Bearingless transverse flux permanent magnet machine for large direct-drive

The aim of this paper is to develop and verify a new concept of bearingless machine for large direct-drive wind turbines. The new bearingless machine is constructed with double-sided air-gaps and flux concentrating transverse flux permanent magnet (TFPM) linear machine configuration. Unlike the windings of conventional bearingless machines, the main windings of the new bearingless machine are used to simultaneously control both the thrust force and the bearing force. In order to control the bearing force of the new bearingless machine, a phase angle shift algorithm is developed and applied for the control of the normal force in the air-gap. The thrust force and the normal force are obtained through three-dimensional finite element analyses to identify the forces as a function of the mover position, the air-gap length and the magneto-motive force by currents. The control algorithm is implemented by simulations using the Matlab/Simulink. To verify the algorithm and simulations, a flux concentrating TFPM linear machine is built, and the new bearingless drive concept is achieved experimentally. The maximum displacement of the air-gap is 0.16mm which is about 5% of the air-gap length, 3mm, in operating at 0.2m/s speed and 0.2m stroke.