A New Multiple-Output Resonant Matrix Converter
Topology Applied To Domestic Induction Heating
F. Almazán, O. Lucía, J. Acero, J.M. Burdío, and C. Carretero
Group of Power Electronics and Microelectronics
Aragon Institute of Engineering Research (I3A).
University of Zaragoza, Mariano Esquillor s/n, 50018, Zaragoza, Spain.
Tel. +34-976762707, Fax +34-976762043, e-mail: olucia@unizar.es
Abstract
Most of the ac-ac converters used in home-appliances are based on single-output dc-link
inverters, which provides a cost-effective and straight-forward solution. However, this twostage power conversion decreases power density and efficiency. Direct ac-ac conversion has
been thoroughly studied in the past. However, the complex control scheme and higher cost has
prevented it from being used in low-cost applications, such as home appliances.
This paper proposes the direct ac-ac conversion by means of a multiple-output resonant matrix
converter applied to multiple-inductive load systems. The proposed topology reduces
significantly the number of devices and complexity, leading to an efficient, versatile and costeffective solution. The analytical and simulation results have been verified by means of a
prototype applied to a novel total-active-surface induction heating appliance.
Keywords: Induction heating, resonant power conversion, matrix converter, digital control.
1.
Introduction
Many electronic-fed home appliances are based on dc-link inverters which provide frequencyadjustable excitation required for motors, air conditioning systems, or induction heating devices
(Wang et al. 2009). This architecture provides a straight forward implementation, but also
implies a two-stage power conversion which decreases power density and efficiency.
Direct ac-ac conversion has been thoroughly studied in the past in order to provide an efficient
and compact solution with no energy storage elements. These converters have been compared to
other alternatives (Lai et al. 2008) and successfully applied to drives (Kolar et al. 2007),
aerospace applications (Lee et al. 2010), or power supplies (Andreu et al. 2008;
Ratanapanachote et al. 2006). Matrix converters have also been applied to series resonant loads
for 3-phase systems in (Ecklebe et al. 2009). Considering the induction heating application,
several resonant matrix converters featuring MOSFETs (Nguyen-Quang et al. 2006; NguyenQuang et al. 2007) or RB-IGBTs (Gang et al. 2008; Sugimura et al. 2008) have been proposed.
All the proposals previously described show some common positive points including
improved power factor and harmonic distortion, increased power density, and reduction of
electrolytic bus capacitors. However, the main drawback is the use of additional switching
devices to implement the matrix converter, which lead to increased control complexity and cost.
This issue becomes critical for certain cost-oriented applications. This may be the main reason
A New Multiple-Output Resonant Matrix Converter Topology
Applied To Domestic Induction Heating
for the low percentage of use of matrix converters compared to classical dc-link inverters in
some areas as the home appliances segment.
The aim of this paper therefore is to propose a new multiple-output resonant matrix
converter topology based on the series resonant multi-inverter (O. Lucía et al. 2010) to modify
traditional power conversion based on a dc-link inverter (Fig. 1 (a)). The proposed multipleoutput resonant matrix converter (Fig. 1 (b)) combines the advantages of matrix converters
with the improved cost and power control of the series resonant multi-inverter. Since the matrix
converter block is shared with a high number of induction loads, the overall cost is significant
reduced, and the proposed topology can target the home appliances market.
This paper is organized as follows. Section II presents the proposed multiple-output resonant
matrix converter topology, including the converter schematic and its control strategies. Section
III summarizes de design procedure for the main components, and Section IV presents the main
experimental results used to validate the converter operation. Finally, conclusions of this paper
are drawn in Section V.
Mains
230 V
50/60 Hz
AC-DC
DC-AC
Converter
Converter
Induction load
v
f kHz
(a)
Mains
230 V
50/60 Hz
AC-AC
Converter
Induction
load 1
V1
f1 kHz
Induction
load 2
V2
f2 kHz
…
Induction
load n
Vn
fn kHz
(b)
Fig. 1. Induction heating appliance block diagram: (a) classical dc-link resonant inverter and (b) proposed
multiple-output resonant matrix converter.
2.
Multiple-Output Resonant Matrix Converter
2.1 Topology
The proposed multiple-output resonant matrix converter (Fig. 2) is divided into two blocks: the
common matrix converter block (CMCB) and the resonant load block (RLB). The CMCB has a
half-bridge structure, and it is composed of the common switches Smh and Sml. The switches have
been implemented by means of two IGBTs with antiparallel diode featuring common-emitter
configuration. This configuration has the best ratio between cost and efficiency.
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A New Multiple-Output Resonant Matrix Converter Topology
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+
Smh
vl1
cmh+
Cs/2
cmh-
S1
c1
-
+
Cr1
Leq1
Req1
i l1
vl3
S3
c3
-
Cr3
Leq3
Sml
vo
S2
Cs/2
+
cml+
cml-
vl2
-
-
i l3
Sn-1
Cr,n-1
Leq,n-1
Req,n-1
i l,n-1
cn-1
…
c1
+
+
vl,n-1
Req3
io
~ Vmains
…
-
cn
c4
i l2
Req2
Leq2
Cr2
S4
+
vl4
-
Sn
i l4
+
Req4
Leq4
Cr4
…
i l,n
Req,n
Vl,n
Leq,n
-
Cr,n
Fig. 2. Multiple-output resonant matrix converter topology.
Thb
ThbDhb
cmh+
cml+
cmhcml-
td,hb2
Vmains > 0
~
td,hb1
vmains
~
v o , io
c1
Vmains < 0
φ1 td1
T1
vmains
T1D1
~
c3
i1
i2
~
t
Fig. 3. Control parameters and main waveforms for the multiple-output resonant matrix converter with
positive and negative mains voltage.
The resonant load block is composed of the electrical equivalent for each induction load Req,iLeq,i, the resonant capacitor Cr,i, and the specific switches Si. This provides adjustable output
power for each load while reducing the number of devices.
The main benefit of the proposed topology lies in the use of the CMCB, as it significantly
reduces the ratio of switching devices count per load, avoids the rectifier stage and energy
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A New Multiple-Output Resonant Matrix Converter Topology
Applied To Domestic Induction Heating
storage elements, and simplifies the control strategy. Compared to the classical half-bridge
inverter, and the single-phase single-output matrix converter, for an n-load system the proposed
topology has 4 + n switching devices, while the others requires 2n and 4n respectively. This
implies also a significant reduction in the auxiliary circuits such as control and driver circuits,
and snubber networks.
2.2
Control strategy
The control strategy proposed for the multiple-output resonant matrix converter is based on the
high frequency pulse density modulation (HF-PDM) (O. Lucía et al. 2010; O. Lucía et al. 2011).
This scheme allows performing a fine output power tuning for each load while optimizing the
power converter efficiency. The complete set of control parameters is ψ = {Thb, Dhb, td,hb1, td,hb2,
Ti, Di, td,i, φi| i = 1 .. n} (Fig. 3). Thb and Dhb are the CMCB switching period and duty cycle
respectively, and Ti, Di, φi are the RLB switching period, duty cycle, and phase shift
respectively. Besides, a certain dead times td,hb1, td,hb2 and td,i are defined for safety reasons.
The control signals of the CMCB, cmh+, cml+, cmh-, cml-, are modified according to the sign of the
mains voltage. The CMCB operational conditions determines the overall output power delivered
by the power converter to the set of induction loads. In addition to that, the specific switches Si
are selectively switched on in order to activate the different heating areas and to perform precise
output power control.
Fig. 4 shows the configuration sequence for the multiple output resonant matrix converter
depending on the sign of the mains voltage. It is important to note that there are three switches
activated at the same time. Besides, the common switches withstand the current for all the set of
induction loads, whereas the specific switches only have to withstand the current associated to
its induction load.
The main benefit of the proposed control scheme is the parallel load operation with a voltage
source. This provides independent operation for each load and becomes a simple and effective
method to control the output power for each induction load Po,i.
3.
Design procedure
The following lines give a brief description of the design procedure for the proposed
converter:
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A New Multiple-Output Resonant Matrix Converter Topology
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3.1 Resonant tank
The inductor-pot equivalent Req,i-Leq,i and the resonant capacitor Cr,i make up an individual
resonant tank for each induction load. These have to be designed in order to obtain the desired
output power and switching frequency range. The inductor is designed to achieve the Req,i
required to obtain the maximum output power Po,i,max. Considering the output voltage provided
by the CMCB, the necessary equivalent resistance is:
Vmains > 0
I
II
+
Smh
Leq1
vl1
cmh+
-
io
~ Vmains
Sml
+
cml+
cml-
Req1
S1
cmh-
i l1
Smh
vl2
-
i l2
Req2
cml-
v l1
cmh+
-
S1
io
+
Cs
Cs
vo
vl2
-
-
i l2
Req2
Leq1
i l1
vl1
cmh+
S1 -
cmhio
Sml
c2
S2
+
vo
v l2
-
-
i l2
Req2
+
cml+
cml-
Cs
cml-
Leq2
i l1
c1
c2
S2
+
vo
vl2
-
-
Cr1
Leq1
Req1
i l1
+
Smh
vl1
cmh+
S1 -
cmhio
~ Vmains
Sml
c2
S2
+
vo
-
Cr2
Cs
c1
vl2
Leq2
+
cml+
-
i l2
Req2
Leq2
Cr2
VI
Smh
~ Vmains
io
Cr2
+
c1
Leq1
Req1
Sml
+
Cr1
S1
cmh-
~ Vmains
c2
+
v l1
cmh+
c1
Cr1
Req1
cmh-
cml-
i l1
Smh
V
Smh
Sm,l
Req1
S2
Cr2
+
cml+
+
cml+
IV
~ Vmains
io
Leq2
-
Leq1
-
Sml
c2
+
vl1
S1
cmh~ Vmains
Cs vo
Cr1
cmh+
c1
S2
III
+
Cr1
-
i l2
Req2
+
cml+
cml-
Cs
Req1
i l1
c2
S2
+
vo
-
Cr2
Leq1
c1
vl2
Leq2
Cr1
i l2
Req2
Leq2
-
Cr2
+
Cr1
(a)
Vmains < 0
I
II
Smh
+
Cr1
v l1
Leq1
cmhh
cmhl
i l1
1
io
~ Vred
Sm,l
+
cmlh
cmll
Req1
S
Cs
Smh
cmhh
+
vo
-
i l2
Req2
cmll
Leq2
v l1
cmhh
cmhh
Req1
S1 -
cmhl
io
+
vo
+
vl2
-
i l2
Req2
cmll
vl1
cmhh
S1 -
cmhl
io
Sm,l
c2
S2
+
-
i l2
Req2
Leq2
Cr2
+
cmlh
cmll
Cs
Cs
-
c1
c2
S2
+
vo
vl2
Leq2
i l1
-
-
i l2
Req2
Leq2
Cr2
VI
Sm,h
~ Vred
+
cmlh
Cr2
+
c1
v l2
-
i l1
io
Sm,l
c2
Leq1
Req1
S1
cmhl
~ Vred
Cr1
Leq1
vl1
c1
vo
-
Sm,h
V
Smh
Cs
Cs
Leq1
i l1
S2
Cr2
+
cmll
+
cmlh
IV
Sml
io
Sm,l
S2
-
cmlh
S1
cmhl
Cr1
Req1
-
~ Vred
v l2
~ Vred
vl1
c1
c2
III
+
vo
Leq1
Req1
i l1
+
Sm,h
vl1
cmhh
S1 -
cmhl
c1
io
~ Vred
Sm,l
c2
S2
+
vl2
-
Cr1
-
i l2
Req2
Leq2
Cr2
+
cmlh
cmll
Cs
vo
Leq1
Req1
i l1
c1
c2
S2
+
vl2
-
Cr1
-
i l2
Req2
Leq2
Cr2
(b)
Fig. 4. Configuration sequence for the multiple output resonant matrix converter: (a) positive mains voltage
and (b) negative mains voltage.
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Req ,i  Vo21,rms Po ,i ,max ,
(1)
which leads to an inductor design with a certain number of turns and Leq. Then, the resonant
capacitor is chosen to set the resonant frequency fo,i above the audible range (20 kHz):
Cr ,i  1 4 2 f o2,i Leq ,i .
3.2
(2)
Switching devices
The switching devices are selected according to the converter specifications. The common
switches operate with both switching and conduction losses, whereas the switching losses in the
specific devices can be neglected (O. Lucía et al. 2010). Considering the usual switching
frequencies and stress, 600-V IGBTs are selected.
The specific switches are selected considering the maximum output power per load. Then,
the maximum current that they have to withstand is:
iSi ,rms ,max  Po ,i ,max Req ,i
(3)
The maximum current through the common switches iSm,rms,max depends on the maximum
n
converter output power Po,max. Typically it is selected as Po ,max   Po ,i ,max in order to avoid over
i 1
sizing the converter. Considering symmetrical duty cycle and unity power factor (resonant
conditions), the rms current can be estimated as:
iSm , rms ,max  Po ,max
2 Vo ,rms .
(4)
3.3 Snubber network
The snubber network is intended to reduce the converter switching losses and therefore to
increase the converter efficiency. Considering that the specific switches have no switching
losses, and the common switches operate with zero voltage switching (ZVS) during the turn on,
a capacitive snubber network (Cs) is selected to reduce the switching losses that occur during the
common switches (Smh, Sml) switch-off transition. The maximum capacitance value is given by
the ZVS condition, which can be calculated as:
Cs,max 
2td iswoff
vmains
.
(5)
min
where td is the dead time associated to that transistor and isw-off is the switch-off current. As a
consequence, Cs is selected within this range order to optimize the efficiency and the power
control region with the ZVS condition (O Lucía et al. 2009).
3.4 Control scheme
Control signals are generated using an FPGA-based control platform. The digital control block
was described using VHDL. This block is based on a multi-phase Digital Pulse Width
Modulator (DPWM) to control the common and specific switching devices. Besides, a mainsvoltage feedback circuit provides the information needed to change the control signals
according to the sign of the mains voltage (nMCS signal). Fig. 5 shows the control block used to
generate the CMCB control signals.
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A New Multiple-Output Resonant Matrix Converter Topology
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Fig. 5. Digital block to generate the control signals for the CMCB.
4.
Experimental Results
A multiple-output resonant matrix converter was designed and implemented featuring 500-W
output power per load, and switching frequency range between 30 and 150 kHz. The selected
switching devices are IGBTs with antiparallel diode FAIRCHILD HGTG20N60. The resonant
tanks are made up by 8-cm 48-turns coils and 44-nF resonant capacitors. Two 3.3-nF snubber
capacitors have also been added in parallel with the common switches Smh, Sml.
The series resonant matrix converter prototype is shown in Fig. 6. Fig. 6 (a) shows a detailed
view of the CMCB prototype, and Fig. 6 (b) shows the complete test bench for the 4-load series
resonant matrix converter.
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A New Multiple-Output Resonant Matrix Converter Topology
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(a)
(b)
Fig. 6. Experimental 4-load induction heating test-bench: (a) Common Matrix Converter Block (CMCB),
and (b) multiple induction heating load experiment.
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Applied To Domestic Induction Heating
(a)
(b)
Fig. 7. Multiple-output resonant matrix converter prototype: (a) main control signals and waveforms (from
top to bottom: cmh+, cml+, cmh-, cml-, nMCS, 40 V/div, vmains, 400 V/div, io, 8 A/div, and vo, 400 V/div), and (b)
control signals transition (from top to bottom: cmh+, cml+, cmh-, cml-, nMCS, 40 V/div).
Fig. 7 shows the main waveforms for the proposed converter. Fig. 7 (a) shows the control
signals, mains voltage and voltage-sign signal, the output current, and the output voltage. This
figure shows the proper converter operation during both, the positive and the negative mains
cycle. In addition, a detailed view of the control signals transition is shown in Fig. 7 (b).
Finally, Fig. 8 shows the converter operation with different operational conditions for a load
with Req,i = 14 Ω, Leq,i = 125 µH, and Cr,i = 44 nF. On one hand, Fig. 8 (a) shows the converter
operation near the resonant frequency with fs,hb = 75 kHz and Po,i = 500W, where a sinusoidal
output current can be seen. On the other hand, Fig. 8 (b) shows the converter operation with a
higher switching frequency fs,hb = 100 kHz in order to reduce the output power to Po,i = 100 W.
For this condition, a higher harmonic content can be observed in the output current.
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(a)
(b)
Fig. 8. Main control signals and waveforms for the multiple-output resonant matrix converter: (a) fs,hb = 75
kHz and Po,i = 500W, and (b) ) fs,hb = 100 kHz and Po,i = 100W. From top to bottom: : cmh+ (40 V/div), cml+ (40
V/div), cmh- (40 V/div), cml- (40 V/div), io (10 A/div), and vo (100 V/div); time 10 µs/div.
5.
Conclusions
Direct ac-ac conversion has proven to be a convenient technique which can be extended to
the ubiquitous dc-link inverters present in most household appliances. It combines higher power
density with a reduced number of conversion stages and energy-storage elements. However, the
higher number of switching devices and complex control scheme has prevented it from being
widely used.
In this paper, a multiple-output resonant matrix converter has been proposed. It combines the
benefits of matrix converters, with the improved control and cost reduction associated to this
multiple output stage. The feasibility of this proposal has been tested by means of a 4-load
prototype. As a conclusion, the multiple-output resonant matrix converter is proposed as a costeffective and high-power density converter for multiple-load systems.
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5 Acknowledgments
This research was supported by the I3A Fellowship Program and the Spanish MICINN under
Project TEC2010-19207 and Project CSD2009-00046, by DGA under Project PI065/09, and by
Bosch and Siemens Home Appliances Group.
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