Forward action to make time-delay systems positive-real or negative-imaginary

Positive-real and negative-imaginary systems are characterized by properties which make them particularly important in modeling physical devices, such as large-scale flexible structures or electric networks. This paper focuses on a strategy developed in order to ensure the positive-real or negative-imaginary property to systems with external time-delays. A forward action is taken into consideration in order to make systems with time-delay positive-real or negative-imaginary, guaranteeing also closed-loop stability performance. Numerical examples are included.