This paper proposes a filtered-sequence phase-locked loop (FSPLL) structure for detection of the positive sequence in
three-phase systems. The structure includes the use of the Park
transformation and moving average filters (MAF). Performance
of the MAF is mathematically analyzed and represented in Bode
diagrams. The analysis allows a proper selection of the window
width of the optimal filter for its application in the dq transformed
variables. The proposed detector structure allows fast detection
of the grid voltage positive sequence (within one grid voltage cycle).
The MAF eliminates completely any oscillation multiple of the
frequency for which it is designed; thus, this algorithm is not affected
by the presence of imbalances or harmonics in the electrical
grid. Furthermore, the PLL includes a simple-frequency detector
that makes frequency adaptive the frequency depending blocks.
This guarantees the proper operation of the FSPLL under large
frequency changes. The performance of the entire PLL-based detector
is verified through simulation and experiment. It shows very
CitationRobles, E. [et al.]. Variable-Frequency Grid-Sequence Detector Based on a Quasi-Ideal Low-Pass Filter Stage and a Phase-Locked Loop. "IEEE transactions on power electronics", Setembre 2010, vol. 25, núm. 10, p. 2552-2563.
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