  This paper deals with the design of robust tracking and model following
(RTMF) controller for linear time-invariant (LTI) systems with uncertainties.
The controller is based on the second order sliding mode (SOSM) algorithm
(super twisting) which is the most effective and popular in the family of
higher order sliding modes (HOSM). The use of super twisting algorithm (STA)
eliminates the chattering problem encountered in traditional sliding mode
control while retaining its robustness properties. The proposed robust tracking
controller can guarantee the asymptotic stability of tracking error in the
presence of time varying uncertain parameter and exogenous disturbances.
Finally, this strategy is implemented on a magnetic levitation system (MagLev)
which is inherently unstable and nonlinear. While implementing this proposed
RTMF controller for MagLev system, a super twisting observer (STO) is used to
estimate the unknown state i.e the velocity of the ball which is not directly
available for measurement. It has been observed that the RTMF controller based
on STA-STO pair, is not good enough to achieve SOSM for a chosen sliding
surface using continuous control. As a remedy, continuous RTMF controller based
on STA is implemented with a higher order sliding mode observer (HOSMO). The
simulated as well as the experimental results are provided to illustrate the
effectiveness of the proposed controller-observers pair.
