Rotor skewed pole mode method for reducing noise of permanent magnet synchronous motor

Abstract

The invention discloses a rotor skewed pole mode method for reducing noise of a permanent magnet synchronous motor, which analyzes and designs a generation source of radial vibration of the integer slot permanent magnet synchronous motor, and mainly solves the problem of high-frequency squeal generated by the integer slot permanent magnet synchronous motor at a high speed. The rotor specifically comprises a rotor iron core and a deviation angle segmented skewed pole of a permanent magnet. The method is applied to the built-in permanent magnet synchronous motor, and a permanent magnet and a rotor core of the built-in permanent magnet synchronous motor are segmented. When the permanent magnet motor adopts the rotor segmented structure, a radial force harmonic component which plays a main role in vibration of the motor can be effectively offset, radial vibration caused by specific radial force harmonic waves is weakened, and torque pulsation of the motor is optimized, so that the running stability of the motor is improved, and the whole quietness of the motor is improved.

Description

Technical Field

[0001] The invention relates to a method for reducing the noise of a permanent magnet synchronous motor by using a rotor skewed pole mode, and belongs to the technical field of manufacturing new high-quality and low-noise motors. Background Art

[0002] With the development of new energy vehicles, the performance of drive motors has been significantly improved in all aspects, and higher requirements have been put forward for the vibration and noise of motors. Permanent magnet synchronous motors have the characteristics of high efficiency, high power density, and large output torque, and are widely used in the field of electric vehicles. However, at the same time, the noise problem brought about by them has also attracted more and more attention. In order to break through the technical difficulties of low vibration and noise of permanent magnet synchronous motors, providing a design method for low vibration and noise permanent magnet synchronous motors has become a problem that needs to be solved urgently. In order to suppress the vibration and noise of permanent magnet motors, it is mainly to reduce the harmonic content and reduce the amplitude of the low-order radial electromagnetic force of the motor. Therefore, it is of great significance to study the generation mechanism of vibration and noise of permanent magnet synchronous motors and its suppression method.

[0003] As a method to reduce motor torque pulsation, rotor segmented skewed pole technology is often used in the design of industrial motors. Its mechanism of action is to stagger the rotor segments, so that the permanent magnetic field of each rotor segment interacts with the armature magnetic field of the stator core to produce torque waveforms with the same amplitude and different phases. When a specific offset angle is adopted, the phases of each torque waveform are different, so after superposition and synthesis, the torque pulsation is effectively suppressed. This method can be used for reference transplantation and used in the offset of radial electromagnetic force, thereby suppressing the vibration and noise of permanent magnet motors. Summary of the invention

[0004] The purpose of the present invention is to improve the deficiencies of the prior art and propose a method for reducing the noise of a permanent magnet synchronous motor by using a rotor skewed pole method. The method is easy to process and has strong portability. For an integer slot permanent magnet motor, the effect of reducing the motor vibration is significant. In addition, the structure can further reduce the torque pulsation, optimize the electromagnetic performance, take into account both reducing vibration and improving torque performance, and greatly improve the stability of the motor operation.

[0005] Specifically, the present invention is implemented by adopting the following technical solution: a method for reducing the rotor pole skew mode of permanent magnet synchronous motor noise, the specific steps of the method are as follows: Step 1: According to the operating conditions of the integer slot motor, determine the size of the motor, including the stator size, rotor size and arrangement of the permanent magnets, and then select the appropriate slot-pole combination; Step 2: In the design stage, the integer slot permanent magnet motor must be modeled by finite element, the material properties of the motor must be determined, and finite element simulation must be performed to obtain the electromagnetic performance parameters of the motor, and to observe the air gap synthetic magnetic flux density distribution and the two-dimensional radial electromagnetic force distribution of the motor; Step 3: After determining the main harmonic components of the air gap flux density and radial force, theoretically analyze the source of the harmonic generation, predict its main impact on the motor vibration, and import the electromagnetic calculation results obtained by finite element simulation into the acoustic boundary element software to further verify the consistency between the main vibration components in the motor and the prediction; Step 4: Analyze the vibration reduction capabilities of different numbers of segments and different offset angles under the original rotor structure, and select the best solution as the final optimization solution.

[0006] The operating condition of the integer slot motor in step 1 is the automotive permanent magnet drive condition. The stator size of the motor includes the stator outer diameter, the stator inner diameter and the main parameters of the stator teeth; the rotor size includes the rotor outer diameter and the rotor inner diameter; the permanent magnet arrangement and placement method in the embodiment is a V-shaped embedded arrangement method; according to the specific design requirements of the integer slot permanent magnet motor, in the embodiment, the outer diameter of the motor stator core is 195mm, the inner diameter of the stator core is 120mm, the outer diameter of the rotor core is 118.8mm, and the inner diameter of the rotor core is 38mm. The number of stator slots of the motor is 48 slots, the number of rotor poles is 8 poles, the winding winding method is a double-layer integer slot span, and the winding span is 6; Further, in step 2, the material properties of the motor include parameters such as the materials used for the stator, rotor and permanent magnets, material density and the residual magnet size of the permanent magnet. In the embodiment, the stator and rotor material model of the motor is M250-35A, the rotor permanent magnet material is N38UH, and the stator winding is wound with copper wire. The material density of silicon steel sheet M250-35A is 7600kg / m3, the density of permanent magnet is 7500kg / m3, and the density of copper wire is 8900kg / m3. The residual magnet size of permanent magnet N38UH is 1.26T. In addition, the electromagnetic properties of the motor mainly include parameters such as no-load back electromotive force waveform, cogging torque and rated torque. Due to the use of an integer slot structure, the air gap flux density waveform and the radial electromagnetic force waveform of the motor are periodically distributed; the number of cycles of the air gap flux density waveform is the number of permanent magnet poles of the rotor, and the period of the radial electromagnetic force waveform is the number of permanent magnet poles of the rotor.

[0007] Furthermore, in step 3, it can be seen from the frequency domain distribution diagram of the electromagnetic force that in the 8-slot 8-pole integer-slot permanent magnet motor of embodiment 48, the frequency band with relatively large vibration noise appears at 12 times the operating frequency.

[0008] In step 4, for an integer slot permanent magnet motor, the radial force harmonic content of the slot number order has the greatest impact on the motor vibration, and the slot number order radial force harmonics are mainly generated by the interaction between the fundamental component of the air gap flux density and the tooth harmonic component of the air gap flux density. When the number of segments is k, the tooth torque is minimum when the adjacent staggered angle is 7.5° / k. The simulations were performed for six cases with the number of segments k=1, 2, 3, 4, 5, and 6, and the results are shown in Table 1 below: Table 1 Effect of segment number on torque performance Number of rotor segments Pole Angle° Cogging torque / N‧m Average torque / N‧m Torque ripple 1 0 3.09 196.77 5.54% 2 3.75 0.11 193.28 3.14% 3 5 0.11 192.52 2.62% 4 5.625 0.06 192.29 2.59% 5 6 0.02 192.16 2.60% 6 6.25 0.03 192.10 2.57% Further comparison and selection of appropriate skew angles are made to offset the synthetic radial force harmonics, thereby weakening the vibration of the integer slot permanent magnet motor. In the embodiment, four cases, namely, 1 segment, 2 segments, 3 segments, 4 segments, 5 segments and 6 segments, are selected for comparison, and the final number of segments is determined to be 4 segments. When the offset angle is 0.75 degrees, the radial force offset effect is best; The present invention has the following beneficial effects: 1. After the permanent magnet motor rotor is segmented in the present invention, the vibration of the motor under no-load and load operating conditions is significantly weakened, and the operating stability is significantly improved.

[0009] 2. The present invention reduces the vibration of the integer-slot permanent magnet motor while improving the electromagnetic performance, which is specifically manifested in reducing the cogging torque and torque pulsation of the integer-slot permanent magnet motor and improving the sinusoidality of the no-load back electromotive force.

[0010] 3. The rotor segmentation method adopted by the present invention has simple processing technology and high portability, can overcome the limitations of traditional vibration reduction and noise reduction methods, and has a wide range of applications.

[0011] In summary, the rotor pole skewing method for reducing the noise of the permanent magnet synchronous motor of the present invention can not only significantly reduce the vibration of the integer-slot permanent magnet motor, but also take into account the optimization and improvement of the electromagnetic performance. It has a wide range of applications and a simple processing technology, and can overcome the limitations of the traditional methods of complex processing and small application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 (a) is a schematic diagram of the radial structure of the permanent magnet motor of the present invention, Figure 1 (b) is a schematic diagram of the axial structure; Figure 2 It is a schematic diagram of the rotor segment structure; Figure 3 It is a comparison diagram of cogging torque under different skew angles; Figure 4 The torque ripple comparison diagram under different skew angles; Figure 5 Comparison diagram of electromagnetic force harmonic distribution under different oblique polarity angles; Figure 6 This is the noise waterfall diagram at full speed of the motor; Figure 7 This is a comparison chart of the sound pressure levels at different oblique polar angles; DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. In order to more simply and clearly illustrate the beneficial effects of the present invention, a specific integer slot permanent magnet synchronous motor is described in detail below.

[0014] Figure 1 The meaning of each structure is as follows: 1. rotor permanent magnet steel, 2. permanent magnet slot, 3. stator core, 4. rotor surface auxiliary slot, 5. rotor core, 6. stator winding. Among them, the rotor permanent magnet 1 is embedded in the permanent magnet slot 2. The permanent magnet slot 2 has a large area, and there is a gap space after the rotor permanent magnet steel is embedded. The rotor surface auxiliary slot 4 can improve the electromagnetic performance of the motor. The rotor core 5 is used to conduct magnetism in the permanent magnetic field when the motor is idling, reducing the rotor magnetic resistance of the motor. When the motor is running under load, the rotor core 5 also provides a path for the distribution of the armature magnetic field inside the motor. The stator winding 6 is wound around the stator core 3 in an integer slot double-layer winding manner. The stator core 3 includes stator teeth and a stator yoke. The stator winding 6 is wound around the stator teeth to generate a stable excitation magnetic field. The stator yoke provides a path for the distribution and transmission of the permanent magnet and armature magnetic fields, reducing the flow obstruction of the magnetic field.

[0015] A rotor pole skewing method for reducing noise of a permanent magnet synchronous motor of the present invention comprises the following specific steps: Step 1, analyze the design requirements of the integer slot motor. In this embodiment, the integer slot motor is used for electric drive of electric vehicles. After clarifying the design requirements, determine the various dimensional parameters of the motor. Specifically, the stator core outer diameter of the motor is 195mm, the stator core inner diameter is 120mm, and the rotor core outer diameter is 118.8mm, the rotor core inner diameter is 38mm, the motor single-sided air gap is 0.6mm, 9 strands of 0.75mm insulated copper wire are wound in parallel, 48 slots and 8 poles are selected, the winding is wound with integer slot distributed winding, and the span is 6; Step 2, confirm the motor size model, use finite element software to model and analyze the motor. In the embodiment, the stator and rotor material models of the motor are M250-35A, the rotor permanent magnet material is N38UH, and the stator winding is wound with copper wire. The material density of silicon steel sheet M250-35A is 7600kg / m3, the permanent magnet density is 7500kg / m3, and the density of copper wire is 8900kg / m3. The residual magnetism of permanent magnet N38UH is 1.26T. After assigning material properties to each component, further simulation is performed to obtain the various electromagnetic properties and radial electromagnetic force parameters of the integer slot permanent magnet motor; Step 3: Import the electromagnetic radial force data obtained by simulation into the acoustic boundary module for vibration response analysis. In order to test the accuracy of the data, simulation verification is required under multiple working conditions. Multiple working conditions include: no-load working condition, load working condition and high-speed operation working condition. Further obtain the frequency band components that have the main impact on the vibration, analyze their sources theoretically, and find the sources from the two-dimensional decomposition of the spatial radial force; Step 4: According to the results of vibration simulation, the vibration at the 12-fold frequency band is relatively large. Analyze the vibration reduction capabilities of different segment numbers and different offset angles under the original rotor structure, and select the best solution as the final optimization solution.

[0016] Further analysis of the torque pulsation size at the skew angle of different segment numbers that makes the theoretical cogging torque 0 shows that it is more reasonable when the segment number is 4. The acoustic simulation results of the effect of different skew angles on the sound pressure level show that the best effect is obtained when the skew angle is 7.5°.

[0017] Figure 1 (a) Figure 1 (b) is a schematic diagram of the radial and axial models of the motor in this embodiment. The armature winding of this motor adopts a double-layer distributed winding form, the winding span is 6, the magnetic steel adopts a V-shaped built-in structure, the angle is 157 degrees, the permanent magnet material is N38UH, and the material of the stator core and the rotor core are both M250-35A. The main function of the auxiliary groove on the rotor surface is to reduce noise while facilitating installation and positioning; Figure 2 The schematic diagram of the rotor segment structure design is shown. The skew angles of different angles are simulated and analyzed. The theoretical calculation of different numbers of rotor segments is performed. When the number of rotor segments is 4, the skew angle of 7.5° is more reasonable.

[0018] Figure 3 The figure shows the comparison of the cogging torque under four different rotor skew angles. It can be seen from the figure that after adopting the rotor segmented skew, the cogging torque gradually decreases. When the skew angle is 5°, the cogging torque tends to 0; Figure 4The figure shows the comparison of torque pulsation with four different rotor skew angles. It can be seen from the figure that after adopting the rotor segmented skew angle, the torque pulsation gradually decreases. As the skew angle increases, the peak torque also gradually decreases. Figure 5 This is a comparison of the radial electromagnetic force at four different rotor skew angles. It can be seen from the figure that as the skew angle increases, the amplitude of the high-order electromagnetic force wave decreases more significantly, which is beneficial to improving the noise characteristics; Figure 6 The noise waterfall diagram of the motor shows that the noise is mainly caused by the 48th order noise. As long as the 48th order electromagnetic force wave is reduced, the noise will be significantly improved. Figure 7 The figure shows the comparison of sound pressure levels for four different rotor skew angles. It can be seen from the figure that the peak noise is mainly caused by the 48th order. As the skew angle increases, the peak noise in the high-speed zone is significantly reduced.

[0019] In summary, the rotor segmentation method for weakening the vibration of an integer-slot permanent magnet motor of the present invention includes analysis of motor design requirements, analysis and determination of main dimensional parameters, and quantitative analysis of the vibration weakening effects under different segmentation schemes; the optimal design scheme is confirmed, and the air gap flux density and radial electromagnetic force are calculated and analyzed to determine the degree of the shock absorption effect; the difference between the motor torque conditions and the initial structure is compared; the computer case surface vibration acceleration test is performed using an experimental test method to calibrate and verify the consistency between theory and practice. The provided scheme can provide a reference study for suppressing vibration and improving electromagnetic performance of integer-slot permanent magnet motors.

[0020] Although the present invention has been disclosed as above with preferred embodiments, the embodiments are not intended to limit the present invention. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention shall fall within the scope of protection defined by the appended claims of this application.

Claims

1. A method for reducing the rotor pole skewness of a permanent magnet synchronous motor noise, the specific steps are as follows: Step 1: According to the operating conditions of the integer slot motor, determine the size of the motor, including the stator size, rotor size and arrangement of the permanent magnets, and then select the appropriate slot-pole combination; Step 2, design stage, it is necessary to carry out finite element modeling of the integer slot permanent magnet motor, establish the various material properties of the motor, and perform finite element simulation to obtain the electromagnetic performance parameters of the motor, observe the air gap synthetic magnetic flux density distribution and the two-dimensional radial electromagnetic force distribution of the motor; Step 3, after determining the main harmonic components of the air gap flux density and radial force, theoretically analyze the source of the harmonic generation, predict its main impact on the motor vibration, import the electromagnetic calculation results obtained by finite element simulation into the acoustic boundary element software, and further verify the consistency between the main vibration components in the motor and the prediction; Step 4: Analyze the vibration reduction capabilities of different segment numbers and different offset angles on the original rotor structure, and select the best solution as the final optimization solution.

2. The method for weakening the vibration of an integer-slot permanent magnet motor by segmenting the rotor according to claim 1, characterized in that: The operating condition of the integer slot motor in step 1 is the automotive permanent magnet drive condition. The stator size of the motor includes the main parameters of the stator outer diameter, the stator inner diameter and the stator teeth; the rotor size includes the rotor outer diameter and the rotor inner diameter; the permanent magnet arrangement and placement method is a V-shaped embedded arrangement in the embodiment; a 48-slot stator slot is selected to match the slot-pole combination of 8 rotor permanent magnets.

3. The method of weakening the vibration of an integer-slot permanent magnet motor by segmenting the rotor according to claim 1, characterized in that: In the step 2, the stator and rotor material models of the motor are both M250-35A, the rotor permanent magnet material is N38UH, and the stator winding is wound with copper wire; the electromagnetic properties of the permanent magnet motor mainly include no-load back electromotive force waveform, cogging torque and rated torque parameters; in addition, the air gap flux density waveform and radial electromagnetic force waveform of the integer slot permanent magnet motor show periodic distribution, the number of air gap flux density waveform cycles is the number of permanent magnet pole pairs of the rotor, and the period of the radial electromagnetic force waveform is the number of permanent magnet poles of the rotor.

4. The method of weakening the vibration of an integer-slot permanent magnet motor by segmenting the rotor according to claim 1, characterized in that: In step 4, for an integer-slot permanent magnet motor, the radial force harmonic content of the slot number order has the greatest impact on the motor vibration, and the slot number order radial force harmonics are mainly generated by the interaction between the fundamental component of the air gap magnetic flux density and the tooth harmonic component of the air gap magnetic flux density.

5. The method of weakening the vibration of an integer-slot permanent magnet motor by segmenting the rotor according to claim 1, characterized in that: In step 4, after the rotor is segmented, the expression of the cogging torque is:

6. The method for reducing rotor pole skewness of a permanent magnet synchronous motor according to claim 5, characterized in that: The number of segments was finally determined to be 4, and the offset angle was 7.5 degrees.

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