Transcript Course introduction

Course Introduction
• Meetings: Monday and Wednesdays from 3:00 to 4:30 PM in
ENS 145
• Professor: Alexis Kwasinski (ENS348, [email protected],
Ph: 232-3442)
• Course Home Page:
http://users.ece.utexas.edu/~kwasinski/EE394J11Fa13.html
• Office Hours: Mondays and Wednesdays (1:30 – 3:00 pm); or
by appointment.
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© Alexis Kwasinski, 2013
Course Introduction
Prerequisites (or consent from the instructor):
• Fundamentals of power electronics and power systems.
• Fundamentals of power electronics means basic knowledge of control systems, circuits
and electronic devices.
• Familiarity with at least one computer simulation software and basic modeling
approaches.
• Knowledge on how to browse through professional publications.
Course Description:
• Graduate level course.
• Goal #1: To discuss advanced topics in power electronics.
• Goal #2: To prepare the students to conduct research or help them to improve and/or
develop their research skills.
• Both goals are equally important
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Course Introduction
Implications of the second goal:
• There are no midterm exams or final but…..
• You will have to carry out a project throughout the semester which mimics a research
work that you would do for a conference.
• The project’s deliverables include:
• A preliminary report
• A final report (term paper)
• A presentation to the rest of the class during the last week of classes
• Homework assignments tend to be more intense than what you were used to have in
undergraduate courses, but you will have about 2 weeks to complete it.
• You will receive minimal guidance to answer the questions ask in your homework
assignments. This is done on purpose in order to help you develop your research skills.
• In most homework problems the process you take to answer the questions being ask is
more important that the end numerical result. So be sure to explain clearly your train of
thoughts.
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Course Introduction
Grading:
Homework: 25%
Project preliminary evaluation: 15%
Project report: 30%
Presentation: 20%
Class participation: 10%
Letter grades assignment: 100% – 96% = “A+”, 95% – 91% = A, 90% – 86% = A-, 85%
– 81% = B+, and so on.
Homework:
• Homework will be assigned approximately every 2 weeks.
• The lowest score for an assignment will not be considered to calculate the homework
total score. However, all assignments need to be submitted in order to obtain a grade
for the homework.
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Course Introduction
Project:
• The class includes a project that will require successful students to survey current
literature.
• The project consists of carrying out a short research project throughout the course.
• The students need to identify some advanced topic in power electronics.
• The project is divided in two phases:
Preliminary phase. Due date: Sept. 30. Submission of references, application
description, and problem formulation (1 to 2 pages long).
Final phase. Due date: Nov. 25. Submission of a short paper (the report), at
most 10 pages long, single column.
Presentations:
• Each and every student is expected to participate in the final presentation discussing
their project to the rest of the class as if it were a conference presentation of a paper.
• The format of the presentations will be announced during the semester.
• The presentation of the course project to the rest of the class replaces the final exam.
• Presentations are scheduled during regular class times on the last week of classes.
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Course Introduction
Schedule:
Wednesday, Aug. 28
Week 1 (begins Sept. 2)
Week 2 (begins Sept. 9)
Week 3 (begins Sept.16)
Week 4 (begins Sept 23)
Week 5 (begins Sept 30)
Week 6 (begins Oct 7)
Week 7 (begins Oct 14)
Week 8 (begins Oct 21)
Week 9 (begins Oct 28)
Week 10 (begins Nov. 4)
Week 11 (begins Nov. 11)
Week 12 (begins Nov. 18)
Week 13 (begins Nov 25)
Week 14 (begins Dec 2)
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Introduction. Course description. Power electronics
perspectives. Review of fundamental concepts.
Continuation of the review of fundamental concepts.
Switched model. (Monday is a holiday)
Average and linear models
Semiconductor switches model (diodes, MOSFETs and IGBTs).
Real loads, sources, and passive components. Rectifiers
Rectifiers. Single-input dc-dc converters.
Single-input dc-dc converters. Multiple-input converters.
Inverters (Dr. K at INTELEC 2013)
Thermal design. Reliability
Linear and nonlinear control methods in power electronics
Linear and nonlinear control methods in power electronics. Power
electronics converters for renewable and alternative energy.
Power electronics converters for renewable and alternative energy.
Maximum power point tracking
Grid interaction. Islanding. EMI and power factor control.
Power electronics for energy storage (batteries, ultracapacitors and
flywheels). Thanksgiving week
Presentations
© Alexis Kwasinski, 2013
Course Introduction
• The schedule is tentative and may be adjusted depending how fast or slow the
pace of the class needs to be.
• When I cannot be present either I will teach the class remotely or the TA will
teach the class
• Already confirmed lost classes are:
• Sept. 18: ECCE (may be Wednesday only)
• Week of Oct. 14: INTELEC 2013
• I may be absent in one or two other classes due to research commitments
(hurricane damage assessments)
• Additional significant dates:
• Sept. 2: Labor day (shouldn’t affect us other than for the office hours)
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Power electronics
• Power electronics is a technical field dedicated to study, analyze, construct,
and maintain electronic circuits capable of controlling electric energy flow.
• Related fields include:
• Devices and materials
• Controls and systems
• Power and energy
• Power electronic circuits critical components include
• Switches often commutated at a high rate (kHz or faster).
• Energy storage components (capacitors and inductors).
• Use of power electronics are linked to power systems development.
• There are two main group of power electronic applications
• Static applications (output is primarily electric power)
• dynamic/mobile applications (output is primarily mechanical
power)
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History
Competing technologies for electrification in 1880s:
• Edison:
• dc.
• Relatively small power plants (e.g. Pearl Street Station).
• No voltage transformation.
• Short distribution loops – No transmission
• Loads were incandescent lamps and possibly dc motors (traction).
Pearl Street Station:
6 “Jumbo” 100 kW, 110 V
generators
“Eyewitness to dc history” Lobenstein, R.W. Sulzberger, C.
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History
Competing technologies for electrification in 1880s:
•Tesla:
• ac
• Large power plants (e.g. Niagara Falls)
• Voltage transformation.
• Transmission of electricity over long distances
• Loads were incandescent lamps and induction motors.
Niagara Falls historic power plant:
38 x 65,000 kVA, 23 kV, 3-phase
generatods
http://spiff.rit.edu/classes/phys213/lectures/niagara/niagara.html
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History
Edison’s distribution system characteristics: 1880 – 2000 perspective
• Power can only be supplied to nearby loads (< 1mile).
• Many small power stations needed (distributed concept).
• Suitable for incandescent lamps and (dc) traction motors only.
• Cannot be transformed into other voltages (lack of flexibility).
• Higher cost than centralized ac system.
• Used inefficient and complicated coal – steam actuated generators (as
oppose to hydroelectric power used by ac initial centralized systems).
• Not suitable for induction motor.
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History
Traditional technology: the
electric grid:
• Generation, transmission, and
distribution.
• Centralized and passive
architecture.
• Extensive and very complex
system.
• Complicated control.
• Not reliable enough for some
applications.
• Relatively inefficient.
• Stability issues.
• Vulnerable.
• Lack of flexibility.
• Unique, fixed frequency.
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History
Edison’s distribution system characteristics: 2000 – future perspective
• Power supplied to nearby loads is more efficient, reliable and secure than long
power paths involving transmission lines and substations.
• Many small power stations needed (distributed concept).
• Existing grid not suitable for dc loads (e.g., computers) or to operate induction
motors at different speeds. Power electronics allows varying speeds in
induction motors and to feed dc loads.
• Power electronics allows for voltage and current signals to be transformed
(flexibility).
• Transportation electrification needs.
• Can use renewable and alternative power sources.
• Can integrate energy storage.
• Power electronics is the one single technology that Edison needed in the late
1800s.
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Power electronic applications
• Dynamic:
• Variable speed drives in industries
• Arguably for wind generation
• Electric and hybrid electric cars (and other transportation
applications)
• Stationary:
• UPS
• Energy storage integration
• Information and communication technologies power plants
• Power supplies
• Solar power
• Micro-grids
•
•
•
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Power electronics basics
• Types of interfaces:
• dc-dc: dc-dc converter
• ac-dc: rectifier
• dc-ac: inverter
• ac-ac: cycloconverter (used less often)
• Power electronic converters components:
• Semiconductor switches:
• Diodes
• MOSFETs
• IGBTs
Diode
• SCRs
• Energy storage elements
• Inductors
• Capacitors
• Other components:
• Transformer
IGBT
• Control circuit
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MOSFET
SCR
Power electronics basics
• dc-dc converters
• Buck converter
Vo  DE
• Boost converter
E
Vo 
1 D
• Buck-boost converter
DE
Vo  
1 D
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Power electronics basics
• Rectifiers
v
v
v
t
t
Rectifier
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Filter
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t
Power electronics basics
• Inverters
• dc to ac conversion
• Several control techniques. The simplest technique is square wave
modulation (seen below).
•The most widespread control technique is Pulse-Width-Modulation (PWM).
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Power electronics basic concepts
• Energy storage
• When analyzing the circuit, the state of each energy storage element
contributes to the overall system’s state. Hence, there is one state variable
associated to each energy storage element.
• In an electric circuit, energy is stored in two fields:
• Electric fields (created by charges or variable magnetic fields and
related with a voltage difference between two points in the space)
• Magnetic fields (created by magnetic dipoles or electric currents)
• Energy storage elements:
• Capacitors:
Inductors:
L
C
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Power electronics basic concepts
•Capacitors:
• state variable: voltage
• Fundamental circuit equation:
dvC
iC  C
dt
• The capacitance gives an indication of electric inertia. Compare the
above equation with Newton’s
dv
F m
dt
• Capacitors will tend to hold its voltage fixed.
• For a finite current with an infinite capacitance, the voltage must be
constant. Hence, capacitors tend to behave like voltage sources
(the larger the capacitance, the closer they resemble a voltage source)
• A capacitor’s energy is
1
WC  Cv 2
2
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Power electronics basic concepts
• Inductors
• state variable: current
• Fundamental circuit equation:
diL
vL  L
dt
• The inductance gives an indication of electric inertia. Inductors will
tend to hold its current fixed.
• Any attempt to change the current in an inductor will be answered with
an opposing voltage by the inductor. If the current tends to drop, the
voltage generated will tend to act as an electromotive force. If the
current tends to increase, the voltage across the inductor will drop, like
a resistance.
• For a finite voltage with an infinite inductance, the current must be
constant. Hence, inductors tend to behave like current sources (the
larger the inductance, the closer they resemble a current source)
• An inductor’s energy is
1 2
WL 
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2
Li
© Alexis Kwasinski, 2013
Power electronics basic concepts
• Since capacitors behave like constant voltage sources you shall never
connect a switch in parallel with a capacitor. Any attempt to violate this load will
lead to high currents. Likewise, you shall never connect a switch in series with
an inductor. Any attempt to violate this rule will lead to high voltages.
•Steady state:
• In between steady states there are transient periods,
• In steady state the energy in each of the energy storage elements is
the same at the beginning and end of the cycle T. That is, ideally power
input = power output
• Of course, during the transient periods (if they could be called
“periods”) there is a difference between the initial and final energy.
• E.g. inductor:
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WL 
1 2
Li
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Power electronics basic concepts
• The average voltage across an inductor operating in periodic steady state is zero.
dW (t )  0
WL 
 vL (t ) 
1 2
Li
2
P0
i(T )  i(0)
1 T
1 T
L
v
(
t
)
dt

Ldi

(i (T )  i (0))
L


0
0
T
T
T
 vL (t )  0
• Likewise, the average current through a capacitor operating in periodic steady state is
zero.
 iC (t )  0
• Hence, Both KCL and KVL apply in the average sense.
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Power electronics basic concepts
• Time constants: In power electronics we tend to work in many circuits with
“large” capacitances and inductances which leads to “large” time constants.
• What does “large” means? Large means time constants much larger than the
period (whatever the period is. For example, a switching period.
C    RC
L  
Time constant time scale
L
R
Period time scale
• If you look close and for a short time interval, exponentials look like lines
2
t
et  1  t  
2
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for small t

 et  1  t
© Alexis Kwasinski, 2013
Power electronics basic concepts
• Switch matrix
• It is a very useful tool to represent a power electronics circuit operation
and to related (input) variables and (output) signals.
• Analysis with a switch matrix involves:
• 1) Identify and define all possible states. States are defined based on
all possible combinations of the switches in the matrix. Switches have
two possible states: ON (1) or OFF (0).
• 2) For each possible state relate (output) signals to (input) variables
by taken into consideration the time at each state (i.e. the portion of the
time with respect to the switching period).
• 3) Combine the previous relationship in order to calculate average
values for the (output) signals.
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Power electronics basic concepts
• Switch selection
• There are two criteria:
• Current conduction direction
• There are two possible directions:
• Forward – Usually from source to load
• Bi directional – Both directions
• (if current only circulates in the reverse direction, just reverse
the switch and make it a forward conducting switch).
• Voltage present at the switch when it is blocking the current flow.
• The definition relies on the voltage polarity off the switch when it is
blocking current flow and with respect to the forward current
direction convention.
• Can be reverse blocking (RB - diode), forward blocking (FB – BJT
or MOSFET), or bi-directional blocking (BB - GTO).
+
-
• Switches power rating is significantly higher than their losses.
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Power electronics basics
• Harmonics
• Concept: periodic functions can be represented by combining
sinusoidal functions

f (t )  c0   cn cos(nt   n )
n1
• Underlying assumption: the system is linear (superposition principle
is valid.)
• e.g. square-wave generation.
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Power electronics basics
• Additional definitions related with Fourier analysis

f (t )  a0   (an cos(nt )  bn sin(nt ))
n 1
1  T
a0   f (t )dt
T 
2  T
an   f (t )cos(nt )dt
T 
2  T
bn   f (t )sin(nt )dt
T 
a0  c0
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(dc components)
cn  a  b
2
n
2
n
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 bn 
 n   tan  
 an 
1
Power electronics basic concepts
• In power electronic circuits, signals usually have harmonics added to the
desired (fundamental) signal.
• Energy storage elements are used to
• Provide intermediate energy transfer buffers.
• Filter undesired harmonics
• There are two approaches:
• Linear approximation (based on time constants considerations).
I.e., current and voltage ripples)
VC
IC  C
T
I L
VL  L
T
• Harmonic superposition

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Power electronics basics
• Additional definitions
1  T
 f (t )   f (t )dt
T 
• Average
• RMS value
2
f (t ) RMS


1 T 2
1  2
2
  f (t )dt  c0   cn  c0   cn, RMS   cn2, RMS
T 0
2 n1
n 1
n 0
• Instantaneous power
p(t )  v(t )i (t )
• (Average) power

Vn I n
1  T
P   v(t )i (t )dt  V0 I 0  
cos(Vn   In )

T
n 1 2
• Total harmonic distortion

THD 
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2
c
n
n2
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Power electronics basics
• Additional definitions
T
p(t )dt
Average Power

0
p. f 

Apparent Power VRMS I RMS
• Power factor
1
T
• Line regulation
LiR(%)  100
VOUT (Highest input )  VOUT (Lowest input )
VOUT ( Nominal)
• Load regulation
LoR(%)  100
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VOUT (Min Load)  VOUT (Full Load)
VOUT ( Nominal)
© Alexis Kwasinski, 2013