-
附录
A
英文文献
A Novel Dual-LLC Resonant Soft
Switching
Converter for Super High
Frequency
Induction Heating Power
Supplies
Zhengshi
Wang
，
Zhenli
Lou
，
Huiming Chen
College of Electrical
Engineering
，
Zhejiang
University
，
Hangzhou 310027
，
P
。
R
。
China
Email: eew
zs@yahoo
。
com
，
zjulzl@yahoo
。
com
。
cn
，
huiming@c
ee
。
zju
。
edu
。
cn
Abstract-
A
novel
dual-LLC
resonant
tanks
zero
voltage
soft-switching
converter for
super high-frequency solid-state induction heating
power supplies
is proposed in this
paper
。
The
proposed converter is capable of absorbing the
inductive and capacitive parasitical
components in the circuit
。
Switch devices
operate in
zero-voltage soft switching
mode
。
The
problems of high voltage and
current
spikes
caused by oscillation of
parasitic inductors or
capacitors
，
and
huge switching loss in super high-
frequency operation
，
which are troublesome
in
super high-frequency
circuits
，
can be
solved
。
Moreover
，
a large inductor
is
inset
in
the
input
，
this
novel
converter
shares
the
benefits
of
both
voltage-type
and
current-type
inverters
simultaneously
，
and
the
dead-time
between
two
switches
does
not
need
，
therefore
，
this
converter
is
suit
to
operate
in
super
high
frequency
conditions
。
The
working
principle
of
the
converter is
introduced
，
simulation and experimental results
operating around 1
MHz frequency are
given
。
I
INTRODUCTION
Mega-level super high frequency
induction heating is with particular advantages
in metal surface
processing
。
However
，
radio tube oscillators still
predominate
in
these
applications
because
of
the
frequency
reasons
。
It
is
a
fact
that
，
equipment based on radio tubes has many
drawbacks
，
such
as low efficiency
(50%
，
normally)
，
short-lived
，
and pre-heat
needed
。
Using
fast switching
power
electronic
devices
such
as
MOSFET
to
implement
the
solid-state
induction
heating
power
supplies
will
greatly
improve
the
equipment
- 1
-
performance
，
especially in the power
efficiency
。
Many
achievements have
been made in low
power apparatus [1]- [11]
。
Comparing with low frequency
circuits
，
super high frequency converters have to
meet some special problems
in circuit
design and producing craft
。
The first is the inductive and
capacitive
parasitic
parameters
in
devices
and
circuit
wires
or
routes
。
The
equivalent
impedance
of
these
inductive
and
capacitive
parasitic
parameters
cannot
be
neglected
，
they will cause severe
oscillations
，
the
voltage and current spikes
may damage
the switch devices
。
The second is the huge power loss
caused by
high frequency
switching
。
So
，
in
super high frequency power supply
design
，
the
circuit should have abilities to absorb these
parasitic components
，
decrease
the switching loss
of the converters
。
Class-D and Class-E circuits both are
quite
good
topologies
in
high
frequency
applications[2]-[5]
，
< br>
and
have
been
got
widely
used
in
RF
areas
，
but
they
are
not
suit
for
induction
heating
applications
，
because the loads are variable
seriously
。
A
novel dual-LLC resonant tank soft switching
converter
，
which
can absorb the
parasitic components in
circuits and devices
，
all MOSFET devices operate in
zero
voltage
soft
switching
，
is
proposed
in
this
pa
per
。
Moreover
，
this
topology has other two
advantages: a large value inductor is inset in the
input
，
so the
converter shares the benefit of current-fed
circuit
，
the
dead-time between
the two switches does
not need
。
In the
load tank
，
a
series inductor is used as
one
part
of
the
compensator
，
it
will
greatly
improved
load
short
circuit
abilities
。
Detail principle of the converter is
introduced
，
and
key waveforms in
two LLC resonant tanks
are analyzed
，
Simulation and experimental results are
given in this
paper
。
II
。
THE
PRICINPLE
AND
KEY
WA
VEFORMS
OF
THE
CONVERTER
The proposed novel converter is shown
in Fig
。
1
。
Comparing with normal
H-bridge
converter
，
two
inductors
，
La1
and La2
，
are
employed to replace the
upside
switches
。
There
are two LLC tanks in the converter: one is called
load
LLC tank
，
which is made up of
Ls
，
C
，
Lp
，
and R (Lp and R are equivalent
inductor
and
resistor
of
the
induction
wire
and
load)
。
Another
LLC
tank
is
called auxiliary resonant
tank
，
including
La (la1 or La2)
，
Ca (ca1 or Ca2)
，
and load equivalent impedance Z
L
。
It is the
auxiliary LLC resonant tank that
help
Q1 and Q2 work in zero voltage soft switching
mode
。
Inductor
La1
，
La2
and Ls can absorb the parasitic
inductive components of the
circuit
，
and
Ca1
，
Ca2 can
absorb the parasitic capacitors in switch
devices
。
All
these parasitic
components
are
used
as
one
part
of
the
resonant
loop
，
and
parasitic
- 2
-
oscillations
，
high voltage/current surges due to
these parasitic components can
be
effectively eliminated
。
The dead time between Q1 and
Q2
，
which is
quite
common in voltage-fed
converter
，
is not
needed because the inductor Ld is set
in the input
。
Therefore
，
this topology is competent in super
high frequency
working
。
Other benefits of this topology are in
that series-connected
inductor
，
Ls in
load tank
，
can
improve the load short-circuit protection
abilities of the
converter
，
and Ls also has the same function as
normal matching transformer
。
A.
The Impedance
Characteristic of Load LLC Tank
The
load LLC tank is made up of induction coil
(equivalent inductor Lp
，
and
equivalent
resistance
Re)
，
parallel
compensator
capacitor
C
，
and
series
compensator inductor
Ls
。
This
series
and
parallel compensator not
only
can
improve
power
factor
of
the
load
loop
，
but
also
can
improve
the
load
short-circuit
ability
。
Moreover
，
this structure has the same function as
normal
transformer to transform the
voltage value
。
Thus
，
the output
transformer
，
used
for load matching purpose
，
can be omitted
。
Consequently
，
the power
efficiency will be
improved
，
and
weight and size of the power supply can be
decreased
。
The impedance characteristic of load
LLC tank plays important role
in the
converter operation and power
deliver
。
The
impedance of load LLC tank
(ZL)
，
can be expressed
as
，
-
3 -
Fig
。
2
shows the load LLC tank magnitude and phase
characteristic with
different
frequency: There are two resonant poles in load
LLC tank
，
one is
series pole (
?
0
)
，
and
another is parallel resonant
pole(
?
p
):
?
0
?
1/
< br>(
L
p
/
/
L
s
)
C
,
?
p
?
1/
L
p
C
In order to reduce the
reactive power delivery between load and power
supply
，
and get
the maxim output power in the
load
，
the switching frequency of the
converter is set at series pole (
?
0
)
。
If the output
power should
be regulated
，
one
can choose;
?
?
?
0
。
in
fact that
，
maxim
output at
?
0
can be
expresses as
2
U
AB
L
?
(
P
)
2
(3)
R
L
S
P
max
- 4 -
Equation
(3)
shows
that
inductors
Lp
and
Ls
have
the
voltage
transformation
function
，
just like normal voltage
transformer
。
B.
Analysis of
the Auxiliary Resonant LLC Tank
There is another LLC tank in the
proposed converter
，
called auxiliary resonant
LLC tank
，
including La
，
Ca and ZL
。
Fig
。
3(a) shows
the circuit while Q1
is off and Q2 is
on
。
Fig
。
3
(b) is the equivalent circuit of
Fig
。
(a)
，
where
'
2
2
?
?
R
e
?
(
R
e<
/p>
?
(
?
L
e
)
)
/
R
e
(4)
?
2
2
2
?
?<
/p>
C
a
1
?
C
a
1
?
(
L
e
/
((
?
L
e
< br>)
?
R
e
))
There is a similar equivalent
circuit when Q1 is on and
Q2 is off
。
Base
on the
topology and symmetry of the
converter
，
one can get:
U
AB
?
U
Q
1
?
U
< br>Q
2
(5)
U
P
?
0.5(
U
Q
1
?
U
Q
2
)
(6)
In Auxiliary resonant
tank
，
the voltage
and current are governed by
di
La
?
L
?
?
a
dt
?
u
Q
(
t
)
?
u
p
?
u
Q
du
Q
?
< br>,
?
i
La
?
,
?
C
a
(7)
R
e
dt
?<
/p>
?
u
?
0.5<
/p>
u
Q
?
p
?
di
Lb
?
u
p
?
L
b
dt
?
One can
get
- 5 -
d
2
u
Q
(
t
)
dt
2
< br>?
1
du
Q
(
t
)
1
?
u
?
0
(8)
,
'
,
Q
(
t
)<
/p>
R
e
C
a
dt
2
L
a
C
a
When
R
e
,
?
L
a
/
2
C
a
，
the
solution
of
this
second
order
differential
equation
can be expressed as
u
Q
(
t
)
?
U
AM
e
?
t
sin(
?
d
t
?
?
)
(9)
Where
?
?
?
1
1
2
2
1
?
?
(
)
?
，
，
d
,
,
,
2
R
e
,
C
a
L
a
C
< br>a
2
R
e
,
C
a
U
A
M
is the
magnitude
。
The
initial value is:
du
(0)
i
La
1
(0)
，
U
Q
(0)
?
0
，
Q
?
,
< br>dt
C
a
There are
three kinds of frequency in this converter: the
frequency of Q1/ Q 2 on
and off (the
switching frequency of the converter
(
f
s
); the load
LLC resonant
frequency
(
f
L
); and the
auxiliary resonant tank frequency (
f
d
)
。
In induction
heating
application
，
phase-lock-loop
(PLL)
is
often
implemented
to
keep
f
S
?
f
L
。
Moreover
，
in order to let Q1 and Q2 operate in
zero voltage soft
switching
mode
，
these
frequencies should be
f
S
?
f
L
?
f
d
(9)
D is defined as
D
?
f
S
/
f<
/p>
d
?
1
。
Obviously
，
as
f
S
?
f
d
，
there is an
interval when the body diode of the MOSFET turns
on
，
u
Q
(
t
)
is
zero
。
Thus
，
In
half
cycle
，
the
waveform
of
u
Q
(
t
)
has
two
different
parts:
one
is
resonant
trail
，
and
governed by Equation(8); Another part is zero
voltage trail
。
Because the average voltage of inductor
is zero in steady state
，
one can get
V
dc
?
1
2
?
?
2
?
0
(
u
LD
?
u
P
)
d
wt
?
0
?
1
2
?
?
2
?
0
u
p
d
?
t
(10)
When the value of
?
?
?
1
< br>is not so large
，
the
magnitude of
u
Q
(<
/p>
t
)
is
,<
/p>
R
e
,
C
a
U
AM
?
?
2
D
V
dc
(11)
Thus
，
in one
cycle
，
the voltage of
< br>u
Q
1(
t
)
，
u
Q
2(
t
)
，
u
p
(
t
)
and
u
AB
(<
/p>
t
)
can be expressed
as
- 6 -
- 7 -
Fig
。
4 shows the
waveforms of control signal of Q1/Q2(Ug1
，
Ug2)
，
Uqa
，
Uab
，
Up
。
C.
Six Operation
Modes of the Converter
In the proposed
converter
，
there
are six different work modes in one operation
cycle
。
Mode 1 [t1~t2]: Q1 turns on
at this time
，
however
，
the current flows through
the body diode
D1
。
So
，
Q1
turns on in zero voltage
condition
。
When
t=t1
，
Q2 turns
off
。
Because a
large value capacitor Ca2 is paralleled with
Q2
，
the
voltage across the Q2 rises
slowly
。
The
switching loss of Q1 and Q2 will be
quite small
。
- 8 -
Mode
2
[t2~t3]:
at
time
of
t2
，
the
current
flowing
through
D1
decreases
to
zero
，
and start to flow into
Q1
。
Mode 3 [t3~t4]: at time of
t3
，
UQ2 decrease
to zero
，
and D2
starts to turn on
。
U Q2 is clamped to
zero
，
and
auxiliary resonant stops
。
Fig5 Equivalent circuit of
6 modles
Mode 4 [t4~t5]: Q1 is turned
off at t4
，
the
current switches to Ca
，
and the
,
,
auxiliary
resonant of in
C
a
1
R
e
L
a
1
starts working
，
U
Q
1
rises
，
and
governed by
Eq
。
(8)
。
Mode
5
[t5~t6]:
at
time
of
t5
，
the
current
flowing
through
D
2
decreases
to
zero
，
and start to switch
to
Q
2
。
- 9 -
Mode 6 [t6~t7]: at time of t6
，
U
Q
1
d
ecreases to zero
，
and
D
1
starts to
turn on
。
U
Q
1
is clamped
to zero
，
and
auxiliary resonant stops
working
。
Fig
。
5 shown the
equivalent circuit of six operation
modes
，
and
Fig
。
6 shows
key
waveforms
in
the
converter
during
one
operation
cycle:
Ug1/Ug2are
gate
signals of
Q
1/
Q
2
，
U
AB
，
U
C
is the
U
Q
1
/
U
Q
2
are the voltage across the
switches
，
i
voltage
AB point
，
and
capacitor C
。
i
D
1
，
i
D
2
，
i
Q
1
，
i
Q
2
，
C
1
，
i
C
2
ar
e the currents
flowing
through the devices of
Q
1
，
Q
2
，
D
1
，
D
2
，
C
1
，
C
2
，<
/p>
respectively
。
III
。
SIMULATION
A ND
E XPERIMENTAL R ESULTS
The parameters
of the converter in simulation are
V
dc
?
150
V
,
L
d
?
200
uH
,
L
a
1
?
L
a
2
?
< br>5
uH
,
L
s
?
35
uH
,
L
P
?
2.4
uH
,
C
?
12
nF
,
switching
C
a
1
?
C
a
2
?
2.5
nF
,
frequency
=1
。
0MHz
Fig
。
7 shows the
simulation results
。
< br>Obviosly
，
Q
1
turns
- 10 -
on in
ZVS mode
，
and
turns off with very low dv/dtrising
ratio
。
Since the
parasitic parameters are absorbed by
circuit components
(
L
< br>a
,
L
s
,
C
a
)
，
the
voltage and
current traces are all quite
clear
。
Fig
。
8
is experimental waveforms of UQ1 and U p when Vdc
=54V
。
Two
times
magnitude
relationship
of
UQ1
and
Up
verifies
validity
of
theory
analysis
aforementioned
。
Fig
。
9
shows
U
AB
and
U
C
waveforms
in
different
switching
frequency
< br>cases:
f
s
?
973
kHz
,1.008
MHz
,1.008
MHz
when
the
phase
lock
loop
(PPL)
is
removed
。
As the inherent resonant frequency
(
f
L
) of load LLC
tank is away
- 11 -
form
the
switching
fre
quency(
f
S
)
。
The
voltage
across
the
load
(
U
C
)
decreases
。
Fig
。
10
shows
different
load
voltage
(
U
C
)
with
different
compensation
inductor
:
L
S
U<
/p>
C
increases
from
128V
to
232V
while
L
S
changing from 35uH to
26uH
。
From this
view
，
L
S
has the
function of normal
voltage
transformation
。
IV
。
CONCLUSIONS
A novel dual-LLC
resonant tank zero voltage soft switching
converter
，
which
can absorber the parasitic components
in the circuit and devices
，
all MOSFET
devices
operate
in
zero
voltage
soft
switching
，
is
proposed
for
induction
heating power
supplies
。
In
addition
，
the
proposed converter has other two
advantages: an inductor is inset in the
input
，
so the
converter shares the benefit
of
current-fed circuit
，
the dead time between the two switches
is not needed
。
On
the other hand
，
a
series inductor is used in the load tank as one
part of the
compensator
。
This series-connected inductor will
greatly improved load short
circuit
abilities
。
Working principle of the converter is
introduced
，
and
key
waveforms
of
in
two
LLC
resonant
tanks
are
analyzed
，
Simulation
and
experimental results are
given
。
- 12 -
- 13 -
-
-
-
-
-
-
-
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