Nonlinear function controller: a simple alternative to fuzzy logic controller for a power electronic converter

Recently, there has been an increase in the application of fuzzy logic controllers (FLCs) for control of power electronic converters. Due to the FLCs' complex algorithm, their realization often calls for a compromise between cost and performance. In this paper, it is shown that the rule table of most of the two-input FLCs used with power converters can be approximated into a single nonlinearity. This allows the controller to be easily realized using simple, fast, and inexpensive analog circuits. The simplified 'nonlinear function controller (NLFC)' developed in this manner is shown to be equivalent in performance to the original FLC through simulations. The NLFC concept is then applied to PI-FLC, a type of FLC popular in power converter control applications. This results in the PI-FLC being replaced by a simple 'nonlinear PI controller (NPIC).' Using this simplification, the design of NPICs to obtain good dynamic performance in power converters is explained. An example design of NPIC for controlling a dc-dc boost power converter is presented. Experimental results are also presented to demonstrate the superior dynamic performance of the converter with NPIC versus that of a linear-PI controller. Index Terms--Dynamic response, fuzzy control, fuzzy logic, pulsewidth-modulated (PWM) power converters, switched-mode power supplies, Topelitz matrices.