چكيده انگليسي :
In this research, hybrid control of dual system unmanned aerial vehicles (UAVs) was studied. Since UAVs do not need a pilot, they are useful in various missions that humans are unable to perform. UAVs are divided into three main categories: fixed-wing, rotary-wing, and hybrid. Compared to rotary-wing UAVs, fixed-wing UAVs have higher speed and flight continuity, less energy consumption, more load-carrying ability, and the ability to fly at higher altitudes. On the other hand, unlike fixed-wing UAVs, rotary-wing UAVs do not have the ability to hover, and their take-off and landing is horizontal. Therefore, they need a runway and more flight knowledge. Hybrid UAVs combine these two structures. Hybrid UAVs use less energy than rotary-wing UAVs and as a result have higher flight continuity, better load carrying, and high-speed flight ability. Moreover, unlike fixed-wing UAVs, hybrid UAVs have the hovering ability and their take-off and landing is vertical. These abilities prepare them to perform different missions that fixed-wing and rotary-wing UAVs are not able to complete alone. For example, in a mission where it is necessary for a UAV to deliver a cargo in an urban environment and the destination is far away, it requires the flight continuity of a fixed-wing UAV and the ability to vertically take-off and land required in an urban environment. Hybrid UAVs are divided into four categories: tail sitter, tilt rotor, tilt wing, and dual system. Dual system UAVs have some advantages over other structures, including easier repairability of their propulsions, smaller size with less noise, and superiority in terms of safety, reliability, and redundancy. Thus, in this study we focus on dual system UAVs. In order to examine and control this structure, modelling of dual system UAVs was studied first. Modelling can be done either individually for each subsystem or full integrated modelling. Integrated model can suitably represent the existing couplings, and does not ignore the rich dynamics of the UAV. Also, with the help of an integrated model, both propulsions can be used at the same time to perform specific missions, or to continue the mission in case of a failure in the propulsions, or aerodynamic surfaces. In the next step, the motors used in propulsions were selected and their parameters were extracted for better representation of the reality. By completing the UAV model, control strategies and control structure for vertical and horizontal flight were proposed. The transition from vertical to horizontal flight and vice versa, as a main challenge in hybrid UAVs, was addressed by using the appropriate allocation between the two vertical and horizontal flight modes, combining the two controllers, and choosing the correct strategy. Using the proposed strategy the transition from horizontal to vertical flight was performed smoothly. In its horizontal flight mode, dual system UAV has different dynamic modes, each of which affects the stability and behaviour of the UAV. Therefore, it is necessary to control it by closing the appropriate loop and using its own actuators. In order to achieve the desired behaviour, the designed controller needs to be approved by flight quality standards. Finally, the integrated model and hybrid controller for a complete flight mission including vertical take-off, transition and entry into horizontal flight, turning manoeuvre with and without altitude increase in a spiral path, turning with the combination of two propulsions as an advantage of the structure, transition and re-entry into vertical flight, and vertical landing was verified by simulation.
