Command filtered backstepping-based flight control of unmanned helicopters with disturbance observers

A Command filtered backstepping control augmented with disturbance observer (CFBC+DO) is presented to deal with the problem of robust trajectory tracking for unmanned helicopters. The main work relies on the way to reduce the control calculation works and compensate the disturbances acting on the helicopter, which are the main reason of causing the tracking errors. Firstly, a nonlinear DO is presented to estimate the lumped disturbances which are composed of external disturbances and neglected model uncertainties. Then a CFBC is designed for the helicopter´s trajectory tracking. Since the CFBC uses a command filter to calculate the derivatives of the virtual control signal, instead of using the analytical differentiation, it significantly simplifies the backstepping implementation. Furthermore, by integrating the estimated disturbances into CFBC, the global exponential stability of the compensated tracking errors are proved by using Lyapunov theory. At last, simulation results illustrate the efficiency of the proposed method.