N-phase transformer assembly and n-phase llc resonant converter

Abstract

This invention relates to an N-phase LLC resonant converter with an N-phase transformer assembly, where N is a natural number greater than or equal to 1. The N-phase transformer assembly includes a soft magnetic core structure, N primary windings, and N secondary windings. The soft magnetic core structure includes N openings through the soft magnetic core structure and a closed-loop magnetic circuit surrounding each of the N openings. At least one air gap exists within the soft magnetic core structure. Each primary winding is wound around the soft magnetic core structure such that it passes through a corresponding opening. The N secondary windings are not wound around the soft magnetic core structure, and each secondary winding passes through a corresponding opening. The corresponding primary winding and the corresponding secondary winding pass through the same opening among the N openings and are part of the same phase in the N phases.

Description

Technical Field

[0001] This invention relates to an N-phase transformer assembly for an N-phase LLC resonant converter. The invention also relates to an N-phase LLC resonant converter comprising the N-phase transformer assembly according to the invention. Prior Technology

[0002] Miniaturizing electronic components while simultaneously improving their performance is one of the fundamental trends in modern electronics. For example, transformers play a crucial role in modern electronics, used to change alternating current (AC) voltage levels or to provide current isolation between circuits. In many applications, transformers need to be able to deliver high power and large current, such as for charging batteries in battery-electric or hybrid electric vehicles, or powering servers in large data centers.

[0003] The size of a transformer is typically determined by the magnetic core around which its electromagnetic coils are wound. To provide compact transformers with reduced core losses, the miniaturization and design of transformer cores have been studied in detail in the prior art.

[0004] LLC resonant converters are commonly used DC-to-DC converters because soft switching can be used in such converters, where soft switching reduces losses during power conversion. A very important component of an LLC resonant converter is the transformer.

[0005] Transformers known in the prior art specifically designed for LLC resonant converters are typically not optimized for high current. Therefore, transformers known in the prior art for LLC resonant converters are generally not optimized for applications requiring high current, and thus suffer higher losses when used in such applications. Summary of the Invention

[0006] The purpose of this invention is to create a transformer assembly for LLC resonant converters that mitigates at least some of the disadvantages of transformer assemblies known in the prior art. In particular, the object of this invention is to create a compact transformer assembly capable of providing high current to LLC resonant converters.

[0007] This invention relates to an N-phase transformer assembly for an N-phase LLC resonant converter, where N is a natural number greater than or equal to 1. The N-phase transformer assembly includes: (i) a soft magnetic core structure comprising N openings through the soft magnetic core structure and a closed-loop magnetic circuit surrounding each of the N openings, wherein at least one air gap exists within the soft magnetic core structure; and (ii) N primary windings and N secondary windings, wherein the N primary windings and N secondary windings: a) correspond to each other in a bi-firing manner; b) correspond to the N openings in a bi-firing manner; and c) correspond to the N phases in a bi-firing manner. Each of the N primary windings is wound on the soft magnetic core structure such that it passes through a corresponding opening. The N secondary windings are not wound on the soft magnetic core structure, and each of the N secondary windings passes through a corresponding opening. The corresponding primary winding and the corresponding secondary winding pass through the same opening among the N openings and are part of the same phase among the N phases. For each of the N phases, (iii) the corresponding primary winding is spaced apart from the corresponding secondary winding to provide resonant inductance for the resonant cavity of the LLC resonant converter through leakage, and (iv) a soft magnetic core structure is designed to provide magnetizing inductance for the resonant cavity of the LLC resonant converter.

[0008] The N-phase transformer assembly according to the present invention can be used in a single-phase system or a multi-phase system including at least two phases. The N-phase transformer assembly can be particularly implemented as a single-phase, two-phase, or three-phase transformer assembly. When used in an LLC resonant converter, different phases are provided by the switching structure of the LLC resonant converter.

[0009] The N-phase transformer assembly according to the invention is specifically designed for use in an N-phase LLC resonant converter. An LLC resonant converter is a resonant converter with a resonant cavity comprising an inductor and a capacitor, the cavity being designed to resonate at a specific frequency, and the cavity being connected to a transformer. LLC resonant converters are used for DC-to-DC power conversion. LLC resonant converters are suitable for high switching frequencies and typically have low switching losses because soft switching is possible. Therefore, LLC resonant converters are suitable for high-power applications and can be used as part of a charging infrastructure, for example, for charging batteries in battery electric vehicles or hybrid vehicles, or for powering servers in data centers. The N-phase transformer assembly according to the invention can be preferably used in such high-power applications as part of an N-phase LLC resonant converter.

[0010] The resonant cavity of an LLC resonant converter typically includes a resonant inductor and a magnetizing inductor, the resonant inductor being positioned in series with (i) a resonant capacitor and (ii) the primary winding of a transformer connected to the resonant cavity. The magnetizing inductor is positioned in parallel with the primary winding of the transformer. For an N-phase LLC resonant converter, each phase of the N-phase LLC resonant converter may include its own resonant capacitor, resonant inductor, and magnetizing inductor.

[0011] The N-phase transformer assembly according to the invention is designed to provide resonant inductance and magnetizing inductance for the resonant cavity of an N-phase LLC resonant converter. Therefore, the N-phase transformer assembly according to the invention facilitates the assembly of a compact N-phase LLC resonant converter. The leakage inductance in the N-phase transformer assembly is intentionally enhanced by appropriately spacing the primary winding from the corresponding secondary winding, thereby providing the desired resonant inductance. The desired magnetizing inductance is provided by appropriately providing air gaps in the soft core structure; these air gaps also delay the onset of saturation in the soft core structure. The appropriate selection of the soft magnetic material used in the soft core structure, particularly concerning the relative permeability of the soft magnetic material, can also affect the magnetizing inductance. Therefore, this at least one air gap provides the desired magnetizing inductance for the resonant cavity of the N-phase LLC resonant converter and mitigates saturation of the soft core structure.

[0012] Soft magnetic materials are materials that are easily magnetized by external magnetic fields. Magnetization of soft magnetic materials produces a magnetic flux density that is stronger than that of an external magnetic field in air. Compared to hard magnetic materials, soft magnetic materials exhibit low hysteresis losses. As soft magnetic materials for soft core structures, ferrites, particularly manganese-zinc ferrites or nickel-zinc ferrites, or other materials with high permeability can be used. Magnetic cores known in the art, such as ferrite cores, amorphous cores, nanocrystalline cores, or powder cores, are also suitable, for example, for assembling soft magnetic core structures.

[0013] Each of the N primary windings has a corresponding secondary winding among the N secondary windings. There is a one-to-one relationship between the N primary windings and the N secondary windings, also known as a bi-radial relationship. The corresponding primary and secondary winding pairs are successively paired with the N phases in a one-to-one relationship, and also with the N open circuits in a one-to-one relationship. Therefore, there is also a one-to-one relationship between the N open circuits and the N phases.

[0014] Each of the N primary windings is wound around a soft magnetic core structure in such a manner that it passes through a corresponding opening. Each primary winding may have a number of turns greater than or equal to 1, and in a preferred embodiment, much greater than 1. Each primary winding surrounds a portion of the soft magnetic core structure around which it is wound. When current, particularly alternating current, flows through each primary winding, a magnetic field is generated around the primary winding, and due to the high permeability of the soft magnetic core structure, most of this magnetic field passes through the soft magnetic core structure. The soft magnetic core structure around each opening results in a closed-loop magnetic circuit around each opening. Therefore, the soft magnetic core structure is implemented such that most of the field lines of the magnetic field generated by the current flowing through each primary winding pass through the soft magnetic core structure, and more specifically, along the closed-loop magnetic circuit around the corresponding opening. The soft magnetic core structure is preferably implemented such that all openings have substantially the same shape and size.

[0015] Each of the N secondary windings is not wound on a soft magnetic core structure and passes through its corresponding opening. The current flowing through each primary winding results in a potential difference between the terminals of each secondary winding, at which the corresponding secondary winding can be connected to an external circuit. Preferably, each secondary winding passes through its corresponding opening only once. When the terminals of the secondary windings are connected to an external circuit, large currents, especially hundreds of amperes, can flow through the secondary windings, particularly when the number of turns in the corresponding primary winding is much greater than 1. Since the secondary windings are not wound on a soft magnetic core structure, their total length is also reduced, which is beneficial for reducing Joule heating in the secondary windings. To facilitate the flow of such large currents through the secondary windings, the secondary windings may need to have a sufficient cross-section. The secondary windings for the N-phase transformer according to the invention can preferably be formed as a plurality of parallel conductive strips, particularly metal strips, separated by an electrically insulating material, to mitigate the skin effect in the secondary windings. The skin effect may be caused by the high switching frequency in the LLC resonant converter.

[0016] For a three-phase LLC resonant converter that can use the three-phase transformer assembly according to the invention, the three primary windings of the three-phase transformer assembly can be connected in a star or delta configuration, for example. Similarly, for a three-phase LLC resonant converter that can use the three-phase transformer assembly according to the invention, the three secondary windings of the three-phase transformer assembly can be connected in a star or delta configuration, for example.

[0017] Using a larger number of phases can generally lead to a reduction in total losses because the power flow can be distributed more evenly across the different phases. However, a larger number of phases often requires more complex magnetic and electrical circuits, especially more complex switching structures to provide the inversion and rectification functions of an LLC resonant converter.

[0018] In an embodiment of the N-phase transformer assembly according to the present invention, each of the N secondary windings passes through the corresponding opening once.

[0019] Since the length of each secondary winding can be reduced, it is beneficial to reduce losses in the secondary winding, especially losses caused by Joule heating, especially considering the large current that may flow through the secondary winding.

[0020] In another embodiment of the N-phase transformer assembly according to the present invention, each of the N secondary windings is formed by a plurality of parallel conductive strips, wherein an electrically insulating material exists between any two parallel conductive strips.

[0021] In another embodiment of the N-phase transformer assembly according to the invention, each of the N secondary windings is formed by eight parallel conductive strips.

[0022] In another embodiment of the N-phase transformer assembly according to the present invention, the N-phase transformer assembly further includes N tertiary windings, the N tertiary windings being: (i) bi-firingly corresponding to the N phases; (ii) bi-firingly corresponding to the N primary windings and the N secondary windings; and (iii) bi-firingly corresponding to the N openings; wherein each of the N tertiary windings is wound on a soft magnetic core structure such that it passes through the corresponding opening; wherein the corresponding primary winding, the corresponding secondary winding, and the corresponding tertiary winding pass through the same opening in the N openings and are part of the same phase in the N phases.

[0023] Therefore, each phase in the N phases can be associated with a triple consisting of a primary winding, a secondary winding, and a tertiary winding. Each of the N tertiary windings can be wound around a soft magnetic core structure through a corresponding opening. Each tertiary winding can have a number of turns greater than or equal to 1. The corresponding tertiary winding and the primary winding can pass through the same opening among the N openings. Each tertiary winding can be wound around the soft magnetic core structure in such a way that the corresponding closed-loop magnetic circuit around the opening corresponding to the corresponding tertiary winding is surrounded by the corresponding tertiary winding and the corresponding primary winding. Based on the ratio of the number of turns in the primary winding to the number of turns in the corresponding tertiary winding, the transformer assembly can be used as a step-up or step-down transformer assembly between the primary winding and the tertiary winding. For a three-phase transformer assembly, the tertiary windings can be connected, for example, in a star or delta connection. Having secondary and tertiary windings allows the transformer assembly to be used to provide a large current at a low voltage to one load via the secondary winding and a smaller current at a higher voltage to another load via the tertiary winding. This type of transformer assembly can be considered as an N-phase multi-port transformer assembly.

[0024] In another embodiment of the N-phase transformer assembly according to the invention, the N primary windings are made of enameled wire, or the N primary windings are made of Litz wire, or the N primary windings are provided as edgewise-wound coils.

[0025] In another embodiment of the N-phase transformer assembly according to the invention, the N tertiary windings are made of enameled wire, or wherein the N tertiary windings are made of Litz wire, or wherein the N tertiary windings are provided as flat vertical winding coils.

[0026] In another embodiment of the N-phase transformer assembly according to the invention, the Litz wire is implemented as a triple-insulated Litz wire.

[0027] In another embodiment of the N-phase transformer assembly according to the invention, a soft magnetic leakage enhancement element is placed in at least one of the N openings and located between the primary winding passing through at least one opening and the secondary winding passing through at least one opening.

[0028] In another embodiment of the N-phase transformer assembly according to the invention, a soft magnetic leakage enhancement element is placed in at least one of the N openings, located between the secondary winding passing through at least one opening and the tertiary winding passing through at least one opening.

[0029] The soft magnetic leakage enhancement element can be implemented as, for example, a ferrite board. For example, since the soft magnetic leakage enhancement element placed in the opening gap between the primary and secondary windings can be reduced, it is advantageous to increase the leakage inductance and make the N-phase transformer assembly more compact.

[0030] In another embodiment of the N-phase transformer assembly according to the invention, the soft core structure includes a main extension direction, wherein the main extension direction passes through N openings.

[0031] Therefore, the N-phase transformer assembly can extend along the main extension direction. Thus, by attaching a modular soft core structure element providing another opening to the soft core structure of the N-phase transformer, the N-phase transformer assembly can be easily modified into an N+1 phase transformer assembly.

[0032] In another embodiment of the N-phase transformer assembly according to the present invention, the soft core structure includes a plurality of soft core structure elements arranged continuously along the main extension direction, such that each of the plurality of soft core structure elements includes one or two adjacent soft core structure elements, and each of the N openings is formed by two adjacent soft core structure elements.

[0033] When a soft magnetic core structure is made of multiple soft magnetic core structure elements, it is advantageous to assemble the soft magnetic core structure in a simplified manner, especially when the soft magnetic core structure elements correspond to commercially available standard shapes.

[0034] The soft magnetic core structure may include N U-shaped soft magnetic core structural elements and one I-shaped soft magnetic core structural element. For example, each of the N U-shaped soft magnetic core structural elements includes two legs and a yoke. Any two adjacent U-shaped soft magnetic core structural elements are arranged such that the yoke of one of the two adjacent U-shaped soft magnetic core structural elements faces the two legs of the other U-shaped soft magnetic core structural element. Furthermore, the two legs of an outer U-shaped soft magnetic core structural element face the I-shaped soft magnetic core structural element.

[0035] In another embodiment of the N-phase transformer assembly according to the invention, at least one of the N openings is provided by two adjacent U-shaped soft magnetic core structural elements, wherein each of the two adjacent U-shaped soft magnetic core structural elements includes a yoke and two legs, and wherein the two adjacent U-shaped soft magnetic core structural elements are arranged such that the yoke of one of the two adjacent U-shaped soft magnetic core structural elements faces the two legs of the other of the two adjacent U-shaped soft magnetic core structural elements.

[0036] In another embodiment of the N-phase transformer assembly according to the invention, at least one of the N openings is provided by two adjacent U-shaped soft magnetic core structural elements, wherein each of the two adjacent U-shaped soft magnetic core structural elements includes a yoke and two legs, and wherein the two adjacent U-shaped soft magnetic core structural elements are arranged such that their respective two legs face each other.

[0037] In another embodiment of the N-phase transformer assembly according to the invention, at least one of the N openings is provided by a U-shaped soft magnetic core structural element and an I-shaped soft magnetic core structural element, wherein the U-shaped soft magnetic core structural element includes a yoke and two legs, and wherein the U-shaped soft magnetic core structural element and the I-shaped soft magnetic core structural element are arranged such that the two legs of the U-shaped soft magnetic core structural element face the I-shaped soft magnetic core structural element.

[0038] In another embodiment of the N-phase transformer assembly according to the invention, at least one of the N openings is provided by (i) an H-shaped soft magnetic core structure element and (ii) an adjacent U-shaped soft magnetic core structure element or another adjacent H-shaped soft magnetic core structure element; wherein the H-shaped soft magnetic core structure element includes four legs and a yoke.

[0039] In another embodiment of the N-phase transformer assembly according to the invention, N equals 3. When N equals 3, the N-phase transformer corresponds to a three-phase transformer.

[0040] In another embodiment of the N-phase transformer assembly according to the invention, the soft magnetic core structure extends along a simple closed planar curve and surrounds a central hole.

[0041] A simple closed plane curve can be defined as a plane curve, that is, a curve lying in a plane that is topologically equivalent to the unit circle, i.e., a homeomorphic image of the unit circle. Such simple closed plane curves do not intersect each other.

[0042] In another embodiment of the N-phase transformer assembly according to the invention, the soft magnetic core structure is formed as a ring, wherein the ring has a rotation axis passing through a central hole; wherein each of the N openings passing through the ring soft magnetic core structure: (i) includes a corresponding axis of symmetry passing through the opening; and (ii) connects an outer region outside the soft magnetic core structure to the central hole; wherein the N axes of symmetry lie in a common plane, the common plane being substantially orthogonal to the rotation axis, and wherein the N axes of symmetry are spaced apart from each other at an angle of 360º / N.

[0043] In another embodiment of the N-phase transformer assembly according to the invention, the soft magnetic core structure is formed as a ring with a rectangular cross-section.

[0044] A ring surrounds the central hole. Each opening is symmetrical with respect to the axis of symmetry passing through it. Each opening results in a closed-loop magnetic circuit around it.

[0045] In another embodiment of the N-phase transformer assembly according to the invention, N equals 3, and the central hole is formed as a right prism with two opposing polygonal bases of at least three sides; wherein the shape of the bulge of the soft magnetic core structure is similar to the shape of the central hole; and wherein each of the three openings through the soft magnetic core structure: (i) includes a corresponding axis of symmetry passing through the opening, and (ii) connects the outer region outside the bulge to the central hole; wherein the three axes of symmetry lie in a common plane, which is substantially orthogonal to the connecting edge of the right prism; and wherein the three axes of symmetry are spaced apart from each other at an angle of 120º.

[0046] In another embodiment of the N-phase transformer assembly according to the invention, N equals 3, and the polygonal base is a hexagonal polygonal base.

[0047] In another embodiment of the N-phase transformer assembly according to the invention, N equals 3, and the three primary windings are connected in a star or delta configuration, and / or the three secondary windings are connected in a star or delta configuration.

[0048] In another embodiment of the N-phase transformer assembly according to the invention, the three tertiary windings are connected in a star or delta configuration.

[0049] According to a second aspect of the present invention, the present invention relates to an N-phase LLC resonant converter, comprising: (i) a first switching structure; (ii) a resonant cavity connected to the first switching structure; (iii) an N-phase transformer assembly according to the present invention, the N-phase transformer assembly being connected to the resonant cavity through its N primary windings; and (iv) a second switching structure being connected to the N-phase transformer assembly through the N secondary windings of the N-phase transformer assembly.

[0050] In another embodiment of the N-phase LLC resonant converter according to the present invention, the N-phase LLC resonant converter is implemented as a bidirectional N-phase LLC resonant converter.

[0051] In another embodiment of the N-phase LLC resonant converter according to the present invention, the N-phase LLC resonant converter further includes (v) a third switching structure, which is connected to the N-phase transformer assembly through N three-stage windings of the N-phase transformer assembly.

[0052] In the case of a unidirectional N-phase LLC resonant converter, the second switching structure can also be implemented as a rectifier structure. In the case of a bidirectional N-phase LLC resonant converter, the first and second switching structures can be implemented in a similar manner, particularly as a half-bridge or full-bridge inverter structure. For example, the N-phase LLC resonant converter can be used in battery electric vehicles or hybrid electric vehicles. The N-phase LLC resonant converter according to the second aspect of the invention can generally be used in applications requiring high power efficiency and high power density, such as applications for powering servers in big data centers.

[0053] Other advantageous embodiments and combinations of features are derived from the following detailed description and all claims. Simple Explanation of the Diagram

[0054] Figures 1(a) and 1(b) show cross-sectional schematic diagrams of the first embodiments of the two-phase transformer assembly and the three-phase transformer assembly. Figures 2(a) and 2(b) show cross-sectional schematic diagrams of a second embodiment of a two-phase transformer assembly and a three-phase transformer assembly. Figures 3(a) and 3(b) show cross-sectional schematic diagrams of different embodiments of a two-phase transformer assembly. Figures 4(a) and 4(b) show cross-sectional schematic diagrams of different embodiments of a three-phase transformer assembly. Figures 5(a), 5(b), and 5(c) show three views of a three-phase transformer assembly. Figure 6 illustrates the manufacturing steps of the three-phase transformer assembly shown in Figures 5(a), 5(b), and 5(c). Figure 7 shows two views of a three-phase transformer assembly. Figure 8 illustrates the manufacturing steps of the three-phase transformer assembly shown in Figure 7. Figures 9(a) and 9(b) show cross-sectional views of a three-phase transformer assembly with a toroidal soft magnetic core structure and a three-phase transformer assembly with a hollow prismatic soft magnetic core structure. Figure 10 shows three views of the three-phase transformer assembly in Figure 9(a). Figure 11 illustrates the manufacturing steps of the three-phase transformer assembly shown in Figures 9(b) and 10. Figure 12 shows circuit diagrams of a single-phase LLC resonant converter and an N-phase LLC resonant converter. In the accompanying drawings, the same parts are given the same reference numerals. Implementation

[0055] Figure 1(a) shows a cross-sectional schematic diagram of a first embodiment of a two-phase transformer assembly 1'. The two-phase transformer assembly 1' in Figure 1(a) is assembled from two U-shaped soft magnetic core structural elements 2' and one I-shaped soft magnetic core structural element 2''. These three U-shaped soft magnetic core structural elements 2' and I-shaped soft magnetic core structural elements 2'' are assembled along a main extension direction 15, specifically, in the order of U-shaped soft magnetic core structural elements 2', U-shaped soft magnetic core structural elements 2', and I-shaped soft magnetic core structural elements 2''. The U-shaped soft magnetic core structural elements 2' and I-shaped soft magnetic core structural elements 2'' extend along the main extension direction 15, which is drawn adjacent to the U-shaped soft magnetic core structural elements 2' and I-shaped soft magnetic core structural elements 2'' for visualization purposes. For example, the U-shaped soft magnetic core structural elements 2' and I-shaped soft magnetic core structural elements 2'' in Figure 1(a) can be implemented as ferrite cores. Two U-shaped soft magnetic core structural elements 2' are arranged such that the two legs of one U-shaped soft magnetic core structural element 2' face the yoke of the other U-shaped soft magnetic core structural element 2', and the I-shaped soft magnetic core structural element 2'' faces the two legs of the other U-shaped soft magnetic core structural element 2'.

[0056] Between the two U-shaped soft magnetic core structural elements 2', more specifically between the two legs of one U-shaped soft magnetic core structural element 2' and the yoke of the other U-shaped soft magnetic core structural element 2', two air gaps 6 are provided. Air gaps 6 are also arranged between the two legs of the other U-shaped soft magnetic core structural element 2' and the I-shaped soft magnetic core structural element 2''. In Figure 1(a), a total of four air gaps 6 exist. Typically, different numbers of air gaps 6 can be used instead of the four air gaps 6 shown in Figure 1(a). For example, more small air gaps can be used instead of fewer large air gaps. By appropriately determining the dimensions of these four air gaps 6, two magnetizing inductors are provided for the two-phase LLC resonant converter.

[0057] The two-phase transformer assembly 1' includes two openings 3 passing through a U-shaped soft magnetic core structural element 2' and an I-shaped soft magnetic core structural element 2'', which are a result of the shapes of the U-shaped and I-shaped soft magnetic core structural elements 2' and their relative arrangement to each other. The specific arrangement of the U-shaped and I-shaped soft magnetic core structural elements 2' and 2'' in Figure 1(a) provides a closed-loop magnetic circuit 13 around each of the two openings 3.

[0058] The two-phase transformer assembly 1' comprises two phases: a first phase associated with a first primary winding 4' and a second primary winding 5', and a second phase associated with a second primary winding 4'' and a third primary winding 5''. The first primary winding 4' is wound around the two legs of one U-shaped soft magnetic core structure element 2', and the second primary winding 4'' is wound around the two legs of another U-shaped soft magnetic core structure element 2'. The portion of the first primary winding 4' wound on one of the two legs can be connected in series with the portion of the first primary winding 4' wound on the other leg, or the two portions of the first primary winding 4' can be connected in parallel.

[0059] The primary winding 5' and the secondary winding 5'' are not wound on the U-shaped soft magnetic core structure element 2' and the I-shaped soft magnetic core structure element 2''. Instead, the primary winding 5' passes directly through one opening 3, and the secondary winding 5'' passes directly through another opening 3. Both the primary winding 5' and the secondary winding 5'' are formed by multiple conductive strips / lamps arranged parallel to each other. In the cross-sectional schematic diagram of Figure 1(a), three laminations are shown for illustrative purposes. Electrically insulating material is arranged between the conductive strips. Therefore, the primary winding 5' and the secondary winding 5'' can thus have sufficiently large cross-sections to allow large currents to flow through the secondary windings, while mitigating eddy currents in the primary winding 5' and the secondary winding 5'' that may be caused by the rapid switching of the two-phase LLC resonant converter (in which a two-phase transformer assembly 1' may be used). Preferably, the first primary winding 5' and the second primary winding 5'' can extend in the main extension direction 15 along a length similar to that of the corresponding first primary winding 4' and second primary winding 4'', as illustrated in Figure 1(a). By appropriately spacing the first primary winding 5' and the second primary winding 5'' from their corresponding first primary winding 4' and second primary winding 4'', two resonant inductors are provided for the two-phase LLC resonant converter.

[0060] Figure 1(b) shows a cross-sectional schematic diagram of a first embodiment of the three-phase transformer assembly 1''. The three-phase transformer assembly 1'' in Figure 1(b) is structurally similar to the two-phase transformer assembly 1' in Figure 1(a) and includes three U-shaped soft magnetic core structural elements 2', one I-shaped soft magnetic core structural element 2'', and six air gaps 6. Typically, different numbers of air gaps 6 can be used instead of the six air gaps 6 shown in Figure 1(b). For example, more small air gaps can be used instead of fewer large air gaps. The first primary winding 4', the second primary winding 4'', and the third primary winding 4''' are wound on the six legs of the three U-shaped soft magnetic core structural elements 2', and the first primary winding 5', the second primary winding 5'', and the third primary winding 5''' pass directly through the three openings 3.

[0061] Figures 2(a) and 2(b) are structurally similar to Figures 1(a) and 1(b), respectively. The second embodiment in Figures 2(a) and 2(b) differs from the first embodiment in Figures 1(a) and 1(b) in that Figure 2(a) has a first tertiary winding 7' and a second tertiary winding 7'', while Figure 2(b) has a first tertiary winding 7', a second tertiary winding 7'', and a third tertiary winding 7'''. Compared to Figure 1(a), in Figure 2(a), the first primary winding 4' is wound only on one leg of the U-shaped soft magnetic core structure element 2', and the first tertiary winding 7' is wound on the other leg of the U-shaped soft magnetic core structure element 2'. Compared to Figure 1(a), in Figure 2(a), the second primary winding 4'' is wound only on one leg of the U-shaped soft magnetic core structure element 2', and the second tertiary winding 7'' is wound on the other leg of the U-shaped soft magnetic core structure element 2'. Figure 2(b) differs from Figure 1(b) in a similar manner.

[0062] Figure 3(a) illustrates different construction embodiments of the two-phase transformer assembly 1. In the embodiment shown at the top of Figure 3(a), two U-shaped soft magnetic core structural elements 2' and one I-shaped soft magnetic core structural element 2'' are used. In the embodiment shown in the middle of Figure 3(a), one U-shaped soft magnetic core structural element 2' as in the top embodiment and two U-shaped soft magnetic core structural elements 2''' with shorter legs are used. In the embodiment shown at the bottom of Figure 3(a), two U-shaped soft magnetic core structural elements 2''' with short legs and one H-shaped soft magnetic core structural element 2'''' are used as in the middle embodiment of Figure 3(a). The windings can be implemented as shown in Figures 1(a) and 1(b) or Figures 2(a) and 2(b), i.e., primary and secondary windings as in Figures 1(a) and 1(b), or primary, secondary, and tertiary windings as in Figures 2(a) and 2(b).

[0063] Figure 3(b) illustrates how the secondary winding is spaced apart from the primary winding, or optionally from the tertiary winding. This spacing 8 allows for the provision of resonant inductance through leakage. To make the transformer assembly more compact, a soft magnetic leakage enhancement element 9, particularly a ferrite plate, can be placed between the secondary and primary windings, or optionally between the secondary and tertiary windings. While the soft magnetic leakage enhancement element 9 in Figure 3(b) is placed in an opening formed between two identical U-shaped soft magnetic core structure elements, it can also be placed in openings provided by other core structures.

[0064] Figure 4(a) illustrates different construction embodiments of the three-phase transformer assembly 1. In the embodiment shown at the top of Figure 4(a), three U-shaped soft magnetic core structural elements 2' and one I-shaped soft magnetic core structural element 2'' are used. In the embodiment shown in the middle of Figure 4(a), two U-shaped soft magnetic core structural elements 2' as in the top embodiment and two U-shaped soft magnetic core structural elements 2''' with shorter legs are used. In the embodiment shown at the bottom of Figure 4(a), two U-shaped soft magnetic core structural elements 2''' with short legs and two H-shaped soft magnetic core structural elements 2'''' are used as in the middle embodiment of Figure 4(a). The windings can be implemented as shown in Figures 1(a) and 1(b) or Figures 2(a) and 2(b), i.e., primary and secondary windings as in Figures 1(a) and 1(b), or primary, secondary, and tertiary windings as in Figures 2(a) and 2(b). As shown in Figure 4(b), as in Figures 3(a) and 3(b), the soft magnetic leakage enhancement element 9 can be placed in the opening 3 to enhance the resonant inductance while making the three-phase transformer assembly more compact.

[0065] Figures 5(a), 5(b), and 5(c) show three views of a three-phase transformer assembly. Figure 6 shows the construction steps of the three-phase transformer assembly shown in Figures 5(a), 5(b), and 5(c). Figure 5(a) shows a perspective view, Figure 5(b) shows a top view, and Figure 5(c) shows another perspective view of the three-phase transformer assembly with output connector 11. The first stage winding 5', the second stage winding 5'', and the third stage winding 5''' are interconnected in a star configuration and include a star point portion 12 extending along a space on one side of the three-phase transformer assembly, while the output connector 11 is arranged on the other side. For example, the star point portion 12 may be grounded. At the output connector 11, rectified voltage and current may be present. For example, the output connector 11 may be connected to a vehicle's low-voltage battery for charging the low-voltage battery. Between the first-stage winding 5', the second-stage winding 5'', and the third-stage winding 5''' and the output connector 11, a second switching structure electrically connected to the first-stage winding 5'', the second-stage winding 5'', and the third-stage winding 5''' and the output connector 11 is arranged. Different second switching structures can be used, such as including an active switch, or only including diodes for rectification. In Figures 5(a), 5(b), 5(c), and 6, the primary winding and optionally the tertiary winding are provided by edgewise-wound coils 10 placed on a soft core structure. As shown in Figure 6, the soft core structure of Figures 5(a), 5(b), and 5(c) corresponds to the soft core structure shown in the intermediate embodiment of Figure 4(a).

[0066] Figures 7 and 8 correspond to Figures 5(a), 5(b), 5(c), and 6, respectively. The main difference is that the first-stage winding 5', the second-stage winding 5'', and the third-stage winding 5''' are not connected in a star configuration, and the output connector 11 is arranged on both sides of the three-phase transformer assembly. Therefore, the switches of the second switching structure can be arranged on both sides of the three-phase transformer assembly.

[0067] Figure 9(a) shows a cross-sectional view of a three-phase transformer assembly 1''''' with a toroidal soft magnetic core structure 2'''''', and Figure 9(b) shows a cross-sectional view of a three-phase transformer assembly 1'''''' with a hollow prismatic soft magnetic core structure 2'''''''. Figure 10 shows the three-phase transformer assembly 1''''' corresponding to the cross-sectional view of Figure 9(a), and Figure 11 shows the manufacturing steps of the three-phase transformer assembly of Figure 10.

[0068] The toroidal soft magnetic core structure 2''''' and the hollow prismatic soft magnetic core structure 2'''''' in Figures 9(a) and 9(b) surround the central hole 14. The cross-sectional views in Figures 9(a) and 9(b) correspond to the plane passing through the first-stage winding 5', the second-stage winding 5'', and the third-stage winding 5''', which are interconnected in a star configuration. Figure 9(a) shows a three-phase transformer assembly, and Figure 9(b) shows another cross-sectional view of the three-phase transformer assembly, which corresponds to the section (cut) of the three-phase transformer assembly along the dashed lines shown in Figures 9(a) and 9(b). In this other cross-sectional view, the third-stage winding 5''' through an opening is shown, which connects the respective outer sides of the three-phase transformer assembly to their respective central holes 14.

[0069] The central hole 14 of the three-phase transformer assembly in Figure 9(b) is a right prism with two hexagonal bases. The convex hull of the hollow prism-shaped soft magnetic core structure 2''''' of the three-phase transformer assembly 1''''' in Figure 9(b), that is, the minimum convex set around the soft magnetic core structure, is similar to a right prism, that is, the only difference between it and the right prism of the central hole 14 is the scale factor.

[0070] In Figure 10, the star-shaped dot section 12 is visible, in which the first-stage winding 5', the second-stage winding 5'', and the third-stage winding 5''' are connected to each other. A flat, vertically wound coil 10' is placed on a soft magnetic core structure element, which in turn provides a toroidal soft magnetic core structure 2'''''. A second switching structure is arranged between the output connector 11 and the first-stage winding 5', the second-stage winding 5'', and the third-stage winding 5''', as shown on the left side of Figure 10. On the right side of Figure 10, two openings 3' through which the secondary winding passes are visible. Around each of the three openings in the three-phase transformer assembly of Figure 10, there exists a closed-loop magnetic circuit 13, which passes through the soft magnetic core structure element and air gap as shown in Figures 9(a), 9(b), 10, and 11.

[0071] Figure 12(a) shows a circuit diagram of a single-phase LLC resonant converter, and Figure 12(b) shows a circuit diagram of an N-phase LLC resonant converter. The portions highlighted in gray in Figures 12(a) and 12(b) can be provided by a transformer assembly according to the invention. In Figure 12(a), the DC power supply marked with VIN is connected to the switching structure and the resonant capacitors, and is adjacent to the single-phase transformer assembly according to the invention. In Figure 12(b), the DC power supply marked with VIN is connected to the switching structure and N resonant capacitors, and is adjacent to the N-phase transformer assembly according to the invention. For the N-phase as shown in Figure 12(b), after the switching structure, the signal entering the N primary windings ideally has a phase offset of 0º, 360º / N, 2*360º / N, ..., (N-1)*360º / N. For each phase, corresponding secondary and tertiary outputs are provided.

[0072] In the circuit diagrams of Figures 12(a) and 12(b), all resonant inductors are moved to the secondary side S and the tertiary side T, respectively. The N secondary sides S are connected to the low-voltage (LV) battery via a second converter including a second switching structure, and the N tertiary sides T are connected to the high-voltage (HV) battery via a third converter including a third switching structure. The second and third switching structures can provide rectification. The first switching structure in the first converter, the second switching structure in the second converter, and the third switching structure in the third converter enable the provision of bidirectional or unidirectional LLC resonant converters.

[0073] It should be noted that the above are merely preferred embodiments for illustrative purposes, and the scope of this application is not limited to the described embodiments. The scope of this application is determined by the claims of the appended patent application. Furthermore, this application may be modified in various ways by those skilled in the art, but all such modifications shall not depart from the protection sought by the claims of the appended patent application.

[0074] 1': Two-phase transformer assembly 1, 1'', 1''''', 1'''''': Three-phase transformer assembly 2', 2''': U-shaped soft magnetic core structural element 2'': I-shaped soft magnetic core structural element 2'''': H-shaped soft magnetic core structural element 2''''': Ring-shaped soft magnetic core structure 2'''''': Hollow prismatic soft magnetic core structure 3, 3': Opening 4': First primary winding 4'': Second primary winding 4''': Third primary winding 5': First stage winding 5'': Secondary winding 5''': Third stage winding 6: Air gap 7': First and third stage windings 7'': Second and third stage windings 7''': Third-stage winding 8: Interval 9: Soft magnetic leakage enhancement element 10, 10': Flat vertical winding coil 11: Connector 12:Star point part 13: Closed-loop magnetic circuit 14: Center Hole 15: Main extension direction

Claims

1. An N-phase transformer assembly suitable for an N-phase LLC resonant converter, wherein N is a natural number greater than or equal to 1, wherein the N-phase transformer assembly comprises: (i) a soft magnetic core structure comprising N openings through the soft magnetic core structure and a closed-loop magnetic circuit surrounding each of the N openings, wherein at least one air gap exists within the soft magnetic core structure, and (ii) N primary windings and N secondary windings, wherein the N primary windings and the N secondary windings: a) correspond to each other in a bi-firing manner; b) correspond to the N openings in a bi-firing manner; c) correspond to the N phases in a bi-firing manner, wherein each of the N primary windings is wound around the soft magnetic core structure through a corresponding opening; wherein the N secondary windings are not wound around the soft magnetic core structure, and each of the N secondary windings passes through a corresponding opening; wherein the corresponding primary winding and the corresponding secondary winding pass through the same opening among the N openings and are part of the same phase among the N phases, and wherein, for each of the N phases, (iii) The corresponding primary winding is spaced apart from the corresponding secondary winding to provide resonant inductance for a resonant cavity of the LLC resonant converter through leakage, and (iv) the soft magnetic core structure is designed to provide magnetizing inductance for the resonant cavity of the LLC resonant converter.

2. The N-phase transformer assembly as described in claim 1, wherein, Each of the N secondary windings passes through the corresponding opening once.

3. The N-phase transformer assembly as described in claim 2, wherein, Each of the N secondary windings is formed by a plurality of parallel conductive strips, wherein an electrically insulating material exists between any two parallel conductive strips.

4. The N-phase transformer assembly as described in claim 1, wherein, The N primary windings are made of enameled wire, or of Litz wire, or are provided as a flat, vertically wound coil; wherein the Litz wire is implemented as triple-insulated Litz wire.

5. The N-phase transformer assembly as described in claim 1 further comprises N tertiary windings, wherein the N tertiary windings: (i) correspond to the N phases in a bi-firing manner; (ii) correspond to the N primary windings and the N secondary windings in a bi-firing manner; and (iii) correspond to the N openings in a bi-firing manner; wherein, Each of the N tertiary windings is wound around the soft magnetic core structure in such a way that it passes through a corresponding opening; wherein the corresponding primary winding, the corresponding secondary winding, and the corresponding tertiary winding pass through the same opening among the N openings and are part of the same phase among the N phases.

6. The N-phase transformer assembly as described in claim 5, wherein, A soft magnetic leakage enhancement element is placed in at least one of the N openings, located between the secondary winding passing through at least one opening and the tertiary winding passing through at least one opening.

7. The N-phase transformer assembly as described in claim 1, wherein, A soft magnetic leakage enhancement element is placed in at least one of the N openings, located between the primary winding passing through the at least one opening and the secondary winding passing through the at least one opening.

8. The N-phase transformer assembly as described in claim 1, wherein, The soft magnetic core structure includes a main extension direction that passes through the N openings; and wherein the soft magnetic core structure includes a plurality of soft magnetic core structural elements arranged continuously along the main extension direction, such that each of the plurality of soft magnetic core structural elements includes one or two adjacent soft magnetic core structural elements, and wherein each of the N openings is formed by two adjacent soft magnetic core structural elements.

9. The N-phase transformer assembly as described in claim 8, wherein, At least one of the N openings is provided by two adjacent U-shaped soft magnetic core structural elements, wherein each of the two adjacent U-shaped soft magnetic core structural elements includes a yoke and two legs, and wherein the two adjacent U-shaped soft magnetic core structural elements are arranged such that the yoke of one of the two adjacent U-shaped soft magnetic core structural elements faces the two legs of the other of the two adjacent U-shaped soft magnetic core structural elements.

10. The N-phase transformer assembly as described in claim 8, wherein, At least one of the N openings is provided by two adjacent U-shaped soft magnetic core structural elements, wherein each of the two adjacent U-shaped soft magnetic core structural elements includes a yoke and two legs, and wherein the two adjacent U-shaped soft magnetic core structural elements are arranged such that their respective two legs face each other.

11. The N-phase transformer assembly as described in claim 8, wherein, At least one of the N openings is provided by a U-shaped soft magnetic core structural element and an I-shaped soft magnetic core structural element, wherein the U-shaped soft magnetic core structural element includes a yoke and two legs, and wherein the U-shaped soft magnetic core structural element and the I-shaped soft magnetic core structural element are arranged such that the two legs of the U-shaped soft magnetic core structural element face the I-shaped soft magnetic core structural element.

12. The N-phase transformer assembly as described in claim 8, wherein, At least one of the N openings is provided by (i) an H-shaped soft magnetic core structure element and (ii) an adjacent U-shaped soft magnetic core structure element or another adjacent H-shaped soft magnetic core structure element; wherein the H-shaped soft magnetic core structure element includes four legs and a yoke.

13. An N-phase LLC resonant converter, comprising: i) A first switch structure; (ii) A resonant cavity connected to the first switching structure; (iii) The N-phase transformer assembly according to claim 1, wherein the N-phase transformer assembly is connected to the resonant cavity via N primary windings; (iv) A second switching structure connected to the N-phase transformer assembly via the N secondary windings of the N-phase transformer assembly.

14. The N-phase LLC resonant converter as described in claim 13, wherein, The N-phase LLC resonant converter is implemented as a bidirectional N-phase LLC resonant converter.

15. The N-phase LLC resonant converter as claimed in claim 13, comprising (v) a third switching structure connected to the N-phase transformer assembly via N tertiary windings of the N-phase transformer assembly.

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