Patent Publication Number: US-2022224162-A1

Title: Contactless power transfer system and method for controlling the same

Description:
BACKGROUND 
     Embodiments of the present specification relate to a power transfer system, and more particularly to a contactless power transfer system and method of controlling the same. 
     Contactless power transfer systems are used to transmit power from one location to another location without a physical connection such as wires between the two locations. The contactless power transfer systems may be classified as inductive coupling systems and resonance based coupling systems based on their principle of operations. 
     Inductive coupling systems are well known and work based on the principle of induction. However, in such inductive coupling systems, power can be transmitted only between two closely coupled coils. Further, the inductive coupling systems have poor power transmission efficiency. 
     The resonance based coupling systems employ resonant coils, which are operated at a system frequency to transmit power between the two locations via a magnetic field. Such resonance based coupling systems are used to transmit power over relatively long distances and are thus used in various applications. In such applications, the resonance based coupling systems are used to provide power to a load, where the system frequency varies based on a power rating of the load. Moreover, for applications of the resonance based coupling systems such as charging a battery, the system frequency may vary based on a required load power for charging the load. In such applications, the required load power varies for the same load during a single charging cycle; and the system frequency is varied during the single charging cycle for the same load based on the required load power at different instants of time in the single charging cycle. Such variations in the system frequency lead to undesirable effects on the power transmission efficiency of the resonance based coupling systems as the power transmission efficiency of the resonance based coupling systems is dependent on a frequency at which the resonant coils operate. 
     BRIEF DESCRIPTION 
     Briefly, in accordance with one aspect of the present specification, a contactless power transfer system is provided. The contactless power transfer system includes a first power exchanger coil configured to exchange power. The contactless power transfer system also includes a first power converter operatively coupled to the first power exchanger coil and configured to convert a direct current power to an alternating current power at a system frequency. The contactless power transfer system further includes a controller configured to control an operating state of the first power converter to vary an alternating current power provided to the first power exchanger coil at the system frequency. 
     In another aspect of the specification, a method for contactless power transfer is provided. The method includes operating a first power exchanger coil at a system frequency. The method also includes detecting a second power exchanger coil. The method further includes generating an alternating current power at the system frequency using a first power converter. The method also includes transferring the alternating current power from the first power exchanger coil to the second power exchanger coil at the system frequency via a magnetic field. The method further includes controlling a time period of an operating state of the first power converter operating at the system frequency for varying the alternating current power generated by the first power converter, wherein controlling the operating state of the first power converter comprises altering a first time period of an activated state of the first power converter and altering a second time period of a deactivated state of the first power converter to vary the alternating current power generated by the first power converter. 
     In yet another aspect of the specification, a contactless power transfer system is provided. The contactless power transfer system includes a first power converter configured to convert a direct current power received from a power source to an alternating current power at a system frequency. The contactless power transfer system also includes a first power exchanger coil operatively coupled to the first power converter and configured to receive the alternating current power from the first power converter. The contactless power transfer system further includes a second power exchanger coil configured to receive the alternating current power from the first power exchanger coil via a magnetic field at the system frequency. The contactless power transfer system also includes a second power converter operatively coupled to the second power exchanger coil and configured to convert the alternating current power to an output direct current power transmitted to a load. The contactless power transfer system further includes a sensor operatively coupled to the second power converter and configured to measure at least a voltage of the output direct current power. The contactless power transfer system further includes a controller operatively coupled to the first power converter and configured to control an operating state of the first power converter for varying the alternating current power generated by the first power converter based on at least a sensed voltage received from the sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention 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 contactless power transfer system, according to aspects of the present specification; 
         FIG. 2A  is a graphical representation depicting a frequency signal for generating an alternating current power in the contactless power transfer system of  FIG. 1 , according to aspects of the present specification; 
         FIG. 2B  is a graphical representation depicting a control signal for generating the alternating current power in the contactless power transfer system of  FIG. 1 , according to aspects of the present specification; 
         FIG. 2C  is a graphical representation depicting a modulated signal for generating the alternating current power in the contactless power transfer system of  FIG. 1 , according to aspects of the present specification; 
         FIG. 3  is an exemplary graphical representation depicting simulations performed to generate 2.8 kilowatts of alternating current power using a first power converter in the contactless power transfer system of  FIG. 1 , according to aspects of the present specification; 
         FIG. 4  is an exemplary graphical representation depicting simulations performed to generate 280 watts of alternating current power using a first power converter in the contactless power transfer system of  FIG. 1 , according to aspects of the present specification; 
         FIG. 5  is a block diagram representation of an embodiment of a contactless power transfer system of  FIG. 1  configured to detect a second power exchanger coil, according to aspects of the present specification; 
         FIG. 6  is a block diagram representation of another embodiment of the contactless power transfer system of  FIG. 5  including a bias coil configured to detect the second power exchanger coil, according to aspects of the present specification; 
         FIG. 7  is a block diagram representation of yet another embodiment of the contactless power transfer system of  FIG. 5  including a bias transformer configured to detect the second power exchanger coil, according to aspects of the present specification; and 
         FIG. 8  is a flow chart representing steps involved in a method for contactless power transfer using the contactless power transfer system, according to aspects of the present specification. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present specification include a contactless power transfer system and a method for contactless power transfer using the same. The contactless power transfer system includes a first power converter configured to convert a direct current power received from a power source to an alternating current power at a system frequency. As used herein, the term “system frequency” refers to a frequency at which the contactless power transfer system is operated. The contactless power transfer system also includes a first power exchanger coil operatively coupled to the first power converter and configured to receive the alternating current power from the first power converter. Further, the contactless power transfer system includes a second power exchanger coil configured to receive the alternating current power from the first power exchanger coil via a magnetic field, at the system frequency. Moreover, the contactless power transfer system also includes a second power converter operatively coupled to the second power exchanger coil and configured to convert the alternating current power to an output direct current power, where the direct current power may be transmitted to a load. Further, the contactless power transfer system further includes a sensor operatively coupled to a first node located between the second power converter and the load. The sensor is configured to sense at least a voltage or a current at the first node. The contactless power transfer system further includes a controller operatively coupled to the first power converter and configured to control an operating state of the first power converter for varying the alternating current power generated by the first power converter based on at least the sensed voltage or the sensed current received from the sensor. 
     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 disclosure 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 “exchange” and “transfer” may be used interchangeably in the specification and convey the same meaning. Unless specified otherwise, the term “exchange” may be defined as a contactless exchange of power for the purposes of this specification. 
       FIG. 1  is a block diagram representation of a contactless power transfer system  10 , according to an aspect of the present specification. The contactless power transfer system  10  includes a first power exchanger coil  20  and a second power exchanger coil  24 , where the contactless power transfer system  10  enables transfer of power from the first power exchanger coil  20  to the second power exchanger coil  24 . Further details of the operation of the contactless power transfer system  10  are discussed later in the specification. 
     The contactless power transfer system  10  includes a first power converter  12  operatively coupled to a direct current power source  14 . The first power converter  12  receives a direct current power, generally represented by reference numeral  16 , from the direct current power source  14  and converts the direct current power  16  to an alternating current power, generally represented by reference numeral  18 , based on a system frequency of the contactless power transfer system  10 . The first power converter  12  is operatively coupled to the first power exchanger coil  20  and transmits the alternating current power  18  to the first power exchanger coil  20 . The first power exchanger coil  20  receives the alternating current power  18  and generates a magnetic field  22  based on the received alternating current power  18 . The contactless power transfer system  10  also includes the second power exchanger coil  24 . The second power exchanger coil  24  located at a determined distance from the first power exchanger coil  20  receives the magnetic field  22  generated by the first power exchanger coil  20  and converts the magnetic field  22  to a corresponding alternating current power  19  representative of the alternating current power  18  generated by the first power converter  12 . As used herein, the term “determined distance” refers to a distance up to which the alternating current power  18  is desired to be transmitted. In certain embodiments, the first power exchanger coil  20  and the second power exchanger coil  24  may be resonant coils. In one example, the first power exchanger coil  20  may transmit the magnetic field  22  to a plurality of second power exchanger coils  24 . In another example, a plurality of first power exchanger coils  20  may transmit the magnetic field  22  to the second power exchanger coil  24 . Each of the aforementioned configurations is applied based on the application, where contactless power transfer is used. For example, the first power exchanger coil  20  may act as a transmitter and may transfer power in a contactless fashion to the plurality of second power exchanger coils  24  disposed in corresponding devices. Further, each of the plurality of second power exchanger coils  24  may receive the alternating current power  19  simultaneously in a similar time interval or sequentially in same or different time intervals using modulation techniques. 
     Furthermore, the first power exchanger coil  20  and the second power exchanger coil  24  may be configured to operate as the transmitter coil or the receiver coil in different embodiments based on system requirements. In some embodiments, the first power exchanger coil  20  and the second power exchanger coil  24  may act as both transmitter and receiver simultaneously allowing for simultaneous bidirectional exchange of power, data, or both. In one embodiment, the contactless power transfer system  10  may further include a field focusing element (not shown in  FIG. 1 ) to enhance magnetic coupling between the first power exchanger coil  20  and the second power exchanger coil  24 . In same or different embodiment, one or more repeater resonators (not shown in  FIG. 1 ) may be added to the contactless power transfer system  10  to increase the determined distance between the first power exchanger coil  20  and the second power exchanger coil  24  for contactless exchange of power. In some embodiments, the field focusing element, the one or more repeater resonators, or both may be operatively coupled to the first power exchanger coil  20 , the second power exchanger coil  24 , or a combination thereof. 
     Moreover, in the contactless power transfer system  10 , the second power exchanger coil  24  is operatively coupled to a second power converter  26 . The second power converter  26  is configured to receive the alternating current power  19  transmitted by the second power exchanger coil  24 . Further, the second power converter  26  may convert the alternating current power  19  to an output direct current power  28  which is used to operate a load operatively coupled to the contactless power transfer system  10 . During operation, power, also referred to as load power, is required to drive the load  30 . The load power required by the load  30  may vary with time based on a condition of the load  30  at a particular time. For example, if the load  30  is a battery, which is discharged, the required load power for charging the battery may depend on the extent of discharge or charge expended by the battery. In particular, a required load power for charging the battery is higher when the battery is nearly discharged, as compared to the required load power for the battery when the battery is 90% to 95% charged, for example. 
     Further, a sensor  32  is operatively coupled at a first node  34  between the second power converter  26  and the load  30 . The sensor  32  senses at least a voltage  36  at the first node  34 . It may be noted that in some embodiments, the sensor  32  may be configured to sense other electrical parameters, such as but not limited to, current, at the node  34 . A voltage at the first node  34  is induced based on the load power required by the load  30 . Accordingly, the sensed voltage  36  at the node  34  is representative of the power required by the load  30 . Further, a signal  37  representative of the sensed voltage  36  is transmitted to a controller  38  in the contactless power transfer system  10 . In one embodiment, the contactless power transfer system  10  may include a data transmitter operatively coupled to the sensor  32  for transmitting the signal  37  representative of the sensed voltage  36  to the controller  38 . Further, the contactless power transfer system  10  may include a data receiver operatively coupled to the controller  38  for receiving the signal  37  representative of the sensed voltage  36  from the data transmitter. In such embodiments, the signal  37  representative of the sensed voltage  36  is transmitted at a data frequency, which is different from the system frequency. 
     The controller  38  receives the sensed voltage  36  from the sensor  32  and computes the load power required by the load  30  based on the sensed voltage  36 . Further, the controller  38  determines the output direct current power  28 , which is equivalent to the required load power. Moreover, based on the determined output direct current power  28  that is required to drive the load  30 , the controller  38  computes the alternating current power  18  that is required to be generated by the first power converter  12 . In some embodiments, a processing unit (not shown in  FIG. 1 ) may be operatively coupled to the controller  38 , the sensor  32 , or both for computing the required load power, the output direct current power  28 , or the alternating current power  18  that is required to be generated by the first power converter  12  based on the sensed voltage  36 . Further, in some of these embodiments, a signal representative of the load power, the output direct current power  28 , or the alternating current power  18  required to be generated by the first power converter  12  may be transmitted by the processing unit to the controller  38  based on which the controller may control the first power converter  12 . Based on the alternating current power  18  that needs to be generated by the first power converter  12 , the controller  38  controls an operating state of the first power converter  12  to facilitate generation of the required alternating current power  18 . The operating state may be an activated state of the first power converter  12  or a deactivated state of the first power converter  12 . Furthermore, the controller  38  controls a first time period associated with the activated state of the first power converter  12  and the second time period associated with the deactivated state of the first power converter  12 . 
     As used hereinabove, the term “activated state” may be defined as a state of the first power converter  12 , in which the first power converter  12  generates the alternating current power  18  at the system frequency. Such activated state is different from a duty cycle modulation technique such as a pulse width modulation technique. The first time period of the activated state is dependent on the load power required by the load and may vary based on the load power requirement. In contrast, the duty cycle modulation technique includes a fixed duty cycle, which further includes an “ON” time interval and an “OFF” time interval, which may be varied within the fixed duty cycle. Therefore, the first time period of the activated state is different from the duty cycle, thereby making the activated state different from the duty cycle modulation. 
     Similarly, as used hereinabove, the term “deactivated state” may be defined as a state of the first power converter  12 , in which the first power converter  12  does not generate the alternating current power  18 . Such deactivated state is different from the duty cycle modulation technique such as the pulse width modulation technique. The second time period of the deactivated state is dependent on the load power required by the load and may vary based on the load power requirement. In contrast, the duty cycle modulation technique includes the fixed duty cycle, which further includes the “ON” time interval and the “OFF” time interval, which may be varied within the fixed duty cycle. Therefore, the second time period of the deactivated state is different from the duty cycle, thereby making the deactivated state different from the duty cycle modulation. 
     The controller  38  operates the first power converter  12  at the system frequency and alters the first time period and the second time period for generating pulses of alternating current power  18 , which are transmitted to the second power exchanger coil  24  by the first power exchanger coil  20 . Such a configuration allows the contactless power transfer system  10  to operate at a fixed system frequency for different values of required load power, thereby improving a power transfer efficiency of the contactless power transfer system  10 . In one embodiment, the required output direct current power  28  is an average of the pulses of the alternating current power  18  generated by the first power converter  12 . Further details of the operation of the contactless power transfer system are discussed below. 
       FIG. 2A-2C  are graphical representations depicting a system frequency signal for generating the alternating current power  18  in a contactless power transfer system  10  of  FIG. 1 . Referring to  FIG. 2A  the graph  42  represents a system frequency  44 , where X axis  46  of the first graph represents time and Y axis  48  represents a system frequency  44 . 
     In  FIG. 2B  the graph  50  represents a control signal  52  for controlling an operating state of the first power converter  12  of  FIG. 1 , where X axis  54  represents time and Y axis  56  represents an operating state of the first power converter  12 . 
     Referring to  FIG. 2C , the third graph  58  represents a modulated signal  60  based on the system frequency  44  and the control signal  52 , where X axis  62  represents time and Y axis  64  represents the modulation signal  60 . 
     From a combined reading of the first graph  42 , the second graph  50 , and the third graph  58 , it can be seen that the first power converter  12  is operated in an activated state at the system frequency  44  for a first time interval  66 . Furthermore, in a second time interval  68 , the first power converter  12  is operated in a deactivated state, where no alternating current power is generated by the first power converter  12 . Subsequently, in a third time interval  69 , the first power converter  12  is again operated in the activated state, thereby generating alternating current power  18  at the system frequency  44 . Such time intervals  66 ,  68 ,  69  are controlled by the controller  38  to vary the alternating current power  18  generated by the first power converter  12  based on the power required by a load. 
       FIG. 3  is an exemplary graphical representation  70  for a method of generating the alternating current power  18  using the first power converter  12 , according to aspects of the present specification. The graphical representation  70  depicts simulations performed to generate 2.8 kilowatts of alternating current power  18  using the first power converter  12 , where X axis  72  represents time in milliseconds and Y axis  74  represents converter voltage in volts. 
     As illustrated, in a first time interval  76 , the first power converter  12  is operated in an activated state, which generates a current  78  at an output of the first power converter  12 , thereby generating a first pulse  79  of the alternating current power  18 . Further, upon initiation of a deactivation state of the first power converter  12  by the controller  38 , the current  78  in the first power converter  12  decays during a transition time period  80 . 
     During a second time interval  82 , the first power converter  12  is in the deactivated state, where the current  78  is zero. Similarly, in a third time interval  84 , the first power converter  12  is again operated in the activated state, thereby generating the current  78  at the output of the first power converter  12 . Therefore, the first power converter  12  generates a second pulse  85  of the alternating current power  18  in the third time interval  84 . The first pulse  79  and the second pulse  85  provides the desired alternating current power  18  to the first power exchanger coil  20 . 
     The controller  38  controls a duration of the time intervals  76 ,  82 , and  84  depicting the activated state and the deactivated state of the first power converter  12  to generate the desired alternating current power  18  at the system frequency  44  (see  FIG. 2A ). 
       FIG. 4  represents another exemplary graphical representation  90  depicting simulations performed to generate 280 watts of alternating current power  18  using the first power converter  12 . In the graphical representation  90 , X axis  92  represents time in milliseconds and Y axis  94  represents the first converter voltage in volts. 
     As can be seen, in a first time interval  96 , the first power converter  12  is operated in an activated state, which generates a current  98  at an output of the first power converter  12 , thereby generating a first pulse  97  of the alternating current power  18 . Furthermore, upon initiation of a deactivation state of the first power converter  12 , the current  98  in the first power converter  12  decays during a transition time period  100 . It may be noted that the first time interval  96  in the graphical representation  90  is less than the first time interval  76  in the graphical representation  70 , which enables the controller  38  to control the first power converter  12  to generate less alternating current power  18  in the first pulse  97  in comparison to the first pulse  79  of  FIG. 3 . 
     During a second time interval  102 , the first power converter  12  is in the deactivated state, where the current  98  is zero. It may be noted that the second time interval  102  in that graphical representation  90  is more than the second time interval  82  in graphical representation  70 . Furthermore, in a third time interval  104 , the first power converter  12  is again operated in the activated state, thereby generating the current  98  at the output of the first power converter  12 . The first power converter generates a second pulse  105  of the alternating current power  18  during the third time interval  104 . It may be noted that the first time interval  96  and the third time interval  104  in the graphical representation  90  are lesser than the first time interval  76  and the third time interval  84  in the graphical representation  70 , which enables the controller  38  to control the first power converter  12  to generate lesser alternating current power  18  in the first pulse  97  and the second pulse  105  in comparison to the first pulse  79  and second pulse  85  of  FIG. 3 . 
       FIG. 5  is a block diagram representation of an embodiment of a contactless power transfer system  110 , according to aspects of the present specification. The contactless power transfer system  110  includes a first power exchanger coil  120  and a second power exchanger coil  124 , where the contactless power transfer system  110  enables transfer of power from the first power exchanger coil  120  to the second power exchanger coil  124 . Further details of the operation of the contactless power transfer system  110  are discussed later in the specification. 
     The contactless power transfer system  110  includes a first power converter  112  operatively coupled to a direct current power source  114 . The first power converter  112  receives a direct current power, generally represented by reference numeral  116 , from the direct current power source  114  and converts the direct current power  116  to an alternating current power, generally represented by reference numeral  118  based on a system frequency of the contactless power transfer system  110 . The first power converter  112  is operatively coupled to a first power exchanger coil  120  and transmits the alternating current power  118  to the first power exchanger coil  120 . The first power exchanger coil  120  receives the alternating current power  118  and generates a magnetic field  122  based on the alternating current power  118 . The contactless power transfer system  110  also includes the second power exchanger coil  124 . The second power exchanger coil  124  located at a determined distance from the first power exchanger coil  120  receives the magnetic field  122  generated by the first power exchanger coil  120  and converts the magnetic field  122  to a corresponding alternating current power  119  representative of the alternating current power  118  generated by the first power converter  112 . The second power exchanger coil  124  receives the magnetic field  122  generated by the first power exchanger coil  120  and converts the magnetic field  122  to the alternating current power  119  representative of the alternating current power  118  generated by the first power converter  112 . Further, the second power exchanger coil  124  is operatively coupled to a second power converter  126 . The second power converter  126  is configured to receive the alternating current power  119  transmitted by the second power exchanger coil  124  and convert the alternating current power  119  to an output direct current power  128 , which is used to operate a load  130  operatively coupled to the contactless power transfer system  110 . 
     Further, a sensor  132  is operatively coupled at a first node  134  between the second power converter  126  and the load  130 . The sensor senses at least a voltage  136  at the first node  134 . Moreover, a signal  137  representative of the sensed voltage  136  is transmitted to a controller  138  in the contactless power transfer system  110 . The controller  138  receives the signal  137  representative of the sensed voltage  136  from the sensor  132  and computes the load power required by the load  130  based on the sensed voltage  136 . Furthermore, the controller  138  determines the output direct current power  128 , which is equivalent to the required load power. Moreover, based on the output direct current power  128  that is required to drive the load  130 , the controller  138  computes the alternating current power  118  that is required to be generated by the first power converter  112 . Based on the alternating current power  118  that needs to be generated by the first power converter  112 , the controller  138  controls an operating state of the first power converter  112  to generate the required alternating current power  118 . The operating state may be an activated state of the first power converter  112  or a deactivated state of the first power converter  112 . Furthermore, the controller  138  controls a first time period associated with the activated state of the first power converter  112  and the second time period associated with the deactivated state of the first power converter  112 . 
     The contactless power transfer system  110  further includes a first bias processing unit  140  operatively coupled to the controller  138 . The first bias processing unit  140  is configured to provide an operating power  141  to the controller  138  from the power source  114 . During an idle state of the contactless power transfer system  110 , the controller  138  controls the first power converter  112  to generate a bias power, which is transmitted to the second power exchanger coil  124  via the first power exchanger coil  120 . As used hereinabove, the term “bias power” may be defined as a power which is lower than the alternating current power transmitted during operation of the contactless power transfer system  110 . Such bias power is used for the purpose of detecting a second power exchanger coil  124  in the contactless power transfer system  110  during the idle state of the contactless power transfer system  110  and forms a portion of the alternating current power  118  transmitted to the second power exchanger coil  124  during operation of the contactless power transfer system  110 . Furthermore, the contactless power transfer system  110  also includes a second bias processing unit  144  operatively coupled to the second power exchanger coil  124 , where the second bias processing unit  144  is configured to receive a bias power  143 , representative of the bias power  142  from the first power exchanger coil  120  via the second power exchanger coil  124 . The second bias processing unit  144  receives the bias power  143  from the second power exchanger coil  124 , which is further used to activate the sensor  132  for measuring the voltage at the first node  134 . The bias power  143  is also used to generate a signal  146  representative of at least the sensed voltage  136  and transmit the signal  146  to the controller  138 . In one embodiment, the contactless power transfer system  110  may include a wireless communication kit, which may be energized using the bias power  142  to generate and transmit the signal  146  to the controller  138 . The controller  138  receives the signal  147 , representative of the signal  146  and recognizes that the second power exchanger coil  124  is available for transferring power. 
       FIG. 6  is a block diagram representation of an embodiment of a contactless power transfer system  150  of the present specification. The contactless power transfer system  150  includes a first power exchanger coil  160  and a second power exchanger coil  164 , where the contactless power transfer system  150  enables transfer of power from the first power exchanger coil  160  to the second power exchanger coil  164 . Further details of the operation of the contactless power transfer system  150  are discussed later in the specification. 
     The contactless power transfer system  150  includes a first power converter  152  operatively coupled to a direct current power source  154 . The first power converter  152  receives a direct current power, generally represented by reference numeral  156 , from the direct current power source  154  and converts the direct current power  156  to an alternating current power, generally represented by reference numeral  158  based on a system frequency. The first power converter  152  is operatively coupled to the first power exchanger coil  160  and transmits the alternating current power  158  to the first power exchanger coil  160 . The first power exchanger coil  160  receives the alternating current power  158  and generates a magnetic field  162  based on the alternating current power  158 . The contactless power transfer system  150  also includes the second power exchanger coil  164 . The second power exchanger coil  164  located at a determined distance from the first power exchanger coil  160  receives the magnetic field  162  generated by the first power exchanger coil  160  and converts the magnetic field  162  to a corresponding alternating current power  159  representative of the alternating current power  158  generated by the first power converter  152 . The second power exchanger coil  164  receives the magnetic field  162  generated by the first power exchanger coil  160  and converts the magnetic field  162  to the alternating current power  159  representative of the alternating current power  158  generated by the first power converter  152 . Further, the second power exchanger coil  164  is operatively coupled to a second power converter  166 . The second power converter  166  is configured to receive the alternating current power  158  transmitted by the second power exchanger coil  164  and convert the alternating current power  159  to an output direct current power  168 , which is used to operate a load  170  operatively coupled to the contactless power transfer system  150 . 
     Further, a sensor  172  is operatively coupled at a first node  174  between the second power converter  166  and the load  170 . The sensor  172  senses at least a voltage  176  at the first node  174 . Moreover, a signal  177  representative of the sensed voltage  176  is transmitted to a controller  178  in the contactless power transfer system  150 . The controller  178  receives the signal  177  representative of the sensed voltage  176  from the sensor  172  and computes the load power required by the load  170  based on the sensed voltage  176 . Furthermore, the controller  178  determines the output direct current power  168 , which is equivalent to the required load power. Moreover, based on the output direct current power  168  that is required to drive the load  170 , the controller  178  computes the alternating current power  158  that is required to be generated by the first power converter  152 . Based on the alternating current power  158  that needs to be generated by the first power converter  152 , the controller  178  controls an operating state of the first power converter  152  to generate the required alternating current power  158 . The operating state may be an activated state of the first power converter  152  or a deactivated state of the first power converter  152 . Furthermore, the controller  178  controls a first time period associated with the activated state of the first power converter  152  and the second time period associated with the deactivated state of the first power converter  152 . 
     The contactless power transfer system  150  further includes a first bias processing unit  180  operatively coupled to the controller  178 . The first bias processing unit  180  is configured to provide an operating power  181  to the controller  178  from the power source  154 . The operating power  181  is used to operate the controller  178 . During an idle state of the contactless power transfer system  150 , the controller  178  controls the first power converter  152  to generate a bias power  182 , which is transmitted to the second power exchanger coil  164  via the first power exchanger coil  160 . Furthermore, the contactless power transfer system  150  also includes a second bias processing unit  184  operatively coupled to the second power exchanger coil  164 , where the second bias processing unit  184  is configured to receive the bias power  183 , representative of the bias power  182  received from the first power exchanger coil  160 . The contactless power transfer system  150  also includes a bias coil  186  operatively coupled to the second power exchanger coil  164  and the second bias processing unit  184 , where the bias coil  186  is configured to receive the bias power  183  from the first power exchanger coil  160  and transmit the bias power  183  to the second bias processing unit  184 . The second bias processing unit  184  receives the bias power  183  from the second power exchanger coil  164 , which is further used to activate the sensor  172  for measuring the voltage at the first node  174 . The bias power  183  is also used to generate a signal  188  representative of at least the sensed voltage  176  and transmit the signal  188  to the controller  178 . In one embodiment, the contactless power transfer system  150  may include a wireless communication kit, which may be energized using the bias power  183  to generate and transmit the signal  188  to the controller  178 . The controller  178  receives a signal  189 , representative of the signal  188  and recognizes that the second power exchanger coil  164  is available for transferring power. 
       FIG. 7  is a block diagram representation of an embodiment of a contactless power transfer system  200 , according to aspects of the present specification. The contactless power transfer system  200  includes a first power exchanger coil  210  and a second power exchanger coil  214 , where the contactless power transfer system  200  enables transfer of power from the first power exchanger coil  210  to the second power exchanger coil  214 . Further details of the operation of the contactless power transfer system  200  are discussed later in the specification. 
     The contactless power transfer system  200  includes a first power converter  202  operatively coupled to a direct current power source  204 . The first power converter  202  receives a direct current power, generally represented by reference numeral  206 , from the direct current power source  204  and converts the direct current power  206  to an alternating current power, generally represented by reference numeral  208  based on a system frequency. The first power converter  202  is operatively coupled to the first power exchanger coil  210  and transmits the alternating current power  208  to the first power exchanger coil  210 . The first power exchanger coil  210  receives the alternating current power  208  and generates a magnetic field  212  based on the alternating current power  208 . The contactless power transfer system  200  also includes the second power exchanger coil  214 . The second power exchanger coil  214  located at a determined distance from the first power exchanger coil  210  receives the magnetic field  212  generated by the first power exchanger coil  210  and converts the magnetic field  212  to a corresponding alternating current power  209  representative of the alternating current power  208  generated by the first power converter  202 . The second power exchanger coil  214  receives the magnetic field  212  generated by the first power exchanger coil  210  and converts the magnetic field  212  to the alternating current power  209  representative of the alternating current power  208  generated by the first power converter  202 . Further, the second power exchanger coil  214  is operatively coupled to a second power converter  216 . The second power converter  216  is configured to receive the alternating current power  208  transmitted by the second power exchanger coil  214  and convert the alternating current power  209  to an output direct current power  218 , which is used to operate a load  220  operatively coupled to the contactless power transfer system  200 . 
     Further, a sensor  222  is operatively coupled at a first node  224  between the second power converter  216  and the load  220 . The sensor  222  senses at least a voltage  226  at the first node  224 . Moreover, a signal  227  representative of the sensed voltage  226  is transmitted to a controller  228  in the contactless power transfer system  200 . The controller  228  receives the signal  227  representative of the sensed voltage  226  from the sensor  222  and computes the load power required by the load  220  based on the sensed voltage  226 . Furthermore, the controller  228  determines the output direct current power  218 , which is equivalent to the required load power. Moreover, based on the output direct current power  218  that is required to drive the load  220 , the controller  228  computes the alternating current power  208  that is required to be generated by the first power converter  202 . Based on the alternating current power  208  that needs to be generated by the first power converter  202 , the controller  228  controls an operating state of the first power converter  202  to generate the required alternating current power  208 . The operating state may be an activated state of the first power converter  202  or a deactivated state of the first power converter  202 . Furthermore, the controller  228  controls a first time period associated with the activated state of the first power converter  202  and the second time period associated with the deactivated state of the first power converter  202 . 
     The contactless power transfer system  200  further includes a first bias processing unit  230  operatively coupled to the controller  228 . The first bias processing unit  230  is configured to provide an operating power to the controller  228  from the power source  204 . During an idle state of the contactless power transfer system  200 , the controller  228  controls the first power converter  202  to generate a bias power  232 , which is transmitted to the second power exchanger coil  214  via the first power exchanger coil  210 . Furthermore, the contactless power transfer system  200  also includes a second bias processing unit  234  operatively coupled to the second power exchanger coil  214 , where the second bias processing unit  234  is configured to receive the bias power  232  received from the first power exchanger coil  210 . The contactless power transfer system  200  also includes a bias transformer  236 . The bias transformer  236  includes a primary winding  238  operatively coupled to the second power exchanger coil  214  and configured to receive the bias power  232  from the first power exchanger coil  210 . The bias transformer  236  also includes a secondary winding  240  operatively coupled to the second bias processing unit  234  and configured to transmit the bias power  232  to the second bias processing unit  234 . In one embodiment, the second bias processing unit  234  may include a switched-mode power supply. The second bias processing unit  234  receives the bias power  233  from the second power exchanger coil  214 , which is further used to activate the sensor  222  for measuring the voltage at the first node  224 . The bias power  233  is also used to generate a signal  242  representative of at least the sensed voltage  226  and transmit the signal  242  to the controller  228 . In one embodiment, the contactless power transfer system  200  may include a wireless communication kit, which may be energized using the bias power  233  to generate and transmit the signal  242  to the controller  228 . The controller  228  receives a signal  243 , representative of the signal  243  and recognizes that the second power exchanger coil  164  is available for transferring power. 
       FIG. 8  is a flow chart representing steps involved in a method  250  for contactless power transfer using a contactless power transfer system of the present specification, such as the contactless power transfer system  110  of  FIG. 5 , according to aspects of the present specification. The method  250  includes operating a first power exchanger coil  120  at a system frequency in step  252 . The method  250  also includes detecting a second power exchanger coil  124  in step  254 . In one embodiment, a bias power using a first bias processing unit  140  is generated and the bias power  142  is transmitted from the first power exchanger coil  120  to the second power exchanger coil  124 . In another embodiment, the bias power from the first power exchanger coil  120  is received using a second bias processing unit  144  and a signal  146  representative of a detected second power exchanger coil  124  is transmitted to a controller  138 . 
     The method  250  further includes generating an alternating current power  118  at the system frequency using a first power converter  112  in step  256 . The method  250  also includes transferring the alternating current power  118  from the first power exchanger coil  120  to the second power exchanger coil  124  at the system frequency via a magnetic field  122  in step  258 . The method  250  further includes controlling a time period of an operating state of the first power converter  112  using the controller  138  for varying the alternating current power  118  generated by the first power converter  112 , wherein controlling the operating state of the first power converter  112  comprises altering a first time period of an activated state of the first power converter  112  and altering a second time period of a deactivated state of the first power converter  112  to vary the alternating current power  118  generated by the first power converter  112  in step  260 . In one embodiment, the time period of the operating state of the first power converter  112  is controlled based on a load power required by a load  130  for varying the alternating current power  118  generated by the first power converter  112 . In another embodiment, a voltage at a first node  134  located between the second power exchanger coil  124  and the load  130  is sensed and the alternating current power  118  is varied based on at least a sensed voltage  136 . 
     It is to be understood that a skilled artisan will recognize the interchangeability of various features from different embodiments and that the various features described, as well as other known equivalents for each feature, may be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this specification. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.