Integration of Distributed Energy Resources and provision of Ancillary Services: control strategies for Microgrids and Electric System management

Nowadays, the expansion of the electric power systems is globally heading towards a more sustainable and reliable development. The increasing interest for an environmentally conscious and sound use of the available assets is fostering the penetration of the renewable energy sources (RES), bringing significant benefits to economy and society, as: the reduction of the greenhouse gases emissions; public health improvement; more stable energy prices; the diversification of the energy supply; and more efficient and resilient electric grids. The transmission and distribution grids, once dominated by conventional fossil fuel-fired power plants, are now experiencing important transformations. Renewable resources, especially wind and solar, are displacing the traditional thermal generation, leading to considerable changes in the power systems dynamic behavior. The growing number of inverter-based devices connected to the grid, that have a great impact on the stability of the electric networks, as well as the variability, unpredictability and intermittency which characterize the RES, are posing new challenges to the system operators. As opposed to synchronous generators, which inherently provide inertia to the system, renewable power plants are usually decoupled from the grid through power electronic converters, causing critical stability issues in terms of voltage control, load balancing and frequency regulation. The recent developments in the information and communication technologies, as well as the wide spread of intelligent measurement devices, are contributing to improve the performance of the power system operation and leverage the opportunities coming from the exploitation of the new assets and the great amount of available data. Moreover, notable changes are also occurring on the demand side, as advanced digital technologies and control strategies are fostering their active participation to the system management and to a more inclusive and competitive electric market. The present thesis addresses the issue of the energy transition and the consequent significant transformation that the power systems are currently undergoing, focusing on the possible solutions that can be implemented in order to face the increasing challenges and take full advantage of the electric grid available resources. The aim of this study is providing both a general overview of the recent technological developments that have characterized the global evolution of the electric power systems in the last decades, as well as a more detailed description of the advanced control algorithms, regulation logics and innovative strategies that can be implemented for their optimal management. In particular, the focus will be on the efficient exploitation of renewable energy sources, electric storage devices and controllable loads. The thesis is structured considering the different trends and innovations that have taken place in the transmission systems, and the advanced management techniques and technological developments that have had a significant impact on the distribution systems. After a thorough introduction of the present electric networks and energy markets design and operation given in Chapter 1, Chapter 2 and Chapter 3 focus on the integration and exploitation of the new assets available at the transmission level, while Chapter 4 and Chapter 5 investigate the modern control methods and operation management strategies implemented at the distribution level. In particular, the chapters are organized as follows: in Chapter 2, different load control strategies for the provision of frequency regulation services are illustrated, tested and discussed; Chapter 3 deals with the integration of wind power plants and their potential contribution to the system reliability; Chapter 4 presents the design, implementation and operation of an optimization platform for distribution networks management; Chapter 5 describes an Energy Resources Management technique applied to the controllable assets of a Microgrid; the overall conclusions and final remarks are reported in Chapter 6. The present work is the outcome of the scientific research that I developed during the three years long Ph.D. program that was in collaboration with and funded by ABB S.p.A.