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Versatile Hardware and Software Tools for
Educating Students in Power Electronics
Joshua M. Williams, Student Member, IEEE, James L. Cale, Member, IEEE,
Nicholas D. Benavides, Student Member, IEEE, Jeff D. Wooldridge, Andreas C. Koenig, Student Member, IEEE,
Jerry L. Tichenor, Member, IEEE, and Steven D. Pekarek, Member, IEEE
Abstract—A new power electronics laboratory has been constructed at the University of Missouri—Rolla. Key components
of the laboratory are a set of custom-designed hardware and
software tools. The novel hardware tools include five mobile power
electronics testbeds that each contain the semiconductor devices,
gate-drive boards, voltage and current sensors, and computer
interface connections required to study a wide range of circuit
topologies and control techniques. Novel software tools include a
set of virtual instruments used for control, data capture, and data
analysis. A description of these tools, along with their use in power
electronics courses, laboratory exercises, and student research
projects, is presented.
Index Terms—Digital control, laboratories, motor drives, operational amplifiers, power electronics.
I. INTRODUCTION
P
OWER electronics systems (PESs) are increasingly being
used in many applications, including vehicular propulsion
and power distribution, home appliances, and manufacturing.
Designing these systems requires significant knowledge in
multiple areas of electrical and computer engineering. These
include understanding of electronics, control theory, linear and
nonlinear system theory, and electromagnetics. In addition,
knowledge of the behavior of electric machinery, modeling
techniques, and microprocessors for control algorithm implementation must be established to create efficient designs.
Recently, a new power electronics and drives laboratory has
been constructed at the University of Missouri—Rolla (UMRolla). The purpose of the laboratory is twofold. First, it is a
resource for undergraduate and graduate students to develop
Manuscript received March 7, 2003; revised September 1, 2003. This work
was supported in part by the National Science Foundation under Grant 995077
and by the Ameren Foundation.
J. M. Williams was with the Department of Electrical and Computer Engineering, University of Missouri—Rolla, Rolla, MO 65409-0040 USA. He is
now with Caterpillar Electronics, Peoria, IL 61602 USA.
J. L. Cale, A. C. Koenig, and S. D. Pekarek were with the Department of Electrical and Computer Engineering, University of Missouri—Rolla, Rolla, MO
65409-0040 USA. They are now with Purdue University, West Lafayette, IN
47907-2035 USA.
N. D. Benavides was with the Department of Electrical and Computer Engineering, University of Missouri—Rolla, Rolla, MO 65409-0040 USA. He is
now with the University of Illinois at Urbana-Champaign, Urbana, IL 61801
USA.
J. D. Wooldridge was with the Department of Electrical and Computer Engineering, University of Missouri—Rolla, Rolla, MO 65409-0040 USA. He is
now with Empire District Electric Company, Joplin, MO 64801 USA.
J. L. Tichenor is with the Department of Electrical and Computer Engineering, University of Missouri—Rolla, Rolla, MO 65409-0040 USA.
Digital Object Identifier 10.1109/TE.2004.825552
the skills that are required to analyze and design power-electronic-based systems. Second, it is a tool to support research in
the areas of power electronics and electric drives. To facilitate
both objectives, several custom-designed hardware and software
tools have been developed for the laboratory. The novel hardware includes five mobile power electronics testbeds that each
contain semiconductor devices, gate-drive boards, voltage and
current sensors, and computer interface connections. In addition, digital-signal-processing (DSP)-based control boxes have
been designed to interface directly with one or multiple power
electronics testbeds. Novel software includes customized virtual instruments (VIs) that utilize the commercial package LabVIEW [1] for control, data capture, and data analysis. MATLAB
[2] is used for time-domain simulations.
The advantages offered by these tools are numerous. For one,
the power electronics testbeds can be configured using simple
connections on a faceplate to construct a wide variety of converters and inverters. In addition, the testbed can operate from
a single-phase (120-V) source, which is useful in a classroom
setting. Op-amps contained in the testbed have been configured to act as a four-channel computer-based function generator. This generator is convenient for demonstrations or short
courses where two- or three-phase power is required but not
readily available. Finally, the devices are rated at voltage and
current levels that are consistent with those required in many
industrial, automotive, and home appliance applications. Therefore, the testbeds are useful as a tool for undergraduate and graduate student research.
In this paper, a description of these tools, along with
their use in power electronics courses, laboratory exercises, and student research projects is presented. All software, circuit schematics, rack layout drawings, and miscellaneous technical information are posted on the website
http://www.ece.umr.edu/places/Power_Electronics_Lab/. The
ultimate goal is to promote adaptation of this testbed at other
institutions, to evaluate the testbed’s components, and to develop additional tools.
One unique aspect of the laboratory is that undergraduate
students, under the direction of a graduate student and faculty,
designed and constructed a majority of the hardware and software. This accomplishment has helped to spark student interest
in power-related research and has led several students to pursue
graduate schools in this area. An assessment of the laboratory’s
influence on student interest and achievement is provided in
Section VI.
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II. LABORATORY DESIGN CONSIDERATIONS
Over the past decade, several educators have proposed curriculum and laboratories to train students in the analysis and design of PESs [3]–[13]. In [6]–[10], the described educational approach supplements course lectures with computer exercises to
demonstrate the behavior of power electronic circuits and design
control algorithms. Pedagogical approaches emphasizing concurrent simulation and hardware are described in [11]–[13]. In
the courses that utilize hardware-based experiments described
in [11]–[13], students are trained to perform the following:
1) to analyze to establish expected results;
2) to simulate to verify the analysis;
3) to validate through hardware experiments.
At UM-Rolla, prior to the development of the laboratory, only
a single course on power electronics had been co-listed in the
undergraduate/graduate curriculum. In addition, a course had
been listed on electric machines/drives. Both have utilized computer exercises to supplement course lectures. Although these
courses were useful in establishing an understanding of the behavior of the circuits and systems, instructors recognized that
students gain a much better understanding of the complexity of
designing a physical system if they are exposed to hardware.
Specifically, they can observe the effects of parasitics, the physical limitations of devices, and the differences between poorly
and well-designed circuits and software. In addition, they further develop their skills to obtain meaningful and accurate measurements and learn safety measures that are required to work
with power electronics.
Given the motivation to create a curriculum that utilizes
hardware-based experiments, a laboratory containing five of
the power electronics stations shown in Fig. 1 was developed.
From the figure, one can see that each station contains a computer for control and data capture/analysis, an oscilloscope for
observing/capturing wave forms for analysis with the computer,
and an equipment rack containing power electronic devices,
sensing equipment, power supplies, and a load box. Also shown
is a DSP box that is used for supervisory and switch level
control, as well as data acquisition. Sections III–VI provide a
description of the custom-designed components of the power
electronic testbed shown in Fig. 1. Included are the equipment
rack, DSP box, and the software used for data capture, analysis,
and control.
III. POWER ELECTRONIC TESTBED
The main component in each station is the power electronic
testbed shown in Fig. 2. As shown, the testbed consists of multiple racks. The control/sensor rack provides sensors for voltage
and current-based control and fault detection, the inverter and
discrete device racks contain the devices to construct a wide variety of circuit topologies, a BUS-level rack provides a means
to make nodal connections, the op-amp rack acts as an arbitrary
wave form generator, and the Sorensen DHP series direct current (dc) supply with 400-V/25-A ratings can be used to provide
power for research applications. Overall, the testbed is spacious
and divided into sections; each can be used independently or
in conjuction with other testbeds. Removable side panels and
pull-out shelves give access to the interior, facilitating design
Fig. 1.
Power electronic station.
Fig. 2.
Power electronic testbed.
changes and allowing the laboratory to be modified as technologies change. Safety issues resulting from inadvertent contact
with energized circuits is minimized since all the equipment is
mounted inside the enclosure. Details of each rack are described
in Sections III-A–D.
A. Control/Sensor Rack
The control/sensor rack consists of two independent systems
that provide the following functions through the panel shown in
Fig. 3(a):
• control power;
• manual enable/disable switch for each insulated gate
bipolar transistor (IGBT);
• a start/stop for IGBTs;
• voltage and current sensor inputs;
• digital switching inputs and analog sensor outputs.
The switches and digital/analog (D/A) input/output (I/O) connections on the left half of the rack control the devices located
in the inverter rack, while the switches and D/A I/O connections
on the right half control the devices located in the discrete devices rack. The voltage and current sensors shown can be used
with either rack or an external circuit.
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Fig. 4. Inverter rack: (a) front panel and (b) interior.
Fig. 3. Control/sensor rack: (a) front panel and (b) interior.
An interior view of the control/sensor rack is shown in
Fig. 3(b). At the top are four sensor boards, each containing
two current sensors and one voltage sensor. The measurement
range of the sensors is adjusted by selecting an appropriate
output scaling resistance. Measurements are accessible through
a D-subminiature (D-SUB) connector on the front panel. In the
middle of the rack are the device control boards for the inverter
and discrete device racks, left to right, respectively. Each
control board receives transistor–transistor-logic (TTL)-level
switching signals from the digital input port and provides fault
protection for each of the IGBTs.
studied by students. The gate-drive boards and snubbers are connected to the semiconductor devices using small circuit boards
with terminal blocks and collector, base, emitter (CBE) connectors. These boards are placed atop the devices, simplifying the
wiring dramatically.
C. Discrete Device Rack
The discrete device rack is similar to the inverter rack. However, the discrete device rack contains fewer semiconductor
devices, and each device is connected separately. Each of the
IGBTs and diodes are wired directly to the front panel as shown
in Fig. 5(a). An interior view is shown in Fig. 5(b). This rack is
primarily used to create dc/dc converters.
B. Inverter Rack
D. Op-Amp Rack
The inverter rack consists of a three-phase full bridge inverter
constructed with discrete 600-V, 30-A IGBTs and 600-V, 50-A
antiparallel diodes. Discrete devices were chosen to minimize
cost if an IGBT or diode should fail. The inverter connections
are made behind the panel shown in Fig. 4(a), thereby minimizing the number of front-panel connections. An input filter
capacitor is also included.
The inverter rack connections and gate-drive circuitry are
shown in Fig. 4(b). Isolated 20-V gate-drive supplies are shown
in the bottom right, and the gate-drive boards are at the top
right.
The gate-drive circuits were designed using application notes
[14] from the vendor. The gate resistance can be changed so
that the effects of snubber circuits and device rise times can be
The front panel and interior of the op-amp rack is shown in
Fig. 6. Each amplifier circuit is built using an Apex Microtechnology [15] PA12A high-power op-amp, setup as a noninverting
amplifier. The devices are rated at 90 V peak to peak, 15 A, and
have a bandwidth of 500 kHz. A current-limiting resistor can
be used to limit output current to safe levels for inexperienced
students.
The amplifiers are controlled using the station computer
through a 25-pin D-SUB connector on the front panel. The
signal for each op-amp is generated using a custom-designed
LabVIEW VI, shown in Fig. 7. Using the VI, students choose
the wave form to generate the peak amplitude, phase shift, dc
offset, and duty cycle. The VI also contains a plot window
that indicates the wave form being generated for each channel.
WILLIAMS et al.: EDUCATING STUDENTS IN POWER ELECTRONICS
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Fig. 6.
Op-amp rack: (a) front panel and (b) interior.
Fig. 5. Discrete device rack: (a) front panel and (b) interior.
Presently, this module can generate sinusoidal, square, triangular, and sawtooth wave forms. The speed of the computer
(1 GHz) and data acquisition card limit the fundamental frequency of the wave forms to 10 kHz.
The flexibility provided by the op-amp rack is significant.
First, it provides a means to generate two- and three-phase signals with arbitrary harmonic content. This capability is useful
for classroom demonstrations where multiphase power is typically not available. It is also useful for short courses that are
often held in hotels or conference centers without multiphase
power. Further, since the wave forms generated can have arbitrary harmonic content, the racks can be used to study the effects of voltage harmonics on the behavior of a system (power
quality).
IV. DATA ACQUISITION, ANALYSIS, AND
SWITCH-LEVEL CONTROL
Along with the power electronic testbed, each laboratory station is equipped with a digital oscilloscope, a computer with
data acquisition cards, and a DSP box. This equipment is designed to provide relatively fast data collection, support analysis, and changes in switch level and supervisory control. Customized tools are highlighted in Section IV-A and B.
A. Instrumentation and Analysis Software
Efficient data collection is important. It helps maintain student interest, and for research projects where multiple studies
and vast data storage are sometimes required, it reduces the time
required to perform experiments. Each station in the power electronics laboratory contains the instrumentation/computer combination listed in Table I. The VIs used in the power electronics
laboratory are listed in Table II.
Data collection and analysis is performed using VIs coupled
with the general-purpose interface bus (GPIB) computer cards.
Once a wave form is captured on the oscilloscope and the probe
scales are set in the GetScope VI, the data is downloaded into
an ASCII file. This downloading allows the data to be read into
MATLAB or another VI for analysis.
Fig. 8 shows two profiles obtained from the data analysis
VI. The top VI displays the time-domain data for each channel.
The same VI is then used to display frequency-domain data, as
shown in Fig. 8(b). All of the VIs were written by UM-Rolla
undergraduate students as part of their senior design projects.
B. Computer and DSP Control
The computer and data acquisition card at each station can be
programmed to implement open-loop, switch-level control. This
procedure is useful for illustrating basic concepts, such as 180
conduction and sine-triangle pulsewidth modulation. LabVIEW
VIs have been written for this purpose and are listed in Table III.
Although many aspects of power electronics can be learned
using open-loop control of circuits and systems, students obtain a sense of accomplishment and a better understanding of
control theory by designing and programming closed-loop controls and implementing them in hardware. To obtain experience
with closed-loop control design, a DSP is incorporated into the
laboratory. Since the objective of the laboratory is not to learn
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Fig. 7.
IEEE TRANSACTIONS ON EDUCATION, VOL. 47, NO. 4, NOVEMBER 2004
Function generator virtual instrument FunGen VI.
TABLE I
INSTRUMENTATION AND COMPUTER SPECIFICATIONS
TABLE II
LABVIEW VIs FOR POWER ELECTRONICS LABORATORY
the intricacies of DSP programming, the DSPs are set up so that
the students only need to determine and code the control law
using C. The code necessary to access data ports, handle interrupts, etc., are provided to students, minimizing the program’s
complexity.
The DSP board used is manufactured by Technosoft and utilizes a Texas Instrument (TI) TMSA320LF2407 DSP chip. It is
a 30-MHz fixed-point DSP with 3.3-V I/O levels. Since it is a
fixed-point DSP, students are required to use integer values and
adjust measured values for scales and dc offsets.
As shown in Fig. 9, each board is contained in its own
housing, along with a power supply and interface board. Communication with the PC occurs through a nine-pin D-SUB
connector on the front panel, and the two 25-pin D-SUB connectors carry the digital outputs and analog I/O signals. The
external interface board, which was designed and built by an
undergraduate student, provides buffering and signal conditioning for the DSP I/O. Each digital output is buffered with a
unity gain op-amp to prevent a short circuit or low impedance.
WILLIAMS et al.: EDUCATING STUDENTS IN POWER ELECTRONICS
Fig. 8. Data analysis VI: (a) time display and (b) fast Fourier transform (FFT).
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TABLE III
LABVIEW SWITCH-LEVEL CONTROL VIs
Fig. 10.
Single-phase half-wave rectifier.
Fig. 11. Rectifier circuit with sinusoidal input.
implement the control of brushless dc machines, stepper motors,
and volts/Hertz control of induction machines. To demonstrate
the utilization of the testbed in representative applications, two
examples are provided.
A. Single-Phase Half-Wave Controlled Rectifier
Fig. 9.
DSP & Interface board: (a) front and (b) inside.
from damaging the DSP. Similarly, the eight 10-b analog inputs are isolated through an Analog Devices AD215 amplifier
and provide a differential voltage measurement. The two 12-b
analog outputs are buffered through unity gain op-amp circuits.
Since the TI DSP chip does not have D/A converters built in,
D/A I/Os were created by using the Technosoft board’s D/A
converters, These are accessed through a serial digital output
from the TI DSP.
V. SAMPLE EXPERIMENTS
In the new power electronics course, experiments are used to
validate analysis and design controls for converters, inverters,
and rectifiers. In addition, experiments are performed to demonstrate the influence of parasitics on system performance (electromagnetic interference, power quality, acoustic noise, etc.). In
the machines/drives course, experiments are being designed to
Although quite simple, a single-phase half-wave controlled
rectifier circuit demonstrates many of the testbed’s features, the
most important of which is the op-amp rack. Other tools utilized include the LabVIEW modules FunGen, GetScope, and
Data_Analysis, the op-amp rack, and the discrete device rack.
Fig. 10 shows the schematic of the circuit. The source voltage
is produced by using the op-amp rack to amplify the waveform
produced by the “FunGen” output.
wave form is produced by FunGen, the
Since the original
timing information is known, and it can be synchronized with
the second channel in FunGen that is used for controlling the
switch. This procedure allows for phase control to be implemented easily.
To illustrate the flexibility of the FunGen module and op-amp
rack, two different wave forms were input to the rectifier circuit. The results for a sinusoidal input are shown in Fig. 11. The
output voltage for firing angles of 0 and 30 are shown below
the input voltage.
The results for a square-wave input, with the same firing angles, are shown in Fig. 12. In the figure, the upper trace is one
cycle of input voltage, the middle trace is the 0 phase-delay
half-wave rectified output voltage, and the bottom trace is the
30 phase-delay rectified output voltage, respectively.
In the 30 firing angle studies, the output voltage is applied
to the load for a shorter duration of time; therefore, the average
output voltage over a cycle is less. This finding is supported
by the harmonic calculation shown in Fig. 13. As can be seen,
WILLIAMS et al.: EDUCATING STUDENTS IN POWER ELECTRONICS
Fig. 12.
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Rectifier circuit with square-wave input.
Fig. 15.
Fig. 13.
Step change voltage.
Rectifier output harmonics.
Fig. 16. Step change inductor current.
Fig. 14.
dc/dc converter.
in both the sinusoidal and square-wave input, the 30 phasedelayed case has a reduced dc component. Also of note, and
shown in Fig. 12, the phase delay introduces significant even
harmonics in the output voltage with a square-wave input. The
spectral components are obtained using the spectrum analysis
tool within the Data_Analysis VI.
B. dc/dc Converter
Another experiment that demonstrates the capabilities of the
is a
testbed is a dc/dc converter, shown in Fig. 14. The input
dc voltage provided by the Sorenson power supply. Open-loop
control is achieved by controlling the switch with a square wave
created in FunGen.
Closed-loop control of the switch is accomplished using
the DSP. Specifically, the sensors on the control rack are set
to match the analog inputs of the DSP. A template program
has been set up that provides the students with access to all
digital and analog I/O. Students are then required to create
code implementing a proportional-integral control. Controller
parameters are selected using Nyquist-based techniques based
upon a linearized average-value model of a buck converter
(assuming continuous conduction). The parameter selection is
tested in simulation before running the system in hardware.
The students create simulations in MATLAB and compare predicted responses with measured data. A typical wave form that
is established in the laboratory is shown in Fig. 15. Depicted
is the output voltage response when the load undergoes a step
change from 150–100 . The corresponding inductor current
response is shown in Fig. 16. Both the simulation and measured
data are plotted. The responses compare favorably, which help
to ensure confidence in the students that the analysis performed
is valid.
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VI. STUDENT ASSESSMENT OF LABORATORY COURSE
Initially, this laboratory course has produced a favorable
response from students. The course has had full enrollment the
two semesters it has been offered and has received a 3.6/4.0
rating for its educational value from student evaluations. This
rating compares with an average rating of 2.9/4.0 for electrical
and computer engineering courses at UM-Rolla. One of the
course’s stated goals is to help students develop the skills necessary to design and analyze power-electronic-based systems.
Written comments on the evaluations indicate that the course is
meeting this goal. Students have found that the course provides
significant practical experience and effectively integrates the
many topics associated with power electronic systems. In particular, students have commented that the closed-loop control
design experiments are particularly beneficial. Although students have had classes in linear systems and control theory, very
few have practical experience applying this knowledge to the
complete design of a system. In terms of student achievement,
all of the students involved in the laboratory’s development
have chosen to pursue graduate school or a career in power-related fields.
VII. SUMMARY
In this paper, key components of a new power electronics laboratory at UM-Rolla are described. The novel hardware tools
include five mobile power electronics testbeds that each contain the semiconductor devices, gate-drive boards, voltage and
current sensors, and computer interface connections required to
study a wide range of circuit topologies and control techniques.
Novel software tools include a set of virtual instruments (VIs)
used for control, data capture, and data analysis. The results of
experiments are used to explain their use in a power electronics
laboratory.
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Joshua M. Williams (S’96) was born in Peoria, IL, on September 1, 1977. He
received the B.S., M.S., and Ph.D. degrees in electrical engineering from the
University of Missouri–Rolla, in 1999, 2001, and 2004, respectively.
He was a National Science Foundation Integrative Graduate Education
and Research Traineeship (IGERT) Program Fellow at the University of
Missouri-Rolla. His interests include finite-element and magnetic-equivalent
circuit modeling techniques, machine design and optimization, and hybrid
electric vehicle propulsion systems. He is currently with Caterpillar Electronics,
CGT-Advanced Engineering Division.
Dr. Williams is a Member of Eta Kappa Nu, Phi Kappa Phi, and Tau Beta Pi.
He received the Grainger Award for Outstanding Power Engineering Student in
2001.
James L. Cale (M’03) received the B.S. (highest distinction) degree in electrical
engineering from the University of Missouri—Rolla in 2001 and the M.S. degree
in electrical engineering from Purdue University, West Lafayette, IN, in 2003.
He is currently working toward the Ph.D. degree in electrical engineering at
Purdue University under a National Science Foundation Integrative Graduate
Education and Research Traineeship (IGERT) fellowship.
He served in the United States Army Reserves from 1994 to 2003 and interned
at the Cooper Nuclear Reactor, Brownville, NE, in 2000. His interests include
electric machinery and drives, power electronics, electromagnetics, and genetic
algorithms.
Nicholas D. Benavides (S’00) was born in St. Louis, MO, on August 17, 1981.
He received the B.S. degree in electrical engineering from the University of
Missouri—Rolla, in 2003. He is currently working toward the M.S. degree in
electrical engineering from the University of Illinois at Urbana-Champaign.
He worked as a Research Assistant under Dr. S. Pekarek while at the University of Missouri—Rolla from 2001 to 2003. He is currently working as a
Research Assistant under Dr. P. Chapman at the University of Illinois at Urbana-Champaign.
Mr. Benavides received the Grainger Award for Outstanding Power Engineering Students in 2003.
Jeff D. Wooldridge was born in Springfield, MO. He received the B.S. degree
in electrical engineering from the University of Missouri—Rolla in 2001.
He was a co-op student with City Utilities of Springfield, MO, from 1999
to the end of 2000 and was a Research Assistant while an undergraduate. He
is currently a System Protection and Planning Engineer at the Empire District
Electric Company, Joplin, MO.
Mr. Wooldridge is an active Member of the Joplin Chapter of the Missouri
Society of Professional Engineers as an engineer-in-training. He received the
Grainger Outstanding Power Student Award in 2001.
Andreas C. Koenig (S’99) was born in New Orleans, LA, on August 15, 1979.
He received the B.S. and M.S. degrees in electrical engineering from the University of Missouri—Rolla in 2001 and 2003, respectively.
He is currently a National Science Foundation Graduate Research Fellow at
Purdue University, West Lafayette, IN. His interests include hardware design,
numerical analysis, and automated control of power electronic systems and electric machinery.
WILLIAMS et al.: EDUCATING STUDENTS IN POWER ELECTRONICS
Jerry L. Tichenor (S’94–M’96) was born in Springfield, MO, on August 26,
1971. He received the B.S. and M.S. degrees in electrical engineering from the
University of Missouri—Rolla in 1994 and 1996, respectively.
He is currently an Associate Research Engineer at the University of Missouri—Rolla. His research interests include power electronics and electric drive
systems.
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Steven D. Pekarek (M’92) was born in Oak Park, IL, on December 22, 1968.
He received the B.S.E.E., M.S.E.E., and Ph.D. degrees from Purdue University,
West Lafayette, IN, in 1991, 1993, and 1996, respectively.
He is currently an Associate Professor of Electrical Engineering at Purdue
University. His interests include power electronics, electric machines, numerical
analysis, and automated control.