Wireless power transmission system based on self-resonant PCB coil and half-bridge rectification and control method thereof

Abstract

The application discloses a wireless power transmission system based on a self-resonant PCB coil and a half-bridge rectifier and a control method thereof, and relates to the technical field of wireless power transmission. The system comprises a direct-current power supply, a full-bridge inverter, a self-resonant PCB coil, a half-bridge rectifier and a control circuit. The coil uses interlayer distributed parasitic capacitance to replace discrete compensation capacitance to form an inherent series-series resonant network. The control method turns off the switching tube when the load voltage is lower than a threshold value, and the system operates in a constant-current mode; after the threshold value is reached, a sliding mode constant voltage control module adaptively adjusts the duty cycle, and constant voltage output is realized through secondary side short circuit freewheeling, without original and secondary side communication throughout the process. The application absorbs high-frequency transient impact with the help of distributed parasitic capacitance to avoid device failure, simultaneously realizes smooth switching between constant-current and constant-voltage modes, and suppresses voltage instability under large-range load jump.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, specifically to a magnetically coupled resonant wireless power transmission system, and also to a wireless power transmission control method for the system. Background Technology

[0002] Magnetic-coupled resonant wireless power transfer (WPT) technology has been widely used in electric vehicle charging, industrial automation equipment, and intelligent monitoring systems due to its advantages such as contactless power supply and safety and reliability. To achieve stable power transfer, existing WPT systems typically employ resonant compensation networks, with series-series (SS) compensation topologies being the most widely used.

[0003] In traditional SS compensation schemes, the resonant network relies on discrete compensation capacitors and coil inductance to form a resonant circuit. Output regulation is achieved by adjusting the operating frequency or the control parameters of the primary-side inverter. To obtain a stable constant voltage output, most systems require a communication link between the primary and secondary sides to feed back information such as load-side voltage and current to the primary-side controller, which then adjusts the inverter's operating state accordingly. However, this type of scheme suffers from problems such as complex system structure, communication delay, and sensitivity to electromagnetic interference. In complex environments such as industrial sites, insufficient reliability of the communication link can easily lead to control instability or even failure.

[0004] To reduce system complexity and eliminate reliance on communication links, existing technologies have proposed communication-free control methods based on secondary-side regulation, with semi-synchronous rectification voltage regulation technology being a representative example. This method introduces a controllable switch into the secondary-side rectifier circuit. By controlling the switch to conduct at specific times, a short-circuit freewheeling path is formed on the secondary side, allowing part of the resonant current to circulate internally within the secondary side instead of flowing to the load, thereby regulating the output voltage. This method only requires acquiring a voltage signal on the secondary side to complete closed-loop control, achieving constant voltage output without requiring communication between the primary and secondary sides, offering the advantage of structural simplification.

[0005] However, the aforementioned semi-synchronous rectification voltage regulation strategy faces insurmountable physical implementation obstacles in traditional SS resonant systems employing discrete compensation capacitors. Specifically, at the instant the short-circuit freewheeling path is formed, the equivalent impedance of the resonant circuit rapidly decreases, generating transient voltages and pulse currents with high rates of change. For traditional structures using discrete capacitors, these transient stresses concentrate at the edges of the capacitor electrodes and the pin connection areas. Due to the non-uniform electric field distribution and non-negligible parasitic inductance inherent in the structure of discrete capacitors, voltage spikes and thermal stress concentrations are easily formed locally, leading to dielectric breakdown, parameter drift, and even device failure. Furthermore, these problems cannot be solved simply by increasing the capacitor's voltage rating or optimizing its parameters; rather, they are inherent to the lumped parameter characteristics and physical structure of discrete capacitors. Under high-frequency, high-current, and periodic impact conditions, discrete capacitors cannot stably withstand such stresses over long periods, thus limiting the engineering application of semi-synchronous rectification voltage regulation technology in traditional SS compensation topologies.

[0006] On the other hand, most existing non-communication control methods are designed only for constant voltage output, and usually rely on relatively complex control algorithms to achieve voltage regulation. They lack systematic support for the "constant current first, then constant voltage (CC / CV)" requirement in practical charging applications. There is still a technological gap in achieving smooth automatic switching between constant current mode and constant voltage mode without significantly increasing the complexity of secondary-side control or relying on primary-secondary-side communication.

[0007] Furthermore, in practical engineering, when a system faces conditions such as coil misalignment or large-scale load fluctuations, the system's equivalent impedance will experience significant nonlinear perturbations. Traditional linear control strategies (such as PI control), due to their fixed control parameters, struggle to adapt to such large parameter changes, easily leading to steady-state divergence and continuous oscillations, resulting in output voltage instability.

[0008] In summary, existing technologies still have unresolved technical problems in achieving a stable combination of semi-synchronous rectification voltage regulation and traditional SS compensation topology, automatic smooth switching of CC / CV under no communication conditions, and maintaining robust voltage regulation control under a wide range of load fluctuations. Summary of the Invention

[0009] This invention proposes a wireless power transfer system and its control method based on a self-resonant PCB coil and semi-synchronous rectification. Its purpose is to address the problems of dielectric breakdown, parameter drift, and decreased device reliability in existing wireless power transfer systems employing semi-synchronous rectification voltage regulation strategies, where traditional discrete compensation capacitors suffer from electric field concentration, significant parasitic parameters, and insufficient resistance to transient impacts, leading to these issues under high-frequency, high-current transient conditions. Simultaneously, it addresses the difficulty in stably integrating the semi-synchronous rectification voltage regulation strategy with the traditional SS compensation topology due to physical characteristic mismatch. Furthermore, it resolves the difficulty of achieving automatic and smooth switching between constant current and constant voltage modes in existing communication-free control schemes while simplifying the system structure, as well as the issues of divergence and lack of dynamic robustness in traditional linear control strategies when facing large-scale load jumps or coil parameter perturbations.

[0010] The technical solution of this invention is as follows:

[0011] A wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification includes a DC power supply, a full-bridge inverter, a transmitter self-resonant PCB coil, a receiver self-resonant PCB coil, a semi-synchronous rectifier, and a control circuit. The input terminal of the full-bridge inverter is connected to the DC power supply, and the output terminal is connected to the transmitter self-resonant PCB coil. The output terminal of the receiver self-resonant PCB coil is connected to the input terminal of the semi-synchronous rectifier. The transmitter and receiver self-resonant PCB coils are arranged opposite to each other.

[0012] Both the transmitting end self-resonant PCB coil and the receiving end self-resonant PCB coil are double-substrate structures composed of multi-layer planar spiral windings. Distributed parasitic capacitance is formed through the interlayer dielectric of the windings to replace discrete compensation capacitors, so that the system forms an inherent series-series resonant network at the operating frequency.

[0013] The control circuit includes a sliding mode constant voltage control module, which is configured to: execute a model-free incremental integral sliding mode control law based on the sampled load voltage, and adaptively adjust the duty cycle of the switching transistor in the semi-synchronous rectifier to form a periodic short-circuit freewheeling path on the secondary side to adjust the output voltage;

[0014] During the formation of the short-circuit freewheeling path and the high-frequency switching of the sliding mode constant voltage control module, the high-frequency transient voltage impact generated in the resonant circuit and the high-frequency chattering associated with the sliding mode control are carried and absorbed in situ by the distributed parasitic capacitance of the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end in the three-dimensional space, so as to suppress local electric field concentration and voltage spikes and maintain the stability of the resonant parameters.

[0015] The system exhibits constant current output characteristics when the switching transistor is turned off. After the load voltage reaches a set threshold, the sliding mode constant voltage control module adjusts the duty cycle to achieve constant voltage output, thereby completing the automatic switching between constant current mode and constant voltage mode without the need for primary and secondary side communication.

[0016] As a further improvement to the wireless power transmission system based on self-resonant PCB coils and semi-synchronous rectification: both the transmitting and receiving self-resonant PCB coils include two PCB boards with an air gap between them and fixed connection; each PCB board includes two layers of planar metal spiral windings, and the four winding layers are sequentially the first PCB inner layer winding, the first PCB outer layer winding, the second PCB outer layer winding, and the second PCB inner layer winding; among the four winding layers, the inner end of the first PCB inner layer winding and the inner end of the second PCB outer layer winding are connected in series to form a first series group, and the inner end of the first PCB outer layer winding and the inner end of the second PCB inner layer winding are connected in series to form a second series group; a dielectric layer is provided between adjacent winding layers and on the side of the outermost winding layer away from the adjacent winding layer, and the overlapping area between each winding layer forms the distributed parasitic capacitance through the dielectric layer, making the coil equivalent to a series RLC resonant unit; the outer ends of the first PCB inner layer winding and the second PCB inner layer winding serve as the two external connection terminals of the self-resonant PCB coil.

[0017] As a further improvement to the wireless power transmission system based on self-resonant PCB coil and semi-synchronous rectification: the outer end of the outer winding of the first PCB board and the outer end of the outer winding of the second PCB board are kept in an open circuit state to form a series distributed capacitor structure and realize the self-resonant characteristics of the coil.

[0018] As a further improvement to the wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification, the control circuit further includes a voltage sampling module and a comparison module. The voltage sampling module is used to acquire the load voltage across the load terminals in real time. The comparison module is used to compare the load voltage with a set threshold. When the load voltage is lower than the set threshold, the sliding mode constant voltage control module does not output a control signal, the switch of the semi-synchronous rectifier remains off, the system operates in a self-resonant state and presents a constant current output. When the load voltage reaches or exceeds the set threshold, the sliding mode constant voltage control module outputs a pulse width modulation signal to drive the switch to adjust the duty cycle to achieve constant voltage output.

[0019] As a further improvement to the wireless power transmission system based on self-resonant PCB coils and semi-synchronous rectification: the inherent quality factor of the self-resonant PCB coils at the transmitting end and the self-resonant PCB coils at the receiving end... Coupling coefficient with respect to the system at the nominal working distance The square of the product is limited by the maximum load factor set by the system. And satisfy the following constant current fidelity conditions:

[0020]

[0021] In the above formula, , The maximum allowable equivalent load resistance during the constant current charging phase. The equivalent internal resistance of the self-resonant PCB coil is... The constant current fidelity threshold set for the system.

[0022] The present invention also provides a control method based on the above-mentioned wireless power transmission system, comprising the following steps:

[0023] After the system is powered on, the full-bridge inverter operates at the inherent self-resonant frequencies of the self-resonant PCB coils at the transmitting and receiving ends. The system outputs high-frequency alternating current; the switching transistors in the semi-synchronous rectifier remain off, and the system operates in a natural series-series resonance state, outputting a constant current to the load in a non-communication manner.

[0024] The control circuit acquires the load voltage across the load terminals in real time. and compare it with the set target constant pressure threshold. Compare;

[0025] when When the control circuit does not output a control signal, the switching transistor remains off, and the system continues to operate in constant current mode.

[0026] when At that time, the control circuit initiates sliding mode constant voltage control to generate a fixed frequency and duty cycle. An adjustable pulse width modulation signal drives the switching transistor in the semi-synchronous rectifier to periodically turn on and off; during the period when the switching transistor is on, a partial short-circuit freewheeling current is formed in the secondary resonant circuit, and the resonant current does not flow to the load; during the period when the switching transistor is off, the resonant current is rectified and supplies power to the load, thereby maintaining a constant voltage output.

[0027] As a further improvement to the control method: the sliding mode constant pressure control adopts a model-free incremental integral sliding mode control law, the execution logic of which includes:

[0028] Calculate voltage error ;

[0029] Constructing an integral sliding surface ,in The sliding surface scaling factor is set to adjust the system's response damping to transient errors; the initial value of the integral term is set to zero.

[0030] Calculate and output the duty cycle. ,in The adjustment rate of the duty cycle is determined to approximate the gain of the law. Boundary layer thickness; It is a saturation limiting function;

[0031] The duty cycle The initial integral value is set as the duty cycle of the cycle preceding the instant the system switches from constant current mode to constant voltage mode; when the calculated value is obtained... touch At the boundary, anti-saturation processing is performed by truncating the integral term;

[0032] The model-free incremental integral sliding mode control law, in adjusting the duty cycle, does not rely on the mutual inductance between the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end. and load resistance The precise value.

[0033] As a further improvement to the control method: the reaching law gain The following reachability conditions must be met:

[0034]

[0035] In the above formula, This represents the maximum absolute value of the error caused by the system's maximum allowable load jump. This is the lower bound of the system control gain. The sliding surface scaling factor Based on the system's expected adjustment time Set, satisfy .

[0036] As a further improvement to the control method: during constant current mode operation, all the switching transistors in the semi-synchronous rectifier remain off, while the body diodes of the switching transistors are on. The semi-synchronous rectifier is equivalent to a full-bridge uncontrolled rectifier circuit, and the system maintains constant current output by relying on the constant current characteristics of the resonant point of the inherent series-series resonant network.

[0037] As a further improvement to the control method: in constant voltage output mode, the pulse width modulation signal simultaneously drives the two switching transistors in the semi-synchronous rectifier to conduct synchronously to form the local short-circuit freewheeling current; during the positive half-cycle of AC, the first switching transistor conducts normally, and the body diode of the second switching transistor acts as a freewheeling current; during the negative half-cycle of AC, the second switching transistor conducts normally, and the body diode of the first switching transistor acts as a freewheeling current.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. This invention employs a self-resonant PCB coil for both the transmitter and receiver, constructed from a dual-substrate multilayer planar spiral winding. It utilizes the distributed parasitic capacitance formed by the dielectric between the winding layers to replace traditional discrete compensation capacitors. This distributed parasitic capacitance is spatially continuous, with the electric field uniformly distributed along the winding area. It eliminates the localized electric field concentration at electrode edges and pins found in traditional discrete capacitors, while also avoiding the parasitic inductance introduced by discrete components. During semi-synchronous rectification and voltage regulation, when the switching transistor conducts, forming a short-circuit freewheeling path and generating high-rate transient voltage and pulse current surges, the aforementioned distributed parasitic capacitance disperses and absorbs the transient surge energy in situ within a three-dimensional space. The electric field strength and thermal stress experienced by each local unit are significantly lower than the physical tolerance limit of the dielectric, effectively suppressing voltage spikes and localized overheating. This avoids the dielectric breakdown and parameter drift problems that easily occur with traditional discrete capacitors under high-frequency surge conditions, improving system reliability and service life.

[0040] 2. This invention overcomes the physical mismatch bottleneck between traditional discrete compensation capacitors and semi-synchronous rectification voltage regulation strategies by deeply coordinating distributed parasitic capacitance with semi-synchronous rectification and sliding mode control in both hardware and software. During the high-frequency switching process of the sliding mode constant voltage control module to adjust the duty cycle, the high-frequency switching chattering associated with the sliding mode control law is dispersed and absorbed in three-dimensional space through the distributed parasitic capacitance of the self-resonant PCB coil. Each local capacitor unit only bears a small portion of the total chattering energy, and the electric field strength in any local area is far below the dielectric's tolerance limit. Therefore, the sliding mode control law provides stronger robustness and dynamic voltage regulation capability than traditional PI control at the software control level, while the distributed capacitance of the self-resonant PCB coil dissipates the high-frequency stress associated with the control in situ at the hardware physical level, enabling the nonlinear sliding mode control with strong anti-disturbance capability to be implemented safely and stably in the semi-synchronous rectification voltage regulation system.

[0041] 3. This invention utilizes the inherent constant current output characteristic of a self-resonant series-series topology at the resonant point. During system startup and when the load voltage is below a set threshold, constant current output can be maintained naturally without the intervention of control circuitry. Once the load voltage reaches the set threshold, the control circuit automatically initiates sliding mode constant voltage control, achieving constant voltage output by adjusting the duty cycle of the switching transistors in the semi-synchronous rectifier. The entire switching process between constant current and constant voltage modes relies solely on the secondary-side voltage sampling signal, eliminating the need for any communication link or feedback channel between the primary and secondary sides. This fundamentally eliminates problems such as communication delay, electromagnetic interference, and data packet loss, significantly simplifying the system structure and improving control reliability.

[0042] 4. The sliding mode constant voltage control module of this invention adopts a model-free incremental integral sliding mode control law. This control law, in adjusting the duty cycle, does not rely on the mutual inductance between the self-resonant PCB coils at the transmitting and receiving ends, nor on the precise value of the load resistance. It only utilizes the inherent negative monotonicity of the system output voltage with respect to the duty cycle to achieve adaptive adjustment. When facing nonlinear perturbations in the system's equivalent impedance caused by coil offset or large-scale load jumps, this sliding mode control law can effectively clamp the output voltage with its nonlinear switching characteristics, achieving fast voltage stabilization and recovery without overshoot. This fundamentally solves the problem of divergence and misalignment that easily occurs in traditional linear PI control under such extreme conditions due to fixed parameters.

[0043] 5. By setting constant current fidelity conditions, this invention clarifies the constraint relationship between the inherent quality factor of the self-resonant PCB coils at the transmitting and receiving ends, the coupling coefficient at the nominal working distance, and the maximum load factor of the system. This guides the optimized design of coil parameters, maximizing the quality factor and effectively resisting the attenuation of constant current fidelity caused by the increase in load impedance during the constant current charging stage. It also ensures the initial tracking accuracy of the system when switching to sliding mode constant voltage control and eliminates control misalignment caused by mode switching.

[0044] 6. This invention utilizes PCB technology to manufacture self-resonant PCB coils at both the transmitting and receiving ends, which simultaneously possess inductive and capacitive characteristics. This eliminates the need for discrete compensation capacitors and their associated components required in traditional solutions, and the entire control process does not require primary and secondary communication modules. The system structure is extremely simple, compact, and low-cost, making it particularly suitable for wireless power supply scenarios with stringent requirements for space utilization, reliability, and anti-interference capabilities, such as electric vehicles, AGVs, and industrial online monitoring equipment. Attached Figure Description

[0045] Figure 1 The schematic diagram of a wireless power transfer system based on a self-resonant PCB coil and a semi-synchronous rectifier circuit is provided for an embodiment of the present invention.

[0046] Figure 2 This is an exploded view of a self-resonant PCB coil according to an embodiment of the present invention.

[0047] Figure 3 This is a schematic diagram of the structure of a self-resonant PCB coil according to an embodiment of the present invention.

[0048] Figure 4 This is a simulation waveform of the high-frequency chattering transient voltage generated by the system when switching to the sliding mode constant voltage control mode in an embodiment of the present invention.

[0049] Figure 5 This is a simulation diagram of the internal electric field distribution of the self-resonant PCB coil under high-frequency transient impact according to an embodiment of the present invention.

[0050] Figure 6This is a simulation diagram of the structure and internal electric field distribution of a conventional MLCC discrete capacitor under high-frequency transient impact, as shown in the embodiment of the present invention.

[0051] Figure 7 This is a graph showing the relationship between the constant current fidelity threshold, quality factor, and load factor at the nominal working distance in an embodiment of the present invention.

[0052] Figure 8 The output voltage waveform diagram is shown in the embodiment of the present invention using sliding mode control.

[0053] Figure 9 The output voltage waveform diagram is shown for an embodiment of the present invention using PI control.

[0054] Figure 10 This is an equivalent circuit diagram of the receiving end when the switching transistor of the semi-synchronous rectifier is turned off in an embodiment of the present invention.

[0055] Figure 11 This is an equivalent circuit diagram of the receiving end when the semi-synchronous rectifier switch is turned on in an embodiment of the present invention.

[0056] Figure 12 This is a graph showing the changes in load voltage and load current with load in an embodiment of the present invention. Detailed Implementation

[0057] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0058] This embodiment provides a wireless power transfer system based on a self-resonant PCB coil and a semi-synchronous rectifier circuit. For example... Figure 1 As shown, the system includes a DC power supply, a full-bridge inverter, a self-resonant PCB coil at the transmitter end, a self-resonant PCB coil at the receiver end, a semi-synchronous rectifier, and an output filter capacitor. The system includes a load and control circuitry. The control circuitry comprises a voltage sensor, an ADC (Analog-to-Digital Converter), an MCU (Microcontroller Unit) control chip, and a gate drive circuit.

[0059] The input of the full-bridge inverter is connected to a DC power supply, and the output is connected to the two external terminals of the transmitter's self-resonant PCB coil. The two external terminals of the receiver's self-resonant PCB coil are connected to the two input terminals of the semi-synchronous rectifier. The transmitter and receiver self-resonant PCB coils are positioned opposite each other, and energy is transferred between them through magnetic coupling resonance. An output filter capacitor is connected in parallel to the output of the semi-synchronous rectifier. The load is then connected. The semi-synchronous rectifier consists of two NMOS transistors (hereinafter collectively referred to as switching transistors). A body diode is connected in parallel between the drain and source of each switching transistor. This body diode provides a natural freewheeling path when the switching transistor is turned off.

[0060] The structure of the self-resonant PCB coil is described in detail below.

[0061] like Figure 2 and Figure 3 As shown, the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end use the exact same structural parameters. Each self-resonant PCB coil consists of two identical PCB boards, namely the first PCB board (PCB1) and the second PCB board (PCB2). The two PCB boards are fixedly connected by nylon screws, with an air gap between them. Each PCB board contains two layers of planar metal spiral windings. PCB1 includes winding layer 1 and winding layer 2, with a dielectric layer between layer 1 and layer 2, and on the side of layer 1 facing away from layer 2. PCB2 includes winding layer 3 and winding layer 4, with a dielectric layer between layer 3 and layer 4, and on the side of layer 4 facing away from layer 3. Thus, the coil as a whole contains four layers of windings. When PCB1 is located above PCB2, the four layers of windings from top to bottom are: inner winding layer 1 of PCB1, outer winding layer 2 of PCB1, outer winding layer 3 of PCB2, and inner winding layer 4 of PCB2. The dielectric material of the coil is FR4.

[0062] The four winding layers are connected in series as follows: the inner ends of Layer 1 and Layer 3 are connected in series via pin headers to form the first series group (Group 1); the inner ends of Layer 2 and Layer 4 are connected in series via pin headers to form the second series group (Group 2). The outer ends of Layer 1 and Layer 4 serve as the two external connection terminals of the self-resonant PCB coil. The outer ends of Layer 2 and Layer 3 remain open-circuited and are not electrically connected. Through this open-circuit design, the overlapping areas between Layer 2 and Layer 3, as well as between adjacent winding layers, form spatially distributed series parasitic capacitances through the FR4 dielectric layer, making the entire coil equivalent to a series RLC resonant unit with a self-resonant frequency. From the equivalent inductance of the coil and equivalent capacitance Joint decision:

[0063]

[0064] In the above formula, This is the equivalent series inductance of the coil. This is the equivalent series capacitance of the coil.

[0065] Specifically, the outer ends of Layer 1 and Layer 4 of the self-resonant PCB coil at the transmitting end are connected to the two output terminals of the full-bridge inverter, respectively, while the outer ends of Layer 1 and Layer 4 of the self-resonant PCB coil at the receiving end are connected to the two input terminals of the semi-synchronous rectifier, respectively. Through the above-mentioned winding series connection and open-circuit design, the self-resonant PCB coil achieves resonance using its own distributed inductance and the equivalent capacitance between layers and turns. No discrete resonant compensation capacitors are set in the system, thus forming an inherent series-series (SS) resonant network at the system operating frequency.

[0066] Equivalent inductance of self-resonant PCB coil Equivalent capacitance and equivalent resistance It is determined by the structural parameters of the coil. Specifically, the self-inductance of Layer 1 winding... It can be described by the following formula:

[0067]

[0068] In the above formula, Let be the magnetic permeability of copper. The number of turns of the planar winding. The average diameter of the planar winding is defined as follows: , and These are the inner and outer diameters of the planar winding, respectively. The fill factor is defined as follows: .

[0069] The self-inductance of the first series group (Group 1) The self-perception of Layer 1, the self-perception of Layer 3, and the mutual perception between them are jointly determined to satisfy the following conditions. ,in This represents the mutual inductance between Layer 1 and Layer 3. The overall equivalent inductance of the coil. .

[0070] Equivalent capacitance Mainly composed of the planar area corresponding to the first series group Group1 Determined by the parameters of the dielectric layer:

[0071]

[0072] In the above formula, The vacuum permittivity, The relative permittivity of the FR4 dielectric layer is... The thickness of the medium layer between Layer1 and Layer2.

[0073] Equivalent resistance It consists of both ohmic loss and dielectric loss of the copper conductor:

[0074]

[0075] In the above formula, The resistivity of copper. This is the total length of a single-layer winding. For winding line width, For system operating frequency The depth of the skin below, For the thickness of the winding copper foil, This represents the loss tangent of the dielectric layer material.

[0076] In the specific design, the inner diameter of the coil is determined according to the system installation dimensions. and outer diameter The number of winding turns is determined based on the required range of the target resonant frequency. Line width and turn spacing and by quality factor ( ,in Maximize the optimization of each structural parameter to achieve the objective. In this embodiment, the outer diameter is used as the target. , inner diameter To meet constraints and considering actual manufacturing capabilities, a self-resonant PCB coil was designed, with the following specific parameters:

[0077] outer diameter of coil 10cm, inner diameter of the coil 60mm, number of turns 5, line width 2mm, turn spacing 2mm, dielectric layer thickness 0.0994mm, Air layer thickness: 1mm, PCB size: 10cm×10cm, Quality factor 25.8, self-resonant frequency 910kHz.

[0078] Under the above structural design, the distributed parasitic capacitance formed by the interlayer dielectric of the winding is continuously distributed in space, and its electric field is uniformly spread along the winding area. This avoids the local electric field concentration phenomenon at the electrode edges and pin connections found in traditional discrete capacitors, and also avoids the parasitic inductance introduced by discrete components. This distributed capacitance characteristic provides the physical basis for the high-frequency transient stress withstand capability of this invention under semi-synchronous rectification voltage regulation and sliding mode control conditions.

[0079] The following combination Figures 4 to 6This paper elaborates on the absorption mechanism of distributed parasitic capacitance for high-frequency transient impacts generated by semi-synchronous rectification voltage regulation and sliding mode control.

[0080] In this system, the semi-synchronous rectifier regulates the output voltage by periodically turning on the switching transistor to create a short-circuit freewheeling path on the secondary side. At the instant the switching transistor turns on, the equivalent impedance of the resonant circuit decreases rapidly, generating a high-rate-of-change transient voltage and pulse current in the circuit. Simultaneously, when the system operates in sliding mode constant voltage control, high-frequency switching chattering inevitably occurs as the sliding control law approaches the sliding surface. This chattering is injected into the resonant circuit in the form of high-frequency pulse current. These two high-frequency transient stresses—semi-synchronous rectification short-circuit freewheeling impact and sliding mode control high-frequency chattering—if applied to a traditional lumped-parameter capacitor, will create an extremely concentrated distorted electric field at the capacitor electrode edges and pins, easily leading to dielectric breakdown or parameter drift.

[0081] Figure 4 The simulated transient voltage waveform across the resonant circuit is shown in this embodiment of the invention when the system enters the sliding mode constant voltage control mode. The simulation conditions are: DC input voltage... System operating frequency Nominal coupling coefficient .exist During the constant current phase, the switching transistor of the semi-synchronous rectifier remains off, and the system operates in a natural resonance state. The resonant voltage waveform is smooth and there are no high-frequency chattering components. When the load voltage reaches the set threshold, the system switches to constant voltage mode. The incremental integral sliding mode control law is started and dynamically adjusts the duty cycle of the semi-synchronous rectifier. At this time, obvious high-frequency chattering voltage components appear in the resonant circuit.

[0082] To clarify the different behaviors of the high-frequency chattering associated with the above-mentioned sliding mode control in the traditional discrete capacitor structure and the self-resonant PCB coil structure of the present invention, this embodiment performs a comparative simulation of the high-frequency transient electric field distribution of the two. Figure 6 This diagram illustrates the internal electric field distribution of a conventional MLCC discrete compensation capacitor under the same high-frequency transient impact. Due to the extremely thin dielectric layer (micrometer scale) of the MLCC, an extremely concentrated distorted electric field is formed inside it under the action of transient voltage spikes, with the maximum field strength at the center reaching a high level. This significantly exceeds the physical breakdown limit of conventional ceramic dielectrics. Furthermore, high-frequency electromagnetic extraction data indicates that the equivalent series resistance (ESR) of this MLCC at a 500kHz operating frequency has surged to [value missing]. When a large current flows through the high-frequency dithering pulse of the sliding mode control, it is very easy to cause thermal stress damage due to severe local heating.

[0083] In comparison, Figure 5This diagram illustrates the internal electric field distribution of the self-resonant PCB coil of the present invention under transient impact of the same amplitude. Due to the use of an FR4 dielectric layer between four copper foil traces to construct distributed parasitic capacitance, the electric field exhibits a large-area, uniform spatial distribution along the winding plane. Its local maximum transient electric field intensity decreases to approximately [missing value]. This is far below the physical breakdown threshold of FR4 dielectric (approximately...). This multi-layer planar spiral winding structure disperses transient high-frequency impacts across a vast three-dimensional dielectric space—each local capacitor unit bears only a small portion of the total impact energy, and the electric field strength and thermal stress in any local area are far below the dielectric's tolerance limit. Simultaneously, the large-area PCB traces significantly expand the heat dissipation area, fundamentally eliminating the potential for localized electric field concentration and thermal stress breakdown that easily occur in traditional discrete capacitor structures.

[0084] Therefore, in this invention, the distributed parasitic capacitance provides in-situ dispersed absorption of the short-circuit freewheeling impact of semi-synchronous rectification and the high-frequency chattering of sliding mode control at the hardware physical level. This allows the resonant network to maintain parameter stability during voltage regulation, thereby achieving a safe and stable combination of the semi-synchronous rectification voltage regulation strategy and the highly robust sliding mode control law within the same system. This deep hardware-software synergy mechanism is something that traditional SS topologies using discrete compensation capacitors cannot achieve.

[0085] The following explains the working principle of the system's constant current output and the conditions for constant current fidelity.

[0086] The system adopts a series-series (SS) topology, and the operating frequency is equal to the self-resonant frequency of the self-resonant PCB coil. In the resonant state, the inductive and capacitive reactances of the self-resonant PCB coils at the transmitting and receiving ends cancel each other out. The system exhibits natural constant current output characteristics.

[0087] According to the fundamental frequency analysis method, the amplitude of the fundamental frequency voltage output by the full-bridge inverter... for ,in This is the DC input voltage of the full-bridge inverter. Ignoring the equivalent internal resistance of the coils... Ideally, the amplitude of the AC current at the transmitting end is for:

[0088]

[0089] In the above formula, This is the equivalent impedance reflected from the secondary side to the primary side. The equivalent AC impedance of the receiving end. The mutual inductance between the self-resonant PCB coils at the transmitting and receiving ends. This is the operating angular frequency.

[0090] Secondary side induced voltage Therefore, the amplitude of the high-frequency alternating current on the secondary side for:

[0091]

[0092] From the above equation, it can be seen that under ideal lossless conditions, the amplitude of the secondary AC current is It is a constant value, determined solely by the input voltage. and mutual induction The decision is related to the load resistance. It is irrelevant. Therefore, when the switching transistor of the semi-synchronous rectifier is turned off and the body diode is turned on to form a full-bridge uncontrolled rectifier, the system naturally exhibits constant current output characteristics at the resonant point.

[0093] However, in practical systems, the equivalent internal resistance of the self-resonant PCB coils at the transmitting and receiving ends... This objectively exists and cannot be ignored. According to the fundamental equivalent analysis method, when the switching transistor is turned off, the uncontrolled full-bridge rectifier and DC load... The AC equivalent impedance referred to the secondary resonant circuit is: Taking into account the coil's internal resistance Then, based on Kirchhoff's voltage law, the primary-secondary coupled frequency domain equations are established:

[0094] Equation of the original edge loop:

[0095] Secondary loop equation:

[0096] Eliminate by combining the above two equations The actual AC current amplitude on the secondary side can be obtained. for:

[0097]

[0098] As can be seen from this formula, the actual AC current on the secondary side will vary with the load impedance. The increase in current leads to nonlinear decay, causing the system to deviate from the ideal constant current output state. To quantify the degree of this deviation, this invention introduces constant current fidelity. Defined as the actual constant current output amplitude Compared with the ideal lossless constant current output amplitude The ratio:

[0099]

[0100] Divide both the numerator and denominator of the above equation by... Dimensionless processing is performed. According to the physical definition, the intrinsic quality factor of a self-resonant PCB coil... Since the parameters of the transmitting and receiving coils are the same, there are ,in This is the nominal coupling coefficient. Further, a dimensionless load factor is defined. Substituting into the above equation, we can obtain the constant current fidelity condition:

[0101]

[0102] The above relationship reveals the nonlinear coupling effect in the actual system: during constant current charging, as the equivalent impedance of the load gradually increases (i.e., the load factor...), Increase), constant current fidelity It will inevitably decrease. If the constant current fidelity decays too much, it will disrupt the constant current charging characteristics. In practical engineering applications, the coupling coefficient is limited by the physical transmission distance and spatial dimensions of the equipment. Typically, the maximum load factor is small and has a physical limit. Therefore, it needs to withstand the maximum load factor. The resulting attenuation effect should be addressed to ensure the system meets the set fidelity threshold throughout the constant current phase, thereby improving the quality factor of the self-resonant PCB coil. For the design objectives. In specific implementation, the inherent quality factors of the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end are... Coupling coefficient with respect to the system at the nominal working distance The square of the product is limited by the maximum load factor set by the system. And satisfy:

[0103]

[0104] In the above formula, , The maximum allowable equivalent load resistance during the constant current charging phase. The equivalent internal resistance of the self-resonant PCB coil is... The constant current fidelity threshold set for the system. Figure 7 The constant current fidelity at the nominal working distance is shown. With quality factor and load factor The relationship.

[0105] The following explains the principle of semi-synchronous rectification and voltage regulation.

[0106] Once the system enters constant voltage output mode, the control circuit outputs a fixed frequency and duty cycle. An adjustable pulse width modulation (PWM) signal drives the switching transistors in a semi-synchronous rectifier to periodically turn on and off. Within one AC half-cycle ( arrive Within ), the electrical angle at which both switching transistors are simultaneously conducting is . During this short-circuit time, the secondary resonant current does not flow to the load, but forms a local freewheeling loop in the switching transistor channel; while during the remaining conduction angle... Inside, the resonant current flows to the load after being rectified by the body diode.

[0107] The output DC load current can be obtained by averaging the current flowing to the load over one and a half cycles. :

[0108]

[0109] The amplitude of the secondary AC current under the aforementioned constant current mode Substituting into the above formula, we can obtain the DC load voltage output by the semi-synchronous rectifier. Duty cycle Relationship:

[0110]

[0111] Figure 10 The equivalent circuit of the receiver is shown when the switch is turned off. At this time, the body diode of the switch is conducting, and the semi-synchronous rectifier is equivalent to a full-bridge uncontrolled rectifier circuit. The resonant current is rectified by the body diode and then supplied to the load. Figure 11 The equivalent circuit of the receiver is shown when the switch is turned on. At this time, a partial short-circuit freewheeling current is formed in the secondary resonant circuit, and the resonant current circulates in the switch channel and inside the coil, without flowing to the load.

[0112] The design of the sliding mode constant pressure control law is explained in detail below.

[0113] From the above and The relation will For control variables Find the partial derivative:

[0114]

[0115] Within the semi-synchronous rectification and voltage regulation operating range, the duty cycle Therefore The principle of constancy is established. Because... , , , All are positive physical quantities, therefore the output voltage is positive throughout the entire operating domain. duty cycle It exhibits strict negative monotonicity:

[0116]

[0117] The above formula physically reveals: duty cycle Increase, output voltage The duty cycle will inevitably decrease; conversely, as the duty cycle decreases, the output voltage will inevitably increase. This inherent negative monotonicity is the core basis for the design of sliding mode control laws, allowing the control law to operate without requiring precise mutual inductance of the system. With load resistance The parameters can be adjusted stably.

[0118] The tracking error of the system output voltage is defined as:

[0119]

[0120] In the above formula, The target constant pressure threshold is defined. To eliminate the steady-state error of the system, an integral sliding surface is constructed. :

[0121]

[0122] In the above formula, The sliding surface scaling factor is set to adjust the system's response damping to transient errors; the integral term is initially set to zero and is updated in real time with the error after the system starts.

[0123] To prove the existence and reachability of the sliding surface, the Lyapunov function of the system is defined as follows: Differentiating it, we get:

[0124]

[0125] According to the chain rule, the rate of change of the output voltage is mainly driven by the rate of change of the duty cycle, i.e. Because the system exhibits strict negative monotonicity. ,make ,but:

[0126]

[0127] To ensure Lyapunov stability conditions The following incremental reaching law is designed:

[0128]

[0129] In the above formula, To determine the rate of adjustment of the duty cycle for the approach law gain; Boundary layer thickness; Let be the saturation limiting function, which is defined as: when hour, ;when hour, This enables soft switching within the boundary layer to reduce high-frequency chattering.

[0130] Outside the sliding mode boundary layer (i.e.) When, substituting the reaching law into the Lyapunov derivative equation:

[0131]

[0132] Desire to The principle of constant approximation means that the system can reach the sliding surface under any initial state, and the reaching law gain is also true. Accessibility conditions must be met:

[0133]

[0134] In the above formula, This represents the maximum absolute value of the error caused by the system's maximum allowable load jump. This is the lower bound of the system control gain. .

[0135] The above derivation mathematically proves that even if the systems are mutually inductant... With unknown load parameters, as long as the reaching law is configured based on negative monotonicity, the system state can necessarily be constrained to the sliding surface. Integrating the reaching law yields the control law equation:

[0136]

[0137] In actual engineering implementation, duty cycle initial value of integral This is set to the duty cycle of the cycle preceding the instant the system switches from constant current mode to constant voltage mode. When the calculated... touch At the boundary, the control circuit performs anti-saturation processing by truncating the integral term.

[0138] The selection mechanism for sliding mode control parameters is as follows:

[0139] Slip surface ratio factor It determines the dynamic convergence speed of the system state after it reaches the sliding surface. The larger the error Faster convergence is desirable, but excessively high values ​​can amplify high-frequency noise. The optimal value should be selected based on the system's expected settling time. Set, satisfy In this embodiment, the selected range is .

[0140] Approaching Law Gain This determines the rate at which the system state approaches the sliding surface. A larger value results in a faster response, but the increased switching chatter will be absorbed by the distributed parasitic capacitance of the self-resonant PCB coil. The upper limit of its selection is not limited by the physical constraints of traditional discrete capacitor structures.

[0141] Boundary layer thickness Used to perform soft switching near the sliding surface to reduce high-frequency chattering. The selection is based on the inherent output voltage ripple amplitude of the system, and a value slightly larger than the system's steady-state natural ripple (e.g., This ensures voltage regulation accuracy while preventing the controller from responding excessively at high frequencies to unavoidable natural ripples.

[0142] To fully verify the dynamic voltage regulation capability of the sliding mode control strategy of this invention under extreme nonlinear perturbations, this embodiment conducts a comparative experiment between incremental integral sliding mode control and traditional PI control. The experimental conditions are as follows: system DC input voltage The voltage is constant at 50V; the self-resonant PCB coils at the transmitter and receiver are maintained at the nominal working distance, and the coupling coefficient is [missing information]. Mutual induction The system operating frequency remains constant; the system operating frequency is locked to the coil's inherent self-resonant frequency. The system sets the target threshold for constant voltage output. To isolate variables, this experiment introduces only extreme continuous load steps as a single disturbance source: during the steady-state operation of the system, the electronic load is controlled to reduce the system load resistance. according to The sequence underwent a dramatic mutation.

[0143] Experimental results are as follows Figure 8 and Figure 9 As shown. Figure 9 This is the output voltage waveform when using traditional linear PI control. Because the PI control parameters are fixed, it is difficult to adapt to the nonlinear perturbation of the system's equivalent impedance caused by drastic load changes. When the load changes to... When this happens, the system loses its stability margin, and the output voltage waveform exhibits severe low-frequency divergence and continuous oscillation, leading to system instability. Figure 8 This is the output voltage waveform when the incremental integral sliding mode control law of this invention is used. The system experiences each load step phase ( to When the output voltage is subjected to overshoot, it can be effectively clamped and restored to a stable state within milliseconds, demonstrating excellent robustness to a wide range of load disturbances. More importantly, observation... Figure 8 The waveform envelopes during high-frequency switching and voltage regulation in each stage of the sliding mode control did not exhibit any destructive high-frequency voltage spikes or glitches. This indicates that the electrical chattering associated with high-frequency duty cycle adjustment in the software layer of the sliding mode control has been completely absorbed in real-time and smoothly in situ by the self-resonant PCB coil at the receiving end using its distributed parasitic capacitance.

[0144] The following describes the complete workflow of the system and the CC / CV mode switching logic.

[0145] After the system is powered on, the DC power supply supplies power to the full-bridge inverter, which inverts the DC power into a frequency equal to the inherent self-resonant frequency of the self-resonant PCB coil. The high-frequency alternating current is fed into the self-resonant PCB coil at the transmitting end. The transmitting coil and the receiving coil transmit energy through magnetic coupling resonance.

[0146] In constant current mode, the voltage sensor in the control circuit collects the load voltage across the load terminals in real time. After being converted by the ADC, the data is sent to the MCU control chip. The MCU will... With the internally set target constant pressure threshold Comparison. When At this time, the MCU does not output a PWM signal, and both switches in the semi-synchronous rectifier remain off. The body diodes of the switches are on, and the semi-synchronous rectifier is equivalent to a full-bridge uncontrolled rectifier circuit. The system outputs a constant current to the load based on the inherent constant current characteristic of the SS topology resonant point. The equivalent circuit at the receiving end in this state is as follows: Figure 10 As shown. The energy received is rectified by the body diode and then filtered by the output filter capacitor. The filtered and smoothed material is then supplied to the load.

[0147] As constant current charging continues, the load voltage... Gradually rising. When At this time, the MCU initiates sliding mode constant voltage control, executes the aforementioned model-free incremental integral sliding mode control law, and outputs a fixed frequency (equal to...). Duty cycle An adjustable PWM signal simultaneously drives two switching transistors in a semi-synchronous rectifier via a gate drive circuit. During one cycle of the PWM signal, the switching transistors periodically turn on and off: during the on-side, a partial short-circuit freewheeling current forms in the secondary resonant circuit, circulating internally through the transistor channel and not flowing to the load; during the off-side, the resonant current is rectified by the body diode and supplies power to the load. The duty cycle is dynamically adjusted. The control circuit performs closed-loop regulation of the output voltage to achieve constant voltage output.

[0148] In constant voltage output mode, the two switching transistors function differently during the positive and negative half-cycles of the AC circuit: during the positive half-cycle, the first switching transistor conducts normally, and the body diode of the second switching transistor provides freewheeling; during the negative half-cycle, the second switching transistor conducts normally, and the body diode of the first switching transistor provides freewheeling. The equivalent circuit at the receiver in this state is as follows: Figure 11 As shown.

[0149] Figure 12The system is shown in The system displays complete load voltage and load current curves under various load conditions. The maximum current fluctuation rate is 5.8% during the constant current phase and 0.2% during the constant voltage phase. The system achieves automatic and smooth switching between constant current and constant voltage modes throughout operation, requiring no communication link or feedback channel between the primary and secondary sides.

[0150] It should be noted that, as will be apparent to those skilled in the art, the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics thereof. The scope of the present invention is defined by the claims rather than the foregoing description.

Claims

1. A wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification, comprising a DC power supply, a full-bridge inverter, a transmitter self-resonant PCB coil, a receiver self-resonant PCB coil, a semi-synchronous rectifier, and a control circuit; the input terminal of the full-bridge inverter is connected to the DC power supply, and the output terminal is connected to the transmitter self-resonant PCB coil; the output terminal of the receiver self-resonant PCB coil is connected to the input terminal of the semi-synchronous rectifier; The self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end are arranged opposite to each other; characterized in that: Both the transmitting end self-resonant PCB coil and the receiving end self-resonant PCB coil are double-substrate structures composed of multi-layer planar spiral windings. Distributed parasitic capacitance is formed through the interlayer dielectric of the windings to replace discrete compensation capacitors, so that the system forms an inherent series-series resonant network at the operating frequency. The control circuit includes a sliding mode constant voltage control module, which is configured to: execute a model-free incremental integral sliding mode control law based on the sampled load voltage, and adaptively adjust the duty cycle of the switching transistor in the semi-synchronous rectifier to form a periodic short-circuit freewheeling path on the secondary side to adjust the output voltage; During the formation of the short-circuit freewheeling path and the high-frequency switching of the sliding mode constant voltage control module, the high-frequency transient voltage impact generated in the resonant circuit and the high-frequency chattering associated with the sliding mode control are carried and absorbed in situ by the distributed parasitic capacitance of the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end in the three-dimensional space, so as to suppress local electric field concentration and voltage spikes and maintain the stability of the resonant parameters. The system exhibits constant current output characteristics when the switching transistor is turned off. After the load voltage reaches a set threshold, the sliding mode constant voltage control module adjusts the duty cycle to achieve constant voltage output, thereby completing the automatic switching between constant current mode and constant voltage mode without the need for primary and secondary side communication.

2. The wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification according to claim 1, characterized in that: Both the transmitting and receiving self-resonant PCB coils comprise two PCB boards with an air gap between them and fixedly connected. Each PCB board contains two layers of planar metal spiral windings, and the four winding layers are sequentially defined as an inner winding of the first PCB board, an outer winding of the first PCB board, an outer winding of the second PCB board, and an inner winding of the second PCB board. Among the four winding layers, the inner ends of the inner windings of the first PCB board and the outer windings of the second PCB board are connected in series to form a first series group, and the inner ends of the outer windings of the first PCB board and the inner windings of the second PCB board are connected in series to form a second series group. Dielectric layers are provided between adjacent winding layers and on the side of the outermost winding layer facing away from the adjacent winding layer. The overlapping areas between the winding layers form the distributed parasitic capacitance through the dielectric layers, making the coil equivalent to a series RLC resonant unit. The outer ends of the inner windings of the first and second PCB boards serve as the two external connection terminals of the self-resonant PCB coil.

3. The wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification according to claim 2, characterized in that: The outer end of the outer winding of the first PCB board and the outer end of the outer winding of the second PCB board are kept in an open circuit state to form a series distributed capacitor structure and realize the self-resonance characteristics of the coil.

4. The wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification according to claim 1, characterized in that: The control circuit further includes a voltage sampling module and a comparison module; the voltage sampling module is used to collect the load voltage across the load terminals in real time; the comparison module is used to compare the load voltage with the set threshold; when the load voltage is lower than the set threshold, the sliding mode constant voltage control module does not output a control signal, the switch of the semi-synchronous rectifier remains off, the system operates in a self-resonant state and presents a constant current output; when the load voltage reaches or exceeds the set threshold, the sliding mode constant voltage control module outputs a pulse width modulation signal to drive the switch to adjust the duty cycle to achieve constant voltage output.

5. The wireless power transfer system based on a self-resonant PCB coil and semi-synchronous rectification according to claim 1, characterized in that: The inherent quality factor of the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end Coupling coefficient with respect to the system at the nominal working distance The square of the product is limited by the maximum load factor set by the system. And satisfy the following constant current fidelity conditions: ； In the above formula, , The maximum allowable equivalent load resistance during the constant current charging phase. The equivalent internal resistance of the self-resonant PCB coil is... The constant current fidelity threshold set for the system.

6. A control method for the wireless power transmission system according to claim 1, characterized in that, Includes the following steps: After the system is powered on, the full-bridge inverter operates at the inherent self-resonant frequencies of the self-resonant PCB coils at the transmitting and receiving ends. The system outputs high-frequency alternating current; the switching transistors in the semi-synchronous rectifier remain off, and the system operates in a natural series-series resonance state, outputting a constant current to the load in a non-communication manner. The control circuit acquires the load voltage across the load terminals in real time. and compare it with the set target constant pressure threshold. Compare; when When the control circuit does not output a control signal, the switching transistor remains off, and the system continues to operate in constant current mode. when At that time, the control circuit initiates sliding mode constant voltage control to generate a fixed frequency and duty cycle. An adjustable pulse width modulation signal drives the switching transistor in the semi-synchronous rectifier to periodically turn on and off; during the period when the switching transistor is on, a partial short-circuit freewheeling current is formed in the secondary resonant circuit, and the resonant current does not flow to the load; during the period when the switching transistor is off, the resonant current is rectified and supplies power to the load, thereby maintaining a constant voltage output.

7. The control method according to claim 6, characterized in that: The sliding mode constant pressure control adopts a model-free incremental integral sliding mode control law, and its execution logic includes: Calculate voltage error ; Constructing an integral sliding surface ,in The sliding surface scaling factor is set to adjust the system's response damping to transient errors; the initial value of the integral term is set to zero. Calculate and output the duty cycle. ,in The adjustment rate of the duty cycle is determined to approximate the gain of the law. Boundary layer thickness; It is a saturation limiting function; The duty cycle The initial integral value is set as the duty cycle of the cycle preceding the instant the system switches from constant current mode to constant voltage mode; when the calculated value is obtained... touch At the boundary, anti-saturation processing is performed by truncating the integral term; The model-free incremental integral sliding mode control law, in adjusting the duty cycle, does not rely on the mutual inductance between the self-resonant PCB coil at the transmitting end and the self-resonant PCB coil at the receiving end. and load resistance The precise value.

8. The control method according to claim 7, characterized in that: The reaching law gain The following reachability conditions must be met: ； In the above formula, This represents the maximum absolute value of the error caused by the system's maximum allowable load jump. This is the lower bound of the system control gain. The sliding surface scaling factor Based on the system's expected adjustment time Set, satisfy .

9. The control method according to claim 6, characterized in that: During constant current mode operation, all the switching transistors in the semi-synchronous rectifier remain off, while the body diodes of the switching transistors are on. The semi-synchronous rectifier is equivalent to a full-bridge uncontrolled rectifier circuit. The system maintains constant current output by relying on the constant current characteristics of the resonant point of the inherent series-series resonant network.

10. The control method according to claim 6, characterized in that: In constant voltage output mode, the pulse width modulation signal simultaneously drives the two switching transistors in the semi-synchronous rectifier to conduct synchronously to form the partial short-circuit freewheeling current; during the positive half-cycle of AC, the first switching transistor conducts normally, and the body diode of the second switching transistor acts as a freewheeling current; during the negative half-cycle of AC, the second switching transistor conducts normally, and the body diode of the first switching transistor acts as a freewheeling current.

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