Sliding Mode Control with a Time-Varying Ellipsoidal Sliding Surface

In this paper, sliding mode control (SMC) with time varying ellipsoidal sliding surface is presented. When a sliding mode cannot be maintained because of excessive disturbance, this SMC moves the sliding surface closer to the current states by adjusting the vertical radius of the ellipsoidal sliding surface, thereby improving robustness. The advantages of the proposed method are verified through simulation of the second-order time variant linear system with bounded disturbances. Simulation results show that the robustness of the proposed method is improved compared to a conventional time invariant method.