Intelligent Control and Automation, 2013, 4, 55-62 doi:10.4236/ica.2013.41008 Published Online February 2013 (http://www.scirp.org/journal/ica) H 2 and H ∞ Controller Design of Twin Rotor System (TRS) Usman Ahmad 1 , Waqas Anjum 1 , Syed Mahad Ali Bukhari 2 1 Center for Advanced Studies in Engineering, Islamabad, Pakistan 2 University of South Asia, Lahore, Pakistan Email: usman.ahmad@msn.com, waqas.anjum@iub.edu.pk, smab_engineer@yahoo.com Received September 5, 2012; revised October 5, 2012; accepted October 13, 2012 ABSTRACT Control engineering had been the core of all engineering fields all the time. As the name depicts, control of different parameters of various industrial or commercial equipment like plants, vehicles, aircrafts and etc is obtained. Robust and optimal control of these equipments plays a vital role. This paper presents a design of H 2 and H ∞ control for a Twin Rotor System (TRS). TRS is a multi input multi output (MIMO) nonlinear system. The main objective is to control the angular position of the lever bar of TRS. It is having strong coupling between inputs and outputs. The model is first linearized and then controllers are designed to control the positions of lever bar. Simulations are made in MAT- LAB/SIMULINK. Model parameters are also provided in the end. Keywords: Robust; Optimal Control; TRS; MIMO; Linearization; Controller 1. Introduction The question of Multi-Input-Multi-Output (MIMO) con- trol has always been a thought-provoking sub-field sur- rounded by the field of control engineering. Among the systems that involve MIMO control, the helicopter rises out as one of the striking models. This kind of aircraft needs two rotors, spinning in perpendicular planes, there- fore, cannot depend on Single-Input-Single-Output con- trollers to steer in the deep space. Also, un-manned heli- copters have not yet been viewed in armies globally; this fact gives the job of designing MIMO control systems for helicopters a large space to stimulate [1]. The twin rotor system establishes the conventions of a nonlinear MIMO system with considerable cross cou- pling. Its operation approaches a helicopter but the angle of attack of the rotors is fixed, and the aerodynamic for- ces are regulated by changing the speed of motors. The entire mechanical model for this machine has been ma- tured. Based on this mechanical model, various control designs are devised to control the apparatus using MAT- LAB-Simulink [2]. These control strategies are formed to prepare the Twin-Rotor system go to prearranged objec- tives and chase periodic input signals. The exercise of scheming the control designs demands the author to do much labor on state-space formation linearization and exploratory works. Mathematical esti- mation is also executed to achieve the approximated polynomials for variables association. In most of the re- alistic control systems such as flight control systems, there survives saturation restriction on controller outputs [3,4]. If a feedback controller intended without taking into consideration such restraint is employed the closed- loop system may be inconsistent in the case where large external signal is supplemented. One method to treat with such a difficulty is to formulate a low-gain controller which does not outrage input limitations for all extrinsic signals that will be introduced. However, it is clear that this approach culminates in unprogressive control opera- tion. The TRS comprises of a beam centered on its core in such a way that it can gyrate freely both in the horizontal and vertical planes. At both ends of the beam, there are rotors (main rotor and tail rotor) steered by DC motors. A counterbalance arm with a weight on its end is rooted to the beam at the axis [5]. The state of the beam is charac- terized by four system variables: horizontal and vertical angles calculated by position sensors provided at the pivot, and two corresponding angular velocities. Two conventional state variables are the angular velocities of the rotors, regulated by tachometers linked with the DC motors [6]. In a standard helicopter, the aerodynamic force is re- gulated by varying the angle of attack. However, where the angle of attack is fixed then the aerodynamic force is controlled by varying the speed of motors. Therefore, the control inputs are supply voltages of the DC motors. A modification in the voltage use ends in a change of the spinning speed the rotor which culminates in a change of the complementary position of the beam. To overcome the conservative design approach, dif- ferent control approaches that employ on-line optimiza- Copyright © 2013 SciRes. ICA