Fractional order adaptive fuzzy sliding mode controller for a position servo system subjected to aerodynamic loading and nonlinearities

An adaptive fuzzy fractional order sliding mode control (FFOSMC) is introduced for a high performance servo actuation system that is subjected to aerodynamic loads and uncertainties. During flight, aerodynamic loads are exerted on control surfaces which directly affect the performance of position servo loop. Moreover, since these loads are not linear so qualification of servo actuators is an important process in aerospace industry. This article focuses on formulating a servo position controller using fractional calculus and verifying its performance under system uncertainties, nonlinear friction and aerodynamic loads. Utilizing the advantages of fractional order proportional-integral PIα sliding surface and fractional order proportional-derivative PDλ sliding surface, a novel sliding surface is proposed. To reduce chattering phenomenon in sliding mode control, fuzzy logic controller (FLC) is used to deal with uncertain nonlinearities, parametric uncertainties and external disturbances. FLC makes it possible to use small switching gain of the discontinuous control in the presence of large upper bounded uncertainties. Adaptive laws are formulated using Lyapunov function to guarantee the sliding condition. Efficiency of the proposed controller is demonstrated through numerical simulations.