Using LQG Control as the Inner Loop Controller in Quadrotor Navigation

LQG (linear Quadratic Gaussian) control is an optimizing control technique able to consider the noise included in the control input and in the output measurement as well. In this paper it is discussed its usage to close the inner control loop of an inner-outer control scheme applied to a quadrotor. The focus is to show that such a controller is efficient in dealing with measurement noise, which degrades the feedback quality, thus affecting the performance of the control system. The proposed control structure adopts an outer control loop based on the inverse kinematics, which produces velocity references for position control, and an inner control loop based on LQG, which controls the attitude and thrust of the vehicle, ensuring that the vehicle velocity converges asymptotically to the velocity reference while keeping the control signals within physical constraints. Experimental results of applying such a control structure to a micro aerial vehicle, Crazyflie 2.1, are presented and discussed, which validate the proposed control system.