Floating membership fuzzy logic controller for adaptive control of AC drive

Abstract

An industrial application of a fuzzy logic based controller with a “floating membership” function is described in this paper. A vector controlled AC motor drive is chosen as the plant under control. Generally, two independent controllers are required to obtain good tracking and regulating responses, thereby imparting two-degrees-of freedom to the overall controller. The fuzzy logic controller proposed in this paper incorporates both the features of tracking and regulating in one controller only. This is achieved by allocating “floating membership” functions to selected fuzzy variables. These dynamic or “on-the fly” adjustments of membership functions allow the use of a fuzzy variable that directly measures the difference between two inputs. The controller, therefore, can closely follow a trajectory produced by a reference model to achieve good tracking. Its sensitivity to load changes reduces considerably to achieve excellent regulating response. A stand-alone fuzzy logic controller (FLC, AL-220, adaptive logic) having a built-in hardware feature of “floating membership” function is used to design the proposed controller. The fuzzy control algorithms are developed using the INSIGHT IIe development system suitable for the above stand-alone fuzzy logic controller. The simplest model of an indirect vector controlled AC motor drive as a plant is selected for simulation purposes. Responses for various cases of tracking and regulation are presented and these show highly encouraging results Author(s) Keskar, A.G. Dept. of Electron. & Comput. Sci. Eng., Visvesvaraya Regional Coll. of Eng., Nagpur, India Asanare, K.L.