WO2009144266A1

WO2009144266A1 - High power rectifier circuit particularly for aluminium electrolysis

Info

Publication number: WO2009144266A1
Application number: PCT/EP2009/056519
Authority: WO
Inventors: Claude Nicolas; Henri Baerd; Jacques Du Parc
Original assignee: Areva T&D Sas
Priority date: 2008-05-29
Filing date: 2009-05-28
Publication date: 2009-12-03
Also published as: FR2932033B1; EP2289161A1; FR2932033A1

Abstract

The invention relates to a three-phased rectifier circuit that comprises two or more transformers (TR1, TR2) to be connected in parallel to an alternating electric network (R) on the primary side (Pl, Pl', P2), and each to at least one semi-conductor rectifying bridge (PR1, PR2) on the secondary side (S1, S2), wherein the rectifying bridges (PR1, PR2) connected to different transformers are mounted in series on the direct side and are intended to power a user device (10) with direct current. One of the rectifying bridges (PR1) is a thyristor rectifying bridge and the remaining rectifying bridge(s) (PR2) are diode rectifying bridges. The diode rectifying bridge(s) (PR2) supply a voltage higher than that provided by the thyristor rectifying bridge (PR1). The invention further comprises a switching means (12) associated with each diode rectifying bridge (PR2) in order to enable the diode rectifying bridge (PR2) to operate in an idle mode in one position, and to enable the diode rectifying bridge (PR2) to operate as a rectifier in another position. The invention can particularly be used for the power supply in series of aluminium electrolysis tanks.

Description

HIGH POWER RECTIFIER CIRCUIT, IN PARTICULAR FOR ELECTROLYSIS OF ALUMINUM

DESCRIPTION

TECHNICAL AREA

The present invention relates to a high power rectifier circuit especially for the electrolysis of aluminum. The tanks in which the electrolysis of aluminum is carried are traversed by a continuous current of very high intensity of the order of 350,000 amperes for a voltage of 4 volts, many tanks being fed in series. This current value is reached gradually from the start.

For example, for an electrolysis plant with 200 tanks mounted in series, powered by a current of 300 000 amps at a voltage of 4 volts, or 800 volts for the series of electrolysis, it is necessary to have a power of 250 MW. The plant must have a final power of 300 MW if we add the auxiliaries including cooking anodes and foundry. This power corresponds to about a third of the power produced by a nuclear power plant slice, which is huge.

The high power rectifier circuit could of course be used to power anything other than electrolysis cells, for example electric arc furnaces or plasma generators which also require high power. STATE OF THE PRIOR ART

Currently, the tank feed is supplied by the three-phase AC high-voltage power grid R. The three-phase alternating current of the network R passes through a rectifying circuit such as that illustrated in FIG. 1. This circuit comprises, from the three-phase alternating network R, a three-phase transformer or auto-transformer 2 provided on the secondary side with a regulator in charge by sockets (known by the acronym OLTC for "on line tap change"), this secondary powering a three phase rectifier transformer 3. The expression regulator transformer 2 for the transformer or the autotransformer with the regulator in charge will be used later. It should be noted that such a load adjuster mounted at the primary of a transformer increases the design power of the transformer while such a secondary-mounted adjuster would not increase its design power. A secondary regulator of the rectifier transformer 3 would be unrealistic given the current levels. But the adjuster can perfectly be the secondary of the trimmer transformer 2.

It is recalled that a three-phase transformer has at least one primary per phase and at least one secondary per phase, these primaries can be mounted for example in a triangle or star. In the example described, the rectifier transformer 3 comprises two three-phase primary 3.1 connected to the secondary of the regulating transformer and two three-phase secondary 3.2. The two secondary 3.2 of the transformer rectifier 3 are connected to a rectifying bridge 4 dodecaphasic parallel. In fact each three-phase secondary 3.2 is connected to a semiconductor semiconductor semiconductor three-phase bridge and the two bridges are connected in parallel continuous side. Each of the bridges is of the Graetz bridge type. This 12-phase rectifier bridge is represented as having diodes. Self-saturable reactances 5 are inserted between the two secondarys 3.2 of the rectifier transformer 3 and the rectifier bridge 4, making it possible to rapidly adjust the DC voltage, but with a small amplitude to limit the size of the reactances, the adjustment of the large amplitudes being ensured. by the regulator transformer, but in a slower manner and by successive studs. The rectifier bridge 4 supplies direct current, an electrolysis installation or series of electrolysis (not shown specifically) or any other user device 10. Switching means 6 are inserted between the three-phase electrical network R and the primary of the transformer provided with the Adjuster 2. A four-phase thyristor pulse bridge is sometimes used, which makes it possible to dispense with the self-saturable reactances 5 and to reduce the number of taps taken by the adjuster. The thyristors are able to quickly adjust the DC voltage over the entire voltage range from 0 volts, but while consuming a prohibitive reactive power, while the adjuster allows this setting, without reactive power consumption but more slowly. The primary of the regulating transformer 2 may be equipped with a tertiary 8 three-phase connected via protective switch means 9 to a three-phase compensation / filtering battery 7 with one or more branches in parallel, comprising for each branch a capacitor C in series with a inductance L and possibly a damping resistor (not shown). The compensation-filtering battery 7 may be star-shaped, only one branch being shown in FIG. 1. The compensation-filtering battery 7 simultaneously performs the functions of compensation of the reactive power and harmonic filtering. Another compensation-filtering battery of the same type could also be provided at the high voltage level.

To provide the very high current required by the electrolysis series, a single circuit such as that shown in FIG. 1 is not sufficient, even by arranging several thyristors in parallel to form one of the six functional components of the Graetz bridges. Several circuits, called groups, are then used in parallel, these groups being out of phase with each other in order to eliminate the harmonics more completely. These phase shifts are usually made at the primary level of the regulating transformers by zigzag couplings. For example, four dodecaphase groups with a phase shift of -11.25 °, -3.75 °, + 3.75 °, + 11.25 ° respectively are used, which gives a "48-pulse reaction", ie an elimination harmonics to rank 46 and remaining harmonics of ranks 47, 49, 95, 97 etc.

A disadvantage of these phase shifts is to have to use different regulating transformers, especially at the level of the leakage lines, and requiring more spares.

Now a synthetic description of the operation of this circuit will be made. Before closure of the switch means 6, that is to say before powering the regulator transformer 2, the latter is set in the position corresponding to the minimum output voltage.

Once the switching means 6 are closed, the AC voltage supplied by the regulating transformer 2 increases, saturating the self-saturable reactances 5. The current delivered by the rectifier circuit increases until the self-saturable reactances 5 no longer saturated. The regulator transformer 2 stabilizes. The variations in current delivered by the rectifier circuit due to the three-phase electrical network or to the user device are first controlled rapidly by the self-saturable reactances 5, with a limited amplitude, and then by the regulating transformer 2. The disadvantage of this rectifier circuit is that all the power required by the user device passes through both the trimmer transformer and the rectifier transformer, so that these transformers are very bulky and they can not be in a common tank. This congestion notably poses transport problems at the time of installation.

Another disadvantage is the cost of these two transformers which can reach more than half of the overall cost of the installation which uses such a rectifier circuit as power supply.

Another disadvantage is that technological limits appear at the fuses of the diodes or thyristors used in the rectifier bridges, these limits being related to the increase of the rectified voltages.

To eliminate these disadvantages, a path to explore is that all the power does not pass through the same transformer, it is possible to reduce its size.

Three-phase rectifier circuits with a single transformer associated with at least one rectifier bridge are known. In the document FR 2 704 710, the transformer has two three-phase secondaries, each of them being connected to a thyristor-type hexaphase bridge rectifier. The primary of the transformer is directly connected to the three-phase electricity network. All the power goes through the transformer.

In documents EP 0 080 925, EP 0 620 635 and US 4,459,652, there are two bridge rectifiers, one of which is connected to the primary of the transformer and the other to the secondary, these two bridge rectifiers. being mounted either in series or in parallel. The primary of the transformer is directly connected to the three-phase electrical network. There is a lack of galvanic isolation between the power network and the circuit powered. Another disadvantage is that for high power systems powered by a high voltage network, as is the case for aluminum electrolysis plants, the voltage ratio between primary and secondary is very large and there is need interposing a transformer or an autotransformer between the high voltage network and the rectifier circuit.

In patent applications GB 2 383 477 and GB 2 383 695, there are two transformers each having a secondary supplying a thyristor-based hexaphase rectifier bridge, these rectifier bridges being connected in parallel. The primary of the transformers are connected in parallel to the three-phase electrical network. Bridge rectifiers are also connected in parallel. These patent applications seek to reduce the effects of distortions on the network by optimizing the leakage inductances of the transformer. In GB 2 383 695, a chopper with transistors IGBT (for insulated gate bibolar transistor or bipolar transistor insulated gate) is provided. These rectifier circuits do not show how to obtain an output voltage and a current adjustable according to the needs of the user device.

But it must be possible to provide the power and all the functionalities required by the user device. SUMMARY OF THE INVENTION

The present invention has as its main object to provide a rectifying circuit capable of passing very high power, which does not have the disadvantages of space and cost mentioned below and which allows to deliver variable voltages so as to adjust the current value according to the needs of the user device that it contributes to power. In the case of aluminum electrolysis series, the need for rapid adjustment and in charge of the DC voltage results from variations of the high voltage, at most ± 10%, and variations due to the electrolysis process. about 50 volts, about 5% of the total voltage since all the tanks are in series. In addition, it must be possible to ensure the startup periods during which the tanks are successively put in series, the voltage is then reduced. One can then provide several voltage ranges, the passage from one range to another can be performed off load, while maintaining in the range the possibility of fast adjustment and load.

To achieve this, the basic idea is to eliminate the regulating transformer and to use several transformers cooperating with rectifier bridges so that the power is distributed between them, the rectifier bridges being connected in series on the continuous side, one being a thyristor and the other or the other diodes, each diode rectifier bridge can operate freewheel and deliver a voltage substantially zero. More precisely, the present invention proposes a three-phase rectifying circuit comprising two or more transformers intended to be connected in parallel on the primary side to an alternating and secondary electrical network, each having at least one semiconductor rectifier bridge, the rectifier bridges. connected to different transformers being connected in series on a continuous side and being intended to continuously supply a user device. One of the rectifier bridges is thyristors and the remaining rectifier bridges are diodes, the diode rectifier bridge or the set of diode rectifier bridges providing a voltage greater than that provided by the rectifier bridge thyristors. It further comprises a switch means associated with each diode rectifier bridge, comprising a pair of disconnectors, operating in opposition, connected on the DC side to the diode rectifier bridge, making it possible in a freewheeling position to isolate the diode rectifier bridge. thyristor rectifier bridge and, in another position to put it in series with the thyristor rectifier bridge so that the rectifier bridge operates as a rectifier, in the freewheeling position, current flows in one of the disconnectors of the pair which bypassed the rectifier bridge with diodes and not in the other nor in the rectifier diode bridge.

It is advantageous for a transformer connected to a diode rectifier bridge to be equipped with voltage divider means so that the diode rectifier bridge to which it is connected delivers either a full voltage or a fraction of the full voltage.

The voltage divider means may comprise a pair of disconnectors, per phase, and the transformer may comprise a primary formed of two identical primary windings, the pair of disconnectors being able to put in series the two primary windings so that the diode rectifier bridge delivers one half of the full voltage or in parallel so that the diode rectifier bridge delivers the full voltage.

Alternatively, the voltage divider means may comprise a non-load regulator with two sockets, per phase, mounted at the secondary of the transformer.

For the rectifier bridges to be 12-phase, the transformers have secondary phase shifted by 30 ° by appropriate couplings at their secondary or primary, the rectifier bridges may each comprise a first and a second rectifier bridge hexaphase, the first rectifier bridges hexaphase are all mounted in a first series assembly, the second rectifier bridges all being mounted in a second series assembly, the first series assembly and the second series assembly being connected in parallel.

A twelve-phase transformer may comprise two primary and two tertiary compensation, the two tertiary compensation being connected in series and feed a single filter compensation battery. The present invention also relates to a set of two rectifier circuits thus characterized, with 12-phase rectifier bridges, in which the transformers of a rectifier circuit are identical to the transformers of the other rectifier circuit and in which the primary of the transformers are out of phase with the current. , 5 ° with respect to the network, two phases of the network being exchanged between the primary of the transformers of one of the circuits and the primary of the transformers of the other circuit, so that the phase shift of the primary of the transformers of a circuit is positive with respect to the network and the phase shift of the primary of the transformers of the other circuit is negative with respect to the network.

The present invention also relates to a control precursor of a rectifier circuit thus characterized comprising, to make it work, the steps of: a) connecting the user device to the rectifier circuit and the transformer connected to the thyristor rectifier bridge to the network but not the transformer or transformers connected to a diode rectifier bridge, b) regulating the current flowing in the user device by controlling the thyristors of the thyristor rectifier bridge, c) when the voltage required by the user device exceeds the maximum voltage that can be supplied by the thyristor rectifier bridge, to control thyristors of the thyristor rectifier bridge to minimize the current in the device user, the disconnector which when closed shorts the rectifier bridge with diodes, being open and the other disconnector of the couple being closed, d) connect to the network a transformer connected to a rectifier bridge with diodes, if the transformer connected the diode rectifier bridge is equipped with voltage divider means, the latter being positioned beforehand so that the transformer delivers the voltage half, e) regulating the current flowing in the user device by controlling the thyristors of the thyristor rectifier bridge, f) when the voltage demanded by the user device exceeds the maximum voltage that can be provided by all the rectifier bridges connected to the network, controlling the thyristors of the thyristor rectifier bridge to reduce as much as possible the current in the user device, the disconnector which, when it is closed, short circuit the diode rectifier bridge, being open and the other disconnector of the couple being closed, g) if the transformer connected to the diode rectifier bridge which is connected has voltage divider means and is positioned to output the voltage half, disconnect and adjust it by positioning its voltage divider means so that it delivers the full voltage, h) reconnect the transformer connected to the rectifier bridge with diodes and adjusted to the network, i) regulating the current flowing in the user device by controlling the thyristors of the thyristor rectifier bridge, j) if the rectifier circuit has another transformer connected to a diode rectifier bridge not yet connected to the network and the voltage required by the device user exceeds the maximum voltage that can provide the rectifier bridges that are connected to the network, control the thyristors of the thyristor rectifier bridge to minimize the current in the user device, the disconnector which is connected in parallel with the diode rectifier bridge being open and the other disconnector of the couple being closed, k) connect the other transformer connected to a diode rectifier bridge, if this other transformer connected to the diode rectifier bridge is equipped with voltage divider means, position these first to that this other transformer delivers the voltage fraction, then the full voltage,

1) Repeat steps e) through k) until all transformers connected to a diode rectifier bridge are all connected to the network and all are set to provide full voltage.

The method also includes, for stopping the operation of the rectifier circuit, the steps of: m) controlling the thyristors of the thyristor rectifier bridge to minimize the current in the user device, n) disconnect from the network any transformer connected to a diode rectifier bridge then the transformer connected to the thyristor rectifier bridge o) disconnect the user device from the rectifier circuit.

The present invention also relates to the use of a rectifier circuit thus characterized, with as user device one or more aluminum electrolysis cells. The present invention also relates to the use of a set of rectifier circuits thus characterized, with as user device one or more series of aluminum electrolysis cells. The present invention also relates to the use of a method thus characterized with one or more series of aluminum electrolysis cells as a user device.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments given, purely by way of indication and in no way limiting, with reference to the appended drawings in which:

Figure 1 is a diagram of a rectifying circuit of the prior art;

Figure 2A is a diagram of a first variant of a rectifying circuit of the invention;

FIG. 2B is a diagram of a second variant of a rectifying circuit of the invention; Figure 3 is a more detailed diagram of the rectifier bridges shown in Figures 2A and 2B; FIGS. 4A, 4B illustrate a variant of a primary phase of the transformer connected to a diode rectifier bridge of FIGS. 2A, 2B, this primary being equipped with voltage divider means and being respectively in a series assembly and in a mounting parallel;

FIG. 4C illustrates a variant of a secondary phase of the transformer connected to a diode rectifier bridge of FIGS. 2A, 2B, this secondary being equipped with voltage divider means;

FIG. 5 shows the shape of the voltage delivered by the rectifier circuit according to the variants of FIGS. 4A to 4C as a function of the mode of operation of the transformer connected to the diode rectifier bridge;

FIG. 6A shows another variant of a rectifying circuit of the invention;

FIG. 6B shows a further variant of a rectifier circuit according to the invention with three transformers connected to rectifier bridges;

Figure 7 is a diagram of a variant of the transformer connected to the thyristor bridge of Figure 6A whose primary are equipped with tertiary; FIG. 8 represents a set of two twelve-phase rectifier circuits (12 pulses) constituting a set with 24 pulses.

Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the passage from one figure to another. The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable. These different variants presented must be understood as not necessarily exclusive of each other.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Reference will now be made to FIG. 2A, which schematically shows a first example of a three-phase rectifier circuit according to the invention. It comprises two transformers TR1 and TR2 intended to be connected on the primary side P1, P2 each to the same three-phase AC electrical network R. Secondary side S1, S2, each of the transformers TR1, TR2 is connected to at least one semiconductor rectifier bridge PR1, PR2. The semiconductor rectifier bridges PR1, PR2 are connected in series, they are intended to supply a user device 10, such as one or more series of aluminum electrolysis cells. One of the rectifier bridges referenced PR1 is connected to the positive terminal + of the user device 10, the other rectifier bridge referenced PR2 to the negative terminal. The user device could be different, for example an arc furnace or a plasma furnace.

In the example described in FIGS. 2A, 2B, it is assumed that each transformer TR1, TR2 is connected to a single hexaphase rectifier bridge PR1, PR2. In this variant, each transformer TR1, TR2 comprises a secondary Sl, S2 comprising at least one winding per phase.

According to the invention, one of the rectifier bridges PR1 is thyristors Thy and the other referenced PR2 is diode d. By diode rectifier bridge is meant a rectifier bridge whose semiconductor components are of the family of diodes or function as diodes. Thus the diodes could be replaced by thyristors controlled so that they function as diodes.

Similarly, a thyristor rectifier bridge means a rectifier bridge whose semiconductor components are in the family of thyristors or function as thyristors. The number of transformer and diode rectifier assemblies may be greater than one as shown in Figure 6B described later.

The rectifying bridge PR1 thyristors is intended to provide a voltage whose amplitude is adjustable quickly and charged by the control thyristors. The diode rectifier bridge or bridges are intended to provide a rectified voltage whose amplitude is constant. But this voltage can be changed out of charge or at low load. We will describe the means to obtain this change later.

In FIG. 3, each of the rectifying bridges PR1, PR2 is illustrated. These are classic Graetz bridges hexaphase. Their series assembly is clearly visible. The tensions that feed each of arm of a bridge are alternating voltages out of phase by 60 °.

The primers P1, P2 of the transformers TR1, TR2, high voltage side, are preferably mounted in a star and the secondary S1, S2, low voltage side, are preferably mounted in a triangle.

Primary side P1, P2, each transformer TR1, TR2 is connected to the three-phase electrical network R via input switch means II, 12, 13. A switch means associated with the transformer TR1 connected to the rectifier bridge with thyristors PR1 is referenced II, it makes it possible to disconnect it from the network R. The referenced switch means 12, associated with the rectifier bridge with diodes PR2 and connected to a transformer TR2 connected to a rectifier bridge with diodes PR2 makes it possible to operate the rectifier bridge with diodes PR2 in freewheel. The switch means 13 is optional, it makes it possible to disconnect the rectifier circuit R. Each switching means II, 12, 13 comprises a circuit breaker per phase.

In FIGS. 2A, 2B, which represent only one phase, only one of the circuit breakers II, 12, 13 of each of the switch means is seen. The three circuit breakers II, 12, 13 have a common end, the first 13 having its other end connected to the three-phase electrical network R, the second one having its other end connected to the primary P1 of the transformer TR1, the third 12 having its other end connected at primary P2 of transformer TR2. If the circuit breaker 13 is omitted, the common end of the circuit breakers 12 and 13 is connected directly to the network R.

When the diode rectifier PR2 operates freewheeling, the circuit breakers 12 of the switch means associated with the transformer TR2 concerned are open. On the other hand, the circuit-breakers II of the switch means associated with the transformer TR1 connected to the thyristor rectifier bridge PR1 are closed.

It is preferable to provide, on the primary side P1, P1, P2 of each of the transformers TR1, TR2, a tertiary compensation T1, T2. A compensation-filtering battery F1, F2 is connected to each tertiary compensation T1, T2. This compensation-filtering battery F1, F2 comprises one or more branches connected in parallel, preferably in a star, each branch comprising in series an inductance L1, L2 and a capacitor C1, C2 per phase and optionally a damping resistor (not represented). Switching means 110, 120 are inserted between each tertiary compensation T1, T2 and each compensation-filtering battery F1, F2. The switch means 110, 120 are formed, for each transformer, a switch per phase.

Alternatively, it is also possible to place compensation-filtering batteries on the input mains R.

The variant of FIG. 2B is identical to that of FIG. 2A, except that on the network side R only the switch means 13 for disconnecting the rectifier circuit of the network R are present. It comprises a circuit breaker 13 phase, mounted between the network R and the primary P1, P2 transformers TR1, TR2. Only one circuit breaker per phase is sufficient.

Another difference is that the switch means for operating each PR2 diode rectifier bridge freewheel is directly associated with the diode rectifier bridge PR2 because it placed on the DC side. It comprises a pair of disconnectors 14, 15 whose disconnectors operate in opposition. One of the disconnectors 14 is mounted between the rectifying bridge PR2 with diodes, on the user device side 10, and the negative terminal of the user device 10 and the other disconnector 15 is mounted between the rectifying bridge PR2 with diodes, reclining bridge side PR1 to thyristors, and the negative terminal of the user device 10.

In the freewheel position of the rectifier bridge with diodes PR2, it is the disconnector 14 which is open and when the rectifier bridge with diodes PR2 operates as a rectifier, it is the disconnector 15 which is open. In the freewheeling position, current flows in the disconnector 15 but not in the disconnector 14 or in the diode rectifier bridge PR2.

The PR2 diode rectifier bridge or bridges as a whole provide a voltage greater than that provided by the rectifier bridge with thyristors PR1. This reduces the reactive power, the harmonics returned to the network and the undulation of the DC currents. Reference will be made to FIGS. 4A, 4B which show two configurations of a primary phase of the transformer TR2 connected to the rectifier bridge PR2 diodes illustrated in Figures 2A, 2B. Each phase of the primary comprises two windings P2, P2 'capable of being connected either in series or in parallel by switching means MC. The windings are identical. When the windings P2, P2 'are in series, they supply the secondary voltage half and when the windings P2, P2' are in parallel, they provide the secondary full voltage. In these figures 4A, 4B, the switching means MC are formed of two inverter switches 16 and 16 '. In FIG. 4A, the two windings P2, P2 'are in series and in FIG. 4B they are in parallel. Each winding P2, P2 'has a first end permanently connected to the network R and a second end connected to either the second end of the other winding (FIG. 4A) or to the first end of the other winding (FIG. 4B). ), that is to say the network R according to the position of the switching means 16, 16 '. The switching means MC allow in one position to the transformer TR2 and thus to the rectifier bridge with diodes PR2 to deliver a full voltage and in another position to deliver a voltage half of the full voltage. The coupling of three phases thus described can be done in star, in triangle or even in zigzag. Extended triangle coupling is possible, but it would require more complicated MC switching means. FIG. 4C shows a secondary phase of transformer TR2 connected to the bridge rectifier PR2 diode shown in Figures 2A, 2B and it comprises a secondary winding S2 equipped with switching means MC of the type off-load controller with two sockets, taking the form of an inverter switch 17. This off-load regulator two outlets 17 allows in one position to divide the maximum voltage that can deliver the transformer TR2 and in another position to the transformer TR2 to deliver the full voltage. One of the sockets is at one end of the secondary winding S2 and the other taken along the secondary winding S2 in the middle. Such an arrangement makes it possible to have either the full voltage or a fraction of the full voltage, this fraction of the full voltage may be half or not.

The presence of the adjuster in secondary school is only possible if the current level is not too high. In the prior art with the self-saturable reactants, this was not possible because the adjuster should have had a large number of outlets and operate in charge. In the present invention, two outlets are sufficient and the change can take place off load.

It is understood that the switching means MC allowing, in one position, to divide in half the voltage delivered by the transformer TR2 connected to the rectifier bridge with diodes PR2 and, in another position to let it deliver the full voltage, are not mandatory on transformers connected to diode rectifier bridges as the rectifier circuit several transformers connected to diode rectifier bridges as in Figure 6B.

We will now describe the operation illustrated in Figure 5, such a rectifier circuit in the example of Figures 2A, 2B or 6A (which will be described in more detail later). In these examples, there is only one rectifier diode bridge. The user device 10 is connected to the rectifier circuit which is the subject of the invention, on the rectifier bridge side PR1, PR2. The transformer TR1 connected to the thyristor rectifier bridge PR1 will be connected to the network R, but not the transformer TR2 connected to the rectifier bridge with diodes PR2. The transformer TR2 connected to the diode rectifier bridge PR2 is positioned to deliver a half voltage if it conforms to that of the variants of FIGS. 4A, 4B or 4C. Switches II, 13 of the switch means are open in the configurations of Figures 2A, 2B. The switch 12 is open in the configuration of Figure 2A. The disconnector 14 is open and the disconnector 15 is closed in the configuration of Figure 2B.

We start by turning on at time tl, the transformer TRl connected to the rectifying bridge thyristor PRl by closing the circuit breaker 13 and the circuit breaker II. Direct current flows in the thyristor rectifier bridge PR1, in the user device 10 via the disconnector 15 (FIG. 2B) and in the rectifier bridge with diodes PR2 (FIGS. 2A, 6A) in freewheel mode. The current increase is controlled by the Thy thyristor control of the SCR thyristor rectifier bridge. One can refer to FIG. 5. The voltage across the user device 10 increases from 0 volts until it reaches the maximum voltage that can be delivered by the thyristor rectifier bridge PR1.

It is advantageous for the transformers TR1, TR2 and the rectifier bridges PR1, PR2 to be sized so that the rectifier bridge with diodes PR2 cooperating with the switching means MC in their variant of FIGS. 4A, 4B or 4C can deliver either a full voltage a voltage of half, the full voltage being equal to about two thirds of the maximum voltage Umax necessary for the user device 10, and the half voltage being equal to about one third of the maximum voltage Umax.

As soon as the transformer TR1 connected to the thyristor rectifier bridge PR1 is energized, the voltage delivered by the thyristor rectifier bridge PR1 can be increased from 0 to approximately 1/3 of Umax as a function of the thyristor control.

When the user device 10 requests a voltage higher than that which can be provided by the thyristor rectifier bridge PR1, the thyristors of the rectifier bridge PR1 are controlled so as to reduce as much as possible the current in the user device 10.

In the case of the configurations of FIG. 2A or 6A, circuit breaker 12 is closed at time t2. In the case of the configuration of FIG. 2B, the circuit breaker 13 is opened, then the disconnector 15, then the disconnector 14 is closed, then the circuit breaker 13 at time t2. The transformer TR2 connected to the diode rectifier bridge PR2 is then energized. The rectifier bridge with diodes PR2 delivers a half tension. The supply voltage of the user device 10 is about 1/3 of Umax. By controlling the thyristors of the rectifier bridge PR1, the voltage delivered by the thyristor rectifier bridge PR1 is regulated to increase the current in the user device 10 to a setpoint value.

When the voltage requested by the user device 10 exceeds the capacity of the thyristor rectifier bridge PR1 added to that of the diode rectifier bridge PR2, ie about 2/3 of the maximum voltage Umax, the thyristors of the rectifier bridge PR1 are controlled so as to minimize the current in the user device 10.

In the case of the configurations of FIGS. 2A and 6A, the circuit-breaker 12 is opened, the transformer TR2 is positioned so that it delivers the full voltage by acting on the switching means MC or on the off-load regulator with sockets 17 and then closing the circuit breaker 12 at time t3. In the case of the configuration of FIG. 2B, the circuit breaker 13 is opened, the transformer TR2 is positioned to deliver the full voltage by acting on the switching means MC or on the off-load regulator with sockets 17, then, the disconnector 14 remaining closed and the disconnector 15 open, the circuit breaker 13 is closed at time t3. The rectifier bridge with diodes PR2 then delivers about 2/3 of Umax. The thyristors of the thyristor rectifier bridge PR1 can then be controlled so that the supply current of the user device can increase. The transition control sequence of the transformer TR2 from its voltage half to its full voltage must be done as quickly as possible so as to retain, if necessary, the counter electromotive force in the user device 10. If this counter-electromotive force has Too much decreased due to too long downtime, it may be necessary to add a "recharge" sequence of this counter-electromotive force using a lower voltage range before moving to the desired higher voltage range.

Thus, during operation within the three voltage ranges, the transformer TR1 and the thyristor rectifier bridge PR1 are still active. They allow the DC voltage to be set quickly and continuously in the user device 10 in all ranges. The transition from one range to the other at the level of the diode rectifier bridges takes place without load. The ever-present thyristor rectifier bridge TRl ensures fast adjustment and charging with limited reactive power. The transformer TR2 and the diode rectifier PR2 operate in three modes corresponding to the three voltage ranges: freewheel providing a rectified voltage close to 0 volts, at half tension and at full voltage. To stop the operation of the rectifier circuit, the thyristors of the thyristor rectifier bridge PR1 are first controlled to minimize the current in the user device. A transformer connected to a diode rectifier bridge acting on the switch means is disconnected from the network R, that is to say by opening the circuit breaker 12 or the disconnector 14. The transformer TR1 connected to the thyristor rectifier bridge PR1 of the transformer is disconnected. network by acting on the switch means II and 13 (if the latter is present), that is to say by opening the disconnectors II and possibly 13. Finally, the user device 10 of the rectifier circuit is disconnected. As a variant, it is possible for the rectifier bridges instead of being hexaphase to be twelve-phase with a single thyristor rectifier bridge and one or more PR2 diode rectifier bridges. Such rectifier bridges make it possible to reduce the ripple rate on the output current and to limit mainly the amplitude of the harmonics of rank five and seven reinjected on the network. The voltages that supply each of the arms of a rectifier bridge PR1 or PR2 are alternating voltages phase shifted by 30 °. Referring to FIG. 6A, which shows the rectifying circuit of the invention in this latter twelve-phase configuration. In this example, there is only one PR2 diode rectifier bridge, but there could be several. In fact each twelve-phase rectifier bridge PR1 or PR2 is formed of a first PR1.1 PR2.1 hexaphase rectifier bridge and a second hexaphase rectifier bridge PRl.2, PR2.2. All the first rectifier bridges PRl.1, PR2.1 are mounted in a first set PESl series. All second rectifier bridges PR1.2, PR2.2 are mounted in a second set PES2 series. The first set PESl series and the second set PES2 series are mounted in parallel. Twelve-phase rectifier bridges of this nature do not pose a problem to a person skilled in the art.

As illustrated in FIG. 6A, it is preferable to mount the two sets PES1, PES2 series in parallel rather than to form two parallel assemblies, one comprising the two thyristor rectifier bridges and the other the two diode rectifier bridges and fit the two parallel sets in series. It is thus possible to dynamically regulate the equality of the currents in the first and second diode bridges by the first and second thyristor bridges and to reduce the current ripple in the bridges.

The use of rectifying bridges PR1, PR2 12-phase only requires that the transformers TR1, TR2 each have a pair of secondary S1 and S1 ', S2 and S2', phase shifted by 30 °, which can be achieved by different couplings to the primary or in high school. The example of FIG. 6A represents the simplest of these couplings: each of the transformers TR1, TR2 has only one star primary P1, P2 and two secondary ones, one of which is referenced S1, S2 is in a triangle and the other is referenced S1. ', S2' is in star. Other couplings could be used, with two primaries, one star and the other in a triangle or one in zigzag triangle and the other in zigzag star, or one in zigzag and the other no, or long triangles. The couplings providing the phase shift of 30 ° between the secondary may be different at the TR1 transformer connected to the rectifier bridge thyristor PRl and at the transformer TR2 connected to the rectifier bridge with diodes PR2.

In FIG. 6A, the switch means 12 enabling free-wheel operation of the diode rectifier bridge PR2 are illustrated as in the variant of FIG. 2A. It is of course possible to use the configuration illustrated in Figure 2B with the disconnecting couple in opposition continuous side. In this FIG. 6A, there is no representation of tertiary compensation and their compensation-filtering batteries, but there is no disadvantage in introducing them as in FIGS. 2A, 2B. As already indicated, they are optional and it is sometimes preferred to use compensation-filtering batteries connected to the electrical network R.

FIG. 6B shows a rectifying circuit according to the invention with always a transformer TR1 connected to a rectifier bridge with thyristors PR1 but with several transformers TR2, TR3, (in example two), each connected to a bridge rectifier with diodes PR2, PR3. The transformers TR2, TR3 are connected in parallel on the network side 10. The diode rectifier bridges PR2, PR3 are connected in series with each other and with the thyristor rectifier bridge PR1 on the user device 10. To operate the rectifier circuit is carried out as described above, with a first transformer connected to a first diode rectifier bridge. As soon as the user device needs more voltage, another one is connected after having reduced the current in the user device by controlling the thyristors. This can be done until all transformers connected to diode rectifier bridges are connected. FIG. 7 illustrates a clever arrangement of two tertiaries T1, T1 'of a transformer TR1 connected to a rectifier bridge with thyristors PR1. The transformer TR1 comprises two primary P1, P1 and two secondary S1, S1 '. The tertiary two Tl, Tl 'have the same coupling, star in the example. They are connected in series which requires opening the star of one of them, the one called Tl '. The set of two tertiaries T1, T1 'feeds a single filtering-filtering battery F which then only supports the phase harmonics, of ranks 11, 13, 23, 25, etc., but not the harmonics in phase opposition. of ranks 5, 7, 17, 19, etc., which would have been unnecessarily the case with two tertiary and two separate compensation-filtering batteries. The harmonics in phase opposition generate opposite voltages in the two tertiaries Tl, Tl ', they are therefore globally canceled and not supported by the filtering compensation battery F. The harmonics in phase, of ranks 11, 13, 23, 25 etc. ...., are normally filtered by the filtering compensation battery F. FIG. 8 illustrates a rectifier assembly comprising two twelve-phase rectifier circuits or groups G1, G2, 15 ° out of phase, which gives an overall harmonic reaction at 24 pulses. The harmonics of rank 11 and 13 that remained in the twelve-phase assemblies described above are eliminated and the first harmonics that remain have the ranks 23 and 25. The advantage of such a rectifier assembly is that the transformers TRl.1, TR2.1 TR1.2, TR2.2 of both groups are physically identical.

Transformers TRl.1, TRl .2 connected to thyristor rectifier bridges PRIa, PRIb, PRIc, PRId have two primaries, named respectively Pl.1, Pl.2 and Pl.1 ', Pl.2' and two secondary named respectively Sl.1, Sl.2 and Sl.1 ', Sl.2'.

Transformers TR2.1, TR2.2 connected to diode rectifier bridges PR2a, PR2b, PR2c, PR2d each have a primary element named P2, P2 ', respectively.

The primers Pl.1, Pl.2, Pl.1 ', Pl.2' of transformers TRl.1, TRl .2 connected to thyristor rectifier bridges PRIa, PRIb, PRIc, PRId are respectively coupled in zigzag and triangle zigzag to obtain at the same time the phase shift of 30 ° between the two secondary Sl.1, Sl.2, Sl.1 ', Sl.2' and a phase shift of 7.5 ° between each transformer TRl.1, TRl .2 and the network R and two network phases are switched on one of the two groups G1, G2, which reverses the direction of the phase shift. One of the groups is out of phase compared to the network of + 7.5 ° and the other of -1.5 °, or 15 ° between the two groups G1, G2.

In the example of FIG. 8, different dodecaphase couplings have been chosen for the secondary of the TR1.1, TR1.2 transformers connected to the PRI, PRIb, PRIc, PRId thyristor rectifier bridges and to the PR2a, PR2b diode rectifier bridges. , PR2c, PR2d. The secondary Sl.1, Sl.2, Sl.1 ', Sl.2' connected to the thyristor rectifiers PRIa, PRIb, PRIc, PRId are coupled in identical triangle because of the lower voltage, the phase shift of 30 ° secondary S1, S1, S1, S1, S2 'being made by primaries P1, P1 and P1', P1.2 coupled in zigzag and zigzag triangle. This solution leads to decoupled secondary, which is preferable to avoid thyristor switching failures.

For the secondaries S2.1, S2.2, S2.1 ', S2.2' of transformers TR2.1, TR2.2 connected to diode rectifier bridges PR2a, PR2b, PR2c, PR2d, triangle and star couplings are preferred. as illustrated in Figure 6. The secondary voltage being higher for transformers connected to diode rectifier bridges than for transformers connected to thyristor rectifier bridges, this makes it easier to couple star with a single primary P2, P2 'star zigzag. This single primer P2, P2 'coupled in zigzag star makes it easier to add the variant to two windings connectable in series or in parallel with the switching means MC as shown in Figures 2A, 2B. The configuration of Figure 8, gives secondary S2.1, S2.2, S2.1 ', S2.2' uncoupled without danger with the diodes. But of course, one could have chosen identical couplings for the secondary transformers connected to thyristor rectifier bridges and diode rectifier bridges.

The diagram of FIG. 8 must be completed, according to the invention, by the switch means allowing the freewheeling operation of the diode rectifying bridges PR2a, PR2b, PR2c, PR2d, using either the variant of FIGS. 2A or 6, or that of Figure 2B.

It may optionally be completed with the means for dividing the voltage delivered by the transformers TR2.1, TR2.2 connected to the diode rectifier bridges PR2a, PR2b, PR2c, PR2d according to the variants of FIGS. 4A and 4B or that of FIG. 4C. It can also be completed with tertiary compensation as illustrated in Figures 2A, 2B or 7.

An advantage of the rectifier circuit according to the invention is its lower cost since the high voltage side support regulator illustrated in FIG. 1 is no longer used and the sizing power of the transformers is lower.

Another advantage is that the transport and installation of the transformers are facilitated, their size being smaller.

In addition, the suppression of the self-saturable reactants 5 of FIG. 1, normally integrated in the transformers 3, implies that the Transformers used in the rectifier circuit according to the invention are more conventional transformers whose supply is much easier since a greater number of suppliers offer this type of transformer.

Yet another advantage of the rectifier circuit of the invention is that the DC voltage delivered can be increased without being limited by the fuse technology of diodes or thyristors which are conventionally equipped rectifier bridges. This was not the case in the prior art since all the power passed through the same bridge rectifier.

Another advantage is to reduce the harmonics produced, on the one hand because the switching times of the diode rectifier bridges are longer, on the other hand because the harmonics of the two rectifier bridges are not in phase, which allows use identical transformers for parallel circuits. The undulations of the DC currents are also reduced because a diode rectifier bridge generates much less ripples than a thyristor rectifier bridge, which reduces the disturbances with respect to the environment in the structures related to the magnetic field of the electromagnetic fields. continuous busbars.

Another advantage is the control of the rectifier circuit in its fast regulation and charging range, which is much simpler than in the past. The previous structure used two coordinated means on the one hand the regulator transformer equipped with the on the other hand, the self-saturable reactants or the thyristors. The rectifier circuit according to the invention uses only one control means, the ignition of the thyristors of the rectifier bridge TR1. This results in fewer studies and a much simpler exploitation.

The reliability of the rectifier circuit according to the invention is increased and its maintenance facilitated by the suppression of the trimmer transformer. Of course, more semiconductor components are employed but this fact, which can be considered as a disadvantage, has very limited consequences since the voltage supported by each of the rectifier bridges is reduced. Although several embodiments of the present invention have been shown and described in detail, it will be understood that various changes and modifications can be made without departing from the scope of the invention.

Claims

A three-phase rectifier circuit comprising two or more transformers (TR1, TR2) intended to be connected in parallel on the primary side (P1, P1, P2) to an alternating (R) and secondary (S1, S2) electrical network, each at least one semiconductor rectifier bridge (PR1, PR2), the rectifier bridges (PR1, PR2) connected to different transformers being connected in series on a DC side and being intended to continuously supply a user device (10), characterized in that one of the rectifier bridges (PR1) is thyristors and the remaining rectifier bridge (s) (PR2) are diode-shaped, the diode rectifier bridge or the set of diode rectifier bridges (PR2) providing a voltage greater than that provided by the thyristor rectifier bridge (PRl) and in that it comprises a switch means (12) associated with each diode rectifier bridge (PR2) having a pair of disconnectors (14, 15) operating in opposition, connected to the conti nd to the rectifier diode bridge (PR2), allowing in a freewheeling position to isolate the diode rectifier bridge (PR2) of the thyristor rectifier bridge (PR1) and in another position to put it in series with the bridge rectifier with a thyristor (PR1) so that the rectifier bridge operates as a rectifier, in the freewheel position, of the current flowing in one of the disconnectors (15) of the pair (14, 15) which bypasses the diode rectifier bridge and not in the other disconnector (14) nor in the diode rectifier bridge (PR2).

2. rectifier circuit according to claim 1, wherein a transformer (TR2) connected to a diode rectifier bridge (PR2) is equipped with voltage divider means ((16, 16 '), 17) so that the bridge Diode rectifier (PR2) to which it is connected delivers either a full voltage or a fraction of the full voltage.

3. rectifier circuit according to claim 2, wherein the voltage divider means comprise a pair of disconnectors (16, 16 ') per phase and the transformer (TR2) has a primary formed of two identical primary windings (P2, P2'). , the pair of disconnectors (16, 16 ') being adapted to put the two primary windings (P2, P2') in series so that the diode rectifier bridge (PR2) delivers one half of the full voltage or else in parallel, for the rectifier diode bridge (PR2) delivers the full voltage.

A rectifier circuit as claimed in claim 3, wherein the voltage divider means includes a two-tap, non-load adjuster, per phase, mounted at the secondary (S2) of the transformer (TR2).

5. rectifier circuit according to one of claims 1 to 4, wherein the transformers (TRl, TR2) have secondary (Sl, Sl ', S2, S2') phase shifted by 30 ° by appropriate couplings at the level of their secondary (S1, S1 ', S2, S2') or their primary (P1, P2), the rectifier bridges (PR1, PR2) being twelve-phase and each comprise a first and a second hexaphase rectifier bridge ((PR1.1 , PR1.2) and (PR2.1), (PR2.2)), the first hexaphase rectifier bridges (PR1.1, PR2.1) being all mounted in a first series assembly (PES1), the second rectifier bridges ( PR1.2, PR2.2) being all mounted in a second series assembly (PES2), the first series assembly (PES1) and the second series assembly (PES2) being connected in parallel.

6. Rectifier circuit according to one of the preceding claims, wherein at least one transformer (TRl) comprises, per phase, two primary (P1, P1) and two tertiary compensation

(Tl, Tl '), the two tertiary compensation (Tl,

Tl ') being connected in series and feeding a single filter compensation battery (F).

7. Set of two rectifier circuits (G1, G2) according to one of claims 1 to 6, with rectifier bridges (PR1, PR2, PR1 ', PR2') 12-phase, wherein the transformers (TRl.1, TR2. 1) of a rectifier circuit (G1) are identical to the transformers (TR1.2, TR2.2) of the other rectifier circuit (G2) and in which the primers (P1.1, P1.2, P2, P1. 1 ', Pl.2', P2 ') transformers are phase shifted by 7.5 ° with respect to the network (R), two phases of the network (R) being swapped between the primary of the transformers of one of the circuits and the primary of the transformers of the other circuit, so that the phase shift of the primary (P1, P1, P2) of the transformers (TR1.1, TR2.1) of a circuit (G1) is positive with respect to network (R) and the phase shift of the primary (Pl.1 ', Pl.2', P2 ') transformers

(TR1.2, TR2.2) of the other circuit (G2) is negative with respect to the network (R).

8. Control method of a rectifying circuit according to one of claims 1 to 6 comprising for its operation the steps of: a) connecting the user device (10) to the rectifier circuit and the transformer (TRl) connected to the bridge thyristor rectifier (PR1) to the network (R) but not the transformer or transformers (TR2) connected to the diode rectifier bridge (PR2), b) regulating the current flowing in the user device (10) by controlling thyristors of the rectifier bridge (c) when the voltage demanded by the user device (10) exceeds the maximum voltage that can be supplied by the thyristor rectifier bridge (PR1), controlling the thyristors of the thyristor rectifier bridge (PR1) to decrease to a maximum the current in the user device, the disconnector (15) which when closed bypasses the rectifier diode bridge (PR2) being open and the other disconnector (14) of the pair being closed, d) connect to the network (R) a transformer (TR2) connected to a rectifier bridge to diodes (PR2), if the transformer (TR2) connected to the rectifier diode bridge (PR2) is equipped with voltage divider means (MC), the latter are positioned beforehand so that the transformer (TR2) delivers the voltage half, e ) regulating the current flowing in the user device (10) by controlling thyristors of the thyristor rectifier bridge (PR1), f) when the voltage demanded by the user device (10) exceeds the maximum voltage that can be provided by the rectifier bridges (PR1) , PR2) connected to the network (R), controlling the thyristors of the thyristor rectifier bridge (PR1) to minimize the current in the user device (10), the disconnector (15) which when closed bypasses the diode rectifier bridge (PR2) being open and the other disconnector (14) of the pair being closed, g) if the transformer (TR2) connected to the diode rectifier bridge (PR2) which is connected comprises voltage divider means ( MC) and that i ls are positioned to deliver the voltage half, disconnect and adjust it by positioning its voltage divider means (MC) so that it delivers full voltage, h) reconnect the transformer (TR2) connected to the bridge rectifier with diodes (PR2) thus set to the network (R), i) regulating the current flowing in the user device (10) by controlling the thyristors of the thyristor rectifier bridge (PR1), j) if the rectifier circuit has another transformer (TR3) connected to a diode rectifier bridge (PR3) not yet connected to the network (R) and the voltage requested by the user device (10) exceeds the maximum voltage that can be supplied by the rectifier bridges (PR1, PR2) connected to the network (R), controlling the thyristors of the thyristor rectifier bridge (PR1) to minimize the current in the user device (10), the disconnector (15) which is connected in parallel with the diode rectifier bridge (PRl) being open and the other disconnector (14) of the pair being closed, k) connecting the other transformer (TR3) connected to a diode rectifier bridge (PR3), if this other transformer ( TR3) connected to the diode rectifier bridge

(PR3) is equipped with voltage divider means (MC), position these beforehand so that the other transformer delivers the voltage fraction, then the full voltage, 1) repeat steps e) to k) until all transformers connected to a diode rectifier bridge are all connected to the network and all are set to provide full voltage.

9. A method of controlling a rectifying circuit according to claim 8, comprising for stopping its operation the steps of: m) controlling the thyristors of the thyristor rectifier bridge (PR1) to minimize the current in the user device (10) ) n) disconnect from the network (R) any transformer (TR2) connected to a diode rectifier bridge (PR2), then the transformer (TRl) connected to the thyristor rectifier bridge (PR1) o) disconnect the user device

(10) of the rectifier circuit.

10. Use of a rectifier circuit according to one of claims 1 to 6, with as user device (10) one or more series of aluminum electrolysis cells.

11. Use of a set of rectifier circuits (G1, G2) according to claim 7, with as user device (10) one or more series of aluminum electrolysis cells.

12. Use of the method according to claim 8, with as user device (10) one or more series of aluminum electrolysis cells.