Electromagnetic Noise from Permanent Magnet Motors

Abstract: With today’s increase in rail traffic the impact of noise on the people near railway lines is increasing. To control this problem European Union regulations, including TSI (Technical Specifications for Interoperability) Noise, has come into force by implementing many strict norms on new railway vehicles put on the market. One TSI regulation is limiting the acceleration noise, which in turn calls for low noise solutions for drive systems which typically governs the vehicle noise at low speeds, up to around 80 Km/hr. This regulation on railway noise has become a major challenge for many train manufacturers. This calls for electromagnetic-Vibration-Acoustics multi physics analysis of the motor. The thesis mainly focuses on numerical modelling of the electromagnetic-vibro-acoustics system. Ideally such models can compute the audible magnetic sound power radiated from the motor as a function of its speed, PWM strategy applied and geometry. Here a pulse modulated permanent magnet traction motor was modelled with finite elements (FE), using a commercial software. Thereafter, the dynamic characteristics of the motor was analysed by FE modal analysis (eigen-frequencies and eigen-modes) as well as by point force frequency response analysis. The FE model was validated by comparing the Eigen-modes, Eigen-frequencies and point accelerance with the experimental modal analysis results. Thereafter, frequency response analysis was performed to calculate the vibration velocities on the surface of the stator frame using realistic electromagnetic forces. These forces were calculated with a dedicated motor analysis tool (FLUX). Moreover, the vibration velocities calculated were used in boundary element model to calculate the radiated sound power and the directivity. Finally the calculated vibration and sound power levels were compared with measurement results.