NL2034163B1

NL2034163B1 - An insulated winding assembly with improved electromagnetic shielding and current balancing.

Info

Publication number: NL2034163B1
Application number: NL2034163A
Authority: NL
Inventors: Rothmund Daniel; Lomonova Elena; Cremasco Andrea
Original assignee: Univ Eindhoven Tech
Priority date: 2023-02-16
Filing date: 2023-02-16
Publication date: 2024-09-03

Abstract

An insulated winding assembly, comprising a magnetic core, a foil winding package comprising N foil conductors in parallel, wherein each of the N foil conductors are wound around the magnetic core, N first Litz wires, wound around the magnetic core, and electrically connected to the N foil conductors, at first ends of the N foil conductors, respectively, N second Litz wires, wound around the magnetic core, and electrically connected to the N foil conductors, at second ends of the N foil conductors, respectively, N balancing capacitors electrically connected, at first ends thereof, to the N first Litz wires, respectively, such that each of the N balancing capacitors is connected in series with one of the N first Litz wires, wherein N is at least

Description

Title

An insulated winding assembly with improved electromagnetic shielding and current balancing.

Technical field

The present disclosure generally relates to the field of electrical devices and more specifically to foil windings and methods for forming the same, for use, for example, in a transformer and/or an inductor.

Background

High-power converter systems: The rapidly growing share of electricity demanded by emerging high-power Direct Current, DC, applications, such as megawatt charging and hydrogen-to-gas, and the continuous increase of power available from renewables have led to an interest in new highly efficient and compact solutions for medium-voltage high-power converters, such as solid-state transformers.

The so-called Solid-State Transformers, SSTs, i.e., galvanically isolated high-power AC/DC and DC/DC converters, could replace the state-of-the-art technology based on Low-Frequency Transformers, LFTs, due to several benefits such as smaller volume and weight.

Medium-frequency transformers: The power conversion in an SST is supported by transformers operating with MV PWM waveforms in the kilohertz range.

Therefore, this category of transformer is called Medium-Frequency Transformer,

MFT, see for example Figure 1a. The coil of a typical MFT consists of an inner secondary winding, LV, connected to the low voltage side of the converter ( for example < 1.1 kV) and an outer primary winding, HV, radially stacked to LV and connected to the side of the converter with the highest voltage; the coil is installed around the magnetic core of the MFT. The cross-section of the MFT is shown in Figure 1b.

The use of foil windings has gained interest as an alternative to litz wire windings, thanks to the reduced cost of foil conductors compared to litz wire. The main disadvantages of foil conductors are: 1. The increased ohmic losses due to the edge effect, and the electric field hotspots at the foil corners. 2. In high-current foil MFTs, the need for multiple foil conductors connected in parallel requires additional strategies for balancing the current sharing among them.

Reference is made to the following paper: “A. Cremasco, D. Rothmund,

M. Curti, and E. A. Lomonova, “Hybrid Foil-Litz Windings for Highly Efficient and

Compact Medium-Frequency Transformers,” IEEE Open J. Power Electron., (early access), 2023.”

Summary

It is an object of the present disclosure to provide for an insulated winding assembly using foil conductors, that can be applied in different solutions, especially in high-current MFT’s.

In a first aspect of the present disclosure, there is provided an insulated winding assembly, comprising: - a magnetic core; - a foil winding package comprising N foil conductors in parallel, wherein each of the N foil conductors are wound around the magnetic core; - N first Litz wires, wound around the magnetic core, and electrically connected to the N foil conductors, at first ends of the N foil conductors, respectively; - N second Litz wires, wound around the magnetic core, and electrically connected to the N foil conductors, at second ends of the N foil conductors, respectively; - N balancing capacitors electrically connected, at first ends thereof, to the N first Litz wires, respectively, such that each of the N balancing capacitors is connected in series with one of the N first Litz wires, wherein N is at least 2.

The inventors have found that the above described disadvantages of foil conductors can be overcome by using an insulated winding assembly in accordance with the present disclosure.

First, it is noted that the insulated winding assembly comprises multiple

Litz wires. In essence, the actual windings of the winding assembly, i.e. the N foil conductors, are extended by one or two turns of litz wire at both ends thereof. These litz wire may act as equipotential shielding rings, for example, to combat the increased ohmic losses due to the edge effect, and the electric field hotspots at the foil corners.

Second, it is noted that the total cross-section of the conductor in the turns of high-current foil MFTs may require using multiple foil conductors, e.g., two or three foil conductors in parallel as schematized in Figure 3a, insulated from each other, and radially overlapped.

The equivalent impedances of the individual foil sections, indicated by

Zi, are normally unequal; consequently, the total current is not shared uniformly among the paralleled foils, which leads to increased losses and thermal hotspots.

A solution to equalize the current sharing among each branch consists in connecting each foil to a balancing capacitor, as schematized in Figure 3b, located outside the winding; each capacitance is rated so that the total impedance of the paralleled sections is equal.

The inventors have found a way to combine both the above described solutions in an insulated winding assembly in accordance with the present disclosure.

The capacitor may be provided outside the actual package to improve connectivity.

Foil conductors are known to the person skilled in the art in the relevant technical field and are formed by a planar conductor that is insulated. The core material maybe any suitable material as required by the application. As an example, the core material may be air, or any suitable ferromagnetic material with a suitable permeability of magnetic field.

As an advantage over the known prior art documents, the present disclosure achieves lesser loss without a reduction in the cross-sectional area of the conductor. This therefore ensures a higher current carrying capacity. As a further advantage, the present disclosure achieves forming a winding assembly without the need of any mechanical joining, such as welding, between the different elements. The winding assembly is thus formed integrally, ensures a higher current carrying capacity and lower losses due to eddy currents.

In an example, the N balancing capacitors are electrically connected, at second ends thereof, to each other.

The above described example provides for a single connection to the insulated winding assembly. Each of the capacitors, the litz wires and the foil conductors are thus placed in parallel to one another.

In a further example, the N first Litz wires and the N second Litz wires are connected to the N foils conductors by wrapping and soldering the foil conductor around each corresponding Litz wire.

The advantage of this particular example is that a rigid connection is made between the litz wire and the corresponding foil conductor.

In a further example, the N second Litz wires are electrically connected to each other.

In yet another example, the N first Litz wires and/or the N second Litz wires are wound around the magnetic core with at least one turn.

It is noted that the foil conductors may radially overlap.

In a second aspect of the present disclosure, there is provided an electrical transformer comprising a primary and a secondary winding, wherein at least one of the primary or the secondary winding is an insulated winding assembly according to any of examples provided above.

It is noted that the advantages as explained with reference to the first aspect of the present disclosure, being the insulated winding assembly are also applicable to the other aspects of the present disclosure, for example the electrical transformer.

In a third aspect of the present disclosure, there is provided a switched mode power supply comprising an electrical transformer in accordance with the present disclosure.

Such a switched mode power supply is, for example, based on a topology like any of a Flyback Converter, a Forward Converter, a Resonant Converter (LC, CRM, LLC), a Full-Bridge Converter, a Half-Bridge Converter or a Push-Pull

Converter, or anything alike.

In a further aspect of the present disclosure, there is provided a method of forming an insulated winding assembly in accordance with any of the examples provided above, wherein the method comprises the steps of: - winding the N foil conductors in parallel around the magnetic 5 core; - winding the N first Litz wires around the magnetic core and electrically connecting the N first Litz wires to the N foil conductors, at first ends of the

N foil conductors, respectively; - winding the N second Litz wires around the magnetic core and electrically connecting the N second Litz wires to the N foil conductors, at second ends of the N foil conductors, respectively; - electrically connecting the N balancing capacitors at first ends thereof, to the N first Litz wires, respectively, such that each of the N balancing capacitors is connected in series with one of the N first Litz wires.

In an example, the method comprises the step of: - electrically connecting the N balancing capacitors, at second ends thereof, to each other.

In a further example, the method comprises the step of: - wrapping and soldering the foil conductors around each corresponding Litz wire, respectively.

In yet another example, the N second Litz wires are electrically connected to each other

The present disclosure is described in conjunction with the appended figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

The above and other aspects of the disclosure will be apparent from and elucidated with reference to the examples described hereinafter.

Brief description of the drawings

Fig. 1a and 1b disclose an MFT prototype with a foil conductor and a cross-section indicating a primary and secondary winding of the transformer;

Fig. 2 discloses a hybrid foil winding with a litz ring;

Fig. 3a and 3b disclose a schematic of a foil winding with three sections in parallel and a foil winding with three sections in parallel connected to the respective capacitor for current balancing, wherein the capacitors are located outside of the actual winding;

Fig. 4 discloses a schematic of litz rings connected to a parallel foil winding;

Fig. 5a discloses a hybrid winding with parallel foil conductors and litz ring and an electrical schematic of the assembly in accordance with the present disclosure.

Detailed description

It is noted that in the description of the figures, same reference numerals refer to the same or similar components performing a same or essentially similar function.

A more detailed description is made with reference to particular examples, some of which are illustrated in the appended drawings, such that the manner in which the features of the present disclosure may be understood in more detail. It is noted that the drawings only illustrate typical examples and are therefore not to be considered to limit the scope of the subject matter of the claims. The drawings are incorporated for facilitating an understanding of the disclosure and are thus not necessarily drawn to scale. Advantages of the subject matter as claimed will become apparent to those skilled in the art upon reading the description in conjunction with the accompanying drawings.

The ensuing description above provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the disclosure, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the disclosure.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." As used herein, the terms "connected," "coupled," or any variant thereof means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, electromagnetic, or a combination thereof.

Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed

Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list.

These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced in many ways. Details of the system may vary considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed in the specification, unless the Detailed Description section explicitly defines such terms.

Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims.

Figures 1a, 1b and 2, 3a and 3b have been cited and explained in the previous sections. The present disclosure is further elaborated with respect to the remaining figures.

The hybrid winding concept illustrated in Figure 2 cannot be applied to parallel foil windings and the concept shown in Figure 3b, as schematized in Figure 4, the litz rings are connected in series to the paralleled foil, so they cannot be connected to separate capacitors.

The present disclosure is directed to an insulated winding assembly that consists in having a foil winding package with N paralleled foil conductors. Each individual paralleled foil conductor is connected in series, at both ends, to one or more turns of litz wire, placed one above and one below the foil winding package. The resulting winding sections can be connected to the respecting balancing capacitor to balance the current sharing in the paralleled sections.

The present disclosure is thus directed to the insulated winding assembly that comprises: . A foil winding package with N paralleled foil conductors, e.g, N = 3, as shown in Figure 5aa. . Each individual paralleled foil conductor is connected in series, at both ends, to one or more turns of litz wire, placed one above and one below the foil winding package. . The resulting winding sections are connected to the respecting balancing capacitor, as shown in Figure 5b.

To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. For example, while some aspect of the technology may be recited as a computer-readable medium claim, other aspects may likewise be embodied as a computer-readable medium claim, or in other forms, such as being embodied in a means-plus-function claim.

In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

CONCLUSIONS

1. An insulated winding assembly, comprising: - a magnetic core; - a foil winding package having N parallel connected foil conductors, each of the N foil conductors being wound around the magnetic core; - N first Litz wires, wound around the magnetic core, and electrically connected to the N foil conductors, respectively at the first ends of the N foil conductors; - N second Litz wires, wound around the magnetic core, and electrically connected to the N foil conductors, respectively at the second ends of the N foil conductors; - N balancing capacitors electrically connected, at their first ends, to the N first Litz wires, respectively, such that each of the N balancing capacitors is connected in series with one of the N first Litz wires, where N is at least 2.

2. An insulated winding assembly as claimed in claim 1, wherein the N balancing capacitors are electrically connected to each other at their second ends.

3. An insulated winding assembly as claimed in any preceding claim, wherein the N first Litz wires and the N second Litz wires are connected to the N foil conductors by wrapping and soldering the foil conductor around each corresponding Litz wire.

4. An insulated winding assembly as claimed in any preceding claim, wherein the N second Litz wires are electrically connected to each other.

5. Insulated winding assembly according to any of the preceding claims, wherein the N first Litz wires and/or the N second Litz wires are wound around the magnetic core with at least one turn.

6. Insulated winding assembly according to any one of the preceding claims, wherein the N foil conductors overlap radially.

7. An electrical transformer comprising a primary and a secondary winding, at least one of the primary and secondary windings being an insulated winding assembly according to any one of claims 1 to 6.

8. Switched power supply comprising an electrical transformer according to claim 7.

9. A method of forming an insulated winding assembly according to any one of claims 1 to 6, the method comprising the steps of: - winding the N foil conductors in parallel around the magnetic core; - winding the N first Litz wires around the magnetic core and electrically connecting the N first Litz wires to the N foil conductors, respectively at the first ends of the N foil conductors; - winding the N second Litz wires around the magnetic core and electrically connecting the N second Litz wires to the N foil conductors, respectively at the second ends of the N foil conductors; - electrically connecting the N balancing capacitors at their first ends to the N first Litz wires, respectively, such that each of the N balancing capacitors is connected in series with one of the N first Litz wires.

10. A method according to claim 9, wherein the method comprises the step of: - electrically connecting the N balancing capacitors, at their second ends, to each other.

11. A method according to any one of claims 9 to 10, wherein the method comprises the step of: - winding and soldering the foil conductors around each corresponding Litz wire, respectively.

12. A method according to any one of claims 9 to 11, wherein the N second Litz wires are electrically connected to each other.

13. Method according to any of claims 9 to 12, wherein the N first Litz wires and/or the N second Litz wires are wound around the magnetic core with at least one turn.