Analysis of electromagnetic noise of DC permanent magnet motor

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[Abstract] there are many specific forms such as motor noise, electromagnetic noise, aerodynamic noise and mechanical noise in motor stator and rotor on the time-varying electromagnetic force caused by electromagnetic vibration, so that the electromagnetic noise of motor electromagnetic radiation, so the vibration motor is the main vibration motor, noise source, it is necessary for us to the research and control of the. The problem of noise caused by motor relates to the coupling problem of electromagnetic vibration, acoustics, multi physical field, the Maxwell module of ANSYS software has powerful electromagnetic analysis ability, Mechanical module has experienced structural vibration engineering practice shows the analysis ability and strong acoustic analysis module of Acoustics ACT, and you can accomplish seamless transmission of data between them to coupled field analysis, which provides a good solution for the problem of electromagnetic vibration and noise of motor. In this paper a DC permanent magnet motor noise case analysis to complete the whole process of the analysis, harmonic response and acoustic and electromagnetic coupling between them, get the frequency corresponding to the sound pressure level of sound, etc..

Electromagnetic field; vibration; noise

1 Introduction

Noise is a combination of different sound frequency and intensity of the out of order, it will disturb people talk, reduce people's thinking, make the person fatigue, thus affecting the rest, work and sleep, long-term exposure in the noise environment, will make the damaged [1] human hearing, so we need to research and control of the. The electromagnetic noise is mainly caused by the electromagnetic field in the air gap, which results in the vibration of the yoke. This process involves the analysis of electromagnetic field analysis, vibration and acoustic transfer medium, is a complex problem of multi field, multi learning coupling, this paper uses the ANSYS multidisciplinary analysis ability provides a perfect solution for motor noise problems.

2 electromagnetic force analysis

The air gap magnetic field of the motor exists in the micro air gap of the stator and rotor of the motor. Air gap magnetic field is the medium of electromechanical energy conversion, and also produces radial and tangential electromagnetic force on the stator and rotor of the motor. These electromagnetic forces in the conversion of electrical energy into mechanical energy, but also on the structure of the stator and rotor, causing electromagnetic vibration. The rotor vibration is transferred to the shell mainly through the bearing. Because the bearing has the elasticity and the certain damping function, the high frequency vibration of the shell will be obviously attenuated. The stator is directly connected to the motor housing, compared with the rotor vibration, the stator vibration is more likely to cause the decoupling vibration and noise.

The rotor teeth are subjected to an ampere force to form an electromagnetic torque. In the permanent magnet and the stator core by Maxwell, vibration and noise. For the permanent magnet DC motor, the main force of the motor vibration is on the permanent magnet, including radial and tangential electromagnetic force.

2.1 motor model simplification

The analysis of the electromagnetic force of the motor only takes into account the main part of the motor, such as stator, rotor, winding, magnetic steel and so on.  Analysis by Maxwell2D, using the 1/4 model of the motor, calculation of magnetic steel inner surface of radial and tangential magnetic force, with the help of NX software simplified model (simplified stator casing, such as the removal of fine lines, small round face, etc.)

2.2 Maxwell electromagnetic force analysis

Specific steps are as follows:

1) meshing, in which the single magnetic steel mesh encryption

2 coupling analysis options for transient electromagnetic field and harmonic response analysis

3) Maxwell automatically calculates the transient electromagnetic force of the last full cycle

4) the software automatically completes the Fourier transform, and the electromagnetic force in time domain is transformed into frequency domain electromagnetic force

In this paper, the radial and tangential magnetic force density distributions of the inner surface of the stator in Maxwell are calculated as the excitation source, and the harmonic response analysis is carried out in Mechanical.

3 harmonic response analysis

Select the Harmonic response in Workbench Analysis System window, and drag the Harmonicresponse to Maxwell Project in the Schematic window on the right, D4 and B5 to realize the connection of electromagnetic force to the seamless transmission of harmonic response analysis.

3.1 model reduction

Harmonic response analysis only consider the motor stator casing, magnetic steel, ignoring the rest of the structure, with the help of NX software to simplify the model (including the removal of small surface, line, small fillet, etc.)

3.2 Mechanical harmonic response analysis

Specific steps are as follows:

1) meshing

2) import Maxwell electromagnetic force

3) define the noise source transfer file

4) harmonic response analysis to set up and submit the solution

3.2.1 harmonic response analysis boundary condition

3.2.2 谐响应分析材料参数

The displacement, velocity and acceleration of the outer surface of the stator shell, which is calculated by the Mechanical harmonic response, will be used as the excitation source and coupled to the Acoustics ACT acoustic calculation module for acoustic calculation.

4 acoustic analysis

Select the Harmonic response in the Analysis System Workbench window, and drag the Harmonicresponse to the Project Schematic window as shown in the following figure.

4.1 create acoustic models

The acoustic analysis of Acoustics ACT only considers the noise propagation medium (air) outside the stator housing, without considering the internal structure of the motor. With the help of NX model, the acoustic area outside the stator casing is created, and several key observation areas are cut out as shown below.

4.2 Acoustics ACT acoustic analysis

Specific steps are as follows:

1) meshing

2) coupling noise sources

3) noise is calculated by applying boundary conditions

4) noise analysis settings and submit the solution

4.2.1 acoustic analysis boundary conditions

4.2.2 材料参数

4.3 声学分析结果

Based on the Acoustics ACT acoustic calculation, the sound pressure, sound pressure level and speed of the motor stator outer air area at different frequencies are obtained.

5 Conclusion

1) through the 2D electromagnetic field simulation, the transient electromagnetic force on the stator of the motor is obtained;

2), through the electromagnetic structural coupling analysis of transient electromagnetic force, will automatically import Mechanical calculated by 2D electromagnetic magnet on the harmonic response analysis results obtained in response to the motor stator parts of the displacement, velocity and acceleration.

3, through the structural and acoustic coupling analysis, the harmonic response analysis results of the motor stator shell are automatically imported into the AcousticsACT acoustic calculation module.

Finally, through functional analysis of ANSYS electromagnetic vibration and noise of the strong coupling field, completed the analysis of the vibration noise of permanent magnet DC motor, the stator outer air area of the frequency of the sound pressure level size and velocity etc..