Interior permanent magnet motor rotor optimization design method for achieving low torque ripple and low noise

Abstract

An interior permanent magnet motor rotor optimization design method for achieving low torque ripple and low noise, comprising suppressing torque ripple and vibration noise key-order electromagnetic forces on the basis of rotor quadrature-axis surface profiling, and suppressing maximum mechanical stress under high-speed operating conditions on the basis of relief grooves inside a rotor. The rotor quadrature-axis surface profiling is based on the principle of magnetic permeance modulation; by directionally reducing the quadrature-axis magnetic permeance of the rotor, the amplitude of the quadrature-axis air-gap flux density is suppressed, and rotor surface profiling parameters are further optimized to achieve suppression of torque ripple and vibration noise key-order electromagnetic forces. The relief grooves inside the rotor are based on a rotor stress distribution mechanism; by forming the relief grooves around a stress concentration region inside the rotor, the relief grooves and permanent magnet flux barriers constitute a generalized flux barrier in a stress propagation direction, reducing local stress concentration of the rotor, and thus lowering the maximum mechanical stress under high-speed operating conditions.

Description

Rotor optimization design method of low torque ripple and low noise interior permanent magnet motor TECHNICAL FIELD

[0001] The present application relates to a rotor optimization design method of low torque ripple and low noise interior permanent magnet motor, and belongs to the technical field of motor rotor design. BACKGROUND

[0002] In recent years, the fossil energy crisis and climate change have become more and more serious, and higher requirements have been put forward for China's sustainable development strategy and green new energy development. Electric vehicles, as a kind of new energy vehicle, are a technical alternative to non-renewable fossil fuel vehicles. At the same time, China has taken the lead in the electric vehicle industry, and the development of electric vehicles will help to upgrade the automobile industry and break the industrial blockade of western developed countries.

[0003] Permanent magnet synchronous motor has become the mainstream solution of new energy vehicle motor in the market due to its high power density and high efficiency, and has been widely used in products of first-line manufacturers such as Tesla, BYD and Huawei. In order to consolidate the leading advantage of China's new energy vehicle industry and further improve the power density, efficiency, power output quality and NVH characteristics of new energy electric vehicle motors, it is crucial to study the key order electromagnetic force suppression method of electric vehicle torque ripple, vibration and noise. The existing torque ripple suppression method usually selects the rotor skew pole method, but the rotor skew pole technology easily leads to the reduction of motor torque density, and further reduces the motor power density. The existing vibration and noise key order electromagnetic force suppression method usually has the rotor straight axis surface modification method, but the rotor straight axis surface modification also leads to the reduction of torque density, which is not conducive to the improvement of motor power density. At the same time, considering that the maximum speed of the existing electric vehicle drive motor can reach more than 20000rpm, the maximum mechanical stress of its rotor can exceed the yield strength, causing the risk of rotor structure failure under high speed working condition. Therefore, the research on the method for reducing the maximum mechanical stress of the rotor is helpful to ensure the safe and stable operation of the new energy vehicle drive motor. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a rotor optimization design method of low torque ripple and low noise interior permanent magnet motor, which can provide a set of general and efficient torque ripple, vibration and noise key order electromagnetic force stress suppression method for new energy vehicle interior permanent magnet drive motor, and also can ensure the safe and stable operation of the drive motor under high speed working condition.

[0005] The present application adopts the following technical solution to solve the above technical problems:

[0006] The rotor optimization design method of low torque ripple and low noise interior permanent magnet motor comprises the following steps:

[0007] Step 1, parameterize the surface of the motor rotor to be shaped, including the depth and width of the surface to be shaped, and round the edges of the surface to be shaped to make the edges smooth;

[0008] Step 2, use electromagnetic finite element analysis to calculate the average torque, torque ripple and vibration noise key order electromagnetic force of the motor under peak working condition and rated working condition under different depth and width combinations, and obtain the average torque, torque ripple and vibration noise key order electromagnetic force curve under different depth and width combinations;

[0009] Step 3, use mechanical stress finite element analysis to calculate the maximum rotor mechanical stress of the motor under high speed working condition under different depth and width combinations, and obtain the maximum rotor mechanical stress curve under different depth and width combinations;

[0010] Step 4, under the premise of ensuring that the average torque is greater than the design requirement of the motor, according to the torque ripple and vibration noise key order electromagnetic force curve obtained in step 2, select the optimal depth and width combination, so that the optimal depth and width combination considers the torque ripple and vibration noise key order electromagnetic force suppression under peak working condition and rated working condition;

[0011] Step 5, according to the maximum rotor mechanical stress curve obtained in step 3, obtain the maximum rotor mechanical stress of the optimal depth and width combination selected in step 4 under high speed working condition, and judge whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If yes, the current optimal combination has a structural failure risk and enters step 6, otherwise the optimization design is completed;

[0012] Step 6, set unloading grooves around the stress concentration area of the rotor, use electromagnetic finite element analysis to calculate the average torque, torque ripple and vibration noise key order electromagnetic force under different unloading groove position and size parameter combinations, and obtain the average torque, torque ripple and vibration noise key order electromagnetic force curve under different unloading groove position and size parameter combinations;

[0013] Step 7, use mechanical stress finite element analysis to calculate the maximum rotor mechanical stress under different unloading groove position and size parameter combinations, and obtain the maximum rotor mechanical stress curve under different unloading groove position and size parameter combinations;

[0014] Step 8, under the premise of ensuring that the average torque is greater than the design requirement of the motor, according to the torque ripple and vibration noise key order electromagnetic force curve obtained in step 6, select the optimal unloading groove position and size parameter combination, so that the optimal unloading groove position and size parameter combination considers the torque ripple and vibration noise key order electromagnetic force suppression under peak working condition and rated working condition;

[0015] Step 9, according to the maximum rotor mechanical stress curve obtained in step 7, the maximum rotor mechanical stress under the high-speed working condition of the optimal unloading slot position and size parameter combination selected in step 8 is obtained, and it is judged whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet, if yes, step 10 is entered, otherwise the optimization design is completed;

[0016] Step 10, the number of unloading slots set is increased and step 6 is returned until the structural failure risk is eliminated.

[0017] As a preferred scheme of the method of the application, the shape of the to-be-repaired plane in step 1 includes but is not limited to a triangle, a square and an ellipse.

[0018] As a preferred scheme of the method of the application, in step 4, according to the torque pulsation curve under the peak working condition, a first minimum torque pulsation is found, and a first torque pulsation range is set with the first minimum torque pulsation as the center; similarly, a first vibration noise key order electromagnetic force range under the peak working condition is set; according to the torque pulsation curve under the rated working condition, a second minimum torque pulsation is found, and a second torque pulsation range is set with the second minimum torque pulsation as the center; similarly, a second vibration noise key order electromagnetic force range under the rated working condition is set.

[0019] An optimal depth and width combination is selected, so that under the premise that the average torque under the peak working condition and the rated working condition is greater than the design requirement of the motor, the torque pulsation under the peak working condition of the optimal depth and width combination belongs to the first torque pulsation range, the vibration noise key order electromagnetic force under the peak working condition belongs to the first vibration noise key order electromagnetic force range, the torque pulsation under the rated working condition belongs to the second torque pulsation range, and the vibration noise key order electromagnetic force under the rated working condition belongs to the second vibration noise key order electromagnetic force range.

[0020] As a preferred scheme of the method of the application, the unloading slot and the permanent magnet magnetic barrier form a generalized magnetic barrier in the stress propagation direction, and the shape of the unloading slot includes but is not limited to a triangle, a square and an ellipse, and the vertex of the unloading slot is rounded.

[0021] As a preferred scheme of the method of the application, in step 8, the method for selecting the optimal unloading slot position and size parameter combination is the same as the method for selecting the optimal depth and width combination in step 4.

[0022] As a preferred scheme of the method of the application, the interior permanent magnet motor includes but is not limited to a V-shaped embedded permanent magnet motor, a Delta-shaped embedded permanent magnet motor and a double-layer V-shaped embedded permanent magnet motor.

[0023] An embedded permanent magnet motor rotor, the rotor is designed by the low torque ripple, low noise embedded permanent magnet motor rotor optimization design method.

[0024] An embedded permanent magnet motor, adopting the embedded permanent magnet motor rotor.

[0025] Compared with the prior art, the above technical scheme has the following technical effects:

[0026] 1. The optimization design method can efficiently optimize the electromagnetic force of key orders of motor torque ripple, vibration and noise, while ensuring the stability and safety of the motor under high-speed operation conditions.

[0027] 2. The optimization design method uses the new energy vehicle driving motor obtained by the optimization design method, which has high torque output quality, small key order electromagnetic force amplitude of vibration and noise, and small mechanical stress of the rotor under high-speed working conditions, and can quickly realize the performance optimization of the new energy vehicle driving motor product.

[0028] 3. The optimization design method has the characteristics of being intuitive and easy to implement. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a flowchart of the low torque ripple, low noise embedded permanent magnet motor rotor optimization design method of the present application;

[0030] Figure 2 is a double V-shaped embedded permanent magnet driving motor rotor topology related to an embodiment of the present application;

[0031] Figure 3 is the torque ripple variation law of the permanent magnet flat wire driving motor under different modification depths and modification widths based on the electromagnetic field finite element analysis method;

[0032] Figure 4 is the average torque variation law of the permanent magnet flat wire driving motor under different modification depths and modification widths based on the electromagnetic field finite element analysis method;

[0033] Figure 5 is the highest mechanical stress variation law of the permanent magnet flat wire driving motor under different modification depths and modification widths based on the mechanical stress finite element analysis method at 20000 rpm;

[0034] Figure 6 is a comparison of the key order electromagnetic force amplitude before and after the use of the rotor surface cross-axis cutting;

[0035] Figure 7 is a comparison of the electromagnetic torque waveform before and after the use of the rotor surface cross-axis cutting;

[0036] Figure 8 is a schematic diagram of the shape and position of the unloading groove in the rotor;

[0037] Figure 9 is the highest mechanical stress variation law of the permanent magnet flat wire driving motor under different unloading groove plane positions based on the mechanical stress finite element analysis method at 20000 rpm;

[0038] Fig. 10 is a three-dimensional schematic diagram of an embedded permanent magnet motor rotor obtained based on the optimization design method of the application;

[0039] Fig. 11 is a two-dimensional plane schematic diagram of an embedded permanent magnet motor rotor obtained based on the optimization design method of the application. DETAILED DESCRIPTION

[0040] Embodiments of the application are described in detail below with reference to the accompanying drawings, in which the same or similar elements or elements having the same or similar functions are denoted by the same or similar reference numerals throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the application, and cannot be interpreted as a limitation on the application.

[0041] The application proposes an embedded permanent magnet motor rotor optimization design method with low torque ripple and low noise. The optimization design process is shown in Fig. 1, which is mainly divided into two parts. One part is the motor electromagnetic characteristic optimization part by introducing the rotor quadrature axis surface modification, and the other part is the structural stress optimization part considering the maximum rotor rotating mechanical stress. The specific steps are as follows:

[0042] S1, parameterize the modified geometric surface parameters, including the modified depth and width parameters. For the unsmooth surface curve of the modified rotor, a chamfer curve is used to make the surface smooth.

[0043] The geometric surface can be any shape such as triangle, square, ellipse, spline curve, etc.

[0044] S2, carry out electromagnetic finite element analysis calculation under different modified depth and width parameters, and analyze the torque ripple, average torque, vibration noise key order electromagnetic force of the motor under peak working condition and rated working condition;

[0045] S3, carry out mechanical stress finite element analysis calculation under different modified depth and width parameters, and analyze the maximum rotor mechanical stress of the motor under high speed working condition;

[0046] S4, according to the torque ripple, vibration noise key order electromagnetic force distribution under different modified depth and width parameter combinations, obtain the optimal parameter curve of the torque ripple, vibration noise key order electromagnetic force amplitude, and select the parameter combination on the curve to consider the torque ripple and vibration noise key order electromagnetic force suppression, avoid reducing the average torque, and investigate the relationship between the maximum rotor mechanical stress and the silicon steel sheet yield strength to ensure the torque output performance and safe and stable operation of the motor;

[0047] S5, if the maximum mechanical stress of the rotor silicon steel sheet in the high-speed working condition of the wide-speed operation working condition of the driving motor is higher than the yield strength of the silicon steel sheet, there is a risk of structural failure, then a parameterized unloading slot is arranged around the highest stress distribution area between the double-layer permanent magnets, and the influence of the planar position and size parameters of the unloading slot on the average torque, torque ripple, vibration noise key order electromagnetic force is studied by using electromagnetic finite element analysis;

[0048] The shape of the unloading slot can be any shape such as a triangle, a square, an ellipse, a spline curve type, etc.

[0049] S6, the influence of the planar position and size parameters of the unloading slot on the maximum mechanical stress in the high-speed working condition is studied by using mechanical stress finite element analysis;

[0050] S7, according to the maximum mechanical stress of the rotor, the optimal unloading slot planar position and size parameters are selected to ensure the torque output performance and safe and stable operation of the motor.

[0051] Embodiment

[0052] S1, first, the motor rotor cross-axis modification planar parameterized modeling is performed, mainly including modification depth and modification width. As shown in FIG. 2, it is a double-V embedded permanent magnet driving motor rotor topology, 1 represents the position of the rotor q-axis, 2 represents the position of the rotor d-axis, 3 represents the modification depth, and 4 represents the modification length. The modification plane is located on the surface of the rotor cross-axis, and the initial itself is a triangular plane. In order to ensure the smooth connection of the rotor surface curve, the three vertices of the triangle are rounded.

[0053] S2, based on the established motor rotor model, the torque ripple and average torque distribution under different modification depths and modification length-width ratios are analyzed by using electromagnetic finite element analysis as shown in FIGS. 3 and 4. Among them, the average torque only has more drops in the case that the modification depth and the modification length-width ratio are both large. Therefore, the optimal modification parameters of the torque ripple can be selected within a wide modification parameter range.

[0054] S3, based on the structural stress finite element analysis, the rotor maximum mechanical stress under different modification depths and modification widths at 20000 rpm is shown in FIG. 5. It can be seen that the rotor surface cross-axis modification will lead to a higher rotor maximum mechanical stress. It is worth noting that the rotor maximum mechanical stress increases with the increase of the modification depth and the modification length-width ratio.

[0055] S4, according to the electromagnetic finite element analysis results, preferably the depth of the shape modification, the shape modification length-width ratio parameter realizes the torque ripple suppression, and the average torque change is small. In the embodiment, the optimal shape modification depth is 2.5 mm, and the optimal shape modification length-width ratio is 1.5. The amplitude of the key order electromagnetic force before and after optimization is shown in Figure 6, the torque waveform is shown in Figure 7, and the torque ripple before and after optimization is 16.27% and 6.27%, respectively. However, the highest mechanical stress of the rotor under the optimal shape modification plane is as high as 418 MPa under 20000 rpm, which exceeds the yield strength 370 MPa of the rotor silicon steel sheet, and there is a risk of running stability under high-speed working condition.

[0056] S5, the unloading groove inside the rotor core is modeled based on the triangular unloading groove shape, as shown in Figure 8, which is located in the stress concentration area near the rotor magnetic bridge, in order to ensure the smoothness of the unloading groove curve, the vertex is rounded, 5 represents the rotor core, 6 represents the permanent magnet barrier, 7 represents the original shape of the unloading groove, 8 represents the shape of the unloading groove after rounding, 9 represents the permanent magnet. By changing the x, y coordinates of the plane position, the change trend of the highest mechanical stress of the rotor under 20000 rpm and the displacement of the x, y coordinate axis is analyzed, as shown in Figure 9. It can be seen that the highest mechanical stress of the rotor core topology using the unloading groove under 20000 rpm can be optimized to below 370 MPa. In the embodiment, the preferred displacement of the x direction is 0.5 mm, and the displacement of the y direction is-0.84 mm. The three-dimensional schematic diagram of the rotor structure of the inner-embedded permanent magnet motor using the rotor surface modification and unloading groove technology of the application is shown in Figure 10, 10 represents the rotor surface modification, 11 represents the weight-reducing hole, and the two-dimensional plane schematic diagram is shown in Figure 11.

[0057] The method of the application is suitable for common inner-embedded permanent magnet synchronous motor topological structures such as V-type embedded, Delta-type embedded, double-layer V-type embedded, etc. The technology involved is not only suitable for new energy vehicle driving motors, but also suitable for conventional servo motors, two-wheeled vehicle motors and other application occasions. It is not only suitable for high-speed working conditions of high-speed motors, but also suitable for safety and stability of conventional motor operating intervals.

[0058] The above embodiments only illustrate the technical idea of the application, and cannot limit the protection scope of the application. Any modification made according to the technical idea of the application on the basis of the technical scheme falls within the protection scope of the application.

Claims

1. A method for optimizing the rotor design of an embedded permanent magnet motor with low torque ripple and low noise, characterized in that, Includes the following steps: Step 1: Perform parametric modeling on the cross-axis surface of the motor rotor to be modified, including the depth and width of the plane to be modified, and round the corners of the uneven edges of the plane to be modified to make the edges of the plane to be modified smoothly connected. Step 2: Use electromagnetic finite element analysis to calculate the average torque, torque pulsation, and key order electromagnetic force of the motor under peak and rated operating conditions under different depth and width combinations, and obtain the curves of the average torque, torque pulsation, and key order electromagnetic force of vibration noise under different depth and width combinations. Step 3: Use mechanical stress finite element analysis to calculate the maximum rotor mechanical stress of the motor under high-speed conditions under different combinations of depth and width, and obtain the maximum rotor mechanical stress curves under different combinations of depth and width. Step 4: Under the premise of ensuring that the average torque is greater than the motor design requirements, select the optimal depth and width combination based on the key order electromagnetic force curves of torque pulsation and vibration noise obtained in Step 2, so that the optimal depth and width combination can take into account the suppression of key order electromagnetic forces of torque pulsation and vibration noise under both peak and rated operating conditions. Step 5: Based on the maximum rotor mechanical stress curve obtained in Step 3, obtain the maximum rotor mechanical stress under high-speed conditions for the optimal depth and width combination selected in Step 4. Determine whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If so, the current optimal combination has a risk of structural failure and proceed to Step 6; otherwise, the optimization design is completed. Step 6: Set up unloading grooves around the stress concentration area inside the rotor. Use electromagnetic finite element analysis to calculate the average torque, torque pulsation and key order electromagnetic force of vibration noise under different combinations of unloading groove position and size parameters, and obtain the curves of average torque, torque pulsation and key order electromagnetic force of vibration noise under different combinations of unloading groove position and size parameters. Step 7: Use mechanical stress finite element analysis to calculate the maximum rotor mechanical stress under different combinations of unloading groove positions and size parameters, and obtain the maximum rotor mechanical stress curves under different combinations of unloading groove positions and size parameters. Step 8: Under the premise of ensuring that the average torque is greater than the motor design requirements, select the optimal combination of unloading groove position and size parameters based on the key order electromagnetic force curves of torque pulsation and vibration noise obtained in Step 6, so that the optimal combination of unloading groove position and size parameters can take into account the suppression of key order electromagnetic forces of torque pulsation and vibration noise under both peak and rated conditions. Step 9: Based on the maximum rotor mechanical stress curve obtained in Step 7, obtain the maximum rotor mechanical stress under high-speed conditions using the optimal combination of unloading groove position and size parameters selected in Step 8. Determine whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If so, proceed to Step 10; otherwise, the optimization design is complete. Step 10: Increase the number of unloading grooves set and return to step 6 until the risk of structural failure is eliminated.

2. The low torque pulsation and low noise embedded permanent magnet motor rotor optimization design method according to claim 1, characterized in that, The shape of the plane to be modified in step 1 includes, but is not limited to, triangles, squares, and ellipses.

3. The low torque pulsation and low noise embedded permanent magnet motor rotor optimization design method according to claim 1, characterized in that, In step 4, based on the torque pulsation curve under peak operating conditions, the first minimum torque pulsation is found, and the first torque pulsation range is set with the first minimum torque pulsation as the center; similarly, the range of the first vibration and noise key order electromagnetic force under peak operating conditions is set; based on the torque pulsation curve under rated operating conditions, the second minimum torque pulsation is found, and the second torque pulsation range is set with the second minimum torque pulsation as the center; similarly, the range of the second vibration and noise key order electromagnetic force under rated operating conditions is set. The optimal combination of depth and width is selected such that, under the premise that the average torque under both peak and rated operating conditions is greater than the motor design requirements, the torque pulsation under peak operating conditions falls within the first torque pulsation range, and the critical order electromagnetic force for vibration and noise under peak operating conditions falls within the first critical order electromagnetic force range for vibration and noise. At the same time, the torque pulsation under rated operating conditions falls within the second torque pulsation range, and the critical order electromagnetic force for vibration and noise under rated operating conditions falls within the second critical order electromagnetic force range for vibration and noise.

4. The low torque pulsation and low noise embedded permanent magnet motor rotor optimization design method according to claim 1, characterized in that, The unloading groove and the permanent magnet magnetic barrier form a generalized magnetic barrier in the stress propagation direction. The shape of the unloading groove includes, but is not limited to, triangle, square and ellipse. The vertices of the unloading groove are rounded.

5. The low torque pulsation and low noise embedded permanent magnet motor rotor optimization design method according to claim 1, characterized in that, In step 8, the method for selecting the optimal combination of unloading groove position and size parameters is the same as the method for selecting the optimal combination of depth and width in step 4.

6. The low torque pulsation and low noise embedded permanent magnet motor rotor optimization design method according to claim 1, characterized in that, The embedded permanent magnet motor includes, but is not limited to, V-type embedded permanent magnet motor, Delta-type embedded permanent magnet motor, and double-layer V-type embedded permanent magnet motor.

7. An embedded permanent magnet motor rotor, characterized in that, The rotor is designed using the low torque pulsation and low noise embedded permanent magnet motor rotor optimization design method as described in any one of claims 1-5.

8. An embedded permanent magnet motor, characterized in that, The embedded permanent magnet motor rotor as described in claim 7 is used.

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