System Design of Electric Assisted Bicycle using the EDLCs as Power Source
Kenji Noguchi *Koji Orikawa*

Jun-ichi Itoh**Nagaoka University of Technology
Abstract:- The proposed system uses electric double layer capacitors (EDLCs), which is rapidly charged by using wirelesspower transmission. This paper compares the volume and power loss of the three kinds of DC-DC converters which are
step-down type, boost-type and buck-boost type for the charging and discharging of EDLCs. The number and the output voltage
range of the EDLCs is designed that the charge and discharge energy of EDLCs meet more than 53.0 kJ by literature [4]. The
results showed that the total volume of the boost-type DC-DC converter is the small when the output power is less than 1.1 kW.
On the other hand, the total volume of the step-down type is small when the output power is larger than 1.1 kW. Finally, therelationship between the total volume of proposed system and the output power is clarified.
Keywords : Electric assisted bicycle, Electric double layer capacitors, DC-DC converter, Wireless power transfer
Wireless power transfer

1.

IntroductionRecently, DC-DC converters for the control the output voltageof electric double layer capacitors (EDLCs) are actively
researched [1]. However, there are only few literatures which
consider the total volume of DC-DC converters and EDLCs fromthe viewpoint of the mounting them on a moving object such as
electric vehicles and electric bicycles. Authors have been
investigated the application of the EDLCs to the electric assisted
bicycle so far. This paper evaluates the volume and power loss ofstep-down type, boost-type and buck-boost type of DC-DC
converters which is used as charging/discharging operation for
EDLCs.

2.

Transmitting
antennaConverter to consider
DC-DC DC-ACEDLCsーーー～(Battery)Receiving
antennaFig. 1. Proposed system configuration.
Boost-Type DC-DC Converter

iL2aEDLCs(9 seriesconnection)
Capacitance: 256F

Proposed system configuration

iouta
ica

S1a
iL1a

C1a +L1aS2a22.5V(vouta-1.5)~
8V

Fig. 1 shows the proposed system configuration. The proposedsystem uses a high frequency power source in front of thetransmitting antenna for wireless power transmission [2]. Also, theproposed system is constituted by a rapid rechargeable AC-DC
converter and EDLCs in the latter part of the receiving antenna.
Also, during an assist of the energy for drivers, the DC-DC
converter for assist performs the discharge control of the EDLCs
when a brushless DC (BLDC) motor is driven. BLDC motor andDC-AC converter are commercial products [3].

3.

AC-DC～ーRFpower
supplyvouta
24V

vconvavina(a) Boost-Type
Step-down Type DC-DC Converter

iL2bEDLCs(15 seriesconnection)
Capacitance: 153F

S1biL1bvinb
S2b37.5V~25.5V(voutb+1.5)

Circuit configuration of the DC-DC converters

Fig. 2 shows the circuit configuration of three kinds of DC-DCconverters. This paper considers step-down type, boost-type andbuck-boost type as a circuit for the charging and discharging
DC-DC converter using EDLCs as a power source. The number
and the output voltage range of the EDLCs is designed that thecharge and discharge energy of EDLCs meet more than 53.0 kJ
based on the literature [4]. The DC-DC converters of three kinds
are designed that the charge and discharge energy of EDLCs isalmost equal (the energy of boost-type is 58.0 kJ, the energy ofstep-down type is 56.5 kJ, the energy of buck-boost type is 55.2kJ). In addition, the specification of the input voltage of theDC-AC converter is 24 V (Vouta, Voutb, Voutc), and the output
voltage of the DC-DC converter is controlled to 24 V the constant.

ioutb
icb

L1b
C1b +vconvb

voutb
24V(b) Step-down Type
Buck-boost Type DC-DC Converter

iL2c

EDLCs
(12 series connection)
Capacitance : 192F30V(voutc+6)
vinc~
ioutc 18V(voutc-6)

S1ciL1cS2ciccL1cC1c +vconvc

voutc
24V

(c) Buck-boost Type
Fig. 2. Investigated circuit configuration.

1BLDC
motor

Comparison of volume and power loss

20

Power loss [W]4.

Fig. 3 shows the results of power loss analysis on the threekinds of DC-DC converters when the voltage of the EDLCs Vin inFigure 2 is changed. The power loss is analyzed under theconditions that the output power of the DC-DC converter is 384 W
constant. In addition, it is noted that dead time is ignored. FromFig. 3, in the boost-type, it is confirmed that the switching loss andthe conduction loss of the MOSFET is dominated. Also, in thestep-down type and buck-boost type, it is confirmed that theswitching loss of the MOSFET is dominated. The reason is thatthe input current of the boost-type is increased for the input
voltage which is lower than the step-down type and buck-boosttype.
Fig. 4 shows the relationship between the volume and theoutput power for the three kinds of DC-DC converters. It is notedthat the power loss is maximum in case of the voltage of EDLCsin Fig. 4. In addition, the volume of the Fig. 4 is the sum ofvolume of EDLCs and DC-DC converter (smoothing capacitor,heat sink, reactor). The design approach refers to literature [5].
From Fig. 4 (b), around the output power of 100 W, the volume of
the EDLCs is dominant in the converter of all types. The numberof EDLCs for the boost-type is the fewest in all of other DC-DC
converters. Therefore, the volume of boost-type is small. However,if the output power is 1.1 kW or more than 675 W, the volume ofstep-down type is small than the boost-type and the buck-boost
type. In case of the boost-type and buck-boost type, the ripple
current of the smoothing capacitor is increased when the output
power is increased. Therefore, the ratio of the volume of thesmoothing capacitor is increased. On the other hand, in case of thestep-down type, the ripple current of the smoothing capacitor does
not depend on the output power. Therefore, when the output power
is increased, the volume of heat sink which is very small andreactor compared to the volume of the EDLCs is increased.
However, the volume of the converter does not increase too much.
Furthermore, if the output voltage of the DC-DC converter is set
over 24V, the cross over point of the volume of three kinds of
DC-DC converter is shifted toward high output power. The reason
is that the volume of the capacitor is decreased depends on its
ripple current according to the high output voltage of the DC-DCconverter.

Conduction loss of
the reactor
Switching loss of
the MOSFET
Conduction loss ofthe MOSFET

105081522.5
Input voltage vina [V](a) Boost-TypePower loss [W]

20voutb = 24 V, fsw = 100 kHz, Pout = 384 W

5Conduction loss of
the reactor
Switching loss of
the MOSFET

0Conduction loss of
the MOSFET

151025.5

3137.5
Input voltage vinb [V](b) Step-down TypePower loss [W]

20voutc = 24 V, fsw = 100 kHz, Pout = 384 W
Conduction loss of
the reactor
Switching loss of
the MOSFET

15105

Conduction loss of
the MOSFET

0182430
Input voltage vinc [V](c) Buck-boost Type
Fig. 3. Results of power loss analysis of the three kinds of
DC-DC converters16000

vout = 24 V, fsw = 100 kHz
Volume of EDLCs
Boost-Type: 3039 cm3
Buck-boost Type: 4053 cm3
Step-down Type: 5066 cm3

Total Volume [cm3]

14000

12000
10000

Buck-boost Type(vinc : 18 V )

8000
6000
4000

2000

5.

vouta = 24 V, fsw = 100 kHz, Pout = 384 W

15Conclusion

100 500

Step-down Type
Boost-Type(vinb : 37.5 V)(vina : 8 V)
1000 1500 2000 2500 3000 3500 4000
Output power [W](a) The total volume
Total Volume [cm3]

The results showed that the total volume of the boost-type
DC-DC converter is the smallest up to the output power of 1.1 kW.
On the other hand, the total volume of the step-down type is small
when the output power is larger than 1.1 kW. Therefore, from theview point of the minimum volume of the system, the DC-DC
converter of boost-type is the most suitable. Note that, the crossover point of the volume of three kinds of DC-DC converter ischanged according to the output voltage of DC-DC converter.
In the future work, the DC-DC converter of boost-type will bemade as a prototype and it will be verified by experiments.

16000
14000
12000
10000
800060004000
2000
0Inductor

Heatsink
Capacitor
EDLC
Center: Buck-boost TypeLeft: Boost-Type
Right: Step-down Type

100

1000
Output power [W]2000(b) Ratio of the volume
Fig. 4. Relationship between the volume and the output power
for the three kinds of DC-DC converters.

References(http://www.yamaha-motor.jp/pas/lineup/wagon/)[4] K. Noguchi, K.Orikawa, J. Itoh: "Study of the System of Electric Assisted
Bicycle with an Electric Double Layer Capacitor", IEEJ JIASC, No. Y-22
(2013)[5] Y. Kashihara, J. Itoh: "The comparison of the efficiency and power density ofthe multilevel converter topologies for PV inverter", SPC shimane, No.
SPC-11-157 (2011)[1] S. Funabiki, M. Yamamoto: "Estimation of Bidirectional Buck/boost DC/DCConverters with Electric Double-Layer Capacitors for Energy Storage
Systems", IEEJ Trans. D, Vol. 129, No. 6, pp. 658-663 (2009)[2] K.Noguchi, K. Kusaka, J. Itoh: JHES2012, No. A-66 (2012)[3] Yamaha Motor Co., Ltd. PAS wagon.

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