Non-linear observer based control of magnetic levitation systems

Active magnetic levitation AML systems have been widely used in magnetic levitation
vehicles, wind turbine, medical applications, micro robot actuation and turbo-machinery.
Contactless support of objects continues to be a fantasy for several centuries. The utilization of magnetic forces seems to be the ideal solution in many situations to such a goal.
Using magnetic forces to support an object without any mechanical contact is constrained
by the laws of magnetism. Earnshaw’s theorem states that when the inverse-square-law
forces govern several charged particles, they can never be within a stable equilibrium. The
interaction between ferromagnetic objects and electromagnets of either the active or passive type, is associated with an unstable nature. This unstable behaviour can be represented
by highly non-linear differential equations. In the literature many researches are based on
linearised models around a specific nominal operating point then linear controller is utilized to control the system. The associated problem with the linear control technique is
that the system only be adequately controlled in a small region around the equilibrium
point but the variation of operating regions in such non-linear system is wide following a
major disturbance. In this research, two kinds of non-linear observer-based excitation controller are proposed for Maglev to ensure the stability of non-linear system in the presence
of large disturbance and over larger operation regions. A combination of full-order Nonlinear high-gain observer (NHGO) with LQR-feedback linearisation is considered as first
proposal. Second proposed controller is based on the Lyapunov stability theorems, and a
further non-linear full-order observer-based controller via a non-linear fuzzy sliding mode
controller is developed for Maglev system. The proposed control approaches are tested
and validated through simulated exercises of a magnetic levitation system. Comparative
assessments of the approaches are presented and discussed through the thesis