This paper presents an adaptive nonlinear delayed feedback control scheme for
stabilizing the UPO of unknown fractional-order chaotic systems. The proposed
control scheme uses the Lyapunov approach and sliding mode control technique to
ensure that the closed-loop control system is asymptotically stable on a
periodic trajectory sufficiently close to the UPO of the fractional-order
chaotic system. It is guaranteed that the closed-loop system will be robust to
external disturbances with unknowable bounds. Finally, the proposed method is
used to stabilize the UPO of the fractional-order Duffing and Gyro systems, and
extensive simulation results are used to evaluate its performance