A wireless charging system

Abstract

The present invention relates to a wireless power charging assembly (400) and a wireless charging unit (200). The wireless power charging assembly (400) comprises a coil assembly (402) and a power storage unit (418). The coil assembly (402) comprises a secondary coil (410) for coupling with a magnetic field (412) generated by a primary coil (210) of a wireless charging unit (200) and an auxiliary coil (414) positioned around a periphery of the secondary coil (410). The coupling of the magnetic field (412) results into flow of an inductive current (406) into the secondary coil (410). An auxiliary current (416) flows through the auxiliary coil (414) in a direction opposite to that of the inductive current flowing through the secondary coil (410). An auxiliary magnetic field produced from the auxiliary current reduces sideways spreading of the magnetic field (412). The power storage unit (418) stores the inductive current.

Description

[0001] A WIRELESS CHARGING SYSTEM

[0002] The present invention relates to a wireless charging system. More particularly, the present invention relates to a charging coil and a powering mechanism of a wireless charging unit.

[0003] The subject matter discussed in the background section should not be assumed to be prior art merely because of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may correspond to implementations of the claimed technology.

[0004] Wireless charging technology is used for charging of devices such as laptops, smartphones, and Electric Vehicles (EVs). Wireless charging technology offers mobility, convenience, safety, and advancement that allows devices to transfer power without necessitating a direct contact as compared to wired charging technology, which inevitably involves human intervention and associated risks of electrocution.

[0005] In wireless charging technology, a primary coil and a secondary coil are utilized for charging a device. The primary coil is assembled in a wireless charging unit and the secondary coil is assembled in a wireless power transfer appliance. When current passes through the primary coil, a magnetic field is generated in a direction perpendicular to a plane of the primary coil. The magnetic field gets coupled with the secondary coil and power is transferred from the primary coil to the secondary coil through mutual induction. As a result, an inductive current flows into the secondary coil. The inductive current is utilized for charging of a battery of the device. Fig. 1 illustrates a schematic diagram of a secondary coil 102 installed in a device, in accordance with prior art. The secondary coil 102 receives a magnetic field generated by a primary coil. Due to mutual induction between the primary coil and the secondary coil 102, an inductive current 104 flows through the secondary coil 102. The inductive current 104 may be passed through a capacitor 106 and an inverter / rectifier 108 prior to storing into a battery of the device.

[0006] During coupling of the magnetic field with the secondary coil 102, a portion of the magnetic field may get leaked in a lateral direction of the secondary coil 102 i.e. sideways spreading of magnetic field (as illustrated by 110). Magnetic field generated from electric current may be calculated using equation (1) as provided below:

[0007] B = pol / (27rr) Equation (1)

[0008] In equation (1), B denotes magnetic field strength, I denotes electric current flowing through a coil, and r denotes a distance from the secondary coil 102. It may be observed from equation (1) that the magnetic field strength is directly proportional to an amount of electric current flowing through the secondary coil 102. Leakage of the magnetic field becomes a serious concern especially in high power devices, such as EVs since high electric current flows through the secondary coil 102.

[0009] Leakage of magnetic field results in wastage of power. In addition, leaked magnetic field is hazardous to human health and has to be mitigated to a minimum at all conditions as per the limitations prescribed by Society of Automotive Engineers (SAE) & International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. Conventional shielding methods, such as metallic shielding and magnetic shielding are not effective in reducing leakage of magnetic field and rather results in reduced power transfer efficiency, and increase in weight and cost of wireless power transfer system owing to use of expensive and heavy shielding components. Thus, there exists a need of a wireless charging mechanism that reduces the above- mentioned shortcomings associated with conventional wireless charging mechanisms.

[0010] An object of the present invention is to provide a wireless power charging assembly and a wireless charging unit capable of reducing sideways spreading of magnetic field.

[0011] Another object of the present invention is to minimize sideways spreading of the magnetic field without increasing size, weight, and cost of the wireless power transfer unit and wireless charging unit.

[0012] Another object of the present invention is to maximize power transfer efficiency and power transfer capacity between a primary coil and a secondary coil.

[0013] The summary is provided to introduce aspects related to a wireless charging system, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0014] In one embodiment, a wireless power charging assembly is described. The wireless power charging assembly includes a coil assembly and a power storage unit. The coil assembly comprises a secondary coil for coupling with a magnetic field generated by a primary coil of a wireless charging unit. This coupling of the magnetic field results into flow of an inductive current into the secondary coil. The coil assembly further comprises an auxiliary coil positioned around a periphery of the secondary coil. A direction of an auxiliary current flowing through the auxiliary coil is opposite to a direction of the inductive current flowing through the secondary coil. An auxiliary magnetic field produced from the auxiliary current reduces sideways spreading of the magnetic field. The power storage unit stores the inductive current.

[0015] In another embodiment, a wireless power charging assembly is described. The wireless power charging assembly includes a coil assembly and a power storage unit. The coil assembly comprises a secondary coil with an outermost turn of the secondary coil positioned in a direction opposite to inner turns of the secondary coil. The secondary coil couples with a magnetic field generated by a primary coil of a wireless charging unit. The coupling of the magnetic field results into flow of an inductive current into the secondary coil. The inductive current flows through the outermost turn of the secondary coil in a direction opposite to the inductive current flowing through the inner turns. The inductive current flowing through the outermost turn produces an auxiliary magnetic field for reducing sideways spreading of the magnetic field. The power storage unit stores the inductive current.

[0016] In an aspect, the coil assembly of the wireless power charging assembly includes at least one of a shielding layer and a magnetic layer positioned above the coil assembly for reducing spreading of the magnetic field over the coil assembly.

[0017] In an aspect, the auxiliary current is generated by a current control circuitry based on a phase angle and a frequency of the inductive current.

[0018] In an aspect, the wireless power charging assembly is an electric vehicle.

[0019] In an aspect, the secondary coil is selected from a group consisting of Circular-type coil, D type coil, and Double-D type coil. In an aspect, the wireless power charging assembly includes a rectifier and a DC-DC converter for processing the inductive current before storing into the power storage unit.

[0020] In another embodiment, a wireless charging unit is described. The wireless charging unit includes a coil assembly comprising a primary coil for producing a magnetic field for coupling with a secondary coil of a wireless power transfer appliance. The magnetic field is produced by flow of a current generated by a power source. The wireless charging unit further comprises an auxiliary coil positioned around a periphery of the primary coil. A direction of an auxiliary current flowing through the auxiliary coil is opposite to a direction of the inductive current flowing through the primary coil. An auxiliary magnetic field produced from the auxiliary current reduces sideways spreading of the magnetic field.

[0021] In another embodiment, a wireless charging unit is described. The wireless charging unit includes a coil assembly comprising a primary coil with an outermost turn of the primary coil positioned in a direction opposite to inner turns of the primary coil. The primary coil produces a magnetic field for coupling with a secondary coil of a wireless power transfer appliance. The magnetic field is produced by flow of a current generated by a power source. A current flows through the outermost turn of the primary coil in an opposite direction to the current flowing through the inner turns of the primary coil. An auxiliary magnetic field produced from the current flowing through the outermost turn of the primary coil reduces sideways spreading of the magnetic field.

[0022] In an aspect, the primary coil is selected from a group consisting of Circular-type coil, D type coil, and Double-D type coil. In an aspect, the auxiliary current in the wireless charging unit is generated by a current control circuitry based on a phase angle and a frequency of the current.

[0023] In an aspect, the wireless charging unit includes a rectifier and a DC-DC converter for processing the current before providing to the primary coil.

[0024] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention, which are used to describe the principles of the present invention. The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this invention are not necessarily to the same embodiment, and they mean at least one. In the drawings:

[0025] Fig. 1 illustrates a schematic diagram of a secondary coil installed in a device, in accordance with prior art;

[0026] Fig- 2 illustrates a block diagram of a wireless charging unit, in accordance with an embodiment of the present invention;

[0027] Fig- 3 illustrates a block diagram of a primary coil current control circuitry of the wireless charging unit, in accordance with an embodiment of the present invention;

[0028] Fig. 4 illustrates a block diagram of a wireless power transfer appliance, in accordance with an embodiment of the present invention; Fig- 5 illustrates a block diagram of a secondary coil current control circuitry of the wireless power transfer appliance, in accordance with an embodiment of the present invention;

[0029] Fig. 6 illustrates a block diagram of a wireless power transfer appliance, in accordance with an embodiment of the present invention;

[0030] Fig. 7 illustrates an exploded view of a packaging of the coil assembly of the wireless power transfer appliance, in accordance of an embodiment of the present invention;

[0031] Figs. 8A and 8B illustrate leakage magnetic flux distributions of wireless charging system without auxiliary coil, in accordance with an embodiment of the present invention;

[0032] Figs. 8C and 8D illustrate leakage magnetic flux distributions for wireless charging system having auxiliary coil, in accordance with an embodiment of the present invention

[0033] Figs. 9A through 9C illustrate leakage magnetic flux distributions for a fully aligned condition of a primary coil and a secondary coil, in accordance with an embodiment of the present invention;

[0034] Fig. 10A illustrates leakage magnetic flux distributions of a wireless charging system without an auxiliary coil for a partially aligned condition, in accordance with an embodiment of the present invention; and Fig. 10B illustrates leakage magnetic flux distributions of a wireless charging system having an auxiliary coil for the partially aligned condition, in accordance with an embodiment of the present invention.

[0035] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0036] The terms “or” and “and / or” as used herein are to be interpreted as inclusive or meaning any one or any combination. Therefore, “A, B or C” or “A, B and / or C” mean “any of the following: A; B; C; A and B; A and C; B and C; A, B and C.” An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.

[0037] Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words “comprising”, “having”, “containing”, and “including” and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. The present invention provides a wireless power charging assembly and a wireless charging unit capable of reducing sideways spreading of a magnetic field.

[0038] Fig. 2 illustrates a block diagram of a wireless charging unit 200, in accordance with an embodiment of the present invention. The wireless charging unit 200 may comprise a coil assembly 202 and a primary coil current control circuitry 204. The coil assembly 202 may obtain an electric current 206 from the primary coil current control circuitry 204 through a capacitor 208. The primary coil current control circuitry 204 has been explained in detail successively with respect to Fig. 3.

[0039] The coil assembly 202 may comprise a primary coil 210. When the electric current 206 passes through the primary coil 210, a magnetic field 212 may be generated in a direction perpendicular to a plane of the primary coil 210.

[0040] The magnetic field 212 may spread in lateral direction of the primary coil 210 i.e. sideways spreading of the magnetic field 212. The present invention proposes utilization of an auxiliary coil 214 for reduction of the sideways spreading of the magnetic field 212. For reducing the sideways spreading, the auxiliary coil 214 may be positioned around a periphery of the primary coil 210 and an auxiliary current 216 may be provided to the auxiliary coil 214. Flow of the auxiliary current 216 into the auxiliary coil 214 may produce an auxiliary magnetic field in a direction opposite to the magnetic field 212. The auxiliary magnetic field may result in reduction of the sideways spreading of the magnetic field 212.

[0041] Fig. 3 illustrates a block diagram of the primary coil current control circuitry 204, in accordance with an embodiment of the present invention. The primary coil current control circuitry 204 may comprise a rectifier 302 for receiving Alternating Current (AC) received from a power source, such as a power grid and converting the AC to Direct Current (DC). The primary coil current control circuitry 204 may further comprise a DC / DC converter 304 for stepping down the DC at a required power level. The primary coil current control circuitry 204 may further comprise a High Frequency (HF) inverter 306 for generating the electric current 206 of a high frequency. The electric current 206 may be provided to the primary coil 210.

[0042] The primary coil current control circuitry 204 may further comprise a current injector 308 for generating the auxiliary current 216. The auxiliary current 216 may be generated based on a frequency and a phase angle of the electric current 206. In an implementation, the current injector 308 may receive information related to the frequency and the phase angle of the electric current 206 from the HF inverter 306 and may generate the auxiliary current 218 having same frequency and phase angle. The auxiliary current 216 may be provided to the auxiliary coil 214 for reduction of sideways spreading of the magnetic field 212.

[0043] Fig. 4 illustrates a block diagram of a wireless power charging assembly 400, in accordance with an embodiment of the present invention. The wireless power charging assembly 400 may comprise a coil assembly 402 comprising a secondary coil 410. When the secondary coil 410 is placed in proximity to the primary coil 210, a magnetic field 412 may be coupled with the secondary coil 410. As a result, an induction current 406 may flow into the secondary coil 410. The induction current 406 may be provided to a secondary coil current control circuitry 404 through a capacitor 408. The secondary coil current control circuitry 404 may process the induction current 406 before storing it to a power storage unit 418, such as a battery.

[0044] The magnetic field 412 may spread in a lateral direction of the secondary coil 410, i.e. sideways spreading of the magnetic field 412. The present invention proposes utilization of an auxiliary coil 414 for reduction of the sideways spreading of the magnetic field 412. For reducing the sideways spreading, the auxiliary coil 414 may be positioned around a periphery of the secondary coil 410 and an auxiliary current 416 may be provided to the auxiliary coil 414. Flow of the auxiliary current 416 into the auxiliary coil 414 may produce an auxiliary magnetic field in a direction opposite to the magnetic field 412. The auxiliary magnetic field may result in reduction of the sideways spreading of the magnetic field 412.

[0045] Fig. 5 illustrates a block diagram of the secondary coil current control circuitry 404, in accordance with an embodiment of the present invention. The secondary coil current control circuitry 404 may comprise a monitoring unit 502 for monitoring a frequency and a phase angle of the induction current 406. The secondary coil current control circuitry 404 may further comprise a rectifier 504 for converting the induction current 406 to a DC. The secondary coil current control circuitry 404 may further comprise a DC / DC converter 506 for stepping down the DC at a required power level. After being processed by the DC / DC converter 506, the DC may be provided to the power storage unit 418 for storage.

[0046] The secondary coil current control circuitry 404 may further comprise a current injector 508 for generating the auxiliary current 416. The auxiliary current 218 may be generated based on the frequency and the phase angle of the induction current 406. In an implementation, the current injector 508 may receive information related to the frequency and the phase angle of the induction current 406 from the monitoring unit 502 and may generate the auxiliary current 416 having same frequency and phase angle. The auxiliary current 416 may be provided to the auxiliary coil 414 for reduction of the sideways spreading of the magnetic field 412.

[0047] Fig. 6 illustrates a block diagram of a wireless power charging assembly 600, in accordance with an alternate embodiment of the present invention. The wireless power charging assembly 600 may comprise a coil assembly 602 including a secondary coil 604. A magnetic field 606 generated by a primary coil of a wireless charging unit may couple with the secondary coil 604. Coupling of the magnetic field results into flow of an inductive current 608 into the secondary coil 604. The induction current 608 may be provided to a processing circuitry 610 through a capacitor 612. The processing circuitry 610 may process the induction current 608 before storing it to a power storage unit 614.

[0048] The magnetic field 606 may spread in a lateral direction of the secondary coil 604 i.e. sideways spreading of the magnetic field 606. In the alternate embodiment, an outermost turn 616 of the secondary coil 604 may be positioned in a direction opposite to inner turns of the secondary coil 604. The inductive current 608 flows through the outermost turn 616 in an opposite direction to the inductive current 608 flowing through the inner turns. As a result, an auxiliary magnetic field may be produced in a direction opposite to the magnetic field 606. Thus, the sideways spreading of the magnetic field 606 may be reduced.

[0049] Similarly, a wireless charging unit may be provided according to the alternate embodiment. The wireless charging unit may comprise a primary coil for producing a magnetic field. Similar to the secondary coil, an outermost turn of the primary coil may be positioned in a direction opposite to inner turns of the primary coil for reducing sideways spreading of the magnetic field.

[0050] Fig. 7 illustrates an exploded view of a packaging of the coil assembly 402 of the wireless power charging assembly 400, in accordance of an embodiment of the present invention. A shielding layer 702 may be provided at a top of the coil assembly 402. In one implementation, the shielding layer 702 may be made of Aluminium. A magnetic layer 704 may be mounted below the shielding layer 702 for reducing spreading of the magnetic field over the coil assembly 402. The material layer 704 may be made of ferromagnetic, ferrite, or other magnetic materials.

[0051] A spacer 706 may be disposed between the magnetic layer 704 and the secondary coil 410. The spacer 706 may be made of rubber, plastic, or other similar materials. Further, a support member 708 may be disposed at the bottom for supporting the secondary coil 410.

[0052] For analysing effect of introducing an auxiliary coil in a wireless charging system, leakage magnetic flux distributions of a wireless charging system having the auxiliary coil and a wireless charging without auxiliary coil were plotted.

[0053] Figs. 8A and 8B illustrate leakage magnetic field distributions of a wireless charging system without auxiliary coil, in accordance with an embodiment of the present invention. As evident from Fig. 8B, a magnitude of the leakage magnetic field measured at a distance of 800 mm from a coil in the wireless charging system without the auxiliary coil was found to be approximately 112 pT. Figs. 8C and 8D illustrate leakage magnetic flux distributions for wireless charging system having auxiliary coil, in accordance with an embodiment of the present invention. As depicted from Fig. 8D, a magnitude of the leakage magnetic field measured at the distance of 800 mm from the coil in the wireless charging system with the auxiliary coil was found to be approximately 74 pT. It was observed that the leakage magnetic field gets reduced by 34% due to usage of the auxiliary coil with the coil.

[0054] Figs. 9A through 9C illustrate leakage magnetic flux distributions for a fully aligned condition of a primary coil and a secondary coil, in accordance with an embodiment of the present invention. In fully aligned condition, the primary coil was completely aligned with the secondary coil. The leakage magnetic flux distributions were plotted for different configurations. In first configuration, auxiliary coil was not present in periphery of both of the primary coil and the secondary coil. Fig. 9A illustrates leakage magnetic flux distribution for the first configuration. In second configuration, an auxiliary coil was not present at the periphery of the primary coil and an auxiliary coil was present at the periphery of the secondary coil. Fig. 9B illustrates leakage magnetic flux distribution for the second configuration. In third configuration, an auxiliary coil was present at the periphery of the primary coil and an auxiliary coil was present at the periphery of the secondary coil. Fig. 9C illustrates leakage magnetic flux distribution for the third configuration.

[0055] Magnetic fields for each configuration were measured at a distance of 800mm from a coil and results of the measurement were included in Table 1 , as provided below.

[0056] Table 1

[0057] It was observed that the leakage magnetic field is reduced by 28% due to usage of the auxiliary coil at the periphery of the secondary coil and reduced by 36% due to usage of the auxiliary coil at the periphery of both the primary coil and the secondary coil. Fig. 10A illustrates leakage magnetic flux distributions of a wireless charging system without an auxiliary coil for a partially aligned condition, in accordance with an embodiment of the present invention. In partially aligned condition, the primary coil is half aligned with the secondary coil. Fig. 10B illustrates leakage magnetic flux distributions of a wireless charging system having an auxiliary coil for the partially aligned condition, in accordance with an embodiment of the present invention. Magnetic fields for the wireless charging system without the auxiliary coil and the wireless charging system having the auxiliary coil were measured at a distance of 800mm from a coil and results of the measurement were included in Table 2, as provided below.

[0058] Table 2

[0059] It is evident from Table 1 and Table 2 that the leakage magnetic field reduces with the presence of an auxiliary coil around a secondary coil and / or the primary coil without undergoing change in a coil inductance of the primary coil and the secondary coil and a coupling coefficient. In an implementation, the wireless power charging assembly may be an electric vehicle and the wireless charging unit may be a charging station for the electric vehicle.

[0060] The present invention provides a wireless power charging assembly and a wireless charging unit capable of reducing sideways spreading of a magnetic field. The wireless power charging assembly and the wireless charging unit do not utilize additional bulky components for reducing of the sideways spreading of the magnetic field. Due to reducing of the sideways spreading of the magnetic field, a power transfer efficiency and a power transfer capacity is maximized.

[0061] It would be appreciated by a person skilled in the art that the wireless power charging assembly and the wireless charging unit of the present invention is not only restricted to automobiles or machines but also applicable to any power consuming and storage devices such as laptops, smartphones and the like.

[0062] In view of the present disclosure, which describes the present invention, all changes, modifications and variations within the meaning and range of equivalency are considered within the scope and spirit of the invention. It is to be understood that the aspects and embodiment of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiment may be combined together to form a further embodiment of the disclosure.

Claims

Claims1. A wireless power charging assembly (400) comprising: a coil assembly (402) comprising: a secondary coil (410) for coupling with a magnetic field (412) generated by a primary coil (210) of a wireless charging unit (200), wherein the coupling of the magnetic field (412) results into flow of an inductive current (406) into the secondary coil (410); and an auxiliary coil (414) positioned around a periphery of the secondary coil (410), wherein a direction of an auxiliary current (416) flowing through the auxiliary coil (414) is opposite to a direction of the inductive current flowing through the secondary coil (410), and an auxiliary magnetic field produced from the auxiliary current reduces sideways spreading of the magnetic field (412); and a power storage unit (418) for storing the inductive current.

2. The wireless power charging assembly (400) as claimed in claim 1, wherein the coil assembly (402) comprises at least one of a shielding layer (702) and a magnetic layer (704) positioned above the coil assembly (402) for reducing spreading of the magnetic field over the coil assembly.

3. The wireless power charging assembly (400) as claimed in claim 1, wherein the auxiliary current is generated by a secondary coil current control circuitry (404) based on a phase angle and a frequency of the inductive current (406).

4. The wireless power charging assembly (400) as claimed in claim 1, wherein the wireless power charging assembly (400) is an electric vehicle.

5. The wireless power charging assembly (400) as claimed in claim 1, wherein the secondary coil (410) is selected from a group consisting of Circular-type coil, D type coil, and Double-D type coil.

6. The wireless power charging assembly (400) as claimed in claim 1, further comprises a rectifier (504) and a DC-DC converter (506) for processing the inductive current before storage into the power storage unit (418).

7. A wireless power charging assembly (600) comprising: a coil assembly (602) comprising: a secondary coil (604) for coupling with a magnetic field (606) generated by a primary coil (210) of a wireless charging unit (200), wherein the coupling of the magnetic field (606) results into flow of an inductive current (608) into the secondary coil (604), wherein an outermost turn (616) of the secondary coil (604) is positioned in a direction opposite to inner turns of the secondary coil (604), wherein the inductive current (608) flows through the outermost turn (616) in an opposite direction to the inductive current (608) flowing through the inner turns, the inductive current flowing through the outermost turn produces an auxiliary magnetic field for reducing sideways spreading of the magnetic field (606); and a power storage unit (614) for storing the inductive current.

8. The wireless power charging assembly (600) as claimed in claim 7, wherein the secondary coil (604) is selected from a group consisting of Circular-type coil, D type coil, and Double-D type coil.

9. The wireless power charging assembly (600) as claimed in claim 7, further comprises a rectifier and a DC-DC converter for processing the inductive current before storage into the power storage unit (614).

10. A wireless charging unit (200) comprising: a coil assembly (202) comprising: a primary coil (210) for producing a magnetic field (212) for coupling with a secondary coil of a wireless power transfer appliance, wherein the magnetic field is produced by flow of a current generated by a power source; and an auxiliary coil (214) positioned around a periphery of the primary coil (210), wherein a direction of an auxiliary current (216) flowing through the auxiliary coil (214) is opposite to a direction of the inductive current flowing through the primary coil, and an auxiliary magnetic field produced from the auxiliary current reduces sideways spreading of the magnetic field (212).

11. The wireless charging unit (200) as claimed in claim 10, wherein the primary coil (210) is selected from a group consisting of Circular-type coil, D type coil, and Double-D type coil.

12. The wireless charging unit (200) as claimed in claim 10, wherein the auxiliary current (216) is generated by a primary coil current control circuitry (204) based on a phase angle and a frequency of the current.

13. A wireless charging unit (200) comprising: a coil assembly (202) comprising:a primary coil (210) for producing a magnetic field for coupling with a secondary coil of a wireless power transfer appliance, wherein the magnetic field is produced by flow of a current generated by a power source, wherein an outermost turn of the primary coil is positioned in a direction opposite to inner turns of the primary coil, wherein the current flows through the outermost turn in an opposite direction to the current flowing through the inner turns, the current flowing through the outermost turn produces an auxiliary magnetic field for reducing sideways spreading of the magnetic field.

14. The wireless charging unit (200) as claimed in claim 13, wherein the primary coil is selected from a group consisting of Circular-type coil, D type coil, and Double-D type coil.

15. The wireless charging unit (200) as claimed in claim 13, further comprises a rectifier (302) and a DC-DC converter (304) for processing the current before providing to the primary coil.

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