Qiu Tang

Siyu Guo

Yaonan Wang

CiteSeerX

Design of Power System Harmonic Measurement System  
Based on LabVIEW 
 
 
Qiu Tang, Yaonan Wang, Siyu Guo 
College of Electrical and Information Engineering, Hunan University, Changsha, China 
tangqiu07@hnu.cn, yaonan@hnu.cn, syguo@hotmail.com 
 
 
Abstract 
 
Harmonic measurement plays an important part in 
power systems. In this paper, a brief introduction on 
sources and harms of harmonics is given. A harmonic 
measurement method based on interpolating windowed 
FFT is proposed and analyzed. According to the 
analytic results, a multifunctional virtual instrument 
system for harmonic measurement of voltage and 
current signals is designed and implemented in 
LabVIEW environment. Furthermore, the function of 
remote transfer of measured results is implemented 
using the AppletVIEW Toolkit in LabVIEW adopting a 
B/S framework. Measurement results show the 
feasibility and validity of the system. 
 
 
1. Introduction 
 
Rapid growth in the industrial and civil electrical 
power load and the applications of various electrical 
and electronic equipment have been witnessed during 
the last years. With the surge of the total number and 
capacity of the nonlinear components, the electrical 
harmonic pollution is becoming more and more serious 
a problem, and has been a great threat to the safety of 
electric power systems and the national economy as a 
whole. Treatment of harmonics in power systems is 
thus a major concern of power system administrators 
as well as engineers [1]. In this task, the measurement 
of harmonics in power networks, as the basic data 
provider for harmonic analysis and control, is one of 
the issues of fundamental importance. 
Traditional methods of measuring power system 
harmonics employ power harmonic analyzers or 
software packages such as Matlab. However, these 
methods usually do not have powerful graphical 
programming capabilities and network functions for 
remote monitoring and control [2]. This paper presents 
a novel approach using a virtual instrument (VI) 
system with data transfer ability to perform power 
system harmonic measurement based on the 
interpolating windowed fast Fourier transform (FFT). 
The virtual instrument system is designed and 
implemented in LabVIEW environment. Harmonic 
parameters of three-phase voltage and current signals, 
such as the total harmonic distortion (THD) and the 
distortions of the 1st to the 13th harmonics can be 
measured. A B/S network scheme is adopted for data 
transfer, which is implemented using the AppletVIEW 
toolkit in LabVIEW. This data transfer option enables 
remote monitoring via the Internet Explorer. 
Experimental measurement results show accurate and 
stable measurement performance of the system.  
The paper is organized as follows. Section Ⅱ 
describes the sources and effects of power system 
harmonics. Section Ⅲ presents the harmonic analysis 
method with interpolating windowed FFT. Section Ⅳ 
gives the design of our harmonic measurement system 
using LabVIEW. In SectionⅤ, the method of remote 
data transfer is provided. Conclusions are given in 
Section Ⅵ. 
 
2. Sources and Effects of Power System 
Harmonics 
 
In ideal situation, the electric power in a network is 
supplied at a constant system frequency, known as the 
fundamental frequency, and at specified voltage 
magnitudes. In a realistic power system, however, the 
frequency and voltages are deviated from their 
designated values. The deviation of a wave form from 
its perfect sinusoid is generally expressed in terms of 
harmonics. Harmonics in a power system deteriorate 
the quality of electric energy and can result in 
communication interference, transformer overheating, 
or the malfunction of control devices, and so on [3, 4].  
There are two general categories of harmonic 
sources: saturable devices and power electronic 
devices [5]. Saturable devices produce harmonics due 
mainly to iron saturation, as is the case for 
transformers, rotating machines, and fluorescent 
lightings (with magnetic ballasts). Power electronic 
Fourth International Conference on Natural Computation
978-0-7695-3304-9/08 $25.00 © 2008 IEEE
DOI 
489
10.1109/ICNC.2008.230
loads draw power only during portions of the applied 
voltage waveform. Thus, the current drawn by the load 
is no longer sinusoidal and appears chopped or 
flattened. The non-sinusoidal current can interact with 
system impedance to give rise to voltage distortion 
and, in some cases, resonance. These power electronic 
loads include switch-mode power supplies, fluorescent 
lightings (with electronic ballasts), voltage source 
converters and equipments with non-linear 
components. Today, harmonics induced by non-linear 
power electronic loads present inefficient operations of 
local and global power supply systems. 
Harmonics have a number of effects on power 
system components and loads. Power system problems 
such as communication interference, heating, and 
solid-state device malfunctions can be the direct result 
of harmonics [2]. These problems are categorized and 
listed below. 
a) communication interference; 
b) excessive losses and heating in motors, 
capacitors, and transformers; 
c) degraded meter accuracy; 
d) blown capacitor fuses and failed capacitor; 
e) solid-state device malfunctions. 
 
3. Harmonic Analysis Method Using 
Interpolating Windowed FFT 
 
The discrete Fourier Transform (DFT) is a popular 
method in the harmonic analysis of electric power 
system. The amplitude, frequency, and phase of each 
spectral component can be evaluated by the fast 
Fourier transform (FFT). When the sampling frequency 
is two times greater than the highest constituent 
frequency, and the sampling period is an integer 
multiple of the signal period, the harmonic components 
can be determined by the FFT with high accuracy, 
efficiency and simplicity. 
The power system voltage and current can be 
expressed as  
)2cos()(
0
i
i
ii tfAtx ϕπ += ∑
∞
=
                    (1) 
Where if , iA , iϕ are the frequency, amplitude, and 
phase of the i-th harmonic component, respectively. 
 Considering a signal x(t) sampled with a sampling 
period Ts, we have the following sequence x(n). 
)cos()()(
0
i
i
iis nAnTxnx ϕω +== ∑
∞
=
          (2) 
where sii Tfπω 2=  
The DFT, or the discrete spectrum of the signal, is 
thus as follows: 
)](
2
)(
2
[)(
0
i
ji
i
j
i
ij ii e
A
e
A
eX ωωδωωδ ϕϕω −+−= −
∞
=
∑       (3) 
A weighting window function w(n) is then applied 
on x(n) to truncate the infinite sequence, and the 
following result is obtained:  
( ) ( ) ( ) 1,,1,0, −== Nnnwnxnxw                (4) 
Following the product theorem of the Fourier 
transform, the spectrum of )(nxw is given by 
( ) ( ) ( )ωωω jjjW eWeXeX ∗=  
)](
2
)(
2
[
0
i
ji
i
i
ji WeAWeA ii ωωωω ϕϕ ++−= −
∞
=
∑         (5) 
Where )(ωW is the spectrum of the window 
function )(nw . 
Considering the spectrum )( ωjw eX sampled with a 
sampling interval N/2πω =Δ , the discrete 
spectrum )(kX w is 
ωω
ω
Δ== k
j
ww eXkX )()(  
)],()([
20
i
i
i
ji kWkWe
A
i ωωωωϕ +Δ+−Δ= ∑
∞
=
 
k = 0, 1, 2,…N-1                  (6) 
Assuming the sampling rate is sufficiently higher 
than the Nyquist rate, and the truncation length of the 
signal is equal to an integer multiple of the signal 
period, the amplitude and phase of the k-th harmonic 
obtained from )(kX w are given as: 
ij
w e
A
kX ϕ
2
)( 0=                       (7) 
Because of the picket fence effect and energy 
leakage of DFT, however, the results are not precise 
and cannot fulfill the requirements of harmonic 
analysis. To improve the precision of the DFT 
algorithm, the windowed interpolating algorithm was 
proposed. The interpolation can eliminate the errors 
caused by picket fence effects [6], and the errors 
produced by energy leakage can be reduced through 
signal windowing [7]. Various window functions have 
been proposed [8], among which the Hanning window 
is a popular one because of its relatively low side lobe 
amplitudes, fast attenuation, significantly less energy 
leakage compared with rectangular windows, and the 
easiness to access. The Hanning window is defined as 
1,,1,0,2cos5.05.0)( −=⎟
⎠
⎞
⎜
⎝
⎛−= Nn
N
nnw π          (8) 
and its Fourier transform is 
)]2()2([25.0)(5.0)(
N
U
N
UUeW j πωπωωω ++−+=            (9) 
Where 
)
2
sin(/)
2
sin()( 2/ ωωω ω NeU j=               (10) 
After windowing, the spectrum of the sampled 
sequence )( ωjw eX is: 
490
πδδ
πδ
πω
ω
)1(2
)sin(
)(
22
mm
mm
k
j AeX
Nm −
≈
=
            (11) 
πδδδ
πδ
πω
ω
)2)(1(2
)sin(
)(
2)1( mmm
mm
k
j AeX
Nm −−
≈
+=
     (12) 
Let 
ππ ω
ω
ω
ωβ 22 )()( )1( NmNm k
j
k
j
m eXeX =+=
=     (13) 
and we have 
m
m
m β
β
δ
+
−
=
1
12
                        (14) 
From Equations (11) and (12), the amplitude and 
phase of the harmonic are as follows. 
)sin(
)1(2
)( 2
m
mm
k
j
m
Nm
eXA
πδ
δπδ
πω
ω −=
=
          (15) 
NNeXangle mk
j
m
Nm
/)1(])([ 2 −−= = πδϕ πω
ω        (16) 
 
4. Design of Harmonic Measurement 
System using LabVIEW 
 
The proposed method was implemented and 
integrated into our new virtual instrument developed in 
LabVIEW. The overall block diagram of the virtual 
harmonic measurement system is shown in Figure 1. 
The system consists of conditioning circuit, data 
acquisition component, processing computer, etc. 
Voltage and current signals of the power network are 
converted to 0~100V voltage and 0~5A current 
through voltage and current transformers, and are then 
forwarded to the conditioning circuit, where pre-
processing on the signals are performed, and the 
signals are transformed into -5~5V voltage input 
signals. The input signals are fed into the data 
acquisition card for conversion into digital signals, 
which are afterwards analyzed, computed, and output 
by the computer. Measurement results can be 
displayed, printed as reports, stored, or transferred to 
remote station. 
As the central component of the system, the 
systems software was completely implemented using 
the LabVIEW graphical programming language. 
The software can be divided into four main modules,  
Figure 1 Block diagram of the virtual power system 
harmonic measurement system 
being the data acquisition card driving program, data   
acquisition program, harmonic measuring program, 
and harmonic analyzing program. The data acquisition 
card driving program and data acquisition program 
execute continuous data acquisition of the voltage and 
current signals to be measured, and the harmonic 
measuring program and analyzing programs carry out 
filtering of the acquired signals and the computation of 
the harmonic parameters of the three-phase voltage and 
current signals. There are also some other auxiliary 
modules, such as the storing module, which uses the 
LV Report Generation Toolkit for Microsoft Office 
toolbox to store the measured results in MS Word 
documents, and the remote transfer module adopting 
the distributing tool AppletVIEW in LabVIEW to 
transfer measurement results to remote stations in B/S 
mode. The block diagram for the software system is 
shown in Figure 2. 
 
Figure 2 Block diagram of the system software 
The harmonic analyzing module is coded using a set 
of functions provided by LabVIEW. Measurement of 
THD, total distortions of even harmonics and odd 
harmonics, and the distortions of the 1st to the 13th 
harmonics of three-phase voltage and current signals 
are realized using the given interpolating windowed 
FFT algorithm. Before the data analysis, signals are 
pre-processed to reduce spectrum energy leakage by 
the Hanning window function (Hanning Window.vi) 
provided in LabVIEW’s Functions panel. The auto 
power spectrum function (Auto Power Spectrum.vi) is 
called to compute the auto power spectrum of the 
acquired temporal signals, followed by the call to the 
harmonic analyzing function (Harmonic Analyzer.vi) 
to obtain the frequencies and phases, THD, and each 
individual distortion of the harmonics. The THD and 
the n-th voltage harmonic distortion are given by 
Equations (17) and (18), respectively 
0
0
1
100×=
U
UTHDU                 (17) 
0
0
1
100×=
U
UTHD nUn               (18) 
Where 
∑
∞
=
=
2
2
n
nUU                           (19) 
491
Un is the effective voltage of the n-th harmonic, and U1 
is the effective voltage of the fundamental harmonic.  
Distortions of current harmonics can be computed 
in the same way. 
Measurement results for harmonics from the 
fundamental harmonic to the 13th harmonic are 
displayed on the VI panel of the system. Harmonic 
distortions of voltage and current signals are shown in 
Figure 3. 
 
(a) Distortions of voltage harmonics 
 
(b) Distortions of current harmonics 
Figure 3 LabVIEW VI panel for harmonic 
measurement results 
 
5. Remote Data Transfer 
 
For convenient remote monitoring and control, a 
remote data transfer module adopting B/S framework 
is implemented using AppletVIEW, the network 
distributing tool in LabVIEW. The client program is 
developed also through AppletVIEW. The combination 
of AppletVIEW and Java & TCP/IP enables users to 
interact with remote LabVIEW programs via network 
browsers such as Internet Explorer free from plug-ins, 
security setting up, and extra download and license. 
The virtual instrument system, standard Web server, 
and Web browser are thus incorporated to form a 
single system. 
The Java applet used by AppletVIEW is compatible 
to Java 1.1 standard, and can be run in any browser 
supporting the standard. The Applet Builder in 
AppletVIEW package generating the instrument 
interfaces can embed the Java applets created by 
LabVIEW VI panels into Web pages, resulting in 
virtual instruments in B/S mode. 
Besides, Applet Builder requires Java 1.4 JRE 
runtime environment, which means that a Java 1.4 
Runtime should be installed at the server end. By 
incorporating the proxy functions of AppletVIEW in 
LabVIEW platform at the server end, multi-user 
situations can be handled more elegantly. 
Our system is implemented using LabVIEW 7.1 and 
AppletVIEW 4.1. The remote measurement and 
control system program, Temp.vi, is coded in 
LabVIEW. Run Temp.vi, start AppletVIEW Server, 
and then start Applet Builder, Temp.viml and 
corresponding HTML code are created in Applet 
Builder. Save the HTML code in an html file, and 
refine the page through FrontPage or other Web page 
design software. 
When temperature.vi is opened and AppletVIEW is 
started at the server end, remote clients can easily 
actualize remote measurement and control through a 
browser. The interface appearing at the client end is as 
shown in Figure 4.  
 
Figure 4 Client interface of the remote harmonic 
measurement system based on AppletVIEW 
 
6. Conclusions 
 
Harmonic detection and measurement is becoming 
more and more intelligent, networked, multifunctional, 
and practical. The virtual harmonic measurement 
system designed in this paper is of the following 
advantages: the simplicity of the system hardware, 
user-friendly interfaces, easy-to-use options, 
continuous or timed measurement of the amplitudes, 
phases, THD, and distortions of the fundamental 
harmonic and other harmonics of voltage and current 
signals in power systems. In addition to the functions 
of traditional harmonic measurement system, further 
software implementation enables the remote transfer, 
wave form display, numeric display and storing of the 
measurement results of voltage and current signals. 
The application results show the feasibility and 
veracity of the system. By sufficiently exploiting the 
capabilities of the latest computer technologies and 
measurement/control technologies, virtual instruments 
492
realize and enrich the functions of traditional 
instruments. Power system harmonic measurement 
based on virtual instruments is now an obvious 
development direction. 
 
References 
 
[1] J. Arrillaga, D.A.Bradley, and P. S. Bodger, Power 
System Harmonics, New York: John Wiley ＆ Sons, 1985, 
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graghical programming tool”, Proceedings of the IEEE 
Conference on Cybernetics and Intelligent System, 
Singapore, 1-3 December, 2004, pp.885-889. 
[3] A. Gonzalez and J. C. MeCall, “Design of filters to 
reduce harmonic distortion in industrial power system”, 
IEEE Tran. Ind Appl., IA-23(3), 1987, pp.504-511. 
[4] J. R. Subjak and J. S. McQuilkin, “Harmonics-causes, 
effects, measurements, and analysis:update”, IEEE Trans. 
Ind. Appl.,  26(6), 1990, pp.1034-1042. 
[5] W. M. Grady and Surya Santoso, “Understanding power 
system harmonics”, IEEE Power Engineering Review, 
November 2001, pp.8-11. 
[6] V. K. Jain, W. L. Collins, and D. C. Davis, “High-
accuracy analog measurements via interpolated FFT”, 
IEEE Trans. Instrum. Meas., vol.28, pp.226-232, 1979. 
[7] T. Grandke, “Interpolating algorithms for discrete Fourier 
transforms of weighted signals”, IEEE Trans. Instrum. 
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[8] Zhang Fu-sheng, Geng Zhong-xing, Ge Yao-zhong, “FFT 
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Design of Power System Harmonic Measurement System Based on LabVIEW

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Design of Power System Harmonic Measurement System Based on LabVIEW

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