Power supply system for electrolyzer plant and control method thereof

Abstract

A power supply system (100) for an electrolyzer plant is provided. The system (100) comprises at least one AC / AC converter (111) having a first AC side (111A) coupled to a power network (200) and a second AC side (111B) coupled to a first group of electrolyzers (311_A, 311_B) of the electrolyzer plant through a first group of AC / DC converters (113_1A, 113_1B); and a control system (160) configured to control the at least one AC / AC converter (111) to provide at le st one of a grid service to the power network (200) and control of the power supplied to the first group of electrolyzers. The at least one AC / AC converter (111) is configured to operate with a fraction of the total power being transferred from the power network to the first group of electrolyzers.

Description

P2025,0064 WO E / P240135W001 January 27, 2025- 1 - POWER SUPPLY SYSTEM FOR ELECTROLYZER PLANT AND CONTROL METHOD THEREOFTECHNICAL FILED

[0001] The present disclosure generally relates to the field of electrical power conversion and, in particular, to a power supply system for an electrolyzer plant and a method for controlling the power supply system.BACKGROUND

[0002] Global warming drives the shift to sustainable energy, promoting green hydrogen produced through electrolysis using renewable energy. The hydrogen electrolyzers (H2E) decarbonize sectors like transportation, power generation, and steel / ammonia production, and can also enhance grid stability when dynamically controlled to manage grid requirements. Large-scale hydrogen production takes place in an electrolyzer plant with numerous H2E stacks, powered by AC / DC converters. An electrolyzer plant can be provisioned in units, each unit supplied by a power transformer, for example when connected to a high-voltage grid, the power transformer converts the high-voltage (HV) grid voltage to a medium-voltage (MV) level and further downstream the transformers to convert MV level voltages to a low-voltage (LV) level which can power the H2E stacks with respective AC / DC converters. The transformers powering the AC / DC converter can be referred to as rectifier transformers. The connected AC / DC converter may be operated in a multi-pulse configuration to power the electrolyzer and to an extent regulate the voltage applied to the electrolyzer. To improve the voltage regulation at the input of the AC / DC converters, the effect of voltage variations in the grid can be minimized by providing the transformers with onload tap changers but such provisions will increase the overall cost of the plant though better regulation is expected to increase the H2E lifespan. Thyristor rectifiers, commonly used as AC / DC converters, can control DC power but might cause reactive power consumption and increased current distortion at light loads, resulting in the heating of transformers and other power supply components and shortening theirP2025,0064 WO E / P240135W001 January 27, 2025- 2 -lifespan. To address such power quality issues, the electrolyzer plant employs additional power quality conditioning devices such as harmonic filters and STATCOM, which can lead to increased costs and footprint. Moreover, thyristor-based devices have limited fault tolerance and can't support the grid during contingencies. A flexible and reliable power supply solution is desired for powering the H2E wherein a power supply system can be connected to a grid at an MV or HV level and effectively controls hydrogen production and supports maintaining grid power quality.SUMMARY

[0003] It is therefore a goal of the present disclosure to provide a system and a method for an electrolyzer plant that can provide a controlled power conversion to provide a grid service and control of the power supplied to the electrolyzer plant.

[0004] According to an embodiment of the present disclosure, a power supply system for an electrolyzer plant is provided. The system includes at least one AC / AC converter, with a first AC side coupled to a power network and a second AC side coupled to a first group of electrolyzers of the electrolyzer plant through a first group of AC / DC converters. The system further includes a control system configured to control the at least one AC / AC converter to provide one or both of a grid service to the power network and control of the power supplied to the first group of electrolyzers. The at least one AC / AC converter is configured to operate with a fraction of the total power being transferred from the power network to the first group of electrolyzers.

[0005] According to another embodiment of the present disclosure, a method for controlling a power supply system integrated with an electrolyzer plant is provided. The system includes at least one AC / AC converter having a first AC side coupled to a power network and a second AC side coupled to a first group of electrolyzers of the electrolyzer plant through a first group of AC / DC converters, the at least one AC / AC converter being configured to operate with a fraction of the total power being transferred from the power network to the first group of electrolyzers. The method includes the step of controlling the at least one AC / AC converter (111) to provide atP2025,0064 WO E / P240135W001 January 27, 2025- 3 -least one of a grid service to the power network and control of the power supplied to the first group of electrolyzers.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The disclosed aspects will hereinafter be described in connection with the appended drawings that are provided to illustrate but not to limit the scope of the present disclosure.

[0007] Figure 1 is a block diagram of a power supply system according to an embodiment of the present disclosure.

[0008] Figures 2a and 2b illustrate exemplary implementations of the AC / DC converter of the power supply system shown in Figure 1.

[0009] Figures 3~5 show exemplary implementations of the power supply system shown in Figure 1.

[0010] Figures 6A-6D show exemplary implementations of the AC / AC converter shown in Figure 1.

[0011] Figures 7A-7B show exemplary implementations of an energy storage system included in the power supply system shown in Figure 1.

[0012] Figures 8 and 9 show exemplary implementations of the control system of the power supply system shown in Figure 1.

[0013] Figure 10 shows a scenario where the power supply system shown in Figure 1 is applicable.

[0014] Figure 11 is a flowchart of a method for controlling a power supply system integrated with an electrolyzer plant according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0015] A hydrogen electrolyzer is referred to as an electrolyzer or electrolyzer unit in some places below, and an electrolyzer plant refers to a plurality of electrolyzers thatP2025,0064 WO E / P240135W001 January 27, 2025- 4 -are provided for producing hydrogen and can also refer to a hydrogen plant that includes other units such as a water desalination units, hydrogen storage units, and also a power substation to power electrolyzers and other various units. Figure 1 shows a power supply system 100 (referred to as system 100 in some places below) that can be a part of a power substation to power several electrolyzers according to an embodiment of the present disclosure. The power supply system 100 is connected to a power network 200, which is at a voltage level higher than that needed for powering electrolyzers in an electrolyzer plant. As mentioned earlier, the electrolyzer plant in another embodiment can also include the power supply system 100 which includes an AC / AC converter 111 to help with regulating the voltage level for powering the electrolyzers and a control system 160 to control the AC / AC converter 111 to provide grid services to the power network 200 and / or to control the electrical power supplied to a group of hydrogen electrolyzers 311_A and 311_B.

[0016] The control system 160 can be implemented as including local controllers for providing control signals (e.g., gate signals) for operating the AC / AC converters and a supervisory controller that participates in coordinating with other local controllers operating the hydrogen plant or / and the power network. In an example, the local controllers are mainly responsible for operating the AC / AC converter 111 and can coordinate with the supervisory controller. The coordination can be for example receiving a setpoint to regulate the output voltage of the AC / AC converter 111 that gets provided to the downstream units and affects the power supplied to the electrolyzers, and thereby the hydrogen production. Coordination also includes the exchange of measured values or other operations, fault or asset-related information that can help efficiently operate the power supply system. In another embodiment, the control system 160 coordinates with a power network controller (for e.g. by receiving set points, or exchanging power supply system, power source or load-related information) and / or receives measured power network electrical parameters such as power network / grid voltage, electrical current being drawn from the power network, active power values, reactive power values, power frequency values, harmonics, etc. to operate the AC / AC converter 111. In some other embodiments, the control system 160 is included in theP2025,0064 WO E / P240135W001 January 27, 2025- 5 -hydrogen plant control system or in the power network control system (e.g. when the power network is a microgrid). These embodiments will be described in more detail later in this document.

[0017] The power network 200 is an AC power grid (for example MV grid) in an embodiment and in another embodiment is a microgrid with renewable energy sources. In yet another embodiment, the power network 200 is an AC power grid with an HV grid and coupled with an HV power transformer that steps down the voltage from an HV level to an MV level. In yet another embodiment, the power network 200 can include an AC power grid, DC power grid, and a microgrid connected with each other in various combinations and connect one or more power sources in the power network 200 for powering the electrolyzer plant. In some examples, the power network 200 integrates one or more renewable energy sources, such as photovoltaic cells and wind turbine generators to provide green power for the hydrogen electrolyzer plant. In other examples, one or more renewable power sources are part of the AC power grid. Power flow and power quality in the power network 200 are regulated with a power network controller (not shown in Figure 1), the power network controller can coordinate and optimize the electric energy from different sources to the loads (e.g. electrolyzers) connected to the power network 200.

[0018] According to embodiments of the present disclosure, an electrolyzer may include multiple electrolyzers connected in series, parallel, or a combination of series and parallel to form an electrolyzer unit. In this way, the electrolyzer has flexibility and diversity in configuration to be applicable in various scenarios.

[0019] Referring to Figure 1, the AC / AC converter 111 is provided as a fractional converter i.e. a converter that is rated to handle only a fraction of the power that is being supplied downstream to the electrolyzers (e.g., an electrolyzer group). To enable the working of the AC / AC converter, the AC / AC converter is connected in one of the two branches, namely branches 117 and 118, supplying power from the power network 200 to the electrolyzer group. The branch 117 carries the majority of the total power being supplied to the electrolyzer group and is therefore referred to as the main branch or first branch. The branch 118, in which power is controlled by the operation of the AC / ACP2025,0064 WO E / P240135W001 January 27, 2025- 6 -converter, carries only a fraction of the total power, so it is herein referred to as the secondary branch. The AC / AC converter 111, connected to the secondary branch 118 has a first AC side 111 A coupled to the power network 200 and a second AC side 11 IB coupled to downstream units through a transformer 114. The transformer 114 is connected in series in the main branch 117 and is therefore referred to as a series transformer. Specifically, a winding on one side of the transformer 114 is connected in series in the main branch 117, while one terminal of a winding on the other side of the transformer 114 is connected to the output at the second AC side 11 IB of the AC / AC converter 111. The AC / AC converter Ill is operated preferably at an MV voltage level as it is coupled with the power network 200 which may be at an MV voltage level or an HV voltage level in which case a power transformer is used to step down the voltage for connecting at the inputs of the AC / AC converter 111.

[0020] Continuing with Figure 1, for powering the group of electrolyzers 311_A and 311_B, downstream to the AC / AC converter 111, a transformer 112 and a group of AC / DC converters 113_1A and 113_1B for the electrolyzers 311_A and 311_B are provided. The transformer 112 is used to step down the voltage from the AC / AC converter 111, such as stepping down medium- voltage to low- voltage, and then transmits this reduced voltage to the plurality of AC / DC converters which are operating at the low voltage level corresponding to the voltage and power rating of the electrolyzers. Therefore, the transformer 112 can also be referred to as a downstream step-down transformer. Figure 1 illustrates an exemplary power system configuration where a fractional AC / AC converter is used upstream to connect with a power network that can be at an MV or an HV voltage level and downstream a further step-down transformer can be used along with an AC / DC converter to power an electrolyzer. The exemplary power system configuration in Figure 1 and other figures though illustrated with a certain number of electrolyzers and downstream transformer with a certain number of secondary winding, a person skilled in the art would recognize that the power system configuration will work well with a different number of electrolyzers, a different number of secondary windings of the downstream transformer or more number of downstream transformers connected to a bus (e.g. MV bus).P2025,0064 WO E / P240135W001 January 27, 2025- 7 -

[0021] The power supply system can further comprise circuit breakers, switchgears or disconnectors (115 and 116), also referred to as switches to electrically connect or disconnect supply of power to the electrolyzers. These switches 115 and 116 can also be operated to decouple the AC / AC converter 111 from the power network 200. Switches can be provided at multiple locations in the power supply system. For example, a switch 115 is provided on the bus between the power network 200 and the series transformer 114, and a switch 116 is provided on the bus between the series transformer 114 and the downstream step-down transformer 112. Setting these switches can improve the flexibility and reliability of the operation of the system 100. For example, during maintenance or troubleshooting, the faulty part can be isolated by operating the corresponding switches to ensure the normal operation of other parts.

[0022] The control system 160 obtains power network-related parameters and electrolyzer-related parameters and determines control signals (gate signals) for controlling the AC / AC converter 111 based on the obtained parameters, thereby providing a grid service and / or controlling the power provided to the group of electrolyzers.

[0023] The parameters measured at the first AC side 111 A of the AC / AC converter 111 and received by the control system 160 are referred to as power network-related parameters and relate to grid support. These parameters also include estimated values derived from the measured values. For example, some parameters that are not available via measurements can be obtained through an estimation process in the control system 160. Similarly, the parameters measured downstream of the AC / AC converter, for example at DC sides of the group of AC / DC converters and received by the control system 160 are referred to as electrolyzer-related parameters and relate to controlling the power supplied to the group of electrolyzers. These parameters also include estimated values derived from the measured values. For example, some parameters that are not available via measurements can be obtained through an estimation process in the converter controller 161. In an example, the control system 160 can receive one or more power network-related parameters and electrolyzer-related parameters from other controllers communicatively connected with the control system 160. The otherP2025,0064 WO E / P240135W001 January 27, 2025- 8 -controllers can be associated with the power network 200, renewable energy sources, electrolyzers, or / and with loads and other resources (energy storage systems) connected to the system 100. In another example, one or more power network-related parameters or electrolyzer-related parameters can be obtained from user inputs or through a presetting in the control system 160.

[0024] Referring to Figure 2a, in one embodiment, each AC / DC converter is implemented as a diode rectifier. In the power supply system 100, although the diode rectifier itself does not have controllability and therefore cannot directly adjust the output DC voltage to the connected electrolyzer, the voltage delivered to the group of electrolyzers in such a configuration is controlled by controlling the output voltage of the AC / AC converter 111. The output voltage of the AC / AC converter 111 arranged on the secondary branch 118 is controlled by the voltage injected by a back-end series converter of the AC / AC converter 111, which will be described in the following.

[0025] Referring to Figure 2b, in another embodiment, each AC / DC converter is implemented as a thyristor rectifier. The output voltage of the thyristor rectifier can be adjusted by the control system 160, thus enabling individual control of the power supply voltage to each electrolyzer. For example, when an electrolyzer in the group of electrolyzes have different degrees of aging, by controlling the firing angle of the corresponding thyristor rectifier, individual electrolyzers can be operated according to the degree of aging or other such dynamic parameters that may affect performance of the electrolyzers and required power compensation to achieve desired level of efficiency, longer life or balance in the overall operation of the electrolyzers. In an example, the thyristor rectifier can operate as a diode rectifier most of the time, and the firing angle control of the thyristor rectifier is only used when it is necessary to independently control each electrolyzer in the group.

[0026] Figure 3 shows an embodiment of the system 100 of Figure 1. As shown in Figure 3, the AC / AC converter 111 is coupled to an electrolyzer group with a greater number of electrolyzers through a plurality of downstream step-down transformers 112_1 to 112_n that are connected to an AC bus. Specifically, the second AC side 11 IB of the AC / AC converter 111 is connected to the AC bus and thereby to the primaryP2025,0064 WO E / P240135W001 January 27, 2025- 9 -windings of these downstream step-down transformers. Each of the multiple secondary windings of a downstream step-down transformer is connected to an AC / DC converter, which is then connected to an electrolyzer at its DC side. For example, one secondary winding of the downstream step-down transformer 112_1 is connected to the AC / DC converter 113_1A, which is connected to the electrolyzer cell 311_A; the other secondary winding of downstream step-down transformer 112_1 is connected to the AC / DC converter 113_1B, which is connected to the electrolyzer 311_B; and so on, until the downstream step-down transformer 112_n, where one secondary winding is connected to the AC / DC converter 113_nA, which is connected to the electrolyzer 31n_A; and the other secondary winding is connected to the AC / DC converter 113_nB, which is connected to the electrolyzer 31n_B.

[0027] According to embodiments of the present disclosure, the system 100 can be expanded by coupling more AC / AC converters and related components, which have different sizes and layouts and are adaptable to electrolyzer plants. The following describes some embodiments of the system 100.

[0028] Figure 4 shows an embodiment of the system 100. In this embodiment, the system 100 includes a first conversion unit, a second conversion unit, and a transformer 130. The first conversion unit and the second conversion unit transfer power from the power network 200 to a first group of electrolyzers (311_A, 311_B, ... 3 ln_A, 3 ln_B) and a second group of electrolyzers (321_A, 321_B, ... 32n_A, 32n_B), respectively, through the transformer 130 that is shown to have multiple secondary windings, where each secondary winding can power a group of electrolyzers.

[0029] The first conversion unit includes a first AC / AC converter 111 and its associated components. As shown in Figure 4, the first conversion unit includes the first AC / AC converter 111, a plurality of first downstream step-down transformers (112_1 to 112_n), a first group of AC / DC converters (113_1A, 113_1B, ...113_nA, 113_nB), a first series transformer 114, and switches 115 and 116.

[0030] Similarly, as shown in Figure 4, the second conversion unit includes the second AC / AC converter 121, a plurality of second downstream step-down transformers (122_1 to 122_n), a second group of AC / DC converters (123_1A,P2025,0064 WO E / P240135W001 January 27, 2025- 10 - 123_1B, •••123_nA, 123_nB), a second series transformer 124, and switches 125 and 126.

[0031] The primary winding of the transformer 130 is coupled to the power network 200, and the two secondary windings are respectively coupled to the first AC / AC converter 111 and the second AC / AC converter 121. The transformer 130 is used to step down the voltage (e.g., high voltage) from the power network 200, and transfer the reduced voltage to the first AC / AC converter 111 and the second AC / AC converter 121. Therefore, the transformer 130 can be referred to as an upstream step-down transformer.

[0032] In addition, as shown in Figure 4, the system 100 may also include a switch 140 connected before connecting the upstream step-down transformer to the power network 200. The switch 140 can be operated together with the switches 115 and 116 and the switches 125 and 126, further improving the flexibility and reliability of the system 100 by isolating the power supply system or other major units of the electrolyzer plant upon detection of a fault in the plant or during the energization of the plant.

[0033] Figure 5 shows another embodiment of the system 100. In this embodiment, the system 100 is further expanded by including two or more sub- stations, for example, sub-stations 101, ... lOn as shown in Figure 4. Each sub-station can be implemented as including two or more AC / AC converters coupled with a plurality of electrolyzer groups. In this case, more electrolyzers can be powered by the further expanded system. Such configurations are useful to effectively power a large-scale electrolyzer plant.

[0034] According to examples of the present disclosure, in one scenario, the system 100 may include high-voltage circuits, medium-voltage circuits, and low-voltage circuits. Specifically, the upstream step-down transformer reduces high voltage to medium voltage, and the downstream step-down transformer reduces medium voltage to low voltage. In another scenario, the system 100 may include multiple mediumvoltage circuits with decreasing voltage ranges in sequence, such as a first voltage circuit, a second voltage circuit, and a third voltage circuit. Specifically, the upstream step-down transformer steps down the voltage from the first voltage to the second voltage, and the downstream step-down transformer steps down the voltage from the second voltage to the third voltage.P2025,0064 WO E / P240135W001 January 27, 2025- 11 -

[0035] According to examples of the present disclosure, since the power supply voltage of a group of electrolyzers can be adjusted overall by controlling a corresponding AC / AC converter, there is no need to provide on-load tap-changers on the upstream and downstream step-down transformers. In this way, the system 100 can reduce a number of tap-changers, thereby effectively reducing costs.

[0036] According to examples of the present disclosure, an AC / AC converter can have multiple implementations, such as a 2-level converter, a 3-level converter, or a 5-level converter. For example, it can be implemented as a 2-level voltage source converter (VSC) connected in a back-to-back (B2B) configuration; two 3-level neutral point clamped (NPC) converters connected in a B2B configuration; a matrix converter; or modular multilevel converters (MMC) connected in a B2B configuration.

[0037] Next, referring to Figures 6A-6D, examples of AC / AC converters are described, with the AC / AC converter 111 as an example.

[0038] Referring to Figure 6A, in an example, the AC / AC converter 111 includes a front-end AC-DC converter 1110 and a back-end DC-AC converter 1112, which is connected to the front-end AC-DC converter 1110 through a DC link 1114. The converter controller 161 controls the front-end AC-DC converter 1110 in a current mode to provide current-related compensation and thus provides a grid service to the power network 200. The grid service includes one or more of the following: active power compensation; reactive power compensation; grid frequency control; grid voltage regulation; providing inertia to the grid; active harmonic filtering; and power factor correction. The converter controller 161 controls the back-end DC-AC converter 1112 in a voltage mode to adjust the voltage provided to the connected electrolyzer group.

[0039] Figure 6B shows an embodiment of the AC / AC converter 111. In this embodiment, the AC / AC converter 111 is implemented as an MMC converter connected in a B2B configuration, that is, it includes two MMC units arranged face-to-face, with the DC side connected through a DC link and one AC side connected to the power network 200 while the other AC side is connected to a group of AC-DC converters. As shown in Figure 6B, the AC / AC converter 111 includes a front-end shuntP2025,0064 WO E / P240135W001 January 27, 2025- 12 -converter 1110, a back-end series converter 1112, and a storage device 1116 connected to the DC side of the AC / AC converter 111. The storage device 1116 includes one or more capacitors. Both the front-end and back-end converters 1110 and 1112 are identical in terms of topology (i.e. YY MMC configuration). Each converter includes three upper arms and lower arms connected in Y configuration. The upper and lower arms are connected together through reactors 1117. The Y points of upper and lower arms are used to obtain the DC bus and the connection points between the upper and lower arms are used to connect to the ac side which is coupled with the power network 200. Each arm 1111 includes a plurality of converter cells. Each converter cell 1115 can be implemented as a half-bridge circuit (see 1115A) or a full-bridge circuit (see 1115B).

[0040] Figure 6C shows another embodiment of the AC / AC converter 111. In this embodiment, the AC / AC converter 111 is implemented as a two-level converter connected in B2B configuration. The front-end converter 1110 and back-end converter 1112 are identical in terms of topology and are connected by a common DC link. The front-end shunt converter 1110 can provide grid support functionalities as described above and the back-end series converter 1112 can regulate the voltage provided to a plurality of electrolyzers by controlling the voltage injection. Since the fractional power AC / AC converter is connected to the MV bus, and is a MV converter, the switch for each half-bridge circuit comprises several series connected switches 1113 and 1114 in the front-end and back-end converters 1110 and 1112.

[0041] Figure 6D shows yet another embodiment of the AC / AC converter 111. In this embodiment, the AC / AC converter 111 is implemented as two 3L-NPC converters connected in B2B configuration. The front-end shunt converter 1110 and the back-end series converter 1112 are intended for the same application as discussed earlier.

[0042] According to examples of the present disclosure, the front-end shunt AC-DC converter can provide current-related compensation and act as an active power filter. For example, it provides active harmonic filtering to cancel the low-order current harmonics caused by the downstream rectification process and offers reactive power compensation to meet the unity power factor requirement at the PCC point. Since low-P2025,0064 WO E / P240135W001 January 27, 2025- 13 -order harmonics can be canceled out by the downstream step-down transformer connected in a multi-pulse configuration, the filtering burden of the front-end shunt converter can be greatly reduced. This helps reduce the power rating requirements of the front-end shunt converter. Since the harmonic filtering and reactive power compensation are provided by the front-end shunt converter, harmonic trap filters and high-power centralized STATCOM converters are not required, which would require a large amount of space in the electrolyzer plant. In addition, the front-end shunt converter can provide dynamic active harmonic compensation in the case of asymmetric faults, which are difficult to achieve with commonly used passive harmonic trap filters.

[0043] According to examples of the present disclosure, the back-end series converter can provide voltage-related compensation to regulate the voltage fed to the downstream step-down transformer. By controlling the output voltage of the back-end series converter, the power supply voltage to an electrolyzer group can be regulated. Since the back-end series converter can regulate the voltage, the upstream or downstream step-down transformers do not require tap switches, thus helping reduce the overall cost of the system.

[0044] According to examples of the present disclosure, the rated power of the AC / AC converter is only a fraction of the total power of the electrolyzer group connected to it. For example, referring to Figure 4, the rated power of the AC / AC converters 111 is a fraction of the total power transferred to the first group of electrolyzers coupled to it. The rated power of the AC / AC converter 121 is a fraction of the total power transferred to the second group of electrolyzers coupled to it. The rated values of the front-end shunt converter can be determined by the active harmonic filtering requirements and the provision of reactive power to meet the unity power factor at the PCC. The rated values of the back-end series converter can be determined by the DC voltage regulation range of the connected electrolyzer group, for example, in direct proportion to the required voltage of the electrolyzer group.

[0045] According to examples of the present disclosure, since the rated power of the AC / AC converter is only a fraction of the total power of the connected group ofP2025,0064 WO E / P240135W001 January 27, 2025- 14 -electrolyzers, it has a much smaller size than that of a full-power converter, allowing for an integrated arrangement to implement the AC / AC converter. For example, an AC / AC converter that includes a front-end shunt converter, a back-end series converter, and an associated converter controller is arranged in the same housing to form a single device. Compared with the commonly used STATCOM solutions for full-power and high-power converters, this helps reduce the footprint, lower engineering and construction costs, and simplify installation and debugging.

[0046] In addition, the rated power of an AC / AC converter can be further reduced by decreasing the total power of the group of electrolyzers connected to it. For example, this can be achieved by reducing the number of electrolyzers in the group or by decreasing the size of each electrolyzer, which allows for a reduction in the rated power and dimensions of the AC / AC converter.

[0047] Figure 7 A shows an embodiment where the system 100 includes an energy storage system, which includes one or more energy storage groups connected to the bus 153, such as a first energy storage group 151 and a second energy storage group 152. Each energy storage group may consist of a series of energy storage units connected in series, in parallel, or as a combination of both. The specific combination and size of each energy storage group can be determined according to energy and power requirements.

[0048] In an embodiment, each energy storage group may be implemented as an energy storage string and include a switch for connecting to or disconnecting from the system 100. Additionally, each energy storage group may also include a converter to regulate the string current and match the voltages between adjacent strings.

[0049] In an embodiment, the first energy storage group 151 is coupled to the frontend shunt converter of an AC / AC converter, and the second energy storage group 152 is coupled to the back-end series converter of the AC / AC converter. The two energy storage groups may be implemented with the same type of energy storage units or different types of energy storage units. For example, both strings can be implemented with energy storage units based on supercapacitors or lithium-ion batteries, or one can be implemented with supercapacitors and the other with lithium-ion batteries.P2025,0064 WO E / P240135W001 January 27, 2025- 15 -

[0050] Different types of energy storage units have their own advantages. For example, energy storage units based on supercapacitors are suitable for fast grid services that require high power injection or absorption, such as fast frequency response (FFR). When a large amount of energy is required, battery -based energy storage units are suitable. In an embodiment, the first energy storage group 151 is coupled to the front-end shunt converter and includes energy storage units based on supercapacitors for providing auxiliary grid support services, and the second energy storage group 152 is coupled to the back-end series converter and includes energy storage units based on lithium-ion batteries to provide fault ride-through capability for the electrolyzers, allowing them to continue operating longer or safely shut down during grid failures.

[0051] Figure 7B shows another embodiment where the system 100 includes the energy storage system. As shown in Figure 7B, the system 100 also includes a switch 170 on the bus to decouple the front-end shunt converter from the back-end series converter. When the front-end shunt converter and the back-end series converter are decoupled, the first energy storage group 151 can feed its stored energy into the power network 200 through the front-end shunt converter, while the energy stored in the second energy storage group 152 can be transmitted to the corresponding electrolyzer group through the back-end converter.

[0052] According to an example of the present disclosure, in the case of a fault in the power network 200, such as a short-term power outage that prevents the system 100 from receiving electrical energy, the energy storage system helps to safely ride through the fault. For example, when a fault occurs in the power network 200, the electrolyzers at the end are safely isolated from the power network 200 by operating corresponding switches, and the electrical energy in the second energy storage group 152 is transmitted to the electrolyzers through the back-end series converter to safely shut down these electrolyzers.

[0053] In an example where renewable energy sources are coupled in the power network 200, during the low power output period of the renewable energy sources, the energy stored in the energy storage system 150 can be used to supplement the power output. In addition, the front-end shunt converter and the associated energy storageP2025,0064 WO E / P240135W001 January 27, 2025- 16 -group can also provide grid-forming capabilities to enhance the stability of the grid, which can be achieved by configuring the rated power and voltage of the front-end shunt converter and the associated energy storage group. Furthermore, in view of the instability problems that renewable energy may bring to the power grid, integrating energy storage groups with AC / AC converters offers advantages such as providing virtual inertia, fast frequency response, power oscillation damping, and improving system reliability.

[0054] Next, some examples of the control system 160 are introduced.

[0055] In an example, the control system 160 includes converter controllers associated with AC / AC converters. Referring to Figure 8, for example, the control system 160 includes a converter controller 161 associated with the first AC / AC converter 111 and a converter controller 162 associated with the second AC / AC converter 121.

[0056] In another example, the control system 160 includes converter controllers associated with AC / AC converters and a supervisory controller in communication with these converter controllers. Referring to Figure 9, for example, the control system 160 includes a converter controller 161 associated with the first AC / AC converter 111, a converter controller 162 associated with the second AC / AC converter 121, and a supervisory controller 163 that is communicatively connected to the converter controllers 161 and 162, respectively.

[0057] According to examples of the present disclosure, the control system 160 may receive information from other controllers. For example, the control system 160 communicates with electrolyzer controllers (not shown) to obtain electrolyzer-related parameters, such as those indicative of the aging state of each electrolyzer. The control system 160 communicates with a power network controller (not shown) to obtain power network-related parameters, such as the amount of green energy available from the power network 200.

[0058] According to examples of the present disclosure, the coordinated control of the system 100 can be achieved either through communication between the individual converter controllers or through communication between the supervisory controller andP2025,0064 WO E / P240135W001 January 27, 2025- 17 -the individual converter controllers.

[0059] Figure 10 shows an example of the power network 200 as a microgrid. In a microgrid, two or more power supply systems can be coupled in a geographically distributed manner, and each power supply system 100 may be implemented in a configuration as described earlier and provides power to an electrolyzer plant. The microgrid can also be coupled with multiple energy sources, such as renewable energy sources 400 (e.g., solar energy, wind energy) and battery energy storage systems or fuel cell generators 500. In this example, the control system 160 of the power supply system 100 can be implemented as a part of the power network controller 202 and may control power utilization by each power supply system 100 based on various aspects such as available power from the renewable power sources, location of the renewable power sources and energy storage systems, capacity of the power distribution lines at various locations etc., thereby operating the microgrid along with the connected renewable power sources, energy storage systems and the loads including the electrolyzers in a flexible and optimal manner.

[0060] Next, methods for controlling a power supply system integrated with a hydrogen electrolyzer plant according to examples of the present disclosure are described. These methods can be carried out by the control system 160 controlling the power supply system 100.

[0061] Figure 11 is a flowchart of a control method 600 according to an embodiment of the present disclosure. The control method 600 will be described using an example where the control system 160 controls the power system 100.

[0062] At block 602, the supervisory controller 163 obtains information on the available power from the power network 200. For example, the supervisory controller 163 receives the amounts of total available power and green power from a controller associated with the power network 200, such as a power network controller.

[0063] At block 604, the supervisory controller 163 determines whether the total available power is sufficient to meet the power requirements for both the target hydrogen production rate and the provision of grid services.

[0064] In a case where there are strict requirements on carbon footprint and theP2025,0064 WO E / P240135W001 January 27, 2025- 18 -production of green hydrogen is required, the supervisory controller 163 also determines whether the available green power is sufficient to meet the power requirement for the target hydrogen production rate.

[0065] If the determination result in block 604 is negative, meaning the total available power is not sufficient to meet both the power requirements for the target hydrogen production rate and providing the grid services, the method 600 proceeds to block 606. In an example, a negative determination also includes cases where the available green power is insufficient to meet the power requirement for the target hydrogen production rate.

[0066] At block 606, the supervisory controller 163 determines whether the total available power is sufficient to provide the grid services.

[0067] If the determination result in block 606 is negative, meaning the available power is not sufficient to meet the power required for the grid services, the method 600 returns to block 602.

[0068] If the determination result in block 606 is affirmative, meaning the available power is sufficient for providing the grid services, the method 600 proceeds to block 608.

[0069] At block 608, the supervisory controller 163 determines the active power setpoint and reactive power setpoint for providing grid services and sends these setpoints to the corresponding converter controllers. For example, the supervisory controller 163 splits the determined active power setpoint into two components (first and second active power setpoints) and splits the determined reactive power setpoint into two components (first and second reactive power setpoints) either equally or in a weighted manner. The supervisory controller 163 then sends the first active and reactive power setpoints to the first converter controller 161 and the second active and reactive power setpoints to the second converter controller 162.

[0070] According to an example of the present disclosure, the supervisory controller 163 can obtain the power network-related parameters; determine a frequency droop control parameter and an inertia control parameter based on the power network-related parameters to determine the active power setpoint based on the frequency droopP2025,0064 WO E / P240135W001 January 27, 2025- 19 -control parameter and inertia control parameter; and determine a voltage droop control parameter based on the power network-related parameters to determine the reactive power setpoint based on the voltage droop control parameter.

[0071] At block 610, each AC / AC converter controller determines a gate signal based on the received active and reactive power setpoints to control the corresponding AC / AC converter. For example, the first converter controller 161 determines a gate signal based on the first active and reactive power setpoints and controls the AC / AC converter 111 using the determined gate signal.

[0072] If the determination result in block 604 is affirmative, meaning the total available power is sufficient to meet both the power requirements for the target hydrogen production rate and providing the grid services, the method 600 proceeds to block 612.

[0073] At block 612, the supervisory controller 163 determines active and reactive power setpoints for providing the grid services and producing hydrogen with the target hydrogen production rate and sends these determined setpoints to the corresponding AC / AC converters.

[0074] In an example, the supervisory controller 163 can obtain power network-related parameters and electrolyzer-related parameters; determine a frequency droop control parameter and an inertia control parameter based on the power network-related parameters; determine a reference power corresponding to the target hydrogen production rate based on the electrolyzer-related parameters; and determine the active power setpoint based on the frequency droop control parameter, the inertia control parameter, and the reference power. The supervisory controller 163 can determine a voltage droop control parameter based on the power network-related parameters to determine the reactive power setpoint. Next, the supervisory controller 163 can divide the determined active and reactive power setpoints into first and second active power setpoints and first and second reactive power setpoints according to the overall aging condition of each electrolyzer group, and then send the first active and reactive power setpoints to the first converter controller 161 and the second active and reactive power setpoints to the second converter controller 162. The overall aging condition of anP2025,0064 WO E / P240135W001 January 27, 2025- 20 -electrolyzer group can be calculated based on the total current of the electrolyzers in the group, which is measured on the bus (as a decrease in efficiency correlates with increased current draw due to aging). The overall aging condition of an electrolyzer group can also be determined by assessing the individual aging degrees of each electrolyzer in the group (e.g., by calculating the average aging degree of the electrolyzers).

[0075] At block 614, each AC / AC converter controller determines a gate signal based on the received active and reactive power setpoints to control the corresponding AC / AC converter. For example, the first converter controller 161 determines a gate signal based on the first active and reactive power setpoints and controls the AC / AC converter 111 using the determined gate signal.

[0076] At block 616, the supervisory controller 163 determines whether the total hydrogen rate of the whole electrolyzer plant has reached the target hydrogen production rate. In one embodiment, the current on the bus connected to each electrolyzer group is measured to obtain the hydrogen production rate of that group, and the sum of the hydrogen production rate from each group is calculated to determine the total hydrogen rate. In another embodiment, the current of each electrolyzer is measured to obtain its hydrogen production rate, and the sum of the hydrogen production rate from each electrolyzer is calculated to determine the total hydrogen produced rate.

[0077] If the determination result in block 616 is affirmative, the method 600 proceeds to block 618.

[0078] At block 618, the first and second converter controllers maintain the current setpoints for controlling the first and second AC / AC converters.

[0079] If the determination result of block 616 is negative, the method 600 proceeds to block 620.

[0080] At block 620, the supervisory controller 163 adjusts the active power setpoint to obtain a new active power setpoint and divides the new active power setpoint into new first and second active power setpoints according to the overall aging condition of each electrolyzer group, and then sends the new first active power setpointP2025,0064 WO E / P240135W001 January 27, 2025- 21 -to the first converter controller 161 and the new second active power setpoint to the second converter controller 162.

[0081] At block 622, each AC / AC converter controller determines a new gate signal based on the new active power setpoint to control the corresponding AC / AC converter. Then, the method 600 returns to block 616 to determine whether the total hydrogen production rate of the entire electrolyzer plant has reached the target hydrogen production rate. If it has, the method 600 proceeds to block 618. If not, blocks 620 and 622 are performed again.

[0082] Although the control system embodiment shown in Figure 9 is used to introduce the method 600, the method 600 can also be implemented using the control system embodiment shown in Figure 8. For example, each AC / AC converter controller obtains power network-related parameters and electrolyzer-related parameters and communicates with the others to collaboratively determine and divide the aforementioned setpoints.

[0083] According to examples of the present disclosure, the control method 600 can further include a process of controlling AC / AC converters and corresponding switches to cope with power network failures. For example, the supervisory controller 163 receives a signal indicating a grid fault and controls the corresponding switches to decouple the front-end converter and the back-end converter of at least one AC / AC converter. Next, the supervisory controller 163 controls a corresponding switch to allow energy in the first energy storage group 151 to be transferred to the power network 200 through the front-end converter and controls a corresponding switch to allow energy in the second energy storage group 152 to be transferred to the electrolyzer group coupled to the at least one AC / AC converter through the back-end converter. Then, the supervisory controller 163 determines whether the grid fault has been resolved within a predetermined period of time. If so, the coupling of the front-end and back-end converters is restored. If not, energy in the second storage group 152 is used to safely shut down the electrolyzer group. In addition, the supervisory controller 163 can record and report the fault to an upper-level controller.

[0084] Although the above description has introduced that the control process forP2025,0064 WO E / P240135W001 January 27, 2025- 22 -riding through grid faults is implemented by the supervisory controller, this control process can also be implemented by the converter controller associated with one or more AC / AC converters.

[0085] According to examples of the present disclosure, the control method 600 can further include a control process for detecting an asymmetric fault and controlling the corresponding AC / AC converter to address such a fault. When a fault occurs in one electrolyzer of an electrolyzer group or in one AC / DC converter of an AC / DC converter group, low-order current harmonics (e.g., harmonic components below a predetermined harmonic order) will be generated on the primary side of the corresponding downstream step-down transformer. The predetermined harmonic order can be obtained based on the specific layout of the system 100. Therefore, once the converter controller detects harmonic components below the predetermined order based on the measurement of the bus current, it can determine that an asymmetric fault has occurred. In this case, the converter controller will calculate a reference current for filtering the current harmonics, effectively preventing them from being injected into the power network.

[0086] 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

P2025,0064 WO E / P240135W001 January 27, 2025- 23 - WHAT IS CLAIMED IS:

1. A power supply system (100) for an electrolyzer plant, comprising:at least one AC / AC converter (111) having a first AC side (111 A) coupled to a power network (200) and a second AC side (11 IB) coupled to a first group of electrolyzers (311_A, 311_B) of the electrolyzer plant through a first group of AC / DC converters (113_1A, 113_1B); anda control system (160) configured to control the at least one AC / AC converter (111) to provide at least one of a grid service to the power network (200) and control of the power supplied to the first group of electrolyzers;wherein the at least one AC / AC converter (111) is configured to operate with a fraction of the total power being transferred from the power network to the first group of electrolyzers.

2. The power supply system (100) of claim 1, wherein the total power is carried out through a main branch (117) and a secondary branch (118), andwherein the at least one AC / AC converter (111) is connected in the secondary branch (118) and coupled with the main branch (117), andthe second AC side (11 IB) of the at least one AC / AC converter (111) is connected to a series transformer (114) such that the secondary branch (118) carries a fraction of the total power.

3. The power supply system (100) of claim 1, wherein the at least one AC / AC converter (111) is coupled to the first group of electrolyzers through the first group of AC / DC converters and at least one downstream step-down transformer (112), and wherein the second AC side (11 IB) of the at least one AC / AC converter (111) is connected at a medium voltage level and the at least one downstream step-downP2025,0064 WO E / P240135W001 January 27, 2025- 24 -transformer (114) converts the medium voltage level to a low voltage level for powering the first plurality of electrolyzers.

4. The power supply system (100) of claim 1, wherein the control system (160) is configured to control at least one electrical parameter with a converter controller of the at least one AC / AC converter to provide the grid service to the power network (200), and the at least one electrical parameter is associated with at least one of active power, reactive power, power frequency, electrical voltage, active harmonics filtering, power factor correction and emulated inertia.

5. The power supply system (100) of claim 1, wherein the control system (160) is configured to control the at least one AC / AC converter (111) to regulate the voltage at the second AC side (11 IB) and provide the regulated voltage to the first group of AC / DC converters.

6. The power supply system (100) of claim 5, wherein each AC / DC converter in the first group of AC / DC converters is connected to at least one electrolyzer from the first group of electrolyzers, andthe control system (160) is configured to control each AC / DC converter with a set point to provide a controlled DC voltage to the connected electrolyzer to control hydrogen production of the connected electrolyzer.

7. The power supply system (100) of claim 1, wherein the at least one AC / AC converter (111) is a 2-level voltage source converter (VSC) connected in a back-to-back (B2B) configuration; two 3 -level neutral point clamped (NPC) converters connected in a B2B configuration; a matrix converter; or modular multilevel converters (MMC) connected in a B2B configuration.P2025,0064 WO E / P240135W001 January 27, 2025- 25 - 8. The power supply system (100) of claim 1, wherein the at least one AC / AC converter (111) is a modular multilevel converter (MMC) and comprises a front-end shunt converter (1110) at the first AC side (111 A) coupled to the power network (200) and a back-end series converter (1112) at the second AC side (11 IB) coupled to the first group of electrolyzers.

9. The power supply system (100) of claim 8, wherein the control system (160) is configured to control the front-end shunt converter (1110) in a current control mode to provide current-related compensation to the power network (200) for active harmonics filtering and reactive power compensation.

10. The power supply system (100) of claim 8, wherein the control system (160) is configured to:detect harmonics components in the current on the second AC side (11 IB) of the at least one AC / AC converter (111);determine that an asymmetrical fault has occurred in the first group of electrolyzers or the first group of AC / DC converters when a harmonic below a predetermined order is detected in the current on the second AC side (11 IB) of the at least one AC / AC converter (111); anddetermine a reference current to be injected into the power network (200) by the front-end shunt converter (1110) to filter out the current harmonics caused by the asymmetrical fault.

11. The power supply system (100) of claim 8, wherein the control system (160) is configured to control the back-end series converter (1112) in a voltage control mode to control the DC voltage supplied to the first group of electrolyzers by regulating the output voltage of the back-end series converter (1112).P2025,0064 WO E / P240135W001 January 27, 2025- 26 - 12. The power supply system (100) of claim 1, wherein the power supply system (100) comprises a first AC / AC converter (111) and a second AC / AC converter (121);the first AC / AC converter (111) has a first AC side coupled to the power network (200) and a second AC side coupled to the first group of electrolyzers through the first group of AC / DC converters; andthe second AC / AC converter (121) has a first AC side coupled to the power network (200) and a second AC side coupled to a second group of electrolyzers of the electrolyzer plant through a second group of AC / DC converters;wherein the first and second AC / AC converters are coupled to the power network through an upstream step-down transformer (130), and the upstream step-down transformer (130) comprises secondary windings for transferring power to the first and second groups of electrolyzers controlled by the first and second AC / AC converters, andwherein the control system (160) controls converter controllers associated with the first and second AC / AC converters to balance power loading in the secondary windings of the upstream step-down first transformer.

13. The power supply system (100) of claim 12, wherein the control system (160) comprises a first converter controller (161) associated with the first AC / AC converter (111), a second converter controller (162) associated with the second AC / AC converter (121), and a supervisory controlled 163) in communication with the first and second converter controllers, andwherein the supervisory controller (163) is configured to calculate setpoints for controlling the first and second AC / AC converters and transmit the setpoints to the first and second converter controllers.

14. The power supply system (100) of claim 13, wherein the supervisory controller (163) is configured to calculate the setpoints based on one or more ofP2025,0064 WO E / P240135W001 January 27, 2025- 27 - - currents and voltages measured at the first and second AC sides of the first AC / AC converter;- currents and voltages measured at the first and second AC sides of the second AC / AC converter;- state information on states of the first group of electrolyzers from the first converter controller;- state information on states of the second group of electrolyzers from the second converter controller;- voltage measured in the power network;- frequency measured in the power network; and- reference active power and reactive power from a power network controller.

15. The power supply system (100) of claim 1, the power supply system comprising an energy storage system,wherein the energy storage system comprises at least one of a first energy storage group (151) coupled at the first AC side of the at least one AC / AC converter to provide ancillary grid support services to the power network and a second energy storage group (152) coupled at the second AC side of the at least one AC / AC converter to provide fault ride through capability to the first group of electrolyzers.

16. The power supply system (100) of claim 15, wherein each of the first and second energy storage groups is connected with a controllable switch; andthe first energy storage group (151) comprises supercapacitor-based or batterybased energy storage units, and the second energy storage group (152) comprises supercapacitor-based or battery -based energy storage units.

17. The power supply system (100) of claim 16, wherein the control system (160) is configured to, in the case that there is a fault in the power network (200),P2025,0064 WO E / P240135W001 January 27, 2025- 28 -control the second energy storage group (152) to provide power to the first group of electrolyzers to safely shut them down.

18. A method for controlling a power supply system (100) integrated with an electrolyzer plant,the power supply system (100) comprising at least one AC / AC converter (111) having a first AC side (111 A) coupled to a power network (200) and a second AC side (11 IB) coupled to a first group of electrolyzers of the electrolyzer plant through a first group of AC / DC converters, the at least one AC / AC converter being configured to operate with a fraction of the total power being transferred from the power network (200) to the first group of electrolyzers.the method comprising controlling the at least one AC / AC converter (111) to provide at least one of a grid service to the power network and control of the power supplied to the first group of electrolyzers.

19. The method of claim 18, controlling the at least one AC / AC converter (111) to provide at least one of the grid service and control of the power supplied to the first group of electrolyzers comprises:determining whether the available power from the power network is sufficient to meet the power requirements for both the target hydrogen production rate and the provision of the grid service;if the determination result is affirmative, controlling the at least one AC / AC converter to provide both the grid service and control of the power supplied to the first group of electrolyzers;if the determination result is negative but the available power is sufficient to meet the power requirement for the provision of the grid service, controlling the at least one AC / AC converter to provide only the grid service.P2025,0064 WO E / P240135W001 January 27, 2025- 29 - 20. The method of claim 18, controlling the at least one AC / AC converter (111) to provide at least one of the grid service and control of the power supplied to the first group of electrolyzers comprises:determining whether green energy from the power network is sufficient for the first group of electrolyzers to produce a target volume of hydrogen;if the determination result is affirmative, determining a setpoint for controlling the at least one AC / AC converter to regulate the DC voltage transmitted to the first group of electrolyzers; andif the determination result is negative, determining a setpoint for controlling the at least one AC / AC converter to manage the current injected into the power network.

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