Optimization of the Guiding Stability of a Horizontal Axis HTS ZFC Radial Levitation Bearing

This document presents a study on the optimization of the 3D geometry of a horizontal axis radial levitation superconducting magnetic bearing with zero-field cooled (ZFC) high-temperature superconductor (HTS) bulks in the stator and radially magnetized permanent magnet (PM) rings in the rotor. A previous study on optimizing the 3D geometry for minimization of volume or cost considering variable dimensions of components and variable spacing was done. This initial optimization concerned only the maximization of the levitation force with a given restriction for the minimum levitation force. Although the used geometry promotes the creation of guidance with ZFC, guiding forces depend on the spacings between PM rings in the rotor and between the rings of HTS bulks in the stator. This new optimization study aims to find the optimum spacings that maximize the guiding force for specific HTS bulk and PM ring dimensions while maintaining the minimum required levitation force. All the optimizations are based on using the non-dominated sorting genetic algorithm (NSGA-II) over 3D finite element analysis (FEA). A simplified electromagnetic model of equivalent relative permeability, calibrated with experimental measurement of magnetic levitation forces, is used on 3D FEA to reduce significantly numerical processing and optimization time. Specifically optimized geometries for the experimental prototype were tested to validate optimization results. The experimental prototype is made of a stator of high-density polyurethane walls containing chambers where yttrium boron copper oxide (YBCO) bulks are immersed in liquid nitrogen (LN2). To hold the neodymium iron boron (NdFeB) PM rings, the rotor structure is made of polylactic acid plastic printed by a 3D computer numeric control (CNC) printer. An analysis of stable and unstable geometries domains depending on the spacings between HTS rings and PM rings is also done for two HTS bulk sizes.