DESC:FIELD OF THE INVENTION
The invention relates to a hybrid power plant, a method for operating 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 solar power systems (e.g. 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
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 first embodiment of a hybrid power plant having a hybrid plant controller, a wind power plant, a solar power plant, and a storage power plant and one junction for all plants;

Fig. 3 shows a second embodiment of a hybrid power plant having a hybrid plant controller, a wind power plant, a solar power plant, and a storage power plant and two junctions, one of them connecting the solar power plant and the storage power plant;

Fig. 4 shows a third embodiment of a hybrid power plant having a hybrid plant controller, a wind power plant, a solar power plant, and a storage power plant and two junctions one of them connecting the wind power plant and the solar power plant;

Fig. 5 shows a fourth embodiment of a hybrid power plant having a hybrid plant controller, a wind power plant, a solar power plant, and a storage power plant and one unified transformer connecting the wind power plant, the solar power plant and the storage power plant;

Fig. 6 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. 7 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. 8 shows a schematic diagram of active power reserves profiles of wind, solar and storage systems;

Fig. 9 shows a schematic diagram of reactive power reserves profiles of wind, solar and storage systems; and

Fig. 10 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 eight 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.

Since there is a drive to install more renewable power systems, the capability of the grids to absorb transient electrical power supplies is challenged.

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

This object is solved by a hybrid power plant according to the present invention.

Such a hybrid power plant comprises at least two of a wind power plant, a solar power plant and a storage power plant. Further it comprises 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.

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 (a value of) an individual power reserve for each of the at least two of the wind power plant, the solar power plant and the storage power plant; and communicate (the values of) the individual power reserves to the at least two of the wind power plant, the solar power plant and the storage power plant.

By centrally determining individual power reserves 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 constantly provide a predetermined power reserve despite the intermitting nature of wind and solar power systems and thus to help enforcing the grid variables of the electrical grid the hybrid power plant is providing power to. The control system may thus support a stable frequency and voltage at the point of common connection to the electrical grid even when wind speed and/or solar irradiation change. Stringent GCs may be fulfilled, particularly in a fast and accurate manner. Optionally, the control system is adapted for controlling the storage power plant comprising at least two (e.g. different) power-storage systems.

The wind power plant and the solar power plant may be operated in different modes (e.g. power factor control, reactive power as a function of voltage, reactive power as a function of power or reactive power reference) in order to provide reactive power support in case it is required. In the hybrid power plant, reactive power may be provided by means of a power electronic converter. In case of the wind power plant, the converter may control the amount of reactive power injected or absorbed by the wind turbine(s). In case of the solar power plant and the storage power plant it may control the amount of reactive power available in the hybrid power plant based on an operation point (e.g. maximum power point production or state of charge of the battery) and state of operation (e.g. start-up, shut-down or night-time operation). When a TSO is demanding a constant active and/or reactive power reserve, the storage power plant may compensate possible shortages in the wind and solar active and/or reactive power reserves.
The individual power reserves may comprise individual active power reserves and/or individual reactive power reserves, optionally for each of the wind power plant, the solar power plant and the storage power plant. It is worth mentioning that the voltage amplitude is usually a local phenomenon, whereas the frequency magnitude usually has a more global nature in the electrical grid. Therefore, reactive power reserves may be used for the local conditioning for the power system characteristics ensuring proper voltage characteristics at the level of connection.

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 further adapted to determine each of the individual power reserves as a percentage value indicating a percentage of a maximum possible power production (of the wind power plant, the solar power plant or the storage power plant, respectively). The maximum possible power production may be a current maximum (active and/or reactive) power production, e.g. based on present wind speed, solar irradiation or the like.

The control system may be further adapted to receive a value for a hybrid power plant power reserve (a value for active power and/or a value for reactive power) to be provided by the hybrid power plant, e.g. from a TSO or an external grid controller. Optionally, the control system is adapted to determine each of the individual (active or reactive) power reserves in dependence of this hybrid power plant (active or reactive) power reserve. The control system may be adapted to maintain a constant value for a hybrid power plant (active and/or reactive) power reserve by determining individual active and/or reactive power reserves which change over time.

Optionally, the control system is adapted to set the hybrid (active and/or reactive) power plant power reserve to a value of at least 1%. Correspondingly, when operating with a 1% power reserve, the hybrid power plant will be controlled to be operated at 99% of the maximum possible power production. By this, a minimum power reserve may constantly be provided.

The control system may be adapted to determine an active and/or a reactive power loss correction factor accounting for losses of (active or reactive) power between the wind power plant, the solar power plant and/or the storage power plant, respectively, and an electrical grid, in particular a point of common connection to the electrical grid where power of all plants of the hybrid power plant is supplied to the electrical grid. For example, losses may occur at a medium voltage (MV) feeder of the hybrid power plant. In this way, systematically too low reserves supplied to the electrical grid can be avoided.

According to an embodiment, the control system is adapted to determine an active power forecast correction factor and/or a reactive power forecast correction factor accounting for a forecasted maximum possible power production of the wind power plant and/or the solar power plant. The forecast correction factor may be determined by the control system using a forecast of an environmental variable, e.g. a variable indicative for a weather condition. By this, the control system may prepare the hybrid power plant for expected changes in the (active and/or reactive) power production.

The control system may be adapted to determine a total power reserve as a sum of individual power reserves of (the at least two of) the wind power plant, the solar power plant and the storage power plant. This allows a simple calculation of the individual reserves.

In accordance with an embodiment, the control system is further adapted to determine an individual power reserve from the total power reserve and a coefficient of the wind power plant, the solar power plant or the storage power plant. Optionally, the sum of the coefficients equals to 1, which may represent the exact amount of power reserve requested by the TSO and which the hybrid plant controller is subjected to.

Optionally, the control system is further adapted to determine one or all of the coefficients based on maximum possible power productions of the wind power plant and the solar power plant.

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 common connection point with the electrical grid.

Optionally, the storage power plant comprises at least one (e.g., one, two or all) of a battery, an engine-generator (e.g. a diesel generator) and a supercapacitor. 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 and one or more supercapacitors.

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 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 (e.g. a current and/or a predicted power) of the wind power plant, the solar power plant and/or the storage power plant.

Determine (a value of) an individual power reserve 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 values of) the individual power reserves (or the at least two thereof) to the wind power plant, the solar power plant and/or the storage power plant.

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.

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-131C power-storage system
132 battery
133 engine-generator
134 supercapacitor
135 curtailment algorithm
14 converter
15 transformer
16 plant transformer
17 junction (second junction)
17’ first junction
18 hybrid park feeder
19 substation
190 collector
191 transformer
195 unified voltage transformer
2 electrical grid
Kwind, Ksolar, Kadd coefficient
P active power
?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
Q reactive power
?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 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), comprising at least one junction (17, 17’) and / or at least one unified voltage transformer (195) each or both adapted for receiving the generated power from the wind power plant (11), the solar power plant (12) and the storage power plant (13) connected to the junction (17, 17’) and / or unified voltage transformer (195).

2. A hybrid power plant (1, 1’) according to claim 1, wherein the at least one junction (17, 17’) is part of a middle voltage network of the power plant (1, 1’), in particular in a 33 kV network of the power plant (1, 1’).

3. A hybrid power plant (1, 1’) according to claim 1 or 2, wherein the at least one unified voltage transformer (195) transforms low-voltage to medium-voltage, in particular 33 kV.

4. A hybrid power plant (1, 1’) according to at least one of the preceding claims, wherein the output of the at least one junction (17) and / or unified voltage transformer (195) is transmitted to a transformer (191) to high voltage and subsequently the electrical grid (2).

5. The hybrid power plant (1, 1’) according to at least one of the preceding claims, wherein the generated power from each of the wind power plant (11), the solar power plant (12) and / or the storage power plant (13) is received by one junction (17) and / or by one unified transformer (195).

6. The hybrid power plant (1, 1’) according to at least one of claims 1 to 4, wherein the generated power from two of the wind power plant (11), the solar power plant (12) and the storage power plant (13) is transmitted to a first junction (17’), the output of the first junction (17’) is then transmitted to a further junction (17) which has the output of at least one of the wind power plant (11), the solar power plant (12) and the storage power plant (13) as an additional input.

7. The hybrid power plant (1, 1’) according to at least one of the preceding claims, further comprising a control system (10) 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), wherein the control system (10) is adapted to:

- determine a value for an individual power reserve (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qsto) 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 values for the individual power reserves (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qsto) to the at least two of the wind power plant (11), the solar power plant (12) and the storage power plant (13).

8. The hybrid power plant (1, 1’) according to claim 7, wherein the individual power reserves (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) comprise individual active power reserves (?Pwind, ?Psolar, ?Padd) and/or individual reactive power reserves (?Qwind, ?Qsolar, ?Qadd).

9. The hybrid power plant (1, 1’) according to claim 7 or 8, 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).

10. The hybrid power plant (1, 1’) according to any of the preceding claims, the control system (10) further adapted to determine each of the values for the individual power reserves (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) as a percentage value indicating a percentage of a maximum possible power production of the wind power plant (11), the solar power plant (12) or the storage power plant (13).

11. The hybrid power plant (1, 1’) according to any of the preceding claims, the control system (10) further adapted to receive a value for a hybrid power plant power reserve (?PHP, ?QHP) to be provided by the hybrid power plant (1; 1’), and to determine the values for the individual power reserves (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) in dependence of the hybrid power plant power reserve (?PHP, ?QHP).

12. The hybrid power plant (1, 1’) according to claim 11, further adapted to set the hybrid power plant power reserve (?PHP, ?QHP) to a value of at least 1%.

13. The hybrid power plant (1, 1’) according to any of the preceding claims, the control system (10) further adapted to determine a value for a power loss correction factor (?Pcorr_loss, ?Qcorr_loss) accounting for losses of power between the wind power plant (11), the solar power plant (12) and/or the storage power plant (13) and a point of common connection to an electrical grid (2).

14. The hybrid power plant (1, 1’) according to any of the preceding claims, the control system (10) further adapted to determine a value for a power forecast correction factor (?Pcorr_forecast, ?Qcorr_forecast) accounting for a forecasted maximum possible power production of the wind power plant (11) and/or the solar power plant (12).

15. The hybrid power plant (1, 1’) according to any of the preceding claims, the control system further adapted to determine a value of a total power reserve (?Ptot, ?Qtot) as a sum of the values of the individual power reserves (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) of the at least two of the wind power plant (11), the solar power plant (12) and the storage power plant (13).

16. The hybrid power plant (1, 1’) according to claim 15, the control system (10) further adapted to determine a value of an individual power reserve (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) from the value of the total power reserve (?Ptot, ?Qtot) and a coefficient (Kwind, Ksolar, Kadd) of the wind power plant (11), the solar power plant (12) or the storage power plant (13), wherein the sum of the coefficients (Kwind, Ksolar, Kadd) equals to 1.

17. The hybrid power plant (1, 1’) according to claim 16, the control system further adapted to determine the coefficients (Kwind, Ksolar, Kadd) based on maximum possible power productions of the wind power plant (11) and the solar power plant (12).

18. The hybrid power plant (1; 1’) according any of the preceding claims, wherein the storage power plant (13) comprises at least one of a battery (132) and an engine-generator (133), a supercapacitor (134).

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

20. The hybrid power plant (1’) according to any of the preceding claims, 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’) according to any of the preceding claims, the method comprising the following steps:

- determine a value for an individual power reserve (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) 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 values for the individual power reserves (?Pwind, ?Psolar, ?Padd, ?Qwind, ?Qsolar, ?Qadd) 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.