A CONVERTER DEVICE

Abstract: A device for converting current and voltage between a first one-phase side (1) and a second one- or plurality-phase side (3) comprises at least two converter modules (7, 7', 7'') connected between these sides and each having two converters (8, 9) interacting with one of said sides and an intermediate link (10) interconnecting them. The converter modules are connected in series on said first side (1).

Description: A Converter Device FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a device for converting current and voltage between a first one-phase side ana a second one- or plurality-phase side, which comprises at least two converter modules connected between these sides ana each having two converters interacting with one of said sides each and an intermediate link interconnecting them In order to illuminate but not m any way restrict the invention two fields of use of such devices will hereinafter be described, but it is emphasised that a number of otner fields of use for such devices are conceivable withm the scope of the invention. A first such field of use consists of the use of such a de¬ vice in a so called power convertor station, which are placed along lines for electric railway traffic, primarily railway lines, so as to convert or transform voltage and current of a three-phase supply line to one phase having a suitable frequency and voltage of a one phase supply line for providing electrical energy to the vehicles driven on the railway. Such a device may have two converter modules, which at said second side are through the secondary winding of a transformer connected to the three phases of the three phase supply, said transformer being adapted to carry out a transformation of the alternating voltage from for example about 20 kV to for example about 1-3 kV. The converter at said second side of the respective converter module causes a rectifying and this direct voltage is then led to a nurnoer, for instance four, converters connected m parallel between the direct voltage potentials of the intermediate link, said converters being controlled by pulse with modulation to emit an alternating voltage, formed by alternating positive and negative voltage pulses, which are added through primary windings of a transformer, the secondary winding of whicn is connected to the railway supply line and ground. The con¬ verters of the one-phase side are then controlled to produce an alternating current having a desired frequency, usually 16 2/3 Hz, while the three-phase supply line have a fre¬ quency of 50 Hz. Through the transformer on the one-phase side a voltage addition takes place while simultaneously ob¬ taining a stair case curve shape, which will come closer to a sinus shape the greater is the number of converters ai - ranged at said first side. A voltage adaption also takes place, so that the voltage at the one-phase side usually will be about 16 kV The two transformers also ensure gal- vanical separation between the converter modules and between the one-phase and the plurality-phase side. Another field of use for a device defined m the πtroαuc- tion is m an electrically driven vehicle, such as a locomo¬ tive, but such devices already known for tms field of use have had a single converter module, which have been con- nected to the one-phase supply line through a transformer, said transformer having transformed the voltage down from for example 16 kV to 3 kV, and m which converters in the form of three-phase-bridges have been connected m parallel at the second side of the converter module and connected to a three-pnase motor each for driving the vehicle Although these already known devices function well, it would of course be interesting to simplify them for saving costs SUMMARY OF THE INVENTION The object of the present invention is to provide a device of the type mentioned m the introduction, which is easier and primarily may be manufactured to a lower cost than such devices already known, without lowering the requirements of a good function of the device. This object is according to the invention obtained by con- nectmg the converter modules m series on said first side Thanks to such a connection m series of the converter modules is made no transformer is needed at said first side for adding voltages for achieving a good curve shape when the device is used so that the converters at said first side function as inverters and m the opposite case, i.e. when the latters function as rectifiers no transformer is needed either at said first side for transforming down the voltage to a desired level, since a voltage division to the differ¬ ent converter modules will now take place Tnuε, the train advantage of the invention is that no transformer is needed any longer in such a device for co-operation with said first one-phase side, which means a considerable saving of costs with respect to such devices according to the prior art According to a preferred embodiment of the invention the second side is a plurality-phase side, the number of con¬ verter modules of the device is a multiple of the number of phases of the second side, and each converter module is adapted to co-operate through one converter thereof with the phase of this side and just as many converter modules are adapted to co-operate with each phase of the other side The load on the phase of a plurality-phase side will in this way be symmetrical with the same number of levels per phase as the number of converter modules connected to the respective phase. A balanced load is in this way obtained on a plural ity-phase side, usually a three-phase network According to another preferred embodiment of the invention the second side is a plurality-phase side, the number of converter modules of the device is a multiple of the number of phases of said second side, and each converter module is adapted to co-operate through one converter thereof with one phase of this side and the same number of converter modules are mtende to co-operate with each phase of this second side. This embodiment constitutes an alternative way to achieve balancing, wherein a balancing is in this case obtained irrespective of the number of converter modules, so that there is no requirement that these are a multiple of the number of phases . According to a further preferred embodiment of the invention the converters of the converter modules co-operating with sa d second side are adapted to co operate with the second phase side through a transformer by being connected to the secondary winding thereof, and m the two embodiments last mentioned m the first one said transformer has at least a primary and a secondary winding per phase and each converter of the converter modules co-operating with said second phase side is connected to one such secondary winding of its own belonging to a phase of the second side with the secondary windings galvamcally separated from each other and m the second embodiment said transformer has at least a primarily and a secondary winding per phase and each branch of said bridge is connected to such a secondary winding belonging to a phase of the second side with secondary windings belonging to different converter modules galvamcally separated from each other. Thanks to these constructions of the transformer the two embodiments mentioned further above are enabled while ensuring the mutually galvanical separation of the different converter modules required, which is necessary for enabling connection I series The definition of "the trans¬ former" is intended to cover that a plurality thereof are arranged, since the galvamcal separation may take place either by separating the secondary windings in one and the same transformer or by using separate transformers According to another preferred embodiment of the invention, the converters of the converter modules are adapted to enable transmission of power m both directions between tne first and second side, i. e. to function both as rectifiers and inverters This embodiment is to prefer and it may be achieved by using conventional controllable semiconductor switching elements, such as thyristors that may be turned off (GTO's) and bipolar transistors with an insulated gate (IGBT's) but it is withm the scope of the invention to use conventional thyπstor or diode rectifiers as converters of the second side in the case that only power transmission from the second to the first side is necessary According to another preferred embodiment of the invention said first side is formed by a one-phase railway supply line for vehicles electrically driven, the second side is formed by a three-phase supply line and the device is a part of a power convertor station for delivering electrical energy from the three-phase line to the one-phase line oi con¬ versely Accordingly, such a device makes it possible to ob tain a good curve-shape of the one-phase side if the modula¬ tion patterns for the different converters of this side have a suitable mutual phase shift and the output voltages thereof are after that added by a series connection, which accordingly is possible in this case without any transformer on the one-phase side. The more converter modules used the better will the curve-shape be and the higher m the fre¬ quency interval will the harmonics generated be located, which means that the problem to take care thereof is re¬ duced According to another preferred embodiment of the invention the converters of the converter modules co-operating with the second side are connected to an electrical motor each forming said second side. It is by that possible to drive a plurality of electrical motors through a one-phase side without any transformer for bringing the voltage to a level suitable for the motors, since the connection m series ac¬ cording to the invention obtains a division of the voltage of the one-phase side of the different converter modules to a suitable level. Thus, vehicles, such as railway engines, having no transformers may be built . According to another preferred embodiment of the invention the respective converters of the converter modules co-oper- ating with the second side are formed by a bridge having a plurality of branches, which are each connected to a phase winding each of a motor separate for each converter module and having a number of phases corresponding to said plural¬ ity. The separate electrical motor may this way be driven by each converter module, said motor being preferably of the three-phase type, so that the bridge has three branches, i.e. is a three-phase bridge, and a suitable voltage level for the motors may be achieved by the voltage division obtained by the connection in series at the first side. It is of course possible, which is indicated another em¬ bodiment of the invention, that the converters of the con¬ verter modules co-operating with the second side are con¬ nected to a phase winding each of an electrical motor be- longing to the second side, so that for example three con¬ verter modules are arranged for transferring electrical en¬ ergy to one single three-phase motor cr receiving energy therefrom when it is slowed down. Further advantages and advantageous characteristics of tne invention will appear from the following description as well as the other dependent claims RRTEF DESCRIPTION OF THE DRAWINGS With reference to the appended drawings, below follows a de¬ scription of preferred embodiments of the invention cited as examples In the drawings Fig 1 is a circuit diagram illustrating a device according to a first preferred embodiment of the invention, and Fig 2 is a circuit diagram illustrating a device according to a second preferred embodiment of the invention DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION A device for converting current voltage between a first one- phase side 1, which is illustrated through two terminals 2, and a second three-phase side 3 is illustrated in Fig 1 Such a device is suited for being a part of a power con verter station for delivering electrical energy from a three-phase line to a one-phase railway supply lme for ve¬ hicles electrically driven or conversely The device has at the second side a transformer , with three primary windings 5, one for each phase, and three secondary windings 6 gal vanically separated from each other Thus, the transformer is arranged to transform the alternating voltage of one phase to an alternating voltage of another level through eacn couple of primary winding/secondary winding In the case of a power converter station of the type mentioned the voltage of the three-phase line is about 20 kV, and this is transformed m this way to about 2,5 kV alternating voltage between the ends of the respective secondary winding, so that the components arranged the converter modules de- scribed hereinafter will not be damaged. The device also comprises three converter modules 7, one for each phase, which each consists of a first converter 8 co¬ operating with the one-phase side 1, a second converter 9 co-operating with the three-phase side, and an intermediate link 10 arranged therebetween and formed by capacitors and induction coils and being here of the type making the con¬ verter modules voltage-stiff. "Converters" is here defmed as a means being able to function as an inverter and/or a rectifier. The transformer ensures a galvamcal separation required of different converter modules. Galvanical connec¬ tion may only take place one point, namely between the different converters on the first side (see the description further below of this embodiment and the one according to Fig. 2) . Each converter is formed by a bridge having two branches 11, 12, which by a man skilled the art are called phases, but they are here called branches for avoiding confusion. Each such branch has two controllable semiconductor switching de¬ vices 13, 14 in series, which their turn are called branches by the men skilled in the art. The different semi¬ conductor switching devices have a controllable switching element, and preferably a free-wheeling diode connected anti-parallelly thereto. The controllable semiconductor switching element may advantageously be a turn-off thyns- tor, a so called GTO, or a bipolar transistor with an insu¬ lated gate, a so called IGBT. Each converter branch 11, 12 is provided with a branch output 15, 16 a point between these two devices 13, 14, and one branch output of the second converters 9 is connected to one side of the respec- tive secondary winding and the other branch output to the other side thereof. By controlling the semiconductor switch¬ ing devices at the second converter of the respective con¬ verter module a conventional way, a rectifying of the al- ternat g voltage connected thereto is obtained, so that a direct voltage is achieved over the respective intermediate link 10. This direct voltage will the case mentioned above be about 3 kV The intermediate link smoothes out and filtrates the direct voltage, by absorption of the energy pulsations, which are related to the frequency of the alter¬ nating current networks, especially of the one-phase side, by the components thereof The first converters 8 are constructed m the same way as the second converters 9, but a branch output 17 of a first of the converter modules is connected to the one-phase line, the second branch output 18 is connected to a first branch output 19 of the first converter of a second converter module 7' , the second branch output 20 of which is connected to a first branch output 21 of the first converter of tne third converter module 7", and finally a second branch output 22 of this converter is connected to ground 2 Thus, a connection m series of the one-phase side of the con¬ verter device is by this obtained. The semiconductor switch- ing devices of the first converter are preferably controlled by means of pulse with modulation to deliver positive or negative rectangular pulses of the direct voltage of the in¬ termediate link 10 or zero voltage pulses By giving the pulses determined by the different first converters a suit- able mutual displacement by using suitable modulation pat¬ terns, the voltages added through the connection in series will have a staircase shape on the one-phase 1 The peak value thereof will in the present case be apout 9 kV Ac cord gly, the connection m series of the one-phase side of the converter modules makes a voltage addition without any existence of any transformer possible The converters aie preferably designed to enable transferring of electrical en¬ ergy m both directions, although this is not absolutely necessary, but in the case feeding is only intended to take place one direction the converters arranged on the input side may be formed by for example conventional thyristor rectifiers, which accordingly may not function as inverters It is possible to provide the device with another number than three converter modules, and a connection will then take place in the way shown Fig. 1 with just as many sec¬ ondary windings as the number of converter modules so as to achieve galvanical separation of the second converters the different converter modules, which the number of con¬ verter modules is preferably a multiple of three for obtain- ing a symmetrical load on the three-phase network. However, it would theoretically of course be possible to have other numbers of converter modules, but any desired symmetrical load is then not obtained The desired voltage at the one- phase side at a given maximum voltage taken by the se^.ccn ductor switching elements of the converter modules may m this way be obtained by a suitable choice of the number of converter modules The greater number of converter modules means also a better curve shape on the one-phase side It would for example be appropriate to have six converter modules with a voltage of about 2,7 kV per module the case mentioned above for obtaining a one-phase voltage of about 16 kV. It would as an alternative however also be possible to re- place the converters of the three-phase side snown in Fig 1 by conventional thyristor rectifiers connected to a three phase winding each or so called three-phase bridges, i.e bridges having three branches, which each are connected to a phase each of the three-phase side Symmetry the load upon the three-phase network is in this way achieved inde¬ pendently of the number of converter modules, through which the number of converter modules m some cases could be kept lower than in devices of the same type as that shown in Fig. 1, when there is a requirement to have such a load symmetry. The device has the embodiment shown in Fig. 1 two line sides, while Fig. 1 illustrates a device according to a sec¬ ond preferred embodiment of the mvention having a line- and a machine side and in which parts corresponding to parts of the device shown m Fig. 1 are provided with the same refer- ence numerals. The connection in series of the one-phase side 1 of the converter modules is here achieved in the same way as in Fig. 1. The device is here intended to be arranged an electrically driven vehicle intended to receive energy from a one-phase railway supply lme 23. This may for exam- pie have a voltage of 16 kV. Thus, the first branch output 17 is in this case connected to the one-phase railway supply line, while the branch output 22 of the third converter mod¬ ule is connected to ground. The voltage division on the re¬ spective converter modules is in this way obtained without any transformer, which is to compare with the case in con¬ ventional such vehicles, in which a transformer has to be arranged so as to transform down the voltage to a suitable level in the single converter module . The converters 9 of the second side of the device are formed by so called three- phase bridges, i.e. they have here three branches of the type defined above, and each branch output is connected to a phase-wmdmg of a three-phase motor 24. The motors 24 may in this way receive electrical energy from the railway supply line 23 and drive the vehicle. Conventional thyristor converters may in this case not be used on the motor side, but converters having components that may be turned off are required, since normal alternating current motors may not form the electromotive force needed for commutation cf a converter bridge. By arranging a plurality of converter mod- ules and connect the one-phase side thereof series in this way the motors of a vehicle fed through a one-pnase railway supply line may in this way receive driving force with the correct voltage level without using any trans¬ former. The motors have been given an isolation level adapted to the total connection voltage. In a modification of the embodiment according to Fig. 2 the converter of each converter module located at the second side 3 could be connected to only one phase winding of a mo¬ tor, which could be driven through a plurality of converter modules. It would then also be possible to arrange for example six converter modules for driving two three-phase motors. The invention is of course not any way restricted to the preferred embodiments described above, but several possi¬ bilities to modifications thereof would be apparent to a man skilled in the art without departing from the basic idea of the invention. Besides the possible modifications of the device according to the invention mentioned above, it may here also be added that the number of phases of the second side of course may be arbitrary, although it would in practice most often be constituted by a three-phase side. Thus, it could well be a one-phase side, and it is not at all necessary that the de¬ vice produces another frequency of the alternating voltage output than of the alternating voltage input.

Claims: Claims 1. A device for converting current and voltage between a first one-phase side (1) and a second one- or plurality- phase side (3) , which comprises at least two converter modules (7, 7' , 7") connected between these sides and each having two converters (8,9) interacting with one of said sides each and an intermediate link (10) interconnecting them, characterized in that the converter modules are con- nected in series on said first side. 2. A device according to claim 1, characterized in that said second side (3) is a plurality-phase side, that the number of converter modules (7, 7' , 7") of the device is identical to the number of phases of said second side, and that each phase of this side is intended to have a converter (9) of an old converter module co-operating therewith. 3. A device according to claim 1, characterized in that said second side (3) is a plurality-phase side, that the number of converter modules (7, 7' , 7") of the device is a multiple of the number of phases of said second side, and that each converter module is adapted to co-operate through one con¬ verter (9) thereof with one phase of this side and the same number of converter modules are intended to co-operate with each phase of this second side . 4. A device according to claim 1, characterized in that said second side (3) is a plurality-phase side, that the con- verter (9) of each converter module co-operating with said second side is formed by a bridge having just as many branches (11, 12) as the number of phases of the second side, and that the branches of each such bridge co-operate with a phase of said second side each. 5. A device according to any of claims 1-4, characterized m that the converters of the converter modules co-operating with said second side are adapted to co-operate with said second phase side (3) through a transformer (4) by being connected to the secondary winding (6) thereof. 6. A device according to claim 5 and any of claims 2 and 3, characterized in that said transformer (4) has at least a primary (5) and a secondary winding (6) for each phase, and that each converter (9) of the converter modules co-operat¬ ing with said second phase side (3) is connected to such a secondary winding of its own belonging to a phase of said second side with the secondary windings being galvamcally separated from each other. 7. A device according to claims 4 and 5, characterized in that said transformer (4) has at least a primary (5) and a secondary winding (6) for each phase, and that each branch (11, 12) of said bridge is connected to such a secondary winding belonging to a phase of said second side with the secondary windings belonging to different converter modules galvanically separated from each other. 8. A device according to any of the precedmg claims, char- acterized m that the converters (8, 9) of the converter modules (7, 7' , 7") are designed to enabling transfer of power in both directions between the first and second side, i.e. to function both as rectifiers and inverters. 9. A device according to any of the preceding claims, char¬ acterized that each converter (8, 9) includes at least two branches (11, 12) connected parallel between the di¬ rect current voltage potentials of the converter module in¬ cluding m series two controllable semiconductor switching devices (13, 14) and that each such converter branch is pro- vided with a branch tap (15-22) at a pomt between said two apparatuses . 10. A device according to claim 9, characterized m that each of said controllable semiconductor switching devices (13, 14) are formed by a controllable semiconductor switching element and a free-wheel diode connected m anti- parallel therewith. 11. A device according to claim 9 or 10, characterized in that the converter modules (7, 7' , 7") are connected m se¬ ries at the first side (1) by a connection of a second branch tap (18) of the respective converter (8) m a first converter module (7) to a first branch tap (19) of a con- verter m a second converter module (7') and so on, and that the total output voltage from the converter modules (7, 7' , 7") connected in series is obtamed between the first branch tap (17) of the converter of the first converter module (7) and the second branch tap (22) of the converter of a last converter module (7") so obtained. 12. A device according to any of the preceding claims, characterized in that said first side (1) is formed by a one-phase railway supply l ne (23) for vehicles electrically driven. 13. A device according to claims 5 and 12, characterized that said second side (3) of the device is formed by a three-phase supply line, and that the device is a part cf a power converter station for delivering electrical energy from the three-phase line to the one-phase lme or con¬ versely. 14. A device according to any of claims 1-4 or 8-12, charac- terized in that the converters (9) of the converter modules co-operatmg with said second side (3) are connected to an electrical motor (24) each forming said second side. 15. A device according to claim 14, characterized in that the converters (9) of the converter modules co-operating with said second side are each formed by a bridge having a plurality of branches, each of which is connected to a phase winding each of a motor (24) being separate for each con¬ verter module with a number of phases corresponding to sa d plurality. 16. A device according to any of claims 1-4 or 8-12, charac¬ terized in that the converters (9) of the converter modules co-operating with said second side (3) are connected to a phase winding each of an electrical motor (24) belonging to said second side. 17. A device according to claim 12 and any of claims 14-16, characterized that it is adapted to be arranged m such a vehicle for driving said motor/motors (24) and by that the vehicle through the railway supply lme (23) and that one end of the series connection of the converter modules is adapted to be directly, without any intermediate trans¬ former, connected to the railway supply line and the second end thereof is adapted to be connected to ground. 18. A device according to any of the preceding claims, characterized in that said second side (3) is a three-phase side . 19. A device according to any of the preceding claims, characterized in that the converter modules (7, 7' , 7") is of a voltage-stiff type.

Inventors: IVNER SVEN, LEJONBERG TOMMY, IVNER, SVEN, LEJONBERG, TOMMY
Applicants: ABB DAIMLER BENZ TRANSP, IVNER SVEN, LEJONBERG TOMMY, ABB DAIMLER-BENZ TRANSPORTATION (SWEDEN) AB, IVNER, SVEN, LEJONBERG, TOMMY
Application year: 1996
Main classification: H02M5
IPC codes: H02J3, H02M5