2DOF IMC and Smith-Predictor-Based Control for Stabilised Unstable First Order Time Delayed Plants

The article brings a brief revision of the two-degree-of-freedom (2-DoF) internal model control (IMC) and 2-DoF Smith-Predictor-based (SP) unstable systems. It shows that first important reason for distinguishing between these approaches is limitations action. However, it also reminds that, in addition to seemingly lucrative dynamics transients, proposed can conceal tricky behavior with structural instability, which may manifest itself only after longer period time. Instead, as one possible reliable alternatives, two-step IMC filtered Smith predictor (FSP) design are applied first-order time-delayed (UFOTD) Firstly, P controller yielding double real dominant closed loop pole applied. Only then or FSP controllers designed, providing slightly slower, but more robust transients. These remain stable even long run, while showing increased robustness.