A method and a control arrangement for controlling a renewable power plant

Abstract

A method (200) and a control arrangement (150) for controlling a renewable power plant (100) comprising one or more renewable electric power generating units (103) and one or more gas-to-power units (140) are presented. The renewable power plant (100) is connected to an electric power grid (116) and to a gas transmission network (126). The method (200) comprises: determining (210) one or more parameters of the electric power grid (116); based on the one or more determined parameters of the electric power grid (116), controlling (220) the one or more gas-to-power units (140) to convert gas from the gas transmission network (126) to electric power; and based on the one or more determined parameters of the electric power grid (116), controlling (230) the renewable power plant (100) to introduce, in addition to electric power provided by the one or more renewable electric power generating units (103), at least a portion of the converted electric power into the electric power grid (116) so as to improve a stability of the electric power grid (116).

Description

[0001] A METHOD AND A CONTROL ARRANGEMENT FOR CONTROLLING A RENEWABLE POWER PLANT

[0002] Technical field

[0003] Aspects of the present invention relate to a method and a control arrangement for controlling a renewable power plant comprising one or more renewable electric power generating units and one or more gas-to-power units, where the renewable power plant is connected to an electric power grid and to a gas transmission network. Further aspects of the invention relate to a renewable power plant comprising the control arrangement, and to a computer program or a computer-readable medium implementing the method.

[0004] Background

[0005] Renewable power plants rely on renewable energy sources such as wind and / or sun to produce electricity by usage of wind turbine generators and / or photovoltaic power generators. Renewable power plants may also comprise one or more power-to-gas units. Renewable power plants may also comprise one or more gas-to-power units. Besides electricity, the renewable power plants may produce additional energy vectors, such as green hydrogen, produced from water, and other green synthetic fuels, produced by mixing green hydrogen with additional chemical compounds and / or elements. Byproducts of renewable power plants may include recoverable low-grade heat and oxygen, both resulting from the electrolysis of water. Additional gasses, such as ethane, propane and / or butane, may further be produced from hydrogen.

[0006] The renewable power plant may be connected via one or more interfaces to an external electricity grid, an external hydrogen or natural gas grid, an external heat distribution network and / or a grid for industrial products, such as e-fuels.

[0007] The integration of multiple energy vectors / products provides the renewable power plants with the possibility of exchanging different kinds of energy vectors via one or more energy exchange nodes. For example, electricity, hydrogen and / or heat may be exchanged in such nodes. The interfaces may be implemented as a physical point where the flow of energy between the renewable power plant and the surroundings, such as for example external grids of various kinds, is formally regulated. Thus, an energy vector may only be exchanged to another energy vector if it has a specific set of attributes, for example a certain voltage, frequency, pressure, flow, and / or temperature, depending on the energy vector. This specific set of attributes may correspond to, be comprised in, or comprise, network / grid codes for one or more energy vectors.

[0008] The regulation of renewable power plants may for example be controlled by one or more transmission system operators for electricity or gas, which may be responsible for regulating the energy nodes configured for exchanging electricity and gaseous fuels, such as hydrogen. The one or more transmission system operators may in some countries include national transmission system operators. Also, a local district heating company may regulate / control energy nodes configured for exchanging low- grade heat. Since the energy exchange may cross national borders, the national transmission system operators for electricity or gas may be coordinated by supranational bodies.

[0009] Depending on the configuration of the renewable power plant and the available energy infrastructure, it is necessary to develop control systems and control strategies that can simultaneously comply with network / grid codes of electricity and gas distribution systems, as well as potential heat distribution systems. Thus, renewable power plants are required to produce energy with a specific set of attributes, such as for example voltage, frequency, flow, pressure and / or temperature, depending on the energy vector, for a reliable operation of the renewable power plant.

[0010] Summary

[0011] In certain situations, imbalance in the electric power grid to which the renewable power plant is connected may occur. Imbalances may for example be caused by a large electric power consumption unit being stopped, for example if the operation of the large electric power consumption unit is deliberately reduced or if there is a sudden accident or loss of production in the large electric power consumption unit. Imbalances may also be caused by a large electric power consumption unit being started, i.e. when it suddenly starts consuming large amounts of electric power. The imbalance in the electric power grid may for example result in instable voltages, currents and / or frequency in the electric power grid. Thus, voltages, currents and / or frequencies changing quickly over time may be an indication of imbalance in the electric power grid.

[0012] An object of the invention is to provide a solution which mitigates or solves such imbalance problems.

[0013] An object of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

[0014] The above and further objects are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

[0015] According to a first aspect of the invention, a method for controlling a renewable power plant comprising one or more renewable electric power generating units and one or more gas-to-power units is presented. The renewable power plant is connected to an electric power grid and to a gas transmission network. The method comprises: determining one or more parameters of the electric power grid; based on the one or more determined parameters of the electric power grid, controlling the one or more gas-to-power units to convert gas from the gas transmission network to electric power; and based on the one or more determined parameters of the electric power grid, controlling the renewable power plant to introduce, in addition to electric power provided by the one or more renewable electric power generating units, at least a portion of the converted electric power into the electric power grid so as to improve a stability of the electric power grid. Hereby, electric power may be produced in the renewable power plant by converting gas from the gas transmission network to electric power in one or more gas-to-power units. The electric power may then be introduced into the electric power grid. The production of electric power and the introduction of the produced electric power into the electric power grid is based on the one or more parameters of the electric power grid, which may indicate a level of stability of the electric power grid.

[0016] Thus, if the electric power grid is instable, i.e. if there is an imbalance in the electric power grid, e.g. if there are quickly varying voltages, currents and / or frequencies in the electric power grid, the instability may be counteracted by the introduction of the produced electric power into the electric power grid. The renewable power plant may thus mitigate the imbalance of the electric power grid, and possibly bring the electric power grid into balance.

[0017] Especially, short term changes in the electric power grid that are impossible, or at least very hard, to predict / forecast may hereby be taken care of. Such short term changes may for example be caused by starting or stopping a large electric power consumption unit in the electric power grid. By monitoring the electric power grid, i.e. by determining the one or more parameters of the electric power grid, such sudden changes in the electric power grid can be handled by the renewable power plant.

[0018] Since the production of electric power and the introduction of the produced electric power into the electric power grid is based on the one or more parameters of the electric power grid, a real time or near real time balancing of the electric power grid is hereby achievable by the renewable power plant.

[0019] According to an embodiment of the first aspect, the method further comprises: determining, based on the one or more determined parameters of the electric power grid, an instability of the electric power grid; and controlling the one or more gas-to-power units to convert gas to electric power based on the determined instability of the electric power grid. By determining that there is an instability of the electric power grid, and by, based on this identified instability, converting gas to electric power and to introduce the converted electric power into the electric power grid, the instability of the electric power grid is efficiently counteracted.

[0020] Imbalances in the electric power grid, for example associated with quickly varying voltages, currents and / or frequencies, may be stabilized / evened out by the introduction of the produced electric power into the electric power grid. Especially, instability caused by short term changes in the electric power grid may be counteracted by the introduction of electric power into the electric power grid. According to an embodiment of the first aspect, the wherein the electric power grid is determined instable if at least one of the one or more determined parameters of the electric power grid fluctuates with an amplitude A exceeding a fluctuation amplitude threshold Ath; A>Ath.

[0021] Some of the one or more determined parameters of the electric power grid have naturally fluctuating values. The fluctuation amplitude threshold Ath is utilized for identifying the parameters that fluctuate too much, i.e. that fluctuate abnormally, such as e.g. varying frequencies and / or mean power oscillations, thereby indicating that there is an instability problem in the electric power grid.

[0022] According to an embodiment of the first aspect, the instability is determined if one or more situations or events of the following group are valid:

[0023] • at least one of the one or more determined parameters of the electric power grid has a value D deviating from a desired value Ddes by at least a predetermined deviation value Ddev;

[0024] • at least one frequency parameter of the one or more determined parameters of the electric power grid has a gradient value Gfreq exceeding a desired gradient value Gfreq_des; Gfreq>Gfreq_des; and

[0025] • at least one frequency parameter of the one or more determined parameters of the electric power grid has a change of gradient value AGfreq exceeding a desired change of gradient value AGfreq. desi AGfreq>AGfreq_des. Hereby, various instabilities regarding for example frequencies and / or voltages may be easily and efficiently determ ined / detected. In an example the value D may be a frequency or a voltage of the electric power grid.

[0026] According to an embodiment of the first aspect, the gas being converted to electric power has been temporarily stored in a gas storage of the renewable power plant.

[0027] Hereby, gas may be input to the gas storage when there is plenty gas available in the gas transmission network, i.e. when the price for gas is relatively lower, and may then be stored in the gas storage until it is later converted to electric power. The conversion to electric power may be chosen to take place at a point in time when less gas is available in the gas transmission network, i.e. when the gas price is relatively higher, and when the price for electric power is also higher.

[0028] According to an embodiment of the first aspect, the method further comprises: based on the one or more determined parameters of the electric power grid, importing gas from the gas transmission network to the renewable power plant; and based on the one or more determined parameters of the electric power grid, controlling the one or more gas-to-power units to convert at least a portion of the gas imported from the gas transmission network to electric power.

[0029] Since the renewable power plant is connected to the gas transmission network, there are a number of possibilities to counteract instability of the electric power grid available. Gas available for conversion into electric power may then be provided by the gas transmission network and possibly also the power-to-gas units of the renewable power plant. Thus, gas may be imported from the gas transmission network to the renewable power plant, and this imported gas may, possibly in combination with additional gas produced in the renewable power plant, be converted into electric power.

[0030] A higher level of flexibility is hereby achieved for the renewable power plant. For example, when the wind turbine generators and / or the photovoltaic power generators do not produce enough electric power to stabilize the electric power grid, for example when there is little wind and / or at night or during cloudy days, the instability of the electric power grid may still be counteracted and / or improved by converting imported gas into electric power and by introducing the converted electric power into the electric power grid.

[0031] According to an embodiment of the first aspect, the method further comprises: determining one or more parameters of the gas transmission network; and based on the one or more determined parameters of the gas transmission network, importing gas from the gas transmission network to the renewable power plant for the conversion of at least a portion of the gas imported from the gas transmission network to electric power.

[0032] By taking also the one or more parameters of the gas transmission network into consideration when importing gas from the gas transmission network, the state and / or condition of the gas transmission network are also utilized as a basis for the decisions associated with gas import. Thus, the states and / or conditions of both of the gas transmission network and the electric power grid are taken into consideration when the gas is imported from the gas transmission network. The import of gas, and thus also the conversion of the imported gas into electric power, are hereby optimized to current situations occurring in one or both of the gas transmission network and the electric power grid.

[0033] According to an embodiment of the first aspect, the one or more determined parameters of the electric power grid are fluctuating over time, the fluctuations being indicative of a level of stability of the electric power grid.

[0034] By analyzing the naturally fluctuating values for the one or more parameters of the electric power grid, the parameters changing in an abnormal way may be identified as an indication of instability, while normally changing parameters are detected as an indication of stability for the electric power grid.

[0035] According to an embodiment of the first aspect, the method further comprises: based on the one or more determined parameters of the electric power grid, allocating a power producing capability of the renewable power plant; controlling the one or more renewable electric power generating units to produce electric power by utilization of the allocated power producing capability; and controlling the renewable power plant to introduce the produced electric power into the electric power grid.

[0036] Hereby, a power backup is created by this allocation of power producing capability, which can be utilized for producing electric power, if needed. Thus, a reserve of power is allocated for production of electric power, which may be introduced in the electric power grid to compensate for instability / imbalance in the electric power grid.

[0037] According to an embodiment of the first aspect, the method further comprises: determining that there is an imbalance in the electric power grid if one or more situations or events of the following group are valid:

[0038] • at least one of the one or more determined parameters of the electric power grid has a value D being below a predetermined threshold Dth; D<Dth; and

[0039] • at least one of the one or more determined parameters of the electric power grid is fluctuating with a gradient having a change over time with a magnitude M which exceeds a predetermined magnitude of change threshold Mth; M>Mth; and when it is determined that there is an imbalance in the electric power grid, controlling, based on the one or more determined parameters of the electric power grid, the one or more gas-to-power units to convert gas to electric power; and based on the one or more determined parameters of the electric power grid, controlling the renewable power plant to introduce at least a portion of the converted electric power into the electric power grid so as to counteract the determined imbalance in the electric power grid.

[0040] By determining that there is an imbalance in the electric power grid, and by, based on this identified imbalance, converting gas to electric power and to introduce the converted electric power into the electric power grid, the imbalance of the electric power grid is efficiently counteracted. For example, short term changes in the electric power grid, such as e.g. varying frequencies and / or mean power oscillations, may be identified by comparing the one or more determined parameters of the electric power grid with corresponding thresholds. Some of the one or more determined parameters of the electric power grid are naturally fluctuating. However, if they fluctuate too quickly, this may be a sign of imbalance in the electric power grid. Therefore, the fluctuation gradient may be analyzed, and if the parameter value changes over time with a magnitude M exceeding a corresponding threshold Mth; M>Mth; then an imbalance of the electric power grid is quickly and reliably determined. For other parameters of the electric power grid, an imbalance may be easily identified by concluding that the parameters have a value D being below a predetermined threshold Dth; D<Dth.

[0041] According to an embodiment of the first aspect, the one or more determined parameters of the electric power grid comprise one or more of the group of:

[0042] • a voltage of the electric power of the electric power of grid;

[0043] • a current of the electric power of the electric power grid;

[0044] • a frequency of the electric power of the electric power grid; and

[0045] • a set point for the renewable power plant.

[0046] Thus, various parameters of the electric power grid may be utilized as a basis for the conversion of gas to electric power and / or for the introduction of the converted electric power into the electric power grid, which offers a flexibility and reliability for the production and / or introduction of electric power. The one or more determined parameters of the electric power grid may be generally fluctuating parameters. The one or more determined parameters of the electric power grid may correspond to, may be comprised in, and / or may be part of the network / grid codes for the electric power grid, i.e. may define a specific set of attributes that the electric power distributors must fulfill on the energy market. According to an embodiment of the first aspect, each of the one or more gas-to- power units is configured to convert gas to electric power by utilization of one or more in the group of:

[0047] • a thermal energy conversion device;

[0048] • a gas turbine;

[0049] • an electrochemical energy conversion device;

[0050] • a fuel cell; and

[0051] • a gas driven generator.

[0052] These gas-to-power conversion devices provide for efficient conversions of gas into electric power, which has a small amount of conversion losses. Hydrogen from the gas transmission network and / or methanol produced from hydrogen provided by the gas transmission network may for example be utilized for driving the gas-to-power conversion devices, such as e.g. being used as input gases in the electrochemical energy conversion device, the fuel cell and / or the gas turbine, or for being used as fuel in the gas driven generator. Utilizing hydrogen and / or methanol as input gases and / or fuel has advantages related to performance, cost and emissions.

[0053] According to an embodiment of the first aspect, the method further comprises: based on the one or more determined parameters of the electric power grid, controlling the one or more gas-to-power units to convert gas to electric power, wherein the gas comprises or consists of one or more of the group of:

[0054] • hydrogen;

[0055] • oxygen; and

[0056] • methane.

[0057] Hydrogen, oxygen and / or methane gases may be utilized in a large number of implementations. Also, these gases may be easily transformed into electric power with little losses.

[0058] According to an embodiment of the first aspect, the one or more renewable electric power generating units comprise one or more in the group of: • a wind turbine generator of the renewable power plant;

[0059] • a photo-voltaic generator of the renewable power plant; and

[0060] • an electric battery energy storage system of the renewable power plant.

[0061] The renewable power plant may thus comprise a number of different renewable electric power generating units utilizing a corresponding number of different renewable power sources, respectively. Hereby, renewable electric power may be produced by the renewable power plant under various weather conditions, for example under varying wind and sun conditions.

[0062] According to an embodiment of the invention, the method further comprises: determining the one or more parameters of the electric power grid at a point of interest where one or more requirements of the electric power grid are to be fulfilled; based on the one or more determined parameters at the point of interest, dispatching one or more references to the renewable power plant; based on the one or more dispatched references, controlling the one or more gas-to-power units to convert gas to electric power; and based on the one or more determined parameters of the electric power grid at the point of interest, controlling the renewable power plant to introduce at least a portion of the converted electric power into the electric power grid so as to fulfil one or more requirements at the point of interest.

[0063] When the one or more parameters of the electric power grid are determined at the point of interest where the renewable power plant and the electric power grid are connected, the requirements may correspond to and / or be comprised in grid codes for the electric power grid. The dispatched references may correspond to, or comprise, set points intended for control of the entire renewable power plant and / or reference points intended for control of individual entities of the renewable power plant.

[0064] Thus, based on grid codes of the electric power grid, electric power is here produced by conversion of gas, and the electric power is then introduced into the electric power grid. Hereby, the renewable power plant is controlled to produce electric power, which is introduced into the electric power grid, such that the electric power grid complies with its grid codes. In other words, the electric power grid is balanced by the renewable power plant based on its electric power grid codes, such that the electric power grid securely provides electric power complying with its specific set of attributes, such as for example voltage, current and / or frequency attributes.

[0065] According to a second aspect of the invention, a control arrangement for controlling a renewable power plant is presented. The renewable power plant comprises one or more renewable electric power generating units and or more gas-to-power units. The renewable power plant is connected to an electric power grid and to a gas transmission network. The control arrangement is configured to: determine one or more parameters of the electric power grid; based on the one or more determined parameters of the electric power grid, control the one or more gas-to-power units to convert gas from the gas transmission network to electric power; and based on the one or more determined parameters of the electric power grid, control the renewable power plant to introduce at least a portion of the converted electric power into the electric power grid so as to improve a stability of the electric power grid.

[0066] The control arrangement of the second aspect has corresponding advantages as the ones mentioned above for the method for controlling a renewable power plant according to the first aspect of the invention.

[0067] It is to be appreciated that all the embodiments described for the method aspect of the invention are applicable also to the control arrangement aspect of the invention. Thus, all embodiments described for the method aspect of the invention may be performed by the control arrangement, which may include one or more controllers, control units, or control devices. The embodiments of the control arrangement have advantages corresponding to advantages mentioned above for the method and its embodiments. According to a third aspect of the invention, a renewable power plant is presented. The renewable power plant comprises one or more renewable electric power generating units and one or more gas-to-power units, and is connected to an electric power grid and to a gas transmission network. The renewable power plant further comprises a herein described control arrangement.

[0068] The renewable power plant of the third aspect has corresponding advantages as the ones mentioned above for the method for controlling a renewable power plant according to the first aspect of the invention and its embodiments.

[0069] According to a fourth aspect of the invention, the above mentioned and other objects are achieved with a computer program or a computer-readable medium comprising instructions which, when the program or the instructions is / are executed by a computer, cause the computer to carry out one or more of the methods according to any one of the aspects and embodiments disclosed above or below. Advantages of the computer program or the computer-readable medium according to the fourth aspect correspond to advantages of the method according to the first aspect and its embodiments mentioned above or below.

[0070] According to an aspect of the present invention, the above-mentioned computer program and / or the computer-readable medium are / is configured to implement the method and its embodiments described herein.

[0071] The above-mentioned features and embodiments of the method, the computer program, the computer-readable medium, the control arrangement and the renewable power plant, respectively, may be combined in various possible ways providing further advantageous embodiments.

[0072] Further advantageous embodiments of the method for controlling the renewable power plant and the control arrangement, and further advantages of the embodiments of the present invention, emerge from the detailed description of embodiments. Brief Description of the Drawings

[0073] Embodiments of the invention will now be illustrated, for exemplary purposes, in more detail by way of embodiments and with reference to the enclosed drawings, where similar references are used for similar parts, in which:

[0074] Figure 1 is a schematic diagram illustrating an embodiment of a renewable power plant, to which herein described embodiments may be applied;

[0075] Figure 2 is a schematic diagram illustrating an embodiment of a wind turbine generator of the power plant of figure 1 ;

[0076] Figure 3 is a schematic diagram illustrating an embodiment of a power-to-x unit of the power plant of figure 1 ;

[0077] Figure 4 is a schematic diagram illustrating an embodiment of a fuel cell;

[0078] Figure 5 is a schematic flow chart illustrating methods according to various aspects and embodiments of the invention;

[0079] Figure 6 is a schematic diagram illustrating frequency instability control; and

[0080] Figure 7 is a schematic diagram illustrating an embodiment of a control arrangement according to the second aspect of the invention, in which a method according to any one of the herein described aspects and embodiments may be implemented.

[0081] Detailed Description

[0082] Figure 1 schematically illustrates a non-limiting example of a renewable power plant 100, in which aspects and embodiments of the present invention may be implemented. The aspects and embodiments of the present invention may, of course be implemented in any suitable renewable power plant, in which one or more renewable electric power generating units and one or more gas-to-power units are utilized, and which is connected to an electric power grid and to a gas transmission network. The aspects and embodiments of the present invention are thus not limited to implementation in the renewable power plant example in figure 1 .

[0083] The renewable power plant 100 is arranged for providing electric power, or electrical energy, to an electric power grid 116. The renewable power plant 100 includes one or more renewable electric power generating units 103, such as e.g. one or more wind turbine generators 101. According to some embodiments, the renewable power plant 100 may also comprise one or more other renewable electric power generating units / assets 103, for example a photo-voltaic generator 102, such as a photo-voltaic panel, a solar panel, or a solar cell panel. The wind turbine generators 101 and the photo-voltaic generator 102 may also be generally described as renewable power sources 103 of the renewable power plant 100, or as renewable power generators 103 of the renewable power plant 100. The renewable power plant 100 may also comprise one or more additional renewable power sources or power generators 103, such as one or more electric battery energy storage systems 106, which may comprise an electric battery energy storage system, possibly including one or more electric battery units.

[0084] The renewable power plant 100 may also comprise further assets / units / components, such as for example one or more harmonic filters and / or one or more reactive power compensation units. Such further assets / units / components are schematically referred to as further assets / units / components 107 in figure 1 .

[0085] The renewable power plant 100 may be connected, i.e. is connectable, possibly via an internal grid 110 of the renewable power plant 100, to the electric power grid 116 via a point of common coupling (PCC) 115. The renewable electric power generating units 103 feed / provide electric power produced by them to the internal grid 110, which is connected via the point of common coupling 115 to the external electric power grid 116. For some embodiments, the electric power grid 116 may be referred to as a utility grid, an electrical grid, a power grid, or an electric power network.

[0086] The one or more gas-to-power units 140 may according to some embodiments comprise one or more fuel cells 144. The one or more fuel cells 144 may for example comprise one or more gas fuel cells. Such gas fuel cells may, depending on the type of fuel cell, run on essentially any suitable gas, including hydrogen and / or natural gas. For example, the gas fuel cell may include one or more hydrogen fuel cells, which is configured for converting hydrogen and oxygen into electric power by utilizing redox reactions, as described in detail below. The gas / hydrogen 400 may be provided from the gas transmission network 126 via one or more external interfaces 125 to the gas transmission network 126. The gas / hydrogen 400 provided by the gas transmission network 126, may be temporary stored in a gas storage 122. Some of the gas / hydrogen 400 used in this conversion may also have been produced by one or more power-to-gas units (P2G) 120 in the renewable power plant 100, and may possibly be temporarily stored in an internal gas / hydrogen storage 122 of the renewable power plant 100, as explained below.

[0087] The gas-to-power unit 140 may further comprise devices for, i.e. may be configured for, converting gas 400 from the gas transmission network 126 to electric power. The gas-to-power unit 140 may therefore comprise a thermal energy conversion device 141 utilizing heat in gas 400 from the gas transmission network 126 for creating electric power. The gas-to-power unit 140 may further comprise a gas turbine 142, e.g. a single fuel or double fuel turbine being driven by hydrogen 400 from the gas transmission network 126 and / or methanol produced from hydrogen 400 provided by the gas transmission network 126, creating electric power by having pressurized gas spinning the turbine. The gas-to-power unit may further comprise an electrochemical energy conversion device 143 converting chemical energy in gas 400 from the gas transmission network 126 into electric power. The gas-to-power unit 140 may further comprise a gas driven generator 145, which may be driven by various gasses 400, such as e.g. hydrogen from the transmission network 126 and / or methanol produced from hydrogen 400 provided by the transmission network 126.

[0088] The renewable power plant 100 may further comprise one or more power-to-x units, including one or more power-to-gas units 120. The power-to-x units are configured to convert electric power from the renewable power plant 100 to x, i.e. to gas in this case. The power-to-x unit may thus comprise a power-to-gas (P2G) unit 120, including an electrolyzer system 121 configured to convert electric power from the renewable power plant 100 to gas. The power-to-gas units 120 may be described as dynamic electrical loads. The one or more electrolyzer systems 121 are arranged to break down water molecules into its constituents, i.e. into hydrogen and oxygen, by consuming electricity. The power-to-gas units 120, each comprising one or more electrolyzer systems 121 , may also produce heat in the electrolysis process. Optionally, the renewable power plant 100 may also comprise one or more plant extension units 130 that can transform hydrogen produced by the one or more power-to-gas units 120, i.e. produced by the one or more electrolyzer systems 121 , respectively, into other products by consuming electricity. The plant extension units 130 may be described as static or semi-static electric loads, and may comprise one or more chemical units / plants that utilize hydrogen and possibly other compounds or elements, such as e.g. nitrogen or carbon dioxide, to produce other industrial products, such as e.g. e-fuels. The plant extension units 130 may also comprise e.g. an ammonia production plant and / or a methanol production plant. The produced industrial products, e.g. e-fuels, may be stored locally in a product storage 131 , or may be provided for direct onward transportation. Additional gasses, such as ethane, propane and / or butane, may also be produced from the hydrogen.

[0089] One or more interfaces, such as the point of common coupling 115, to the external electricity grid 116, may provide the possibility to export surplus power produced by the renewable electrical generators 103 and by the gas-to-power units 140 of the renewable power plant, which is not used by the one or more power-to-gas units 120, including the electrolyzer systems 121 , and the downstream plant extension units 130, to the electricity grid 116. Corresponding one or more external interfaces 125 may be implemented to export gas 400, i.e. hydrogen or natural gas, produced by the power-to-gas units 120, i.e. by the electrolyzer systems 121 , in the renewable power plant 100 to a gas transmission / distribution network / grid 126, i.e. to a hydrogen or natural gas grid 126. One or more external interfaces 127 may further be implemented to export heat produced by the one or more power-to-gas units 120 in the renewable power plant to a heat grid 128, i.e. to a heat transmission / distribution network 128. Also, one or more interfaces 135 may be implemented to export industrial products, such as for example e-fuels, produced by the plant extension units 130 to a grid 136 for industrial products such as e.g. e-fuels.

[0090] The one or more interfaces 115 to the external electricity grid 116, may also provide the possibility to import electric power from the external power grid 116 to the renewable power plant 100. Correspondingly, the one or more external interfaces 125 to the gas transmission / distribution network 126 may provide the possibility to import gas 400, such as e.g. hydrogen or natural gas, from the gas transmission / distribution network 126 to the renewable power plant 100. Further, the one or more external interfaces 127 to the heat transmission / distribution network 128 may provide the possibility to import heat from the heat transmission / distribution network 128 to the renewable power plant 100. Also, the one or more interfaces 135 to the grid 136 for industrial products may provide the possibility to import industrial products from the grid 136 for industrial products to the renewable power plant 100.

[0091] The renewable power plant 100 may include a control arrangement 150 configured to control the renewable power plant 100. According to some embodiments, the control arrangement 150 may comprise, or be referred to as, a power plant controller (PPC). As schematically illustrated in figure 1 , the control arrangement 150 in form of a power plant controller controls the renewable power generating units 103, the battery system 106, the further assets / units / components 107, the internal grid 110, the one or more power-to-gas units 120, the plant extension units 130, the one or more gas- to-power units 140 and / or the product storage 131 . The power plant controller 150 may also communicate with the external electric power grid 116, the gas transmission network 126, the heat grid 128 and / or the grid 136 for industrial products, and / or their respective interfaces 115, 125, 127, 135. Also, measurements, for example of electric power or other system parameters and / or attributes, are provided to the control arrangement 150 from one or more of the renewable power generating units 103, the battery system 106, further assets / units / components 107, the internal grid 110, the one or more power-to-gas units 120, the one or more gas- to-power units 140, the plant extension units 130, and the product storage 131. Measurements may also be provided by one or more of the external electric power grid 116, the gas transmission network 126, the heat transmission / distribution 128 and the grid 136 for industrial products, and / or from their respective interfaces 115, 125, 127, 135.

[0092] The renewable power plant 100 thus utilizes renewable energy sources, such as wind and sun, for producing electricity by the use of renewable electrical generators 103, such as e.g. the wind turbine generators 101 and / or the photovoltaic power generators 102. The produced electricity may be provided to the external electricity grid 116 and / or may be used for producing hydrogen, natural gas, heat, and / or industrial products such as for example e-fuels. The produced electricity, hydrogen, natural gas, heat and / or industrial products may then be exported to the external electric power grid 116, the external gas transmission network 126, the external heat transmission / distribution 128 and / or an external industrial product grid 136, respectively. Conversely, electricity, hydrogen, natural gas, heat and / or industrial products may also be imported from the external electric power grid 116, the external gas transmission network 126, the external heat transmission / distribution 128 and / or an external industrial product grid 136, respectively.

[0093] In figure 2, an embodiment of the wind turbine generator 101 of the renewable power plant 100 of figure 1 is schematically illustrated. The wind turbine generator 101 may comprise a rotor 161 including one or more blades 162, or rotor blades 162, for example two or more blades 162, such as three blades, or more. The wind turbine generator 101 may comprise a tower 163 and a nacelle 164 mounted to the top of the tower 163. The rotor 161 may be connected, such as rotatably connected or mounted, to the nacelle 164. The wind turbine generator 101 may comprise an electric generator 165 to which the rotor 161 is connected. The rotor 161 is configured to drive the electric generator 165. The nacelle 164 may house the electric generator 165.

[0094] The rotor 161 is rotatable by action of the wind. The wind-induced rotational energy of the blades 162 and rotor 161 may be transferred via a coupling 166, for exampling including one or more shafts, to the electric generator 165. Thus, the wind turbine generator 101 may be described to be configured to convert kinetic energy of the wind to mechanical energy, or rotational energy, by way of the blades 162 and, subsequently, to electric power by way of the electric generator 165. The wind turbine generator 101 may comprise one or more power converters 167 connected to the electric generator 165. The wind turbine generator 101 and / or the electric generator 165 may be connected to the electric power grid 116 via the one or more power converters 167. The one or more power converters 167 may comprise a first power converter for converting AC power from the electric generator 165 to DC power. The one or more power converters 167 may comprise a second power converter for converting DC power from the first power converter to AC power to be provided to the electric power grid 116. The nacelle 164 may house the one or more power converters 167, or the one or more power converters 167 may be located elsewhere.

[0095] The wind turbine generator 101 may be controlled by, or may comprise, a control arrangement 168 for controlling the wind turbine generator 101. The control arrangement 168 of the wind turbine generator 101 may comprise a wind turbine generator controller. The control arrangement 168 of the wind turbine generator 101 may be configured to communicate with and / or be connected to, or be part of, the control arrangement 150 of the power plant 100. For some embodiments, the wind turbine generator 101 may be referred to as a variable-speed wind turbine generator. It is to be understood that the wind turbine generator 101 may include further units, components and / or devices, such as for example sensors, required for a wind turbine generator 101. For some embodiments, and as schematically illustrated in figure 2, the power-to-x units 120, i.e. the power-to-gas unit 120s, may be connected, more specifically electrically connected, to a connection point of the wind turbine generator 101 , such that it may draw electric power produced by the wind turbine generator 101 for producing x. For some embodiments, the wind turbine generator 101 and the power-to-x unit 120 may be arranged together as a unit. However, for some embodiments, the power-to-x unit 120 may be located and / or connected elsewhere in the renewable power plant 100.

[0096] Figure 3 schematically discloses an embodiment of the power-to-x (P2X) unit, here being a power-to-gas unit (P2G) 120 of the power plant 100 of figure 1 , which is configured to convert electric power from the renewable power plant 100 to gas. According to various herein described embodiments, the power-to-gas unit 120 may be configured to convert electric power produced by the renewable power plant 100 itself, and / or may be configured to use imported electric power, to produce a gas or gas mixture comprising or consisting of hydrogen, oxygen and / or methane. In the embodiment illustrated in figure 3, the power-to-gas unit 120 is configured to convert electric power from the renewable power plant 100, i.e. electric power produced within and / or imported to the renewable power plant 100, to a gas mixture comprising hydrogen and oxygen. The power-to-gas unit 120 may be described to be configured to use electricity to break water into hydrogen and oxygen in a process called electrolysis in an electrolyzer system 121. Thus, through the electrolysis, hydrogen is created, which may be used for example as a fuel. The power-to-gas unit 120 may include a container 322 configured to hold or contain water. The power-to-gas unit 120, i.e. the electrolyzer system 121 , may include one or more anodes 323 and one or more cathodes 324 separated from one another by a membrane 325. The container 322 may include an outlet 326 for hydrogen and an outlet 327 for oxygen. The produced hydrogen may be stored in an internal hydrogen storage 122 of the renewable power plant 100.

[0097] With reference to figure 3, for some embodiments, the power-to-gas unit 120 comprises an electrolyzer system 121 comprising one or more of the group of:

[0098] - an alkaline electrolyzer;

[0099] - an unpressurized alkaline electrolyzer;

[0100] - a pressurized alkaline electrolyzer;

[0101] - a proton exchange membrane electrolyzer;

[0102] - an unpressurized proton exchange membrane electrolyzer;

[0103] - a pressurized proton exchange membrane electrolyzer;

[0104] - a polymer electrolyte membrane electrolyzer;

[0105] - an unpressurized polymer electrolyte membrane electrolyzer;

[0106] - a pressurized polymer electrolyte membrane electrolyzer; and

[0107] - a solid oxide electrolyzer (SOEC).

[0108] As illustrated in figures 2 and 3, for some embodiments, the power-to-gas unit 120 may be connected, more specifically electrically connected, to a connection point of the wind turbine generator 101 . For some embodiments, the power-to-gas unit 120 may be connected, more specifically electrically connected, to a connection point of the renewable power plant 100. For some embodiments, the power-to-gas unit 120 may be connected, more specifically electrically connected, to a connection point / external interface, such as the point of common coupling 115, between the renewable power plant 100 and the electric power network / grid 116, and to a connection point / external interface 125 between the renewable power plant 100 and the gas transmission / distribution network 126. It is to be understood that the power-to-gas unit 120 may include further units than the ones herein described, such as e.g. other components and / or devices, for example pumps, vents, storage tanks and / or separators, required for the power-to- gas unit 120 to work efficiently. It is to be understood that other embodiments of the power-to-gas unit 120 than the one disclosed in figure 3 are possible.

[0109] Figure 4 schematically illustrates an example of a gas to power unit 140 comprising a gas fuel cell 144. As mentioned above, there are a number of possible devices that may be used for converting gas 400 from the gas transmission network 126 into electric power, such as a thermal energy conversion device 141 , a gas turbine 142, an electrochemical energy conversion device 143, a fuel cell 144 and / or a gas driven generator 145. In the following, the function of a gas fuel cell 144, and in particular a hydrogen fuel cell, is explained as an example of one possible gas-to-power unit 140 implementation.

[0110] A gas fuel cell is an electromechanical cell, which converts chemical energy of a gas fuel, in this example hydrogen H2 from the gas transmission network 126, and an oxidizing agent, in this example oxygen O2, into electricity through a pair of redox reactions. Fuel cells are different from most batteries since they require a continuous supply of input fuel and oxidizing agent to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from substances that are already present within the battery. Fuel cells can thus produce electricity continuously as long as fuel and oxygen are supplied.

[0111] The example gas fuel cell 144 in figure 4 comprises an anode 401 and a cathode 402. Between the anode 401 and the cathode 402, an electrolyte 403 is arranged. The anode side 410 of the fuel cell 144 comprises a fuel inlet 411 , in which gas fuel, such as hydrogen H2 from the gas transmission network 126 in this example, is input. The anode side 410 further comprises an outlet 412 through which excess fuel is output from the fuel cell 144. At the anode 401 , a first catalyst causes the input gas fuel H2 to take part in oxidation reactions that generate ions, in this example positively charged hydrogen ions H+, and electrons e-. The positively charged hydrogen ions H+, move from the anode 401 to the cathode 402 through the electrolyte 403. At the same time, electrons e- flow from the anode 401 to the cathode 402 through an external circuit 430, producing direct current (DC) electricity by utilization of the passing electrons e-.

[0112] The cathode side 420 of the fuel cell 144 comprises an air inlet 421 , in which air comprising oxygen O2 is input to the gas fuel cell 144. The cathode side 420 further comprises an outlet 422 through which unused gases are output from the gas fuel cell 144. At the cathode 402, a second catalyst causes the hydrogen ions H+coming from the anode 401 via the electrolyte 403, electrons e- coming from the anode 401 via the external circuit 430, and oxygen O2 from the input air to react, thereby forming water H2O and possibly other products, such as e.g. heat.

[0113] Thus, a gas fuel cell, such as the hydrogen fuel cell illustrated in figure 4, comprises two electrodes, i.e. a negative electrode / anode 401 and a positive electrode / cathode 402, being sandwiched around an electrolyte 403. The gas fuel, in this example being hydrogen H2 from the gas transmission network 126, is fed to the anode 401 , and air is fed to the cathode 402. In this example, a first catalyst at the anode 401 then separates hydrogen molecules H2 into protons H+and electrons e; which travel different paths to the cathode 402. The electrons e- travel through an external circuit 430, comprising e.g. one or more coils or the like, in which a flow of electricity is created, whereas the protons H+travel through the electrolyte 403 to the cathode 402, at which they unite with oxygen O2and the electrons e- to produce water H2O and heat. The gas fuel cell 144 thus converts gas, in this example hydrogen H2, into electric power, and this process is utilized in the gas-to-power unit 140.

[0114] There are various types of fuel cells, such as e.g. polymer electrode membrane (PEM) type fuel cells or solid oxide fuel cells (SOFC). In some implementations, two or more fuel cells are grouped together into a fuel cell stack to produce a desired voltage output.

[0115] As understood by a skilled person, the gas fuel cell 144 exemplified as a hydrogen fuel cell schematically illustrated in figure 4 is only one example of many possible fuel cell types that may be utilized in the gas-to-power unit 140. For example, other kinds of hydrogen fuel cells arranged for converting hydrogen from the gas transmission network 126 into electric power, other types of gas fuel cells arranged for converting natural from the gas transmission network 126 into electric power and / or various kinds of methanol fuel cells arranged for converting methanol produced from gas provided by the gas transmission network 126 into electric power may be utilized.

[0116] As mentioned above, the regulation of renewable power plants may be controlled by national transmission system operators for electricity or gas, local district heating companies, and / or supranational bodies. Control systems and control strategies that can provide compliance with network codes, comprising for example specific sets of attributes, for transmission / distribution networks / grids for electricity, gas and / or heat are therefore needed for providing a reliable regulation of the renewable power plant.

[0117] For example, in a European context, the energy nodes configured for exchanging electricity and gaseous fuel of renewable power plants may be regulated by the European national transmission system operators for electricity or gas. Also, energy nodes configured for exchanging low-grade heat may be regulated by the European local district heating company. The European national transmission system operators for electricity and gas are coordinated by supranational bodies, such as the European Network of Transmission System Operators for Electricity (ENTSO-E) and European Network of Transmission System Operators for Gas (ENTSO-G).

[0118] Both the ENTSO-E and the ENTSO-G monitor and analyze the implementation of network codes that clearly define the specific set of attributes that electricity and gas distributors must fulfill to have a harmonized and integrated energy market within the European Union.

[0119] The renewable power plants within Europe may thus have to comply with network codes of the ENTSO-E, the ENTSO-G, both of the ENTSO-E and the ENTSO-G, or none of the ENTSO-E and the ENTSO-G, depending on the configuration of the renewable power plant 100 and on the energy infrastructure available. Outside of Europe, corresponding organizations / bodies may determine corresponding network codes for other countries / regions / continents, which must be complied with by renewable power plants in those countries / regions / continents. It may thus be necessary to develop control systems and control strategies that can simultaneously comply with network codes for electricity, gas and / or heat distribution transmission / distribution networks / grids. In cases where no network codes are enforced by regulators, renewable power plants 100 will still need to produce energy with a specific set of attributes, such as for example voltage, frequency, pressure and / or temperature, depending on the energy vector, for a reliable operation of the renewable power plant 100.

[0120] Imbalances in the external electric power grid 116 to which the renewable power plant 100 is connected, are not allowed according to the grid codes for the electric power grid 116. For example, instable frequencies, voltages and / or currents due to such imbalances may cause the electric power grid 116 not to comply with its grid codes.

[0121] Figure 5 shows a flow chart diagram for a method 200 for controlling the renewable power plant 100, where the renewable power plant 100 comprises one or more renewable electric power generating units 103 and one or more gas-to-power units 140. The renewable power plant 100 is further connected to an electric power grid 116 and to a gas transmission network 126, as explained above.

[0122] In a first step 210 of the method 200, one or more parameters of the electric power grid 116 are determined.

[0123] According to various embodiments, the one or more determined parameters of the electric power grid 116 may comprise a voltage of the electric power of the electric power of grid 116, a current of the electric power of the electric power grid 116, a frequency of the electric power of the electric power grid 116 and / or a set point for the renewable power plant 100. At least some of the one or more determined parameters may be generally fluctuating / non-stationary parameters, that vary relatively slowly over time. At least one of the one or more determined parameters may correspond to at least one of the grid codes for the electric power grid 116. In a second step 220, the one or more gas-to-power units 140 are, based on the one or more determined parameters of the electric power grid 116, controlled to convert gas from the gas transmission network 126 to electric power. According to various embodiments, the one or more power-to-gas units 120 are thus controlled 220, based on the one or more determined parameters of the electric power grid 116, to convert a gas or gas mixture comprising or consisting of hydrogen, oxygen and / or methane to electric power.

[0124] The one or more gas-to-power units 140 are therefore, according to various embodiments, connected to the gas transmission network 126, and are configured to draw / import gas from the gas transmission network 126 when producing electric power. The one or more gas-to-power units 140 may also be connected to the one or more power-to-gas units 120 and / or to the gas storage 122, and may be configured to, in addition to the gas provided by the gas transmission network 126, also draw gas from the one or more power-to-gas units 120 and / or from the gas storage 122. Thus, the gas-to-power unit 140 may be configured to convert gas to electric power, where the gas is provided by the gas transmission network 126, and possibly also by the one or more power-to-gas units 120 and / or by the gas storage 122. The gas storage 122 may be configured to temporarily store gas from the gas transmission network 126 and / or the one or more power-to-gas units 120. Thus, according to an embodiment, at least a portion of the gas being converted to electric power has been temporarily stored in the gas storage 122 of the renewable power plant 100.

[0125] In a third step 230, the renewable power plant 100 is, based on the one or more determined parameters of the electric power grid 116, controlled to introduce at least a portion of the converted electric power into the electric power grid 116 so as to improve a stability of the electric power grid 116. Thus, the renewable power plant 100 here provides / injects electric power into the electric power grid 116, and hereby counteracts the imbalance / instability of the electric power grid 116.

[0126] According to an embodiment illustrated by the flow chart of figure 5, the method 200 further comprises the step of determining 211 an instability / imbalance of the electric power grid 116 based on the one or more determined parameters of the electric power grid 116. The determination 211 of such an instability / imbalance may be performed by detecting if the one or more determined parameters of the electric power grid 116 exceed their respective limits / thresholds.

[0127] According to an embodiment, an instability is determined 211 if at least one of the one or more determined parameters of the electric power grid has a value D deviating from a desired value Ddes by at least a predetermined deviation value Ddev. As a non-limiting example, wherein the value D is the frequency f; a frequency instability is determined if a frequency f of the electric power deviates in relation to its desired frequency value fdes, which may be e.g. 50 Hz or 60 Hz, with more than a predetermined deviation frequency fdev, e.g. 0.2 Hz. As another non-limiting example, wherein the value D is the voltage V; a voltage instability is determined if a voltage of the electric power deviates in relation to its desired voltage value Vdes with more than a predetermined deviation voltage Vdev.

[0128] Figure 6 schematically illustrates a non-limiting example of a frequency instability control. In the diagram, the y-axis indicates the required power output in relation to a present setpoint, and the x-axis indicates the frequency, fdes is the desired frequency value at the setpoint, e.g. 50 Hz. fdev is the allowed deviation frequency, e.g. 0.2 Hz, such that there is an allowed frequency band between a second frequency f2 and a third fs frequency, which is 2*fdev wide, e.g. a 0.4 Hz wide band between 49.8 Hz and 50.2 Hz, around the desired frequency fdes 50Hz.

[0129] According to the required power output curve, additional power should be provided at frequency instability, such that the renewable power plant is able to output a higher power for frequencies being lower than the allowed frequency band, and such that the renewable power plant is able to output a maximum power at a first frequency fi, which is further away from the desired frequency fdes than the second frequency f2. The first frequency fi may e.g. be at 49.5Hz. If the frequency gets very low, i.e. much lower than the first frequency fi, the renewable power plant is allowed to disconnect from the electric power grid.

[0130] The herein presented method for controlling the renewable power plant makes it possible to provide frequency support, i.e. to meet the output power requirements during frequency instability, also when the one or more renewable electric power generating units 103 are not able to increase the power output enough because they are limited at the max power or because the wind or solar irradiation is not high enough. Thus, if the one or more renewable electric power generating units 103 are not able to themselves increase the output power to fulfil the output power requirements outside of the allowed frequency band f2-fs, electric power is produced in the one or more gas-to-power units 140, which is introduced in the electric power grid 116 such that the output power is increased. In other words, the converted electric power produced in the one or more gas-to-power units 140 may be utilized for increasing the output power such that it reaches the maximum power at the first frequency fi when there is a determined frequency instability, i.e. when the frequency f deviates from its desired frequency value fdes, e.g. 50 Hz, with more than the predetermined deviation frequency fdev, e.g. 0.2 Hz.

[0131] According to an embodiment, a frequency instability is determined if at least one frequency parameter of the one or more determined parameters of the electric power grid has a gradient value Gfreq exceeding a desired gradient value Gfreq_deS; Gfreq > Gfreq_des. The gradient value Gfreq here corresponds to the time derivative of the frequency

[0132] According to an embodiment, a frequency instability is determined if at least one frequency parameter of the one or more determined parameters of the electric power grid has a change of gradient value AGfreq exceeding a desired change of gradient value Gfreq_deS; AGfreq > AGfreq_des. The change of gradient value AGfreq here d2f corresponds to the second time derivative of the frequency f; AGyreq= determination of an instability of the frequency of the electric power may thus be based on detecting that the frequency f deviates more than a predetermined deviation frequency fdev from its desired frequency value fdes. According to some embodiments, the determination of the instability of the frequency also comprises detecting that the frequency gradient value Gfreq exceeds its desired gradient value Gfreq_deS; Gfreq > Gfreq_deS; and / or that the change of the frequency gradient value AGfreq exceeds a desired change of gradient value AGfreq. desi AGfreq>AGfreq_des. A determination of an instability of the voltage of the electric power may correspondingly be based on detecting that the voltage V deviates more than a predetermined deviation voltage Vdev, normally between 2% to 5% , from its desired voltage value Vdes, which is normally between 110 and 420kV.

[0133] It should be noted that at least one of the one or more determined parameters is a generally fluctuating / varying parameter. The fluctuations / variations of the parameter values may then be indicative of the level of stability of the electric power grid 116. For such generally fluctuating / varying parameters, corresponding limits / thresholds may be defined to detect if the determined parameters fluctuate / vary too much. Thus, according to an embodiment, the limits / thresholds for normally fluctuating parameters may indicate an amplitude Ath for some of these fluctuations / variations that should not be exceeded by the amplitude A of the parameters. In other words, the electric power grid 116 is determined 211 to be instable / imbalanced if at least one of the one or more determined parameters of the electric power grid 116 fluctuates with an amplitude A exceeding its fluctuation amplitude threshold Ath; A>Ath. Further, the limits / thresholds may also indicate a change over time for some of these fluctuations / variations that should not be exceeded by the parameters, respectively.

[0134] After the possible instability / imbalance has been determined 211 , the control 220 of the conversion of gas to electric power performed by the one or more gas-to-power units 140 is based on the determined instability / imbalance of the electric power grid 116.

[0135] According to an embodiment illustrated by the flow chart of figure 5, the renewable power plant 100 is connected to a gas transmission network 126, as illustrated in figure 1 . The method 200 then further comprises the step of importing 212 gas from the gas transmission network 126 to the renewable power plant 100 based on the one or more determined parameters of the electric power grid 116.

[0136] Then, the one or more gas-to-power units 140 are controlled to convert at least a portion of the gas imported from the gas transmission network 126 to electric power. The one or more gas-to-power units 140 may also be controlled to convert, in addition to the imported gas, gas provided by the one or more power-to-gas units 120 to electric power. The conversion of gas imported from the gas transmission network 126 and possibly also gas produced by the one or more power-to-gas units 120 of the renewable power plant 100 to electric power is based on the one or more determined parameters of the electric power grid 116. The converted electric power is then introduced 230 into the electric power grid 116.

[0137] According to an embodiment illustrated by the flow chart of figure 5, the method 200 further comprises the step of determining 213 one or more parameters of the gas transmission network 126, in addition to the determined one or more parameters of the electric power grid. Then, the import 214 of gas from the gas transmission network 126 to the renewable power plant 100 for the conversion of at least a portion of the imported gas to electric power is based also on the one or more determined parameters of the gas transmission network 126. Thus, gas is here imported 214 from the gas transmission network 126 based on determined parameters of the electric power grid 116 and on the determined parameters of the gas transmission network 126. Then, gas imported 214 from the gas transmission network 126 is converted to electric power based on the determined parameters of the electric power grid 116. At least a portion of the converted electric power is then introduced 230 into the electric power grid 116 based on determined parameters of the electric power grid 116.

[0138] According to an embodiment illustrated by the flow chart of figure 5, the method 200 further comprises the step of allocating 215 a power producing capability of the renewable power plant 100 based on the one or more determined parameters of the electric power grid 116. This allocation is provided by controlling the renewable power plant 100 to run in a so-called derated mode, i.e. in a reduced / non-maximal production mode for which not all of the production capabilities of the renewable power plant are fully utilized. Then, the one or more renewable electric power generating units 103 are controlled 216 to produce electric power by utilization of the allocated power producing capability, which may then be introduced 230 into the electric power grid 116. Thus, a possible / imaginary power backup / reserve is hereby created / released in the renewable power plant 100, which can be utilized for producing electric power if needed. In other words, a reserve of power is allocated, which is possible to utilize for production of electric power, which may be introduced in the electric power grid 116 if needed.

[0139] According to an embodiment illustrated by the flow chart of figure 5, the method 200 further comprises the step of determining 217 that there is an imbalance in the electric power grid 116 if one or more situations or events occur. These situations or events may comprise that at least one of the one or more determined parameters of the electric power grid 116 has a value D being below a predetermined threshold Dth; D<Dth. These situations or events may also comprise that at least one of the one or more determined parameters of the electric power grid 116 is fluctuating with a gradient having a change over time with a magnitude M which exceeds a predetermined magnitude of change threshold Mth; M>Mth.

[0140] When it is determined that there is an imbalance in the electric power grid 116, the method 200 comprises the step of controlling 220, based on the one or more determined parameters of the electric power grid 116, the one or more gas-to-power units 140 to convert gas to electric power. Further, the method 200 comprises the step of controlling 230, based on the one or more determined parameters of the electric power grid 116, the renewable power plant 100 to introduce at least a portion of the converted electric power into the electric power grid 116, so as to counteract the determined imbalance in the electric power grid 116.

[0141] According to an embodiment illustrated in by the flow chart of figure 5, the one or more parameters of the electric power grid 116 are determined 210 at a point of interest 115 where one or more requirements of the electric power grid 116 are to be fulfilled. According to some embodiments, the requirements may correspond to and / or may be comprised in electric power grid codes.

[0142] In this document, all of the points of interest, the point of common connection (PCC), and the point of interconnection, refers to a point, e.g. a point / node / place / location where at least two networks meet, for example the point at which the obligations / responsibilities of the renewable power plant 100 terminates and obligations / responsibilities of the electric power provider and / or the electric power grid 116 starts. This may also be described as the point at which the renewable power plant 100 stops and the electric power grid 116 starts.

[0143] Then, based on the one or more determined parameters of the electric power grid at the point of interest 115, one or more references are dispatched 221 to the renewable power plant 100. According to an embodiment, the dispatched references may be, correspond to and / or comprise set points intended for the entire renewable power plant 100 and / or reference points intended for individual entities of the renewable power plant 100. According to an embodiment, the step of dispatching 221 the references further comprises calculating the references based on the one or more determined parameters of the electric power grid 116 at the point of interest

[0144] 115.

[0145] In the renewable power plant 100, the one or more gas-to-power units 140 are then controlled 222, based on the one or more dispatched references, to convert gas to electric power. Thus, the dispatched references are received by the renewable power plant 100, and are used for controlling the conversion of gas to electric power in the one or more gas-to-power units 140.

[0146] Then, the renewable power plant 100 is controlled 230, based on the one or more determined parameters of the electric power grid 116 at the point of interest 115, to introduce at least a portion of the converted electric power into the electric power grid

[0147] 116, so as to fulfil the one or more requirements at the point of interest 115.

[0148] According to a second aspect, a control arrangement 150 configured for controlling a renewable power plant 100 is presented. As mentioned above, the renewable power plant 100 comprises one or more renewable electric power generating units 103 and one or more gas-to-power units 140. The renewable power plant 100 is connected to an electric power grid 116 and to a gas transmission network 126. The control arrangement 150 is configured to determine 210 one or more parameters of the electric power grid 116, as described above.

[0149] The control arrangement 150 is further configured to control 220, based on the one or more determined parameters of the electric power grid 116, the one or more gas- to-power units 140 to convert gas from the gas transmission network 126 to electric power, as described above.

[0150] The control arrangement 150 is also configured to control 230, based on the one or more determined parameters of the electric power grid 116, the renewable power plant 100 to introduce at least a portion of the converted electric power into the electric power grid 116 so as to improve a stability of the electric power grid 116.

[0151] With reference to Figure 1 , the renewable power plant 100 may comprise a control arrangement 150 for controlling the power plant 100 according to any one of the aspects and / or embodiments disclosed herein. The control arrangement 150 may comprise, or be referred to as, a power plant controller (PPC).

[0152] According to a third aspect, a renewable power plant 100 is presented. The renewable power plant 100 comprises one or more renewable electric power generating units 103 and one or more gas-to-power units 140, and is connected to an electric power grid 116 and to a gas transmission network 126, as schematically illustrated in figure 1 . The renewable power plant 100 further comprises a control arrangement 150 as herein described.

[0153] The control arrangement 150 may further be configured to, e.g. it comprises units / means / devices 610, 611 , 612, 613, 614, 615, 616, 617, 620, 621 , 622, 630 to, execute / provide / implement the further herein mentioned method steps 210, 211 , 212, 213, 214, 215, 216, 217, 220, 221 , 222, 230 according to various above-described embodiments.

[0154] The person skilled in the art will appreciate that the herein described method aspects and embodiments of the control arrangement controlling a renewable power plant 100 may also be implemented in a computer program, which, when it is executed in a computer, instructs the computer to execute the method. The computer program is usually constituted by a computer program product 503 (shown in figure 7) stored on a non-transitory / non-volatile digital storage medium, in which the computer program is incorporated in the computer-readable medium of the computer program product. The computer-readable medium comprises a suitable memory, such as, for example: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk unit, etc.

[0155] Figure 7 shows in schematic representation an embodiment of the control arrangement 150 according to an aspect of the invention, which may include a control unit 500, which may be arranged / configured for performing / executing one or more of the above-mentioned method steps 210, 211 , 212, 213, 214, 215, 216, 217, 220, 221 , 222, 230. The control unit 500 may comprise a computing unit 501 , which can be constituted by essentially any suitable type of processor or microcomputer, for example a circuit for digital signal processing (Digital Signal Processor, DSP), or a circuit having a predetermined specific function (Application Specific Integrated Circuit, ASIC). The computing unit 501 is connected to a memory unit 502 arranged in the control unit 500. The memory unit 502 provides the computing unit 501 with, for example, the stored program code and / or the stored data which the computing unit 501 requires to be able to perform computations. The computing unit 501 is also arranged to store partial or final results of computations in the memory unit 502.

[0156] In addition, the control unit 500 may be provided with devices 511 , 512, 513, 514 for receiving and transmitting input and output signals. These input and output signals may comprise waveforms, impulses, or other attributes which, by means of the devices 511 , 513 for the reception of input signals, can be detected as information and can be converted into signals which can be processed by the computing unit 501 . These signals are then made available to the computing unit 501 . The devices 512, 514 for the transmission of output signals are arranged to convert signals received from the computing unit 501 in order to create output signals by, for example, modulating the signals, which, for example, can be transmitted to other parts and / or systems of, or associated with, the electric power grid 116, the gas transmission network 126, the heat transmission / distribution network 128, the grid 136 for industrial products and / or the renewable power plant 100 (see figure 1 ). Each of the connections to the devices for receiving and transmitting input and output signals can be constituted by one or more of a cable, a data bus, and a wireless connection.

[0157] Here and in this document, control units are often described as being provided for performing steps of the method according to herein described aspects and embodiments of the invention. This also includes that the units are designed to and / or configured to perform these method steps. For example, the control units may comprise one or more control entities arranged for performing one or more of the herein described method steps 210, 211 , 212, 213, 214, 215, 216, 217, 220, 221 , 222, 230, respectively. These control entities may for example correspond to groups of instructions, which may be in the form of programming code, that are input into, and are utilized / executed by the processor / computing unit 501 of the control unit 500 when the entities are active and / or are utilized for performing their method steps, respectively. Such control entities may be implemented as separate entities in multiple control units, or may be logically separated but physically implemented in the same control unit, or may be both logically and physically arranged together.

[0158] With reference to figure 1 , the control arrangement 150, which may include one or more control units or control entities 610, 611 , 612, 613, 614, 615, 616, 617, 620, 621 , 622, 630, such as for example one or more devices, controllers or control devices, may be arranged to perform all of the method steps mentioned above, in the claims, and in connection with the herein described aspects and embodiments. The control arrangement 150 is associated with the above-described advantages for each respective embodiment of the method.

[0159] The herein described aspects and embodiments may be applied also in other power plant domains than the renewable power plant domains mentioned herein. For example, the herein described aspects and embodiments may be applied to virtual power plants or aggregations of flexible energy loads with their corresponding constraints.

[0160] The present invention is not limited to the above-described embodiments. Instead, the present invention relates to, and encompasses all different embodiments being included within the scope of the independent claims.

Claims

Claims1. A method (200) for controlling a renewable power plant (100) comprising one or more renewable electric power generating units (103) and one or more gas-to- power units (140), the renewable power plant (100) being connected to an electric power grid (116) and to a gas transmission network (126), wherein the method (200) comprises: determining (210) one or more parameters of the electric power grid (116); based on the one or more determined parameters of the electric power grid (116), controlling (220) the one or more gas-to-power units (140) to convert gas from the gas transmission network (126) to electric power; and based on the one or more determined parameters of the electric power grid (116), controlling (230) the renewable power plant (100) to introduce, in addition to electric power provided by the one or more renewable electric power generating units (103), at least a portion of the converted electric power into the electric power grid (116) so as to improve a stability of the electric power grid (116).

2. A method (200) according to claim 1 , further comprising: determining (211 ), based on the one or more determined parameters of the electric power grid (116), an instability of the electric power grid (116); and controlling (220) the one or more gas-to-power units (140) to convert gas to electric power based on the determined instability of the electric power grid (116).

3. A method (200) according to claim 2, wherein the electric power grid (116) is determined (211 ) instable if at least one of the one or more determined parameters of the electric power grid (116) fluctuates with an amplitude A exceeding a fluctuation amplitude threshold Ath; A>Ath.

4. A method (200) according to any one of claims 1-2, wherein the instability is determined (211 ) if one or more situations or events of the following group are valid:• at least one of the one or more determined parameters of the electric power grid (116) has a value D deviating from a desired value Ddes by at least a predetermined deviation value Ddev;• at least one frequency parameter of the one or more determined parameters of the electric power grid (116) has a gradient value Gfreq exceeding a desired gradient value Gfreq_des; Gfreq>Gfreq_des; and• at least one frequency parameter of the one or more determined parameters of the electric power grid (116) has a change of gradient value AGfreq exceeding a desired change of gradient value AGfreq. desi AGfreq>AGfreq_des.

5. A method (200) according to any one of claims 1-4, wherein the gas being converted to electric power has been temporarily stored in a gas storage (122) of the renewable power plant (100).

6. A method (200) according to any one of claims 1-5, further comprising: based on the one or more determined parameters of the electric power grid(116), importing (212) gas from the gas transmission network (126) to the renewable power plant (100); and based on the one or more determined parameters of the electric power grid (116), controlling (220) the one or more gas-to-power units (140) to convert at least a portion of the gas imported from the gas transmission network (126) to electric power.

7. A method (200) according to any one of claims claim 1 -6, wherein the method (200) further comprises: determining (213) one or more parameters of the gas transmission network (126); and based on the one or more determined parameters of the gas transmission network (126), importing (214) gas from the gas transmission network (126) to the renewable power plant (100) for the conversion of at least a portion of the gas imported from the gas transmission network (126) to electric power.

8. A method (200) according to any one of claims 1-7, wherein the one or more determined parameters of the electric power grid (116) are fluctuating over time, the fluctuations being indicative of a level of stability of the electric power grid (116).

9. A method (200) according to any one of claims 1 -8, wherein the method (200) further comprises: based on the one or more determined parameters of the electric power grid (116), allocating (215) a power producing capability of the renewable power plant (100); controlling (216) the one or more renewable electric power generating units (103) to produce electric power by utilization of the allocated power producing capability; and controlling (230) the renewable power plant (100) to introduce the produced electric power into the electric power grid (116).

10. A method (200) according to any one of claims 1-9, wherein the method (200) further comprises: determining (217) that there is an imbalance in the electric power grid (116) if one or more situations or events of the following group are valid:• at least one of the one or more determined parameters of the electric power grid (116) has a value D being below a predetermined threshold Dth; D<Dth; and• at least one of the one or more determined parameters of the electric power grid (116) is fluctuating with a gradient having a change over time with a magnitude M which exceeds a predetermined magnitude of change threshold Mth; M>Mth; and when it is determined that there is an imbalance in the electric power grid (116), controlling (220), based on the one or more determined parameters of the electric power grid (116), the one or more gas-to-power units (140) to convert gas to electric power; and based on the one or more determined parameters of the electric power grid (116), controlling (230) the renewable power plant (100) to introduce at least aportion of the converted electric power into the electric power grid (116) so as to counteract the determined imbalance in the electric power grid (116).

11. A method (200) according to any one of claims 1 -10, wherein the one or more determined parameters of the electric power grid (116) comprise one or more of the group of:• a voltage of the electric power of the electric power of grid (116);• a current of the electric power of the electric power grid (116);• a frequency of the electric power of the electric power grid (116); and• a set point for the renewable power plant (100).

12. A method (200) according to any one of claims 1-11 , wherein each of the one or more gas-to-power units (140) is configured to convert gas to electric power by utilization of one or more in the group of:• a thermal energy conversion device (141 );• a gas turbine (142);• an electrochemical energy conversion device (143);• a fuel cell (144); and• a gas driven generator (145).

13. A method (200) according to any one of claims 1-12, wherein the method (200) further comprises: based on the one or more determined parameters of the electric power grid (116), controlling (220) the one or more gas-to-power units (140) to convert gas to electric power, wherein the gas comprises or consists of one or more of the group of:• hydrogen;• oxygen; and• methane.

14. A method (200) according to any one of claims 1 -13, wherein the one or more renewable electric power generating units (103) comprise one or more in the group of:• a wind turbine generator (101 ) of the renewable power plant (100);• a photo-voltaic generator (102) of the renewable power plant (100); and• an electric battery energy storage system (106) of the renewable power plant (100).

15. A method (200) according to any one of claims 1-14, wherein the method (200) further comprises: determining (210) the one or more parameters of the electric power grid (116) at a point of interest (115) where one or more requirements of the electric power grid (116) are to be fulfilled; based on the one or more determined parameters at the point of interest(115), dispatching (221 ) one or more references to the renewable power plant (100); based on the one or more dispatched references, controlling (222) the one or more gas-to-power units (140) to convert gas to electric power; and based on the one or more determined parameters of the electric power grid(116) at the point of interest (115), controlling (230) the renewable power plant (100) to introduce at least a portion of the converted electric power into the electric power grid (116) so as to fulfil one or more requirements at the point of interest (115).

16. A computer program (703) or a computer-readable medium comprising instructions which, when the program or the instructions is / are executed by a computer, cause the computer to carry out the method according to any one of the claims 1 to 15.

17. A control arrangement (150) for controlling a renewable power plant (100), wherein the renewable power plant (100) comprises one or more renewable electric power generating units (103) and or more gas-to-power units (140), the renewable power plant (100) being connected to an electric power grid (116) and to a gas transmission network (126), wherein the control arrangement (150) is configured to: determine (210) one or more parameters of the electric power grid (116);based on the one or more determined parameters of the electric power grid (116), control (220) the one or more gas-to-power units (140) to convert gas from the gas transmission network (126) to electric power; and based on the one or more determined parameters of the electric power grid (116), control (230) the renewable power plant (100) to introduce at least a portion of the converted electric power into the electric power grid (116) so as to improve a stability of the electric power grid (116).

18. A renewable power plant (100) comprising one or more renewable electric power generating units (103) and one or more gas-to-power units (140), and being connected to an electric power grid (116) and to a gas transmission network (126), wherein the renewable power plant comprises a control arrangement (150) according to claim 17.

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