Designing the Non-Linear PID Controller for a Missile Kaveh Kianfar Imam Hossein University Ghadr Aerodynamic Researching Center Tehran, Iran Kaveh_Kianfar2006@yahoo.com Reza Amiri Imam Hossein University,Fajr Electronic And Communication Center Tehran, Iran Amiri_Reza61@yahoo.com Ali Bozorgmehr Shahed University M.Sc. graduated student in Electrical Engineering Tehran, Iran Ali110Bozorgmehr @yahoo.com Abstract— PID controllers are the most prevailing & operative controllers in industry in recent 50 years. NPID Method that is an optimized method of usual PID, leads to get better operation in response quickness and, also overshoot simultaneously. In this paper, it is used NPID method that is an efficient method for control. NPID includes a non-Linear gain and a defined linear gain that connected serial. Using this method results in setting responses based on closed loop system control operation, that k_d (.) , K_i (.) and K_P (.) are control gains varies with time and have constant values in linear proportional, integral, derivative controller. The missile control system contains a linear system to non- linear one. The missile control System responses to PID and NPID controller are shown at the end to compare their behaviors & effects. Keywords- Saturation, Describing Function, Popov, Linearization, Nonlinear Gain I. INTRODUCTION In most engineering applications, there is a nonlinear system It certain way, thus these systems should linearized by special methods after that a PID controller is designed for that linearized system. Even though, in some situation this method is acceptable but in many cases due to the highly nonlinear behavior of the system, using a simple PID is not a good choice.[1] Using gain schedule table for PID controllers is a common method in flight control systems.(controller parameter gains such as KP, KD, and KI are set according to missile states.[2],[3],[4]) PID controllers are the most prevailing & operative controllers in industry in recent 50 years. The term I, guarantees tracing the steady state, while terms D&P provide stability & proper transition behavior. PID controllers are used for various types of dynamic systems. While the gain of PID controllers is linear & constant, it results in the most equations that control the physical process look unreal. To increase control system operation, we need to change the work condition or peripheral parameters that mostly are beyond the simple PID controller ability. When the error between input & the actual volume is high, the gain will be amplified. This error actually leads producing a great correction directive order. For system output that arms to increase rate to reduce error, this correction causes the gain get declined automatically & prevents large overshoot in response .[5],[6] One of the important issues in controller design is considering the system limitation, which may make the system unstable. This designing method is based on considering system limitation. A wide range of modern missiles flight in addition to their high maneuverability, lead to a large gain table is needed while such tables are too complicated, so use of combinations of nonlinear PID controller to improve the effectiveness of adaptive control and robust control is necessary. The purpose of this paper is to design nonlinear controllers which improve the operation of flight control systems. II. NPID CONTROLLER The non-liner proportional integral derivate controllers could have such structure. (1) That and are the control gains that change with time, that are constant in liner proportions integral derivative controllers. The reason of being variable with time is using a non- liner factor in front of linear proportional, integral, derivative controller. U (t) and e (t) are system input & error, respectively. NPID controllers could gather this condition for system [7]. • Damping augmentation • Decrease in lift time for step input • Optimizing the tracing precision • Compensating the friction factor The non-liner PID controllers may have plentiful uses in industry base on their individual feature [8] , [9]. System studied in this paper, uses two non-linear saturated blocks in its own structure. The two saturated block in the system above, are the inherent limitation. There are different methods to design non-linear controller [10]. One, that is used to design the non-linear gain of stated controller, is to design linear PID controller 2011 First International Conference on Informatics and Computational Intelligence 978-0-7695-4618-6/11 $26.00 © 2011 IEEE DOI 10.1109/ICI.2011.36 171 2011 First International Conference on Informatics and Computational Intelligence 978-0-7695-4618-6/11 $26.00 © 2011 IEEE DOI 10.1109/ICI.2011.36 171