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Electromagnetic fields in the air gap of an electric machine produce electromagnetic forces between the rotor and stator. The total force exerted on the rotor due to the eccentric rotor position is called the unbalanced magnetic pull. This eccentricity force is directed roughly over the shortest air gap. At low frequencies, the vibration amplitudes of flexural modes may be large enough to couple the electromagnetic system to the mechanical one. This electromechanical interaction changes the vibration behaviour of the system.The main purpose of this dissertation is to reveal the main rotordynamic consequences induced by the electromechanical interaction in cage induction motors. Another goal is to achieve this by deriving a simple and representative electromechanical rotor model with physical variables and parameters.In this study, a new parametric model was derived for the unbalanced magnetic pull induced by an arbitrary rotor motion in transient operation. The parameters of this model can be determined analytically from the basis of the machine characteristics or estimated numerically as in this study. To estimate the parameters, an efficient numerical method was developed from the analysis of impulse response. The numerical results showed that the simple electromagnetic force model, together with the estimated parameters, predicts the unbalanced magnetic pull fairly accurately.An electromechanical rotor model was derived by combining the Jeffcott rotor model with the simple electromagnetic force model, including two additional variables for the harmonic currents of the rotor cage. Applying this model, the rotordynamic effects of electromechanical interaction were studied. Three induction motors were used in the numerical examples. The results obtained show that the electromechanical interaction may decrease the flexural frequen-4 cies of the rotor, induce additional damping or cause rotordynamic instability. These interaction effects are most significant in motors operating at, or near, the first flexural critical speed. Excluding the potential rotordynamic instability, the numerical results indicate that the electromechanical interaction effectively reduces the unbalance response close to the first flexural critical speed. 5 PrefaceThis work was carried out during the period 2001-2003 as a part of the research project "Electromechanical interaction in vibration control of electric machines". The aim of this project was to enhance our understanding of the effects of electromechanical interaction in general, and electromagnetic damping in particular, on the vibration control of electrical machines. The research partners were the

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An iron-loss model for laminated ferromagnetic cores of electrical machines is presented and applied to estimate the core losses of an induction machine with finite element analysis. Skin effect in the cross section of the core lamination is modeled using a set of sinusoidal basis functions while locally considering both the hysteretic material properties and the excess field caused by domain wall motion. After spatial and time discretization, a single nonlinear equation system is obtained. An accurate vector Preisach model, the differential reluctivity tensor and the Newton-Raphson method guarantee excellent convergence of the iteration procedure. Results from the model correspond well to iron-loss data obtained by measurements.

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