The performance of quadrotors can be significantly disturbed in the presence of wind. In this article, a simple-toimplement attitude controller is proposed to render a robust and accurate trajectory tracking in the presence of disturbance and model uncertainties. The attitude controller design is based on quantitative feedback theory. A fuzzy logic controller is further employed to provide a satisfactory position trajectory tracking for the quadrotor. The performances of the controllers, in terms of disturbance rejection and trajectory tracking, are experimentally studied. Finally, a flight scenario is performed that compares the performance of the designed quantitative feedback theory-fuzzy control scheme with the ArduCopter controller.
Although, robust controllers that have been designed for hydraulic actuators based on quantitative feedback theory (QFT) have shown satisfactory performance, their stability is limited to certain set of inputs-outputs. This paper explores, for the first time, the stability of a QFT controller using stability theorem of Takagi-Sugeno (T-S) fuzzy systems. To do this, first the hydraulic closed-loop system is represented by a T-S fuzzy model that is formed through a nonlinear combination of some local linear models. Next, the stability of the resulting T-S fuzzy system is analyzed simply by stability analysis of its local linear models. This approach is used to study the stability of a QFT position controller previously developed for hydraulic actuators. Results show guaranteed stability of the QFT controller over a wide range of operation and in the presence of parametric uncertainties.
Although high bandwidth for the pressure tracking of hydraulic actuators is highly desirable in many industrial applications, it has been a challenge to achieve, mainly due to the natural velocity feedback path in these actuators. In this paper, we investigate the extent to which a fixed-gain linear controller designed based on quantitative feedback theory (QFT) can improve the pressure tracking bandwidth while considering other design criteria including closed-loop stability, disturbance rejection, and robust tracking. Simulation and experimental results are presented to demonstrate that the designed QFT controller satisfies the mentioned design criteria over a wide range of parametric uncertainties, and at the same time provides 6 Hz pressure tracking bandwidth.
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