POWER QUALITY
HARMONICS ANALYSIS
AND REAL
MEASUREMENTS DATA

Edited by Gregorio Romero Rey
and Luisa Martinez Muneta

Power Quality Harmonics Analysis and Real Measurements Data
Edited by Gregorio Romero Rey and Luisa Martinez Muneta Published by InTech
Janeza Trdine 9, 51000 Rijeka, Croatia

Copyright © 2011 InTech
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Contents

Preface IX
Part 1 Measurements 1
Chapter 1 Electric Power Systems Harmonics
- Identification and Measurements 3
Soliman Abdelhady Soliman
and Ahmad Mohammad Alkandari
Chapter 2 On the Reliability of Real Measurement Data
for Assessing Power Quality Disturbances 69
Alexandre Brandao Nassif
Chapter 3 Voltage Harmonics Measuring Issues
in Medium Voltage Systems 89
Jarosław Łuszcz
Part 2 Converters 109
Chapter 4 Study of LCC Resonant Transistor DC / DC
Converter with Capacitive Output Filter 111
Nikolay Bankov, Aleksandar Vuchev and Georgi Terziyski
Chapter 5 Thermal Analysis of Power
Semiconductor Converters 131 Preface

Nowadays, the rapid growth of power electronics in industry and the presence of
products based on electronic components in enterprises, institutions, shops, small
businesses, residences, etc. and transport systems has been welcomed by the people
who already use it due to its increased productivity within all areas. The problem of
this increasing use of power electronics equipment is the important distortions
originated; the perfect AC power systems are a pure sinusoidal wave, both voltage
and current, but the ever-increasing existence of non-linear loads modify the
characteristics of voltage and current from the ideal sinusoidal wave. This deviation
from the ideal wave is reflected by the harmonics and, although its effects vary
depending on the type of load, it affects the efficiency of an electrical system and can
cause considerable damage to the systems and infrastructures. Logic and electronic
control circuits, among others, may be affected if the supply voltage has distortions,
leading to, for example, damage in the consumer equipment, and noise in the different
installations or unsafe working conditions. In other cases the harmonic current passes
through transmission lines and causes harmonic voltage on the loads connected at the
end of the line, but this will be dealt with in another book.
Ensuring optimal power quality after a good design and devices means productivity,
efficiency, competitiveness and profitability. Nevertheless, nobody can assure the
optimal power quality when there is a good design if the correct testing and working
process from the obtained data is not properly assured at every instant; this entails
processing the real data correctly. To ensure a precise measurement of the electrical
power quantities, different processing techniques are necessary. The possibilities range
from the design of the overall system to the testing and training of devices, checking
the influence of the final design and behaviour laws in a virtual environment similar to

of the output characteristics, as well as outlining the area of natural commutation of
the controllable switches. Finally, a laboratory prototype of the converter under
consideration is built after suggesting a methodology for designing it. Chapter 5
investigates the thermal behaviour of the power semiconductor as a component part of
the power converter (rectifier or inverter), and not as an isolated part, from different
structures of power rectifiers. To do this, the parametric simulations for the transient
thermal conditions of some typical power rectifiers are presented and the 3D thermal
modelling and simulations of a power device as main component of power converters
are described too.
Chapter 6 discusses the principle and control method of a Unified Power Quality
Conditioner (UPQC), mainly used in low-voltage low-capacity applications and effective
in reducing both harmonic voltage and harmonic current, but applied in this case to high
power nonlinear loads. In this UPQC, a shunt Active Power Filter (APF) is connected to
a series LC resonance circuit in grid fundamental frequency so as to make a shunt APF in
lower voltage and lower power, and uses a hybrid APF which includes a Passive Power
Filter (PPF). Chapter 7 summarizes the research of parallel and series resonances and
unifies the study providing a similar expression to the series resonance case, but
substantially improved for the parallel resonance case, and unique to their location. It is
completed with the analysis of the impact of the Steinmetz circuit inductor resistance on
the resonance and a sensitivity analysis of all variables involved in the location of the
parallel and series resonance. Finally, the chapter ends with several experimental tests to
validate the proposed expression and several examples of its application. Chapter 8
Preface XI

presents a generic stochastic analysis to model the effect of nonlinear electronic devices
in power distribution systems by using circuit models comprising several passive
current sources for the electronic devices. The chapter also analyzes different
combinations of loads and transmission lines and results in a method for performing the
primary estimations for the planning and dimensioning of power systems with the
flexibility of being able to choose the numbers of different devices.

Dra. Mª Luisa Martinez Muneta
Universidad Politécnica de Madrid
Spain


Part 1
Measurements

1
Electric Power Systems Harmonics -
Identification and Measurements
Soliman Abdelhady Soliman
1

and Ahmad Mohammad Alkandari
2

1
Misr University for Science and Technology,
2
College of Technological Studies,
1
Egypt
2
Kuwait
1. Introduction
The presence of non-linear loads and the increasing number of distributed generation power
systems (DGPS) in electrical grids contribute to change the characteristics of voltage and
current waveforms in power systems, which differ from pure sinusoidal constant amplitude
signals. Under these conditions advanced signal processing techniques are required for

Harmonic sources are divided into two categories:
1. Established and known
2. New and Future
A review of the literature indicates that the known sources of harmonics include:
1. Tooth ripple or ripples in the voltage waveform of rotating machines.
2. Variations in air-gap reluctance over synchronous machine pole pitch.
3. Flux distortion in the synchronous machine from sudden load changes.
4. Non-sinusoidal distribution of the flux in the air gap of synchronous machines.
5. Transformer magnetizing currents.
6. Network nonlinearities from loads such as rectifiers, inverters, welders, arc furnaces,
voltage controllers, frequency converters, etc.
While the established sources of harmonics are still present on the system, the power
network is also subjected to new harmonic sources:
1. Energy conservation measures, such as those for improved motor efficiency and load
matching, which employ power semiconductor devices and switching for their
operation. These devices often produce irregular voltage and current waveforms that
are rich in harmonics.
2. Motor control devices such as speed controls for traction.
3. High-voltage direct-current power conversion and transmission.
4. Interconnection of wind and solar power converters with distribution systems.
5. Static var compensators which have largely replaced synchronous condensors as
continuously variable-var sources.
6. The development and potentially wide use of electric vehicles that require a significant
amount of power rectification for battery charging.
7. The potential use of direct energy conversion devices, such as magneto-hydrodynamics,
storage batteries, and fuel cells that require dc/ac power converters.
8. Cyclo-converters used for low-speed high-torque machines.
9. Pulse-burst-modulated heating elements for large furnaces.
Today’s power system harmonic problems can be traced to a number of factors:
1. The substantial increase of nonlinear loads resulting from new technologies such as

microprocessor-controlled systems.
9. Interference with large motor controllers and power plant excitation systems. (Reported
to cause motor problems as well as non-uniform output.)
10. Mechanical oscillations of induction and synchronous machines.
11. Unstable operation of firing circuits based on zero voltage crossing detection or
latching.
These effects depend, of course, on the harmonic source, its location on the power system,
and the network characteristics that promote propagation of harmonics.
3. Estimation of harmonics and sub-harmonics; the static case
3.1 Time domain model [3]
In this model, it is assumed that the waveform under consideration consists of a
fundamental frequency component and harmonic components with order of integral
multiples of the fundamental frequency. It is also assumed that the frequency is known and
constant during the estimation period. Consider a non-sinusoidal voltage given by a
Fourier-type equation:

  
0
0
sin
N
nn
n
vt V n t





(1)

cos
nn n
xV

 (3a)

Power Quality Harmonics Analysis and Real Measurements Data

6
sin
nn n
yV


(3b)
Then, equation (2) can be written as



00
0
sin cos
N
nn
n
vt x n t y n t





21 2 22 2 22 1 2
2 1
12 21

N
N
m
mm mm mN m
N
y
at at a t
vt
x
at at a t
vt y
vt
at at a t
y










where the elements of the A matrix are the sine and cosine expansion of equation (4). In the
a’s vector form, equation (5) can be written as







vv
v
Zt At t



(6)
where
Z
v
(t) is m  1 vector of sampled voltage measurement, A(t) is m  (2N + 1) matrix of
measurement coefficients,

v
is (2N +1) vector to be estimated, 
v
(t) is m  1 error vector to
be minimized. The order of the matrix A(t) depends n the number of harmonics to be
estimated. Furthermore, the elements of the matrix
A(t) depend on the initial sampling time
t



(7)
where
1
() [ () ()] ()
TT
At AtAt At

 is the left pseudo inverse. Having obtained the
*
v

, the
magnitude of any harmonic of order
n can be calculated as

1
22
2
nnn
Vxn





; 1, ,nN

 (8)

t
n
n
vt Ve V n t








(10)
where
V
0
is the amplitude of decaying dc component at t = 0

Is the time constant of the decaying dc component
The exponential term in equation (10) can be expanded using Taylor series and its first two
terms can be used as

 
0
00
1
sin
N
nn
n

11 12 0 0
1
sin cos
N
nn
n
vt x tx x n t
y
nt


  

(13)
If the voltage v(t) is samples at a pre-selected rate t, then m sample would be obtained at t
1
,
t
2
= t
1
+ t, …, t
m
= 1 + (m – 1)t, in this case equation (13) becomes








Power Quality Harmonics Analysis and Real Measurements Data

8
Having obtained the parameters vector Y
*
, the harmonics magnitude and phase angle can be
obtained as

1
22
2
nnn
Vxy





(16)

1
tan
n
n
n
y
x




 
1
11
21
() cos cos cos
NM
tit
iiikkk
ik
ft Ae wt Ae wt B wt




 
 

 

 

(19)
where
A
1
, A
2
, …, A
N

frequency domain.