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FI20205998A1 - A power balancing reserve for an electrical grid - Google Patents

A power balancing reserve for an electrical grid Download PDF

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Publication number
FI20205998A1
FI20205998A1 FI20205998A FI20205998A FI20205998A1 FI 20205998 A1 FI20205998 A1 FI 20205998A1 FI 20205998 A FI20205998 A FI 20205998A FI 20205998 A FI20205998 A FI 20205998A FI 20205998 A1 FI20205998 A1 FI 20205998A1
Authority
FI
Finland
Prior art keywords
fcr
support
subsystems
subsystem
electrical grid
Prior art date
Application number
FI20205998A
Other languages
Finnish (fi)
Swedish (sv)
Inventor
Jarmo Saari
Oscar Karlsson
Original Assignee
Sympower Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sympower Oy filed Critical Sympower Oy
Priority to FI20205998A priority Critical patent/FI20205998A1/en
Priority to PCT/FI2021/050676 priority patent/WO2022079352A1/en
Publication of FI20205998A1 publication Critical patent/FI20205998A1/en

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/12—Circuit arrangements for AC mains or AC distribution networks for adjusting voltage in AC networks by changing a characteristic of the network load
    • H02J3/14—Circuit arrangements for AC mains or AC distribution networks for adjusting voltage in AC networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
    • H02J3/144—Demand-response operation of the power transmission or distribution network
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • H02J3/472—For selectively connecting the AC sources in a particular order, e.g. sequential, alternating or subsets of sources
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
    • H02J2310/10—The network having a local or delimited stationary reach
    • H02J2310/12—The local stationary network supplying a household or a building
    • H02J2310/16—The load or loads being an Information and Communication Technology [ICT] facility
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
    • H02J2310/50—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads
    • H02J2310/52—The controlling of the operation of the load not being the total disconnection of the load, i.e. entering a degraded mode or in current limitation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
    • H02J2310/50—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads
    • H02J2310/56—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads characterised by the condition upon which the selective controlling is based
    • H02J2310/58—The condition being electrical
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
    • Y02B70/3225—Demand response systems, e.g. load shedding, peak shaving
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
    • Y04S20/20—End-user application control systems
    • Y04S20/222—Demand response systems, e.g. load shedding, peak shaving

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

According to an example embodiment, a method (200, 400, 600) for operating a power balancing reserve system for an electrical grid (100) is provided, the power balancing reserve system comprising a support system (120, 320, 520) comprising a plurality of support subsystems (121, 321, 521) arranged for serving a back-end system (125, 325, 525) that has a time-varying requirement for a functionality provided by the support system (120, 320, 520) and a control subsystem (122, 322, 522) for controlling input power supply to said plurality of support subsystems (121, 321, 521) from the electrical grid, the method (200, 400, 600) comprising: assigning (202, 402, 602) each support subsystem (121-k, 321-k, 521-k) to one of a plurality of subgroups of said plurality of support subsystems (121, 321, 521); selecting (204, 404, 604) one of said subgroups for FCR operation to be carried out during a predefined time period; controlling (206, 406, 606) respective input powers supplied to the support subsystems (121-k, 321-k, 521-k) assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid (100); and controlling (208, 408, 608) respective input powers supplied to the support subsystems (121-k, 321-k, 521-k) assigned to subgroups not selected for the FCR operation in accordance with requirements of the back-end system (125, 325, 525).

Description

A power balancing reserve for an electrical grid
TECHNICAL FIELD The example and non-limiting embodiments of the present invention relate to provision of reserve supply to an electrical grid.
BACKGROUND An electrical grid, especially a large one such as a national or a transnational electrical grid requires careful control in order to balance the electricity production from generating stations to the grid and the electricity consumption from the grid by consumers: electricity production to the grid needs to match the electricity consumption from the grid in order to keep the grid operational, whereas in a practical situation instantaneous electricity production and electricity consumption do not fully match each other.
In general, in a balanced condition of the grid the frequency of alternating current (AC) transferred via the grid remains at a nominal system frequency, which e.g. in the European electrical grids is typically 50 Hz, whereas any imbalance between the production and consumption results in a small deviation from the nominal system frequency: in case the consumption exceeds the production (i.e. the grid is heavily loaded) the AC frequency in the grid falls below the nominal system frequency, whereas in case the production S 20 exceeds the consumption (i.e. the grid is lightly loaded) the AC frequency in N the grid raises above the nominal system freguency. Since exact balancing of 2 instantaneous production and consumption in a complex network is practically S impossible, a minor deviation between the nominal system freguency and the E AC freguency of the grid is typically allowed without considering the grid to be © 25 out of balance. As an example, assuming the nominal system frequency of 50 3 Hz, the AC frequency of the grid may be allowed to vary between 49.9 and S 50.1 Hz.
N
Typically, the grid operator aims at ensuring balance in the grid via planning the production and consumption within the network in advance, for example on a daily basis and/or an hourly basis. Nevertheless, in a real-life environment the AC frequency of the grid involves temporary deviations from the nominal system frequency on regular basis, typically such deviations occur during each hour of operation of the grid. A known technique for ensuring balance in the grid despite such deviations involves usage of power balancing reserve that is able to increase or decrease its planned power supply to or demand from the grid in accordance with the AC frequency of the grid. An example of such a power balancing reserve is a frequency control reserve (FCR) that is able to selectively increase or decrease its power consumption in dependence of the observed AC frequency of the grid: in case the AC frequency of the grid drops below the nominal system frequency (indicating the consumption currently exceeding the production), a FCR entity may decrease its power consumption in order to contribute towards decreasing the load of the grid, whereas in case the AC frequency of the grid rises above the nominal system frequency (indicating the production currently exceeding the consumption), the FCR entity may increase its power consumption in order to contribute towards increasing the load of the grid.
SUMMARY It is an object of the present invention to provide a system that is able to serve S as a power balancing reserve for an electrical grid in addition to its primary O function, which system enables one of increasing or decreasing its power O consumption in a flexible manner in without disturbing its internal operation.
N TY 25 According to an example embodiment, a power balancing reserve system for E: an electrical grid is provided, the power balancing reserve system comprising % a support system arranged for serving a back-end system that has a time- 2 varying requirement for a functionality provided by the support system and the support system comprising: a plurality of support subsystems arranged for serving the back-end system, each support subsystem assigned to one of a plurality of subgroups of said plurality of support subsystems; and a control subsystem for controlling input power supply to said plurality of support subsystems from the electrical grid, the control subsystem arranged to select one of said subgroups for FCR operation to be carried out during a predefined time period, the control subsystem comprising a FCR control subsystem arranged to control respective input powers supplied to the support subsystems assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid, and a support function control subsystem for controlling respective input powers supplied to the support subsystems assigned to subgroups not selected for the FCR operation in accordance with requirements of the back-end system. According to another example embodiment, a method for operating a power balancing reserve system for an electrical grid is provided, the power balancing reserve system comprising a support system comprising a plurality of support subsystems arranged for serving a back-end system that has a time-varying requirement for a functionality provided by the support system and a control subsystem for controlling input power supply to said plurality of support subsystems from the electrical grid, the method comprising: assigning each support subsystem to one of a plurality of subgroups of said plurality of support subsystems; selecting one of said subgroups for FCR operation to be carried out during a predefined time period; controlling respective input powers supplied to the support subsystems assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid; and controlling S respective input powers supplied to the support subsystems assigned to N subgroups not selected for the FCR operation in accordance with reguirements 2 25 of the back-end system.
N I According to another example embodiment, a computer program for a © measuring wind speed is provided, the computer program comprising S computer readable program code configured to cause performing at least the N method according to the example embodiment described in the foregoing N 30 when said program code is executed on one or more computing apparatuses.
The computer program according to the above-described example embodiment may be embodied on a volatile or a non-volatile computer- readable record medium, for example as a computer program product comprising at least one computer readable non-transitory medium having the program code stored thereon, which, when executed by one or more computing apparatuses, causes the computing apparatuses at least to perform the method according to the example embodiment described in the foregoing. The exemplifying embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" and its derivatives are used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features described hereinafter are mutually freely combinable unless explicitly stated otherwise. Some features of the invention are set forth in the appended claims. Aspects of the invention, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of some example embodiments when read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF FIGURES The embodiments of the invention are illustrated by way of example, and not a by way of limitation, in the figures of the accompanying drawings, where
O 5 Figure 1 illustrates a block diagram of some logical elements coupled to an W electrical grid according an example; E Figure 2A illustrates a block diagram of some logical elements of a refrigeration © 25 — system arranged for cooling a back-end system according to an example; o
LO N Figure 2B illustrates a block diagram of some logical elements of a refrigeration N system arranged for cooling one or more back-end subsystems according to an example;
Figure 3 illustrates a method according to an example; Figure 4A illustrates a block diagram of some logical elements of an aeration system arranged for aerating a back-end system according to an example; Figure 4B illustrates a block diagram of some logical elements of an aeration 5 system arranged for aerating one or more back-end subsystems according to an example; Figure 5 illustrates a method according to an example; Figure 6A illustrates a block diagram of some logical elements of a support system arranged for supporting a back-end system according to an example; Figure 6B illustrates a block diagram of some logical elements of a support system arranged for supporting one or more back-end subsystems according to an example; Figure 7 illustrates a method according to an example; and Figure 8 illustrates a block diagram of some components of an apparatus according to an example.
DESCRIPTION OF SOME EMBODIMENTS Figure 1 illustrates a block diagram of some logical elements coupled to an o electrical grid 100 according an example. The electrical grid 100 provides an O interconnected network that enables transfer and distribution of electric power O 20 from producers to consumers. In the example of Figure 1, the electrical grid N 100 has coupled thereto power producer entities 102-1, 102-2, 102-3 for I generation of electric power for delivery via the electrical grid 100 and power N consumer entities 104-1, 104-2, 104-3 for consuming the electric power 3 generated by the power producer entities 102-1, 102-2, 102-3. In this regard N 25 — the power producer entities 102-1, 102-2, 102-3 represent a plurality of power N producer entities and the power consumer entities 104-1, 104-2, 104-3 represent a plurality of power consumer entities. In the example of Figure 1 the electrical grid 100 further has a frequency containment reserve (FCR) system 110 coupled thereto, which FCR system 110 represents one or more FCR systems that may be coupled to the electrical grid 100. The plurality of power producer entities may comprise respective power stations or power plants for production of electric power while the plurality power consumer entities may comprise any industrial, commercial and/or private establishment that consume the electric power.
The electrical grid 100 may be alternatively referred to as an electric grid, as a power grid or, simply, just as a grid.
The electrical grid 100 may be provided for transfer and distribution of alternating current (AC) at a predefined nominal system frequency, which may be, for example, 50 Hz (e.g. in Europe) or 60 Hz (e.g. in the United States). Along the lines described in the foregoing, in the course of operation of the electrical grid 100 the actual AC frequency therein may exhibit small deviation from the nominal system frequency due to temporary imbalance between the electric power supplied to the electrical grid 100 and the electric power consumed from the electrical grid 100. Figure 2A illustrates a block diagram of some logical elements of a refrigeration system 120 arranged for cooling a back-end system 125 according to an example.
In this example, the refrigeration system 120 comprises a first refrigeration subsystem 121-1, a second refrigeration subsystem 121-2 and a control subsystem 122. The refrigeration subsystems 121-1, 121-2 represent S a plurality of (i.e. two or more) refrigeration subsystems that may be jointly O referred to by a reference numeral 121, whereas any single refrigeration O subsystem may be referred to by a reference numeral 121-k.
In the example N 25 of Figure 2A, each of the refrigeration subsystems 121-k may be arranged for I cooling of the back-end system 125 in general and each of the refrigeration © subsystems 121-k is arranged to operate under control of the control S subsystem 122. Hence, the cooling capacity provided by the plurality of N refrigeration subsystems 121 is applicable for refrigeration required in the N 30 back-end system 125.
Figure 2B illustrates a block diagram of some logical elements of a refrigeration system 120 arranged for cooling back-end subsystems 125-1, 125-2 according to an example.
In this example, the back-end subsystems 125-1, 125-2 represent a plurality of (i.e. two or more) back-end subsystems that jointly constitute the back-end system 125, whereas any single back-end subsystem may be referred to by a reference numeral 125-j.
As a difference to the example of Figure 2A, in the example of Figure 2B each of the refrigeration subsystems 121-k may be arranged for cooling of respective one or more back-end subsystems 125-j instead of serving for cooling of the back-end system 125 in general.
In the example of Figure 2B, the back-end subsystems 125-j may be co-located with each other or they may be provided in different locations with respect to each other.
On the other hand, the refrigeration subsystem 121-k is typically co-located with those ones of the back-end subsystems 125-j it serves to cool.
In the following, the operation of the refrigeration system 120 is predominantly described with references to the (single) back-end system 125, whereas the description readily generalizes into an arrangement that involves the plurality of back-end subsystems 125-j,
mutatis mutandis.
The back-end system 125 is typically one provided for a certain industrial or commercial purpose that may reguire constant availability of refrigeration but where the reguired cooling capacity may vary over time, for example, with the instantaneous load of the back-end system 125 and/or with ambient S temperature.
A maximum cooling capacity reguired from the refrigeration N system 120 by the back-end system 125 depends on a type and/or 2 25 characteristics of the back-end system 125. The joint cooling capacity of the = plurality of refrigeration subsystems 121 may be dimensioned in view of the E reguired maximum cooling capacity, possibly further over-dimensioned in 9 order to account for unexpected events in the plurality of refrigeration 3 subsystems 121 and/or in the back-end system 125, such as malfunction in O 30 oneormore of the refrigeration subsystems 121-k and/or unexpected increase in required cooling capacity due to a malfunction or misuse of the back-end system 125. Consequently, there may be prolonged periods of time during which even a significant part of the cooling capacity of the refrigeration system 120 is not needed for cooling of the back-end system 125. As non-limiting examples, the back-end system 125 may comprise a warehouse providing cool storage, a food production facility, a chemical industry facility, or another establishment that requires constant refrigeration at a power that may vary over time e.g. with the usage of the back-end system 125 and/or with the ambient temperature.
Each of the refrigeration subsystems 121-k may comprise respective one or more cooling apparatuses of a suitable type known in the art that enable providing a respective maximum cooling capacity Pout,maxk at a respective input power Pinmaxk, whereas each of the refrigeration subsystems 121-k may be arranged to apply the respective one or more cooling apparatuses to provide, under control of the control subsystem 122, a respective instantaneous cooling capacity Poutk(f) at an instantaneous input power Pink(f). As an example, the — maximum input power Pinmaxk Of the refrigeration subsystem 121-k may be in a range from a few kilowatts (kW) to several megawatts (MW), where an applicable value may depend e.g. on the number of refrigeration subsystems 121-k included in the refrigeration system 120, on the maximum cooling capacity reguired from the refrigeration system 120 by the back-end system 125 and/or on the respective maximum cooling capacities of other ones of the plurality of refrigeration subsystems 121. The control subsystem 122 may be arranged to control the respective instantaneous input power Pink(f) to the S refrigeration subsystem 121-k according to reguirements of the back-end N system 125 such that the refrigeration subsystem 121-k provides a reguired 2 25 instantaneous cooling capacity Poutk(t). In this regard, each of the refrigeration = subsystems 121-k may be arranged to operate under respective one or more E control signals issued by the control subsystem 122. 00 3 The refrigeration system 120 described in the foregoing may further serve as N the FCR system 110 coupled to the electrical grid 100 in order to provide a N 30 power balancing reserve for the electrical grid 100. In other words, a primary purpose of the refrigeration system 120 is the cooling of the back-end system
125 whereas it may have a secondary purpose of serving as the FCR system 110 for the electrical grid 100. Hence, the control subsystem 122 needs to account for both the cooling requirements of the back-end system 125 and power balancing requirements arising from the state of the electrical grid 100. In this regard, the plurality of refrigeration subsystems 121 may be divided into a first group of refrigeration subsystems 121-k that are currently allocated for FCR operation (while also providing cooling capacity to the back-end system 125) and into a second group of refrigeration subsystems 121-k that are operated only to provide the cooling capacity to the back-end system 125. In this regard, each of the plurality of refrigeration subsystems 121 may be assigned into one of a plurality of subgroups and, consequently, each of the plurality of subgroups may comprise respective one or more refrigeration subsystems 121-k of the plurality of refrigeration subsystems 121 that are not assigned to any of the other subgroups.
The control subsystem 122 may be arranged to select one of the plurality of subgroups for the FCR operation for a predefined time period, whereas other subgroups are not selected for the FCR operation for the same time period but they (only) serve for refrigeration of the back-end system 125. The selection of one of the subgroups for the FCR operation may be made for the predefined time period in its entirety or to a — sub-period thereof, whereas the selection may be changed from one time period to another and/or from one sub-period to another, as described in more detail via examples provided in the following.
S The control subsystem 122 may include, at least conceptually, a FCR control O subsystem 122-1 and a refrigeration control subsystem 122-2: the FCR control N 25 subsystem 122-1 may be arranged to control (e.g. adjust) the respective I instantaneous input powers Pink(f) supplied to the refrigeration subsystems © 121-k assigned to the subgroup selected for the FCR operation such that their S combined power consumption contributes towards balancing the state of the N electrical grid 100, whereas the refrigeration control subsystem 122-2 may be N 30 arranged to control (e.g. adjust) the respective instantaneous input powers
Pink(t) supplied to the refrigeration subsystems 121-k assigned to the subgroups that are not assigned for the FCR operation such that the respective instantaneous cooling capacities Poutk(f) of the (all) refrigeration subsystems 121k provide sufficient overall cooling capacity Pout(f) for the back-end system
125. In other words, the FCR control subsystem 122-1 and the refrigeration control subsystem 122-2 jointly operate to guarantee sufficient cooling capacity for the back-end system 125 while operating the refrigeration subsystems 121-k assigned to the subgroup selected for the FCR operation such that a power balancing function according to the state of the electrical grid 100 is provided.
The operation of the FCR control subsystem 122-1 may at least in part depend on the state of the electrical grid 100 via an indication of an observed AC frequency in the electrical grid 100. In this regard, the FCR control subsystem 122-1 may be arranged to control the respective instantaneous input powers Pin x(t) supplied to the refrigeration subsystems 121-k assigned to the subgroup — selected for the FCR operation in accordance with a difference between the nominal system frequency of the electrical grid 100 and the observed AC frequency in the electrical grid 100. In particular, the FCR control subsystem 122-1 may be arranged to carry out one of the following control actions in dependence of the difference between the nominal system frequency of the electrical grid 100 and the observed AC frequency in the electrical grid 100: - Keep the respective instantaneous input powers Pink(f) supplied to the S refrigeration subsystems 121-k assigned to the subgroup selected for O the FCR operation unchanged in response to the observed AC O freguency of the electrical grid 100 being egual or substantially egual to N 25 the nominal system frequency; I - Decrease the respective instantaneous input powers Pin(f) supplied to © the refrigeration subsystems 121-k assigned to the subgroup selected S for the FCR operation in response to the observed AC freguency of the N electrical grid 100 being below a first threshold freguency that is smaller N 30 than or egual to the nominal system freguency;
- Increase the respective instantaneous input powers Pink(f) supplied to the refrigeration subsystems 121-k assigned to the subgroup selected for the FCR operation in response to the observed AC frequency of the electrical grid 100 being above a second threshold frequency that is larger than or equal to the nominal system frequency; Consequently, the refrigeration system 120 may serve as the power balancing reserve that contributes towards improved balance between the electric power supplied to the electrical grid 100 and the electric power consumed from the electrical grid 100 in case the observed AC frequency of the electrical grid 100 (substantially) differs from the nominal system frequency of the electrical grid
100. The first and second threshold frequencies may be set to respective predefined values. According to an example, each of the first and second threshold frequencies may be set a value that is equal to the nominal system frequency of the electrical grid 100, thereby activating the power balancing reserve functionality in the refrigeration system 120 when the observed AC frequency of the electrical grid 100 differs from the nominal system frequency. In another example, the fist threshold frequency may be set to a value that is smaller than the nominal system frequency and the second threshold frequency may be set to a value that is larger than the nominal system frequency, thereby activating the power balancing reserve functionality in the refrigeration system 120 when 5 the observed AC freguency of the electrical grid 100 differs from the nominal O system freguency by more than the respective margin(s) defined via the first O and second threshold freguencies. In a non-limiting example assuming the N 25 nominal system frequency of 50 Hz, the first threshold frequency may be a I value chosen from a range from 49.500 to 50.000 Hz and the second threshold © frequency may be a value chosen from a range from 50.000 to 50.500. In a S further example both the first and second threshold freguencies may be set to N 50.000 Hz, in another example the first threshold frequency may be set to N 30 49.900 Hz and the second threshold freguency may be set to 51.100 Hz,
whereas in a further example the first threshold frequency may be set to 49.500 Hz and the second threshold frequency may be set to 51.100 Hz.
The FCR control subsystem 122-1 may be arranged to adjust the respective instantaneous input powers Pink(f) supplied to the refrigeration subsystems 121-k assigned to the subgroup selected for the FCR operation in accordance with a respective predefined range of allowable input powers available for the FCR operation for the respective refrigeration subsystem 121-k, which may be referred to as a FCR range for the respective refrigeration subsystem 121-k.
In an example, the respective FCR range for the refrigeration subsystem 121- k may be defined via a minimum allowable input power Pror mink for the FCR operation and a maximum allowable input power Proc maxk for the FCR operation, where a nominal input power Pror mid.k for the FCR operation may be defined as the mid-point between the minimum and maximum allowable input powers e.g. as Pror mid.k = (Prer_mink + Prcr max.k) / 2. Alternatively, the respective FCR range for the refrigeration subsystem 121-k may be defined via the nominal input power Pro miak for the FCR operation together with the (symmetric) input power margin Pror mra.k that defines the FCR capacity available for the refrigeration subsystem 121-k, resulting in the FCR range from Prcr_mink = Prcr mid.k — Prcr mrg.k to Ptor mid,k + Prer_mrg.k.
An applicable FCR range depends on usage and characteristics of the refrigeration system 120 and/or on characteristic of the plurality of refrigeration S subsystems 121 therein.
As non-limiting examples, the nominal input power O Prer_mia k May be a predefined value chosen from a range from a few kW to O several MW, whereas the input power margin Prcr mrg,k may be a predefined N 25 — value chosen from a range from a few kW to a few hundred kW (depending on I the applied nominal input power Prr_midk). In an example, the nominal input a © power Pror mid.k may be 200 kW and the input power margin Prcr mra.k may be > 150 kW. £ N In this regard, in case the electric grid 100 is in a balanced state (e.g. when the observed AC frequency of the electrical grid 100 is (substantially) equal to the nominal system frequency) without involvement of the power balancing function provided via the refrigeration system 120, the FCR control subsystem 122-1 operates the refrigeration subsystem 121-k assigned to the subgroup selected for the FCR operation at respective nominal FCR input powers Prcr mid.k.
In contrast, a loss of balanced state in the electrical grid 100 due to one or more other components coupled thereto may cause the FCR control subsystem 122-1 one of increasing or decreasing the respective instantaneous input powers Pink(t) supplied to the refrigeration subsystems 121-k assigned to the subgroup selected for the FCR operation within the limits set by the respective minimum FCR input power Pro mink and the respective maximum input power Prr_maxk in accordance with the difference between the observed AC freguency of the electrical grid 100 and the nominal system freguency of the electrical grid 100. According to an example, any change in the respective instantaneous input power Pin,k(t) may be implemented using a step of a predefined size.
According to an example, the step size towards a higher input power (i.e. an upwards step) and the step size towards a lower input power (i.e. a downwards step) are the same or substantially the same, whereas in another example the upwards step is different from the downwards step.
As an example of the latter, the downwards step may be larger than the upwards step.
The size of the applied step may depend on the respective nominal input power Pror mid,k and/or on the respective input power margin Prcr mra.k May be a predefined value chosen from a range from a few kW to a few tens of kW.
S The respective FCR range for each of the refrigeration subsystems 121-k O assigned to the subgroup selected for the FCR operation remains the same N 25 throughout the predefined time period, where both the FCR ranges and the I predefined time period may be ones agreed in advance between an operator a © of the refrigeration system 120 and an operator of the electrical grid 100. In S this regard, both the duration of the predefined time schedule and its starting N and ending times may be defined based on reguirements of the electrical grid N 30 100 and/or on reguirements set by an operator of the electrical grid 100. In an example, the predefined time period may cover a predefined time slot within a time schedule that includes a plurality of consecutive time slots, whereas the time period may be further divided into a sequence of sub-periods, i.e. into a plurality of sub-periods.
In an example in this regard, the respective operators of the refrigeration system 120 and the electrical grid 100 may agree on provision of the FCR functionality using a certain FCR range for one or more time slots of a time schedule, depending e.g. on expected cooling capacity required by the back-end system 125 during the time schedule and/or on expected balancing power requirements of the electrical grid 100. In an example, the time schedule may comprise a given day and the plurality of time slots therein may comprise respective time portions of the given day, e.g. the hours of the given day or half-an-hour periods of the given day.
Consequently, the agreement between the respective operators of the refrigeration system 120 and the electrical grid may be made separately for a plurality of time schedules (e.g. days) and/or for respective one or more time slots (e.g. hours of the day) therein and it may define different FCR ranges for different time slots of the time schedule, e.g. in dependence of expected cooling capacity required by the back-end system 125 during the respective time schedules and/or the respective time slots and/or the expected power balancing requirements of the electrical grid 100 (e.g. respective different FCR ranges for different hours of the day on weekdays and on weekends). The operation of the refrigeration control subsystem 122-2 may aim at S operating the refrigeration subsystems 121-k assigned to the subgroups not O selected for the FCR operation such that the cooling capacity provided O therefrom complements that provided from the refrigeration subsystems 121- N 25 —kassignedto the subgroup selected for the FCR operation and operated under z control of the FCR control subsystem 122-1. This may be provided, for © example, by the refrigeration control subsystem 122-2 continuously receiving S feedback concerning one or more temperatures that are descriptive of a N temperature in the back-end system 125 and controlling respective N 30 instantaneous input powers Pink(f) supplied to the refrigeration subsystems 121-k assigned to the subgroups not selected for the FCR operation such that said one or more temperatures are kept within or brought into respective predefined temperature ranges, thereby ensuring sufficient overall cooling capacity for the back-end system 125. Such temperature feedback may be received from the refrigeration subsystems 121-k and/or from the back-end system 125. As an example in this regard, the refrigeration control subsystem 122-2 may continuously receive feedback concerning respective temperatures in (cooling liquids of) the refrigeration subsystems 121-k and it may control the respective instantaneous input powers Pin(t) supplied to the refrigeration subsystems 121-k assigned to the subgroups not selected for the FCR operation such that respective temperatures therein are kept within or brought into respective predefined temperature ranges.
In another example, the refrigeration control subsystem 122-2 may continuously receive feedback concerning one or more temperatures in the back-end system 125 and it may control the respective instantaneous input powers Pink(f) supplied to the refrigeration subsystems 121-k assigned to the subgroups not selected for the FCR operation such that the one or more temperatures in the back-end system 125 are kept within or brought into respective predefined temperature ranges.
Hence, the cooling capacity available in the refrigeration subsystems 121-k assigned to the subgroups not selected for the FCR operation is fully available for cooling of the back-end system 125 under control of the refrigeration control subsystem 122-2, whereas the instantaneous cooling capacity produced via operation of the refrigeration subsystems 121-k assigned to the subgroup > selected for the FCR operation depends on the state of the electrical grid 100 N but is nevertheless available to complement the cooling capacity obtained from 2 25 the refrigeration subsystems 121-k assigned to the subgroups not selected for = the FCR operation.
Conversely, the instantaneous cooling capacity produced E via operation of the refrigeration subsystems 121-k assigned to the subgroup D selected for the FCR operation under control of the FCR control subsystem 3 122-1 does not directly reflect the needs of the back-end system 125 but rather O 30 depends on the state of the electrical grid 100, whereas the instantaneous cooling capacity produced via operation of the refrigeration subsystems 121-k assigned to the subgroups not selected for the FCR operation operating under control of the refrigeration control subsystem 122-2 may be adjusted in view of the cooling capacity provided by the refrigeration subsystems 121-k assigned to the subgroup selected for the FCR operation.
Along the lines described in the foregoing, the selection of a subgroup of refrigeration systems 121-k for the FCR operation may be made for the predefined time period in its entirety or to a sub-period thereof, whereas the selection may be changed from one time period to another and/or from one sub-period to another. If the time period is further divided into the plurality of sub-periods, depending on the usage scenario, the sub-periods may have an equal duration or the sub-periods may vary in duration. In a scenario where the subgroup of refrigeration systems 121-k selected for the FCR operation remains the same throughout the predefined time period, the predefined time period may be considered to consist of a single sub-period that covers the certain time slot in its entirety. Alternatively, in such a scenario the predefined time period may be considered as one that is at least conceptually divided into the plurality of time periods while the same subgroup of refrigeration systems 121-k is selected for the FCR operation throughout the sub-periods of the predefined time period. In another example, the predefined time period may be divided into the plurality of (e.g. two or more) sub-periods and the control subsystem 122 may be arranged to change selection of the subgroup of refrigeration systems 121-k assigned for the FCR operation from S one sub-period to another. In this regard, the selection may be made such that O a different one of the plurality of subgroups is selected for the FCR operation O in consecutive sub-periods of the seguence of sub-periods, thereby ensuring N 25 that the same one or more refrigeration subsystems 121-k are not allocated z for the FCR operation in two consecutive sub-periods of the predefined time © period. According to an example, the control subsystem 122 may be arranged S to make the selection of the subgroup for the FCR operation over the seguence N of sub-periods in a round-robin manner, thereby evenly allocating each of the N 30 subgroups (and hence each of the refrigeration subsystems 121-k) for the FCR operation over the predefined time period. Such an approach may especially advantageous in a scenario of the type exemplified via Figure 2B, where each of the refrigeration subsystems 121-k may be dedicated for serving one or more back-end subsystem 125-j and, hence, where a prolonged allocation of a certain subgroup of refrigeration subsystems 121-k to the FCR operation might risk compromising the cooling capacity provided to those ones of the back-end subsystems 125-j that are served by the refrigeration subsystems 121-k assigned to the subgroup that is allocated to the FCR operation for prolonged period of time.
As a non-limiting example, there may be two subgroups of refrigeration systems 121-k, where a first subgroup includes the first refrigeration subsystem 121-1 and a second subgroup includes the second refrigeration subsystem 121-2. Moreover, the predefined time period may have a duration of one hour and it may be further divided into the plurality of sub-periods equal length, e.g. into four sub-periods of fifteen minutes or into six sub-periods of ten minutes.
The control subsystem 122 may be arranged to change the selection of the subgroup from the first sub-group to the second one or vice versa when moving from one sub-period of the predefined time period to another, thereby alternately using either the first refrigeration subsystem 121- 1 or the second refrigeration subsystem 121-2 as the one allocated for the FCR operation whereas the other one may serve solely for refrigeration of the back- end system 125. Such an alternating usage of the first and second refrigeration sub-systems 121-1, 121-2 for the FCR operation may be especially S advantageous in scenarios of the type shown in Figure 2B, where each of the N first and second refrigeration sub-systems 121-1, 121-2 may be dedicated to 2 25 serve a respective one of the back-end subsystem 125-1, 125-2 and where a = prolonged allocation of one of the first and second refrigeration sub-systems E 121-1, 121-2 to the FCR operation might risk compromising the cooling 9 capacity provided to the respective one of the back-end subsystems 125-1, o = 125-2. N 30 Operation of the refrigeration system 120 described in the foregoing and/or in the following may be, alternatively, described as steps of a method.
As an example in this regard, Figure 3 depicts a flowchart illustrating a method 200, which may be carried out, for example, by the control subsystem 122. Respective operations described with references to blocks 202 to 208 pertaining to the method 200 may be implemented, varied and/or complemented in a number of ways, for example as described with references to the refrigeration system 100 in the foregoing and/or in the following. The method 200 serves as one for operating a power balancing reserve system for the electrical grid 100, the power balancing reserve system comprising the refrigeration system 120 that comprises the plurality of refrigeration subsystems 121 arranged for cooling the back-end system 125 and the control subsystem 122 for controlling input power supply to said plurality of refrigeration subsystems 121 from the electrical grid 100. The method 200 comprises assigning each refrigeration subsystem 121-k to one of a plurality of subgroups of said plurality of refrigeration subsystems 121, as indicated in block 202, and selecting one of said subgroups for FCR operation to be carried out during a predefined time period, as indicated in block 204. The method 200 further comprises controlling respective input powers supplied to the refrigeration subsystems 121-k assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid 100, as indicated in block 206, and controlling respective input powers supplied to the refrigeration subsystems 121-k assigned to subgroups not selected for the FCR operation in accordance with requirements of the S back-end system 125, as indicated in block 208.
O
N O The examples described in the foregoing pertain to usage of the refrigeration N 25 system 120 as the FCR system 110 coupled to the electrical grid 100 in order I to provide a power balancing reserve for the electrical grid 100, thereby making © use of flexibility allowed by the cooling requirements of the back-end system S 125 via adjusting the input power supply provided by the plurality of N refrigeration subsystems 121 to account for the state of the electrical grid 100.
N As another example of a system that may serve as the FCR system 100 coupled to the electrical grid, Figure 4A illustrates a block diagram of some logical elements of an aeration system 320 according to an example.
In this example, the aeration system 320 comprises a first aeration subsystem 321- 1, a second aeration subsystem 321-2 and a control subsystem 322. The aeration subsystems 321-1, 321-2 represent a plurality of (i.e. two or more) aeration subsystems that may be jointly referred to by a reference numeral 321, whereas any single aeration subsystem may be referred to by a reference numeral 321k.
In the example of Figure 4A, each of the aeration subsystems 321-k may be arranged for aeration of the back-end system 325 in general while each of the aeration subsystems 321-k may be arranged to operate under control of the control subsystem 322. Hence, the aeration capacity provided by the plurality of aeration subsystems 321 is applicable for aeration of the back-end system 325. While the example of Figure 4A may be considered as one where the aeration system 320 is provided for aeration of the back-end system 325 in general, Figure 4B illustrates a block diagram of some logical elements of a variant of the aeration system 320 where the back-end system 325 includes a plurality of back-end subsystems, represented in the example of Figure 4B by back- end subsystems 325-1, 325-2 and where any single back-end subsystem may be referred to by a reference numeral 325+. As a difference to the example of Figure 4A, in the example of Figure 4B each of the aeration subsystems 321- k may be arranged for aeration of respective one or more back-end subsystems 325+ instead of serving for aeration of the back-end system 325 S in general.
As in the case of the refrigeration system 120 according to the N example of Figure 2B, in the example of Figure 4B the back-end subsystems 2 25 325-j may be co-located with each other or they may be provided in different = locations with respect to each other.
On the other hand, the aeration E subsystem 321-k is typically co-located with those ones of the back-end 9 subsystems 325-j it serves to aerate.
In the following, the operation of the 3 aeration system 320 is predominantly described with references to the back- O 30 end system 325 in general, whereas the description readily generalizes into an arrangement that involves the plurality of back-end subsystems 325-j, mutatis mutandis.
The aeration system 320 according to the respective examples of Figures 4A and 4B may serve to provide aeration for a wastewater treatment procedure applied for removing contaminants from the wastewater, whereas the back- end system 325 may comprise a single aeration basin served by the plurality of aeration subsystems 321 while the plurality of back-end subsystems 325-j may comprise respective plurality of aeration basins, where each of the aeration subsystems 321-k may be arranged for aeration of respective one or more aeration basins 325-j. In this regard, the aeration system 320 may serve to aerate wastewater included in the aeration basin(s) in order to ensure sufficient oxygen level therein to enable wastewater treatment via usage of suitable bacteria or micro-organisms of other type injected into the aeration basin(s). The wastewater treatment procedure typically requires constant availability of aeration whereas the aeration capacity required from the aeration system 320 — varies over time, depending e.g. on the amount of wastewater currently in the aeration basin(s), on temperature of the wastewater included in the aeration basins and/or on ambient temperature. A maximum aeration capacity reguired from the aeration system 320 depends e.g. on the type of the wastewater treatment procedure applied and/or capacity of the aeration basin(s) and hence the joint aeration capacity enabled by the plurality of aeration subsystems 321 may be dimensioned in view of the maximum reguired aeration capacity, possibly further over-dimensioned in order to account for S unexpected events in the aeration system 320 and/or in the aeration basin(s). N Conseguently, there may be prolonged periods of time during which even a 2 25 significant part of the aeration capacity of the aeration system 320 is not = needed for aeration of the wastewater included in the aeration basin(s).
T : While using the aeration basins(s) of the wastewater treatment system as an 3 example of the back-end system 325 and the back-end subsystems 325-j, this N serves as a non-limiting example and the description in this regard provided in N 30 the foregoing and/or in the following readily generalizes of aeration of a back-
end system 325 and/or back-end subsystems 325-j of other type, mutatis mutandis.
Each of the aeration subsystems 321-k may comprise respective one or more aeration pumps or aeration devices of other type that enable providing a respective maximum aeration capacity at a respective input power Pinmaxk, whereas each of the aeration subsystems 321-k may be arranged to apply the respective one or more aeration pumps (or aeration devices of other type) to provide, under control of the control subsystem 322, a respective instantaneous aeration capacity at an instantaneous input power Pink(t). As an example, assuming the wastewater treatment use case described above, the maximum input power Pinmaxk Of the aeration subsystem 321-k may be in a range from a few kilowatts (kW) to several megawatts (MW), where an applicable value may depend e.g. on the number of aeration subsystems 321- k included in the aeration system 320, on the maximum aeration capacity required from the aeration system 320 and/or on the respective maximum aeration capacities of other ones of the plurality of aeration subsystems 321. The control subsystem 322 may be arranged to control the respective instantaneous input power Pink(t) to the aeration subsystem 321-k according to requirements of the back-end system 325 such that the aeration subsystem 321-k provides a required instantaneous aeration capacity.
In this regard, each of the aeration subsystems 321-k may be arranged to operate under respective one or more control signals issued by the control subsystem 322. S Like the refrigeration system 120 described in the foregoing, also the aeration O system 320 may further serve as the FCR system 110 coupled to the electrical N 25 grid 100 in order to provide a power balancing reserve for the electrical grid I 100. In other words, a primary purpose of the aeration system 320 is the a © aeration of the back-end system 325 whereas it may have a secondary S purpose of serving as the FCR system 110 for the electrical grid 100. Hence, N the control subsystem 322 needs to account for both the aeration reguirements N 30 of the back-end system 325 and power balancing requirements arising from the state of the electrical grid 100. In this regard, the plurality of aeration subsystems 321 may be divided into a first group of aeration subsystems 321- k that are currently allocated for FCR operation (while also providing aeration capacity to the back-end system 325) and into a second group of aeration subsystems 321-k that are operated only to serve the back-end system 325.
Hence, the plurality of aeration subsystems 321 may be assigned into the plurality of subgroups in the manner described in the foregoing for grouping of the refrigeration subsystems 121-k and the control subsystem 322 may be arranged to select one of the plurality of subgroups for the FCR operation for a predefined time period, whereas other subgroups are not selected for the FCR operation for the same time period but they (only) serve for aeration of the back-end system 325. In this regard, the selection may be made and varied over time in a similar manner as described in the foregoing for the refrigeration system 120.
The control subsystem 322 may include, at least conceptually, a FCR control subsystem 322-1 and an aeration control subsystem 322-2: the FCR control subsystem 322-1 may be arranged to control (e.g. adjust) the respective instantaneous input powers Pin k(t) supplied to the aeration subsystems 321-k assigned to the subgroup selected for the FCR operation such that their combined power consumption contributes towards balancing the state of the electrical grid 100, whereas the aeration control subsystem 322-2 may be arranged to control (e.g. adjust) the respective instantaneous input powers S Pin x(t) supplied to the aeration subsystems 321-k assigned to the subgroups O that are not assigned for the FCR operation such that the respective O instantaneous aeration capacities Poutk(t) of the (all) aeration subsystems 321- N 25 — k provide sufficient overall aeration capacity Pout(f) for the back-end system z 325. In other words, the FCR control subsystem 322-1 and the aeration control © subsystem 322-2 jointly operate to guarantee sufficient aeration capacity for S the back-end system 325 while operating the aeration subsystems 321-k N assigned to the subgroup selected for the FCR operation such that a power N 30 balancing function according to the state of the electrical grid 100 is provided.
In this regard, the FCR control subsystem 322-1 may operate in the manner described in the foregoing for the FCR control subsystem 122-1 of the refrigeration system 120, mutatis mutandis.
Moreover, the aeration control subsystem 322-2 may operate the aeration subsystems 321-k assigned to the subgroups not selected for the FCR operation such that the aeration capacity provided therefrom complements that provided from the aeration subsystems 321-k assigned to the subgroup selected for the FCR operation and operated under control of the FCR control subsystem 322-1. This may be provided, for example, by the aeration control subsystem 322-2 continuously receiving feedback concerning the current aeration requirement of the back-end system 325 and controlling respective instantaneous input powers Pin k(t) supplied to the aeration subsystems 321-k assigned to the subgroups not selected for the FCR operation such that the aeration requirement of the back-end system 325 is satisfied to ensure sufficient overall aeration capacity for the back-end system 325.
Hence, the aeration capacity available in the aeration subsystems 321-k assigned to the subgroups not selected for the FCR operation is fully available for aeration of the back-end system 325 under control of the aeration control subsystem 322-2, whereas the instantaneous aeration capacity produced via operation of the aeration subsystems 321-k assigned to the subgroup selected for the FCR operation depends on the state of the electrical grid 100 but is nevertheless available to complement the aeration capacity obtained from the S aeration subsystems 321-k assigned to the subgroups not selected for the O FCR operation.
O T Operation of the aeration system 320 described in the foregoing and/or in the = 25 following may be, alternatively, described as steps of a method. As an example E: in this regard, Figure 5 depicts a flowchart illustrating a method 400, which may 3 be carried out, for example, by the control subsystem 322. Respective S operations described with references to blocks 402 to 408 pertaining to the method 400 may be implemented, varied and/or complemented in a number of ways, for example as described in the present disclosure with references to the aeration system 320 and/or with references to the refrigeration system 120,
mutatis mutandis. Like the method 200 described in the foregoing, the method 400 serves as one for operating a power balancing reserve system for the electrical grid 100, the power balancing reserve system comprising the aeration system 320 that comprises the plurality of aeration subsystems 321 arranged for aeration of the back-end system 325 and the control subsystem 322 for controlling input power supply to said plurality of aeration subsystems 321 from the electrical grid 100. The method 400 comprises assigning each aeration subsystem 321-k to one of a plurality of subgroups of said plurality of aeration subsystems 321, as indicated in block 402, and selecting one of said subgroups for FCR operation to be carried out during a predefined time period, as indicated in block 404. The method 400 further comprises controlling respective input powers supplied to the aeration subsystems 321-k assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid 100, as indicated in block 406, and controlling respective input powers supplied to the aeration subsystems 321-k assigned to subgroups not selected for the FCR operation in accordance with requirements of the back-end system 325, as indicated in block 408. While the FCR operation to provide a power balancing reserve for the electrical grid 100 has been described in the foregoing using the refrigeration system 120 and the aeration system 320 as representative but non-limiting examples, S the refrigeration system 120 according to the example of Figure 2A and the O aeration system according to the example of Figure 4A readily generalize into O a support system 520 illustrated by an exemplifying block diagram of Figure N 25 BA, whereas the refrigeration system 120 according to the example of Figure I 2B and the aeration system according to the example of Figure 4B readily © generalize into a support system 520 illustrated by an exemplifying block S diagram of Figure 6B.
S N In the example of Figure 6A, the support system 520 comprises a first support subsystem 521-1, a second support subsystem 521-2 and a control subsystem
522. The support subsystems 521-1, 521-2 represent a plurality of (i.e. two or more) support subsystems that may be jointly referred to by a reference numeral 521, whereas any single support subsystem may be referred to by a reference numeral 521-k. In the example of Figure 6A, each of the support subsystems 521-k may be arranged for serving the back-end system 525 in general, whereas each of the aeration subsystems 521-k may be arranged to operate under control of the control subsystem 522. Hence, the capacity provided by the plurality of support subsystems 521 is applicable for serving the back-end system 525 in general. In the example of Figure 6B, the support system 520 serves a plurality of back- end subsystems, represented in the example of Figure 6B by back-end subsystems 525-1, 525-2, where any single back-end subsystem may be referred to by a reference numeral 525-j. As a difference to the example of Figure 6A, in the example of Figure 6B each of the support subsystems 521-k may be arranged for serving respective one or more back-end subsystems —525-j instead of serving the back-end system 525 in general. As in the case of the refrigeration system 120 according to the example of Figure 2B and the aeration system 320 according to the example of Figure 4B, in the example of Figure 6B the back-end subsystems 525-j may be co-located with each other or they may be provided in different locations with respect to each other. On the other hand, the support subsystem 521-k is typically co-located with those ones of the back-end subsystems 525-j it serves to support. In the following, the operation of the support system 520 is predominantly described with S references to the back-end system 525 in general, whereas the description N readily generalizes into an arrangement that involves the plurality of back-end 2 25 subsystems 525-j, mutatis mutandis.
N = The support system 520 according to the respective examples of Figures 6A © and 6B and the plurality of support subsystems 521 therein may serve to any S technical support function for the back-end system 525 or for the back-end N subsystems 525-j that have time-varying requirements for the functionality N 30 provided by the support system 520, along the lines described in the foregoing for the refrigeration function provided by the refrigeration subsystems 121-k of the refrigeration system 120 and for the aeration function provided by the aeration subsystems 321-k of the aeration system 320. While the back-end system 525 typically requires constant availability of the function provided by the support system 520, the required extent (or amount) of support may vary over time.
The maximum capacity of the support system 520 needs to be dimensioned in view of the maximum requirement by the back-end system 525, which typically results in prolonged periods of time during which even a significant part of the capacity of the support system 520 is not needed for by the back-end system 525 Each of the support subsystems 521-k may be arranged to operate under control of the control subsystem 522 such that a respective instantaneous service capacity at an instantaneous input power Pink(f) is provided for the back-end system 525, e.g. based at least in part on current requirements indicated by the back-end system 525 such that service capacity currently required by the back-end system 525 is provided from the support system 520. In this regard, each of the support subsystems 521-k may be arranged to operate under respective one or more control signals issued by the control subsystem 522. Like the refrigeration system 120 and the aeration system 320 described in the foregoing, also the support system 520 may further serve as the FCR system 110 coupled to the electrical grid 100 in order to provide a power balancing S reserve for the electrical grid 100. In other words, in addition to its primary O purpose of supporting the back-end system 525, the support system 520 may O have a secondary purpose of serving as the FCR system 110 for the electrical N 25 grid 100. Hence, the control subsystem 522 needs to account for both the I requirements of the back-end system 525 and power balancing requirements © arising from the state of the electrical grid 100. In this regard, the plurality of S support subsystems 521 may be divided into a first group of support N subsystems 521-k that are currently allocated for FCR operation (while also N 30 serving the back-end system 525) and into a second group of support subsystems 521-k that are operated only to serve the back-end system 525.
Hence, the plurality of support subsystems 521 may be assigned into the plurality of subgroups in the manner described in the foregoing for grouping of the refrigeration subsystems 121-k and/or for grouping of the aeration subsystems 321-k and the control subsystem 522 may be arranged to select one of the plurality of subgroups for the FCR operation for a predefined time period, whereas other subgroups are not selected for the FCR operation for the same time period but they (only) serve for supporting the back-end system
525. In this regard, the selection may be made and varied over time in a similar manner as described in the foregoing for the refrigeration system 120 and/or for the aeration system 320. The control subsystem 522 may include, at least conceptually, a FCR control subsystem 522-1 and a support function control subsystem 522-2: the FCR control subsystem 522-1 may be arranged to control (e.g. adjust) the respective instantaneous input powers Pink(f) supplied to the support subsystems 521-k assigned to the subgroup selected for the FCR operation such that their combined power consumption contributes towards balancing the state of the electrical grid 100, whereas the support function control subsystem 522-2 may be arranged to control (e.g. adjust) the respective instantaneous input powers Pink(t) supplied to the support subsystems 521-k assigned to the subgroups that are not assigned for the FCR operation such that the respective instantaneous capacities Poutk(f) of the (all) support subsystems 521-k provide sufficient service capacity Pout(f) for the back-end oO system 525.
S O In other words, the FCR control subsystem 522-1 and the support function N 25 control subsystem 522-2 jointly operate to guarantee sufficient support I capacity for the back-end system 525 while operating the support subsystems © 521-k assigned to the subgroup selected for the FCR operation such that a S power balancing function according to the state of the electrical grid 100 is N provided. In this regard, the FCR control subsystem 522-1 may operate in the N 30 manner described in the foregoing for the FCR control subsystem 122-1 of the refrigeration system 120, mutatis mutandis.
Moreover, the support function control subsystem 522-2 may operate the support subsystems 521-k assigned to the subgroups not selected for the FCR operation such that the service capacity provided therefrom complements that provided from the support subsystems 521-k assigned to the subgroup selected for the FCR operation and operated under control of the FCR control subsystem 522-1. This may be provided, for example, by the support function control subsystem 522-2 continuously receiving feedback concerning the current requirement of the back-end system 525 and controlling respective instantaneous input powers Pink(t) supplied to the support subsystems 521-k assigned to the subgroups not selected for the FCR operation such that the service requirement of the back-end system 525 is satisfied to ensure sufficient overall service capacity for the back-end system 525. As an example in this regard, the feedback obtained from the back-end system 525 may comprise one or more parameters that are descriptive of one or more conditions in the back-end system 525, whereas the control by the support function control subsystem 522-2 may comprise controlling respective instantaneous input powers Pink(f) supplied to the applicable support subsystems 521-k such that the one or more conditions are kept within or brought into respective predefined (value) ranges.
Hence, the support capacity available in the support subsystems 521-k assigned to the subgroups not selected for the FCR operation is fully available for serving the back-end system 525 under control of the support function S control subsystem 522-2, whereas the instantaneous support capacity N produced via operation of the support subsystems 521-k assigned to the 2 25 subgroup selected for the FCR operation depends on the state of the electrical = grid 100 but is nevertheless available to complement the service capacity E obtained from the support subsystems 521-k assigned to the subgroups not D selected for the FCR operation.
o
LO N Operation of the support system 520 described in the foregoing and/or in the N 30 following may be, alternatively, described as steps of a method. As an example in this regard, Figure 7 depicts a flowchart illustrating a method 600, which may be carried out, for example, by the control subsystem 622. Respective operations described with references to blocks 602 to 608 pertaining to the method 600 may be implemented, varied and/or complemented in a number of ways, for example as described in the present disclosure with references to the support system 520, to the refrigeration system 120 and/or to the aeration system 320, mutatis mutandis.
Like the methods 200 and 400 described in the foregoing, the method 600 serves as one for operating a power balancing reserve system for the electrical grid 100, the power balancing reserve system comprising the support system 520 that comprises the plurality of support subsystems 521 arranged for supporting the back-end system 525 and the control subsystem 522 for controlling input power supply to said plurality of support subsystems 521 from the electrical grid 100. The method 600 comprises assigning each support subsystem 521-k to one of a plurality of subgroups of said plurality of support subsystems 521, as indicated in block 602, and selecting one of said subgroups for FCR operation to be carried out during a predefined time period, as indicated in block 604. The method 600 further comprises controlling respective input powers supplied to the support subsystems 521-k assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid 100, as indicated in block 606, and controlling respective input powers supplied to the support subsystems 521-k assigned to subgroups not selected for the FCR operation in accordance with requirements of the back-end system 525, as S indicated in block 608. & O Figure 8 schematically illustrates some components of an apparatus 700 that N 25 may be employed to implement the control subsystem 122, 322, 522 or one or z more portions thereof, e.g. the FCR control subsystem 122-1, 322-1, 522-1 © and/or one of the refrigeration control subsystem 122-2, the aeration control S subsystem 322-2 and the support function control subsystem 522-2. The N apparatus 700 comprises a processor 702 and a memory 704. The memory N 30 704 may store data and computer program code 706. The apparatus 700 may further comprise communication means 708 for wired or wireless communication with other apparatuses and/or user I/O (input/output) components 710 that may be arranged, together with the processor 702 and a portion of the computer program code 706, to provide the user interface for receiving input from a user and/or providing output to the user.
In particular, the user I/O components may include user input means, such as one or more keys or buttons, a keyboard, a touchscreen or a touchpad, etc.
The user I/O components may include output means, such as a display or a touchscreen.
The components of the apparatus 700 are communicatively coupled to each other via a bus 712 that enables transfer of data and control information between the components.
The memory 704 and a portion of the computer program code 706 stored therein may be further arranged, with the processor 702, to cause the apparatus 700 to perform at least some aspects of operation of the control subsystem 122, 322, 522 or one or more portions thereof.
The processor 702 is configured to read from and write to the memory 704. Although the processor 702 is depicted as a respective single component, it may be implemented as respective one or more separate processing components.
Similarly, although the memory 704 is depicted as a respective single component, it may be implemented as respective one or more separate components, some or all of which may be integrated/removable and/or may provide permanent / semi- permanent/ dynamic/cached storage.
S The computer program code 706 may comprise computer-executable O instructions that implement at least some aspects of operation of the control O subsystem 122, 322, 522 or one or more portions thereof when loaded into the N 25 processor 702. As an example, the computer program code 706 may include I a computer program consisting of one or more sequences of one or more a © instructions.
The processor 702 is able to load and execute the computer S program by reading the one or more seguences of one or more instructions N included therein from the memory 704. The one or more seguences of one or N 30 more instructions may be configured to, when executed by the processor 702, cause the apparatus 700 to perform at least some aspects of operation of the control subsystem 122, 322, 522 or one or more portions thereof. Hence, the apparatus 700 may comprise at least one processor 702 and at least one memory 704 including the computer program code 706 for one or more programs, the at least one memory 704 and the computer program code 706 configured to, with the at least one processor 702, cause the apparatus 700 to perform at least some aspects of operation of the control subsystem 122, 322, 522 or one or more portions thereof. The computer program code 706 may be provided e.g. a computer program product comprising at least one computer-readable non-transitory medium having the computer program code 706 stored thereon, which computer program code 706, when executed by the processor 702 causes the apparatus 700 to perform at least some aspects of operation of the control subsystem 122, 322, 522 or one or more portions thereof. The computer-readable non- transitory medium may comprise a memory device or a record medium such as a CD-ROM, a DVD, a Blu-ray disc or another article of manufacture that tangibly embodies the computer program. As another example, the computer program may be provided as a signal configured to reliably transfer the computer program. Reference(s) to a processor herein should not be understood to encompass only programmable processors, but also dedicated circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal S processors, etc. Features described in the preceding description may be used O in combinations other than the combinations explicitly described. 2 a j > 2
S

Claims (15)

Claims
1. A power balancing reserve system for an electrical grid (100), the power balancing reserve system comprising a support system (120, 320, 520) arranged for serving a back-end system (125, 325, 525) that has a time- varying requirement for a functionality provided by the support system (120, 320, 520), the support system (120, 320, 520) comprising: a plurality of support subsystems (121, 321, 521) arranged for serving the back-end system (125, 321, 521), each support subsystem (121-k, 321-k, 521-k) assigned to one of a plurality of subgroups of said plurality of support subsystems (121, 321, 521); and a control subsystem (122, 322, 522) for controlling input power supply to said plurality of support subsystems (121, 321, 521) from the electrical grid (100), the control subsystem (122, 322, 522) arranged to select one of said subgroups for FCR operation to be carried out during a predefined time period, the control subsystem (122, 322, 522) comprising: a frequency containment reserve, FCR, control subsystem (122-1, 322-1, 522-1) arranged to control respective input powers supplied to the support subsystems (121-k, 321-k, 521-k) assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid (100), and N a support function control subsystem (122-2, 322-2, 522-2) for N controlling respective input powers supplied to the support 2 subsystems (121-k, 321k, 521-k) assigned to subgroups not selected = 25 for the FCR operation in accordance with requirements of the back- E: end system (125, 325, 525). 00 N
2. A power balancing reserve system according to claim 1, wherein the s control subsystem (122, 322, 522) is arranged to select the same one of the subgroups for the FCR operation throughout the predefined time period.
3. A power balancing reserve system according to claim 1 or 2, wherein the predefined time period is divided into a sequence of sub-periods and wherein the control subsystem (122, 322, 522) is arranged to select different one of the plurality of subgroups for the FCR operation in consecutive sub-periods of the predefined time period.
4. A power balancing reserve system according to claim 3, wherein the control subsystem (122, 322, 522) is arranged to select one of the plurality of subgroups is selected for the FCR operation over the sequence of sub-periods in a round-robin manner.
5. A power balancing reserve system according to any of claims 1 to 4, wherein each of the plurality of subgroups comprises respective one or more support subsystems (121-k, 321-k, 521-k) that are not assigned to any of the other subgroups.
6. A power balancing reserve system according to any of claims 1 to 5, o wherein the FCR control subsystem (122-1, 322-1, 522-1) is arranged to O control the respective input powers supplied to the support subsystems © (121, 321, 521) assigned to the subgroup selected for the FCR operation N in accordance with a difference between a nominal system frequency of I 25 the electrical grid (100) and an observed alternating current, AC, 2 frequency in the electrical grid (100).
o N 7. A power balancing reserve system according to claim 6, wherein the FCR control subsystem (122-1, 322-1, 522-1) is arranged to decrease the respective input powers supplied to the support subsystems (121-k, 321-k, 521-k) assigned to the subgroup selected for the FCR operation in response to the observed AC frequency of the electrical grid (100) being below a first threshold frequency that is smaller than or equal to the nominal system frequency, and increase the respective input powers supplied to the refrigeration subsystems (121-k, 321-k, 521-k) assigned to the subgroup selected for the FCR operation in response to the observed AC frequency of the electrical grid (100) being above a second threshold frequency that is larger than or equal to the nominal system frequency.
8. Apower balancing reserve system according to claim 7, wherein the FCR control subsystem (122-1, 322-1, 522-1) is arranged to keep the respective input powers supplied to the support subsystems (121-k, 321- k, 521-k) assigned to the subgroup selected for the FCR operation unchanged in response to the observed AC frequency of the electrical grid (100) being equal to the nominal system frequency.
9. A power balancing reserve system according to any of claims 1 to 8, wherein the FCR control subsystem (122-1, 322-1, 522-1) is arranged to control the respective input powers supplied to the support subsystems o (121-k, 321-k, 521-k) assigned to the subgroup selected for the FCR S operation in accordance with a respective predefined FCR range 2 allocated for the respective support subsystem (121-k, 321-k, 521-k).
N ” 25 E 10. A power balancing reserve system according to claim 9, wherein the & respective FCR range for a support subsystem (121-k, 321-k, 521-k) S defines at least the following: © a minimum allowable input power supply to the respective support subsystem (121-k, 321-k, 521-k) under the FCR operation, and a maximum allowable input power supply to the respective support subsystem (121-k, 321-k, 521-k) under the FCR operation.
11. A power balancing reserve system according to claim 10, wherein the respective FCR range for a support subsystem (121-k, 321-k, 521k) further defines a nominal FCR input power for the respective support subsystem (121-k, 321-k, 521-k), wherein the nominal FCR input power for the respective support subsystem (121-k, 321-k, 521-k) is the mid- point between the minimum and maximum FCR input powers for the respective support subsystem (121-k, 321-k, 521-k).
12. A power balancing reserve system according to any of claims 1 to 11, wherein the support function control subsystem (122-2, 322-2, 522-2) is arranged to: receive feedback on one or more parameters that are descriptive of one or more conditions in the back-end system (125, 325, 525); and control the respective input powers supplied to the support subsystems (121, 321, 521) assigned to the subgroups not selected for the FCR operation such that said one or more conditions are kept within or brought into respective predefined ranges.
S S 13. A power balancing reserve system according to any of claims 1 to 12, O wherein one of the following applies: = the support system comprises a refrigeration system (120) comprising a = 25 plurality of refrigeration subsystems (121) arranged for cooling the back- 2 end system (125) and wherein the support function control subsystem 2 comprises a refrigeration control subsystem (122-2); or N the support system comprises an aeration system (320) comprising a plurality of aeration subsystems (321) arranged for aeration of the back- end system (325) comprising one or more aeration basins (325, 325+) for holding wastewater and wherein the support function control subsystem comprises an aeration control subsystem (322-2).
14. A method (200, 400, 600) for operating a power balancing reserve system for an electrical grid (100), the power balancing reserve system comprising a support system (120, 320, 520) comprising a plurality of support subsystems (121, 321, 521) arranged for serving a back-end system (125, 325, 525) that has a time-varying requirement for a functionality provided by the support system (120, 320, 520) and a control subsystem (122, 322, 522) for controlling input power supply to said plurality of support subsystems (121, 321, 521) from the electrical grid (100), the method (200, 400, 600) comprising: assigning (202, 402, 602) each support subsystem (121-k, 321-k, 521-k) to one of a plurality of subgroups of said plurality of support subsystems (121, 321, 521); selecting (204, 404, 604) one of said subgroups for FCR operation to be carried out during a predefined time period; controlling (206, 406, 606) respective input powers supplied to the support subsystems (121-k, 321-k, 521-k) assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid (100); and N controlling (208, 408, 608) respective input powers supplied to the N support subsystems (121-k, 321-k, 521-k) assigned to subgroups not 2 selected for the FCR operation in accordance with requirements of the - 25 back-end system (125, 325, 525). = > 3
15. A computer program for operating a power balancing reserve system for O an electrical grid (100), the power balancing reserve system comprising a support system (120, 320, 520) comprising a plurality of support subsystems (121, 321, 521) arranged for serving a back-end system
(125, 325, 525) that has a time-varying requirement for a functionality provided by the support system (120, 320, 520) and a control subsystem (122, 322, 522) for controlling input power supply to said plurality of support subsystems (121, 321, 521) from the electrical grid (100), the computer program comprising computer readable program code (306) configured to cause performing of the following when said program code (306) is run on one or more computing apparatuses (300): assign each support subsystem (121-k, 321-k, 521-k) to one of a plurality of subgroups of said plurality of support subsystems (121, 321, 521); select one of said subgroups for FCR operation to be carried out during a predefined time period; control respective input powers supplied to the support subsystems (121- k, 321-k, 521-k) assigned to the subgroup selected for the FCR operation in accordance with a state of the electrical grid (100); and control respective input powers supplied to the support subsystems (121- k, 321-k, 521-k) assigned to subgroups not selected for the FCR operation in accordance with requirements of the back-end system (125, 325, 525).
O
QA
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