FREQUENCY METHODS FOR ROBUST ANALYSIS UDC 681.5.037

The following paper aims at giving analytical expression and confirming unequivocally the results achieved through frequency methods for robust analysis of stability and industrial control systems' performance in conditions under uncertainty. A numerical example of robust analysis of a system with internal model is presented. Methods of Nyquist- and Black-Nichols- analysis and the analisis through sensitivity functions for evaluation of robust properties of control systems are examined.