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

• Published in: IEEE transactions on energy conversion Vol. 36; no. 3; pp. 2047 - 2058
• Main Authors: Zhang, Chen, Foyen, Sjur, Suul, Jon Are, Molinas, Marta
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analytical models; Converters; Dynamic stability; Feedback; FLL; frequency feedback; Frequency locked loops; Frequency locking; LTP; Mathematical models; Numerical stability; Phase locked loops; Phase locked systems; PLL; Power system stability; Quadratures; SOGI; stability; Stability analysis; Synchronism; Synchronization
• ISSN: 0885-8969; 1558-0059
• DOI: 10.1109/TEC.2020.3041797

Second-order Generalized Integrator (SOGI)-based quadrature-signal-generator (QSG) together with either a phase-locked-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 article 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 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 article 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.