A TIME-VARYING SLIDING SURFACE FOR FAST AND ROBUST TRACKING CONTROL OF 2ND-ORDER UNCERTAIN SYSTEMS

A time-varying sliding surface for a variable structure control (VSC) law is proposed to achieve fast and robust tracking in a class of second-order uncertain dynamic systems. The surface initially passes arbitrary initial states and subsequently moves towards a predetermined surface via rotating and/or shifting. The existence of sliding mode with the time-varying sliding surface is proved, and moving procedures are presented in detail as well as salient features. Using the proposed surface favorable fast and robust tracking behaviors are accomplished without increasing the magnitude of the discontinuous control gain, hence undesirable chattering. To illustrate the advantages of the proposed method, a simple second-order nonlinear system subjected to parameter variations and extraneous disturbance is considered.