Modeling and Analysis of SOGI-PLL/FLL-Based Synchronization Units: Stability Impacts of Different Frequency-Feedback Paths

Second-order Generalized Integrator (SOGI)-based quadrature-signal-generator (QSG) together with either a phase-locked-loop (PLL) or frequency-locked-loop (FLL) constitute two types of typical synchronization units (i.e., SOGI-PLL and -FLL) that have been widely used in grid-tied converter systems. This article will reveal clarify the stability issue these arising from different implementations frequency-feedback-path (FFP) connecting SOGI-QSG PLL/FLL. In this regard, four FFP be discussed. Although not affect steady-state frequency adaptation, their dynamical effects on small-signal SOGI-PLL/FLL remain concealed. To end, present comprehensive assessment comparative analysis focusing issue. extend applicability accuracy discussions, all analyses fulfilled by using parameter space-oriented method formulated linear-time periodic (LTP) framework. The obtained results are verified time-domain simulations, main findings further interpreted appropriate analytical models.