Supply unit for a DC load, method for operating same, and electrolysis system

Abstract

The invention relates to a supply unit (20) for a DC load (50). The supply unit (20) comprises: - a DC terminal (21) for connecting to the DC load (50), - a first AC terminal (22) which is connected to a DC bus (26) via a first AC / DC converter (24), - a second AC terminal (23) which is designed for connecting to a second AC voltage (U2) and which is connected to the DC terminal (21) via a second AC / DC converter (25), - an energy storage device (29) which is connected to the DC bus (26) via a first DC / DC converter (27), - a second DC / DC converter (28) which connects the DC bus (26) to the DC terminal (21) and which can be operated so as to provide the current with respect to the DC terminal (21), and - a control unit (30) for controlling the supply unit (20). The supply unit is characterized in that - the first DC / DC converter (27) is designed in the form of a bidirectional DC / DC converter, and the control unit (30) is designed to operate the first DC / DC converter (27) so as to provide the voltage with respect to the DC bus (26), and - the first AC / DC converter (24) is designed in the form of a bidirectional AC / DC converter, and the control unit (30) is designed to operate the first AC / DC converter (24) so as to provide the voltage with respect to the first AC terminal (22). The invention additionally relates to an operating and starting method and to an electrolysis system comprising such a supply unit (20).

Description

[0001] SUPPLY UNIT FOR A DC CONSUMER, METHOD FOR OPERATION THEREOF AND ELECTROLYSIS SYSTEM

[0002] Technical field of the invention

[0003] The invention relates to a supply unit for a DC consumer, in particular—but not exclusively—an electrolyzer. The invention also relates to methods for operating and starting such a supply unit and to an electrolysis system with one or more supply units.

[0004] State of the art

[0005] To produce hydrogen from water using an electrolysis reaction, electrolysis plants are known in which an electrolyzer is supplied with electrical power via a supply unit from an alternating current (AC) network. Since such electrolyzers are usually operated as direct current (DC) consumers during the electrolysis reaction, the supply unit has one or more rectifying power converters. Depending on their size and design, the electrolyzers can have nominal outputs of up to several tens of MW. The supply unit can be used to specifically adjust the hydrogen production rate, i.e. the amount of hydrogen produced per unit of time. For this purpose, the power converter can be operated in a current-adjusting manner at its DC connection connected to the electrolyzer.Depending on the electrolyzer design, an electrical DC voltage corresponding to the supplied current is generated at the electrolyzer's DC terminal, and thus also at the DC terminal of the supply unit. The DC voltage typically increases with increasing hydrogen production rate and can range between a few hundred and 1500 V.

[0006] To meet the growing demand for green hydrogen—that is, hydrogen produced exclusively from renewable energy sources through electrolysis—large electrolysis plants are being designed with numerous electrolyzers and a variety of supply units. Such electrolysis plants have total outputs in the range of several hundred megawatts. Photovoltaics and wind power are used primarily as renewable energy sources. Within the electrolysis plants, the energy consumers and energy producers are linked via an internal AC grid.Depending on the availability and / or distance of a higher-level energy supply network (ESN), the internal AC network can either have no electrical connection at all with the higher-level ESN, i.e. be designed as a pure island network, or it can have an electrical connection designed for only a low power exchange between the internal AC network and the higher-level ESN. This is the case, for example, with electrolysis plants operated offshore. In particular, there is usually a requirement for the internal AC network to have black start capability, or at least brown start capability. It must therefore be able to start up without any energy supply or with only a limited energy supply from the higher-level ESN. The supply units used in such an island network are therefore subject to special requirements. Specifically, they should.

[0007] - allow a high-efficiency electrical supply to the electrolyzer assigned to them,

[0008] - enable pre-charging of the electrolyzer assigned to them,

[0009] - ensure that the internal AC network is started up with little or no external power supply - if necessary in conjunction with other supply units assigned to the internal AC network.

[0010] The technical article: Meng, X. [et al.]; “A Novel Multi-Scale Frequency Regulation Method of Hybrid Rectifier and Its Specific Application in Electrolytic Hydrogen Production”; IEEE Transactions on Power Electronics, Vol. 38, 2023, No. 1 , pp. 123-129 lEEE Xplore [online], DOI: 10.1109 / TPEL.2022.3207601 , In: IEEE; discloses a hybrid rectifier with a thyristor-based and a transistor-based rectifier. The transistor-based rectifier of the hybrid rectifier is used to provide frequency support for an AC grid connected to the hybrid rectifier on a short-term / low-power scale, e.g., to smooth the rate of frequency change and to gain time for the thyristor-based rectifier to take effect. The thyristor-based rectifier is used to provide frequency support for the AC grid on a long-term / high-power scale.

[0011] The publication DE 10 2020 124964 A1 also discloses a hybrid rectifier with a thyristor rectifier and a transistor rectifier for supplying a DC load from an AC network. When the DC voltage at a DC output of the hybrid rectifier is below a voltage threshold, the hybrid rectifier is operated in a first operating state in which a total active power is transported from the AC input to the DC output of the hybrid rectifier via the thyristor rectifier and not via the transistor rectifier. When the DC voltage at the DC output of the hybrid rectifier reaches or exceeds the voltage threshold, the total active power is transported from the AC input to the DC output of the hybrid rectifier via both the thyristor rectifier and the transistor rectifier.

[0012] The document DE 10 2018 133 641 A1 discloses a method for operating an electrolysis device with a converter connected to an AC voltage grid via a decoupling impedance, and an electrolyzer connected to the converter on the DC voltage side. At a grid frequency that corresponds to a nominal frequency of the AC voltage grid and is constant over time, the electrolysis device is operated with an electrical power that is between 50% and 100% of the nominal power of the electrolyzer. The converter is operated with a voltage-imprinting effect, so that the AC active power drawn from the AC voltage grid changes directly as a function of a change and / or a rate of change in the grid frequency in the AC voltage grid.

[0013] Object of the invention

[0014] The invention is based on the object of providing a supply unit for a DC consumer, in particular an electrolyzer, that meets the above-mentioned requirements in an improved manner. It is also an object of the invention to provide a method for operating the supply unit and an electrolysis system with such a supply unit.

[0015] Solution

[0016] The object of providing a supply unit for a DC consumer, in particular an electrolyzer, is achieved according to the invention with the features of independent patent claim 1. The object of providing a method for operating the supply unit is achieved according to the invention with the features of claims 11 and 14. The object of providing an electrolysis system with such a supply unit is achieved according to the invention with the features of claim 15. Advantageous embodiments of the supply unit are recited in claims 2 to 10. Advantageous embodiments of the method are recited in claims 12 and 13, and advantageous embodiments of the electrolysis system are recited in claims 16 and 17.

[0017] Description of the invention

[0018] A supply unit according to the invention for a DC consumer comprises: a DC connection for connection to the DC consumer, a first AC connection which is connected to a DC bus via a first AC / DC converter, a second AC connection which is connected to the DC connection via a second AC / DC converter, an energy storage device which is connected to the DC bus via a first DC / DC converter, a second DC / DC converter which connects the DC bus to the DC connection and can be operated to adjust the current with respect to the DC connection, and a control unit for controlling the supply unit, in particular the first and second AC / DC converters, the first and second DC / DC converters and the respectively associated isolating units.The supply unit is characterized in that the first DC / DC converter is designed as a bidirectional DC / DC converter and the control unit is configured to operate the first DC / DC converter in a voltage-regulating manner with respect to the DC bus, and the first AC / DC converter is designed as a bidirectional AC / DC converter and the control unit is configured to operate the first AC / DC converter in a voltage-regulating manner with respect to the first AC connection.

[0019] The term DC load refers to a device that consumes direct current (DC) electrical power during operation, in particular one that is powered by DC electrical power. However, this does not mean that it is designed exclusively to consume DC power. Rather, it is also possible for the device to operate both as a DC load and as a DC source, consuming DC power in some periods and generating DC power in others. The DC load can, in particular, be an electrolyzer. However, the application is not limited to an electrolyzer as a DC load. For example, certain electrolyzers can operate both as DC loads and as DC sources, in particular as fuel cells.The first DC connection can be designed for connection to a first secondary winding of a transformer unit, which provides a first AC voltage Ui from an AC network to the first AC connection of the supply unit. The second AC connection can be designed for connection to a second secondary winding of the transformer unit in order to provide a second AC voltage U2 from the AC network to the second AC connection of the supply unit. The first AC / DC converter as well as the second AC / DC converter can in particular be transistor-based AC / DC converters. The second AC / DC converter can also be designed as a bidirectional AC / DC converter, as is the case for the first AC / DC converter. The first DC / DC converter as well as the second DC / DC converter can each be designed as transistor-based DC / DC converters.

[0020] A method according to the invention for operating the supply unit is aimed, in a first aspect, at the electrical supply of the DC load, in particular an electrolyzer. In the method, the supply unit is connected to the DC load, i.e., in particular, the electrolyzer as a DC load, via its DC connection. A first AC voltage Ui is provided at the first AC connection of the supply unit, for example, by connecting the first AC connection to a first secondary winding of a transformer unit. Furthermore, a second AC voltage U2 is provided at the second AC connection of the supply unit, for example, by connecting the second AC connection to a second secondary winding of the transformer unit. The method comprises the following steps:

[0021] Supplying the DC consumer, in particular the electrolyzer, in partial load operation or during its pre-charging with a power flow through the first AC / DC converter, which is operated in a voltage-regulating manner with respect to the first AC connection, wherein a power flow through the second AC / DC converter is suppressed, and

[0022] Supplying the DC load, in particular the electrolyzer, in normal operation with a simultaneous power flow through the first AC / DC converter and the second AC / DC converter. The control unit of the supply unit is configured to operate the supply unit in a state connected to the AC grid and the DC load according to the operating method. The control unit can additionally be configured to operate the supply unit—optionally in a state connected to the AC grid and the DC load—according to the start-up method.

[0023] A method according to the invention for starting such a supply unit aims, in a second aspect, at a black start or brown start of the supply unit and also of an AC network comprising the supply unit. In the method, the supply unit is connected via its DC connection to the DC load, in particular an electrolyzer as a DC load. Furthermore, the supply unit is connected with its first AC connection to a first secondary winding and with its second AC connection to a second secondary winding of a transformer unit. The method for the black start or brown start comprises the following steps:

[0024] Charging the energy storage of the supply unit, if it is not already sufficiently charged,

[0025] Providing a DC bus voltage UDC-BUS on the DC bus by a voltage-setting operation of the first DC / DC converter

[0026] Providing a first AC voltage Ui at the first AC terminal of the supply unit by a voltage-adjusting operation of the AC / DC converter with respect to the first AC terminal,

[0027] Closing an AC disconnect unit assigned to the supply unit and / or the first AC / DC converter, if it is not already closed. The control unit of the supply unit is configured to operate the supply unit—if necessary, in a state connected to the AC grid and the DC load—according to the startup method. The control unit can additionally be configured to operate the supply unit in a state connected to the AC grid and the DC load according to the operating method.

[0028] With a supply unit designed in this way and the method, the problem mentioned above can be solved in a particularly efficient way. The supply unit thus allows a highly efficient electrical supply to the DC load assigned to it, which can in particular be designed as an electrolyzer. Specifically, in partial load operation the DC load is only supplied via a power flow from the first AC / DC converter, with a power flow from the second AC / DC converter being suppressed. As a result, the first AC / DC converter can be operated particularly efficiently and with a high degree of efficiency due to the lower operating voltage in the partial load range. Only during normal operation of the DC load is its electrical supply provided via simultaneous power flows through the first and second AC / DC converters.Since both AC / DC converters are connected to different AC voltages Ui, U2 via their respective assigned AC terminals, for example via different, in particular galvanically isolated, secondary windings of a transformer unit, the first AC / DC converter and the second AC / DC converter are decoupled from one another in such a way that voltage-regulating operation of the first AC / DC converter and, at the same time, current-regulating operation of the second AC / DC converter is possible. Furthermore, the overall losses incurred during conversion can be reduced. In order to achieve their respective assigned DC voltages, both AC / DC converters can be operated from their respective assigned AC voltages in such a way that excessive boosting and the associated conversion losses are avoided for each of the two AC / DC converters.

[0029] Pre-charging of the DC load assigned to the supply unit, in particular the electrolyzer, can also be carried out particularly efficiently. Because the first DC / DC converter is bidirectional and can be operated with voltage regulation with respect to the DC bus, it can maintain the DC bus voltage UDC.BUS applied to the DC bus at a constant value, particularly during voltage fluctuations in the internal AC network and / or voltage changes due to the energy content of the energy storage device. The second DC / DC converter can draw on this constant DC voltage and is then operated with current regulation with respect to the DC connection, i.e., is operated in such a way as to provide a predefined current at its output—and thus at the DC connection of the supply unit. In this way, the second DC / DC converter operates as a current source during pre-charging, enabling controlled pre-charging without uncontrolled current fluctuations.This also applies to partial load operation and / or normal operation of the supply unit, since the second DC / DC converter can also be operated in a current-controlling manner with respect to the DC connection. Because the supply unit itself has a suitably dimensioned energy storage unit, it is also guaranteed that the internal AC grid can be started up with little or no external power supply - if necessary in conjunction with other supply units assigned to the internal AC grid. If the energy storage unit is not sufficiently charged, it can be charged via an auxiliary energy source, such as a generator with a combustion engine or a fuel cell. The auxiliary energy source can be coupled to the internal AC grid for this purpose. It can have only a small nominal power, since charging the energy storage unit does not have to be 100% and also does not have to be completed within a short time.Regardless of this, with a large number of appropriately designed supply units connected to the internal AC grid, there are usually individual supply units with a sufficiently charged energy storage device, which can then be used as supply unit(s) for black start or brown start. During black or brown start, the first DC / DC converter can provide a predefined DC voltage on the DC bus by drawing power from the energy storage device. Due to its voltage-regulating operation with respect to the DC bus, the first DC / DC converter can keep this DC voltage constant on the DC bus – especially even in the event of a drop in the DC voltage at the energy storage device caused by the energy extraction.The first AC / DC converter can draw power from the constant DC bus voltage UDC-BUS of the DC bus and, due to its bidirectional operation, provide a first AC voltage Ui at the first AC connection - and via the first secondary winding also at the primary side of the transformer unit. This is possible in particular because the first AC / DC converter can be operated in a voltage-regulating manner with respect to the first AC connection and can thus ensure suitable premagnetization of the transformer unit. Advantageously, the first AC voltage Ui can be kept constant, at least temporarily. After that, an AC isolation unit arranged on the primary side of the transformer unit can be closed, provided it is not already closed, so that the AC voltage is present in the internal AC network, or at least in a sub-area of ​​the internal AC network.Other supply units assigned to the internal AC grid can synchronize and connect to the AC voltage present in the internal AC grid after generating an AC voltage Ui at their first AC connection in the same way. Energy generation units assigned to the internal AC grid, such as photovoltaic (PV) systems and / or wind turbines, can also synchronize and connect to the AC voltage present in the internal AC grid and maintained by the supply units already connected to it.

[0030] Advantageous embodiments of the invention are specified in the following description and the subclaims, the features of which can be used individually and in any combination with one another.

[0031] In one embodiment of the supply unit, the second AC / DC converter can be operated in a current-setting manner with respect to the DC connection. Accordingly, the control unit can also be configured to operate the second AC / DC converter in a current-setting manner with respect to the DC connection, such that a predetermined current is provided at its DC connection. This is advantageous if a power flow is also provided by the second AC / DC converter, for example during normal operation of the supply unit. In particular, with an electrolyzer as a DC consumer, a production rate in the electrolysis process can also be specified via the second AC / DC converter, just as is the case with the second DC / DC converter with its current-setting operation with respect to the DC connection. Alternatively or cumulatively, it is possible for the second DC / DC converter to be designed as a bidirectional DC / DC converter with respect to its power flow.In this way, particularly when an electrolyzer is used as a DC consumer, an electrical charge that may be available in the electrolyzer can be used in addition to the energy storage device when starting up the internal AC network. It can be advantageous for the second DC / DC converter to be able to operate to regulate the voltage with respect to the DC bus when power flows in the direction of the DC bus. In particular, the control unit can be configured to operate the second DC / DC converter to regulate the voltage with respect to the DC bus. In this way, the second DC / DC converter can optimally support the first DC / DC converter in setting a DC voltage on the DC bus. In addition, it is also possible to use a bidirectional second DC / DC converter to discharge an input capacitance of the DC consumer in a controlled manner and to transfer the charge via the DC bus and the first DC / DC converter into the energy storage device in order to store it there.For this purpose, the energy storage device can advantageously comprise one or more supercapacitors and / or one or more accumulators.

[0032] In one embodiment, the second DC / DC converter can be designed to reduce a DC voltage UDC.BUS applied to the DC bus to a DC voltage UDC,2I applied to the DC connection, i.e. to operate in a step-down manner from the DC bus towards the DC connection. When power flows from the DC connection towards the DC bus, it can correspondingly operate in a step-up manner. In this way, the second DC / DC converter can, on the one hand, pre-charge an input capacitance of the DC load starting from a discharged, i.e., voltage-free input capacitance in a controlled manner. On the other hand, it is also possible to completely, or at least almost completely, discharge the input capacitance of the DC load again if necessary.

[0033] It is possible for the AC grid itself to have two different AC voltages, in particular two AC voltages with different voltage amplitudes. In this case, the AC voltage with the smaller voltage amplitude can be connected to the first AC terminal and the AC voltage with the larger voltage amplitude to the second AC terminal. Alternatively, however, it is also possible for the supply unit to additionally comprise a transformer unit or to be connected to a transformer unit. The transformer unit can have a primary side for connection to an AC grid and a secondary side with a first secondary winding and a second secondary winding. The first secondary winding can be designed to provide the first AC voltage Ui and can be connected to the first AC terminal.The second secondary winding can be designed to provide the second AC voltage U2 and be connected to the second AC terminal. In this case, a winding ratio of the transformer unit can be designed such that a second amplitude Ü2 of the second AC voltage U2 is greater, in particular by at least a factor of 1.3, than a first amplitude Ü1 of the first AC voltage Ui. This can be advantageous, for example, when a DC bus voltage exceeds a DC voltage applied to the electrolyzer while the electrolyzer is operating at its maximum possible power, for example its nominal power. Alternatively, however, a winding ratio of the transformer unit can also be designed such that a second amplitude Ü2 of the second AC voltage U2 is smaller, in particular by at least a factor of 1.3, than a first amplitude Üi of the first AC voltage Ui.This can be advantageous, for example, when a DC bus voltage falls below a DC voltage applied to the electrolyzer while the electrolyzer is operating at its maximum possible power, for example, its nominal power. Within the scope of the invention, however, it is also possible for the first amplitude Üi of the first AC voltage Ui to be equal to the second amplitude Ü2 of the second AC voltage U2.

[0034] In this case, a total power flow provided by the supply unit during normal operation, for example at a nominal power of the DC consumer, in particular the electrolyzer, can be provided to a share of 25% to 40% via the first AC / DC converter and to a share of 60% to 75% via the second AC / DC converter.

[0035] In order to suppress the power flow through the second AC / DC converter during partial load operation and / or when pre-charging the DC consumer, the second AC / DC converter can be connected to the DC connection of the supply unit via a circuit breaker. Alternatively or additionally, an AC circuit breaker can also be arranged between the second AC connection and the second AC / DC converter. The circuit breaker can be arranged in a connection module of the supply unit. The supply unit can also comprise further circuit breakers, for example between the first AC / DC converter and the first AC connection, between the first DC / DC converter and the energy storage device and / or between the second DC / DC converter and the DC connection. If necessary, several of the circuit breakers, including several fuses, can be arranged in the connection module of the supply unit.

[0036] Various DC loads also require electrical power to AC loads during operation. For example, in an electrolyzer, pumps for conveying and removing the media, and possibly even a heater, must be electrically powered as DC loads. Advantageously, the supply unit can also have an additional AC auxiliary supply connection to supply one or more AC loads assigned to the DC load.

[0037] An electrolysis plant according to the invention comprises: one or more electrolyzers as DC consumers, one or more supply units, and one or more transformer units that are part of the one or more supply units or via which the one or more supply units can be connected to an AC grid. This results in the advantages already mentioned in connection with the supply unit and the method.

[0038] In one embodiment, the electrolysis system can comprise multiple supply units, wherein at least one of the one or more transformer units has more than two secondary windings, and wherein a plurality of supply units can be connected to the AC grid via a common transformer unit. The electrolysis system can additionally comprise an auxiliary energy source for charging the energy storage device(s). The auxiliary energy source can be configured as an auxiliary energy source operable with hydrogen and can comprise, for example, an internal combustion engine or a fuel cell.

[0039] Short description of the characters

[0040] The invention is illustrated below with the aid of figures, of which

[0041] Fig. 1 shows a first embodiment of an electrolysis plant according to the invention;

[0042] Fig. 2 shows a second embodiment of an electrolysis plant according to the invention.

[0043] Character description

[0044] Fig. 1 shows a first embodiment of an electrolysis system 100 according to the invention with a plurality of supply units 20, each connected to a DC consumer 50 - here, for example, an electrolyzer 51. The electrolyzer is part of an electrolysis unit 55, which, in addition to one or more pumps 53 for conveying electrolysis reactants and for removing electrolysis products, a heater 54 for controlling the temperature of the electrolysis reactants and, if applicable, the electrolyzer 50, also includes a control unit 52 for controlling the electrolysis unit 53. The plurality of supply units 20 can each be of the same type, or at least largely of the same type, which is why only one of the plurality of supply units 20 is shown in Fig. 1. Additional supply units 20 are symbolized in Fig. 1 by the three dots.The supply unit 20 has a first AC connection 22, which is connected to a DC bus 26 via a first bidirectionally operable AC / DC converter 24. A second AC connection 23 of the supply unit 20 is connected to a DC connection 21 of the supply unit 20 via a second AC / DC converter 25 and a circuit breaker 31. Furthermore, the first DC connection 22 is connected to an auxiliary AC supply connection 32, via which AC loads assigned to the DC load—here, for example, the pump 53 and the heater 54—can be supplied.

[0045] The DC bus 26 is connected to an energy storage device 29 via a bidirectionally operable first DC / DC converter 27. Depending on the voltage ratio between the energy storage device 29 and a voltage UDC-BUS applied to the DC bus 26, the first DC / DC converter 27 can be a DC / DC converter that boosts the voltage towards the DC bus 26 or a DC / DC converter that bucks the voltage towards the DC bus 26. Within the scope of the invention, a combined boost / buck converter can also be used as the first DC / DC converter 27. The first DC / DC converter 27 can be operated in a voltage-regulating manner with respect to the DC bus 26, i.e., it is capable of setting and maintaining a constant predefined voltage UDC-BUS on the DC bus 26. For this purpose, it can transfer electrical power from the energy storage device 29 to the DC bus 26 or back. The DC bus 26 is also connected to the DC connection 21 of the supply unit 20 via a second DC / DC converter 28.The second DC / DC converter 28 is designed as a step-down DC / DC converter from the DC bus 26 toward the DC connection 21 and can be operated in a current-setting manner with respect to the DC connection 21. It is thus able to set and maintain a predefined current at its connection connected to the DC connection 21. Optionally, the second DC / DC converter 28 can also be designed to be bidirectionally operable, so that not only electrical power can be transferred from the DC bus 26 toward the DC connection 21, but also from the DC connection 21 toward the DC bus 26. The supply unit 20 further has a control unit 30 for its control. For the purposes of controlling the electrolysis system 100, this control unit is connected to the control unit 53 of the electrolysis unit 55, which is symbolized in Fig. 1 by a dashed line.To supply power to the DC load 50, the supply unit 20 is connected via a transformer unit 40 and an AC isolating unit 41 to an AC grid 60 having an AC voltage Lhetz with an amplitude ÜNetz. The transformer unit 40 has a primary side 40P coupled to the AC grid 60 and a secondary side 40S that can be coupled to several supply units 20 and comprises several secondary windings—four secondary windings, for example. Of the four secondary windings 45-48, the AC voltage Ui with an amplitude Üi is applied to the secondary winding 45, while the second AC voltage U2 with an amplitude Ü2 is applied to the secondary winding 46. The secondary winding 45 is connected to a first AC terminal 22 of the supply unit 20, the secondary winding 46 is connected to the second AC terminal 23 of the supply unit 20.Furthermore, the secondary winding 47 can be connected to a first AC terminal 22 and the secondary winding 48 to a second AC terminal 23 of a further supply unit 20 (not shown in Fig. 1). The secondary winding 47 can have a first AC voltage Ui and the secondary winding U2 can have a second AC voltage. The amplitudes of the first AC voltages Ui at the secondary windings 45 and 47 can be the same or different. Analogously, the amplitudes of the second AC voltages U2 at the secondary windings 46 and 48 can be the same or different. The further supply unit 20 can be connected to the same electrolyzer 51 of the supply unit 20. Alternatively, the further supply unit 20 can also have a separate further electrolyzer 51 or a further electrolysis unit 55 assigned to it.

[0046] During partial load operation of the electrolyzer 51 and / or during its pre-charging, the isolating switch 31 is open, preventing power flow through the second AC / DC converter 25. In these cases, the supply is via the second DC / DC converter 28, which is operated in a current-regulating manner and draws electrical power from the DC bus 26. The power drawn from the DC bus 26 is fed back to it by the first AC / DC converter 24 from the AC grid 60, and if necessary also by the first DC / DC converter 27 from the energy storage device 29. The first DC / DC converter 27 is operated in a voltage-regulating manner on the DC bus 26. Should the DC bus voltage UDC-BUS increase and exceed a predefined value, the first DC / DC converter 24 can counteract the increase by directing power flow into the energy storage device 29.Conversely, should the DC bus voltage UDC-BUS drop, the first DC / DC converter 24 can counteract the drop by directing power from the energy storage device 29 into the DC bus 26. During normal operation, the electrolyzer 51 is supplied by a simultaneous power flow from both the first AC / DC converter 24 and the second AC / DC converter 25. For this purpose, a voltage at the output of the second AC / DC converter 25 was previously adjusted to match a voltage present at the DC terminal 21, and the isolating switch 31 was closed. Even during normal operation, the first DC / DC converter can be operated in a voltage-regulating manner with respect to the DC bus 26.

[0047] During a black and / or brown start, an internal AC network 60 is to be established on the primary side 40P of the transformer unit 40, and the transformer unit is to be pre-magnetized. For this purpose, a predefined DC bus voltage UDC-BUS is established on the DC bus 26 via the first DC / DC converter 27. The first AC / DC converter 24 is operated in a voltage-regulating manner with respect to the first DC terminal 22, thus generating an AC voltage at the first secondary winding 45—and thus also on the primary side 40P of the transformer unit 40. In the event that the supply unit 20 is the first of the several supply units 20 to build up the internal AC network, i.e. if there is no AC voltage in the AC network yet, the AC separation unit 41 can be closed and the AC voltage in the AC network can develop together with the AC voltage generated on the primary side of the transformer unit 40.In the event that an AC voltage is already present in the AC network, the AC separation unit 41 can be open and only closed after the AC voltage on the primary side 40P of the transformer unit 40 has been synchronized with the AC voltage UNetz in the AC network 60. Alternatively, it is also possible for the supply unit 20 to have a further AC separation unit (not shown in Fig. 1) arranged between the first AC / DC converter 24 and the first AC connection 22. For synchronization (with the AC separation unit closed), an AC voltage applied to the AC-side connection of the first AC / DC converter 24 can be synchronized with an AC voltage applied to the first secondary winding 45 and thus to the first AC connection 22 of the supply unit 20. After synchronization has taken place, the further AC separation unit can then be closed.The formation of the AC voltage in the internal AC grid 60 does not necessarily have to take place up to a nominal voltage of the AC grid 60 solely by the supply unit 20 that is first connected to the internal AC grid 60 and using only its assigned energy storage device 29. Rather, it is possible for the build-up of the nominal AC voltage Ugrid to take place in stages. For example, the supply unit 20 that is first connected to the internal AC grid 60 can generate only a fraction of the nominal voltage of the AC grid 60, to which other supply units 20 assigned to the internal AC grid 60 can then synchronize. After their synchronization, these can also be connected to the internal AC grid 60 and, with their respective energy storage devices 29, support a further increase in the AC voltage llgrid in the AC grid 60. Alternatively or cumulatively, other energy generation systems, for example photovoltaics (PV) or.

[0048] Wind turbines are synchronized with the internal AC grid 60 and connected to it.

[0049] Fig. 2 shows a second embodiment of an electrolysis unit 100 according to the invention. It is similar in many respects to the first embodiment of the electrolysis unit 100, which is why reference is made to the description of Fig. 1 with regard to the similar features. Only the differences from the embodiment shown in Fig. 1 are explained below.

[0050] The second embodiment of the electrolysis system 100 shown in Fig. 2 has only one supply unit 20, which, however, in contrast to the supply unit 20 of Fig. 1, itself comprises a transformer unit 40 and an AC isolating unit 41. The transformer unit 40 is connected with its primary side 40P to the AC grid 60 via the AC isolating unit 41. The secondary side 40S of the transformer unit 40, in contrast to that of Fig. 1, has only two secondary windings 45, 46, namely a first secondary winding 45 connected to the first AC terminal 22 and a second secondary winding 45 connected to the second AC terminal 23. Partial load operation, normal operation, as well as pre-charging of the electrolyzer 51 can take place analogously to the manner described in Fig. 1. The same also applies to starting up an internal AC grid 60 during a black or brown start. In the electrolysis plant 100 in Fig.2, only one supply unit 20 with a correspondingly associated electrolysis unit 55 is shown. Alternatively, however, it is also possible for the electrolysis system to comprise additional supply units 20, each with an associated electrolysis unit 55, which are coupled to the AC grid 60 in parallel with the illustrated supply unit 20.

[0051] List of reference symbols

Claims

Patent claims 1. Supply unit (20) for a DC consumer (50), wherein the supply unit (20) comprises: a DC connection (21) for connection to the DC consumer (50), a first AC connection (22) which is connected to a DC bus (26) via a first AC / DC converter (24), a second AC connection (23) which is connected to the DC connection (21) via a second AC / DC converter (25), an energy storage device (29) which is connected to the DC bus (26) via a first DC / DC converter (27), a second DC / DC converter (28) which connects the DC bus (26) to the DC connection (21) and can be operated in a current-setting manner with respect to the DC connection (21), and a control unit (30) for controlling the supply unit (20), characterized in that the first DC / DC converter (27) is designed as bidirectional DC / DC converter and the control unit (30) is configured to operate the first DC / DC converter (27) in a voltage-regulating manner with respect to the DC bus (26),and the first AC / DC converter (24) is designed as a bidirectional AC / DC converter and the control unit (30) is configured to operate the first AC / DC converter (24) in a voltage-regulating manner with respect to the first AC terminal (22).

2. Supply unit (20) according to claim 1, wherein the control unit (30) is configured to operate the second AC / DC converter (25) in a current-setting manner with respect to the DC connection (21).

3. Supply unit (20) according to claim 1 or 2, wherein the second DC / DC converter (28) is designed as a bidirectional DC / DC converter.

4. Supply unit (20) according to one of claims 1 to 3, wherein the supply unit (20) additionally comprises a transformer unit (40) or is connected to a transformer unit (40), wherein the transformer unit (40) has a primary side (40P) for connection to an AC network (60) and a secondary side (40S) with a first secondary winding (45) and a second secondary winding (46), wherein the first secondary winding (45) is connected to the first AC terminal (22) and the second secondary winding (46) is connected to the second AC terminal (23).

5. Supply unit (20) according to claim 4, wherein a winding ratio of the transformer unit (40) is designed such that a second amplitude Ü2 of the second AC voltage (U2) is greater, in particular by at least a factor of 1.3, than a first amplitude Ü1 of the first AC voltage (Ui).

6. Supply unit (20) according to claim 4, wherein a winding ratio of the transformer unit (40) is designed such that a second amplitude Ü2 of the second AC voltage (U2) is smaller, in particular by at least a factor of 1.3, than a first amplitude Ü1 of the first AC voltage (Ui).

7. Supply unit (20) according to one of the preceding claims, wherein the energy storage device (29) comprises a supercapacitor and / or an accumulator.

8. Supply unit (20) according to one of the preceding claims, wherein the second DC / DC converter (28) is designed to reduce a DC voltage (UDC-BUS) applied to the DC bus (26) to a DC voltage (UDC,2I) applied to the DC terminal (21).

9. Supply unit (20) according to one of the preceding claims, wherein the second AC / DC converter (25) is connected to the DC connection (21) via a circuit breaker (31), wherein optionally the circuit breaker (31) is arranged together with one or more circuit breakers and / or one or more fuses in a connection module of the supply unit (20).

10. Supply unit (20) according to one of the preceding claims, additionally comprising a further AC auxiliary supply connection (32) for supplying one or more AC consumers (53, 54) associated with the DC consumer (50).

11. A method for operating a supply unit (20) according to one of the preceding claims, which is connected via its DC connection (21) to an electrolyzer (51) as a DC consumer (50), and which is connected to a first AC voltage (Ui) with its first AC connection (22) and to a second AC voltage (U2) with its second AC connection (23), comprising the steps: Supplying the electrolyzer (51) in partial load operation or when precharging the electrolyzer (51) with a power flow through the first AC / DC converter (24), which is operated in a voltage-regulating manner with respect to the first AC connection (22), wherein a power flow through the second AC / DC converter (25) is suppressed, and Supplying the electrolyzer (51) in normal operation with a simultaneous power flow through the first AC / DC converter (24) and the second AC / DC converter (25).

12. The method according to claim 11, wherein a pre-charging of the electrolyzer (51) takes place by means of a power flow through the current-setting second DC / DC converter (28).

13. The method according to claim 11 or 12, wherein a total power flow provided by the supply unit (20) during normal operation of the electrolyzer (51) takes place to a proportion of 25% - 40% via the first AC / DC converter (24) and to a proportion of 60% to 75% via the second AC / DC converter (25).

14. A method for starting up a supply unit (20) according to one of claims 1 to 10, which is connected via its DC connection (21) to an electrolyzer (51) as a DC consumer (50), and which is connected via its first AC connection (22) to a first secondary winding (45) and via its second AC connection (23) to a second secondary winding (46) of a transformer unit (40), wherein a black start or brown start of the supply unit (20) comprises the following steps: Providing a DC bus voltage (UDC-BUS) on the DC bus (26) by a voltage-setting operation of the first DC / DC converter (27) Providing a first AC voltage (Ui) at the first AC terminal (22) of the supply unit (20) by a voltage-adjusting operation of the first AC / DC converter (24) with respect to the first AC terminal (22), Closing an AC separation unit (41) associated with the supply unit (20) and / or one of the first AC / DC converter (24), if it is not already closed.

15. Electrolysis plant (100) comprising: one or more electrolyzers (51) as DC consumers (50), one or more supply units (20) according to one of claims 1 to 10, and one or more transformer units (40) which is / are part of the one or more supply units (20) and / or via which the one or more supply units (20) can be connected to an AC network.

16. Electrolysis plant (100) according to claim 15 with a plurality of supply units (20), wherein at least one of the one or more transformer units (40) has more than two secondary windings (45 - 48), and wherein a plurality of supply units (20) can be connected to the AC network (60) via a common transformer unit (40).

17. Electrolysis plant (100) according to claim 15 or 16, additionally comprising an auxiliary energy source for charging the energy storage device(s) (29), in particular an auxiliary energy source operable with hydrogen, for example an internal combustion engine or a fuel cell.

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