Battery Management System with Flying Capacitor
Converter Operated in Discontinuous Current Mode
Taisuke Shioi, Mitsuru Miyashita, Satoshi Nagai,
Keisuke Kusaka, Jun-ichi Itoh
Dept. of Electrical, Electronics and Information Engineering
Nagaoka University of Technology
Niigata, Japanshioi@stn.nagaokaut.ac.jp, miyashita@stn.nagaokaut.ac.jp
satoshi_nagai@stn.nagaokaut.ac.jp,
kusaka@vos.nagaokaut.ac.jp, itoh@vos.nagaokaut.ac.jp

Toshiki Nakanishi, Kazuhiro Kobayashi
Dept. of system development
San-Eisha, Ltd.
Tokyo, Japannakanishi-toshiki@san-eisha.co.jp,
kobayashi-kazuhiro@san-eisha.co.jp

Abstract— This paper proposes a novel battery management
system (BMS) based on a three-level flying-capacitor three-port
converter operated in discontinuous current mode (DCM). In
BMS, the reduction of the inductor volume is required in a DCDC converter. In particular, the proposed three-port converter
contributes to the reduction of the inductor volume by sharing
the inductor for the power conversion among solar cells, battery
and DC-link. In addition, DCM is applied to further minimize
the inductor volume. The validity of the proposed three-port
converter and the inductor design for DCM operation isdemonstrated with a 750-W prototype. In particular, it was
mentioned that the prototype circuit achieves DCM in all
operation modes. Furthermore, the inductor volume with DCM
is reduced by 53 % compare to that with CCM.

problem of this circuit is that it cannot convert power between
two DC input ports. Therefore, this multi-port converter isinapplicable to BMS which requires the energy charge to thebattery from PV is required. Thus, it is required to reduce theinductor volume by decreasing inductance and number of
inductors, while realizing the bidirectional power conversion
between battery and PV.

Keywords—Multi-port converter, Discontinuous current mode,
DC-DC converter

I. INTRODUCTION
Recently, photovoltaics (PV) system has been actively
applied to emergency power supply system to generate
electricity during disaster [1]. However, generated electric
power by PV system fluctuates due to the weather conditions.
In order to absorb generated electric power fluctuation,
auxiliary energy storage systems using batteries or doublelayer capacitors are typically employed [2]-[3]. Therefore,
battery management system (BMS) is required to control thepower flow between the PV, the energy storage system, andan AC output side. In principle, BMS operated as DC-DC
conversion which has two DC input ports and one DC output
port. The DC input port is connected to PV panel and batteries,
the DC output port is connected to single-phase inverter.
Conventional emergency power supply systems, which isconsist of a single-phase inverter and two DC-DC converters
operating as PCS for PV and BMS, is introduced in [4]. The
conventional BMS results in a large volume due to two boost
inductors in the DC-DC converters. The Reduction of thenumber of inductors is required in order to minimize thecircuit volume. Hence, multi-port converters have been
actively researched to reduce the circuit volume [5-8]. In
ref.[6], the multi-port converter achieves the bidirectional
power flow between two DC input ports by using only one
converter. However, two inductors are still necessary for two
input ports. In ref.[7], the bidirectional operation is achievedby two inductors. Furthermore, this multi-port converter
might not be achieved the reduction of inductor volume
because these multi-port converter requires large inductancedue to the operation of Continuous Current Mode (CCM). In
ref.[8], reduction of the number of inductors is achieved byconnecting each DC input port in series. However, the

XXX-X-XXXX-XXXX-X/XX/$XX.00 ©20XX IEEE

This paper proposes a novel multi-port converter based on
the Flying Capacitor Converter (FCC) [9] topology to reduceof inductor volume. The battery is connected to the low
voltage port of FCC and PV is replaced with the flying
capacitor in the proposed three-port converter. The circuit
volume is reduced because the power conversion between PV
and battery uses only one inductor. In addition, Discontinuous
Current Mode (DCM) [10-11] is applied to further reduce
inductance. Moreover, the power conversion from PV to DClink without battery is also achieved by time-sharing
technique. The originality of this paper is that 1) FCC is usedas three-port converter, 2) the DCM operation is employedwith the FCC topology to achieve the bidirectional power flow
among PV, the battery and the DC-link while using only one
inductor.
This paper is organized as follows; first, the descriptionsof the circuit configuration and the circuit operation are
introduced. Secondly, the design method of the inductor tooperate the DCM is derived. In addition, the inductor volume
comparison between DCM and CCM is discussed. Finally, theoperation of the three-port converter is demonstrated with a
750-W prototype. It is mentioned that the three-port converter
achieves each mode operation and DCM control. Furthermore,
it is also obtained that the inductor volume is reduced by 53 %with DCM compare to CCM.
II. CIRCUIT CONFIGURATION AND OPERATION MODE
A. Configuration of conventional circuit
Fig. 1 shows a conventional emergency power supply
system. The conventional system is composed by a singlephase inverter and two DC-DC converters operating as BMS
and PCS for PV. A large volume is required in theconventional system due to two boost inductors in the DC-DC
converters. Both the number of inductors and the inductancevalue should be reduced to minimize the inductor volume.
B. Configuration of proposed three-port converter
Fig. 2 shows the configuration of the proposed three-port
based on three-level FCC. The battery is connected to the FCC
low voltage port and the PV is connected to the flying
capacitor nodes. The circuit volume is reduced because there

III. CONTROL METHOD AND INDUCTOR DESIGN
Proposed three-port converter applies the DCM operation.
In this section, the duty ratio calculation is explained. In

PV

vAC

V
t

Fig. 1. Conventional battery management system using two chopper.
BMS
S1
S2
L
Battery

VBat

VPV
S3

+
-

VDC

V
vAC

t

S4

Fig. 2. Proposed three-port converter circuit based on three-level FCC.
S1

S1

iL S
2
L
Battery
S
Vbat

iL S
2
VPV

3

V
PVDC

L
Vbat

S4

S3

V
VPV VACVDC
Inverter1) Mode I(Fig.3(a)): The power flow of Mode Ⅰ is fromthe battery to DC-link. In this mode, the three-port converter
operates as the boost converter. The current flows througheither the two series MOSFETs or two series body diodes
depending on the switching modes: synchronous switching
operation or asynchronous switching operation. Note that thismode achieves biderectional operation.
2) Mode II(Fig.3(b)): The power flow of Mode Ⅱ is fromthe battery and PV to DC-link. In this mode, the three-port
converter operates as the FCC discharging the flying
capacitor. That is the power is sending from PV to DC-link.
Similarly, the current flows through either the switches S1 by
the synchronous switching operation or the asynchronous
switching operaion with body diode.
3) Mode III(Fig.3(c)): The power flow of Mode Ⅲ isfrom PV to the battery. In this mode, the three-port converter
operates as the buck converter. Similarly, the current flows
through either the switches S3 and S4 by the synchronous
switching operation or the asynchronous switching operaion
with body diode4) Mode IV(combination of Mode II and Mode III): The
power flow of Mode IV is from PV to DC-link, combining
Mode Ⅱ and Mode Ⅲ. First, the power from PV is
temporarily transferred to the battery by Mode Ⅲ. Next, thispower outputs to DC-link through Mode II. Thus, the direct
power flow from PV to DC-link is achived by the
combination of Mode II and Mode III. Note that the battery
does not charge or discharge in Mode IVbecause the energy
from PV is temporarily stored in the filter capacitor which isconnected in parallel to the battery. In practical, the power
flows from PV to DC-link and charge battery from PV are
also achieved by the current ratio of Mode II and the Mode
III in Mode IV.
Table I lists the switching pattern and the power flow ofeach mode. Note that the asynchronous switching operation is
employed to evaluate the basic operation. In Table I, ON
describes the on-state of the switch, whereas OFF describes
the off-state of the switch, and Duty describes the switching
operation with duty ratio of the switch. In addition, S1 isemployed by either a switch or a diode because switch S1 isalways OFF in Table. I.

Battery

InverterC. Operation modes of proposed three-port converter
Fig. 3 shows each operation modes of the three-port
converter. The three-port converter has four operation modes
according to the power flow.

BMS

Inverteris only one inductor in this system. Furthermore, the numberof switching devices does not increase compared to theconventional circuit shown in Fig. 1. The proposed three-port
converter uses the switching devices which the voltage ratingis half of those in the typical boost converter because of theseries connection of four switches. The volume of the inductor
is further reduced due to the low inductance of the boost
inductor with the DCM application. Note that the proposed
three-port converter achieves zero current switching(ZCS)
because the inductor current falls to zero before turning ON in
DCM.

t

S4

(i) Fig.1. Conventional circuit.
(ii)(a) Mode Ⅰ : power flow From battery to DC-link.
S1

S1
iL S
2
L

iL S
2
VPV

S3

Vbat

VDC

L
Vbat

S4

S3

VPV

VDC

S4

(i)
(ii)
(b) Mode Ⅱ : power flow From battery and PV to DC-link.

S1

S1

iL S
2

iL S
2
L
Vbat

S3

VPV

VDC

L
Vbat

S4

S3

VPV

VDC

S4

(i)
(ii)
(c) Mode Ⅲ : power flow From PV to the battery.
Fig. 3. Operation modes of the three-port converter. The power flowfrom PV to DC-link (Mode IV) is achieved combining Mode II and III.
Table. I. Switching pattern in each modes.
S1

S2

S3

S4

Power flow

Mode I

OFF

OFF

ON

Duty

Battery → DC link

Mode II

OFF

OFF

Duty

Duty PV+Battery → DC link

Mode III

OFF

Duty

OFF

ON

OFF

OFF

Duty

Duty

OFF

Duty

OFF

ON

Mode IV

DC link → Battery
PV → DC link

addition, the inductor volume calculation is mentioned toclarify the validity of the proposed circuit. Finally, the control
diagram of the three-port converter is introduced.

A. Derivation of duty ratio
Fig. 4 shows the inductor current waveform in DCM
including zero-current interval. In this section, the duty ratio
is obtained from the average inductor current iLave, inductor
peak current ipk, battery voltage Vbat, PV voltage VPV, and DClink voltage VDC.
1) Duty ratio of Mode I: In Mode I, the interval D1_m1Tsw
is for Mode I(i) in Fig. 3(a), whereas the interval D2_m1Tsw isMode Ⅰ(ii) in Fig. 3(a). The duty ratio D1 is calculated fromaverage inductor current ILave. Circuit equation in Mode I(i)and Mode I(ii) are represented asdiV Vbat  L L
 L _ D1_ m1
dt
(1)

diL
V

V

V

L
L _ D 2 _ m1
DC
bat

dt

where iL is the inductor current, Vbat is the battery voltage, and
VDC is the DC-link voltage. Then, the inductor peak current Ipk
is given by (2) from (1).
Vbat
 I pk  L D1_ m1Tsw I  VDC  Vbat D T
2 _ m1 sw
 pk
L

(2)

where Tsw is the switching period, D1_m1 is the duty ratio during
the inductor charge period, and D2_m1 is the duty ratio during
the inductor discharge period. The average inductor current
iLave is obtained by averaging the inductor current during theswitching period. The average inductor current is calculatedby the inductor peak current Ipk, the duty ratio D1_m1, D2_m1,
and the switching period Tsw in Fig. 4. The average inductor
current is given by (3)I Lave 1
I pk  ( D1_ m1  D2 _ m 2 )2(3)

The duty ratio D1_m1 of the inductor energy charge intervalin Mode I is calculated from on (2) and (3). The duty ratio
D1_m1 is given by (4).

D1_ m1 

2 LI Lave VDC  Vbat
TswVbat
VDC(4)

The duty ratio D2_m1 of the inductor energy dischargeinterval in Mode I is calculated from (2) and (3).The duty ratio
D2_m1 is given by (5).

D2 _ m1 

2 LI Lave
Vbat
TswVDC VDC  Vbat

(5)

Both duty ratios D1_m1 and D2_m1 are calculated from theaverage inductor current ILave that is command value. In theMode Ⅰ, the average inductor current ILave is controlled byswitching S3 and S4 from (4).
2) Duty ratio of Mode II: The duty ratio of Mode Ⅱ is forcalculated by similar method as Mode Ⅰ. The interval D1_m2Tsw
is Mode II(i) in Fig. 3(b). The interval D2_m2Tsw and zerocurrent interval is Mode Ⅱ(ii) in Fig. 3(b). The inductor peakcurrent of Mode Ⅱ is given by (6) based on faraday’s law.

i [A]
Ipk
ILave

D1 Tsw

D2 Tsw

D3 Tsw

t [s]Tsw
Fig. 4. Inductor current waveform with DCM.

VI  bat D1_ m 2Tsw

 pk
L

V
 I  DC  VPV  Vbat D
pk
2 _ m 2Tsw

L


(6)

where VPV is the voltage of the PV. The duty ratio D1_m2 andD2_m2 are given by (7) and (8) from (3) and (6).

2 LI Lave VDC  VPV  Vbat
TswVbat
VDC  VPV

(7)

2 LI Lave
Vbat
Tsw (VDC  VPV )(VDC  VPV  Vbat )(8)

D1_ m 2 
D2 _ m 2 3) Duty ratio of Mode III: The duty ratio of Mode Ⅲ is
calculated by similar method as Mode Ⅰ. The interval D1_m3Tsw
is Mode Ⅲ(i) in Fig. 3(c). The duty ratio D2_m3Tsw and zerocurrent interval is Mode III(ii) in Fig. 3(c). The inductor peakcurrent in Mode Ⅲ is given by (9).
V  VbatI  PV
D1_ m3Tsw

 pk
L
(9)

 I  Vbat D T
pk
2 _ m 3 swL
The duty ratio D1_m3 and D2_m3 are given by (10) and (11)from (3) and (9).

D1_ m3 

2 LI Lave Vbat
TswVPV VPV  Vbat

(10)

D2 _ m3 

2 LI Lave VPV  Vbat
TswVPV
Vbat(11)

B. Derivation of average inductor current and power
In this section, the average inductor current is calculated
to obtain the desired output power. Note that the conversion
loss is neglected for the sake of simplicity.
1) Output power of Mode Ⅰ : The power flow of Mode Ⅰ
is from the battery to DC-link. Therefore, the relationship of
the average inductor current ILave and the output power Pout1 isgiven by (12).
P
I Lave  out1
(12)
Vbat
The average inductor current is decided by the desired
output power.

2) Output power of Mode Ⅱ : The power flow of Mode Ⅱ
is from the battery and PV to DC-link. Therefore, therelationship of the input power and the output power is givenby (13)
Pout 2  Pbat  PPV(13)
where Pout2 is the output power to DC-link, Pbat is the powerfrom the battery, and PPV is power from PV. The power of PV
is given by (14) and the power of battery is given by (15).

PPV  VPVPout 2VDC(14)Pbat  Vbat I Lave(15)
Next, the relationship between the average inductor
current ILave and the output power Pout2 is given by (16) from(13), (14) and (15).
P  V I Lave  out 2 1  PV 
(16)
Vbat  VDC 3) Output power of Mode Ⅲ : The power flow of Mode
Ⅲ is from PV to the battery. Therefore, the average inductor
current iLave is derivated by the power of battery Pout3. The
relationship between the average inductor current ILave andoutput power Pout3 is given by (17)P
I Lave  out 3
(17)
Vbat
4) The inductor current required in Mode Ⅳ : Fig. 5.
shows the inductor current waveform in Mode Ⅳ. Mode Ⅳ
outputs the power to DC-link from only PV by combining
Mode Ⅱ and Mode Ⅲ. The control period becomes twotimes longer than that in other modes due to the combinationof two modes. In the control period, the DC-link receives thepower only during Mode Ⅱ . Therefore, the relationshipbetween Mode Ⅱ and Mode Ⅳ is given by (18).
Pout 2  2 Pout 4(18)
In Mode Ⅳ, the double value of the desired power Pout4 isrequired in Mode Ⅱ. In addition, the output power of thebattery in Mode Ⅱ is charged by Mode Ⅲ. Therefore, therelationship of the power Pout2 and Pout3 is given by (19) from
(13)
Pout 2  Pout 3  PPV(19)
Therefore, the average inductor current ILave which is
required to obtain the output power Pout2 is given by (20)based on (16), (17), (18) and (19).

2 Pout 4  VPV  I Lave 
1 
 , (@ Mode2)
Vbat  VDC (20)
2 Pout 4  VPV  I Lave   V 1  V  , (@ Mode3)
bat 
DC 

Note that the direction of the inductor current is defined
as positive when it flows from the battery. The inductor
current becomes negative in Mode Ⅲ because current flows
into the battery from PV. In order to satisfy (21), theinflowing current to the battery in Mode Ⅲ is required to beequal to the current which is output from battery in Mode Ⅱ.
In each modes, the average inductor current which is thecommand value of duty ration is decided from the output
power based on (13), (17), (18) and (21), respectively.
Therefore, the desired output power is obtained byiLave(ModeⅡ)i [A]iLave(Mode Ⅳ)
Mode III

Mode IIt [s]Mode IV

Fig. 5. Inductor current waveform in Mode Ⅳ.

controlling the average inductor current based on theseequations.
C. Design of inductance
The inductance should be designed properly to ensure theDCM operation. In particular, the minimum inductanceprovides Boundary Conduction Mode (BCM) operation with
rated current rms value.
1) Design of inductance in Mode Ⅰ: In order to achieve
DCM, D1_m1Tsw+D2_m1Tsw should be smaller than Tsw. The
condition for the achievement of BCM is given by (21) from
(4) and (5).

D1_ m1  D2 _ m1 

2 LI Lave VDC
1
TswVbat VDC  Vbat

(21)

In Mode I, the inductance L which achieves DCM is givenby (22) from (21).

L

TswVbat (VDC  Vbat )2I LaveVDC(22)2) Design of inductance in ModeⅡ: The inductance toachieve BCM in the Mode Ⅱ is calculated by similar method
as Mode Ⅰ. The condition of inductor current achieving the
BCM is given by (23) from (7) and (8).

D1_ m 2  D2 _ m 2 

2 LI Lave VDC  VPV
1
TswVbat VDC  VPV  Vbat

(23)

In Mode Ⅱ, the inductance L which achieves DCM is givenby (24) from (23).

L

TswVbat (VDC  VPV  Vbat )2I Lave (VDC  VPV )(24)3) Design of inductance in Mode Ⅲ: The inductance toachieve BCM in the Mode Ⅲ is calculated by similar method
as Mode Ⅰ. The condition of inductor current achieving BCM
is given by (25) from (10) and (11).

D1_ m3  D2 _ m3 

2 LI Lave VPV1
TswVbat VPV  Vbat

(25)

In Mode Ⅲ, the inductance L which achieves DCM isgiven by (26) from (25).

L

TswVbat (VPV  Vbat )2I LaveVPV(26)

The inductance condition is considered in BCM in eachmode. The minimum inductance among modes is selected toachieve DCM. On the other hand, the inductor peak current
will be increased if the inductance is designed as smaller value.
Thus, the lower limit of inductance is decided by themaximum current rating of the semiconductor device and thesaturation magnetic flux density of the core.

34

 2W 
VolL  KV 
(27)
 K u Bm J w 
where KV is the coefficient which depends on the shape ofcore, W is inductor energy, Ku is the window utilization factor,
Bm is the maximum flux density, and Jm is the current density.
The inductor volume is proportional to the three-fourths of
the inductor storage energy. Therefore, the reduction ratio of
the inductor volume is obtained by comparing the inductor
storage energy between DCM and CCM.
Next, the inductor energy in CCM which is the target forcomparison is calculated. Note that the ripple ratio of inductor
current in CCM is assumed as peak-to-peak 30%. In CCM,
The inductance to achieve CCM is given by (28) inconsideration of the current ripple ratio.
V
VDC  Vbat
L  bat(28)
I L f sw VDC
where ΔIL is the current ripple. The inductor storage energy
is calculated from inductor peak current. The inductor
volume is compared in next chapter according to theexperimental conditions.

E. Control block diagram
Fig. 6 shows the control block diagram of the three-port
converter which is applied with DCM. The control block
diagram consists of the duty selector, a PWM generator and aswitching pattern selector. The duty ratio is calculated basedon the mode select signal and the command average inductor
current. Next, the PWM signal is generated based on the mode
selector signal and the duty ratio. Note that the applied switch
is decided by the mode selector signal as shown in the Table
1. Furthermore, the gate interruption is added to protect thecircuit. In this paper, the inductor current is generated by openloop control based on (12), (16) and (17).
IV. EXPERIMENTAL RESULTS
A. Design method of prototype
Table II lists the experimental conditions. The proposed
three-port converter operation with DCM is demonstrated
with a 750-W prototype. In this paper, DC-link of 150 V is
selected with the single-phase AC 100 V. In the experiment,
the battery and PV are replaced by the DC power supplies.
The inductance is designed with the consideration of 1.2 times
higher rating power by (22), (24) and (26) to achieve DCM.
In particular, DCM is achieved by the inductance of under
32.0 μH in Mode Ⅰ, 43.5 μH in Mode Ⅱ, and 30.0 μH in ModeⅢ. Therefore, the inductance is required to lower than 30.0
μH to achieves DCM in all mode. In the experiment, theinductance of 14.5 μH is selected to achieves DCM. Note thatthe inductance is measured from the inductor current gradientat the average value of 15 A.
B. Comparison of inductor volume
The inductor volume is obtained by substituting theparameter in Table 2 into (1) and (28). The inductor peakSW pattern selector
0
0

D1_m1

Mode I eq. (5)
iref

D1_m2

Mode II eq. (8)D1_m3Mode III eq. (11)

D1

0

S1
S2

PWM generator
Mode selector

D. Calculation of inductor volume
In this section, the inductor volume is estimated in termsof inductor storage energy. The inductor volume is given by(27) based on Area Product concept [12].

FPGA

DSP

1

+
-

Mode protector

Carrier

SelM1
SelM2
SelM3

0

S3

1

S4

Fig. 6. Control block diagram of FCC with DCM.
Table II. Experimental conditions.
Parameter

SymbolValue

Output power

Pout

750 W

Output voltage

VDC

150 V

Battery voltage

Vbat

48 V

PV voltage
Boost up inductor

VPV
L1

Battery decoupling capacitor

90 V

Cbat

14.5 mH
1500 mF

PV decoupling capacitor

CPV

1500 mF

DC link decoupling capacitor
PWM Carrier Frequency

CDC

650 mFfsw

20 kHzMode I current command

Iref1

15.8 A

Mode II current command

Iref2

8.0 A

Mode III current command

Iref3

14.1 A

Mode IV current command

Iref4

16.1 Acurrent in DCM is 60.2 A from (2), whereas the inductor peakcurrent in CCM is 20.5 A. In addition, the inductance in DCM
is 14.5 μH, whereas the inductance in CCM is 340 μH from
(28). Hence, the inductor energy in DCM is 26.1 mJ, and theinductor energy in CCM is 71.4 mJ from (27). Consequently,
the inductor volume of the proposed circuit with DCM is
reduced by 53%.
C. Evaluation of operation waveform
Fig. 7 shows the operation waveforms in Mode Ⅰ. In ModeI, the power is transferred from the battery to DC-link. Thus,in this mode, the three-port converter operates as same as theboost converter. It is mentioned that the inductor current
achieves DCM as shown in Fig. 7. The average inductor
current is 15.2 A which is 3.8% lower than the current
command of 15.8 A. This error occurs due to the switchingloss and conduction loss of the switching devices. Note thatthe output power error is not occur due to the dead time
because proposed circuit does not have switches which needinverse duty.
Fig. 8 shows the operation waveforms in Mode Ⅱ. In ModeⅡ, the power is output from PV and the battery to DC-link. Fig.
8 mentioned that the inductor current achieves DCM. The
average inductor current is 6.1 A which is 23.6% lower thanthe current command of 8 A. The inductor current error ofMode Ⅱ is larger than Mode I. The conduction route isdifferent in each modes; therefore, the inductor current error
is different due to the also difference of the conduction loss.
Fig. 9 shows operation waveforms in Mode Ⅲ. In ModeⅢ, the battery is charged by PV. It is mentioned that theinductor current achieves DCM as shown in Fig. 9. In addition,
the inductor current is negative because the direction of
inductor current is inverse to Mode I and Mode Ⅱ. The average
inductor current is -12.3 A which is 23.6% lower than current

command of -16.1 A. The reason of the error is same as
mentioned in above paragraph.
Fig. 10 shows the operation waveforms in Mode Ⅳ. In
Mode Ⅳ, the power is output from PV to DC-link by
operating alternately between Mode Ⅱ and Mode Ⅲ. Note thatthe inductor current is negative in Mode Ⅲ, whereas thecurrent direction is different from Mode Ⅱ because the current
flows from PV to the battery. Theoretically, the average
inductor current should become 0 A because the current
command of the average inductor current in Mode Ⅱ andMode Ⅲ are equal. However, the average inductor current is-1.6 A in Mode Ⅳ in the experiment. This current error occurs
from the loss difference between Mode Ⅱ and Mode Ⅲ.
V. CONCLUSION
In this paper, the three-port converter based on the flying
capacitor converter was proposed. The three-port converter
reduced the inductor volume by 53% with the sharing use of
the inductor and the application of DCM. The duty ratio andthe inductance of the three-port converter were calculated toachieve DCM. The validity of the calculation method of the
duty ratio and the inductance was demonstrated with the 750W prototype.
As the future works, improvement of the circuit efficiency
by synchronous rectifier, efficiency evaluation, loss analysis,
and error compensation of inductor will be considered.
REFERENCES[1]

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DC link voltage [50 V/div]
PV voltage [50 V/div]
Battery voltage [50 V/div]
0V
Inductor current [20 A/div]

0A[100 ms/div]

ILave=15.2 A [400 ms/div]

Fig. 7. Operation waveform of the Mode I.
DC link voltage [50 V/div]
PV voltage [50 V/div]
Battery voltage [50 V/div]
0V

Inductor current [10 A/div]

0A

ILave=6.1 A [400 ms/div][100 ms/div]

Fig. 8. Operation waveform of the Mode II.
DC link voltage [50 V/div]
PV voltage [50 V/div]
Battery voltage [50 V/div]
0V
0A

ILave=-12.3 A

Inductor current [20 A/div][400 ms/div][100 ms/div]

Fig. 9. Operation waveform of the Mode III.
DC link voltage [50 V/div]
PV voltage [50 V/div]
Battery voltage [50 V/div]
0V

ILave=-1.6 A

Inductor current [20 A/div][400 ms/div][100 ms/div]

0A

Mode II Mode III
Fig. 10. Operation waveform of the Mode IV.

International Power Electronics Conference, No. 21A4-5, pp. 36613666 (2014)[12] Wm. T. Mclyman: “Transformer and inductor design handbook”,
Marcel Deller Inc. (2004)