A Control Method for Buck-boost Type Direct Interface Converter With DC Power Supply
Koji Kato*

Jun-ichi Itoh**Nagaoka University of Technology
Keywords: AC and DC power supply interface, Indirect Matrix Converter, Active snubber circuit
Abstract – This paper proposes a novel control method for an interface converter that is using an indirect matrix converter (IMC) with a
DC power supply. The proposed converter is constructed based on an indirect matrix converter and a combined of a boost type converter
and a step-down type converter. The proposed converter connects an active snubber to the DC link part of IMC along with a boost typeconverter. The voltage transfer ratio from the AC power sources to the load can be improved by an active snubber. In addition, theproposed control method able to control the power distribution ratio and output voltage at a same time. The basic operation of the
proposed method has confirmed by simulation and experimental results. Moreover, in order to confirm the validity of the proposedsystem, the mileage evaluation at 10-15 mode for a hybrid electric vehicle has been implemented based on the simulation.

1. Introduction
Recently, renewable energies and hybrid electric vehicle(HEV) systems are receiving significant interest, withconsiderations of global warming and environmental problems.
There are two types of power sources for renewable energies; AC
power sources such as a wind turbine and DC power sources
such as batteries, and fuel cells. In these systems, interface power
converters have been intensely studied. A conventional power
converter system, which consists of a pulse width modulation(PWM) rectifier, a DC/DC converter and an inverter, requires anelectrolytic capacitor. However, this electrolytic capacitor in theconventional system interferes in several subjects, such as down
sizing, long life time and low costs.
On the other hand, there is an AC/AC direct converter
without a large energy buffer such as a matrix converter, whichuses nine bidirectional switches, and an IMC, which consists of acurrent source rectifier and a voltage source inverter without acapacitor in the DC link part[1]-[4]. The utilization of these AC/AC
direct converter in renewable energy systems can achieve thefollowing; downsizing, long-life cycle and low costs.
There are some approaches to interface DC power supply
using the matrix converter as mentioned in [5], [6]. A voltage
source inverter is connected to the input or output side of thematrix converter. In this system, the matrix converter operates inparallel with and the inverter. However, there are somedisadvantages such as large size and constituting of many
components. The inverter is used to interconnect with the DC
power supply because the matrix converter has no DC
component. As a result, this is a high cost structure in the matrix
converter.
On the other hands, there are two types of interface
converters using an IMC have been proposed, which areclassified as the boost type converter[7] and step-down typeconverter[8]. Since the IMC has a DC link part, it is easy tointerconnect with a DC power supply. The proposed boost typeconverter connects a DC/DC converter using a chopper to the DC
link part of the IMC. The inverter and the DC/DC converter
operate at the same time as a four-phase voltage source inverter,
including the DC/DC converter. With regard to the voltage
relationship between the DC power supply and the DC link, theproposed circuit provides a boost up converter for the DC power
supply. However, the proposed boost type converter does not

improve the voltage transfer ratio of the IMC. That is, the voltage
transfer ratio of IMCs, which defines the ratio between the output
and the input voltage, is well known as being constrained to
0.866.
The proposed step-down type converter interface the DC
power supply using an active snubber circuit in the IMC. The
active snubber circuit is composed by a capacitor connected to an
IGBT in series. This snubber circuit with the IGBT works as a
step-down chopper for the DC power supply. In addition, thevoltage transfer ratio can be improved by the DC power supply.
In the step-down type converter, the DC power supply should behigher than the DC link voltage to avoid short circuit. However,when the battery is used for the DC power supply in this system,
a lot of batteries have to be connected in series. In this case, thebattery volumes will increase.
This paper proposes a converter which is combined by aboost type converter and a step-down type converter. The
proposed converter connects an active snubber to the DC linkpart in the boost type converter. The voltage transfer ratio fromthe AC power source to the load can be improved by the active
snubber. Besides, the high voltage battery is not required because
the DC voltage source is boosted up by this DC/DC converter.
That is, the proposed system covers the disadvantage of the boost
type and step-down type from one to each other. The basic
operation of the proposed method has confirmed by simulationand experimental results. Moreover, in order to confirm thevalidity of the proposed system, the mileage evaluation at 10-15
mode for a hybrid electric vehicle is implemented based on thesimulation.

2. Circuit topology
A. AC and DC power supplies direct interface system
Figure 1 shows the block diagram of the proposed directinterface converters for the energy management system. Thissystem consists of two AC power sources or loads and the DC
power source without a large energy buffer, such as anelectrolytic capacitor. In case of a hybrid EV system, the energy
flow of the interface converter must be maintained in three
directions, as shown Fig. 1. Two types of the DC/DC converter,
which are boost type converter and step-down type converter, canbe applied to this system.

Figure 2 shows the proposed boost type converter. a chopperis connected to the DC link part in the IMC. In this system, theDC link voltage becomes higher than the DC power supply.
Therefore, it is referred to as a “boost type AC/DC/AC directconverter”. The chopper leg is controlled as a fourth leg of thevoltage source inverter. Therefore, the control is implemented ina way that the voltage command of the chopper compares with
the inverter carrier to obtain the desired PWM pattern.
However, the proposed converter has the problem. The
voltage transfer ratio between the power grid to the motor, isconstrained to 0.866 because the current source rectifier has no aboost up function. As a consequence, the output current of the
IMC is higher than the back-to-back type converter, which
consists of a voltage type PWM rectifier and an inverter, for thesame output power. As a result, the motor loss and the converter
loss are increased. Besides, the low voltage transfer ratio limits
the applications of an IMC.

operates as a conventional IMC. In this case, the DC/DC
converter becomes a conventional snubber circuit, as shown in
Fig. 4(a). On the other hand, the proposed converter operates as aconventional inverter when the DC/DC converter switch Sbp isturned on, because all switches in the rectifier are turned off. In
this case, the DC/DC converter is similar to a DC power supply,
as shown in Fig. 4(b). That is, the proposed circuit operates as aconventional IMC or a conventional inverter alternately insequence.

Input filter

B. Boost type AC/DC/AC direct converter

C. Step-down type AC/DC/AC direct converter.

Input filter

Fig. 2. Boost type AC/DC/AC direct converter.

Fig. 3. Step down type AC/DC/AC direct converter.

Input filter

Figure 3 shows the proposed step-down type converter. The
DC/DC converter is constructed with an active snubber circuit in
the IMC. 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 should be higher thanthe peak of the AC input line voltage, because a 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”. The DC/DC
converter is controlled as the fourth leg of the rectifier side
converter. Time sharing is applied to the control of the snubber
circuit.
Figure 4 shows the equivalent circuits of the proposed
converter. The rectifier stage converter is similar to a four phasecurrent source rectifier including the DC/DC converter.
Therefore, the switch in the three-phase PWM rectifier and
DC/DC converter must be separately turned on in order to avoid
a short circuit between the AC and DC power supplies. When the
DC/DC converter switch Sbp is turned off, the proposed converter(a) Sbp is turn off.

Dc power
supplyFig. 1. Block diagram of AC and DC power supply interface
system.

U
VW

M(b) Sbp is turn on.
Fig. 4. Equivalent circuit of the proposed circuit

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 the average value of theoutput voltage between the rectifier stage and the DC/DC
converter. Therefore the average value of the DC link voltage
Edc in the proposed circuit can be expressed as,*

Edc = Drec vin + D*vb

(1),

where Drec* is the rectifier stage converter duty ratio, and Db*isas follows.
(1) vout*≧0.866vin : boost type operation mode(2) vout*<0.866vin : buck-boost type operation mode
When the output voltage command is lower than 0.866 of the
input voltage vin, the proposed circuit operates as the boost type
AC/DC/AC direct converter. In this case, the active snubber
circuit becomes a conventional snubber circuit. In other words,
active snubber duty command Db* becomes ‘0’. In addition, thethe DC/DC converter duty ratio.
In the step-down type converter, DC power supply becomes
higher than the DC link voltage. Therefore, a lot of batteries need
to be connected in series to provide high voltage DC power
supply. In this case, battery volumes increase.
D. Buck-boost type AC/DC/AC direct converter.

Input filter

Fig. 5. Principle of the step-down type AC/DC/AC directconverter.

Fig. 6. Proposed circuit.

Input filter

Figure6 shows the proposed circuit configuration. As
previously discussed, the voltage transfer ratio of the boost type
AC/DC/AC direct converter is constrained to 0.866, and a DC
power supply of step-down type AC/DC/AC direct converter isrequires by a lot of batteries to obtain high DC voltage.
Thus, the proposed converter combines both the boost type
AC/DC/AC direct converter with step-down type AC/DC/AC
direct converter. In other words, the proposed buck-boost type
AC/DC/AC direct converter is composed by a boost type
AC/DC/AC direct converter with an active snnuber circuit. The
proposed converter can operate as the boost type AC/DC/AC
direct converter and step-down type AC/DC/AC direct converter.
The proposed circuit improves the voltage transfer ratio by using
an active snubber circuit.
Figure 7 shows the equivalent circuits of the proposed
converter. The rectifier stage converter is similar to a four phasecurrent source rectifier including the active snubber. Therefore,
the switches in the three-phase PWM rectifier and active snubber
must be separately turned on in order to avoid a short circuit
between the AC power supplies and capacitor. When the DC/DC
converter switch Sc is turned off, the proposed converter operates
as a boost type AC/DC/AC direct converter. In this case, theDC/DC converter becomes a conventional snubber circuit, asshown in Fig. 7(a). On the other hand, the proposed converter
operates as a conventional inverter with boost copper when theactive snubber switch Sc is turned on, because all switches in therectifier are turned off, as shown in Fig. 7(b). That is, theproposed circuit operates as boost type AC/DC/AC directconverter or an inverter with boost chopper under alternately
control.

(a) Sc is turn off.

3. Control strategy
Figure 7 shows the control block diagram of the proposed
converter. The proposed control method is based on the control
method of a boost type AC/DC/AC direct converter[7]. The
inverter stage and DC/DC converter stage can be controlled
independently and to apply the carrier comparison method. In
addition, the voltage transfer ratio of the proposed converter can
improve by the active snubber circuit.
The proposed circuit has two types of operation modes. The
operation mode is changed by the output voltage command vout*(b) Sc is turn on.
Fig. 7. Equivalent circuit of the proposed circuit.

DC/DC converter uses an ACR (Automated current regulator).
The power distribution ratio is decided by the DC/DC converter
current command.
On the other hand, the proposed converter operates as abuck-boost type AC/DC/AC direct converter when the output
voltage command is higher than 0.866 of input voltage vin. In the
proposed method, the power distribution ratio is decided by theactive snubber duty ratio and the inverter stage output voltage
vout*. To control the output voltage and the power distribution
ratio at the same time, the output voltage command and theactive snubber duty command is described as follows.
In the buck-boost type operation, the power distribution ratio
is controlled by the operation time division of each operation
mode. The output voltage is obtained by the average output
voltage of inverter stage for the boost type mode and step-down
type mode. Thus, when the active snubber duty is defined as Db,
the output voltage is obtained by (2).
*
* E
*
* E
vout = λsdt Db c + λbt (1 − Db ) rec
2
2
(2),
*
*
= Db vsdt _ out + (1 − Db )vbt _ out
where, vout is the inverter stage output voltage of the proposed
circuit, vbt_out is the inverter stage output voltage of the boost type
operation, vsdt_out is the inverter stage output voltage of step-down
type operation, λsdt is the modulation index of the step-down type
operation, λbt is the modulation index of the step-down type
operation, Ec is the capacitor voltage of active snubber, Erec is theoutput voltage of rectifier stage and the subscript ’*’ represents
the command.
The power distribution ratio is calculated by multiplying theoutput voltage of each operation and the active snubber duty ratio
Db*. The power distribution ratio is expressed by (3) when the
instantaneous power is assumed to constant during one carrier
cycle.
******
Psdt : Pbt = Db vsdt _ out : (1 − Db )vbt _ out(3),
where, Pstd is the output power of the boost type operation and
Pbt is the output power of the boost type operation.
From Eq.(4), the operation time ratio of the active snubber
circuit Db can be determined by Eq.(4).
*vbt _ out Psdt

*

Db =

*

*

*

(4).

*

Thus, the output voltage of the proposed converter isconstrained by the power distribution ratio. In order ｔo control
the output voltage and the power distribution ratio at the sametime, the output voltage command vout* and active snubber dutycommand Db* of the active snubber circuit is leaded by (5) from
(2) and (4).
*vout Psdt

*

*

*

*

*

Psdt + Pbt (1 −

*

vout

*

vbt _ out

*

)

2
Ec

(6).

In addition, active snubber capacitor voltage vc is controlled
by AVR (Automated voltage regulator). It is noted that themodulation index λbt is fixed at ‘1’ to output maximum voltage.
Therefore, the power distribution ratio and the output voltage cancontrol at same time. The relation between the output voltage andthe active snubber duty ratio is shown in fig. 9.

4. Simulation and experimental results
Table 1 provides the parameters and conditions for simulationand experimental circuit. The operation of the proposed circuit isdemonstrated by the simulation and experimental results.
Figure 10 shows the simulation results of the proposed
control strategy. In the simulation, an ideal current source load
and a main circuit are used to confirm the proposed strategy. At
first, the proposed converter operates as the boost type
AC/DC/AC direct converter. After 0.05msec, the proposed
converter operate as the buck-boost type AC/DC/AC directconverter. Good sinusoidal waveforms are obtained for the input
current and the output voltage. The total harmonic distortion*

vsdt _ out Pbt + vbt _ out Psdt

vsdt _ out =*vout Psdt*

λsdt =

Psdt + Pbt (1 −Fig. 8. Control block diagramof the buck-boost AC/DC/AC direct converter.
Vc
Vin
Edc

1
0.866

*

vout

vbt _ out

controllable range

(5).

*
*

)

The modulation index of inverter can be determined by
Eq.(6) from Eq.(5).

0

0.2

0.4

0.6

0.8

Active snubber duty ratio : Db

Fig. 9. Relation between output voltage and active
snubber duty ratio.

1

(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 output voltage.
Figure 12 shows the waveform of the basic operation for the
proposed circuit. Figure 12(a) is obtained in the single operationof the boost type AC/DC/AC direct converter; fig. 12(b) is
obtained in the single operation of the step-down type
AC/DC/AC direct converter. Good sinusoidal waveforms and DC
waveform are obtained for the input and output current of theboth operation mode as shown in Fig. 11. As a results in fig.
11(a), it is confirmed that the input, output and dc output current
T.H.D. are 2.4%, 1.9%, 1.9% respectively. The input power
factor is 99% and efficiency is 96.3%. Moreover, the input,
output and dc output current T.H.D. are 2.4%, 1.9%, 1.9%, theinput power factor is 99% and efficiency is 95.2% as shown infig. 11(b).
These experimental results confirm the validity and basic
operation of the proposed circuit.
5. Loss comparison of hybrid system
This chapter shows a comparison between the converter lossof an IMC and a Buck to Buck converter (BTB) to confirm thevalidity of the proposed system for a HEV system. The converter
loss of an IMC and a BTB system are calculated for 10-15 modeof the HEV. It is noted that battery power of the HEV system is
not considered in this comparison. The converter loss iscalculated by PSIM(powersim Inc.), as refer to [9].
Figure 12 shows the configuration for the loss calculation
method. At first, power semiconductor characteristics for theswitching loss and conduction loss are measured by a chopper
test under the various current and voltage. Next, theinstantaneous values of the current and the voltage at the switch
timing are captured to the DLL (dynamic linked library) file. In
the DLL file, the power semiconductor characteristics and a loss
calculation program are described as below. The switching loss isestimated by referring to the values of the voltage and current,
which are obtained by the chopper test results. The conduction
loss is estimated by the V-I characteristics from the current value.
This method can estimate the power semiconductor loss
regardless of the circuit configuration.
Figure 13 shows the 10-15 mode cycle, which is one of thetest driving patterns for the vehicle to measure fuel expenses[10].
The calculation parameters are refried by “Toyota Prius[11]” asshown in Table 2. The requirement motor power is calculated by
the driving pattern and the weight of the vehicle. The assumed
conditions of the fuel expenses calculation are as follows.
1) The generator voltage is converted in proportion to the bucke.m.f. of 150V when the vehicle speed is 70km/h.
2) The motor buck e.m.f. is supposed to 0.866 times ofgenerator buck EMF.
3) For the DC link voltage of the BTB system, the generator
buck e.m.f. is set to 1.5 times higher by the PWM rectifier.
4) The wind drags the rolling friction, and other resistances forthe drive are neglected.
5) The converter loss consists of only switching loss andconduction loss.

Table1

Experimental parameter.

Input voltage
Input frequency

200[V]
50[Hz]

Carrier frequency

7.5[kHz]

Output frequency

40[Hz]DC power supply
Power ratio

LC filter
Cut-off
frequencyload
Commutation
time
1:2

350[V](AC:DC)

2 [mH]
13.2 [µF]
1[kHz]
R-L
2.5 [µs]

Input voltage vr,vs,vt [V]
200
0
-200

Input current ir,is,it [A] (LPF)20-2

Output line voltage vuv,vvw,vwu [V] (LPF)
200
0
-200

Output current iu,iv,iw [A]
5
0
-5
8

DC power supply current iL [A]40

DC link voltageEdc [V]
300
0
0.04

0.05
[sec]

0.06

Fig. 10. Simuration waveform(a) Boost type AC/DC/AC direct converter.

(b) Step down type AC/DC/AC direct converter.
Fig. 11. Experimental waveformDLL fileFigure 14 shows the loss calculation results based on the
10-15 mode cycle. The power loss of the IMC is lower than the
BTB system regardless the speed and torque. Table 3 indicates
the total energy loss, the total efficiency and fuel expense of the
proposed system in comparison to the BTB. The loss energy isimproved by approximately 30% by applying the IMC. Theenergy conversion efficiency is improved by approximately 3%.
These results confirm the validity of the IMC when the IMC
applies HEV system. It should be noted that the performance of
IMC is decreased when the battery power ratio is increasing.

6. Conclusion
This paper proposes the novel control method and theconverter which is combined by the boost type converter andstep-down type converter. The proposed converter connects anactive snubber to the DC link of the boost type converter. The
voltage transfer ratio of the boost type converter can be improvedby this active snubber. In addition, the validity of the IMC
applying in HEV system has confirmed. The basic operation of
the proposed method has confirmed by simulation andexperimental results.

(1) P. W. Wheeler, J. Rodriguez, J. C. Clare, L. Empringham: "Matrix Converters:

Speed [km/h]

References

Fig. 12. Principle of loss calculation mehod.

A Technology Review" IEEE Transactions on Industry Electronics Vol. 49, No. 2,
pp274-288, 2002
(2) J.Itoh, I.Sato, H.Ohguchi, K,Sato, A.Odaka, N.Eguchi:「A Control Method for

Fig.13. 10-15mode running pattern.

the Matrix Converter Based on Virtual AC/DC/AC Conversion Using Carrier
Comparison Method」IEEJ Vol.124-D No.5,2004(in Japanese)

Table 2. Calculation parameter.

(3) J. W. Kolara, T. Friedli, F. Krismer and S. D. Round:” The Essence ofThree-Phase AC/AC Converter Systems” Power Electronics Motion Control

Car weight[11]Car heighConference 2008 pp.27-42(4) L.Wei, Y.Matsusita, T.A.Lipo: “Investigation of Dual-bridge Matrix Converter
Operating under Unbalanced Source Voltage” IEEE Power Electronics Specialist
Conference 2003, 1293(2003).

1280 kg[11]

Max motor output
power [11]Car width[11]1725 mm[11]1490 mm

Fuel expenses

35.5 km/L

50 kW

Coefficient ofwind drag[11]0.26

Coefficient of rolling friction

0.01(5) S. Goto, S. Ogasawara, and H. Funato, "A New Power Converter Circuit
Combining an Inverter with a Matrix Converter," IEEJ SPC-06-101, 2006.
(6) Jun-ichi Itoh, Hiroshi Tamura: "A Novel Control Strategy for a Combined
System Using Both Matrix Converter and Inverter without Interconnection
Reactors", IEEE PESC2008, pp.1741-1747, 2008
(7) Koji Kato, Jun-ichi Itoh, "A Novel Control Method of Direct Interface
Converters for Several Power Supplies" 12th European Conference on PowerElectronics and Applications 2007(8) Koji Kato, Jun-ichi Itoh, " Control Method for a Three-Port Interface Converter
Using an Indirect Matrix Converter with an Active Snubber Circuit", THE 13th
IEEE Power Electronics and Motion Control Conference,448, 2008.
(9) J. Itoh, T. Iida, A. Odaka:" Realization of High Efficiency AC link Converter
System based on AC/AC Direct Conversion Techniques with RB-IGBT" Industrial

Fig.14. 10-15 mode loss calculation result.
Table 3. Calculation results*.

Electronics Conference, Paris, ,PF-012149,2006(10)

Ministry

of

Land,

Infrastructure,

Transport

and

http://www.mlit.go.jp/jidosha/nenpi/nenpilist/nenpilist.html(11) TOYOTA MOTOR CORPORATION : http://toyota.jp/prius

Tourism (Japan):

Loss energy kJ

IMC

BTB

156.6

223.4

Energy conversion efficiency %

93.1

90.6

Fuel expenses km/L

36.6

35.5

* In these results, all motor energy is provided by a generator.