Optimization Design Method for the Rotor of Interior Permanent Magnet Motor with Low Torque Ripple and Low Noise

Abstract

The present invention discloses an optimized design method for the rotor of an interior permanent magnet motor with low torque ripple and low noise, including the suppression of key order electromagnetic forces of torque ripple, vibration and noise based on the modification of the rotor quadrature axis surface, and the suppression of the highest mechanical stress under high-speed conditions based on the relief grooves inside the rotor. Among them, the modification of the rotor quadrature axis surface is based on the principle of permeance modulation. By directionally reducing the permeance of the rotor quadrature axis, the suppression of the quadrature axis air-gap magnetic density amplitude is achieved. Further optimizing the rotor surface modification parameters realizes the suppression of key order electromagnetic forces of torque ripple and vibration and noise. The relief grooves inside the rotor are based on the rotor stress distribution mechanism. By opening relief grooves around the stress concentration area inside the rotor and forming a generalized magnetic barrier with the permanent magnet magnetic barrier in the stress propagation direction, the local stress concentration phenomenon of the rotor is reduced, and thus the highest mechanical stress under high-speed conditions is reduced. The method of the present invention has the advantages of being easy to implement, good suppression effect of key order electromagnetic forces of torque ripple and vibration and noise, and general applicability.

Description

Technical Field

[0001] The invention relates to a low-torque pulsation and low-noise embedded permanent magnet motor rotor optimization design method, belonging to the technical field of motor rotor design. Background Art

[0002] Permanent magnet synchronous motors have become the mainstream solution for new energy vehicle motors in the market due to their high power density and high efficiency. In order to consolidate the first-mover advantage of my country'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 electromagnetic force suppression methods for key orders of torque pulsation and vibration noise of electric vehicles. The existing torque pulsation suppression methods usually use the rotor skew method, but the rotor skew technology can easily lead to a decrease in the torque density of the motor, thereby reducing the power density of the motor. The existing electromagnetic force suppression methods for key orders of vibration and noise usually only have rotor direct shaft surface modification methods, but rotor direct shaft surface modification can also lead to a decrease in torque density, which is not conducive to improving the power density of the motor. At the same time, considering that the maximum speed of existing electric vehicle drive motors can reach more than 20,000 rpm, the maximum mechanical stress of the rotor can exceed the yield strength, resulting in the risk of rotor structure failure under high speed conditions. Therefore, studying the method of reducing the maximum mechanical stress of the rotor will help ensure the safe and stable operation of the new energy vehicle drive motor. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an optimization design method for an embedded permanent magnet motor rotor with low torque pulsation and low noise, which can provide a universal and efficient method for suppressing the key order electromagnetic force stress of torque pulsation and vibration noise for the embedded permanent magnet drive motor of new energy vehicles, and at the same time ensure the safe and stable operation of the drive motor under high speed conditions.

[0004] The present invention adopts the following technical solutions to solve the above technical problems:

[0005] The low torque ripple and low noise embedded permanent magnet motor rotor optimization design method comprises the following steps:

[0006] Step 1, parametric modeling is performed on the plane to be modified on the surface of the motor rotor cross-axis, including the depth and width of the plane to be modified, and rounding is performed on the rough edges of the plane to be modified to make the edges of the plane to be modified smoothly connected;

[0007] Step 2, using electromagnetic finite element analysis to calculate the average torque, torque pulsation and key order electromagnetic force of vibration noise of the motor under peak working conditions and rated working conditions under different depth and width combinations, and obtaining the average torque, torque pulsation and key order electromagnetic force curves of vibration noise under different depth and width combinations;

[0008] Step 3: Use finite element analysis of mechanical stress to calculate the maximum rotor mechanical stress of the motor under high-speed conditions for different combinations of depth and width, and obtain the maximum rotor mechanical stress curve for different combinations of depth and width;

[0009] Step 4: On the premise of ensuring that the average torque is greater than the motor design requirements, according to the torque ripple and vibration noise key order electromagnetic force curves obtained in Step 2, select the optimal combination of depth and width, so that the optimal combination of depth and width takes into account the suppression of torque ripple and vibration noise key order electromagnetic force under peak conditions and rated conditions;

[0010] Step 5: According to the maximum rotor mechanical stress curve obtained in Step 3, obtain the maximum rotor mechanical stress of the optimal combination of depth and width selected in Step 4 under high-speed conditions, and judge whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If so, that is, the current optimal combination has a risk of structural failure and enters Step 6, otherwise the optimization design is completed;

[0011] Step 6: Set unloading grooves around the internal stress concentration area of the rotor, and use electromagnetic finite element analysis to calculate the average torque, torque ripple and vibration noise key order electromagnetic force for different combinations of unloading groove positions and size parameters, and obtain the average torque, torque ripple and vibration noise key order electromagnetic force curves for different combinations of unloading groove positions and size parameters;

[0012] Step 12: Use finite element analysis of mechanical stress to calculate the maximum rotor mechanical stress for different combinations of unloading groove positions and size parameters, and obtain the maximum rotor mechanical stress curve for different combinations of unloading groove positions and size parameters;

[0013] Step 15: On the premise of ensuring that the average torque is greater than the motor design requirements, according to the torque ripple and vibration noise key order electromagnetic force curves obtained in Step 6, select the optimal combination of unloading groove positions and size parameters, so that the optimal combination of unloading groove positions and size parameters takes into account the suppression of torque ripple and vibration noise key order electromagnetic force under peak conditions and rated conditions;

[0014] Step 18: According to the maximum rotor mechanical stress curve obtained in Step 7, obtain the maximum rotor mechanical stress of the optimal combination of unloading groove positions and size parameters selected in Step 8 under high-speed conditions, and judge whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If so, enter Step 10, otherwise the optimization design is completed;

[0015] Step 21: Increase the number of set unloading grooves and return to Step 6 until the risk of structural failure is eliminated.

[0016] As a preferred solution of the method of the present invention, the shape of the plane to be modified in Step 1 includes, but is not limited to, triangle, square and ellipse.

[0017] As a preferred embodiment of the method of the present invention, in step 4, according to the torque ripple curve under peak operating conditions, the first minimum torque ripple is found, and with the first minimum torque ripple as the center, a first torque ripple range is set; similarly, a first vibration and noise key order electromagnetic force range under peak operating conditions is set; according to the torque ripple curve under rated operating conditions, the second minimum torque ripple is found, and with the second minimum torque ripple as the center, a second torque ripple range is set; similarly, a second vibration and noise key order electromagnetic force range under rated operating conditions is set.

[0018] An optimal depth and width combination is selected such that, on the premise that the average torques under peak operating conditions and rated operating conditions are both greater than the motor design requirements, the torque ripple of the optimal depth and width combination under peak operating conditions belongs to the first torque ripple range, and at the same time, the vibration and noise key order electromagnetic force under peak operating conditions belongs to the first vibration and noise key order electromagnetic force range, and at the same time, the torque ripple under rated operating conditions belongs to the second torque ripple range, and at the same time, the vibration and noise key order electromagnetic force under rated operating conditions belongs to the second vibration and noise key order electromagnetic force range.

[0019] As a preferred embodiment of the method of the present invention, 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, and the vertices of the unloading groove are rounded.

[0020] As a preferred embodiment of the method of the present invention, in step 8, the method for selecting the optimal unloading groove position and size parameter combination is the same as the method for selecting the optimal depth and width combination in step 4.

[0021] As a preferred embodiment of the method of the present invention, the embedded permanent magnet motor includes, but is not limited to, V-shaped embedded permanent magnet motor, Delta-shaped embedded permanent magnet motor, and double-layer V-shaped embedded permanent magnet motor.

[0022] An embedded permanent magnet motor rotor is designed by using the optimized design method of the embedded permanent magnet motor rotor with low torque ripple and low noise.

[0023] An embedded permanent magnet motor uses the above-mentioned embedded permanent magnet motor rotor.

[0024] Compared with the prior art by adopting the above technical solutions, the present invention has the following technical effects:

[0025] 1. The optimized design method of the present invention can efficiently optimize the torque ripple and the vibration and noise key order electromagnetic force of the motor, while ensuring the stable safety of the motor under high-speed operating conditions.

[0026] 2. The new energy vehicle drive motor obtained by using the optimization design method of the present invention has high torque output quality, small electromagnetic force amplitude of key vibration and noise orders, and small mechanical stress under high-speed rotor conditions, and can quickly optimize the product performance of the new energy vehicle drive motor.

[0027] 3. The optimization design method of the present invention has the characteristics of being intuitive and easy to implement. Description of the Drawings

[0028] Figure 1 is the flowchart of the optimization design method of the interior permanent magnet motor rotor with low torque ripple and low noise of the present invention;

[0029] Figure 2 is the rotor topology of the double-V interior permanent magnet drive motor involved in the embodiment of the present invention;

[0030] Figure 3 is the torque ripple change law of the permanent magnet flat wire drive motor under different modification depths and modification widths based on the finite element analysis method of electromagnetic field;

[0031] Figure 4 is the average torque change law of the permanent magnet flat wire drive motor under different modification depths and modification widths based on the finite element analysis method of electromagnetic field;

[0032] Figure 5 is the highest mechanical stress change law of the permanent magnet flat wire drive motor at 20000 rpm under different modification depths and modification widths based on the finite element analysis method of mechanical stress;

[0033] Figure 6 is the comparison of the electromagnetic force amplitude of key orders before and after cross-axis pole cutting on the rotor surface;

[0034] Figure 7 is the comparison of the electromagnetic torque waveforms before and after cross-axis pole cutting on the rotor surface;

[0035] Figure 8 is the schematic diagram of the shape and position of the relief groove inside the rotor;

[0036] Figure 9 is the highest mechanical stress change law of the permanent magnet flat wire drive motor at 20000 rpm under different relief groove plane positions based on the finite element analysis method of mechanical stress;

[0037] Figure 10 is the three-dimensional schematic diagram of the interior permanent magnet motor rotor obtained by using the optimization design method of the present invention;

[0038] Figure 11 is the two-dimensional plane schematic diagram of the interior permanent magnet motor rotor obtained by using the optimization design method of the present invention. Detailed Embodiments

[0039] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as a limitation to the present invention.

[0040] The present invention proposes an optimization design method for an interior permanent magnet motor rotor with low torque ripple and low noise. The optimization design process is as Figure 1 shown, which is mainly divided into two parts. One part is the electromagnetic characteristic optimization part of the motor by introducing the cross-axis surface modification of the rotor, and the other part is the structural stress optimization part considering the highest rotational mechanical stress of the rotor. The specific steps are as follows:

[0041] S1. Parametrize the geometric surface parameters, including the modification depth and modification width parameters. For the non-smooth part of the rotor surface curve after modification, use a chamfer curve to make its surface smooth;

[0042] The geometric surface can be any shape such as triangular, square, elliptical, spline curve type, etc.

[0043] S2. Conduct electromagnetic finite element analysis and calculation under different modification depths and modification width parameters, and analyze the torque ripple, average torque, and key order electromagnetic forces of vibration and noise of the motor under peak conditions and rated conditions;

[0044] S3. Conduct mechanical stress finite element analysis and calculation under different modification depths and modification width parameters, and analyze the maximum rotor mechanical stress of the motor under high-speed conditions;

[0045] S4. According to the torque ripple and the distribution of key order electromagnetic forces of vibration and noise under different combinations of modification depth and modification width parameters, obtain the optimal parameter curve of the key electromagnetic force amplitudes of torque ripple and vibration and noise. The preferred parameter combination on the curve takes into account both the suppression of torque ripple and key order electromagnetic forces of vibration and noise, and examines the relationship between the maximum rotor mechanical stress and the yield strength of the silicon steel sheet while avoiding reducing the average torque, so as to ensure the torque output performance and safe and stable operation of the motor;

[0046] S5. If the maximum mechanical stress of the rotor silicon steel sheet is higher than the yield strength of the silicon steel sheet under high-speed conditions in the wide speed operation condition of the drive motor, there is a risk of structural failure. Then, set a parametric relief groove around the highest stress distribution area between the double-layer permanent magnets, and use electromagnetic finite element analysis to study the influence of the plane position and size parameters of the relief groove on the average torque, torque ripple, and key order electromagnetic forces of vibration and noise;

[0047] The shape of the relief groove can be any shape such as triangular, square, elliptical, spline curve type, etc.

[0048] S6. Use mechanical stress finite element analysis to study the influence of the plane position and size parameters of the relief groove on the maximum mechanical stress under high-speed conditions;

[0049] S7. According to the maximum mechanical stress of the rotor, optimize the optimal plane position and size parameters of the relief groove to ensure the motor torque output performance and safe and stable operation.

[0050] Embodiment

[0051] S1. First, perform parametric modeling of the cross-axis modification plane parameters of the motor rotor, mainly including the modification depth and modification width. As Figure 2 shown, it is the topology of the rotor of a double-V type embedded permanent magnet drive motor. 1 represents the position of the q-axis axis of the rotor, 2 represents the position of the d-axis axis of the rotor, 3 represents the modification depth, and 4 represents the modification length. The modification plane is located on the cross-axis surface of the rotor, and its initial itself is a triangular plane. To ensure the smooth connection of the rotor surface curve, fillet processing is performed on the three vertices of the triangle.

[0052] S2. Based on the established motor rotor model, use electromagnetic finite element analysis to analyze the torque ripple and average torque distribution under different modification depths and modification length-width ratios as Figure 3 and Figure 4 shown. Among them, the average torque only drops significantly when both the modification depth and the modification length-width ratio are relatively large. Therefore, the optimal modification parameters for torque ripple can be selected within a relatively wide range of modification parameters.

[0053] S3. Based on structural stress finite element analysis, analyze the maximum mechanical stress of the rotor under different modification depths and modification widths at 20,000 rpm as Figure 5 shown. It can be seen that the cross-axis modification on the rotor surface will result in a relatively high maximum mechanical stress of the rotor. It should be noted that the maximum mechanical stress of the rotor increases with the increase of the modification depth and the modification length-width ratio.

[0054] S4. According to the results of electromagnetic finite element analysis, optimize the modification depth and modification length-width ratio parameters to achieve torque ripple suppression, while the change in average torque is relatively small. In this embodiment, the optimal modification depth is 2.5 mm and the optimal modification length-width ratio is 1.5. The comparison of the electromagnetic force amplitudes of the key orders before and after optimization is as Figure 6 shown, and the torque waveform is as Figure 7 shown. The torque ripples before and after optimization are 16.27% and 6.27% respectively. However, the maximum mechanical stress of the rotor under the optimal modification plane at 20,000 rpm is as high as 418 MPa, exceeding the yield strength of the rotor silicon steel sheet of 370 MPa, posing a risk to the operation stability under high-speed conditions.

[0055] S5. Model the relief groove inside the rotor core based on the triangular relief groove shape, as Figure 8As shown, its position is in the stress concentration area near the rotor magnetic isolation bridge. To ensure a smooth transition of the unloading groove curve, its vertex is rounded. 5 represents the rotor core, 6 represents the permanent magnet magnetic barrier, 7 represents the original shape of the unloading groove, 8 represents the shape of the unloading groove after rounding, and 9 represents the permanent magnet. By changing the x and y coordinates of its planar position, the variation trends of the highest mechanical stress and the displacements along the x and y coordinate axes of the rotor at 20,000 rpm are analyzed, as Figure 9 shown. It can be seen that for the rotor core topology with the unloading groove, the highest mechanical stress at 20,000 rpm can be optimized to below 370 MPa. In this embodiment, the displacement in the x direction is preferably 0.5 mm, and the displacement in the y direction is -0.84 mm. The three-dimensional schematic diagram of the interior permanent magnet motor rotor structure applying the rotor quadrature axis surface modification and unloading groove technology of the present invention is as Figure 10 shown, 10 represents the rotor surface modification, 11 represents the weight reduction hole, and its two-dimensional planar schematic diagram is as Figure 11 shown.

[0056] The method of the present invention is applicable to common interior permanent magnet synchronous motor topologies such as V-type embedded, Delta-type embedded, and double-layer V-type embedded. The technologies involved are applicable not only to the drive motors of new energy vehicles, but also to various application scenarios such as conventional servo motors and two-wheeler motors. It is applicable not only to the high-speed operating conditions of high-speed motors, but also to the safety and stability of the operating range of conventional motors.

[0057] The above embodiments are only used to illustrate the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the present invention.

Claims

1. An optimization design method for the rotor of an interior permanent magnet motor with low torque ripple and low noise, characterized in that, The steps are as follows: Step 1: Parametrically model the plane to be modified on the quadrature axis surface of the motor rotor, including the depth and width of the plane to be modified, and round the non-smooth parts of the 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 ripple, and key order electromagnetic forces of vibration and noise of the motor under peak and rated operating conditions for different combinations of depth and width, and obtain the average torque, torque ripple, and key order electromagnetic force curves of vibration and noise for different combinations of depth and width; Step 3: Use mechanical stress finite element analysis to calculate the maximum rotor mechanical stress of the motor under high-speed operating conditions for different combinations of depth and width, and obtain the maximum rotor mechanical stress curves for different combinations of depth and width; Step 4: On the premise of ensuring that the average torque is greater than the motor design requirements, according to the torque ripple and key order electromagnetic force curves of vibration and noise obtained in Step 2, select the optimal combination of depth and width, so that the optimal combination of depth and width takes into account the suppression of torque ripple and key order electromagnetic forces of vibration and noise under peak and rated operating conditions; Step 5: According to the maximum rotor mechanical stress curve obtained in Step 3, obtain the maximum rotor mechanical stress of the optimal combination of depth and width selected in Step 4 under high-speed operating conditions, and judge whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If so, that is, the current optimal combination has a risk of structural failure and enter Step 6, otherwise the optimization design is completed; Step 6: Set relief grooves around the area of internal stress concentration in the rotor, and use electromagnetic finite element analysis to calculate the average torque, torque ripple, and key order electromagnetic forces of vibration and noise for different combinations of relief groove positions and size parameters, and obtain the average torque, torque ripple, and key order electromagnetic force curves of vibration and noise for different combinations of relief groove positions and size parameters; Step 7: Use mechanical stress finite element analysis to calculate the maximum rotor mechanical stress for different combinations of relief groove positions and size parameters, and obtain the maximum rotor mechanical stress curves for different combinations of relief groove positions and size parameters; Step 8: On the premise of ensuring that the average torque is greater than the motor design requirements, according to the torque ripple and key order electromagnetic force curves of vibration and noise obtained in Step 6, select the optimal combination of relief groove positions and size parameters, so that the optimal combination of relief groove positions and size parameters takes into account the suppression of torque ripple and key order electromagnetic forces of vibration and noise under peak and rated operating conditions; Step 9: According to the maximum rotor mechanical stress curve obtained in Step 7, obtain the maximum rotor mechanical stress of the optimal combination of relief groove positions and size parameters selected in Step 8 under high-speed operating conditions, and judge whether the obtained maximum rotor mechanical stress is greater than the yield strength of the rotor silicon steel sheet. If so, enter Step 10, otherwise the optimization design is completed; Step 10: Increase the number of relief grooves set and return to Step 6 until the risk of structural failure is eliminated.

2. The optimized design method of the interior permanent magnet motor rotor with low torque ripple and low noise according to claim 1, characterized in that The shape of the plane to be modified described in Step 1 includes, but is not limited to, triangle, square, and ellipse.

3. The optimized design method of the interior permanent magnet motor rotor with low torque ripple and low noise according to claim 1, characterized in that, In step 4, according to the torque ripple curve under peak operating conditions, find the first minimum torque ripple. Taking the first minimum torque ripple as the center, set the first torque ripple range; similarly, set the first electromagnetic force range of the key vibration and noise orders under peak operating conditions; according to the torque ripple curve under rated operating conditions, find the second minimum torque ripple. Taking the second minimum torque ripple as the center, set the second torque ripple range; similarly, set the second electromagnetic force range of the key vibration and noise orders under rated operating conditions. Select the optimal depth and width combination such that, on the premise that the average torque under peak operating conditions and rated operating conditions is greater than the motor design requirements, the torque ripple of the optimal depth and width combination under peak operating conditions belongs to the first torque ripple range, and at the same time, the electromagnetic force of the key vibration and noise orders under peak operating conditions belongs to the first electromagnetic force range of the key vibration and noise orders, and at the same time, the torque ripple under rated operating conditions belongs to the second torque ripple range, and at the same time, the electromagnetic force of the key vibration and noise orders under rated operating conditions belongs to the second electromagnetic force range of the key vibration and noise orders.

4. The optimized design method of the interior permanent magnet motor rotor with low torque ripple and low noise 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, and the vertices of the unloading groove are rounded.

5. The optimized design method of the interior permanent magnet motor rotor with low torque ripple and low noise according to claim 1, characterized in that, In step 8, the method of selecting the optimal unloading groove position and size parameter combination is the same as the method of selecting the optimal depth and width combination in step 4.

6. The optimized design method for the rotor of an embedded permanent magnet motor with low torque ripple and low noise 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 by using the low torque ripple and low noise embedded permanent magnet motor rotor optimization design method described in any one of claims 1-5.

8. An embedded permanent magnet motor, characterized in that, Adopt the embedded permanent magnet motor rotor described in claim 7.

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