PATENT DOCUMENT

Publication Number: US-12184111-B2
Application Number: US-202318154383-A
Country: US
Kind Code: B2

Title: Frequency management for wireless power transfer

Abstract:
A wireless power transmitter can include a coil, an inverter coupled to the coil, and control circuitry coupled to the inverter that, responsive to receiving a burst request pulse from a wireless power receiver, initiates inverter operation, driving the coil and powering the receiver. The control circuitry can operate inverter switches so bandwidth of the wireless power transfer signal falls within a specified range by: (a) extending a minimum on time of the switches, (b) modifying pulse width modulation (PWM) drive signals supplied to the switches to shape a coil current burst envelope, and/or (c) modifying PWM signal amplitude supplied to the switches. Modifying the PWM drive signals can include using a symmetrical PWM scheme in which the positive and negative pulses are symmetrical in width on a cycle-by-cycle basis or using a complementary PWM scheme in which the positive and negative pulse widths are complementary on a cycle-by-cycle basis.

Claims:
The invention claimed is: 
     
       1. A wireless power transmitter comprising:
 a wireless power transfer coil; 
 an inverter coupled to the wireless power transfer coil; and 
 control circuitry coupled to the inverter that, responsive to receiving a request from a wireless power receiver, initiates operation of the inverter to drive the wireless power transfer coil, thereby delivering a wireless power transfer signal to the wireless power receiver; 
 wherein the control circuitry operates one or more switching devices of the inverter to deliver the wireless power transfer signal to the wireless power receiver, wherein bandwidth of the wireless power transfer signal is controlled to fall within a specified bandwidth range by extending a minimum on time of each pulse of the one or more switching devices during operation of the inverter. 
 
     
     
       2. The wireless power transmitter of  claim 1  wherein the control circuitry operates one or more switching devices of the inverter to deliver power to the wireless power receiver such that the bandwidth of the wireless power transfer signal falls within the specified bandwidth range by modifying drive signals supplied to the switching devices to shape a coil current burst envelope. 
     
     
       3. The wireless power transmitter of  claim 2  wherein the control circuitry modifies the drive signals supplied to the switching devices to shape the coil current burst envelope using a symmetrical pulse width modulation switching scheme in which the inverter-generated positive and negative pulses are symmetrical in width on a cycle-by-cycle basis. 
     
     
       4. The wireless power transmitter of  claim 2  wherein the control circuitry modifies drive signals supplied to the switching devices to shape the coil current burst envelope using a complementary pulse width modulation switching scheme in which the inverter-generated positive and negative pulse widths are complementary on a cycle-by-cycle basis. 
     
     
       5. The wireless power transmitter of  claim 1  wherein the control circuitry operates one or more switching devices of the inverter to deliver power to the wireless power receiver such that the bandwidth of the wireless power transfer signal falls within the specified bandwidth range by modifying an amplitude of pulse width modulation signals supplied to the switching devices. 
     
     
       6. A method of operating a wireless power transmitter in a burst mode, the method comprising:
 receiving a request from a wireless power receiver; 
 responsive to the request, operating one or more switching devices of the transmitter during an on time; and 
 subsequent to the on time, idling the one or more switching devices during an off time; 
 wherein operating one or more switching devices of the transmitter during an on time comprises operating the one or more switching devices to constrain electromagnetic emissions from the wireless power transmitter within a specified bandwidth range by extending a minimum on time of each pulse of the one or more switching devices during operation. 
 
     
     
       7. The method of  claim 6  wherein operating the one or more switching devices to constrain electromagnetic emissions from the wireless power transmitter within the specified bandwidth range comprises modifying drive signals supplied to the switching devices to shape a coil current burst envelope. 
     
     
       8. The method of  claim 7  wherein modifying the drive signals supplied to the switching devices to shape the coil current burst envelope comprises using a symmetrical pulse width modulation switching scheme in which the inverter-generated positive and negative pulses are symmetrical in width on a cycle-by-cycle basis. 
     
     
       9. The method of  claim 7  wherein modifying the drive signals supplied to the switching devices to shape the coil current burst envelope comprises using a complementary pulse width modulation switching scheme in which the inverter-generated positive and negative pulse widths are complementary on a cycle-by-cycle basis. 
     
     
       10. The method of  claim 7  wherein modifying the drive signals supplied to the switching devices to shape a coil current burst envelope comprises modifying an amplitude of pulse width modulation signals supplied to the switching devices. 
     
     
       11. A wireless power transmitter comprising:
 a wireless power transfer coil; 
 an inverter comprising a plurality of switching devices coupled to the wireless power transfer coil; and 
 control circuitry that drives the plurality of switching devices; to cause a frequency bandwidth of a wireless power transfer signal to fall within a predetermined range by extending a minimum on time of each pulse of the plurality of switching devices during operation of the inverter. 
 
     
     
       12. The wireless power transmitter of  claim 11  wherein the control circuitry employs a symmetrical pulse width modulation scheme to shape a burst current envelope such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range. 
     
     
       13. The wireless power transmitter of  claim 12  wherein the symmetrical pulse width modulation scheme includes generating positive and negative pulses that are symmetrical in width on a cycle-by-cycle basis. 
     
     
       14. The wireless power transmitter of  claim 11  wherein the control circuitry employs a complementary pulse width modulation scheme to shape a burst current envelope such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range. 
     
     
       15. The wireless power transmitter of  claim 14  wherein the complementary pulse width modulation scheme includes generating positive and negative pulses having complementary widths on a cycle-by-cycle basis. 
     
     
       16. The wireless power transmitter of  claim 11  wherein the control circuitry employs an amplitude modulation scheme to shape a burst current envelope such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 17/644,005 filed Dec. 31, 2021, entitled “Frequency Management for Wireless Power Transfer”; which claims priority to U.S. Provisional Application No. 63/261,541, filed Sep. 23, 2021, entitled “Occupied Bandwidth Reduction for Wireless Power Transmitters,” the disclosure of which is incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     Wireless power transfer, in which power is delivered via magnetic/inductive coupling between a power transmitter (PTx) and a power receiver (PRx), is useful for powering battery powered electronic devices. In some applications, burst mode wireless power transfer may be provided to enhance operating efficiency. Bursty operation of wireless power transmitters may result in undesired electromagnetic emissions. 
     SUMMARY 
     A wireless power transmitter can include a wireless power transfer coil, an inverter coupled to the wireless power transfer coil, and control circuitry coupled to the inverter that, responsive to receiving a burst request pulse from a wireless power receiver, initiates operation of the inverter to drive the wireless power transfer coil, thereby delivering power to the wireless power receiver. The control circuitry can operate one or more switching devices of the inverter to deliver power to the wireless power receiver such that a bandwidth of the wireless power transfer signal falls within a specified bandwidth range. The control circuitry can operate one or more switching devices of the inverter to deliver power to the wireless power receiver such that a bandwidth of the wireless power transfer signal falls within the specified bandwidth range by extending a minimum on time of the switches. The control circuitry can operate one or more switching devices of the inverter to deliver power to the wireless power receiver such that the bandwidth of the wireless power transfer signal falls within the specified bandwidth range by modifying drive signals supplied to the switching devices to shape a coil current burst envelope. The control circuitry can modify the drive signals supplied to the switching devices to shape the coil current burst envelope using a symmetrical pulse width modulation switching scheme in which the inverter-generated positive and negative pulses are symmetrical in width on a cycle-by-cycle basis. The control circuitry can modify the drive signals supplied to the switching devices to shape the coil current burst envelope using a complementary pulse width modulation switching scheme in which the inverter-generated positive and negative pulse widths are complementary on a cycle-by-cycle basis. The control circuitry can operate one or more switching devices of the inverter to deliver power to the wireless power receiver such that the bandwidth of the wireless power transfer signal falls within the specified bandwidth range by modifying an amplitude of pulse width modulation signals supplied to the switching devices. 
     A method of operating a wireless power transmitter in a burst mode can include receiving a burst request pulse from a wireless power receiver; responsive to the burst request pulse, operating one or more switching devices of the transmitter during an on time; and subsequent to the on time, idling the one or more switching devices during an off time. Operating one or more switching devices of the transmitter during an on time can include operating the one or more switching devices to constrain electromagnetic emissions from the wireless power transmitter within a specified bandwidth range. Operating the one or more switching devices to constrain electromagnetic emissions from the wireless power transmitter within the specified bandwidth range can include extending the on time. Operating the one or more switching devices to constrain electromagnetic emissions from the wireless power transmitter within the specified bandwidth range can include modifying drive signals supplied to the switching devices to shape a coil current burst envelope. Modifying the drive signals supplied to the switching devices to shape the coil current burst envelope can include using a symmetrical pulse width modulation switching scheme in which the inverter-generated positive and negative pulses are symmetrical in width on a cycle-by-cycle basis. Modifying the drive signals supplied to the switching devices to shape the coil current burst envelope comprises using a complementary pulse width modulation switching scheme in which the inverter-generated positive and negative pulse widths are complementary on a cycle-by-cycle basis. Modifying the drive signals supplied to the switching devices to shape a coil current burst envelope can include modifying an amplitude of pulse width modulation signals supplied to the switching devices. 
     A wireless power transmitter can include a wireless power transfer coil, an inverter comprising a plurality of switching devices coupled to the wireless power transfer coil, and control circuitry that provides drive signals to the plurality of switching devices. The drive signals can be controlled such that the frequency bandwidth of the wireless power transfer signal falls within a predetermined range. The control circuitry can extend a minimum on time during which the plurality of switching devices are operated such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range. The control circuitry can employ a symmetrical pulse width modulation scheme to shape a burst current envelope such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range. The symmetrical pulse width modulation scheme can include generating positive and negative pulses that are symmetrical in width on a cycle-by-cycle basis. The control circuitry can employ a complementary pulse width modulation scheme to shape a burst current envelope such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range. The complementary pulse width modulation scheme can include generating positive and negative pulses having complementary widths on a cycle-by-cycle basis. The control circuitry can employ an amplitude modulation scheme to shape a burst current envelope such that the frequency bandwidth of the wireless power transfer signal falls within the predetermined range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a high level schematic of a wireless power transfer system. 
         FIG.  2    illustrates burst mode operation of a WPT system, showing the rectifier output voltage. 
         FIG.  3    illustrates an exemplary burst envelope and corresponding frequency spectrum. 
         FIG.  4    illustrates an exemplary improved burst envelope and corresponding frequency spectrum. 
         FIG.  5    illustrates an exemplary burst envelope with further improved performance. 
         FIG.  6    illustrates a high level schematic of an exemplary wireless power transfer system. 
         FIG.  7    illustrates a first envelope shaping technique for improving performance. 
         FIG.  8    illustrates a second envelope shaping technique for improving performance. 
         FIG.  9    illustrates a third envelope shaping technique for improving performance. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure&#39;s drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose. 
     Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a given drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
       FIG.  1    illustrates a high level schematic of a wireless power transfer system  100 . The left side of the figure illustrates a power transmitter (PTx)  103 , which receives an input voltage Vin and transmits energy to a receiver via magnetic induction, i.e., by coupling between transmit and receive coils represented by inductors L 1  and L 2 , respectively. (Each coil/inductor also has a corresponding intrinsic/parasitic resistance: R 1 /R 2 . These are illustrated in the schematic of  FIG.  1    but are not separate physical components.) The right side of the figure depicts a power receiver (PRx)  105  that receives power via the aforementioned inductive coupling and delivers power to a load depicted by current source Iload. An input voltage Vin is supplied to inverter  102 . Inverter  102  generates an AC output having a predetermined frequency and a magnitude that is determined by input voltage Vin, which may be regulated by a separate regulator (not shown). This AC output voltage of inverter  102  is provided the transmit coil, represented by inductor L 1 , which is magnetically coupled a corresponding receive coil, represented by inductor L 2 . This results in energy transfer to the PRx  105 . PRx  105  includes a receive coil, represented by inductor L 2 , which has a voltage induced therein by magnetic induction via transmit coil L 1 . This AC voltage may be provided to a rectifier  106 , discussed in greater detail below, that converts the received AC voltage to an output DC voltage (Vrect) that may be supplied to a load. The wireless power transfer system  100  may include additional components, such as transmitter tuning capacitor Cpri and receiver tuning capacitor C 2  that may be used to tune the resonant frequency of the transmit and receive circuits to improve operating efficiency of the system. 
     In the illustrated embodiment, inverter  102  is a full bridge inverter made up of four switching devices Q 1 -Q 4 , although other inverter topologies could be used as appropriate for a given application. Also depicted at a high level is PWM controller  108 , which provides pulse width modulation signals to the switching devices Q 1 -Q 4  to generate a desired output voltage and/or current. These switching devices are illustrated as MOSFETs (metal-oxide-semiconductor field effect transistors), though other types switching devices (including, for example, IGBTs (insulated gate bipolar transistors), junction field effect transistors (JFETs), etc. could be used as appropriate for a given embodiment. Likewise, any suitable semiconductor technology, such as silicon, silicon carbide (SiC), gallium nitride (GaN), could be used depending on the specific application. The same applies to all other switching devices (including diodes) discussed in the present application. Switching devices Q 1 -Q 4  may be alternately switched to connect an input DC voltage (e.g., from boost regulator  108 ) to the transmit winding L 1 , producing an AC voltage that may be coupled to the PRx as described above. 
     Operation of inverter  102  will induce an AC voltage in magnetically coupled PRx receiver coil L 2 . This AC voltage may be coupled to a rectifier  106 . In the illustrated embodiment, rectifier  106  is a full bridge active rectifier made up of four switches Q 5 -Q 7 . Although illustrated as MOSFET switches, other rectifier types, constructed using any suitable semiconductor technology, could also be used. These alternative configurations can provide for increased operating efficiency in some applications. 
     Operating a wireless power transfer system in a burst mode can address inefficiencies associated with at the system under certain loading conditions. In burst mode, power is transmitted in short bursts instead of continuously. Thus, a burst can include one or more AC pulses from the inverter. Following the one or more burst pulses, there may be an intervening time period during which no AC power is transmitted. This intervening time period may then be followed by another burst of one or more AC pulses. This can mitigate light load inefficiencies by decreasing switching losses and quiescent current losses. Additionally, carefully controlled use of burst mode can allow the system to effectively be loaded at its optimum output resistance, thus allowing the AC/AC system to be operated at or near its peak efficiency, regardless of actual output power. Finally, the use of burst mode can be used to control the voltage gain of the system, i.e., the ratio of the output voltage Vrect to the input voltage Vin. 
       FIG.  2    shows burst mode operation, with the switching on and off times and showing the rectifier output voltage  210 . Beginning, for example, at time t 1 , an on time of the inverter may begin, triggered by a burst request pulse from the receiver. During this on time, switching on the inverter side may transfer power to the receiver side, causing the rectifier voltage Vrect to increase to a peak value at time t 2 , corresponding to when the burst is terminated, i.e., the inverter stops switching. Then, during the off time (from t 2  to t 3 ), when the inverter is not switching, the rectifier voltage Vrect may decrease to a valley threshold (Vth valley) that causes the receiver to send another burst request pulse at time t 3 , repeating the cycle. 
     In a typical implementation of burst mode wireless power transfer, the power receiving device can communicate to the power transmitting device that power is required by initiating a burst request pulse. This pulse may be created by the receiver by using the rectifier switches to apply a predetermined switching pattern, sequence, or state to the receiver coil. This predetermined switching pattern, sequence, or state alters the reflected impedance magnetically coupled via the transmitter and receiver windings to the power transmitter/inverter. Upon detection of this pulse, the transmitter/inverter initiates a burst of pulses as described above. Exemplary implementations of burst mode control circuitry are disclosed in Applicant&#39;s co-pending U.S. patent application Ser. No. 17/386,542, entitled “Efficient Wireless Power Transfer Control,” filed Jul. 28, 2021 and 63/216,831, entitled “Wireless Power Transfer with Integrated Communications,” filed Jun. 30, 2021, which are incorporated by reference in their entirety. 
     Burst mode operation may be characterized in part by an on time, that is the duration during which the inverter in the power transmitter is switching to provide power to the receiver. There is also a corresponding off time during which the inverter in the power transmitter is not switching and no power is delivered to the receiver. In some embodiments, it may be desirable for a minimum duration of the on time to be relatively short. For example, this may provide for improved ripple performance with respect to the rectified DC voltage appearing at the receiver. The on time corresponds to a burst envelope, the envelope being defined in terms of the current delivered to the transmit coil being non-zero and in terms of the current over that interval.  FIG.  3    illustrates an exemplary burst envelope  320 . Burst envelope  320  may, for example, have a minimum duration of 4 μs, although other minimum durations are possible. 
     The illustrated burst envelope  320  results in an H-field spectrum  322 , also depicted in  FIG.  3   . The H-field generated by the device is a function of the current delivered to the transmit coil during the burst on time, i.e., when the inverter is switching. In the illustrated example, it may be desirable for a certain percentage of the total H-field energy to occupy the bandwidth between a lower frequency limit  324  and an upper frequency limit  326 . In the illustrated example, the lower frequency limit may be 1.7 MHz, and the upper frequency limit may be 1.8 MHz, although other values are also possible. It may be beneficial for the emissions energy associated with operation of the wireless power transmitter, including burst mode operation, to fall within a certain band, i.e., between the lower and upper limits. Spectrum  322 , shown in  FIG.  3   , illustrates an exemplary burst envelope  320  whether a relatively larger amount of emission energy falls outside the 1.7 to 1.8 MHz band. 
     One way in which the burst mode operation may be modified to focus is the emission band is to extend the minimum on time associated with burst mode operation.  FIG.  4    illustrates such an arrangement. In  FIG.  4   , the minimum on time of the burst mode can be extended so as to be approximately 30 μs, roughly 8× longer than in  FIG.  3   . This corresponds to the lengthened burst envelope  420 . Lengthened burst envelope  420  can correspond to an H-field spectrum  422 . As illustrated in the frequency domain plot in the lower portion of  FIG.  4   , more of the energy associated with the time-lengthened burst envelope falls in the band between lower frequency limit  424  and upper frequency limit  426 . Increasing the minimum on time may, in some applications, lead to increased ripple voltage of the Vrect voltage appearing at the output of the rectifier in the power receiver. To some degree this ripple may be mitigated, e.g., by larger output capacitors or other techniques. However, in some of these applications, it may not be feasible to tolerate higher ripple or to otherwise mitigate the ripple voltage. 
     An additional or alternative approach that may be employed is to modify switching of the inverter to shape the vertical profile of the burst envelope. This corresponds to changing the rate at which the transmit coil current increases at the beginning of the burst period and/or decreases at the end of the burst period. Such an example is illustrated in  FIG.  5   . In  FIG.  5   , burst envelope  520  has been extended in time as compared to burst envelope  320  of  FIG.  3   . Additionally, the burst envelope has been shaped so that the coil current (and correspondingly the power transmitted) ramps up gradually at the beginning of the burst envelope and ramps down gradually at the end of the burst envelope, rather than being a sharp on/off transition as depicted above in the burst envelopes  320  ( FIG.  3   ) and  420  ( FIG.  4   ). Spectrum  522  depicts the effect of such envelope shaping on the H-field spectrum. As a result of the envelope shaping, significantly more of the H-field energy is contained in the bandwidth between lower frequency limit  324  and upper frequency limit  326 . 
     Such envelope shaping may be achieved by specific control of the inverter switching devices described in greater detail below.  FIG.  6    depicts a simplified schematic of the wireless power transfer system that identifies voltages and terminals relevant to the discussion. The techniques described below may also be employed in systems having differing circuit configurations or topologies than those described herein, which are merely exemplary. The transmitter inverter is made up of four switching devices Q 1 -Q 4 . The input terminals of the inverter correspond to the drain terminals of switches Q 1  and Q 3  and the source terminals of switches Q 2  and Q 4 . (As noted above, MOSFETs are used as exemplary switching devices, but other switching device types could be used as appropriate for a given application.) The output terminals of the inverter correspond to the connection points of switches Q 1  and Q 2  (denoted TXac 1 ) and the connection points of switches Q 3  and Q 4  (denoted TXac 2 ). The inverter output voltage (an AC voltage) appearing across these terminals is denoted Vinv_out. This voltage is applied to the transmitter winding Ltx and tuning capacitor Ctx. Other tuning arrangements and/or configurations may also be used as appropriate for a given embodiment. 
     The receiver includes an active rectifier made up of switches Q 5 -Q 8 . The input terminals of this rectifier, RXac 1  and RXac 2 , corresponding to the connection points of switches Q 5 /Q 6  and Q 7 /Q 8 , respectively, receive an input voltage Vrect in that is induced in the receive coil Lrx by the voltage appearing across transmit coil Ltx by virtue of operation of the inverter. The illustrated receiver side circuitry also includes tuning capacitor Crx, although other tuning arrangements or configurations could be used as appropriate to a given application. The outputs of the rectifier correspond to the drain terminals of switches Q 5  and Q 7  and the source terminals of switches Q 6  and Q 8 , where the voltage Vrect, ultimately supplied to the load, appears. (As above switching devices other than MOSFETs could be used as appropriate for a given application. 
     Returning to the transmitter side, inverter switches Q 1 -Q 4  may be operated by suitable control circuitry, such as PWM control circuitry  108  depicted above in  FIG.  1   . This PWM circuitry may provide control/gate drive signals to inverter switches Q 1 -Q 4  to generate pulses of varying width that determine the average current delivered to the transmit coil Ltx.  FIG.  7    illustrates one exemplary envelope shaping scheme including a first on-time, during which a pulse sequence  731  having varying pulse widths are provided to the inverter switching devices, an off-time during which the inverter switching devices are idle, and a second on-time during which the switches are again operated with varying pulse widths.  FIG.  7    depicts a symmetrical PWM switching scheme, in which the inverter-generated positive and negative pulses are symmetrical in width on a cycle-by-cycle basis. Additionally, pulse amplitude may be constant and equal to the inverter input voltage. Positive pulses correspond to turning on switches Q 1  and Q 4  to apply a positive voltage across transmit winding Ltx, while negative pulses correspond to turning on switches Q 2  and Q 3  to apply a negative voltage across transmit winding Ltx, resulting in an AC current flowing through the winding. 
     Pulse sequence  731  begins with relatively narrower pulses, with the applied pulse widths expanding over time, before again decreasing towards the end of the on-time cycle. The result of this pulse width modulation scheme is to produce a burst envelope  732 . Burst envelope  732  may be characterized by its on time, start step  733 , a flat top  735 , and the shape of the curve between the start step and flat top. The start step is the initial current magnitude, which can range from zero to the full current that the inverter is able to supply. Smaller start steps can result in a narrower frequency bandwidth, but may also reduce the power supplied to the transmitter, so a balance may be struck. Flat top  735  corresponds to the peak power level of the transmitter. Similarly to the start step, a balance may be struck between the length of the flat top versus average power delivery rate. Longer flat tops may increase the net power transfer level while also increasing frequency bandwidth, while shorter flat tops may decrease the net power transfer level while also decreasing frequency bandwidth. Finally, the shape of the curve between the start step and the flat top can also influence power transfer level and frequency bandwidth. The curve may be shaped to be linear, sinusoidal, or any other desirable curve shape. As a general principle, a sinusoidal curve shape (as illustrated in  FIG.  7   , which depicts a cosine curve between start step  733  and flat top  735 ) will result in a lower frequency bandwidth while a linear shape may increase occupied bandwidth. Using the principles described above, a system can be designed such that the control circuitry generates a pulse sequence  731  that results in the desired shape of burst envelope  732  and a corresponding frequency bandwidth spectrum that complies with an applicable specification or requirement. 
     The lower portion of  FIG.  7    depicts the rectifier voltage Vrect corresponding to the burst mode operation. During the on time (i.e., while switches Q 1 -Q 4  are active), Vrect is increasing, as depicted by rising portion  737 . During the off time (i.e., while switches Q 1 -Q 4  are idle), Vrect is decreasing, as depicted by falling portion  739 . This ripple in the Vrect voltage is a characteristic of burst mode operation and may be controlled to within desired limits by circuit design (e.g., controlling system capacitance and other parameters) or by circuit operation (e.g., by controlling the on time, off time, and duty cycle). 
       FIG.  8    illustrates an alternative exemplary envelope shaping scheme including a first on-time, during which a pulse sequence  831  having varying pulse widths are provided to the inverter switching devices, an off-time during which the inverter switching devices are idle, and a second on-time during which the switches are again operated with varying pulse widths.  FIG.  8    depicts a complementary PWM switching scheme, in which the inverter-generated positive and negative pulse widths are complementary on a cycle-by-cycle basis. Additionally, pulse amplitude may be constant and equal to the inverter input voltage. Positive pulses correspond to turning on switches Q 1  and Q 4  to apply a positive voltage across transmit winding Ltx, while negative pulses correspond to turning on switches Q 2  and Q 3  to apply a negative voltage across transmit winding Ltx, resulting in an AC current flowing through the winding. 
     Pulse sequence  831  begins with relatively narrower positive pulses, with the applied pulse widths expanding over time. Correspondingly, the negative pulses begin with a broader width decreasing to a narrower width through the on time cycle. The result of this pulse width modulation scheme is to produce a burst envelope  832 . As with burst envelope  732  described above, burst envelope  832  may be characterized by its on time, start step  833 , a flat top  835 , and the shape of the curve between the start step and flat top. Using the principles described above, a system can be designed such that the control circuitry generates a pulse sequence  831  that results in the desired shape of burst envelope  832  and a corresponding bandwidth spectrum. 
     The lower portion of  FIG.  8    depicts the rectifier voltage Vrect corresponding to the burst mode operation. During the on time (i.e., while switches Q 1 -Q 4  are active), Vrect is increasing, as depicted by rising portion  837 . During the off time (i.e., while switches Q 1 -Q 4  are idle), Vrect is decreasing, as depicted by falling portion  739 . This ripple in the Vrect voltage is a characteristic of burst mode operation and may be controlled to within desired limits by circuit design (e.g., controlling system capacitance and other parameters) or by circuit operation (e.g., by controlling the on time, off time, and duty cycle). 
       FIG.  9    illustrates an alternative exemplary envelope shaping scheme including a first on-time, during which a pulse sequence  931  having varying pulse amplitudes are provided to the inverter switching devices, an off-time during which the inverter switching devices are idle, and a second on-time during which the switches are again operated with varying pulse amplitudes. (Pulse widths may optionally also be modulated using this switching scheme.).  FIG.  9    depicts an input voltage modulation scheme, in which the inverter-generated positive and negative pulse widths are symmetrical in width and the pulse amplitudes are varied on a cycle-by-cycle basis to produce the desired window shape. Positive pulses correspond to turning on switches Q 1  and Q 4  to apply a positive voltage across transmit winding Ltx, while negative pulses correspond to turning on switches Q 2  and Q 3  to apply a negative voltage across transmit winding Ltx, resulting in an AC current flowing through the winding. 
     Pulse sequence  931  begins with relatively shorter pulse amplitudes, for both positive and negative pulse widths, with the applied pulse amplitudes increasing over time. Although not shown in  FIG.  9   , pulse widths could also be modulated in addition to the amplitudes. The result of this pulse modulation scheme is to produce a burst envelope  932 . As with burst envelopes  732  and  832  described above, burst envelope  932  may be characterized by its on time, start step  933 , a flat top  835 , and the shape of the curve between the start step and flat top. Using the principles described above, a system can be designed such that the control circuitry generates a pulse sequence  931  that results in the desired shape of burst envelope  932  and frequency bandwidth spectrum. 
     Pulse amplitude may be varied in different ways. In some embodiments, a voltage pre-regulator may be inserted upstream of the inverter power rails, and the voltage pre-regulator may be controlled to produce a rail voltage input to the inverter that corresponds to the desired pulse amplitude. This voltage pre-regulator could be a switching converter, such as a buck converter, or could be a form of linear regulator. However, a switching converter would typically be more efficient in such configurations. 
     The lower portion of  FIG.  9    depicts the rectifier voltage Vrect corresponding to the burst mode operation. During the on time (i.e., while switches Q 1 -Q 4  are active), Vrect is increasing, as depicted by rising portion  937 . During the off time (i.e., while switches Q 1 -Q 4  are idle), Vrect is decreasing, as depicted by falling portion  939 . This ripple in the Vrect voltage is a characteristic of burst mode operation and may be controlled to within desired limits by circuit design (e.g., controlling system capacitance and other parameters) or by circuit operation (e.g., by controlling the on time, off time, and duty cycle). 
     The foregoing example inverter pulse modulation techniques allow shaping of the current window applied by the inverter to the transmit coil during the on time of burst mode operation. The particular window shape can be selected from among a variety of window shapes, including square, trapezoidal, sinusoidal, Gaussian, sinc (i.e., sin(x)/x), Tukey, Kaiser, Hamming, Hann, DPSS, and other suitable window shapes known to those familiar with the signal processing arts. As discussed above window shapes having more gradual transitions (e.g., sinusoidal, Hamming windows) may result in better performance with shorter minimum on times as opposed to window shapes having sharper transitions (e.g., square, trapezoidal, or Kaiser windows). Nonetheless, any suitable window shape may be employed for a given system as appropriate to meet design requirements. 
     The foregoing describes exemplary embodiments of wireless power transfer transmitters, receivers, and systems using burst mode based communications in which burst envelope shaping is employed. Such systems may be used in a variety of applications but may be particularly advantageous when used in conjunction with wireless power transfer systems personal electronic devices such as a mobile phones, smart watches, and/or tablet computers including accessories for such devices such as wireless earphones, styluses, and the like. However, any wireless power transfer system for which increased overall efficiency is desired may advantageously employ the techniques described herein. Although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined in various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims.

Metadata:
Filing Date: 20230113
Publication Date: 20241231
Grant Date: 20241231
Priority Date: 20210923
Inventors: LI, YE
RUSSELL, ANTOIN J.
TERRY, STEPHEN C.
SCHWARTZ, ADAM L.
RANGANATHAN, SUMANT
LISI, GIANPAOLO
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00711", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/80", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/00711", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 85383753