Converter system and control method thereof

Abstract

The present disclosure provides a converter system (100) for powering a plurality of hydrogen electrolyzers that are electrically coupled together to form at least one electrolyzer string (200). The converter system (100) includes a main power supply unit (10) configured to provide bulk power to the at least one electrolyzer string (200) such that a main current flows through the at least one electrolyzer string (200); an auxiliary power supply unit (20) comprising at least one DC / DC converter (21), which is electrically coupled with the at least one electrolyzer string (200) to inject or extract an adjustable current to or from the at least one electrolyzer string (200); 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 control method for controlling the converter system.BACKGROUND

[0002] The energy sector is currently undergoing a significant transformation with the emergence of hydrogen (FL) as a viable energy carrier and storage medium. Consequently, substantial research is being dedicated to exploring various aspects of technologies related to hydrogen generation, with a particular focus on diverse electrolyzer technologies. By utilizing electricity from renewable sources, the production of "green hydrogen," which is the most environmentally friendly option, becomes possible.

[0003] Regardless of the chemical reaction employed in the process, at least one power electronic converter is needed to transform AC (or DC) current from the electrical power grid into a DC current with the appropriate voltage and current characteristics.

[0004] A large hydrogen production system, also referred to as a hydrogen electrolyzer plant, typically comprises electrolyzer strings having several electrolyzer units connected in series, and possibly also in parallel. These electrolyzer strings are connected to the DC terminals of a converter system for power, and the potential across individual electrolyzer units is a divided potential according to the resistance offered by the individual electrolyzer unit. However, such division of the potential in series-connected electrolyzers presents certain challenges regarding overall system protection and control due to their potentially non-uniform physical behavior and aging characteristics. As a result, different electrolyzers may experience varying DC voltage drops, leading to either overload or reduced production for those electrolyzers. Such variations complicate the design of control and protection for the hydrogen production system, especially when considering the need for a solution that is highly scalable and modular for use in large-scale hydrogen production.SUMMARY

[0005] One aspect of the present disclosure provides a converter system for powering a plurality of hydrogen electrolyzers that are electrically coupled together to form at least one electrolyzer string. The converter system includes a main power supply unit configured to provide bulk power to the at least one electrolyzer string such that a main current flows through the at least one electrolyzer string; an auxiliary power supply unit comprising at least one DC / DC converter, which is electrically coupled with the at least one electrolyzer string to inject or extract an adjustable current at the 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.

[0006] 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 the at least one electrolyzer string, or a fraction of the total plant power.

[0007] 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 current flowing through a segment of the at least one electrolyzer string.

[0008] 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.

[0009] 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 between the at least one electrolyzer string and the additional electrolyzer string or between the at least one electrolyzer string and the energy storage string.

[0010] In an example, the main power supply unit comprises a main converter coupled between a power network and the at least one electrolyzer string.

[0011] In an example, the main converter includes one or more modular multilevel converters (MMCs).

[0012] 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.

[0013] 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 which require active power exchange, without disrupting hydrogen production.

[0014] 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.

[0015] In an example, the auxiliary power supply unit comprises: a first DC / DC converter coupled between a positive DC terminal or a negative DC terminal of the main converter and an end electrolyzer of the at least one electrolyzer string; and a second DC / DC converter coupled with the at least one electrolyzer string in a location different from that of the first DC / DC converter.

[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 at least one electrolyzer, 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 control system is configured to: control the first DC / DC converter to inject a first current to a first segment of the at least one electrolyzer string; and control the second DC / DC converter to draw a second current from a second segment of the at least one electrolyzer string.

[0018] In an example, the first current is equal to the second current.

[0019] In an example, the first current is not equal to the second current; and the difference between the first current and the second current is compensated by an energy source included in the auxiliary power supply unit.

[0020] In an example, the control system is configured to adjust the first and second currents individually based on the difference in the degree of aging of the electrolyzers in the first segment and the second segment such that the maximum production efficiency for each electrolyzer string segment is achieved.

[0021] Another aspect of the present disclosure provides a control method for controlling the converter system described above. The control method includes the step of controlling at least one of the main power supply unit and the auxiliary power supply unit for operating the converter system.

[0022] In an example, the step of controlling comprises: obtaining electrolyzer-related parameters including parameters that indicate the operating and / or health state of each electrolyzer in the at least one electrolyzer string; determining the degree of aging of each segment of the at least one electrolyzer string based on the electrolyzer-related parameters; determining an adjustment current based on the difference in aging degrees between adjacent segments; determining a setpoint for the at least one DC / DC converter based on the adjustment current; and controlling the at least one DC / DC converter according to the setpoint.

[0023] In an example, the step of controlling comprises monitoring and / or estimating the difference in aging degrees between adjacent segments; determining a new adjustment current based on the monitored change in the difference; determining a new setpoint for the at least one DC / DC converter based on the new adjustment current; and controlling the at least one DC / DC converter according to the new setpoint.

[0024] In an example, determining the degree of aging of each segment comprises: calculating an arithmetic average of the aging degrees of all the electrolyzers in the segment.

[0025] In an example, determining the degree of aging of each segment comprises: calculating a weighted average of the aging degrees of all the electrolyzers in the segment; and wherein the more serious the aging degree of an electrolyzer, the greater the weight.

[0026] In an example, the step of controlling comprises coordinately controlling the converter controller associated with the main converter and the converter controller associated with the at least one DC / DC converter such that the hydrogen production efficiency of the at least one electrolyzer string is improved while providing a required grid service.

[0027] In an example, the step of controlling comprises in the case of a fault in a segment of the at least one electrolyzer string, controlling the at least one DC / DC converter such that the faulty segment is bypassed.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 1 is a block diagram of a converter system according to an embodiment of the present disclosure.

[0030] Figures 2A and 2B illustrate exemplary implementations of the main power supply unit of the converter system shown in Figure 1.

[0031] Figure 3 illustrates an example of the converter system shown in Figure 1.

[0032] Figure 4 illustrates an exemplary implementation of the auxiliary power supply unit of the converter system shown in Figure 1.

[0033] Figures 5A, 5B and 5C illustrate exemplary implementations of the energy source of the converter system shown in Figure 1.

[0034] Figures 6A and 6B illustrate some other examples of the converter system shown in Figure 1.

[0035] Figure 7 illustrates an exemplary implementation of the control system of the converter system shown in Figure 1.

[0036] Figure 8 is a flowchart of a method for controlling a converter system integrated with at least one electrolyzer string according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0037] The inventor found that when a string of hydrogen electrolyzers (hereinafter referred to as “electrolyzers”) connected in series is powered, due to the same current flowing through them in a string, differences if any in their degree (rate) of aging will lead to uneven voltage distribution between electrolyzers connected in series in the electrolyzer string. Specifically, the more severely aged electrolyzer will experience a greater voltage drop due to an increase in internal resistance, while the healthier ones will experience a smaller voltage drop. This unbalanced state limits the hydrogenproduction capacity of healthy or lightly aged electrolyzers, as the current input to the entire electrolyzer group has to be reduced to prevent the voltage of severely aged electrolyzer from exceeding its maximum limit. In response to this challenge, the present disclosure proposes a converter system and a control method thereof, which can adjust the current flowing through different segments (a subset of electrolyzer units) of the electrolyzer string, thereby effectively improving the hydrogen production efficiency of the electrolyzer string.

[0038] Examples of one aspect of the present disclosure relate to a converter system for powering a plurality of hydrogen electrolyzers that are electrically coupled together to form at least one electrolyzer string. The converter system includes a main power supply unit, an auxiliary power supply unit and a control unit. The main power supply unit provides bulk power to the at least one electrolyzer string such that a main current flows through the at least one electrolyzer string. The auxiliary power supply unit includes at least one DC / DC converter, which is electrically coupled with the at least one electrolyzer string to inject or extract an adjustable current at the point of coupling with the at least one electrolyzer string. The control system controls at least one of the main power supply unit and the auxiliary power supply unit for operating the converter system.

[0039] The at least one DC / DC converter connected in an electrolyzer string is a partial power converter 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. In this 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.

[0040] Below, detailed examples of the converter system are described.

[0041] Figure 1 shows a converter system 100 according to an example of the present disclosure, which is used to power an electrolyzer string 200 and can regulate the current flowing through one or more segments of the electrolyzer string 200.

[0042] With reference to Figure 1 , the electrolyzer string 200 includes a plurality of electrolyzer units 201 to 20n coupled together. In the example of Figure 1, these electrolyzers are shown connected in series to form the electrolyzer string 200. According to other examples of the present disclosure, several electrolyzer units connected in parallel may also be included in the electrolyzer string 200. Additionally, each electrolyzer unit (for simplicity also referred to as electrolyzer) in the electrolyzer string 200 may include multiple electrolyzer cells connected in series, multiple electrolyzer cells connected in parallel, or a combination of both series and parallel configurations.

[0043] Continuing with reference to Figure 1, the converter system 100 includes a main power supply unit 10, an auxiliary power supply unit 20, and a control system 30. The main power supply unit10 is used to provide the main current I for the electrolyzer string 200, while the auxiliary power supply unit 20 is used to inject or draw adjustable current Al’ into or from the point of coupling in the electrolyzer string 200. The control system 30 manages the operation of the main and auxiliary power supply units to optimize the hydrogen production efficiency of the electrolyzer string 200, especially when there is an aging imbalance in the electrolyzer string 200. Additionally, the converter system 100 can provide grid services to the power network connected to the main power unit 10.

[0044] Below, embodiments of the main power supply unit 10 are described.

[0045] The main power supply unit 10 includes a main converter, also referred to as a front -end converter, with a DC positive terminal 10A and a DC negative terminal 10B for providing the main current I to the electrolyzer string 200. 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 converter includes an MMC. The present disclosure does not limit the specific implementation of the MMC; therefore, the description of its topology is omitted.

[0046] 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 strings include supercapacitor strings 11 and 12, battery strings 13 and 14, and a PV string 15.

[0047] 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 one electrolyzer string 200 through the main converter to offer a fault ride -through function when the power network fails and cannot provide power.

[0048] 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.

[0049] In an embodiment, the hydrogen production plant can be arranged at the AC terminal of an HVDC system to provide grid services, functioning similarly to a STATCOM or E-STATCOM.

[0050] It is noted that the power network can be an HVDC link, a micro-grid, a DC network, or an AC distribution network.

[0051] 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 string 200 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.

[0052] 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. Additionally, the hydrogen production plant can also be operated in island mode as long as energy from the ESS is available.

[0053] In another example, power is provided to the ESS during the peak of renewables. The ESS can be used for ancillary services (also referred to as ancillary gird services or grid services) that require active power exchange with the grid, such as GFM, peak-shaving, 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.

[0054] 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 Modular Multilevel 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).

[0055] Below, embodiments of the auxiliary power supply unit 20 are described.

[0056] In one embodiment, the auxiliary power supply unit 20 includes a first DC / DC converter and a second DC / DC converter. The first DC / DC converter is coupled to the top and / or bottom of theelectrolyzer string 200. Specifically, the first DC / DC converter located at the top can be connected between the positive DC terminal 10A of the main converter and the end electrolyzer that is coupled to this terminal. The first DC / DC converter located at the bottom can be connected between the negative DC terminal 10B of the main converter and the end electrolyzer coupled to this terminal. The second DC / DC converter may consist of one or more DC / DC converters, each coupled at a different location between the positive and negative terminals of the main converter than the first DC / DC converter.

[0057] Moreover, there is at least one electrolyzer in the electrolyzer string 200 located between the second DC / DC converter and the first DC / DC converter or between any two second DC / DC converters. One side of each of these DC / DC converters is coupled to the electrolyzer string, while the other sides are connected in parallel to each other. These DC / DC converters divide the electrolyzer string into multiple segments; for example, the electrolyzers between two adjacent DC / DC converters can form one segment, while the electrolyzers in front of or behind a DC / DC converter can also form a segment.

[0058] The control system 30 regulates the current flowing through each segment by controlling these DC / DC converters. By controlling each converter, it is possible to inject current into one or more segments or draw (extract) current from one or more segments. The sum of the injected current equals the sum of the drawn current, thereby regulating the current flowing through each segment. The main current I drew from the positive DC terminal 10A of the main converter by the entire electrolyzer string 200 is equal to the current injected into the negative DC terminal 10B of the main converter.

[0059] Figure 1 shows an example in which the auxiliary power supply unit 20 includes the first and second DC / DC converters described above. Referring to Figure 1, the auxiliary power supply unit 20 consists of a first DC / DC converter 21 and a second DC / DC converter 22. The first DC / DC converter 21 is coupled between the positive DC terminal 10A and the top -end electrolyzer 201. The second DC / DC converter 22 is coupled between the electrolyzers 202 and 203 at an intermediate position of the electrolyzer string 200. Additionally, the first side of the first DC / DC converter 21 and the first side of the second DC / DC converter 22 are coupled to the electrolyzer string 200, respectively, while the second side of the first DC / DC converter 21 and the second side of the second DC / DC converter 22 are connected in parallel.

[0060] As shown in Figure 1, the electrolyzers 201 and 202 between the first DC / DC converter 21 and the second DC / DC converter 22 form the first segment, while the electrolyzers 203 to 20n after the second DC / DC converter 22 form the second segment. The control system 30 manages the first and second DC / DC converters 21 and 22 so that the current II flowing through the first segment and the current 12 flowing through the second segment satisfy the following equations (1) and (2).

[0061] I1=I+AF ( 1)

[0062] 12=11 -AF=I (2)

[0063] I represents the current drawn from the positive DC terminal 10A of the main converterand injected into the negative DC terminal 10B of the main converter by the entire electrolyzer string 200. Through such control, currents of different magnitudes can flow through the first and second segments. This is particularly suitable for situations where the aging degrees of the electrolyzers in the first and second segments differ significantly, thereby optimizing the hydrogen production efficiency, maximizing the hydrogen production rate, and balancing the aging degrees of electrolyzers of the entire electrolyzer string 200.

[0064] Al’ represents the current injected into the first segment. The magnitude of Al’ can be adjusted by controlling the first and second DC / DC converters. For example, the magnitude of Al’ can be dynamically adjusted according to the difference in aging degrees between the first and second segments. The greater the difference in aging degrees between the two segments, the larger Al’ will be. As the aging degrees of both segments decrease, Al’ also decreases.

[0065] According to an embodiment of the present disclosure, the position of the second DC / DC converter 22 can be adjusted by changing the point at which the first side of the second DC / DC converter 22 is coupled to the electrolyzer string 200. Through such adjustments, the first segment can contain a larger or smaller number of electrolyzers, and correspondingly, the second segment can contain a smaller or larger number of electrolyzers. These adjustments can optimize the hydrogen production efficiency of the entire electrolyzer string 200 in a more flexible manner, maximizing the hydrogen production rate and balancing the aging degrees of the entire electrolyzer string 200. It should be noted that such adjustments will place higher requirements on the electrical isolation of the second DC / DC converter; thus, the electrical isolation characteristics of the converter must fully account for the isolation requirements at different coupling points to the electrolyzer string 200.

[0066] According to an embodiment of the present disclosure, a larger number of first and / or second DC / DC converters can be configured in the electrolyzer string to create additional segments. This allows for more precise control over the operation of the entire electrolyzer string, further optimizing the hydrogen production efficiency and better balancing the aging degrees of the electrolyzer string.

[0067] The control mode of injecting current into the first segment and drawing current from the second segment has been described above as an example. According to embodiments of the present disclosure, the control mode of drawing current from the first segment and injecting current into the second segment can also be implemented in a similar manner. The choice between the two control modes is determined by the relative aging status of the electrolyzers in the two segments. When the relative aging status of the two segments changes, the control system can switch from one control mode to another.

[0068] In another embodiment, the auxiliary power supply unit 20 includes an energy source in addition to the first and second DC / DC converters described above. The previous descriptions of the first and second DC / DC converters also apply here, including their location settings, quantityadjustments, and so on, which will not be repeated. Additionally, the second sides of these 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.

[0069] One scenario of this embodiment is that the control system 30 manages each DC / DC converter to either draw current from the energy source and inject it into a corresponding segment or draw current from a segment and inject it back into the energy source. The current exchanged between each DC / DC converter and the energy source can be individually controlled and adjusted, ensuring that the total current drawn from the energy source equals the total current injected into it. In other words, the net current exchanged between these converters and the energy source remains zero. In this case, the energy source serves as an energy buffer.

[0070] Another scenario in this embodiment is that the control system 30 manages each DC / DC converter to either draw current from the energy source and inject it into a corresponding segment or draw current from a segment and inject it back into the energy source. The current drawn or injected between each DC / DC converter and the energy source can be individually controlled and adjusted. In this case, the total current drawn from the energy source may not equal the total current injected into it, meaning the net current exchanged between these DC / DC converters and the energy source is not zero. Consequently, the difference between the total current drawn from the energy source and the total current injected into it can be compensated by the energy source, allowing it to provide additional current or draw additional current as needed.

[0071] Figure 4 shows an example in which the auxiliary power supply unit 20 includes first and second DC / DC converters along with an energy source. Referring to Figure 4, the auxiliary power supply unit 20 includes first DC / DC converters 21 and 23, a second DC / DC converter 22, and an energy source 26. The first DC / DC converter 21 is connected between the positive DC terminal 10A of the main converter and the top end electrolyzer 201. The first DC / DC converter 23 is connected between the negative DC terminal 10B of the main converter and the bottom end electrolyzer 20n. The second DC / DC converter 22 is coupled between electrolyzers 202 and 203. Furthermore, the first sides of the first DC / DC converters 21 and 23 and the first side of the second DC / DC converter 22 are connected to the electrolyzer string, respectively. The second sides of the first DC / DC converters 21 and 23 and the second side of converter 22 are connected in parallel to each other while also being connected in parallel to the energy source 26.

[0072] As shown in Figure 4, the electrolyzers 201 and 202 located between the top first DC / DC converter 21 and the second DC / DC converter 22 form a first segment, while the electrolyzers 203 to 20n between the second DC / DC converter 22 and the bottom first DC / DC converter 23 form a second segment. The control system 30 manages these DC / DC converters 21-23 to ensure that the current flowing through each segment and the current interacting with the energy source 26 satisfy the following equations (3)-(6):

[0073] 11=1+ All (3)

[0074] 12=11 -AI2 (4)

[0075] I2+AI3=I (5)

[0076] AI=AI1-AI2+AI3 (6)

[0077] where II presents the current flowing through the first segment, 12 presents the current flowing through the second segment, All presents the first current drawn by the DC / DC converter 21 from the energy source 26, AI2 presents the second current injected by the DC / DC converter 22 into the energy source 26, AI3 presents the third current drawn by the DC / DC converter 23 from the energy source 26, and Al presents the sum of currents exchanged between these DC / DC converters and the energy source 26.

[0078] According to an embodiment of the present disclosure, each of the first to third currents can be independently controlled and adjusted. In other words, the current exchanged between each DC / DC converter and the energy source 26 is also independently controlled and adjustable. This control allows for more precise management of each segment's operation, optimizing the hydrogen production efficiency of the entire electrolyzer string, maximizing the hydrogen production rate, and better balancing the aging of the entire electrolyzer string.

[0079] As mentioned above, the sum of the currents exchanged between these DC / DC converters and the energy source 26, denoted as Al, can be zero. In this case, the sum of the first current All drawn by the DC / DC converter 21 from the energy source 26 and the third current AI3 drawn by the DC / DC converter 23 from the energy source is equal to the second current AI2 injected by the DC / DC converter 22 into the energy source 26. The sum of the currents exchanged between these DC / DC converters and the energy source 26, Al, may not be zero. In this case, the sum of the first current All drawn by the DC / DC converter 21 and the third current AI3 drawn by the DC / DC converter 23 from the energy source 26 will be either greater than or less than the second current AI2 injected by the DC / DC converter 22 into the energy source 26.

[0080] According to an embodiment of the present disclosure, the energy source 26 can be implemented in various ways.

[0081] 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.

[0082] 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.

[0083] In an embodiment, power for an isolated energy source 26 can be sourced from the DCoutput of the main converter, through a separate converter, or from the electrolyzer string 200 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.

[0084] In another example, the energy source 26 can be implemented by means of an energy storage string, an electrolyzer string or other components capable of providing and storing energy.

[0085] 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 200.

[0086] 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.

[0087] In this example, as shown by the dashed line in Figure 5B, the energy source 26, which serves 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.

[0088] For example, referring to Figure 5C, the energy source 26 can be implemented by means of an additional electrolyzer string 210. In this example, the DC / DC converter 21 divides the electrolyzer string 200 into two segments, 200A and 200B, and the additional electrolyzer string 210 into two segments, 210A and 210B. The segments 200A and 200B include electrolyzers before and after the DC / DC converter 21, respectively. The segments 210A and 210B include electrolyzers before and after the DC / DC converter 21, respectively. The DC / DC converter 21 can be operated to regenerate the current flowing through one or more of these segments.

[0089] According to an embodiment of the present disclosure, multiple electrolyzer strings can be connected on the DC side of the main converter. One or more DC / DC converters can be coupled to each electrolyzer string in the manner described above to regulate the current flowing through one or more segments of the electrolyzer string. This approach allows for the simple and flexible expansion of the number and scale of electrolyzers.

[0090] Figure 6A illustrates an example of coupling multiple electrolyzer strings on the DC side of the main converter. As shown in Figure 6 A, x electrolyzer strings S_1 to S_x are connected between the positive and negative DC terminals 10A and 10B of the main converter. These electrolyzer stringsare arranged in parallel, with each string coupled to multiple DC / DC converters. The coupling of these DC / DC converters is similar to that described for the DC / DC converters with reference to Figure 4. The regulation of the current in several segments of each electrolyzer string, as well as the interaction between the DC / DC converters and their corresponding energy sources, follows a similar approach to that described with reference to Figure 4. For example, the segment currents Ill and 112, along with the regulation currents All 1, AI12, and AI13 for the electrolyzer string S_l, satisfy Equations similar to those in Equations (3)-(6). Similarly, the segment currents Ixl and 1x2 of the electrolyzer string S_x , along with the regulated currents AIxl, AIx2, and AIx3, also satisfy Equations similar to those in Equations (3)-(6).

[0091] Figure 6B shows another example of coupling multiple electrolyzer strings on the DC side of the main converter. As shown in Figure 6B, the DC side of the main converter provides a bipolar DC power supply, allowing multiple electrolyzer strings S_l~S_x, as illustrated in Figure 6A, to be connected in parallel between each pair of positive and negative DC terminals. Multiple DC / DC converters are coupled to each electrolyzer string, and the relevant descriptions provided earlier also apply here. In the configuration shown in Figure 6B, 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.

[0092] Below, embodiments of the control system 30 are described.

[0093] 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.

[0094] In an embodiment of the present disclosure, the system controller 34 can receive information from other controllers. Other controllers include, for example, electrolyzer controllers (not shown) and a power network controller (not shown).

[0095] 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 the electrolyzer string 200, 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 electrolyzercontrollers 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.

[0096] 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.

[0097] 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.

[0098] Additionally, a segment of an electrolyzer string can be operated separately if there are faulty or compromised electrolyzers within that segment. For example, the control system 30 can manage the DC / DC converters to reduce the current of the compromised segment to zero. This allows the current flow from the main converter to be directed through an auxiliary path and then injected into healthy segments.

[0099] For example, referring to Figure 1 , if there is a faulty or severely aged electrolyzer in the first segment, the control system 30 manages the DC / DC converters 21 and 22 to direct the main current I from the positive DC terminal 10A into the auxiliary path, which is then injected into the second segment.

[0100] Examples of another aspect of the present disclosure relate to control methods for controlling a converter system for powering at least one electrolyzer string.

[0101] 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 Figures 7 and 8.

[0102] 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 notbe repeated.

[0103] At block 804, the system controller 34 determines the degree of aging of each segment of the electrolyzer string, for example, the degree of aging of the first segment and the second segment, based on the obtained electrolyzer-related parameters.

[0104] In an embodiment of the present disclosure, the aging degree of a segment refers to the overall aging degree of all the electrolyzers contained in the segment. For example, the aging degree of a segment can be represented by the arithmetic average of the aging degrees of all the electrolyzers in the segment. For another example, the aging degree of a segment can be represented by the weighted average of the aging degrees of all the electrolyzers in the segment. One way of weighted averaging is that the more serious the aging degree of the electrolyzer, the greater the weight. Another way of weighted averaging is to first assign equal weights to all the electrolyzers in the segment, then increase the weight of the most severely aged electrolyzer and decrease the weight of the least severely aged electrolyzer.

[0105] In an embodiment, 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).

[0106] At block 806, the system controller 34 determines the adjustment current based on the difference in aging degrees between adjacent segments of the electrolyzer string 200, so as to increase the hydrogen production efficiency of the entire electrolyzer string. For example, referring to Figure 7, the system controller 34 determines the current AF based on the difference between the aging degree of the first segment and the aging degree of the second segment, so that the total hydrogen production rate of the two segments is maximized, for example, by light-loading the severely aged segment and heavy-loading the healthy segment, thereby maximizing the hydrogen production rate and balancing the life of the entire electrolyzer string 200.

[0107] In an embodiment, the system controller 34 determines the adjustment current by referencing a pre-created lookup table that correlates aging degree differences to adjustment current values. The lookup table, which serves as a database, contains optimal adjustment current values for various differences in aging degrees. Upon detecting a difference in aging degrees between adjacent segments within the electrolyzer string 200, the system controller 34 will retrieve the corresponding adjustment current value from the lookup table.

[0108] In another embodiment, the system controller 34 employs a trained Al model to determine the adjustment current. This Al model, by learning and analyzing a large amount of historical data, canpredict the optimal current regulation strategy for different aging degrees. When the system controller 34 detects a difference in aging degrees between adjacent segments, it inputs this difference information into the Al model. The Al model then outputs the optimal adjustment current value.

[0109] 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 AF.

[0110] 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.

[0111] 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.

[0112] At block 814, the system controller 34 monitors the difference in aging degrees of adjacent segments and determines a new adjustment current based on the monitored change in the difference.

[0113] According to examples of the present disclosure, DC-DC converters and their control systems can also provide information regarding the health and aging of the electrolyzers to which they are connected. For instance, a DC-DC converter can measure various operational parameters, such as the voltage across an electrolyzer or a group of electrolyzers, and the current flowing through them. These measurements can be used for monitoring and estimating internal resistance and other electrolyzer-related parameters. This information can then be utilized by the electrolyzer controller or system controller for condition-based operation of the electrolyzer system / hydrogen production plant.

[0114] At block 816, the system controller 34 determines a new setpoint for each DC / DC converter.

[0115] At block 818, the system controller sends the new setpoints to corresponding converter controllers. Then, each converter controller controls the associated converter according to the received setpoint (i.e., the new setpoint).

[0116] According to an embodiment, the control method 800 further includes a process for providing grid services while adjusting the current of each segment in the electrolyzer string 200 to reduce (minimize) losses and improve (maximize) hydrogen production efficiency. 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 improved hydrogen production efficiency and capacity for the hydrogen plant, while also providing grid services.

[0117] For example, the system controller 34 receives power network-related parameters from thepower 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 the electrolyzer string 200 can meet the active and reactive power setpoints. The power change capability of the electrolyzer string 200 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 200.

[0118] 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.

[0119] If the evaluation indicates that the active and reactive power setpoints cannot be met, the system 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.

[0120] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein. All structural and functional equivalent transformations to the elements of the various aspects of the present disclosure, which are known or to be apparent to those skilled in the art, are intended to be covered by the claims.

Claims

WHAT IS CLAIMED IS:

1. A converter system (100) for powering a plurality of hydrogen electrolyzers that are electrically coupled together to form at least one electrolyzer string (200), comprising:a main power supply unit (10) configured to provide bulk power to the at least one electrolyzer string (200) such that a main current flows through the at least one electrolyzer string (200);an auxiliary power supply unit (20) comprising at least one DC / DC converter (21), which is electrically coupled with the at least one electrolyzer string (200) to inject or extract an adjustable current to or from the at least one electrolyzer string (200); 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 (21) is sized based on, and operated with, a fraction of the total power transferred to the at least one electrolyzer string (200).

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 (21) is configured to exchange power with the energy source (26) to adjust current flowing through a segment of the at least one electrolyzer string (200).

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; and- 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 (21) is connected to another DC / DC converter that is coupled with the energy storage string; orthe energy source (26) comprises or is integrated with an additional electrolyzer string (210), and the at least one DC / DC converter (21) is coupled between the at least one electrolyzer string (200) and the additional electrolyzer string (210).

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 one electrolyzer string (200).

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 converter is coupled to a fuel cell string, andthe control system (30) is configured to control the main converter, either to inject fuel cell-generated power into the power network (300), through the main converter, to provide grid services, or to deliver the fuel cell-generated power to the at least one electrolyzer string (200), through the main converter, to enable a fault ride-through function in the power network.

9. 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.

10. The converter system (100) of claim 9, 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.

11. 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.

12. The converter system (100) of claim 6, wherein the auxiliary power supply unit (20) comprises: a first DC / DC converter (21) coupled between a positive DC terminal (10A) or a negative DC terminal (10B) of the main converter and an end electrolyzer of the at least one electrolyzer string (200); anda second DC / DC converter (22) coupled with the at least one electrolyzer string (200) in a location different from that of the first DC / DC converter (21).

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 at least one electrolyzer, 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 control system (30) is configured to: control the first DC / DC converter (21) to inject a first current to a first segment of the at least one electrolyzer string (200); andcontrol the second DC / DC converter to draw a second current from a second segment of the at least one electrolyzer string (200).

15. The converter system (100) of claim 14, wherein the first current is equal to the second current.

16. The converter system (100) of claim 14, wherein the first current is not equal to the second current; andthe difference between the first current and the second current is compensated by an energy source included in the auxiliary power supply unit (20).

17. The converter system (100) of claim 14, wherein the control system (30) is configured to adjust the first and second currents individually based on the difference in the degree of aging of the electrolyzers in the first segment and the second segment.

18. A control method for controlling a converter system (100) of any of claims 1-17, the control method comprising:controlling at least one of the main power supply unit (10) and the auxiliary power supply unit (20) for operating the converter system (100).

19. The control method of claim 18, wherein the step of controlling comprises:obtaining electrolyzer-related parameters including parameters that indicate the operating state of each electrolyzer in the at least one electrolyzer string (200);determining the degree of aging of each segment of the at least one electrolyzer string (200) based on the electrolyzer-related parameters;determining an adjustment current based on the difference in aging degrees between adjacent segments;determining a setpoint for the at least one DC / DC converter based on the adjustment current; and controlling the at least one DC / DC converter according to the setpoint.

20. The control method of claim 19, wherein the step of controlling comprises:monitoring the difference in aging degrees between adjacent segments;determining a new adjustment current based on the monitored change in the difference; determining a new setpoint for the at least one DC / DC converter based on the new adjustment current; andcontrolling the at least one DC / DC converter according to the new setpoint.

21. The control method of claim 18, wherein determining the degree of aging of each segment comprises calculating an arithmetic average of the aging degrees of all the electrolyzers in the segment; orcalculating a weighted average of the aging degrees of all the electrolyzers in the segment, wherein the more serious the aging degree of an electrolyzer, the greater the weight.

22. The control method of claim 18, wherein the step of controlling comprises: coordinately controlling the converter controller associated with the main converter and the converter controller associated with the at least one DC / DC converter such that the hydrogen production efficiency of the at least one electrolyzer string is improved while providing a required grid service.

23. The control method of claim 18, wherein the step of controlling comprises:in the case of a fault in a segment of the at least one electrolyzer string, controlling the at least one DC / DC converter such that the faulty segment is bypassed.

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