Parallel feedforward and simplified adaptive control

What is it about?

Simple adaptive control systems were recently shown to be globally stable and to maintain robustness in the presence of disturbances if the controlled plant is ‘almost strictly positive real’, namely, if there exists a positive definite static output feedback (unknown and not needed for implementation) such that the resulting closed-loop transfer function is strictly positive real. This paper is an attempt to show in an intuitive way how to use parallel feedforward and the stabilizability properties of systems in order to satisfy the ‘almost positivity’ condition. The feedforward configuration may be stationary, if some prior knowledge is given, or adaptive, in general. This way, simple adaptive controllers can be implemented in a large number of complex control systems, without requiring the order of the plant or the pole excess as prior knowledge.

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