Hectowatt-level wireless power transmission system in room-level space and parameter design method

Abstract

The invention provides a hectowatt-level wireless power transmission system in a room-level space and a parameter design method. The technical problem that a power transmission system in an existing room-level space is low in safety level and transmission power is solved. Comprising a transmitting end and a receiving end, and the transmitting end comprises a plurality of transmitting coils arranged at equal intervals in the vertical direction; the inner sides of the plurality of transmitting coils form a room-level charging space, the receiving end comprises a plurality of receiving circuits, and the plurality of receiving ends are all located in the room-level charging space. According to the parameter design method, a system electromagnetic field safety limit value and coil geometric dimension parameters are set, and parameter optimization design is carried out by constructing conditions for realizing decoupling compensation and ZPA in the system and adopting capacitance distributed compensation for each coil, so that uniform current distribution between the coils is realized under a high mutual coupling condition; and the security level and the transmission efficiency of the power transmission system in the room-level space are improved.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission, and in particular to a hundred-watt wireless power transmission system in a room-level space and a parameter design method. Background Art

[0002] Wireless power transfer (WPT) technologies can provide wireless power or charging capabilities for electronic devices in personal living spaces, such as laptops and smartphones. Among these technologies, near-field wireless power transfer, especially magnetic resonance wireless power transfer (MR-WPT), has received extensive research attention due to its potential in improving power transfer efficiency and reducing health effects.

[0003] MR-WPT technology uses magnetic field coupling at frequencies from kHz to low MHz to achieve wireless power transmission within a specific distance or area. For example, in existing literature, omnidirectional transmitters are used to control the magnetic field to provide wireless charging for low-power devices (such as sensors). And the power supply range is extended by grid planar transmitters, which is suitable for desktop scenarios. Although these methods are effective in local spaces, the public's long-standing expectation of achieving wireless power supply throughout the room still faces major challenges. These challenges include safety assurance when humans are in the electromagnetic (EM) environment, and maintaining power transmission and efficiency that meets the needs of various devices in most areas of the room.

[0004] In the field of EM safety, in order to protect the public from the impact of the EM environment, countries and industry organizations have established electromagnetic exposure safety standards, such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP), the Federal Communications Commission (FCC) and the Institute of Electrical and Electronics Engineers (IEEE). Under the framework of these standards, numerous studies are devoted to reducing EM exposure in wireless power transmission. Most studies focus on reducing the electromagnetic field emitted from the outside of the coil, such as through electromagnetic shielding and power control, to ensure compliance with safety standards. However, there are relatively few studies on the spatial distribution of electromagnetic fields, especially in terms of actively reducing human EM exposure by optimizing the spatial distribution of electromagnetic fields.

[0005] In the context of large-space power transmission, dipole coil-based structures have been used to achieve simultaneous charging of multiple receivers and multiple degrees of freedom in a space of nearly 1 cubic meter. A quasi-static cavity resonance (QSCR) method was used to generate a widely distributed magnetic field in the room, providing tens of watts of power to devices placed near the walls of the space. Circuit models of QSCR-based wireless power transmission systems have also been explored, and dual circular coils have been used as transmitters to create a relatively uniform magnetic field in a room-scale space, providing 40 watts of power to the receiver. Although these studies have laid a solid foundation for wireless power transmission in large-scale spaces, they have not explored EM safety issues in depth, and the potential for increasing power transmission under existing safety standards has not been fully studied. Summary of the invention

[0006] The purpose of the present invention is to provide a 100-watt wireless power transmission system and parameter design method in a room-level space, so as to solve the technical problems of low safety level and low transmission power of the existing power transmission system in the room-level space.

[0007] A 100-watt wireless power transmission system in a room-level space comprises a transmitting end and a receiving end, wherein the transmitting end comprises a plurality of transmitting coils arranged at equal intervals in a vertical direction;

[0008] A room-level charging space is formed inside the plurality of transmitting coils. The receiving end includes a plurality of receiving circuits. The plurality of receiving ends are all located in the room-level charging space.

[0009] Optionally, the transmitting end further includes a DC power supply, an inverter and a plurality of primary side compensation circuits;

[0010] The output ends of the primary compensation circuits are respectively connected to the transmitting coils, the input ends of the primary compensation circuits are all connected to the output end of the inverter, and the input end of the inverter is connected to the DC power supply.

[0011] Optionally, the receiving circuits each include a receiving coil, a secondary side compensation circuit, a rectifier and a load connected in sequence;

[0012] The primary compensation circuit and the secondary compensation circuit are LCC-S topology structures, the primary compensation circuits each include a primary compensation inductor, a primary first compensation capacitor and a primary second compensation capacitor, and the secondary compensation circuits each include a secondary compensation capacitor.

[0013] Optionally, the plurality of transmitting coils are single-turn coils.

[0014] A parameter design method for a 100-watt wireless power transmission system in a room-level space is used for parameter design of the above-mentioned 100-watt wireless power transmission system in a room-level space, and the specific steps are:

[0015] S1: Set the system electromagnetic field safety limit, including the magnetic field strength limit and electric field strength limit in the safe charging area, as well as the local SAR limit;

[0016] S2: Set the geometric size parameters of the transmitting and receiving coils according to the requirements, and calculate the system resonant frequency and transmitting coil current when the system transmission power is maximum based on the system electromagnetic field safety limit as a constraint;

[0017] S3: Select any receiving coil and given the output voltage of the inverter, extract the electromagnetic parameters of the transmitting and receiving coils through finite element analysis, including the self-inductance of the transmitting and receiving coils, and the mutual inductance between the transmitting and receiving coils;

[0018] S4: Construct the conditions for realizing decoupling compensation and ZPA in the system, calculate the parameters of the primary and secondary compensation circuits, and use the distributed compensation method of compensation capacitors to perform segmented compensation on the transmitting coil;

[0019] S5: Taking the local SAR limit as a constraint, calculate the optimal operating current of the receiving coil.

[0020] Optionally, the geometric dimension parameters of the transmitting coil and the receiving coil in step S2 include: the radius of the transmitting coil, the number of transmitting coils, the safe distance between the human body and the transmitting coil, the spacing between the transmitting coils, the total height of several transmitting coils, the total height of the safe charging space and the radius of the receiving coil.

[0021] Optionally, the specific method for calculating the system resonant frequency and the transmitting coil current when the system transmission power is maximum in step S2 is:

[0022] According to the geometrical dimension parameters of the transmitting coil and the receiving coil, the magnetic field and electric field strength at any transmitting coil current and the system resonant frequency, as well as the effective power flow received by the receiving coil are calculated;

[0023] With the magnetic field and electric field strengths being less than the electromagnetic field safety limit as the constraint condition and the maximum effective power flow received by the receiving coil as the optimization goal, the system resonant frequency and transmitting coil current when the system transmission power is maximum are obtained.

[0024] Optionally, in step S4, the conditions for achieving decoupling compensation and ZPA in a wireless power transmission WPT system with multiple transmitting coils and multiple receiving coils are constructed through the system resonance relationship:

[0025]

[0026] Where ω is the angular frequency, L fn is the nth primary compensation inductance, C fnis the first compensation capacitor value of the nth primary side, L rm is the self-inductance of the mth receiving coil, C rm is the mth secondary compensation capacitor value, C sn is the second compensation capacitor value of the nth primary side, L sn is the self-inductance of the nth transmitting coil, M nk is the mutual inductance between the nth transmitting coil and the kth transmitting coil, N s is the total number of transmitting coils;

[0027] The conditions for achieving decoupling compensation and ZPA are f satisfy in: and The transmitting coil current and the inverter output voltage are respectively obtained through step S2, the transmitting coil current when the transmission power is maximum, the inverter output voltage set in step S3, and the self-inductance of the transmitting and receiving coils, as well as the conditions for realizing decoupling compensation and ZPA, calculate the primary first compensation capacitance value, the primary compensation inductance value, the secondary compensation capacitance value and the primary second compensation capacitance value.

[0028] Optionally, in step S4, the distributed compensation method of the compensation capacitor is used to perform segmented compensation on the transmitting coil. sn_seg The values ​​are:

[0029]

[0030] In the formula, C sn_seg is the value of the segmented compensation capacitor, and Q is the number of segments of the transmitting coil and the primary second compensation capacitor.

[0031] Optionally, the specific method for calculating the optimal operating current of the receiving coil in step S5 is:

[0032] S5.1: Set the operating current of the receiving coil according to the exposure scenario;

[0033] S5.2: Calculate the peak local SAR under the current receiving coil operating current;

[0034] S5.3: Determine whether the peak local SAR is equal to the local SAR limit value. If so, output the current receiving coil operating current as the optimal operating current; if not, return to step S5.1 to reset the receiving coil operating current.

[0035] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0036] 1. This application constructs a wireless power transmission system by combining multiple large single-turn circular coil structures with magnetic resonance wireless power transmission technology, which can achieve safe wireless power transmission of more than 100W in a room-level space.

[0037] 2. This application sets the electromagnetic field safety limit and coil geometry parameters of the system, builds the conditions for decoupling compensation and ZPA in the system, and optimizes the parameters for each coil using capacitor distributed compensation to achieve uniform current distribution between coils under high mutual coupling conditions. This improves the safety level and transmission efficiency of the power transmission system in the room-level space.

[0038] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings of the present invention are as follows.

[0040] Figure 1 FIG. 4 is an equivalent circuit diagram of the multi-transmitting coil and multi-receiving coil system of the present invention.

[0041] Figure 2 The present invention is a flow chart of the system parameter design method.

[0042] Figure 3 It is a schematic diagram of the structure of multiple large single-turn circular transmitting coils of the present invention.

[0043] Figure 4 FIG. 4 is an equivalent circuit diagram of distributed compensation of a specific transmitting coil after compensation and decoupling according to the present invention.

[0044] Figure 5 FIG. 4 is a diagram showing simulation results of a system with three transmitting coils according to the present invention.

[0045] Figure 6 It is a local SAR simulation analysis diagram during the power transmission process of the present invention.

[0046] Figure 7 It is a simulation analysis diagram of the metal object of the present invention.

[0047] Figure 8 This is a temperature distribution diagram of a metal object under natural convection of the present invention.

[0048] Fig. 9 This is a graph showing the analysis results of current, power and efficiency of the present invention.

[0049] Fig.10 The present invention has a single RX Plot of experimental test results in the xoz plane of the coil.

[0050] Fig.11 This is the electromagnetic field intensity distribution diagram in the xoz plane at different heights of the hair.

[0051] Fig.12 This is a thermal image of a metal object in a stable state according to the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0053] Embodiment 1:

[0054] like Figure 1 A 100-watt wireless power transmission system in a room-level space as shown includes a transmitting end and a receiving end, wherein the transmitting end includes a plurality of transmitting coils T arranged at equal intervals in the vertical direction. X , a number of the transmitting coils T X All are single-turn coils, several transmitting coils T X The number is N s , L sn is the nth transmitting coil T X The self-inductance, where: n∈(1,2,...,N s );

[0055] Several transmitting coils T X A room-level charging space is formed inside the receiving end, and the receiving end includes a plurality of receiving circuits, and the plurality of receiving ends are all located in the room-level charging space.

[0056] In this embodiment, under ideal conditions, the solenoid can generate a uniform and widely distributed high-frequency electromagnetic field inside it. Based on this concept, this paper uses multiple large single-turn circular coils as the transmitting coil T X , which is equivalent to the size of a room, such as Figure 3 As shown in (a), Figure 3 (a) is a schematic diagram of the three-dimensional structure of the coupling mechanism.

[0057] The transmitting end also includes a DC power supply U dc , an inverter and a plurality of primary compensation circuits, wherein the output ends of the plurality of primary compensation circuits are respectively connected to a plurality of transmitting coils T X The input ends of the primary compensation circuits are connected to the output end of the inverter, and the input end of the inverter is connected to the DC power supply U dc connect.

[0058] The receiving circuits each include a receiving coil R connected in sequence X , secondary side compensation circuit, rectifier and load RLm , several receiving coils R X The number is N r , L rm is the mth receiving coil R X The self-inductance, where: m∈(1,2,...,N r ).

[0059] The primary compensation circuit and the secondary compensation circuit are LCC-S topology structures. The nth primary compensation circuit includes a primary compensation inductor L fn , the first compensation capacitor C fn And the primary side second compensation capacitor C sn The mth secondary compensation circuit includes a secondary compensation capacitor C rm .

[0060] In this embodiment, since the transmitting coil L sn Large size and coaxial configuration, the transmitting coil L sn On the contrary, in practical applications, the coupling between the receiving coil L rm The distance between them is large or they are placed on the same plane. The receiving coil L rm The mutual coupling between them can usually be ignored. Let k (range from 1 to N s ) represents any transmitting coil. M nk Indicates different transmitting coils L sn The mutual induction between is the mutual inductance between the transmitting coil and the receiving coil.

[0061] Embodiment 2:

[0062] like Figure 2 The parameter design method of a 100-watt wireless power transmission system in a room-level space shown is used to perform parameter design on a 100-watt wireless power transmission system in a room-level space described in Example 1, and the specific steps are as follows:

[0063] S1: Set the system electromagnetic field safety limit, including the magnetic field strength limit H in the safe charging area inc and electric field strength limit E inc , and local SAR limits.

[0064] In this embodiment, if Figure 3 (b) shows the spatial distribution of the electromagnetic field of the transmitting coil. The intensity of the electric field (E field) and the magnetic field (H field) gradually increases from the center to the coil winding. When approaching the coil, the field strength may become strong enough to affect the electromagnetic safety of the human body. Therefore, this application defines a safe charging space Ωs to limit the harmful electromagnetic exposure that may be caused when approaching the coil. The safe charging space is composed of a shaded cylindrical surface A sSurrounded by a radius slightly smaller than the transmitting coil T X The radius of the xoz plane is the safety boundary line l. Figure 3 As shown in (b), when the electromagnetic field strength at the safety boundary line meets the relevant safety standards, it can ensure that the human body in the charging space is protected from the transmitting coil T X When the receiving coil R X When placed in a safe charging space, they can harvest energy through magnetic field coupling.

[0065] The International Commission on Non-Ionizing Radiation Protection (ICNIRP) is an authoritative body that regulates electromagnetic exposure to the human body. In its 2020 guidelines, it defines basic limits and reference levels for electromagnetic exposure to the public, as shown in Table 1. The basic limits include whole-body specific absorption rate SAR and local SAR, where whole-body specific absorption rate SAR is used to prevent heat stress and local SAR is used to prevent local thermal damage. Since SAR is an internal exposure indicator and difficult to measure directly, the guidelines derive reference levels based on the basic limits to ensure that the electromagnetic field intensity is significantly lower than the basic limits. Compliance with the electromagnetic field thresholds specified by these reference levels can ensure that exposure is well below the basic limits, thereby meeting the guidelines.

[0066] Table 1 Basic limits and reference levels for public exposure in the frequency range of 100KHZ to 10MHZ

[0067]

[0068] In a room-scale wireless charging system, the human body may absorb the power generated by the transmitting coil T X and the receiving coil R X The electromagnetic energy emitted. Due to the transmitting coil T X The electromagnetic field generated by the transmitting coil T is widely distributed in the entire space, and its electromagnetic exposure level may reach the regulatory standard even in the absence of a receiving load. In order to minimize the exposure of the human body to electromagnetic radiation, this application adopts a reference level to limit the electromagnetic radiation generated by the transmitting coil T X Specifically, at any point p in space, if its H field strength is H p , the E field strength is E p , then the electromagnetic field strength in the charging area must meet specific constraints:

[0069]

[0070] Receiving coil R X The size of the receiving coil R is usually small, similar to electronic equipment. They are usually wound into a planar multi-turn coil structure to increase the receiving power. XThe H field strength nearby may exceed the reference level. However, the human body has a significant impact on the receiving coil R X Exposure to the generated electromagnetic fields is usually short-term and local. Therefore, we use local SAR to limit the exposure to the electromagnetic fields generated by the receiving coil R X Specifically, the receiving coil R X The local SAR exposure of any part of the human body must meet specific constraints:

[0071] Local SAR≤2W kg -1 (2)

[0072] Where Local SAR is the local SAR exposure value of any part of the human body.

[0073] S2: Set the transmitting coil T according to the requirements X and the geometrical dimension parameters of the receiving coil, and based on the system electromagnetic field safety limit as a constraint, calculate the system resonant frequency f when the system transmits the maximum power op and the transmitting coil current I s-op ;

[0074] The transmitting coil T X The geometrical dimension parameters include: the radius of the transmitting coil R s , the number of transmitting coils N s , the safe distance D between the human body and the transmitting coil, the spacing d between the transmitting coils s , the total height of several transmitting coils h s 、Total height of safe charging space h l and the receiving coil radius R r .

[0075] In this embodiment, if Figure 3 (c) shows the two-dimensional projection of the transmitting coil on the xoz plane. The current flowing through all coils has the same amplitude and phase, expressed as a phasor, and the effective value of the current is I s . With the transmitting coil T X Coaxial single-turn receiving coil R X Radius R r Much smaller than the transmitting coil T X Radius R s . Receiving coil R X The size is small, ensuring that its presence does not significantly affect the transmitting coil T X Generated spatial electromagnetic distribution. Receiving coil R X The effective value of the current is I r .Shaded area A sIt represents the safe distance D that should be maintained between the human body and the transmitting coil. Its projection on the xoz plane is the left boundary line l. The total height of the safe charging space is h. l .

[0076] Assume that the current distribution in the coil is uniform and the receiving coil R X In the transmitting coil T X Current and receiving coil R X The maximum energy can be obtained when the current phase difference is 90°. If the phase difference of the coil is set to 90°, according to the Biot-Savart law, Maxwell equations and superposition principle, the electric field (E field) and magnetic field (H field) at the midpoint p in space are:

[0077]

[0078] in:

[0079]

[0080] Where i is the type identifier s or r, where s is the transmitting coil identifier and r is the receiving coil identifier. The spatial position function T i ,H x , T i ,H z , T i ,E y They are respectively the transmitting coil T X Or receiving coil R X The spatial position function in the x, y, and z directions. i (k) is the transmitting coil T X Or receiving coil R X is the z-axis position of the kth turn of the coil, θ is the azimuth angle around the central axis of the coil, and μ0 is the magnetic permeability of the air.

[0081] The average Poynting vector at a point p in space is:

[0082]

[0083] In the xoz plane, the average Poynting vector at a point p in space has components only in the x and z directions, as Figure 3 (c) If we take the unit normal vector n pointing inward and perpendicular to line l, the effective power flow into space Ωs has only S av,x Therefore, the receiving coil R X The effective power flow received is:

[0084]

[0085] In the above formula, the current I of the receiving coil is set ris the unit current. When the coil size and safety distance are fixed, the effective power flow into the energy collection space is With the resonant frequency f and the transmitting coil current I s According to formula (3), it can be seen that the resonant frequency f and the transmitting coil current I s It is directly related to the electromagnetic field in space. There is an optimal f and I s combination, maximizing the electromagnetic field while ensuring that it meets safety standards Therefore, the optimization process is constrained by the electric and magnetic field strengths at the safety boundary line l. s Effective power As the goal, the optimization model with electromagnetic safety constraints is obtained as follows:

[0086]

[0087] In this embodiment, in order to maintain universality, the present application consists of three single-turn transmitting coils T X The scenario of a multi-transmitting coil system composed of N s = 3. Transmitting coil radius R s is 1.5 meters, and the total height of several transmitting coils h s =1 meter, transmitting coil radius R s The spacing between s is 0.5 m, and the single-turn receiving coil R X Radius R r The safe distance D between the human body and the transmitting coil system is 100 mm. Based on these coil structure parameters, we use MATLAB software to visualize equation (7), as shown in Figure 3 (d) shows the relationship between the effective power flow, the transmitting coil current and the frequency under specific parameters. The horizontal axis in the figure represents the resonant frequency, and the vertical axis represents the current of the transmitting coil. The red curve represents the safety limit of the electric field, and the white curve represents the safety limit of the magnetic field. These two curves divide the graph into four regions. Region 1 and Region 4 correspond to situations where only the magnetic field strength or the electric field strength exceeds its safety limit, respectively. Region 2 is the region where both the electric field and magnetic field strengths exceed their limits, while Region 3 indicates that both the electric field and the magnetic field are within the safety limit (including the boundaries). Within this safe operating region 3, the optimal operating curve for achieving maximum power transfer and meeting electromagnetic safety standards is located at the interface between regions 3 and 4. When the system operates at the frequency and current corresponding to this curve, maximum power transfer can be achieved under the constraints of the electromagnetic exposure reference level. The red asterisk indicates the optimal operating point, whose resonant frequency is f op =1.38MHz, current is I s-op =9.1A.

[0088] exist Figure 3 In (d), each point on the red curve corresponds to the same power level. This means that in the room-level space, in order to ensure that the receiving coil R has unit current X To receive the same power, choosing a lower frequency (such as the hundreds of kilohertz range recommended by the Qi standard) requires a larger transmitting coil T. X excitation current. This will result in a stronger H field, which may exceed the ICNIRP2020 limit and cause nerve stimulation to the human body. Conversely, choosing a higher frequency (such as 6.78MHz) can reduce the transmitting coil T X The current required will increase the receiving coil R X The electric field strength nearby leads to higher SAR exposure. At the point marked by the red asterisk, the system not only achieves the maximum power transmission under the reference level limit, but also ensures that the receiving coil R X The generated electric field is minimized. Therefore, the optimal operating point in this application is a balance between power transmission and electromagnetic safety, ensuring compliance with safety standards while minimizing electromagnetic exposure.

[0089] S3: Select any receiving coil R X , and the output voltage U of the inverter is given S , the transmitting coil T is extracted by finite element analysis X and the receiving coil R X The electromagnetic parameters of the transmitting coil T X Self-sensitivity sn , receiving coil R X Self-sensitivity rm and the transmitting coil T X With receiving coil R X Mutual inductance M ij .

[0090] S4: Construct the conditions for realizing decoupling compensation and ZPA in the system, calculate the parameters of the primary and secondary compensation circuits, and use the distributed compensation method of compensation capacitors to perform segmented compensation on the transmitting coil;

[0091] S4.1: This application mainly studies the steady-state power transmission characteristics. Since the compensation circuit filters out the higher harmonics, the fundamental wave approximation FHA is used to analyze the compensation and decoupling conditions. dc Converted to AC voltage via inverter Its effective value is U dc of times and used as the reference phase. After rectification, the AC power on the receiving side is converted into DC power to supply the load. The input voltage of each receiving circuit rectifier is marked as Compensation inductance L fn and each transmitting coil L sn The current phasors in are marked as and Receiving side capacitor C rm The current phasors in

[0092] With a single transmitting coil T X and the receiving coil R X Different systems have strong mutual coupling between multiple large transmit coils in multi-transmit and multi-receive wireless power transfer systems. In order to achieve current balance and zero phase angle (ZPA) compensation, the system must derive the resonant condition. Figure 1 As shown in the circuit diagram, according to Kirchhoff's voltage law KVL, with the primary compensation inductor L fn The relevant circuit equation is:

[0093]

[0094] From formula (8), it can be seen that when the primary compensation inductance L fn And the primary first compensation capacitor C fn When resonating at frequency ω, any transmitting coil T X The current in the And the primary first compensation capacitor C fn Decision. If each C fn The value of is equal, denoted as C f (Similarly, each L fn Equal, denoted as L f ), then each transmitting coil T X The current in the The phase is 90°, recorded as The first compensation condition is obtained as shown in equation (9). When this condition is met, any transmitting coil T X The current in is shown in formula (10):

[0095]

[0096] From formula (10), we can see that at the angular frequency ω, and the compensation parameter C f When each transmitting coil T X The current in the same Control. Apply Kirchhoff's voltage law KVL, combined with equations (9) and (10), and any transmitting coil T X and any receiving coil R X The relevant circuit equations are:

[0097]

[0098] In formula (11), is the kth transmitting coil T X and the mth receiving coil R X The mutual inductance between them, when L rm and C rm When resonating at frequency ω, the output voltage is given by equation (13) and is proportional to the input voltage Same phase.

[0099]

[0100] When equation (10) satisfies equation (13), the current flowing through any primary compensation inductor is given by equation (14).

[0101]

[0102] According to Ohm's law R rm is the AC equivalent resistance, which is R Lm Combining formulas (13) and (14), the input impedance Z of the inverter is s It is expressed by formula (16).

[0103]

[0104] According to formula (16), the input impedance Z s Only the real part, and with multiple transmitting coils T X Mutual inductance M sn This realizes the zero phase angle ZPA and decoupling compensation between the coils. Therefore, summarizing the derivation process from equations (8) to (16), the conditions for achieving decoupling compensation and ZPA in the strongly mutually coupled multi-transmitting coil and multi-receiving coil wireless power transmission WPT system are:

[0105]

[0106] S4.2: In the actual circuit, the large size transmitting coil T X The stray parameters between the transmission coil and the environment will not only introduce additional losses, but also affect the electromagnetic field distribution, thereby interfering with the electronic devices being charged in the space. In order to reduce the parasitic effects of large-sized coils at high frequencies, the transmitting coil T X Approximately as an ideal conductor, to ensure uniform current distribution, each transmitting coil T X Divided into Q segments to minimize parasitic effects. The primary side second compensation capacitor C sn Evenly distributed over these parts for segmented compensation, e.g. Figure 4 (a) shows the specific T after considering the compensation and decoupling of parasitic parameters. X Equivalent circuit diagram of distributed compensation. sn_seg Indicates the nth transmitting coil T XEquivalent self-inductance when divided into Q parts, M sn_seg Represents the corresponding equivalent mutual inductance. C sn_seg The second compensation capacitor on the primary side is divided into Q segments and connected to the nth transmitting coil T X The associated segment compensation capacitor. R sn_g and C sn_g represents the parasitic resistance and capacitance of each conductor segment to the environment. sn_seg 、M sn_seg and C sn_seg The series resonance between them bypasses the parasitic effects and ensures that the large size transmitting coil T X The uniform current distribution, the equivalent circuit is further simplified as follows Figure 4 As shown in (b), Figure 4 (b) is the specific T after compensation and decoupling ignoring parasitic parameters X Equivalent circuit diagram of distributed compensation. For the nth transmitting coil T in each segment X , C sn_seg Compensation L sn_seg and M sn_seg Therefore, the segment compensation capacitor C sn_seg The values ​​are:

[0107]

[0108] S5: Taking the local SAR10g limit as a constraint, calculate the receiving coil R X The best operating current.

[0109] In this embodiment, the simulated receiving coil R X 5-10 mm from the head or hand, this distance usually represents the minimum contact distance between the current-carrying conductor and the human body in practical applications. Following these steps can ensure that the multi-transmitting coil T X The resulting electromagnetic exposure complies with the reference level, while the specific receiving coil R X Basic limits are met, allowing for maximum power transfer in large spaces.

[0110] S6 simulation and verification:

[0111] S6.1 Electromagnetic distribution of large-size transmitting coil and human SAR simulation at the optimal working point:

[0112] In Ansys HFSS software, the transmitting coil T was simulated and verified. X The electromagnetic distribution and its impact on the human body standard SAR. The radius of each large-sized transmitting coil is 1.5 meters and the spacing is 0.5 meters. These transmitting coils are located in Figure 3(d) The optimal operating point is determined in (current is 9.1A and frequency is 1.38MHz). The safe charging space is a cylindrical area coaxial with the transmitting coil, with a radius of 1.4 meters and a height of 2 meters. The safety boundary is 100 mm away from the transmitting coil. Since the electromagnetic field reaches its maximum at the safety boundary, the human body and its key tissues (torso, head, legs and arms) are placed in this position for simulation, as shown in Figure 2. Figure 5 (a) shows the simulation model. Figure 5 (b) The field intensity distribution diagram in the xoz plane shows that the closer to the transmitting coil, the stronger the electric and magnetic fields are, and they reach the reference level (H) at point A of the safety boundary. inc =21A / m, E inc =83V / m), while other locations in the charging space are below these levels. Figure 5 (c) is the local SAR10g diagram of key human tissues, with a peak value not exceeding 0.072W / kg, which is far below the basic limit of 2W / kg. The local SAR10g of the integrated whole body has an absorbed power of 0.0187W, and the average whole body SAR of a standard human body mass of 78kg is only 0.00024W / kg, which is far below the basic limit of 0.08W / kg. These results show that the proposed room-level electromagnetic environment meets safety requirements.

[0113] S6.2 Human SAR simulation during power transmission:

[0114] like Figure 6 As shown, Figure 6 (a) is the local SAR simulation model diagram during power transmission. Figure 6 (a) shows the selected receiving coil R X , is a traditional planar spiral structure with an outer diameter of 100 mm, an inner diameter of 5 mm, a wire diameter and a coil spacing of 2 mm, and its size is comparable to that of a tablet computer. Assuming the exposure scenario is a receiving coil R X The current-carrying conductor plane is about 10 mm away from the top of the head, and the receiving coil R in the parameter design method is used. X The current optimization method determines the R X The best working current I r_op , its effective value is 3.5A. X At 3.5A, the local SAR10g peak at the top of the head reaches 2.0W / kg, while other areas are lower than this value. X , keeping the coil current below 3.5A ensures compliance with the local SAR10g limit.

[0115] In order to verify the electromagnetic safety during power transmission, we set up a three-receiving coil R XSimultaneous working scenarios, such as Figure 6 (a) These coils are placed horizontally in the area with the highest field strength (at the safety boundary), with a spacing of 50 mm between each coil, simulating the distance when multiple electronic devices are used simultaneously. The simulation takes into account multiple receiving coils R X The working positions are placed at the waist, chest, near the eyes and top of the head, with a distance of R from the receiving coil. X The simulation results show that when the three receiving coils R X When placed on the top of the head, the local SAR10g peak is about 2W / kg. In other simulated usage scenarios, the local SAR10g is well below the basic limit of 2.0W / kg. These results show that even in extreme exposure scenarios, human electromagnetic exposure meets relevant guidelines, and in typical daily use (such as three receiving coils R X placed at the waist and chest), the exposure values ​​are well below the basic limit.

[0116] S6.3 Metal object simulation analysis:

[0117] In high-frequency electromagnetic environments, eddy currents in metal objects can cause harmful thermal effects. Therefore, it is necessary to evaluate common or potential metal objects in the room, including aluminum, iron, nickel, and alloy materials. Table 2 lists these objects and their approximate sizes, including small household items such as aluminum foil, coins, cans, aluminum blocks, steel nails, wrenches, and larger items such as cooking utensils. These objects are placed within the safety boundary for simulation analysis based on their typical usage locations, such as Figure 7 (a) shows a model diagram of placing a metal object at the safety boundary for simulation. Figure 7 (b) shows the loss distribution simulation results of various objects. Figure 7 (c) shows these losses on a logarithmic scale. Ferromagnetic objects such as nickel coins and iron cookware exhibit higher eddy current effects than non-magnetic metals. Aluminum blocks and some stainless steel objects (such as nails or wrenches) show smaller eddy current losses, no more than 50mW. In the area of ​​strongest field strength, large ferromagnetic objects such as iron cookware have eddy current losses of about 1.64W, while when placed in the center of the room, the losses are only 0.73W. In general, as the size of the metal object increases, the losses also increase. For objects of the same size, ferromagnetic metals exhibit stronger eddy current effects than non-ferromagnetic metals. To further evaluate the thermal effects, the temperature distribution of these metal objects was simulated using Ansys Icepak. Figure 7 (c) and set the ambient temperature under natural convection conditions to 29°C. The simulation results are shown in Figure 8As shown, the temperature rise of all objects is kept within 1°C. This shows that even under conservative heat dissipation conditions, the thermal effect can be ignored, ensuring the safety of the system.

[0118] Table 2 Types of metal objects

[0119]

[0120] S6.4 Build an experimental prototype for experiment:

[0121] S6.4.1 Build the experimental prototype:

[0122] The experimental prototype uses a 20-sided polygonal structure with an inscribed circle to simulate a room, with a radius of 1.5 meters, a height of 2.4 meters, and a total volume of about 17 cubic meters. A 2.4-meter-high square wooden support is installed at each vertex, and three layers of wire ducts are arranged around it. The transmitting coil T in each wire duct X The conductor is 0.04mm*3000 Litz wire, three T X The total weight of the coil is approximately 0.96 kg. The lowest wire slot is located 0.7 meters above the ground, and the gap between adjacent wire slots is 0.5 meters. For easy access, a door is designed to allow the current of three separate single-turn circular coils to return to the power supply through the slot above the door. The overall structure is connected by 3D printed parts and pneumatic nails to ensure stability.

[0123] The structural parameters of the receiving coil are as follows: Figure 6 As shown in (a), the coil is wound on a 3D printed reel. An oscilloscope and power analyzer are used for data recording. The developed wireless power transfer technology is capable of wirelessly charging portable devices such as laptops and smartphones in a room. During the experiment, a charging protocol conversion interface was added between the rectifier and the electronic device without affecting the experimental setup. In addition, when the mobile phone is directly placed against the receiving coil R X When connected, it can charge normally without interfering with the device's touch screen or communications. Figure 1 The equivalent circuit connection of the system is shown in Table 3. The main electrical parameters are shown in Table 3. These parameters include self-inductance and mutual inductance, compensation inductance and capacitance of the transmitting coil, and self-inductance and compensation capacitance of the receiving coil. The optimal resonant frequency of the system is 1.38MHz, and the optimal operating currents of the transmitting coil and the receiving coil are 9.1A and 3.5A respectively.

[0124] Table 3 Parameters of room-level wireless charging system prototype

[0125]

[0126] S6.4.2 Experimental results analysis:

[0127] S6.4.2.1 Verification of current sharing for multiple large single-turn circular coils:

[0128] like Fig. 9 As shown, Fig. 9 (a) shows the three transmitting coils T at an operating frequency of 1.38 MHz. X The effective current in each coil is about 9.1A, and the phases are consistent, achieving current balance. This also verifies the effectiveness of the parallel coil compensation and decoupling method proposed in this paper. Fig. 9 (b) shows the voltage and current waveforms of the inverter output, inductor L1, and receiving coil 1, where the inverter achieves zero voltage switching ZVS, and the 90° phase difference between the transmitting coil and the receiving coil achieves maximum power transfer. Fig. 9 (c) and (d) show the received power and efficiency of a single receiver and three identical receivers, respectively. The maximum power of a single receiver reaches 140W (46% efficiency). The total transmission power of the three receivers reaches 375W, with an efficiency of over 70%. It can be foreseen that as the number of receivers increases, the transmission power and efficiency will also increase.

[0129] S6.4.2.2 Spatial distribution of transmission power and efficiency in room-scale space:

[0130] like Fig.10 (a) and (b) are the power reception diagram and efficiency distribution diagram on the xoz plane evaluated using a single receiver. The z=0 plane and the first transmitting coil T X Planar alignment. Near the coil, the receiver achieved over 100W of power reception. Within a common living space, extending from z=0m to a height of z=1m, the receiver consistently received over 40W of power, with an efficiency of over 20%. However, at locations farther from the coil along the z-axis, particularly at the top and bottom of the room, the power dropped to around 10W.

[0131] S6.4.2.3 Measurement of electromagnetic field strength in space and electromagnetic heating test of metal objects:

[0132] In order to verify the electromagnetic safety, the electric and magnetic fields in the xoz plane were measured using a high-frequency electromagnetic field meter NF-5035. Fig.11 Results are shown at three typical z coordinates (corresponding to the positions of the three transmitting coils, z = 0m, 0.5m, 1.0m). In the charging space (x∈[-1.4m,1.4m]), the electromagnetic field strengths are kept below 21A / m and 83V / m, respectively, in line with the ICNIRP 2020 guidelines.

[0133] The metal objects listed in Table 2 are Figure 7The positions shown in (a) were placed in the room. The thermal images of these objects were recorded using a UTi384G thermal imager in a steady state (about 10 minutes). Fig.12 As shown. The ambient temperature is about 29-30℃. Transmitting coil T X1 The temperature of the metal objects slightly increased to 33.7°C, and the temperature of all metal objects was close to the ambient temperature, with no risk of fire, thermal burns or damage, and no adverse effects on the system. These results show that the impact of typical metal objects in the weak magnetic field environment proposed in this study is negligible.

[0134] In summary, this application demonstrates that safe wireless power transmission of more than 100W can be achieved in room-level spaces by combining multiple large single-turn circular coil structures with magnetic resonance wireless power transfer (MR-WPT) technology. Our analysis and testing established an electromagnetic optimization model with the goal of maximizing electromagnetic power flow and subject to electromagnetic exposure limits, which can determine the optimal resonant frequency and coil current of the system to ensure the maximum electromagnetic power flow under ICNIRP 2020 limits. The introduced distributed capacitance compensation and parallel excitation method of each coil turn effectively mitigate the parasitic parameters and electric field effects in large-sized coils. In addition, the proposed compensation parameter design method achieves decoupling under strong coupling conditions, ensuring uniform current distribution between coils. The power transmission capability of the system was verified by a cylindrical room model (3 meters in diameter and 2.4 meters in height). The test results show that the system achieves more than 100W of wireless power transmission (efficiency over 46%) at the optimal position near the transmitting coil using a specific tablet-sized receiver. When three specific iPad-sized receivers work simultaneously, the system successfully transmits 375W (efficiency over 70%). In the main device usage area (height from z = 0 meters to z = 1 meter), a single receiver can continuously receive more than 40W of power with efficiency maintained above 20%. This result shows the potential application of the system in smart homes, office environments, and public places, especially for wireless power environments that require large spatial freedom and multiple electronic devices. Future research will focus on exploring larger-scale wireless power transmission systems, improving system efficiency, developing receiving coils with lower electromagnetic exposure, and integrating these coils with various electrical devices.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A 100-watt wireless power transmission system in a room-level space, comprising a transmitting end and a receiving end, characterized in that: The transmitting end includes a plurality of transmitting coils arranged at equal intervals in the vertical direction; A room-level charging space is formed inside the plurality of transmitting coils. The receiving end includes a plurality of receiving circuits. The plurality of receiving ends are all located in the room-level charging space.

2. A 100W wireless power transmission system in a room-level space according to claim 1, characterized in that: The transmitting end also includes a DC power supply, an inverter and a plurality of primary compensation circuits; The output ends of the primary compensation circuits are respectively connected to the transmitting coils, the input ends of the primary compensation circuits are all connected to the output end of the inverter, and the input end of the inverter is connected to the DC power supply.

3. The 100-watt wireless power transmission system in a room-level space according to claim 2, characterized in that: The receiving circuits all include a receiving coil, a secondary side compensation circuit, a rectifier and a load connected in sequence; The primary compensation circuit and the secondary compensation circuit are LCC-S topology structures, the primary compensation circuits each include a primary compensation inductor, a primary first compensation capacitor and a primary second compensation capacitor, and the secondary compensation circuits each include a secondary compensation capacitor.

4. The 100-watt wireless power transmission system in a room-level space according to claim 1, characterized in that: The transmitting coils are all single-turn coils.

5. A parameter design method for a 100-watt wireless power transmission system in a room-level space, characterized in that: The parameters of a 100-watt wireless power transmission system in a room-level space as described in any one of claims 1 to 4 are designed, and the specific steps are as follows: S1: Set the system electromagnetic field safety limit, including the magnetic field strength limit and electric field strength limit in the safe charging area, as well as the local SAR limit; S2: Set the geometric size parameters of the transmitting and receiving coils according to the requirements, and calculate the system resonant frequency and transmitting coil current when the system transmission power is maximum based on the system electromagnetic field safety limit as a constraint; S3: Select any receiving coil and given the output voltage of the inverter, extract the electromagnetic parameters of the transmitting and receiving coils through finite element analysis, including the self-inductance of the transmitting and receiving coils, and the mutual inductance between the transmitting and receiving coils; S4: Construct the conditions for realizing decoupling compensation and ZPA in the system, calculate the parameters of the primary and secondary compensation circuits, and use the distributed compensation method of compensation capacitors to perform segmented compensation on the transmitting coil; S5: Taking the local SAR limit as a constraint, calculate the optimal operating current of the receiving coil.

6. The parameter design method of a 100-watt wireless power transmission system in a room-level space according to claim 5, characterized in that: The geometrical dimension parameters of the transmitting coil and the receiving coil in step S2 include: the radius of the transmitting coil, the number of transmitting coils, the safe distance between the human body and the transmitting coil, the spacing between the transmitting coils, the total height of the transmitting coils, the total height of the safe charging space and the radius of the receiving coil.

7. The parameter design method of a 100W wireless power transmission system in a room-level space according to claim 5, characterized in that: The specific method for calculating the system resonant frequency and the transmitting coil current when the system transmission power is maximum in step S2 is: According to the geometrical dimension parameters of the transmitting coil and the receiving coil, the magnetic field and electric field strength at any transmitting coil current and the system resonant frequency, as well as the effective power flow received by the receiving coil are calculated; With the magnetic field and electric field strengths being less than the electromagnetic field safety limit as the constraint condition and the maximum effective power flow received by the receiving coil as the optimization goal, the system resonant frequency and transmitting coil current when the system transmission power is maximum are obtained.

8. The parameter design method of a 100W wireless power transmission system in a room-level space according to claim 5, characterized in that: In step S4, the conditions for achieving decoupling compensation and ZPA in a wireless power transmission WPT system with multiple transmitting coils and multiple receiving coils are constructed through the system resonance relationship: Where ω is the angular frequency, L fn is the nth primary compensation inductance, C fn is the first compensation capacitor value of the nth primary side, L rm is the self-inductance of the mth receiving coil, C rm is the mth secondary compensation capacitor value, C sn is the second compensation capacitor value of the nth primary side, L sn is the self-inductance of the nth transmitting coil, M nk is the mutual inductance between the nth transmitting coil and the kth transmitting coil, N s is the total number of transmitting coils; The conditions for achieving decoupling compensation and ZPA are f satisfy in: and The transmitting coil current and the inverter output voltage are respectively obtained through step S2, the transmitting coil current when the transmission power is maximum, the inverter output voltage set in step S3, and the self-inductance of the transmitting and receiving coils, as well as the conditions for realizing decoupling compensation and ZPA, calculate the primary first compensation capacitance value, the primary compensation inductance value, the secondary compensation capacitance value and the primary second compensation capacitance value.

9. The parameter design method of a 100W wireless power transmission system in a room-level space according to claim 8, characterized in that: In step S4, the distributed compensation method of the compensation capacitor is used to perform segmented compensation on the transmitting coil. sn_seg The values ​​are: In the formula, C sn_seg is the value of the segmented compensation capacitor, and Q is the number of segments of the transmitting coil and the primary second compensation capacitor.

10. The parameter design method of a 100W wireless power transmission system in a room-level space according to claim 5, characterized in that: The specific method for calculating the optimal operating current of the receiving coil in step S5 is: S5.1: Set the operating current of the receiving coil according to the exposure scenario; S5.2: Calculate the peak local SAR under the current receiving coil operating current; S5.3: Determine whether the peak local SAR is equal to the local SAR limit value. If so, output the current receiving coil operating current as the optimal operating current; if not, return to step S5.1 to reset the receiving coil operating current.

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