Transient response of revolving magnetic field in induction type bearingless motors with secondary resistance variations

Optimal parameter selection in a field oriented control method for induction type bearingless motors is proposed to realize stable magnetic suspension. It is experimentally shown that the magnetic suspension is stable with a slight increase in a reference value of a secondary resistance. With the proper value in the secondary resistance reference, a phase angle of generated revolving magnetic field can be adjusted. There is an optimal reference value in the secondary resistance, which realizes the exact correspondence between the controller flux reference and generated revolving magnetic field. It is shown that a flux waveform, obtained from a search coil wound around a stator tooth, is corresponding to the direction of flux reference if operated with the optimal value. It is also shown that successful magnetic suspension without coupling in two orthogonal radial axes can be realized with the optimal reference value.