Method for reducing eddy-current loss of annular magnetic core by opening air gap

Abstract

The invention provides a method for reducing eddy current loss of an annular magnetic core by opening an air gap, which comprises an annular magnetic core (1) and a thin layer air gap (2), the annular magnetic core (1) is an annular ferrite magnetic core, the thin layer air gap (2) is arranged on the inner ring surface of the annular magnetic core (1), the thin layer air gap (2) is an air ring and surrounds the inner ring of the annular magnetic core (1) for a circle, and the thin layer air gap (2) is arranged on the inner ring surface of the annular magnetic core (1). The inner diameter of the thin-layer air gap (2) is the same as that of the annular magnetic core (1), the width of the thin-layer air gap (2) is smaller than one half of the magnetic core width of the annular magnetic core (1), and the magnetic core is structurally kept complete. According to the invention, a layer of thin-layer air gap surrounding the magnetic core is formed near the inner side surface of the annular magnetic core, so that the circulation path of eddy current is cut off, and the eddy current loss is reduced. Meanwhile, the method does not damage the structure of the annular magnetic core, the structure of the annular magnetic core is kept complete, and due to the fact that the air gap is extremely thin, the influence on the magnetic conductivity of the magnetic core can be ignored.

Description

Technical Field

[0001] The invention relates to the technical field of high-frequency transformer magnetic cores, and in particular to a method for reducing eddy current loss of a ring-shaped magnetic 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 moving 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 loss. In low-frequency and low-magnetic density applications, the iron loss generated by magnetic components accounts for a small proportion, but with the development of power electronics technology, the rated frequency of electrical equipment is getting higher and higher, and the proportion of iron loss is increasing. The accurate calculation of iron loss becomes more and more 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. At present, there are many methods for calculating the loss of magnetic components, such as: Steinmetz equation method, loss separation model, Preisach model and Jiles-Atherton (JA) model. The parameters of these methods or models are mostly derived from the magnetic flux density B and magnetic field strength H This means that if the loss data of the device is unknown, these methods are unlikely to provide accurate estimates of the core losses of the device, such as in the early verification design of a new electromagnetic device or in the optimization design of an existing electromagnetic device.

[0003] The finite element method is often used by researchers and engineers to design and optimize electrical equipment. Commercial software such as ANSYS and JMAG are widely used due to their powerful integration functions. Although these software bring convenience, their core algorithms are black boxes, which will limit researchers to conduct research within their frameworks. In addition, the existing finite element software for calculating iron loss essentially integrates some loss calculation methods, 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 Cheng Ming and others from Southeast University (Qin Wei, Cheng Ming, Wang Zheng, et al. A preliminary study on vector magnetic circuit and its application [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 with electromagnetic field theory and introduces a vector magnetic circuit model. Unlike 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 better understand the characteristics and physical significance of eddy current effect and hysteresis effect, as well as the magnetoelectric 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 the magnetic circuit loss, and can directly obtain the values ​​and distributions of the 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 the eddy current loss of a ring-shaped ferrite core by opening an air gap based on an electromagnetic field calculation method derived from vector magnetic circuit theory, that is, opening a thin annular air gap near the inner surface of the ring-shaped core to reduce the eddy current loss inside the core under high-frequency conditions.

[0006] Technical solution: A method of reducing eddy current loss of a ring-shaped magnetic core by opening an air gap in the present invention is achieved by the following, including a ring-shaped magnetic core and a thin layer of air gap, wherein the ring-shaped magnetic core is a ring-shaped ferrite core, and the thin layer of air gap is arranged on the inner ring surface of the ring-shaped magnetic core, and the thin layer of air gap is an air ring, which surrounds the inner ring of the ring-shaped magnetic core, and the inner diameter of the thin layer of air gap is the same as the inner diameter of the ring-shaped magnetic core, and the width of the thin layer of air gap is less than half of the core width of the ring-shaped magnetic core, and the core structure remains intact.

[0007] 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.

[0008] The two-dimensional electromagnetic field equation constructed by the vector magnetic circuit theory is specifically: ; ; ; ; ; ; 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.

[0009] The hysteresis loss P h , eddy current loss P e The calculation formula is as follows: ; ; In the formula, is the core volume, For the cycle, is the conductivity.

[0010] 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: ; In the formula, is the flux path length, is the number of winding turns, is the winding current, is the magnetic field strength; for toroidal cores, there are: ; In the formula, It is the distance from a point on the two-dimensional cross section to the center axis of the ring.

[0011] The thin 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 air gap is opened in this concentrated area, and the maximum air gap depth does not exceed half of the core width.

[0012] The thin layer air gap has one or more thin layers.

[0013] The air gap thickness of the thin layer air gap is the minimum value that can be achieved by the production process.

[0014] Beneficial effects: The present invention adopts the above technical solution, and the beneficial effects compared with the prior art are as follows: 1. The two-dimensional electromagnetic field calculation method based on vector magnetic circuit theory described in the present invention can simultaneously consider the hysteresis effect and eddy current effect of the magnetic core, and then directly obtain the specific values ​​and distribution of the hysteresis loss and eddy current loss of the magnetic core. There is no need to use a loss calculation model, and the decoupling of loss calculation and electromagnetic field calculation is avoided, making the analysis and design of magnetic components more accurate.

[0015] 2. The method of opening a thin air gap inside the ring-shaped magnetic core proposed in the present invention can effectively reduce the eddy current inside the magnetic core under high frequency conditions. This method has little change to the original structure of the magnetic core, so it is more convenient to process the original magnetic core and has little impact on the performance of the original magnetic core. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a three-dimensional diagram of the ring-shaped magnetic core with an air gap of the present invention.

[0017] Figure 2 It is a two-dimensional cross-sectional view of the ring-shaped magnetic core with an air gap of the present invention.

[0018] Figure 3 The figure is a flow chart of an embodiment of the present invention.

[0019] Figure 4 This is a diagram showing the calculation results of the eddy current loss distribution of a 400kHz non-gapped ring core using the two-dimensional electromagnetic field calculation method described in the present invention. Figure 4 (1) is the hysteresis loss distribution and diagram of the two-dimensional cross section of the magnetic ring. Figure 4 (2) in the figure is the eddy current loss distribution diagram of the two-dimensional cross section of the magnetic ring.

[0020] Figure 5 This is a comparison chart of the calculation results of the magnetic flux density distribution of the ring-shaped magnetic core before and after the air gap is opened at 400kHz using the two-dimensional electromagnetic field calculation method described in the present invention. Figure 5 (1) is the magnetic flux density distribution diagram of the two-dimensional cross section of the magnetic ring without air gap. Figure 5 (2) is the magnetic flux density distribution diagram of the two-dimensional cross section of the magnetic ring with an air gap depth of 1 / 4 of the magnetic ring width. Figure 5 (3) is the magnetic flux density distribution diagram of the two-dimensional cross section of the magnetic ring with two air gaps and a depth of 1 / 4 of the magnetic ring width. Figure 5 (4) is the magnetic flux density distribution diagram of the two-dimensional cross section of the magnetic ring with an air gap depth of 1 / 2 the width of the magnetic ring.

[0021] The figure includes: a toroidal magnetic core 1 and a thin air gap 2. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0023] The present invention proposes a method for reducing eddy current loss of a toroidal magnetic core by opening an air gap, comprising a toroidal magnetic core 1 and a thin-layer air gap 2, wherein the toroidal magnetic core 1 is a toroidal ferrite core, the thin-layer air gap 2 is arranged on the inner ring surface of the toroidal magnetic core 1, the thin-layer air gap 2 is an air ring, surrounding the inner ring of the toroidal magnetic core 1, the inner diameter of the thin-layer air gap 2 is the same as the inner diameter of the toroidal magnetic core 1, the width of the thin-layer air gap 2 is less than half of the core width of the toroidal magnetic core 1, and the core structure remains intact.

[0024] 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.

[0025] The magnetic core is a ring-shaped ferrite core, such as Figure 1 3D image of a gapped toroidal core and Figure 2 The two-dimensional cross-section of a toroidal core with an air gap shows that the thin air gap is near the inner ring surface, the air gap surrounds the core, and the width is less than the difference between the inner and outer diameters. The core is not divided into two by the air gap. Figure 3 In this embodiment, the toroidal core works under sinusoidal excitation, and the core shape, parameters and operating frequency are shown in Table 1: Table 1 Parameters of toroidal core 3E6 .

[0026] According to the parameters in Table 1, the boundary conditions of the inner and outer ring magnetic fields can be obtained as follows: ; Furthermore, under sinusoidal excitation, the proposed two-dimensional electromagnetic field calculation formula can be transformed into a phasor form: ; ; ; ; ; ; 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. From this we can get Figure 5 From the two-dimensional cross-sectional magnetic flux density distribution diagram of the magnetic ring shown in (1), it can be seen that under the high-frequency condition of 400kHz, an obvious skin effect phenomenon occurs inside the 3E6 ferrite core, and the magnetic flux density shows a distribution characteristic of concentrating inward and on the surface.

[0027] Furthermore, the hysteresis loss under sinusoidal excitation P h , eddy current loss P e The calculation formula is as follows: ; ; In the formula, is the core volume, For the cycle, is the conductivity. From this we can get Figure 4 The hysteresis loss distribution of the two-dimensional cross section of the magnetic ring shown in (1) and Figure 4 The eddy current loss distribution of the two-dimensional cross section of the magnetic ring is shown in (2). Figure 4 It can be seen that the distribution of hysteresis loss and the distribution of magnetic flux density have almost the same characteristics. This is because the hysteresis loss comes from the rotational friction of the 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.

[0028] Furthermore, according to the distribution of eddy current loss, we try to open an air gap with a depth of 1 / 4 of the magnetic ring width, 1 / 2 of the magnetic ring width, or 2 air gaps with a depth of 1 / 4 of the magnetic ring width on the inner side of the magnetic ring, and re-perform electromagnetic field analysis and loss calculation on the magnetic field after opening the air gap. The magnetic flux density distribution diagram of the two-dimensional cross section of the magnetic core after opening the air gap is shown in the figure. Figure 5 (2) Figure 5 (3) Figure 5 As shown in (4) in the figure, according to the loss calculation results, the effect after opening the air gap is shown in Table 2.

[0029] Table 2 Effect of air gap inside the magnetic ring on magnetic ring loss at 400kHz high frequency .

[0030] As can be seen from Table 2, the hysteresis loss inside the magnetic ring will increase slightly after the air gap is opened. This is because the slots force part of the magnetic flux to flow from the outside of the magnetic ring. Since the flow path of the outer layer of the magnetic ring becomes longer, 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 eddy current concentration area, and the eddy current is forced to flow to the area with greater impedance, which makes the eddy current itself smaller, and ultimately reduces the eddy current loss. Since the eddy current loss of the 3E6 magnetic ring under high-frequency conditions also accounts for a large proportion, the total loss is ultimately reduced.

[0031] From the above examples, it can be seen that the gapped toroidal magnetic core proposed by the present invention has significantly reduced eddy current loss and reduced total loss under high frequency conditions compared to the non-gap magnetic core. In addition, compared with other methods, such as the laminated magnetic core method, the method proposed by the present invention has less modification to the magnetic core, is easy to process, and the original properties of the magnetic core are basically unchanged.

[0032] The preferred embodiments of the present invention are described in detail above. The protection scope of the present invention is not limited to the above embodiments. Any technical solutions that can be obtained by ordinary technicians in this field through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the existing technology should be within the protection scope 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.

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 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.

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 two-dimensional electromagnetic field equation constructed by the vector magnetic circuit theory is specifically: ； ； ； ； ； ； 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.

4. 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 hysteresis loss P h , eddy current loss P e The calculation formula is as follows: ； ； In the formula, is the core volume, For the cycle, is the conductivity.

5. 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 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: ； In the formula, is the flux path length, is the number of winding turns, is the winding current, is the magnetic field strength; for toroidal cores, there are: ； In the formula, It is the distance from a point on the two-dimensional cross section to the center axis of the ring.

6. 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 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.

7. The method for reducing eddy current loss of a ring-shaped magnetic core by opening an air gap as claimed in claim 6, characterized in that: The thin layer air gap (2) has one or more thin layers.

8. The method for reducing eddy current loss of a ring-shaped magnetic core by opening an air gap as claimed in claim 7, 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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