WO2022250640A1

WO2022250640A1 - A novel wireless capacitive power transfer system

Info

Publication number: WO2022250640A1
Application number: PCT/TR2022/050483
Authority: WO
Inventors: Mehmet Zahid EREL; Kamil Cagatay BAYINDIR; Mehmet Timur AYDEMIR
Original assignee: Ankara Yildirim Beyazit Universitesi
Priority date: 2021-05-26
Filing date: 2022-05-25
Publication date: 2022-12-01

Abstract

The present invention relates to a power transfer system developed for wireless capacitive power transfer applications.

Description

A NOVEL WIRELESS CAPACITIVE POWER TRANSFER SYSTEM Technical Field of the Invention

State of the Art

Each passing day, the significance of renewable energy and charging has increased due to many disadvantages such as air pollution and health problems caused by fossil fuels. Wired charging applications may cause security problems in conditions such as rain, humidity, and snowfall, in addition to causing cable complexity, therefore, establishing a ground for new wireless power transfer studies in the industrial and academic fields. Wireless power transfer studies are divided into many areas, especially inductive and capacitive power transfer studies. The sensitive behavior of inductive power transfer applications around conductive materials causes eddy current losses due to magnetic field, especially in metal materials close to the system, and this may lead to a significant increase in temperature, which may lead to danger in practice. On the other hand, capacitive power transfer studies have started to be preferred in many application areas such as electric vehicles since there is no significant power loss around metal objects in capacitive power transfer studies where electric field is used. Instead of the costly Litz cable used in inductive power transfer, inexpensive and light metal plates have been used in power transfer and this has added much flexibility to the application. Also, it grows in importance recently in both academic and industrial studies by reducing the size of the circuit due to the success of capacitive power transfer at high frequencies.

Applications on wireless power transfer are categorized as near-field and far-field. While optical (laser) power transfer applications can be given as an example for far- field applications, inductive and capacitive power transfer applications become prominent in near-field applications. Studies on capacitive power transfer have mostly focused on a new resonance topology and optimizing the resonance elements used. There are also studies within the scope of protection related to the design and control of power electronics converters. However, in the current system, there are no studies on the use of metal plates as external capacitors in primary and secondary resonance circuits by means of using the geometric structure and bringing cost advantage to the total system.

Capacitive power transfer applications provide many advantages over inductive power transfer applications inherently. The direct propagation of the electric field relative to the magnetic field and the use of low-cost elements such as aluminum plate for power transfer instead of expensive litz cable can be given as example. Recent studies have begun to focus on capacitive power transfer due to these advantages. In the state of the art, there are studies on capacitive power transfer system based on LC-LC compensation topology. In these systems, there are generally elements such as full bridge inverter structure, primary resonance coil, primary resonant external capacitor assembly, four metal plates that provide power transfer, secondary resonant external capacitor assembly and secondary resonant coil, full bridge passive rectifier that converts alternating voltage to direct voltage and load. Considering the state of the art, the general scheme of the system is illustrated in Figure-1 .

Studies on capacitive power transfer have intensified since 2015 and the main principle in the proposed studies is to reduce the cost and losses of the system by reducing the required resonance inductance. Since the capacity of the capacitive power transfer system is very small at picofarad levels, external capacitors are generally required in medium and high-power capacitive power transfer applications. This situation is solved by integrating external capacitor assemblies connected in series and parallel to the primary and secondary resonant circuits in the system.

In the state of the art, in the document numbered ΈR 2745417 A2” there are transmitter and receiver electrode pairs between two non-conductive layers by means of two conductive layers, and this causes the capacitive impedance to arise. There is a wireless power transfer from the transmitter electrode pair to the receiver electrode pair to feed the load. The system can be installed in places where open electrical connections are not preferred or desired, such as bathrooms and stores, where regular changes are required to illuminate, while enabling power transmission over a large area. The capacitive wireless power transfer system can transfer power over a wide range of brittle transparent solid infrastructure such as windows, mirrors, glass flooring or any other infrastructure made of glass. The first layer constituting the system is a non-conductive transparent material, which includes glass, mirror, or a brittle material made of glass. It is interconnected by a second layer comprising a transparent conductive material. The second layer, which is conductive, comprises two pairs of emitting electrodes, and the power is transmitted when the receiver, catches the series resonance frequency via the driver in order to feed the charge to the two pairs of electrodes. Said study provides the opportunity to transmit power in a wide environment in bathrooms where open electrical contacts are not preferred, and in stores related to lighting. However, there is no design related to a power transfer system that creates the resonance capacity of the primary and secondary resonance systems by means of the bent structures thereof. Also, there is no information regarding its usability in places covering wireless capacitive power transfer applications.

The document titled "Design and Analysis of Capacitive Power Transfer System with and without the Impedance Matching Circuit" in the state of the art mentions the low power capacitive power transfer applications. In this low-power application, the air gap is provided with a thickness of 1 mm by using paper, and it is used to both capacity and separate aluminum plates by utilizing the insulation constant of the paper. However, there is no mention of obtaining power transfer by using twisted geometric structure in said system. In the study, there are applications on low power capacitive power transfer by using class E converter.

The document numbered "W02020139247A1 " in the state of the art is a power transfer system developed for rail systems. It is based on the principle of meeting the energy need of the motor by transferring the electrical energy through the shaft. It is designed to safely provide capacitive power transmission. The working principle of the system mentioned in said document can be explained by the state of meeting the energy need of the engine safely by transferring the power from the air gap between the metal plates. However, said system does not mention resonance situations, and an insulator material is used to prevent short circuit. Consequently, the disadvantages disclosed above and the inadequacy of available solutions in this regard necessitated making an improvement in the relevant technical field.

Brief Description and Objects of the Invention The most important object of the present invention is to eliminate the need for external capacitors used in primary and secondary resonant circuits in similar systems by means of the plate design that is developed.

Another object of the present invention is to use the existence of leakage capacities in primary and secondary circuits as resonance capacity for wireless capacitive power transfer applications by means of positioning metal plates with the developed system.

Yet another object of the present invention is to provide the desired adjustment of the capacity values in the primary and secondary resonance circuits according to the insulation coefficient by placing an insulating material between two conductive plates such as aluminum or copper. Yet another object of the present invention is to increase the efficiency of the total system by eliminating the ESR losses and degradation problems of the external capacitors since no external capacitors are used in the primary and secondary resonant circuits.

Yet another object of the present invention is to improve the overall system size, thereby providing ease of installation of the total system, and providing flexibility in both academic and industrial studies since the number of elements used will be reduced by deactivating the external capacitors.

Yet another object of the present invention is to enable it to lead many more studies since the proposed capacity structure is compatible with all power electronics and resonance topologies.

Yet another object of the present invention is to increase the low-cost advantage of capacitive power transfer over inductive power transfer by not using external capacitors. Structural and characteristic features of the present invention as well as all advantages thereof will become clear through the attached figures and the following detailed description provided by making references thereto. Therefore, the assessment should be made by taking these figures and the detailed description into consideration. Description of the Figures

FIGURE -1 is the drawing that illustrates the view of LC-LC compensation topology based capacitive power transfer system in the state of the art.

FIGURE -2 is the drawing that illustrates the view of a novel capacitive power transfer system of the present invention. FIGURE -3 is the drawing that illustrates the view of a novel capacitive power transfer system integrated into the capacitive power transfer system, which is the subject of the invention.

FIGURE -4 is the drawing that illustrates the leakage capacities in the structure developed in the system of the present invention. FIGURE -5 is the drawing that illustrates the view of a novel capacitive power transfer structure of the present invention in Ansys Maxwell.

FIGURE -6 is the drawing that illustrates the port capacity model in the system of the present invention.

FIGURE -7 is the drawing that illustrates the model used to extract leakage capacities by using port capacities in the system of the present invention.

FIGURE -8 is the drawing that illustrates the simplified leakage capacity model, (a) simple model, (b) combined model.

FIGURE -9 is the drawing that illustrates the simplified leakage capacity model, (a) simple model, (b) combined model. FIGURE -10 is the drawing that illustrates the simplified leakage capacity model. FIGURE -11 is the drawing that illustrates the voltage and current of the primary resonant circuit obtained by using the Plexim PLECS software program.

FIGURE -12 is the drawing that illustrates the voltage and current of the secondary resonant circuit obtained by using the Plexim PLECS software program. FIGURE -13 is the drawing that illustrates the voltage and current of the primary resonance circuit obtained as a result of experimental studies.

FIGURE -14 is the drawing that illustrates the voltage and current of the secondary resonance circuit obtained as a result of experimental studies.

FIGURE -15 is the drawing that illustrates the output current on the load side obtained as a result of the experimental studies.

Description of Elements/Parts of the Invention

Parts shown in the figures are enumerated and numbers corresponding the respective parts are provided below in order to provide a better understanding for the wireless capacitive power transfer system developed with the present invention.

1. Transmitter plates providing primary resonance

2. Insulating material

3. Receiver plates providing secondary resonance

4. Full bridge inverter structure

5. Primary resonant coil

6. Developed resonance capacity structure

7. Secondary resonant coil

8. Full bridge rectifier

9. Load Detailed Description of the Invention

The present invention relates to a capacitive power transfer system developed for wireless capacitive power transfer applications. The need for external capacitors to be used will be eliminated by means of this developed system, thereby reducing the total system cost. In addition, the total system loss is improved by reducing the losses caused by the series resistance of the capacitors. By eliminating the need for external capacitors, flexibility has been added to the total system in terms of application.

Considering the wireless power transfer application areas, said system can be used especially in electric vehicle charging, drone charging applications, laptop charging applications, mobile phone charging applications, electric bike and scooter charging applications as well as underwater wireless charging applications.

Since the developed system will be compatible regardless of the resonance topology of the wireless power transfer system and the power electronics converter, it is thought that it will benefit the industry in wireless charging applications and many other applications due to the advantages it provides.

Since the resonance capacity value can be adjusted as desired with the developed system, the required resonance inductance value can also be adjusted as desired according to the selected switching frequency. In addition, it provides an opportunity to further improve the cost issue, which is one of the biggest advantages of wireless capacitive power transfer applications over inductive power transfer applications.

In said system, it is provided to be used as an external capacitor in primary and secondary resonant circuits by using an insulating material (2) between two aluminum conductive plates. The plates used are the transmitter plates (1 ) providing the primary resonance, and the receiver plates (3) providing the secondary resonance. Aluminum material was chosen for the plates in order to reduce the total system cost. The insulating material (2) to be used here was chosen as a Teflon plate for prototype purposes. The amount of capacitor can be increased according to the insulation constant (ε_r) of the insulating material (2) used. For example, ε_r= 2.1 for Teflon, ε_r= 3 for paper, ε_r= (4-7) for glass, e_r=11.2 for silicone, ceramic materials; ε_r>1500 for barium titanate (BaTi0₃), 86 < ε_r < 173 for titania (Ti0₂). Thus, the amount of inductance required for resonance can be reduced and the overall system size can be reduced. The present invention works on the principle that it can be used as a resonance capacitor for primary and secondary resonant circuits by means of by bending the 2 transmitter plates (1 ) providing the primary resonance and the 2 receiver plate (3) providing the secondary resonance in L shape, and placing the insulating material (2) in the form of a plate between the bent parts. The study works according to the principle of obtaining a capacitor if there is an insulating material (2) between two conductive metal plates, that is, between the transmitter plates (1 ) providing the primary resonance and the receiver plates (3) providing the secondary resonance.

Figure-3 illustrates the primary resonance coil (5), the developed resonance capacity structure (6), the secondary resonance coil (7), the full bridge rectifier (8), and the load (9).

Dimensions of the capacitive plate design created by bending the transmitter plates (1) providing the primary resonance and the receiver plates (3) providing the secondary resonance in an “L” shape may vary depending on application and intended power transfer. Here, the dimensions of the plate design vary according to the application. For example, it can increase up to 50 mm x 50 mm in small power applications such as phone charging applications, 150 mm x 150 mm in medium power applications, and up to 610 mm x 610 mm in high power applications.

In addition, the insulating material (2) used between the transmitter plates (1 ) providing the primary resonance and the receiver plates (3) providing the secondary resonance also affects the plate dimensions. In the dimensions given in Table 4, 2 transmitter plates (1 ) providing primary resonance and 2 receiver plates (3) providing secondary resonances were bent in an “L” shape, and the capacity structure for the primary and secondary resonance circuits is obtained by placing Teflon as an insulating material (2) between them. The resonant capacity structure (6) developed later was integrated into the LC-LC compensation based capacitive power transfer system.

It is intended to be used as a resonant capacity for wireless capacitive power transfer applications with the developed system by using the presence of leakage capacities that occur with the positioning of metal plates. The obtained leakage capacity values revealed the power transfer structure of the invention, which is a new design. In the equation below, primary and secondary resonance capacity values obtained using leakage capacities are given. C_P represents the primary resonance capacity value, C_s represents the secondary resonance capacity value, and C_M represents the mutual capacity value.

Two different methods were used to calculate the primary and secondary resonance capacity values and mutual capacity values given in Equation-1. One of them is to solve the leakage capacity values as a matrix using the finite element method of the power transfer system designed by using the Ansys Maxwell software program shown in Figure-5 and is to calculate the primary and secondary resonance capacity values and the mutual capacity value by means of equation-1 with these determined leakage capacity values. The second method is to calculate the primary and secondary resonance capacity values and the mutual capacity value according to equation-1 in the developed power transfer system by using the port capacity values measured with the LCR meter, by obtaining the leakage capacity values through the “Wolfram Mathematica” program. In this study, both methods were tried, but the second method was taken as a basis.

The developed wireless capacitive power transfer system is integrated into the system using LC compensation topology in primary and secondary resonance circuits. The 110 W capacitive power transfer system has been achieved as a prototype by means of the developed system, and a lower cost than expected study has been introduced.

The developed wireless capacitive power transfer system is given in Figure-2. Flere, Teflon plate is preferred as the insulating material (2). The leakage capacities in the developed system are given in Figure 4. Flere, the capacity C₁₂ and C₃₄ are the place where the insulating material (2) is integrated, and constitute an important part of the resonance capacity value obtained for the primary and secondary resonance circuits. In addition, capacitances C₁₂ and C₃₄ are also called main capacity, and it is seen that it has an important place in determining the resonant capacity for the primary and secondary circuit. While this makes the developed system important, it provides the opportunity to use insulating material (2) in the desired size and thickness by means of the flexibility of the power transfer system, and it helps to increase the overall system efficiency and capacity value, thereby increasing the output power easily.

Obtaining leakage capacities: It is shgwn in Figure-6 that the capacity value measured by LCR meter between bcth plates is the pert capacity and the six specified capacity values are defined as C_T12, C_T13, C_TI4, C_T23, C_T24, and C_T34. Figure-7 shews leakage capacities C₁₂, C₁₃, C₁₄, C₂₃, C₂₄, and C₃₄ to be ebtained by using pert capacities.

According to the circuit model in Figure-7, the star-connected C₁₂, C₁₃, and C₁₄ capacities have been converted into delta-connected capacity connections in Figure-8 (a), and this converted structure was later simplified as a model in Figure-8 (b). The C_23Y, C_24Y, and C_34Y capacities seen in Figure-8 (a) are the conversions of the C₁₂, C₁₃, and C₁₄capacities. The relationship between them is given in equation-2.

Also, as seen in Figure-8 (a), the capacities C₂₃ and C_23Y, C₂₄ and C_24Y, C₃₄ and C_34Y are in parallel connection. Accordingly, these capacities can be simplified asC_1S, C_2S andC_3S as given in equation-3. By using the C_1S, C_2S and C_3S capacities shown in Figure- 8(b), C_T23, C_T24 andC_T34 port capacity values can be derived as given in equation-4.

Similarly, star-connected C₁₄, C₂₄ andC₃₄capacities seen in Figure 7 are converted into delta-connected capacity connections and shown in Figure-9(a). C_12Y, C_13Y andC_23eY capacities are transformations of C₁₄, C₂₄ and C₃₄capacities and the relationship between them is given in equation-5. In addition, the capacities of C₁₂and C_12Y, C₁₃and C_13Y, C₂₃ andC_23eY were in parallel connection as seen in Figure-9 (a), and these are simplified as C_4S, C_5S andC_6S capacities as given in equation-6. By using the C_4S, C_5S andC_6S capacities shown in Figure-9(b), C_T12, C_T13 and C_T23 port capacity values can be derived as given in equation-7.

It is stated that C_T23 given in equation-4 and C_T23 given in equation-7 are calculated in different manners. Although both derive from different star capacity connections, both constitute the same port originating from terminal b and terminal c. Therefore, the C_T23 values derived from Figure-8 and Figure-9 are the same, and can also be verified by using equation-4 and equation-7. The delta connected capacity connection consisting of C₁₂, C₁₃ and C₂₃ seen in Figure- 9 (a) has been converted to star connected capacity connection and shown in Figure- 10. The transformation relationship is given in equation-8.

Also, the C_T14 port capacity value obtained from here is expressed in equation 9.

By using the equations given above, the leakage capacity parameters were drawn from the related equations and solved by using Wolfram Mathematica program. The values obtained were determined according to the 110 W study designed as a prototype, accordingly, the port capacity values measured with the LCR meter are given in Table- 1 and the solved leakage capacity values are given in Table-2.

Analysis and experimental studies:

A novel wireless capacitive power transfer system developed for wireless capacitive power transfer applications is shown in Figure-2. In Table-3, the design parameters of the developed system are given.

Table 3. The design parameters of the developed system

Table 4 shows the parameters used when the invention is integrated into an LC-LC compensation topology based wireless capacitive power transfer system. Here, input and output voltage values, parameter values of the developed power transfer system, air gap (power transfer distance), resonance capacitance value for primary and secondary circuit, the mutual capacitance value, the coupling constant (kc), the required primary and secondary resonance inductance value, and finally the switching frequency are given.

Analysis Studies:

In case of integrating the system, which was developed by using the Plexim PLECS software program, into the capacitive power transfer system, analysis studies were carried out and guidance was provided for experimental studies. Figure-11 shows the voltage and current graph of the primary resonant circuit, and this graph also represents the inverter output voltage and current. In Figure-11, the current has been scaled 2 times in order to observe the primary resonance state more clearly. Figure- 12 shows the voltage and current graph of the secondary resonant circuit. In Figure 12, the current has been scaled 2 times in order to observe the secondary resonance state more clearly. Also, this graph represents the full bridge rectifier input voltage and current. Rds (on) resistance of Silicon carbide (SiC) Mosfets used with the idea that analysis studies will guide experimental studies, the ESR resistances of the primary and secondary resonance coils (7), and the forward voltage values of silicon carbide (SiC) diodes used were taken into account in the analysis studies. Experimental Study

The integrated state of the developed wireless capacitive power transfer system into the LC-LC compensation topology based system is given in Figure-3. As content, STM32F4 Discovery microprocessor board is utilized to generate the switching frequency. The inductance required for the primary and secondary resonant circuits is obtained by using an air core coil. Flere, the air-core coil is preferred since it provides linear change and control. When we consider the coil design, litz cable is preferred because of its advantages against skin effect and proximity effect problems that may be encountered at high frequency.

C2M0080120D CREE brand Silicon carbide (SiC) Mosfet is preferred due to its success in high frequencies in the full bridge inverter structure (4). The new generation IDH06G65C6XKSA1 INFINEON brand silicon carbide (SiC) diodes are used in the full bridge passive rectifier part, which provides the output voltage and current to be rectified and given to the load (8), and this provides an advantage in terms of system losses by means of its very low voltage drop feature of 1 ,25V. The resistive load, which creates the value of 33.1 ohms, is used as the load. Considering the full bridge inverter and passive rectifier board design, it has been tried to avoid losses by designing it as small as possible (10x10 cm) due to effects that may be encountered at high frequencies, such as acting as an antenna.

Figure-13 shows the voltage and current graph of the primary resonance side obtained as a result of experimental studies, and this graph also represents the output voltage and current in the full bridge inverter structure (4). Figure-14 shows the voltage and current graph of the secondary resonant side, and this graph also represents the rectifier input voltage and current. Figure-15 shows the output current on the load side of the system. As can be seen here, low current fluctuation has been achieved.

Results:

A novel wireless capacitive power transfer system has been developed for wireless capacitive power transfer applications. The prominent feature of the developed system is that there is no need for external capacitor groups, which have a very high cost and occupy an important place in the system for primary and secondary resonant circuit structures. Depending on the insulation coefficient of the insulating material used, the resonance capacitance value can be increased significantly. Thus, the required resonance inductance value will be significantly reduced. The invention is integrated into the capacitive power transfer system using LC-LC compensation topology. Here, the input voltage is measured as 60 V, the input current is measured as 1.83 A, and the output voltage is measured as around 50 V, and the output current is measured as 1.51 A. Accordingly, as a result of experimental studies, a wireless capacitive power transfer system with 110 W input power and a total system efficiency close to 70% has been achieved. Also, the efficiency and power of the total system can be easily increased according to the insulating material to be selected. Consequently, the developed power transfer system adapts regardless of the type of resonance topology to be used and the type of power electronics converter by means of its flexible structure, and it is thought that it will constitute an important place in the literature in studies on wireless capacitive power transfer. Also, it is expected that the developed capacitive power transfer system will make significant contributions to industrial and academic studies due to the many advantages it offers.

It is thought that it will be easily bent with a twisting machine in the industry and will provide ease of use in wireless capacitive power transfer studies, and it will be superior to other studies in terms of total system cost by means of the flexibility and lightness of metal materials such as aluminum or copper used in the developed wireless capacitive power transfer system.

Claims

1. A capacitive power transfer system developed for wireless capacitive power transfer applications, characterized in that, it comprises;

• At least two transmitter plates (1 ) providing primary resonance, which is bent in an "L" shape, and between the bent parts of which an insulating material (2) is placed in order to be used as a resonance capacitor in primary or secondary resonant circuits,

• Insulating material (2) in the form of a plate for use as an external capacitor in primary and secondary resonance circuits by using it between the plates (1) providing the primary resonance and between the plates (3) providing the secondary resonance,

• At least two receiver plates (3) providing secondary resonance, which is bent in an "L" shape, and between the bent parts of which an insulating material (2) is placed in order to be used as a resonance capacitor in primary or secondary resonant circuits.

2. A wireless capacitive power transfer system according to Claim 1 , characterized in that, it comprises a transmitter plate (1 ) that is made of aluminum or copper and that provides primary resonance.

3. A wireless capacitive power transfer system according to Claim 1 , characterized in that, it comprises a receiver plate (3) that is made of aluminum or copper and that provides secondary resonance.

4. A wireless capacitive power transfer system according to Claim 1 , characterized in that, it comprises an insulating material (3) produced in the form of plates in order to reduce the amount of inductance required for resonance by providing a capacity.