عنوان مقاله [English]
This study aims to improve operational efficiency and enhance the flight performance of variable pitch Quadrotors in hover with the scope of achieving sustainable inverted flight, or fulfilling a special mission in automated mass flights. The objectives of this study, a robust control system design for a candidate variable pitch quad rotors is paced classically. The methodology is based on mathematical modeling developments extracted specifically for a candidate variable pitch Quadrotors. Trim calculation and linearization of equations along with design, implementation and integration of a robust controller for the quad rotor are therefore following steps in this study. The challenges associated with the dynamic modeling of rotors, aerodynamic modeling
in small Reynolds numbers and modeling of the electric propulsion system are removed using the Blade Element-Momentum Theory (BEMT). To improve the performance, two control loops including an attitude control system and a control motion were implemented using H$infty$ optimization and $mu$ synthesis. Results showed that H$infty$ optimization is a suitable approach to reducing the unstructured uncertainties, and thus it can be used for control system design with 30 percent of
uncertainty relevant to the aerodynamic coefficients. Results also revealed that the stabilized inverted flight as a novel ability of operation in variable pitch Quadrotors could be obtained. In both approaches Bilin transformation is aimed to pole shifting and avoidance of singularity in H$infty$ optimization and $mu$ synthesis. By using the Bilin transform, design of weight functions is avoidable, thus controller design would be easier. On the other hand, robust controllers frequently have the high order transfer functions which make the implementation of it difficult, thus the model reduction approach was applied to reduce the order of controller designed with $mu$ synthesis method. Overall, without problem caused from gyroscopic effect in fixed pitch Quadrotor, a variable pitch mechanism to develop the bigger Quadrotor, with the less problems in control system.