3526
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`IEEE TRANSACTIONS ON MAGNETICS, VOL. 35. NO. 5. SEPTEMBER l999
`
`Large Air—Gap Coupler for Inductive Charger
`
`H. Sakamoto, K. Harada, S. Washimiya, K. Takehara
`Kumamoto Institute of Technology, 4-22—1 Ikeda, Kumamoto 860-0082, Japan
`
`‘
`
`‘
`
`Y. Matsuo and F. Nakao
`
`.
`
`FDK Corporation, 2281, Washimizu, Kosai-Shi, Shizuoka 431-04, Japan
`
`Abstract—_—A novel magnetic coupler with large air gap-is
`presented. It is developed for the electric vehicle’s automatic
`inductive charger. The new inductive coupler proposed here has
`sufficient exciting inductance even if it has a large air gap.
`Calculated exciting inductance is 40 pH at 2 turns of winding and
`5 mm air gap, which agrees well with measured value. In order
`to assess the generation of heat caused by the eddy current, the
`magnetic flux densities in the inductive charger and also a flat
`iron plate,
`to which the inductive charger is attached, are
`calculated. The conversion efficiency with the coupler and a
`MOSFETs full-bridge inverter of 100 kHz, is 97% at 8.3 kW
`output.
`
`[ne'er Term--inductive charger, inductive coupler, large air
`gap coupler
`
`I. INTRODUCTION
`
`Inductive charging is safe, efficient and easy to use for
`the electric vehicle (EV).- Fig. l shoWs possible means of
`inductive chargingfor EV applications. Generally in the
`inductive charging,
`increasing of the air gap in the
`magnetic coupler,
`results
`is decreasing in the self-
`inductance, at the same time leakage inductance is
`increased. Therefore a . conduction loss due to the
`proximately effect will not be negligible and a transferring
`power is limited by the leakage inductance. Presently, most
`ofthe inductive chargers for electric vehicle is ofhand held
`insert-type as shownin Fig. 2 (A) [1]. Although in-this type
`of charger,'the air gap of the coupler is easy to make small,
`it will be troublesome to do inserting operations by hand.
`Further, if the power becomes large, it will be too heavy to
`carry it by hand. On the other hand, an automatic charging
`at parking site as shown in Fig. 2 (B) is'more preferable
`and .convenient because it has a mechanical carrying and
`adjusting tools [2][3].
`In this system, however,
`it
`is
`necessary to have a, small gap. In order to salve these
`problems, we examine a large ferrite pot core of a flat
`construction, by' which the self—inductance becomes
`sufficiently large due to the short magnetic path and to the
`large
`cross
`sectional
`area of'
`the
`core. With this
`construction, leakage inductance can be small 'at a long air
`gap, because the gap length is compensated effectively by a
`large cross sectional area. As results, inductive charging of
`high efficiency and large power is possible without any
`mechanical adjustment as shown in Fig. 2 (C).
`Manuscript received February 25, 1999
`Hiroshi Sakamoto, Telephone number: +81 96 326 311 lEx.2750
`Fax number: +81 96 326 3004, Email: hiroshi@ee.kumamoto-it.ac.jp
`
`Inverter
`
`DC IN
`
`
`
`Magnetic
`'- coupler
`
`
`Battery
`
`:-
`i.
`__|"_
`.1.
`._"l'_
`
`
`Primary Coil
`
`(C) Automatic Charger with Large Air-Gap Coupler
`
`Fig. 2 Inductive charging system for electric vehicle.
`
`0018-9464199$10.00 © 1999 IEEE
`
`   ÿ

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`Authorized licensed use limited to: Reprints Desk. Downloaded on April 26,2021 at 15:42:54 UTC from IEEE Xplore. Restrictions apply.
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 001
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 001
`
`

`

`II. New INDUCTIVE COUPLER DIMENSION
`AND CHARACTERISTICS
`
`III. CALCULATION AND MEASUREMENT
`OF COUPLER INDUCTANCE '
`
`3527
`
`The self-inductance L and the leakage inductance L1 have
`been measured and calculated using the software package
`for magnetic field analysis ELF/TVIAGIC.:The calculated
`values of the self—inductance L and the leakage inductance
`L] are plotted as a function of the air gap; The calculated
`result and experimental result are showa in Fig. 4.
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`Air gap 1ength[mm]
`
`L
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`
`Fig. 4 Self-inductance and leakagewinductance.
`
`Fig. 5 shost measured coupler self—inductance L and
`leakage inductance L, when secondary side is shifted
`horizontally. L does not change almost but L1 increases
`from 1 pH to 10 pH when secondary side shifts
`horizontally from 0 mm to 50 mm.
`'
`
`
`
`1000
`
`The new inductive coupler is composed of two thin large
`ferrite pot cores and two windings as shown in Fig. 3.
`In
`this figure, the primary core is for primary coil of charger
`side, the secondary core is for secondary coil ofthe electric
`vehicle side, and the iron plate is the body of the electric
`vehicle shown in Fig. 2 (C). The. primary and secondary
`cores have large cross sectional areas, as shown in plain'D
`and plain E. On the other hand, the thickness of the bottom
`of the slot for winding seems to be thin. However, this
`portion being. a periphery Of the circle,
`the total cross
`seetional area of the cOre in plain C is not always small.
`Therefore, the magnetic reluctance of the fluxpath through
`the cores become small. So in this coupler,
`the self-
`inductance is large and the leakage-inductance is small
`even if air gap is of considerable length. Fig. 3 and table I
`show the dimension and design parameters of the core.
`
`
`
`Primarycore
`Secondary core
`
`Fig. 3 Dimension of the magnetic coupler.
`
`Table I Design parameters of the core
`
`§.
`
`IL] 1.
`Inductance(pH) 5
`
`l 6 ll16212631364146515661667176'81'
`
`_ Silied length between priinary core
`and secondary core [mm]
`
`Fig. 5 Experimental result ML and L1.
`
`
`366 cm3
`
`Core volume
`_.
`Core weight
`Core cross section C
`
`17.2kg
`' 100cm 2
`801cm2
`Core cross section D
`
`Core cross section E-
`.
`738'cm2 '
`Flux path length
`37 cm
`
`-
`
`Specific permeability
`Core loss
`
`
`.
`
`2300
`0.003 SW/cm 2
`
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`   ÿ

  ÿ ÿ ÿÿ ÿÿ   ÿ ÿÿÿÿÿ !ÿ"ÿ#$$$ÿ%ÿÿ

 ÿ&ÿ
`
`Authorized licensed use limited to: Reprints Desk. Downloaded on April 26,2021 at 15:42:54 UTC from IEEE Xplore. Restrictions apply.
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 002
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 002
`
`

`

`
`
` RatioofMagneticFluxDensity
`
`0
`
`5
`
`10
`
`15
`
`20
`
`25
`
`Gap between core and iron plate[ mm ]
`
`Fig. 8 Magnetic flux densities retio.
`
`V. CONCLUSION
`
`A new inductive coupler is proposed which has sufficient
`exciting inductance and low leakage inductance at large air
`gap length. The coupler is tested as an inductive charger,
`and high conversion efficiency is measured namely 97 %
`at 8.3 kW output when gap length is 3 mm and switching
`frequency is 100 kHz. It proves that this coupler can be
`used in large air gapped application such as automatic
`charging EV at parking area.
`
`REFERENCES
`
`[1] F. Anan, K. Yamasaki, “An inductive charger for electric
`vehicles”, Proceedings of the 13‘11 international electric vehicle
`symposium, pp.7l9-724
`[2] C. A. Bleijs, 0. Normand, “A fiilly automatic station using
`inductive
`charging techniques", Proceedings of
`the
`13"1
`international electric vehicle symposium, pp. 742-747
`[3] J. Beretta, F. Quentin, “A complete automatic charging system
`for electric vehicles?’, Proceedings of the 13'h international
`electric vehicle symposium, pp.550—552
`
`3528
`
`Fig. 6 shows measured coupler inductance when upper
`side is tilted vertically. The self-inductance L decreases
`when increasing tilt angle but the leakage inductance L1
`does not change so much. L and L1 are 40 IuI-l and 1.5 pH
`respectively at tilt angle of 1.6 degrees and tilt length of 14
`Him. So it
`is
`important
`to keep low tilt angle for
`guaranteeing a sufficient inductance.
`
`1
`
`1000
`
`’5: 100
`E;
`
`10
`
`1
`
`i 3
`
`3
`
` 0
`
`2
`
`3
`
`Tilt angle between primary core
`and secondary core.
`[ degrees ]
`
`Fig. 6 Experimental result of L and L1.
`
`IV. CALCULATION or FLUX DENSITIES
`
`In order to assess the generation of heat caused by the
`eddy current, the magnetic flux densities in the inductive
`charger and a flat iron plate, to which the inductive charger
`is attached, are calculated using the software package for
`magnetic field analysis ELF/MAGIC. In these calculations,
`the radius and thickness of the iron plate are 520 mm and 5
`mm, respectively. Initial permeability of the ferrite pot core
`is 2300 and that of the iron plate is 5218. The coil of pot
`core has 2 turns and a constant current of 0.1 A flows in the
`
`therefore,
`saturated,
`coil. The magnetization" is not
`Newton-Raphson iteration technique is not necessary. The
`air gap of the inductive charger is fixed to 2 mm. Fig. 7
`shows. the flux density plot of the coupler at
`the gap
`between the inductive charger and the iron plate is 1 mm.
`And the gap between the inductive charger and the iron
`plate is varied 0 mm to 30 mm. When the gaps are 0 mm
`and 5 mm, the calculated values of the flux densities at the
`plane H are 4.17 x 10'4 T and 4.29 x 10'5 T respectively. The
`calculated ratios of the magnetic flux densities at the plane
`F, G, H to those at the plane f, g, h shown in Fig. 7
`respectively, are shown in Fig. 8. It may be concluded that
`the inductive charger is attached to the iron plate at few
`millimeters apart, in order to prevent the generation of heat
`caused by the eddy current.
`
`Authorized licensed use limited to: Reprints Desk. Downloaded on April 26,2021 at 15:42:54 UTC from IEEE Xplore. Restrictions apply.
`
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 ÿ&ÿ
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 003
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 003
`
`