Study of Contactless Inductive Charging Platform
`with Core Array Structure for Portable Products
`
`Jia-You Lee
`Department of Electrical Engineering
`National Cheng Kung University
`Tainan, Taiwan
`leejy@mail.ncku.edu.tw
`
`
`
`Tsung-Wen Chang
`Department of Electrical Engineering
`National Cheng Kung University
`Tainan, Taiwan
`n2694421@mail.ncku.edu.tw
`
`22.83% comparing to the quantity of cell phone sold (1.095
`billion) in 2007. Therefore, a common charging platform which
`possesses compatibility of different electronic products be-
`comes rather imperative.
`
`II. THE FRAMEWORK OF CONTACTLESS INDUCTIVE
`CHARGING PLATFORM
`Traditional chargers rely on the contact of metals, oxidi-
`zation or corrosion frequently occur on the contacting point of
`metals, causing the increase in the resistance between two
`contacting points and thus causing heat consumption or
`inefficiency in charging. In recent years, electromagnetic
`induction theory is adopted to develop contactless inductive
`power system, and successfully applied on electronic tooth-
`brush, electronic shaver, cell phone, telephone and other
`portable electronic products [1-6].
`The contactless inductive charging technique mentioned in
`this research aims to provide convenient and uniform charging
`method for portable electronic products. Upon designing
`contactless inductive charging system, the analysis of magnetic
`allocation for inductive structure is the first consideration,
`relying on the result of analysis to obtain appropriate inductive
`structure and to consider the impact of current direction of
`array core on the allocation of magnetic fields. Next, closed-
`loop control structure is applied, enabling the system to work in
`the domain of high efficiency. The structure of contactless
`inductive charging platform proposed in this research is shown
`as Fig. 1. The primary of Fig. 1 shows that the converter trans-
`forms AC into DC, then the inverter again transforms the DC
`into AC for driving inductive core of the primary. In the
`secondary, the inductive core picks up power from primary and
`the power is then rectified in order to charge the lithium bat-
`tery. The charging scheme utilized in this research is constant
`current and constant voltage.
`
`Figure 1. The framework of contactless inductive charging platform.
`
`
`
`Hung-Yu Shen
`Department of Electrical Engineering
`National Cheng Kung University
`Tainan, Taiwan
`n28991366@mail.ncku.edu.tw
`
`Abstract—In this research, contactless power transmission tech-
`nique is applied in the charging of lithium battery for portable
`electronic products and the concept of common charging
`platform is proposed. The charging platform is comprised of
`several pot type cores with array structure, allowing circuit to be
`charged within a permitted region of displacement on the
`charging platform. However, a larger air gap exists in contactless
`structure compared to other contact structures, i.e. poor power
`transmission efficiency. In order to overcome the weakness,
`phase-locked loop (PLL) is applied to enable the operation
`frequency of circuit to be maintained above primary resonant
`frequency and microprocessor
`is utilized to
`improve the
`transmission efficiency when charging platform is standby. In
`addition, printed-circuit-board (PCB) is utilized on the secondary
`to reduce the thickness of the secondary circuit, forming PCB
`coil. Experimental results show that the transmission efficiency
`between contactless inductive structures is 55% under the
`condition of charging current 200mA and air gap 2.5mm.
`
`Keywords-contactless power transmission; charging platform;
`array structure;, PCB coil
`
`I.
`INTRODUCTION
`In the past decade, electronic products have progressed in a
`tremendous speed. Portable electronic products, such as
`multimedia cell phones, MP3, digital camera, notebooks and
`etc, have almost become a necessity for people of modern age.
`Accompanying the growing demand for portable electronic
`products, the demand of rechargeable batteries has also
`increased.
`Despite the fact that rechargeable batteries pollute the
`environment to a lesser extent, comparing to non-rechargeable
`batteries, they still have some weaknesses that are not yet
`overcome. Portable electronic products of different brand
`require different type of chargers due to different requirements
`of voltage, current and connector types. Not only the chargers
`for portable electronic products of different brands are not
`compatible, but also chargers for portable electronic products
`with of same brand but different modules. This leads to vast
`number of battery chargers and thus causing problems. Users
`with many portable electronic products have to carry a number
`of chargers is a problem. Besides, the metal and electrolyte
`components cause environmental problems. According to the
`survey of research center, IDC, the quantity of cell phone sold
`globally in 2009 has raised to 1.345 billion, an increase of
`
`978-1-61284-459-6/11/$26.00 ©2011 IEEE
`
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`III. ANALYSIS OF CONTACTLESS INDUCTIVE STRUCTURE
`Contactless
`inductive charging, using electromagnetic
`induction for power transmission, can be regarded as a loosely
`couple transformer. Comparing to the structure of traditional
`transforms, its contactless inductive structure yields larger gap,
`causing difficulties for primary inductive coil to establish
`magnetic circuit and to produce magnetic field. Therefore, this
`research investigates the influence of different inductive
`structure on the magnetic allocation based on the analysis of
`characteristics magnetic allocation for different types of
`inductive structure.
`
`A. Primary inductive structure
`Generally, commonly used inductive structures are (a) type
`I, (b) type E and (c) Pot type, as shown in Fig. 2. Under con-
`stant length, inductive coil has to produce enough flux and low
`leakage flux. Software Maxwell 3D is utilized to analyze the
`magnetic allocation of different core type and to decide on the
`core of primary. The simulation of magnetic field for each core
`is shown as (a) type I, (b) type E and (c) Pot type of Fig. 3.
`Type I inductive structure, has poor magnetic field closeness
`and large leakage flux, leading to difficulties in establishing
`magnetic circuit and a decrease in overall coupling coefficient.
`Comparing to the inductive structure of type I, the inductive
`structure of type E has better magnetic field closeness and
`better coupling effect. However, it’s large in size and is easily
`affected by horizontal displacement, therefore, is suitable for
`larger and constant load. Pot type has a closer structure,
`therefore magnetic circuit becomes easily established and
`produce lower leakage flux comparing to type E. If it is applied
`in contactless power transmission, the disturbance of leakage
`flux on surrounding electronic equipments can be reduced.
`
`The charging platform of this research is composed of
`several pot type cores, allowing charging to be done in fixed
`distance of displacement. The arrangement of array core is
`shown as Fig. 4, with an area of 100(cid:152)70mm2. The characteris-
`tic of magnetic field allocation for the charging platform is
`affected by arrangement of core as well as the direction of
`driving current.
`Fig. 5 indicates the allocation of magnetic field of different
`driving current within a distance of 2.5mm on top of the
`platform. It is observed that the induced magnetic field for the
`current of the same direction is smaller near the center of the
`core. On the other hand, the current of different direction
`produces larger flux on the outside of the coil and smaller flux
`in the center of the coil, resulting in a depletion region.
`However, magnetic field is easily formed in the center of the
`core, thus, yielding larger induced magnetic field than current
`of the same direction.
`
`B. Secondary inductive coil
`The design of secondary inductive coil is mainly flat and
`this research adopts the design of PCB coil. As the coupling
`effect of the PCB coil is poor, a double sided structure is
`adopted to increase induced current. In addition, the induced
`field formed by the pot type cores is weaker in the center of the
`core, resulting in an increase of resistance of PCB coil.
`Therefore, increase wiring on the outer side of the structure, as
`shown in Fig. 6. Fig. 7 represents the secondary structure.
`Plane core is used to cover the surface of the structure, in order
`to increase the coupling coefficient of the PCB coil and to
`increase shielding of the magnetic field.
`
`
`
`
`
`
`
`(a)Type I
`
`
`
`(b)Type E
`
`
`
`(c)Pot type
`
`Figure 2. Commonly used inductive structures.
`
`
`Figure 4. The arrangement of array core.
`
`(a)Type I
`
`
`
`(b)Type E
`
`
`
`
`
`(a)same direction
`
`(b)different direction
`
`
`
`Figure 5. The simulation of magnetic field for different direction of current.
`
`(c)Pot type
`
`
`
`
`
`Figure 3. The simulation of magnetic field for each core type.
`
`Figure 6. The PCB coil of secondary with double sided structure.
`
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`B. Charging circuit
`As it is desirable for secondary to be as thin as possible,
`charging management IC (BQ2057) produced by company TI
`is utilized to implement charging circuit. The charging scheme
`adopts constant current and constant voltage. The process of
`charging includes three steps: pre-charged mode, constant
`current mode and constant voltage mode. At the start of
`charging, BQ2057 would switch to the pre-charged mode to
`charge the battery with constant current if the voltage of battery
`is too low. In the process, the voltage of the battery increases
`gradually to the default value. When default value is reached,
`BQ2057 would switch to constant current mode to charge the
`battery with current of default value. At the end of charging
`process, constant voltage is utilized to charge the battery and
`the charging current decades along with time. If the charging
`current reduced to the lowest value of the set current, BQ2057
`would terminate charging and switch to standby mode. Fig. 10
`illustrates the charging circuit of BQ2057.
`
`Figure 9. The flow chart of the control scheme.
`
`
`
`Figure 10. The charging circuit [7].
`
`V. EXPERIMENTAL RESULT
`Fig. 11 is the contactless inductive charging platform
`structure proposed by this research. The main structure is class
`D inverter, which drives the contactless inductive structure to
`transfer energy to secondary. Next, the battery is charged by
`the charging circuit. As the charging current decades along
`with the process of charging, the system equivalent impedance
`alters. Therefore, the system can be adjusted by the feedback
`circuit.
`Fig. 12 is the waveform of the experiment. Fig. 12(a) shows
`the complementary of signals of gate (i.e. vgs1 and vgs2). This is
`to avoid short circuit of switches. Fig. 12(b) represents the
`waveform of vgs2 and vds2. When the voltage of vds2. decreased
`to zero, vgs2 would be triggered, resulting in inverter possessing
`the effect of ZVS. Fig. 13 illustrates the charging procedure of
`
`IV. PRIMARY CONTROL SCHEME AND CHARGING CIRCUIT
`
`A. Control scheme
`The control circuit of primary is controlled by PLL,
`enabling the system to be operated in resonant frequency.
`However, when secondary inductive coil is removed from the
`charging platform, operating under resonant frequency would
`cause quality factor of charging platform to increase, leading to
`the increase of primary voltage. In addition, due to the removal
`of secondary,
`loadless condition
`leads
`to unnecessary
`consumption of power rate and heating of the inductive coil. In
`order to solve the aforementioned problems, this research
`replied on PIC16F876A microprocessor as a remedy and the
`control circuit is shown as Fig. 8. The removal of secondary
`would lead to changes in the voltage of primary inductive coil,
`therefore, can be detected by the level of voltage. Feedback
`voltage, VF connects to analog input of microprocessor, AD
`converter transfers feedback voltage into digital signal for
`control processing. If the voltage exceeds the upper limit of
`default value, microprocessor defines that primary is removed
`and send out low- level signal to switch off the optocoupler.
`Aforementioned produces a voltage into a control circuit of
`PLL, leading to the offset enlargement of phase, in order to
`remove operating frequency from resonant frequency to reduce
`the consumption of power.
`The primary inductive array core is comprised of several
`pot type cores, i.e. magnetic field locates mainly in the center
`of the core. Besides, the primary is driven by different direction
`of current, resulting in poor magnetic field in the connecting
`region between core and core. This connecting region leads to
`insufficient energy supply for the secondary. The control
`scheme proposed in this research includes a function to show
`the coupling effect, for the purpose of misplacing secondary in
`the connecting region. Fig. 9 illustrates the flow chart of the
`control scheme.
`
`Figure 7. The structure of secondary.
`
`Figure 8. The diagram of micropocessor control circuit.
`
`
`
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`
`Apple v. GUI Global Products
`IPR2021-00471, 472, 473
`GUI Ex. 2033
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`

`VI. CONCLUSION
`Firstly, this research analyzes the magnetic field allocation
`of different core and considers the impact of induced magnetic
`field on other electronic equipments. From the result of
`analysis, the charging platform is designed by several pot type
`cores with magnetic enclosure. Secondly, the influence of
`current direction of the coil on the allocation of magnetic field
`is investigated to choose appropriate induced structure and
`current direction of the coil. Primary control circuit adopts PLL
`control to reduce resonant frequency offset caused by loading
`effect, to reach the goal of high transfer efficiency. Thirdly,
`microprocessor control circuit is utilized to adjust input power
`when the secondary is removed from the charging platform,
`and to reduce energy depletion. The coupling effect of each
`part of the charging platform is shown to provide the best
`position to place the secondary.
`As for part of secondary, constant current and constant
`voltage charging schemes are implemented by charging
`management IC. In addition, the induced structure is imple-
`mented by PCB, leading to plane circuit. Finally, the result of
`experiment shows that the contactless inductive charging
`platform is able to charge a battery with charging current of
`200mA under the condition of a gap 2.5mm between the
`secondary and the charging platform. The highest transfer
`efficiency is 55% between primary and secondary, and is able
`to work normally within a large enough displacement. Part of
`energy is lost in leakage inductance of induced structure.
`Therefore, transfer efficiency can be improved if the above
`weakness can be overcome and other type of induced structure
`and magnetic material are added to increase the coupling
`coefficient.
`
`ACKNOWLEDGMENT
`This work was partially sponsored by the National Science
`Council, Taiwan, under awards number NSC 98-2221-E-006-
`248.
`
`[2]
`
`REFERENCES
`[1] C. Sonntag, E. A. Lomonova, and J. L. Duarte, “Variable-phase contact-
`less energy transfer desktop part I:design,” in Proc. IEEE ICEMS, 2008,
`pp. 4460-4465.
`J. Achterberg, E. A. Lomonova, and J. de Boeij, “Coil array structures
`compared for contactless battery charging platform,” IEEE Trans.
`Magn., vol. 44, no. 5, pp. 617-622, 2008.
`[3] S. Y. R. Hui and W. C. Ho, “A new generation of universal contactless
`battery charging platform for portable consumer electronic equipment,”
`IEEE Trans. Power Electron., vol. 20, no. 3, pp. 620-627, 2005.
`[4] B. Choi, J. Nho, H. Cha, T. Ahn, and S. Choi, “Design and implementa-
`tion of low-profile contactless battery charger using planar printed
`circuit board windings as energy transfer device,” IEEE Trans. Ind.
`Electron., vol. 51, no. 1, pp. 140-147, 2004.
`[5] A. P. Hu, Z. J. Chen, S. Hussmann, G. A. Govic, and J. T. Boys, “A
`dynamically on-off controlled
`resonant converter designed
`for
`coalmining battery charging applications,” in Proc. PowerCon, 2002,
`vol. 2, pp. 1039-1044.
`[6] T. W. Chang and J. Y. Lee, “Study of contactless charging platform with
`coil array structure for mobile phone”, Symposium on Power Electronics
`Conference, Taiwan, pp. 907-910, 2007.
`[7] BQ2057 Data Sheet, Texas Instruments Inc., 2002.
`
`the contactless inductive charging platform, with a voltage of
`3.1V under the pre-charged mode. When the voltage of battery
`is lower than 3.1 V, BQ2057 would start the pre-charged mode
`automatically. The largest charging current is set as 200mA
`and terminating current is set as 30mA. Fig. 14 represents the
`3D distribution diagram of energy transfer efficiency of the
`charging platform, with a highest transfer efficiency of 55%
`and the lowest transfer efficiency in the connecting region of
`the core. The lowest transfer efficiency is resulted from current
`of the different direction.
`
`Figure 11. The structure contactless inductive charging platform.
`
`
`
`
`
`
`(a)vgs1 and vgs2
`
`
`
`(b)vgs2 and vds2
`
`
`
`Figure 12. The waveform of the experiment.
`
`
`Figure 13. The charging procedure of the inductive charging platform.
`
`Figure 14. The 3D distribution diagram of efficiency of the charging platform.
`
`
`
`
`759
`
`Apple v. GUI Global Products
`IPR2021-00471, 472, 473
`GUI Ex. 2033
`
`