Abstract:
A method for adaptively optimizing wireless charging efficiency is disclosed. The method may comprise providing an input power to a power transmitter, the power transmitter comprising a transmitter-side coil wirelessly coupled to a receiver-side coil of a power receiver, determining, at the power receiver, a real power transferred from the power transmitter, transmitting information associated with the determined real power to the power transmitter through the coupling between the receiver-side coil and the transmitter-side coil, and adjusting, at the power transmitter, the input power in response to determining, according to the transmitted information, that the real power differs from an expected power corresponding to the input power by over a first threshold, causing the real power to tune towards the expected power.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority to U.S. Provisional Application No. 62/339,056, filed May 19, 2016, entitled “WIRELESS CHARGING SYSTEMS AND METHODS WITH ADAPTIVE EFFICIENCY OPTIMIZATION,” the entire contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates generally to a wireless charging method and apparatus, particularly, to a wireless charging method and apparatus with adaptive efficiency optimization. 
       BACKGROUND 
       [0003]    Wireless charging is an evolving technology that may bring a new level of convenience of charging millions of electronic devices. In a wireless charging system, in particular, in an inductive wireless charging system, energy is transferred from a power transmitter, through magnetic coils coupled to the power transmitter, to one or multiple power receivers. Charging efficiency, which is the ratio of received power over transmitted power, is the most critical parameter in wireless charging. Improving the charging efficiency will effectively reduce the energy wasted during transmission, prevent heat discharges or over-voltage damages of the charging and to-be-charged devices. Also the improved efficiency could eliminate unnecessary electromagnetic radiations, avoiding potential influences on human&#39;s health. 
         [0004]    There are mainly two approaches for efficiency optimization: (1) hardware approach, by using high efficiency components such as integrated circuits (ICs); (2) software approach, by tuning input power based on an optimization method. Most of the Qi protocol based wireless-charging systems in today&#39;s market rely on the hardware approach, and only tune to achieve a stable output voltage at the receiver rectifier. These systems use a power transmission pad and a compatible receiver in a portable device. In operation, a to-be-charged device is placed on top of the power transmission pad, which charges it via resonant inductive coupling. The hardware approach is greatly limited by cost, product design, and IC technology. On software approach, wireless charging systems based on AirFuel protocol uses Bluetooth Low Energy (BLE) to provide feedback information from a power receiver to a transmitter, so power transmitter can calculate a current efficiency and tune the input power when receiving the feedback packet. However, the BLE feedback packet interval is large due to the low energy characteristics, and the tuning step is small because of the inconsistency of receiver (RX) load condition under different input power, so this mechanism takes a long time to converge to good efficiency. 
         [0005]    Therefore, it is desirable to have a wireless charging system with optimal charging efficiency, fast convergence time, and reliable output power. 
       SUMMARY 
       [0006]    One aspect of the present disclosure is directed to a method for adaptively optimizing wireless charging efficiency. The method may comprise providing an input power to a power transmitter, the power transmitter comprising a transmitter-side coil wirelessly coupled to a receiver-side coil of a power receiver, determining, at the power receiver, a real power transferred from the power transmitter, transmitting information associated with the determined real power to the power transmitter through the coupling between the receiver-side coil and the transmitter-side coil, and adjusting, at the power transmitter, the input power in response to determining, according to the transmitted information, that the real power differs from an expected power corresponding to the input power by over a first threshold, causing the real power to tune towards the expected power. 
         [0007]    Another aspect of the present disclosure is directed to a system for adaptively optimizing wireless charging efficiency. The system may comprise a power transmitter configured to receive an input power, the power transmitter comprising a transmitter-side coil wirelessly coupling to a receiver-side coil, and a power receiver comprising the receiver-side coil. The power receiver may be configured to: determine a real power transferred from the power transmitter, and transmit information associated with the determined real power to the power transmitter through the coupling between the receiver-side coil and the transmitter-side coil. The power transmitter may be further configured to adjust the input power in response to determining, according to the transmitted information, that the real power differs from an expected power corresponding to the input power by over a first threshold, causing the real power to tune towards the expected power. 
         [0008]    It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Preferred and non-limiting embodiments of the invention may be more readily understood by referring to the accompanying drawings in which: 
           [0010]      FIG. 1  is a diagram of a wireless charging system, according to one exemplary embodiment. 
           [0011]      FIG. 2  is a diagram of a wireless charging system, according to another exemplary embodiment. 
           [0012]      FIG. 3  is a flow chart of a wireless charging process, according to one exemplary embodiment. 
           [0013]      FIG. 4  is diagram of comparison results between a conventional wireless charging method and an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0014]    Specific, non-limiting embodiments of the present invention will now be described with reference to the drawings. It should be understood that particular features and aspects of any embodiment disclosed herein may be used and/or combined with particular features and aspects of any other embodiment disclosed herein. It should also be understood that such embodiments are by way of example and are merely illustrative of but a small number of embodiments within the scope of the present invention. Various changes and modifications obvious to one skilled in the art to which the present invention pertains are deemed to be within the spirit, scope and contemplation of the present invention as further defined in the appended claims. 
         [0015]      FIG. 1  shows a wireless charging system. As shown in  FIG. 1 , the wireless charging system includes a transmitter side and a receiver side. The transmitter side and receiver side are coupled by coils therebetween. In one exemplary embodiment, the transmitter side includes input nodes (+ and −), a power amplifier, and a transmitter matching network (TX matching network). The receiver side includes a receiver matching network (RX matching network), a rectifier, and a buck converter. The power are input at the input nodes of the transmitter side, wirelessly transmitted through the coils to the receiver side, and applied to a load at the output. As shown in  FIG. 1 , at each stage, there are power losses, for example, capacitor losses (cap losses) and heat losses. 
         [0016]      FIG. 2  shows a wireless charging system  200  according to some other embodiments of the present disclosure. As shown in  FIG. 2 , the wireless charging system  200  includes a transmitter side  202  and a receiver side  204 . The transmitter side  202  and receiver side  204  are coupled by coils  206 ,  208  therebetween. In one exemplary embodiment, the transmitter side  202  includes input nodes (+ and −), a power amplifier  212 , a load demodulator  214 , and a transmitter matching network  216 . The receiver side  204  includes a receiver matching network  222 , a load modulator  224 , a rectifier  226 , a buck converter  228 , and a load  230 . The transmitter side  202  may be implemented in a charging device. The receiver side  204  may be implemented in a consumer electronic device, such as a cell phone, headset, watch, tablet device, laptop, electronic brush, car, or any other consumer electronic devices that may be wirelessly charged. Alternatively, the receiver side may be implemented as a stand-along charging device for a user to attach to a consumer electronic device. For example, a user can attach an electronic device as the load  230  as shown in  FIG. 2 . 
         [0017]    In addition, as shown in  FIG. 2 , the transmitter side  202  further includes a transmitter control block  300 , and the receiver side  204  also includes a receiver control block  400 . The transmitter control block  300  includes an analog-to-digital detection circuit  312 , a transmitter micro controller unit (TX MCU)  314 , a general purpose input and output (GPIO)  316 , a radio frequency circuit (RF Core)  318 , and a radio transceiver  320 . The receiver control block  400  includes an analog-to-digital detection circuit  412 , a receiver micro controller unit (RX MCU)  414 , a general purpose input and output (GPIO)  416 , a radio frequency circuit (RF Core)  418 , and a radio transceiver  420 . The transmitter control block  300  and the receiver control block  400  each can be integrated on one chip. There are available chips on the market, which, with programming, can be used to function as the transmitter control block  300  and the receiver control block  400 , for example, Broadcom BCM20737S, NXP QN9021, TI CC2540, etc. The functionalities of the circuit blocks shown in  FIG. 2  are described below in connection with the flow chart in  FIG. 3 . 
         [0018]    As shown in  FIG. 2 , the input nodes receive an input voltage Vin. The input nodes are connected to the power amplifier  212 , which amplifies the input voltage Vin. The power amplifier  212  is connected to the load demodulator  214 , which is connected to the TX matching network  216 . The load demodulator  214  demodulates feedback signals transmitted from the load modulator  224  through the coils  208 ,  206  and RX and TX matching networks  222 ,  216 . The transmission is shown as power-line communication in  FIG. 2 . The TX matching network  216  is connected to the coil  206 . The TX matching network  216  may include one or more capacitors. Capacitance of one or more of the capacitors may be adjustable. The TX matching network  216  and the coil  206  form an LC circuit. The frequency of the LC circuit can be adjusted by adjusting the capacitance of the TX matching network  216 . The coil  206  transmits the energy to the coil  208  on the receiver side  204 . 
         [0019]    On the receiver side  204 , similar to the transmitter side  202 , the coil  208  is connected to the RX matching network  222 , which has one or more capacitors. One or more of the capacitors may have adjustable capacitance. The capacitors are used to adjust the frequency of an LC circuit formed by the coil  208  and RX matching network  222 . The RX matching network  222  is connected to the load modulator  224 , which is controlled by the receiver control block  400 , and generates the feedback signals to be transmitted to the load demodulator  214 . The operation of the load modular  224  and the receiver control block  400  will be described in detail below. The load modulator  224  is connected to the rectifier  226 , which is connected to the buck converter  228 . The energy is received by the coil  208  and transmitted to the rectifier  226 , which converts the alternating current (AC) to direct current (DC). The buck converter (e.g., DC-to-DC power converter)  228  steps down the voltage from the rectifier  226  and outputs it to the load  230 . 
         [0020]    As shown in  FIG. 2 , the ADC detection circuit  412  of the receiver control block  400  is connected to the positive and negative terminals of the load  230  and to the positive and negative terminals at the input side of the buck converter  228 . The ADC detection circuit  412  monitors the output voltage and/or current signals of the rectifier  226  (VRECT and IRECT) and the buck converter  228  (VBUCK and IBUCK), and generates digital signals that are fed to the RX MCU  414 . The RX MCU  414  generates control signals based on the digital signals from ADC detection circuit  412 . In some embodiments, the control signals correspond to the voltage/current variations of the load  230 . The control signals are sent to the load modulator  224  and buck converter  228  through GPIO  416  to control the load modulator  224  and buck converter  228 . For example, RX MCU  414  reads VBUCK and IBUCK from ADC detection circuit  412 , calculates the current output power, and then calculates the difference between expected output power and current output power. The difference can be defined as a value “output power error”, the length of which is one byte. RX MCU  414  will change the GPIO level based on the binary format of “output power error” (1-0 series). As an example, the unit of output power is 100 mW. If the expected output power is 5 W, which is 50*100 mW. The current output power is 4.8 W, which is 48*100 mW. The output power error is 2, the binary format of which is 00000010. To send this one byte value, RX MCU  414  pulls GPIO connected to the load modulator  224  down when it sees a “0”, and pulls the GPIO up when it sees a “1”. 
         [0021]    As discussed above, the ADC detection circuit  412  also monitors VRECT and IRECT. The RX MCU  414  reads the monitored signals and includes them in BLE packet and send them through Bluetooth radio  420  to the transmitter control block  300 . The transmitter control block  300  monitors the VRECT and IRECT to make sure they do not exceed certain limits. If they exceed preset limits, the transmitter control block  300  can control the input voltage to lower VRECT and IRECT. 
         [0022]    GPIO  416 , although shown as one block, may include multiple GPIOs. The RX MCU  414  may use different GPIOs to control load modulator  224  and buck converter  228 . For load modulation, the RX MCU  414  may use a GPIO to control one pair of load modulation switches (since the AC currents are positive and negative, so the system uses one pair of switches for AC+ and AC− respectively). When the switch is closed, AC+ or AC− will be connected to GND. When the switch is open, AC+ or AC− is not connected to GND and will supply power to the rectifier  226 . 
         [0023]    The load modulator  224  modulates the control signals, for example, by applying the control signals to a higher frequency signal. The modulated signals are transmitted through the RX matching network  222  and coil  208  to the transmitter side  202 . 
         [0024]    The RX MCU  414  may also send the control signals to RF core  418 . The RX MCU  414  may also generate signals representing status, e.g., voltage and/or current across the load, and send them to RF core  418 . RF core  418  may generate Bluetooth signals and transmit them through radio transceiver  420  to the transmitter side  202 . According to some embodiments, the Bluetooth signals are BLE (i.e., Bluetooth version 4.0+) signals and the RF cores and transceivers at the transmitter and receiver sides are configured to send and receive BLE signals. 
         [0025]    On the transmitter side  202 , the load demodulator  214  receives the feedback signals from the power-line communication (the coil  206  and TX matching network  216 ), demodulates the feedback signals, and sends the demodulated signals to TX MCU  314  through GPIO  316 . The TX MCU  314  also receives the Bluetooth signals from the radio transceiver  320  and RF core  318 . The TX MCU  314  generates adjustment signals to the input voltage, and sends it to the ADC detection circuit  312 . The ADC detection circuit  312  converts the adjustment signals into analog signals, and applies them to the input voltage. The transmitter control block  300  also detects the input voltage and current through the ADC detection circuit  312 . 
         [0026]    As described above and shown in  FIG. 2 , in the embodiments of the present disclosure, there are two communication channels from the receiver side to the transmitter side: (1) BLE communication channel: BLE packets are delivered through the out-of-band 2.4 GHz BLE wireless channel; (2) Power-line communication: power-line packets are delivered through the in-band wireless power transfer channel. 
         [0027]    In an exemplary embodiment, the optimization procedure may be initialized by the BLE communication. For example, once the power transmitter side  202  receives the reported charging voltage and current at the receiver side  204 , TX MCU  314  calculates the current efficiency and starts tuning input power instantly without waiting for the next BLE packet. During the optimization procedure, the receiver side is constantly reporting the error between received power and expected power through power-line communication. The tuning step is varying based on the efficiency and load condition. The charging efficiency could quickly converge to optimal value while maintaining stable output power. In some exemplary embodiments, the optimization procedure may be terminated by the next BLE packet that the transmitter side  202  receives from the receiver side  204 . 
         [0028]      FIG. 3  shows a flow chart of an exemplary optimization method. As shown in  FIG. 3 , after start, the receiver side sends a BLE packet including information on the voltage and current on the load. At step  612 , the transmitter side receives the BLE packet. At step  614 , the TX MCU decodes the BLE packet and retrieves the information on current output power and expected output power. At step  616 , the transmitter control block detects the input voltage and current. At step  618 , the transmitter control block calculates the efficiency. The efficiency is output power divided by input power. At step  620 , the transmitter control block determines whether the efficiency is low. If the efficiency is low, for example, lower than 55%, the process goes to step  622 . If the efficiency is high, for example, 55% or higher, the process goes to step  624 , at which, the optimization process ends. At step  622 , the TX MCU calculates the transmitter side load (TX load). The TX load can be calculated by dividing the input voltage by the input current (V in /I) detected by the ADC detection circuit  312  at the transmitter side. At step  626 , the load demodulator demodulates the feedback signals from the power-line communication and sends the demodulated signals to TX MCU. The feedback signals indicate the errors/differences of the expected power and the real power across the load. The expected power can be set by the user. For example, if the charging system is used to charge a smartphone, the expected power may be set as 5 W. At step  628 , TX MCU determines whether difference ratio ((expected power−real power)/expected power) is below a threshold. If no, the TX MCU will adjust the input voltage to the last input voltage V in,prev  at step  634 . If yes, the TX MCU will generate adjustment signals to adjust the input voltage to be V in, new  (calculated by the formulas below). 
         [0029]    The tuning step ΔV at the transmitter side is determined by three parameters: (1) the difference between current efficiency and target efficiency e η  (unit is %), (2) load condition of the receiver side and coil system Z L  (unit is Ω), (3) RX power error coefficient C ep , which is determined by the error between expected RX power and real output power e P . 
         [0000]    
       
         
           
             
               C 
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         [0030]    If e P ≧200 mW, which means the output power variation is more than 200 mW compared with expected value, TX MCU will assume RX output power is unstable, and thus roll back to last input voltage and terminate optimization. 
         [0000]    The tuning of input voltage in each iteration can be expressed in the following equation: 
         [0000]    
       
         
           
               
             
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         [0031]    Where final value V in,new  is the newly determined input voltage in this tuning iteration, V in,prev  is the previous input voltage in last tuning iteration, ΔV max  is the maximum tuning step defined by user, ΔV min  is the minimum tuning step defined by user. Z L  is TX load. Z L,max  is the maximum TX load in wireless charging system, Z L,min  is the minimum TX load in wireless charging system. k is the coefficient to determine the impact of three parameters e η , e P  and Z L . k is the coefficient to determine the impact of three parameters e η , C ep  and Z L . If k is larger, the input voltage will be reduced faster. Typical values for coefficient k is 250˜350. For example, in a wireless power transfer system, whose Z L,min  is 5Ω and Z L,max  is 60Ω, the target efficiency is 50%. In this system the coefficient k is set to 290. Power receiver target output power is 5 W. When input voltage is 20V, the input current is 0.9 A, so Z L =22.2Ω, currently the RX output power is 4.95 W, current efficiency is 27.5%, from equation shown above, and the voltage tuning step is 2244 mV. When input voltage is reduced to 14V, the input current is 0.8 A, so Z L =17.5Ω, the RX output power is 4.92 W, current efficiency is 43.9%, from equation shown above, and the voltage tuning step is 435 mV. As shown in the above calculations, the voltage tuning will be smaller when efficiency is close to optimal efficiency (50%). 
         [0032]    The parameters k, ΔV min , ΔV max , Z L,min , and Z L,max  can all determined by user&#39;s requirements. These are design parameters that can be determined based on the charging system condition and are related to the charging area, charging distance, voltage rating, TX Coil shape etc. These values can be tuned during system tests to achieve best performance to meet user&#39;s requirement. 
         [0033]      FIG. 4  shows a comparison of efficiency optimization speed between adaptive optimization method and traditional optimization method. As shown in  FIG. 4 , traditional optimization method uses BLE signals, which have a frequency of 2.4 GHz and are sent in a time interval of 200 milliseconds (ms), to adjust the input power. The embodiments in this disclosure additionally use power-line signals, which have a frequency of 6.78 MHz (or another frequency between 50 kHz to 10 MHz), and are sent at a much higher frequency, for example, at intervals, e.g., 20 ms. Thus, the system in this disclosure can quickly adjust the output power to an expected level. As an example, known that the optimal input voltage is 11V to achieve maximum efficiency, when power receiver is moved to another place that triggers the input voltage to 18V, two methods initialize optimization procedure at the same time to reduce input voltage and improve efficiency. For the traditional optimization method, it requires around 2400 ms to terminate optimization procedure and reduce input voltage to 11V, while the adaptive optimization method takes only around 200 ms to reach optimal efficiency condition. In addition, the adaptive optimization method is monitoring the stability of RX output power in real time while tuning the input power. If RX output power has large variation or drops under expected value, the input voltage will roll back to last stable level to ensure the stability of wireless charging performance. 
         [0034]    The present disclosure introduces an adaptive efficiency optimization method for wireless charging systems, which can be used to improve the overall system efficiency in a fast and reliable approach. By adaptively tuning the input power and real-time output power monitoring, the wireless charging system can optimize the efficiency under different load condition at a faster speed. In some exemplary embodiments, the adaptive efficiency optimization method can be fully implemented by software, so it will not increase the circuit cost of product. In addition, this optimization method can be adopted to different charging scenarios by changing the pre-defined parameters to satisfy different types of requirements. 
         [0035]    The invention described and claimed herein is not to be limited in scope by the specific preferred embodiments disclosed herein, as these embodiments are intended as illustrations of several aspects of the invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.