Design and Implementation of Hybrid Magnetic Bearing Control Part

Abstract

Experiments with magnetic levitation for stabilization of rotating parts of electrical machines started in the middle of 20th century, but first practical application started with powerful digital microprocessors. Recently, price and quality of micro-controllers and other supporting circuits allow to design a number of magnetic bearings in all power classes. However, more complicated construction (and higher price) classifies magnetic bearings to be used in special applications of high speed and power drives or aggressive ambient or vacuum. There are just a few companies producing magnetic bearings on the worldwide market (e.g. Synchrony Magnetic Bearings, Waukesha Magnetic Bearings, Calnetix Technologies or Levitronix). Industrial using of active magnetic bearings is defined by international standard ISO 14839. The standard describes technical terms, measurement and diagnostic of machine equipped by active magnetic bearings and evaluation criteria. Worldwide there are a few patents and technical papers describing the theory of hybrid magnetic bearings, but a real product still does not take a significant place on the market. Also the industrial standard doesn't describe any flux-combined type of the magnetic bearing. The aim of this doctoral thesis is to analyse capability of the permanent-magnet-based active magnetic bearing with three-phase stator winding. Diagnostic by the international standard for the active magnetic bearing was used as a method of the bearing evaluation features. For this purpose a new electrical part of the hybrid magnetic bearing was designed and constructed. It was driven together with a three-phase magnetic part and tests and diagnostics of the complete system according to the actual international standard were made. It was found that the hybrid magnetic bearings are able to fulfil all requirements of the standard ISO 14839, which proves that they could be used in the same application as active bearings, since the standard defines only the active ones. The practical outcome of this paper is a description of a perspective way how to develop the hybrid magnetic bearing for real industrial applications.