Method for supplying a consumer, in particular an electrolyser, with a DC voltage, and device for carrying out the method
Patent Information
- Application Number
- EP2024702510
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-21
- Filing Date
- 2024-01-26
- Publication Date
- 2025-12-31
AI Technical Summary
Existing systems for supplying direct voltage to electrolyzers face challenges in ensuring safe and efficient operation across both single-stage and two-stage configurations, particularly in managing voltage and current characteristics to achieve high performance at varying power levels.
The method involves using inverters and converters in conjunction with switching means, allowing for parallel or series operation depending on current capacity, with a selected characteristic curve that enables seamless switching between single-stage and two-stage modes within a defined switching range, ensuring reliable operation and easy design rule implementation for voltage and current combinations.
This approach allows for high-performance operation at both low and high voltages by evenly utilizing rectifier and converter capabilities, ensuring safe and efficient power delivery to electrolyzers across the entire power spectrum, with parameters like voltage and power limits defining the switching range for reliable operation.
Smart Images
Figure EP2024051837_29082024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] title
[0003] Method for supplying a consumer, in particular an electrolyzer, with a direct voltage and a device for carrying out the method
[0004] The invention relates to a method for supplying a consumer, in particular an electrolyzer, with a direct voltage and a device for carrying out the method according to the preamble of the independent claims.
[0005] State of the art
[0006] EP 3752665 B1 discloses a circuit arrangement, a method for operating a circuit arrangement, and an electrolysis device. For supplying direct current to a plurality of electrolyzers connected in parallel, the circuit arrangement comprises a rectifier that converts an input AC voltage into a first output DC voltage. Each electrolyzer is connected in parallel to the output of the rectifier via a step-down converter that converts the first DC voltage into a second DC voltage such that the second DC voltage drops across the electrolyzer. Each of the step-down converters is designed to be controllable and / or adjustable to adjust the level of its second DC voltage. The circuit arrangement comprises a plurality of switches, each step-down converter being bridgeable by a respective switch.
[0007] The invention is based on the object of ensuring safe operation of the consumer, in which both single-stage and two-stage operation can be reliably achieved. This object is achieved by the features of the independent claims.
[0008] Disclosure of the invention
[0009] The method according to the features of independent claim 1 has the advantage that a more uniform utilization of the inverter and converter as well as the associated switching means is possible. In single-stage operation, the converter is operated in parallel with the rectifier, whereas in two-stage operation the converter is operated sequentially in series after the rectifier. Assuming the rectifier or converter has a current carrying capacity of 50% of the maximum current, 50% of the maximum current can be served in the two-stage configuration, making it particularly suitable for the lower half of the power spectrum, whereas in single-stage operation 100% of the maximum current can be served by adding the individual currents. This means that low voltages as well as high power outputs can be achieved at high voltages due to a high maximum current.According to the invention, the characteristic curve of the load, in particular of the electrolyzer, is selected such that it runs through a switching range, wherein a change from single-stage operation to two-stage operation and vice versa is possible in the switching range. This makes it particularly easy to describe corresponding design rules, in particular for voltage and current, for the combination of load and power electronics (rectifier and converter with associated switching devices, etc.). Safe operation that covers both operating cases is reliably achieved. According to the invention, a characteristic curve of the load is selected such that it runs through a switching range in which a change between single-stage operation and two-stage operation is possible.This makes it particularly easy to define appropriate design rules for voltage and current for the combination of the respective load, especially the electrolysis stack, and the power electronics. It is particularly preferable to select the load's characteristic curve so that it does not enter a range where switching between single-stage and two-stage operation is not possible. This allows the aforementioned advantages to be achieved.
[0010] In a practical development, it is provided that the switching range depends on at least one voltage limit, in particular as a function of a phase voltage of the power source, and / or in particular as a function of a maximum voltage for which the rectifier and / or the DC-DC converter or their switching means are designed. This allows for easy parameterization depending on the respective power source and / or the respective power electronics used. Particularly preferably, the switching range depends on at least one power limit.
[0011] A practical development provides for the switching range to be selected so that the voltage at the load lies between an upper voltage limit and a lower voltage limit, and the power at the load lies below a power limit. These parameters enable reliable switching between the two modes.
[0012] Further useful developments arise from further dependent claims and from the description.
[0013] Short description of the drawing
[0014] They show:
[0015] Figure 1 shows the cell voltage as a function of cell current density and temperature,
[0016] Figure 2 shows the voltage of the electrolyzer as a function of current and temperature,
[0017] Figure 3 shows a schematic diagram of the circuit arrangement,
[0018] Figure 4 shows a concrete circuit arrangement of the principle shown in Figure 3,
[0019] Figure 5 shows the circuit arrangement according to Figure 4 in a two-stage operation,
[0020] Figure 6 shows the circuit arrangement according to Figure 4 in a single-stage operation, in which the converter is operated as a rectifier connected in parallel with the rectifier, Figure 7 shows an alternative embodiment of a circuit arrangement with a common output coil,
[0021] Figure 8 shows an example limit characteristic curve for two-stage operation,
[0022] Figure 9 shows an example limit characteristic curve for single-stage operation,
[0023] Figure 10 shows the relationship between the voltage characteristic of a consumer, in particular an electrolyzer, and the characteristic of the alternating concept of the operating stages, as well as
[0024] Figure 11 shows an illustration of an inappropriate matching of the characteristic curves with possible remedial measures.
[0025] Embodiment of the invention
[0026] The invention is illustrated schematically using several embodiments and is described in detail below with reference to the drawing.
[0027] Figure 1 shows the dependence of the cell voltage Uz of a cell of a possible consumer, in particular an electrolyzer 40, as a function of the current density j and the temperature T. An electrolyzer 40 is used in the electrolysis of water to produce hydrogen and oxygen using electrical current. The electrolyzer 40 is formed by a large number of individual cells connected in series, each having a cell voltage Uz. In principle, the cell voltage Uz increases with the cell current density j and with decreasing temperature T. In reality, the cell voltage Uz depends on the state of aging. With increasing age, the cell voltage Uz also increases. However, this relationship is not shown in Figure 1.
[0028] Figure 2 shows the voltage U of the consumer, in particular the electrolyzer 40, as a function of current I and temperature T. The dependence on current I, temperature T and aging state is maintained during the transition from the cell to the electrolyzer 40. The relationships shown in Figures 1 and 2 demonstrate that, especially at low voltages U, particularly with certain inverter types, special efforts are necessary to make these low voltages U available to the consumer, in particular the electrolyzer 40. As an example, a dashed line is drawn which indicates that, in particular at low currents (for example, less than between 375 and 400 A), two-stage operation 23 is expedient, and at higher currents, single-stage operation 21 is expedient to ensure sufficient supply to the consumer, in particular the electrolyzer 40.
[0029] For consumers, in particular electrolyzers 40, powerful current sources or power sources 12, such as a grid connection, are required. Rectifiers are used to convert the alternating voltage into a direct voltage U suitable for the consumer, in particular electrolyzer 40. If an active bridge circuit, in particular an active B6 bridge, is used as the bridge circuit, this results in a lower voltage limit that cannot be undercut. For conventional 400 V phase voltages, this lower voltage limit is in the range of approximately 600 V. Looking at Figure 2, it is clear that two-stage rectifier concepts must be used, using an additional step-down converter.
[0030] Figure 3 shows a schematic of the circuit layout as specified in more detail in Figures 4-7. The upper layout is designed for two-stage operation 23. Via coils 14, which enable boost converter operation, a rectifier 16 is supplied like a mains connection from a power source 12 providing alternating current. The alternating voltage rectified by the rectifier 16 is fed via an intermediate circuit 26 to a converter 30, which is operated as a DC-DC converter in two-stage operation 23. The load, in particular electrolyzer 40, is supplied with DC voltage via the additional coils 38 and a common output coil 46. The lower layout is designed for single-stage operation 21. The converter 30 is then operated as a rectifier 30, connected in parallel to the rectifier 16, via the additional coils 38.The DC voltage then reaches the consumer, in particular electrolyzer 40, via the intermediate circuit 26 and the common output coil 46 to supply it.
[0031] Figure 4 shows an example of the circuit implementation of the concept shown in Figure 3. The power source 12 is schematically designed as a three-phase mains connection. The circuit arrangement for supplying the electrolyzer 40 comprises at least one rectifier 16 designed as a bridge circuit, which is connected via an intermediate circuit 26 to a converter 30, which is also designed as a bridge circuit. The converter 30 serves as a step-down converter if necessary to access the lower voltages U. The rectifier 16 serves as a power converter and comprises, for example, three rectifier branches 20, 22, 24 connected in parallel. In each of the rectifier branches 20, 22, 24, two switches 18 are arranged in series.In Figure 4, semiconductor switches such as IGBTs (Insulated Gate Bipolar Transistors) are used as switches 18 by way of example, but other controllable power semiconductors such as MOSFETs, for example made of SiC, GaN, etc., can just as well be used. Between the two switches 18 of a rectifier branch 20, 22, 24, the individual phases of the power source 12 are electrically contacted via a coil 14 each. The rectifier 16 is thus constructed as an active B6 bridge. The two outputs of the rectifier 16 are connected to the intermediate circuit 26. The rectifier 16 therefore converts the alternating voltage of the power source 12 into a direct voltage, which is used to feed the intermediate circuit 26. An intermediate circuit capacitor 28 is connected to the two outputs of the rectifier 16 in the intermediate circuit 26. The intermediate circuit 26 in this exemplary embodiment is therefore a direct voltage intermediate circuit.
[0032] A further converter 30 is provided, which again comprises, for example, three parallel branches 32, 34, 36. In each of the parallel branches 32, 34, 36, two switches 18 are arranged in series. The common potentials of the branches 32, 34, 36 are in turn connected to the intermediate circuit 26. Like the rectifier 16, the converter 30 can also be connected to the power source 12. For this purpose, an electrically conductive contact is made between the two switches 18 of a branch 32, 34, 36 with the respective phases of the power source 12, which contact is each conducted via corresponding further coils 38 and each via a first switch 41.The three phases, each routed via the first switch 41, are, on the one hand, fed to the converter 30 via the respective additional coils 38, and, on the other hand, are routed at a branching point via additional switches 42 provided for each phase. After the additional switch, they are brought together at the same potential for further contacting the input of the electrolyzer 40. Via a third switching means 43, the common (upper) potential of the intermediate circuit 26 located between the rectifier 16 and the converter 30 is routed to the input of the electrolyzer 40. The additional input of the electrolyzer 40 is at the same (lower) potential as the reference potential of the intermediate circuit 26 or of the two bridge circuits 16, 30, which are also connected to the additional input of the electrolyzer 40.
[0033] The switches 41, 42, 43 are components of a switch unit that enable the optional operation of the converter 30 as a rectifier or AC / DC converter, in particular connected in parallel to the rectifier 16, which also functions as a boost converter or AC / DC converter, and as a DC / DC converter, in particular as a step-down converter. The switch unit enables both single-stage operation 21 (parallel connection of the two bridge circuits 16, 30 and operation as a rectifier or AC / DC converter) and two-stage operation 23 (the converter 30 forms the further stage and functions as a DC / DC converter or DC / DC converter, in particular a step-down converter, sequentially coupled to the intermediate circuit 26). The different operating modes with the associated positions of the switches 41, 42, 43 of the switch unit are shown in the following Figures 5 and 6.
[0034] Figure 5 shows the switch positions in two-stage operation 23. The first switches 41 are open. Therefore, there is no feed-in or supply of the converter 30 from the power source 12 via the additional coils 38. Likewise, there is no conductive connection between the intermediate circuit 26 and the first input of the load, in particular the electrolyzer 40. The output voltage (DC voltage) of the rectifier 16 serves as the input voltage for the converter 30. The associated third switch 43 is open. However, the additional switches 42 are all closed, so that the rectified voltage waveforms, each for the branches 32, 34, 36 of the converter 30 between two switching devices 18 via the additional coils 38, are combined (after the additional switch 42 is closed) and fed to the input of the load, in particular the electrolyzer 40. The rectifier 16 and the converter 30 are therefore connected in series.Rectifier 16 functions as an AC / DC converter in boost converter mode. Converter 30 functions as a DC / DC converter. In DC / DC converter mode, the additional coils 38 have a smoothing effect and prevent the formation of circulating currents. Preferably, the coils 14 upstream of the AC / DC side (of rectifier 16) and downstream of the DC / DC side (of converter 30) are constructed identically.
[0035] Figure 6 shows the switch positions in single-stage operation 21. The first switches 41 are closed. The remaining switches 42 are open. The third switch 43 is closed. The arrows symbolize the corresponding current flows.
[0036] The phases are each fed in parallel via coils 14 to the rectifier 16. The phases of the power source 12 are also fed to the converter 30 via the additional coils 38 and, after AC / DC conversion (by appropriately controlling the switching means 18 in the respective B6 bridges at the appropriate times), equally feed the intermediate circuit 26. The positive intermediate circuit potential is fed via the third switch 43 to the input of the consumer, in particular the electrolyzer 40. The reference potential of the intermediate circuit 26 is fed to the additional input of the electrolyzer 40. If the coils 14 and the additional coils 38 have the same dimensions, the boost converter coils are also identical.
[0037] Unlike the prior art, the rectifier 16 and the converter 30 are used equally in each of the operating modes (single-stage operation, two-stage operation). Assuming a current carrying capacity of 50% of the maximum current of the two bridge circuits 16, 30, 50% of the maximum current can be served in the two-stage configuration, i.e., the lower half of the power spectrum, whereas in single-stage operation, 100% of the maximum current can be served by summing the individual currents.
[0038] The embodiment according to Figure 7 is characterized by a common output coil 46. This common output coil 46 is arranged between the common potential of the further switches 42 and the third switch 43 and the input of the consumer, in particular electrolyzer 40, and serves to smooth the output current.
[0039] Figure 8 shows an example limit characteristic curve for two-stage operation 23. A UI diagram shows the permissible voltage range U (voltage drop across the load or electrolyzer 40) as a function of the current I across the load or electrolyzer 40. The permissible range 63 in two-stage operation 23 is essentially characterized by two conditions: first, the voltage U must be below the voltage limit Us, which is defined by the switching devices 18 used or installed. In the exemplary embodiment, the voltage limit Us is 800 V.
[0040] On the other hand, the required power P must be below the power limit Pg2 of the power electronics in two-stage operation 23. This condition results in a hyperbola in the current-voltage diagram according to Figure 8, since: P = U * I. In the present example, a power limit Pg2 of 1.5 MW was chosen. This power limit Pg2 depends on the respective topology and type of rectifier 16 or converter 30 used. For example, it is assumed that there are six parallel converters, each with a power of 250 kW per inverter. For example, in single-stage operation 21, 12 inverters can be connected in parallel. In two-stage operation 23, two inverters must be connected in series, 6 of them in parallel.
[0041] This results in a permissible voltage range of 63 for two-stage operation 23 if both of the following conditions are met:
[0042] U < Us AND P <Pg2.
[0043] Figure 9 shows the permitted voltage range 61 for single-stage operation 21. The permitted range is essentially characterized by three conditions: the voltage U must be below the voltage limit Us, which is defined by the switching devices 18 used or installed. In the exemplary embodiment, the voltage limit Us is 800 V. the voltage U must be above the rectified voltage Ug of the network or power source 12. The rectified voltage llg is calculated as a function of the phase voltage Up of the network or power source 12 as follows: Ug = Up * root (2). In the present example, with a phase voltage of 400 V and a voltage fluctuation of the network 12 of +-10%, this results in a maximum voltage Ug of approximately 620 V, which is shown as an example in Figure 9.
[0044] The required power P must be below the power limit Pg1 of the power electronics in single-stage operation 21. As a first approximation, this power limit Pg1 is twice as high in single-stage operation 21 due to the parallel connection of rectifier 16 and converter 30 than in the two-stage case (2*Pg2). This condition results in a hyperbola in the current-voltage diagram, since again: P = U * I. In this diagram, a power limit Pg1 of 3 MW was chosen as an example.
[0045] This results in a permissible voltage range 61 for the two-stage operation 23 if both of the following conditions are met:
[0046] Ug < U < Us AND P <Pg1.
[0047] Figure 10 shows the relationship between the permissible ranges (switchover range 60, permissible range 61 for single-stage operation 21, permissible range 63 for two-stage operation 23) and the impermissible range 62, as shown in Figures 8 and 9 for the different modes of operation. The switchover range 60 is understood to be the range where both permissible ranges 61, 63 of single-stage and two-stage operation 21, 23 overlap, i.e., where switching between single-stage operation 21 and two-stage operation 23 and vice versa is possible.
[0048] In detail, for the two-stage operation 23, there is a permissible voltage range, which is represented by the permissible range 63 and the switching range 60 (as part of the permissible range 63 as shown in Figure 8) with, for example,
[0049] U < Us (800V) AND P < Pg2 (1.5 MW).
[0050] For the single-stage operation 21, a permissible voltage range 61 results, which is described by the permissible range 61 and the switching range 60 (as part of the permissible range 61 as shown in Figure 9) with, for example, Ug (620 V) < U < Us (800 V) AND P < Pg1 (3 MW).
[0051] This results in a current-voltage range that can be served by both the single-stage operation 21 and the two-stage operation 23 and is referred to as switching range 60. The switching range 60 satisfies the following conditions, for example:
[0052] Ug (620 V) < U < Us (800 V) AND P < Pg2 (1.5 MW).
[0053] This also results in a current-voltage range that cannot be served by either the single-stage operation 21 or the two-stage operation 23. This range is therefore referred to as the prohibited range 62. The prohibited range satisfies, for example, the following conditions:
[0054] U < Ug (620 V) AND P > Pg2 (1.5 MW).
[0055] In order to be able to operate the consumer, in particular electrolyser 40, in combination with the switching concept between the single-stage operation 21 and the two-stage operation 23, two conditions for a desired characteristic curve 66 of the consumer, in particular electrolyser 40, must be met: the characteristic curve 66 must pass through the switching area 60 in order to enable switching between the two operations 21, 23 the characteristic curve 66 must never pass through the prohibited area 62.
[0056] These conditions are met for the desired characteristic curve 66 shown in Figure 10. In addition, a latest switching point 70 is shown, at which switching is just possible within the switching range 60 before the forbidden range 62 is reached.
[0057] The following assumptions have been made for the design as an example. There are six parallel inverters (number of inverters) with an output of 250 kW per inverter and a maximum voltage U_max (or Us) of 800 V. One inverter represents a converter 30 or rectifier 16. For two-stage operation 23, the following is calculated: Pmax or Pg2 = 6 * 250 kW = 1.5 MW. For single-stage operation 21, the maximum output is calculated: Pg1 = 12 * 250 kW = 3 MW. In single-stage operation, voltages < 620 V (Ug as the rectified phase voltage of the network 12) are no longer achievable. Voltages Us greater than 800 V cannot be achieved either. The maximum output Pmax of 3 MW cannot be exceeded either.In addition to these boundary conditions, it is essential that the characteristic curve 66 of the consumer, in particular electrolyzer 40, is selected such that the characteristic curve 66 passes through the switching area 60 and at the same time does not pass through the prohibited area 62.
[0058] Figure 11 shows a critical design of the stage change concept for a specific consumer, specifically electrolyzer 40. In addition to the boundary lines for single-stage operation 21 and two-stage operation 23, a problematic characteristic curve 68 at 50 °C and a problematic associated characteristic curve 69 at 70 °C (temperature of the consumer or electrolyzer 40) are shown. The problematic characteristic curve 69 clearly passes through the prohibited area 62 in a problematic area 72. The problematic characteristic curve 68 also slightly touches the prohibited area 62.
[0059] In the following, countermeasures 74, 76, 78 are explained, which are shown in the form of arrows in Figure 11 and are intended to indicate how the characteristic curves 68, 69 can be brought out of the forbidden area 62 or how the forbidden area 62 can be shifted so that the characteristic curves 68, 69 are no longer in the forbidden area.
[0060] A possible countermeasure 74 could be an increase in the number of cells installed in the stack of the electrolyzer 40, which would lead to an upward parallel shift of the characteristic curve 68, 69. For the same current I, a higher voltage U is achieved with a higher number of cells in the stack.
[0061] A further possible countermeasure 74 could consist in a reduction of the temperature T of the consumer, in particular of the electrolyzer 40 or the stack temperature in the critical range, which also leads to a parallel shift of the characteristic curve 68, 69 upwards.
[0062] A further possible countermeasure 76 could consist in increasing the performance of the power electronics or switching means 18, which leads to a parallel shift of the hyperbola and thus of the limit value Pg1, Pg2 or Pmax to the top right.
[0063] Another possible countermeasure 78 could be the use of a voltage converter or a transformer at the input with a modified winding ratio, which leads to a reduction of the phase voltage Up and thus of the rectified voltage Ug.
[0064] Another possible countermeasure could be the use of power electronics or switching means 18 with higher dielectric strength, which leads to an increase in the limit value Us.
[0065] If necessary, the measures or individual measures 74, 76, 78 can also be combined with each other.
[0066] The circuit arrangement described is particularly suitable for the operation of an electrolyzer 40 or comparable systems which must be supplied from an alternating voltage network with direct voltage over a wide voltage range at high power levels.
Claims
Claims 1. A method for supplying a consumer, in particular an electrolyzer (40), with a direct voltage, comprising at least one rectifier (16) for converting an alternating voltage provided by a power source (12) into a direct voltage, comprising at least one converter (30) which can be connected to the rectifier (16) via an intermediate circuit (26), wherein in a single-stage operation (21) the converter (30) is operated in parallel with the rectifier (16), so that the converter (30) is used as a rectifier (30) to convert the alternating voltage provided by the power source (12) into a direct voltage, or in a two-stage operation (23) the converter (30) is operated as a direct voltage converter (30) connected downstream of the rectifier (16), for supplying the consumer, in particular the electrolyzer (40), with a voltage (U), wherein a characteristic curve (66) of the consumer (40) has a switching range (60) goes through,in which a change between single-stage operation (21) and two-stage operation (23) is possible., 2. Method according to claim 1, characterized in that the characteristic curve (66) of the consumer (40) does not pass through a region (62) in which no change between the single-stage operation (21) and the two-stage operation (23) is possible.
3. Method according to one of the preceding claims, characterized in that the switching range (60) depends on at least one voltage limit value (Ug, Us), in particular as a function of a phase voltage (Up) of the power source (12), and / or in particular as a function of a maximum voltage (Us) for which the rectifier (16) and / or the DC-DC converter (30) or their switching means (18) is designed.
4. Method according to one of the preceding claims, characterized in that the switching range (60) depends on at least one power limit value (Pg1, Pg2).
5. Method according to one of the preceding claims, characterized in that the switching range (60) is selected such that a voltage (U) at the consumer (40) lies both between an upper voltage limit value (Us) and a lower voltage limit value (Ug) and that a power (P) at the consumer (40) lies below a power limit value (Pg2).
6. Method according to one of the preceding claims, characterized in that the lower voltage limit value (Ug) depends on a phase voltage (Up) of the power source (12), in particular on a rectified phase voltage (Up).
7. Method according to one of the preceding claims, characterized in that the upper voltage limit value (Us) depends on a voltage limit of at least one switching means (18) used in the rectifier (16) and / or in the converter (30).
8. Method according to one of the preceding claims, characterized in that the power limit value (Pg1, Pg2) depends on a power limit or maximum power of the rectifier (16) and / or the converter (30) or inverter and / or on a number of rectifiers (16) and / or converters (30) used.
9. Method according to one of the preceding claims, characterized in that the range (62) in which no change between the single-stage operation (21) and the two-stage operation (23) is possible is defined such that the power (P) at the consumer (40) is above a power limit value (Pg2) and the voltage (U) at the consumer (40) is below the lower voltage limit value (Ug).
10. Method according to one of the preceding claims, characterized in that the characteristic curve (66) of the consumer (40) represents the relationship between the voltage (U) dropping across the consumer (40) of a describes the current (I) flowing through the consumer (40) and / or that the switching range (60) and / or the range (62) in which no switching between the single-stage operation (21) and the two-stage operation (23) is possible is described via the relationship between the voltage (U) dropping across the consumer (40) and a current (I) flowing through the consumer (40).
11. Method according to one of the preceding claims, characterized in that at least one countermeasure (74, 76, 78) is taken if the characteristic curve (66) does not run at least partially through the switching region (60).
12. Method according to one of the preceding claims, characterized in that as countermeasures a number of the rectifiers (16) and / or converters (30) is changed and / or that the number of cells installed in the electrolyzer (40) is changed and / or that the consumer (40) is operated at a changed, in particular lower, temperature and / or that switching means (18) used for the rectifier (16) and / or for the converter (30) are used with a changed, in particular higher, current-carrying capacity or dielectric strength and / or that the phase voltage (Up) of the power source (12) is reduced, for example by providing a voltage converter such as a transformer.
13. Method according to one of the preceding claims, characterized in that at least one coil (14, 38) is provided between the rectifier (16) and / or the converter (30) and the power source (12), and / or that at least one switching means (41) of a switch unit, which is provided for changing between the single-stage operation (21) and the two-stage operation (23), is provided between the power source (12) and the converter (30), and / or that at least one coil (38), in particular for each phase, is arranged, and / or that at least one switching means (42, 43) of the switch unit is arranged between the converter (30) and the consumer, in particular the electrolyzer (40), and / or that at least one switch (42) of the switch unit is arranged between the further coil(s) (38) and an input of the consumer, in particular the electrolyzer (40).
14. A device for supplying a consumer, in particular an electrolyzer (40), with a direct voltage, comprising at least one rectifier (16) for converting an alternating voltage provided by a power source (12) into a direct voltage, comprising at least one converter (30), characterized in that at least one switch unit (41, 42, 43) is provided, which either connects the converter (30) in parallel with the rectifier (16) in a single-stage operation (21), so that the converter (30) is used as a rectifier (30) to convert the alternating voltage provided by the power source (12) into a direct voltage, or in a two-stage operation (23) to operate the converter (30) as a direct-voltage converter (30) connected downstream of the rectifier (16), wherein the output voltage of the converter (30) serves to supply the electrolyzer (40),further configured to carry out the method according to one of the preceding claims.,