In this paper, a new output feedback control system design method for a VTOL quadrotor aircraft is proposed. A nonlinear observer is developed to estimate the unmeasurable vehicle speed vector. Based on the speed estimation, a cascade control strategy consisting of a kernel loop and a reference command generator is presented for the control system design. A nonlinear approach using model reference control and control allocation techniques is proposed to design the kernel loop control. The control allocation technique adopted in this paper can handle actuator saturations and is applicable to both overactuated and underactuated systems. The designed kernel control law is in the form of dynamic update law. The reference of the kernel loop control is generated by a reference command generator consisting of attitude and position controls. Dynamic inversion method is used in the design of the reference command generator. The proposed approach is applied to a quadrotor aircraft and simulation results show the effectiveness of the proposed approach.
Nomenclature
, ,= position of the origin of the body-fixed frame ( , , ) with respect to the inertial frame ( , , ) , , = components of aircraft velocity along , and body axes, / = roll angle, / = pitch angle, / = yaw angle, / = aircraft roll rate along body axis, / = aircraft pitch rate along body axis, / = aircraft yaw rate along body axis, / = gravity, / 2 = mass, = air speed, / = distance from rotors to the center of mass of the aircraft, = moment of inertia of rotor, . 2 = moment of inertia about body axis, .= moment of inertia about body axis, . 2 = moment of inertia about body axis, . 2 , = proportionality constants relating rotor speeds and resulting thrust and torque = angular speed of the rotor