A Novel Control Strategy for Direct Interface Converters Used for DC and AC Power Supplies

KATO Kouji

A Novel Control Method for Direct Interface Converters
used for DC and AC Power Supplies
Koji Kato,
Jun-ichi Itoh
Nagaoka University of Technology
1603-1 Kamitomioka-cho
Nagaoka city Niigata, Japan
Tel./FAX: +81/ (258) . 47.9533
E-Mail: itoh@vos.nagaokaut.ac.jp
URL: http://pelab.nagaokaut.ac.jp/itohlab/

Keywords«Matrix converter», «Converter control», «Power factor correction», «Energy converters for HEV»

Abstract
This paper proposes a novel control method for a direct interface converter for management of theenergy flow in either an AC or DC supply. The proposed converter is constructed based on an indirect
matrix converter. Therefore a proposed control strategy is based on an indirect control method with atriangular carrier wave. This paper proposes two control methods, using a boost up and a step down
type DC/DC converter. The basic operation of the proposed control method is confirmed bysimulation and experimental results.
In addition, this paper also proposes a commutation error compensation method for an output
voltage error and an input current error for an indirect matrix converter. In the proposed method, theoutput voltage and input current error by the commutation can be compensated at the same time,
because the PWM pulse of each switch is directly compensated. The validity of the proposed method
is confirmed by experimental results. Those results prove that the proposed compensation method candecrease total harmonic distortion (THD) of the input and output current.

I. Introduction
Recently, interface power converters for renewable energy and hybrid electric vehicle (EV) systems
have been studied intensely. Power sources can different types; AC power sources such as wind
power, and DC power sources such a photovoltaic cells, a batteries, and fuel cells. Therefore, aconventional power converter system composed of AC/DC, DC/DC and DC/AC converters requires alarge energy buffer, such as an electrolytic capacitor. However, the electrolytic capacitor in aconventional system interferes with down sizing, long-life time and low costs.
On the other hand, there is an AC/AC direct converter with a DC link, known as an indirect matrix
converter [1-10]. The indirect matrix converter, which does not have a large energy buffer such as anelectrolytic capacitor, can solve these problems. This converter is suitable to realize direct interface
converters with multi-port for several power supplies. However, it is difficult to be added a DC/DC
converter, because the conventional control method for the indirect matrix converter uses the space
vector modulation [1], which is expressed by three dimensions.
This paper proposes tri-port converters using a simple control method based on the indirect control
method with a triangular carrier wave [11]. By using a triangular carrier, the PWM pulse can begenerated without relationship to the number of phases. As a result, the proposed control system canbe easy added to a DC/DC converter. In addition, this paper proposes the commutation error
compensation method for the output voltage error and the input current error of the indirect matrix
converter. The commutation causes the output voltage error and the input current error, such as thedead-time in a conventional inverter. In the proposed method, the output voltage and input current
error are compensated at the same time, because the PWM pulse of each switch is directly

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A Novel Control Strategy for Direct Interface Converters Used for DC and AC Power Supplies

KATO Kouji

compensated. As a result, the influence of the commutation for the input and output current can be
decreased by the proposed commutation method.
Experimental results with an AC power grid, a motor, and a battery are also provide. The basic
operation and validation of the proposed method are confirmed by simulation and experimental results.
As a result, input, output and DC output current total harmonics distortion (THD) are 1.4, 1.8%, 2.3%,
were confirmed. In addition, an input power factor of over 99% and an efficiency of 95.4% wereobtained.

II. Circuit topology
Figure 1 shows the proposed direct interface 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 an electrolytic capacitor. In case of a hybrid EV system, the energy flow of theinterface converter must be maintained in three directions, as shown Fig. 1.
Figure 2 shows the main circuits of the proposed system. There are two operation methods in thissystem. The first operation method is to operate the inverter side converter as a four-phase voltage
source inverter, including the DC/DC converter. For this operation, the DC link voltage becomes
higher than the DC power supply. Therefore, it is referred to as a “boost type AC/DC/AC directconverter”. The second operation method is to operate the rectifier side converter as the four-phasecurrent source rectifier, including the DC/DC converter. In this case, DC link voltage becomes lower
than DC power supply, and thus, is referred to as a “step down type AC/DC/AC direct converter” inthis paper.
The proposed control strategy, which is based on an indirect control method with the triangularcarrier wave, easily realizes the addition of a DC/DC converter. The conventional indirect control
Energy Flow

Wind power
Engine generatoretc.

No energy buffer
AC/DC
ConverterG

DC/AC
Converter

Photovoltaics
Fuel cell
Battery
etc.

Load
or
Power line

DC/DC
converter

Current source DC/DC Voltage source
rectifierinverterconverter

Current source DC/DC Voltage source
rectifierconverter inverter

Srp Ssp Stp

Srp Ssp Stp

Sbp

Sup

Svp Swp

U
V

R
S
T

W

Srn Ssn

Sun Svn Swn

Stn Sbn
Bn

M

Bp
Lb

Input filter

Input filter

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

Sup

Svp Swp

U
V

R
S
T

W

Srn Ssnvbatt
BatteryM

Sun Svn Swn

Stn

Bp

vbatt
BatterySbpBn(a)Boost type AC/DC/AC direct converter.
(b) Step down type AC/DC/AC direct converter.
Fig. 2. Proposed circuits.

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strategy, which uses space vector control, must calculate the PWM pulse width to include a DC/DC
converter. In addition, it is difficult to define the output voltage command vector to include a DC
output. However, the proposed control system can include a DC/DC converter by using a commandfor the comparison of the carrier wave and the voltage. This chapter describes two types of control
method for the DC/DC converter.

A. Boost type AC/DC/AC direct converter
Figure 3 shows a block diagram of the boost type DC/DC converter with the indirect matrix
converter. This converter operates the inverter side converter as a four-phase voltage source inverter
including the DC/DC converter. The relation between the input voltage [vr vs vt]t and the output
voltage [vu vv vw vb’ ]t can be expressed as⎡v u ⎤ ⎡ sup sun ⎤⎡v r ⎤⎥⎢ ⎥ ⎢s⎢v v ⎥ = ⎢ vp svn ⎥ ⎡ srp s sp stp ⎤ ⎢v ⎥(1),
⎢v w ⎥ ⎢ s wp s wn ⎥ ⎢⎣ s rn s sn s tn ⎥⎦ ⎢ s ⎥⎢⎣v t ⎥⎦⎥
⎢ ⎥ ⎢⎣⎢v b '⎦⎥ ⎣⎢ sbp sbn ⎦⎥where Sxy is the switching function of the switch Sxy in Fig. 2. Sxy = 1 when Sxy is turned on, and Sxy = 0
when Sxy is turned off. The output voltage vb’ is the battery voltage vbatt based on that the motor neutral
point.
The rectifier side converter uses single-phase modulation, as shown in Ref. [11]. Thus, the DC link
voltage contains the ripple, which contains sixth order component of a power supply frequency. The
output voltage commands of the inverter side converter including the DC/DC converter mustcompensate for this ripple. Moreover, the output voltage commands of the four-phase voltage source
inverter are based on the neutral point of the motor. In contrast, the DC/DC converter output voltage
commands are based on the point Bn, as shown in Fig. 2. Therefore, the DC/DC converter voltage
command vbout** is converted by the following equation:*****
vbatt = 2vbatt − 1(2).
Rectifier side pulse commands(current type)

DC/DC converter sidepulse commands

PWM rectifier Pulse patternconversion
controller

DC/DC
converter
controller

Inverter
controller

Input current commands

+

+

×

×

Single leg
modulation+
dc_rip×++

Carrier

DC linkripple cal

Inverter side pulse
commands (voltage type)

Carrier
generator
1/X

Duty
conversion

Chopper comands

Output voltage commands

Fig. 3. Control block diagram of boost type AC/DC/AC direct converter.

B. Step down type AC/DC/AC direct converter
Figure 4 shows a block diagram of the step down type AC/DC/AC direct converter. This converter
operates the rectifier side converter as a four-phase current source rectifier including the DC/DC
converter. The relation between the input voltage [vr vs vt vb’ ]t and the output voltage [vu vv vw]t can be
expressed as:⎡v r ⎤⎡v u ⎤ ⎡ sup sun ⎤⎢ ⎥⎥ ⎡ srp s sp s tp sbp ⎤ ⎢v s ⎥
⎢ ⎥ ⎢
v
s
s
=
(3),
vn ⎥ ⎢⎢ v ⎥ ⎢ vp
s rn s sn stn sbn ⎥⎦ ⎢v t ⎥⎣⎢⎣v w ⎥⎦ ⎢ s wp s wn ⎥⎢ ⎥⎣⎦⎣⎢v b '⎦⎥

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A Novel Control Strategy for Direct Interface Converters Used for DC and AC Power Supplies

KATO Kouji

where the input voltage vb’ is the battery voltage vbatt based on the input voltage neutral point. To
avoid short circuit of the power supply, the rectifier side converter and DC/DC converter must be
switched separately.
Figure 5 shows the relation of the carrier signals between the inverter and the rectifier. Usually, acurrent type rectifier is controlled under the constant DC link current. However, the DC link current
must be zero when the inverter controller selects zero voltage vectors. In the proposed method, this isachieved by controlling the slope of the inverter carrier signal as shown in Figure 5. By adopting thismethod, the zero current period of the DC link is distributed by the same ratio as each input current, as
described in Eq. (4).
Tr 0 Ts 0 Tb 0 Tr 0 + Ts 0 + Tb 0
=
=
=
(4).
T1
T2
T3
T1 + T2 + T3

Rectifier side pulse commands(current type)

Inverter side pulse
commands (voltage type)

DC/DC converter
pulse pattern
DC/DC
converter
controller

PWM rectifier Pulse patternconversion
controller

Inverter
controller

Carrier
Carrier
generator

dc_ripDC linkripple calSingle leg
modulation

Input current commands

1/X

Chopper comands

Output voltage commands

Fig. 4. Control block diagram of step down type AC/DC/AC direct converter.
T
ib*

Rectifierside
carrier andcommands

irec*
T1
Srp

Rectifier
side
pulse

T2/2

Ssp

T2/2

Stn

ir 0
is 0
i 0

Input
current

T3/2

T3/2

Sbp

Tr0
Ts0/2

Ts0/2

t

ib 0
Dc link
current

Tb0/2

Tb0/2

0
vu*

Inverter side
carrier andcommands

vv*
vw*

Fig. 5. Relation between inverter carrier and rectifier pulse.

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III. Improvement of waveform for boost type AC/DC/AC direct converter
Figure 6 shows a part of the pulse pattern and behavior of the voltage error for the proposed indirectconverter. In an indirect matrix converter, the rectifier side converter can achieve the zero current
switching when the inverter generates the zero voltage vectors [4]. In other words, the dc-link current
must be zero when the inverter controller selects the zero voltage vectors. However, the dc-linkcurrent flows in the proposed circuit when the inverter generates the zero voltage vectors of the upper(P) arms. Therefore, the proposed circuit has to choose only lower (N) arms zero voltage vectors. It isshould be note that the conventional dead-time is applied for the commutation of the inverter side.

A. Analysis of the commutation error
In order to realize the low harmonics input and output current, the voltage error by the commutation
is important as a conventional inverter. At first, this paper analyzes the commutation error of theindirect matrix converter. The relation between input voltage and output voltage of the indirect matrix
converter can be expressed as Eq. (5) using "Dmn",which is duty ratio for switch Smn.
⎡v u ⎤ ⎡ Dup Dun ⎤⎡v r ⎤⎥ ⎡ Drp Dsp Dtp ⎤ ⎢ ⎥
⎢ ⎥ ⎢
vs
(5).
⎢v v ⎥ = ⎢ Dvp Dvn ⎥ ⎢ D
Dsn Dtn ⎥⎦ ⎢ ⎥rn⎣⎢⎣v w ⎥⎦ ⎢ Dwp Dwn ⎥⎢⎣v t ⎥⎦⎣⎦As shown in Figure 4, the error by the dead time occurs to the inverter side and rectifier side duty
ratio. In this case, the duty ratio considering the dead time error can be expressed by Eq. (6).
**⎡v u ⎤ ⎡ D u + ΔD u 1 - D u − ΔD u ⎤⎡v ⎤⎤⎢ r ⎥⎢⎥ ⎡ Drp * + ΔD rp D sp * + ΔD sp
0
⎢ ⎥
*
*
⎥ ⎢v s ⎥*⎢v v ⎥ = ⎢ Dv + ΔDv 1 - Dv − ΔDv ⎥ ⎢
+
Δ
D
D
0
0
*
*
⎢
tn
tn
⎢
⎥
⎣
⎦⎥ ⎢v ⎥⎢⎣v w ⎥⎦
D + ΔD w 1 - D w − ΔD w
⎣ t⎦
⎣ w
⎦
⎡ ( D * + ΔD )( D * + ΔD ) ( D * + ΔD )( D * + ΔD ) (1 - D * − ΔD )( D * + ΔD ) ⎤ ⎡ ⎤
u rp
rp
u
u
s
sp
u
u tn
tn ⎥ vr
⎢ u
⎥⎢ ⎥
⎢
*
*
*
*
*
*
= ⎢ ( D + ΔD )( D
+ ΔD ) ( D + ΔD )( D + ΔD ) (1 - D − ΔD )( D + ΔD ) ⎥ ⎢v ⎥
v
v
rp
rp
v
v
s
sp
v
v
tn
tn ⎢ s ⎥
⎥ v
⎢
*
*
*
*
*
*
⎢( Dw + ΔDw )( Drp + ΔDrp ) ( Dw + ΔDw )( Ds + ΔDsp ) (1 - Dw − ΔDw )( Dtn + ΔDtn )⎥ ⎢⎣ t ⎥⎦
⎦
⎣

(6),

where ΔDmn represents the duty error by the dead time, and the suffix ’*’ represents the command.
From Eq. (6), the output voltage vu can be determined by Eq. (7).
vu= v * + ΔD ( D *v + D *v − D *v ) + ΔD (ΔD v + ΔD v − ΔD v )uu rp r
sp s
tn t
u
rp r
sp s
tn t
+ D * (ΔD v + ΔD v ) + (1 - D * )ΔD v
u
rp r
sp s
u
tn t

{

}

(7).

Fig. 6. Commutation example.

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The second term in the right side of Eq. (7) means the voltage error directly affected by the inverter
dead time, the third term means the influence of the input side, and the fourth term means mixed error
between the input and output side.
On the other hand, the relation between the input and output current of the indirect matrix converter
can be expressed as Eq. (8). It should be noted that Eq. (8) is the transposed matrix of Eq. (6).
*
*
*
*
*
*
( Dv + ΔDv )( Drp + ΔDrp )( Dw + ΔDw )( Drp + ΔDrp ) ⎤ ⎡iu ⎤⎡ir ⎤ ⎡ ( Du + ΔDu )( Drp + ΔDrp )
⎥⎢ ⎥
⎢
⎢ ⎥
*
*
*
*
*
*
( Dv + ΔDv )( Ds + ΔDsp )( Dw + ΔDw )( Ds + ΔDsp ) ⎥ ⎢iv ⎥ (8).
⎢rs ⎥ = ⎢ ( Du + ΔDu )( Ds + ΔDsp )⎢⎣it ⎥⎦ ⎢(1 - Du* − ΔDu )( Dtn* + ΔDtn ) (1 - Dv * − ΔDv )( Dtn* + ΔDtn ) (1 - Dw* − ΔDw )( Dtn* + ΔDtn )⎥ ⎢⎣iw ⎥⎦⎥⎦⎢⎣From Eq. (8), for example, the input current ir can be determined by Eq. (9).
*

*

*

*

*

*

*

*

*

*

ir = i r + ΔDrp ( Du iu + Dv iv + Dw i w ) + ΔDrp ( ΔDu iu + ΔDv iv + ΔDv i w ) + ΔDu ( Drp iu + Drp iv + Drp i w ) (9).

In the conventional compensation methods, the output voltage error is compensated by Eq. (7).
That is, the voltage error adds to the voltage commands of the inverter. From Eq. (7), thecompensation duty ratio Ducomp can be determined by Eq. (10) because duty factor is obtained by
dividing the duty ratio by the DC-link voltage. In the indirect matrix converter, the compensation
values contain not only the inverter voltage error ΔDu but also the influence error ΔDrucomp of the input
side. Similarly, other compensation duty ratio can be calculated.
D{}= ΔD + D (ΔD v + ΔD ΔD v ) + (1 - D * )ΔD v e
ucomp
u
u
rp r
u sp sutn
dc= ΔD + ΔDurucomp(10).

This method can compensate the output voltage, however, the input current can not compensate
because the compensation values is decided without consideration for the input current. In this case,the input current ir can be expressed by Eq. (11).
i r = i r * + ΔDrp Du*i u + Dv *iv + Dw *i w
(11).
*
*
*
− ΔDrucomp ( Drp i u − ΔDrp i u ) − ΔDrvcomp ( Drp iv − ΔDrp iv ) − ΔDrwcomp ( Drp i w − ΔDrp i w ){}The additional input current error occurs to Eq. (11) since the output voltage is compensated by Eq.
(10). Moreover, the commutation error of the rectifier side can not compensate because thecommutation error of the rectifier side does not depend on the inverter side duty ratio. Therefore, theinput current error remains as shown in Eq. (11).
B. Proposed compensation method
In this paper, the voltage error is directly compensated by the PWM pulse. The input current andoutput voltage error can compensate at the same time because the PWM pulse of each switch is
directly compensated.
Figure 7 shows the proposed commutation error compensation method. The inverter side and
DC/DC converter side pulse commands are compensated directly based on the load current directionin Commutation compensator as shown Fig. 7(a).
Figure 7(b) shows behavior of the commutation compensator. In case of load current direction is
Rectifier sidepulse
commands

6

4

Inverter and
DC/DC converter
side pulse
commands
Load current
direction
signal

iu
iv
iw
ib

FPGA

Commutationcompensator

Commutation
generator

20

Sup

*

Inverter side Sup**pulse withcompensation

4(Iload<0)(Iload>0)
Inverterside pulse
commands

Td
increasing

Td

decreasing

Commutation Td
time(a) Configuration of proposed commutation(b) Behavior of compensator
error compensation.
Fig. 7. Proposed commutation error compensation method.

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A Novel Control Strategy for Direct Interface Converters Used for DC and AC Power Supplies

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plus, the compensator adds the dead-time period to the pulse command, because actual pulse isdecreased by the dead-time period. In case of load current direction is minus, the compensator
subtracts the dead-time period to the pulse command, because actual pulse is increased by the deadtime period.

IV. Simulation and experimental results
Figure 8 shows the simulation results of the proposed control strategy. In the simulation, an ideal
current source load and a main circuit are used to check the proposed strategy. Good sinusoidal
waveforms are obtained for the input current and the output voltage. The THD of the input and theoutput current are less than 1%, respectively. In addition, a good DC waveform, without low
frequency ripple, is obtained for the DC output voltage.
Table 1 provides the experimental parameters. The operation of a boost type DC/DC converter withindirect matrix is shown by the experimental results. This converter has six operation modes asfollows. (P: power grid, B: battery, M: motor)
I:
II:
III:
IV:
V:
VI:

P: generation,
P: generation,
P: generation,
P: regeneration,
P: regeneration,
P: regeneration,

B: charge,
B: charge,
B: discharge,
B: charge,
B: discharge,
B: discharge,
vr [V]
200

vr [V]

200

M: motoring
M: generating
M: motoring
M: generating
M: motoring
M: generating

0
-200

0
-200
ir [A] (LPF)

4

10
0
-10

0
-4

vuv [V] (LPF)
200

200

0
-200

0
-200

10

iu [A]

0-10
vbatt [V] (LPF)

iu [A]

vbatt [V]

400
200
0

200
100
0
ibatt [A]
4
2
0
0.02

vuv [V] (LPF)

10

0
-10

ir [A] (LPF)

0.04
[sec]

0.06

ibatt [A] (LPF)

2
1
0
0.02

(a) boost mode

0.04
[sec]

0.06

(b) step down mode
Fig. 8. Simulation results.

Table1 Experimental parameter.
Input voltage
200[V]
2 [mH]
LC filter
Input frequency
50[Hz]
6.6 [μF]
Carrier frequency
10[kHz]Cut-off frequency
1.3[kHz]
Output frequency
40[Hz]
DC loadR-L
AC load1.5[kW]motor
DC source
DC power supply
Commutation time
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Figure 9 shows the waveforms for operation modes I, II, and VI, as typical modes. Good sinusoidal
and dc waveforms were obtained for the input and output current. The other operation modes werealso confirmed. As a result, generation and regeneration of a power grid, the charge and discharge of abattery, and motoring and generating operations are obtained for each operation waveform.
Figure 10 shows the efficiency and the input power factor when the dc/dc converter leg is stopped
in the proposed converter. The input power factor of over 99% and the high efficiency of 95.4% wereobtained. It should be noted that the efficiency of a conventional AC/DC/AC interface converter witha large electrolytic capacitor is approximately 90%. Therefore, the proposed converter can decrease
the converter loss of 1/2.
0

Input voltage(phase)200 [V/div]0

Input voltage(phase)200 [V/div]0

Input current
10 [A/div]0

Input current
5 [A/div]0

AC Output
current
10 [A/div]0

AC Output
current
10 [A/div]

DC Output
current
5 [A/div]0

DC Output
current
5 [A/div]

0

10 [ms/div]

10 [ms/div](a) Mode I(b) Mode III

0

Input voltage(phase)200 [V/div]0

Input current
5 [A/div]0

AC Output
current
10 [A/div]0

DC Output
current
5 [A/div]
10 [ms/div](c) Mode VI
Fig. 9. Experimental results.

Fig. 10. Efficiency and input power factor.

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Figure 11 shows the comparison among the THD of the proposed circuit without voltage andcurrent error compensation, with the conventional compensation, which only add the voltage error tothe output voltage command, and proposed compensation methods, as described in chapter III. In the
input current THD, the conventional compensation methods is not effective, because the conventional
compensation method only compensates the output voltage without consideration for the input current.
In contrast, the THD for the input current is improved by approximate 50%, using the proposedcompensation method. On the other hand, the conventional compensation method decreases theoutput current THD by approximate 50%. In addition, the proposed compensation method also
decrease the input current THD by approximate 60%. However, almost same THD are obtained in the
DC output current. This causes that an auto current regulator is used in the DC/DC converter control.
In the proposed compensation, low THD is obtained for the input and output currents.
These experimental results confirm that the validity of the proposed circuit and commutation error
compensation method.
10
Input current with conventional compensation( )5Input current without
conventional compensation( )Input current with proposed compensation( )
0

500
1000
Output Power[W]1500

AC output current THD [%](a) THD of input current.

(b) THD of AC output current.

(c) THD of DC output current.
Fig. 11. THD of input and output current using a R-L load.

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A Novel Control Strategy for Direct Interface Converters Used for DC and AC Power Supplies

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V. Conclusion
This paper proposes a novel control strategy for the energy management of an AC and DC power
supply direct interface converters. The proposed control strategy, which is based on an indirectcontrol method with a triangular carrier wave, is easy to expand to the multi-phase system. This paper
proposes the two control methods using a boost up and step down type DC/DC converters. Moreoverthe compensation method for the output voltage and the input current error by the commutation werealso proposed. The proposed compensation method can be used in the indirect matrix converter. The
proposed compensation methods compensate directly the PWM pulse of each switch. The validity ofthe proposed strategy was confirmed by both the simulation and experimental results. As a result, it isconfirmed that the AC input, output current, and the DC output current THD are 1.4%, 1.8%, 2.3%,
respectively, and the input power factor is over 99% and the maximum efficiency is 95.4%. Moreover,the influence of the commutation for the input and output current can be decreased by the proposed
commutation method. In addition, three directions of energy flow in this circuit are confirmed.
This study was supported by Industrial Technology Grant Program in 2005 from New Energy andIndustrial Technology Development Organization (NEDO) of Japan.

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Unbalanced Source Voltage" IEEE PESC2003, 1293(2003)[3] K. Iimori, K. Shinohara, O. Tarumi, Z. Fu, and M. Muroya, ”New current-controlled PWM rectifier- voltage
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[4] K. Iimori, K. Shinohara, K. Yamamoto,:" Study of Dead Time of PWM Rectifier of Voltage-Source Inverter
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EPE 2007 - Aalborg

ISBN : 9789075815108

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