Popov's Method and its Subsequent Development

摘要

A simple proof of the quadratic criterion for absolute stability is given for the nondegenerate case. A similar result was proved earlier (for both degenerate and nondegenerate cases) by the author (1967) by using completely different methods. The proof given has some similarities with the ideas used by Popov (1959-1961) in the proof of his now widely known frequency-domain criterion of absolute stability. The new frequency-domain criterion of absolute stability is given for the system with the periodic coefficient. One illustrative example is considered.