Nonlinear fuzzy logic control of a PWM inverter with a nonlinear load

Abstract

Capacitor input filter loads (nonlinear) typically cause voltage distortion in DC to AC inverter waveshape. Nonlinear fuzzy logic control fields promise in reducing this compared with conventional PID control. Comparisons between nonlinear fuzzy logic proportional derivative controllers and conventional linear PID controllers are made by simulating a buck converter subjected to large step load current changes. It was found that the choice of freewheeling switch (uncontrolled diode or synchronous rectifier) is a major factor in improved output voltage control. Fuzzy Logic controllers are investigated as arbitrary transfer characteristic generators. Membership function shape, degree of overlap, and number of overlaps, are examined, along with choice of rule table values, as to the effect on the transfer characteristic of the controller. Results are presented as transfer characteristic plots, 3D control surface plots, Bode plots, and step response plots for the buck converter.