ISBN 978-80-261-0722-4, © University of West Bohemia, 2018 Experimental Verification of the Hybrid Magnetic Bearing Operation Jan Vitner, Jirí Pavelka, Jiri Lettl Department of Electric Drives and Traction Faculty of Electrical Engineering, CTU in Prague Prague, Czech Republic jan.vitner@cvut.cz Abstract – This paper discusses the proposal, realization, controlling system implementation and function verification of a hybrid magnetic bearing. The hybrid magnetic bearing in comparison with active and passive magnetic bearings exploits both passive and active magnetic fluxes. This type of bearing is not given too much attention in the literature despite of its many advantages. The issue of active and passive magnetic bearings is widely elaborated against the issue of hybrid magnetic bearings. The hybrid magnetic bearing is the special kind of a radial magnetic bearing. This magnetic bearing exploits permanent magnets to produce the basic magnetic flux acting the rotor and 3-phase double layer winding to influence this flux by an active magnetic flux. Basically, the hybrid magnetic bearing was developed for high speed bearing-less devices. According to that, we are expecting the achievement the highest rotor levitation stability in wide range of rotational speed and in various driving modes. The quality of the levitation is evaluated by international standards [ISO 14839]. In this paper, results of experimental verification of the levitation stability are presented. Keywords - magnetic bearing; positional stabilization; magnetic levitation; power electronic I. INTRODUCTION Magnetic bearings have been found very applicable for suspending high-speed rotary systems, such as flywheel systems [1], vacuum pumps or turbo- compressors [2]. They are being increasingly used in applications where minimum friction is desired or in chemically aggressive environments where traditional bearings are unacceptable for their lubrication system or other features [3]. Passive magnetic bearings (PMB) feature very little loss due to no current, but have no active control ability and low damping stiffness [4]. Active magnetic bearings (AMB) have the control ability and high stiffness characteristic, but the existence of biased current brings power losses [5-6]. Therefore, more attention is paid to the permanent magnet biased hybrid magnetic bearing (HMB), which combines the merits of PMB and AMB. Hybrid magnetic bearings, while usually being more complex to construct, require smaller ampere-turns per unit force than equivalent active magnetic bearings, have higher sensitivity as a function of the drive coil current, usually exhibit better linearity as a function of the drive coil current, and can be made more compact. If the rotor is laminated, they can also provide lower rotor hysteresis and eddy current losses. Since HMB bearings can operate in the virtual zero power mode (VZP), where the static bearing load is supported by the permanent magnet field, thus they can operate with very low energy consumption. Most of the previously published works deals with levitation control adjustment of the active magnetic bearing [7-8], whereas this paper is primarily focused on the control system adjustment of the real permanent magnet based active magnetic bearing with the 3-phase stator winding [9]. The chapter II. of this paper describes the structure of the HMB and fundamental function of its parts. Following chapter III. deals with mathematical description of the two major forces acting the rotor and their significant features. The simulation (see chapter IV.) of the HMB behavior is followed by chapter V. with description of the realized system and with the presentation of the HMB levitation measurement results. II. DESCRIPTION OF THE HYBRID MAGNETIC BEARING The magnetic circuit is assembled from two identical parts with above mentioned winding in each part. Eighteen permanent magnets are placed around the perimeter between both parts [10], as shown in Fig. 1. Figure 1. View of the whole hybrid magnetic bearing The 3-phase winding creates a source for magnetic circuit (red line in Fig. 2) and produces controlled magnetic field in this circuit. This active magnetic field is closing in radial plane. Magnetic resistivity of the magnetic circuit for this active magnetic field is independent on the rotor shaft motion. The active magnetic field flows through both horizontally