Download Slides, chapter 20 - University of Colorado Boulder

Resonant and Soft-Switching Techniques in Power
Electronics ECEN 5817
Instructors: Mariko Shirazi
Professor Robert Erickson
ECEE 1B65A
303-492-1661
[email protected]
Course web site: http://ece.colorado.edu/~ecen5817
• Lecture schedule
• Lecture slides and supplementary materials
• Homework assignments and solutions
• Announcements
Textbook:
Erickson and Maksimovic, Fundamentals of Power Electronics, second edition,
Chapters 19 and 20
Extensive supplementary notes and chapters on course web site
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
1
Lecture 1: Introduction
Preliminaries
Prerequisites
• ECEN 5797 Introduction to Power Electronics is a required prerequisite to
this course
• Note that ECEN 5807 is not a prerequisite
Grading
• Homework 50%
– Approximately 12 weekly assignments
– Assignments posted each week on course web page
• Midterm exam 17%
– One-week take-home exam
• Final exam 33%
– One-week take-home exam
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
For off-campus students
Delivery options
• Web: lectures posted on web site within 24 hours. High resolution.
Students electing this option will typically run 1-2 days behind the oncampus students.
• VHS or DVD: lectures mailed to off-campus students. Low resolution
(NTSC: conventional analog TV). Students electing this option will
typically run one week behind the on-campus students.
With either approach: set a schedule for yourself — a regular time when you will
watch the lectures, that is a fixed time behind the on-campus schedule. You
will be expected to mail or fax your homework on the day that you would
normally watch the lecture where the homework of the on-campus students is
collected. Ditto for exams.
Final grades for off-campus students are due 7-10 days after the on-campus
grades.
If you decide to quit the course, please submit the paperwork to formally drop.
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Homework: off-campus students
On the day you would normally watch the lecture in which the homework
assignment is due, mail or fax your completed homework to:
Mariko Shirazi
ECE Department
Campus Box 425
University of Colorado
Boulder, CO 80309-0425
Fax:
303-492-2758
(cover page should list Mariko Shirazi as the recipient)
Please don’t scan and email your homework.
Homework solutions will be posted on the course web site, and solution passwords
will be sent to you with your graded homework (if you put an email address on
the first page of your homework, we will email the password when we receive
your homework).
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Office hours
Thursdays, 12:00 - 2:00 pm
ECEE 1B65
Telephone office hour: Thursdays, 2:00 to 3:00 pm Mountain time
Off-campus students are welcome to call at this time or at other times; I’ll at least
be there to answer the phone at the above time.
Questions via email are also encouraged. I will try to respond to them within a
day.
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
5
Lecture 1: Introduction
Acknowledgement
Most of the material for this class has been developed by Professor
Robert Erickson and/or taken directly from the course textbook
Fundamentals of Power Electronics by Professor Erickson and
Professor Dragan Maksimovic.
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Introduction to Resonant Conversion
Resonant power converters contain resonant L-C networks whose
voltage and current waveforms vary sinusoidally during one or more
subintervals of each switching period. These sinusoidal variations are
large in magnitude, and the small ripple approximation does not apply.
Some types of resonant converters:
• Dc-to-high-frequency-ac inverters
• Resonant dc-dc converters
Another application of resonant techniques: Soft-switched PWM
converters
• Resonant switch converters
• Other soft-switching converters
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
A basic class of resonant inverters
NS
is(t)
Basic circuit
+
dc
source
vg (t)
NT
+
–
vs(t)
L
i(t)
Cs
+
Cp
v(t)
–
–
Switch network
Resistive
load
R
Resonant tank network
Several resonant tank networks
L
Cs
L
L
Cp
Series tank network
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
Parallel tank network
8
Cs
Cp
LCC tank network
Lecture 1: Introduction
Input impedance
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Tank network responds only to fundamental
component of switched waveforms
Switch
output
voltage
spectrum
fs
3fs
5fs
f
Resonant
tank
response
fs
3fs
5fs
f
fs
3fs
5fs
f
Tank current and output
voltage are essentially
sinusoids at the switching
frequency fs.
Output can be controlled
by variation of switching
frequency, closer to or
away from the tank
resonant frequency
Tank
current
spectrum
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Derivation of a resonant dc-dc converter
Rectify and filter the output of a dc-high-frequency-ac inverter
The series resonant dc-dc converter
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Quasi-resonant converters
In a conventional PWM
converter, replace the
PWM switch network
with a switch network
containing resonant
elements.
Buck converter example
i1 (t)
i2 (t)
+
+
vg (t) +
–
v1 (t)
–
Switch
network
v2 (t)
–
L
i(t)
+
C
R
v(t)
–
Two switch
networks:
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Applications of resonant and
soft-switching converters
Electronic ballasts for gas-discharge lamps
• Produce high-frequency ac
Other high-frequency ac applications
• Electrosurgical generators
• Induction heaters
• Piezoelectric transformers
High-frequency high-density dc–dc converters
• Reduce switching loss and improve efficiency
High-voltage and other specialized converters
• Transformer nonidealities lead to ringing waveforms
Converters using IGBTs
• Mitigate switching loss caused by current tailing
Low-harmonic rectifiers
• Mitigate switching loss caused by diode stored charge
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Resonant inverter: An electronic ballast
• Must produce
controllable highfrequency (50 kHz)
ac to drive gas
discharge lamp
• DC input is
typically produced
by a low-harmonic
rectifier
• Similar to resonant
dc-dc converter,
but output-side
rectifier is omitted
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
Half-bridge, driving LCC tank circuit and gas
discharge lamp
14
Lecture 1: Introduction
Motivation for resonant DC-DC converters
and soft-switching techniques
• Increasing switching frequency reduces value and size of
filter inductances and capacitances
• Up to a point, increasing switching frequency reduces
transformer size
• Increasing switching frequency increases switching loss
• Much R&D effort has been devoted to increasing the
switching frequency and reducing the loss in high-density
power supplies
• Approaches to achieve these goals include use of resonant
converters and soft switching techniques
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Reducing the size of a dc-dc converter
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Effect of switching frequency on transformer size
Ferrite core for Cuk converter example
• As switching frequency is
increased from 25 kHz to
250 kHz, core size is
dramatically reduced
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
• As switching frequency is
increased from 400 kHz to
1 MHz, core size
increases
17
Lecture 1: Introduction
High power density requires high efficiency
Pin
Converter
Pout
A goal of current converter technology is to construct converters of small size and weight,
which process substantial power at high efficiency
High density power conversion
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
4.3. Switching loss
• Energy is lost during the semiconductor switching transitions,
via several mechanisms:
• Transistor switching times
• Diode stored charge
• Energy stored in device capacitances and parasitic
inductances
• Semiconductor devices are charge controlled – controlling
charge must be inserted or removed to switch a device
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Classical but misleading example: Transistor switching
with clamped inductive load (4.3.1)
Buck converter example
transistor turn-off
transition
Loss:
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
4.3.4. Efficiency vs. switching frequency
Add up all of the energies lost during the switching transitions of one
switching period:
Average switching power loss is
Total converter loss can be expressed as
where
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
Pfixed = fixed losses (independent of load and fsw)
Pcond = conduction losses
21
Lecture 1: Introduction
Efficiency vs. switching frequency
Switching losses are equal to
the other converter losses at the
critical frequency
This can be taken as a rough
upper limit on the switching
frequency of a practical
converter. For fsw > fcrit, the
efficiency decreases rapidly
with frequency.
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Soft switching:
Zero-voltage
and zero-current switching
vs1 (t)
Vg
vs(t)
Soft switching can mitigate some
t of the mechanisms of switching loss and
possibly reduce the generation of EMI
Semiconductor devices are switched on or off at the zero crossing of their
or current waveforms
–voltage
V
g
is(t)
t
Conducting D 1
devices: D
4
“Soft”
turn-on of
Q 1, Q 4
t
Q1
Q4
D2
D3
Q2
Q3
Conduction sequence: D1–Q1–D2–Q2
Q1 is turned on during D1 conduction
interval, without loss
“Hard”
“Soft”
“Hard”
turn-off of turn-on of turn-off of
Q 1, Q 4
Q 2, Q 3
Q2, Q3
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Soft switching in a PWM converter
Example: forward converter with active clamp circuit
Forward converter
Switching transitions are resonant, remainder
of switching period is not resonant
Transistors operate with zero voltage
switching
Beware of patent issues
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Classical but misleading example: Transistor switching
with clamped inductive load (4.3.1)
Buck converter example
transistor turn-off
transition
Loss:
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
25
Lecture 1: Introduction
Analysis of resonant converters
Series resonant dc-dc converter example
• Complex!
• Small ripple
approximation
is not valid
Need new
approaches:
• Sinusoidal
approximation
• State plane
analysis
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Outline of course
1. Analysis of resonant converters using the sinusoidal approximation
• Classical series, parallel, LCC, and other topologies
• Sinusoidal model
• Zero voltage and zero current switching
• Resonant converter design techniques based on frequency response
2. Sinusoidal analysis: small-signal ac behavior with frequency modulation
• Spectra and envelope response
• Phasor transform method
3. State-plane analysis of resonant converters
• Fundamentals of state-plane and averaged modeling of resonant circuits
• Exact analysis of the series and parallel resonant dc-dc converters
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Outline, p. 2
4. State plane analysis of resonant switch and other soft-switching converters
• Quasi-resonant topologies and their analysis via state-plane approach
• Quasi-square wave converters
• Zero voltage transition converter
• Soft switching in forward and flyback converters
• Multiresonant and class E converter
5. Server systems, portable power, and green power issues (time permitting)
• Modeling efficiency vs. load, origins of loss
• Variable frequency approaches to improving light-load efficiency
– DCM
– Burst mode
• Effects of parallel modules
• DC transformers
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction
Upcoming Assignments
Preparation for next lecture:
Read Section 19.1, Sinusoidal analysis of resonant converters
Preparation for Lecture 3:
Read Section 19.2, Examples
Homework assignment, due Lecture 5:
Homework set #1, Review
ECEN 5817 Resonant and Soft-Switching
Techniques in Power Electronics
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Lecture 1: Introduction