This paper presents two novel fast converging robust controllers for Caputo derivative based
fractional-order nonlinear systems. These fractional-order systems are high-relative-degree with model
uncertainties and external disturbances. First, a new fractional-order model is derived from the original
model based on block transformation strategy. Employing the block transformation technique makes the highrelative-degree systems versatile for sliding mode controllers design. In the second step, two different nonlinear
sliding manifolds are proposed to reach a short time convergence. Subsequently, appropriate nonlinear
sliding mode control laws are developed to assure the robustness and fast converging behaviors. It is
worthy to notify that the mentioned sliding manifolds guarantee the fractional-order system last state
convergence, and the other states convergence can be assured by control gains of the block
transformation. The stability of closed-loop system for both controllers is achieved by the fractionalorder stability theorems. Finally, two comprehensive numerical simulations are carried out to indicate the
superiority and effectiveness of the suggested robust controllers.