Vasile Mihai Popov (born July 7, 1928, Galaţi, Romania) is a leading systems theorist and control engineering specialist.
Motivated by stability issues in nuclear reactors and by his participation in a seminar series on qualitative theory of differential equations run by A. Halanay, Popov started working in stability of nonlinear feedback systems, in particular on the Lur'e-Postnikov problem.
In 1958/59 he obtained, through a very original approach, the first frequency stability criterion for a class of nonlinear feedback control systems.
He continued this work and obtained the equivalence between the state space (Lyapunov function based) approach and the frequency domain approach for stability and obtained a very perceptive characterization of passive systems, nowadays known as the celebrated Kalman–Yakubovich–Popov lemma.
In the early 1960s, Popov also conceived the notion of hyperstability, a concept that he viewed as generalization of absolute stability.