WO2025002887A1

WO2025002887A1 - Converter-hydrogen system

Info

Publication number: WO2025002887A1
Application number: PCT/EP2024/066832
Authority: WO
Inventors: Nicklas Johansson; Weichi ZHANG; Jan Svensson; Wene-Wen JIANG; Vijesh JAYAN; Yuan-Chih Lin; Akif Zia KHAN; Bochen LIU
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2023-06-26
Filing date: 2024-06-17
Publication date: 2025-01-02
Anticipated expiration: 2025-12-26

Abstract

A converter-hydrogen system is provided. The converter-hydrogen system includes a converter unit comprising a plurality of electrically connected converter cells, the converter unit being configured to be electrically coupled to a power network; and a hydrogen unit comprising a plurality of electrolyzer stacks and/or fuel cell stacks with auxiliary equipment is coupled to the converter unit. At least one electrolyzer stack or fuel cell stack is configured to be mechanically coupled to a frame structure, and to be electrically coupled with at least another electrolyzer stack or fuel cell stack in the hydrogen unit. The frame structure of the at least one electrolyzer stack or fuel cell stack is configured to be at a pre-configured electric potential based on the electrical coupling with the at least another electrolyzer stack or fuel cell stack and comprises an insulating means for electrically isolating the at least one electrolyzer stack or fuel cell stack from a ground potential.

Description

CONVERTER-HYDROGEN SYSTEM

TECHNICAL FILED

[0001] The present disclosure relates to converter-hydrogen systems for medium- or high-voltage power supply solutions.

BACKGROUND

[0002] The global push towards energy transition to a more sustainable energy paradigm, caused by global warming, has led to the exploration and adoption of alternative sources of energy. In this regard, hydrogen produced by electrolyzer stations using renewable energy holds great potential for decarbonizing various sectors of the global energy system, including long-haul transportation, power generation, and steel/ammonia production, etc.

[0003] The electrolyzer is typically a DC load and is generally fed by a power electronic converter that is connected to an AC grid. Traditionally, low voltage (LV) power supply solutions, such as multi-pulse thyristor rectifiers, are used to supply the required DC current to the electrolyzer to generate a desired amount of hydrogen. A large-scale electrolyzer station can be formed by having multiple electrolyzers, where each of them is powered by an LV power supply. Integrating such a large-scale electrolyzer plant into a power grid at a transmission level has numerous drawbacks. For example, the large-scale electrolyzer station may include a number of substations, which require numerous switchgears, busbars, and transformers to facilitate the integration of LV power supplies into the power grid that operates at a high voltage level.

[0004] In this context, a solution utilizing a medium-voltage and high-voltage power supply, such as a Modular Multilevel Converter (MMC), has been proposed. The MMC typically comprises several hundred series-connected converter cells, each cell contributing a portion of the converter's overall output. These series-connected converter cells can directly integrate multiple electrolyzer stacks into the power grid at the transmission level. By employing such a power supply solution, the need for numerous switchgears, busbars, and transformers can be eliminated.

[0005] However, the direct utilization of the medium-voltage and high-voltage MMC power supply solution, in the layout of a traditional large-scale electrolyzer station, poses a risk of introducing significant incompatibility relating to potential voltage imbalance among various components within the electrolyzer station. Consequently, there is a demand for a novel system configuration for the medium-voltage and high- voltage MMC power supply solution.

SUMMARY

[0006] According to an embodiment of the present disclosure, a converter-hydrogen system is provided. The converter-hydrogen system includes a converter unit comprising a plurality of electrically connected converter cells, the converter unit being configured to be electrically coupled to a power network; and a hydrogen unit comprising a plurality of electrolyzer stacks and/or fuel cell stacks with auxiliary equipment is coupled to the converter unit. At least one electrolyzer stack or fuel cell stack is configured to be mechanically coupled to a frame structure, and to be electrically coupled with at least another electrolyzer stack or fuel cell stack in the hydrogen unit. The frame structure of the at least one electrolyzer stack or fuel cell stack is configured to be at a pre-configured electric potential based on the electrical coupling with the at least another electrolyzer stack or fuel cell stack and comprises an insulating means for electrically isolating the at least one electrolyzer stack or fuel cell stack from a ground potential.

[0007] In an example, the at least one electrolyzer stack or fuel cell stack has two electrode terminals, and at least one electrode terminal is at an electric potential resulting from the electrical coupling with the at least another electrolyzer stack or fuel cell stack in the hydrogen unit. The frame structure of the at least one electrolyzer stack or fuel cell is electrically connected to one of the two electrode terminals stack of the at least one electrolyzer stack or fuel cell, and the pre-configured electric potential of the frame structure is different than the electric potential of the other one of the two electrode terminals of the at least one electrolyzer stack or fuel cell.

[0008] In an example, the frame structure is configured to be at an electric potential within a range of 10 to 100%, optionally 20% to 80%, of the maximum electric potential of the converter unit.

[0009] In an example, the at least one electrolyzer stack or fuel cell stack has two electrode terminals, and at least one electrode terminal of the two electrode terminals is at an electric potential resulting from a series and/or parallel configuration of the converter cells. The frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, is pre-configured to be at an electric potential equal to the electric potential of the at least one electrode terminal.

[0010] In an example, the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, is pre-configured to be at a floating potential.

[0011] In an example, the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, is pre-configured to be at a ground potential.

[0012] In an example, the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, comprises the insulating means capable of withstanding the maximum electric potential of the converter unit.

[0013] In an example, the plurality of electrolyzer stacks or fuel cell stacks are connected in series, and an end terminal of the series-connected electrolyzer stacks or fuel cell stacks are connected to a DC terminal of the converter unit.

[0014] In an example, the frame structure of the at least one electrolyzer stack is extended to mechanically couple to at least another electrolyzer stack in the hydrogen unit, or the frame structure of the at least one electrolyzer stack is mechanically coupled to a common platform, which is at a pre-configured electric potential and supports a frame structure of at least another electrolyzer stack.

[0015] In an example, the frame structure of the at least one fuel cell stack is extended to mechanically couple to at least another fuel cell stack in the hydrogen unit, or the frame structure of the at least one fuel cell stack is mechanically coupled to a common platform, which is at a pre-configured electric potential and supports a frame structure of at least another fuel cell stack.

[0016] In an example, the common platform or extended frame structure is preconfigured to be at an electric potential equal to one of the electric potentials of electrode terminals of the electrolyzer stacks or fuel cell stacks that are arranged on the common platform or extended frame structure.

[0017] In an example, the hydrogen unit comprises the plurality of electrolyzer stacks with the auxiliary equipment, and the auxiliary equipment comprises one or more of: one or more electrolyte tanks for storing electrolyte; one or more liquid pumps configured to circulate electrolyte and/or water, and cooling water in the hydrogen unit; and one or more gas pumps configured to transport H2 gas and 02 gas from the hydrogen unit. At least a portion of the auxiliary equipment is coupled with the frame structure configured at the pre-configured electric potential.

[0018] In an example, the auxiliary equipment comprises common auxiliary equipment shared by two or more electrolyzer stacks or fuel cell stacks and dedicated auxiliary equipment for each of the two or more electrolyzer stacks or fuel cell stacks, wherein the dedicated auxiliary equipment is coupled to the frame structure of the electrolyzer stack or fuel cell stack. The common auxiliary equipment is fluidly coupled to the dedicated auxiliary equipment for each of the two or more electrolyzer stacks or fuel cell stacks through a pipe of the converter-hydrogen system, wherein the pipe is electrically isolated from the common auxiliary equipment.

[0019] In an example, the converter unit is a chain-link converter unit coupled to a medium- or high-voltage and comprises at least one converter arm comprising series- connected converter cells, and a converter cell is electrically coupled to one of the plurality of electrolyzer stacks or fuel cell stacks.

[0020] In an example, the converter cell, as well as said one electrolyzer stack or fuel cell stack, along with auxiliary equipment to support the operation of said one electrolyzer stack or fuel cell stack, is integrated into a module, and the integrated module has fluid connections for electrolyte, water and gas.

[0021] In an example, the integrated module is arranged on a frame structure to which said one electrolyzer stack or fuel cell stack is coupled.

[0022] In an example, the converter-hydrogen system comprises an auxiliary converter or an isolation transformer for providing an isolated low-voltage power supply to electrical elements of the auxiliary equipment.

[0023] In an example, the converter unit is a double-Y connection converter unit having an AC side and a DC side, the AC side is coupled to a medium- or high-voltage, the double-Y connection converter unit comprising a plurality of parallel arms coupled between the AC side and the DC side, and each arm comprises the plurality of converter cells connected in series. The plurality of electrolyzer stacks and/or fuel cell stacks are coupled to the DC side.

[0024] In an example, two or more of the plurality of electrolyzer stacks are vertically arranged in a group, and the electrolyzer stack with the electrode terminal having the closest potential to the ground potential in the group is arranged at the bottom. [0025] In an example, insulation is provided between adjacent electrolyzer stacks in the group, and frame structures coupled to respective electrolyzer stacks are configured to be at different electric potential, or adjacent electrolyzer stacks in the group are vertically stacked without insulation between the adjacent electrolyzer stacks, and frame structures coupled to respective electrolyzer stacks are configured to be at the same electric potential.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The disclosed aspects will hereinafter be described in connection with the appended drawings, which are provided to illustrate but not to limit the scope of the present disclosure.

[0027] Figures 1 A, IB and 2A-2D illustrate converter-hydrogen systems according to embodiments of the present disclosure.

[0028] Figure 3 illustrates an exemplary configuration for one electrolyzer stack.

[0029] Figures 4-6 and 7A-7B illustrate exemplary configurations for series- connected electrolyzer stacks. [0030] Figure 8 illustrates a modular configuration for a chain-link converter unit according to an embodiment of the present disclosure.

[0031] Figures 9A-9C illustrate exemplary configurations for auxiliary equipment according to embodiments of the present disclosure.

DETAILED DESCRIPTION

[0032] The present disclosure proposes a new configuration, where a frame structure or common platform is set at a pre-configured electric potential for MV/HV power supply solutions interfaced with MV/HV-based AC or DC grids. This configuration ensures proper isolation of all conductive components in a large-scale converterhydrogen system from the ground. The proposed configuration is a key enabler for MV/HV power supply solutions in the large-scale converter-hydrogen system. In examples of the present disclosure, the medium voltage ranges between IkV and 35 kV and the high voltage ranges between 35 kV and 300 kV.

[0033] Moreover, the MV/HV power supply solutions eliminate the need for substations, harmonic filters, STATCOMs, and rectifier transformers, thereby providing a much more compact and cost-effective solution compared to legacy LV power supply solutions.

[0034] According to an embodiment of the present disclosure, a converter-hydrogen system for a medium- or high-voltage network is proposed. The converter-hydrogen system includes a converter unit and a hydrogen unit. The converter unit includes a plurality of electrically connected converter cells and is connectable to the network. The hydrogen unit is coupled to the converter unit and includes a plurality of electrolyzer stacks and/or fuel cell stacks. The hydrogen unit further includes auxiliary equipment to support the operation of the hydrogen unit. At least one electrolyzer stack or fuel cell stack is mechanically coupled to a frame structure. Moreover, the at least one electrolyzer stack or fuel cell stack is configured to be electrically connected with at least another electrolyzer stack or fuel cell stack from the plurality of electrolyzer stacks and/or fuel cell stacks. The frame structure of the at least one electrolyzer stack or fuel cell stack is configured to be at a pre-configured electric potential based on the electrical connection with the at least another electrolyzer stack or fuel cell stack and comprises an insulating means for electrically insulating the at least one electrolyzer stack or fuel cell stack from a ground potential.

[0035] Embodiments of the present disclosure will now be described with reference to the drawings. In the following description, examples of the electrolyzer stack are mainly introduced, and examples of the fuel cell stack can be implemented in a similar way. Moreover, embodiments of the present invention are applicable to various electrolyzer stacks, such as alkaline (ALK) and proton exchange membrane (PEM) electrolyzer stacks.

[0036] Figure 1A shows a converter-hydrogen system 100 (hereinafter, also simply referred to as system 100) according to an embodiment of the present disclosure. The system 100 mainly includes a converter unit and a hydrogen unit. The hydrogen unit includes a plurality of electrolyzer stacks and auxiliary equipment to support the operation of the electrolyzer stacks. Each electrolyzer stack can include one or more electrolysis cells.

[0037] With reference to Figure 1 A, the converter unit is implemented as a modular multilevel chain-link converter (may alternatively be called chain link MMC). The chain link MMC includes a plurality of converter arms (may alternatively be called legs, branches). Each arm includes a plurality of series-connected converter cells, such as converter cells 1 l~ln, 21~2n and 3 l~3n. Each arm can also include an inductor 71, 72 or 73. For each arm, the voltage across the converter unit is divided among the series- connected converter cells. For example, as shown in Figure 1A, the voltage Vsc is divided among the series-connected converter cells l l~ln; the voltage Vsb is divided among the series-connected converter cells 21~2n; and the voltage V_sa is divided among the series-connected converter cells 31~3n.

[0038] The chain-link MMC can be connected to an MV and HV power grid. The power grid can be part of a local, regional, national, or international electrical power grid, to which the system 100 is connected. The power grid, for example, delivers power generated by renewable energy sources such as wind or solar power. The power grid can have three connection lines for three phases. It is also understood that the system 100 can be used in other applications with fewer or more phases. In an example, the system 100 can also include a transformer 80 connectable to the MV and HV power grid for galvanically isolating the system 100 from the power grid and for adapting an input voltage level associated with an alternating current received from the power grid. Each chain-link arm is connected to an AC line of the transformer 80.

[0039] Each converter cell can be implemented as including a single-stage power converter (e.g., an AC/DC converter) or a two-stage power converter (e.g., an AC/DC converter and a DC/DC converter). In this exemplary illustration, each converter cell is electrically connected with one electrolyzer stack of the plurality of electrolyzer stacks and provides a DC output to said one electrolyzer stack. For example, each of the series- connected converter cells 1 l~ln is electrically connected with one of a set of electrolyzer stacks 41~4n and provides a direct current to the electrolyzer stack. Similarly, each of the series-connected converter cells 21~2n is electrically connected with one of a set of electrolyzer stacks 51~5n and provides a direct current to the electrolyzer stack. Each of the series-connected converter cells 31~3n is electrically connected with one of a set of electrolyzer stacks 61~6n and provides a direct current to the electrolyzer stack. In some examples, a converter cell can be connected to more than one electrolyzer stack, for example, to two or more electrolyzer stacks connected together in series and/or parallel. The two or more electrolyzer stacks connected to the converter cell are electrically coupled with another electrolyzer stack connected to another converter cell through the converter cell.

[0040] Figure IB shows an example of the system 100. In Figure IB, the system 100 has similar features as have been described with reference to Figure 1A. However, in the system 100 shown in Figure IB, at least one converter cell may be electrically connected with a fuel cell stack. In this case, the at least one converter cell receives power from the fuel cell stack. For example, as shown in Figure IB, the converter cell In of the series-connected converter cells 1 l~ln is electrically connected with a fuel cell stack 4n and receives power from the fuel cell stack 4n. Further, in the system 100 shown in Figure IB, at least one converter cell may be connected to a battery. For example, as shown in Figure IB, the converter cell 2n of the series-connected converter cells 21~2n is connected to the battery 5n.

[0041] In some other embodiments, at least some of the converter cells of the converter unit are connected with one electrolyzer stack or one fuel cell stack, and the remaining converter cells may either be unconnected or connected to other types of components (such as batteries or other fuel cells/electrolyzer stacks). In some embodiments, some of the converter cells may be connected with electrolyzer stacks and some of the converter cells may be connected with fuel cell stacks. In some other embodiments, one electrolyzer stack or fuel cell stack may be connected across several of the series-connected converter cells. There may, for example, be two, three, four or more of the series-connected converter cells that together drive the electrolyzer stack or fuel cell stack. In other words, in an example, two or more series-connected converter cells from one chain link arm may be connected to drive a single electrolyzer stack or a single fuel cell stack. This can be advantageous in that it allows a better match between the converter cell rating and the electrolyzer stack or fuel cell stack rating.

[0042] Figure 2A shows a converter-hydrogen system 100’ (hereinafter, also simply referred to as system 100’) according to an embodiment of the present disclosure. The system 100’ has similar features as the system 100 described with reference to Figure 1A. Similarly, the system 100’ mainly includes a converter unit and a hydrogen unit. The hydrogen unit includes a plurality of electrolyzer stacks. Each electrolyzer stack can include one or more electrolysis cells. However, the converter unit in Figure 2A has another topology.

[0043] With reference to Figure 2A, the converter unit is implemented as a double Y-connection MMC. The double Y-connection MMC includes a DC side having two DC terminals to provide a unipolar or a bipolar DC power supply. The double Y- connection MMC also includes an AC side connected to an MV and HV power grid. The above descriptions of the MV and HV power grid can also be applied here. In an example, the system 100’ also includes a transformer 80’ connectable to the MV and HV power grid for galvanically isolating the system 100’ from the power grid and for adapting an input voltage level associated with an alternating current received from the power grid. The AC side of the double Y-connection MMC is connected to the MV and HV power grid through the transformer 80’ .

[0044] The double Y-connection MMC includes a plurality of parallel phase arms (may alternatively be called legs or branches), here three, where each phase arm includes an upper arm connected to one of the DC terminals and a lower arm connected to the other one of the DC terminals. The upper and lower arms respectively include a plurality of series-connected converter cells. For example, the converter arm of phase a includes the upper and lower arms each including a plurality of series-connected converter cells 3 l’~3n’ . The converter arm of phase b includes the upper and lower arms each including a plurality of series-connected converter cells 21’~2n’. The converter arm of phase c includes the upper and lower arms each including a plurality of series-connected converter cells 1 l’~ln’. Each converter cell can be implemented as a half-bridge (HB) cell or a full-bridge (FB) cell. Each converter arm can also include two or more inductors. For example, the converter arm of phase a includes the upper and lower arms each including an inductor 73’. The converter arm of phase b includes the upper and lower arms each including an inductor 72’. The converter arm of phase c includes the upper and lower arms each including an inductor 71’. The midpoint of each phase arm can form an AC output of the converter unit.

[0045] With continued reference to Figure 2 A, the plurality of electrolyzer stacks include one string of series-connected electrolyzer stacks 41’~4n’ connected at the DC side and between the two DC terminals. The DC voltage Vdc across the converter unit is divided among the series-connected electrolyzer stacks.

[0046] Figure 2B shows an example of the system 100’. In Figure IB, the system 100’ has similar features as those have been described with reference to Figure 2A. However, in the system 100’ shown in Figure 2B, the plurality of electrolyzer stacks include two or more strings of series-connected electrolyzer stacks 41’ ~4n’, 5 l’~5n’ and 61’~6n’ connected at the DC side and between the two DC terminals. The DC voltage Vdc across the converter unit is divided among the series-connected electrolyzer stacks of each string. Additionally, the system can further involve converters or bypass arrangements on the DC side for balancing and controlling the DC voltage and/or current to each branch (not shown in the figure).

[0047] Figure 2C shows another example of the system 100’. In Figure 2C, the system 100’ mainly includes a converter unit and a fuel cell system. The fuel cell system includes a plurality of fuel cell stacks and auxiliary equipment such as pumps and electrolyte tanks. The converter unit is implemented as a double Y-connection MMC as described above. The plurality of fuel cell stacks includes one string of series-connected fuel cell stacks connected at the DC side and between the two DC terminals.

[0048] Figure 2D shows yet another example of the system 100’. In Figure 2D, the system 100’ mainly includes a converter unit, an electrolyzer system and a fuel cell system. The electrolyzer system includes a plurality of electrolyzer stacks and auxiliary equipment such as pumps and electrolyte tanks. The fuel cell system includes a plurality of fuel cell stacks and auxiliary equipment such as pumps and electrolyte tanks. The converter unit is implemented as a double Y-connection MMC as described above. The plurality of electrolyzer cell stacks include one string of series-connected electrolyzer stacks connected at the DC side and between the two DC terminals. The plurality of fuel cell stacks includes one string of series-connected fuel cell stacks connected at the DC side and between the two DC terminals. The system 100’ in Figure 2D also includes two isolating switches 91’ and 92. The isolating switch 91’ is connected to the string of electrolyzer stacks and used to disconnect the string of electrolyzer stacks from the converter unit. The isolating switch 92’ is connected to the string of fuel cell stacks and used to disconnect the string of fuel cell stacks from the converter unit. In this example, the system 100’ can be operated to connect with the electrolyzer stacks to provide power to the electrolyzer stacks or can be operated to connect with the fuel cell stacks to receive power from the fuel cell stacks. Additionally, there may be bypass switches (not shown in the figure) to bypass malfunctioning units. [0049] In some other embodiments, the DC side of the converter unit can be connected with a string of series-connected DC units. The DC units can include one or more electrolyzer stacks and/or one or more fuel cell stacks. When the system 100’ is required to operate in a power-to-gas mode, the electrolyzer stacks can be connected to the converter unit to generate hydrogen and the fuel cell stacks can be bypassed. When the system 100’ is required to operate in a gas-to-power mode, the fuel cell stacks can be connected to the converter unit to consume hydrogen previously produced by the electrolyzer stacks and generate power, and the electrolyzer stacks can be bypassed.

[0050] In various examples of the systems 100 or 100’ described above, electrolyzer stacks or fuel cell stacks coupled to one arm of the converter unit share the total HV DC power, where both electrode terminals of each electrolyzer stack or fuel cell stack will be at a high voltage potential and the electrolyzer stack or fuel cell stack connected in series next will be at a slightly higher or a lower higher voltage potential. In this case, because the electrode terminals of an electrolyzer stack or fuel cell stack might be at a much higher voltage potential than the designed or typical potential rating of an electrolyzer stack or fuel cell stack, the electrolyzer stack or fuel cell stack may need much higher insulation between the electrode terminals and its frame structure on which it is mounted. If not properly insulated, there can be a short circuit between the electrode terminals and the grounded parts in the system. In this regard, the inventors discovered that the potential difference between the two electrode terminals of an electrolyzer stack or fuel cell stack can be much smaller (e.g., 500V, IkV), even though both two terminal are at HV/MV potentials (e.g. lOkV or 50kV), and proposed a new solution to effectively utilize electrolyzer stacks or fuel cells in the series configuration to meet the insulation requirements for operating the system at a HV/MV DC voltage.

[0051] For brevity and illustration purpose, an example is given using several electrolyzer stacks connected in series (though there may be nearly hundreds of electrolyzer stacks connected across a high voltage power supply) between the positive (DC+) and negative (DC-) terminals of the DC side of a double Y-connection MMC, which shares a bipolar power supply ranging from +18kV to -18kV on the DC side. If each electrolyzer stack is assumed to be a resistive load and all the electrolyzer stacks are assumed to be equal, an approximately equal voltage distribution across each electrolyzer can be expected. For example, an electrolyzer stack is shown to have a IkV potential difference across its power terminals. It is noted that, in an example where each electrolyzer stack is rated at 500V, there will be at least 72 electrolyzer stacks connected in series across a +18kV and -18kV bipolar DC power supply. A person skilled in the art would recognize that several electrolyzer stacks can be coupled together in series and/or parallel as needed to achieve the rated/desired level of voltage drop across individual electrolyzer stacks in view of the designed electric potential difference between the electrode terminals of the electrolyzer stacks.

[0052] It is noted that the specific numerical values mentioned in the drawings and the description (e.g., the value of electric potential or the number of electrolyzer stacks, etc.) are intended to serve as examples for better understanding of the present invention and are not intended to limit the present invention.

[0053] It is noted that the drawings are shown for an illustrative purpose where the insulation is shown by a gray-filled block indicative of an insulation bulk. For example, the gray-filled block illustrates an insulator for electrically insulating electrolyzer electrodes from the frame structure or one or more insulating stands for electrically insulating the frame structure from the ground.

[0054] Figure 3 shows an exemplary configuration for one electrolyzer stack according to an embodiment of the present disclosure, taking the electrolyzer stack 41’ as an example.

[0055] With reference to Figure 3, the electrolyzer stack 41’ is electrically connected with the electrolyzer stack 42’ (this electrical connection can be seen in Figure 2A) and has two electrode terminals, i.e., a first electrode terminal 411’ and a second electrode terminal 412’. The first electrode terminal 411’ is electrically connected with the converter unit and the second electrode terminal 412’ is electrically connected with an electrode terminal of the electrolyzer stack 42’. Each of the first and second electrode terminal 411’ and 412’ is at an electric potential resulting from a series and/or parallel configuration of the converter unit. For example, the first electrode terminal 411’ is at an electric potential equal to that of the positive terminal of the DC side of the converter (i.e., 18kV). The second electrode terminal 412’ is at an electric terminal equal to that of the connected terminal of the electrolyzer stack 42’ (i.e., 17.5kV). The electrolyzer stack 41’ is arranged on a frame structure 410’. The frame structure 410’ is a mechanical support structure for the electrolyzer stack 41’. One or both of the first and second electrode terminals 411’ and 412’ are electrically insulated from the frame structure 410’ and the frame structure 410’ is electrically insulated from the ground. The short circuit issue can be eliminated by electrically insulating the frame structure 410’ from the ground. For example, the frame structure 410’ comprises an insulating means for insulating the frame structure 410’ from a ground potential. The frame structure 410’ can be supported by one or more insulating stands 415’. A plurality of insulating stands may be stacked to increase the insulation capability based on the preconfigured electric potential of the frame structure 410’. That is to say, the number of stacked insulating stands is associated with the preconfigured electric potential of the frame structure 410’. [0056] In an example, the frame structure 410’ is configured to be at an electric potential based on at least one of electric potentials of electrode terminals of the electrolyzer stack 41’ and the connected electrolyzer stack 42’. In this example, the frame structure 410’ can be configured to be at an electric potential equal to or very close to the electric potential of the second electrode terminal 412’ of the electrolyzer 41’. [0057] In another example, the frame structure 410’ is configured to be at an electric potential within a range of 10-100%, optionally 20%~80%, of the maximum electric potential (e.g., 18kV) of the hydrogen unit. Specifically, in one embodiment, different frame structures can be pre-configured to different electric potentials within a first range of 10-100% of the maximum electric potential of the hydrogen unit. In another embodiment, different frame structures can be pre-configured to different electric potentials within a second range of 20-80% of the maximum electric potential of the hydrogen unit. The first range and the second range can be predetermined based on measurement results and/or model calculations. In other words, the electric potential of each frame structure can be an electric potential within a predetermined potential range, and electric potentials of different frame structures can be different electric potentials within the predetermined potential range.

[0058] In yet another example, the frame structure 410’ is configured to be at an electric potential equal to the electric potential of one of the first and second electrode terminals 411’ and 412’ of the electrolyzer stack 41’.

[0059] In yet another example, the frame structure is configured to be at an electric potential based on the electric potentials of both first and second electrode terminals 411 ’ and 412’ of the electrolyzer 41’. In this example, the frame structure can be configured to be at an electric potential equal to an average of the electric potentials of both first and second electrode terminals 411’ and 412’ of the electrolyzer 41’.

[0060] In yet another example, the frame structure 410’ is configured to be at a floating potential.

[0061] In yet another example, the frame structure 410’ is configured to be at a ground potential.

[0062] With continued reference to Figure 3, in an example, both the first and second electrode terminals 411’ and 412’ are electrically insulated from the frame structure 410’. For example, the first electrode terminal 411’ is insulated from the frame structure 410’ through a first insulator 413’, and the second electrode terminal 412’ is electrically insulated from the frame structure 410’ through a second insulator 414’. The frame structure 410’ is electrically insulated from the ground through one or more insulating stands 415’ supporting the frame structure 410’, and the electric potential of the frame structure 410’ is pre-configured to be equal to the electric potential of the second electrode terminal 412’. In this embodiment, the insulation level of the electrical insulation between the first electrode terminal 411’ and the frame structure 410’ (i.e., the electrical insulation level of the first insulator 413’) only needs to withstand the potential difference (e.g., 500V) between the first electrode terminal 411’ and the frame structure 410’. The electrical insulation level between the second electrode terminal 412’ and the frame structure can refer to the electrical insulation level between the first electrode terminal 411’ and the frame structure 410’. The electrical insulation level between the frame structure 410’ and the ground (e.g., the electrical insulation level of the insulating stands 415’) needs to withstand the potential difference (e.g., 17.5kV) between the frame structure and the ground. That is to say, the one or more insulating stands 415’ supporting the frame structure 410’ are provided to withstand the high voltage potential applied to the frame structure 410’.

[0063] In addition, it is also feasible to electrically connect one of the first and second electrode terminals 411’ and 412’ to the frame structure 410’, for example, connecting the second electrode terminal 412’ to the frame structure 410’. In this way, no electrical insulation is required between the second electrode terminal 412’ and the frame structure 410’ and the corresponding insulator 414’ can be omitted.

[0064] Figure 4 shows an exemplary configuration for series-connected electrolyzer stacks 41’ and 42’, in which respective electrolyzer stacks are arranged on different frame structures configured to be at different electric potentials.

[0065] With reference to Figure 4, the electric potential of the frame structure 410’ on which the electrolyzer stack 41’ is arranged can be preconfigured to be equal to the electric potential (e.g., 17kV) of the second electrode terminal 412’ of the electrolyzer stack 41’, and the electric potential of the frame structure 420’ on which the electrolyzer stack 42’ is arranged can be preconfigured to be equal to the electric potential (e.g., 16kV) of the second terminal 422’ of the electrolyzer stack 42’, which is lower than that of the electrode terminal 412’. In this way, the electric potential of the frame structure 420’ is lower than that of the frame structure 410’ due to the series configuration of the two electrolyzer stacks connected. Therefore, the insulation level between the frame structure 420’ and the ground can be lower than that between the frame structure 410’ and the ground. In this case, the number of stacked insulating stands 425’ of the frame structure 420’ can be less than that of stacked insulating stands 415’ of the frame structure 410’. As shown in Figure 4, the height of the stacked insulating stands 425’ is lower than that of the insulating stands 415’.

[0066] Although the arrangement of placing each electrolyzer stack on a frame structure is shown in Figures 3 and 4, according to embodiments of the present disclosure, the frame structure can also be extended to mechanically support two or more electrolyzer stacks.

[0067] In some other embodiments, considering the unequal voltage distribution caused by dynamic changes in the system, the electric potential of the frame structure can be pre-configured with a margin that can compensate for the dynamic changes. The reasons for the dynamic changes are varied, for example, the operation status of complex distribution networks will change with changes in environmental conditions, increases or decreases in load demand, adjustments in power output, changes in operation modes, and faults or disturbances, as well as the significant asymmetry in the parameters of the distribution network resulting from the integration of renewable energy, and so on. In an example, the electric potential of the frame structure may be pre-configured based on the electric potential of one electrode terminal of the electrolyzer stack supported by the frame structure under the condition of equal voltage distribution and a redundancy value. The redundancy value is determined according to the specific application scenario of the system, to ensure that the redundancy can accommodate unequal voltage distribution during system dynamics. In this example, the redundancy value can be determined using a trained machine learning model, which can predict the voltage distribution of the HVDC or MVDC output of the converter unit according to the current state of the system. [0068] In some other embodiments, the insulation level of each frame structure from ground can withstand the maximum electric potential generated by the converter unit.

[0069] Figure 5 illustrates an exemplary configuration where series-connected electrolyzer stacks are arranged on a common platform, and the electric potential of the common platform is pre-configured. The common platform is a mechanical support on which a group of electrolyzer stacks (e.g., two or more electrolyzer stacks) is arranged, and the common platform is electrically insulated from the ground. The advantage of adopting the common platform lies in improving space utilization and reducing the overall system footprint, especially when there are a large number of electrolyzer stacks. [0070] With reference to Figure 5, the series-connected electrolyzer stacks corresponding to one converter arm of the MMC converter unit are divided into several groups, with each group of electrolyzer stacks arranged on a common platform. The electric potentials of these platforms can be different. For example, the electric potential of each common platform can be pre-configured to be equal to the electric potential of one electrode terminal of an electrolyzer stack in the respective group.

[0071] With continued reference to Figure 5, the series-connected electrolyzer stacks are divided into three groups, with three electrolyzer stacks in each group, and each group of electrolyzer stacks is arranged on a common platform. Specifically, a first group of electrolyzer stacks 4T-43’ is arranged on a first common platform CPI, and this group can include more electrolyzer stacks, for example, one or more electrolyzer stacks can be coupled between the electrolyzer stacks 42’ and 43’. A second group of electrolyzer stacks 44’-46’ is arranged on a second common platform CP2, and this group can include more electrolyzer stacks, for example, one or more electrolyzer stacks can be coupled between the electrcolyzer stacks 45’ and 46’. A third group of electrolyzer stacks 47’-49’ is arranged on a third common platform CP3, and this group can include more electrolyzer stacks, for example, one or more electrolyzer stacks can be coupled between the electrcolyzer stacks 48’ and 49’. To minimize the required insulation level for electrode terminals of the electrolyzer stacks arranged on one common platform, the electric potential of said one common platform can be preconfigured to be equal to the electric potential of one electrode terminal of the electrolyzer stack located in the middle position among those series-connected electrolyzer stacks arranged on said one common platform. For example, the electric potential of the first common platform CPI is pre-configured to be equal to the electric potential (e.g., 16kV) of one terminal of the electrolyzer stack 42’ located in the middle position among the electrolyzers 4F-43’. Similarly, the electric potential of the second common platform CP2 is pre-configured to be equal to the electric potential (e.g. 4kV) of one terminal of the electrolyzer stack 45’ located in the middle position among the electrolyzer stacks 44’-46’. The electric potential of the third common platform CP3 is pre-configured to be equal to the electric potential (e.g., -8kV) of one terminal of the electrolyzer stack 48’ located in the middle position among the electrolyzer stacks 47’- 49’.

[0072] The short circuit issue can be eliminated by electrically insulating each common platform from the ground through insulating means. For example, the first common platform CPI includes insulating stands 401 for insulating the first common platform CPI from a ground potential. The second common platform CP2 includes insulating stands 402 for insulating the second common platform CP2 from a ground potential. The third common platform CP3 includes insulating stands 403 for insulating the third common platform CP3 from a ground potential. In an example, the insulating stands of each common platform may be stacked to increase the insulation capability based on the preconfigured electric potential of the common platform. That is to say, the number of stacked insulating stands is associated with the preconfigured electric potential of the platform. As shown in Figure 5, the height of the insulating stands 401 is greater than that of the insulating stands 402, but the same as that of the insulating stands 403.

[0073] In an example, each common platform is configured to be electrically connected with one electrode terminal of the electrolyzer stack located in the middle position among those series-connected electrolyzer stacks arranged on the common platform. In this way, each common platform is configured to be at an electric potential equal to that of the connected electrode terminal.

[0074] In another example, at least one common platform is configured to be at a floating potential.

[0075] In yet another example, at least one common platform is configured to be at a ground potential. For example, in the YY-connection configuration with a bipolar power supply, there might be a power terminal of an electrolyzer stack, in the series- connected electrolyzer stacks, that is at the ground potential.

[0076] In some other embodiments, considering the unequal voltage distribution caused by dynamic changes in the system, the electric potential of the common platform can be pre-configured with a margin that can compensate for the dynamic changes. The determination of this margin can be similar to that of the redundancy value discussed above, with the difference being that in the aforementioned implementation, only the voltage distribution fluctuation of a single electrolytic cell was considered when determining the redundancy value, whereas in this implementation, the determination of the redundancy value needs to consider the voltage fluctuation of a group of electrolyzer stacks arranged on one common platform.

[0077] An embodiment similar to the common platform shown in Figure 5 is to extend the frame structure used to support a single electrolyzer stack to support two or more electrolyzer stacks. For example, the frame structure 410' that originally only supported the electrolyzer stack 41' is extended to support multiple electrolyzer stacks 41’ -43’. In this embodiment, the extended frame structure 410’ is equivalent to the first common platform CPI described above.

[0078] In some other embodiments, the common platform is implemented with frame structures of a group of electrolyzer stacks (e.g., two or more of the plurality of electrolyzer stacks) being electrically interconnected with cables, to maintain these frame structures at a same pre-configured potential.

[0079] It is noted that the frame structure or the common platform is a part of the hydrogen unit, and thus also a part of the system.

[0080] Figure 6 shows an example of the configuration in Figure 5. The configuration shown in Figure 6 has similar features to those have been described with reference to Figure 5. However, in the configuration shown in Figure 6, each common platform is configured to be at the same electric potential, for example, ranging between 20%-100% of the DC voltage at the DC side (e.g. 36kV).

[0081] Figures 4-6 illustrate exemplary configurations in which series-connected electrolyzer stacks are horizontally arranged. Next, Figures 7A and 7B illustrate exemplary configurations in which series-connected electrolyzer stacks are vertically arranged. In Figures 7A and 7B, taking nine series-connected electrolyzer stacks coupled to the DC side of the double-Y connection converter unit as an example, the voltage between the positive and negative electrodes on the DC side is between 0 and 18kV. Therefore, when each electrolyzer stack is considered as a DC load with equal resistance, the voltage drop across each electrolyzer stack is 2kV.

[0082] Figure 7A shows an embodiment of the vertical configuration, in which a plurality of electrolyzer stacks are divided into several groups, electrolyzer stacks in each group are arranged in a vertical manner and the bottommost one is arranged on the ground through an insulating support, and insulation is also provided between adjacent electrolyzer stacks in the group. In this embodiment, the frame structures in one group can be configured at different electric potentials.

[0083] With reference to Figure 7A, the series-connected electrolyzer stacks 41 ’—43 ’ are vertically arranged in a first group, and the electrolyzer stack 43’ with the lowest potential is arranged at the bottom (i.e., closest to the ground). The frame structure can be configured at an electric potential equal to that of one electrode terminal of the electrolyzer stack to which the frame structure is coupled. For example, the frame structure 410’ is configured at an electric potential of 16kV, which is equal to the electric potential of one electrode terminal of the electrolyzer stack 41’; the frame structure 420’ is configured at an electric potential of 14kV, which is equal to the electric potential of one electrode terminal of the electrolyzer stack 42’; and the frame structure 430’ is configured at an electric potential of 12kV, which is equal to the electric potential of one electrode terminal of the electrolyzer stack 43’. Insulation is provided between adjacent electrolyzer stacks and between the bottommost electrolyzer stack 43’ and the ground. For example, insulating stands 415’ are provided between the electrolyzer stacks 41’ and 42’, and the electrical insulation level of the insulating stands 415’ can withstand the potential difference between the electric potential of the frame structure 410’ and the electric potential of the frame structure 420’. Similarly, insulating stands 425’ are provided between the electrolyzer stacks 42’ and 43’, and the electrical insulation level of the insulation members 425’ can withstand the potential difference between the electric potential of the frame structure 420’ and the electric potential of the frame structure 430’. The insulation level of the insulating stands 435’ can withstand the potential difference between the electric potential of the frame structure 430’ and a ground potential.

[0084] With continued reference to Figure 7A, the series-connected electrolyzer stacks 44’~46’ are vertically arranged in a second group, and the electrolyzer stack 46’ with the lowest potential is arranged at the bottom (i.e., closest to the ground). The series-connected electrolyzer stacks 47’~49’ are vertically arranged in a second group, and the electrolyzer stack 49’ with the lowest potential is arranged at the bottom (i.e., closest to the ground). The implementation of the second and third groups is similar to that of the first group described above, with the exception that the frame structures 460’ and 490’ of the bottommost electrolyzer stacks 46’ and 49’ have lower potentials than the frame structures 430’ in the first group, and therefore require a lower insulation level relative to ground. As shown in Figure 7A, the height of insulating stands 495’ is lower than that of the insulating stands 465’ and even lower than that of the insulating stands 435’.

[0085] Figure 7B shows an example of the vertical configuration depicted in Figure 7A. The configuration shown in Figure 7B has similar features to those that have been described with reference to Figure 7A. However, in the configuration depicted in Figure 7B, there is no insulation provided between adjacent electrolyzer stacks in one group, that is to say, one electrolyzer stack is directly arranged on another one without insulating stands. In such a configuration, all frame structures in one group are configured at the same electric potential, for example, equal to the electric potential of one electrode terminal of an electrolyzer stack in that group. In an example, all frame structures in the first group are configured at an electric potential of 14kV, which is equal to the electric potential of one electrode terminal of the electrolyzer stack 42’; all frame structures in the second group are configured at an electric potential of 8kV, which is equal to the electric potential of one electrode terminal of the electrolyzer stack 45’; and all frame structures in the third group are configured at an electric potential of 2kV, which is equal to the electric potential of one electrode terminal of the electrolyzer stack 48’ . In this case, the required electrical insulation level of insulating stands for insulating the bottommost frame structure from the ground can be different. As shown in Figure 7B, the height of insulating stands 495’ is lower than that of the insulating stands 465’ and even lower than that of the insulating stands 435’.

[0086] It is noted that the examples introduced above are applicable to both the chain link and double-Y topologies of the converter unit mentioned above. In the double-Y topology, the electrolyzer stacks are connected in series between the positive terminal and the negative terminal of the DC side of the converter unit. In the chain-link topology, in each converter arm, the converter cells are connected in series and share a high voltage, and each electrolyzer stack is connected to a corresponding one of the converter cells and thus obtains the same voltage distribution as the converter cell to which it is connected.

[0087] Figure 8 shows a modular configuration according to an embodiment of the present disclosure. The modular configuration is applicable to the above-mentioned system 100 (e.g., the system 100 shown in Figures 1A and IB) in which the converter unit is implemented in the chain-link topology. In this embodiment, each electrolyzer stack along with the converter cell, which is electrically coupled to the electrolyzer stack to provide a power supply to the electrolyzer stack, as well as the auxiliary equipment to support the operation of the electrolyzer stack are integrated into a module, and the module is arranged on the frame structure to which the electrolyzer stack is coupled. Moreover, the frame structure is configured at an electric potential based on the position of the converter cell in the chain-link arm, and electrically insulated from the ground through insulating stands. As shown in Figure 8, the electrolyzer stack 41 along with the converter cell 11 as well as the auxiliary equipment (AUX) to support the operation of the electrolyzer stack 41 are integrated into a module M41. The module M41 is arranged on the frame structure 410 of the electrolyzer stack 41. The frame structure 410 is configured to be at an electric potential equal to that of one electrode terminal of the electrolyzer stack 41 and is electrically insulated from the ground through insulating stands 415.

[0088] Examples of the present disclosure also propose new solutions for the layout, insulation, and power supply of auxiliary equipment in the above-mentioned systems. Below, in some examples, the embodiment of auxiliary equipment to support the operation of electrolyzer stacks is introduced as an example, and the embodiment of auxiliary equipment to support the operation of fuel cell stacks can be implemented in a similar manner.

[0089] The auxiliary equipment can include one or more of the following components: pumps (e.g., liquid pumps and gas pumps), sensors (e.g., temperature sensors and pressure sensors), control and protection units (e.g., control panel, anodic protection unit), storage devices (e.g., electrolyte tanks and hydrogen tanks), cooling system (e.g., heat exchangers), gas-liquid separators (e.g., H2/Lye separators and O2/Lye or H2/water separators and O2/water separators), scrubbers, compressors, dryers, etc. Some require power supply, while others do not. In an example, for PEM electrolyzer stacks, the electrolyte can be non-conductive distilled water and at least part of the distilled water can be used as cooling water. For ALK electrolyzer stacks, the electrolyte can be conductive alkaline electrolyte. In an example, a heat exchanger can be coupled with a pump for circulating cooling water in the hydrogen unit and for adjusting the temperature and flow rate of the cooling water.

[0090] Moreover, among the above-mentioned components, some have conductive housings, such as metal housings, while others have non-conductive housings, such as ceramic or plastic housings. In addition, the hydrogen unit includes pipes where electrolytes or gases flow. The pipes, which are insulating, are used for connecting two components with different electric potentials, or insulating connectors can be provided at the connections of two components with different electric potentials.

[0091] In an example, the hydrogen unit comprises a plurality of electrolyzer stacks and auxiliary equipment to support the operation of the electrolyzer stacks. The auxiliary equipment comprises one or more of: one or more electrolyte tanks for storing electrolyte; one or more liquid pumps configured to circulate electrolyte and/or water, and cooling water in the hydrogen unit; and one or more gas pumps configured to transport H2 gas and 02 gas from the hydrogen unit. For at least one electrolyzer stack, at least a portion of the auxiliary equipment used to support the operation of the at least one electrolyzer stack is coupled with the frame structure of the at least one electrolyzer stack configured at a pre-configured electric potential.

[0092] In an example, the auxiliary equipment includes common auxiliary equipment shared by two or more electrolyzer stacks or fuel cell stacks and dedicated auxiliary equipment for each of the two or more electrolyzer stacks or fuel cell stacks, and the dedicated auxiliary equipment is coupled to the frame structure of the electrolyzer stack or fuel cell stack. The common auxiliary equipment is fluidly coupled to the dedicated auxiliary equipment for each of the two or more electrolyzer stacks or fuel cell stacks through a pipe of the converter-hydrogen system, and the pipe is electrically isolated from the common auxiliary equipment. The pipe can be a non- conductive pipe (ceramic or plastic pipe; or non-conductive material covers its inner surface) or provided with an insulating connector at the place before linking to the common auxiliary equipment.

[0093] For clarity, with reference to Figure 4, the auxiliary equipment for the electrolyzer stacks 41’ and 42’ are introduced. The dedicated auxiliary equipment for the electrolyzer stack 41 ’ can include one or more gas/liquid separators (e.g., for an alkaline electrolyzer stack, the liquid would be electrolyte and for a PEM electrolyzer stack, the liquid would be water), and a liquid tank. The dedicated auxiliary equipment for the electrolyzer stack 41’ can further include fluid pumps, a cooling system, a control device, a sensing device and a protection circuit. The dedicated auxiliary equipment is arranged on (coupled to) the frame structure of the electrolyzer stack 41’ . Similarly, the dedicated auxiliary equipment for the electrolyzer stack 42’ can include one or more gas/liquid separators (e.g., for an alkaline electrolyzer stack, the liquid would be electrolyte and for a PEM electrolyzer stack, the liquid would be water), and a liquid electrolyte tank. The dedicated auxiliary equipment for the electrolyzer stack 42’ can further include fluid pumps, a cooling system, a control device, a sensing device and a protection circuit. The dedicated auxiliary equipment is arranged on (coupled to) the frame structure of the electrolyzer stack 42’. The common auxiliary equipment for both the electrolyzer stack 41’ and the electrolyzer stack 42’ includes one or more of a scrubber, a compressor, a dryer and a storage (e.g., an H2 storage and an 02 storage), and the common auxiliary equipment is put on the ground. The dedicated auxiliary equipment for the electrolyzer stack 41’ is coupled to the common auxiliary equipment with pipes which are non-conductive pipes or provided with insulating connectors at the places before linking to the common auxiliary equipment. Similarly, the dedicated auxiliary equipment for the electrolyzer stack 42’ is coupled to the common auxiliary equipment with pipes which are non-conductive pipes or provided with insulating connectors at the places before linking to the common auxiliary equipment.

[0094] It is noted that the dedicated auxiliary equipment can be seen as the so-called BOS (balance of stack) which is dedicated to an electrolyzer stack, and the common auxiliary equipment can be seen as the so-called BOP (balance of plant) which is shared by more than one electrolyzer stacks.

[0095] It is noted that, in some examples, at least a portion of the dedicated auxiliary equipment can be provided in the common auxiliary equipment. For example, in the case of ALK electrolyzer stacks, the dedicated auxiliary equipment includes a liquid (electrolyte) tank, while in the case of PEM electrolyzer stacks, the dedicated auxiliary equipment may not include a dedicated liquid (water) tank, instead the common auxiliary equipment includes a liquid (water) tank, allowing several electrolyzer stacks to share this liquid (water) tank.

[0096] Figures 9A-9C show some embodiments of the auxiliary equipment related to the electrolyzer stack 41’, where isolation is provided to avoid short circuiting through the electrical/mechanical couplings in the system and through electrolytes/fluids if they are conducting (e.g. lye solution). Similar arrangements may be used for fuel cell stacks to isolate auxiliary equipment of fuel cell stacks to avoid any possible short circuiting through the electrical/mechanical couplings in the system or through any of the fluids which may be conducting.

[0097] With reference to Figure 9A, in an embodiment, each electrolyzer stack is configured with an individual pump 101 and an individual electrolyte tank 102 that is arranged on the ground and the tank housing can isolate the electrolyte from the ground potential. In an example where the electrolyte is non-conducting (e.g., distilled water), a plurality of or group of electrolyzer stacks may share a common electrolyte tank 102, which may be arranged on the ground and has the ground potential. The electrolyte flows from the electrolyte tank 102 into the pump 101 through a pipe 106 and then is pumped into the electrolyzer stack 41’ through a pipe 107. The pipe 107 is used to connect the pump 101 and the electrolyzer stack 41’, which are at different electric potentials, and thus is a non-conductive pipe (ceramic or plastic pipe; or non-conductive material covers its inner surface) or provided with an insulating connector 103 at the place before linking to the electrolyzer stack 41’. An auxiliary power supply 105 can be provided to power electrical elements of the auxiliary equipment and is also arranged on the ground.

[0098] With reference to Figure 9B, in another embodiment, each electrolyzer stack has its dedicated pump and the pump is arranged on the frame structure to which the electrolyzer stack is coupled. As shown in Figure 9, the pump 101 dedicated to the electrolyzer stack 41’ is arranged on the frame structure 410. A plurality of or group of electrolyzer stacks share a common electrolyte tank 102 when the electrolyte is nonconducting (e.g., distilled water), which is arranged on the ground and has the ground potential. The electrolyte flows from the electrolyte tank 102 into the pump 101 through a pipe 106 and then is pumped into the electrolyzer stack 41’ through a pipe 107. The pipe 106 is used to connect the electrolyte tank 102 and pump 101, which are at different electric potentials, and thus is a non-conductive pipe (ceramic or plastic pipe; or non- conductive material covers its inner surface) or provided with an insulating connector 103 at the place before linking to the pump 101.

[0099] With reference to Figure 9C, in yet another embodiment, each electrolyzer stack has its dedicated pump and the pump is arranged on the frame structure to which the electrolyzer stack is coupled. As shown in Figure 9, the pump 101 dedicated to the electrolyzer stack 41’ is arranged on the frame structure 410. Moreover, each electrolyzer stack has its dedicated electrolyte tank and the electrolyte tank is also arranged on that frame structure. As shown in Figure 9, the electrolyte tank 102 dedicated to the electrolyzer stack 41’ is arranged on the frame structure 410. Moreover, an auxiliary power supply 105 can be provided to power electrical elements of the auxiliary equipment and is also arranged on the frame structure 410’.

[00100] In some examples, the H2 gas and 02 gas can be transported through insulating gas pipes.

[00101] In some examples, in the case where the dedicated pump is arranged on the frame structure along with the electrolyzer stack (e.g., the layout shown in Figure 9B), an auxiliary converter dedicated to the pump can be provided. For example, for each dedicated pump, an auxiliary converter is coupled between the converter unit and the pump to provide a low- voltage power supply to that pump.

[00102] In some examples, in the case where the dedicated pump is arranged on the frame structure along with the electrolyzer stack (e.g., the layout shown in Figure 9B), an isolation transformer dedicated to the pump can be provided. For example, for each dedicated pump, an isolation transformer is coupled between a power grid and the pump to provide an isolated low-voltage power supply to that pump.

[00103] In some examples, the auxiliary equipment can also include a protection circuit, such as an RC circuit, to protect the system under dynamic or fault scenarios. For example, the RC circuit can be coupled with an electrolyzer stack and arranged on the frame structure along with the electrolyzer stack.

[00104] It should be understood that a zero potential may occur in a series connection, which means that the value is approximately zero, but it does not necessarily mean that it must be grounded.

[00105] It should be understood that in the same figure, different heights of insulating stands indicate different insulation levels (insulation capabilities), with higher height corresponding to stronger insulation strength. However, the heights of insulating stands are not comparable between different figures.

[00106] It should be understood that “providing electrical isolation” can include providing electrical insulation through an insulating component such as the insulting stand described above.

[00107] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein. All structural and functional equivalent transformations to the elements of the various aspects of the present disclosure, which are known or to be apparent to those skilled in the art, are intended to be covered by the claims.

Claims

WHAT IS CLAIMED IS:

1. A converter-hydrogen system comprising: a converter unit comprising a plurality of electrically connected converter cells, the converter unit being configured to be electrically coupled to a power network; and a hydrogen unit comprising a plurality of electrolyzer stacks and/or fuel cell stacks with auxiliary equipment is coupled to the converter unit, wherein at least one electrolyzer stack or fuel cell stack is configured to be mechanically coupled to a frame structure, and to be electrically coupled with at least another electrolyzer stack or fuel cell stack in the hydrogen unit, and wherein the frame structure of the at least one electrolyzer stack or fuel cell stack is configured to be at a pre-configured electric potential based on the electrical coupling with the at least another electrolyzer stack or fuel cell stack and comprises an insulating means for electrically isolating the at least one electrolyzer stack or fuel cell stack from a ground potential.

2. The converter-hydrogen system of claim 1, wherein the at least one electrolyzer stack or fuel cell stack has two electrode terminals, and at least one electrode terminal is at an electric potential resulting from the electrical coupling with the at least another electrolyzer stack or fuel cell stack in the hydrogen unit, and wherein the frame structure of the at least one electrolyzer stack or fuel cell is electrically connected to one of the two electrode terminals of the at least one electrolyzer stack or fuel cell, and the pre-configured electric potential of the frame structure is different than the electric potential of the other one of the two electrode terminals of the at least one electrolyzer stack or fuel cell.

3. The converter-hydrogen system of claim 1, wherein the frame structure is configured to be at an electric potential within a range of 10 to 100%, optionally 20% to 80%, of the maximum electric potential of the converter unit.

4. The converter-hydrogen system of claim 1, wherein the at least one electrolyzer stack or fuel cell stack has two electrode terminals, and at least one electrode terminal of the two electrode terminals is at an electric potential resulting from a series and/or parallel configuration of the converter cells, and wherein the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, is pre-configured to be at an electric potential equal to the electric potential of the at least one electrode terminal.

5. The converter-hydrogen system of claim 1, wherein the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, is pre-configured to be at a floating potential.

6. The converter-hydrogen system of claim 1, wherein the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, is pre-configured to be at a ground potential.

7. The converter-hydrogen system of claim 1, wherein the frame structure, to which the at least one electrolyzer stack or fuel cell stack is coupled, comprises the insulating means capable of withstanding the maximum electric potential of the converter unit.

8. The converter-hydrogen system of claim 1, wherein the plurality of electrolyzer stacks or fuel cell stacks are connected in series, and an end terminal of the series- connected electrolyzer stacks or fuel cell stacks are connected to a DC terminal of the converter unit.

9. The converter-hydrogen system of any of claims 1-8, wherein the frame structure of the at least one electrolyzer stack is extended to mechanically couple to at least another electrolyzer stack in the hydrogen unit, or the frame structure of the at least one electrolyzer stack is mechanically coupled to a common platform, which is at a pre-configured electric potential and supports a frame structure of at least another electrolyzer stack.

10. The converter-hydrogen system of any of claims 1-8, wherein the frame structure of the at least one fuel cell stack is extended to mechanically couple to at least another fuel cell stack in the hydrogen unit, or the frame structure of the at least one fuel cell stack is mechanically coupled to a common platform, which is at a pre-configured electric potential and supports a frame structure of at least another fuel cell stack.

11. The converter-hydrogen system of claim 9 or 10, wherein the common platform or extended frame structure is pre-configured to be at an electric potential equal to one of the electric potentials of electrode terminals of the electrolyzer stacks or fuel cell stacks that are arranged on the common platform or extended frame structure.

12. The converter-hydrogen system of any of claims 1-11, wherein the hydrogen unit comprises the plurality of electrolyzer stacks with the auxiliary equipment, and the auxiliary equipment comprises one or more of: one or more electrolyte tanks for storing electrolyte; one or more liquid pumps configured to circulate electrolyte and/or water, and cooling water in the hydrogen unit; and one or more gas pumps configured to transport H2 gas and 02 gas from the hydrogen unit; and wherein at least a portion of the auxiliary equipment is coupled with the frame structure configured at the pre-configured electric potential.

13. The converter-hydrogen system of claim 1, wherein the auxiliary equipment comprises common auxiliary equipment shared by two or more electrolyzer stacks or fuel cell stacks and dedicated auxiliary equipment for each of the two or more electrolyzer stacks or fuel cell stacks, wherein the dedicated auxiliary equipment is coupled to the frame structure of the electrolyzer stack or fuel cell stack; and the common auxiliary equipment is fluidly coupled to the dedicated auxiliary equipment for each of the two or more electrolyzer stacks or fuel cell stacks through a pipe of the converter-hydrogen system, wherein the pipe is electrically isolated from the common auxiliary equipment.

14. The converter-hydrogen system of claim 1, wherein the converter unit is a chain-link converter unit coupled to a medium- or high-voltage power network and comprises at least one converter arm comprising series-connected converter cells, and a converter cell is electrically coupled to one or more electrolyzer stacks or fuel cell stacks.

15. The converter-hydrogen system of claim 14, wherein the converter cell, as well as said one or more electrolyzer stacks or fuel cell stacks, along with their auxiliary equipment to support the operation of said one or more electrolyzer stacks or fuel cell stacks, is integrated into a module, and the integrated module has fluid connections for transporting electrolyte and/or water and gas.

16. The converter-hydrogen system of claim 15, wherein the integrated module is arranged on a frame structure to which said one or more electrolyzer stacks or fuel cell stacks are coupled.

17. The converter-hydrogen system of claim 1, wherein the converter-hydrogen system comprises an auxiliary converter or an isolation transformer for providing an isolated low-voltage power supply to electrical elements of the auxiliary equipment.

18. The converter-hydrogen system of claim 1, wherein the converter unit is a double-Y connection converter unit having an AC side and a DC side, the AC side is coupled to a medium- or high-voltage power network, the double-Y connection converter unit comprising a plurality of parallel arms coupled between the AC side and the DC side, and each arm comprises the plurality of converter cells connected in series; and wherein the plurality of electrolyzer stacks and/or fuel cell stacks are coupled to the DC side.

19. The converter-hydrogen system of claim 1, wherein two or more of the plurality of electrolyzer stacks are vertically arranged in a group, and the electrolyzer stack with the electrode terminal having the closest potential to the ground potential in the group is arranged at the bottom.

20. The converter-hydrogen system of claim 1, wherein insulation is provided between adjacent electrolyzer stacks in the group, and frame structures coupled to respective electrolyzer stacks are configured to be at different electric potential, or adjacent electrolyzer stacks in the group are vertically stacked without insulation between the adjacent electrolyzer stacks, and frame structures coupled to respective electrolyzer stacks are configured to be at the same electric potential.