Multi-rotor Aircraft Design Based On Sliding Mode Variable Structure Control

With the progress of science and technology,the small multi-rotor UAV is more and more appearing in people’s life and has attracted more and more researchers’ attention.Quadrotors,represented by small multi-rotor UAVs,are widely used in military and civilian fields and become the mainstream of today’s small UAVs.Quadrotor has many advantages,the system structure is relatively simple,the volume is relatively small and it can be easily manipulated.However,the quadrotor system also has many problems,such as the difficulty of establishing accurate models,the complex nonlinearity of the system,etc.Sliding mode variable structure control is a kind of control method that can effectively solve the problem of complex nonlinear systems and is widely used in control field.It can improve the performance of the system by designing the sliding modes to realize discontinuous control.Although sliding mode control can make the system get very good robustness,it will make the system produce chattering,which is the biggest disadvantage of sliding mode control.The use of boundary layer sliding mode can effectively weaken the jitter.At the same time,in order to reduce the influence of system uncertainty,adaptive control is added based on sliding mode control.In this paper,a four-rotor aircraft is chosen as the research object,an adaptive sliding mode controller is designed to get a better control effect.First of all,the principle of quadrotor is analyzed,then the force analysis of the aircraft and the establishment of coordinate system and the method of mutual conversion between coordinate systems are given.According to the aircraft line motion and angular motion equations,the mathematical model of the aircraft is deduced.Due to the complexity of the system and the influenced by the outside world,in order to facilitate the study of the system,some external factors are ignored and the system model is simplified based on the assumption.Then,for the system of aircraft,a sliding mode controller is designed based on sliding mode control theory and system mathematical model.Simulink is used in MATLAB to simulate the designed controller and the result was compared with the PID controler.In order to solve the problem of sliding mode control chattering and to reduce the impact of system uncertainty,adaptive control is added to the system.The principle of adaptive control and the adaptive control strategy are introduced.Then,an adaptive sliding mode controller is designed for the aircraft and the controller is simulated and compared with PID and sliding mode.In order to verify the controller’s effect,a four-rotor aircraft experimental platform was built.The principle of each module of the aircraft is analyzed,and the debugging of the system isintroduced.The designed controller is applied to the aircraft to be measured,and then the control effect of the three controllers is compared and analyzed.The experimental results show that the designed adaptive sliding mode controller has better robustness than the PID controller and the sliding mode controller.