Claims:We Claim:

1. Method for controlling a hybrid power plant (1), comprising at least two different power plants (2, 3, 4) including at least one renewable energy power plant and (2, 3) and a hybrid power plant controller (15), comprise the following steps:
- providing a ramp rate control for active power output,
- calculating ramp rate control set point (Psetpoint), characterized in that
-- collecting and/or calculating sampling data,
-- reading in actual power (Pactual) and power forecast (Pforecast),
-- determining forward filter (PFWmin),
-- selecting minimum power set point forward filter (PFWmin),
-- determining backward filter (PBWmin),
-- selecting minimum power set point backward filter (PBWmin),
-- determining ramp rate control set point (Psetpoint) by selecting minimum power set point from minimum power set point backward filter (PBWmin) or minimum power set point forward filter (PFWmin) and
- using ramp rate control set point (Psetpoint) as active power value for con-trolling hybrid power plant (1).

2. The method for controlling a hybrid power plant (1) according to claim 1, wherein repeating the steps of calculating ramp-rate control set point (Pset-point) periodically.

3. The method for controlling a hybrid power plant (1) according to claim 1 or 2, wherein processing of data by checking if all data is available.

4. The method for controlling a hybrid power plant (1) according to one of the claims 1 to 3, wherein read in the actual power (Pactual) from the at least two different power plants, in particular the wind power plant (2) and the solar power plant (3).

5. The method for controlling a hybrid power plant (1) according to one of the claims 1 to 4, wherein determining forward filter by calculating power set point forward step (PFWstep) and read in power set point forward forecast (PFWforecast).

6. The method for controlling a hybrid power plant (1) according to one of the claims 1 to 5, wherein determining the backward filter by calculating power set point backward step (PBWstep) and read in power set point backward fore-cast (PBWforecst).

7. The method for controlling a hybrid power plant (1) according to claim 5, wherein selecting minimum power set point forward filter (PFWmin) by se-lecting the minimum power set point of power set point forward step (PFW-step) or power set point forward forecast (PFWforecast).

8. The method for controlling a hybrid power plant (1) according to claim 6, wherein selecting minimum power set point backward filter (PBWmin) by se-lecting the minimum power set point of power set point backward step (PBW-step) or power set point backward forecast (PBWforecst).

9. The method for controlling a hybrid power plant () according to one of the claims 7 or 8, wherein determining ramp rate control set point (Psetpoint) by selecting minimum of minimum power set point from backward filter (PBWmin) or minimum power set point forward filter (PFWmin).

10. A hybrid power comprising at least two types of power plants (1) including at least one renewable energy power plant and (4) and a hybrid power plant controller (15), characterized in that the hybrid power plant controller (15) is configured to execute the method according to one of the claims 1 to 9.

11. The hybrid park power plant (1) according to claim 10, wherein the hybrid power plant controller (15) comprises an automatic ramp rate control element (27) for calculating ramp-rate control set point (Psetpoint).

12. The hybrid park power plant (1) according to claim 10 or 11, wherein the hybrid power plant (1) comprises at least one solar power plant (3) and at least one wind power plant (2) or comprises at least one solar power plant (3) and at least one energy storage plant (4) or comprises at least one wind pow-er plant (2) and at least one solar power plant (3) and at least one energy storage plant (4).

13. The hybrid park power plant according to claims 10 or 11, wherein the hy-brid power plant controller (15) comprises an active power set point element (29) for providing active power set points to a set point distribution element (30) for distributing active power set points of wind power plant (2) and/or active power set points of solar power plant (3), and/or an energy storage control element (31) for distributing active power set points of energy stor-age system (2).

Dated this 15th day of April 2022

For Suzlon Energy Limited

Nandan Pendsey
(IN/PA726)
AZB & Partners
Agents for the applicant
To,
The Controller of Patents
The Patent Office
Mumbai
, Description:TITLE OF INVENTION

Ramp Rate Control for Renewable Energy Using Forecast

FIELD OF INVENTION

The present invention is directed to a method for controlling a hybrid power plant, comprising at least two different power plants including at least one renewable energy power plant and a hybrid power plant controller for ramp rate control using forecast.

BACKGROUND

Several ramp rate control methods are known from the prior art. EP 3 087 436 A1 is directed to an intermittent energy management system and method. The method for controlling an operating condition of an electric power grid, the electric power grid having an intermittent power supply coupled thereto, the method comprising: using an energy variability controller, controlling variability of a delivered power output of the intermittent power supply to the electric power grid by: monitoring an actual environmental value for a location proximate the intermittent power sup-ply, an available power output of the intermittent power supply being dependent on the actual environmental value; when the actual environmental value is increas-ing and hence the available power output is increasing, increasing the delivered power output according to a predetermined rate of increase; monitoring a forecast environmental value for the location; when the forecast environmental value is decreasing, decreasing the delivered power output according to a predetermined rate of decrease; and, limiting the delivered power output to below a predeter-mined threshold. US 2015/0019034 A1 is directed to a device for smoothing fluc-tuations in renewable energy power production. The device collects data on re-newable power production, meteorological and other information, forecasts short timescale renewable power production then mitigates costs incurred by power fluctuations by modulating the power output, while maximizing power production revenue. Mitigation may be effected by an AC/DC inverter, an energy storage system, demand response or a FACTS device. The magnitude and costs for modu-lating response required from energy storage, FACTS or other power modulation equipment is thereby reduced. US 2013/0162043 A1 is directed to a multiple re-newables site electrical generation and reactive power control. The method of con-figuring a renewable energy curtailment and control system uses a master control-ler and a plurality of controllers configured to control a cluster of renewable ener-gy resources to deliver predetermined amounts of actual power and reactive power to a point of interconnect with a grid in accordance with contractual requirements with users of electrical power while reducing reactive power flow between renew-able resources in the cluster.

A disadvantage of the cited prior art is a loss of annual energy production during the fulfillment of the strict grid code requirements.

OBJECT OF THE INVENTION

An object of the present invention is to maintain a ramp response according to grid code requirements with a minimum loss of annual energy production.

SUMMARY OF THE INVENTION

This object shall be solved by a method for controlling a hybrid power plant ac-cording to a first aspect of the present invention. The hybrid power plant compris-es at least two different power plants including at least one renewable energy power plant and a hybrid power plant controller, wherein the renewable power plant could be a wind power plant or a solar power plant or a combination thereof. In particular, the hybrid power plant maybe comprises at least one wind power plant and at least one solar power plant or at least one wind power plant and at least one energy storage plant or at least one solar power plant and at least one energy storage plant or at least one wind power plant and at least one solar power plant and at least one energy storage plant. The method comprises the following steps:
- providing a ramp rate control for active power output,
- calculating ramp rate control set point Psetpoint, wherein
-- collecting and/or calculating sampling data,
-- reading in actual power Pactual and power forecast Pforecast,
-- determining forward filter (PFWmin),
-- selecting minimum power set point forward filter PFWmin,
-- determining backward filter (PBWmin),
-- selecting minimum power set point backward filter PBWmin,
-- determining ramp rate control set point Psetpoint by selecting minimum power set point from backward filter PBWmin or minimum power set point forward filter PFWmin and
- using ramp rate control set point Psetpoint as active power value for control-ling hybrid power plant.

Advantageously, the steps for calculating the ramp rate control takes place in time steps, in particular for time steps for a minute and will be repeated for example for a time range at least of 10 minutes in advance. More advantageously, the calcula-tion of ramp-rate control set point Psetpoint will be executed by the hybrid power plant controller. And with the ramp-rate control set points Psetpoint the active power output of the hybrid power plant will be given and maintain the ramp rate to be followed under all operating conditions. This method provides an active and au-tomatic control of power demand with the integration of the forecast, while moni-toring the ramp rate. This guarantees fulfillment of grid code requirements with a minimum loss of annual energy production at the same time.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step of repeating the steps of calculating ramp-rate control set point Pset- point periodically. In particular, the read in step for the power forecast Pforcast values takes place every minute for a time range of 10 minutes in advance or longer.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises processing of data by checking if all data is available.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step of read in the actual power Pactual from the at least two different power plants, in particular the wind power plant and the solar power plant.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step of determining forward filter by calculating power set point for-ward step PFWstep and determining power set point forward forecast PFWforecast.

Advantageously, the calculation of the power forward step PFWstep will be done stepwise for example for a time range of at least 10 minutes, wherein the time steps are for one minute, so e.g. in ten steps (i) 1 to 10. The power forward step PFWstep will be calculated according to equation EQ1

EQ1: PFWstep(i+1) = PFWstep(i) ± x% PN, wherein “i+1” indicates the step for the value of set point to be calculated and wherein “i” indicates the step for the cur-rent set point value or actual power value if i=0 and PN indicates rated power. Ac-cording to this, for example the value of power forward step PFWstep at step i+1=3 is equal to the value of power forward step PFWstep at step i=2 plus minus x percent of the rated power PN. The value x indicates the variance of the injected power from the rated power PN which depends on a respective grid code requirement. This can vary from country to country. For example, according to grid code CEA2019 10% is allowed. This means that the injected power shall differ maxi-mal 10% from rated power. The selection of plus minus depends on increasing or decreasing power.

For example, in case of increasing max power and allowed variation of 10% of the rated power PN, then, the power set point forward step PFWstep will be calculated according to equation EQ1a:

EQ1a: PFWstep(i+1) = PFWstep(i) + 10% PN

For example, in case of decreasing max power and allowed variation of 10% of the rated power PN, then, the power set point forward step PFWstep will be calculat-ed according to equation EQ1b:

EQ1b: PFWstep(i+1) = PFWstep(i) - 10% PN
Advantageously, the power set point forward forecast PFWforecast will be determined according to equation EQ2

EQ2: PFWforecast(i+1) = Pforecast(i+1)

wherein “i+1” indicates step for the value of set point to be calculated. According to this, for example the value of power set point forward forecast PFWforecast at step i+1 = 3 is equal to the value of the power forecast Pforecast at step i+1 = 3 provided by a power estimator.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step of determining the backward filter comprising calculating power set point backward step PBWstep and determining power set point backward forecast PBWforecst.

Advantageously, the power set point backward step PBWstep will be calculated ac-cording to equation EQ3:

EQ3: PBWstep(i-1) = PBWstep(i) ± x% PN
wherein “i-1” indicates the step for the value of set point to be calculated and wherein “i” indicates step for the current set point value and PN indicates rated power. According to this, for example the value of power set point backward step PBWstep at step i-1 = 3 is equal to the value of power set point backward step PBWstep at step i = 4 plus minus x percent of the rated power PN. The value x indicates the variance of the injected power from the rated power PN which depends on a re-spective grid code requirement. This can vary from country to country. For exam-ple, according to grid code CEA2019 10% are allowed. This means that the in-jected power shall differ maximal 10% from rated power. The selection of plus minus depends on decreasing or increasing power.

For example, in case of increasing max power and allowed variation of 10% of the rated power PN, then, the power set point backward step PBWstep will be calculated according to equation EQ3a:

EQ3a: PBWstep(i-1) = PBWstep(i) - 10% PN

For example, in case of decreasing max power and the grid code allowed a varia-tion of 10% of the rated power PN, then the power set point backward step PBWstep will be calculated according to equation EQ3b:

EQ3b: PBWstep(i-1) = PBWstep(i) + 10% PN

Advantageously, the power set point backward forecast PBWforecast will be deter-mined according to equation EQ4

EQ4: PBWforecast(i-1) = Pforecast(i-1)

wherein “i-1” indicates the step of the value of set point to be calculated. Accord-ing to this, for example the value of power set point backward forecast PBWforecast at step i-1 = 3 is equal to the value of power forecast Pforecast at step i-1 = 3 provided by a power estimator.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step of selecting minimum power set point forward filter PFWmin by se-lecting the minimum power set point of power set point forward step PFWstep or power set point forward forecast PFWforecast.

Advantageously, the minimum power set point forward filter PFWmin will be select-ed according to equation EQ5

EQ5: PFWmin(i+1) = min [PFWstep(i+1), PFWforecast(i+1)]

wherein “i+1” indicates the step for value of set point to be calculated. According to this, for example the value of minimum power set point forward filter PFWmin at step i+1 = 3 is equal to the minimum value of power set point forward step PFWstep at step i+1 = 3 or power set point forward forecast PFWforecast at step i+1 = 3.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step of selecting minimum power set point backward filter PBWmin by selecting the minimum power set point of power set point backward step PBWstep or power set point backward forecast PBWforecst.

Advantageously, the minimum power set point backward filter PBWmin will be se-lected according to equation EQ6

EQ6: PBWmin(i-1) = min[PBWstep(i-1), PBWforecast(i-1)]

wherein “i-1” indicates the step for the value of the set point to be calculated. Ac-cording to this, for example the value of minimum power set point backward filter PBWmin at step i-1 = 3 is equal to the minimum value of power set point backward step PBWstep at step i-1 = 3 or power set point backward forecast PBWforecast at step i-1 = 3.

In a preferred embodiment, the method for controlling a hybrid power plant com-prises the step calculating ramp rate control set point Psetpoint by selecting minimum of minimum power set point from backward filter PBWmin or minimum power set point forward filter PFWmin.

Advantageously, the ramp rate control set point Pset point will be selected according to equation EQ7

EQ7: Psetpoint(i) = min[PFWmin(i+1), PBWmin(i-1)]

wherein “i” indicates the step for the value of set point to be calculated. Accord-ing to this, for example the value of ramp rate control set point Psetpoint at step i = 3 is equal to the minimum value of minimum power set point from backward filter PBWmin at step i-1 = 3 or minimum power set point forward filter PFWmin at step i+1 = 3.

A further aspect of the present invention is directed to a hybrid power plant.

The hybrid power plant comprises at least two different power plants including at least one renewable energy power plant, in particular at least one wind power plant, at least one solar power plant and a hybrid power plant controller, wherein the hybrid power plant controller is configured to execute said method for control-ling a hybrid power plant.

Advantageously, the hybrid power plant controller executes the calculation of ramp-rate control set point Psetpoint for controlling the hybrid power plant. More advantageously, the ramp rate control set point Psetpoint will be calculated at an au-tomatic ramp control of the hybrid power plant controller. The ramp rate control set point Psetpoint will be forwarded to an active power set point element which is connected to a set point distribution element and an energy storage control ele-ment for distributing the ramp rate control set point Psetpoint to these elements. The set point distribution element provides the ramp rate control set point Psetpoint to an active power set point element for the at least one wind power plant and to an active power set point element for the at least one solar power plant. The energy storage control element provides ramp rate control set point Pset point to the active power set point for the energy storage system.

In a preferred embodiment, the hybrid park power plant controller has an automat-ic ramp rate control element for calculating ramp-rate control set point Psetpoint.

In a preferred embodiment, the hybrid power plant maybe comprises at least one wind power plant and at least one solar power plant or at least one wind power plant and at least one energy storage plant or at least one solar power plant and at least one energy storage plant or at least one wind power plant and at least one solar power plant and at least one energy storage plant.

In a preferred embodiment, the hybrid park power plant controller has an active power set point element for providing active power set points to a set point distri-bution element for distributing active power set points of wind power plant and active power set points of solar power plant, and an energy storage control ele-ment for distributing active power set points of energy storage system.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be explained in more detail with respect to exemplary em-bodiments with reference to the enclosed drawings, wherein:

Figure 1 shows hybrid power plant;

Figure 2 shows hybrid power plant controller of the hybrid power plant ac-cording to Fig. 1;

Figure 3 shows a method of controlling the hybrid power plant and

Figure 4 shows a diagram of power ramp rate.

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

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 depicts a schematic view of a hybrid power plant 1. In this embodiment the hybrid power plant comprises a wind power plant 2, a solar power plant 3 and an energy storage plant 4 as well as a sub-station 5. Latter is connected to the utili-ty grid 8 via a power transmission line 6 (hereinafter HPP-power transmission line) over a transformer 7 (hereinafter: HPP-transformer) for controlling the power out-put of the hybrid power plant 1. Further the wind power plant 2 is connected to the sub-station 5 via a power transmission line 9 (WPP-power transmission line) over transformer 10 (hereinafter: WPP-transformer) for supplying the output pow-er of the wind power plant 2. The solar power plant 3 is connected to the sub-station 5 via a power transmission line 11 (hereinafter: SPP-power transmission line) via a transformer 12 (hereinafter: SPP-transformer) for supplying the power output of the solar power plant 3. The energy storage plant 4 is connected to the sub-station 5 via a power transmission line 13 (hereinafter: ESP-power transmis-sion line) over a transformer 14 (hereinafter: ESP-transformer) for supplying the power output of the energy storage plant 4 as well as the power input to the ener-gy storage plant 4. The sub-station 5 comprises a junction (not shown) for receiv-ing the generated power from the wind power plant 2, the solar power plant 3 and the energy storage power plant 4 and for supplying the total generated power to the electrical grid 8. Therefore, the junction connects the WPP-power transmission line 9, the SPP-power transmission line 11 and ESP-power transmission line 13 to the HPP-power transmission line 6.

Furthermore, the hybrid power plant 1 includes a hybrid power plant controller 15. In this embodiment the hybrid power plant controller 15 is arranged within the sub-station 5. However, it is possible to arrange the hybrid power plant controller 15 at another place within the hybrid power plant 1. The wind power plant 2 con-tains at least one wind turbine (not shown). Maybe the wind power plant 2 further contains a power estimator (not shown). Latter could be for example a wind esti-mator. Further the wind power plant 2 contains a wind power plant controller 16. This controller 16 is connected to the hybrid power plant controller 15 via a data transmission line 17 (hereinafter: WPP-data transmission line). Over the WPP-data transmission line 17 the actual measured WPP power output can be transmitted to the hybrid power plant controller 15 and power set points especially ramp rate control set points Pset point can be received from the hybrid power plant controller 15. The solar power plant 3 contains at least one photovoltaic module (not shown) and a solar power estimator 18 for forecasting the power output as power forecast Pforcast of the solar power plant 3. The solar power estimator 18 is for example a weather estimator for monitoring the sky and weather conditions known from the prior art. Especially, the power estimator is at least one sky imager like a camera, which monitors changes in sky and weather conditions for delivering crucial ob-servations data from the sky for example ratio of clouds. The solar power plant 3 further contains solar power plant controller 19. This controller 19 is connected to the hybrid power plant controller 15 via a data transmission line 20 (hereinafter: SPP-data transmission line). Over the SPP-data transmission line 20 the actual measured SPP power output can be transmitted to the hybrid power plant control-ler 15 and power set points especially ramp rate control set points Psetpoint can be received from the hybrid power plant controller 15. The energy storage plant 4 contains at least one of the groups of mechanical, electrical, electromagnetic, bio-logical, electrochemical, thermal and/or chemical energy storage. Additional, the energy storage plant 4 contains an energy storage plant controller 21. Latter is connected to the hybrid power plant controller 15 via a data transmission line 22 (hereinafter: ESP-data transmission line). Over the ESP-data transmission line 22 the actual measured ESP power output can be transmitted to the hybrid power plant controller 15 and power set points especially ramp rate control set points Psetpoints can be received from the hybrid power plant controller 15. The hybrid power plant controller 15 is also connected with the transmission system operator TSO of the utility grid 8 for providing or receiving relevant data like power set points via a data transmission line 23 (hereinafter HPP-data transmission line). The solar power estimator 18 is connected to the hybrid power plant controller 15 via a data transmission line 24 (hereinafter PE-data transmission line) to provide fore-casted power output of the solar power plant 3 to the hybrid power plant control-ler 15. Data between the controllers 16, 19, 21, 15 and the transmission system operator TSO of the utility grid 8 can be transmitted wired or wirelessly. Same applies for the solar power estimator 18.

Figure 2 depicts a detailed view of the hybrid power plant controller 15. That comprises a curtail element 25 for identifying if the hybrid power plant 1 is cur-tailed. The curtail element 25 is connected to a ramp control element 26 for receiv-ing external power set points. These external set points maybe are ramp rate con-trol set points for increasing or decreasing ramp rate. In particular, the ramp con-trol element 26 is connected with transmission system operator TSO of the utility grid 8 via the HPP-data transmission line 23. Further the curtail element 25 is con-nected to an automatic ramp control element 27 for calculating power set points, in particular ramp rate control set points Psetpoint of the hybrid power plant 1. These ramp rate control set points Psetpoint are parameters for an increasing or decreasing ramp rate. As input data, the automatic ramp control element 27 receives parame-ters from the forecast of the solar power plant 3 and/or wind power plant 2 (if applicable) as well as actual power Pactual available from the hybrid power plant 1. The ramp control element 26 and the automatic ramp control element 27 are con-nected to a switch element 28, which is connected to an active power set point element 29. Depending on the status of the hybrid power plant 1, namely if the hybrid power plant 1 is curtailed or not the active power set point element 29 re-ceived power set points from the ramp rate control element 26 or from the auto-matic ramp control element 27. The status of the hybrid power plant 1 is identified by the curtail element 25. If the hybrid power plant 1 is curtailed then the active power set point element 29 receives power set points from the ramp control ele-ment 26. If the hybrid power plant is not curtailed then the active power set point element 29 receives power set points from the automatic ramp control element 27. The active power set point element 29 is connected to a set point distribution ele-ment 30 for distributing active power set points to the wind power plant 2 and the solar power plant 3. Therefore, the set point distribution element 30 prioritizes power set points for the wind power plant 2 and the solar power plant 3. After this, the set point distribution element 30 sends the respective active power set points to the wind power plant controller 16 of the wind power plant 2 via the WPP-data transmission line 17 and the solar power plant controller 19 of the solar power plant 3 via the SPP-data transmission line 20. Further the active power set point element 29 is connected to an energy storage control element 31 for distrib-uting active power set points to the energy storage plant 4. Therefore, the energy storage control element 31 sends the respective active power set points to the en-ergy storage plant controller 21 of the energy storage plant 4 via the ESP-data transmission line 22. The hybrid power plant controller 15 further contains a power metering element 32 for providing actual power Pactual of the hybrid power plant 1. For distributing the actual power Pactual to the respective elements the power meter-ing element 32 is connected to the ramp control element 26, the automatic ramp control element 27, the set point distribution element 30 and the energy storage control element 31. As input data the power metering element 32 receives the ac-tual power Pactual from respective controllers of the wind power plant 2 and solar power plant 3 as well as the actual power from the utility grid 8.

Figure 3 depicts a flow diagram of the method for controlling a hybrid power plant 1 according to an embodiment of the present invention and which complies with the grid code CEA2019. Advantageously, this method will be executed at the automatic ramp control element 27 of the hybrid power plant controller 15.

The method starts with step S1, which contains providing a ramp rate control for active power output, therefore calculating ramp rate control set points Psetpoint ac-cording to the following steps. These steps for calculating the ramp rate control takes place in time steps periodically, in particular for time steps for a minute and will be repeated for example for a time range of 10 minutes in advance or more.

Step S2 contains collecting and/or calculating sampling data for one minute. Therefore, in step S3 contains reading in the actual power Pactual of the wind power plant 2 and the solar power plant 3. These data will be provided by the respective controllers 16, 19 of the wind power plant 2 and the solar power plant 3. Further-more, step 3 contains reading in the power forecast values Pforecast of the solar pow-er plant 3 and the wind power plant 2 (if applicable). In the descried embodiment only the solar power plant 3 has the solar power estimator 18, which provides power forecast values Pforecast(i) in time steps of i=1 to i=10 minute, so for 10 minutes in advance or longer.

Step S4 contains preparing of data to check if all data is available.

Step S5 contains determining forward filter, which comprises selecting minimum power set point forward filter PFWmin. The minimum power set point forward filter PFWmin will be selected according to equation EQ5

EQ5: PFWmin(i+1) = min [PFWstep(i+1), PFWforecast(i+1)]

wherein the minimum power set point of power set point forward step PFWstep(i+1) and power set point forward forecast PFWforecast(i+1) will be selected maybe for every minute i=1 to i=10.

The selection will be made first calculating power set point forward step PFWstep(i) and read in power set point forward forecast PFWforecast(i) for maybe every minute i=1 to i=10. In other words, the calculation of the power set point forward step PFWstep will be done stepwise maybe for every minute, for 10 minutes in advance or longer. Depending on increasing or decreasing maximal power the power set point forward step PFWstep will be calculated according to equation EQ1a or EQ1b. In case of an increasing maximal power EQ1a will be used and in case of decreasing maximal power EQ1b will be used, namely

EQ1a: PFWstep(i+1) = PFWstep(i) + 10% PN

EQ1b: PFWstep(i+1) = PFWstep(i) - 10% PN

wherein minute i = 0 indicates the actual power Pactual and PN indicates rated power of the utility grid 8. If the power set point forward step PFWstep at minute 3 should be calculated at increasing maximal power, then the value of power set point for-ward step PFWstep at minute i+1 = 3 is equal to the value of power set point forward step PFWstep at minute i = 2 plus 10 percent of the rated power PN. Or if the power set point forward step PFWstep at minute 3 should be calculated at decreasing max-imal power, then the value of power set point forward step PFWstep at minute i+1 = 3 is equal to the value of power set point forward step PFWstep at minute i = 2 minus 10 percent of the rated power PN.

Furthermore, the selection will be made first read in the power set point forward forecast PFWforecast. This will be determined according to equation EQ2

EQ2: PFWforecast(i+1) = Pforecast(i+1)

wherein “i” indicates the value of minute i=1 to minute i=10. According to this, the value of power set point forward forecast PFWforecast at minute i+1 = 3 is equal to the value of the power forecast Pforecast at minute i+1 = 3 provided by a solar power estimator 18 of the solar power plant 3.

Back to equation EQ5, for selecting the minimum power set point forward filter PFWmin at minute i+1 = 3, the minimum value of power set point forward step PFW-step at minute i+1 = 3 and power set point forward forecast PFWforecast at minute i+1 = 3 will be selected. This will be done for every minute i=1 to i=10.

Step S6 contains determining backward filter, which comprises selecting minimum power set point backward filter PBWmin. The minimum power set point forward filter PBWmin will be selected according to equation EQ6:

EQ6: PBWmin(i-1) = min[PBWstep(i-1), PBWforecast(i-1)]

wherein the minimum power set point of power set point backward step PBWstep(i-1) and power set point backward forecast PBWforecast(i-1) will be selected maybe for every minute i=10 to i=1.

The selection will be made first calculating power set point backward step PBW-step(i) and read in power set point backward forecast PBWforecast(i) for maybe every minute i=10 to i=1. In other words, the calculation of the power set point back-ward step PBWstep will be done stepwise for every minute, for 10 minutes in ad-vance or longer. Depending on increasing or decreasing maximal power the power set point backward step PBWstep will be calculated according to equation EQ3a or EQ3b. In case of an increasing maximal power EQ3a will be used and in case of a decreasing maximal power EQ3b will be used, namely

EQ3a: PBWstep(i-1) = PBWstep(i) - 10% PN

EQ3a: PBWstep(i-1) = PBWstep(i) + 10% PN

wherein minute i=0 indicates the actual power Pactual and PN indicates rated power of the utility grid 8. If the power set point backward step PBWstep at minute 3 should be calculated at increasing maximal power, then the value of power set point backward step PBWstep at minute i-1 = 3 is equal to the value of power set point backward step PBWstep at minute i = 4 minus 10 percent of the rated power PN. If the power set point backward step PBWstep at minute 3 should be calculated at decreasing maximal power, then the value of power set point backward step PBWstep at minute i-1 = 3 is equal to the value of power set point backward step PBWstep at minute i = 4 plus 10 percent of the rated power PN.

Furthermore, the selection will be made first read in the power set point backward forecast PBWforecast. This will be determined according to equation EQ4

EQ4: PBWforecast(i-1) = Pforecast(i-1)

wherein “i” indicates the value of minute i=10 to minute i=1. According to this, the value of power set point backward forecast PBWforecast at minute i-1 = 3 is equal to the value of the power forecast Pforecast at minute i-1 = 3 provided by a solar power estimator 18 of the solar power plant 3.

Back to equation EQ6, for selecting the minimum power set point backward filter PBWmin at minute i-1 = 3, the minimum value of power set point backward step PBWstep at minute i-1 = 3 and power set point backward forecast PBWforecast at minute i-1 = 3 will be selected. This will be done for maybe every minute i=10 to i=1.

Step S7 contains determining ramp rate control set point Psetpoint by selecting mini-mum power set point from minimum power set point backward filter PBWmin or minimum power set point forward filter PFWmin. The ramp rate control set point Psetpoint will be selected according to equation EQ7

EQ7: Psetpoint(i) = min[PFWmin(i+1), PBWmin(i-1)]

wherein ramp rate control set point Psetpoint will be selected maybe for every minute i=1 to minute i=10, so for 10 minutes in advance or longer. According to this, for example the value of ramp rate control set point Psetpoint at minute i = 3 is equal to the minimum value of minimum power set point from backward filter PBWmin at minute i-1 = 3 or minimum power set point forward filter PFWmin at minute i+1 = 3.

Step S8 contains using ramp rate control set point Psetpoint as active power value for controlling hybrid power plant 1. The active power set point element 29 receives ramp rate control set points Psetpoint from the automatic ramp control element 27. The active power set point element 29 sends the ramp rate control set point Psetpoint to the set point distribution element 30, which distributing ramp rate control set point Psetpoint to the wind power plant 2 and the solar power plant 3. Therefore, the set point distribution element 30 prioritizes ramp rate control set points Psetpoint for the wind power plant 2 and the solar power plant 3. After this, the set point distri-bution element 30 sends the respective ramp rate control set points Psetpoint to the wind power plant controller 16 of the wind power plant 2 via the WPP-data transmission line 17 and the solar power plant controller 19 of the solar power plant 3 via the SPP-data transmission line 20. Further the active power set point element 29 sends ramp rate control set point Psetpoint to the energy storage control element 31, which distributes ramp rate control set point Psetpoint to the energy stor-age plant 4. Therefore, the energy storage control element 31 sends the respective ramp rate control set point Psetpoint to the energy storage plant controller 21 of the energy storage plant 4 via the ESP-data transmission line 22.

The above described method guarantees a smooth control of the injected active power of the hybrid power plant 1 to the utility grid 8 during a change of maximal available power which complies with the grid code requirements of CEA2019. As a result of this, is a ramp rate control 33 according to Figure 4.

Fig. 4 shows a solid line 34, which indicates actual injected power of the hybrid power plant 1. This actual injected power 34 corresponds to the actual power Pactual of the hybrid power plant 1. A dashed line 35 indicated a desired ramp rate for the active power to be injected to the utility grid 8. If the power estimator of the solar power plant 3 or the wind power plant 2, especially the solar power estimator 18 of the solar power plant, indicates a drop in available power of the hybrid pow-er plant 1 then the above-mentioned method for calculating the ramp rate control set points Psetpoint starts. The ramp rate control set points Psetpoint determine the de-sired ramp rate 35.

For calculating ramp rate control set points Psetpoint the above described equation EQ7 will be used and will be repeated between times t1 and t3. Based on equa-tion EQ7 the minimum power set point forward filter PFWmin will initially deter-mine according to equation EQ5. The required power set point forward step PFW-step will be calculated according to equation EQ1b. Further the required power set point forward forecast PFWforecast will be determined according to equation EQ2. Then the minimum power set point backward filter PBWmin will initially determine according to equation EQ6. The required power set point backward step PBWstep will be calculated according to equation EQ3b. Further the required power set point backward forecast PBWforecast will be determined according to equation EQ4. Then according to EQ7 the minimum value of minimum power set point forward filter PFWmin and minimum power set point backward filter PBWmin will be selected.

At time t1 the desired ramp rate 35 begins to reduce the injected active power to the utility grid 8. Between the times t1 and t2 the actual injected power 34 is higher than the desired ramp rate 35. In other words, the ramp rate control set points Psetpoint are lower than the actual injected power 34 produced by the hybrid power plant 1. The surplus energy will be used for charging the energy storages of the energy storage plant 4. This is indicated by the left hatched area 36. At time t2 the maximal available power 35 is equal to the desired ramp rate 35, but the avail-able power drops further. However, the desired ramp rate 35 is higher than the actual injected power 34. So from time t2 to time t3 the missing active power will be injected by the energy storage plant 4 by discharging the energy storages. This is indicated by a right hatched area 37. Between the times t3 and t4 the hybrid power plant 1 injects the actual injected power 34 to the utility grid 8 until the power estimator of the solar power plant 3 or the wind power plant 2, especially the solar power estimator 18 of the solar power plant, indicates a rise in available power of the hybrid power plant 1. Then the above-mentioned method for calcu-lating the ramp rate control set point Psetpoint starts again and the ramp rate control set points Psetpoint will be calculated.

For calculating these ramp rate control set points Psetpoint the above described equa-tion EQ7 will be used and will be repeated between times t4 and t6. Based on equation EQ7 the minimum power set point forward filter PFWmin will initially de-termine according to equation EQ5. The required power set point forward step PFWstep will be calculated according to equation EQ1a. Further the required power set point forward forecast PFWforecast will be determined according to equation EQ2. Then the minimum power set point backward filter PBWmin will initially determine according to equation EQ6. The required power set point backward step PBWstep will be calculated according to equation EQ3a. Further the power set point back-ward forecast PBWforecast will be determined according to equation EQ4. According to EQ7 the minimum value of minimum power set point forward filter PFWmin and minimum power set point backward filter PBWmin will be selected.

At time t4 the desired ramp rate 35 is higher than the actual injected power 34. In other words, the ramp rate control set points Psetpoint are higher than the actual in-jected power 34 produced by the hybrid power plant 1. So between the times t4 and t5 the missing active power will be compensated by the energy storage plant 4 by discharging the energy storages. This is indicated by the right hatched area 37. At time t5 the desired ramp rate 35 is equal to the maximal available power, but the actual injected power 34 increases faster than the desired ramp rate 35. The surplus active power at times between t5 and t6 will be injected to the energy storage plant 4 for charging the energy storages. This is indicated by the left hatched area 36. After time t6 the actual injected power power 34 will be injected to the utility grid 8.

LIST OF REFERENCE SIGNS

1 hybrid power plant
2 wind power plant
3 solar power plant
4 energy storage plant
5 sub-station
6 power transmission line (HPP-power transmission line)
7 transformer (HPP-transformer)
8 utility grid
9 power transmission line (WPP-power transmission line)
10 transformer (WPP-transformer)
11 power transmission line (SPP-power transmission line)
12 transformer (SPP-transformer)
13 power transmission line (ESP-power transmission line)
14 transformer (ESP-transformer)
15 hybrid power plant controller
16 wind power plant controller
17 data transmission line (WPP data transmission line)
18 solar power estimator
19 solar power plant controller
20 data transmission line (SPP-data transmission line)
21 energy storage plant controller
22 data transmission line (ESP-data transmission line)
23 data transmission line (HPP-data transmission line)
24 data transmission line (PE-data transmission line)
25 curtail element
26 ramp control element
27 automatic ramp control element
28 switch element
29 active power set point element
30 set point distribution element
31 energy storage control element
32 power metering element
33 ramp rate control
34 actual injected power
35 desired ramp rate
36 left hatched area
37 right hatched area