Coaxial winding structures for modular MV converters

Abstract

Disclosed herein is a high-voltage withstand coaxial winding transformer (HVW- CWT), comprising a first dielectric tube, a first inner nonmagnetic conductive layer disposed on an interior surface of the first dielectric tube, and a first outer nonmagnetic conductive layer disposed on an exterior surface of the first dielectric tube. The first inner and outer conductive layers can be coaxial.

Description

COAXIAL WINDING STRUCTURES FOR MODULAR MV CONVERTERSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 665,493, filed on 28 June 2024, which is incorporated herein by reference in its entirety as if fully set forth below.FIELD OF THE DISCLOSURE

[0002] The various embodiments of the present disclosure relate generally to a novel high- frequency transformer design that can sustain high voltage across the primary and secondary windings, where the electric field can be sustained across a desired insulator (and not in air) such as a ceramic tube. The disclosed coaxial winding transformer (CWT) can be used with solid-state transformers, e.g., MV2DC.BACKGROUND

[0003] There is a growing need for solid-state transformers (SSTs) that can connect directly to the medium voltage grid and provide isolated low-voltage DC or AC voltages for a myriad of applications related to the energy transition. Examples of important applications include, but are not limited to, DC fast charging of EVs, DC feeds into Al data centers, hybrid PV and energy storage plants, and green hydrogen electrolyzers. These plants are rated at 500 kW to 500 MW, with individual modular SSTs rated at 500 kW to 5 MW or so, connected to AC voltages in the range of 12 kV to 34 kV AC on the medium voltage (MV) side, and 400 V to 1500 V on the DC side.

[0004] As is well known, power-electronics-based SSTs involve high-frequency switching with AC and DC side converters and a compact high-frequency transformer, isolating the AC and DC sides. The AC side uses stacked converter modules to manage the peak voltage stress and parallel the outputs to achieve higher currents on the DC side. It is well known to one skilled in the art that MV SSTs face tough technical challenges, including the need to withstand high transient voltages from the grid; inrush current and voltage sharing during startup, normal operation, and during faults; breakdown of transformer insulation due to dielectric stress and partial discharge; response to DC and AC side faults; thermal management while preserving dielectric withstand capability over the long term in the field; and ability to achieve all this in a compact and cost-effective package. Several examples of such high-voltage, high-frequencytransformers can be found in the literature, showing the difficulty and challenges of achieving the desired attributes. See Zhu, Charles. High-Efficiency, Medium- Voltage-Input, Solid-State- Transformer-Based 400-kW / 1000V / 400A Extreme Fast Charger for Electric Vehicles. United States: N. p., 2023. Web. doi: 10.2172 / 1987553.

[0005] A previous disclosure has shown the concept of a Medium Voltage (MV) to DC (MV2DC) converter (See US Provisional App. No. 63 / 526,770, which is incorporated herein by reference in its entirety as if fully set forth below), which uses the Isolated Inertialess Converter (IIC) as the building block to reflect a DC voltage Vdc as + / -Vdc on the AC side, including high-frequency isolation. The IIC module control is based on ‘flipping logic’ that ensures no low-frequency excitation of the HF transformer core and achieves the desired AC side output voltage. Multiple IIC modules are stacked in series, with the + / -Vdc adding or subtracting to realize a ‘staircase’ waveform that approximates the desired sinewave voltage. This approach to the synthesis of an AC voltage is well known to one skilled in the art. The novelty of the IIC -based MV2DC converter lies in the ability to realize precise and well- controlled voltages + / -Vdc at each module level without requiring significant energy storage on the AC side bridge (which is significantly different from typical Modular Multilevel Converters (MMC) that are often used in such series stacked converter implementations).

[0006] However, achieving precise control of the AC voltage can still require adequate magnetizing inductance, voltage and current handling, as well as extremely low trapped energy in the high-frequency transformer leakage inductance - ‘inertialess’ operation. At the same time, it can be desirable for the transformer to meet other operational requirements for isolation, partial discharge, and thermal management.BRIEF SUMMARY

[0007] A first aspect of the present disclosure provides a high-voltage withstand coaxial winding transformer (HVW-CWT), comprising a first dielectric tube, a first inner nonmagnetic conductive layer disposed on an interior surface of the first dielectric tube, and a first outer nonmagnetic conductive layer disposed on an exterior surface of the first dielectric tube. The first inner and outer conductive layers can be coaxial.

[0008] According to the first aspect, various embodiments can have various additional features or combinations of features, including the following exemplary features. In some embodiments, the first inner conductive layer is disposed on the interior surface of the first dielectric tube such that no air gap is present between the first inner conductive layer and the interior surface of the first dielectric tube. In some embodiments, the first outer conductivelayer is disposed on the exterior surface of the first dielectric tube such that no air gap is present between the first outer conductive layer and the exterior surface of the first dielectric tube. In some embodiments, the first inner conductive layer forms, at least in part, a first winding of the HVW-CWT. In some embodiments, the first outer conductive layer forms, at least in part, a second winding of the HVW-CWT. In some embodiments, the second winding is a low voltage winding of the HVW-CWT. In some embodiments, the HVW-CWT further comprises a first winding disposed in an interior of the first inner conductive layer. In some embodiments, the HVW-CWT further comprises an air gap disposed between the first winding and the first inner conductive layer. In some embodiments, the HVW-CWT further comprises at least one spacer located in the air gap. In some embodiments, the first winding is formed by one or more conductive wires. In some embodiments, the HVW-CWT further comprises a second winding disposed exterior to the first outer conductive layer. In some embodiments, the HVW-CWT further comprises an air gap disposed between the second winding and the first outer conductive layer. In some embodiments, the second winding is a low voltage winding of the HVW-CWT. In some embodiments, the first dielectric tube comprises a material selected from the group consisting of ceramic, fiberglass, polymers, and composites. In some embodiments, the first dielectric tube comprises a composite material selected from the group consisting of: fiberglass reinforced plastic, silica-filled epoxy, and alumina-filled epoxy. In some embodiments, the HVW-CWT further comprises a core surrounding an exterior of the outer conductive layer. In some embodiments, the first outer conductive layer is electrically coupled to one of an AC bridge and a DC bridge of a power converter, and the first inner conductive layer is electrically coupled to the other of the AC bridge and the DC bridge of the power converter. In some embodiments, the first outer conductive layer comprises a first length extending in a longitudinal direction of the first dielectric tube, the first inner conductive layer comprises a second length extending in the longitudinal direction of the first dielectric tube, the first dielectric tube comprises a third length extending in the longitudinal direction of the first dielectric tube, the second length is greater than the first length, and the third length is greater than the second length. In some embodiments, the HVW-CWT can further comprise a second dielectric tube, a second inner nonmagnetic conductive layer disposed on an interior surface of the second dielectric tube and electrically coupled to the first inner conductive layer, and a second outer nonmagnetic conductive layer disposed on an exterior surface of the second dielectric tube and electrically coupled to the second inner conductive layer, in which the second inner and outer conductive layers are coaxial.

[0009] A second aspect of the present disclosure provides a power converter, comprising a plurality of converter modules stacked in series. Each converter module comprises a first bridge, a second bridge, and any of the HVW-CWTs disclosed herein. The first inner conductive layer of each HVW-CWT is electrically coupled to one of the first bridge and the second bridge and the first outer conductive layer of each HVW-CWT is electrically coupled to the other of the first bridge and the second bridge.

[0010] According to the first aspect, various embodiments can have various additional features or combinations of features, including the following exemplary features. In some embodiments, the first bridge is an AC bridge and the second bridge is a DC bridge. In some embodiments, the first inner conductive layer is electrically coupled to the DC bridge, and the first outer conductive layer is electrically coupled to the AC bridge.

[0011] These and other aspects of the present disclosure are described in the Detailed Description below and the accompanying drawings. Other aspects and features of embodiments will become apparent to those of ordinary skill in the art upon reviewing the following description of specific, exemplary embodiments in concert with the drawings. While features of the present disclosure may be discussed relative to certain embodiments and figures, all embodiments of the present disclosure can include one or more of the features discussed herein. Further, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used with the various embodiments discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments, it is to be understood that such exemplary embodiments can be implemented in various devices, systems, and methods of the present disclosure.DRAWINGS

[0012] The following detailed description of specific embodiments of the disclosure will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, specific embodiments are shown in the drawings. It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.

[0013] FIGS. 1A-D provide an exemplary (A) circuit schematic of isolated inertia-less converter (IIC) unit, and key waveforms of II C showing (B) positive, (C) zero, and (D) negative voltage level generation, utilized with some embodiments of the present disclosure.

[0014] FIG. 2 provides a schematic diagram of an exemplary Stacked IIC in an MV2DC, utilized with some embodiments of the present disclosure.

[0015] FIG. 3 provides a schematic diagram of an exemplary MV2DC three-phase IIC module with one DC bridge feeding three AC bridges (one per-phase), utilized with some embodiments of the present disclosure.

[0016] FIG. 4 provides a schematic of a conventional SST HF transformer prototype for 15 kW CLLC with 13.2 kV input.

[0017] FIG. 5 provides an exploded view of a conventional CWT.

[0018] FIGS. 6A-B provides a schematic diagram of a HVW-CWT, in which FIG. 6A illustrates a full body rendering of three HVW-CWTs and FIG. 6B illustrates a zoomed-in view of windings, conductive layers / shields, dielectric insulation tube, and cores, in accordance with some embodiments of the present disclosure.

[0019] FIG. 7 provides a schematic of a cross-sectional view of a portion of an HVW-CWT, in accordance with some embodiments of the present disclosure.

[0020] FIG. 8 provides a schematic diagram of a single layer of an MV2DC stack with three HVW-CWTs (one per HV cell), in accordance with some embodiments of the present disclosure.

[0021] FIG. 9 provides a schematic diagram of a MV2DC 14-layer stack, in accordance with some embodiments of the present disclosure.

[0022] FIG. 10 provides a schematic diagram of a three-phase MV2DC stacked system cabinet system, in accordance with some embodiments of the present disclosure.

[0023] FIG. 11 provides a schematic of a cross-sectional view of a portion of an HVW-CWT, in accordance with some embodiments of the present disclosure.

[0024] FIG. 12 provides a schematic of a cross-sectional view of a portion of an HVW-CWT, in accordance with some embodiments of the present disclosure.

[0025] FIG. 13 provides a schematic of a cross-sectional view of a portion of an HVW-CWT, in accordance with some embodiments of the present disclosure.DETAILED DESCRIPTION

[0026] Although preferred exemplary embodiments of the disclosure are explained in detail, it is to be understood that other exemplary embodiments are contemplated. Accordingly, it is not intended that the disclosure is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. Thedisclosure is capable of other exemplary embodiments and of being practiced or carried out in various ways. Also, in describing the preferred exemplary embodiments, specific terminology will be resorted to for the sake of clarity.

[0027] To facilitate an understanding of the principles and features of the present disclosure, various illustrative embodiments are explained below. The components, steps, and materials described hereinafter as making up various elements of the embodiments disclosed herein are intended to be illustrative and not restrictive. Many suitable components, steps, and materials that would perform the same or similar functions as the components, steps, and materials described herein are intended to be embraced within the scope of the disclosure. Such other components, steps, and materials not described herein can include, but are not limited to, similar components or steps that are developed after development of the embodiments disclosed herein.

[0028] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0029] Also, in describing the preferred exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

[0030] Ranges can be expressed herein as from “about” or “approximately” one particular value and / or to “about” or “approximately” another particular value. When such a range is expressed, another exemplary embodiment includes from the one particular value and / or to the other particular value.

[0031] By ‘ ‘comprising” or “containing” or “including” is meant that at least the named compound, member, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

[0032] Mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a device or system does not preclude the presence of additional components or intervening components between those components expressly identified.

[0033] The materials described as making up the various members of the invention are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of the invention. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the invention.

[0034] Reference will now be made in detail to exemplary embodiments of the disclosed technology, examples of which are illustrated in the accompanying drawings and disclosed herein. Wherever convenient, the same references numbers will be used throughout the drawings to refer to the same or like parts.

[0035] The present disclosure provides novel techniques for realizing viable high-frequency transformers that meet the low leakage inductance requirement, while also providing a simple manufacturable design that addresses isolation, partial discharge, and thermal management issues.

[0036] High-Frequency (HF) Transformers for MV Applications:

[0037] A typical IIC module and its operation are shown in FIGS. 1A-D, with a target rating of 800 VDC and + / -800 V on the AC side by using an HF transformer and flipping logic. The target switching frequency for the IIC is in the 10-50 kHz range. The IIC modules depicted in FIG. 1A can be stacked together, as shown in FIG. 2, to realize higher AC side voltages. For three three-phase operation, three AC side IIC stacks can be utilized used. While many methods are possible for how the DC bridge and AC bridges of the converter are paired together, a preferred approach is to take three AC bridges from the three phases and couple them to a single DC bridge so as to reduce double line frequency currents in the DC bridge capacitors. This approach is shown in FIG. 3.

[0038] A typical MV2DC system could be rated to operate at, say 13-34 kV, with peak voltages that components can withstand of >50 kV in the steady-state, and 100 kV+ under transient conditions for 34 kV systems. In addition, the HF switching in the IIC cell causes high dv / dt, which can also cause accelerated failure and dielectric breakdown to occur. Of particular concern are air voids that remain as the components are assembled, as air ‘breaks down’ at much lower field intensities, as compared to many dielectric materials. Many components that operate at high voltage, such as transformers, use vacuum pressure impregnation (VPI) with suitable thermoset polymers, such as mineral-filled epoxy resins, to ensure that air voids are eliminated and long life is obtained. Other solutions relv on dielectric fluids, typically oils, toachieve the same goal while also improving heat transfer from the windings by convection and reject it to the environment.

[0039] Power electronic components and circuits are typically not designed for immersion in oil and are often liquid-cooled using heat sinks and cold plates. This can be seen in current designs for HVDC and VSC systems, where entire buildings are used to house converters, elaborate cooling loops are used with deionized water and heat exchangers, and high-voltage bushings are used to isolate the stacked modules of a typical MMC-type of design. In the case of high-frequency SSTs, unlike for MMCs, each stacked AC module is also coupled to the LV DC side with an HF transformer and DC bridge. This dramatically increases the complexity of the design and the challenge of simultaneously managing the insulation, power transfer, and cooling requirements for the system. Perhaps the most problematic element is the HF transformer itself, the point where all the dielectric stresses need to be managed.

[0040] A typical HF transformer used in more traditional SST implementations is shown in FIG. 4. Planar transformers are often preferred in HF converter designs due to higher power density. The example shown in FIG. 4 exemplifies some of the challenges, including eliminating air from the potting compound, use of electrostatic shields, dielectric breakdown due to fringing, air trapped in Litz wires, partial discharge, high dv / dt issues, thermal management and manufacturability.

[0041] The transformer in FIG. 4 has a magnetizing inductance of 100 pH, but is silent on leakage inductance. It can be seen that the use of a CLLC resonant circuit in a series resonant converter implementation suggests that the leakage inductance is high (estimate ~5 H) and is an actual energy transfer element. This shows that the DC and AC sides are decoupled and can require independent control of the voltage on the stacked AC side, which is accomplished with an MMC-like structure, a lot of energy stored in DC capacitors. The design of the transformer, especially to avoid partial discharge is very complex, requiring epoxy encapsulation of the winding that is free of air voids.

[0042] Exemplary HV Withstand CWT (HVW-CWT):

[0043] Disclosed herein are various MV2DC systems, based on the IIC, which can employ a coaxial winding transformer (CWT) structure for the HF transformer to realize ultra-low leakage inductance - target <200 nH. A traditional CWT structure, as has been used for a while, is shown in FIG. 5. While this has been shown to be very suitable for high current levels of 100 - 3,000 A in low- voltage applications (e.g., 100-1,000 V), extending the design to medium andhigh voltage levels, as can be required by the MV2DC SST, raises serious challenges. The peak voltage stress between the primary and secondary windings traverses through the air, which limits the ability to withstand high peak voltages. Previous designs that have used special Litz wires with high breakdown strength of 50 kV, still see the same issues, as the air will ionize and breakdown. A design approach is needed that addresses all the above-identified issues at the same time.

[0044] Various embodiments of the present disclosure utilize the coaxial winding structure for several reasons. The circular cross-section of the windings can provide a very smooth E-field profile with even stresses. The coaxial geometry can assure the lowest leakage inductance, a key parameter for the IIC. The design can be extended such that there is no air in the path that supports the voltage and electric field between the AC and DC sides. A detailed design approach with discussion is given below.

[0045] Various embodiments of the present disclosure provide high voltage withstand coaxial winding transformers (HVW-CWTs). As used herein the term “high voltage” alone should not be construed as limiting the scope of the present disclosure. Rather, as those skilled in the art, various embodiments of the present disclosure can be applied to various applications involving wide ranges of voltage levels. Embodiments of the present disclosure, however, can be particularly improved over conventional systems for use in medium voltage applications, e.g., up to 34 kV, such as 13-34kV, though the disclosure is not so limited.

[0046] At the heart of various embodiments of the HWV-CWTs is a tube that is made of a dielectric material, such as a ceramic that has high voltage withstand (typically in the range of 15-25 kV / mm). A thin layer of a non-magnetic conductive material, such as copper (or a partially conducting material), can be plated on the inside of the tube and can be processed (e.g., with sintering or electroless or electroplating) such that the conductive layer bonds with the dielectric without any air voids or gaps therebetween. A similar layer can be coated on the outside of the dielectric tube as well. One of the inner or outer layers, e.g., the inside conductive layer can be connected to a potential that is at the LV DC level (e.g., midpoint of the DC bus voltage), while the other of the inner or outer layers, e.g., the outside layer, is at the HV AC level (e.g., midpoint of the AC bridge output voltage). The voltage stress can then be completely taken across the ceramic (with no possibility of airgaps), which can be selected to have the desired breakdown level. The voltages between the windings and the ceramic surface layers can be in the range of 800 volts, well within the range of standard insulation designs.

[0047] FIGS. 6A-B shows an exemplary design a HVW-CWT. The transformer can comprise a first dielectric tube 105, a first inner nonmagnetic conductive layer 110 disposed on an interior surface of the first dielectric tube 105, and a first outer nonmagnetic conductive layer 115 disposed on an exterior surface of the first dielectric tube 105. The first inner 110 and outer 115 conductive layers can be coaxial with each other.

[0048] The use of high permittivity materials, e.g., the dielectric tube or other exterior materials, can allow for electric field shaping, thus allowing for a partial discharge free environment. As shown in FIG. 6B, in some embodiments, the inside layer 110 can extend out beyond the outside layer 115 on both sides. For example, the first outer conductive layer 110 has a first length extending in a longitudinal direction of the first dielectric tube 105, the first inner conductive layer 1 10 has a second length extending in the longitudinal direction of the first dielectric tube 105, the first dielectric tube 105 has a third length extending in the longitudinal direction of the first dielectric tube 105, the second length is greater than the first length, and the third length is greater than the second length. As those skilled in the art would understand, however, the disclosure is not limited to these relative lengths, and various embodiments can have various relative lengths between the first dielectric tube 105, first inner layer 110, and first outer layer 115.

[0049] The dielectric tube can be made of many different dielectric materials known in the art, including, but not limited to, ceramic, fiberglass, polymers, and composites. Composites can include, but are not limited to, fiberglass reinforced plastics (such as FR4 and GPO3), silica- filled epoxy, alumina-filled epoxy, and the like.

[0050] In some embodiments, the first inner 110 and outer 115 layers can be formed by a coating of a conductive non-magnetic material on the inner and outer surfaces, respectively, of the first dielectric tube 105. Exemplary conductive non-magnetic materials that can form the first inner 110 and outer 115 layers, include, but are not limited to, copper, aluminum, gold, silver, brass, bronze, graphene, carbon nanotubes, nickel alloys, tantalum, and the like.

[0051] Additionally, as discussed above, the inner 110 and outer 115 layers can be disposed about the inner and outer surfaces of the dielectric tube 105, respectively, such that no air gap is present between the layers 110 115 and respective surface of the dielectric tube 105. As used herein, the term “air gap” refers to any gap, void, pocket, or other volume that can be filled with air (or any gas) affecting electric fields. These air gaps can result from either manufacturing defects, operation of the device, or an intended design choice.

[0052] The inside and outside conductive layers are terminated to power converters (see FIGS. 1-3), as discussed above. For example, the first outer conductive layer 115 is electrically coupled to one of an AC bridge and a DC bridge of a power converter, and the first inner conductive layer 110 is electrically coupled to the other of the AC bridge and the DC bridge of the power converter. As used herein, and as appreciated by persons skilled in the art, the terms AC bridge and DC bridge refer to respective stages of a power converter.

[0053] Insulating panels can be used to create a ‘high-voltage cell’, where the AC side bridge and related components are located, isolated from all components that are at the LV DC side voltage potentials. The HVW-CWTs can also include a core 120 220, e.g., a magnetic cores, such as a nanocrystalline core.

[0054] As shown in FIGS. 6A-7B, the HVW-CWT can further comprise a second dielectric tube 205, a second inner nonmagnetic conductive layer 210 disposed on an interior surface of the second dielectric tube 205 and electrically coupled to the first inner conductive layer 110, and a second outer nonmagnetic conductive layer 215 disposed on an exterior surface of the second dielectric tube 205 and electrically coupled to the first outer conductive layer 215, in which the second inner 210 and outer 215 conductive layers are coaxial. As those skilled in the art would understand, the second dieletric tube 205, second inner layer 210, and second outer layer 215 can mimic and have similar properties / materials / connections / functions as the first dielectric tube 105, first inner layer 110, and first outer layer 115.

[0055] While in some embodiments, the inner 1 10 and outer 1 15 layers can serve as respective first 111 and second 116 windings of the HVW-CWT, in some embodiments, these layers can serve as electric field shields (instead of primarily current carrying windings), and the transformer can comprise distinct first 111 and second 116 windings.

[0056] An exemplary HVW-CWT may have a 4:4 turns ratio. As shown in FIGS. 6A-B, in some embodiments, the inner 110 210 and outer 115 215 layers can form first and second windings, respectively. In some embodiments, however, as shown in FIG. 7, the HVW-CWT can further comprise a first winding 111 disposed on an interior of the first inner conductive layer 110, and a second winding 1 16 disposed on an exterior of the first outer layer 115. In some embodiments, the first 1 11 and second 116 windings can be formed by additional conductive materials or layers, e.g., copper. For example, to make a 4:4 turns ratio, as shown in FIG. 7, the first winding 111 can comprise a copper layer that has portions around the circumference of the layer removed / notched so as to make four segments, which can be interconnected with respective components of a second side of the transformer (e.g., a secondtube 205, second inner conductive layer 210, and second outer conductive layer 215), to form the four turns needed. For example, the AC bridge side windings can be terminated inside the HV cell, while the LV windings can be outside the HV cell (or vice versa), separated by insulation barriers and large air gaps. The LV windings can directly connect to the DC side bridge (or vice versa). The tubular structure of the windings can minimize the leakage inductance, maximize the surface area for cooling, and simplify assembly and manufacture. It also allows the use of non-conductive material plated to the right depth to minimize AC resistance and cost.

[0057] FIGS. 11-13 provide alternative configurations for HVW-CWTs in accordance with various embodiments of the present disclosure. Each of these configurations comprises a dielectric tube 105, inner conductive layer 110, first winding 111, outer conductive layer 115, and second winding 116. The spacing and makeup of these components, however, can vary. For example, as shown in FIG. 11, an air gap 126 can exist between the inner nonmagnetic conductive layer 110 and the first winding 111. That air gap can be formed, at least in part, by one or more spacers 125 disposed between the first winding 110 and the inner layer 110. In this embodiment, the HVW-CWT further comprises a first winding support 112 configured to maintain the dimensional integrity of the first winding. The support 112 can be made of many materials, such as a dielectric material. As shown in FIG. 12, the HVW-CWT can include an air gap 126 between the first winding 111 and the inner conductive layer 110 and another air gap 127 between the outer conductive layer 115 and the second winding 116. FIG. 13 provides an alternative configuration to FIG. 12 in which the first winding 111 is formed by a plurality of wires.

[0058] As shown in FIG. 8, each HVW-CWT can be connected to a printed circuit board with the AC bridge, gate drivers, and associated control, filtering, and clamping circuits. Together, this can form the HV cell. Three HV cells can be connected on the LV side to a single DC bridge that provides excitation to all three HVW-CWTs. The three HV cells and one LV cell together form an integrated module that represents a single layer of the MV2DC stack. Multiple layers can be stacked together to match the AC-side line voltage and device ratings. For instance, with readily available 1.7 kV devices, a 14-layer stack can be used to realize a 13 kV (line-line) system, see FIG. 9. This approach has already been discussed in the MV2DC provisional disclosure referenced above but now includes integration with the HVW-CWT.

[0059] The entire MV2DC stacked system can be housed in a sealed IP-67 enclosure to maintain a dust and humidity-free environment, nrimarily to avoid the accumulation of dustand degradation of high-voltage withstand capability in the MV2DC system. Airflow can be maintained inside the cabinet to cool the devices with an externally mounted chiller or other heat exchanger. An embodiment of a three-phase MV2DC stacked system is shown in FIG. 10.

[0060] As shown in FIGS. 8-9, in some embodiments, the transformers disclosed herein can comprise one or more dielectric plates disposed exterior to the dielectric tube proximate ends of said tube. These dielectric plates can be configured to shape electric fields exterior to the dielectric tube. In some embodiments, the dielectric tube and the dielectric plates can be integral with each other (i.e., formed of a continuous piece of material). For example, in some embodiments, the dielectric tube and dielectric plates can be inj ection molded together. In some embodiments, the inner conductive layer can be first formed, then the dielectric plate and tube can be injection molded around the inner conductive layer, and then the outer conductive layer can be electroplated around the exterior of the dielectric tube. In some embodiments, the dielectric tube and plates can be injection molded and then the inner and outer conductive layers can be injection molded around the layers.

[0061] The embodiments disclosed herein provide several advantages over conventional devices. For example, the disclosed MV2DC systems, based on the IIC, can use a coaxial winding transformer (CWT) structure for the HF transformer to realize ultra-low leakage inductance - target <200 nH. A traditional CWT structure, as has been used for a while. While this has been shown to be very suitable for high current levels of 100 - 3,000 A in low- voltage applications (e.g., 100-1,000 V), extending the design to medium and high voltage levels, as can be needed by the MV2DC, raises serious challenges. The peak voltage stress between the primary and secondary windings traverses through the air, which limits the ability to withstand high peak voltages. Previous designs that have used special Litz wires with a high breakdown strength of 50 kV still see the same issues, as the air will ionize and break down. Various embodiments disclosed above can address all the above-identified issues at the same time. A coaxial winding structure can be useful for several reasons. The circular cross-section of the windings can provide a very smooth E-field profile with even stresses. The coaxial geometry can assure the lowest leakage inductance, a key parameter for the IIC. The design can be extended such that there is no air in the path that supports the voltage and electric field between the AC and DC sides.

[0062] It is to be understood that the embodiments and claims disclosed herein are not limited in their application to the details of construction and arrangement of the components set forth in the description and illustrated in the drawings. Rather, the description and the drawingsprovide examples of the embodiments envisioned. The embodiments and claims disclosed herein are further capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purposes of description and should not be regarded as limiting the claims.

[0063] Accordingly, those skilled in the art will appreciate that the conception upon which the application and claims are based may be readily utilized as a basis for the design of other structures, methods, and systems for carrying out the several purposes of the embodiments and claims presented in this application. It is important, therefore, that the claims be regarded as including such equivalent constructions.

[0064] Furthermore, the purpose of the foregoing Abstract is to enable the United States Patent and Trademark Office and the public generally, and especially including the practitioners in the art who are not familiar with patent and legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is neither intended to define the claims of the application, nor is it intended to be limiting to the scope of the claims in any way.

Claims

CLAIMSWhat is claimed is1. A high-voltage withstand coaxial winding transformer (HVW-CWT), comprising: a first dielectric tube; a first inner nonmagnetic conductive layer disposed on an interior surface of the first dielectric tube; and a first outer nonmagnetic conductive layer disposed on an exterior surface of the first dielectric tube, wherein the first inner and outer conductive layers are coaxial.

2. The HVW-CWT of claim 1 wherein the first inner conductive layer is disposed on the interior surface of the first dielectric tube such that no air gap is present between the first inner conductive layer and the interior surface of the first dielectric tube.

3. The HVW-CWT of claim 1 wherein the first outer conductive layer is disposed on the exterior surface of the first dielectric tube such that no air gap is present between the first outer conductive layer and the exterior surface of the first dielectric tube.

4. The HVW-CWT of claim 1, wherein the first inner conductive layer forms, at least in part, a first winding of the HVW-CWT.

5. The HVW-CWT of claim 1, wherein the first outer conductive layer forms, at least in part, a second winding of the HVW-CWT.

6. The HVW-CWT of claim 5, wherein the second winding is a low voltage winding of the HVW-CWT.

7. The HVW-CWT of claim 1, further comprising a first winding disposed in an interior of the first inner conductive layer.

8. The HVW-CWT of claim 7, further comprising an air gap disposed between the first winding and the first inner conductive layer.

9. The HVW-CWT of claim 8, further comprising at least one spacer located in the air gap-10. The HVW-CWT of claim 1, wherein the first winding is formed by one or more conductive wires.

11. The HVW-CWT of claim 1, further comprising a second winding disposed exterior to the first outer conductive layer.

12. The HVW-CWT of claim 11, further comprising an air gap disposed between the second winding and the first outer conductive layer.

13. The HVW-CWT of claim 11, wherein the second winding is a low voltage winding of the HVW-CWT.

14. The HVW-CWT of claim 1, wherein the first dielectric tube comprises a material selected from the group consisting of ceramic, fiberglass, polymers, and composites.

15. The HVW-CWT of claim 14, wherein the first dielectric tube comprises a composite material selected from the group consisting of: fiberglass reinforced plastic, silica- filled epoxy, and alumina-filled epoxy.

16. The HVW-CWT of claim 1, further comprising a core surrounding an exterior of the outer conductive layer.

17. The HVW-CWT of claim 1, wherein the first outer conductive layer is electrically coupled to one of an AC bridge and a DC bridge of a power converter, and wherein the first inner conductive layer is electrically coupled to the other of the AC bridge and the DC bridge of the power converter.

18. The HVW-CWT of claim 1, wherein the first outer conductive layer comprises a first length extending in a longitudinal direction of the first dielectric tube, the first inner conductive layer comprises a second length extending in the longitudinal direction of the first dielectric tube, and the first dielectric tube comprises a third length extending in the longitudinal direction of the first dielectric tube, wherein the second length is greater than the first length, and wherein the third length is greater than the second length19. The HVW-CWT of claim 1, further comprising: a second dielectric tube; a second inner nonmagnetic conductive layer disposed on an interior surface of the second dielectric tube and electrically coupled to the first inner conductive layer; and a second outer nonmagnetic conductive layer disposed on an exterior surface of the second dielectric tube and electrically coupled to the second inner conductive layer, wherein the second inner and outer conductive layers are coaxial.

20. The HWV-CWT of claim 1, further comprising one or more dielectric plates disposed in an area exterior to the first dielectric tube, the one or more dielectric plates configured to shape an electric field external to the first dielectric tube.

21. The HWV-CWT of claim 20, wherein the at least one dielectric plate in the one or more dielectric plates and the first dielectric tube are integral with each other.

22. A power converter, comprising: a plurality of converter modules stacked in series, each converter module comprising: a first bridge; a second bridge; and the HVW-CWT of any of claims 1-21, wherein the first inner conductive layer is electrically coupled to one of the first bridge and the second bridge and the first outer conductive layer is electrically coupled to the other of the first bridge and the second bridge.

23. The power converter of claim 22, wherein the first bridge is an AC bridge and the second bridge is a DC bridge.

24. The power converter of claim 23, wherein the first inner conductive layer is electrically coupled to the DC bridge, and wherein the first outer conductive layer is electrically coupled to the AC bridge.

Images