Detailed requirements and constraints for the control of flexibility

Abstract

This Electra internal report includes the work of Task T6.1 describing the nature, availability and contribution of flexibility resources. This task also models the interactions across control boundaries and identifies sources of control conflicts, giving also an overview of experiences from the ELECTRA partners regarding the realization of controllers in demonstration and field test projects. The work was carried out during the period from May to December 2014. The different type of flexibility resources, their characteristics, affecting market mechanisms and potential for aggregation were researched using a survey among project partners. The parameters used to characterise flexibility include the amount of power modulation, the duration, the rate of change, the response time, the location, the availability, the controllability, etc. Views were also received how these parameters will develop until 2030 and what are the general trends for development of amount and controllability of this resource types. The parameters characterising different energy resources provide the technical requirements for their applicability to flexible operation 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 as reciprocating engines can be started quickest. The speed of power change is clearly the highest for heat motors and their minimum power is low. Also steam and combined heat and power plants can be utilised in the relatively quick increasing of the electricity generation. Slower power changes are possible also with the nuclear power but they cannot be carried out continuously. The regulation characteristics of hydro power are superb in comparison to the other electricity generation methods. Besides the sun power, wind power is increasing most quickly in the world in the 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 and discharging 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 provide secondary and tertiary frequency control. Static compensation devices maintain desired voltage level by feeding the grid with necessary reactive power. FACTS devices and cross-border connections based on HVDC converter schemes can play an important role in frequency and voltage support. Demand response, including industrial loads and household devices and electric vehicles, will have great influence in flexible operation of the grid. This report describes appropriate models that characterize the interactions across control boundaries under normal and emergency situations, introducing suitable data rates and models of use by real-time control functions. In the future power system scheme, TSOs will be able to control significantly 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, will influence the balance between day-ahead production and consumption schedule and will leave energy markets with higher and less predictable need for balancing power. The actors involved in the future grid control are balance responsible Party (BRP), cell system operator (CSO), cell operational information system (COIS), distribution system operator (DSO). Their respective roles are described and these actors play roles both to technical and market operations. Considering the web of cells concept developed in this project, the generation units will be smaller and in many cases these will be renewable resources which are less suitable for frequency control [1]. For that reason a more important role for participation at the demand side will be expected for voltage and frequency control in the future. The report describes “model based interfaces”, where the flexibility user and the flexibility contributor agree on a simplified model which describes the actual behaviour and 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 are also presented. The report describes the methodology proposed to construct such a dynamic model for the purposes of extracting conflicting interactions of interest from the point of view frequency and voltage stability. From the voltage stability perspective there are many factors which may significantly influence the environment for voltage stability. It seems quite certain, that possible conflicts affecting voltage stability may occur mainly due to lack of proper coordination among players in the system voltage control and reactive power reserves management which are TSOs, DSOs, Generators and Aggregators. Generally the scenery foreseen for frequency, voltage and 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 in demonstration and field test projects are also provided. It summarizes best practices and lessons learned which will provide valuable inputs for the implementation of control concepts and their testing and validation. The main requirements for controllers are reliability, fault tolerance and robustness.