A Disturbance Observer Based Control scheme using an Active Disturbance Rejection Controller: An underactuated moving crane example

This article proposes a Disturbance Observer Based Controller (DOBC) improved by the inclusion of an Active Disturbance Rejection Controller (ADRC), in classical transfer function form, as a feedback controller. Typically, the DOB controller uses a disturbance observer (DO) obtained by subtracting the low pass filtered plant inverse from the similarly filtered input signal. After direct disturbance cancellation, the feedback controller part of the DOB controller scheme is usually prescribed in an independently free manner. The use, in classical transfer function form, of a Reduced Order Extended State Observer based Active Disturbance Rejection Controller (ROESO-ADRC) as a feedback controller, in place of an unrelated controller, is shown to vastly improve the total disturbance attenuation in the closed loop system, thus enhancing the output reference trajectory tracking performance. The method is tested in the trajectory tracking control of an under-actuated, nonlinear, moving crane.