Capacitive coupling wireless power transmission system and method based on stable working frequency

Abstract

The invention discloses a capacitive coupling wireless power transmission system and method based on stable working frequency. The wireless power transmission system comprises a transmitter and a receiver. The receiver comprises a capacitor plate P3, a capacitor plate P4 and a receiving end resonator; the transmitter comprises a capacitor plate P1, a capacitor plate P2, a transmitting end resonator and a frequency detuning controller; the frequency detuning controller is connected to the transmitting terminal resonator in parallel and comprises an inductor LD and a switch S1; by closing the switch S1 and disconnecting the switch S1 after oscillation of the system is stable, the wireless electric energy transmission system is detuned between resonant frequencies of the transmitter and the receiver, switching of the wireless electric energy transmission system from a low-frequency branch to a high-frequency branch is completed, and the system always works at the high-frequency branch with relatively stable frequency when working in an over-coupling state. And the working frequency is stable and is approximate to the self-resonant frequency.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and in particular relates to a capacitive coupling wireless power transmission system and method based on a stable operating frequency. Background Art

[0002] Compared with traditional power transmission, Wireless Power Transfer (WPT) technology uses wireless methods to supply energy without the need for physical connection. This avoids a series of problems such as line aging and damage, extends the service life of the equipment, and improves safety, eliminates the risk of exposed wires, and reduces the risk of electric shock. It is particularly suitable for some high-risk environments (such as medical equipment, power tools, etc.). At the same time, the wireless charging device and the receiving end do not need direct contact and can be designed into a sealed structure, which is suitable for occasions with high requirements for waterproofing and dustproofing (such as electric vehicles, outdoor equipment, etc.).

[0003] Near-field wireless power transmission technology can be mainly divided into two types: magnetic field (inductive) coupling (Inductive Power Transfer, IPT) and electric field (capacitive) coupling (Capacitive Power Transfer, CPT), which are also the two mainstream WPT technologies and are widely used in the field of wireless power transmission. At the same time, these two near-field WPT technologies have dual properties and have commonalities in many aspects.

[0004] In order to reduce the skin effect of AC current, the inductive coupling device uses a large amount of Litz wire. In order to increase the coupling ability of the inductive coupling mechanism, high-frequency ferrite is added to the coil. This leads to high manufacturing cost of the inductive coupling mechanism, large core loss, large volume and weight of the mechanism, and high-frequency magnetic field will produce eddy current loss in the metal foreign matter in the magnetic field, resulting in reduced transmission efficiency and even causing metal objects to heat up and generate electric sparks, which is dangerous under certain conditions. The magnetic field leakage of the coupling mechanism not only generates electromagnetic interference to the environment and affects the operation of other electronic products, but also causes certain harm to humans, animals and plants. High-power transmission mechanisms also need to design special aluminum plates as magnetic field shielding structures.

[0005] At the end of the 20th century, Paul Curry, an American electrical engineer, first proposed a wireless power transmission method that uses high-frequency electric fields as an energy transmission channel. However, due to the lack of relevant supporting theories and technical limitations at the time, the electric field coupling wireless power transmission technology developed relatively slowly compared with the magnetic field coupling wireless power transmission technology. Since the 21st century, with the emergence of high-power high-frequency switching devices, capacitors with excellent high-frequency characteristics, magnetic cores and other hardware and electromagnetic field numerical analysis theory, high-performance computers and simulation software, support has been provided for further research on CPT technology. Compared with the IPT system, the CPT system uses cheaper metal plates in the coupling mechanism. When metal foreign matter exists in the electric field between the coupling plates, it will not cause eddy current loss, and the electric field attenuation at the edge of the plate is fast and the radiation range is small. Compared with the Litz coil and ferrite of the magnetic coupling mechanism, the metal plate has a simple structure, low cost, and greatly reduced volume and weight. It is more suitable for applications in dynamic charging, electric vehicle charging, etc. Therefore, in recent years, electric field coupling wireless power transmission technology has become one of the main research directions of wireless power transmission methods.

[0006] However, the CPT system also has some disadvantages, which are as follows: 1) The system transmission power and efficiency are poorly robust and are easily affected by changes in distance and coupling mechanism angle; 2) The system will produce frequency splitting under strong coupling, resulting in a decrease in transmission power. The wireless energy transfer system based on parity time symmetry (PTs-WPT) has strong robustness and the system has the characteristics of frequency adaptation. Specifically, when the coupling reaches a certain intensity and the system undergoes frequency splitting, the PTs-WPT system will adaptively track and adjust to the frequency after splitting, avoiding the occurrence of frequency splitting and thus maintaining a high transmission power. The characteristics of PTs-WPT enable it to solve the two major problems of traditional WPT. PTs-WPT has also become a research hotspot in the field of wireless energy transmission in recent years. With the continuous improvement of PTs-WPT system research, in-depth research on the two mainstream transmission methods and the expansion of higher-order PT symmetric systems have also been launched.

[0007] However, although the PTs-WPT system has excellent transmission characteristics, the commonly used self-oscillating PT symmetric system will automatically track the split frequency in the PT symmetric area. Although it avoids the output efficiency and power reduction caused by frequency splitting, it leads to the instability of its operating frequency. Such a result is unacceptable in some commercial applications or special applications. For example, for the Qi standard frequency band (110-205kHz range) for wireless charging or the NFC device and RFID technology frequency band (near 13.56MHz), when the changing operating frequency is too large, the system cannot meet the requirements. Summary of the invention

[0008] The object of the present invention is to provide a capacitive coupling wireless power transmission system and method based on a stable operating frequency.

[0009] In a first aspect, the present invention provides a capacitive coupling wireless power transmission system based on a stable operating frequency, which includes a transmitter and a receiver; the receiver includes a capacitor plate P 3 、Capacitor plate P 4 and the capacitor plate P 3 and capacitor plate P 4 The receiving end resonator connected; the transmitter includes a capacitor plate P 1 、Capacitor plate P 2 and the capacitor plate P 3 and capacitor plate P 4 The transmitter resonator connected; the transmitter also includes a frequency detuning controller; the frequency detuning controller is connected in parallel to the transmitter resonator; the frequency detuning controller includes an inductor L D and switch S 1 ; Through switch S 1 The closing and opening of the wireless power transmission system causes the wireless power transmission system to be detuned between the resonant frequencies of the transmitter and the receiver, completing the switching of the wireless power transmission system from the low-frequency branch to the high-frequency branch.

[0010] As a preferred embodiment, when the system is operating in the low frequency branch, by closing the switch S 1 After disconnecting again, the control system works in the high frequency branch.

[0011] Preferably, the capacitor plate P 1 and capacitor plate P 2 The coupling capacitor C 12 , and the capacitor plate P 3 and capacitor plate P 4 The coupling capacitor C 34 Equal; capacitor plate P 1 and capacitor plate P 3 The coupling capacitor C 13 , and the capacitor plate P 2 and capacitor plate P 4 The coupling capacitor C 24 equal.

[0012] Preferably, the natural frequencies ω of the transmitting end resonator and the receiving end resonator are 0 Equal, the resonant frequency ω' 0 equal.

[0013] As a preferred embodiment, the operating frequencies of the low-frequency branch and the high-frequency branch are ω2 and ω 3 , which is obtained as follows: Among them, ω 0 is the natural frequency; k is the coupling coefficient between the transmitter and the receiver; γ L is the loss factor of the receiver.

[0014] Preferably, the receiving end resonator includes a compensation inductor L R , compensation capacitor C RE and load resistance R L ; Capacitor plate P 3 and capacitor plate P 4 Connect the compensation capacitors C RE The transmitting end resonator includes a compensation inductor L connected in series T , compensation capacitor C TE and negative resistance -R T ; Capacitor plate P 1 and capacitor plate P 2 Connect the compensation capacitors C TE The two ends of the inductor L connected in sequence D and switch S 1 Connect in parallel to the compensation inductor L T Both ends.

[0015] As a preference, the capacitor plate P 1 and capacitor plate P 3 Placed opposite each other, capacitor plates P 2 and capacitor plate P 4 The two capacitor plates are placed opposite each other and completely overlap each other.

[0016] In a second aspect, the present invention provides a capacitive coupling wireless power transmission method based on a stable operating frequency, which uses the above-mentioned wireless power transmission system; the wireless power transmission method comprises the following steps: adjusting the transmitter and the receiver so that the wireless power transmission system operates in a parity-time symmetric state; in the initial state, the switch S in the frequency detuning controller 1 In the disconnected state; if the system works in the high frequency branch, wireless power transmission is performed directly; otherwise, the switch S is closed. 1 , disconnect switch S after the system oscillation stabilizes 1 , so that the system works on high frequency branching for wireless power transmission.

[0017] Preferably, the conditions for working in the parity-time symmetric state are as follows: The transmitter gain factor γ T Equal to the loss factor γ of the receiver L; The coupling coefficient k between the transmitter and the receiver is greater than the critical coupling coefficient k c , critical coupling coefficient k c The expression is: .

[0018] As a preferred method, the method for determining whether the system is working in the high frequency branch is as follows: if the operating frequency ω is less than the resonant frequency ω' 0 Or if the transmitter phase lags behind the receiver phase, the system works in the low-frequency branch; otherwise, the system works in the high-frequency branch.

[0019] The present invention has the following beneficial effects: 1. Based on the self-resonant frequency offset phenomenon existing in the CPT system itself, the present invention adds a transient frequency detuning control method, so that the system always works in a high-frequency branch with a relatively stable frequency when working in an over-coupled state, and the operating frequency is stable and close to the self-resonant frequency.

[0020] 2. The present invention adopts a horizontal four-plate energy transfer structure, which has a simple structure and low cost, and can achieve a higher electric field strength and energy transmission efficiency within a shorter distance. Moreover, since the quadrupole plate structure can form a current loop only by itself, it can be applied to more complex and general application scenarios, such as working on water.

[0021] 3. The present invention uses a self-oscillating transmitting source to work, which can perform frequency tracking and avoid frequency splitting. At the same time, it meets the parity-time symmetry conditions, can achieve relatively stable output, and does not require complex external control circuits, and has strong robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the quadrupole plate coupling structure and its equivalent circuit used in the present invention.

[0023] Figure 2 The figure is a schematic diagram of the system circuit for realizing frequency regulation of the present invention.

[0024] Figure 3 This is a theoretical diagram of the frequency and gain solution of the present invention.

[0025] Figure 4 The two working modes of the present invention under a certain coupling coefficient and the voltage and current waveform diagram of frequency switching.

[0026] Figure 5 It is a comparison diagram of the theoretical value and the simulation value of the working frequency of the present invention changing with the coupling coefficient. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] like Figure 1 and Figure 2 As shown, the capacitive coupling wireless power transmission system based on the stable working frequency includes a transmitter (Tx) and a receiver (Rx); the transmitter includes a capacitor plate P 1 、Capacitor plate P 2 , a transmitter resonator and a frequency detuning controller; the frequency detuning controller includes an inductor L D and switch S 1 The transmitting end resonator includes a compensation inductor L connected in series T , compensation capacitor C TE and negative resistance -R T ; Capacitor plate P 1 and capacitor plate P 2 Connect the compensation capacitors C TE The two ends of the inductor L connected in sequence D and switch S 1 Connect in parallel to the compensation inductor L T The receiver includes capacitor plates P 3 、Capacitor plate P 4 and a receiving end resonator; the receiving end resonator includes a compensation inductor L R , compensation capacitor C RE and load resistance R L ; Capacitor plate P 3 and capacitor plate P 4 Connect the compensation capacitors C RE both ends of .

[0029] In this embodiment, the capacitor plate P 1 (P 2 ) and capacitor plate P 3 (P 4 ) are placed opposite each other, and the two capacitor plates in the opposite position completely overlap.

[0030] Capacitor plate P i and capacitor plate P j Forming coupling capacitance C ij ; where i,j = 1, 2, 3, 4, and i ≠ j. The coupling capacitance between the capacitor plates on the same side (C 12 and C 34 ) and the cross capacitance between the opposite side cross capacitance plates (C 14 and C 23 ) is much smaller than the coupling capacitance of the opposite plate (C 13 and C 24 ). The equivalent self capacitance at the transmitter end is C TS , the equivalent self capacitance at the receiver end is C RS , the equivalent mutual capacitance between the transmitter and the receiver is C M , equivalent self capacitance CTS , equivalent self capacitance C RS and mutual capacitance is C M The calculation method of is as follows;

[0031] Special styles Due to the relatively small self-capacitance C TS and C RS Not only is it easily affected by the environment, but it also introduces a large reactive impedance. Therefore, an RLC resonator is added in the transmitter and receiver; negative resistance – R T A self-oscillating power source capable of adaptively tracking the bifurcation frequency. This coupled RLC resonator is an instantiation of the concept of parity-time (PT) symmetry in electronics.

[0032] For the opposite capacitor plates P 1 (P 2 ) and P 3 (P 4 ), coupling capacitor C 12 and coupling capacitor C 34 Equal and denoted as C s ; Coupling capacitor C 13 and coupling capacitor C 24 Equal and denoted as C m Due to the cross capacitance C 14 and the crossover capacitance C 23 Compared with the coupling capacitance of the positive plate, the value is small and can be ignored, then equation (1) can be simplified to:

[0033] Special styles From formula (2), we can see that the equivalent self-capacitance C TS and equivalent self capacitance C RS With mutual capacitance C M This is the essential difference between inductive coupling and capacitive coupling, and this will introduce significant differences in the bifurcation frequency behavior. The natural frequency and resonant frequency of the transmitter resonator and the receiver resonator are the same, ω 0 and ω' 0 , natural frequency ω 0 and the resonant frequency ω' 0 The expression is:

[0034] Natural frequency ω 0 and the resonant frequency ω' 0 The relationship between them satisfies ω' 0 = (1−k) 0.5 ω 0 ; Where k is the coupling coefficient, and its expression is: Formula (4) When the mutual capacitance is C M = 0, the natural frequency ω 0 and the resonant frequency ω' 0 equal.

[0035] The state equation of the wireless power transmission system is expressed as: Formula (5) Where, ω is the operating frequency of the system; I T For the equivalent negative resistance –R T The current on L For load R L The current on T is the gain coefficient at the transmitter end, γ T = (R T −R 1 ) / (ω 0 L T ); γ L is the loss coefficient at the receiver end, γ L = (R L +R 2 ) / (ω 0 L R );R 1 and R 2 They are respectively the compensation inductance L T and compensation inductor L R parasitic resistance.

[0036] Since the coefficient matrix in equation (5) remains unchanged after performing both parity inversion (swapping the subscripts "T" and "L" or "R") and time reversal (changing the sign of j), this means that the system is a parity-time symmetric system, i.e., a PT symmetric system. For a solution to equation (5), the determinant of the coefficient matrix must be zero. After separating the real and imaginary parts of the determinant equation and setting them both to zero, we obtain:

[0037] Formula (6) At this time, there are two frequency solutions.

[0038] For the first case, the system works in the PT-broken state and is also undercoupled, and the gain coefficient is γ T1 = k 2 / γ L , has a non-bifurcation solution ω 1 : Formula (7) Working frequencyω 1As the coupling coefficient k changes, it is no longer a fixed constant, which is different from the inductively coupled wireless power transfer system, i.e., IPT. When k = 0, ω 1 = ω 0 is the natural resonant frequency without coupling effects.

[0039] For the second case, the system works in the PT-symmetric state and is also in the over-coupled state, and the gain coefficient γ T2,3 and loss coefficient γ L Equal (γ T2,3 = γ L ), and has a bifurcated frequency solution ω 2,3 : Formula (8) The high-frequency branch and low-frequency branch in formula (7) are represented by ω 2 and ω 3 .

[0040] Figure 3 is the gain factor γ L =0.0274. The gain coefficient γ corresponding to different coupling coefficients k is also plotted. T1 and gain factor γ T2,3 From (7), we can see that there is a critical coupling coefficient k c , so that the operating frequency ω 2 and the operating frequency ω 3 merged to the same frequency.

[0041] Formula (9) When k < k c ,ω 2 and ω 3 becomes a complex value.

[0042] from Figure 3 It can be seen that k c ≈0.0276; when there are two possible gain coefficients, the system prefers to choose the gain mode with the lower value. c When γ T1 >γ T2,3 , the system gives priority to γ T2,3 , there is a bistable state at this time, and the corresponding frequency is ω 2 and ω 3 When k <k c When the system works at ω 1 , because only ω 1 is a real value. When the coupling coefficient k is equal to the critical coupling coefficient k cWhen k = k c When 2 Reach the minimum valueω 2,min , whose expression is:

[0043] Formula (10) from Figure 3 It can be seen that the operating frequency ω 2 is approximately a constant value that is insensitive to the coupling coefficient k. In the overcoupled state, the operating frequency behavior is different from that of the IPT system. In the IPT system, the operating frequency in the undercoupled state is almost unchanged, and it bifurcates into a high-frequency branch and a low-frequency branch in the overcoupled state. However, in the CPT system, the operating frequency changes in the undercoupled state, and the high-frequency branch and the low-frequency branch in the overcoupled state are also different from those of the IPT. In fact, for an effective CPT system, the loss is much less than 1, that is, γ L <<1. Solve the bifurcation frequency in equation (8) 2,3 Simplified to:

[0044] Formula (11) Equation (11) verifies that for an effective CPT system, its high-frequency branch ω in the over-coupled state is 2 The conclusion is that it is not sensitive to the coupling coefficient k. The coupling coefficient k takes the output power P on the load resistance under different ranges L The expression is:

[0045] Formula (12) Current|I T |Insensitive to coupling coefficient, especially for stable operating frequency and unchanged equivalent impedance.

[0046] The key to achieve stable operating frequency and load power is to make the system work in the high frequency branch. The frequency selection method between the high frequency branch and the low frequency branch of the system through the frequency detuning controller is as follows:

[0047] Through the working frequency ω and the resonant frequency ω' 0 The size or phase between the transmitter and the receiver determines whether the system is working in the high-frequency branch; if the operating frequency ω is less than the resonant frequency ω' 0 Or the transmitter phase lags behind the receiver phase, the system works in the low-frequency branch (operating frequency is ω 3 ); otherwise, the system works in the high-frequency branch (the working frequency is ω 2 ). If the system works in the low-frequency branch, the switch S is closed briefly. 1After that, disconnect it again, causing the system to detune between the resonant frequencies of the transmitter and receiver. A sufficiently large frequency detune will cause the system to move from the operating frequency ω 3 Become a new high-frequency branch, although this frequency is not the working frequency ω for the time being 2 After the system oscillation is stable, switch S 1 is disconnected to eliminate the resonant frequency detuning. Due to the hysteresis characteristics of the bistable system, the system will continue to operate in the high frequency branch and stabilize at the operating frequency ω 2 Through this high-frequency branch selection method, the system will always operate at the operating frequency ω 2,min and the natural frequency ω 0 between the frequency range while maintaining a stable power output.

[0048] In order to further reflect the characteristics of the present invention, as an example, a system proposed by the present invention is designed using Multisim simulation software. The negative resistance is realized by connecting an amplifier with positive feedback, and the resistance value is R f1 =5Ω、R f2 =47Ω and R f3 =255 kΩ. Device parameters: Inductance is L T =L R =203μH, the corresponding total resonant capacitance value is C TE +C TS (C RE +C RS ) is about 500pF, and the natural resonant frequency is f 0 =500kHz, Tx (Rx) end inductance L T (L R ) of the parasitic resistance R 1 =R 2 =7.5Ω, load resistance R L =10Ω, detuned inductor L D =4uH. When the coupling coefficient k>k c That is, the system is in an over-coupled state, and the system may randomly select low frequency or high frequency to work. Through frequency detuning control, the system can be artificially made to select the high frequency branch to work. Figure 4 It is the voltage waveform diagram of the transmitting and receiving ends when the system switches from low frequency to high frequency in the over-coupled state. Figure 5 The coupling coefficient is in the range of 0~0.2. Under this series of parameters, the results of theoretical analysis and simulation show that the theoretical value is consistent with the simulation value, which can achieve the goal of the system operating at a high-frequency branch of about 500kHz in an over-coupled state, and the error is less than 5‰.

Claims

1. A capacitive coupling wireless power transmission system based on a stable operating frequency, comprising a transmitter and a receiver; the receiver comprises a capacitor plate P3, a capacitor plate P4 and a receiving-end resonator connected to the capacitor plate P3 and the capacitor plate P4; the transmitter comprises a capacitor plate P1, a capacitor plate P2 and a transmitting-end resonator connected to the capacitor plate P3 and the capacitor plate P4; characterized in that: The transmitter also includes a frequency detuning controller; the frequency detuning controller is connected in parallel to the transmitting end resonator; the frequency detuning controller includes an inductor L D and switch S1; by closing and opening the switch S1, the wireless power transmission system is detuned between the resonant frequencies of the transmitter and the receiver, completing the switching of the wireless power transmission system from the low-frequency branch to the high-frequency branch.

2. The capacitive coupling wireless power transmission system based on stable operating frequency according to claim 1, characterized in that: When the system works in the low-frequency branch, by closing the switch S1 and then opening it again, the control system works in the high-frequency branch.

3. The capacitive coupling wireless power transmission system based on stable operating frequency according to claim 1, characterized in that: The coupling capacitance C between the capacitor plate P1 and the capacitor plate P2 12 , and the coupling capacitance C between the capacitor plate P3 and the capacitor plate P4 34 Equal; coupling capacitance C between capacitor plate P1 and capacitor plate P3 13 , and the coupling capacitance C between the capacitor plate P2 and the capacitor plate P4 24 equal.

4. The capacitive coupling wireless power transmission system based on stable operating frequency according to claim 3, characterized in that: The transmitting-end resonator and the receiving-end resonator have the same natural frequency ω0 and the same resonance frequency ω'0.

5. The capacitive coupling wireless power transmission system based on stable operating frequency according to claim 1, characterized in that: The operating frequencies of the low-frequency branch and the high-frequency branch are ω2 and ω3 respectively, which are obtained as follows: Where ω0 is the natural frequency; k is the coupling coefficient between the transmitter and the receiver; γ L is the loss factor of the receiver.

6. The capacitive coupling wireless power transmission system based on stable operating frequency according to claim 1, characterized in that: The receiving end resonator includes a compensation inductor L R , compensation capacitor C RE and load resistance R L ; Capacitor plates P3 and P4 are connected to compensation capacitors C RE The transmitting end resonator includes a compensation inductor L connected in series T , compensation capacitor C TE and negative resistance -R T ; Capacitor plates P1 and P2 are connected to compensation capacitors C TE The two ends of the inductor L connected in sequence D And switch S1 is connected in parallel with the compensation inductor L T Both ends.

7. The capacitive coupling wireless power transmission system based on stable operating frequency according to claim 1, characterized in that: The capacitor plate P1 and the capacitor plate P3 are placed opposite to each other, and the capacitor plate P2 and the capacitor plate P4 are placed opposite to each other, and the two capacitor plates in the opposite position completely overlap.

8. A capacitively coupled wireless power transmission method based on a stable operating frequency, characterized in that: A capacitive coupling wireless power transmission system based on a stable operating frequency as described in claim 1 is used; the wireless power transmission method comprises the following steps: adjusting a transmitter and a receiver so that the wireless power transmission system operates in a parity-time symmetric state; in an initial state, a switch S1 in a frequency detuning controller is in an open state; if the system operates in a high frequency branch, wireless power transmission is performed directly; otherwise, the switch S1 is closed, and after the oscillation of the system is stabilized, the switch S1 is opened, so that the system operates in a high frequency branch and then wireless power transmission is performed.

9. The capacitive coupling wireless power transmission method based on stable operating frequency according to claim 8, characterized in that: The conditions for working in the parity-time symmetric state are as follows: The transmitter gain factor γ T Equal to the loss factor γ of the receiver L ; The coupling coefficient k between the transmitter and the receiver is greater than the critical coupling coefficient k c , critical coupling coefficient k c The expression is: 。 10. The capacitive coupling wireless power transmission method based on stable operating frequency according to claim 8, characterized in that: The method for judging whether the system works in the high frequency branch is as follows; if the operating frequency ω is less than the resonant frequency ω'0 or the transmitter phase lags the receiver phase, the system works in the low frequency branch; otherwise, the system works in the high frequency branch.

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