Surge Voltage Suppression Methods for
Three-phase to Single-phase Matrix Converter
Yoshiyuki Kadoshima

Kazuhiro Koiwa

Jun-ichi Itoh

Dep. of Electrical Engineering
Nagaoka University of Technology
Nagaoka, Niigata, Japanykadoshima@stn.nagaokaut.ac.jp

Dep. of Electrical Engineering
Nagaoka University of Technology
Nagaoka, Niigata, Japan
newkoiwa@stn.nagaokaut.ac.jp

Dep. of Electrical Engineering
Nagaoka University of Technology
Nagaoka, Niigata, Japan
itoh@vos.nagaokaut.ac.jp

Francois Anne

Antoine Gerlaud

Junya Sasaki

Dep. of R&D and design engineer
MERSEN St Sylvain d’Anjou France
St Sylvain, d’Anjou, France
Francois.ANNE@mersen.com

Dep. of electrical protection
MERSEN St Sylvain d’Anjou France
St Sylvain, d’Anjou, France
antoine.gerlaud@mersen.com

Managing director
MERSEN Japan K.K.
Shinjuku, Tokyo, Japanjunya.sasaki@mersen.com

Abstract—This paper discusses surge voltage suppression
methods in order to design a large capacity three-phase to singlephase matrix converter which is used in AC-DC converters. In
order to reduce the surge voltage, the design criteria based on theflow chart of a laminated bus bar (LBB) for the three-phase to
single-phase matrix converter is clarified to achieve the lowest
stray inductance. As a result, the maximum stray inductance of
the LBB for 200-V, 50-kW is achieved to 59 nH in simulation and58.3 nH in experiment. Besides, when the surge voltage exceeds
the tolerance, a snubber capacitor is used in order to limit thesurge voltage. In this paper, the design method of the snubber
capacitor is also proposed. Concretely, the relationship amongsnubber capacitance, surge voltage and turn-on loss is derived.
As the result, it is confirmed that the surge voltage becomes 231
V when the output current is 310 A by experiment. Thus, thedesign method of snubber capacitor to suppress the surge voltage
is validated.
Keywords—three-phase to single-phase matrix converter; surge
voltage suppression; laminated bus bar; simple AC snubber

I.

INTRODUCTION

Three-phase AC-DC converters have been applied in many
applications such as telecommunication power system, DC
power transmission and quick battery charger for electricvehicle [1-2]. In the three-phase AC-DC converter, an isolatedtransformer is required in terms of protection and noise
elimination. However, the commercial frequency isolatedtransformer is bulky. In order to solve this problem, a system,
which is composed of a PWM rectifier, a PWM inverter and ahigh frequency transformer, has been discussed [3]. In thissystem, small transformer is used owing to the increase of thefrequency. However, large boost up inductors and anelectrolytic capacitor are required.
On the other hand, an AC-DC converter using a threephase to single-phase matrix converter has been attracted [4-5].
The advantages of matrix converters are as follows: highefficiency, small size and long life-time owing to the absenceof boost up inductors and an electrolytic capacitor [6].
However, in comparison with the conventional AC-DC
converter, the current loops of the three-phase to single phasematrix converter become longer. This is because the bidirectional switching device, which is unavailable in module,
is used with two switching devices. Thus, the surge voltage
becomes larger when the three-phase to single-phase matrix
converter is applied for large capacity application. In otherwords, large snubber and protection circuit are required inorder to suppress the surge voltage which is dominated by thestray inductance. Therefore, in order to achieve highefficiency and reduced size, it is necessary to decrease thestray inductance of current loops or use the snubber circuit tosuppress the surge voltage. For this reason, LBBs, which have
low stray inductance owing to the laminated structure of
conductors and isolators, has been applied in an inverter [710]. However, the LBBs for a matrix converter cannot beeasily designed in the same way as an inverter because of bidirectional switching devices. On the other hand, generalsnubber circuit for matrix converters, which is composed by
the diode rectifier, clamped capacitor and discharge resistor,
becomes complication structure compared to the inverter due
to use of the AC snubber.
In this paper, a design method of LBBs for the three-phaseto single-phase matrix converter, which have low strayinductance, is revealed. The design point of LBB for matrix
converters is differ to that of the conventional PWM rectifiers
and inverters because of the current type converter in the view
from input side. In addition, the simple AC snubber circuit,which connects a capacitor with a switching device in parallel,
is proposed. This technology becomes important when thesurge voltage suppression is needed in order to achieve highpower output of several hundred-kW direct AC-AC converters.
This paper is organized as follows. First, a LBB is designed tofocus on layout of filter capacitor and switching device on
current loops which affect surge voltages. Then, in order toevaluate the operation of the LBB, stray inductances andInput LC filter

Cs
Ssn'

+

Rp

C

Stn'

San

In order to reduce the size of the snubber and protection
circuit, a surge voltage suppression method is discussed in thissection. First, the surge voltage Vs occurs when the energy,
which is stored in stray inductor ls, transfers to a parasitic
capacitance of switching device CCE. Thus, the surge voltage
Vs is expressed asls
I off 
CCE

Sbn

Cp

Fig. 1. Configuration of the conventional AC-DC converter
Srp

Ssp

Stp

Cs

SURGE VOLTAGE SUPPRESSION METHODS

Vs 

Sbp

Rs

Fig. 2 shows the circuit configuration of the AC-DC
converter with a three-phase to single-phase matrix converter.
The three-phase to single-phase matrix converter can convert
three-phase AC into high frequency AC of several-ten-kHz
directly. In addition, the three-phase to single-phase matrix
converter does not need large passive components such as
boost up inductors and an electrolytic capacitor. As a result, theadvantages of this system are as follows: (i) high efficiency
owing to directly conversion AC into AC, (ii) small size andlong life-time owing to absence of an electrolytic capacitor andboost-up inductors. Thus, it is expected that the three-phase to
single-phase matrix converter is applied in large capacity
applications. In order to apply the three-phase to single-phasematrix converter for large capacity application, it is necessary
to suppress a surge voltage with a snubber circuit. However,the conventional snubber circuit, which is composed by acapacitor and a resistor, for each bi-directional switching
device leads to increase the loss of the snubber.



Srn'

Sap

Stp'

CIRCUIT TOPOLOGY

Fig. 1 shows the circuit configuration of the conventional
AC-DC converter. The three-phase AC-AC converter iscomposed of an input LC filter, boost-up inductors, a PWM
rectifier, an electrolytic capacitor and a PWM inverter. The
features of the conventional system are as follows: (i) large
converter loss owing to many conversion times, (ii) large sizeand short life-time owing to the electrolytic capacitor and theboost-up inductors, however (iii) the simple snubber circuit for
reducing the surge voltage.

III.

L

Ssp'



where, the turn-off current Ioff is constant. According to (1), in
order to suppress the surge voltage, it is necessary to decrease
the stray inductance ls or increase the capacitance CCE. Thus,
this paper discusses two methods in details.

vi
ii

vo
io

Lf

vl
il

Load

II.

Srp'

Load

temperature of the LBB are simulated. Second, the snubber
circuit, which is composed by a capacitor for a bi-directional
IGBT, is evaluated. In particular, the relationship among thesnubber capacitance, surge voltage and turn-on loss istheoretically calculated. Next, the validity of the theoreticalformulas is validated by switching test. Third, the validity ofdesign of the LBB is confirmed by comparing the experimental
result and the simulation results. Finally, the surge voltage ismeasured by adopting the designed LBB and the designed
snubber capacitor. Based on these results, the design method of
LBB and snubber circuit is confirmed.

Srn

Ssn

Stn

Cp Rp
Cf

Fig. 2. Configuration of the AC-DC converter with the three-phase to
single-phase matrix converter

Fig. 3 shows the flow chart to design the three-phase to
single-phase matrix converter for suppression of the surge
voltage. First, all components are selected by specification ofsystem in order to design LBBs. Additionally, the voltage andcurrent at worst case are calculated in order to design the surge
voltage. Next, the LBB, which has low stray inductance, isdesigned for the three-phase to single-phase matrix converter.
Then, temperature TLBB of the designed LBB is calculated bysimulation [11]. If the maximum temperature TLBB is higher
than the allowable temperature of the components Tc which areconnected with the LBB, it is necessary to modify the design of
the LBB. Second, stray inductances ls of the designed LBB iscalculated by simulation [11]. Then, the maximum allowableinductance ls’ is calculated by parasitic capacitance which is
obtained by switching test using the selected switching device.
It is noted that, in case of ls ≥ ls’, the design of the snubber
capacitor Cs, as shown in Fig. 2, is applied because the surge
voltage is larger than that of the design value. However, theturn-on loss increases owing to the additional snubber capacitor.
Thus, it is necessary to limit the junction temperature Tj to theallowable junction temperature Tj’ by redesigning the coolingsystem.
A. Laminated Bus Bar
In this section, the design method of a LBB for the threephase to single-phase matrix converter is discussed. In order todesign the LBB, it is important to decide the terminal positionof all components. Thus, all components are selected based on
the specification before the design of LBBs. First, the highfrequency transformer is designed the specification which theexcitation current is 20% of the rated output current. Second,the cut-off frequency of input LC filter is designed to assure
the input ripple current is less than 5% of the rated input
current. At first, the input filter capacitance Cf is designed byassuming that the input ripple voltage is 10% of the rated input
voltage. Next, the input filter inductance Lf is designed fromthe cut-off frequency and the filter capacitance Cf. Third, theclamped capacitance Cp of the protection circuit is designed
based on the surge voltage which is generated by excitationinductance of high frequency transformer. Moreover, thedischarge resistance Rp is calculated by the loss of protection
circuit. Furthermore, the snubber diode is selected based on
the current squared times at the worst case. It is noted that theamplitude and conduction time of the diode current at theworst case are confirmed by simulation. Next, the switching
device is selected based on the maximum switching voltage
and current at the worst case. Finally, the loss is analyzed bysimulation using loss characteristic of the switching device[12]. Based on the loss analysis result, the cooling system isdesigned by thermal analysis for heat-sink. Table I lists the
specification of the system and Table II lists the selectedcomponents for the system.
The design of LBBs for matrix converters is explained. In
Fig. 1, LBBs for the PWM rectifier and the PWM inverter aredesigned to make the loop area, which is composed by the DC
link capacitor and the upper and lower arm (Srp', Srn'), become
small. On the other hand, in Fig. 2, energy, which is stored instray inductor in input layers, transfers to parasitic capacitor ofswitching device owing to resonant circuit which composedby the stray inductor, the input filter capacitor and the parasitic
capacitor of the upper or lower arm (Srp, Ssp, Stp). Therefore,
LBBs for the three-phase to single-phase matrix converter aredesigned to make six loop areas, in which two bi-directional
IGBTs in upper or lower arm are in pair with each input filter
capacitor, become small.
Fig. 4 shows the configuration of two designed LBBs forthe three-phase to single-phase matrix converter and current
loop at the maximum stray inductance. It is noted that thedifference between Fig. 4(a) and (b) is the direction of theswitching devices. In Fig. 4(a), the switching device isarranged by assuming that the distance among each terminalsof switching device becomes short. On the other hand, in Fig.
4(b), the distance between each terminals of switching device
becomes longer than that of Fig. 4(a). This is because theswitching devices rotate 90 degrees for an angle of switching
device in Fig. 4(a) in order to improve performance of coolingsystem. As a result, the maximum stray inductance in Fig. 4(a)and Fig. 4(b) is calculated to 59 nH and 65 nH by simulation,
respectively. Thus, the configuration of the LBB in Fig. 4(a) is
adopted because the maximum stray inductance of Fig. 4(a) islower than Fig. 4(b).
Fig. 5 shows the thermal simulation result of the LBB of
Fig. 4(a). The current in simulation condition is the rated
current of three-phase to single-phase matrix converter i.e. thecurrent of the input layers is 50 Hz and 144 A, and the currentof the output layers is 10 kHz and 202 A. Thus, the current
density of the output layers is higher than the input layers. As
a result, the temperature of the output layer trends to be higher
than the input layer. Additionally, the maximum temperatureof the LBB TLBB is 54 °C when ambient temperature is theworst case 40 °C because terminal for switching device isnarrow. Therefore, the maximum temperature 54 °C is lower
than the allowable temperature of all components 85 °C is
confirmed.

Start
Input of parameters
Design of a high frequency transformer
Design of an input filter
Design of a protection circuit
Selection of a switching device
Design of a cooling system
by loss analysis
Design of a laminated bus bars
Simulation of the temperature TLBBNTLBB ≤ Tc
Y
Simulation of the stray inductance ls
Switching test of switching device
Calculation of
the allowable stray inductance ls’Nls ≤ ls’Y
Design of a snubber
Loss analysisN
Tj ≤ Tj’
Y
Redesign of thecooling system

End

Fig. 3. Flow chart to design the three-phase to single-phase matrix
converter for suppression of the surge voltage

TABLE I. SPECIFICATION OF THE SYSTEM
Item
voltagefrequency
Input
power factor
current THD
ripple voltage
voltageLoadoutput power
Switching frequency
temperature
Ambient
altitude

SymbolValu
200V(±10%)Vi50 or 60Hz
fi
cosφ
≥0.95
≤ 5%
THDi
28.2V
Vr
500V
Vl
50kW
Pl
10kHz
fs
-10~40°C
Ta≥1000mAa

TABLE II. SELECTED COMPONENTS FOR THE SYSTEM
Part

SymbolCalculated
value

IGBT

S(rst/pn)-

Heat sink

-

-

Fan

-

-

Cf

160μF

Lf

10μH

-

-

Cp

2.2μF

Rp1
Rp2

47kΩ
10kΩ

Input filter
capacitor
Input filter
reactorProtection
diode
Protection
capacitor
Protection
resistermodel number of device
MITSUBISHI“CM400C1Y-24S”
MERSEN“MF250T13A80AF32D”
SUNON“PMD1204PPB1-A”
Cornell-Dubilier“944U161K801ABM”

Maximum
ration1200V
350A
26.5cfm
230V
160μFac

STS induktivitaeten
10μH
350A
IXYS
1200V
28A
”DSEI2X30-12B”
EPCOS
850V
2.2μFdc“B32656S8225J561”
47kΩ
10W
TE Connectivity “YP1047KJ” 825V
1900V
10kΩ
100W
Arcol “HS100 10K J”

B. Simple AC Snubber Circuit
In order to limit the surge voltage to the design value, thesimple AC snubber circuit, which connects a capacitor inparallel, is adopted when the maximum stray inductance bysimulation is larger than the allowable stray inductance.
However, the snubber capacitor Cs increases the turn-on loss
Eon because a short current flows at turn-on by the snubber
capacitor. Accordingly, the switching device is broken owing
to large current. Therefore, in terms of the surge voltage andthe switching loss, it is important to design Cs. In addition, an
adjustment of gate resistance also suppresses the surge voltage.
However, adjustment of dv/dt is limited by gate resistance inrecent IGBTs. Additionally, the surge voltage suppression bygate resistance leads to increase the both turn-on loss and turnoff loss. Owing to this, an adjustment of gate resistance for the
suppression of surge voltage is not considered.

T

D

S

C

B

R

Vs 

2ls
CCE
I off Vs 0 
CCE  Cs
CCE  Cs



Eon 

1
CCE  Cs Von 2  CCE  Cs Eon0 
2
CCE

10

5

8

3

9
12

7

P
N

11

(a) Design 1 of LBB
T
S

D

R

B

C

F

A

1
2

4

E

3

5
6

8
7

9

10

12

P

11

N

(b) Design 2 of LBB

R
S
T

where, Ioff is the current at turn-off, Vs0 is the surge voltage
without snubber capacitor. It is noted that CCE is previously
measured by switching tests. According to (2), surge voltage
Vs can be suppressed by increasing Cs. On the other hand,energy, which is stored in a capacitor, transfers Eon. Thus, Eon
is expressed as



6

1

4

E

Fig. 6 shows the test circuit for evaluating the snubber
capacitor. It composes the buck chopper. It is noted that theupper switching device Sp is always on-state. On the other
hand, the lower switching device Sn is switched. The surge
voltage Vs and turn-on loss Eon are evaluated from themeasured voltage and current of the lower switching device Sn,
and the relationship between each Cs. Thus, Vs is expressed as



2

A

F

C

B
Cfrs

5

9

Srp

Ssp

Stp

2

6

10

3

7

11

Srn

Ssn

Stn

4

8

12

P

Cfst

A

D
F

1

Cftr

E

N

(c) Maximum inductance loop
Fig. 4. LBB for the matrix converter
TLBB(Δ T)[°C]

58(18)
56(16)

where, Von is the voltage at turn-on, Eon0 is the turn-on loss
when the snubber capacitor is not connected.
Fig. 7(a) shows the switching waveform at turn-off when
the snubber capacitor Cs is not connected. The surge voltage
Vs0 is 96 V when the turn-off current Ioff is 11 A. In Fig. 7(b),the surge voltage Vs is reduced to 26 V because the snubber
capacitor Cs of 50 nF for the parasitic capacitor CCE of 4.21nF
is connected.
Fig. 8(a) and (b) show the switching waveform at turn-on.
In Fig. 8(a), the turn-on current Ion0 is 18.8 A when thesnubber capacitor is not connected. In Fig.7(b), the turn-on
current Ion is increase to 74.8 A because of the short current
owing to the snubber capacitor Cs of 50 nF for the parasitic
capacitor CCE of 4.21 nF.
Fig. 9 shows the surge voltage and turn-on loss
characteristics based on Cs and CCE by the experiment. It isnoted that the sum of CCE and Cs was normalized by CCE. In
addition, Vs and Eon are normalized by switching voltage

54(14)
52(12)
50(10)
48(8)Fig. 5. Temperature TLBB of the Fig .4(a) LBB
The ambient temperature is 40 °C.
Ll=1.2mH

Sp
Vg=-15V

Cs

Vdc=200V
Vg=±15V
d =50%
fs=10kHzls

Rg=24Ω

Sn

v
i

Cs

Rl=10ΩIGBT
Fuji Electric Co.
“2MBI150U2A-060”
Maximum voltage : VCE=600V
Maximum current : IC=150A
Parasitic capacitance : CCE=4.21nF

Fig.6. Test circuit for evaluating the snubber circuit

Von(off), current Ion(off) and Vs0 or Eon0. As the result, theexperimental results are almost agreed with the theoreticalvalue. However, the experimental results of Vs and Eon are

96V

Voltage 40[V/div]

11A

18.8A

Current 15[A/div]0
Current 2[A/div]

Voltage 40[V/div]

400[ns/div]

400[ns/div]0(a) Without snubber capacitor

26V(a) Without snubber capacitor

Voltage 40[V/div]
Current 15[A/div]
74.8A

11A
0
Voltage40[V/div]

Current 2[A/div]0400[ns/div]

400[ns/div](b) With Cs of 50 nF for CCE of 4.21nF
Fig. 7. Switching waveform at turn-off(b) With Cs of 50 nF for CCE of 4.21nF
Fig. 8. Switching waveform at turn-on

VSurge voltage V I s V [p.u.]
off off s0

IV.

1.4

EXPERIMENTAL RESULTS

A. Evaluation of the Laminated Bus Bar
In this section, the stray inductance and temperature rise of
the LBB, which is shown in Fig. 4(a), is evaluated byexperiment. First, the stray inductance is measured byswitching tests with the LBB.
Fig. 10 shows an example of the test circuit for measuring
the stray inductance of the designed LBB. It is noted that thecircuit model considers parasitic capacitor and strayinductance. It composes the buck chopper. Additionally, theupper switching device Sp is always on-state, and the lower
switching device Sn is switched in the same way as theexperiment of evaluating the snubber capacitor. The surge
voltage Vs and the turn-off current Ioff are measured. Then, thestray inductance on the current loop l is derived by (4).
2

2C f CCE  Vs  lC f  2CCE  I off 



14

1.2

Surge voltage(Experiment)
Surge voltage(Calculation)

1.0
0.8
0.6

12

Turn on loss
(Calculation)
Turn on loss
(Experiment)

10
8
6

0.4

4

0.2

2

0.0

E
Turn on loss V I onE [p.u.]
on on on0

lower a little than the theoretical value. This is because allenergy, which is stored in stray inductor, is not transferred into
the capacitor of the switching device owing to theinterconnection resistance and the switching loss. Therefore,
the required snubber capacitance to suppress the surge voltage
at the worst case is designed by (2).

0
0

2

4
6
Capacitance

8
10
CCE+Cs [p.u.]
CCE

12

14

Fig. 9. Surge voltage and turn-on loss characteristics based on capacitanceby experiment

where, the stray inductance on the current loop l is sum of thestray inductance of the LBB ls and the equivalent series
inductance (ESL)of the input filter capacitor lC and the IGBTlIGBT. Therefore, the stray inductance of the LBB ls is derivedby (5).
ls  l  lC  l IGBT  Fig. 11 shows the stray inductance comparison between
the simulation and experiment. As the results, it is confirmedthat the stray inductance is minimum value when the distance
between each input layer and the distance of switching devices
Srn and Ssn from the filter capacitor Cfrs are minimum.
Moreover, the stray inductance error between the simulation

R

B. Evaluation of the Simple AC Snubber Circuit
The snubber capacitor is designed based on the measured
maximum stray inductance by experiment. Furthermore, thesuppression effect of the surge voltage is evaluated using thesnubber capacitor by assuming the current at the worst case. It
is assumed that the maximum surge voltage is 60% of theworst case voltage of switching device or less. In this paper,
the capacitor of 50 nF is connected. In addition, the designed
value of the surge voltage is 359 V at the worst case.
Fig. 14 shows the switching waveforms at turn-off on theeach loop. From Fig. 14(a), (b) and (c), it is confirmed that thesurge voltage on the loop V, which is shown by Fig. 11, is thelargest when the turn-off current is same value. This is because
the stray inductance of the LBB on loop V is the largest in allloops. Accordingly, the surge voltage becomes 231 V when the
output current is 310 A on the loop V. The measured value issmaller than the designed value. This is because all energy,
which is stored in stray inductor, is not transferred into thecapacitor of the switching device owing to the interconnection
resistance and the switching loss. Thus, the surge voltage islower than design value. Therefore, the design method ofsnubber capacitor to suppress the surge voltage can bevalidated.

Rg

Srp

N

CCE=114nF

off

A

Lo=0.55mH

lIGBT=4.64nH

Cfrs=160μF
lC=29.6nH

Rg

Vg=-15V

B

4

1
P
5
off

Vg=±15V
d =50%
fs=10kHz

Rg

Ssp

CCE

SW

v

lIGBT
ls

IGBT
MISTUBISHI“CM400C1Y-24S”

i

S

6

Fig. 10. An example of the test circuit for measuring the stray inductance ofthe designed LBB
70: Simulation

60

: 25A

: 50A

: 75A

Stray inductance ls [nH]Fig. 13 shows the analysis result of the temperature of the
LBB by the experiment. As the result, the temperature of the
LBB agrees with the simulation result. However, thetemperature of the LBB around terminal in experiment is alittle higher than the simulation result. This is because theinterconnection, screw and fuse become the heat sources. On
the other hand, the temperature of the LBB except terminal inexperiment is a little lower than the simulation result. This isbecause the ambient wind velocity is ideally 0 m/s and theconvection by generation of heat is not considered insimulation.

on

Vg=-15V

Vdc=282V

3

Rg=4.9Ω

Vg=15V

Next, the validity of the temperature rise simulation of
LBB is revealed by experiment.
Fig. 12 shows the test circuit for analysis of temperaturerise of the LBB. It is noted that the diode was used instead of
the switching device. In addition, the current is adjusted byusing slid regulator assuming that the root mean squared valueof current is the current which the three-phase to single phasematrix converter operates at rated condition.

2

50
40
30
20
10
0

Srp(1-2)
Srn(3-4)
Ssp(5-6)
Ssn(7-8)
Cfrs(A-B)
I
II

Ssp(5-6)
Ssn(7-8)
Stp(9-10)
Stn(11-12)
Cfst(C-D)
III
IV

Stp(9-10)
Stn(11-12)
Srp(1-2)
Srn(3-4)
Cftr(E-F)
V
VI

Fig. 11. Stray inductance comparison between the simulation andexperiment
I to VI are number of the current loop which affect surge voltages.

Slideregulator

Fuse

Buck
transformer

CT

R
S
T

3-phase
144 A
50 Hz

P

1

5

9

2

6

10

3

7

11

4

8

12

CT

N

Fig.12. Test circuit analyzing temperature rise

47
44
13.1
11.5

10.8

41

16.8
15.4

10.9

CONCLUSIONS AND FUTURE WORKS

This paper proposed the methods of the surge voltage
suppression in order to design a large capacity three-phase to38
35: Temperature rise [ºC]

V.

195 A
DC

Fig. 13. Experimental result of temperature rise of the LBB
The ambient temperature is 26 °C.

32

Temperature [ºC]and experiment is 4.8%. This error is because all energy,
which is stored in stray inductor, is not transferred into theparasitic capacitor of the switching device owing to theinterconnection resistance and the turn-off loss and the valuesof the parasitic capacitors are not constant. It is noted that themeasured surge voltage is dominated by the stray inductanceof the LBB and an ESL of the filter capacitor and the IGBT
module on the current loop. For this reason, in order tosuppress the surge voltage, the switching device and capacitor,
which have low ESL, should be selected.

single-phase matrix converter which is used in AC-DC
converters. In order to suppress the surge voltage, it isnecessary to reduce the stray inductance. Thus, the LBB, inwhich layout of components and laminating layer isconsidered by assuming that current loop to affect surge
voltage, was designed. As the result, it was confirmed that the
maximum stray inductance was 59 nH in simulation and 58.3
nH in experiment.. On the other hand, the surge voltage can be
reduced by adopting the snubber circuit which connects a
capacitor for a switching device. Thus, the snubber capacitor
was designed and evaluated by experiment. As the result, therelationship among Cs, Vs and Eon was revealed. Thus, it was
confirmed that the snubber capacitor can be designed by ontime switching test in which parasitic capacitance of switching
device is measured. Finally, the surge voltage can besuppressed to design value or less by adopting the designed
LBB and snubber capacitor. Based on these results, the threephase to single-phase matrix converter can be applied for 50kW system.

Surge voltage
228 V

Voltage 70[V/div]

Turn-off current
313 A
Current
040[A/div]

800[ns/div](c) Loop I which is composed of Srp, Ssp and Cfrs
Surge voltage
228 V

Voltage 70[V/div]

In future work, the stray inductance and temperature rise of
the LBB and surge voltage will be evaluated when the threephase to single-phase matrix converter is operated at rated
power.
Turn-off current
311 A

ACKNOWLEDGMENT

Current

This study was supported by Mersen. Mr. Anne Francois
was given me advices of design of LBBs. In addition, Mr.
Gerlaud Antoine supported the inductance and thermal
simulation of the LBB.

040[A/div]

800[ns/div](b) Loop III which is composed of Ssp, Stp and Cfst
Surge voltage
231 V

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[2]

[3]

[4]

[5]

[6]

[7]

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Voltage 70[V/div]

Turn-off current
310 A
Current
040[A/div]

800[ns/div](c) Loop V which is composed of Stp, Srp and Cftr
Fig. 14. Switching waveform at turn-off[8]

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