WO2023174529A1

WO2023174529A1 - A system comprising a hydrogen electrolyser unit and an enhanced static compensator and a method for controlling the system

Info

Publication number: WO2023174529A1
Application number: PCT/EP2022/056867
Authority: WO
Inventors: Nicklas Johansson; Bertil Berggren; Jan Svensson
Original assignee: Hitachi Energy Switzerland Ag
Priority date: 2022-03-16
Filing date: 2022-03-16
Publication date: 2023-09-21

Abstract

A system (100), a control unit (130) and a method (1000) for controlling the system (100) is provided. The system comprises a hydrogen electrolyser unit (110), an enhanced static compensator, E-STATCOM, (120), and a control unit (130). The hydrogen electrolyser unit (110) is connected to an electrical power grid (101) at a point of common coupling, PCC, (102) and is configured to consume active power, P_el, from the electrical power grid. The E-STATCOM (120) is connected to the electrical power grid at the PCC, comprising an energy storage unit (121), and configured to supply or consume active power, P_ESS, to the electrical power grid via the energy storage unit and to adjust a reactive power contribution to the electrical power grid. The control unit (130) configured to control an active power contribution from the hydrogen electrolyser unit and the E-STATCOM based on a reference value.

Description

A SYSTEM COMPRISING A HYDROGEN ELECTROLYSER UNIT AND AN ENHANCED

STATIC COMPENSATOR AND A METHOD FOR CONTROLLING THE SYSTEM

TECHNICAL FIELD

The present disclosure generally relates to the field of power system control.

BACKGROUND

In order to limit the impact and the negative effects of climate change, a reduction of emission of CO2 and other gases which contribute to global warming is needed. Therefore, the use of renewable energy sources, such as solar and wind, have increased in recent years, and will continue to increase. Renewable energy sources are a type of non-synchronous generation, NSG, wherein the amount of power generated by a NSG may fluctuate. A high level of NSG within a power system, or power grid, brings challenges, such as, frequency stability of the power system, voltage stability of the power system, short-circuit power levels and harmonic stability of the power system.

In traditional power systems, this has not been as big of an issue due to the prevalence of synchronous generation, which provides a high amount of rotating inertia in the power system, and for which the output may be increased, relatively fast, in response to an increased power demand. Therefore, synchronous generation may provide a high level of power system control.

It is therefore of interest to provide an improved level of power system control, especially in a power system with a high penetration of NSG.

SUMMARY

It is therefore a goal of the present disclosure to provide a system, a control unit and a method which may provide power system control.

To achieve this goal, the present disclosure provides a system comprising a hydrogen electrolyser unit and an enhanced static compensator, E-STATCOM, a control unit, and a method for controlling the system, as defined by the independent claims. Further embodiments are provided in the dependent claims.

According to an aspect of the present disclosure, a system is provided. The system provides a hydrogen electrolyser unit connected to an electrical power grid at a point of common coupling, PCC. The hydrogen electrolyser unit is configured to consume active power from the electrical power grid. The system further comprises an enhanced static compensator, E-STATCOM, connected to the electrical power grid at the PCC. The E-STATCOM comprises an energy storage unit, and is configured to supply or consume active power to the electrical power grid, via the energy storage unit, and to adjust a reactive power contribution to the electrical power grid. The system further comprises a control unit configured to control an active power contribution from the hydrogen electrolyser unit and the E-STATCOM based on a reference value. The control unit is configured to, upon determining whether a grid frequency of the electrical power grid at the PCC deviates from a reference frequency: update the reference value, determine a target value for the power consumption of the hydrogen electrolyser unit from the electrical power grid based on the updated reference value, and cause the hydrogen electrolyser unit to decrease or increase its active power consumption from the electrical power grid towards the determined target value. Until the active power consumption of the hydrogen electrolyser unit has reached the determined target value, the control unit is configured to cause the E-STATCOM to supply or consume active power to or from the electrical power grid such that the collective active power contribution from the hydrogen electrolyser unit and the E-STATCOM corresponds to the updated reference value. The control unit is further configured to control the reactive power contribution from the E-STATCOM.

According to a second aspect of the present disclosure, a method for controlling a system is provided, wherein the system comprises a hydrogen electrolyser unit and an E-STATCOM being connected to an electrical power grid at a PCC and comprising an energy storage unit. The method comprises, upon determining whether a grid frequency of the electrical power grid at the PCC deviates from a reference frequency, determining a reference value for controlling an active power contribution from the system to the electrical power grid, determining a target value for active power consumption of the hydrogen electrolyser unit from the electrical power grid based on the reference value, and causing the active power consumption of the hydrogen electrolyser unit to decrease or increase towards the target value. Until the active power consumption of the hydrogen electrolyser unit has reached the target value, the method comprises causing the E-STATCOM to supply or consume active power to or from the electrical power grid such that the collective active power contribution of the hydrogen electrolyser unit and E-STATCOM corresponds to the reference value. The method further comprises causing the E-STATCOM to adjust a reactive power contribution to the electrical power grid.

According to a third aspect of the present disclosure, a control unit is provided. The control unit is configured to perform the method according to the second aspect of the present disclosure. The control unit may be connected to and/or in communication with a system according to the first aspect of the present disclosure.

The amount of hydrogen produced via electrolysis is expected to increase dramatically within the next few years. Thus, hydrogen electrolyser units are expected to act as large electric loads in electrical power grids. Electrical power grids comprising hydrogen electrolyser unit(s) acting as large electrical load(s), and/or a high degree of NSGs, may have a large need for electrical power grid control, i.e. frequency control, such as fast supply or consumption of active and/or reactive power. However, due to the increasing amount of NSGs in the electrical power grids, the ability to rapidly supply active power into an electrical power grid, in case of, for example, a dip in power production, will be diminished. A dip in power production may be indicated by a decrease of the grid frequency of the electrical power grid. When a dip in power production occurs, the required duration of supplying active power may last at least 15 minutes. Therefore, there is a need of providing fast electrical power grid control in an electrical power grid which may comprise one or more hydrogen electrolyser unit(s) and/or a high degree of NSGs.

The control method of the present disclosure is based on coordination of fast electrical power grid control via an E-STATCOM, which is able to quickly supply or consume reactive power and to supply or consume active power, and adjustment of the active power consumed by a hydrogen electrolyser unit, thereby providing in combination faster and more time-extended electrical power grid control. This coordinated combination provides a faster response as if an adjustment of the active power consumed was only made by a hydrogen electrolyser unit, since a hydrogen electrolyser unit may not be able to change its active power consumption sufficiently fast. Thus, the faster response of the E-STATCOM provides electrical power grid control until the adjustment of the active power consumption by the hydrogen electrolyser unit has been accomplished, thereby providing both faster and more time-extended electrical power grid control. In other words, the coordinated combination may thereby be utilized in the electrical power grid as a large flexible load in the system. The coordinated combination may be eligible to bid, or act, in several frequency (or electrical power) control market segments, which may lead to increased profits in comparison to solely a hydrogen electrolyser unit or solely an E-STATCOM.

The present disclosure is not limited to a system comprising a single hydrogen electrolyser unit, and may comprise a plurality of hydrogen electrolyser units or a hydrogen electrolyser plant. Further, the present disclosure is not limited to a system comprising a single E-STATCOM, and may comprise a plurality of E- STATCOMs. The E-STATCOM may comprise a plurality of energy storage units, which may be connected to each other in series or in parallel. Additionally, the system may comprise one or more STATCOM(s). The control unit may be communicatively connected to the hydrogen electrolyser unit and/or the E-STATCOM.

The energy storage unit may be an electrical energy storage unit. The energy storage unit may store electrical energy. An energy storage unit which is supplying active power may understood as discharging of the energy storage unit. Correspondingly, an energy storage unit which is consuming active power may be understood as charging of the energy storage unit.

The system may comprise an internal controlled resistive circuit, such as a chopper, which is configured to burn, or consume, electrical energy, and may be connected to the electrical power grid at the PCC. The system may be configured to cause the internal controlled resistive circuit to consume active power from the electrical power grid, which may, sometimes, be more efficient than storing electrical energy in the energy storage unit of the E-STATCOM.

The control unit may be configured to receive information pertaining to the active power consumption of the hydrogen electrolyser unit, determining whether active power consumption of the hydrogen electrolyser unit has reached the determined target value. Additionally, the control unit may be configured to receive information pertaining to the active power contribution of the E-STATCOM, for determining that the collective active power contribution from the hydrogen electrolyser unit and the E-STATCOM corresponds to the updated reference value.

The reference value for controlling an active power contribution from the system to the electrical power grid may be based on the determined grid frequency deviation. Consequently, the control unit may be further configured to update the reference value based on the determined grid frequency deviation. A larger determined grid frequency deviation may lead to a more significant update of the reference value. For example, a grid frequency deviation of -1 Hz may lead to the updated reference value being 70% of the previous reference value. The update may be based on a predetermined data table which indicates to which degree the reference value should be updated if a given grid frequency deviation is determined. Further, the degree by which the reference value is updated based on a determined grid frequency may be predetermined by a transmission system operator, TSO, responsible for the electrical power grid.

A renewable energy plant may be connected to the electrical power grid, at the PCC, and configured to supply active power to the electrical power grid. The control unit may be further configured to receive information indicative of a deviation of active power supplied to the electrical power grid by the renewable energy plant. The control unit may be further configured to update the reference value based on the received information. Correspondingly, the method may further comprise receiving information indicative of a deviation of active power supplied to the electrical power grid by the renewable energy plant, and determining the reference value for controlling an active power contribution from the system to the electrical power grid based on the received information. Thus, the reference value may be based on a determined grid frequency deviation and/or information indicative of a deviation of active power supplied to the electrical power grid by the renewable energy plant, thereby allowing for a more finely-tuned updated reference value, which may increase the response speed and/or the efficiency of the system.

The present disclosure provides the benefits of running a reliable microgrid comprising one or more hydrogen electrolyser unit(s), one or more E-STATCOM(s) and one or more renewable energy plant(s), wherein the output of the microgrid is hydrogen produced by the one or more hydrogen electrolyser unit(s). Due to instability of a microgrid with a high degree of, or exclusive, power production from renewable energy plant(s), such a microgrid would rely heavily on the reactive power control provided by the one or more E-STATCOM(s), as well as the combined and coordinated active power control provided by the hydrogen electrolyser unit(s) and the E-STATCOM(s).

The reactive power supplied to the electrical power grid may be based on the active power consumption of the hydrogen electrolyser unit, a reactive power consumption of the hydrogen electrolyser unit, and a voltage at the PCC. Correspondingly, the control unit may be further configured to control the reactive power contribution from the E-STATCOM based on the active power consumption of the hydrogen electrolyser unit, a reactive power consumption of the hydrogen electrolyser unit, and a voltage at the PCC. Therefore, the E-STATCOM may provide a more finely adjusted reactive power control, which may improve the stability in the electrical power grid.

The control unit may be further configured to cause the E-STATCOM to inject a harmonic current to the electrical power grid at the PCC based on phase currents at the PCC, the active power consumption of the hydrogen electrolyser unit, a reactive power consumption of the hydrogen unit, and a voltage at the PCC. Correspondingly, the method may further comprise causing the E-STATCOM to inject a harmonic current to the electrical power grid at the PCC based on phase currents at the PCC, the active power consumption of the hydrogen electrolyser unit, the reactive power consumption of the hydrogen unit, and a voltage at the PCC. Therefore, the E-STATCOM may provide increased stability within the electrical power grid, thereby reducing losses within the electrical power grid, i.e. improving the efficiency in the electrical power grid.

The hydrogen electrolyser unit may be connected to the PCC via a rectifier. The rectifier may, alternatively, be referenced to as a "rectifier converter". The rectifier may be a thyristor-based converter, a diode rectifier which may comprise a DC/DC converter or a DC/DC buck converter, or a Pulse-Width Modulation-, PWM-, based AC/DC converter comprising insulated-gate bipolar transistors, IGBTs.

The hydrogen electrolyser unit may be an alkaline hydrogen electrolyser unit or a proton exchange membrane, PEM, hydrogen electrolyser unit. Further, the system may comprise a plurality of hydrogen electrolyser units, or a hydrogen electrolyser plant, comprising one or more alkaline hydrogen electrolyser unit(s) or one or more PEM hydrogen electrolyser unit(s). Advantages of alkaline electrolyser units, in comparison to other types of hydrogen electrolyser units, are that they comprise cheaper catalysts, have a higher lifespan, and produces hydrogen gas with a high purity. Advantages of PEM electrolyser units, in comparison to other types of hydrogen electrolyser units, are that they have a higher current density, they are more compact, have a smaller footprint, have a fast response, and allow for dynamic operation. However, PEM electrolyser units are more expensive.

The energy storage unit of the E-STATCOM may comprise at least one of a supercapacitor or a battery. An advantage of supercapacitors is their fast response time with regards to supplying and/or consuming active power. On the other hand, batteries may provide a higher energy storage capability, or active power capacity. A combination of one or more supercapacitor and one or more batteries may thereby provide the advantages of both.

The control unit may be configured to, upon determining a grid frequency deviation, cause the E-STATCOM to supply or consume active power to the electrical power grid such that the collective active power contribution from the hydrogen electrolyser unit and the energy storage unit corresponds to the updated reference value within 2 seconds, 1 second, or 0.5 seconds of updating the reference value.

Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, module, action, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, action, etc., unless explicitly stated otherwise. The actions of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present disclosure will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the disclosure.

Figs. 1 to 3 schematically show systems according to exemplifying embodiments of the present disclosure.

Fig. 4 shows a flowchart of a method according to an exemplifying embodiment of the present disclosure.

Fig. 5 shows a graph disclosing a method according to an exemplifying embodiment of the present disclosure.

DETAILED DESCRIPTION

Fig. 1 schematically shows a system 100 according to an exemplifying embodiment of the present disclosure.

The system 100 comprises a hydrogen electrolyser unit 110, and an enhanced static compensator, E-STATCOM, 120, which are both connected to an electrical power grid 101 at a point of common coupling, PCC, 102. The electrical power grid 101 may be understood as being part of regional, national, or international electrical power grid, to which the system 100 is connected. The hydrogen electrolyser unit 110 is configured to consume active power from the electrical power grid 101. The E-STATCOM 120 comprises an energy storage unit 121, and is configured to supply or consume active power to/from the electrical power grid 101, via the energy storage unit 121, and to adjust a reactive power contribution to the electrical power grid 101. The hydrogen electrolyser unit 110 may be an alkaline hydrogen electrolyser unit or a proton exchange membrane, PEM, hydrogen electrolyser unit. Additionally, the hydrogen electrolyser unit 110 is shown in Fig. 1 to be connected to the PCC 102 via a rectifier 103. However, the hydrogen electrolyser unit 110 may be connected to the PCC 102 in a different manner, such as, for example, directly to the PCC 102, and/or via a transformer (not shown). The energy storage unit 121 of the E-STATCOM 120 may comprise at least one of a supercapacitor or a battery. Further, the E-STATCOM 120 may be connected to the PCC 102 via a transformer (not shown). Additionally, the system

100 may comprise a transformer (not shown) connected between the PCC 102 and the electrical power grid 101.

The system 100 further comprises a control unit 130 configured to control an active power contribution from the hydrogen electrolyser unit 110 and the E-STATCOM 120 based on a reference value. The control unit 130 may be communicatively connected to the hydrogen electrolyser unit 110 and/or the E- STATCOM 120, wherein the communicative connection may be wireless and/or via wire.

The control unit 130 is configured to determine a grid frequency of the electrical power grid 101 at the PCC 102. The determination of a grid frequency of the electrical power grid 101 may be determined by a sensor unit (not shown) arranged at the PCC 102 which may be communicatively connected to the control unit 130. The control unit 130 is further configured to, upon determining whether a grid frequency of the electrical power grid 101 at the PCC 102 deviates from a reference frequency: update the reference value, which may be based on the determined grid frequency deviation, determine a target value for the power consumption of the hydrogen electrolyser unit 110 from the electrical power grid

101 based on the updated reference value, and cause the hydrogen electrolyser unit 110 to decrease or increase its active power consumption from the electrical power grid 101 towards the determined target value. The control unit 130 is further configured to, until the active power consumption of the hydrogen electrolyser 110 unit has reached the determined target value, cause the E-STATCOM 120 to supply or consume active power to/from the electrical power grid 101 such that the collective active power contribution from the hydrogen electrolyser unit 110 and the E-STATCOM 120 corresponds to the updated reference value.

The control unit 130 is further configured to control the reactive power contribution from the E-STATCOM. The control unit 130 may be further configured to control the reactive power contribution from the E-STATCOM 120 based on the active power consumption of the hydrogen electrolyser unit 110, a reactive power consumption of the hydrogen electrolyser unit 110, and a voltage at the PCC 102, wherein the voltage may be measured, and/or determined, by a sensor unit (not shown) communicatively connected to the control unit 130. The control unit 130 may be further configured to cause the E-STATCOM 120 to inject a harmonic current to the electrical power grid 101 at the PCC 102 based on phase currents at the PCC 102, the active power consumption of the hydrogen electrolyser unit 110, a reactive power consumption of the hydrogen unit 110 and a voltage at the PCC 102. The phase currents at the PCC 102 may be measured, and/or determined, by a sensor unit (not shown) communicatively connected to the control unit 130. Additionally, the control unit 130 may be configured to, upon determining a grid frequency deviation, cause the E-STATCOM 120 to supply or consume active power to the electrical power grid 101 such that the collective active power contribution from the hydrogen electrolyser unit 110 and the energy storage unit 120 corresponds to the updated reference value within, for example, 2 seconds or 1 second of updating the reference value.

The present disclosure is not limited to a system 100 comprising one hydrogen electrolyser unit 110, as shown in Fig. 1. The system 100 may comprise a plurality of hydrogen electrolyser units 110. Each hydrogen electrolyser unit 110 may be connected to the PCC 102. Further, the present disclosure is not limited to a system comprising one E-STATCOM 120, as shown in Fig. 1. The system 100 may comprise a plurality of E-STATCOMs 110, wherein each E-STATCOM 110 may be connected to the PCC 102. Furthermore, an E-STATCOM 120 may comprise one or more energy storage unit(s) 121.

The control unit 130 may, alternatively, be configured as a control system comprising a plurality of communicatively connected control units 130, wherein each control unit 130 may be connected to one or more of the parts of the system 100.

Fig. 2 schematically shows a system 200 according to an exemplifying embodiment of the present disclosure. It should be noted that Fig. 2 comprises features, elements and/or functions as shown in Fig. 1 and described in the associated text. The features are identified by reference numbers made up of the number of the figure to which it relates followed by the number of the feature, which are equivalents for all exemplifying embodiments, e.g. the common feature "10" is indicated by "110" in Fig. 1 while the corresponding feature is indicated by "210" in Fig. 2. Hence, it is also referred to Fig. 1 and the description relating thereto for an increased understanding. A difference between the system 200 shown in Fig. 2 and the system 100 shown in Fig. 1 is that the system 200 comprises two hydrogen electrolyser units 210. The hydrogen electrolyser units 210 are connected in parallel, but may, alternatively, be connected in series. Further, the system 200 may comprise one or more additional hydrogen electrolyser unit(s) 210. Each hydrogen electrolyser unit 210 is connected to a respective rectifier 203. An E-STATCOM 220, comprising an energy storage unit 221, and the two hydrogen electrolyser units 210 are connected to a PCC 202 of an electrical power grid 201. However, the hydrogen electrolyser units 210 are connected to the PCC 202 via a transformer 204, while the E-STATCOM 220 is connected directly to the PCC 202. It is to be understood that the present disclosure is not limited to a system 200 comprising a transformer 204 connected as shown in Fig. 2, and that the system 200 may comprise more, or fewer transformers 204. For example, the E-STATCOM 220 may be connected to the PCC via a transformer (not shown). Further, the system 200 comprises a control unit 230 which is communicatively connected to the hydrogen electrolyser units 210 and the E-STATCOM 220.

Fig. 3 schematically shows a system 300 according to an exemplifying embodiment of the present disclosure. It should be noted that Fig. 3 comprises features, elements and/or functions as shown in Figs. 1 and 2 and described in the associated texts. The features are identified by reference numbers made up of the number of the figure to which it relates followed by the number of the feature, which are equivalents for all exemplifying embodiments, e.g. the common feature "10" is indicated by "110" in Fig. 1 while the corresponding feature is indicated by "310" in Fig. 3. Hence, it is also referred to Figs. 1 and 2 and the descriptions relating thereto for an increased understanding.

A difference between the system 300 shown in Fig. 3 and the systems 100, 200 shown in Figs. 1 and 2, respectively, is that a renewable energy plant 340 is connected to the electrical power grid 301, at the PCC 302 of the electrical power grid 301. The renewable energy plant 340 is configured to supply active power to the electrical power grid 301. Although the renewable energy plant 340 is shown in Fig. 3 to be directly connected to the PCC 302, the renewable energy plant 340 may be connected to the PCC 302 via, for example, a transformer (not shown; see e.g. Figs. 1 and 2). Further, the renewable energy plant 340 may comprise a plurality of parts, each being configured to supply active power to the electrical power grid 301.

Another difference between the system 300 shown in Fig. 3 and the systems 100, 200 shown in Figs. 1 and 2, respectively, is that an electrical power grid 301 of the system 300 may be a closed electrical power grid, a microgrid or a local electrical power grid. However, the present disclosure is not limited to a system 300 connected to a closed electrical power grid, and the system 300 may, alternatively, be connected to a regional, national, or international electrical power grid to which one or more renewable energy plant(s) 340 is/are connected.

The system 300 further comprises a control unit 330 which is communicatively connected to the hydrogen electrolyser unit 310, the E-STATCOM 320 and the renewable energy plant 340.

The electrical power grid 301 being a closed electrical grid may be facilitated by the renewable energy plant 340 supplying active power to the electrical power grid 301. Further, a coordinated control of a hydrogen electrolyser unit 310, an E- STATCOM 320 and the renewable energy plant 340 may allow for providing power grid control within the (closed) electrical power grid 301.

Fig. 4 shows a flowchart of a method 1000 according to an exemplifying embodiment of the present disclosure for controlling a system according to an exemplifying embodiment of the present disclosure, such as those shown in Figs. 1 to 3 and the descriptions relating thereto.

The method comprises, upon determining 1010 whether a grid frequency of an electrical power grid at a PCC deviates from a reference frequency, determining 1020 a reference value for controlling an active power contribution from the system to the electrical power grid, determining 1030 a target value for active power consumption of a hydrogen electrolyser unit of the system from the electrical power grid based on the reference value, causing 1040 the active power consumption of the hydrogen electrolyser unit to decrease or increase towards the target value. The method further comprises, until the active power consumption of the hydrogen electrolyser unit has reached the target value, causing 1050 an E-STATCOM of the system to supply or consume active power to/from the electrical power grid such that the collective active power contribution of the hydrogen electrolyser unit and E- STATCOM corresponds to the reference value.

The method further comprises causing 1060 the E-STATCOM to supply reactive power to the electrical power grid, which may be performed simultaneously and/or intermittently as any other step of the method 1000. The reactive power supplied to the electrical power grid may be based on the active power consumption of the hydrogen electrolyser unit, a reactive power consumption of the hydrogen electrolyser unit, and a voltage at the PCC. The method 1000 may further comprise causing 1061 the E-STATCOM to inject a harmonic current to the electrical power grid at the PCC based on phase currents at the PCC, the active power consumption of the hydrogen electrolyser unit, the reactive power consumption of the hydrogen unit and a voltage at the PCC.

The reference value for controlling an active power contribution from the system to the electrical power grid may be based on the determined grid frequency deviation. Therefore, the determination 1020 of the reference value may be based on the determination 1010 of the grid frequency.

The method 1000 may further comprise receiving information 1070 indicative of a deviation of active power supplied to the electrical power grid by a renewable energy plant, which may be connected to the electrical power grid, at the PCC, and configured to supply active power to the electrical power grid. Determining 1020 the reference value for controlling an active power contribution from the system to electrical power grid may, alternatively or additionally, be based on the received information.

Fig. 5 shows a graph illustrating the active power control obtained by a method 2000 according to an exemplifying embodiment of the present disclosure. It should be noted that Fig. 5 comprises features and/or functions as shown in Fig. 4 and described in the associated text. Hence, it is also referred to Fig. 4 and the description relating thereto for an increased understanding.

The graph shows the effect of the method 2000 being performed with regards to amounts of active power being supplied to an electrical power grid by an hydrogen electrolyser unit and an E-STATCOM of a system according to an exemplifying embodiment of the present disclosure. The vertical axis of the graph indicates amount of relative active power, ranging from 0 to 100, and the horizontal axis of the graph indicates time, ranging from 0 to 15 seconds.

The graph discloses three lines. A first line P_ei of the three lines indicates a level of active power consumption of the hydrogen electrolyser unit from the electrical power grid. A second line PESS of the three lines indicate a level of active power supply of the E-STATCOM to the electrical power grid. A third line Ppiant of the three lines indicates a level of active power contribution of the hydrogen electrolyser unit and the E-STATCOM, which is equal to the active power consumption of the hydrogen electrolyser unit minus the active power supply of the E-STATCOM. The graph further discloses a target value Ptar, which is shown as being equal to 70. However, it should be understood that the target value Ptar shown in Fig. 5 is an example, and that the target value Ptar may be substantially any value, such as, for example, between 50 and 90.

At time equal to zero, a step of causing the active power of the hydrogen electrolyser unit to decrease towards a target value for active power consumption of the hydrogen electrolyser unit, which may be equal to 70 as shown in Fig. 5, is performed. It may therefore be understood that a step of determining the target value has been performed, based on a determined reference value for controlling an active power contribution from the system to the electrical power grid. Therefore, the level of active power consumption of hydrogen electrolyser unit decreases, as indicated by the first line P_ei. The reference value may have been determined upon a determination that a grid frequency of the electrical power grid at a PCC deviates from a reference frequency.

In Fig. 5 the reference value and the target value Ptar are equal, but the present disclosure is not limited to their values being equal. For example, the reference value may be less than the target value Ptar, such as, for example, between 70 and 90 percent of the target value Ptar, which would mean that the active power supply by the E-STATCOM PESS is equal to between 10 and 30 percent of the active power consumption of the hydrogen electrolyser unit P_ei.

The method 2000 further comprises, until the active power consumption of the hydrogen electrolyser unit has reached the target value, causing the E-STATCOM to supply or consume active power to the electrical power grid such that the collective active power contribution of the hydrogen electrolyser unit and the E- STATCOM corresponds to the reference value. It will be appreciated that the E- STATCOM needs some time to ramp up its active power supply, and the active power supply provided by the E-STATCOM PESS reaches a determined level at time tl. Thus, at time tl, the level of active power contribution of the hydrogen electrolyser unit and the E-STATCOM Ppiant reaches the targe value Ptar, as indicated by the third line. The response time of the system may therefore be understood as equal to tl. The active power supply provided by the E-STATCOM PESS decreases in coordination with the decrease of the active power consumption of the hydrogen electrolyser unit P_ei, such that the active power contribution of the hydrogen electrolyser unit and the E-STATCOM Ppiant is equal to the targe value Ptar, until the active power consumption of the hydrogen electrolyser unit P_ei is equal to the target value Ptar. Performing active power control by controlling the active power consumption of a hydrogen electrolyser unit P_ei is limited by a time it takes for the hydrogen electrolyser unit to ramp down its active power consumption P_ei, wherein the time is equal to t2 in the illustrated example. However, by coordinating the active power supply provided by the E-STATCOM PESS and the decrease of the active power consumption of the hydrogen electrolyser unit P_ei, a faster response is obtained. While the present invention has been illustrated in the appended drawings and the foregoing description, such illustration is to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the appended claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A system (100) comprising: a hydrogen electrolyser unit (110) connected to an electrical power grid (101) at a point of common coupling, PCC, (102) and configured to consume active power, Pei, from the electrical power grid; an enhanced static compensator, E-STATCOM, (120) connected to the electrical power grid at the PCC, comprising an energy storage unit (121), and configured to supply or consume active power, PESS, to the electrical power grid via the energy storage unit and to adjust a reactive power contribution to the electrical power grid; and a control unit (130) configured to control an active power contribution from the hydrogen electrolyser unit and the E-STATCOM based on a reference value, P plant; wherein, upon determining whether a grid frequency of the electrical power grid at the PCC deviates from a reference frequency, the control unit is configured to: update the reference value; determine a target value for the power consumption of the hydrogen electrolyser unit from the electrical power grid based on the updated reference value; cause the hydrogen electrolyser unit to decrease or increase its active power consumption from the electrical power grid towards the determined target value; and until the active power consumption of the hydrogen electrolyser unit has reached the determined target value, cause the E-STATCOM to supply or consume active power to/from the electrical power grid such that the collective active power contribution from the hydrogen electrolyser unit and the E-STATCOM corresponds to the updated reference value, and wherein the control unit is further configured to control the reactive power contribution from the E-STATCOM.

2. The system according to claim 1, wherein the control unit is further configured to update the reference value based on the determined grid frequency deviation.

3. The system according to claim 1 or 2, wherein a renewable energy plant (340) is connected to the electrical power grid, at the PCC, and configured to supply active power to the electrical power grid.

4. The system according to claim 3, wherein the control unit is further configured to: receive information indicative of a deviation of active power supplied to the electrical power grid by the renewable energy plant; and wherein the control unit is further configured to update the reference value based on the received information.

5. The system according to any of the preceding claims, wherein the control unit is further configured to control the reactive power contribution from the E-STATCOM, QESS, based on the active power consumption of the hydrogen electrolyser unit, P_ei, a reactive power consumption of the hydrogen electrolyser unit and a voltage at the PCC.

6. The system according to any one of the preceding claims, wherein the control unit is further configured to, cause the E-STATCOM to inject a harmonic current to the electrical power grid at the PCC based on phase currents at the PCC, the active power consumption of the hydrogen electrolyser unit, a reactive power consumption of the hydrogen unit, and a voltage at the PCC.

7. The system according to any one of the preceding claims, wherein the hydrogen electrolyser unit is connected to the PCC via a rectifier (203).

8. The system according to any one of the preceding claims, wherein the hydrogen electrolyser unit is an alkaline hydrogen electrolyser unit or a proton exchange membrane, PEM, hydrogen electrolyser unit.

9. The system according to any one of the preceding claims, wherein the energy storage unit of the E-STATCOM comprises at least one of a supercapacitor or a battery.

10. The system according to any one of the preceding claims, wherein the control unit is configured to, upon determining a grid frequency deviation, cause the E- STATCOM to supply or consume active power to the electrical power grid such that the collective active power contribution from the hydrogen electrolyser unit and the energy storage unit corresponds to the updated reference value within 2 seconds of updating the reference value.

11. A method (1000) for controlling a system (100) comprising a hydrogen electrolyser unit (110) and an enhanced static compensator, E-STATCOM, (120) connected to an electrical power grid at a point of common coupling, PCC, and comprising an energy storage unit (121), wherein the method comprises: upon determining (1010) whether a grid frequency of the electrical power grid at the PCC deviates from a reference frequency: determining (1020) a reference value for controlling an active power contribution from the system to the electrical power grid; determining (1030) a target value for active power consumption of the hydrogen electrolyser unit from the electrical power grid based on the reference value; causing (1040) the active power consumption of the hydrogen electrolyser unit to decrease or increase towards the determined target value; and until the active power consumption of the hydrogen electrolyser unit has reached the target value, causing (1050) the E-STATCOM to supply or consume active power to/from the electrical power grid such that the collective active power contribution of the hydrogen electrolyser unit and the E-STATCOM corresponds to the reference value; and causing (1060) the E-STATCOM to adjust a reactive power contribution to the electrical power grid.

12. The method according to claim 11, wherein the reference value for controlling an active power contribution from the system to the electrical power grid is based on the determined grid frequency deviation.

13. The method according to claim 11 or 12, further comprising: receiving information (1070) indicative of a deviation of active power supplied to the electrical power grid by a renewable energy plant connected to the electrical power grid, at the PCC, and configured to supply active power to the electrical power grid; and determining (1020) the reference value for controlling an active power contribution from the system to the electrical power grid based on the received information.

14. The method according to any of claims 11 to 13, wherein the reactive power supplied to the electrical power grid is based on the active power consumption of the hydrogen electrolyser unit, a reactive power consumption of the hydrogen electrolyser unit, and a voltage at the PCC

15. The method according to any of claims 11 to 14, further comprising causing (1061) the E-STATCOM to inject a harmonic current to the electrical power grid at the PCC based on phase currents at the PCC, the active power consumption of the hydrogen electrolyser unit, the reactive power consumption of the hydrogen unit and a voltage at the PCC.

16. A control unit (130) configured to perform the method according to any of claims

11 to 15.