Electrolysis system
Patent Information
- Application Number
- EP2023745169
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-08-09
- Filing Date
- 2023-07-21
- Publication Date
- 2025-04-23
AI Technical Summary
Existing electrolysis systems face challenges in achieving energy-efficient and cost-effective operation, particularly in large-scale systems, due to the complexity and high costs associated with thyristor-based rectification, which results in significant harmonic disturbances and reactive power requirements, limiting operational flexibility and network stability.
The use of a voltage source converter (VSC), specifically a modular multilevel converter (MMC) with IGBT-based technology, for direct current supply to multiple electrolysis systems connected in parallel, allowing for individual power control and bidirectional power transfer, thereby reducing harmonic emissions and reactive power needs, and enabling network services like voltage support.
This approach enhances energy efficiency, reduces operational complexity and costs, improves flexibility, and allows for the provision of network services, such as voltage support and active power control, while maintaining high reliability and efficiency in large-scale electrolysis systems.
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Abstract
Description
[0001] Description
[0002] Electrolysis system
[0003] The invention relates to an electrolysis system comprising at least two electrolysis plants and a power supply source.
[0004] Electrolysis, processes in which a chemical reaction is induced using electrical current, is used in many technical fields and is used, for example, to produce various substances. For example, hydrogen and oxygen can be produced through the electrolysis of water. For the operation of electrolysis devices, also called electrolysis stacks, electrolyzers, or electrolysis plants, it is desirable, especially on a large-scale basis, that they can be operated as energy-efficiently and safely as possible.
[0005] Nowadays, hydrogen is produced from water using methods such as proton exchange membrane (PEM) electrolysis, an anion exchange membrane, or alkaline electrolysis. The electrolysis plants use electrical energy to produce hydrogen and oxygen from the water supplied. This process takes place in a so-called electrolysis stack, made up of several electrolysis cells. The electrolysis stack can in turn consist of several electrolysis modules, which in turn are made up of many electrolysis cells. Water is introduced as the reactant into the electrolysis stack, which is subjected to a direct current (DC voltage). After passing through the electrolysis cells, two fluid streams consisting of water and gas bubbles (O2 and H2 respectively) emerge.
[0006] It is currently known that several electrolyzers or electrolysis systems can be electrically connected in parallel, for example. Each electrolyzer is supplied via its own galvanically isolated circuit consisting of a transformer with a tap changer for coarse control of the electrolyzers and a rectifier with a thyristor circuit for fine control of the electrolysis system. This represents a very complex implementation. Alternatively, to reduce the circuit complexity, it is also known that the electrolyzers can be connected in parallel and operated via a rectifier. However, this can result in current distribution based on the resistance ratios of the electrolyzers, thus leading to significant derating and the risk of one or more electrolyzers operating outside their safe operating ranges.
[0007] Water electrolysis plants require high direct current to operate. Since the electrical grid typically operates as an alternating current system, the use of power electronic rectifiers is necessary to connect the electrolysis plant to the grid. In future large-scale plants, this will require the use of numerous parallel rectifier systems with existing designs.
[0008] For example, EP 3 752 665 A1 discloses a grid connection for an electrolysis system with several electrolyzers connected in parallel. The rectifier comprises a thyristor set with a plurality of thyristors. By controlling the rectifier, the level of the DC voltage at the output can be adjusted. The controllability of the rectifier is achieved by selecting the firing times of the thyristors in the thyristor set. To stabilize the DC voltage generated by the rectifier, EP 3 753 665 A1 further provides a capacitor connected in parallel to the rectifier output. Furthermore, an adjustable filter device is provided, having an inductance and a capacitor, by means of which a harmonic generated by the rectifier, which is generated during operation by the switching of the thyristor set of the rectifier, can be dampened.In future large-scale plants with a large number of electrolysis plants in one electrolysis system, a corresponding number of power electronic rectifiers would have to be provided for the grid connection. These rectifiers would be used in a complex rectifier system and connected in parallel in order to be able to provide the high direct current requirements for the electrolysis plants. Due to the grid feedback caused by the harmonics of the thyristors, this can only be achieved with a correspondingly large amount of filtering effort and is associated in particular with considerable additional costs for the installation and operation of the filter system. In large-scale plants, the technical limitations and the effort involved in widely used thyristor-based rectification are therefore very disadvantageous. However, this is accepted in the concepts known to date because thyristor technology is a tried and tested technology.
[0009] The invention is therefore based on the object of specifying an electrolysis system with a direct current supply for several electrolysis plants connected in parallel, which is designed for large-scale plants and has cost advantages over the known approaches, while at the same time offering improved operating behavior with regard to energy-efficient operation.
[0010] The object is achieved according to the invention by an electrolysis system comprising at least two electrolysis plants, a power supply source with a direct voltage output and a central supply line, wherein the central supply line is connected to the direct voltage output of the power supply source, so that a direct current at a first direct voltage can be fed into the central supply line, and wherein the electrolysis plants are electrically connected in parallel to the central supply line, wherein for the direct current supply from the public power grid at a grid connection point a voltage source converter (VSC), in particular a modular multilevel converter (MMC), is connected which converts an input-side alternating voltage into the output-side first direct voltage at the direct voltage output, wherein each electrolysis plant has a,a DC / DC converter which converts the first DC voltage into a respective second DC voltage is connected in parallel to the DC voltage output of the voltage source converter (VSC), in particular of the modular multilevel converter (MMC), such that the second DC voltage drops across the electrolysis system, wherein each of the DC / DC converters is controllable and / or adjustable to adjust the level of its second DC voltage, wherein controllable bypass switches are provided so that when the bypass switch is closed, a respective DC / DC converter can be bypassed such that the connected electrolysis system can be directly supplied with the first DC voltage.
[0011] With the invention, individual power control for the electrolysis systems is achieved for the first time in an electrolysis system through the advantageous interaction of a voltage-source converter (VSC) - in particular an IGBT-based converter, for example a modular multilevel converter (MMC converter) at the grid connection point, with the respective DC / DC converters of the electrolysis systems. Thanks to the central voltage-source converter (VSC), embodied, for example, as a modular multilevel converter (MMC), the AC current is converted to DC current only once at a grid connection at the grid connection point. For this purpose, an IGBT-based rectifier, provided, for example, by a modular multilevel converter, is used at the connection.A central connection of the voltage-source converter (VSC), particularly one designed as a modular multilevel converter (MMC), to an AC grid is thus possible, providing the electrical DC power for electrolysis at the DC voltage output on the central supply line with the first DC voltage. The central supply line therefore functions as a DC bus line, providing the electrical power at the first DC voltage.
[0012] The invention is based on the realization that, due to the high direct currents required for electrolysis, rectifiers based on thyristor technology are currently primarily used. While the previously preferred thyristor-based rectification and AC connection technology is proven, reliable, and exhibits comparatively low losses during operation, the use of thyristors results in strong grid perturbations due to harmonics, as well as high reactive power requirements. This will create a significant additional filter and compensation requirement, particularly for future large electrolysis systems with multiple electrolysis units or electrolyzers, which will increase both costs and space requirements accordingly.Since both the reactive power demand and harmonics depend on the operating point, the filter systems must be designed for all operating points of a connected large electrolysis plant in order to achieve the required operational flexibility and grid stability in a large-scale plant on an industrial scale.
[0013] Furthermore, the increasing elimination of rotating masses, for example, due to the shutdown of nuclear and coal-fired power plants, is expected to lead to a significant decrease in grid short-circuit power and thus grid stability in future grids. It is therefore becoming increasingly important for large plants – in addition to their primary function – to be able to provide grid services for the public power grid. This is only possible to a limited extent with current thyristor technology (active power control). Furthermore, in very weak grids, additional measures are required to even be able to use thyristor technology.
[0014] When combining renewable energy generation systems (RE systems), such as photovoltaic systems, which sometimes already provide direct current, with electrolysis systems, the use of thyristor technology also requires multiple conversion of the voltage form (DC-AC-DC), which leads to increased costs and losses.
[0015] If several thyristor rectifiers are operated in parallel, such as in large systems, they can be supplied with phase-shifted AC voltages to reduce filter requirements. However, with such a concept, it is necessary to keep all the rectifiers at comparable, uniform operating points or to draw a similar power output. If operation with different operating points must be considered, for example, due to different aging of the individual electrolysis modules, the filter requirements increase again. This significantly limits operational flexibility and can only be improved with considerable systemic effort and expense.
[0016] The invention is the first to use a voltage-source converter (VSC), specifically a modular multilevel converter (MMC), to transfer power between the AC and DC grids in an electrolysis system. This offers numerous advantages over a thyristor-based supply topology. A particular advantage is that this enables bidirectional power transfer between the public power grid and the central supply line in an electrolysis system, enabling grid services such as voltage support or the assumption of grid-providing functions.
[0017] The use of insulated-gate bipolar transistors (IGBTs) in the modular multilevel converter that supplies the electrolysis with direct current has proven particularly advantageous for the operating behavior of the electrolysis system. The IGBT is a semiconductor component used in power electronics because it combines the advantages of a bipolar transistor, such as good conduction behavior, high blocking voltage, robustness, and the advantages of a field-effect transistor through almost power-free control. The use of IGBTs is widespread, for example, in a so-called three-phase B6 bridge circuit with an IGBT-based rectifier, which achieves very precise control of the electrolysis current with good rectification.The distinctive advantages of IGBTs are their high voltage and current limits: voltages of up to 6500 V and currents of up to 3600 A at a power of up to several megawatts, which makes IGBTs ideal for use in electrolysis systems. Therefore, the use of IGBTs for the voltage-source converter (VSC), particularly implemented as an IGBT-based modular multilevel converter (MMC), is very advantageous in the context of the electrolysis system proposed here.
[0018] On the electrolysis side, the respective DC / DC converters individually reduce the first DC voltage for an electrolysis system to a respective second DC voltage to the desired values without any significant conversion losses. This means that the electrolysis systems in the electrolysis system can be regulated in terms of electrolysis output and can also be switched on and off. Partial load capability or partial load control is achieved by regulating the electrolysis current. By coordinating the power controllers, island grid capability can also be ensured if required - in addition to or alternatively to a grid connection to the public grid. This offers considerable cost advantages, for example, in remote on-shore or off-shore systems. To provide higher electrolysis currents, several DC / DC converters can be connected in parallel and used in a respective connecting line.
[0019] To further improve energy efficiency in the electrolysis system, it is additionally provided that it comprises several controllable bypass switches so that a respective DC / DC converter, e.g. an IGBT-based step-down converter, can be bridged in a connecting line by a respective controllable bypass switch if required. When a DC / DC converter is bypassed, the first DC voltage then drops completely across the electrolysis system connected to the bridged DC / DC converter. With bridged DC / DC converters, the second DC voltage therefore corresponds to the first DC voltage. Operating the DC / DC converter in such a way that the second DC voltage, i.e. the output voltage of the DC / DC converter, is as equal as possible to the first DC voltage, i.e. the input voltage of the DC / DC converter, can be replaced by bridging the DC / DC converter.This avoids the electrical losses that would occur during normal operation when the DC / DC converter is powered. For particularly energy-efficient operation, this advantageously means that, for example, only the electrolysis systems with the lowest resistances can be supplied via the DC / DC converter, while the others are supplied directly via the first DC voltage. The respective bypass switches can be controlled, for example, by a central computing device in the electrolysis system, which computing device is also designed, in particular, to control and / or regulate the DC / DC converters. This provides the electrolysis system with a bypass device having a number of controllable bypass switches, enabling particularly advantageous and energy-efficient load control of the electrolysis systems connected to the central DC supply line.
[0020] In a particularly preferred embodiment of the electrolysis system, the DC / DC converter is designed as an IGBT-based step-down converter for individual power control of the electrolysis system.
[0021] Preferably, the voltage-source converter (VSC), particularly embodied as a modular multilevel converter (MMC), is designed for bidirectional operation and connected to a central grid connection point, allowing voltage support to be achieved by providing reactive power to the public grid. Advantageously, other grid services are also possible, such as assuming grid-providing functions.
[0022] More preferably, the voltage-source converter (VSC) is designed as an IGBT-based modular multilevel converter, so that electrical power from the central supply line can be fed into the public power grid at the grid connection point as needed. This is a special and advantageous form of bidirectional operation of the electrolysis system. This is possible when surplus power is available on the central supply line that cannot be taken up by the electrolysis plant, for example through additional feed-in of electrical direct current power from a renewable energy plant (RE plant) into the central supply line or during partial load operation or maintenance of individual electrolysis plants or modules of the electrolyzer. During normal operation, an MMC therefore transfers power optionally from the DC side to the AC side or vice versa, which favors particularly flexible operation of the electrolysis system.
[0023] In a preferred embodiment, the electrolysis plants are connected in parallel with each other with respect to the central supply line in such a way that an electrolysis plant is connected to the central supply line via a respective connecting line.
[0024] This leverages the advantages of the DC bus principle with its central direct current supply line, which allows for and also provides for an independent connection line for each electrolysis plant. In the electrolysis system, the central DC supply network can be flexibly expanded as needed and can be expanded to include additional electrolysis plants, possibly by adjusting the feed-in power of the power sources feeding into the DC grid to the required power consumption of the electrolysis plants or electrolyzers.
[0025] In the case of power consumption via the grid connection point to the public power grid, this can be done and adjusted flexibly via the central modular multilevel converter.
[0026] In this case, a respective IGBT-based step-down converter is preferably connected in a connecting line, the input voltage of which corresponds to the first direct voltage and the second direct voltage of which can be adapted to a respective operating voltage of the electrolysis system.
[0027] Thus, the required operating voltage at the output of the IGBT-based buck converter in the respective connecting line can be individually adjusted and set at the level of the individual electrolysis system. Precise regulation and control of the second DC voltage, and thus the operation of the electrolysis system in this connecting line, is achieved.
[0028] The use of multiple modular high-current DC / DC converters connected in parallel in a single connecting cable is particularly advantageous. This enables industrial application in combination with a number of electrolysis units in an electrolysis system.
[0029] The buck converter (also known as a step-down converter) converts the first DC voltage on the central DC supply line as input voltage into a second DC voltage, a lower output voltage. It is also called a step-down converter.
[0030] A connecting line advantageously forms a DC line or a DC branch from the central supply line for one or more electrolysis systems or electrolyzers operating with direct current in the respective connecting line. Thus, any number of electrolysis systems of any size can be advantageously connected to one or more such central DC branch lines using controllable IGBT-based DC / DC converters, particularly so-called buck converters or step-down converters, thus expanding the electrolysis system accordingly.
[0031] In a particularly preferred embodiment, the step-down converter is designed in a modular manner in a connecting line, wherein a step-down converter has at least two DC / DC step-down converters connected in parallel, the input voltage of which corresponds to the first DC voltage.
[0032] Preferably, the at least two parallel-connected DC / DC step-down converters of the modular step-down converter are electrically connected to one another on the output side and are each designed to regulate the second DC voltage.
[0033] This enables precise regulation of the electrolysis power in a single connecting cable to the respective operating voltage of the supplied electrolysis system, depending on the operating situation. The IGBT-based and modular supply topology allows power regulation as well as operational fault or failure tolerance, so that individual modules of the electrolysis system can continue to operate in the event of a fault. This increases operational reliability and cost-effectiveness. A further advantage is that the parallel-connected DC / DC converters can be operated in an "interleaved" mode. This increases the DC power quality, improves the efficiency of the electrolysis cells, and simplifies the design of passive elements, such as inductors.
[0034] The use of IGBT-based DC / DC converters in a connecting line allows for individual power control of the individual electrolysis strings in the connecting lines without significantly impacting grid disturbances. A modular design of the DC / DC converters can also reduce costs. Furthermore, the modular approach allows for reduced continued operation of the electrolysis plant in the event of individual semiconductor failures. In currently selected solutions using thyristors, a semiconductor failure leads to a total failure of the rectifier string or the associated module series of the electrolysis plant, which can only be remedied through complex repairs, so downtimes must be factored in.
[0035] To improve energy efficiency in the electrolysis system, it can be provided that it comprises several bypass switches, whereby the IGBT-based buck converter can be bridged by one switch each in a connecting line if required. When a buck converter is bypassed, the first DC voltage drops completely across the electrolysis system connected to the bridged buck converter. In bridged buck converters, the second DC voltage therefore corresponds to the first DC voltage. Operating the buck converter in such a way that the second DC voltage, i.e. the output voltage of the buck converter, is as equal as possible to the first DC voltage, i.e. the input voltage of the buck converter, can be replaced by bridging the buck converter, so that the losses that would arise from such operation of the buck converter can be avoided.For particularly energy-efficient operation, for example, only the electrolysis systems with the lowest resistances can be supplied via the step-down converter, while the others are supplied directly via the first DC voltage. The switches can be controlled, for example, by a computing device in the circuit arrangement, with the computing device also being designed, in particular, to control and / or regulate the step-down converters.
[0036] The proposed electrical supply topology in an electrolysis system offers increased flexibility in a wide range of areas compared to existing approaches. The use of an IGBT-based modular multilevel converter (MMC) at the central grid connection point enables the provision of additional grid services for the public power grid. Renewable energy systems, such as wind turbines or photovoltaic systems, can also feed their generated electrical energy directly into the central supply line, which is designed as a DC bus, and the electrolysis systems in the respective connecting lines can be individually controlled from one another.
[0037] Preferably, therefore, a modular step-down converter is connected to an electrolysis system having a plurality of electrolysis modules electrically connected in series.
[0038] This creates a regulated direct current supply to the electrolysis system and the electrolysis modules in a connecting line. This makes it possible to precisely adjust the total electrolysis output in a connecting line using the regulated direct current output as needed. In particular, partial load operation can be achieved in an electrolysis system, for example if the electrical power supply on the central DC supply line drops or if hydrogen production is to be temporarily reduced. It is also possible and particularly advantageous for the electrolysis modules of an electrolysis system to be individually bridged by a bridging circuit with a switchable bridging line and a controllable electrical switch, allowing an electrolysis module of an electrolysis system to be taken out of operation if necessary, for example for maintenance purposes or partial load operation of the electrolysis system.
[0039] In a preferred embodiment, the step-down converter is therefore designed as a controllable buck converter, so that the supply of electrolysis current to the electrolysis system can be adapted to any fluctuating feed-in power from the power supply source into the central supply line. The controllability of the step-down converter enables a flexible supply of electrolysis direct current to the electrolysis system in a connecting line, which can be adjusted with regard to the electrolysis power. Whether the step-down converter operates continuously or intermittently depends on the inductance, switching frequency, input voltage, output voltage and the flowing output current. Since these parameters can sometimes change rapidly, the transition between the two operating modes must generally be taken into account (e.g. prevented) when designing the circuit, especially a regulator.The two operating modes differ in terms of the control characteristic, i.e. the dependence of the output voltage on the duty cycle, as well as in terms of the interference emission.
[0040] Preferably, the step-down converter is designed as a controllable buck converter with output voltage control via pulse-width modulation in continuous operation. This allows for continuous operation of the buck converter and controllability of the electrolysis current supplied to an electrolysis system via the respective connecting line.
[0041] In a further preferred embodiment of the electrolysis system, the power supply source comprises a wind turbine as a power generator, to which a rectifier with a DC voltage output is connected, wherein the DC voltage output is designed for the first DC voltage.
[0042] In this way, a connection or direct current connection and supply of the electrolysis systems from a wind turbine or wind farm is achieved in the electrolysis system via the central DC supply line, whereby isolated grid operation is advantageously possible. If the electrolysis system is operated in an isolated grid, there is no connection to the public power grid or connection activation, so the grid connection can be interrupted at the grid connection point as needed, i.e. the central modular multilevel converter can be taken out of operation or even eliminated. However, bidirectional operation is possible at any time, so that feed-in to the public power grid is also possible. It is also possible that the renewable energy system already supplies direct current at a suitable voltage level, so that in these cases no additional rectifier is required to feed in renewable electricity.
[0043] In a further preferred embodiment, the power supply source comprises a photovoltaic system as a power generator, the DC voltage output of which is designed for the first DC voltage, wherein the DC voltage output is connected to the central supply line.
[0044] This allows the DC voltage level at the DC output to be flexibly adjusted to the specified first DC voltage on the central DC supply line. If necessary, boost converters, known as boost inverters, are connected downstream of the PV generator to adjust the specified DC voltage level at the DC output. This is necessary if the DC output of the photovoltaic system itself does not provide a sufficiently high DC voltage level to feed into the central supply line.
[0045] With this design, an advantageous connection or connection to and supply of an electrolysis system with electricity generated from a photovoltaic system is achieved in the electrolysis system via the central DC grid on the central supply line. If necessary, off-grid operation based on photovoltaics is also possible. Analogously and in line with the advantages of connecting the electrolysis system to a wind turbine described above, an off-grid operation is independent of the public power grid, which enables particularly great design flexibility and self-sufficient deployment options away from the public power grid if required or in addition to a grid connection, which is still possible in the electrolysis system for bidirectional operation via the modular multi-level converter.When feeding PV power into the central supply line, a step-up converter (DC / DC converter) may need to be provided on the PV side to increase the voltage of the PV generator as needed, in order to ensure that direct current is fed into the central supply line at a given first direct voltage.
[0046] Preferably, the central supply line in the electrolysis system is designed for operation with a first DC voltage in the medium-voltage range of 20 kV, in particular between 1.5 kV and 30 kV. In this case, an adaptation to the operating voltage of the electrolysis systems in the electrolysis system must be made during the design. Designs for higher operating voltages of 10 kV to 30 kV are flexibly possible if required.
[0047] The DC voltage level at the DC output of the voltage source converter (VSC), particularly the modular multilevel converter, can be flexibly adapted to the respective requirements of the electrolysis system and the transmission line, with a high output voltage preferably being selected as the specified first DC voltage, which is preferably greater than at least 1.5 kV. When designing and constructing the DC voltage level on the central supply line, the nominal voltages of the grid levels commonly used in energy transmission can be used, for example, or these values can serve as a guide for the DC voltage level of the first DC voltage.Electrical energy is transmitted via high-voltage lines at various medium-voltage and high-voltage grid levels with the following typical nominal voltages: medium voltage of 3 kV, 6 kV, 10 kV, 15 kV, 20 kV, 30 kV; high voltage of 60 kV, and 110 kV. The central supply line functions very advantageously as a central DC bus line, enabling a direct high-voltage direct current supply to the electrolysis systems in the electrolysis system.
[0048] Further advantages, features and details of the invention emerge from the following description of preferred embodiments and from the drawings. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the single figures can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention.
[0049] Embodiments of the invention are explained in more detail with reference to a drawing. It shows schematically and in a highly simplified manner:
[0050] FIG 1 an electrolysis system with an electrolysis plant and a wind turbine;
[0051] FIG 2 an electrolysis system with an electrolysis plant and a photovoltaic plant;
[0052] FIG 3 the DC bus supply topology with the central supply line for direct current and with electrolysis plants connected to it;
[0053] FIG 4 shows a section of the supply topology according to FIG 1 with a modular step-down converter comprising several DC / DC converters;
[0054] FIG. 5 shows a schematic block diagram of the supply topology of an electrolysis system with a central modular multilevel converter (MMC) at the grid connection point. FIG. 6 shows a supply topology of an electrolysis system according to FIG. 5 with a bridging device.
[0055] The same reference symbols have the same meaning in the figures.
[0056] FIG. 1 shows an electrolysis system 100 according to the invention. The electrolysis system 100 comprises an electrolysis unit 1 with two electrolysis systems 1A, 1B and a power supply source 3 connected to the electrolysis unit 1. The power supply source 3 has a wind turbine 19 as the power generator, which serves as a renewable energy system (RE system) and a source of green electricity. The electrolysis system 100 is supplied with electrolysis current via a central supply line 5, which is supplied with direct voltage. Thus, the central supply line 5 forms a central DC bus line, by means of which a direct current for the electrolysis process can be supplied directly to the electrolysis unit 1.
[0057] Each of the electrolysis systems 1A, 1B of the electrolysis system 100 is connected to a supply connection 23A, 23B on the central supply line 5 via a respective connecting line 9A, 9B, so that a parallel connection of the electrolysis systems 1A, 1B is realized. The electrolysis system 1A has at least one electrolyzer 15A and the electrolysis system 1B has at least one electrolyzer 15B. The electrolyzers 15A, 15B can be designed either as PEM electrolyzers, as AEM electrolyzers (AEM: Anion Exchange Membrane) or as alkaline electrolyzers, with combinations also being possible. It is possible for a plurality of electrolyzers 15A, 15B to be connected in series in a branch of the respective electrolysis system 1A, 1B to be supplied via the corresponding connecting line 9A, 9B.On the power supply source 3 side, a rectifier 13A having a DC voltage output 7 is connected downstream of the wind turbine 19 on the output side of a generator of the wind turbine 19. This allows an alternating current generated by the generator of the wind turbine 19 to be converted into a direct current at a predetermined first DC voltage 31 at the DC voltage output 7 and fed into the central supply line 5. This creates a central DC network designed for a predetermined first DC voltage 31, for example a DC medium voltage. In order to couple the electrical power generated by the wind turbine 19 and fed into the central supply line 5, no further active components, such as transformers, are required when connecting the wind turbine 19 to the central supply line 5, so that a particularly simple supply topology is implemented.
[0058] The DC voltage level at the DC voltage output 7 of the rectifier 13A can be flexibly adapted to the respective requirement in the electrolysis system 100, with a high output voltage at the medium voltage level being preferably selected as the predetermined first DC voltage 31, which is at least greater than 1.5 kV. Typically, a medium voltage level of 20 kV is set for the first DC voltage 31. For the first DC voltage 31 on the central supply line 5, the nominal voltages of the network levels commonly used in energy transmission can also be used, for example, when designing and constructing the central DC network through the central supply line 5, or these values can serve as a guide for the DC voltage level.Here, electrical energy is transmitted via high-voltage lines at various medium-voltage and high-voltage network levels with the following typical nominal voltages: medium voltage of 3 kV, 6 kV, 10 kV, 15 kV, 20 kV, 30 kV; high voltage of 60 kV, 110 kV. The central supply line 5 functions very advantageously as a central DC bus line, which directly enables a high-voltage direct current supply to the connected electrolysis systems 1A, 1B in an electrolysis system 100.
[0059] For a connection and direct current supply of the electrolysis systems 1A, 1B matched to the respective second direct voltage 33A, 33B as the operating voltage, a step-down converter 11A is connected in the connecting line 9A and a step-down converter 11B is connected in the connecting line 9B. The step-down converters 11A, 11B, also called step-down converters, are based on IGBT technology, i.e. on transistor technology as opposed to the previously used thyristor technology, so that individual power control of the individual electrolysis strands is provided in the connecting lines 9A, 9B. The input of the step-down converter 11A is connected to the supply connection 23A and, analogously, the input of the step-down converter 11B is connected via the supply connection 23B to the central supply line 5.On the output side, the step-down converters 11A, 11B are each connected to the electrolyzer 15A, 15B in the connecting line 9A, 9B, so that a respective direct current is provided for the electrolysis in the electrolyzers 15A, 15B at a respective adjustable voltage level of a second direct voltage 33A, 33B for the operating voltage. During operation of the electrolysis system 100, a medium-voltage direct current network is provided on the central supply line 5 as a central DC network at the first direct voltage 31 and is used to supply the electrolysis systems 1A, 1B connected in parallel to the central supply line 5 with electrolysis current. By using a high voltage, a direct current can be provided and electrical direct current power can be fed into the central supply line 5. The electrolysis system 100 can be designed and constructed particularly flexibly.Expandable, for example, by connecting additional electrolysis systems 1A, 1B, comprising additional electrolyzers 15A, 15B, via a connecting line 9A, 9B. Optionally, grid-independent island grid operation is possible with the electrolysis system 100, provided no power is drawn from the public power grid 25. Preferably, however, a draw of electrical power and a connection to the public power grid 25 at a central grid connection point 25 is provided.
[0060] The step-down converters 11A, 11B connected to the connecting lines 9A, 9B are implemented as DC / DC converters (step-down converters) and are each designed such that their input voltage corresponds to the specified first DC voltage 31 in the central DC network on the central supply line 5, and their respective output voltage is adjusted or set to a respective second DC voltage 33A, 33B as the respective operating voltage of the connected electrolysis system 1A, 1B. The step-down converters 11A, 11B are designed as controllable step-down converters, so that the supply of the electrolysis system 1A, 1B with electrolysis current can be adjusted and tracked to a fluctuating feed-in power of the power supply source 3 into the central supply line 5.The step-down converters 11A, 11B can be configured, for example, as adjustable buck converters with output voltage control via pulse-width modulation in continuous operation, which enables continuous operation with exceptional performance. The step-down converters 11A, 11B are IGBT-based, thus achieving individual power control in the electrolysis system 1A, 1B. The IGBT-based design of the step-down converters 11A, 11B limits the influence of grid perturbations from the public power grid 25 and achieves the greatest possible decoupling, thus enabling stable operation.
[0061] In the electrolysis system 100 shown in FIG. 1, it is also possible for an electrolysis system 1A, 1B to be arranged, for example, at the base of the tower of a respective wind turbine 19, and there directly connected to the central supply line 5. This is advantageous, for example, for onshore applications and the installation of wind turbines 19 in remote areas and for island grid operation. A wind turbine 19 here also refers to a wind farm or wind park—onshore or offshore—with a plurality of wind turbines 19.
[0062] According to the embodiment of FIG. 1, a connection to the public power grid 25 is additionally set up on the power supply source 3 side in the electrolysis system 100. For this purpose, as illustrated in FIG. 1 in dashed lines, a separate supply connection 23C is provided in the central supply line 5. The connection to the public power grid 25 is made via a connecting transformer 27 at the grid connection point 35 and a downstream central modular multilevel converter 13, which has a DC voltage output 7. The central modular multilevel converter 13 is based on IGBT technology and has a corresponding number of IGBTs as power components. The modular multilevel converter (13) is a possible and preferred specific embodiment of a voltage source converter (VSC).In principle, other VSC-based converters can therefore also be used at the grid connection point 35 to feed power from the public power grid 25 into the central supply line 5.
[0063] The modular multilevel converter 13 is designed and flexibly adjustable in such a way that the first direct voltage 31 is delivered to its direct voltage output 7 and fed into the central supply line 5. Corresponding voltage levels for the first direct voltage can be selected, for example, from medium-voltage levels of 3 kV, 6 kV, 10 kV, 15 kV, 20 kV, 30 kV, or high-voltage levels of 60 kV or 110 kV. The voltage level is flexibly adaptable and changeable. Furthermore, the modular multilevel converter 13 enables bidirectional operation when using the supply connection 23C as a grid connection, so that direct current from the public power grid 25 can be fed into the central supply line 5 as needed, as well as direct current from the DC grid of the central supply line 5 can be fed out at the first direct voltage 31.Thus, if required, electricity from the public power grid 25 can also be fed into the central supply line 5 at the supply connection 23C with the appropriate voltage and made available for use for electrolysis purposes in the electrolysis system 1. The advantage here is that by providing a connection to the public power grid 25, for example, replacement requirements can be met, for example when the wind turbine 19 is not producing electricity or is producing only a very limited amount of electricity due to maintenance, or during phases of darkness, so that a backup solution is maintained to ensure the most continuous supply and uniform operation of the electrolysis systems 1A, 1B for hydrogen production. If necessary, even in the event of an undersupply of electrical DC power on the central supply line 5, one or more electrolysis systems 15A, 15B can be operated at partial load or taken off the DC grid.An adapted partial load operation is achieved as required in the respective connecting line 9A, 9B by means of the controllable step-down converters 11A, 11B, by means of which the direct current power can be adjusted via the respective second direct voltage 33A, 33B at the output of the step-down converter 11A, 11B. In a pure island grid operation of the system network, there is generally no need for a backup due to the lack of an available connection option to a public grid 29. Here, however, a specially set up and provided "redundancy" or the provision of a system reserve in the island grid for the feeding wind turbine 19 or a photovoltaic system 21 (see FIG. 2), e.g. Through the modular design of these renewable energy feed-in systems and the installation of some reserve modules in the electrolysis plants 15A, 15B, a largely maintenance-independent supply and uninterrupted, largely self-sufficient operation can be achieved.In this case, common reserve modules can also be bundled and provided for several central supply lines 5, which are either switchable or contribute to the supply of several supply lines by coupling the central supply lines 5.
[0064] When using the Modular Multilevel Converter s 13, an IGBT-based rectifier, at grid connection point 35, only minimal harmonic emissions occur. Additional filtering is not required at all, or at most, to a significantly lesser extent than with comparable thyristor-based systems. The reactive power demand of this connection and supply topology can be flexibly adjusted. Consequently, very little or no reactive power compensation is required.
[0065] Thanks to the individually adjustable reactive power requirement of the IGBT-based Modular Multilevel Converter 13 as a central rectifier system, it can contribute not only to control power but also to voltage support of the public power grid 25. In isolated grids, such as local renewable energy grids, these IGBT-based Modular Multilevel Converters 13 can also have a grid-shaping effect.
[0066] In this concept, renewable energy systems that themselves provide direct current can feed directly into the DC bus. The inverter required when using thyristor-based rectifiers is eliminated. This eliminates additional conversion losses. If more power is fed into the central supply line 5, which acts as a DC bus, than is consumed by the electrolysis in the electrolysis unit 1, the IGBT-based converter 13 at the grid connection point 35 is also able to feed the excess power into the public power grid 25. This type of linking or electrical interconnection of the individual electrolysis systems 1A, 1B via the central supply line 5 decoupling the systems takes place. The electrolysis lines of the electrolysis system 1A, 1B or the respective electrolyzers 15A, 15B can be operated at their respective individual operating points. This also increases the controllability of the entire electrolysis system 100.In a further exemplary embodiment of an electrolysis system 100 according to the invention, FIG. 2 shows an alternative power supply source 3 for supplying the electrolysis unit 1 with direct current. The power supply source 3 comprises a photovoltaic system 21 with a large number of PV modules (not shown in detail). The photovoltaic system 21 can, for example, be designed as a large-area and powerful free-field system - preferably in sunny regions - so that PV outputs of 10 MW and more are available for the electrolysis. On the electrolysis unit 1 side, a substantially analogous system concept to that in FIG. 1 is applied, and corresponding system components, ie the electrical connection and supply of the electrolysis systems 1A, 1B, are provided via the central supply line 5, which in turn is designed as a central DC bus line or DC connection string.To achieve this, the electrolysis system 1A is electrically connected to the supply connection 23A and, correspondingly, the electrolysis system 1B is electrically connected to the supply connection 23B via a respective connecting line 9A, 9B, into which respective IGBT-based step-down converters 11A, 11B are connected.
[0067] Thus, in the electrolysis system 100 configured in this way, the power supply source 3 comprises a photovoltaic system 21, a so-called PV generator, as the power generator. This already supplies a DC voltage at the generator output, which is already designed for the predetermined first DC voltage 31. The DC voltage output 7 is then formed by the PV generator output and is directly connected to the central supply line 5.
[0068] In order to achieve a desired and advantageous DC voltage level at the first DC voltage 31 for feeding DC power into the central supply line 5 with respect to the photovoltaic system 21 as the power supply source 3, it is also possible, as shown in the exemplary embodiment in FIG. 2, for a boost converter 17 to be connected to the DC output of the PV generator of the photovoltaic system 21.
[0069] The boost converter 17, also called a step-up converter or boost regulator, is a special type of DC-DC converter in power electronics. The output voltage is always greater than the input voltage, so that the step-up converter 17 provides the first DC voltage 31 of the desired DC voltage level specified for a feed-in at the DC voltage output 7. A higher voltage reduces the material requirements and thus the cost of the lines downstream of the feed-in from the power supply source 3.
[0070] The boost converter 17 is designed for the voltage level and supplies the first DC voltage 31 at the output. The boost converter 17 is designed to be controllable, allowing flexible adjustment of the supplied output voltage. The power of the photovoltaic system 21 is coupled and fed into the central supply line 5 directly at the DC voltage output 7 of the boost converter 17. For the transmission and collection of electrical power by the electrolysis unit 1, the electrolysis systems 1A, 1B are connected to the central supply line 5 via a respective connecting line 9A, 9B, as described in more detail above. The respective step-down converters 11A, 11B also decouple the regulation of the electrolysis current requirements in the connecting lines 9A, 9B, thus enabling individual operation of these DC connecting lines, which is particularly important for partial load requirements.Feeding grid power from the public grid 23 into the central supply line 5 is also possible in the PV application and is implemented in a similar manner to that described in FIG. 1, with a central modular multilevel converter 13 at the grid connection point. The basic concept of supplying and coupling multiple electrolysis plants 1, 1A, 1B using a central DC bus supply line 5 is shown schematically and simplified in FIG. 3. A three-phase AC connection is made at the grid connection point 35. A central IGBT-based modular multilevel converter 13 is connected to the AC input at the grid connection point 25, to whose DC output 7 the central supply line 5 is connected and leads off as a DC bus. The modular multilevel converter 13 supplies the first DC voltage 31, for example a medium voltage at 20 kV, as the output voltage.The electrolysis unit 1 comprises several electrolysis systems 1A, IB, IC, which in turn comprise a plurality of electrolysis modules 29A, 29B, 29C, 29D, 29E electrically connected in series. Each electrolysis system 1A, IB, IC is connected to the central supply line 5 via a respective connecting line 9A, 9B, 9C. To provide a respective second DC voltage 33A, 33B, 33C, a step-down converter 11A, 11B, 11C based on IGBT technology is connected to the connecting lines 9A, 9B, 9C. Thus, the level of the second DC voltage 33A, 33B, 33C can be controlled or regulated. Bidirectional operation is achieved by the modular multilevel converter 13 based on IGBTs, so that excess power on the central supply line 5 can be fed into the public power grid 25 via the grid connection point 35.
[0071] Not shown in detail in FIG 3 is a possibility of feeding direct current from a renewable energy plant (RE plant) into the central supply line 5. In this regard, reference is made to the exemplary embodiments in FIG 1 and FIG 2.
[0072] The concept of supplying and coupling multiple electrolysis systems 1A, IB, IC achieves a regulated direct current supply to the supplied electrolysis system 1A, IB, IC with the electrolysis modules 29A - 29E in a respective connecting line 9A, 9B, 9C, whereby two direct voltage levels must be taken into account. This makes it possible to adjust the total electrolysis power in a connecting line 9A, 9B, 9C precisely as needed using the regulated direct current power via the respective regulation of the second direct voltage 33A, 33B, 33C. In particular, partial load operation can be achieved in an electrolysis system 1A, IB, IC, for example, if the supply of electrical power on the central DC supply line 5 decreases, or if hydrogen production is to be temporarily reduced.It is also possible and particularly advantageous that the electrolysis modules 29A - 29E of an electrolysis system 1A, IB, IC can be bridged individually and module by module by means of a bridging circuit - not shown in detail in FIG 3 - with a switchable bridging line and with a controllable electrical switch, and as a result, if required or optionally, one or more of the electrolysis modules 29A - 29E of an electrolysis system 1A, IB, IC can be taken out of operation, for example for maintenance purposes or to bring about a required partial load operation of the respective electrolysis system 1A, IB, IC or also selected electrolysis modules 29A - 29E, e.g. according to the degree of aging or an upcoming maintenance interval.
[0073] The concept of a modular DC / DC conversion in a step-down converter 11 will be explained using FIG. 4 as an example. A section of the supply topology shown in FIG. 3 shows a modular step-down converter 11 comprising several DC / DC converters 11A, 11B, 11C connected in parallel, which supplies an electrolysis system 11A. Two DC voltage lines with corresponding positive and negative polarity are provided for the central supply line 5, to which the DC / DC converters 11A, 11B, 11C are each connected with their DC voltage inputs with the correct polarity as modules of the one step-down converter 11. This parallel connection forms a connecting line 9A for supplying the electrolysis system 1A. The electrolysis system 1A comprises an electrolyzer 15A having several electrolysis modules 29A-29E.The use of IGBT-based DC / DC converters 11A, 11B, 11C allows individual power control of the electrolysis system 1A connected via a connecting line 9A without significantly impacting grid disturbances. The modular design of the step-down converter 11, comprising multiple DC / DC converters 11A, 11B, 11C, enables greater system flexibility with reasonable cost reduction and provides redundancy for reliable operation. Thus, the modular design of the step-down converter 11 enables at least reduced continued operation of the electrolysis systems 1A in the event of individual semiconductor component failures. This is advantageous over known concepts in which semiconductor failures lead to a failure of the rectifier string or the associated electrolyzer 15A, which would require repair during a system shutdown.
[0074] The DC / DC converters 11A, 11B, 11C each comprise a transistor 37 embodied as an IGBT, a storage choke 39, and a diode 41, as illustrated in the exploded view of FIG. 4. The transistors 37 and the storage chokes 39 are each arranged in series with the electrolyzer 15A, which is to be supplied via a respective step-down converter 11. The diodes 41 are correspondingly connected in parallel with the respective electrolyzer 15A. The level of the second DC voltage 33, which is provided by the step-down converter 11 and drops across the electrolyzer 11A, can be regulated via the transistor 37. For this purpose, the transistors 37 can be connected, for example, to a computing device 43 (not shown in detail in FIG. 4) - see FIG. 5 and the corresponding description - wherein the corresponding control for regulating and / or controlling the step-down converter 11 is carried out via the computing device 43.It is possible for individual electrolysis modules 29A-29E of electrolysis system 1A or electrolyzer 15A to be bypassed by a bridging circuit, although this is not shown in detail in FIG 4. The bypass circuit can be equipped with a switchable bypass line and with a controllable electrical switch, so that bridging can be effected individually and module by module. This means that one or more of the electrolysis modules 29A-29E of electrolysis system 1A can be taken out of operation as needed or optionally. This is very advantageous, for example, for maintenance purposes or to bring about the necessary partial load operation of the respective electrolysis system 1A or selected electrolysis modules 29A-29E, e.g. depending on the degree of aging or an upcoming maintenance interval.
[0075] In combination with the IGBT-based modular multilevel converter 13 at the grid connection point 35 according to the embodiments shown in FIGS. 1 to 3, it is possible to offer additional grid services for the public power grid 25. Renewable energy systems (RE systems) can additionally and as needed feed directly into the central supply line 5 as a DC bus - not explicitly shown in FIGS. 3 and 4 - and the electrolysis systems 1A, 1B, and 1C can be individually controlled from one another. In this case, the rectification of the alternating current from the public grid 25 is performed only once, centrally at the grid connection point 35. For this purpose, an IGBT-based modular multilevel converter 13 is used as a central component when the system is connected to a medium-voltage grid to supply the first DC voltage to the central supply line 5.
[0076] Fig. 5 shows a schematic and highly simplified representation of a section of an electrolysis system 100. Only one particularly advantageous circuit and bridging concept in the electrolysis system 100 is intended to be demonstrated. This circuit provides a direct current supply to several electrolyzers 15A, 15B connected electrically in parallel, wherein the electrolyzers 15A, 15B are each connected via an IGBT-based step-down converter 11A, 11B in parallel to the output of a central modular multilevel converter 13, which acts as a rectifier. The modular multilevel converter 13 converts an AC voltage applied on the input side from the public power grid 25 into a first DC voltage 31 and is IGBT-based.This first DC voltage 31 is applied via the parallel connection branches 45A, 45B defined by the connecting lines 9A, 9B, each branch comprising one of the electrolyzers 15A, 15B and one of the step-down converters 11A, 11B. The first DC voltage 31 is converted by the step-down converter 11A into the second DC voltage 33A, which is applied across the electrolyzer 15A. Accordingly, the first DC voltage 31 is also converted by the second step-down converter 11B into the second DC voltage 33B, which is applied across the electrolyzer 11B. In addition to the two electrolyzers 11A, 11B shown, the supply topology shown in the electrolysis system 100 can of course also be used to supply DC voltage to further electrolyzers, which are likewise connected via a step-down converter as a further branch in parallel to the output of the central modular multilevel converter 13, corresponding approximately to FIG. 3.
[0077] In order to be able to operate the electrolyzers 15A, 15B at a desired operating point, which for example lies within a safe operating range, the step-down converters 11A, 11B are controllable and / or regulatable to adjust the level of the second direct voltage 33A or 33B. In addition, the modular multilevel converter 13 can also be controllable and / or regulatable to adjust the level of the first direct voltage 31. Thus, direct current power can be fed into the central supply line 5 at a predetermined first direct voltage 31. In particular, it can be provided that both the modular multilevel converter 13 and the step-down converters 11A, 11B, as well as any additional step-down converters of additional connection branches that may be present, are controllable or regulatable.For controlling the rectifier 13 and / or the step-down converters 11A, 11B, the supply topology of the electrolysis system 100 can, for example, comprise a computing device 43, via which the modular multilevel converter 13 and / or the step-down converters 11A, 11B can be controlled or regulated. For this purpose, the computing device 43 can be connected to one or more measuring devices - not shown in more detail here - via which, for example, a quantity of substance produced by one of the electrolyzers 15A, 15B, a respective resistance of one or more of the electrolyzers 15A, 15B and / or a respective current flow through one or more of the electrolyzers 15A, 15B can be determined. The control and / or regulation of the modular multilevel converter 13 for adjusting the level of the first DC voltage 31 orControl or regulation of the step-down converters 11A, 11B to adjust the level of the second DC voltages 33A, 33B can be carried out, for example, depending on the specific amount of substance and / or depending on the respective resistance or, if applicable, other influencing variables of the electrolyzers 11A, 11B and / or the respective current flow through the electrolyzers 11A, 11B. External factors include, for example, the current electricity price and the availability of electricity generation from renewable energy. This also applies accordingly to additional electrolyzers and additional step-down converters that may be present in addition to the connection branches 45A, 45B. The step-down converters 11A, 11B and any additional step-down converters that may be present are part of the supply topology of the electrolysis system 100, to which the electrolyzers 11A, 11B and any additional electrolyzers that may be present can be connected.
[0078] FIG. 6 shows a supply topology of an electrolysis system 100 corresponding to FIG. 5 with a bypass device. In this case, according to the exemplary embodiment shown in FIG. 6, it is additionally provided that controllable bypass switches 47A, 47B are provided with a respective activatable switching element, which can also be controlled via the computing device 43, so that the step-down converters 11A, 11B can be bypassed when a correspondingly closed switch is used. When the step-down converter 11A, 11B is bypassed by the bypass switch 47A, 47B, i.e., when a switching element for a respective bypass path is activated for bypassing, the first DC voltage 31 generated by the modular multilevel converter 13 drops directly across the electrolyzer 11A or 11B, specifically bypassing the respective step-down converter 11A, 11B.During bridging, the corresponding electrolyzers 15A, 11A are therefore supplied as needed and optionally directly from an intermediate circuit of the first DC voltage 31 via the respective connecting line 9A, 9B. Thus, in FIG 6, the bridging switch 47A is activated as an example, i.e. the corresponding switch for the bridging path is closed and the step-down converter 11A is bridged. The bridging switch 47B is not activated. The switching element of the bridging switch 47B is switched here in a switching state for supplying current to the step-down converter 11B. As a result, a bridging device with a number of controllable bridging switches 47A, 47B is provided in the electrolysis system 100, and a particularly advantageous and energy-efficient load control of the electrolysis systems 1A, 1B connected to the central DC supply line is enabled.
[0079] In the electrolysis system 100, an electrolysis unit 1 comprises, in addition to the described supply topology, all electrolyzers connected to it. These can, for example, each comprise at least one proton exchange membrane, wherein the proton exchange membrane is designed in particular for generating hydrogen through the electrolysis of deionized and / or distilled water. However, it is also possible to use electrolyzers based on alkaline electrolysis or anion exchange membrane electrolysis.
[0080] The use of a modular multilevel converter 13 (MMC converter) enables the central direct current supply and direct current transmission in the electrolysis system 100, specifically bidirectionally. The modular multilevel converter 13 can be used to offer grid services that go beyond the actual transmission task. The use in combination with electrolysis systems in an electrolysis system 100 with a central supply line 5 designed as a DC bus according to the present invention is particularly advantageous. The use of parallel modular high-current DC / DC converters for the second direct voltage 22 in the electrolysis system 100 is of great advantage for an industrial application in combination with an electrolysis system 11A, 11B. The coupling of electrolysis systems 11A, 11B in a large hydrogen production plant via a DC bus is thus possible.
[0081] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.
Claims
Patent claims 1. Electrolysis system (100) comprising at least two electrolysis units (1A, 1B), a power supply source (3) with a direct voltage output (7) and a central supply line (5), wherein the central supply line (5) is connected to the direct voltage output (7) of the power supply source (3) so that a direct current at a first direct voltage (31) can be fed into the central supply line (5), and wherein the electrolysis units (1A, 1B) are electrically connected in parallel to the central supply line (5), wherein for the direct current supply from the public power grid (25) a voltage-source converter (13) is connected to a grid connection point (35), which converts an input alternating voltage into the output-side first direct voltage (31) at the direct voltage output (7), wherein each electrolysis unit (1A, 1B) in each case converts the first direct voltage (31) into a second direct voltage (33A,33B) is connected in parallel to the DC voltage output (7) of the voltage-source converter (13) in such a way that the second DC voltage (33A, 33B) drops across the electrolysis system (1A, 1B), wherein each of the DC / DC converters (11A, 11B) is controllable and / or adjustable to adjust the level of its second DC voltage (33A, 33B), wherein controllable bypass switches are provided so that when the bypass switch is closed, a respective DC / DC converter (11A, 11B) can be bypassed in such a way that the connected electrolysis system (1A, 1B) can be directly supplied with the first DC voltage (31).
2. Electrolysis system (100) according to claim 1, wherein the DC / DC converter (11A, 11B) is designed as an IGBT-based step-down converter (11A, 11b) for individual power control of the electrolysis system (HA, 11b).
3. Electrolysis system (100) according to claim 1 or 2, wherein the voltage-source converter (13) is designed for a bidirectional Operation is designed and connected to a central grid connection point (35) so that voltage support can be effected by providing reactive power to the public power grid (25).
4. Electrolysis system (100) according to claim 3, wherein the voltage source converter (13) is designed as an IGBT-based modular multilevel converter (13), so that electrical power from the central supply line (5) can be fed into the public power grid (25) at the grid connection point (35) as needed.
5. Electrolysis system (100) according to one of the preceding claims, in which the electrolysis systems (1A, 1B) are connected in parallel with one another with respect to the central supply line (5) in such a way that an electrolysis system (1A, 1B) is connected to the central supply line (5) via a respective connecting line (9A, 9B).
6. Electrolysis system (100) according to claim 5, wherein a respective IGBT-based step-down converter (11A, 11B) is connected into a connecting line (9A, 9B), the input voltage of which corresponds to the first DC voltage (31) and the second DC voltage (33B, 33C) of which is adaptable to a respective operating voltage of the electrolysis system (1A, 1B).
7. Electrolysis system (100) according to claim 6, wherein in a connecting line (9A, 9B) the step-down converter (11A, 11B) is designed in a modular manner, wherein a step-down converter (11A, 11B) has at least two DC / DC step-down converters (21A, 21B, 21C) connected in parallel, the input voltage of which corresponds to the first DC voltage (31).
8. Electrolysis system (100) according to claim 7, wherein the at least two parallel-connected DC / DC step-down converters (21A, 21B) of the modular step-down converter (11A, 11B) are electrically connected to one another on the output side and are each designed to regulate the second DC voltage (33A, 33B).
9. Electrolysis system (100) according to claim 8, wherein the modular step-down converter (11A, 11B) is connected to an electrolysis system (1A, 1B) having a plurality of electrolysis modules (29A, 29B, 29C, 29D, 29E) electrically connected in series.
10. Electrolysis system (100) according to one of the preceding claims, wherein the power supply source (3) comprises a wind turbine (19) as a power generator, to which a rectifier (13A) having a DC voltage output (7) is connected, wherein the DC voltage output (7) is designed for the first DC voltage (31).
11. Electrolysis system (100) according to one of the preceding claims, wherein the power supply source (3) comprises a photovoltaic system (21) as a power generator, the DC voltage output (7) of which is designed for the first DC voltage (31), wherein the DC voltage output (7) is connected to the central supply line (5).
12. Electrolysis system (100) according to one of the preceding claims, wherein the central supply line (5) is designed for operation with a first DC voltage (31) in the medium voltage of 20 kV, in particular between 1.5 kV and 30 kV.