The application of electrodynamic levitation in magnetic bearings
Storm, Markus Erasmus
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Currently the MBMC (Magnetic Bearing, Modelling and Control) research group in the School of Electrical, Electronic and Computer Engineering of the North-West University is developing a Magnetic Bearing research laboratory. The aim is to ascertain a proper knowledge and understanding of magnetic bearings for development and implementation in industry. Magnetic levitation can be realised through using either EMS (Electromagnetic Suspension) which functions on attracting forces or EDS (Electrodynamic Suspension) that functions on repulsive forces. Since all the research done by the MBMC research group were until now focused on EMS AMBs (Active Magnetic bearings) there was a need to also explore the possibilities of an EDS implementation. The project objectives are the design and verification of a vertically suspended EDS magnetic bearing laboratory model. Different possible methods of EDS exist and by studying each the most promising alternative was selected, the Inductrack technique. A combination of a special high grade permanent magnet arrangement, the Halbach array, and a unique conducting track construction forms the Inductrack concept. This method uses electrodynamic interaction between a moving Halbach array and a close-packed array of coils consisting of shorted electrical circuits to attain levitation. The lnductrack technique must be revised into a circular implementation to realize a functioning magnetic bearing since the method was developed for magnetically levitated trains. This involves altering the linear Halbach array and conducting track into circular elements with the same levitation characteristics. Since exceptionally little literature could be found on this specific implementation it was decided that the project will not entail the physical building of a demonstration model. However, the focus of the project was to create a sound design foundation and to veri® the applicability of the design in magnetic bearings. Attaining this knowledge involved the all the design phases of a laboratory demonstration model except that the model was not physically built and implemented. The revised design was verified by analytical calculations, MATLAB® simulations and comparing the system parameters with a linear Inductrack scale model. The circular Halbach array implementation was verified by using two different FEM (Finite Element Method) software packages and performing several 2D and 3D simulations. The magnets should be specially assembled into the circular array through a complex process due to the immense strength of the magnets. Since no information is available on this, the process was uniquely developed through using a FEM analysis to determine the forces present between the permanent magnets within the array during the assembly process. An assembly model was developed and the assembly process simulated in the CAD software package SOLIDWORKS® to eliminate any interference. A mechanical design was performed on the different model parts and was used to combine the assembly and demonstration model. This was done by using analytical calculations and incorporating a stress and strain analysis with SOLIDWORKS® and COSMOSXpress®. After different design sections of the project were completed a design review board meeting was held. The purpose of this meeting was to evaluate and verify the different aspects of the project and to obtain inputs where possible improvements could be made. Due to the diversity of the project (including electrical to mechanical aspects) members from both disciplines constituted the review panel. The design was approved by the review panel with minor implementation recommendations.
- Engineering