Reduced-order observer for dynamic output feedback of variable-structure control systems

In this paper nonlinear non-affine systems, for which the state vector is not completely available, are considered. It is assumed that the systempsilas mathematical model is perfectly known and conditions hold, which assure the global injectivity of any required state transformation. The proposed strategy combines two approaches and designes a reduced-order observer, which relies on second order sliding mode differentiators just to provide the necessary, otherwise unavailable, artificial outputs exploited to steer to zero a lower dimensional estimation error vector under an simplified set of convergence conditions.