Comparative Verification of Radiation Noise Reduction Effectusing Spread Spectrum for Inductive Power Transfer System
Keisuke Kusaka 1) Kent Inoue 2) Jun-ichi Itoh 3)1)Nagaoka Univesity of Technology, Dept. of Electrical, Electronics and Information
1603-1 Kamitomioka-machi, Nagaoka, Niigata, 940-2188, Japan (E-mail: kusaka@vos.nagaokaut.ac.jp)
2) Nagaoka University of Technology, Dept. of Electrical, Electronics and Information
1603-1 Kamitomioka-machi, Nagaoka, Niigata, 940-2188, Japan (E-mail: k_inoue@stn.nagaokaut.ac.jp)
3) Nagaoka University of Technology, Dept. of Electrical, Electronics and Information
1603-1 Kamitomioka-machi, Nagaoka, Niigata, 940-2188, Japan (E-mail: itoh@vos.nagaokaut.ac.jp)

Presented at EVS 31 & EVTeC 2018, Kobe, Japan, October 1 - 3, 2018

ABSTRACT: This paper evaluated radiation noise reduction methods for inductive power transfer systems using a spread spectrum
technique. In the spread spectrum methods, the radiation noise is reduced by changing a switching frequency, which is generated bypseudorandom numbers at random, continuously. The effects of the radiation noise reduction are evaluated with the IPT system with aseries-parallel compensation and series-series compensation topology. As the results, the harmonics components of the radiation noisearound the fundamental frequency are reduced by 7.8 and 8.1 dBA in maximum with the series-series compensation method and theseries-parallel compensation method, respectively in comparison with the constant frequency transmission. From the results, theproposed methods are effective for both the series-series compensation and series-parallel compensation method.

KEY WORDS: Inductive power transfer, Radiation noise, Spread spectrum, Series-series (SS) compensation, Series-parallel (SP)compensation

allowable radiation noise has been legislated. The regulations are

1. INTRODUCTION

currently under discussion for the international standardization. A
85-kHz frequency band will be used as the transmission frequency

In recent years, inductive power transfer (IPT) systems forelectric vehicles (EVs) have been actively studied and developed[1–7]. In particular, practical realization of the IPT systems for
EVs or plug-in hybrid EVs (PHEVs) is highly desired because the
IPT systems are capable of improving the usability of the EVs andthe PHEVs. However, the IPT systems emit radiation noise.
Therefore, in order to employ the IPT systems into practicalapplications, the radiation noise must be suppressed to satisfy
existing standards, such as the well-known standard based on
CISPR11, i.e., a standard regulated by the International special
committee in radio interference. Otherwise, the IPT systems might
affect other wireless communication systems or electronicequipment.

in the international standard. This regulation is basicallycorresponding to CISPR 11 Group 2, Class B [8].
In previous studies, suppression methods using a magnetic
material or metal shield have been proposed [9–12]. In order tosuppress the radiation noise, transmission coils are surrounded byplates composed of a magnetic material or metal plate. The
radiation noise can be suppressed because these shields convert themagnetic flux from the radiation noise into eddy currents.
However, the eddy currents increase the power loss of the IPT
systems. Moreover, the additional shields (magnetic or metal) leadto an increase in cost. So far, the authors have proposed two
radiation noise reduction methods, in which the power istransmitted with changing switching frequency of the inverter

Figure 1 shows the maximum allowable radiation noise for thecontinuously; it is also called as a spread spectrum [13–14]. The

IPT systems of 7 kW or less for EVs in Japan. In Japan, theproposed methods do not need additional components. Moreover,

Copyright © 2018 Society of Automotive Engineers of Japan, Inc. All rights reserved

16mm

Radiation noise [dBA/m] (at 10 m)

80
68.4

Fundamental

60

40
2nd 3rd
4th
5th

23.1
20

0

CISPR Class B Group2

-10
10

100

Fundamental

79 kHz – 90 kHz

2nd

158 kHz – 180 kHz

3rd

237 kHz – 270 kHz

4th

316 kHz – 360 kHz

5th

395 kHz – 450 kHz

CISPR Class B
Group2 + 10 dB

1000

10000

Frequency[kHz]Fig. 1. Maximum allowable radiation noise for IPT system of 7 kW or less for use in EVs in Japan (under discussion).

the effect on the efficiency by using the proposed method is small

Rz-p

Rz-p+1 ···· Rz-q···· Rz-1

Rz

compensation topology. However, the effectiveness of the

Sz-p

Sz-p+1 ····

Sz-q···· Sz-1

Sz

proposed radiation noise reduction methods for the IPT system

····

····

····

····

····

at the rated power [14]. In a previous paper, the radiation noise

Xz-p

Xz-p+1 ···· Xz-q···· Xz-1

Xz

reduction effect of these two proposed methods have been

LSB
(1bit)

evaluated with the IPT system with a series-series (SS)with a series-parallel (SP) compensation topology had not been
evaluated.
In this paper, the proposed radiation noise reduction technique
is used for the IPT system with the SP compensation topology .

MSB(7bit)

Fig. 2. Generation method of pseudorandom numbers basedon maximal length sequence.

The contribution of this paper is that the radiation noise reduction
effect is compared between the SS and the SP compensation
Figure 3 shows the probability distribution of the switching

topology.

frequency of the inverter in two proposed radiation noise reduction

2. RADIATION NOISE REDUCTION METHODS

methods. Fig. 3 (a) shows the probability distribution of spread
spectrum with a uniform distribution (SSUD) [2]. The probability

2.1. Generation method of pseudorandom number

distribution is a discrete uniform distribution from 80 kHz to 90

In the proposed method, the radiation noise is spread over thekHz. Therefore, the spectrum of the voltage applying to thefrequency domain from 80 kHz to 90 kHz by changing thetransmission coil is uniformly spread. Fig. 3 (b) shows theswitching frequency of the inverter in two different ways. The

probability distribution of spread spectrum with a biased

switching frequency is changed according to pseudorandom

distribution (SSBD) [3]. The input impedance depends on thenumbers, which are generated by using a maximum lengthswitching frequency. Thus, the probability distribution is insequence (M-sequence). The M-sequence random number is

proportional to the impedance of resonance circuit.

generated as
X z  X z  p  X z  q ......................................................... (1),where Xz-p and Xz-q are the present values of Xz delayed by periodsof p and q, respectively (p > q). In this paper, p = 7 and q = 1 areused. Note that a number of bits of the pseudorandom number isseven.

3. DESIGN OF TRANSMISSION COIL
Figure 4 shows the equivalent circuit for designing the IPT
system. Fig. 4 (a) and (b) show the SS compensation topology andthe SP compensation topology, respectively.
3.1. SS compensation method

2.2. Probability distributions for reduction method

Copyright © 2018 Society of Automotive Engineers of Japan, Inc. All rights reservedFrom the circuit equations of the equivalent circuit, which isshown in Fig. 4 (a), the primary current and the secondary current1 
r2  Req  j   L2 

C2 

I1 
V1



1  
1  

2 2
r

j

L

r

R

j

L



L
 1
  2
 2

1
eq
m
C1  
C2  





I2 




1  
1 



2 2
 r2  Req  j   L2     Lm
r1  j   L1 

C

C

1  
2 






40
35

15
0.15

30

650 Hz

25

10
0.10

20
15

5
0.05

....................................................................................... (2),

j Lm

20
0.20

Probability distribution

are calculated as

10
5

00
79

V1

80
80

81

82
82

84
84

83

85

86
86

87

88
88

89

90
90

0
91

Frequency[kHz](a) Proposed method I: SSUD....................................................................................... (3),winding, r2 is the equivalent series resistance of the secondary
winding, L1 is the primary inductance, L2 is the secondary
inductance, C1 is the primary compensation capacitor, C2 is thesecondary compensation capacitor, Lm is the mutual inductance,and  is the angular frequency of the power supply. Note that the

40
40
35

Probability distribution

resistance, r1 is the equivalent series resistance of the primary

20
0.20

15
0.15

30
30
25
20
20

10
0.10

15

10
10

5
0.05

voltage V1 is the fundamental component of the output voltage of

5
00
79

80
80

81

the inverter.

82
82

84
84

83

85

86
86

87

88
88

89

90
90

00
91

Frequency[kHz]The parameters of the transmission coil are designed with theequivalent circuit. The resistance Req indicates that equivalent load
resistance considering the full-bridge rectifier. Then the equivalent(b) Proposed method II: SSBD
Fig. 3. Probability distributions for proposed methods.
Changing range of switching frequency of inverter is from 80
kHz to 90 kHz.

load resistance is given by [15]
2

Req 

8 VDC ,2............................................................... (4), 2 P2where VDC,2 is the DC voltage on the secondary side and P2 is the

I1 C
1

r1

I2 L2-Lm

L1-Lm

r2

C2
Req

f
Lm

V1

output power.
The inductances of the primary and the secondary coils aredesigned according to the following equations

L1 
L2 

2
DC ,1
2
DC ,2

Req V

k V
Req

k

(a) SS compensation method.

I1 C
1............................................................... (5),r1

I2 L2-Lm

L1-Lmf........................................................................ (6),

I3

r2
C2

V1

Req

Lm

where VDC,1 is the DC voltage on the primary side and k is thecoupling coefficient.
The compensation capacitors are selected in order to cancel out(b) SP compensation method.
Fig. 4. Equivalent circuit for designing the IPT system.

the reactive power at the input frequency. Thus, the value of thecompensation capacitors is calculated asC1 1..................................................................... (7),
 2 L1C2 

1.................................................................... (8).
 L22Copyright © 2018 Society of Automotive Engineers of Japan, Inc. All rights reserved

Impedance[W]where V1 is the primary voltage, Req is the equivalent load

The compensation capacitors are selected in order to cancel out

3.2. SP compensation method
The circuit equations of the equivalent circuit, which is shown

the reactive power at the input frequency. Thus, the value of theFig. 4 (b) are calculated ascompensation capacitors is calculated as



 
1 
1


   Req  j 2 2r2  j   L1 

C

C

C2

2 
2 


I1  
V1 .... (9),.................................................................... (17).

4.1. Experimental Setup
Figure 5 and Table I show the circuit configurations for the
1 
r1  j  L1  2 
 C1  j Lm

prototype and specifications, respectively. The self-inductance of0

the primary side and secondary side in Table I is measured from1 
1r2  j  L2  2 
j

C

C2
2 

1
1
j
Req  j
 C2
 C2

0

1

 2 L2........................................................ (16),

4. EXPERIMENTAL RESULTS

1 Lm
I3 
V1 ............................................................... (11), C2 j Lm

 L1 1  k 2 
2

C2 


1 
j Lm  Req  j


C2 

I2 
V1 .......................................... (10),




1

C1 

the prototype of the transmission coils. The silicon carbide

Table I. Specifications of prototype.

....................................................................................... (12).

SymbolValue

Input DC voltage

Vin

420 V

Rated powerP

3.0 kW

Coupling coefficient

k

0.20

Primary inductanceL1

392 H

Secondary inductanceL2

Primary capacitance

C1

Secondary capacitance

C2

Note that the voltage V1 is the fundamental component of theoutput voltage of the inverter.
The parameters of the transmission coil are designed with theequivalent circuit. The resistance Req indicates the equivalent load
resistance considering the full-bridge rectifier. Then the equivalentload resistance is given by [15]

 2 VDC ,2

401 H (SS)

2

Req 

8

P2

............................................................... (13).

The inductances of the primary and the secondary coils are

24.2 H (SP)designed according to the following equations

8.78 nF (SS)

2

 8 V

L1  L2  2 DC ,1  ..................................................... (14), k V
DC ,2 


L2 

Req

k



1 k2

+

145 nF (SP)l

Transmission distance

150 mm.......................................................... (15),C1
Vin

8.96 nF

i1

v1

C2

k
L1

C1
R

L2

Vin
vo

+

i1

v1

k
L1

R
L2

C2

(a) SS compensation method.
(b) SP compensastion method.
Fig. 5. Circuit configrations of prototype.

Copyright © 2018 Society of Automotive Engineers of Japan, Inc. All rights reservedvoMOSFETs are used as the switching devices in the inverter. Also,
Secondarywinding

the silicon carbide schottky barrier diodes are used in the rectifier.
Figure 6 shows the primary and secondary coils for the
prototype. The common solenoid-type coils are used for the bothcompensation topology. In order to obtain the common output

Ferriteplate

power, the number of turns of the secondary coil is different
between the SS compensation and SP compensation topology. The
transmission distance is 150 mm, assuming transmission from thePrimary
windingroad to the bottom of the EV or PHEV.
4.2. Radiation Noise Measurement Conditions

Fig. 6. Transmission coils with rated power of 3 kW. Lowerside is transmitter coil, upper side is receiver coil. White
winding in secondary side is used SS compensation method.
Red winding in secondary side is used SP compensation
method.

Figure 7 shows the setup of the probe used for the measurementof the radiation noise. The radiation noise was measured at two
points. The each distance from the edge of the transmission coils
and to each measurement position is 500 mm.
4.3. Experimental Results

order harmonics components, similarly. As a result, the proposed

Figure 8 shows the radiation noise with the SS compensation

radiation noise reduction methods are effective for both the SP andmethod. Fig. 8 (a) shows the result with a constant switching

SS topology. The reduction effect of the radiation noise is almost

frequency operation, whereas Fig. 8 (b) and (c) show the results

equivalent.

using the spread spectrum with SSUD and SSBD, respectively. As
a result, by using the SSUD and SSBD, the radiation noise on the

5. CONCLUSION

fundamental frequency is reduced by 4.8 dBA and 7.8 dBA in
comparison with the conventional method. In addition, the effect

So far, the authors have proposed two radiation noise reductionof reduction is confirmed at low-order harmonics components,

methods, in which the power is transmitted by a continuously

similarly.

changing switching frequency of the inverter over a spread
spectrum.

Figure 9 shows the radiation noise with the SP compensation
method. Fig. 9 (a) shows the result with a constant switching

In this paper, the radiation noise reduction effect of two

frequency operation, whereas Fig. 9 (b) and (c) show the results

proposed methods (the SSUD and the SSBD) was experimentallyobtained using the SSUD and SSBD, respectively. As a result, bydemonstrated with the IPT system of 3 kW prototype employing

using the SSUD and SSBD, the fundamental frequency is reduced

SP compensation method. In addition, the reduction effect wasby 4.8 dBA and 8.1 dBA in comparison with the conventional

evaluated in comparison with employing the SS compensation

method. In addition, the effect of reduction is confirmed at low-method. As a result, the harmonics components around theTransmission coil
Probe
500

mm

500 mmWinding
z

z

y
x

y
x

(a) Measurement point: A.
(b) Measurement point: B.
Fig. 7. Measurement environment of radiation noise. The distance from edge of transmission coils to each measurement position is
500 mm.

Copyright © 2018 Society of Automotive Engineers of Japan, Inc. All rights reserved

[dBA]
60

40

Reduced by 4.8 dBA

Reduced by 7.8 dBA

20

0

-20
100

225

350

475 [kHz]

100

225

350

475 [kHz]

100

225

350

475 [kHz][dBA]
60

40

20

0

-20
80.0

82.5

85.0

87.5

[kHz]

80.0

82.5

85.0

87.5

[kHz]

80.0

82.5

85.0

87.5

[kHz]

(a) Conventional method.
(b) Proposed method I: SSUD.
(c) Proposed method II: SSBD.
Fig. 8. Radiation noise at measurement point A in y-z plane with SS compensation topology.
fundamental frequency of the radiation noise with the SS
compensation method were suppressed by 4.8 and 7.8 dBA by
applying the SSUD and the SSBD, respectively. On the other hand,in the SP compensation method, the harmonics components
around the fundamental frequency of the radiation noise were
suppressed by 4.8 and 8.1 dBA by applying the SSUD and the
SSBD, respectively. From the results, the radiation noise reduction
effect is expected using the two proposed methods the IPT system
employing the SP compensation method as with the SS
compensation method.

Copyright © 2018 Society of Automotive Engineers of Japan, Inc. All rights reserved

[dBA]
60

40

Reduced by 4.8 dBA

Reduced by 8.1 dBA

20

0

-20
100

225

350

475 [kHz]

100

225

350

475 [kHz]

100

225

350

475 [kHz][dBA]
60

40

20

0

-20
80.0

82.5

85.0

87.5

[kHz]

80.0

82.5

85.0

87.5

[kHz]

80.0

82.5

85.0

87.5

[kHz]

(a) Conventional method.
(b) Proposed method I: SSUD.
(c) Proposed method II: SSBD.
Fig. 9. Radiation noise at measurement point A in y-z plane with SP compensation method.
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