On the stability of time-delay systems using Nyquist criterion

This work presents different results on the stability of linear time-delay systems by a simple method derived from the Nyquist criterion. The main characteristic is the simplicity of the stability tests, maintaining analysis rigour. Based on this simple stability test, delay-independent and delay-dependent stability criteria are derived, being possible the statement of those criteria as numerically treatable problems. Although the presented study concerns systems with different point delays, the extension to systems with distributed delays is possible.