Description of Generalized concepts for Bearingless Drives

The bearingless electric motor, which provides not only the generation of torque but also the necessary magnetic bearing forces by its winding system, still has a very young history. Not before the signal and power electronics had achieved an appropriate level of performance in the early nineties, the mentioned technology was ready for practical use. In this context the bearingless slice motors with permanent magnetic excitation are of particular importance, as they require active stabilization in only three degrees of freedom through the utilization of reluctance forces. The generation of electromagnetic torque and radial force components has required closed stator rings so far. This design implies disadvantages, in particular when motors with large diameters are used, because of the huge manufacturing and material costs. The figure below depicts an example of a typical area of application: a bearingless motor for hermetically encapsulated process chambers, which are required in the chemical industry, biotechnology or in medical engineering, for instance. The outstanding demands of such large drive systems have been a strong incentive for the FWF project P17523-N07, to work out a general mathematical description, coupled with modelling and simulation foundations, which provide the design of bearingless motors with high integrated winding systems, not only in closed but also in segmented architecture. Special scientific challenges have resulted from the general development of suitable non-linear dynamic motor models for current as well as voltage impression, from the design of transformation and control algorithms which are necessary for high performance operation and also from rotor dynamic investigations. The latter are of great importance for the run-up as well as for the dynamic and steady-state operation as - in order to keep the mechanical complexity as small as possible - only a few active control interventions have been permitted in the bearingless system. In general, the passive stabilizations of such systems are slightly damped. Therefore, deep knowledge in the analysis and suppression of mechanical vibrations are required.