Converter system and control method thereof

Abstract

A converter system (100) for powering a plurality of hydrogen electrolyzers is provided. The plurality of hydrogen electrolyzers are electrically coupled together to form at least two electrolyzer strings (210, 220). The converter system (100) comprises: a main power supply unit (10) comprising a main converter that provides bulk power to the at least two electrolyzer strings (210, 220) such that a main current flows through each of the at least two electrolyzer strings; an auxiliary power supply unit (20) comprising at least one DC / DC converter, which is electrically coupled with one electrolyzer string from the at least two electrolyzer strings to inject or extract an adjustable current to or from the one electrolyzer string; and a control system (30) configured to control at least one of the main power supply unit (10) and the auxiliary power supply unit (20) for operating the converter system (100).

Description

CONVERTER SYSTEM AND CONTROL METHOD THEREOFTECHNICAL FILED

[0001] The present disclosure relates to a converter system for powering hydrogen electrolyzers and a method for controlling the converter system.BACKGROUND

[0002] The energy sector is currently undergoing a significant transformation with the emergence of hydrogen as a viable energy carrier and storage medium. Consequently, considerable research is being dedicated to exploring various aspects of hydrogen generation technologies, particularly focusing on different electrolyzer technologies. Typically, hydrogen electrolyzer units are arranged in various configurations to optimize their size and production efficiency. However, the potential for serial and parallel connections of electrolyzer units poses challenges regarding overall system protection and control. This is mainly due to their non-uniform physical behaviors and aging characteristics. As a result, different electrolyzer strings (branches) may draw varying DC currents from a common DC bus, which complicates control and protection design, especially considering the scalability and modularity of hydrogen generation plants.SUMMARY

[0003] It is therefore one objective of the present disclosure to provide a solution that enhances the efficiency, reliability, availability, and flexibility of operation for a hydrogen production system comprising at least two electrolyzer strings.

[0004] According to examples of one aspect of the present disclosure, a converter system for powering a plurality of hydrogen electrolyzers is provided. The plurality of hydrogen electrolyzers are electrically coupled together to form at least two electrolyzer strings. The converter system comprises: a main power supply unit comprising a main converter that provides bulk power to the at least two electrolyzer strings such that a main current flows through each of the at least two electrolyzer strings; an auxiliary power supply unit comprising at least one DC / DC converter, which is electrically coupled with one electrolyzer string from the at least two electrolyzer strings to inject or extract an adjustable current at a point of coupling; and a control system configured to control at least one of the main power supply unit and the auxiliary power supply unit for operating the converter system.

[0005] In an example, the at least one DC / DC converter is sized based on and operated with, a fraction of the total power transferred to said one electrolyzer string.

[0006] In an example, the auxiliary power supply unit comprises an energy source, and the at least one DC / DC converter is configured to exchange power with the energy source to adjust the currentflowing through said one electrolyzer string.

[0007] In an example, the energy source comprises or is integrated with one or more of the following: 1) an energy storage unit comprising one or more of a supercapacitor and a super battery; 2) a DC source with a dedicated DC / DC converter, wherein the DC source comprises one or more of: a separate DC power supply, a DC grid, and a fuel cell; 3) an AC source with a dedicated AC / DC converter; for example, the AC source is an AC grid or an AC feed.

[0008] In an example, the energy source comprises or is integrated with an additional electrolyzer string or an energy storage string. The at least one DC / DC converter is coupled with the additional electrolyzer string or the energy storage string.

[0009] In an example, the main power supply unit comprises a main converter coupled between a power network and the at least two electrolyzer strings.

[0010] In an example, the main converter includes one or more modular multilevel converters (MMCs).

[0011] In an example, the main power supply unit is coupled with an energy storage system (ESS) which is coupled with the main converter, and the ESS comprises one or more of a battery string, a capacitor string, a supercapacitor string, and a string of energy storage units associated with photovoltaic (PV) systems.

[0012] In an example, the control system is configured to: control the main converter to receive power from the ESS in the case of a fault in the power network; and / or control the main converter such that power is exchanged between the ESS and the power network to provide grid services that require active power exchange, without disrupting hydrogen production.

[0013] In an example, the main converter is coupled to a renewable source, which is coupled to the power network; and optionally, the renewable source comprises a wind farm.

[0014] In example, the main converter is coupled to a fuel cell, and the control system is configured to control the main converter so that fuel cell-generated power is either injected into the power network through the main converter to provide grid ancillary services or delivered to the at least two electrolyzer strings through the main converter to offer a fault ride -through function when the power network fails and cannot provide power.

[0015] In an example, the auxiliary power supply unit comprises: a first DC / DC converter coupled to a first electrolyzer string from the at least two electrolyzer strings; and a second DC / DC converter coupled to a second electrolyzer string from the at least two electrolyzer strings.

[0016] In an example, a first side of the first DC / DC converter and a first side of the second DC / DC converter are coupled to the first and second electrolyzer strings, respectively; and a second side of the first DC / DC converter and a second side of the second DC / DC converter are coupled to each other in parallel.

[0017] In an example, the first DC / DC converter is connected with an end electrolyzer or an intermediate electrolyzer of the first electrolyzer string and the second DC / DC converter is connected with an end electrolyzer or an intermediate electrolyzer of the second electrolyzer string.

[0018] In an example, the control system is configured to: control the second DC / DC converter to draw an adjustment current from the second electrolyzer string; and control the first DC / DC converter to inject the adjustment current into the first electrolyzer string.

[0019] In an example, the control system is configured to: control the first DC / DC converter to draw a first adjustment current from an energy source included in the auxiliary power supply unit and inject the first adjustment current into the first electrolyzer string; and control the second DC / DC converter to draw a second adjustment current from the energy source and inject the second adjustment current into the second electrolyzer string.

[0020] In an example, the control system is configured to: control the first DC / DC converter to draw a first adjustment current from the first electrolyzer string and inject the first adjustment current into an energy source included in the auxiliary power supply unit; and control the second DC / DC converter to draw a second adjustment current from the energy source and inject the second adjustment current into the second electrolyzer string.

[0021] In an example, the control system is configured to: control the first DC / DC converter to draw a first adjustment current from the first electrolyzer string and inject the first adjustment current into an energy source included in the auxiliary power supply unit; and control the second DC / DC converter to draw a second adjustment current from the second electrolyzer string and inject the second adjustment current into the energy source.

[0022] In an example, the control system is configured to: regulate each of first and second adjustment currents according to changes in the aging states of the first and second electrolyzer strings.

[0023] In an example, the auxiliary power supply unit comprises a plurality of sets of DC / DC converters, and each set of DC / DC converters comprises: a first DC / DC converter coupled to a first electrolyzer string from the at least two electrolyzer strings; and a second DC / DC converter coupled to a second electrolyzer string from the at least two electrolyzer strings.

[0024] In an example, the control system is configured to: control the plurality of sets of DC / DC converters such that the current flowing through one or more segments of each electrolyzer string is controlled.

[0025] According to examples of another aspect of the present disclosure, a control method for controlling a converter system as described above is provided. The control method comprises the step of controlling at least one of the main power supply unit and the auxiliary power supply unit for operating the converter system.

[0026] In an example, the step of controlling comprises: obtaining electrolyzer-related parametersincluding parameters that indicate the operating state of each electrolyzer in the at least two electrolyzer strings; determining the degree of aging of each electrolyzer string based on the electrolyzer-related parameters; and determining an adjustment strategy for adjusting the operation of each electrolyzer string or segment based on the determined aging degree of each electrolyzer string and a predetermined control objective.

[0027] In an example, the step of controlling comprises: coordinately controlling a converter controller associated with the main converter and a converter controller associated with the at least one DC / DC converter such that the operation of the at least two electrolyzer strings is controlled according to the predetermined control objective while providing a required grid service.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] Figure 1A is a block diagram of a converter system according to an embodiment of the present disclosure.

[0030] Figures IB and 1C illustrate embodiments of the converter system shown in Figure 1A.

[0031] Figures 2A and 2B illustrate exemplary implementations of the main power supply unit of the converter systems shown in Figure 1A.

[0032] Figure 3 illustrates an example of the converter system shown in Figure 1A.

[0033] Figure 4A is a block diagram of a converter system according to another embodiment of the present disclosure.

[0034] Figures 4B-4D illustrate embodiments of the regulation based on the converter system shown in Figure 4A.

[0035] Figures 5A and 5B illustrate exemplary implementations of the energy source of the converter system, as shown in Figure 4A.

[0036] Figures 6A, 6B, and 6C illustrate some other examples of the converter system according to the present disclosure.

[0037] Figure 7 illustrates an exemplary implementation of the control system of the converter system shown in Figure 1A.

[0038] Figure 8 is a flowchart of a method for controlling a converter system integrated with at least two electrolyzer strings according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0039] The inventor found that when using a converter such as MMC to power multiple electrolyzers in a hydrogen production plant, it is possible to connect the multiple electrolyzers in a single string on the DC side of the MMC converter. However, connecting multiple electrolyzer strings on the DC side can lead to various problems. For example, when two electrolyzer strings are connected in parallel on the DC side, if their performance is imbalanced (such as one electrolyzer string being new while the other has been in use for some time and shows signs of aging), the two electrolyzer strings will draw unequal currents from the converter (common DC bus wherein the strings are connected) according to physical characteristics of individual electrolyzers (such as their aging states) that are connected in the string. Further, electrolyzers may be connected in series and parallel in an electrolyzer string and electric current distributions in the string are based on the respective physical characteristics (e.g., internal resistance) of individual electrolyzers. Internal resistance of an electrolyzer changes with its aging, resulting in differences in the equivalent internal resistance between two electrolyzers in a string. For example, in a parallel configuration of two electrolyzers, the electric current distribution may not be uniform when there are changes in their respective internal resistance. The aged electrolyzer will have a higher resistance and increased losses compared to a new electrolyzer. In another case, when two electrolyzers are connected in parallel, internal resistance of an electrolyzer may exhibit negative temperature dependence and increase in temperature due to increased losses, or limited performance of a cooling system for the electrolyzers will decrease the internal resistance and cause increased electric current flow through the electrolyzers. This will result in increased losses which will subsequently decrease internal resistance, leading to a risk of triggering thermal runaway. Consequently, the stability and reliability of the entire system are facing greater challenges.

[0040] In response to these challenges, the present disclosure proposes a converter system and a corresponding control method that can intelligently adjust the current flowing through different electrolyzer strings, thereby achieving flexible control of the operation of the entire hydrogen production system and avoiding the need to increase cooling performance to mitigate thermal risks caused by imbalances in electric current distribution within the strings.

[0041] Examples of one aspect of the present disclosure relate to a converter system for powering a plurality of hydrogen electrolyzers that are stacked together to form at least two electrolyzer strings. The converter system includes a main power supply unit, an auxiliary power supply unit, and a control system. The main power supply unit includes a main converter that provides bulk power to the at least two electrolyzer strings such that a main current flows through each of the at least two electrolyzer strings. The auxiliary power supply unit includes at least one DC / DC converter, which is electrically coupled with one electrolyzer string from the at least two electrolyzer strings to inject or extract an adjustable current at a point of coupling. The control system controls at least one of the main power supply unit and the auxiliary power supply unit for operating the converter system.

[0042] The at least one DC / DC converter connected in an electrolyzer string is a partial powerconverter, i.e., the at least one converter operates with a much smaller power rating compared to the total power provided by the main power supply unit for the electrolyzer string to which it is coupled. For example, the rated power of the at least one DC / DC converter is a fraction of the total power that will be consumed by all the electrolyzers in the electrolyzer string to which it is coupled, or a fraction of the total plant power.

[0043] In an example, the size and rated power of the at least one DC / DC converter can be determined according to the upper limit value of a predetermined range of adjustable current that may be required for compensating in a segment of the electrolyzer string to have the electrolyzer units in the segment for efficiently perform.

[0044] Below, detailed examples of the converter system are described.

[0045] Figure 1A shows a converter system 100, according to an embodiment of the present disclosure, that is used to power an electrolyzer system (e.g., a hydrogen production plant) comprising multiple electrolyzer strings and can regulate the current flowing through each string. In Figure 1A and other figures, two electrolyzer strings, namely, a first electrolyzer cell string 210 and a second electrolyzer string 220, are shown by way of example.

[0046] With reference to Figure 1, the first electrolyzer string 210 and the second electrolyzer string 220 are coupled in parallel. The first electrolyzer string 210 includes a plurality of electrolyzer units 211 to 21n that are connected together. The second electrolyzer string 220 includes a plurality of electrolyzer units 221 to 22n that are connected together. In the example shown in Figure 1, the electrolyzer units (for simplicity also referred to as electrolyzers) in both the first and second electrolyzer strings are connected in series. However, in other examples of the present disclosure, each electrolyzer string may also include several electrolyzer units connected in parallel. Furthermore, each electrolyzer unit may include multiple electrolyzer cells connected in series, multiple electrolyzer cells connected in parallel, or a combination of both series and parallel configurations

[0047] Continuing to refer to Figure 1, the converter system 100 comprises a main power supply unit 10, an auxiliary power supply unit 20, and a control system 30.

[0048] The main power supply unit 10 outputs a main current I from its positive DC terminal 10 A. This main current I is split into a first main current II and a second main current 12, which are supplied to the first electrolyzer string 210 and the second electrolyzer string 220, respectively. When the aging or performance of the first electrolyzer string 210 and the second electrolyzer string 220 is the same (for example, if both are new electrolyzer strings and their equivalent resistances are equal), the first main current II and the second main current 12 will be equal. When the aging or performance of the first electrolyzer string 210 and the second electrolyzer string 220 differs (for example, as they operate, the aging of the two strings may diverge, or one of the two strings may be new while the other has been in use for some time, resulting in unequal equivalent resistances), the first main current II and the second main current 12 will be unequal.

[0049] The auxiliary power supply unit 20 can adjust the current flowing through each electrolyzer string. For example, the auxiliary power supply unit 20 can increase the current flowing through one string while reducing the current flowing through another string; increase the current flowing through all strings; or decrease the current flowing through each string.

[0050] The control system 30 controls one or both of the main power supply unit 10 and the auxiliary power supply unit 20 to control the operation of the converter system 100. For example, when there is a performance / aging imbalance between two electrolyzer strings, resulting in unequal hydrogen production rates for the two electrolyzer strings, the auxiliary power supply unit 20 can be controlled to equalize the hydrogen production rates of the two electrolyzer strings. For another example, by cooperatively controlling the main power supply unit 10 and the auxiliary power supply unit 20, it is possible to provide grid services while controlling the operation of each electrolyzer string. For yet another example, by controlling the main power supply unit 10 to transfer power to the electrolyzers from other sources such as an energy storage system (ESS) when there is a failure in the power network, it is possible to have fault ride-through capability for ensuring that these electrolyzers can be safely shut down or operated at minimum power consumption with continued power supply.

[0051] Below, embodiments of the main power supply unit 10 are described.

[0052] The main power supply unit 10 includes a main converter, which can also be referred to as a front-end converter. The main converter has a DC positive terminal 10A and a DC negative terminal 10B. The main current I is output from the DC positive terminal 10A and then is split and flows into each electrolyzer string. The current returning to the DC negative terminal 10B can be equal to the main current I or different from it.

[0053] In one embodiment, the main converter can be a main DC / DC converter coupled to a DC power network. In another embodiment, the main converter can be an AC -DC converter coupled to an AC power network. The main AC-DC converter can be implemented to include one or more modular multilevel converters (MMCs). Figure 2A shows an example where the main converter includes an MMC. The present disclosure does not limit the specific implementation of the MMC; therefore, the description of its topology is omitted.

[0054] According to some embodiments of the present disclosure, the main power supply unit 10 can be coupled with an energy storage system (ESS) or include the ESS. The ESS can have one or more strings of energy storage units coupled between the positive and negative DC terminals of the main converter. These energy storage units can include different types, such as DC capacitors, supercapacitors, batteries, as well as those associated with photovoltaic (PV) systems for storing energy generated. Figure 2B shows an example of coupling multiple strings of energy storage units between the positive and negative DC terminals of the MMC. In this example, the energy storage strings include supercapacitor strings 11 and 12, battery strings 13 and 14, and a PV string 15.

[0055] The ESS can be utilized to damp the oscillations or any potential AC components in theDC output of the main converter, such as the pole voltage, so that the pole voltage seen from the electrolyzer strings appears DC. The ESS can also be used to provide Fast Frequency Response (FFR), inertia support, and to enable GFM (Grid-Forming) behavior for the hydrogen production plant.

[0056] According to some embodiments of the present disclosure, the main power supply unit 10 may be coupled with a fuel cell, for example, a string of fuel cells connected between the positive and negative DC terminals of the main converter. Fuel cell -generated power can be injected into the power network through the main converter to provide grid ancillary services, such as active power compensation, reactive power compensation, frequency regulation, voltage support, black start capabilities, and load following. The power generated by the fuel cells can also be supplied to the electrolyzer strings through the main converter, which is particularly useful in the event that the power network fails and cannot provide power, thus offering a fault ride -through function.

[0057] According to some embodiments of the present disclosure, the main power supply unit 10 can also be coupled with renewable energy sources at its input or through the power network to which it is connected to produce green hydrogen. Renewable energy may include as an example one or more of wind power, solar power, and hydropower.

[0058] Figure 3 shows an example where the main power supply unit 10 is coupled to a wind farm (WF) to allow the electric energy generated by the wind farm to be used by the electrolyzer strings 210 and 220 for producing green hydrogen. The main power supply unit 10 is also coupled to the energy storage system (ESS) to obtain electric energy from the ESS when the output of the wind farm is unstable (for example, during seasons with weak winds for a time being). Additionally, the wind farm is coupled to the power grid so that when the electric energy generated exceeds the amount required for target hydrogen production during strong wind seasons, the excess electric energy can be transferred to the power grid.

[0059] In an example, if there is a fault in the grid, the hydrogen production will not be disrupted because the ESS can supply the electrolyzer strings during the fault till the fault is cleared, and the main converter can remain connected to the grid during the fault to provide reactive current to the grid.

[0060] In another example, power is provided to the ESS during the peak of renewables. The ESS can be used for ancillary services that require active power exchange with the grid, such as GFM, peakshaving, demand response, FFR, inertia support, and power oscillation damping. This can be achieved without disruption of hydrogen production with coordinated and optimized control in the hydrogen plant to provide grid service and for hydrogen production.

[0061] The configuration shown in Figure 3 offers many advantages. For example, the efficiency of "green hydrogen" production can be enhanced by locating renewable energy generation close to hydrogen production sites, as this proximity reduces the need for extensive network infrastructure. Furthermore, local energy production and consumption contribute to a reduction in infrastructure requirements. To support the grid, the main converter (i.e., front-end converter), such as a ModularMultilevel Converter (MMC), coupled with the energy storage system (ESS), can provide grid-forming capabilities and auxiliary services. The integration of one or more DC / DC converters introduces several control features that further improve the system's performance. For instance, the ESS can dampen power oscillations, stabilizing power delivery from renewable sources to electrolyzers. Additionally, the ESS enhances the stability and performance of renewables, which is particularly useful in scenarios like black starts. It also enables grid-forming behavior by providing inertial response and frequency control for the hydrogen plant. Smooth power control is achieved through the DC / DC converters, which manage power consumption and allow the main converter (e.g., MMC) to replicate the behavior of Static Synchronous Compensators (STATCOM).

[0062] Additionally, the hydrogen production plant can also operate in island mode as long as the ESS energy is available.

[0063] Below, embodiments of the auxiliary power supply unit 20 are described.

[0064] In one embodiment, the auxiliary power supply unit 20 includes multiple DC / DC converters, each coupled to an electrolyzer string. Each DC / DC converter can be located at the top, bottom, or middle of the electrolyzer string to which it is coupled. The DC / DC converter located at the top can be connected between the positive DC terminal of the main converter and the end electrolyzer of the electrolyzer string that is coupled to the positive DC terminal. The DC / DC converter located at the bottom can be connected between the negative DC terminal of the main converter and the end electrolyzer of the electrolyzer string that is coupled to the negative DC terminal. The DC / DC converter located in the middle may include one or more DC / DC converters, each coupled between the positive and negative terminals of the main converter, positioned differently from the top or bottom DC / DC converter.

[0065] These DC / DC converters form multiple converter groups, with each group including a DC / DC converter coupled to each electrolyzer string. In each converter group, the first side of each DC / DC converter is connected to an electrolyzer string, while the second side is connected in parallel to each other. For example, referring to Figure 1A, the DC / DC converter 21, which is coupled to the first electrolyzer string 210, and the DC / DC converter 22, which is coupled to the second electrolyzer string 220, together form a converter group.

[0066] One or more DC / DC converters coupled to each electrolyzer string can divide the electrolyzer string into multiple segments. For example, the electrolyzers located between two adjacent DC / DC converters can form one segment, while the electrolyzers located before or after a DC / DC converter can also form a segment.

[0067] These DC / DC converters can regulate the current flowing through each electrolyzer string under the control of the control system 30. In some examples, the current flowing through one or more segments of each electrolyzer string can also be regulated by these DC / DC converters. Additionally, one or more segments of an electrolyzer string can be bypassed using these DC / DC converters.

[0068] Figure 1 A shows an example in which the auxiliary power supply unit 20 includes multiple DC / DC converters. Referring to Figure 1A, the auxiliary power supply unit 20 includes a first DC / DC converter 21 coupled to the first electrolyzer string 210 and a second DC / DC converter 22 coupled to the second electrolyzer string 220. The first DC / DC converter 21 is connected between the positive DC terminal 10A of the main converter and the end electrolyzer 211 of the first electrolyzer string 210. The second DC / DC converter 22 is connected between the positive DC terminal 10A of the main converter and the end electrolyzer 221 of the second electrolyzer string 220. Moreover, the first sides of the first DC / DC converter 21 and the second DC / DC converter 22 are respectively coupled to the electrolyzer strings 210 and 220, while the second sides of the first DC / DC converter 21 and the second DC / DC converter 22 are connected in parallel.

[0069] In an embodiment, as shown in Figure 1A, the control system 30 regulates the current flowing through the first and second electrolyzer strings 210 and 220 by controlling the first and second DC / DC converters 21 and 22. The control process and principles can be expressed by the following formulas (l)-(3):

[0070] 1=11+12 (1)

[0071] I1’=I1+AI (2)

[0072] I2’=I2-AI (3)

[0073] where I represents the main current output from the positive DC terminal 10A of the main converter. In this embodiment, the current output from the positive DC terminal 10A of the main converter is equal to the current returning to the main converter through the negative DC terminal 10B.

[0074] Il and 12 represent the first and second main currents distributed to the first and second electrolyzer strings 210 and 220, respectively, before being regulated by the first and second DC / DC converters 21 and 22. When II and 12 are not equal, it indicates differences in the performance of the first and second electrolyzer strings 210 and 220, including variations in equivalent internal resistances and hydrogen production rates. Specifically, if the second main current 12 is greater than the first main current II, it indicates that the overall hydrogen production rate of the second electrolyzer string 220 is higher than that of the first electrolyzer string 210. Conversely, if the second main current 12 is less than the first main current II, it indicates that the overall hydrogen production rate of the second electrolyzer string 220 is lower than that of the first electrolyzer string 210.

[0075] II' and 12' represent the currents flowing through the first and second electrolyzer strings 210 and 220 after being adjusted by the first and second DC / DC converters 21 and 22.

[0076] Al represents the current drawn from one electrolyzer string and injected into another. An example of drawing the current Al from the second electrolyzer string 220 and injecting it into the first electrolyzer string 210 is shown in Figure 1A. The current Al is adjustable; for instance, the minimum value of Al can be zero, while the maximum value is constrained by the rated current of either the first or second DC / DC converter.

[0077] According to an embodiment, when 12 is greater than II, the second DC / DC converter 22 is controlled to draw a current Al from the second electrolyzer string 220, while the first DC / DC converter 21 is controlled to inject this current Al into the first electrolyzer string 210. Through this control, the currents II' and 12' flowing through the first and second electrolyzer strings after adjustment can be made equal. In this case, the value of Al may be equal to half the difference between II and 12.

[0078] According to another embodiment, when 12 is greater than II, the second DC / DC converter 22 is controlled to draw a current Al from the second electrolyzer string 220, while the first DC / DC converter 21 is controlled to inject this current Al into the first electrolyzer string 210. Through this control, the difference in current flowing through the first and second electrolyzer strings after adjustment can be reduced; that is, the difference between II' and 12' becomes less than the difference between II and 12. In this case, the value of Al can be adjusted based on the dynamic changes in the aging state of the two electrolyzer strings.

[0079] According to yet another embodiment, when 12 is greater than II, the first DC / DC converter 21 is controlled to draw a current Al from the first electrolyzer string 210, while the second DC / DC converter 22 is controlled to inject this current Al into the second electrolyzer string 220. Through this control, it is possible to heavily load the electrolyzer string with a higher hydrogen production rate (less aging) while lightly loading the electrolyzer string with a lower hydrogen production rate (more serious aging). Consequently, the difference between the currents II' and 12' flowing through the first and second electrolyzer strings after this adjustment will increase, meaning that the difference between II' and 12' becomes greater than the difference between II and 12. In this case, the value of Al can be adjusted based on the dynamic changes in the aging state of the two electrolyzer strings.

[0080] According to an embodiment, the first and second DC / DC converters may be positioned at intermediate locations on the first and second electrolyzer strings, respectively. This arrangement allows each DC / DC converter to regulate the current flowing through a segment of an electrolyzer string rather than the current flowing through the entire string. An example of this configuration is shown in Figure IB.

[0081] Referring to Figure IB, the first DC / DC converter 21 is positioned at an intermediate location on the first electrolyzer string 210, for example, between the electrolyzers 212 and 213. The second DC / DC converter 22 is similarly positioned on the second electrolyzer string 220, for instance, between the electrolyzers 222 and 223. The first DC / DC converter 21 can adjust the current flowing through a segment of the first electrolyzer string 210, specifically through the electrolyzers 213 to 2 In. Likewise, the second DC / DC converter 22 can adjust the current flowing through a segment of the second electrolyzer string 220, specifically through the electrolyzers 223 to 22n. The regulation of the current flowing through each segment is similar to the previously described method for regulating thecurrent through each electrolyzer string, so the relevant descriptions above also apply here.

[0082] According to an embodiment, the position of a DC / DC converter in an electrolyzer string can be adjusted, for example, by modifying the coupling position where the first side of the DC / DC converter is connected to the electrolyzer string. Through such adjustments, it is possible to increase or decrease the number of electrolyzers included in the segment. These adjustments allow for a more flexible matching of the current regulation capability of the DC / DC converter. It is noted that such adjustments will place higher demands on the electrical isolation of the DC / DC converter, so the design will fully consider the electrical isolation requirements at different locations within the electrolyzer string.

[0083] In addition, for the DC / DC converter positioned at the midpoint between the positive and negative DC terminals 10A and 10B, the requirement for electrical isolation is low or may not be necessary, as this point is close to or equal to ground potential.

[0084] In Figures 1A and IB, the arrangement of each DC / DC converter in a converter group is shown to be symmetrical on the electrolyzer strings. According to an embodiment, the DC / DC converters in a converter group can also be arranged in asymmetrical positions. For example, for two DC / DC converters in a converter group, one DC / DC converter may be located at the top of one electrolyzer string, while the other DC / DC converter is positioned in the middle of another electrolyzer string. Alternatively, both DC / DC converters could be located at asymmetrical middle positions on the two electrolyzer strings. Figure 1C illustrates such an example. Referring to Figure 1C, the first DC / DC converter 21 is located between electrolyzers 212 and 213 on the first electrolyzer string, while the second DC / DC converter 22 is located between electrolyzers 221 and 222 on the second electrolyzer string. This means that the first DC / DC converter 21 is closer to the bottom of its respective string compared to the second DC / DC converter. In this embodiment, the regulation of current flowing through each segment is similar to the method described above for regulating current through each electrolyzer string; thus, the relevant descriptions above also apply here.

[0085] In another embodiment, the auxiliary power supply unit 20 includes an energy source in addition to the DC / DC converters described above. The previous descriptions of the DC / DC converters also apply here, including their location settings, quantity adjustments, and so on, which will not be repeated. Additionally, the second sides of these DC / DC converters are connected in parallel with the energy source, as well as in parallel with each other, allowing each DC / DC converter to independently exchange energy with the energy source. Each DC / DC converter can draw current from or inject current into the energy source independently and in a controlled manner. In this embodiment, the current output from the positive DC terminal 10A may or may not be equal to the current injected into the negative DC terminal 10B.

[0086] Figure 4A illustrates such an embodiment. As shown in Figure 4A, the auxiliary power supply unit 20 includes the first DC / DC converter 21, the second DC / DC converter 22, and an energysource 26. The previous descriptions of the first and second DC / DC converters 21 and 22 also apply here and will not be repeated. Additionally, the second sides of the first and second DC / DC converters 21 and 22 are connected in parallel with the energy source 26, as well as in parallel with each other, allowing each DC / DC converter to independently exchange energy with the energy source 26. Below, some examples of current regulation based on the auxiliary power supply unit 20 shown in Figure 4A will be described with reference to Figures 4B-4D.

[0087] In an example, some of these DC / DC converters draw current from the energy source 26, while others inject current into it. For instance, referring to Figure 4B, the first DC / DC converter 21 draws a first current All from the energy source 26, while the second DC / DC converter 22 injects a second current AI2 into the energy source 26. The total current drawn from the energy source 26, such as the first current All, may be equal to the total current injected into the energy source, such as the second current AI2. In this case, the energy source 26 can act as an energy buffer. Alternatively, the total current drawn from the energy source 26 may not be equal to the total current injected into it. In this case, the energy source 26 can compensate for the difference between the total current drawn and the total current injected.

[0088] The current regulation and principles shown in Figure 4B satisfy the following formulas (4) ~ (6):

[0089] H’=I1+AI1 (4)

[0090] 12 =12- AI2 (5)

[0091] AI=AI1-AI2 (6)

[0092] where II and II' represent the current flowing through the first electrolyzer string 210 before and after regulation by the first DC / DC converter 21, respectively. 12 and 12' represent the currents flowing through the second electrolyzer string 220 before and after regulation by the second DC / DC converter 22. All represents the first current drawn by the first DC / DC converter 21 from the energy source 26, while AI2 represents the second current injected by the second DC / DC converter 22 into the energy source 26. Al represents the sum of the currents that these DC / DC converters interact with the energy source 26.

[0093] When Al is zero, that is, when the first current drawn by the first DC / DC converter is equal to the second current injected by the second DC / DC converter, the current I' flowing back to the negative DC terminal 10B of the main converter is equal to the main current I output from the positive DC terminal 10A of the main converter. When Al is not zero, that is, when the first current drawn by the first converter is not equal to the second current injected by the second converter, the current I' flowing back to the negative DC terminal 10B of the main converter is not equal to the main current I output from the positive DC terminal 10A of the main converter.

[0094] In another example, each DC / DC converter is operated to draw current from the energy source 26. For example, referring to Figure 4C, the first DC / DC converter 21 is operated to draw a firstcurrent All from the energy source 26, and the second DC / DC converter 22 is operated to draw a second current AI2 from the energy source 26.

[0095] The current regulation and principles shown in Figure 4C satisfy the following formulas (7) ~ (9):

[0096] H’=I1+AI1 (7)

[0097] I2’=I2+AI2 (8)

[0098] AI=AI1+AI2 (9)

[0099] where II and II' represent the current flowing through the first electrolyzer string 210 before and after regulation by the first DC / DC converter 21, respectively. 12 and 12' represent the currents flowing through the second electrolyzer string 220 before and after regulation by the second DC / DC converter 22. All represents the first current drawn by the first DC / DC converter 21 from the energy source 26, and AI2 represents the second current drawn by the second DC / DC converter 22 from the energy source 26. Al represents the sum of the currents that these DC / DC converters interact with the energy source 26. In this example, the current I' flowing back to the negative DC terminal 10B of the main converter is greater than the main current I output from the positive DC terminal 10A of the main converter, because each DC / DC converter is operated to increase the current flowing through the electrolyzer string to which it is coupled.

[0100] In yet another example, each DC / DC converter is operated to inject current from the energy source 26. For example, referring to Figure 4D, the first DC / DC converter 21 is operated to inject a first current All into the energy source 26, and the second DC / DC converter 22 is operated to inject a second current AI2 into the energy source 26.

[0101] The current regulation and principles shown in Figure 4D satisfy the following formulas (10) ~ (12):

[0102] H’=I1-AI1 ( 10)

[0103] I2’=I2-AI2 ( 11 )

[0104] AI= - (AI1+AI2) ( 12)

[0105] where II and II' represent the current flowing through the first electrolyzer string 210 before and after regulation by the first DC / DC converter 21, respectively. 12 and 12' represent the currents flowing through the second electrolyzer string 220 before and after regulation by the second DC / DC converter 22. All represents the first current injected by the first DC / DC converter 21 into the energy source 26, and AI2 represents the second current injected by the second DC / DC converter 22 into the energy source 26. Al represents the sum of the currents that these DC / DC converters interact with the energy source 26. In this example, the current I' flowing back to the negative DC terminal 10B of the main converter is less than the main current I output from the positive DC terminal 10A of the main converter, because each DC / DC converter is operated to reduce the current flowing through the electrolyzer string to which it is coupled.

[0106] In the examples above, each of the first and second currents can be independently controlled and adjusted. In other words, the control system 30 can independently manage the current exchanged between each DC / DC converter and the energy source 26, and the exchanged current is adjustable. Through such control, the operation of each electrolyzer string can be managed more precisely, thereby achieving at least one of the following: optimizing the overall hydrogen production efficiency of multiple electrolyzer strings, balancing the hydrogen production rate of each electrolyzer string, and balancing the aging of each electrolyzer string.

[0107] According to an embodiment of the present disclosure, the energy source 26 can be implemented in various ways.

[0108] In an example, as shown in Figure 5A, the energy source 26 may include one or more of the following: 1) an energy storage unit comprising a supercapacitor and / or a super battery; 2) a DC source with a dedicated DC-DC converter, the DC source comprising one or more of a separate DC power supply, a DC grid, and a fuel cell; 3) an AC source with a dedicated AC / DC converter; for example, the AC source is an AC feed or an AC grid.

[0109] There will be situations where the energy source 26 needs to be charged. Below are embodiments of how the energy source 26 can be charged.

[0110] In an embodiment, power for an isolated energy source 26 can be sourced from the DC output of the main converter, through a separate converter, or from an electrolyzer string via a DC-DC converter. In another embodiment where the energy source 26 is a battery, the DC-DC converter coupled with the battery can function as a charger until the battery is fully charged. Once fully charged, the battery can be used for string current regulation. In this case, the charging of the battery is managed to ensure that the efficiency and availability of the electrolyzers are not compromised.

[0111] In another example, the energy source 26 can be implemented by means of an energy storage string or other components capable of providing and storing energy.

[0112] For example, referring to Figure 5B, the energy source 26 can be implemented by means of an energy storage string (e.g., a battery string 14) coupled with the DC side of the main converter 101, that is, by exchanging energy between the DC / DC converter 21 and the DC / DC converter 141 coupled to the energy storage string to regulate the current flowing through the electrolyzers after the DC / DC converter 21 in the electrolyzer string 210.

[0113] It is noted that one DC / DC converter 21 is shown coupled with the electrolyzer string 200, and one DC / DC converter 141 is shown coupled with the energy storage string 14, respectively. However, according to some examples of the present disclosure, both the electrolyzer string 200 and the energy storage string 14 can each be coupled with two or more DC / DC converters. Additionally, each of the two or more DC / DC converters coupled with the electrolyzer string 200 is connected to a corresponding one of the two or more DC / DC converters coupled with the energy storage string 14.

[0114] In this example, as shown by the dashed line in Figure 5B, the energy source 26, whichserves as an energy buffer and can be coupled with the DC / DC converter 141, is an optional element. In other words, it can be implemented with or without the energy buffer.

[0115] In addition, the energy source 26 can also be implemented by means of a string of energy storage units in the ESS or other components capable of providing and storing energy. For example, the energy source 26 can be implemented by means of a string of energy storage units, such as a battery string 14 shown in Figure 2B, that is, by exchanging energy between the DC / DC converter 21 and a converter coupled to the energy storage string 14 to regulate the current flowing through the electrolyzers after the DC / DC converter 21 in the electrolyzer string 210.

[0116] According to an example of the present disclosure, the auxiliary power supply unit 20 can be implemented to include multiple sets of DC / DC converters, thereby enabling the regulation of the current flowing through one or more segments of an electrolyzer string. Next, some embodiments of the auxiliary power supply unit 20, which includes multiple sets of DC / DC converters, will be described with reference to Figures 6A-6C.

[0117] In an embodiment, the auxiliary power supply unit 20 includes multiple sets of DC / DC converters. Each set of DC / DC converters includes a DC / DC converter coupled to each of the first and second electrolyzer strings, respectively, and an energy source coupled to each of these DC / DC converters. For example, referring to Figure 6A, the auxiliary power supply unit 20 includes multiple sets 20A-20C of DC / DC converters. The DC / DC converter set 20 A includes DC / DC converters 21 A and 22A coupled to the first and second electrolyzer strings, respectively, along with an energy source 26 A coupled to each of the DC / DC converters 21 A and 22 A. The DC / DC converter set 20B includes DC / DC converters 21B and 22B coupled to the first and second electrolyzer strings, respectively, along with an energy source 26B coupled to each of the DC / DC converters 21B and 22B. Similarly, the converter set 20C includes DC / DC converters 21C and 22C coupled to the first and second electrolyzer strings, respectively, and an energy source 26C coupled to each of the DC / DC converters 21C and 22C. The control system 30 manages each set of DC / DC converters to adjust the current flowing through the corresponding segments of the electrolyzer strings. For example, the control system 30 controls the DC / DC converter set 20A to adjust the current flowing through the segment of the first electrolyzer string that includes electrolyzers 211 and 212, as well as the current flowing through the segment of the second electrolyzer string that includes electrolyzers 221 and 222. The configuration and control strategy of each set of DC / DC converters are similar to those described with reference to Figures 4A-4D, so the above description of Figures 4A-4D is also applicable here.

[0118] In another embodiment, the auxiliary power supply unit 20 includes multiple sets of DC / DC converters. Each set of DC / DC converters includes a DC / DC converter coupled to each of the first and second electrolyzer strings, respectively. For example, referring to Figure 6B, the auxiliary power supply unit 20 includes multiple sets 20A-20C of DC / DC converters. The DC / DC converter set 20 A includes DC / DC converters 21 A and 22A coupled to the first and second electrolyzer strings,respectively. The DC / DC converter set 20B includes DC / DC converters 21B and 22B coupled to the first and second electrolyzer strings, respectively. Similarly, the converter set 20C includes DC / DC converters 21C and 22C coupled to the first and second electrolyzer strings, respectively. The control system 30 manages each set of DC / DC converters to adjust the current flowing through the corresponding segments of the electrolyzer strings. For example, the control system 30 controls the DC / DC converter set 20A to adjust the current flowing through the segment of the first electrolyzer string that includes electrolyzers 211 and 212, as well as the current flowing through the segment of the second electrolyzer string that includes electrolyzers 221 and 222. The configuration and control strategy of each set of DC / DC converters are similar to those described with reference to Figures 1A-1C, so the above description of Figures 1A-1C is also applicable here.

[0119] In yet another embodiment, the auxiliary power supply unit 20 includes multiple sets of DC / DC converters, which are implemented in a combined form of Figures 6A and 6B. For example, referring to Figure 6C, the auxiliary power supply unit 20 includes multiple sets 20A-20C of DC / DC converters. The DC / DC converter set 20 A includes DC / DC converters 21 A and 22 A coupled to the first and second electrolyzer strings, respectively, along with an energy source 26 A coupled to each of the DC / DC converters 21 A and 22 A. The DC / DC converter set 20B includes DC / DC converters 21B and 22B coupled to the first and second electrolyzer strings, respectively. The converter set 20C includes DC / DC converters 21C and 22C coupled to the first and second electrolyzer strings, respectively, and an energy source 26C coupled to each of the DC / DC converters 21C and 22C. The control system 30 manages each set of DC / DC converters to adjust the current flowing through the corresponding segments of the electrolyzer strings. The configuration and control strategy of the sets 20A and 20C are similar to those described with reference to Figures 4A-4D, so the above description of Figures 4A-4D is also applicable here. The configuration and control strategy of the set 20B are similar to those described with reference to Figures 1 A-1C, so the above description of Figures 1 A-1C is also applicable here.

[0120] Below, embodiments of the control system 30 are described.

[0121] In an embodiment, the control system 30 includes converter controllers associated with the main converter and each DC / DC converter, along with a system controller that is communicatively connected to each converter controller. This system controller may also be referred to as a supervisory controller. For example, as illustrated in Figure 7, the control system 30 comprises a converter controller 31 associated with the first DC / DC converter 21, a converter controller 32 associated with the second DC / DC converter 22, a converter controller 33 associated with the main converter 10, and a system controller 34 that is communicatively connected to the converter controllers 31-33. In some examples, the system controller 34 is implemented as a controller that is included in a hydrogen plant controller.

[0122] In an embodiment of the present disclosure, the system controller 34 can receive information from other controllers. Other controllers include, for example, electrolyzer controllers (notshown) and a power network controller (not shown).

[0123] In an example, the system controller 34 communicates with the electrolyzer controllers to obtain electrolyzer-related parameters. The electrolyzer -related parameters include parameters that can indicate the operating state or performance of each electrolyzer of each electrolyzer string, such as the current, voltage, temperature, internal resistance, cooling efficiency, hydrogen production rate, water consumption, and internal pressure of each electrolyzer. The electrolyzer-related parameters may include parameters measured by sensors coupled to each electrolyzer, such as voltage sensors, current sensors, and temperature sensors. These measured parameters will be transmitted by the electrolyzer controllers to the system controller. In addition, the electrolyzer-related parameters can also include parameters calculated based on measured parameters. For example, some parameters cannot be directly obtained through measurement; instead, they can be derived by calculating the measured parameters. The aging state of each electrolyzer can be calculated based on the electrolyzer-related parameters. The aging state of each electrolyzer can be calculated by the electrolyzer controllers and sent to the system controller or calculated by the system controller based on the received electrolyzer-related parameters.

[0124] In an example, the system controller 34 can communicate with a power network controller to obtain power network-related parameters. The power network-related parameters may include parameters measured in the power network. The measured parameters are sent by the power network controller to the system controller 34. The power network -related parameters may also include parameters calculated based on the measured parameters. For example, some parameters cannot be directly obtained through measurement; instead, they can be derived by calculating the measured parameters. The power network-related parameters may include parameters representing the power supply capacity of the power grid, including the green power that can be provided, such as power from renewable energy sources. Furthermore, the power network-related parameters can include the electricity price fluctuation curve, upon which the most cost-effective hydrogen production strategy can be formulated.

[0125] Additionally, the system controller 34 can also obtain the electrolyzer -related parameters and the power network-related parameters according to user input or preset values in the electrolyzer controllers and the power network controller.

[0126] Examples of another aspect of the present disclosure relate to control methods for controlling a converter system for powering at least two electrolyzer strings.

[0127] Figure 8 is a flow chart of a control method 800 for controlling the converter system 100 according to an example of the present disclosure. The method 800 can be performed by the control system 30 described above. Next, the method 800 will be described with reference to Figure 8.

[0128] Referring to Figure 8, at block 802, the system controller 34 obtains electrolyzer -related parameters. The above descriptions of the electrolyzer-related parameters also apply here and will not be repeated.

[0129] At block 804, the system controller 34 determines the degree of aging of each electrolyzer string, such as the first and second electrolyzer strings, based on the obtained electrolyzer -related parameters. Additionally, in cases where an electrolyzer string includes multiple segments, as described above, the aging degree of each segment can also be determined.

[0130] In an embodiment of the present disclosure, the aging degree of an electrolyzer string refers to the overall aging degree of all the electrolyzers included in the string. For example, the aging degree of a string can be represented by the arithmetic average of the aging degrees of all the electrolyzers in the string. For another example, the aging degree of a string can be represented by the weighted average of the aging degrees of all the electrolyzers in the string. One way of weighted averaging is that the more serious the aging degree of an electrolyzer, the greater the weight. Another way of weighted averaging is to first assign equal weights to all the electrolyzers in the string, then increase the weight of the most severely aged electrolyzer and decrease the weight of the least severely aged electrolyzer.

[0131] In an embodiment of the present disclosure, the aging degree of a segment refers to the overall aging degree of all the electrolyzers included in the segment. The aging degree of a segment can be obtained in a manner similar to that for an electrolyzer string described above, and will not be repeated here.

[0132] The aging degree of an electrolyzer is a parameter that quantitatively expresses the aging condition of the electrolyzer. As mentioned above, the aging degree of each electrolyzer can be calculated by the electrolyzer controller and sent to the system controller. Alternatively, the aging degree of each electrolyzer can be calculated by the system controller. The aging degree of each electrolyzer can be determined based on its internal resistance, temperature, and hydrogen production efficiency (e.g., the ratio of its actual hydrogen production to its theoretical hydrogen production).

[0133] At block 806, the system controller 34 determines an adjustment strategy for adjusting the operation of each electrolyzer string based on the aging degrees of the first electrolyzer string 210 and the second electrolyzer string 220, as well as a predetermined control objective. Next, some embodiments of block 806 (blocks 8061-8065) will be described.

[0134] In an embodiment, referring to block 8061, when the aging degree of the first electrolyzer string is greater than that of the second electrolyzer string (for example, when the current 12 flowing through the second electrolyzer string is greater than the current II flowing through the first electrolyzer string) and the control objective is to equalize the hydrogen production rates of the first and second electrolyzer strings after adjustment, the adjustment strategy includes determining the value of the adjustment current as half of the difference between the currents flowing through the two electrolyzer strings, drawing this adjustment current from the second electrolyzer string 220, and injecting the drawn adjustment current into the first electrolyzer string 210.

[0135] In another embodiment, referring to block 8062, when the aging degree of the first electrolyzer string is greater than that of the second electrolyzer string (for example, when the current12 flowing through the second electrolyzer string is greater than the current II flowing through the first electrolyzer string) and the control objective is to reduce the difference between the hydrogen production rates of the first and second electrolyzer strings at a predetermined rate after adjustment, the adjustment strategy includes determining the adjustment current based on the dynamic change in the difference between the currents flowing through the two electrolyzer strings. This ensures that the difference between the hydrogen production rates of the first and second electrolyzer strings decreases at the predetermined rate. The adjustment strategy also includes drawing the adjustment current from the second electrolyzer string 220 and injecting the drawn adjustment current into the first electrolyzer string 210. This strategy is especially applicable in situations where the current flowing through the second electrolyzer string is much greater than that flowing through the first electrolyzer string, and it is necessary to consider the constraint of the power change rate limit of the electrolyzers while reducing the hydrogen production rate difference between the two electrolyzer strings.

[0136] In yet another embodiment, referring to block 8063, when the aging degree of the first electrolyzer string is greater than that of the second electrolyzer string (for example, when the current 12 flowing through the second electrolyzer string is greater than the current II flowing through the first electrolyzer string) and the control objective is to balance the aging conditions of the two electrolyzer strings, the adjustment strategy includes determining an adjustment current, drawing this adjustment current from the first electrolyzer string 210, and injecting the drawn adjustment current into the second electrolyzer string 220. Through such control, it is possible to heavily load the electrolyzer string with less aging while lightly loading the electrolyzer string with more aging. In this embodiment, the value of the adjustment current can vary with the dynamic changes in the aging state of the two electrolyzer strings.

[0137] In yet another embodiment, referring to block 8064, when the aging degree of each of the first and second electrolyzer strings exceeds a first predetermined aging degree, and the aging degree of the first electrolyzer string is greater than that of the second electrolyzer string, with the control objective being to slow down aging and balance the aging conditions of the two electrolyzer strings, the adjustment strategy includes determining a first and a second adjustment current. The adjustment strategy also includes drawing the first adjustment current from the first electrolyzer string and injecting it into the energy source, as well as drawing the second adjustment current from the second electrolyzer string and injecting it into the energy source. The value of the first adjustment current is greater than that of the second adjustment current.

[0138] In yet another embodiment, referring to block 8065, when both the first and second electrolyzer strings are healthy (for example, when the aging degrees of the two electrolyzer strings are less than a second predetermined aging degree) and the control objective is to maximize and balance the hydrogen production rates of the two electrolyzer strings, the adjustment strategy includes determining a first and a second adjustment current. The adjustment strategy also involves drawing thefirst adjustment current from the energy source and injecting it into the first electrolyzer string, as well as drawing the second adjustment current from the energy source and injecting it into the second electrolyzer string. The value of the first adjustment current is greater than that of the second adjustment current.

[0139] At block 808, the system controller 34 determines the setpoint for each DC -DC converter, such as a voltage setpoint, a current setpoint, or a power setpoint, based on the determined adjustment current. For example, referring to Figure 7, the system controller 34 determines the setpoint for the DC / DC converter 21 and the setpoint for the DC / DC converter 22 according to the adjusted current.

[0140] At block 810, the system controller 34 sends the determined setpoints to corresponding converter controllers. For example, referring to Figure 7, the system controller 34 sends the setpoint for the DC / DC converter 21 to the converter controller 31 and sends the setpoint for the DC / DC converter 22 to the converter controller 32.

[0141] At block 812, each converter controller controls the associated DC / DC converter according to the received setpoint. For example, referring to Figure 7, the converter controller 31 controls the DC / DC converter 21 according to the received setpoint, and the converter controller 32 controls the DC / DC converter 22 according to the received setpoint.

[0142] It is noted that the adjustment strategy for segments of the electrolyzer strings can be implemented in a manner similar to that described above and will not be repeated here.

[0143] According to an embodiment, the control method 800 further includes a process for providing grid services while performing the adjustment described above. Referring to Figure 7, the system controller 34 collaborates with the converter controller 33 associated with the main converter, as well as the converter controllers 31 and 32 associated with the DC / DC converters 21 and 22. This collaboration enables optimal control that achieves both the control of the operation of the electrolyzer strings and the provision of grid services.

[0144] For example, the system controller 34 receives power network-related parameters from the power network controller and determines the control parameters needed for the required grid services, such as an active power setpoint and a reactive power setpoint, based on these parameters. Subsequently, the system controller 34 evaluates if the power change capability of each electrolyzer string can meet the active and reactive power setpoints. The power change capability of the electrolyzer string includes assessing the maximum power ramp-up and ramp-down values, which are predetermined based on the physical characteristics of each electrolyzer in the string.

[0145] If the evaluation indicates that the active and reactive power setpoints can be met, the system controller 34 sends the active and reactive setpoints to the converter controllers 33, 31, and 32. This enables the converter controllers 33, 31, and 32 to control the corresponding converters according to the received active and reactive power setpoints.

[0146] If the evaluation indicates that the active and reactive power setpoints cannot be met, thesystem controller 34 implements an optimal control strategy that utilizes the energy storage system (ESS) to enhance hydrogen production efficiency while providing the required grid service. In this approach, the system controller 34 divides each of the active and reactive power setpoints into two parts, i.e., first and second active power setpoints, and first and second reactive power setpoints. The first active and reactive power setpoints are used to control the converter controllers 31 -33, while the second active and reactive power setpoints are utilized to manage the ESS, including the dedicated converter coupled to the ESS. This control strategy allows the system to offer grid services in a more flexible manner while optimizing hydrogen production efficiency in the hydrogen plant.

[0147] 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

WE CLAIM:

1. A converter system (100) for powering a plurality of hydrogen electrolyzers that are electrically coupled together to form at least two electrolyzer strings (210, 220), comprising:a main power supply unit (10) comprising a main converter that provides bulk power to the at least two electrolyzer strings (210, 220) such that a main current flows through each of the at least two electrolyzer strings;an auxiliary power supply unit (20) comprising at least one DC / DC converter, which is electrically coupled with one electrolyzer string from the at least two electrolyzer strings to inject or extract an adjustable current to or from the one electrolyzer string; anda control system (30) configured to control at least one of the main power supply unit (10) and the auxiliary power supply unit (20) for operating the converter system (100).

2. The converter system (100) of claim 1, wherein the at least one DC / DC converter is sized based on and operated with, a fraction of the total power transferred to said one electrolyzer string.

3. The converter system (100) of claim 1, wherein the auxiliary power supply unit (20) comprises an energy source (26), and the at least one DC / DC converter is configured to exchange power with the energy source (26) to adjust current flowing through said one electrolyzer string.

4. The converter system (100) of claim 3, wherein the energy source (26) comprises or is integrated with one or more of the following:- an energy storage unit comprising one or more of a supercapacitor and a super battery;- a DC source with a dedicated DC / DC converter, wherein the DC source comprises one or more of a separate DC power supply, a DC grid, and a fuel cell;- an AC source with a dedicated AC / DC converter, wherein the AC source is an AC power grid.

5. The converter system (100) of claim 3, wherein the energy source (26) comprises or is integrated with an energy storage string, and the at least one DC / DC converter is connected to another DC / DC converter that is coupled with the eneigy storage string; orthe energy source (26) comprises or is integrated with an additional electrolyzer string, and the at least one DC / DC converter (21) is coupled between the one electrolyzer string and the additional electrolyzer string.

6. The converter system (100) of claim 1, wherein the main power supply unit (10) comprises a main converter coupled between a power network (300) and the at least two electrolyzer strings (210, 220).

7. The converter system (100) of claim 6, wherein the main converter includes one or more modular multilevel converters (MMCs).

8. The converter system (100) of claim 6, wherein the main power supply unit (10) is coupled with an energy storage system (ESS) which is coupled with the main converter, andthe ESS comprises one or more of a battery string, a capacitor string, a supercapacitor string, and a string of energy storage units associated with photovoltaic (PV) systems.

9. The converter system (100) of claim 8, wherein the control system (30) is configured to: control the main converter to receive power from the ESS in the case of a fault in the power network (300); and / orcontrol the main converter such that power is exchanged between the ESS and the power network (300) to provide grid services that require active power exchange, without disrupting hydrogen production.

10. The converter system (100) of claim 6, wherein the main converter is coupled to a renewable source, which is coupled to the power network (300);and optionally, the renewable source comprises a wind farm.

11. The converter system (100) of claim 6, wherein the main converter is coupled to a fuel cell, andthe control system is configured to control the main converter so that fuel cell -generated power is either injected into the power network through the main converter to provide grid services or delivered to the at least two electrolyzer strings through the main converter to offer a fault ride-through function when the power network fails and cannot provide power.

12. The converter system (100) of claim 1, wherein the auxiliary power supply unit (20) comprises:a first DC / DC converter (21) coupled to a first electrolyzer string (210) from the at least two electrolyzer strings; anda second DC / DC converter (22) coupled to a second electrolyzer string (220) from the at least two electrolyzer strings.

13. The converter system (100) of claim 12, wherein a first side of the first DC / DC converter (21) and a first side of the second DC / DC converter (22) are coupled to the first and second electrolyzer strings, respectively; anda second side of the first DC / DC converter (21) and a second side of the second DC / DC converter (22) are coupled to each other in parallel.

14. The converter system (100) of claim 12, wherein the first DC / DC converter (21) is connected with an end electrolyzer or an intermediate electrolyzer of the first electrolyzer string (210); and the second DC / DC converter (22) is connected with an end electrolyzer or an intermediate electrolyzer of the second electrolyzer string (220).

15. The converter system (100) of claim 12, wherein the control system is configured to: control the second DC / DC converter (22) to draw an adjustment current from the second electrolyzer string (220); andcontrol the first DC / DC converter (21) to inject the adjustment current into the first electrolyzer string (210).

16. The converter system (100) of claim 12, wherein the control system is configured to: control the first DC / DC converter (21) to draw a first adjustment current from an energy source included in the auxiliary power supply unit (20) and inject the first adjustment current into the first electrolyzer string (210); andcontrol the second DC / DC converter (22) to draw a second adjustment current from the energy source and inject the second adjustment current into the second electrolyzer string (210).

17. The converter system (100) of claim 12, wherein the control system is configured to: control the first DC / DC converter (21) to draw a first adjustment current from the first electrolyzer string (210) and inject the first adjustment current into an energy source included in the auxiliary power supply unit (20); andcontrol the second DC / DC converter (22) to draw a second adjustment current from the energy source and inject the second adjustment current into the second electrolyzer string (210).

18. The converter system (100) of claim 12, wherein the control system is configured to:control the first DC / DC converter (21) to draw a first adjustment current from the first electrolyzer string (210) and inject the first adjustment current into an energy source included in the auxiliary power supply unit (20); andcontrol the second DC / DC converter (22) to draw a second adjustment current from the second electrolyzer string (220) and inject the second adjustment current into the energy source.

19. The converter system (100) of any of claims 16-18, wherein the control system is configured to:regulate each of first and second adjustment currents according to changes in the aging states of the first and second electrolyzer strings (210, 220).

20. The converter system (100) of claim 1, wherein the auxiliary power supply unit (20) comprises a plurality of sets of DC / DC converters, and each set of DC / DC converters comprises: a first DC / DC converter (21) coupled to a first electrolyzer string (210) from the at least two electrolyzer strings; anda second DC / DC converter (22) coupled to a second electrolyzer string (220) from the at least two electrolyzer strings.

21. The converter system (100) of claim 20, wherein the control system (30) is configured to: control the plurality of sets of DC / DC converters such that the current flowing through one or more segments of each electrolyzer string is controlled.

22. A control method for controlling a converter system of any of claims 1-21, the control method comprising:controlling at least one of the main power supply unit and the auxiliary power supply unit for operating the converter system.

23. The control method of claim 22, wherein the step of controlling comprises:obtaining electrolyzer-related parameters including parameters that indicate the operating state of each electrolyzer in the at least two electrolyzer strings;determining the degree of aging of each electrolyzer string based on the electrolyzer-related parameters; anddetermining an adjustment strategy for adjusting the operation of each electrolyzer string based on the determined aging degree of each electrolyzer string and a predetermined control objective.

24. The control method of claim 23, wherein the step of controlling comprises: coordinately controlling a converter controller associated with the main converter and a converter controller associated with the at least one DC / DC converter such that the operation of the at least two electrolyzer strings is controlled according to the predetermined control objective while providing a required grid service.

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