A principal source of vibration in permanent magnet (PM) motors
and generators is the traveling forces on the stator induced by the
rotating permanent magnets. These forces are transmitted through the
stator and to the surrounding system. The magnetic forces were
calculated from the flux density by finite element methods (FEMs). The
dynamic reactions at the motor mounting points, which provide the
forcing function to the base system, were also calculated by FEMs. The
vibration characteristics and the transmissibility of each frequency
component were investigated using Fourier decomposition of the traveling
magnetic force. The results showed that for a radially centered rotor
the frequency components of the magnetic force were integer multiples of
the rotor speed multiplied by the number of magnetic poles. Higher
harmonics were more difficult to transmit, except when stator structure
resonance occurred. The edge shape of the PM determined the shape of the
magnetic force and the magnitude of the frequency components. By proper
shaping of the magnetic edges, the composition of the magnetic force
spectrum can be assigned to higher frequencies, reducing the overall
transmission to the base system
"The influence of the PM shape on the electromagnetic force excitation and on the vibrational behavior of PMSM has been analyzed , e.g. radially magnetized magnets showed a frequency spectrum of force excitations with higher components at higher frequencies, due to the block shaped B-field. "
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a methodology for the acoustic optimization of PMSM applying two steps: hybrid modeling to obtain the magnetic field and forces at comparatively small computational effort and FEM-to-measurement transfer functions to assess the structural behavior and the radiation characteristics of the machine at once. Both steps are explained and applied to a specific PMSM design, which is subject to optimization. The proposed approach relies on a (virtual) protoype. The resulting optimized geometry shows significant reduction potential in terms of total sound pressure level, up to 18dB(A), but at the cost of a larger magnet volume. Limitations of this procedure are discussed.
Electrical Machines (ICEM), 2010 XIX International Conference on; 10/2010
"Therefore, reduction of electromagnetic exciting force is considered in this paper. Two types of exciting force are produced during operation of ISG which are global force such as torque ripple and local force that is including radial force and tangential force . This paper deals with reduction design of vibration and noise of ISG by decreasing both global force and local force. "
[Show abstract][Hide abstract] ABSTRACT: Integrated starter and generator (ISG) is working as starter after vehicle idle stopping and generator during vehicle driving. When ISG works as starter to operate engine, ISG produces maximum power at the operating speed 4000 rpm to remove vibration of initial starting of the engine. In that time ISG produces whine noise which can be detected inside a vehicle. There are two methods to reduce the vibration and noise. One is improving the stiffness of stator and the other is reduction of electromagnetic exciting force. Although improvement of stiffness using mechanical design is utilized effectively to reduce whine noise, the electromagnetic design using the reduction of exciting forces is more reasonable in the same motor size. Because ISG produces torque ripple, radial force and tangential force on operating condition, this paper deals with the reduction design of electromagnetic exciting forces which affect the noise and vibration. Two design variables are selected to optimize the rotor shape especially geometry of flux barrier, and response surface methodology (RSM) is applied as an optimization method. Finally, quantity of the vibration and noise of optimized model are compared with prototype model, and the noise measured in the vehicle engine bay was reduced from 27 dB(A) to 25 dB(A).
"Several researchers – have investigated the harmonic contents of UMF by numerical and analytical methods. Prior researchers did not measure UMF directly; they just presumed the existence and characteristics of the UMF by analyzing the measured vibration or the acoustic characteristics of an electric motor. "
[Show abstract][Hide abstract] ABSTRACT: This paper investigates the characteristics of the unbalanced magnetic force (UMF) of a brushless dc (BLDC) motor due to uneven magnetization of a permanent magnet (PM), rotor eccentricity, stator eccentricity, and interactions between these factors. An experimental device is developed to measure the UMF of an electric motor directly. Finite-element analysis is performed to compare experimental and simulated results. The characteristics of the measured UMF match those of the simulated one. The UMF always exists in the symmetric design of pole, slot and winding of BLDC motors if there are manufacturing or operating errors such as uneven magnetization of the PM, or rotor and stator eccentricities. This research shows that the driving frequencies of the UMF due to uneven magnetization of the PM are the first harmonic and the harmonics of slot number plusmn 1. It also shows that rotor and stator eccentricities mainly generate the first harmonic and the harmonics of the pole number, respectively.
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