Synthesis of Robust Quadcopter Control Algorithms Considering Speeds and Lift Force Constraints

The paper presents the synthesis of a tracking system for a quadrocopter considered as a solid body with six degrees of freedom and four control actions (rotor lift forces), considering design constraints on velocities and controls. The plant operates under conditions of parametric and external disturbances, as well as incomplete measurements. The trac king loop is designed in a typical way and consists of translational and rotational motion subsystems with three inputs and three outputs each. Reference trajectories are independently specified for the spatial position of the quadrocopter’s center of mass and yaw angle. The pitch and roll angles have a dual function: in the translational motion subsystem they, together with the total lift force, act as controls, which are considered as reference actions in the rotational motion subsystem. Scientific novelty is related to the developed method of dynamic feedback design using piecewise linear feedback with saturation in regulators, state and disturbance observers, as well as dynamic differentiators of reference actions. Application of the block control principle with combined piecewise linear feedbacks with saturation for design of tracking subsystems of spatial and angular positions allowed to provide stabilization of tracking errors at imposed constraints on velocities and controls. Reduced dynamic observers with piecewise linear correction reduce the computational load. Based on tracking error measurements, they recover composite signals including unmeasured velocities, uncertain parameters, and external disturbances to a specified accuracy without the need for individual identification of uncertain parameters. The feedback formation on the variables of such observers ensures robustness of the tracking system. Instead of numerical differentiation operations, which are problematic to implement, dynamic differentiators with piecewise linear correction are used to recover derivatives of reference actions, which are capable of processing piecewise differentiable signals and do not generate surges of estimation signals at special points. The presented results of numerical modeling confirm the effectiveness of the developed algorithms

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