Control Method for a Three-Port Interface
Converter Using an Indirect Matrix Converterwith an Active Snubber Circuit
Koji Kato*, Jun-ichi Itoh**Nagaoka University of Technology, Nagaoka City Niigata, Japan, e-mail: itoh@vos.nagaokaut.ac.jp

Abstract— This paper proposes a novel control method for
an interface converter using an indirect matrix converterwith three power supplies, which consist of two AC and one
DC supplies. An active snubber circuit in the indirect matrix
converter is used as an interface with the DC power supply.
The proposed control method is based on the indirectcontrol method with a triangular carrier wave [10].
Therefore the proposed method can be easily applied to a
DC/DC converter. In addition, this paper proposes reducing
the number of switching during one carrier period for the
inverter stage converter. In the proposed method, theinverter stage carrier is controlled asymmetry to reduce theswitching times in the inverter stage. To apply the proposed
method, the switching loss of the inverter stage can be
decreased to 2/3 times in comparison with a conventional
method. The validity of the proposed method is confirmedby simulation and experimental results.
Keywords—Matrix converter, Converter control, Powerfactor correction, Energy converters for HEV.

I. INTRODUCTION
Recently, renewable energies and hybrid electricvehicle (HEV) systems are receiving significant interest,with consideration of global warming and environmental
problems. There are two types of power sources forrenewable energies; AC power sources such as wind
power generator, and DC power sources such aphotovoltaic cells, batteries, and fuel cells. Therefore, toimplement these applications, interface power converters
have been intensely studied. A conventional power
converter system, which consists of a pulse widthmodulation (PWM) rectifier, a DC/DC converter and an
inverter, requires a large energy buffer, such as anelectrolytic capacitor. However, the electrolytic capacitor
in a conventional system has disadvantages such as large
size, short-life time and high costs.
On the other hand, there is an AC/AC direct converterwith a DC link, which is referred to as an “indirect matrix
converter” [1-5]. The indirect matrix converter iscomposed by the current source rectifier and voltage
source inverter without energy buffer in DC link part. The
utilization of an indirect matrix converter, which has nolarge energy buffer such as an electrolytic capacitor, canbring advantages such as size reduction, long-life time andcost reduction. We have already proposed an interface
converter using an indirect matrix converter [6]. The
proposed interface converter connects a DC/DC converter
to DC link of the indirect matrix converter. With regard to
the voltage relationship between the battery and the DC

link, the proposed circuit works as a boost up converter
for the battery. However, the proposed converter has thesame problem due to an indirect matrix converter. That is,the voltage transfer ratio of indirect matrix converters,
which defines the ratio between the output and input
voltage, is well known as being constrained to 0.866.
Improvement of the voltage transfer ratio for indirect
matrix converters has been widely discussed [7,8].
However, it seems that the proposed methods increase thenumber of components, due to the insertion of voltage
transfer ratio compensator, which consists of an H-bridge
inverter and a capacitor, to the DC link of the indirect
matrix converter.
Meanwhile, a snubber circuit is required in order toprotect the indirect matrix converter from over-voltage
and over-current. In Ref. [9], a snubber circuit was used inorder to compensate the imbalance in the supply voltage.
However there was no discussion of the DC power supply
interface using a snubber circuit.
This paper proposes a novel control method for multipower supply interface system using an indirect matrix
converter with a step-down chopper. The proposed
converter is constructed based on an indirect matrix
converter that does not have a large energy buffer, such as
an electrolytic capacitor. The active snubber circuit of theindirect matrix converter is used as a step-down chopper
for a DC power supply. In addition, the voltage transfer
ratio can be improved by the DC power supply. An
indirect control method with a triangular carrier wave [10]is expanded into the proposed control method. In the
proposed control system, a DC/DC converter can be easily
added to the indirect matrix converter.
In addition, this paper also proposes a control method
reducing the number of switching for the inverter stage
converter. In the proposed converter which is composedby a current source rectifier, a voltage source inverter anda step-down chopper, the switching frequency of theinverter stage increases in comparison with rectifier stage.
Because the zero current switching operation of therectifier stage can be achieved when the inverter output
zero voltage vectors, which are generated by every upperor lower peak of the inverter carrier. Therefore, in the
proposed method, the switching frequency is reduced byusing a transformed asymmetry inverter carrier in order tocontrol the zero voltage vector timing.
The basic operation of the proposed method is
confirmed by the simulation and experimental results; thetotal harmonic distortion (THD) of the input, output anddc output currents are 7.4%, 4.8%, 1.9%, respectively, andthe input power factor is 99% and efficiency is 93.8%. In

596
c 2008 IEEE
978-1-4244-1742-1/08/$25.00 addition, bidirectional energy flow characteristic among
the power supplies in this circuit is confirmed.
II. CIRCUIT TOPOLOGY
Figure1 shows AC and DC power supply interface
systems. A conventional interface system consists of a
PWM rectifier, a DC/DC converter and an inverter, as
shown in Fig. 1(a). This system requires a large
electrolytic capacitor in DC link part in order to smooth
DC link voltage. This system is very flexible in term ofvoltage condition among the AC input AC output side andDC power source because of using voltage typeconverters. However, the problem for an electrolytic
capacitor in DC link part is large volume, short lifetime inhigh temperature and high cost.
Figure 1(b) shows the proposed AC and DC power(a) Conventional system.

(b) Proposed system.
Fig. 1. Block diagrams of AC and DC power supply interface
system.

㪚㫌㫉㫉㪼㫅㫋㩷㫊㫆㫌㫉㪺㪼㩷 㪛㪚㪆㪛㪚㫉㪼㪺㫋㫀㪽㫀㪼㫉㪺㫆㫅㫍㪼㫉㫋㪼㫉
Srp

Ssp

Stp

Sbp

Sup

Svp

Swp
U
V
W

vbatt
㪛㪺㩷㫇㫆㫎㪼㫉㩷㫊㫌㫇㫇㫃㫐

Sun

Stn
Bp

(a) Sbp is turned off㪭㫆㫃㫋㪸㪾㪼㩷㫊㫆㫌㫉㪺㪼㩷㫀㫅㫍㪼㫉㫋㪼㫉RS
T

Srn Ssn

supply direct interface converters for the energy
management system. The proposed interface converter isconstructed based on an indirect matrix converter withouta large energy buffer such as an electrolytic capacitor. The
DC/DC converter connects to DC link of the indirect
matrix converter.
Figure 2 shows the specific main circuit of the proposedinterface converter. The DC/DC converter is built as anactive snubber circuit in the indirect matrix converter. An
IGBT is connected anti-parallel to the snubber circuit
diode. This snubber circuit with the IGBT is used as a
step-down chopper of the DC power supply. In this case,
the DC power supply voltage of the snubber circuit ishigher than the peak of the AC input line voltage, becausea rush current occurs between the AC and the DC input
power supplies when the peak of the AC input line voltage
is higher than the DC power supply voltage. Therefore,
this converter is referred to as a “step-down type
AC/DC/AC direct converter”.
Figure 3 shows the equivalent circuits of the proposed
converter. The rectifier stage converter is similar to a fourphase current source rectifier including the DC/DC
converter. Thus, the switches in the three-phase PWM
rectifier and DC/DC converter must be separately turnedon in order to avoid a short circuit of the AC and DC
power supplies. When the DC/DC converter switch Sbp isturned off, the proposed converter operates as aconventional indirect matrix converter. In this case, theDC/DC converter becomes a conventional snubber circuit,as shown in Fig. 3(a). On the other hand, the proposed
converter operates as a conventional inverter when the
DC/DC converter switch Sbp is turned on, when all
switches in the rectifier are turned off. In this case, theDC/DC converter is similar to a DC power supply, as
shown in Fig. 3(b). That is, the proposed circuit operates
as an indirect matrix converter or inverter alternately. In

M

Svn Swn

Bn

Fig. 2. Proposed circuit configuration.

(b) Sbp is turned on
Fig. 3. Equivalent circuits of the proposed converter.

2008 13th International Power Electronics and Motion Control Conference (EPE-PEMC 2008)597

addition, the input power ratio between the AC and DC
power supplies and the voltage transfer ratio between the
input and the output voltage are controlled by the duty
ratio of the DC/DC converter.

result, the current command for each phase is decreasedby the working time of the DC chopper. Therefore, theinput current command irec** for one phase is converted byIII. CONTROL STRATEGY

i rec ** = irec * ⋅ (1 − i b* )The proposed control strategy, which is based on an
indirect control method with a triangular carrier wave, caneasily realize the addition of the DC/DC converter. The
conventional indirect control strategy, which uses space
vector modulation, must calculate the pulse width for eachswitch, including the DC/DC converter. In addition, it isdifficult to define the input current command vector,
because it is four-phase, consisting of the three-phase AC
power supply and the DC power supply. Therefore, thecontrol in this paper can be achieved by using an
independent command for the DC/DC converter based oncarrier comparison modulation.

(2),
where irec* is rectifier stage current command, and ib* is the
DC/DC converter input current command.
Figure 5 shows the relationship between the DC link
voltage and the DC/DC converter duty ratio for the
proposed converter. The DC link voltage is decided by theaverage value of the output voltage between the rectifier
stage and the DC/DC converter. Therefore the averagevalue of the DC link voltage Edc in the proposed circuit
can be expressed as

A. Control method for the rectifier stage and DC/DC
converter
Figure 4 shows a block diagram of the step-down type
AC/DC/AC direct converter. The rectifier stage converterin the proposed interface converter functions as a fourphase current source rectifier including the DC/DC
converter. The relation between the input voltage [vr vs vtvb’]t and the output voltage [vu vv vw]t can be expressed asª v u º ª sup« » «« vv » = « svp«¬v w »¼ « swp
¬

sun º
»ªs
svn » « rpsrn
swn »¼ ¬

s sp

stp

ssn

stn

ª vr º« »sbp º « v s »»« »0 ¼ vt« '»«¬vb »¼(1),
where the input voltage vb’ is the DC power supply
voltage vbatt based on the neutral point of the input voltage.
To avoid a short circuit of the AC and DC power supplies,
the switches in the rectifier stage converter and theDC/DC converter are not turned on at the same time. As a

Fig. 5. The relationship between the DC link voltage
and the DC/DC converter duty ratio.

Fig. 6. DC link voltage waveform.

Fig. 4. Control block diagram of step-down mode.

598

Fig. 7. Output voltage range for proposed converter.

2008 13th International Power Electronics and Motion Control Conference (EPE-PEMC 2008)

***E dc = D rec v in + D b v b(3),
where Drec** is the rectifier stage converter duty ratio
based on input current command converted by equation(2), and Db* is the DC/DC converter duty ratio, and vin is
input voltage for maximum value, and vb is DC power
supply voltage.
Figure 6 shows a comparison between the DC link
voltage of the proposed circuit and the indirect matrix
converter, where the maximum value of the indirect
matrix converter is defined as 1 [p.u.]. The DC link
voltage contains a ripple, which is constrained by the sixthorder component of the AC power supply frequency.
Therefore, the output voltage is limited to 0.866 times thatof the maximum DC link voltage. On the other hand, theproposed circuit can operate alternately between theindirect matrix converter and inverter as discussed andshown early in Fig. 3. The DC link voltage waveform of
the proposed circuit is shown in Fig. 6 when Db* is set to
0.5 and the DC power supply voltage vb is assumed to be 2
times that of the indirect matrix converter. In this case, theDC link voltage of the proposed circuit obtains 1.43 times
that of the indirect matrix converter. Thus, the proposed
circuit can improve the voltage transfer ratio from the AC
input side to the AC output side by using the DC power
supply voltage.
Figure 7 shows the DC link voltage range for the
proposed converter. In the proposed converter, the DC
power supply voltage of the snubber circuit has to keep
higher than the peak of the AC input line voltage in orderto prevent a rush current. Thus, the range of the DC link
voltage is defined from the output voltage of rectifier
stage to battery voltage, as expressed by equation (3).
Therefore, the range of the output voltage is defined fromzero volts to battery voltage as show in Fig. 7.
It should be noted that the ratio between the rectifier
duty Drec* and the DC/DC converter duty Db* is the sameas the input power ratio between the AC and DC power
supplies.
B. Basic control method of the inverter stage
Figure 8(a) shows the relation of carrier signals
between the inverter and the rectifier stages. The rectifier
stage is controlled under the condition of constant DC linkcurrent. However, the actual DC link current must be zero
when the inverter stage controller selects the zero voltage
vectors. In the proposed method, this is achieved bycontrolling the slope of the inverter carrier signal, as
shown in Fig. 6. By adopting this method, the zero current
period of the DC link is distributed to each input current
by the same ratio, as expressed by equation (4).
T r 0 T s 0 Tb 0 Tr 0 + T s 0 + T b 0
=
=
=
Tr
Ts
Tb
Tr + Ts + Tb

(4),

where Tr is turn on period in Srp, Ts is tern on period in Ssp,,
Tb is tern on period in Sbp,, Tr0 is zero current period in Tr,
Ts0 is zero current period in Ts, Tb0 is zero current period inTb.
C. Proposed switching loss reduction method forinverter stage
In the Fig. 8(a), two-phase modulation is introduced inorder to reduce the switching loss in the inverter stage
besides the zero current period distribution. However, the(a) Conventional method(b) Proposed method
Fig.8. Relation between inverter carrier and rectifier pulse.

number of switching of the inverter stage increases to 3
times in compared with rectifier stage. For example, theU-phase switching devices in the inverter stage arechanged in one rectifier carrier period 6 times though thatof the rectifier stage is 2 times. The switch timings of therectifier and DC/DC converter stage are only agree withthe bottom of the inverter carrier in order to achieve thezero current switching. As a result, the switching loss of
the inverter stage increases.
Figure 8(b) shows proposed switching loss method
using the carrier signals. In the proposed method, theinverter stage carrier is controlled asymmetry to reduce
the number of switching of the inverter stage, as shown in
Fig. 8(b). The switch timings of the rectifier and DC/DC
converter stage are agree with both bottom and top of theinverter carrier. In this case, the U-phase switching
devices in the inverter stage are changed 4 times. It isshould be noted that the zero current period of the DC linkis also distributed to each input current by the same ratio
in the proposed method, as expressed by equation (4).
As a result, the switching loss of the inverter stage canbe decreased to 2/3 times in the comparison with aconventional method because the number of the switchingin one carrier period is 4 times though that of theconventional method 6 times. Note that the proposed
method requires the zero voltage vectors at both top andbottom of the inverter carrier. This means that the twophase modulation can not be applied to the inverter
voltage command. That is, the proposed method iseffective in low voltage aria such as low speed in motor

2008 13th International Power Electronics and Motion Control Conference (EPE-PEMC 2008)599

drive applications because the three phase modulation isused in low speed aria.
D. Commutation method
In indirect matrix converter, the rectifier stage converter
can achieve zero current switching when the inverter
generates the zero voltage vectors [11]. In other words, theDC link current must be zero when the inverter controller
selects the zero voltage vectors. The proposed circuit
alternately operates between an indirect matrix converter
and an inverter. The switching of Sbp in the DC/DC
converter is also achieved when the inverter outputs thezero vectors. Therefore, switching losses do not occur inthe rectifier stage converter and the DC/DC converter. It isshould be noted that a conventional dead time is applied
for the commutation of the inverter stage. The
conventional dead time for the inverter stage causes
output voltage error and input current error. To overcome
it, the commutation error compensation method [6] isapplied for proposed circuit. As a result, the influence ofthe commutation for the input and output current can becompensated.

Figure 11 shows the DC link voltage waveform for theconventional indirect matrix converter and proposed
converter. In consideration of the low frequency
Table 1. Experimental parameters.
Input voltage
Input frequency

200 [V]50 [Hz]Carrier frequency

10 [kHz]

Output frequency

30 [Hz]DC power supply

300 [V]Power ratio (AC:DC)LC filter

2 [mH]
6.6 [ F]

Cut-off
1.3 [kHz]
frequency
load
R-L
Commutation
2.5 [ s]time
2:1

IV. SIMULATION AND EXPERIMENTAL RESULS
Table 1 provides the simulation and experimental
circuit parameters and conditions. The operation of the
proposed circuit is demonstrated by the simulation andexperimental results.
A. Basic operation simulation results for the proposed
converter
Figure 9 shows the simulation results of the proposed
converter. In the simulation, an ideal current source load
and a main circuit are used to check the proposed control
strategy. Good sinusoidal waveforms are obtained for the
input current and the output voltage. The THD of the input
and the output current are less than 1%, respectively. In
addition, a good DC waveform, without low frequency
ripple, is obtained for the DC power supply current.
In the waveform of Fig. 9(a), power grid generation,battery discharge, and motoring operations are obtained.
Similarly, power grid regeneration, battery charge, andgenerating operations are obtained for waveform of Fig.
9(b). As a result, bidirectional energy flow among thepower supplies in this circuit is confirmed.
These simulation results confirm the basic operation of
the proposed circuit.

Waveform when power grid generation, battery discharge, and motoring
operations

B. Basic operation experimental results for the
proposed converter
This chapter shows the basic operation of the proposed
converter. The proposed switching loss reduction method
is not applied in experimental results of this chapter as
rated voltage range. However the validity of the proposed
switching number reduction method is confirmed by next
chapter.
Figure 10 shows the input current, the output current
and the DC current waveforms. Good sinusoidal and dc
waveform are obtained for input and output current. In the
waveform of Fig. 9(a), power grid generation, battery
discharge, and motoring operations are obtained.
(b) Waveform when power grid regeneration, battery charge,
and generating operations
Fig. 9. Simulation results.

600

2008 13th International Power Electronics and Motion Control Conference (EPE-PEMC 2008)

components, a low pass filter was applied to the lower
waveform in Fig. 10. As a result, the DC link voltage ofthe conventional indirect matrix converter is 245 [V]. On
the other hands, the results shown in Fig.11 (b) confirm
that the DC power supply voltage and the input voltage
are alternated to the DC link voltage. As a result, theminimum average value of the DC link voltage is 260 [V],as shown by the upper waveform of Fig. 11(b). The DC
link voltage of the conventional indirect matrix converter
is 245 [V]; therefore, the proposed circuit can improve thevoltage transfer ratio.
Figure 12 shows the efficiency and the input power
factor of the proposed circuit. An input power factor (P.F.)
over 99% and high efficiency of 93.8% were obtained. In
comparison, the efficiency of a conventional multi-power
supply interface converter with a large electrolytic
capacitor is approximately 90%. In addition, the efficiency
can be improved by the applying of reverse blocking
IGBTs to the rectifier stage.
Figure 13 shows the THD of the input and output
current confirming that the input, output and DC input
current THD are 7.5%, 3.7% and 1.9%, respectively.
These experimental results confirm the validity andbasic operation of the proposed circuit.

(a) Conventional indirect matrix converter.

C. The proposed switching loss reduction method
This chapter shows the validity of the proposed
switching loss reduction method. The validity of proposed
method is confirmed by the indirect matrix converter. Thismeans that the DC/DC converter duty ratio is just zero.
The reason is that the effect of switching loss ruction isdepends on the DC/DC converter duty ratio. Therefore, toclear the effect of the proposed method, the DC/DC
converter stage was stopped.
Figure 14 shows the input current and the output
current waveforms of the proposed method. Goodsinusoidal waveform are obtained for input and output
current. In addition, it is confirmed in Figure 15 that the
input and output current THD are 1.8% and 1.3%
respectively. In the input and output waveform, almost asimilar waveform is obtained in comparison with theconventional method. Thus, the good experimental
waveforms are confirmed, in case of the reducing ofswitching number for inverter stage.

(b) Proposed converter.
Fig. 11. DC link voltage waveform.

Fig. 12. Efficiency and input power factor. (IMC=indirect matrix
converter; INV=inverter. )10
Input current

5Output current

DC Input current0(a) Waveform when power grid regeneration, battery charge,
and generating operations.
Fig. 10. Experimental waveform.

500

1000

Output Power[W]Fi

g. 13. THD of input and output current.

2008 13th International Power Electronics and Motion Control Conference (EPE-PEMC 2008)

601

Figure 16 shows the efficiency and the input power
factor of the proposed circuit. In the conventional method,
the input power factor over 99% and high efficiency of
93.8% were obtained. On the other hand, the efficiency isimproved by about 0.5 point by applying the proposed
method. In addition, the input power factor over 99% is
obtained.
Figure 17 shows the loss analysis for the proposed
circuit using circuit simulator (PSIM, Powersim
Technologis Inc) and DLL file (Dynamic Link
Library)[12]. The three phase modulation, two phasemodulation, and proposed switching loss reduction
method are applied for the inverter stage control. The twophase modulation decreases the switching loss of inverter
stage by about 2/3 in compared with a three phasemodulation. On the other hands, the switching loss of theinverter stage is improved by about 1/2 by applying of the
proposed switching loss reduction method. In the view ofloss on rectifier stage, there is no difference in eachmethod, since the switching losses do not occur in therectifier stage during zero current switching. In case of theheavy load, the conduction loss is dominant to theswitching loss. In contrast, the switching loss is dominant
to conduction loss when the light load is used. Therefore,
proposed method is valid in the low speed and light loadarea, because the two-phase modulation can not apply inthe low speed area to avoid the output current bias to one
switching device and to keep the output voltage accuracy.
These experimental results confirm the validity of the
proposed circuit and proposed switching loss reduction
method.
V. CONCLUSIONSThis paper proposes a novel control method for a multipower supply interface converter using an indirect matrix
converter. An active snubber circuit in the indirect matrix
converter is used as the interface of the DC power supply.
The proposed control method can be easily applied tomulti-port systems, due to the use of carrier comparison
modulation. Therefore the proposed method can beapplied easily to a DC/DC converter. In addition, thispaper proposes a control method of switching loss
reduction for the inverter stage converter. Applying the
proposed method, the switching loss of the inverter stage
can be decreased to 2/3 times in the comparison withconventional method. The validity of the proposed method
was confirmed by the simulation and experimental results.
The experimental results of the proposed system using
1kW class prototype circuit are obtained as follows,i)
The bidirectional energy flow among the power
supplies in this circuit is confirmed.
ii) The input, output and dc output current THD are
7.5%, 3.7%, 1.9%, the input power factor is 99%,
and the efficiency is 93.8%.
iii) The efficiency is improved by about 0.5 point by
application of the proposed method.
iv) The proposed switching number reduction method
is valid in the low speed and light load area.
This study was supported by Industrial Technology
Grant Program in 2005 from New Energy and Industrial
Technology Development Organization (NEDO) of Japan.

602(a) Conventional method.

(b) Proposed method.
Fig. 14. Experimental waveform.

(a) Input current THD.

(a)
Output current THD.
Fig.15. THD of input and output current.

2008 13th International Power Electronics and Motion Control Conference (EPE-PEMC 2008)

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Fig.
16. Efficiency and input power factor.

(a)Loss analysis of heavy load.

(b) Loss analysis of light load.
Fig. 17. Loss analysis.

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