Wireless power transfer device

Abstract

A wireless power transfer device for capacitive inductive power transfer has a primary and a secondary device separated by a conductive member. The primary device has at least two transmitter plates configured to capacitively couple with the conductive member to induce a current and generate a magnetic field in the conductive member. The secondary device is connectable to a load and has a receiving coil configured to inductively couple with the conductive member.

Description

Technical Field

[0001] The present invention relates to wireless power transfer systems and is particularly, but not exclusively, relevant to systems using inductive or capacitive (wireless) power transfer topologies.

[0002] Specifically, although not exclusively, the present invention is directed to providing an improved circuit topology that enables the use of combined capacitive and inductive coupling to wirelessly transfer power across a conductive surface. In addition, this approach also reduces the effects of eddy currents and system losses, thereby reducing system size and cost, and improving energy density and reliability. Background Art

[0003] Wireless power transfer (WPT) was first proposed by Tesla in 1891, with the goal of using near-field electromagnetic induction to transfer power without direct electrical connection. With the development of power electronics technology, WPT technology has been widely studied and applied in many fields, such as electric motors, consumer electronics, medical implants, and transportation systems, due to its advantages in flexibility, convenience, and safety.

[0004] Inductive power transfer (IPT) and capacitive power transfer (CPT) are the two most popular WPT technologies based on magnetic field coupling and electric field coupling, respectively. Most WPT systems have non-conductive power transfer channels, such as air and insulating materials. But in many practical applications, there is usually a metal barrier between the primary power source and the secondary electrical load, such as for charging mobile electronic devices through a metal back cover, powering fish finders through a metal hull, and delivering power to metal containers. In these applications, power is usually delivered by direct connection or even by drilling a hole to pass the drive cable through the metal barrier. However, this solution may cause watertightness, structural and maintenance issues, so it is hoped that wireless power transfer can be achieved in these applications.

[0005] Nevertheless, existing WPT power sources are not suitable for transmitting power through conductive barriers. IPT systems involve large eddy currents inside the metal barrier, which may cause high losses and safety issues, and the metal barrier shields the power flow. Similarly, for a typical CPT system with two pairs of coupling plates, some literature claims that the CPT system can transmit power through the metal barrier. In fact, as long as the coupled electric field is not completely shielded, the conventional CPT system can only transmit power through the metal barrier. When both transmission plates are completely covered by the metal barrier, the conventional CPT system cannot transmit power through the metal barrier because the electric field density near the receiving plate is almost the same and the power is blocked.

[0006] Researchers in the field have attempted to improve IPT systems by reducing the eddy current effects in the metal barrier. Some previous implementations in the field include:

[0007] i. A large inductive power delivery system with a low operating frequency of 50 Hz for supplying power to an electrical sensor or device operating in a space covered by a metal wall; results of this embodiment show that 3 W of electrical power can be supplied to an LED through a 1 mm thick stainless steel wall,

[0008] ii. Power transfer through a steel pipe can be performed using two coupled coils; the results of this embodiment indicate that a maximum open circuit electromagnetic force (EMF) of 10V is achieved at a frequency of 100Hz, but the ultimate power transfer capacity is not given, and

[0009] iii. IPT system delivering power through a stainless steel disk 20 mm thick and 130 mm in diameter; results indicate that for sensor applications, output powers of several milliwatts are achieved at an operating frequency of 500 Hz.

[0010] However, the limitations of the above methods can be mainly attributed to the low operating frequency. In addition, all these IPT systems operate at very low operating frequencies in the order of 50 Hz to 500 Hz to reduce eddy current losses. Increasing the operating frequency of these systems can be an expensive solution. Due to the low operating frequency, the size of the transmission coil must be relatively large to generate sufficient EMF on the pickup coil, otherwise the output power will be very low.

[0011] The present invention is directed to overcoming one or more of the problems set forth above by providing an improved circuit topology that addresses some of the shortcomings found in previously developed IPT systems.

[0012] In this specification, where reference has been made to patent specifications, other external documents or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents or such sources of information are prior art, or form part of the common general knowledge in the field, in any jurisdiction. Summary of the invention

[0013] Purpose of the Invention

[0014] It is an object of the present invention to provide an apparatus, method or system which will at least go some way to overcome the disadvantages of existing systems, or will at least provide a useful alternative to existing systems.

[0015] Further objects of the present invention will become apparent from the following description. Summary of the invention

[0017] Thus, in one aspect, the invention may broadly reside in a wireless power transfer device for wirelessly transferring power through a conductive member, the device comprising:

[0018] a primary device and a secondary device separated by said conductive member;

[0019] The primary device is connectable to a power source, the primary device having at least two transmitter plates configured to capacitively couple with the conductive member to induce a current and generate a magnetic field in the conductive member; and

[0020] The secondary device is connectable to a load and has a receiving coil configured to inductively couple with the conductive component.

[0021] Preferably, the frequency of the power supply is selected so that the magnetic flux density near the edge of the conductive member is higher than the magnetic flux density in the middle region of the conductive member.

[0022] Preferably, the two transmitter plates are located at the distal end of the passage through the conductive member and form a capacitor arranged in series with the conductive member.

[0023] Preferably, the primary device further comprises a primary compensation circuit for cancelling the reactance of the transmitter and reducing high-order harmonics in the transmitter.

[0024] Preferably, the primary compensation circuit comprises a compensation inductor or an inductor or a capacitor.

[0025] Preferably, the secondary device further comprises a secondary compensation circuit connected to the receiving coil and the load.

[0026] Preferably, the secondary compensation circuit is at or near resonance with the receiving coil.

[0027] Preferably, the primary device further comprises a control component for adjusting an operating frequency of the wireless power transmission apparatus.

[0028] Preferably, said control means for regulating said operating frequency comprises a rectifier and a subsequent inverter.

[0029] Preferably, the control means for adjusting the operating frequency further comprises an AC-AC converter.

[0030] Preferably, the receiving coil comprises a reflection coil positioned on a side of the receiving coil opposite to the conductor component.

[0031] Preferably, the reflective coil further comprises ferrite and / or non-ferrite reflective material.

[0032] Preferably, the receiving coil is positioned relative to the conductive component so that the eddy current in the conductive component is below a threshold value.

[0033] Preferably, said primary arrangement is directly connected to said conductive member.

[0034] Preferably, the conductive component comprises a conductive layer or a conductive surface.

[0035] In another aspect, the invention may broadly be described as a primary device for wirelessly transferring power through a conductive member, the primary device being connectable to a power source and comprising:

[0036] At least two transmitter plates are configured to capacitively couple with the conductive member to induce a current and generate a magnetic field in the conductive member.

[0037] Preferably, the primary device is separable from a secondary device connected to a load and having a receiving coil via the conductive member, and the secondary device is inductively coupled to the conductive member.

[0038] In another aspect, the invention may be broadly described as a secondary device for wirelessly transferring power through a conductive member, the secondary device being connectable to a load and comprising:

[0039] A receiving coil is configured to be inductively coupled to the conductive component.

[0040] Preferably, the secondary device is isolatable via the conductive member from a primary device having at least two transmitter plates capacitively coupled to the conductive member to induce a current and generate a magnetic field in the conductive member.

[0041] Preferably, the secondary device further comprises the conductive component and the receiving coil.

[0042] In another aspect, the invention may broadly be described as a method for wirelessly transferring power through a conductive member, the method comprising:

[0043] providing a primary device connectable to a power source and having at least two transmitter plates, the transmitter plates being configured to capacitively couple with the conductive member to induce a current and generate a magnetic field in the conductive member;

[0044] providing a secondary device connectable to a load and having a receiving coil configured to inductively couple with the conductive member; and

[0045] wherein said primary and secondary devices are separated by said conductive member.

[0046] In another aspect, the invention may broadly be described as a power delivery device for delivering power through a conductive member, the device being operable in first and second connection modes, the device comprising:

[0047] a primary device connectable to a power source and having at least two transmitter plates configured to selectively capacitively couple with the conductive member to induce a current and generate a magnetic field in the conductive member;

[0048] a switch member, the switch member switching between the first and second connection modes;

[0049] wherein in the first connection mode the primary device is connected to the at least two transmitter plates and in the second connection mode the primary device is directly connected to the conductive component.

[0050] In another aspect, the invention may broadly be described as a power delivery device for delivering power through a conductive member, the device being operable in first and second connection modes, the device comprising:

[0051] A power delivery device for delivering power through an electrically conductive member, the device being operable in first and second connection modes, the device comprising:

[0052] a secondary device connectable to a load and having a receiving coil configured to inductively couple with the conductive member;

[0053] a primary device connectable to a power source and having at least two transmitter plates configured to selectively capacitively couple with the conductive member to induce a current and generate a magnetic field in the conductive member;

[0054] a switch member, the switch member switching between the first and second connection modes;

[0055] wherein in the first connection mode the primary device is connected to the at least two transmitter plates and in the second connection mode the primary device is directly connected to the conductive component.

[0056] Preferably, the reflective coil further comprises ferrite and / or non-ferrite reflective material.

[0057] As used herein, the term "and / or" means "and" or "or" or both.

[0058] As used herein, "or" preceding a noun refers to the plural and / or singular form of the noun.

[0059] As used in this specification, the term "comprising" means "consisting at least in part of..." When interpreting statements in this specification that include the term, the features introduced by the term in each statement need to be present, but other features may also be present. Related terms such as "comprise" and "comprised" should be interpreted in the same manner.

[0060] It is intended that reference to a numerical range disclosed herein (e.g., 1 to 10) also incorporates reference to all rational numbers within that range (e.g., 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9, and 10) as well as any range of rational numbers within that range (e.g., 2 to 8, 1.5 to 5.5, and 3.1 to 4.7).

[0061] The entire disclosures of all applications, patents, and publications cited above and below, if any, are hereby incorporated herein by reference.

[0062] The disclosed subject matter also provides a method or system, which can be broadly said to consist in the parts, elements and features referred to or indicated in this specification individually or collectively, and in any or all combinations of two or more of these parts, elements or features. When a specific integral thing mentioned in this specification has a known equivalent in the field to which the present invention relates, such known equivalent is deemed to be incorporated into this specification.

[0063] Other aspects of the invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Various embodiments of the present invention will now be described, by way of example, with reference to the following drawings.

[0065] Figure 1 A block diagram of a system that can deliver power across a metallic barrier based on the proposed method is depicted.

[0066] Figure 2 The direction of the AC current in the metal barrier and the direction of the AC magnetic field on the barrier are depicted.

[0067] Figure 3 The equivalent circuit of the proposed system with combined CPT-IPT coupler is depicted.

[0068] Figure 4 A metal barrier is shown having a rectangular cross-section in a 3D coordinate system.

[0069] Figure 5 A square sub-bar of a metal barrier is shown.

[0070] Figure 6 3D geometry depicting the current density vector and magnetic flux density vector.

[0071] Figure 7 is a simulation model of the current CPT-IPT setup in CST Studio Suite.

[0072] Figure 8 The current density distribution in the metal barrier is shown.

[0073] Fig. 9 A to 9D show simulated and theoretical contour and vector diagrams of the magnetic flux density distribution on the xz cross section. The color gradient is shown in (a), the simulated contour diagram is shown in (b), the simulated vector diagram is shown in (c), and the theoretical contour and vector diagram of the magnetic flux density distribution on the xz cross section are shown in (d).

[0074] Fig.10 a to 10D show simulation and theoretical results of magnetic flux density distribution on the xy cross section. The color gradient is shown in (a), the simulated contour map is shown in (b), the simulated vector map is shown in (c), and the theoretical contour and vector map of magnetic flux density distribution on the xy cross section (the cross section is 5 mm higher than the cross section of the metal barrier) are shown in (d).

[0075] Fig.11 A to 11E depict the exact magnetic flux density magnitudes on the xz cross section at different heights. The simulated magnetic flux density magnitudes at different heights are shown in (a) and the theoretical magnetic flux density magnitudes at different heights are shown in (b).

[0076] Fig.12 A practical prototype of the proposed CPT-IPT combined system for wirelessly delivering power through a metallic barrier is shown.

[0077] Fig.13 Simulations, theory, and experimental results (actually measured magnetic flux density on the metal barrier at different points) of the magnetic flux distribution above the metal barrier are depicted.

[0078] Fig.14 The simulation results of the magnetic field distribution (magnetic flux density distribution) and the ferrite core of the receiving coil are shown.

[0079] Fig.15 A graph depicting the harvested power at different locations is shown.

[0080] Fig.16 The experimental waveform of the prototype is shown when the coil is mounted at the edge of the barrier and the distance Δz tends to zero.

[0081] Fig.17 The experimental waveforms of the prototype are shown when the coil is mounted in the middle zone of the barrier with a distance Δz equal to 20 mm. DETAILED DESCRIPTION

[0082] A novel method and apparatus for wireless power transfer through a conductive component, such as a conductive component that is conductive itself or is connected by a conductive wire such as a Figure 1 As shown ( Fig.12 An object having a conductive layer or surface with a combined capacitive and inductive coupling topology (100) is also shown in FIG. Figure 1 The system in the block diagram shown in describes the proposed method. A metal barrier (101) (conductive layer or conductive surface) divides the entire system into two sides: a transmission side (210) and a receiving side (220), which are connected by a coupling interface (102). The transmission side (210) contains an AC-DC converter (110), which can be considered as providing a DC voltage source. The DC voltage is then converted to an AC voltage by an inverter module (120). The metal barrier (101) is capacitively coupled to two primary structures, in this example in the form of transmission plates (130) forming two series capacitors (240).

[0083] In order to offset the large reactance of the coupling capacitor (240) and enhance the AC current in the circuit, a primary compensation circuit (140) is provided in the transmission side (210). On the receiving side (220), the receiving coil (150) on the conductive barrier (101) is connected to the secondary compensation circuit (160) and the load (170) in sequence. The secondary compensation network (160) is in or near resonance with the receiving coil to enhance the power delivery capability of the system. In another embodiment, the wireless power delivery device (100) of the present invention is configured to be operable in the first and second connection modes ( Figure 1 ) and includes a switch member (not shown) that switches between the first and second connection modes Figure 1 ), wherein in a first connection mode the primary device (210) is connected to at least two transmitter plates (130), and in a second connection mode the primary device (310) is directly connected to the conductive layer.

[0084] How it works

[0085] As described above, the inverter (120) converts the DC voltage into a high-frequency AC voltage, which is connected to the compensation circuit (140), so that an alternating voltage can be excited between the two transmission plates (130). Then, since the metal barrier (101) is coupled with the transmission plate (130), an AC current flows along the metal barrier (101) between two coupling regions corresponding to the positions of the plates 130. According to Ampere's law, an alternating magnetic field can be excited around the metal barrier (101). Figure 2 The direction of the magnetic field on the barrier and the direction of the AC current in the barrier are shown in FIG. 2 , which are orthogonal to each other. The combination of the transmission circuit (210) and the metal barrier (101) forms a magnetic field generator, which has a function similar to that of a conventional IPT transmission circuit. Unlike the multi-turn coils in a typical IPT system, the metal barrier in the proposed system is more like a primary single-turn coil, similar to a current transformer (CT). On the receiving side (220), the pickup coil (150) is located near the metal barrier, and the magnetic field is transmitted through the coil, so that EMF can be excited on the coil based on Faraday's law. Finally, through an appropriate compensation module (160) in the receiving circuit (150), a certain power level can be delivered to the load (170).

[0086] Unlike selecting two transmission plates (130) on the primary side (210), the transmission coil will generate uncontrollable eddy currents in the barrier, which may cause high losses and safety issues. Because the AC current excited by the metal barrier can be controlled by adjusting the inverter, a capacitive interface is selected on the primary side. The magnetic field is excited by the current and distributed around the metal barrier, however, the metal barrier almost shields the electric field on the secondary side. Therefore, the inductive coupling interface on the secondary side is more suitable for extracting power from the alternating magnetic field than the capacitive interface.

[0087] In the coupling interface (102), the transmission plate and the metal barrier form a capacitive coupler, while the barrier and the receiving coil form an inductive coupler. Therefore, the combination of the capacitive coupler and the inductive coupler can be considered a capacitive-inductive (CPT-IPT) coupler.

[0088] Based on the above working principle, Figure 3 An equivalent circuit (200) with certain subcircuits is shown in order to make the system easier to understand. Figure 3 The DC voltage source E in dc express Figure 1 The output of the AC-DC converter (110) in FIG. 1 is an H-bridge inverter having four switches S1-S4, and its output voltage is U in The primary compensation circuit consists of a coupling capacitor C connected in series s1 and C s2 Sensor L t Formed, coupling capacitor Cs1 and C s2 and Figure 1 The inductor 105 represents a primary single-turn coil. On the receiving side, L r is the receiving coil (in Figure 1 is marked as (150)), and Cr is Figure 1 The compensation network or circuit (160) corresponds to a series compensation capacitor. L is the resistive load of the system, and Figure 1 The load (170) corresponds to R t and R r Indicates the internal resistance of the transmission and reception loops respectively.

[0089] The left side of each of the two capacitors Cs1 and Cs2 represents two transmission plates (130). The right side of the two capacitors enclosed by the dotted box and the primary coil of the inductive coupling interface correspond to the metal barrier (101). Because the metal barrier can be regarded as a single turn wire, the primary self-inductance of the inductive coupling interface (105) is extremely small and can be ignored. The secondary coil of the equivalent transformer refers to the receiving coil (150) on the metal barrier. The combination of the above objects represents the combined CPT-IPT coupling interface (102).

[0090] Analysis of combined coupling

[0091] exist Figure 1 In the system proposed in , the power transfer characteristics and capabilities depend on the current in the barrier and the magnetic field around it. Due to the high operating frequency, the skin effect in the conductor cannot be ignored and should be considered. Therefore, this section will analyze the current density distribution and magnetic flux density distribution.

[0092] A. Analysis of current density distribution in metal barriers

[0093] Due to the skin effect at high operating frequencies, the current density is not uniformly distributed in the conductive part. In fact, it tends to be larger near the surface of the conductor and decreases as it goes deeper into the conductor. In this section, a conductor with a rectangular cross section and a small thickness is used as the metal barrier in the analysis, which is similar to the metal back cover or back shell of some consumer electronic devices such as mobile phones or tablets. The width, length and thickness of the barrier are defined as a, b and h respectively.

[0094] Since regions A and B on the barrier are coupled to the transmission plate, the voltage potentials of the two regions are different and they can be regarded as current input ports that can inject current into the metal barrier. Due to the severe skin effect and the small thickness of the metal barrier, it is reasonable to assume that most of the current flows between regions A and B along the y direction. Therefore, the problem can be simplified to knowing the current density distribution in a conductor with a rectangular cross-section through mathematical calculation. According to the article by Antonini et al., (G. Antonini, A. Orlandi and CR Paul, entitled "Internal impedance of conductors of rectangular cross-section", IEEE Trans. Microw. Theory Tech., Vol. 47, No. 7, pp. 979-985, 1999), the continuous current density distribution function on the xz cross-section can be expressed as:

[0095]

[0096] Where μAl and σAl represent the magnetic permeability and electrical conductivity of the metal barrier, respectively. S is the cross section of the conductor. in is the average current density on the boundary. It is difficult to find an analytical solution to this integral equation, but it is easier to give a numerical solution. To obtain a numerical solution, the cross section of the conductor is divided into N rectangular subsections with square cross sections, as Figure 5 shown.

[0097] The cross section of the mth sub-bar is defined as ΔS m , and the area of ​​all sub-cross sections is ΔS. The coordinates of the mth sub-column are (x m , z m ), and the current flowing into it is Jm. Then, through the discretization of the continuous expression equation (1), the current J can be derived as follows m expression.

[0098]

[0099] where m∈[1,N], and

[0100]

[0101] By converting the summation symbol into a matrix form, equation (2) can be rewritten as:

[0102]

[0103] Since J represents the current density as a complex vector, J can be expressed as:

[0104] J=J real +iJ imag (6)

[0105] Among them J real and J imag The vectors representing the real and imaginary parts of vector J. The matrix equation can then be rewritten as:

[0106] J real -ψAJ imag +iJ imag +ψAJ real =J in (7)

[0107] Define Jreal and Jimag as:

[0108]

[0109] Substituting equation (8) into equation (7), the matrix equation (7) can then be expanded to:

[0110]

[0111] Finally, the magnitude of the current density on each sub-bar can be expressed as:

[0112]

[0113] B. Analysis of magnetic flux density distribution around the barrier

[0114] According to the Biot-Savart law, the magnetic flux density near the metal plate can be calculated. Figure 6 The 3D geometric diagram of the current density vector and the magnetic flux density vector is shown in . The magnetic flux density vector at any point D with coordinates (xd, yd, zd) excited by the current on the mth subcolumn is:

[0115]

[0116] In equation (11),

[0117]

[0118] and

[0119]

[0120] Among them, μ air is the magnetic permeability of air, ex and ez represent unit vectors in the x and y directions, respectively. m,dIndicates the Euclidean distance between the point (xd,yd,zd) and the mth sub-column. The coordinates of the mth sub-column are (xm,zm). 3D geometry of the current density vector and the magnetic flux density vector.

[0121] Then the horizontal and vertical components of the vector Bm,d(xd,yd,zd) can be expressed as:

[0122]

[0123] Therefore, the total magnetic flux density vector at point (xd, yd, zd) induced by the currents in all sub-columns can be expressed as:

[0124]

[0125] Simulation study

[0126] In order to verify the above theoretical analysis and solutions, a 3D simulation model was established using the CST software package, which is an electromagnetic field simulation software, and the simulation results were compared with the theoretical results according to the analysis in the above combined coupling analysis section.

[0127] Analysis of current density distribution in metal barriers

[0128] Figure 7 The simulation model is shown in Figure 2. In the simulation model, the metal barrier and transmission plate are made of aluminum, whose conductivity is 3.56×10 7 S / m, magnetic permeability is 1.26×10 -6 H / m. The current source is connected to the midpoint of the transmission plate. Table I lists the preset parameters of the model.

[0129] Table I

[0130] Preset parameters of the analog modules in the CSP software package

[0131]

[0132] Calculation of current density

[0133] Based on the calculation steps in the above section on current distribution analysis in metal barriers, the current density distribution inside a conductor with a rectangular cross section can be shown as equation (10). Substituting the size of the metal barrier into the equation, Figure 8 The unit current distribution of the metal barrier is shown in FIG.

[0134] exist Figure 8 It is obvious that the unit current on the edge of the cross section is higher than that in the middle region, which means that most of the current flows along the surface of the metal barrier. In particular, the current on the edge varies from 0.35 to 1.0, which is much higher than the current in other regions.

[0135] Comparison between theoretical and simulation results

[0136] In addition to the simulation results of the magnetic flux distribution, the theoretical magnetic field distribution was also calculated based on the analysis of the combined coupling with the same preset parameters in Table I (as discussed above).

[0137] Fig. 9 Simulated and theoretical contours and vector diagrams showing the magnetic flux density distribution on the xz cross section. Fig. 9 (a) shows the color gradient of the simulation results. Fig. 9 As can be seen in (b), the magnetic flux density near the edge of the metal barrier is stronger than that in the middle. Fig. 9 In (c), it can be found that the horizontal magnetic field component is the main part, especially the horizontal magnetic field component in the middle region. The component in the z direction tends to become larger near the edge of the barrier. Fig. 9 Theoretical contours and vector diagrams calculated based on equation (15) are shown in (d), which produce similar results compared to the simulation results.

[0138] Fig.10 The simulation and theoretical results of the magnetic flux density distribution on the xy cross section are shown. Fig. 9 (b) Similarly, Fig.10 (b) shows that the magnetic flux density near the edge of the metal barrier is stronger than that in the middle. Fig.10 In (c), it is clear that the component of the magnetic field vector in the y direction can be neglected. Fig.10 Theoretical contours and vector diagrams are shown in (d), which are also similar to the simulation results.

[0139] Fig.11 The exact magnetic flux density values ​​on the xz cross section at different heights are shown. Fig.11 In both (a) and (b), Δz represents the distance between the measured point and the metal barrier. The results show that the magnetic flux density reaches its maximum value at the two edges. As Δz increases, the magnitude of the magnetic flux density tends to become significantly smaller at the edges, while the magnitude decreases slightly in the middle area.

[0140] Experimental studies

[0141] In order to practically verify the theoretical analysis and simulation results, a prototype has been built and two experiments have been conducted. The first experiment was designed to detect the magnetic flux density distribution on the metal barrier and compare it with the theoretical and simulated distribution. The second experiment was conducted to confirm the feasibility of power transfer in this approach.

[0142] Experimental setup

[0143] Experimental prototypes have been constructed, such as Fig.12As shown in . The metal barrier (40) is a rectangular thin aluminum plate with a size of 295×195×2 mm. The transmission plate (30) is also made of aluminum material and has a size of 295×100×2 mm, which is larger than the theoretical and simulation preset values. However, their effective coupling areas are both 195×50 mm. Therefore, the larger actual size of the transmission plate (30) does not affect the power transfer characteristics. We used a larger plate in the experimental setup because the larger size is conducive to fixing the transmission plate (30) on the wooden substrate. The metal barrier plate (40) and the transmission plate (30) are separated by a piece of polyethylene terephthalate (PET) film. On the transmission side, a full-bridge inverter (10) with four silicon carbide (SiC) MOSFETs (C2M0080120D) is used to generate high-frequency voltage. The high reactance of the capacitive coupling interface is compensated by an air-core inductor (20) with a Litz wire winding. For the first experiment, a 35-turn air-core open-circuit coil of size 155×45×10 mm was used as the detection coil. In the second experiment, due to the small self-inductance of the metal barrier (40), the mutual coupling between the barrier and the receiving coil is weak, which means that the flux density passing through the receiving coil (50) will be low. Therefore, a ferrite core is used in the pickup coil of the receiving part to enhance the magnetic flux passing through the coil. The type of ferrite core is TDK-I-N87 (MnZn material), with a relative magnetic permeability of 2000 (±25%) and a size of 95×56×16 mm. The receiving coil (50) is also fully tuned by a mica capacitor (60) suitable for high-frequency applications. The circuit parameters of the prototype are listed in Table II.

[0144] Table II

[0145] Parameters of the actual prototype

[0146]

[0147] Magnetic flux density measurement

[0148] Before measuring the output power, measure the magnetic flux density B on the metal barrier x To verify the calculation and simulation of the above magnetic flux density distribution. It is difficult to measure B directly at each point x , so the measurement method here is to set up an open-circuit detection coil inside the magnetic field and measure the open-circuit voltage on the output port of the detection coil. Then, the average magnetic flux density passing through the detection coil can be calculated according to the following formula:

[0149]

[0150] Where S coil is the cross section of the detection coil, U open is the EMF on the coil and N coil is the number of turns of the coil. Fig.13The simulation, theoretical and experimental results of the magnetic flux distribution above the metal barrier are shown in Figure 1, respectively. In this figure, the actual value of the magnetic flux density is not strictly symmetrical, however, the coupling structure is symmetrical and the magnetic field should be distributed symmetrically. The reason is that there may be several factors in the experimental setup that affect the symmetrical distribution of the magnetic field: the transmission plate is not strictly parallel to the metal barrier and the external electromagnetic field, etc. In summary, the experimental results are in good agreement with the theoretical and simulation results.

[0151] After adding a ferrite core to the receiving coil, the magnetic field distribution will change due to the influence of the ferrite core on the magnetic field. Fig.14 The simulation results of magnetic field distribution are shown in Fig.14 In the case of a ferrite core, the magnetic field is attracted to the ferrite core, which results in a higher flux density through the ferrite core and a higher EMF in the receiving coil. The output power of the system with a ferrite core on the secondary side is measured in the next section.

[0152] When a conductive layer is inserted between two coils of an IPT system, the eddy currents in the conductive layer depend on both the operating frequency and the position of the receiving coil. Therefore, the distance between the conductive surface and the receiving coil affects the eddy currents. For example, a larger distance provides smaller eddy currents on the conductive surface and vice versa. Therefore, by changing the coupling configuration, the eddy currents will also change.

[0153] Output power measurement

[0154] based on Fig.12 The prototype in the figure can also measure the output power according to the change of the receiving coil position. For the receiving coil with different positions relative to the metal barrier, the inductance of the coil will change within a certain range due to the influence of the barrier on the coil. In this prototype, when the coil moves from the edge to the middle area, the inductance L r It varies between 72.1-95.2μH. Therefore, the compensation capacitor C r It should also be modulated between 1.16-1.53nF to ensure that the receiving circuit works under fully tuned conditions. When y=0, the position of the receiving coil changes in the x and z directions, and the receiving coil moves between the two edges of the metal barrier, and the distance between the coil and the barrier changes between 0-20mm. The measured results are listed in Table III. According to the data in Table III, Fig.15 The obtained power at different positions is shown in FIG.

[0155] Table III

[0156] Experimental results with receiving coil moving in X and Z directions (power in W)

[0157]

[0158] Fig.15The output power of the load at different positions is shown. Obviously, more power can be obtained near the edge of the metal barrier and less power can be obtained in the middle area, which is similar to the magnetic flux density distribution analyzed above. In addition, as the distance Δz between the receiving coil and the metal barrier increases, the output power also decreases, especially the output power near the edge. When Δz is equal to 1mm, 11.09W of power is obtained at the edge and 3.41W of power is obtained at the middle point, which is a decrease of about 69.25%. When Δz increases to 20mm, the maximum power obtained at the edge is reduced to 2.15W, while the power received in the middle area drops to 1.38W. The output power only drops by 35.81%, which is smaller than the drop when Δz is 1mm. This means that when the distance between the coil and the barrier is small, the power obtained tends to be more sensitive to the position in the x direction.

[0159] In addition, the output power near the edge of the metal barrier is more sensitive to the distance Δz than the output power in the middle region. Fig.15 In the figure, as the distance Δz at the edge increases from 1-20mm, the power obtained decreases from 11.09W to 2.15W, a decrease of 80.61%. However, when the receiving coil is in the middle area, when the distance Δz increases, the power obtained only decreases by 59.53%, from 3.41W to 1.38W. In addition, when the output power reaches the peak (11.09W), the system efficiency is 41.6%.

[0160] Therefore, when the coil is mounted at the edge of the barrier, the power extracted is sensitive to the coil position. However, in this case, the maximum power can be received when the distance Δz tends to zero. Fig.16 The experimental waveform under this condition is shown in . In addition, when the coil is set in the middle area of ​​the barrier, the output power level is reduced to a lower level compared to the previous condition. But the acquired power is more stable. Fig.17 The actual waveform under this condition is shown in FIG.

[0161] The experimental results show that a maximum output power of 11.09 W is delivered through the metal barrier. This power level is sufficient to meet the power requirements of portable electronic devices such as mobile phones with metal back covers, and it can also be used to slowly charge tablets and digital cameras. The power delivery capability of the proposed wireless power delivery method can be further improved for other higher power applications such as laptops and logistics robots. The system can potentially be used for specific applications such as delivering power through the metal hull of a boat to drive a fish finder.

[0162] A wireless power transfer method for transmitting power through a metal barrier by combined capacitive and inductive coupling is proposed. The current density distribution in the metal barrier is analyzed considering the skin effect. The magnetic field distribution around the metal surface is then determined based on the current density distribution. A simulation model in the CST software package and an actual wireless power transfer system with combined IPT-CPT coupling are constructed to verify the theoretical analysis. The simulation results and actual measurements of the magnetic flux density are compared with the theoretically calculated values, and consistent results are obtained. The results show that the magnetic flux density near the edge is higher than that in the middle, although the flux density is more sensitive to the changes in the distance and position of the receiving coil around the edge. Finally, it has been demonstrated that more than 11W of power can be transmitted through a 2mm thick aluminum plate when the power acquisition position is at one edge of the plate. The results of the above analysis demonstrate the feasibility of transmitting power through a metal barrier, which can potentially be used to design various wireless power supplies for portable electronic devices with metal covers, which are lacking in existing WPT systems.

[0163] Throughout the specification, like reference numerals are used to refer to like features in different embodiments.

[0164] Unless the context clearly requires otherwise, throughout the specification, the words "comprise", "comprising" and the like should be interpreted in an inclusive sense as opposed to an exclusive or exhaustive sense, ie, as "including, but not limited to".

[0165] Although the present invention has been described by means of examples and with reference to its possible embodiments, it should be understood that it can be modified or improved without departing from the scope of the present invention. The present invention can also be broadly said to be individually or jointly in the specification of the present application, the parts, elements and features referred to or indicated, in any or all combinations of two or more of the parts, elements or features. In addition, when reference has been made to a specific assembly or complete object of the present invention with known equivalents, such equivalents are incorporated herein as individually set forth.

[0166] Any discussion of the prior art throughout the specification should not be considered as an admission that this prior art is widely known or forms part of the common general knowledge in the field.

Claims

1. A wireless power transfer apparatus for wirelessly transferring power to a secondary device through a metal barrier, the apparatus comprising: A primary device is connectable to a power source, the primary device having at least two transmitter plates, the transmitter plates being configured to capacitively couple with the metal barrier to induce current and generate a magnetic field in the metal barrier, the metal barrier being inductively coupled with a receiving coil of the secondary device. 2 . The wireless power transfer device of claim 1 , wherein a frequency of the power source is selected so that a magnetic flux density near an edge of the metal barrier is higher than a magnetic flux density in a middle region of the metal barrier. 3 . The wireless power transfer device of claim 1 , wherein the two transmitter plates are located at a distal end of passing through the metal barrier and form a capacitor arranged in series with the metal barrier. 4 . The wireless power transfer apparatus of claim 1 , wherein the primary device further comprises a primary compensation circuit for counteracting a reactance of a transmitter board. 5 . The wireless power transfer device of claim 4 , wherein the primary compensation circuit is configured to reduce high-order harmonics. The wireless power transfer apparatus of claim 4 , wherein the primary compensation circuit comprises an inductor or a capacitor. 7 . The wireless power transfer apparatus of claim 1 , wherein the secondary device further comprises a secondary compensation circuit connected to the receiving coil and a load.

8. The wireless power transfer device of claim 7, wherein the secondary compensation circuit is at or near resonance with the receive coil. 9 . The wireless power transmission device according to claim 1 , wherein the primary device further comprises a control component for adjusting an operating frequency of the wireless power transmission device. 10 . The wireless power transfer device of claim 9 , wherein the control means for adjusting the operating frequency comprises a rectifier and an inverter. 11 . The wireless power transfer device of claim 9 , wherein the control means for adjusting the operating frequency further comprises an AC-AC converter. 12 . The wireless power transfer device of claim 1 , wherein the receiving coil comprises a reflection coil positioned on a side of the receiving coil opposite to the metal barrier.

13. The wireless power transfer device of claim 12, wherein the reflective coil further comprises ferrite and / or non-ferrite reflective material. 14 . The wireless power transfer device of claim 1 , wherein the receiving coil is positioned relative to the metal barrier to provide an eddy current of a desired magnitude in the metal barrier.

15. The wireless power transfer apparatus of claim 1, wherein the primary device is directly connected to the metal barrier.

16. The wireless power transfer device of claim 1, wherein the metal barrier comprises a conductive layer or a conductive surface.

17. The wireless power transfer apparatus of claim 1, wherein the metal barrier comprises a barrier between the primary device and the secondary device.

18. A primary device for wirelessly transferring power across a metal barrier, the primary device being connectable to a power source and comprising: at least two transmitter plates configured to capacitively couple with the metal barrier to induce a current and generate a magnetic field in the metal barrier; as well as ； The primary device may be separated from a secondary device connected to a load and having a receiving coil by the metal barrier, and the secondary device is inductively coupled to the metal barrier.

19. The primary device of claim 18, wherein the transmitter plates are spaced apart from each other and are configured to provide spaced apart capacitors in series with the metal barrier.

20. The primary device of claim 18, further comprising a compensation circuit.

21. A secondary device for wirelessly transferring power across a metal barrier, the secondary device being connectable to a load and comprising: a receiving coil configured to inductively couple with the metal barrier; as well as The secondary device may be separated from the primary device by the metal barrier having at least two transmitter plates capacitively coupled to the metal barrier to induce current and generate a magnetic field in the metal barrier.

22. The secondary device of claim 21, wherein the secondary device further comprises the metal barrier and the receiving coil.

23. A method for wirelessly transmitting power across a metallic barrier, the method comprising: providing a primary device connectable to a power source and having at least two transmitter plates configured to capacitively couple with the metal barrier to induce a current and generate a magnetic field in the metal barrier; inductively coupling a coil to the metal barrier; and The power source and the coil are separated by the metal barrier.

24. A power delivery device for delivering power across a metallic barrier, the device being operable in first and second connection modes, the device comprising: a primary device connectable to a power source and having at least two transmitter plates configured to selectively capacitively couple with the metal barrier to induce a current and generate a magnetic field in the metal barrier; a switch member, the switch member switching between the first and second connection modes; wherein in the first connection mode the primary device is connected to the at least two transmitter plates and in the second connection mode the primary device is directly connected to the metal barrier.

25. A power delivery device for delivering power across a metallic barrier, the device being operable in first and second connection modes, the device comprising: a secondary device connectable to a load and having a receiving coil configured to inductively couple with the metal barrier; a primary device connectable to a power source and having at least two transmitter plates configured to selectively capacitively couple with the metal barrier to induce a current and generate a magnetic field in the metal barrier; a switch member, the switch member switching between the first and second connection modes; wherein in the first connection mode the primary device is connected to the at least two transmitter plates and in the second connection mode the primary device is directly connected to the metal barrier.

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