CHATTERING AVOIDANCE BY 2ND-ORDER SLIDING MODE CONTROL

Relying on the possibility of generating a second-order sliding motion by using, as control, the first derivative of the control signal inst ead of the actual control, a new solution to the problem of chattering elimination in variable structure control (VSC) is presented. Such a solution, inspired by the classical bang-bang optimal control strategy , is first depicted and expressed in terms of a control algorithm by i ntroducing a suitable auxiliary problem involving a second-order uncer tain system with unavailable velocity. Then, the applicability of the algorithm is extended, via suitable modifications, to the case of nonl inear systems with uncertainties of more general types. The proposed a lgorithm does not require the use of observers and differential inequa lities and can be applied in practice by exploiting such commercial co mponents as peak detectors or other approximated methods to evaluate t he change of the sign of the derivative of the quantity accounting for the distance to the sliding manifold.