Design of a Quadrotor Attitude Controller and Throttle Acceleration Autopilot Based on Forward Modeling

Quadrotors are currently of widespread use in many commercial and military applications, thus, any development aiming at increasing their flight performance is of considerable relevance. Both the model structure and main dynamical parameters of a quadrotor during forward flight are different from those present when hovering. This results in a poor performance of any controller designed for hovering equilibrium, when applied to forward flight scenarios. Aiming at this problem, we propose a design methodology for a quadrotor attitude controller and throttle acceleration autopilot, based on forward modeling. Firstly, the forward dynamics is modeled via system identification and designed experiment. Then, utilizing the linearization results, a frequency domain analysis method is investigated for tuning the parameters of attitude cascade PID controller of quadrotor. The three-layer structure requires it to be designed separately, where the inner loop solves the stability problem and the outer one improves the response performance. And this work regards crossover frequency and phase margin as indicators. Next, a novel closed-loop throttle autopilot with acceleration feedback is constructed to control the vertical movement fast and accurately. The control command in throttle channel is given from the relationship between equilibrium throttle and vertical acceleration, which will be processed by a PI correction and a first-order low-pass filter. Finally, the numerical simulations and comparisons are carried out to demonstrate the strong stability and transient behavior of the proposed scheme in different working regimes.