DESC:FIELD OF THE INVENTION
The invention relates to a control system for controlling a hybrid power plant, a hybrid power plant, a method for controlling a hybrid power plant, and a computer program product.

BACKGROUND
A mix of power generation between solar and wind power plants becomes more and more present in the modern power systems. Each year Transmission System Operators (TSOs) observe increased amounts of renewable energy produced by wind turbines and photovoltaic systems to be connected to their grid. Consequently, the stability of the grid is being challenged and for this purpose grid codes (GCs) are constantly adapting to more stringent requirements.

The nature of wind power and solar power has an intermittent character. The variability of the active power production from both wind and solar is a result of the changing nature mainly of wind speed, wind direction and solar irradiation.

BRIEF DESCRIPTION OF THE INVENTION
Fig. 1 shows a schematic diagram of power production profiles of wind and solar systems;

Fig. 2A and 2B show droop characteristics for frequency and voltage regulation, respectively;

Fig. 3 shows a hybrid power plant having a hybrid plant controller, a wind power plant, a solar power plant, and a storage power plant;

Fig. 4 shows a hybrid power plant having a hybrid plant controller, a wind power plant having a plurality of wind-turbine generator systems, a solar power plant having a plurality of photovoltaic systems, and a storage power plant having a plurality of power-storage systems; and
Fig. 5 shows a method for controlling a hybrid power plant.

DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 shows exemplary power production profiles of wind and solar power systems. The horizontal axis shows the time over an exemplary duration of three days. The vertical axis shows the active power in an arbitrary scale. Therein, the solid line indicates the active power provided by an exemplary wind power plant comprising one or more wind turbines. As the wind changes, there can be seen strong variations in the produced power. The dashed line, on the other hand, indicates the active power of an exemplary solar, e.g. photovoltaic, power plant. During the night, no power is produced and during daytime, power is produced depending on the position of the sun relative to the solar power plant and on the presence of clouds and the like (note the kink in the curve at the time around 38:00). The dotted line shows the sum of active power produced by the wind power plant and by the solar power plant. As can be seen in Fig. 1, the sum of wind and solar power may balance fluctuations in both of the individual sources in certain circumstances. However, there are situations in which there is no or only little sunlight, and no or only little wind.

It is an object to provide a solution for further improving grid stability based on renewable power sources.

This object is solved by a control system of the present invention.

Accordingly, a control system adapted for controlling a hybrid power plant is provided, the hybrid power plant comprising at least two of a wind power plant, a solar power plant and a storage power plant. Therein, the control system is further adapted to: determine (e.g., estimate) an individual droop parameter for each of the at least two of the wind power plant, the solar power plant and the storage power plant, and communicate the individual droop parameters to the wind power plant, the solar power plant and/or the storage power plant.

By centrally determining individual droop parameters for each of the at least two of the wind power plant, the solar power plant and the storage power plant of a hybrid power plant, it is possible to effectively share the fraction of the response to deviations in grid variables and thus to help enforcing the grid variables of the electrical grid the hybrid power plant is providing power to. The control system may support the frequency and voltage at the point of common connection to the electrical grid. Stringent GCs may be fulfilled, particularly in a fast and accurate manner. The control system may provide an aggregated droop control for two or three types of power sources of the hybrid power plant. Optionally, the control system is adapted for controlling the storage power plant comprising at least two (e.g. different) power-storage systems.

The hybrid power plant may comprise (each of) the wind power plant, the solar power plant and the storage power plant. The control system may be adapted for controlling the hybrid power plant comprising (each of) the wind power plant, the solar power plant and the storage power plant. By this, the control system may help supporting the grid variables in an even more effective manner.

The control system may be adapted to determine each of the individual droop parameters as a percentage value indicating the percentage amount a grid variable would have to change to cause a 100% change in a controlled quantity. This enables a simple control.

The controlled quantity may be an active power or a reactive power (e.g. of the corresponding power plant). The grid variable may be a grid frequency or a grid voltage. Optionally, the control system is adapted to control more than one quantity. Both active power and reactive power may be controlled quantities. The control system may be adapted to determine individual droop parameters separately for active power and for reactive power.

According to an embodiment, the control system is adapted to set each of the individual droop parameters to a value in the range of 1% to 20%. The control system may individually control the percentage of droop needed for each power source (wind power plant, solar power plant and storage power plant). The control system may be adapted to set the individual droop parameters such that the hybrid power plant has a predetermined aggregated droop parameter (e.g., the control system is adapted to receive a predetermined aggregated droop parameter from an external grid controller, e.g. a TSO). The predetermined aggregated droop parameter may be, e.g., in the range of 1% to 20%.

The control system may determine, e.g. estimate, the individual droop parameters online, e.g. based on variables that may change in time. Optionally, the control system is adapted to determine the individual droop parameters based on at least one grid variable and/or at least one environmental variable and/or at least one operating condition.

According to an embodiment, the control system is adapted to receive and/or determine (e.g. monitor) at least one operation status of the wind power plant, the solar power plant and/or the storage power plant. Optionally, the control system is adapted to determine the individual droop parameters based on the at least one operation status. The control system may manage the internal resources of active and reactive power of the hybrid power plant based on their actual condition of production. By this, a very reliable response of the hybrid power plant may be achieved.

At least one operation status may comprise one or more of a current active power production, an active power production profile, a state of charge, SOC (e.g. of a battery or a supercapacitor), and a state of health, SOH (e.g. of a battery). More specifically, the at least one operation status may comprise an active power production of the wind power plant and/or the solar power plant and a state of charge of the storage power plant.

Further, the control system may be adapted to forecast at least one of the at least one operation status, e.g. based on a current or preceding operation status and/or on an environmental variable (or its forecast).

The control system may be further adapted to receive and/or determine (e.g. measure) at least one grid variable of an electrical grid. Further, the control system may be adapted to determine the individual droop parameters based on the at least one grid variable.

At least one grid variable may comprise a grid frequency and/or a grid voltage. The control system may measure the grid variable(s) at medium voltage level (e.g. from 1 kV to 35 kV).

The control system may be further adapted to receive and/or determine (e.g. measure) at least one environmental variable. Optionally, the control system is further adapted to determine the individual droop parameters based on the at least one environmental variable.

At least one environmental variable may comprise one or more of a wind speed, a wind direction, an air density, a temperature and a solar irradiation variable (e.g. a position of the sun, the presence of clouds, etc.).

Optionally, the control system is adapted to forecast at least one of the one or more environmental variables. The forecast may be based, e.g., on previous data and/or current measurements. This may further improve the accuracy of the power delivery.

The control system may be adapted to determine at least two of the individual droop parameters (or each of the individual droop parameters) at a given point in time such as to be different from one another.

According to an aspect, a hybrid power plant is provided. The hybrid power plant comprises at least two of (or all of) a wind power plant, a solar power plant and a storage power plant. Further, the hybrid power plant comprises the control system according to any embodiment or variant described herein.

Each of the wind power plant, the solar power plant and the storage power plant may comprise one single power generating unit (such as one wind turbine) or a plurality of power generating units (e.g., a plurality of wind turbines). The storage power plant may be adapted for delivering 20% or up to 20% of the active power of the hybrid power plant (e.g. with reference to rated power outputs).

The hybrid power plant may further comprise a junction adapted for receiving the generated power from each of the wind power plant, the solar power plant and the storage power plant and for supplying the total generated power to an electrical grid. The hybrid power plant may provide the total power delivered by the wind power plant, the solar power plant and the storage power plant at one connection point with the electrical grid.

Optionally, the storage power plant comprises at least one (e.g., one, two, three or all) of a battery, an engine-generator (e.g. a diesel generator), a supercapacitor and a curtailment algorithm. A storage power plant comprising a battery or a plurality of batteries for storing power and providing power to the grid may also be referred to as battery plant.

More specifically, the storage power plant may comprise at least two of one or more batteries, one or more engine-generators, one or more supercapacitors and one or more curtailment algorithms.

At least one of the wind power plant, the solar power plant and the storage power plant may comprise more than one wind-turbine-generator system, more than one solar system (e.g. photovoltaic and/or thermal solar systems) or more than one power-storage system, respectively. The control system of the hybrid power plant may effectively control the individual plants to cooperate in supporting the grid voltage and/or frequency.

Further, the hybrid power plant may comprise the at least one junction and / or at least one unified voltage transformer each of them adapted for receiving the generated power from the wind power plant, the solar power plant and the storage power plant which are connected to the at least one junction and / or the at least one unified voltage transformer.

In one embodiment the hybrid power plant comprises at least one junction being part of a middle voltage network of the power plant, in particular in a 33 kV network of the power plant. That can imply that the voltage at the output of the wind power plant, the solar power plant and / or the storage power plant is transformed to medium voltage before being transmitted to the at least one junction.

In a further embodiment the at least one unified voltage transformer transforms from low-voltage to medium-voltage, in particular to 33 kV. Again, that can imply that the voltage at the output of the wind power plant, the solar power plant and / or the storage power plant is transformed to medium voltage before being transmitted to the at least one unified transformer.

With junctions and / or unified transformers a number of different network layouts are possible.

With such a network layout it is e.g. possible to evaluate the layouts also from an efficiency point of view. Given the often remote location and the availability of the power grid, the junction boxes connected coupled with step up transformers can provide a proper solution for loss reductions. A secondary benefit can e.g. be that land constraints are a well known issue in some countries and therefore the wind power plant might be several kilometers away for the solar power plant.

In one embodiment the output of the at least one junction and / or unified voltage transformer is transmitted to a transformer to high voltage and subsequently to the electrical grid.

It is also possible that the generated power from each of the wind power plant, the solar power plant and / or the storage power plant is received by one junction and / or by one unified transformer.

Alternatively, the generated power from two of the wind power plant, the solar power plant and / or the storage power plant is transmitted to a first junction, the output of the first junction is then transmitted to a further junction which has the output of at least one of the wind power plant, the solar power plant and the storage power plant as an additional input.

According to an aspect, a method for controlling a hybrid power plant comprising a wind power plant, a solar power plant and a storage power plant (or at least two of those) is provided. The method comprises the following steps:

Optionally, receive and/or determine (e.g. measure) at least one grid variable of an electrical grid, at least one environmental variable and/or at least one operation status of the wind power plant, the solar power plant and/or the storage power plant.

Determine an individual droop parameter for each of the wind power plant, the solar power plant and the storage power plant (or the at least two thereof), in particular based on the at least one grid variable, the at least one environmental variable and/or the at least one operation status.

Communicate the individual droop parameters to the wind power plant, the solar power plant and/or the storage power plant (or the at least two thereof).

By this, grid stability may be effectively improved using renewable energy sources.

In the method the control system according to any embodiment or variant described herein, or the hybrid power plant according to any embodiment or variant described herein may be used.

According to an aspect, a computer program product is provided. The computer program product comprises instructions which, when executed by one or more computers, cause the one or more computers to carry out the steps of the aforementioned method.

DETAILED DESCRIPTION
The frequency of a power system is directly controllable by the amount of active power produced and consumed in the system. To maintain a constant frequency value, equilibrium between generation and consumption has to be achieved. In the moment when this equilibrium is broken, the grid frequency can experience excursions into the under-frequency area (under, e.g., 50 Hz or 60 Hz, depending on the nominal frequency), or the grid frequency can experience excursions into the over-frequency area (above, e.g., 50 Hz or 60 Hz). The power production units then have to bring the power system back to its equilibrium point by quickly adjusting their output power.

As commonly known, the frequency of a synchronous AC generator is directly proportional to the speed of the rotating electrical field(s). If a load requirement on the generator is increased maintaining a constant voltage, then the current increases, so electrical torque increases and therefore the rotor of the generator tends to decelerate. As a result, the frequency decreases. In response, the power to the generator is increased so that the increased load requirement is met. For controlling the frequency, the frequency of the rotor is compared to a set point. If the frequency is below or above the set point, power to the generator is increased or decreased, respectively, until the frequency again meets the set point.

Similarly, voltage may be controlled by adjusting the reactive power supplied by the generator, e.g. by setting the exciting current of the generator.

Droop control is a control strategy that may be applied to a plurality of generators for primary frequency and/or voltage control to allow parallel generator operation for load sharing.

Fig. 2A and 2B show exemplary droop characteristics for frequency (Fig. 2A) and voltage regulation (Fig. 2B), respectively.

Therein, P denotes the active power, Q the reactive power, f the grid frequency and V the grid voltage. Further, fN and VN correspond to the nominal grid frequency, e.g. 50 Hz or 60 Hz, and to the nominal grid voltage, e.g. 220 kV or 380 kV. Pmax and Qmax indicate the maximum active and reactive power of the respective power production unit.

A first exemplary droop characteristic is indicated by R1% and shown as a solid line both for active power P and for reactive power Q. This characteristic in each case defines how the set points for the active and reactive power, respectively, are modified when the grid frequency f and/or grid voltage V deviate from the nominal grid frequency fN and/or voltage VN. For this purpose, the power production unit provides power reserves of +/- ?P and +/- ?Q. Given these reserves, and with the slope of R1%, the set points of P and Q are adapted in dependence of the frequency or voltage deviation up to +/- |?f|/fN and +/- |?V|/VN, respectively. Within the reserves, the dependency of the set points for the active and reactive power on the grid frequency f and grid voltage V are linear. The slope in this area may be referred to as droop parameter. The droop parameter may be defined as a percentage value indicating the percentage amount the grid variable (fN and/or VN) would have to change to cause a 100% change in the corresponding controlled quantity (P and/or Q, respectively).

The active power P and reactive power Q are linearly dependent on grid frequency fN and voltage VN, respectively, within +/- |?f|/fN and +/- |?V|/VN, respectively. Outside of this interval, the power reserves would be exceeded and thus the droop characteristics comprise flat areas, which may be referred to as outer horizon. In these flat areas the set points for active and reactive power P, Q are not changed, even when the grid frequency fN or voltage VN change.

R2% indicates a second exemplary droop characteristic as a dashed line. In comparison to the first exemplary droop characteristic R1%, it has a smaller slope, corresponding to a smaller droop parameter. Further, the droop characteristic comprises a deadband (thick horizontal line), i.e., a range of grid frequencies f around the nominal grid frequency fN and a range of grid voltages V around the nominal grid voltage VN wherein the set points for the active and reactive power P, Q are not modified. By this, control actions are kept at a minimum within a region of tolerable grid frequency or grid voltage deviations.

Fig. 3 shows a hybrid power plant 1. The hybrid power plant 1 comprises a control system 10, a wind power plant 11, a solar power plant 12 and a storage power plant 13.

The wind power plant 11 generally comprises at least one wind-turbine generator system, in the following referred to as WTG system 111 and in the example according to Fig. 3, the wind power plant 11 comprises exactly one WTG system 111. The WTG system 111 may be a horizontal-axis wind turbine comprising a nacelle rotatably mounted on a tower. The WTG system 111 comprises a turbine 112 (rotatably mounted on the nacelle) and a generator 113 driven by the turbine 112. The turbine 112 is rotated by the wind so as to produce electrical power by means of the generator 113. The generator 113 is electrically coupled to an optional transformer 15. Further, the wind power plant 11 comprises a wind-power-plant controller, in the following referred to as WPP controller 110. The WPP controller 110 is adapted to control the turbine 112 (e.g., a pitch angle of one or more turbine blades) and/or the generator 113 (e.g., a set point, e.g. of a torque). Optionally, the WPP controller 110 is further adapted to control the output power at the terminal of transformer 15.

The solar power plant 12 generally comprises at least one thermal solar or photovoltaic system, the latter in the following referred to as PV system 121. In the example according to Fig. 3, the wind power plant 11 comprises exactly one PV system 121. The PV system 121 comprises a plurality of PV arrays 122. A set of PV arrays 122 are connected to one another in a series and a plurality of such serial PV arrays 122 are connected to one another in parallel. The plurality of PV arrays 122 are connected to a converter 14, in the example according to Fig. 3 a DC-to-AC converter. The converter 14 is electrically coupled to an optional transformer 15. Further, the solar power plant 12 comprises a photovoltaic-power-plant controller, in the following referred to as PVPP controller 120. The PVPP controller 120 is adapted to control the converter 14 and/or optional switches for coupling or decoupling at least one PV array 122. Optionally, the PVPP controller 120 is further adapted to control the output power at the terminal of transformer 15.

The storage power plant 13 generally comprises at least one power-storage system 131A. In the example according to Fig. 3, the storage power plant 13 comprises exactly one power-storage system 131A. The power-storage system 131 is neither a WTG system nor a solar power system such as a PV system. According to Fig. 3, the power-storage system 131A comprises an electrochemical power storage device, more precisely, a rechargeable battery 132, e.g. a lithium-ion battery. The battery 132 is connected to a converter 14, in the example according to Fig. 3 a DC-to-AC converter. The converter 14 is electrically coupled to an optional transformer 15. Further, the storage power plant 13 comprises a storage-power-plant controller, in the following referred to as SPP controller 130. The SPP controller 130 is adapted to control the converter 14 and/or optional charging and recharging electronics. Optionally, the SPP controller 120 is further adapted to control the output power at the terminal of transformer 15.

Each of the wind power plant 11, solar power plant 12 and storage power plant 13 are electrically coupled to a junction 17 such as to supply their produced power to the junction 17. The junction 17 is adapted to receive the produced power from each of the wind power plant 11, solar power plant 12 and storage power plant 13, and to output a total produced power. For example, the junction 17 is a 33 kV junction box. The junction 17 is connected to an electrical grid 2 by means of a substation 19. The substation 19 in the present example is a MV substation and comprises a transformer 191 to transform the current supplied by the junction 17 to HV, e.g., 220 kV or 380 kV. The substation 19 further comprises a collector 190 which connects the junction 17 to the transformer 190. The substation 19 is electrically coupled to the electrical grid 2. According to an alternative, the junction 17 and the substation 19 may be designed as one device.

As already mentioned, the hybrid power plant 1 comprises a control system 10. The control system 10 may be arranged at the substation 19. The control system 10 is communicatively coupled to the WPP controller 110, the PVPP controller 120 and the SPP controller 130. The control system 10 is adapted to control each of the WPP controller 110, the PVPP controller 120 and the SPP controller 130. The control system 10 may also be referred to as hybrid plant controller or HyPC. The control system 10 may be implemented in or as a programmable logic controller, PLC.

The control system 10 is further communicatively coupled to the substation 19 and/or (in the present example to both) an anemometer 100 (or any other environmental variable detector). Thereby, the control system 10 receives at least one grid variable from the substation 19. For example, the at least one grid variable comprises a grid frequency and/or a grid voltage. Alternatively, the control system 10 comprises a measurement device coupled to the electrical grid 2 and adapted for measuring the at least one grid variable. As a further alternative, the control system 10 may receive at least one grid variable value from a TSO, e.g. by means of a corresponding SCADA interface (indicated with the open dashed line in Fig. 3). The anemometer 100 provides measured values of the wind speed to the control system 10. The anemometer 100 may be arranged on or near the WTG system 111, e.g. on the nacelle of the WTG system 111.

A measurement of the environmental variable, in this example the wind speed, may be indicative for the status at the time of the measurement. Alternatively or in addition, the control system 10 may determine an environmental variable by forecasting a value of the environmental variable. For example, a current value of the environmental variable may be forecasted using past measurements. Alternatively, a future value of the environmental variable may be forecasted using past and/or current measurements. For example, the forecast may be based on measurements taken one day ago or one year ago (in particular at the same time of day). Optionally, these measurements are corrected, e.g. for different temperatures. Further optionally, the forecast may include a weather forecast. The forecast may be a short-term forecast for a value of the environmental variable, e.g. 15 to 30 minutes after the forecast. Alternatively, the forecast may be a medium-term forecast for a value of the environmental variable, e.g. 2 to 4 hours after the forecast.

Further, the control system 10 is adapted to receive and/or determine at least one operation status of the wind power plant 11, the solar power plant 12 and/or the storage power plant 13. The at least one operation status may comprises one or more of a current active power production (of the wind power plant 11, the solar power plant 12 and/or the storage power plant 13), an active power production profile (of the wind power plant 11, the solar power plant 12 and/or the storage power plant 13), a state of charge (of the storage power plant 13), a state of health (of the storage power plant 13) and a life-cycle cost of energy. The current active power production (profile) may be determined at MV level.

The control system 10 is thus adapted to receive and/or determine, in particular measure, at least one operation status, at least one grid variable of the electrical grid 2 and at least one environmental variable.

The control system 10 may also be adapted to forecast at least one grid variable, and/or at least one operation status, the latter for example based on a forecast of the environmental value.

Further, the control system is adapted to determine, in particular estimate, droop parameters. The droop parameters comprise, e.g., the slope of a droop characteristic (e.g. of the droop characteristic according to Fig. 2A and/or according to Fig. 2B) either for all grid frequencies/voltages or for a certain range or certain ranges of grid frequencies/voltages. More precisely, the control system 10 is adapted to determine at least one individual droop parameter RWPP, RPVPP, RSPP for each of the wind power plant 11, the solar power plant 12 and the storage power plant 13, respectively. Therein, the determination of the droop parameters RWPP, RPVPP, RSPP may be based on the at least one grid variable and/or the at least one environmental variable and/or the at least one operation status (current and/or forecasted). Optionally, the control system 10 is adapted to determine individual droop parameters RWPP, RPVPP, RSPP separately for active power and for reactive power.

The droop parameters RWPP, RPVPP, RSPP may be percentage values indicating the percentage amount the grid variable would have to change to cause a 100% change in a controlled quantity. According to this example, an RWPP, RPVPP or RSPP of 5% would mean that a 5% frequency deviation would cause a 100% change in active power output and/or that a 5% voltage deviation would cause a 100% change in reactive power output. Optionally, the control system 10 is adapted to set each of the individual droop parameters RWPP, RPVPP, RSPP to a value in the range of 1% to 20%. The individual droop parameters may be set by the control system 10 such that an aggregated droop R, which may be the sum of the individual droop parameters, is in the range of 1% and 20%.

It will be appreciated that the control system 10 may be adapted to control active power and/or reactive power based on the droop parameters RWPP, RPVPP, RSPP.

For example, the determination of the individual droop parameters RWPP, RPVPP, RSPP may be based on the at least one environmental variable. In this regard, as an example, a (e.g. short-term or medium-term) forecasted wind speed may be taken into account for determining the droop parameter RWPP for the wind power plant 11. If the forecast indicates that the wind speed will allow a substantial increase in (active and/or reactive) power produced by the wind power plant 11, the control system 10 may set the droop parameter RWPP for the wind power plant 11 to a higher value. The wind power plant 11 will then provide a larger portion of the hybrid power plant 1 response to a deviation in the grid variable. The individual droop parameters for the solar power plant 12 and/or the storage power plant 13 may be reduced in a corresponding manner. On the other hand, if wind forecast (and optionally, solar irradiation forecast) indicate that one or both of the wind power plant 11 and the solar power plant 12 are likely to produce less power, the droop parameters RWPP, RPVPP, RSPP may be set by the control system 10 such that the storage power plant 13 will provide a larger portion of the hybrid power plant 1 response to a deviation in the grid variable. The storage power plant 13 may be controlled accordingly, e.g. by timely charging the battery 132. Thus, the control system 10 may control the individual power sources (wind power plant 11, solar power plant 12 and storage power plant 13) based on their actual (and/or forecasted) conditions of power production.

The individual droop parameters RWPP, RPVPP, RSPP may be different from one another, e.g. at a given point in time.

Correspondingly, the control system 10 is further adapted to communicate the individual droop parameters RWPP, RPVPP, RSPP to the wind power plant 11, the solar power plant 12 and/or the storage power plant 13, in particular to the respective WPP controller 110, PVPP controller 120 and/or SPP controller 130. The control system 10 is communicatively coupled to the wind power plant 11, the solar power plant 12 and/or the storage power plant 13, in particular to the respective WPP controller 110, PVPP controller 120 and/or SPP controller 130, e.g. by means of ethernet and/or one or more optic fibers.

The WPP controller 110, the PVPP controller 120 and the SPP controller 130 are adapted to control the WTG system 111, the PV system 121 and the power-storage system 131A, respectively, based on the corresponding droop parameter RWPP, RPVPP, RSPP.

Optionally, the WPP controller 110, the PVPP controller 120 and the SPP controller 130 may comprise (e.g. store in a memory) the droop characteristics for active and/or reactive power P, Q, wherein the droop characteristics may comprise the position of the outer horizon and/or of an optional deadband. The slope of the droop characteristic(s) may be set by the corresponding droop parameter RWPP, RPVPP, RSPP provided by the control system 10.

Fig. 4 shows a hybrid power plant 1’ similar to the hybrid power plant 1 according to Fig. 3, so in the following only the differences to hybrid power plant 1 according to Fig. 3 will be described.

The wind power plant 11 of the hybrid power plant 1’ according to Fig. 4 comprises a plurality of WTG systems 111. Each of the WTG systems 111 are controlled by the WPP controller 110. That is, each of the plurality of WTG systems 111 is controlled in dependence on the droop parameter RWPP set by the control system 10.

Further, the wind power plant 11 comprises a plant transformer 16, which may be, e.g., a MV or HV transformer. Each of the generators 113 of the plurality of WTG systems 11 is electrically coupled to the plant transformer 16 (via an optional transformer 15).

The solar power plant 12 comprises a plurality of PV systems 121. Each of the PV systems 121 has a plurality of PV arrays 122 coupled to a plant transformer 16 via a converter 14 and an optional transformer 15. Each of the PV systems 121 is controlled by the PVPP controller 120.

Further, the storage power plant 13 comprises two power-storage systems 131A having a battery 132 each, a power-storage system 131B having a supercapacitor 134, a power-storage system 131C having an engine-generator 133 (such as a diesel generator), and a power-storage system 131D having a curtailment algorithm 135.
For curtailment, some or all of the turbines 112 within the wind power plant 11, some or all of the PV systems 121 of the solar power plant 12 and/or some or all of the (other) power-storage systems 131A-131C may be operated with lower-than-possible power production. This enables the hybrid power plant 1’ to increase power production when needed in order to react on changes in grid frequency and/or grid voltage. The amount or fraction of the power kept for curtailment is determined by the curtailment algorithm 135. This may be based on the droop parameter RSPP for the storage power plant 13 provided by the control system 10 and/or based on a grid variable. By means of the curtailment algorithm 135, the accuracy of the droop operation may be further improved. The control system 10 may be adapted to determine the amount of curtailment.

Fig. 5 shows a method for controlling the hybrid power plant 1, 1’ comprising the wind power plant 11, the solar power plant 12 and the storage power plant 13 according to Fig. 3 and/or according to Fig. 4, the method comprising the following steps:

Step S100: Receive and/or determine at least one operation status, at least one grid variable of an electrical grid 2 and/or at least one environmental variable;

Step S101: Determine an individual droop parameter RWPP, RPVPP, RSPP for each of the wind power plant 11, the solar power plant 12 and the storage power plant 13 based on the at least one operation status, the at least one grid variable and/or the at least one environmental variable; and

Step S102: Communicate the individual droop parameters RWPP, RPVPP, RSPP to the wind power plant 11, the solar power plant 12 and/or the storage power plant 13.

The method may further comprise a step S103 of controlling at least one WTG system of the wind power plant 11, at least one PV system 121 (or other solar power system) of the solar power plant 12 and/or at least one power-storage system 131A-131D of the storage power plant 13 based on the individual droop parameters RWPP, RPVPP, RSPP.

A computer program product 102 that may be stored on a non-volatile storage 101 of the control system 10 may comprise instructions which, when executed by one or more computers (the control system 10, the WPP controller 110, the PVPP controller 120 and/or the SPP controller 130 may be or comprise computers) cause the one or more computers to carry out the steps of the aforementioned method.

By means of the hybrid power plant 1; 1’ according to Figs. 3 and 4 and in particular by means of the control system 10, by the method according to Fig. 5 and by the computer program product it is possible to effectively smooth power production based on renewable power sources.

LIST OF REFERENCE NUMERALS

1, 1’ hybrid power plant
10 control system
100 anemometer
101 storage
102 computer program product
11 wind power plant
110 WPP controller
111 WTG system
112 turbine
113 generator
12 solar power plant
120 PVPP controller
121 PV system
122 PV array
13 storage power plant
130 SPP controller
131A-131D power-storage system
132 battery
133 engine-generator
134 supercapacitor
135 curtailment algorithm
14 converter
15 transformer
16 plant transformer
17 junction
19 substation
190 collector
191 transformer
2 electrical grid
f grid frequency
P active power
Q reactive power
RWPP, RPVPP, RSPP droop parameter
R aggregated droop
V grid voltage
,CLAIMS:CLAIMS

We claim:

1. A control system (10) for controlling a hybrid power plant (1; 1’) comprising at least two of a wind power plant (11), a solar power plant (12) and a storage power plant (13), wherein the control system (10) is adapted to:

- determine an individual droop parameter (RWPP, RPVPP, RSPP) for each of the at least two of the wind power plant (11), the solar power plant (12) and the storage power plant (13); and
- communicate the individual droop parameters (RWPP, RPVPP, RSPP) to the at least two of the wind power plant (11), the solar power plant (12) and the storage power plant (13).

2. The control system (10) according to claim 1, wherein the control system (10) is adapted for controlling the hybrid power plant (1; 1’) comprising the wind power plant (11), the solar power plant (12) and the storage power plant (13).

3. The control system (10) according to claim 1 or 2, further adapted to determine each of the individual droop parameters (RWPP, RPVPP, RSPP) as a percentage value indicating the percentage amount a grid variable would have to change to cause a 100% change in a controlled quantity.

4. The control system (10) according to claim 3, wherein the controlled quantity is an active power (P) or a reactive power (Q) and the grid variable is a grid frequency (f) or a grid voltage (V).

5. The control system (10) according to claim 3 or 4, wherein the control system (10) is adapted to set each of the individual droop parameters (RWPP, RPVPP, RSPP) to a value in the range of 1% to 20%.

6. The control system (10) according to any of the preceding claims, wherein the control system (10) is adapted to determine the individual droop parameters (RWPP, RPVPP, RSPP) based on at least one operation status, at least one grid variable and/or at least one environmental variable.

7. The control system (10) according to any of the preceding claims, further adapted to receive and/or determine at least one operation status of the wind power plant (11), the solar power plant (12) and/or the storage power plant (13), and to determine the individual droop parameters (RWPP, RPVPP, RSPP) based on the at least one operation status.

8. The control system (10) according to claim 7, wherein the at least one operation status comprises one or more of a current active power production, an active power production profile, a state of charge and a state of health.

9. The control system (10) according to claim 7 or 8, wherein the control system (10) is adapted to forecast the at least one operation status.

10. The control system (10) according to any of the preceding claims, the control system (10) being further adapted to receive and/or determine at least one grid variable of an electrical grid (2), and to determine the individual droop parameters (RWPP, RPVPP, RSPP) based on the at least one grid variable.

11. The control system (10) according to claim 10, wherein the at least one grid variable comprises a grid frequency (f) and/or a grid voltage (V).

12. The control system (10) according to any of the preceding claims, the control system (10) being further adapted to receive and/or determine at least one environmental variable, and to determine the individual droop parameters (RWPP, RPVPP, RSPP) based on the at least one environmental variable.

13. The control system (10) according to claim 12, wherein the one or more environmental variable comprises one or more of a wind speed, a wind direction, an air density, a temperature and a solar irradiation variable.

14. The control system (10) according to claim 12 or 13, wherein the control system (10) is adapted to forecast the one or more environmental variables.

15. The control system (10) according to any of the preceding claims, wherein, at a given point in time, at least two of the individual droop parameters (RWPP, RPVPP, RSPP) are different from one another.

16. A hybrid power plant (1; 1’) comprising at least two of a wind power plant (11), a solar power plant (12) and a storage power plant (13), wherein the hybrid power plant (1; 1’) further comprises the control system (10) according to any of the preceding claims.

17. The hybrid power plant (1; 1’) according to claim 16, further comprising a junction (17) adapted for receiving the generated power from each of the wind power plant (11), the solar power plant (12) and the storage power plant (13) and for supplying the total generated power to an electrical grid (2).

18. The hybrid power plant (1; 1’) according to claim 16 or 17, wherein the storage power plant (13) comprises at least one of a battery (132), an engine-generator (133), a supercapacitor (134) and a curtailment algorithm (135).

19. The hybrid power plant (1’) according to claim 18, wherein the storage power plant (13) comprises at least two of one or more batteries (132), one or more engine-generators (133), one or more supercapacitors (134) and one or more curtailment algorithms (135).

20. The hybrid power plant (1’) according to any of claims 18 to 19, wherein at least one of the wind power plant (11), the solar power plant (12) and the storage power plant (13) comprises more than one wind-turbine-generator system (111), more than one solar system (121) or more than one power-storage system (131), respectively.

21. A method for controlling a hybrid power plant (1; 1’) comprising at least two of a wind power plant (11), a solar power plant (12) and a storage power plant (13), the method comprising the following steps:

- determine an individual droop parameter (RWPP, RPVPP, RSPP) for each of the at least two of the wind power plant (11), the solar power plant (12) and the storage power plant (13); and
- communicate the individual droop parameters (RWPP, RPVPP, RSPP) to the at least two of the wind power plant (11), the solar power plant (12) and the storage power plant (13).

22. A computer program product (102) comprising instructions which, when executed by one or more computers, cause the one or more computers to carry out the steps of the method of claim 21.