Systems for green-hydrogen production and control methods thereof

Abstract

The disclosure relates to efficient systems (10, 100) and methods for green-hydrogen production. A system (10) for off-grid green-hydrogen production is provided, the system (10) comprising: a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources, an electrolyser module (2) configured to produce green hydrogen based on the power provided by the renewable-energy source module (1), a grid-forming energy-storage module (3) configured to provide grid-forming capabilities to the renewable-energy source module (1) and the electrolyser module (2), a plurality of power-converter modules (C1, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the grid-forming energy-storage module (3), which are electrically connected to each other, and a central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (C1, C2, C3).

Description

[0001] SP3227

[0002] SYSTEMS FOR GREEN-HYDROGEN PRODUCTION AND CONTROL METHODS THEREOF

[0003] Field of the invention

[0004] The invention relates to systems for green-hydrogen production and control methods thereof.

[0005] Background art

[0006] Hydrogen production by electrolysis of water and powered by renewable-energy sources is referred to as green-hydrogen production, as opposed to grey-hydrogen produced from fossil fuels such as natural gas. An advantage of green hydrogen is its versatility, as hydrogen can for example be used to store and transport renewable energy, which increases sustainable energy security by reducing dependence on fossil fuels. Moreover, hydrogen has applications in various industrial sectors such as transportation fuelled by hydrogen and delocalized power generation, for example for energy-intensive industries such as steel production. For at least such advantages, green hydrogen is expected to play a vital role in a future renewable-energy mix that involves electrification to reach net-zero emissions. In general, low-carbon hydrogen such as green-hydrogen is positioned to play a key role in the energy transition, for, among other things, decarbonizing production of fertilisers and chemicals, oil refining, and in sectors where electrification is not possible or prohibitively expensive to achieve at scale. Further background on green-hydrogen production facilities can be found for example in the review article [Viteri et al] or the article [Ceylan et al] and references therein.

[0007] However, green-hydrogen production facilities usually need large amount of investments and materials, making the installing of new facilities unfeasible / non-practicable. Therefore, there is interest in systems and methods for green-hydrogen production that enable production of green-hydrogen in an efficient manner.

[0008] Summary of the invention

[0009] A task set forth by the inventors is to provide efficient systems and methods for green-hydrogen production. The inventors solved the task by devising systems and methods according to the appended set of claims, with advantageous aspects as set out in the dependent claims. The systems and methods enable efficient green-hydrogen production without relying on connecting to an external electrical grid or only relying on a reduced / limited / weak grid connection. The technical advantages are discussed in more depth further below in the detailed description.

[0010] Brief description of the drawingsThe present invention is discussed in more detail below, with reference to the attached drawings, in which:

[0011] Fig- 1 shows a system for off-grid green-hydrogen production based on a grid-forming energy -storage module, according to the present disclosure.

[0012] Fig- 2 shows a system for reduced-grid green-hydrogen production according to the present disclosure.

[0013] Fig- 3 shows an example of a renewable-energy source module (1).

[0014] Fig. 4 shows an example of an electrolyser module (2).

[0015] Fig. 5 shows an example of an energy-storage module (3).

[0016] Figs. 6-7 show, schematically, methods of controlling the systems.

[0017] Fig. 8 shows an apparatus of the present disclosure, such as a central controller.

[0018] Figs. 9-12 show numerical scenarios for illustrative purposes.

[0019] Detailed description

[0020] Embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. However, the embodiments of the present disclosure are not limited to the specific embodiments and should be construed as including all modifications, changes, equivalent devices and methods, and / or alternative embodiments of the present disclosure.

[0021] The terms “have,” “may have,” “include,” and “may include” as used herein indicate the presence of corresponding features (for example, elements such as numerical values, functions, operations, or parts), and do not preclude the presence of additional features.

[0022] The terms “A or B,” “at least one of A or / and B,” or “one or more of A or / and B” as used herein include all possible combinations of items enumerated with them. For example, “A or B,” “at least one of A and B,” or “at least one of A or B” means (1) including at least one A, (2) including at least one B, or (3) including both at least one A and at least one B.

[0023] The terms such as “first” and “second” as used herein may modify various elements regardless of an order and / or importance of the corresponding elements, and do not limit the corresponding elements. These terms may be used for the purpose of distinguishing one element from another element. For example, a first element may be referred to as a second element without departing from the scope the present invention, and similarly, a second element may be referred to as a first element.

[0024] It will be understood that, when an element (for example, a first element) is “(operatively or communicatively) coupled with / to” or “connected to” another element (for example, a second element), the element may be directly coupled with / to another element, andthere may be an intervening element (for example, a third element) between the element and another element. To the contrary, it will be understood that, when an element (for example, a first element) is “directly coupled with / to” or “directly connected to” another element (for example, a second element), there is no intervening element (for example, a third element) between the element and another element.

[0025] The expression “configured to (or set to)” as used herein may be used interchangeably with “suitable for” “having the capacity to” “designed to” “adapted to” “made to,” or “capable of’ according to a context. The term “configured to (set to)” does not necessarily mean “specifically designed to” in a hardware level. Instead, the expression “apparatus configured to...” may mean that the apparatus is “capable of...” along with other devices or parts in a certain context.

[0026] The terms used in describing the various embodiments of the present disclosure are for the purpose of describing particular embodiments and are not intended to limit the present disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. All of the terms used herein including technical or scientific terms have the same meanings as those generally understood by an ordinary skilled person in the related art unless they are defined otherwise. The terms defined in a generally used dictionary should be interpreted as having the same or similar meanings as the contextual meanings of the relevant technology and should not be interpreted as having ideal or exaggerated meanings unless they are clearly defined herein. According to circumstances, even the terms defined in this disclosure should not be interpreted as excluding the embodiments of the present disclosure.

[0027] The person skilled in the art will understand that the features described above and / or below may be combined in any way deemed useful. The drawings of the present disclosure show examples / embodiments of the invention, which will be described in detail hereinafter. It is to be understood that one or more of elements / components shown and / or described in one or more of these examples / embodiments and not in others may be used in those others too unless mechanical or other limitations prevent such an implementation. Moreover, describing features of different examples / embodiments in a single passage does not automatically mean that those features are inextricably linked. They may be applied separately from one another.

[0028] Green-hydrogen production facilities usually need large amount of investments and materials, making the installing of new facilities unfeasible / non-practicable. Therefore, there is interest in systems and methods for green-hydrogen production that enable production of green-hydrogen in an efficient manner.The inventors devised systems for green-hydrogen production that make efficient greenhydrogen production feasible on a large scale. First, an off-grid system is discussed with reference to Fig.1, e.g., for installing at remote places where no public grid is available. Second, a system with a reduced-grid-connection is discussed with reference to Fig.2.

[0029] Fig- 1 illustrates a system (10) for off-grid green-hydrogen production, according to the present disclosure. The system (10) comprises:

[0030] a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources,

[0031] an electrolyser module (2) configured to produce green hydrogen based on the power provided by the renewable-energy source module (1),

[0032] a grid-forming energy-storage module (3) configured to provide grid-forming capabilities to the renewable-energy source module (1) and the electrolyser module (2), a plurality of power-converter modules (Cl, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the gridforming energy-storage module (3), which are electrically connected to each other, and

[0033] a central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (Cl, C2, C3).

[0034] The system (10) enables green-hydrogen production without relying on connecting the system (10) to an external electrical grid such as a public grid. Thereby, large-scale green hydrogen production can be deployed at remote locations where no electrical grid is available. That is, the off-grid system (10) is suitable for locations in which a grid may not be available, as in remote locations, e.g. in desert regions. The off-grid system (10) may also be referred to as an islanded system.

[0035] The grid-forming energy-storage module (3) is specifically configured / devised to provide the grid-forming capabilities - thus not powering the green-hydrogen production -which enables the green-hydrogen production without relying on connecting to an external electrical grid that requires both investments into materials and time due to relatively long delivery times of providing electrical connections to external electrical grids such as public grids.

[0036] As compared to conventional off-grid plants, in which energy storage units are scaled to enable feeding electrolysers, the system (10) employing the grid-forming energy -storage module (3) enables to scale down the overall size of the energy-storage module (3). Thereby, the system (10) provides the technical advantage that it can be installed at shorter time scales and at reduced costs with a lower footprint. Moreover, the grid-forming capabilities providedby the grid-forming energy-storage module (3) ensure that a system- voltage stability is maintained without relying on external electrical grids.

[0037] The grid-forming energy-storage module (3) is thus different from for example a synchronous condenser, which would add extra costs for extra equipment, installation, maintenance, and increases footprint. The power provided by the renewable-energy source module (1) is accordingly primarily used for powering green-hydrogen production of the electrolyser module (2), however may also be used for providing energy to various other components, including to supporting and auxiliary components (Balance of Plant (BOP), Balance of System (BOS)) and to the grid-forming energy -storage module (3) that may include batteries of various types and super capacitors and the like.

[0038] The plurality of power-converter modules (Cl, C2, C3) allows power flow, for example by converting power from one form to another, such as from alternating current (AC) to direct current (DC) and vice versa from DC to AC. Which type of power-converter is employed may depend on which conversion is to be implemented. For example, a photovoltaic-power converter (Cl-11) may be employed to convert photovoltaic-based power provided by a photovoltaic array from DC to AC, but a wind-turbine-power converter (Cl-21) may be employed to convert wind-based power provided by a wind-turbine array. Power converters are further described below.

[0039] The central controller (5) enables control of the system (10) by controlling the power flow specifically between modules (1, 2, 3) of the system (10) via the plurality of powerconverter modules.

[0040] Preferably, the plurality of power-converter modules (Cl, C2, C3) comprises:

[0041] a renewable-energy source power-converter module (Cl) configured to regulate a first active power (Pi-ren) flowing from the renewable-energy source module (1);

[0042] an electrolyser power-converter module (C2) configured to regulate a second active power (P2-eiy) flowing to the electrolyser module (2); and

[0043] a grid-forming power-converter module (C3) configured to output a reference voltage and a reference frequency for the providing of the grid-forming capabilities.

[0044] The active powers can be regulated / controlled by adjusting set points of the respective power-converters. A set point of a power-converter module determines an amount of power that is output / transferred by the power-converter module. For example, if a set point is set to 100%, then the full power available at the power-converter is output; e.g., the full power available from the renewable-energy sources and / or available at input terminals of the renewable-energy source power-converters are transferred to output terminals of the renewable-energy source power-converters. Similarly for set points of other power-converters. If the set point is set to 50%, then only half of the full power available is output / transferred at the respective power-converter. In general, a set point of X% means that X% of the full power available is output / transferred.

[0045] So, the power-converter modules enable the system (10) to focus the power flow by controlling active powers (Pi-ren, P2-eiy) between renewable-energy sources and electrolysers, while the grid-forming power-converter module (C3) specifically focuses on providing the system stability via the reference voltage and the reference frequency. Such functionality of the grid-forming power-converter module (C3) and the grid-forming energy-storage module (3) distinguishes from a general-purpose energy-storage module that would be designed to instead power the green-hydrogen production if needed. For example, during hydrogen-production mode of the system (10), the central controller (5) can control the set points of the powerconverter modules to keep the first and second active powers in balance (P i-ren=P2-eiy) while maintaining the reference voltage and reference frequency.

[0046] Preferably, the central controller (5) is configured to control the grid-forming powerconverter module (C3) to adjust supply of electrical energy from the grid-forming energystorage module (3) in dependence on a voltage level at a point of common coupling (PCC123) so as to maintain operational stability during the green-hydrogen-production.

[0047] By focusing on the voltage level of the point of common coupling (PCC123), the gridforming power-converter module (C3) and the grid-forming energy-storage module (3) can efficiently fulfil their function of only maintaining stability during green-hydrogen production while not powering the green-hydrogen production. The point of common coupling conceptually refers to a point at which the modules (1-3) are electrically coupled to each other.

[0048] Preferably, for the maintaining of the operational stability, the central controller (5) is configured to control the grid-forming power-converter module (C3) if the voltage level at the point of common coupling (PCC123) deviates from the reference voltage by a respective threshold. By controlling and checking for deviations of the voltage level by respective thresholds, the operational stability is efficiently monitored.

[0049] Preferably, for the maintaining of the operational stability, the central controller (5) is configured to control the grid-forming power-converter module (C3) so as to:

[0050] in response to the voltage level at the point of common coupling dropping below a first threshold value, deliver electrical energy by the grid-forming energy-storage module (3); and in response to the voltage level at the point of common coupling exceeding a second threshold value, absorb electrical energy by the grid-forming energy -storage module (3).Thereby, the grid forming capabilities are efficiently provided for the islanded system, as the grid-forming power-converter module (C3) and the grid-forming energy-storage module (3) are specifically adapted to absorb and deliver electrical energy based on voltage swells and sags at the point of common coupling in order to maintain the system stability. In other words, the central controller (5) is configured to stabilize the reference voltage and reference frequency during for maintaining of the operational stability, by controlling the grid-forming powerconverter module (C3) accordingly.

[0051] Preferably, the central controller (5) is configured to control the plurality of powerconverter modules (Cl, C2, C3) to keep, during the green-hydrogen-production, a third active power (Ps-es) flowing from the grid-forming power-converter module (C3) at zero.

[0052] Thereby, the grid-forming energy -storage module (3) is efficiently put to use by only providing the grid-forming capabilities but not providing any power for green-hydrogen production. For example, any fluctuations of energy supply from the renewable-energy sources are not balanced by temporarily raising the third active power (P3.es), but instead the third active power (Ps-es) is kept at zero. Such control by the central controller (5) is advantageous as it enables the system (10) to produce green-hydrogen but at lower costs due to the capability of employing down-scaled grid-forming power-converter and grid-forming energy-storage modules.

[0053] Preferably, the central controller (5) is configured to control the plurality of powerconverter modules in a green-hydrogen-production operation mode to keep a steady state (Pi-ren=P2-eiy) in which the first active power (Pi-ren) is substantially equal to the second active power (P2-eiy) while the third active power (Ps-es) is kept at zero.

[0054] Thereby, the system’s green-hydrogen production relies on the renewable-energy supply and maximizes green-hydrogen output, but does not require to provide an up-scaled energy -storage module and connections that are adapted to power green-hydrogen production. Instead, during green-hydrogen-production, the amount of energy consumed by the electrolyser module (2) follows the amount of energy supplied by the renewable-energy sources (Pi-ren=P2-eiy) while the grid-forming power-converter and grid-forming energy -storage modules do not power the production (P3-es=0) but merely form the reference voltage and reference frequency.

[0055] Preferably, the central controller (5) is configured to: in response to the power provided by the renewable-energy source module (1) dropping below a minimum-power threshold, keep the third active power (Ps-es) at zero and initiate a stand-by control sequence configured to put the electrolyser module (2) in a stand-by mode.Thereby, the central controller (5) is ensuring that no power is used from the gridforming energy-storage module (3) to power hydrogen production, supporting the latter’s functional role of providing grid strength and stability sufficient for green-hydrogen production while not unnecessarily loosing energy and resources for powering itself the production. So, when the energy-supply from the renewable-energy sources drops below a certain threshold, the system (10) does not react by drawing energy from the energy -storage module (3), but instead is put into the stand-by mode, thus avoiding usage of energy from the energy -storage module (3) for a hydrogen-production purpose.

[0056] The central controller (5) can maintain the power equilibrium in the system (10) such that Pi-ren=P2-eiyand P3-es=0 based on fast measurements (i.e. with a relatively -fast sampling rate for real-time responsiveness) of the current and voltage in the system at different nodes / points / locations that are indicative of active powers. The current and voltage measurements at different nodes / points / location in the system (10) can be input to the central controller (5) and, based on an algorithm programmed inside the central controller (5), set points for the renewable-energy source power-converter (Cl), electrolyser power-converter (C2) and grid-forming power-converter module (C3) can be generated.

[0057] Preferably, an energy-storage-capacity of the grid-forming energy-storage module (3) is adapted to its functional role of only providing the grid-forming capabilities.

[0058] By adapting the energy-storage-capacity accordingly, the size of the energy -storagecapacity can be significantly reduced as opposed to a general-purpose energy-storage module. For example, the grid-forming energy -storage module (3) can be sized to only a minimum size that is required to enable stable operation of the green-hydrogen production, e.g. to enable startup operations from minimum to maximum load conditions. However, a larger size is not required thanks to the dedicated control function provided by the central controller (5). Thereby, a larger size that would be sufficient for sustaining the green-hydrogen-production, for example to compensate for low energy supply by the renewable-energy sources, can be avoided. As a consequence of adapting the energy-storage-capacity to providing only the grid-forming capabilities, materials and resources required for larger-scale energy storage systems can be saved. In other words, the grid-forming energy-storage module (3) can be scaled down as compared to configuring it to provide production-powering capabilities, which would require stronger connections and more resources. Thereby, the system (10) can be installed quicker and with less resources, making the system (10) more feasible and scalable as compared to systems in which hydrogen-production is also maintained by energy modules.So, preferably, an energy -providing capacity of the grid-forming energy-storage module (3) is, relative to a minimum-production energy-demand of the electrolyser module (2), insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production. In other words, that means a size of the grid-forming energy -storage module (3) is scaled-down to even below enabling hydrogen production by itself; that is, to a range in which it is dedicated to only providing the grid-forming capabilities, but its scaled-down size is too small to power green-hydrogen production. The energy -providing capacity may also be referred to as energy-deliver capacity or powering capacity.

[0059] In general, the minimum-production energy-demand corresponds to a certain minimum amount of energy delivery required for running the electrolyser module (2) and its precise value may generally depend on manufacturing details of the electrolyser module (2). The minimum may for example correspond to 1%, 5%, 10%, 15%, 20%, 30%, 40% of a maximum-production energy -demand. Below the minimum, the electrolyser module (2) can for example not be run in a safe manner or cannot produce hydrogen, e.g. because otherwise hydrogen-oxygen crossover may occur which may lead to explosive conditions. The grid-forming energy -storage module (3) is thus preferably physically scaled-down to a below-minimum size in terms of powering abilities of hydrogen production. Typically, for state-of-the-art electrolysers, the minimum-production energy-demand is about 20-40% of the maximum demand. So, more preferably, the energy -storage capacity of the grid-forming energy -storage module (3) is less than 20% of the minimum-production energy-demand of the electrolyser module (2). However, the precise percentage value may depend on manufacturing aspects of the electrolyser module (2).

[0060] The minimum-production energy-demand may also be referred to as a “turn-down” of the electrolyser. The tum-down refers to a threshold value below which the electrolyser cannot be operated for the reasons as outlined above.

[0061] In addition to an off-grid system, the present disclosure further provides a system (100) for reduced-grid green-hydrogen production. Fig.2 illustrates such as system. The system (100) comprises:

[0062] a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources,

[0063] an electrolyser module (2) configured to produce hydrogen based on the power provided by the renewable-energy source module (1),

[0064] a grid-supporting energy-storage module (3) configured to provide grid-supporting capabilities to the renewable-energy source module (1) and the electrolyser module (2),a reduced-grid-connection (4) configured to provide a reference voltage and a reference frequency to a point of common coupling (PCC1234) of the renewable-energy -module (1), the electrolyser module (2), the grid-supporting energy-storage module (3), and the reduced-grid-connection (4);

[0065] a plurality of power-converter modules (Cl, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the gridsupporting energy-storage module (3), which are electrically connected to each other, and a central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (Cl, C2, C3).

[0066] Specifically by the combination of the reduced-grid-connection (4) providing the reference voltage and frequency and the grid-supporting energy-storage module (3) providing the grid-supporting capabilities, the system (100) enables to take advantage of a public grid (40) providing reference voltage and frequency, but via only a weak / reduced / limited connection by the reduced-grid-connection (4) that thus can be installed quicker, using less resources, and at reduced connection-fee costs, as the reduced-grid-connection (4) requires less resources than a full grid connection. The reduced-grid-connection (4) may also be referred to as a weak-grid-connection (4) or a limited-grid-connection (4).

[0067] The system (100) can be installed in the locations where either a strong grid or a weak grid is available. For example, the public grid in Fig. 2 can relate to the strong grid or the weak grid. In general, strong grids refers to grids with a relatively-larger short-circuit capacity (SCC) and weak grids refer to grids with a relatively weaker SCC.

[0068] Preferably, the reduced-grid-connection (4) has a size that, relative to a minimumproduction energy-demand of the electrolyser module (2), is insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production. In other words, that means a size of the reduced-grid-connection (4) is on a physical level scaled-down relative to the electrolyser module (2) to a range in which it is dedicated to only providing the reference voltage and reference frequency (providing an electric grid based on which power can be transferred between the modules 1-3 of the system (100)), but its scaled-down size is too small to power green-hydrogen production. Similarly, the grid-supporting energy-storage module (3) is also preferably scaled-down to a size that is insufficient to satisfy the minimum-production energy -demand, in a manner as already outlined above in the context of the off-grid system (10) for the grid-forming energy-storage module, which is therefore not repeated here.

[0069] Preferably, the reduced-grid-connection (4) has a size that, relative to a minimumproduction energy-demand of the electrolyser module (2), is insufficient to satisfy theminimum-production energy-demand for powering green-hydrogen production, and the energy-providing capacity of the grid-forming energy -storage module (3) is, relative to a minimum-production energy-demand of the electrolyser module (2), insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production. More preferably, both the size and the energy-providing capacity are together insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production.

[0070] The system (100) thus has the technical advantage of enabling to get only a very small electrical grid connection and install an energy storage as small as possible to maintain the system stability by its grid-supporting functionality. Thereby, the system (100) can be installed resource efficiently and long waiting times for installing large-scale electric-grid connections can be avoided. As illustrated in Fig. 2, a public grid (40) does not need to be connected by a full / strong connection that would enable powering the green-hydrogen production, but the reduced-grid-connection (4) providing the reference voltage and frequency can physically be scaled-down relative to the size of the electrolyser module (2) and yet is sufficient for the whole system (100) to provide green-hydrogen production. The grid-supporting energy -storage module (3) can stabilize against unwanted fluctuations, as outlined further below.

[0071] In contrast, state-of-the-art hydrogen-production systems require a conventional strong grid connection that is substantially scaled according to the size of electrolysis plant to enable powering the electrolysis plant, the conventional grid connection thus not being a reduced-grid-connection and not being installed in combination with a dedicated grid-supporting energystorage module (3).The reduced grid connection (4) is thus installed with its dedicated functional role of providing a voltage and frequency reference for system stability. The system (100) has the further technical advantage of enabling a trade-off between a size of gridsupporting energy -storage module (3) and a size / strength of the reduced grid connection (4), as these two participating components can support each other to fulfil their common primary goal of providing the reference voltage and reference frequency for the renewable-energy source power-converter (Cl) and the electrolyser power-converter (C2). Thereby, the system (100) enables powering hydrogen production only by the renewables, without relying on full / large-scale electric connections from a strong grid and / or a scaled-up energy-storage module that would by themselves enable powering of hydrogen-production. Thereby, up-scaling of the whole system (100) is facilitated as less resources are needed by the system (100) for enabling green-hydrogen production, which also reduces connection time and costs.

[0072] By the provided system (100), a dependency on a public grid is removed. For example, conventional hydrogen-production plants typically use a strong grid for hydrogen productionand energy storage is used during fault scenarios, so that the energy storage could feed the electrolyser during fault periods.

[0073] One or more of the preferred functionalities of the off-grid system (10), as described further above, can also be employed for the reduced-grid-system (100). Below, additional aspects are emphasized.

[0074] Preferably, the grid-supporting energy-storage module (3) is configured to supress unwanted fluctuations during the green-hydrogen production introduced due to the reduced-grid-connection (4). For suppressing the unwanted fluctuations, the grid-supporting energystorage module (3) is preferably configured to absorb or deliver power at the PCC ( PCC1234) in case of voltage swell or voltage sag at the PCC ( PCC 1234), respectively. Therefore, the gridsupporting energy -storage module (3) enables smoothing of the system voltage and the frequency and providing a stable system for the green-hydrogen production.

[0075] Thanks to their specific functional roles, the reduced-grid-connection (4) and the gridsupporting energy-storage module (3) have the synergetic effect of efficiently maintaining system stability for the green-hydrogen production. The reduced-grid-connection (4) has a size adapted to providing a reduced grid strength, reduced relative to a public-grid strength, the reduced grid strength for providing the grid-supporting capabilities but not for sustaining green-hydrogen-production.

[0076] Thereby, only a physically limited and reduced grid connection is used, so that one ultimately exploits a grid by a weak connection to only provide voltage and frequency stability and efficiently omits the need of establishing strong grid connections.

[0077] Preferably, the central controller (5) is configured to control the power-converter modules (Cl, C2, C3) such that the reduced-grid-connection (4) and the energy storage module (3) only provide, during the green-hydrogen-production, the reference voltage and the reference frequency but zero active power (P3.es = 0 and P4-grid=0).

[0078] Thereby, the central controller (5) ensures that any green-hydrogen production does not rely on power delivery by the reduced-grid-connection (4) and the energy storage module (3) but is fuelled solely by the renewable-energy sources. However, the reduced-grid-connection (4) may be employed in energy-storing-operations to store energy in the grid-supporting energy -storage module (3), for example in case of the unavailability of the enough renewable source power.

[0079] Preferably, the renewable-energy source module (1) comprises at least one of: one or more photovoltaic arrays (1-11; 1-1M); and / or

[0080] one or more wind-turbine arrays (1-21; 1-2N).Preferably, the renewable-energy source power-converter module (Cl) comprises at least one of:

[0081] one or more photovoltaic-power converters (C1-11; C1-1M) connected to the respective one or more photovoltaic arrays (1-11; 1-1M); and / or

[0082] one or more wind-turbine-power converters (Cl -21; C1-2N) connected to the respective one or more wind-turbine arrays (1-21; 1-2N).

[0083] Each power-converter may respectively contribute to the first active power (Pi-ren), thereby enabling more precise control of the first active power (Pi-ren).

[0084] Preferably, the electrolyser module (2) comprises one or more electrolyser submodules (2-1; 2-L).

[0085] Preferably, the electrolyser power-converter module (C2) comprises one or more electrolyser power-converter sub-modules (C2-1; C2-L) connected to the respective one or more electrolyser sub-modules (2-1; 2-L).

[0086] Thus, one or more green-hydrogen plants may be employed and connected, each contributing respectively to the second active power (P2-eiy), and enabling more precise control of the second active power (P2-eiy) by control of the respective converters.

[0087] Preferably, the energy -storage module (3) comprises one or more energy-storage submodules (3-1; 3-K).

[0088] Preferably, the grid-forming power-converter module (C3) comprises one or more grid-forming power-converter sub-modules (C3-1; C3-K) connected to the respective one or more energy-storage sub-modules (3-1; 3-K).

[0089] Preferably, the renewable-energy sources comprise at least one of:

[0090] one or more solar-energy sources,

[0091] one or more wind-energy sources,

[0092] one or more hydropower-energy sources,

[0093] one or more biomass-energy sources,

[0094] one or more geothermal-energy sources, and / or

[0095] one or more wave-energy sources.

[0096] Accordingly, the renewable-energy source module (1) may comprise respective submodules according to the used sources.

[0097] In addition to the systems (10, 100), the present disclosure provides methods of operating the systems (10, 100) so as to enable efficient green-hydrogen production by the systems. Aspects of the methods are schematically depicted in the flowcharts Figs. 6-7. Theflowcharts may be extended to further include one or more of the aspects as described hereinbelow.

[0098] First, provided is a method of controlling any one of the systems (10, 100), the controlled system preferably containing one or more of the aforementioned preferred aspects. The method is for controlling according to a start-up sequence. The method comprises:

[0099] initializing (Al) power-output set points (SPi, SP2, SP3) of the plurality of powerconverter modules (Cl, C2, C3) to zero; and

[0100] increasing (A2), gradually, the first power-output set point (SPi) and adjusting the second set point (SP2) to balance the first active power (Pi-ren) and the second active power (P2-eiy), until reaching a desired power supply for a green-hydrogen-production mode.

[0101] The start-up sequence may be initiated numerous times, for example after standby / shut-down triggered by a too-low energy supply from the renewable-energy sources. The method provides an efficient / smooth way of enabling green-hydrogen production by gradually increasing the power delivered by the renewable-energy sources. Thereby, the power delivered to the electrolyser module (2) can efficiently and smoothly follow the power delivered by the renewable-energy source module (1). For example, fluctuations in the renewable-energy source supply can be dealt with while operating the system. In other words, by the gradually increasing, the first and second active powers are efficiently balanced, until reaching the desired power supply.

[0102] Preferably, the adjusting of the second power-output set point (SP2) is based on one or more difference values (Al, AP) calculated from a plurality of parameters comprising electric currents and / or electric voltages at the point of common coupling (PCC123, PCC1234) of the system (10, 100). For example, the central controller (5) may collect data indicative of currents or power values flowing from or to the involved power-converter modules, and may adjust the set points of the power-converter modules accordingly.

[0103] Preferably, the method comprises:

[0104] check whether a stability parameter of the system (10, 100) indicates instability; if yes, adjust one or more of the first to third power-output set points (SPi, SP2, SP3) until the stability parameter indicates stability.

[0105] By checking a stability parameter, one can take developing instabilities into account and adjust energy supply to counter the instabilities. For example, one can control the energystorage module (3) to stabilize the reference voltage and / or reference frequency.Preferably, the stability parameter is related to power-oscillation levels at the point of common coupling (PCC123, PCC1234). These power-oscillation levels are an efficient indicator of stability.

[0106] Preferably, the desired power supply for the green-hydrogen-production mode relates to reaching a pre-set and / or configurable maximum value for the first power-output set point (SP 1). Setting a configurable maximum value is more preferred as it enables adapting to variable system requirements.

[0107] Preferably, the gradually increasing comprises one or more stepwise increments, each stepwise increment comprising: increasing the first power-output set point (SP 1) by a respective percentage increment, such as in between 1-5%, and adjusting the second set point (SP2) to balance the first active power and the second active power [Pi -ren P 2-ely ] .

[0108] For example, considering the off-grid system (10), such stepwise increase of the startup sequence enables to reach a steady state in which the hydrogen-production is powered by the renewable-energy source, e.g. solar energy, while the grid-forming energy-storage module (e.g. any kind of battery or supercapacitor, etc.) provides the reference voltage and reference frequency for operation stability. Small stepwise increases in the first power setpoint (SP1) for the renewable-energy source power converter (Cl) from zero to a maximum value during the startup allows a smooth start of the islanded green hydrogen plant.

[0109] Furthermore, provided is a further method of controlling any one of the systems (10, 100), the controlled system preferably containing one or more of the aforementioned preferred aspects. The further method is for controlling according to a green-hydrogen production mode. The method comprises:

[0110] adjusting (Bl), by controlling the power-converter module (C3), supply or absorption of electrical energy by the energy -storage module (3) in dependence on the voltage level at the point of common coupling (PCC123, PCC1234) so as to maintain operational stability of the green-hydrogen production during the green-hydrogen-production mode.

[0111] Preferably, the method comprises:

[0112] for the maintaining of the operational stability, controlling (B2) the power-converter module (C3) if the voltage level at the point of common coupling (PCC123, PCC1234) deviates from the reference voltage by a respective threshold

[0113] Preferably, the method comprises, for the maintaining of the operational stability: in response to the voltage level at the point of common coupling dropping below a first threshold value, delivering electrical energy by the energy-storage module (3); andin response to the voltage level at the point of common coupling exceeding a second threshold value, absorbing electrical energy by the energy -storage module (3).

[0114] Preferably, the method comprises:

[0115] keeping, during the green-hydrogen-production, the third active power (Ps-es) flowing from the power-converter module (C3) at zero.

[0116] Preferably, the method comprises:

[0117] keeping, during the green-hydrogen-production, a steady state (P i-ren=P2-eiy) in which the first active power (Pi-ren) is substantially equal to the second active power (P2-eiy) while the third active power (P3.es) is kept at zero.

[0118] Preferably, the method comprises:

[0119] in response to the power provided by the renewable-energy source module (1) dropping below a minimum-power threshold, keeping the third active power (P3.es) at zero and initiating a stand-by control sequence configured to put the electrolyser module (2) in a stand-by mode.

[0120] Preferably, the method comprises:

[0121] checking if the power from the one or more renewable-energy sources is less than a minimum required power;

[0122] if yes, initiating a delay timer, and,

[0123] upon expiry of the delay timer, if the power from the one or more renewable-energy sources is less than a minimum required power, setting the first power-output set point (SP i) and the second power-output set point (SP2) to zero.

[0124] By triggering shut-down based on power-value of renewable-energy sources, one can more efficiently ensure that electrolyser module (2) operates only based on renewable-energy sources and not based on power of the reduced-grid-connection (4) and the grid-supporting energy -storage module [reduced-grid system (100)] or the grid-forming energy-storage module [off-grid system (10)]. Moreover, the delay timer allows for power fluctuations for a configurable time during which less than the minimum power is delivered.

[0125] The present disclosure further provides a computer program product, a computer-readable medium, and an apparatus.

[0126] The computer program product comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of the preceding method claims.

[0127] The computer-readable medium has stored thereon the computer program product. The apparatus (1000) comprises a processor (1001) and a memory (1003) storing instructions which, when executing by the processor, cause the processor to perform the methodaccording to any one of the preceding method claims. Moreover, preferably, the instructions may further cause the processor to perform any one of the control operations of the central controller (5) as described further above in the context of the systems (10, 100).

[0128] For example, the apparatus (1000) may correspond to the central controller (5). The apparatus (1000) may be located close to the system (10, 100) but may also be placed remotely away from the system (10, 100). The apparatus (1000) may also be implemented as a decentralized computer system.

[0129] Preferably, the apparatus (1000) of the preceding claims, wherein the apparatus (1000) corresponds to a central controller (5) configured to perform any one of the aforementioned methods preferably containing one or more of the aforementioned preferred aspects and / or to perform one of the aforementioned preferred aspects of the central controller (5) as described further above in the context of the systems (10, 100).

[0130] The present disclosure further provides a method of installing any one of the systems (10, 100), the installed system preferably containing one or more of the aforementioned preferred aspects. The method comprises:

[0131] installing the renewable-energy source module (1),

[0132] installing the electrolyser module (2),

[0133] installing the energy-storage module (3),

[0134] installing the plurality of power-converter modules (Cl, C2, C3), and

[0135] installing the central controller (5).

[0136] The method preferably comprises installing one or more of the aforementioned preferred aspects of any one of the systems (10, 100).

[0137] Figs. 9-12 show numerical scenarios for illustrative purposes, one for a system (100) for reduced-grid green-hydrogen production (“Weak Grid”) and one for a system (10) for off-grid green-hydrogen production (“Off Grid”). The values are merely taken for illustrative purposes to showcase by example the principles as outlined above. Power values are indicated as P_PV (photovoltaic), P Elec (electrolyser), P Grid (reduced-grid-connection), P_SC (supercapacitor as energy storage).

[0138] The following table provides an overview of the numerical scenarios in terms of sizes of the involved components:

[0139]

[0140] Scenario A. Operation of a system (100) for reduced-grid green-hydrogen production, i.e. based on a reduced-grid-connection (4) and a grid-supporting power-converter and energystorage module.

[0141] Figs.9a-9c show a IkVA weak grid + 25kW grid-supporting power converter + 300Wh energy storage module (“SC” for supercapacitor).

[0142] Fig.9a shows a gradual start-up and full load operation of the electrolyser. Fig. 9a shows a relatively-larger step increase in the power setpoint (SP1) of the renewable source power converter (Cl) and corresponding increase in the power setpoint (SP2) of the electrolyser power converter, during which the green hydrogen production from the electrolyser closely follows the available renewable energy.

[0143] Fig.9b shows a step-wise increase from 0-100% of the electrolyser power-converter set point. Fig. 9b showcases that the step-wise increase of a start-up sequence enables to reach a steady state in which hydrogen production is powered by the renewable-energy source, e.g. solar energy, while the reduced grid connection and the supercapacitor exemplifying the gridsupporting energy-storage module provide operating stability. The small step increase in the first power setpoint (SP1) for the renewable-energy source power converter (Cl) from zero to a maximum value during the startup allows a smooth start of the green hydrogen plant.

[0144] Fig. 9c shows a step-wise decrease from 100-0% of the electrolyser power-converter set point.

[0145] Figs. lOa-lOb show a start-up and full load operation, for different combinations of sizes of the reduced-grid-connection and the grid-supporting power converter, each with a 300Wh energy storage module.

[0146] Fig. 10a shows a IkVA weak grid + 15kW grid-supporting power converter.

[0147] Fig. 10b shows a 3kVA weak grid + 9kW grid-supporting power converter.Figs. 10a- 10b thus illustrate that one can balance sizes of the involved components, e.g. by increasing the reduced-grid-connection while decreasing the grid-supporting power converter.

[0148] Scenario B. Operation of a system (10) off-grid green-hydrogen production, i.e. based on a grid-forming power-converter and grid-forming energy-storage module.

[0149] Figs, lla-llc show a 25kW grid-forming power converter +300Wh energy storage module (“SC” for supercapacitor).

[0150] Fig. Ila shows a start-up and full load operation of the electrolyser. Fig. 1 la showcases a relatively-larger step increase in the first power setpoint (SP1) of the renewable source power converter (Cl) and corresponding increase in the power setpoint (SP2) of the electrolyser power converter, so that the green hydrogen production from the electrolyser closely follows the available solar power in off grid scenarios.

[0151] Fig. 11b shows a step-wise increase from 0-100% of the electrolyser power-converter set point. Fig. 11b showcases that the stepwise increase of the start-up sequence enables to reach a steady state in which the hydrogen production is powered by the renewable-energy source, in this example solar energy, while the supercapacitor exemplifying the grid-forming energystorage module provides reference voltage and reference frequency for operation stability. The small step increase in the first power setpoint (SP1) for the renewable source power converter (Cl) from zero to a maximum value during the startup in the top graph allows a smooth start of the islanded green hydrogen plant.

[0152] Fig. 11c shows a step-wise decrease from 100-0% of the electrolyser power-converter set point.

[0153] Fig. 12 shows a start-up and full load operation, for a 22kW grid-forming power converter + 300Wh energy storage module.

[0154] Clauses.

[0155] 1. System (10) for off-grid green-hydrogen production, the system (10) comprising: a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources,

[0156] an electrolyser module (2) configured to produce green hydrogen based on the power provided by the renewable-energy source module (1),

[0157] a grid-forming energy-storage module (3) configured to provide grid-forming capabilities to the renewable-energy source module (1) and the electrolyser module (2),a plurality of power-converter modules (Cl, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the gridforming energy-storage module (3), which are electrically connected to each other, and

[0158] a central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (Cl, C2, C3).

[0159] 2. The system (10) of clause 1, wherein the plurality of power-converter modules (Cl, C2, C3) comprises:

[0160] a renewable-energy source power-converter module (Cl) configured to regulate a first active power (Pi-ren) flowing from the renewable-energy source module (1);

[0161] an electrolyser power-converter module (C2) configured to regulate a second active power (P2-eiy) flowing to the electrolyser module (2); and

[0162] a grid-forming power-converter module (C3) configured to output a reference voltage and a reference frequency for the providing of the grid-forming capabilities.

[0163] 3. The system (10) of clause 2, wherein the central controller (5) is configured to control the grid-forming power-converter module (C3) to adjust supply of electrical energy from the grid-forming energy-storage module (3) in dependence on a voltage level at a point of common coupling (PCC123) so as to maintain operational stability of the green-hydrogen production during the green-hydrogen-production.

[0164] 4. The system (10) of the preceding clause, wherein, for the maintaining of the operational stability, the central controller (5) is configured to control the grid-forming powerconverter module (C3) if the voltage level at the point of common coupling (PCC 123) deviates from the reference voltage by a respective threshold.

[0165] 5. The system (10) of the preceding clause, wherein, for the maintaining of the operational stability, the central controller (5) is configured to control the grid-forming powerconverter module (C3) so as to:

[0166] in response to the voltage level at the point of common coupling dropping below a first threshold value, deliver electrical energy by the grid-forming energy-storage module (3); and in response to the voltage level at the point of common coupling exceeding a second threshold value, absorb electrical energy by the grid-forming energy -storage module (3).

[0167] 6. The system (10) of any one of the preceding clauses, wherein the central controller (5) is configured to control the plurality of power-converter modules (Cl, C2, C3) to keep, during the green-hydrogen-production, a third active power (P3.es) flowing from the gridforming power-converter module (C3) at zero.7. The system (10) of the preceding clause, wherein the central controller (5) is configured to control the plurality of power-converter modules in a green-hydrogen-production operation mode to keep a steady state (Pi-ren=P2-eiy) in which the first active power (Pi-ren) is substantially equal to the second active power (P2-eiy) while the third active power (Ps-es) is kept at zero.

[0168] 8. The system (10) of the preceding clause, wherein the central controller (5) is configured to:

[0169] in response to the power provided by the renewable-energy source module (1) dropping below a minimum-power threshold, keep the third active power (Ps-es) at zero and initiate a stand-by control sequence configured to put the electrolyser module (2) in a stand-by mode.

[0170] 9. The system (10) of any one of the preceding clauses, wherein an energy-storage-capacity of the grid-forming energy-storage module (3) is adapted to its functional role of only providing the grid-forming capabilities.

[0171] 10. The system (10) of any one of the preceding clauses, wherein an energy-providing capacity of the grid-forming energy-storage module (3) is, relative to a minimum-production energy-demand of the electrolyser module (2), insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production.

[0172] 11. System (100) for reduced-grid green-hydrogen production, the system (100) comprising:

[0173] a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources,

[0174] an electrolyser module (2) configured to produce green hydrogen based on the power provided by the renewable-energy source module (1),

[0175] a grid-supporting energy-storage module (3) configured to provide grid-supporting capabilities to the renewable-energy source module (1) and the electrolyser module (2), a reduced-grid-connection (4) configured to provide a reference voltage and a reference frequency to a point of common coupling (PCC1234) of the renewable-energy -module (1), the electrolyser module (2), the grid-supporting energy-storage module (3), and the reduced-grid-connection (4);

[0176] a plurality of power-converter modules (Cl, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the gridsupporting energy-storage module (3), which are electrically connected to each other, and a central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (Cl, C2, C3).12. The system (100) for reduced-grid green-hydrogen production of clause 11, wherein the plurality of power-converter modules (Cl, C2, C3) comprises:

[0177] a renewable-energy source power-converter module (Cl) configured to regulate a first active power (Pi-ren) flowing from the renewable-energy source module (1);

[0178] an electrolyser power-converter module (C2) configured to regulate a second active power (P2-eiy) flowing to the electrolyser module (2); and

[0179] a grid-supporting power-converter module (C3) configured to support the reference voltage and the reference frequency.

[0180] 13. The system (100) for reduced-grid green-hydrogen production of the preceding clause, wherein the grid-supporting energy-storage module (3) is configured to supress unwanted fluctuations during the green-hydrogen production introduced due to the reduced-grid-connection (4).

[0181] 14. The system (100) for reduced-grid green-hydrogen production of any one of the preceding clauses, wherein the reduced-grid-connection (4) has a size adapted to providing a reduced grid strength, reduced relative to a public-grid strength, the reduced grid strength for providing the grid-supporting capabilities but not for sustaining green-hydrogen-production.

[0182] 15. The system (100) for reduced-grid green-hydrogen production of the preceding clause, wherein the reduced-grid-connection (4) is configured to provide, during the green-hydrogen-production, the reference voltage and the reference frequency but zero active power (P4-grid=0).

[0183] 16. The system (100) for reduced-grid green-hydrogen production of any one of the preceding clauses, wherein the reduced-grid-connection (4) has a size that, relative to a minimum-production energy-demand of the electrolyser module (2), is insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production.

[0184] 17. The system (100) for reduced-grid green-hydrogen production of the preceding clause, wherein the energy-providing capacity of the grid-forming energy-storage module (3) is, relative to the minimum-production energy-demand of the electrolyser module (2), such that both the size of the reduced-grid-connection (4) and the energy -providing capacity are together insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production.

[0185] 18. The system (10, 100) of any one of the preceding clauses, wherein the renewableenergy source module (1) comprises at least one of:

[0186] one or more photovoltaic arrays (1-11; 1-1M); and / or

[0187] one or more wind-turbine arrays (1-21; 1-2N).19. The system (10, 100) of the preceding clause, wherein the renewable-energy source power-converter module (Cl) comprises at least one of:

[0188] one or more photovoltaic-power converters (C1-11; C1-1M) connected to the respective one or more photovoltaic arrays (1-11; 1-1M); and / or

[0189] one or more wind-turbine-power converters (Cl -21; C1-2N) connected to the respective one or more wind-turbine arrays (1-21; 1-2N).

[0190] 20. The system (10, 100) of any one of the preceding clauses, wherein the electrolyser module (2) comprises one or more electrolyser sub-modules (2-1; 2-L).

[0191] 21. The system (10, 100) of the preceding clause, wherein the electrolyser powerconverter module (C2) comprises one or more electrolyser power-converter sub-modules (C2-1; C2-L) connected to the respective one or more electrolyser sub-modules (2-1; 2-L).

[0192] 22. The system (10, 100) of any one of the preceding clauses, wherein the energystorage module (3) comprises one or more energy-storage sub-modules (3-1; 3-K).

[0193] 23. The system (10, 100) of the preceding clause, wherein the grid-forming or gridsupporting power-converter module (C3) comprises one or more power-converter sub-modules (C3-1; C3-K) connected to the respective one or more energy-storage sub-modules (3-1; 3-K).

[0194] 24. The system (10, 100) of any one of the preceding system clauses, wherein the renewable-energy sources comprise at least one of:

[0195] one or more solar-energy sources,

[0196] one or more wind-energy sources,

[0197] one or more hydropower-energy sources,

[0198] one or more biomass-energy sources,

[0199] one or more geothermal-energy sources, and / or

[0200] one or more wave- energy sources.

[0201] 25. Method of controlling the system (10, 100) of any one of the preceding system clauses according to a start-up sequence, the method comprising:

[0202] initializing (Al) power-output set points (SPi, SP2, SP3) of the plurality of powerconverter modules (Cl, C2, C3) to zero; and

[0203] increasing (A2), gradually, the first power-output set point (SPi) and adjusting the second set point (SP2) to balance the first active power (Pi-ren) and the second active power (P2-eiy), until reaching a desired power supply for a green-hydrogen-production mode.

[0204] 26. The method of the preceding method clause for controlling the system according to the start-up sequence, wherein the adjusting of the second power-output set point (SP2) is based on one or more difference values (Al, AP) calculated from a plurality of parameters comprisingelectric currents and / or electric voltages at the point of common coupling (PCC123, PCC1234) of the system (10, 100).

[0205] 27. The method of any one of the preceding method clauses, comprising:

[0206] check whether a stability parameter of the system (10, 100) indicates instability; if yes, adjust one or more of the first to third power-output set points (SPi, SP2, SP3) until the stability parameter indicates stability.

[0207] 28. The method of the preceding clause, wherein the stability parameter is related to power-oscillation levels at the point of common coupling (PCC123, PCC1234).

[0208] 29. The method of any one of the preceding method clauses, wherein the desired power supply for the green-hydrogen-production mode relates to reaching a pre-set and / or configurable maximum value for the first power-output set point (SP 1).

[0209] 30. Method of controlling the system (10, 100) of any one of the preceding system clauses according to a green-hydrogen production mode, the method comprising:

[0210] adjusting (Bl), controlling the grid-forming power-converter module (C3), supply of electrical energy from the energy-storage module (3) in dependence on the voltage level at the point of common coupling (PCC123) so as to maintain operational stability of the green-hydrogen production during the green-hydrogen-production mode.

[0211] 31. The method of the preceding method clause for controlling the system according to the green-hydrogen production mode, comprising:

[0212] for the maintaining of the operational stability, controlling (B2) the grid-forming powerconverter module (C3) if the voltage level at the point of common coupling (PCC 123) deviates from the reference voltage by a respective threshold

[0213] 32. The method of the preceding method clause for controlling the system according to the green-hydrogen production mode, comprising for the maintaining of the operational stability:

[0214] in response to the voltage level at the point of common coupling dropping below a first threshold value, delivering electrical energy by the energy-storage module (3); and

[0215] in response to the voltage level at the point of common coupling exceeding a second threshold value, absorbing electrical energy by the energy -storage module (3).

[0216] 33. The method of any one of the preceding method clauses for controlling the system according to the green-hydrogen production mode, further comprising:

[0217] keeping, during the green-hydrogen-production, the third active power (Ps-es) flowing from the grid-forming power-converter module (C3) at zero.34. The method of any one of the preceding method clauses for controlling the system according to the green-hydrogen production mode, further comprising:

[0218] Keeping, during the green-hydrogen-production, a steady state (Pi-ren=P2-eiy) in which the first active power (Pi-ren) is substantially equal to the second active power (P2-eiy) while the third active power (P3.es) is kept at zero.

[0219] 35. The method of any one of the preceding method clauses for controlling the system according to the green-hydrogen production mode, further comprising:

[0220] in response to the power provided by the renewable-energy source module (1) dropping below a minimum-power threshold, keeping the third active power (Ps-es) at zero and initiating a stand-by control sequence configured to put the electrolyser module (2) in a stand-by mode.

[0221] 36. The method of any one of the preceding method clauses for controlling the system according to the green-hydrogen production mode, further comprising:

[0222] checking if the power from the one or more renewable-energy sources is less than a minimum required power;

[0223] if yes, initiating a delay timer, and,

[0224] upon expiry of the delay timer, if the power from the one or more renewable-energy sources is less than a minimum required power, setting the first power-output set point (SP i) and the second power-output set point (SP2) to zero.

[0225] 37. Computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of the preceding method clauses.

[0226] 38. Computer-readable medium having stored thereon the computer program product of the preceding clause.

[0227] 39. Apparatus (1000) comprising a processor (1001) and a memory (1003) storing instructions which, when executing by the processor, cause the processor to perform the method according to any one of the preceding method clauses.

[0228] 40. The apparatus (1000) of the preceding clauses, wherein the apparatus (1000) corresponds to a central controller (50) configured to perform the method according to any one of the preceding method clauses.

[0229] 41. Method of installing the system (10, 100) of any one of the preceding system clauses, the method comprising:

[0230] installing the renewable-energy source module (1),

[0231] installing the electrolyser module (2),

[0232] installing the energy-storage module (3),installing the plurality of power-converter modules (Cl, C2, C3), and installing the central controller (5).

[0233] The following list of references is referred to in the present document and is incorporated herein by way of reference.

[0234] List of references

[0235] [A] Authors. Title. Publisher. Date.

[0236] [Ceylan et al] Ceren Ceylan, Yilser Devrim. Green hydrogen based off-grid and on-grid hybrid energy systems. International Journal of Hydrogen Energy. Volume 48, Issue 99, 25 December 2023, Pages 39084-39096.

[0237] [Viteri et al] Juan P. Viteri, Sofia Viteri, Carlos Alvarez-Vasco, Felipe Henao. A systematic review on green hydrogen for off-grid communities - technologies, advantages, and limitations. International Journal of Hydrogen Energy. Volume 48, Issue 52, 22 June 2023, Pages 19751-19771.

Claims

SP3227CLAIM S1. System (10) for off-grid green-hydrogen production, the system (10) comprising:a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources,an electrolyser module (2) configured to produce green hydrogen based on the power provided by the renewable-energy source module (1),a grid-forming energy-storage module (3) configured to provide grid-forming capabilities to the renewable-energy source module (1) and the electrolyser module (2), a plurality of power-converter modules (Cl, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the gridforming energy-storage module (3), which are electrically connected to each other, anda central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (Cl, C2, C3).

2. The system (10) of claim 1, wherein the plurality of power-converter modules (Cl, C2, C3) comprises:a renewable-energy source power-converter module (Cl) configured to regulate a first active power (Pi-ren) flowing from the renewable-energy source module (1);an electrolyser power-converter module (C2) configured to regulate a second active power (P2-eiy) flowing to the electrolyser module (2); anda grid-forming power-converter module (C3) configured to output a reference voltage and a reference frequency for the providing of the grid-forming capabilities.

3. The system (10) of claim 2, wherein the central controller (5) is configured to control the grid-forming power-converter module (C3) to adjust supply of electrical energy from the gridforming energy -storage module (3) in dependence on a voltage level at a point of common coupling (PCC123) so as to maintain operational stability of the green-hydrogen production during the green-hydrogen-production.

4. The system (10) of the preceding claim, wherein, for the maintaining of the operational stability, the central controller (5) is configured to control the grid-forming power-converter27module (C3) if the voltage level at the point of common coupling (PCC123) deviates from the reference voltage by a respective threshold.

5. The system (10) of the preceding claim, wherein, for the maintaining of the operational stability, the central controller (5) is configured to control the grid-forming power-converter module (C3) so as to:in response to the voltage level at the point of common coupling dropping below a first threshold value, deliver electrical energy by the grid-forming energy-storage module (3); and in response to the voltage level at the point of common coupling exceeding a second threshold value, absorb electrical energy by the grid-forming energy -storage module (3).

6. The system (10) of any one of the preceding claims, wherein the central controller (5) is configured to control the plurality of power-converter modules (Cl, C2, C3) to keep, during the green-hydrogen-production, a third active power (P3.es) flowing from the grid-forming powerconverter module (C3) at zero.

7. The system (10) of the preceding claim, wherein the central controller (5) is configured to control the plurality of power-converter modules in a green-hydrogen-production operation mode to keep a steady state (Pi-ren=P2-eiy) in which the first active power (Pi-ren) is substantially equal to the second active power (P2-eiy) while the third active power (P3.es) is kept at zero.

8. The system (10) of the preceding claim, wherein the central controller (5) is configured to:in response to the power provided by the renewable-energy source module (1) dropping below a minimum-power threshold, keep the third active power (P3.es) at zero and initiate a stand-by control sequence configured to put the electrolyser module (2) in a stand-by mode.

9. The system (10) of any one of the preceding claims, wherein an energy-storage-capacity of the grid-forming energy-storage module (3) is adapted to its functional role of only providing the grid-forming capabilities.

10. The system (10) of any one of the preceding claims, wherein an energy-providing capacity of the grid-forming energy-storage module (3) is, relative to a minimum-production energydemand of the electrolyser module (2), insufficient to satisfy the minimum-production energydemand for powering green-hydrogen production.

11. System (100) for reduced-grid green-hydrogen production, the system (100) comprising: a renewable-energy source module (1) configured to provide power from one or more renewable-energy sources,an electrolyser module (2) configured to produce green hydrogen based on the power provided by the renewable-energy source module (1),a grid-supporting energy-storage module (3) configured to provide grid-supporting capabilities to the renewable-energy source module (1) and the electrolyser module (2), a reduced-grid-connection (4) configured to provide a reference voltage and a reference frequency to a point of common coupling (PCC1234) of the renewable-energy -module (1), the electrolyser module (2), the grid-supporting energy-storage module (3), and the reduced-grid-connection (4);a plurality of power-converter modules (Cl, C2, C3) configured to allow power flow between the renewable-energy source module (1), the electrolyser module (2), and the gridsupporting energy-storage module (3), which are electrically connected to each other, and a central controller (5) configured to control the power flow by controlling the plurality of power-converter modules (Cl, C2, C3).

12. The system (100) for reduced-grid green-hydrogen production of claim 11, wherein the plurality of power-converter modules (Cl, C2, C3) comprises:a renewable-energy source power-converter module (Cl) configured to regulate a first active power (Pi-ren) flowing from the renewable-energy source module (1);an electrolyser power-converter module (C2) configured to regulate a second active power (P2-eiy) flowing to the electrolyser module (2); anda grid-supporting power-converter module (C3) configured to support the reference voltage and the reference frequency.

13. The system (100) for reduced-grid green-hydrogen production of the preceding claim, wherein the grid-supporting energy -storage module (3) is configured to supress unwanted fluctuations during the green-hydrogen production introduced due to the reduced-grid-connection (4).

14. The system (100) for reduced-grid green-hydrogen production of any one of the preceding claims, wherein the reduced-grid-connection (4) has a size adapted to providing a reduced gridstrength, reduced relative to a public-grid strength, the reduced grid strength for providing the grid-supporting capabilities but not for sustaining green-hydrogen-production.

15. The system (100) for reduced-grid green-hydrogen production of the preceding claim, wherein the reduced-grid-connection (4) is configured to provide, during the green-hydrogen-production, the reference voltage and the reference frequency but zero active power (P4-grid=0).

16. The system (100) for reduced-grid green-hydrogen production of any one of the preceding claims, wherein the reduced-grid-connection (4) has a size that, relative to a minimumproduction energy-demand of the electrolyser module (2), is insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production.

17. The system (100) for reduced-grid green-hydrogen production of the preceding claim, wherein the energy-providing capacity of the grid-forming energy -storage module (3) is, relative to the minimum-production energy-demand of the electrolyser module (2), such that both the size of the reduced-grid-connection (4) and the energy -providing capacity are together insufficient to satisfy the minimum-production energy-demand for powering green-hydrogen production.

18. The system (10, 100) of any one of the preceding claims, wherein the renewable-energy source module (1) comprises at least one of:one or more photovoltaic arrays (1-11; 1-1M); and / orone or more wind-turbine arrays (1-21; 1-2N).

19. The system (10, 100) of the preceding claim, wherein the renewable-energy source powerconverter module (Cl) comprises at least one of:one or more photovoltaic-power converters (C1-11; C1-1M) connected to the respective one or more photovoltaic arrays (1-11; 1-1M); and / orone or more wind-turbine-power converters (Cl -21; C1-2N) connected to the respective one or more wind-turbine arrays (1-21; 1-2N).

20. The system (10, 100) of any one of the preceding claims, wherein the electrolyser module (2) comprises one or more electrolyser sub-modules (2-1; 2-L).

21. The system (10, 100) of the preceding claim, wherein the electrolyser power-converter module (C2) comprises one or more electrolyser power-converter sub-modules (C2-1; C2-L) connected to the respective one or more electrolyser sub-modules (2-1; 2-L).

22. The system (10, 100) of any one of the preceding claims, wherein the energy-storage module (3) comprises one or more energy-storage sub-modules (3-1; 3-K).

23. The system (10, 100) of the preceding claim, wherein the grid-forming or grid-supporting power-converter module (C3) comprises one or more power-converter sub-modules (C3-1 ; C3-K) connected to the respective one or more energy -storage sub-modules (3-1; 3-K).

24. The system (10, 100) of any one of the preceding system claims, wherein the renewableenergy sources comprise at least one of:one or more solar-energy sources,one or more wind-energy sources,one or more hydropower-energy sources,one or more biomass-energy sources,one or more geothermal-energy sources, and / orone or more wave- energy sources.

25. Method of controlling the system (10, 100) of any one of the preceding system claims according to a start-up sequence, the method comprising:initializing (Al) power-output set points (SPi, SP2, SP3) of the plurality of powerconverter modules (Cl, C2, C3) to zero; andincreasing (A2), gradually, the first power-output set point (SPi) and adjusting the second set point (SP2) to balance the first active power (Pi-ren) and the second active power (P2-eiy), until reaching a desired power supply for a green-hydrogen-production mode.

26. The method of the preceding method claim for controlling the system according to the startup sequence, wherein the adjusting of the second power-output set point (SP2) is based on one or more difference values (Al, AP) calculated from a plurality of parameters comprising electric currents and / or electric voltages at the point of common coupling (PCC123, PCC1234) of the system (10, 100).

27. The method of any one of the preceding method claims, comprising:check whether a stability parameter of the system (10, 100) indicates instability; if yes, adjust one or more of the first to third power-output set points (SP i, SP2, SP3) until the stability parameter indicates stability.

28. The method of the preceding claim, wherein the stability parameter is related to poweroscillation levels at the point of common coupling (PCC123, PCC1234).

29. The method of any one of the preceding method claims, wherein the desired power supply for the green-hydrogen-production mode relates to reaching a pre-set and / or configurable maximum value for the first power-output set point (SP 1).

30. Method of controlling the system (10, 100) of any one of the preceding system claims according to a green-hydrogen production mode, the method comprising:adjusting (Bl), controlling the grid-forming power-converter module (C3), supply of electrical energy from the energy-storage module (3) in dependence on the voltage level at the point of common coupling (PCC123) so as to maintain operational stability of the green-hydrogen production during the green-hydrogen-production mode.

31. The method of the preceding method claim for controlling the system according to the green-hydrogen production mode, comprising:for the maintaining of the operational stability, controlling (B2) the grid-forming powerconverter module (C3) if the voltage level at the point of common coupling (PCC 123) deviates from the reference voltage by a respective threshold32. The method of the preceding method claim for controlling the system according to the green-hydrogen production mode, comprising for the maintaining of the operational stability:in response to the voltage level at the point of common coupling dropping below a first threshold value, delivering electrical energy by the energy-storage module (3); andin response to the voltage level at the point of common coupling exceeding a second threshold value, absorbing electrical energy by the energy -storage module (3).

33. The method of any one of the preceding method claims for controlling the system according to the green-hydrogen production mode, further comprising:32keeping, during the green-hydrogen-production, the third active power (Ps-es) flowing from the grid-forming power-converter module (C3) at zero.

34. The method of any one of the preceding method claims for controlling the system according to the green-hydrogen production mode, further comprising:Keeping, during the green-hydrogen-production, a steady state (Pi-ren=P2-eiy) in which the first active power (Pi-ren) is substantially equal to the second active power (P2-eiy) while the third active power (P3.es) is kept at zero.

35. The method of any one of the preceding method claims for controlling the system according to the green-hydrogen production mode, further comprising:in response to the power provided by the renewable-energy source module (1) dropping below a minimum-power threshold, keeping the third active power (Ps-es) at zero and initiating a stand-by control sequence configured to put the electrolyser module (2) in a stand-by mode.

36. The method of any one of the preceding method claims for controlling the system according to the green-hydrogen production mode, further comprising:checking if the power from the one or more renewable-energy sources is less than a minimum required power;if yes, initiating a delay timer, and,upon expiry of the delay timer, if the power from the one or more renewable-energy sources is less than a minimum required power, setting the first power-output set point (SP i) and the second power-output set point (SP2) to zero.

37. Computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any one of the preceding method claims.

38. Computer-readable medium having stored thereon the computer program product of the preceding claim.

39. Apparatus (1000) comprising a processor (1001) and a memory (1003) storing instructions which, when executing by the processor, cause the processor to perform the method according to any one of the preceding method claims.

40. The apparatus (1000) of the preceding claims, wherein the apparatus (1000) corresponds to a central controller (50) configured to perform the method according to any one of the preceding method claims.

41. Method of installing the system (10, 100) of any one of the preceding system claims, the method comprising:installing the renewable-energy source module (1),installing the electrolyser module (2),installing the energy-storage module (3),installing the plurality of power-converter modules (Cl, C2, C3), andinstalling the central controller (5).34

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