Command-filter-based trajectory-tracking control of quadrotor subject to internal and external disturbances

Abstract

Purpose – We propose a command-filter backstepping controller that integrates a disturbance observer (DO) and a high-gain observer (HGO) to handle unknown internal and external disturbances acting on a quadrotor. Design/methodology/approach – To build the controller, we first define tracking errors between the measured and desired quadrotor outputs. These errors let us rewrite the system in a new set of state variables. Using that transformed model, we apply the Lyapunov theory and derive a backstepping control law. To avoid taking repeated time-derivatives of states and virtual controls, we insert a first-order command filter. Since the controller also needs disturbance estimates, we add a nonlinear DO. Finally, we replace every state that appears in the controller or observer with its estimate from a HGO. Findings – The main result is a control law that lets the quadrotor follow its path even when both internal and external disturbances act on it. Every sub-model is allowed its own type of disturbance, so the design stays realistic. We introduce a new state transformation and, with Lyapunov arguments, build a backstepping controller that includes a first-order filter; the filter keeps the design from suffering the usual “explosion of complexity.” A HGO then reconstructs the unmeasured states and their rates, yielding an output feedback implementation. In parallel, the nonlinear DO attenuates constant and nonlinear disturbances and band-limited white noise. Practical implications – The method reduces reliance on high-precision sensors and mitigates the impact of wind, model error and rotor noise during flight. Originality/value – Previous studies typically address either disturbance rejection or partial sensing, rarely both. Our design brings the filter, DO and HGO together, so it tackles disturbances, limited sensors and the well-known complexity spike in backstepping all at once.