Grid-voltage Synchronization Algorithms Based on Phase-locked Loop and Frequency-locked Loop for Power Converters

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Journal Title
Journal ISSN
Volume Title
Sähkötekniikan korkeakoulu | Master's thesis
Date
2014-06-16
Department
Major/Subject
Electrical Drives
Mcode
S3016
Degree programme
EST - Master’s Programme in Electrical Engineering
Language
en
Pages
45+10
Series
Abstract
The purpose of this thesis is to study and find the appropriate grid-voltage synchronization method for grid-connected converters under different kinds of faults like phase unbalancing, harmonics, offset and voltage sags. The main purpose of grid-synchronization algorithms is to estimate the positive- and negative-sequence components of the utility voltage under unbalanced and distorted condition. The existing most advanced phase-locked loop (PLL) and frequency-locked loop (FLL) methods are well known method for grid-synchronization. The fundamental variable estimated by the PLL is the grid-phase angle, whereas the grid frequency is the one for the FLL. The most extended technique used for grid synchronization in three-phase three wire system is a synchronous reference frame PLL (SRF-PLL). The SRF-PLL works accurately during balanced condition, but cannot estimate voltage components during unbalanced condition. The Decoupled Double Synchronous Reference Frame PLL (DDSRF-PLL) is might be a substantiation solution for the estimation of the sequence components of the utility voltage under unbalanced condition. Another method based on the FLL, a double second-order generalized integrator FLL (DSOGI-FLL) has also the ability to detect the positive- and negative-sequence components of the utility voltage under unbalanced condition. DDSRF-PLL and DSOGI-FLL algorithms are tested under different kinds of faults and compared with each other. The results show that their performance under harmonic-distorted condition is not really acceptable. A new algorithm based on SRF-PLL, decoupled multiple synchronous reference frame PLL (DMSRF-PLL) might be a better solution for accurate detection of the positive- and negative-sequence voltage components under unbalanced and harmonic distortion condition.
Description
Supervisor
Hinkkanen, Marko
Keywords
decoupling network, frequency-locked loop, grid-connected converter, phase-locked loop, second order generalized integrator.
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