Tampere University of Technology

TUTCRIS Research Portal

Online Frequency-Response Measurements of Grid-Connected Systems in Presence of Grid Harmonics and Unbalance

Research output: Contribution to journalArticleScientificpeer-review


Original languageEnglish
Pages (from-to)3343 - 3347
Number of pages5
JournalIEEE Transactions on Power Electronics
Issue number4
Early online date25 Sep 2019
Publication statusPublished - 2020
Publication typeA1 Journal article-refereed


Grid characteristics have a drastic impact on the stability and control performance of grid-connected systems. Because the grid conditions typically vary over time, online measurements are most desirable for the stability assessment, protection design, and control-system optimization of the systems. Previous studies have presented methods based on Fourier techniques and broadband sequences with which the frequency responses of the grid-connected systems, such as the grid impedance or inverter control loops, can be measured. However, online measurements under unbalanced grids with harmonic voltages have not been comprehensively considered. The present paper demonstrates how the previously applied online-measurement methods fail in the presence of unbalanced grid and voltage harmonics due to the spectral leakage caused by Fourier transform. This work also proposes a simple signal-design method to avoid the leakage. Experimental results based on a high-power grid-connected system are shown to demonstrate the effectiveness of the proposed method.

Publication forum classification