Method and arrangement for supplying a load from a power supply source

Abstract

The invention relates to a method for supplying a load (250) from a power supply source (280) with alternating voltage, using a plurality of rectifier groups connected in parallel and one or more transformers (260), wherein each of the plurality of rectifier groups (270.1, 270.2, 270.3) each has one or more active rectifiers connected in parallel, wherein one or more selected ones of the plurality of rectifier groups each have a plurality of active rectifiers connected in parallel, wherein the active rectifiers of the plurality of rectifier groups are electrically connected to the load (250) on the DC voltage side, wherein the active rectifiers of each of the plurality of rectifier groups are each electrically connected to the power supply source (280) on the AC voltage side via the one or more transformers (260), wherein different ones of the plurality of rectifier groups each have separate secondary windings (264.1, 264.2, 264.3) of the one or more transformers, wherein the active rectifiers of the one or each of the plurality of selected rectifier groups are each controlled synchronously with one another for rectification, and wherein active rectifiers of different ones of the plurality of rectifier groups are controlled offset from one another for rectification.

Description

The present invention relates to a method for supplying an AC voltage to a load from a power supply source, using a plurality of active rectifiers, to an arrangement for this and to a system having such an arrangement.BACKGROUND OF THE INVENTIONFor various applications, for example for operating electrolysers, high-power current sources or energy supply sources are required. The energy supply source can be, for example, a mains connection.Disclosure of the InventionAccording to the invention, a method for supplying a load from a power supply source, an arrangement for this, and a system having such an arrangement having the features of the independent patent claims are proposed. Advantageous embodiments are the subject matter of the dependent claims and of the following description.The invention is concerned with supplying an alternating voltage, e.g. one or more electrolysers, to a load from a power supply source. By means of electrolysers, for example, hydrogen (and oxygen) can be obtained from water and then, for example, also temporarily stored or provided for further use.A power supply source here can be, for example, a mains connection or, in general, a power or voltage mains. Particularly when used on an industrial scale, high-power current sources or energy supply sources are required. In the classic technique, rectifiers used to convert the alternating voltage of the energy supply source into a direct voltage for the load can be constructed with the aid of thyristors. However, this has the disadvantage that severe mains disturbances can occur because of the pulse width modulation required in this case.If active rectifiers, e.g. with so-called B6 bridges, are used, high-performance switches (power switches) such as e.g. IGBTs, MOS-FETs or other semiconductor switches are usually necessary. Since the size of circuit breakers is limited, circuit breakers or generally active rectifiers can be connected in parallel. However, so-called circulating currents can occur between the rectifiers.A circulating current occurs in particular whenever a high-side switch is closed in two rectifiers connected in parallel in the same phase in one rectifier and a low-side switch is closed in the other rectifier. This results in a current path via which, for example, the intermediate circuit capacitor can be discharged. There are several reasons why such a switching state may occur. Thus, for example, the drive signals (in particular the underlying carrier signals or carrier signals) of the two rectifiers can be shifted with respect to one another, or the modulation degrees (duty cycles) of the two rectifiers are different. Component tolerances of the rectifiers can also result in a time offset of the activation edges.Within the scope of the present invention, a special control in a special topology is now proposed, which can prevent circulating currents. In order to supply a load from a power supply source with alternating voltage, a plurality of active rectifiers are also used here. In addition, however, one or more transformers are used. In this case, the active rectifiers are divided into a plurality of rectifier groups, wherein each rectifier package comprises at least one, but preferably a plurality of active rectifiers connected in parallel. At least one of the plurality of rectifier groups should, however, comprise a plurality of, i.e. at least two, active rectifiers connected in parallel. Such rectifier groups will also be referred to below as selected rectifier groups. In practice, however, it will be expedient if all of the plurality of rectifier groups are selected rectifier groups, that is to say comprise a plurality of active rectifiers.The active rectifiers of the plurality of rectifier groups are, as usual, electrically connected on the DC voltage side to the load and on the AC voltage side electrically connected via the one or more transformers to the energy supply source. In this case, separate secondary windings of the one or more transformers are assigned to different ones of the plurality of rectifier groups. In particular, the various secondary windings assigned to the plurality of rectifier groups are galvanically isolated from one another. Here, it does not matter how many active rectifiers are assigned to the rectifier groups.In this way, the phases or phase connections of the active rectifiers of the different rectifier groups are galvanically separated from one another, so that circulating currents cannot occur between rectifiers of different rectifier groups.The connection to the energy supply source is then effected via one or more primary windings of the one or more transformers. Depending on the number of phases of the alternating voltage of the energy supply source, one or more primary windings can be provided; typically, one primary winding is provided for each phase. It should be mentioned here that one or more secondary windings must then also be provided for each rectifier group; one secondary winding is then provided for each rectifier group, wherein all secondary windings can be assigned to one phase of the one primary winding of the same phase.In addition, however, the active rectifiers of the one or each of the plurality of selected rectifier groups are each driven synchronously with one another for rectification. Synchronous driving here means in particular that the half bridges of different active rectifiers of the same selected rectifier packet, which half bridges are assigned to the same phases, are synchronously driven; i.e. high-side and low-side switches are synchronously opened and closed, so that no circulating currents can occur within the respective rectifier group.In addition, active rectifiers of different rectifier groups are controlled to be rectified in a manner offset with respect to one another. In this way, EMC interference on the primary side of the one or more transformers can be reduced. Since the superposition of the offset switching operations takes place only in the magnetic circuit of the transformer, a positive EMC effect can be achieved there on account of the switching operations offset with respect to one another, without having the negative effects of circuit currents.It should be mentioned at this point that, when active rectifiers are mentioned, they can also generally be converters which can, however, also be operated at least as rectifiers; for example, a converter can also be operated as rectifier and as inverter. Inverters are frequently also referred to in inverters.In one embodiment, the active rectifiers of different rectifier groups are controlled to be rectified in a manner offset with respect to one another by mutually corresponding phases being controlled in a manner offset with respect to time. In this case, similar drive patterns, but ones offset with respect to one another in time, can be used. This is also referred to as carrier shift.In one embodiment, the active rectifiers of different ones of the plurality of rectifier groups are biased to perform rectification offset from one another using different drive frequencies. In this case, the drive frequency for the plurality of active rectifiers in the one or in one of the plurality of selected rectifier groups can be varied, in particular swept, synchronously. The term "wobbling" is understood here in particular to mean a periodic frequency change of an oscillation about an average frequency. This is also possible for a plurality or all of the plurality of selected rectifier groups, wherein, however, the variation for the different plurality of selected rectifier groups then takes place in particular independently of one another, i.e. the variation takes place synchronously for the active rectifiers in a selected rectifier packet, but independently of a variation in the other selected rectifier groups. In particular, the variations in different selected rectifier groups can then also be different.In one embodiment, the active rectifiers of different ones of the plurality of rectifier groups are driven to rectify in a staggered manner by using different drive values. A duty cycle is in particular a number between zero and one, which indicates the duty cycle of a drive signal. This can lead to the different rectifier groups each supplying a different direct current component. In this case, it is then necessary to take care that the sum of the currents of the plurality of rectifier groups corresponds to the desired load current. In one embodiment, the modulation of the individual rectifier groups can also be varied with respect to one another in time.Each of the explained possibilities for driving active rectifiers of different ones of the multiple rectifier groups offset with respect to one another for rectification reduces the EMC interference. The various possibilities can also be combined with one another as desired.In one embodiment, the energy supply source has a plurality of phases, for example three phases, as is frequently the case with high-power AC voltage grids. However, it should be mentioned that the principle also works in a single-phase or n-phase power supply source.Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.The invention is schematically illustrated in the drawing on the basis of exemplary embodiments and is described below with reference to the drawing.Brief Description of the DrawingsFIG. 1 shows schematically an arrangement for explaining the invention. FIG. 2 schematically shows an arrangement according to the invention in one embodiment. FIGS. 3 a, 3 b, 3 cschematically show diagrams for sequences of methods according to the invention in various embodiments.Embodiment(s) of the InventionIn FIG. 1, an arrangement 100 for explaining the invention is shown schematically. The arrangement 100 has, for example, two active rectifiers 110, 120 which are connected in parallel. The arrangement 100 serves for supplying a load 150, e.g. one or more electrolyzers, with alternating voltage from a power supply source 130. By way of example, the energy supply source 130 has three phases 180 a, 180 b, 180 c.The rectifier 110 comprises, corresponding to the three phases of the power supply 130, three half bridges 110 a, 110 b, 110 c, which may also be referred to as phases. Each half bridge has, by way of example, two power semiconductor switches, a high-side switch T H and a low-side switch T L.The rectifier 120 comprises, corresponding to the three phases of the power supply 130, three half bridges 120 a, 120 b, 120 c, which may also be referred to as phases. Each half bridge has, by way of example, two power semiconductor switches, a high-side switch T H and a low-side switch T L.The rectifiers 110 and 120 can therefore be constructed in the same way. By means of the power semiconductor switches, which can be controlled for opening and closing by means of a control device 142 by means of a control pattern 144 (separate control devices for the rectifiers are also conceivable), an AC voltage can be rectified; they are thus active rectifiers. In particular, however, the rectifiers 110 and 120 are connected in parallel on the DC voltage side and can be electrically connected to the load 150. In addition, an intermediate circuit capacitor 140 can be interposed. The rectifiers 110 and 120 have connections 114 and 124, respectively, on the DC voltage side for this purpose, by means of which they can be connected to the load 150.On the AC voltage side, on the other hand, the rectifiers 110 can be electrically connected to the energy supply source 180. In particular, the mutually corresponding phases are connected here, i.e. the phases or half bridges 110 aand 120 aare connected to the phase 180 a. The same applies to the half bridges 110 band 120 band 110 cand 120 c, and to the phases 180 band 180 c, respectively. Suitable phase connections 112, 122 of the rectifiers 110, 120 are provided for this purpose. These phase connections are connected in the respective rectifier to the center taps of the respective half bridges, i.e. in each case between high-side switch T H and low-side switch T L. Inductances 116, 126 are provided by way of example downstream of the phase connections 122 and 122, respectively.In this arrangement 100, it can now be connected to the aforementioned circuit currents. For this purpose, for example, the high-side switch T H of the half bridge 110 aof the rectifier 110 and the low-side switch T L of the half bridge 120 aof the rectifier 120 can be simultaneously closed, i.e. conducting; this can also be the case only briefly, for example. In this case, a circulating current I K can form, which can discharge the intermediate circuit capacitor 140.FIG. 2 schematically illustrates an arrangement 200 according to the invention in an embodiment with which a method according to the invention can also be carried out.The arrangement 200 has, by way of example, three rectifier groups 270.1, 270.2, 270.3, each of these three rectifier groups in turn having three active rectifiers. Rectifier group 270.1 includes active rectifiers 210.1, 220.1, 230.1, rectifier group 270.2 includes active rectifiers 210.2, 220.2, 230.2, and rectifier group 270.3 includes active rectifiers 210.3, 220.3, 230.3. In this case, the three active rectifiers within a rectifier group are each connected in parallel. Thus, each of the rectifier groups 270.1, 270.2, 270.3 is, for example, a selected rectifier group; as mentioned, however, one of the rectifier groups can also have only one active rectifier, for example.The arrangement 200 serves for supplying a load 250, e.g. one or more electrolyzers, with alternating voltage from a power supply source 280. The energy supply source 280 is shown only roughly schematically here. Moreover, the arrangement 200 comprises a transformer 260, wherein the transformer comprises terminals 266 for electrically connecting to the power supply source 280. In addition, the rectifier has a primary winding.The active rectifiers of the plurality of rectifier groups, i.e. all active rectifiers 210.1, 220.1, 230.1, 210.2, 220.2, 230.2, 210.3, 220.3, 230.3 shown here, have connections 274 on the DC voltage side for the electrical connection to the load 250. By way of example, only two connections are shown here, i.e. the active rectifiers can also be connected internally in the arrangement, but individual connections can also be provided.The active rectifiers of each of the plurality of rectifier groups are additionally electrically connectable or connected to the transformer 260 on the AC voltage side in each case. In this case, separate secondary windings of the transformer 260 are assigned to different ones of the plurality of rectifier groups. For example, the rectifier group 270.1 is assigned the secondary winding 264.1, the rectifier group 270.2 is assigned the secondary winding 264.2, and the rectifier group 270.3 is assigned the secondary winding 264.3. By way of example, the rectifier groups or their rectifiers are connected to the secondary winding via terminals 272 on the AC voltage side.The secondary windings are galvanically separated from one another, so that circulating currents cannot occur between active rectifiers of different rectifier groups.It should be mentioned at this point that, on account of the schematic illustration, specifically only one primary winding and three secondary windings are shown for the transformer 260. As mentioned, one primary winding is typically provided for each phase. In the case of a three-phase alternating voltage of the energy supply source 280, three primary windings must therefore be provided. Accordingly, there are then nine secondary windings--in the example shown--three per phase.In this case, for example, each of the nine active rectifiers 210.1, 220.1, 230.1, 210.2, 220.2, 230.2, 210.3, 220.3, 230.3 by way of example can be constructed in the same way as the active rectifiers 110, 120 according to FIG. 1. With more or fewer phases of the alternating voltage, a different number of active rectifiers would have to be provided accordingly.The arrangement 200 additionally has a control device 242, by means of which, for example, all active rectifiers can be controlled for rectification. It is also conceivable to use a plurality of control devices for this purpose. The specific type of control of the various active rectifiers will be explained in more detail below.FIGS. 3 a, 3 b, 3 cschematically show diagrams for sequences of methods according to the invention in various embodiments. In particular, different drive patterns for half bridges of active rectifiers of different rectifier groups are shown here.Here, switching states 302 are shown above a time axis 301. In this case, a distinction is to be made between switching states 303 and 304. Switching state 303 means, the low-side switch of a half bridge of an active rectifier is switched on, the high-side switch is switched off, switching state 304, on the other hand, the high-side switch of a half bridge of an active rectifier is switched on, the low-side switch is switched off.In FIG. 3 a, a drive pattern for a half bridge of an active rectifier of one rectifier group is shown at 310, and a drive pattern for a half bridge of an active rectifier of another rectifier group is shown at 312. Both control patterns 310, 312 are identical per se, but are offset in time. This is also known as a carrier shift. The regions between vertical lines of the two drive patterns mark time regions in which an asynchrony of the drive is present.In FIG. 3 c, 320 shows a drive pattern for a half bridge of an active rectifier of one rectifier group, and 322 shows a drive pattern for a half bridge of an active rectifier of another rectifier group. It can be seen here that the control pattern 312 has a higher frequency than the control pattern 310. The regions between vertical lines of the two drive patterns mark time regions in which an asynchrony of the drive is present.In FIG. 3 c, 330 shows a drive pattern for a half bridge of an active rectifier of one rectifier group, and 332 shows a drive pattern for a half bridge of an active rectifier of another rectifier group. It can be seen here that the activation pattern 330 and the activation pattern 332 have different modulation values. Thus, in the case of the drive pattern 330, the high-side switch is closed for a longer time than in the case of the drive pattern 332; the situation is the opposite for the low-side switches. The regions between vertical lines of the two drive patterns mark time regions in which an asynchrony of the drive is present.

Claims

A method for supplying an AC voltage to a load (250) from a power supply source (280), using a plurality of rectifier groups connected in parallel and one or more transformers (260), wherein each of the plurality of rectifier groups (270.1, 270.2, 270.3) respectively has one or more active rectifiers connected in parallel, wherein one or more selected ones of the plurality of rectifier groups respectively have a plurality of active rectifiers connected in parallel, wherein the active rectifiers of the plurality of rectifier groups are electrically connected to the load (250) on the DC voltage side, wherein the active rectifiers of each of the plurality of rectifier groups are electrically connected to the power supply source (280) via the one or more transformers (260) on the AC voltage side, wherein separate secondary windings (264.1, 264.2, 264.3) of the one or more transformers are respectively assigned to different ones of the plurality of rectifier groups, wherein the active rectifiers of the one or each of the plurality of selected rectifier groups are each driven for rectification synchronously with one another, and wherein active rectifiers of different ones of the plurality of rectifier groups are driven for rectification offset with respect to one another.The method of claim 1, wherein the different secondary windings associated with the plurality of rectifier groups are galvanically isolated from each other.Method according to claim 1 or 2, wherein the active rectifiers of different ones of the plurality of rectifier groups are controlled to be rectified in a manner offset with respect to one another by mutually corresponding phases being controlled in a manner offset with respect to time.The method of claim 3, wherein the active rectifiers of different ones of the plurality of rectifier groups are biased to perform rectification using similar but time-biased drive patterns (310, 312).The method of any preceding claim, wherein the active rectifiers of different ones of the plurality of rectifier groups are biased to rectify in a staggered manner using different drive frequencies.The method of claim 5, wherein the drive frequency for the plurality of active rectifiers in the one or in one of the plurality of selected rectifier groups is synchronously varied, in particular swept; or wherein the drive frequency for the plurality of active rectifiers of each of the plurality of selected rectifier groups is respectively synchronously varied, in particular swept, but independently of the other ones of the plurality of rectifier groups.The method of any preceding claim, wherein the active rectifiers of different ones of the plurality of rectifier groups are biased to rectify in a staggered manner using different drive values.Method according to claim 7, wherein the drive values of different ones of the plurality of rectifier groups are varied with respect to one another in time.The method of any preceding claim, wherein the load (150) comprises one or more electrolyzers.Arrangement (200) for supplying a load (150) from a power supply source (130) with alternating voltage, wherein the arrangement comprises a plurality of rectifier groups connected in parallel, wherein each of the plurality of rectifier groups comprises in each case one or more active rectifiers connected in parallel, wherein one or more selected ones of the plurality of rectifier groups comprise in each case a plurality of active rectifiers connected in parallel, and wherein the arrangement comprises one or more transformers, wherein the active rectifiers of the plurality of rectifier groups comprise connections on the direct voltage side for electrically connecting to the load, wherein the active rectifiers of each of the plurality of rectifier groups are in each case electrically connectable or connected to the one or at least one of the plurality of transformers (160) on the alternating voltage side, wherein separate secondary windings of the one or more transformers are assigned to different ones of the plurality of rectifier groups, wherein the one or more transformers comprise connections (166) for electrically connecting to the power supply source (130), and wherein the arrangement has a drive device which is configured to drive the active rectifiers of the one or each of the plurality of selected rectifier groups synchronously with one another for rectification, and to drive active rectifiers of different ones of the plurality of rectifier groups offset with respect to one another for rectification.The system comprising one or more electrolyzers and an assembly (200) according to claim 10, wherein the one or more electrolyzers as a load (150) are electrically connected to the DC side terminals (114, 124).

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