Method for supplying power to an electrolysis system, and power supply for an electrolysis system

Abstract

The invention relates to a method for supplying power (20) to an electrolysis system (100) having a plurality of electrolyzers (12.1, 12.2,... 12.n) and a plurality of power converters (10.1, 10.2,... 10.n). The electrolyzers (12.1, 12.2,… 12.n) are connected to respective power converters (10.1, 10.2,... 10.n) via respective DC lines (DC+, DC-). The power converters (10.1, 10.2,… 10.n) are electrically connected in parallel with one another to an AC network (18) on the AC side, in particular via a transformer (16). During the operation of the electrolysis system (100), at least one DC line (DC+, DC-) has a fixed reference to a ground potential (PE), in particular in that at least one DC_minus line (DC-) is connected to a ground potential (PE). The method has the steps of: - setting respective DC currents for the electrolyzers (12.1, 12.2,... 12.n) by means of the respective power converter (10.1, 10.2,... 10.n) in order to supply the respective electrolyzers (12.1, 12.2,... 12.n) on the basis of respective electrolyzer target values (SP1, SP2,... SPn), - determining a current ground reference of the electrolyzers (12.1, 12.2,... 12.n), and - limiting absolute values of DC_minus ground voltages (MU1, MU2,... MUn) of the DC_minus lines (DC-) with respect to the ground potential (PE) to a specifiable ground voltage limit value. The invention also relates to a power supply (20) for an electrolysis system (100) and to an electrolysis system (100).

Description

[0001] 24-065-P-WO - 1 - submitted version

[0002] METHOD FOR POWER SUPPLY OF AN ELECTROLYSIS PLANT AND POWER SUPPLY FOR AN ELECTROLYSIS PLANT

[0003] TECHNICAL AREA

[0004] The application relates to a method for supplying power to an electrolysis plant, a power supply for an electrolysis plant, and an electrolysis plant itself. The application specifically relates to the power supply of an electrolysis plant with a variable ground connection.

[0005] STATE OF THE ART

[0006] In an electrolysis plant, such as a power-to-gas plant, electrical energy, particularly from renewable sources, can be converted into storable gases, especially hydrogen. For this purpose, an electrolysis plant typically has a power supply that draws electrical power from a source, for example an alternating current (AC) grid, and feeds it as direct current (DC) into an electrolyzer.

[0007] An electrolyzer can comprise an array of multiple cells that work together to convert electrical energy into chemical reactions. Such an array of cells in an electrolyzer is called an electrolysis stack, or simply stack. This allows, for example, water to be split into its components – hydrogen and oxygen. Each stack consists of several electrolysis cells connected in series or parallel. The cells contain electrodes where the electrolysis reactions take place, as well as membranes that separate the resulting gases and ions.

[0008] The grounding of such systems plays a crucial role for several reasons. German patent DE881826 already describes an electrolysis system with a series connection of electrolysis baths, in which a midpoint of the series connection is kept at ground potential as close as possible, and a shift of the midpoint relative to ground potential represents a ground fault. EP 4200463 B1 discloses an electrolysis system connected to ground potential via an ohmic resistor. WO 2024 / 17633 A1 discloses an electrolysis system with a ground connection that can be switched on and / or adjusted as needed, which is used as a protective earth and is intended, in particular, to prevent corrosion caused by any stray currents.

[0009] In electrolysis plants with multiple electrolyzers that are to have a specified DC ground reference, power converters with AC-DC bridge circuits are used, in particular, for the transfer of electrical power between the electrolyzers and an AC network, as described in 2-24-065-P-WO - 2 - submitted version.

[0010] Level topology and / or DC-DC converters are used between the DC terminal and the AC-DC bridge circuit to decouple the DC potentials of the electrolyzers from each other and / or from the AC potentials.

[0011] TASK

[0012] The application is based on the task of providing a method for power supply and a power supply for electrolyzers that enables individual operation of the electrolyzers while simultaneously ensuring a predetermined ground reference for the electrolyzers.

[0013] SOLUTION

[0014] The problem is solved by a method with the features of independent claim 1 and a service provision with the features of independent claim 23. Embodiments are specified in the dependent claims.

[0015] DESCRIPTION

[0016] An electrolysis plant comprises several electrolyzers and several power converters. The electrolyzers are connected to their respective power converters via DC lines, with the power converters being electrically connected in parallel to each other on the AC side, in particular via a transformer, to an AC network. During operation of the electrolysis plant, at least one DC line has a fixed reference to earth potential, in particular by connecting at least one DC negative line of an electrolyzer to earth potential.

[0017] A method for supplying power to such an electrolysis plant exhibits:

[0018] A) Setting the respective DC currents to the electrolyzers by the respective power converter to supply the assigned electrolyzers depending on the respective electrolyzer setpoints,

[0019] B) Determining the current ground reference of the electrolyzers, and

[0020] C) Limiting the absolute values ​​of DC_minus earth voltages of the DC_minus lines relative to earth potential to a predefinable earth voltage limit value.

[0021] The term "ground reference" refers to a potential difference relative to ground potential. Each electrolyzer has a ground reference in that the connection between each power converter and the electrolyzer, via the respective DC lines, maintains a current potential difference relative to ground potential. Specifically, the DC_minus and DC_plus lines of each electrolyzer have a DC_minus-ground connection. (24-065-P-WO - 3 - submitted version)

[0022] Voltage or a DC_positive earth voltage relative to earth potential is present, which differs by the DC voltage applied to this electrolyzer at a set DC current. In step C) of the application procedure, the earth reference of the electrolyzers is adjusted so that none of the DC_negative lines exhibits a DC_negative earth voltage whose absolute value is greater than the predefinable earth voltage limit.

[0023] The power converter transforms electrical power supplied via the AC grid into DC power for the associated electrolyzer. The power converter thus acts as a rectifier. The power conversion within the power converter is achieved, for example, by means of a bridge circuit with controllable power switches. The power conversion can be controlled, for example, by switching the power switches of the bridge circuit. The control of the power switches can be carried out by a control unit within the power converter. By controlling the power switches, the DC current supplying the associated electrolyzer can be adjusted. This adjustment of the DC current can be dependent on a specific electrolyzer setpoint, which can be specified directly as the electrolyzer DC current setpoint or indirectly as the electrolyzer power setpoint.The power converter can be specifically designed to convert and transfer electrical power in any of the possible directions. In particular, it can be operated as both a rectifier and an inverter.

[0024] The described method enables a defined DC grounding of the electrolyzers in an electrolysis plant with various types of power converters, particularly without an additional DC converter. This method allows the intermediate circuits of the individual power converters to be decoupled from each other, while simultaneously maintaining a determinate ground reference for the electrolysis plant as a whole. The decoupling can also include monitoring and limiting of the respective ground current.

[0025] Limiting the absolute voltage values ​​of the DC_negative lines relative to ground potential can reduce corrosion and other degradation effects in the electrolyzers. Furthermore, the insulation requirements can be reduced, as lower voltages of the DC_negative lines relative to ground can be ensured.

[0026] Limiting the absolute voltage values ​​of the DC negative lines relative to ground potential to the predefinable ground voltage limit can be achieved in various ways. For example, it can be implemented with autonomous control of the DC voltages of the electrolyzers in the respective control unit within the respective power converter, thus eliminating the need for a higher-level control unit in the electrolysis plant. Alternatively or additionally, limiting can be achieved with a superimposed 24-065-P-WO - 4 - submitted version

[0027] Control can be implemented in a higher-level control unit, where the electrolyzer setpoints are predefined and / or the ground reference is adjusted. Alternatively or additionally, the respective voltages can be limited via adjustable grounding resistors.

[0028] In one embodiment of the method, the power converters are essentially identical in construction. With essentially identical power converters, the method for limiting the absolute values ​​of the voltages of the DC negative lines relative to ground potential can be implemented more easily due to the identical construction of the power converters. However, embodiments with power converters that differ in their design are also conceivable.

[0029] The power converters feature semiconductor bridge circuits with a three-level topology and shared DC links. The described method enables defined DC grounding of the electrolyzers even with power converters with a three-level topology, which, in particular, do not require an additional DC regulator. Although the DC links of the individual power converters with a three-level topology are connected to the center potential of the AC lines via galvanic coupling of the respective DC link centers and subsequently to each other via the AC-side parallel connection, allowing, among other things, circulating currents to flow between the DC links, the DC currents and thus the DC voltages can be set independently of each other, while simultaneously maintaining a deterministic ground reference.The decoupling of the DC voltages from the DC_minus-earth voltages achieved in this way can also include monitoring and limiting of a respective earth current and corresponding circulating currents via the AC-side parallel connection between the power converters.

[0030] Specifically, when using power converters with a 3-level topology, each with a shared DC link, the center points of the shared links can have a largely identical ground reference via the AC-side parallel connection. The described method also enables safe DC-side grounding when using such power converters that have a common reference potential for the DC link via the AC lines, whereby the DC negative ground voltages are limited to the predefined ground voltage limit. Additionally, circulating currents arising via the AC-side parallel connection can be detected and limited.

[0031] In one embodiment of the method, adjusting the respective DC currents to the electrolyzers includes adjusting the respective DC voltages at the electrolyzers by the respective power converter. In this embodiment, the respective DC current, by means of which the respective electrolyzer is supplied with electrical power for carrying out the electrolysis, is generated via the respective DC voltage set by the respective power converter (24-065-P-WO - 5). The adjustment of the respective DC voltage and the respective DC current generated thereby can be carried out by the respective control unit of the power converter. The adjustment of the respective DC voltage can, in particular, be dependent on the respective electrolyzer DC current setpoint.

[0032] In one embodiment of the method, adjusting the respective DC currents involves adjusting AC currents by appropriately switching the semiconductor switches of the respective bridge circuit of the respective power converter. In this embodiment, the respective DC current, which supplies the respective electrolyzer with electrical power for electrolysis, is generated from the AC current set by the respective power converter and drawn from the AC grid. The adjustment of the respective AC current and the resulting respective DC current can be performed by the control unit of the respective power converter. The adjustment of the respective AC current can, in particular, be dependent on the respective electrolyzer DC current setpoint.

[0033] In one embodiment of the method, determining the current ground reference of the electrolyzers includes determining the respective DC-negative ground voltage of the respective DC-negative line of the respective power converter relative to ground potential. In this embodiment, the ground reference of each electrolyzer can be determined by determining the DC-negative ground voltage of the associated DC-negative line relative to ground. This determination of the ground reference of the electrolyzers can be performed, in particular, for each electrolyzer in the electrolysis plant. If the DC-negative ground voltage of one or more DC-negative lines is known, for example, because at least one direct connection between a DC-negative line and ground has been explicitly established, it is sufficient for the step of determining the current ground reference if the DC-negative ground voltages are determined only for the remaining DC-negative lines.In other words, if the DC_minus ground voltage of one or more DC_minus lines is known, this known ground reference can be used in the step of determining the ground reference of the entire electrolyzers and does not need to be determined separately again.

[0034] In one embodiment of the method, the DC negative-earth voltages of the power transformers are measured. Alternatively or additionally, the DC negative-earth voltages of the power transformers are determined from measurements of the voltage at the center point of a split DC link relative to ground potential and the voltage of the lower half of the split DC link of the respective power transformer. The center points of the split DC links of the power transformers can have a common reference to ground via the AC-side parallel connection. From the respective voltage of the lower half of the split DC link of a power transformer, the 24-065-P-WO - 6 - submitted version can then be determined.

[0035] The DC negative ground voltage of the DC negative line of the respective power converter can be derived. This embodiment is particularly advantageous for power converters with a split intermediate circuit, as a direct measurement of the DC negative ground voltage can be omitted and the voltage of the lower half of the intermediate circuit can be used, which may already be present, for example, in the control unit of the power converter. Furthermore, the voltage at the center point of the split DC intermediate circuit of a power converter relative to ground potential can be determined either directly by a DC-side measurement between the respective center point and ground potential, or indirectly by an AC-side measurement of the voltage at the center potential of the AC lines relative to ground potential.

[0036] In one embodiment of the method, several, in particular all, DC negative lines can each be connected to earth potential, especially via individual grounding resistors, the respective grounding resistors being optionally adjustable. A connection of each DC negative line to earth potential can be established, for example, via a DC switch, with a grounding resistor being arranged in series with the DC switch. If such a grounding resistor is adjustable, its resistance value can be set. This allows for flexible configuration of the ground reference of the respective electrolyzers.

[0037] In one embodiment of the method, determining the ground reference of the electrolyzers involves measuring the DC negative ground currents across the respective grounding resistances. The respective DC negative ground voltage can be determined, in particular, from the DC negative ground currents flowing through the grounding resistance.

[0038] In one embodiment of the method, the DC negative earth voltages of the power converters are determined by multiplying the respective measured differential currents by the respective grounding resistances, whereby the respective differential currents can include AC differential currents, DC differential currents, and / or DC negative earth currents. In this embodiment, differential currents can therefore be used, which are easier and more accurately determined than the DC negative earth voltages themselves.

[0039] In one embodiment of the method, to limit the absolute magnitudes of the DC negative-earth voltages, the respective DC voltages and / or the respective DC currents are adjusted such that the respective DC negative-earth voltages are limited in magnitude to the predefinable earth voltage limit value, e.g., a maximum of 50 V, preferably a maximum of 30 V. The adjustment of the respective DC voltages and / or DC currents can be achieved, in particular, by controlling, e.g., by clocking, the semiconductor switches of the bridge circuits of the respective power converters. 24-065-P-WO - 7 - submitted version

[0040] To limit the absolute magnitude of the negative DC-to-earth voltages, the respective electrolyzer setpoint, in particular the respective electrolyzer DC current setpoint, can be reduced if the predefined earth voltage limit is exceeded by a negative DC-to-earth voltage and / or if a respective differential current caused by a negative DC-to-earth voltage exceeds a predefined differential current limit. If the potential of the negative DC line is too far below earth potential, the DC current generated by the power converter, and thus the DC voltage of the respective power converter, can be reduced.

[0041] To limit the absolute magnitude of the DC negative-earth voltages, the respective electrolyzer setpoint, in particular the respective electrolyzer DC current setpoint, can be increased if the predefinable earth voltage limit is exceeded by a positive DC negative-earth voltage and / or if a differential current caused by a positive DC negative-earth voltage exceeds the predefinable differential current limit. If the potential of the DC negative line is too far above earth potential, the DC current generated by the power converter, and thus the DC voltage of the respective power converter, can be increased.

[0042] In one embodiment of the method, limiting the absolute values ​​of the DC negative-earth voltages includes limiting the maximum voltage difference between the DC voltages of the power converters, in particular by means of a control unit superior to the power converters, to a predefinable maximum difference. For this purpose, the electrolysis plant can include the superior control unit, which is connected to the respective control units of the power converters via communication links. Through these communication links, the superior control unit can receive the DC voltage values ​​from the power converters and transmit control commands to the individual control units to limit the differences between the DC voltages. The individual control units can then adjust the control of the semiconductor switches of their respective bridge circuits in response to the control commands received from the superior control unit.

[0043] To limit the maximum voltage difference between the DC voltages, the electrolyzer setpoint, in particular the electrolyzer DC current setpoint, can be reduced for the power converter(s) with the highest DC voltage. Alternatively or additionally, to limit the maximum voltage difference between the DC voltages, the electrolyzer setpoint, in particular the electrolyzer DC current setpoint, can be increased for the power converter(s) with the lowest DC voltage. Such reduced or increased electrolyzer DC current setpoints (as per the version submitted in 24-065-P-WO - 8) can be transmitted from the higher-level control unit to the control units of the respective power converters.

[0044] In one embodiment of the method, limiting the absolute values ​​of the DC negative-earth voltages involves asymmetry of the intermediate circuit halves of one or more power converters. This embodiment can be applied to power converters with a split intermediate circuit, where the respective intermediate circuit halves can be deliberately set asymmetrically to change the potential difference to earth. This asymmetry can also be set by the control unit of the respective power converter by appropriately controlling the circuit breakers of the bridge circuit. The control unit can thus, for example, respond to control commands received from the higher-level control unit.

[0045] In one embodiment of the method, the asymmetry of the DC link halves comprises a redistribution of energy between the DC link halves of a respective power converter, wherein the redistribution is effected in particular by means of a balancing circuit connected to the DC link halves and / or by generating an AC-side zero system through the bridge circuit of the respective power converter. The AC-side zero system generated by each power converter can, in particular, be accompanied by a voltage difference between its associated upper DC link half and its associated lower DC link half, which is transmitted to the center potential of the AC lines.

[0046] In one embodiment of the method, the asymmetry includes approximating or aligning the DC voltages of the lower intermediate circuit halves of the power converters connected to the respective DC_minus lines with each other and, in particular, with a predefinable common setpoint.

[0047] In one embodiment of the method, limiting the absolute values ​​of the negative DC-to-earth voltages involves symmetricalizing the total negative DC-to-earth voltages around the earth potential. Here, the negative DC-to-earth voltages of the electrolysis plant are adjusted using one or more of the described methods so that they are as symmetrical as possible around the earth potential. This prevents equalizing currents, fault currents, etc., and thus increases safety.

[0048] The balancing of the total DC negative earth voltages around earth potential can, for example, involve setting adjustable grounding resistors located between the DC negative lines and earth potential. The resistance value of each grounding resistor is chosen to be particularly high the greater the deviation of the respective DC voltage from a mean value of the DC voltages (see 24-065-P-WO - 9 - submitted version). The determination of the mean value of the DC voltages can be performed by the higher-level control unit.

[0049] Balancing the total DC-negative-earth voltage can further include selectively connecting at least one of the DC-negative lines to earth potential, in particular, exactly one of the DC-negative lines being selectively connected to earth potential. Connecting and disconnecting the respective DC-negative line from earth potential can be accomplished via the respective associated DC switch, which is controlled, for example, by the control unit of the associated power converter or the higher-level control unit.

[0050] The selective connection can be chosen by a control algorithm based on the determined current ground reference of the electrolyzers such that the maximum absolute values ​​of the DC_minus-ground voltages of all electrolyzers are minimized for the selected selective connection compared to the maxima of the absolute values ​​of the DC_minus-ground voltages for all other possible selective connections. To select the DC_minus line that should be selectively connected to ground potential to meet this condition, expected values ​​of the DC_minus-ground voltages for different selective connection scenarios can be determined and compared. Typically, the DC_minus line of the electrolyzer whose DC voltage is closest to the mean or median value of the DC voltages of all electrolyzers should be selectively connected to ground potential.To ensure that the optimal selective compound is maintained even when the operating point of one or more electrolyzers changes, the control algorithm can be executed continuously or repeatedly, particularly by the higher-level control unit.

[0051] Optionally, during operation of the electrolysis plant, the single DC negative line selectively connected to ground potential can be changed as needed, particularly to minimize the absolute value of the maximum DC negative-to-ground voltage. The selective connection of this single DC negative line to ground potential can be achieved via a switch. The DC negative line can be connected directly to ground potential via the switch without an intermediate resistor. Alternatively, the DC negative line can also be connected to ground potential via a series circuit consisting of a switch and a resistor.

[0052] The electrolysis plant as registered has several electrolyzers and several power converters. Each electrolyzer is assigned its own power converter. The electrolyzers are connected via separate DC lines to one of the power converters in the version submitted (24-065-P-WO - 10 -).

[0053] Power converters are connected, and the power converters are designed and arranged for parallel power exchange with an AC network on the AC side. During operation of the electrolysis plant, at least one of the DC lines has a fixed reference to earth potential, in particular by at least one DC negative line being connected to earth potential.

[0054] A power supply for such an electrolysis plant has been established:

[0055] - To adjust the DC currents to the respective electrolyzers via the respective power converter to supply the assigned electrolyzer, depending on the respective electrolyzer setpoints,

[0056] - to determine the current ground reference of the electrolyzers, and

[0057] - To limit the absolute values ​​of the voltages of the DC_minus lines relative to earth potential to a predefinable limit value.

[0058] The electrolysis plant comprises several electrolyzers and the described power supply. In particular, the electrolysis plant may further include a control unit superior to the power converters, which is designed and configured to supply the electrolysis plant with electrical power in a state connected to the AC grid according to the described procedure.

[0059] Limiting the absolute values ​​of the DC negative voltages relative to ground potential to a predefined ground voltage limit can be achieved in various ways. For example, it can be implemented with a control unit within the respective power converter, thus eliminating the need for a higher-level control unit. Alternatively or additionally, limiting the absolute values ​​of the DC negative ground voltages can be achieved with a higher-level control unit, where the electrolyzer setpoints, particularly the electrolyzer DC current setpoints, and / or the ground reference itself are set. Alternatively or additionally, the absolute values ​​of the DC negative voltages can be limited using adjustable grounding resistors.

[0060] BRIEF DESCRIPTION OF THE FIGURES

[0061] The registration process is further explained and described below using the examples shown in the figures.

[0062] Fig. 1 schematically shows a first embodiment of an electrolysis plant.

[0063] Fig. 2 schematically shows a second embodiment of the electrolysis plant. 24-065-P-WO - 11 - submitted version

[0064] Fig. 3 schematically shows a third embodiment of the electrolysis plant.

[0065] Fig. 4 schematically shows a fourth embodiment of the electrolysis plant.

[0066] Fig. 5 schematically shows a fifth embodiment of the electrolysis plant.

[0067] Fig. 6 schematically shows a method for supplying power to an electrolysis plant.

[0068] The same reference symbols are used in the figures for identical or similar elements. Representations in the figures may not be to scale.

[0069] FIGURE DESCRIPTION

[0070] Fig. 1 schematically shows an electrolysis plant 100. The electrolysis plant 100 comprises electrolyzers 12.1, ... 12.n and power converters 10.1, ... 10.n individually assigned to the electrolyzers 12.1, ... 12.n. The power converters 10.1, ... 10.n primarily act as rectifiers and are connected in parallel on the AC side via the optional transformer 16 to a three-phase AC network 18. The optional transformer 16 itself has no ground reference.

[0071] A power supply 20 of the electrolysis plant 100 includes power converters 10.1, ... 10.n. The power converters 10.1, ... 10.n supply the electrolyzers 12.1, ... 12.n with DC current via their respective DC lines DC+, DC-. This current is adjustable via the electrolyzer setpoint SP1, ... SPn by the power converters 10.1, ... 10.n. The respective electrolyzer setpoint SP1, ... SPn can be specified, for example, as the electrolyzer DC current setpoint or as the electrolyzer power setpoint and / or received by the control unit via a communication link.

[0072] The DC lines DC+ and DC- comprise a DC+ conductor and a DC- conductor. The power converters 10.1, ... 10.n each have split intermediate circuits 14.1.0, ... 14.nO, 14.1.U, ... 14.nU and each a bridge circuit in a 3-level topology. Each split intermediate circuit has an upper half 14.1.0, ... 14.n.0 and a lower half 14.1.U, ... 14.nU. The upper half 14.1.0, ... 14.n.0 of each intermediate circuit is located between the respective DC+ conductor and a midpoint of the intermediate circuit. The lower half 14.1.U, ... 14.nU of the respective intermediate circuit is arranged between the center of the intermediate circuit and the respective DC_minus conductor DC-.

[0073] Optionally, the electrolysis plant 100 can include, in addition to the electrolyzers 12.1, ... 12.n, further DC-side units which can act as DC sources. Such DC sources can include, for example, fuel cells. The power converters 10.1, ... 10.n can be configured as 24-065-P-WO - 12 - submitted version

[0074] Inverters and / or rectifiers are used and thus for current conversion from DC to AC and / or AC to DC. The power converters 10.1, ... 10.n can therefore also convert DC current generated by fuel cells into AC current and feed it into the AC grid 18.

[0075] The electrolysis system 100 has a fixed ground connection on the DC side, as the respective DC negative conductors are directly connected to earth potential PE. The potential of the DC negative lines DC- to earth PE MU1, ... MU2 is inherently limited by the fact that all DC negative lines are grounded.

[0076] In the (hard) DC grounding shown in Figure 1, circular currents can occur, which may be undesirable as explained below.

[0077] The DC voltages U1, ... Un can differ from each other, especially if the electrolyzer setpoints SP1, ... SPn are different. Even with identical electrolyzer setpoints SP1, ... SPn, e.g., identical electrolyzer DC current setpoints, (slightly) different DC voltages U1, ... Un can result due to different characteristic curves of the connected electrolyzers 12.1, ... 12.n. If the DC voltages U1, ... Un are different, then the partial voltages U12 and Un2 in the lower intermediate circuit halves 14.1.U, ... 14.nU are also different, especially if the respective DC voltages U1, ... Un are distributed symmetrically to the respective intermediate circuit halves by means of the control of the power converters 10.1, ... 10.n. This voltage difference between the partial voltages U12-Un2 can cause a circulating current in the system, which flows through the DC_minus lines connected via the earth connections, the intermediate circuits 14.1.0, ... 14.n.Current flows through the power transformers 10.1, ... 10.n and their AC-side parallel connection. Such circulating currents can lead to increased system losses and asymmetries in the intermediate circuits 14.1.0, ... 14.nO, 14.1.U, ... 14.nU of the power transformers 10.1, ... 10.n, and can, for example, cause detrimental saturation of the EMC filters of the power transformers 10.1, ... 10.n. Furthermore, a DC component can occur in the AC current, which places a heavy load on the transformer 16.

[0078] For an example of two parallel-connected power converters 10.1 and 10.2, the following values ​​can result. If the DC voltages U1 and U2 are identical and both DC voltages are, for example, U1 = U2 = 700 V, the situation is symmetrical and initially no circulating currents occur. With different DC voltages, for example, U1 = 700 V and U2 = 705 V, a significant circulating current with an amplitude of approximately 3 A can arise. The circulating current depends on the magnitude of the voltage difference |U_12 - U_22| in the lower intermediate circuit halves 14.1.U and 14.2.U. The circulating current can, in principle, be influenced and limited by minimizing the difference between the DC voltages U1 and U2, whereby, as the version 24-065-P-WO - 13 - submitted shows, there is a conflict of objectives between the limited choice of DC voltages U1, U2 and the setting of the specified electrolyzer setpoints.

[0079] Fig. 2 schematically shows a second embodiment of the electrolysis system 100. Compared to the electrolysis system 100 of Figure 1, the grounding of the electrolysis system 100 according to Figure 2 has additional passive components. The power supply 20 of the electrolysis system 100 includes the power converters 10.1, ... 10.n and the passive components.

[0080] In the second embodiment, the respective grounding of the DC-negative lines is implemented using passive components arranged in the respective grounding paths between the DC-negative line and earth (PE). These passive components are exemplified here as grounding resistors R1, ... Rn. When a current flows through each grounding resistor R1, ... Rn, a DC-negative-to-earth voltage MU1, ... MUn drops across it.

[0081] These passive components in the grounding path decouple the DC voltages U1, ... Un from each other, meaning that the DC voltages U1, ... Un can be adjusted independently to a certain extent. In contrast to the "hard" grounding shown in Fig. 1, the grounding of the electrolysis plant 100 is now designed as a "soft" ground.

[0082] The circulating currents described in connection with Figure 1 are limited in their current intensity by the soft grounding according to Figure 2. At the same time, the DC_minus-to-earth voltages MU1, ... MUn of the DC_minus lines relative to earth PE are now determined by the selection and design of the passive components, e.g., the grounding resistors R1, ... Rn.

[0083] For an example of two parallel-connected power converters 10.1 and 10.2, the following values ​​can result. If the DC voltages U1 and U2 are identical and both DC voltages are, for example, 700V, then the situation is symmetrical. No or almost no circulating currents occur, and the DC negative-earth voltages MU1 and MU2 across R1 and R2 are zero or very low.

[0084] If the DC voltages U1, U2, and thus also the partial voltages U12 and U22, differ in the lower intermediate circuit halves 14.1.U, 14.2.U, circulating currents can occur across the grounding resistances R1, R2. The resulting circulating current depends on the magnitude of the voltage difference |U_12— U_22| in the lower intermediate circuit halves 14.1.U, 14.2.U and on the sum of the grounding resistances R1+R2. A voltage drop across the grounding resistances R1, R2, due to the circulating currents, corresponds to the resulting DC negative ground voltages MU1, MU2. The circulating current and the version submitted 24-065-P-WO - 14 -

[0085] DC negative earth voltages MU1, MU2 can be influenced and limited by controlling the difference between the DC voltages U1 and U2.

[0086] As an example of dimensioning two parallel-connected power converters 10.1 and 10.2, it can be shown that, for example, with grounding resistors R1 = R2 = 25 ohms, the difference between the DC voltages U1 and LI2 can be a maximum of approximately 100 V if the circuit current is limited to a maximum of 1 A, for example, for device protection reasons. The absolute values ​​of the DC negative ground voltages MU1 and MU2 are then a maximum of 25 V. In contrast, the grounding resistors R1 and R2 could be increased, for example to R1 = R2 = 50 ohms, which would reduce the circuit current. This would increase the difference between the DC voltages U1 and LI2 to 200 V without the circuit current exceeding 1 A, but the absolute values ​​of the DC negative ground voltages MU1 and MU2 would then be approximately 50 V.

[0087] In the embodiment according to Fig. 2, the DC negative potentials thus deviate from the ground potential PE by the respective voltage drop MU1, ... Miln across the grounding resistors R1, ... Rn. Adjusting the DC currents to the electrolyzers 12.1, ... 12.n with the potentially necessary different DC voltages U1, ... 11n results in a ground reference of the electrolyzers 12.1, ... 12.n, which is determined by the voltage drop MU1, ... Miln across the grounding resistors R1, ... Rn. This voltage drop MU1, ... Miln, in particular its absolute value, can be determined, for example, by measuring the DC negative ground voltages or by measuring the ground currents through the grounding resistors, and its magnitude can be limited to a predefinable ground voltage limit, e.g., 50 V. In particular, the differences in the DC voltages U1, ... 1ln can be limited, for example by limiting the respective electrolyzer setpoints SP1, SP2, ...SPn can be reduced for those electrolyzers 12.1, ... 12.n whose DC_minus-earth voltages MU1, ... Miln have a negative sign and whose absolute value exceeds the earth voltage limit. Alternatively or cumulatively, the respective electrolyzer setpoints SP1, ... SPn can be increased for those electrolyzers 12.1, ... 12.n whose DC_minus-earth voltages MU1, ... Miln have a positive sign and whose absolute value exceeds the earth voltage limit. In this way, the variation in the total DC_minus-earth voltages MU1, ... Miln around the earth potential PE, and thus the overall earth reference of the electrolyzers, can be reduced.

[0088] Fig. 3 schematically shows a third embodiment of the electrolysis plant 100. Compared to the electrolysis plant 100 according to Figure 2, the grounding resistances R1, R2, ... Rn are adjustable. The transformer 16 is not shown in Figure 3 but can be included optionally. The intermediate circuits of the power transformers 10.1, 10.2, ... 10.n can optionally be divided (see version 24-065-P-WO - 15 - submitted version) and have the upper half 14.1.0, ... 14.n.0 and the lower half 14.1.U, ... 14.nU, see Figures 1 and 2.

[0089] The embodiment of the electrolysis system 100 according to Fig. 3 can, for example, include a higher-level control unit (not shown) which is connected to the control units of the power converters 10.1, 10.2, ... 10.n via a communication link. The respective electrolyzer setpoints SP1, SP2, ... SPn can be transmitted from the higher-level control unit to the respective power converters 10.1, 10.2, ... 10.n. The respective electrolyzer setpoint SP1, SP2, ... SPn can, for example, be specified as the electrolyzer DC current setpoint or as the electrolyzer power setpoint and adjusted by a control unit of the respective power converter 10.1, 10.2, ... 10.n. Overall, depending on the characteristic curves of the associated electrolyzers 12.1, 12.2, ... 12.n, the DC voltages U1, U2, ... Un at the electrolyzers 12.1, 12.2, ... 12.n are obtained, as well as depending on the DC voltages U1, U2, ...Un and the set earth resistances R1 , R2, ... Rn the DC_Minus-earth voltages MU1 , MU2, ... MUn.

[0090] Particularly for the operation of electrolyzers 12.1, 12.2, ... 12.n, from a regulatory perspective, for the purpose of plant protection and / or from a safety perspective, it may be desirable to avoid high earth voltages, especially high absolute values ​​of the DC negative earth voltages of the DC negative conductor to earth PE. In the embodiment according to Fig. 3, the absolute values ​​of the DC negative earth voltages MU1, MU2, ... , MUn can now be limited to a predefinable earth voltage limit value of, for example, 50 V. After determining the current ground reference of the electrolyzers 12.1, 12.2, ... 12.n, the respective set resistance value of the respective grounding resistor R1, R2, ... Rn can be chosen to be larger the greater the deviation of the respective DC voltage U1, U2, ... Un from an average value of the DC voltages U1, U2, ... Un. This allows for adjustments within the setting ranges of the grounding resistors R1, R2, ...Rn effectively balances the total DC negative earth voltages MU1, MU2, ... MUn around the earth potential PE. If, even in such a largely symmetrical situation, one of the DC negative earth voltages MU1, MU2, ... MUn should exceed the predefinable earth voltage limit of, for example, 50 V, one of the other described measures for limiting the absolute values ​​of the DC negative earth voltages MU1, MU2, ... MUn can optionally be initiated, for example, by reducing or increasing the corresponding electrolyzer setpoint SP1, SP2, ... SPn.

[0091] Fig. 4 schematically shows a fourth embodiment of the electrolysis plant 100. Compared to the electrolysis plant 100 according to Figure 2, the grounding of the electrolysis plant 100 shown here has additional DC switches S1, S2, ... Sn. The power supply 20 of the version submitted in 24-065-P-WO - 16 -

[0092] Electrolysis system 100 includes the power converters 10.1 , 10.2, ... 10. n, the passive components and the DC switches S1 , S2, ... Sn.

[0093] In the embodiment shown in Fig. 4, the respective grounding of the DC negative lines can be achieved by the DC switches S1, S2, ... Sn, which are arranged in the respective grounding paths between the respective DC negative line and earth PE. By opening and closing the DC switches S1, S2, ... Sn, one or more of the DC negative lines can be selectively connected to earth potential PE via the respective grounding resistor R1, R2, ... Rn.

[0094] By selectively connecting the DC switches S1, ... Sn, the voltages MU1, MU2, ... Miln of the DC negative conductors (DC- to ground potential PE) can be set and limited in magnitude. The selective connection can be chosen by a control algorithm based on the determined current ground reference of the electrolyzers 12.1, 12.2, ... 12.n such that the maximum DC negative-to-ground voltage MU1, MU2, ... Miln of all electrolyzers 12.1, 12.2, ... 12.n is minimal compared to all other possible selective connections. The control algorithm can be executed continuously or repeatedly, particularly by a higher-level control unit (not shown).

[0095] In the operation of electrolysis plant 100, in particular, exactly one of the DC_minus lines can be selectively connected to earth potential PE, whereby the one DC_minus line selectively connected to earth potential PE can be changed as needed in order to minimize an absolute value of the maximum DC_minus earth voltages MU1, MU2, ... MUn. This allows the totality of the DC_minus earth voltages MU1, MU2, ... MUn to be effectively balanced around earth potential PE within the given distribution of the DC voltages U1, U2, ... Un. If one of the DC negative earth voltages MU1, MU2, ... MUn should exceed the predefinable earth voltage limit of, for example, 50 V in such a largely symmetrical situation, one of the other described measures for limiting the absolute values ​​of the DC negative earth voltages MU1, MU2, ... MUn can optionally be initiated, for example by adjusting the corresponding electrolyzer setpoint SP1, SP2, ...SPn is reduced or increased.

[0096] In Fig. 4, each of the DC negative lines is connected to ground (PE) via a series circuit of a respective resistor R1, R2, ... Rn and a respective switch S1, S2, ... Sn. Alternatively, according to the invention, it is also possible to omit the resistors R1, R2, ... Rn, so that the DC negative lines are connected to ground (PE) only via a respective switch S1, S2, ... Sn, i.e., without a respective resistor R1, R2, ... Rn in their switchable connection to ground (PE) (24-065-P-WO - 17 - submitted version). This is particularly advantageous when, during operation of the electrolysis plant, exactly one of the DC negative lines is selectively connected to ground (PE) via its closed switch S1, S2, ... Sn.

[0097] Fig. 5 shows a fifth embodiment of the electrolysis plant 100. Compared to the electrolysis plant 100 according to Figure 2, the electrolysis plant 100 here has at least one balancing circuit 15, which for example includes a resonantly switched converter (RSC) known per se.

[0098] The balancing circuits 15 can be controlled such that the circulating currents occurring during operation of the electrolysis plant 100 at different DC voltages U1, U2, ... 11n of the electrolyzers 12.1, 12.2, ... 12.n are minimized. It has been shown that this is usually equivalent to ensuring that the negative intermediate circuit halves 14.1.U, ... 14.nU of all power converters 10.1, 10.2, ... 10.n have approximately the same voltages U12, U22, ... Un2 (compare Figures 1 and 2). The balancing circuits 15 therefore do not have the usual task of balancing the intermediate circuit halves, but rather the task of keeping the voltages U12, U22, ... Un2 of the negative intermediate circuit half of all power transformers 10.1 , 10.2, ... 10. n as equal as possible, in particular regulating them to a common setpoint, so that no circulating current flows or a flowing circulating current is minimized.Alternatively or additionally, a certain circulating current below a circulating current limit can be allowed by keeping balancing circuits 15 inactive as long as the circulating current of a respective power transformer is below the circulating current limit.

[0099] Fig. 6 schematically shows a method for supplying power to an electrolysis plant 100.

[0100] The electrolysis plant 100, see Figures 2 to 5, comprises electrolyzers 12.1, 12.2, ... 12.n and individually assigned power converters 10.1, 10.2, ... 10.n to each electrolyzer 12.1, 12.2, ... 12.n. These power converters are connected in parallel on the AC side via an optional transformer 16 to a three-phase AC network 18. The power converters 10.1, 10.2, ... 10.n supply the electrolyzers 12.1, 12.2, ... 12.n with DC current, which can be adjusted via electrolyzer setpoints SP1, SP2, ... SPn by the power converters 10.1, 10.2, ... 10.n. The electrolyzer setpoints SP1, SP2, ... SPn can include, in particular, electrolyzer DC current setpoints or electrolyzer power setpoints and can optionally be individually adjustable for each power converter 10.1, 10.2, ... 10.n. Especially with identical electrolyzers 12.1, 12.2, ... 12.n, the electrolyzer setpoint SP1, SP2, ... SPn can also be set for several electrolyzers 12.1, 12.2, ... 12.n.n be identical. 24-065-P-WO - 18 - submitted version.

[0101] The electrolysis system 100 has a fixed earth reference on the DC side, for example by connecting at least one DC conductor DC+, DC- to earth potential PE.

[0102] The method for supplying power to the electrolyzers 12.1 , 12.2, ... 12.n exhibits:

[0103] A) Setting the respective DC currents depending on the respective electrolyzer setpoints SP1, SP2, ... SPn

[0104] B) Determining the current ground reference of electrolyzers 12.1, 12.2, ... 12. n

[0105] C) Limiting the absolute values ​​of the DC_minus-earth voltages MU1, MU2, ... Miln of the DC_minus conductor DC- relative to earth potential PE to a predetermined limit value

[0106] The DC currents in A) can be adjusted, for example, by appropriately adjusting the DC voltages U1, U2, ... 11n by the respective power converters 10.1, 10.2, ... 10.n. In particular, the DC currents in A) can be achieved by adjusting the AC currents and thus the regulated DC voltages by clocking the semiconductor bridge of the respective power converters 10.1, 10.2, ... 10.n.

[0107] The current ground reference of electrolyzers 12.1, 12.2, ... 12.n in B) can be determined, for example, by measuring the DC negative ground voltages MU1, MU2, ... MUn. Alternatively or additionally, the current ground reference of electrolyzers 12.1, 12.2, ... 12.n can be determined by measuring the voltages at the intermediate circuit center points to ground (PE) on the DC or AC side and subtracting half the respective intermediate circuit voltage U1 / 2, U2 / 2, ... Un / 2. Alternatively or additionally, the current ground reference of electrolyzers 12.1, 12.2, ... 12.n can be determined by measuring differential currents or DC negative ground currents on the DC or AC side and multiplying them by the respective ground resistance R1, R2, ... Rn. In the event that the earth reference of a DC_minus line DC- is known, e.g. because a DC_minus line DC- has been selectively connected to earth PE, it is sufficient to determine the DC_minus earth voltages only for the remaining DC_minus lines DC-.The same applies if the earth reference for several of the DC_minus lines is known.

[0108] To limit the absolute values ​​of the DC_minus earth voltages MU1 , MU2, ... MUn of the DC_minus lines DC- relative to earth potential PE to a predefinable earth voltage limit value, various embodiments were explained with reference to Figures 1 to 5.

[0109] Limiting the absolute values ​​of the DC-negative earth voltages MU1, MU2, ... MUn of the DC-negative conductors DC- to earth potential PE can, in particular, comprise one or more of the following steps. -065-P-WO - 19 - submitted version i) Individual adjustment of the DC voltages U1, U2, ... 11n by the power transformers 10.1, 10.2, ... 10.n depending on the current earth reference a. Reducing the respective DC voltage if the absolute value of the respective DC-negative earth voltage is too high and the respective DC-negative earth voltage is negative, i.e., if the potentials of the corresponding DC-negative lines DC- are too far below the earth potential PE; b. Reducing the respective DC voltage if the corresponding differential current flowing from the relevant DC_minus line towards earth is too high and has a sign that correlates with a negative DC_minus-earth voltage; c.ii) Increasing the respective DC voltage if the absolute value of the respective DC negative ground voltage or the resulting differential current flowing from the relevant DC negative line towards ground PE is too large and the respective DC negative ground voltage is positive (to equalize relatively low DC voltages U1, U2, ... Un) ii) Reducing the “spread” of the DC voltages U1, U2, ... Un occurring during the operation of the electrolysis plant 100 by the higher-level control unit a. by reducing the electrolyzer setpoints SP1 , SP2, ... SPn (and thus the DC voltages U1 , U2, ... Un) for those electrolyzers 12.1, 12.2, ... 12. n with strongly negative DC negative ground voltages MU1, MU2, ... MUn b. by increasing the electrolyzer setpoints SP1, SP2, ... SPn (and thus the DC voltages U1, U2, ... Un) for those electrolyzers 12.1, 12.2, ... 12. n with high positive DC_minus-earth voltages MU1, MU2, ...MUn iii) Generating or increasing an asymmetry of split intermediate circuits 14.1.0, ... 14.nO, 14.1.U, ... 14.nU by: a. Charge transfer between the upper intermediate circuit halves 14.1.0, ... 14.n.0 and the respective associated lower intermediate circuit halves 14.1.U, ... 14.nU, e.g. driven by balancing circuits 15 on the DC intermediate circuits 14.1.0, ... 14.n.0, 14.1.U, ... 14.nU, wherein the balancing circuits 15 are not used for balancing, but for the targeted asymmetry of the respective associated intermediate circuit halves 14.1.0, ... 14.nO, 14.1.U, ... 14.nU. b. Clocking of the respective bridge circuits of the power converters 10.1, 10.2, ... 10.n with generation of an AC zero system c. Approximation or equalization of the DC voltages U1, U2, ... Un of the lower intermediate circuit halves 14.1.U, ... 14. n.U to each other, in particular to a common setpoint 24-065-P-WO - 20 - submitted version iv) overarching symmetry of the earth reference of the entirety of the electrolyzers 12.1 , 12.2, ... 12. n , i.e. all occurring DC_minus earth voltages relative to earth potential PE a. by asymmetric distribution of the earth references with variable earth resistances R1 , R2, ... Rn , which are set depending on the deviation from the mean value of the DC voltages U1 , U2, ... 11n ; b. by earthing exactly one DC_minus line DC- i. with selection of the optimal DC_minus line to be earthed DC- ii. with regular or continuous verification of the optimal earthing, in particular regular or continuous verification of the selection of exactly one earthed DC_minus line DC- iii. with changing the exactly one grounded DC_minus line DC-.

[0110] Using the higher-level control unit (not shown), e.g., a plant controller, and a higher-level control algorithm executed on it, one or more of the following steps can be performed: a. Specifying the electrolyzer setpoints SP1, SP2, ... SPn b. Specifying a common DC voltage setpoint U12, U22, ... Un2 for the lower intermediate circuit halves 14.1.U, ... 14.nU c. Dispatching of a plant setpoint by distributing the plant setpoint to the electrolyzers 12.1, 12.2, ... 12.n and / or the power converters 10.1, 10.2, ... 10.n of the electrolysis plant 100 depending on the DC_minus-earth voltages MU1, MU2, ... Miln, in particular with reduction of individual electrolyzer setpoints SP1, SP2, ... SPn in the case of excessively negative values ​​of the DC_minus-earth voltages MU1, MU2, ... Miln and / or with increase of individual electrolyzer setpoints SP1, SP2, ...SPn occurs when the DC_Minus-Earth voltages MU1, MU2, ... Miln are too strongly positive.

[0111] 4-065-P-WO - 21 - submitted version

[0112] REFERENCE MARK LIST

[0113] 10.1, 10.2, ... 10.n Power converters

[0114] 12.1, 12.2, ... 12.n Electrolyzer 14.1.0, ... 14.n.0 Intermediate circuit upper half

[0115] 14.1 , U, ... 14.nU Intermediate circuit lower half 15 Balancing circuit

[0116] 16 Transformer 18 AC network

[0117] 20 Benefit provision

[0118] A, B, C process steps

[0119] DC+ DC_Plus line

[0120] DC - DC_Minus line

[0121] U1, U2, ... Un DC voltage PE earth potential

[0122] R1, R2, ... Rn Earth resistance

[0123] S1, S2, ... Sn DC switch

[0124] MU1, MU2, ... MUn DC_Minus-Earth Voltage SP1 , SP2, ... SPn Electrolyzer DC Current Setpoint

Claims

24-065-P-WO - 22 - submitted version PATENT CLAIMS 1. Method for supplying power to an electrolysis plant (100) with several electrolyzers (12.1, 12.2, ... 12.n) and several power converters (10.1, 10.2, ... 10.n), wherein the electrolyzers (12.1, 12.2, ... 12.n) are connected to respective power converters (10.1, 10.2, ... 10.n) via respective DC lines (DC+, DC-), wherein the power converters (10.1, 10.2, ... 10.n) are electrically connected in parallel to each other on the AC side, in particular via a transformer (16), to an AC network (18), wherein during operation of the electrolysis plant (100) at least one DC line (DC+, DC-) has a fixed reference to an earth potential (PE), in particular by connecting at least one DC_minus line (DC-) to earth potential (PE). the procedure exhibits: - Setting the respective DC currents to the electrolyzers (12.1, 12.2, ... 12.n) by the respective power converter (10.1, 10.2, ... 10.n) to supply the associated electrolyzers (12.1 , 12.2, ... 12.n) depending on the respective electrolyzer setpoints (SP1, SP2, ... SPn), - Determining the current ground reference of the electrolyzers (12.1, 12.2, ...

12. n), and - Limiting the absolute values ​​of DC_minus earth voltages (MU1, MU2, ... MUn) of the DC_minus lines (DC-) relative to earth potential (PE) to a predefinable earth voltage limit value.

2. Method according to claim 1, wherein the power converters (10.1 , 10.2, ...

10. n) are essentially identical in construction and in particular each comprise a semiconductor bridge circuit with three-level topology and a split intermediate circuit (14.1.0, ... 14.nO , 14.1.U, ... 14.nU).

3. Method according to claim 1 or 2, wherein the adjustment of the respective DC currents comprises adjusting the respective DC voltages (U1 , U2, ... Un) at the electrolyzers (12.1, 12.2, ...

12. n) by the respective power converter (10.1, 10.2, ...

10. n).

4. Method according to one of the preceding claims, wherein the adjustment of the DC currents comprises adjusting AC currents by suitable clocking of semiconductor switches of the respective power converter (10.1, 10.2, ...

10. n).

5. Method according to one of the preceding claims, wherein determining the current ground reference of the electrolyzers (12.1 , 12.2, ...

12. n) comprises determining the respective DC_minus ground voltage (MU1, MU2, ... MUn) of the respective DC_minus line (DC-) of the respective power converter (10.1 , 10.2, ...

10. n) against ground potential (PE). 24-065-P-WO - 23 - submitted version 6. Method according to claim 5, wherein the DC_minus-earth voltages (MU1 , MU2, ... Miln) are measured or determined from measurements of the voltage of the midpoint of a split DC intermediate circuit relative to earth potential (PE) and the voltage of the lower half of the split DC intermediate circuit (14.1.U, ... 14.nU) of the respective power transformer (10.1 , 10.2, ...

10. n).

7. Method according to one of the preceding claims, wherein several DC negative lines (DC-) can be connected to the earth potential (PE) in particular via respective earth resistances (R1 , R2, ... Rn ), wherein the respective earth resistances (R1 , R2, ... Rn ) are in particular adjustable.

8. Method according to claim 7, wherein determining the earth reference of the electrolyzers (12.1 , 12.2, ...

12. n) comprises measuring the DC_minus earth currents across the respective earth resistances (R1 , R2, ... Rn).

9. Method according to claim 7, wherein DC_minus-earth voltages (MU1 , MU2, ... Miln) of the power transformers (10.1 , 10.2, ...

10. n) are determined by multiplying the respective measured differential currents with the respective grounding resistances (R1 , R2, ... Rn), wherein the respective differential currents include AC differential currents, DC differential currents and / or DC_minus-earth currents.

10. Method according to one of the preceding claims, wherein, to limit the DC negative earth voltages (MU1, MU2, ... MUn), the respective DC voltages (U1, U2, ... Un) and / or the respective DC currents are adjusted such that the respective DC negative earth voltages (MU1 , MU2, ... MUn) are limited in magnitude to the predefinable earth voltage limit value, e.g. a maximum of 50 V, preferably a maximum of 30 V.

11. Method according to claim 10, wherein the respective electrolyzer setpoint is reduced if the predefinable earth voltage limit is exceeded in magnitude by a negative DC_minus earth voltage (MU1 , MU2, ... MUn) and / or if a respective differential current caused by a negative DC_minus earth voltage (MU1 , MU2, ... MUn) exceeds in magnitude a predefinable differential current limit.

12. Method according to claim 10 or 11, wherein the respective electrolyzer setpoint is increased if the predefinable earth voltage limit is exceeded in magnitude by a respective positive DC_minus earth voltage (MU1 , MU2, ... MUn) and / or if a respective differential current caused by a positive DC_minus earth voltage (MU1 , MU2, ... MUn) exceeds in magnitude the predefinable differential current limit. 24-065-P-WO - 24 - submitted version 13. Method according to one of the preceding claims, wherein limiting the DC_minus-earth voltages comprises limiting the maximum voltage difference between the DC voltages (U1, U2, ... 11n) of the power converters (10.1 , 10.2, ...

10. n), in particular by a control unit superior to the power converters (10.1 , 10.2, ...

10. n), to a predefinable maximum difference.

14. Method according to claim 13, wherein limiting the maximum voltage difference of the DC voltages (U1 , U2, ... Un) comprises a reduction of the electrolyzer setpoint for the power converter(s) (10.1 , 10.2, ...

10. n) with the highest DC voltage (U1, U2, ... Un) and / or an increase of the electrolyzer setpoint for the power converter(s) (10.1 , 10.2, ...

10. n) with the lowest DC voltage (U1, U2, ... Un).

15. Method according to any of the preceding claims, insofar as it refers back to claim 2, wherein limiting the DC_minus-earth voltages (MU1 , MU2, ... MUn) comprises asymmetry of the intermediate circuit halves (14.1.0, ... 14.n.0 , 14.1.U, ...

14. nU) of a power converter (10.1 , 10.2, ...

10. n) or of several power converters (10.1 , 10.2, ... 10.n).

16. Method according to claim 15, wherein the asymmetry of the intermediate circuit halves (14.1.0, ... 14.n.0 , 14.1.U, ... 14.nU) comprises a redistribution of energy between the intermediate circuit halves (14.1.0, ... 14.n.0 , 14.1.U, ... 14.nU) of a respective power converter (10.1 , 10.2, ... 10.n) wherein the redistribution is carried out in particular by means of a balancing circuit (15) connected to the intermediate circuit halves (14.1.0, ... 14.n.0 , 14.1.U, ... 14.nU) and / or comprises the generation of an AC-side zero system by the bridge circuit of the respective power converter (10.1 , 10.2, ... 10.n).

17. Method according to claim 15 or 16, wherein the asymmetry comprises an approximation or an equalization of the DC voltages (U12, U22, ... Un2) of the lower intermediate circuit halves (14.1.U, ...

14. nU) of the power converters (10.1 , 10.2, ...

10. n) connected to the respective DC_minus lines (DC-) to each other and in particular to a predefinable common setpoint.

18. Method according to any one of claims 1 to 14, wherein limiting the DC_minus-earth voltages (MU1 , MU2, ... MUn) comprises symmetry of the totality of the DC_minus-earth voltages (MU1 , MU2, ... MUn) around the earth potential (PE).

19. Method according to claim 18, wherein the symmetry of the totality of the DC_Minus- Earth voltages (MU1, MU2, ... MUn) are set between the DC- 24-065-P-WO - 25 - submitted version The system comprises adjustable earth resistances (R1, R2, ... Rn) arranged between negative lines (DC-) and earth potential (PE), wherein the set resistance value of the respective earth resistance (R1, R2, ... Rn) is chosen to be larger, in particular, the greater the distance of the respective DC voltage (U1, U2, ... 11n) from an average value of the DC voltages (U1, U2, ... 11n).

20. Method according to claim 18, wherein the symmetry of the totality of the DC_minus earth voltages (MU1 , MU2, ... Miln) comprises selectively connecting at least one of the DC_minus lines (DC-) to the earth potential (PE), wherein in particular exactly one of the DC_minus lines (DC-) is selectively connected to the earth potential (PE).

21. Method according to claim 20, wherein the selective compound is selected by a control algorithm depending on the determined current ground reference of the electrolyzers (12.1 , 12.2, ...

12. n) such that a maximum of the absolute values ​​of the DC_minus-ground voltages (MU1 , MU2, ... Miln) of the totality of the electrolyzers (12.1 , 12.2, ...

12. n) is minimal, wherein the control algorithm is executed in particular continuously or repeatedly by the higher-level control unit.

22. Method according to claim 20 or 21, wherein in the operation of the electrolysis plant (100) the exactly one DC_minus line (DC-) selectively connected to the earth potential (PE) is changed as required, in particular to minimize an absolute amount of the maximum DC-minus-earth voltages (MU1 , MU2, ... Miln).

23. Power supply (20) for an electrolysis plant (100) with several electrolyzers (12.1, 12.2, ... 12.n) and several power converters (10.1, 10.2, ... 10.n), wherein the electrolyzers (12.1, 12.2, ... 12.n) are connected via respective DC lines to each of the power converters (10.1, 10.2, ... 10.n), wherein the power converters (10.1, 10.2, ... 10.n) are designed and arranged for parallel power exchange on the AC side with an AC network, wherein during operation of the electrolysis plant (100) at least one of the DC lines has a fixed reference to earth potential (PE), in particular by at least one DC negative line (DC-) being connected to earth potential (PE), wherein the power supply is set up, - DC currents to the respective electrolyzers (12.1 , 12.2, ...

12. n) through the respective power converter (10.1 , 10.2, ...

10. n) to supply the associated electrolyzer (12.1 , 12.2, ...

12. n) depending on the respective electrolyzer setpoints, - to determine a current ground reference of the electrolyzers (12.1 , 12.2, ...

12. n), and 24-065-P-WO - 26 - submitted version - To limit the absolute values ​​of voltages of the DC_minus lines (DC-) relative to earth potential (PE) to a predefinable limit value.

24. Electrolysis system (100) comprising several electrolyzers (12.1 , 12.2, ...

12. n) and a power supply according to claim 23, in particular further comprising a control unit superior to the power converters (10.1, 10.2, ...

10. n) which is designed and configured to operate the electrolysis system (100) in a state connected to the AC network (18) according to the method according to one of claims 1 to 22.

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