Inductor structure

Abstract

The invention provides an inductor structure. The inductor structure includes a plurality of magnetic cores, wherein each magnetic core includes a central post. Any two adjacent magnetic cores are separated by a first gap, and the size of the first gap enables the magnetic flux of a magnetic flux path formed by the first gap to be half of the magnetic flux flowing through the central column.

Description

Technical Field

[0001] The present invention relates to a matrix inductor design with medium voltage isolation, and more particularly to an inductor structure for medium voltage and high voltage applications. Background Art

[0002] The development of power semiconductor devices using wide bandgap materials such as silicon carbide (SiC) has opened a new era for the field of power conversion. With such materials, it has become possible to fabricate power devices with high blocking voltages and reasonable on-resistances at high switching frequencies. The advantages of such power devices themselves have prompted many industries to switch to using SiC-based power semiconductor devices.

[0003] SiC power devices have led to extensive research in the field of medium voltage solid state transformers. For applications such as electric vehicle charging infrastructure, power supply for data centers, grid interconnection, etc., medium voltage solid state transformers are advantageous solutions. Compared to traditional line frequency transformers (the current solutions), the main advantages of solid state transformers are the reduction in the size of the power conversion stage while also having advantages such as reactive power control and renewable energy integration. The reduction in the size of the solid state transformer is mainly achieved by replacing the traditional line frequency transformer with a high frequency transformer. In addition, a power electronic interface is required to interface the high frequency transformer with the grid, where the power electronic interface and the high frequency transformer together are regarded as the solid state transformer. Generally, a solid state transformer has an AC / DC stage and a DC / DC stage, where the AC / DC stage is used to interface the solid state transformer with the grid, and the DC / DC stage is used to provide the required electrical isolation. In the AC / DC stage, in order to interface the power electronic interface with the grid, inductors are often used to filter out high frequency current components generated by the power electronic interface. Depending on the topology of the DC / DC stage, inductors can also be used for power conversion. Since the converter operates at high frequencies, the current flowing through the inductor is mostly a high frequency current. In a medium voltage system, the inductors are used to block the medium voltage level and have medium voltage isolation between them. To achieve reliable medium voltage isolation, not only can the voltage be blocked through system design, but also the degradation of the isolation structure can be avoided through operation without partial discharge. Therefore, this isolation is usually designed to ensure that the electric field in the system (or the surrounding air) does not exceed its rated operating voltage (allowing for some tolerance).

[0004] Medium-voltage inductance systems have been used in power systems for many years and, like traditional line-frequency transformers, are also designed to operate at line frequency, especially in high-power applications. As mentioned above, the introduction of silicon carbide technology has made it possible to operate high-frequency converters, but medium-voltage inductance technology based on line-frequency operation is not suitable for medium- and high-frequency operation. For example, due to the low-frequency characteristics of the current flowing through the medium-voltage inductor, the volume of the medium-voltage inductor is relatively large, and power density is not the main concern in typical applications. The magnetic core can be made of silicon steel and paired with solid copper windings. In the inductor, the solid copper windings are sealed with an insulating material, and a sufficient air gap is provided between the windings and the magnetic core to achieve medium-voltage isolation.

[0005] In medium-voltage medium-frequency inductors, it is not an optimal practice to use a magnetic core made of silicon steel and solid copper windings, for at least two reasons. First, at medium-frequency operation, a magnetic core made of silicon steel and solid copper windings will cause relatively large losses and thus is not adopted. Specifically, due to the skin effect, solid copper is not commonly used in medium- and high-frequency applications. Affected by the skin effect, in medium- and high-frequency currents, since the current only flows on the surface of the winding, the effective cross-sectional area of the solid copper winding will decrease, resulting in an increase in the effective resistance of the winding and thus an increase in losses. In addition, silicon steel has a high saturation magnetic flux density and can thus operate at high peak magnetic fluxes, but due to the relatively large flux swings, the core losses are also relatively large. Since the core losses are relatively large, high-frequency operation will significantly increase the core losses, so silicon steel or similar materials are not suitable (or at least not favored) in such applications.

[0006] In addition, most applications related to medium-frequency inductors (such as solid-state transformers) usually focus more on the power density of magnetic components. Therefore, providing an air gap for medium-voltage isolation, which causes an excessive increase in the size of the magnetic components, is not feasible.

[0007] To alleviate the problems faced by existing inductor designs, some methods for low-voltage (e.g., less than 2 kV) applications have been developed. For example, the silicon steel used as the magnetic core can be replaced with other materials, such as ferrite, nanocrystalline, or amorphous cores, which have relatively small core losses and can thus be used in high-frequency operation. The solid copper windings can be replaced with litz wire, which is designed for medium- and high-frequency operation. Although the parameters of the litz wire need to be determined according to the operating frequency, the structure of the litz wire is designed to eliminate (or substantially eliminate) the skin effect at a specific frequency and minimize the AC resistance. However, medium-voltage (e.g., about greater than 3.3 kV) inductors have additional isolation requirements and need to achieve partial-discharge-free operation (to ensure continuous and reliable operation). How to achieve reliable medium-voltage operation while achieving high efficiency and high power density remains a major challenge.

[0008] In the existing literature, many efforts have been made in the design of medium-voltage inductors and transformers. The most basic method of designing an inductor to achieve the required voltage isolation is to follow the traditional design and provide gaps between the magnetic core and the winding, as well as between the layers of each winding, as shown in Figure 1A (front view) and Figure 1B (top view of one of the windings). Specifically, Figure 1A and Figure 1B show an inductor 10, which includes a magnetic core 12 and a winding group 16. As shown in Figure 1A , the magnetic core 12 includes a magnetic core pair formed by a top part and a bottom part, and there is a gap 14 between the top part and the bottom part. Figure 1B shows a leg of the magnetic core 12. The winding group 16 surrounds each leg (left and right legs) of the magnetic core 12. The winding group 16 includes a winding support structure (or simply referred to as a support structure) for supporting a plurality of winding layers. For example, in Figure 1A and Figure 1B , the winding support structure includes a bobbin support 18 and a plurality of supports 20 (including supports 20a, 20b), where the bobbin support 18, support 20a, and support 20b are separated by spacers 22. Support 20a supports a winding layer 24, and support 20b supports another winding layer 26. It should be noted that the air gaps between the various structures are represented by white spaces in the figure, and in some cases, in applications using encapsulation, the plurality of air gaps are filled with encapsulation materials. Medium-voltage isolation can be achieved by using the bobbin support 18. Although in some applications, the bobbin support 18 can also be replaced by other support structures (which can be one or more layers of paper sheets, such as Nomex paper or mica paper). In addition, in some variant structures, the windings and / or the magnetic core are encapsulated or filled with oil to reduce the air gap distance or increase the medium-voltage isolation ability. However, considering environmental factors and / or fire risks, inductors / transformers encapsulated or filled with oil are generally not preferred, and dry isolation is more preferred. In applications where the inductor 10 mainly carries low-frequency current, solid copper windings can be used, so encapsulation (or dry isolation) is a viable option. However, if Litz wire is used (such as in high-frequency designs), the encapsulation process is usually unreliable and not used. If isolation is carried out without encapsulation and exposed to air, it will be difficult to expand the application to higher voltages and partial-discharge-free operation. SUMMARY OF THE INVENTION

[0009] According to an embodiment of the present invention, the present invention provides an inductor including a plurality of magnetic cores, where each magnetic core includes a central column. Any two adjacent magnetic cores are separated by a first gap, and the size of the first gap is such that the magnetic flux of the magnetic flux path formed is half of the magnetic flux flowing through the central column.

[0010] Aspects of the present invention will be described in the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Aspects of the present invention may be more readily understood with reference to the following schematic diagrams, in which the components are used to illustrate the present invention and are not necessarily drawn to scale. Further, in the various schematic diagrams, like reference numerals are used to denote corresponding parts.

[0012] Figure 1A and Figure 1B shows an inductor / transformer approach that achieves the required isolation by providing gaps between windings and between the windings and the magnetic core.

[0013] Figure 2A and Figure 2B shows the concept of splitting a medium - voltage inductor into multiple low - voltage series inductors.

[0014] Figure 3 is Figure 2A and Figure 2B a schematic diagram of the series inductors and the magnetic flux paths flowing through each magnetic core in

[0015] Figure 4 is for Figure 3 a schematic diagram of arranging and connecting the magnetic cores adjacent to each other in

[0016] Figure 5 is for reducing the overall volume of the series inductor structure shown in Figure 4 by combining magnetic cores and removing part of the magnetic core columns.

[0017] Figure 6 is a schematic diagram of an inductor according to an embodiment of the present invention.

[0018] Figure 7 is Figure 6 a schematic diagram of the reluctance model of the inductor in

[0019] Figure 8 is a schematic diagram of an inductor according to another embodiment of the present invention.

[0020] Figure 9 is Figure 8 a schematic diagram of the reluctance model of the inductor in

[0021] Figure 10 is a schematic diagram of an inductor according to another embodiment of the present invention.

[0022] Figure 11 is Figure 10 a schematic diagram of the simulated magnetic flux density distribution of the inductor shown in

[0023] Figure 12A and Figure 12B show two implementation methods of the inductor according to the embodiment of the present invention.

[0024] Figure 13 Schematic diagram of a method for increasing the electrical clearance and creepage distance between high-voltage potentials while maintaining the required high-voltage isolation between cores.

[0025] Figure 14 Schematic diagram of a method for increasing the electrical clearance and creepage distance between high-voltage potentials while maintaining the required high-voltage isolation between cores and maintaining PD-free operation.

[0026] Figure 15 Schematic diagram of a method for increasing the thickness of the spacer outside the gap when the spacer in the gap is not sufficient to achieve the required effect.

[0027] Figure 16 Schematic diagram of a method for encapsulating adjacent parts of the core to achieve the required high-voltage isolation.

[0028] The reference numerals are as follows:

[0029] 10: Inductor

[0030] 12: Core

[0031] 16: Winding group

[0032] 14: Gap

[0033] 18: Spool support

[0034] 20, 20a, 20b: Support

[0035] 22: Spacer

[0036] 24, 26: Winding layer

[0037] 30: Medium-voltage inductor

[0038] 32: Core

[0039] 33: Gap

[0040] 34: Winding group

[0041] 35: Winding layer

[0042] 36: Series inductor structure

[0043] 37: Series connection

[0044] 38, 38a, 38b, 38c, 38d: Inductor

[0045] 35a: First winding layer

[0046] 35b: Second winding layer

[0047] 35c: The third winding layer

[0048] 35d: The fourth winding layer

[0049] Vmax: Voltage

[0050] 50: Matrix inductor

[0051] 52: Magnetic core

[0052] 60: Matrix inductor

[0053] 61, 61a, 61b, 61c, 61d: Central column

[0054] 62, 62a, 62b, 62c, 62d: Magnetic core

[0055] 64, 64a, 64b, 64c, 64d: Central column gap

[0056] 66, 66a, 66b, 66c, 66d: Winding group

[0057] 63, 63a, 63b: Side column

[0058] 68, 68a, 68b: Side column gap

[0059] 69, 69a-1, 69b-1, 69c-1, 69a-2, 69b-2, 69c-2: Magnetic core gap

[0060] 70: Magnetic resistance model

[0061] R1, R2, R3: Magnetic resistance

[0062] 80: Matrix inductor

[0063] 82, 82a, 82b, 82c, 82d: Magnetic core

[0064] 84, 84a, 84b, 84c, 84d: Central column

[0065] 83, 83a, 83b: Side column

[0066] 90: Magnetic resistance model

[0067] 100: Matrix inductor

[0068] 102, 102a, 102b, 102c, 102d: Magnetic core

[0069] 104, 104a, 104b, 104c, 104d: Central column

[0070] 102e, 102f: Side magnetic core

[0071] 108, 108a, 108b: Side posts

[0072] 106, 106a-1, 106b-1, 106a-2, 106b-2: Side clearances

[0073] 110: Magnetic flux density distribution

[0074] 112, 114, 116: Magnetic field strength markings

[0075] 120A, 120B: Matrix inductors

[0076] 102g: Magnetic core

[0077] 130: Spacer

[0078] 132: Semiconductor coating

[0079] 134: Encapsulation material Detailed implementation manners

[0080] The present invention discloses some embodiments related to matrix medium-voltage inductors (hereinafter also simply referred to as inductors or matrix inductors), which can achieve a partial discharge-free design without additional encapsulation and use a non-uniform magnetic core structure with a smaller volume. In some embodiments, the matrix inductor confines the electric field in the air to an operating voltage level lower than the air breakdown voltage to achieve partial discharge-free operation. Since there is no need to encapsulate the winding, this structure can utilize the advantages of Litz wire to achieve low loss and good heat dissipation performance. Moreover, due to the use of multiple magnetic cores and windings, this structure provides a modular design method for medium-voltage inductors. In addition, compared with the series magnetic core structure, the overall volume of this structure is smaller.

[0081] It should be noted that the so-called "non-uniform" magnetic core structure refers to a magnetic core structure used for medium / high-voltage inductors and can be at different potentials, rather than the overall magnetic core having a consistent potential due to the continuity of the magnetic core like a "unified core".

[0082] As mentioned above, generally speaking, it is challenging to achieve medium-voltage isolation in a conversion system. There are currently various methods for constructing medium-voltage inductors. Although some methods perform well in terms of efficiency and partial discharge-free operation, they are not easy to mass-produce and / or cannot achieve modularization. To solve the problems faced in the design of medium-voltage inductors, the present invention proposes some embodiments of matrix medium / high-voltage inductors, which have significant advantages compared with existing designs. In one embodiment, the disclosed matrix medium / high-voltage inductor provides an efficient, modular and encapsulation-free approach. Since the modular characteristics of the inductor are more favored in some embodiments, a single magnetic core (or even a unified magnetic core) structure is not considered.

[0083] Note that the medium voltage mentioned refers to the voltage value or voltage range commonly accepted in the power conversion industry. For example, in some embodiments, the medium voltage includes voltages between approximately 3.3 kV and 22 kV, and the high voltage is considered to be a voltage higher than this range.

[0084] After outlining the characteristics of the matrix inductor of the disclosed embodiments of the present invention, the matrix inductor illustrated in the drawings will be described in detail below. Although the matrix inductor includes a specific number of magnetic cores and / or winding layers in the description made according to the drawings, the present invention is not limited thereto. For example, the embodiments are equally applicable to inductor structures with different numbers of magnetic cores and / or winding layers. In addition, although the description focuses on medium voltage inductors, those of ordinary skill in the art should understand that high voltage inductors can also achieve their effects according to the description of the present invention, and thus are also within the scope of the present invention. Additionally, although specific details in one or more embodiments are determined or described during the description, the multiple specific details are not limited to being essential parts of each embodiment, and the various advantages stated are not limited to being achieved by a single embodiment. The present invention aims to cover various alternatives, modifications, and equivalent solutions within the principles and protection scope defined by the appended claims of the present invention. For example, two or more embodiments may interchange features or be combined in any combination. Furthermore, it should be noted that the appended claims are not limited to a specific embodiment described in the present invention.

[0085] Regarding the concept of the matrix medium voltage inductor, it can be described based on series-connected low voltage inductors. Generally speaking, a series-connected low voltage inductor is formed by dividing a medium voltage inductor into multiple smaller low voltage inductors and connecting them in series. Since the voltage to be blocked between multiple low voltage inductors is smaller, this approach has advantages in terms of modularity and isolation ability of the structure. In some embodiments, it should also be noted that the magnetic core should not be grounded to avoid violating the purpose of using a series structure, and medium voltage isolation is still required between the winding and the magnetic core for each inductor. The magnetic core can be maintained floating or connected to a terminal of one of the inductors (to define the potential of the magnetic core). In addition to modularity, the present invention has some special advantages. For example, since each inductor can be regarded as multiple independent low voltage inductors, there is no need for potting or encapsulation. Furthermore, due to the absence of potting, this structure can use Litz wire. In some embodiments, since the magnetic core is floating (or at a high potential), the placement of the inductor needs to be fully considered (such as the position of the actual grounding surface). In addition, the overall volume of the series structure is usually larger than the volume of a single medium voltage inductor.

[0086] The series inductor structure is further described below. Please refer to Figure 2A and Figure 2B . Figure 2A is the front view of a single inductor, Figure 2B is the front view of the series inductor structure, Figure 2A andFigure 2B illustrates the concept of splitting a medium - voltage inductor into multiple low - voltage series - connected inductor structures. As Figure 2A shown, it shows a medium - voltage inductor 30. The medium - voltage inductor 30 includes a magnetic core 32, and the magnetic core 32 includes a magnetic - core pair. The top part and the bottom part of the magnetic - core pair are separated by a gap 33. Generally, the magnetic - core structure includes a top post, a center post, a bottom post, and two side posts. It should be noted that multiple posts are sometimes also referred to as legs. The magnetic core 32 also includes a winding group 34, where the winding group 34 includes a support structure (such as including a bobbin support) for supporting multiple winding layers 35 wound helically around or about the center post, similar to Figure 1A and Figure 1B shown. In this example, the medium - voltage inductor 30 has four winding layers 35, with a turn number of N, an inductance value of L, and the cross - sectional area of the center post being Ac.

[0087] To obtain the same inductance value L in a series structure, the cross - sectional area of the magnetic core is the same, and the windings can be split according to the Figure 2B illustrated series - inductor structure 36. Among the four inductors 38a, 38b, 38c, and 38d (collectively referred to as inductors 38) with a series connection 37 within the series - inductor structure 36, the number of turns of the winding on each inductor 38 is N / 4. For such a series structure, since four smaller inductors 38 (using the first to the fourth magnetic cores respectively) are used, the volume increases to Figure 2A four times the volume of a single magnetic core 32 in Figure 2A . In this example, the inductor 38a includes a first winding layer 35a, the inductor 38b includes a second winding layer 35b (connected to the first winding layer 35a through the series connection 37), the inductor 38c includes a third winding layer 35c (connected to the second winding layer 35b through the series connection 37), and the inductor 38d includes a fourth winding layer 35d (connected to the third winding layer 35c through the series connection 37). Such a structural arrangement causes an increase in the volume and core loss of the series - inductor structure 36. For a single medium - voltage inductor 30 in medium - voltage applications, corresponding designs need to be made for the isolation of the inductor. To withstand the voltage Vmax, the isolation between windings and the isolation between windings and the magnetic core need to be designed according to the voltage Vmax. However, in medium - voltage applications, the voltage Vmax is usually very high, so it is actually difficult to design to achieve such a high level of isolation. This is one of the advantageous features of the series - inductor structure 36. For example, since Figure 2A the medium - voltage inductor 30 is split into Figure 2BFour inductors 38 connected in series, so each inductor 38 is designed to block only a voltage of Vmax / 4 and the corresponding isolation is designed. In some embodiments, one of the limitations of using this series inductor structure 36 is that the magnetic core cannot be grounded. If the magnetic core is grounded, medium voltage isolation between the winding and the magnetic core still needs to be achieved in the series inductor structure. The magnetic core can be kept floating (not connected to a specific potential) or connected to the potential of one of the local ends. It should be noted that if the magnetic core is connected to the potential of the local end, it should be ensured that all magnetic cores are connected to the terminals of relatively lower voltage or higher voltage (i.e., according to the selected connection, all magnetic cores are connected to the lower voltage, or all magnetic cores are connected to the higher voltage). In addition to the lower isolation requirements, the series structure also has advantages in terms of parasitic capacitance. Since the same four inductors are connected in series, it helps to significantly reduce the parasitic capacitance. For example, in this example, if Figure 2A the parasitic capacitance in is C, then Figure 2B the parasitic capacitance in is C / 4.

[0088] The matrix inductor solves the problems of large volume and core loss of the series inductor. Please refer to Figure 3 which shows Figure 2B the series inductor structure 36 in (the same components are labeled with the same reference numerals), and adds the magnetic flux paths flowing through each series inductor 38. It should be noted that there is no magnetic flux in the gaps between the magnetic cores. Based on the series connection method, the direction of the magnetic flux path can be changed.

[0089] In Figure 4 (the components corresponding to Figure 2B and Figure 3 are represented by the same reference numerals), the gaps between the magnetic cores of the series-connected multiple inductors 38 are removed, and the magnetic cores are adjacent to each other. It should be noted that as Figure 4 shown, in the part (or column) where the gaps between the magnetic cores are removed, the magnetic fluxes cancel each other out. If the columns where the magnetic fluxes cancel each other out are combined, the magnetic flux in the multiple columns is zero. Furthermore, since the magnetic flux in the multiple columns is zero, multiple columns can be eliminated, thereby generating a matrix inductor 50 as shown in Figure 5 . The matrix inductor 50 includes a magnetic core 52 and multiple winding groups, where the magnetic core 52 has a magnetic core pair (including a top part and a bottom part), and the multiple winding groups include multiple winding layers 35. The magnetic core 52 can be regarded as a uniform magnetic core structure (the potential of the magnetic core is the same everywhere inside), compared with the previous structure including the series-connected inductors 38 ( Figure 2B) has a smaller volume compared to it. By changing the gap, the direction and magnitude of the magnetic flux can be designed according to requirements. In an ideal case, if the gap is designed in this way, the required inductance value remains unchanged at L. From a structural perspective, it should be noted that the magnetic core 52 is a consistent structure. To achieve medium-voltage isolation, the isolation between the winding and the magnetic core needs to be designed according to the maximum voltage Vmax. The transition from a non-consistent magnetic core to a consistent magnetic core loses one of the important advantages of using series inductors in medium-voltage applications. However, the arrangement of the matrix inductor 50 has advantages in low-voltage applications, mainly reducing the parasitic capacitance of the matrix inductor 50.

[0090] Figure 6 Figure 60 shows a matrix inductor 60 according to an embodiment of the present invention. The matrix inductor 60 includes a single medium-voltage inductor that adopts the concept of a medium-voltage matrix inductor. In this embodiment, the matrix inductor 60 includes four central columns (or central pins) 61 (such as central columns 61a, 61b, 61c, and 61d). The specific number of central columns 61 is not limited to this, but can be determined according to actual requirements. Specifically, in this embodiment, the matrix inductor 60 includes a plurality of magnetic cores 62 (such as magnetic cores 62a, 62b, 62c, and 62d). Each magnetic core 62 includes a pair of magnetic cores, where each pair of magnetic cores includes a top part and a bottom part, and the top part and the bottom part are separated by a corresponding central column gap 64 (such as central column gaps 64a, 64b, 64c, and 64d). In addition, the matrix inductor 60 further includes a plurality of winding groups 66 (such as winding groups 66a, 66b, 66c, and 66d). In some embodiments, each winding group 66 includes a bobbin support, where the bobbin support includes a corresponding winding layer and a winding layer support (which can also be simply referred to as a support). In some embodiments, one or more layers of paper sheets (such as Nomex paper or mica paper) can also be used as a support structure, for example, to replace the bobbin support. The winding groups 66a, 66b, 66c, and 66d respectively include a first winding layer 35a, a second winding layer 35b, a third winding layer 35c, and a fourth winding layer 35d. In the shown embodiment, the support structure of the winding group 66 supports the winding layer 35, and the winding layer 35 surrounds the central column 61 of the magnetic core 62. In this embodiment, the first winding layer 35a surrounds the central column 61a, the second winding layer 35b surrounds the central column 61b, the third winding layer 35c surrounds the central column 61c, and the fourth winding layer 35d surrounds the central column 61d. The matrix inductor 60 further includes two side columns 63 (such as side columns 63a and 63b), and the side columns 63a and 63b respectively have side column gaps 68a and 68b (collectively referred to as side column gaps 68), where the side column gaps 68a and 68b are on the same straight line as the central column gaps 64.

[0091] The matrix inductor 60 further includes core gaps 69 (such as top core gaps 69a-1, 69b-1, and 69c-1, and core gaps 69a-2, 69b-2, and 69c-2 respectively located below the corresponding top core gaps), and these core gaps are located between the top portions and the bottom portions of adjacent cores 62. For example, core gaps 69a-1 and 69a-2 are arranged along the vertical axis in Figure 6 and are respectively located between the top portions and the bottom portions of adjacent cores 62a and 62b. Further illustration, core gap 69a-1 vertically extends between the top portion of core 62a and the top portion of core 62b, and core gap 69a-2 vertically extends between the bottom portion of core 62a and the bottom portion of core 62b. Although core gaps 69a-1 and 69a-2 are aligned along the vertical axis, there is a separation space between them, and a part of the adjacent winding groups is accommodated in the separation space. For example, there is a separation space between core gaps 69a-1 and 69a-2, and a part of winding group 66a (including the first winding layer 35a) and a part of winding group 66b (including the second winding layer 35b) are accommodated in the separation space. From Figure 6 it can be seen that there is a magnetic flux path (the magnetic flux is ) passing through the central column 61 and spanning the core gaps 69 on each side of the central column 61, where the magnetic flux passing through the central column 61 is, for example, (with the corresponding direction or polarity), and the magnetic flux spanning the core gap 69 is, for example, (with the corresponding direction or polarity). For example, the magnetic flux path (the magnetic flux is ) passes through the central column 61b of core 62b and flows to core 62a via core gap 69a-1 (for example, the magnetic flux is ), and at the same time flows to core 62c via core gap 69b-1 (for example, the magnetic flux is ). There is no magnetic flux path in the separation space. Based on a similar manner, core gaps 69b-1 and 69b-2 separate cores 62b and 62c, and core gaps 69c-1 and 69c-2 separate cores 62c and 62d. In addition, in this embodiment, the direction of core gap 69 is perpendicular to the directions of central column gap 64 and side column gap 68.

[0092] In some embodiments, the winding group 66 includes Litz wire wound around or surrounding the central column 61 of the magnetic core 62. Depending on the application requirements, PCB-type winding can be used. As shown in the figure, the magnetic core 62 presents a non-uniform concept, where the required inductance value is obtained by designing the size of the magnetic core gap 69 and the necessary voltage isolation between the magnetic cores 62 is provided. In other words, the size of the magnetic core gap 69 is determined by the required inductance value and voltage isolation. In fact, the requirement of voltage isolation should be considered during the design stage of such a matrix inductor 60.

[0093] Figure 7 The reluctance model 70 of the matrix inductor 60 (such as Figure 6 shown) for medium voltage is shown. The reluctances R1, R2, and R3 can be determined by the length of the gap and the cross-sectional area (Ac) of the central column 61, where the reluctance R1 corresponds to the four central column gaps 64, the reluctance R2 corresponds to the side column gap 68, and the reluctance R3 corresponds to the top and bottom magnetic core gaps 69. According to Figure 7 the shown reluctance model 70, the reluctance R1 can be obtained from the following formula:

[0094]

[0095] Similarly, the reluctance R2 is:

[0096]

[0097] The reluctance R3 is:

[0098]

[0099] where lg1, lg2, and lg3 are the lengths of the corresponding gaps respectively, Ac is the cross-sectional area of the central column 61, and Ac / 2 is the cross-sectional area of the side column 63 and the columns at the top and bottom (as Figure 6 shown). Since the winding is wound around the central column 61, Figure 7 the reluctance model 70 of Figure 7 also shows the magnetic flux sources (with corresponding polarities). The reluctance R3 needs to be equal to the reluctance R2 to maintain Figure 6 the shown magnetic flux distribution (the magnetic flux passing through the side column 63 is equal to the magnetic flux passing through the columns at the top and bottom). According to Figure 6 and Figure 7 it can be seen that the magnetic flux across the magnetic core gap 69 is equal to half of the magnetic flux flowing through the central column 61. For example, in the shown embodiment, the magnetic flux flowing through the magnetic core gap 69 (such as the magnetic core gap 69a-1) is half of the magnetic flux flowing through the central column 61 (such as the central column 61b), which is a preferred situation for the size and operation of a medium voltage matrix inductor. The values of the reluctances R1, R2, and R3 can be designed according to the required inductance value, peak magnetic flux density, and cross-sectional area.

[0100] Figure 8The matrix inductor 80 showing another embodiment of the present invention is Figure 6 a variation of the matrix inductor 60 shown, where the reluctance R1 is equal to zero. The matrix inductor 80 includes a plurality of magnetic cores 82 (such as magnetic cores 82a, 82b, 82c, and 82d), a plurality of central columns 84 (such as central columns 84a, 84b, 84c, and 84d), and a plurality of side columns 83 (such as side columns 83a and 83b), similar to Figure 6 that shown. In Figure 8 , the winding group is similar to that shown in Figure 6 , so it will not be labeled separately here and will not be elaborated further. It should be noted that in the embodiment shown in Figure 8 , the central column gap 64 in Figure 6 is removed. Preferably, a medium-voltage matrix inductor such as that shown in Figure 8 should have side column gaps 68 (air gaps) on the side columns 83 and core gaps 69 (air gaps) on the top and bottom columns to provide voltage isolation. A plurality of side column gaps 68 and core gaps 69 are also used to provide the required inductance value. In addition, removing the central column gap 64 (air gap) as shown in Figure 6 can reduce the total number of required air gaps, making the inductor easier to design and manufacture. It should be noted that when manufacturing the matrix inductor 80, it is not mandatory for the central columns 84 (such as central columns 84a, 84b, 84c, and 84d) to be integrally formed, as this may increase the difficulty of automatic assembly. In some embodiments, the central column 84 may include two or more components, and the gap between the multiple components is much smaller than the core gap 69, thus maintaining the reluctance R1 close to zero.

[0101] Figure 9 Shows Figure 8 the reluctance model 90 of the medium-voltage matrix inductor 80 shown. As shown in Figure 9 , since the reluctance R1 is equal to zero, it is replaced by a short circuit wire. By adjusting the reluctances R2 and R3 according to the required inductance value, cross-sectional area, and peak current flowing through the winding, the same magnetic flux distribution as in Figure 6 can be maintained. Additionally, in this embodiment, the magnetic flux flowing through the core gap 69 is half of the magnetic flux flowing through the central column 84, similar to the embodiments shown in Figure 6 and Figure 7 .

[0102] Figure 10 The matrix inductor 100 showing another embodiment of the present invention is Figure 8A variation example of the matrix inductor 80 shown. Similar to FIGS. 6 and 8, the matrix inductor 100 includes a plurality of magnetic cores 102 (such as magnetic cores 102a, 102b, 102c, and 102d), each magnetic core 102 includes a corresponding central column 104 (such as central columns 104a, 104b, 104c, and 104d), and there is a magnetic core gap 69 between adjacent magnetic cores 102. Additional side magnetic cores 102e and 102f are respectively located on opposite sides of the matrix inductor 100, and the side magnetic cores 102e and 102f respectively include side columns 108a and 108b (collectively referred to as side columns 108). As can be seen from Figure 8 the side column 83 has a side column gap 68 (air gap), and this air gap results in a complex magnetic core shape at both ends of the medium-voltage matrix inductor 80. Considering the manufacturing complexity, this arrangement is not the most ideal. Figure 10 Each magnetic core of the matrix inductor 100 shown has a symmetric structure, and it replaces the side column gap 68 in Figure 8 with side gaps 106 (such as side gaps 106a-1 and 106b-1 between the top parts and side gaps 106a-2 and 106b-2 between the bottom parts), and the side gaps 106 are parallel to the magnetic core gap 69. In fact, to achieve the overall structure, basically two simple magnetic core shapes are required. One magnetic core shape is suitable for magnetic cores 102a, 102b, 102c, and 102d, and the other magnetic core shape is suitable for side magnetic cores 102e and 102f. In this embodiment, the cross-sections of the side magnetic cores 102e and 102f are rectangular, and the cross-sections of the magnetic cores 102a, 102b, 102c, and 102d are I-shaped. Similar to Figure 8 , the central column 104 can be manufactured using two or more components, but the air gap between the components should be minimized as much as possible to make the magnetic resistance R1 close to zero. In addition, Figure 10 the winding group shown is similar to that in Figure 6 , so it will not be labeled separately here and will not be elaborated further. In addition, similar to the previous embodiment, the magnetic flux flowing through the magnetic core gap 69 is half of the magnetic flux flowing through the central column 104.

[0103] Figure 11 For Figure 10 a simulation schematic diagram of the magnetic flux density distribution 110 of the matrix inductor 100 shown, where the matrix inductor 100 has a specific number of turns (N = 19), current (I = 18 A), and air gap lengths lg and lg / 2. It can be noted that the magnetic flux densities on each central column 104 and side column 108 are similar (about between 200 mT and 220 mT). According to the correspondence between the magnetic field strength and the gray scale marked on the left side in Figure 11 and the marked magnetic field strength marks 112, 114, and 116, the magnetic field strengths in different regions can be understood. In Figure 11 (also refer toFigure 10 ), the cross-sectional area (Ac) of the central column 104 is twice that of the side columns 108 and the columns at the top and bottom (Ac / 2). As shown in the figure, such a magnetic flux density distribution can be achieved only when the air gap (lg) between the central columns is twice that between the side column and the adjacent central column (lg / 2), which confirms the foregoing description about Figure 6 that is, if the magnetic resistance R3 is equal to the magnetic resistance R2, the magnetic flux density on each column is similar, and the magnetic flux flowing through each column can be determined according to the size of the cross-sectional area.

[0104] Figure 12A and Figure 12B show two ways to physically implement the aforementioned medium-voltage matrix inductor. Please refer to Figure 12A , which shows a matrix inductor 120A (similar to the inductor shown in Figure 10 ), including a plurality of magnetic cores 102 and a plurality of corresponding winding groups 66 arranged linearly, where the magnetic core 102 includes magnetic cores 102a, 102b, 102c, and 102d with a magnetic core gap 69 and side magnetic cores 102e and 102f with a side gap 106. In this embodiment, this design can provide the minimum overall volume of the matrix inductor 120A and only requires the use of two types of simple magnetic core structures (one suitable for magnetic cores 102a, 102b, 102c, and 102d, and the other suitable for side magnetic cores 102e and 102f). However, in some cases, a linear structure may not be suitable, such as when the installation environment has a short size, is more cube-shaped, or is more compact. Figure 12B shows another arrangement, where the matrix inductor 120B has the same composition as the matrix inductor 120A, but its magnetic cores are arranged in a folded or non-linear structure, such as a U-shaped structure. In this design, although the overall volume of the matrix inductor 120B is larger than that of the matrix inductor 120A in Figure 12A , the structure of the matrix inductor 120B is more cube-shaped. In addition, as shown in Figure 12B , the matrix inductor 120B requires three types of magnetic core structures (such as magnetic core 102a, side magnetic core 102e, and newly introduced magnetic core 102g). As described above, compared with the matrix inductor 120A, the advantage of using the matrix inductor 120B is that it can be arranged in a smaller cubic space.

[0105] According to the foregoing various embodiments of the matrix inductor, a plurality of magnetic cores forming a non-uniform structure (such as a plurality of magnetic cores at different potentials respectively) can be used, and the required isolation can be achieved by using the air gap between the magnetic cores. Figures 13 to 16 illustrates some methods for increasing the electrical clearance and creepage distance while maintaining high-voltage isolation.

[0106] Before describing these methods, an overview of the prior art and certain deficiencies of these methods will be presented first. In some designs, specific parts of an inductor may be encapsulated. For example, the winding of the inductor is encapsulated, and a shielding layer is provided on the surface to ensure that the electric field in the air is limited to less than 2 kV / mm, and the encapsulating material can withstand a large electric field. Such a design can provide partial discharge-free operation, but it may also have some drawbacks. For example, the structure needs to be encapsulated, and measures must be taken to ensure that there are no air bubbles inside the encapsulated structure. In addition, the shielding layer usually increases the parasitic capacitance of the inductor structure. In some existing designs of planar structures, a high-frequency transformer provides shielding for the windings of a PCB-type structure, where the ends need to be treated (such as encapsulating the edges of the shielding layer) to eliminate surface partial discharge that may occur at the edges of the shielding layer.

[0107] Existing designs also include medium-voltage transformers, where the primary winding and the secondary winding are dry-cast separately to provide the required high-voltage isolation. This concept can be applied to inductors, for example, dry-casting the winding of the inductor and maintaining a certain distance between the winding and the magnetic core. In some transformer designs, spacers are used to separate the low-voltage winding and the medium-voltage winding to meet the isolation requirements.

[0108] All of the aforementioned existing structures can be immersed in oil to achieve the required partial discharge level and higher-voltage isolation, but since dry magnetic components are preferred in medium-voltage applications considering maintainability, putting the magnetic structure in oil is not the most practical solution.

[0109] Please refer to Figures 13 to 15 , which shows a part of a matrix inductor 80 (but the other embodiments shown in the present invention are equally applicable), where an insulating sheet 130 is inserted into the core gap 69 (such as core gaps 69a-1 and 69a-2) between adjacent cores 82 (such as cores 82a and 82b) to increase the electrical clearance and creepage distance between the cores 82 while maintaining the required high-voltage isolation. The thickness of the insulating sheet can be determined according to the material and the required insulation. In some embodiments, the material of the insulating sheet 130 includes polyamide, FR4, Nomex paper, or similar insulating materials. In some cases, the core gap 69 is not sufficient to achieve the required isolation or partial discharge-free operation, so it is necessary to insert the insulating sheet 130 into the core gap 69. As shown in Figure 13 , the insulating sheet 130 passes through the core gap 69 and the isolation space). However, if only the insulating sheet is inserted into the core gap 69 without other considerations, as shown in Figure 13 , it may cause a decrease in the partial discharge voltage. Therefore, in addition to inserting the insulating sheet 130 into the core gap 69 (there are still air holes between the core 82 and the insulating sheet 130), semiconductor coatings (or layers) 132 are also applied on both sides of the insulating sheet 130, as shown in Figure 14As shown. Then, the magnetic core 82 is pressed against the spacer 130 to bring the semiconductor coating 132 to the corresponding (different) magnetic core potential. Through the provided spacer 130, this method helps to increase the electrical clearance and creepage distance. In addition, as Figure 15 shown, by increasing the thickness of the portion of the spacer 130 located outside the magnetic core gap 69, the partial discharge ability can be improved.

[0110] Figure 16 Another method of achieving the required electrical clearance and creepage distance while maintaining PD-free operation is shown. Specifically, as Figure 16 shown, the encapsulant 134 is filled in the magnetic core gap 69 (such as the magnetic core gap 69a-1) between adjacent magnetic cores 82 (such as magnetic cores 82a and 82b). Although the inductive structure does not necessarily require encapsulation to achieve medium voltage isolation, the portions of the magnetic cores 82 adjacent to the magnetic core gap 69 (air gap) can still be encapsulated. The thickness and shape of the encapsulant 134 depend on the required voltage insulation.

[0111] Although the present invention describes the application of SiC power devices in the field of medium voltage solid state transformers, the implementation of the inductive embodiments shown in the present invention is not limited to medium voltage solid state transformers using SiC power devices. The inductive embodiments shown in the present invention can also be applied to traditional power converters or other types of solid state transformers using other power devices (such as GaN (gallium nitride) power devices or silicon-based power devices).

[0112] Based on the foregoing embodiments of the matrix inductor and with reference to at least Figure 6 , a first embodiment of an inductor is proposed according to the present invention, wherein the inductor (60) includes a plurality of magnetic cores (62), the plurality of magnetic cores (62) includes a first magnetic core (62a) and a second magnetic core (62b), the first magnetic core (62a) includes a first central column (61a), the second magnetic core (62b) includes a second central column (61b), the first magnetic core (62a) is separated from the second magnetic core (62b) by a first gap (69a-1), and the size of the first gap (69a-1) is such that the magnetic flux of the magnetic flux path formed thereby is half of the magnetic flux flowing through the first central column or the second central column.

[0113] This first embodiment may include a combination of one or more of the following features.

[0114] In the inductor of the first embodiment, the potential of the first magnetic core (62a) is different from the potential of the second magnetic core (62b).

[0115] In the inductor of the first embodiment, the size of the first gap (69a-1) is determined by the inductance value and insulation required for the inductor.

[0116] In the inductor of the first embodiment, the plurality of magnetic cores (62) further includes a third magnetic core (62c) adjacent to the second magnetic core (62b). The third magnetic core (62c) includes a third central column (61c). The second magnetic core (62b) and the third magnetic core (62c) are separated by a second gap (69b-1). The magnetic flux of the magnetic flux path formed by the second gap (69b-1) is equal to the magnetic flux flowing through the first gap (69a-1).

[0117] In the inductor of the first embodiment, the first magnetic core includes a first magnetic core pair, the second magnetic core includes a second magnetic core pair. Two parts of the first magnetic core pair are separated by a first central column gap (64a), and two parts of the second magnetic core pair are separated by a second central column gap (64b).

[0118] In the inductor of the first embodiment, the first magnetic core includes a first magnetic core pair, the second magnetic core includes a second magnetic core pair. Two parts of the first magnetic core pair are in contact with each other, and two parts of the second magnetic core pair are in contact with each other.

[0119] In the inductor of the first embodiment, the plurality of magnetic cores (82) includes a plurality of side columns (83a, 83b). Each side column (83) includes a side column gap (68a, 68b), and the direction of the side column gaps (68a, 68b) is perpendicular to the direction of the first gap (69a-1).

[0120] In the inductor of the first embodiment, the plurality of magnetic cores (102) includes a plurality of side columns (108). Each side column (108) includes a side column gap (106), and the direction of the side column gaps (106a-1, 106a-2) is parallel to the direction of the first gap (69a-1).

[0121] In the inductor of the first embodiment, both the first magnetic core and the second magnetic core include a single body structure.

[0122] In the inductor of the first embodiment, the plurality of magnetic cores (102a, 102b, 102c, 102d) are arranged linearly (120A).

[0123] In the inductor of the first embodiment, the plurality of magnetic cores (102a, 102e, 102g) are arranged non-linearly (120B).

[0124] In the inductor of the first embodiment, the first gap (69a-1) is occupied by a spacer (130).

[0125] In the inductor of the first embodiment, the spacer (130) includes a semiconductor coating (132).

[0126] In the inductor of the first embodiment, the spacer including the semiconductor coating extends beyond the first gap.

[0127] In the inductor of the first embodiment, the first gap contains a packaging material (134).

[0128] In the inductor of the first embodiment, it further includes a plurality of winding groups (66) isolated from a plurality of magnetic cores, wherein the plurality of winding groups (66) includes a first winding group (66a) and a second winding group (66b). The first winding group includes a first winding layer (35a) surrounding a first central column, and the second winding group includes a second winding layer (35b) surrounding a second central column.

[0129] In the inductor of the first embodiment, the first winding layer and the second winding layer include Litz wires.

[0130] In the inductor of the first embodiment, both the first winding group and the second winding group include a bobbin support (18).

[0131] Referring to at least Figure 6 , the present invention provides a second embodiment of an inductor, wherein the inductor (60) includes a plurality of magnetic cores (62). Each magnetic core (62) includes a pair of magnetic cores, and two parts of the pair of magnetic cores are separated by a first gap (64). The first gap (64) is arranged along a first direction. Each magnetic core further includes a central column (61). Any two adjacent magnetic cores are separated by a second gap (69). The second gap (69) is arranged along a second direction, and the second direction is perpendicular to the first direction. The size of the second gap is such that the magnetic flux of the magnetic flux path formed thereby is half of the magnetic flux flowing through the central column.

[0132] Referring to at least Figure 8 , the present invention provides a third embodiment of an inductor, wherein the inductor (80) includes a plurality of magnetic cores (82). Each magnetic core includes a central column (84). Any two adjacent magnetic cores are separated by a first gap (69). The size of the first gap is such that the magnetic flux of the magnetic flux path formed thereby is half of the magnetic flux flowing through the central column.

[0133] It should be noted that the above are only preferred embodiments proposed for illustrating the present invention. The present invention is not limited to the described embodiments. The scope of the present invention is determined by the appended claims. And the present invention can be variously modified by those skilled in the art, but all do not depart from what the appended claims are intended to protect. In addition, the disclosed embodiments can be arbitrarily combined. Referring to one embodiment does not mean excluding the features in other embodiments. In the claims, the word "comprising" does not exclude other elements or steps, and the "a" prefixed to an element name does not exclude a plurality.

Claims

1. An inductor structure comprising: A plurality of magnetic cores include a first magnetic core and a second magnetic core, wherein the first magnetic core includes a first central column, the second magnetic core includes a second central column, the first magnetic core and the second magnetic core are separated by a first gap, and the size of the first gap is such that a magnetic flux of a magnetic flux path formed by the gap is half of a magnetic flux flowing through the first central column or the second central column. 2 . The inductor structure as claimed in claim 1 , wherein a potential of the first magnetic core is different from a potential of the second magnetic core. 3 . The inductor structure as claimed in claim 1 , wherein a size of the first gap is determined by the inductance and insulation required by the inductor.

4. The inductor structure as described in claim 1, wherein the multiple magnetic cores further include a third magnetic core adjacent to the second magnetic core, the third magnetic core includes a third center column, the second magnetic core and the third magnetic core are separated by a second gap, and a magnetic flux of a magnetic flux path formed by the second gap is equal to the magnetic flux flowing through the first gap.

5. The inductor structure as claimed in claim 1, wherein the first magnetic core comprises a first magnetic core pair, the second magnetic core comprises a second magnetic core pair, two parts of the first magnetic core pair are separated by a first center column gap, and two parts of the second magnetic core pair are separated by a second center column gap. 6 . The inductor structure as claimed in claim 1 , wherein the first magnetic core comprises a first magnetic core pair, the second magnetic core comprises a second magnetic core pair, two parts of the first magnetic core pair are abutted against each other, and two parts of the second magnetic core pair are abutted against each other. 7 . The inductor structure as claimed in claim 6 , wherein the plurality of magnetic cores comprise a plurality of side pillars, each of the side pillars comprises a side pillar gap, and a direction of the side pillar gap is perpendicular to a direction of the first gap. 8 . The inductor structure as claimed in claim 6 , wherein the plurality of magnetic cores comprise a plurality of side pillars, each of the side pillars comprises a side pillar gap, and a direction of the side pillar gap is parallel to a direction of the first gap. 9 . The inductor structure as claimed in claim 1 , wherein the first magnetic core and the second magnetic core both comprise a single main body structure.

10. The inductor structure as claimed in claim 1, wherein the plurality of magnetic cores are arranged linearly. The inductor structure as claimed in claim 1 , wherein the plurality of magnetic cores are arranged nonlinearly. 12 . The inductor structure as claimed in claim 1 , further comprising a spacer, wherein the first gap is occupied by the spacer.

13. The inductor structure of claim 12, wherein the spacer comprises a semiconductor coating. 14 . The inductor structure as claimed in claim 13 , wherein the isolation film comprising the semiconductor coating extends out of the first gap. The inductor structure as claimed in claim 1 , wherein the first gap comprises a packaging material.

16. The inductor structure as described in claim 1 further includes a plurality of winding groups isolated from the plurality of magnetic cores, wherein the plurality of winding groups include a first winding group and a second winding group, the first winding group includes a first winding layer surrounding the first center column, and the second winding group includes a second winding layer surrounding the second center column. 17 . The inductor structure of claim 16 , wherein the first winding layer and the second winding layer comprise Litz wires. 18 . The inductor structure of claim 16 , wherein the first winding set and the second winding set both comprise a bobbin support.

19. An inductor structure comprising: A plurality of magnetic cores, each of which comprises a magnetic core pair, two parts of the magnetic core pair are separated by a first gap, and the first gap is arranged along a first direction, each of the magnetic cores further comprises a central column, any two adjacent magnetic cores are separated by a second gap, the second gap is arranged along a second direction, the second direction is perpendicular to the first direction, and the size of the second gap is such that a magnetic flux of a magnetic flux path formed by the second gap is half of a magnetic flux flowing through the central column.

20. An inductor structure comprising: A plurality of magnetic cores, each of which comprises a central column, any two adjacent magnetic cores are separated by a first gap, and the size of the first gap is such that a magnetic flux of a magnetic flux path formed by the first gap is half of a magnetic flux flowing through the central column.

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