A design approach for general type-2 fuzzy logic controllers with an online scheduling mechanism

This paper proposes a systematic approach to solve the design problem of General Type-2 (GT2) Fuzzy Logic Controllers (FLCs) with an online scheduling mechanism for performance enhancements. We firstly suggest constructing the GT2-FLC over its baseline type-1 and interval type-2 FLCs, and then to tune a single design parameter which defines the shape of the secondary membership functions. We present how the shape of the secondary membership function changes with respect to the design parameter and show resulting effect on the control surface generation. The presented comparative analysis on the control surfaces show that aggressive and smooth control surfaces can be easily generated by tuning the design parameter. We suggest tuning the design parameter by providing a tradeoff between robustness and performance of the control system. Also, to achieve satisfactory control performances for various steady-state points, we propose an online scheduling mechanism that tunes the design parameter with respect to the operating points. We perform a simulation study on a nonlinear system to validate our analyses and proposed design methods. The simulation results show that GT2-FLC has a potential to improve overall system performances in comparison to its type-1 and interval type-2 counterparts, while the developed scheduling mechanism provides an opportunity to achieve satisfactory results for various operating points.