JID:AESCTE AID:3292 /FLA [m5G; v1.149; Prn:1/04/2015; 13:48] P.1(1-7) Aerospace Science and Technology ••• (••••) •••–••• Contents lists available at ScienceDirect Aerospace Science and Technology www.elsevier.com/locate/aescte 1 67 2 68 3 69 4 70 5 71 6 72 7 73 8 74 9 75 10 76 11 77 12 78 13 79 14 80 15 81 16 82 17 83 18 84 19 85 20 86 21 87 22 88 23 89 24 90 25 91 26 92 27 93 28 94 29 95 30 96 31 97 32 98 33 99 34 100 35 101 36 102 37 103 38 104 39 105 40 106 41 107 42 108 43 109 44 110 45 111 46 112 47 113 48 114 49 115 50 116 51 117 52 118 53 119 54 120 55 121 56 122 57 123 58 124 59 125 60 126 61 127 62 128 63 129 64 130 65 131 66 132 Fractional order adaptive fuzzy sliding mode controller for a position servo system subjected to aerodynamic loading and nonlinearities Nasim Ullah a , Wang Shaoping b , Muhammad Irfan Khattak c , Muhammad Shafi d a City University of Science and Information Technology, Peshawar, Pakistan b Beihang University, Beijing, China c NWFP UET, Peshawar, Bannu Campus, Pakistan d Zirve University, Turkey a r t i c l e i n f o a b s t r a c t Article history: Received 10 October 2014 Received in revised form 17 January 2015 Accepted 25 March 2015 Available online xxxx Keywords: Sliding mode control Fractional calculus Chattering Friction Robustness Position servo system Aerodynamic loading 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.  2015 Published by Elsevier Masson SAS. 1. Introduction A high performance servo actuation system is crucial part of a guided vehicle which is used to drive control surfaces. During real flight, aerodynamic forces and torques are applied on con- trol surfaces which indirectly load the actuators. Apart from forces and loads there are some other factors which affect control per- formance of position servo loop. These factors include system un- certainties, system noise and nonlinear friction. It is difficult to formulate high performance position servo system without con- sidering the effect of these nonlinearities. Fractional calculus (FC) is a mathematical topic which finds ap- plications in many areas of science and technology [1–3]. In many applications its higher degree of freedom is very advantageous [4–9]. In 1988, Oustaloup presented a new idea about fractional- order (FO) controllers for the first time [10]. He formulated a robust fractional-order control scheme called Command Robuste d’Ordre Non-Entier (CRONE) [11]. Authors of [12] suggested fre- quency domain approach for the design of fractional order con- E-mail addresses: nasimullah@cusit.edu.pk (N. Ullah), shaopingwang@vip.sina.com (W. Shaoping), m.i.khattak@nwfpuet.edu.pk (M.I. Khattak), muhammad.shafi@gmail.com (M. Shafi). trollers. The concept of variable fractional order controllers is in- troduced by Valério and Sá da Costa [13]. Padula et al. introduced fractional order-PID controller and its tuning scheme [14]. A model predictive control of fractional order nonlinear discrete time sys- tems has been proposed by authors of [15]. The concept of sliding mode control (SMC) is based on variable structure control which is robust against upper bounded uncertain- ties [16]. A linear manifold is used to formulate classical sliding mode control and asymptotic stability is guaranteed. Due to the fact that robust part of sliding mode controller is based on a discontinuous function; high frequency chattering is introduced in control signal. To overcome this limitation and to have more degrees of freedom, sliding mode control is formulated using frac- tional calculus. The idea is to achieve better performance with more degrees of freedom. Earlier research work is focused on frac- tional order proportional-derivative (FOPD) manifold, which has been applied in antilock braking systems [17], twin-tank model [18] and robotic flexible joint manipulators [19]. The above men- tioned FOPD controllers design doesn’t take uncertainties into ac- count. System nonlinearities, parametric uncertainties and external disturbances affect control performance of dynamic systems. Clas- sical sliding mode controller has a discontinuous control compo- http://dx.doi.org/10.1016/j.ast.2015.03.020 1270-9638/ 2015 Published by Elsevier Masson SAS.