MOVING SWITCHING SURFACES FOR ROBUST-CONTROL OF 2ND-ORDER VARIABLE-STRUCTURE SYSTEMS

Most of the switching surfaces proposed so far for a variable structure control system (VSCS) have been determined independently of initial conditions. The VSCS with these typical switching surfaces may be sensitive to parameter variations and extraneous disturbances during the reaching phase. To overcome this drawback, we propose a new switching surface which is initially designed to pass arbitrary initial conditions, and subsequently move towards a predetermined switching surface by rotating or/and shifting. We call it a moving switching surface (MSS). Using the MSS a low sensitivity system is obtained through shortening the reaching phase. Furthermore, the system robustness is guaranteed during whole intervals of control action by eliminating the reaching phase. To illustrate the advantages of the proposed method, a simple second-order linear system subjected to external disturbance is considered as a preliminary example followed by a two-link manipulator.