Design Method of Cooling Structure Considering
Load Fluctuation of High-power
Wireless Power Transfer System
Jun-ichi Itoh
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Nagaoka, Japan
itoh@vos.nagaokaut.ac.jp

Kosuke Mizoguchi
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Nagaoka, Japannagaoka_mizo@stn.nagaokaut.ac.jp

Le Hoai Nam
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Nagaoka, Japanlehoainam@stn.nagaokaut.ac.jp

Keisuke Kusaka
Dept. of Electrical, Electronics, andInformation Engineering
Nagaoka University of Technology
Nagaoka, Japan
kusaka@vos.nagaokaut.ac.jp
Abstract— This paper proposes a thermal design method fortransmission coils with thermally conductive plastic platesconsidering load fluctuation of high-power wireless powertransfer (WPT) systems. The high power transmission may
cause melting of an insulation coating film of litz wires due tothe heat generation of the windings and cores. For this reason, a
cooling structure for the transmission coils is required. As thecooling structure, thermally conductive plastic plates with highthermal conductivity and resistivity are inserted between thecore and the aluminum plates for an improvement of heattransfer. By representing the cooling structure as a thermal
equivalent circuit, it facilitates a thermal design that takes into
account load fluctuations. The thermal equivalent circuit iscomposed of a two-stage ladder circuit divided into the WPTsystem part and a cooling part. The peak temperature and the
maximum allowable loss of load fluctuation are derived bysimplifying the two-stage ladder circuit. In addition, thethickness of the thermally conductive plastic plates is designedby the design flowchart for the 15-kW WPT system.
Keywords— Wireless power transfer, thermally conductive
plastic, high-power, load fluctuation, thermal equivalent circuit

I. INTRODUCTION
Recently, high-power WPT systems have been actively
studied [1]. A wireless power transfer (WPT) provides
convenience because the power is fed without metal contacts
and connectors. Thus, WPT is superior to wired power supply
systems, and its application in various fields is expected. For
the applications requiring high power such as electric vehicles
and construction machines [2–3], the design to achieve highpower is considered. As an example, the WPT system forlarge-capacity excavator has been proposed [3]. Currently, thedevelopment of the WPT system with an input power of 3.3
or 7.7 kW is moving towards a commercial for light-duty
vehicles with a standardization. Meanwhile, the transmission
power of the bus is much higher than the light-duty electricvehicles [4–5].
However, there is a problem that the ferrite cores and thewindings in the high-power WPT system generate heat due tocopper loss and iron loss [6]. In particular, the temperature riseof the litz wire may melt the insulating film of the litz wire,
eventually causing insulation breakdown between thewindings. Thus, a cooling structure is required to suppress the
978-1-7281-3153-5/19/$31.00 ©2019 IEEE

heat of the high-power WPT system. Thermal design istypically performed by simulation using the finite element
method (FEM) [7]. The optimal solution is unclear since the
FEM requires various conditions such as mesh and heattransfer conditions. In addition, the load of the WPT system isassumed to be a charger or a motor for construction machines.
For this reason, the WPT system repeats the operation andstandby. When temperature analysis is performed using FEM
for repeat operations, the analysis may take a long time.
This paper proposes a thermal design method consideringload fluctuations of a high-power WPT system with a coolingstructure using thermally conductive plastic plates.
Considering the cooling structure with the thermal equivalentcircuit, it is possible to easily perform thermal design evenwhen the load fluctuates. Moreover, the thermal design withthe thermal equivalent circuit shortens the thermal analysis
time. By expressing the system by the thermal equivalentcircuit, the thermal design is optimized by solving the thermal
equivalent circuit with a differential equation. The appliedcooling structure for this paper consists of winding, ferritecore, thermally conductive plastic plates, and aluminum plates.
Each material is represented by a thermal resistance and a heat
capacity on the thermal equivalent circuit. The equivalentcircuit consists of a two-stage ladder circuit divided into the
WPT system part and the cooling part. In order not to exceed
the limitation on temperature, the maximum loss must be
determined from the steady peak temperature of the two-stage
ladder circuit. However, it is mathematically difficult to derive
the peak temperature of the two-stage ladder circuit. Thus, thepeak temperature is obtained by approximating the two-stage
ladder circuit. The allowable loss in order to make the coils
under the temperature limitation is derived from the peaktemperature. Then, the cooling structure is designed byelectromagnetic field analysis. The proposed flowchartadjusts the thickness of the thermally conductive plastic tobring the cooling structure below the maximum loss.

II.

WIRELESS POWER TRANSFER SYSTEM FOR
HIGH-POWER EV CHARGER

Lf

A. System configuration
Figure 1 shows a circuit configuration of the WPT system.
The system consists of a single-phase inverter on the primaryside and a rectifier on the secondary side. In this system, theseries resonance compensation is applied to the primary side,
whereas the parallel resonance compensation to the secondaryside, i.e. SP resonance compensation, in order to supply aconstant voltage to the battery charging system. Thus, the load
voltage is constant regardless of the load fluctuation when aconstant voltage is applied to the primary coil. As a result, it
is possible to obtain the maximum efficiency at the designed
output power.

C1 Req  L2 

L1

 V
2

2
2, DC

8

P2



Req

k

0

1 k2

Cf

C2 v2

C1

r1

I2

l1

l2



f

Req

C2

Lm

V2

Fig. 2. Equivalent circuit of the WPT system.
TABLE I.

DESIGN PARAMETERS OF THE WPT SYSTEM.

SymbolValue

Primary DC voltage

V 1,DC

640 V

Secondary DC voltage

V 2,DC

640 V

Rated Output power

P out

15 kW

Switching frequencyf

20 kHzCoupling coefficientk

0.4

Primary inductanceL1 H

Secondary inductanceL2 H

Primary capacitance

C1

184 nF

Secondary capacitanceC2636 nF

Primary

Ferrite core

Insulating sheet





1
 C1  2
0 L1 (1  k 2 ) C2 

1

02 L2Secondary(a) Conventional cooling structure: Aluminum plates (worst condition).
PrimaryFerrite core

d



C. Cooling structure of WPT system
Figure 3 shows the structures of two cooling structures.
Fig. 3(a) shows the conventional cooling structure using only
the aluminum plates [10]. This structure transfers heat directly
to the aluminum plates. However, eddy current loss occurs in
the cooling aluminum plates. In particular, when the core isplaced close to the aluminum plates, eddy currents are
generated in the aluminum plates, causing the decrease in thetransmission efficiency and the heat generation of theAluminum
plates
Coil
Board



Then, the resonant capacitors are determined according to(4) and (5) so that the power factor stand from the primary sideis unity.

R

r2

2

 8 V

 L1  L2  2 1. DC   k V
2, DC 


+

V2,DC

I1





L2

Fig. 1. WPT system with SP resonance compensation.

The self-inductances of the primary side coil and thesecondary side coil are designed to be equal to the impedanceof the equivalent load resistance Req and the excitationinductance [9]. As a result, it is possible to obtain the
maximum efficiency at the designed output power. The selfinductances of the primary side coil and the secondary sidecoil are expressed by (2),(3).


v1

V1

Figure 2 shows the equivalent circuit of the WPT system.
Table Ⅰ shows the specifications of the WPT system. In thissystem, as one of the example, an output power of 15 kW isassumed. The equivalent resistance of the load-side rectifier isreplaced by the equivalent series resistance Req [8]. The
equivalent load resistance Req of the full-bridge rectifier isexpressed by (1).

k

V1,DC

B. Design of WPT system



I1

+

I2

Insulating sheet

Aluminum
platesThermally
conductive
plastic plates
Coil
Board

Secondary(b) Proposal cooling structure: Aluminum plates + Thermally conductive
plastic plates
Fig. 3. Structure of cooling systems.

aluminum plates themselves. Fig. 3 (b) shows the proposedcooling structure using the thermally conductive plastic plates.
The thermally conductive plastic plates, which are made of amaterial with a high resistivity of 2.2 × 106 Ωm and highthermal conductivity of 21 W/mK [11], are inserted between
the cores and the aluminum plates. Meanwhile, it is difficult
to transfer the heat from the heat source to the outside when
only the thermally conductive plastic plates are used. Thus,
the proposed structure also uses the aluminum plates, whichhave a high thermal conductivity of 138 W/mK. The proposedcooling method suppresses the eddy current loss generated in
the aluminum plates while cooling the primary and secondary
coils. In addition, the eddy current loss is reduced byincreasing the thickness of the thermally conductive plastic
plates.
D. Thermal equivalent circuit
Figure 4 shows a thermal equivalent circuit in which theproposed structure is divided into the WPT system part and acooling part. The thermal equivalent circuit is easily possible
to design even when the load fluctuates repeatedly. When thethermal equivalent circuit is solved in consideration of the heat
capacity, the cycle time to the steady temperature is derived.
In addition, the thermal design is optimized by solving thedifferential equations of the thermal equivalent circuit. The
thermal equivalent circuit is a two-stage ladder circuitcomposed of the WPT system part and a cooling part The
operating condition of the WPT system applies the total loss
Q [W], and the standby condition applies the heat source as
0W. Total loss Q [W] consists losses from windings, core, andaluminum plate. The heat capacity of the winding and ferrite
core is C1 [J/K], the thermal resistance is R1 [K/W], and thetemperature is T1 [°C]. The heat capacity of thermallyconductive plastic plates and aluminum plates is C2 [J/K], thethermal resistance is R2 [K/W], and the temperature is T2 [°C].
The equation for T1 and T2 is expressed by nodal equations.
The equations for operating conditions T1 and T2 is expressedas (6).

dT1 T1  T2Q  C1 dt  R1 

T

T
dT
T2
2
 1 2 C

2
 R1
dt R2



Equation (6) is Laplace transform, and the temperature at thestart of operation is expressed as (7).



T1 ( s )  T2 ( s)Q
 s  sC1T1 ( s ) R1 

T
(
s
)

T
(
s
)
T ( s)2
 1
 sC2T2 ( s )  2

R1
R2



Each T1(s) and T2(s) are derived from (7). When inverse
Laplace transform is performed, T1(t) and T2(t) are obtained.
Except for the start of the operation, it is necessary to apply
the initial temperature in the heat capacity. The initial
temperature of the winding and ferrite core is T01. The initial
temperature of the thermally conductive plastic plates andaluminum plates are T02. Considering the initial temperatures
T01 and T02 in (6), the result of Laplace transform is expressed
as (8).

Operation mode

Thermally
conductive
plastic plates+
Aluminum

Ferrite core+
Winding
R1

T1

R2

T2

Q
C1

C2

WPT system part

Cooling structureStandby mode
R1

T1

C1

R2

T2

C2

Fig. 4. Thermal equivalent circuit corresponding to load fluctuationof the WPT system.



T1 ( s )  T2 ( s )Q s  C1  sT1 ( s )  T01  
R1  T1 ( s )  T2 ( s )  C  sT ( s )  T   T2 ( s )
2
2
02

R1
R2



Each T1(s) and T2(s) are derived from (8). When inverse
Laplace transform is performed, temperature rise T1(t) andT2(t) from the initial temperature are obtained.
The temperature of the WPT system during a standby
condition drops because the total loss Q [W] in the standby
condition is 0 W. The loss in Fig. 4 is opened. The temperatureduring the standby condition is expressed as (9).



dT1 T1  T2
0  C1 dt  R1 

T

T
dT
T
1
2
2

 C2
 2
 R1
dt R2



Considering the initial temperatures T01 and T02 in (9), theresult of Laplace transform is expressed as (10).



T1 ( s )  T2 ( s )0  C1  sT1 ( s )  T01  
R1  T1 ( s )  T2 ( s )  C  sT ( s )  T   T2 ( s )
2
2
02

R1
R2



Each T1(s) and T2(s) are derived from (10). When inverse
Laplace transform is performed, temperature drop T1(t) andT2(t) from the initial temperature are obtained. From the above,
the temperature rise and drop by the load fluctuation is
calculated by the above equation. In other words, the time toreach the peak temperature is calculated.
E. Derivation of peak temperature and allowable loss
Figure 5 shows a thermal equivalent circuit with anapproximation of the peak temperature. Figure 6 shows anexplanatory diagram for deriving the peak temperature. If theoperation continues for a long time until the steady
temperature is reached, the peak temperature is determined.
However, the above method of obtaining the peak temperaturetakes a long time. Thus, it is necessary to derive anapproximate expression for the peak temperature.
Furthermore, it is necessary to design the heat by deriving the
maximum allowable loss of the cooling structure. The
maximum allowable loss is derived from the peak temperature.
The thermal equivalent circuit for obtaining the peaktemperature assumes that R2 and C2 parts on the secondaryside of the two-stage ladder circuit are the average temperature
T2. The thermal equivalent circuit in Fig. 5 is expressed as (11).

T1
Q
C1

T2

Fig. 5. Thermal equivalent circuit for determining peak temperature.

Temperature rise[°C]

dT1 T1  T2Q  C1 dt  R1 
dTT0  C 1  1 T2
1

dt
R1

Averagetemperature: T2

R1



Tpeak

T1(ta)

T1(tb)T0

T0ta

The peak temperature is obtained from the simultaneous
equations of temperature rise and drop in the steady-state. The
Laplace transform of (11) is expressed as (12).

tb

Time[s]Fig. 6. Derivation of peak temperature on steady-state.
Start



T1 ( s ) T2
Q
 s  C1  sT1 ( s )  T01   R  sR11 0  sC T ( s )  C T  T1 ( s )  T2
1 1
1 0

R1
sR1

Setting the winding with the half-length of the core

Deriving R1,2, C1,2 of cooling system using only
aluminum plates (Worst condition)
Deriving the maximum loss by approximate
expression (R,C,Duty,Tpeak→Qmax)

The temperature rise and drop of T1(s) is express as (13) from
(12) with inverse Laplace transform.



Creating the worst condition by electromagnetic
field analysist 
T1 (t )  T2  QR1  exp   T2  T0  QR1  C1R1   

t 

T
(
t
)

T

exp

T

T

 0 2 
2
 1
 C1R1 Deriving L1 by electromagnetic field analysis
L1>L1,nominal

As shown in Fig. 6, when the temperature after ta is the peaktemperature Tpeak and the temperature after tb is the lower limit
value T0, the temperature expressed as (14).



Tpeak T2 1  AB   QR1 1  A1  AB

NO

Increasing the thickness
Δd of the thermallyAnalyzing loss Q of the cooling structure
conductive plastic plates
by electromagnetic field analysis
NO

Q<QmaxYES
Completed a cooling structure with maximum
allowable loss and peak temperatureloss Qmax is expressed as (16).





The approximation formula for peak temperature is
extremely precise [12]. The maximum allowable loss isobtained by the deformation of (15). The maximum allowable

Increasing
L1

Fig. 7. Flowchart of thermal design.

Solving for Tpeak from the simultaneous equations in (14), theapproximate equation for peak temperature is expressed as(15).
Electromagnetic
field analysis

YES ta 
T1 (ta )  Tpeak  T2  QR1  exp   T2  T0  QR1  C1R1   
 tb 

T1 (tb )  T0  T2  exp   C R  Tpeak  T2 
 1 1


 t 
 t 
 A  exp   a  , B  exp   b  CR 1 1
 C1R1 

Thermaldesign Qmax 

Tpeak (1  AB)  T2 (1  AB)
R1 (1  A)





F. Thermal design
Figure 7 shows the flowchart of the thermal design for the
WPT system with the proposed cooling structure. In order todesign the cooling structure, thermal analysis, andelectromagnetic field analysis are used for the evaluation of
the cooling performance. The advantage of the proposed
design flow is a one-loop thermal analysis. Thus, there is no

III.

THERMAL ANALYSIS AND LOSS ANALYSIS

A. Thermal analysis
The primary side and secondary current of k = 0.4 are I1 =37.3 A, I2 = 85.6 A, and the gap of the WPT system is 100mm. This condition is not changed even if the coolingstructure changes. In this condition, the loss on the primaryside is larger than the secondary side due to a large number ofturns and winding resistance. Thus, the thermal design targets
the primary WPT system.
Table Ⅱ shows the density, specific heat, volume, and heat
capacity of each part of the WPT system. Table Ⅲ shows the
thickness, thermal conductivity, thermal transfer area, andthermal resistance of each material. The heat capacity of eachpart is expressed by (17) using the density ρ [kg/m3], specificheat c [J/(kg·K)], and volume V [m3] in Table Ⅲ. The heat
capacity and thermal resistance are calculated from the worst
condition structure.
 C   cV The thermal resistance R [K/W] of each material is expressedby (18) using the thickness L [m], thermal transfer surface A[m2], and thermal conductivity K [W/(m·K)] in Table Ⅲ.


R

L

KA



There is a difference in the heat transfer area between thewinding and the core. Thus, the thermal resistance R’[K/W]
when heat spreads in the thickness direction and the surface
direction is expressed as (19).


R' 

L

ka(2 L  a)

By the above formula, the thermal conductivity and heat
capacity of the worst condition shown in Fig. 4 are R1 = 0.157
K/W and C1 = 6299 J/K, R2 = 0.0405 K/W, and C2 = 5849 J/K.

TABLE II.

THERMAL CAPACITY OF EACH MATERIAL.

Copper (winding)
Ferrite coreDensity[kg/m 3 ]Specificheat[J/(kg･K)]

Volume[m 3 ]

8960

380

255.6×10 -6

870.3

600

1998×10-65753.1-65849.14800

Aluminum

2680

900

2425×10

T hermallyconductive plastic

1490

950

-

TABLE III.

T hermalcapacity[J/K]-

THERMAL RESISTANCE OF EACH MATERIAL.
T hermalT hermalT hickness
conductivity transfer area[m]
[W/mK][m 2 ]

T hermalresistance[K/W]

Primary winding

0.004

403

0.04

0.00025Ferrite core

0.01

5

0.20

0.0154

Aluminum

0.01

138.3

0.24

0.0003

Silicon grease

-

0.84

-

0.0402

Osculating plane

-

-

-

0.0755Insulating sheet

0.00020.2

0.20

0.0050T hermallyconductive plastic

-

21

0.20

-

180

Primary side winding
Primary side aluminum
Primary side core
Qmax

16.7
160
16.8

Loss[W]

need to perform thermal analysis many times. According to
the flowchart of Fig. 7, the thickness of the thermallyconductive plastic plates in the proposed cooling structure isdetermined. At the first, the model with aluminum plates,
which directly connected to the core, is analyzed. The
thickness of the thermally conductive plastic plates is set to 0mm. In other words, it is as same as the conventional structure
shown in Fig. 3. This cooling structure assumes that the ferrite
winding area is half of the core. Heat capacity and thermal
resistance are taken from the cooling model and taken into
account in the thermal equivalent circuit. The maximum
allowable loss of the cooling structure is derived fromconditions such as peak temperature. The next step is to model
the cooling structure of the worst condition withelectromagnetic field analysis. The inductance value of the
primary winding is analyzed with the electromagnetic field
analysis. If the inductance value exceeds the nominal value,
the loss analysis of the cooling structure is analyzed byelectromagnetic field analysis. If the analyzed loss exceeds the
maximum allowable loss, the thickness of the thermallyconductive plastic plates is increased in order to reduce theeddy current loss. If the maximum allowable loss is notreached, the cooling structure that lowers the winding
temperature below the allowable temperature is determined.

140

16.6

16.6

39.2
24.1

22.7

19.0

118.8

118.7

118.8

118.8

0

10

20

30

120

100
Thermally conductive plastic plates thickness[mm]Fig. 8. Total loss due to the thickness of thermally conductive plastic
plates.

Load fluctuation is designed to operate and standby in a
30-minute cycle. The duty ratio of this paper is 90%. This duty
ratio is the operation time in one cycle time. In other words, it
operates for 27-minutes in 30-minutes, and standby for 3minutes. Under these conditions, to suppress the temperaturerise of the WPT system below 30°C, the allowable power loss
is 158.0 W by (16). Thus, the loss from the cooling structure
must be less than this maximum allowable loss.
B. Loss analysis
Figure 8 shows an analyzed power loss with the different
thickness of the thermally conductive plastic plates. The
power loss is lower than the maximum allowable loss when
the thickness is larger than 30-mm. As a result, the eddy

Primary

Ferrite core

Thermally
conductive
Aluminumplastic30mm
446mm
Gap:100mm

459mm

Winding

446mm

SecondaryFig. 9. Cooling structure with less than maximum allowable loss by electromagnetic field analysis.

current loss is reduced by 51.5% and the total loss is
suppressed to 154.3 W.
Figure 9 shows the cooling structure with the 30-mm
thermally conductive plastic plates. The thickness of thethermally conductive plastic plates is 30-mm, and it is placed
between the aluminum plates and the core. The primarywinding is 42-turns and the inductance value is 421µH.
IV. CONCLUSION
This paper proposed a thermal design method consideringload fluctuations of a high-power WPT system with a coolingstructure using thermally conductive plastic plates.
Considering the cooling structure with the thermal equivalentcircuit, it is possible to easily perform thermal design evenwhen the load fluctuates. Moreover, the thermal design withthe thermal equivalent circuit shortens the thermal analysis
time. By expressing the system by the thermal equivalentcircuit, the thermal design is optimized by solving the thermal
equivalent circuit with a differential equation. The proposed
flowchart is designed for the thickness of the thermallyconductive plastic plates that is below the maximum allowable
loss. The maximum allowable loss should not exceed 158.0
W. As a result, eddy current loss is reduced by 51.5% and thetotal loss is suppressed to 154.3 W when the thickness of thethermally conductive plastic plates is 30-mm.
In the future, we will verify and evaluate the proposed
design method by prototype experiments.
REFERENCES
[1]

[2]

[3]

[4]

[5]

Keisuke Kusaka, Jun-ichi Itoh, “Development Trends of Inductive
Power Transfer Systems Utilizing Electromagnetic Induction with
Focus on Transmission Frequency and Transmission Power,” IEEJ
Journal Industry Applications, vol. 6, no. 5, pp. 328-339, 2017.
Mostak Mohammad, Seungdeog Choi, Md Zakirul Islam, Sangshin
Kwak, Jeihoon Baek, “Core Design and Optimization for Better
Misalignment Tolerance and Higher Range of Wireless Charging of
PHEV,” IEEE Trans. Transportation Electrification, vol. 3, no. 2, pp.
445-453, 2017.
Keisuke Kusaka, Kent Inoue, and Jun-ichi Itoh, “Inductive Power
Transfer System for an Excavator by considering Large Load
Fluctuation,” IEEJ Journal Industry Applications, vol. 8, no. 3, pp. 413420, 2019.
Chunting Chris Mi, Giuseppe Buja, Life Fellow, Su Y. Choi, Chun T.
Rim, “Modern Advances in Wireless Power Transfer Systems for
Roadway Powered Electric Vehicles,” IEEE Trans. Industrial Electron.,
vol. 63, no. 10, pp.6533-6545, 2016.
J. Shin, S. Shin, Y. Kim, S. Ahn, S. Lee, G. Jung, S. Jeon, D. Cho,
“Design and Implementation of Shaped Magnetic-Resonance-Based
Wireless Power Transfer System for Roadway-Powered Moving
Electric Vehicles,” IEEE Trans. Industrial Electron., vol. 61, no. 3, pp.
1179-1192, 2014.

[6]

Kosuke Mizoguchi, Keisuke Kusaka, Jun-ichi Itoh, “Evaluation of
Cooling Method for Wireless Power Transfer System using Thermally
Conductive Plastics,” Technical Committee on Semiconductor Power
Converter , SPC-19-044, MD-19-044, 2019.
[7] B. Dong, K. Wang, B. Han and S. Zheng, "Thermal Analysis andExperimental Validation of a 30 kW 60000 r/min High-Speed
Permanent Magnet Motor With Magnetic Bearings," IEEE Access, vol.
7, pp. 92184-92192, 2019.
[8] R. L. Steigerwald, “A comparison of half-bridge resonant converter
topologies,” IEEE Trans. Power Electron., vol. 3, no. 2, pp. 174-182,
1988.
[9] Roman Bosshard, Johann Walter Kolar, Jonas Muhlethaler, Ivica
Stevanovic, Bernhard Wunsch, Fransisco Canales, “Modeling and η-αPerato Optimization of Inductive Power Transfer Coils for Electric
Vehicles,” IEEE Journal Emerging and Selected Topics in PowerElectron., vol. 3, no. 1, pp. 50-64, 2015.
[10] Tomohiro Yamanaka, Itaru Fujita, Yasuyoshi Kaneko, Shigeru Abe,
Tomio Yasuda, “Cooling Structure for Large Capacity H-shaped Core
Contactless Power Transformers for Electric Vehicles,” IEEJ Trans.
Industry Applications, vol. 134, no. 3, pp. 370-375, 2014.
[11] Yamashita Materials Corporation, “Thermal Conductive Plastic,”
http://www.yamashita-net.co.jp/english/[12] Kosuke Mizoguchi, Keisuke Kusaka, Jun-ichi Itoh, “Design Method of
Cooling Structure Considering Load Fluctuation of High-power
Wireless Power Transmission System,” Technical Committee on
Semiconductor Power Converter , SPC-19-123, MD-19-089, 2019.