Abstract:
A wireless energy transfer receiver includes an input configured to receive alternating current (AC) electric energy and an output configured to make available direct current (DC) electric energy. The receiver further includes a rectification component configured to convert the AC energy received at the input into DC energy available at the output, the DC energy made available as DC voltage; and a multiplication component configured to amplify a peak voltage of the AC energy received at the input, the DC voltage made available at the output correspondingly being higher than the peak voltage of the AC energy received at the input.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims benefit to U.S. provisional application 61/428,139 filed Dec. 29, 2010 entitled Voltage Multiplication for Increasing the Charging Power Received at a Wireless Receiver, the contents of which is incorporated herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    Energy transfer between two coupled inductors may occur through the use of a transmitter generating an oscillating magnetic field and a receiver converting the oscillating magnetic field into electric power. In many energy transfer systems the conversion is from oscillating magnetic field into a direct current (DC) voltage. 
         [0003]    The DC voltage is at least in part a function of magnetic field intensity and the coupling between the inductors. If the magnetic field intensity decreases or the coupling between the inductors decreases, then DC voltage may also decrease. If the DC voltage drops below the minimum voltage required by the load then energy transfer ceases. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0004]      FIG. 1  illustrates an exemplary wireless energy transfer system. 
           [0005]      FIG. 2  illustrates a representative exemplary implementation of a wireless energy transfer system. 
           [0006]      FIG. 3  illustrates another representative exemplary implementation of a wireless energy transfer system. 
           [0007]      FIG. 4  illustrates an exemplary circuit for voltage doubling. 
           [0008]      FIG. 5  illustrates another exemplary circuit for voltage doubling. 
           [0009]      FIG. 6  illustrates another exemplary circuit for voltage doubling. 
           [0010]      FIG. 7  illustrates another exemplary circuit for voltage doubling. 
           [0011]      FIG. 8A  illustrates one exemplary wireless energy transfer system in which a voltage doubler rectifier is included in the receiver. 
           [0012]      FIG. 8B  illustrates the effective circuit of an exemplary receiver including a voltage doubler rectifier when a voltage source is in a negative phase of its cycle. 
           [0013]      FIG. 8C  illustrates the effective circuit of an exemplary receiver including a voltage doubler rectifier when a voltage source is in a positive phase of its cycle. 
           [0014]      FIG. 9A  illustrates an exemplary implementation of a receiver which adaptively enables and disables a voltage multiplication component of a voltage multiplier rectifier circuit. 
           [0015]      FIG. 9B  illustrates an exemplary implementation of an adaptive receiver in a first mode. 
           [0016]      FIG. 9C  illustrates an exemplary implementation of an adaptive receiver in a second mode. 
           [0017]      FIG. 10  illustrates another exemplary implementation of a receiver with rectification multiplication circuitry. 
           [0018]      FIG. 11  illustrates an exemplary synchronous rectification circuit that may be used as a rectification multiplication circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    A wireless energy transfer system may include coupled inductors or coils, a transmitter capable of generating a high-intensity oscillating magnetic field, and a receiver capable of converting the magnetic field into usable electric power. The electric power is provided to a load. 
         [0020]    The conversion of the magnetic field into usable electric power may include a rectification process if the load requires a continuous voltage source. 
         [0021]    In many systems the load requires a minimum voltage for proper operation. However, as the magnetic field intensity and/or the coupling between the inductors decreases, the voltage to the load may also decrease to a value below the minimum operational voltage of the load. It would be beneficial in some circumstances to have the capability on the receiver side to increase the voltage to the load so that the voltage to the load exceeds the minimum operational voltage requirements of the load. 
         [0022]    Additionally, the capability on the receiver side to increase the voltage to the load would beneficially allow for the transmitter to at least one of (i) generate a lower intensity magnetic field, (ii) allow for lesser coupling between the coils, and (iii) design the receiver coil with fewer turns, therefore saving cost and reducing losses. 
         [0023]      FIG. 1  illustrates an exemplary wireless energy transfer system  100  including a transmitter  105 , a receiver  110 , a load  115 , and coils  120  and  125 . Transmitter  105  provides a magnetic field at coil  120 , which is magnetically coupled to coil  125 . Receiver  110  converts the magnetic field coupled on coil  125  to electric power provided to load  115 . 
         [0024]    Receiver  110  includes a conversion component  130 , which further includes a rectification component  135  and a multiplication component  140 . Components  130 ,  135 , and  140  each represent at least one of or a combination of circuitry, firmware, and software that perform the underlying function of the respective component. Circuit elements of rectification component  135  and a multiplication component  140  may be implemented within one circuit including within one integrated circuit or may be implemented within separate circuits. Receiver  110  may include digital or analog circuits or a combination of digital and analog circuits. Components  130 ,  135 , and  140  are described further below. 
         [0025]    Receiver  110  is connected to load  115  at least via connections  145  and  150 . Power provided to load  115  is represented in  FIG. 1  as a potential voltage difference Vout between a node ‘a’ on connection  145  and a node ‘b’ on connection  150 . 
         [0026]      FIG. 2  illustrates a representative exemplary implementation of a system  100  in the form of a circuit diagram, system  100  including a transmitter  105 , a coil  120 , a coil  125 , a conversion component  130  with rectification component  135 , and a load  115 , as identified below the circuit diagram. 
         [0027]    Components of transmitter  105  include a voltage source  205  and a transmitter resonant network  210 . Coil  120  has self-inductance L 1 . A high-intensity oscillating magnetic field is established within transmitter resonant network  210  and coil  120  by applying voltage source  205  to transmitter resonant network  210 . 
         [0028]    The magnetic field is coupled to coil  125  having self-inductance L 2 . The coupling coefficient between coils  120  and  125  is represented as ‘k’ on the circuit diagram. 
         [0029]    Coil  125  is connected to a receiver resonator network  220 . As the magnetic field is coupled onto coil  125  it is converted into a high voltage oscillating signal within receiver resonator network  220  and coil  125 . 
         [0030]    A rectifier  225  converts the oscillating signal into a direct current (DC) voltage. A capacitor  230  is used to reduce ripple in the DC voltage, and the DC voltage, Vout in  FIG. 2 , may be applied to a load. 
         [0031]    The circuitry illustrated in  FIG. 2  is representative. Many other topologies are possible for implementing voltage source  205 , resonator networks  210  and  220 , rectifier  225 , and capacitor  230 . Further, one or both of coils  120  and  125  may represent multiple coils. Coils  120  and  125  may be different sizes and shapes. Load  115 , although represented by resistance R, may be a complex load. 
         [0032]      FIG. 3  is a simplified equivalent of the circuit of  FIG. 2 . The simplification is based on an assumption that the higher order harmonics of the square-wave voltage at the input of the rectifier are suppressed by the narrow-band filter formed by receiver resonant network  220  and coil  125 . Only the fundamental sinusoidal component is taken into account in determining an equivalent circuit. The assumption as stated allows rectifier  225 , capacitor  230 , and load  115  to be approximated by a resistor R_eq=R·8/π 2 . 
         [0033]    Vout applied to the load is then described by equation (1), where ω is the operating frequency of the circuit expressed in radians per second (rad/s). 
         [0000]        V out —   eq ( t )= V out·4/π·sin(ω t )   (1)
 
         [0034]    It can be shown that Vout is a strong function of the transmitter voltage source, such as voltage source  205  in  FIG. 2 . Vout can also be shown to be a strong function of the coupling between coils  120  and  125 , for example as represented by coefficient k in  FIG. 2 . Thus, the amplitude of Vout varies with the amplitude of the magnetic field and the strength of the coil coupling. 
         [0035]    The magnetic field may be affected by the number and type of objects near the transmitter, the tuning of the resonant circuit, and the stability and efficiency of the voltage source, to name a few influencing factors. The coupling between the coils may be affected by distance between the coils, orientation of the coils with respect to each other, geometry of the coils, size difference between the coils, and the medium in the space between the coils (e.g., air, metal housing, and magnetic materials), to name a few influencing factors. 
         [0036]    As the magnetic field intensity decreases and/or the coupling between the coils weakens the magnitude of Vout decreases. When Vout drops below the minimum operational voltage required by the load, energy transfer ceases. 
         [0037]    Much research has been performed with the goal of increasing magnetic field intensity at the transmitter or increasing coupling between the coils of the transmitter and receiver. However, many influences affect magnetic field intensity and coupling in an actual user environment. Thus, even for a system in which the transmitter is designed to ideally generate a high intensity magnetic field and the system is designed to ideally achieve a strong coupling between the coils, the actual energy transfer predicted by the ideal design may not occur. 
         [0038]    As can be seen, there are many ways in which even a well-designed system may not effectively transfer energy to the receiver. 
         [0039]    It would therefore be desirable to provide for a multiplication of the voltage at the receiver. Not only would voltage multiplication at the receiver allow the system to perform effectively in an actual environment but also may allow the design requirements of the system to be relaxed, and may further allow the performance of the system to be improved with little or no change to the transmitter. 
         [0040]    A receiver including voltage multiplication may allow, for example, a lower transmitter source voltage, a greater distance between transmitter and receiver, and misalignment of the transmitting and receiving devices. Additionally or alternatively, because multiplication of the voltage at the receiver allows for weaker coupling between the coils, the coils may be smaller and/or may be designed using less costly material. 
         [0041]    Having identified the need for and benefit of voltage multiplication at the receiver, a suitable multiplier is selected. Referring again to  FIG. 1 , conversion component  130  may include rectification component  135  and multiplication component  140 . As mentioned above, rectification component  135  and multiplication component  140  may be implemented within one circuit and may share circuit elements, or may be implemented separately. Combination voltage multiplier and rectifier circuits may allow for a reduced overall circuit element count, which in turn may allow for reduced size and/or cost. Representative examples of combination voltage multiplier and rectification circuits are illustrated in  FIGS. 4-7 . 
         [0042]      FIG. 4  illustrates an exemplary Villard circuit. A Villard circuit is a voltage doubler circuit with rectification. The capacitor in the circuit of  FIG. 4  may also be used as resonant capacitor for the receiver coil, effectively limiting the rectifier to a simple diode. In the Villard circuit, the capacitor charges during negative phases of the coil voltage to the peak voltage of the negative phase. Effectively, the capacitor voltage provides a direct current (DC) offset for the coil voltage approximately equal to the absolute value of the peak voltage of the negative phase. The output voltage Vout of a Villard circuit oscillates between zero and roughly double the positive peak coil voltage. 
         [0043]    Large voltage swings at Vout such as from a Villard circuit may be difficult or impossible for a load to manage. There are a number of voltage multiplier circuits that reduce or minimize voltage ripple by using additional components. Illustrative examples are provided in  FIGS. 5-7 . 
         [0044]      FIG. 5  illustrates an exemplary Greinacher circuit for voltage doubling, described below. 
         [0045]      FIG. 6  illustrates an exemplary Delon voltage doubler circuit. One capacitor is charged during negative cycle phases and one capacitor is charged during positive cycle phases, each capacitor charged to the peak value of its respective phase. Vout is the sum of the voltages on the two capacitors, roughly the positive phase peak voltage plus the absolute value of the negative phase peak voltage. 
         [0046]      FIG. 7  illustrates another exemplary voltage doubler circuit, similar to the circuit of  FIG. 6  but with a split coil. Both capacitors are charged during both phases, reducing the ripple on the output voltage Vout. 
         [0047]    Many other circuit topologies may be implemented to multiply the voltage applied at Vout, not limited to voltage doublers. Further, multipliers may be cascaded. Different circuit topologies may include different filtering mechanisms to shape the voltage at Vout as desired. 
         [0048]      FIG. 8A  illustrates one exemplary wireless energy transfer system in which a Greinacher voltage doubler rectifier  805  as illustrated in  FIG. 5  is included in the receiver.  FIGS. 8B and 8C  provide a simplified explanation of the voltage doubling function of the Greinacher circuit. 
         [0049]      FIG. 8B  illustrates the voltage across the receiver coil as a voltage source Vin that is in a negative phase of its cycle with peak voltage −Vp. Current flows into receiver  110  as shown by arrow  810 . Diode  815  is forward biased and begins to conduct, and develops a forward bias voltage Vd. Capacitor  820  is charged from the current flowing through diode  815  to a voltage of amplitude Vp−Vd, biased as shown in  FIG. 8B . Near the end of the negative phase of the cycle diode  815  stops conducting, leaving capacitor  820  charged to Vp−Vd. Reciever coil voltage Vin then transitions to a positive phase of its cycle as illustrated in  FIG. 8C . 
         [0050]      FIG. 8C  illustrates Vin as positive, which establishes a forward bias on diode  830  so that diode  830  begins to conduct and develops a forward bias voltage Vd as shown. Current flows as illustrated by arrow  835 . Capacitor  840  begins to charge from the series connection of coil voltage Vin and capacitor  820  which still is charged to approximately Vp−Vd. In the simple case where the peak negative and positive voltages of Vin are equal, capacitor  840  charges to a maximum voltage of (Vp+(Vp−Vd)−Vd)=2Vp−2Vd. In this way capacitor  840  is charged to roughly double the peak input voltage. The capacitor  840  voltage is Vout provided to the load. 
         [0051]    Although the Greinacher circuit implementation is illustrated and described in detail, other voltage multipliers or multiplier/rectifiers may be used instead. 
         [0052]    The use of voltage multiplier circuits allows receiver  110  to be placed at greater distances before the load voltage drops below usable voltage levels. However, when a voltage-multiplied receiver  110  is then placed closer to a transmitter  105  the receiver  110  circuitry may be subjected to higher voltage stresses. In such a situation it is possible that the voltage on a circuit element may exceed the element&#39;s voltage rating, causing the element and thus receiver  110  to operate undesirably. To avoid this circumstance receiver  110  may be designed to withstand high voltages. However, high voltage designs may be cost, size, or otherwise prohibitive. 
         [0053]    It would therefore be advantageous to have the capability to enable voltage multiplication at receiver  110  only when needed, or conversely to disable voltage multiplication at receiver  110  when close to a transmitter  105 . The receiver  110  circuitry may then be designed for lower voltages. 
         [0054]      FIG. 9A  illustrates an exemplary implementation of a receiver  110  which adaptively enables and disables a voltage multiplication component  140  of a voltage multiplier rectifier circuit. In the example of  FIG. 9  receiver  110  includes a switching circuit  905  with a switch  910  and controller  915 . Switch  910  may be any semiconductor or other switching device and is illustrated as a field effect transistor (FET) merely for convenience. A controller  915  monitors the voltage at a point within the receiver, and turns switch  910  on or off according to the monitored voltage, as described below. Controller  915  may include hysteresis such that the voltage must cross a first voltage threshold for controller  915  to turn switch  915  on, and must cross a second threshold for controller  915  to turn switch  915  off. 
         [0055]    Monitoring of the voltage may be performed by a separate circuit outside of the receiver  110  circuitry. For example, in a smart phone there may be a voltage monitoring circuit that monitors voltages at various locations within the circuitry of the smart phone, and one such monitoring location may be at receiver  110 . In the smart phone example, a processor may evaluate the voltage measurements made by the monitoring circuit and provide signals according to the evaluation. One such signal may be an indication provided to controller  915  to turn switch  910  on or off. Other implementations are also possible. For example, controller  915  may be one circuit on a receiver  110  integrated circuit chip that performs voltage monitoring and controls switch  910 . 
         [0056]    The receiver of  FIG. 9A  further includes diodes  920 ,  925 ,  930 , and  935 , and capacitors  940  and  945 . These circuit elements are discussed with respect to  FIGS. 9B and 9C . 
         [0057]      FIG. 9B  represents the receiver of  FIG. 9A  when switch  910  is turned on. With switch  910  on, diode  930  is short-circuited. Diode  925  is not used for rectification or multiplication when switch  910  is turned on. The effective rectification multiplication circuit includes only diodes  920  and  935  and capacitors  940  and  945 , and is recognizable as a Greinacher circuit that roughly doubles the peak input voltage as discussed above. 
         [0058]      FIG. 9C  represents the receiver of  FIG. 9A  when switch  910  is turned off. With switch  910  off, receiver  110  provides rectification with no multiplication. When the voltage across the receiver coil is in a negative phase, diodes  925  and  935  conduct, charging capacitor  945  to some voltage less than the absolute value of the receiver coil negative peak voltage. When the voltage across the receiver coil is in a positive phase, diodes  920  and  930  conduct, charging capacitor  945  to some voltage less than the receiver coil positive peak voltage. The voltage on capacitor  945  depends at least in part on the ratio of the capacitance of capacitors  940  and  945 . 
         [0059]    In some implementations, an active rectifier topology is used such that, for example, metal oxide semiconductor FETs (MOSFETs) may be used to replace one or more of diodes  920 ,  925 ,  935 , and  930 . In such implementations the adaptive multiplication may be implemented with potentially no additional cost. 
         [0060]      FIG. 10  illustrates another exemplary implementation of a receiver  110  with rectification multiplication circuitry. In this example, receiver  110  includes a rectification circuit as described above with respect to  FIG. 9C  and also includes a switch  1005  (Qaux) that provides the multiplication function. 
         [0061]    Without switch  1005 , receiver  110  is a rectifier as described above. When switch  1005  is closed, the receiver coil and capacitor  1010  form a resonant tank circuit. The quality factor of this resonant tank is very high and after a few cycles a large amount of energy is stored in the resonant tank. During the time switch  1005  is closed capacitor  1015  delivers power to the load. 
         [0062]    When switch  1005  is opened from a closed position the energy stored in the resonant tank gets transferred to capacitor  1015 . Thus, the voltage across capacitor  1015 , load voltage Vout, increases. 
         [0063]    The switching frequency of switch  1005  may be independent of the resonant frequency of the transmitter and receiver circuits and may be chosen to achieve a certain regulation accuracy and output voltage ripple. 
         [0064]    To minimize switching losses, switch  1005  may be, for example, switched on at zero voltage and off at zero current. 
         [0065]      FIG. 11  illustrates an exemplary synchronous rectification circuit that may be used as a rectification multiplication circuit similar to the circuit of  FIG. 10 . Receiver  110  in  FIG. 11  includes switches  1105 ,  1110 ,  1115 , and  1120 , one switch for each diode in a full wave rectifier. In this manner, the voltage drop across the diodes in forward bias mode is eliminated. 
         [0066]    In the synchronous rectification circuit of  FIG. 11 , if switches  1115  and  1120  are closed (shorting diodes Q 2  and Q 4 , respectively) then the effective circuit is substantially similar to the circuit of  FIG. 10  with switch  1005  closed. The circuit of  FIG. 11  may operate in a voltage multiplication mode by closing switches  1115  and  1120  (or switches  1105  and  1110 ) to charge the resonant tank, then opening switches  1115  and  1120  (or switches  1105  and  1110 ) to charge capacitor  1130 . While capacitor  1130  is charging, synchronous operation of switches  1105 ,  1110 ,  1115 , and  1120  may occur as described above. Thus, the synchronous rectification circuit of  FIG. 11  may also be used to provide for multiplication with little or no additional cost. 
         [0067]    An active rectifier topology may be used such for one or more of the circuits described above. For example, metal oxide semiconductor FETs (MOSFETs) may be used to replace one or more diodes. 
       CONCLUSION 
       [0068]    A receiver has been described that improves wireless energy transfer by providing the capability of multiplication of the receiver coil voltage. Such a receiver provides improved performance and may reduce the price of wireless energy transfer systems. The multiplication capability of the receiver may be adaptively turned on and off. A plurality of exemplary implementations has been provided to illustrate a few of the possible topologies that enable multiplication within the receiver. 
         [0069]    The above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the technologies discussed herein, and that the disclosed systems and methods will be incorporated into such future embodiments. In sum, it should be understood that the invention is capable of modification and variation. 
         [0070]    All terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those knowledgeable in the technologies described herein unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary.