How to power an electrical load from a renewable energy device

Abstract

An HVDC system is provided that includes an AC / DC converter subsystem electrically connected to a renewable energy equipment and a VSC subsystem, the method including the steps of: operating the renewable energy equipment to function as a voltage source for energizing an HVDC link between the AC / DC converter subsystem and the VSC subsystem, operating the VSC subsystem as a voltage source to energize at least one electrical load electrically connected to the VSC subsystem, operating the equipment to follow the VSC subsystem such that controlling an AC power output affects the power generation rate if it is determined that a power generation rate of the renewable energy equipment is not within specified parameters, and operating the VSC subsystem to follow the renewable energy equipment such that the VSC subsystem adjusts characteristics of its AC electrical output to match characteristics of power generated by the renewable energy equipment if the power generation rate is within specified parameters.

Description

[Technical field]

[0001] The present invention relates to a method of supplying power from a renewable energy device to an electrical load, and in particular to a method of supplying power through the use of an HVDC system electrically connected to both for at least the transmission of power. [Background technology]

[0002] This section is intended to introduce various aspects of art that may be related to exemplary embodiments of the present invention. This description is believed to be helpful in providing a framework to facilitate a better understanding of certain aspects of the present invention. As such, it should be understood that this section should be read in this light, and not necessarily as an admission of any prior art.

[0003] Renewable or "green" energy sources, such as electricity produced by photovoltaic panels or wind turbines, are of increasing interest in efforts to decarbonize global energy consumption. Also of great interest is "green" hydrogen, produced using water electrolysis powered by "green" electricity.

[0004] The characteristics of electrical power from renewable energy sources such as the sun or wind can vary throughout the day, particularly due to the intermittent nature of such energy sources. Intermittency and other factors present challenges for directly interconnecting renewable energy sources with electrical loads, particularly large electrical loads such as those with annual electrical consumption in the gigawatt (multi-gigawatt) range. In addition, existing power electronics interfaces (also known as grid-following) utilized in wind and solar applications require connection to a utility power grid for their power generation and transmission to energy users. Thus, renewable energy devices that generate energy from renewable energy sources ("green" energy) are typically connected to the utility power grid as an intermediary for the broader distribution of green energy to the general population served by that utility power grid, rather than such green energy being directly transmitted from the renewable energy device to one or more electrical consumers, particularly electrical consumers with energy demands in the gigawatt range.

[0005] Currently, "green" hydrogen production facilities receive green energy indirectly from the utility power grid system, rather than directly from the renewable energy source itself. Relying on the power grid system for the supply of green power has certain drawbacks, such as being subject to interruptions in the power grid system, including power outages and other grid disturbances (e.g., voltage dips, power quality, voltage oscillations, etc.) and failures. Furthermore, grid dependency will also depend on the timing and availability of grid connection extensions, as well as the availability of such grid connections to the locations where the renewable energy equipment is located. In addition, there are inefficiencies associated with connecting to the power grid due to multiple conversions between alternating current (AC) and direct current (DC) between the flow of electricity from the renewable generators to the power grid system and then distributed to the electricity consumers.

[0006] Furthermore, the intermittency of renewable energy sources may make it difficult for electricity consumers that receive electricity directly from a solar power plant without receiving power from a power grid system to restart the system, such as at the beginning of a day. In the absence of power from the power grid, a so-called black start needs to be performed to energize and operate the electricity consumers, including controlling both the renewable generators and the electricity consumers to match power generation with power consumption during operation of both.

[0007] For example, U.S. Patent No. 9,379,633 discloses a method for black starting an AC network, but does not address the challenges associated with energizing and operating an HVDC system connected to renewable energy equipment to power electrical loads. Similarly, U.S. Patent No. 9,960,603 discloses an installation including a rectifier and a VSC for transmitting power between two AC voltage networks, but does not address the challenges associated with energizing and operating such an installation. S. Bernal-Perez et al., "Off-shore Wind Farm Grid Connection using a Novel Diode-Rectifier and VSC-Inverter based HVDC Transmission Link," IECON, 2011, pp. 3186-3191, discloses an installation including a rectifier and a VSC for transmitting power from an offshore wind turbine to a utility power grid, where a synchronous generator is assumed to maintain the power grid voltage amplitude and angle. However, it does not address the challenges associated with energizing and operating such an installation to directly transmit power from an offshore wind turbine to an electrical load.

[0008] Another example is US Patent No. 10566799, which discloses a method for black starting a wind farm to generate electricity to supply a connected supply network.Similarly, US Patent No. 10566799 does not address the challenges associated with energizing and operating an HVDC system connected to renewable energy equipment to supply electrical loads.

[0009] Yet another example is US Patent No. 9,197,068, which discloses a method for controlling a multi-terminal HVDC system having multiple converter stations, including identifying disruptions in the HVDC system from measurements. However, US Patent No. 9,197,068 also does not address the challenges associated with energizing and operating an HVDC system connected to renewable energy equipment to supply power to electrical loads.

[0010] US Patent No. 8,305,778 discloses a method of influencing power generation of at least one variable speed generator, where the at least one variable speed generator supplies power at a constant frequency to a local AC bus, the local AC bus being connected to a DC link via a first voltage source converter, and the DC link being connected to an AC grid via a second voltage source converter. However, US Patent No. 8,305,778 also does not address the challenges associated with powering and operating an HVDC system connected to renewable energy equipment to power electrical loads without a utility power grid connection.

[0011] Therefore, there remains a need for a method of controlling an HVDC system to directly power electrical loads from renewable energy equipment, including, but not limited to, utility power grid connections. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Pat. No. 9,379,633 [Patent Document 2] U.S. Pat. No. 10,566,799 [Patent Document 3] U.S. Patent No. 9,197,068 [Patent Document 4] U.S. Patent No. 8,305,778 [Non-patent literature]

[0013] [Non-Patent Document 1] BERNAL-PEREZ, S., et al. Off-shore wind farm grid connection using a novel diode-rectifier and VSC-inverter based HVDC transmission link. In: IECON 2011-37th Annual Conference of the IEEE Industrial Electronics Society. IEEE, 2011. p. 3186-3191. Summary of the Invention

[0014] The present disclosure describes a method of controlling an HVDC system to supply power from renewable energy equipment to an electrical load, the method including providing a direct electrical connection between the equipment and the load. The methods disclosed herein may be used to provide a point-to-point connection for transmitting power from renewable energy equipment to an electrical load, as well as other configurations including additional terminals other than a point-to-point connection as would be understood by one of ordinary skill in the art. The presently described methods address challenges to such electrical connections, including fluctuations and intermittent availability of electricity generation, such as electricity generated by wind or sun. Such direct electrical connections provided by the HVDC systems and methods of controlling such HVDC systems described herein allow electrical consumers in general, and in particular large electrical consumers having nominal capacity in the gigawatt (GW) range, to be independent from the utility power grid, whereby grid independence minimizes grid-related disruptions experienced by the large electrical consumers, such as planned or unplanned power outages, failures, and other grid disturbances. The methods and systems described herein also allow electrical power to be sourced directly from renewable energy equipment, thereby enabling the option of eliminating the infrastructure required to connect to the utility power grid. This decouples the operation of facilities receiving power from renewable energy devices from the availability and capacity of existing and additional grid infrastructure to implement such grid connection. Such options for grid independence allow for the development of certain locations as renewable energy facilities that were previously considered inaccessible due to a lack of existing utility power infrastructure to enable the distribution of green energy to end consumers of electricity.

[0015] Furthermore, having the option of independence from the power grid allows electricity consumers, especially the larger ones, to control and manage their own electrical network to meet their electricity consumption demands, which can lead to improved overall system efficiency and overall production as well as reduced CAPEX and OPEX. Furthermore, a direct electrical connection with a renewable generator allows the option of co-locating the electricity consumer with the renewable generator. Both the co-location and / or grid independence options can reduce the footprint and demand on the existing power grid system as additional renewable energy equipment and / or electricity consumers, especially the larger ones, come online. Without such a point-to-point connection option with a renewable generator, a large expansion of the power grid may be required to accommodate the receipt of "green" electricity from additional renewable energy equipment or facilities and distribution to additional consumers. The co-location option is extended to allow facilities to be built in locations where renewable generators are available but where power grid connection is insufficient or unavailable.

[0016] Furthermore, where the electricity consumer is an electrolyser, a direct electrical connection between the electrolyser and a renewable generator is likely to provide the most efficient conversion of renewable energy (such as wind or solar) to hydrogen. As used herein, electrolyser has its ordinary meaning, which includes systems that use electricity to split water into hydrogen and oxygen in a process called electrolysis.

[0017] The methods and systems for connecting renewable energy equipment to an electrical load described herein allow for independence from the power grid, but also provide the option of being connected to the grid if such grid connection is desired.

[0018] Accordingly, the present invention provides a method for supplying power to an electrical load from a renewable energy device, the method comprising: (a) providing an HVDC system comprising an AC / DC converter subsystem and a VSC subsystem, the AC / DC converter subsystem comprising at least one AC / DC converter unit, an input electrically connected to a renewable energy device, and an output electrically connected to the VSC subsystem; a VSC subsystem comprising at least one VSC, an input electrically connected to the AC / DC converter subsystem, and an output electrically connected to at least one electrical load; (b) determining an initial voltage magnitude and phase angle of electricity generated by the renewable energy device; (c) operating the renewable energy equipment to generate power having the predetermined initial voltage magnitude and phase angle from step (b) to energize the HVDC link between the AC / DC converter subsystem and the VSC subsystem, thereby supplying DC power to the VSC subsystem, wherein the renewable energy equipment generates power at a power generation rate; (d) operating the VSC subsystem to convert the DC power to an AC power output for powering at least one electrical load, the AC power output having an initial voltage swing; (e) determining whether a power generation rate of the renewable energy equipment is within specified parameters, and if the result of the determination is "no," operating the renewable energy equipment in accordance with the VSC subsystem such that controlling the AC power output of the VSC subsystem affects the power generation rate of the renewable energy equipment; (f) modifying the AC power output of the VSC subsystem, thereby introducing a power imbalance to the renewable energy equipment; (g) in response to at least the power imbalance from step (f), adjusting a power generation rate of the renewable energy equipment to restore a power balance to the renewable energy equipment; (h) repeating steps (e)-(g) until a rate of power generation of the renewable energy device is determined to be within specified parameters.

[0019] Optionally, step (f) may include operating the VSC subsystem to provide an AC power output including a new voltage amplitude selected based at least on the desired incremental change to the AC voltage output, and step (g) may include operating the renewable energy equipment to generate power having a new voltage amplitude and phase angle corresponding to the new voltage amplitude of the VSC subsystem from step (f) to restore power balance to the renewable energy equipment. Suitably, the desired incremental change may be determined based at least on a difference between the actual AC voltage output and a specified AC voltage output of the VSC subsystem.

[0020] Preferably, the method comprises the steps of: (i) upon determining that the power generation rate of the renewable energy equipment is within specified parameters, operating the VSC subsystem to follow the renewable energy equipment such that changes in power generated by the renewable energy equipment affect an AC power output of the VSC subsystem; (j) maintaining the HVDC link in a steady state in response to a detected power imbalance in the HVDC link caused by at least a change in the power generated by the renewable energy equipment by operating the VSC subsystem to adjust a voltage amplitude of its AC power output to correspond to the power generated by the renewable energy equipment.

[0021] Optionally, step (j) comprises: - identifying changes in voltage amplitude and phase angle of the electricity generated by the renewable energy equipment that cause the detected power imbalance; - adjusting the AC power output of the VSC subsystem to restore the HDVC link to a steady state by operating the VSC subsystem to provide an AC power output having a new voltage amplitude based on the identified change.

[0022] Optionally, the specified parameter may be within a range of −10% to +10%, preferably −5% to +5%, more preferably −1% to +1% of the power generation threshold of the renewable energy equipment. Suitably, the power generation threshold may be determined by maximum power point tracking (MPPT).

[0023] According to another aspect, there is provided a method of controlling an HVDC system to supply power from renewable energy equipment to an electrical load, particularly an electrical load that is independent of a power grid, the method comprising: (a) providing an HVDC system comprising an AC / DC converter subsystem and a VSC subsystem, the AC / DC converter subsystem includes at least one AC / DC converter unit, an input electrically connected to the renewable energy device, and an output electrically connected to the VSC subsystem; a VSC subsystem comprising at least one VSC, an input electrically connected to the AC / DC converter subsystem, and an output electrically connected to at least one electrical load; (b) operating the renewable energy equipment to generate power having a voltage magnitude and phase angle that maintains the HDVC link in a steady state and supplying DC power to the VSC subsystem; (c) operating the VSC subsystem to convert the DC power to an AC power output for supply to at least one electrical load, the AC power output comprising a first voltage amplitude; (d) monitoring a condition of the HVDC link to detect deviations from a steady state caused by changes in at least the voltage magnitude and phase angle of the power generated by the renewable energy equipment; (e) upon detecting the deviation, restoring the HVDC link to a steady state, the restoring step including the steps of identifying a change from step (d) and operating the VSC subsystem to convert the DC power to an AC power output having a new voltage amplitude selected based on the identified change.

[0024] In this respect, it should be noted that the electrical loads used in accordance with the present invention are preferably independent of the power grid, unlike, for example, US Patent No. 8,305,778, where an AC grid is used.

[0025] It should further be noted that in step (b) of the above method according to the invention, the change in voltage amplitude and phase angle of the power generated by the renewable energy equipment is due to the renewable energy equipment itself. This is in contrast to e.g. US Pat. No. 8,305,778 (see col. 2, line 65 to col. 3, line 2), where the invention is based on the idea of ​​modifying the power generated by the ASG [adjustable speed generator used to convert wind energy into electrical power] by modifying the AC voltage at the local AC bus. This modification is performed by controlling the first voltage source converter.

[0026] Further, it should be noted that in step (d) of the above method according to the present invention, the power output change of the renewable energy equipment is due to the intermittent nature of the natural resource, which can either increase or decrease. In contrast, according to US Pat. No. 8,305,778, only power reduction is performed. See, for example, column 3, lines 22-30 of US Pat. No. 8,305,778: "Using the present method, a rapid and effective reaction to a disturbance in the AC grid is achieved, whereby a reduction in the reference value of the AC voltage at the local AC bus results in a response of the first voltage source converter to reduce the AC voltage amplitude at the local AC bus. This again leads to a reduction in the generator by at least one ASG."

[0027] Furthermore, in step (e) of the method according to the present invention, the restoration of the HVDC link to a steady state is achieved via modification of the VSC subsystem output voltage amplitude interfacing to the electrical load. In contrast, US8305778 focuses on control methods to counter such changes as a result of the natural intermittency of renewable energies, which can manifest either as an increase or decrease in power output.

[0028] Optionally, step (d) may comprise continuously monitoring, where the condition of the HVDC link is continuously monitored at a time interval of less than 1 second, preferably less than 0.01 seconds, more preferably less than 1 millisecond (ms), such as in the range of 1 microsecond (μs) to 1 second, preferably 10 μs to 0.01 seconds, more preferably 50 μs to 1 ms.

[0029] Suitably, an HVDC link is in steady state when its operating voltage amplitude is within + / -0.01% to + / -10%, preferably + / -0.01% to + / -5%, more preferably + / -0.01% to + / -0.1% of its nominal voltage rating.

[0030] Optionally, the at least one electrical load is one or more electrical consumers. Suitably, the one or more electrical consumers may comprise an electrolyser having a nominal capacity of at least 10 megawatts, preferably in the range of 10 megawatts (MW) to 10 gigawatts (GW). Suitably, the electrolyser does not receive power from a utility power grid to produce hydrogen.

[0031] Optionally, the AC / DC converter subsystem (102) is a rectifier subsystem comprising at least one rectifier unit. Preferably, the rectifier subsystem comprises a plurality of rectifier units connected in series, and / or the VSC subsystem comprises a plurality of VSCs connected in series. [Brief description of the drawings]

[0032] [Figure 1]1 illustrates an exemplary HVDC system suitable for use with the methods described in this disclosure. [Diagram 2] 1 illustrates a chart of an example HVDC link voltage at steady state as described in accordance with various aspects disclosed herein. [Diagram 3] 1 illustrates an embodiment of a method for energizing an HVDC system (such as that shown in FIG. 1) according to various aspects disclosed herein. [Figure 4] 1 illustrates an embodiment of a method for controlling a power generation rate of renewable energy equipment supplying power to an HVDC system (such as that shown in FIG. 1 ) according to various aspects disclosed herein, including the embodiment illustrated in FIG. 3 . [Diagram 5] 1 illustrates an embodiment of a method for controlling an HVDC system (such as that shown in FIG. 1) to maintain an HVDC link in a steady state, according to various aspects disclosed herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. References to "one embodiment", "embodiment", "exemplary embodiment", etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but not all embodiments necessarily include the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment. Moreover, when a particular feature, structure, or characteristic is described in connection with one embodiment, the effect of such feature, structure, or characteristic on other embodiments, whether or not explicitly described, is within the knowledge of one of ordinary skill in the art. Other suitable modifications and adaptations of various conditions and parameters normally encountered in the art will be apparent to those skilled in the art and are within the spirit and scope of the present invention.

[0034] Although the description herein provides numerous specific details that are set forth for a thorough understanding of the exemplary embodiments, it will be apparent to one of ordinary skill in the art that the embodiments may be practiced without some or all of these specific details. In other instances, well-known process steps and / or structures have not been described in detail in order not to unnecessarily obscure the invention. The features and advantages of the embodiments may be better understood with reference to the following drawings and description.

[0035] Furthermore, where a similar element is used in more than one figure, the same reference number is used in each figure, and a detailed description of the element is provided only at its first occurrence. Certain features or components of the systems or processes described herein may be omitted in certain illustrated configurations for clarity. Furthermore, certain features, such as, but not limited to, pumps, valves, gas bleeds, gas inlets, fluid inlets, fluid outlets, etc., are not necessarily shown in the figures, although their presence and function will be understood by those skilled in the art. Similarly, the depiction of some of such features in a figure does not indicate that all of them are depicted.

[0036] FIG. 1 and associated description describes an exemplary system and various optional features (embodiments) of such a system that can be used to provide electricity generated by a renewable energy device directly to an end user. FIGs. 3-5 and associated description describe an exemplary method and various optional features (embodiments) for use to operate the system shown in FIG. 1 and described herein (and any embodiment or optional features thereof) to provide such electricity. As described in the "Summary of the Invention" section, the present disclosure, among other things described herein, enables large electricity consumers (such as electrolyzers) to be powered by renewable energy devices without receiving electricity from a power grid, but having the option to do so.

[0037] Referring to FIG. 1, an HVDC system 100 is shown that includes an AC / DC converter subsystem 102 and a VSC subsystem 104. In a preferred embodiment, the AC / DC converter subsystem 102 is a rectifier subsystem. The AC / DC converter subsystem 102 includes at least one AC / DC converter unit 106, preferably multiple (two or more) AC / DC converter units 106 connected in series with each other. In a preferred embodiment, the rectifier subsystem 102 includes multiple rectifier units 106 connected in series with each other. The VSC subsystem 104 includes at least one "Voltage Source Converter" (VSC) 118, preferably multiple VSCs 118 connected in series with each other. Although the remainder of the disclosure refers to the "rectifier subsystem 102," it is understood that the rectifier subsystem is a preferred embodiment of the AC / DC converter subsystem and that other suitable devices for converting alternating current (AC) to direct current (i.e., AC / DC converters) may be used as known to those skilled in the art.

[0038] The rectifier subsystem 102 includes an input (unsigned) electrically connected to the renewable energy device 108 to receive generated power therefrom, and an output (unsigned) electrically connected to the VSC subsystem 104 to provide power thereto. The VSC subsystem 104 includes an input (unsigned) electrically connected to the rectifier subsystem 102 to receive power therefrom, and an output (unsigned) electrically connected to at least one electrical load 122 to provide power thereto.

[0039] The power generated by the renewable energy equipment 108 is provided to the rectifier subsystem 102 via equipment known to those skilled in the art, such as step-up transformers and power cables. The HVDC system 100 can be used with any suitable renewable energy equipment 108 that generates power from a renewable energy source and allows for control of the output voltage, angle, and / or frequency of the generated power. The renewable energy source can be wind energy, solar energy, biomass, electrochemical (e.g., fuel cells), or a combination thereof. For example, the renewable energy equipment 108 can include a wind turbine that includes components (such as an internal DC link and a VSC) that allow for control of the output voltage, angle, and / or frequency of the generated power.

[0040] The amount of power generated by any given renewable energy source may vary depending on the equipment 108 used, in addition to any applicable variability inherent to the renewable energy source itself. For example, if the equipment 108 comprises a wind turbine, the amount of power generated will depend at least on the size of the turbine and the length of its blades, as well as the number of turbines used. Similarly, if the equipment 108 comprises PV panels, the amount of power generated will depend at least on the size and number of PV panels.

[0041] Referring to FIG. 1 , the rectifier subsystem 102 of the HVDC system 100 is electrically connected to the renewable energy equipment 108 to receive power generated by the equipment 108. Power transmission equipment 112 and 114, known to those skilled in the art, such as transformers and power lines, including transformers for stepping up or stepping down voltage as applicable, may be used to provide power from the equipment 108 to the rectifier subsystem 102. The renewable energy equipment 108 may preferably be operated to function as a voltage source in generating power having an initial voltage amplitude and phase angle that depends on the nominal voltage output of the equipment 108 and may be determined by one skilled in the art taking into account at least the active and reactive power flows into the rectifier subsystem 102. One skilled in the art will understand the relationship between the voltage amplitude of the power generated by the renewable energy equipment 108 and the active power flowing into the rectifier subsystem 102, and will be able to select a suitable initial voltage amplitude to achieve a desired active power flow based on the nominal voltage output of the equipment 108. Similarly, one skilled in the art will understand the relationship between the phase angle of the power generated by the renewable energy equipment 108 and the reactive power flowing through the rectifier subsystem 102 and will be able to select an appropriate initial phase angle to achieve the desired reactive power flow in relation to the active power flow.

[0042] As used herein, the term "reactive power" refers to a type of power flow used to facilitate the transmission of real power (i.e., active power) through an alternating current (AC) generating and / or transmission system. In AC circuits, power is temporarily stored in inductive and capacitive elements, resulting in periodic reversals in the direction of power flow. The remaining portion of the power flow is real power or energy that can be used to perform work on a load (e.g., to operate a component or equipment). Conversely, the portion of the power flow that is temporarily stored in the form of a magnetic or electric field due to inductive and capacitive network elements is known as reactive power.

[0043] As used herein, "nominal voltage output" has its ordinary meaning, including a voltage output value assigned to a component or system (such as equipment 108) that conveniently designates its voltage class (typically assigned by the equipment manufacturer). As used herein, "voltage source" has its ordinary meaning, including a component capable of maintaining a fixed voltage, ideally independent of load resistance or output current. It should be understood that such initial voltage magnitude and phase angle may be determined by a computer program or controller of system 100, as described herein.

[0044] Any number and / or type of transformers may be used to preferably step up the voltage of the power from the equipment 108 before it is provided to the rectifier subsystem 102. The electrical connections between the equipment 108 and the rectifier subsystem 102 may be configured as known to those skilled in the art. For example, a unit of equipment 108 (such as one or a selected group of wind turbines or PV panels, shown as 110 in FIG. 1) may be connected to each rectifier unit 106 as shown in FIG. 1, or the units of equipment 108 may be connected to multiple rectifier units 106 (not shown).

[0045] The AC / DC converter subsystem, or preferably the rectifier subsystem 102, converts the AC power input to direct current (DC) power. The output of the rectifier subsystem 102 is high voltage DC power, which may result from a series connection of two or more rectifier units 106 and / or the voltage of the AC power input being high voltage. As used herein, the term "high voltage" or "HV" refers to a voltage of at least 1500V DC voltage.

[0046] Preferably, at least one (including all) of the rectifier units 106 may comprise (including consist essentially of) a plurality (two or more) of rectifiers connected in series, thereby providing two levels of series connection where the rectifier units 106 themselves are connected in series with one another in a configuration with multiple rectifier units 106. It is understood that at least one (including all) of the rectifier units 106 may comprise (or consist essentially of) one rectifier. Thus, the rectifier subsystem 102 may have a plurality (two or more, five, etc.) of rectifier units 106 having at least the following combinations: (a) At least one unit 106 has one rectifier and the remaining units 106 have two or more rectifiers. (b) Every unit 106 has multiple (two or more) rectifiers. (c) Every unit 106 has one rectifier.

[0047] The number and / or size of rectifiers in the rectifier unit 106, and correspondingly, the number and / or size of rectifier units 106 in the rectifier subsystem 102, are design choices that can be made by those skilled in the art based on factors such as the ampere rating and DC link voltage of the HVDC system. For example, for an HVDC system with a nominal capacity of 1.2 GW, the rectifier subsystem may include six rectifier units connected in series, each rectifier unit including 10-12 rectifiers connected in series, each rectifier rated at 6.5 kV. As used herein, "rated" voltage has its ordinary meaning, including the maximum voltage at which a component or device (such as a rectifier) ​​can be safely operated. As used herein, "nominal capacity" has its ordinary meaning, including the intended full-load sustained output of a system or component when the context refers to a power source, or the intended full-load sustained annual consumption of a system or component when the context refers to an electrical load. Nominal capacity is a number registered with an authority to classify the power output of a power source or the power consumption of an electrical load, and is usually expressed in watts, including megawatts (MW).

[0048] Suitable rectifiers for use in the rectifier unit 106 and rectifier subsystem 102 are preferably unidirectional rectifiers known to those skilled in the art, more preferably diode rectifiers. The selected rectifiers preferably allow power to be transported in one direction, which offers the advantages of lower weight and lower complexity in the circuit control system when compared to converters that allow bidirectional flow of power, such as self-commutated converters. Furthermore, relatively compact power semiconductors can be used for the unidirectional rectifiers.

[0049] 1, the high voltage DC power output of the rectifier subsystem 102 is provided to the VSC subsystem 104 via an HVDC link 116. The HVDC link 116 may comprise one or more cable circuits or HVDC transmission lines. In the example shown in FIG. 1, the HVDC link 116 includes three HVDC transmission lines. The HVDC link 116 may be or include any suitable combination of DC cables, DC overhead lines, DC cables and DC overhead lines connected in series, overcurrent limiting reactors, etc., as known to those skilled in the art.

[0050] As will be appreciated by those skilled in the art, there are various suitable configurations for the HVDC link 116, including bipole, fixed bipole, and monopole. For example, as shown in FIG. 1, the HVDC system 100 may optionally include a dedicated metallic return (DRM) 130 and grounding points 131 and 132. During operation, either point 131 or 132 may be bypassed (not used) to allow current to flow through the DMR 130. Under this configuration of the DMR 130 and one grounding point (131 or 132), the HVDC system 100 effectively becomes a bipole configuration with the DMR 130. Alternatively, the HVDC system 100 may operate without the DMR 130 and need not include the DMR 130, but may still include the grounding points 131 and 132. Under this alternative configuration, the HVDC system 100 effectively becomes a fixed bipole system. HVDC system 100 may also be effectively a symmetrical monopolar system if optional DMR 130 is removed and both grounding points 131 and 132 are bypassed.

[0051] Furthermore, one may choose to add additional parallel terminals to the existing HVDC system 100, either on the rectifier subsystem 102 side (examples 140 and 141 in FIG. 1 ) or on the VSC subsystem 104 side (examples 150 and 151 in FIG. 1 ), where 140, 141, 150, 151 may comprise at least one or more rectifier units, thyristor units, VSCs, or combinations thereof.

[0052] The VSC subsystem 104 converts the HVDC power to an AC power output. Preferably, the VSC subsystem 104 is operable to function as a voltage source in converting the DC power to AC power having an initial voltage magnitude capable of initiating power flow to the electrical loads 122, as may be determined by one skilled in the art by considering at least the specifications of the HVDC system 100, the equipment 108, and the loads 122. One skilled in the art will appreciate that the AC power output of the VSC subsystem 104 also has a phase angle.

[0053] When the VSC subsystem 104 comprises multiple VSCs 118 connected in series with each other, the DC power supplied to the VSC subsystem 104 may be distributed across the VSCs 118 in the subsystem 104. Preferably, DC power input may be provided to each of the VSCs 118 in the subsystem 104, however, there are situations, such as equipment failure, where DC power is supplied to some but not all of the VSCs 118. In these situations, at least one VSC 118 does not receive any DC power and is considered to be in bypass mode. The value of the AC voltage output of each VSC 118 may be adjusted by controlling the amount of DC power supplied to it, according to design choices known to those skilled in the art.

[0054] On the other hand, the VSC 118 may be suitable to be any self-commutated converter that uses semiconductor materials to convert power between AC and DC. For example, the VSC 118 may include, for example, several half H-bridges or full H-bridges, or a combination thereof, connected in series with a common AC output going to the power load 122. The semiconductor valves may include a branch of gate turn-on / turn-off semiconductor elements, such as insulated gate bipolar transistors (IGBTs), and diodes connected in anti-parallel to these elements. The VSC 118 preferably comprises a modular multi-stage converter, in particular a multi-level modular converter VSC (MMC-VSC), which comprises a chain of modules of semiconductor circuits connected in a half H-bridge or full H-bridge or a combination topology thereof to enable high power quality voltage AC-DC conversion or vice versa, as desired.

[0055] Typically, a modular multi-stage converter comprises a number of phase modules corresponding to the number of phases of the second AC voltage network attached. Each phase module is configured as a three-pole unit and comprises two outer DC voltage terminals and a central AC voltage terminal. A phase module branch extends between each of the AC and DC voltage terminals and comprises a series circuit of two-pole submodules. An energy storage device, for example a monopolar capacitor, and a power semiconductor circuit configured in parallel therewith are attached to each submodule. The power semiconductor circuit can be configured, for example, as a half-bridge circuit or a full-bridge circuit or a combination thereof. In the half-bridge circuit, a series circuit of two switchable power semiconductor switches, for example IGBTs, IGCTs, is provided, with each switchable power semiconductor switch being connected in parallel with a freewheeling diode of opposite polarity. Here, a first submodule connection terminal is directly connected to one pole of the energy storage device and the other submodule connection terminal is connected to a potential node between the switchable power semiconductor switches. In the full bridge circuit, two series circuits each consisting of two power semiconductor switches that can be turned on and off are provided, one submodule connection terminal is connected to a potential node between the power semiconductor switches that can be turned on and off in the first series circuit, and a second submodule connection terminal is connected to a potential node between the power semiconductor switches that can be turned on and off in the second series circuit.

[0056] The number and / or size of VSCs 118 in the VSC subsystem 104 is a design choice for one skilled in the art and can be made based on factors such as the ampere rating and DC link voltage of the HVDC system. For example, for an HVDC system transmitting 1.2 GW, the VSC subsystem may include 12 VSCs connected in series.

[0057] Referring to FIG. 1, the AC power output from the VSC subsystem 104 is provided to an electrical load 122. The electrical load 122 may include any suitable equipment that uses and / or stores electricity, as known to those skilled in the art. Preferably, the electrical load 122 includes at least one electrolyzer that uses electricity to split water into hydrogen and oxygen in a process called electrolysis, thereby producing hydrogen gas. The hydrogen production capacity is dependent on the equipment manufacturer. As known to those skilled in the art, the energy consumption and corresponding specifications of the renewable energy equipment can be determined based on the desired hydrogen production capacity and the specifications of the potential electrolyzer equipment. Conversely, if renewable energy is a limiting factor, the electrolyzer equipment can be selected and designed based on the renewable energy, as known to those skilled in the art. For example, a typical electrolyzer can produce approximately one kilogram of hydrogen for every 45-60 kWh of energy that is fed to the electrolyzer. When the renewable energy equipment is used to generate energy, factors in selecting the nominal capacity of the renewable energy equipment typically include taking into account the potential intermittency of the renewable energy source. For example, if wind and / or solar are the renewable energy sources, it may be preferable to adjust the nominal capacity by 50% to account for when no power can be generated. However, this factor is likely to vary depending on the renewable energy source, such as biofuel. In a scenario where the renewable energy equipment consists essentially of one or more wind turbines, a renewable energy equipment with a nominal capacity of 200 MW can be reasonably expected to produce approximately 50 tons of hydrogen per day (assuming approximately 50 kWh of power is provided to produce 1 kg of hydrogen).

[0058] The systems and methods described in this disclosure, including optional features and various embodiments, enable one or more large-scale electricity consumers 122. For example, the electrical load 122 can comprise at least one electrolyzer, including two, three, four, five, six, seven, eight, nine, ten, or more, connected to the system 100 and powered by electricity generated by the renewable equipment 108. Preferably, each of the at least one electrolyzer has a nominal capacity of at least 10 megawatts, preferably in the range of 10 megawatts (MW) to 10 gigawatts (GW). As mentioned in this disclosure and elsewhere in this disclosure, the electrical consumers of the electrical load 122, such as the one or more connected electrolyzers, do not receive power from a utility power grid to produce hydrogen.

[0059] Optionally, the electrical loads 122 may include an AC electrical network (such as a utility power grid) or may include an energy storage device, such as a battery. The AC electrical network and / or energy storage device act as an electrical load by accepting AC power output from the VSC subsystem 104, thereby allowing the flow of electricity to continue through the system 100. These options may be useful when the equipment 108 generates more power than can be used by the electrical loads 122 that comprise the equipment being powered by the system 100 and / or when, due to circumstances where a power grid connection is feasible, it may be more cost effective to "sell" the green power generated by the equipment 108 rather than using or storing it. It is understood that if the electrical load 122 includes one or more electrical consumers, such as electrolyzers, and one also chooses to connect the electrical consumers to a utility power grid, excess energy generated by the equipment 108 but not used by the connected consumers can be sent to the utility power grid (as described in WO202143912(A1)), and vice versa, if the electrical consumer(s) need more energy, it can be drawn from the utility power grid. However, it is understood that the methods and systems described herein preferably provide all power to operate one or more electrical consumers as described herein, rather than power coming from the utility power grid (grid independent).

[0060] To provide power from the VSC subsystem 104 to the electrical loads 122, power transmission equipment known to those skilled in the art, such as a transformer 120, may be used. If the electrical loads 122 include equipment that requires power for their operation, any number and / or type of suitable converter transformers 120 may be used to preferably step down the voltage of the power from the VSC subsystem 104 to an amount suitable for use by the electrical loads 122. Suitable converter transformers 120 include those that have DC voltage offset tolerance capabilities. It is understood that the electrical loads 122 may include their own converters for converting AC power to DC power for use where applicable. If the electrical loads 122 include another AC electrical network, a step-up transformer 120 may be used to provide power at an appropriate voltage accepted by the AC electrical network. If the electrical loads 122 include energy storage equipment, a step-down transformer is typically expected to interface to an energy storage unit.

[0061] Although FIG. 1 shows one electrical load 122 connected to one VSC 118 to receive the AC power output therefrom, it is understood that other configurations are available including one electrical load 122 connected to two or more VSCs 118 to receive the AC power output therefrom, or two or more electrical loads 122 connected to one VSC 118.

[0062] Although not shown, it is understood that the system 100 may employ a computer program to control various components of the system 100, such as the VSC subsystem 104, and to interact with the equipment 108 to control the voltage magnitude and phase of the electricity output from the equipment 108. This computer program may be referred to as a controller. For example, the power flowing through the HVDC transmission link 116 may be controlled by the control unit 130 independently of the phase angle between the equipment 108 and the electrical loads 122. Such control allows for stabilization of the HVDC system 100, the power source (the equipment 108), and the electrical loads 122 (collectively the electrical network 10) against disturbances due to sudden changes in power and as described further herein.

[0063] The system 100 may employ any suitable computer program for performing the applicable steps of the methods described herein when the computer program is executed by a data processor. As used herein, reference to a computer program is intended to be equivalent to a reference to a program element and / or a computer readable medium that includes instructions for controlling a computer system to coordinate the execution of the above-mentioned methods. The computer program may be implemented as a computer readable instruction code by using any suitable programming language, such as, for example, JAVA, C++, etc., and may be stored in a computer readable medium (removable disk, volatile or non-volatile memory, embedded memory / processor, etc.). The instruction code is operable to program a computer or any other programmable device to perform the intended functions. The computer program may be available from a network, such as the World Wide Web, or may be downloaded therefrom. The various aspects described herein may each be realized by a software computer program, however, they may also each be realized by one or more specific electronic circuits or hardware. Furthermore, the present invention may be realized in a hybrid form, i.e., a combination of software and hardware modules.

[0064] One challenge for an electrical network that relies on renewable sources of power and is independent of a power grid such as the power grid 10 is the intermittent nature of renewable energy that disrupts the network, from shutdowns when energy sources such as wind or solar are not available to fluctuating electricity production rates corresponding to weather. To maintain the HVDC transmission link 116 in a steady state, the active power flow into the HVDC transmission link 116 should be balanced, meaning that the active power leaving the link 116 and going to the electrical loads 122 through the VSC subsystem 104 is preferably equal to the power received by the link 116. As used herein, "steady state" in the context of the HVDC link 116 means when its operating voltage amplitude is within + / -0.01% to + / -10%, preferably + / -0.01% to + / -5%, more preferably + / -0.01% to + / -0.1% of its nominal voltage rating (or rated voltage). For example, referring to FIG. 2, an HVDC link for a wind turbine with a nominal voltage output of 690V by design choice has a rated voltage of 640kV (determined by considering the power losses due to the transmission equipment and the direct step-up relationship due to the transformer). The steady state of the HVDC link in FIG. 2 is when its operating voltage amplitude is between 640.2kV and 639.8kV. As used herein, "operating voltage" has its ordinary meaning, including the voltage at which a device or component is operating at a given moment. "Rated voltage" has its ordinary meaning, including the voltage at which a device or component can safely operate. Those skilled in the art know how to determine the rated voltage of the HVDC link 116 based on the specifications of the equipment 108, including the nominal voltage output, and the rated voltages of the components supporting the HVDC link 116.

[0065] Furthermore, if the electrical network 10 experiences a shutdown, restoring power is potentially problematic because the network 10 is not connected to a power grid. In particular, when power is available again after a shutdown, it is undesirable for the devices 108 to generate power at or near their power generation threshold because that amount of power would likely overwhelm the devices in the network 10 and cause a power surge that could lead to equipment failure rather than returning the network 10 to its steady state operation.

[0066] The present disclosure provides a method of using an HVDC system 100 to supply power from renewable energy equipment 108 to electrical loads 122, including restoring the flow of power to the network 10 after experiencing an outage (e.g., where there is no or minimal availability of renewable energy, such as wind or solar), without using power from the power grid.

[0067] According to one aspect, the present disclosure provides a method for energizing an HVDC system 100 to supply power from a renewable energy equipment 108 to an electrical load 122. As described herein, an HVDC system 100 is provided that includes a rectifier subsystem 102 and a VSC subsystem 104. The rectifier subsystem 102 includes at least one rectifier unit 116, an input (unsigned) electrically connected to the renewable energy equipment 108, and an output (unsigned) electrically connected to the VSC subsystem 104. As described, the VSC subsystem 104 includes at least one VSC 118, an input (unsigned) electrically connected to the rectifier subsystem 102, and an output (unsigned) electrically connected to at least one electrical load 122.

[0068] Referring to FIG. 3, in block 302, the HVDC system 100 and the electrical loads 122 need to be energized to start operating, such as after a shutdown of the network 10 due to a system failure or a shutdown of the equipment 108. The process of energizing the HVDC system 100 can be supported by auxiliary systems that first energize the renewable energy equipment 108 to start generating power. As shown in FIG. 1, the electrical loads 122 are only connected to the HVDC system 100 to receive its power, so when the HVDC link 116 is down, it also has no power and needs to be energized. Energizing the HVDC link 116 includes providing electrical power with appropriate characteristics (such as voltage magnitude and phase angle) to energize the electrical loads 122. As used herein, "energize" or its grammatical equivalents means to provide power to dormant equipment that does not have electricity flowing through it.

[0069] As shown in block 304, an initial voltage amplitude and phase angle of the power output of the renewable energy device 108 is determined based at least on a nominal voltage of the renewable energy device 108, as described herein. In block 306, the renewable energy device 108 is configured to generate a predetermined initial voltage amplitude and phase angle (V (電源)i and θ (電源)IThe renewable energy equipment 108 operates to function as a voltage source by generating power having a specific power generation rate at any instant in time, energizing the rectifier subsystem 102 and the HVDC link 116, thereby providing DC power to the VSC subsystem 104. The renewable energy equipment 108 generates power at a specific power generation rate at any instant in time. The computer program or controller components of the system 100 described herein can be programmed to determine this initial voltage magnitude and phase angle based on the nominal output voltage of the renewable energy equipment 108, as known to those skilled in the art, including at least considering the real and reactive power flows to the rectifier subsystem 102, as described herein. The computer program or controller components can transmit the predetermined initial voltage magnitude and phase angle to applicable components of the renewable energy equipment 108 (such as the internal VSC of the wind turbine) to generate such power having predetermined characteristics. The generated power is provided to the rectifier subsystem 102 via transmission equipment 112 and 114, such as transformers and wires, as referred to herein. The rectifier subsystem 102, powered by power from the renewable energy equipment 108, converts the AC power input to HVDC power, thereby powering the HVDC link 116 and providing the HVDC power to the VSC subsystem 104. In block 308, an initial voltage magnitude for the AC power output of the VSC subsystem 104 is preferably one that can initiate power flow to the electrical loads 122, as can be determined by one of ordinary skill in the art, at least as described herein. A computer program or controller component of the system 100 described herein can be programmed to determine this initial voltage magnitude. It is understood that the AC power output of the VSC subsystem 104 includes a phase angle in addition to a voltage magnitude.In block 310, the VSC subsystem 104 is operated to function as a voltage source for energizing one or more electrical loads 122 electrically connected to the VSC subsystem 104, where the VSC subsystem 104 provides an AC power output having an initial voltage magnitude to the connected electrical load(s) 122 via transmission equipment 120, such as a transformer and electrical lines as described herein, thereby energizing the electrical loads 122.

[0070] In block 312, it is determined whether the power generation rate of the renewable energy equipment 108 is within the specified parameters. If the answer is "yes" in block 314, the HVDC link 116 may be maintained in a steady state against a power imbalance caused by a change in the power generated by the renewable energy equipment 108, as further described in FIG. 5. If it is determined that the power generation rate of the renewable energy equipment 108 is not within the specified parameters, in block 314, the renewable energy equipment 108 is operated to follow the characteristics of the AC power output such that the power generation rate of the renewable energy equipment 108 can be controlled by controlling the characteristics of the AC power output of the VSC subsystem 104. That is, the VSC subsystem 104 is the "master" and the renewable energy equipment 108 is the "slave". Preferably, the renewable energy equipment 108 can be put into a "slave" mode until the power generation rate is within the specified parameters. Those skilled in the art will know how to use the computer program or controller components of the system 100 and / or the associated components of the renewable energy equipment 108 to achieve such a master / slave relationship.

[0071] 4 illustrates an exemplary process flow for controlling the AC power output of the VSC subsystem 104 to bring the power generation rate within specified parameters, and in particular, illustrates an option for implementing block 316 of FIG. 3 to operate the renewable energy equipment 108 to comply with the AC power output of the VSC subsystem 104. In block 316A, the VSC subsystem 104 is operated to provide an AC power output having a new voltage magnitude selected based at least on a desired incremental change to the AC voltage output. Preferably, the desired incremental change includes an incremental increase or decrease to the AC voltage output of the VSC subsystem 104, ultimately bringing the operating AC voltage output of the VSC subsystem 104 within specified parameters based at least on the nominal capacity (or nominal power consumption) of the load 122, which is an electrical consumer. For example, if the electrical load 122 consists essentially of one electrolyzer with a nominal capacity of 1 GW (10%-100%) per equipment manufacturer, hydrogen production can begin when provided with electrical power having a voltage swing equivalent to that of a 100 MW consumption, and can be increased to 100% as the voltage swing of the electrical power increases. In this scenario, the voltage swing of the AC electrical output of the VSC subsystem 104 can be adjusted (with incremental increases and decreases to accommodate system variations) until the voltage swing of the AC electrical output of the VSC subsystem 104 reaches the desired parameters, which may result in 1 GW or some percentage desired (e.g., 90%-99%, etc.). It is understood that designing a grid independent electrical network such as network 10 preferably takes into account the desired electrical load or demand and / or the desired renewable energy generation nominal capacity, which can aid in equipment selection and operating conditions.

[0072] In block 316A, the new voltage amplitude of the AC power output of the VSC subsystem 104 is different from the initial voltage amplitude from block 308. For example, the initial voltage amplitude is V (VSC)i and the new voltage swing is V (VSC)1The new voltage swing value may be determined based at least on the difference between the actual voltage output of the VSC subsystem 104 and the specified voltage output. In a preferred embodiment, the specified voltage output of the VSC subsystem 104 is a user-defined value based on the nominal capacity value of the electrical load 122, including the electrical consumer. The difference between the actual AC voltage output value and the specified AC voltage output value may be used to determine an appropriate incremental change in the AC voltage output value for the VSC subsystem 104. For example, this difference may be an input to a closed loop control system that provides as an output a voltage adjustment value (i.e., an incremental change) for the AC power output of the VSC subsystem 104 having the new voltage swing. It is to be understood that the computer program or controller component of the system 100 may be programmed to perform these and other steps as described herein.

[0073] As the VSC subsystem 104 begins to convert the DC power to AC power having a new voltage amplitude, the power output leaving the system 100 via the VSC subsystem 104 no longer corresponds to the power input entering the system 100 from the renewable energy equipment 108. Such a power imbalance is experienced by the renewable energy equipment 108 when in the "slave" mode because the remaining components in the system 100 are configured to maintain the HVDC link 116 in a steady state while in such mode. In block 316B, in response to at least the power imbalance from block 316A, the power generation of the renewable energy equipment 108 is adjusted to restore a power balance to the renewable energy equipment 108. Preferably, the power balance of the renewable energy equipment 108 is adjusted by operating at least the renewable energy equipment 108 to at least adjust the power generation of the renewable energy equipment 108 to the new voltage amplitude (V (VSC)1 ) corresponding to the new voltage amplitude and phase angle (V (電源)1 and θ (電源)1 ) is restored by generating power having a new voltage amplitude and phase angle (V (電源)1 and θ (電源)1), the power balance is restored to the equipment 108 and its power generation rate has been changed accordingly to match the new AC voltage output of the VSC subsystem 104.

[0074] The process may return to block 312, and if it is determined that the power generation rate of the renewable energy device 108 is not within the specified parameters, the process may return to block 316A, and the VSC subsystem 104 is operated to provide an AC power output having another new voltage amplitude configured to provide an incremental change in the amount of AC voltage output of the VSC subsystem 104, as described herein. This other new voltage amplitude may be V (VSC)2 This can be seen as the new voltage amplitude V (VSC)1 A change in the characteristics of the AC power output of the VSC subsystem 104 introduces a power imbalance to the renewable energy equipment 108, resulting in a corresponding change in the rate of power generation, and a new voltage amplitude and phase angle (V (電源)2 and θ (電源)2 to restore the power balance to the device 108.

[0075] Thus, blocks 312 and 316 (including 316A and 316B) may be implemented as a loop that controls the power generation rate of the equipment 108 (including steering the power generation rate of the renewable energy equipment 108 to the specified parameters) by controlling the characteristics of the AC output of the VSC subsystem 104 until the power generation rate is within the specified parameters. Preferably, the specified parameters include when the power generation rate is within + / - 10%, more preferably within + / - 5%, and most preferably within + / - 1% of the power generation threshold of the renewable energy equipment 108. Preferably, the power generation threshold is determined by maximum power point tracking (MPPT). It is understood that the specified parameters may be a design choice, such as any desired power generation rate, or may be subject to specific system and operational limitations (such as to accommodate variations in renewable energy sources such as wind or solar) as known to those skilled in the art. The loop of blocks 312 and 316 (including 316A and 316B) can be used to generally increase the power generation rate of the renewable energy equipment 108, which it will be understood can include cycles of decreasing and increasing the voltage amplitude of the AC output of the VSC subsystem 104 (and correspondingly the voltage amplitude of the renewable energy equipment 108) according to the operating conditions to accommodate rapid achievement of a steady state for the entire system 10.

[0076] If, in block 312, it is determined that the power generation rate is within the specified parameters, the system 100 may operate in a steady state operation in which the HVDC link 116 is maintained in a steady state against power imbalances caused at least by changes in the characteristics of the power generated by the renewable energy equipment 108, as further described with respect to FIG.

[0077] In steady state operation of the system 100, the VSC subsystem 104 can be operated to be a "slave" and follow the power output of the renewable energy equipment 108 that is currently the "master". That is, when the renewable energy equipment 108 is operating as a "slave", it is instructed to stop following the VSC subsystem 104 so that its power generation rate is not affected by changes in the AC electrical output. As a "master", changes to the electrical power generated by the renewable energy equipment 108 (including changes to the voltage amplitude and / or phase angle) affect the AC electrical output of the VSC subsystem 104. For example, in the "slave" mode, the VSC subsystem 104 can be programmed to adjust the voltage amplitude and phase angle of its AC electrical power output to correspond to the characteristics of the electrical power generated by the renewable energy equipment 108. The computer program or controller components of the system 100, the VSC subsystem 104, and / or associated components of the renewable energy equipment 108 can be programmed to implement this configuration of the renewable energy equipment 108 acting as a "master" and the VSC subsystem 104 acting as a "slave" as described above, as known to those skilled in the art.

[0078] 5, in block 502, during steady state operation, the renewable energy equipment generates power to keep the HVDC link 116 powered and provides DC power to the VSC subsystem. The generated power has a voltage magnitude and phase angle, V, respectively, that maintains the HVDC link 116 in a steady state. (電源)s and θ (電源)V. As will be appreciated by those skilled in the art, changes to the characteristics of the power generated by the renewable energy equipment 108 may be caused at least by changes in active power input from the dynamic nature of the renewable energy equipment, such as aerodynamic torque input from wind if the equipment 108 includes a wind turbine, with respect to voltage amplitude, and at least by a redistribution of reactive power across all applicable units of the renewable energy equipment with respect to phase angle. In block 504, the condition of the HVDC link 116 is monitored to detect power imbalances in the HVDC link 116 caused by changes in at least the voltage amplitude and phase angle of the power generated by the renewable energy equipment. Suitable systems and methods for monitoring the condition of the HVDC link 116 and detecting such power imbalances are known to those skilled in the art.

[0079] The renewable energy device 108 has a new voltage amplitude and phase angle, V (電源)新 and θ (電源)新 where, if the change is large enough, it can cause the HVDC link 116 to deviate from steady state. This can occur when the power output leaving the system 100 via the VSC subsystem 104 no longer corresponds to the power input entering the system 100 from the renewable energy equipment 108. Such a power imbalance is experienced by the HVDC link 116 when the VSC subsystem 104 is in a "slave" mode. This is in contrast to when the renewable energy equipment 108 is in a "slave" mode. An amount of power imbalance experienced by the HVDC link 116 that exceeds a certain threshold can cause a deviation of the HVDC link 116 from steady state.

[0080] If a deviation from steady state caused by at least a change in voltage amplitude and phase angle of the power generated by the renewable energy equipment 108 is detected in block 506, steady state of the HVDC link 116 is restored in block 508. If the HVDC link remains in steady state, no action is required. It is understood that the system may be programmed to perform monitoring steps as desired, including with respect to whether or not the process proceeds to block 508.

[0081] In block 508, if a deviation is detected in block 506, the steady state of the HVDC link 116 is restored by identifying the change in voltage amplitude and phase angle of the power generated by the renewable energy equipment 108 that caused the deviation in block 510. In block 512, the voltage amplitude of the AC power output of the VSC subsystem 104 is adjusted in response to the identified change, thereby restoring the HVDC link 116 to the steady state. That is, the VSC subsystem 104 adjusts the new voltage amplitude and phase angle (V (電源)新 and θ (電源)新 ) corresponding to the new voltage swing (V (VSC)新 ) to provide an AC power output having a

[0082] Optionally and preferably, the status of the HVDC link 116 is continuously monitored. More preferably, the continuously monitoring includes checking the status of the HVDC link 116 at time intervals of less than 1 second, preferably less than 0.01 seconds, more preferably less than 1 millisecond (ms), such as in the range of 1 microsecond (μs) to 1 second, preferably 10 μs to 0.01 seconds, more preferably 50 μs to 1 ms. Under such continuous monitoring, in block 508, when the HVDC link 116 is restored to a steady state, new voltage amplitudes and phase angles (V (電源)新 and θ (電源)新 ) become the new steady state voltage amplitudes and phase angles for which changes are identified in block 510 to restore the HVDC link 116 to a steady state again.

[0083] The process shown in FIG. 5 and described herein may be useful for maintaining the HVDC system 100 in a steady state in situations where variations in voltage amplitude and phase angle equipment 108 generate electricity from variable renewable energy sources such as wind or sun.

[0084] As explained, the methods provided herein address the challenges associated with directly supplying power from renewable energy equipment to electricity consumers, especially those that have a large annual energy consumption for their operation, such as in the GW range, and that receive their power only from the renewable energy equipment rather than alternatively or additionally connected to the utility power grid for their power supply. In particular, the methods described with respect to Figs. 3 and 4 enable black starting of the HVDC link with power from the renewable energy equipment and transmit that power to black starting the connected electricity consumers. Furthermore, the methods described with respect to Figs. 3 and 4 enable controlling the power generation rate of the renewable energy equipment to be within specified parameters, preferably its power generation threshold, to maximize the rate of energy that can be produced at a given moment. The method described with respect to Fig. 5 enables the steady state of the HVDC link to be maintained even when the system experiences power imbalances caused at least by potential variable power generation that may take the HVDC link out of steady state. Maintaining the HVDC link in steady state also helps to ensure a steady supply of power from the renewable energy equipment to the electricity consumers. As can be appreciated, the systems and methods described in this specification section, including all described features and embodiments, achieve the objects and / or advantages described in the Summary of the Invention section.

[0085] Although specific embodiments have been described herein, it is understood that such description is not intended to limit the described embodiments. Instead, any combination of the features and elements provided above, whether related to different embodiments or not, is contemplated for implementing and practicing the contemplated embodiments. Furthermore, the embodiments disclosed herein may achieve other possible solutions or advantages over the prior art, but whether or not a particular advantage is achieved by a given embodiment does not limit the scope of the disclosure. Thus, the aspects, features, embodiments, and advantages described herein are merely exemplary and are not considered elements or limitations of the appended claims unless expressly recited in the claim(s).

Claims

1. 1. A method for supplying electrical power from a renewable energy device (108) to an electrical load (122), the method comprising: (a) providing an HVDC system (100) comprising an AC / DC converter subsystem (102) and a VSC subsystem (104); the AC / DC converter subsystem comprises at least one AC / DC converter unit (106), an input electrically connected to the renewable energy equipment (108), and an output electrically connected to the VSC subsystem (104); the VSC subsystem comprising at least one VSC (118), an input electrically connected to the AC / DC converter subsystem (102), and an output electrically connected to at least one electrical load (122); (b) determining an initial voltage magnitude and phase angle of electrical power generated by the renewable energy device (108); (c) operating the renewable energy equipment (108) to generate power having the predetermined initial voltage magnitude and phase angle from step (b) for energizing an HVDC link (116) between the AC / DC converter subsystem (102) and the VSC subsystem (104), thereby supplying DC power to the VSC subsystem (104), wherein the renewable energy equipment (108) generates power at a power generation rate; (d) operating the VSC subsystem (104) to convert the DC power to an AC power output for energizing the at least one electrical load (122), the AC power output comprising an initial voltage swing; (e) determining whether the power generation rate of the renewable energy equipment is within specified parameters, and if the result of the determination is "no", operating the renewable energy equipment in accordance with the VSC subsystem (104) such that controlling the AC power output of the VSC subsystem (104) affects the power generation rate of the renewable energy equipment (108); (f) varying the AC power output of the VSC subsystem (104), thereby introducing a power imbalance to the renewable energy equipment (108); (g) in response to at least the power imbalance from step (f), adjusting a power generation rate of the renewable energy equipment (108) to restore a power balance to the renewable energy equipment (108); (h) repeating steps (e) through (g) until the power generation rate of the renewable energy device (108) is determined to be within the specified parameters; A method comprising:

2. step (f) includes operating the VSC subsystem (104) to provide an AC power output including a new voltage amplitude selected based at least on a desired incremental change to the AC voltage output; step (g) includes operating the renewable energy equipment (108) to generate power at a new voltage amplitude and phase angle corresponding to the new voltage amplitude of the VSC subsystem (104) from step (f) to restore a power balance to the renewable energy equipment (108); The method of claim 1.

3. The method of claim 2 , wherein the desired incremental change is determined based at least on a difference between an actual AC voltage output and a commanded AC voltage output of the VSC subsystem.

4. (i) upon determining that the power generation rate of the renewable energy equipment (108) is within the specified parameters, operating the VSC subsystem (104) to follow the renewable energy equipment (108) such that changes in power generated by the renewable energy equipment (108) affect the AC power output of the VSC subsystem (104); (j) maintaining the HVDC link in a steady state in response to a detected power imbalance in the HVDC link caused by at least a change in the power generated by the renewable energy equipment by operating the VSC subsystem (104) to adjust a voltage swing of its AC power output to correspond to the power generated by the renewable energy equipment (108); The method of any one of claims 1 to 3, further comprising:

5. Step (j) is - Identifying changes in the voltage amplitude and phase angle of the power generated by the renewable energy equipment that cause the detected power imbalance; - adjusting the AC power output of the VSC subsystem (104) to restore the HDVC link (116) to a steady state by operating the VSC subsystem (104) to provide an AC power output having a new voltage amplitude based on the identified change; The method of claim 4 , comprising:

6. The method according to any one of claims 1 to 5, wherein the specified parameter is within a range of -10% to +10%, preferably -5% to +5%, more preferably -1% to +1% of a power generation threshold of the renewable energy equipment.

7. The method of claim 6 , wherein the power generation threshold is determined by maximum power point tracking (MPPT).

8. 1. A method for controlling an HVDC system to supply power from a renewable energy device to an electrical load, in particular an electrical load that is independent of a power grid, the method comprising: (a) providing an HVDC system (100) comprising an AC / DC converter subsystem (102) and a VSC subsystem (104); the AC / DC converter subsystem comprises at least one AC / DC converter unit (106), an input electrically connected to the renewable energy equipment (108), and an output electrically connected to the VSC subsystem (104); the VSC subsystem comprising at least one VSC (118), an input electrically connected to the AC / DC converter subsystem (102), and an output electrically connected to at least one electrical load (122); (b) operating the renewable energy equipment (108) to generate power having a voltage magnitude and phase angle that maintains the HDVC link (116) in a steady state and supplying DC power to the VSC subsystem (104); (c) operating the VSC subsystem (104) to convert the DC power to an AC power output for supply to at least one electrical load (122), the AC power output comprising a first voltage amplitude; (d) monitoring a condition of the HVDC link (116) to detect deviations from steady state caused by changes in voltage magnitude and phase angle of electrical power generated by at least the renewable energy equipment (108); (e) upon detecting the deviation, restoring the HVDC link (116) to a steady state, the restoring step including the steps of identifying the change from step (d) and operating the VSC subsystem (104) to convert the DC power to an AC power output having a new voltage amplitude selected based on the identified change; A method comprising:

9. 9. The method of claim 8, wherein step (d) comprises continuously monitoring, wherein the condition of the HVDC link is continuously monitored at a time interval of less than 1 second, preferably less than 0.01 seconds, more preferably less than 1 millisecond (ms), such as in the range of 1 microsecond (μs) to 1 second, preferably 10 μs to 0.01 seconds, more preferably 50 μs to 1 ms.

10. 10. A method according to any one of claims 1 to 9, wherein the HVDC link is in steady state when its operating voltage amplitude is within the range of + / -0.01% to + / -10%, preferably + / -0.01% to + / -5%, more preferably + / -0.01% to + / -0.1% of its nominal voltage rating.

11. The method according to any one of claims 1 to 10, wherein the at least one electrical load is one or more electrical consumers.

12. 12. The method of claim 11 , wherein the one or more electricity consumers comprise electrolysers having a nominal capacity of at least 10 megawatts, preferably in the range of 10 megawatts (MW) to 10 gigawatts (GW).

13. 13. The method of claim 12, wherein the electrolyzer does not receive power from a utility power grid to produce hydrogen.

14. The method of any one of claims 1 to 13, wherein the AC / DC converter subsystem (102) is a rectifier subsystem comprising at least one rectifier unit.

15. The method of claim 14 , wherein the rectifier subsystem comprises a plurality of rectifier units connected in series and / or the VSC subsystem comprises a plurality of VSCs connected in series.

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