Printed circuit board based winding structure for inductors.

Abstract

To provide a highly reliable, potting-free, partial discharge-free PCB-based medium voltage inductor and medium voltage inductor assembly.SOLUTION: A PCB-based medium voltage inductor according to an embodiment includes a PCB 305 having through holes, a winding 310 made of any other suitable conductive material with conductive layers embedded within the PCB, and a magnetic core 320. Each of the conductive layers is patterned to have a spiral shape around the through holes and is arranged within an annular region having an annular radius. The conductive layers are arranged in a staggered pattern such that the annular radius of the conductive layers increases from the centermost one of the conductive layers to the outermost one of the conductive layers.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] This disclosure relates to printed circuit board (PCB)-based planar winding structures for use in inductors. More particularly, this disclosure relates to PCB-based planar winding structures for use in inductors for medium voltage applications. [Background technology]

[0002] With the advancement of wide-bandgap semiconductors, power electronic devices with high blocking voltages capable of switching at high frequencies have opened up new application areas and become increasingly common in industry. These wide-bandgap semiconductor-based converter systems are finding applications in power converters, including but not limited to renewable energy integration, active filters, shore-to-ship power systems, and solid-state transformers. Solid-state transformers (SSTs) are considered the most profitable solution to achieve all these requirements because they can provide a direct power electronics interface from the medium-voltage AC (MVac, 4.16 kV / 13.8 kV grid) stage to the low-voltage DC (LVdc, 400 V / 800 V) stage. A key advantage of SSTs is that they eliminate the need for traditional bulky low-frequency transformers, replacing them with high-frequency magnets and power electronics interfaces. A typical connection from the MVac grid to the power electronics converter system requires a medium-voltage inductor interface.

[0003] MV inductors have been used in power systems since their inception. Traditionally, these inductors have been designed for high-power applications, and most importantly, they are widely used in low-frequency applications. Because these inductors are used for low-frequency currents, silicon steel material is used as the core material along with solid copper windings. However, with SiC devices, to minimize the size of the magnetic components, the converters operate at high switching frequencies. This not only results in low-frequency currents flowing through the inductors, but also in high switching-frequency ripple. In this scenario, traditional medium-voltage inductors fail.

[0004] Much research has been conducted to compensate for these high-frequency losses, primarily in low-voltage applications (i.e., <2 kV). The use of Litz wire offers an excellent solution for reducing high-frequency winding losses, and various core materials, such as ferrite and nanocrystalline, can be used to reduce high-frequency core losses. However, medium-voltage inductors require additional insulation and partial-discharge-free operation (reliable continuous operation). Achieving good efficiency and adequate power density, along with medium-voltage insulation requirements, remains a major challenge. Also, considering cost and ease of manufacturing, PCB-based solutions are typically preferred over traditional wire-wound solutions because they offer reliable and repeatable designs.

[0005] Various studies have been conducted in the literature on the design of medium-voltage inductors. High-frequency medium-voltage transformers have also been included in this research because they have similar design criteria. The primary focus is on the insulation design of inductors / transformers. The most basic method for achieving the required voltage isolation is to provide some distance between windings and layers [Reference 1]. In [Reference 1], the medium-voltage isolation between the winding and core is achieved using a 3D-printed bobbin. Figure 1A is a schematic perspective view of the medium-voltage inductor in [Reference 1], and Figure 1B is a schematic cross-sectional view of the medium-voltage inductor in Figure 1 along plane A-A'. Interlayer isolation is achieved by providing spacers between layers, as shown in Figures 1A and 1B. In this case, voltage stress is handled not only by the spacers but also by the air gap. This method is simple and easy to implement, but it cannot be scaled to higher voltages. It also increases the volume of the inductor due to the large air gap. Note that instead of an air gap, insulating material can be used between layers to reduce the spacing. However, such a structure cannot achieve partial discharge-free operation considering the air gap between the windings.

[0006] Another commonly used approach to magnetic design is based on encapsulating or potting the inductor using an encapsulation material. References 2 and 3 present transformer / inductor designs employing this concept. As discussed in References 4 and 5, a shielding layer can be added to the surface of this encapsulation structure to ensure that the electric field is confined within the encapsulant, resulting in partial discharge-free operation of the magnetic component. However, achieving partial discharge-free operation in these structures requires the creation of an air-free space within the encapsulation structure. This is quite difficult to achieve and unreliable, especially when multilayer winding structures are used. Figure 2 shows an example of one of these structures.

[0007] In [Reference 6], a medium voltage transformer is designed with separate dry-cast primary and secondary windings to provide the necessary insulation. This concept can also be used for inductors where the inductor windings are dry-cast and placed a fixed distance from the core.

[0008] Another approach is presented in [Reference 7], where a medium-voltage air-core transformer is demonstrated. This concept can also be extended to air-core inductors. From an insulation perspective, this structure proves beneficial because the absence of a core removes the constraints on winding-to-core insulation. While this has some benefits in terms of insulation design, air-core-based inductors are impractical for use in many applications due to their significantly larger size and the omnidirectional magnetic field resulting from the absence of a core. It is also impractical to scale the concept to achieve higher inductance values. For these reasons, air-core magnets are typically not preferred for most applications.

[0009] [Reference 8] demonstrated a high-frequency planar PCB transformer with medium-voltage isolation. A high-voltage dielectric material is used to withstand the medium voltage between the primary and secondary windings. The core is encapsulated with an epoxy material to prevent arcing from the ends of the windings to the core, and the windings are spaced apart to prevent partial discharges between the windings and the core. However, this construction does not provide partial-discharge-free operation at the interface between the low-voltage and medium-voltage windings.

[0010] Typically, these structures can be immersed in oil to achieve the required partial discharge rating, but in medium voltage applications, dry magnets are preferred, so immersing the magnets in oil is not the most effective or reliable solution.

[0011] References

[0012] [Reference 1] H. Zhao et al., "Physics-Based Modeling of Parasitic Capacitance in Medium-Voltage Filter Inductors", IEEE Transactions on Power Electronics, vol. 36, no. 1, pp. 829-843, Jan. 2021, doi: 10.1109 / TPEL.2020.3003157.

[0013] [Reference 2] D. Rothmund, T. Guillod, D. Bortis and J. W. Kolar, "99% Efficient 10kV SiC-Based 7kV / 400V DC Transformer for Future Data Centers", IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 7, no. 2, pp. 753-767, June 2019, doi: 10.1109 / JESTPE.2018.2886139.

[0014] [Reference 3] D. Rothmund, T. Guillod, D. Bortis and J. W. Kolar, "99.1% Efficient 10kV SiC-Based Medium-Voltage ZVS Bidirectional Single-Phase PFC AC / DC Stage", IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 7, no. 2, pp. 779-797, June 2019, doi: 10.1109 / JESTPE.2018.2886140.

[0015] [Reference 4] H. Li, P. Yao, Z. Gao and F. Wang, "Medium Voltage Converter Inductor Insulation Design Considering Grid Requirements", IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 10, no. 2, pp. 2339 - 2350, April 2022, doi: 10.1109 / JESTPE.2021.3131602.

[0016] [Reference 5] Q. Chen, R. Raju, D. Dong and M. Agamy, "High Frequency Transformer Insulation in Medium Voltage SiC enabled Air-cooled Solid-State Transformers", 2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018, pp. 2436 - 2443, doi: 10.1109 / ECCE.2018.8557849.

[0017] [Reference 6] T. B. Gradinger, U. Drofenik and S. Alvarez, "Novel Insulation concept for an MV dry-cast medium-frequency transformer", 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe), 2017, pp. P.1 - P.10, doi: 10.23919 / EPE17ECCEEurope.2017.8099006.

[0018] [Reference 7] P. Czyz, T. Guillod, F. Krismer, J. Huber and JWKolar, "Design and Experimental Analysis of 166kW Medium-Voltage Medium-Frequency Air-Core Transformer for 1:1-DCX Applications", IEEE Journal of Emerging and Selected Topics in Power Electronics, doi:10.1109 / JESTPE.2021.3060506.

[0019] [Reference 8] S. Mukherjee et al., "A High-Frequency Planar Transformer with Medium-Voltage Isolation", 2021 IEEE Applied Power Electronics Conference and Exposition (APEC), 2021, pp. 2065-2070, doi:10.1109 / APEC42165.2021.9487061. Summary of the Invention [Problem to be solved by the invention]

[0020] The present disclosure provides a reliable, potting-free, partial discharge-free PCB-based solution that is easily manufactured with excellent repeatability and good performance at operating voltages. [Means for solving the problem]

[0021] In one aspect, the present disclosure provides a PCB-based medium-voltage inductor including: a PCB having a through hole; a plurality of conductive layers embedded within the PCB and stacked on one another, the plurality of conductive layers electrically connected to one another through one or more embedded vias, each of the plurality of conductive layers patterned to have a spiral shape around a central through hole and arranged within an annular region having an annular radius; a first terminal electrically coupled to an outermost conductive layer of the plurality of conductive layers; and a second terminal electrically coupled to a centralmost conductive layer of the plurality of conductive layers, the plurality of conductive layers arranged in a staggered pattern.

[0022] In one embodiment, the staggered pattern is a concave staggered pattern, and the concave staggered pattern is defined such that annular radii of the plurality of conductive layers increase from the central-most conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers.

[0023] In one embodiment, the plurality of conductive layers are spatially separated in the vertical direction.

[0024] In one embodiment, the PCB-based medium-voltage inductor further includes a magnetic core magnetically coupled to the plurality of conductive layers, the magnetic core having an air gap.

[0025] In one embodiment, the magnetic core is electrically connected to the first terminal or the second terminal.

[0026] In one embodiment, the PCB-based medium-voltage inductor further includes a coating layer coated on a surface of the magnetic core, the coating layer being made of a conductive material or a semiconductor material, and the magnetic core being electrically connected to the first terminal via the coating layer.

[0027] In one embodiment, each conductive layer has a spiral shape around the through hole in a horizontal plane and is patterned to have multiple peripheries, corresponding peripheries of the multiple conductive layers are aligned with each other, and sides of the corresponding peripheries of the multiple conductive layers are arranged in a V-shaped or U-shaped staggered pattern.

[0028] In another aspect, the present disclosure provides a medium-voltage inductor assembly including a plurality of the above-described PCB-based medium-voltage inductors, a bobbin structure that holds the plurality of PCB-based medium-voltage inductors, and a magnetic core assembly magnetically coupled to the plurality of PCB-based medium-voltage inductors.

[0029] In one embodiment, a window area is formed between the bobbin structure, the plurality of PCB-based medium voltage inductors, and the magnetic core assembly, the window area being configured to remove heat generated from the plurality of conductive layers.

[0030] In yet another aspect, the present disclosure provides a medium-voltage inductor assembly including a plurality of the PCB-based medium-voltage inductors described above, wherein the first terminals of the plurality of PCB-based medium-voltage inductors are electrically connected to one another and the second terminals of the plurality of PCB-based medium-voltage inductors are electrically connected to one another.

[0031] In yet another aspect, the present disclosure provides a PCB-based medium-voltage inductor including: a PCB having a through hole; a plurality of conductive layers embedded in the PCB and stacked on one another, the plurality of conductive layers electrically connected to one another through one or more embedded vias, each of the plurality of conductive layers patterned to have a spiral shape around the through hole and arranged within an annular region having an annular radius; a first terminal electrically coupled to an outermost conductive layer of the plurality of conductive layers; and a second terminal electrically coupled to a centralmost conductive layer of the plurality of conductive layers, the annular radius of the plurality of conductive layers increasing from the centralmost conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers.

[0032] In one embodiment, the PCB-based medium-voltage inductor further includes a winding extension protruding from an end of the plurality of conductive layers, and the second terminal is electrically coupled to the central-most conductive layer of the plurality of conductive layers via the winding extension.

[0033] In one embodiment, the PCB-based medium-voltage inductor further includes winding extensions protruding from ends of the plurality of conductive layers, wherein side surfaces of the winding extensions are arranged in a concave staggered pattern and front surfaces of the winding extensions are arranged in a convex staggered pattern.

[0034] In yet another aspect, the present disclosure provides a PCB-based medium-voltage inductor including: a PCB having a through hole; a plurality of conductive layers embedded in the PCB and stacked on one another, the plurality of conductive layers electrically connected to one another through one or more embedded vias, each of the plurality of conductive layers patterned to have a spiral shape around the through hole and arranged within an annular region having an annular radius; a winding extension protruding from an end of the plurality of conductive layers; a first terminal electrically coupled to an outermost conductive layer of the plurality of conductive layers; and a second terminal electrically coupled to a centralmost conductive layer of the plurality of conductive layers via the winding extension, the annular radius of the plurality of conductive layers increasing from the centralmost conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers.

[0035] In one embodiment, the side surfaces of the winding extensions are arranged in a concave staggered pattern and the front surfaces of the winding extensions are arranged in a convex staggered pattern. [Brief explanation of the drawings]

[0036] The present disclosure is better understood upon consideration of the following detailed description and the accompanying drawings.

[0037] [Figure 1A] 1 shows a conventional transformer solution whereby insulation is achieved by providing spaces between windings and between the windings and the core. [Figure 1B] 1 shows a conventional transformer solution whereby insulation is achieved by providing spaces between windings and between the windings and the core.

[0038] [Figure 2] 1 shows a conventional transformer solution with an encapsulant to encapsulate the windings and a shielding layer on top of the encapsulant.

[0039] [Figure 3]1 illustrates a PCB-based medium voltage inductor according to one embodiment of the present disclosure.

[0040] [Figure 4] 4 illustrates an exemplary voltage gradient in one layer of the PCB-based medium-voltage inductor of FIG. 3 when a 15 kV voltage is applied across the electrical terminals of the PCB-based medium-voltage inductor.

[0041] [Figure 5A] 4 shows a cross-sectional view of the PCB-based medium-voltage inductor along plane AA′ of FIG. 3. [Figure 5B] 4 shows a cross-sectional view of the PCB-based medium-voltage inductor along plane BB' of FIG. 3. [Figure 5C] 4 shows a cross-sectional view of the PCB-based medium-voltage inductor along plane CC′ of FIG. 3 .

[0042] [Figure 6] 1 illustrates a PCB-based medium-voltage inductor according to another embodiment of the present disclosure.

[0043] [Figure 7] 1 illustrates a cross-sectional view of a PCB-based medium-voltage inductor that uses a bobbin structure to hold multiple PCB windings and a magnetic core assembly, according to one embodiment of the present disclosure.

[0044] [Figure 8] 1 illustrates a PCB-based medium-voltage inductor assembly including two identical PCB-based inductors connected in parallel, according to one embodiment of the present disclosure.

[0045] [Figure 9] 1 illustrates an equivalent circuit of two PCB-based windings connected in parallel, according to one embodiment of the present disclosure.

[0046] [Figure 10A] Simulation results of the electric field distribution in the conductive layers of a PCB-based medium-voltage inductor arranged in a "concave" staggered pattern are shown. [Figure 10B] Figure 1 shows the simulated electric field distribution in the conductive layers of a PCB-based medium-voltage inductor arranged in a "convex" staggered pattern. DETAILED DESCRIPTION OF THE INVENTION

[0047] The present disclosure is generally directed to PCB-based medium-voltage inductors that provide a partial discharge-free design without requiring additional encapsulation. To produce partial discharge-free operation, embodiments of the present disclosure limit the electric field on the surface of the PCB windings to less than the air breakdown voltage at the operating voltage level. A magnetic core is connected to one of the inductor's terminals to define a potential across the core, creating an electric field at and / or near the surface of the PCB. It should be understood that the PCB winding structure can be designed in any suitable manner to create an electric field.

[0048] FIG. 3 illustrates a PCB-based medium-voltage inductor 300 according to one embodiment of the present disclosure. The windings 310 of the PCB-based medium-voltage inductor 300 are embedded within a PCB 305, and a magnetic core 320 provides a path for the magnetic field to flow. In certain embodiments, the windings 310 can be constructed of copper or any other suitable conductive material, including multiple conductive layers embedded in the PCB 305 and stacked on top of each other. The conductive layers are electrically connected to each other using embedded vias. To achieve the required inductance, a small air gap 330 is required within the magnetic core 320. The PCB 305 includes a through-hole to accommodate the magnetic core 320. The magnetic core 320 includes two E-shaped magnetic cores arranged in a mirror-image configuration, one above the other. The central magnetic pillars of the two E-shaped magnetic cores are housed within a through-hole in the PCB 305, and there are air gaps between the central magnetic pillar and the side pillars of the two E-shaped magnetic cores.

[0049] Each conductive layer of winding 310 may be patterned to have a spiral shape that makes several turns in a horizontal plane to wrap successively increasing or decreasing distances around a through-hole in PCB 305. In one embodiment, each spiral-shaped conductive layer of winding 310 is confined to an elliptical or rectangular annular region having an annular radius.

[0050] First and second terminals 301 and 302 are provided for passing current to and from winding 310. In one embodiment, first terminal 301 is electrically connected to the top and bottom layers of winding 310, and second terminal 302 is electrically connected to the center layer(s) of winding 310. Essentially, PCB-based medium-voltage inductor 300 includes two windings 310 connected in parallel with each other.

[0051] Depending on the particular design and / or requirements, PCB 305 may have any suitable shape and / or thickness. Note that when a current / voltage is applied to PCB-based medium-voltage inductor 300, the voltage is distributed among windings 310, resulting in a voltage gradient across windings 310. Figure 4 shows an example voltage gradient in one conductive layer of PCB-based medium-voltage inductor 300 when a 15 kV voltage is applied between first terminal 301 and second terminal 302.

[0052] 5A, 5B, and 5C show cross-sectional views of PCB-based medium-voltage inductor 300 along planes AA′, BB′, and CC′ of FIG. 3, respectively. As shown in FIG. 5A, winding 310 of PCB-based medium-voltage inductor 300 is arranged in a specific “staggered” pattern to confine or shape the electric field in, on, and / or near PCB 305, thereby providing partial-discharge-free operation of PCB-based medium-voltage inductor 300 without the need for additional potting. In this embodiment, winding 310 includes 12 conductive layers (including conductive layers 1 through 12 from top to bottom) arranged in a “concave” staggered pattern. That is, the ends of the top (e.g., first conductive layer) and bottom (e.g., twelfth conductive layer) conductive layers of winding 310 define a larger annular radius R than the center layers (e.g., sixth and seventh conductive layers). Furthermore, each lap of the spiral conductive layer is generally aligned with one another, except that when viewed in cross section from the side (i.e., the side of the lap), the first through twelfth conductive layers appear to form a concave (e.g., "V" or "U") shape. It is understood that any appropriate amount of conductive layers can be used depending on design preferences. Furthermore, the first through twelfth conductive layers of winding 310 are spatially separated from one another in the vertical direction (or Z direction) using PCB material and are electrically connected at specific points using buried vias (to provide a continuous current path). These buried vias can be filled with an encapsulating material, such as epoxy, to avoid air bubbles in the PCB material.

[0053] It will be appreciated that partial discharge free operation is possible primarily because the voltage applied to first terminal 301 and second terminal 302 is distributed between windings 310, thereby creating a voltage gradient across windings 310. The staggered windings utilize this voltage gradient to create an electric field within and on the surface of PCB 305. The selection of the distance between winding spacings in the X direction is a design choice and can be varied depending on requirements.

[0054] 5B and 5C focus on the region where the ends of the central conductive layer of the winding 310 protrude outward to form winding extensions 340, as shown in FIG. 3, to provide the necessary connection to a terminal (e.g., second terminal 302). The high electric field around this region can exceed the breakdown voltage of air and cause partial discharges. To prevent such strong electric fields, field-limiting techniques (such as staggering) are applied to this region of the winding extensions 340. As shown in FIG. 4, because the different conductive layers of the PCB-based medium-voltage inductor 300 are at different voltages due to the voltage gradient across the winding 310, the individual layers are extended to form equipotential surfaces on each layer, and these extensions are designed in a specific manner to limit the electric field within the region. In one embodiment, the sides of the winding extensions 340 are arranged in a "concave" staggered pattern, as shown in FIG. 5B. Meanwhile, the front surfaces of the winding extensions 340 are arranged in a "convex" staggered pattern, as shown in FIG. 5C. 10A and 10B show computer simulation results of the electric field distribution at a peak voltage of 15 kV for conductive layers of a PCB-based medium voltage inductor arranged in a "concave" and "convex" staggered pattern, respectively.

[0055] FIG. 6 illustrates a PCB-based medium-voltage inductor 600 according to another embodiment of the present disclosure. The PCB-based medium-voltage inductor 600 of FIG. 6 is substantially identical to the PCB-based medium-voltage inductor 300 of FIG. 3, except that the magnetic core 320 is coated with a layer 610 of conductive or semiconductive material. Furthermore, an electrical connection 620 is required between the magnetic core 320 and one of the terminals (e.g., the first terminal 301). This is because the staggered winding structure shown in FIG. 6 can reduce the electric field in the air below the air breakdown voltage only when the magnetic core 320 is connected to one of the terminals. In certain embodiments, the electrical connection 620 can be made using a conductor wire or a metal rod. The conductive / semiconductive coating (i.e., layer 610) on the surface of the magnetic core 320 can provide a reliable connection for maintaining the electric potential of the magnetic core 320. Note that the electrical connection 620 should be made to both components of the magnetic core 320. The choice of the terminal to which the magnetic core 320 can be connected is not arbitrary. In one embodiment, the magnetic core 320 should be connected to the terminal closest to the outer surface of the PCB 305 (eg, the first terminal 301).

[0056] 7 illustrates a cross-sectional view of a medium-voltage inductor assembly 700 that uses a bobbin structure 730 to hold multiple PCB-based medium-voltage inductors 711 and 712 and a magnetic core assembly 720, according to one embodiment of the present disclosure. The bobbin structure 730 can be coated with a semiconductive or conductive surface and can be electrically connected to the magnetic core assembly 720 so that they share the same electrical potential. Additionally, because the medium-voltage inductor assembly 700 is a potting-less solution, the remaining window area 740 can be used as a forced-air cooling solution to directly remove heat generated by the PCB-based medium-voltage inductors 711 and 712. Alternatively, a thermally conductive material, such as aluminum nitride, can be bonded to the PCB-based medium-voltage inductors 711 and 712 with some thermal interface material, and a heat sink placed on the thermally conductive material away from the medium-voltage inductor assembly 700 can be used to remove heat.

[0057] FIG. 8 illustrates a medium-voltage inductor assembly 800 including two identical PCB-based medium-voltage inductors 810 and 820 connected in parallel, according to one embodiment of the present disclosure. As shown, the first terminals 301 of the PCB-based medium-voltage inductors 810 and 820 are connected together, as are the second terminals 302 of the PCB-based medium-voltage inductors 810 and 820. Paralleling two PCB-based medium-voltage inductors reduces the current flowing through each PCB-based medium-voltage inductor, thereby helping to reduce total winding losses. However, increasing the number of parallel-connected PCB-based medium-voltage inductors requires a larger window area, which increases not only the volume of the magnetic core but also the overall size of the inductor. Optimization is required to determine the appropriate amount of parallel-connected PCB-based medium-voltage inductors for a given medium-voltage inductor assembly.

[0058] 9 shows an equivalent circuit 900 of two PCB-based medium-voltage inductors 910 and 920 connected in parallel, according to one embodiment of the present disclosure. Depending on the available and / or required window area, more PCB-based medium-voltage inductors can be connected in parallel, which helps reduce the total winding losses of the medium-voltage inductor assembly.

Claims

1. a PCB having through holes; a plurality of conductive layers embedded within the PCB and stacked on one another, the plurality of conductive layers being electrically connected to one another through one or more embedded vias, each of the plurality of conductive layers being patterned to have a spiral shape around the through hole and disposed within an annular region having an annular radius; a first terminal electrically coupled to an outermost conductive layer of the plurality of conductive layers; a second terminal electrically coupled to a central most conductive layer of the plurality of conductive layers; Including, the plurality of conductive layers are arranged in a staggered pattern; the offset pattern is a concave offset pattern, and the concave offset pattern is defined such that annular radii of the plurality of conductive layers increase along an axial direction of the spiral shape from the central-most conductive layer of the plurality of conductive layers to the outermost conductive layer of the plurality of conductive layers; annular radii of the plurality of conductive layers in a direction of a first axis increase from the central conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers, and annular radii of the plurality of conductive layers in a direction of a second axis perpendicular to the first axis decrease from the central conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers. PCB based medium voltage inductor.

2. The PCB-based medium-voltage inductor of claim 1 , wherein said plurality of conductive layers are spatially separated in the vertical direction.

3. The PCB-based medium-voltage inductor of claim 1 , further comprising a magnetic core magnetically coupled to the plurality of conductive layers, the magnetic core having an air gap.

4. The PCB-based medium-voltage inductor of claim 3 , wherein the magnetic core is electrically connected to the first terminal or the second terminal.

5. 5. The PCB-based medium-voltage inductor of claim 4, further comprising a coating layer coated on a surface of the magnetic core, the coating layer being made of a conductive material or a semiconductor material, and the magnetic core being electrically connected to the first terminal via the coating layer.

6. 2. The PCB-based medium-voltage inductor of claim 1, wherein each of the plurality of conductive layers has a spiral shape around the through-hole in a horizontal plane and is patterned to have multiple turns, and corresponding turns of the plurality of conductive layers are aligned with each other.

7. A plurality of PCB-based medium voltage inductors according to claim 1; a bobbin structure for holding the plurality of PCB-based medium voltage inductors; a magnetic core assembly magnetically coupled to the plurality of PCB-based medium-voltage inductors; Including, Medium voltage inductor assembly.

8. 8. The medium-voltage inductor assembly of claim 7, wherein a window area is formed between the bobbin structure, the plurality of PCB-based medium-voltage inductors, and the magnetic core assembly, the window area configured to remove heat generated from the plurality of conductive layers.

9. 10. A medium voltage inductor assembly comprising a plurality of PCB-based medium voltage inductors according to claim 1, the first terminals of the plurality of PCB-based medium-voltage inductors are electrically connected to one another; the second terminals of the plurality of PCB-based medium-voltage inductors are electrically connected to one another. Medium voltage inductor assembly.

10. further comprising a winding extension protruding from an end of the plurality of conductive layers; The PCB-based medium-voltage inductor of claim 1 , wherein the second terminal is electrically coupled to the central-most conductive layer of the plurality of conductive layers via the winding extension.

11. The PCB-based medium-voltage inductor of claim 1 , further comprising a winding extension protruding from an end of said plurality of conductive layers.

12. a PCB having through holes; a plurality of conductive layers embedded within the PCB and stacked on one another, the plurality of conductive layers being electrically connected to one another through one or more embedded vias, each of the plurality of conductive layers being patterned to have a spiral shape around the through hole and disposed within an annular region having an annular radius; a winding extension protruding from an end of the plurality of conductive layers; a first terminal electrically coupled to an outermost conductive layer of the plurality of conductive layers; a second terminal electrically coupled to a central conductive layer of the plurality of conductive layers via the winding extension; Including, the annular radii of the plurality of conductive layers increase along an axial direction of the spiral shape from the central-most conductive layer of the plurality of conductive layers to the outermost conductive layer of the plurality of conductive layers; annular radii of the plurality of conductive layers in a direction of a first axis increase from the central conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers, and annular radii of the plurality of conductive layers in a direction of a second axis perpendicular to the first axis decrease from the central conductive layer of the plurality of conductive layers toward the outermost conductive layer of the plurality of conductive layers. PCB based medium voltage inductor.

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