# Circuit Example Introduction to Soft Switching

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```					Circuit Example: Introduction to Soft Switching
f s  100 kHz, D  0.5
1
fo             16 kHz
2 LC
C
QR   5
L

1                              ECEN 5817
L = 10 H, C = 10 F, R = 5  Zero-Voltage Switching (ZVS) Quasi-Square-Wave Operation

2                                     ECEN 5817
L = 10 H, C = 10 F, R = 5 : ZVS-QSW M1 turn-off, M2 turn-on

3                                        ECEN 5817
L = 10 H, C = 10 F, R = 5 : ZVS-QSW M2 turn-off, M1 turn on

4                                       ECEN 5817
ZVS-QSW: M2 turn-off, M1 turn-on transition

M1         D1

iL   L
+                              Voutt
VDC     vs
–

M2         D2

5                ECEN 5817
Hard-switched: M2 turn-off, M1 turn-on transition

M1        D1

iL   L
+                             Voutt
VDC    vs
–

M2        D2

6            ECEN 5817
Circuit Example: Introduction to Resonant Converters
f s  100 kHz D  0.5
kHz,
1
fo             71 kHz
2 LC
C
QR         1.1
L

7                                 ECEN 5817
L = 10 H, C = 0.5 F, R = 5  Resonant Converter Operation

8                                        ECEN 5817
L = 10 H, C = 0.5 F, R = 5 : M1 turn-off, M2 turn-on

9                                     ECEN 5817
L = 10 H, C = 0.5 F, R = 5 : M2 turn-off, M1 turn on

10                                    ECEN 5817
Comparison of Losses

Hard-switching PWM                ZVS QSW         Parallel resonant inverter
L = 100 H, C = 10 F        L = 10 H, C = 10 F L = 10 H, C = 0.5 F
Ploss (U1) [W]              57.5                         34.3                    45.9
( )[ ]
Ploss (U2) [W]               6.1                         8.6                     12.0
Ploss, total [W]           63.6                         42.9                    57.9
Pout [W]              1750                         1970                    2610
 [%]              96 5
96.5                         97.9
97 9                    97.8
97 8

11                                          ECEN 5817
f s  100 kHz D  0.5
kHz,
1
fo             5 kHz
2 LC
C
QR        16
L

12                               ECEN 5817
L = 100 H, C = 10 F, R = 50 Standard Hard-Switched Converter at Light Load

13                                      ECEN 5817
L = 10 H, C = 10 F, R = 50 ZVS-QSW at Light Load

14                                     ECEN 5817
L = 10 H, C = 0.5 F, R = 50 Resonant Converter at Light Load

15                                      ECEN 5817
Comparison of Losses
Hard-switching PWM            ZVS QSW              Parallel resonant
L = 100 H, C = 10 F    L = 10 H, C = 10 F   L = 10 H, C = 0.5 F
Plloss (U1) [W]             57.5
57 5                      34.3
34 3                  45.9
45 9
Ploss (U2) [W]               6.1                      8.6                   12.0
Ploss, total [W]           63.6                      42.9                  57.9
Pout [W]              1750                     1970                   2610
h [%]              96.5                      97.9                  97.8

Hard-switching PWM            ZVS QSW              Parallel resonant
L = 100 H, C = 10 F    L = 10 H, C = 10 F   L = 10 H, C = 0.5 F
Ploss (U1) [W]               13
1.3                      20.2
20 2                  37.5
37 5
Ploss (U2) [W]               0.2                      13.9                  34.3
Ploss, total [W]            7.4                      34.1                  71.8
Pout [W]              188                       203                   369
 [%]              99.2                      85.6                  83.7
16                                     ECEN 5817

Reduced switching loss
Zero current
Zero-current switching: switch current is zero prior to turn off
Zero-voltage switching: switch voltage is zero prior to turn on
Possible operation at higher switching frequency, may enable reduced size of passive
components, higher power density
Zero-voltage switching also reduces converter-generated EMI
applications
In specialized applications, resonant networks may be unavoidable
Resonant inverters in electronic ballasts for gas-discharge lamps, other high-
frequency ac applications
High voltage converters: significant transformer leakage inductance and winding

17                                        ECEN 5817

Can optimize performance at one operating point, but in most cases not over wide
range of input voltage or load power variations
Significant currents may circulate through the tank elements, even when the load is
Quasi sinusoidal
Quasi-sinusoidal waveforms exhibit higher peak and RMS values than equivalent
rectangular waveforms
All of the above lead to increased conduction losses, which can offset the reduction in
switching loss
Variable frequency operation may be required
Complexity: need different analysis and modeling methods

18                                         ECEN 5817
Applications of resonant and soft-switching converters

High-frequency ac inverter applications
• Electronic ballasts for gas-discharge lamps
• Electrosurgical generators
• Induction heaters
• Piezoelectric transformers
Efficiency improvements
• Mitigation of switching losses caused by diode stored charge in PFC rectifiers
DC-DC
• Mitigation of switching losses due to leakage inductance in isolated DC DC
converters
• Mitigation of switching losses due to current tailing and diode reverse
recovery in IGBT-based DC-DC converters and DC-AC inverters
High-frequency high-density dc–dc converters
• Reduced switching loss, improved efficiency, higher-frequency operation
High-voltage and other specialized converters
High voltage
• Transformer non-idealities incorporated into resonant tanks

19                                    ECEN 5817
Course Outline
1. Analysis of resonant converters using the sinusoidal approximation
, parallel, LCC, and other topologies
• Classical series, p       ,    ,             p g
• Modeling based on sinusoidal approximation
• Zero voltage and zero current switching concepts
• 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

20                                       ECEN 5817
Course Outline
4. Configurations and state plane analysis of soft-switching converters
Q              (               ) p g
• Quasi-resonant (resonant-switch) topologies
• Quasi-square wave converters
• Soft switching in forward and flyback converters
• Zero voltage transition converter
• DC-DC converter with fixed conversion ratio (“DC transformer”)
5. Energy-Efficiency                                  (time-permitting)
5 Energy Efficiency and Renewable Energy Applications (time permitting)
• Computer server power distribution, efficiency optimization techniques
• Soft-switching techniques for improved efficiency in DC-AC inverters

21                                        ECEN 5817
Chapter 19
Resonant Conversion

Introduction
19.1   Sinusoidal analysis of resonant converters
19.2   Examples
Series resonant converter
Parallel resonant converter
19.3   Soft switching
Zero current switching
Zero voltage switching

19.4   Load-dependent properties of resonant converters

19.5 Exact characteristics of the series and parallel resonant
converters

22                              ECEN 5817
A class of resonant DC-to-AC inverters

23                       ECEN 5817
A resonant DC-DC converter

A resonant dc-dc converter:
Transfer function
H(s)
H( )

is(t)                       iR(t)                           i(t)
+
+         L       Cs        +
dc
d
source +–                    vs(t)                       vR(t)                           v(t)   R
vg(t)
–
–
–
NS                        NT                           NR         NF
Switch network        Resonant tank network          Rectifier network Low-pass dc
network

If tank responds primarily to fundamental component of switch
network output voltage waveform, then harmonics can be neglected
g                      pp
Section 19.1: modeling based on sinusoidal approximation

24                                                         ECEN 5817
The sinusoidal approximation

Switch
output
voltage                           Tank current and output
spectrum                            voltage are essentially
fs     3fs    5fs
sinusoids at the switching
f
frequency fs
Resonant                            Neglect harmonics of
tank
response                                      p        g
switch output voltage
waveform, and model only
the fundamental
fs     3fs    5fs   f   component
Tankk
current
Remaining ac waveforms
spectrum                            can be found via standard
phasor analysis
fs     3fs    5fs   f

25                              ECEN 5817
19.1.1 Controlled switch network model

NS
is(t)
1
+

vg   +      2              vs(t)
–               2

–
1

Switch network

Fourier series expansion of              The fundamental component is
it h t
square-wave switch network  k
output voltage vs(t):

So model switch network output port
with voltage source of value vs1(t)

26                                  ECEN 5817
Model of switch network input port

Find dc (average) component of
NS                     the switch network input current
is(t)
1
+

vg   +     2              vs(t)
–               2

–
1

Switch network

Fundamental component of the
output current:

27                                ECEN 5817

```
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