A wireless power transmission system capable of automatically compensating for the influence of metal obstacles

Abstract

The present invention discloses a wireless power transmission system capable of automatically compensating for the influence of metal obstacles, which includes a signal generator, a power amplifier, a voltage-controlled variable capacitor, a first compensation capacitor, a second compensation capacitor, a transmitting coil, a receiving coil, and a load. The output end of the signal generator is connected to the input end of the power amplifier, and the voltage-controlled variable capacitor and the first compensation capacitor are connected in parallel to form an equivalent variable capacitor. C (NEW) , and this equivalent variable capacitor C (NEW) is connected in series with the transmitting coil to form a transmitting circuit, and both ends of the transmitting circuit are correspondingly connected to the output end of the power amplifier; the receiving coil is connected in series with the second compensation capacitor to form a receiving circuit, and both ends of this receiving circuit are correspondingly connected to both ends of the load. By using the voltage-controlled variable capacitor, the present invention changes the frequency characteristics of the system without adding additional components and feedback networks, improves the energy transmission efficiency of wireless power transmission, has high safety, and broad market prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless power transmission, and particularly relates to a wireless power transmission system capable of automatically compensating for the influence of metal obstacles. Background Art

[0002] Like wireless communication technology, getting rid of the bondage of physical media and realizing wireless power transmission has been a beautiful pursuit of mankind for many years. Wireless power transmission technology, also known as non-contact power transmission technology, refers to a way of energy transmission in which electrical energy is transmitted from a power source to a load without direct electrical contact. Wireless power transmission technology can be divided into electric field coupling type, microwave radiation type, magnetic coupling resonance type, etc. In the electric field coupling type of wireless power transmission technology, a metal plate on the power source side and a metal plate on the load side form a capacitor, and the electric field of the capacitor is used for power transmission, but it can only be applied in low-power occasions; the microwave radiation type of wireless power transmission technology uses the far field for transmission, and its transmission distance is much larger than the geometric size of the transmission device, but its directivity is poor, and the transmission power is generally relatively small; the magnetic coupling resonance type of wireless power transmission technology transmits energy through the near-field magnetic coupling between two inductance coils resonating at the same frequency. Compared with the electric field coupling type of wireless power transmission technology, the transmission distance has been greatly extended; compared with the microwave radiation type of wireless power transmission technology, it has less impact on the electromagnetic environment and has a larger transmission power, so it has received more and more extensive attention and research.

[0003] Although the magnetic coupling resonance type of wireless power transmission technology has increased the transmission distance, especially the axial distance, and its practicability has been greatly improved. However, there should be no metal obstacles between the transmitting coil and the receiving coil in this wireless power technology. Once there are metal obstacles, the equivalent parameters of the wireless power transmission system will be affected, the power transmission efficiency will drop rapidly, and the transmission performance will deteriorate extremely. In order to enable the wireless power transmission system to automatically compensate for the influence of metal obstacles, frequency tracking control or impedance adjustment devices can be adopted. Frequency tracking control is to automatically adjust the power supply frequency to maintain the resonant state of the system, and the impedance adjustment device is to add adjustable elements to dynamically adjust the input impedance of the system to keep the input impedance in a pure resistance state. However, the existing wireless power transmission technologies all require components and feedback networks, which greatly increase the complexity and failure rate of the wireless power transmission system, and the cost will also increase significantly. Summary of the Invention

[0004] The object of the present invention is to propose a wireless power transmission system capable of automatically compensating for the influence of metal obstacles in view of the problem that when a non-ferromagnetic metal obstacle exists between the transmitting coil and the receiving coil, the system performance drops significantly due to the change of equivalent parameters.

[0005] The present invention adopts the following technical solutions to achieve the above object: A wireless power transmission system capable of automatically compensating for the influence of metal obstacles, characterized by comprising a signal generator, a power amplifier, a voltage-controlled variable capacitor, a compensation capacitor 1, a compensation capacitor 2, a transmitting coil, a receiving coil, and a load. The output end of the signal generator is connected to the input end of the power amplifier. The voltage-controlled variable capacitor is connected in parallel with the compensation capacitor 1 to form an equivalent variable capacitor C (NEW) , and this equivalent variable capacitor C (NEW) is connected in series with the transmitting coil to form a transmitting circuit, and the two ends of the transmitting circuit are correspondingly connected to the output end of the power amplifier; the receiving coil is connected in series with the compensation capacitor 2 to form a receiving circuit, and the two ends of this receiving circuit are correspondingly connected to the two ends of the load; the transmitting coil is used to convert electrical energy into magnetic field energy and transmit it to the receiving coil, the voltage-controlled variable capacitor is used to change the frequency characteristics of the wireless power transmission system and suppress the influence of the change in the equivalent parameters of the transmitting coil and the receiving coil caused by non-ferromagnetic metal obstacles, and the receiving coil is used to receive the magnetic field energy transmitted by the transmitting coil and convert it into electrical energy.

[0006] The design method of the wireless power transmission system capable of automatically compensating for the influence of metal obstacles according to the present invention is characterized in that the specific steps are as follows:

[0007] Step S1: Establish a KVL equation set of the wireless power transmission system considering metal obstacles, that is:

[0008]

[0009] In the formula, i1, i2, and i3 are respectively the current of the transmitting coil, the current of the receiving coil, and the equivalent current induced on the metal obstacle; L1 and L2 are respectively the self-inductance of the transmitting coil and the self-inductance of the receiving coil; L ob is the equivalent inductance of the metal obstacle; R1 and R2 are respectively the equivalent series resistance of the transmitting coil and the equivalent series internal resistance of the receiving coil; R L [[ID=2G]] is the load resistance; R ob is the equivalent resistance of the metal obstacle; u c(NEW) is the voltage across the equivalent variable capacitor C (NEW) ; u c2 is the voltage across the compensation capacitor 2 C2; M is the mutual inductance between the transmitting coil and the receiving coil; M 1ob and M 2ob are respectively the equivalent mutual inductance between the metal obstacle and the transmitting coil and the equivalent mutual inductance between the metal obstacle and the receiving coil; u s is the output voltage of the power amplifier, that is, u s = U s cos(ωt), U s is the amplitude of the output voltage of the power amplifier, ω is the angular frequency of the output voltage waveform of the signal generator, ω = 2πf;

[0010] Step S2: Combine the equations in step S1 to obtain:

[0011]

[0012] in

[0013]

[0014] Where ΔL1 and ΔR1 are the changes in the equivalent inductance of the transmitting coil and the equivalent resistance of the transmitting coil caused by the metal obstacle, respectively; ΔL2 and ΔR2 are the changes in the equivalent inductance of the receiving coil and the equivalent resistance of the receiving coil caused by the metal obstacle, respectively;

[0015] Step S3: The coulomb-volt characteristic curve of the voltage-controlled variable capacitor is expressed as u1(q)=a1q+a3q 3 , where a1 and a3 are constant coefficients determined by the voltage-controlled variable capacitor parameters, u1 is the voltage across the voltage-controlled variable capacitor, and q is the charge stored in the voltage-controlled variable capacitor, expressed as q = Qcos(ωt+θ), where Q is the amplitude of the charge stored in the voltage-controlled variable capacitor. On this basis, the KVL equation for the transmitting circuit without metal obstacles is established, namely:

[0016]

[0017] in

[0018]

[0019] Where, L Σ is the equivalent inductance of the circuit connected to the output of the power amplifier; R Σ is the equivalent resistance of the circuit connected to the output terminal of the power amplifier;

[0020] Step S4: Solve the steady-state solution of the differential equation in step S3 to obtain the amplitude-frequency characteristic function of the circuit, namely:

[0021]

[0022] Step S5: Use the implicit function derivation method to find the equation in step S4 And make is 0, we get:

[0023]

[0024] Arranging the above formula, we get:

[0025]

[0026] Step S6: Substitute the sorted expression obtained in Step S5 into the amplitude-frequency characteristic function of the circuit in Step S4, and solve for the angular frequency ω0 corresponding to the maximum charge amplitude, that is:

[0027]

[0028] Step S7: Considering the change amounts ΔL1, ΔL2, ΔR1, and ΔR2 of the equivalent parameters of the transmitting coil and the receiving coil caused by the metal obstacle, obtain the shifted angular frequency ω1, that is:

[0029]

[0030] where

[0031]

[0032] In the formula, L Σ ’ is the equivalent inductance of the circuit connected to the output end of the power amplifier after the change; R Σ ’ is the equivalent resistance of the circuit connected to the output end of the power amplifier after the change, L ref is the intermediate variable of the inductance part, R ref is the intermediate variable of the resistance part;

[0033] Step S8: Let ω1 = ω0, and obtain the equation about the compensation capacitor C1, that is:

[0034]

[0035] The values of L1 and L2 are determined by winding the coil, and the value of C2 needs to satisfy Adjust the compensation capacitor C1 to make the equation in Step S8 hold, and obtain the value of the compensation capacitor C1, thereby completing the design of the wireless power transmission system. This wireless power transmission system can suppress the influence caused by non-ferromagnetic metal obstacles, and thus improve the power transmission efficiency.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects: The wireless power transmission system capable of automatically compensating for the influence of metal obstacles provided by the present invention uses a voltage-controlled variable capacitor to change the frequency characteristics of the system without adding additional components and feedback networks, improves the energy transmission efficiency of wireless power transmission, has high safety, and broad market prospects. Brief Description of the Drawings

[0037] Figure 1 is the structural diagram of the wireless power transmission system of the present invention;

[0038] Figure 2 is the schematic diagram of the positions of the transmitting coil, the receiving coil, and the metal obstacle of the present invention;

[0039] Figure 3 is the equivalent circuit diagram of the metal obstacle considered in the present invention;

[0040] Figure 4 is the equivalent circuit diagram of the transmitting circuit of the metal obstacle considered in the present invention;

[0041] Figure 5 is the data analysis diagram of the power transmission efficiency in the embodiment of the present invention. Detailed implementation manners

[0042] In order to make the content and advantages of the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0043] As Figure 1 shown, the signal generator provides high-frequency sinusoidal alternating current for the entire wireless power transmission system; the power amplifier amplifies and converts the sinusoidal signal output by the signal generator into alternating current suitable for the system requirements; the voltage-controlled variable capacitor is used to change the frequency characteristics of the wireless power transmission system to compensate for the influence of the metal obstacle on the system, and forms an equivalent variable capacitor C in parallel with the compensation capacitor one (NEW) ; the transmitting coil is used to convert high-frequency sinusoidal alternating current into magnetic field energy and transmit it to the receiving coil.

[0044] The non-ferromagnetic metal plate is located between the transmitting coil and the receiving coil, and its positional relationship is as Figure 2 shown; the receiving coil is used to convert the magnetic field energy emitted by the transmitting coil into electrical energy; and the resonance frequency of the receiving coil is matched with the frequency of the sinusoidal signal output by the signal generator through the compensation capacitor two; the load is connected in series with the compensation capacitor two.

[0045] As Figure 3 shown, in order to solve the technical problems existing in the prior art, extensive exploration has been carried out. When a non-ferromagnetic metal obstacle is located between the transmitting coil and the receiving coil, it can be regarded as a form of series connection of an inductor and a resistor in the circuit, and has a coupling relationship with the coil. For a wireless power transmission system including a non-ferromagnetic metal obstacle, its KVL equation set is:

[0046]

[0047] In the formula, i1, i2, and i3 are the currents of the transmitting coil, the receiving coil, and the equivalent current induced on the metal obstacle respectively; L1 and L2 are the self-inductances of the transmitting coil and the receiving coil respectively; L ob is the equivalent inductance of the metal obstacle; R1 and R2 are the equivalent series resistance of the transmitting coil and the equivalent series internal resistance of the receiving coil respectively; R L is the load resistance; R obis the equivalent resistance of the metal obstacle; u c(NEW) is the equivalent variable capacitance C (NEW) is the voltage across both ends; u c2 is the voltage across the compensation capacitor C2; M is the mutual inductance between the transmitting coil and the receiving coil; M 1ob and M 2ob are respectively the equivalent mutual inductance between the metal obstacle and the transmitting coil and the equivalent mutual inductance between the metal obstacle and the receiving coil; u s is the output voltage of the power amplifier, that is, u s = U s cos(ωt), U s is the amplitude of the output voltage of the power amplifier, ω is the angular frequency of the output voltage waveform of the signal generator, ω = 2πf; decouple the part of the metal obstacle in the circuit from the transmitting coil and the receiving coil to obtain:

[0048]

[0049] where

[0050]

[0051] In the formula, ΔL1 and ΔR1 are respectively the change in the equivalent inductance of the transmitting coil caused by the metal obstacle and the change in the equivalent resistance of the transmitting coil caused by the metal obstacle; ΔL2 and ΔR2 are respectively the change in the equivalent inductance of the receiving coil caused by the metal obstacle and the change in the equivalent resistance of the receiving coil caused by the metal obstacle;

[0052] The Coulomb-voltage characteristic curve of the voltage-controlled variable capacitor is expressed as u1(q) = a1q + a3q 3 , where a1 and a3 are both constant coefficients, which can be determined by the parameters of the voltage-controlled variable capacitor, u1 is the voltage across the voltage-controlled variable capacitor, q is the electric charge stored in the voltage-controlled variable capacitor, expressed as q = Qcos(ωt + θ), where Q is the amplitude of the electric charge stored in the voltage-controlled variable capacitor. On this basis, establish the KVL equation of the transmitting circuit without the metal obstacle, that is:

[0053]

[0054] where

[0055]

[0056] In the formula, L Σ is the equivalent inductance of the circuit connected to the output end of the power amplifier; R Σ is the equivalent resistance of the circuit connected to the output end of the power amplifier. The steady-state solution of the above equation is the amplitude-frequency characteristic function:

[0057]

[0058] Use the implicit function differentiation method to obtain and let be 0, and we get:

[0059]

[0060] Rearrange the above formula to get:

[0061]

[0062] Substitute Q 2 the rearranged expression obtained from the expression of into the amplitude-frequency characteristic function, and solve for the angular frequency ω0 corresponding to the maximum charge amplitude, that is:

[0063]

[0064] Furthermore, considering Figure 4 the changes in the equivalent parameters ΔL1, ΔL2, ΔR1, and ΔR2 of the transmitting coil and the receiving coil caused by the metal obstacle in, we get the offset angular frequency ω1, that is:

[0065]

[0066] where

[0067]

[0068] In the formula, L Σ ’ is the equivalent inductance of the circuit connected to the output end of the power amplifier after the change; R Σ ’ is the equivalent resistance of the circuit connected to the output end of the power amplifier after the change, L ref is an intermediate variable of the inductance part, and R ref is an intermediate variable of the resistance part;

[0069] Let ω1 = ω0, and we get an equation about the compensation capacitor C1, that is:

[0070]

[0071] Adjust the compensation capacitor C1 to make the above equation hold, and obtain the value of the compensation capacitor C1, thereby completing the design of the wireless power transmission system. This wireless power transmission system can suppress the influence caused by non-ferromagnetic metal obstacles, and thus effectively improve the power transmission efficiency.

[0072] Based on the system platform built thereby, relevant experimental data are obtained. The data analysis is as Figure 5 shown. It can be seen that the present invention greatly improves the power transmission efficiency when the metal obstacle is located at different positions.

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A wireless power transmission system capable of automatically compensating for the influence of metal obstacles, characterized in that It includes a signal generator, a power amplifier, a voltage-controlled variable capacitor, a compensation capacitor 1, a compensation capacitor 2, a transmitting coil, a receiving coil and a load. The output end of the signal generator is connected to the input end of the power amplifier. The voltage-controlled variable capacitor and the compensation capacitor 1 are connected in parallel to form an equivalent variable capacitor C (NEW) , and this equivalent variable capacitor C (NEW) is connected in series with the transmitting coil to form a transmitting circuit, and the two ends of the transmitting circuit are correspondingly connected to the output end of the power amplifier; the receiving coil and the compensation capacitor 2 are connected in series to form a receiving circuit, and the two ends of this receiving circuit are correspondingly connected to the two ends of the load; the transmitting coil is used to convert electrical energy into magnetic field energy and transmit it to the receiving coil, the voltage-controlled variable capacitor is used to change the frequency characteristics of the wireless power transmission system, suppress the influence of the equivalent parameter changes of the transmitting coil and the receiving coil caused by non-ferromagnetic metal obstacles, and the receiving coil is used to receive the magnetic field energy transmitted by the transmitting coil and convert it into electrical energy; The specific design steps of the wireless power transmission system that can automatically compensate for the influence of metal obstacles are as follows: Step S1: Establish the KVL equations of the wireless power transmission system considering metal obstacles, that is: Where, i1, i2, and i3 are the currents of the transmitting coil, the receiving coil, and the equivalent current induced on the metal obstacle, respectively; L1 and L2 are the self-inductances of the transmitting coil and the receiving coil, respectively; L ob is the equivalent inductance of the metal obstacle; R1 and R2 are the equivalent series resistance of the transmitting coil and the equivalent series internal resistance of the receiving coil, respectively; R L is the load resistance; R ob is the equivalent resistance of the metal obstacle; u c(NEW) is the voltage across the equivalent variable capacitor C (NEW) ; u c2 is the voltage across the compensation capacitor C2; M is the mutual inductance between the transmitting coil and the receiving coil; M 1ob and M 2ob are the equivalent mutual inductances between the metal obstacle and the transmitting coil and between the metal obstacle and the receiving coil, respectively; u s is the output voltage of the power amplifier, i.e., u s = U s cos(ωt), U s is the amplitude of the output voltage of the power amplifier, ω is the angular frequency of the output voltage waveform of the signal generator, ω = 2πf; Step S2: Combine the equations in Step S1 to obtain: Where In the formula, ΔL1 and ΔR1 are the change in the equivalent inductance of the transmitting coil caused by the metal obstacle and the change in the equivalent resistance of the transmitting coil caused by the metal obstacle, respectively; ΔL2 and ΔR2 are the change in the equivalent inductance of the receiving coil caused by the metal obstacle and the change in the equivalent resistance of the receiving coil caused by the metal obstacle, respectively; Step S3: The Coulomb-voltage characteristic curve of the voltage-controlled variable capacitor is expressed as u1(q) = a1q + a3q 3 , where a1 and a3 are both constant coefficients determined by the parameters of the voltage-controlled variable capacitor. u1 is the voltage across the voltage-controlled variable capacitor, and q is the electric charge stored in the voltage-controlled variable capacitor, expressed as q = Qcos(ωt + θ), where Q is the amplitude of the electric charge stored in the voltage-controlled variable capacitor. On this basis, the KVL equation of the transmitting circuit without metal obstacles is established, that is: Where where L Σ is the equivalent inductance of the circuit connected to the output terminal of the power amplifier; R Σ is the equivalent resistance of the circuit connected to the output terminal of the power amplifier; Step S4: Solve the steady-state solution of the differential equation in Step S3 to obtain the amplitude-frequency characteristic function of the circuit, that is: Step S5: Use the implicit differentiation method to find the derivative of the equation in step S4 And let be 0, we get: Rearrange the above formula to obtain: Step S6: Substitute the rearranged expression obtained in Step S5 into the amplitude-frequency characteristic function of the circuit in Step S4, and solve for the angular frequency ω0 corresponding to the maximum value of the charge amplitude, that is: Step S7: Considering the change amounts ΔL1, ΔL2, ΔR1, and ΔR2 of the equivalent parameters of the transmitting coil and the receiving coil caused by the metal obstacle, obtain the offset angular frequency ω1, that is: Where Wherein, L Σ ’ is the equivalent inductance of the circuit connected to the output terminal of the power amplifier after change; R Σ ’ is the equivalent resistance of the circuit connected to the output terminal of the power amplifier after change, L ref is the intermediate variable of the inductance part, and R ref is the intermediate variable of the resistance part; Step S8: Let ω1 = ω0 to obtain an equation about the compensation capacitor C1, that is: The values of L1 and L2 are determined by winding the coil, and the value of C2 needs to satisfy Adjust the compensation capacitor C1 to make the equation in step S8 hold, and obtain the value of the first compensation capacitor C1, thereby completing the design of the wireless power transmission system. This wireless power transmission system can suppress the influence caused by non-ferromagnetic metal obstacles, and further improve the power transmission efficiency.

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