Design and sensorless control of a reluctance synchronous machine for a magnetically levitated drive

Magnetically levitated drives are usually used in high speed applications and/or for special environmental conditions, e.g in turbo pumps. This paper discusses a prototype setup of a sensorless controlled reluctance synchronous machine (RSM) equipped with sensorless controlled active magnetic bearings (AMB) for such target applications. The utilization of sensorless control methods to the AMB and also to the RSM results in a significant simplification of the system architecture and a hardware cost reduction. Additionally by using a three phase AMB topology the same three phase voltage source inverters can be used for the RSM as well as for the AMBs. In this work the focus is set to the sensorless control of the RSM. The basic principle of the two sensorless position detection methods applied to a magnetically levitated RSM prototype for high rotational speeds are investigated. Experiments in the sensorless operation are performed and by the results design criteria for RSM machines with big airgaps are identified, because this is required for the magnetic levitation. Thus, an improved machine design is introduced and simulation results are presented to confirm the improved machine design for such magnetically levitated high speed applications.