Vibration control in electrical machines using built-in actuator

The magnetic field within electrical machines causes an electromechanical interaction between the electrical and mechanical dynamics of the system. A relatively small asymmetry of flux distribution in the air gap creates an unbalanced magnetic force which tends to pull the rotor towards the stator in the direction of the highest flux density. This unbalanced magnetic force (or pull) in an electrical machine is exploited in so-called self-bearing or bearing-less electrical machine where, as well as functioning as a motor or generator, the machine can also produce transverse forces perpendicular to the rotation axis. The presence of magnetic field of pole pair p is due to the main supply of the motor and the presence of magnetic field of pole pair p±1 is due to the asymmetry present in the magnetic field or due to the eccentric rotor motion. So, the presence of magnetic field of pole pair p±1 will produce an unbalanced magnetic force in the air gap. This paper addresses a special type of stator winding scheme having parallel branches and a novel Wheatstone-bridge type connection in order to achieve direct control on the unbalanced components of stator magnetomotive force (MMF) whilst having no effect on the torque-producing components of the stator MMF. An Finite Element code has been developed in MATLAB and used as the basic tool for this investigation. It has been demonstrated in case of an induction motor that a controllable force in the air gap can be produced. The results from numerical model have been verified by experimental results.