Ferrite magnetic block design method for relieving magnetic heat nonuniformity of wireless charging magnetic core

Abstract

The invention discloses a ferrite magnetic block design method for relieving magnetic heat unevenness of a wireless charging magnetic core, which is characterized by comprising the following steps of: dividing the magnetic core into a middle magnetic field weak area and an edge magnetic field strong area; constructing a multi-objective optimization function, and determining the sizes of ferrite magnetic blocks in the middle magnetic field weak area and the edge magnetic field strong area and air gap parameters between the adjacent magnetic blocks through weight distribution optimization; based on the optimization result, a first ferrite magnetic block is arranged in the middle magnetic field weak area, a second ferrite magnetic block is arranged in the edge magnetic field strong area, the size of the first ferrite magnetic block is larger than that of the second ferrite magnetic block, and the air gap width of the edge magnetic field strong area is gradually increased in a gradient mode from inside to outside; and combining the optimized non-uniform air gap mixed size ferrite magnetic block with a transmitting coil and a receiving coil to form a wireless electric energy transmission magnetic coupling mechanism.

Description

Technical Field

[0001] The present invention relates to the field of wireless charging, and particularly to a design method of ferrite magnetic blocks for alleviating magnetic heat non-uniformity of a wireless charging magnetic core. Background Art

[0002] In the field of wireless power transmission, ferrite and nanocrystalline materials are most commonly used as magnetic core materials. Considering the high manufacturing cost and large process complexity of nanocrystalline materials, and the large eddy current loss caused by large conductivity, although the relative magnetic permeability and saturation magnetic flux density of ferrite are relatively lower than those of nanocrystalline materials, their characteristics are also fully applicable to wireless power transmission systems with medium-high frequencies and medium-high powers. Therefore, ferrite is still generally used as the magnetic core structure in wireless power transmission to increase electromagnetic coupling and reduce magnetic leakage.

[0003] In order to alleviate the problem of non-uniform magnetic heat on the magnetic block, in addition to the selection of materials, the design optimization of the magnetic core shape is also carried out. Regarding the shape design of ferrite, there are already shapes such as U-shaped, I-shaped, E-shaped, and stepped shapes. Among them, the U-shaped, E-shaped, and stepped ferrites have increased volume and weight and increased manufacturing process complexity. The I-shaped ferrite has serious magnetic leakage due to its large air gap. Based on considerations of shielding effect, economic cost, and performance, etc., block array type ferrites are most commonly used.

[0004] Due to the limitation of the material processing technology of zinc-manganese ferrite blocks, the side length of a single fired ferrite is mostly 50 mm or 100 mm, and then arranged in a matrix to form the entire magnetic core. Inevitably, there are air gaps between the ferrites. In the existing technologies and designs, ferrites of the same size and uniform adjustment of the air gap are used to make the magnetic heat as balanced as possible and reduce magnetic leakage. Summary of the Invention

[0005] To achieve the above and other related purposes, the present invention discloses a design method of ferrite magnetic blocks for alleviating magnetic heat non-uniformity of a wireless charging magnetic core, including: S1: Divide the magnetic core into a weak magnetic field region in the middle and a strong magnetic field region at the edge; S2: Construct a multi-objective optimization function, which comprehensively considers the thermal equilibrium coefficient C(T), the maximum magnetic leakage density B at the back of the magnetic core, the highest temperature T on the surface of the magnetic core, the system transmission efficiency η, and the air gap of 0.5 mm, the side length of the ferrite magnetic block of 5 cm, the maximum magnetic density B and the highest temperature T on the surface of the magnetic core, and determines the size of the ferrite magnetic blocks in the weak magnetic field region in the middle and the strong magnetic field region at the edge and the air gap parameters between adjacent magnetic blocks through weight allocation optimization; max 、 max 、 S3: Based on the optimization results, arrange the first ferrite magnet in the weak intermediate magnetic field region and arrange the second ferrite magnet in the strong edge magnetic field region, where the size of the first ferrite magnet is larger than that of the second ferrite magnet, and the air gap width in the strong edge magnetic field region increases gradually from the inside out; S4: Combine the optimized non-uniform air gap hybrid-size ferrite magnets with the transmitting coil and the receiving coil to form a wireless power transfer magnetic coupling mechanism.

[0006] Furthermore, the multi-objective optimization function is: ; ζ 1 ,ζ 2 ,ζ 3 ,ζ 4 are the weight coefficients of C(T), B max ,T max ,η respectively, and satisfy the constraint conditions: ζ 1 + ζ 2 + ζ 3 + ζ 4 = 1, the maximum leakage magnetic density at 400 mm from the back of the magnetic core should be less than 27 μT, the highest temperature on the surface of the magnetic core is less than 60 °C, and the air gap between ferrite blocks is 0 - 2.5 mm.

[0007] Furthermore, the calculation method of the thermal equilibrium coefficient is: ; T min is the lowest temperature on the surface of the magnetic core.

[0008] Furthermore, in step S2, a magnetic-thermal coupling model is constructed by using finite element simulation software to simulate the influence of different ferrite sizes and air gaps on the magnetic flux density distribution and temperature field, and the multi-objective function is iteratively optimized based on the simulation data.

[0009] Furthermore, the materials of the first ferrite magnet and the second ferrite magnet are zinc-manganese ferrite.

[0010] On the other hand, the present invention provides a wireless power transfer magnetic coupling mechanism, which uses the non-uniform air gap hybrid-size ferrite magnetic core designed by the above method, and includes: (a) A transmitting end magnetic core, which is composed of a transmitting coil and the non-uniform air gap hybrid-size ferrite magnetic core; (b) A receiving end magnetic core, which is composed of a receiving coil and the non-uniform air gap hybrid-size ferrite magnetic core.

[0011] Furthermore, the operating frequencies of the transmitting coil and the receiving coil are 85 kHz, and the maximum transmission power is 11 kW.

[0012] By adopting the above technical solution, in the core design with non-uniform air-gap and mixed-size ferrite magnet blocks arranged, the phenomenon of uneven magnetic heat on the core is greatly alleviated. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In combination with the accompanying drawings and with reference to the following detailed description, the above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent. The drawings are used to better understand the solution and do not limit the present disclosure. In the drawings, the same or similar reference numerals denote the same or similar elements, where: Figure 1 is the flowchart of the present invention; Figure 2 is the T distribution on the surface of the ferrite block t core = 5 cm with different air gaps l g on the core surface; Figure 3 is the T distribution on the surface of the ferrite block t core = 5 cm with different air gaps l g on the core surface; Figure 4 is the T distribution on the surface of the ferrite block t core = 10 cm, l g and the |B| distribution on the core surface with a = 0.5 mm Figure 5 is the variation of the maximum magnetic flux density B on the plane perpendicular to the ferrite core at a distance of 5 cm and the local maximum temperature T on the ferrite core with the air gap l g ; Figure 6 is the non-uniform air-gap and mixed-size ferrite core structure; Figure 7 is the overall structure of the non-uniform air-gap and mixed-size ferrite core; Figure 8 is the temperature T and magnetic density B distribution on the upper surface of the non-uniform air-gap and mixed-size ferrite core under the excitation of 11 kW / 85 kHz. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

[0015] Reference Figure 1 , an embodiment of the present invention provides a ferrite magnetic block design method for alleviating uneven magnetic heat in a wireless charging magnetic core, including: S1: Divide the magnetic core into a weak magnetic field region in the middle and a strong magnetic field region at the edge; S2: Construct a multi-objective optimization function, which comprehensively considers the thermal equilibrium coefficient C(T), the maximum leakage magnetic density B at the back of the magnetic core max , the highest temperature T on the surface of the magnetic core max , the system transmission efficiency η, as well as an air gap of 0.5 mm, the side length of the ferrite magnetic block of 5 cm, the maximum magnetic density B and the highest temperature T on the surface of the magnetic core. Through weight allocation optimization, determine the sizes of the ferrite magnetic blocks in the weak magnetic field region in the middle and the strong magnetic field region at the edge and the air gap parameters between adjacent magnetic blocks; S3: Based on the optimization results, arrange the first ferrite magnetic block in the weak magnetic field region in the middle and arrange the second ferrite magnetic block in the strong magnetic field region at the edge, where the size of the first ferrite magnetic block is larger than that of the second ferrite magnetic block, and the air gap width in the strong magnetic field region at the edge increases gradually from the inside to the outside; S4: Combine the optimized non-uniform air gap mixed-size ferrite magnetic blocks with the transmitting coil and the receiving coil to form a magnetic coupling mechanism for wireless power transmission.

[0016] First, build a magnetic heat model of the magnetic coupling mechanism for wireless power transmission with the help of comsol finite element simulation software, and study the influence of the air gap and size on the magnetic heat characteristics of the ferrite magnetic core based on the simulation model.

[0017] According to Ampere's law (∇×H = J) and the principle of continuity of the magnetic field, the magnetic flux of the magnetic field must be conserved in the magnetic circuit, that is, the magnetic flux (Φ = B⋅A) should be consistent on any cross-section. When the magnetic flux passes through the air gap of the magnetic core, since the magnetic permeability of the air gap is much lower than that of the ferrite, the magnetic field intensity must increase to maintain the consistency of the magnetic flux, that is, the "constraint" of the magnetic field at the air gap will cause the magnetic flux density to increase. In addition, the "contraction effect" of the magnetic field lines also increases the magnetic field density at the air gap. Due to the hindrance of the low magnetic permeability air gap to the magnetic field, the magnetic field lines will "contract" at the air gap, the spacing becomes smaller, and the magnetic field density becomes more concentrated. Usually, the smaller the air gap, the greater the magnetic field density. Due to the concentration of the magnetic field density at the air gap, the loss in this area also increases accordingly, and the air gap loss becomes the main source of local overheating. The expression of the air gap loss is where, P gap is the air gap loss, k gap is a fixed constant, l g is the air gap width, t core is the side length of the ferrite, B mis the peak value of magnetic flux density on the magnetic core at frequency f. From the formula, l g , t core and B m all affect the magnitude of the air-gap loss, and thus affect the temperature. Among them, the magnetic flux density B m is mainly related to the magnetic permeability μ and the magnetic field strength H. On the premise that μ is determined, B m is mainly related to the magnetic field strength, and the air-gap width l g and position affect the distribution of the magnetic field strength H, and thus affect the magnitude of B m , and finally affect the air-gap loss and temperature. Therefore, the local high temperature of the magnetic core is related to the air-gap width lg and the side length t of the ferrite core , that is: where k g is a fixed constant, and К, δ, ς are the power exponents of the corresponding parameters respectively. From the formula, under the condition that the magnetic permeability is determined, the air-gap width l g and the side length t of the ferrite core mainly affect the local high temperature.

[0018] Through simulation, Figure 2 and Figure 3 show the distributions of the magnetic core surface T and |B| under the excitation of 11kW / 85kHz, with the side length t of the ferrite block core = 5cm and different air-gaps l g . The values of l g are 0.5mm, 1.5mm and 2.5mm in sequence. It shows that as the air-gap increases, the magnetic flux density and temperature on the magnetic core surface will become more uniform, the concentration is not obvious, and the maximum values all show a downward trend. Figure 4 shows the distributions of T and |B| on the surface of the ferrite with t core = 10cm and l g = 0.5mm under the excitation of 11kW / 85kHz. Comparing with Figure 2 (a) and Figure 3 (a) shows that under the same air-gap condition, the maximum values of temperature and magnetic flux density of multiple small-sized ferrite magnetic cores are smaller than those of a small number of large-sized ferrite magnetic cores, and the magnetic-thermal distribution is more uniform. However, Figure 5 it shows that the influence of the air-gap on the magnetic core temperature and the maximum leakage magnetic flux on the vertical 5cm plane of the back of the ferrite shows an opposite trend, and it is a game process between the two. Therefore, overall consideration should be given and the ferrite should be reasonably arranged.

[0019] Secondly, define the thermal equilibrium formula as From the formula, the smaller C is, the better the magnetic-thermal equilibrium effect of the magnetic core is.

[0020] To comprehensively consider the overall performance of the system, a multi-objective optimization function \(H(C(T), B\) max , T\) max , η)\) is proposed, and its specific expression is as follows. To achieve a better design, the magnetic core is divided into two regions: a region with a strong edge magnetic field and a region with a weak middle magnetic field. For the middle region with a weak magnetic field, input parameters \(t\) core1 and \(l\) g1 are defined; while for the edge region with a stronger magnetic field, input parameters \(t\) core2 and \(l\) g2 are defined. On this basis, the constraint conditions of the system are that the maximum leakage magnetic density at 400 mm from the back of the magnetic core should be less than 27 μT, the highest temperature on the surface of the magnetic core should be less than 60 °C, and the air gap between ferrite blocks is 0 - 2.5 mm. According to this optimization function, it can be concluded that the smaller the value of \(H\), the better the overall performance of the system and the better the magnetic-thermal equilibrium effect. where \(C(T)\) is the equilibrium coefficient, \(B\) max is the maximum leakage magnetic of the back of the magnetic core, \(T\) max is the highest temperature on the surface of the magnetic core, η is the system transmission efficiency, \(B\) and \(T\) are the maximum magnetic density and the highest temperature on the surface of the ferrite magnetic core when the air gap is 0.5 mm, \(ζ\) 1 , \(ζ\) 2 , \(ζ\) 3 , \(ζ\) 4 are the weight coefficients of \(C(T)\), \(B\) max , \(T\) max , η respectively. According to the focus of this design, let \(ζ\) 1 = 0.4, \(ζ\) 2 = 0.3, \(ζ\) 3 = 0.2, \(ζ\) 4 = 0.1.

[0021] According to the objective function, the optimal parameters \(t\) core1 , \(l\) g1 , \(t\) core2 , \(l\) g2 are obtained to form the structure of the wireless power transfer magnetic core. The side length \(t\) core1 of the first ferrite in the region with a weak middle magnetic field is 10 cm, and the air gap \(l\) g1 is 0.5 mm; the side length \(t\) core2 of the second ferrite in the region with a strong surrounding magnetic field is 5 cm, and the air gap \(l\) g2 is 1.2 mm, as shown in Figure 6 and Figure 7 .

[0022] Figure 8For the temperature T and magnetic flux density B distributions on the upper surface of the proposed magnetic core excited at 11 kW / 85 kHz, according to previous studies, an air gap lg = 0.5 mm under a uniform air gap is the optimal solution to alleviate magnetic heat and suppress magnetic leakage. Therefore, the proposed magnetic core structure is compared with two magnetic cores of different sizes with lg = 0.5 mm, and the magnetic heat non-uniformity is alleviated, and the magnetic leakage is within the safe range.

[0023] Finally, the ferrite magnetic core with non-uniform air gaps of multiple sizes is combined with the energy transfer coil to form a magnetic coupling mechanism.

[0024] The present invention also provides a magnetic coupling mechanism for wireless power transmission, which uses the non-uniform air gap hybrid-size ferrite magnetic core designed by the above method and includes: (a) A transmitting-end magnetic core composed of a transmitting coil and the non-uniform air gap hybrid-size ferrite magnetic core; (b) A receiving-end magnetic core composed of a receiving coil and the non-uniform air gap hybrid-size ferrite magnetic core.

[0025] Among them, the operating frequencies of the transmitting coil and the receiving coil are 85 kHz, and the maximum transmission power is 11 kW.

[0026] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used here have the same meaning as the general understanding of those of ordinary skill in the art to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless specifically defined.

[0027] For the method embodiments, for simplicity of description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the embodiments of the present invention are not limited by the described action sequences, because according to the embodiments of the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily essential for the embodiments of the present invention.

[0028] From the description of the above embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of this application.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for designing a ferrite magnetic block for alleviating magnetic and thermal unevenness of a wireless charging magnetic core, characterized in that: include: S1: Divide the magnetic core into a middle area with weak magnetic field and an edge area with strong magnetic field; S2: Construct a multi-objective optimization function, which combines the thermal equilibrium coefficient C(T), the maximum magnetic flux leakage density B at the back of the magnetic core max , Maximum core surface temperature T max , system transmission efficiency η, air gap 0.5mm, maximum magnetic density B and maximum temperature T on the core surface of ferrite magnet block with side length 5cm, and the size of ferrite magnet block in the middle weak magnetic field area and the edge strong magnetic field area and the air gap parameters between adjacent magnet blocks are determined by weight distribution optimization; S3: Based on the optimization result, a first ferrite block is arranged in the middle weak magnetic field area, and a second ferrite block is arranged in the edge magnetic field strong area, wherein the size of the first ferrite block is larger than that of the second ferrite block, and the air gap width of the edge magnetic field strong area increases gradually from the inside to the outside; S4: Combine the optimized non-uniform air gap mixed-size ferrite magnet block with the transmitting coil and the receiving coil to form a wireless power transmission magnetic coupling mechanism.

2. The method according to claim 1, characterized in that The multi-objective optimization function is: ； ζ1, ζ2, ζ3, ζ4 are C(T), B max , T max , the weight coefficient of η, and satisfy the constraints: ζ1 + ζ2 + ζ3 + ζ4 = 1, the maximum leakage magnetic density at 400mm on the back of the core should be less than 27μT, the maximum temperature of the core surface is less than 60℃, and the air gap between ferrite blocks is 0~2.5mm.

3. The method according to claim 1, characterized in that The calculation method of the thermal equilibrium coefficient is: ； T min It is the minimum temperature of the core surface.

4. The method according to claim 1, characterized in that: In step S2, a magnetothermal coupling model is constructed by finite element simulation software to simulate the influence of different ferrite sizes and air gaps on the magnetic flux density distribution and temperature field, and the multi-objective function is iteratively optimized based on the simulation data.

5. The method according to claim 1, characterized in that The first ferrite block and the second ferrite block are made of zinc-manganese ferrite.

6. A wireless power transmission magnetic coupling mechanism, characterized in that: The non-uniform air gap mixed size ferrite core designed by the method of claim 1 comprises: (a) a transmitting end magnetic core, which is composed of a transmitting coil and the non-uniform air gap mixed size ferrite core; (b) The receiving end magnetic core is composed of a receiving coil and the non-uniform air gap mixed size ferrite core.

7. The magnetic coupling mechanism according to claim 6, characterized in that: The operating frequency of the transmitting coil and the receiving coil is 85kHz, and the maximum transmission power is 11kW.

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