Research On Modeling And Flight Control Technology Of Multi-Rotor Aircraft

Due to its simple structure, superior maneuverability and unique flying way, multi-rotor aircrafthas attracted increasing attention from scholars and research institutions at home and abroad and it isbecoming one of the attractive research fields. However, the greater disparity exists when comparingthe autonomous flight control of the multi-rotor aircraft domestic with that of abroad. Besides, it isdifficult to implement fault-tolerant flight control when any of the actuator breaks down because ofthe rotor assembly of the quad-rotor without any redundancy. Therefore, the configuration and theadvanced flight control method of the multi-rotor aircraft is to be studied furtherly. Accordingly, thedissertation carries out a series of research work in modelling and advanced flight control to meet thetarget of the actual flight for a novel multi-rotor aircraft which was awarded a national inventionpatents.First of all, the aerodynamics forces, torques of the rotor and the whole airframe are analyzedand derived on the basis of the detailed analysis of the configuration and the principles of flight of theplane symmetrical multi-rotor aircraft. Then, the systemic nonlinear mathematical model with sixdegree of freedom and the flight control model are developed for the aircraft, respectively. At thesame time, the open-loop characteristic of the mathematical model and control model are proved andanalyzed. They demonstrate that the developed model can embody the characteristics of the aircraft,such as serious nonlinearity, intense state-coupling and uncertainties and can meet the requirements offlight control system design.Secondly, an attitude control system model with composite disturbance of the aircraft is deducedunder taking full account of the uncertainties and external disturbance factors for the aircraft. And, arobust adaptive attitude controller with compensation the disturbance based on fully tuned radial basisfunction neural network is proposed for the uncertain attitude system and the center vector and thewidth vector of the neural network all can be adjusted online. Simulation results show that theproposed method can restrain the disturbance effectively and can meet the requirement of the attitudemotion control.Thirdly, a method of trajectory tracking control for the aircraft is proposed based onbackstepping terminal sliding mode control to achieve the requirement of tracking the desiredtrajectory accurately. Thereinto, an adaptive sliding mode algorithm for disturbance reconstruction isdeveloped to restrain the impact of the composite disturbance on the aircraft. The algorithm does notneed the boundary of the composite disturbance just like the RBF neural network. But, compared with RBF neural network, the proposed algorithm is simple and fit for engineering. In order to achieve theattitude stabilization and to track the desired attitude and trajectory quickly as well as accurately, anattitude controller is designed which use a combined adaptive sliding mode algorithm for disturbancereconstruction, backstepping, dynamic surface control and terminal sliding mode control. After that, aposition controller is designed based on backstepping. The effectiveness and correctness of theproposed methods are verified through the simulation results.In the following, a problem of trajectory tracking is further considered under the condition ofcomposite disturbance impact, the state constraints to better reflect and meet both the actual flightcharacteristics and requirements. Aiming at the composite disturbance of the system, a sliding modedisturbance observer is designed to reconstruct the composite disturbance and to bulid thecompensatory control law. Considering the special form of the position control model, a positioncontroller is referred from the designing ideas of the sliding mode control and developed. The impactof the composite disturbance and the requirements of the attitude angles and angular velocitiesconstraints are considered in the attitude controller design. Then, a backstepping attitude controller isdesigned based on composite disturbance reconstruction and compensation, as well as constrainedcommand filter. The simulation results demonstrate that the proposed methods can make the aircrafttracking the desired trajectory under the case of composite disturbance and the state constraints.Finally, aiming at the problem of actuator fault of the attitude control system, a novel faultdiagnosis, identification and fault tolerant control strategy is presented. In ref.[199], there is aswitching function in the control variable of the sliding mode disturbance observer which may lead tothe problem of chattering phenomena of the composite disturbance reconstruction value. A modifiedsliding mode disturbance observer is proposed to reconstruct the composite disturbance. Consideringthe actuator fault models include both the loss of actuator effectiveness fault and the actuator-stuckfault, a local actuator fault estimation algorithm is presented which is similar to the mode referenceadaptive control. Then, an attitude controller based on the proposed composite disturbancereconstruction algorithm, the actuator fault estimation algorithm and backstepping is designed. Thestability of closed-loop system is analysed via Lyapunov method and the excellent performance isdemonstrated by simulation.