Analysis of Force and Torque Harmonic Spectrum in an Induction Machine for Automotive NVH Purposes
Examensarbete för masterexamen
Electric power engineering (MPEPO), MSc
Garcia De Madinabeita, Inigo
Currently, hybrid and fully electric vehicles are being developed in a great variety regarding topology, power and range. This requires a new methodology for NVH (Noise Vibration and Harshness) evaluation of potential problems early in the design phase. This methodology requires reliable simulation approaches for hybrid and electric drivetrains, concerning the whole automobile, and not limited to the electric machine. One of the main NVH sources is the electric drive, as the excitations in the electric motor, caused by the electromagnetic forces, excite its housing and that of the drivetrain, causing a structure-borne vibration. Torque ripple generates excitations in the shaft and gearbox, which are then transmitted to the whole drivetrain housing. It is seen that a low-torque-ripple design aim might not be enough for reducing the NVH issues, and specially radiated noise, in a fully electric or hybrid drivetrain, since Maxwell forces experienced by the stator can be present in frequencies where there is no torque harmonic. Since analytic models cannot represent accurately the non-linearity of the magnetic field and the detailed design of the stator and rotor geometries, the FEM (Finite Element Method) simulations are unavoidable to study the electrical motors in detail. A FEM tool is used in this project to design and assess the performance of an induction machine, focusing on the effect that driving profile and control unit cause on the electric drive, magnetic field and forces in the system for different driving conditions. The produced forces are evaluated to assess the noise and vibration in the system. It is seen that FEM results correlate with what theory predicts, as force harmonic orders are 0, 2 and n ± 1, where n is any magnetic flux density harmonic. The center tooth point only experiences radial forces, whereas the corner points have tangential stress as well, due to saturation. An example of 15μm dynamic eccentricity illustrates alterations force and torque harmonic magnitudes due to shaft assembly eccentricity or shaft bending caused by bearing clearance and/or stiffer gear contact vibration.
Elkraftteknik , Electric power engineering