Journal of International Council on Electrical Engineering Vol. 3, No. 3, pp.257~261, 2013
http://dx.doi.org/10.5370/JICEE.2013.3.3.257
Analysis of Inductive Power Transfer according to Resistance loads and
air gaps at 50 kHz Frequency
Dong-Uk Jang†, Joao Victor Pinon Pereira Dias*, Sang-Hoon Chang* and
Hyung-Chul Kim*
Abstract – Contactless systems use electromagnetic fields to transport power from railway substation to
the traction system. The proto type of inductive power transfer (IPS) system has been developed in order
to use train power feeding. It is based on a contactless transformer with a fixed coreless primary and
different secondary core like E shape and U shape. The primary coil is supply with 50 kHz current which
produces a magnetic flux in the secondary core. Further this flux induces a current in the secondary coil.
This paper presents results of experiment for developed inductive power transfer system experiments.
The IPS has a large air gap, so it is required a high magnetization current and compensate the leakage
flux of primary and secondary coil. The proto type IPS has an air gap with range 1 to 5 mm and core
material is ferrite with maximum power of 5 kW. The power supply to IPS is designed by constant
current control inverter with compensation capacitance. We measure inductance of IPS and coupling
coefficient in order to calculate the compensation parameter according to variable air gap. The analysis of
output for the proto type IPS is performed regarding different loads.
Keywords: Inductive power transfer, Air gap, Railway, Resonance power converter
coil. This paper presents results of experiment for
developed inductive power transfer system experiments.
The IPS has a large air gap, so it is required a high
magnetization current and compensate the leakage flux of
primary and secondary coil. The proto type IPS has an air
gap with range 1 to 5 mm and core material is ferrite with
maximum power of 5 kW. The power supply to IPS is
designed by constant current control inverter with
compensation capacitance. We measure inductance of IPS
and coupling coefficient in order to calculate the
compensation parameter according to variable air gap. The
analysis of output for the proto type IPS is performed
regarding different loads.
1. Introduction
The power supply system in railway has been developed
for high speed train such as wheel type and MAGLEV. The
conventional power collection with contact between
pantograph and contact wire was disadvantage for increase
the speed. Also, it’s system had problems with wear of
contact points, noise generation, arc discharge generation
due to incomplete contact. Therefore the contactless power
transfer system was proposed to solve these problems in
transportation system. There were inductive coupling,
capacitive coupling, electromagnetic wave transmission
with resonance coupling and plasma bridge between vehicle
and wire in contactless power transfer method.
Contactless systems use electromagnetic fields to
transport power from railway substation to the traction
system. The proto type of inductive power transfer (IPS)
system has been developed in order to use train power
feeding. It is based on a contactless transformer with a fixed
coreless primary and different secondary core like E shape
and U shape. The primary coil is supply with 50 kHz
current which produces a magnetic flux in the secondary
core. Further this flux induces a current in the secondary
2. Measurements
In order to test and compare with different the core type
used in the IPS the output, voltage and current were
measured. The test was divided to two steps. Firstly, the
core parameters were measured for different air gaps. Next,
the system was assembled and the output parameters were
measured for different air gaps and loads.
The parameters measured in the cores were the selfinductances and the series aiding and series opposing
inductances between primary coil and secondary coil. To
measure the inductance, the LCR meter was used. The
measurements were done to a frequency of 50 kHz and the
†
Corresponding Author: Metropolitan Railroad Systems Research
Center, Korea (dujang@krri.re.kr)
* Metropolitan Railroad Systems Research Center, Korea
Received: June 14, 2013; Accepted: June 24, 2013
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Analysis of Inductive Power Transfer according to Resistance loads and air gaps at 50 kHz Frequency
defined as well due to manufacture characteristic of the
MOSFET switching device. The maximum output voltage
is was limited to 150 V.
air gap was increase from 1 mm to 5 mm with 1 mm step.
With the measured values the values of mutual
inductance (M) and coupling coefficient (k) were calculated
as following equations respectively.
M = (La − Lb )/4
(1)
k = M L1 /L2
(2)
Here, La is the inductance of the coils in series-adding
mode and Lb is series-opposite mode. L1 and L2 are the
primary and secondary self-inductances respectively
The measurements were done for the two types of the
cores and the results were presented in a previous work of
the author [2]. The values of the inductances are reproduced
in the table below.
Table 1. Measured inductance values
Core Distance of
Llp [μH] Lm [μH]
type
air gap
E-I
1 mm
0.343
9.731
E-I
3 mm
1.123
4.256
E-I
5 mm
1.456
2.496
U-I
1 mm
1.914
6.2745
U-I
3 mm
1.596
4.683
U-I
5 mm
1.819
2.980
Fig. 1. The experimental system.
The cores were tested for 3 different air gap sizes, 1, 3,
and 5 mm. The high power resistance has two possible
connections configurations, allowing utilization of two
different resistance values, 3 and 6 
Lms [μH]
0.431
1.865
2.810
2.033
1.800
2.167
With the values of the inductances the value of the
equivalent inductance was calculated for each one of the
values of the air gap size. The equivalent inductance was
calculated from inductance of Table 1.
The next step was determining the value of the compensation capacitance. The values are presented in table 2.
Table 2 Compensation capacitance values
Distance of Compensation capacitance
Core type
air gap
[μF]
E-I
1 mm
13.758
E-I
3 mm
4.186
E-I
5 mm
3.648
U-I
1 mm
2.937
U-I
3 mm
3.499
U-I
5 mm
3.296
Fig. 2. Waveforms E-I core at 5mm and 3 Ohm.
The IPS circuit was mounted with the compensation
values showed in table 2 for each one of the air gaps.
Following the scheme presented in Fig. 1 the IPS was
mounted.
The switching frequency of the inverter was 50 kHz. To
be able to compare the results of the both cores was decided
to fix the output current of the inverter using the DSP
program.
The output current of inverter (primary input current)
was set to 50 A. The maximum output voltage had to be
Fig. 3. Waveforms E-I core at 5mm and 6 Ohm.
The measurements were performed with oscilloscope
DL850 made by YOKOGAWA, the RMS value of the
current and voltage of the input, output of the contactless
258
Dong-Uk Jang, Joao Victor Pinon Pereira Dias, Sang-Hoon Chang and Hyung-Chul Kim
transformer and the average value of the DC current and
voltage of the load were measured.
The Figs below exemplify the wave forms measured. The
results were gathered in an electronic table and the graphs
with the results are presented in the next section.
resistance.
Fig. 7. Primary values vs. air gap with 6[Ω] of load
resistance.
Fig. 4. Waveforms U-I core at 5mm and 3 Ohm.
Fig. 8. Secondary values vs. air gap with 3[Ω] of load
resistance.
Fig. 5. Waveforms U-I core at 5mm and 6 Ohm.
3. Results and Discuss
The measurements of the currents and voltage for the
different air gaps and loads in the prototype are presented in
the graphs below.
Fig. 9. Secondary values of vs. air gap with 6[Ω] of load
resistance.
To analyze the results the discussion will be divided the
results in three topics: input, output and load. The analysis
will focus the comparison of the two cores, and how the
load and the air gap size influence the results.
The input values presented in Figs 6 and 7 show the
operation boundaries defined. The current is maintained
Fig. 6. Primary values vs. air gap with 3[Ω] of load
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Analysis of Inductive Power Transfer according to Resistance loads and air gaps at 50 kHz Frequency
steady near the rated value, 50A. The inverter works as a
current source so the voltage levels change to maintain the
rated value for the change of air gap and load.
The E-I core has a smaller voltage then the U-I core,
moreover less power should be supplied to ensure the rated
voltage in the input of the contactless transformer.
The change of the load increase the voltage as expected
and the current maintain the same value, due to operation
interests. As the air gap increases the voltage decreases.
The output showed in Figs 8 and 9 presents again a U-I
core with bigger values of voltage in comparison with the
E-I core for an air gap of 1 mm, however for the other
values of the air gap size the E-I have a bigger value. The
currents have similar value for the both core types.
With the change in the load the voltage increases as in
the input, although the input the current decrease,
respecting the Ohm’s Law.
4. Conclusions
The proto type IPS has an air gap with range 1 to 5 mm
and core material is ferrite with maximum power of 5 kW.
The power supply to IPS is designed by constant current
control inverter with compensation capacitance. We
measure inductance of IPS and coupling coefficient in order
to calculate the compensation parameter according to
variable air gap. The analysis of output for the proto type
IPS is performed regarding different loads. From results we
obtain that the cores supply similar currents to the load
moreover the voltage levels change according to the value
of the air gap. The changes in the load value produce same
response for the different cores.
References
[1] J. V. P. P. Dias, H. Kim and D Jang, “Computer Model
for Railway Inductive Power Supply Using the Valtchev
Model”, ICEMS 2011: International Conference on
Electrical Machines and Systems, 20-23 August,
Beijing, China.
[2] D. Jang, J. V. P. P. Dias, H. Kim, D. Lee and S. Jung,
“The Characteristics Analysis and Design for 5kW
Contactless Transformer”, 2011 Autumn Conference &
Annual Meeting of the Korean Society for Railway, 2022 October , Jeju, South Korea2011.
[3] M. Bauer, P. Becker and Q. Zhengl, “Inductive Power
Supply (IPS®) for the Transrapid”, MAGLEV 2006:
The 19th International Conference on Magnetically
Levitated Systems and Linear Drives, 13-15 September
2006, Dresden, Germany.
[4] Dongsu Lee , Dong-Uk Jang , Hyung-Chul Kim , and
Sang-Yong Jung, “Numerical Analysis and Design of
Moving Contactless High Power Transformer”, Journal
of Magnetics 16(4), December 2011.
Fig. 10. DC output values vs. air gap with 3[Ω] of load
resistance.
Donguk Jang received his B.S degree
and M.S degree in electrical
engineering from Chungbuk National
University. His research interests
include power supply systems, high
voltage engineering and insulation
diagnosis for railway systems.
Fig. 11. DC output values vs. air gap with 6[Ω] of load
resistance.
Lastly, the Figs 10 and 11 represent the measurements in
the load. Being DC values the results are similar to the
output of the contactless transformer reducing the converter
voltage and small losses.
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Dong-Uk Jang, Joao Victor Pinon Pereira Dias, Sang-Hoon Chang and Hyung-Chul Kim
Joao Victor Pinon Pereira Dias
received his B.S degree in electrical
engineering from State University of
Campinas, Brazil in 2008 and his M.S
degree from University of Science &
Technology, KRRI Campus, Korea. His
research interests are Electric Traction
systems and Transformers for Railway applications.
Sang-Hoon Chang received his M.S
and Ph.D degree in department of
electrical engineering from Yonsei
university and Hongik university
respectively in Korea. He had worked
at Korea Railroad Corporation since
1982 as a power system research
engineer for electric railroad from 1982 to 1994. He has
been working for Korea Railroad Research Institute in
Korea since 1994. His special fields of interests include
power supply system design and analysis for electric
railway system.
Hyungchul Kim received the B.S. and
M.S. degrees in electrical engineering
from Korea University, Seoul, Korea,
in 1991 and 1993, respectively, and his
Ph.D. degree from Texas A&M
University, College Station, USA in
2003. He is presently working for
Korea Railroad Research Institute, Korea.
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