Patent Application
20240235199
This patent application claims priority of European Patent Application No. 21425027.6 filed on May 24, 2021, the entire disclosure of which is incorporated herein by reference.
The present invention relates to a plant for the production of electrical energy and a method for operating said plant.
Known to the art are hybrid plants for the production of electrical energy, which are connected to an electrical distribution grid.
The hybrid solutions combine different sources of energy and storage within the same plant, keeping a single point of interconnection with the electrical grid.
Hybrid plants normally comprise at least one programmable energy source (like a gas turbine supplied with at least one fossil fuel) and a storage Often, hybrid plants comprise also renewable energy sources, like photovoltaic plants, wind farms, geothermal plants, and/or other types of energy sources, like gas engines, solar CSP solutions, etc.
Managing in real time these different kind of energy sources is not simple as the behaviour of each one of these energy sources can be completely different one from another.
Power plants comprising different programmable and non-programmable energy sources can cause severe management issues for the operators of the power plant.
Flexibility of the traditional programmable power sources is essential as the contribution of the renewable energy sources is volatile. Moreover, renewable energy sources are also often characterized by a high concentration of power production in some periods, not always predictable.
Hybrid plants have to guarantee a stable and reliable connection to the electrical distribution network in all operating conditions and taking into account all the peculiarities above described.
In particular, it is fundamental to properly react to transient situations in which a fast and significant variation of the energy produced by the plant is required to counterbalance the variation of the frequency of the electrical grid.
Therefore, in hybrid plants it is required to carry out grid adjustment interventions and responding to extremely variable load requests with a very dynamic response and, at the same time, to optimize the use of the storage system to provide multiple services, while minimizing its exploitation to preserve its limited capacity.
The object of the present invention is therefore to provide a hybrid plant for the production of electrical energy wherein the different energy sources are properly managed in order to obtain an improved flexibility and power capacity of the plant.
According to said object, the present invention relates to a hybrid plant for the production of electrical energy and configured to be connected to an electrical grid; the hybrid plant comprising:
Advantageously, the control device of the hybrid plant according to the present invention is configured to manage the at least one programmable energy source and the storage assembly in an optimized way to satisfy the grid requirements for the frequency stabilization and/or to correct load unbalances.
In particular, the management of the storage assembly according to the present invention is a key factor to strongly increase the plant flexibility.
According to the present invention, in fact, the total load demand is distributed among the sources such that their load variation is performed in optimal manner at the same time.
The use of the storage assembly is bidirectional such to provide both sudden power increase or decrease depending on the specific load variation request.
It is a further object of the present invention to provide a method for operating a hybrid plant for the production of electrical energy which is able to manage the different energy sources so as to obtain an improved flexibility and power capacity of the plant.
According to said object, the present invention relates to a method for operating a hybrid plant for the production of electrical energy as claimed in claim 13.
The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limitative embodiment, in which:
In
The hybrid plant 1 comprises at least one programmable energy source 4 and at least one energy storage assembly 5.
The programmable energy source 4 is configured to produce a predictable amount of electrical energy.
Preferably, the hybrid plant 1 comprises also at least one non-programmable energy source 7.
The amount of energy produced by the non-programmable energy source 7 is not predictable.
In the non-limiting example here disclosed and illustrated, the hybrid plant 1 comprises a plurality of programmable energy sources 4.
Each programmable energy source 4 is provided with a respective generator (not illustrated) able to produce respective load PL1, PL2, . . . PLn.
Each programmable energy source 4 is configured to produce electrical energy on the basis of a programmable load reference value PLRef1, PLRef2, . . . PLRefn.
Preferably, at least one of the plurality of programmable energy sources 4 is a gas turbine assembly.
In the non-limiting example here disclosed and illustrated the programmable energy sources 4 are two gas turbine assemblies.
Each gas turbine assembly comprises a compressor, a combustor, a turbine and a generator (not illustrated).
In particular, the compressor comprises an inlet, supplied with air, and a plurality of blades compressing the passing air. The compressed air leaving the compressor flows into a plenum, i.e. a closed volume, and from there into the combustor, where the compressed air is mixed with at least one fuel and combusted. The resulting hot gas leaves the combustor unit and is expanded in the turbine, producing mechanical work on a shaft connected to the generator.
According to a variant not shown, at least one of the programmable energy sources 4 can be an internal combustion engine or a coal fired or hydroelectric power generation unit.
The energy storage assembly 5 comprises at least one energy storage device (not illustrated) configured to selectively store or release energy. In the non-limiting example here disclosed and illustrated, the energy storage device is a battery.
According to a variant not shown, the energy storage assembly 5 can be an electro-chemical storage system or a CO2 storage system.
In the non-limiting example here disclosed and illustrated, the hybrid plant comprises a plurality of non-programmable energy sources 7, each of which is configured to produce a non-predictable load NPL1, NPL2, . . . . NPLn.
Preferably, at least one of the plurality of non-programmable energy sources 7 is a steam turbine assembly operating in natural sliding pressure.
In the non-limiting example here disclosed and illustrated the non-programmable energy sources 7 are two: a steam turbine assembly and a renewable energy source.
The steam turbine assembly comprises at least one heat boiler and at least one steam turbine (not illustrated).
The heat boiler is configured to exploit the heat from a hot gas stream for producing steam, which is used to drive the steam turbine producing mechanical work on a shaft connected to a generator.
In the non-limiting example here disclosed and illustrated, the heat boiler of steam turbine assembly is supplied with the hot gas flow coming from the gas turbines of the programmable energy sources 4. Therefore, the operation of the steam turbine assembly closely depends on the operating conditions of the gas turbine assembly because the exhaust gas provides the thermal energy needed for steam production.
Typically, the number of heat boilers equals the number of gas turbines of the plant. In the example here disclosed and illustrated, therefore, the steam turbine assembly comprises two heat boilers exploiting the exhaust gas coming from the two gas turbine assemblies 4.
The hybrid plant 1 comprises also a control device 8 configured to control the operating conditions of the hybrid plant 1 on the basis of the demand of the grid 2, a transformer 9 configured to transform the electrical energy produced by the hybrid plant 1 into electrical energy having the requirements of the grid 2 (e.g. having a higher voltage) and a plurality of auxiliary devices 10 (schematically illustrated as a unit).
Auxiliary devices 10 are devices such as pumps, valves, fans, etc., which are electrically fed and designed to assist the energy production of the programmable energy sources 4, the non-programmable energy sources 7, the energy storage assembly 5, etc.
As schematically represented in
As detailed better in the following, the transformer 9 can be supplied also with the energy released by the energy storage assembly 5, if the requirements of the grid 2 demands it.
The transformer 9 supplies to the grid 2 a current NET load CNL.
The current Net load CNL is obtained by the difference between the current gross load CGL supplied by the programmable energy sources 4, by the non-programmable energy sources 7 and by the energy storage assembly 5 and the load absorbed by the auxiliary devices 10.
In other words, the current net load CNL supplied to the grid 2 is the result of the following formulas:
Current gross load (CGL)=(programmable current loads)+(non-programmable current loads)+(energy storage load) (1)
Current Net load (CNL)=Current gross load (CGL)−(auxiliary consumption). (2)
With reference to
In detail, the control device 8 comprises a plant net load reference calculation module 11, configured to calculate a plant net load reference value NETLoadRef on the basis of the requirements of the grid 2, and a source managing module 12, which is configured to manage the different programmable energy sources 4 and the energy storage assembly 5, at least on the basis of the plant net load reference value NETLoadRef and on the basis of the current Net load CNL.
The net load reference calculation module 11 calculates a plant net load reference value NETLoadRef taking into account the load requirements of the grid 2.
The requirements of the grid 2 are calculated by a primary module 14 and/or a secondary module 15 and/or an energy market module 16.
The primary module 14 is configured to calculate a primary reference load PFC REF of the current net load on the basis of the frequency gf of the grid 2 with the purpose to stop the frequency deviation from the reference value (e.g. 50 Hz).
Preferably, the primary module 14 is configured to calculate a primary reference load PFC REF so as to perform the plant primary frequency control. In other words, the primary module 14 is configured to calculate a primary reference load PFC REF so as to obtain an automatic regulation performed by the plant sources.
The secondary module 15 is configured to calculate a secondary reference load SFC REF on the basis of the level signal received by a Transmission System Operator (TSO) 17 of the electrical grid 2. The Transmission System Operator (TSO) is an entity entrusted with transporting energy in the form of electrical power on a national or regional level, using fixed infrastructure.
The secondary module 15 is configured to perform the plant secondary frequency control which consists of centralized automatic control that allows to the control area (i.e. the national one) to increase or decrease its total power generation in order to satisfy the power exchanges with the near control areas on the programmed values, also contributing to the control of the grid frequency.
The energy market module 16 is configured to calculate an energy reference load profile SAPP Ref on the basis of the energy sold se by the plant 1 to the energy market 18.
The calculator module 11 is configured to calculate the plant net load reference value NETLoadRef on the basis of the data provided by the primary module 14 and/or by the secondary module 15 and/or by the energy market module 16.
In order to calculate the effective load variation needed by the plant 1, the plant net load reference value NETLoadRef shall be corrected by taking into account the current net load CNL supplied to the grid 2 by the plant 1.
In other words, the required load variation Δload is calculated as the difference between the plant net load reference value NETLoadRef and the current net load CNL.
As already detailed before the current net load CNL is defined by the formula (2).
The source management module 12 is configured to provide programmable load reference PLRef1, PLRef2, . . . PLRefn to the programmable energy sources 4 and, if needed, a reference integrating load RIL to the storage assembly 5.
With reference to the flow chart of
In this way, the source management module 12 performs a sort of control of the state of charge of the energy storage assembly 5 in order to guarantee that the energy storage assembly 5 be able to react properly in case of need.
In other words, it is important to keep the state of charge of the energy storage assembly 5 in an intermediate condition that allows at any time a proper release or storage of energy.
The step of controlling the energy storage assembly 5 so as to store or release energy until the storage current load SCL to zero is reached, is performed by providing a reference integrating load RIL to the energy storage assembly 5, which is equal to the requested state of charge. In other words the variation of the reference integrating load ΔRIL is calculated by modifying the storage current load SCL and has negative sign (−) in case of storing energy and positive sign (+) in case of releasing energy.
The step of controlling the energy storage assembly 5 is performed if the programmable sources assembly does not require the storage assembly contribution to satisfy the grid requirements (primary frequency control, secondary frequency control, energy market control).
The step of calculating programmable load reference PLRef1, PLRef2, . . . PLRefn to the programmable energy sources 4 and a reference integrating load RIL to the storage assembly 5 comprises:
The calculation of the programmable energy source reference loads PLRef1, PLRef2, . . . PLrefn and the calculation of the integrating load RIL is substantially made by calculating a variation of the programmable energy source reference loads ΔPLRef1, ΔPLRef2 . . . ΔPLrefn and of the integrating load ΔRIL on the basis of the calculated required load variation Δload and then adding the calculated variation of the programmable energy source reference loads ΔPLRef1, ΔPLRef2 . . . ΔPLrefn and of the integrating load ΔRIL to the temporally previous programmable energy source reference loads PLRef1 (t−1), PLRef2 (t−1), . . . PLrefn (t−1) and of the integrating load RIL(t−1) stored in a storing unit (not illustrated).
Once calculated the reference integrating load RIL, the control device 8 is further configured to control the programmable energy sources 4 so as to follow the programmable energy source reference load PLRef1, PLRef2, . . . PLrefn and to control the storage assembly 5 so as to selectively increase the calculated reference integrating load RIL of a ARIL value if the sum of the programmable energy source reference load variations ΔPLRef1, ΔPLRef2, . . . ΔPLrefn is lower than the required load variation Δload or to decrease the calculated reference integrating load RIL of a ARIL value if the sum of the programmable energy source reference load variations ΔPLRef1, ΔPLRef2, . . . ΔPLrefn is greater than the required load variation Δload.
The step of checking if the programmable energy sources 4 are able to satisfy the required load variation Δload comprises:
In the non-limiting here example disclosed and illustrated wherein the programmable energy sources 4 are gas turbine assemblies, the calculated gas turbine load reference value takes into account the limits of each gas turbine assembly. The maximum admissible load and the minimum admissible load are normally predefined according to the type of gas turbine assembly and are supplied manually by an operator during the initial basic settings entry operations. Analogously, the maximum increasing or decreasing gradient obtainable by gas the turbine assembly is normally predetermined and is manually supplied by an operator during the initial basic settings entry operations.
In other words, the storage assembly 5 is configured to participate to the load supply to the grid 2 only if the programmable energy sources 4 are not sufficient to react properly to the load requirements of the grid 2. In this way, the energy storage assembly 5 is used only if the programmable energy sources 4 are not sufficient to satisfy the load profile needed by the grid 2.
When the energy storage assembly 5 intervenes, its load variation is, as soon as possible, compensated in order to bring the stored energy close to its nominal status of charge.
This allow to preserve the duration of the energy storage system 5.
Advantageously, the plant managing module 12 distributes the required load variation Δload between the available energy sources (at least one programmable energy source 4 and an energy storage system 5) to optimize the plant response to the requirements of the grid 2.
Essentially, the plant managing module 12 is configured to limit the use of the storage assembly 5 for fast load variations to maximize its runtime and minimize its life consumption.
Advantageously, the control device 8 is configured to manage all the energy sources to react to the requirements of the grid 2. In particular, the requirements of the grid 2 comprises also the primary frequency control, which is normally managed by the programmable energy source only, as common current practice.
This allow to avoid, for example, the common limitation of the gas turbine assembly 4 by setting aside a primary reserve of load for the primary frequency control.
Thanks to the present invention, the primary frequency reserve is assigned to the energy storage assembly 5 and only in case the energy storage assembly 5 reaches its full charge or full discharge conditions, the primary frequency reserve is transferred to the gas turbine assembly 4 in a bumpless way.
In other words, thanks to the fact that the primary frequency reserve is assigned to the energy storage device 5 the exploitable operating range of the gas turbine assembly 4 is extended from the minimum to the maximum technical load allowing an augmented power contribution to the grid 2.
Finally, it is clear that modifications and variants can be made to the plant and to the method described herein without departing from the scope of the present invention, as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21425027.6 | May 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/054797 | 5/23/2022 | WO |
