Single-capacitor wpt system for underwater mobile device charging and parameter design method

Abstract

The application provides a single-capacitor WPT system and a parameter design method for charging a mobile device underwater, and is characterized in that: for a mobile device in an underwater environment, a wireless power supply coupling mechanism design method considering an insulating layer is provided, and taking a double-sided LC-compensated single-capacitor coupling WPT system underwater as an example, a system parameter design method for making the system reach a zero phase angle state is given. The effect is that: compared with a traditional underwater electric field coupling wireless power transmission mode, the application realizes wireless power supply of a mobile device in an underwater three-dimensional space, improves the flexibility of the system, reduces the cost of the system, has a lower requirement for a structural space, and improves the energy transmission distance; compared with a single-capacitor WPT transmission mode in air, the energy transmission power and efficiency and the energy transmission distance are improved under the same conditions.

Description

Technical Field

[0001] This invention relates to wireless power transfer technology, specifically to a single-capacitor WPT system and parameter design method for charging underwater mobile devices. Background Technology

[0002] Wireless Power Transfer (WPT) technology combines power electronics and modern control theory and technology to achieve wireless power transmission via carriers such as magnetic fields, electric fields, microwaves, and lasers. This technology has become a global research hotspot, as it can solve many problems associated with direct electrical contact in traditional wires and has broad application prospects. Electric-field Coupled Wireless Power Transfer (EC-WPT) technology utilizes a high-frequency alternating electric field between metal plates as the energy transmission carrier to achieve wireless power transmission. Its coupling mechanism is generally composed of metal plates, featuring low cost, light weight, and flexible shape. During system operation, eddy current losses are minimal in the metal conductors between and around the coupling mechanism, with the majority of the current flux distributed between the plates, resulting in minimal impact on environmental electromagnetic interference and the ability to transfer energy across metal surfaces. Due to these advantages, EC-WPT systems have attracted numerous researchers both domestically and internationally, and EC-WPT technology has already been applied in consumer electronics, medical devices, and electric vehicles.

[0003] Compared to research on EC-WPT technology in air, research on underwater electric field-coupled wireless power transfer technology is still in its early stages. EC-WPT technology offers numerous advantages for underwater applications. It utilizes high-frequency electric fields for power transfer, resulting in less eddy current loss in water. The coupling mechanism uses metal plates, which are simple in structure and require only an insulating layer for underwater applications. The metal plates are also robust, capable of withstanding the high pressure of deep water. Furthermore, the coupling capacitance between the plates is a key factor in power transfer in EC-WPT systems, and the relatively high permittivity of water significantly increases this capacitance, thereby improving the system's power transmission and efficiency. In addition, the increased coupling capacitance allows for compensation with smaller inductors, further reducing system size and cost, and ultimately improving power density.

[0004] However, existing EC-WPT systems for underwater applications primarily use four opposing parallel metal plates as the coupling mechanism, suitable for situations where the relative positions of the coupling mechanism are fixed. However, for wireless power supply systems of underwater mobile devices, the energy transmitting plates are typically fixed in a specific location, such as in underwater power base stations, while the energy receiving end frequently moves in and out, or even changes direction. This causes changes in the relative positions of the transmitting and receiving plates, resulting in the energy receiving end being in a different orientation relative to the transmitting end in three-dimensional space. The cross-coupling capacitance between the two pairs of metal plates reduces the flexibility of the system's power supply, severely limiting the application of EC-WPT technology for wireless power supply of mobile devices in three-dimensional space. Summary of the Invention

[0005] Based on the above requirements, the primary objective of this invention is to propose a single-capacitor WPT system for charging underwater mobile devices. By improving the structure of the coupling mechanism, the system's power supply flexibility is enhanced, thereby meeting the wireless power supply requirements of mobile devices in underwater three-dimensional space.

[0006] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0007] A single-capacitor WPT system for charging underwater mobile devices includes a power transmitter and a power receiver. The key feature is that the power transmitter includes a power supply base station and a power transmitting sphere. The power supply base station is equipped with a power transmitting circuit, which includes a power supply, a high-frequency inverter, and a primary-side resonant network. The power transmitting sphere is connected to the primary-side resonant network via a conductive cable and is covered with a first insulating protective layer. The power receiver is mounted on the underwater mobile device and includes a power receiving sphere protruding from the outer surface of the underwater mobile device and a power receiving circuit located inside the underwater mobile device. The power receiving circuit includes a secondary-side resonant network, a rectifier filter circuit, and a load. The power receiving sphere is covered with a second insulating protective layer. The power transmitting sphere and the power receiving sphere form a single-capacitor coupling structure to achieve wireless power transmission.

[0008] Optionally, the high-frequency inverter adopts a full-bridge inverter structure, and the rectifier and filter circuit includes a full-bridge rectifier and a filter capacitor.

[0009] Optionally, the primary-side resonant network includes a resonant inductor L1 and a resonant capacitor C1 connected in series, and the energy transmitting ball is connected to the common connection terminal of the resonant inductor L1 and the resonant capacitor C1 via a conductive cable; the secondary-side resonant network includes a resonant inductor L2 and a resonant capacitor C2 connected in series, and the energy receiving ball is connected to the common connection terminal of the resonant inductor L2 and the resonant capacitor C2.

[0010] Optionally, the structure and size of the power transmitting ball and the power receiving ball are the same.

[0011] Based on the above system, this invention also proposes a parameter design method for a single-capacitor WPT system for charging underwater mobile devices, the key of which includes the following steps:

[0012] S1: Determine the target output power and load R based on the application requirements of underwater mobile equipment. L ;

[0013] S2: Determine the size and material of the power transmitting sphere and the power receiving sphere based on the transmission distance requirements and the target output power determined in S1; including the thickness d of the first and second insulating protective layers. s and relative permittivity ε s The radius R of the energy transmitting sphere and the energy receiving sphere, and the transmission distance range d. w and the relative permittivity ε of the transmission medium w ; and in accordance with Estimate the coupling capacitance value, where ε0 is the dielectric constant in vacuum;

[0014] S3: Determine the system angular frequency based on experience; select the resonant inductor L2 value based on the coupling capacitance value estimated in step S2, the system angular frequency, and experience, and according to ω 2 L2C2=1 determines the capacitance value of the resonant capacitor C2, where ω is the system angular frequency;

[0015] S4: Set the capacitance value of resonant capacitor C1 to be equal to the capacitance value of resonant capacitor C2, initially set the inductance value of resonant inductor L1 to be equal to the inductance value of resonant inductor L2, and construct an experimental device with two-port characteristics in an underwater environment.

[0016] S5: Use an LCR bridge to measure the input impedance of the experimental device. By adjusting the size of the resonant inductor L1, observe the impedance value displayed on the LCR bridge. When the circuit is resistive, determine the inductance value of the resonant inductor L1.

[0017] S6: Adjust the input voltage of the power supply to ensure the system output power meets the target;

[0018] S7: Provide the final system parameters.

[0019] The effects of this invention are:

[0020] This invention proposes a single-capacitor WPT system and parameter design method for charging underwater mobile devices. The coupling mechanism has a simple structure and is easy to install. It can eliminate the cross-coupling capacitance generated by traditional coupling mechanisms, improve the flexibility of system power supply, and make it adaptable to wireless charging of mobile devices in underwater three-dimensional space. Through parameter design, it can enable the system to operate in ZPA state while ensuring the underwater energy transmission distance, reduce reactive power, and improve system transmission performance. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0022] Figure 1 A schematic diagram of a single-capacitor WPT system for charging underwater mobile devices provided by the present invention;

[0023] Figure 2 A circuit block diagram of a single-capacitor WPT system for charging underwater mobile devices provided by the present invention;

[0024] Figure 3 This is a circuit topology diagram in a specific embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the structure of the power transmitting ball and the power receiving ball in a specific embodiment of the present invention;

[0026] Figure 5 This is a flowchart illustrating the parameter design process of the present invention.

[0027] Figure 6 Diagram of the capacitance analysis model of the underwater spherical coupling mechanism;

[0028] Figure 7 for Figure 3 The equivalent circuit model diagram;

[0029] Figure 8 A diagram of an experimental setup with two-port characteristics in an underwater environment;

[0030] Figure 9 The inverter output voltage u for power supply in three-dimensional space in Inverter output current i in System output current i o Waveform diagram;

[0031] Figure 10 A graph showing the output power of a three-dimensional space power supply system as a function of input voltage;

[0032] Figure 11 A graph showing the efficiency of a three-dimensional power supply system as a function of output power.

[0033] Figure 12 A schematic diagram showing power supply from six directions;

[0034] Figure 13 The output power and efficiency of the system are given in six directions. Detailed Implementation

[0035] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0036] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0037] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, this embodiment provides a single-capacitor WPT system for charging underwater mobile devices, including a power transmitter and a power receiver. The power transmitter includes a power supply base station device and a power transmitting ball. The power supply base station device is equipped with a power transmitting circuit, which includes a power supply, a high-frequency inverter, and a primary-side resonant network. The power transmitting ball is connected to the primary-side resonant network through a conductive cable. A first insulating protective layer is wrapped around the outside of the power transmitting ball. The power transmitting ball is usually fixed above the power supply base station by a mechanical device. The height of the power transmitting ball relative to the power supply base station can be adjusted to adapt to different diving and buoyancy depths of the underwater mobile device.

[0038] The power receiving end is installed on the underwater mobile device and includes a power receiving ball protruding from the outer surface of the underwater mobile device and a power receiving circuit located inside the underwater mobile device. The power receiving circuit includes a secondary resonant network, a rectifier filter circuit and a power load. A second insulating protective layer is wrapped around the outside of the power receiving ball. The power transmitting ball and the power receiving ball form a single capacitor coupling structure to realize wireless power transmission.

[0039] pass Figure 3As can be seen, the high-frequency inverter in this embodiment adopts a full-bridge inverter structure. The rectifier and filter circuit includes a full-bridge rectifier and a filter capacitor. Since the bilateral LC compensation network has advantages such as good boost effect and fewer reactive components, and this topology is conducive to improving the power density of the system and has stronger robustness, the primary side resonant network in this embodiment includes a resonant inductor L1 and a resonant capacitor C1 connected in series. The power transmitting ball is connected to the common connection terminal of the resonant inductor L1 and the resonant capacitor C1 through a conductive cable. The secondary side resonant network includes a resonant inductor L2 and a resonant capacitor C2 connected in series. The power receiving ball is connected to the common connection terminal of the resonant inductor L2 and the resonant capacitor C2.

[0040] from Figure 3 As can be seen from this, the power supply E dc The system's power transmitting end consists of a full-bridge inverter (composed of four MOSFETs S1-S4), resonant inductor L1, resonant capacitor C1, and power transmitting sphere P1. The power receiving end consists of power receiving sphere P2, resonant inductor L2, resonant capacitor C2, a full-bridge rectifier (composed of four diodes D1-D4), and filter capacitor C. o and load resistance R L The system's power receiving end is formed. The DC input voltage of this single-capacitor charging system is converted into high-frequency AC power after passing through a full-bridge inverter and a resonant network at the transmitting end. Under the action of the high-frequency AC power, an interactive electric field is formed between the coupling mechanism formed by the power transmitting ball P1 and the power receiving ball P2. Displacement current is generated under the action of the interactive electric field, realizing the wireless transmission of electrical energy.

[0041] To facilitate parameter design, the structure, size, and material of the power transmitting sphere and the power receiving sphere are identical during implementation. Figure 1 and Figure 4 As can be seen, by using a spherical coupling mechanism, the energy transmitter is fixed, and the energy receiver can flexibly supply power around the transmitter in multiple degrees of freedom, increasing the wireless power supply range of the device. The sphere of the spherical coupling mechanism can be a solid or hollow sphere. In order to reduce the weight of the system, the material is generally a lightweight metal. Because it can provide wireless power in all directions, it can be widely used in application scenarios with high flexibility or multi-load charging, such as underwater sensor groups.

[0042] Based on the above system, this embodiment also proposes a parameter design method for a single-capacitor WPT system for charging underwater mobile devices, as detailed below. Figure 5 As shown, it includes the following steps:

[0043] S1: Determine the target output power and load R based on the application requirements of underwater mobile equipment. L For example, if the system's target output power is set to 150W or 200W, and the load R... LSet to 64Ω;

[0044] S2: Determine the size and material of the power transmitting sphere and the power receiving sphere based on the transmission distance requirements and the target output power determined in S1; including the thickness d of the first and second insulating protective layers. s and relative permittivity ε s The radius R of the energy transmitting sphere and the energy receiving sphere, and the transmission distance range d. w and the relative permittivity ε of the transmission medium w ; and in accordance with Estimate the coupling capacitance value, where ε0 is the dielectric constant in vacuum;

[0045] In practical implementation, both the power transmitting sphere and the power receiving sphere are 2mm thick hollow copper spheres with a radius of 5cm; the first and second insulating protective layers are made of resin material with a thickness of 1mm; the structure between the spherical coupling mechanisms is as follows: Figure 6 As shown, the transmission medium from the transmitter to the receiver is an insulating layer-water-insulating layer.

[0046] Two capacitors, each with a value of C, are formed using two insulating layers as dielectrics. s Capacitor C is formed using water as the dielectric. t Total capacitance C in This is equivalent to three capacitors connected in series. Although the numerical solutions for spherical capacitors and parallel-plate capacitors differ, the capacitance C formed by the insulating layer can be derived from the calculation of the parallel-plate capacitor. s The capacitance C formed by water as a dielectric t The relationship between their magnitudes can be determined using the formula for calculating the capacitance of a parallel plate:

[0047]

[0048] Where S is the equivalent area of ​​the opposite side, and ε is the relative permittivity of the insulating layer. s The relative permittivity ε of water is generally between 4 and 6. w The value is 81, due to the insulation layer d s The thickness is generally very small, often between 1 and 2 mm, while in practical applications, the transmission distance d of the system is much greater. w It's around tens of centimeters, so even ε s Less than ε w According to d s and d w The relationship between the insulating layer and the capacitance C s Much larger than the capacitance C formed by the water medium w According to the formula for calculating capacitors in series, we get:

[0049] Because of C s Much larger than Cw Therefore, C in Approximately equal to C w Only C needs to be calculated. w The capacitance can be calculated using the principle of mirrors. Existing research indicates that the capacitance of two conducting spheres in water can be calculated using the mirror principle, yielding C. in The calculation formula is:

[0050]

[0051] Where k = R / d, R is the radius of the sphere, and d is the distance between the centers of the two spheres. As k approaches 0, C... in The faster the convergence, the better. Since the radius of a spherical coupling mechanism is generally a few centimeters, and the distance between the centers of the spheres can reach tens of centimeters, the higher order can be ignored, and C can be used to... in Simplified to:

[0052]

[0053] This allows us to estimate the coupling capacitance value.

[0054] S3: Determine the system angular frequency based on experience; select the resonant inductor L2 value based on the coupling capacitance value estimated in step S2, the system angular frequency, and experience, and according to ω 2 L2C2=1 determines the capacitance value of the resonant capacitor C2, where ω is the system angular frequency;

[0055] For example, if the system operating frequency f is set to 1MHz, the system angular frequency ω = 2πf; combined with Figure 3 The circuit structure shown is analyzed using the Fundamental Harmonics Approximation (FHA) method. The equivalent circuit is as follows: Figure 7 As shown, Figure 7 The power supply u can be used in the middle in Considered as a sinusoidal AC power supply, the rectifier and filter stages and the load R L It can be equivalent to an equivalent resistance R. eq The relationship between the equivalent resistance and the load resistance is given by R. eq =8R L / π 2 ;

[0056] Although the transmission mechanism of a single-capacitor electric field coupled WPT system is not yet clear, according to basic electrical engineering theory, there must be current flowing from the receiver back to the transmitter. Therefore, this invention analyzes the unclear part as an equivalent module of the coupling mechanism.

[0057] During parameter design, after determining parameters such as coupling mechanism dimensions, materials, and transmission distance range through steps S1-S3, the single-capacitor coupled WPT system constitutes an equivalent capacitance C. S The capacitance value can only be roughly estimated to be within a certain range. The capacitance value usually changes with different transmission distances. Therefore, it is not possible to accurately determine the internal structure of the equivalent module directly using the coupling capacitance value. Therefore, this invention designs the receiver and transmitter separately when designing parameters.

[0058] For the receiving end, based on the parameters given above, the estimated coupling capacitance value in step S1 is approximately 200pF. Considering the system angular frequency and experience, the resonant inductor L2 can be selected within the range of 50uH to 100uH to reduce the inductor's size, weight, and internal resistance, which is beneficial for reducing system losses and increasing system power density. And according to ω... 2 L2C2=1 determines the capacitance value of the resonant capacitor C2.

[0059] S4: Set the capacitance of resonant capacitor C1 to be equal to that of resonant capacitor C2, initially set the inductance of resonant inductor L1 to be equal to that of resonant inductor L2, and construct an experimental setup with two-port characteristics in an underwater environment; in this example, the experimental setup with two-port characteristics in an underwater environment is as follows: Figure 8 As shown; Figure 8 The input impedance is the system's input impedance Z. in ;

[0060] To reduce reactive power and improve transmission performance, the system can be operated in ZPA mode, i.e., by configuring parameters to make the system input impedance Z... in Since it is purely resistive, the values ​​of C1, L2, and C2 have been determined through the above analysis. At this time, the input impedance is changed by adjusting L1, thus proceeding to step S5.

[0061] S5: Use an LCR bridge to measure the input impedance of the experimental device. By adjusting the size of the resonant inductor L1, observe the impedance value displayed on the LCR bridge. When the circuit is resistive, determine the inductance value of the resonant inductor L1.

[0062] Since the structure in the equivalent module of the coupling mechanism is unclear, the inductance value of the resonant inductor L1 cannot be accurately calculated directly using the formula. This invention uses an LCR bridge to conveniently determine the inductance value of the resonant inductor L1, thereby ensuring that the system operates in the ZPA state.

[0063] S6: Adjust the input voltage of the power supply to ensure the system output power meets the target;

[0064] S7: Provide the final system parameters.

[0065] To further verify the technical effect of the present invention, this embodiment also conducts actual tests by building an experimental platform. When the power transmitting ball is fixed, the power receiving ball can rotate freely around it in all directions to achieve omnidirectional free power supply.

[0066] Fresh water was used in the experiment. The distance between the two spherical coupling mechanisms, i.e. the transmission distance, was 70cm. The experiment was carried out in a transparent water tank. The coupling mechanism could move in the water to simulate the wireless power supply situation when the power receiver was in different positions, as well as the energy transmission situation when the receiver moved dynamically.

[0067] The input terminal uses an IT6535D DC power supply as the power source. A light bulb and resistor are connected as loads at the output terminal. External capacitors C1 and C2 and inductors L1 and L2 are used to establish circuit resonance and compensate for reactive power in the system. The high-frequency full-bridge inverter uses four C2M0080120D MOSFETs. The drive signal is generated by the DSP and controlled by the driver chip to switch the MOSFETs on and off. To reduce inductor losses caused by the skin effect and proximity effect, the inductors are made of 0.03mm*3000 strand high-frequency Litz wire. The capacitors are high-frequency high-voltage capacitors, model CCG81-1U. The full-bridge rectifier consists of diodes of model GHXS030A120S.

[0068] By changing the relative positions of the two spherical coupling mechanisms on the water surface and underwater, the experiment simulated two scenarios: Scenario 1 is an application scenario where the transmitter is underwater and the receiver is on the water surface, which can be applied to the wireless power supply of underwater base stations to surface equipment; Scenario 2 is the most widespread application scenario where both the transmitter and receiver are underwater, which can be applied to the wireless power supply of underwater equipment by underwater base stations, or the wireless power supply between underwater equipment.

[0069] Based on experience and the parameter design method mentioned in this invention, a set of system parameters are obtained as shown in Table 1. The coupling capacitance and corresponding resonant inductance L1 of the coupling mechanism under two different scenarios are shown in Table 2. As can be seen from Table 2, the coupling capacitance of the coupling mechanism under the two position scenarios changes significantly, but the corresponding compensation inductance does not change much.

[0070] Table 1: Parameter Table of Three-Dimensional Spatial Single-Capacitor Coupled WPT System

[0071]

[0072] Table 2: Coupling capacitance and compensation inductance in two cases

[0073]

[0074] The experiment mainly focuses on omnidirectional power supply in three-dimensional space when both the transmitter and receiver are underwater. During the experiment, the transmitter is fixed, and a sphere is formed with the transmitter as the center and the transmission distance as the radius. The receiver moves on this sphere to simulate omnidirectional power supply.

[0075] Based on the two different application scenarios mentioned above, when the input voltage E dc When a certain voltage is applied, the 40W bulbs in both scenarios can light up normally, indicating that energy can be transmitted from the transmitter to the receiver in both scenarios.

[0076] To further investigate the system's output characteristics, the bulb was replaced with a 64Ω resistive load, and the system's output power was calculated by measuring the output current. Figure 9 Input voltage E dc Inverter output voltage u at 140V in Inverter output current i in and load current i o Waveform diagram.

[0077] from Figure 9 As can be seen from this, the inverter output voltage u in and inverter output current i in The fact that the system is in phase indicates that it is in the ZPA state, demonstrating the rationality and effectiveness of the parameter design method. Figure 9 The input voltage is 140V, and the load current i is... o It has a current of 1.25A and an output power of 100.7W.

[0078] Figure 10 The graph shows the output power of a three-dimensional spatial power supply system as a function of input voltage. Figure 10 It can be seen that the system's output power increases with the input voltage E dc The output power increases with the increase of voltage; when the input voltage is 100V, the output power is 52.4W, and when the input voltage is 140V, the output power reaches 100.7W. Figure 11 The graph shows the efficiency of a three-dimensional power supply system as a function of output power. Figure 11 It can be seen that the system efficiency first increases with the increase of output power. When the output power is 52.4W, the system efficiency is the highest at 40.1%. After that, the efficiency decreases slightly with the increase of output power, but the efficiency remains above 35% throughout the experiment.

[0079] When providing three-dimensional power to mobile devices, the receiver can move in any direction. Figure 12The experiment simulated six power supply scenarios from different orientations, with energy receivers ① to ⑥ positioned relative to the transmitting sphere in six different directions: front, back, left, right, up, and down. In the experiment, the energy transmitter was fixed, and the energy receivers were moved to positions ① to ⑥ respectively, with the input voltage E uniformly applied. dc Set the voltage to 100V, the load to 64Ω, and the transmission distance to 70cm, and observe the system output power and efficiency from different orientations.

[0080] Figure 13 The curves showing the changes in system output power and efficiency under six different orientations are presented. From... Figure 13 As can be seen, when the energy receiver is in six different positions, under the same conditions, the output power ranges from a minimum of 51.4W to a maximum of 53.2W, a difference of about 2W; the efficiency ranges from a minimum of 39.1% to a maximum of 40.9%, with no significant difference. In summary, the system can stably supply power when the receiver's position changes in six different directions. Because the coupling mechanism is spherical, the spherical transmitter can be used as the center, and a spherical surface with a radius of 70cm can be formed. The system can stably supply power when the receiver moves to different positions on this spherical surface.

[0081] In summary, the experimental results verify the effectiveness of the single-capacitor WPT system and parameter design method for charging underwater mobile devices proposed in this invention. The coupling mechanism uses only a pair of metal balls, which is simple in structure and easy to align. It eliminates the cross-coupling capacitance between the energy transmission plates, improves the flexibility of the system, and can be effectively applied to wireless power supply of mobile devices in underwater three-dimensional space.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and such transformations should be covered within the scope of the claims and specification of the present invention.

Claims

1. A single-capacitor WPT system for charging an underwater mobile device, comprising a power transmitting end and a power receiving end, characterized in that, The power transmitting end comprises a power supply base station device and a power transmitting ball, the power supply base station device is configured with a power transmitting circuit, the power transmitting circuit comprises a power supply, a high-frequency inverter and a primary side resonance network, the power transmitting ball is connected in the primary side resonance network through a conductive cable, and a first insulation protective layer is coated on the outside of the power transmitting ball; the power receiving end is arranged on an underwater mobile device and comprises a power receiving ball protruding from the outer surface of the underwater mobile device and a power receiving circuit located in the underwater mobile device, the power receiving circuit comprises a secondary side resonance network, a rectification filter circuit and a power load, a second insulation protective layer is coated on the outside of the power receiving ball, a single-capacitor coupling structure is formed between the power transmitting ball and the power receiving ball to realize wireless power transmission, and system parameters are configured according to a predicted coupling capacitance value, wherein ε0 is the dielectric constant in vacuum, R is the radius of the power transmitting ball and the power receiving ball, d is the distance between the power transmitting ball and the power receiving ball, and εr is the relative dielectric constant of the transmission medium. w d is the transmission distance range, ε w r is the relative dielectric constant of the transmission medium.

2. The single-capacitor WPT system for charging underwater mobile devices of claim 1, wherein: The high-frequency inverter adopts a full-bridge inverter structure, and the rectification filter circuit comprises a full-bridge rectifier and a filter capacitor.

3. The single-capacitor WPT system for underwater mobile device charging of claim 1, wherein: The primary side resonant network comprises a resonant inductor L1 and a resonant capacitor C1 connected in series with each other, and the electric energy transmitting ball is connected to a common connection end of the resonant inductor L1 and the resonant capacitor C1 through a conductive cable; the secondary side resonant network comprises a resonant inductor L2 and a resonant capacitor C2 connected in series with each other, and the electric energy receiving ball is connected to a common connection end of the resonant inductor L2 and the resonant capacitor C2.

4. The single-capacitance WPT system for charging underwater mobile devices of claim 3, wherein: The electric energy transmitting ball and the electric energy receiving ball are identical in structure and size.

5. The parameter design method of single-capacitance WPT system for underwater mobile device charging according to claim 4, wherein, The method comprises the following steps: S1: Determine target output power and load R according to the application requirements of the underwater mobile device L ; S2: determining the size and material of the power transmitting ball and the power receiving ball according to the transmission distance requirement and the target output power determined in S1, including the thickness d of the first and second insulation protective layers s and the relative dielectric constant ε s ; the radius R of the power transmitting ball and the power receiving ball, the transmission distance range d w and the relative dielectric constant ε w of the transmission medium; and according to estimating the coupling capacitance value; S3: determine the system angular frequency according to experience; determine the resonant inductance L2 according to the coupling capacitance value estimated in step S2, the system angular frequency and the resonant inductance L2 selected according to experience, and calculate the resonant capacitance C2 according to the following formula: C2 = 1 / (2 * pi * f * L2) wherein f is the system angular frequency. S4: setting the capacitance value of the resonant capacitor C1 to be equal to the capacitance value of the resonant capacitor C2, initially setting the inductance value of the resonant inductor L1 to be equal to the inductance value of the resonant inductor L2, and constructing an experimental device having a two-port characteristic in an underwater environment; S5: measuring the input impedance of the experimental device by using an LCR bridge, adjusting the size of the resonant inductor L1, and observing the impedance value displayed on the LCR bridge; when the circuit is resistive, the inductance value of the resonant inductor L1 is determined; S6: adjusting the input voltage of the power supply to make the system output power meet the target; S7: giving the final system parameters.

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