Using on-line estimation techniques for output feedback VSC design

The conventional VSS is always limited to the system with full-state feedback, however in practical applications, full measurement of state might be neither possible nor feasible. To deal with the unavailability of state, some asymptotic observers and dynamic compensators have been used in VSS (variable structure system) recently. However, those methods possibly increase the complexity of system. On the other hand, in conventional VSS design, the knowledge of the upperbound of uncertainty is required to determine the gain of control. In general, this may not be easy to obtain. Then, the on-line estimation technique relaxed from the point that no knowledge of uncertainty upperbound is needed. In this paper, a direct output feedback variable structure control is proposed with an on-line estimation technique to stabilize a class of nonlinearly uncertain systems robustly. Here the hyperplane is composed of the output instead of the state, and the estimation uses the time delay concept to evaluate a function which represents the effects of the inaccessible state and uncertainty, under which the output feedback design is completed.