Patent Publication Number: US-2018041065-A1

Title: System and method for charging receiver devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to India patent application entitled “SYSTEM AND METHOD FOR CHARGING RECEIVER DEVICES” filed concurrently herewith under attorney docket number 314788-1. 
     BACKGROUND 
     Embodiments of the present invention relate generally to wireless power transfer systems and more particularly to a system and method for charging receiver devices. 
     In general, power transfer systems are widely used to transfer power from a power source to one or more receiver devices, such as for example, mobile devices, biomedical devices, and portable consumer devices. Typically, the power transfer systems may be contact based power transfer systems or wireless power transfer systems. In certain applications, where instantaneous or continuous power transfer is required but interconnecting wires are inconvenient, the wireless power transfer systems are desirable. 
     In the wireless power transfer systems, a charging device is used to convert an input power to a transferrable power which is further transmitted to charge one or batteries in the receiver devices. However, these receiver devices are compatible with one of the wireless frequency standards. For example, there are currently three competing frequency standards: the Alliance for Wireless Power (A4WP), the Wireless Power Consortium (WPC), and the Power Matters Alliance (PMA). The WPC standard (Qi) is defined in a frequency range of 100 kHz to 200 kHz. The PMA standard is defined in a frequency range of 200 kHz to 400 kHz. Further, the A4WP standard is defined at a frequency of about 7 MHz. A conventional charging device cannot be used to charge the receiver devices operating at different frequency standards. 
     Thus, there is a need for an improved system and method for charging receiver devices operating at different frequency standards. 
     BRIEF DESCRIPTION 
     In accordance with one embodiment of the present invention, a charging pad is disclosed. The charging pad includes at least one first frequency coil operable at a first frequency band. Further, the charging pad includes at least one second frequency coil operable at a second frequency band different from the first frequency band. Also, the charging pad includes an excitation unit operationally coupled to the at least one first frequency coil and the at least one second frequency coil and configured to drive the at least one first frequency coil and the at least one second frequency coil. 
     In accordance with another embodiment of the present invention, a wireless charging device is disclosed. The wireless charging device includes a charging pad including an excitation unit configured to convert a DC voltage of an input power to at least one of a first AC voltage having a frequency from a first frequency band and a second AC voltage having a frequency from a second frequency band. Also, the charging pad includes a transmitting unit operatively coupled to the excitation unit, wherein the transmitting unit comprises at least one first frequency coil configured to transmit the first AC voltage having the frequency from the first frequency band. Further, the transmitting unit includes at least one second frequency coil configured to transmit the second AC voltage having the frequency from the second frequency band. In addition, the wireless charging device includes a control unit operatively coupled to the excitation unit and configured to feed at least one of a first frequency control signal and a second frequency control signal to the excitation unit. 
     In accordance with another embodiment of the present invention, a method for charging one or more receiver devices is disclosed. The method includes receiving, by an excitation unit, at least one of a first frequency control signal and a second frequency control signal. Further, the method includes converting, by the excitation unit, a DC voltage of an input power to a first AC voltage having a frequency from a first frequency band if the first frequency control signal is received. Also, the method includes converting, by the excitation unit, the DC voltage of the input power to a second AC voltage having a frequency from a second frequency band if the second frequency control signal is received. Furthermore, the method includes transmitting, by at least one first frequency coil, the first AC voltage having the frequency from the first frequency band, to a first receiver device. In addition, the method includes transmitting, by at least one second frequency coil, the second AC voltage having the frequency from the second frequency band, to a second receiver device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a block diagram representation of a wireless power transfer system; 
         FIG. 2  is a schematic representation of a wireless power transfer system; 
         FIG. 3  is a schematic representation of a wireless power transfer system; 
         FIG. 4  is a diagrammatic representation of a charging pad having first frequency and second frequency coils; 
         FIG. 5  is a diagrammatic representation of a charging pad having first frequency and second frequency coils; 
         FIG. 6  is a diagrammatic representation of a charging pad having first frequency and second frequency coils inductively coupled to receiver devices; 
         FIG. 7  is a flow chart illustrating a method for charging a plurality of receiver devices; and 
         FIG. 8  is a graphical representation of different control signals. 
     
    
    
     DETAILED DESCRIPTION 
     As will be described in detail hereinafter, various embodiments of a system and method for charging one or more wireless receiver devices are disclosed. In particular, the system and method disclosed herein employ an excitation unit that is capable of driving first frequency and second frequency coils enabling charging of the wireless receiver devices designed based on different frequency standards. 
     Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this specification belongs. The terms “first”, “second”, and the like, as used herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. Also, the terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “or” is meant to be inclusive and mean one, some, or all of the listed items. The use of “including,” “comprising” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. Furthermore, terms “circuit” and “circuitry” and “controlling unit” may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together to provide the described function. In addition, the term operationally coupled as used herein includes wired coupling, wireless coupling, electrical coupling, magnetic coupling, radio communication, software based communication, or combinations thereof. 
       FIG. 1  is a diagrammatical representation of a wireless power transfer system  100  in accordance with an embodiment of the present invention. The wireless power transfer system  100  is used to transmit an electrical power from a power source  102  to one or more receiver devices such as mobile devices, biomedical devices, and portable consumer devices. Particularly, in an automobile industry, a vehicle includes one or more charging pads that are used for supplying electrical power from the power source  102  to the mobile devices like cell phones, laptops, heating ventilation and air-conditioning (HVAC) units etc. In one embodiment, the wireless power transfer system  100  may also be referred to as a contactless power transfer system. 
     In the illustrated embodiment, the wireless power transfer system  100  includes a wireless charging device  104  that is wirelessly coupled to a first receiver device  106  and a second receiver device  108 . It may be noted that the wireless power transfer system  100  is not limited to the first receiver device  106  and the second receiver device  108  and may include any number of receiver devices. 
     The first and second receiver devices  106 ,  108  may be compatible with one of the wireless frequency standards. For example, one of the receiver devices may be compatible with Alliance for Wireless Power (A4WP) standard that is defined at a frequency of about 7 MHz. Similarly, another receiver device may be compatible with Wireless Power Consortium (WPC) standard (Qi) that is defined in a frequency range of 100 kHz to 200 kHz. One of the receiver devices may be compatible with Power Matters Alliance (PMA) standard that is defined in a frequency range of 200 kHz to 400 kHz. One of the other receiver devices may be compatible with Air Fuel Alliance standard that is defined at a frequency of about 6.7 MHz. For ease of understanding of the embodiment of the invention, the first receiver device  106  is considered to be compatible with a first frequency standard such as Air Fuel Alliance standard defined at a frequency of about 6.7 MHz. The first frequency standard may also be referred to as a high frequency standard. Similarly, the second receiver device  108  is considered to be compatible with a second frequency standard such as WPC standard defined in a frequency range of 100 kHz to 200 kHz. The second frequency standard may also be referred to as a low frequency standard. It may be noted that the receiver devices  106 ,  108  may be of any frequency standard and are not limited to the frequency standards mentioned herein. Further, any number of receiver devices that are compatible with any number of frequency standards may be envisioned for charging. 
     In conventional power transfer systems that are compatible with different frequency standards for each of the receiver devices/gadgets, a charging device may not supply power to each of the receiver devices at their corresponding frequency standards. In one of the conventional power transfer systems, separate charging devices having a dedicated converter and dedicated frequency coils for each frequency standard, are employed to supply power to the corresponding receiver device. However, using separate charging devices for each frequency standard may substantially increase set-up cost and maintenance cost of the conventional power transfer systems. 
     To overcome the above problems/drawbacks associated with conventional systems, the exemplary power transfer system  100  includes the wireless charging device  104  that is configured to charge the first and second receiver devices  106 ,  108  of any frequency standard. The wireless charging device  104  includes a charging pad  130  and a control unit  112  that are used for supplying electrical power from the power source  102  to the first and second receiver devices  106 ,  108 . The charging pad  130  may be referred to as an electrical enclosure upon which the one or more receiver devices  106 ,  108  may be placed for charging one or more batteries in the corresponding receiver devices  106 ,  108 . In one embodiment, the control unit  112  may be positioned within the charging pad  130 . In another embodiment, the control unit  112  may be positioned external to the charging pad  130 . Further, the charging pad  130  includes an excitation unit  110  and a transmitting unit  114 . In one embodiment, the excitation unit  110  may include one or more converters (not shown) that are used for providing electrical power at a desired frequency to the first and second receiver devices  106 ,  108 . 
     The excitation unit  110  is electrically coupled to the power source  102  and the control unit  112 . The power source  102  is configured to supply an input power  120  having a DC voltage to the excitation unit  110 . In some embodiments, the input power  120  may be in a range from about 1 W to 200 W. In one embodiment, the power source  102  may be a part of the wireless charging device  104 . In another embodiment, the power source  102  may be positioned external to the wireless charging device  104 . 
     Furthermore, the excitation unit  110  is configured to receive the input power  120  having the DC voltage from the power source  102 . Further, the excitation unit  110  is configured to convert the DC voltage of the input power  120  to a first AC voltage having a frequency in a first frequency band and/or a second AC voltage having a frequency in a second frequency band. It may be noted that the first frequency band may be referred to as a range of frequencies from about 4 MHz to about 9 MHz. In a similar manner, the second frequency band may be referred to as a range of frequencies from about 100 kHz to about 1 MHz. Also, it may be noted that the terms “frequency in a first frequency band” and “first frequency” may be used interchangeably in the below specification. Similarly, the terms “frequency in a second frequency band” and “second frequency” may be used interchangeably in the below specification. 
     Additionally, the excitation unit  110  is configured to receive a first frequency control signal  122  and/or a second frequency control signal  124  from the control unit  112 . If the first frequency control signal  122  is received from the control unit  112 , the excitation unit  110  is configured to convert the DC voltage of the input power  120  to the first AC voltage having the first frequency. In a similar manner, if the second frequency control signal  124  is received from the control unit  112 , the excitation unit  110  is configured to convert the DC voltage of the input power  120  to the second AC voltage having the second frequency. In one example, the first and second AC voltages may be in a range from about 5 Volts to about 50 Volts. The details pertaining to converting the DC voltage to the first AC voltage or the second AC voltage are explained in greater detail below with reference to  FIGS. 2 and 3 . 
     In one embodiment, the control unit  112  is configured to alternately send the first frequency control signal  122  and the second frequency control signal  124  at regular time intervals to the excitation unit  110 . In one specific embodiment, the control unit  112  is configured to send a modulation signal including the first frequency control signal  122  and the second frequency control signal  124 . In another embodiment, the control unit  112  is configured to concurrently send the first frequency control signal  122  and the second frequency control signal  124  to different sets of switches in the excitation unit  110 . 
     The excitation unit  110  is further configured to transmit the input power having the first AC voltage or the second AC voltage to the transmitting unit  114 . The transmitting unit  114  includes one or more first frequency coils  116  and one or more second frequency coils  118  that are electrically coupled to the excitation unit  110 . In one embodiment, the one or more first frequency coils  116  and the one or more second frequency coils  118  may be stacked one above the other. In another embodiment, the one of more first frequency coils  116  and the one or more second frequency coils  118  may be positioned side-by-side on a same plane or on a different plane. Further, the one or more first frequency coils  116  are inductively coupled to a receiver coil (not shown in  FIG. 1 ) in the first receiver device  106 . One or more second frequency coils  118  are inductively coupled to a receiver coil (not shown in  FIG. 1 ) in the second receiver device  108 . Further, the first frequency and second frequency coils  116 ,  118  are used to wirelessly transmit the input power having the first AC voltage or the second AC voltage to the first and second receiver devices  106 ,  108 . Particularly, if the excitation unit  110  converts the DC voltage to the first AC voltage having the first frequency, the first frequency coils  116  are excited to transmit the first AC voltage having the first frequency to the first receiver device  106 . In a similar manner, if the excitation unit  110  converts the DC voltage to the second AC voltage having the second frequency, the second frequency coils  118  are excited to transmit the second AC voltage having the second frequency to the second receiver device  108 . 
     Further, the first and second receiver devices  106 ,  108  are configured to use the first AC voltage having the first frequency or the second AC voltage having the second frequency for charging one or more batteries  126 ,  128  included in the first and second receiver devices  106 ,  108 . In one embodiment, the first and second receiver devices  106 ,  108  such as mobile phones and laptops may be inductively coupled to the first frequency coils  116  and/or the second frequency coils  118  based on the frequency standards for which the first and second receiver devices  106 ,  108  are designed. For example, if the first receiver device  106  is designed to the first frequency standard such as Air Fuel Alliance standard, the first receiver device  106  receives the first AC voltage having the first frequency from the first frequency coils  116 . Similarly, if the second receiver device  108  is designed to a second frequency standard such as WPC standard, the second receiver device  108  receives the second AC voltage having the second frequency from the second frequency coils  118 . In one example, the first and second receiver devices  106 ,  108  may be placed on the charging pad  130  for charging the batteries  126 ,  128  in the first and second receiver devices  106 ,  108 . 
     Thus, by employing the exemplary wireless power transfer system  100 , the single charging device  104  is configured to transfer power to the first and second receiver devices  106 ,  108  that are compatible with one or more frequency standards. 
     Referring to  FIG. 2 , a detailed schematic representation of the wireless power transfer system  100  in accordance with an embodiment of the present invention is depicted. The wireless power transfer system  100  is used to transmit the input power  120  from the power source  102  to the first and second receiver devices  106 ,  108 . 
     The wireless power transfer system  100  includes the wireless charging device  104 , the first receiver device  106 , and the second receiver device  108 . The wireless charging device  104  is wirelessly coupled to the first receiver device  106  and the second receiver device  108 . The first receiver device  106  and the second receiver device  108  may be compatible with one of the wireless frequency standards. 
     Further, the wireless charging device  104  includes the charging pad  130  and the control unit  112  that are used for supplying electrical power from the power source  102  to the first and second receiver devices  106 ,  108 . The charging pad  130  includes the excitation unit  110  and the transmitting unit  114 . It may be noted that the wireless power transfer system  100  may include other components and is not be limited to the components shown in  FIG. 2 . 
     In the illustrated embodiment, the excitation unit  110  includes only a single converter  216  that is electrically coupled to the power source  102  and configured to receive the input power  120  having the DC voltage from the power source  102 . The single converter  216  is defined as an electrically coupled device that has single DC or line frequency input. It may be noted that in other embodiments, the excitation unit  110  may include any number of converters and is not limited to a single converter. Further, the single converter  216  includes a first switch  208 , a second switch  210 , a plurality of diodes  212 , and a plurality of capacitors  214  that are arranged to form a half bridge inverter circuit. The first and second switches  208 ,  210 , the diodes  212 , and the capacitors  214  are electrically coupled between input terminals  217  and output terminals  218  of the excitation unit  110 . In one embodiment, the switches  208 ,  210  may include electronic switches such as MOSFETs or IGBTs. It may be noted that the switches  208 ,  210  may include other semiconductor switches and is not limited to MOSFETs and IGBTs. Further, the first switch  208  and the second switch  210  are operated complimentary to each other. For example, if the first switch  208  is activated for a time duration T on , the second switch  210  is deactivated for this time duration T on . Similarly, if the second switch  210  is activated for the time duration T off , the first switch  208  is deactivated for this time duration T off . 
     Furthermore, the control unit  112  is configured to alternately and repeatedly send a first frequency control signal  122  and a second frequency control signal  124  to the first switch  208  and the second switch  210 . In one embodiment, the control unit  112  may generate the first and second frequency control signals  122 ,  124  based on change in characteristics of the first and second frequency coils  116 ,  118 . For example, if the first receiver device  106  and/or the second receiver device  108  are placed on the charging pad  130 , the characteristics such as electrical current in the first and/or second frequency coils  116 ,  118  may change. Further, the change in the characteristics of the first and second frequency coils  116 ,  118  may be used by the control unit  112  to generate the first and second frequency control signals  122 ,  124 . 
     Furthermore, the control unit  112  sends the first frequency control signal  122  to the first switch  208  for a first time period. Concurrently, the control unit  112  sends a signal that is complimentary to the first frequency control signal  122  to the second switch  210  for the first time period. In one example, the first frequency control signal  122  may have a high switching pulse frequency of about 6.7 MHz. During the first time period, the first switch  208  and the second switch  210  are operated complimentary to each other to convert the DC voltage of the input power  120  to the first AC voltage having a first frequency. In one embodiment, the first frequency may be in a range from about 4 MHz to about 9 MHz. In one specific embodiment, the first switch  208  and the second switch  210  is configured to modulate the DC voltage of the input power  120  based on the first frequency control signal  122  to generate the first AC voltage having the first frequency at the output terminals  218  of the excitation unit  110 . 
     In a similar manner, the control unit  112  sends the second frequency control signal  124  to the first switch  208  for a second time period. Concurrently, the control unit  112  sends a signal that is complimentary to the second frequency control signal to the second switch  210  for the second time period. In one embodiment, the second frequency control signal  124  may have a low switching pulse frequency of about 100 kHz. During the second time period, the first switch  208  and the second switch  210  are operated complimentary to each other to convert the DC voltage of the input power  120  to the second AC voltage having a second frequency. In one embodiment, the second frequency may be in a range from about 100 kHz to about 1 MHz. In one embodiment, the first switch  208  and the second switch  210  are configured to modulate the DC voltage of the input power  120  based on the second frequency control signal  124  to provide the second AC voltage having the second frequency at the output terminals  218  of the excitation unit  110 . 
     Further, the input power having the first AC voltage or the second AC voltage is transmitted from the excitation unit  110  to the transmitting unit  114 . The transmitting unit  114  includes the first frequency coils  116  and the second frequency coils  118 . In the illustrated embodiment, only one first frequency coil  116  and one second frequency coil  118  are shown. The first frequency coils  116  are electrically coupled to the excitation unit  110  and inductively coupled to a corresponding receiver coil  224  in the first receiver device  106 . The first frequency coils  116  are used to transfer the power having the first AC voltage to the receiver coil  224  in the first receiver device  106 . Further, the power having the first AC voltage is then transmitted from the receiver coil  224  to an electric load  228  such as a battery in the first receiver device  106  via a power conditioner  232 . 
     In a similar manner, the second frequency coils  118  are electrically coupled to the excitation unit  110  and inductively coupled to a corresponding receiver coil  226  in the second receiver device  108 . The second frequency coils  118  are used to transfer the power having the second AC voltage to the receiver coil  226  in the second receiver device  108 . Further, the power having the second AC voltage is then transmitted from the receiver coil  226  to an electric load  230  such as a battery in the second receiver device  108  via a power conditioner  234 . 
     During normal operation of the wireless power transfer system  100 , the control unit  112  is configured to periodically and/or alternately send the first frequency control signal  122  and the second frequency control signal  124  to the excitation unit  110 . Particularly, the control unit  112  sends the first frequency control signal  122  to the first switch  208  and a signal that is complimentary to the first frequency control signal  122  to the second switch  210  for the first time period. Further, during the first time period, the first switch  208  and the second switch  210  toggles between ON state and OFF state based on switching pulse of the first frequency control signal  122  to convert the DC voltage of the input power to the corresponding first AC voltage having the first frequency. It may be noted that the ON state may be referred to as a state where the switches  208 ,  210  are activated. The OFF state may be referred to as a state where the switches  208 ,  210  are deactivated. Furthermore, the first AC voltage having the first frequency is provided to the first frequency coil  116  to transmit the power having the first AC voltage to the receiver coil  224  in the first receiver device  106 . Thereafter, the receiver coil  224  transmits the first AC voltage having the first frequency to the load  228  via the power conditioner  232 . 
     Furthermore, at the end of the first time period, the control unit  112  sends the second frequency control signal  122  to the first switch  208  and a signal that is complimentary to the first frequency control signal  122  to the second switch  210  for the second time period. Further, during the second time period, the first switch  208  and the second switch  210  toggles between ON state and OFF state based on switching pulse of the second frequency control signal  124  to convert the DC voltage of the input power to the corresponding second AC voltage having the second frequency. The second AC voltage having the second frequency is provided the second frequency coil  118  to transmit the power having the second AC voltage to the receiver coil  226  in the second receiver device  108 . Thereafter, the receiver coil  226  transmits the second AC voltage having the second frequency to the load  230  via the power conditioner  234 . In one embodiment, the control unit  112  may alternately send the first frequency control signal  122  and the second frequency control signal  124  to the excitation unit  110  to provide the first AC voltage having the first frequency and the second AC voltage having the second frequency to the corresponding receiver devices  106 ,  108 . 
     In the exemplary power transfer system  100 , the excitation unit  110  drives the first frequency coils  116  and the second frequency coils  118  to transfer the power from the power source  102  to the receiver devices  106 ,  108  of different frequency standards. 
     Referring to  FIG. 3 , a schematic representation of a wireless power transfer system  300  in accordance with another embodiment of the present invention is depicted. The wireless power transfer system  300  of  FIG. 3  is similar to the wireless power transfer system  100  of  FIG. 2  except that the excitation unit  302  includes a single converter  304  having a full bridge inverter circuit. Particularly, the single converter  304  includes a first leg of switches  306  and a second leg of switches  308 . The first leg of switches  306  is configured to receive a first frequency control signal  122  from the control unit  112  and the second leg of switches  308  is configured to receive a second frequency control signal  124  from the control unit  112 . In this embodiment, the first frequency control signal  122  is a continuous signal having a high switching pulse frequency of about 6.7 MHz and the second frequency control signal  124  is a continuous signal having a low switching pulse frequency of about 200 kHz. 
     The first leg of switches  306  is activated if the first frequency control signal  122  is received. Further, the first leg of switches  306  is configured to convert a DC voltage of the input power  120  to a first AC voltage having a first frequency. In one embodiment, the first frequency may be in a range from about 4 MHz to about 9 MHz. The first AC voltage having the first frequency is transmitted to the first frequency coil  116  which in turn inductively transfers the power having the first AC voltage to the first receiver device  106 . 
     In a similar manner, the second leg of switches  308  is activated if the second frequency control signal  124  is received. Further, the second leg of switches  308  is configured to convert the DC voltage of the input power  120  to a second AC voltage having a second frequency. In one embodiment, the second frequency may be in a range from about 100 kHz to about 1 MHz. The second AC voltage having the second frequency is transmitted to the second frequency coil  118  which in turn inductively transfers the power having the second AC voltage to the second receiver device  108 . 
     Referring to  FIG. 4 , a schematic representation of a charging pad  402  in accordance with an exemplary embodiment is depicted. The charging pad  402  may be similar to the charging pad  130  of  FIG. 1 . Further, the charging pad  402  includes the one or more first frequency coils  116  and the one or more second frequency coils  118 . Particularly, the charging pad  402  includes a first layer  404  having the one or more first frequency coils  116  and a second layer  406  having the one or more second frequency coils  118 . The first and second layers  404 ,  406  may be referred to as electrical carrier having one or more frequency coils. The first layer  404  and the second layer  406  are positioned proximate to each other in the charging pad  402 . In one embodiment, the first layer  404  may include a plurality of first frequency coils  116  that are arranged in parallel configuration and/or serial configuration. Similarly, the second layer  406  may include a plurality of second frequency coils  118  that are arranged in parallel configuration and/or serial configuration. In one embodiment, the charging pad  402  may also include the excitation unit that is capable of independently driving the one or more first frequency coils  116  and/or the one or more second frequency coils  118 . 
     The one or more first frequency coils  116  and the one or more second frequency coils  118  are stacked one above the other within the charging pad  402 . The receiver devices are placed at a predefined location on a top surface of the charging pad  402  in such a way that the one or more first frequency coils  116  and the one or more second frequency coils  118  are disposed below the predefined location, within the charging pad  402 . The excitation unit  130  drives the one or more first frequency coils  116  and/or the one or more second frequency coils  118  based on the frequency standard of the receiver devices. 
     Referring to  FIG. 5 , a schematic representation of a charging pad  502  in accordance with another embodiment is depicted. The charging pad  502  includes a single layer  504  having the one or more first frequency coils  116  and the one or more second frequency coils  118 . Particularly, the first frequency coils  116  and the second frequency coils  118  are alternately positioned in the single layer  504  of the charging pad  502 . Specifically, the one or more first frequency coils  116  and the one or more second frequency coils  118  are embedded within the charging pad  502 . In one embodiment, the one of more first frequency coils  116  and the one or more second frequency coils  118  may be positioned side-by-side on a same plane or on a different plane. The single layer  504  may be referred to as an electrical carrier having different frequency coils. 
     Referring to  FIG. 6 , a schematic representation of the charging pad  402  in accordance with an exemplary embodiment is depicted. The charging pad  402  includes a first layer  404  having the one or more first frequency coils  116  and a second layer  406  having the one or more second frequency coils  118 . Further, the first frequency coils  116  are inductively coupled to the first receiver device  106  and the second frequency coils  118  are inductively coupled to the second receiver device  108 . In one embodiment, the charging pad  402  includes a surface upon which the first and second receiver devices  106 ,  108  are positioned. 
     Referring to  FIG. 7 , a flow chart illustrating a method for charging a plurality of receiver devices in accordance with an embodiment of the present invention is depicted. The method  700  is described with reference to  FIGS. 1 and 2 . At step  702 , the excitation unit  110  receives at least one of the first frequency control signal  122  and the second frequency control signal  124  from the control unit  112 . Particularly, the control unit  112  sends the first frequency control signal  122  and the second frequency control signal  124  alternately and repeatedly to the excitation unit  110 . The power source  102  supplies the input power  120  having the DC voltage to the excitation unit  110 . 
     Subsequently, at step  704 , the excitation unit  110  converts the DC voltage of the input power  120  to the first AC voltage having a first frequency if the first frequency control signal  122  is received. Particularly, the control unit  112  sends the first frequency control signal  122  to the first switch  208  and a signal that is complimentary to the first frequency control signal  122  to the second switch  210  for the first time period. Further, during the first time period, the first switch  208  and the second switch  210  in the excitation unit  110  toggles between ON state and OFF state based on switching pulse of the first frequency control signal  122  to convert the DC voltage of the input power to the corresponding first AC voltage having the first frequency. In one embodiment, the first frequency may be in a range from about 4 MHz to about 9 MHz. 
     Furthermore, at step  706 , the excitation unit  110  converts the DC voltage of the input power to the second AC voltage having a second frequency if the second frequency control signal  124  is received. Particularly, the control unit  112  sends the second frequency control signal  122  to the first switch  208  and a signal that is complimentary to the first frequency control signal  122  to the second switch  210  for the second time period. Further, during the second time period, the first switch  208  and the second switch  210  in the excitation unit  110  toggles between ON state and OFF state based on switching pulse of the second frequency control signal  124  to convert the DC voltage of the input power to the corresponding second AC voltage having the second frequency. In one embodiment, the second frequency may be in a range from about 100 kHz to about 1 MHz. 
     At step  708 , at least one first frequency coil  116  transmits the first AC voltage having the first frequency to the first receiver device  106 . Further, the excitation unit  110  drives the first frequency coil  116  in the transmitting unit  114  to transfer the first AC voltage having the first frequency to the receiver coil  224  of the first receiver device  106 . Further, the first AC voltage is conditioned by the power conditioner  232  and supplied to the load  228  such as a battery in the first receiver device  106 . 
     Furthermore, at step  710 , at least one second frequency coil  118  transmits the second AC voltage having the second frequency to the second receiver device  108 . Further, the excitation unit  110  drives the second frequency coil  118  in the transmitting unit  114  to transfer the second AC voltage having the second frequency to the receiver coil  226  of the second receiver device  108 . Further, the second AC voltage is conditioned by the power conditioner  234  and supplied to the load  230  such as a battery in the second receiver device  108 . 
     In accordance with the exemplary embodiments discussed herein, the exemplary system and method facilitate to charge the receiver devices of any frequency standard, using the excitation unit  110 . 
     Referring to  FIG. 8 , a graphical representation of different control signals in accordance with aspects of the present invention is shown. Reference numeral  802  is representative of a first frequency control signal transmitted from the control unit to the excitation unit for converting the DC voltage of the input power to the first AC voltage. The first frequency control signal  802  includes a plurality of switching pulses  804  during a first time period represented by  806 . Further, reference numeral  808  is representative of a second frequency control signal transmitted from the control unit to the excitation unit for converting the DC voltage of the input power to the second AC voltage. The second frequency control signal  808  includes a single switching pulse  810  during a second time period represented by  820 . It should be noted herein that the second frequency control signal  808  includes more number of switching pulses within the second time period  820 . However, the number of switching pulses of the second frequency control signal  808  within the second time period  820  is less than the number of switching pulses for the first frequency control signal  802  within the first time period  806 . Reference numeral  812  is representative of a modulation signal which includes the first frequency control signal  814  and the second frequency control signal  816 . Particularly, the first frequency control signal  814  is generated during the first time period  806  and the second frequency control signal  816  is generated during the second time period  820 . 
     This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.