電気学会論文誌●（●●●●●●●部門誌）
IEEJ Transactions on ●●●●●●●●●●●●●●●
Vol.●● No.● pp.●-●●
DOI: ●.●●/ieejeiss.●●.●Paper

A 22kW Three-phase Wireless Power Transfer System
in Compliance with CISPR 11 and ICNIRP 2010
Keisuke Kusakaa)＊ Member, Rintaro Kusui＊ Student-member,
Jun-ichi Itoh＊ Senior-member, Daisuke Sato＊＊ Member, Tetsu Shijo＊＊＊ Non-member,
Shuichi Obayashi＊＊＊ Non-member,
Masaaki Ishida＊＊＊ Non-member(Manuscript received Jan. 00, 20XX, revised May 00, 20XX)
Techniques to reduce electromagnetic emission in high-power wireless power transfer (WPT) systems are required because theradiated emission of the WPT must comply with the regulation published by CISPR (International Special Committee on RadioInterference) and ICNIRP (International Commission on Non-ionizing Radiation Protection.) In this paper, a three-phase WPTsystem, which complies with CISPR 11, group 2, class A is developed. The three-phase WPT system has six solenoid coils on the
primary side and six solenoid coils on the secondary side. The use of 12 coils allows radiation noise reduction as the radiation noise
is emitted to the opposite direction of the pairs of coils. Moreover, the cross-coupling among six coils on the common side iscanceled by adjusting the position of coils. The electromagnetic compatibility of the 22kW prototype is evaluated in a 10 m anechoic
chamber according to the CISPR 11 guideline. The prototype fully complies with CISPR 11, class A, group 2 with respect toelectromagnetic emission. Moreover, it also complies with ICNIRP guidelines in 2010 at a distance of 340 mm or more from theedge of the coils.
Keywords : Electromagnetic compatibility, Electromagnetic induction, Inductive power transmission, wireless power transmission

1.

the guidelines published by ICNIRP and CISPR. The guideline
published by ICNIRP focuses on the effect on human bodies. In
contrast, the guidelines by CISPR focuses on the effect on theinterference with radio communications and malfunction ofelectrical equipment. The high-power WPT system must comply
with both regulations.
For WPT5, high-power wireless power transfer systems havebeen developed(10–16). In (11–13), the WPT systems with an input
power of 22 to 50 kW have been reported. However, the radiatedemission test has not been mentioned in the literature. In (14–15),
only the magnetic field near WPT systems has been evaluated tocompare with ICNIRP guidelines. The compatibility with the
CISPR guidelines has not been discussed; nevertheless, theradiation noise from WPT systems may interfere with the radio
communications. The two-channel 44-kW WPT system isdemonstrated in (16). The radiated emission at 10 m from the WPTsystem is evaluated in an anechoic chamber for the compatibility
test with the regulation in Japan. However, the compatibility with
the CISPR guidelines has not been discussed in this paper.
Nevertheless, compliance with both guidelines is essential to put
the high-power WPT system into practical use.
In this paper, the 22-kW three-phase WPT system (WPT5) isdeveloped. The developed 22-kW system reduced the radiativeemission using multiple coils. Moreover, the cross-coupling effectby the multiple coils is cancelled using three-phase transmission
and coil structure. It is demonstrated that the 22-kW prototype
satisfies CISPR 11, class A, group 2 published in 2009, andguideline for general public exposure published by ICNIRP in 2010.

Introduction

The sales volume of electric vehicles (EVs) has been slowly
increasing in this decade due to global warming and environmental
issues. One of the reasons that are hindering the rapid adoption of
EVs is their short travel distance. Since users of EVs are frequently
required to charge onboard batteries, they are not still substituted
for conventional vehicles. As one of the solutions to improve theconvenience of EV users, wireless power transfer (WPT) withmagnetic induction has been actively studied in this decade(1–8).
In the international standardization for the WPT system by
ISO/IEC, the WPT systems are classified into five classes (WPT1–
5) based on the input power(9). The largest class is WPT5, with an
input power of 22 kW or more. One of the specific difficulties ofhigh-power WPT is electromagnetic compatibility (EMC). An
increase in the transmission power exposes EMC problems due tothe radiated emission because the WPT system transmits powerusing magnetic coupling. The electromagnetic emission may causeinterference with radio communications, malfunction of electricalequipment, or harm to human bodies. In order to ensure that the
WPT system does not affect equipment or the human body, theelectromagnetic radiation from the WPT system must comply witha) Correspondence to: Keisuke Kusaka. E-mail:kusaka@vos.nagaokaut.ac.jp＊
Nagaoka University of Technology
1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan＊＊
Nagaoka Motor Development Co., Ltd.,2085-16, Fukasawa, Nagaoka, Niigata 940-2135, Japan＊＊＊
Toshiba Corporation
1, Komukai-Toshiba-cho, Saiwai-ku, Kawasaki, Kanagawa 2128582, Japan© 200● The Institute of Electrical Engineers of Japan.

1Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)2.

Three-phase WPT System with EMI Reduction
Capability

iu1

u1

2.1 Circuit Configuration
Figure 1 shows the threephase WPT system. The WPT system has six solenoid-typetransmission coils for the primary side and six coils for thesecondary side. The positions of six coils for the primary andsecondary side are fixed, respectively, as shown in Fig. 1 (a). The
primary and secondary sides are connected in star winding forthree-phase transmission. Note that the delta-delta, star-delta, ordelta-star windings can be used for the system, whereas the star-starwindings are used in this paper. The six coils are used for each of
the primary and secondary sides to reduce the effect of the crosscoupling among the coils. In conventional three-phase WPTsystems(17–19), the circulating current due to the cross-coupling
among the primary coils or secondary coils degrades thetransmission efficiency. The WPT system has the reduced effect ofcross-coupling by optimizing the positional relationship and figuresof the six coils, as explained in the next section.
In the proposed system, only the magnetic couplings M between
the paired coils such as Lu1A and Lu2A contribute to supplying powerfrom the primary side to the secondary side. Other couplings,
typically called cross-coupling, cause the unintended induced
voltage on each coil. In WPT systems with multiple transmission
coils, the induced voltage alternates by the current on the other coil.
The unintended induced voltage is not compensated by the resonantcapacitors. In other words, the other magnetic couplings should bezero for the power transmission with a unity power factor.
The three-phase inverter is used on the primary side. The inverter
is operated with a square wave output voltage. On the secondaryside, the diode bridge rectifier is used. The resonant capacitors Cu1,
Cv1, and Cw1 are connected to the output of the inverter for thecompensation of a weak magnetic coupling M. Consequently, theresonant capacitors Cu2, Cv2, and Cw2 are connected into the input of
the three-phase diode bridge rectifier for the compensation. The
inverter is operated in a zero-voltage switching (ZVS) condition by
operating the inverter with a slightly higher frequency than theresonant frequency owing to the series resonance. In the ZVS
condition, the switching loss of MOSFETs is reduced because aparasitic capacitor is discharged before them switching due to thecirculating current during the deadtime(20).
2.2 Radiation Noise Reduction
Figure 2 is a schematicof the primary and secondary coils. The key technique to reduce theradiation noise is the six pairs of solenoid coils placed in the
opposite. The series-connected two coils on the common phase aremagnetically differential. Because the amplitude of the current oneach coil and the direction of the magnetic flux is in the opposite
direction, radiation noise measured at 10 m from the center of coils
is suppressed(16). Note that the measurement distance isprovided by the guideline for radiation noise such as CISPR.
Moreover, the proposed system has six coils for three-phasetransmission. The transmission coils are placed every 60 degrees.
In the conventional three-phase WPT system, the cross-couplingcannot be ignored because the cross-coupling degrades thetransmission efficiency because of the circulating current on the
primary side or the secondary side. In the proposed system, theeffect of cross-coupling Man, Mbn, Mcn, Ma12, Mb12, or Mc12 (n = 1 or
2) is reduced to approximately zero, as explained in the next section.
Figure 3 compares the magnetic field analyzed by anelectromagnetic analysis (JSOL Corp., JMAG) between the three-

Cu1

VDC1

v1

iu2

M

u2

Lu1A

Lu2A

Lu1B
Lv1B
Lv1A

Lw2B
Lw2A

Cv1

w1

Cu2

Lu2B
Lw1B
Lw1A

Lv2B

Lv2A

Cv2

VDC2

v2
w2

Cw2

Cw1

(a) Circuit configuration2rxFerrite core
Lw1B

Acrylic plate

Lv1A

y

Windings

Lu1A

Lu1B
Lw1A
Lv1B

(b) Figure of primary coils and secondary coils

Fig. 1. Three-phase wireless power trasnfer systemwith 12 coils. The two coils connected in series isdifferentially connected for radiation noise reduction.
The secondary coils is the same to the primary coils
except the number of turns.
v1

iv1
Cv1
M b1

Lw1B

iu1

Lu1A

Lv1A

M c1

u1
Cu1

Lu1B

M a1

iw1

w1
M

iv2

Cw1

Lw1A

Lv1B

M b12

M a12

M c12

v2

Cv2
Lw2B

iu2

Lu2A

u2

M b2

Cu2

Lu2B
M a2

iw2

Lv2A

M c2

Lw2A
Lv2B

w2
Cw2

Fig. 2. Transmission coils and magnetic couplings
among 12 coils. The magnetic couplings except the main
couplings M do not contribute transmitting power.
phase WPT system with six coils and the proposed WPT systemwith 12 coils. In the three-phase WPT system with six coils, the2

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.) vu1 A   L1Ys  vu1B   M c1
 vv1 A   M b1
 
 vv1B   M a1
 vw1 A   M b1
 
 vw1B   M a1
v  = M
 u2A  
 vu 2 B   M c12
v  M
 v 2 A   b12
 vv 2 B   M a12  vw 2 A   M b12
v  M w 2 B   a12

M c1

M b1

M a1

M b1

M a1

M

M c12

M b12

M a12

M b12

L1Ys

M a1

M b1

M a1

M b1

M c12

M

M a12

M b12

M a12

M a1

L1Ys

M c1

M b1

M a1

M b12

M a12

M

M c12

M b12

M b1

M c1

L1Ys

M a1

M b1

M a12

M b12

M c12

M

M a12

M a1

M b1

M a1

L1Ys

M c1

M b12

M a12

M b12

M a12

M

M b1

M a1

M b1

M c1

L1Ys

M a12

M b12

M a12

M b12

M c12

M c12

M b12

M a12

M b12

M a12

L2Ys

M c2

M b2

M a2

M b2

M

M a12

M b12

M a12

M b12

M c2

L2Ys

M a2

M b2

M a2

M a12

M

M c12

M b12

M a12

M b2

M a2

L2Ys

M c2

M b2

M b12

M c12

M

M a12

M b12

M a2

M b2

M c2

L2Ys

M a2

M a12

M b12

M a12

M

M c12

M b2

M a2

M b2

M a2

L2Ys

M b12

M a12

M b12

M c12

M

M a2

M b2

M a2

M b2

M c2

M a12   iu1  
M b12   −iu1 
M a12   iv1  
M b12   −iv1 M c12   iw1  
M  d  −iw1 ···························· (1)M a 2  dt  iu 2  
M b 2   −iu 2 
M a 2   iv 2 
M b 2   −iv 2  
M c 2   iw 2 L2Ys   −iw 2 

200

Magnetic field [dBmA/m]

coils Lu1B, Lv1B, Lw1B, Lu2B, Lv2B, and Lw2B are removed from thesystem with 12 coils. In this analysis, a current with a frequency of
85 kHz is provided into each winding. The primary and thesecondary current are 28 and 46 A, respectively. The magnetic fieldstrength at 10 m from the center of the coil has been compared. The
proposed WPT system has approximately the same magnetic fieldas the conventional WPT near the coils because the distance
between the two magnetomotive forces is relatively far apartcompared to the measurement distance. The proposed WPT systemwith 12 coils has a lower magnetic flux density than theconventional WPT system away from the center of the coils. Notethat the radiation noise from the WPT system is measured andevaluated at 10 m in the CISPR 11 guidelines.
2.3
Reduction in Effect of Cross-coupling
The WPT
system with multiple coils on the primary side or the secondary side
has a critical problem that the transmission coils have crosscoupling, which is also called cross-coupling” among the coils(16,
21–22). In (22), it is reported that the analytical results of efficiency
and voltage transfer ratio of the three-phase WPT system has anerror to the experimental results due to the cross-coupling. The
circulating current causes a decrease in transmission efficiency.
In this paper, the effect of cross-coupling is reduced toapproximately zero by six coils, which are circularly placed, and athree-phase current on the six coils. Here, the reduction method is
explained, focusing on Lu1A in Fig. 2. The cross-coupling on the
primary side for Lu1A is from others on the primary side Lu1B, Lv1A,
Lv1B, Lw1A, and Lw1B. Note that the types of cross-coupling arelimited to three types, Ma1, Mb1, and Mc1, by placing the coils in acircle. The sum of the magnetic flux from these coils on Lu1A is zeroby designing the figures of coils, such as the radius of six coils, thewidth, and the length of each coil.
The reduction method of the interference is described using theinduced voltage on Lu1A in this section. Equation (1) presents theinduced voltage on the 12 coils. The variables M is the main
coupling for power transmission, Man, Mbn, Mcn, Ma12, Mb12, andMc12 are the cross-coupling, LnYs is the self-inductance of each coil.
Here, the cross-coupling Ma12, Mb12, Mc12 can be ignored because
the different heights and the different directions of the solenoid
coils cause significant small coupling. Note that the effect of crosscoupling Ma12, Mb12, Mc12 is also canceled by the design oftransmission coils, although it can be ignored in this paper.
From the first line of (1), the induced voltage of the coil Lu1A isexpressed by

180
160
140
Measurement distancein CISPR 11

120
100

6-coils
12-coils

80
60

r r+x

0

2000

4000
6000
8000
10000
Distance from center of coils [mm]Fig. 3. Comparison in magnetic field strength between
the six-coils WPT and proposed 12-coils WPT.
diu1
di
+ M u2
dt
dt
di 
di
 div1 diw1  di− M a1 ++ M b1  v1 + w1  − M c1 u1

dt 
dt 
dt
 dt
 dt

vu1 A  L1Ys................................................................................................ (2).
As shown in (2), the terms on the first line represent the induced
voltage by the self-inductance and the mutual inductance, which
contributes to transmitting power to the secondary side. The termson the second line are from the interferences. The induced voltage
by the interferences Ma1, Mb1, and Mc1 does not transmit power tothe secondary side. On the contrary, the third to fifth terms cause
the circulating current. The sum of these terms must be zero.
Adjusting the sum of the third to fifth to zero using the three-phasetransmission characteristic reduces the effect of the cross-coupling.
The three-phase current is an equilibrium when the transmission
coils have no position misalignment. Equation (2) is modified as (3),where Im1 is the primary current amplitude.
vu1 A = L1Ys

diu1di
+ M u2
dt
dt


2 

− I m1  M c1 cos t + ( M a1 − M b1 ) cos  t −  
3 


4 

+ ( M a1 − M b1 ) cos  t −   3 
... (3)Equation (3) has three cosine waves with a phase delayed by 120
or 240deg. Thus, the condition for canceling the effect of the crosscoupling is satisfying

3

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)

Ploss

Pin

=

iu1

u1
Cu1

vuv

200 V

Powe r sou rce i nanec hoic chamber

Lv1A

VDC1

Pout

iu2

M

u2

Lu 1A

Lu2A

Lu1B
Lv1B

Lw2B

Cv1

v1

Pout
Pin

Cu2

Lu2B
Lw1B
Lw1A

Lw2A

Lv2B

Lv2A

Cv2

VDC2
v2

w1

w2
Cw1

Cw2

Buck and boost chopper for power circulation

Fig. 4. Circuit configuration of the 22-kW WPT system. The buck and boost chopper is used for power circulation for the test in
the anechoic chamber with limited power capacity.

M a1 = Mb1 + M c1 ........................................................... (4).
The cancellation condition is (5) with the coupling coefficients
ka1, kb1, and kc1 because the self-inductance of the primary coils iscommon.

ka1 = kb1 + kc1 ............................................................... (5)In the same manner, the cancellation condition of the induced
voltage on the secondary side iska 2 = kb 2 + kc 2 .................................................................. (6).
(a) Primary inverter

By satisfying both (5) and (6), the induced voltage on the Lu1A is
simplified as

vu1 A  L1Ys(b) Secondary rectifier

diu1
di+ M u 2 ............................................... (7).
dtdtThis is the same as the induced voltage of a single-phase WPTsystem. It means that the interference among the primary coils andthe secondary coils can be canceled by the structure of 12 coils.
Eqs. (5–6) provides the limitation on the figure of transmission
coils. In Fig. 1, the coupling kan (n = 1, 2) tends to be the strongest
among the cross-coupling because kan is the coupling between theadjacent coils in the same plane. In order to satisfy (5–6), only the
coupling kbn and kcn should be improved without increasing thecoupling kan. It prevents shrinking the total radius r + x of thetransmission coils.
For the prototype, physical parameters of the transmission coils,
such as the width, the depth, the thickness, and the distance between
the coils, have been determined by cut-and-try with anelectromagnetic analysis in this paper. The end of the cut-and-try
design is determined by the remaining coupling. The ideal
conditions are kan = kbn + kcn, as shown in (5–6). From theseequations, the remaining magnetic coupling is kan – kbn – kcn. The
transmission coils are designed so that the remaining coupling kan –kbn – kcn is less than 1/10 of the coupling k (= M / (L1YsL2Ys)0.5). Herethe coupling k is the main coupling between the primary coils andthe secondary coils.
It should be noted that the misalignment of coils and parameter
errors on resonance may cause the degradation on the transmission
power and efficiency because the cancellation conditions of thecross-coupling, as shown by (5–6), are developed based on theassumption of three-phase equilibrium. Besides, the reduction inradiated emission will not be affected by the misalignment of coils(c) Transmission coils

Fig. 5. The 22-kW prototype.
because the cancellation of the radiated emission is satisfied bypairs of coils connected in series with the same current, such as Lu1A
and Lu1B.

3. 22-kW Prototype
3.1
System Configuration
In this chapter, the 22-kW
WPT system is experimentally demonstrated. Figures 4 and 5 show
the system configuration and prototype for the evaluation,
respectively. The input is connected to the variable transformer toadjust the input DC voltage. Note that a PWM rectifier will be
installed instead of the adjustable transformer and diode-bridge
rectifier for a product. The prototype has a diode bridge rectifier andbidirectional buck-boost chopper for the test in an anechoic
chamber with limited input power.
The bidirectional buck-boost chopper circuit plays a role incirculating power between the output and the input of the system.
4

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)Table I. Specification of 22-kW prototype.
Parameters

Symbols

Value

Input power

Pm

25

kW

Primary voltage at rated power

VDC1

650

V

Secondary voltage

VDC2

200-400

V

Transmission frequency

f

80

kHz

Air gap
Core width

g

90

mm

x

500

mm

Core length

y

250

mm

Core thickness

z

10

mm

RadiusNumber of turns
Self-inductance
Main coupling

r

750

mm

Primary

N1

8

turn

Secondary

N2

5

turn

Primary

L1Y

21.8

mH

Secondary

L2Y

8.52

mH

k

0.55

TDK, PC95

Litz wire

2UEWLZ 7×130 (0.1)

MOSFETs

ROHM, BSM300D12P2E001

DiodesInfineonTechnologies,
IDW40G120C5BFKSA1
Td

500

L2Y = Lu 2 = Lv 2 = Lw2 =

2
6 VDC
1
.......................... (10).
 k Pm
2

Then, the resonant capacitors Cu1, Cv1, Cw1, Cu2, Cv2, and Cw2 areselected to resonate with the self-inductance of each coil. Seriesseries compensation(24) is used in this paper. The reactance of thecapacitors must be equals to the reactance of the inductance of thecoils at the transmission frequency in the series-series
compensation.

ns

Cu1 = Cv1 = Cw1 =The secondary DC voltage VDC2 is adjustable between 200 to 400 V
by the bidirectional buck-boost chopper because it is a typicalvoltage range of onboard batteries. The AC power source in theanechoic chamber supplies only the power loss in the WPT systemand the bidirectional buck-boost chopper due to the configuration.
Figures 5 (c) shows the transmission coils for the 22-kW test. The
cross-coupling is ka1 = 0.0043, kb1 = 0.0026, kc1 = 0.0026, ka2 =0.0090, kb2 = 0.0013, and kc2 = 0.0006. The developed transmission
coils satisfy the cross-coupling reduction condition expressed in (5–6). Air gaps between the primary coils and the secondary coils are
90 mm because the physical parameters of the coils are determinedby the cut-and-try method in this paper. The proposed configurationis also effective for WPT systems with different air-gap. The air gap
does not affect the reduction performance of the radiation noise andcross-coupling. The radiation noise reduction is achieved by thepairs of two coils, placed opposite, on each the primary and thesecondary side. Although, the interference reduction condition
expressed in (5) and (6) are satisfied on each the primary side andthe secondary side, respectively, even if the air gap is changed.
3.2
Parameter Design
In this chapter, the design ofthe 22-kW three-phase WPT system is explained. Table I shows theparameters of the prototype. First, the inductance of coils isdesigned. The three-phase diode bridge rectifier is represented as an
AC resistance. The equivalent AC resistance Req of the rectifier is(8).

1

 2 L1Y, Cu 2 = Cv 2 = Cw2 =1

 2 L2Y............................................................................................... (11)For the ZVS operation of the inverter, the operating frequency of
the inverter is slightly higher than the resonant frequency, which isdetermined by (9–11).

4.

Experimental Verification of 22-kW Prototype

4.1
Rated Power Test
Figure 6 shows the operation
waveforms with a 22-kW of the output power, a 650-V of the
primary DC voltage VDC1, and a 400-V of the secondary DC voltage
VDC2. The bidirectional buck-boost chopper controls the secondary
DC voltage to 400 V in order to emulate the onboard battery. The
waveform in Fig. 6(a) is the line voltage. The zero-cross of the
primary current is synchronized with the voltage rise and fall of theline voltage. It means that the primary inverter operates in theresonant condition. From Fig. 6 (b), it is confirmed that the threephase primary current is at equilibrium. The output voltage slowly
steps up or down by the ZVS operation.
4.2
Efficiency Evaluation
The system efficiency ofthe 22-kW prototype is evaluated. The DC-to-DC efficiency, which
is defined as the ratio between the input power and the output powerof the DC stage, is measured by the power analyzer (Yokogawa,
WT1600). Figure 7 shows the efficiency characteristic of the WPTsystem. The efficiency indicated in Fig. 7 contains the power loss
in the inverter and the diode bridge rectifier. The secondary DC
voltage is controlled at 200, 300, 400 V to emulate the constantvoltage load, such as an onboard battery. When the battery voltage
is lower than 400 V, the output power is derated by the current limitof the secondary coils and diodes. The maximum DC-to-DC
efficiency is 91.3% at an output power of 5.0 kW, 91.3% at 10 kW,
and 91.1% at 22 kW when the secondary DC voltage is 200, 300,
and 400 V.

2
8 (VDC 2 2 )6 VDC
2............................................ (8)= 2 Pm 3
 2 Pm
2

Req =

2
6 VDC
2
......................... (9),
 2 k Pm

Half of the L2Y is the inductance for each coil connected in series
on the phase. The primary inductance should be designed from thevoltage gain from the primary side to the secondary DC.
From (9), the primary inductance is

L1Y = Lu1 = Lv1 = Lw1 =Core

Deadtime

secondary DC voltage. The system has a margin on the output
power, considering the power loss in the system. Thus, theequivalent resistance is calculated with VDC2 = 400 V and Pm = 25kW.
Equation (9) is introduced from the impedance matchingcondition, where  ( = 2f) is the angular transmission frequency,
and k is the nominal value of the coupling coefficient. The
equivalent resistance of the rectifier should be equals to the selfinductance of the secondary coils for the impedance matching. For
simplicity, the parasitic resistances of the coils are ignored.

The AC resistance is introduced by expanding the analysis of theequivalent resistance of the single-phase rectifier in (23) with a
rated output power Pm and the DC output voltage VDC2 on thesecondary side. The rated output power is 22 kW with a 400-V of5

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)Inverter output voltage vuv1 [1kV/div]

 = 92.0%
2000

Iron loss

Inverter output current iu1 [50A/div]

Power loss [W]1600

Rectifier input current iu2 [50A/div]

Copper loss

(Conduction)

Iron loss
Copper loss

800

Inverter(switching)400

4ms/div

0Fig. 8.

Inverter output voltage vuv1 [1kV/div]iv1 [50A/div]
iw1 [50A/div]

4ms/div(b) Inverter output voltage and output current on each phaseFig. 6. Operation waveforms of the proposed threephase WPT system. The output power is 22 kW, primary
DC voltage is 650 V, and secondary DC voltage is 400
V.

DC-to-DC Effciency  [%]

95
400 V

90

85

0

4

Fig. 7.

Efficiency characteristic with different
secondary DC voltage.

8

12
16
Output Power P [kW]20

InverterExperimentCalculation

Breakdown of power loss of 22-kW prototype.

In the calculation, the conduction loss of the MOSFETs
dominates the power loss. It accounts for 26.9% of the total loss.
The second-largest power loss is the copper loss of the secondary
coil because the secondary current I2 is larger than I1. It accounts
for 22.3% of the total loss.
4.3
Electromagnetic Emission Test for CISPR
guidelines
The magnetic and electric field is measured in the
10-m anechoic chamber of the Industrial research institute of
Niigata prefecture in Niigata, Japan. The measurements are fullycompliant with CISPR 11 et. 6.0 published in 2015, and AMD. 1
published in 2016, class A, group 2 (25). Especially, this paper
focuses on only the WPT system used in all locations other thanthose allocated in residential environments. Thus, the WPT systemis evaluated with the regulations for class A. The measurement
results can be compared with WPT systems, which will be
developed from this point of time, with the fair condition because
the fairness of the measurement conditions is guaranteed by CISPR
11.
The transmission coils are placed on the turntable and rotated by
360 degrees during the measurement. The highest recorded level ofthe electromagnetic radiation at each frequency is recorded. The
loop antenna (ETS Lindgren, 6502) and Broadband antenna (Teseq,
CBL6111D) are used for the measurement of a magnetic field andelectric field, respectively. The measurement distance from the edgeof the system is 10 m, according to the CISPR 11. The emission
with a 22 kW of output power and a 400 V of the secondary DC
voltage is measured. Note that the diode bridge rectifier, inverter,
high-frequency rectifier, and buck-boost chopper circuit are put inan underground pit in order to evaluate the emission from only thetransmission coils.
Figure 9 shows the magnetic field measured in the 10-m anechoic
chamber with the peak detection. The line highlighted by gray is the
background noise, which is measured even when the WPT system
is not operated. The dotted line represents the regulation of CISPR
11, class A, group 2. In the CISPR 11, the regulation on the radiatedmagnetic field within 150 kHz to 30 MHz has been set up. The
regulation on the frequency lower than 150 kHz is under discussion.
The magnetic field on the x-axis, y-axis, z-axis at the fundamental
frequency is 74.9, 70.1, and 60.9dBmA/m, respectively.
Figure 10 shows the electric field measured in the 10-m anechoic
chamber. The line highlighted by gray is the background noise,
which is measured even when the WPT system is not operated. The

Inverter output current iu1 [50A/div]

80

Primaryside(Conduction)(a) Inverter output voltage, current, rectifier input current and output
voltage.

300 V

Secondaryside

Rectifier1200

Output voltage VDC2 [250V/div]

VDC2 = 200 V

91.1%
Others24

Figure 8 shows a power loss breakdown of the system when the
output power is 22 kW. In this analysis, the primary DC voltage is
650 V, and the DC voltage on the secondary side is 400 V. The total
power loss measured by the experiment is 2.16 kW. On the other
hand, the sum of the calculated power loss is 1.90 kW. The error
between the calculation and the experiment is 260 W, where it is
1.2% of the output power. In other words, the measured efficiency
is 91.1%, as against the calculation value of 92.0%.
6

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)80
CISPR11, Class A, Group 2(150kHz-30MHz)

60

Radiated emission [dBmV/m]Radiated emission [dBmA/m]

80
40
20
0
-20
-40
0.01

Background noise

0.1

1

Freaquency [MHz]

10

40
20
Background noise

0
30

30

(a) x-axis

Freaquency [MHz]60

CISPR11, Class A, Group 2(150kHz-30MHz)

40
20
0
-20

Background noise

0.1

1

Freaquency [MHz]10

CISPR11, Class A, Group 2

60
40
20

Background noise

0
30

30

100

Freaquency [MHz](b) y-axis

Fig. 10. Electric field measured in the 10-m anechoic
chamber. The measurement is fully compliant withCISPR 11.

CISPR11, Class A, Group 2(150kHz-30MHz)

40
20

Magnetic field strength H [A/m]Radiated emission [dBmA/m]

60

0
-20
0.1

1

1000

(b) Vertical polarized wave

80

-40
0.01

1000

80
Radiated emission [dBmV/m]Radiated emission [dBmA/m]

100(a) Horizontal polarized wave

80

-40
0.01

CISPR11, Class A, Group 2

60

10

30

Freaquency [MHz](c) z-axis

Fig. 9. Magnetic field measured in the 10-m anechoic
chamber. The measurement is fully compliant withCISPR 11.

40
30
Reference level for
general public exposure at 85 kHz

20

10
0
200

300
400
500
Distance from the edge of coil DM [mm]600

Fig. 11. Magnetic field strength regarding distancefrom the edge of coil and reference level for generalpublic exposure at 85 kHz published by ICNIRP in 2010.

dotted line represents the regulation of CISPR 11, class A, group 2.
In the CISPR 11, the regulation on the radiated electric field within
30 MHz to 1 GHz has been set up. The electric field of the prototype
fully satisfies the regulation of CISPR 11 with a large margin. From
the above results, the proposed WPT system fully satisfies theregulation of CISPR 11, class A, group 2.
4.4
Electromagnetic Emission Test for ICNIRP
guideline
Figure 11 shows the magnetic field strength
regarding the distance from the edge of coils and the reference levelfor general public exposure to time-varying magnetic fields
published by ICNIRP in 2010(26). The radiation noise is measured
with ELT-400 (Narda Safety Test Solutions). Note that themeasurement has been held in the semi-anechoic chamber withlimited area. The measurement result shows that the proposed WPTsystem complies with the reference levels for general public
exposure at 85 kHz published by ICNIRP in 2010 by ensuring aseparation distance of 340 mm or more from the edge of the coils.

5.

Conclusion

In this paper, the 22-kW three-phase WPT system, which fullycomplies with CISPR and ICNIRP guidelines without the effect of
the cross-coupling is developed and demonstrated. The WPTsystem transmits power through 12 coils, which are circularly
placed every 60 degrees, to reduce electromagnetic emission andcross-coupling effect. The maximum efficiency of the proposedsystem from the primary DC side to the secondary DC side is 91.1%
with an output power of 22 kW and an output voltage of 400 V.
Finally, the electromagnetic compatibility of the 22-kW prototype
is evaluated in the anechoic chamber according to the measurement
method in CISPR 11. The magnetic field and the electric field fullycomply with the guideline of CISPR 11, class A, group 2. Besides,
the WPT system satisfies the regulation in magnetic field strength
regulated by ICNIRP 2010 by ensuring a separation distance of 340

7

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)
Vehicle Symposium and Exhibition (EVS27), pp. 1-8 (2013)(22) J. Kim, H. C. Son, D. H. Kim and Y. J. Park, “Impedance matchingconsidering cross coupling for wireless power transfer to multiple receivers,”
2013 IEEE Wireless Power Transfer (WPT), pp. 226-229 (2013)(23) R. L. Steigerwald, “A Comparison of Half-Bridge Resonant Converter
Topologies,” IEEE Trans. on Power Electronics, Vol. 3, No. 2, pp. 174-182(1988)(24) Y. H. Sohn, B. H. Choi, E. S. Lee, G. C. Lim, G. Cho, C. T. Rim, “General
Unified Analyses of Two-Capacitor Inductive Power Transfer Systems:
Equivalence of Current-Source SS and SP Compensations,” IEEE Trans. on
Power Electronics, Vol. 30, No. 11, pp. 6030-6045 (2015)(25) Comité international spécial des perturbations radioélectriques (CISPR),“Industrial, scientific and medical equipment - Radio-frequency disturbancecharacteristics - Limits and methods of measurement,” CISPR 11, Ed. 6.2(2019)(26) ICNIRP, “ICNIRP guidelines for limiting exposure to time-varying electricand magnetic fields (1 Hz to 100 kHz),” Health physics, Vol. 99, No. 6, pp.
818-836 (2010)

mm or more from the edge of coils.
In future work, the effect of a misalignment and parameter error
for resonance on the transmission efficiency and electromagnetic
emission will be evaluated.

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(15)

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(17)

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Keisuke Kusaka(Member) received his B.S. and M.S. degrees inelectrical,
electronics
andinformationengineering from Nagaoka University ofTechnology, Niigata, Japan in 2011, 2013,
respectively. From 2015 to 2016, he was with
Swiss Federal Institute of Technology in
Lausanne (EPFL), Switzerland as a Trainee. In
2016, he received his Ph.D. degree in energy andenvironment science from Nagaoka University ofTechnology. He had been with Nagaoka University of Technology, Niigata,Japan as a researcher from 2016 to 2018, and an assistant professor from2018 to 2021. He is currently a tenure track lecturer at the same university.
His current research interests include the areas of inductive power transfer
systems and high-frequency converters. Dr. Keisuke is a member of theInstitute of Electrical Engineers of Japan and Society of Automotive
Engineers of Japan. He received the second prize paper award in IPECNiigata 2018.
Rintaro Kusui(Student-member) was received his B.S. degree inelectrical,
electronics
andinformationengineering from Nagaoka University ofTechnology, Niigata, Japan in 2020. Presently, he
is a Ph.D. candidate at Nagaoka University ofTechnology, Niigata, Japan. He is the student
member of IEEJ and IEEE.

Jun-ichi Itoh

(Senior-member) was born in Tokyo, Japan, in 1972.
He received his M.S. and Ph.D. degree in electricaland electronic systems engineering from Nagaoka
University of Technology, Niigata, Japan in 1996,
2000, respectively. From 1996 to 2004, he waswith Fuji Electric Corporate Research andDevelopment Ltd., Tokyo, Japan. He was with
Nagaoka University of Technology, Niigata, Japanas an associate professor. Since 2017, he has beena professor. His research interests are matrix
converters, dc/dc converters, power factor correction techniques, energy
storage system and adjustable speed drive systems. He received IEEJ
Academic Promotion Award (IEEJ Technical Development Award) in 2007.
In addition, he also received Isao Takahashi Power Electronics Award in
8

IEEJ Trans. ●●, Vol.●●, No.●, ●●●Three-phase wireless power transfer with 12 coils (Keisuke Kusaka et al.)
IPEC-Sapporo 2010 from IEEJ, 58th OHM Technology Award from The
Foundation for Electrical Science and Engineering, November, 2011,
Intelligent Cosmos Award from Intelligent Cosmos Foundation for the
Promotion of Science, May, 2012, and Third prize award from Energy
Conversion Congress and Exposition-Asia, June, 2013. Prizes for Scienceand Technology (Development Category) from the Commendation for
Science and Technology by the Minister of Education, Culture, Sports,
Science and Technology, April 2017. Dr. Itoh is a senior member of theInstitute of Electrical Engineers of Japan, the Society of Automotive
Engineers of Japan and the IEEE.
Daisuke Sato

(Member) was born in Hokkaido, Japan, in 1989. Hereceived his B.S. and M.S. degrees in 2012, 2014,
respectively in electrical, electronics andinformationengineeringfrom
Nagaoka
University of Technology, Nagaoka, Japan. In
2017, he received his Ph.D. degree in energy andenvironment science from Nagaoka University ofTechnology. In 2017, he launched Nagaoka Motor
Development Co., Ltd. as a co-founder. He iscurrently CEO.
Tetsu Shijo(non-member) received B.S. M.S., and Ph.D.
degrees from Tokyo Institute of Technology,
Tokyo, Japan in 2002, 2004, and 2007,
respectively. From 2007, he is with Toshiba
Corporation.

Shuichi Obayashi(non-member) received his degree in Master ofEngineering from Kyoto University, Kyoto, Japan
in 1987. From 1987, he is with Toshiba
Corporation.

Masaaki Ishida(non-member) received his B.S. degree from Keio
University, Tokyo, Japan in 1987. From 1987, heis with Toshiba Corporation.

9

IEEJ Trans. ●●, Vol.●●, No.●, ●●●