Abstract
The work presented in this paper focuses on the design of a robust nonlinear flight control system for a small fixed-wing UAV against uncertainties and external disturbances. Toward this objective, an integrated UAV waypoints guidance scheme based on Carrot Chasing guidance law (CC) in comparison with the pure pursuit and line of sight-based path following (PLOS) guidance law is analyzed. For path following based on CC, a Virtual Track Point (VTP) is introduced on the path to let the UAV chase the path. For PLOS, the pure pursuit guidance law directs the UAV to the next waypoint, while the LOS guidance law steers the vehicle toward the line of sight (LOS). Nonlinear Dynamic Inversion (NLDI) awards the flight control system researchers a straight forward method of deriving control laws for nonlinear systems. The control inputs are used to eliminate unwanted terms in the equations of motion using negative feedback of these terms. The two-time scale assumption is adopted here to separate the fast dynamics—three angular rates of aircraft—from the slow dynamics—the angle of attack, sideslip, and bank angles. However, precise dynamic models may not be available, therefore a modification of NLDI is presented to compensate the model uncertainties. Simulation results show that the modified NLDI flight control system is robust against wind disturbances and model mismatch. PLOS path-following technique more accurately follows the desired path than CC and also requires the least control effort.
Highlights
Unmanned aerial vehicles (UAVs) are widely used by military and civilian industries in a huge number of applications such as aerial surveillance and photography and payload deployment [1].with low-cost sensors and electronics, there is a significant interest in using low-costUAVs among aircraft hobbyists, academic researchers, and industrials
In the first part of this section, the comparison between Nonlinear Dynamic Inversion (NLDI) and modified NLDI (MNLDI) tracking performance is covered while focusing on the coupling between channels, in addition to the robustness of the designed flight control system against external wind disturbances and model uncertainties
To design a complete flight control system, the guidance commands generated by either pursuit and line-of-sight (PLOS) or Chasing guidance law (CC) path following algorithm are achieved by adopting MNLDI flight controller due to its robustness
Summary
Unmanned aerial vehicles (UAVs) are widely used by military and civilian industries in a huge number of applications such as aerial surveillance and photography and payload deployment [1]. The combination of pure pursuit and line of sight-based path following (PLOS) is a geometric technique for generating guidance law. A robust UAV flight control methodology is still required to track a severe acute maneuver command with the existence of external disturbance and model uncertainties. For this objective, the main contribution of the current research is to design a fully autonomous guidance and control algorithm by combining simple geometric path following guidance law and a modified. The concept of Pure pursuit and line-of-sight (PLOS) path following algorithm vanishes the cross-track error distance using LOS control law, in addition to eliminating the LOS angle error using pure pursuit guidance law.
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