Mechanism of Eddy Current-induced Electromagnetic Force and Vibration Noise of Large-Capacity Transformer Oil Tanks

With the improvement of internal combustion engine noise, the noise of claw pole alternator which is universally used on modern automobiles is becoming more distinct. Extensive experimental results show that the noise of claw pole alternator is annoying at low to middle speed and mainly originates from the electromagnetic noise. In this paper, a complete methodology for electromagnetic vibration and noise prediction of claw pole alternator is presented. It is a three-step multiphysics simulation. The first step is to calculate the magnetic force exerted on the inner surface of the stator using 3D FEM. The second step is the structural analysis, which is to investigate the natural resonant frequencies and modal shapes of the alternator system taking into account the real mechanical boundary conditions. The third is the electromagnetic vibration and noise calculation by using modal superposition method and boundary-element method, respectively. Simulation results agree well with those measured by experiments. Furthermore, the mechanisms of electromagnetic vibration and noise are analyzed by using the electromagnetic theory. The method can be used in the initial design stage of claw pole alternator and is also suitable for other types of motor.

This paper presents a method based on the finite element simulation, the electromagnetic field, electromagnetic force, electromagnetic vibration and electromagnetic noise characteristics of a double-rotor permanent magnet synchronous in-wheel motor under multiple operating conditions are systematically studied. On the integration of previous methods, a program of multi-physics modeling and analysis of electromagnetic vibration and noise of motor is set up. Firstly, a new electromagnetic structure design of double-rotor permanent magnet synchronous in-wheel motor is proposed. Based on Maxwell stress equation, the analytical model of the radial electromagnetic force of the motor is established. The spatial domain, time domain and frequency domain analysis of the internal and external electromagnetic force and torque ripple of the double-rotor permanent magnet synchronous in-wheel motor are carried out by means of finite element simulation. Analysis shows that the radial electromagnetic force before the 5th order is mainly influential, tangential electromagnetic force before the 4th order is mainly influential. With the increasing of order, the amplitude is gradually reduced. The amplitude of the first order is the highest. According to the different modeling methods of stator windings, four finite element models in 3D structural field are designed for the double-rotor permanent magnet synchronous in-wheel motor. Then, the effects of quality and stiffness of the effective length and end of stator windings on the stator modal frequency are summarized and compared. The results show that the effect of winding mass and stiffness on the overall modal frequency of the stator is nearly canceled. After that, the 3D structural field model of the double-rotor permanent magnet synchronous in-wheel motor is used to simulate the transient dynamics under radial concentrated force loading. Based on the simulation results, the inner and outer lateral deformation of stator is analyzed in time domain and frequency domain. Finally, the harmonic response analysis of 3D structural field model of the double-rotor permanent magnet synchronous in-wheel motor is proposed, and the 3D sound field boundary element model of electromagnetic noise is established. The acoustic boundary element analysis under multiple operating conditions is carried out, including sound pressure analysis of stator surface, sound pressure analysis of field point and analysis of sound pressure frequency response characteristics at different field points. The results show that the electromagnetic noise of motor is more sensitive to the high frequency excitation, and the sensitivity of the electromagnetic noise in the radial position is significantly larger than that of the axial position. The analysis process proposed in this paper can provide support for the prediction, optimization and analysis of influencing factors of electromagnetic vibration and noise during the period of motor design.

Aiming at the electromagnetic vibration and noise problem of an 8-pole 48-slot permanent magnet synchronous motor for a vehicle, the multi-physics coupling simulation model of the motor is introduced to optimize the rotor structure of the motor to reduce the vibration and noise of the permanent magnet synchronous motor. The effectiveness of the research method is verified by the bench test in the anechoic chamber. Finite element software was used to establish the stator core and system model considering the anisotropy of materials, and the simulation model was verified by modal experiment. For the 2in1 electric drive system, the electromagnetic-structure-acoustic multi-physics coupling noise prediction model is established. Based on the three-dimensional distributed electromagnetic force excitation, the electromagnetic radiation noise of the motor under full load acceleration is calculated, and the characteristics of electromagnetic noise are analyzed. The accuracy of the electromagnetic-structure-acoustic multi-physics coupling model of permanent magnet synchronous motor is verified by the bench test results of the anechoic chamber. By changing the angle and shape of the motor rotor, the cogging torque ripple between the stator and the rotor is reduced, and the 48th order harmonic amplitude is reduced. Finally, the optimized sample is tested on the vehicle, and the 48th order electromagnetic noise can be reduced by 5–15 dB(A). The accuracy of the electromagnetic-structure-acoustic multi-physics coupling model of permanent magnet synchronous motor is verified by the bench test results of the anechoic chamber. Therefore, the research results can be further used for the design and development of a vehicle permanent magnet synchronous motor and the research on the mechanism of electromagnetic vibration and noise.

In the paper, the numerical simulation is conducted on the motor electromagnetic force firstly. Radial force waves of the motor are the main reason for causing electromagnetic vibration and noise. Then, electromagnetic forces are mapped into a structural model for computing electromagnetic vibration. Computational results are compared with experimental results, so the correctness of the computational model is verified. Then, electromagnetic noises are computed according to the vibration data of the motor. Electromagnetic noises of the motor are axis-symmetric in plane X and plane Z. In plane Y, the electromagnetic noise of the motor is skew-symmetric relative to a 45° angle. In plane X and plane Z, the noise is caused by the vibration of the end cap, while noise in plane Y is caused by electromagnetic radial forces. In addition, the motor electromagnetic noise has an obvious directivity. The motor also has obvious peak noises at 300 Hz, 400 Hz, 500 Hz, 600 Hz, 900 Hz, 1200 Hz, 1500 Hz and 1800 Hz. Peak noises are corresponding to 6th, 8th, 10th, 12th, 18th, 24, 30th and 36th orders of the motor. Finally, modal participation factors of the motor within the analyzed frequency are computed. Results showed that modals at the 3rd, 5th, 12th and 15th orders of the motor have most obvious impacts on electromagnetic noises. In particular, the 3rd order modal shape obviously affects electromagnetic noises. The electromagnetic noise is reduced by applying reinforced bars and damping layer to these key modal shapes, especially the peak noise. The total noise of the original structure is 58 dB, while the total noise of the improved structure is 52.3 dB. Obviously, the total noise is reduced by 9.8 %.

To investigate the electromagnetic vibration and noise issues in induction motors, this study employs a combined methodology of experimental, theoretical, and simulation approaches to analyze the characteristics of electromagnetic noise. Initially, a theoretical analysis of the radial electromagnetic force of the motor is conducted, followed by a simulation of the motor’s electromagnetic vibration and noise at a working condition of 3000 rpm, incorporating a Multiphysics coupled analysis of electromagnetic-vibration-noise. Vibration testing on a specific compressor motor reveals that the primary vibration noise characteristic frequency is centered around 2000 Hz. A comparison between simulation and experimental results shows a high degree of congruence, indicating the reliability of the simulation method. Subsequently, an acoustic camera kit, Brüel & Kjær PULSE Reflex, based on a beamforming method, is employed for noise source identification and acoustic holography testing at 3000 rpm, which successfully localizes the noise sources. The analysis and experiments provided herein can serve as a reference for the development of electromagnetic vibration noise suppression techniques in induction motors.

The electromagnetic noise of motor is mainly caused by the main magnetic fluxing into the air gap along the radial direction, generating radial force in the tooth of stator and rotor, which causes electromagnetic vibration and noise. The paper analyzes the theory of the production principle of electromagnetic force by selecting different slot combination to verify the influence on the electromagnetic wave, further conducts through the finite element analysis and modal analysis to prove the validity of the theory, and finally to prove that the choice of slot combination has an important influence on the noise of squirrel cage induction motor through noise test tank. Keywords-Slot Combination; Electromagnetic Force; Finite Element Analysis; Modal Analysis; Noise Test I. INT RODUCT ION At present, harmonic magnetic field of stator and rotor of the squirrel cage induction motor will interact with each other which will produce radial electro magnetic wave changing with time and space when it is electricity in engineering. Radial electro magnetic wave will cause vibration of stator, which will cause the noise. This is the main reason for the motor to generate electromagnetic noise. Intrinsic mode of motor stator structure and radial electromagnetic wave on the surface of the stator core are two major factors to determine the size of induction motor electromagnetic noise .At the same time the selection of slot coordination of the motor is mainly based on experience, and sometime the electromagnetic noise will exceeds standard. Therefore, it is necessary to research the slot coordination selection method of squirrel-cage motor. At the same time, the appropriate or not of slot coordination, not only should consider the order, amplitude and size of the wave force, must also consider the frequency of force wave and the natural frequency of the stator size, to avoid resonance. The generation of electromagnetic noise have a close relationship with the radial electro magnetic force wave and the existing mechanical mode, these two aspects should be in consider when choosing low noise slot coordination. Literature 2 studied effect on noise of 8 poles with 28 slots, 8 poles with 36 slots and 8 poles with 48 slots, when this three pole with slot coordination. Literature 3 only studied the electromagnetic wave through groove cooperates select to limit the influence of noise, but did not consider the modal effect. Literatures 4 studied the mode of traction drive motor, but had no contrast on slots with different effects on noise. Based on the squirrel cage induction motor as an examp le for slot coordination which is commonly used in engineering analysis the influence of the electromagnetic wave in theoretically in this paper, And in this paper a calculation is made for a company to provide prototype theory analysis and simulation, and through the prototype experiments validate the importance of selecting slot coordination and shorten the design cycle, to reduce the electromagnetic noise in the primary stage fullest.

A complete methodology for electromagnetic vibration and noise prediction of claw pole alternators is presented. It is a 3-step multiphysics simulation. The first step is to calculate the distributed magnetic force exerted on the inner surface of the stator using 3D FEM. The second step is the structural analysis which is to investigate the natural resonant frequencies and modal shapes of the alternator system taking into account the real mechanical boundary conditions. The third is the electromagnetic vibration and noise calculation by using modal superposition method and boundary element method respectively. The modeling can ensure the temporal and spatial distribution characteristics of the electromagnetic force and reflect the structural mechanic characteristics of claw pole alternators. Simulation results agree well with those measured by experiments. Furthermore, the mechanisms of electromagnetic vibration and noise are analyzed by using the electromagnetic theory. The method can be used in the initial design stage of claw pole alternators and is also suitable for other type of motor.

Modeling and analysis of radial electromagnetic force and vibroacoustic behaviour in switched reluctance motors

In this study, a multiphysics finite element method is proposed to predict and evaluate the electromagnetic vibration and noise of the permanent magnet synchronous motors. First, the expressions of radial electromagnetic force waves were derived based on the established mathematical models of airgap magnetic field using the analytical methods. Subsequently, the main circumferential spatial orders influencing electromagnetic noise were analyzed and discussed. Then, a multiphysics simulation model that consists of mechanical field, electromagnetic field, and acoustic field was established for the calculation of the electromagnetic radiation noise. Finally, the multiphysics simulation model developed for the electromagnetic vibration and noise prediction was validated by comparing the finite element analysis and experimental data. It is shown that, although the local differences exist, the results from the finite element calculation and test analysis have a good agreement on the analytical mechanism overall, both in amplitude and main orders. In addition, this paper has made a detailed analysis to the electromagnetic noise generation mechanism, which lays the basis for further study in predicting and suppressing the electromagnetic vibration and noise of the drive motors of pure electric vehicle.

The permanent magnet vernier synchronous machine (PMVSM) has the characteristics of high torque density and high power density and has advantages in the field of low-speed and high-torque applications. The PMVSM utilizes rich harmonics for torque enhancement, but it can also cause an increase in radial electromagnetic force and vibration noise. In this paper, we take a 12-slot 10-pole PMVSM as an example to analyze the source of radial electromagnetic force, vibration and noise. The electromagnetic finite-element model and structural finite-element model of the PMVSM are established for calculation. Through the analysis and calculation of two-dimensional electromagnetic fields, the radial electromagnetic force distribution of the PMVSM is obtained. We derive the radial electromagnetic force formula of the PMVSM and verify the correctness of the formula through harmonic analysis of the radial electromagnetic force. The sources of radial electromagnetic forces at various orders and frequencies within the PMVSM are analyzed and summarized by coupling the radial electromagnetic force obtained from the electromagnetic finite-element model to the structural finite-element model and conducting electromagnetic vibration harmonic response analysis on the PMVSM. The measured acceleration spectrum of the prototype is compared with the finite-element method (FEM) results, verifying the correctness of the finite-element simulation results for electromagnetic vibration.

In this paper, a multi-physics simulation model capable of electromagnetic noise prediction is established, and the effectiveness of the established simulation model in predicting and evaluating electromagnetic noise is verified. Based on the verified motor model, a rotor step skewing model which can affect electromagnetic noise is proposed, and the influence of the skewing angle on electromagnetic noise is investigated in detail. By studying the spectral characteristics of the low-order radial magnetic force which has a great influence on electromagnetic noise, the distribution of electromagnetic noise characteristics of the permanent magnet synchronous motor (PMSM) with or without the rotor step skewing is compared and analyzed. Therefore, it lays a technological foundation for predicting and suppressing the electromagnetic vibration noise of electric vehicle (EV) driving motor in the electromagnetic design.

The reduction in the electromagnetic vibration and noise in three-phase squirrel-cage induction motors (IMs) has become very important from an environmental standpoint. Although electromagnetic vibration in IMs has been studied for several years, the relationship between the electromagnetic force and the radial distributions of the resulting electromagnetic vibration and noise has not yet been analyzed in sufficient detail. Our results clearly show that the radial distributions of the dominant electromagnetic vibration and noise components caused by an IM under load conditions match the mode shape of the dominant electromagnetic force producing these components.

A multiphysics simulation model that consists of electromagnetic field, mechanical field, and acoustic field was established to predict the electromagnetic vibration and noise of claw pole alternators. First, magnetic force exerted on the stator inner surface was calculated by three-dimensional (3-D) transient electromagnetic field analysis and the characteristic of magnetic force was analyzed. Second, finite-element modal analysis of alternator assembly was conducted while taking into account the anisotropy of the stator core and armature winding and the installation condition. Simulation result was validated by modal test. Afterward, magnetic force was transferred to the structural mesh using mesh mapping method and the vibration and noise were predicted by using mode superposition method and boundary-element method, respectively. Simulation results agree well with those measured by experiments. Finally, the mechanism of electromagnetic vibration and noise of the claw pole alternator was revealed with the help of 2-D Fourier transform of magnetic force and the mode participation factor of each mode. Results show that for three-phase 12-pole/36-slot claw pole alternator, electromagnetic vibration, and noise are mainly caused by the zeroth-order (circumferential spatial order) force harmonics whose frequencies are 36 kfr ( k = 1, 2, 3,…) and the sixth-order (circumferential spatial order) force harmonics whose frequencies are (36 k ± 6) fr ( k = 1, 2, 3,…).

Reduction of electromagnetic vibration and acoustic noise from three-phase squirrel-cage induction motors (IMs) is very important, particularly from the standpoint of environmental considerations. Although the electromagnetic vibration of IMs has been studied for several years, the relationships between the radial distribution of the electromagnetic vibration and noise and the electromagnetic forces responsible for them have not yet been analyzed in sufficient detail. In the present study, we investigated this relationship experimentally for a small IM under different load conditions. Our results clearly show that the radial distributions of the dominant electromagnetic vibration and noise components match the mode shape of the dominant electromagnetic force producing these components.

As a nondestructive testing method, the magnetic flux leakage (MFL) testing technique is widely used for the testing of surface and near-surface areas in ferromagnetic materials. The MFL field is influenced by parameters of defects, strength of excitation, sensor lift-off value and electromagnetic noises etc. A 2-D finite element method (FEM) simulation model is established in this paper to analyze the influence of lift-off values under the condition of mechanical vibration and electromagnetic noises. The distribution of the MFL field peak for different lift-off values and different depth defects is presented. The defect quantization errors caused by the mechanical vibration and electromagnetic noises are introduced to analyze the influence of lift-off values and electromagnetic noises. The best range of lift-off values can be determined from the results of error analysis. It is effective to improve the measuring accuracy in practical MFL testing.