Experimental Verification of Wireless Charging
System for Vehicle Application using EDLCs
Jun-ichi Itoh, Kenji Noguchi and Koji Orikawa
Department of Electrical, Electronics and Information Engineering
Nagaoka University of Technology
Nagaoka, Niigata, Japan
itoh@vos.nagaokaut.ac.jp，k_noguchi@stn.nagaokaut.ac.jp，orikawa@vos.nagaokaut.ac.jp

Abstract— This paper discusses an vehicle application
which uses electric double layer capacitors (EDLCs) as a
power source. EDLCs are charged through a rapid charger byusing wireless power transmission. In this paper, as vehicle
application, the electric assisted bicycle is considered. First, theantenna for the wireless power transmission and the charger
are introduced. Next, this paper compares the volume and thepower loss of the three kinds of DC-DC converters which are abuck-type, a boost-type and a buck-boost type for the charging
and discharging of EDLCs. As a result, such as an electric
assisted bicycle for small-capacity system, the boost-type issmall. On the other hand, such as electric vehicles for largecapacity system, the buck-type is small. Finally, the proposedsystem is experimentally verified as a prototype. As a result,the proposed system can shorten to 1/4 the charging time of
the conventional system.
Keywords— Vehicles, Supercapacitors,
transmission, DC-DC power converters

I.

Inductive

power

INTRODUCTION

Recently, in consideration of global warming, the vehicle
application system using battery has been studied actively [1].
The vehicle application uses a lithium-ion battery as an energy
source. The lithium-ion battery is suitable for a long assist
time owing to high energy density. However, the lithium-ion
battery is the short lifetime and it needs long charging time.
On the other hand, the kHz-class wireless charging systemusing rapid rechargeable electric double layer capacitors(EDLCs) which has long cycle life has been developed forvehicular applications [2]. This system uses EDLCs instead ofthe lithium-ion battery. In this system, a disadvantage of low
energy density of EDLCs is solved by frequent fast wirelesscharging. However, the kHz-class antenna for wireless powertransfer is large and heavy because of a large core. On theother hand, the MHz-class antenna for wireless power transfer
for the purpose of weight reduction and miniaturization of theantenna has been studied [3].
The authors have been proposed an electric assisted bicyclewith EDLCs and MHz-class wireless charging system as avehicle application [4]. This system has two concepts asfollows; First, it is assumed that the EDLCs are used as only
the assist of starting acceleration and slopes for the electric

Wireless powertransferRF
power
supplyTransmitting
antenna

EDLCs
DC

Receiving
antennaDC
AC
DC

Wireless charging area

DC
AC

BLDC
motor

Vehicle application side

Fig. 1. Configuration of the proposed system.

assisted bicycle in order to suppress the total energy of the
EDLCs; Second, the wireless power transfer system is applied
to rapid charger for the EDLCs because of small capacity andthe short charging time. However, the MHz-class wirelesscharging for EDLCs has not been actually verified in terms oftransmission efficiency of the antenna, an efficiency and a
volume of an interface power converter for EDLCs.
This paper evaluates three items as follows in order toclarify advantages of MHz-class wireless charging for EDLCs;
1) The antenna using a print circuit board (PCB) andcharger design for the wireless power transmission,2) The circuit topology of the interface DC-DC converter
for EDLCs in the proposed system configuration in terms ofthe volume and efficiency corresponding to output power,
3) The comparison of the charging time of the proposedsystem and the conventional system.
Also, the wireless power transfer system has problems thatthe voltage of the receiving antenna is varied by variation of
the coupling factor and a load. Therefore, a control method forcharging controlling an input impedance of the receiving side
to constant value by using a DC-DC converter is proposed.
The effectiveness of the proposed control is experimentally
verified.
II.

PROPOSED SYSTEM CONFIGURATION

Fig. 1 shows the configuration of the proposed system. The
proposed system uses a Radio Frequency (RF) power supply
at the input stage of the transmitting antenna for wirelesspower transmission [5-9]. Also, the proposed systemcomprises a rapid rechargeable AC-DC converter and EDLCs
in the latter part of the receiving antenna. The EDLCs arecharged when the vehicle application stops on the wirelesscharging area. Also, the voltage of EDLCs is controlled to beconstant by the DC-DC converter when the motor is driven.
III.

Open Type
R/2

DESIGN OF ANTENNA FOR WIRELESS POWER
TRANSMISSION AND CHARGER

L/2

Cs L/2 R/2

RF power supply connection

A small receiving antenna is preferred in order to mount thevehicle application. Therefore, the authors have been proposed
a formula spiral antenna made of a printed circuit board,which is flat, compact and easy design.

Short Type
R/2

L/2

L/2

R/2

Cp

Line of cut

RF power supply connection

d : Thickness of copper trace
S: Space between copper trace
W: Width of copper trace

Cross section cut

Fig. 2. Structure of the antenna for wireless power transmission.
Input

Start

E
T

Decision P ( V, I )∙∙∙step 1

Antenna size
(Domax)

Decision W, d , S , Di∙∙∙step 2

Decision N∙∙∙step 3

Decision L，Cp，R∙∙∙step 4

Decision Cv∙∙∙step 5

Decision f0，h∙∙∙step 6

Parameters
E: Charging energy
T: Charging time
P: Charging power
V: Rated voltage
I: Rated current
N: Number of turns
L: Inductance
Cp: Parasitic capacitance of the parallel
Cv: Capacitance of the external capacitor
f0: Self-resonant frequency
h : Transmitting efficiency

h > Required hNo

YesFinishFig. 3. Design flow chart of charger and antenna forwireless power transmission.
FunctionRF
generator power supply
50W

Power
Meter

Wireless powertransfer

LoadPF

Coaxial Cable

PLoad

50mm

PR

Open typeor
Short type with
Cv = 500pF

h = PLoad /PF×100 [%]PCB Antenna

Fig. 4. System configuration of the experiments.
The system of the experiment circuit is matched at 50Ω.
100
Transmission distance: 50 mm
Short type with
Input power: 100 W
80
Cv = 500pF
Load: 50 W
Open type
Domax: 200 mm
60Transmission
efficiency h [%]B. Comparison of Transmission Efficiency
Fig. 4 shows the system configuration of the experiments.
Arbitrary frequency is output using a function generator. The
output power cannot output 1 kW (The average output powerof the charger) because of capacity limit of RF power supply.
Therefore, the output of the RF power supply is scaled to 100
W (10% of 1 kW). Reflected power PR is measured using a
power meter in the front stage of the power transmission
antenna. Also, the antenna of short type is connected in series

Domax: Outer diameter
Di: Inner diameter

50W

A. Design of Wireless Charger
Fig. 2 shows the structure and equivalent circuits of thetransmitting antenna for wireless power transmission. The
connection point of the short type and open type is the output
of a RF power supply. For the receiving antenna, theequivalent circuit is the same. The antenna has a two-layer
structured wiring in order to increase the inductance value.
Fig. 3 shows the design flow chart of the charger and theantenna for the wireless power transmission. From Fig. 3, thecharging power P is determined by the charging time T andthe charging energy E. The antenna is designed from thespecifications of the antenna size Domax and the charging
power P. The charger considers the short charging time andthe volume of power conversion system for the charging
power. In this paper, the specification example of the system
is designed as follows.
1) The target of charging time T is 60 sec,
2) The charging energy E is supplied to 56.5 kJ. This energy
is the maximum energy in the proposed system. Also, theEDLCs are used product of Nippon Chemi-Con Corporation[10].
In addition, the average output power of the charger E/T isapproximately 1 kW. If the discharging power is less than 1
kW, the size of the circuit becomes large when the charging
circuit combines with the discharging circuit. Therefore, thecharging control should be placed in RF power supply of thepower transmission side of the wireless power transfer system.
On the other hand, if the discharging power is more than 1 kW,
the size of the circuit does not become large when the
charging circuit combines with the discharging circuit. So, a
compact system can be realized. Therefore, bi-directional
system for charging and discharging is designed in this paper.
Also, the antenna size Domax depends on the mounting
position of the power receiving side. The antenna for wirelesspower transmission is experimentally compared between the
short type and open type with the same size.

40
20
0
0.6

1.1

1.6

2.1

2.6

3.1

3.6

Frequency f [MHz]Fig. 5. Experimental results of the frequency characteristics ofthe transmission efficiency.

with the capacitor of capacitance 500 pF.
Fig. 5 shows the experimental results of the frequency

EDLCs(9 series
connection)
Capacitance: 256F
22.5V(vouta-1.5)~
8V
Energy:56.5 kJ

iL2a

iouta

EDLCs
(15 seriesconnection)
Capacitance: 153F
37.5V
~
25.5V
(voutb+1.5)
Energy:58.0 kJ

ica

S1a
iL1a

C1a +

L1a
S2a

vouta
24V

vconva

vina

iL2b

iL2c

S1b

S1c
iL1b

vinb
S2b

ioutb

iL1c

icb

L1b
C1b +

vconvb

L1c

S2c

EDLCs
(12 series connection)
Capacitance : 192F
30V(voutc+6)~
vinc
ioutc 18V(voutc-6)
Energy: 55.2kJ
icc

C1c +
vconvc
voutc
24V

voutb
24V

(a) Boost-Type.

(b) Buck-Type.
(c) Buck-boost Type.
Fig. 6. Investigated circuit configuration.
The energy of EDLCs for a circuit of three types is designed with the same energy.
As shown in Fig. 9, a BLDC motor is connected to the output of the DC-DC converter.
20
20
20
vouta = 24 V, fsw = 100 kHz, Pout = 384 W
voutb = 24 V, fsw = 100 kHz, Pout = 384 W
voutc = 24 V, fsw = 100 kHz, Pout = 384 W

10Conduction loss of
the MOSFET

5
0

15

Power loss [W]

Switching loss of
the MOSFET

Power loss [W]Power loss [W]Copper loss of the reactor

15

10

5
0

8

15

22.5

Input voltage vina [V]

15
10
5
0

25.5

31

Input voltage vinb [V]

37.5

18

24

30

Input voltage vinc [V](a) Boost-Type.

(b) Buck-Type.
(c) Buck-boost Type.
Fig. 7. Results of power loss analysis of the three kinds of DC-DC converters.
The power loss is neglected iron loss of the reactor, the conduction loss of the diode, recovery loss.

characteristics of the transmission efficiency. The power isamplified by the amplifier. The antenna is designed according
to the flowchart of Fig. 4. From Fig. 5, it is confirmed that the
short type can realize the low resonance frequency comparedto the open type at the same transmission efficiency andantenna size. In general, if resonant frequency is the low
frequency, the efficiency of RF power supply is high.
Therefore, the short type can be high efficiency of the systemthan the open type. So, the proposed system is adopted theshort type. In Section 5, the antenna is redesigned in order to
use the inexpensive low voltage RF power supply.
IV.

DESIGN OF THE INTERFACE CONVERTER FOR EDLCS

A. Comparison of Circuit Configuration
Fig. 6 shows the circuit configuration of three kinds of DCDC converters. This paper investigates the interface DC-DC
converter which a buck-type, a boost-type and a buck-boost
type for EDLCs. In this paper, when the voltage of EDLCs issmaller than the output voltage of the DC-DC converter, it isdefined as a boost-type. The number and the output voltage
range of the EDLCs are designed when the charging anddischarging energy of EDLCs meet more than 53.0 kJ. Thus,
the DC-DC converters are designed that the charging anddischarging energy of EDLCs is as follows: the energy of theboost-type, buck-type and buck-boost type are 56.5 kJ, 58.0 kJ
and 55.2 kJ, respectively. In addition, the specification of the
input voltage of the DC-AC converter is 24 V (Vouta, Voutb,
Voutc), and the output voltage of the DC-DC converter iscontrolled to 24 V at constant. Further, the reactors of all types
are designed to the current ripple value (1.5 A) as same as thebuck-type. Therefore, the reactors of all types are designedthat the current ripple of the reactor meets less than 1.5A. On
the other hand, the smoothing capacitor is designed from theallowable ripple current.
In this system, the load of BLDC motor is changed. It isnecessary to increase the capacitance of the smoothing
capacitor in order to reduce the variation in the output voltageof the DC-DC converter owing to load variations. However,the volume of the smoothing capacitor should be reduced interms of volume implementation. Therefore, when the load
fluctuations occur, it is important to reduce the volume of thesmoothing capacitor by implementing the fast control responseof the output voltage [11].
B. Comparison of Power Loss
Fig. 7 shows the power loss analysis of three kinds of DCDC converters when the voltage of the EDLCs Vin is changed.
The power loss is analyzed under the conditions that theoutput power of the DC-DC converter is 384 W. It is notedthat dead time is neglected. As shown in Fig. 7, it is confirmedthat the switching loss and the conduction loss of the
MOSFET dominates the total loss in the boost-type. Also, it isconfirmed that the switching loss of the MOSFET isdominates the total losses in the buck-type and buck-boost
type. This is because the input current of the boost-type isincreased owing to the input voltage, which is lower than the
buck-type and buck-boost type.

Ploss1
vol cooling ==Rth  CSPI T j  Ta  CSPI

Condition: vout = 24 V, fsw = 100 kHz
Buck-boost Type
Volume of EDLCs(vinc : 18 V )Boost-Type: 3.0 dm3

8

Buck-boost Type: 4.1 dm3
Buck-Type: 5.1 dm3

7

Total volume [dm3]

C. Comparison of Total Volume
Fig. 8 shows the relationship between the total volume andthe output power for the three kinds of DC-DC converters. It
is noted that the power loss is maximum for the voltage of
EDLCs in Fig. 7. In addition, the volume of the Fig. 8 is thesum of volume of EDLCs and DC-DC converter (Reactor,
Heat sink, Electrolytic capacitor).
In this paper, CSPI (Cooling System Performance Index),
which is a reciprocal of the product of the volume and thethermal resistance, is introduced to estimate the volume ofcooling system. The CSPI indicates the cooling performance
per unit volume of the cooling system. It means that a highperformance cooling system shows high CSPI. Therefore, thecooling system is miniaturized when CSPI become higher.
The volume of the cooling system volcooling is given by (1)from the relationship between the power loss and the rise intemperature [12].

65Buck-Type(vinb : 37.5 V)

4Boost-Type(vina : 8 V)

3

2

100

500

(1)

(2)

2000

7

Heatsink

Capacitor

EDLCs

Right: Buck-Type
Left: Boost-Type
Center: Buck-boost Type

6
5
4
3
2

(3)

where  VCE is the proportionality factor between the rms
value of the ripple current and the volume, and ICRMS is the rms
value of the ripple current of the electrolytic capacitor.
From Fig. 8(b), around the output power of 100 W, thevolume of the EDLCs is dominant in the converter of all types.
The number of EDLCs for the boost-type is the fewest in all ofother DC-DC converters. Therefore, the volume of the boosttype is the smallest. However, if the output power is 1.1 kW or
more than 675 W, the volume of the buck-type is smaller thanthat of the boost-type and the buck-boost type. For the boosttype and the buck-boost type, the ripple current of thesmoothing capacitor is increased when the output power isincreased. Therefore, the ratio of the volume of the smoothing
capacitor is increased. On the other hand, for the buck-type,-1

8

Total volume [dm3]34where Kv is the constant value depending on the shape ofcores, W is the maximum energy of the reactor, Ku is theoccupancy of the window, Bm is the maximum flux density of
the core, and J is the current density of the wire.
The capacitor volume is calculated based on commerciallyavailable electrolytic capacitors [14]. The volume of theelectrolytic capacitor is proportional to the rms value of theripple current of the electrolytic capacitor. The volume volCEof the electrolytic capacitor is given by (3).
1
vol CE =  VCE
I CRMS

1500(a) Total volume.
Reactor

where Rth is the thermal resistance of the cooling system, Tj
is the junction temperature of the switching device, Ta is theambient temperature, Ploss is the power loss of the switching
device.
In this paper, the reactor is designed by the Area Productconcept [13] using a window area and a cross-sectional area.
Then volume of the reactor volL is given by (2).

 2W 
vol L = K v 
 K u Bm J 

1000

Output power [W]

1

0

100

1000

Output power [W]2000(b) Ratio of the volume.
Fig. 8. Relationship between the total volume and the output power
for the three kinds of DC-DC converters.
In this figure, it is noted the voltage of EDLCs at the maximum
power loss is considered.

the ripple current of the smoothing capacitor does not dependon the output power. Therefore, when the output power isincreased, the volume of heat sink and reactor which is verysmall compared to the volume of the EDLCs is increased.
However, the volume of the converter does not increase toomuch. Furthermore, if the output voltage of the DC-DC
converter is set to over 24 V, the cross over point of thevolume of three kinds of DC-DC converter is shifted toward
high output power. The reason is that the volume of thecapacitor is decreased depends on its ripple current according
to the high output voltage of the DC-DC converter. Also, theboost-type is the most compact in the power capacity (384W)
of the electric assisted bicycle. Also, even if the energy of the
EDLCs is small capacity further, the boost-type is the mostcompact. Therefore, the boost-type is adopted in the proposedsystem.

FunctionRF
generator power supply
Coaxial Cable

Wireless
power
transfer

Rectifier circuit

iRF
vRF
PCB Antenna(Short type)
SS topology

50mm

Bi-directional DC-DC converter

iout

EDLCs
S
(7 series connection) 1
Capacitance : 100F
iL1
17.5V
(vout -6.5)
L1
~
S2
8V
vin
Energy:12.1 kJ

ic

iL2

Motor drive(Products on the market)

C1 +
vout
24V

BLDC
motor

vconv

Fig. 9. The entire circuit diagram of the proposed system.
The proposed system is designed based on the system design to chapter 5.
The semiconductor switches are silicon MOSFETs.

M
5

C2

Charging time [min]C1
4

RF power supply
connection

3

Be shortened
to 1/42

10lithium-ion battery(Conventional system)

EDLCs(Proposed system)

Fig. 10. Comparison of the charging time for charging the 12.1kJ of
the proposed system and conventional system.

V.

WIRELESS CHARGING VERIFICATION OF SYSTEM

A. Design of the Whole System
Fig. 9 shows the circuit diagram of the entire system basedon the system design to chapter 4. By the system design, thetotal volume of boost type is minimum in three kinds of DCDC converters at the maximum power (384W) of electric
assisted bicycle. Therefore, boost type is adopted for the bidirectional DC-DC converter. In the antenna for wirelesspower transmission, the short type can be high efficiency of
the RF power supply than the open type. Therefore, theantenna of short type is adopted. The running distance of aslope is more than 200 m as prototype specifications in thispaper. Thus, the energy of the EDLCs (Nippon Chemi-Con Co,
DDLE2R5LGN701KAA5S) is designed in 12.1 kJ [10]. In
addition, the specification of the charging time is 1 minute.
The wireless power transfer system is adopted the primary andsecondary series resonant capacitors (SS topology) [15].
Fig. 10 shows the comparison of the charging time forcharging the 12.1 kJ of the proposed system and conventional
system. The charging energy of the conventional system iscalculated from specification of the product. From Fig. 10, theproposed system can shorten to 1/4 the charging time of theconventional system.
Fig. 11 shows the equivalent circuit diagram of the SS
topology. The transmitting antenna is connected to the RF

L1

L2 Rectifier circuit
connection

Transmitting
antenna

Receiving
antennaFig. 11. Equivalent circuit diagram of the SS topology.
The capacitor is connected to an external antenna.
Table I. Specification of antenna.

Items
Outline (Length)

Values
250mm

Outline (Side)

200

mm

Number of turns (surface)

5

turn

Number of turns (reverse face)

5

turn

Space between copper trace

5mm

Width of copper trace3

mm

Thickness of PCB (FR-4)

2mm

Thickness of copper trace70m

Self-inductance L1

8.6

H

Self-inductance L2

8.6

H

Mutual inductance M

1.4

H

Designed coupling factor k0

0.16

Primary capacitance C1

2.9

nF

Secondary capacitance C2

2.9

nF

power supply. The receiving antenna is connected to therectifier.
Table I shows the specification of antenna for wirelesspower transmission. The designed coupling factor and the selfinductance are measured by a LCR meter. The capacity C1 andC2 of the series capacitor is given by (4).
C1 =

1
L1

2
0

= C2 =

1
L202

(4)

where L1 is the self-inductance of receiving antenna, 0 is
the resonance angular frequency, L2 is the self-inductance oftransmitting antenna.
Fig. 12 shows the control block diagram of wirelesscharging. In the SS topology, if the voltage of transmitting
antenna is not controlled, the voltage of the receiving antenna

vin
1
+
1  sTicvout

PI

vconv* + 1 iL1
sL1

a

iL2+

30
1 voutsC1

iL1

Fig. 12. Control block diagram.
The output voltage of bi-directional DC-DC converter is controlled toa constant 24V.
Table II. Conditions of the experiment.
Items
ValuesFrequency of the FG

1

MHz

Resonant frequency

1

MHz

Voltage of the FG

380

mVrms

Gain of the RF power source

100

Transmission distance

50

Input and output
voltage or current [V],[A]

PI

iL1*

25

Output voltage vout

20

Input voltage (EDLCs) vin

15

Start charging

Stop charging

10

Input current (reactor) iL1

5

Output current iL2

0
0

100
Time [sec]200(a) Voltage and current waveform of the input and output
for the bi-directional DC-DC converter.

100

mm

is varied by variation of the coupling factor and load [2]. In
this problem, the breakdown voltage of the switching device
must be designed by taking into account the variation of thecoupling factor and the load. Therefore, charging control by
the combination of two points as below is proposed.
1) The output voltage of the bi-directional DC-DC
converter is controlled to be constant.
2) The voltage of the receiving antenna is set higher thanthe output voltage of the bi-directional DC-DC converter.
Thus, the design of the breakdown voltage of the switching
device can be simplified. The charging experiment is based on
the experimental conditions shown in Table II.
B. Experimental Results of Wireless charging
Fig. 13 shows the experimental results of the wirelesscharging to the EDLCs.
Fig. 13(a) shows the voltage and current waveform of the
input and output for the bi-directional DC-DC converter. From
Fig. 13(a), the output voltage of the bi-directional DC-DC
converter is controlled to be constant, and the EDLCs arecharged.
Fig. 13(b) shows the input impedance of the bi-directional
DC-DC converter during the wireless charging to the EDLCs.
From Fig. 13 (b), the input impedance of bi-directional DCDC converter is controlled to be constant is confirmed.
Therefore, the transmission efficiency can be kept constant.
Fig. 13(c) shows the energy storage capacity of EDLCs
from the start of charging to the end of charging. From Fig. 13(c), the energy capacity of the EDLCs are charged from 0% to100% in about 4 minutes is confirmed. The reason thatcharging time is not within 1 minute is power transmission
frequency of the prototype is 1 MHz. Therefore, if the powertransmission frequency is adjusted within the Industry Science
Medical band, the full charging of 1 minute is achieved.
Fig. 13(d) shows the voltage and current waveforms of theoutput of the RF power source, the voltage and current
waveforms of the output of bi-directional DC-DC converter.
From Fig. 13(d), the input power factor of the high frequency
power source is approximately 1 is confirmed.

Input impedance of bi-directional
DC-DC converter [W]1+
1  sTiv

80
Start charging

60

Stop charging

40
Input impedance is constant

20
0
0

100
Time [sec]200(b) Input impedance of the bi-directional DC-DC converter.

Energy capacity of EDLCs [%]

vout*

iout

100
Start charging

80

Stop charging

60
40

20
Charging time: About 4 minutes

0
0

50

100
150
Time [sec]200(c) Energy capacity of EDLCs.
RF output voltage vRF [50V/div]0
RF output current iRF [10A/div]0
Output voltage vout [20V/div]0
Output current iout [2A/div]0400[nsec/div](d) Voltage and current waveforms of the outputof the RF power source.
Fig. 13. Experimental results of the wireless charging to the EDLCs.

C. Wireless Charging Method
Fig. 14 shows the wireless charging method to the electric
assisted bicycle. The receiving antenna is connected to thesides of the front basket of the electric assisted bicycle. The
proposed system is introduced to a charging side. There are
the following advantages by this method.
1) The foreign body (Dust, etc) is less likely to adhere to
the power transmitting and receiving antenna, as compared toa system for power transmission from the ground (Therefore,
it does not affect the transmission efficiency)
2) The variation of transmission distance and the positional
deviation of between the transmitting and receiving antenna
can be reduced by the front wheel is fixed using bicycle
parking stand.
3) It is low cost because the antenna and wiring are notplaced into the ground.
VI.

CONCLUSION

This paper evaluated the energy capacity of EDLCs, theantenna for wireless power transmission and the charger, theinterface converter for EDLCs in proposed system
configuration. The proposed system was experimentally
verified as the prototype. The results showed following
conclusions;1) The results showed that the short type as the antenna forwireless power transmission is higher efficiency than the open
type with the same size.
2) The results showed that such as an electric assisted
bicycle for small-capacity system, boost-type is small. On theother hand, such as electric vehicles for large-capacity system,
buck-type is small.
3) The results showed that the charging time of EDLCs inproposed system can be shorten by 1/4 compared to theconventional system.
Finally, effectiveness of the proposed control was
confirmed experimentally.
In the future work, the running test using the proposedsystem in an actual road will be experimentally verified.
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Transmitting
antenna

EDLCs

Receiving
antennaTransmission distance: 50mm
To RF power
supplyFig. 14. Wireless charging method to the electric assisted bicycle.
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