3526
`
`IEEE TRANSACTIONS ON MAGNETICS, VOL. 35, NO. 5, SEPTEMBER [999
`
`Large Air-Gap Coupler for Inductive Charger
`
`H. Sakamoto, K. Harada, 8. Washimiya, K. Takehara
`Kumamoto Institute of Technology, 4-22-1 Ikeda, Kumamoto 860-0082, Japan
`
`Y. Matsuo and F, Nakao
`:
`FDK Corporation, 2281, Washimizu, Kosaji-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, Thenew inductive coupler proposed here has
`sufficient exciting inductance even if it has a large air gap.
`Calculated exciting inductance is 40 WH at 2 turns ofwinding 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
`MOSFETsfull-bridge inverter of 100 KHz, is 97% at 8.3 kW
`output.
`
`Index Terms---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. 1 shows possible means of
`inductive charging for 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 anda transferring
`poweris limited by the leakage inductance. Presently, most
`ofthe inductive chargers for electric vehicle is ofhand held
`insert-type as shown.in Fig. 2 (A) [1]. Although inthis type
`of charger,the air gap ofthecoupler is easy to make small,
`it will be troublesome to do inserting operations by hand.
`Further,if the power becomeslarge,it will be too heavy to
`carry it by hand. On the other hand, an automatic charging
`at patking 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 compensatedeffectively 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 1Ex.2750
`Fax slumber: +81 96 326 3004, Email: hiroshi@ee.kumgmoto-it,ac.jp
`
` I Magnetic,
`
`coupler
`
`hhBHHE
`
`
`Primary Coil
`(C) Automatic Charger with Large Air-Gap Coupler
`
`Fig. 2 Inductive charging system for electric vehicle.
`
`0018-9464/99$10,00 © 1999 IEEE
`
`   ÿ

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`Authorized licensed uselimited 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
`
`

`

`Tl. NEW INDUCTIVE COUPLER DIMENSION
`AND CHARACTERISTICS
`
`TI, CALCULATION AND MEASUREMENT
`OF COUPLER INDUCTANCE —
`
`3527
`
`The self-inductance L and the leakage inductance L, have
`‘been measured and calculated using the software package
`for magnetic field analysis ELF/MAGIC. The calculated
`values ofthe self-inductance L and the leakage inductance
`L, are plotted as a function of the air gap. The calculated
`result and experimental result are shownin Fig.4.
`
`The new inductive coupler is composed oftwothin large
`ferrite pot cores and two windings as shownin 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). Theprimary and secondary
`cores have large cross sectional areas, as shownin plain D
`and plain E. Onthe 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
`sectional 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 parametersofthe core.
`
`“1000
`
`.
`
`~
`
`a
`
`
`
`
`
`@ 1. meas. ML, meas. — cale.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`=
`
`
`
`
`
`
`1 REEF ia
`=f SFE
`rT
`
`
`3 sistatele!| eter ilbree
`Teh Co
`Co Cer
`TH
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`ot
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`ee
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`peamanae
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`ESR ae
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`“ae
`+ | on yo
`:
`Air gap length [mm ]
`
`Authorized licensed uselimited 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
`
`--
`
`0.1
`
`pp
`
`Fig, 4 Self-inductance and leakage-inductance.
`
`Fig. 5 shows measured coupler self-inductance L and
`leakage inductance L, when secondary side is shifted
`horizontally. 1 does not change almost but L, increases
`from 1 wH to 10 wH when secoridary side shifts
`horizontally from 0 mm to 50 mm,
`,
`
`1000
`
`5Inductance(uH) =
`
`w i,
`
`1 4
`
`1 6 11 16 21 26 31 36 41 46 SI 56 GI O71 OBI
`
`__ Sifted length between primary core
`and secondary core [mm |
`
`Fig. 5 Experimental result of L and 1,
`
`oO"Brimarycore|
`Secondary core
`
`
`
`Fig. 3 Dimension of the magnetic coupler.
`
`Table I Design parameters ofthe core
`
`
`Core yolume
`:
`366 cm3
`Core weight
`17.2 kg
`
`
`_|_ Core cross section C
`100 cm?
`
`Core cross section D
`801 cm2
`Core cross section E-.
`738 cm2
`Fiux path length
`37m
`Saturating flux density
`Specific permeability.
`‘Core loss
`
`
`_
`
`_
`
`
`
`
`
`2300
`0.0035W/em ”
`
`
`
`
`
`
`
`
`
`
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`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 002
`
`

`

`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 L,
`does not change so much. L and L, are 40 WH and 1.5 uH
`respectively attilt angle of 1.6 degrees andtilt length of 14
`mm. So it
`is
`important
`to keep low tilt angle for
`guaranteeing a sufficient inductance.
`
`1000
`
`Inductance(wH)
`
`100
`
`10
`
`0
`
`1
`
`2
`
`3
`
`Tilt angle between primary core
`and secondary core.
`[ degrees]
`
`Fig. 6 Experimental result ofL and L,.
`
`IV. CALCULATION OF FLUX DENSITIES
`
`In order to assess the generation of heat caused by the
`eddy current, themagnetic 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 ofthe 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
`coil. The magnetization.
`is not
`saturated,
`therefore,
`Newton-Raphson iteration technique is not necessary. The
`ait 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 | 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% T and 4.29 x 10° 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.
`
`[fetTs
`
`rare
`
`
`f<[-t|
`
` Afiz[e[le
` RatioofMagneticFixDensity
`
`0
`
`25
`20
`15
`10
`5
`Gap between core and iron plate[ mm ]
`
`Fig. 8 Magnetic flux densities retio.
`
`V. CONCLUSION
`
`A new inductive coupleris proposed which has sufficient
`exciting inductance and low leakage inductanceatlarge 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 iength 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" international electric vehicle
`symposium, pp.719-724
`[2] C. A. Bleijs, O. Normand, “A fully automatic station using
`inductive
`charging techniques”, Proceedings of
`the
`13"
`international electric vehicle symposium, pp.742-747
`[3] J. Beretta, F. Quentin, “A complete automatic charging system
`for electric vehicles”, Proceedings of the 13" international
`electric vehicle symposium, pp.550-552
`
`Authorized licensed uselimited to: Reprints Desk. Downloaded on April 26,2021 at 15:42:54 UTC from IEEE Xplore. Restrictions apply.
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`Momentum Dynamics Corporation
`Exhibit 1023
`Page 003
`
`Momentum Dynamics Corporation
`Exhibit 1023
`Page 003
`
`