Fuzzy control of AC-DC converters supplying high precision DC drive systems

The paper describes an application of fuzzy set theory in a DC speed control system supplied by an AC-DC converter. The fuzzy control is used to linearize the external characteristics of the converter in discontinuous-conduction mode occurring at light load and/or high speed. The nonlinear characteristics in discontinuous-conduction mode affect the control loop gain. The solution is to linearize the converter's characteristics, meaning to prolong the characteristic of the continuous-conduction mode over the characteristics of the discontinuous-conduction mode. Algorithms have been developed in detail and verified with MatLab Fuzzy Toolbox. The simulation study indicates that fuzzy control is a good alternative to conventional control methods, being used particularly in nonlinear complex systems which are ill defined or totally unknown.