Linear perturbation models for a.c. magnetic suspension systems: experimental and theoretical results

Open-loop transfer functions are presented for various a. c. magnetic suspension systems. These transfer functions, relating changes in control voltage to changes in airgap, are used to demonstrate the differences between the various a. c. magnetic suspension systems and to show the effect of parameter variation (such as airgap or carrier frequency) on the open-loop poles and zeros. The transfer functions developed are used in a closed-loop linear model to predict the transient behaviour of an experimental system. Several different compensations and frequencies are used. LCR tuned-circuit as well as RL circuit-suspension systems are analysed. Good agreement is achieved for natural frequencies, gains and damping.