Yokeless radial electrodynamic bearing

When null-flux, passive electrodynamic bearings include a ferromagnetic yoke in front of the permanent magnets, the stiffness associated with the radial centering force becomes negative under a critical speed. This yields a strong instability and the necessity of using mechanical launch bearings at low speeds. In this paper, an electrodynamic bearing without ferromagnetic yoke is proposed. An analytical 2D model of the bearing is presented and some hypotheses are validated. The model is then used to perform a first analysis of the bearing performance. The force predictions correspond to expectations: the stiffness never reaches negative values. It is also shown that for given geometrical parameters, the performance of the studied bearing can be improved by choosing the appropriate number of phases and number of pole pairs of the winding.