Problems of Startup and Phase Jumps in PLL Systems

An adaptive phase-locked loop (PLL) structure is proposed which offers fast and smooth tracking of phase-angle jumps. Correlatively, it offers soft startup stage and avoids undesired frequency swings caused by phase jumps. The adaptive mechanism adjusts the gain of frequency estimation loop in order to mitigate large transients of frequency during sudden phase angle variations. This reduces the coupling of phase and frequency variables and allows tremendously faster and smoother estimation of both variables. The proposed adaptive mechanism can be applied to different PLL and adaptive notch-filter systems three of which including the enhanced PLL (EPLL), the synchronous reference frame PLL (SRF-PLL), and the second order generalized integrator frequency-locked loop (SOGI-FLL) are studied in this paper.