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Classification of Resonant‐Switch Converters

ZVS‐QR 

Buck

Boost

Buck‐Boost

Cuk

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20.3.1  The zero‐voltage‐switchingquasi‐resonant switch cell

Lr

Cr

D2

SW

When the previously‐described operations are followed, then the converter reduces to

Lr

Cr

D2+–

L

C R

+

V

–

Vg

I

+

v2(t)

–

i1(t) i2(t)

+

v1(t)

–

+ vCr(t) –

iLr(t)D1

Q1

A full‐wave version based on the PWM buck converter:

ZVS‐QR

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ZVS‐QR State Plane Trajectory

The average output voltage

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Results:Quasi‐resonant switches

Output characteristics: Full‐wave ZVS buck

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20.3.2  The ZVS multiresonant switch

When the previously‐described operations are followed, then the converter reduces to

A half‐wave version based on the PWM buck converter:

Lr

Cs

D2

SW

Cd

Lr

D2+–

L

C R

+

V

–

Vg

I

+

v2(t)

–

i1(t) i2(t)

+

v1(t)

–

Cd

Cs

D1

Q1

ZVS‐MR Operating ModesD Maksimovic, "Synthesis of PWM and Quasi‐Resonant DC‐to‐DC Power Converters," Ph.D. thesis, California Institute of Technology, 1989.

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ZVS QSW Converters: Already Studied

Lecture 21

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20.2.3  Quasi‐square‐wave resonant switches

Lr Cr

D2

SW

Lr Cr D2SW

When the previously‐described operations are followed, then the converter reduces to

ZCS

ZVS

A quasi‐square‐wave ZCS buck with input filter

+–

Lr

Cr

Vg

Cf

Lf D1

D2

Q1 L

C R

+

V

–

I

• The basic ZCS QSW switch cell is restricted to 0 ≤ µ ≤ 0.5

• Peak transistor current is equal to peak transistor current of PWM cell

• Peak transistor voltage is increased

• Zero-current switching in all semiconductor devices

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Ac modeling of quasi‐resonant converters

Use averaged switch modeling technique: apply averaged PWM model, with d replaced by µ

Buck example with full‐wave ZCS quasi‐resonant cell:

+–

L

C R

+

v(t)

–

vg(t)

i(t)

+

v2(t)

–

i1(t) i2(t)

+

v1(t)

–

Lr

Cr

Full-wave ZCS quasi-resonant switch cell

+

v1r(t)

–

i2r(t)

D1

D2

Q1

Frequencymodulator

Gatedriver

vc(t)

µ = F

Ac modeling of QR converters

Quasi‐resonant converters inherit properties of PWM parents, withswitch conversion ratio μ playing the role of the PWM switch duty cycle d

AC modeling approach:

• Start from μ(v,i,fs) found for the resonant switch

• Perturb and linearize

• Replace d with � in the small‐signal AC dynamic model of the PWMparent converter

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Example 1: Half‐wave ZCS quasi‐resonant buck

Buck Converter Small Signal Model

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ZVS‐QR buck AC model

Example 2: Half‐wave ZCS‐QR buck

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Perturb and Linearize

AC SSM of half‐wave ZCS‐QR buck

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Summary of results