Robust Frequency-Adaptive Quadrature Phase-Locked-Loops With Lyapunov-Certified Global Stability

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