Robust stability and desired model method

The paper deals with a determination of robust stability regions in a plane of conventional analog controller adjustable parameters for common controlled plants with time delay. There are derived rather general formulas, which allow to render both stability regions and regions for specified gain or phase margin. Knowledge of these regions allows to verify a robustness of different controller tuning methods for plants with uncertainties. For the most common plants with time delay of the first and the second order with time delay user-friendly formulas are given. The use of a described approach is shown in the example.