  This paper is concerned with fault estimation in a class of nonlinear
fractional order systems using a new super twisting algorithm based second
order step by step sliding mode observer. Since the existing sliding mode
observers are troubled with the chattering phenomenon, here a new observer
structure is proposed and finite time convergence of error dynamics is proved
using fractional order super twisting algorithm (FSTA). Two numerical examples
of chaotic fractional order systems and a comparison with respect to a similar
observer justify the effectiveness of the proposed observer
