One of the important results of classical systems theory is the (finite-dimensional) Internal Model Principle (IMP). It states that a feedback controller stabilizing the closed-loop system is robust if and only if it incorporates a copy of exogenous reference signals. The IMP is used to design control systems, but it can also be seen as a guideline for understanding how nature has implemented this principle to accomplish robust regulation.
The aim of the research is to develop the theory of robust regulation for infinite-dimensional systems. In addition we let the reference and disturbance signals be nonsmooth periodic or almost periodic functions. This allows an extremely rich class of signals to be used in the analysis.
The extension of the theory is crucial since many important processes, such as diffusion, heat transfer and vibration, are infinite-dimensional. Applications include heat diffusion and flexible structures.