FR3069696A1 - VOLTAGE ELEVATOR AUTOTRANSFORMER, AND CONTINUOUS ALTERNATIVE CONVERTER COMPRISING SUCH A AUTOTRANSFORMER - Google Patents

Abstract

The invention relates to a voltage-boosting autotransformer topology, as well as to a continuous AC converter comprising such an autotransformer. The autotransformer is configured to input three-phase alternating current (e.g., 115 Vac at constant frequency), and to output nine output voltage, supplied to a set of 18-pulse rectifier bridges to provide high DC voltage (e.g. +270 Vdc / -270 Vdc). The invention is particularly suitable for AC / DC converters in the field of aeronautics.

Description

VOLTAGE LIFTING AUTOTRANSFORMER, AND CONTINUOUS ALTERNATIVE CONVERTER COMPRISING SUCH AN AUTOTRANSFORMER.

The invention relates to a voltage-boosting autotransformer, as well as to a DC alternating converter comprising such an autotransformer.

In the aeronautical field, electricity is gradually taking a predominant place in terms of energy with regard to hydraulic or pneumatic energy. On-board electrical networks in aeronautics are currently evolving towards the use of direct current associated with a high voltage level, as proposed by the new HVDC networks (High Voltage Direct Current or high voltage direct current in French). The three-phase alternating current (for example 115 Vac at constant frequency), generated using the turbines, is thus converted into a high direct voltage (for example +270 Vdc / -270 Vdc). To carry out such a conversion operation, it is common to use an assembly consisting of an autotransformer and of a rectifier bridge assembly, assembly which can be designated under the name of ATRU (“Auto Transformer Rectifier Unit”, or “ autotransformer-rectifier ”). As a reminder, an autotransformer is a special case of transformer, in which the entire winding plays the role of primary and the part of the winding up to the intermediate point plays the role of secondary; the primary winding and the secondary winding thus have a common part, without any galvanic isolation between them. At equal nominal power, it is thus less bulky and lighter than a conventional transformer, which is advantageous in aeronautical applications.

Placing a capacitor-based rectifier at the output of the autotransformer would reintroduce into the AC circuit currents with harmonic frequencies of the frequency of the AC supply current.

Thus, the value of the angular phase shift between the voltage and the current intensity (also called "cos phi"), would be degraded, as well as the total harmonic distortion voltage (also called "THDv" for "Total Harmony Distorsion voltage") . So as not to have to use a filter cell with an autotransformer, and still reduce the residual ripples of the direct current (also called "ripple") and the harmonics reinjected into the network, different solutions consisting in artificially creating in an autotransformer, using additional outputs, one or two other three-phase networks, most often offset by 20 °, 37 ° or 40 °, have already been proposed. This structure can then be coupled to a twelve rectifier (for a three-phase network in addition to the main network) or eighteen wells (for two three-phase networks in addition to the main network).

An autotransformer, taking a three-phase voltage as input can, in known manner, be represented by a vector diagram. The three input voltages of the three-phase AC network form an equilateral triangle with the neutral voltage point at the center. The different output voltages can be represented by a vector originating from the center of the triangle, the length of the vector representing the maximum amplitude of the output voltage, and the angle of the vector relative to a reference vector representing the phase. of the output voltage. The windings present on the same leg of the autotransformer, and therefore magnetically coupled because crossed by the same magnetic flux, are represented in parallel on the vector diagram by different segments. The electrical interconnections between the windings are represented on the vector diagram by segment intersections. The length of these segments represents the number of turns of the windings.

Document US 2002/0186112 A1 thus discloses an autotransformer artificially recreating two three-phase networks in addition to the main network, the second three-phase network thus recreated being offset by a phase between 35 ° and 40 ° (preferably 37 °) relative to the main network, the third recreated three-phase network being offset by a phase between 35 ° and 40 ° (preferably 37 °) relative to the second recreated three-phase network. The amplitudes of the output voltages of the second and third networks are between 0.73 and 0.78 times the output voltage of the first main network, preferably equal to 0.767 times the output voltage of the first main network. The autotransformer is also coupled to an 18-pin rectifier. The document therefore describes a so-called “37 °” topology. The autotransformer described in this document does not, however, provide a solution to contain the mass of the autotransformer. However, this parameter is decisive in aeronautical applications. Manufacturers usually play on the dimensioning in nominal power of the autotransformer, at the price of a slight degradation of the output, compensated by an efficient cooling system using cold plates more often or specific heatsinks presenting a compromise power 'extraction / high mass. The problem with this choice of dimensioning is the use of complex and expensive cooling solutions or even, in the case of cold plates, difficult to integrate into an already existing system given the heaviness of the modifications to be made.

The invention therefore aims to optimize the mass of an autotransformer by reducing the length of the vectors by modifying its vector diagram, without making its industrialization more complex.

An object of the invention is therefore a voltage-boosting autotransformer, comprising a magnetic core formed by a first, a second and a third leg, said autotransformer being intended to be connected to a three-phase power supply of given amplitude supplied to a first, a second and a third input point and supplying nine output voltages, the nine output voltages being able to be broken down into a first group of three amplitude output voltages (Va, Vb, Vc) maximum a and 120 ° out of phase with each other, a second group of three output voltages (Vap, Vbp, Vcp) of maximum amplitude

0.767.a and phase-shifted by 120 °, and a third group of three output voltages (Vapp, Vbpp, Vcpp) of maximum amplitude 0.767.a and phase-shifted by 120 °, the second group of three output voltages (Vap, Vbp, Vcp) being 37 ° out of phase with respect to the first group of three output voltages (Va, Vb, Vc) and the third group of three output voltages (Vapp , Vbpp, Vcpp) being 37 ° out of phase with respect to the second group of three output voltages (Vap, Vbp, Vcp), the first leg comprising a first main winding delimited by the second input point and by a first separate terminal from the second input point by a number of turns such that the voltage taken from the first terminal has the same maximum amplitude as the output voltages of the second and third groups of output voltages (Vap, Vbp, Vcp, Vapp, Vbpp, Vcpp), the first main winding further comprising a first po intermediate int separated from the first entry point by a number of turns such that the first intermediate point is electrically connected to a first auxiliary winding magnetically coupled to a second main winding of the second leg having as said second entry point , said first auxiliary winding having a number of turns identical to the portion of second main winding situated between the second and the third entry point, the second main winding being delimited by the third entry point and by a second terminal separate from the third input point of a number of turns such that the voltage taken from the second terminal has the same maximum amplitude as the output voltages of the second and third groups of output voltages (Vap, Vbp, Vcp, Vapp, Vbpp, Vcpp), the second main winding having a second intermediate point separate from the second point d input of a number of turns such that the second intermediate point is electrically connected to a second auxiliary winding magnetically coupled to a third main winding of the third leg having as intermediate point said third entry point, said second auxiliary winding having a number of turns identical to the portion of the third main winding situated between the third and the first entry point, the third main winding being delimited by the first entry point and by a third terminal separated from the first entry point of a number of turns such that the voltage taken from the third terminal has the same maximum amplitude as the output voltages of the second and third groups of output voltages (Vap, Vbp, Vcp, Vapp, Vbpp, Vcpp), the third main winding having a third intermediate point separated from the third entry point by a number of turns such that q ue the third intermediate point is electrically connected to a third auxiliary winding magnetically coupled to the first main winding of the first leg having as an intermediate point said first entry point, said third auxiliary winding having a number of turns identical to the portion of the first winding main located between the second and first entry point, the portion of the first main winding located between the second and the first entry point, the portion of the third main winding located between the third and first entry point and the portion of the second main winding located between the second and the third entry point being electrically connected to each other in a triangle arrangement, the autotransformer also comprising:

a first additional winding, electrically connected to the first terminal, magnetically coupled to the third main winding and delimited by a first additional terminal, the first additional winding comprising a number of turns such that the voltage taken from the first additional terminal has the same amplitude maximum than the output voltages of the first group of three output voltages (Va, Vb, Vc),

- a second additional winding, electrically connected to the second terminal, magnetically coupled to the first winding

FIG. 1 shows a simplified example of a three-phase autotransformer, equipped with coils B23, B12 and B31 comprising input terminals E1, E2 and E3, and coils S23, S12 and S31 which are not linked to the invention but which illustrate the operating principle of an autotransformer. The autotransformer includes a closed ferromagnetic circuit comprising:

- a first central leg M12 receiving the windings corresponding to a first phase;

a second lateral M23 leg receiving the coils of a second phase;

and a side leg M31 receiving the coils of a third phase.

In the case of a three-phase input voltage, the magnetic fluxes which flow in each of the legs of the autotransformer are identical but 120 ° out of phase with each other. Thus, in the diagram of FIG. 2, the vectors OE1, OE2 and OE3, representing the input voltages have the same amplitude, and have an angle of 120 ° between them. As previously indicated, the windings of the same leg are all traversed by the same magnetic flux, and are thus magnetically coupled. For example, in FIG. 2, the segments representing the main winding B12 and an auxiliary winding X3 are shown in parallel; this illustrates the magnetic coupling between the main winding B12 and the auxiliary winding X3, the latter corresponding for example to the winding S12 in the vector representation of the circuit of FIG. 1. It has also been indicated previously that each input or output voltage can be represented by a vector, whose length represents the amplitude, and whose orientation represents the phase from 0 ° to 360 °. Thus, for an autotransformer configured to produce nine phases from three input phases spaced 120 ° apart, vector compositions are sought which, from the three input phases, make it possible to manufacture the nine phases sought. In FIG. 2, the three-phase power supply is applied to the terminals of the windings at E1, E2 and E3.

An arbitrary neutral point of origin O is also defined arbitrarily for the vectorial composition and the simple input and output voltages of the autotransformer will be referenced with respect to this point. The three points E1, E2 and E3 form an equilateral triangle, originating from point O, which implies that the vector sum of the voltages OE1, OE2 and 03 is zero.

For the autotransformer according to the invention, it is sought to obtain a first group of three output voltages (Va, Vb, Vc), a second group of three output voltages (Vap, Vbp, Vcp) and a third group of three output voltages (Vapp, Vbpp, Vcpp). The voltages of the first group of three output voltages (Va, Vb, Vc) have the same phase as the input voltages. The length of the vectors representing the voltages of the first group of three output voltages (Va, Vb, Vc) depends on the desired output voltage. For example, for a supply voltage of 115 Vac, and an output voltage of 270 Vdc, there is a coefficient of 2.34 between the length of the vectors representing the voltages of the first group of three output voltages (Va, Vb, Vc) and the length of the vectors representing the input voltages, which corresponds to the case of a step-up autotransformer. The vectors representing the voltages of the first group of three output voltages (Va, Vb, Vc) and the vectors of the input voltages are thus collinear. The second group of three output voltages (Vap, Vbp, Vcp) is then constructed from the first group of three output voltages (Va, Vb, Vc). The vector representing the first voltage Vap of the second group of three output voltages (Vap, Vbp, Vcp) has an angle of 37 ° relative to the vector representing the first voltage Va of the first group of three output voltages (Va, Vb, Vc), and a length equal to 0.767 times the length of the vector designating the first voltage Va of the first group of three output voltages (Va, Vb, Vc). Alternatively, the angle of 37 ° can be replaced by an angle of 40 °. The vector representing the voltage Vbp is then deduced from the vector representing the voltage Vap, by an identical length and an angle of 120 °; similarly, the vector representing the voltage Vcp is deduced from the vector representing the voltage Vbp, by an identical length and an angle of 120 °. The process of constructing the vectors representing the voltages of the third group of three output voltages (Vapp, Vbpp, Vcpp) is similar. The vector representing the voltage Vapp has a length equal to 0.767 times the length of the vector designating the first voltage Va, with an angle of -37 ° between the two vectors (or 40 ° depending on a variant). The vector representing the voltage Vbpp is then deduced from the vector representing the voltage Vapp, by an identical length and an angle of -120 °; similarly, the vector representing the voltage Vcpp is deduced from the vector representing the voltage Vbpp, by an identical length and an angle of -120 °.

FIG. 3 illustrates another mode of representation of the autotransformer. Having illustrated the magnetic circuit with its legs M12, M13 and M23 in FIG. 1, we pass to FIG. 3 where only the coils are represented opposite the three legs which they equip, the parallel segments in FIG. 2 corresponding to windings arranged on the same leg. These windings are also represented by segments in FIG. 2, the amplitude of which is representative of the length of the windings, the length of a winding being defined by its number of turns surrounding a leg.

The first leg M12 comprises a first main winding B12 also shown in FIG. 2. The first main winding B12 extends from the second entry point E2 to a first terminal KT. The length of the first main winding B12, namely between the entry point E2 and the first terminal K1 ', is determined so that the point representing the first terminal KT is on the iso-amplitude circle of the second group of three voltages output (Vap, Vbp, Vcp) and the third group of three output voltages (Vapp, Vbpp, Vcpp). Likewise, the second leg M23 comprises a second main winding B23 also shown in FIG. 2. The second main winding B23 and delimited by a first additional terminal, the second additional winding comprising a number of turns such as the voltage drawn at the second additional terminal has the same maximum amplitude as the output voltages of the first group of three output voltages (Va, Vb, Vc), a third additional winding, electrically connected to the third terminal, magnetically coupled to the second main winding and delimited by a third additional terminal, the third additional winding comprising a number of turns such that the voltage taken from the third additional terminal has the same maximum amplitude as the output voltages of the first group of three output voltages (Va, Vb, Vc ).

The invention also relates to a continuous AC converter comprising such an autotransformer.

Other characteristics, details and advantages of the invention will emerge on reading the description made with reference to the accompanying drawings given by way of example and which represent, respectively:

Figure 1 shows a simplified three-phase autotransformer;

FIG. 2 illustrates a vector diagram representative of a first embodiment of an autotransformer according to the invention;

Figure 3 schematically illustrates the windings provided for the first embodiment;

FIG. 4 illustrates a vector diagram representative of a second embodiment of an autotransformer according to the invention;

FIG. 5 schematically illustrates the windings provided for the second embodiment;

FIG. 6 schematically illustrates an autotransformer-rectifier 18 pulses according to the invention.

extends from the third entry point E3 to a second terminal K2 ’. The length of the second main winding B23, namely between the third input point E3 and the second terminal K2 ', is determined so that the point representing the second terminal K2' is on the iso-amplitude circle of the second group of three output voltages (Vap, Vbp, Vcp) and the third group of three output voltages (Vapp, Vbpp, Vcpp). Finally, the third leg M31 comprises a third main winding B31 also shown in FIG. 2. The second main winding B31 extends from the first entry point E1 to a third terminal K3 ’. The length of the third main winding B31, namely between the first input point E1 and the third terminal K3 ', is determined so that the point representing the third terminal K3' is on the iso-amplitude circle of the second group of three output voltages (Vap, Vbp, Vcp) and the third group of three output voltages (Vapp, Vbpp, Vcpp).

There is a first auxiliary winding X1 on the first leg M12; there is thus magnetic coupling between the first auxiliary winding X1 and the second main winding B23. The length of the first auxiliary winding X1, in number of turns, is identical to the length of the portion of second main winding B23 located between the second entry point E2 and the third entry point E3. The voltages Vap and Vapp are taken from the terminals of the first auxiliary winding X1. The first auxiliary winding X1 is also electrically connected to the first main winding B12 via a first intermediate point K1. In FIG. 2, the first intermediate point K1 is located at the intersection of the segment representing the first main winding B12 and the segment representing the first auxiliary winding X1. The location of the first main winding B12 and the first auxiliary winding X1 being known, the number of turns separating the first entry point E1 from the first intermediate point K1 is therefore deduced by measuring the distance separating the points E1 and K1 on the vector diagram. Thus, the first intermediate point K1 in the first main winding B12 is at a position such that the ratio n1 / N between the number n1 of turns lying between E1 and K1 and the total number N of turns of the first main winding B12 is: n1 / N = E1K1 / E2KT. The number of turns n1 is therefore equal to the integer value of ΝΈ1Κ1 / Ε2ΚΓ. In the same way, by repeating the operations by circular permutation, the number of turns separating the second entry point E2 from the second intermediate point K2 is deduced by measuring the distance separating the points E2 and K2 on the vector diagram, and the number of turns separating the third entry point E3 from the third intermediate point K3 by measuring the distance separating the points E3 and K3 on the vector diagram. The turns of the various windings of the autotransformer according to the present invention can be produced with an aluminum strip, or else with copper wires.

We then have a first additional winding Y1, delimited by the first terminal KT, the location of which is known on the vector diagram, and by a first additional terminal K1 ". The first additional winding Y1 is magnetically coupled to the third main winding B31, and is located on the third leg M31. The location of the first additional terminal K1 ”is therefore deduced by construction of a segment representing the first additional winding Y1 parallel to the segment representing the third main winding B31, the first additional terminal K1” being located at the intersection of the segment representing the first additional winding Y1 and the point of taking the voltage Va. Similarly, by repeating the operations by circular permutation, the location of the second additional terminal K2 "and of the third additional terminal K3" is deduced. This topology advantageously makes it possible to reduce the length of the vectors transiting the total current and therefore the length and the associated winding volume in the autotransformer and then to distribute the power as best as possible, in the other windings, to the outputs of the autotransformer, c that is to say distribute the currents as best as possible and reduce the apparent electrical power of the transformer (“kVa rating” in English). A better distribution of the currents makes it possible to minimize the section of the windings and therefore their total volume. A reduction in the mass of the windings is thus obtained. This reduction in mass can advantageously be of the order of 10 to 15%.

FIG. 3 schematically illustrates the windings provided for the first embodiment as described relative to FIG. 2, making it possible to visualize the way in which the different points are connected, on the different legs of the autotransformer in accordance with the description above . In the same way, FIG. 5 schematically illustrates the windings provided for the second embodiment as described relative to FIG. 4.

FIG. 4 illustrates a vector diagram representative of the topology of a second embodiment of the invention. The representation convention of the three-phase supply in E1, E2 and E3 is identical to the previous embodiment. For this embodiment, it is sought to obtain a first group of three output voltages (Va, Vb, Vc), a second group of three output voltages (Vap, Vbp, Vcp) and a third group of three output voltages (Vapp, Vbpp, Vcpp), the voltages of the three groups this time all having the same maximum amplitude. The construction of the vectors representing the different groups of output voltages is identical to the previous embodiment. The vector representing the first voltage Vap of the second group of three output voltages (Vap, Vbp, Vcp) has an angle of a with respect to the vector representing the first voltage Va of the first group of three output voltages (Va, Vb, Vc ), and a length equal to the length of the vector designating the first voltage Va of the first group of three output voltages (Va, Vb, Vc). The angle a can be equal to 37 °, or equal to 40 °. The vector representing the voltage Vbp is then deduced from the vector representing the voltage Vap, by an identical length and an angle of 120 °; similarly, the vector representing the voltage Vcp is deduced from the vector representing the voltage Vbp, by an identical length and an angle of 120 °. The process of constructing the vectors representing the voltages of the third group of three output voltages (Vapp, Vbpp, Vcpp) is similar to the embodiment described above.

The second embodiment differs from the first embodiment in that the first entry point E1 is merged with the first intermediate point K1. The number of interconnections between the different legs of the autotransformer is therefore reduced compared to the previous embodiment. The auxiliary winding X1 is magnetically coupled to the second main winding B23, and is thus located on the second leg M23. Two additional windings V1a and V1b, represented respectively by the segments R11-R12 and R13-R14 in the diagram of FIG. 4, are magnetically coupled to the first main winding B12 and to the third main winding B31 respectively, and are therefore located respectively on the legs M12 and M31 of the autotransformer. One thus obtains a symmetry of the windings on either side of the auxiliary winding X1, and therefore a better distribution of the currents by the proximity of the values of the impedances. The points K1 ”(representing the voltage Va), K2” (representing the voltage Vb), K3 ”(representing the voltage Vc), R11 (representing the voltage Vap), R34 (representing the voltage Vcpp), R31 (representing the voltage Vcp), R24 (representing the voltage Vbpp) and R21 (representing the voltage Vbp) are of known location, insofar as they are all inscribed in the center circle O. The point R12, which is one of the two terminals of the additional winding V1a with point R11, is determined geometrically by construction of the intersection between the auxiliary winding X1 and the additional winding V1a. The number of turns of the additional winding V1a is such that the ratio n1a / N between the number nia of turns forming the additional winding V1a and the total number N of turns of the first main winding B12 is: n1a / N = R12R11 / E2KT. The number of turns nia is therefore equal to the integer value of N * R12R11 / E2KT. By symmetry, we deduce the number of turns of the additional winding V1b. Likewise, by repeating the operations by circular permutation, the number of turns of the additional windings V2a, V2b, V3a and V3b is deduced therefrom. The angle a can be 37 ° or 40 °. To switch from one to the other, it is enough to play on the lengths of segments representing the auxiliary windings and the additional windings. For example, to go from 37 ° to 40 °, it suffices to reduce the length of the segment representing the additional winding V1a, and to increase the length of the segment representing the auxiliary winding X1. Switching to an angle a equal to 40 ° advantageously makes it possible to remove the common mode voltage, and therefore to do without a bulky, heavy and expensive common mode filter.

FIG. 6 represents a block diagram of an AC-DC converter, comprising an autotransformer according to the second embodiment, illustrated by FIGS. 4 and 5, followed by three rectifying bridges, one bridge being associated with each group of three-phase voltages. The autotransformer is thus advantageously used to carry out an AC / DC voltage conversion. The three-phase power supply is thus connected to the autotransformer at inputs E1, E2 and E3. According to the second embodiment, illustrated in Figures 4 and 5, the three output voltage groups are recovered at the output of the autotransformer. The voltages of the first group of three output voltages (Va, Vb, Vc) are connected to a first bridge PA1 conventionally composed of six diodes. The phase-shifted outputs of + 37 ° (or + 40 °) are connected to a second PA2 bridge of six diodes, and the phase-shifted outputs of -37 ° (or -40 °) are connected to a third bridge ditto of six diodes. The three rectifier bridges have common outputs which constitute the outputs of the converter. The set of three bridges with six diodes delivers a pseudo-continuous voltage with 18 pulses.

The different parameters of the autotransformer, such as the angle of 37 ° or 40 ° (phase), and the ratio between the AC input voltage and the desired DC output voltage (gain) can be selected in order to minimize the amount of energy passing through the autotransformer, and at the same time ensuring a conversion with 18 pulses.

This description applies to a step-up autotransformer. However, it could also be applied to a voltage reducing autotransformer. This would require modifying the windings of the vectors representing the voltages Va, Vb, Vc so that these vectors are shorter than for a voltage booster, or else putting windings which will cause these vectors to be in the triangle, and then modify the length consequently of the vectors Vap, Vapp while also playing on the length of the vectors creating them.

Claims (2)

1. Voltage-boosting autotransformer, comprising a magnetic core formed by a first (M12), a second (M23) and a third (M31) leg, said autotransformer being intended to be connected to a three-phase supply of given amplitude supplied to a first (E1), a second (E2) and a third (E3) entry point and providing nine output voltages, the nine output voltages being able to be broken down into a first group of three voltages of output (Va, Vb, Vc) of maximum amplitude a and phase shifted from one another by 120 °, a second group of three output voltages (Vap, Vbp, Vcp) of maximum amplitude 0.767.a and phase shifted one from the other by 120 °, and a third group of three output voltages (Vapp, Vbpp, Vcpp) of maximum amplitude 0.767.a and phase shifted from one another by 120 °, the second group three output voltages (Vap, Vbp, Vcp) being 37 ° out of phase with the first ier group of three output voltages (Va, Vb, Vc) and the third group of three output voltages (Vapp, Vbpp, Vcpp) being 37 ° out of phase with respect to the second group of three output voltages (Vap, Vbp, Vcp), the first leg (M12) comprising a first main winding (B12) delimited by the second entry point (E2) and by a first terminal (KT) separated from the second entry point (E2) by a number of turns such that the voltage taken from the first terminal (KT) has the same maximum amplitude as the output voltages of the second and third groups of output voltages (Vap, Vbp, Vcp, Vapp, Vbpp, Vcpp), the first main winding (B12) further comprising a first intermediate point (K1) separated from the first entry point (E1) by a number of turns such that the first intermediate point (K1) is electrically connected to a first auxiliary winding (X1) coupled magnetically to a second main winding (B23) d e the second leg (M23) having as its intermediate point said second entry point (E2), said first auxiliary winding (X1) having a number of turns identical to the portion of second main winding (B23) located between the second (E2 ) and the third entry point (E3), the second main winding (B23) being delimited by the third entry point (E3) and by a second terminal (K2 ') separate from the third entry point (E3) a number of turns such that the voltage taken from the second terminal (K2 ') has the same maximum amplitude as the output voltages of the second and third groups of output voltages (Vap, Vbp, Vcp, Vapp, Vbpp, Vcpp ), the second main winding (B23) having a second intermediate point (K2) separated from the second entry point (E2) by a number of turns such that the second intermediate point (K2) is electrically connected to a second auxiliary winding (X2) coupled magn ethically to a third main winding (B31) of the third leg (M31) having as intermediary point said third entry point (E3), said second auxiliary winding (X2) having a number of turns identical to the portion of the third main winding (B31) located between the third (E3) and the first (E1) entry point, the third main winding (B31) being delimited by the first entry point (E1) and by a separate third terminal (K3 ') of the first input point (E1) of a number of turns such that the voltage taken from the third terminal (K3 ') has the same maximum amplitude as the output voltages of the second and third groups of output voltages (Vap, Vbp, Vcp, Vapp, Vbpp, Vcpp), the third main winding (B31) having a third intermediate point (K3) separated from the third entry point (E3) by a number of turns such that the third intermediate point (K3 ) either electrically connected ment to a third auxiliary winding (X3) magnetically coupled to the first main winding (B12) of the first leg (M12) having as an intermediate point said first entry point (E1), said third auxiliary winding (X3) having a number of identical turns to the portion of the first main winding (B 12) located between the second (E2) and the first (E1) entry point, the portion of the first main winding (B12) located between the second (E2) and the first (E1) entry point, the portion of the third main winding (B31) located between the third (E3) and the first (E1) entry point and the portion of the second main winding (B23) located between the second (E2 ) and the third (E3) entry point being electrically connected to each other in a triangle configuration, characterized in that the autotransformer also includes: - a first additional winding (Y1), electrically connected to the first terminal (KT), magnetically coupled to the third main winding (B31) and delimited by a first additional terminal (K1 ”), the first additional winding (Y1) comprising a number turns such that the voltage taken from the first additional terminal (K1 ”) has the same maximum amplitude as the output voltages of the first group of three output voltages (Va, Vb, Vc), - a second additional winding (Y2), electrically connected to the second terminal (K2 '), magnetically coupled to the first main winding (B12) and delimited by a first additional terminal (K2 ”), the second additional winding (Y2) comprising a number of turns such that the voltage taken from the second additional terminal (K2 ”) has the same maximum amplitude as the output voltages of the first group of three output voltages (Va, Vb, Vc), - a third additional winding (Y3), electrically connected to the third terminal (K3 '), magnetically coupled to the second main winding (B23) and delimited by a third additional terminal (K3 ”), the third additional winding (Y3) comprising a number of turns such that the voltage taken from the third additional terminal (K3 ”) has the same maximum amplitude as the output voltages of the first group of three output voltages (Va, Vb, Vc). 2. AC-DC converter characterized in that it uses an autotransformer according to the preceding claim, a direct diode being connected between each output of the autotransformer and a positive output of the converter, and a reverse diode being connected between each output of the autotransformer and a negative output of the converter.