Method and apparatus for wireless power transfer with resonant capacitance switching

Abstract

The present application provides an apparatus for wireless power transfer, the apparatus comprising a resonant circuit and a control circuit, the resonant circuit comprising: a transmitter coil; a first capacitor connected in series with the transmitter coil; and a second capacitor connected in series with the first switch. The second capacitor and the first switch are connected in parallel with the first capacitor. A control circuit is connected to the resonant circuit and configured to: detect whether a voltage across the first capacitor or a current event of the transmitter coil occurs; and when the occurrence of the event is detected, controlling to turn on the first switch in response to the signaling to turn on the first switch. A method for controlling switching in a second capacitor is also provided.

Description

Technical Field

[0001] The present application relates generally to wireless power transfer and, in particular embodiments, to wireless power transfer techniques and mechanisms utilizing resonant capacitive switching. Background Art

[0002] As technology further develops, wireless power transmission has become an efficient and convenient mechanism for powering or charging battery-based electronic devices such as mobile phones, smart phones, smart watches, laptops, digital cameras, MP3 players, tablets, e-readers, handheld game consoles, and / or similar devices. A wireless power transmission system typically includes a primary-side transmitter and a secondary-side receiver. The primary-side transmitter is magnetically coupled to the secondary-side receiver. The magnetic coupling can be implemented as a loosely coupled transformer having a primary-side coil formed in the primary-side transmitter and a secondary-side coil formed in the secondary-side receiver.

[0003] The primary side transmitter may include a power conversion unit, such as a primary side power converter. The power conversion unit is coupled to the power source and is capable of converting electrical energy into a wireless power signal. The secondary side receiver is capable of receiving the wireless power signal through a loosely coupled transformer and converting the received wireless power signal into power suitable for the load. Summary of the invention

[0004] Embodiments of the present application describe methods and apparatus for wireless power transfer using resonant capacitor switches, thereby generally achieving technical advantages.

[0005] According to one aspect of the present application, a device for wireless power transmission is provided, the device comprising a resonant circuit and a control circuit, the resonant circuit comprising: a transmitter coil; a first capacitor connected in series with the transmitter coil; and a second capacitor connected in series with a first switch, wherein the second capacitor and the first switch are connected in parallel with the first capacitor; the control circuit is connected to the resonant circuit and is configured to: detect whether a voltage event across the first capacitor or a current event of the transmitter coil occurs; and when the occurrence of the event is detected, turn on the first switch in response to a signaling control to turn on the first switch.

[0006] According to another aspect of the present application, a method for a wireless power transmitter is provided. The wireless power transmitter includes: a first capacitor and a transmitter coil connected in series; and a second capacitor connected in series with a first switch, wherein the second capacitor and the first switch are connected in parallel with the first capacitor. The method includes: detecting whether an event of a voltage across the first capacitor or a current of the transmitter coil occurs; and when the event occurs, turning on the first switch in response to a signaling control to turn on the first switch.

[0007] According to another aspect of the present application, there is provided a device for wireless power transmission, the device comprising a resonant circuit, the resonant circuit comprising: a transmitter coil; a first capacitor connected in series with the transmitter coil; and a second capacitor connected in series with a first switch, wherein the second capacitor and the first switch are connected in parallel with the first capacitor. The device also includes a detection circuit configured to detect the voltage across the first capacitor or the current of the transmitter coil; and a control circuit connected to the detection circuit. The control circuit is configured to: determine whether the voltage across the first capacitor or the current of the transmitter coil meets a predetermined condition, and based on the condition, control the first switch to be turned on in response to receiving a signaling to turn on the first switch.

[0008] According to another aspect of the present application, a controller is provided, comprising: a circuit configured to: detect a voltage across a first capacitor in a capacitor group or a current of a transmitter coil, wherein the capacitor group is connected in series with the transmitter coil, the capacitor group further comprises a second capacitor connected in series with a first switch, the second capacitor and the first switch are connected in parallel with the first capacitor; determine whether the voltage across the first capacitor or the current of the transmitter coil satisfies a predetermined condition; and when the voltage across the first capacitor or the current of the transmitter coil satisfies the predetermined condition, control the first switch to be turned on in response to a received signaling to turn on the first switch.

[0009] The foregoing has been summarized in a rather broad manner the features and technical advantages of the present application, so that the detailed description of the present application below is better understood. Other features and advantages of the present application will be described below, and these features and advantages constitute the subject matter of the claims of the present application. It should be understood by those skilled in the art that the disclosed concepts and specific embodiments can be easily used as the basis for modifying or designing other structures or processes to achieve the same purpose of the present application. It should also be recognized by those skilled in the art that such equivalent structures do not deviate from the spirit and scope of the present application as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a more complete understanding of the present application and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

[0011] Figure 1 is a schematic diagram of an exemplary wireless power transmission system according to an embodiment of the present application;

[0012] Figure 2 is a schematic diagram of an exemplary circuit of a power transmitter in a wireless power transmission system according to an embodiment of the present application;

[0013] Figure 3is a schematic diagram showing an exemplary switch that can be used to implement an embodiment of the present application;

[0014] Figure 4 is a flow chart of an exemplary method for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application;

[0015] Figure 5 is a schematic diagram of an exemplary control circuit for a power transmission system according to an embodiment of the present application;

[0016] Figure 6 is a schematic diagram of an exemplary circuit on the transmitter side of a power transmission system according to an embodiment of the present application;

[0017] Figure 7 This is a diagram showing the embodiment of the present application. Figure 6 A schematic diagram of exemplary waveforms of a circuit in;

[0018] Figure 8 is a schematic diagram of another exemplary circuit on the transmitter side of the power transmission system according to an embodiment of the present application;

[0019] Fig. 9 is a flow chart of another exemplary method for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application;

[0020] Fig.10 is a flowchart of another exemplary method for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application; and

[0021] Fig.11 is a flow chart of yet another exemplary method for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application.

[0022] Corresponding numerals and symbols in the different figures generally indicate corresponding parts unless otherwise indicated.The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. DETAILED DESCRIPTION

[0023] The making and use of the embodiments of the present application will be discussed in detail below. However, it should be understood that the concepts disclosed herein can be embodied in various specific situations, and the specific embodiments discussed herein are merely illustrative and are not intended to limit the scope of the claims. In addition, it should be understood that various changes, substitutions and modifications may be made to this document without departing from the spirit and scope of the present application as defined by the appended claims.

[0024] In addition, one or more features of one or more embodiments described below may be combined or used to create alternative embodiments not explicitly described, and features applicable to the embodiments are understood to be within the scope of the present application. Therefore, the appended claims include any such modifications or embodiments.

[0025] The present application will be described with respect to embodiments in a specific context, namely a method and apparatus for wireless power transmission with resonant capacitor switching. However, the present application may also be applied to various power systems. Various embodiments will be explained in detail below with reference to the accompanying drawings.

[0026] Figure 1 A block diagram of an exemplary wireless power transmission system 100 according to various embodiments of the present disclosure is shown. The wireless power transmission system 100 includes a power converter 104 and a wireless power transmission device 101 connected in cascade between an input power source 102 and a load 118. In some embodiments, the power converter 104 is used to further improve the performance of the wireless power transmission system 100. In other embodiments, the power converter 104 is an optional element. In other words, the wireless power transmission device 101 can be directly connected to the input power source 102.

[0027] The wireless power transmission device 101 includes a power transmitter 110 (also referred to as a transmitter in this application) and a power receiver 120 (also referred to as a receiver in this application). Figure 1 As shown, the power transmitter 110 includes a transmitter circuit 106, a resonant capacitor group (also referred to as a capacitor bank or bank) 108, and a transmitter coil L1. The resonant capacitor group 108 and the transmitter coil L1 are connected in series, and a resonant cavity (or resonant circuit) can be formed on the transmitter side. In one embodiment, the capacitor group 108 may include a plurality of capacitors connected in parallel, wherein two or more capacitors may be connected to the transmitter coil L1 via a switch. Figure 2 An example of a capacitor bank 108 is provided, where capacitor bank 206 is shown. By selectively switching in and out capacitance in the capacitor bank, the resonant capacitance on the transmitter side can be dynamically controlled during power transmission in the power transmission system 100. This can improve wireless power transmission efficiency and maintain appropriate output gain in a power transmission system (e.g., a 25W magnetic field power configuration (MPP) system).

[0028] According to design requirements and different applications, the transmitter-side resonant cavity may further include a resonant inductor. In some embodiments, the resonant inductor may be implemented as an external inductor. In other embodiments, the resonant inductor may be implemented as a connecting line. The transmitter circuit 106 and the resonant cavity are connected in a cascade manner. The input end of the transmitter circuit 106 is coupled to the output end of the power converter 104. The first output end of the transmitter circuit 106 is connected to the first end of the capacitor bank 108. The second output end of the transmitter circuit 106 is connected to the second end of the capacitor bank 108 through the transmitter coil L1.

[0029] The power receiver 120 includes a receiver coil L2, a resonant capacitor Cs, a rectifier 112, and a power converter 114 connected in cascade. Figure 1 As shown, the resonant capacitor Cs is connected in series with the receiver coil L2 and is further connected to the input of the rectifier 112. The resonant capacitor Cs may also be referred to as a receiver capacitor or a secondary resonant capacitor. The resonant capacitor Cs may help achieve soft switching of the wireless power transmission system 100. The output of the rectifier 112 is connected to the input of the power converter 113. The output of the power converter 113 is coupled to the load 118.

[0030] When the power receiver 120 is placed near the power transmitter 110, the power transmitter 110 is magnetically coupled with the power receiver 120 through a magnetic field. A loosely coupled transformer is formed by the transmitter coil L1 as a part of the transmitter 110 and the receiver coil L2 as a part of the receiver 120. Therefore, power can be transmitted from the transmitter 110 to the receiver 120.

[0031] In some embodiments, the power transmitter 110 can be within a charging pad. The transmitter coil L1 is placed below the top surface of the charging pad. The power receiver 120 can be embedded in an electronic device (e.g., a mobile device) that requires wireless charging, such as a smartphone, tablet computer, smart watch, e-reader, laptop computer, game console, etc. When the electronic device is placed near the charging pad, magnetic coupling is established between the transmitter coil L1 and the receiver coil L2. In other words, the transmitter coil L1 and the receiver coil L2 can form a loosely coupled transformer through which power transfer is generated between the transmitter 110 and the receiver 120. The coupling strength between the transmitter coil L1 and the receiver coil L2 is quantified by the coupling coefficient k. In some embodiments, k is in the range of about 0.05 to about 0.9.

[0032] In some embodiments, after establishing magnetic coupling between the transmitter coil L1 and the receiver coil L2 , the transmitter 110 and the receiver 120 may form a power system through which power is wirelessly transferred from the input power source 102 to the load 118 .

[0033] The input power source 102 may be a power adapter that converts a utility line voltage into a direct current (DC) voltage. The input power source 102 may also be a renewable power source, such as a solar panel array. In addition, the input power source 102 may be any suitable energy storage device, such as a rechargeable battery, a fuel cell, any combination thereof, and / or the like.

[0034] The load 118 represents the power consumed by the electronic device coupled to the power receiver 120. As an example, the load 118 may be a rechargeable battery and / or battery pack connected in series / parallel and coupled to the output of the power receiver 120. As another example, the load 118 may be a downstream power converter, such as a battery charger.

[0035] According to some embodiments, the transmitter circuit 106 may include a primary side switch of a full-bridge converter. The transmitter circuit 106 may include a primary side switch of any other suitable power converter, such as a half-bridge converter, a push-pull converter, any combination thereof, and / or the like.

[0036] It should be noted that the power converters described above are only examples. Those having ordinary skill in the art will recognize that other suitable power converters based on class E topology (eg, class E amplifiers) may be used instead according to design requirements and different applications.

[0037] The transmitter circuit 107 may further include a resonant capacitor ( Figure 2 Not shown, but Figure 3 ). Throughout the specification, the resonant capacitor may be alternatively referred to as a transmitter resonant capacitor or a first resonant capacitor. The magnetic induction of the resonant capacitor and the transmitter coil may form a resonant cavity. According to design requirements and different applications, the resonant cavity may further include a resonant inductor. In some embodiments, the resonant inductor may be implemented as an external inductor. In another embodiment, the resonant inductor may be implemented as a connecting wire.

[0038] The power receiver 120 includes a receiver coil L2, which is magnetically coupled to the transmitter coil L1 after the power receiver 120 is placed near the power transmitter 110. Thus, power can be transmitted to the receiver coil L2 and further transferred to the load 118 through the rectifier 112. Figure 2As shown, the receiver 120 may include a secondary resonant capacitor Cs. Throughout the specification, the secondary resonant capacitor Cs may be alternatively referred to as a receiver resonant capacitor or a second resonant capacitor. The power receiver 120 may further include a communication device (not shown) connected between the input terminal of the rectifier 112 and the ground. The communication device is configured to send a control signal from the receiver 120 to the transmitter 110. For example, the communication device may be configured to transmit the control signal through an appropriate modulation scheme such as amplitude shift keying (ASK). The ASK modulation scheme can be implemented by adjusting the impedance coupled to the receiver coil L2. After adjusting the impedance coupled to the receiving coil L2, the gain of the wireless power transmission system 100 will also change accordingly. The transmitter 110 detects the change in gain by analyzing the current flowing through the transmitter coil L1 and / or the voltage on the transmitter coil L1. The gain change can be demodulated to retrieve the control signal sent by the receiver.

[0039] The rectifier 112 converts the alternating polarity waveform received from the resonant cavity including the receiver coil L2 and the receiver resonant capacitor Cs into a unipolar waveform. The rectifier 112 may be a full-wave diode bridge or a half-wave diode bridge. In some embodiments, the rectifier 112 includes a full-wave diode bridge and an output capacitor. In other embodiments, the full-wave diode bridge may be replaced by a full-wave bridge formed by a switching element such as an n-type metal oxide semiconductor (NMOS) transistor.

[0040] In addition, the rectifier 112 may be formed by other types of controllable devices, such as metal oxide semiconductor field effect transistor (MOSFET) devices, bipolar junction transistor (BJT) devices, super junction transistor (SJT) devices, insulated gate bipolar transistor (IGBT) devices, gallium nitride (GaN) based power devices, and / or the like. The detailed operation and structure of the rectifier 112 are well known in the art and are therefore not discussed herein.

[0041] The power converter 114 is coupled between the rectifier 112 and the load 118. The power converter 113 is a non-isolated power converter. It will be appreciated by those skilled in the art that the following description of the receiver-side power converter 114 is equally applicable to the power converter 104 on the transmitter side, and the power converter 104 can be implemented in a similar manner according to the needs and applications of the transmitter side. The power converter 114 can be used to further adjust the voltage / current applied to the load 118. The power converter 114 can be a non-isolated power converter. In some embodiments, the power converter 114 can be implemented as a step-down power converter (such as a buck converter). In other embodiments, the power converter 114 can be implemented as a four-switch buck-boost power converter.

[0042] In addition, the power converter 114 can be implemented as a hybrid power converter. The hybrid converter is a non-isolated power converter. By controlling the on or off of the switch of the hybrid converter, the hybrid converter can be configured as a buck converter, a charge pump converter or a hybrid converter.

[0043] Depending on design requirements and different applications, the hybrid converter can operate in different operating modes. In particular, when the load current is less than a predetermined current threshold and / or the input voltage is less than a predetermined voltage threshold, the hybrid converter can operate in a buck mode. In buck mode, the hybrid converter is configured as a buck converter. When the input voltage is greater than a predetermined voltage threshold and / or the load current is greater than a predetermined current threshold, the hybrid converter can operate in a charge pump mode or a hybrid mode. In particular, in some embodiments, when the ratio of the output voltage of the hybrid converter to the input voltage of the hybrid converter is less than 0.5, the hybrid converter can operate in a charge pump mode or a hybrid mode. In charge pump mode, the hybrid converter is configured as a charge pump converter. In hybrid mode, the hybrid converter is configured as a hybrid converter.

[0044] In some embodiments, the hybrid converter includes a first switch, a capacitor, and a second switch connected in series between the output terminal of the rectifier 112 and the input terminal of the load 118. The hybrid converter also includes a third switch and a fourth switch. The third switch is connected between a common node of the first switch and the capacitor, and a common node of the second switch and the output terminal of the hybrid converter. The fourth switch is connected between a common node of the capacitor and the second switch and ground.

[0045] In addition, the power converter 114 may include a first power stage and a second power stage connected in cascade. The first power stage is configured to operate in different modes to effectively charge the load 118 (e.g., a rechargeable battery). In some embodiments, the first stage may be implemented as a step-down power converter (e.g., a buck converter), a four-switch buck-boost converter, a hybrid converter, and any combination thereof. The second stage power supply is configured as a voltage divider or an isolation switch.

[0046] In some embodiments, the wireless power transmission device 101 may include a control circuit 130 connected to the power transmitter 110. For example, the control circuit 130 may be specifically connected to the resonant cavity of the power transmitter 110. The control circuit 130 is configured to control the switching in and out of the capacitors in the capacitor bank 108 in response to the switching signaling. The switching signaling may be a system command for turning on or off a switch in the capacitor bank to switch in or out the capacitor associated with the switch. The control circuit 130 may be configured to detect parameters on the transmitter side, determine whether to switch the capacitor based on the detected parameters, and generate corresponding control signaling based on the determination result and the switching signaling. For example, the control signaling may be an instruction / command to instruct to open the switch by applying a drive signal. Further details will be provided below.

[0047] Figure 2 2 is a schematic diagram of an exemplary circuit 200 of a power transmitter in a wireless power transmission system according to an embodiment of the present application. The circuit 200 can be used to implement Figure 1 The power transmitter 110 shown. In this example, the circuit 200 includes a switch circuit 204 (which can be used to implement Figure 1 1 ), a capacitor bank 206, and a transmitter coil 208 (Ltx). Here, the capacitor bank may also be referred to as a bank. The switch circuit 204 includes power switches 212, 214, 216, and 218. For example, the power switches may be implemented using MOSFETs. The power switches 212 and 214 are connected in series between the input power source 202 and the ground. The power switches 216 and 218 are connected in series between the input power source 202 and the ground. The common node between the power switches 212 and 214 is SW1. The common node between the power switches 216 and 218 is SW2. The voltage Vin of the input power source 202 may be controlled according to various needs and applications. The input power source 202 may be the output of a power converter (e.g., the power converter 104), an applicable energy storage device, or an applicable energy source.

[0048] The capacitor bank 206 is connected in series with the transmitter coil 208. The capacitor bank 206 in this example includes four capacitors, namely Ctx1, Ctx2, Ctx3 and Ctx4. The capacitor Ctx1 is connected in series with the transmitter coil 208 between nodes SW1 and SW2. The capacitor Ctx2 is connected in series with the first switch S1 between the two terminals T1 and T2 of the capacitor Ctx1. The capacitor Ctx3 is connected in series with the second switch S2 between the two terminals T1 and T2 of the capacitor Ctx1. The capacitor Ctx4 is connected in series with the third switch S3 between the two terminals T1 and T2 of the capacitor Ctx1. That is, Ctx1, Ctx2 and their associated switches S1, Ctx3 and their associated switches S2, and Ctx4 and their associated switches S3 are connected in parallel between nodes T1 and T2. Figure 2 Four capacitors included in the capacitor bank 206 are shown for illustration purposes only, and various numbers of capacitors, such as 2, 3, 5, or 6 capacitors, may be included in the capacitor bank 206 according to design needs and applications. As an example, the capacitors Ctx1-Ctx4 may have capacitances of 68 nanofarads (nF), 33 nF, 390 nF, and 33 nF, respectively.

[0049] Switches S1-S3 may each be implemented as a single switch or as back-to-back switches and may be implemented using field effect transistors (FETs). Figure 3 is a schematic diagram showing an example switch that can be used to implement switches S1-S3 according to an embodiment of the present application. Switch 302 is an example of an N-type switch, including an N-MOSFET and an integral diode. Switch 304 is an example of a P-type switch, including a P-MOSFET and an integral diode. Switch 312 is an example of a back-to-back switch, including two N-MOSFETs, whose sources are directly connected to each other. Switch 314 is an example of a back-to-back switch, including two N-MOSFETs, whose drains are directly connected to each other. Switch 316 is an example of a back-to-back switch, including two P-MOSFETs, whose sources are directly connected to each other. The structure and operation of the switches are well known in the art and will not be described in detail here.

[0050] The power transmission system can be configured to switch in or out one or more capacitors Ctx2, Ctx3, and Ctx4 during power transmission of the power transmission system. By selectively switching in or out a capacitor on the power transmitter side, the power transmitter provides a dynamically adjustable resonant capacitance in the capacitor bank 206 to adapt to different load requirements and / or scenarios with different coupling strengths of the transformer, which enables the power transmission system to maintain a suitable system output gain and obtain an ideal wireless charging efficiency.

[0051] For example, the power transmission system may determine whether to cut in or cut out one of the capacitors Ctx2-Ctx4 based on the power requirements of the load and / or the coupling strength of the transformer. For example, in the case of a high-power load and a coupling coefficient K>0.81*α, the power transmission system may choose to cut in capacitor Ctx3 to provide a resonant capacitance of 458nF. The power transmission system may issue a switching command / signaling to trigger the switching on or off of the switch S2 associated with the capacitor Ctx3. During the power transmission process of the power transmission system, a driving voltage may be applied to the switch S2 to turn on the switch S2, thereby cutting in the capacitor Ctx3 in the resonant cavity on the transmitter side. The switching command / signaling may indicate the switching in of one or more capacitors in the capacitor bank.

[0052] Switching capacitors during power transfer in a power transfer system may stress the devices (e.g., switches) of the resonant cavity. For example, one problem that may occur during the turn-on process is that a surge current may be generated through the switch that is turned on (e.g., switch S2), which may be large and may cause huge transient power losses and damage the switch. This problem may generally be caused by a large difference between the voltage on capacitor Ctx1 and the voltage on the capacitor that is cut in. For example, if switch S2 is turned on to switch capacitor Ctx3 when the voltage on capacitor Ctx1 is zero-crossing or close to zero and the voltage on capacitor Ctx3 is approximately the input voltage Vin, a large surge current may be generated through switch S2, thereby stressing switch S2.

[0053] To alleviate or avoid such stress, in some embodiments, a control circuit (or controller) may be provided, such as Figure 1 The control circuit 130 shown is further configured to control the switching-in of the capacitors of the capacitor bank when a command (or signaling) to switch on the relevant switches of the capacitors (capacitors to be switched in) is received. Specifically, the control circuit can control whether or when to switch in the capacitors when a command is received. For example, when the difference between the voltage on the capacitor Ctx1 and the voltage on the capacitor to be switched in is zero or less than a threshold, the capacitor needs to be switched in so as to reduce the pressure on the switch of the capacitor to be switched in when the switch is turned on during the operation of the power transmission system.

[0054] Various embodiments are described below by taking the command indicating to turn on the switch S2 to switch in the capacitor Ctx3 as an example. These embodiments are also applicable to the switching of other capacitors in the capacitor bank.

[0055] In some embodiments, upon receiving a command, the control circuit may control the capacitor Ctx3 to be switched in (e.g., fully opening the switch S2) when a predetermined event occurs. The event may be determined based on one or more parameters of the power transmitter, such as the voltage across the capacitor Ctx1 or the current flowing through the transmitter coil Ltx 208. Other applicable parameters may also be used to determine the event if they can be detected and used to determine whether a capacitor of the capacitor bank can be switched in with a tolerable / acceptable inrush current. The implementation of determining whether to switch a capacitor based on whether a predetermined event occurs is referred to as event-based switching. When enabled, the power transmitter may operate in an event-based switching mode.

[0056] When one or more parameters meet the predetermined conditions, an event may occur, as shown below. Figure 2 Give an example.

[0057] In one embodiment, when a command is received, the control circuit may control the capacitor Ctx3 to be switched in when the voltage across the capacitor Ctx1 reaches the peak voltage of the capacitor Ctx1. In another embodiment, when a command is received, the control circuit may control the capacitor Ctx3 to be switched in when the voltage across the capacitor Ctx1 is greater than a voltage threshold. Depending on the design requirements or application of the power transmission system, the voltage threshold may be determined according to the peak voltage of the capacitor Ctx1. For example, the voltage threshold may be set to 80%, 90%, or 95% of the peak voltage of the capacitor Ctx1.

[0058] In another embodiment, when a command is received, the control circuit may control the capacitor Ctx3 to be switched in when the current flowing through the transmitter coil 208 of the power transmitter crosses zero value (0) (i.e., crosses zero). In another embodiment, when a command is received, the control circuit may control the capacitor Ctx3 to be switched in when the current flowing through the transmitter circuit 204 (bridge current, such as the current flowing through the switches 212, 214, 216, or 218) crosses zero value (0) (i.e., crosses zero). The current flowing through the transmitter circuit 204 is the same as the current flowing through the power transmitter transmitting coil. In another embodiment, when a command is received, the control circuit may control the capacitor Ctx3 to be switched in when the current flowing through the transmitter coil (or bridge current) is less than a current threshold. Depending on the design requirements or application of the power transmission system, the current threshold may be determined according to the peak current of the transmitter coil Ltx. For example, the current threshold may be set to 1%, 5%, or 10% of the peak current of the transmitter coil Ltx.

[0059] When the switch S2 is a back-to-back switch, the following embodiments may be provided.

[0060] In one embodiment, when a command is received, the control circuit may control the switch-in capacitor Ctx3 when the voltage across the capacitor Ctx1 crosses zero (0) (i.e., crosses zero). In another embodiment, when a command is received, the control circuit may control the switch-in capacitor Ctx3 when the voltage across the capacitor Ctx1 is less than a voltage threshold. Depending on the design requirements or application of the power transmission system, the voltage threshold may be determined based on the peak voltage of the capacitor Ctx1. For example, the voltage threshold may be set to 1%, 5%, or 10% of the peak voltage of the capacitor Ctx1.

[0061] In another embodiment, when a command is received, the control circuit may control the cut-in capacitor Ctx3 when the current (or bridge current) flowing through the transmitter coil of the power transmitter reaches the peak current of the transmitter coil. In another embodiment, when a command is received, the control circuit may control the cut-in capacitor Ctx3 when the current (or bridge current) flowing through the transmitter coil is greater than a current threshold. Depending on the design requirements or application of the power transmission system, the current threshold may be determined according to the peak current of the transmitter coil. For example, the current threshold may be set to 80%, 95%, or 98% of the peak current of the transmitter coil Ltx.

[0062] In some embodiments, when a command is received, the control circuit may control the cut-in capacitor Ctx3 when the difference between the voltage on the capacitor Ctx1 and the voltage on the capacitor to be cut-in is less than a voltage threshold. The voltage threshold may be determined based on the tolerance of the power transmission system to the inrush current caused by the switching capacitor and / or the required power transmission efficiency.

[0063] In some embodiments, the control circuit can control the driving speed of the switch (such as S2) to turn on the switch slowly or gradually to avoid generating a large surge current. Taking the use of field effect transistors to implement switch S2 as an example, according to the gate drive voltage, the field effect transistor can operate in one of at least three modes: conduction mode (field effect transistor is used as a fully turned-on switch), cut-off mode (field effect transistor is used as a disconnected switch) and ohmic mode (field effect transistor is used as a switch with variable on-resistance and controllable by the gate drive voltage). In some embodiments, by changing the gate drive voltage under the control of the control circuit, the switch S2 can be driven to generate various on-resistances, so that the current flowing through the switch S2 increases at a predetermined rate or a predetermined mode. This implementation method can be referred to as drive-based switching. When enabled, the power transmitter can operate in a drive-based switching mode. Whether or not event-based switching is enabled, the power transmitter can perform drive-based switching.

[0064] As an example, when it is determined to cut in the capacitor Ctx3, the control circuit may control the switch S2 to be initially turned on at a first drive voltage within a first time interval, wherein the first drive voltage causes the switch S2 to have a first on-resistance, which limits the current flowing through the switch S2 to the first current I1. The first drive voltage may be set so that the first current I1 is small and does not cause any stress to the turned-on switch S2. In the next time interval (second time interval), the control circuit may control the gate drive voltage of the switch S2 to become a second drive voltage, so that the switch S2 has a second on-resistance that is smaller than the first on-resistance. The second on-resistance limits the current flowing through the switch S2 to a second current I2 that is greater than the first current I1. Then, the control circuit may control the drive voltage of the switch S2 to be similarly changed within the next time interval (third time interval) to allow the current flowing through the switch S2 to increase (e.g., greater than the second current I2), and so on.

[0065] In one embodiment, the control circuit may continue to control the change of the driving voltage of switch S2 until the current flowing through switch S2 reaches the threshold level, or until switch S2 is fully turned on. In another embodiment, each time before changing the driving voltage of switch S2 for the next time interval, the control circuit may detect whether the difference between the voltage on capacitor Ctx1 and the voltage on capacitor Ctx3 is less than the voltage threshold. If the difference is less than the voltage threshold, the control circuit may control switch S2 to be fully turned on. If the difference is not less than the voltage threshold, the control circuit may control the change of the driving voltage of switch S2 in the next time interval to increase the current flowing through switch S2, as described above.

[0066] The lengths of the time intervals may be the same or different. The lengths of the time intervals, the number of time intervals used (i.e., the number of different drive voltages used to change the on-resistance of the switch), the difference between the drive voltages used in the time intervals, and / or the increment of the current (the rate of current increase) may be predetermined and configured according to various design needs and practical applications. As a principle, these parameters are selected / determined to avoid or reduce the stress caused by turning on the switch S2 when the power transmitter is operating to transfer power.

[0067] In the above embodiment, when operating in the drive-based switching mode, the control circuit can control a set of drive voltages to be applied to the switch S2 in sequence, so that the switch S2 has a set of corresponding on-resistances, so that the current flowing through the switch S2 gradually increases, thereby avoiding a large surge current when the switch S2 is turned on.

[0068] In some embodiments, when it is determined that the switch S2 is turned on, the control circuit can control the switch S2 to be turned on at a predetermined driving voltage, so that the switch S2 has an on-resistance, thereby limiting the current flowing through the switch S2 to below the current threshold. The current threshold can be determined by considering the switch S2's ability to withstand surge current, power transmission efficiency, allowable power loss, or other applicable factors. In one embodiment, the switch S2 can be controlled to remain in a conducting state driven by a predetermined driving voltage until it is turned off, for example in response to a command to disconnect the switch S2. In another embodiment, after the switch S2 is turned on at a predetermined driving voltage, the control circuit can continuously or periodically detect whether the difference between the voltage across the capacitor Ctx1 and the voltage across the capacitor Ctx3 is less than the voltage threshold. If the difference is less than the voltage threshold, the control circuit can control the switch S2 to be fully turned on. If the difference is not less than the voltage threshold, the control circuit can control the switch S3 to remain turned on by a predetermined driving voltage.

[0069] In the power transmitter, one or both of the event-based switching mode and the drive-based switching mode can be enabled. Which mode the power transmitter enables can be predetermined and configured.

[0070] Figure 4 4 is a flow chart of an example method 400 for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application. The method 400 may be performed by a controller / processor of a power transmission system (including a control circuit of an embodiment). By using the method 400, the power transmission system may perform capacitor bank switching according to an embodiment of the present disclosure, or fall back to conventional switching. One or more switching modes may be configured / enabled for the power transmission system.

[0071] The method 400 starts from step 402 and proceeds to step 404 to determine whether a switching command for capacitor switching is received. If a switching command is not received, the method 400 will continue to monitor the switching command (step 404). If a switching command is received, the method 400 proceeds to step 406 to determine whether an event-based switching mode is enabled. If the event-based switching mode is not enabled, the method 400 may determine whether a drive-based switching mode is enabled in step 408. If the drive-based switching mode is not enabled, the method 400 may perform conventional switching in step 410, wherein the control circuit controls the relevant switch of the capacitor to be switched in with a drive voltage in response to the received switching command.

[0072] If the drive-based switching mode is enabled, the method 400 performs drive-based switching at step 412 as described above. As an example, the control circuit can control the switch to be turned on by applying various drive voltages to the switch so that the switch presents various on-resistances, thereby increasing the current flowing through the switch gradually or at a predetermined rate. The control circuit can continuously change the drive voltage until the current flowing through the switch increases to a threshold value, or until the switch is fully turned on. For another example, the control circuit can control the switch to be turned on at a predetermined drive voltage, which limits the current flowing through the switch to be less than a current threshold to avoid generating a large surge current. As another example, the control circuit can control the switch to be turned on at a predetermined drive voltage, allowing a small current to flow through the switch, and fully turning on the switch when the difference between the voltage on the capacitor Ctx1 and the voltage on the capacitor to be cut in is less than a voltage threshold.

[0073] If the event-based switching mode is enabled, the method 400 may proceed to step 414 to detect whether an event occurs. As described above, in the case where the switch is implemented as a single switch, an event occurs when the voltage on the capacitor Ctx1 is greater than or equal to a threshold value, which may be the peak voltage of the capacitor Ctx1 or may be determined based on the peak voltage of the capacitor Ctx1; or, an event occurs when the current through the transmitter coil Ltx passes zero or is less than a threshold value. In the case where the switch is implemented as a back-to-back switch, an event occurs when the voltage on the capacitor Ctx1 is zero or less than a threshold value, or when the current through the transmitter coil Ltx is greater than or equal to a threshold value, which may be the peak current of the transmitter coil Ltx or may be determined based on the peak current of the transmitter coil Ltx. If an event occurs, the method 400 proceeds to step 416 to switch in the capacitor by fully turning on the switch. Which event will be used for the event-based switching mode may be pre-configured by the controller or may be configured by the controller.

[0074] If the event does not occur, the method 400 may proceed to step 418 to determine whether the drive-based switching mode is enabled. If the drive-based switching mode is enabled, the method 400 may proceed to step 412 to perform the above-mentioned drive-based switching. If the drive-based switching mode is not enabled, the control circuit may control not to cut in the capacitor in step 420. In this case, the method 400 may proceed to step 414, in which the control circuit may continue to monitor whether an event occurs and determine whether to cut in the capacitor based on this.

[0075] Although the steps of method 400 described above are as follows Figure 4As shown, a person of ordinary skill in the art will recognize that one or more steps may be removed and / or the steps may be optionally rearranged depending on the operating mode of the power transmitter. For example, when the power transmitter is preconfigured for an event-based switching mode, steps 406-412 and step 418 may be deleted. In this case, method 400 switches the capacitor when an event occurs. As another example, when the power transmitter is preconfigured for an event-based switching mode and a drive-based switching mode, steps 406-410 and steps 418 and 420 may be deleted. In this case, when it is detected that an event has not occurred, method 400 may perform drive-based switching. As yet another example, step 420 may be optional. As yet another example, when the power transmitter is preconfigured for a drive-based switching mode, method 400 may only perform steps 404 and 412.

[0076] Figure 5 is a schematic diagram of an exemplary control circuit 500 of a power transmission system according to an embodiment of the present application. Figure 5 The power transmitter 200 is used as an example for illustration purposes only. When the event-based switching mode is enabled, the control circuit 500 may be applied. As shown in the figure, the control circuit 500 includes a detection circuit 510 and a control logic circuit 520. The detection circuit 510 is configured to receive a parameter of the power transmitter, detect whether an event occurs according to the parameter, and output a signal D indicating whether the event occurs. event . Output signal D event It can be a logic signal indicating whether an event has occurred. event It can be a logic high signal (1) indicating that an event has occurred, or a logic low signal (0) indicating that an event has not occurred.

[0077] The control logic circuit 520 can be configured to event The control signals C1, C2, and C3 are generated by the switching commands for turning on / off the switches for cutting in the corresponding capacitors to control the on / off of the switches S1-S2. The control signals C1, C2, or C3 can be a logic high signal (1) indicating turning on the switch; or a logic low signal (0) indicating turning off the switch. A person skilled in the art will recognize that the signal D event Other configurations of the control signals C1, C2, C3 may also be applicable. For example, the signal may be a logic low signal indicating that an event has occurred, or a logic high signal indicating that an event has not occurred.

[0078] Taking capacitor Ctx3 / switch S2 as an example, when a switching command to cut in capacitor Ctx3 (i.e., turn on the relevant switch S2) is received and an event occurs, the control logic circuit may generate a control signal C2 (e.g., a logic high level) to trigger the switch S2 to be turned on. When no switching command is received or the event does not occur, the control logic circuit may generate a control signal C2 (e.g., a logic low level) to instruct to keep switch S2 turned off, or to instruct to perform drive-based switching (if the drive-based switching mode is enabled). In one example, the control logic may be implemented using an AND logic gate, where the two input terminals (e.g., G1 and G2) of the AND logic gate receive signals D respectively. event The AND logic gate outputs a control signal C1, C2 or C3 at the output terminal of the AND logic gate. When there is a switching command, the terminal G2 of the AND logic gate can receive a logic high level signal; when there is no switching command, the terminal G2 of the AND logic gate can receive a logic low level signal.

[0079] The detection circuit 510 may include a scaling circuit 512, a sampling / holding circuit 514, and a comparator circuit 516 connected in cascade. The scaling circuit 512 is configured to adjust / regulate (e.g., amplify or reduce) the value of an input parameter so that it is within a range suitable for subsequent circuit processing, and to generate an output signal Dsc having an adjusted value of the input parameter. The scaling circuit 512 may be optional. The sampling / holding circuit 514 is configured to receive a signal Dsc, sample the signal Dsc to generate a sampling value / sampling signal Dsa, and hold the sampling value / sampling signal Dsa and feed it to the comparator circuit 516. The comparator circuit 516 is configured to compare the sampling value Dsa with a threshold value to determine whether an event occurs, and output a signal D indicating the determination result accordingly. event .

[0080] Table 1 below shows Figure 2 Taking the power transmitter 200 in FIG. 1 as an example, nine situations are provided, including example parameters that can be used to detect the occurrence of an event, corresponding events, and corresponding thresholds that can be used for detection. These situations have been discussed above and will not be repeated here. The controller of the power transmitter can be configured to detect one or more events to control the switching of the capacitor bank in response to a switching command.

[0081] Table 1

[0082]

[0083] In some embodiments, when it is determined (e.g., using method 400) that event-based switching mode, drive-based switching mode, or both are enabled for the power transmitter, the controller / processor may be configured to issue a control signal to connect the control circuit to the power transmitter, and the control circuit begins operating in the corresponding enabled mode. For example, Figure 1 A switch may be connected between the control circuit 130 and the power transmitter 100. In response to a control signal, the switch is controlled to be turned on, and the control circuit starts receiving parameters, detecting events, and controlling the switching of the capacitor bank.

[0084] Figure 6 6 is a schematic diagram of an example circuit 600 of a transmitter side of a power transmission system according to an embodiment of the present application. Circuit 600 shows an example implementation of control circuit 500, in which an event-based switching mode is enabled. Circuit 600 includes a power transmitter 610 of a power transmission system and a control circuit, the control circuit including a proportional circuit 620, a sample / hold circuit 630, a comparator 640, and an AND logic gate 650.

[0085] The power transmitter 610 is similar to the power transmitter 200, so it is not described again here. In this embodiment, the circuit 600 is configured to detect an event of the voltage across the capacitor Ctx1, and determine whether to switch the capacitor, such as Ctx3, in response to a switching command based on the detection result. The voltage event across the capacitor Ctx1 may include the example events shown in Table 1 above.

[0086] The proportional circuit 620 includes an amplifier 622 and resistors R1, R2, R3 and R4. Resistors R1 and R2 are connected in series between a reference voltage (VREF) and a node T2 of the power transmitter 610. The common node of the resistors R1 and R2 is connected to a first input terminal of the amplifier 622. Resistors R3 and R4 are connected in series between an output terminal of the amplifier 622 and a node T1 of the power transmitter 610. The common node of the resistors R3 and R4 is connected to a second input terminal of the amplifier 622. Therefore, the first input terminal of the proportional circuit 620 receives a divided voltage of the voltage of the node T2 (i.e., one terminal of Ctx1), and the second terminal of the proportional circuit 620 receives a divided voltage of the voltage of the node T1 (i.e., another terminal of Ctx1). When VREF=0 and the resistance values ​​of the resistors R1-R4 are the same, the voltage of the output signal Dsc of the proportional circuit 620 is approximately equal to V T2 -V T1 .

[0087] The sample / hold circuit 630 samples the output signal Dsc to generate a sampled signal / voltage Dsa and feeds it to the comparator 640. The sample / hold circuit 630 can be implemented using various conventionally known circuits or any other applicable circuits. The comparator 640 compares the sampled signal Dsa with a threshold value to determine whether an event occurs and outputs a signal D indicating the comparison result at its output terminal. event In this case, the threshold value may be any threshold value shown in Table 1. For example, the threshold value may be the peak voltage of Ctx1, a zero value (0) in the case of back-to-back switching, or a predetermined voltage threshold. The output terminal of the comparator 640 is connected to the first input terminal G1 of the AND logic gate 650. The second input terminal G2 of the AND logic gate 650 is connected to the switching command signal. When the sampling signal Dsa meets the threshold value, the output signal D event It can be a logic high signal and is fed to port G1 of the AND logic gate. In response to the switching command appearing on port G2 (i.e., the logic high level on G2), the AND logic gate 650 outputs a logic high signal C 1,2,3 , which can be used to trigger / control the switching on of the capacitor to be switched in, such as Ctx3 indicated by the switching command. When the sampling signal Dsa does not meet the threshold, the AND logic gate 650 can output a logic low signal for controlling the switch to be turned off or performing drive-based switching (if enabled).

[0088] Figure 7 is a schematic diagram showing an exemplary waveform of a circuit 600 according to an embodiment of the present application. In this example, the control circuit detects that the voltage across Ctx1 reaches its peak voltage, and controls the switch S2 to be turned on in response to a switching command indicating that the capacitor Ctx3 is turned on. In Figure (a), the vertical axis represents the current. In Figure (b), the vertical axis represents the voltage. The horizontal axis of both figures represents time. Curve 710 represents the current flowing through the transmitter coil Ltx. Curve 712 represents the current flowing through the capacitor Ctx3. Curve 720 represents the voltage across the capacitor Ctx1. Curve 722 represents the drive voltage for turning on the switch S2. Curve 724 represents the voltage across the capacitor Ctx3. The control circuit detects that the voltage across the capacitor Ctx1 reaches the peak voltage at time T1, and in response to receiving the switching command, the control circuit may generate a control signal to control the application of the drive voltage immediately after time T1 to fully open the switch S2. By using event-based switching, the inrush current can be greatly reduced.

[0089] Figure 88 is a schematic diagram of another example circuit 800 of the transmitter side of the power transmission system according to an embodiment of the present application. The circuit 800 shows an example implementation of the control circuit 500, in which the event-based switching mode is enabled. The circuit 800 includes a power transmitter 610 of the power transmission system, and a control circuit including a sample / hold circuit 630, a comparator 640, and an AND logic gate 650, as shown in FIG. Figure 6 Circuit 800 differs from circuit 600 in that circuit 800 does not include a proportional circuit and circuit 800 is configured to detect current events flowing through transmitter coil Ltx. Current events may include the example events shown in Table 1 above. Based on the detection result, circuit 800 determines whether to switch a capacitor, such as Ctx3, in response to a switching command.

[0090] As shown in the figure, Figure 8 In the example of FIG. 6 , the sample / hold circuit 630 may be configured to sample the current I1 flowing through the transmitter coil Ltx to generate and hold a sampled signal / current Dsa, which is fed into the comparator 640. The comparator 640 compares the sampled signal Dsa with a threshold value to determine whether an event occurs, and outputs a signal D indicating the comparison result at its output terminal. event In this case, the threshold value may be any threshold value shown in Table 1. For example, the threshold value may be a peak current of Ltx, a zero value (0) in the case of back-to-back switching, or a predetermined current threshold value.

[0091] When the sampling signal Dsa meets the threshold, the output signal D event It can be a logic high signal and is fed to terminal G1 of the AND logic gate. In response to the switching command appearing on terminal G2 (logic high level on G2), the AND logic gate 650 outputs a logic high signal C 1,2,3 , which can be used to trigger / control the switching of the capacitor to be switched, such as Ctx3 indicated by the switching command. When the sampling signal Dsa does not meet the threshold, the AND logic gate 650 can output a logic low signal for controlling the switch to be turned off or performing drive-based switching (if enabled).

[0092] Since the current I1 is the same as the current I2 flowing through the bridge circuit in the transmitter circuit, the control circuit can also detect the current I2 to detect whether the event occurs.

[0093] In some embodiments, the power transmission system may include a control circuit that is a combination of circuit 600 and circuit 800. That is, the control circuit may be configured to detect a voltage event across Ctx1 and to detect a current event flowing through the transmitter coil Ltx. For example, the control circuit may include a first control branch that includes elements 620, 630, 640, and 650 connected as shown in circuit 600 for switching control based on detection of a voltage event across Ctx1; and a second control branch that includes elements 630, 640, and 650 connected as shown in circuit 800 for switching control based on detection of a current event flowing through the transmitter coil Ltx.

[0094] In some embodiments, a switching command may be received to switch multiple switches. In this case, multiple AND logic gates may be provided, each AND logic gate being associated with a switch. Figure 6 For example, the switching command may indicate switching between Ctx2 and Ctx3. event The two AND logic gates associated with switches S1 and S2 can be fed respectively. Each AND logic gate can be based on the control signal D event And the switching command outputs the corresponding control signal.

[0095] Figure 6 and Figure 8 Example implementations of the control circuit in some cases are provided, such as the several cases shown in Table 1, and those skilled in the art can easily implement other cases based on the concepts and principles of the present application. Various changes, modifications and alterations can be made without departing from the principles and spirit of the present application to provide a control circuit configured to perform event-based switching and drive-based switching.

[0096] Fig. 9 900 is a flowchart of another exemplary method 900 for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application. The method 900 can be applied to circuit 600 or circuit 800 and can be performed by the control circuit as described above. As shown in the figure, in step 902, the control circuit can monitor the voltage event across the first capacitor (e.g., Ctx1) of the capacitor bank (e.g., capacitor bank 206) or the current event flowing through the transmitter coil (e.g., Ltx) of the power transmitter (e.g., power transmitter 200 or 610). The control circuit can determine whether the event occurs in step 904. When the event occurs, in response to the switching command / signal of the capacitor (e.g., Ctx3), the control circuit controls the switching capacitor by controlling the switch S2 associated with Ctx3 to be fully turned on in step 906. When the event does not occur, the control circuit executes step 902 to continue monitoring the event. Step 902 can be performed continuously or periodically, or when a switching command is received.

[0097] Fig.10 1 is a flowchart of another exemplary method 1000 for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application. The method 1000 may be applied to the circuit 600 or the circuit 800 and may be performed by the control circuit as described above. As shown in the figure, in step 1002, the control circuit may monitor a voltage event across a first capacitor (e.g., Ctx1) of a capacitor bank (e.g., capacitor bank 206) or a current event through a transmitter coil (e.g., Ltx) of a power transmitter (e.g., power transmitter 200 or 610). In step 1004, the control circuit may determine whether an event occurs. When an event occurs, in response to a switching command / signal of a capacitor (e.g., Ctx3), the control circuit controls the switching capacitor by controlling the switch S2 associated with Ctx3 to be fully turned on in step 1006. When the event does not occur, the control circuit executes step 1008 to control the execution of actuation-based switching to turn on the switch S2. Step 1002 may be performed continuously or periodically, or may be performed when a switching command is received.

[0098] Fig.11 1 is a flowchart of another exemplary method 1100 for switching control of a capacitor bank in a power transmitter according to an embodiment of the present application. The method 1100 may be applied to the circuit 600 or the circuit 800 and may be performed by the control circuit as described above. As an example, the wireless power transmitter may include: a first capacitor and a transmitter coil connected in series; and a second capacitor connected in series with a first switch, wherein the second capacitor and the first switch are connected in parallel with the first capacitor. As shown in the figure, in step 1102, the control circuit may monitor whether a voltage event across the first capacitor or a current event of the transmitter coil occurs. In step 1104, when the event occurs, the control circuit may control the first switch to be turned on in response to a signal to turn on the first switch.

[0099] Although the present application has been described in detail, it should be understood that various changes, substitutions and modifications may be made without departing from the spirit and scope of the present application as defined by the appended claims. In addition, the scope of the present application is not intended to be limited to the specific embodiments described herein, as those of ordinary skill in the art will readily understand from the present application that currently existing or later developed processes, machines, manufactures, material compositions, means, methods or steps may be utilized according to the present application, which processes, machines, manufactures, material compositions, means, methods or steps may perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein. Therefore, the appended claims are intended to include such processes, machines, manufactures, material compositions, means, methods or steps within their scope.

Claims

1. A device for wireless power transmission, characterized in that: Including resonant circuit and control circuit, The resonant circuit comprises: a transmitter coil; a first capacitor connected in series with the transmitter coil; and a second capacitor connected in series with a first switch, wherein the second capacitor and the first switch are connected in parallel with the first capacitor; The control circuit is connected to the resonant circuit and is configured as follows: detecting whether a voltage event across the first capacitor or a current event of the transmitter coil occurs; and When the occurrence of the event is detected, the first switch is turned on in response to a signaling control for turning on the first switch.

2. The device according to claim 1, characterized in that The event includes a voltage across the first capacitor reaching a peak voltage of the first capacitor.

3. The device according to claim 1, characterized in that The event includes a voltage across the first capacitor being greater than a voltage threshold.

4. The device according to claim 1, characterized in that The event comprises a current zero crossing of the transmitter coil.

5. The device according to claim 1, characterized in that The event includes a current of the transmitter coil being less than a current threshold.

6. The device according to claim 1, characterized in that The first switch is a back-to-back switch, and The event comprises a voltage across the first capacitor crossing zero.

7. The device according to claim 1, characterized in that The first switch is a back-to-back switch, and The event includes the current of the transmitter coil reaching a peak current of the transmitter coil.

8. The device according to claim 1, characterized in that The event includes a difference between a voltage across the first capacitor and a voltage across the second capacitor when the first switch is off being less than a voltage threshold.

9. The device according to claim 1, characterized in that The apparatus further comprises a transmitter switching circuit connected to the resonant circuit, wherein the transmitter switching circuit comprises: a first power switch and a second power switch connected in series between a power source and ground, wherein a common node of the first power switch and the second power switch is connected to a first terminal of the transmitter coil; and A third power switch and a fourth power switch are connected in series between the power source and ground, wherein a common node of the third power switch and the fourth power switch is connected to the second terminal of the transmitter coil via the first capacitor.

10. The device according to claim 1, characterized in that The control circuit is further configured as: When the event does not occur, and in response to a signal to turn on the first switch, the first switch is turned on with a variable driving voltage to adjust the on-resistance of the first switch so that the current flowing through the first switch increases at a predetermined rate.

11. The device according to claim 10, characterized in that The control circuit is further configured as: When the difference between the voltage across the first capacitor and the second voltage is less than a voltage threshold, the first switch is controlled to be fully turned on, and the second voltage is the voltage across the second capacitor when the first switch is turned on by the driving voltage.

12. The device according to claim 1, characterized in that The control circuit is further configured as: When the event does not occur, and in response to the signaling to turn on the first switch, the control turns on the first switch with a predetermined driving voltage, the predetermined driving voltage generates an on-resistance of the first switch, and the on-resistance limits the current flowing through the first switch to below a current threshold.

13. A method for a wireless power transmitter, wherein the wireless power transmitter comprises: a first capacitor and a transmitter coil connected in series; and a second capacitor connected in series with the first switch, wherein the second capacitor and the first switch are connected in parallel with the first capacitor; and The method comprises: detecting whether a voltage event across the first capacitor or a current event of the transmitter coil occurs; as well as When the event occurs, the first switch is turned on in response to a signaling control for turning on the first switch.

14. The method according to claim 13, characterized in that Detecting whether the event occurs includes: The occurrence of the event is detected when the voltage across the first capacitor reaches a peak voltage of the first capacitor, or The occurrence of the event is detected when the current in the transmitter coil passes through zero.

15. The method according to claim 13, characterized in that The first switch is a back-to-back switch; and Detecting whether the event occurs includes: The event is detected when the voltage across the first capacitor passes through zero, or The occurrence of the event is detected when the current of the transmitter coil reaches a peak current of the transmitter coil.

16. The method according to claim 13, characterized in that Detecting whether the event occurs includes: The occurrence of the event is detected when a difference between a voltage across the first capacitor and a voltage across the second capacitor when the first switch is turned off is less than a voltage threshold.

17. The method according to claim 13, further comprising: When it is detected that the event does not occur, and in response to a signal to turn on the first switch, controlling the first switch to be turned on with a variable driving voltage so as to adjust the on-resistance of the first switch so that the current flowing through the first switch increases at a predetermined rate; as well as When the difference between the voltage across the first capacitor and the second voltage is less than a voltage threshold, the first switch is controlled to be fully turned on, and the second voltage is the voltage across the second capacitor when the first switch is turned on by the driving voltage.

18. A controller comprising: The circuit is configured as: detecting a voltage across a first capacitor in a capacitor bank or a current of a transmitter coil, wherein the capacitor bank is connected in series with the transmitter coil, the capacitor bank further comprising a second capacitor connected in series with a first switch, the second capacitor and the first switch being connected in parallel with the first capacitor; determining whether the voltage across the first capacitor or the current of the transmitter coil satisfies a predetermined condition; as well as When the voltage across the first capacitor or the current of the transmitter coil satisfies the predetermined condition, the first switch is controlled to be turned on in response to the received signaling control to turn on the first switch.

19. The controller according to claim 18, wherein: When the voltage across the first capacitor reaches the peak voltage of the first capacitor, the voltage across the first capacitor satisfies the predetermined condition; as well as When the current of the transmitter coil passes through zero, the current of the transmitter coil satisfies the predetermined condition.

20. The controller according to claim 18, wherein: The first switch is a back-to-back switch; When the voltage across the first capacitor passes through zero, the voltage across the first capacitor satisfies the predetermined condition; as well as When the current of the transmitter coil reaches the peak current of the transmitter coil, the current of the transmitter coil satisfies the predetermined condition.

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