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					            The Rockwell Motors and Drives Laboratory
                     at Clemson University
       National Science Foundation Workshop on Teaching of Power Electronics
             And Electric Drives and Their Applications in Power Systems
                                   Las Vegas, NV
                               February 20 – 21, 2004


                         E. R. (Randy) Collins Jr., PhD, PE
                                 Associate Professor
                  Department of Electrical and Computer Engineering
                                 Clemson University
                              Clemson, SC 29634-0915
                          randy.collins@ces.clemson.edu




I. Introduction

A generous equipment donation from Rockwell Automation Power Systems has enabled
the Department of Electrical and Computer Engineering at Clemson University to
develop a new motors and drives laboratory using state-of-the-art industrial motor
controls. As a result, a laboratory has been renovated and equipped with three-phase
power to house the workstations. The hardware for each of these workstations is mostly
complete, but refinements are continuing on the human-machine interface, controls, and
data acquisition system. Additionally, laboratory experiments are being developed for
the workstations. These experiments will supplement junior- and senior-level
undergraduate lecture classes.

II. Overview of the Curriculum

The Electrical Engineering undergraduate degree program offers three courses in the
power systems area and one optional laboratory. During the junior year, EE students are
required to take an introductory course on power systems and electric machines. An
optional laboratory course can be taken concurrently with the class. At the senior year,
students are required to take two technical electives. Two power engineering courses are
among these elective choices. One of these is a traditional power system analysis course
and the other is a power electronics and drives course. These courses are described in
additional detail below.

ECE 360 (Energy Conversion) This class is a three-hour required course for juniors
majoring in electrical engineering. The topics include a review of three-phase circuit
analysis and power computations, magnetic circuits, transformers, dc motors, ac
induction motors, ac synchronous motors and generators, and transmission lines.
ECE 412 (Energy Conversion Laboratory) This laboratory is a one-credit hour
elective lab which is to be taken concurrently with or after ECE 360. This laboratory
focuses on experiments with motors and generators, using Lab-Volt brand equipment.
The experiments are typical introductory machines experiments: torque-speed
characteristics, equivalent circuit parameter determination and verification, synchronizing
generators to the line, etc. The motors are all run “across the line” and drives are not
discussed.

ECE 418 (Power System Analysis) This course is a three-credit hour elective class that
is taken by approximately 20% of the EE seniors. Topics covered include power system
modeling and the per-unit system, symmetrical components, load-flow, fault analysis and
some basics of economic dispatch. It is used as an introduction to the many facets of
power engineering and as a foundation for graduate study.

ECE 419 (Power Electronics and Drives) This course is a three-credit hour elective
class that is taken by about 25% of EE seniors. Topics include power electronic devices
(diodes, thyristors, power transistors, etc.), power electronic circuits and converters
(rectifiers, inverters, dc/dc, etc.), and the use of the power electronics as drives for
motors. Aspects of motor control are discussed, focusing primarily on the basics of ac
induction motor control using V/Hz schemes and dc motor control using thyristor-based
rectifiers.

III. The New Laboratory

Rockwell Automation Power Systems, headquartered in Greenville SC, has familiar
product lines such as Reliance Electric and Dodge. A few years ago, Rockwell donated
funding for a large scholarship endowment and an in-kind equipment gift to Clemson.
This gift was targeted specifically for Mechanical Engineering and Electrical and
Computer Engineering, with the ultimate goal of equipping a multi-disciplinary senior
capstone design project laboratory in mechatronics. As an intermediate step toward that
final goal, each department was able to enhance their own laboratories using the
equipment gift.

The ECE department chose to use the donation to develop a modern motors and drives
laboratory to supplement the existing motors lab. The Rockwell equipment was well
suited for such a deployment. Since most laboratories have approximately 10 to 15
students per section, we decided to create 5 workstations, with a sixth station as a
development prototype and a spare.

The original machines lab at Clemson was housed in the basement of our 1927-vintage
Riggs Hall. At that time, the basement was the logical place to locate the large motors
due to proximity to three-phase power, noise and vibration, and access to the loading
dock. In the ensuing years, the large motors were ultimately replaced by the small Lab-
Volt brand workstations, but the location of the lab remained the same.
Recently, we had an opportunity to move the laboratory to a location on the main
teaching floor of Riggs Hall. During the past year, the lab space was renovated to
remove an existing senior project lab and house the new power lab. Three-phase 208V
power was installed, with twist-lock outlets located around the periphery of the room and
at a central location. The facility is highly visible to ECE students and now houses both
the older Lab-Volt workstations and the new Rockwell lab stations. It is perhaps the
finest teaching lab in the department.

IV. The Workstation Details

The purpose of the workstations is to enable students to explore the operation of ac and
dc motors when fed from adjustable speed drives. The workstations contain ac and dc
motors, ac and dc drives, measuring instruments, data acquisition and control, a computer
and laser printer, and a digital oscilloscope.

Because of the equipment grant, the workstations utilize Reliance Electric and Dodge
components almost exclusively. Third party vendors, such as National Instruments,
Tektronics, and Eaton/Lebow, were used where comparable components were not
available from Rockwell. If the workstations were to be duplicated, equipment from a
variety of vendors could be used with similar functionality. Clemson University faculty,
undergraduates, and graduate students have designed and constructed these workstations,
developed a solid understanding of how they operate and what can be done with them,
and are presently debugging the systems and creating laboratory experiments. An
electrical engineering Master’s degree student has been instrumental in bringing this
project together and wrote an MS thesis on the subject. Another MS student is now
working on the completion of the project and the development of the experiments.

An overview of the basic functionality of the workstation is as follows. A block diagram
of the system is shown in Figure 1. Two small (1 hp) electric motors, one three-phase ac
induction motor and one dc motor, are coupled together via a clutch and a rotary torque
sensor. The torque sensor also contains a pulse encoder. Mechanical torque and speed
are measured using the torque sensor. A dc tach generator is also connected to the
system to give an analog speed signal. The induction motor can be line-connected or
driven from a variable frequency drive. The dc motor is driven from an adjustable speed
dc drive. The dc drive is a thyristor-based, four-quadrant device and is line-regenerative.
The ac drive is a 2-quadrant drive and is not capable of regeneration. The drive can be
operated in a volts/hertz or vector control mode. Dynamic braking resistors have been
added to the ac drive to provide 4-quadrant functionality. Therefore, either machine can
be operated as a controllable load (generator) while the opposite machine is used as a
motor.

The entire workstation is interfaced to a computer using a data acquisition card. The data
acquisition and control is performed using National Instruments LabView. The drives’
analog and digital I/O ports are connected to the PC, which acts as a master controller
(much like a PLC would operate an industrial system). Therefore, the speed and torque
of the motor and the load can be controlled via the LabView Human-Machine interface
(HMI) that we designed specifically for use with the workstation. Additionally, electrical
parameters (voltages and currents) at various locations on the workstation, as well as
torque and speed, can be acquired by LabView. LabView displays these measurements
on the computer screen (similar to an oscilloscope) as well as stores the sampled data.
Since the computers are on the university’s network, this data can be uploaded to a
website or emailed for use by the students outside of the laboratory.



                                          208V
                                       Three-Phase
                                         Supply




                                                                                         Resistive
                                                                                         Braking
                                                                                          Module

             Reliance                   Computer                           Reliance
           FlexPak 3000               Control (PLC),                     GV3000 AC
           Regenerative               HMI, and Data                       Adjustable
           DC Adjustable                Aquisition                       Speed Drive
            Speed Drive               using LabView                      (non-regen)




                                       Eaton/Lebow   Speed
  Tacho-
                            Clutch        Torque   Encoder
  meter        1.0 hp                                                        1.0 hp
                                          Sensor   (integrated into
            Reliance DC                                 torque sensor)    Reliance AC
             Motor with                                                  3 φ Induction
            Shunt Field                                                      Motor
Figure 1. Block Diagram of the Workstation.


V. Features of the Workstations

In this section, some photographs and descriptions of some of the salient features of the
workstations are provided. Figure 2 shows an overall view of the workstation, with the
drives mounted on the backplane, the motors, clutch, torque sensor and tachometers
mounted at the bottom. The computer and printer are located just beneath the countertop,
and a LCD monitor on a pivoting arm is mounted to the backplane. Much of the wiring
has been placed behind lexan covers so that students can see how the components are
interconnected. Safety sockets have been used so that students can connect to these wires
with modern “banana” plugs to measure voltages without the risk of contacting exposed
conductors. Voltage isolators are used to connect the voltage probes to the data
acquisition system. This eliminates the chance of ground loops and other short circuits as
well as overvoltage to the input ports. Loops have been brought out at various locations
so that students can clamp current transformers to measure currents.
DC Drive
                                                                                                         AC Drive

LabView
Display                                                                                                  Braking
                                                                                                         Modules

Probe
Interface
                                                                                                         Laser
                                                                                                         Printer
Computer




DC Motor
                                                   Torque
                       Clutch                                                         AC Motor
                                                   Transducer
           Figure 2. A Rockwell Automation Motor Drive Workstation. This workstation
           consists of a Reliance Flexpak 3000 four-quadrant dc drive, a Reliance GV 3000 ac drive
           with dynamic braking, a Dell computer using National Instruments data acquisition
           running LabView, and a Reliance three-phase AC induction motor coupled to a Reliance
           DC Motor via a Dodge Clutch and Eaton/Lebow torque sensor. A pulse speed encoder
           and dc tach generator provide speed information. Tektronix voltage isolators and Extech
           hall effect current probes provide electrical signals to the data acquisition (DAQ) card. A
           custom-designed input/output interface between the instrumentation and the DAQ card
           provides overvoltage protection. A Tektronix digital oscilloscope and Fluke multimeter
           are available for conventional measurements. A laser printer is connected to the
           computer and oscilloscope for local hardcopies. The computer is connected to the
           campus network.
                                                                                        Lexan
                                                                                        Safety
                                                                                        Shield

Regenerative
DC Drive


                                                                                        Loops for
                                                                                        Current
                                                                                        Probe
                                                                                        Connections

   Moveable
   Current
   Probe                                                                                Sockets for
                                                                                        Voltage
                                                                                        Probe
                                                                                        Connections




                                                                                        Digital
                                                                                        Oscilloscope




     Figure 3. Details of the DC Drive portion. The left side of the workstation contains
     the Flexpak 3000 four-quadrant dc drive and access to the input and output electrical
     wiring. The wiring is behind a lexan cover so that students can see the actual wiring but
     can only access the live parts via safety plugs mounted on the lexan. Optically isolated
     voltage probes and current transformers enable students to safely measure voltages and
     currents at a variety of locations on the digital oscilloscope or on the computer. The dc
     drive’s input voltage and current on all three phases, the armature voltage and current,
     and the field voltage and current are accessible for measurement. The speed and torque
     of the dc motor are also available via transducers.
                         Braking Resistors




                                                                                        AC Drive



    Current
    Probe




Power and
Control
Connections
and Relays



                                                                                           Isolated
                                                                                           Voltage
                                                                                           Probe




        Figure 4. Details of the AC Drive portion. The right side of the workstation contains
        the GV 3000 ac drive and access to the input and output electrical wiring. As shown
        previously, the wiring is behind a lexan cover so that students can see the actual wiring
        but can only access the live parts via safety plugs mounted on the lexan. The ac drive’s
        input and output voltage and currents, the dc link voltage, and dynamic braking resistor
        voltage and current are available for measurement, in addition to the motor’s mechanical
        parameters.
                                                                   Torque
    DC Tach                                Clutch                  Sensor &
                                                                   Encoder




Figure 5. Details of the Motors. The motors are mounted on the bottom of the
workstation behind Lexan safety shields to prevent inadvertent contact with rotating
parts. The Reliance DC motor is on the left and the Reliance AC induction motor is on
the right, with a Dodge Clutch connected between the DC motor and the Eaton/Lebow
torque sensor. A Reliance dc tach is mounted to the dc motor and a pulse encoder is
contained in the torque sensor. The clutch enables easy no-load testing of the motors and
is controlled from the HMI on the computer.




Figure 6. HMI Display, showing part of the LabView interface. This screen shows
the start, stop, jog, and speed control for the two drives and the oscilloscope shot of the
GV 3000 ac drive’s output voltage and current. The data acquisition card can accept 4
channels of analog input and students can choose to connect the voltage and/or current
probes to any location on the system for display or data capture. The digital data shown
on the graphs can be exported to files for students to use away from the lab.
VI. Sample Experiments

We are presently developing experiments for students to use with the workstations.
During the Spring of 2004, the workstations will be integrated into the ECE 419 Power
Electronics and Drives class. The plan is to use the workstations for 4 exercises (outside
of normal class-time). These exercises will include: dc drive operation and control, ac
drive operation and control, regenerative and dynamic braking, and drive control systems.
Initially, we envision the labs being used to primarily demonstrate concepts that have
been taught in class and to enable students to explore the drives’ operation. The figures
that follow demonstrate some of the items that could be explored.




                                                                Legend:
                                                                •   Red: AC Input Line Voltage
                                                                •   Green: AC Input Line Current
                                                                •   Blue: PWM Output Voltage of
                                                                    AC Drive
                                                                •   Magenta: AC Motor Current




Figure 7. Normal ac drive input and output waveforms. This image was captured
from the workstation and shows the input voltage and current waveforms and the output
voltage and current waveforms. Concepts such as harmonics could be explored from the
data.




                                                                Legend:
                                                                •   Red: AC Input Line Voltage
                                                                •   Green: AC Input Line Current
                                                                •   Blue: Output Armature Voltage of DC
                                                                    Drive
                                                                •   Magenta: DC Motor Armature
                                                                    Current




Figure 8. Normal dc drive input and output waveforms. This image was captured
from the workstation and shows the input voltage and current waveforms and the output
voltage and current waveforms from the drive. While cluttered, it demonstrates the 4-
channel capability of the data acquisition system. Students can choose these or many
other parameters, such as field voltage, torque, speed, etc.
                      Switching frequency 8KHz                                   Switching frequency 2KHz

        0.6                                                               0.8                       AB line voltage (1V/500V)

                                                                          0.6                       AN line current (.1V/A)
        0.4
                                                                          0.4
        0.2                                                               0.2
Volts




                                                                  Volts
         0.0                                                        0.0
           0.015                             0.02                     0.010
                                                             0.025 -0.2
        -0.2
                                                                   -0.4
        -0.4                                                              -0.6

        -0.6                                                              -0.8
                                        Time (seconds)                                   Time (seconds)

         Figure 9. Switching frequency effects. These graphs show the ac drive’s output
         voltage when the switching frequency has been changed from 8 kHz to 2 kHz. The
         students can see the effect of this change on the voltage PWM waveform and the increase
         of ripple in the motor’s current waveform, and they can audibly hear the change from the
         motor and drive.

                                                                          DC Link Voltage
                                     0.9
                                     0.8
                                     0.7
               DC Link Volts (pu)




                                     0.6
                                     0.5
                                     0.4
                                     0.3
                                                       Resistor Voltage
                                     0.2
                                     0.1
                                       0
                                    -0.1 0      0.01      0.02       0.03         0.04       0.05        0.06
                                                                 Time (sec)

         Figure 10. Dynamic Braking Resistor Operation. This figure shows the voltage and
         current waveforms captured from the dynamic braking resistor when the ac drive is
         operated in a regenerative mode (being driven by the dc motor). Students can observe
         changes in this waveform as the loading is increased, and compute the amount of
         regenerated power, among other things.
VII. Conclusion

The Rockwell Automation laboratory will provide an excellent opportunity for our
students to learn about modern motor control and power electronic applications in a safe
and flexible environment. The workstations offer many possibilities for experimentation
on motors and drives similar to those that students will encounter in “the real world.” We
are just beginning to incorporate these workstations into our classes. We do not
anticipate that these workstations will replace the older motor and generator workstations,
but they will enable students to learn about the next step in the evolution of modern
rotating machinery.

Already, we have seen a change in enrollment in our senior-level power electronics and
drives class due to these workstations. The mere visibility of these modern platforms,
and the digital oscilloscopes, printers, etc., have made students excited about using them.
It is our hope that this excitement will go beyond the initial “look through the window”
excitement. Indeed, we hope that students will become more interested in modern power
engineering, power electronics and drives, and find that power engineering is much more
than ugly wires hanging from the poles.

VIII. Acknowledgements

Special thanks to Mr. Joseph Swann, Joe Razum and others at Rockwell Automation for
their generous gift. Thanks to Dr. John Gowdy for providing departmental support for
the laboratory space and expenses involved in peripheral equipment, construction of the
workstations, and development activities. And, without the assistance of two fine
graduate students, Adam Baier and Ryan Yocco, this project would not have been
possible. My sincerest thanks to both of you for dedication “above and beyond” the call
of duty.