6 EVOLUTION OF THE ELECTRICITY DISTRIBUTION NETWORKS
6.3 Operation of the future electricity distribution networks
The operation and control of the ADNs and the microgrids is a complex task involving several stakeholders and actors. The stakeholders are considered system actors (or are affected by the operation of the system) having expectations, such as economic or social benefits. Further, actors can be personal roles and systems, devices, software, and events, which perform operations that change the system’s state, for example.
Various scenarios should be modelled and analysed based on the electricity distribution evolution and the network’s operational targets. The UC analysis helps to identify and analyse the network operations and functions and visualise the interactions between the network actors.
Publication VIII presents a comprehensive UC analysis for the microgrid concept.
The UC modelling and analysis method and a tool (Enterprise Architect) were utilised for microgrid management analysis top-down, from an abstract/concept level closer to practice. First, the general microgrid functions were presented as HL-UCs defining the microgrid functions, regardless of the practical solution.
Further down, PUCs were developed for the Sundom Smart Grid, and finally, TUCs of DR and overcurrent (OC) protection of the Sundom case study with real-time simulation. Regarding the different UC levels, the relationship between the concept and the functionality was emphasised with a microgrid management analysis case study. Figure 31 presents the UC analysis’ method application.
Figure 31. Functional analysis method for the microgrid concept. Adapted from (Publication VIII).
The TUCs were applied to the Sundom Smart Grid with measured data, including the previously developed a reactive power flow controller for the WT converter and the schematically developed DR controller for the household loads. These AS UCs were tested in the SIL co-simulation setup in the phasor and EMT platform with one-year measurement data. Also, protection case studies were analysed based on the CHIL test with the EMT platform.
The management system for the ADNs and microgrids is formed from different subsystems, that is, “a system of systems”, taking care of the operational targets.
To recognise, analyse and realise the different levels of functions that can affect each other, a methodology for expressing the system's functions like those presented in Publication VIII is needed. For example, a case study can be developed to analyse residential customers who own the inverter-connected generation and controllable loads aiming to participate in different ASs. As demonstrated (TUCs) in Publication VIII, the customer’s ASs provision options can be both system-wide and local – DR programmes for the TSO and reactive power management for the DSO, controlled simultaneously by different stakeholders.
The potential entities can be detected by utilising this kind of functional analysis to develop or improve the concrete ADNM solutions. For applying the microgrid concept to the real case management system, the publication suggests that HL-UCs and PHL-UCs should be specified, considering only the specific application requirements. TUCs for real-time simulations and testing is appropriate to prepare models, simulations and testing plans. Multi-objective control of microgrids puts pressure to develop management system test cases in a central, distributed, comprehensive, and dedicated manner, as shown in Publication VIII. In the future, different configurations regarding the depth of UCs needed, and a time-domain
analysis should be used to examine various microgrid functions running in parallel.
This thesis defines the following terms for the ADNM, based on Publication VIII and Figure 18:
A technical concept is an innovation described, planned or implemented. An ADN concept can be a microgrid or a VPP, for example.
An ADNM high-level concept can be microgrid management or DR programmes.
Application is a concept’s real-life utilisation.
Operation is the method by which a device or system performs its function. ADN operation refers to a concept(s) of multiple systems working together to achieve the operational target, which can be set economic, technical, or environmental. A high-level technical target can be improving power quality and power supply reliability, economic target to minimise operational cost, and environmental target to reduce carbon footprint. Power quality assurance and improvement refer to the functionalities to manage voltage amplitude and frequency. Power supply reliability refers to the functionalities to manage the failures in the power system, by asset and protection management, for example.
Functionality is a set of functions implemented through the control and management systems. An ADNM functionality can be voltage regulation or active and reactive power control.
A function is a multi-level term, which describes what an element does or for what it is used
A method means a process by which a task is completed, whereas a procedure means a particular method for performing a task.
Publication IX presents a method for analysing the evolution of the distribution networks holistically. The analysis utilises the UML, and it consists of the dynamic descriptions of network operations and the static illustrations of the actors and their relationships. The dynamic descriptions are the systems’ behavioural descriptions, the operational scenarios by UC stories and modelling. The static relationships among classified actors illustrate the network structure, the communications between the actors operating the system described by the class diagrams. A class diagram is the system’s backbone and points out attributes (values), operations (the processes, which a class executes) of a particular class, generalisations, and constraints connecting the classes.
Four distribution network evolution phases: Traditional, Self-sufficient, Microgrid and Intelligent Microgrid Network were defined. Further, their operation and structure were modelled and analysed by a UML tool with the Sundom Smart Grid case study. The analysis is based on the network’s normal state operation, which are energy management and power balance management and the network disturbance situations, which are OC fault situations. Publication IX presents the evolving network operations through the developed HL-UCs and PUCs by the UC descriptions and the evolving network structure through the classified actors and their associations with the class diagrams.
The generated method, graphical models of the ADNM schemes and the microgrid control functionalities in Publication IX can be applied for: a) scenario building in roadmap development, b) creating a common understanding of the distribution system operation, c) real-time simulations, d) management system development, and e) developing and analysing several parallel running control algorithms of distributed energy resources for ASs in the developing distribution networks, for example.