A method for reducing eddy current loss of a toroidal magnetic core by opening an air gap

Abstract

The present invention provides a method for reducing eddy current loss of a toroidal core by opening an air gap, which includes a toroidal core (1) and a thin-layer air gap (2). The toroidal core (1) is a toroidal ferrite core, and the thin-layer air gap (2) is arranged on the inner ring surface of the toroidal core (1). The thin-layer air gap (2) is an air ring that surrounds the inner ring of the toroidal core (1) for one week. The inner diameter of the thin-layer air gap (2) is the same as the inner diameter of the toroidal core (1), and the width of the thin-layer air gap (2) is less than half of the core width of the toroidal core (1), and the core structure remains intact. By opening a thin-layer air gap that surrounds the core for one week near the inner surface of the toroidal core, the present invention truncates the circulation path of eddy currents, and thus the eddy current loss is reduced. At the same time, this method does not damage the structure of the toroidal core, and the toroidal core structure remains intact. Since the air gap is extremely thin, the influence on the magnetic permeability of the core can be ignored.

Description

Technical Field

[0001] The present invention relates to the technical field of high-frequency transformer cores, and particularly to a method for reducing eddy current loss of a toroidal core by opening an air gap. Background Art

[0002] In recent years, with the rapid development of silicon carbide (SiC) and gallium nitride (GaN), power electronic devices are developing towards high frequency, miniaturization, and high power. However, in modern power converters, the essential magnetic components (transformers, inductors, etc.) account for about half of the volume and weight and generate most of the power losses. In applications with low frequency and low magnetic flux density, the proportion of iron loss generated by magnetic components is relatively small. However, with the development of power electronic technology, the rated frequency of electrical equipment operation is getting higher and higher, and the proportion of iron loss is getting larger and larger. The accurate calculation of iron loss becomes increasingly important. Accurately predicting the loss distribution characteristics of magnetic components and considering the adverse effects of losses on the magnetic field are crucial for the design, analysis, and optimization of magnetic components. Accurate modeling of magnetic components is challenging because their own parameters, including permeability, conductivity, saturation, and most importantly, core loss, are affected by various conditions such as excitation, size and shape, temperature, etc. Currently, there are many methods for calculating the loss of magnetic components, such as the Steinmetz equation method, loss separation model, Preisach model, and Jiles-Atherton (J-A) model. Most of the parameters of these methods or models need to be extracted or fitted from the relationship curve between magnetic flux density B and magnetic field strength H or the loss data of specific measurement equipment. This means that if the loss data of the equipment is unknown, it is difficult for these methods to provide an accurate estimate of the core loss of the equipment, such as in the early verification design of new electromagnetic equipment or the optimized design of existing electromagnetic equipment.

[0003] The finite element method is often used by researchers and engineers for the design and optimization of electrical equipment. Commercial software such as ANSYS and JMAG is widely used due to its powerful integration function. Although these software bring convenience, their internal core algorithms are a black box, which will limit the research of researchers within their framework. In addition, the existing finite element software calculates iron loss by integrating some loss calculation methods in essence, and it is not clear whether the hysteresis effect and eddy current effect are considered in the electromagnetic field calculation process.

[0004] In recent years, Professor Ming Cheng of Southeast University et al. (Qin Wei, Ming Cheng, Zheng Wang, et al. Preliminary Exploration of Vector Magnetic Circuit and Its Applications [J]. Proceedings of the CSEE, 2024, 44(18): 7381-7395. DOI: 10.13334 / j.0258-8013.pcsee.232113.) proposed a new vector magnetic circuit theory, which combines magnetic circuit theory and electromagnetic field theory and introduces a vector magnetic circuit model. Different from the previous scalar magnetic circuit model that only considers magnetic resistance, this model consists of three components: magnetic resistance, magnetic induction, and magnetic capacitance. This model helps to more deeply understand the characteristics and physical meanings of eddy current effect and hysteresis effect, as well as the magnetic power law. This theory attempts to explain eddy current loss, hysteresis loss, and the phase difference between magnetomotive force and magnetic flux. Based on the vector magnetic circuit theory, a two-dimensional electromagnetic field analytical calculation model for core loss under sinusoidal excitation is proposed. This analytical calculation method does not require the use of empirical formulas to fit magnetic circuit losses and can directly obtain the numerical values and distributions of hysteresis loss and eddy current loss of the magnetic core. Summary of the Invention

[0005] Technical Problem: The purpose of the present invention is to provide a method for reducing eddy current loss of a toroidal ferrite core by opening an air gap based on the electromagnetic field calculation method derived from the vector magnetic circuit theory, that is, by opening a circular thin-layer air gap near the inner surface of the toroidal core to reduce the eddy current loss inside the core under high-frequency conditions.

[0006] Technical Solution: A method for reducing eddy current loss of a toroidal core by opening an air gap according to the present invention is achieved as follows. It includes a toroidal core and a thin-layer air gap. The toroidal core is a toroidal ferrite core. The thin-layer air gap is provided on the inner ring surface of the toroidal core. The thin-layer air gap is an air ring that surrounds the inner ring of the toroidal core for one week. The inner diameter of the thin-layer air gap is the same as the inner diameter of the toroidal core. The width of the thin-layer air gap is less than half of the core width of the toroidal core, and the core structure remains intact.

[0007] The method includes the following steps:

[0008] S1: Based on the vector magnetic circuit theory, construct a two-dimensional electromagnetic field calculation equation to obtain the magnetic density and eddy current calculation formulas of the toroidal core;

[0009] S2: Based on the magnetic density and eddy current calculation formulas of the toroidal core, further obtain the magnetic flux density, hysteresis loss, and eddy current loss distributions of the two-dimensional cross-section;

[0010] S3: Based on the eddy current loss distribution of the two-dimensional cross-section of the toroidal core, in the part where the eddy current loss is concentrated, open a thin-layer air gap with a certain depth to block the original eddy current path to achieve the purpose of reducing eddy current loss. P e of the purpose.

[0011] The two-dimensional electromagnetic field equations constructed by the vector magnetic circuit theory are specifically as follows:

[0012] ;

[0013] ;

[0014] ;

[0015] ;

[0016] ;

[0017] ;

[0018] In the formula, is the magnetic permeability, is the hysteresis angle, is the vector magnetic potential, is the source current density, is the eddy current density, is the magnetic field strength, is the magnetic flux density, is the angular frequency.

[0019] The hysteresis loss P h and the eddy current loss P e The calculation formulas are specifically as follows:

[0020] ;

[0021] ;

[0022] In the formula, is the core volume, is the period, is the conductivity.

[0023] The two-dimensional cross-sectional magnetic flux density, hysteresis loss, and eddy current loss distributions are specifically obtained by assigning boundary conditions to the two-dimensional cross-section and then calculating the magnetic density and loss values at each position within the cross-section. The boundary conditions are obtained based on Ampere's circuital law:

[0024] ;

[0025] In the formula, is the magnetic flux path length, is the number of turns of the winding, is the winding current, is the magnetic field strength; for a toroidal core, there is:

[0026] ;

[0027] In the formula, is the distance from a certain point on the two-dimensional cross-section to the axis of the ring center.

[0028] For the thin-layer air gap with a certain depth, specifically, according to the eddy current loss distribution of the two-dimensional cross-section obtained in step S2, under high-frequency conditions, the eddy current loss will concentrate near the inner ring surface. A thin-layer air gap is opened in this concentrated area, and the maximum depth of the air gap does not exceed one-half of the core width.

[0029] There is one or more of the thin-layer air gaps.

[0030] The thickness of the opened thin-layer air gap is the minimum value that can be achieved by the production process.

[0031] Beneficial effects: The present invention adopts the above technical solutions, and the beneficial effects compared with the prior art are as follows:

[0032] 1. The two-dimensional electromagnetic field calculation method based on the vector magnetic circuit theory described in the present invention can simultaneously consider the hysteresis effect and the eddy current effect of the core, and thus can directly obtain the specific values and distribution of the hysteresis loss and the eddy current loss of the core. Without relying on a loss calculation model and avoiding the decoupling of loss calculation and electromagnetic field calculation, the analysis and design of magnetic components are made more accurate.

[0033] 2. The method of opening a thin-layer air gap on the inner side of the toroidal core proposed in the present invention can effectively reduce the eddy current inside the core under high-frequency conditions. This method makes less change to the original structure of the core. Therefore, it is more convenient to process the original core and has less impact on the performance of the original core. Description of the Drawings

[0034] Figure 1 is a three-dimensional view of the toroidal core with an air gap opened according to the present invention.

[0035] Figure 2 is a two-dimensional cross-sectional view of the toroidal core with an air gap opened according to the present invention.

[0036] Figure 3 is a schematic flow chart of an embodiment of the present invention.

[0037] Figure 4 is a calculation result diagram of the eddy current loss distribution of the toroidal core without an air gap at 400 kHz according to the two-dimensional electromagnetic field calculation method described in the present invention. Figure 4 In (1) is the hysteresis loss distribution diagram of the two-dimensional cross-section of the magnetic ring, and Figure 4 in (2) is the eddy current loss distribution diagram of the two-dimensional cross-section of the magnetic ring.

[0038] Figure 5This is a comparison chart of the calculation results of the magnetic flux density distribution of the toroidal core before and after opening the air gap for the two-dimensional electromagnetic field calculation method described in the present invention. Figure 5 In (1), it is the two-dimensional cross-sectional magnetic flux density distribution diagram of the magnetic ring without an air gap. Figure 5 In (2), it is the two-dimensional cross-sectional magnetic flux density distribution diagram of the magnetic ring with one air gap with a depth of 1 / 4 of the magnetic ring width. Figure 5 In (3), it is the two-dimensional cross-sectional magnetic flux density distribution diagram of the magnetic ring with two air gaps with a depth of 1 / 4 of the magnetic ring width. Figure 5 In (4), it is the two-dimensional cross-sectional magnetic flux density distribution diagram of the magnetic ring with one air gap with a depth of 1 / 2 of the magnetic ring width.

[0039] In the figure: there are toroidal core 1 and thin-layer air gap 2. Detailed implementation mode

[0040] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the present invention, and gives a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0041] The present invention proposes a method for reducing the eddy current loss of a toroidal core by opening an air gap, including toroidal core 1 and thin-layer air gap 2. The toroidal core 1 is a toroidal ferrite core. The thin-layer air gap 2 is arranged on the inner ring surface of the toroidal core 1. The thin-layer air gap 2 is an air ring that surrounds the inner ring of the toroidal core 1 for one week. The inner diameter of the thin-layer air gap 2 is the same as the inner diameter of the toroidal core 1. The width of the thin-layer air gap 2 is less than half of the core width of the toroidal core 1, and the core structure remains intact.

[0042] The method includes the following steps:

[0043] S1: Based on the vector magnetic circuit theory, construct a two-dimensional electromagnetic field calculation equation to obtain the magnetic density and eddy current calculation formulas of the toroidal core.

[0044] S2: Based on the magnetic density and eddy current calculation formulas of the toroidal core, further obtain the magnetic flux density, hysteresis loss, and eddy current loss distributions of the two-dimensional cross-section.

[0045] S3: Based on the eddy current loss distribution of the two-dimensional cross-section of the toroidal core, in the part where the eddy current loss is concentrated, open a thin-layer air gap with a certain depth to block the original eddy current path to achieve the purpose of reducing the eddy current loss. P e The purpose.

[0046] The core is a toroidal ferrite core, such as Figure 1 The three-dimensional diagram of the toroidal core with an air gap opened and Figure 2As shown in the two-dimensional cross-sectional view of the ring-shaped magnetic core with an open air gap, the thin air gap is near the inner ring surface. The air gap surrounds the magnetic core for one week, and its width is less than the difference between the inner and outer diameters. The magnetic core is not divided into two by the air gap. Refer to Figure 3 , in this embodiment, the ring-shaped magnetic core operates under sinusoidal excitation. The shape, parameters, and operating frequency of the magnetic core are shown in Table 1:

[0047] Table 1 Parameters of Ring-shaped Magnetic Core 3E6

[0048] .

[0049] According to the parameters in Table 1, the magnetic field boundary conditions of the inner and outer rings can be obtained as:

[0050] ;

[0051] Furthermore, under sinusoidal excitation, the proposed two-dimensional electromagnetic field calculation formula can be transformed into phasor form:

[0052] ;

[0053] ;

[0054] ;

[0055] ;

[0056] ;

[0057] ;

[0058] In the formula, is the magnetic permeability, is the hysteresis angle, is the vector magnetic potential, is the eddy current density, is the magnetic field strength, is the magnetic flux density, is the angular frequency. Thus, the magnetic flux density distribution diagram of the two-dimensional cross-section of the magnetic ring as shown in Figure 5 can be obtained. It can be seen that under the high-frequency condition of 400 kHz, obvious skin effect phenomena occur inside the 3E6 ferrite magnetic core, and the magnetic flux density shows a distribution characteristic of concentrating towards the inner ring and the surface.

[0059] Furthermore, the calculation formulas for hysteresis loss P h and eddy current loss P e under sinusoidal excitation are specifically:

[0060] ;

[0061] ;

[0062] Wherein, is the core volume, is the period, is the conductivity. From this, the hysteresis loss distribution of the two-dimensional cross-section of the magnetic ring as shown in (1) of Figure 4 and the eddy current loss distribution of the two-dimensional cross-section of the magnetic ring as shown in (2) of Figure 4 can be obtained. It can be seen from Figure 4 that the distribution of hysteresis loss almost maintains the same characteristics as the distribution of magnetic flux density. This is because the hysteresis loss comes from the rotational friction of magnetic domains. Therefore, where the magnetic flux density is larger, the hysteresis loss is correspondingly larger. However, the eddy current loss is more concentrated on the surface around the cross-section, especially the inner surface.

[0063] Furthermore, according to the distribution of eddy current loss, an attempt is made to open an air gap with a depth of 1 / 4 of the magnetic ring width, 1 / 2 of the magnetic ring width or two air gaps with a depth of 1 / 4 of the magnetic ring width on the inner side of the magnetic ring, and the electromagnetic field is re-analyzed and the loss is calculated for the magnetic field after opening the air gap. The distribution diagram of the magnetic flux density of the two-dimensional cross-section of the core after opening the air gap is as shown in (2) of Figure 5 , Figure 5 in (3) of Figure 5 in (4) of

[0064] Table 2 Influence of opening an air gap on the inner side of the magnetic ring on the magnetic ring loss under the condition of 400 kHz high frequency

[0065] .

[0066] It can be seen from Table 2 that the hysteresis loss inside the magnetic ring will increase slightly after opening the air gap. This is because the grooving causes part of the magnetic flux to be forced to flow outside the magnetic ring. Since the outer layer of the magnetic ring has a longer flow path, according to the vector magnetic circuit theory, the magnetic capacitance becomes smaller and the hysteresis loss increases. However, the eddy current loss will be significantly reduced. This is because the air gap interrupts the original area where the eddy current is concentrated, and the eddy current is forced to flow to the area with a greater impedance, making the eddy current itself smaller, and finally reducing the eddy current loss. Since the proportion of the eddy current loss of the 3E6 magnetic ring under high-frequency conditions is also relatively large, the final total loss decreases.

[0067] It can be seen from the above examples that the air-gap ring-shaped core proposed by the present invention, compared with the core without an air gap, under high-frequency conditions, the eddy current loss is significantly reduced, and the total loss will also be reduced. In addition, compared with other methods, such as the laminated core method, the method proposed by the present invention makes less modification to the core, is easy to process, and the original properties of the core are basically unchanged.

[0068] The preferred embodiments of the present invention have been described in detail above. The scope of protection of the present invention is not limited to the above embodiments. Any technical solutions that can be obtained by those of ordinary skill in the art based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art shall fall within the scope of protection determined by the claims.

Claims

1. A method for reducing eddy current loss of a ring-shaped magnetic core by opening an air gap, characterized in that: The invention comprises a ring-shaped magnetic core (1) and a thin-layer air gap (2), wherein the ring-shaped magnetic core (1) is a ring-shaped ferrite magnetic core, the thin-layer air gap (2) is arranged on the inner ring surface of the ring-shaped magnetic core (1), the thin-layer air gap (2) is an air ring, surrounding the inner ring of the ring-shaped magnetic core (1), the inner diameter of the thin-layer air gap (2) is the same as the inner diameter of the ring-shaped magnetic core (1), the width of the thin-layer air gap (2) is less than half of the magnetic core width of the ring-shaped magnetic core (1), and the magnetic core structure remains intact; The method comprises the following steps: S1: Based on the vector magnetic circuit theory, a two-dimensional electromagnetic field calculation equation is constructed to obtain the magnetic flux density and eddy current calculation formulas of the toroidal magnetic core; S2: Based on the magnetic flux density and eddy current calculation formulas of the toroidal core, the magnetic flux density, hysteresis loss and eddy current loss distribution of the two-dimensional cross section are further obtained; S3: Based on the eddy current loss distribution of the two-dimensional cross section of the toroidal core, a thin layer of air gap of a certain depth is opened in the part where the eddy current loss is concentrated to block the original eddy current path and reduce the eddy current loss P e purpose; The two-dimensional electromagnetic field equation constructed by the vector magnetic circuit theory is specifically: Where μ is the magnetic permeability, γ is the hysteresis angle, A is the vector magnetic potential, J s is the source current density, J e is the eddy current density, H is the magnetic field intensity, B is the magnetic flux density, and ω is the angular frequency; The hysteresis loss P h , eddy current loss P e The calculation formula is as follows: Where V is the core volume, T is the period, and σ is the conductivity; The distribution of the magnetic flux density, hysteresis loss and eddy current loss of the two-dimensional cross section is specifically obtained by assigning boundary conditions to the two-dimensional cross section, and then obtaining the magnetic flux density and loss values ​​at each position in the cross section. The boundary conditions are obtained according to Ampere's circuit theorem: ∮ l H·dl=NI; Where l is the length of the magnetic flux path, N is the number of winding turns, I is the winding current, and H is the magnetic field strength. For a toroidal core, we have: Where r is the distance from a point on the two-dimensional cross section to the center axis of the ring.

2. The method for reducing eddy current loss of a ring-shaped magnetic core by opening an air gap as claimed in claim 1, characterized in that: The thin layer air gap of a certain depth is specifically, according to the eddy current loss distribution of the two-dimensional cross section obtained in step S2, under high frequency conditions, the eddy current loss will be concentrated near the inner ring surface, and a thin layer air gap (2) is opened in this concentrated area, and the maximum air gap depth does not exceed half of the core width.

3. The method for reducing eddy current loss of a ring-shaped magnetic core by opening an air gap as claimed in claim 2, characterized in that: The thin layer air gap (2) has one or more thin layers.

4. The method for reducing eddy current loss of a ring-shaped magnetic core by opening an air gap as claimed in claim 3, characterized in that: The air gap thickness of the thin layer air gap (2) is the minimum value that can be achieved by the production process.

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