This work describes and compares two phaselocked-
loop (PLL) algorithms aimed at tracking a biased sinusoidal
signal with unknown frequency, amplitude and phase,
with inherent robustness to dc-offset. The proposed methods
endow Quadrature PLLs, renowned for their excellent tracking
performance, with frequency-adaptation capability, while providing
robust global stability certificates. The large-gain global
stability, proven by Lyapunov-like arguments borrowed from
adaptive control theory, represents a major benefit compared
to conventional PLLs, whose convergence instead can be proven
only locally by small-signal analysis or small-gain assumptions.
In this connection, the proposed algorithms represent the first
frequency-adaptive and DC-bias rejecting PLL-type architectures
with Lyapunov-certified global stability. When used for
signal tracking, the proposed methods are shown to outperform
the adaptive observer, especially in noisy conditions. Moreover,
they provide more accurate frequency estimates than existent
frequency-adaptive PLLs, showing enhanced robustness in facing
both phase-noise and measurement perturbations.
