Zero Voltage Switching over Entire Load Range andWide Voltage Variation of Parallelly-Connected
Dual-Active-Bridge Converter using PowerCirculating Operation
Hayato Higa and Jun-ichi Itoh
Department of Electrical Engineering
Nagaoka University of Technology
Niigata, Japanhhiga@stn.nagaokaut.ac.jp, itoh@vos.nagaokaut.ac.jp
Abstract— This paper proposes a power-circulating
operation at light load operation for a parallelly-connecteddual-active-bridge (DAB) converter in order to achieve zerovoltage switching (ZVS) over entire load range and widebattery-voltage variation. At the light load, a power flow ofeach DAB converter is controlled in such a way that thetransferred power of each DAB converter satisfies thecondition for ZVS, i.e. the power-circulating operation.
Consequently, MOSFET with low voltage rating can beused due to no surge voltage in ZVS. At the heavy load, thepower-circulating operation is no longer required due to thehigh power flow of each DAB converter. The heavy load
efficiency is not only improved but also the light load is
operated without the recovery surge. From experimental
results, at 75% of the nominal voltage, the ZVS range is
extended by 380% compared to the ZVS range of only thesame power flow operation. Moreover, the converter
efficiency is over 95.6% from the rated power of 29% to therated power at the nominal voltage.
Keywords—Dual Active Bridge converter;
switching; Parallel connection;

I.

Zero

voltage

INTRODUCTION

Recently, energy storage systems have been actively
installed to electric vehicles and DC micro-grid systems [1]. A
bi-directional isolated DC-DC converter is used as the battery
conversion systems. Due to its flexibility, a dual active bridge(DAB) converter is generally applied in such systems [2-3]. The
DAB converter can obtain the high efficiency because zerovoltage switching (ZVS) is achieved without additional
components. ZVS not only reduces the turn-on loss but also
reduces the surge voltage which occurs in the recovery mode of
the body diode into MOSFET. As a result, the low voltage
rating of MOSFET can be selected. However, the ZVS range islimited when the voltage fluctuates widely [3]. Due to the hardswitching operation at the fluctuated voltage, the high voltage
rating of MOSFET which has high on-state resistance has to be
selected. Therefore, the converter efficiency at the heavy load
region is decreased due to the worse performance of the highvoltage rating of MOSFET. In addition, the error of the phaseshift angle occurs in the output voltage of the inverter which is
the hard switching operation due to the dead-time error [4]. In
the energy storage system, the DAB converter is operated inwide load range. Therefore, the extension of the ZVS range overentire load range is required with wide voltage range.
In order to extend ZVS range, the some modulation
schemes have been presented [5-8]. Pulse width modulation is
employed with the phase-shift control [5-6]. However, it is notalways possible to achieve ZVS for all switches by the widevoltage range because the direction of the inductor current
which discharges the junction capacitor cannot be controlled at
the light load. On the other hand, pulse frequency modulation
is applied depending on the voltage condition in order to keep
the operation point at the ZVS condition [7-8]. However, thevolume of the transformer becomes large because the volumeof the transformer is decided by the minimum switchingfrequency. In a difference approach, the coupling coefficient of
the transformer kc is designed to be low [9]. However, due tolarge magnetizing current, the converter efficiency at the heavy
load region decreases compared to that of the high coupling
coefficient (kc≥0.99).
In this paper, with the aiming for the extension of ZVS
range over wide battery-voltage variation, the powercirculating operation of a parallelly-connected DAB converter
is proposed. The original contribution in this paper is that thepower-circulating operation of each DAB converter is used inorder to achieve ZVS over entire load range and wide batteryvoltage variation. In particular, when the power-circulating
operation is active, the power flow of each DAB converter ischanged in such a way that ZVS for all DAB converters isachieved. In addition, the low voltage rating of MOSFET canbe selected because no surge voltage occurs in ZVS. This paper
is organized as follows; firstly, the circuit configuration and thepower-circulating operation are explained. Secondly, a flow
chart to determine the power flow and the output power isintroduced. Finally, the experiment is conducted in order toverify the ZVS operation at the light load with the variation of
the battery voltage.
II.

PROPOSED CIRCUIT

Fig. 1 shows the circuit configuration of the parallellyconnected DAB converter. By employing the parallel
connection to the DAB converter, the conduction loss and thecopper loss are reduced in compared to those when only one
DAB converter is applied. However, the ZVS range is limited
when the battery voltage fluctuates from the nominal voltage.
Fig. 2 shows the operation waveforms of each DAB
converter. The transferred power is controlled in bidirectional
direction by the phase angle between the high voltage (HV) side
inverter and the low voltage (LV) side inverter.
Fig. 3 shows the power flow diagrams of the parallellyconnected DAB converter corresponding to the output power.
Fig. 3(a) shows the parallel operation at heavy load where ZVS
is simply achieved due to the high power flowing through eachconverter. Fig. 3(b) shows the single operation in which, only
one DAB converter is operated under the ZVS condition of theeach individual DAB converter with the parallel operation. Fig.
3(c) shows the power-circulating operation applied at light load.
In the power-circulating operation, the power flow of each
DAB converter is changed in order to achieve ZVS. The
transferred power of each DAB converter P1 and P2 aredesigned to satisfy the condition for the ZVS achievement. It isnoted that only two DAB converters are operated at light load
because the transferred power P1 will have to be increased if thenumber of the active converters increases. In other words, atlight load, the No. 3~No. m DAB converter is inactive.
Fig. 4 shows the determination of the operation mode undercondition that ZVS is achieved over entire load range. The
operation mode is changed depending on the relationshipbetween the reference transferred power Pref and the lower limitof the transferred power for ZVS PZVS. The conditions based on
Pref and PZVS are explained as follows
 Condition1: Pref<PZVS Power-circulating operation
When the condition 1 is met, ZVS is not achieved in eachindividual DAB converter if each DAB converter flows thesame power in the same direction, i.e. the parallel operation or
the single operation. Therefore, the power-circulating operation
is used. In the power-circulating operation, the transferred
power of each DAB converter P1 and P2 are adjusted to be larger
than PZVS. As a result, the transferred power of each DAB
converter P1 and P2 are calculated by (1).

P1  Pref  PZVSP2   PZVS

(1) Condition 2: PZVS ≤ Pref <2PZVS Single operation
In this condition, ZVS is achieved if only one DAB converter
is active, i.e. the single operation. Therefore, only one DAB
converter is operated. The other is operated that zero voltage is
output in each inverter. In the single operation, the transferred
power of each DAB converter P1 and P2 are calculated by (2).

High voltage (HV) side

Cell No.1

Low voltage (LV) side

Cds_High
N=N1/N2
N1:N2

Vin

L

i1_pr

Vout

Cds_Lowv1_se

Lm v1_pr

Cell No.2
Cell No.m

Fig. 1. Circuit configuration of parrallelly-connected DAB converter.
The voltage of the HV side is 380V, whereas the voltage of the LV sidevaries from 36 V to 60 V.

d1
Vin/N
Vout

d1

v1_pr
v1_se

0

-Vout
-Vin/N

v1_se

t0

t

i_pr

i_pr

0

v1_pr

t

t 0

(a) Discharge operation(b) Charge operation
Fig. 2. Simplified waveforms of individually DAB converter The
transferred power is controlled in bidirectional direction by the phaseangle.

Pin

P1

Cell No.1 DAB
Charge operation

P2

Cell No.2 DAB
Charge operation

Pout(a) Parallel operation

Pin

P1

Cell No.1 DAB
Charge operation

Pout

Cell No.2 DAB
Not operate(b) Single operation

Pin

P1

Cell No.1 DAB
Charge operation
Cell No.2 DAB
Discharge operation

Pout

P2

(c) Power-circulating operation
Fig. 3. Power flow diagrams of parrallelly-connected DAB converter.
At heavy load where ZVS is simply achieved, the power flow of each
DAB converter is the same. At light load, the power flow of each DAB
converter is controlled in such a way that each DAB converter can stillachieve ZVS.

P1  Pref
P2  0(2)

 Condition 3: 2PZVS ≤Pref ≤ Prated Parallel operation
In the condition 3, ZVS is achieved in each individual DAB
converter. Therefore, the parallel operation is active. In theparallel operation, the transferred power of each DAB converter
P1 and P2 are calculated by (3).

P1  Pref / 2(3)

P2  Pref / 2

DERIVATION OPERATION MODE

This section introduces the flowchart, which derives thephase-shift angle of each DAB converter under the condition
that ZVS is achieved over entire load range. Firstly, the deadtime Td is calculated by (4) in the wide ZVS range [10].

Td 

2

LCds

 


2 Lm
Vin
 4f swTd 
1 2
2  2 Lm  N L NV o u t(5)At the condition of NVout<Vin, the phase-shift angle of lower limit
with ZVS condition dZVS is calculated by (6) excluding theparasitic capacitance [3].
  2 Lm  N 2 L NV ou t
 4  f swTd 
1 
2 
2 Lm
Vin


(6)

where  and  are coefficient which is decided by the power
flow. The coefficient is decided to be =1 =-1 in the charge
operation. On the other hand, the coefficient is decided to be =1 =1 in the discharge operation. It should be noted that leakage
inductance of the transformer is neglected when the phase-shift
angle is calculated because the additional inductor L is muchlarger than the leakage inductance of the high frequency
transformer. Then, the lower limit of the transferred power PZVS
is calculated by (7) using dZVS
PZVS 

Pref

P1
PZVS
P2


d ZVS VinVout
d ZVS 1 


NL




2PZVS

Prated Pref

(4)

Fig. 5 shows the flowchart for deriving the transferred
power of each DAB converter. If the parallel number is changed.
The number of the operated DAB converters is changed
depending on the reference of the transferred power. The ZVS
condition is decided by the inductor current and the exciting
current. In addition, the inductor current waveform is variedcorresponding to the relationship among the input voltage, theoutput voltage and the power flow. At the condition of
NVout>Vin the phase-shift angle of lower limit with ZVS
condition dZVS is calculated by (5) excluding the parasitic
capacitance [3].

d ZVS Condition 3
Parallel operation
2PZVS ≤Pref≤ Prated

2PZVS

PZVS



d ZVS Condition 2
Single operation
PZVS≤ Pref<2PZVS

PratedPref, P1 and P2

III.

Condition 1
Power-circulating
Operation
Pref<PZVS

PZVSFig. 4. Determination of operation mode depending on the referencetransferred power Pref in order to achieve ZVS over entire load range. In
the light load condition of Pref<PZVS, the power-circulating operation is
active. The single operation is applied at the condition of PZVS
≤Pref<2PZVS. In the heavy load of 2PZVS ≤Pref≤Prated, the parallel operation
is employed. At the condition of Pref<0, the power flows of P1 and P2 areswitched.

Start
Input parameter
Vin, Vout, N, fsw, L, Lm, Pref
Cal. of lower limit of the phase shift angle for ZVS
dZVS , Eq. (5),(6)Cal. of lower limit of the output power for ZVS
PZVS , Eq. (7)Selection of three operation modes
Calculation of the reference transferred power
P1，P2 Eq. (1),(2) or (3)Cal. of phase shift angle of each DAB converter
d1 ,d2 Eq.(8)End
Fig. 5. Flowchart for deriving of transferred power under the condition
that ZVS is achieved over entire load range
Table 1 Simlation condition(7)

where  is the switching angular frequency, N is transformer
turn ratio. From (7), the references of the transferred power of
each DAB converter Pref are compared with PZVS. The parallel
operation is active at the condition of Pref>2PZVS. In contrast, thepower-circulating operation is active at the condition ofPref<PZVS. Next, the references transferred power of each DAB

Input voltage Vin

380 V

Additional inductor L

2.19 µH

Output voltage Vout

36 V

Rated power

3 kW

Switching frequency fsw
Dead-time Td
Parallelly connected
numberParastic capacitance
Cds_high

50 kHz Magnetizing inductance Lm

3 mH

100 nsTurn ratio of transformer N

8

2

Battery voltage range

36V to 60V

200 pF

Parastic capacitance
Cds_Low

1200 pF

converter P1, P2 are calculated by (1), (2) or (3). Finally, thephase-shift angle d1, d2 are calculated by (8) [10].
d1 


2



2
4



NL
P1
VinVout

IV.

v1_pr

Vin
NVout

v1_se

-NVout
-Vin

(8)
v2_se

Vin
NVout

v2_pr

SIMULATION RESULTS-NVout-Vin

In this section, the simulation results are demonstrated inorder to evaluate the power-circulating operation. Table 1 shows
the simulation conditions. The parallel number of DAB
converter is two. It is noted that the output power which ZVS isachieved is 875 W from Eq. (5) and (6).
Fig. 6 shows the output voltage of each inverter v1_pr, v1_se,v2_pr, v2_se and the inductor current at the HV side i1_pr, i2_pr when
the power-circulating operation is active at the output power ofabout 205 W, i.e. the power which cannot achieve ZVS for eachindividual DAB converter. It is confirmed that the output powerof 205 W at light load can be generated by changing thetransferred power and the power flow of each DAB converter.
Fig. 7 shows waveforms of the gate signal and drain-source
voltage with the power-circulating operation and the parallel
operation. In Fig. 7(a), hard switching is confirmed because
MOSFET is turned on at the output voltage Vout. In Fig. 7(b),The ZVS operation is confirmed by the power-circulating
operation because MOSFET of each inverter are turned on at thezero voltage. Therefore, ZVS at light load is achieved by powercirculating operation.
Fig. 8 shows characteristics of the input power Pin and thereference transferred power Pref. The ZVS range is extended by
110% compared to the parallel operation. The ZVS achievement
not only reduces the switching loss but also eliminates the deadtime error of the phase-shift angle. Therefore, compared to whenusing only the parallel operation, the error between the input
power and the reference transferred power is reduced to 12 % byusing the power-circulating operation.
V.

EXPERIMENTAL RESULTS

Table 2 shows the experimental parameters. A 1.5 kW
prototype of two parallelly-connected DAB converter is tested
in order to confirm the validity of the power-circulating
operation. When the output voltage is 36 V, the lower limit oftransferred power for ZVS PZVS is 411 W with the single
operation. When the output voltage is 48 V, ZVS is achieved
over entire load range at the charge operation. Therefore, thepower-circulating operation is inactive at the nominal voltage. It
is noted that the additional inductor is connected in series to LVside of the high frequency transformer. In the LV-side inverterof MOSFET, IRFP4110PbF (Infenion) is selected.
IRFP4110PbF has the on-state resistance Ron =3.7 mΩ, thevoltage rating Vrate=100 V and the current rating Irate=120A. On
the other hand, SCT3030AL-E (Rohm) is selected at the HVside inverter. SCT3030AL-E has the on-state resistance Ron =30mΩ, the voltage rating Vrate=650 V and the current rating
Irate=70A.

No.1 DAB P1

Input power Pin

20ms

No.2 DAB P21080 W
205 W-875 W

Fig. 6. Operation waveforms with power-circulating operation. The
lower limit of the output power for ZVS condition is 875 W. The lightload operation is confirmed even with the power-circulating operation.
40

Drain-source voltage at LV side inverter (No. 2 DAB)

20
0

Hard switching
Gate signal at LV side inverter (No.2 DAB)1040Drain-source voltage at LV side inverter (No. 1 DAB)

20
0

Hard switching
Gate signal at LV side inverter (No. 1 DAB)

1

1 ms

0

(a)Parallel operation(Pout=380 W)
40

Drain-source voltage at LV side inverter (No. 2 DAB)

20
0
1

0
40
20
0
1

ZVS
Gate signal at LV side inverter (No.2 DAB)

Drain-source voltage at LV side inverter (No. 1 DAB)ZVSGate signal at LV side inverter (No. 1 DAB)

1 ms
0(b) Power-circulating operation (Pout =205 W)
Fig. 7. Waveforms of gate signal and drain-source voltage. With
applying the only parallel operation, ZVS is not achieved. Furthermore,
the recovery surge in MOSFET occurs. On the other hand, ZVS isachieved by using the power-circulating operation, which results in noturn-on loss.

Error between Pref and Pin [%]

60
60
60
50
50
50
40
40
40

Table 2 Experiment condition

ZVS range of power-circulating operation
Extended by 110%

ZVS range of only
parallel operation

10
10
10
00 0
00 0

380 V

Additional inductor L

2.03 µH

Output voltage Vout

36, 48 V

Rated power

1.5 kW

Switching frequency fsw 100 kHz Magnetizing inductance Lm

Only parallel operation

30
30
30

20
20
20

Input voltage Vin

Power-circulaitng operation
Reduced to12%

1.6 mH

Turn ratio of transformer N N1/N2=15/2

Dead-time at HV side

100 nsDead-time at LV side

150 ns Parallely connected number

Parastic capacitance
Cds_Low

100 pF

Parastic capacitance
Cds_Low

2
400 pF

Output voltage of high voltage side inverter (No.1 DAB ) 500 V/div

500
1000
1500
2000
2500
3000
500
500 1000
1000 1500
1500 2000
2000 2500
2500 3000
3000
Refference transferred power Pref [W]Fig. 8. Characteristics of reference transferred power and error
between input power Pin and reference transferred power Pref. The
ZVS range is exrtended by 110%. In addition, the error between Pin
and Pref is reduced to 12%.

Fig. 9 shows the operation waveforms with three operationsat 380 V of the input voltage and 36 V of the output voltage. Fig.
9 (a) shows that of the parallel operation at the output power of1048 W. Fig. 9 (b) shows that of the single operation at theoutput power of 542 W. Fig. 9 (c) shows that of the powercirculating operation at 235 W, i.e. the achievement of ZVS ineach individual DAB converter. In Fig. 9 (a), the parallel
operation is confirmed at the same power flow. As a result, theconduction loss and copper loss can be reduced in compared toonly single operation. In Fig. 9(b), the single operation is
confirmed because only one DAB converter is operated. On theother hand, the power-circulating operation is obtained because
the each individual DAB converter is difference power flow. In
three operations, the transferred power of the each individual
DAB converter P1 and P2 are over the lower limit of thetransferred power PZVS. By using the power-circulating
operation, the light load operation is not used in the eachindividual DAB converter. As a result, the ZVS is achieved overentire load range.
Fig. 10 shows operation waveforms of the gate signal andthe drain-source voltage with/without the power-circulating
operation. Fig. 10(a) shows that with parallel operation. Fig.
10(b) shows that with the power-circulating operation. In Fig.
10(a), the hard switching is confirmed that MOSFET is turnedon at the output voltage. Furthermore, the high voltage surge
occurs in MOSFET due to the recovery mode. In Fig. 10(b),ZVS is confirmed because MOSFET is turned on at the zerovoltage. Therefore, the high voltage rating of MOSFET is not
required because the recovery surge is avoided by the powercirculating operation. It is noted that the turn-off loss can be
reduced by connecting snubber capacitors in parallel to
MOSFET in order to delay the rise of the drain-source voltage
Fig.11 shows efficiency characteristics of two parallellyconnected DAB converter. Fig. 11(a) shows that when the
output voltage is 48 V and the input voltage is 380 V, i.e. thenominal voltage. Fig. 11(b) shows that when the output voltage
is 36 V and the input voltage is 380 V. In Fig. 11(a), the lightload efficiency is improved by using the single operation
because the iron loss is reduced by no operation of one DAB00
Output voltage of low voltage side inverter (No.1 DAB) 50 V/div
Inductor current of high voltage side (No.2 DAB) 5 A/div

0
0
Inductor current of high voltage side (No.1 DAB) 5 A/div

4 ms/div(a) Parallel operation at 1048 W
Output voltage of high voltage side inverter (No.1 DAB ) 500 V/div

00
Output voltage of low voltage side inverter (No.1 DAB) 50 V/div

0

Inductor current of high voltage side (No.2 DAB) 5 A/div

0
Inductor current of high voltage side (No.1 DAB) 5 A/div(b)

4 ms/div

Single operation at 542 W

Output voltage of high voltage side inverter (No.1 DAB ) 500 V/div

00
Output voltage of low voltage side inverter (No.1 DAB) 50 V/div
Inductor current of high voltage side (No.2 DAB) 5 A/div

0
0
Inductor current of high voltage side (No.1 DAB) 5 A/div

4 ms/div(c) Power-circulating operation at 235 W
Fig. 9. Operation waveforms for two parallelly-connected DAB converter.
Three operations are confirmed by changing the power flow of the eachindividual DAB converter. In the power-circulating operation, thetransferred power of the each individual DAB converter P1 and P2 are 805
W, 537 W, i.e. the ZVS achievement in the each individual DAB converter.

converter. Therefore, the converter efficiency is over 95.6%
from the rated power of 29% to the rated power by changing thepower flow of the each DAB converter depending on the output
power. In addition, the ZVS is achieved over entire load range.
In Fig. 11(b), the ZVS range is extended by 380% comparedwith only the parallel operation. In addition, the maximum
efficiency 96.2% is achieved. However, the light load efficiency
is low by the power-circulating operation because theconduction loss and copper loss is increased due to large thelower limit of the transferred power. In order to improve theconverter efficiency with the power-circulating operation, thedesign of the magnetizing inductance Lm and the additional
inductance L are important from (5), (6).

Upper arm drain-source voltage (No.1 DAB) 25 V/div

Hard switching0

Lower arm gate-source voltage (No.1 DAB) 25 V/div

0

0
Reduce recorvery surge

00Lower arm drain-source voltage (No.1 DAB) 25 V/div
400 ns/div
400 ns/div

Meiqin Mao, etc. "Accurate Output Power Control of Converters
for Microgrids Based on Local Measurement and Unified
Control", IEEJ Journal of Industry Applications, Vol. 4, No. 4,
pp.331-338, 2015.
[2] R. W. D. Doncker, etc. "A three-phase soft-switched high-powerdensity dc/dc converter for high-power applications", IEEE Transon Industry Applications, Vol, 27, No. 1, pp. 63-73, 1991.
[3] Kheraluwala M.N, etc :“Preformance Characterization of a HighPower Dual Active Bridge dc-to-dc Converter”, IEEE Trans. I.P.,
Vol. 28, No. 6, pp. 1294-1301, 1992.
[4] Biao Zhao, etc.: "Dead-Time Effect of the High-Frequency
Isolated Bidirectional Full-Bridge DC–DC Converter:
Comprehensive Theoretical Analysis and Experimental
Verification", IEEE Trans. PELS., Vol. 29, No. 4, pp. 1667-1680,
2014.
[5] Yoichi Ishizuka, etc, "Static Characteristic Analysis of Proposed
Bi-Directional Dual Active Bridge DC-DC Converter", IEEJ
Journal of Industry Applications, Vol.4,No. 5, pp.602-610, 2015.
[6] Florian Krismer, Johann W. Kolar: "Closed Form Solution for
Minimum Conduction Loss Modulation of DAB Converters",
IEEE Trans. PELS., Vol. 27, No. 1, pp. 174-188, 2012
[7] Xiao-Fei He, etc., "A Variable Switching Frequency Hybrid
Control for ZVS Dual Active Bridge Converters to Achieve High
Efficiency in Wide Load Range", APEC2014 , Vol. , No. , pp.
1095-1099, 2014
[8] Felix J and Jurgen B, "Generalized Modeling and Optimizationof a Bidirectional Dual Active Bridge DC-DC Converter
IncludingFrequency
Variation",
IEEJ
JournalofIndustryApplications, Vol.4, No.5, pp.593-601, 2015.
[9] J. Riedel, etc: "Wide Range ZVS Operation of Dual Active Bridge
DC-DC Converter using Adaptive Modulation and Low Coupling
Factor Transformers", EPE2016, 2016.
[10] Hirofumi Akagi, etc.:"Power-Loss Breakdown of a 750-V 100kW 20-kHz Bidirectional Isolated DC–DC Converter Using SiC-(a) Without circulating operation (b) With circulating operation
Fig. 10. Waveforms of gate signal and drain-source voltage at light load.
In Fig. (a), ZVS is not achieved when the power-circulating operation is
not applied, whereas ZVS is achieved if the power-circulating operation
is applied, which results in no turn-on loss. In addition, the turn-off loss
can be reduced by connecting a snubber capacitor parallel to MOSFET.
100
100
100

Highest-efficiency operation
Single operation
Parallel operation

95
9595 Maximum eff.
96.2%

Parallel operation

90
9090

Efficiency[%]
Efficiency[%]
Efficiency [%]REFERENCES

ZVS
0CONCLUSTIONThis paper proposed the power-circulating operation for theparallelly-connected DAB converter with the aiming ofachieving ZVS over entire load range and wide battery-voltage
variation. In the proposed method, the power flow and thetransferred power were changed depending on the output power
in order to operate all DAB converters at the ZVS condition. In
the experimental results, the ZVS range was extended by 380%
compared to that when using only parallel operation. At thenominal voltage, the converter efficiency is over 95.6% from
29% the rated power to the rated power by changing the power
flow of the each individual DAB converter. In the future work,
the design of the magnetic components will be consider in orderto achieve the high efficiency in wide load.

[1]

0

0

Single operation

85
8585

ZVS range
with single operation

80
8080

ZVS range
with parallel operation

75
7575

70
70700
00

300
300
300

600
900
1200
600
1200
600 power900
900
1200
Output[W]
OutputOutputpower
power[W][W](a) Vin=380 V, Vout=48 V (Nominal voltage)

100
100
100

Parallel operation is not operated
Recovery surge is over 90 V at LV side
(Withstand voltage of MOSFET. :100 V)

95
9595

Maximum eff.
96.0%

90
9090

Efficiency[%]
Efficiency[%]
Efficiency[%]VI.

Upper arm gate-source voltage (No.1 DAB) 25 V/div

Paralleloperation

Power-circulating
operation80
8080

ZVS range
with single operation

75
7575
70
7070

Single operation

Extended by 380%

85
8585

1500
1500
1500

ZVS range withpower-circulating operation

000

ZVS range
with parallel operation

200
200
200

400
600
800
1000 1200 1400
400 Output
600power[W]800 1000
1000 1200
1200 1400
1400
400
600
800
Outputpower[W]power[W]Output(b) Vin=380 V, Vout=36 V (75% nominal voltage)
Fig. 11. Efficiency characteristics of two parallelly-connected DAB
converter with fluctuation of output voltage. At the nominal voltage, thelight load efficiency is improved by the single operation compared with
only parallel operation. The maximum efficiency is 96.2% at 678 W. At
75% of the nominal voltage, ZVS range is extended by 380% comparedwith only parallel operation. In addition, the parallel operation at the lightload is not operated because the surge voltage in MOSFET is 90 V due tothe recovery mode.

MOSFET/SBD Dual Modules", IEEE Trans.IAS., Vol. 51, No. 1,
pp. 420-428, 2015