Full Text - IDOSI Publications

Middle-East Journal of Scientific Research 20 (12): 1935-1939, 2014
ISSN 1990-9233
© IDOSI Publications, 2014
DOI: 10.5829/idosi.mejsr.2014.20.12.981
Reduced Component Induction Heater for Domestic Applications
B. Vamsikrishna and R. Renuka
Department of Electrical and Electronics Engineering,
Bharath University, Chennai, Tamilnadu, India
Abstract: A new proposed topology is used to improve the efficiency while reducing the power device count
for induction heating applications. In the proposed system, the rectifier is constructed using two independent
diodes and sharing the other two diodes with snubber diodes of MOSFET switches. So it has minimized
components. Also, for the high frequency inversion process, the series inverter topology is selected which will
further reduce the number of MOSFET switches required for the inverter. The inverter is provided with
resonant circuit to resonate the current and voltage at the switching frequency to achieve ZVS (Zero Voltage
Switching) and ZCS (Zero Current Switching) which will greatly reduce the switching losses. In Simulation,
pulse generators are used to generate pulses for the inverter switches and the PID is used in the closed loop
to achieve the desired output.
Key words: Home appliances
Induction heating
Inverters
INTRODUCTION
Induction heating appliance market is increasing
due to its fastest heating time and efficiency. Domestic
induction hobs are now becoming a standard option,
especially in Asia and Europe. The development of high
frequency AC/AC converters for kitchen equipments is
the need of the hour [1]. The development of the new
high frequency induction heating cooker, boiler and
super heated steamer, that is high-performance, high
power density and high efficiency compared with the
conventional gas cooking equipment are much more
attractive for home and business uses. By such
technological background, high-frequency soft switching
power supply for the electromagnetic induction
heating with the control schemes has been developed.
Nowadays, most designs use the half-bridge series
resonant topology because of its control simplicity and
high efficiency. In the past, several ac-ac topologies have
been proposed to simplify the converter and improve the
efficiency. The efficiency and cost are compromised due
to the use of a higher number of switching devices [2-7].
Other approaches, commonly used in electronic ballasts,
simplify the rectifier stage in order to improve the
converter performance. This topology, known as halfbridge boost rectifier, reduces the switch count while
Resonant power conversion
keeping the same performance as more complex solutions.
Induction heating is the process of heating an electrically
conducting object (usually a metal) by electromagnetic
induction, where eddy currents (also called Foucault
currents) are generated within the metal and resistance
leads to Joule heating of the metal. An induction heater
(for any process) consists of an electromagnet, through
which a high-frequency alternating current (AC) is
passed. Heat may also be generated by magnetic
hysteresis losses in materials that have significant relative
permeability. The frequency of AC used depends on the
object size, material type, coupling (between the work coil
and the object to be heated) and the penetration
depth.Induction heating is a non-contact heating process.
It uses high frequency electricity to heat materials that
are electrically conductive [1]. Since it is non-contact,
the heating process does not contaminate the material
being heated. It is also very efficient since the heat is
actually generated inside the work piece. This can be
contrasted with other heating methods where heat is
generated in a flame or heating element, which is then
applied to the work. Conventional converters for radio
frequency induction heating usually follow an AC-DC-AC
structure, which can exhibit non-unity power factor and
introduce large harmonic currents into the utility supply.
Then the matrix converter have an additional switches,
Corresponding Author: R. Renuka, Department of Electrical and Electronics Engineering,
Bharath University, Chennai, Tamilnadu, India.
1935
Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014
so it have an increased the control complexity and cost of
the system.Next the single phase boost chopper converter
produces the harmonic distortion and high input peak
current. So the switching losses are high. In the existing
system the DC - AC inverter is operated in open loop with
fixed PWM ON time for a fixed power output and hence
the power output cannot be varied and moreover, for any
error or deviation, the output is not corrected
automatically. Generally the induction heaters running
on 50 Hz ac mains will have a full wave rectifier using
4 diodes followed by high frequency inverter using
4 MOSFET switches.
Proposed Power Converter: A new topology is proposed
to improve the efficiency and to reduce the power device
count for induction heating applications. The proposed
system is based on the series resonant half-bridge
topology and requires only two rectifier diodes.
Because of the reduction of number of diodes, the
system components are minimized. It also reduces the
switch count while keeping the same performance as
more complex solutions.
This topology implements resonant capacitors and
may use a bus capacitor, due to the symmetry between
positive and negative mains voltage, both resonant
capacitors have the same value. An input inductoris
used to reduce the harmoniccontent to fulfill the
electromagnetic compatibility regulations. The inverter
is provided with resonant circuit to resonate the current
and voltage at the switching frequency to achieve ZVS
(Zero Voltage Switching) and ZCS (Zero Current
Switching) which will greatly reduce the switching losses.
The proposed system employs closed loop system
with two microcontrollers: One to generate PWM pulses
for MOSFET switches and to read the input voltage,
current and output voltage. The other controller is used
to compute input and output power and display on the
LCD. Serial communication interface is provided
between two controllers for data transfer between
them.For closed loop operation the desired output power
can be entered through keys. The closed loop control is
implemented using software based PID control algorithm,
which compare the set power with actual power to
generate an error signal which in turn is used to modify
the ON time of PWM pulses in order to maintain the
output at desired value.
Analysis: The proposed topology is a series-parallel
resonant converter. The inductor-pot system is modeled
as an equivalent series resistance Reqand inductance
Leq, as shown in Fig. 3.1 [15]. This topology implements
resonant capacitors Cr and may use a bus capacitor Cb.
Fig. 3.1: Proposed ac-ac converter.
Fig. 3.2: States and transition conditions
Due to the symmetry between positive and negative
mains voltage, both resonant capacitors have the same
value. An input inductor Lsis used to reduce the harmonic
content to fulfill the electromagnetic compatibility
regulations [2].
A 230v,50Hz Ac supply is given to the circuit.
The harmonics in the supply is reduced by input
inductance Ls. The input Ac supply is converted in to Dc
by Half bridge rectifier. Bus capacitor Cb is act as a filter
which is used to remove ripples from the Dc voltage.
MOSFET is used as switching device in our project.
MOSFET performs switching operation at Zero voltage
switching condition (ZVS). The diode DH and DL act as
inverter in different modes of operation which it
convert DC to AC. The AC voltage is given to RL load.
The switching operation performed in three different
operating modes.The topology presents symmetry
between positive and negativeac voltage supply. Its
symmetry simplifies analysis and makes possible to
redraw the circuit.
Although this topology uses different resonant
configurations, parallel and series and different resonant
tanks for each of them, it is possible to use a normalized
nomenclature based on series resonance. Fig. 3.2 shows
the simple transition conditions for each state [3].
STATE I: SHActivated : SL Deactivated: State I operates
with the high-side switching device SH triggered-on
and activated and the low-side switching device (SL)
triggered-off. The parallel resonant circuit is set by an
1936
Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014
equivalent capacitor Ceq, obtained from Cr and Cband
expressed and the inductor electrical parameters, Req and
Leq. The current flowing through SH is the same as the
one flowing through the load.State I begins when SL is
triggered OFF. In this moment, the anti parallel diode DH
conducts and SH can be triggered ON ensuring ZVS
switching-on conditions. Transitions from this state can
lead either to state II or state III. If voltage across SL
reaches zero and DL starts conducting, the transition
condition to state II is fulfilled. On the other hand, if SH is
switched OFF whenTH conducts, the next state is state III
[4].
STATE II: SH Activated: SL Activated: State II is
characterized by the conduction of both switching
devices, although only SH is triggered ON. That is,
TH and DL conduct at the same time. Current through
load is supplied by both devices (TH and DL ) and
consequently, low conduction stress for the devices is
achieved. The equivalent parallel resonant circuit is set
by the inductor electrical parameters in parallel with
both resonant capacitors. Cbis short-circuited by both
switching devices. This state starts when the voltage
across SL reaches zero. At this moment, DL starts
conducting at the same time as TH is triggered ON.
This state finishes when SH is triggered OFF and the
next state is state III. The main benefit results of the
lower switch-off current achieved when SH is triggered
OFF, due to the fact that the load current is supplied by
both devices. In addition, SH achieves ZVS conditions
during both switch-on and switch-off transitions,
reducing consequently the switching losses [5].
STATE III: SH Deactivated: SL Activated: State III is
defined by the conduction of SL while SH is deactivated.
The equivalent resonant circuit is set by one resonant
capacitor in parallel with the series connection of the
Cbcapacitor and the parallel connection of the inductor
and the other one resonant capacitance. Note that when
Cbis zero (á = 0), theequivalent resonant circuit is a series
RLC circuit composed of the inductor-pot system and
one resonant capacitor. This state starts when SH is
triggered OFF. At this moment, DL starts conducting
and SL can be triggered ON achieving ZVS switch-on
conditions. This state finishes when SL is deactivated and
the next state is state I [6].
The operating principles of the circuit are illustrated
by Fig. 3.1 Fig, 3.2 Fig, 3.3 and the theoretical waveforms
are shown in Fig. 3.4
The first operation mode uses the three states
described earlier: I, II and III. It makes possible to achieve
ZVS conditions for the high-side switch in state II [7].
Fig. 3.3: Theoretical Analysis Wave form
Simulation Results: The Resonant converter fed
induction heater is simulated using Matlabsimulink and
their results are presented here. The circuit model of
resonant converter is shown in Fig.4 Scopes are
connected to measure output voltage, driving pulses and
capacitor voltage.The principle of operation is based on
the generation of a variable magnetic field by means of a
planar inductor below a metallic vessel. The mains
voltage is rectified and after that an inverter provides a
medium-frequency current to feed the inductor. The usual
operating frequency is higher than 20 kHz to avoid the
audible range and lower than 100 kHz to reduce switching
losses. The diode rectifier is used to convert AC to DC
source. The filter capacitor is used to reduce the
ripples and given it to the inverter. The MOSFET
switches are used because of its fast switching capability.
The snubbers in the mosfet is used to protection.
The inverter converts dc to ac output. The switching
pulses required for the inverter operation are generated
by the V-ZCD and a PWM pulse at particular frequency.
Each switching pulse is logically ORed with PWM pulse
and applied to the gate of MOSFET switches for
triggering. PIC16F877A controller is used here for
generating PWM pulses. The resonant condition is
satisfied using resonant circuit. It can operate with
zero-voltage switching conditions during turn-on for
both switching devices and also during turn-off
transitions for one of them. As a consequence, the
efficiency is improved while the device count is reduced.
1937
Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014
Fig. 4.1: Open loop circuit
Fig. 4.5: AC output waveform
Fig. 4.2: AC input
Fig. 4.6: Closed loop circuit
Fig. 4.3: Switching pulse waveform
Fig. 4.7: AC input
Fig. 4.4: Current to load
The output waveform is obtained by using CRO. The ac
input voltage, current and ac output voltage are then
measured and fed to the controller via internal ADC to
obtain the desired output voltage in the closed loop.
Fig. 4.8: Current to load
1938
Middle-East J. Sci. Res., 20 (12): 1935-1939, 2014
ACKNOWLEDGEMENT
I articulated my gratitude to Mr.B. Vamsi Krishna,
M. Tech., Assistant Professor of Electrical and electronics
Engineering who had thought as the way to do a
successful project and without whose constant
encouragement and whole idea, the project would not
have been possible. I wish to express my sincere thanks
to our project co-coordinator Prof.T.Ramamoorthy and
External Guide Prof.Dr.S.Arumugam who had helped me
lot and has given valuable suggestion, which made me to
accomplish this project in very successful and next way.
Fig. 4.9: AC output waveform
REFERENCES
1.
2.
3.
Fig. 4.10: Hardware layout
PIC16F628A controller is used to compute the efficiency
and power factor of the system. It achieves unity power
factor when the voltage and current are in phase with
each other.
4.
5.
CONCLUSION
Thus an embedded based induction heater with
reduced components suitable for domestic applications
is developed successfully. The efficiency and cost are
compromised due to the use of a less number of switching
devices. Other approaches, commonly used in electronic
ballasts, simplify the rectifier stage in order to improve
the converter performance. This topology, known as
half-bridge boost rectifier, reduces the switch count while
keeping the same performance compared to the other
complex solutions. It also improves the power factor of
the system.
6.
7.
1939
Acero, J., J.M. Burdio, L.A. Barragan, D. Navarro,
R. Alonso, J. R. Garcia, F. Monterde, P. Hernandez,
S. Llorente and I. Garde, 0000. Domestic induction
appliances, IEEE Ind. Appl. Mag., 16(2): 39-47.
Fujita, H., N. Uchida and K. Ozaki, 2009. A new
zone-control induction
heating system using
multiple inverter units applicable under mutual
magnetic coupling conditions, IEEE Trans. Power
Electron., 26(7): 2009-2017.
Mill´ An, I., J.M. Burd´ýo, J. Acero, O. Luc´ýa
and S. Llorente, 2011. Seriesresonant inverter with
selective harmonic operation applied to all-metal
domestic induction heating, IET Power Electron.,
4: 587-592.
Steigerwald, R.L., 0000. A comparison of half-bridge
resonant convertertopologies, IEEE Trans. Power
Electron., 3(2): 174-182.
Koertzen, H.W., J.D. van Wyk and J.A. Ferreira.,
1995. Design of the halfbridge series resonant
converters for induction cooking, in Proc. IEEE
Power Electron. Spec. Conf. Records, pp: 729-735.
Pham, H., H. Fujita, K. Ozaki and N. Uchida, 0000.
Phase angle control ofhigh-frequency resonant
currents in a multiple inverter system for
zonecontrolinduction heating, IEEE Trans. Power
Electron., 26(11): 3357-3366.
Yunxiang, W., M.A. Shafi, A.M. Knight and
R.A. McMahon, 0000. Comparison of the effects of
continuous and discontinuous PWM schemeson
power losses of voltage-sourced inverters for
induction motor drives, IEEE Trans. Power Electron.,
26(1): 182-191.