Dual Active Bridge DC-DC Converter using Both
Full and Half Bridge Topologies to Achieve High
Efficiency for Wide Load
Hayato Higa

Shunsuke Takuma, Kouji Orikawa and Jun-ichi Itoh

Dept. of Electrical Electronic Information Engineering
Nagaoka University of Technology
Nagaoka, Niigata, Japanhhiga@stn.nagaokaut.ac.jp

Dept. of Science of Technology Inovation
Nagaoka University of Technology
Nagaoka, Niigata, Japan
takuma_s@stn.nagaokaut.ac.jp
orikawa, itoh@vos.nagaokaut.ac.jp

Abstract—This papar proposes which the Dual Active Bridge(DAB) converter changes between Full Bridge (FB) converter’s
operation and Half Bridge (HB) converter’s operation on thesecondary side of the high frequency transformer depending on
the output power. With the HB converter operation’s, the ironloss of the transformer becomes small because the secondary
voltage of the transformer becomes half compared to the FB
converter’s operation. In addition, Zero Voltage Switching (ZVS)
is achieved at the light load. Therefore, the proposed circuit canobtain the high efficiency for the wide load by the changing the
HB and the FB converter’s operation depending on the output
power. In this paper, the changing point between the HB and the
FB converter is derived using the loss calculation. The validity ofthe proposed circuit is verified by 800-W prototype. From theexperimental results, it is confirmed that the proposed circuit has
the two local maximum efficiencies which are 92.9% and 93.4%
at the light load and the heavy load using the proposed circuit.

circulating current [6]. In order to solve these problems, Pulse
Width Modulation (PWM) is added to the phase shift control inorder to extend the ZVS range and reduce the circulating
current in [7-8]. However, it is not always possible to achieve
the ZVS for all switches due to the error between the primaryvoltage and the secondary voltage including the turn ratio of
the transformer. Besides, the efficiency is not discussed interms of the high voltage boost up. In [9-10], the reactive
power is suppressed by voltage compensation using an
auxiliary transformer. However, the additional switching
devices and the auxiliary transformer are required in order toreduce the circulating current. In addition, the iron loss isincreased by the auxiliary transformer. In [11-12], the variableswitching frequency control is introduced and a relay switch isconnected to the transformer in order to change the leakage
inductance depending on the output power. However, thevariable switching frequency makes the design EMC filter
difficult in the high power application. In [13], a FB converter
and a HB converter are combined using a bidirectional switch.
The bidirectional switch can be on-state or off-state during thewhole switching period when the input voltage is maximum or
minimum. However, the bidirectional switch works based on
the PWM switching while the input voltage is changed.
Therefore, the switching loss occurs in the bidirectional switch
although the ZVS is achieved on the main switches. In [14-16],
a three-level DAB converter with a neutral-point-clamped
topology has been proposed in order to improve the total
harmonic distortion of the inductor current. However, thenumber of switching devices is increased.

Keywords—Dual Active Bridge Converter; Zero Voltage
Swtichng (ZV S);I.

INTRODUCTION

Recently, the high efficiency and the high power density
bidirectional isolated DC/DC converters are increasingly
desired in the application of power grid system that found in
the smart grid system and electric vehicles. Therefore, thepower conversion system requires the isolation andbidirectional operation. In order to achieve the bi-directional
power transmission and the isolation, a bi-directional isolated
DC-DC converter is used as power conversion systems [1-3]. A
Dual Active Bridge (DAB) converter has been presented suchas a bidirectional isolated DC-DC converter [4-5]. The DAB
converter can achieve the bidirectional power conversion,
isolation and high voltage boost up using active switches and ahigh frequency transformer. In addition, in order to reduce theswitching loss, the DAB converter achieves Zero Voltage
Switching (ZVS) during the dead time using an additional
capacitance or a parasitic capacitance of the switching devices[5]. However, the ZVS cannot be achieved at the light load in
the conventional DAB converter because the capacitor
connected in parallel to the switching devices is not completely
charged or discharged due to the small transformer current.
Moreover, the conduction loss also increases due to the large
978-1-4673-7151-3/15/$31.00 ©2015 IEEE

This paper proposes a new isolated bidirectional DC-DC
converter based on the DAB converter. The secondary side of
the circuit topology is changed from the FB converter or the
HB converter depending on the load conditions. The
bidirectional switch without the PWM operation is used to
select the circuit topology. By changing between the FB
converter and the HB converter depending on the load, theproposed circuit can achieve the high efficiency for the wide
load because the ZVS range is extended and the iron loss of thetransformer is reduced at the light load. This paper is organized
as follows; first, the configuration and the operations of the
proposed circuit are explained. Second, the principle of thepower loss reduction in the proposed circuit is described.
Thirdly, the proposed calculation method that is used toevaluate the power loss is confirmed. Finally, the experimental
results show the fundamental operation and the efficiency
characteristics of the prototype circuit.
II.

B. Output power for Full Bridge Mode and Half Bridge mode
Fig. 2 shows the operation modes of the proposed circuit.
The FB converter and the HB converter are combined on thesecondary side of the transformer.
Fig. 2 (a) shows the operation mode when the secondaryside of the transformer is operated as the FB converter. During
this mode, Sw5 is always off. Therefore, the power loss does
not occur on Sw5. The capacitors C1 and C2 work as a smooth
capacitance to E2.
When the secondary side of the transformer is operated as
the FB converter, the transferred power to the secondary side
PDC_FB is expressed by (1) [17].

nV1_ maxV2 _ FB _ max

Ll

nV
V


 (1  )  1_ max 2 _ FB _ max  (1  )
2f swLl

where V1_max is the maximum value of the secondary
voltage of the transformer, V2_FB_max is the maximum value ofthe secondary voltage of the transformer, Ll is the sum of theleakage inductance and that of the additional inductor,  is thephase difference between the primary voltage and thesecondary voltage of the transformer, n is the turn ratio of thetransformer,  is the switching angular frequency and fsw is theswitching frequency.
When the primary side of the transformer is operated as the
FB converter, V2_FB_max is E2. Therefore, the higher power istransferred using the FB converter to the secondary side of thetransformer. On the other hand, the ZVS cannot be achieved at
the light load because the capacitors connected in parallel tothe switches are not completely charged or discharged due tolow current in the conventional dual active bridge converter. In

Turn ratio n 

N1
N2

Sw1

iTr1

Secondary side
Sw3
C1

N1：N2

E1

R Ll

Sw5

v2

v1p

PROPOSED DUAL ACTIVE BRIDGE CONVERTER

A. Circuit configulation
Fig. 1 shows the configuration of the proposed isolatedbidirectional DC-DC converter based on the DAB converter.
The proposed converter consists of the DAB converter, abidirectional switch Sw5 and two capacitors C1 and C2. The
capacitances of C1 and C2 are same. The proposed circuit canachieve the ZVS in the same manner with the conventional
DAB converter when the switches are modulated at the highoutput power. The maximum rating voltage of the bidirectionalswitch is same to that of C1 and C2 which is half of otherswitches on the secondary side of the transformer. In addition,
the bidirectional switch does not require the high speed
switching because the PWM is not applied to Sw5. Therefore,
the bidirectional switch which has low on-resistance can beselected in order to reduce the conduction loss of Sw5 when
Sw5 is on-state.

PDC _ FB 

Primary side

Sw2

E2

C2

Sw4

Fig. 1. . Configuration of proposed bidirectional DC-DC converter
based on dual active bride converter (E1 < E2).
Smoothingcapacitor

Full bridge converter

C1

Sw3

Sw1

Sw5
v2

E2

C2

Sw2

Sw4

(a) FB converter operation. C1 and C2 work as smoothing capacitor
to E2.
Half bridge converter

Sw1

C1

Sw3
Sw5

v2

Sw2

E2

C2
Sw4

(b) HB converter operation. C1 and C2 work as a part of HB converter
operation.
Fig. 2. Operation mode of secondary side of transformer.

addition, the iron loss becomes large due to high E2. As a result,the efficiency is sharply decreased at the light load.
Fig. 2 (b) shows the operation mode when the secondaryside of the transformer is operated as the HB converter. During
this mode, Sw5 is always on. Therefore, the power loss occurs
on Sw5. However, the conduction loss can be reduced due tolow on-resistance because Sw5 does not require the highswitching speed. The capacitors C1 and C2 work as a part of theHB converter. When the secondary side of the transformer isoperated as the HB converter, the maximum value of thesecondary voltage of the transformer V2_HB_max becomes E2/2.
When the secondary side of the transformer is operated as the
HB converter, the output power to the secondary side PDC_HB isexpressed by (2).


PDC _ HB 

nV1 _ max V2 _ HB _ maxLl (1 


)




From (2), it is understood that PDC_HB is half of PDC_FB when
the FB converter’s operation is selected. Moreover, the ironloss of the transformer is reduced because V2_HB_max becomes
half of E2. As a result, the lower power is transferred while theiron loss becomes lower compared with that of the FB
converter.
In addition, the transformer current with the HB converter’s
operation becomes higher than the FB converter’s operation.
Therefore, the ZVS is achieved in the lower power region
compared to the conventional DAB converter.
From above mentioned explanation, it is understood thatthe operation modes of the proposed circuit are changed
according to the output power. In high output power region, theproposed circuit is operated as the conventional dual active
bridge converter. In the low output power region, the proposed
circuit is operated as a hybrid of the FB converter on the
primary side of the transformer and the HB converter on thesecondary side of the transformer. In the proposed method, It is
required to derive the changing point between the HB
converter and the FB converter from the converter loss
C. ZVS range
In order to achieve the ZVS for all switching devices in the
FB converter’s operation, the condition of the output power ispresented by (3) [5].
2 nV1 _ maxV2 _ FB _ max    nV1_ max  
nV1 _ maxV2 _ FB _ max 
1  
  PDC _ FB 

4L
4L
  V2 _ FB _ max  









From (3), the lower limit of the output power to achieve theZVS increases due to the ratio of the primary and thesecondary voltage including the turn ratio of the transformer
nV1_max/V2_FB_max .
On the other hands, the condition of the output power ispresented by (4) in order to achieve the ZVS in the HB
converter’s operation.
nV1 _ max V2 _ HB _ max   nV1 _ max 
1  
4L  V2 _ HB _ max 






2


nV1 _ max V2 _ HB _ max   PDC _ HB 
4L





From (4), The ZVS range at the HB converter’s operation is
wider than the FB converter’s operation at light load whennV1_max/V2_HB_max is close to 1

III. DESIGN PROCEDURE OF MAXIMUM EFFICIENCY POINT FOR
TWO MODESThe power loss of the proposed circuit consists of theswitching loss, the conductions loss of MOSFETs, the copper
loss, the iron loss. Other power losses are not considered forsimplification. Those power losses are divided into three kindsof a power loss. First, the switching loss is a power loss which
is proportional to current. Next, the conduction loss of
MOSFETs and the copper loss are a power loss which is
proportional to the square of current. In the end, the iron loss isa power loss which is not related to current. Therefore, the total
power loss Ploss considering a single converter is expressed by(5)
2

Ploss  K2 Pout  K1Pout  K0

(5)

where K2 is the constant coefficient for the power loss which is
proportional to the square of current, K1 is the constantcoefficient for the power loss which is proportional to current
and K0 is the power loss which is not related to current.
In addition, the efficiency is expressed by (6) using (5).



Pout
Pout

(6)
2
Pout  Ploss K 2 Pout  (1  K1 ) Pout  K0

By differentiating (6) with respect to Pout, the condition of
the output power which achieves the maximum efficiency
Pmax, is expressed by (7).
2K2 P max  K0

(7)

From (7), Pmax is determined the relationship between K0
and K2. Eq. (7) is re-expressed by (8)P max 

K0
K2

(8)

Fig. 3(a) shows the relationship among above three kinds ofpower loss and the efficiency in the case of a single converter.
In the case of the general DAB converters, K1 is zero at thehigher output power due to ZVS. Therefore, Pmax can be
designed by adjusting relationship among the conduction lossof MOSFETs, the copper loss and the iron loss while the region
which achieves the ZVS is independently designed.
Fig. 3(b) shows the efficiency characteristics considering
the proposed circuit. The proposed circuit has two local
maximum efficiencies at the light load and the heavy load
because the HB converter’s or the FB converter’s operation is
selected depending on the output power. Therefore, theefficiency is higher compared with the conventional DAB
converter by changing two circuits on the secondary side of thetransformer at Psw_HB-FB. In the proposed circuit, the efficiency
can be improved for wide load variation by designing the ZVS
range and adjusting the ratio among the conduction loss, thecopper loss and the iron loss of the transformer. Therefore, it isnecessary to calculate the each loss.

A. MOSFET Loss in primary and secondary inverter
The power loss of the MOSFET consists of the conduction
loss. In the secondary voltage side inverter of Fig. 1, theconduction loss of the secondary voltage side MOSFET
Pcondloss_pr can be obtained by (7) using the on-resistance of thesecondary side MOSFET Ron_pr. Thus, the power loss per
secondary MOSFET Pcondloss_se can be obtained by (5), (6) using
the on-resistance of the secondary side MOSFET

Pcondloss_ pr  Ron_ pr I L 





Pcondloss_ se  Ron_ se NI L  



2

2

In the HB converter’s operaiton, it should be noted that the
conduction loss does not occur at two switches Sw1, Sw2
because the two switches are always off. However, the inductor
current is double compared to the FB converter’s operation atsame load.
B. Transformer loss
The power loss of the transformer consists of the iron loss
and the copper loss. The iron loss occurs because of the fluxchange in the core. The copper loss occurs in the winding
resistance of transformer. At first, when the square wave isinputted to the transformer, the flux density Bac is obtained by
(7).


Bac 

V2 _ FB _ max  ton
2 N 2 Ac

Ptrans _ fe  PcvVe 





Pcopper _ se  Rwire _ se NI L  



2

2

C. Additional inductor loss
The power loss of the additional inductor consists of thecopper loss and the iron loss. In order to neglect the saturationof the flux in the core, the air coil is used. Thus, the copper loss
occurs only in the additional inductor. The copper loss of theadditional inductor is obtained by similarly to (10).
V.

EFFICIENCY ESTIMATION BY LOSS CALCULATION

The proposed circuit in Fig. 1 is investigated using the loss
calculation. The circuit parameters are shown in Table 1. Itshould be noted that the primary side wire resistance is larger
than the secondary side because the additional inductor is seriesconnected to the primary side of the transformer. The rating
power is 800 W. The primary voltage has 36 V to 60 V and thesecondary voltage has a fluctuation of 340 V to 380V. In the
primary side inverter, IRFP4568 (IR co.) of MOSFET is


max





In the half bridge mode, the iron loss is decreased bydecrement of the flux density.
The copper loss of the transformer is obtained from thewinding resistance with the skin effect. The primary winding
copper loss Pcopper_pr in the main circuit is obtained by (9) using
the primary winding resistance of the main circuit with skineffect Rwire_pr. The secondary winding copper loss Pcopper_se in
the main circuit is obtained by (10) using the primary winding
resistance of the main circuit with skin effect Rwire_se.

Pout
2
K 2 Pout  (1  K1 ) Pout  K0

Ploss
K2Pout2



K1PoutPloss

K0
K
Pmax  0
K2

Pmax
Output power Pout (W)(a) Single converter.



where N2 is the secondary wire turns, Ac[m2] is the effective
cross-section of the core. Therefore, the iron loss of thetransformer Ptrans_fe is obtained by (14) using the characteristicsof the flux density - core loss value Pcv[W/m3] and the effective
volume of the core Ve[m3].
Pcopper _ pr  Rwire _ pr I L Power loss (W)This section explains the power loss expression of the
proposed circuit. The switching loss is ideally zero, because theswitching devices can achieve the ZVS. The power loss of the
proposed circuit consists of the conduction loss and theconstant loss. The conduction loss is generated in the onresistance of MOSFET, the wire resistance of the transformer.
The constant loss is generated within the iron loss of thetransformer and the no load loss.

Efficiency (%)

EXPLESSION FOR POWER LOSS

max_FBmax_HB
Efficiency  (%)

IV.

Pout
 FB 
2
K 2 _ FB Pout  (1  K 1 _ FB ) Pout  K 0 _ FB
Pout
HB 
2
K2 _ HB Pout  (1  K1_ HB ) Pout  K0 _ HBP max_HB 

K0_ HBP max_FB 

K2_ HB

Half bride mode

K0_ FBK2_ FB

Full bride modePmax_HB

Psw_HB-FB Pmax_FB
Output power Pout (W)(b) Proposed converter (max_HB <max_FB).
Fig. 3 Efficiency curve.

selected. On the other hands, STB45N65M5 (ST co.) of
MOSFET is selected in the secondary side.

converter’s operation is increased when the ratio of the primary
and the secondary inverter voltage including the turn ratio is
close to 1.

Fig. 4 shows the loss calculation results against the output
power at the fluctuation of the primary and the secondary
voltage. From the results, the maximum efficiency of over 95%
is achieved against the voltage fluctuation. From Fig. 4, thechanging point between the HB converter’s and the FB
converter’s operation is decided by the primary/the secondaryside voltage including the turn ratio of the transformer.

TABLE I.

Fig.4 (a) shows the efficiency against the output power
when E2 is 380 V, E1 is 32 V. the efficiency of the HB
converter‘s operation is much higher than the FB converter’s
operation at the light load. This is because the iron loss isdecreased compared to the FB converter’s operation. However,
the efficiency at the FB converter’s operation is low. This iscause that the reactive current is large due to the error between
the primary voltage and the secondary voltage including theturn ratio of the transformer. Moreover, the ZVS range isnarrow from (3). Thus, the switching loss occurs at the light
load.

Half bridge mode

Parameter

SymbolPrimary voltage

E1
E2
fsw

32

kHz

Additional Inductor

Ll

15

µH

Rated power
On resistance of primaryswitching devices

Prated800

W

Ron_pr

0.25

mW

On resistance of secondary
switching devices
primaryside wire resistanceRon_se11mW

Rwire_pr150mW

primaryside wire resistancen
Rwire_se

5
170

mW

Half bridge mode

Full bridge mode

100.0

changing pointchanging point

95.0
Efficiency [%]Full bridge

Half bridge

85.0

Half bridge

90.0
85.0

80.0

Full bridge

80.0
0

200

400
600
Output power [W]8000(a)E1=36 V E2=380 V NE1/E2=0.47
Half bridge mode

100.0

200

400
600
Output power [W]800(b) E1=36 V E2=340 V NE1/E2=0.53

Full bridge mode

Full bridge mode

100.0

Full bridgechanging point

95.0

95.0
Efficiency [%]Efficiency [%]Efficiency [%]

95.0
90.0

Unit
V
V

Turn ratio of transformer

Full bridge modeValue
36 to 60
340 to 380

Secondary voltage
Switching frequency

For the same reasons, the efficiency of the FB converter’s
operation becomes low at close to nE1/E2=0.5 (In Fig.4 (b) and(c)). On the other hand, In Fig. 4 (d), the efficiency of the FB

100.0

SPECIFICATION PARAMETERS OF THE POWER LOSSCALCULATION FOR PROPOSED CIRCUIT

Half bridge

90.0

Full bridge

85.0
80.0
0

200

400
600
Output power [W](c) E1=48 V E2=380 V NE1/E2=0.63

800

90.0
Half bridge

85.0
80.0
0

200

400
600
Output power [W](d) E1=60 V E2=340 V NE1/E2=0.88

Fig. 4 Calculation results of proposed circuit.

800

VI.

EXPERIMENTAL RESULTSTABLE II.

A. Operation waveforms of the proposed circuit
Fig. 5 shows the experimental waveforms of a prototype
circuit. Table 1 shows the experimental conditions. From theresults, it is confirmed that V2_HB_max is E2/2 = 190 V (In Fig.
5(a)) while V2_FB_max is E2 = 380 V (In Fig. 5(b)). From Fig.
5(a) and Fig. 5(b), the primary current of the transformer islarger than the HB converter’s operation because the secondary
voltage of the transformer is different.

SymbolValue
E1
48
E2(Fig. 7(a))
340Secondary terminal voltage
E2(Fig. 6, 7(b)) 380
Turn ration532
Switching frequency
fsw
/4
Phase shift angleAdditional inductor
Ll
15
Parameter
Primary terminal voltage

B. Efficiency of each mode
Fig. 6 (a) shows the measurement efficiency against theoutput power when the secondary terminal voltage E2 is 340 V.
From the results, the local maximum efficiencies of 92.9% and93.4% are achieved. At below Pmax_FB, the efficiency at the FB
converter’s operation is decreased because the iron loss of thetransformer is large compared with the total loss. Therefore, thesecondary side of the transformer is operated as the HB
converter in order to output the lower power and reduce theiron loss of the transformer. At the HB converter’s operation,
another local maximum efficiency exists because the constantcoefficients for the power loss are different from that of the FB
converter’s operation. Therefore, it is confirmed that the
proposed circuit improves the efficiency at the light load. On
the other hand, the efficiency is decreased at the output powerof more than Pmax_FB. This is because the conduction losses of
MOSFETs on the secondary side and the copper loss on thesecondary side of the transformer are dominant in the total
power loss.
Fig. 6 (b) shows the measurement efficiency against theoutput power when the secondary voltage E2 is 380 V. From
the results, the local maximum efficiencies of 93.8% and92.4% are achieved. The maximum efficiency at the FB modein Fig. 6 (b) is lower than that of Fig. 6 (a). This is because theiron loss in Fig. 5 (b) becomes large compared with that in Fig.
5 (a) due to higher secondary terminal voltage. At the output
power of more than 650 W, the efficiency in Fig. 6 (b) ishigher than that in Fig. 6 (a) because the conduction loss of
MOSFETs and the copper loss the transformer are reduced dueto the low inductor current. At the HB converter’s operation,
the high efficiency is achieved compared with Fig. 6 (a).
The changing point which the FB converter and the HB
converter are switched Psw_HB-FB, is not same between Fig. 6(a)and (b). This is because the minimum current which achieves
the ZVS is different from the two conditions. When thesecondary terminal voltage E2 is high, the current of the
primary side and the secondary side are lower than that whenE2 is low. Therefore, the ZVS range is extended when the FB
converter is operated on the secondary side of the transformer.
As a result, the changing point between the FB converter andthe HB converter are higher output power in Fig. 6 (b).
The output power which achieves the maximum efficiency
at the FB converter PmaxFB, is also different. This is becausethat the iron loss of the transformer is larger and the conduction
loss is lower due to E2 is high. Therefore, K0_FB is large and
K2_FB is lower. As a result, the higher E2 becomes, PmaxFB
moves toward. On the other hand, the output power which
achieves the maximum efficiency PmaxHB is almost same at the

EXPERIMENTAL CONDITIONSTransformer primary voltage

Unit
V
V
V
kHz
rad
mH

50[V/div]

0
Transformer secondary voltage 250[V/div]00Transformer primary current

10[A/div]

20[μsec/div](a) HB converter’s operation.
Transformer primary voltage

50[V/div]

0
Transformer secondary voltage 500[V/div]00Transformer primary current

20[A/div]

20[μsec/div](b) FB converter’s operation.
Fig. 5 Experimental waveforms of prototype circuit (E2 is 380 V).

HB converter’s operation. This is because the iron loss, theconduction loss of MOSFETs and the copper loss are notdifferent much because E2 is low.
C. Loss analysis of alternation point
In order to evaluate the power loss at changing point which
the HB and the FB converter’s operation, the loss measures andanalysis each part was implemented under the experimental
conditions as shown in Table 1.
Fig.7 shows the loss analysis of the DAB converter with the
FB converter and the HB converter. This is case that thesecondary side voltage is changed while the primary voltage isconstant. Fig.7(a) shows the loss analysis results at thecondition of E1=48 V,E2=340 V. Fig.7(b) illustrates theanalysis results with the HB converter’s operation and the FB

Psw_HB-FB

Half bridge
mode

94

Efficiency  (%)

converter’s operation when the primary side voltage E1 is 48 V,
the secondary voltage E2 is 380 V. From the loss analysis, theiron loss of the transformer at the HB converter’s operation isdecreased compared to the FB converter’s operation. In
addition, the switching loss is reduced by achievement of theZVS. However, the copper loss and the conduction loss are
increased because the transformer current is large in the case of
the same output power compared to the FB converter’s
operation. Moreover, the copper loss of the primary sidetransformer is predominant. It account for over 50% of the total
loss. This is causes that the wire resistance of the additional
inductor is large. Therefore, in order to achieve the higher
efficiency, it is necessary to optimize the transformer and the
additional inductor design.

Finally, the principle of the proposed circuit isexperimentally confirmed. It is confirmed that the two local
maximum efficiencies are achieved by changing point between
the two circuits. From the experimental results, the maximum
efficiency of 93.8% at 280W is obtained. From the loss
analysis results, the relationship between the switching point
and the each part loss.
In future work, the converter efficiency will be improvedby the optimizing design of the transformer and the additional
inductor.

[3]

[4]

[5]

90

Half bridge

400600
Output power Pout (W)Efficiency  (%)

94

800

Full bridgemodePmax_FB
Full bridge

93
92
91

Half bridge

90
89
200

E1=48V
E2=380V
n=5
fsw=32 kHz

400
600
Output power Pout (W)800(b) E2 = 380 V.
Fig. 6

Measured efficiency of prototype circuit.

30
Switching loss

25

Iron loss(Trans.)
Copper loss
(Primary side Trans.)

20
15

Copper loss
(secondary side Trans.)

10

Conduction loss
(Primary side)

5

Conduction loss
(secondary side)

321W
Half bridge mode

312W
Full bridge mode(a) E2 = 340 V.
40Loss [W][2]

E1=48V
E2=340V
n=5
fsw=32 kHz

91(a) E2 = 340 V.

REFERENCES
R. W. D. Doncker, D. M. Divian, M. H. Kheraluwala: "A three-phase
soft-switched high-power-density dc/dc converter for high-power
applications", IEEE Trans on Industry Applications, Vol, 27, No. 1, pp.
63-73 (1991)
S. Inoue, H. Akagi: "A Bidirectional DC-DC Converter for an Energy
Storage System With Galvanic Isolation", IEEE Trans on PowerElectronics, Vol, 22, No. 6, pp. 2299-2306 (2007)
T. Babasaki, T. Tanaka, Y. Nozaki, T. Tanaka, T. Aoki, F. Kurokawa:"Developing of Higher Voltage Direct-Current Power-feeding Prototype
System", Proc. 31st INTELEC 2009, (2009)
D. Aggeler, J. Biela, S. Inoue, H. Akagi, J.W. Kolar : "Bi-Directional
Isolated DC-DC Converter for Next-Generation Power Distribution Comparison of Converters using Si and SiC Devices", Power
Conversion Conference - Nagoya, 2007, pp.5 10-517, 2007
Kheraluwala, M.N., Gascoigne, R.W., Divan, D.M., Baumann, E.D.:「Preformance Characterization of a High Power Dual Active Bridge
dc-to-dc Converter」, IEEE Trans. I.P., Vol. 28, No. 6, pp. 1294-1301(1992)

92

P
Pmax_HB Half bridge sw_HB-FB
mode

0

[1]

Full bridge

93

200

Loss [W]In order to derive the changing point of the FB converter
and the HB converter, the loss calculation of the proposed
circuit are investigated and evaluated in term of losses. From
the results, it is clarified that the relationship among the
primary, the secondary side voltage and the changing point of
the FB converter’s operation and the HB converter’s operation.
The validity of the loss calculation was confirmed thetheoretically with the maximum efficiency of over 95%.

Pmax_FB

89

VII. CONCLUSION
This paper proposed isolated bidirectional DC-DC
converter based on the DAB converter combining the FB
converter and the HB converter on the secondary side of thetransformer. The proposed converter changes the FB
converter’s operation and the HB converter’s operation
depending on the output power in order to extend the ZVS
range and reduce the iron loss.

Pmax_HB

Full bridge
mode

35

Switching loss

30

Iron loss(Trans.)
Copper loss
(Primary side Trans.)

25
20

Copper loss
(secondary side Trans.)

15
10

Conduction loss
(Primary side)

5

Conduction loss
(secondary side)

0

410 W
Half bridge mode

415 W
Full bridge mode(b) E2 = 380 V.
Fig. 7 Loss analysis of DAB converter with FB converterand HB converter at changing point

[6]Biao Zhao, Qiang Song, Wenhua Liu and Weixin Sun “CurrentStressOptimized Switching Strategy of Isolated Bidirectional DC-DC
Converter With Dual-Phase-Shift Control”, IEEE Trans. on PowerElectronics, vol. 60, no. 10, pp.4458-4467, Oct 2013.
[7] Tomohiro Matsuda, Giuseppe Guidi, Atsuo Kawamura Tomofumi
Imakubo, Yuuji Imakubo, Yuuji Sasaki, Takehiro Jikumaru:「Improvement of Efficiency of Dual Active Bridge DC-DC Converter
by Using Pulse Width Modulation in AC Voltage」, JIASC2011, Vol. ,No. , pp. 307-312 (2011)[8] A. K. Jain, R. Ayyanar: "PWM Control of Dual Active Bridge:
Comprehensive Analysis and Experimental Verification", IEEE Transon Power Electronics, Vol, 26, No. 4, pp. 1215-1227 (2011)[9] A. Jones, B. Smith, C. Maxwell: 「Reactive Power Loss Optimization
Method for Bi-directional Isolated DC-DC Converters」, IEEE Trans.
PE., Vol. 23, No. 6, pp. 2905-2914 (2008)[10] A. Tripathi, K. Mainali, S. Bhattacharya: "A Series Compensation
Enabled ZVS Range Enhancement of a Dual Active Bridge Converter
for Wide Range Load Conditions", ECCE, pp. 5384-5391 (2014)[11] Xiao-Fei He, Zhiliang Zhang, Yong-Yong Cai, Yan-Fei Liu“A Variable
Switching Frequency Hybrid Control for ZVS Dual Active Bridge
Converters to Achieve High Efficiency[12] G. Guidi, M. Pavlovsky, A. Kawamura, T. Imakubo, H. Wan:
"Improvement of Light Load Efficiency of Dual Active Bridge DC-DC
Converter by Using Dual Leakage Transformer and Variable Frequency",
ECCE, pp. 830-837 (2010)[13] W. Song, B. Lehman: "Dual-Bridge DC-DC Converter: A New
Topology Characterized With No Deadtime Operation", IEEE Trans on
Power Electronics, Vol, 19, No. 1, pp. 94-103 (2004)[14] X. Zhang, T-C. Green: "The Modular Multilevel for High Step-Up Ratio
DC-DC Conversion", IEEE Trans on Industry Electronics, Vol, PP, No.
1, pp. PP-PP (2015)[15] Moonem, M.A, Krishnaswami, H: 「Analysis and Control of Multilevel Dual Active Bridge DC-DC Converter」, ECCE2012, pp. 15561561 (2012)[16] Moonem, M.A, Krishnaswami, H., Fang Zheng Peng: 「Control andConfiguration of Three-Level Dual-Active Bridge Converter as a Frontend Interface for Photovoltaic System」, APEC2014, pp. 3017-3020(2014)[17] Kheraluwala, M.N., Gascoigne, R.W., Divan, D.M., Baumann, E.D.:「Preformance Characterization of a High Power Dual Active Bridge
dc-to-dc Converter」, IEEE Trans. I.P., Vol. 28, No. 6, pp. 1294-1301(1992)