IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 4, NOVEMBER 2005
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Development, Implementation, and Assessment of a
Web-Based Power Electronics Laboratory
William Gerard Hurley, Senior Member, IEEE, and Chi Kwan Lee
Abstract—A Web-based laboratory exercise with remote access
is presented, through which a student of Electrical/Electronic Engineering is introduced in both a theoretical and practical way, to
many fundamental aspects of power electronics. The system is flexible and can expand the range of laboratory exercises where fullscale laboratories are not feasible. In the electrical environment,
limits can be placed on voltages and currents for safety reasons.
Prelaboratory investigations allow students to take an active involvement in the learning process by addressing some challenging
and critical aspects of the design before approaching the physical
system. Further understanding is gained by studying the circuit
in a Web-based, interactive power electronics seminar (iPES) by
simulating the circuit using PSpice and then analyzing the control
and feedback issues with MATLAB. In the final stage, a real power
converter is tested remotely over the Web, and the cycle of design,
simulation, and test is completed using Web-based tools.
Index Terms—Control engineering, dc–dc converters, distance
learning, power electronics, Web-based laboratory.
NOTATION
The instantaneous variable is lower case; the quiescent or average value is upper case; and the incremental component is
. The Laplace translower case with a tilde, e.g.,
form of the incremental variable is upper case with the variable
, e.g.,
.
I. INTRODUCTION
A
WEB-BASED real-time laboratory is described where all
of the instrumentation used in the experiment is remotely
accessed over the Web, and the student can carry out the measurements in his or her own time while continuously refining
the design as the measurements are made. The student sees all
the instruments on the screen and controls the inputs as required
to see the results of actions taken. The experiential learning setting afforded by the Web stimulates the student in a highly interactive environment. Further advantages over the traditional
laboratory setting are that scheduled time slots are eliminated,
safety with live electrical circuits is not an issue, and the number
of users is not limited. Web-based laboratories have been developed in the area of control [1], [2]. The emphasis in the paper is
on the broader concepts and assessment of Web-based learning
and comparison with traditional learning methods.
In a traditional laboratory exercise, the students carry out a
prelaboratory assignment consisting of design and simulation.
Manuscript received July 20, 2004; revised July 6, 2005. This work has been
funded by Enterprise Ireland.
The authors are with the Department of Electronic Engineering, National University of Ireland, Galway, Ireland (e-mail: ger.hurley@nuigalway.ie).
Digital Object Identifier 10.1109/TE.2005.856147
The student then goes to the laboratory with up to 20 others,
who work in groups of two and measure the results to confirm
the calculations, normally in a two-hour slot. The major drawback of this process is that the student does not have an opportunity to repeat the design component if the theory and measurements do not match, because of time constraints; in other
words, the essential feedback link between theory and practice
is missing. The feedback link is provided by Web-based laboratory measurements. The student sees all the instruments on the
screen, controls the inputs as required, and monitors the results
of actions taken. Unlike simulation tools, the instruments are
operating in real time on real hardware.
A power supply must be designed to have good line regulation, good load regulation, and good transient response to
system disturbances and be basically stable under all operating
conditions. All these requirements are satisfied by using a
closed-loop controlled converter, which compares a reference
voltage to the actual output voltage, thereby varying the duty
ratio of the power transistor switch, which restores the output
voltage to the desired value. Pulsewidth modulation (PWM)
feedback control achieves this goal [3]–[6].
In the course of the exercise from prelaboratory to postlaboratory assignments, the student is introduced to the basic
principles of power electronics, the dynamics of switching
systems, the averaged and linearized circuit model techniques,
and the application of compensation techniques in a typical
control system. An excellent Web-based interactive power
electronics seminar (iPES) with animated applets is available
at [7]. The use of modern Web-based tools for circuit design
(PSpice1) and control systems (MATLAB2) has removed the
traditional paper-based approach, which normally requires
sweeping approximations, while motivating the student in an
innovative learning setting to gain insights into the underlying
principles. Combining the simulation tools with iPES gives the
student widely transferable skills beyond the specifics of the
experiment under investigation.
II. THE WEB-BASED POWER ELECTRONICS
LABORATORY SETUP
A. Equipment and dc–dc Power Converter
The development of the remote-access laboratory is based
on general-purpose interface bus (GPIB) instruments and LabVIEW 7.3 All the instruments, including a four-channel digital
1http://www.orcad.com/
2http://www.mathworks.com/
3http://www.labview.com/
0018-9359/$20.00 © 2005 IEEE
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IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 4, NOVEMBER 2005
Fig. 1. Hardware setup in the laboratory.
TABLE I
TECHNICAL SPECIFICATIONS OF THE dc–dc BUCK CONVERTER
Fig. 2.
dc–dc buck converter circuit.
oscilloscope, a dc power supply, and a digital voltmeter, communicate with the host computer using LabVIEW 7 and the
GPIB interface to perform data exchange. Fig. 1 shows the hardware setup in the laboratory. In Fig. 1, the actual dc–dc power
converter and associated power supply, resistive load, and oscilloscope are shown on the left; the host computer running
LabVIEW 7 is shown on the right. The gate voltage, input current, output current, and output voltage ripple waveforms of the
converter are measured. The input voltage of the dc–dc power
converter can be varied by the dc power supply from 8 to 15 V.
The power conversion part of the system is implemented by
a dc–dc buck converter, using a power metal–oxide–semiconductor field-effect transistor (MOSFET) as the switching device,
as shown in Fig. 2. The detailed technical specifications of the
dc–dc buck converter are listed on Table I.
B. LabVIEW and LabVIEW Internet Toolkit
LabVIEW by National Instruments (NI), Austin, TX, is a
graphical development environment for data acquisition, instrument control, measurement analysis, and data presentation.
Fig. 3 shows two examples of virtual instrument (VI) setups,
which are used to send a command and receive a data string
from the instruments through the GPIB interface. Fig. 3(a) is a
VI setup that sends the value of voltage and current limits to the
dc power supply. The output voltage and current of the dc power
supply can be measured and received using a simple receive
command, which is shown in Fig. 3(b). All the functionality,
configuration, and appearance of the system are simply assembled by connecting different blocks. The LabVIEW Internet
Toolkit incorporates the VI setups on the Internet Web browser.
Fig. 4 shows the final instruments and control front panel as
they appear on the Web browser interface.
III. CIRCUIT ANALYSIS AND CONTROL
A. Circuit Analysis
The dc–dc buck regulator circuit operates in two different
modes. An analysis of these modes, found in any undergraduate text [3], [4], reveals the following equation, where is the
duty cycle of the switch:
and
(1)
The iPES [7] is an ideal vehicle for the student to become
familiar with the circuit; a sample screen is shown in Fig. 5. The
dynamic behavior of the circuit is based on perturbations about
the steady state or average values of voltage, current, and duty
cycle. The process of linearization is described in [6], resulting
in the linearized equivalent circuit shown in Fig. 6.
HURLEY AND LEE: A WEB-BASED POWER ELECTRONICS LABORATORY
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Fig. 3. Example of LabVIEW VI. (a) Setup 1: Sending a command to an instrument. (b) Setup 2: Receiving a data string from an instrument.
Fig. 4. Final instruments and control front panel on the Web browser.
The transfer function of control to output
will
be required for stability analysis and may be found by setting
, yielding
(2)
where
and
.
B. Block Diagram
Fig. 7 shows a closed-loop system of a regulated dc–dc buck
converter, consisting of a compensation error amplifier, a PWM
generator/comparator, and the converter transfer function. The
full circuit and the derivations of the transfer functions are described in the Appendix.
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IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 4, NOVEMBER 2005
Fig. 5.
Interactive power electronics seminar (iPES) [7].
Fig. 6.
Linearized equivalent circuit.
Fig. 8. PSpice waveforms of buck converter (upper trace output voltage and
lower trace output current).
Fig. 7. Block diagram of the converter.
IV. PRELABORATORY ASSIGNMENT AND STUDENT EXERCISE
Before carrying out the Web-based laboratory, students are
required to complete a set of prelaboratory assignments. The
set of prelaboratory assignments provides a good fundamental
and theoretical background to the design of a dc–dc switching
mode converter, which is later remotely tested on the Web. The
assignments include theoretical circuit analysis, computer simulation, averaged and linearized circuit modeling, control-loop
design and compensation, and inductor design.
and specifications. A PSpice model for an idealized dc–dc buck
regulator includes a voltage-controlled switch, an ideal diode,
an ideal inductor, and an ideal output capacitor. The switch is
controlled by a pulse voltage source. Fig. 8 shows the PSpice
output for the output capacitor voltage and the inductor current.
The student is expected to compare the voltage ripple and
current ripple with the well-known calculations based on the
output capacitor and inductor values. The calculations may be
compared with the actual measurements later.
B. Stability Analysis With MATLAB
A. Computer Simulation With PSpice
Students are asked to perform a circuit simulation using
PSpice. Students can observe the operation principle of the
converter from the simulation and verify the design equation
In this exercise, students are required to select the values
of
,
,
, and
of the compensating error amplifier
(Fig. 10) to ensure a phase margin of at least 45 and a gain
margin of at least two to ensure stability. Stability is achieved
HURLEY AND LEE: A WEB-BASED POWER ELECTRONICS LABORATORY
Fig. 9.
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Bode plot of converter control system (MATLAB).
by the proper selection of the pole and zero of the compensation error amplifier. The student must generate a Bode plot of the
open-loop converter control system (Fig. 9) using MATLAB.
V. REMOTE LABORATORY SESSION
In the laboratory exercise, the student observes and records
waveforms from probe points on the power conversion board.
Fig. 4 shows the input current, output current, output voltage
ripple, and gate voltage of the converter on the Web browser
10 V regulated to give an output
screen for an input of
of 5 V (read from the dc voltmeter) across the 3.3- resistive load. The students can repeat the measurements for various
input voltages from 8 to 15 V, noting the little or no change in
the regulated 5-V output voltage. The objective is to observe the
change in duty cycle of the converter according to the change
of input voltage. Students are asked to calculate the inductor
value (using the slope of the input current/inductor current), average input/output current, average diode current, input/output
power, and efficiency of the converter. Other experiments may
be considered, such as step response to input voltage changes
and changes in load using an electronic load.
VI. ASSESSMENT AND EVALUATION
Independent assessment of the Web-based laboratory exercise was based on the principles enunciated in [8], with
emphasis on usability. The students were required to write a
detailed project report for assessment purposes. Student evaluation was carried out by the National University of Ireland,
Galway’s Centre for Excellence in Teaching and Learning
(CELT). Feedback from the students dealt with the effectiveness of the approach as a teaching tool and the relative strengths
and weaknesses of the curriculum content. The students were
also asked to identify the principal advantages of Web-based
learning over traditional approaches. The students rated each
component highly (iPES, PSpice, MATLAB, and measurements) and identified flexibility in terms of access and time as
the main advantages. The students were asked to 1) express
their confidence level using the new system, 2) rate the quality
of the materials, and 3) indicate their overall satisfaction. The
results are summarized in Table II, indicating that over 80%
of the students were satisfied with the exercise. The students
suggested that the live experiment be made available over an
extended period to gain full benefit from the experiment. The
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Fig. 10.
IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 4, NOVEMBER 2005
Circuit for dc–dc converter.
feedback has been very useful to the instructors for the future
running of the experiment.
TABLE II
ASSESSMENT DATA
VII. CONCLUSION
A Web-based power electronics laboratory with remote access has been described. A board-mounted power conversion
system has been developed, offering an interactive teaching and
demonstration facility to the students. The complete exercise
includes interactive simulation (iPES and PSpice) and control
software (MATLAB) for electronic systems. The paper verifies
that the design and control realization of the physical system
performs in a correct and robust manner and can thus be used as
an educational tool to highlight the various concepts of switch
mode power supplies and their control. The paper demonstrates
that Web-based laboratory exercises remove the traditional limitations on space, time, and staff costs, while offering the individual student more flexibility.
HURLEY AND LEE: A WEB-BASED POWER ELECTRONICS LABORATORY
APPENDIX
The block diagram of Fig. 7 represents the full circuit diagram
shown in Fig. 10. The transfer function of the main DC-DC
converter has already been established in (2). The compensation
error amplifier is a straightforward inverting amplifier, and the
transfer function is readily established, yielding
(A1)
where is
and is
.
The operation of the Pulse Width Modulated (PWM) controller is fully explained in [6]. In summary the control voltage
is compared to a repetitive ramp waveform and the output
of the comparator controls the duty cycle of the switch. The
transfer function of the PWM circuit is [4], [6]
(A2)
where
is the peak value of the ramp waveform.
ACKNOWLEDGMENT
The authors would like to thank W. H. Wölfle, M. Hynes, and
S. C. Tang for their contributions. They also would like to thank
Dr. I. MacLabhrain and M. Keating of the Centre of Excellence
in Teaching and Learning (CELT) at the National University of
Ireland, Galway for their assistance.
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[4] N. Mohan, T. M. Undeland, and W. P. Robbins, Power Electronics, Converters, Applications and Design. New York: Wiley, 1995.
[5] R. Erickson and D. Maksimovic, Fundamentals of Power Electronics,
2nd ed. New York: Chapman & Hall, 1997.
[6] W. G. Hurley, M. Hynes, and W. H. Wölfle, “PWM control of a magnetic
suspension system,” IEEE Trans. Educ., vol. 47, no. 2, pp. 165–173, May
2004.
[7] U. Drofenik and J. W. Kolar, “Interactive power electronics seminar
(iPES)—A Web-based introductory power electronics course employing
Java-applets,” in Proc. 2002 IEEE Power Electronics Specialists Conf.
(PESC’02), vol. 2, Jun. 2002, pp. 443–448.
[8] Y. Amigud, G. Archer, J. Smith, M. Szymanski, and B. Servatius, “Assessing the quality of Web-enabled laboratories in undergraduate education,” in Proc. 32nd Annu. ASEE/IEEE Frontiers in Education (FIE’02),
vol. 2, Nov. 2002, pp. F3E-12–F3E-16.
William Gerard Hurley (M’77–SM’90) was born in Cork, Ireland. He received
the B.E. degree (first-class honors) in electrical engineering from the National
University of Ireland, Cork, in 1974; the M.S. degree in electrical engineering
from the Massachusetts Institute of Technology, Cambridge, in 1976; and the
Ph.D. degree from the National University of Ireland, Galway, in 1988.
From 1977 to 1979, he was a Product Engineer for Honeywell Controls,
Toronto, ON, Canada. From 1979 to 1983, he was a Development Engineer in
transmission lines at Ontario Hydro, Toronto, ON, Canada. He lectured in Electronic Engineering at the University of Limerick, Ireland, from 1983 to 1991
and is currently Vice-President and Professor of Electrical Engineering at the
National University of Ireland, Galway, and the Director of the Power Electronics Research Center. His research interests include high-frequency magnetics, power quality, and automotive electronics.
Prof. Hurley is a Fellow of the Institution of Engineers of Ireland and a
Member of Sigma Xi. He has served as a Member of the Administrative
Committee of the IEEE Power Electronics Society and was General Chair
of the Power Electronics Specialists Conference in 2000. He received a Best
Paper Prize for the IEEE TRANSACTIONS ON POWER ELECTRONICS in 2000.
REFERENCES
[1] C. C. Ko, B. M. Chen, J. Chen, Y. Zhuang, and K. C. Tan, “Development
of a Web-based laboratory for control experiments on a coupled tank
apparatus,” IEEE Trans. Educ., vol. 44, no. 1, pp. 76–86, Feb. 2001.
[2] K. W. E. Cheng, C. L. Chan, N. C. Cheung, and D. Sutanto, “Virtual
laboratory development for teaching power electronics,” in Proc. 2002
IEEE Power Electronics Specialists Conf. (PESC’02), vol. 2, Jun. 2002,
pp. 461–465.
[3] D. W. Hart, Introduction to Power Electronics. Englewood Cliffs, NJ:
Prentice-Hall, 1997.
Chi Kwan Lee received the B.Eng. degree (with honors) and the Ph.D. degree, both in electronic engineering, from the City University of Hong Kong,
Kowloon, Hong Kong, in 1999 and 2004, respectively.
He then joined the National University of Ireland, Galway, where he is currently a Postdoctoral Research Fellow in the Department of Electronic Engineering. His research interests include random-switching techniques, analysis of
multilevel inverter, flexible ac transmission systems (FACTs), and active power
filter design.