Synchronization Stability Analysis of SRF-PLL and DSOGI-PLL Using Port-Hamiltonian Framework

This article proposes port-Hamiltonian (pH) stability analysis of synchronous reference frame-phase-locked loop (SRF-PLL) and double second-order generalized integrator-PLL (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 interactions with the converter controllers under nonideal operating conditions. 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 synchronization 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.