Design Of Aircraft Pitch Channel Based On Variable Structure Control Theory

The emergence of the flight control system is accompanied by the invention of theairplane. Flight control system is used to improve the performance of the aircraft and toreduce the workload of the pilot. With the expansion of the flight envelop, the flight missionsbecome more and more complex, the values of the parameter perturbation and the externaldisturbance which are caused by the complex flight environment are very large. All above andthe nonlinear and multi parameters characteristics of the aircraft put forward higherrequirements to the flight control system. The performance of the flight mainly depends onthe reliable guarantee of the flight control system. Flight control system is one of the mostimportant parts of the airplane, it plays a decisive role to the performance and the security ofthe airplane and it is particularly important to the technology research of the flight controlsystem.In this paper, we design a flight control system with the variable structure control theory,especially focus our attention on the pitch channel control system, and the simulation resultsand analysises of the control system designed are given.First of all, the mathematical model of the aircraft is established and decoupled in orderto get the linear equations of the pitch channel.Secondly, on the basis of a certain understanding of the constitution, working principleand basic analysis method of the aircraft control system, we focus our attention on the shortperiod mode of the pitch channel. Automatic flight control system is designed by using thetraditional PD control method and the control results are given by using simulation analysis.Then, the variable structure control theory is introduced. As we know, the variablestructure control has an advantage called invariance that the internal parameter perturbationand the external disturbance have no effect on the system. In practical application, we makeuse of this feature to design the flight control system. In this paper, index reaching lawmethod is used in the design of the switching manifold in order to weaken the chattering.Considering the factor that the control input is limited so that we couldn’t get a satisfied resultby using the index reaching law only, a composite method is proposed to reduce chattering,that is sign function’s high gain method.At last, the control result of the variable structure control system designed is simulated inthe environment of Matlab and is compared with the traditional PD control system. Thesimulation results show that the variable structure control system has a perfect performance ofautonomous and anti-interference capability and it can smoothly follow the instructions in different flight environments. The system has a certain theoretical and practical significance.