  Robust online estimation of an oscillation frequency belongs to classical
problems of the system identification and adaptive control. The given harmonic
signal can be noisy and amplitude-varying, at the same time, like e.g. in case
of the damped oscillations. A novel robust frequency estimation algorithm is
proposed, motivated by the existing globally convergent frequency estimator.
Advantage of the proposed estimator is in requiring one design parameter only
and being robust against the measurement noise and initial conditions. The
proven global convergence is insensitive to the amplitude variations, which
comes in favor of applications with damped oscillations or additionally shaped
harmonic signals. The proposed analysis is simple and discloses an exponential
convergence rate, which depends analytically from the sought frequency,
adaptation gain, and oscillations amplitude. Numerical and experimental
examples demonstrate robustness and efficiency of the proposed estimator for
amplitude-varying and noisy signals.
