A rotor slot structure and design method of a large hollow low-iron-loss permanent magnet synchronous motor

Abstract

This invention relates to a rotor slot structure and design method for a large hollow, low-iron-loss permanent magnet synchronous motor, aiming to suppress motor losses and improve performance through slot optimization. The structure determines the optimal elliptical rotor slot structure by comparing the no-load and load performance of motors with different rotor slot shapes. Using single-factor experiments, quadratic regression analysis, and response surface methodology, the influence of the positions a1 and a2 of the first and second rotor slots, the short radii b1 and b2, and the long radii c1 and c2 on motor performance is systematically investigated, and the optimal combination of structural parameters is selected. After applying this optimal elliptical rotor slot structure, the core performance of the motor is significantly optimized: iron loss is reduced by 11.87%, cogging torque by 44.98%, and torque ripple by 1.3%, with almost no negative impact on motor operating efficiency and output torque. Furthermore, this slot structure is simple to manufacture, widely applicable, and can precisely adapt to the rotor structure design requirements of large hollow permanent magnet synchronous motors, balancing performance improvement and engineering applications.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic design technology for permanent magnet synchronous motors used in new energy commercial vehicles, specifically to a rotor slot structure and design method for a large hollow, low iron loss permanent magnet synchronous motor. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs), with their unique advantages of high efficiency, high power density, and high output torque, have been widely used in the drive systems of new energy vehicles. Currently, the new energy vehicle industry is continuously raising its requirements for the comprehensive performance of drive motors, driving PMSMs towards higher speeds, higher power density, and lower NVH (noise, vibration, and harshness). Under this development trend, motor design faces many core technological challenges: high power density design inevitably increases the motor's heat dissipation pressure, and iron loss, as one of the main heat sources of PMSMs, increases significantly with increasing motor speed, further exacerbating the motor's temperature rise and heat dissipation burden; simultaneously, as drivers increasingly demand higher levels of driving comfort, the cogging torque generated by the change in magnetic resistance between the stator slots and permanent magnets can easily cause vibration and noise problems during low-speed operation, seriously affecting the driving experience and potentially leading to poor motor start-up smoothness; furthermore, torque pulsation reduces the smoothness of motor power output, accelerates the wear of transmission components in the electric drive system, shortens their service life, and also affects the stability of the vehicle's power response. Therefore, developing designs for low iron loss, low cogging torque, and low torque pulsation in permanent magnet synchronous motors is of great practical significance for improving motor performance and engineering application value.

[0003] Rotor slotting technology optimizes the magnetic circuit characteristics of a motor by altering the air gap reluctance distribution and cancels out stator slotting harmonics of specific orders, effectively reducing the air gap magnetic flux density harmonic content. This dual effect significantly reduces iron losses, cogging torque, and torque ripple. Rotor slotting technology is now widely used in permanent magnet synchronous motors for new energy vehicles. This method can be adapted and applied to large hollow permanent magnet synchronous motors to suppress their iron losses, cogging torque, and torque ripple. Summary of the Invention

[0004] To address the problems of high iron loss, large cogging torque, and torque pulsation in existing large hollow permanent magnet synchronous motors, the technical problem to be solved by this invention is to provide a rotor slot structure and design method for a large hollow low iron loss permanent magnet synchronous motor. By selecting the slot type and optimizing the design of the rotor slot structure parameters, the iron loss, cogging torque, and torque pulsation of the motor are synergistically suppressed, thereby achieving a comprehensive improvement in multiple performance indicators of the motor.

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a rotor slot structure for a large hollow, low-iron-loss permanent magnet synchronous motor, comprising a rotor core and multiple sets of rotor slots; the rotor core is an annular structure, the rotor slots are formed on the outer circular surface of the rotor core, and the rotor slots are elliptical.

[0006] Based on the above technical solution, the present invention can be further improved as follows:

[0007] Furthermore, each set of rotor slots includes a first rotor slot and a second rotor slot located at different positions, and the first rotor slot and the second rotor slot have different dimensions.

[0008] The second objective of this invention is to provide a design method for the rotor slot structure of the above-mentioned large hollow low iron loss permanent magnet synchronous motor, comprising the following steps:

[0009] Step 1: Construct motor simulation models with rotor slots as triangular slots, rectangular slots, inner and outer offset slots, elliptical slots, and no rotor slots. Compare the no-load and load weighted performance indicators of each model under seven typical working conditions: rated operating point, rated limit point, low speed high torque point, high speed low torque point, maximum torque point, maximum speed point, and peak power point. At the same time, combine the processing manufacturability for comprehensive evaluation to obtain the elliptical rotor slot with the best comprehensive performance.

[0010] Step 2: Based on the elliptical rotor slots obtained in Step 1, conduct single-factor experiments on the positions a1 and a2 of the first and second rotor slots, the minor radii b1 and b2 of the first and second rotor slots, and the major radii c1 and c2 of the first and second rotor slots. Generate an experimental table and construct a quadratic regression model. After verifying the significance of the model, perform response surface calculations to obtain the optimal combination of structural parameters of the elliptical rotor slots.

[0011] Step 3: Based on the optimal combination of structural parameters of the elliptical rotor slot obtained in Step 2, construct a motor simulation model to carry out simulation verification under no-load and full-load conditions. Compare the simulation results with the model prediction results to obtain the optimal design scheme of the elliptical rotor slot that is verified accurately and can be applied in engineering.

[0012] Furthermore, step 1 specifically involves:

[0013] Step 1.1, Model Construction: Build simulation models of five types of large hollow permanent magnet synchronous motors, including those with triangular slots, rectangular slots, inner and outer offset slots, elliptical slots as rotor slots, and those without rotor slots. Except for the shape of the rotor slots, the core dimensions, material selection, permanent magnet arrangement, slot pole fit, and other structural parameters of all models remain consistent.

[0014] Step 1.2, performance index determination: Define two types of weighted performance indices: no-load and load. The no-load indices are weighted cogging torque and weighted no-load air gap magnetic flux density total harmonic distortion. The load indices are weighted torque pulsation, weighted torque, weighted efficiency, and weighted iron loss. All weighted indices are the average values ​​of the corresponding performance indices under seven typical operating conditions of the motor.

[0015] Step 1.3, Slot Selection: Compare all weighted performance indicators of five large hollow permanent magnet synchronous motor simulation models under no-load and load conditions, evaluate them from the aspects of comprehensive performance and manufacturability, and finally select the elliptical rotor slot with the best comprehensive performance.

[0016] Furthermore, step 2 specifically involves:

[0017] Step 2.1, determine the optimization parameters: For the elliptical rotor slot, determine six core optimization parameters, namely the positions a1 and a2 of the first rotor slot and the second rotor slot, the short radii b1 and b2 of the first rotor slot and the second rotor slot, and the long radii c1 and c2 of the first rotor slot and the second rotor slot.

[0018] Step 2.2, Conduct single-factor experiments: Conduct single-factor experiments on the six parameters respectively, that is, keep other parameters unchanged and only change the value of the target parameter, record the weighted performance index of the motor under different operating conditions, and generate a standardized experimental table;

[0019] Step 2.3, Construct and validate the regression model: Construct a quadratic regression model based on the results of the single-factor experiment, and validate the significance of the model;

[0020] Step 2.4, Response Surface Calculation Optimization: Analyze the validated quadratic regression model through response surface calculation, solve for the optimal solution of the model, and obtain the optimal combination of the six structural parameters of the elliptical rotor slot that enables the motor to achieve the best performance.

[0021] Furthermore, in step 2.4, the optimal combination of six structural parameters of the elliptical rotor slot that enables the motor to achieve the best performance is obtained, specifically: a1 = 7.6348deg, b1 = 0.531mm, c1 = 3.239mm, a2 = 16.6894deg, b2 = 0.4999mm, c2 = 3.9925mm.

[0022] Furthermore, step 3 specifically involves:

[0023] Step 3.1, Constructing the verification model: Based on the optimal combination of structural parameters of the elliptical rotor slot obtained in Step 2, a new simulation model of the large hollow permanent magnet synchronous motor is built. The core dimensions, materials, and permanent magnet arrangement of the model are consistent with those in Steps 1 and 2.

[0024] Step 3.2, Simulation and Comparative Verification: Perform full-condition simulations of the verification model under no-load and load conditions to obtain the actual weighted performance indicators. Compare the simulation results with the prediction results of the quadratic regression model in Step 2 to verify the accuracy of the prediction results.

[0025] Step 3.3, Conclusion Confirmation: The simulation results are consistent with the prediction results, confirming the effectiveness of the optimal parameter combination.

[0026] The beneficial effects of this invention are: by selecting the slot shape of the rotor slot and optimizing the structural parameters, a large hollow permanent magnet synchronous motor rotor slot structure with low iron loss, low cogging torque, and low torque pulsation is constructed. This not only solves the problems of high iron loss, large cogging torque, and large torque pulsation in existing large hollow permanent magnet synchronous motors, but also has the advantages of simple processing technology and strong portability. Attached Figure Description

[0027] Figure 1 Schematic diagrams of different slot shapes for large hollow permanent magnet synchronous motors;

[0028] Figure 2 for Figure 1 Enlarged view A (a) shows the rotor slots as the prototype, i.e., trapezoidal slots; b) shows the rotor slots as triangular slots; c) shows the rotor slots as rectangular slots; d) shows the rotor slots as inner and outer offset slots; e) shows the rotor slots as elliptical slots; f) shows no rotor slots.

[0029] Figure 3 A comparison chart of weighted indices under no-load and load conditions for large hollow permanent magnet synchronous motors with different slot shapes;

[0030] Figure 4 A schematic diagram of optimized parameters for an elliptical rotor slot;

[0031] Figure 5 for Figure 4 Enlarged image;

[0032] Figure 6 A comparison of the no-load and load performance of a large hollow permanent magnet synchronous motor under different elliptical slot positions;

[0033] Figure 7 A comparison of the no-load and load performance of large hollow permanent magnet synchronous motors with different short radii of elliptical slots;

[0034] Figure 8 A comparison of the no-load and load performance of large hollow permanent magnet synchronous motors with different elliptical slot radii;

[0035] Figure 9 A comparison chart showing the no-load and load performance of the large hollow permanent magnet synchronous motor before and after optimization.

[0036] The attached diagram lists the components represented by each number as follows:

[0037] 1. Rotor core, 2. Magnetic barrier, 3. Permanent magnet slot, 4. Permanent magnet, 5. First rotor slot, 6. Second rotor slot. Detailed Implementation

[0038] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0039] like Figure 1 As shown, a rotor slot structure for a large-hollow, low-iron-loss permanent magnet synchronous motor includes a rotor core 1 and multiple sets of rotor slots. The rotor core 1 is an annular structure, and the rotor slots are formed on the outer circular surface of the rotor core 1, and the rotor slots are elliptical. Each set of rotor slots includes a first rotor slot 5 and a second rotor slot 6 located at different positions. The dimensions of the first rotor slot 5 and the second rotor slot 6 are different. A magnetic barrier 2 is provided in the rotor core 1. The magnetic barrier 2 is used to increase the magnetic reluctance of the rotor yoke, reduce leakage flux, prevent local magnetic saturation of the rotor yoke, and thus optimize the output torque and torque pulsation of the motor. The rotor permanent magnet 4 is embedded in the permanent magnet slot 3. The permanent magnet slot 3 has a large internal area, and a gap is left between it and the permanent magnet 4. This gap is filled with epoxy resin potting compound. The auxiliary slots on the rotor surface, namely the first rotor slot 5 and the second rotor slot 6, can improve the electromagnetic performance of the motor. The rotor core 1 provides a path for the permanent magnet flux when the motor is idling, reducing the rotor magnetic reluctance of the motor. When the motor is under load, the rotor core 1 provides a flow path for both the permanent magnet field and the armature reaction field to achieve electromagnetic energy exchange.

[0040] The large hollow permanent magnet synchronous motor is used in the permanent magnet drive mode of new energy commercial vehicles. Its core dimensions, including the stator inner and outer diameters, stator slot dimensions, and rotor inner and outer diameters, are as follows: stator outer diameter 230mm, stator inner diameter 156.2mm, rotor outer diameter 154.6mm, rotor inner diameter 95.46mm, stator slot depth 16.9mm, stator slot width 3.5mm, and single-sided air gap length 0.8mm. The permanent magnets of the large hollow permanent magnet synchronous motor are arranged in a U+V type embedded arrangement: several permanent magnets 4 are provided, with some permanent magnets 4 embedded in the permanent magnet slots 3 in a U-shape, and others embedded in the permanent magnet slots 3 in a V-shape. The slot-pole configuration of the large hollow permanent magnet synchronous motor is an integer slot configuration of 72 stator slots and 8 rotor poles. The stator and rotor core material of the large hollow permanent magnet synchronous motor is B27AHV1400, which has high magnetic permeability and low iron loss characteristics, and its density is 7650 kg / m³. 3 The rotor permanent magnet material is N42UH, with a remanence of 1.30T and a density of 7500 kg / m³. 3It provides a stable rotor magnetic field and has high heat resistance. The stator winding is made of copper wire with an 8-layer distributed winding structure and a winding pitch of 9, which reduces winding losses and improves motor efficiency. The copper wire density is 8900 kg / m³. 3 .

[0041] The design method for the rotor slot structure of the aforementioned large-diameter, low-iron-loss permanent magnet synchronous motor includes the following steps:

[0042] Step 1: Construct motor simulation models with rotor slots as triangular slots, rectangular slots, inner and outer offset slots, elliptical slots, and no rotor slots. Compare the no-load and load weighted performance indicators of each model under seven typical operating conditions: rated operating point, rated limit point, low speed high torque point, high speed low torque point, maximum torque point, maximum speed point, and peak power point. At the same time, combine the processing manufacturability for comprehensive evaluation to obtain the elliptical rotor slot with the best comprehensive performance.

[0043] The seven typical operating points of the aforementioned large and medium-sized hollow permanent magnet synchronous motor are as follows: Rated operating point, which is rated speed + rated torque + rated power, representing the rated output capacity of the motor; Rated limit point, which is rated speed + limit torque + limit power, representing the limit torque output capacity of the motor at rated speed; Low speed high torque point, which is 50% of rated speed + rated torque, representing the rated torque output capacity of the motor at low speed; High speed low torque point, which is 150% of rated speed + rated power, representing the rated power output capacity of the motor at high speed with field weakening; Maximum torque point, which is 500 rpm + peak torque, representing the limit torque output capacity of the motor; Maximum speed point, which is 12000 rpm, representing the limit speed output capacity of the motor; Peak power point, which is 5791 rpm + peak power, representing the limit power output capacity of the motor.

[0044] Step 1 is as follows:

[0045] Step 1.1, Model Building: (e.g.) Figure 2 As shown, five simulation models of large hollow permanent magnet synchronous motors were constructed, featuring triangular slots, rectangular slots, internally and externally offset slots, elliptical slots as rotor slots, and no rotor slots. Except for the shape of the rotor slots, all models maintained consistent core dimensions, material selection, permanent magnet arrangement, slot pole fit, and other structural parameters to ensure fair comparison. The motor's armature winding uses an 8-layer distributed winding configuration with a winding pitch of 9. The permanent magnets (4) are arranged in a U+V type embedded configuration, with the first layer of permanent magnets having a pole angle of 74.438° and the second layer having a pole angle of 120°. The permanent magnets are made of N42UH neodymium iron boron material. Both the stator and rotor cores are made of B27AHV1400 silicon steel sheets. Figure 1 The large hollow permanent magnet synchronous motor shown has the same structural parameters and material selection as the rotor slots, except for the difference in the rotor slot structure.

[0046] Step 1.2, Performance Indicator Determination: Define two types of weighted performance indicators: no-load and load. The no-load indicators are weighted cogging torque and weighted no-load air gap magnetic flux density total harmonic distortion (THD). The load indicators are weighted torque pulsation, weighted torque, weighted efficiency, and weighted iron loss. All weighted indicators are the average values ​​of the corresponding performance indicators under seven typical operating conditions of the motor (rated operating point, rated limit point, low speed high torque point, high speed low torque point, maximum torque point, maximum speed point, and peak power point), covering the full operating condition requirements of permanent magnet drive for new energy commercial vehicles.

[0047] Step 1.3, Slot Selection: Compare all weighted performance indicators of five large hollow permanent magnet synchronous motor simulation models under no-load and load conditions, evaluate them from the aspects of comprehensive performance and manufacturability, and finally select the elliptical rotor slot with the best comprehensive performance.

[0048] Figure 3 This is a comparison chart of weighted indices under no-load and load conditions for large hollow permanent magnet synchronous motors with different slot shapes. Figure 3 It can be seen that the shape of the rotor slot has little impact on the weighted efficiency and weighted torque of the motor, but a more significant impact on the weighted iron loss. Among them, the motor with no rotor slot structure has the highest weighted iron loss among all groups, and the motor with rotor slots of the inner and outer offset structure has the highest weighted cogging torque among all groups. The motors with rotor slots of trapezoidal slot (original slot), triangular slot, rectangular slot and elliptical slot structure have similar comprehensive performance, while the performance indicators of the rotor slot structure of triangular slot structure are slightly inferior to those of elliptical slot structure. The rotor slots of trapezoidal slot and rectangular slot structure are excluded due to complex processing technology and poor engineering implementation. Based on this, the elliptical rotor slot is determined to be the optimal rotor slot shape for large and medium hollow permanent magnet synchronous motors.

[0049] Step 2: Based on the elliptical rotor slots obtained in Step 1, single-factor experiments are conducted on the positions a1 and a2 of the first rotor slot 5 and the second rotor slot 6, the minor radii b1 and b2 of the first rotor slot 5 and the second rotor slot 6, and the major radii c1 and c2 of the first rotor slot 5 and the second rotor slot 6. An experimental table is generated, and a quadratic regression model is constructed. After the model's significance is verified, response surface methodology is performed to obtain the optimal combination of the elliptical rotor slot structural parameters. Specifically:

[0050] Step 2.1, determine the optimization parameters: For the elliptical rotor slots, six core optimization parameters are defined, namely the positions a1 and a2 of the first rotor slot 5 and the second rotor slot 6, the short radii b1 and b2 of the first rotor slot 5 and the second rotor slot 6, and the long radii c1 and c2 of the first rotor slot 5 and the second rotor slot 6 (the motor's single rotor pole has a left-right symmetrical structure, and only the parameters on one side of the symmetry axis need to be optimized to achieve overall rotor pole optimization).

[0051] Step 2.2, Conduct single-factor experiments: Conduct single-factor experiments on the six parameters respectively, that is, keep other parameters unchanged and only change the value of the target parameter, record the weighted performance index of the motor under different operating conditions, and generate a standardized experimental table.

[0052] Step 2.3, Construct and validate the regression model: Construct a quadratic regression model based on the results of the single-factor experiment, validate the significance of the model, ensure that the model can accurately reflect the mathematical relationship between the parameter values ​​and the motor performance indicators, and eliminate model errors that are not statistically significant.

[0053] Step 2.4, Response Surface Calculation Optimization: The validated quadratic regression model is analyzed through response surface calculation to find the optimal solution of the model and obtain the optimal combination of the six structural parameters of the elliptical rotor slot that enables the motor to achieve the best performance. Specifically, a1 is 7.6348 degrees, b1=0.531 mm, c1=3.239 mm, a2 is 16.6894 degrees, b2=0.4999 mm, and c2=3.9925 mm.

[0054] Figure 4 and 5 This is a schematic diagram of the optimized parameters for the elliptical rotor slots. The single rotor pole of the large hollow permanent magnet synchronous motor has a symmetrical structure, so only the rotor slot parameters on one side of the axis of symmetry need to be adjusted to achieve the structural optimization of the entire rotor pole. Each side of the single-pole rotor of this motor has two elliptical rotor slots, and six optimization parameters are set accordingly, namely the position a1, short radius b1, and long radius c1 of the first rotor slot 5; and the position a2, short radius b2, and long radius c2 of the second rotor slot 6.

[0055] Figure 6 This figure compares the no-load and load performance of a large hollow permanent magnet synchronous motor under different elliptical slot positions. As shown in the figure, the position parameters a1 and a2 of the first rotor slot 5 and the second rotor slot 6 have almost no effect on the motor's weighted efficiency and weighted torque, but have the most significant impact on weighted iron loss. They have a slight impact on weighted cogging torque, weighted no-load air gap magnetic flux density (THD), and weighted torque ripple. Therefore, by optimizing the elliptical slot position parameters a1 and a2, significant suppression of motor iron loss, cogging torque, and torque ripple can be achieved without reducing motor efficiency and torque output.

[0056] Figure 7This figure compares the no-load and load performance of a large hollow permanent magnet synchronous motor with different short radii of elliptical slots. As shown in the figure, the short radii b1 and b2 of the first rotor slot 5 and the second rotor slot 6 have almost no effect on the motor's weighted efficiency and weighted torque, but have the most significant impact on weighted iron loss. They have a slight impact on weighted cogging torque, weighted no-load air gap magnetic flux density (THD), and weighted torque ripple. Therefore, by optimizing the design of the short radii b1 and b2 of the elliptical slots, significant suppression of motor iron loss, cogging torque, and torque ripple can be achieved without reducing motor efficiency and torque output.

[0057] Figure 8 This figure compares the no-load and load performance of a large hollow permanent magnet synchronous motor with different elliptical slot radii. As shown in the figure, the radii c1 and c2 of the first rotor slot 5 and the second rotor slot 6 have almost no effect on the motor's weighted efficiency and weighted torque, but have the most significant impact on weighted iron loss. They have a slight impact on weighted cogging torque, weighted no-load air gap magnetic flux density (THD), and weighted torque ripple. Therefore, by optimizing the design of the elliptical slot radii c1 and c2, significant suppression of motor iron loss, cogging torque, and torque ripple can be achieved without reducing motor efficiency and torque output.

[0058] Step 3: Based on the optimal structural parameter combination of the elliptical rotor slots obtained in Step 2, construct a motor simulation model and conduct full-condition simulation verification under no-load and load conditions. Compare the simulation results with the model prediction results to obtain an accurate and engineering-applicable optimal design scheme for the elliptical rotor slots. Details are as follows:

[0059] Step 3.1, Constructing the verification model: Based on the optimal combination of structural parameters of the elliptical rotor slot obtained in Step 2, a new simulation model of a large hollow permanent magnet synchronous motor is built. The core dimensions, materials, permanent magnet arrangement and other parameters of the model are consistent with those in Steps 1 and 2.

[0060] Step 3.2, Simulation and Comparative Verification: Perform full-condition simulations of the verification model under no-load and load conditions to obtain the actual weighted performance indicators. Compare the simulation results with the prediction results of the quadratic regression model in Step 2 to verify the accuracy of the prediction results.

[0061] Step 3.3, Conclusion Confirmation: If the simulation results are consistent with the prediction results, the effectiveness of the optimal parameter combination is confirmed. In this invention, this step verifies that the prediction results are accurate and the optimal parameter combination can be applied in practice.

[0062] Figure 9The figure shows a comparison of the no-load and load performance of the large hollow permanent magnet synchronous motor before and after optimization. As can be seen from the figure, after adopting the elliptical rotor slot structure of this invention, the weighted iron loss of the motor is reduced to 471.77W, a decrease of 11.87%; the weighted cogging torque is reduced to 3.47Nm, a decrease of 44.98%; the weighted torque ripple is reduced to 8.54%, a decrease of 1.3%; while the weighted efficiency increases slightly, and the weighted torque decreases from 171.71Nm to 171.14Nm, a negligible change, demonstrating a significant optimization effect.

[0063] In summary, this invention, through rotor slot shape simulation screening, obtains the elliptical rotor slot with the best comprehensive performance indicators. Then, combining single-factor experiments, quadratic regression analysis, and response surface methodology, it optimizes the optimal parameter combination of the elliptical slot, achieving significant suppression of motor iron loss, cogging torque, and torque ripple, with almost no adverse impact on efficiency and torque. Furthermore, the elliptical rotor slot manufacturing process is simple and widely applicable, precisely adaptable to the rotor structure design requirements of large and medium-sized hollow permanent magnet synchronous motors. Details are as follows:

[0064] 1. After the large hollow permanent magnet synchronous motor has elliptical rotor slots, the performance of the motor under no-load and load operation is significantly improved. The weighted iron loss is reduced from 535.31W to 471.77W, a reduction of 11.87%; the weighted cogging torque is reduced from 6.32Nm to 3.48Nm, a reduction of 44.98%; and the weighted torque ripple is reduced from 9.38% to 8.54%, a reduction of 9.04%, which significantly improves the motor's heat dissipation pressure and operating stability.

[0065] 2. The elliptical slot structure design balances efficiency improvement and torque output stability; while suppressing iron loss, cogging torque and torque pulsation, the weighted efficiency is increased from 90.14% to 90.16%, and the weighted torque is reduced from 171.71Nm to 171.14Nm, with almost no adverse effects on the motor's operating efficiency and output torque.

[0066] 3. The elliptical rotor slotting method described above has a simple processing technology, high portability, and can be precisely adapted to the rotor structure design requirements of large hollow permanent magnet synchronous motors.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rotor slot structure for a large hollow, low-iron-loss permanent magnet synchronous motor, characterized in that, It includes a rotor core (1) and multiple sets of rotor slots; the rotor core (1) is a circular ring structure, the rotor slots are opened on the outer circular surface of the rotor core (1), and the rotor slots are elliptical.

2. The rotor slot structure of the large hollow low-iron-loss permanent magnet synchronous motor according to claim 1, characterized in that, Each set of rotor slots includes a first rotor slot (5) and a second rotor slot (6) in different positions, and the first rotor slot (5) and the second rotor slot (6) have different dimensions.

3. A design method for the rotor slot structure of a large hollow low-iron-loss permanent magnet synchronous motor according to any one of claims 1-2, characterized in that, The steps include the following: Step 1: Construct motor simulation models with rotor slots as triangular slots, rectangular slots, inner and outer offset slots, elliptical slots, and no rotor slots. Compare the no-load and load weighted performance indicators of each model under seven typical working conditions: rated operating point, rated limit point, low speed high torque point, high speed low torque point, maximum torque point, maximum speed point, and peak power point. At the same time, combine the processing manufacturability for comprehensive evaluation to obtain the elliptical rotor slot with the best comprehensive performance. Step 2: Based on the elliptical rotor slots obtained in Step 1, single-factor experiments are conducted on the positions a1 and a2 of the first rotor slot (5) and the second rotor slot (6), the short radii b1 and b2 of the first rotor slot (5) and the second rotor slot (6), and the long radii c1 and c2 of the first rotor slot (5) and the second rotor slot (6). An experimental table is generated and a quadratic regression model is constructed. After the model significance is verified, the response surface is calculated to obtain the optimal combination of the structural parameters of the elliptical rotor slots. Step 3: Based on the optimal combination of structural parameters of the elliptical rotor slot obtained in Step 2, construct a motor simulation model to carry out simulation verification under no-load and full-load conditions. Compare the simulation results with the model prediction results to obtain the optimal design scheme of the elliptical rotor slot that is verified accurately and can be applied in engineering.

4. The rotor slot structure of the large hollow low-iron-loss permanent magnet synchronous motor according to claim 3, characterized in that, Step 1 is as follows: Step 1.1, Model Construction: Build simulation models of five types of large hollow permanent magnet synchronous motors, including those with triangular slots, rectangular slots, inner and outer offset slots, elliptical slots as rotor slots, and those without rotor slots. Except for the shape of the rotor slots, the core dimensions, material selection, permanent magnet arrangement, slot pole fit, and other structural parameters of all models remain consistent. Step 1.2, performance index determination: Define two types of weighted performance indices: no-load and load. The no-load indices are weighted cogging torque and weighted no-load air gap magnetic flux density total harmonic distortion. The load indices are weighted torque pulsation, weighted torque, weighted efficiency, and weighted iron loss. All weighted indices are the average values ​​of the corresponding performance indices under seven typical operating conditions of the motor. Step 1.3, Slot Selection: Compare all weighted performance indicators of five large hollow permanent magnet synchronous motor simulation models under no-load and load conditions, evaluate them from the aspects of comprehensive performance and manufacturability, and finally select the elliptical rotor slot with the best comprehensive performance.

5. The rotor slot structure of the large hollow low-iron-loss permanent magnet synchronous motor according to claim 3, characterized in that, Step 2 is as follows: Step 2.1, determine the optimization parameters: For the elliptical rotor slot, determine six core optimization parameters, namely the positions a1 and a2 of the first rotor slot (5) and the second rotor slot (6), the short radii b1 and b2 of the first rotor slot (5) and the second rotor slot (6), and the long radii c1 and c2 of the first rotor slot (5) and the second rotor slot (6). Step 2.2, Conduct single-factor experiments: Conduct single-factor experiments on the six parameters respectively, that is, keep other parameters unchanged and only change the value of the target parameter, record the weighted performance index of the motor under different operating conditions, and generate a standardized experimental table; Step 2.3, Construct and validate the regression model: Construct a quadratic regression model based on the results of the single-factor experiment, and validate the significance of the model; Step 2.4, Response Surface Calculation Optimization: Analyze the validated quadratic regression model through response surface calculation, solve for the optimal solution of the model, and obtain the optimal combination of the six structural parameters of the elliptical rotor slot that enables the motor to achieve the best performance.

6. The rotor slot structure of the large hollow low-iron-loss permanent magnet synchronous motor according to claim 5, characterized in that, In step 2.4, the optimal combination of six structural parameters of the elliptical rotor slots that enables the motor to achieve the best performance is obtained, specifically: a1 = 7.6348deg, b1 = 0.531mm, c1 = 3.239mm, a2 = 16.6894deg, b2 = 0.4999mm, c2 = 3.9925mm.

7. The rotor slot structure of the large hollow low-iron-loss permanent magnet synchronous motor according to claim 3, characterized in that, Step 3 specifically involves: Step 3.1, Constructing the verification model: Based on the optimal combination of structural parameters of the elliptical rotor slot obtained in Step 2, a new simulation model of the large hollow permanent magnet synchronous motor is built. The core dimensions, materials, and permanent magnet arrangement of the model are consistent with those in Steps 1 and 2. Step 3.2, Simulation and Comparative Verification: Perform full-condition simulations of the verification model under no-load and load conditions to obtain the actual weighted performance indicators. Compare the simulation results with the prediction results of the quadratic regression model in Step 2 to verify the accuracy of the prediction results. Step 3.3, Conclusion Confirmation: The simulation results are consistent with the prediction results, confirming the effectiveness of the optimal parameter combination.

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