Patent Application
20160359467
The present disclosure relates to wireless power transfer, and in particular to dynamic control in the power transfer system to manage over voltage conditions.
Wireless power transfer is becoming increasingly popular in portable electronic devices, such as mobile phones, computer tablets, etc., which typically require long battery life and low battery weight. The ability to power an electronic device without the use of wires provides a convenient solution for users of portable electronic devices. Wireless power transfer gives manufacturers a tool for developing creative solutions to problems due to having limited power sources in consumer electronic devices.
Wireless power transfer capability can improve the user's charging experience. In a multiple device charging situation, for example, wireless power transfer may reduce overall cost (for both the user and the manufacturer) because conventional charging hardware such as power adapters and charging chords can be eliminated. There is flexibility in having different coil sizes and shapes on the transmitter and/or the receiver in terms of industrial design and support for a wide range of devices from mobile handheld devices to computer laptops.
An apparatus for wireless power transfer in accordance with the present disclosure may include a resonator circuit for coupling with an externally generated magnetic field to produce a time varying signal. The apparatus may include a rectifier for converting the time varying signal into a DC signal. A variable impedance circuit may be electrically connected to an output of the rectifier to limit the voltage level at the output of the rectifier. The variable impedance circuit may vary its impedance dependent on the DC signal at the output of the rectifier.
In some embodiments, the variable impedance circuit may present a resistive load to the output of the rectifier. In some embodiments, the variable impedance circuit may modulate its impedance in a predetermine manner.
In some embodiments, the variable impedance circuit may be controller based on one or more electrical characteristics of the DC signal. In some embodiments, the electrical characteristic of the DC signal may be its voltage level. In some embodiments, the electrical characteristic of the DC signal may be its current flow.
A method for wireless power transfer in accordance with the present disclosure may include coupling to an externally generated magnetic field to produce a time varying signal. A DC signal may be produced from the time varying signal; the DC signal being presented at an output of a circuit. One or more characteristics of the DC signal may be used to vary an impedance electrically connected to the output of the circuit.
In some embodiments, the method may include rectifying the time varying signal to produce the DC signal.
In some embodiments, the impedance may be modulated in a predetermined manner. In some embodiments, the modulation may depend on the DC signal.
An apparatus for wireless power transfer in accordance with the present disclosure may include a resonator circuit configured to generate a magnetic field that can couple to an external circuit. A power circuit may provide power to the resonator. A sense circuit may be configured to sense a parameter such as a voltage and/or current provided to the resonator coil or current drawn by the power circuit. A controller may be configured to control the power circuit in accordance with an indication that a predetermined voltage condition exists at an output of the external circuit, based on one or more of the sensed parameters.
In some embodiments, the indication may be based on one or more of the sensed voltage level in the resonator circuit, the sensed current flow in the resonator circuit, and the sensed current flow in the power circuit being modulated in a predetermined manner.
In some embodiments, the controller may gradually decrease the power provided to the resonator. In some embodiments, the controller may reduce the power provided to the resonator circuit by an amount proportional to a strength of the sensed parameter.
The following detailed description and accompanying drawings provide a better understanding of the nature and advantages of the present disclosure.
With respect to the discussion to follow and in particular to the drawings, it is stressed that the particulars shown represent examples for purposes of illustrative discussion, and are presented in the cause of providing a description of principles and conceptual aspects of the present disclosure. In this regard, no attempt is made to show implementation details beyond what is needed for a fundamental understanding of the present disclosure. The discussion to follow, in conjunction with the drawings, makes apparent to those of skill in the art how embodiments in accordance with the present disclosure may be practiced. In the accompanying drawings:
In the following description, for purposes of explanation, numerous examples and specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be evident, however, to one skilled in the art that the present disclosure as expressed in the claims may include some or all of the features in these examples, alone or in combination with other features described below, and may further include modifications and equivalents of the features and concepts described herein.
Wireless power transfer may refer to transferring any form of energy associated with electric fields, magnetic fields, electromagnetic fields, or otherwise from a transmitter to a receiver without the use of physical electrical conductors (e.g., power may be transferred through free space). The power output into a wireless field (e.g., a magnetic field or an electromagnetic field) may be received, captured by, or coupled by a “power receiving element” to achieve power transfer.
In one illustrative embodiment, the transmitter 104 and the receiver 108 may be configured according to a mutual resonant relationship. When the resonant frequency of the receiver 108 and the resonant frequency of the transmitter 104 are substantially the same or very close, transmission losses between the transmitter 104 and the receiver 108 are reduced. As such, wireless power transfer may be provided over larger distances. Resonant inductive coupling techniques may thus allow for improved efficiency and power transfer over various distances and with a variety of inductive power transmitting and receiving element configurations.
In certain embodiments, the wireless field 105 may correspond to the “near field” of the transmitter 104. The near-field may correspond to a region in which there are strong reactive fields resulting from the currents and charges in the power transmitting element 114 that minimally radiate power away from the power transmitting element 114. The near-field may correspond to a region that is within about one wavelength (or a fraction thereof) of the power transmitting element 114.
In certain embodiments, efficient energy transfer may occur by coupling a large portion of the energy in the wireless field 105 to the power receiving element 118 rather than propagating most of the energy in an electromagnetic wave to the far field.
In certain implementations, the transmitter 104 may output a time varying magnetic (or electromagnetic) field with a frequency corresponding to the resonant frequency of the power transmitting element 114. When the receiver 108 is within the wireless field 105, the time varying magnetic (or electromagnetic) field may induce a current in the power receiving element 118. As described above, if the power receiving element 118 is configured as a resonant circuit to resonate at the frequency of the power transmitting element 114, energy may be more efficiently transferred. An alternating current (AC) signal induced in the power receiving element 118 may be rectified to produce a direct current (DC) signal that may be provided to charge or to power a load.
The front-end circuit 226 may include a filter circuit to filter out harmonics or other unwanted frequencies. The front-end circuit 226 may include a matching circuit to match the impedance of the transmitter 204 to the power transmitting element 214. As will be explained in more detail below, the front-end circuit 226 may include a tuning circuit to create a resonant circuit with the power transmitting element 214. As a result of driving the power transmitting element 214, the power transmitting element 214 may generate a wireless field 205 to wirelessly output power at a level sufficient for charging a battery 236, or otherwise powering a load.
The receiver 208 (also referred to herein as power receiving unit, PRU) may include receive circuitry 210 that may include a front-end circuit 232 and a rectifier circuit 234, and a load control module 235. The front-end circuit 232 may include matching circuitry to match the impedance of the receive circuitry 210 to the power receiving element 218. As will be explained below, the front-end circuit 232 may further include a tuning circuit to create a resonant circuit with the power receiving element 218. The rectifier circuit 234 may generate a DC power output from an AC power input to charge the battery 236, as shown in
The receiver 208 may be configured to determine whether an amount of power transmitted by the transmitter 204 and received by the receiver 208 is appropriate for charging the battery 236. Transmitter 204 may be configured to generate a predominantly non-radiative field with a direct field coupling coefficient (k) for providing energy transfer. Receiver 208 may directly couple to the wireless field 205 and may generate an output power for storing or consumption by a battery (or load) 236 coupled to the output or receive circuitry 210.
As discussed above, transmitter 204 and receiver 208 may be separated by a distance and may be configured according to a mutual resonant relationship to minimize transmission losses between the transmitter and the receiver.
When the power transmitting or receiving element 352 is configured as a resonant circuit or resonator with tuning circuit 360, the resonant frequency of the power transmitting or receiving element 352 may be based on inductance and capacitance. Inductance may be simply the inductance created by a coil or other inductor forming the power transmitting or receiving element 352, and the capacitance (e.g., a capacitor) may be provided by the tuning circuit 360 to create a resonant structure at a desired resonant frequency. As a non limiting example, the tuning circuit 360 may comprise a capacitor 354 and a capacitor 356 may be added to the transmit and/or receive circuitry 350 to create a resonant circuit.
The tuning circuit 360 may include other components to form a resonant circuit with the power transmitting or receiving element 352. As another non limiting example, the tuning circuit 360 may include a capacitor (not shown) placed in parallel between the two terminals of the circuitry 350. Still other designs are possible. In some embodiments, the tuning circuit in the front-end circuit 226 may have the same design (e.g., 360) as the tuning circuit in front-end circuit 232. In other embodiments, the front-end circuit 226 may use a tuning circuit design different than in the front-end circuit 232.
For power transmitting elements, the signal 358, with a frequency that substantially corresponds to the resonant frequency of the power transmitting or receiving element 352, may be an input to the power transmitting or receiving element 352. For power receiving elements, the signal 358, with a frequency that substantially corresponds to the resonant frequency of the power transmitting or receiving element 352, may be an output from the power transmitting or receiving element 352.
As explained above, in accordance with aspects of certain embodiments, a wireless power system 200 (
A solution may be to limit the voltage at the receiver 208. For example, limits may be designed in (e.g., hardcoded limits in the transmitter 204) so that the highest transmit current will not cause destructive voltages on the receiver 208. Designs may use a regular but slow voltage feedback via a feedback channel 219 (e.g., a Bluetooth channel). Another solution may be to use an over-voltage protection (OVP) alert, in which a Bluetooth signal is sent to shut down the transmitter 204 before damage can result from the over-voltage condition.
However, such solutions may not be adequate for certain transient conditions, where rapid high voltage excursions caused by transmitter currents that are below maximum values may nonetheless be detrimental to the electronics in the receiver 208. For example, the use of feedback via a communication channel 219 may be too slow to respond to such transients. An OVP alert mechanism can cause a system shutdown, which may protect the system from such transients, but is likely to result in a poor user experience (shutdown but no charge).
The discussion will now turn to a description of receive circuitry (e.g., 210,
In some embodiments, the receive coil 402 may have a fixed resonant frequency, Fresonant. Accordingly, the reactive network 404 and receive coil 402 may define a resonant circuit having a frequency Fresonant in order to achieve a given level of coupling with the magnetic field 42. The reactive network 404 may comprise any suitable network of one or more resistive devices and/or reactive devices, such as inductors, capacitors, etc.
The receive circuitry 400 may include a rectifier circuit 406 electrically connected to the resonator circuit 422. The rectifier circuit 406 may include an output 408. The rectifier circuit 406 may be configured to produce a DC signal at its output 408 in response to the time varying signal 44 from the resonator circuit 422.
The receive circuitry 400 may include a variable impedance circuit 424 electrically connected as an electrical load to the output 408 of the rectifier circuit 406. In accordance with the present disclosure, an impedance of the variable impedance circuit 424 may vary and thus change the loading on rectifier circuit 406. This aspect of the present disclosure will be discussed in more detail.
In some embodiments, the variable impedance circuit 424 may comprise a variable load 412 and a controller (control circuit) 414. In some embodiments, the variable load 412 may act as a resistive load. In other embodiments, the variable load 412 may act as a reactive load. In still other embodiments, variable load 412 may act as a combination of resistive load and reactive load.
In some embodiments, the controller 414 may be configured to sense a voltage level Vout at the output 408 of the rectifier circuit 406 and produce a control signal 414a based on the sensed voltage level. In other embodiments, the controller 414 may be configured to sense a current flow Iout at the output 408; the control signal 414a may be based on current flow. In still other embodiments, the controller 414 may generate a control signal 414a based on Vout and Iout. The control signal 414a may be provided to the variable load 412 to control the impedance presented by the variable load 412. Although not illustrated, in other embodiments, the voltage level Vout and current flow Iout may be sensed using separate sense circuits. See
Operation of the receive circuitry 400 shown in
At block 504, the rectifier circuit 406 may produce a DC signal at its output 408 in response to the time varying signal 44. The DC signal, for example, may provide DC power to device electronics (not shown) in a PRU that incorporates the receive circuitry 400. Merely as examples, the DC power may be used recharge a battery, drive a display, and so on.
At block 506, the controller 414 may sense an electrical characteristic of the DC signal. In some embodiments, for example, the controller 414 may be configured to sense a voltage level of the DC signal. In other embodiments, the controller 414 may be configured to sense a current flow of the DC signal. In other embodiments, the controller 414 may be configured to sense both the voltage level of the DC signal and the current flow of the DC signal.
At block 508, the controller 414 may generate a control (ctl) signal based on the sensed electrical characteristic(s) of the DC signal. In some embodiments, for example, the controller 414 may compare (e.g., using a suitable comparator circuit, not shown) a sensed voltage level with a predetermined threshold value. In response to the sensed voltage exceeding the predetermined threshold value, the controller 414 may assert or otherwise generate a control signal 414a, for example, to indicate an overvoltage condition.
In some embodiments, the predetermined threshold value in the controller 414 may be set equal to an overvoltage value that represents the overvoltage condition. Accordingly, the variable impedance circuit 424 may operate as a “limiting load” to limit the voltage level at the output 408 to a safe operating voltage of the PRU. In other embodiments, the predetermined threshold value may be set to a value lower than the overvoltage value. Using a value lower than the overvoltage limit may allow for preemptive action in order to reduce the output voltage before an overvoltage condition occurs.
In other embodiments, the controller 414 may use a sensed current flow of the DC signal as a criterion to control the variable load 412, e.g., in order to maintain a certain current flow at the output 408. The controller 414 may use a sensed voltage level and a sensed current flow (e.g., sensing a power level) of the DC signal as a criterion to control the variable load 412, e.g., in order to maintain a certain level of power delivered to the device electronics of the PRU. The controller 414 may use still other criteria for controlling the variable load 412, or combinations of these and other criteria for controlling the variable load 412.
At block 510, the variable load 412 may be configured to respond to the asserted control signal 414a that results in a change in its impedance. In some embodiments, for example, the impedance of the variable load 412 may decrease. Since there is an equivalent source resistance Requiv at the output 408 of the rectifier circuit 406, the source resistance and the impedance of the variable load 412 define a voltage divider, and so decreasing the impedance of the variable load 412 can reduce the output voltage Vout.
In some embodiments, instead of using a threshold as the trigger for generating the control signal 414a, voltage limiting action of the variable impedance circuit 424 can be continuous. There need not be a discrete change in load resistance of the variable load 412 due to crossing a threshold, but rather a continuously changing load resistance of the variable load 412. In some embodiments, the variable load 412 may be varied as a function Vout. In other embodiments, the variable load 412 may be varied as a function Iout. In other embodiments, the variable load 412 may be varied as a function of power (e.g., Vout×Iout).
In some embodiments, the control signal 414a may be a pulse width modulated (PWM) waveform. The controller 414 (
Referring to
Referring to
Referring to
In accordance with the present disclosure, the controller 414 (
The discussion will now turn to a description of transmit circuitry (e.g., 206,
In some embodiments, the transmit coil 708 may have a fixed resonant frequency, Fresonant. Accordingly, the reactive network 706 and transmit coil 708 may define a resonant circuit in order to generate a magnetic field 72 at the frequency Fresonant, allowing for a receiver (e.g., 400,
The transmit circuitry 700 may include a controller 712. In some embodiments, the transmit circuitry 700 may include a sense circuit 722 configured to sense a voltage VsenseTX across the transmit coil 708. In other embodiments, the transmit circuitry 700 may include a sense circuit 724 configured to sense a current flow IsenseTX into the transmit coil 708. In other embodiments, the transmit circuitry 700 may be configured to sense both the voltage VsenseTX across the transmit coil 708 and the current flow IsenseTX into the transmit coil 708. Referring for a moment to
If the receive coil of the external circuit 74 draws more or less power from the magnetic field 72, the change in power drawn can manifest itself as a change in the impedance of transmit coil 708. Consider receive circuitry 400 in
As noted above, the controller 414 in receive circuitry 400 may further modulate the control signal 414a to not only provide overvoltage protection by controlling the impedance of variable load 412, but at the same time incorporate a message, or more generally any kind of data, that can be conveyed to and detected by the PTU. As explained above, the duty cycle of the control signal 414a may be modulated to control the impedance of variable load 412 to provide overvoltage protection. At the same time, the control signal 414a may be further modulated (or the modulation for the overvoltage protection may be done in such a way or have a particular characteristic/signature) to incorporate a message or other data that can be detected by the PTU. This aspect of the present disclosure will be described in more detail below.
Operation of transmit circuitry 700 will now be explained in connection with the process depicted in
At block 804, the controller 712 may detect a high voltage (HV) condition in the external circuit 74 (e.g., of a PRU). For example, if a predetermined voltage condition exists at output 408 of receive circuitry 400 (e.g., the voltage at output 408 exceeds a predetermined threshold), the variable impedance circuit 424 may vary its impedance and thus alter the power drawn from the magnetic field 72 by receive coil 402. A resulting corresponding change in the impedance of transmit coil 708 may appear as changes in VsenseTX, IsenseTX, and IsensePA. An HV condition in a PRU may be signaled when a sensed parameter (VsenseTX, IsenseTX, IsensePA) crosses a predetermined threshold value. In some embodiments, an HV condition may be signaled based on parameters (e.g., power, impedance, etc.) calculated from the sensed parameters.
At block 806, the controller 712 may assert a control signal to control the power output of the power amp 704 in response to an HV condition. In some embodiments, the transmit circuitry 700 may be embodied in a PTU configured for coupling to multiple PRUs. Accordingly, at block 808, in accordance with the present disclosure, the controller 712 may reduce the power (e.g., transmit current) to the transmit coil 708 when an HV condition occurs in a PRU, rather than cutting off power completely, so as to minimize disruption to other PRUs in the wireless charging system. In some embodiments, the controller 712 may reduce the power to the transmit coil 708 at a fixed rate (e.g., some number of units of current per unit of time) until the HV condition is no longer present. In other embodiments, the controller 712 may modulate or otherwise control current into the transmit coil 708 in a continuously variable fashion using an appropriate control algorithm.
When power to the transmit coil 708 is reduced, that in turn can reduce the amount of power that is received at the receive circuitry 400. Accordingly, the sensed voltage at output 408 in the receive circuitry 400 may drop, which in turn may cause the controller 414 to disable or otherwise adjust the amount of resistance presented by the load circuit 412. This can restore the original impedance of the transmit coil 708, which in turn may restore the original values of VsenseTX, IsenseTX, and IsensePA, thus signaling the end of the HV condition.
As explained above, in accordance with the present disclosure, the variable impedance circuit 424 (
In other embodiments, the variable impedance circuit 424 may modulate its impedance in a time varying manner. Referring to
More generally, the modulation may serve as a low bit rate signaling method to communicate data from the PRU to the PTU at the same time that overvoltage protection is happening. Accordingly, the variable impedance circuit 424 can be modulated (e.g., using control signal 414a) in a way that simultaneously provides overvoltage protection and conveys a message or other data to the PTU. Thus, modulations in the variable impedance circuit 424 detected by the PTU may (1) inform the PTU to adjust its transmit power in order to avoid overvoltage and/or (2) provide information to the PTU that does not necessarily relate to overvoltage protection. This may allow for a configuration that may accomplish both the signaling and protection in overvoltage conditions while not having to immediately rely on other communication mechanisms that may introduce delays in the ability to protect circuitry in more extreme overvoltage conditions.
The above description illustrates various embodiments of the present disclosure along with examples of how aspects of the particular embodiments may be implemented. The above examples should not be deemed to be the only embodiments, and are presented to illustrate the flexibility and advantages of the particular embodiments as defined by the following claims. Based on the above disclosure and the following claims, other arrangements, embodiments, implementations and equivalents may be employed without departing from the scope of the present disclosure as defined by the claims.
