Course Introduction

1
Course Introduction

• Meetings Tuesdays and Thursdays from 330 to
  500 PM in ENS 116
• Professor Alexis Kwasinski (ENS528,
  akwasins_at_mail.utexas.edu, Ph 232-3442)
• Course Home Page http//users.ece.utexas.edu/kw
  asinski/EE394VAPEFa09.html
• Office Hours Mondays (130 to 300 PM) and
  Wednesdays (1200 to 130 PM) or by appointment.

2
Course Introduction

• Prerequisites
• Fundamentals of power electronics and power
  systems or consent from the instructor.
• Familiarity with at least one computer
  simulation software.
• 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

3
Course Introduction

• Grading
• Homework 25
• Project preliminary evaluation 15
• Project report 25
• Final exam 25
• 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.

4
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 Oct. 13. Submission
  of references, application description, and
  problem formulation (1 to 2 pages long).
• Final phase. Due date Nov. 24. Submission of a
  short paper (the report), at most 10
  pages long, single column.
• Final Exam
• The format of the final exam will be announced
  during the semester.
• The official date and time for the final can be
  found at http//registrar.utexas.edu/schedules/09
  9/finals/index.html. (W 12/9, 2-5 pm)
• Prospect for working in teams
• Depending on the course enrollment, I may allow
  to do both the project and the final exam in
  groups of 2. I will announce my decision within
  the first weeks of classes.

5
Course Introduction
Schedule Thursday, August 27 Introduction.
Course description. Power electronics
perspectives. Review of fundamental
concepts. Week 1 (begins August 31) Continuation
of the fundamental concepts review. Power
electronic circuits modeling. Week 2 (begins
September 7) Power electronic circuits modeling.
Single-input and multiple-input dc-dc
converters Week 3 (begins September 14) Power
electronics control. Linear methods Week 4
(begins September 21) Power electronics control.
Nonlinear methods. Week 5 (begins September
28) Real components. Real loads. Week 6 (begins
October 5) Real components. Real sources Week 7
(begins October 12) Real components. Inductors
and capacitors Week 8 (begins October 19) Real
components. Diodes and MOSFETS Week 9 (begins
October 26) Real components. IGBTs and other
switches. Week 10 (begins November 2) Snubbers.
Losses and thermal issues. Week 11 (begins
November 9) Inverter topologies. PWM Week 12
(begins November 16) Inverters control Week 13
(begins November 23) Induction machines
control. Week 14 (begins November 30) Induction
machines control. Reliability issues
6
Course Introduction

• The schedule is tentative and may be adjusted
  depending how fast or slow the pace of the class
  needs to be.
• Some dates to makeup lost classes will be set up
  in a few weeks. Tentatively this date is Wed. 4
  to 530 pm.
• Already confirmed lost classes are
• Week of Sept. 21 ECCE (may be Tuesday only)
• Week of Oct. 19 INTELEC 2009
• Nov. 17 INTELEC 2010 Management Committee (may
  also miss a class before or a class after).
• Additional few classes might need to be
  rescheduled due to research commitments
  (hurricane damage assessments)
• Additional significant dates
• Sept. 7 Labor day (shouldnt affect us other
  than for the office hours)
• Nov. 26 Thanksgiving

7
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)

8
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.
9
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/niag
ara/niagara.html
10
History

• Edisons distribution system characteristics
  1880 2000 perspective
• Power can only be supplied to nearby loads (lt
  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.

11
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.

12
History

• Edisons 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 voltages to be
  transformed (flexibility).
• Cost competitive with centralized ac system.
• 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.

13
Power electronic applications

• Dynamic
• Variable speed drives
• Arguably for wind generation
• Electric and hybrid electric cars
• 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
• SCRs
• Energy storage elements
• Inductors
• Capacitors
• Other components
• Transformer
• Control circuit

Diode
MOSFET
SCR
IGBT
15
Power electronics basics

• dc-dc converters

• Buck converter

• Boost converter

• Buck-boost converter

16
Power electronics basics

• Rectifiers

v
v
v
t
t
t
Rectifier
Filter
17
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).

18
Power electronics basic concepts

• Energy storage
• When analyzing the circuit, the state of each
  energy storage element contributes to the overall
  systems 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
19
Power electronics basic concepts

• Capacitors
• state variable voltage
• Fundamental circuit equation
• The capacitance gives an indication of electric
  inertia. Compare the above equation with Newtons
  
• 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 capacitors energy is

20
Power electronics basic concepts

• Inductors
• state variable current
• Fundamental circuit equation
• 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 inductors energy is

21
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
• That is, in steady state the energy in each of
  the energy storage elements is the same at the
  beginning and end of the cycle T.
• Of course, during the transient periods (if they
  could be called periods) there is a difference
  between the initial and final energy.

or
22
Power electronics basic concepts

• The average voltage across an inductor
  operating in periodic steady state is zero.
• Likewise, the average current through a
  capacitor operating in periodic steady state is
  zero.
• Hence, Both KCL and KVL apply in the average
  sense.

23
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.
• If you look close and for a short time interval,
  exponentials look like lines

Time constant time scale
Period time scale
24
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.

25
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.

-
26
Power electronics basics

• Harmonics

• Concept periodic functions can be represented
  by combining sinusoidal functions
• Underlying assumption the system is linear
  (superposition principle is valid.)
• e.g. square-wave generation.

27
Power electronics basics

• Additional definitions related with Fourier
  analysis

28
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)
• Harmonic superposition

29
Power electronics basics

• Additional definitions
• Average
• RMS value
• Instantaneous power
• (Average) power
• Total harmonic distortion

30
Power electronics basics

• Additional definitions
• Power factor
• Line regulation
• Load regulation