Discussion on 'State feedback control with time delay'

This note is a short discussion on the paper 'State feedback control with time delay', in which an a posteriori analysis on the primary closed-loop eigenvalues is proposed to ensure that the chosen location is accurately achieved by state feedback. The goal is twofold. First, a qualitative evaluation of closed-loop stability can be carried out by using classical control techniques, as systems margins or Nyquist plot, without the necessity of evaluating the primary closed-loop eigenvalues; and second, the well-known Pade approximants for time delay in frequency domain is shown to be as accurate as that the truncation of the Taylor exponential expansion proposed in that work. (C) 2017 Elsevier Ltd. All rights reserved.