The VPF Harmonic Analysis Algorithm Based on Quasi-Synchronous DFT

Zhongjun Fu1, 3, Jianyu Wang1, *, Yun Ou2, Genyuan Zhou3, Feng'e Bai3, Xiaorong Zhao3
1 School of Automation, Nanjing University of Science and Technology, Nanjing, 210094 China
2 Changzhou Foreign Languages School, Changzhou 213017, China
3 School of Computer Engineering, Jiangsu University of Technology, Changzhou 213001, China

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© 2017 Fu et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the School of Automation, Nanjing University of Science and Technology, Nanjing, 210094 China, 200, Xiaolingwei Rd., Nanjing, 210094 China, Tel: +8613951716181; E-mail:



The main source of spectral leakage in Quasi-synchronous DFT (QSDFT) harmonic analysis is the short-range leakage resulting from the fluctuating signals.


The QSDFT discrete spectrum stretching theorem, as is demonstrated in this paper, shows that the peak in frequency domain changes synchronously with the signal frequency drift. Based on QSDFT, an improved algorithm—Variable Picket Fence (VPF) is proposed.


The VPF means the sampling position in the frequency domain will synchronously change with the signal frequency drift. In this way, we can accurately capture the spectrum peak, thereby inhibiting short-range spectral leakage. Hence signal frequency drift can be obtained by measuring the fundamental phase difference between the adjacent sample points.


Simulation and application results prove that this proposed algorithm increases the accuracy of harmonic analysis by inhibiting short-range spectral leakage efficiently in the range of 45 to 55HZ.

Keywords: Harmonic Analysis, Fourier Transforms, Power system parameter estimation, Spectral Analysis, Synchronization.