A multivariable fuzzy logic controller (MFLC) for a buck DC-DC converter

This paper describes the design and construction of a multivariable fuzzy controller (MFLC) for the control of a DC-DC buck converter. An off-the-shelf hardware-based MFLC system has been developed that is used to model the variable switching structure of the buck converter. The MFLC design criterion is based on the error in output voltage and the change of error in the output voltage as inputs of the controller, and the changes in the duty cycle ratio as output of the controller. The error and change of error are two membership functions bounded in the interval [0, 1]. The two inputs have two fuzzy subsets, negative fuzzy subset N and positive fuzzy subset P. The output is made up of fuzzy subsets of singletons. It will be shown that when the error and change of error have the same signs, the output moves away from a set point and therefore the same reasoning or rules can be used to change the output. The results will show that the MFLC technique provides robust control for nonlinear power electronics variable switching structure like the DC-DC buck converter.