FR3129244A1 - PLANAR TRANSFORMER AND BIDIRECTIONAL DC-DC ELECTRIC CONVERTER COMPRISING SUCH A PLANAR TRANSFORMER - Google Patents

Abstract

This planar transformer (1) comprising an interlacing of primary layers (11) and secondary layers (12) which comprise conductive turns and which are separated and covered by a dielectric material, the primary layers (11) comprising only successive conductive turns connected in series, and the secondary layers comprising only conductive turns connected in parallel with each other. Figure for abstract: [Fig 1]

Description

PLANAR TRANSFORMER AND BIDIRECTIONAL DC-DC ELECTRIC CONVERTER COMPRISING SUCH A PLANAR TRANSFORMER

The present invention relates to planar transformers using interlaced stacks of primary and secondary layers separated by a dielectric to interface a primary network and a secondary network in direct current.

The present invention aims to constitute a planar transformer which has a transformation ratio greater than five between the primary and the secondary while minimizing the skin effect produced by the high chopping frequencies present in certain on-board aircraft systems.

Prior techniques

It is known to use planar transformers in power converters, when galvanic isolation is necessary.

This is particularly the case when the converter is used to connect a battery supply to a low-voltage, high-current electrical network, for example the so-called twenty-eight-volt "low-voltage differential transmission" network of an aircraft.

However, the current trend is to use silicon carbide or gallium nitride components, known as "Grand Gap" in power converters on board aircraft systems, allowing high switching frequencies, at lower loss, which allows a significant gain in terms of mass and volume of these on-board converters.

But this has the disadvantage of strongly increasing the influence of the skin effect and proximity effects in planar transformers.

The geometric arrangement of the primary and secondary layers of the transformer then has a major impact on the level of power dissipated by the Joule effect, which must absolutely be controlled to minimize the mass of the magnetic elements.

However, it is difficult to predict the distribution of the current in the windings connected in parallel, and a strong skin effect and proximity effects generating overheating tend to appear.

Faced with the complexity of modeling the magnetic effects in the windings, it is known on the other hand to overcome the problem of heating by the direct addition of cooling means to the planar transformer, such as those described in patent application EP3300090A1 .

This solution is nevertheless cumbersome, energy-intensive and sub-optimal, since it does not solve the causes of the appearance of undesirable magnetic effects.

Published mathematical models of electrical transformers, such as those of Dowel (1966), Weichen (2003), Chen (2015) or Djuric (2012) only allow a posteriori modeling of losses on a defined case, and do not allow to determine in advance an optimal architecture to be implemented in order to achieve target performances, in particular in a planar transformer.

The object of the invention is to overcome at least some of the aforementioned drawbacks and to propose a planar transformer capable of combining the advantages of compactness, reliability and efficiency for its implementation.

In view of the foregoing, the subject of the invention is a planar transformer comprising an interlacing of primary layers and secondary layers which comprise conductive turns and which are separated by a dielectric material, the primary layers comprising only successive conductive turns connected in series and the secondary layers comprising only conductive coils connected in parallel with respect to each other.

Preferably, the interlacing comprises five primary layers and five secondary layers superposed alternately with the primary layers.

For example, each primary layer has two conductive turns in series, the set of primary layers totaling ten turns.

Advantageously, each secondary layer comprises a single conductive turn.

According to one embodiment, each secondary layer is alternated with a single primary layer.

In one embodiment, two successive secondary layers are alternated with two primary layers.

Advantageously, the conductive turns have a copper thickness of between seventy and three hundred micrometers, preferably of the order of one hundred and seventy-five micrometers.

The planar transformer can also provide that two turns of two primary layers are separated by a distance of between two hundred micrometers and five millimeters.

Preferably, at least one of the primary and secondary layers comprises copper foil.

The invention also relates to a bidirectional electrical DC-DC converter comprising a planar transformer. The invention also relates to an aircraft comprising such an electrical converter or a planar transformer as described above.

The invention will be better understood on detailed study of two embodiments taken by way of non-limiting examples and illustrated by the appended drawings, in which:

represents the planar transformer according to a first embodiment.

represents a primary layer of the planar transformer.

represents a secondary layer of the planar transformer.

represents the planar transformer according to a second embodiment.

represents the planar transformer integrated in an electrical circuit of the “dual active bridge” type.

Claims (11)

Planar transformer (1) comprising an interlacing of primary layers (11) and secondary layers (12) which comprise conductive turns (13,15,17) and which are separated by a dielectric material (7), characterized in that the primary layers (11) comprise only conductive coils (13,15) successively connected in series, and in that the secondary layers (12) comprise only conductive coils (17) connected in parallel with each other. Planar transformer (1) according to Claim 1, in which the interleaving comprises five primary layers (11) and five secondary layers (12) alternately superposed with the primary layers (11). Planar transformer (1) according to one of Claims 1 and 2, in which each primary layer (11) comprises two conductive turns (13,15) in series. Planar transformer (1) according to any one of Claims 1 to 3, in which each secondary layer (12) comprises a single conductive turn (17). Planar transformer (1) according to any one of Claims 1 to 4, in which each secondary layer (12) is alternated with a single primary layer (11). Planar transformer (1) according to any one of Claims 1 to 4, in which two successive secondary layers (12) are alternated with two primary layers (11). Planar transformer (1) according to any one of Claims 1 to 6, in which the conductive coils (13,15,17) comprise a copper thickness of between seventy and three hundred micrometers, preferably of the order of one hundred and seventy-five micrometers. Planar transformer (1) according to any one of Claims 1 to 7, in which two turns (13,15) of two primary layers (11) are separated by a distance of between two hundred micrometers and five millimeters. A planar transformer (1) according to any one of claims 1 to 8, wherein at least one of the primary (11) and secondary (12) layers comprises copper foil. Bi-directional DC-DC electric converter (29) comprising a planar transformer (1) according to any one of the preceding claims. Aircraft comprising at least one of a planar transformer according to any one of claims 1 to 9 or a converter according to claim 10.