ABSTRACT: Noise and vibration of electrical machines is a major concern. Changes in the machine design to improve its efficiency can lead to unacceptable vibrations. Tools to predict its vibratory and acoustic performance at the design stage need to be developed. An improved finite element model has been developed to analyse the vibration behaviour of a Permanent Magnet Synchronous Machine of a lift installation using the finite element software ABAQUS. All components and subsets of the machine have been modelled and validated by experimental modal analysis (EMA) performed on them. Some modelling issues have been overcome so that an accurate enough model has been reached. The laminated stator, as it is formed by a pack of several steel sheets, has been treated as an orthotropic material. Windings have been considered as a solid orthotropic part as well. The rotor and the stator and end-shields assemblies have also been validated comparing the calculated natural frequencies and modes shapes and those obtained by EMA. The bearings that join the rotor to the assembly of the stator have been represented by radial springs. The electromagnetic forces are applied in order to obtain the vibration response of the mechanical model. These forces are obtained from the magnetic air-gap flux density which has been obtained with a 2D finite element model developed by FLUX. Then, the vibration response has been used to calculate the radiated noise with an acoustic model in Virtual.Lab. The results given by the acoustic numerical model are compared with sound power measurements made in an anechoic chamber. KEY WORDS: Permanent magnet synchronous motor (PMSM); Vibrations; Forced response; Electromagnetic noise. 1 INTRODUCTION An improved finite element model is developed to calculate the vibro-acoustic response of a Permanent Magnet Synchronous Machine. Years ago the increasing use of inverters introduced more excitation harmonics which originated vibration and noise problems. Noise and vibration have a direct influence on users’ perception of quality and comfort. Nowadays, in order to reduce costs, the efficiency of the machine needs to be improved and the quantity of magnets has to be minimised, as these materials are becoming more and more expensive. Because of this, it is really important to optimise the geometry of the stator, being the vibration behaviour a restriction, as some geometry modifications can lead to unacceptable vibrations. Noise and vibration in electric motors have different origins that can be classified in three groups: • Electromagnetic noise: Originated by magnetic forces acting on the stator and rotor • Mechanical noise: Originated by bearings, shaft misalignment… • Aerodynamic noise: Originated by the cooling fan. The contribution of these sources changes depending on the working conditions. In the analysed case due to the absence of a fan the aerodynamic noise does not exist, so the generated noise is electromagnetic and mechanical. According to Gieras et al. [2] and Timar and Lai [5], mechanical and aero- dynamical noises increase with speed. However, Timar and Lai [5] affirm that in the very-low-speed domain mechanical and electromagnetic noises are present. The presence of mechanical noise at low speed machines is usually related to unhealthy mechanical elements. Other authors as Kawasaki et al. [3] assess that “noise below 1000Hz is due to radial electromagnetic excitation” and according to Lakshmikanth et al. [4], the electromagnetic source is the dominating source in low to medium power rated machines. As in the analysed machine the rotational speed of the motor is low, for a healthy machine mechanical noise should be low, so the analysis is focused on the electromagnetic noise calculation. For this task a structural finite element model needs to be developed which will be validated by experimental modal analysis (EMA). In order to model the electric motor some modelling issues need to be overcome so that an accurate enough model is reached. First, the laminated stator presents different stiffness in radial and axial directions, according to Gieras et al. [2], Verdyck and Belmans [6] and Wang and Lai [7], as it is formed by a pack of several steel sheets. Thus, orthotropic material properties are applied to the solid part representing the laminated stator. Those properties are adjusted according to the experimental results as that stiffness depends on the compression pressure acting in the axial direction (Wang and Williams [8] and Watanabe et al. [9]) during manufacturing and the procedure used to tie these pack of steel sheets and, therefore, is hard to determine. Then, different modelling strategies are found in literature for the windings. Belmans et al. [1] and Wang and Lai [7] consider that the mass supplement due to windings is more Vibro-acoustic finite element analysis of a Permanent Magnet Synchronous Machine Alex McCloskey 1 , Xabier Arrasate 1 , Gaizka Almandoz 2 , Xabier Hernandez 3 , Oscar Salgado 4 1 Department of Mechanical Eng., Faculty of Engineering, Mondragon Unibertsitatea, Loramendi 4, 20500 Arrasate/Mondragón, Spain 2 Department of Electrical Eng., Faculty of Engineering, Mondragon Unibertsitatea, Loramendi 4, 20500 Arrasate/Mondragón, Spain 3 Department of Mechanical Eng., Orona EIC, Polígono Lastaola, 20120 Hernani, Spain 4 Department of Mechanical Engineering, Ik4 Ikerlan, Pº J. M.Arizmendiarrieta 2, 20500 Arrasate-Mondragón, Spain email: amccloskey@mondragon.edu, jarrasate@mondragon.edu, galmandoz@mondragon.edu, xhernandez@orona- group.com, osalgado@ikerlan.es