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Title: Linear models for A.C. magnetic suspension.
Author: Henn, J. W.
ISNI:       0000 0001 3553 2945
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 1979
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The research presented in this thesis is aimed at predicting the transient behaviour of attractive a.c. magnetic suspension systems. The non-linear characteristics of the suspension system were linearised by considering small displacement from an equilibrium position. Impedance measurements were taken as the physical basis and transfer functions were developed by either using Suppressed Carrier Modulation Theory (Modulation theory model) or by taking the RMS values of the a.c. quantities (simple model). Open loop transfer functions relating changes in control voltage to changes in magnet airgap were developed. These transfer functions were used in closed loop linear models to obtain stability limits and to predict the transient behaviour of: 1) Non-linear analogue simulation of an idealised onedimensional magnetic suspension system controlled by an ideal, variable amplitude, voltage source - Resistance inductance (RL) circuit. 2) An experimental apparatus (cantilever) where the airgap was measured using a Hall effect device and the control signal modulated using a linear multiplier. The resultant amplitude modulated signal was then amplified using a class AB power amplifier - both RL and LCR tuned circuit systems were investigated. 3) The same experimental apparatus but using thyristor bridge networks instead of the linear modulator and the class AB power amplifier (only the RL circuit was investigated) . The transient responses of these systems were investigated by comparing the closed loop step responses and frequency responses of the linear model and the experimental system. It was found that the gains natural frequencies and damping ratios obtained from the experimental system were mostly within 20% of that value predicted by the linear model. At the lower stability limit gains and natural frequencies obtained from experiment were within 10% of that predicted from the linear model. At the upper limit discrepancies between experiment and theory were observed. Open loop transfer functions were also developed for suspension systems affected by eddy currents. Repulsive as well as attractive suspension systems were analysed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available