System and method for providing electrical power from renewable energy sources to electrical loads

Abstract

This invention provides a generation-to-load system. The system comprises a renewable energy source RES platform comprising a plurality of renewable energy sources; and a load platform comprising a plurality of electrical loads, the plurality of electrical loads comprising at least one of a first type of electrical load having a narrow input operation power range and at least one of a second type of electrical load having a wide input operation power range, wherein at least two of the plurality of electrical loads are connected in series with one another. The system comprises a High Voltage DC HVDC bus system configured to provide electrical connection between the RES platform and the load platform, to receive incoming power from the RES platform, and to output power to the load platform; and a controller operatively coupled to the HVDC bus system. The controller is configured to automatically regulate the power output by the HVDC bus system to the electrical loads in the load platform, and maintain a power balance between the RES platform and the load platform. A corresponding method of operating such a system is also provided.

Description

[0001] SP3186

[0002] 1

[0003] SYSTEM AND METHOD FOR PROVIDING ELECTRICAL POWER FROM RENEWABLE ENERGY SOURCES TO ELECTRICAL LOADS

[0004] Field of the Invention

[0005] This invention relates to a system for delivering electrical power from renewable energy sources to electrical loads. This invention also relates to methods for controlling such a system.

[0006] Background of the invention

[0007] Global energy systems are facing increasing challenges to meet strict carbon reduction targets. This results in the need to integrate massive amounts of renewable energy into the electrical power grid. However, the integration of such large-scale renewable energy -with its inherent stochastic and intermittent nature - is a huge challenge for the current ( supply-demand) electricity systems.

[0008] In some instances, it has been found that connecting the renewable energy sources directly to the electrical loads -i. e., implementing a 'generation-to-load' system -can reduce the pressure to the electricity grid. As an example, wind power can be generated by renewable energy sources corresponding to (offshore) wind turbines and converted into hydrogen (H₂) using electrical loads corresponding to water electrolyzers. This method allows grid supply-demand balance to be achieved in a cost-effective way without expensive grid expansions. In addition, the hydrogen generated in this (relatively) environmentally friendly manner can in turn be used as the feedstock and e-fuel to further decarbonize certain hard-to-abate sectors.

[0009] An example implementation of such a renewable generation-to-load system may be based on a medium-voltage50 / 60Hz AC collection structure, although other possible designs of the collection structure are possible. In a specific example involving a wind-to-hydrogen system, a plurality of wind turbines could be connected to a medium voltage (MV) AC bus, with the connection for each wind turbine involving two back-to-back inverters and a gridfrequency transformer. A plurality of water electrolyzers could constitute the loads and could be powered by rectifiers with step-down grid-frequency transformers. These transformers match the voltage between the terminals of the electrolyzers and the MVAC bus, and provide galvanic insulation between the MVAC bus and the electrolyzers to ensure the safety of the electrolyzers and their operators.

[0010] These grid-frequency transformers have a low operating frequency which results in them having a huge size and weight. This can be a challenge for implementations involving limited space and / or with high installation and maintenance difficulties, such as offshore scenarios. It has been considered to increase the AC frequency to reduce the transformer size. However, high frequency AC transmission is not currently feasible for long distance power transmission (thereby also resulting in a barrier for offshore applications ). AC collection systems also need to deal with high reactive power compensation, which increases the rating of the equipment.

[0011] Other energy collection system designs are therefore desirable to investigate and implement, and it is against this background that the present disclosure has been set.

[0012] Summary of the Invention

[0013] According to an aspect of the invention, there is provided a generation-to-load system. The system comprises a renewable energy source RES platform, itself comprisinga plurality of renewable energy sources; a load platform itself comprising a plurality of electrical loads; a High Voltage DC (HVDC) bus system; and a controller operatively coupled to the HVDC bus system. The plurality of electrical loads comprises at least one of a first type of electrical load having a narrow input operation power range and at least one of a second type of electrical load having a wide input operation power range. At least two of the plurality of electrical loads are connected in series with one another.

[0014] The High Voltage DC (HVDC) bus system is configured to provide electrical connection between the RES platform and the load platform, to receive incoming power from the RES platform, and to output power to the load platform.

[0015] The controller is configured to automatically regulate the power output by the HVDC bus system to the electrical loads in the load platform, and to maintain a power balance between the RES platform and the load platform. In order to provide this functionality, the controller is configured to: determine reference input electrical signals for each of the first and second electrical load types respectively, the reference input electrical signals indicating a desired input power for the associated electrical load type; determine, based on the reference input electrical signals, first and second control variables arranged to enable the controller to regulate the power output to first and second electrical load types respectively; and vary a voltage of the HVDC bus system and control the power output to the first and second electrical load types using the respective first and second control variables.

[0016] The above-described system is able to easily handle multiple loads of different types and having different properties (e. g., flexibility). Additionally, the systemis able to effectively manage the power balance between the RE platform and the electrical load platform, thereby allowing any given electrical load to be operated as effectively as possible, across a variety of wind power conditions. As such, the above-described system is able to increase operational efficiency of the individual loads (and hence of the load platform as a whole). Additionally, the loads can be operated so as to minimise the need for operational maintenance, hence also increasing their individual lifetimes (as well as that of the overall load platform).

[0017] It should be appreciated that the pair of terms 'flexible' and 'unflexible', and the pair of terms 'wide' vs 'narrow' as used above and hereinafter are intended to indicate a rela tive difference in the operational power range of different types of loads. Furthermore, the 'flexibility' (or lack thereof ) for any given load is intended to provide an indication of the ability of the load to operate substantially continuously at a low power, as well as an indication of the dynamic performance (ramp-up / down rates ) of the load.

[0018] It is further noted that although the system involves at least some of the loads being connected in series with one another, it is not mandatory for all loads to be connected in series with one another (although this is a possible implementation). Some loads may instead be connected in parallel.

[0019] Moreover, in this document, the term 'High Voltage' has been used to refer to systems with operational voltages equal to or above 1kV. This is generally in line with accepted standards within the industry, although it should be noted that this voltage range also includes systems having what is sometimes referred to in the industry as 'Medium Voltage' (MV). The term 'High Voltage'as used herein therefore should be understood to encompasses both HV and MV systems.

[0020] Finally, it should be noted that the above-mentioned reference 'electrical signals' are indicative of reference values for certain parameters / properties of the system component, for example, current, voltage and / or power.

[0021] In some instances, the load platform may further comprise a plurality of DC-DC converters, each DC-DC converter being electrically connected to one of the plurality of electrical loads. In such a configuration, the DC-DC converters would control the power / voltage / current that each associated load draws from the HVDC bus system.

[0022] In some instances, the load platform may further comprise at least one energy storage system configured to store excess electrical energy and to provide the stored energy to one or more of the plurality of electrical loads. With the energy storage system, the loads can draw on the stored energy, which allows them to operate under conditions when it is not possible for the HVDC bus voltage to reduce further (e. g., low wind power or during a start-up procedure).

[0023] Optionally, the at least one energy storage system corresponds to: (i) a combined energy storage system configured to provide the stored energy to multiple ones of the plurality of electrical loads; and / or (ii) a distributed energy storage system comprising a plurality of energy storage sub-units, each energy storage sub-unit being connected to one of the plurality of electrical loads and configured to provide the stored energy to the connected electrical load. In more detail and where applicable, the energy storage system may be connected to input terminals of the DC-DC converters that are associated with the loads. Additionally, or alternatively,the energy storage system may be connected (directly) to an input terminal of the corresponding electrical load.

[0024] The energy storage systems provide particular benefit when connected to the first electrical load type, since the operation of these types of loads is inherently less flexible under low wind power conditions. However, the energy storage system may be connected to the second electrical load type, as an additional or alternative implementation.

[0025] In some specific examples, the system may correspond to a wind-to-hydrogen system. In these examples, the plurality of renewable energy sources may correspond to a plurality of wind turbines, and the plurality of electrical loads may correspond to a plurality of water electrolyzers. The above-described overall system is particularly useful when implemented in relation to such a wind-to-hydrogen system, since wind power is inherently very intermittent and difficult to regulate.

[0026] Other options for renewable energy sources also exist, particularly in relation to other example system implementations, such as for industrial power-to-heat scenarios or electrical-vehicle charging stations. In such instances, the renewable energy sources can take the form of PV panels or hydropower sources; whilst the loads can correspond to electrically heated furnaces or kilns, electrical vehicles. Where the electrical loads are water electrolyzers, the first electrical load type may correspond to an alkaline electrolyzer, and the second electrical load type may correspond to a PEM electrolyzer.

[0027] Optionally, the controller may be configured to determine the reference input electrical signals for each of the first and second electrical load types based on: (a) degradation rates of each of the first and second electrical load types; and / or (b) an aging model of eachof the first and second electrical load types. The system can additionally or alternatively take other features into account when considering how to calculate those reference input electrical signals. For example, it can make changes to mitigate the effects of degradation and / or aging to the electrical loads and thereby optimise load lifetimes as well as the overall maintenance schedule for the load platform.

[0028] In some examples, the controller is configured to apply a current rate (di / dt) limiter when determining the first control variable. The di / dt limiter can be used in this manner to limit the rate of current flowing through the loads (and specifically through the first type of load) to avoid too fast a ramp-up rate for those loads when altering the power and voltage distributions, since those loads are also inherently 'unflexible' and have slow dynamic performance.

[0029] In some instances, the controller is configured to monitor the voltage of the HVDC bus system and voltages of each of the plurality of electrical loads to determine the reference input electrical signals. The ability of the system to monitor (or sample ) the actual voltages of the system components in substantially real-time, means that the system can also change the reference input electrical signals that are determined and implemented automatically based on real-time fluctuations in those voltages. Optimum operational efficiency of the individual loads, and of the system as a whole, can therefore be achieved despite fluctuations in the power generated by the renewable energy sources.

[0030] In some cases, the reference input electrical signals correspond to reference input voltages. In those cases, the controller is further configured to perform the following functions to determine the first and secondcontrol variables: determine first and second reference input currents for the first and second electrical load types respectively based on the corresponding reference input voltages; and compare each of the first and second reference input currents with a monitored actual current for the first and second electrical load types respectively.

[0031] More specifically, in some of those instances the controller is further configured to perform the following functionality to determine the corresponding first and second reference input current: determine a reference current by sampling a voltage of the HVDC bus system and comparing the sampled HVDC bus system voltage with a reference HVDC bus voltage; monitor voltages of the first and second electrical load types; compare the reference input voltages with the corresponding monitored voltages to determine an associated compensation current component for each of the first and second electrical load types; and perform a summation of the compensation current component for each of the first and second electrical load types with the reference current.

[0032] According to another aspect of the present invention, there is provided a method for operating a generation-to-load system. The generation-to-load system comprises a renewable energy source RES platform, itself comprising a plurality of renewable energy sources; a load platform itself comprising a plurality of electrical loads; a High Voltage DC (HVDC) bus system; and a controller operatively coupled to the HVDC bus system. The plurality of electrical loads comprises at least one of a first type of electrical load having a narrow input operation power range and at least one of a second type of electrical load having a wide input operation power range. At least two of the plurality of electrical loads areconnected in series with one another. The High Voltage DC (HVDC) bus system is configured to provide electrical connection between the RES platform and the load platform, to receive incoming power from the RES platform, and to output power to the load platform.

[0033] The method enables automated regulation of power distribution by the HVDC bus system to the electrical loads in the load platform, whilst maintaining a power balance between the RES platform and the load platform. In order to achieve this function, the method comprises: determining reference input electrical signals for each of the first and second electrical load types respectively, the reference input electrical signals corresponding to a desired input power for the associated electrical load type; determining, based on the reference input electrical signals, first and second control variables for regulating the power output to first and second electrical load types respectively; and varying a voltage of the HVDC bus system and controlling the power input to the first and second electrical load types using the respective first and second control variables.

[0034] Any and all of the features and advantages set out above in relation to the generation-to-load system are equally applicable to its method of operation.

[0035] In some instances, the reference input electrical signals correspond to reference input voltages. In such cases, the method further comprises: determining first and second reference input currents for the first and second electrical load types respectively based on the corresponding reference input voltages; and comparing each of the first and second reference input currents with a monitored actual current for the first and second electrical load types respectively to determine the first and second control variables.In some specific instances, the method may further comprise determining the first and second reference input currents by: determining a reference current for the plurality of electrical loads by sampling a voltage of the HVDC bus system and comparing the sampled HVDC bus system voltage with a reference HVDC bus voltage; monitoring voltages of the first and second electrical load types; comparing the reference input voltages with the corresponding monitored voltages to determine an associated compensation current component for each of the first and second electrical load types; and summing the compensation current component for each of the first and second electrical load types with the reference current.

[0036] The above-described methods provide a mechanism for ensuring that the control variable takes into consideration changes are occurring elsewhere in the system.

[0037] Brief Description of the Drawings

[0038] Figure 1 schematically illustrates an example HVDC generation-to-load system, according to an aspect of the present invention;

[0039] Figures 2 and 3 each schematically illustrate specific implementations of the system of Figure 1 in the context of a wind-to-hydrogen system;

[0040] Figures 4 illustrates an example method for controlling the systems of any of Figures 1 to 3, according to an aspect of the present invention;

[0041] Figure 5 illustrates a control scheme configured to automatically regulate the power distribution between the loads in the system of Figure 3, according to an aspect of the present invention;

[0042] Figures 6A and 6B illustrate respectively circuit diagrams for an example DC-DC converter and anelectrolyzer that may be used to simulate the HVDC generation-to-load system shown in Figure 3;

[0043] Figure 7 illustrates an example implementation of electronic components that can be utilised to simulate implementation of the HVDC generation-to-load system shown in Figure 3; and

[0044] Figure 8 illustrates simulation results for the example implementation of the system shown in Figure 7.

[0045] These drawings depict one or more implementations in accordance with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.

[0046] Detailed Description of the Drawings

[0047] In view of the potential drawbacks of the AC collection system that were discussed above, DC power transmission and collection systems have also been investigated for use in generation-to-load systems.

[0048] Generally, a smaller platform and corresponding lower investment can be achieved for a DC collection system due to the reduced weight and volume of the constituent electrical devices, such as transformer.

[0049] An example high voltage DC generation-to-load collection system (hereafter simply referred to as an 'HVDC system' for ease of reference ) is described in copending patent application WO 2023 / 144359 Al by the present Applicant.

[0050] This HVDC system comprises renewable energy equipment; a voltage source converter (VSC) sub-system; and an AC / DC converter sub-system comprising a plurality of AC / DC converter units connected in series between the renewable energy equipment and the VSC sub-system. The renewable energy equipment includes a plurality of renewable energy sources (RES ) such as wind turbines or PVpanels. The VSC sub-system comprises a plurality of VSCs connected to one another in series.

[0051] The connection between the AC / DC converter subsystem and the VSC sub-system corresponds to an HVDC link (e. g., one or more HVDC transmission lines ). Electric power transmission equipment is used to provide the electric power from the VSC sub-system to a plurality of electrical loads.

[0052] In this HVDC system, although long distance power transmission is possible due to the high voltages, a bulky grid-frequency transformer still needs to be used, which maintains the challenges discussed in the background section above. Moreover, the HVDC system described above is controlled in a manner that involves maintaining a substantially steady-state HVDC link voltage (i. e., within a specific narrow voltage range), as well as maintaining a power production rate within a designated parameter. It is desirable to be able to make improvements to the abovedescribed system for efficiency and ease of operation.

[0053] When designing a load platform, it is possible to use loads with different properties. For example, in a hydrogen generation load platform, different types of electrolyzers can be used. Typically, a first type of electrolyzer would have a relatively narrower operational power range, such that the electrolyzer cannot operate continuously with a low power, and slow dynamic performance ( such that ramp up and down times are slow). An example of this type of electrolyzer would be an alkaline electrolyzer. A second type of electrolyzer would have a relatively wider operational power range, such that the electrolyzer could be operated continuously under both high and low power conditions (for example, a PEM electrolyzer). Those electrolyzers with the wider operational ranges are typically considered to be more'flexible' than their narrower operational range counterparts. For ease of reference hereafter, electrolyzers having relatively narrow operational voltage ranges will be referred to as 'unflexible', whilst electrolyzers having relatively wide operational voltage ranges will be referred to as 'flexible'.

[0054] When designing the load platform, two options are available: ( 1 ) to use only flexible loads; and (2 ) to use a combination of flexible and unflexible loads. In different application examples, one option or the other might be preferable. Implementing a system based on option ( 1 ) would likely improve power tracking performance; however, sometimes option (2 ) may have to be used in cases where there is no ability to select the load type.

[0055] Furthermore, the use of different load types in option (2 ) helps to reduce costs (as unflexible loads are typically less costly), improves energy management, enhances dynamic operation and potentially may increase the working life of electrolyzers. Implementing option (2 ) may however still pose a challenge in the cases in which the RES generates energy outside the bounds of the unflexible loads.

[0056] AU 2008 / 313636 Al describes a production system for electric energy and hydrogen in which a hybrid electrolyzer system is implemented and two different kinds of electrolyzers are used. Specifically, a 'rapid dynamic response' type of electrolyzer (e. g., a 'flexible' PEM electrolyzer) and a ' slow dynamic response' type of electrolyzer (e. g., an 'unflexible' alkaline electrolyzer).

[0057] However, in this known system, the issues associated with implementing large heavy transformers still apply; and there is also a need to implement active energy management to handle energy fluctuations that arise from the intermittent nature of the RES. The system thereforeincludes a control device which manages the hydrogen production of the electrolyzers as a function of the requirements of the electricity network operator or the internal requirements of the wind farm. The hydrogen production of the electrolyzers can therefore be increased or decreased in such a way that, on the one hand, the fluctuations of power inj ected to the electricity network are eliminated and, on the other hand, an active power reserve is maintained. More specifically, the control device can control the energy in such a way that when excess energy is generated, it is utilized to produce hydrogen. Conversely, when there is insufficient energy, the hydrogen is reconverted into electric energy for inj ection to the electricity network.

[0058] The current Applicant has appreciated the limitations that are associated with the above prior art systems. For example, difficulties arise in operating the control device to control the operation and hydrogen production of the electrolyzers at a rate that will match the speed of energy fluctuations - ramping down when the wind power drops and ramping up when the wind power increases. This is particularly true in instances of offshore RES (and onshore electrolyzers ) that do not have a direct grid connection to help absorb the power differentials. The current Applicant has therefore developed a new cost-effective and reliable generation-to-load system and a corresponding control method / strategy. This improved system and method achieves a balance between the generated power from the sources and the consumed power by the loads; and also enables automated regulation of the power distribution between different loads in the load platform. As a result, improved operation of the system is achieved.Aspects of this improved system and control method according to aspects of the present invention are illustrated in Figures 1 to 5.

[0059] Referring first to Figure 1, a generalised generation-to-load system according to an example implementation of the present invention will be described. In its most general sense, the system 100 comprises a renewable energy (RE) platform 10, the RE platform 102 itself comprising a plurality of renewable energy sources (RES ) 104 that are arranged to generate electrical power from renewable energy (e. g., wind turbines, PV panels etc. ). The system 100 also comprises a load platform 106 that itself comprises a plurality of electrical loads 108, each load being configured to utilise the generated electrical power (for example, each load 108 may correspond to one or more water electrolyzers that use electrical power to produce hydrogen H₂).

[0060] The RE platform 102 is operatively connected to the load platform 106 via a DC connection system, and specifically via an HVDC bus system 110, which may take the form of one or more DC electrical communication buses or links. In the example shown in Figure 1, the HVDC bus system 110 comprises a pair of HVDC buses 110a, 110b that are connected to one another, and to a respective one of the RE and load platforms 102, 106.

[0061] Additionally, the RE platform 102 and the load platform 106 each comprise power converters. Specifically, the RE platform 102 comprises a plurality of AC-DC converters 112, whereby each AC-DC converter 112 is connected to a corresponding RES 104. The AC-DC converters 112 are configured to receive incoming AC power generated by the RES 104, and to convert it to DC power for output to the HVDC bus system 110 (via the RES-side HVDC bus 110a). The load platform 106 comprises a plurality of DC-DC converters 114, whereby each DC-DC converter 114 is connected to a corresponding load 108. The DC-DC converters 114 are configured to receive incoming power from the HVDC bus system 110 (via the load-side HVDC bus 110b), and to provide the converted DC power to their corresponding load 108. More specifically (and as can be seen in Figure 1 ), input terminals 115a of each DC-DC converter 114 are connected to the load-side HVDC bus 110b in series; and an output terminal 115b of each DC-DC converter is connected to the corresponding load 108. As such, the loads 108 are considered to be connected in series.

[0062] The specific form taken by the components in the system 100 may vary depending on desired implementation context. Alternative implementations or variations of the system 100 shown in Figure 1 are illustrated in the systems 100a, 100b that are shown in Figures 2 and 3 respectively.

[0063] In the system variations 100a, 100b illustrated in Figures 2 and 3, each RES 104 corresponds to a wind turbine string, which in turn comprises several or tens of individual wind turbines. The load platform 106 corresponds to a 'Hydrogen (H2) generation platform', where each load 108 corresponds to a water electrolyzer and the load platform 106 as a whole may comprise tens or hundreds of water electrolyzer loads 108 and their respective DC-DC converters 114.

[0064] Furthermore, the topologies of the AC-DC converters 112 and DC-DC converters 114 are not fixed. In some specific implementations (for example, those shown in Figures 2 and 3 ), these converters 112, 114 may each operate at medium ( switching) frequencies to allow for a reduced size and weight (in comparison with similar components operating at higher frequencies ). Such 'medium'frequencies may fall in the range of 200 Hz to 10 kHz. It is also envisaged that in such implementations, the input voltages of the DC-DC converters 114 would typically range from hundreds of Volts to several kilo Volts (kV). This would allow for utilization of relatively low-voltage commercially available semiconductor switches within them; for example, 3. 3kV or 4.5kV-level IGBTs ( insulated-gate bipolar transistors ) or IGCTs (integrated gate-commutated thyristors ). This would reduce the difficulty of manufacturing the necessary DC-DC converters (particularly in comparison to converters that have higher input voltages).

[0065] In some implementations, the system 100 may comprise multiple different types of (electrolyzer) loads, whereby each type of electrolyzer load has a different input operational power range and therefore has a different 'flexibility' ( in line with the terminology introduced earlier in this document). For example, in the systems 100a, 100b that are shown in Figures 2 and 3, two different types of electrolyzer loads 108a, 108b are envisaged for implementation - denoted as Electrolyzer 1 (El ) and Electrolyzer 2 (E2 ) loads - whereby the El loads 108a correspond to unflexible loads having relatively narrow (er) input power ranges, while the E2 loads 108b correspond to flexible loads having relatively wide ( r) input power ranges. As an example, a narrower input power range would correspond to 50% to 100% of the rated power for that load, whereas a wider input power range would correspond to 0% to 100% of the rated power for that load. It should be appreciated however that more or fewer different types of electrolyzer loads may be implemented as desired.

[0066] One challenge in an islanded system ( 'islanded' being used in this context to mean a power system that hasno grid connection, as is the case for the currently described systems 100, 100a, 100b of this application) is to match the power profiles of the RES platform 102 and the load platform 106. Power generation by an RES 104 is typically controlled to maximize power production (for example, via the application of a maximum power point tracking algorithm). There is hence a need to control the power provided to the corresponding loads 108 to match the power generation profile of the RES 104. However, power matching is a challenge, particularly when the generation profile does not necessarily follow a theoretical / desired maximum power point.

[0067] To address this challenge, one or more energy storage systems 116a, 116b, 116c may be incorporated into the load platform 106.

[0068] As shown in Figure 3, there are several options for the connection of the energy storage systems. A first option involves implementing a ( single) centralized energy storage system 116a, connected in parallel with the input terminals 115a of the series-connected DC-DC converters 114a that are associated with El loads 108a, due to their narrower operational power ranges and slow dynamic performance. A second option involves implementing a distributed energy storage system comprising a plurality of energy storage system sub-units 116b, each sub-unit 116b being connected in parallel with one of the associated DC-DC converters 114a that are associated with El loads 108a. A third option also involves implementing a distributed energy storage system comprising a plurality of energy storage system sub-units 116c, but in this case, each sub-unit 116c is connected to an input of the associated El load 108a.

[0069] Although not shown in Figure 3, it is also possible to connect the energy storage systems 116a, 116b, 116c tothe DC-DC converters 114b associated with the E2 loads 108b, in accordance with any of the three options set out above. The three options may also be combined within the same load platform as desired.

[0070] The implementation of energy storage system ( s ) allows for the compensation of a power differential that might arise due to a mismatch of power regulation rate between the RES platform 102 and the load platform 106. Specifically, this mismatch may result from a relatively slow power ramp-up rate of the El loads 108a (resulting from their slow dynamic performance ), and the fast power variation rate of the RES 104 (by its nature).

[0071] Such a power differential would typically arise when the wind power falls due to a reduction in wind speed. In such circumstances, the electrolyzer loads would ideally decrease their power consumption to maintain a substantially stable voltage of the HVDC bus system 110. However, since the regulation rate of the power for El loads 108a is also typically limited (usually by a di / dt limiter), these electrolyzer loads are unable to decrease as fast as the wind power drops, leading to the power differential. It would be desirable for the E2 loads 108b to compensate for this power differential by decreasing their consumption power faster to ensure more power is transferred to the El loads 108a. However, this process tends to fail when ( 1 ) the wind power decreases too fast; and / or (2 ) when the consumption power of the El loads 108a is larger than the input wind power.

[0072] By implementing energy storage system ( s ), fluctuations in the voltage of the HVDC bus system 110 and correspondingly of the input voltages of the DC-DC converters 114a, 114b can be suppressed. Moreover, the presence and function of the energy storage system ( s ) can be used for charging the RES grid during a start-upprocedure. This mitigates challenges that are typically associated with the start-up procedure: the power generated by the wind turbines alone may not be sufficient to initiate the start-up process of the overall system, since the power is needed to charge all capacitors present in the system (and hence needs to provide a high charging current over a long charging period). The use of energy storage systems provides additional power that can reduce the pressure on the wind turbines and increase the likelihood of a successful start-up process.

[0073] A control strategy has also been developed by the current Applicant to allow the system to operate under low wind powers. In its most general sense, the control scheme involves implementing a mixed load platform 106 (i. e., incorporating loads of different flexibilities) - for example as shown in the systems 100a, 100b of Figures 2 and 3, in combination with allowing flexibility and variation in the voltage of the HVDC bus system 110.

[0074] The devised control strategy aims to control the operation of, and power provided to, the load platform 106 such that it matches the power generation profile of the RES platform 102 as closely as possible. The control strategy is able to achieve this desired result whilst nevertheless maintaining flexibility in the design of the load platform such that it can include different types of electrolyzer loads and thereby achieve the associated benefits derived therefrom. More specifically, the El loads 108a are more cost effective whilst the E2 loads 108b have good power tracking performance and a wide operating power range.

[0075] To summarise, the control strategy that has been devised involves each RES 104 (i. e., the wind turbine strings ) being operated at maximum power tracking mode as far as possible to realize sufficient utilization of windpower, whilst allowing the voltage of the HVDC bus system 110 to be controlled or altered based on the needs of the series-connected DC-DC converters 114 on the load platform 106. These DC-DC converters 114 are, in turn, operated in such a way as to regulate the power supply for the different types of electrolyzer loads 108. A balance can therefore be maintained between the generated and consumed power.

[0076] Implementing the control strategy can involve operating the DC-DC converters 114 on the load platform 106 in one of two main operation modes: ( 1 ) a first 'Balanced power distribution' mode in which the power and / or voltages to the El loads 108a and the E2 loads 108b is maintained the same; and (2 ) a second 'Variable power distribution' mode in which the input power and / or voltages for the El loads 108a can be regulated to be different to those of the E2 loads 108b. The first operation mode is typically adopted when it is desired to simply consume as much of the generated power as possible; and when the wind power is at a sufficiently high level. The second operation mode is typically adopted in order to optimise the operating efficiency of the load platform 106, and is particularly advantageous under conditions where the wind power is not at a maximum level.

[0077] When implementing the second operation mode, the voltage of the HVDC bus system 110 is allowed to vary. This is in contrast to other, more conventional, solutions where the HVDC system bus voltage is typically only allowed to vary within a very strict tolerance and the power distribution to the loads is not allowed to vary. By adopting the present control strategy, the DC-DC converters 114b connected to the E2 loads 108b can keep reducing their input voltage, since the power distribution ratio of the two types of electrolyzer is not fixed. As aresult, the input power of the El loads 108a would be maintained at or above their minimum operation value and the system can continue operating.

[0078] As a further advantageous aspect, even in the first 'balanced' mode, the HVDC bus system 110 voltage is allowed to vary within a relatively narrow range (i. e., within certain tolerances that avoid triggering system protection equipment) such that a wider range of values exists within which the HVDC bus system 110 can maintain a power match between the RE platform 102 and the load platform 106. This increased ability to perform power matching even in relation to small scale fluctuations increases the overall efficiency of the system.

[0079] In more detail, in the present systems 100, 100a, 100b, the HVDC system bus 110 voltage is allowed to decrease actively such that the DC-DC converters 114b connected to the E2 loads 108b can continue to reduce their input voltage. Operation of the system as a whole can thus be maintained by increasing the power output to the El loads 108a (via their associated DC-DC converters 114a) which allows these loads to work above their minimum power points. The present systems 100, 100a, 100b can therefore continue to operate substantially normally even in situations where the generated power from the RE platform 102 is low. On the other hand, when the wind power is high, the voltage of the HVDC system bus 110 can be allowed to increase to reduce the current flowing through the various connections and converters, decreasing the power loss and achieving high efficiency.

[0080] By implementing this dual-mode control strategy, it is unnecessary to cut off any electrolyzer loads from the system or to have to shut down the whole system under a low wind power situation (that nevertheless remains above the minimum operating power of the system). The dynamicperformance of the system is also improved under the low wind power situation.

[0081] A further benefit of utilising a control strategy incorporating the second operation mode is that a balance can be achieved in the degradation rates among different electrolyzers. It is important to emphasise that varying degradation rates of electrolyzer loads within the load platform 106 can have a significant impact on the likelihood of equipment failures and can disrupt the regular maintenance schedule, ultimately leading to increased operating costs. To address this issue, the above-described second operation mode can be utilised to dynamically adj ust the power allocation to any given electrolyzer. Specifically, the input power of an electrolyzer that is aging at a faster rate can be actively reduced, while the input power of an electrolyzer aging at a slower rate can be increased. Discrepancies in degradation rates of electrolyzers across the load platform 106 as a whole can be minimised, ensuring a more uniform and efficient operation across the load platform 106.

[0082] In another example use case, the second operation mode can also be employed to optimize the operating efficiency of the load platform 106 as a whole. The efficiency of the DC-DC converters 114 and of the electrolyzer loads 108 depends on their operating points -different converters and loads will have different efficiencies at different power points, therefore resulting in some operating points having a much better overall efficiency than others. The power losses of the DC-DC converters 114 and electrolyzer loads 108 can be modelled, in ways that the skilled person will be familiar with. Based on the results of this modelling, the appropriate power distribution to certain DC-DC converters114 and electrolyzer loads 108 can be determined to optimise the operating efficiency of the load platform 106.

[0083] A description of a control method, which utilises the above-described dual-mode control strategy, will now be provided with specific reference to a wind-to-hydrogen system, such as those shown in Figures 2 and 3. When implementing this method, it is assumed that power distribution will be balanced amongst a given type of electrolyzer load (i. e., power across all El loads 108a is balanced and power is also separately balanced across all E2 loads 108b). The efficiencies of the DC-DC converters, as well as the characteristics of the same type of electrolyzer loads, are also assumed to be the same. As such, the input voltages of the DC-DC converters 114 are expected to be the same amongst electrolyzer loads of the same type, but may differ when comparing different electrolyzer load types.

[0084] Before illustrating details of the control method, the meaning of some relevant parameters will first be defined in Table A. Boundary conditions associated with some of these parameters (particularly under specific operation modes ) are also defined below.

[0085] Parameters Meaning

[0086] Vbus Voltage of the HVDC bus system

[0087] Vbus_r Rated voltage of the HVDC bus system

[0088] Vbus_min Minimum voltage of the HVDC bus system

[0089] PWT Power generated by wind turbines

[0090] PwT_r Rated power of wind turbines

[0091] The minimum wind power to maintain normal PWT_min operation of system (When Pwi< PwT_m, the whole system will be shut down)

[0092] Pa Power for each El load

[0093]

[0094] Pp Power for each E2 load

[0095] Pa_r Rated power for each El load

[0096] Pp_r Rated power for each E2 load

[0097] Vin_aInput voltage of each El load

[0098] Vin_p Input voltage of each E2 load

[0099] Pa_mi n Minimum operating power of one El load Maximum input voltage of a DC-DC converter on Vin_max

[0100] H2 platform

[0101] Minimum input voltage of a DC-DC converter on Vin_min

[0102] H2 platform

[0103] N Number of El loads

[0104] M Number of E2 loads

[0105]

[0106] Table A: Meanings of parameters in a wind-to-hydrogen system

[0107] It is noted that the parameters

[0108]

[0109] and Vbus_min are usually defined by constraints associated with constants of the system and its components. For example, is typically defined based on the probability of a low-wind-power situation occurring and a desire to maximise expected returns. Pamin is typically set as a percentage (e. g., 20% ) of the rated power of an El load; and Vbus_min usually depends on various requirements of safe operation and the fault-handling equipment. As part of the following calculations, optimization of the parameters N and M - the number of each type of electrolyzer; and

[0110]

[0111] and Vinmax- the minimum and maximum input voltages of the DC-DC converters 114a, 114b on the load platform 106 - is particularly desirable.

[0112] The effects on these parameters will now be considered under a variety of wind power conditions, such that an understanding of the desired control method can be achieved.In a low power scenario when the wind power decreases to PWT_min, the second control mode discussed above would be adopted such that the power to the E2 loads 108b can be actively reduced to ensure that the El loads 108a can operate at the minimum power that they require, i. e., Pa_min. Due to the series-connection structure of the components in the load platform 106, the input voltages of the DC-DC converters 114a, 114b will be proportional to the power consumed. Correspondingly, the input voltage of the DC-DC converters 114a connected to the El loads 108a will reach their maximum values; and the input voltage of the DC-DC converters 114b connected to the E2 loads 108b will reach their minimum values. Simultaneously, the voltage of the HVDC bus system 110 will also decrease to its minimum Vbus min.

[0113] In such a low wind power scenario, the input voltages Vina and Vinb of the DC-DC converters 114a, 114b for each the El and E2 loads can be calculated using the below pair of equations in ( 1 ). Boundary conditions for these input voltages can then also be defined: the voltage value Vin a of the El loads 108a will always need to be less than Vin max,’ and the voltage value Vin_pof the E2 loads 108b will always need to be greater than

[0114]

[0115] V

[0116] 1 NP

[0117] Vm- - K < V

[0118] K -NV

[0119] Vm

[0120]

[0121] M

[0122] On the other hand

[0123]

[0124] a 'normal' ( higher ) wind power we can obtain other boundary conditions:

[0125] NP +MP > P F (^ +M )F,,_nlln< Fte-r< (V +M )F,,

[0126]

[0127] in which the value FWT is a capacity factor of the wind power (relating to utilisation), considering the investment and profit of the whole system.

[0128] A general control method that varies depending on the level of wind power in any given scenario can then be defined considering these boundary conditions.

[0129] In a first scenario, the wind power is relatively high - i. e., the wind power PWT is greater than a certain predefined value PWT b, determined using the following equation:

[0130] PWT _b = (M +min

[0131]

[0132] ( 4 )

[0133] In this scenario, as there is sufficient wind power available, there is no need to vary the power distribution between the two types of electrolyzer loads, and the first ( 'power balanced' ) operation mode discussed previously can be implemented. In this mode, the method would aim to simply balance the input voltages of the DC-DC converters 114a, 114b that are connected to different the different electrolyzer load types, such that an appropriate voltage can be drawn by each converter and load.

[0134] In a second scenario, the wind power P T is less than the predefined value PWT b but greater than the minimum operating power PWT min. In this scenario, there is now a need to vary the power distribution between the two types of electrolyzer loads 108a, 108b, and the second

[0135] ( 'variable power' ) operation mode is therefore implemented. The method would involve controlling the group of DC-DC converters 114a that are connected to the El loads 108a to increase their input voltage proportions (in terms of the HVDC bus system 110 voltage) whilst maintaining voltage balancing amongst those El loads 108a. Correspondingly, the method would also involve controlling the group of DC-DC converters 114b that are connected tothe E2 loads 108b to reduce their input voltages (proportions ), whilst also maintaining voltage balancing amongst those E2 loads 108b. In other words, the DC-DC converters 114a connected to the El loads 108a will be controlled to have higher input voltages than the DC-DC converters 114b connected to the E2 loads 108b; but there will nevertheless be voltage balancing amongst the group of El loads 108a and separately amongst the group of E2 loads 108b.

[0136] In a third scenario, the wind power PWT is less than the minimum wind power PWT min necessary for the system to operate. In this scenario, the entire system will shut down.

[0137] In any of the above-described three scenarios, the method would aim to allow the voltage of the HVDC bus system 110 to vary. This voltage can be defined by the following equation:

[0138] V

[0139]

[0140] , =V, ~km / T\P„^ -PJI / T\=V, -k, \I, -i, | r l-sVT where the kPWT and kibus are droop coefficients; Ibus_r is the given boundary current and ibus is the current of the HVDC bus system 208. As the skilled person will be aware, 'droop' is a control mechanism used in relation to power generators (wind turbines ) to share the load between multiple generators that are connected (in parallel).

[0141] As will be appreciated from equation (5 ), a decrease in the wind power P T results in a corresponding decrease in the HVDC bus system voltage Vbus. This also results in a corresponding decrease in the voltage stress for the DC-DC converters 114a that are associated with the El loads 108a.

[0142] Taking all the above information about operation modes, parameter values and dependencies into consideration, along with the various boundary conditions and scenarios that apply, a general control method can bedefined. This method 400 is illustrated in Figure 4, and is currently envisaged as being implementable for any of the systems 100a, 100b that comprises loads having different flexibilities. The method 400 is configured to enable automatic regulation of power distribution, by the HVDC bus system 110, to the electrical loads 108a, 108b in the load platform 106; and whilst maintaining a power balance between the RES platform 102 and the load platform 106.

[0143] The method 400 is intended to be implemented by a processor, in communication with a memory storing instructions that when implemented cause the processor to implement the corresponding desired method functionality. For example, control variables are envisaged as being derived and provided to a controller (which may correspond to the above-described processor, or to a different processing entity entirely) to implement the desired power distribution and balancing that is to be achieved by the method 400.

[0144] The method 400 comprises a first step 402 in which reference input values of certain properties / parameters - i. e., voltages, reference input powers and / or reference input currents - for each type of load (e. g., El loads 108a and E2 loads 108b) are determined, via one or more different mechanisms that will be described subsequently with reference to Figure 5. These reference input values (voltages, powers and / or currents ) correspond to a desired input voltage, power and / or current for each type of load 108a, 108b.

[0145] The method 400 comprises a subsequent step 404 in which control variables, for regulating the power output to each type of load (e. g., El loads 108a and E2 loads 108b), are derived using the previously determined reference input values. For example, control variablesrelating to current control can be derived and used for regulating the current input to each type of load.

[0146] Thereafter, the method 400 comprises a step 406 in which the HVDC bus system 110 voltage is varied; and a step 408 in which the power input to each type of load (e. g., El loads 108a and E2 loads 108b) is controlled and altered using the respective control variable. These final two steps 406, 408 may also be performed substantially simultaneously.

[0147] Turning now to Figure 5, this illustrates a control diagram 500 highlighting the detailed control actions and calculations that are taken, according to one specific implementation scenario, to achieve the desired results of the overall (general) control strategy and control method 400 set out above.

[0148] The control diagram 500 comprises four sub-diagrams. One sub-diagram shows a first control loop 502 comprising controls and calculations performed in relation to the voltage of the HVDC bus system 110. This first control loop 502 is therefore also referred to in Figure 5 as the 'HVDC bus voltage control' loop. A primary aim of the first control loop 502 is to determine and output an appropriate reference current value Iob for the electrolyzer loads 108a, 108b.

[0149] Another sub-diagram shows a second control loop 504 comprising controls and calculations performed in relation to power and / or voltage balancing for the two different electrolyzer load types 108a, 108b. This second control loop 504 is therefore also referred to in Figure 5 as the ' Variable voltage / power power distribution and vol tage balancing control' loop. A primary aim of the second control loop 504 is to use the Iob generated by the first control loop 502 to determine appropriate control variables Daj and Dpkfor regulating current input to the Elloads 108a and E2 loads 108b respectively. This second control loop 504 therefore enables automatic regulation of the power distribution between the El and E2 loads 108a, 108b, as well as voltage balancing for the groups of DC-DC converters 114a, 114b that are connected to the same type of load.

[0150] Another sub-diagram shows a third control loop 506 comprising controls and calculations performed in relation to further controlling the current that is drawn by the DC-DC converters 114a, 114b associated with the two types of loads 108a, 108b. This third control loop 506 is therefore also referred to in Figure 5 as the ' Inner output current control' loop. A primary aim of the third control loop 506 is to ensure ( safe ) regulation of the current to the electrolyzer loads 108a, 108b.

[0151] Considering the first control loop 502 in more detail, a reference voltage for the HVDC system bus Vbusis defined according to equation (5 ); and this value Vbusis limited to lie between Vbus_min and Vbus_max. The real-time (actual ) voltage of the HVDC system bus Vbus is then monitored or sampled by the first control loop 502, and compared with the reference voltage

[0152]

[0153] The difference between the theoretical and actual values is used to generate and output the reference current value IoThereafter, the second control loop 504 is configured to use the value of the reference voltage

[0154]

[0155] to determine reference input voltages for the DC-DC converters 114a, 114b connected to each of the El and E2 loads 108a, 108b. In the specific example shown in Figure 5, the reference input voltage

[0156]

[0157] for the DC-DC converters 114a connected to the El loads 108a can be determined using the following equation:

[0158]

[0159] ( 6)Correspondingly, the reference input voltage Vinp_reffor the DC-DC converters 114b connected to the E2 loads 108b can be determined using the following equation:

[0160] V. — (Kf-NV J

[0161]

[0162] In equation ( 6), Iina_b is a boundary current that is defined to trigger the desired active increase in Vina_refunder the appropriate conditions; and kiais a positive droop coefficient. Based on equation ( 6), when the realtime (actual) current of the HVDC bus system ibus is less than the boundary current Iina_b, the reference input voltage Vina_ref of the DC-DC converters 114a connected to the El loads 108a will increase to allow the electrolyzers to obtain more input power.

[0163] A limiter L2 is also introduced to ensure that the reference input voltage Vina_refremains larger than a multiple N / (M+N) of the reference voltage of the HVDC bus system Vbus_r f. This multiple is defined based on the proportion of the number of El loads 108a in the load platform. The presence of the limiter L2 helps avoid active reduction of the input voltage Vina_ref when the current of the HVDC bus system ibus is greater than the boundary current Iina_b. It will also be appreciated that throughout the second control loop 504, the reference input voltages Vi naref and Vinp ref should be limited to lie between in min and Vin_maxto ensure the safe operation of the associated DC-DC converters 114a, 114b.

[0164] The second control loop 504 is further configured to ascertain the actual measured (real-time) input voltage of each associated DC-DC converter 114a, 114b, and to compare the reference voltages Vina_refand Vinp_ref with those measured values. For subsequent reference, the measured input voltage for the jthEl load' s associated DC-DC converter will be denoted as Vina_j, and the measured inputvoltage for the kthE2 load' s associated DC-DC converter will be denoted as vinp_k.

[0165] This voltage comparison is used by the second control loop 504 to generate a 'compensation current component' for each type of electrolyzer load - namely Gvaand GVp for El loads 108a and E2 loads 108b respectively. The second control loop 504 is then configured to determine reference output currents Ioa_ref_j and Iop_ref_k, for the jthEl load and the kthE2 load (where j=1, 2, …, N; and k=1, 2, …, M), by summing each compensation current component Gvaand Gvpwith the output reference current Io_b that was generated earlier by the first control loop 502.

[0166] Thereafter, the third control loop 506 is configured to use the appropriate reference output currents Ioa_ref_j, Iop_ref_k for the electrolyzer type under consideration as inputs for comparison against the real-time (actual) currents ( ioa_j or iop_k) for the El loads 108a and E2 loads 108b respectively. Based on this comparison, a control variable Daj or Dpkis generated for regulating the corresponding DC-DC converters 114a, 114b of the El loads 108a and E2 loads 108b respectively.

[0167] As shown in Figure 5, a di / dt limiter is also adopted by the third control loop 506 when calculating the control variable Daj, to limit the rate of change of the current Ioa_ref_j that flows through the El loads 108a. This prevents the El loads 108a from ramping their power up or down too quickly (e. g., above their intrinsic desirable ramp-up or ramp-down rates ). This in turn helps to prevent accelerated degradation of those electrolyzers.

[0168] In some implementations, a fourth control loop 508 also forms part of the control strategy. This is shown in Figure 5 as the 'Energy storage system control' loop and is utilised in instances where one or more energy storage systems 116a, 116b, 116c are incorporated into the loadplatform 106 in relation to the El loads 108a (e. g., as shown in the system 100b of Figure 3 ).

[0169] This fourth control loop 508 comprises controls and calculations performed in relation to determining a reference current Diessfor the energy storage systems. More specifically, the reference current

[0170]

[0171] for the energy storage system associated with the

[0172]

[0173] El load is obtained by subtracting the reference current

[0174]

[0175] for the

[0176]

[0177] El load from its value after the di / dt limiter has been applied (in the third control loop 506). A control variable

[0178]

[0179] is then determined by comparing the monitored current

[0180]

[0181] with the measured / monitored actual (realtime) value

[0182]

[0183] of the current to that El load 108a.

[0184] The various control variables that were calculated as part of the control loops described above constitute direct control / modulation electrical signals. These signals are output to a controller, and thereafter to the corresponding DC-DC converters, to control their operation. These control signals can, for example, relate to controls for the duty cycles of the DC-DC converters.

[0185] The present Applicant has appreciated that there are multiple technical benefits that can be achieved as a result of implementing the above-described aspects of the present invention.

[0186] For example, the use of an HVDC power collection system can reduce the size of the equipment ( such as transformers ) that are used in the system. As such, a correspondingly smaller platform and lower initial investment can be realised. This makes the HVDC power collection system described hereinabove particularly suitable for implementation in relation to offshore RES-to-load systems (particularly offshore wind-to-Hydrogen systems ): the investments in the load platforms in such systems are closely tied to the size and weight of theequipment used, and can be very high (particularly in the more typically seen 50 / 60 Hz AC collection systems ).

[0187] Implementing the series-connected structure of the (electrolyzer) loads 108 in the load platform 106 of the present invention - where the inputs of the DC-DC converters 114 are connected in series with one another -has the beneficial effect that the input voltages of each DC-DC converter are usually in the order of only a few kV (e. g., around 2 kV). As a result, commercially available semiconductor switches (e. g., 4.5kV IGBTs or IGCTs ) can be used, thereby reducing the voltage conversion ratios. This is also particularly useful in relation to (offshore ) wind-to-hydrogen implementations where, as noted above, the size and weight of equipment gains in importance. The corresponding voltage stresses are also lower, and the transformers that are needed are also correspondingly much easier to design and implement.

[0188] Furthermore, implementing the above-described control strategies and methods means that the power distribution among different types of electrolyzer loads can be actively regulated. This allows the unflexible El loads 108a to still work above their minimum operating power under low wind power situations. Different degradation rates of different electrolyzers can also be managed and mitigated as has been discussed in detail above. The above-described embodiments therefore increase the ease with which electrolyzer loads having different properties ( specifically, different input voltage ranges and hence different flexibilities ) can be more easily incorporated into a single load platform to take advantage of the associated benefits that such loads can provide.

[0189] It is noted that various modifications may be made to the above-described specific examples andimplementations, without necessarily departing from the inventive concept.

[0190] For example, it is noted that the control strategy shown and described with reference to Figure 5 only gives one possible realization method of the general control strategy concept. In view of balancing degradation rates among different electrolyzers, the reference voltages for different DC-DC converters 114a, 114b could instead be generated by other methods, such as by ranking the degradation rates of electrolyzers, and / or based on aging models of electrolyzers. These methods change the generation method of the reference voltages, but do not substantively affect the underlying aim and results / outputs achieved by the control strategy, or the broad steps of the methods that are involved.

[0191] The present Applicant has conducted a simple simulation to verify the feasibility of, and advantages associated with, the above-described invention. This will now be briefly described in relation to Figures 6 to 8.

[0192] An example model of the DC-DC converters 114 provided in the load platform 106 is shown in Figure 6A, and an example model of the electrolyzers which constitute the loads 108 is shown in Figure 6B. In this simulation, the rated power ratings of the electrolyzers are set to 20 MW, and the minimum operating power for the El loads 108a is set as 20% of the rated value, namely 4 MW. An example of the entire simulation model that was tested (using the software PLECS ) is shown in Figure 7, and includes a simulation of a RE platform 702, one of each electrolyzer type (El load 704 and E2 load 706), and an energy storage system 708 connected to the input of the El load 704.

[0193] The simulation parameters are given in Table B below, and the simulation results are shown presented in Figure 8.Item Value Item Value

[0194] C₁ 3.6μF n 16

[0195] 11.1mH L₁ / L₂ / L_ess 1mH / 0.1mH / 10μH 1.75Ω Ls1 / Ls2 0 C₁₁ / C₁₂ 20mF 10F / 0.5F

[0196] 20mΩ / 24mΩ / 10mΩ 6mΩ / 5mH 66kV 600V / 600V / 1kV 303.03A k_ia 2

[0197]

[0198] 75.76A 425

[0199] Table B: Key simulation parameters

[0200] The simulation itself was carried out in the following manner:

[0201] (a) Initially (at time t=0s ), the simulated input wind power was set as 40 MW, and the system was able to operate in the (first ) 'power balanced' operation mode. The input voltages vc1and vc2to the El load 704 and the E2 load 706 respectively were maintained the same.

[0202] However, it will be appreciated that due to inherent inconsistencies between the two electrolyzers, the output currents and power will not necessarily also remain the same.

[0203] (b) At time t=ls, the input wind power was stepped down to 10 MW, however as shown in the graphs of Figure 8, the El load was still able to be operated above its minimum operating point of 4 MW. Hence, the system was still able to operate in that first 'power balanced' operation mode, although the HVDC bus voltage had to decrease slightly (as required by the controls implemented and discussed previously).

[0204] (c) During the regulation process ( from time t=ls to t=1. 6s ), the power Poi to the type 1 electrolyzer El decreased much slower than the power to the type 2 electrolyzer E2 (as shown in the bottom graph of Figure 8 ). The energy storage system 708 therefore had to compensate for the power differential between Poi and P02 to suppress the overshoot / undershoot regulation of vciandVc2. This can be seen from the third graph in Figure 8 (which shows the control variables that are implemented during the simulation), where the Mi and M3 lines followed opposite trends.

[0205] (d) At t=2s, the input wind power was further decreased to 5 MW, and the system then converted to operating in the ( second) 'variable power distribution' operation mode. As shown in the top and bottom graphs of Figure 8, the input voltage and power of the E2 load therefore started decreasing, to still allow the El load to operate at its minimum power point of 4 MW.

Claims

SP318639C L A I M S1. A generation-to-load system comprising:a renewable energy source RES platform comprising a plurality of renewable energy sources;a load platform comprising a plurality of electrical loads, the plurality of electrical loads comprising at least one of a first type of electrical load having a narrow input operation power range and at least one of a second type of electrical load having a wide input operation power range, wherein at least two of the plurality of electrical loads are connected in series with one another;a High Voltage DC HVDC bus system configured to provide electrical connection between the RES platform and the load platform, to receive incoming power from the RES platform, and to output power to the load platform; anda controller operatively coupled to the HVDC bus system and configured to automatically regulate the power output by the HVDC bus system to the electrical loads in the load platform, and maintain a power balance between the RES platform and the load platform, the controller being configured to:determine reference input electrical signals for each of the first and second electrical load types respectively, the reference input electrical signals indicating a desired input power for the associated electrical load type;determine, based on the reference input electrical signals, first and second control variables arranged to enable the controller to regulate the power output to first and second electrical load types respectively; and vary a voltage of the HVDC bus system and control the power output to the first and second electricalload types using the respective first and second control variables.

2. The system of claim 1, wherein the load platform further comprises a plurality of DC-DC converters, each DC-DC converter being electrically connected to one of the plurality of electrical loads.

3. The system of claim 1 or claim 2, wherein the load platform further comprises at least one energy storage system configured to store excess electrical energy and to provide the stored energy to one or more of the plurality of electrical loads.

4. The system of claim 3, wherein the at least one energy storage system corresponds to any one or more of the following: (i) a combined energy storage system configured to provide the stored energy to multiple ones of the plurality of electrical loads; (ii ) a distributed energy storage system comprising a plurality of energy storage sub-units, each energy storage sub-unit being connected to one of the plurality of electrical loads and configured to provide the stored energy to the connected electrical load.

5. The system of any preceding claim and corresponding to a wind-to-hydrogen system, wherein the plurality of renewable energy sources correspond to a plurality of wind turbines and the plurality of electrical loads correspond to a plurality of water electrolyzers.

6. The system of any preceding claim, wherein the controller is configured to determine the reference input electrical signals for each of the first and second electrical load types based on: (a) degradation rates of each of thefirst and second electrical load types; and / or (b) an aging model of each of the first and second electrical load types.

7. The system of any preceding claim, wherein the controller is configured to apply a current rate di / dt limiter when determining the first control variable.

8. The system of any preceding claim, wherein the controller is configured to monitor the voltage of the HVDC bus system and voltages of each of the plurality of electrical loads to determine the reference input electrical signals.

9. The system of claim 8, wherein the reference input electrical signals correspond to reference input voltages and the controller is further configured to:determine first and second reference input currents for the first and second electrical load types respectively based on the corresponding reference input voltages; andcompare each of the first and second reference input currents with a monitored actual current for the first and second electrical load types respectively to determine the first and second control variables.

10. The system of claim 9, wherein the controller is further configured to:determine a reference current by sampling a voltage of the HVDC bus system and comparing the sampled HVDC bus system voltage with a reference HVDC bus voltage;monitor voltages of the first and second electrical load types;compare the reference input voltages with the corresponding monitored voltages to determine anassociated compensation current component for each of the first and second electrical load types; andsum the compensation current component for each of the first and second electrical load types with the reference current to determine the corresponding first and second reference input current respectively.

11. A method for operating a generation-to-load system, the generation-to-load system comprising:a renewable energy source RES platform comprising a plurality of renewable energy sources;a load platform comprising a plurality of electrical loads, the plurality of electrical loads comprising at least one of a first type of electrical load having a narrow input operation power range and at least one of a second type of electrical load having a wide input operation power range, wherein at least two of the plurality of electrical loads are connected in series with one another; anda High Voltage DC HVDC bus system providing electrical connection between the RES platform and the load platform and configured to receive power from the RES platform and output power to the load platform;wherein the method enables automated regulation of power distribution by the HVDC bus system to the electrical loads in the load platform, whilst maintaining a power balance between the RES platform and the load platform, and the method comprises:determining reference input electrical signals for each of the first and second electrical load types respectively, the reference input electrical signals corresponding to a desired input power for the associated electrical load type;determining, based on the reference input electrical signals, first and second control variables forregulating the power output to first and second electrical load types respectively; andvarying a voltage of the HVDC bus system and controlling the power input to the first and second electrical load types using the respective first and second control variables.

12. The method of claim 11, wherein the reference input electrical signals correspond to reference input voltages and the method further comprises:determining first and second reference input currents for the first and second electrical load types respectively based on the corresponding reference input voltages; andcomparing each of the first and second reference input currents with a monitored actual current for the first and second electrical load types respectively to determine the first and second control variables.

13. The method of claim 12, and further comprising determining the first and second reference input currents by:determining a reference current for the plurality of electrical loads by sampling a voltage of the HVDC bus system and comparing the sampled HVDC bus system voltage with a reference HVDC bus voltage;monitoring voltages of the first and second electrical load types;comparing the reference input voltages with the corresponding monitored voltages to determine an associated compensation current component for each of the first and second electrical load types; and summing the compensation current component for each of the first and second electrical load types with thereference current to determine the corresponding first and second reference input current respectively.

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