EP2602801B1

EP2602801B1 - Planarer and modularer transformer

Info

Publication number: EP2602801B1
Application number: EP12194186.8A
Authority: EP
Inventors: Davide Fantino; Vincenzo Giorgianni; Emanuele Musca
Original assignee: Magneti Marelli SpA
Current assignee: Marelli Europe SpA
Priority date: 2011-12-05
Filing date: 2012-11-26
Publication date: 2015-07-15
Anticipated expiration: 2032-11-26
Also published as: EP2602801A1; ITTO20111114A1; EP2602801A8

Description

The present invention relates to a transformer of the type comprising at least one primary winding, at least one secondary winding, and a magnetic core that connects the primary winding magnetically to the secondary winding, and in which the primary winding is of the wire-type sort, whilst the secondary winding is formed by a planar element. In such transformers of a known type, the primary winding is wound in a helix; such a configuration is affected, however, by considerable losses due to parasitic currents, above all in high-frequency applications.
The document of the known art No. US 2010/127813 describes a transformer having a regular alternation of primary wire-type windings wound in a helix and of secondary planar windings. The planar windings are spaced apart via a spacer around which a primary winding is wound, thus forming as a whole a coil structure.
The above structure varies each time according to the type of application, being more or less complex according to the number of primary and secondary windings envisaged. One and the same type of spacer can in fact be set also on an outer side of one of the planar windings so that a further primary winding can be wound around it. Likewise, on one and the same spacer there can then be connected another planar winding, and on this there can be fixed another spacer with yet a further primary winding.
The object of the present invention is to provide a transformer according to claim 1, which will present efficiency of operation higher than that of transformers of a known type. Moreover, a further object of the present invention is to provide a transformer with modular structure, at a contained cost.
The objects referred to above are achieved via a transformer having the characteristics of one or more of the annexed claims.
The claims form an integral part of the technical teaching provided herein in relation to the invention.
Further characteristics and advantages of the invention will emerge from the ensuing description with reference to the annexed drawings, which are provided purely by way of non-limiting example and in which:

Figures 1 and 2 are two perspective views of an example of embodiment of the transformer described herein;
Figures 3 and 4 are perspective views of components of the transformer of Figure 1;
Figure 5 is a schematic illustration of a cross section of half of the transformer described herein;
Figure 6a and 6b illustrate the schematic configuration of a conventional transformer and of the transformer described herein, respectively.

In the ensuing description various specific details are illustrated aimed at providing an in-depth understanding of the embodiments. The embodiments may be obtained without one or more specific details, or with other methods, components materials, etc. In other cases, known structures, materials, or operations have not been described in detail so that various aspects of the embodiments will not be obscured.
The references used herein are provided merely for convenience and hence do not define the sphere of protection of the embodiments.
The transformer described herein, designated as a whole by the reference number 10, comprises at least one primary winding 2, at least one secondary winding 4, and a ferromagnetic core 6 that connects the primary winding magnetically to the secondary winding. Moreover, in said transformer the primary winding 2 is of the wire-type sort, whilst the secondary winding 4 is formed by a planar element made of electrically conductive material; in various embodiments, as in the one illustrated, the aforesaid element forms as a whole a turn and has a substantially rectangular cross section, the longer side of which is set substantially parallel to the plane containing the turn.
In the transformer described herein, the primary winding is formed by a wire - i.e., by an elongated element made of electrically conductive material - with a substantially circular cross section, which is wound in a spiral along the secondary winding. The wire is preferably coated with a sheath of insulating material; for example, it is enamel painted with insulating material or else coated with a proper insulating sheath so that it can be wound on itself in turns in contact with or in any case very close to one another; as primary winding it is hence possible to use a normal electrical cable, of the type widely available on the market.
As will be seen hereinafter, such a configuration enables reduction of the losses due to the parasitic currents and makes it possible to obtain, as a consequence, an efficiency of operation higher than that of transformers of a known type, discussed above.
With reference to Figures 6a and 6b (which are schematic illustrations of sections of half transformer), illustrated therein is a comparison between the configuration of a transformer of a conventional type and the configuration of the transformer described herein. As mentioned previously, in conventional transformers, the wire of the primary is wound in a helix; as a result of said geometry, the turns of the helix are subjected to significant, i.e., non-negligible, levels of parasitic current induced by the magnetic flux generated by the adjacent turns; the losses of energy due to said currents are considerable and the equivalent electrical resistance is consequently markedly higher than the resistance measured in direct current. In particular, the dissipation of energy is greater in the turns close to the secondary because the currents induced are higher there. Said condition is schematically represented in Figure 6a, where in the turn closest to the secondary there are three "+" and two "-", and in the turn below two "+" and one "-", the useful current in the winding being hence as a whole equal to just one "+". In the transformer of the type described herein, schematically represented in Figure 6b, said losses are instead considerably reduced, since each turn of the primary finds itself facing the secondary winding so that the effects of the magnetic flux generated by each turn vanish in the first layer of primary winding, without creating parasitic currents in so far as the current induced in the turns of the primary due to the vicinity to the secondary is all useful current.
In various preferred embodiments, as in the one illustrated, the transformer comprises at least one bobbin element 8 having:

a central cylindrical portion (not visible in the figures); and
a first widened end portion 12 and a second widened end portion 12', set respectively at the opposite ends of the aforesaid central portion and defining, respectively, a first plane surface 12a and a second plane surface 12'a facing one another.

In the above preferred embodiment, the two end portions of the bobbin element each carry a secondary winding, i.e., the turn with planar cross section, whilst the wire of the primary winding is wound in a spiral around the central portion, along at least one of the two facing plane surfaces. In particularly preferred embodiments, the two plane surfaces 12a, 12a' are at a distance apart D that is such as to prevent overlapping of said wire in the axial direction of the spiral formed by it.
In various embodiments, as in the one illustrated, the bobbin element 8 has an opening 14 that traverses the central portion and both of the end portions 12, in a direction substantially coinciding with the axis of the three windings carried by the bobbin element, and is prearranged, as may be seen from the figures, to receive a column 6' of the ferromagnetic core.
In various embodiments, as in the one illustrated, the end portions 12 are both formed by a disk made of insulating material with a hole at the centre, within which the respective secondary winding is embedded, whilst the central portion is constituted by a tubular element, once again made of insulating material, on the opposite ends of which are respectively fixed, in a region corresponding to their central holes, the two disk-shaped end portions.
As schematically represented in Figure 5, the bobbin element described above enables provision of a completely modular transformer structure, in which said element constitutes a single module that can be repeated any number of times, according to the application for which the transformer is designed. In particular, as may be seen in the example illustrated in the figures, the individual elements are prearranged for being stacked on top of one another, on the central column of the ferromagnetic core, by which the respective central openings 14 of said elements are traversed. In this connection, Figure 1 illustrates an example of transformer with three elements 8 stacked on top of one another.
Moreover, once again as schematically represented in Figure 5, it should be noted that the number of turns of the primary winding can vary according to the application required, and likewise differ between the bobbin elements that make up the transformer; in the same way, one or more bobbin elements of the transformer may present the secondary winding even on just one of the two end portions 12.
Finally, according to the required applications, the secondary windings and, likewise, the primary windings of the resulting ensemble, may then be connected in series and/or in parallel. In various embodiments, as in the one illustrated, the ferromagnetic core is formed by two distinct parts 6a, 6b separated in a plane P that is transverse to the column 6' of the core that carries the elements 8 and that cuts or delimits one end of said column. In assembly of the transformer, the two parts of the transformer are first separate so that it is possible to arrange the elements 8 on the column 6', and then said parts are coupled so as to close said elements within the ring structure formed thereby.
A transformer of the type described herein can be used in a DC-DC converter, designed to convert a direct-current source from one level or value of voltage to another. DC-DC converters are extremely widespread in the automotive sector, for example for electric cars, where it is frequently necessary for said converter apparatuses to be bidirectional, making the conversion between one side at a higher voltage level and one side at a lower voltage level in both directions. For example, in hybrid vehicles there are usually present two electrical wiring systems, namely, an electrical wiring system of a traditional type for loads such as the lights or the electronic control unit of the thermal engine and a high-voltage wiring system for the electric engine, which can operate, for example, at a voltage of around 600 V. In such a context, systems for conversion of energy are needed, preferably bidirectional ones, which set the two wiring systems in communication, in particular for transferring energy from the high-voltage wiring system supplied by a specific battery, for example a lithiumion battery, to the conventional wiring system at a lower voltage. In the above example of application, the transformer described herein can preferably be assembled according to a so-called "central tap" configuration.
Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary, even significantly, with respect to what has been illustrated herein purely by way of non-limiting example, without thereby departing from the scope of the invention, as defined by the annexed claims.

Claims

A transformer comprising:
- at least one primary winding (2);

- at least one secondary winding (4); and

- a magnetic core (6) designed to connect said primary winding magnetically to said secondary winding,
wherein the primary winding is formed by a wire, whilst the secondary winding is formed by a planar element that identifies as a whole a turn, said planar element having a rectangular cross section or in any case an elongated cross section, the longer side of which is set substantially parallel to the ideal plane containing said turn, said primary winding being formed by a wire wound in a spiral along said secondary winding,
said transformer being characterized in that it has a modular structure comprising at least one first bobbin element (8) and one second bobbin element (8), each bobbin element having:
- a central cylindrical portion; and

- a first widened end portion (12) and a second widened end portion (12'), set respectively at the opposite ends of said central portion, and defining, respectively, a first plane surface (12a) and a second plane surface (12'a) facing one another, where said first and second widened portions each carry one of said at least one secondary winding, and the wire of said primary winding is wound in a spiral around said central portion, along and between said first and second plane surfaces (12a, 12'a).
The transformer according to Claim 1, wherein said first and second bobbin elements are stacked on top of one another on said magnetic core.
The transformer according to any one of the preceding claims, wherein one of said first and second bobbin elements rests with one end portion thereof on an end portion of the other one of said first and second bobbin elements.
The transformer according to any one of the preceding claims, wherein said first and second surfaces (12a, 12'a) are at a distance apart (D) such as to prevent overlapping of said wire in the axial direction of said spiral.
The transformer according to any one of the preceding claims, wherein said bobbin element has an opening (14) that traverses said central portion and both of said end portions, in a direction substantially coinciding with the axis of said windings, and is traversed by a branch of said magnetic core.
The transformer according to any one of the preceding claims, wherein said end portions (12) are both formed by a disk made of insulating material with a hole at the centre, within which the respective secondary winding is embedded, whilst said central portion is constituted by a tubular element, made of insulating material, on the opposite ends of which said end portions are respectively fixed, in a region corresponding to their central holes.
The transformer according to any one of the preceding claims, wherein said magnetic core (6) comprises two distinct parts (6a, 6b), coupled to one another, together defining a ring structure that encloses within it said first and second bobbin elements (8).
The transformer according to any one of the preceding claims, comprising three or more of said bobbin elements (8).
The transformer according to any one of the preceding claims, wherein said first and second bobbin elements are identical to one another.
The transformer according to any one of the preceding claims, wherein said first and second bobbin elements are constituted by respective separate and distinct bodies.