Perfect tracking control using multirate control in magnetic levitation system

This paper presents a tracking control design method for nonminimum phase systems based on multirate control. Traditionally, perfect tracking control schemes cannot be applied to nonminimum phase plants because of unstable pole-zero cancellations. Although methods of zero assignment based on multirate control and the method of state matching using multirate feedforward control to realize perfect tracking control have been proposed, the oscillation restraint and the feasibility in nonminimum phase systems cannot be satisfied at same time. We propose a method using the difference of state variables to generate a smooth desired state variable trajectory in the discrete-time systems. The techniques we proposed are applicable to nonminimum phase discrete-time systems and the oscillations between the sampling points are restrained well. Finally, computer simulations and experiment results based on magnetic levitation apparatus are presented.