The Practical Design of High Power Inductive Heating-Facility with
Half-bridge Inverter
HSU CHUN-LIANG1 SHIEH-SHING LIN2 CHENG-CHIAN KUO3
E.E Department of Saint John’s University
No. 499, Sec. 4, Tang-kin Rd. Taipei County, Taiwan
REPUBLIC OF CHINA
+886-2-28013131 #6500, liang@mail.sjsmit.edu.tw
Abstract: - Today the inductive heating facilities have been applied in many manufacturing field in Taiwan,
and this promoted research in this field directing to higher power, higher frequency, and higher efficiency as
well. But most of the circuit structures in large capacity devices were adapted with Full-bridge structures in
Inverter. In this study, a half-bridge inverter driven by fixed-frequency was implemented in a variable power
inductive heating-facility in which the circuit was adapted Resonant- Transition in Zero-Voltage-Switching,
Clamped-Voltage (ZVS-CV). The main part of this study was the practical design work through complete
experiments step by step. The generating power was controlled by adjusting the turn-on timing of IGBT, in
this way, the power factor of power-source side was highly promoted, and the driving signal was generated by
TMS320F240 (DSP), so as well as detected the status of whole system with sampling in AD converter
channels of DSP. Due to the design of this model the high performance was easily gained. The analysis of
power change by adjusting Duty-cycle, the loading current waves, EMC under different operating frequency
were verified and matched with the original theory through simulation with Is-Spice Software.
Key-Words: Resonant-Transition, Isolated Gate Bipolar Transistor, Zero-Voltage-Switching, Clamped-Voltage
1 Introduction
Owing to the progress of semi-conductor
components in recent decades, more power elements
could be applied in products of higher-power device.
So as well the increase of endurance of voltage and
ampere of components prompted the rapid
development of power electronics field. That leads
to higher frequency, response, and efficiency
performance of a larger capacity heating device. For
instance, most of products in industry machineries
were used the inverter technique such as AC
inductive motors, non-brush DC motors, washing
machine, inductive heaters, UPS, switching power
suppliers, and sonar power system.。Especially the
popular application of inductive heater was in
illustration of the development of industry. Since the
heating methods such as gas or electricity in family
would leak heat around the heater itself, the heater
got lower energy transformed efficiency. The
inductive heating method which uses rectifiers and
high frequency inverter to convert 60Hz AC input
current into 20~40KHz high frequency energy
output to supply the inductive coils which would
generate the inductive eddy current so as to heat the
pan over coils.
Nowadays the power electronic technique is to
implement the electronics into huge power circuits
or systems. So to speak, it’s a process how to deal
with power transformation with semiconductor
components. Electronic technique has been
developed since the first Silicon Control Rectifier
(SCR) was invented in 1956. Today power
electronics can be divided into Traditional and
modern stage. The former was mainly developed
power capability with SCR such as fast-speed SCR,
inversed-conduct SCR, bi-direction SCR etc. Not
with standing the improvement with parameter as
voltage, current, dv/dt, di/dt, and switching feature,
yet there were many choke points such as lack of
ways of up-grade running frequency. That led to add
capacities, conductors, and some auxiliary switches
in circuits, and led to improper size of products and
in-application controlled frequency, and finally the
new generation electronic technique was initiated.
The latest electronic technique has broken away
the traditional constrains since new type
components invented in 1980 such as power
field-effect-transistor,
insulated-gate
field-effect-transistor (IGFET), isolated-gate bipolar
transistor (IGBT), Power Metal-Oxygen-Silicon
FET (Power MOSFET) etc. The new components
advocated Pulse-Width-Modulation (PWM), zero
voltage, zero current, and switching resonance [2,8].
Furthermore, those new type components own
superiorities such as integrated, high controlled
frequency, fully-controlled circuit, digital control,
upgrading
switching
frequency,
decreasing
audio-frequency noise lower current ripple and cost
down.
The most easily damaged components in power
electronic driver circuits are switching ones, and
under the consideration of both high voltage and
current endurance and easily driven, the related
design were mainly taken advantage of Insulated
Gate Bipolar Transistor-IGBT and Power MOSFET.
IGBT owns features of high speed, driving
capability, and input resistance, so was viewed as
most proper for high power switching components.
In addition, it also owns high voltage endurance at
off condition while loading high current at on
condition. But IGBT has two defects, one is huge
off current and longer delay time that lead to much
waste power and the other is latch-up effect, that
would causes out of control of Gate polar or even
complete damage to components. Sum up, the
purpose of this study is to design a high power
stable heating device with safety and intelligence.
Generally speaking, An intelligent and stable high
power magnetic inductive heating facility with
IGBT as switching components would provide well
protection for driver circuit to avoid damage of
components even under any troubleshooting
including incorrect programming, and this
performance would be the motivation of this study.
Since magnetic inductive heating facility belongs
to application of high frequency electronic power
components which combine of both inerter and
technique of switching so as to convert low
frequency DC power into high frequency AC power.
Finally, crossing the coils with changed magnetic
field and generating eddy current on the surface of
ovens, in the process, through coupled magnetic
field to convert electric energy into magnetic energy,
further more convert magnetic energy into heat
transferred to loads to accomplish heating effect.
But, the higher frequency of switching components
is, the more switching lose is. Driving signal
couldn’t control on and off of IGBT on account of
latched effect resulting from over-loading and noise,
and this condition led to damage of IGBT
themselves and larger stress of components resulting
from current or voltage glitches. So how to design a
high frequency, power, and performance inverter
with Zero-Voltage-Switching (ZVS) is the purpose
of this research.
The structure of this paper was called Class-D
half-bridge resonate Inverter [1], and the resonation
circuit has both resonated interval and
non-resonated interval during in a switching period,
and this resonated method was classified into to
Zero-Voltage-Switching,
Clamped-Voltage,
(ZVS-CV) [3] conversion circuit. The method in
this paper is to adopt soft switching so as to get
current resonated and ZVS, which would reduce the
switching loss of IGBT and promote the system
efficiency. Furthermore, we drove gate polar of
IGBT with symmetrical Pulse Width Modulation
(PWM) signals to reduce current harmonic of
supply power and improve its power factor.
2 Study Motivation
Most traditional inverter adopted hard switching,
and it would increase loss of power electronic
components and couldn’t run under high power and
frequency condition. Moreover, even resulted in
increasing harmonic of supply power and damage of
IGBT because of overheat. This paper tried to adopt
soft switching strategy of series resonance and the
designed structure is Class-D Half-bridge series
resonance inverter. Owing to simple structure and
high efficiency, the resonance current was
approximate to sine-wave as to improving power
factor and efficiency of whole system. From
literature review [9], inductive heating own
superiority as (1) fast heating process (2) safety (3)
low pollution (4) accurate temperature control (5)
proper power control (6) no-limitation by
environment. So how to convert DC current
rectified from AC power supply to high frequency
AC current needed by load and produce less
harmonic during conversion process so as to cut
down the loss of IGBT and finally design a high
power, easily driven, high efficient heating
technique of inverter taken advantage by inductive
heating method that is superior to traditional ones
was the main motivation of this study.
3 Literature Review
There were three main direction of power
electronics research as follow: (1) Power elements
such as IGBT, Power MOSFET, and GTO. (2)
Circuit topology such as Half-bridge, Full-bridge. (3)
Control technique such as PWM, PAM, PFM, and
PDM.
Present research papers for inductive heating
most focus on full-bridge [9] or half-bridge [1,5]
and the driving signals were used Pulse Width
Modulation (PWM), and Sinusoid Pulse Width
Modulation (SPWM). The driving types can be
divided into Symmetric and Non-symmetric [7, 8].
The switching methods are Zero-voltage and
Zero-current. The switching frequency are
Fixed-frequency switching and Variable-frequency
to adjust output power. As to the power control are
PWM with fixed-frequency control and SPWM
technique in which the switching ON timing was
adjustable to control power output. The other one is
Pulse Frequency Modulation (PFM) [2] that is
varying the switching frequency according to load
variety, and in this way, switching frequency would
automatically correspond to the change of resonated
frequency to get the maximal power output.
As to now, the control method for half-bridge
structure is using variable-frequency with fixed
turn-off timing on IGBT [13], and this method could
protect switching components. But the power is
limited due to being limited of turn-off current. The
switching frequency of PFM [2] would vary
according to the varying of load to get maximal
power and generally adopted variable power
constant frequency (VPCF), fixed-frequency PWM
[11,12]. In literature [1], the switching way adopted
that switching frequency was more than resonated
frequency, so we could get to the effect of ZVS. As
to the control signals of PWM have symmetric and
non-symmetric. It was easy for symmetric way to
control power output that most multi-half-bridge
control structure will adopt this method [4].
The control method in full-bridge structure was
phase-shifting ZVS inverter which uses the stray
capacity on IGBT and stray inductance in circuit to
achieve the ZVS and soft switching to low down the
switching loss, so would the full-bridge structure
use fixed-frequency to achieve phase-angle shifting
of output voltage to control the power output. In the
literature [1], the inverter adopted half-bridge with
forced switching, in which the switching frequency
is more than resonated frequency, and there are
many superiority as follow: (1) Zero Voltage
Switching could low down the switching loss of
IGBT. (2) Excluding the reversed current of
flywheel diode could cost down the components. (3)
Power control range becomes larger, and this
condition is suitable for larger variety of power
control. (4) Using two resonated capacities could
reduce the effective value of ripple current on
DC-LINK capacity and increase power fact of
supply power. (5) It could provide driving signal
with 50% duty-cycle. In the literature [2], it
presented PFM technique as control strategy for
power control. The control theory is basically on
how step after the load change, that means the
control circuit would feedback the loading current
and then vary frequency that steps after the
resonated frequency to achieve the optimal power
output point. This kind of varying system switching
frequency to control power output is most suitable
for heating iron pans made of magnetic-admittance
materials and for aluminum pans made of nonmagnetic-admittance materials.
This paper adopted the structure presented in
literature [1], in which we selected fixed switching
frequency, and the reason why we selected this way
was as follow: (1) it is easy to design the EMI filter
and minimize size of filter. (2) when we developed
multi-oven in one system, the noise generated by
switching frequency among ovens could be
minimized.
We learned that there was no difference of the
efficiency of inverter performance between fixed
DC voltage and non-fixed voltage. But the current
flowed into fixed DC voltage inverter and IGBT is
larger than that of non-fixed DC voltage inverter
and this would upgrade the selection of components
even would increase the extra cost. So we adopted
non-fixed DC voltage inverter as our research
direction.
From literature [1], the Q value in Fig. 3 was
affected by combined resistance. If the pan existed
and had the better magnetic-admittance, the value of
its resistance would be larger and result in smaller Q
value. If switching frequency were larger than
resonated frequency (fs>fr) and the Q value were
very small, the change range of switching frequency
would be larger and lead to broader range of power
control. So in this paper we adopted the method that
switching frequency was larger than resonated
frequency. It would let circuit operate in high power
under ZVS and cut down the turn-on loss on IGBT
which would be embedded with clipping resonated
circuit to cut down turn-off loss of IGBT.
4 Practical Design
4.1 Inverter Structure of System
In Fig. 1, it is called Half-bridge Resonate Inverter
structure. The circuit topology of inductive
heating-facility could be equivalent to RLC
series-resonated circuit as shown in Fig. 2. Where
the resonated frequency of circuit is f 0 , the
impedance characteristics is Z 0 , and the quality
factor is Q . The values of them can be calculated
as follow:
1
f0 =
L,
2π r
Cr
Z0 =
Lr
Cr
S1
,
Q=
Z0
R
C
L
R
S2
C
Fig. 1 Half-bridge Resonate Inverter structure
Leq
Req
Cr
Fig. 2 RLC series-resonated equivalent circuit
Fig. 3 shows the relation between output power
and ratio value of system operating frequency f s and
resonated frequency f o . From that, we learned that
different Q value would cause much difference of
power curves. The less Q is, the lower sensitivity
of output power is. We could gain the largest output
power when switching frequency was equal to
resonated frequency.
Fig.3. Relation between output power and
poer
3 phases
220V
Converter
circuit
Power source
circuit
filter
inverter
fs
4.3.1 Design of rectifier
Since the system power is 3-phase AC power, it is
necessary to use 3-phase full-wave rectification
circuit and there were three important parameters
need to be considered as follow:
(1) Forward average current: its value was
designed according to power of load, and generally
designer would use twice of stable current
endurance when choosing proper rectifier
(2) Backward peak voltage: because almost all
rectifiers were operating in high voltage condition,
designer must consider the backward voltage in the
turn-off condition of rectifier.
fo
LC
Resonated
circuit
Fig 6 DC output voltage wave after rectification
IGBT driving
circuit
Load
detecter
DSP
controller
4.3 Design of rectifier and filter
Without
Load
detecter
Over-current
protecter
(3) Surge current: because the last rectifier was
connected to inverter, designer should consider
much higher surge current endurance to avoid
damage to rectifier at instant turn-on condition. The
average voltage after rectification in Fig 6 was as
follow:
Terminal
controller
Key-scan
Displayer
Speaker
=
Fig. 4 Heating System circuit structure
Fig. 4 shows the whole system structure of
designed inductive heating-facility, and the main
parts of design details described as follow:
4.2 Input DC power for inverter
The input source power of system is 3 phases, 60Hz
AC power which was adjusted into Vline=220V by
auto-transformer and then the power was input to
inverter after full-wave rectification shown in Fig. 5.
π
1
Vdo =
π
3
π
∫π
6
−
3
6
2 VLL cos wt dwt
2 VLL
(1)
= 1.35VLL
where Vd o is the DC output average voltage and
VLL is the Root mean square of Vline.
If the Po as the heating-facility power were 5KW,
and the efficient factor of inverter η = 0.9 ,
V LL =220V. We can calculate as follow:
Vd ＝ 1.35VLL = 297 V
The input power of inverter can calculate as:
Po
5kw
= 5.6kw
(2)
0.9
η
And the output current of rectifier I d would be
Pin =
=
as
Fig. 5 Input DC power circuit of system
Id =
Pin 5.6kw
=
= 18.855 A
Vd
297v
According to results mentioned above, we can
choose proper rectifier.
4.3.2 Design of Filter
Filter capacity has both filtering and voltage
regulator function. Since we used 3-phase source
power, the ripple rate was accepted, we chose one
capacity (2.2uf/400V) as shown in Fig. 7.
3-phase rectifier
filter
R
S
T
Fig. 7 3-phase rectifier and filter
4.3.3 Design of Inverter
The inverter in the heating-facility was adopted
half-bridge series-resonated structure as shown in
Fig. 8 and all components in circuit would describe
as follow:
S1
Lr
Cr/2
R
Cr/2
R
C
S2
Fig. 8 Half-bridge series-resonated structure
4.4 Operating Frequency
As we mentioned before, the operating frequency of
inductive heating-facility has much to do with
output power. When the operating frequency is
equal to resonated frequency, heating system would
gain the largest output power. Supposed that we
used frequency to control various power output,
there are two models as follow:
(1)
(2)
the system highest operating frequency
generates largest power output.
the system smallest operating frequency
generates largest power output.
The superiority of model (2) is that system owns the
smallest operating frequency at largest output power,
and that makes smaller loss of IGBT than that of
model (1). Because the current endurance of IGBT
has much to with conjunction temperature which is
resulted from IGBT loss and the more loss is, the
less current endurance will be. So we chose model
(2) as our operating frequency in system
The resonated frequency could be calculated
according to formula (3). We designed the resonated
frequency to be 16.97 KHz.
f =
1
2π Lr C r
(3)
where f is the resonated frequency, Lr is the coils
inductance, and C r is the resonated capacity.
5 Simulation & Analysis of inverter
circuit
Since the switching way of IGBT and frequency
were the key factor that affected the circuit
operation, we first used Is-Spice to simulate the
circuit function and analyze the wave of half-bridge
circuit structure driving with set driving signals
including Symmetric and non-symmetric PWM,
SPWM. Then comparing the current flowing
through IGBT and analyzing current wave on coils
and noise under fixed power output to learn the
whole theory and adjusted the related parameters in
the circuit according to the wave change. Then we
experimented with the RLC series resonation in
order to learn the switching loss generated from the
switching signals for IGBT, and found solution of
how the noise low down and power factor become
better to promote the efficiency of power system.
Finally, we designed the resonation capacities and
inductance in the circuit to decide (a) power output
(b) RMS value of output current (c) system
switching
frequency.
Then
we
designed
Clamped-voltage slow-resonated circuit to change
ON and OFF timing of IGBT so as to low down
switching loss during switching of IGBT and
restrain over-voltage of IGBT that generates high
dv/dt doing damage to IGBT. We judged whether
the pan really exist or not by response of RLC
circuit and whether the pan was taken away or not
by calculate the power change through voltage and
current sampled from AD channel of DSP. We used
photo-couple circuit to isolate driver circuit with IC
(HCPL-3120) and designed voltage, current
over-loading and overheating circuits after learning
the dynamic and static features of IGBT. Meanwhile
we adopted DSP (TMS320F240) to develop the core
program of whole system to generate PWM signal
needed by controlling IGBT and CPLD as
protecting PWM circuit to avoid simultaneously ON
of up-IGBT and bottom-IGBT that would result in
damage of IGBT.
When DC power supplies to AC load, it must
process DC to AC converting. This function
accomplishing DC to AC converter is DC-AC
conversion circuit or called inverter. Supposed we
classify inverter with feature of DC power, it could
be divided voltage-type and current-type, and in this
6
AC POWER
Load
Inductor-coils
Power Transistors
Recitifier
X11
KBPC2506
12
Cf
4.7u
I_in
3
3
3
25
14
14
14
14
14
X5
IRG4BC30UD
14
14
13
Rg2
10
Eddy current
generating heat
In Fig. 9, AC power (110V/220V, 60Hz/50Hz)
converted into half-cycle positive AC power by
rectification, and the power was converted into
smooth DC power after passing through LC
low-pass filter which coupled with a high-voltage
endurance shunt capacity. Finally, the inverter
generated a high frequency current by switching of
IGBT or Power MOSFET and generated a changed
magnetic-field with electric-magnetic induction,
which would induct cross-over inductor-coils and
generated eddy-current on the surface of magnetic
materials to accomplish heating effect. Fig. 10
shows the voltage and current wave change during
electric energy converting into heat energy.
As Fig. 11, in this paper we adopted turn-on-off
resonation converter, which generated high
frequency AC signals for load by LC resonation
pool with switches turning on and off. DSP
generated driving signal and judged present
condition of system by voltage feedback signals
generated by sampling from power current and load
current that flowed through Current Transformer
(CT). The primary function of EMI circuit is to get
rid of noise generating from high frequency
switching as well as from AC power.
LC resonation pool
N:1
Feedback signal of
power current
Half-bridge
inverter
Driving
signal
TMS320F240 DSP
Control circuit
R10
0.01
6
C1
0.3u
21
10
21
9
14
14
14
Rs2
14
9
9
7
1
X9
COUPLEDL
9
X8
HFA15TB60M
C2
0.3u
1
Cs2
Fig. 12 the simulation circuit of main system
In Fig. 12, the design of the half-bridge inverter
simulation circuit including selection of gate driving
resistor of IGBT and clamped RCD slow-resonation
circuit could decide output power, switching
frequency, the value of resonation capacity and
inductance which combined the half-bridge inverter.
Then it will convert non-smooth DC voltage into
high frequency current for load by high frequency
PWM switching signals.
Fig. 10 the voltage wave during Resonated
Heating-process
EMI adjusting
circuit
14
14
7 7
∆
High frequency
current
Fig. 9 Structure of Half-bridge Resonated
Heating-process
AC
I_out
X6
HFA15TB60M
High Frequency
Switching 20kHz
C
T
2
Cs1
14
POWER
MOSFET
DC Power
6
Pout
10
2
g1
g2
60/50Hz AC
POWER
6
Rs1
6
B2
Voltage
-
IGBT
AC
6
6
11 11
Rg1
10
6
6
14
IN
∆
Vsin
3
5
+
∆
12
6
6
X4
IRG4BC30UD
B1
Voltage
Lf
300u
V220
12
X7
HFA15TB60M
X3
HFA15TB60M
Vd
*
paper we adopted the former.
L1
L2
R
C
T
Equivalent
Circuit of Pan
Feedback signal of
Inductor coils current
Fig. 11 the Development Chart of System
C urren t feedback sen sor
H eating coil
IG B T T em perature sensor
P an T em p erature sensor
In verter C ircuit
(H alf B ridg e S ystem )
P an d etect sen sor
IG B T D river
F an m otor
10M H z
A /D
P W M D river
CPLD
IN T 1
E nable signal circuit
PW M 1
PW M 2
T M S 3 20F 24 0
P W M T rig
B uzzer
R S 232 介 面
P o w er o n
PC
Low
M id
H ig h
L E D D isplay
K ey
Fig. 13 system development structure
In Fig. 13, we used DSP to generate the driving
signals for IGBT and design protection circuit with
CPLD to prevent the upper and lower IGBT from
switching ON simultaneously even burn down IGBT.
On the other hand, through external interrupt signals
CPLD would detect the load condition (whether
there is a pan or not) and send back the detected
signal into DSP; further more, it also feedback
sampled temperature, voltage, current signals into
10 bits AD channels inside DSP to avoid system in
danger condition. All the immediate information
sampled by DSP would send to PC terminal through
RS-232 interface to let user learn the power change
situation on line immediately.
6 Experiment Results
In Fig. 14, the pink color (channel 3) wave pointed
out the driving signal of IGBT, ranged +15v ~ -11v,
frequency 20K Hz. And the yellow color wave
(channel 1) was voltage between collector and
emitter of IGBT (Vce), it’s about 297V. From the
figure, it was obvious that if the Vce hadn’t
descended to zero while the driving signal was ON,
this meant IGBT was not precisely operating on
soft-switching point and that’s why so large
harmonic appeared on Vce wave, in addition, the
slop of Vce became larger at switching-point and
this meant dv/dt became larger.
showed inductor-coil current wave with pan on
heating stove. Comparing the two figures, we
learned that the peak value of inductor-coil current
were quite different, so we could detected whether
there was a pan on stove or not by detecting peak
value of voltage gained from converting
inductor-coil current to voltage through CT. The
circuit was shown in Fig. 18.
S1
C1
L
DC
CT
S2
C2
5v
R1
+
R2
Fig. 14 The lower IGBT control signals without at
soft-switching
Under same condition, in Fig. 15, it was obvious
that if the driving signal was ON while dv/dt went
down to zero, the harmonic on Vce wave was less
than that in Fig. 14 and slop kept smooth leading to
the output power became stable. This meant the
IGBT was under controlled at precise soft
switching-point. The result was shown in Fig. 15.
Fig. 15 The lower IGBT control signals at
soft-switching
Fig. 16 Inductor-coils current wave without pan
Fig. 17 Inductor-coils current wave with pan
The blue color pulses (channel 2) was the
shooting pulses designed to generate the driving
signals for lower-IGBT and the red wave (channel 3)
was inductor-coil current wave
converted by
current transformer (CT). Fig. 16 showed
inductor-coil current wave without pan and Fig. 17
To dsp
-
R3
Fig. 18 Detect circuit for condition of pan on
7 Conclusion & Suggestion
In this study, a half-bridge driven by
fixed-frequency was implemented in a variable
power, constant frequency inductive heating facility
in which the circuit was adapted ResonantTransition
in
Zero-Voltage-Switching,
Clamped-Voltage (ZVS-CV). After simulation with
Is-Spice and practical experiment, we gained the
conclusion as following : (1) In the heating process,
if we took away the pan, the combined resistance
and inductance in the circuit would decrease that
caused Q value increase and make switching
frequency near to resonated frequency, and the
pan-inductor-coil current instantly rose upward.
Provided that the Ic of IGBT were more over than Ic
maximum, the IGBT would occur to latch effect that
led to out of control of power or even damage to
IGBT themselves. So the most important design
factor of software is the detecting of putting away of
the pan. It is necessary to immediately judge pan’s
being put away and stop the PWM control signal to
avoid the damage of IGBT.
(2) The detected method for pan putting away in
this paper utilized the current transformer to decade
current flowing through primary winding and
convert into the voltage signal with resistors and
capacities, finally amplified the signal with OP to
0~5 volt level which would sampled by DSP AD
channels, and the current change amount would be
used to compare with the former sampled current
and then judge whether the pan was put away or not.
(3) The practical design of large-scale power
resonated pan can be divided into three types: (a) to
pull up the primary power supply (b) to pull up the
capacities value on DC BUS (c) to decrease
inductance of pan-inductor-coil or enlarge the
resonated capacity. But the inductor-coil is made of
winding copper and it couldn’t be too thin;
otherwise, the coil would be burnt down because of
overheating, so the inductance can’t be decreased
too much.
(4) The duty-cycle must increase gradually when
upgrade the fire of stove to avoid doing damage to
IGBE because of high di/dt which causes fast rising
of current of IGBT.
(5) The system should immediately detect the
putting away of pan and turn off the PWM control
signal lest the current of resonation pool should
suddenly increase to cause the latch effect of IGBT,
so there must be hardware or software design to
detect the putting away of pan.
(6) The practical design for high power inductive
heating devices should focus on voltage-proof and
current-proof class of components, especially the
layout should separate the power wire and signal
wire to avoid the noise generated from power lines.
(7) The clamped RCD slow resonated circuit
should be near to IGBT as could as possible when
layout to avoid generating stray inductance that
would cause high di/dt resulting in burning down of
IGBT.
(8) Restraining the stray oscillation generated by
high frequency switching of IGBT has three
methods as follow: (a) Shortening the pin wire of
gate polar of IGBT as could as possible (b) Using
ferrite bead (c) Setting series resistor onto gate polar
of IGBT.
(9) The strategies preventing the system from
operation trouble-shooting are as follow: (a)
Reducing stray capacities between driver circuit and
ground. (b) Low down the resistor of driver circuit
(c) Up-grade the rated voltage of driver circuit.
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