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`US 7,915,858 B2
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`a2) United States Patent
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`Mar. 29, 2011
`(45) Date of Patent:
`Liu et al.
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`US007915858B2
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`FOREIGN PATENT DOCUMENTS
`(54) LOCALIZED CHARGING, LOAD
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`GB
`2388716 A
`11/2003
`IDENTIFICATION AND BI-DIRECTIONAL
`GB
`2389720 A
`12/2003
`COMMUNICATION METHODSFOR A
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`GB
`12/2003
`2389767 A
`PLANAR INDUCTIVE BATTERY CHARGING
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`GB
`2/2004
`2392024 A
`SYSTEM
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`8/2004
`2398 176 A
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`cn
`5 3b x30 ‘ el
`Inventors: Xun Liu, Guizhou (CN); Wing Choi
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`GB
`2399 446 A
`9/2004
`Ho, Hong Kong (HK); Ron Shu Yuen
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`Hui, Hong Kong (HK); Wing Cheong WO 03/105308 Al—12/2003WO
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`Chan, Hong Kong (HK) WO—WO 2004/038888 A2 5/2004
`WO 2007/019806 Al
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`(73) Assignee: City University of Hong Kong,
`OTHER PUBLICATIONS
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`Kowloon (HK)
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`Chang-Gyun Kim; Dong-Hyun Seo; Jung-Sik You; Jong-Hu Park;
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`Cho, B.H., “Design of a contactless battery charger for cellular
`Subject to any disclaimer, the term ofthis
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`patent is extended or adjusted under 35
`phone,” IEEE Transactions on Industrial Electronics, vol. 48, Issue
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`U.S.C. 154(b) by 585 days.
`6 , Dec. 2001, pp. 1238-1247.
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`S. C. Tang, S. Y. R. Hui and H. Chung,“Evaluation of the Shielding
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`Effects on Printed-Circuit-Board Transformers using Ferrite Plates
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`and Copper Sheets,” IEEE Transactions on Power Electronics, vol.
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`17, No. 6, Nov. 2002, pp. 1080-1088.
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`(75)
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`(*) Notice:
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`(21) Appl. No.: 11/929,466
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`(22)
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`Filed:
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`Oct. 30, 2007
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`Prior Publication Data
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`US 2009/0108805 Al
`Apr. 30, 2009
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`Int. Cl
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`HOIM 10/46
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`(52) US. C1. ceceeeeesseeeeceeceeceeceeestensesseeseenes 320/108
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`(58) Field of Classification Search .................. 320/107,
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`320/108, 112, 114, 115, 116
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`See applicationfile for complete search history.
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`References Cited
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`U.S. PATENT DOCUMENTS
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`9/2000 Brockmannetal. .......... 320/108
`6,118,249 A
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`6,301,128 Bl
`10/2001 Jang et al.
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`ve 363/17
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`een Bi eos yeu al.
`” 3vo
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`7.164255 B2*
`1/2007 Ub veecccccscssesessenien 320/108
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`2003/0210106 Al
`11/2003 Cheng etal.
`333/24 R
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`2009/0121675 Al*
`5/2009 Hoetal. wee 320/108
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`(Continued)
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`Primary Examiner — Edward Tso
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`(74) Attorney, Agent, or Firm — Heslin Rothenberg Farley
`& Mesiti PC.
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`ABSTRACT
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`Methodsandprinciples are described for systematizing local-
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`ized charging, load identification and bi-directional commu-
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`nication in a planar battery charging system. Also described is
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`control circuitry for selectively energizing a primary winding
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`whena load is placed on the platform. The optimization ofthe
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`size of the receiver winding compared to the transmitter
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`winding is discussed, while the associated communication
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`methods include techniques for load identification, compat-
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`ibility checks, hand-shaking and communication ofcharging
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`Status.
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`25 Claims, 7 Drawing Sheets
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`Transmitter
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` weenie+ control signal
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`Page 1 of 15
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`US 7,915,858 B2
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`Page 2
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`OTHER PUBLICATIONS
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`S.Y. R. Hui and W.C. Ho, “A New Generation of Universal Contact-
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`less Battery Charging Platform for Portable Consumer Electronic
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`Equipment,” IEEE Power Electronics Specialists Conference, 2004,
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`vol. 1, Jun. 20-25, 2004, pp. 638-644.
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`T. Sekitani, M. Takamiya, Y. Noguchi, S. Nakano,Y. Kato, K. Hizu,
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`H. Kawaguchi, T. Sakurai, T. Someya, “A large-areaflexible wireless
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`power transmission sheet using printed plastic MEMSswitches and
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`organic field-effect transistors,’ IEDM 2006, International Electron
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`Devices Meeting, Dec. 2006, pp. 1-4.
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`* cited by examiner
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`U.S. Patent
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`Mar.29, 2011
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`Sheet 1 of 7
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`US 7,915,858 B2
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`FIG.2(a)
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`U.S. Patent
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`Sheet 2 of 7
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`US 7,915,858 B2
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`eeeSoe 1 . .
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`Primary shielding
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`__-~ Secondary shielding
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`FIG.2(b)
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`FIG.3
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`FIG.4
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`U.S. Patent
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`Sheet 3 of 7
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`FIG.S5
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`FIG.6
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`U.S. Patent
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`11.13cm
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`FIG.8
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`FIG.9
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`Trai
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`Controllable
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`waneese* control signal
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`System scan mode
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`Passible load
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`Data exchange mode
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`FIG.10
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`FIG.11
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`detected?
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`US 7,915,858 B2
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`1
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`LOCALIZED CHARGING, LOAD
`IDENTIFICATION AND BI-DIRECTIONAL
`
`
`COMMUNICATION METHODS FOR A
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`PLANAR INDUCTIVE BATTERY CHARGING
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`SYSTEM
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`2
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`Electronics, Vol. 17, No. 6, November 2002, pp. 1080-1088;
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`S. C. Tang and S. Y. R. Hui, “Planar printed-circuit-board
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`transformers with effective electromagnetic interference
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`(EMI) shielding” U.S. Pat. No. 6,501,364; S. Y. R. Hui,
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`“Apparatus and methodof an inductive battery charger,” PCT
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`patent application WO03/105308; S. Y. R. Hui and W. C. Ho,
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`“A New Generation of Universal Contactless Battery Charg-
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`ing Platform for Portable Consumer Electronic Equipment,”
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`IEEE Power Electronics Specialists Conference, 2004, Vol-
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`ume: 1 , 20-25 Jun. 2004, Pages: 638-644]. In practice, the
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`area of the battery pack or the back cover of a portable
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`electronic product can be used for the energy-receiving coil.
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`This vertical flux approach makesit easier than the horizontal
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`flux approach to design a slim energy-receiving module.
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`Electro-magnetic shielding 6 is provided on the side of the
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`charging surface opposite from the side on which a device to
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`be chargedis placed. This shielding prevents flux from being
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`directed in the wrong direction (which would be a safety
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`issue—especiallyif the battery charging platform wasplaced
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`on a metal surface) and enhances the magnetic flux that is
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`available for battery charging. Electromagnetic shielding is
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`also added on the side of the energy-receiving coil opposite
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`from the side to be placed on the charging surface as shown
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`for example in FIG. 2(4). In such a battery charging platform
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`a secondary winding is provided that is associated with a
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`battery to be charged. The secondary winding picks up the
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`magnetic flux and generates a charging voltage that is pro-
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`vided to the battery. Generally the secondary winding would
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`be formedintegrally with the battery such that a battery or a
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`device containing the battery is placed on the charging sur-
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`face with the secondary coilparallel to the surface suchthatit
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`receives a maximum amount of magnetic flux. Alternatively,
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`however, the secondary winding may be electrically con-
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`nected to the battery but physically separate therefrom. In
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`such a case the secondary winding may be formed as part of
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`a secondary charging module that is placed on the charging
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`surface. This possibility is particularly useful to allow the
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`charging platform to be used with older electronic devices
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`that are not otherwise designed for use with such a platform.
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`In both cases, the entire surface of the charging surface is
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`energized for energy transfer. Although the concept of a
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`“localized charging principle”has been disclosed previously
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`in GB2389720A, U.S. Pat. No. 7,1642,55 and WO2007/
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`019806, so far there is no systematic approach in designing an
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`inductive battery charging pad that can meet the energy-
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`efficiency,
`safety, electromagnetic compatibility require-
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`ments simultaneously.
`In “T. Sekitani, M. Takamiya, Y.
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`Noguchi, S. Nakano, Y. Kato, K. Hizu, H. Kawaguchi, T.
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`Sakurai, T. Someya, “A large-area flexible wireless power
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`transmission sheet using printed plastic MEMSswitches and
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`organic field-effect transistors,’ JEDM °06, International
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`Electron Devices Meeting, December 2006, pp. 1-4,” a
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`MEMS method has been proposed for inductive charging
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`system, but such approach is restricted to relatively low-
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`powerandis very costly.
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`SUMMARY OF THE INVENTION
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`According to the present invention there is provided, in a
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`first aspect, a planar battery charging system comprising a
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`primary powertransmission side formed of an array ofpri-
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`mary windings adapted to generate magnetic flux substan-
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`tially perpendicular to a charging surface, and a secondary
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`powerreceiving side comprising a secondary winding asso-
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`ciated with a battery to be charged and being adapted to
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`receive the magnetic flux when placed on the charging sur-
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`face, the secondary winding being provided with electromag-
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`FIELD OF THE INVENTION
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`This invention relates to localized charging, load identifi-
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`planar battery charging system.
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`BACKGROUND OF THE INVENTION
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`The increasing popularity of portable consumerelectronic
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`products such as mobile phones, MP3 players and PDAshas
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`prompted new concerms on the huge variety and number of
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`battery chargersthat are required. This numberis both incon-
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`venient to users and eventually leadsto electronic waste prob-
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`lems. Inductive or wireless charging apparatus that can
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`charge more than one electronic product have been proposed.
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`Twodifferent approaches have been proposedfor the ac mag-
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`netic flux generation, namely “horizontal flux” and “vertical
`flux” method.
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`Inductive electronic chargers have been developedfor use
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`with some types of portable electronic equipment such as
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`electric toothbrushes. Inductive chargers have also been pro-
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`posed in U.S. Pat. Nos. 6,356,049, 6,301,128, and 6,118,249.
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`These inductive type chargers, however, usetraditional trans-
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`former designs with windings wound aroundferrite magnetic
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`cores. The main magnetic flux between the primary (energy-
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`transmitting) winding and secondary (energy-receiving)
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`winding has to go through the magnetic core materials. An
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`alternative contactless charger [Chang-Gyun Kim; Dong-
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`HyunSeo; Jung-Sik You; Jong-Hu Park; Cho, B. H., “Design
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`of a contactless battery charger for cellular phone,” JEEE
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`Transactions on Industrial Electronics, Volume: 48, Issue: 6,
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`December 2001 Page(s): 1238-1247.] proposed also uses
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`magnetic cores as the main structure for the coupled trans-
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`former windings. However, these battery chargers do not use
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`a planarstructure and each charger is able to charge only one
`electronic load at a time.
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`Two different approaches to planar battery charging
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`devices have recently been proposed. The first type of planar
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`battery charger modifies the rotating machine concept by
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`flattening the “round shape” of the motor into a “pancake
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`shape,” as shown in FIG.1(a) and reported in GB2399225A,
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`GB2398176A, WO2004/038888A, GB2388716A, US2003-
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`210106A, GB2392024A, and GB2399230A. The magnetic
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`flux lines 1 flow along (i.e., roughly parallel to) the planar
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`charging surface 2. However, such a horizontal flux approach
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`requires a vertical surface to pick up the ac flux for voltage
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`induction (FIG. 1(4)) andthis limitation makesit difficult to
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`design a slim energy-receiving module that can be unobtru-
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`sively housed inside the equipmentto be charged. Typically,
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`as shown in FIG. 1() the secondary winding needs to be
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`wound round a magnetic core 3.
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`The second approach (shown for example in WO03/
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`105308A, GB2389720A, GB2399446A,USS. Pat. No. 7,164,
`60
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`255, GB2389767A, WO2007/019806) creates an ac mag-
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`netic field with theflux lines 4 flowing substantially vertically
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`out of a planar charging surface 5 (FIG. 2(a)). Since the lines
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`of flux leave the charging surfacevertically, the entire surface
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`of the load in principle can be used to pick up the flux [S. C.
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`Tang, S. Y. R. Hui and H. Chung,“Evaluation ofthe Shielding
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`Effects on Printed-Circuit-Board Transformers using Ferrite
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`Plates and Copper Sheets,” ZEEE Transactions on Power
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`Page 10 of 15
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`Page 10 of 15
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`4
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`of columns, wherein the matrix switching array comprises
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`one switch per row and one switch per column, and wherein
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`a windingto be excited is selected by closing the switches in
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`the row and column corresponding to the location of the
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`winding. The switches may be controlled by a microproces-
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`sor control unit and the matrix switching array preferably
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`includesfilter means to prevent the generation of EMIinter-
`ference.
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`According to a still further aspect of the invention, there is
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`provided a planar battery charging system comprising a pri-
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`mary powertransmission side formed of an array of primary
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`windings adapted to generate magnetic flux substantially per-
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`pendicular to a charging surface, and a secondary power
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`receiving side comprising a secondary winding associated
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`with a battery to be charged and being adaptedto receive the
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`magnetic flux when placed on the charging surface. The bat-
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`tery charging system further comprises data communication
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`meansfor enabling data communication betweenthe primary
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`side and the secondary side.
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`The data transfer from the primary side to the secondary
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`side may be achieved by modulating the excitation of a pri-
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`mary winding. The data transfer from the secondary side to
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`the primary side may be achieved by modulating a parameter
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`(such as, for example, the loading conditions) on the second-
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`ary side.
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`Preferably, the data communication comprises detection
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`by the primary side of a load to be charged on the secondary
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`side. The detection of a load to be charged may include the
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`detection of the location of the load on the charging surface.
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`Preferably, the data communication comprises hand-shak-
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`ing and compatibility checks between the primary side and a
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`load to be charged and/or determination ofthe charging status
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`of a battery.
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`3
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`netic shielding on the side of the winding opposite from the
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`side to be placed on the charging surface. Therelative dimen-
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`sions of the primary windingsand the secondary winding are
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`chosen to meet the conditionsthat(a) the area enclosed by the
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`secondary winding is greater than the area enclosed by a
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`primary winding, (b) the secondary windingor the shielding
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`will always fully enclose a primary winding when a second-
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`ary windingis placed on the charging surface, and (c) a single
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`primary winding generates sufficient power to charge a the
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`battery.
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`Preferably, in order to optimize the performance of the
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`battery charging system, the ratio of the area enclosed by the
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`secondary windingto the area enclosed by a primary winding
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`is minimized while being consistent with conditions (a) and
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`(b).
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`In preferred embodiments of the invention, the primary
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`windingsare arrangedin a regulararray of identical size and
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`shape. The array of primary windings mayalso be divided
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`into a plurality of zones and within each zone the primary
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`windings are of identical size and shape, though different
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`zones may feature windingsofdifferent sizes and shapes.
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`In some embodimentsof the invention, the primary wind-
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`ings are provided in a stacked structure which may, for
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`example, be formed oftwo or more connected coils separated
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`by a substrate.
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`Preferably, only a single primary windingis excited when
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`a secondary windingis placed on the charging surface.
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`In embodiments of the invention,
`the electromagnetic
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`shielding provided with the secondary winding extends
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`beyond the dimensionsofthe secondary winding. Preferably,
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`only a primary windingthat is covered either by the second-
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`ary winding, or by the electromagnetic shielding, when a
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`secondary winding is placed on the charging surface is
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`excited. More than one primary winding may be excited,
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`provided that only primary windings covered by the second-
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`ary winding and/or shielding are excited.
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`According to another aspect of the present invention, there
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`is provided a planar battery charging system comprising a
`Some embodiments of the invention will now be described
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`primary powertransmission side formed ofan array ofpri-
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`by way of example and with reference to the accompanying
`mary windings adapted to generate magnetic flux substan-
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`drawings, in which:
`tially perpendicular to a charging surface, and a secondary
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`FIGS. 1(@) and (6) show (a)the direction ofthe flux lines in
`powerreceiving side comprising a secondary winding asso-
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`a first prior art battery charging platform, and (b) a corre-
`ciated with a battery to be charged and being adapted to
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`sponding secondary device,
`receive the magnetic flux when placed on the charging sur-
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`FIGS. 2(@) and (6) show (a) the direction ofthe flux lines in
`face. When a secondary winding is placed on the charging
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`a secondpriorart battery charging platform, and (b) a corre-
`surface, only a single primary winding is excited to generate
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`sponding secondary device,
`magnetic flux to charge the battery.
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`FIG. 3 shows one example of a single- or multiple layer
`Preferably, a matrix switching array is provided for
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`winding array for a charging platform based on hexagonal
`enabling a selected primary winding to be excited. When
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`windings,
`excited, a single primary winding maypreferably provide
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`FIG. 4 shows examples of rectangular or circular receiver
`sufficient magnetic flux to charge thebattery.
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`windings,
`In preferred embodiments of the invention, meansare pro-
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`FIG. 5 illustrates the dimensional relationship between
`vided to detect the presence and location on the charging
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`large receiver windings and smaller transmitter windings
`surface of the secondary winding.
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`based on a square packing of circular windings,
`According to a further aspect of the invention, there is
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`FIG. 6 illustrates the dimensional relationship between
`provided a planar battery charging system comprising a pri-
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`large receiver windings and smaller transmitter windings
`mary powertransmission side formed of an array of primary
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`based on hexagonal packing of hexagonalspiral windings,
`windings adapted to generate magnetic flux substantially per-
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`FIG.7 illustrates an example of load-dependentselection
`pendicular to a charging surface, and a secondary power
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`of transmitter windings for energization,
`receiving side comprising a secondary winding associated
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`FIG. 8 shows one example of a switching circuit for trans-
`with a battery to be charged and being adaptedto receive the
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`mitter winding selection and excitation,
`magnetic flux when placed on the charging surface. Thepla-
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`FIG. 9 shows another example of a switching circuit for
`nar battery charging system further comprises a matrix
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`transmitter winding selection and excitation,
`switching array for selectively exciting individual primary
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`FIG. 10 illustrates an example of a methodofbi-directional
`windings.
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`communication between the transmitter windings and the
`In preferred embodiments of the invention, the array of
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`primary windings compriseaplurality of rows anda plurality receiver winding, and
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`US 7,915,858 B2
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`Page 11 of 15
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`Page 11 of 15
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`

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`5
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`FIG.11 is a flow diagram for the operation of one example
`of the invention.
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`DETAILED DESCRIPTION OF PREFERRED
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`EMBODIMENTS
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`Preferred embodiments of the present invention provide a
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`systematic methodology that covers a range of technical
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`aspects of an inductive battery charging system. Such a sys-
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`tem includes a charging platform or pad that generates verti-
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`cal flux from the planar surface of the charging pad and at
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`least
`in preferred embodiments
`the present
`invention
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`addresses several basic principles for achieving localized
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`charging in a charging pad system. Althoughthese principles
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`and corresponding techniques can be implemented individu-
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`ally, their collective use is synergistic and enables the devel-
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`opment of an inductive charging pad system that can meet
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`various international regulatory requirements.
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`FIG. 3 showsa typical single-layer windingarray structure
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`with many individual primary energy-transmitting coils 7
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`(named transmitter windings hereafter) in an inductive bat-
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`tery charging pad.It is also proposed that a multilayer wind-
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`ing array can also be used. For example, a stacked winding
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`where each primary winding comprises a pair of coils pro-
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`vided respectively on two sides of a substrate, such as a
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`printed-circuit board, can be adopted to enhance the magnetic
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`flux for the same foot-print area. In a stacked structure one
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`coil in the pair may generally overly the other, but this need
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`not necessarily be exact and there may be a small offset. It
`should also be notedthat a stacked structure can be extended
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`to more than twocoils.
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`In order for the charging pad to charge a wide range of
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`portable electronic loads, a methodology is proposed that
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`involves the combined use of several basic principles and
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`technical features. In the following description, the primary
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`energy-transmitting windings in the charging pad will be
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`called “transmitter windings” and the secondary energy-re-
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`ceiving windings inside the electronic loads will be called
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`“receiver windings”.
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`In embodiments of this invention,(i) the receiver winding
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`are larger than the transmitter windings, (ii) the receiver
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`winding should fully cover at least one transmitter winding
`whereverthe electronic load that contains the receiver wind-
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`ing is placed on the charging surface of the charging pad and
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`(11) one transmitter winding is sufficient to provide enough
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`powertransfer for the electronic load under consideration for
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`the charging pad. As discussed above a multilayer structure of
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`stacked windings can be used to enhance the magnetic flux for
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`the same foot-print area. Preferably the area ratio of the
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`receiver winding and one transmitter winding must be mini-
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`mized provided that condition(ii) is satisfied.
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`The basic conceptof the localized chargingprinciple is to
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`energize only the relevant transmitter windings that are
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`directly underneath the receiving windings ofthe electronic
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`loads for energy transfer. In other words, the localized charg-
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`ing principle is load-position dependent.It only energizes the
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`areas on the charging surface where the electronic loads are
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`placed. In preferred embodimentsofthis invention, it is pro-
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`posedto energize only one transmitter winding for each elec-
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`tronic load or at least only those covered by the electronic
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`load. This offers the following advantages:
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`(a) Since the transmitter winding is fully covered by the
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`receiver winding (with electromagnetic shielding that should
`extendat least for the same dimensionsas the receiver wind-
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`ing and preferably should extend beyondthe receiver wind-
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`ing), this avoids unnecessary electromagnetic radiation from
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`Page 12 of 15
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`US 7,915,858 B2
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`6
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`the charging surface that is not covered by the electronic load.
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`This reducesthe generationofpossible electromagnetic inter-
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`ference (EMI).
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`(b) Unnecessary switching and conduction powerlosses
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`are avoidedor at least mitigated in transmitter windings that
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`play no part in energy transfer. This improves the overall
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`energy efficiency of the entire charging system.
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`(c) The possibility of human exposure to the transmitted
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`energy from the charging pad due to physical contacts on the
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`charging surface of the charging pad1s either eliminatedor at
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`least reduced. This feature helps meeting the “IEEE C95.1
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`standard for safety levels with respect to human exposure to
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`radio frequency electromagnetic fields, 3 kHz to 300 GHz.”
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`In order to select the appropriate transmitter windings for
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`localized charging,
`suitable power
`inverter circuits are
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`required that can connect and energize the selected transmit-
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`ter windings to excite these selected windings at the appro-
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`priate frequency so as to maximize the magnetic coupling and
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`energy transfer between the transmitter windings of the
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`charging pads and the receiver windings of the electronic
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`loads. The electronic switching circuit should periodically
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`check the existence ofthe loads on the charging pad. Oncethe
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`load compatibility has been favorably checked, the power
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`electronic switching circuit should energize appropriate
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`transmitter winding for energy transfer.
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`Embodimentsof the present invention includethe use of a
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`bi-directional communication system for detecting the pres-
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`ence and location of load(s) on the surface of the charging
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`pad. The communication system must check the identity and
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`compatibility of the loads so that items not designed or
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`intended to be charged on the charging pad will not receive
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`transmitted power. This feature ensures the safety of the
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`users. For example, should a cigarette lighter be accidentally
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`placed on the charging pad it mustnot receive any power from
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`the charging pad. In addition, the bi-directional communica-
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`tion should provide information forthe battery charge condi-
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`tion. Whenthe loadsare fully charged, the selected transmit-
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`ter windings should stop energy transfer in order to reduce
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`unnecessary energy wastage.
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`In the following description, these integrated technical
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`aspects will be explained in moredetail.
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`The three conditions proposed for the windingsare that(i)
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`the receiver winding 8 should be larger than the transmitter
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`windings 7 in the sense that the receiver winding 8 should
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`enclose a greater area than a transmitter winding 7, (ii) the
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`receiver winding 8 must fully cover at least one transmitter
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`winding 7 whereverthe electronic load is placed on the charg-
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`ing surfaceofthe charging pad and(iii) one transmitter wind-
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`ing 7 is sufficient to provide enough powertransfer to charge
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`the battery of an electronic device intended to be chargeable
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`on the charging pad. In this example, it is assumedthat the
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`receiver winding 8 is circular. However,the skilled reader will
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`understandthat the receiver winding 8 can be of other shapes
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`such as any