Flat filtering: A classical approach to robust control of nonlinear systems

Flat filtering constitutes a reinterpretation of Generalized Proportional Integral Control (GPIC) in the form of robust Classical Compensation Networks (CCN). Roughly speaking, any linear controllable system can be output regulated with the help of a well tuned filter and a suitable cascaded linear combinations of the internal states of such filter. Here, it is shown that such classical tool is also capable of efficiently handling control tasks on perturbed nonlinear systems, including unknown nonlinearities and un-modeled dynamics.