A PT-symmetry-based wireless power supply device with multiple transmitting coils in parallel

Abstract

The application relates to a wireless energy supply device based on PT symmetry parallel multi-transmitting coil, which supplies energy for a single load by n transmitting devices; each transmitting device is composed of a resonant capacitor and a transmitting coil connected in parallel. A negative resistance provides energy for the system and can be composed of an operational amplifier or an inverter. The transmitting coils of the n transmitting devices are in a decoupling state. A receiving device is composed of a receiving coil, a resonant capacitor and a load connected in parallel. The application adopts the parity-time symmetry (PTS) principle. Within the symmetry range, the system can not only realize stable transmission power and transmission efficiency, but also improve the receiving load voltage value and the critical transmission distance of the system. In addition, the multiple transmitting devices have flexible placement positions, and the system has greater advantages in the application of wireless power supply with large power.

Description

TECHNICAL FIELD

[0001] The application relates to a PT-symmetry-based wireless power supply device with multiple parallel transmission coils, and belongs to the technical field of wireless power transmission. BACKGROUND

[0002] Compared with traditional wired power transmission, wireless power transmission technology (WPT) omits the connection of wires between the transmission end and the receiving end, avoids the safety hazards and stable power supply problems caused by wire aging and damage, and has the advantages of safety, flexibility and portability. At present, WPT has been applied in many fields, such as implantable medical devices, electric vehicles and mobile phone charging. However, the current traditional wireless power transmission technology still has many defects, such as a large number of devices, small output power, short distance, strict requirements for the placement position of the coil, and a series of problems such as efficiency reduction caused by resonance frequency splitting, which greatly limit the application of wireless power transmission in life and industry.

[0003] In June 2017, researchers from Stanford University proposed a wireless power transmission system based on the parity time symmetry (PTS) theory, which can perfectly solve the problem of large transmission efficiency reduction caused by the position deviation of the transmission coil and the receiving coil. Due to the adaptive characteristics of the PT-symmetric system, when the coupling coefficient changes, the transmission end device can automatically adjust the working frequency, realizing stable and efficient transmission efficiency in the strong coupling region (PT-symmetric region). In this region, the transmission efficiency does not change with the change of the coupling coefficient.

[0004] The transmission distance of the WPT system is limited by the size of the coil, so the transmission distance of the two-coil PTS-WPT system is difficult to meet the application background of most current applications. Some researchers have proposed a PTS-based multiple transmission coil parallel power supply WPT system, which can increase the number of transmission coils to reduce the critical coupling coefficient and thus improve the transmission distance of the system. However, this system requires that the coupling coefficients of all transmission coils be equal, which has strict requirements for the parameter design and physical placement position of the transmission coil, resulting in that the application background and field of the system are limited.

[0005] To solve the above problems, we propose a PT-symmetry-based multi-transmit coil parallel wireless power supply system. Research shows that increasing the number of transmit coils can improve the transmission distance from the transmit end to the receive end of the WPT system. The use of a multi-transmit coil parallel structure can effectively solve the problem of coupling coefficient deviation between transmit coils, making the parameter design and placement of the transmit end coil more flexible. In addition, the proposed wireless power supply device can improve the system's output power while maintaining stable transmission efficiency, broadening the application of wireless power transmission systems in implantable medical and electronic products with larger loads. SUMMARY

[0006] To solve the above problems, we propose a PT-symmetry-based multi-transmit coil parallel wireless power supply system. Research shows that increasing the number of transmit coils can improve the transmission distance from the transmit end to the receive end of the WPT system. The use of a multi-transmit coil parallel structure can effectively solve the problem of coupling coefficient deviation between transmit coils, making the parameter design and placement of the transmit end coil more flexible. In addition, the proposed wireless power supply device can improve the system's output power while maintaining stable transmission efficiency, broadening the application of wireless power transmission systems in implantable medical and electronic products with larger loads.

[0007] The transmit coils of the n transmit end devices are in a decoupled state, i.e.:

[0008] M P1P2 =M P1P3 …=M P1Pn …M PiPj =0 (1)

[0009] where M PiPj represents the mutual inductance between the i-th transmit coil and the j-th transmit coil, i = 1, 2, 3,..., n, j = 1, 2, 3,..., n, and i ≠ j.

[0010] The conditions that the wireless power supply system needs to meet under steady-state operation are:

[0011]

[0012] In formula (2), k P =k P1 (L0 / L P1 ) 0.5 +k P2 (L0 / L P1 ) 0.5 +…+k Pn (L0 / L Pn) 0.5 ; k PS 2 = k P1 2 + k P2 2 + … + k Pn 2 ; k Pn is the coupling coefficient generated between the nth transmitting coil and the receiving coil; k P is the equivalent coupling coefficient of the equivalent transmitting coil of the transmitting end device and the receiving coil; ω0 is the inherent resonance frequency on the transmitting end device loop; ω S is the inherent resonance frequency of the receiving end device loop; γ N represents the total gain of the transmitting end loop; γ L represents the total loss of the receiving end loop; -R N is the equivalent negative resistance value; R L is the load resistance value; R Pn is the equivalent internal resistance of the nth transmitting coil; R S is the equivalent internal resistance of the receiving coil; L S is the inductance value of the receiving coil; C S is the resonance capacitance of the receiving end device; L0 is the equivalent inductance value of the transmitting end device loop; C0 is the equivalent capacitance value of the transmitting end device loop; L Pn is the inductance value of the nth transmitting coil.

[0013] The circuit structure of the negative resistance source can adopt current type or voltage type feedback form operational amplifier, half-bridge or full-bridge inverter, etc., and the equivalent negative resistance value formed meets the prerequisite requirements of the system.

[0014] The device parameters of all the transmitting coils can be designed and adjusted according to the required working frequency and the receiving end device parameters.

[0015] As preferred, the forms of all the transmitting coils can be kept consistent.

[0016] As preferred, the forms of the transmitting coils and the receiving coil can be kept consistent.

[0017] As preferred, the device parameters of all the transmitting devices and the receiving devices can be the same.

[0018] Specifically, the same parameters refer to the same inductance value and capacitance value on all the transmitting devices and the receiving devices.

[0019] The resonance capacitance of the transmitting device and the inductance of the transmitting coil can be inconsistent with the resonance capacitance of the receiving device and the receiving coil.

[0020] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0021] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0022] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0023] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0024] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0025] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0026] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0027] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0028] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0029] The transmitting coil of the transmitting device and the receiving coil of the receiving device can be any one of a plurality of forms such as a PCB coil, a planar coil, a spiral coil, etc.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] Compared with the traditional WPT system, the application does not need to increase the additional complex frequency tracking device, can avoid the efficiency and power reduction problem caused by the frequency splitting phenomenon in the strong coupling state; compared with the existing two-coil PTS-WPT system, the critical transmission distance and output power of the application are obviously improved; compared with the existing multi-transmit coil PTS-WPT system, the placement position of the transmit coil of the application is more flexible, the coil and the resonant capacitor values can be different, the system has fewer limitations, and the application range is wider. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0033] Figure 1 is the equivalent circuit schematic diagram of the wireless power supply device based on PT symmetry of the parallel multi-transmit coil of the present application.

[0034] Figure 2 is the placement position of the transmit coil and the receive coil of the wireless power supply device based on PT symmetry of the parallel multi-transmit coil of the present application.

[0035] Figure 3 is the transmission efficiency and coupling coefficient relationship curve of the wireless power supply device based on PT symmetry of the parallel multi-transmit coil of the present application.

[0036] Figure 4 is the transmission power and coupling coefficient relationship curve of the wireless power supply device based on PT symmetry of the parallel multi-transmit coil of the present application.

[0037] Figure 5 is the output power curve and the equivalent coupling coefficient relationship curve of the two-coil parallel type PTS-WPT system and the present application.

[0038] Figure 6 is the critical coupling coefficient of the two-coil parallel type PTS-WPT system and the present application under different loads. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0040] As Figure 1 shown in the figure, the PT-symmetry based multi-transmit coil parallel wireless power supply system provided by the embodiment includes a transmitting end device and a receiving end device, the transmitting end device includes a negative resistance-R N and a transmitting module connected in parallel, the negative resistance-R N provides energy for the system, each transmitting module is composed of a resonant capacitor C Pi (i=1, 2, 3, ···n) and a transmitting coil L Pi connected in parallel, wherein the transmitting coil has an equivalent internal resistance and the internal resistance R Pi and the transmitting coil L Pi are connected in parallel; the receiving end device includes a receiving coil L S , a resonant capacitor C S and a load R L connected in parallel; the receiving coil has an equivalent internal resistance and the internal resistance R S and the receiving coil L S are connected in series.

[0041] Since the transmitting coils of the n transmitting modules are completely decoupled from each other, according to Figure 1 shown in the figure, it can be obtained from the Kirchhoff's voltage and current law:

[0042]

[0043] In formula (3), -R N is the equivalent negative resistance value, R L is the load resistance value; L Pn is the inductance value of the nth transmitting coil; R Pn is the equivalent internal resistance of the nth transmitting coil; C Pn is the resonant capacitor of the nth transmitting end device; M Pn is the mutual inductance value of the nth transmitting coil and the receiving coil; L S is the inductance value of the receiving coil; R S is the equivalent internal resistance of the receiving coil; C S is the resonant capacitor of the receiving end device; and are the current vectors on the nth transmitting coil and the receiving inductor respectively; is the current vector flowing through the negative resistance; is the current vector flowing through the load resistance; ω is the working frequency of the system.

[0044] γ N represents the total gain of the transmitting end circuit; γ L represents the total loss of the receiving end circuit; ω S =(LS C S ) -0.5 Let ω0 be the inherent resonant frequency of the receiving device circuit; ω0 = (L0C0) -0.5 Let L be the inherent resonant frequency of the transmitting device circuit; where (L0) is the resonant frequency of the transmitting device circuit. -1 =(L P1 ) -1 +(L P2 ) -1 +…+(L Pn ) -1 L0 is the equivalent inductance of the transmitting coil; C0 = C1 + C2 + ... + C n C0 is the equivalent capacitance of the transmitting coil; M Pn k is the mutual inductance generated between the nth transmitting coil and the receiving coil. Pn =M Pn (L Pn C Pn ) -0.5 Let k be the coupling coefficient between the nth transmitting coil and the receiving coil; if we let k P =k P1 (L0 / L P1 ) 0.5 +k P2 (L0 / L P1 ) 0.5 +…+k Pn (L0 / L Pn ) 0.5 ,k PS 2 =k P1 2 +k P2 2 +…+k Pn 2 ;k P Let be the equivalent coupling coefficient between the transmitting and receiving coils of the transmitting device; in this system, the coupling effect has a relatively small impact on the original oscillation of the system, so 1+k P 2 -k PS 2 ≈1, the formula (3) can be simplified to:

[0045]

[0046] When the transmitting and receiving devices satisfy PT symmetry, the following must be met:

[0047]

[0048] For the system to have real-frequency solutions, it must also satisfy:

[0049]

[0050] The real and imaginary parts of equation (6) are separated and simplified to obtain:

[0051]

[0052] According to equation (7), the frequency solution is:

[0053]

[0054] According to equation (9), the condition for the frequency to have a purely real solution is:

[0055]

[0056] Therefore, to make the system work in the PT symmetric region, the following condition (10) needs to be additionally satisfied:

[0057]

[0058] When the transmitter device parameters are consistent, equation (11) can be simplified as

[0059]

[0060] When the system is stably working in the PT symmetric region, the equivalent transmitter loop current effective value V N and the equivalent receiver loop current effective value V S are obtained, and the ratio of the two is:

[0061]

[0062] At this time, the efficiency η of the system is equal to:

[0063]

[0064] The transmission power P O is equal to:

[0065]

[0066] When the coupling coefficients of the transmitter coils are not equal, i.e., k P1 ≠ k P2 ≠ … ≠ k Pn , if the transmitter coils L P1 = mL P2 = … = mL Pn , and the coupling coefficients k Pn of the transmitter coils satisfy the condition (15), the proposed wireless power supply system based on PT symmetry of multiple transmitter coils in parallel can still satisfy PT symmetry, and the critical coupling coefficient becomes smaller and the transmission distance becomes longer.

[0067]

[0068] The proposed PT symmetry based multi-transmit coil parallel wireless power supply system compared with the existing multi-transmit coil power supply system based on the principle of PT symmetry, from formula (2), the coupling coefficient k between the transmit end coil and the receive end coil of the system Pn It is not necessary to meet the equal condition, and each parameter of the transmit end coil does not need to be consistent, and each transmit coil does not need to be in the strong coupling region, only the equivalent coupling coefficient k P In the strong coupling region, the present application has stable energy transmission characteristics and frequency automatic tracking characteristics, which means that the size design and placement position of each transmit coil of the transmit device can be more flexible. From formula (15), by increasing the number of transmit end coils, the system can improve the critical coupling coefficient range, that is, improve the transmission distance.

[0069] The proposed PT symmetry based multi-transmit coil parallel wireless power supply system compared with the traditional two-coil PTS-WPT system: from formulas (13) and (14), when the system is in the PT symmetry state, the transmission efficiency and output power of the system are independent of the coupling coefficient; from formula (13), the transmission efficiency of the system is the same as that of the traditional two-coil PTS-WPT system. From formula (14), the output power of the system can be effectively improved, and the improved output power is related to the equivalent coil parameters of the designed transmit end device.

[0070] In order to further illustrate the advantages of the present application, as an example, a PT symmetry based multi-transmit coil parallel wireless power supply system is designed by using PSpice simulation software. The electrical parameters of the system are as follows: V N = 5V, transmit coil inductance L P1 = L P2 = 1uH, receive coil inductance L S = 1uH, transmit end capacitance and receive end capacitance C P1 = C P2 = C S = 85pF, working frequency ω0= ω S = 13.6MHz, equivalent resistance R P1 = R P2 = R S = 11kΩ, load R L = 1kΩ, negative resistance is realized by power electronic circuit.

[0071] According to the above simulation coefficient, Figure 2 is a schematic diagram of the placement position of the two-parameter symmetric and mutually decoupled transmit coils.Figure 3 , Figure 4 is the system transmission efficiency, transmission power and coupling coefficient relationship curve, from the figure, the system proposed in the application, when the equivalent coupling coefficient of the transmitting coil is in the PT symmetric region, the coupling coefficient of the transmitting coil is different, the application can still achieve constant transmission efficiency and output power, and there is no need to ensure that all transmitting coils are in the PT symmetric region, which reduces the placement position requirement of the coil. Figure 5 is the output power and equivalent coupling coefficient relationship curve of the two transmitting coil wireless power supply system and the two coil PTS-WPT system, from the figure, when in the PT symmetric region, the output power of the system proposed in the application is 1 times higher than that of the traditional two coil PTS-WPT. Figure 6 is the critical coupling coefficient of the two transmitting coil wireless power supply system and the two coil PTS-WPT system under different loads, from the figure, the system proposed in the application can effectively reduce the critical coupling coefficient, that is, the critical transmission distance is greatly improved.

[0072] The embodiments of the application are described in detail above with reference to the drawings, but the application is not limited to the described embodiments. For those skilled in the art, various changes, modifications, replacements and variations of the embodiments can be made without departing from the principles and spirits of the application, and still fall within the protection scope of the application.

Claims

1. A PT-symmetry based wireless power device with multiple transmitting coils in parallel, characterized in that: The application relates to a system comprising a transmitting device and a receiving device; the transmitting device comprises a negative resistance source and n transmitting modules; each transmitting module is composed of a resonant capacitor and a transmitting coil connected in parallel; the receiving device comprises a receiving coil, a resonant capacitor and a load connected in parallel; the transmitting device comprises a negative resistance R N and the transmitting module is connected in parallel, the negative resistance R N provides energy for the system; each transmitting module is composed of a resonant capacitor C Pi (i = 1, 2, 3···n) and a transmitting coil L Pi connected in parallel, wherein the transmitting coil has an equivalent internal resistance and the internal resistance R Pi and the transmitting coil L Pi are connected in parallel; the receiving device comprises a receiving coil L S , a resonant capacitor C S and a load R L connected in parallel; the receiving coil has an equivalent internal resistance and the internal resistance R S and the receiving coil L S are connected in series. The transmitting coils of the n transmitting devices are completely decoupled from each other, and the Kirchhoff voltage and current law can be obtained as follows: ； where -R N is the equivalent negative resistance value, R L is the load resistance value; L Pn is the inductance value of the nth transmitting coil; R Pn is the equivalent internal resistance of the nth transmitting coil; C Pn is the resonance capacitance of the nth transmitting end device; M Pn is the mutual inductance value of the nth transmitting coil and the receiving coil; L S is the inductance value of the receiving coil; R S is the equivalent internal resistance of the receiving coil; C S is the resonance capacitance of the receiving end device; I Pn and I S are the current vectors on the nth transmitting coil and the receiving inductance, respectively; I N is the current vector flowing through the negative resistance; I L is the current vector flowing through the load resistance; ω is the operating frequency of the system, γ N represents the total gain of the transmitting end loop; γ L represents the total loss of the receiving end loop; ω S = (L S C S ) −0.5 is the natural resonant frequency of the receiving end device loop; ω0 = (L0C0) −0.5 is the natural resonant frequency of the transmitting end device loop; wherein (L0) -1 = (L P1 ) -1 + (L P2 ) -1 +∙∙∙+(L Pn ) -1 , L0 is the equivalent inductance value of the transmitting end coil; C0 = C1+C2+∙∙∙+C n , C0 is the equivalent capacitance value of the transmitting end coil; M Pn is the mutual inductance generated between the nth transmitting coil and the receiving coil; k Pn = M Pn (L Pn C Pn ) -0.5 is the coupling coefficient generated between the nth transmitting coil and the receiving coil; if k P = k P1 (L0 / L P1 ) 0.5 +k P2 (L0 / L P1 ) 0.5 +∙∙∙+k Pn (L0 / L Pn ) 0.5 , k PS 2 = k P1 2 +k P2 2 + ∙∙∙ + k Pn 2 ; k P is the equivalent coupling coefficient of the equivalent transmitting coil of the transmitting end device and the equivalent receiving coil; in this system, the effect of coupling is less disturbed to the original oscillation of the system, so 1+k P 2 - k PS 2 ≈ 1, the above formula can be simplified as: .

2. A PT-symmetry based wireless power device with multiple parallel transmitting coils according to claim 1, wherein: The transmitting coils of the n transmitting devices are in a decoupled state from each other, that is: ； where M PiPj represents the mutual inductance between the ith transmit coil and the jth transmit coil, i = 1, 2, 3, ··· n, j = 1, 2, 3, ··· n, and i ≠ j.

3. A PT-symmetry based wireless power device with multiple transmitting coils in parallel according to claim 1, wherein: The equivalent natural frequency ω0of the transmit device transmit loop is related to the natural frequency ω S Consistently, i.e.: ； L S is the inductance value of the receiving coil; C S is the resonant capacitance of the receiving end device; wherein, (L0) -1 = (L P1 ) -1 + (L P2 ) -1 +∙∙∙+(L Pn ) -1 , L0 is the equivalent inductance value of the transmitting end coil; C0 = C1+C2+∙∙∙+C n , C0 is the equivalent capacitance value of the transmitting end coil; L Pn is the inductance value of the nth transmitting coil; C Pn is the resonant capacitance of the nth transmitting end device.

4. The PT-symmetry based wireless power device with multiple parallel transmitting coils of claim 1, wherein: The total gain γ of the transmitting device loop N The total loss γ of the receiving device loop L Consistency is maintained, i.e.: ； - R N R is the equivalent negative resistance value; R L R is the load resistance value; R Pn R is the equivalent internal resistance of the nth transmitting coil; R S R is the equivalent internal resistance of the receiving coil.

5. The PT-symmetry based wireless power device with multiple parallel transmitting coils of claim 1, wherein: The working frequency ω of the wireless power supply device is designed as: ； where k P = k P1 (L0 / L P1 ) 0.5 +k P2 (L0 / L P1 ) 0.5 +∙∙∙+k Pn (L0 / L Pn ) 0.5 ; k PS 2 = k P1 2 + k P2 2 + ∙∙∙ +k Pn 2 ; k Pn is the coupling coefficient between the nth transmit coil and the receive coil; k P is the equivalent coupling coefficient between the transmit equivalent transmit coil and the receive coil.

6. A PT-symmetry based wireless power device with multiple transmitting coils in parallel according to claim 1, wherein: The transmission efficiency η of the wireless power supply device satisfies: ； The output power of the system satisfies P O : ； According to the working frequency ω of the system, the output power P of the system O , the expression of the total loss γ of the system receiving end loop L , the device parameters of the transmitting end device and the receiving device, and the number n of the transmitting end device coils can be determined.

Images