Cascade magnetic element

Abstract

The utility model belongs to the technical field of magnetic elements, and particularly relates to a cascade magnetic element. According to the utility model, a plurality of magnetic elements are stacked to form a cascaded magnetic element; each magnetic element comprises a magnetic core and a winding which are made of magnetic materials, each magnetic element is flattened, and the ratio of the width to the thickness of each magnetic element is larger than 10; air gaps are arranged between two adjacent layers of magnetic elements and on two sides of the winding. According to the utility model, high-efficiency energy conversion under high frequency can be realized, the resonant frequency and energy density of the magnetic element are improved, and eddy current loss is reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of magnetic components, and in particular relates to a cascade magnetic element. Background Art

[0002] Traditional magnetic components (including but not limited to inductors and transformers) are large in size, resulting in a large amount of space waste in the system and requiring a lot of time for reasonable selection and assembly. Existing magnetic components can effectively reduce the system volume, cascade the magnetic components, increase the operating frequency of the magnetic components, and reduce the core loss. Compared with traditional magnetic components, cascaded magnetic components have higher energy density, higher operating frequency, and lower loss.

[0003] However, simply cascading magnetic components brings challenges of electromagnetic thermal coupling: at high frequencies:

[0004] (1) When the physical size of the copper material exceeds the skin depth of the copper material at the operating frequency, a significant eddy current effect will occur inside the wire, causing the current to be distributed only on the surface of the wire, increasing the loss while reducing the value of the magnetic component. From a material point of view, copper material has better conductivity. According to the skin depth formula The skin depth of copper material is smaller and the skin effect is more serious. δ (skin depth): indicates the depth at which the current density in the conductor drops to 1 / e (about 36.8%) of the surface current density. The unit is meter (m). ρ (resistivity): The resistivity of the conductor material, which indicates the material's resistance to the flow of current. The unit is ohm-meter (Ω·m). f (frequency): The frequency of alternating current. The unit is Hertz (Hz). μ r (Relative permeability): The ratio of the magnetic permeability of a material to the magnetic permeability of vacuum μ0. μ0 (vacuum permeability): The magnetic permeability of a vacuum, approximately equal to 4π×10 -7 Henry per meter (H / m).

[0005] (2) Due to the high magnetic permeability of the material, the self-resonance frequency is very low and cannot be used normally at higher frequencies. (The self-resonance frequency of a magnetic component is determined by the magnetic component and its parasitic capacitance. Generally speaking, the higher the first resonant frequency of a magnetic component, the better, because it means that the magnetic component can operate over a wider frequency range without being affected by parasitic capacitance. If the operating frequency is close to or higher than the first resonant frequency, the magnetic component will behave like a capacitor rather than a magnetic component, and its impedance will decrease as the frequency increases. This may cause unnecessary effects such as signal attenuation, distortion or interference. Many magnetic component manufacturers will choose one-tenth of the self-resonance frequency below the operating frequency as the maximum frequency of the magnetic component application, so the higher the self-resonance frequency, the higher the operating frequency that the magnetic component can be applied to)

[0006] (3) The core loss of the material increases at high frequencies, and the eddy current loss of the magnetic material is serious.

[0007] Cascading of magnetic materials: Ferrite materials are mechanically brittle and cannot be made into magnetic component materials. Summary of the invention

[0008] The utility model aims to provide a cascade magnetic element (including but not limited to inductor and transformer) with high energy density and low loss suitable for high frequency.

[0009] The utility model provides a cascaded magnetic element (including but not limited to an inductor and a transformer), which is formed by stacking a plurality of magnetic elements to form a cascaded magnetic element; wherein each magnetic element comprises a magnetic core and a winding made of a magnetic material, and each magnetic element is flattened, specifically, the ratio of width to thickness is greater than 10; air gaps are provided between two adjacent layers of magnetic elements and on both sides of the winding;

[0010] Figure 1 The schematic diagram of the stacked structure of multiple magnetic devices, their current and magnetic field strength direction, yellow is the winding current, gray is the magnetic material structure, combined into a cascaded magnetic component structure. The cross-sectional view of each magnetic component of the cascaded magnetic component is shown in Figure 1. Figure 2 The 3D model is as follows Figure 3 As shown. Among them, the copper foil (winding) has a width of m, a thickness of d, a semi-major axis of a, and a semi-minor axis of b; the gap length is lg; and the stacking layer thickness (magnetic material thickness) is l1.

[0011] refer to Figure 2 In order to solve the problem of uneven current distribution caused by skin effect under high frequency conditions, the thickness of copper foil is designed. Specifically, according to the skin depth formula The skin depth of the copper conductor at the operating frequency can be calculated; where ρ is the resistivity of the conductor material, in ohm-meters (Ω·m), f is the frequency of the alternating current, in Hertz, and μ0 is the magnetic permeability of a vacuum, which is approximately equal to 4π×10 -7 Henry per meter (H / m), μ r It is the ratio of the magnetic permeability of the material to the magnetic permeability of vacuum.

[0012] In the utility model, twice or more of the skin depth is taken as the thickness of the copper foil.

[0013] Determine the air gap length according to the design parameters to obtain an equivalent magnetic permeability that is much smaller than the magnetic permeability, thereby increasing the energy density limit of the magnetic component. According to the desired effective magnetic permeability required by the design, the equivalent magnetic permeability of the magnetic core is determined by the magnetic material and the air gap;

[0014]

[0015] Among them, l Mis the average total magnetic path length, l g is the air gap length, μ effr is the equivalent relative magnetic permeability, μ cr is the relative magnetic permeability. C is the magnetic path length of the core.

[0016] The air gap determines the limit of the energy density of the entire magnetic core, and the air gap length is calculated based on the required effective magnetic permeability and the magnetic permeability of the magnetic material.

[0017] According to different parameter requirements, the dimension parameters of the cascaded magnetic components, copper foil thickness, etc. can be adjusted accordingly. Parameters include: magnetic component value; DC resistance; saturation current; operating frequency, etc.

[0018] Technical features and functional advantages of this utility model:

[0019] The utility model solves the following problems by flattening and cascading the magnetic element structure:

[0020] (1) The structure of the cascaded magnetic device, the stacking of multiple magnetic device units, realizes the mutual cancellation of the magnetic field in the middle layer, which can reduce the thickness of the magnetic material in the middle layer, reduce the total volume of the entire magnetic element, and improve the integration and energy density of the magnetic device. The distributed air gap structure between the stacked structure layers reduces the loss of the magnetic element and improves the overall energy storage density.

[0021] (2) Two-dimensional design. Based on theoretical analysis of the electromagnetic field inside the core material, it is found that the flatter the material's magnetic cross-section, the higher the self-resonance frequency of the magnetic element. By calculating the maximum aspect ratio under the same magnetic element value, the self-resonance frequency of the material can be increased by about two times. Specifically, the core cross-sectional area and magnetic flux circumference can be calculated based on the required magnetic element value and the material's saturation magnetic flux density. Figure 1 , the mutual constraints between the dimensional parameters, and the requirements of the DC resistance, can be used to calculate the maximum aspect ratio that meets the design parameters to satisfy the two-dimensional structure;

[0022] (3) In this design, air gaps are opened on both sides to form cascaded magnetic elements of the structure. Figure 1 The figure shows the distributed air gap structure of the cascaded magnetic components. Figure 2 The air gap position of a single unit is shown. By adding the air gap, the effective magnetic permeability of the entire magnetic core is much smaller than the magnetic permeability of the magnetic material, thereby improving the energy density limit of the magnetic component's energy storage.

[0023] (4) Reduce eddy current loss. According to the flattened design of the magnetic core, the parasitic electric field generated inside the material, which is the source of eddy current loss, is reduced, further reducing the loss. The flattened magnetic cross-section design allows the bound electric field to be distributed in an approximately rectangular shape on the cross-section. The electric field energy on the cross-section is calculated, which is the source of eddy current loss. The eddy current loss of the magnetic core is generated by the eddy current formed by the internal electric field. By reducing the electric field energy, the eddy current loss is further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram of the structure of the cascaded magnetic element provided by the utility model (front view), including a multi-layer cascaded magnetic core structure, a winding structure, and air gaps between layers.

[0025] Figure 2 The cross-sectional view of each submodule of the cascade magnetic element provided by the utility model includes the magnetic material thickness l1, the air gap size l g , schematic diagram of parameters such as winding width m, thickness d, etc.

[0026] Figure 3 This is a 3D schematic diagram of each submodule of the cascaded magnetic element provided by the utility model. DETAILED DESCRIPTION

[0027] For example Figure 2 The sub-unit structure has a square section side length of 1.18mm, a rectangular section width of 17.5mm, and a thickness of 0.08mm for the same core cross-sectional area. According to the flattened design of the core, the parasitic electric field generated inside the material, which is the source of eddy current loss, is reduced by 7 times, further reducing the loss. In the flattened magnetic cross-section design, the bound electric field is distributed in an approximately rectangular shape on the cross-section, and the electric field energy on the cross-section, which is the source of eddy current loss, is calculated. The eddy current loss of the core is generated by the eddy current formed by the internal electric field. By reducing the electric field energy, the eddy current loss is further reduced;

[0028] According to the design, the inductor design is flattened by utilizing the higher material mechanical properties of the strip. For example, the core cross-section width: thickness is 218, which is a dimensional ratio of more than 10 times, achieving approximate two-dimensionalization.

[0029] For example, if the target inductor inductance is 100uH and the current is 50A, 10 sub-units can be stacked, each with an inductance of 10uH and a current of 5A. The middle layer core can be further thinned to reduce the overall volume and improve the overall energy density.

Claims

1. A cascade magnetic element, characterized in that: A cascaded magnetic element is formed by stacking a plurality of magnetic elements; wherein each magnetic element comprises a magnetic core and a winding made of a magnetic material, each magnetic element is flattened, and a ratio of width to thickness is greater than 10; an air gap is provided between two adjacent layers of magnetic elements and on both sides of the winding; Assume the winding is copper foil.

2. The cascaded magnetic element according to claim 1, characterized in that: The thickness of the copper foil is twice or more than twice the skin depth; the skin depth formula is: Where ρ is the resistivity of the conductor material in ohm-meters, f is the frequency of the alternating current in hertz, and μ0 is the magnetic permeability of a vacuum, which is approximately equal to 4π×10 -7 Henry per meter, μ r It is the ratio of the magnetic permeability of the material to the magnetic permeability of vacuum.

3. The cascaded magnetic element according to claim 1, characterized in that: The air gap length l g Calculated based on the required effective magnetic permeability and the magnetic permeability of the magnetic material: Among them, l M is the average total magnetic path length, μ effr is the equivalent relative magnetic permeability, μ cr is the relative magnetic permeability, l C is the magnetic path length of the core.

4. The cascaded magnetic element according to any one of claims 1 to 3, characterized in that: The magnetic element is an inductor or a transformer.

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