Light Load Efficiency Improvement of
Flying Capacitor-type Current-Fed DAB Converterfor 1500V DC-gridTakashi Ohno
Dept. of Science of Technology
Innovation
Nagaoka University of Technology
Nagaoka, Japans225058@stn.nagaokaut.ac.jp

Rintaro Kusui
Dept. of Science of Technology
Innovation
Nagaoka University of Technology
Nagaoka, Japankusui@stn.nagaokaut.ac.jp

Hiroki Watanabe
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Nagaoka, Japanhwatanabe@vos.nagaokaut.ac.jp

Jun-ichi Itoh
Dept. of Science of Technology
Innovation
Nagaoka University of Technology
Nagaoka, Japan
itoh@vos.nagaokaut.ac.jp
Abstract—This paper proposes a three-level current-fed dual
active bridge (DAB) converter to achieve a wide high-efficiency
range for DC voltage and load variation. The proposed control
provides zero voltage switching (ZVS) by triangular current
mode (TCM) under a wide DC voltage range. Additionally, thetransformer root mean square (RMS) current is drasticallyreduced compared with the conventional control because theDC-voltage ratio is regulated by voltage control to match withthe transformer turn ratio. Moreover, the proposed control
improves the light load efficiency using the full-bridge (FB) andthe half-bridge (HB) modes. The loss analysis results show thatthe proposed control reduces switching by 46%. The conduction
losses were reduced by 53%. The proposed three-level currentfed DAB converter achieves an efficiency of 93.5% or higher
over a wide voltage range from 160V to 320V. Finally, theexperimental results indicated that the total loss is reduced by
63% at 0.2p.u.
Keywords—Current-fed dual active bridge converter, Multilevel, Wide range, Zero voltage switching, Triangular current
mode, Medium voltage

I. INTRODUCTION
Recently, 1500-V DC grid systems connecting light railtransit (LRT), electric vehicles (EV), renewable energy
sources, and so on are attracting attention from around theworld for energy decarbonization policies [1][2]. In thesesystems, an isolated DC-DC converter has been widely
developed to interface the converter between the 1500-V DC
grid and energy sources or batteries [3][4]. A dual active
bridge (DAB) converter is one of the strong candidates
because there are attractive advantages, e.g., 1) galvanic
isolation capability, 2) zero voltage switching (ZVS)
operation for low switching losses, and 3) simple
configuration. However, the DAB converter has a narrowhigh-efficiency range due to the soft switching failure andincreasing circulating current under the DC voltage variation.
Additionally, the large ripple current may increase thesmoothing capacitor.
In[5]-[9], several modulation methods have been proposedto achieve ZVS, and current RMS reduction even when thevoltage ratio does not agree with the turn-ratio of thetransformer. The various modulation methods which are theexpanding ZVS range[5]-[7] or achieving minimumtransformer current RMS[8][9], have been proposed.
Specifically, extended-phase shift (EPS) control [5], dualphase shift (DPS) control [6], and triple-phase shift (TPS)
control [7] have been proposed as modulation method that
achieves ZVS over a wide range and minimum current RMS.
However, these methods require complicated calculation tofind the optimal combination of the switching frequency, thephase shift angle of individual legs, and the phase shift angleof each bridge. In ref [10][11], the DAB converter with themultilevel topology of the T-type and the neutral point clump(NPC) converters have been proposed to reduce thetransformer current. These circuits switch the voltage levels
applied to the transformer to reduce the transformer current
RMS. However, the T-type based three-level converter is notenough to achieve high withstand voltage. The NPC based
three-level converter has many additional components.
Additionally, these converters increase the volume of thesoothing capacitor because of the large ripple current.
By contrast, a current-fed DAB converter combined withan interleaved boost chopper with an H-bridge of the DAB has
been proposed to reduce transformer current [12]. The currentfed DAB converter controls the voltage ratio to agree with theturn ratio of the transformer by the boost capacitor voltage
control. For this reason, the current-fed DAB converter
achieves low RMS of the transformer current. The converter
is controlled by the triangular current mode (TCM), whichflows a small negative inductor current. Thereby, the currentfed DAB converter achieves ZVS for the lower-side switch of
the boost chopper. However, TCM is controlled at a variablefrequency to keep the negative current constant. Specifically,
the switching frequency increases for light load because theinductor current ripple needs to be reduced. Thus, the lightload efficiency is decreased due to the turn-off loss isincreased at light load.
This paper proposes the current-fed DAB converter withthe three-level flying capacitor (FC) converter to keep the highefficiency in load fluctuations and wide-range voltage
conditions. The originality of this paper is that the flying
capacitor type current-fed (FCCF) DAB converter reduces theswitching loss by the switching operation of full-bridge andhalf-bridge mode. This paper demonstrates the detailed of loss

analysis, and experimental result with a 12.8-kW prototype toprovide the effectiveness of the proposed control.

Secondary Side

II. CIRCUIT CONFIGURATION
Fig. 1 shows the configuration of a DAB converter with athree-level flying capacitor (FC DAB). This converter consists
a two-level inverter at the primary side and three-level flying
capacitor inverter at the secondary side. The FC DAB
converter is controlled by single phase shift modulation.
Fig. 2 shows the configuration of a current-fed DAB
converter with a three-level flying-capacitor and an H-bridge
integrated with the interleaved DC-DC converter. This
converter controls the boost capacitor voltage so that thevoltage ratio of the primary and the secondary sides to muchthe turn ratio of the transformer. This converter applies thetriangular current mode (TCM) for boost inductor current ofiLCA and iLCB in order to achieve ZVS in all switching of the
primary side. Additionally, the phase shift angle of interleaved
converter sets a 180-degree to significantly reduce the current
ripple of the DC power sources.
Fig. 3 shows the operation waveform of the FCCF DAB
converter. The conventional DAB converter sets the switching
duty at 0.5. In contrast, the FCCF DAB converter changes theswitching duty depending on the boost ratio. In addition, the
FCCF DAB converter operates a variable switching frequency
control to keep a constant negative current at TCM. However,the performance of the power device limits the switchingfrequency. In this paper, the frequency range is set from
10kHz to 30kHz. The relationship between switchingfrequency and input power is expressed asfS =Vin 2 D

LC ( Pin − 2Vin Ibot )**(10kHz  f S  30kHz )(1),

where Vin is the input voltage, LC is the boost inductor, Pin* isthe command of the input power, Ibot* is the command of theboost inductor current bottom value, and D is defined asV
D = 1 − in
VC

(2),

where VC is the boost capacitor voltage.
III. OPERATION MODE AND ANALYSIS
A. Full Bridge (FB) ModeIn Fig. 3, the switching pattern in the full bridge (FB) mode
for the FCCF DAB converter is shown. The triangle carrier forQ2 is the base carrier. The triangle carrier for Q4 shifted by 180
degrees with the base carrier. The switching timing of Q5 havea  phase shift with the base carrier. The switching timing of
Q9 have a  phase shift with the Q4 carrier. According to Fig.
3, the switching devices of Q9 and Q10 are synchronizedswitching in the upper arm. Similarly, the switching devicesof Q11 and Q12 are synchronized switching in the lower arm.
As a result, a three-level waveform with an amplitude equal tothe peak value of the grid voltage (1500V) is applied to thetransformer during FB mode. Thus, the voltage of the primary
boost capacitor is set to 800V due to the winding turn ratio of
8:15 . The power transmission in the FB mode is expressed as

PTr =

1 2
vPr i ( ) iTr ( ) d
2 0

Q5

Primary Side

(3),

Q3

Q1

Q6
iTr N=n1/n2
LDAB
vTr

vPri

Vin

Q4

Q2

Q9
Q10
VfcA

VfcB

vSec

Q7

Q11

Q8

Q12

Vgrid

Figure 1. Conventional DAB converter with three-level
flying capacitor (FC DAB)
Secondary Side

Q5

Primary Side

Q3
Q1
iLCA
LCA
iLCB

Q6
VC
iTr N=n1/n2
LDAB
vTr

vPri

LCB
Q2

Q4

Vin

Q9
Q10
VfcA

VfcB

vSec

Q7

Q11

Q8

Q12

Vgrid

Figure 2. Proposed current-fed DAB converter with threelevel flying capacitor (FCCF-DAB); Vin from 160V to
320V, Vgrid 1500V, rated power 12.8kW.
Q1,Q2

ON

Q3,Q4

OFF

Switching duty : D
ON

ON

OFF

ON

Q5,Q8

ON

OFF

Q6,Q7

ON

OFF

Q9,Q12

OFFON

Q10,Q11OFFON

NVgrid0-NVgrid
Vgrid
0-Vgrid
0
0



vPri
vSec
iTr
iLCA
iLCB

Triangular Current Mode
I1

t0

I2

t1

I3

t2

I4

t3

I5

t4

I6

t5

I7

t6

I8

t7

t8

Figure 3. Key waveform of the FCCF DAB converter in thefull bridge mode.
where PTr is the transmission power, vPri is the output voltageof the primary H-bridge, and iTr is the transformer current of
the primary side. The phase shift angle is expressed from (3)
as

=



2
VC − Vin −VC(VC − Vin ) − P* f S LDAB
2



(4).

Note that (4) is valid when D < 0.5. Furthermore, when thephase shift angle is larger than (1-2D), it is expressed as=V − ( −8D + 8D − 1)V − 8P f L 
2V 



2

C

2

C

*

S

DAB

(5).

C

Table 1 shows the switching condition in the FB mode.
According to the table 1, the primary devices of Q1 to Q4 areachieved ZVS by the TCM. However, the secondary high-side
devices of Q5, Q6, Q9, and Q10 does not achieved ZVS because
the transformer current is zero at the switching timing. Notethat the switching condition of the table 1 is valid for the
power flow from the primary to the secondary sides. Thus, thelower side devices of Q7, Q8, Q11, and Q12 does not achieved
ZVS when the power flow from the secondary to the primarysides.
B. Half Bridge (HB) Mode
Fig. 4 shows the key waveform of the FCCF DAB
converter in the HB mode. The HB mode outputs the flying
capacitor voltage of 750V. Thus, the voltage of the primaryside boost capacitor is set to 400V in order to the voltage ratio
to agree with the turn ratio of the transformer. In the HB mode,the switching patterns for discharging and charging arealternated to keep constant the flying capacitor voltage.
Table 2 shows the switching condition in the HB mode.
The primary side devices of Q1 to Q4 are achieved ZVS by the
TCM as in the FB mode. However, the HB mode does notachieved ZVS for the switching devices of Q5, Q6, Q9, and Q10.
The turn-on losses are only occurred by the energy charged
into the output capacitance because the device current is zero.
C. Control block diagram of the FCCF DAB converter
Fig.5 shows the control block diagram of the FCCF DAB
converter. The primary side of the FCCF DAB converter
consists of the boost inductor current controller on the inner
loop and the boost capacitor voltage controller on the outerloop. The boost capacitor command is switched by theoperating mode to the FB mode of 800V and the HB mode of
400V. The voltage PI controller sends a command of the boost
inductor current. The boost inductor current for both iLCA andiLCB are controlled with each current controller. The voltage
command is calculated by the feedforward (Vc-Vin) from theoutput of the current PI controller. Furthermore, the switching
duty D is calculated by normalizing the voltage commandwith boost capacitor voltage VC. The secondary side of the
FCCF DAB converter is used for the switching duty
calculated on the primary side. The carrier frequency is
calculated by the power command value into (1). The
calculated switching frequency and power command are usedin (4) to calculate the phase shift angle.
D. Loss Analysis with the FC DAB and the FCCF DAB
converters
Table 3 shows the loss analysis and the experimental
parameters in order to compare to the flying capacitor-type(FC) three-level DAB converter of conventional circuit andthe FCCF DAB converter. The input voltage is 160V to 320V
and the dc grid voltage is 1500V. The rated power is 12.8-kW
with a maximum input current limited to 40A because it isdesigned for the battery applications. The switchingfrequencies are designed to agree with the switching

Table 1. the switching condition in the FB mode
timing

iLCA

iLCB

iTr

Turn ont0

positive-zero

Q1 : ZVS

t1--

positive

Q11 , Q12 : ZVS

t2

negative-

positive

Q2 : ZVS

t3

-

-

zero

Q9, Q10 : Non-ZVS

t4-

positivezero

Q3 : ZVS

t5--

negative

Q7, Q8 : ZVS

t6-

negative

negative

Q4 : ZVS

t7

-

-

zero

Q5, Q6 : Non-ZVS

Switching duty : D
Q1,Q2

OFF

ON

OFF

ON

Q3,Q4

ON

OFF

ON

OFF

ON

Q5,Q8

ON

OFF

ON

Q6,Q7

OFF

ON

OFF

Q9,Q12

OFFON

Q10,Q11

ON

OFF

NVgrid/2 vPri0
-NVgrid/2
Vgrid/2 vSec
0
-Vgrid/2



iTr

0

iLCA
i
0 LCB

I1

I2

I3

I4

I5

I6

I7

I8

I9 I10 I11 I12 I13 I14 I15 I16

t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 t13 t14 t15 t16

Figure 4. Key waveform of the FCCF DAB converter in thehalf bridge mode.
Table 2. the switching condition in the HB mode
timing

iLCA

iLCB

iTr

Turn ont0

positive-zero

Q1 : ZVS

t1--

positive

Q12 : ZVS

t2

negative-

positive

Q2 : ZVS

t3

-

-

zero

Q10 : Non ZVS

t4-

positivezero

Q3 : ZVS

t5--

negative

Q8 : ZVS

t6-

negative

negative

Q4 : ZVS

t7

-

-

zero

Q6 : Non ZVS

t8

positive-zero

Q1 : ZVS

t9--

positive

Q11 : ZVS

t10

negative-

positive

Q2 : ZVS

t11

-

-

zero

Q9 : Non ZVS

t12-

positivezero

Q3 : ZVS

t13

-

-

negative

Q7 : ZVS

t14-

negative

negative

Q4 : ZVS

t15

-

-

zero

Q5 : Non ZVS

frequency at rated power between the FCCF DAB and the FC
DAB. The sum of the inductance which is connected in series
with the transformer is 68.5uH. The transformer winding turnratios are designed to agree with the nominal voltage between
the FCCF DAB and the FC DAB. In addition, the FCCF andthe FC DAB transformers are designed to match the maximum
magnetic flux amplitude at rated condition. The switching
device of the FCCF DAB converter and the FC DAB
converter is the hybrid SiC modules (IGBT + SiC SBD:
CMH150DY-24NFH, MITSUBISHI ELECTRIC).
Fig. 6 shows the converter loss comparison of the FCCF
DAB and FC DAB converters at the input voltage of 320V.
The turn-on switching losses become zero at achieving an
ideal ZVS condition because the energy of the output
capacitance of the IGBT is regenerated to the power supply or
sent to the load. However, the other switching losses occur
such as the loss caused by a tail current. The output power of
1.0p.u. is out of the operating range in the HB mode under the
rated power condition. For this reason, only the FB mode iscompared at the rated power operation. From Fig. 6, the FCCF
DAB converter has lower secondary side switching losses
than the FC DAB converter because the FCCF DAB converter
reduces the switching device current at turn-off. Similarly, the
FCCF DAB converter has lower condition loss at the rated
operating point by reduction of the RMS value of thetransformer current.

Q2, Q1VC
Q4, Q3PI
ICLB*

Eq.(1)

P

fS*

1
0
1
0
Carrier(180-deg. shifted)

Q5, Q8

Phase
Phase
Phase
Phase
shift
shift
shift
shift

Eq.(4)

Q6, Q7
Q9, Q12

Q10, Q11

Figure 5. Control block diagram of the FCCF DAB
converter.
Table 3. Loss analysis and experimental parameters

A. Comparison of the FB and HB modes waveform
Fig. 7 shows the operation waveforms of the FCCF DAB
converter with the FB and the HB modes at discharging
operation. Fig.7 shows the primary H-bridge voltage vPri, thesecondary H-bridge voltage vSec, the primary transformer
current iTr and the boost inductor current iLCA and iLCB. Fig 7(a),(c) and (e) show the FB mode waveforms for the input voltage
Vin = 160V, Vin = 240V and Vin = 320V, respectively. Fig. 7(b),(d) and (f) show the HB mode waveforms. The input current
Iin is the same at 0.5 p.u. (20A). In Fig. 7(a), (c) and (e), theamplitude of the primary-side H-bridge voltage is 800V. The
secondary-side transformer voltage is the grid voltage(1500V), as in Fig. 3. In Fig. 7(b), (d) and (f), the amplitudeof the primary-side H-bridge voltage is 400V. The secondaryside transformer voltage is half of the dc grid voltage (750V).
The input current Iin is the same at 0.5p.u. (20A).

According to fig. 3 and fig. 4, all devices of the FCCF
DAB converter are achieved ZVS on the primary side. The
experimental results of fig. 7(a), (b) and (c) show no surge
voltage at the switching timing of the primary H-bridge.
However, the secondary upper arm devices of the FCCF DAB
converter are not achieved ZVS. Therefore, the secondary side
voltage of fig. 7(a), (b) and (c) occurs a surge voltage.
Similarly, the primary devices of the HB mode are achieved
ZVS. In contrast, the secondary upper arm devices are notachieved ZVS. Thus, there is occurred the surge voltage, as
shown in fig. 7(d), (e) and (f).

D

PI
ICLA VC -Vin

VC

IV. EXPERIMENTAL RESULT

Value

Element

SymbolRated power

Prated

12.8kW@Vin=320V

Rated current

Irated40A

Switching frequency

fs

Input voltage

VinDC-grid voltage

Vgrid

FCCF DABFC DAB

10-30kHz

15kHz

160-320V
1500V(HB) 400V−

Boost capacitor voltage

VC(FB) 800V−

Boost inductor

LC

270mH

−

External inductor

LEX

45mH

64.5mH

Leakage InductorLl

23.5mH

4.0mH

Magnetizing Inductance

LMg

48mH

2.6mH

0.532

Turn ratioN

Dead-timeTd

1ms

Hybrid-SiC Modules−

CMH150DY-24NFH

400

Switching device losses[W]The switching duty of the FCCF DAB converter is decided
by the relationship between the input voltage and the boost
voltage. Specifically, the voltage ratio agrees with the turnratio by the boost operation of the primary side. Therefore, theswitching duty of the FCCF DAB converter is varied from 0.2
to 0.8. In addition, the boost inductor current is controlled bya variable switching frequency for the TCM operation. In Fig.
7(a) and (d), the switching frequency is reduced by the HB
mode from 18.2kHz to 13.7kHz. In Fig. 7(b) and (e), theswitching frequency is reduced from 23.9kHz to 13.7kHz. In
Fig. 7(c) and (f), the switching frequency is reduced from
27.4kHz to 10kHz at 0.5p.u.

IC*

PI

VC*

300

0.2p.u.
Conduction
loss

600
500
400

200
100

700

300

-46%

0

Proposed

200

100
Turn off loss
+Recovery loss 0

0.26

Sec. Diodeconduction loss
Pri. Diodeconduction loss
Sec. IGBT
conduction loss
-53% Pri. IGBT
conduction loss
Sec. Diode
recovery loss
Pri. Diode
recovery loss
Sec. IGBT
switching loss
Pri. IGBT
switching loss

1p.u.

Conventional

Figure 6. The converter loss comparison of the FCCF DAB
and FC DAB converters at input voltage of 320V
B. Efficiency characteristics
Fig. 8 shows the efficiency characteristics of the 12.8-kW
prototype. Fig. 8 indicates the input voltage characteristics at
rated input current of 40A. The proposed control achieves ahigh-efficiency operation of up to 93.5% under the wide range
voltage condition from 160V to 320V and the rated current

800V

18.2kHzvpri 1[kV/div]

400V

0

13.7kHz0

vsec 2[kV/div]
1.5kV
Non-ZVS0
iTR 10[A/div]

750V
0

0

0

vpri 500[V/div]

vsec 1[kV/div]
Non-ZVS

iTR 20[A/div]0

iLCA 20[A/div]
iLCB 20[A/div]

6.1Arms0

iLCA 20[A/div]
iLCB 20[A/div]

8.9Arms

20[µsec/div]

30[µsec/div](a) FB mode : Vin = 160V(b) HB mode : Vin = 160V

vpri 1[kV/div] 23.9kHz

800V

400V

0

1.5kV
0

13.7kHz0
vsec 2[kV/div]

750V

Non-ZVS0

iTR 10[A/div]00vpri 500[V/div]

vsec 1[kV/div]

Non-ZVS
iTR 20[A/div]0

iLCA 20[A/div]
iLCB 20[A/div]

7.5Arms0

iLCA 20[A/div]
iLCB 20[A/div]

12.9Arms

10[µsec/div]

20[µsec/div](c) FB mode : Vin = 240V
vpri 1[kV/div]

800V

27.4kHzvpri 500[V/div]

400V

0

1.5kV
0

10kHz

0
vsec 2[kV/div]

750V

Non-ZVS0

iTR 10[A/div]00(d) HB mode : Vin = 240V

vsec 1[kV/div]
Non-ZVS
iTR 40[A/div]0

iLCA 20[A/div]
iLCB 20[A/div]

8.6Arms

010[µsec/div]

iLCA 20[A/div]
iLCB 20[A/div]

25.2Arms
30[µsec/div](e) FB mode : Vin = 320V(f) HB mode : Vin = 320V
Figure 7. operation waveform of the FCCF DAB converter
condition. In contrast, the conventional circuit of the FC DAB
converter has low efficiency compared to the FCCF DAB
converter. The main factor is that the FCDAB converter
operates under the condition where the transformer turn ratio
and voltage ratio did not match. As a result, particularly under
the low voltage conditions, there is an increase in the RMS
value of the transformer current leading to reduced efficiency.
Fig. 9 shows the efficiency characteristics of the output
power characteristics at an input voltage of 160V, 240V and
320V conditions. Fig. 9(a) shows the efficiency characteristicsof the proposed circuit and the conventional circuit in the FB
and the HB modes at input voltage of 160V. The HB mode of
the FCCF DAB converter shows the highest efficiency acrossnearly all operation points. Similarly, the HB mode of the FC
DAB
convertershows
relatively
high-efficiency
characteristics. However, it experiences a sharp dropped inefficiency around 0.5 p.u. The reason for this is that the phaseshift angles on both the primary and the secondary sides haveincreased. As a result, the reactive power is increased due tothe transformer current is increased. Furthermore, theconverter efficiency of FB mode is significantly reduced due

to a deviation from a voltage ratio of 1.0. The converter occursof increasing transformer current RMS and hard switching.
Fig. 9(b) shows the efficiency characteristics at an input
voltage of 240V. The efficiency characteristics in the FB
mode of the FC DAB converter and the FCCF DAB converter
are nearly the same. However, in the HB mode, the FC DAB
converter shows higher efficiency under very light loadconditions, but the efficiency of the FCCF DAB converter
becomes higher at a rated current exceeding 0.6p.u. The
reason for the high efficiency of the FC DAB converter is thefavorable input-to-output voltage ratio. However, the FCCF
DAB converter keeps high efficiency even under high loadconditions because the voltage ratio matches completely.
Fig. 9(c) shows the efficiency characteristics at an input
voltage of 320V. The HB mode of the FCCF DAB converter
improved light load efficiency because the HB mode operates
at a lower switching frequency compared to the FB mode to
reduce turn-off losses. As a result, the loss is reduced by 63%
from the FB mode to the HB mode at 0.2p.u. condition.
However, the FC DAB converter achieved higher efficiency
compared to the FCCF DAB converter at almost all of theHB mode (FCCF DAB)FB mode (FCCF DAB)

100

94

94.9%

92

93.7%
FCCF DAB converter

90
88

FC DAB converter
160

200

240

Input voltage Vin[V]

280

320

operating points. One of the reason is that the operating
frequency of the FC DAB converter differs from the FCCF
DAB converter by up to twice. Thus, it is supposed that theefficiency of the FCCF DAB converter decreases because of
the increased switching losses during turn-off.

80

[3]

[4]

[5]

[6]

[7]

[8]

1.6

3.2

4.8

6.4

(a) Vin = 160V
FCCF DAB with HB mode
FCCF DAB with FB mode
FC with HB mode
94.9%
FC with FB mode

100

94.4%

Efficiency [%]

95

95.6%

90

92.7%

85

80

0

2.4

4.8

7.2

9.6

Output Power [kW](b) Vin = 240V
FCCF DAB with HB mode
FCCF DAB with FB mode
94.9% 94.5%
FC with HB mode
FC with FB mode

100

95

Efficiency [%][2]0

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88.9%

Converter loss was
reduced by 80%

85

V. CONCLUSIONSThis paper proposed a three-level flying capacitor currentfed
DAB
converterfor
mediumvoltageapplications(1500Vdc). The loss analysis results show that the
HB mode of the FCCF DAB converter reduces the loss by
3.8% compared to the FC DAB with the HB mode of theconventional method at 0.2p.u. and the FB mode reduces theloss by 36.4% at 1.0p.u. Additionally, the experiment results
show that the losses are reduced by 63% under the input
voltage condition of 320V and the output power condition of
0.2p.u. Also, the FCCF DAB converter is achieved anefficiency of up to 93.5% under voltage variations from 160V
to 320V and rated input current conditions. In future work,
clarification of the switching point between the FB and the HB
modes will be conducted.

93.9%

90

Figure 8. Efficiency characteristics of the voltage
fluctuations at rated input current of 40A[1]

FCCF DAB with HB mode
FCCF DAB with FB mode
FC with HB mode
94.4%
FC with FB mode95

Efficiency [%]Efficiency [%]

96

94.7%

90

Converter loss was
reduced by 63%

85

80

0

3.2

6.4

9.6

12.8

Output Power [kW](c) Vin = 320V
Figure 9. Efficiency characteristics of the output power
at input voltage of 160V, 240V and 320V conditions.
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