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AC (small-signal dynamic) modeling of quasi-resonant converters ECEN5817 Lecture 37 Quasi-resonant converters inherit properties of PWM parents, with switch conversion ratio playing the role of the PWM switch duty cycle d AC modeling approach: Start from (v if ) found for the resonant switch Start from (v,i,f s ) found for the resonant switch Perturb and linearize Replace d with in the small-signal AC dynamic model of the PWM parent converter (from ECEN5797 Intro to PE) ECEN 5817 1

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Page 1: AC (small-signal dynamic) modeling of quasi-resonant converters

AC (small-signal dynamic) modeling of quasi-resonant converters

ECEN5817Lecture 37

Quasi-resonant converters inherit properties of PWM parents, with switch conversion ratio playing the role of the PWM switch duty cycle d

AC modeling approach:• Start from (v i f ) found for the resonant switchStart from (v,i,fs) found for the resonant switch• Perturb and linearize

• Replace d with in the small-signal AC dynamic model of the PWM parent converter (from ECEN5797 Intro to PE)

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Page 2: AC (small-signal dynamic) modeling of quasi-resonant converters

Example 1: Full-wave ZCS-QR Buck

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Page 3: AC (small-signal dynamic) modeling of quasi-resonant converters

Small-signal AC model of the PWM buck converter

Textbook, Fig.7.17(a)

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Page 4: AC (small-signal dynamic) modeling of quasi-resonant converters

Small-signal AC model of the full-wave ZCS-QR buck

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Page 5: AC (small-signal dynamic) modeling of quasi-resonant converters

Example 2: Half-wave ZCS-QR buck

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Perturb and linearize

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Page 7: AC (small-signal dynamic) modeling of quasi-resonant converters

Small-signal AC model of the half-wave ZCS-QR buck

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A detailed solved example posted on the HW10 page

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Page 10: AC (small-signal dynamic) modeling of quasi-resonant converters

Summary of the linearization/perturbation results

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Page 11: AC (small-signal dynamic) modeling of quasi-resonant converters

How about 2-switch ZVS-QSW?

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Page 12: AC (small-signal dynamic) modeling of quasi-resonant converters

Small-signal AC model of the two-transistor ZVS-QSW

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Page 13: AC (small-signal dynamic) modeling of quasi-resonant converters

Constant-Frequency Soft-Switching Converters

• Introduction and a brief survey

• Active clamp (auxiliary switch) soft switching converters• Active-clamp (auxiliary-switch) soft-switching converters,

• Active-clamp forward converter

• Textbook 20 4 2 and on-line notesTextbook 20.4.2 and on line notes

• The zero-voltage transition full-bridge converter

• Textbook Section 20.4.1 and on-line notes

• “DC Transformer”

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Page 14: AC (small-signal dynamic) modeling of quasi-resonant converters

Soft-switching converters with constant switching frequency

• With two or more active switches, we can obtain zero-voltage switching in converters operating at constant switching frequency

h d i h b h i l d i h• The second switch may be one that is already in the PWM parent converter (synchronous rectifier, or part of a half or full bridge). In other cases, the second switch is an additional “auxiliary” switch

E lExamples:

• Two-switch quasi-square wave (with synchronous rectifier)

• Two-switch multi-resonant (with synchronous rectifier)Two switch multi resonant (with synchronous rectifier)

• Active-clamp switch (forward, flyback, other converters)

• Phase-shifted bridge with zero voltage transitions

• These converters can exhibit stresses and characteristics that approach those of the parent hard-switched PWM converters, but with zero-voltage switching over a range of operating points

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Page 15: AC (small-signal dynamic) modeling of quasi-resonant converters

Two-switch ZVS-QSW converters: already studied

• Q2 can be viewed as a Original one-switch version

• Q2 can be viewed as a synchronous rectifier

• Additional degree of control is possible: let Q2 conduct is possible: let Q2 conduct longer than D2 would otherwise conduct

• Constant switching Add h tifi Constant switching frequency control is possible, with behavior similar to conventional PWM

Add synchronous rectifier

PWM

• Can obtain µ < 0.5

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Page 16: AC (small-signal dynamic) modeling of quasi-resonant converters

The multiresonant switch

Basic single-transistor version

2 switch 2-switch (synchronous rectifier) version

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