Modular power conversion system with high frequency link

Abstract

A modular power conversion system in provided with a high frequency link comprising an electrically insulating tube that encloses a high frequency conductor. Power converter blocks are connected in series and linked to transformers enclosing the insulating tube. The transformers can be toroidal. The outside surface of the insulating tube is provided with conductive or semiconductive layers. A tape or material with high dielectric constant or non-linear resistivity is used to span the gap between adjacent conductive or semiconductive layers on the outer surface of the insulating tube. A conductive shield is provided on the inner surface of the insulating tube and optionally connected to earth or ground with a current sensor in the connection path for detecting the health of the insulation.

Description

Modular Power Conversion System with High Frequency LinkCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 789,468, filed 16-APR-2025, which is incorporated by reference herein in its entirety.STATEMENT OF GOVERNMENT INTEREST

[0002] Portions of this invention were made with government support under DE-SC0025007 awarded by Office of Science, U.S. Department of Energy. The U.S. government has certain rights in the invention.BACKGROUND

[0003] The present disclosure relates to a modular power conversion system with galvanic insulation. Specifically, the present invention relates to a modular power conversion system with building blocks comprising transformers and power converter bridges wherein the building blocks are coupled through a high frequency AC link.

[0004] US 11,735,357, granted to one of the applicants, describes a modular power conversion system which includes a plurality of building blocks comprised of transformers and power conversion bridges, and a high frequency AC link that transfers power and provides galvanic isolation between the building blocks.

[0005] The present invention describes further novel features and enhancements to a modular power conversion system comprising a high frequency link and an insulating tube that was described in US 11,735,357.

[0006] Many electrical applications require step-up or step-down of voltages along with conversion to AC or DC. Traditionally this is accomplished through use of power electronic converters along with line-frequency transformers. For example in a solar farm, DC from solar panels is converted to low voltage AC by inverters and then stepped up by a transformer to higher voltages for connection to the electric grid. In windturbines, variable frequency AC from the wind turbine generators is converted to 50 or 60 Hz by a power electronic converter and stepped up by a transformer for connection to the grid. Line frequency transformers in such applications can be bulky. One approach to achieve a more compact equipment size is to use solid-state transformers. Solid-state transformers use power electronics in combination with high frequency transformers typically operating at several hundred Hz to tens or hundreds of kHz. Generally, high frequency operation instead of line frequency operation can reduce the size and weight of transformers since a smaller magnetic core can be used. In solid-state transformers, incoming DC or low frequency (e.g. 50 or 60 Hz) AC is first converted to a high frequency by power electronics, then stepped-up / down by a high frequency transformer, and finally converted back to DC or AC of a suitable form and frequency for supplying a load or connecting to the grid.Although the magnetic core size can be reduced in a solid-state transformer compared to a line frequency transformer, the insulation needed between the primary and secondary sides can take up substantial space and reduce the power density of the overall system. A system using an insulation tube to separate the primary and secondary sides is described in US 11,735,357. However, there can be high localized dielectric stresses along the surface of the tube described in US 11,735,357 particularly at the edges of conductive foils or layers placed on the surface. Therefore, what is needed are techniques that overcome the above mentioned disadvantages of existing approaches.BRIEF SUMMARY OF THE INVENTION

[0007] Embodiments of the invention provide a power conversion system with modular building blocks comprising arrangement of transformers and power converter bridges, wherein the modular building blocks are coupled with a high frequency AC link with galvanic insulation.

[0008] In accordance with one aspect of the invention, a plurality of modular building blocks that include transformers and power converter bridges are coupled through a galvanically isolated high frequency current link. The high frequency link is magnetically coupled through the transformers in the building blocks but electricallyinsulated from the building blocks with a tube of high dielectric strength. According to another aspect of the invention, sections of the insulating tube are coated with conductive or semiconductive layer on the inner and outer surfaces and each layer is electrically referenced to a respective adjacent winding or high frequency link. This ensures that potential gradient between the windings / core and the high frequency link is impressed substantially across the dielectric tube and any potential gradients across air gaps in the transformers are minimized thus reducing partial discharge or corona effects. In accordance with another aspect of the invention, a high dielectric material or tape is used to span the gap between adjacent conductive or semiconductive layers on the outer surfaces of the insulating tube. In accordance with another aspect of the invention, a nonlinear resistive material is used to span the gap between adjacent conductive or semiconductive layers on the outer surfaces of the insulating tube.

[0009] According to yet another aspect of the invention, the conductive layer on an inner layer or surface of the insulating tube is connected to earth or ground and used as a protective shield to divert fault current in case of failure of the insulating tube.According to yet another aspect of the invention, the connection path of the shield to earth / ground is has current monitoring to check the health of the insulation system.

[0010] Various other features and advantages will be made apparent from the following detailed description and the drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements.

[0012] Figure 1 illustrates a modular power converter system with a high frequency link according to prior art.

[0013] Figure 2 illustrates a modular power converter system with a high frequency link according to prior art, wherein the modular power converter systemconsists of power converter blocks arranged in two arms of series connected power converter blocks.

[0014] Figure 3 illustrates a modular power conversion system with a high frequency link according to one embodiment of the present invention. An insulating tube is used to isolate the high frequency link, wherein multiple power electronic blocks and toroidal transformers are placed along the length of the insulating tube and connected to form two arms of a modular power converter. The high voltage connection for the two arms is positioned near the middle of the insulated tube and stack while the neutral connections of the arms are positioned near the two ends of the tube. Multiple conductive foils or layers are placed along the length of the tube on its surface and a high dielectric constant material or a non-linear resistive material is used to span the gap between adjacent conductive foils or layers.

[0015] Figure 4 illustrates a modular power conversion system with a high frequency link according to yet another embodiment of the present invention. An insulating tube is used to isolate the high frequency link, wherein multiple power electronic blocks and toroidal transformers are placed along a portion of the length of the insulating tube and connected in series to form one arm of a modular power converter. Multiple conductive foils or layers are placed along a portion of the length of the tube on its surface and a high dielectric constant material or a non-linear resistive material is used to span the gap between adjacent conductive foils or layers.DETAILED DESCRIPTION

[0016] Various embodiments and aspects of the inventions will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of various embodiments of the present invention. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present inventions.

[0017] Reference in the specification to “one embodiment” or “an embodiment” or “another embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the invention.

[0018] Figure 1 illustrates, according to prior art, a combination 100 of two building blocks for a modular transformer and power converter arrangement with galvanic insulation. Transformer 110 and power converter module 114 are part of one building block, while transformer 120 and power converter module 124 are part of the second building block. Power converter module 114 transfers power between its AC or DC terminals 116 and transformer 110 through high frequency connection 112. Power converter module 124 transfers power between its AC or DC terminals 126 and transformer 120 through high frequency connection 122. Conductor 130 is shared as a common winding that passes through both transformers 110 and 120 and has high insulation to the other parts of transformers 110 and 120. Conductor 130 when put in a closed circuit serves as a high frequency link for transferring power between two or more modular building blocks in a galvanically isolated manner. A controller 190 may be used for communications, sensing quantities such as voltage or current, and to control the switching devices in the power converter modules. The terminals 116 and 126 of power converter modules 114 and 124 respectively are added in series to obtain a common AC or DC port 132.

[0019] Figure 2 illustrates, according to prior art, a phase leg 200 comprising multiple building blocks for the modular transformer and power converter arrangement with galvanic isolation. Building blocks 210, 220, and 230 have AC or DC ports 212, 222, and 232 respectively which are combined in series to form AC or DC port 272; while blocks 240, 250, and 260 have AC or DC ports 242, 252, and 262 respectively which are combined in series to form AC or DC port 274. Ports 272 and 274 are further placed in parallel to form AC or DC port 276. The building blocks 210, 220, 230, 240, 250, and 260 share a common high frequency link 280 that is coupled to the transformers in the building blocks. The link 280 transfers power between the building blocks in thephase leg 200 or between phase leg 200 and other phase legs. A controller 290 is used to control the switching devices in the power converter modules.

[0020] Figure 3 illustrates, according to one embodiment of the present invention, an improved electrical insulation for a high frequency isolated modular power conversion system, 300. The cross-sectional view of the insulation system, 310, shows an electrical insulation tube 321. The inner surface of the tube has a conductive layer or conductive pipe, 323. A conductor 322 is placed within the tube and can comprise a litz wire. The ends of the conductor 322 can be connected to a power converter. Power converter building blocks 361, 362 and 363 are connected in series to form one arm, while power converter building blocks 364, 365, and 366 are connected in series to form a second arm. Two neutral ends 381 and 382 are formed by the two arms and can optionally be connected together. The other ends of the arms are connected through reactors 371 and 372 to form terminal 383 which serves as an input or output AC or DC port. Power converter blocks 361, 362, and 363 are respectively connected to transformers 351, 352 and 353 whose secondary is formed by conductor 322. In a preferred embodiment, the transformers can be toroidal. Conductive or semi conductive layers 332, 333 and 334 are placed on the surface of the tube and electrically connected or referenced to power converter blocks 361, 362 and 363 or their respective toroids. This arrangement confines the dielectric stress between the power converters and the high frequency link conductor 322 to across the wall of the insulation tube 321 and prevents high dielectric stresses in the air or space adjacent to the tube. High dielectric constant tapes or layer of materials, 341, 342, and 343 are used to span the gaps between the conductive layers on the outer surface of the tube and alleviate the dielectric stress at the edges of the conductive layers thus reducing the risk of corona or partial discharge. In one embodiment non-linear resistive layers can be used for 341, 342 and 343. A similar approach is used along the surface of the tube for the section coupling to power converter blocks 364, 365 and 366. In one embodiment, the copper layer of pipe 323 is connected to ground / earth and serves as a protective shield for diverting the fault current in case of insulation failure in the tube 321. In yet another embodiment, the connection of 323 to ground / earth is provided with a current sensor to monitor the insulation leakage current and to detect the condition of the insulation tube 321 and to take protective measures.

[0021] Figure 4 illustrates, according to another embodiment of the present invention, an improved electrical insulation for a high frequency isolated modular power conversion system, 400. The cross-sectional view of the insulation system, 410, shows an electrical insulation tube 421. An inner layer or the inner surface of the tube has a conductive layer or conductive pipe, 423. A conductor 422 is placed within the tube and can comprise a litz wire. The ends of the conductor 422 can be connected to a power converter. Power converter building blocks 461, 462 and 463 are connected in series to form terminal 481 situated at or near neutral or ground potential and through a reactor 472 to terminal 482 which serves as an input or output connection node. In contrast with Fig. 3, only a single series chain / arm of power converter blocks is used with the blocks coupled to toroids 451, 452, and 453. Conductive or semiconductive layers 431, 432, and 433, and high dielectric constant layers 441, 442, and 443 provide a graded dielectric stress along the surface of tube 421. Conductive shield 423 can be grounded / earthed to shield secondary high frequency link 422 from insulation failure in tube 421. A portion of the tube surface is provided with a high voltage termination 491 to the conductive layer 452 at the end of the tube. In one embodiment, the connection of 423 to ground / earth is provided with a current sensor to monitor the insulation leakage current and to detect the condition of the insulation tube 421.

[0022] The foregoing description of exemplary embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. It will be recognized by those skilled in the art that many modifications and variations are possible without departing from the essential scope of the invention. It is, therefore, to be understood that the scope of the invention is not limited to the particular embodiments disclosed, and that the invention will include all embodiments falling within the scope of the claims appended hereto.

Claims

CLAIMSWhat is claimed is:

1. A modular power conversion system with a high frequency link,wherein the power conversion system comprises two arms of series connected power converter blocks, andwherein the high frequency link comprises an electrical conductor placed in an electrically insulating tube, andwherein the power converter blocks are connected to transformers enclosing the electrically insulating tube, andwherein conductive or semiconductive layers are placed along portions of the outside surface of the tube and electrically referenced to the potential of the transformers or the power converter blocks, andwherein a conductive layer or shield is located on an inner layer or surface of the insulating tube, andwherein a tape or layer of material with a high dielectric constant or a non-linear resistivity is placed to span adjacent layers of the conductive or semiconductive layers on the outside surface of the tube.

2. The modular power conversion system of claim 1;wherein the conductive layer or shield located on the inner layer or surface of the insulating tube is connected to a ground or earth.

3. The modular power conversion system of claim 2;wherein the connection between the conductive layer or shield and the ground or earth is monitored with a current sensor to detect the condition of the insulating tube.

4. A modular power conversion system with a high frequency link,wherein the power conversion system comprises an arm of series connected power converter blocks, andwherein the high frequency link comprises an electrical conductor placed in an electrically insulating tube, andwherein the power converter blocks are connected to transformers enclosing the electrically insulating tube, andwherein conductive or semi conductive layers are placed along portions of the outside surface of the tube and electrically referenced to the potential of the transformers or the power converter blocks, andwherein a conductive layer or shield is located on an inner layer or surface of the insulating tube, andwherein a tape or layer of material with a high dielectric constant or a non-linear resistivity is placed to span adjacent layers of the conductive or semi conductive layers on the outside surface of the tube.

5. The modular power conversion system of claim 4;wherein the conductive layer or shield located on an inner layer or surface of the insulating tube connected to a ground or earth.

6. The modular power conversion system of claim 5;wherein the connection between the conductive layer or shield and the ground or earth is monitored with a current sensor to detect the condition of the insulating tube.

Images