BRNO UNIVERSITY OF TECHNOLOGY
Faculty of Electrical Engineering and Communication
Doc. Dr. Ing. Pavol Bauer
RESEARCH AND EDUCATION OF POWER ELECTRONICS
IN 21ST CENTURY
VÝUKA A VÝZKUM VÝKONOVÉ ELEKTRONIKY V 21. STOLETÍ
TEZE PŘEDNÁŠKY K PROFESORSKÉMU JMENOVACÍMU ŘÍZENÍ
V OBORU
SILNOPROUDÁ ELEKTROTECHNIKA A ELEKTROENERGETIKA
BRNO 2007
Keywords
Power electronics, E-learning, energy storage, renewable energy, multiobjective optimization,
power electronics for power systems, simulation
Klíčová slova
Výkonová elektronika, E-learning, akumulátor - zásobník energie, obnovitelné zdroje elektrické
energie, víceobjektová optimalizace, výkonová elektronika v energetice, simulace
© Pavol Bauer, 2007
ISBN 978-80-214-3553-7
ISSN 1213-418X
CONTENTS
1 INTRODUCTION......................................................................................................................... 5
2 EDUCATION OF POWER ELECTRONICS .............................................................................. 5
2.1
INTRODUCTION ............................................................................................................... 5
2.1.1 Shift from teaching oriented towards learning oriented education. ......................... 6
2.2
ENERGY CHALLENGE PROJECT................................................................................... 7
2.2.1 Specific objectives for the “Electrical Energy” project ........................................... 7
2.2.2 The “Electrical Energy” project............................................................................... 8
2.2.3 Evaluation of the educational objectives ................................................................. 8
2.3
INTERACTIVE ANIMATIONS ......................................................................................... 9
2.4
EXPERIMENTS ................................................................................................................ 10
2.5
FUTURE CHALLENGES................................................................................................. 12
3 RESEARCH OF POWER ELECTRONICS............................................................................... 12
3.1
Efficiency and power density increase of power conversion............................................. 14
3.1.1 New semiconductor devices, soft switching .......................................................... 14
3.1.2 Electro-magneto-thermal-mechanical integration.................................................. 14
3.1.3 Optimized design based on multiobjective optimization and genetic algorithm ... 15
3.1.4 Power management strategies for generator-set with energy storage for 4Qload . 17
3.2
POWER ELECTRONICS FOR RENEWABLE ENERGY.............................................. 18
3.3
POWER ELECTRONICS FOR POWER SYSTEMS....................................................... 19
3.3.1 Electronic tap changer............................................................................................ 20
3.4
SIMULATION OF POWER ELECTRONICS.................................................................. 22
3.4.1 Easy visualization of Simulation results ................................................................ 22
3.4.2 Open Interface for Integrated Simulation .............................................................. 23
4 CONCLUDING REMARKS ...................................................................................................... 24
5 REFERENCES............................................................................................................................ 25
3
Curriculum Vitae
Name:
Date of birth:
Place of birth:
Marital status:
Nationality:
e-mail:
Pavol Bauer, Doc.Dr.Ing.
January 9, 1961
Kosice
Married
Slovak, Dutch
p.bauer@tudelft.nl
Education and degrees:
1976-1980
Secondary school (Gymnasium), Kosice
1980-1985
Technical University of Kosice, Slovakia,
Faculty of Electrical Engineering, specialization Power Electronics
1995
PhD degree at University of Technology in Delft
2005
Doc. (Assoc. Prof.) , Brno University of Technology
Awards:
2007
2007
2006
IEEE Senior member
Medal of the Dean FEI TU Kosice
IEEE W.M. Portnoy prize paper award
Professional experience:
1997 – 2007
Docent, Delft University of Technology
2006 – 2007
Technical University Kosice
2002 - 2003
KEMA Arnhem- industrial experience, part time
1995 - 1997
Researcher, Delft University of Technology
1990 – 1994
PhD student, Delft University of Technology
1986 – 1990
Technical University Kosice, Slovakia
Publication activity
Over 200 publications, author or co-author of 5 books, 35 journal papers, international patent in
40 countries, 155 papers at the international conferences, 7 Tutorial notes.
List of research projects for the industry and other research programs
We@sea, offshore wind parks, 2005-2009; Contactless energy transfer project, 2004-2008;
ERAO 2 (Dynamical model of the wind park), 2002-2004; Smarttrafo project, 2001;DOWEC
Project (Dutch Offshore Wind Energy Converter), 2001-2004; ERAO 1 Electrical infrastructure
of offshore wind park, 1999-2001; Power Electronics for Pulsed Electric Fields, 1999-2000;
Lagerwey windgenerator, 1998; Research project Nonsymmetrical Regulation of Transformers,
1997; Research project DC-flux in the Distribution Transformers, 1997; Power Electronics in
Electrical Power Engineering - FACTS and Custom Power, 1996; Industrial power converter
for transformer tap changer , 1994-1996; Dynamic Analysis of AC power Converters, 19901994
European Leonardo da Vinci projects
EDIPE E-learning Distance Interactive Practical Education «Project Number» CZ/06/B/F/PP168022, 2006-2008; INETELE (Interactive and Unified E-Based Education and Training in
Electrical
Engineering), 2002-2005; ELINA Training in Electrical Engineering
SK/98/2/05381/PI/II.1.1. c/CONT, 1999-2001
4
1
INTRODUCTION
Electric power is the muscle of modern industry and power electronics makes its utilization
smarter. In broad terms, the task of power electronics is to process and control the flow of electric
energy by supplying voltages and currents in a form that is optimally suited for user loads. Power
electronics deals with conversion and control of electrical power in the range of milli-watts to
Giga-watts with the help of power semiconductor switching devices. The focus in power
electronics is on conversion, efficiency of conversion and control of energy. A solid state power
electronic apparatus can be looked upon as a high-efficiency switched mode power amplifier,
where the efficiency may approach as high as 98 to 99 percent. Besides, the equipment is static,
free from audio noise, and has low cost, small size, high reliability and long life compared to
traditional equipment used before for similar functions [1].
The applications of power electronics may include dc and ac regulated power supplies, UPS
systems, electrochemical processes (such as electroplating, electrolysis, anodizing, metal refining,
etc.), generation of some chemical gases, heating and lighting control, electronic welding, power
line static VAR compensators (SVC, STATCOM), active harmonic filters (AHF), HVDC systems,
PV and fuel cell power conversion, solid state dc and ac circuit breakers, high frequency heating,
and motor drives. Motor drives area may include applications in computers and peripherals,
robotics, solid state starters for motors, transportation (Electric Vehicle, Hybrid Vehicle, subway,
etc.), home appliances, paper and textile mills, wind generation system, air-conditioning and heat
pumps, rolling and cement mills, machine tools and robotics, pumps and compressors, ship
propulsion, etc. Besides applications in energy systems and industrial automation, power
electronics is now playing a significant role in global energy conservation. In spite of all the
applications power electronics is “invisible technology”, because is not in the centre of attention
and publicity. At the same time it is “enabling technology” which enables that the mentioned can
happen.
This thesis is divided into two parts. The first part deals with education of power electronics
and the second explores research of power electronics. The aim is to show the authors contribution
in the field of power electronics as well as some future trends.
2
EDUCATION OF POWER ELECTRONICS
2.1
INTRODUCTION
The changing world and fast advance in power electronics requires necessary changes in Power
Electronics education too. The increasing number of contributions at the Power Electronics
conferences proves that the changes in education are in focus of many. It concerns theoretical
(lectures) as well as practical part of the education. My main focus in recent years was the use of
the new media (interactive E-learning ), problem based and project organized learning as the
possible ways to improve the quality of the education [2][3][4][5][6][7][9][10].
Traditionally, in the development of engineering education the key objective was to enable the
teacher to convey knowledge and insight to the students. The main element was (and still often is)
the lecture where the teacher explains, gives examples, shows calculations, discuss mathematical
derivations etc. The accent is on the oral communication, which was supported by on-line hand
written messages using the blackboard and chalk. Due to the low speed of hand writing students
had some (but often not enough) time to try and understand what was going on.
With increasing complexity of the systems to be discussed (more dimensions, dynamical
structures and interactions) teachers began to feel hampered by the speed limitations of
handwriting on the blackboard. They adopted the use of the overhead projector with great
5
enthusiasm, since this enabled them to do a lot of the writing in the preparatory phase of the
lecture. Also students appreciated this, since the, often unclear) handwriting was replaced by wellstructured and clearly readable notes. However, what was projected so easily was still hard to
understand, in particular since the pace of dealing with subjects was increased. A next problem for
teachers was how to convey dynamical structures and interactions. The use of animations (inserted
in power point presentations) seemed to be a solution. But again, from the students’ point of view,
the improvement was only partial.
The conclusion is, that in the design of the education the accent was on the teaching
(particularly the preparation), which leads to beautiful lectures with a disappointing learning yield.
What may be even more serious is, that students got demotivated, since they felt themselves to be
unsuited for subject, they experienced to be too difficult for them. The advance in the teaching
method does not automatically yield better understanding. New advances in the teaching method
allow that more material in the same time is presented. The lectures often happen in the fast tempo
with less time to comprehend (Fig.1). Obviously, the problems mentioned above have been
identified. The introduction of electronic appliances (e.g. computers, networks with connected
student laptops etc.) has facilitated the introduction of interactive teaching and learning
environments. Computer animations were developed so that students can more or less repeat the
demonstrations as given during lectures or even during the lectures [3]. While maintaining lectures
as the primary educational activity, problem and project oriented laboratory exercises have been
introduced [2].
y
x
2 XY
3
2 XY
3
z
ZW
ZW
w
2 XY
3
y
x
2
XY
3
z
ZW
w
?
??
???
Fig. 1Teaching method development
TABLE 1
BLOOM’S TAXONOMICAL LEVELS OF INTELLECTUAL BEHAVIOR IMPORTANT TO LEARNING
Level
Recalling and remembering the information
1
Knowledge
2
Comprehension Explaining the meaning of the information.
3
Application
4
5
Analysis
Synthesis
6
Evaluation
2.1.1
Use of information, solving of problems using required skills or
knowledge.
Breaking down a whole into components.
Putting parts together to create a new and integrated whole.
Making judgments about the merits of ideas, verifying value of
evidence, recognizing subjectivity.
Shift from teaching oriented towards learning oriented education
Traditionally, the main objective was that the students acquired knowledge. The assessment
was based on testing whether the students could reproduce the acquired knowledge. By the end of
the last century engineering educators began to realize, that the demands from industry had
6
changed and that there should be given more emphasis to skills and (deep) understanding rather
than to knowledge. Presently, the main objective of teaching is the development of student skills.
This means that the teacher is a coach in the process of the student development. Obviously, this
has its implications on assessment which has to be different, as has been discussed in [2].
Taxonomical levels of intellectual behaviour important to learning are listed in Table 1 [6]. In this
work six levels (Bloom’s levels) within the cognitive domain are identified. Use of the new media
(interactive E-learning ), problem based and project organized learning are the possible ways to
improve the quality of the education and bring higher levels of understanding and learning. We
introduced a web based learning tool for power electronics and two project oriented labs related to
power electronics education: problem based learning in the first year of study (Energy Challenge
project) and the design oriented practical for the fourth year of study as a supplement to lectures of
power Electronics.
2.2
ENERGY CHALLENGE PROJECT
The first year curricula in engineering consist of numerous and often mutually isolated courses.
Students appear to have great difficulty in understanding the relation of the course contents and the
field they have chosen when they started. This often leads to a lack of motivation. Furthermore, in
the first year engineering students often are more trained in analysis rather than synthesis. Finally,
typical engineering skills such as creativity, communication, teamwork etc. appear to be less
emphasised as the ‘hard issues’ such as mathematics and physics.
The other importance of the project is that fresh students get involved in power electronics something they do not have any experience with in contrary to computer technique, telecom or
information technology. This way the energy technique and particularly power electronics will be
more attractive to the next generation of the students
The mentioned problem is solved by introducing a ‘course’ in the format of small working
groups, which run throughout the first year. The groups carry out small projects and a tutor with an
advisory role supervises them. One of the themes of the project is so called “Energy Challenge“. It
is compulsory for all first year students. The pedagogic philosophy can be best described as ‘teach
me how to do it myself’.
2.2.1
Specific objectives for the “Electrical Energy” project
The image of power engineering is of one traditional, not developing and old fashioned field.
Power Electronics in particular is not known at all. Many students can not even give any answer to
the question what power electronics is and what it studies.
The selection for a direction of the study is however made after second or third year. The
tendency today is that students select subjects they are familiar with such as computer technique,
telecommunication and information technology. This choice has little to do with the actual market
situation and to the needs of the society. Our project can positively contribute to that selection in
benefit of power electronics. The specific objectives are to:
• Propagate energy technique specifically power electronics and to positively influence the
direction and choice of the study for this subject.
• Propagate the renewable energy sources and to place them in context of the power
electronics
• To learn to think in terms of energy and also to effectively deal with the energy. The young
generation can nowadays think in terms of bites and bytes but not in the terms of energy and
most important in terms of amount of energy. The physical understanding of amount of
energy needed for a simple task such as the one described next in the project is beyond the
expertise of most of the students.
The key issues of the educational objectives of this module are:
7
•
•
•
•
•
•
Learning to think in alternatives,
Learning that in real life there are always more solutions to problem than just one,
Learning to evaluate alternative solutions by first formulating criteria,
Learning to think in terms of functions, rather than implementations,
Learning to use knowledge and skills as a means rather than a goal,
Learning to perceive technology in a context.
2.2.2
The “Electrical Energy” project
To meet the general and specific objectives of the project a simple assignment was defined [2].
There is a need to get water from the drain, which is 1 meter deep. The drain is located in a remote
place, in area where no source of electricity is available. As a tool there is a crane with basket or a
water pump available. Available sources of energy are sun or wind energy that is both available for
a limited time interval. The designed system could use any of the two available energy sources
with any of the two loads, viz. the crane and the pump (Fig. 2, Fig.3). There are thus basically four
different combinations. Taking into consideration the rest of the building blocs (dc-dc converter,
energy storage) the number of possible combinations of connection of components (building
blocs) is even larger.
The crane and pump are selected to show the importance of effectiveness of components in an
Electric Drive. Good understanding of the component but also creativity in selecting the optimal
working point in the complex system is here the key point. The power converters (up/down
chopper or dc-dc converter) place power electronics in the context of a larger energy system.
Straightforward linking of any of the two energy sources to the loads does not lead to satisfactory
results because of the mismatch between these sources and the loads. This latter fact is essential.
Therefore, the need of energy conversion becomes apparent. The application of power electronics
conversion is consequently introduced in a natural way. The up/down chopper can change voltage
from 3-25 V to a voltage of 3-50 V. The detailed understanding of the power converter operation
is beyond the expertise and expectation of this project and its function is explained by a simple
imagination of a ‘dc-dc transformer’ able to change voltage and current.
sun
load
pump
crane
wind
Fig. 2: Available sources and load
2.2.3
Fig. 3: Solar cells, wind-generator, dc-dc
converter, crane
Evaluation of the educational objectives
Every group obtained a different solution with a different result. These results in a different
amount of water obtained from the drain. The students learn to think in alternatives and learn that
in real life there are always more solutions to problem than just one. We learned the students to
evaluate alternative solutions by first formulating criteria such as power, energy, time, and voltage,
8
current. Without this many measurements prove to be at the end unusable for the ultimate system
design. The students learn to use knowledge and skills as a means rather than as a goal. The goal is
to get water from the drain the knowledge about the components is only a means of obtaining it.
Specific knowledge about power and energy as well as knowledge about the components e.g.
converter is required. To obtain this knowledge certain skills such as experience with
measurements and measurement technique is necessary. Evaluation of alternative solutions based
on formulated criteria is the essential part of the process. As already mentioned the students learn
to perceive technology in a context of a larger project.
2.3
INTERACTIVE ANIMATIONS
Learning or teaching of a technical subject is often difficult because there are a large number of
possible reactions of a system to parameter changes. If the same dynamics is presented in the form
of a short movie, the dynamic system behaviour can be explained much easier in many cases. We
used animation during simulation that opens up new possibilities for teachers and enables student
to avoid a passive watching the display at learning and pushes him to active participate in the
learning process. Here, interactive animation might help a lot - its utilization in simulation enables
to create an interactive training environment, to replace (partially) the physical laboratories. By
interactive animations the knowledge and understanding are challenged (Table 1). The criteria for
interactive animations are following [3][4][5][6][7]:
• due to multi-dimensional character of the systems, a high degree of interactivity should be
provided, e.g. if simulations or computer-animations are used, the students should have a
possibility to freeze the time or even reverse the time so as to study the causal relation
between different phenomena and states of the circuit under study,
• the e-learning support system should be developed in such a way that it would allow
students to acquire a deep insight into the complex and dynamic interactions of a number of
parameters in power electronic systems,
• the e-learning system should be structured in such way that the learning proceeds with
increased complexity (hierarchical approach),
• the system should give a qualitative impression of level of different quantities,
• the students should get motivation to study these systems in more detail, so as to become
skilled in designing such systems themselves,
• the system should allow a self-assessment of student learning,
• the system should allow including assignments as well as individual assessments.
When studying a certain power electronic circuit, the first question of the student is always for
the different current paths in dependency of the switching states and certain impressed currents
and voltages. With traditional teaching the current paths are drawn using different colours into
some figures of the power circuit, or the teacher’s present slide-shows in the classroom. We used
the approach of interactive animations. Different visualization principles for explaining power
electronic circuits are summarized in [6]. To illustrate the ideas mentioned above, two examples
are shown in Fig. 4. The chain circuit (Fig. 4a) represents a straightforward approach to the
realization of a multi-level converter for use in high power applications without the need for
magnetic combining circuitry and complex transformer arrangement. The animation in Fig. 4a
shows the current path (dotted line) of a chain converter in the interval of maximum output voltage
and positive current. With the slide of the cursor the current path for the other two voltage levels
and different current is shown. With the change of the conduction angle the output voltage level is
varied with fast response. The square wave generation principle shown in Fig. 4b is a basic
switching strategy used for high power converters. Detailed explanation of the circuit behaviour is
contained in the associated secondary screen. The continuously running animation was replaced by
9
a static one where the cursor (vertical line in the time diagram) that can be shifted in time by the
lecturer. This solution gives a possibility to explain circuit behaviour given by switching states of
the power semiconductor devices in the required time instant.
a)
b)
Fig. 4 Screens to demonstrate switching states in power electronics converters: a) A singlephase structure of an m-level cascade inverter. b) Square wave switching in the voltage source
inverter
The following examples come from the module Simulation of Power Electronics. Fig. 5a shows
comparison of different integration methods.
a)
b)
Fig. 5 a) Comparison of integration methods; b) State space model chapter.
The equations describing the circuit are changing according the switching state
This knowledge is essential for proper and effective simulation. The integration step can be
changed by moving the slider on the interactive animation and the accuracy is shown for each
method. At the same time the accuracy is shown graphically too. In the next example a state space
model of a power converter is explained
2.4
EXPERIMENTS
Experiments in traditional physics instruction are used as lecture demonstrations, high-school
classroom demonstrations, and as laboratory experiments. There are two pedagogical techniques
10
used for lecture demonstrations. In a traditional course, students observe an experiment and then
the instructor explains what happened and why. In reformed instruction, students predict what is
going to happen before the experiment, and then reconcile their predictions with the observations. t
It is crucial to let students have real practice.
The real experiment gives the students a sense of
practical testing and they can also see the
Guest 1
influence of the second/higher order effect, real
User
Guest n
time effects, effect of parasitic which is difficult
or impossible to be simulated perfectly. The
reason is that the simulation is always based on
Internet
more or less simplified model. However to build
an experiment is expensive. It is impossible for
data
an educational institute to have the complete
control
scale of experiments. The hardware experiment
Measuring and
should therefore be redesigned such that they
web server
also can be accessed in the Web [9]. This way
the advance in ICT will be combined with the
real world. The proposed virtual (distance)
GPIB interface
laboratory is not a web-based simulation. It is a
real electro-technical experiment conducted in
the laboratory but remotely controlled and
Oscilloscope Oscilloscope
monitored by web-based tools. The experiment
is either conducted online or based on recorded
Control power
values. It allows students to perform experiment
supply
Web camera
safely without any guidance. They can also
experience the appearance of the measurement
Measured circuit
instrument, the electronic components and many
Fig. 6 E-learning and experiments
more factors such as lay-out.
The experiments should be not only analysis oriented (to measure and see the results) but also
synthesis oriented. It should involve a design aspect. Therefore the measurements are designed and
implemented as a project with leading idea and clear targets [9] . The goal is to approach higher
level as depicted in Bloom’s diagram (Table1) and namely application, analysis and synthesis.
Measuring
instrument
Relays
switch
Power
Power
Fig. 7 DelftWebLab system and measuring points
11
2.5
FUTURE CHALLENGES
E-learning has introduced a new access to engineering subjects learning. Interactive animation
and simulation enable to create interactive training environment and partly to replace laboratories
(performing little experiments and system analysis). However the danger is that instead of deep
understanding and physical background, the students could memorize the visualized results. These
tools therefore cannot perform to stand alone education and they must be part of complete
curricula. Most of the interactive tools are focused on “what-if” simulations based on moving bars
to increase or decrease parameters of the circuits. In other words, the circuit situations are
performed without the use of real values for the circuit’s parameters. The sense for real values is
hereby very important. E-learning should be based on knowledge of components properties and
subsystems behaviour to perform synthesis of the final system and to design the new system based
on real (produced) components. E-learning should introduce a possibility of evaluation and
judgments about the merits of ideas, verifying value of evidence, recognizing subjectivity. The key
words are: conclude, criticize, decide, defend, determine, evaluate, dispute, judge, justify,
compare, rate, recommend, agree, appraise, prioritize, assess, estimate, deduct. E-learning should
introduce an active way towards project oriented learning. Instead of using a short problem as a
tool to deliver information and knowledge, a larger scope project should be used. It is well-suited
to the engineering disciplines and the way engineers in the industry work.
It should be noted however, that the E-learning and distance laboratories should enrich the
possibilities, and not completely replace the classical forms of education.
3
RESEARCH OF POWER ELECTRONICS
Fig. 8 The S curve adoption of an innovation
What is the future scenario in power electronics technology? Is it tending to saturate in the
traditional S curve (Fig.8) ? What are the directions of future research in this area? Generally, in
the most opinions, the answer is “yes” to the saturating trends of the technology. Carefully looking
into publications from the field of power electronics, it should be evident from recent publications
that by far the majority of these contributions are incremental in nature. In any technology
evolution, it is always difficult to predict its future course. Our past experience can only guide us
to extrapolate for the future. Any major invention alters the course of a technology, and spurs new
momentum of research activities. For example, the invention of transistors, and then the thyristors,
paved new era in power electronics. However, at the end of thyristor era (mid-1970’s), it was felt
that power electronics technology was getting saturated, and almost coming to a halt. Fortunately,
12
the advent of new and advanced power semiconductor devices opened new frontiers in power
electronics [1]. Of course, new converter topologies, advanced PWM techniques, powerful
processors and chips, personal computers, simulation techniques, etc. gave tremendous momentum
to the technology advancement.
Generally it can be said that a new momentum came from new semiconductor and/or new
application field. Let us evaluate these two aspects. Besides improvement of modern Si-based
power devices in terms of power ratings and characteristics, large band-gap devices (such as SiC)
are expected to bring renaissance in power electronics, as mentioned before. Although power
device is the heart of power electronics, the device research strictly does not fall into the
mainstream of power electronics technology. Devices, research in batteries, fuel cells, solar cells,
microchips, ultra-capacitors, etc. will also significantly impact power electronics evolution. At the
other end of the spectrum, intelligent control and estimation techniques, will significantly impact
power electronics evolution. Sensorless on-line precision estimation of machine variables,
particularly absolute position in synchronous machine and speed in induction machine near zero
frequency region, and estimation of equivalent circuit parameters for ac machines, require further
exploration although significant advances have been made recently in these areas. Sensorless
vector control of ac drives is the clear trend of the future. On-line diagnostics of converter and
machine faults along with utility power quality diagnosis, and the corresponding fault-tolerant
control are important research topics for reliability improvement of power electronic systems. The
control, estimation, monitoring, fault diagnostics, and fault-tolerant control will eventually be
implemented with a single chip. It is expected that converter, control and machine will be
eventually integrated as an intelligent machine of the future, particularly in the lower end of power
rating. There are, of course, myriads of application-oriented research topics.
(V)
voltage
current
(A)
10000
10000
8000
8000
gate turn-off thyristor
6000
6000
4000
4000
insulated gate
bipolar transistor
2000
2000
500
500
1980
jaar
2000
1990
Fig. 9 Power electronic switches
The chances and opportunities in power electronics in the coming years are in the following
areas:
• Efficiency and power density increase of power conversion,
13
• Power electronics for renewable energy,
• Power electronics for power systems.
These areas are further explored next and some results and authors contribution is showed (see
references in the text).
3.1
3.1.1
EFFICIENCY AND POWER DENSITY INCREASE OF POWER CONVERSION
New semiconductor devices, soft switching
As already mentioned a new device based on SiC will bring renaissance in power electronics.
The materials based on SiC have high breakdown electric field, and high electrical and thermal
conductivities compared to silicon. These properties permit devices with higher power capability
(with higher voltage), higher switching frequency and lower conduction drop in unipolar device
(which means automatically higher efficiency), higher junction temperature (350C), and better
radiation hardness. However, processing of these materials is very difficult and challenging. As
one of the bottlenecks of power electronics is thermal design, availability of high temperature
power devices will promote research activities in their applications in high temperature
environment demanding further research in control electronics, passive components, electrical
machines etc. It appears that power electronics based on SiC devices will bring renaissance in
future. Traditionally, converters with self-controlled devices, use simple hard switching principle.
However, hard switching has the inherent disadvantages of high switching loss (that decreases the
converter efficiency and burdens the cooling system), stresses the devices, and causes EMI
problems. To overcome these problems, soft-switching converters have been proposed [13][14].
Soft-switched converters generally require auxiliary resonance circuits and extra devices with
additional control complexity that can increase the converter cost, decrease reliability, and cause
extra losses that can adversely affect the converter efficiency. For these reasons, soft-switched
converters could not find much acceptance for all applications. Soft-switched power conversion,
however, is justified in high frequency link power conversion, where the load requires galvanic
isolation from the source through high frequency transformer.[14]
3.1.2
Electro-magneto-thermal-mechanical integration
The objective of research is to add more functionality to the printed circuit boards of low power
ac-dc power converters by incorporating capacitive and inductive functions into it, to improve the
physical components by making changes to the packaging and integrating of more than one
component in one package, and to adjust the shape and size of component packaging so that the
assembly method lends itself better to automated manufacturing [15][16][17]. The goal of the
miniaturisation of PCB-assembled power converters (increase of the power density) is achieved by:
• Removing all unused space (air) within the converter Exploiting the 3rd dimension for
component placement (Geometrical packaging / 3D puzzle ),
• Removing all excess materials and integrating the functionality of more than one
discrete component into one single component.
The converters on Fig.10 demonstrate means to deal with thermal issues and diverse
geometrical shapes by exploiting inherent features of the printed circuit board (PCB), such as
thermal layers and flexible PCB technology. Furthermore electromagnetic integration of passives
(Fig.11) enabled the realisation of embedded multifunctional structures such as the integrated
transformer in the enhanced converter design.
14
Fig. 10 Technology demonstrators built to demonstrate improvement in power densities and
thermal characteristics [17].
L, C, R layers
integrated into PCB
Capacitive
laminate
(C-ply®)
Inductive laminate
(MagLam®)
Resistive
laminate
(Ω-ply®)
Fig. 11 Electromagnetic integration
3.1.3
Optimized design based on multiobjective optimization and genetic algorithm
The design of complex engineering systems, such electrical drives and power electronics,
requires application of knowledge from several disciplines (multidisciplinary) of engineering
(electrical, mechanical, thermal). The interdisciplinary nature of complex systems design presents
challenges associated with modelling, simulation, computation time and integration of models
from different disciplines. There is a need to develop design methods that can model different
degrees of collaboration and help resolve the conflicts between different disciplines.
The rise of complexity of systems as well as the number of design parameters needed to be coordinated with each other in an optimal way have led to the necessity of using mathematical
modelling of system and application of optimisation techniques. Multiobjective optimisation is the
search for acceptable solutions to problems that incorporate multiple performance criteria. Genetic
algorithm is hereby used and a new biologically motivated algorithm is suggested [18].
Usually the objectives are in competition with one another and trade-off exists between the
objectives, where improvement in one objective cannot be achieved without deteriorating the
other. In the previous work such a new design method is developed and demonstrated on simple
15
example of a BLDC drive with minimum cogging torque, maximum efficiency and minimum
mass [19][20].
A power electronic converter is an assembly of electronic and other components that are
selected on the basis of their working principle, physical parameters and cost. The components
form the starting point of any design process. The development of a power electronic converter is
highly multi-disciplinary. The design of power electronics include: circuit/system analysis, thermal
analysis, EMI (electromagnetic interference) analysis, packaging, manufacturability and price. A
19 inch cabinet with a electric drive system has been drawn in Figure 12. The volume for the
active components is 1/3 of the total volume; 2/3 is needed for EMI and thermal management.
EMI filters
Damping R’s
Active
components
EMI filters
Fig. 12.Power electronic system with a lot of non-functional EMC and thermal components
Thermal and EMC requirements are usually in conflict in the design of power electronic
systems. The conflict leads to time and budget overruns in the design phase and – finally – to
systems in which many components do not play a role in the active circuitry. In industrial systems,
in general, less than half of the volume and mass is used for active circuitry, the remaining part is
due to thermal and EMC constraints such as dissipation of filter resonance dampers. The
conventional industrial design process does not yet allow an integrated circuit, thermal and EMI
design. The results of the proposed research will enable this. The resulting power conversion
systems will be much more compact, use significantly less material and will hereby be more
efficient. Additionally they will be designed in shorter time.
The goal of the future research is to make a first-time-right multi-physical design tool for power
electronics resulting in shorter time-to-market of new products. This concurrent design approach
can be achieved by following an object-oriented design methodology. Three aspects should be
addressed simultaneously:
• Object-oriented power electronics system integration (synthesis),
• EMI analysis and design,
• Thermo-electrical analysis and design.
16
3.1.4
Power management strategies for generator-set with energy storage for 4Q-load
Another way to increase the efficiency is the use of an energy storage for dynamic systems
especially for 4 quadrant loads. The diesel generators in small electricity grids can serve as an
example. The reason for low efficiency is twofold. First of all the efficiency of a diesel generator is
dependent on the ratio between the average power and the peak power of the generator. The
smaller this ratio, the lower the efficiency. Furthermore some loads can regenerate energy. In small
grids this energy is mostly not needed elsewhere and should be dissipated. A solution solving both
above mentioned problems is using an energy storage device in the system. This storage can be
used for peak shaving and storing regenerated energy. Six different power management strategies
are suggested: Only Generator, Peak Power Shaving, Dynamic Solution, Max On or Off, Average
Power and Only Storage. The implications of these algorithms are given for a typical case study.
Calculations show that the Max On or Off, Average Power and Only Storage methods save the
most energy. Calculation of the costs shows that adding an energy storage device lowers the cost
for all methods [21].
Fig. 13 System topology for generator with Liion HP battery
Fig. 14 System topology for generator with
Super capacitor
Energy
Storage
Bi-directional
DC/DC
variable f and V
ON/OFF
constant VDC=570 V
constant VAC=3x400 V/ 50 Hz
A
AC/DC
DC/AC
DC/DC
Filter
B
α
Di esel
Engin e
SGPM
D
D (duty)
Voltage
Control Unit
ω (i nstantaneous velocity)
Optimum c ontrol syste m of EGS
IL
(load curre n t)
ω p (required velocity )
Fig. 15. The generator-set system with peak power delivered to the dc-link of the ac-dc-ac
converter from a storage element
In another example the energy storage connected via a power electronic converter helps the
dynamics of the system. The engine-generator dynamics at a sudden load change (from low load to
high load) remains a challenge in case of variable speed diesel generator. The dynamic behaviour
17
analysis proves that the introduction of an energy storage element into the EGS with variableengine-speed concept eliminates this drawback [22][23][24]
3.2
POWER ELECTRONICS FOR RENEWABLE ENERGY
Renewable energy road map, an integral part of the Strategic European Energy Review [12],
sets out a long term vision for renewable energy sources in the EU. It proposes that the EU
establish a mandatory (legally binding) target of 20% for renewable energy's share of energy
consumption in the EU by 2020. However is this decision questionable from the taxpayer point of
view, it will mean a further boost for power electronics.The application of wind energy throughout
the world is thus expecting a fast growth especially offshore [25] . In this context, cost of wind
energy also plays an important role. The power electronics based electrical system concerns the
electrical power components between the generator shaft and the grid connection and the way
these components are interconnected and operated. Its function is to convert mechanical power
into electric power, to collect electric power from individual turbines, to transmit it to the shore
and to convert it to the appropriate voltage and frequency. The system consists amongst other of
generators, cables, transformers and power electronic converters. Systems are mainly characterized
by the type of the voltage (AC or DC) and the frequency (fixed or variable).
Fancy Horses
price
Talented Horses
T
T6
heat pump
photo voltaics
fG
imported biomass
biomass and waste
12 m/s
8
1
10
6
imported waterpower
Work Horses
wind at sea
0
1
n
n6
Winning Horses
applicability
Fig. 16 Renewable energy sources
Fig. 18 Individual variable speed systems with
back-to-back converters
Fig. 17 Generator and turbine characteristics.
Fig. 19 Individual variable speed systems
with multi-terminal DC..
A load flow model has been developed for the evaluation of thirteen different electrical
architectures for large offshore wind farms. Some of them are depicted in Fig. 18 and Fig. 19. Loss
and cost models of components were suggested [26]. In a case study, these architectures have been
evaluated for two wind farm sizes and two distances to shore (Fig.20) [27].
18
Fig. 20 Production, E-system price, E-losses and LPC of 100 MW systems at 20 km
3.3
POWER ELECTRONICS FOR POWER SYSTEMS
Power grid infrastructure in most countries in the world is in urgent need of modernization and
power electronics can play here an important role. Further it is the integration of dispersed
generation which requires new solutions. Electric utilities, and many of the manufacturing
industries they serve, are on the threshold of revolutionary change brought about by high-power
electronics. Electrical networks are currently evolving into more hybrid networks, including AC
and DC, with energy storage for individual households, office buildings, industry and utility
feeders to interface these different power concepts [28]. This energy-web concept is depicted in
Fig. 21. Distributed power resources include wind, solar, natural gas, petroleum, coal and even
pebble-bed nuclear energy. There is general consensus that the future power grid will need to be
smart and aware, fault tolerant and self healing, dynamically and statically controllable and asset
and energy efficient.
Developments in high power electronic devices and fast micro-controllers can be used to
control large amounts of power within the sophisticated electric power system. The application of
power electronics in high power AC transmission networks is internationally termed Flexible AC
Transmission Systems (FACTS). This technology increases the network options available to the
network planner and can provide viable alternatives to HVDC networks in some network
upgrades. The solutions for power quality are named custom power. FACTS electronic control
devices are costly and the reliability is relatively poor, therefore their low acceptance so far. The
development of new, relatively low-cost methods for power flow control and power quality
without sacrificing system reliability is central in the research attention. Two of such solutions
distributed FACTS and electronic tap changer are shown here.
Distributed FACTS perform instead of one single large device a large number of small
distributed, easy to manufacture devices. They are self powered by induction from the line,
attached to the line via a single turn transformer, float electrically on the transmission conductors,
and are controlled using wireless or power line communication techniques.
19
Factory
CHP
Central
Generation
Microturbine
Substation
Pumped Storage
Commercial
CHP
Decentralized
DER Dispatch
Data Centers
Wind
Storage
Fuel Cell
Flow Batteries
Flywheel
Photovoltaic
Residence
Fuel Cell Car
Fig. 21 Energy web concept
Further, since the series connection to the line (Fig.22) does not require supporting phase–
ground insulation, the distributed FACTS can therefore easily be applied at any transmission
voltage level [29].
Fig. 22 Distributed FACTS concept
3.3.1
Electronic tap changer
Tap changers of utility transformers is one of the new areas where power electronics finds its
way. Studies of the voltage behaviour in the Netherlands show that the voltages on the delivery
points in the network can vary extensively and differ depending on the location in the network.
20
Energetic savings appear in the network and with users if the grid delivers less excessive voltage.
To achieve a fast and continuous control of the transformer voltage and to design a static converter
one must be able to change the transformer taps under the full operation of the transformer and
achieve an on load tap changing. By pending at a high frequency between two taps under the full
operation of the transformer the continuous regulation of secondary voltage is achieved. Voltage
of the PWM modulated tap changed transformer is depicted in Fig.23. By changing the taps, the
transformer turn ratio changes too.
u [V]
L1
S
L2
[ms]
t
L tap
control
Fig. 23: Voltage of the PWM modulated tap changed transformer
Research and application of IGBT switched tap changer for 500 kVA 10kV to 400V
transformer is reported in many papers [30][31][32]. The switch S depicted in Fig. 23 is here
replaced by a semiconductor converter placed at the taps at the high voltage side (10kV). Because
there is no single semiconductor switch with this blocking capability, and series connection is not
considered, this problem has to be solved in a different way. By leaving one semiconductor switch
always on (and this way creating a conducting path in the phase), the voltage on the other switches
is limited only by the voltage of the taps. The maximum voltage to be blocked for a transformer
with 4 taps and a tap voltage of 250 V is assumed to be 1 kV (effective, top=1.41kV). The
switches thus do not need to block a 10 kV voltage. Since the switches have to stay under the
operation and conduct in the case of a short circuit at the secondary terminals of the transformer, at
least one pair of the switches (at one tap) has to be designed for high current (short circuit current).
For this purpose a crowbar is constructed.
Fig. 24: Breadboard of the electronic tap changed transformer and patents
There are two basic conditions for the switching cell: open line is not allowed (there has to be
always a conducting path), since it would result in 10kV on the semiconductor, on the other side
21
and overlap results in a short circuit of the tap. The so called smart commutation cell does not
allow neither so called “dead time commutation’ used by a voltage source inverter nor ‘overlap
current commutation’ used by current source converters [34].
The suggested solution is patented world wide [33] and currently an industrial product based on
the suggested design is available (Fig. 24).
3.4
SIMULATION OF POWER ELECTRONICS
Modern design of a power electronics system is often verified by simulation. There are several
circuit simulation packages in use and each of them has some strong and some weak features.
Standard demands for a simulation package are:
•
•
•
•
•
Fast simulation without convergence problems,
User friendly interface with schematic editor,
Multilevel modelling capability,
Detailed models of the semiconductor switches,
Link with modelling language (C/C++).
The best known simulation packages are Spice, Saber, Matlab/Simulink, Caspoc, Simplorer,
EMTP and there are many others. Nearly all of them fulfil the above mentioned requirements. One
of the latest development and directions in Power Electronic simulations are:
• Easy visualization of Simulation results [35][36],
• Open interface for data exchange for integrated simulation.
As power electronic and drive systems are getting more complex today, the simulation /
animation used is requiring more features. The main directions in the development of simulation
tools are the visualization of the simulation results and the requirement on the interface for the
integrated simulator. The integrated simulation approach is important because of the
multidisciplinary and compact integration of systems.
3.4.1
Easy visualization of Simulation results
Animation based on interactive simulation is a way to go deeper inside a problem. The use of a
general simulation tool is the only way to allow to go deeply inside the operating of a device and
to understand the dynamic interactions between the parameters. The simulation program, Caspoc
allows that the circuit is animated during the simulation. This gives insight in the behavior of the
circuit during its operation. It is possible to follow the current path and see which switches are
opening or closing. The voltage level is given numerically at each node, while a moving dashed
line indicates the direction of the current. The color of the nodes and the current path are
dependent on the level of the voltage and current. This visualizes the operation of the converter in
detail. The user can interact with the simulation/animation by changing parameters during the
simulation/animation and immediately see their influence on the circuit behavior.
The main features of power electronics system simulation are the large number of
simultaneously occurring variables i.e. voltages and currents, in particular:
• the way they vary with time,
• their polarities,
• their mutual dependency (in particular the causal relations),
• their relation to the state of the circuit,
• states of the individual switches,
22
•
control signals.
To perform a simulation of the more complex system requests from the designer to follow very
closely the simulation and run it more then once to understand the causal relations as summarized
above. The designer in that case sits behind the computer and waits for one or other instant
(action) to happen. Visualization of all variables becomes even more important. Therefore earlier
animation is added to the simulation program. To simplify the process of visualization it is
possible to use the so called ‘Freeze and go back feature’.
Fig. 25 Three level converter
The simulation results are stored in the computer and it is possible to use the time cursor and go
back with the time. The state of the all switches, control signals and currents and voltages is shown
again. The animation feature allows top following all the causal relations without sitting behind
the computer during the simulation itself. In Fig.25 such a visualized animation of a three level
converter, with freeze and go back feature is shown.
3.4.2
Open Interface for Integrated Simulation
Typical power electronics system analyses consist of many aspects and is multidisciplinary.
These are, for example, parameters of magnetic actuators, parameters and precise models of
semiconductor switches, electrical machine parameters, thermal effects, different control issues,
packaging and parasitic effects as a result of different layout, to name a few. Designers are usually
concentrating on one or more aspects, but the trend is clearly towards an integrated approach. The
power electronics simulator is central in this case. The interaction and data exchange with different
analysis and design tools is hereby necessary (Fig.26). Standard and open interface for data
exchange is demanded from simulation software.
23
Semiconductor
(Spice)
Electromagnetic
design
(Ansys,IES)
Machine design
and parameters
(Tesla)
Packaging
(Compare)
Power Electronics
Electrical Drives
Simulator
(Caspoc)
Thermal effects
and analysis
(Ansys)
Matlab/Simulink
Third party
products
Toolboxes
Fig. 26 Integrated simulation approach
4
CONCLUDING REMARKS
This publication is divided into two parts and starts with short survey of applications of power
electronics. Then, it gives a brief but comprehensive review of the recent advances in power
electronics education and the ways to make it more attractive. The trends of the E-learning and
respective areas of its application in power electronics have been highlighted, wherever possible.
A number of examples of E-learning tools have been included to supplement the general
discussion.
Performed research and applications show that power electronics is now established as a major
discipline in electrical engineering. It is now an indispensable tool for modern industrial
automation, high efficiency energy systems, and energy conservation, as discussed before. It can
play a dominant role in solving global environmental problem. In future, power electronics is
expected to influence effectively the industrial and energy policies of nations
24
5
REFERENCES
[1]
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Devices (SSID-2007) held in Sunplaza Hotel, Tokyo, Japan on June 29, 2007.
[2]
BAUER P., ROMPELMAN O.: The ''Energy Challenge" in Electrical Engineering
Education; European Journal of Engineering Education - EJEE Journal, December 2002,
Taylor&Francis, ISSN 0343-3797, p.339-347
[3]
BAUER P., KOLAR J.W.: Teaching Power Electronics in 21 century, European Power
Electronics and Drives Journal (EPE Journal),Vol.13,December 04/03, ISSN 0939-8368
[4]
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[5]
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of the IEE, Japan, Volume 126, No5, May 2006, ISSN 0913-6339
[6]
FEDAK V, BAUER P.: E-learning Concept for Electrical Engineering, International Review
of Electrical Engineering (IREE), ISSN: 1827- 6600 October 2006, pp.575-581
[7]
DUDRIK J., BAUER P.: 'New Methods in Teaching Power Electronics and Devices'
International Journal Engineering Education (IJEE), 2007, ISSN: 0949-149X
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BAUER P., FEDAK V, HAJEK V.: Practical Application of E-Learning in Electrical
Engineering, Innovations 2007, Chapter in the book, Innovations 2007 - World Innovations
in Engineering Education and Research (iNEER), ISBN 978-0-9741252-6-8
[9]
BAUER P., DUDAK J., MAGA D., HAJEK V,: Distance practical education for Power
Electronics, International Journal of Engineering Education (IJEE), 2007, ISSN: 0949-149X
[10] DROFENIK U., KOLAR, DUIJSEN VAN P., BAUER P.: New Web-Based Interactive ELearning in Power Electronics and Electrical Machines. IEEE Industry Application Society
Annual Meeting, 2001, Chicago; September 30 – October, 10.p., ISBN: 0-7803-7116-X
[11] BAUER P. FEDAK V.: E – learning for Power Electronics and Electrical Drives; ED&PE
International Conference, High Tatras, 24-26 September 2003, ISBN 80-89061-77-X
[12] Renewable Energy Road Map: Renewable energies in the 21st century: building a more
sustainable future, {SEC(2006) 1719},{SEC(2006) 1720},{SEC(2007) 12}, Brussels,
10.1.2007
[13] BAUER P, KLAASSENS J.B: "A Novel Control Principle for Parallel Resonant Voltage
Link Converters" ; IEEE Industry Application Society Annual Meeting, 1992, Oct. 4-9,
Westin Galleria, Houston, Texas, USA, pp.796-800
[14] KLAASSENS J.B, VAN WESENBEECK M. P. N., BAUER P.: "Soft Switching Power
Conversion" ; European Power Electronics and Drives Journal (EPE Journal), Brussels,
Sept. 1993, Vol. 3, No. 3, ISSN 0939-8368
25
[15] DE JONG E.C.W, FERREIRA J.A., BAUER P.: Thermal Design based on Surface
Temperature mapping, IEEE Power Electronic Letters, Vol 3, Issue 4, ISSN 1540-7985,
pp.125-130
[16] DE JONG E.C.W., FERREIRA J.A., BAUER P.: Design Techniques for Thermal
Management in Switch Mode Converters" IEEE Transactions on Industry Applications,
Volume 42, Number 6, Nov./Dec. 2006, ISBN 0093-9994
[17] DE JONG E.C.W., FERREIRA J.A.,BAUER P.: Towards the next level of PCB usage in
power electronic converters, IEEE Transaction on Power Electronics, accepted paper
[18] KUMAR, P., D.GOSPODARIC, BAUER P.; Improved Genetic Algorithm Inspired by
Biological Evolution; Journal SOFT COMPUTING, Volume 11, Number 10 / August, 2007
ISSN: 1432-7643; Springer Berlin / Heidelberg; pp.923-941
[19] KUMAR, P, BAUER P : Multi-Objective Optimization of Brushless DC Motor, European
Transaction on Electrical Power, Accepted paper 2008, 2007 John Wiley & Sons, Ltd
[20] KUMAR, P, BAUER P.: Multi-objective optimization for ED&PE; International conference
Electrical Drives and Power Electronics (ED&PE), High Tatras, Slovakia, September,
2007,ISBN 978-8073-867-9
[21] BAALBERGEN F.J., BAUER P. : Power Management Strategies for Generator-set with
Energy Storage for 4Q-load; Power Electronics Specialists Conference (PESC 2008),
submitted paper
[22] LEUCHTER J., BAUER P.: Efficiency Investigation of Electrical Generator-Converter Set,
Transactions on Industry Applications of the IEE, Japan, October 2007, ISSN 0913-6339
[23] LEUCHTER J., BAUER P., RERUCHA V, V. HAJEK: Dynamic Behaviour Modeling and
Verification of Advanced Electrical-Generator Set Concepts, IEEE Transaction on Industrial
Electronics, accepted paper
[24] LEUCHTER J., KURKA O, BAUER P., RERUCHA V.: New Generation of Mobile Power
Sources with Variable Speed, Journal of Electrical Engineering (JEE), ISSN 1335-3632,
vol. 57, no. 5, pp. 241-248, 2006.
[25] BAUER P., HAAN S.W.H.DE, DUBOIS M.R.:Introduction to Windenergy and Offshore
Windparks Problematic; PCIM 2003, Nurnberg; May 2003, ISBN 3-928643-37-1
[26] BAUER P., HAAN S.W.H.DE: Tool for Evaluation of Offshore Windpark: Models of the
Components;. European Power Electronics Conference EPE2001, Graz, 27-29 August
2001,10.p., ISBN:90-75815-06-9
[27] DAMEN M., BAUER P., HAAN S.W.H.DE, PIERIK J.,:Steady state electrical design,
power performance and economic modeling of offshore wind farms, European Power
Electronics and Drives Journal ( EPE Journal), ISSN 0939-8368
26
[28] ENSLIN J.H.R; BAUER P.;GROEMAN F.KNIJP J.: Status and operational experiences
with FACTS devices in high voltage networks, Journal RFBE: Revue E tijdschrift, No 3,
2005; ISSN 07700024
[29] DIVAN D., JOHAL H.: Distributed FACTS - A New Concept for Realizing Grid Power
Flow Control, IEEE Transactions on Power Electronics, Vol.22, NO6, November
2007,pp.2253-2260
[30] BAUER P., HAAN S.W.H. DE, Electronic Tap Changer for 500kVA/ 10kV Distribution
Transformer: Design, Experimental Results and Impact in Distribution Networks, IEEE
Industry Application Society Annual Meeting, St. Louis, October 1998
[31] BAUER P., HAAN S.W.H. DE, PAAP G.C.: Electronic Tap Changer for 10 kV Distribution
Transformer, European Power Electronics Conference, EPE 97,Trondheim, September
1997, pp.3.1010-3.1015; ISBN:9075815-02-6
[32] BAUER P., HAAN S.W.H. DE: New Concept for Voltage Control. IEEE Pedes 98, Perth
Australia, November 1998,pp.918-923, ISBN 0-7803-4879-6
[33] PATENT: P.G.J.M.ASSELMAN, BAUER P.,PAAP G.C., HAAN S.W.H. DE ,WATER
C.J.van DE: Method and device for continuous adjustment and regulation of transformer
turns ratio, and transformer provided with such device, United States patent: US5969511, 19
oktober 1999
[34] BAUER P., R.SCHOEVAARS: Bidirectional Switch for a Solid State Tap changer, IEEE
Power Electronics Specialists Conference PESC 2003, Acapulco, june 2003, pp.466473,ISBN 0-78037759-9
[35] BAUER P., DUIJSEN P.J. European Power Electronics and Drives Journal ( EPE Journal),
FEDAK V: Advances and trends in simulation of power electronics and electrical drives (1)
(in Slovak), AT&P Journal, May 2005, June 2005 ISSN 1335-2237, pp.50-53, pp.100-101
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Electronics and Drives Journal ( EPE Journal), 2002, Vol.13 No 04 November 2003; pp.4350, ISSN0939-8368
27
ABSTRACT
The lecture “Research and education of power Electronics in 21st Century” provides a survey of
advances in power electronics research and education and also shows authors contribution in this
field as well as some future trends.
Advance in power electronics and changing demands require necessary changes in education of
power electronics too. It concerns theoretical (lectures) as well as practical part of the education.
Use of the new media (interactive E learning ), problem based and project organized learning are
the possible ways to improve the quality of the education. In this survey web based learning tool
for power electronics and two project oriented practical for power electronics education are
introduced:
• Problem based learning in the first year of study (Energy challenge project),
• Design oriented laboratory for the fourth year of study as a supplement to lectures of power
electronics.
Concerning research the three main areas are explored:
• Efficiency and power density increase of power conversion
• Power electronics for renewable energy
• Power electronics for power systems.
Within the area “Efficiency and power density increase of power conversion“ the following
aspects namely new semiconductor devices, soft switching, electro-magneto-thermal- mechanical
integration, optimized design and synthesis, and finally the power management strategies are
discussed. Power electronics for renewable energy is here limited to wind power and offshore
wind parks. Within the area “Power electronics for power systems“ a patented design of an
electronic tap changer is shown. Finally some advances in power electronics simulation are
illustrated.
28