Variable structure control of nonlinear system with unmatched uncertainties

The robust output tracking control problem for single input single output (SISO) nonlinear system with bounded unmatched uncertainties was discussed. The variable structure control scheme based on Lyapunov theory was adopted, in which the matched and unmatched parts in uncertainties are dealt with separately. The variable structure control law was designed, and it can ensure that the closed-loop system is globally stable, satisfies the sliding reachable condition, and the tracking error converges to zero. The simulation results using MATLAB have confirmed that the performance of the control law is satisfactory.