IEEE PEDS 2011, Singapore, 5 - 8 December 2011
A Series-Resonant Half-Bridge Inverter
for Induction-Iron Appliances
N. Sanajit* and A. Jangwanitlert **
* Department of Electrical Power Engineering, Faculty of Engineering,
Mahanakorn University, Bangkok Thailand, 10530
** Department of Electrical Engineering, Faculty of Engineering,
King Mongkut’s Institute of Technology Ladkrabang, Bangkok Thailand, 10520
Abstract- This paper presents a series-resonant half-bridge
inverter for induction iron appliances. The series-resonant
inverter is implemented to provide Zero Current Switching
(ZCS) for all the switches at turn off conditions and Zero Voltage
Switching (ZVS) at diode turn on. The main features of the
proposed inverter are simple PWM control strategy and high
efficiency. The operation mode of the inverter will be evaluated
corresponding to the duty cycle of the switch. The experimental
results verify the advantages of the proposed topology.
The paper is organized as follows. In Section II, the converter is
chosen. The operation principle of the synthesized converter is
presented in Section III. The experimental results are indicated in sec
IV. Finally, conclusions of the work are provided in Section V.
Index Terms- ZVS, ZCS, induction iron, half-bridge inverter,
resonant
I. INTRODUCTION
INDUCTION heating system can apply for many things such
as induction hardening, induction melting, induction cooking, etc [1].
One thing that is no paper to propose for induction heating systems is
induction iron. Therefore, this is the first time to propose the
induction iron appliance. Induction iron is low-power inductionheating systems with a maximum output power usually less than 1.5kW per load. An induction iron appliance is basically made up of a
flat-type inductor coil, with insulator, in which the iron tray to be
heated is placed. Between the iron tray and the coil, an insulator is
placed in Fig. 1. The heat is generated at the iron tray’s bottom due to
eddy currents and hysteresis losses. These induced currents are
caused by an alternating magnetic field generated by a medium
frequency (20–100 kHz) current through the coil. Iron tray-inductor
coupling is usually modeled as the series connection of an inductor
and a resistor, based on the transformer analogy. The values of the
equivalent inductance and resistance depend on the operating
frequency and the required maximum power.
An arrangement of an induction iron is shown in Fig. 2. An
induction iron takes the energy from the mains voltage, which is
rectified by a bridge of diodes. In this paper, a bus filter is designed to
allow a large voltage ripple to obtain the high input power factor.
Then, the inverter topology supplies the high-frequency ripple current
to the induction coil. The main inverter topologies used in induction
heating system are the resonant inverters, including full-bridge, halfbridge and single-switch inverters. In this case, induction iron
appliance including is possible to use a half- bridge inverter as shown
in Fig. 3.
The purpose of this work is to get a series-resonant inverter for
using it in power electronic converters mainly for induction iron. The
operating frequency is fixed, but the duty cycle control can be
adjusted, based on power desired and load conditions. The required
fixed-frequency control has some additional advantages, as reducing
the electromagnetic noise spectrum and avoiding the acoustic noise
[2] due to different operating frequencies which cause low-frequency
interferences amplified by the iron.
Fig. 1 Iron tray with Coil
Fig. 2 Typical arrangement of an induction iron appliance.
II. CHOICE OF CONVERTER
The half-bridge, series resonant converters were selected
above the single-switch topologies due to the following
reasons [3]:
• The voltage across the semiconductors is clamped.
Even though two switches are needed, at least half
the voltage blocking capability is required.
• Due to switching is done at a duty ratio of 50%,
feedback is not needed.
Anti-parallel composite-switches must be used, as shown in
Fig. 3, consisting of a singular-switch (S) and an anti-parallel
diode (D). Isolated gate bipolar transistors (IGBTs) are shown
because they are well suited for this medium frequency
application. Although an isolated gate drive is needed, an
opto-isolator can be used due to the 50% duty ratio. The
978-1-4577-0001-9/11/$26.00 ©2011 IEEE
46
switching power loss in the semiconductors could be a
disadvantage and is investigated.
kHz. The following changes were made to the converters
described by
• The resonant capacitors (C1+C2) // C) are used, as
shown in Fig. 3, so that current is drawn from the
supply during each half cycle of the switching period,
enhancing the power factor.
III. OPERATION PRINCIPLES
Fig. 3 Half-bridge, series resonant circuit.
The are generally two possible switching schemes for
this converter to obtain the desired output power control
without varying the input voltage, i.e. load commutation and
forced commutation. In this paper, the load commutation
should be applied.
Fig. 5 shows possible current paths of the inverter output
voltage (vAB) and load current (iL) which are only one cycle
(see Fig. 2 or Fig. 6). Also, the operation waveforms are
shown in Fig 6. To simplify it, the following assumptions are
provided:
• The resonant capacitors are ideal
• Inductance L is working coil and work piece
• Resistance R is work piece
• all devices are no losses.
C1
Load Commutation
A typical iCS waveform is shown in Fig. 4. The power is
decreased by decreasing switching frequency (fs) below the
resonant frequency (fr) where
fr = 1
LCT
, CT = (C1 + C2 ) / /C
(1)
Giving the following advantages and disadvantages:
+
No turn-off power loss for the singular-switches
(ZCS) and no turn-off power loss for the anti-parallel
diodes (ZVS) as shown in Fig.4.
- Maximum power is obtained at the upper limit of the
switching frequency.
- Turn-on power loss for the singular-switches and turnoff power loss and reverse recovery current for the antiparallel diodes.
D1
S1
L
R
Vi
D2
C2
C
S2
(a) Mode 1
Fig. 4 Singular-switch and diode current for load commutation.
To be easily operated, the load commutated converter
was applied. The elimination of the reverse recovery current
of the diodes [3,4]and the maximum power was obtained at the
upper point of the switching frequency range, usually about 30
47
IV. EXPERIMENTAL RESULTS
The experimental results are done for the main
components as given below:
C1=C2= 12 uF; C = 0.8 uF, L = 35.62 uH, R = 26 mohm,
Maximum input voltage Vi = 310 V.
Fig. 5 Operation mode.
This inverter can be operated under soft switching
conditions as shown in Fig. 4, and its output power cannot be
regulated continuously due to the fact that the input voltage
(Vi) has a high ripple (as shown in Fig.7) following by the ac
input voltage. However, the duty cycle control for switches is
fixed. The duty cycle D is equal to 0.35. The results from
each voltage and current of switch per cycle are shown in
Fig.8 that is indicated as the soft switching (ZVS and ZCS like
Fig. 4). The characteristics of voltage and current waveform of
the previous cycle is look like the same as the next cycle, but
the amplitude of voltage and current is different. Therefore,
the inverter output voltage and load current waveform are
shown in Fig. 9. That is indicated that switch is operated as the
load commutation.
Fig. 6 Operation waveform.
There are 4 switching modes in a switching period as
described in the following.
Mode 1: (t0-t1) [Fig. 5(a)]: Switch S1 conducts the load current
iL. The output voltage across the load (inverter output voltage)
is Vi/2. The zero current of switch S1 is zero at turn off. In this
mode, the zero current switch (ZCS) of switch S1is achieved.
Mode 2: (t1-t2) [Fig. 5(b)]: switch S1 is off. The voltage across
S1 is zero to prepare the diode D1 going to a zero voltage
switch (ZVS) at turn on. The diode D1 conducts the load
current iL in the opposite direction of mode 1. The output
voltage across the load is still equal to Vi/2.
Fig. 7 High input ripple voltage (Vi) (upper) and current (below).
Mode 3: (t2-t3) [Fig. 5(c)]: Diode D1 is off. Switch S2 conducts
the same side of load current iL and S2 achieves the ZCS
condition. The output voltage across the load is -Vi/2. When
the switch conducts, the voltage across of switch S2 is zero.
Mode 4: (t3-t4) [Fig. 5(d)]: switch S2 is off. The voltage across
S2 is zero to prepare the diode D2 going to a zero voltage
switch (ZVS) at turn on. The diode D2 conducts the load
current iL in the opposite direction of mode 3. The output
voltage across the load is still equal to -Vi/2.
The next cycle will be repeated mode 1 and so on.
Fig. 8 Voltage across switch (upper) and current of each switch (below).
48
Fig. 12 Distributed temperature over the iron sheet from thermo-scan.
Fig.9 The inverter output voltage (vAB) (square wave) and
load current (iL) (almost sine wave).
In addition, the experiment shows the heat from the iron
sheet that is compound of the iron. Fig.10 shows the average
absorbed temperature results from the thick of the iron sheet.
The more thickness of iron sheet had, the more time for
getting high temperature had. Moreover, Fig. 11 shows the
average emitted temperature results from the thickness of the
iron sheet. The more thickness of iron sheet had, the more time
for reducing high temperature to low temperature had. In this
case, the upper limit of temperature is 90 oC while lower limit
of temperature is 30 oC. To use appropriately in this research,
4-mm thickness of iron sheet was used.
Furthermore, the test of heat, which is from iron sheet, is
compared between the induction iron and ordinary electric
iron. The right hand side of Fig. 12 shows the distributed-
temperature over the iron sheet of induction iron and the left
hand side of this Fig. 12 shows the distributed temperature
over the iron sheet of ordinary electric iron. It can be observed
that the yellow color is over the iron sheet of induction iron.
This indicates the temperature is almost the same over the iron
sheet. However, the yellow color shows on the iron sheet of
ordinary electric iron that indicates only topical coil, which is
in body of ordinary electric iron. It describes the temperature
over the iron sheet is too much different
In Fig. 13, the output power of ordinary electric iron is
compared with that of induction iron. When the output power
from induction iron is tested at 385 watts, the output power
from the ordinary electric iron is 880 watts, the induction iron
can save more energy per hour. The energy per hour from
ordinary electric iron is 0.117 kw/h. but the induction iron is
0.092 kW/h. The efficiency of induction iron is 92% as shown
in Fig. 14.
Ordinary Electric Iron vs. Induction Iron
Output Power (W)
1000
800
Po (W) Ordinary
Electric Iron
600
400
Po (W) Induction Iron
200
0
0
20
40
60
80
100
Temperature (C)
Fig. 10 The average temperature absorbed from the thick of iron sheet.
Efficiency
Fig. 13 Output power of both irons.
92.5
92
91.5
91
90.5
90
89.5
89
88.5
88
87.5
0
Fig. 11 The average temperature emitted from the thick of iron sheet.
20
40 Temp (C) 60
80
100
Fig. 14 Efficiency of induction iron.
49
V. CONCLUSION
In this paper the operation principle of the prototype
induction iron is introduced together with the switching
frequency lower than resonant frequency, power desired and
ZCS and ZVS algorithm incorporated in it. Its performance
characteristics are verified by the experimental results for a
prototype induction iron rated at 385 W. The induction iron is
designed to replace ordinary electric iron. The prototype has
been developed and the performance is good. It can provide
the heat like ordinary electric iron, it can reduced to 1/2 of the
power for the same amount of heating capability.
REFERENCES
[1] N.S. Baytndtr, O. Kukrer and M. Yakup, “DSP-based PLL-controlled 50100 kHz 20 kW high-frequency inducton heating system for surface
hardening and welding applications,” IEE Proc-Electr. Power Appl., Vol.
150, No. 3, May 2003.
[2] A. Y. Goharrizi, M. Farasat, S. H. Hosseini, A. K. Sadigh, “A Half bridge
inverter with soft switching auxiliary circuit for induction-cooking
applications,” The Proceedings of the 1st IEEE Power Electronic & Drive
Systems & Technologies Conference, 2010, 80-84.
[3] H. W. Koertzent, J. D. Van Wyk and J. A. Ferreira, “Design of the halfbridge, series resonant converter for induction cooking,” The Proceeding
of the 26th IEEE Power Electronics Specialists Conference, 1995, pp.
729-735.
[4] Y. Lu, K. W. E. Cheng, K.W. Chan, Z.G. Sun, and S.W. Zhao,
Development of a Commercial Induction Cooker, The proceedings of the
3rd International Conference on Power Electronics Systems and
Applications, 2009.
50