DESC:FIELD OF THE INVENTION:
The invention relates to: a control system for controlling a hybrid power plant according to claim 1; to a hybrid power plant; to a method for controlling a hybrid power plant according to claim 19; and to a computer program product according to claim 20.

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.

In current practice common solar and wind power systems are operated based on threshold values, wherein in case one or more parameters from a grid requirement are violated or not complied with, the wind or solar power plant transitions from an active state in which it may produce active power to an inactive state, and disconnects from the electrical grid so that no electrical power can be exchanged between the wind or solar power plant and the electrical grid.

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.

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 according to claim 1.

Accordingly, a control system adapted for controlling a hybrid power plant is provided, the hybrid power plant comprising at least two different types of power plants, the two different types of power plants including at least one renewable-energy power plant (in particular at least two different renewable-energy power plants), wherein the control system comprises a non-interrupting control mode adapted to maintain at least one of the power plants of the hybrid power plant in an active state and in (power) connection to an electrical grid when (and even though) the at least one of the power plants of the hybrid power plant produces no active power or substantially no active power.

In the non-interrupting control mode, one, several or all power plants of the hybrid power plant may be kept active and connected to the electrical grid both when the power plants (individually or in combination) produce active power and when they (individually or in combination) produce no or substantially no active power.

By maintaining the connection to the electrical grid and maintaining the power plant in the active state (and not transitioning it into an inactive state), electrical power (active and/or reactive power) may be exchanged between the electrical grid and the connected power plant. This connection may be established via one or more devices such as a transformer or a junction. The connection of the power plant to the electrical grid may also be referred to as power connection. The non-interrupting control mode may also be referred to as non-stop operation. The respective power plant is kept active and connected to the grid both when it produces power as well as when it produces no power. A threshold may be defined below which the power plant is regarded as producing substantially no active power, e.g. 1% or 0.1% of a nominal power output of the respective power plant. A wind power plant, e.g. produces no active power when all turbine rotors of the wind power plant stand still. A solar power plant, e.g. produces no active power or substantially no active power during the night. Another potential reason for producing no or substantial no active power may be when the hybrid power plant is outside of the production envelope. For example, in the electrical grid there may be more active power available than required. In particular in such a situation the control system may actively control one or more power plants of the hybrid power plant to produce no or substantial no active power (e.g. by feathering wind turbine blades) and enter or stay in the non-interrupting mode to continue to provide grid support.

By means of the control system even in case of zero power production the power plant(s) is/are not disconnected from the electrical grid. Maintaining a power plant in an active state may require active power, so an activated power plant that produces no active power may even consume active power. However, by maintaining such power plants of a hybrid power plant in the active state and connected to the electrical grid, strongly improved grid support may be provided.

The control system thus enables the power plants of the hybrid power plant to support the electrical grid even when no electrical power is produced by one or more of these power plants. For example, the control system may provide (zero) low-voltage ride through (LVRT) at high voltage (HV) terminals, reactive power control, voltage control, frequency support and/or even black start. By the control system it is thus possible, e.g. to damp voltage fluctuations of the electrical grid by allowing reactive power exchange with a power plant of the hybrid power plant even in situations when no active power is produced by this power plant.

The control system is adapted to manage the (internal) resources of the hybrid power plant by means of a communication infrastructure connecting the control system to the individual power plants. The control system is further adapted for controlling the individual power plants of the hybrid power plant such as to damp and/or compensate the intermittent nature of at least some of the power sources.

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 electrical grid in an even more effective manner.

The non-interrupting control mode may be adapted to maintain at least one of the power plants of the hybrid power plant in an active state and in connection to an electrical grid when the at least one of the power plants of the hybrid power plant constantly produces no active power or substantially no active power. The control system may be adapted to determine that the at least one of the power plants constantly produces no or substantially no active power when the at least one of the power plants provides no or substantially no active power to the electrical grid over a predefined period of time, e.g. of more than one minute or more than one hour.

Optionally, the control system is further adapted to operate in the non-interrupting mode longer than 12 hours or longer than 24 hours(or longer than a plurality of days) and/or over a time duration comprising at least one daytime and at least one nighttime.

At least one renewable-energy power plant of the hybrid power plant may comprise at least one wind power plant and/or at least one solar power plant.

The hybrid power plant may comprise at least two of a wind power plant, a solar power plant and a storage power plant and the control system may be adapted to control this hybrid power plant. Further, the hybrid power plant controlled by the control system may comprise at least one wind power plant, at least one solar power plant and at least one storage power plant.

OBJECT OF THE INVENTION

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

SUMMARY OF THE INVENTION

According to an embodiment the control system is adapted to monitor the active power production of one or more (e.g. all) of the power plants of the hybrid power plant. More generally, the control system may be 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. 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. In an embodiment of the present invention, 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 super capacitor), and a state of health, SOH (e.g. of a battery). The control system may be further adapted to receive and/or determine (e.g. measure) at least one grid variable of an electrical grid. 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, MV, (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. 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 is optionally further adapted to measure the active power production of the power plants of the hybrid power plant at medium voltage level (MV level).

According to an embodiment, the control system is further adapted to determine whether or not at least one of the power plants of the hybrid power plant (constantly) produces no active power or substantially no active power, and to set an active power production set point of at least one other power plant of the hybrid power plant in dependence of a determination that at least one of the power plants of the hybrid power plant (constantly) produces no active power. When maintaining a power plant in the active state the power plant consumes active power. The control system may be adapted to compensate this power consumption by a correspondingly adjusted (e.g. increased) set point for another one of the hybrid power plant’s power plants.

Alternatively or in addition, the control system may be adapted to request delivery of active power from the electrical grid to the hybrid power plant when operating in the non-interrupting control mode.

In an embodiment, the control system is further adapted to control the at least one of the power plants of the hybrid power plant that (constantly) produces no active power (or substantially no active power) to provide reactive power to the electrical grid when operating in the non-interrupting control mode. By this, the hybrid power plant may provide grid stability support even when some or all of its power plants provide no active power.

Optionally, the control system is adapted to control the at least one of the power plants of the hybrid power plant that (constantly) produces no active power or substantially no active power to provide grid voltage support when operating in the non-interrupting control mode.

The control system may be further adapted to control the at least one of the power plants of the hybrid power plant that (constantly) produces no active power (or substantially no active power)to perform active filtering, in particular to reduce a total harmonic distortion or individual harmonics of the electrical grid when operating in the non-interrupting control mode.

Optionally, the non-interrupting control mode is adapted to maintain all renewable-energy power plants of the hybrid power plant (or all power plantsof the hybrid power plant) in an active state and in connection to an electrical grid when at least one or all of the power plants of the hybrid power plant (constantly) produce(s) no active power(or substantially no active power).

According to an embodiment, the control system is adapted to determine a value for an individual reactive power reserve for at least one or all of the power plants of the hybrid power plant.Optionally, the control system is adapted to communicate the value(s) for the individual reactive power reserve(s) to the at least one or to all of the power plants of the hybrid power plant.

According to an aspect, a hybrid power plant is provided. The hybrid power plant comprises at least two different types of power plants,including at least one renewable-energy 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. 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.

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 super capacitor 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 super capacitors 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.

According to an aspect, a method for controlling a hybrid power plant comprising at least two different types of power plants including at least one renewable-energy power plant is provided. The method comprises operating the hybrid power plant in a non-interrupting control mode so as to maintain at least one of the power plants of the hybrid power plant in an active state and in connection to an electrical grid (even) when the at least one of the power plants of the hybrid power plant constantly produces no active power.

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 aforementioned method.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention will become apparent from the drawings according to the description. Embodiments of the invention are shown in the figures, where
Fig. 1 shows a schematic diagram of power production profiles of wind and solar systems;

Fig. 2 shows a hybrid power plant having a hybrid plant controller, a wind power plant, a solar power plant, and a storage power plant;

Fig. 3 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;

Fig. 4 shows a schematic diagram of power production profiles of wind and solar systems without the provision of active power reserves and when accounting for active power reserves;

Fig. 5 shows a schematic diagram of active power reserves profiles of wind, solar and storage systems;

Fig. 6 shows a schematic diagram of reactive power reserves profiles of wind, solar and storage systems; and

Fig. 7 shows a method for controlling a hybrid power plant.

The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 2 shows a hybrid power plant 1 comprising a control system 10 and a plurality of power plants 11, 12, 13. More precisely, the hybrid power plant 1 comprises at least two different types of power plants 11, 12, 13, wherein the at least two different types of power plants 11, 12, 13 include at least one renewable-energy power plant 11, 12. In the example according to Fig. 2, the hybrid power plant 1 comprises a wind power plant 11 and a solar power plant 12 as renewable-energy power plants which are accompanied by a storage power plant 13.

The control system 10 is adapted for controlling the hybrid power plant 1. Further, the control system 10 comprises a non-interrupting control mode. The control system 10 may be operating in the non-interrupting control mode. The non-interrupting control mode (and the control system 10 when operating in the non-interrupting control mode) is adapted to maintain (in particular to operate and keep operating) at least one of the power plants 11, 12, 13 of the hybrid power plant 1 in an active state and in connection to an electrical grid 2 when said at least one of the power plants 11, 12, 13 of the hybrid power plant 1 (in particular constantly) produces no active power or substantially no active power.

To enter and maintain the non-interrupting mode, the control system 10 may override deactivation and/or disconnect-from-grid functions.

For example, the control system 10 may determine that the at least one of the power plants 11, 12, 13 of the hybrid power plant 1 constantly produces no active power or substantially no active power, when it provides no active power or substantially no active power to the electrical grid 2 over a predefined duration of time of more than one minute, in particular of more than one hour.

The control system 10 may operate in the non-interrupting mode longer than 24 hours, in particular without interruption. The control system 10 may include other modes such as an interrupting mode in which it disconnects power plants that produce no or substantially active power from the grid and deactivates these power plants. The non-interrupting mode may be selectable by a TSO and/or may be the default control mode.

Optionally, in the non-interrupting control mode the control system 10 maintains all renewable-energy power plants 11, 12 of the hybrid power plant 1 (or all power plants 11, 12, 13 of the hybrid power plant 1) in an active state and in connection to the electrical grid (2) when at least one or all of the power plants 11, 12, 13 of the hybrid power plant 1constantly produce(s) no or substantially no active power.

In the non-interrupting mode, the power plants 11, 12, 13 may provide grid support (in particular voltage support) and/or monitoring functions.

Referring again to Fig. 1, which may correspond to exemplary production profiles of the wind power plant 11 and the solar power plant 12 of the hybrid power plant 1, the solar power plant 12 produces no active power during the nights. The wind power plant 11 produces, e.g., substantially no active power at times of roughly 12 h and 56 h. Depending on a predefined threshold value (e.g. a percentage of a nominal or maximum active power output, or a certain value in Watts), at further (or fewer) time periods the wind power plant 11 may be regarded as producing substantially no active power.

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.

In order to be able to effectively respond to grid frequency and/or grid voltage deviations, it is possible to operate hybrid power plants with a power output below a possible maximum power output. For example, blades of wind turbines may be pitched towards feather by a certain degree, so that only a predefined fraction of the available power at the given wind conditions is produced by the wind turbine, e.g. 90% what would correspond to a reserve of 10%. The reserve may thus be the difference of the maximum possible power production and the actual power production at a given point in time, or in another possible representation, the percentage of this difference with respect to the maximum possible power production. This reserve may be used to stabilize a connected electrical grid when necessary. In this case, the power will be increased to a higher value, e.g. to the maximum possible power (i.e., 100%).

The hybrid power plant 1 of Fig. 2 is adapted to provide active and reactive power reserves, in particular in the non-interrupting mode. This will be described in more detail further below after a more detailed description of the setup of the hybrid power plant 1.

As shown in Fig. 2, 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. 2, 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. 2, 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. 2 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. 2, 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. 2, 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. 2 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.

The power plants 11, 12, 13 of the hybrid power plant 1 may individually and/or collectively be disconnected from the electrical grid by corresponding couplings. Such couplings may be included in one or more of the transformers 15, in the junction 17 and/or in the substation.

As already mentioned, the hybrid power plant 1 comprises the 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, indicated by dashed lines. 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. 2). 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 may be 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 may thus be 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.

The control system 10 may thus monitor the active power production of the power plants 11, 12, 13 of the hybrid power plant 1. In particular, it may measure the active power production of the power plants 11, 12, 13 of the hybrid power plant 1at medium voltage (MV) level.

The control system 10 may determine whether or not at least one of the power plants 11, 12, 13 of the hybrid power plant 1 (in particular) constantly produces no active power or substantially no active power, and to set an active power production set point of at least one other power plant 11, 12, 13 of the hybrid power plant 1in dependence of a determination that at least one of the power plants 11, 12, 13 of the hybrid power plant 1 (constantly) produces no active power. For example, the control system 10 may determine that the solar power plant 12 produces no or substantially no active power and, in reaction, increase an active power production set point of the wind power plant 11 and/or of the storage power plant 13 correspondingly.

Alternatively or in addition, the control system 10 may be able to request delivery of active power from the electrical grid 2 to the hybrid power plant 1 when operating in the non-interrupting control mode, e.g. in a situation in which the hybrid power plant 1 in total consumes more active power than it produces. This may also cover losses, e.g. in the infrastructure of the hybrid power plant 1.

The control system 10 is adapted to provide at least one grid support function when operating in the non-interrupting control mode.

For responding to possible grid frequency and/or grid voltage deviations, the hybrid power plant 1 maintains a hybrid power plant active power reserve ?PHP and a hybrid power plant reactive power reserve ?QHP. These are the power reserves that the hybrid power plant 1 is capable to provide at its point of coupling to the electrical grid 2.

As a base value, the hybrid power plant active power reserve ?PHP and the hybrid power plant reactive power reserve ?QHP are each set by the control system 10 to 1% or to at least 1%. As an example, the control system 10 may set the hybrid power plant active power reserve ?PHP to be in the range of 1% to 20%. Alternatively or in addition, the control system 10 may set the hybrid power plant reactive power reserve ?QHP to be in the range of 1% to 50%. These ranges provide good response capabilities while reducing the annual power yield only little.

Optionally, the control system 10 may be designed such that the provision of power reserves can be switched on (curtailment mode) or off (maximum-power mode). The control system 10 may be adapted to receive a command for selecting the mode.

Optionally, the control system 10 may be adapted to receive from a TSO and/or an external grid control a set point for the hybrid power plant active power reserve ?PHP and/or for the hybrid power plant reactive power reserve ?QHP.

The control system 10 is further adapted to determine an individual active power reserve ?Pwind, ?Psolar, ?Padd and an individual reactive power reserve ?Qwind, ?Qsolar, ?Qsto for each of the wind power plant 11, the solar power plant 12 and the storage power plant 13. It will be appreciated that two or more, or even all of the values for the individual active power reserves ?Pwind, ?Psolar, ?Padd and individual reactive power reserves ?Qwind, ?Qsolar, ?Qsto may be different to one another.

Given the hybrid power plant active power reserve ?PHP and/or the hybrid power plant reactive power reserve ?QHP, the individual power reserves may be calculated by the control system 10 as follows (for active and reactive power):

?PHP = ?Pwind + ?Psolar + ?Padd + ?Pcorr_loss + ?Pcorr_forecast,
?QHP = ?Qwind + ?Qsolar + ?Qsto + ?Qcorr_loss + ?Qcorr_forecast.

Therein, ?Pcorr_loss and ?Qcorr_loss are active and reactive power loss correction factors accounting for losses of power in electrical infrastructure, in particular between the wind power plant 11, the solar power plant 12 and/or the storage power plant 13, and the electrical grid 2, e.g. at a hybrid park feeder 18 between junction 17 and substation 19. The losses may depend of the mode of operation of the control system 10. Further, ?Pcorr_forecast and ?Qcorr_forecast are active and reactive power forecast correction factors accounting for a forecasted maximum possible power production of the wind power plant 11 and/or the solar power plant 12. The forecast may be short-term and/or mid-term. The forecast may comprise a weather forecast, a wind-speed forecast and/or a solar-irradiation forecast.

The control system 10 may also determine total active and/or reactive power reserves, ?Ptot and ?Qtot, as a sum of the power reserves of the individual power plants:

?Ptot = ?Pwind + ?Psolar + ?Padd,
?Qtot = ?Qwind + ?Qsolar + ?Qsto.

It directly follows that:

?Ptot = ?PHP - ?Pcorr_loss - ?Pcorr_forecast,
?Qtot = ?QHP - ?Qcorr_loss - ?Qcorr_forecast.

Optionally, the control system 10 may be adapted to receive from a TSO and/or an external grid control a set point for the total active and/or reactive power reserves ?Ptot, ?Qtot.

For a simplified control scheme, the control system 10 may determine the share of the individual power plants by multiplying the total active and/or reactive power reserves ?Ptot, ?Qtot with corresponding coefficients Kwind, Ksolar, Kadd, wherein 0 = Kwind, Ksolar, Kadd= 1:

?Pwind = Kwind?Ptot,
?Psolar = Ksolar?Ptot,
?Padd = Kadd?Ptot,
?Qwind = Kwind?Qtot,
?Qsolar = Ksolar?Qtot,
?Qsto = Kadd?Qtot.

Therein, Kwind + Ksolar + Kadd = 1.

For determining the coefficients Kwind, Ksolar, Kadd and/or the individual active and reactive power reserves ?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qsto, the control system 10 may monitor the current power production (in particular operation points) of the wind power plant 11 and the solar power plant 12 and, optionally, a status, e.g. the SOC or an optional mix of power-storage systems of the storage power plant 13. Corresponding measurements of the current power production (by the control system 10 or an operatively connected device) may be performed at MV level.

The control system 10 is further adapted to communicate values indicative for the individual active power reserves ?Pwind, ?Psolar, ?Padd and for the individual reactive power reserves ?Qwind, ?Qsolar, ?Qsto 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.

For example, the control system 10 communicates the percentage values for ?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qsto to the respective power plants. It will be appreciated that alternatively or in addition, the control system 10 may e.g. communicate the coefficients Kwind, Ksolar, Kadd and the total active and/or reactive power reserves ?Ptot, ?Qtot as values indicative for the individual active power reserves ?Pwind, ?Psolar, ?Padd and for the individual reactive power reserves ?Qwind, ?Qsolar, ?Qsto to the wind power plant 11, the solar power plant 12 and/or the storage power plant 13.

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 values indicative for the active power reserves ?Pwind, ?Psolar, ?Padd and reactive power reserves ?Qwind, ?Qsolar, ?Qsto.

The control system 10 may control at least one of the power plants 11, 12, 13 of the hybrid power plant 1 that constantly produces no or substantially no active power to provide reactive power to the electrical grid 2, in particular for providing grid voltage support, when operating in the non-interrupting control mode.

Optionally, the control system 10 may control at least one of the power plants 11, 12, 13 of the hybrid power plant 1 that constantly produces no or substantially no active power to reduce a total harmonic distortion (THD) and/or individual harmonics of the electrical grid 2 when operating in the non-interrupting control mode. This may be done by an active control of the harmonics. For example, the power plants 11, 12, 13 may perform active filtering functions.

Fig. 3 shows a hybrid power plant 1’ similar to the hybrid power plant 1 according to Fig. 2, so in the following only the differences to hybrid power plant 1 according to Fig. 2 will be described.

The wind power plant 11 of the hybrid power plant 1’ according to Fig. 3 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 active power reserve ?Pwind and reactive power reserve ?Qwind 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. That is, each of the plurality of PV systems 121 is controlled in dependence on the active power reserve ?Psolar and reactive power reserve ?Qsolar set by the control system 10.

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 and a power-storage system 131C having an engine-generator 133 (such as a diesel generator). Each of the plurality of power-storage systems 131A-131C is controlled in dependence on the active power reserve ?Padd and reactive power reserve ?Qsto set by the control system 10

Fig. 4 shows, similar to Fig. 1, exemplary power production profiles of the wind power plant 11 (thin solid line) and the solar power plant 12 (thin dashed line). The sum of the wind and solar power is indicated by the dotted line. These curves correspond to the maximum possible power production. Further, thick lines indicate the corresponding (active) power production of the wind power plant 11 and the solar power plant 12 within the same time frame when applying active power reserves ?Pwind, ?Psolar of 10% in each case. By applying power reserves, the respective power production is reduced to (the maximum possible power production) 100% - ?Pwind and ?Psolar, i.e., in the present example to 90%.

Fig. 5 shows the active power reserves of the wind power plant 11 (solid line), the solar power plant 12 (dashed line) and the storage power plant 13 (dotted line). When there is only little wind and solar power, the storage power plant 13 supplements a larger fraction of active power and, thus, also of the active power reserve. The example of Fig. 5 is based on a hybrid power plant active power reserve ?PHP of 10 %.

Fig. 6 shows corresponding reactive power reserves, wherein the reactive power reserve of the wind power plant 11 is shown as a thin solid line, the reactive power reserve of the solar power plant 12 as a dashed line and the reactive power reserve of the storage power plant 13 as a thick solid line. The dotted line indicates the sum of wind and solar reactive power reserves. The example of Fig. 6 is based on a hybrid power plant reactive power reserve ?QHP of 50%.

Both for active power and for reactive power, the control system 10 may determine the active and reactive power reserves ?Padd, ?Qsto of the storage power plant 13 based on the active and reactive power reserves ?Pwind, ?Psolar, ?Qwind, ?Qsolar, respectively, of the wind power plant 11 and the solar power plant 12.

Since the control system 10 is adapted to receive and/or determine current power production statuses of the wind power plant 11 and the solar power plant 12, as well as an SOC and/or a SOH of the storage power plant 13, it is able to effectively assign the shares of the individual power plants in providing the hybrid power plant active and reactive power reserves ?PHP, ?PHP.

Fig. 7 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. 2 and/or according to Fig. 3, the method comprising the following steps:

Step S100: Monitoring, by the control system 10, the active power production of the power plants 11, 12, 13 of the hybrid power plant 1; 1’. This may include measuring the active power output of the power plants 11, 12, 13 of the hybrid power plant 1; 1’, in particular at MV level.

Step S101: Determining, by the control system 10, that one or more of the power plants 11, 12, 13 (in particular one of the renewable-energy power plants 11, 12) of the hybrid power plant 1; 1’ (constantly) produce(s) no active power or substantially no active power. This may include to determine that the respective power plant 11, 12, 13 in the active state consumes the same amount or more active power as it produces. This may also include to determine that the respective power plant 11, 12, 13 provides no active power to the electrical grid 2. Optionally, the respective power plant 11, 12, 13 may preserve an active power reserve ?Pwind, ?Psolar, ?Padd. For example, corresponding environmental conditions (e.g. wind and/or solar irradiation) are such that the power plant 11, 12 generally may produce a certain amount of active power, but by preserving an active power reserve ?Pwind, ?Psolar, ?Padd, the power plant 11, 12 does not supply any active power to the electrical grid 2 and the control system 10 may then determine that the respective power plant 11, 12 (constantly) produces no active power or substantially no active power.

Step S102: Operating, by the control system 10, the hybrid power plant 1; 1’ in a non-interrupting control mode so as to maintain at least one of the power plants 11, 12, 13 of the hybrid power plant 1; 1’ in an active state and in connection to an electrical grid 2 when the at least one of the power plants 11, 12, 13 of the hybrid power plant 1; 1’ (constantly) produces no active power or substantially no active power.

Step S103: Optionally, exchanging reactive power between the grid and the at least one of the power plants 11, 12, 13 of the hybrid power plant 1; 1’ which (constantly) produces no or substantially no active power. This may include to determine an individual reactive power reserve ?Qwind, ?Qsolar, ?Qsto for each of the wind power plant 11, the solar power plant 12 and the storage power plant 13, e.g. based on the at least one operation status, the at least one grid variable and/or the at least one environmental variable. Alternatively or in addition, active power reserves ?Pwind, ?Psolar, ?Padd may be used to provide grid frequency support. The method may further comprise 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-131C of the storage power plant 13 based on the individual active power reserve ?Pwind, ?Psolar, ?Padd and/or the individual reactive power reserve ?Qwind, ?Qsolar, ?Qsto.

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. 2 and 3 and in particular by means of the control system 10, by the method according to Fig. 7 and by the computer program product it is possible to improve grid support based on renewable power sources.

Further, in the non-interrupting control mode the control system 10 may be informed by each power plant 11, 12, 13 of the hybrid power plant 1; 1’ about a detection of an abnormal operation with no technical reason. This may lead to a conclusion of an invasive breach or a security breach, e.g. in the case of a theft and/or an un-authorized personnel access. Thus, the provision of the non-interrupting mode may additionally improve the security of the hybrid power plant 1; 1’.

It is worth noting that the control system 10 may be adapted to activate the non-interrupting mode independently of a state of charge of the storage power plant 13.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is to be understood that the description and drawings presented herein represent a presently preferred embodiment of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly not limited.
List of Reference Numbers
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-131C power-storage system
132 battery
133 engine-generator
134 supercapacitor
135 curtailment algorithm
14 converter
15 transformer
16 plant transformer
17 junction
18 hybrid park feeder
19 substation
190 collector
191 transformer
2 electrical grid
Kwind, Ksolar, Kadd coefficient
?Pcorr_forecast active power forecast correction factor
?Pcorr_loss active power loss correction factor
?PHP hybrid power plant active power reserve
?Ptot total active power reserve
?Pwind, ?Psolar, ?Padd active power reserve
?Qcorr_forecast reactive power forecast correction factor
?Qcorr_loss reactive power loss correction factor
?QHP hybrid power plant reactive power reserve
?Qtot total reactive power reserve
?Qwind, ?Qsolar, ?Qsto reactive power reserve
,CLAIMS:CLAIMS
We claim:

1. A control system (10) for controlling a hybrid power plant (1; 1’) comprising at least two different types of power plants (11, 12, 13)including at least one renewable-energy power plant (11, 12), wherein the control system (10) comprises a non-interrupting control mode adapted to maintain at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) in an active state and in connection to an electrical grid (2) when the at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) produces no active power or substantially no active power.

2. The control system (10) according to claim 1,wherein the non-interrupting control mode is adapted to maintain at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) in an active state and in connection to an electrical grid (2) when the at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) constantly produces no active power or substantially no active power.

3. The control system (10) according to claim 1 or 2, further adapted to operate in the non-interrupting mode longer than 24 hours.

4. The control system (10) according to any of the preceding claims, wherein the at least one renewable-energy power plant (11, 12) of the hybrid power plant (1; 1’) comprises at least one of a wind power plant (11) and a solar power plant (12).

5. The control system (10) according to any of the preceding claims, wherein the control system (10) is adapted for controlling the 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).

6. The control system (10) according to any of the preceding claims, further adapted to monitor the active power production of the power plants (11, 12, 13) of the hybrid power plant (1; 1’).

7. The control system (10) according to claim 6, further adapted to measure the active power production of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) at medium voltage level.

8. The control system (10) according to claim 6 or 7, further adapted to determine whether or not at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) produces no active power or substantially no active power, and to set an active power production set point of at least one other power plant (11, 12, 13) of the hybrid power plant (1; 1’)in dependence of a determination that at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) produces no active power.

9. The control system (10) according to any of the preceding claims, further adapted to request delivery of active power from the electrical grid (2) to the hybrid power plant (1; 1’) when operating in the non-interrupting control mode.

10. The control system (10) according to any of the preceding claims, further adapted to control the at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) that produces no active power or substantially no active power to provide reactive power to the electrical grid (2)when operating in the non-interrupting control mode.

11. The control system (10) according to any of the preceding claims, further adapted to control the at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) that produces no active power or substantially no active power to provide grid voltage support when operating in the non-interrupting control mode.

12. The control system (10) according to any of the preceding claims, further adapted to control the at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) that produces no active power or substantially no active power to perform active filtering to reduce a total harmonic distortion or individual harmonics of the electrical grid (2) when operating in the non-interrupting control mode.

13. The control system (10) according to any of the preceding claims, the non-interrupting control mode being further adapted to maintain all renewable-energy power plants (11, 12) of the hybrid power plant (1; 1’), or all power plants (11, 12, 13) of the hybrid power plant (1; 1’) in an active state and in connection to the electrical grid (2) when at least one or all of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) produce(s) no active power or substantially no active power.

14. The control system (10) according to any of the preceding claims, further adapted to determine a value for an individual reactive power reserve (?Qwind, ?Qsolar, ?Qsto) for atleast one or all of the power plants (11, 12, 13) of the hybrid power plant (1; 1’); and to communicate the value for the individual reactive power reserve(s) (?Qwind, ?Qsolar, ?Qsto) to the at least one or all of the power plants (11, 12, 13) of the hybrid power plant (1; 1’).

15. A hybrid power plant (1; 1’) comprising at least two different types of power plants (11, 12, 13),including at least one renewable-energy power plant (11, 12)and the control system (10) according to any of the preceding claims.

16. The hybrid power plant (1; 1’) according to claim 15, further comprising a junction (17) adapted for receiving the generated power from each of the at least two different types of power plants (11, 12, 13) and for supplying the total generated power to an electrical grid (2).

17. The hybrid power plant (1; 1’) according to claim 15 or 16, comprising a storage power plant (13) including at least one of a battery (132), an engine-generator (133), a super capacitor (134) and a curtailment algorithm (135).

18. The hybrid power plant (1’) according to any of claims 15 to 17, comprising at least one of a wind power plant (11) having more than one wind-turbine-generator system (111), a solar power plant (12) having more than one solar system (121) and a storage power plant (13) having more than one power-storage system (131).

19. A method for controlling a hybrid power plant (1; 1’) comprising at least two different types of power plants (11, 12, 13) including at least one renewable-energy power plant (11, 12), wherein the method comprises operating the hybrid power plant (1; 1’) in a non-interrupting control mode so as to maintain at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) in an active state and in connection to an electrical grid (2) when the at least one of the power plants (11, 12, 13) of the hybrid power plant (1; 1’) produces no active power or substantially no active power.

20. 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 method of claim 20.