Isolated DC to Single-phase AC Converterwith Active Power Decoupling Capability
for Battery Storage System
Nagisa Takaoka, Hiroki Watanabe, Jun-ichi Itoh
Dept. of Electrical, Electronics and Information Engineering
Niigata, Japanntakaoka@stn.nagaokaut.ac.jp, hwatanabe@vos.nagaokaut.ac.jp, itoh@vos.nagaokaut.ac.jp
Abstract— This paper proposes a new active power
decoupling topology circuit, which does not require any
additional passive components and switching devices forbattery storage systems. This converter operates as thebidirectional isolated DC to single-phase AC converter with thepower decoupling capability using the coupled inductor. The
pulse density modulation (PDM), which achieves zero voltage
switching (ZVS) is applied for the secondary side converter
using a matrix converter (MC) in order to reduce the switchinglosses. This paper mentioned that the proposed circuit reduces
the double-line frequency power ripple on the input current to10.3% by the experiment. In addition, the output voltage THD
is lower than 3.0% overwide load range.
Keywords—Battery Storage System; Electronic Vehicle;
Single-phase converter; Power ripple compansetion

I. INTRODUCTION
Recently, the research of Electric Vehicle (EV) and Plugin Hybrid Electric Vehicle (PHV) have been rapidly
expanded [1]. An isolated DC to single-phase AC converter
is the main component of a battery storage system for thesevehicles in order to achieve a safe connection.
The converter topologies for the battery storage systemhave been studying for following requirements; (i) long lifetime, (ii) high efficiency, (iii) small volume, (iv) highreliability, (v) galvanic isolation. The EV/PHV with thebattery storage system become increasingly popular to meet
the all following conditions. However, in the conventional
topologies, the large electrolytic capacitor is required toabsorb a double-line frequency power ripple, which is caused
by instantaneous power mismatch between DC and the AC
grid side. As a result, the using large electrolytic capacitor isbrought to limit the life-time and results in low reliability of
the conventional converter.
As one of the solution, active power decoupling
topologies, leading to the elimination of the bulky
electrolytic capacitors in the DC-link have been studying [26]. These active power decoupling topologies charge anddischarge the buffer capacitor by the additional switching
devices and passive components in order to compensate thedouble-line frequency power ripple. It is possible to ensure
the reliability and the life-time compared to the conventional
method by the buffer capacitors, which enable to use of film
or ceramic capacitor instead of the bulky electrolytic
capacitor. The problems of almost conventional active power
decoupling topologies and control methods are the switchinglosses due to hard switching of an entire converter andadditional switching devices for active power decoupling
capability. However, these additional components preventthe high efficiency, high reliability and the downsizing of theconverter system.
This paper proposes a new active power decoupling
topology for an isolated DC to single-phase AC converter
based on matrix converter (MC). The originality of this
proposed active power decoupling topology is not require
any additional components, owing to the employment of thecoupled inductor. The coupled inductor assumes the boost
operation and the power decoupling operation without
additional magnetic component in the proposed converter.
Furthermore, in order to reduce the converter losses, MC isapplying to the secondary side. MC is achieved to reduce inthe number of the conversion from two stages to one stage
compared to a typical converter configuration as a rectifier
and a full bridge converter, In addition, a pulse density
modulation (PDM) is applied to MC in order to achieve thezero voltage switching (ZVS). This paper presents thevalidity of the proposed method by experiment.
II. CIRCUIT CONFIGURATION
A. Conventional circuit
Figure 1 shows an isolated DC to single-phase AC
converter with the conventional power decoupling circuit.
This power decoupling circuit is applied at the primary sidein order to eliminate the bulky electrolytic capacitor. In theconventional power decoupling method, the buffer capacitor
voltage is actively fluctuated in order to absorb the power
ripple. Therefore, the DC-link capacitance is achieved tominimize the comparison with that in Cdc as shown in Fig. 1
because the buffer energy is ensured by the capacitor voltage.
However, the conventional power decoupling methodrequires the additional switching devices and magnetic
components. In addition, the conventional converter
configuration has a number of the four stages power
conversion including the active power decoupling method.
Consequently, this method increases the volume of thecooling system and the converter loss.
B. Proposed circuit
Figure 2 presents the proposed isolated DC/AC converter,
which is composed by a matrix converter and a full-bridge
inverter with the coupled inductor. The third-winding N3 ofthe coupled inductor is galvanic isolation between the
primary side. In particular, the buffer capacitor Cbuf absorbs
the double-line frequency power ripple by charging anddischarging it, whereas full-bridge inverter controls thebuffer capacitor voltage. In the secondary-side, MC isemployed to eliminate the DC-link smoothing capacitors.
Furthermore, the MC is achieved to reduce the number of thepower conversion from two stages to one stage in thesecondary side compared to a general configuration of arectifier and a full-bridge inverter. Thus, MC as a secondary
converter contribute the improvement of the power densityof the converter system and the converter efficiency.
Figure 3 shows the operation modes of full-bridge
inverter with the coupled inductor. The proposed inverter has
four operation modes which generate a phase shift between
the switching of each arm. Fig. 3 (a) and (b) is power transfer
operation mode to secondary side. On the other hand, Fig. 3(c) and (d) is power decoupling operation mode in order tocharge and discharge the buffer capacitor. A leakage
inductor of the coupled inductor is utilized as the boost
inductor Lboost. Note that the main power from the battery to
the AC grid is controlled by the differential mode, whereas
the power ripple component is absorbed by controlling thecommon mode. The inductance of the boost inductor in
worst case, which ripple ratio is maximum is calculated byPower decoupling circuit

idc
Lboostdcom _ muxVdc
2idc f sw

+

L1

Lload

Cdc1

Cbuf

Isolated DC-DC
converter

Boost converter

iripple _ pp / 2
idc _ max

N3
idc

S1ap S1bp
N1

Lboostwhere Δidc is the allowable current ripple ratio, iripple_pp is thepeak to peak value of the input current idc, Vdc is a DC input
voltage and fsw is the switching frequency. Note that thedcom_max is the maximum reference of the common mode in a
one period, which is explained in next section.
C. Principle of power decouplingIf both the grid current and voltage are sinusoidal, thebuffer capacitor voltage vCbuf, which necessary to compensate
the power ripple is calculated based on the energy of thebuffer capacitor. First, the energy of the buffer capacitor
WCbuf is expressed by

S2ap

vdif Cbuf

N2
Vcom

Vdc

S2bp

igrid

Lload
vout

VCbuf

S2an

S1an S1bn

Full bridge Inverter (FBI)

vgrid
S2bn

Matrix converter (MC)Fig. 2.
Configuration of proposed isolated converter. The full-bridge
inverter with the coupled inductor and the buffer capacitor is controlled toconvert the DC input power to the AC power and absorb the power ripple
without additional switching devices and inductors.
S1ap

S1bp

Lboost S1an

vdif
S1bn

vcom

(1)

(2

PWM Inverter

Fig.1 Conventional isolated DC to single-phase AC converter with active
buffer circuit. The conventional converter uses a bulky electrolytic capacitor
Cdc to absorb the power ripple caused by a single-phase load.

S1ap

ic
VCbuf

vcom
Lboost S1an

Cbuf

idc

Vdc

(a) Differential mode 1
S1ap

iripple 

vgrid

Vdc

Vdc

Lboost 

igrid

Cdc2

vcom

S1bp

vdif
Lboost S1an
Vdc

S1ap

ic
vcom
VCbuf
Cbuf

(c) Common mode 1

ic

vdif VCbuf
S1bn
Cbuf

(b) Differential mode 2

S1bn

idc

idc

S1bp

Lboost S1an
Vdc

idc

S1bp

ic

vdif VCbuf
S1bn
Cbuf

(d) Common mode 2

Fig. 3.
Operation modes of primary-side converter with coupled inductor.
The primary side of the proposed system is operated in two modes; thedifferential mode as the power transmission and the common mode as a
power ripple compensation.



dvCbuf ttWCbuf   vCbuf ibuf d   vCbuf  Cbuf
 d
t0
t0
d 

  Pave cos  20  d
t

t0

(3)

where ibuf is the current of Cbuf, Pave is the average power ofthe output-side and ω0 is the grid-side angular frequency.
From (3), the voltage of the buffer capacitor vCbuf for thecompensation of the power ripple is presented byP
vCbuf  VC 0 2  ave sin  20 t   sin  20t0 o CbufP VC 0  ave sin  2o t 0 Cbuf1

Carrierdcom+ddif
dcom

0
A
B

(4)

1
0
1
0
0

vdif

2

MODE

S1ap
S1bp

III. CONTROL STRATEGY
In the control of the differential mode operation as a
power transfer, the three-winding voltages of the coupledinductor are controlled into a three-level wave form byoperation modes as shown in Fig. 3 (a) and (b). On the other
hand, the common mode operation is controlled to absorb thepower ripple. In particular, the power ripple component
occurs in the buffer capacitor voltage because the input
current is regulated into a constant value in the proposed
power decoupling method.
Then, the common mode operation of the proposed
method is employed for the remaining period after thedifferential mode operation. Therefore, the duty ratio of thecommon mode operation is calculated by the following: dcom _ c  1  d dif

*
com

 vv



Cbuf

where ddif is the duty ratio of the differential mode, whereas
dcom_c is the duty ratio of the common mode as shown in Fig.
5(c) and vcom* is a command of the common voltage. This
common mode voltage command vcom* is output by a PI
control of the DC input current as explained in the next
section. In addition, ddif is decided to the maximum value ofthe relationship between the input and output voltage.
Figure 4 shows a relationship among each command, thetriangle carrier and the switching pattern of the primaryconverter in the proposed system. The differential mode
voltage of the each duty ratios as shown in Fig. 3(a) and (b)in a carrier period is equal in order to suppress a DC biased
magnetization of the coupled inductor, especially. The
comprising signals A and B is generated by comprised duties
which the sum of “dcom_c and ddif” and only dcom_c and atriangle carrier as shown in Fig. 4. Thus, the desired
operation in each duties of the primary converter isactualized as described previously. The primary converter ofthe proposed system achieves the power decoupling
operation and the transfer power to the secondary side at thesame time without the additional passive components and theswitching devices.
Figure 5 shows the control block diagram of the proposedsystem with the power decoupling capability. The DC input

PT

APD

PT

APD

C2
0
0

D1
1
0

C1
1
1

D2
0
1

C2
0
0

APD ： Active power decoupling mode
PT : Power transfer mode

Fig. 4.

C1,C2 : Common mode by fig. 3
D1,D2 : Differential mode by fig. 3

Relationship among operation modes, signal and carrier.

voltage control for Cbuf DC current control

vCbuf*

vout*

PI

PI
i *
vCbuf dc
1
vCbuf

Fig. 5.

vout**

vcom*

idc
MAX

ddif*

Fig. 6

Pulse pattern conversion

where VC0 is the buffer capacitor voltage at a start time t0.

APD

S1ap
S1an
S1bp
S1bn

S2ap ,S2an
S2bp ,S2bn

Control block diagram

current control, which absorbs the power ripple component,
is control by using PI controller. The actively fluctuatedvalue of the buffer capacitor voltage command is calculatedby (4). Furthermore, the pulse pattern conversion outputs theeach gate signal using carrier and signals A and B as shownin Fig. 4.
IV. MODULATION METHOD OF MATRIX CONVERTER
Figure 6 shows the signal generation block of the
proposed PDM based on the delta-sigma conversion [6]. In
this PDM method, the output grid voltage waveform isgenerated by using the input voltage pulses of MC as theminimum unit. PDM allows MC to switch at the zero voltage
period of the third-winding of the coupled inductor.
Moreover, the distortion of the grid voltage, which
influences on the output voltage quality of MC is achieved to
become low. A delta-sigma conversion generates the inverse
voltage pulses in order to cancel the quantization error.
Consequently, MC with this PDM method achieves thedecrease of the switching loss and the low output voltage
THD.
V. EXPERIMENTAL RESULT
Table 1 shows the experimental conditions and Figure 7
demonstrates the experimental waveforms of the proposed
converter with/without the power decoupling method at R-LS modulator
ABS

1



ZOH

0
z-1

S2ap
S2an

MUX2

0
Polarity detection

DC input current idc 5A/div.

MUX1

vout**

Buffer capacitor voltage vCbuf 50V/div.

Quantizer

0

S2bp
S2bn

S1bn

0

Fig. 6Gate signal generation block of PDM based on delta-sigma
conversion.
Table 100

4 ms/div.

(a) Without power decoupling method.

Experimental condition

DC input voltage

200 Vdc

Rated power

1 kW

Load current

5 ArmsLoad frequency

50 Hz

Filter inductor Lout

2.0 mH

Boost inductor Lboost

1 mH

Buffer Capacitor Cbuf

200 mF

Turn ratio of coupledinductor N1:N2:N3

1:1:2

Carrier frequency of
primary converter

100 kHz

Carrier frequency of
secondary converter

10 kHzLoad voltage

Output current iload 5A/div.
Output voltage vout 250V/div.

200 Vrms

Buffer capacitor voltage vCbuf 50V/div.
DC input current idc 5A/div.
00load as the single-phase AC load. As shown in Fig. 7 (a), theinput current idc has a double-line frequency power ripple
component without the power decoupling method. The
buffer capacitor voltage fluctuation is small because thepower ripple component is not compensated by the buffer
capacitor in this operation mode, i.e. the passive power
decoupling capability. In contrast, the proposed method
actively fluctuates the vCbuf from Fig. 7 (b). Consequently,
the 2nd-order harmonics as a 100 Hz in the input current issuppressed greatly.

00

Output current iload 5A/div.
Output voltage vout 250V/div.

4 ms/div.

(b) With power decoupling method.
Fig. 7. Experimental waveforms in steady state when output power isabout 1 kW. The fluctuated capacitor voltage is absorb the double-line
frequency power ripple on the input current.

Figure 8 shows the double-line frequency power ripple
component on the input current of the proposed converter.
Note that the fundamental harmonic is based on the output
frequency of 50 Hz. It is verified from the analysis result in
Fig. 8, the double-line frequency power ripple component on
the input current is reduced by 79.2% as compared to thatwithout power decoupling method. However, a small ripple
component still appears in the input current. This is because
the compensation reference shown the (4) has a small error
as compared to the actual power ripple.

sigma conversion is improved by the quantizer. Then, thequantizer outputs the output pulses to cancel the quantization
error from the reference value of vout. As a result, the output
voltage THD is lower than 3.0% overwide load range.

Figure 9 shows the harmonic analysis result of the input
current and the total harmonics distortion (THD) of theoutput voltage in the proposed converter. The double-line
frequency power ripple component as a 100 Hz on the input
current is normalized by the each DC component of the input
current. From the analysis result, the proposed power
decoupling method reduces the double-line frequency power
ripple component to 10.3% in maximum. This is attributedthat the power pulsation are compensated by the active
power decoupling operation. In addition, the output voltage
ripple is low because the pulse is output continuously with
applying the proposed PDM method in MC of a secondary
converter. This PDM method, which based on the delta-

VI. CONCLUSION

Figure 10 shows the extended voltage in MC with PDM.
The experimental results mentioned the ZVS operation ofturn-on at MC with the proposed PDM method. In the all
devices are turn-off period, the drain-source voltages arepulsated when the current of devices is near 0 A.

This paper has proposed a new DC to single-phase AC
isolated converter with the power decoupling capability byusing the coupled inductor. This proposed converter
configuration is chosen because of the following advantages;(i) Boost operation is achieved without additional L,(ii) Elimination of bulky electric capacitors in the circuit,(iii) The buffer capacitor using a low capacitance,(iv) No additional component for the power decoupling,

REFERENCES[1]

K.Shiozaki and others, “Design and Verification of High Frequency
SiC On-board Vehicle Battery Charger for PHV/EV”, SAE of Japan,
pp. 25, (2014)[2] A. Tokumasu and others, “AC/DC Converter Based on Instantaneous
Power Balance Control for Reducing DC-Link Capacitance”, IEEJ
Journal of Industry Applications, Vol. 4, No. 6 pp.745-751 (2015)[3] S. Yamaguchi, T. Shimizu: "Single-phase Power Conditioner with a
Buck-boost-type Power Decoupling Circuit", IEEJ Journal ofIndustry Applications, Vol. 5, No. 3, pp.191-198 (2016)[4] T. Shimizu and others, “Flyback-Type Single-Phase Utility
Interactive Inverter With Power Pulsation Decoupling on the DC
Input for an AC Photovoltaic Module System", IEEE Trans. On
Power Electronics, Vol. 21, No. 5, pp. 1264-1272 (2006)[5] Y. Tang and others, “Decoupling of fluctuating power in single-phasesystems through a symmetrical half-bridge circuit” IEEE Trans.
Power Electron., vol. 30, no. 4, pp.1855–1865,(2015)[6] C.T. Lee and others, “Efficiency Improvement of a DC/AC Converterwith the Power Decoupling Capability", 2012 Twenty-Fourth
Annu.IEEE Appl. Power Electron. Conf Expo., pp1462-1468 (2012)[7] S. Kimura, K. Nanamori, T. Kawakami, J. Imaoka, and M.
Yamamoto"Allowable Power Analysis and Comparison of HighPower Density DC-DC Converters with Integrated Magnetic
Components,"IEEJ J. Industry Applications, vol. 6, no. 6, pp. 463-472,
2017.
[8] H.Radwan, M.A. Sayed, T.Takeshita, A.A. Elbaset, G. Shabib,”
Boost Inverter Topology with High-Frequency Link Transformer for
PV Grid-Tied Applications” IEEJ J. Industry Applications,vol. 8, No.
5, pp. 849-856[9] P. W. Wheeler and others, "Matrix Converters: A Technology
Review", IEEE Trans. Ind. Electron., Vol. 49, No. 2, pp. 274-288(2002)[10] J. Haruna, J. Itoh: "Control Strategy for a Matrix Converter with a
Generator and a Motor", Proc. 26th IEEE APEC, pp. 1782-1789(2011)[11] K. Yamamoto, S. Ehira, and M. Ikeda, "Synchronous Frame Control
for Voltage Sag/Swell Compensator Utilizing Single-Phase Matrix
Converter,"IEEJ J. Industry Applications, vol. 6, no. 6, pp. 353-361,
2017.
[12] Y.Nakata and J.Itoh “A fundamental verification of a single-phase to
three-phase matrix converter with a PDM control based on space
vector modulation”, 2014 International Power Electronics Conference(IPEC-Hiroshima 2014 - ECCE ASIA), pp.138-145, (2014)[13] N.Takaoka, H.Takahashi, J.Itoh: "Isolated Single-Phase Matrix
Converter Using Center-Tapped Transformer for Power Decoupling
Capability", IEEE Transactions on Industry Applications, Vol. 54, No.
2, pp. 1523-1531 (2018)[14] E.C. Nho, J.H.Jung, H.S.Kim: “Switching Loss Minimization of 3phase Interleaved Bidirectional DC-DC Converter” The 2014 IPEC,
pp2763-2764 (2014)

100
Reduced by 79.2%

10

Without the power decoupling method
With the power decoupling method

1

0.1

1 2 3 4 5 6 7 8 9 1011121314151617181920
Harmonic number

Fig. 8Harmonic analysis result when output power is 940W. The
2nd order harmonic of 100 Hz component is reduced by 79.2% by
proposed converter and the power decoupling method.

16
Current ripple component of 100 Hz
14
12
10
8
6
4
Output voltage THD
2
0
200
400
600
800
Output power [W]

4
3.5
3
2.5
2
1.5
1
0.5
0
1000

Output voltage THD [%]In future work, we will analyze the loss distribution of
the proposed converter.

Input current ripple(100Hz)[%](100%: DC current component)

A prototype was constructed to validate the power
decoupling method and fundamental operation in experiment.
As a result, the power ripple component of a secondary-orderharmonics was reduced by 79.2% in comparison to the casewithout the proposed power decoupling method. The resultwith applying the PDM based on the delta-sigma conversion
is verified to achieve ZVS operation in MC and low output
voltage THD, which is lower than 3.0% within the entire
output power range.

Harmonic component[%](100%: DC current component)(v) Low output voltage THD.

Fig. 9Harmonic analysis result of input current and total
harmonics distortion (THD) of output voltage in proposed converter
within output power from 300 W to 1 kW.

Drain-source voltage of S2bp 250V/div.
ZVS
0 Gate-source voltage of S

2bp

25V/div.

0

Drain-source voltage of S2ap 250V/div.

0Gate-source voltage of S2ap
25V/div.
0

ZVS

400 ns/div.

Fig. 10 Gate-source voltages of MC in experiment. The pulse is output
to improve the distortion and ZVS operation of the turn-on is achieved
by applying PDM based on a delta-sigma conversion in MC.