Patent Application
20190267845
The present invention generally relates to systems and methods for high-power wireless power transfer with dual-Qi compatibility.
Wireless power transfer (WPT) involves the use of time-varying magnetic fields to wirelessly transfer power from a source to a device. Faraday's law of magnetic induction provides that if a time-varying current is applied to one coil (e.g., a transmitter coil) a voltage will be induced in a nearby second coil (e.g., a receiver coil). The voltage induced in the receiver coil can then be rectified and filtered to generate a stable DC voltage for powering an electronic device or charging a battery. The receiver coil and associated circuitry for generating a DC voltage can be connected to or included within the electronic device itself such as a smartphone or other portable device.
The Wireless Power Consortium (WPC) was established in 2008 to develop the Qi inductive power standard for charging and powering electronic devices. Powermat is another well-known standard for WPT developed by the Power Matters Alliance (PMA). There also have been some market consolidation efforts to unite into larger organizations, such as the AirFuel Alliance consisting of PMA and the Rezence standard from the Alliance For Wireless Power (A4WP).
Early versions of both the Qi and Powermat standards fixed the peak resonant frequency of the wireless power transfer process at 100 kHz for Qi and 277 kHz for Powermat. These fixed values are based on the nominal values of the primary inductance of the transmitter coil and the primary capacitance of the associated transmitter-side resonant capacitor in series with the transmitter coil. The operating frequency for transmitters called for in these standards is based on these assumed fixed resonant frequencies. In actual wireless power transmitters the peak resonant frequency is not fixed but is rather a function of the nominal inductance and capacitance values of the transmitter coil and capacitor and other factors such as component variations, load, and leakage. Different wireless power receivers may put different loads on a particular wireless power transmitter, and power leakage varies depending on how well-aligned a wireless power receiver's coil is to the transmitter coil. The entire behavior of the wireless power transfer system is affected by variations in the actual resonant frequency of a wireless power transmitter.
Later versions of these standards allow for slight variations in the operating frequency away from the assumed fixed resonant frequency, but these variations still rely on the basic assumption that the resonant frequency of the transmitter is a known, fixed value based on the nominal inductance of the transmitter coil (measured without being magnetically coupled to a receiver coil) and the nominal capacitance of the resonant capacitor. The Qi standard still requires that the receiver is tuned to a fixed frequency, the fixed frequency being tuned to the assumed fixed resonant frequency of the transmitter, i.e., 100 KHz. The assumed resonant frequency is determined from the measurement of the receiver coil inductance without being in proximity to a transmitter coil and the receiver resonant capacitor. In actual operating Qi systems, while the transmitter and receiver are magnetically coupled, variable resonant frequencies are generated, which is not just unpredictable but adversely affects the ability to deliver more power. As maximum power transfer in a wireless power system occurs when the operating frequency is close to or at the resonant frequency, an incorrect assumption about the resonant frequency affects the ability of the system to deliver close to maximum power. The incorrect assumption about the resonant frequency also creates anomalies in the control loop. For example, in the Qi and PowerMat systems, when the receiver requests an increase in power, the Qi and Powermat systems lower the operating frequency of the transmitter to be closer to the assumed fixed resonant frequency. As the actual (and varying) resonant frequency was often higher than the assumed resonant frequency, the delivered power would decrease instead and the transmitter would turn off due to this anomaly, sometimes referred to as “control inversion.” For example, if the actual resonant frequency of a wireless power transfer system is 150 kHz but the assumed resonant frequency is 100 kHz, the system may adjust the operating frequency closer to 100 kHz in an attempt to increase the delivered power but may actually be lowering the delivered power by moving too far away from the actual resonant frequency. An operating frequency that is too far from the actual resonant frequency can also cause large unanticipated voltage peaks in the resonant components in both the receiver and the transmitter. The reliability of the wireless power transfer system thus can also be affected by assuming an incorrect fixed resonant frequency.
Another drawback of assuming a fixed resonant frequency for a wireless power system is that the operating frequency may be set at a frequency lower than the actual resonant frequency, which causes the overall behavior of the wireless power transmitter coil and capacitor (the “LC tank”) to be capacitive. When the overall behavior of the LC tank is capacitive, switching losses occur in the transistor bridge circuit that generate a time-varying current applied to the transmitter coil, lowering efficiency.
Furthermore, in conventional inductive power transfer systems, such as Qi, the Qi standard still requires that the receiver be tuned to a fixed frequency, the same as the assumed fixed resonant frequency of the transmitter, i.e., 100 KHz. Therefore, in order to maintain the fixed frequency while still responding to varying power needs of a receiver, power transfer systems vary the input voltage of the transmitter using a high-powered DC-DC converter. Along with being costly and cumbersome to implement, varying the input voltage of the transmitter while maintaining the fixed frequency ensures that the transmitter cannot possibly cater to conflicting power demands from multiple receivers, limiting the system to be a one-to-one system, where one transmitter can only support the power needs of a single receiver.
Thus, there is a long felt need for a single transmitter to support the power needs of more than one receiver in a wireless power transfer system.
The systems and methods described herein use a wireless power transmitter to provide wireless power. In an aspect, a wireless power transmitter for providing wireless power includes a rectifier comprising a first coil coupled with a second coil and a switch having a first switch state and a second switch state and an output electrically coupled to a node between the first coil and the second coil. In the first switch state, the rectifier is configured to output a first current having a first polarity through the first coil and a second current having a second polarity through the second coil, the first polarity and the second polarity are different, and in the second switch state, the rectifier is configured to output a third current having a third polarity through the first coil and the second coil.
In some implementations, the wireless power transmitter may include a controller coupled to the switch, where the controller is configured to control the configuration of the switch in the first switch state and in the second switch state. For example, the controller may be configured to open/close the switch depending on the type of receiver (e.g., a Qi receiver or a proprietary receiver) present. For example, the controller may transmit a control signal to open the switch (e.g., drive a transistor acting as the switch “on” by applying a high signal to the transistor's gate) when one or more Qi receivers are present.
In some implementations when the controller is coupled to the switch, the switch may further comprise a transistor, where the transistor receives one or more control signals from the controller, and a diode coupled in parallel with the transistor. For example, the controller may transmit control signals to the transistor to turn the transistor “on” or “off” (e.g., sending a control signal to a driver circuit to drive the transistor high or low, respectively). The diode coupled in parallel with the transistor may prevent the transistor from conducting current in either direction when the transistor is “off.”
In some implementations, the diode may comprise at least one of an external diode or a body diode of the transistor. For example, the diode may be an external diode coupled in parallel with the transistor.
In some implementations, when in the first switch state, the controller may further be configured to control the transmitter at a predetermined frequency, where the predetermined frequency is higher than a maximum resonant frequency of the transmitter. For example, the controller may control the transmitter at a predetermined frequency that is higher than the resonant frequency and lower than electromagnetic interference standards testing (e.g., 150 kHz).
In some implementations, the predetermined frequency is a frequency in the range of 141 kHz to 150 kHz. For example, the controller may control the transmitter at a predetermined frequency of 145 kHz.
In some implementations, when in the second switch state, the controller may be further configured to detect a resonant frequency of the transmitter, determine an optimized frequency that is at least 2% greater than the detected resonant frequency, and vary the phase of the rectifier to control the transmitter at the optimized frequency. For example, the controller may determine the resonant frequency from the peak resonant voltage waveform that results from a frequency sweep (e.g., from 300 kHz to 75 kHz).
In some implementations, the wireless power transmitter may include a ferrite wall between the first coil and the second coil, where the ferrite wall is configured to decease a flux leakage between the first coil and the second coil by providing a flux pathway for a first flux from the first coil and a second flux from the second coil.
In some implementations, the wireless power transmitter may include a biasing resistor coupled to the node, where the biasing resistor is configured to set a positive voltage at the node, wherein the node is further coupled to the switch, the first coil, and the second coil.
In some implementations, the wireless power transmitter may include a first LC tank, comprising a first capacitor coupled in series the first coil, wherein the first LC tank has a first resonant frequency and a second LC tank, comprising a second capacitor coupled in series with the second coil, wherein the second LC tank has the first resonant frequency.
In some implementations, the wireless power transmitter may include a ferrite sheet beneath the first coil and the second coil, where the ferrite sheet is magnetically coupled to the first coil and the second coil.
In another aspect, a method for providing wireless power from a transmitter includes controlling the transmitter to operate in a first state at a predetermined frequency, the predetermined frequency being higher than a resonant frequency of the transmitter, controlling the transmitter to operate in a second state at a variable frequency, and, in the second state, modulating a phase of the transmitter such that an operating frequency of the transmitter is at least 2% greater than the resonant frequency of the transmitter.
In some implementations, the predetermined frequency is a frequency in the range of 141 kHz to 150 kHz. For example, a controller may control the transmitter at a predetermined frequency of 145 kHz.
In some implementations, when controlling the transmitter to operate in the first state, the method further includes detecting the presence of at least one Qi receiver. For example, a controller may receive data packets from one or more Qi receivers indicating the presence of one or more Qi receivers.
In some embodiments, in response to detecting the presence of a first Qi receiver, the method further includes controlling a first branch of the transmitter at the predetermined frequency and controlling a second branch of the transmitter such that it transmits a nominal amount of power.
In some implementations, in response to detecting the presence of a first Qi receiver and a second Qi receiver, the method further includes controlling a first branch of the transmitter and a second branch of the transmitter at the predetermined frequency. For example, a controller may operate the transmitter at a predetermined frequency between 141 kHz and 150 kHz.
In some implementations, when controlling the first branch of the first transmitter and the second branch of the second transmitter at the predetermined frequency, the method further includes controlling a first duty cycle of a first rectifier of the first branch and controlling a second duty cycle of a second rectifier of the second branch, where the first duty cycle and the second duty cycle are different.
In some implementations, when operating the transmitter in the first state, the method further includes detecting the resonant frequency of the transmitter, where the resonant frequency varies in response to varying power requests from a receiver. For example, the controller may determine the resonant frequency from the peak resonant voltage waveform that results from a frequency sweep (e.g., from 300 kHz to 75 kHz).
In some implementations, when controlling the transmitter to operate in the second state, the method further includes detecting a resonant frequency of the transmitter and determining the optimized frequency of the transmitter that is at least 2% greater than the detected resonant frequency.
In some implementations, when controlling the transmitter to operate in the second state, the method further includes receiving a request from a receiver coupled to the transmitter requesting that the transmitter transmit more power to the receiver and increasing the phase of the transmitter to transmit more power to the receiver while maintaining the optimized operating frequency. For example, the transmitter may receive one or more data packets from the receiver indicative of a request for more power. In response, the phase of the transmitter may be increased to transmit more power to the receiver.
In some implementations, when controlling the transmitter to operate in the second state, the method further includes receiving a request from a receiver coupled to the transmitter requesting that the transmitter transmit more power to the receiver and decreasing the phase of the transmitter to transmit less power to the receiver while maintaining the optimized operating frequency. For example, the transmitter may receive one or more data packets from the receiver indicative of a request for less power. In response, the phase of the transmitter may be decreased to transmit less power to the receiver.
Transmitter 100 further includes resistor 106 and DC voltage supply 104 to bias link 146, and a switch coupled to link 146, shown in
Transmitter 100 comprises two branches, branch 142 (e.g., the first branch) and branch 144 (e.g., the second branch). Branch 142 comprises transistor 112, transistor 114, and transmitter coil 120 and capacitor 124 (e.g., LC tank 121). Branch 144 comprises transistor 116, transistor 118, and transmitter coil 122 and capacitor 126 (e.g., LC tank 123). In some embodiments, transistors 112 and 114, and transistors 116 and 118, are in a half-bridge configuration. Controller 132 may independently control and operate each half-bridge rectifier in branch 142 and branch 144, thus independently controlling branch 142 and branch 144. For example, in some configurations, branch 142 may transmit power while branch 144 is “off” (e.g., doesn't transmit power). In other configurations, branch 144 may transmit power while branch 142 is “off” (e.g., doesn't transmit power).
In some embodiments, transmitter coils 120 and 122 are nominally identical coils and capacitors 124 and 126 are nominally identical resonant capacitors. Therefore, the resonant frequencies of branch 142 and branch 144 are the same when transmitter coils 120 and 122 and capacitors 124 and 16 are nominally identical, respectively. The resonant frequency of transmitter 100 (e.g., the overall system) is equal to the resonant frequency of branch 142 (e.g., or branch 144, as they are nominally the same), as disclosed in U.S. Patent Publication No. 20160285319, entitled “Tuned Resonant Microcell-Based Array for Wireless Power Transfer,” filed on Mar. 28, 2016, the subject matter of which is hereby incorporated by reference in its entirety. As long as each LC tank is in series with one another, and each LC tank is tuned to the same resonant frequency, the overall resonant frequency of the system is equivalent to the tuned resonant frequency of an individual LC tank.
In other embodiments, LC tanks 121 and 123 include a plurality of transmitter coils and a plurality of capacitors. In some embodiments, capacitor 124 is comprised of a plurality of capacitors, and in some embodiments, capacitor 126 is comprised of a plurality of capacitors.
Voltage supply 102 provides a DC input voltage for transmitter 100, and in one embodiment is a constant value in the range of 12-15 V. In another embodiment, voltage supply 102 is implemented as a DC-to-DC converter (not shown) that provides a variable DC input voltage to full-bridge 110, and controller 130 provides a control signal to voltage supply 102 to select the input voltage value. In other embodiments, duty cycle control or phase modulation of full-bridge circuit 110 may vary the input voltage value to transmitter coil 120 and capacitor 124 and transmitter coil 122 and capacitor 126. In other embodiments, a combination of a variable input voltage from voltage supply 102, duty cycle variation, and/or other phase modulation may be used to vary the voltage input to transmitter coil 120 and capacitor 124 and transmitter coil 122 and capacitor 126.
Controller 132 provides control signals to the full-bridge rectifier 110 via driver circuits 134, 136, 138, and 140 to drive each of transistors 112, 114, 116, and 118 on or off. Controller 132 further provides control signals to driver circuit 148 to drive transistor 108 on or off. Driver circuits are known to persons of ordinary skill and may include but are not limited to constant current drivers, constant resistor drivers, bootstrap circuitry, an amplifier, or any other comparable type of driver circuit.
Each of transistors 108, 112, 114, 116, and 118 is an n-type MOSFET; however any other type of transistor is within the scope of the invention. In some embodiments, transistors 108, 112, 114, 116, and 118 may all be p-type field effect transistors (FETs). In some embodiments, transistors 108, 112, 114, 116, and 118 may be any combination of p-type or n-type FETs. In some embodiments, transistors 108, 112, 114, 116, and 118 may be bipolar junction transistors, heterojunction bipolar transistors, or any comparable transistor.
Controller 132 controls the timing of switching transistors 112, 114, 116, and 118 on and off to provide alternating current to LC tank 121 and LC tank 123, respectively. In one embodiment, controller 132 will turn on (e.g., apply a “high” signal to the gates of) transistor 112 and transistor 118 while turning off (e.g., applying a “low” signal to the gates of) transistor 114 and transistor 116 during a time interval. During the next time interval, controller 132 will turn on transistor 114 and transistor 116 and turn off transistor 112 and transistor 118. Controller 132 may also provide for “dead time” between the time intervals, during which potentially cross-conducting pairs of transistors in full-bridge rectifier 110, for example transistors 112 and 114 and/or transistors 116 and 118, are simultaneously off. In one embodiment, the dead time has a duration in the range of 100 nanoseconds to 1 millisecond. The timing of switching these pairs of transistors in full-bridge rectifier 110 on and off by controller 132 establishes an operating frequency for transmitter 100. In one embodiment, controller 132 provides control signals to full-bridge rectifier 110 such that it operates as two half-bridge rectifiers.
Branch 142 and branch 144 each have a voltage detector, voltage detector 128 and voltage detector 130, respectively. The voltage detectors detect and rectify the voltage at the resonant voltage nodes in their respective branches. For example, in branch 142, voltage detector 128 detects and rectifies the voltage at resonant voltage node 180. In branch 144, voltage detector 130 detects and rectifies the voltage at resonant voltage node 129. The voltages detected by voltage detector 130 and/or voltage detector 128 are used by controller 132 to determine both the operating frequency of transmitter 100 and the resonant frequency of transmitter 100.
Voltage detector 130 receives as an input a voltage measured between node 131 and ground. Voltage detector 130 detects and rectifies the voltage at node 129 and provides a peak voltage value signal to controller 132 through path 131. The peak voltage value signal tracks the peak amplitude values of the rectified voltage waveform measured at node 129. Voltage detector 130 tracks the peak values of the rectified voltage when transmitter 100 is not under load and also when transmitter 100 is under load from a wireless receiver (not shown). Voltage detector 130 also provides a rectified voltage signal to controller 132 through path 133.
In some embodiments, voltage detector 128 receives as an input a voltage measured between node 180 and ground. Voltage detector 128 detects and rectifies the voltage at node 180 and provides a peak voltage value signal to controller 132 through path 182. The peak voltage value signal tracks the peak amplitude values of the rectified voltage waveform measured at node 180. Voltage detector 128 tracks the peak values of the rectified voltage when transmitter 100 is not under load and also when transmitter 100 is under load from a wireless receiver (not shown). Voltage detector 128 also provides a rectified voltage signal to controller 132 through path 183.
In some embodiments, controller 132 may only receive input from one voltage detector (e.g., either voltage detector 128 or voltage detector 130). Controller 132 many only need to receive input from one voltage detector when branch 142 and branch 144 are run synchronously because branch 142 and branch 144 will be driven at the same operating frequency. Therefore, the difference in output control signals from voltage detector 128 and voltage detector 130 should be nominal (e.g., dependent on the tolerance/actual values of each component in the transmitter). An embodiment of voltage detectors 128 and 130 is discussed further below in conjunction with
Controller 132 generates control signals to control full-bridge rectifier 110 and transistor 108. In one embodiment, controller 132 is a microcontroller executing firmware configured to process the peak voltage value signal and the rectified voltage signal from voltage detector 128 and/or voltage detector 130 and to generate the control signals for full-bridge circuit 110. In other embodiments, controller 132 is embodied as a field programmable gate array, a state machine, or an application specific integrated circuit (ASIC) configured to process the signals from voltage detector 128 and/or voltage detector 130 and to generate the control signals.
Controller 132 is configured to detect the varying resonant frequency of transmitter 100. For example, controller 132 is configured to vary the operating frequency of transmitter 100 over a range of frequencies and to process the resulting peak voltage value signal from voltage detector 128 or voltage detector 130 to detect the resonant frequency of transmitter 100.
Controller 132 is further configured to calculate an optimized operating frequency for transmitter 100 based on the detected resonant frequency. The optimized operating frequency for transmitter 100 is approximately 2-15% greater than the actual detected resonant frequency of transmitter 100. In one embodiment, the optimized operating frequency is approximately 5% greater than the detected resonant frequency of transmitter 100. An operating frequency that is approximately 1% to 15% greater than the actual resonant frequency has the effect that LC tank 121 and LC tank 123 appear inductive to full-bridge circuit 110 such that residual current will tend to flow naturally to either of the input supply rails during the dead time, allowing for zero-voltage switching and higher efficiency. By operating transmitter 100 at a frequency that is 2-15% greater than the detected resonant frequency, transmitter 100 provides close to its maximum available power to a wireless power receiver while also enabling zero-voltage switching of full-bridge circuit 110.
An operating frequency that is higher than the actual resonant frequency allows for zero-voltage switching by the transmitter. Zero-voltage switching ensures that the current in any transistor of the bridge switching circuit is momentarily negative (i.e., flowing through its body diode) at the moment that the transistor is switched on. Zero-voltage switching in the transmitter provides minimal switching losses and higher efficiency. If the assumed resonant frequency, which is the incorrect target frequency for maximum power transfer, is significantly less than the actual resonant frequency, there is a higher likelihood that the operating frequency used by the wireless power transmitter will be lower than the actual resonant frequency, preventing zero-voltage switching and lowering efficiency. The control of transmitter circuit 100 is described in more detail below.
Link 146 connects transmitter coil 120 and transmitter coil 122. In some embodiments, link 146 may be a metal link connecting transmitter coil 120 and 122 in a series configuration. For example, conductor 146 may be a wire, a tracing on a printed circuit board, or any other compatible conductive connection. In some embodiments, transmitter coil 120 and transmitter coil 122 are spiral coils laid out on a single ferrite sheet, where the ferrite sheet is magnetically coupled to transmitter coil 120 and transmitter coil 122, as shown in
Resistor 106 may be coupled between transmitter coil 120 and transmitter coil 122 at position 146 in transmitter circuit 100. Resistor 106 may be a biasing resistor connected to DC power supply 104, fixing the value of the voltage at link 146 to be a set voltage. In some embodiments, resistor 106 may range between 1 kΩ to 10 kΩ and connect to a positive biasing voltage (e.g, DC power supply 104). In some embodiments, DC power supply 104 provide a constant voltage of approximately 5-15 V. In some embodiments, resistor 106 may range between 1 kΩ to 10 kΩ and connect to the positive rail of voltage supply 102. Resistor 106 biases the value of the voltage at link 146 such that there is not reverse conduction through diode 109. Biasing the voltage at link 146 further prevents unintended electromagnetic interference at link 146.
Transistor 108 is coupled between link 146 and ground. Transistor 108 is coupled to diode 109 in a parallel configuration. In some embodiments, diode 109 may be an external diode. In some embodiments, diode 109 may be the intrinsic body diode of transistor 108. Controller 132 may turn transistor 108 on or off via driver circuitry 148.
In some embodiments, transmitter coil 120 and transmitter coil 122 are connected, such that the when transistor 108 is conducting (e.g., the gate of the transistor is held high and transistor 108 is “on”), the polarity of the current through transmitter coil 120 and transmitter coil 122 is the same, as shown and described in reference to
Controller 132 may operate transmitter 100 in two distinct modes, (1) Dual-Qi mode and (2) proprietary mode, both of which will be described in detail in the following paragraphs.
When controller 132 detects the presence of one or more Qi receivers, controller 132 operates transmitter 100 in dual-Qi mode. For example, controller 132 may detect the presence of a Qi receiver after receiving a data packet from said receiver. Detecting the presence of one or more Qi receivers is described in more details in reference to
To power two Qi receivers, one Qi receiver on branch 142 and one Qi receiver on branch 144, controller 132 drives the two half-bridge rectifiers in a specific manner. In some embodiments, controller 132 controls the timing of switching transistors 112, 114, 116, and 118 on and off to provide an alternating current to transmitter coils 120 and 122 and capacitors 124 and 126. In one embodiment, controller 132 will turn on (e.g., apply a “high” signal to the gates of) transistor 112 and transistor 114 while turning off (e.g., applying a “low” signal to the gates of) transistor 116 and transistor 118 during a time interval. During a next time interval, controller 132 will turn on transistor 116 and transistor 118 and turn off transistor 112 and 114 (e.g., driving the two half-bridges in unison). Driving the transistors of the two half-bridge rectifiers in unison induces the current in transmitter coil 120 and transmitter coil 122 to be in a same direction (e.g., the same polarity). For example, as shown in
In one embodiment, in dual-Qi mode when two receivers are present, controller 132 uses a fixed frequency mode to control the switching of the two half-bridge rectifiers. In order to synchronously operate the two branches of transmitter 100 (e.g., branch 142 and branch 144), controller 132 may drive both half-bridge rectifiers at the same operating frequency.
In one embodiment, controller 132 is configured to operate transmitter 100 at a fixed frequency. Controller 132 may process the resulting peak voltage signal from voltage detector 128 (e.g., or voltage detector 130) to detect the operating frequency of transmitter 100. Controller 132 may modify the duty cycle of each of the two half-bridge rectifiers to maintain a fixed operating frequency of transmitter 100. Controller 132 may monitor the operating frequency from the voltage signal from voltage detector 128 (e.g., or voltage detector 130) to identify changes to the operating frequency, and adjust the duty cycle of at least one of the two half-bridge rectifiers to maintain the operating frequency at the fixed value.
In some embodiments, the operating frequency may be a fixed frequency chosen from between 141 kHz and 150 kHz. The range of frequencies in the 141 kHz to 150 kHz band are higher than the maximum resonant frequency of a typical Qi system, which may lie anywhere between 100 kHz and 141 kHz depending on the load and inductance leakage. The range of frequencies in the 141 kHz to 150 kHz band are also lower than the lower limit of electromagnetic interference (EMI) standards testing, which begins at 150 kHz. Therefore, operating transmitter 100 at a frequency above the resonant frequency of the Qi system ensures that LC tank 121 in branch 142 and LC tank 123 in branch 144 operate in an overall inductive manner.
In some embodiments, the operating frequency may be a fixed frequency chose to be 2-20% higher than a detected resonant frequency of transmitter 100. Controller 132 may determine the resonant frequency of transmitter 100 from the voltage signals from voltage detector 128 or from the voltage signals from voltage detector 130. Controller 132 may be configured to calculate an optimized operating frequency for transmitter 100 based on the detected resonant frequency. The optimized operating frequency for transmitter 100 is approximately 2-20% higher than the actual detected resonant frequency of transmitter 100. As stated above, operating transmitter 100 at a frequency above the resonant frequency of the Qi system ensures that capacitor 124 and transmitter coil 120 circuit in branch 142 and the capacitor 126 and transmitter coil 122 circuit in branch 144 operate in an overall inductive manner.
In some embodiments, although the operating frequency of branch 142 and branch 144 is the same fixed frequency, the duty cycle of each branch may be varied to respond separately to the load demands of the two Qi receivers coupled to the two branches. Therefore, duty cycle modulation of the two half-bridge rectifiers allows for the power transmitted from branch 142 and the power transmitted from branch 144 to be independently controlled. For example, if the receiver coupled to branch 142 requests more power (e.g., 5 W) than the receiver coupled to branch 144 (e.g., 3 W), then controller 132 may adjust the duty cycle of the half-bridge rectifier in branch 142 to be higher to the maximum power transfer duty cycle (e.g., when the duty cycle is 0.5, the maximum amount of power is transferred) and may adjust the duty cycle of the half-bridge rectifier in branch 144 to be lower than the duty cycle of half-bridge rectifier in branch 142 while maintaining the same fixed operating frequency for each branch. Therefore, controller 132 may independently control the output power of each branch of transmitter 100.
Furthermore, the synchronous operation of the two half-bridge rectifiers in dual-Qi mode forces largely the same current direction (e.g., polarity) between branch 142 and branch 144, thus creating low electromagnetic interference between the two branches, as explained in reference to
In some embodiments, when only one Qi receiver is present, controller 132 “turn off” the inactive branch of transmitter 100 that does not have a receiver coupled to it. For example, to “turn off” a branch, controller 132 may leave the lower transistor (e.g., either transistor 114 or transistor 118) of the inactive branch (e.g., either branch 142 or branch 144) “on” for a majority of the time, with the lower transistor being turned off only for dead time constraints and any need to switch the upper transistor (e.g., either transistor 112 or transistor 116) “on” in order to keep the driver circuitry (e.g., driver circuit 134 and driver circuit 138) functional.
In some embodiments, transmitter 400 may be operated at a fixed frequency, as described above, using duty-cycle control or input-voltage control (e.g., through the use of a DC-DC converter).
In some embodiments, when only a single receiver is present, controller 132 may control transmitter 400 using frequency tracking for the active branch (e.g., the branch with the corresponding receiver), as described above, where the optimized operating frequency is set to be 2-20% higher than the detected resonant frequency, as explained above. When only a single receiver is present, frequency tracking may be utilized as the electromagnetic interference (e.g., cross-talk) between branch 142 and branch 144 is nominal (e.g., the inactive branch creates a nominal amount of magnetic flux that doesn't interfere with the magnetic flux created by the active branch). Therefore controller 132 may implement frequency tracking of a branch of transmitter 100 when a single receiver is present using phase modulation, duty cycle modulation, or input voltage modulation (via a DC-DC converter), or any combination of the above.
There is low interference (e.g., very little cross-talk) between branch 142 and branch 144 because the magnetic flux induced in each branch is in the same vertical direction, as explained above. Therefore, there is little flux leakage from one branch to the other (e.g., there is little flux leakage between magnetic flux 541 and 551). In previous systems, including the Qi system, flux was not induced vertically (e.g., the current in the two coils was not in the same direction), and flux leakage between two branches of a transmitter circuit created noise and interference when receiving amplitude modulation communication pulses from one or more receivers, causing the communication between the transmitter and receiver to break down, and resulting in turning off transmitter (e.g., per the Qi standard). Therefore, in previous systems, the transmitters with two transmitter coils had to place the two transmitter coils a large distance away from each other to attempt to reduce flux leakage. The current invention mitigates the flux leakage issue by creating a vertical flux, and thus allows the transmitter coils (e.g., transmitter coils 120 and 122) to be placed close together.
At step 606, in response to receiving data packets from one or more Qi receivers, controller 132 identifies which branch (e.g., branch 142 and/or branch 144) has a Qi receiver present on it. In some embodiments, when only one Qi receiver is present, controller 132 may turn off the branch that does not have a Qi receiver on it. Transmitter 100 may determine that a branch does not have a Qi receiver on it if controller 132 does not receiver a data packet in response to sending a ping on said branch. For example, if controller 132 determines that branch 144 does not have a Qi receiver on it, controller 132 may turn off branch 144 by providing control signals to driver circuits 138 and 140 to not drive the half-bridge rectifier (e.g., transistors 116 and 118).
If, at step 606, controller 132 determines that “yes,” both branches have a Qi receiver on them, step 606 proceeds to step 308. At step 608, controller 132 pings branch 142 and branch 144 simultaneously to “awaken” both Qi receivers. Controller 132 may ping both Qi receivers by operating transmitter 100 at a frequency higher than the resonant frequency, for example 175 kHz. To avoid the Qi receivers from turning off, controller 132 may sweep the operating frequency of transmitter 100 from 175 kHz to 145 kHz while maintaining a limited duty cycle 20% or less (e.g., to ensure that the Qi receivers receive enough power from the transmitter to create a voltage on the Qi receiver's control circuitry to wake it up, but not enough power to damage the Qi receivers). For example, controller 132 may sweep the frequency of transmitter 100 from 175 kHz to 145 kHz with a duty cycle of 10-15% when the input voltage is between 12-15 V.
At step 610, in response to detecting the presence of one or more Qi receivers, the transmitter is operated at a fixed frequency. In some embodiments, within a finite time of receiving the initial data packets from the one or more Qi receivers, controller 132 provides control signals to transistors 112, 114, 116, and 118 to operate transmitter 100 at a lower operating frequency. For example, controller 132 may operate transmitter 100 at a fixed operating frequency between 141 kHz to 150 kHz, as described above. For example, once controller 132 has completed the frequency sweep from 175 kHz to 145 kHz, both of the Qi receivers will demand more power from transmitter 100 as each Qi receiver connects to their respective load. To provide more power to the Qi receivers while maintaining a fixed frequency (e.g., between 141 kHz and 150 kHz), controller 132 may modulate the duty cycles of each half-bridge rectifier in each branch (e.g., branch 142 and branch 144) to provide the power requested by each Qi receiver. Controller 132 may modulate the duty cycle of each half-bridge rectifier independently based on differing power needs from each Qi receiver (e.g., one branch may have a duty cycle of 30% while the second branch may have a duty cycle of 40% if the second Qi receiver requires more power). Controller 132 may limit the duty cycle for each branch to be between 45-50%. In a half-bridge rectifier configuration, the maximum power transfer occurs at 50% of the duty cycle, and the power transfer at a 40% duty cycle is equivalent to the power transfer at a 60% duty cycle (e.g., same with the power transfer at a 30% duty cycle and a 70% duty, etc.).
Under normal operation, when controller 132 is controlling the half-bridge rectifiers using duty cycle modulation, both branches (e.g., branch 142 and branch 144) normally have different duty cycles (e.g., because each Qi receiver has unique power requirements). In a preferred embodiment, the current through transmitter coil 120 and transmitter coil 122 should be in the same direction for as long as possible (e.g., to reduce interference and EMI, as described above). In one embodiment, to ensure that the currents are in the same direction for as long as possible, controller 132 may send control signals through drive circuits 136 and 140 to ensure that both low-side transistors (e.g., transistor 114 and transistor 118) are turned “on” exactly at the same instant, as shown in
If, at step 606, controller 132 determines that “no,” both branches do not have a Qi receiver on them, then step 606 proceeds to step 612. At step 612, in response to detecting the presence of one Qi receiver, the branch of transmitter 100 corresponding to the detected Qi receiver is operated either at a fixed frequency or is operated using frequency tracking. The branch of transmitter 100 that does not have a corresponding Qi receiver is turned “off” by controller 132. For example, controller 132 may operate the detected branch of transmitter 100 at a fixed operating frequency between 141 kHz to 150 kHz, as described above. As another example, controller 132 may operate the detected branch of transmitter 100 using frequency tracking, as also described above. Controller 132 calculates an optimized operating frequency for transmitter 100 based on the detected resonant frequency. The optimized operating frequency for transmitter 100 is approximately 2-15% greater than the actual detected resonant frequency of transmitter 100, ensuring that the inductive reactance of LC tank 121 or LC tank 123 (e.g., depending on what branch is being operated by controller 132) is greater than the capacitive reactance of LC tank 121 or 123, so the behavior of LC tank 121 or 123 is inductive, therefore allowing for zero-voltage switching of the transistors.
When controller 132 detects the presence of one or more proprietary receivers, controller 132 operates transmitter 100 in proprietary mode. When operating in proprietary mode, controller 132 provides a control signal to driver circuit 148 to drive transistor 108 off (e.g., apply a “low” signal to the gate of transistor 108).
In some embodiments, the proprietary receiver 1040 includes longitudinal receiver coil 1042 that comprises a ferrite core and a helical coil wrapped around the ferrite core. For example, the ferrite core may be in the shape of a cylindrical rod and the helical coil is wrapped around the ferrite core such that the ferrite core and the helical coil share a common longitudinal axis. In one embodiment, proprietary receiver 1040 is optimally oriented such that the longitudinal axis of the ferrite core is substantially parallel to the longitudinal axis of transmitter 100.
In one embodiment, when operating in Proprietary mode, controller 132 may use phase modulation to control full-bridge rectifier 110. As explained above, an output of voltage detector 130 is a peak resonant voltage at node 129 between transmitter coil 122 and capacitor 126. Controller 132 determines the resonant frequency of transmitter 100 from the peak resonant voltage, as described above. In on embodiment, controller 132 may also determine the resonant frequency from an output of voltage detector 128.
The maximum amount of power transferred in a full-bridge rectifier (e.g., full-bridge 110) occurs when the phase of the full-bridge is 1. Therefore, in some embodiments, when the phase of full-bridge rectifier is less than 1, a partial amount of power is transferred to LC tank 121 and/or LC tank 123 (e.g., transmitter coil 120 and capacitor 124 and/or transmitter coil 122 and capacitor 124).
As the phase of the full-bridge rectifier varies, the size and location of effective input power pulse also varies. Therefore, adjusting the operating frequency of transmitter 100 to ensure that the zero-voltage crossing of voltage 1130 is always slightly to the right of center 1111 of effective input power pulse 1110 ensures that the behavior of LC tanks 121 and 123 is inductive (e.g., allows for zero-voltage switching).
At step 1404, controller 132 regulates the peak voltage. For example, after controller 132 determines the optimized operating frequency by first locating the actual resonant frequency based on the peak amplitude of the voltage waveform at node 129 (e.g., or node 180), controller 132 then monitors the shape of the peak voltage waveform at node 129 (e.g., or node 180) by processing the rectified voltage signal from voltage detector 130 (e.g., or 128) to identify any changes to the resonant frequency and adjusts the phase of the full-bridge rectifier 110 as needed to maintain the peak voltage within a hysteretic window (e.g., such that the operating frequency of transmitter 110 is approximately 2-15% greater than the present resonant frequency). For example, controller 132 monitors the shape of the peak voltage waveform at node 129 (e.g., or node 180) to ensure that it is slight to the right of the center 1111 of effective input power pulse 1110 for a varying phase control scheme, as described above in relation to
At step 1406, controller 132 determines whether the peak voltage is higher than the voltage window. If at step 1406, controller 132 determines that “No,” The peak voltage (e.g., the rectified and scaled down peak voltage) is not higher than the upper limit of the voltage window (e.g., if the voltage window is 2.3 V to 3.5 V), then step 1406 proceeds to step 1408. At step 1408, controller 132 determines whether the peak voltage is lower than the voltage window. If, at step 1408, controller 132 determines that “No,” the peak voltage is not lower than the lower limit of the voltage window (e.g., if the voltage window is 2.3 V to 3.5 V), then step 1408 reverts to step 1402.
If, at step 1408, controller 132 determines that “Yes,” the peak voltage is lower than the lower limit of the voltage window, then step 1408 proceeds to step 1410. At 1410, controller 132 adjusts the phase of the full-bridge rectifier to increase the power. For example, controller 132 may increase the phase of the full-bridge rectifier (e.g., to get closer to a phase of 1, where the maximum power is transferred) to increase the power to the receiver, and raise the peak voltage to be within the voltage window.
In some embodiments, at step 1410, controller 132 may increase the power to the receiver by input voltage regulation via a DC-DC regulator, instead of phase modulation of the half-bridge converter. For example, controller 132 may increase the input voltage to increase the power to the receiver.
If at step 1406, controller 132 determines that “Yes,” The peak voltage is higher than the upper limit of the voltage window (e.g., if the voltage window is 2.3 V to 3.5 V), then step 1406 proceeds to step 1412. At step 1412, controller 132 adjusts the phase of the full-bridge rectifier to decrease the power. For example, if a receiver is suddenly removed from transmitter 100, the peak voltage from node 129 (e.g., or node 180) will become “peaky,” a characteristic of unloaded resonant circuits. This causes the peak voltage to suddenly increase. However, controller 132 will sense the sudden peak voltage spike and will keep the peak of the voltage at node 129 (e.g., the resonant voltage) within the voltage window. To reduce the peak voltage, controller 132 will reduce the phase of full-bridge rectifier 110, which in turn causes a smaller period of time during which a magnetization current is drawn into LC tank 121 and/or LC tank 123, thus reducing the peak voltage and reducing the power output by transmitter 100. Further, as the magnetization current component is the residual level responsible for the degradation in deficiency of a typical resonant power converter, reducing the magnetization current improves the efficiency of the power converter. Therefore as transmitter 100 reduces power to the receiver, the input current drawn by the transmitter will automatically decrease, and the efficiency of transmitter 100 will improve at lighter receiver loads. The reliability of transmitter 100 will also improve, as the peak voltage on the components in transmitter 100 (e.g., capacitors 124 and 126) will be controlled.
In some embodiments, at step 1412, controller 132 may decrease the power to the receiver by input voltage regulation via a DC-DC regulator, instead of phase modulation of the half-bridge converter. For example, controller 132 may decrease the input voltage to decrease the power to the receiver.
At 1504, controller 132 determines an amount of time between receiving successive data packets. For example, controller 132 may receiving 10 data packets, each data packet was received 100 ms apart. As another example, controller 132 may determine that only 8 data packets of the 10 data packets were read by transmitter 100 (e.g., a data packet read at 100 ms, 200 ms, 300 ms, 500 ms, 600 ms, 800 ms, 900 ms, and 1000 ms). Controller 132 may still be able to interpret the receiver's request even though two data packets are missing, by determining that each data packet is sent 100 ms apart. Controller 132 may determine based on the pattern that each data packet is sent a fixed amount of time apart (e.g., either 100 ms apart or an integer multiple of 100 ms) that the data packet is indicative of a request for either more or less power from the receiver. Further, the spacing between sending successive data packets has a deliberate tolerance (e.g., typically +/−5 ms) to account for the width of each packet (e.g., the time it takes to send the bits in a single data packet).
At 1506, controller 132 determines whether the amount of time is indicative of a request for less power. For example, controller 132 may determine (e.g., based on a standard or predefined difference in time) that data packets being sent 100 ms apart is indicative of a request for less power, while data packets being sent 125 ms apart is indicative of a request for more power. The difference in time between a request for more power and a request for less power should be chosen such that their multiples rarely overlap (e.g., less than two or fewer overlaps every ten packets). If, at 1506, controller 132 determines that “No,” the amount of time is not indicative of a request for less power, then process 1506 proceeds to 1508. At 1508, controller 132 determines whether the amount of time is indicative of a request for more power. For example, controller 132 may determine (e.g., based on a standard or predefined difference in time) that data packets being sent 125 ms apart is indicative of a request for more power, while data packets being sent 100 ms apart is indicative of a request for less power.
If, at 1508, controller 132 determines that “No,” the amount of time is not indicative of a request for less power, then process 1506 reverts to 1502. If, at 1508, controller 132 determines that “Yes,” the amount of time is indicative of a request for more power, then process 1508 proceeds to 1510. At 1510, transmitter 100 transmits more power to the receiver. Transmitter 100 may transmit more power to the receiver using the methods described above. If, at 1506, controller 132 determines that “Yes,” the amount of time is indicative of a request for less power, then process 1508 proceeds to 1512. At 1512, transmitter 100 transmits less power to the receiver.
The invention has been described above with reference to specific embodiments. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The foregoing description and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
This application claims the benefit of U.S. Provisional Patent Application No. 62/636,057, entitled “High-Power Wireless Power Transfer with Dual-Qi Compatibility,” filed on Feb. 27, 2018, the subject matter of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62636057 | Feb 2018 | US |
