Finely Tuned Cascaded Fuzzy Controllers with VHDL – A Case Study for Linerization of V-I Characteristics of a Convertor

This work proposes cascaded Fuzzy Logic Controllers as new hardware architecture so that it works in an accurate and fast manner. The MAX-MIN interface can be simplified as lookup table operations. Both membership function values and index numbers of input MF's are pre-stored in the lookup table and the observed crisp inputs serve as the addresses for reading them. Each output MF is treated as a singleton located at the center of the MF. So, the computational complexity of COG defuzzification is significantly reduced. As a case study for a single-phase converter, the fuzzy method of Δ∝ angle compensation is used to linearize the converter transfer characteristics in discontinuous conduction mode. On the basis of the information collected from the graphs; the fine tuning of the output of FLC1 is suggested to achieve better linearization. The required fine-tuning is achieved by using another fuzzy controller FLC2 cascaded with first fuzzy controller FLC1. All components of the FLC are simulated in VHDL using the concept of moment of equilibrium principle for MAX and MIN modules. The VHDL analysis shows faster response to conclude that dedicated cascaded hardware processor will give very accurate linear control for the converter under study.