Coil structure enclosed with active shield, and multipurpose optimization method therefor

Abstract

To provide a coil structure enclosed with an active shield, and a multipurpose optimization method therefor.SOLUTION: A coil structure enclosed with an active shield includes a primary coil 01 and active shield coils. The active shield coils are reversely connected in series outside the primary coil, and include an inner shielding coil 02 having a current direction the same as that of the primary coil and an outer shielding coil 03 having a current direction opposite to that of the primary coil. A multipurpose optimization method includes a step of constructing a finite element simulation model of an active shield coil and a wireless power transmission (WPT) system, a step of constructing an optimization proxy model by a data driving method, and a step of realizing multi-objective optimization design by taking the proxy model, a polynomial chaos proxy model as an objective function of a non-dominated sorting genetic algorithm (NSGA-II).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of wireless power transmission, and more particularly to a coil structure surrounded by an active shield and a multi-objective optimization method thereof. [Background technology]

[0002] Wireless power transfer (WPT) technology not only has the advantage of being extremely safe by preventing users from coming into contact with electrical interfaces and mechanical structures, but also has the advantages of convenient charging and space-saving. Therefore, wireless power transfer systems are widely used in various electrical and electronic devices, such as mobile phones, drones, electric bicycles, and electric vehicles.

[0003] However, as the charging power of wireless power transmission systems gradually increases, the leakage magnetic field between the coupling mechanisms can cause significant interference to surrounding electronic devices, and exposure to electromagnetic radiation poses safety risks to people. These issues limit the use of WPT in many fields.

[0004] Therefore, research into shielding technology for WPT systems is extremely important for ensuring safety against electromagnetic wave exposure in WPT.

[0005] Currently, magnetic shielding methods and active magnetic shielding methods are widely used, which use high-permeability magnetic materials to create low-reluctance paths for magnetic flux, or use eddy current counter-magnetic fields induced by non-ferromagnetic conductive materials to reduce leakage flux.

[0006] However, the aluminum plate shield used in the magnetic shielding method tends to generate heat, which increases the size, weight, and cost of the wireless power transmission system.

[0007] The active magnetic shielding method generates a canceling magnetic field in the opposite direction to the leakage magnetic field of the WPT through a shield coil, and has the advantages of flexible placement and good shielding effect.

[0008] Active magnetic shielding methods are divided into passive and active shielding, depending on whether an independent power supply is used. Active shielding devices require complex tuning circuits, and the impedance of the coil system changes significantly with temperature, making it difficult to match the current phase of the shield coil and primary coil in actual use. Both shielding methods reduce the magnetic field between the WPT magnetic coupling mechanism, leading to reduced transmission efficiency.

[0009] To ensure shielding effectiveness while minimizing the impact on transmission efficiency, many researchers have studied the design of WPT devices in combination with finite element simulation and optimization algorithms. While accurate simulation results can significantly reduce the time cost of multiple tests, finite element simulation requires long calculation times, and optimization algorithms require multiple iterations, resulting in high computational costs for optimized WPT device designs. Summary of the Invention [Problem to be solved by the invention]

[0010] SUMMARY OF THE INVENTION An object of the present invention is to provide a coil structure surrounded by an active shield and a multi-objective optimization method thereof in order to solve the problems raised in the background art above. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention employs the following technical means. A coil structure surrounded by an active shield, comprising a primary coil; are connected in reverse series outside the primary coil, The direction of the current is the same as that of the primary coil, and the inner shield coil is used to compensate for the transmission efficiency of the WPT system. The direction of the current is opposite to that of the primary coil, and an outer shield coil is used to weaken the magnetic induction strength around the coil structure area. The antenna further comprises an active shielding coil, including:

[0012] A multi-objective optimization method for a coil structure surrounded by an active shield, comprising: Building a finite element simulation model of the active shield coil and WPT system based on the coil structure surrounded by the active shield; constructing a polynomial chaos surrogate model of the optimization objective in a data-driven manner based on the optimization variables and the optimization horizon; The constructed polynomial chaos surrogate model is used as the objective function of the NSGA-II algorithm to realize the multi-objective optimization design of the active shielding coil; The above method, comprising:

[0013] The optimization variables are the radius r of the inner shield coil, in , the spacing d between the shield coils on the same side, and the vertical distance h between the shield coil and the primary coil.

[0014] The optimization objectives are the amount of change Δη in the WPT system transmission efficiency and the maximum value of the magnetic flux on the observation plane A1.

[0015] In addition, the polynomial chaos surrogate model includes Δη and B max surrogate models are included.

[0016] Furthermore, specific steps of the method include: Using the finite element simulation model as the original model y(ξ), the original model is expanded using the PCE method to obtain the following equation 1.

[0017]

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[0018] Step 2: Assuming that TIFF2025146611000006.tif13170 is a polynomial corresponding to the input variables, we obtain the following equation 2.

[0019]

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[0020] A step of constructing a corresponding orthogonal polynomial basis according to the moment of the degree of each input variable, and obtaining the following Equations 3 and 4 based on the orthogonality conditions of the polynomials.

[0021]

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[0024]

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[0027] Data-driven arbitrary distribution orthogonal polynomial base coefficients After obtaining TIFF2025146611000017.tif16170, continue building the surrogate model from Equation 1, truncate Equation 1, and calculate the truncated polynomial coefficients using the regression method. [Effects of the Invention]

[0028] Compared to the prior art, the advantages of the present invention include: By combining it with a surrogate model to perform multi-objective optimization of the active shielding coil, the time cost of the optimization process can be significantly reduced, and the active shielding coil can effectively weaken the leakage magnetic field of the WPT system in the target area, achieving good shielding effect. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a coil structure surrounded by an active shield of the present invention; [Figure 2](a) A diagram showing a conventional coil structure; (b) A diagram showing an active coil structure connected in anti-series to a primary coil; (c) A diagram showing a shield structure having two active coils; and (d) A diagram showing a coil structure surrounded by an active shield provided by the present invention. [Figure 3] (a) is a diagram showing a WPT system simulation model equipped with an active shield coil on one side, and (b) is a schematic diagram showing the distance relationship between the shield coil and the primary coil. [Figure 4] 1 is a flowchart of the multi-objective optimization design of the coil structure surrounded by the active shield of the present invention. [Figure 5] FIG. 1 is a Pareto front diagram of COMSOL and metamodel in the present invention. [Figure 6] FIG. 1 is a comparison diagram of various algorithm Pareto fronts in the present invention. [Figure 7] Photographs of a WPT system equipped with the active shield coil of the present invention: (a) a coil and a receiving coil surrounded by the active shield, and (b) a coil and a transmitting coil surrounded by the active shield. [Figure 8] (a) Magnetic flux density results for observation surface A1 without a shield, (b) Magnetic flux density results for observation surface A2 without a shield. [Figure 9] (a) Magnetic flux density results for observation surface A1 with an active shield, (b) Magnetic flux density results for observation surface A2 with an active shield. DETAILED DESCRIPTION OF THE INVENTION

[0030] In order to clarify the objectives, technical means and advantages of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings and embodiments. It will be understood that the specific embodiments described herein are only used to interpret the present invention and are not intended to limit the present invention.

[0031] Hereinafter, specific implementations of the present invention will be described in detail with reference to specific embodiments.

[0032] As shown in FIG. 1, a coil structure surrounded by an active shield is provided according to an embodiment of the present invention, comprising a primary coil 01, It is connected in reverse series outside the primary coil 01, The direction of the current is the same as that of the primary coil 01, and the inner shield coil 02 compensates for the transmission efficiency of the WPT system. The direction of the current is opposite to that of the primary coil 01, and an outer shield coil 03 is used to weaken the magnetic induction strength around the coil structure area. The antenna further includes an active shielding coil including:

[0033] In the embodiment of the present invention, the operation principle of the proposed coil structure will be explained by comparing it with a conventional coil structure as shown in FIG.

[0034] FIG. 2(a) shows a conventional coil structure, which does not have a shielding structure, and therefore a large leakage magnetic field occurs between the transmitting coil and the receiving coil.

[0035] Figure 2(b) shows an active coil structure connected in anti-series to the primary coil 01, where the current direction is opposite to that of the primary coil 01, which has a better shielding effect, but at the same time it also weakens the magnetic field between the transmitting coil and the receiving coil, which has a significant negative impact on the efficiency of the WPT system.

[0036] Figure 2(c) shows a shielded structure with two active coils, in which the active coils are powered by an independent system, and the impact on the efficiency of WPT is low, but it is difficult to match the current phase of the shield coil and the primary coil O1 during actual operation.

[0037] Figure 2(d) shows the coil structure surrounded by an active shield provided by the present invention. The coil structure surrounded by an active shield has a double-layer coil, which is connected in reverse series with the primary coil 01. The current direction of the inner shield coil 02 is the same as the current in the primary coil 01, thereby generating a magnetic field in the same direction as the primary coil 01, which has the effect of compensating for the transmission efficiency of the WPT system. The current direction of the outer layer shield coil and the primary coil 01 is opposite, which weakens the strength of the magnetic field outside the coil, thereby providing a shielding effect.

[0038] A multi-objective optimization method for a coil structure surrounded by an active shield is provided according to an embodiment of the present invention, comprising the steps of: The method includes constructing a finite element simulation model of the active shield coil and WPT system based on a coil structure surrounded by an active shield, and constructing a polynomial chaos surrogate model for optimization purposes in a data-driven manner based on optimization variables and optimization intervals.

[0039] The optimization variables are the radius r of the inner shield coil O2 in , the spacing d between the shield coils on the same side, and the vertical distance h between the shield coil and the primary coil O1. The optimization objective is the change Δη in the WPT system transmission efficiency and the maximum magnetic flux value on the observation plane A1, and the leakage magnetic field on the observation plane of the optimized WPT system is minimized, and the impact on the transmission efficiency is also minimized.

[0040] The constructed polynomial chaos surrogate model is used as the objective function of the Non-Dominated Sorting Genetic Algorithms-II (NSGA-II) to realize multi-objective optimization design of the active shield coil.

[0041] In an embodiment of the present invention, referring to Figure 3, the transmitting coil of the WPT system and the transmitting active shield coil connected in series to the transmitting coil are wound with twisted wire having a diameter of 3.7 mm, the transmitting coil has 14 turns and an outer diameter of 198 mm.

[0042] The receiving coil and the receiving-side active shield coil connected in series to the receiving coil are wound with twisted wire having a diameter of 2.9 mm, the receiving coil has 18 turns, and its outer diameter is 148 mm.

[0043] In the simulation model, the operating distance between the transmitting coil and the receiving coil is 40 mm, the resonant circuit is a series compensation circuit, the operating frequency is 70 kHz, the resistance value of the load resistor is 2.8 Ω, and the output power is 300 W.

[0044] Take the WPT system simulation model with an active shield coil on one side as an example, where r in is the radius of the inner shield coil O2, d is the spacing between the shield coils on the same side, h is the vertical distance between the shield coil and the primary coil O1, the coil material is copper, and there is a magnetic shield made of ferrite under the primary coil O1.

[0045] In order to verify the shielding effect of the coil surrounded by the active shield, two observation planes A1 and A2 are set in the simulation model. A1 is perpendicular to the plane on which the primary coil O1 is located, and A2 is parallel to the plane on which the primary coil O1 is located. The distance to the center of the WPT primary coil O1 is 500 mm (d m =500mm), and the size is 500mm x 200mm (S x =200mm,S y =500mm,S z = 200 mm), and point O is a measurement point on the observation plane A1.

[0046] Referring to FIG. 4, there is shown a design flowchart of a multi-objective optimization method for a coil structure surrounded by an active shield.

[0047] This invention uses the NSGA-II algorithm to perform multi-objective optimization design of the active shield coil, first initializing the population and then calculating the fitness of the objective function. It is important to note that this invention uses data-driven polynomial chaos to calculate the change in transmission efficiency Δη of the WPT system equipped with the active shield coil and the maximum magnetic induction strength B of the observation surface. max A surrogate model of the NSGA-II algorithm is constructed and used as the objective function of the NSGA-II algorithm.

[0048] A fast dominance sort is performed according to the fitness of the objective function, and a congestion degree is calculated to generate a new parent population. The algorithm enters an iterative cycle, performing selection, crossover, and mutation on the population, recalculating the fitness of the objective function, performing a fast non-dominated sort on the fitness result, calculating the congestion degree to generate a temporary offspring population, combining the temporary offspring population with the parent population, selecting and generating a new offspring population, and determining whether the number of iterations has reached a default value. If so, the iterative cycle is terminated, and the optimization result for the active shielding coil structure is obtained.

[0049] The optimization variables and optimization ranges of the active shield coil are shown in Table 1.

[0050] [Table 1]

[0051] In a preferred embodiment of the present invention, the polynomial chaos surrogate model includes Δη and B max surrogate models are included.

[0052] In a preferred embodiment of the present invention, the specific steps of the method are as follows: Using the finite element simulation model as the original model y(ξ), the original model is expanded using the PCE method to obtain the following equation 1.

[0053]

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[0054] Unlike probability-driven methods, data-driven methods are not restricted by the distribution type of the variables, and prior art techniques use moments of finite data of one-dimensional variables to construct the corresponding orthogonal polynomial basis.

[0055] Step 2: Assuming that TIFF2025146611000023.tif13170 is a polynomial corresponding to the input variables, we obtain the following equation 2.

[0056]

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[0057] A step of constructing a corresponding orthogonal polynomial basis according to the moment of the degree of each input variable, and obtaining the following Equations 3 and 4 based on the orthogonality conditions of the polynomials.

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[0064] This allows data-driven arbitrary distribution orthogonal polynomial base coefficients After obtaining TIFF2025146611000034.tif16170, we can continue to build a surrogate model from Equation 1, truncate Equation 1, and use the regression method to calculate the truncated polynomial coefficients.

[0065] Example 1 A simulation model of the WPT system and active shielding coil was constructed using the finite element simulation software comsol, and the simulation model was run on an Intel 13900k processor, taking 5 minutes to obtain the corresponding simulation results.A data-driven method was used to construct a surrogate model (Metamodel by Date Driven) of the objective function.

[0066] To verify the accuracy of the surrogate model as the objective function, the present invention first uses the comsol simulation model as the objective function, sets the number of iterations of the NSGA-II algorithm to 30, and the number of populations to 30, and performs a multi-objective optimization calculation using the surrogate model as the objective function. The number of iterations and the number of populations are both 30. The Pareto front diagrams calculated using the two methods are shown in Figure 5, and the statistical characteristic parameters of the optimization results are listed in Table 2. It can be seen that the optimal values ​​calculated by the two methods are very close, and the mean values ​​and standard deviations of the optimization results are basically consistent, proving that the surrogate model is suitable as a substitute for the simulation model.

[0067] However, the calculation time for multi-objective optimization using the surrogate model as the objective function was 12 seconds, while the calculation time for the simulation model as the objective function was 75 hours.

[0068] Due to the computational speed of the surrogate model, the present invention selected the multi-objective artificial hummingbird algorithm and the multi-objective gray wolf algorithm for comparison. The number of algorithm iterations was set to 400, and the population size was set to 50. The comparison results of the calculated Pareto front are shown in Figure 6, and the parameters and computational costs of the optimization results are listed in Table 3.

[0069] The optimal results of the three algorithms are circled in Figure 6. After comparison, it can be seen that the results of the NSGA-II algorithm are superior to the other algorithms, so the present invention also used the NSGA-II algorithm to carry out the optimization design. Taking into account the shielding effect of the active shield coil and its impact on transmission efficiency, the result of the NSGA-II algorithm in Figure 6 was selected as the design value.

[0070] [Table 2]

[0071] [Table 3]

[0072] Referring to the above optimization results, a WPT system equipped with an active shield coil was constructed as shown in Figure 7. Figure 7(a) shows the coil and receiving coil surrounded by the fabricated active shield, and Figure 7(b) shows the coil and transmitting coil surrounded by the fabricated active shield, which were tested and verified from an actual test angle.

[0073] Shielding effectiveness test: The observation surface was divided into 5x4 squares, and the magnetic flux density value of each square was measured with an electromagnetic radiation analyzer without and with the coil surrounded by the active shield, and the comparison results are shown in Figure 8 and Figure 9. The results show that the magnetic flux density of the WPT system with the active shield at the observation surface position was significantly reduced.

[0074] Table 4 shows parameters such as the self-inductance and transmission efficiency of the coil before and after it is surrounded by an active shield. The results in the table show that the changes in transmission efficiency are basically consistent with the optimized calculation results. Measurements taken at the observation point positions of the simulation model showed that the leakage magnetic field was reduced by 87.02%, demonstrating the effectiveness of the coil structure surrounded by an active shield and the optimized design method proposed by this invention.

[0075] [Table 4]

[0076] The above is merely a preferred embodiment of the present invention, and it should be noted that a person skilled in the art may make some modifications and improvements without departing from the technical idea of ​​the present invention, and such modifications and improvements shall also be considered to be included in the protection scope of the present invention, and shall not affect the effect of the implementation of the present invention or the practicability of the patent. [Explanation of symbols]

[0077] 01 Primary coil 02 Inner shield coil 03 Outer shield coil

Claims

1. A multi-objective optimization method for a coil structure surrounded by an active shield, comprising: The method is based on an active shielded coil structure, the active shielded coil structure comprising a primary coil; connected in anti-series outside the primary coil, The present invention further includes an active shield coil including an inner shield coil, the direction of which is the same as the direction of the current in the primary coil, for compensating for the transmission efficiency of the WPT system, and an outer shield coil, the direction of which is opposite to the direction of the current in the primary coil, for weakening the magnetic induction strength around the coil structure area; The method comprises: constructing a finite element simulation model of the active shield coil and the WPT system based on a coil structure surrounded by the active shield; constructing a polynomial chaos surrogate model of the optimization objective in a data-driven manner based on the optimization variables and the optimization horizon; and realizing a multi-objective optimization design of the active shield coil using the constructed polynomial chaos surrogate model as an objective function of the NSGA-II algorithm; The optimization variables are the radius r of the inner shield coil, in , the spacing d between the shield coils on the same side and the vertical distance h between the shield coils and the primary coil; The optimization objective is to determine the change Δη in the transmission efficiency of the WPT system and the observation plane A 1 is the maximum magnetic flux value, The polynomial chaos surrogate model includes Δη and observation plane A 1 Maximum magnetic induction strength B max surrogate models of Multi-objective optimization method for coil structures surrounded by active shielding.

2. The specific steps are: The finite element simulation model is used as an original model y(ξ), and the original model is expanded using the PCE method to obtain the following Equation 1: [Equation 1] [In the formula, 【number】 is the coefficient of the polynomial chaos expansion term, d is the dimension of the model input variable, and ξ is the d-dimensional input variable 【number】 is a multi-index of size d, 【number】 are orthogonal polynomials constructed from orthogonal polynomial bases corresponding to each dimensional variable], 【number】 is a polynomial corresponding to the input variables to obtain the following equation 2: [Equation 2] [In the formula, 【number】 teeth, 【number】 ], constructing a corresponding orthogonal polynomial basis according to the moment of each input variable degree, and obtaining the following Equation 3 and Equation 4 based on the orthogonality condition of the polynomials; [Equation 3] where μ is a weighting function. [Equation 4] Any k-th degree polynomial 【number】 Obtaining the following equation 5 according to the orthogonality of all low-order polynomials in [Equation 5] defining the k-th moment of the input variable ξ as the following equation 6: [Equation 6] rearranging Equation 5 into the following Equation 7 based on Equation 6; [Equation 7] expressing Equation 7 as a matrix to obtain Equation 8: [Equation 8] Data-driven arbitrary distribution orthogonal polynomial base coefficients 【number】 After obtaining [mathematical formula - see original document], continue to build a surrogate model from Equation 1, truncate Equation 1, and calculate the truncated polynomial coefficients using a regression method. The multi-objective optimization method for a coil structure surrounded by an active shield according to claim 1.

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