys Space Claim software, and a 3D thermal analysis model was established using Ansys Fluent software. Simulation boundary conditions were set: mass inlet for inlet type, 7 L / min for inlet flow rate, 80°C for inlet temperature, and outflow boundary for outlet type.

[0063] In the simulation of step 6, three different spray hole numbers of 12, 15, and 18 were selected, and the simulation results shown in Table 3 were obtained:

[0064] Table 3 Simulation results of different nozzle number schemes

[0065]

[0066] Taking temperature as the evaluation criterion, it can be seen that the spray cooling effect is better when the number of spray holes is 15, so it is determined as the optimal number of spray holes.

[0067] Choose two different spray hole diameters of 1mm and 2mm, and a cone-shaped countersunk spray hole shape with an upper hole diameter of 1.6mm and a lower hole diameter of 1mm, such as Figure 3 After simulation of different nozzle aperture schemes, the results are shown in Table 4:

[0068] Table 4 Simulation results of different nozzle aperture schemes

[0069]

[0070] By comparison, it can be determined that the conical countersunk hole is the best shape and size of the spray hole.

[0071] According to the temperature rise cloud map, when the above-mentioned optimal spray ring specifications are used, the steady-state average temperature of the winding has exceeded the threshold of 180°C, so the core oil circuit is further simulated and optimized in step seven. First, 45 axially extended straight oil circuits are evenly arranged on the outside of the stator core. The cross-section of the oil circuit is a fan-shaped circuit with a height of 3mm and an arc of 6°. Based on this straight oil circuit, the stator core staggered oil circuit is designed. Specifically, the stator core laminations are divided into 5 sections, each section is rotated 5°, so that each oil circuit intersects with half of the adjacent oil circuit. The structure and cross-sectional form of the two oil circuits are as follows. Figure 4 The stator temperature field simulation results when two oil circuit layouts are used are shown in Table 5:

[0072] Table 5 Simulation results of different stator core oil channel structures

[0073]

[0074] Combined with the temperature cloud map, the optimal core oil circuit layout and the final optimal oil cooling system were determined, namely, the stator core oil circuit structure with 15 spray holes in the spray ring, a conical countersunk hole structure, a total of 45 staggered holes, and a fan-shaped oil circuit cross-section.

[0075] In step 8, the temperature rise corresponding to rated and peak operating conditions for the optimized oil cooling system was simulated. Under rated operating conditions, the maximum temperature of the flat wire windings was 98.73°C, the maximum temperature of the stator core was 94.13°C, the maximum temperature of the rotor core was 85.78°C, and the maximum temperature of the magnets was 85.6°C. Under peak operating conditions, at a peak power of 94 kW and a speed of 6000 rpm, the maximum temperature of the flat wire windings was 130.67°C, the maximum temperature of the stator core was 118.88°C, the maximum temperature of the rotor core was 100.57°C, and the maximum temperature of the magnets was 99.03°C.

[0076] In the final step nine, a motor temperature rise test platform is constructed, which consists of a test motor entity, a dynamometer, a controller, a thermometer, a power analyzer, and a constant temperature oil tank. The controller is used to drive and control the operation of the test motor entity. The test motor entity is connected to the dynamometer through a coupling, and various motor operating conditions are loaded through the dynamometer. Thermocouples connected to the thermometer are provided at the end windings and stator core slots of the test motor entity to measure the temperature rise at the corresponding positions. The power analyzer is used to measure the motor power and speed under various working conditions. The constant temperature oil tank is connected to the oil cooling system in the test motor entity and provides it with cooling oil.

[0077] Finally, after platform test verification, the results showed that under the rated operating conditions of 4500rpm, 85Nm, and 40kW, the temperature rise curve of the flat wire winding end of the motor after running for 30 minutes was basically consistent with the simulation results. The maximum temperature of the winding end was around 160℃, which was lower than the temperature resistance limit of the winding insulation grade of 180℃, and both met the standard requirements well.

[0078] It should be understood that the size of the serial numbers of the steps in the embodiment of the present invention does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0079] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. The design method of the stator oil circuit structure of a high-speed oil-cooled flat wire motor is characterized by: The specific steps include: Step 1: Use finite element simulation software to establish a high-speed flat wire permanent magnet drive motor model, including a two-dimensional magnetic field model and a three-dimensional structural model of the motor; Step 2: Select the appropriate stator end spray ring type and oil circuit layout, and design the overall structure of the oil cooling system; Step 3: Consider the motor's winding loss, core loss, and permanent magnet eddy current loss to establish a motor electromagnetic loss model; Step 4: Using the motor electromagnetic loss model established in step 3, combined with the motor's speed-torque mechanical characteristics, calculate the loss distribution cloud diagrams under rated and peak operating conditions, and select multiple typical operating conditions corresponding to the rated and peak operating conditions to calculate the motor electromagnetic loss and temperature rise respectively; Step 5: Perform finite element simulation based on the three-dimensional structural model to extract the fluid domain model of the motor and establish a three-dimensional thermal analysis model of the motor for finite element simulation of the motor temperature rise under rated and peak operating conditions; set the simulation boundary conditions and the cooling oil inlet flow rate and inlet temperature; Step 6: Design different combinations of the number, diameter, and shape of the spray ring spray holes, and use the fluid domain 3D thermal analysis model to simulate the winding temperature and stator core temperature cloud map to determine the optimal spray ring specifications; Step 7: When the steady-state average temperature of the winding with the optimal spray ring specification obtained by simulation in step 6 exceeds the corresponding threshold, the stator core oil circuits set at the end windings on both sides are simulated and optimized, including: selecting different stator core oil circuit layouts, performing finite element simulation to calculate the stator temperature field corresponding to each oil circuit layout, and using fluid domain model extraction and three-dimensional thermal analysis model to obtain winding temperature and core temperature cloud maps, thereby determining the optimal stator core oil circuit layout and then determining the optimal oil cooling system structure; Step 8: Based on the determined optimal oil cooling system structure, a three-dimensional thermal analysis model is used to simulate the stator temperature distribution cloud under different typical operating conditions, and the distribution areas corresponding to the maximum temperatures of the windings and stator core are determined, which will serve as the basis for subsequent motor cooling system optimization; Step 9. Build a high-speed flat-wire permanent magnet drive test motor entity based on the optimal oil cooling system structure, and construct a motor temperature rise test platform based on the test motor entity; use the test platform to drive the test motor entity to operate under rated and peak conditions, and measure the temperature rise of the end winding and stator core at the same time, so as to verify the effect of the designed optimal oil cooling system structure.

2. The method according to claim 1, wherein: In step one, Motor CAD software is used to establish a two-dimensional electromagnetic field model of the motor, and Solid Works software is used to establish a three-dimensional structural model of the motor.

3. The method according to claim 1, wherein: In step 2, the oil circuit layout consisting of an oil inlet pipeline, two spray rings, a stator core oil circuit and an oil outlet pipeline is specifically designed; wherein, the spray rings are arranged at both ends of the casing, and the stator core is located between the two spray rings; after the cooling oil flows from the outside of the casing into the inside through the oil pipeline, part of the cooling oil is distributed to a spray ring, and under the action of oil pressure, it is sprayed out from the spray holes distributed circumferentially on the spray ring to cool the end winding on one side close to it; the other part of the cooling oil flows through the stator core oil circuit to the other spray ring, and the stator core and the end winding on the other side are cooled during the flow process; the cooling oil after cooling is discharged from the casing through the oil outlet pipeline and enters the next cooling cycle.

4. The method according to claim 1, wherein: The motor electromagnetic loss model established in step 3 specifically includes: Winding loss model: P Cu =P DC +P AC Where, P Cu is the total winding loss, P DC is the DC loss of the winding; P AC is the winding AC loss; Among them, the DC loss P DC Calculated using the following formula: P DC =mI 2 R DC Where m is the number of motor phases, I is the effective value of the motor phase current, and R DC is the DC resistance of the winding, which is specifically expressed as: Where, l Cu is the average half-turn length of the winding, N Φ is the number of series turns per phase, σ Cu is the electrical conductivity of copper, N is the number of parallel branches, and S is the cross-sectional area of ​​the winding; AC loss P AC Calculated using the following formula: Where k s is the AC loss coefficient, B is the magnetic flux density, ω is the electrical angular frequency, d is the conductor thickness, W is the flat wire width, and l is the conductor length; Core loss model: Where, P ir is the core loss, P h is the hysteresis loss, P e is the eddy current loss, P ex is the additional loss, K h and ɑ is the hysteresis loss coefficient, K e is the eddy current loss coefficient, K ex is the additional loss coefficient, B m is the peak value of magnetic flux density, f is the repetitive magnetization frequency; Permanent magnet eddy current loss model: Where, P PM is the eddy current loss of the permanent magnet, L a is the axial length of the permanent magnet, L b is the average width of the permanent magnet, V is the volume of the permanent magnet, ρ pm is the resistivity of the permanent magnet, K pm is the eddy current loss coefficient of the permanent magnet, f pm is the magnetic field alternating frequency, B pm is the maximum magnetic flux density of the permanent magnet.

5. The method according to claim 1, wherein: In step five, the motor fluid domain model is extracted using Ansys Space Claim software, and a three-dimensional thermal analysis model is established using Ansys Fluent software.

6. The method according to claim 1, wherein: In the simulation of step six, the maximum temperature of 180°C allowed by the motor insulation grade H is used as the threshold of the steady-state average temperature of the winding, and when the determined optimal injection ring specifications exceed this threshold, the core oil circuit simulation optimization of step seven is performed.

7. The method according to claim 1, wherein: The core oil circuit layout selected in step seven includes: a layout in which multiple axially extending straight oil circuits are evenly arranged outside the stator core, and various staggered oil circuit layouts including straight oil circuits, and setting the cross-sectional shape and size specifications at each position of the oil circuit.

8. The method according to claim 1, wherein: In step nine, a motor temperature rise test platform is specifically constructed, which consists of a test motor entity, a dynamometer, a controller, a thermometer, a power analyzer, and a constant temperature oil tank; wherein, the controller is used to drive and control the operation of the test motor entity; the test motor entity is connected to the dynamometer through a coupling, and various motor operating conditions are loaded through the dynamometer; thermocouples connected to the thermometer are provided at the end windings and stator core slots of the test motor entity to measure the temperature rise at the corresponding positions; the power analyzer is used to measure the motor power and speed under various working conditions; the constant temperature oil tank is connected to the oil cooling system in the test motor entity and provides cooling oil circulation for it.

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