Active Disturbance Rejection Control of Nonlinear Systems via linear Endogenous injections and Exogenous feedback : A Classical Viewpoint

This article deals with a linear approach, based on endogenous injections and exogenous feedback (EIEF), for the robust output reference trajectory tracking control of nonlinear systems with controllable (flat) tangent linearizations, obtained around an operating equilibrium point. The approach unifies, under equivalence, the Reduced Order Observer based Active Disturbance Rejection Control approach (ROESO-ADRC), the Generalized Proportional Integral Control (GPI) and the Classical Compensation networks control approach for flat systems, also known as Flat Filters (FF). An illustrative nonlinear rotary crane Lagrangian system example, which is non-feedback linearizable, is presented along with convincing simulations.