FUZZY LOGIC-BASED TUNING OF THE BOUNDARY-LAYER THICKNESS OF THE VARIABLE-STRUCTURE CONTROLLER

The variable structure control (VSC) is a simple and powerful nonlinea r controller, but it leads to a high frequency chattering on the contr ol input. To decrease the chattering phenomenon of the VSC, a boundary layer is commonly introduced. Then its thickness requires a compromis e between the steady state error and the chattering amplitude. In this paper, we propose a new VSC that tunes the boundary layer thickness u sing the fuzzy logic system. The tuning methods presented are two: One uses absolute error and its derivative as fuzzy input variables, whic h decreases the number of tuning rules as compared with using common f uzzy variables of error and change of error. The other uses only a sin gle fuzzy variable of a distance. This variable is derived by the prop erty of two-dimensional rule table which is composed of absolute error and its derivative. Since the second method uses a single variable fo r tuning the thickness, the number of tuning rules is greatly decrease d. Furthermore, we obtain the good tracking performance which is almos t the same as that of the first method. To ensure the control performa nce in both cases, we perform computer simulations using an inverted p endulum as a controlled plant.