Design of radial displacement sensor and control of a switched reluctance machine with one bearing
This project is focused on two objectives: X-Y displacement sensor design and design of switched reluctance motor with a magnetic bearing instead of mechanic bearings to support the rotor at one end. At the other end, a mechanical bearing is still used. Two types of design of low cost sensor for rotor displacement detection are presented. Both of them have very simple structure, which gives very low cost. The first presented sensor has the rotor with 12 poles permanent magnets on its surface. The experimental performance shows this sensor can detect the displacement, but it is not suitable for bearingless control because it doesn't have smooth output and can't work when motor stops. The second sensor design has a solid steel rotor and the experimental performance shows it can detect the displacement for bearingless control in terms of quick response and low cost. A magnetic bearing is realized in a single phase switched reluctance motor. The basic principle is that besides main winding, a radial force winding is employed on each stator tooth, which can generate the flux to balance the radial force in the airgaps so that the rotor can be self-supported. Mathematic analysis and simulation are pretend. The experimental results show that magnetic bearing can support the rotor in the central position regardless of the external force (within 12 N) acting on the rotor shaft. Bearingless control on a two phase switched reluctance motor with only one bearing is also designed. In the experiment, a proper switching point is chosen, which is for the control switching between two phases. Experimental results show that rotor can run with only one magnetic bearing support at 250 rpm. Although the running speed is very low, it is an important step for further research on bearingless control design.