Research On Data Driven Optimal Curved Path Following Logic For The Fixed-wing UAV

Autonomous navigation control system is the core system to achieve UAV autonomous flight.In the implementation of obstacle avoidance,tracking and monitoring tasks,the system needs to ensure that the UAV could scheduled flight.In the complex airspace,how to effectively compensate for external unknown wind disturbance,to ensure that the UAV can accurately follow the scheduled path,known as the UAV path following problem.At present,UAV path following control has become a hot topic in theory and engineering re-search.It is the key point of UAV autonomous navigation system.There are many ways to propose path following control for small fixed-wing UAVs.Small-scale fixed-wing unmanned aircraft in the path following problems are:(1)Most of the methods only for straight and circular path following,it is difficult to directly apply to solve the general curved path following problem.(2)Fixed-wing unmanned aerial vehicles to adjust the movement mechanism is complex,it is easy to be affected by wind disturbance and side slip.(3)To achieve the curved path following,very few studies take into account the UAV input limited situation.In this context,in order to achieve accurate curved path following control,the paper uses the Model Free Adaptive Control(MFAC)method to control the UAV heading,construct the appropriate vector field(VF)To achieve accurate curved path following.In this paper,two methods of con-trol Lyapunov function(CLF)and Nested Saturation(NS)are proposed for the case that the input of two-dimensional plane is restricted.Combined with Model Predictive Con-trol and Integral LOS(Line of Sight)strategy,a three-dimensional curved path following method is proposed.According to the algorithm proposed in this paper,the hardware-in-the-loop simulation system and the physical flight test are used to verify the reliability and effectiveness of the algorithm.The main work of this paper includes:(1)The advantages and disadvantages of data-driven control method are analyzed,and a model-free adaptive control method with output observer is proposed.In order to better estimate the pseudo-partial derivative(PPD)of the time-varying parameter,the output disturbance observer is added and the model-free adaptive controller with output observer is designed and proved to be stable by using Lyapunov theory.According to the characteristics of the fixed wing unmanned aerial vehicle heading control and the advan-tages of the model free adaptive control method,a model free adaptive control(MFAC)method is proposed for small fixed wing unmanned aerial vehicle Heading control.The time-varying dynamic equivalence model is used to replace the original nonlinear time-invariant mathematical model.Based on the estimated PPD,the iterative control method is designed.The stability of the proposed control method and the convergence of the tracking error are proved by discrete Lyapunov technique.(2)A vector field method for tracking the unsteady curved path of UAV is proposed.According to the distance of the UAV to the desired path and the current heading an-gle,the vector field is used to obtain the desired heading angle command.Based on the cross-track error and the along-track error defined in the Frenet-Serret coordinate system,the controller is designed to ensure that the UAV is in any position and any orientation within the two-dimensional space,Both of which eventually converge to zero.When the geometric trajectory of the UAV converges to the desired path,the speed of the UAV is guaranteed to meet the corresponding dynamic characteristics.This method avoids the singularity of the triangular curve in the design process by defining the velocity envelope of a moving point on the desired path.(3)The tracking control method of UAV curved path is designed.Due to the presence of mechanical limits and energy constraints,fixed-wing unmanned aerial vehicles in the process of turning,the control input must be bounded and limited.The restriction of the control input can not be limited by a simple limit function,and a corresponding control state is required.Two methods of controlling Lyapunov function and saturation set are proposed to deal with the situation that the input of the two-dimensional in-plane curve is limited.Furthermore,an integral LOS method based on model predictive control is proposed to solve the problem of curve path tracking in the case of input limited in three-dimensional space.(4)A multi-UAVs cooperative curve tracking control method with high-order non-linear and under-drive characteristics is designed.Compared with the linear full drive system,non-linear underactuated system has a better practical significance.Based on the anti-backward method,Lyapunov theorem and graph theory,the method of tracking con-trol of multi-UAV system is designed,and the position and velocity of the UAV system are proposed.And verifies the validity and rationality of the method.(5)A high-performance hardware in-loop simulation system and flight test are de-signed to verify the effectiveness and responsibility of proposed methods.The moving point described by the arc length parameter is used as the virtual reference point,and the deviation between the UAV and the virtual reference point is used as the tracking er-ror.This solves the singularity introduced when the shortest distance point of the UAV is more than one.The desired path is obtained by using cubic spline interpolation,which has good smoothness and extensibility,and does not need to solve the global expression of the desired path.