Nonlinear resonance wireless power transmission method

Abstract

The invention discloses a nonlinear resonant wireless power transmission method in the field of magnetic coupling resonant wireless power transmission, which mainly solves the problem that the magnetic coupling resonant wireless power transmission technology is easy to generate a frequency splitting phenomenon in an over-coupling state and breaks through the limitation of a linear transmission system. Transmission characteristics of a transmission system are improved by incorporating a non-linear inductor into a receiving resonant topology. Under the same frequency condition, the nonlinear resonant wireless power transmission method can delay the critical coupling state of the transmission system, and has an obvious effect on suppressing the frequency splitting phenomenon.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetically coupled resonant wireless power transmission, and relates to a nonlinear resonant wireless power transmission system, and in particular to a method for improving the transmission characteristics of the wireless power transmission system through a nonlinear resonant topology and suppressing the frequency splitting phenomenon of the wireless power transmission system. Background Art

[0002] In the early days of the concept of wireless power transmission technology, researchers mainly used microwave and inductive wireless power transmission methods. Although both methods can achieve wireless transmission of electric energy, microwave wireless power transmission is easily affected by the natural environment, and inductive wireless power transmission technology has low transmission efficiency, so the development of wireless power transmission technology is slow. With the emergence and development of magnetic coupling resonant wireless power transmission technology, researchers' attention has shifted to this transmission method. This technology uses the resonance principle, and the transmitter and receiver can achieve efficient power transmission under the condition of strong magnetic field coupling. Its high efficiency, large transmission distance, less impact on the human body, and easy implementation have made the magnetic coupling resonant wireless power transmission technology develop rapidly. It has been applied to many fields of society, such as mine production, electronic medical care, electric vehicles, etc. However, as the coupling distance of this transmission method decreases, its transmission efficiency will gradually produce frequency splitting phenomenon, which seriously reduces the transmission efficiency of this technology. In order to suppress the influence of frequency splitting, researchers have proposed a number of suppression methods for magnetic coupling resonant wireless power transmission systems: manually changing the distance between the transceiver coils, using optimization algorithms to optimize system parameters in real time, and using frequency tracking control and impedance matching. However, these methods can only suppress the occurrence of frequency splitting under certain conditions, and are difficult to implement. They are difficult to use as solutions for practical engineering applications, and there are still the following problems:

[0003] 1. The method of manually changing the distance between the transceiver coils is simple in principle and easy to operate, but manual adjustment cannot accurately make the system work at the highest transmission efficiency point, which reduces the utilization efficiency and cannot be used for actual engineering applications. Especially for transmission systems in special environments, the complex environment makes this method impossible to put into practice and can only be used for simple operations in the laboratory.

[0004] 2. For the method of optimizing system parameters in real time using an optimization algorithm, when the parameters change greatly, the algorithm may fall into a local optimum during program operation, resulting in the final converged value not being the global optimal solution, thereby reducing the effect of the system in improving transmission efficiency and making it impossible to suppress frequency splitting.

[0005] 3. The use of frequency tracking control and impedance matching methods will introduce too many inductance and capacitance components, which will not only make it difficult to derive the system transmission efficiency formula and make it impossible to conduct a qualitative analysis of the transmission system, but will also increase the order of the system, increase system losses, and lead to a decrease in overall transmission efficiency.

[0006] At the same time, the above methods are all based on linear wireless power transmission systems. After years of research and application, their performance improvement potential is not great. Based on the above research status, we must find a new research method to better suppress the occurrence of frequency splitting. Summary of the invention

[0007] The technical problem to be solved by the present invention is: the purpose of the present invention is to address the problem that traditional magnetically coupled resonant wireless power transmission systems are prone to frequency splitting in an over-coupled state, resulting in a serious reduction in the transmission efficiency of the transmission system, and considering that the existing solutions are all based on linear transmission systems, the present invention breaks through the limitations of linear systems and proposes a nonlinear resonant wireless power transmission method, which can better improve the transmission characteristics of the transmission system, suppress the frequency splitting phenomenon in the wireless power transmission system, and better meet the transmission power requirements of the equipment.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions:

[0009] The nonlinear resonance wireless power transmission system described in the present invention comprises a transmitting part and a receiving part.

[0010] The transmitting part includes a DC power supply, a transmitting resonant topology, and an inverter.

[0011] The inverter is used to generate a high-frequency signal, an output end of which is connected to a transmitting resonant topology, and an input end of which is connected to a direct current power supply.

[0012] The transmit resonant topology includes a transmit coil and a capacitor.

[0013] The receiving part includes a receiving resonant topology, a nonlinear resonant circuit and a load.

[0014] The nonlinear resonant circuit is composed of a nonlinear inductor with a PC40 ferrite as a magnetic core, and is used to provide nonlinear characteristics for the transmission system.

[0015] The receiving resonant topology includes a receiving coil and a capacitor.

[0016] The load may be a DC or AC load device, but a DC load should be rectified by a rectifier device to provide power for it.

[0017] The transmitting coil and the receiving coil are both wound by Litz wire of the same diameter. The two coils have equal diameters and the same number of turns, so that the transmitting and receiving parts of the transmission system have the same natural frequency and the equivalent resistance of the transmitting and receiving coils is the same.

[0018] The distance between the transmitting coil and the receiving coil is adjustable. By adjusting the distance between the transmitting and receiving coils, the mutual inductance value M between the two coils is changed, so that the system works in a critical coupling state.

[0019] The nonlinear resonant wireless power transmission system is powered by a DC power supply, which obtains a high-frequency current signal through an inverter and transmits it to a receiving part through a transmitting coil. After nonlinear inductance adjustment, better transmission characteristics can be obtained and power can be supplied to the load.

[0020] The nonlinear resonant wireless power transmission system includes a DC power supply, an inverter, a transmitting resonant topology, a receiving resonant topology, a nonlinear resonant topology and a load. The nonlinear resonant wireless power transmission method includes the following steps:

[0021] (1) Analyze the critical coupling state of the traditional magnetic coupling wireless power transmission system: Establish an equivalent circuit model of the transmission system and simplify it to obtain the corresponding equivalent Thevenin circuit. After analyzing the equivalent circuit, the equivalent impedance of the circuit can be obtained: In this method, the transmitting and receiving coils use the same components, so R1 = R2 = R, L1 = L2 = L, C1 = C2 = C, and M is the mutual inductance of L1 and L2. In order to maximize the transmission efficiency of the system, the topology of the transmitting and receiving coils should meet the impedance matching. That is, Z eq The imaginary part is 0. Based on this condition, the critical coupling state condition is: At the same time, according to the maximum output power law, the maximum output power condition can be obtained:

[0022] (2) Determine the component parameters of the traditional magnetic coupling wireless power transfer system by Determine the critical coupling distance of the transmission system, where μ0 is the vacuum permeability, r is the radius of the two coils, N is the number of turns of the two mutual inductance coils, and d is the distance between the two coils (axially symmetric).

[0023] (3) Maxwell is used to calculate the characteristic parameters of the nonlinear inductor, where the nonlinear inductor uses PC40 ferrite as the magnetic core. The actual parameters of the nonlinear inductance value H of the nonlinear inductor model at different current I sizes can be obtained, and the obtained parameters are plotted, laying the foundation for the method.

[0024] (4) The nonlinear inductor is incorporated into the receiving coil of the transmission system to form a nonlinear resonant wireless power transmission system, and the nonlinear inductor parameters obtained in step (3) of the method are set, and the mutual inductance value M of the nonlinear resonant wireless power transmission system is determined to be under the critical coupling condition value.

[0025] The beneficial effects of the present invention are:

[0026] 1. The nonlinear transmission system has better frequency characteristics than the linear transmission system, and can effectively suppress the frequency splitting phenomenon caused by the linear transmission system, which effectively solves the shortcomings of several existing methods for suppressing the frequency splitting phenomenon.

[0027] 2. The method does not require frequent manual changes in system parameters, does not increase the system order, has a simple structure, and does not require the use of complex optimization algorithms. It is more in line with the modeling background of the transmission system under realistic conditions and is more suitable for practical engineering applications. It provides a new perspective and method for solving the frequency splitting phenomenon of the magnetically coupled resonant wireless power transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the composition of the nonlinear resonant wireless power transmission system.

[0029] Figure 2 This is the equivalent circuit model diagram of the nonlinear resonant wireless power transmission system.

[0030] Figure 3 This is the nonlinear resonance characteristic diagram.

[0031] Figure 4 The output efficiency characteristic diagram of the method for a nonlinear resonant wireless power transfer system example. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, specific implementations of the present invention are described in detail below with reference to the accompanying drawings.

[0033] Figure 1 Schematic diagram of the nonlinear resonant wireless power transmission system of the method. Figure 1 As shown, the nonlinear resonant wireless power transmission system of the present invention includes a DC power supply, an inverter, a transmitting resonant topology, a receiving resonant topology, a nonlinear resonant topology and a load. After passing through the inverter, the DC power supply can obtain a high-frequency AC current, which is connected to the transmitting resonant topology, and the electromagnetic induction law is used to transmit the electric energy to the receiving resonant topology, and then the nonlinear resonant topology is used to improve the transmission characteristics of the system. The electric energy is transmitted to the AC load to power the load.

[0034] Figure 2is the equivalent circuit diagram of the nonlinear resonant wireless power transmission system, such as Figure 2 As shown, the nonlinear resonant transmission system adopted by the method is improved on the basis of the traditional SS transmission system structure, and the nonlinear inductor is incorporated into the secondary resonant topology. The equivalent internal resistance of the transmitting end is R1, L1 and C1 constitute the transmitting end resonant circuit, R2 is the equivalent internal resistance of the receiving end, and R L is the load resistor, L2, C2, and L3 form a receiving end resonant circuit, and M is the mutual inductance of inductors L1 and L2. When nonlinear inductance is incorporated into the resonant circuit, the system will produce nonlinear resonance. This phenomenon is also called ferromagnetic resonance, which is a common phenomenon in power transmission systems: the voltage transformer with an iron core is regarded as a nonlinear inductor. Due to the existence of ground capacitance of the transmission line, it can form a nonlinear resonant circuit with the nonlinear inductor, which will lead to nonlinear resonance under certain conditions, thereby causing ferromagnetic resonance overvoltage, and this phenomenon has a self-maintaining effect. As long as the nonlinear resonance condition remains unchanged, the overvoltage will exist for a long time.

[0035] Figure 3 is the nonlinear resonance characteristic diagram, such as Figure 3 As shown, since the capacitance is linear, U C (I) is a straight line, while the nonlinear inductor will saturate when the current gradually increases. L (I) tends to be stable. Let ΔU = U L -U C According to the circuit, U L and U C The phase is opposite, when ωL>1 / ωC, U L >U C , at this time the circuit current is inductive; when ωL<1 / ωC, U L C , at this time the circuit current is capacitive; when ωL=1 / ωC, ΔU=0, at this time the circuit enters a nonlinear resonance state, and the circuit obtains a relatively large current. In addition, when ΔU=E, the system is in a state of equilibrium, so a1, a2, and a3 are three equilibrium points. By using the small perturbation method to analyze these three points, it can be found that the circuit can work stably at points a1 and a3. Therefore, the existence of nonlinear inductance makes the circuit have more than one stable point. When the transmission system increases with the current, the system resonates at multiple current value points, thereby reducing the number of frequency splitting phenomena in the system. At the same time, when the current rises to a certain level, it can be observed that U C (I) In a larger range of variation, U L (I) only changes slightly, so the nonlinear inductor can also play a certain voltage stabilizing role, which allows the system to maintain high-efficiency output over a large frequency range.

[0036] ​The method example is a wireless power transmission system under the condition of resonant frequency f=0.8MHz. The transmitting and receiving coils have the same structure, both are wound with 4mm Litz wire, the coil diameter is 400mm, the number of turns is 12, and the load size is 50Ω.

[0037] Figure 4 The transmission efficiency characteristic diagram of the method example is shown in FIG. The method example first determines the critical coupling distance at which the frequency splitting phenomenon occurs in the linear transmission system according to the critical coupling state condition value, keeps the coupling distance unchanged, incorporates the nonlinear resonant circuit into the receiving resonant topology, and plots the obtained results as shown in FIG. Figure 4 As shown in the figure, it can be seen that when the linear transmission system is in a critical coupling state, the transmission efficiency characteristic curve of the nonlinear transmission system still does not have the frequency splitting phenomenon. Therefore, by utilizing the ferromagnetic resonance characteristics brought by the nonlinear inductance to the transmission system, the transmission characteristics of the linear transmission system can be improved and the occurrence of the frequency splitting phenomenon can be suppressed.

[0038] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific implementation methods of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple replacements and changes can be made without departing from the design concept of the present invention, which should be regarded as belonging to the scope of protection involved in the claims submitted by the present invention.

Claims

1. A nonlinear resonant wireless power transmission method, which is implemented by changing a traditional magnetic coupling wireless power transmission system using a nonlinear resonant circuit. The nonlinear resonant wireless power transmission system includes a DC power supply, an inverter, a transmitting resonant topology, a receiving resonant topology, a nonlinear resonant topology and a load, and is characterized in that: The method comprises the following steps: (1) Analyze the critical coupling state of the traditional magnetic coupling wireless power transmission system: Establish an equivalent circuit model of the transmission system and simplify it to obtain the corresponding equivalent Thevenin circuit. After analyzing the equivalent circuit, the equivalent impedance of the circuit can be obtained: In this method, the transmitting and receiving coils use the same components, so R1 = R2 = R, L1 = L2 = L, C1 = C2 = C, and M is the mutual inductance of L1 and L2. In order to maximize the transmission efficiency of the system, the topology of the transmitting and receiving coils should meet the impedance matching. That is, Z eq The imaginary part is 0. Based on this condition, the critical coupling state condition is: At the same time, according to the maximum output power law, the maximum output power condition can be obtained: (2) Determine the component parameters of the traditional magnetic coupling wireless power transfer system by Determine the critical coupling distance of the transmission system, where μ0 is the vacuum permeability, r is the radius of the two coils, N is the number of turns of the two mutual inductance coils, and d is the distance between the two coils (axially symmetric). (3) Maxwell is used to calculate the characteristic parameters of the nonlinear inductor, where the nonlinear inductor uses PC40 ferrite as the magnetic core. The actual parameters of the nonlinear inductance value H of the nonlinear inductor model at different current I sizes can be obtained, and the obtained parameters are plotted, laying the foundation for the method. (4) Incorporating the nonlinear inductor into the receiving coil of the transmission system to form a nonlinear resonant wireless power transmission system, and setting the nonlinear inductor parameters obtained in step (3) of the method, and determining the mutual inductance value M of the nonlinear resonant wireless power transmission system to be under the critical coupling condition value.

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