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IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 4, NOVEMBER 2005 567

Development, Implementation, and Assessment of aWeb-Based Power Electronics Laboratory

William Gerard Hurley, Senior Member, IEEE,and Chi Kwan Lee

AbstractA Web-based laboratory exercise with remote accessis presented, through which a student of Electrical/Electronic En-gineering is introduced in both a theoretical and practical way, tomany fundamental aspects of power electronics. The system is flex-ible and can expand the range of laboratory exercises where full-scale 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 in-volvement in the learning process by addressing some challengingand critical aspects of the design before approaching the physicalsystem. Further understanding is gained by studying the circuitin a Web-based, interactive power electronics seminar (iPES) by

simulating the circuit using PSpice and then analyzing the controland feedback issues with MATLAB. In the final stage, a real powerconverter is tested remotely over the Web, and the cycle of design,simulation, and test is completed using Web-based tools.

Index TermsControl engineering, dcdc converters, distancelearning, power electronics, Web-based laboratory.

NOTATION

The instantaneous variable is lower case; the quiescent or av-

erage value is upper case; and the incremental component is

lower case with a tilde, e.g., . The Laplace trans-

form of the incremental variable is upper case with the variable

, e.g., .

I. INTRODUCTION

AWEB-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 mea-

surements 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 set-

ting afforded by the Web stimulates the student in a highly in-

teractive 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 devel-

oped 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 beenfunded by Enterprise Ireland.

The authors are withthe Department of ElectronicEngineering,NationalUni-versity of Ireland, Galway, Ireland (e-mail: [email protected]).

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 draw-

back of this process is that the student does not have an oppor-

tunity to repeat the design component if the theory and mea-

surements 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 labora-

tory 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 areoperating in real time on real hardware.

A power supply must be designed to have good line regu-

lation, 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 post-

laboratory assignments, the student is introduced to the basic

principles of power electronics, the dynamics of switchingsystems, 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

LABORATORYSETUP

A. Equipment and dcdc Power Converter

The development of the remote-access laboratory is based

on general-purpose interface bus (GPIB) instruments and Lab-

VIEW 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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570 IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 4, NOVEMBER 2005

Fig. 5. Interactive power electronics seminar (iPES) [7].

Fig. 6. Linearized equivalent circuit.

Fig. 7. Block diagram of the converter.

IV. PRELABORATORYASSIGNMENT ANDSTUDENTEXERCISE

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 dcdc switching

mode converter, which is later remotely tested on the Web. The

assignments include theoretical circuit analysis, computer sim-

ulation, averaged and linearized circuit modeling, control-loop

design and compensation, and inductor design.

A. Computer Simulation With PSpice

Students are asked to perform a circuit simulation using

PSpice. Students can observe the operation principle of theconverter from the simulation and verify the design equation

Fig. 8. PSpice waveforms of buck converter (upper trace output voltage andlower trace output current).

and specifications. A PSpice model for an idealized dcdc 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

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 gainmargin of at least two to ensure stability. Stability is achieved


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HURLEY AND LEE: A WEB-BASED POWER ELECTRONICS LABORATORY 571

Fig. 9. Bode plot of converter control system (MATLAB).

by the proper selection of the pole and zero of the compensa-

tion error amplifier. The student must generate a Bode plot of the

open-loop converter control system (Fig. 9) using MATLAB.

V. REMOTELABORATORYSESSION

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

screen for an input of 10 V regulated to give an output

of 5 V (read from the dc voltmeter) across the 3.3- resis-

tive 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), av-

erage 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 changesand changes in load using an electronic load.

VI. ASSESSMENT AND EVALUATION

Independent assessment of the Web-based laboratory ex-

ercise 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 eval-

uation was carried out by the National University of Ireland,

Galways Centre for Excellence in Teaching and Learning(CELT). Feedback from the students dealt with the effective-

ness 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 measure-

ments) and identifiedflexibility 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 anextended period to gain full benefit from the experiment. The


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HURLEY AND LEE: A WEB-BASED POWER ELECTRONICS LABORATORY 573

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) con-

troller 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. Wlfle, 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.

REFERENCES

[1] C. C. Ko, B. M. Chen, J. Chen, Y. Zhuang, and K. C.Tan,Developmentof a Web-based laboratory for control experiments on a coupled tankapparatus,IEEE Trans. Educ., vol. 44, no. 1, pp. 7686, Feb. 2001.

[2] K. W. E. Cheng, C. L. Chan, N. C. Cheung, and D. Sutanto,Virtuallaboratory development for teaching power electronics,in Proc. 2002

IEEE Power Electronics Specialists Conf. (PESC02), vol. 2, Jun. 2002,pp. 461465.

[3] D. W. Hart,Introduction to Power Electronics. Englewood Cliffs, NJ:Prentice-Hall, 1997.

[4] N. Mohan, T. M. Undeland, and W. P. Robbins,Power Electronics, Con-verters, 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. Wlfle, PWM control of a magneticsuspension system,IEEE Trans. Educ., vol.47,no. 2,pp.165173,May2004.

[7] U. Drofenik and J. W. Kolar, Interactive power electronics seminar

(iPES)A Web-based introductory powerelectronics courseemployingJava-applets,in Proc. 2002 IEEE Power Electronics Specialists Conf.(PESC02), vol. 2, Jun. 2002, pp. 443448.

[8] Y. Amigud, G. Archer, J. Smith, M. Szymanski, and B. Servatius,As-sessing the quality of Web-enabled laboratories in undergraduate educa-

tion,inProc. 32nd Annu. ASEE/IEEE Frontiers in Education (FIE02),vol. 2, Nov. 2002, pp. F3E-12F3E-16.

William Gerard Hurley (M77SM90) wasborn in Cork, Ireland.He receivedthe B.E. degree (first-class honors) in electrical engineering from the NationalUniversity of Ireland, Cork, in 1974; the M.S. degree in electrical engineeringfrom the Massachusetts Institute of Technology, Cambridge, in 1976; and thePh.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 intransmission lines at Ontario Hydro, Toronto, ON, Canada. He lectured in Elec-

tronic Engineering at the University of Limerick, Ireland, from 1983 to 1991and is currently Vice-President and Professor of Electrical Engineering at theNational University of Ireland, Galway, and the Director of the Power Elec-tronics Research Center. His research interests include high-frequency mag-netics, power quality, and automotive electronics.

Prof. Hurley is a Fellow of the Institution of Engineers of Ireland and aMember of Sigma Xi. He has served as a Member of the AdministrativeCommittee of the IEEE Power Electronics Society and was General Chairof the Power Electronics Specialists Conference in 2000. He received a Best

Paper Prize for the IEEE TRANSACTIONS ONPOWERELECTRONICSin 2000.

Chi Kwan Lee received the B.Eng. degree (with honors) and the Ph.D. de-gree, 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 cur-rently a Postdoctoral Research Fellow in the Department of Electronic Engi-neering. His research interests include random-switching techniques,analysis ofmultilevel inverter,flexible ac transmission systems (FACTs), and active powerfilter design.

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