1. Resonant and Soft-Switching Techniques in Power Electronics ECEN 5817
Instructors: Mariko Shirazi
Professor Robert Erickson
ECEE 1B65A
Course web site:
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

2. 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%

3. 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 on-campus 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.

4. 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
Fax:
(cover page should list Mariko Shirazi as the recipient)
Please don’t scan and 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 address on the first page of your homework, we will the password when we receive your homework).

5. 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 are also encouraged. I will try to respond to them within a day.

6. 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.

7. 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

8. A basic class of resonant inverters
Basic circuit
Several resonant tank networks

9. Input impedance

10. Tank network responds only to fundamental component of switched waveforms
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

11. 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

12. Quasi-resonant converters
Buck converter example
In a conventional PWM converter, replace the PWM switch network with a switch network containing resonant elements.
Two switch networks:

13. 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

14. Resonant inverter: An electronic ballast
Must produce controllable high-frequency (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
Half-bridge, driving LCC tank circuit and gas discharge lamp

15. 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

16. Reducing the size of a dc-dc converter

17. 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
As switching frequency is increased from 400 kHz to 1 MHz, core size increases

18. High power density requires high efficiency
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

19. 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

20. Classical but misleading example: Transistor switching with clamped inductive load (4.3.1)
Buck converter example
transistor turn-off transition
Loss:

21. 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 Pfixed = fixed losses (independent of load and fsw)
Pcond = conduction losses

22. 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.

23. Soft switching: Zero-voltage and zero-current switching
Soft switching can mitigate some 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 voltage or current waveforms
Conduction sequence: D1–Q1–D2–Q2
Q1 is turned on during D1 conduction interval, without loss

24. Soft switching in a PWM converter Example: forward converter with active clamp circuit
Switching transitions are resonant, remainder of switching period is not resonant
Transistors operate with zero voltage switching
Beware of patent issues

25. Classical but misleading example: Transistor switching with clamped inductive load (4.3.1)
Buck converter example
transistor turn-off transition
Loss:

26. 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

27. 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

28. 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

29. 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