Research On Fault-tolerant Control Of Multi-propeller Aerostat Based On Sliding Mode Theory

The aerostat is a kind of vehicles flying in the near-space,which has been attracting more and more research.Due to the complex flight environment and long-time mission requirements,it is easy to cause the fault even failure of the aerostat system;one of the most common types of faults is the actuator fault.In this paper,based on the sliding mode control theory,we study the fault diagnosis and fault-tolerant control(FTC)of the flight control system for the multi-propeller aerostat,where the influence of the unknown external disturbances and the input saturation constraint of the actuator are also considered.The main contributions of this paper are as follows:1.This paper studies the types of the multi-propeller aerostat system faults,and establishes a unified mathematical model of the actuator faults.A simplified four degree of freedom model of the aerostat is extracted based on the existing six degree of freedom model,and obtains the relationship between the system faults and the responses of the system states,the analysis results of open-loop system under the actuator faults are given respectively.2.In the view of the loss of efficiency of the actuators and the wind disturbance,an integral sliding mode control allocation method for fault system is proposed.The paper considers the redundant configuration of multi-propellers,and once the faults of actuators occur,the control allocation module will redistribute the control signal to healthy actuators in order to produce the equivalent input of the system.Then,an integral sliding mode controller is developed to eliminate the steady-state errors for the trajectory tracking.The advantage of the fault-tolerant control allocation system is that it doesn’t change the structure of the main controller,and the design of the method is simple and easy to realize.3.An adaptive sliding mode FTC strategy is proposed considering the fault control problem of the system under the condition of various faults of actuators and the influence of external disturbance and propeller input saturation.The integral sliding mode control technology is used to achieve better tracking performance,and the sigmoid function is presented to deal with the problem of input saturation,and an online adaptive control law is designed to eliminate the offset fault and external disturbance.The simulation results show that this strategy can achieve good control performance under the condition of complex actuator faults and can avoid the effect of external disturbance and input saturation.4.In order to solve the problem of fault-tolerant control of unknown actuator faults,an active FTC scheme is proposed by combining the approaches of observer and sliding mode variable structure control.Firstly,an adaptive fault estimator is developed for the fault system,which can estimate the states of system and the size of faults,and then,according to the obtained fault information,an adaptive sliding mode fault-tolerant controller is proposed to achieve the trajectory tracking of closed-loop system.The simulation results indicate that the active FTC scheme has strong robustness and reliability.The results of this paper are of great significance to improve the flight reliability of the aerostat,and the design method can be extended to solve the FTC problems of other types of aircraft.