Quad-rotor MAV trajectory planning in wind fields

This paper addresses the problem of time optimal path planning for a quadrotor helicopter evolving in a region of known winds. Usually, the flight control of quadrotors subject to wind disturbances challenge seeks to find the optimal control to keep track of a desired trajectory in a windy region. This approach has one major disadvantage: the quadrotor flight control has to compensate for trajectory deviations; therefore, the energy consumption becomes an issue. Most unmanned aerial vehicles (UAV) navigation techniques use waypoints to accomplish their missions. In the framework of a waypoint based navigation, a promising path planning strategy would be a time optimal approach in which the UAV would take advantage of wind to reach its next waypoint; therefore, saving time and energy (under constant forward velocity constraint). A model separation is used to simplify the control of the six-degrees-of-freedom (6DOF) dynamics of the quadrotor. Such approach allows to deal with quadrotor´s 3D-motion through two subsystems: dynamic (altitude and MAV-relative forward velocity) and kinematic (nonholonomic navigation) subsystems. In terms of control, a hierarchical control scheme is used to stabilize dynamic and kinematic underactuated subsystems involved in the navigation task. The time optimal path planning is computed using a dynamic optimization method for continuous systems with some state variables specified at an unspecified terminal time. Results have been validated in simulation.