Power Quality Analysis Based on All-phase FFT
1
Zhang Yonghui,Chen Xi,Zhang Xiyuan
College of Information Science & Technology, Hainan University, Haikou, China
zhyhemail@163.com
Abstract- Based on the theory of all-phase
spectrum, this paper analyses frequency and
harmonics of power. All-phase time-shifting phase
difference correcting spectrum analysis is used to
correct the measurements of parameters of power
quality. All-phase FFT based spectrum analysis
and correction has better performance than
traditional methods by considering all complexions
of the input data. By analyzing the power signal
sampling data, it concludes that All-phase FFT
based spectrum analysis is more precise on
detecting higher harmonics and analyzing power
quality than classic FFT.
Key words: all-phase FFT; real frequency analysis;
real harmonic analysis
I. INTRODUCTION
Power system harmonic and power system
frequency are the important parameters of power
quality in China’s power systems. The power
frequency is 50Hz which regulated by
GB/T15945-1995 “power quality
-power system
frequency deviation allowable”. Power
frequency deviate value is 0.2Hz. If the capacity
is lesser, deviation can be eased to ±0.5Hz.
Research found that the waveform distortion and
noise interference can affect the precision of
frequency measurement and the noise disturb is
the main reason.
The presence of harmonics in a power
system will produce additional harmonic losses,
reducing the efficiency of electrical equipment.
Harmonic can make power line radiation and
even can cause a fire. The harmonics produce
mechanical vibration on the electric motor and
physical damage to aging cables insulation.
When people transfer signals in power system,
the background signal contains a large number
of harmonic components. It makes the
transmission very difficult, the information loss
in seriously situation.
The theory of all-phase spectrum with good
suppression of spectral leakage and high
accuracy estimation by considered the input
signal divided by all the circumstances. In the
case of no disturbance, analysis of all-phase FFT
spectral can retain phase information without
distortion. Due to the frequency and amplitude
linked directly by phase correction, the character
it provides a guarantee for accuracy measure for
frequency and amplitude. In this paper, time
shifting and phase difference correction method
has been used to measure the harmonic precisely
[2].
II. BASIC PRINCIPLE OF ALL -PHASE
SPECTRUM
The power supply current is three-phase AC,
frequency of AC is 50Hz, and the actual
waveform has other harmonics except
fundamental 50Hz. The harmonics of multiples
third has the largest component and most
harmful in the all harmonics. Harmonic
detection is the basic of harmonic treatment, so
harmonic accuracy measure is prior to the
harmonic control.
All-phase spectrum analysis need
preprocessing the data for all the sequence which
contain sample point x
0
and length is N, then
take the traditional FFT spectrum analysis and
window comprehensive treatment. It improved
the performance of spectral analysis by the
2010 International Conference on Intelligent System Design and Engineering Application
978-0-7695-4212-6/10 $26.00 © 2010 IEEE
DOI 10.1109/ISDEA.2010.162
69