Study Of Fault Tolerant Control Based On Adaptive Sliding Mode For Near Space Vehicles

In this paper, fault modeling, fault diagnosis and fault tolerant control(FTC) technologies have been researched for near space vehicle(NSV) flight control system under different fault cases. These faulty types of flight control system in this paper have been studied which mainly involves actuator fault, engine fault, and structural fault. Near space vehicle is one of the main international weapons in future wars. In recent years, the technology for near space vehicle of the United States has reached the highest level compared to other military power. It has been successfully tested at different Mach numbers, and the highest Mach number has reached 20. However, the progress of our national near space vehicle development work is not yet optimistic, and all aspects of the study are still struggling. Therefore, near space vehicle technology is an urgent and imperative task in order to lead our country’s military and national security.Compared to conventional aircraft, near space vehicle has its own unique advantages and disadvantages: on the one hand, high march, big flight envelope, strong attack ability, good stealth; on the other hand,complex environment, high demanding of the body material, strong coupling, and nonlinearity. All the above complex factors inevitably make the aircraft be prone to out of control in the process of performing tasks, resulting in catastrophic accidents and casualties. So it is very important to ensure the safety of flight system of near space vehicle, it can be seen that fault diagnosis and fault tolerant control technology is crucial. In the following, against this phenomenon and around this research direction, the main framework for this article is as follows:Firstly we introduce the research background and significance of near space vehicles, and then give an overview of the main fault diagnosis and fault tolerant control methods for near space vehicle.Secondly, this section mainly describes two aspects:on the one hand, detailed attitude model and longitudinal model of near space vehicle are disscussed and by analyzing the characteristics of both, the appropriate control requirements of the dynamic model is select as the research object; on the other hand, different kinds of near space vehicle faulty models are established, which includes actuator faulty model, sensor faulty model, structural damage model, and for different types of faults, introduced its specific physical significance.Third, single actuator fault is taken into account; meanwhile, external interference and model uncertainty are also considered. Based on second-order dynamic terminal sliding mode control, a terminal sliding mode control and an adaptive fault tolerant dynamic sliding mode control are proposed, which can effectively overcome the chattering, and also make the desired signals be quickly and accurately tracked within time. Simulation results show that the designed algorithm has a good fault tolerance.Forth, against near space vehicle with actuator dynamic factor, meanwhile in the case of two kinds of faults, that is,actuator stuck and loss, a sliding mode adaptive fault tolerant control scheme is designed, including the designs of sliding mode observer and adaptive sliding mode fault-tolerant controller. The method can updates the parameters of the FTC controller on line by estimated two fault information timely, which can make the faulty flight control system, be able to successfully complete flight task and return back.Fifth, NSV structural damage has been modeled by comparing the simulation curves to update the coefficients of aerodynamic parameters; the dynamic equations with structural damage can be more close to the real physical model. Further, based on Backstepping and RBF neural network control technologies, a RBF NNs Backstepping fault tolerant control scheme has been proposed aiming for structural damage. Experimental results show that, within a certain degree of damage, the proposed method has the recoverable ability within effective time for flight control system in the event of non-fatal injuries.Finally, the paper summarizes our exsiting work and lookouts the future work. In our future work, via consideing more faulty factors of the flight control system for near space vehicle, a more complete and sophisticated mechanism of fault diagnosis and fault tolerant control will be established, which provides a guarantee for safe and reliable flight control.