Magnetic core for a solid state transformer

Abstract

This invention discloses a magnetic core for a solid-state transformer. The magnetic core for a solid-state transformer has an alloy composition of Fe (atomic percentage). a‑x Si b B c Cu d Nb e V f Ni x Where: 50≤a≤79, 12.4≤b≤16.5, 6.6≤c≤9.7, 0.4≤d≤1.3, 1≤e≤3, 0≤f≤2, 0.5≤x≤20.0, and a+b+c+d+e+f=100. The magnetic core proposed in this invention is suitable for solid-state high-frequency transformers operating at frequencies of 5~100 kHz, and can be applied to fields such as AI data centers and new energy grid connection, filling a gap in related technologies.

Description

Technical Field

[0001] This invention relates to the field of iron-based nanocrystalline alloy technology, and more particularly to a magnetic core for solid-state transformers. Background Technology

[0002] Solid-state transformers (SSTs), as core equipment in next-generation energy systems, have broad application prospects in smart grids, AI data centers, new energy grid connection, electric vehicle charging stations, and electric ships. Compared with traditional power frequency transformers, SSTs utilize power electronic conversion technology, achieving voltage transformation and electrical isolation through medium-to-high frequency transformers (MFTs), offering significant advantages such as small size, light weight, high efficiency, and high functional integration. International giants like NVIDIA are exploring medium-voltage rectifier applications and are committed to using SST technology as a future-oriented power distribution solution for facilities. Delta, Meituan, Qin Huai Data, and Dongyangguang have jointly released the world's first SST-based intelligent DC power supply system solution, achieving a system conversion efficiency of 98.5% and a single power cabinet output power of 1MW.

[0003] High-frequency transformers are the core component of SST (Supervisory Transformer), and their performance directly determines the overall efficiency, power density, and reliability of the SST system. Key technological bottlenecks in high-frequency transformers include small capacity, high loss density, difficulty in designing large-capacity magnetic cores, system complexity, and high cost. Transformers used in SST typically operate between 5 kHz and 100 kHz. While higher frequency operation reduces core size, it also brings challenges such as a dramatic increase in iron losses and exacerbated eddy current effects. Regarding material selection, the core materials currently available for SST high-frequency transformers mainly fall into three categories: ferrite, amorphous alloys, and nanocrystalline alloys. While ferrites have high resistivity and low high-frequency losses, their saturation magnetic flux density is relatively low (typically only 0.3~0.5 T), making it difficult to meet the high power density requirements of SST. Amorphous alloys, although possessing high saturation magnetic flux density (approximately 1.56 T) and low mid-to-low frequency losses, experience a sharp increase in losses at high frequencies above 5 kHz, and their permeability decays rapidly with increasing frequency.

[0004] Iron-based nanocrystalline alloys have attracted much attention due to their unique amorphous / nanocrystalline dual-phase structure. After appropriate crystallization annealing, these alloys can precipitate α-Fe(Si) nanocrystals with a size of approximately 15-25 nm on an amorphous matrix, combining the high resistivity of amorphous materials with the excellent soft magnetic properties of nanocrystalline materials, such as high saturation magnetic induction, high permeability, and low coercivity. Amorphous and nanocrystalline materials possess both the high resistivity provided by amorphous materials to reduce eddy current losses and the excellent soft magnetic properties imparted by nanocrystalline materials, making their advantages even more pronounced in SST applications. Studies have shown that amorphous and nanocrystalline solid-state transformers reduce core losses by 60%–80% at high frequencies compared to traditional silicon steel, reduce no-load losses by more than 40%, and increase transformer efficiency to 98.5%. However, existing iron-based nanocrystalline alloys still face the following prominent problems in high-frequency applications:

[0005] Currently, typical Finemet alloys (composed of B7 or B9 alloys) have an effective permeability of over 150,000 at 1 kHz, with a coercivity of approximately 0.5 A / m. While such high permeability is certainly advantageous in low-frequency applications, in the operating frequency range of high-frequency transformers in SST (typically 5~100 kHz), excessively high low-frequency permeability leads to a sharp increase in eddy current losses in the core at high frequencies. The permeability decreases exponentially with increasing frequency, severely affecting the operational stability and efficiency of the SST system.

[0006] Furthermore, high permeability also leads to easy saturation of the magnetic core under bias magnetic fields, limiting its application in high-power SSTs. Industry data shows that the optimal range for effective permeability of SST core materials at 1 kHz is between 10,000 and 30,000. This range can effectively control high-frequency losses and bias saturation while ensuring sufficient excitation inductance. However, the permeability of existing nanocrystalline materials is generally too high, making it difficult to precisely fall within this range. Secondly, how to maintain a high saturation magnetic induction intensity and low coercivity while controlling the effective permeability at 1 kHz within the optimized range of 10,000 to 30,000 for SST applications has become a critical problem that urgently needs to be solved in the current technological field. Currently, solid-state transformers are booming, and high-frequency amorphous and nanocrystalline alloys will generate an industry scale of hundreds of billions of yuan in the next 5-10 years, representing a significant opportunity for the development of the amorphous and nanocrystalline industries. Therefore, developing iron-based nanocrystalline magnetic core materials with moderate effective permeability (10,000~30,000) and high saturation magnetic induction, low coercivity and low high-frequency loss specifically for SST high-frequency transformers has significant technical value and broad application prospects. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention proposes a magnetic core for solid-state transformers. This invention optimizes the composition of a finemet alloy using Ni, achieving an effective permeability μ at a frequency of 1 kHz.e It is precisely controlled within the range of 10,000 to 30,000, while maintaining a high saturation magnetic induction intensity, low coercivity, and excellent high-frequency loss characteristics.

[0008] The first objective of this invention is to provide a magnetic core for a solid-state transformer, wherein the alloy composition of the magnetic core is Fe by atomic percentage. a-x Si b B c Cu d Nb e V f Ni x , where: 50≤a≤79, 12.4≤b≤16.5, 6.6≤c≤9.7, 0.4≤d≤1.3, 1≤e≤3, 0≤f≤2, 0.5≤x≤20.0, and a+b+c+d+e+f =100.

[0009] The design principle of the alloy composition in the iron-based nanocrystalline magnetic core proposed in this invention is as follows:

[0010] (1) Fe: Iron is the matrix element of the alloy, providing basic ferromagnetism. Its atomic percentage content directly affects the saturation magnetic induction intensity B. s The size of B. Too low an Fe content will lead to B. s A decrease in temperature or an excessively high temperature may lead to coarsening of nanocrystalline grains, resulting in a decrease in the alloy's ability to form amorphous materials and an increase in coercivity, which in turn deteriorates the soft magnetic properties.

[0011] (2) Si: Silicon is a key element in the formation of α-Fe (Si) nanocrystals. Si atoms are dissolved in the α-Fe lattice, which can reduce the magnetocrystalline anisotropy constant and magnetostriction coefficient, thereby reducing coercivity and increasing permeability. At the same time, Si can also increase the resistivity of the alloy and reduce eddy current losses. Therefore, the Si content can directly affect the soft magnetic properties of the material.

[0012] (3) B: Boron is the main element for forming amorphous phases and can significantly improve the amorphous forming ability of alloys. B has a small atomic radius and can fill the interatomic gaps of Fe, increasing the disorder of the alloy and the stability of the supercooled liquid.

[0013] (4) Cu: Copper acts as a nucleating agent in Finemet alloys. Cu and Fe are not solid dissolved at low temperatures. During annealing, Cu atoms preferentially precipitate in clusters, providing nucleation sites for α-Fe nanocrystals and promoting uniform nucleation of nanocrystals.

[0014] (5) Nb: Niobium is a key element for inhibiting grain growth. Nb has a large atomic radius and a low diffusion coefficient. During annealing, it is enriched at the grain boundaries of α-Fe grains. Through the solute dragging effect, it inhibits further grain growth, thereby ensuring the acquisition of fine nanocrystalline structure.

[0015] (6) V: The addition of vanadium is to compensate for the decrease in the grain growth inhibition effect caused by the decrease in Nb, which can maintain the effect of refining the grain structure and improve the resistivity and thermal stability of the alloy. At the same time, it reduces the cost of the material. V has a good synergistic effect with elements such as Nb and can optimize the crystallization behavior of amorphous precursors.

[0016] (7) Ni: Nickel is the controlling element. Ni has a face-centered cubic structure and can be dissolved in the α-Fe lattice in Fe-based alloys, affecting magnetocrystalline anisotropy and magnetic domain structure. Increasing the Ni content will change the Curie temperature of the alloy and change the migration characteristics of the magnetic domain walls. This invention achieves continuous adjustment of the effective permeability at 1 kHz in the range of 0.4 to 100,000 by systematically controlling the Ni content.

[0017] Preferably, the value of x is in the range of 1 ≤ x ≤ 10; the alloy composition of the magnetic core is Fe. 73.5- x Si 15.5 B7Cu1Nb 1.5 V 1.5 .

[0018] Further preferred, the range of x is: 2.5≤x≤5.0.

[0019] Preferably, the magnetic core is made of amorphous ribbon with a thickness of 10~25 μm through winding and crystallization annealing, and the filling factor of the magnetic core is ≥75%.

[0020] Preferably, the saturation magnetic induction intensity Bs ≥ 1.0 T and the coercivity Hc ≤ 2.5 A / m of the magnetic core. The magnetic core is an iron-based nanocrystalline magnetic core with an effective permeability (μ) at a frequency of 1 kHz. e The range is 10,000 to 30,000.

[0021] A second objective of this invention is to provide a method for manufacturing a magnetic core for a solid-state transformer, comprising the following steps:

[0022] S1, according to the alloy composition formula Fe a-x Si b B c Cu d Nb e V f Ni x Convert the atomic percentage of each element to the mass percentage and weigh out industrial pure iron, crystalline silicon, ferroborone alloy, copper, ferroniobium alloy, ferrovanadium alloy and nickel raw materials;

[0023] S2. Place the raw materials weighed in step S1 into a vacuum induction melting furnace and melt them at 1450℃~1600℃ for 120~240 min under inert gas protection to fully melt and homogenize the alloy and obtain the master alloy melt.

[0024] S3. The master alloy melt obtained in step S2 is prepared into an amorphous ribbon by a single-roller rapid cooling method. The surface linear velocity of the copper roller is 22~35 m / s, and a continuous amorphous ribbon with a thickness of 10~25 μm is obtained.

[0025] S4. The amorphous ribbon obtained in step S3 is wound into a ring or rectangular magnetic core, and the filling factor of the magnetic core is ≥75%;

[0026] S5. The magnetic core obtained in step S4 is subjected to a three-step annealing process under vacuum or a protective atmosphere. First, the temperature is increased from room temperature to 400℃~440℃ at a rate of 4~10℃ / min and held for 60~120 min. Then, the temperature is increased to 460℃~500℃ at a rate of 0.5~1.5℃ / min and held for 60~120 min. Next, the temperature is increased to the target temperature of 500℃~570℃ at a rate of 0.5~1.5℃ / min and held for 90~180 min. Finally, the core is cooled to below 300℃ in the furnace and removed.

[0027] S6: The magnetic core annealed in step S5 is impregnated and cured to obtain the magnetic core for the solid-state transformer.

[0028] In step S1, the preferred raw materials for copper and nickel are electrolytic copper and electrolytic nickel.

[0029] Preferably, in step S2, the metallurgy is carried out at 1500℃~1570℃ for 180 min.

[0030] Preferably, step S3 specifically involves: pouring the master alloy melt obtained in S2 onto the surface of a high-speed rotating copper roller using a single-roller rapid cooling method. The linear velocity of the copper roller surface is 25~35 m / s, and the cooling rate is approximately 10 m / s. 6 K / s yields continuous amorphous ribbons with a thickness of 10~25 μm and a width of 5~50 mm.

[0031] Preferably, in step S5, the protective atmosphere is high-purity nitrogen or high-purity argon. First, the temperature is increased from room temperature to 420°C at 8°C / min and held for 60 min; then, it is increased to 460°C at 1°C / min and held for 90 min; then, it is increased to the target temperature of 555°C at 1°C / min and held for 120 min; finally, it is cooled to below 300°C with the furnace and taken out.

[0032] Preferably, in step S6, the impregnation and curing process is as follows: the annealed magnetic core is placed in an epoxy resin or silicone resin impregnation solution, vacuum impregnated for 10 to 30 minutes, and then cured at 120°C to 150°C for 2 to 4 hours.

[0033] This invention also protects the application of the magnetic core in a solid-state transformer, wherein the solid-state transformer operates in the frequency range of 5~100 kHz, the magnetic core is used as the magnetic core of a high-frequency transformer in the solid-state transformer, and / or the solid-state transformer is applied in the fields of AI data centers, new energy grid connection, electric vehicle charging stations or smart grids.

[0034] The magnetic core proposed in this invention is suitable for solid-state high-frequency transformers with operating frequencies of 5 to 100 kHz, and can be applied to fields such as AI data centers and new energy grid connection, filling the relevant technological gap.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] 1. This invention achieves, for the first time, continuous adjustment of the effective permeability of Fe-based nanocrystalline alloys within the range of 0.4 to 100,000 at a frequency of 1 kHz by systematically controlling the amount of Ni added. In particular, when x=5, the effective permeability is controlled within the range of 10,000 to 30,000, which precisely meets the optimal permeability requirements of SST high-frequency transformer core materials.

[0037] 2. This invention achieves the target permeability while maintaining a high saturation magnetic induction intensity (B). s ≥ 1.0 T) and lower coercivity (H c With a strength ≤ 2.5 A / m, it exhibits excellent overall soft magnetic properties. It is suitable as a core material for SST high-frequency transformers within the frequency range of 5–100 kHz.

[0038] 3. The magnetic core preparation method proposed in this invention is stable and reliable. It uses vacuum induction melting combined with single-roll quenching to prepare amorphous ribbon, and has a wide annealing process window (nanocrystalline structure can be obtained at 500℃~570℃), making it suitable for industrial mass production. This invention fills the technological gap in the prior art where there is no iron-based nanocrystalline magnetic core material specifically for SST high-frequency transformers, providing key material support for the industrialization and application of SST. Attached Figure Description

[0039] Figure 1 The graph shows the relationship between the effective magnetic permeability of the alloys in Comparative Example 1 and Examples 1-5 of this invention and the Ni content x at a frequency of 1 kHz.

[0040] Figure 2This is a comparison diagram of the hysteresis loops (BH curves) of the alloys in Comparative Example 1 and Examples 1-5 of the present invention. Detailed Implementation

[0041] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0042] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental materials and reagents used herein are commercially available products conventionally available in this technical field.

[0043] The magnetic cores obtained in the following embodiments or comparative examples were subjected to the following performance tests: the effective permeability μ of the magnetic core at a frequency of 1 kHz was measured using an impedance analyzer or a BH analyzer. e , saturation magnetic induction intensity B s and coercivity H c Isomagnetic properties.

[0044] Comparative Example 1

[0045] According to atomic percentage Fe 73.5 Si 15.5 B7Cu1Nb 1.5 V 1.5 (i.e., x=0) Ingredients: Weigh out industrial pure iron (purity ≥99.9%), industrial silicon (purity ≥99.5%), ferroborone alloy (B content 16~20 wt%), electrolytic copper (purity ≥99.99%), ferroniobium alloy (Nb content 60~68 wt%), and ferrovanadium alloy (V content 50~55 wt%), and then convert the atomic percentages to mass percentages before mixing.

[0046] The prepared raw materials are placed in a vacuum induction melting furnace and heated under vacuum (20 Pa) to a temperature of 1500℃~1570℃ for 180 min to fully melt and homogenize the alloy, thus obtaining the master alloy melt.

[0047] Amorphous ribbons were prepared using a single-roll quenching method: the master alloy was remelted, and then the melt was injected into a spraying ladle and poured through a boron nitride nozzle onto the surface of a high-speed rotating copper roller. The linear velocity of the copper roller surface was 28 m / s, and the cooling rate was approximately 10 m / s. 6 K / s yielded a continuous amorphous ribbon with a thickness of approximately 20 μm and a width of 42 mm.

[0048] The amorphous strip is slit into strips with a width of 10 mm by a slitting machine, and then wound into a toroidal magnetic core with an outer diameter of 30 mm, an inner diameter of 20 mm, and a height of 10 mm on an automatic winding machine. The filling factor of the magnetic core is 79%.

[0049] The magnetic core was placed in a vacuum heat treatment furnace with a vacuum of -0.1 MPa. It was first heated from room temperature to 420°C at a rate of 8°C / min and held for 60 min. Then it was heated to 460°C at a rate of 1°C / min and held for 90 min. Next, it was heated to the target temperature of 555°C at a rate of 1°C / min and held for 120 min. Finally, it was cooled to below 300°C in the furnace and removed.

[0050] The annealed magnetic core was placed in an epoxy resin impregnation solution and impregnated under vacuum (-0.1 MPa) for 20 min, and then cured at 130℃ for 2 h.

[0051] Impedance analyzer (Wayne Kerr 6500B) was used to test the core's μ-voltage at a frequency of 1 kHz and an excitation voltage of 0.3 V. e μ was measured e = 106,000; saturation magnetic induction intensity B was measured using a static BH meter. s = 1.17 T, coercivity H c = 0.8 A / m.

[0052] This embodiment is a reference composition without added Ni, with an effective permeability of over 100,000 at 1 kHz, exceeding the optimal range (10,000~30,000) for SST cores.

[0053] Example 1

[0054] According to atomic percentage Fe 72.5 Si 15.5 B7Cu1Nb 1.5 V 1.5 Ni1 (i.e., x=1) ingredient preparation. Except for the addition of electrolytic nickel (purity ≥99.9%), the other raw materials are the same as those in Comparative Example 1, and the ingredients are prepared according to the mass percentage conversion. Furthermore, the other processes are the same as those in Comparative Example 1.

[0055] Magnetic property test results: Effective permeability μ at 1 kHz e =80,000, saturation magnetic induction intensity B s =1.21 T, coercivity H c =0.6 A / m.

[0056] In this embodiment, after adding 1 at% Ni, the effective permeability μ e =80,000, which still exceeds the target range for SST magnetic cores (10,000 to 30,000).

[0057] Example 2

[0058] According to atomic percentage Fe 71 Si 15.5 B7Cu1Nb 1.5 V 1.5 Ni 2.5 (i.e., x=2.5) Ingredients. Other raw materials are the same as in Comparative Example 1, and are prepared according to the mass percentage conversion. All other processes are the same as in Comparative Example 1.

[0059] Magnetic property test results: Effective permeability μ at 1 kHz e =37,000, saturation magnetic induction intensity B s =1.24 T, coercivity H c =0.4 A / m.

[0060] In this embodiment, after adding 2.5 at% Ni, the effective permeability μ at 1 kHz is... e =37,000, still exceeding the optimal range (10,000~30,000) for SST cores. Meanwhile, the saturation magnetic induction intensity remains at a high level (B s =1.22 T), with a coercivity of only 0.4 A / m.

[0061] Example 3

[0062] According to atomic percentage Fe 68.5 Si 15.5 B7Cu1Nb 1.5 V 1.5 Ni5 (i.e., x=5) was used for ingredient preparation. Other raw materials were the same as in Comparative Example 1, and were prepared according to the mass percentage conversion. All other processes were also the same as in Comparative Example 1.

[0063] Magnetic property test results: Effective permeability μ at 1 kHz e =24,000, saturation magnetic induction intensity B s =1.1 T, coercivity H c =0.75 A / m.

[0064] In this embodiment, after adding 5 at% Ni, the effective permeability μ e The price was further reduced to 24,000, falling within the target range for SST cores (10,000 to 30,000), and the overall performance met the requirements of SST.

[0065] Example 4

[0066] According to atomic percentage Fe 63.5 Si 15.5 B7Cu1Nb 1.5 V 1.5 Ni 10(i.e., x=10) Ingredient preparation. Other raw materials are the same as in Comparative Example 1, and are prepared according to the mass percentage conversion. All other processes are the same as in Comparative Example 1.

[0067] Magnetic property test results: Effective permeability μ at 1 kHz e =14,000, saturation magnetic induction intensity B s =1.16 T, coercivity H c =2.6 A / m.

[0068] In this embodiment, the effective permeability decreased to 14,000 after adding 10 at%Ni, but the coercivity increased significantly, exceeding the target range (10,000~30,000) for SST cores.

[0069] Example 5

[0070] According to atomic percentage Fe 58.5 Si 15.5 B7Cu1Nb 1.5 V 1.5 Ni 15 (i.e., x=15) Ingredient preparation. Other raw materials are the same as in Comparative Example 1, and are prepared according to the mass percentage conversion. All other processes are the same as in Comparative Example 1.

[0071] Magnetic property test results: Effective permeability μ at 1 kHz e =0.4 million, saturation magnetic induction intensity B s =1.01T, coercivity H c =3 A / m.

[0072] In this embodiment, after adding 15 at% Ni, the effective permeability μ e It dropped to 0.4 million, below the lower limit of the target range (10,000~30,000) for SST cores, and the saturation magnetic induction intensity dropped to 1.01 T.

[0073] Example 6

[0074] Similar to Example 1, except that: a three-step annealing process is used, first the temperature is increased from room temperature to 400℃ at 4℃ / min and held for 120 min; then the temperature is increased to 460℃ at 0.5℃ / min and held for 120 min; then the temperature is increased to the target temperature of 500℃ at 0.5℃ / min and held for 180 min; finally, the temperature is cooled to below 300℃ in the furnace and removed. The impregnation and curing process is as follows: the annealed magnetic core is placed in epoxy resin or silicone resin impregnation liquid, vacuum impregnated for 10 min, and then cured at 120℃ for 4 h.

[0075] Example 7

[0076] Similar to Example 1, except that: a three-step annealing process is used, first the temperature is increased from room temperature to 440℃ at 10℃ / min and held for 60 min; then the temperature is increased to 500℃ at 1.5℃ / min and held for 60 min; then the temperature is increased to the target temperature of 570℃ at 1.5℃ / min and held for 90 min; finally, the temperature is cooled to below 300℃ in the furnace and removed. The impregnation and curing process is as follows: the annealed magnetic core is placed in epoxy resin or silicone resin impregnation liquid, vacuum impregnated for 30 min, and then cured at 150℃ for 2 h.

[0077] The magnetic properties of the alloys obtained in Comparative Example 1 and Examples 1-5 are shown in Table 1.

[0078] Table 1. Comparison of magnetic properties between Comparative Example 1 and Alloys of Examples 1-5

[0079]

[0080] From Table 1 and Figure 1 The data shows that as the Ni content x gradually increases from 0 to 15, the effective magnetic permeability μ of the alloy at a frequency of 1 kHz increases. e It exhibits a monotonically decreasing trend, decreasing from 106,000 in Comparative Example 1 to 4,000 in Example 5. When x=5, μ e This perfectly matches the optimal requirement of SST high-frequency transformers for the core material's effective permeability of 10,000 to 30,000 kHz. This indicates that within this range, the permeability can be precisely controlled to the ideal range by adjusting the Ni content.

[0081] like Figure 2 As shown, at saturation magnetic induction intensity B s In terms of T, the overall value fluctuates between 1.01 and 1.24. When x = 2.5, B... s Reaching 1.24 T, it is at a relatively high level; as the Ni content continues to increase, B... s It decreases somewhat, but remains at 1.1 T at x = 5, satisfying B. s The requirement of ≥ 1.0 T indicates that adding an appropriate amount of Ni has little effect on maintaining a high saturation magnetic induction intensity.

[0082] For coercivity H c The coercivity H is minimized at x = 2.5. c The coercivity is 0.4 A / m. As the Ni content further increases, the coercivity gradually increases, reaching 3 A / m at x = 15. Overall, at x = 5, the effective permeability requirement is met while maintaining a low coercivity (Hc ≤ 2.5 A / m).

[0083] In summary, analysis of the magnetic properties of alloys with different Ni contents reveals that x = 5 is the optimal Ni content. Iron-based nanocrystalline magnetic cores prepared near this value can meet the comprehensive performance requirements of high-frequency transformers in solid-state transformers for permeability, saturation magnetic induction, and coercivity. Ni atoms are dissolved in the α-Fe lattice. Due to the difference in their electronic structure compared to Fe, the arrangement of local magnetic moments and the energy state of domain walls are altered, thus changing the resistance to domain wall movement and consequently affecting permeability. This provides an important basis for the research and development of high-frequency transformer core materials for solid-state transformers.

[0084] The above description of the embodiments is only for the purpose of helping to understand the technical solution and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A magnetic core for a solid-state transformer, characterized in that, The alloy composition of the magnetic core, by atomic percentage, is Fe. a-x Si b B c Cu d Nb e V f Ni x , where: 50≤a≤79, 12.4≤b≤16.5, 6.6≤c≤9.7, 0.4≤d≤1.3, 1≤e≤3, 0≤f≤2, 0.5≤x≤20.0, and a+b+c+d+e+f=100.

2. The magnetic core for a solid-state transformer according to claim 1, characterized in that, The range of x is: 1≤x≤10.

3. The magnetic core for a solid-state transformer according to claim 2, characterized in that, The range of x is: 2.5≤x≤5.

0.

4. The magnetic core for a solid-state transformer according to any one of claims 1 to 3, characterized in that, The magnetic core is made of amorphous ribbon with a thickness of 10~25 μm through winding and crystallization annealing, and the filling factor of the magnetic core is ≥75%.

5. The magnetic core for a solid-state transformer according to any one of claims 1 to 3, characterized in that, The magnetic core has a saturation magnetic induction intensity Bs≥1.0 T and a coercivity Hc≤2.5 A / m.

6. The method for preparing a magnetic core for a solid-state transformer according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1, according to the alloy composition formula Fe a-x Si b B c Cu d Nb e V f Ni x Convert the atomic percentage of each element to the mass percentage and weigh out industrial pure iron, crystalline silicon, ferroborone alloy, copper, ferroniobium alloy, ferrovanadium alloy and nickel raw materials; S2. Place the raw materials weighed in step S1 into a vacuum induction melting furnace and melt them at 1450℃~1600℃ for 120~240 min under inert gas protection to obtain the master alloy melt. S3. The master alloy melt obtained in step S2 is prepared into an amorphous ribbon by a single-roller rapid cooling method. The surface linear velocity of the copper roller is 22~35 m / s, and a continuous amorphous ribbon with a thickness of 10~25 μm is obtained. S4. The amorphous ribbon obtained in step S3 is wound into a ring or rectangular magnetic core, and the filling factor of the magnetic core is ≥75%; S5. The magnetic core obtained in step S4 is subjected to a three-step annealing process under vacuum or a protective atmosphere. First, the temperature is increased from room temperature to 400℃~440℃ at a rate of 4~10℃ / min and held for 60~120 min. Then, the temperature is increased to 460℃~500℃ at a rate of 0.5~1.5℃ / min and held for 60~120 min. Next, the temperature is increased to the target temperature of 500℃~570℃ at a rate of 0.5~1.5℃ / min and held for 90~180 min. Finally, the core is cooled in the furnace to below 300℃ and then removed. S6: The magnetic core annealed in step S5 is impregnated and cured to obtain the magnetic core for the solid-state transformer.

7. The preparation method according to claim 6, characterized in that, In step S2, the metallurgy is carried out at 1500℃~1570℃ for 180 minutes.

8. The preparation method according to claim 6 or 7, characterized in that, In step S5, the protective atmosphere is high-purity nitrogen or high-purity argon. First, the temperature is increased from room temperature to 420°C at 8°C / min and held for 60 min; then, it is increased to 460°C at 1°C / min and held for 90 min; then, it is increased to the target temperature of 555°C at 1°C / min and held for 120 min; finally, it is cooled to below 300°C with the furnace and taken out.

9. The preparation method according to claim 6 or 7, characterized in that, In step S6, the impregnation and curing process is as follows: the annealed magnetic core is placed in an epoxy resin or silicone resin impregnation solution, vacuum impregnated for 10 to 30 minutes, and then cured at 120°C to 150°C for 2 to 4 hours.

10. The application of the magnetic core according to any one of claims 1 to 3 in a solid-state transformer, characterized in that: The solid-state transformer operates in the frequency range of 5~100 kHz, and the magnetic core is used as the magnetic core of the high-frequency transformer in the solid-state transformer. And / or, the solid-state transformer is applied in the fields of AI data centers, new energy grid connection, electric vehicle charging stations or smart grids.

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