Finite-Time Sliding Mode Control With Unknown Control Direction

In this paper, a global nonsingular sliding mode controller is developed for a second order system with unknown control direction. A novel terminal sliding mode hypersurface is presented to compensate for the sign uncertainty in the control input and avoid the singularity issue present in the traditional terminal sliding mode control. In contrast to the Nussbaum gain approach where the equilibrium point is reached asymptotically in the presence of input sign uncertainty, the proposed controller guarantees that the equilibrium point can be reached from any initial state in finite time. Simulation results are provided to validate the proposed controller.