Observers with discrete-time measurements in the sliding mode control of nonlinear systems

The paper investigates the problem of designing an observer for nonlinear nonaffine systems with discrete time measurements (continuous-discrete time systems). The paper considers the variable-structure control of nonlinear systems when the state vector is not completely available and the output measurements are discrete time; the use of suitably designed observers is required. The strategy of introducing integrators in the input channel is exploited to enlarge the class of tractable control systems. An observer is proposed and conditions are found under which it is proven the convergence to the unique ideal solution of both system and observer. The control problem is solved by forcing a sliding regime for the observer, while satisfying an exponential stability criterion for the observation error state equation.