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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 phaselocked-loop (PLL) or a 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 paper will reveal and clarify the stability issue of these two
synchronization units arising from different implementations of
the frequency-feedback-path (FFP) connecting the SOGI-QSG
and the PLL/FLL. In this regard, four types of FFP
implementations that are frequently seen in the literature will be
discussed. Although different implementations of the FFP will not
affect the steady-state frequency adaptation, their dynamical
effects on the small-signal stability of SOGI-PLL/FLL remain
concealed. To this end, this paper will present a comprehensive
stability assessment and comparative analysis of SOGI-PLL/FLL
focusing on the FFP issue. To extend the applicability and
accuracy of discussions, all the analyses will be fulfilled by using a
parameter space-oriented stability assessment method formulated
in the linear-time periodic (LTP) framework. The obtained results
are verified by time-domain simulations, and the main findings are
further interpreted by using appropriate analytical models.

Index Terms— FLL, PLL, synchronization, SOGI, stability,
LTP, frequency feedback.
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Academic article





  • Technical University of Denmark
  • Norwegian University of Science and Technology
  • SINTEF Energy Research / Energisystemer



Published in

IEEE transactions on energy conversion



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