Patent Description:
Wireless charging is becoming widely used recently to charge electronic devices including, but not limited to, mobile phones, smart watches, and tablets. A wireless power-receiving device (also referred to as a wireless power receiver) is electromagnetically coupled with a wireless power-transmitting device (also referred to as a wireless power transmitter). During the power transfer, communication between the wireless power-receiving device and the wireless power-transmitting device may be used to adjust the power received at the wireless power-receiving device. Communication may be achieved by varying an internal load of a receiving circuit of the wireless power-receiving device to produce an Amplitude Shift Keying (ASK) signal.

Various industry standards have been developed to specify the protocol between the wireless power transmitters and wireless power receiver, such as how the wireless power transmitters and wireless power receiver communicate with each other to adjust for supply and demand of power. For example, the Qi wireless charging standard defined by the Wireless Power Consortium (WPC) uses in-band communication within the transformer (e.g., transmitter coil and receiver coil) while the AirFuel protocol defined by the AirFuel Alliance uses out-of-band communication through Bluetooth, Near-Field Communication, and so on.

For devices with small rechargeable batteries, caution needs to be exercised for power transfer between the wireless power transmitter and the wireless power receiver, in order to achieve linear and finer power regulation to avoid stressing the battery charging system. There is a need in the art for wireless charging systems that is simple and cost effective, while providing linear and finer power regulation.

<CIT> discloses a wireless power transmitter with discrete supply voltage levels that are applied to the coil driving inverter. The levels are adjusted by feedback from the receiver.

According to one or more embodiments, the above objective is achieved by means of a method having the features specifically set forth in the claims that follow. Embodiments moreover concern a related wireless power transmitter.

The claims are an integral part of the technical teaching of the disclosure provided herein.

In some embodiments, a method for operating a wireless power transmitter includes: receiving a power control command from a wireless power receiver inductively coupled to the wireless power transmitter; computing a target transmitter power for the wireless power transmitter in accordance with the power control command; computing a potential voltage change for a transmitter voltage of the wireless power transmitter in accordance with the target transmitter power; determining if a magnitude of the potential voltage change is equal to or larger than a discrete step size of a supply voltage provided by a power supply, wherein the power supply is coupled to the wireless power transmitter and configured to provide the supply voltage to the wireless power transmitter; and in response to determining that the magnitude of the potential voltage change is equal to or larger than the discrete step size of the supply voltage, adjusting a transmitter power of the wireless power transmitter by: setting the supply voltage provided by the power supply to a first voltage value by changing the supply voltage by one or more discrete steps; computing a first target current value for a transmitter current of the wireless power transmitter in accordance with the target transmitter power and the first voltage value; and controlling a power conversion circuit of the wireless power transmitter using the first target current value, wherein the power conversion circuit is coupled to a coil of the wireless power transmitter, and is configured to provide an alternate current (AC) voltage to the coil of the wireless power transmitter.

In some embodiments, a method for operating a wireless power transmitter includes: receiving, by the wireless power transmitter, a power control command from a wireless power receiver, wherein the wireless power transmitter comprises a power conversion circuit, wherein the power conversion circuit is coupled to a Direct Current (DC) power supply and is configured to convert a DC voltage provided by the DC power supply into an Alternate Current (AC) voltage applied to a coil of the wireless power transmitter, wherein the DC voltage provided by the DC power supply changes in discrete steps and has a discrete step size; computing a target transmitter power for the wireless power transmitter in accordance with the power control command; computing, based on the target transmitter power and a present value of a transmitter current of the wireless power transmitter, a potential voltage change for a transmitter voltage of the wireless power transmitter in order to achieve the target transmitter power; determining if a magnitude of the potential voltage change is equal to or larger than the discrete step size of the DC power supply; and in response to determining that the magnitude of the potential voltage change is equal to or larger than the discrete step size of the DC power supply, adjusting a transmitter power of the wireless power transmitter by: shifting the DC voltage provided by the DC power supply by one or more discrete steps such that the DC voltage has a first voltage value; computing a first target current value for the transmitter current of the wireless power transmitter based on the target transmitter power and the first voltage value; and controlling the power conversion circuit using the first target current value.

In some embodiments, a wireless power transmitter includes: a coil; a power conversion circuit coupled to the coil, wherein the power conversion circuit is configured to receive a Direct Current (DC) voltage from a power supply and convert the DC voltage to an Alternate Current (AC) voltage applied to the coil, wherein DC voltage provided by the power supply is adjustable in discrete steps and has a discrete step size; a communication circuit coupled to the coil and configured to receive a power control command from a wireless power receiver; and a controller coupled to the power conversion circuit and the communication circuit, wherein the controller is configured to: receive the power control command from the communication circuit; compute a target transmitter power for the wireless power transmitter in accordance with the power control command; compute, based on the target transmitter power and a present value of a transmitter current of the wireless power transmitter, a potential voltage change for a transmitter voltage of the wireless power transmitter; compare the potential voltage change with the discrete step size of the power supply; and in response to determining that a magnitude of the potential voltage change is equal to or larger than the discrete step size of the power supply, adjust a transmitter power of the wireless power transmitter by: shifting the DC voltage provided by the power supply by one or more discrete steps such that the DC voltage has a first voltage value; computing a first target current value for the transmitter current of the wireless power transmitter based on the target transmitter power and the first voltage value; and controlling the power conversion circuit using the first target current value.

In the figures, identical reference symbols generally designate the same component parts throughout the various views, which will generally not be re-described in the interest of brevity. For a more complete understanding of the invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:.

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

The present invention will be described in the context of wireless charging, and in particular embodiments, methods and circuits for wireless power transmitters.

<FIG> illustrates a block diagram of wireless charging system <NUM>, in an embodiment. As shown in <FIG>, the wireless charging system <NUM> includes a wireless power transmitter <NUM> and a wireless power receiver <NUM>. The wireless power transmitter <NUM> has a coil <NUM>, which is inductively coupled to a coil <NUM> of the wireless power receiver <NUM>.

In the example of <FIG>, the wireless power transmitter <NUM> is coupled to a power source <NUM> (also referred to as a power supply). In some embodiments, the power source <NUM> is a Direct Current (DC) power supply that provides a DC voltage to power the wireless power transmitter <NUM>. The power source <NUM> may be, e.g., a Universal Serial Bus - Dedicated Charging Port (USB-DCP) power supply. Details of USB-DCP are described in the USB - Battery Charging (USB-BC) standard. In an example embodiment, the power source <NUM> is a USB - Quick Charge (USB-QC) power supply, where the USB-QC standard falls under the USB - BC standard. In some embodiments, the power source <NUM> (e.g., a USB-QC power supply) is plugged into a power outlet (e.g., a wall socket) and provides a DC voltage within a specific range (e.g., +5V to +12V). In some embodiments, the DC voltage provided by the power source <NUM> is adjustable in discrete steps having a discrete step size (e.g., <NUM> mV). The wireless power transmitter <NUM> may request a specific DC voltage from the power source <NUM> through a data line in a signal/data path <NUM> (e.g., for transmitting voltage signal(s) and digital data) between the power source <NUM> and the wireless power transmitter <NUM>. For example, an USB-QC power supply may provide a DC voltage that is adjustable in discrete steps with a discrete step size of <NUM> mV.

In <FIG>, the wireless power transmitter <NUM> includes a power conversion circuit <NUM>, a controller <NUM>, a feedback circuit <NUM>, an in-band communication circuit <NUM>, and the coil <NUM>. In some embodiments, the power conversion circuit <NUM> includes a Pulse Width Modulation (PWM) circuit and a power converter. The PWM circuit is configured to generate a PWM signal having a frequency and a duty cycle. The PWM signal drives the power converter of the power conversion circuit <NUM>, which power converter may be, e.g., a DC-AC power converter that converts the DC voltage provided by the power source <NUM> into an Alternate Current (AC) voltage, where the AC voltage is applied to the coil <NUM> for wireless power transfer. In some embodiments, the output power (may also be referred to as the transmitter power) of the wireless power transmitter <NUM>, which is equal to the multiplication of the voltage across the coil <NUM> (also referred to as transmitter voltage) and the current flowing through the coil <NUM> (also referred to as transmitter current), may be adjusted by adjusting the frequency or the duty cycle of the PWM signal driving the power converter of the power conversion circuit <NUM>. In addition, the transmitter power may be adjusted by adjusting the DC voltage provided to the power conversion circuit <NUM> by the power source <NUM>. Note that in the discussion herein, the word "or" is used in a non-exclusive context. For example, in the above discussion, the output power of the wireless power transmitter <NUM> is said to be adjustable by adjusting the frequency or the duty cycle of the PWM signal, which means that the output power of the wireless power transmitter <NUM> is adjustable by adjusting the frequency of the PWM signal, by adjusting the duty cycle of the PWM signal, or by adjusting both the frequency and the duty cycle of the PWM signal.

Although not illustrated in <FIG>, the wireless power transmitter <NUM> may include a rechargeable battery that is charged by the power conversion circuit <NUM>. The rechargeable battery may replace the power source <NUM> as the DC power supply during wireless charging, when the power source <NUM> is not available. This may be useful in applications where a mobile device (e.g., a mobile phone) wirelessly charges another mobile device (e.g., another mobile phone, True Wireless earbuds, or the like).

The coil <NUM>, which may also be referred to as the primary coil or transmitter coil, is inductively coupled (e.g., electromagnetically coupled) to the coil <NUM> (may also be referred to as a secondary coil or receiver coil) of the wireless power receiver <NUM>. The AC current flowing through the transmitter coil <NUM> create a time-varying (e.g., an oscillating) electromagnetic field and induces a current in the wireless power receiver <NUM>. The current induced in the wireless power receiver <NUM> may then be utilized for charging a load <NUM> (e.g., a rechargeable battery) coupled to the wireless power receiver <NUM>.

In various embodiments, the feedback circuit <NUM> of the wireless power transmitter <NUM> is coupled to the coil <NUM> and is configured to measure the transmitter current and the transmitter voltage. The in-band communication circuit <NUM> is coupled to the coil <NUM> and is configured to perform in-band communication between the wireless power transmitter <NUM> and the wireless power receiver <NUM>.

The controller <NUM> may be a micro-controller, a processor, an Application Specific Integrated-Circuit (ASIC), or the like, and is used to control operation of the wireless power transmitter <NUM>. In some embodiments, the controller <NUM> includes a memory module (e.g., a non-volatile memory) that stores instructions (e.g., computer codes), which when executed by the controller <NUM>, performs signal processing functions and generates control signals/data signals that are used to control the operation of the wireless power transmitter <NUM>. For example, the controller <NUM> may perform the signal processing functions illustrated in <FIG>. The controller <NUM> may generate control signals/data signals that is used to control the wireless power transmitter <NUM> in accordance with the method <NUM> of <FIG>. Details are discussed hereinafter.

Stilling referring to <FIG>, the wireless power receiver <NUM> includes the coil <NUM>, a rectifier circuit <NUM>, a voltage conditioning circuit <NUM>, an in-band communication circuit <NUM>, and a controller <NUM>. In some embodiments, the rectifier circuit <NUM> rectifies (e.g., converts) the AC voltage induced across the coil <NUM> into a DC voltage. The rectifier circuit <NUM> may be any suitable rectifier, such as a full-bridge rectifier, a half-bridge rectifier, or the like. The DC voltage generated by the rectifier circuit <NUM> is conditioned by the voltage condition circuit <NUM> to provide a stable DC voltage for the load <NUM> (e.g., a rechargeable battery of a mobile device). The voltage condition circuit <NUM> may include a DC-DC power converter and a voltage regulator (e.g., a Low-Dropout (LDO) voltage regulator), as an example.

In some embodiments, the in-band communication circuit <NUM> of the wireless power receiver <NUM> communicates with the in-band communication circuit <NUM> of the wireless power transmitter <NUM> through Amplitude Shift Keying (ASK) modulation. In some embodiments, the in-band communication circuit <NUM> includes a capacitor and a switch that are coupled in parallel to an internal load. The switch, under the control of the controller <NUM>, is switched between an "On" state and an "Off" state to connect or disconnect the capacitor from the internal load, which causes a change in the amplitude of the AC voltage across the coil <NUM>. The change in the amplitude of the AC voltage across the coil <NUM> is sensed by the transmitter coil <NUM> (e.g., through electromagnetic coupling) and decoded by the in-band communication circuit <NUM>.

The controller <NUM> of the wireless power receiver <NUM> may be a micro-controller, a processor, an Application Specific Integrated-Circuit (ASIC), or the like, and is used to control operation of the wireless power receiver <NUM>. In some embodiments, the controller <NUM> includes a memory module (e.g., a non-volatile memory) that stores instructions (e.g., computer codes), which when executed by the controller <NUM>, performs signal processing functions and generates control signals/data signals that are used to control the operation of the wireless power receiver <NUM>. In some embodiments, the controller <NUM> monitors the output of the rectifier circuit <NUM> and/or the output of the voltage conditioning circuit <NUM>, and based on, e.g., the DC voltage provided to the load <NUM>, generates a power control command for the wireless power transmitter <NUM>. The power control command is sent via the in-band communication circuits <NUM>/<NUM> using ASK modulation, in some embodiments.

In the illustrated embodiment, the power control command is a request for the wireless power transmitter <NUM> to increase or decrease the transmitted power by a percentage. For example, the power control command may indicate a control message of "power up by X percentage" or "power down by Y percentage. " In some embodiments, due to, e.g., coupling loss between the wireless power transmitter <NUM> and the wireless power receiver <NUM>, it may be difficult to send a request for a specific value (e.g., an absolute value) of the transmitter power in the power control command. The power change in percentage is a simple and flexible way to request a change in the transmitted power. Typically, a first power control command is followed by a few subsequent power control commands, in order for the transmitted power to be adjusted and approach the desired value.

Rechargeable-battery-operated wearable consumer electronic devices, such as smart-watch and True Wireless (TWS) earbuds, are now using wireless power delivery to charge the batteries of the devices. Typically, these wearable device batteries have capacity under <NUM> mAh, and while charging, the charging power should be regulated precisely, since sudden or instantaneous surges in charging power may result in battery damage.

The wireless power transmitters used for recharging wearable device batteries may perform power regulation by changing operating frequency (of the PWM signal), duty-cycle (of the PWM signal), or supply voltage (e.g., provided to the power conversion circuit <NUM>). Due to the small form factor of wearable devices, the receiver coils used on these devices have smaller areas. Due to the small area of the receiver coil, it may not be possible to achieve smooth power regulation by adjusting only the operating frequency and the duty-cycle of the wireless power transmitter, and it may be necessary to control the supply voltage as well.

To control supply voltage smoothly, DC-DC converters are generally used. However, DC-DC converters generally require bulky inductors, and considering the form factors of the wearable devices, those bulky inductors may not be used. Moreover, these bulky inductors will add extra component cost to the wireless power transmitter. Another unwanted side-effect of using DC-DC converters is that it may generate heat at the surface of the wireless power transmitter, which may be closely located to the battery of the wireless power transmitter and could potentially increase the battery temperature.

A potential solution to avoid using DC-DC converter in the wireless power converter but still be able to control supply voltage is to use a variable power supply such as a USB wall-adapter. Low-end USB wall-adapters, such as USB-DCP or USB-QC adaptors, are inexpensive and widely used for mobile device charging, but these USB wall-adapters usually have coarse voltage step size of, e.g., <NUM> mV compared to few mV for DC-DC converters. Adjusting supply voltage provided by these USB wall-adapters in coarse discrete step size (e.g., <NUM> mV) may create power spike at the wireless power receiver and may damage the battery of the wireless power receiver. High-end USB power adapters, such as USB - Power Delivery Programmable Power Supply (USB-PD PPS) power supplies, allows more precise voltage change in discrete step size of <NUM> mV and may be able to provide smooth control of supply voltage. However, the USB-PD PPS adapter has complex circuit design and incurs higher cost.

The present disclosure provides a solution that allows the use of the low-end USB wall-adapters (e.g., USB-QC adapters) with coarse voltage step size (e.g., <NUM> mV) as the power source <NUM> of <FIG>, and still achieve smooth power regulation. The wireless power transmitter <NUM> used in the disclosed solution has low complexity. The controller <NUM>, by performing the signal processing functions of <FIG> and by controlling the wireless power transmitter <NUM> (and the power source <NUM>) in accordance with the method of <FIG>, achieves smooth power regulation. Details are discussed hereinafter.

<FIG> illustrates a flow chart of a method <NUM> for operating a wireless power transmitter, in an embodiment. The method <NUM> may be used to control operation of the wireless power transmitter <NUM> of <FIG>. In particular, the method <NUM> shows the operation performed by the wireless power transmitter <NUM> in response to a power control command. As discussed previously, during operation of the wireless charging system <NUM>, the wireless power receiver <NUM> may send multiple power control commands, one after another, in order to fine-tune the transmitter power of the wireless power transmitter <NUM>, such that smooth power regulation at the wireless power receiver <NUM> is achieved for charging the battery of the wireless power receiver <NUM>. Discussion of the method <NUM> refers to various devices/circuits in the wireless charging system <NUM> of <FIG>.

In <FIG>, at block <NUM>, a power control command is received by the wireless power transmitter <NUM> from the wireless power receiver <NUM>. The power control command comprises a request of transmitter power adjustment, such as "power up by X percentage" or "power down by Y percentage," in some embodiments.

Next, at block <NUM>, the wireless power transmitter <NUM> computes a target power PTARGET (also referred to as a target transmitter power). The controller <NUM> computes the target transmitter power PTARGET by adjusting (e.g., increasing or decreasing) the present transmitter power by the required percentage. For example, the controller <NUM> has knowledge about the present value of the transmitter current (e.g., current flowing in the transmitter coil <NUM>) and the present value of the transmitter voltage (e.g., voltage across the transmitter coil <NUM>), which present values may be provided by the feedback circuit <NUM>. In an embodiment, the controller <NUM> adjusts the present value of the transmitter current by the requested percentage to obtain a modified transmitter current value, then multiplies the modified transmitter current value with the present value of the transmitter voltage to compute the target transmitter power PTARGET. Other ways to compute the target transmitter power are possible, and are fully intended to be included within the scope of the present disclosure. In the discussion herein, the "present value" of the transmitter voltage (or transmitter current) refers to the value of the transmitter voltage (or transmitter current) when the power control command is received and before the wireless power transmitter <NUM> adjusts the transmitter voltage (or transmitter current) in response to the power control command received currently.

Next, at block <NUM>, a potential voltage change ΔV to achieve the target transmitter power PTARGET is calculated. In some embodiments, the calculation of the potential voltage change ΔV is performed by dividing the target transmitter power PTARGET by the present value of the transmitter current to find a potential target voltage VTARGET, then subtract the present value of the transmitter voltage from the potential target voltage VTARGET. In other words, the potential voltage change ΔV represents a voltage change needed to achieve the target transmitter power PTARGET, assuming that the transmitter current remains at the present value.

Next, at block <NUM>, the potential voltage change ΔV is compared with the discrete step size of the power source <NUM>. In embodiments where an USB-QC power supply is used as the power source <NUM>, the discrete step size is <NUM> mV. Denote the discrete step size of the power source <NUM> as VSTEP, the processing of the block <NUM> compares the magnitude (e.g., the absolute value |ΔV|) of the potential voltage change ΔV with the discrete step size VSTEP of the power source <NUM>, in order to determine if the magnitude of the potential voltage change ΔV is equal to or larger than the discrete step size VSTEP.

If the magnitude of the potential voltage change ΔV is equal to or larger than the discrete step size VSTEP, the processing of the method <NUM> proceeds to block <NUM>, where a new voltage value VIN is computed for the output voltage of the power source <NUM> (which is the input voltage for the power conversion circuit <NUM> of the wireless power transmitter <NUM>). In an example embodiment, the new voltage value VIN differs from the presently value of the output voltage of the power source <NUM> by N discrete step sizes VSTEP, where N is an integer. A positive integer number of N indicates that the output voltage of the power source <NUM> should be increased by N discrete steps, and a negative integer number of N indicates that the output voltage of the power source <NUM> should be decreased by N discrete steps. Denote the present value (e.g., the value before changing by N discrete steps) of the output voltage of the power source <NUM> as VIN_OLD, the new voltage value VIN is represented by: <MAT>.

In some embodiments, the integer number N is determined by dividing the potential voltage change ΔV by the discrete step size VSTEP to get a first number (which may be a floating point number or an integer), then rounding the first number into an integer that is equal to or immediately adjacent to (e.g., differs by a magnitude less than <NUM>) to the first number. Different methods for performing the rounding of the first number may be used. As an example, the integer number N may be determined by: <MAT> where the floor(. ) function rounds its input to the nearest integer toward negative infinity. In other words, Equation (<NUM>) finds the integer number N such that the new voltage value VIN is the closest to the potential target voltage VTARGET without going over (e.g., being larger than) the potential target voltage VTARGET.

As another example, the integer number N may be determined by: <MAT> where the ceil(. ) function rounds its input to the nearest integer toward positive infinity. In other words, Equation (<NUM>) finds the integer number N such that the new voltage value VIN is the closest to the potential target voltage VTARGET without going under (e.g., being smaller than) the potential target voltage VTARGET.

As yet another example, the integer number N may be determined by: <MAT> where the fix(. ) function rounds its input to the nearest integer toward zero. In some embodiments, a request to adjust the output voltage by N discrete steps is sent through the signal/data path <NUM> to the power source <NUM>, and the power source <NUM> adjusts its output voltage by N discrete steps as requested. Note that in the illustrated embodiment, the new voltage value VIN is not applied instantly as it is computed, instead, the new voltage value VIN is applied later in a subsequent PID control loop (see, e.g., block <NUM>) to the power source <NUM> at the same time when a control signal v(j) (see <FIG> and discussion thereof) is applied to the power conversion unit <NUM> to adjust the frequency or duty cycle of the PWM signal. Details are discussed hereinafter.

Next, in block <NUM>, a new target transmitter current ITARCET is calculated by dividing the target transmitter power PTARGET by the new voltage value VIN: <MAT>.

Next, in block <NUM>, the new target transmitter current ITARCET is used as an input to drive the power conversion circuit <NUM> such that the transmitter current generated by the power conversion circuit <NUM> approaches the new target transmitter current ITARGET. In the illustrated embodiment, the new target transmitter current ITARCET is used as an input to a Proportional-Integral-Differential (PID) control loop (see <NUM> in <FIG>) to generate a control signal v(j) (see v(j) in <FIG>), which control signal v(j) is sent to the power conversion circuit <NUM> and is used to control the frequency or the duty cycle of the PWM signal generated by the PWM signal generator of the power conversion circuit <NUM>, in order to adjust the transmitter current of the wireless power transmitter <NUM> to approach the new target transmitter current ITARCET. The transmitter voltage of the wireless power transmitter <NUM> may also be adjusted (e.g., fine-tuned within a small range) by the frequency or duty cycle of the PWM signal, as skilled artisans readily appreciate. In some embodiments, after the transmitter current is adjusted by the PID control loop, the wireless power receiver <NUM> evaluates the charging power for its battery, and may send one or more additional power control commands to the wireless power transmitter <NUM> to fine-tune the transmitter power. Usually, within a few adjustments (e.g., a few power control commands), the charging power is within the desired range for the wireless power receiver <NUM>.

In some embodiments, the PID control loop used for adjusting the transmitter power is the PID control loop defined in the Qi wireless charging standard. This allows re-use of the parameters and control algorithms defined in the Qi wireless charging standard, which simplifies the product design, reduces product cost, and shortens product development time significantly. For example, the disclosed method <NUM> may be implemented by modifying the firmware (e.g., computer codes) developed for the Qi wireless charging standard, and the wireless power transmitter <NUM> can use the same simple hardware developed for the Qi wireless charging standard.

For each power control command received, the processing in blocks <NUM>, <NUM>, and <NUM> achieves the target transmitter power VTARGET by two adjustments: First, the DC voltage provided by the power source <NUM> is adjusted (e.g., in the PID control loop) by N discrete steps, which causes a corresponding change in the transmitter voltage (e.g., a voltage shift of N × VSTEP) generated by the power conversion circuit <NUM>, which in turn causes a change in the transmitter power. This change in the transmitter voltage satisfies a first portion (which may be a majority portion) of the required transmitter power change. Second, the transmitter current is adjusted by the control signal generated by a PID control loop (details discussed below with reference to <FIG>), where the PID control loop uses the new target transmitter current ITARCET to compute an error signal that drives the PID control loop. The adjustment of the transmitter current satisfies the remaining portion (which may be a minor portion) of the required transmitter power change. In some embodiments, the PID control loop adjusts the transmitter power by adjusting the frequency or duty cycle of the PWM signal, and therefore, has limited capability in adjusting the transmitter power. The presently disclosed method, by adjusting the output voltage of the power source <NUM>, allows large adjustment of the transmitter power, and the remaining small adjustment needed in the transmitter power is taken care of by the PID control loop. By combining the coarse adjustment capability of the power source <NUM> and the fine-tuning adjustment capability of the PID control loop, a large transmitter power adjustment range is achieved while achieving smooth, highly accurate transmitter power control.

Still referring to <FIG>, if the magnitude of the potential voltage change ΔV is smaller than the discrete step size VSTEP, the processing of the method <NUM> proceeds to block <NUM>, where the potential voltage change ΔV (which may have a positive or negative value) is added to an accumulated voltage value VACCU. The accumulated voltage value VACCU is initialized to zero during a power up or a reset of the wireless power transmitter <NUM>, and is changed by the potential voltage change ΔV during the processing of the block <NUM>, in some embodiments.

Next, in block <NUM>, the magnitude (e.g., the absolute value |ΔVACCU|) of the accumulated voltage value VACCU is compared with the discrete step size VSTEP of the power source <NUM>, in order to determine if the magnitude of the accumulated voltage value VACCU is equal to or larger than the discrete step size VSTEP.

If the magnitude of the accumulated voltage value VACCU is equal to or larger than the discrete step size VSTEP, the processing proceeds to block <NUM>, where a new voltage value VIN for the power source <NUM> is computed by adjusting the present value for the output voltage of the power source <NUM> by one discrete step size. In particular, if the accumulated voltage value VACCU has a positive value (e.g., VACCU ≥ VSTEP), then the new voltage value VIN of the power source <NUM> is increased by one discrete step size of VSTEP, and the accumulated voltage value VACCU is assigned an updated value of VACCU - VSTEP. Conversely, if the accumulated voltage value VACCU has a negative value (e.g., VACCU ≤ -VSTEP), then the new voltage value VIN is decreased by one discrete step size of VSTEP, and the accumulated voltage value VACCU is assigned an updated value of VACCU + VSTEP. Note that the new voltage value VIN is applied to the power source <NUM> later, in the PID control loop (see block <NUM>).

Next, in block <NUM>, a new target transmitter current ITARGET is calculated by dividing the target transmitter power PTARGET by the new voltage value VIN computed in block <NUM>, using Equation (<NUM>).

Next, in block <NUM>, the new target transmitter current ITARCET is used to calculate the error signal that drives the PID control loop. In response to the error signal, the PID control loop generates a control signal v(j) (see <FIG>), which control signal controls the power conversion circuit <NUM> such that the transmitter current generated by the power conversion circuit <NUM> approaches the new target transmitter current ITARGET. The processing is the same as or similar to that of block <NUM>, thus details are not repeated.

The processing in blocks <NUM>, <NUM>, and <NUM> provides additional performance advantage. To appreciate the advantage, consider a scenario where multiple power control command are received, where each power control command corresponds to a respective small potential voltage change ΔV (e.g., smaller than one discrete step size VSTEP), and all of the power control commands request power adjustment in the same direction (e.g. power up or power down). Without the processing of blocks <NUM>, <NUM>, and <NUM>, the wireless power transmitter <NUM> may adjust only the frequency or duty cycle of the PWM signal in the power conversion circuit <NUM> to accommodate the requested transmit power change. However, adjusting only the frequency or duty cycle of the PWM signal can only achieve limited range of adjustment in the transmit power. If the sequence of power control commands all request "power up" or "power down," then after responding to the first few power control commands, the power conversion circuit <NUM> may reach its maximum adjustment range (e.g., reaching the maximum frequency or duty cycle), and may not be able to accommodate additional power adjustment requests. The present disclosure, by combining multiple small power adjustment requests into one discrete step size change in the output voltage VIN of the power source <NUM>, ensures that the power conversion circuit <NUM> only have to accommodate small power adjustment requests within its adjusting capability, thereby ensuring smooth, well-regulated power adjustment.

If, in the processing of block <NUM>, the magnitude of the accumulated voltage value VACCU is determined to be smaller than the discrete step size VSTEP, the output voltage VIN of the power source <NUM> is not changed (e.g., maintain the present value). The processing proceeds to block <NUM>, where a new target transmitter current ITARCET is calculated by dividing the target transmitter power PTARGET by the present value of the output voltage VIN, using Equation (<NUM>).

Next, the processing proceeds to block <NUM>, where the new target transmitter current ITARCET is used for control of the PID control loop. The processing of block <NUM> has been discussed above, thus details are not repeated.

<FIG> illustrates a block diagram of a digital signal processing system <NUM>, in an embodiment. The functional blocks of the digital signal processing system <NUM> are used to implement the various processing steps of the method <NUM> of <FIG>. In some embodiments, the digital signal processing system <NUM> is implemented as the firmware running on the controller <NUM> of the wireless power transmitter <NUM>.

As illustrated in <FIG>, the digital signal processing system <NUM> accepts a power control command c and generates a control signal v(j) as its output, where the superscript (j) indicates the iteration number within the PID control loop <NUM>, details of which are discussed hereinafter. For example, the power control command c represents the power control command received currently, and the control signal v(j) is the j-th control signal calculated by the PID control loop <NUM> in response to the power control command received currently, where j = <NUM>, <NUM>,. , M, and M is the total number of iterations of the PID control loop <NUM> in response to the power control command received currently. The control signal v(j) contains control information, such as frequency or duty cycle of the PWM signal, and is sent to the power conversion circuit <NUM> to control the operation of the power conversion circuit <NUM>.

In <FIG>, the block <NUM> may correspond to a power control command c relayed by the in-band communication circuit <NUM> to the controller <NUM>. In the example of <FIG>, the functional block <NUM> receives the power control command c, which indicates a percentage change in the transmitter power, and scales the present value <MAT> of the transmitter current by the requested percentage change to compute a target transmitter current value <MAT>. For example, in various embodiments, the functional block <NUM> computes the target transmitter current value <MAT> according to the following equation: <MAT>.

For example, in the embodiments considered, the value c uses a signed binary coding having <NUM> bits, and the term c/<NUM> is used to calculate the percentage change in the transmitter power.

Next, in functional block <NUM>, the present value <MAT> of the transmitter voltage is multiplied with the target transmitter current value <MAT> to compute a target transmitter power <MAT>. Accordingly, in the embodiment considered, the functional block <NUM> computes: <MAT>.

Next, in functional block <NUM>, a potential target voltage <MAT> is computed by dividing the target transmitter power <MAT> by the transmitter current value <MAT>. Specifically, in the embodiment considered, the functional block <NUM> computes: <MAT>.

Next, the functional block <NUM> performs the processing in various processing steps of <FIG>, such as the processing steps after the block <NUM> but excluding the processing of "Run PID Loop" in blocks <NUM> and <NUM>. For example, the functional block <NUM> may perform the comparison step (e.g., blocks <NUM>/<NUM>), the processing step of "Compute New VIN" in <FIG> (e.g., blocks <NUM>/<NUM>), and send a signal <NUM>, which indicates the integer number N of discrete voltage steps for the power source <NUM> to adjust its output voltage, to the power conversion circuit <NUM> (which then relays the integer number N to the power source <NUM>). In addition, the functional block <NUM> may perform the processing of "Compute New Target Current" of <FIG> (e.g., blocks <NUM>/<NUM>/<NUM>), and send a signal <NUM>, which indicates a new target current value <MAT>, to an adder <NUM>. The new target current value <MAT> corresponds to the new target transmitter current ITARGET discussed above, in some embodiments. The new target current value <MAT> is used as an input to the PID control loop <NUM>. Note that in the illustrated embodiment, the processing in functional blocks <NUM>, <NUM>, <NUM>, and <NUM> are performed only once (when j = <NUM>) for the power control command received currently, and therefore, the new target current value <MAT> is computed only once when j = <NUM> and is used as the target value for the PID control loop <NUM>. The PID control loop <NUM>, however, may run multiple iterations (e.g., a total of M iterations) within a given period of time to generate the control signal v(j) in each of the iterations, and the control signal v(j) is used to adjust the frequency or duty cycle of the PWM signal of the power conversion unit <NUM> in each of the iterations. For example, in the j-th iteration, the present value <MAT> of the transmitter current is subtracted from <MAT> to generate an error signal e(j), which in turn generates a control signal v(j) for the j-th iteration, as discussed below. Note that the notation <MAT> is used here to clearly indicate that the new target current value <MAT> is calculated only once when j = <NUM> and is used for all of the M iterations of the PID control loop <NUM>.

As illustrated in the <FIG>, within the PID control loop <NUM>, the adder <NUM> computes an error signal e(j) between the new target current value <MAT> and the present value <MAT> of the transmitter current. Next, the error signal e(j) is used as an input signal to drive a PID controller functional block <NUM> and to generate an output signal PID(j). The PID controller functional block <NUM> may include a proportional control block, an integral control block, and a derivative control block to perform the PID control function, as an example. In some embodiments, the PID controller functional block <NUM> uses the parameters and structure described in the Qi wireless charging standard. PID control is known in the art, thus details are not discussed here. For this reason, the functional block <NUM> just shows schematically the proportional component KP, the integral component KI and the derivative component KD of a conventional PID controller.

Next, in the functional block <NUM>, the output signal PID(j) is scaled by a scaling factor Sv, then the scaled value is subtracted from a previous value v(j-<NUM>) (e.g., value in a previous iteration of the PID control loop) of the control signal to generate the control signal v(j) as the output signal of the digital signal processing system <NUM> (also referred to as the output of the PID control loop) in response to the power control command received. Accordingly, in the embodiment considered, the functional block <NUM> computes: <MAT>.

As discussed above, in some embodiments, the PID control loop <NUM> runs multiple iterations. During the j-th iteration, j = <NUM>, <NUM>. , M, a corresponding control signal v(j) is generated to control the frequency or duty cycle of the PWM signal of the power conversion unit <NUM>. Notably, the new voltage value VIN for the power source <NUM> is applied at the same time when the control signal v(j) is applied to the power conversion unit <NUM>, as discussed above. In other words, the output voltage of the power source <NUM> is changed (if voltage change is needed as determined by the processing of <FIG>) at the same time when the frequency or duty cycle of the PWM signal of the power conversion unit <NUM> are changed. In some embodiments, the signal <NUM>, which indicates the integer number N of discrete voltage steps for the power source <NUM> to adjust its output voltage, may be included within the control signal v(j) as part of the control signal v(j).

<FIG> and <FIG> illustrate performance of a wireless charging system without and with the presently disclosed control method for the wireless power transmitter, respectively, in an embodiment. To generate the performance results of <FIG>, a reference signal processing system is formed by modifying the digital signal processing system <NUM> of <FIG> by removing the functional blocks in the dashed region <NUM> and by supplying the output signal <MAT> of the function block <NUM> to the adder <NUM> to replace the signal <MAT>. The power source <NUM> used to obtain the performance results in <FIG> and <FIG> is a USB-QC power supply with a discrete step size of <NUM> mV.

In <FIG>, the curve <NUM> shows the voltage VIN provided by the power source <NUM>, and the curve <NUM> shows the output voltage VOUT (e.g., voltage at the output of the voltage condition circuit <NUM>) of the wireless power receiver <NUM>. In the reference signal processing system, the output signal v(j) of the PID control loop controls the voltage VIN provided by the power source <NUM> and the frequency or duty cycle of the PWM signal of the power conversion circuit <NUM>. A medium load condition of about <NUM> mA is simulated. As shown in the <FIG>, without the disclosed control method, the coarse step size of <NUM> mV of the power source <NUM> is too large to achieve a smooth received voltage at a target level. In fact, as illustrated in <FIG>, due to the coarse step size of <NUM> mV, oscillation in the output voltage VOUT occurs as the wireless power receiver <NUM> sends power control commands that oscillate (e.g., alternate) between a "power up" request and a "power down" request. The large voltage spikes in the output voltage VOUT due to the oscillation may be too large and may damage the rechargeable battery being charged by the output voltage VOUT.

In <FIG>, the curve <NUM> shows the voltage VIN provided by the power source <NUM>, and the curve <NUM> shows the output voltage VOUT (e.g., voltage at the output of the voltage condition circuit <NUM>) of the wireless power receiver <NUM>. To generate the performance results of <FIG>, the load is varied from <NUM> A to <NUM> A, and the method <NUM> (implemented by the digital signal processing system <NUM>) is used to control the wireless power transmitter <NUM>. As shown in <FIG>, as the load sweeps from <NUM> A to <NUM> A, the voltage VIN provided by the power source <NUM> changes from <NUM> V to <NUM> V in discrete step size of <NUM> mV, and a smooth output voltage VOUT is observed throughout the process, with a maximum voltage dip of less than <NUM> mV.

Disclosed embodiments may achieve advantages. For example, the disclosed method <NUM> adjusts the transmitter power by adjusting the output voltage of the power source <NUM> by one or more discrete steps when possible, and by adjusting the frequency or duty cycle of the PWM signal in the power conversion circuit <NUM>. The disclosed method requires no hardware change in the wireless power transmitter, and allows the use of inexpensive, widely available power supply (e.g., USB-QC power supply) as the power source <NUM>. The disclosed control method may be implemented as firmware running on the controller <NUM>, and the firmware may re-use software modules previous designed for the PID control of the Qi wireless charging standard. The above features/advantages reduce cost of the wireless power transmitter and shorten product development time.

<FIG> illustrates a flow chart of a method <NUM> for operating a wireless power transmitter, in an embodiment. It should be understood that the method <NUM> shown in <FIG> is merely an example of many possible embodiment methods. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. For example, various steps as illustrated in <FIG> may be added, removed, replaced, rearranged, or repeated.

Claim 1:
A method for operating a wireless power transmitter, the method comprising:
- receiving (<NUM>) a power control command from a wireless power receiver (<NUM>) inductively coupled to the wireless power transmitter (<NUM>);
- computing (<NUM>) a target transmitter power for the wireless power transmitter in accordance with the power control command;
- computing (<NUM>) a potential voltage change for a transmitter voltage of the wireless power transmitter in accordance with the target transmitter power;
- determining (<NUM>) if a magnitude of the potential voltage change is equal to or larger than a discrete step size of a supply voltage provided by a power supply (<NUM>), wherein the power supply is coupled to the wireless power transmitter and configured to provide the supply voltage to the wireless power transmitter; and
- in response to determining that the magnitude of the potential voltage change is equal to or larger than the discrete step size of the supply voltage, adjusting a transmitter power of the wireless power transmitter by:
- setting (<NUM>) the supply voltage provided by the power supply to a first voltage value by changing the supply voltage by one or more discrete steps;
- computing (<NUM>) a first target current value for a transmitter current of the wireless power transmitter in accordance with the target transmitter power and the first voltage value; and
- controlling (<NUM>) a power conversion circuit (<NUM>) of the wireless power transmitter using the first target current value, wherein the power conversion circuit is coupled to a coil (<NUM>) of the wireless power transmitter, and is configured to provide an alternate current, AC, voltage to the coil of the wireless power transmitter.