Abstract
We develop stability conditions for linear feedback time-delay systems under error in time-delay. The time-delay of a mathematical model does not coincide in general with that of the real plant. Therefore, if the mathematical model is used for control designs, resulting control laws do not necessarily guarantee stability of the real closed-loop system. The important step in our approach lies in descriptions of systems under error in time-delay; the time-delay error is described as an additive or multiplicative plant perturbation. These descriptions enable us to derive the stability conditions based on Nyquist stability criterion. From derived stability conditions, we evaluate the error tolerance of timedelay and consider stability margins for timedelay systems under error in time-delay.
