Transcript Course overview

EE462L/EE394-7, Spring 2014
Overview
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•Question: What are power electronic devices?
•Answer: Fast switches that can handle high voltages
and currents
•Question: Why do we need these fast switches?
•Answer: To efficiently convert AC to DC, DC to DC, or
DC to AC, or to efficiently control average power flow.
(Efficiently usually means greater than 80% – 90%)
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A switch
Rugged, reliable, efficient, long lived, but not very fast
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The ideal power electronic device is a perfect
switch that
• is fast − can open and close instantly (thus no
switching losses), and at a high rate (i.e., operating
frequency)
• when closed, can conduct any amount of current with
no internal voltage drop (thus no conduction losses)
• when open, will conduct no current and can withstand
any voltage without breakdown
• will be unidirectional or asymmetric (that is an inherent
property of power electronic devices, and we can
always place two switches in antiparallel and use
blocking diodes to prevent backward conduction)
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An everyday example – a light dimmer
• Method 1 to dim the light – insert a series resistor between the
120Vac source and the bulb. This method has high insertion
loss and low efficiency.
Rseries
+
120Vac
–
Rbulb
Efficiency = Rbulb ÷ (Rbulb + Rseries)
Efficiency = 50% when light power is half
• Method 2 to dim the light – switch the voltage to the bulb onand-off, faster than the eye can detect, to reduce the rms
voltage at the bulb. This is lossless dimming.
+
120Vac
–
Rbulb
?
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Another example – convert 39Vdc to 13Vdc
Stereo
voltage
Switch closed
Switch open
39
+
39Vdc
–
Rstereo
0
Switch state, Stereo voltage
Closed, 39Vdc
DT
T
Open, 0Vdc
If the duty cycle D of the switch is 1/3, then the average voltage
to the expensive car stereo is 39 ÷ 3 = 13Vdc. This is lossless
conversion. However, is this acceptable?
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Convert 39Vdc to 13Vdc, cont.
+
39Vdc
–
Try adding a large C in parallel with the
load to control ripple. But if the C has
13Vdc, then when the switch closes, the
source current spikes to a huge value
Rstereo
C
L
+
39Vdc
–
C
Rstereo
Try adding an L to prevent the huge
current spike. But now, if the L has
current when the switch attempts to
open, the inductor’s current
momentum and resulting Ldi/dt will
burn out the switch.
Rstereo
By adding a “free wheeling” diode,
the switch can open and the
inductor current can continue to
flow. With high-frequency
switching, the load voltage ripple
can be reduced to a small value.
lossless
L
+
39Vdc
–
C
A DC-DC Buck Converter
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Another example - H-bridge inverter converts DC to AC
Vdc
Vdc
closed
closed
A+
A+
B+
+ Vload −
+ Vload −
closed
A–
B+
B–
closed
A–
B–
A+,B− closed; A−,B+ open
A+,B− open; A−,B+ closed
Vload = Vdc
Vload = −Vdc
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The H-bridge inverter that you will build to
convert DC (e.g. from a solar panel) to AC
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The class is divided into three lab periods in ENS212
(the Power Lab)
•Sections 17060 and 17374: Thur. from 3:30 pm to 6:30 pm
•Sections 17065 and 17370: Wed. from 6:30 pm to 9:30 pm
(some projects, such as the PV project, may require going to
the lab at different times)
But to build and test some of your circuits, you will
also need to work other times during the ECE 2nd floor
laboratory hours
This is not a theoretical course. This is
a practical course.
Circuits and reports are your primary
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form of “homework”
The class is divided into three lab periods, cont.
The optimum situation is:
• Each lab period has the same number of students
• If you have a strong case for permanently and informally
switching lab sections, it will be considered as long as the
numbers are not too unbalanced or your request leads from
even number of students to odd number of students.
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Power labs are unlike other ECE labs – they can
be hazardous and require considerable caution
• Unlike 5V digital labs, power experiments can burn,
go “bang,” blow fuses, melt components, and scare
or hurt you.
• Never test a power circuit by “let’s power it up and
see if it works!”
• It is important that you and your partner triple-check
your wiring before energizing a circuit for the first
time. For the first few experiments, let a TA or me
check it with you.
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Power labs are unlike other ECE labs, cont.
• Never dangle wires or oscilloscope leads over an
energized circuit
• You will have several different “grounds” – so be
careful when taking measurements. Never attach
two oscilloscope ground clips to nodes with
different potentials.
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This is a course where you will
• Learn how to convert AC to AC, AC to DC, DC to DC,
and DC to AC (i.e., the AC – DC – AC “round trip”)
• Learn the theory related to the circuits, and be tested
over it 2 times and at the final exam
• Read the lab document before starting to build!
• Build the circuits in two-person teams. Each team
then prepares a single two-person team report.
• Compare theory to actual circuit performance. In
order to do well in this class you need to have a
critical approach when working with your circuits. If
you just try to do your projects by “following a
recipe” chances are that you will not do well in this
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course.
This is a course where you will, cont.
• Sometimes work with voltages over 100V, and where
short circuit currents are high, so be careful! Remove
hand jewelry and dangling neckchains.
• Use safety glasses 1. when soldering to avoid
accidental hot solder “splashback” in your eyes, or 2.
when getting “up close and personal” to observe an
energized power circuit.
• Wash your hands after soldering (because solder
contains lead)
• Use knowledge of circuit operation, plus your senses
of sight, sound, smell, and touch (carefully), to
observe and debug your circuits
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This is a course where you will, cont.
• Build your circuit together with your partner
• Taking turns, one partner builds, while the other partner
double-checks with the schematic and verifies the
connections
• Not simply build your circuit by blindly copying the
sample circuit or lab document photograph, wire for
wire! (if so, you cheat yourself and you will not
understand the circuit)
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This is a course where you will, cont.
• Write 11 reports that describe 8 circuits plus
photovoltaics (tentative) and 2 additional applications of
the inverter
• Be assigned a partner and be expected to work with
your partner as a team. Solo/a requests will be
considered only and justified only in well justified
circumstances.
• Receive the same report grade as your partner.
• Be permitted to select a partner. Please do so by next
Tuesday. If you don’t indicate a partner preference, your
partner will be selected randomly.
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Concerning Partners
• Bring any partner problems to my attention right away
• If a section has an odd number of partners, then a
randomly chosen graduate student will be requested to
solo.
• In some well justified cases partners may be changed
during the course. However, not liking your partner is
not a justified case. Like in real jobs you will need to
learn how to work with your partner even when you
don’t like each other.
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This is a course where you will, cont.
• At the start of the due date lab period, and as called in
team order, turn in your report (hardcopy only – no
emails), and turn in your circuit
• We will inspect your circuit for construction quality,
and decide if it meets the quality threshold
• Reports and circuits not turned in when a team is
called forward receive
– 1. fractional +/− letter grade reduction if turned in later
during that lab period, or
– 2. full letter grade reduction if turned in during the following
Tuesday’s class. Later reports will not be accepted.
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This is a course where you will, cont.
• Become proficient in soldering and in the use of
oscilloscopes and meters
• Learn the resistor color code to make your life easier
• Understand and appreciate why resistors have power
ratings
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This is a course where you will, cont.
• Learn about solar panels, and how to use the
electricity they produce, with the panels atop ENS
• Learn about sun position in the sky throughout the
year, components of solar radiation, and the effect
that panel angles have on daily energy produced
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The circuits are
• Light dimmer (AC to AC)
• Diode bridge rectifier (AC to DC)
• Photovoltaics (on ENS roof) (actually it is not a circuit).
• MOSFET firing circuit
• Buck, boost, and buck/boost converters (DC to DC)
• Inverter (DC to AC) and its three component circuits
(PWM control, isolated firing circuit, and H-bridge)
• Optional – PI controller for boost converter
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The pace is fast, so don’t get behind
• Because you will build many circuits in a relatively
short time, it isn’t possible for you to design your
own circuits
• Most parts are not available at the regular ECE
checkout counter
• Recommendations for improving the circuits,
construction, testing techniques, lab documents, as
well as ways to improve the overall lab experience
are always appreciated
• Regarding design opportunities, many students use
these circuits as starting points for Senior Lab 464
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Is EE462L for you?
If you do not want to
• build circuits,
• be cooperative,
• be courteous,
• be a good lab citizen,
• be careful, and
• carry your weight, then …
you are in the wrong course!
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Is EE462L for you?
• Some comments about the course’s concept:
• The focus of the course is on lab work and learning through
practical work in the lab.
• This course is NOT a theoretical-based course.
• Although most of the lectures include an overview of the
theoretical background, you are expected to gain further insights
from the lab work and from your own work.
• Lectures are mostly based on Powerpoint presentations. Many
concepts and circuits require time consuming circuit drawings
and text explanations. Without Powerpoint it will be impossible to
cover the course material.
• If you have trouble following Powerpoint presentations, you are
encouraged to consult the recommended books or the lab manual,
or to ask the TAs or the professor.
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Tuesday and Thursday lectures
• The supporting theory and explanations of the
circuits are taught during the lectures.
• There are usually three lectures each week.
• Many times there will be an attendance roster
as you enter the room. You are expected to sign
it at the beginning of the class and no later than
5 minutes after class starts
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Lectures, cont.
• Please be punctual – having many late arrivals for the
first 5-10 minutes is disruptive and, in effect, delays the
start of class
• Cell phones and laptops – turn off (unless you clear it
with Dr. Kwasinski). Students not complying with this
rule may be assigned an “absent” for the class in which
they are using their laptops or cell phones without
asking Dr. Kwasinski first.
• A few times I will need to be away for lectures to attend
conferences or to participate in meetings. These trips
are intended to benefit the power electronics program at
UT so they also benefit you, students in this class.
These trips are not pleasure trips at all. Most of the time
they involve being the entire time at a hotel conference
room. Trips to disaster areas may not even involve a 27
hotel at all.
The course grading formula is
• Lab circuits and reports – 50%
• Two tests. Tentative dates are on Mon. (Feb. 25, April
22) – 20%
• Comprehensive final exam (everybody takes it at the
UT scheduled day and time. However, the final is not
planned for the whole 3-hour slot) – 20%
• Attendance (taken at all lab sessions, and at most
lectures) – 10% (scaled so that perfect attendance
gets full credit, 50% attendance gets zero credit).
• Fractional letter grade (A, A-, B+….) will be used for
the final grade. A is equivalent to 100 % and
according to
http://registrar.utexas.edu/students/grades, B is
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equivalent to 75% and so on.
Concerning tests and the final exam
• One 8.5” x 11” sheet of notes is permitted at each test
and at the final exam
• The questions are sometimes multiple choice, with
several possible answers given, plus an “Other” box.
The correct answer is supposed to be among the given
answers. Adequate work must be shown to justify the
chosen answer.
• Tests and the final exam may be individually curved so
that they have approximately the same average grade
• If it works to your advantage, your lowest (or missing)
test grade will be replaced by your final exam grade
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Concerning tests and the final exam, cont.
Regrade requests are handled as follows:
Within a week of getting your graded test back (but not
the same day),
• Neatly write down on a piece of paper your reasons
for requesting a regrade,
• Staple the paper to your test,
• Return it to me for consideration
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Good citizenship in the power lab
• Be courteous to your fellow students – we all
share the same power lab
• When finished in the lab, clean up your mess
• When finished in the lab, return all equipment
items to their proper place
• When crowded, do not “hog” the lab benches
by doing unnecessary or unrelated work there
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Absences and Other Extenuating
Circumstances
• Please do not ask for excused absences or late
attendance roster sign-ins
• Instead, handle absences, missed attendance roster
sign-ins, and all other extenuating circumstances as
follows:
• Keep a record book with details
• At the end of the semester, prepare a written statement
that itemizes each and gives reasons
• Staple the statement to your final examination
• Your statements will be taken consideration, all at
once, when assigning the final course grades
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Team Tool Kit #1
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Team Tool Kit #2
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More Team Tools
Each student gets a
pair of safety
glasses and keeps
them
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Lab Equipment
120 Vac Variac
120/120 Vac Isolation
Transformer
Panavises
120/25 Vac Transformer
Three-Series Headlight Load
Bank
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Lab Equipment, cont.
Oscilloscope
Ground Fault Interrupter
(GFI)
SEL-421 Relay and Meter
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Questions?
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