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Hybrid Optimal Control of Autopilot Modes for Aircraft Trajectory Design in Air Traffic Control

With the increasing demands for air transportation, air traffic control strategies have been focused on the efficient, safe, and clean operation which can cope with a large amount of traffic. Here, optimal aircraft trajectories generation is one of the important parts in these efforts. An aircraft’s trajectory is dependent on the aircraft’s dynamics and can be controlled by a number of flight modes. The switching of flight modes occurs in normal operation during any flight phase or in any abnormal situation such as obstacle avoidance or go-around, which needs a deviation from a nominal trajectory. In any case, the efficient and safe mode switching should be provided.

In this research, we propose an algorithm that generates an optimal sequence of flight modes and optimal continuous control input for each mode which minimize a given cost function while satisfying constraints. Each flight mode has its own dynamics so that the flight dynamics of an aircraft has the characteristics of a hybrid system. The control input for the hybrid system includes a mode schedule which has two components, a mode sequence and switching times, and a continuous input for each mode as shown in Figure 1. In general, it is difficult to find all these components efficiently and effectively. This is why the most of previous works have solved for the part of these components, for example, finding switching times for a given mode sequence. Here, we apply a bi-level algorithm to solve this hybrid optimal control problem and demonstrate that this approach gives an optimal flight trajectory of an aircraft operating with the national airspace system.

Figure 1. Hybrid Optimal Control Problem


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