ANALYSIS AND DESIGN OF ZERO-ORDER SUGENO TYPE FUZZY LOGIC CONTROLLER

Abstract

Tuning methodology and other aspects of asimple fuzzy logic controller are studied in this thesis. It is established that a zero order Sugeno type fuzzy controller is analytically equivalent to a simple Mamdani type fuzzy controller. Comprehensive analysis comparing the initial outputs of linear and proposed fuzzy controllers in the context of derivative kick is presented. It is shown that simplest fuzzy controller if properly tuned is capable of providing better performance as compared to an equivalent well-tuned linear controller. Based on speed of response as criteria, three methods of tuning are proposed. First two methods require the knowledge ofinitial outputs and gains of a well-tuned linear controller for calculating the parameters of the equivalent fuzzy controller. The third method is more conventional in approach and supports all the conventional control design techniques. The design methodology, such as pole-zero cancellation, damping accuracy, maximum overshoot, settling time, rise time criteria used for linear control design can also be used for fuzzy logic based control design. Simulation results comparing the performance of the fuzzy controller tuned using proposed tuning methodology with equivalent linear and other ill-tuned fuzzy controllers establish the superiority ofthe proposed tuning methodologies. Robustness of proposed controller is studied for uncompensated second order process with dead time against variation in the process dead time and process characteristics. The use of Smith predictor compensator is proposed for making the fuzzy control system insensitive to dead time variations. Simulation results for uncompensated and compensated system clearly show that for larger errors between actual parameter values, the performance ofthe proposed controller is much superior both from the point ofview of response to reference input and unit step disturbance.