Active disturbance rejection control applied to a twin-rotor system

Abstract

The problem of controlling the nonlinear system known as the Twin-Rotor System (TRS) using the Active Disturbance Rejection Control (ADRC) technique is investigated in this work. The TRS is a commercial didactical experiment that is used for studying helicopters control tasks, such as pitch and yaw stabilization or tracking. In this work only one degree-of-freedom is considered, namely the TRS pitch movement, such that the TRS can be represented as a third order Single-Input Single-Output (SISO) nonlinear system. The parameters of a first-principles model are obtained by minimizing the quadratic cost associated with the difference between experimentally acquired response data and simulated ones. Since the TRS output is quantized due to the use of a rotational encoder, an Algebraic Differentiation Procedure (ADP) is used as a filtering technique to smooth out the corresponding abrupt transitions caused by quantization. In addition, a partial dynamics cancellation scheme is employed to reduce the system order considering that the ADRC strategy was originally conceived to be applied in second-order systems. To accomplish this reduction, the time-derivative of a signal is estimated using a Robust and Exact Differentiator (RED) technique. Finally, the ADRC strategy, modified by the inclusion of signal processing stages provided by the ADP and the RED, is tested in practice. Experimental data indicates superior performance with respect to the original ADRC formulation in tracking a desired reference pitch angle.