Controllable rectifier arrangement for hydrogen electrolysis

Abstract

The invention relates to a rectifier arrangement for hydrogen electrolysis, comprising a first transformer (1) for transforming an input voltage U1 into a secondary voltage U1', wherein the transformer (1) has N>1 winding taps (2), and wherein an on-load tap changer (4) is provided that is designed to switch the winding taps (2) of the first transformer (1) such that the output voltage U1' can be switched into N stages, and wherein a second transformer (5) is provided for transforming the secondary voltage U1' into an output voltage U2 having a number M>1 of winding taps (6), wherein a second on-load tap changer (7) connected to the controller (3) is provided, wherein the first transformer (1) is connected in series with the second transformer (5) such that the output voltage U2 can be switched into NxM stages, wherein the transformers (1, 5) are arranged on separate iron cores, and wherein a passive rectifier (8) is provided for generating an output direct current IDC and an output DC voltage UDC.

Description

[0001] 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT)

[0002] Adjustable rectifier arrangement for hydrogen electrolysis

[0003] The invention relates to a controllable rectifier arrangement for hydrogen electrolysis.

[0004] Prior art includes methods for producing hydrogen by electrolysis, in particular PEM (Proton Exchange Membrane) electrolysis and AEL (Alkaline Electrolysis). Such processes require a high and essentially constant direct current, although this current depends on the specific production conditions. Typically, direct currents exceeding 600 A are required at power levels above 1 MW.

[0005] For providing direct current, adjustable rectifier arrangements are known that generate a direct current output voltage from an alternating current input voltage. These arrangements typically use actively controlled electronic circuits, such as circuits with thyristors or IGBTs and downstream filter elements.

[0006] To reduce the losses incurred during the conversion of the input AC voltage to the output DC voltage, it is known from WO WO2024 / 130276 A1 to equip a rectifier arrangement for hydrogen electrolysis with a transformer having several partial windings that are switched by different load tap changers. By cascading load tap changers with different numbers of turns per stage, coarse and fine control of the output voltage can be achieved. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT). However, this has the disadvantage that the transformer design is complex and its manufacture is costly. Several windings cascaded via tap changers must be produced, which leads to complicated troubleshooting and repair in the event of a fault.Furthermore, in practice it has become apparent that load balancing and the exact cancellation of harmonics is difficult in windings that are arranged on one and the same transformer core.

[0007] The object of the invention is therefore to create a simplified design of such a rectifier arrangement, which enables the use of simple and proven components as well as simple troubleshooting and fault correction, and simple correction of unbalanced load situations.

[0008] These and other tasks are solved by a rectifier arrangement according to claim 1.

[0009] A rectifier arrangement according to the invention is designed for hydrogen electrolysis and comprises a first transformer for transforming an input voltage Ui into a secondary voltage UT. The transformer has a number N > 1 of winding taps. For example, the number of turns can be in the range of 1000 to 1500. The number of winding taps N can be greater than 10, for example, about 20. However, up to 35 winding taps or more can also be provided. The winding taps can be provided in a partial section of the transformer winding, so that, for example, only about 200 of about 1000 turns are tapped.

[0010] A load tap changer connected to a controller is provided, designed for the uninterrupted switching of the winding taps of the first transformer. The controller can thus adjust the secondary voltage Ui' in N steps via the load tap changer. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) According to the invention, a second transformer is provided, designed for transforming the secondary voltage Ui' into an output voltage U2 with a number M > 1 of winding taps. A second load tap changer connected to the controller is provided, designed for the uninterrupted switching of the winding taps of the second transformer. This second transformer is connected in series with the first transformer, so that the output voltage U2 can be switched in N x M steps.

[0011] According to the invention, the first and second transformers are arranged on separate iron cores. Preferably, the two transformers are provided as separate components. This allows for simpler manufacturing, maintenance, and repair of the transformers. However, the two transformers can also be combined in a common assembly.

[0012] At the output of the second transformer, a passive rectifier is provided to generate an output DC current (IDC) and an output DC voltage (UDC). The controller can be connected to a voltmeter and an ammeter to measure the output voltage (UDC) and output current (IDC), enabling it to generate the required DC current by adjusting the two tap changers in the two transformers. By eliminating actively controlled electronic circuits and filter elements, electrical losses in the rectifier are reduced, resulting in more efficient power delivery.

[0013] According to the invention, the first transformer can be provided to have a primary winding and a galvanically isolated secondary winding, wherein the secondary voltage Ui' is tapped at the secondary winding and the winding taps are provided at the primary winding.

[0014] According to the invention, the first transformer can also be an autotransformer, with the input voltage Ui and the secondary voltage Ui' being tapped from the same winding. Such autotransformers are also known as autotransformers. This allows for a particularly cost-effective and space-saving implementation of the rectifier arrangement. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) According to the invention, the output voltage U2 can be adjusted in coarse steps via the first load tap changer and in fine steps via the second load tap changer.

[0015] In order to enable such coarse and fine adjustment of the output voltage via the two load tap switches, it can be provided that the voltage levels switched by the two load tap switches are of different heights with respect to the output voltage U2.

[0016] For example, the first transformer can have a transformation ratio of Ui / Ui' = 5:1 and a primary-side voltage range of 0–30 kV. With N = 10 equally distributed primary-side winding taps, the secondary-side voltage levels of the first tap changer are approximately AUi' ≤ 600 V. The second transformer can, for example, have a transformation ratio of UT / U2 = 10:1 and a primary-side voltage range of 0–6 kV. With M = 20 equally distributed primary-side winding taps of the second transformer, the secondary-side voltage levels of the second tap changer are approximately AU2 ≤ 30 V. This allows for 10 coarse taps of ≤ 600 V each and 20 fine taps of ≤ 30 V each. Provided that the input voltage Ui is fully applied, i.e., the winding of the first transformer is not tapped, a fine adjustment of the output voltage is achieved by voltage steps of AU2 = 30 V.With an input voltage of Ui = 30 kV, this corresponds to a fine control of 0.1%.

[0017] The transformation ratios of the two transformers can be the same or different. The number of turns in the windings of the two transformers can also be the same or different. Likewise, the number of winding taps N, M of the two tap changers can be the same or different.

[0018] For example, the two tap changers can have an identical number of winding taps N = M. However, it is also possible for the number of winding taps of the first tap changer N to be greater or less than the number of winding taps of the second tap changer M. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) The number of turns switched per stage by the tap changers can also be the same or different. For example, the first tap changer can switch a higher number of turns per stage than the second tap changer. For example, the first tap changer can switch 100 turns per stage, and the second tap changer can switch fewer than 10 turns, fewer than 5 turns, two turns, or only 1 turn per stage.

[0019] These configurations can also be combined. Preferably, the rectifier arrangement is designed such that switching the first tap changer causes a change in the output voltage U2 of the second transformer in larger steps than switching the second tap changer. For example, the change in the output voltage U2 when switching the first tap changer can be 10, 20, or 30 times greater than when switching the second tap changer.

[0020] By using such cascaded tap changers, both the normal control range and stronger mains-side over- and undervoltages (+ / - 10% of the input voltage) can be covered. Furthermore, the step adjustment within the control range can be very fine, while the coarse steps can be approached very quickly to make larger adjustments. In particular, the voltage steps for fine control can be below approximately + / - 0.1%, especially below approximately 0.01%, and for coarse control approximately + / - 10% of the input voltage.

[0021] The number and division of the stages into fine and coarse stages can be individually adapted to the application area, whereby experience has shown that more than 125 stages are required for the use according to the invention in hydrogen electrolysis.

[0022] Preferably, the rectifier is designed as a passive diode bridge rectifier, without active components such as thyristors. This enables high rectifier efficiency and total losses of preferably less than 1.5%.

[0023] According to the invention, the two separate transformers and the rectifier can be configured as multiphase, in particular two-phase or three-phase. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) The configuration of the on-load tap changers for each transformer can vary. For example, three single-phase devices or one three-phase device can be provided. Other configurations are also provided according to the invention.

[0024] The regulator can be connected to an ammeter to measure the output current IDC and, optionally, also to a voltmeter to measure the output voltage UDC. The output current IDC and the output voltage UDC represent the target values ​​to be achieved by the rectifier arrangement.

[0025] According to the invention, several parallel-connected secondary transformers and rectifiers may be provided, wherein the secondary transformers each have separate iron cores and each have its own secondary load tap changers connected to the controller. In this case, the controller is preferably connected to an ammeter for measuring the output current in each of the parallel-connected bridges and optionally also to a voltmeter for measuring the output voltage in each of the parallel-connected bridges.

[0026] The second transformers can each be designed as two-winding transformers or as multi-winding transformers, in particular as three-winding transformers with one primary winding and two secondary windings.

[0027] The output voltages of the second transformers can be phase-shifted by an angle Acp. A dedicated rectifier can be provided for each of the second transformers. The second transformers and their associated rectifiers can be single-phase or multi-phase, particularly three-phase. To achieve reduced output voltage ripple, the transformers can be phase-shifted. It is possible for the transformers to be configured to achieve an output voltage phase-shifted by an angle of Acp, where Acp is equal to 60° divided by the number of second transformers.

[0028] For example, a 24-pulse circuit can be implemented with four second two-winding transformers and four rectifier bridges. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) A 48-pulse circuit can be implemented by using four second transformers as three-winding transformers with one primary and two secondary windings, or eight second transformers as two-winding transformers, with a separate rectifier bridge provided at the output of each winding.

[0029] With such a rectifier arrangement, an additional load balancing control can be easily implemented by measuring each bridge current of the rectifier bridges and transmitting it to the controller, which then adjusts the respective second tap changers. The setpoint of the generated DC currents can thus be evenly distributed across the individual rectifier bridges by fine-tuning the tap changers of the second transformers, thereby reducing network disturbances, particularly harmonic overtones, and DC current ripple.

[0030] Accordingly, the controller can be connected to an ammeter for measuring the output current of each rectifier and, if necessary, to a voltmeter for measuring the output voltage of each rectifier.

[0031] According to the invention, the controller can thus ensure, in a subordinate control loop, that the electrical power or current in each rectifier bridge is essentially equal, thereby compensating for unbalanced loads. In a superior control loop, the controller can ensure that the target values ​​for the output voltage and output current are achieved. The controller can therefore be configured to perform load balancing between the bridges with the second tap changers of the second transformers and rectifiers in a subordinate control loop, and to set the desired output current IDC with the first and second tap changers of the first and second transformers in a superior control loop.

[0032] According to the invention, several first transformers connected in parallel can also be provided, each having separate iron cores and each having first load tap changers connected to the controller. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) This allows a high input power to be distributed across several first transformers. An unbalanced load can then also be compensated on the primary side by adjusting the first load tap changers via the controller.

[0033] According to the invention, the input AC voltage Ui can have an amplitude of over 10 kV, in particular about 20 kV to 33 kV, and the output DC voltage UDC has a nominal value of about 300 V to about 2000 V, for example about 1200 V. For future applications, the amplitude of the input AC voltage Ui can also be higher, for example up to 115 kV.

[0034] The first transformer can have a rated electrical power of over approximately 1 MVA, preferably over approximately 6 MVA, for example in the range of 15 MVA to 30 MVA. The second transformer can have a rated electrical power that is lower than that of the first transformer, for example in the range of approximately 500 kVA to approximately 10 MVA, depending on the number of parallel transformers.

[0035] According to the invention, it can further be provided that two or more secondary transformers are provided. These can be designed as two-winding or multi-winding transformers. The output voltages of the secondary transformers or their partial windings can be phase-shifted by an angle Acp, wherein a rectifier is provided for each of the secondary transformers or their partial windings to generate the output DC current IDC and the output DC voltage UDC.

[0036] The invention further relates to a system comprising several rectifier arrangements connected in parallel according to the invention, wherein the load tap changers of each rectifier arrangement are connected to a central controller.

[0037] The invention further relates to the use of a rectifier arrangement according to the invention for generating a DC output current (IDC) of more than approximately 600 A, preferably more than approximately 2 kA, preferably more than approximately 20 kA, at an output DC voltage in the range of approximately 300 V to approximately 1500 V for hydrogen electrolysis, in particular PEM electrolysis or alkaline electrolysis. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT). When using a rectifier arrangement according to the invention, fine control of + / - 0.1%, in particular + / - 0.01% and lower of the input voltage can be achieved by means of the first tap switches, and coarse control of + / - 10% and higher of the input voltage can be achieved by means of the second tap switches.

[0038] Further features of the invention will become apparent from the claims, the description of the exemplary embodiments, and the figures. The invention is explained below with reference to figures which show exemplary embodiments:

[0039] Fig. 1 shows a first embodiment of a rectifier arrangement according to the invention;

[0040] Fig. 2 shows a second embodiment of a rectifier arrangement according to the invention;

[0041] Fig. 3 shows a third embodiment of a rectifier arrangement according to the invention;

[0042] Fig. 4 shows an embodiment of a system according to the invention with several rectifier arrangements connected in parallel,

[0043] Fig. 5 shows a further embodiment of a rectifier arrangement according to the invention.

[0044] Fig. 1 shows a first embodiment of a rectifier arrangement according to the invention for hydrogen electrolysis. This arrangement comprises a first transformer 1 for transforming an input voltage Ui into a secondary voltage Ui', wherein the transformer 1 has N > 1 winding taps 2. A load tap changer 4 connected to a regulator 3 is provided, which is designed for the uninterrupted switching of the winding taps 2 of the first transformer 1, so that the output voltage Ui' can be switched in N steps. In this embodiment, the first transformer 1 has a primary winding and a galvanically isolated secondary winding. N = 9 winding taps 2 are provided on the primary winding. A second transformer 5 on a separate iron core is provided for transforming the secondary voltage Ui' into an output voltage U2 with M > 1 winding taps 6.65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) In this embodiment, M = 9 winding taps 6 are provided. A second load tap changer 7, connected to the controller 3, is provided for the uninterrupted switching of the winding taps 6 of the second transformer 5. The first transformer 1 is connected in series with the second transformer 5, so that the output voltage U2 can be switched in N x M steps.

[0045] At the output of the second transformer 5, a passive rectifier 8 is provided to generate an output DC current IDC and an output DC voltage UDC. The controller 3 is connected via data lines to a voltmeter 10 and an ammeter 9 on the output side of the rectifier 8. In this embodiment, the rectifier 8 is designed as a single-phase diode bridge rectifier. The controller 3 receives a desired output DC current as a target variable and adjusts the load tap changer 4 of transformer 1 and the load tap changer 7 of transformer 5 such that this value is reached at the output of the rectifier 8.

[0046] A preferred embodiment of the invention is explained in more detail below. In this embodiment, the first transformer 1 is designed as an autotransformer with a nominal voltage Ui of 33 kV. The output DC voltage UDC is finely adjustable in a range of approximately 657 V to approximately 1057 V, with an output DC current of 20 kA. The rectifier 8 is designed as a passive 3-phase bridge rectifier with 4 phase-shifted B6C bridge rectifier circuits.

[0047] The transformer 1 has 35 winding taps on a section of the primary winding, allowing the secondary voltage Ui' to be switched in N = 35 steps via the first tap changer 4. The number of turns switched per step is the same, so the voltage steps are of equal size. In this embodiment, the secondary voltage Ui' is switched by the first tap changer 4 in approximately 22 equal steps of approximately AUi' = 444 V within a range of approximately 23,228 V to approximately 33,000 V. This enables coarse step control of the output voltage Ui', as shown in Table 1.

[0048] Shown. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT)

[0049] Switching position first Ui[V] Ü1' [V] Ü2 [V] Load tap changer (center position) 29 - 35 (for

[0050] Undervoltage regulation < 33000 33000 1042 to -10%)

[0051] 28 32556 1028

[0052] 27 32112 1014

[0053] 26 31668 1000

[0054] 25 31224 986

[0055] 33000

[0056] 10 25004 790 9 24560 776

[0057] 8 24116 762

[0058] 7 23672 748

[0059] 1 - 6 (for

[0060] Overvoltage regulation > 33000 23228 734 to +10%)

[0061]

[0062] Table 1

[0063] In this embodiment, the first six and the last seven winding taps are used for regulating an undervoltage or an overvoltage, so that the input voltage U1 can fluctuate in the range of 33 kV + / - 10% without affecting the function of the rectifier arrangement.

[0064] Unlike the first transformer 1, the second transformer 5 in this embodiment is not an autotransformer, but has separate primary and secondary windings. This allows the windings to be pivoted. In this embodiment, the second transformer has a turns ratio of approximately 31.6:1 and is configured in a delta connection. Table 1 shows the output voltage U2 values ​​in a mid-position of the second tap changer 7, allowing the output voltage U2 to be finely adjusted by this value. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) In this embodiment, the second transformer 7 has 27 winding taps for fine adjustment. The winding taps are located on the primary winding of the second transformer 7, enabling fine adjustment of the voltage U2 with voltage steps of approximately ΔU2 = 1.17 V per step.Based on an input voltage of 33 kV, this enables highly accurate fine control of the output voltage in the range of approximately 0.003% of the input voltage.

[0065] With an initially coarsely set secondary voltage, the output voltage U2 can thus be regulated with high precision in a voltage step of approximately ΔU2 = 1.17 V to set the desired output current. Table 2 shows, as an example, the voltage steps of the output voltage for a secondary voltage Ui' = 33 kV. To achieve high precision, all 27 steps of the second load tap changer are used for fine-tuning the output voltage.

[0066] Switching position of second Ui' [V] U2 [V] Load tap changer

[0067] 27 1057.78 26 1056.62

[0068] 25 1055.45 24 1054.29 23 1053.12

[0069] 14 33000 1042.64

[0070] 5 1032.15 4 1030.99 3 1029.82

[0071] 2,1028.66

[0072] 1,1027.49

[0073]

[0074] Table 2 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) Fig. 2 shows a second embodiment of a rectifier arrangement according to the invention. In this embodiment, the first transformer 1 is designed as an autotransformer. This transformer, also known as an autotransformer, consists of only one coil, which has one or more taps for taking the output voltage. The primary and secondary sides are thus combined in a single coil. On the primary side, the first transformer 1 again has a number N > 1 of winding taps, wherein a load tap changer 4 connected to a regulator 3 is provided, which is designed for the uninterrupted switching of the winding taps 2 of the first transformer 1, so that the output voltage of the first transformer UT can be switched in N steps.

[0075] Four secondary transformers 5, 5', 5", 5'" are connected in series with the first transformer 1. These transformers convert the secondary voltage Ui' into parallel output voltages U2. Each secondary transformer is a separate component mounted on an iron core and includes a second tap changer (7, 7', 7", 7'") connected to the regulator 3. Passive rectifiers 8', 8", 8'" are connected in series with each of the secondary transformers 5, 5', 5", 5'" and are followed by ammeters 9, 9', 9", 9'" to measure the output current in each bridge. In this example, the four secondary transformers 5, 5', 5", 5'" and the four rectifiers 8, 8', 8", 8'" are single-phase but phase-shifted by 60°. In this exemplary embodiment, this results in a 24-pulse rectifier circuit.To implement a coarse and fine stepping circuit, the second load tap changers 7, 7', 7", 7'" switch a lower value of the output voltage U2 per step than the first load tap changer 4.

[0076] Fig. 3 shows a third embodiment of a rectifier arrangement according to the invention. This embodiment corresponds to that of Fig. 2, except that the second transformers 5, 5', 5", 5'" are designed as phase-shifted 3-winding transformers. This results in a 48-pulse rectifier circuit in this embodiment. For each of the two secondary-side windings, two rectifiers 8, 8', 8", 8'" and two ammeters 9, 9', 9", 9" connected to the regulator 3 are provided. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) Fig. 4 shows an embodiment of a system according to the invention comprising four rectifier arrangements connected in parallel according to the invention, wherein the first load tap changers 4, 4', 4“, 4'“ and the second load tap changers 7, 7', 7“, 7'“ of each rectifier arrangement are connected to a central controller 3.

[0077] Fig. 5 shows another embodiment of a rectifier arrangement according to the invention. This embodiment corresponds to that of Fig. 3, except that the first transformer 1 is designed as a two-winding transformer. The second transformers 5, 5', 5", 5'" are designed as phase-shifted three-winding transformers. This results in a 48-pulse rectifier circuit in this embodiment. For each of the two secondary-side windings, two rectifiers 8, 8', 8", 8'" and two ammeters 9, 9', 9", 9" connected to the regulator 3 are provided. By pivoting the windings of the first transformer 1, a 96-pulse configuration can be achieved.

[0078] The invention is not limited to the embodiments shown here, but encompasses any rectifier arrangement within the scope of the following claims. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT)

[0079] Reference symbol list

[0080] 1, 1', 1", 1"' First transformer

[0081] 2 winding taps of the first transformer 3 regulators

[0082] 4 4 ', 4", 4"< First load tap changer

[0083] 5, 5', 5", 5"' Second transformer

[0084] 6 winding taps of the second transformer 7, 7', 7", 7"' Second load tap changer

[0085] 8, 8', 8", 8"' rectifier

[0086] 9, 9', 9", 9"' ammeter

[0087] 10, 10', 10", 10"' voltmeter

Claims

65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) Patent claims 1. Rectifier arrangement for hydrogen electrolysis, comprising a. a first transformer (1) for transforming an input voltage U1 into a secondary voltage U1', wherein b. the transformer (1) has a number N > 1 winding taps (2), and wherein c. a load tap changer (4) connected to a controller (3) is provided, which is designed for the uninterrupted switching of the winding taps (2) of the first transformer (1) so that the output voltage Ui' can be switched in N steps, characterized by the fact that d. a second transformer (5) is provided for transforming the secondary voltage U1' into an output voltage U2 with a number M > 1 winding taps (6), wherein e. a second load tap changer (7) connected to the regulator (3) is provided, which is designed for the uninterrupted switching of the winding taps (6) of the second transformer (5), wherein f. the first transformer (1) is connected in series with the second transformer (5) so that the output voltage U2 can be switched in N x M steps, wherein g. the first transformer (1) and the second transformer (5) are arranged on separate iron cores, and wherein h. a passive rectifier (8) is provided at the output of the second transformer (5) to generate an output DC current IDC and an output DC voltage UDC.

2. Rectifier arrangement according to claim 1, characterized in that the first transformer (1) has a primary winding and a galvanically isolated secondary winding, wherein the winding taps are provided on the primary winding. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) 3. Rectifier arrangement according to claim 1, characterized in that the first transformer (1) is an autotransformer, wherein the input voltage Ui and the secondary voltage Ui' are tapped from the same winding.

4. Rectifier arrangement according to one of claims 1 to 3, characterized in that the output voltage U2 is adjustable in coarse steps via the first load tap changer (4) and in fine steps via the second load tap changer (7).

5. Rectifier arrangement according to one of claims 1 to 4, characterized in that the rectifier (8) is designed as a passive diode bridge rectifier.

6. Rectifier arrangement according to one of claims 1 to 5, characterized in that the transformers (1, 5) and the rectifier (8) are multiphase, wherein the load tap changers (4, 7) are multiphase, in particular three-phase, or several, in particular three, single-phase load tap changers (4, 7) are provided.

7. Rectifier arrangement according to one of claims 1 to 6, characterized in that the regulator (3) is connected to an ammeter (9) for measuring the output current IDC and optionally also to a voltmeter (10) for measuring the output voltage UDC.

8. Rectifier arrangement according to one of claims 1 to 7, characterized in that several parallel-connected second transformers (5, 5', 5", 5'") and rectifiers (8, 8', 8", 8'") are provided, wherein the second transformers (5, 5', 5", 5'") each have separate iron cores and each have second load tap changers (7, 7', 7", 7'") which are connected to the regulator (3). 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) 9. Rectifier arrangement according to one of claims 1 to 8, characterized in that the second transformer(s) (5, 5', 5“, 5'“) are designed as two-winding transformers or as multi-winding transformers, in particular as three-winding transformers with one primary winding and two secondary windings.

10. Rectifier arrangement according to claim 8 or 9, characterized in that the regulator (3) is connected to an ammeter (9, 9', 9", 9'") for measuring the output current IDC, IDC, IDC", IDC"' of each rectifier (8, 8', 8", 8'") and optionally also to a voltmeter (10, 10', 10", 10'") for measuring the output voltage UDC, UDC', UDC", UDC"' of each rectifier (8, 8', 8", 8'").

11. Rectifier arrangement according to one of claims 8 to 10, characterized in that the controller (3) is configured to perform an unbalanced load compensation between the second transformers (5, 5', 5", 5'") and rectifiers (8, 8', 8", 8'") in a subordinate control loop, and to set the desired output current IDC in a superordinate control loop.

12. Rectifier arrangement according to one of claims 1 to 11, characterized in that several parallel-connected first transformers (1, T, 1“, T“) are provided, each having separate iron cores and each having first load tap changers (4, 4', 4“, 4'“) which are connected to the regulator (3).

13. Rectifier arrangement according to one of claims 1 to 12, characterized in that the input AC voltage Ui has an amplitude of over 10 kV, in particular about 20 kV to 33 kV, and the output DC voltage UDC has a nominal value of about 300 V to about 2000 V, for example about 1200 V. 65210 / AG / - Andritz AG, Stattegger Strasse 18, 8045 Graz (AT) 14. Rectifier arrangement according to one of claims 1 to 13, characterized in that the first transformer (1) has a rated electrical power of over about 6 MVA, for example in the range of 15 MVA to 30 MVA.

15. Rectifier arrangement according to one of claims 1 to 14, characterized in that two or more second transformers (5, 5', 5", 5'") are provided, wherein the output voltages of the transformers (5, 5', 5", 5'") are phase-shifted by an angle Acp and wherein a rectifier (8, 8', 8", 8'") is provided for each of the second transformers (5, 5', 5", 5'") to generate the output DC current IDC and the output DC voltage UDC.

16. Rectifier arrangement according to one of claims 1 to 15, characterized in that the second transformer (5, 5', 5“, 5'“) has a rated electrical power which is lower than that of the first transformer (1), for example in the range of about 500 kVA to about 10 MVA.

17. System comprising several parallel-connected rectifier arrangements according to any one of claims 1 to 16, wherein the load tap changers (4, 4', 4“, 4'“, 7, 7', 7“, 7'“) of each rectifier arrangement are connected to a central controller (3).

18. Use of a rectifier arrangement according to any one of claims 1 to 17 for generating an output direct current IDC of more than about 600 A, preferably more than about 2 kA, preferably more than about 20 kA, at an output direct voltage in the range of about 300 V to about 1500 V, in particular about 1350 V, for hydrogen electrolysis, in particular PEM electrolysis or alkaline electrolysis.

19. Use according to claim 18, characterized in that the first load tap changers (4) provide coarse control of the output voltage with voltage steps of approximately + / - 10% and the second load tap changers (7) provide fine control of the output voltage with voltage steps of less than + / - 0.1%, in particular less than + / - 0.01% of the input voltage.

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