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The introduction of distributed renewable power units (RPU) changes the operation of electrical power systems. RPU take over tasks of conventional power plants such as energy supply and the provision of ancillary services. The ancillary service provision must be reliable in order to guarantee secure system operations. In this thesis, the RelACs-method is introduced to assess coalitions, i.e. aggregations of RPU, with respect of how reliably they are able to provide ancillary services, particularly for the use case of providing primary control reserves. The RelACs-method incorporates uncertainties induced by unit failures and forecast errors as well as dependencies between units. The RelACs-method can be used to guarantee that a coalition is able to fulfil specific reliability requirements. Furthermore, the RelACs-method is used to derive recommendations for the choice of inputs to coalition forming given different conditions.

This Electra internal report includes the work of Task T6.1 describing the nature, availability andcontribution of flexibility resources. This task also models the interactions across controlboundaries and identifies sources of control conflicts, giving also an overview of experiences fromthe ELECTRA partners regarding the realization of controllers in demonstration and field testprojects. The work was carried out during the period from May to December 2014.The different type of flexibility resources, their characteristics, affecting market mechanisms andpotential for aggregation were researched using a survey among project partners. The parametersused to characterise flexibility include the amount of power modulation, the duration, the rate ofchange, the response time, the location, the availability, the controllability, etc. Views were alsoreceived how these parameters will develop until 2030 and what are the general trends fordevelopment of amount and controllability of this resource types. The parameters characterisingdifferent energy resources provide the technical requirements for their applicability to flexibleoperation of the grid and their suitability for frequency and voltage control now and in the future.Regarding the flexibility of electricity generation, gas turbines and other heat motors asreciprocating engines can be started quickest. The speed of power change is clearly the highest forheat motors and their minimum power is low. Also steam and combined heat and power plantscan be utilised in the relatively quick increasing of the electricity generation. Slower power changesare possible also with the nuclear power but they cannot be carried out continuously. Theregulation characteristics of hydro power are superb in comparison to the other electricitygeneration methods. Besides the sun power, wind power is increasing most quickly in the world inthe coming years. The modern wind power plants are able to active and reactive power control.Storage systems can contribute to the frequency and voltage control mechanisms. Charging anddischarging of the storage system at the right moments (response within milli-seconds to seconds)can help to preserve the balance between consumption and generation. Storages can also providesecondary and tertiary frequency control. Static compensation devices maintain desired voltagelevel by feeding the grid with necessary reactive power. FACTS devices and cross-borderconnections based on HVDC converter schemes can play an important role in frequency andvoltage support. Demand response, including industrial loads and household devices and electricvehicles, will have great influence in flexible operation of the grid.This report describes appropriate models that characterize the interactions across controlboundaries under normal and emergency situations, introducing suitable data rates and models ofuse by real-time control functions. In the future power system scheme, TSOs will be able to controlsignificantly smaller part of the generation compared to the traditional centralized configuration,and thus they will not be able any more to compensate large deviations in the power balance.Moreover, increased electricity loads and sources such as EVs and residential PV systems, willinfluence the balance between day-ahead production and consumption schedule and will leaveenergy markets with higher and less predictable need for balancing power. The actors involved inthe future grid control are balance responsible Party (BRP), cell system operator (CSO), celloperational information system (COIS), distribution system operator (DSO). Their respective rolesare described and these actors play roles both to technical and market operations. Considering theweb of cells concept developed in this project, the generation units will be smaller and in manycases these will be renewable resources which are less suitable for frequency control [1]. For thatreason a more important role for participation at the demand side will be expected for voltage andfrequency control in the future. The report describes “model based interfaces”, where the flexibilityuser and the flexibility contributor agree on a simplified model which describes the actual behaviourand constraints of the flexibility resource. Main outcomes of the work are the definition of controller conflict from a flexible power system perspective, a review of state of the art in power system control conflict and an outline of the methodology for identifying these conflicts during system operation and their impact on system stability. The report summaries the main findings from the literature and from project participant’s experience in terms of scenarios or examples of controller interactions resulting in conflict. A measure of controller conflict is presented for each example. This can be used as an indicator of the impact of controller conflict on system stability. Suggestions for resolving controller conflict arealso presented. The report describes the methodology proposed to construct such a dynamicmodel for the purposes of extracting conflicting interactions of interest from the point of viewfrequency and voltage stability. From the voltage stability perspective there are many factors whichmay significantly influence the environment for voltage stability. It seems quite certain, thatpossible conflicts affecting voltage stability may occur mainly due to lack of proper coordinationamong players in the system voltage control and reactive power reserves management which areTSOs, DSOs, Generators and Aggregators. Generally the scenery foreseen for frequency, voltageand reactive power control in 2030+ is much more complicated than it is presently.An overview of experiences from the ELECTRA partners regarding the realization of controllers indemonstration and field test projects are also provided. It summarizes best practices and lessonslearned which will provide valuable inputs for the implementation of control concepts and theirtesting and validation. The main requirements for controllers are reliability, fault tolerance androbustness.