Control and management systems of distribution Smart Grids based on distributed and decentralized architectures

The reference frame of this research is the radical transformation of electrical systems which are evolving toward smart grids. The main motivations behind this development are political and technical in nature including the growth of energy demand, environmental problems, international climate agreements, the diffusion of distributed generation and the diffusion of new components and new technologies, including electric energy storage systems. A contribution to this evolution is the increase of Distributed Generation (DG) from Renewable Energy Sources (RESs) as a form of energy production with zero emissions. In this new scenario, the distribution systems completely change their role and functions, gradually moving from "passive" networks, in which energy flows from the transmission system to the distribution nodes of consumption, to "active" networks", in which the consumer becomes also producer, with consequent bi-directional power flows along the distribution feeders. As the grid has changed compared to traditional operation, new technical problems have emerged, and in particular the voltage control in this new type of grid has been tackled in recent years. In fact, the DGs mainly use "intermittent" RESs which can cause sudden and rapid variations of the power injections thus inducing over/under voltages. Conventional voltage regulation relies on transformer on-load tap-changers in HV/MV substations, step voltage regulators and capacitor banks, which have slow response times. It is therefore necessary to identify new devices, management tools and control strategies in the evolving distribution systems. At the same time, an important issue to consider is the need for economic solutions, which allow to improve the flexibility of existing networks, allowing for a large increase Distributed Energy Resources (DERs), but at the same time require acceptable investments. In this research, taking note of the imminent and necessary evolution of the electricity system, a solution is sought to the problem of optimizing the voltage, starting from a modeling of the system itself, and arriving at control via a decentralized approach with different methodologies. Summarizing, the three main topics treated in this Thesis are: • PART I: the evolution of the traditional electrical systems toward Smart Grids; • PART II: the Distribution System linear modelling, both exact and approximated with and without losses; • PART III: the voltage optimization problem in Smart Distribution Grids using the distributed and decentralized approaches in three different ways. In particular, after studying the characteristics of different control structures, the decentralized approach is preferred, where the distribution system is usually divided into voltage control zones. This approach ensures the optimal solution for each Voltage Control Zone (VCZ) and requires a light communication infrastructure. To model the distribution system, in the presence of DER, after representing it through the equivalent circuit, we started from the branch, considering three different types of modeling. The exact one, the linearized one and the linearized one with losses. By merging more branches, it is obtained the feeder modeling, with and without losses. Finally, the modeling of the lateral is carried out, with and without losses, Finally, a structural load flow algorithm is defined to calculate the Sensitivity Matrices of the Powers to the Injected Powers, Sensitivity Matrices of the Voltages to the Injected Powers and Sensitivity Matrices of the Voltages to the Voltage Regulators. In the last part of this research, the problem of optimizing voltage in distribution networks is tackled adopting the decentralized approach with different methodologies: the alternate direction multiplier method (ADMM) and the auxiliary problem principle (APP). Finally, the problem of optimizing voltage profiles in energy distribution networks has been tackled with a two-step procedure in which traditional and innovative controllers are integrated. Therefore, after an analysis of the reasons that are leading the system to evolve, the problem of optimizing voltage in smart distribution networks is addressed. A method has been defined for modeling the system itself both in the presence and absence of losses, starting from the brach, to the feeder up to the lateral. The control and management of this new system is achieved with the decentralized approach with different methodologies. Concluding with numerical tests on distribution test networks to demonstrate the effectiveness of the proposed tools.