This paper proposes port-Hamiltonian (pH) stability
analysis of Synchronous Reference Frame - Phase-Locked Loop
(SRF-PLL) and Double Second Order Generalised Integrator
- Phase-Locked Loop (DSOGI-PLL), while accounting for the
overlapping converter dynamics under low-inertia and weak-grid
scenarios. The main aim is to highlight the risk of PLL interac tions with the converter controllers under nonideal operating con ditions. The nonlinear pH models of SRF-PLL and DSOGI-PLL
are used to derive analytical stability criteria, which help monitor
the effect of PLL interactions on synchronisation stability. The
stability criteria are substantiated through MATLAB/Simulink
simulations on a 400 V Converter-Grid test system. It is shown
that the stability criteria derived based on time-scale separation
is inexact. In comparison, the proposed criteria, accounting for
converter dynamics, offer better stability predictions and match
closely with the simulation results.