EP1301932B1 - High frequency transformer with integrated rectifiers - Google Patents

Abstract

A high frequency transformer may include an integrated rectifier cell with flat windings and/or slotted copper segments stacked on a core branch to provide alternating primary and secondary windings. This reduces inductance leakage and thus increases the operating frequency of the transformer. Rectifying diodes of the rectifier cell may be arranged according to various configurations between the copper segments, and the collection plates may form one of the rectifier outputs. The other output may be provided by connecting all the midpoints of the windings with conductive spacers pressed together along a first axis. The invention is particularly advantageous in static converters, and, more particularly, in spot welding machines, for example.

Description

TECHNICAL DESCRIPTION

The present invention relates to transformers for static converter and more particularly to the transformer-rectifier assembly.

In known systems of this type, transformers are generally used, the primary and secondary coaxial, ie radially superimposed. The coils are made with enamelled wire or with copper foil (planar coil).

Axially stacked systems have also been described, in particular in the French patent FR1 028950A by C. GOSSELIN which explains the use of copper slats suitably slotted to form a coil capable of being placed around a core, this in the case of transformers at 50 or 60 Hz, single-phase or three-phase.

The US patent US4965712A of DUSPNA WALTER. S and AL also describes the use in turns of copper sheet cut with this time a core making several turns around the copper plate. This transformer was used in a high frequency circuit.

The two systems that have just been described incorporate rectifying diodes between the secondary blades. They have in common the disadvantage of having a high leakage inductance, likely to limit the frequency of use and therefore make the bulky system heavy and expensive.

The invention avoids these disadvantages since it makes it possible to produce very simple and inexpensive transformers thanks to a high operating frequency.

• des diodes de redressement en silicium (4), avantageusement sous forme de pastilles nues, directement comprimées entre les lames conductrices (3) lesquelles peuvent être réalisées en cuivre ou en aluminium.
• un empilement alterné, sur la jambe de noyau (1), des bobines plates (2) et des plaques conductrices (3), avantageusement disposées suivant un nombre élevé d'alternances (2)-(3).

The invention relates to a high-frequency transformer with integrated rectifiers having primary and / or secondary coils consisting of conductive strips (3) surrounding a single leg of the magnetic core, operating at a frequency of between 3 and 50 kHz and comprising:

• silicon rectifying diodes (4), advantageously in the form of bare pellets, directly compressed between the conductive strips (3) which may be made of copper or aluminum.
• an alternating stack, on the core leg (1), flat coils (2) and conductive plates (3), advantageously arranged in a large number of alternations (2) - (3).

According to another characteristic, the rectification is carried out either in a two-diode two-phase type circuit with a secondary mid-point (a), or with a conventional bridge (b), or with a circuit with two filtering inductances (c). ).

According to another characteristic, the rectifying diodes (4) are strongly pressed by suitable means (24) between the conductive blades (3) constituting the secondary and collector blades (14), in order to ensure good thermal and electrical contact.

According to another characteristic, the collecting blades (14) and the conductive blades (3) are cooled either by circulation of air or by a circulation of water in the thickness of the blade by means of channels (25).

According to another characteristic the conductive blades (3) are used as a primary, either directly or in series by means of conductive columns (15) arranged in a staggered manner along the axes Δ ₄ and Δ ₅ .

According to another characteristic, the conductive blades (3) have a U-shape (20) and are used as a primary and attacked by a bridge switching generator constituted by 4 switches (21) arranged between continuous feed blades ( 22) and (23), the pattern constituting the bridge being advantageously reproduced a large number of times, the blades (20) being interposed between coils (2) or plates (3) used as secondary

According to another characteristic, the conductive blades (3) being secondary, the rectifier (a) is made n times by connecting all the middle points by conductive columns (5) according to Δ ₁ while the diodes are stacked according to Δ. ₂ The diodes can be in position (12) or (13) and the middle points respectively (13) or (12).

According to another characteristic, the flat coils (2) are produced either by enamelled wire winding following two superimposed spirals connected in their center, one centriped, the other centrifugal or by two copper plates cut in a spiral and interconnected. by a weld in the center of the coil.

According to another characteristic, the invention is used for the construction of static converters, whether they are voltage boosters or down-converters.

According to another characteristic, the invention is used to supply welding machines, by point or of TIG, MIG, ARC type ... or else plasma machines for shooping, plasma cutting, etc.

According to another characteristic, the conductive plate (3) consists of a flat heat pipe.

• la figure 1 représente le schéma de principe du circuit électronique d'un transformateur avec son circuit de redressement qui peut être de type a, b ou c.
• la figure 2 représente, en vue éclatée, un transformateur abaisseur d'impédance et le redresseur associé.
• la figure 3 représente une coupe du convertisseur schématisé sur la figure 2, montrant notamment la connexion de point milieu du secondaire, dans le cas d'un redresseur de type a.
• la figure 4 représente une des plaques (3) formant le secondaire du convertisseur de la figure 3.
• la figure 5 représente une vue éclatée d'un convertisseur élévateur d'impédance.
• la figure 6 représente deux modes de connexion des cellules de redressement, en parallèle (6a), en série (6b).
• la figure 7 représente un générateur de découpage en pont intégré à la structure du transformateur, qui permet d'attaquer les primaires (20).
• la figure 8 représente une spire de primaire (20) destinée à être attaquée par le générateur de la figure 7, sur laquelle sont représentés les transistors (21) constituant les branches du pont.
• la figure 9 représente les moyens (24) permettant le serrage de l'empilement de diodes ;
• la figure 10 représente les canaux de refroidissement des plaques conductrices (3) et des plaques collectrices (14).
• la figure 11 représente un système utilisant le circuit de redressement de type (c).
• la figure 12 représente une coupe du système précédent dans lequel les inductances sont réalisées au moyen d'une spire traversant les noyaux (25).

The features and advantages of the invention will appear better in the description which follows, referenced in the accompanying drawing in which:

• the figure 1 represents the circuit diagram of the electronic circuit of a transformer with its rectification circuit which may be of type a, b or c.
• the figure 2 represents, in exploded view, an impedance-lowering transformer and the associated rectifier.
• the figure 3 represents a section of the converter schematized on the figure 2 , showing in particular the secondary midpoint connection, in the case of a type of rectifier.
• the figure 4 represents one of the plates (3) forming the secondary of the converter of the figure 3 .
• the figure 5 represents an exploded view of an up-converter.
• the figure 6 represents two connection modes of the rectification cells, in parallel (6a), in series (6b).
• the figure 7 represents a bridge splitter generator integrated in the structure of the transformer, which makes it possible to attack the primers (20).
• the figure 8 represents a primary turn (20) intended to be attacked by the generator of the figure 7 , on which are represented the transistors (21) constituting the branches of the bridge.
• the figure 9 represents the means (24) for clamping the diode stack;
• the figure 10 represents the cooling channels of the conductive plates (3) and the collector plates (14).
• the figure 11 represents a system using the rectification circuit of type (c).
• the figure 12 represents a section of the previous system in which the inductances are made by means of a turn through the cores (25).

The invention can be divided into 2 categories: impedance-lowering converters and impedance boosters. In the 1 ^st case, the output voltage is lower than that which feeds continuously the cutting bridge, while in the second case, it is higher.

In a general way, a converter is constituted by the implementation of several elementary cells such as that shown schematically on the figure 1 . The output connection of the cells can be performed in series in the case of an impedance rise ( figure 6a ) or in parallel for the impedance Fig. 6b ) or infinitely many combinations in series-parallel, so as to better adapt the impedances.

The stacking of these elementary circuits, associated with the splitting of the primary winding makes it possible to stack around the core (1) the primary and secondary circuit slabs by alternating them (a primary, a secondary, a primary etc.). is of paramount importance for a transformer because it reduces the leakage inductance. This limits the performance of the converters.

This stack is also very interesting from a thermal point of view because it allows the evacuation of calories dissipated in the transformer coils, by means of conductive plates (3) which are themselves cooled, either by pulsed air or by a circulation of water inside the plates itself, or again by the use of a process based on heat pipes. These conductive plates (3), both from an electrical and thermal point of view, can advantageously be made of copper or aluminum and constitute both the primary and the secondary or both simultaneously.

This stack is still interesting from an economic and industrial point of view because it allows the construction of a large variety of converters, in a wide range of power from standard elements that can be connected in a large number of serial combinations -parallel, both primary and secondary.

The arrangement of silicon diodes (4), advantageously in the form of thin pellets (fusions on molybdenum, for example), directly in contact with the conductive (3) or collector (14) plates, makes it possible to eliminate the connection wires and consequently to reduce the inductance of connection between the transformer and the rectifiers. This reduction is further increased in some cases by the paralleling of a large number of elementary circuits.

Thus, the invention makes it possible to reduce the parasitic inductance in series with the switching bridge, which is the sum of the leakage inductance of the transformer and the connection inductance. This allows operation at a higher frequency than is achieved with conventional transformers. This results in a reduction in the bulk, the mass and finally the cost of the converters.

For example, it was possible to realize converters operating at 5 kHz, capable of delivering a permanent power of 250 kW, holding in a box of shoes! The elementary cell of the converter represented in figure 1 allows to understand how it works. It consists essentially of a ferromagnetic core (1), ferrite or thin-laminated silicon iron (0.05 to 0.1 mm) or amorphous material.

• un bobinage primaire (P) qui peut suivant les cas être constitué par une plaque métallique (3), avantageusement en cuivre ou en aluminium, refroidie par air ou par eau ou encore une bobine en fil émaillé à double spirale (2).
• un bobinage secondaire (S), comportant un point milieu qui peut être réalisé par l'assemblage de deux plaques (3) connectées entre elles par une colonne conductrice (12) lorsque le primaire est une bobine à double spirale (2) ou deux bobines spirales lorsque le primaire est constitué par une plaque (3). A noter que dans ce dernier cas on peut également n'utiliser qu'une bobine à double spirale (2) à condition d'utiliser un redressement suivant les circuits (b) ou (c) schématisés sur la figure 1. dans certains cas, le circuit secondaire peut être constitué simplement par une spire réalisée par une plaque (3) avec redressement suivant le circuit (c).

Around the core (1) are arranged:

• a primary winding (P) which may, depending on the case, consist of a metal plate (3), advantageously of copper or aluminum, cooled by air or by water, or a double spiral enameled wire coil (2).
• a secondary winding (S), comprising a mid-point which can be realized by assembling two plates (3) interconnected by a conductive column (12) when the primary is a double spiral coil (2) or two coils spirals when the primary is constituted by a plate (3). Note that in the latter case it is also possible to use only a double spiral coil (2) provided that a rectification is used according to the circuits (b) or (c) shown schematically on the figure 1 . in some cases, the secondary circuit may simply consist of a turn made by a plate (3) with rectification according to the circuit (c).

The elementary cell given in figure 1 has a rectifying circuit using two diodes (D). It may comprise a filtering circuit (C), but it may also be placed at the output of the converter, ie after all the elementary cells have been connected in parallel as shown schematically on the figure 6a or in series as schematized on the figure 6b .

According to a first preferred embodiment of the invention, given by way of indication and, of course, in no way limiting, the static converter is used to obtain intense currents at a low voltage. As an example, consider the case of a spot welding power supply capable of delivering 10000 A at a voltage of 10 V.

To reach this intensity we will connect in parallel according to the diagram of the figure 6b , 5 cells constituted as shown exploded on the figure 2 , ie each comprising two copper secondary plates (3) surrounding a primary coil (2). The cut given in figure 3 allows to better understand the realization of this circuit. The 2 plates (3) are represented on the figure 4 . they comprise a slot (10) in which the core (1) passes and a slot (11) for forming a turn. The diodes can be placed either in position (12), in this case the midpoint is in (13), or in position (13) (midpoint in 13) according to the diagram of the figure 2 . Between these two plates is placed a flat coil made either by winding in two superimposed spirals of enamelled wire interconnected by the center, or by the stack of plates of a turn connected together by conductive columns staggered according to the diagram of the figure 5 . this type of coil has the advantage of having a small thickness allowing good evacuation of calories and have its outputs on the outside without causing excess thickness.

The connection of the middle points of the primary which is one of the rectifying outputs is achieved by clamping along the axis Δ ₁ of copper spacer (5) by means of a steel rod passing through the hole (12). formed in the plate (3). The rectifying diodes are made by directly placing the silicon chips (4), often called fusion between the plates (3) and (14) along the axis Δ ₂ . thus the diodes connect the ends (13) of the turns cut between the plates (3), thanks to the slot (11) to the collection blades (14) which constitute the other output of the collector. In order for the diode-copper plate contacts to be of little resistivity, the stack must be tightly tightened along the Δ ₂ axis, using filtered steel screws or rods.

The primaries, all connected in series following the figure 6b , will be powered by a symmetrical bridge cutting off the rectified area. For example, it will operate at a frequency ranging from 3 to 10 kHz. If for example, it is 5 kHz and using a 5cm ² useful section core, working at a peak induction of 1T, it will require that the primary has 55 turns. This will be achieved, for example by 5 coils (2), 11 turns each. Thus, the transformation ratio will be 55.

The cooling of the diodes and the transformer is carried out from the plates (3) and the collectors (14), which are cooled by water or by air.

According to a second preferred embodiment of the invention given here also for purely indicative purposes and of course in no way limiting, the static converter object of the invention is used as a high voltage source, which can also be called " impedance boost converter ".

In this case, the plates (3) are used to constitute the primaries as well as schematized on the figure 5 . To better understand the invention, let us place ourselves in the concrete case of a high voltage power supply delivering a voltage of 5600 volts.

Suppose that the nucleus has a section of 50 cm ² and that it supports a peak induction of 0.28T at the frequency of 5kHz. The number of primary turns, ie plates (3) connected in series by the set of connection columns Δ ₄ and Δ ₅ will be 20. The connections of the plates will be made by a series of spacers (15) alternately insulating or conductive. As previously, the plates (3), comprising a slot (10) to let the core pass and a slot (11) necessary to form a turn, are stacked alternately face F up then down, then up, etc. .. so that the turns turn in the same direction thus forming a spiral winding.

The secondary ones are formed by coils (2) of the "double spiral" type already mentioned above. figure 5 represented a cell using two coils (2) connected in a suitable direction so that the two output wires (16) and (17) deliver squares square in phase opposition. Under these conditions, the diodes (18) and (19) make it possible to perform a so-called "two-phase" rectification.

The connection of all the elementary cells is carried out as shown schematically in Figure 6b. With 10 plates (3) in primary, we can achieve 5 cells. Each coil should have 20 turns.

As before, the cooling of the transformer can advantageously be effected by means of the plates (3); these can be cooled by air or water. on the figure 6 b , there is shown a filtering cell LC placed on the output of the converter.

According to a third embodiment of the invention, again given purely as an indication and, of course, in no way limiting, the transformer integrates between its conductive plates (20) of a slightly different shape, used this time as a primary, a series of generators constituted by bridges in order this time, to reduce the inductance of connection between the generator and the transformer. Indeed, this inductance adds to both (leakage inductance and inductance of connections of the rectifiers), mentioned above.

The figure 7 represents this generator, which as before, is composed of several cells allowing the realization of the primary-secondary alternation which we saw that it constitutes the foundation of the invention. In the figure, there are two points that use transistors (21) in fairly flat packages, say for example S 247. Advantageously, these transistors may be MOS or IGBT. They are connected according to the conventional diagram of the bridge, between continuous supply plates (22) polarity + and (23) polarity -. Capacitors (C) are also available, as close as possible to the transistors (21), between the plates (22) and (23). The secondary is realized as before with integrated rectifiers, provided that it is split up. The fractionation can be obtained even in the case of a single coil, it is sufficient in this case to connect in series flat coils (2) or plates to a turn (3) connected in series by means of conductive columns (15). ).

According to a fourth embodiment of the invention also given purely by way of indication, a rectification is carried out according to scheme (c). In case, the diodes (4) are stacked between the secondary (3) and the collector plates (14) along the axes Δ ₆ and Δ ₇ (see figure 11 ). The plates (3) can be extended in order to realize the inductances L by placing two cores (25) between the rectifier and the output as shown schematically on the figure 12 .

One of the important technological aspects in the embodiment of the invention is the clamping of the diodes. It must ensure a constant pressure contact, whatever the differential dilations. To maintain contact over the entire surface of the diode, it is necessary to have perfect flatness of the conductive blades (3) and (14). The tightening is ensured by means of at least 4 screws (24) with a high elastic limit.

Another important technological aspect lies in the cooling of the conductive plates (3) and (14), which ensures the removal of heat from the transformer coils, but also and above all the diodes (4) which, in some spot welding machines , can release very high power densities. The cooling can be carried out simply by giving the plates (3) and (14) a sufficient surface on which it causes a forced circulation of air. For higher powers, it is necessary to use a coolant (water, glycol, coolanol, freon, oil etc ...).

The plates consist of two sheets of copper. Channels are engraved in one of them (see figure 10 ) and the two sheets are crushed one on the other, so that the liquid can be circulated in the thickness of the sheet. This is introduced for example by the orifice (26) and extracted by (27), this by means of a suitable set of spacers sealed and hollow, not shown in the figures. It is thus possible to channel the liquid to the level of the diode.

• générateur à très faible impédance destiné à équiper les machines à souder par point.
• générateur à faible impédance destiné à alimenter les torches à souder de type MIG ou TIG ainsi que les torches à découper.
• générateur à haute tension
• chargeur de condensateur, chargeur - déchargeur de batteries, etc ....

The invention can be used in all cases where a static converter is required. Let us mention as a guide some typical applications of the invention:

• very low impedance generator for equipping spot welding machines.
• low impedance generator for supplying MIG or TIG welding torches as well as cutting torches.
• high voltage generator
• capacitor charger, charger - battery discharger, etc ....

Claims (11)

1. High-frequency transformer, with integrated rectifier, having primary and/or secondary coils, consisting of conductive plates (3) surrounding a single magnetic core leg, characterized in that it operates at a frequency between 3 and 50 kHz and comprises:

   - silicon rectifier diodes (4), advantageously in the form of bare pads, directly compressed between the conductive plates (3) which can be made of copper or of aluminium,

   - an alternating stack, on the core leg (1), of the flat coils (2) and of the conductive plates (3), advantageously arranged with a high number of alternations (2)-(3).
2. Device according to Claim 1, characterized in that the rectification is carried out either according to a two-diode diphase-type circuit with a secondary having a centre tap a), or with a conventional bridge (b) or with a circuit with two inductors (c).
3. Device according to Claim 2, characterized in that the rectifying diodes (4) are strongly pressed by appropriate means (24) between the conductive plates (3) forming the secondaries and collector plates (14), in order to ensure a good thermal and electrical contact.
4. Device according to Claim 3, characterized in that the collector plates (14) and the conductive plates (3) are cooled by air circulation, or by water circulation in the thickness of the plate using channels (25).
5. Device according to any one of Claims 1 to 4, characterized in that the conductive plates (3) are used as primary, either directly, or with series-connection by means of conductive columns (15), arranged staggered on the axes Δ₄ and Δ₅.
6. Device according to any one of Claims 1 to 4, characterized in that the conductive plates (3) are U-shaped (20) and are used as primary and driven by a bridge-configuration switched-mode generator comprising four switches (21) positioned between DC power supply plates (22) and (23), the pattern forming the bridge being advantageously repeated a large number of times, the plates (20) being inserted between coils (2) or plates (3) used as secondary.
7. Device according to any one of Claims 1 to 6, characterized in that, the conductive plates (3) being secondaries, the rectifier (a) is produced n times by linking all the centre taps using conductive columns (5) on Δ₁, whereas the diodes are stacked on Δ₂, the diodes being able to be in position (12) or (13) and the centre taps respectively (13) or (12).
8. Device according to any one of Claims 1 to 7, characterized in that the flat coils (2) are produced either by the winding of enamelled wire on two superimposed turns linked in their middle, one of them centripetal and the other centrifugal, or by two copper plates cut into a spiral and interlinked by a solder joint at the centre of the coil.
9. Device according to any one of Claims 1 to 8, characterized in that the invention is used for the construction of solid-state converters, whether of voltage step-up or step-down type.
10. Device according to any one of Claims 1 to 8, characterized in that it is used to power spot or TIG, MIG, ARC or other types of welding machines, or even plasma machines for shooping, plasma cutting, and so on.
11. Device according to any one of Claims 1 to 10, characterized in that the conductive plate (3) is a flat heat pipe.

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