Noise and vibration DC-motor(直流电机噪音及振动)

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IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 6, NOVEMBER 2004
Characterization of Noise and Vibration Sources in Interior Permanent-Magnet Brushless DC Motors
Hong-Seok Ko and Kwang-Joon Kim
Abstract—This paper characterizes electromagnetic excitation forces in interior permanent-magnet (IPM) brushless direct current (BLDC) motors and investigates their effects on noise and vibration. First, the electromagnetic excitations are classified into three sources: 1) so-called cogging torque, for which we propose an efficient technique of computation that takes into account saturation effects as a function of rotor position; 2) ripples of mutual and reluctance torque, for which we develop an equation to characterize the combination of space harmonics of inductances and flux linkages related to permanent magnets and time harmonics of current; and 3) fluctuation of attractive forces in the radial direction between the stator and rotor, for which we analyze contributions of electric currents as well as permanent magnets by the finite-element method. Then, the paper reports on an experimental investigation of influences of structural dynamic characteristics such as natural frequencies and mode shapes, as well as electromagnetic excitation forces, on noise and vibration in an IPM motor used in washing machines. Index Terms—Brushless machines, electromagnetic forces, noise, permanent magnet, vibrations.
Fig. 1.
Cross sections of BLDC motors.
I. INTRODUCTION
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ONVENTIONAL direct current commutator motors with permanent magnets are easy to control and require few semiconductor devices. Yet, they have serious operational problems in association with brushes. For examples, the brushes require regular maintenance and induce noise by friction with the commutators. A solution for these problems is brushless direct current (BLDC) motors. BLDC motors can be classified into two types, as shown in Fig. 1 according to the geometric shape and location of permanent magnets. Compared with surface mounted permanent-magnet (SPM) motors, interior permanent-magnet (IPM) motors have several advantages. One advantage comes from the position of magnets. Because permanent magnets are embedded in the rotor, the IPM motors can be used at higher speeds without debonding of the permanent magnets from the rotor due to the centrifugal forces. Another obvious advantage of the IPM motors is higher efficiency. That is, in addition to the mutual torque from the permanent magnets, the IPM motors utilize the reluctance torque generated by the rotor saliency [1].
Manuscript received June 28, 2002; revised June 7, 2004. H.-S. Ko was with the Mechanical Engineering Department, Korea Advanced Institute of Science and Technology (KAIST), Daejon 305-701, Korea. He is now with Samsung Electronics Company Ltd., Suwon 443-742, Korea (e-mail: hskatom@yahoo.co.kr). K.-J. Kim is with the Mechanical Engineering Department, KAIST, Daejon 305-701, Korea (e-mail: kjkim@mail.kaist.ac.kr). Digital Object Identifier 10.1109/TMAG.2004.832991
Regarding the noise and vibration, the IPM motors have more sources than the SPM motors. Furthermore, analysis of magnetic field in the IPM motors is more difficult due to the magnetic saturations, especially in the rotors. In an IPM motor, the electromagnetic excitation sources can be classified into three parts: cogging torque, ripples of mutual and reluctance torque, and fluctuations of radial attractive force between the rotor and stator. In an SPM motor, only the mutual torque is generally considered and an analytical method can be used [2], [3]. For the IPM motors, however, the finite-element method (FEM) is used to account for the magnetic saturation at the rotor core and, besides the mutual torque, the reluctance torque needs to be considered. In addition, although only the permanent magnet may be considered to calculate the radial attractive forces between the rotor and stator in the IPM motors [4], the electromagnetic field due to the currents may become significant depending on the loading and generate serious excitation forces. In this paper, a technique that can efficiently calculate the cogging torque as a function of rotor position by including saturation effects is proposed. Then, a torque equation for characterizing the space and time harmonics with respect to the mutual and reluctance torque ripples is used to extract their fluctuating components. The radial attractive forces due to the electric currents in the stator as well as the permanent magnets in the rotor are calculated by the FEM and its effects on noise and vibration are investigated. The noise and vibration in the motors are mostly generated by the electromagnetic sources and subsequently can be amplified by the dynamic characteristics of the motor structure. Therefore, influences of natural frequencies and mode shapes of the structures are experimentally investigated for the noise and vibration of an IPM motor under study. II. ELECTROMAGNETIC EXCITATION SOURCES Electromagnetic excitations in electric motors are caused by variation of both circumferential and radial forces acting between the stator and the rotor with respect to the time and space.
0018-9464/04$20.00 © 2004 IEEE