Patent Publication Number: US-2020287418-A1

Title: System and method for protecting a wireless power transfer system

Description:
RELATED APPLICATIONS 
     This application is a Continuation of and claims the priority benefit of U.S. application Ser. No. 15/417,246 filed Jan. 27, 2017 which claims the priority benefit of India Application No. 201641003928 filed Feb. 3, 2016. 
    
    
     BACKGROUND 
     Embodiments of the present invention relate generally to wireless power transfer systems and more particularly to a system and method for protecting a wireless power transfer system. 
     In one or more industries, an electric vehicle or a hybrid vehicle includes one or more batteries that supply electrical power to drive the vehicle. In one example, the batteries supply energy to an electric motor to drive a shaft in the vehicle, which in turn drives the vehicle. The batteries are used for supplying the power and hence may be drained and need to be charged from an external power source. 
     In general, power transfer systems are widely used to transfer power from a power source to one or more electric loads, such as for example, the batteries in the vehicle. Typically, the power transfer systems may be contact based power transfer systems or contactless power transfer systems. In the contact based power transfer systems, components, such as plug, socket connectors, and wires are physically coupled to the batteries for charging the batteries. However, due to environmental impact, such connectors and wires may be damaged or corroded. Also, high currents and voltages are used for charging the batteries. Hence, establishing a physical connection between the power source and the batteries in the vehicle may involve cumbersome safety measures. Also, this power transfer system may become bulkier and heavier compared to the contactless power transfer system. 
     In the contactless power transfer systems, power converters are used to convert an input power to a transferable power, which is further transmitted to the electric load, such as the batteries in the vehicle. The power converter includes switches which are operated at a particular switching frequency to convert the input power to the transferable power. Typically, depending upon the load, the switching frequency of the power converter is changed to regulate or control an output voltage of the power transfer system. However, if the electric load is disconnected or varied, the output voltage of the power transfer system may attain a very high value in a very short time period. Such a sudden increase in the output voltage may lead to failure of operation and may also damage one or more components in the power transfer system. 
     Therefore, there is a need for an improved system and method for protecting the power transfer system. 
     BRIEF DESCRIPTION 
     In accordance with one embodiment of the present invention, a wireless power transfer system is disclosed. The wireless power transfer system includes a first converting unit configured to convert a first DC voltage of an input power to a first AC voltage. Further, the wireless power transfer system includes a contactless power transfer unit communicatively coupled to the first converting unit and configured to receive the input power having the first AC voltage from the first converting unit and transmit the input power. Also, the wireless power transfer system includes a second converting unit communicatively coupled to the contactless power transfer unit and configured to receive the input power from the contactless power transfer unit and convert the first AC voltage of the input power to a second DC voltage. The input power having the second DC voltage is transmitted to an electric load. Furthermore, the wireless power transfer system includes a switching unit coupled to the contactless power transfer unit and the second converting unit and configured to decouple the second converting unit from the contactless power transfer unit if the second DC voltage across the electric load is greater than a first threshold value. 
     In accordance with another embodiment of the present invention, a switching unit for protecting a wireless power transfer system is disclosed. The switching unit includes a switch configured to be electrically coupled across a second converting unit configured to be coupled to an electric load. Also, the switching unit includes a controller electrically coupled to the switch and configured to send a first control signal to activate the switch if an output DC voltage determined across the electric load is greater than a first threshold value. The switch is activated to decouple the second converting unit from a contactless power transfer unit. 
     In accordance with another embodiment of the present invention, a method for protecting a wireless power transfer system is disclosed. The method includes converting, by a first converting unit, a first DC voltage of an input power to a first AC voltage. Further, the method includes receiving from the first converting unit and transmitting, by a contactless power transfer unit, the input power having the first AC voltage. Also, the method includes converting, by a second converting unit, the first AC voltage of the input power to a second DC voltage. Furthermore, the method includes transmitting the input power having the second DC voltage from the second converting unit to an electric load. In addition, the method includes decoupling, by a switching unit, the second converting unit from the contactless power transfer unit if the second DC voltage across the electric load is greater than a first threshold value. 
    
    
     
       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 having a switching unit in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic representation of a wireless power transfer system in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic representation of a wireless power transfer system in accordance with another embodiment of the present invention; 
         FIG. 4  is a flow chart illustrating a method for protecting a wireless power transfer system in accordance with an embodiment of the present invention; 
         FIG. 5  is a flow chart illustrating a method for decoupling and coupling a converting unit in a wireless power transfer system in accordance with an embodiment of the present invention; and 
         FIG. 6  is a flow chart illustrating a method for regulating an output voltage of a wireless power transfer system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As will be described in detail hereinafter, various embodiments of a system and method for protecting a wireless power transfer system are disclosed. Also, various embodiments of a system and method for regulating an output voltage of the wireless power transfer system are disclosed. In particular, the system and method disclosed herein employ a switching unit to protect one or more components in the wireless power transfer system. More specifically, the switching unit decouples the one or more components in the system if an output voltage of the wireless power transfer system increases to an undesirable value. Further, the switching unit may be used to control or regulate the output voltage of the wireless power transfer system even if an electric load coupled to the wireless power transfer system changes substantially. 
       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 electric loads  132  such as, batteries, light loads, mobile devices like cell phones, laptops, HVAC systems etc. Particularly, in an automobile industry, an electric vehicle or a hybrid vehicle includes one or more batteries that supply electrical power to drive the vehicle. Such batteries may be electrically charged from the power source  102  via the wireless power transfer system  100 . In one embodiment, the wireless power transfer system  100  may also be referred as a contactless power transfer system. 
     In the illustrated embodiment, the wireless power transfer system  100  includes a first converting unit  104  (inverter), a control unit  106 , a contactless power transfer unit  108 , and a second converting unit  110  (rectifier). The first converting unit  104  is electrically coupled to the power source  102  and the control unit  106 . The power source  102  is configured to supply an input power having a first DC voltage  112  to the first converting unit  104 . In some embodiments, the input power may be in a range from about 100 W to about 6.6 kW. In one embodiment, the power source  102  may be a part of the wireless power transfer system  100 . In another embodiment, the power source  102  may be positioned external to the wireless power transfer system  100 . 
     The first converting unit  104  is configured to receive the input power having the first DC voltage  112  from the power source  102 . Further, the first converting unit  104  is configured to operate at a determined switching frequency to convert the first DC voltage  112  of the input power to a first AC voltage  114 . Particularly, the control unit  106  may determine the switching frequency of the first converting unit  104  based on the electric load  132  coupled to the wireless power transfer system  100 . In one example, the control unit  106  may include a digital circuit or a processor that performs one or more functions based on pre-stored instructions or programs. Upon converting the first DC voltage  112  of the input power to the first AC voltage  114 , the first converting unit  104  is further configured to transmit the input power having the first AC voltage  114  to the contactless power transfer unit  108 . 
     The contactless power transfer unit  108  includes two or more coils or an array of coils  116  that are magnetically coupled to each other. The coils  116  are used for wirelessly transmitting the input power having the first AC voltage  114  from the first converting unit  104  to the second converting unit  110 . The details pertaining to transmitting the power using the coils  116  are explained in greater detail below with reference to  FIG. 2 . 
     The second converting unit  110  is electrically coupled to the contactless power transfer unit  108  via a switching unit  130 . Upon receiving the power having the first AC voltage  114  from the contactless power transfer unit  108 , the second converting unit  110  is configured to convert the power having the first AC voltage  114  to an output power having a second DC voltage  118 . Further, the second converting unit  110  is configured to transmit the output power having the second DC voltage  118  to the electric load  132 . In one example, the output power may be used for charging the electric load including one or more batteries that are coupled to the wireless power transfer system  100 . 
     Additionally, the wireless power transfer system  100  includes a sensor  120 , a first transceiver  122 , and a second transceiver  124  that together form a feedback loop  126 . The sensor  120  is used to sense the second DC voltage (output voltage)  118 . The feedback loop  126  is used to communicate a voltage signal (V o )  128  representative of the second DC voltage  118  from the sensor  120  to the control unit  106  via the first transceiver  122  and the second transceiver  124 . Further, the control unit  106  may be used to adjust or change the switching frequency of the first converting unit  104  based on the received voltage signal (V o )  128  to control or regulate the second DC voltage  118  across the electric load  132 . 
     However, since the voltage signal (V o )  128  is communicated using a wireless communication path between the first transceiver  122  and the second transceiver  124 , the control unit  106  may receive the voltage signal (V o )  128  after a certain time delay. In one embodiment, the delay may be in a range from about 1 millisecond to about 5 milliseconds. 
     The control unit  106  may not be able to timely control the second DC voltage  118  across the electric load  132  due to the delay in communicating the voltage signal (V o )  128 . As result, the second DC voltage  118  may increase above a critical value, which in turn may damage the second converting unit  110  and/or other components in the wireless power transfer system  100 . The critical value may be a voltage value above which the components in the wireless power transfer system  100  may be damaged. In one embodiment, the critical value may be in a range from about 400V to about 500V. 
     To overcome the issues related to increase of the second DC voltage  118  above a critical value, the exemplary wireless power transfer system  100  includes the switching unit  130  to protect the second converting unit  110  from damage. Particularly, the switching unit  130  is electrically coupled to the contactless power transfer unit  108  and the second converting unit  110 . The switching unit  130  is configured to decouple the second converting unit  110  from the contactless power transfer unit  108  if the second DC voltage  118  is greater than a first threshold value (V o Max). The first threshold value (V o Max) may be less than the critical value. In one embodiment, the first threshold value (V o Max) may be in a range from about 350V to about 450V. 
     The input power is not transmitted to the second converting unit  110  or the electric load  132  by decoupling the second converting unit  110  from the contactless power transfer unit  108 . As a result, the second DC voltage  118  across the electric load  132  may be reduced below the first threshold value (V o Max). The switching unit  130  is configured to prevent the second DC voltage  118  from attaining a critical value, which in turn protects the second converting unit  110  from damage. The protection of the second converting unit  110  is described in greater detail with reference to  FIG. 2 . 
     Furthermore, in one embodiment, the switching unit  130  may be used to regulate or control the second DC voltage  118  across the electric load  132 . If the second DC voltage  118  is greater than a voltage reference value (V o ref), the switching unit  130  is configured to regulate or control the second DC voltage  118  without decoupling the second converting unit  110  from the contactless power transfer unit  108 . The regulation of the second DC voltage  118  is described in greater detail with reference to  FIG. 3 . 
     Referring to  FIG. 2 , a schematic representation of a wireless power transfer system  200  in accordance with an embodiment of the present invention is depicted. The wireless power transfer system  200  is similar to the wireless power transfer system  100  of  FIG. 1 . The wireless power transfer system  200  is used to transmit an input power from a power source  202  to an electric load  232  such as one or more batteries in an electric or hybrid vehicle. 
     The wireless power transfer system  200  includes a first converting unit  204 , a control unit  206 , a contactless power transfer unit  208 , a second converting unit  210 , a switching unit  212 , a first transceiver  214 , and a second transceiver  216 . It may be noted that the wireless power transfer system  200  may include other components and may not be limited to the components shown in  FIG. 2 . 
     In the illustrated embodiment, the first converting unit  204  is electrically coupled to the power source  202  and configured to receive the input power having a first DC voltage  218  from the power source  202 . The first converting unit  204  includes a plurality of switches  220  and diodes  222  that are electrically coupled between an input terminal and an output terminal of the first converting unit  204 . In one example, the switches  220  may include electronic switches, such as MOSFETs or IGBTs. The plurality of switches  220  and the diodes  222  are arranged to form a DC-AC converter. 
     The switches  220  are activated and deactivated based on a switching frequency of the first converting unit  204  to convert the first DC voltage  218  of the input power to a first AC voltage  224 . Particularly, the control unit  206  is configured to determine the switching frequency of the first converting unit  204  based on the electric load  232  coupled to the wireless power transfer system  200 . Further, the control unit  206  is configured to send one or more gate signals  226  that are representative of the switching frequency to the plurality of switches  220  in the first converting unit  204  to convert the first DC voltage  218  of the input power to the first AC voltage  224 . The input power having the first AC voltage  224  is transmitted from the first converting unit  204  to the contactless power transfer unit  208 . 
     The contactless power transfer unit  208  is electrically coupled to the first converting unit  204  for receiving the input power having the first AC voltage  224 . The contactless power transfer unit  208  includes a primary coil  228  and a secondary coil  230 . The primary coil  228  is electrically coupled to the first converting unit  204 . In a similar manner, the secondary coil  230  is electrically coupled to the second converting unit  210 . The primary coil  228  and the secondary coil  230  are magnetically coupled to each other. 
     In addition to the primary coil  228  and the secondary coil  230 , the contactless power transfer unit  208  includes a field focusing coil  234  and a compensation coil  236 . The field focusing coil  234  is positioned between the primary coil  228  and the secondary coil  230 . The field focusing coil  234  is magnetically coupled to the primary coil  228  and the secondary coil  230 . In a similar manner, the compensation coil  236  is magnetically coupled to the secondary coil  230 . It may be noted that the contactless power transfer unit  208  may include two or more coils for transferring the power from the first converting unit  204  to the second converting unit  210 . 
     Further, the input power having the first AC voltage  224  from the first converting unit  204  is configured to excite the primary coil  228  and the field focusing coil  234  simultaneously. The magnetic field generated by the primary coil  228  is focused towards the secondary coil  230  via the field focusing coil  234 . The secondary coil  230  is configured to receive the magnetic field and convert the magnetic field to the input power having the first AC voltage  224 . The power having the first AC voltage  224  is then transmitted from the secondary coil  230  to the second converting unit  210 . In one embodiment, the field focusing coil  234  is electrically coupled to one or more resonators that are arranged in an array which are excited by the input power simultaneously to enhance the coupling between the primary coil  228  and the secondary coil  230 . The compensation coil  236  is configured to match an impedance of the contactless power transfer unit  208  with the second converting unit  210 . 
     The second converting unit  210  is configured to convert the power having the first AC voltage  224  to an output power having a second DC voltage  238 . Particularly, the second converting unit  210  includes a plurality of diodes, MOSFETs, or IGBTs  240  that are electrically coupled between an input terminal and an output terminal of the second converting unit  210 . The power having the second DC voltage  238  is transmitted to the electric load  232 . In one embodiment, the electric load  232  may be batteries that are electrically charged by using the power received from the second converting unit  210 . It may be noted that herein the terms “output voltage” and “second DC voltage” may be used interchangeably. 
     Additionally, the wireless power transfer system  200  includes a sensor  244 , a first transceiver  214 , and a second transceiver  216  that together form a feedback loop  242 . The feedback loop  242  is used for communicating load information and/or the second DC voltage information to the control unit  206 . More specifically, the sensor  244  is electrically coupled to the output terminal of the second converting unit  210  to determine the second DC voltage  238  across the electric load  232 . In one embodiment, the sensor  244  may be a voltage sensor. In such an embodiment, the sensor  244  is configured to transmit a voltage signal (V o )  246  that is representative of the determined second DC voltage  238  to the first transceiver  214 . 
     The first transceiver  214  includes an antenna  248  configured to transmit the voltage signal (V o )  246  towards an antenna  250  of the second transceiver  216 . In one embodiment, the first transceiver  214  may be positioned proximate to the electric load  232  and the second transceiver  216  may be positioned proximate to the first converting unit  204  or the power source  202 . The second transceiver  216  is configured to receive the voltage signal (V o )  246  transmitted by the first transceiver  214 . Further, the second transceiver  216  is configured to transmit the received voltage signal (V o )  246  to the control unit  206 . 
     The control unit  206  is configured to determine a change in the electric load  232  based on the voltage signal (V o )  246  representative of the second DC voltage  238 . In response to receiving the voltage signal (V o )  246 , the control unit  206  is configured to determine or adjust the switching frequency of the first converting unit  204 . Further, the control unit  206  is configured to send gate signals  226  that are representative of the switching frequency to the first converting unit  204  to control the first AC voltage  224  of the first converting unit  204 , which in turn controls the second DC voltage  238  across the electric load  232 . In other words, the control unit  206  is configured to control or regulate the second DC voltage  238  of the wireless power transfer system  200  based on the voltage signal (V o )  246  received via the feedback loop  242 . 
     Similar to the embodiment of  FIG. 1 , in order to overcome the issues related to increase of the second DC voltage  2388  above a critical value, the exemplary wireless power transfer system  200  includes the switching unit  212  configured to protect the second converting unit  210  from damage. The switching unit  212  includes a switch  252  and a controller  254 . The controller  254  is electrically coupled to the switch  252  and the sensor  244 . 
     In the illustrated embodiment, the switch  252  is electrically coupled across the second converting unit  210 . The switch  252  is activated if the switch  252  receives a first control signal from the controller  254 . Specifically, the switch  252  is activated or closed to short-circuit the secondary coil  230 , which in turn decouples the second converting unit  210  from the secondary coil  230 . Similarly, the switch  252  may be deactivated if the switch  252  receives a second control signal from the controller  254 . Specifically, the switch  252  is deactivated or opened to couple the secondary coil  230  to the second converting unit  210 . 
     The controller  254  includes a first comparator  256 , a second comparator  258 , and a flip-flop unit  260 . The first comparator  256  and the second comparator  258  is electrically coupled to an input terminal of the flip-flop unit  260 . An input terminal of the controller  254  is coupled to the first comparator  256  and the second comparator  258 . An output terminal of the controller  254  is coupled to the flip-flop unit  260 . 
     The controller  254  is configured to receive the voltage signal (V o )  246  that is representative of the second DC voltage  238  from the sensor  244 . Further, the received voltage signal (V o )  246  is transmitted to the first comparator  256  and the second comparator  258 . The first comparator  256  is configured to compare the second DC voltage  238  with a first threshold value (V o Max). If the second DC voltage  238  is greater than the first threshold value (V o Max), the first comparator  256  is configured to trigger the flip-flop unit  260  to generate the first control signal at the output terminal of the controller  254 . 
     Similarly, the second comparator  258  is configured to receive the voltage signal (V o )  246  that is representative of the second DC voltage  238 . Further, the second comparator  258  is configured to compare the received second DC voltage  238  with a second threshold value (V o Min). It should be noted herein that the second threshold value (V o Min) is less than the first threshold value (V o Max). If the second DC voltage  238  is less than the second threshold value (V o Min), the second comparator  258  is configured to trigger the flip-flop unit  260  to generate the second control signal at the output terminal of the controller  254 . 
     During normal operation of the wireless power transfer system  200 , the switch  252  is deactivated to couple the second converting unit  210  to the contactless power transfer unit  208 . The second DC voltage  238  across the electric load  232  is controlled or regulated by the control unit  206  based on the voltage signal (V o )  246  received from the sensor  244  via the first transceiver  214  and the second transceiver  216 . The controller  254  does not activate or close the switch  252  if the second DC voltage  238  is less than the first threshold value (V o Max). 
     In certain circumstances, if the full load  232  or a portion of the load  232  is disconnected or decoupled suddenly from the second converting unit  210 , the second DC voltage  238  across the load  232  may increase above the first threshold value (V o Max). The sensor  244  determines and send the voltage signal (V o )  246  that is representative of this second DC voltage  238  to the controller  254  and the first transceiver  214 . At the controller  254 , the first comparator  256  compares the second DC voltage  238  with the first threshold value (V o Max). If the second DC voltage  238  is greater than the first threshold value (V o Max), the first comparator  256  triggers the flip-flop unit  260  to generate the first control signal which is transmitted to the switch  252  to deactivate the switch  252 . As a result, the second converting unit  210  is decoupled from the contactless power transfer unit  208 . 
     Concurrently, the first control signal is transmitted from the controller  254  to the first transceiver  214 . Further, the first transceiver  214  transmits the voltage signal (V o )  246  received from the sensor  244  and the first control signal received from the controller  254  to the second transceiver  216 . The voltage signal (V o )  246  and the first control signal are further transmitted to the control unit  206 . 
     Upon receiving the voltage signal (V o )  246  and the first control signal, the control unit  206  determines that the switch  252  is activated in the wireless power transfer system  200  based on the received first control signal. As a result, the control unit  206  deactivates the first converting unit  204 . In one embodiment, the control unit  204  sends the gate signals  226  to the switches  220  in the first power converting unit  204  to deactivate or open the switches  220 . As a result, the first converting unit  204  is deactivated or suspended from transmitting the power to the contactless power transfer unit  208  and the second converting unit  210 . 
     Furthermore, after a predetermined time period, the control unit  206  sends a reset signal  262  to the second transceiver  216 , which is further transmitted to the first transceiver  214 . The first transceiver  216  sends the reset signal  262  to the flip-lop unit  260  in the controller  254 . In response to receiving the reset signal  262 , the flip-flip unit  260  resets and generates the second control signal at the output terminal of the controller  254 . The generated second control signal is transmitted to the switch  252  to deactivate or open the switch  252  so that the second converting unit  210  is coupled to the contactless power transfer unit  208  to permit the second converting unit  210  to continue supplying power having the second DC voltage  238  to the electric load  232 . 
     Concurrently, the generated second control signal at the controller  254  is transmitted to the first transceiver  214 . In addition to the second control signal, the first transceiver  214  receives the voltage signal (V o )  246  representative of the second DC voltage  238  across the load  232 . Further, the first transceiver  214  transmits the voltage signal (V o )  246  and the second control signal to the second transceiver  216 , which is further transmitted to the control unit  206 . 
     Upon receiving the voltage signal (V o )  246  and the second control signal from the second transceiver  216 , the control unit  206  determines whether the second DC voltage  238  is less than or equal to the first threshold value (V o Max). If the second DC voltage  238  is less than or equal to the first threshold value (V o Max), the control unit  206  sends the gate signals  226  to the switches  220  in the first converting unit  204  to activate the first converting unit  204 . Further, the control unit  206  adjusts or changes the switching frequency of the first converting unit  204  based on the second DC voltage  238  across the electric load  232 . In one embodiment, the control unit  206  adjusts or changes the switching frequency of the first converting unit  204  to regulate or control the second DC voltage  238  across the electric load  232 . If the second DC voltage  238  is greater than the first threshold value (V o Max), the control unit  206  waits for the predetermined time period to send another reset signal to the controller  254 . If the second DC voltage  238  continues to be greater than the first threshold value (V o Max) after transmitting the reset signal for a predetermined number of times, the control unit  206  deactivates the system  200 . 
     Accordingly, by employing the switching unit  212  and the control unit  206 , the second DC voltage  238  is prevented from increasing above the critical value. As a result, the second converting unit  210  is protected from damage even if the electric load  232  gets disconnected or decoupled from the wireless power transfer system  200 . 
     Referring to  FIG. 3 , a schematic representation of a wireless power transfer system  300  in accordance with another embodiment of the present invention. The wireless power transfer system  300  is similar to the wireless power transfer system  200  of  FIG. 2  except that a controller  302  in the switching unit  212  is configured to regulate or control the second DC voltage  238  (output voltage) of a second converting unit  210 . 
     During operation, if the electric load  232  gets disconnected from the wireless power system  300 , the second DC voltage  238  across the load  232  may increase above a voltage reference value (V o ref). It is required to control or regulate the second DC voltage  238  so that the second DC voltage  238  is not increased above a critical value. In one example, the voltage reference value (V o ref) is less than the critical value. 
     The sensor  244  determines the second DC voltage  238  across the electric load  232 . Further, the sensor  244  transmits a voltage signal (V o )  246  representative of the second DC voltage  238  to the controller  302 . At the controller  302 , the second DC voltage  238  is compared with the voltage reference value (V o ref). If the second DC voltage  238  is greater than the voltage reference value (V o ref), the controller  302  generates a control signal  304  having a determined duty cycle to control the switch  252 . In one embodiment, the controller  302  may determine or select the duty cycle using a look-up table. For example, if the second DC voltage  238  is 90 volts, a duty cycle of 0.75 corresponding to 90 volts is selected from the look-up table. In another example, if the second DC voltage  238  is 170 volts, a duty cycle of 0.5 corresponding to 170 volts is selected from the look-up table. In yet another example, if the second DC voltage  238  is 250 volts, a duty cycle of 0.25 corresponding to 250 volts is selected from the look-up table. 
     The controller  302  transmits the control signal  304  having the determined duty cycle to the switch  252  to regulate or control the second DC voltage  238  across the load  232 . Particularly, the control signal  304  includes switching pulses having the determined duty cycle. The switching pulses are transmitted to the switch  252  to regulate or control the second DC voltage  238  across the load  232 . 
     Concurrently, the voltage signal (V o )  246  is transmitted from the sensor  244  to the first transceiver  214 . Further, the first transceiver  214  transmits the voltage signal (V o )  246  to the second transceiver  216 , which in turn is transmitted to the control unit  206 . 
     At the control unit  206 , gate signals  226  are generated based on the second DC voltage  238 . Further, the control unit  206  transmit the gate signals  226  to the switches  220  in the first converting unit  204  to adjust or change the switching frequency of the first converting unit  204 . As a result, the first AC voltage  224  from the first converting unit  204  is regulated, which in turn controls or regulates the second DC voltage  238  across the load  232 . However, the regulation of the second DC voltage  238 , using the control unit  206 , occurs after the regulation of the second DC voltage, using the controller  302 . Hence, the controller  302  may perform faster regulation of the second DC voltage  238  compared to the regulation of the second DC voltage  238  by the control unit  206 . 
     Accordingly, the second DC voltage  238  across the load  232  is regulated or controlled by employing the switching unit  212  before the second DC voltage  238  reaches the critical value. As a result, the second converting unit  210  is prevented from damage even if the electric load  232  is disconnected from the wireless power transfer system  300 . 
     Referring to  FIG. 4 , a flow chart illustrating a method  400  for protecting the wireless power transfer system in accordance with aspects of the present invention is depicted. The method  400  is described with reference to the components of  FIGS. 1 and 2 . At step  402 , a first DC voltage of an input power is converted to a first AC voltage. A first converting unit is coupled to a power source for receiving the input power having the first DC voltage. The first converting unit is operated at a determined switching frequency to convert the first DC voltage of the input power to the first AC voltage. 
     Subsequently, at step  404 , the method includes receiving and transmitting the input power having the first AC voltage. Particularly, a contactless power transfer unit is electrically coupled to the first converting unit to receive the input power having the first AC voltage. The contactless power transfer unit transmits the input power having the first AC voltage to a second converting unit. Furthermore, at step  406 , the first AC voltage of the input power is converted to a second DC voltage. A second converting unit is electrically coupled to the contactless power transfer unit to receive the input power having the first AC voltage. Further, the second converting unit converts the first AC voltage of the input power to the second DC voltage. At step  408 , the input power having the second DC voltage is transmitted from the second converting unit to an electric load. In one embodiment, the electric load may be one or more batteries that are electrically charged using the input power having the second DC voltage received from the second converting unit. 
     At step  410 , the second converting unit is decoupled from the contactless power transfer unit if the second DC voltage across the electric load is greater than a first threshold value (V o Max). Specifically, a switching unit is used to decouple the second converting unit from the contactless power transfer unit. As a result, the second DC voltage across the electric load is reduced below the first threshold value (V o Max), thereby protecting the second converting unit from damage due to over voltage. Furthermore, if the determined second DC voltage is less than a second threshold value (V o Min), the switching unit couples the second converting unit to the contactless power transfer unit to continue supplying power having the second DC voltage to the electric load. 
     Referring to  FIG. 5 , a flow chart illustration a method for decoupling and coupling a second converting unit in a wireless power transfer system in accordance with an embodiment of the present invention is depicted. Specifically, the method  500  includes steps involved in the step  410  of  FIG. 4 . At step  502 , a voltage signal (V o ) representative of a second DC voltage across an electric load is transmitted by a sensor. More specifically, the sensor transmits the voltage signal (V o ) to a controller. Further, the sensor transmits the voltage signal (V o ) to a control unit via a first transceiver and a second transceiver. 
     Subsequently, at step  504 , the controller determines whether the voltage signal (V o ) representative of the second DC voltage is greater than a first threshold value (V o Max). If the voltage signal (V o ) representative of the second DC voltage is greater than the first threshold value (V o Max), the controller transmits a first control signal to a switch to activate or close the switch as depicted in step  506 . As a result, the second converting unit is decoupled from the contactless power transfer unit and thereby the second DC voltage across the load is reduced below the first threshold value (V o Max). More specifically, the second DC voltage is prevented from reaching a critical value that is greater than the first threshold value (V o Max). The critical value may be a voltage value above which the second converting unit may be damaged. Concurrently, the controller sends a first control signal to the control unit via the first transceiver and the second transceiver. 
     Furthermore, at step  508 , the controller determines whether the voltage signal (V o ) representative of the second DC voltage is less than a second threshold value (V o Min). If the voltage signal (V o ) representative of the second DC voltage is less than the second threshold value (V o Min), the controller sends a second control signal to the switch to deactivate or open the switch as depicted in step  510 . As a result, the second converting unit is coupled to the contactless power transfer unit to receive and supply the power to the electric load. 
     At step  512 , the control unit receives the voltage signal (V o ) and the first control signal. The control unit receives the voltage signal (V o ) from the sensor via the first transceiver and the second transceiver. The control unit receives the first control signal from the controller via the first transceiver and the second transceiver. 
     Subsequently, at step  514 , the control unit deactivates the first converting unit if the first control signal is received from the controller. The first converting unit is deactivated to prevent the supply of input power to the second converting unit. Furthermore, at step  516 , the control unit, transmits a reset signal to the controller via the first transceiver and the second transceiver after a predetermined time period. In response to receiving the reset signal, the controller generates the second control signal. Further, the controller sends the second control signal to the switch to deactivate or open the switch. As a result, the second converting unit is coupled to the contactless power transfer unit to receive and supply the power to the electric load at step  508 . 
     Concurrently, at step  518 , the controller transmits the second control signal to the control unit via the first transceiver and the second transceiver. Further, the sensor transmits the voltage signal (V o ) to the control unit via the first transceiver and the second transceiver. Subsequently, at step  520 , the control unit determines whether the voltage signal (V o ) representative of the second DC voltage is less than or equal to the first threshold value (V o Max). If the second DC voltage is less than or equal to the first threshold value (V o Max), the control unit transmits gate signals to activate the first converting unit. As a result, the input power is supplied to the second converting unit via the contactless power transfer unit. Further, the electric load receives the power having the second DC voltage from the second converting unit. As a result, one or more components in the wireless power transfer unit are protected from increase in the second DC voltage across the load. 
     Referring to  FIG. 6 , a flow chart illustrating a method for regulating an output voltage of a wireless power transfer system in accordance with an embodiment of the present invention is depicted. At step  602 , a first DC voltage of an input power is converted to a first AC voltage. Specifically, a first converting unit is coupled to a power source for receiving the input power having the first DC voltage. Further, the first converting unit is operated at a determined switching frequency to convert the first DC voltage of the input power to the first AC voltage. 
     Subsequently, at step  604 , the method includes receiving and transmitting the input power having the first AC voltage. Particularly, a contactless power transfer unit is electrically coupled to the first converting unit to receive the input power having the first AC voltage. Further, the contactless power transfer unit transmits the input power having the first AC voltage to a second converting unit. 
     Furthermore, at step  606 , the first AC voltage of the input power is converted to a second DC voltage. The second converting unit is electrically coupled to the contactless power transfer unit to receive the input power having the first AC voltage. Further, the second converting unit converts the first AC voltage of the input power to the second DC voltage. At step  608 , the input power having the second DC voltage is transmitted from the second converting unit to an electric load. In one embodiment, the electric load may be one or more batteries that are electrically charged by the input power having the second DC voltage received from the second converting unit. 
     In addition, at step  610 , the second DC voltage across the electric load is regulated if the second DC voltage across the electric load is greater than a voltage reference value (V o ref). A switching unit is electrically coupled to the second converting unit and configured to regulate the second DC voltage across the electric load. Particularly, a sensor coupled to an output terminal of the second converting unit is used to determine the second DC voltage across the electric load. Further, a controller which is coupled to the sensor, is used to generate a control signal having a determined duty cycle based on the second DC voltage. More specifically, the controller compares the second DC voltage with a voltage reference value (V o ref). If the second DC voltage is greater than the voltage reference value (V o ref), the controller determines or selects a duty cycle corresponding to the second DC voltage. Further, the controller generates the control signal having the selected or determined duty cycle. Thereafter, the controller feeds the control signal having the determined duty cycle to the switch to regulate the second DC voltage across the electric load to protect the second converting from damage due to over voltage. 
     In accordance with the exemplary embodiments discussed herein, the exemplary system and method facilitate to protect one or more components in the wireless power transfer system when the load is disconnected. Further, the exemplary system and method facilitate to control or regulate the output voltage when the load is disconnected. As a result, one or more components in the system are protected without decoupling the components from each other in the system. 
     While only certain features of the present disclosure 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 present disclosure.