Abstract

Abstract
This paper proposes a "grey-box" dynamic equivalent model for medium voltage active distribution networks, taking into account a heterogeneous fleet of generation technologies alongside the latest European grid codes requirements. It aims to properly represent the transient behavior of the system upon large voltage disturbances in the transmission side. The proposed equivalent model is composed by four main components: two equivalent generation units, one for converter-connected units' representation, and another accounting for the synchronous generation units' portfolio; an equivalent composite load model; and a battery energy storage system, also converter-connected to the grid. The model's parameters are estimated by an evolutionary particle swarm optimization algorithm, by comparing a fully-detailed model of a medium voltage distribution network with the equivalent model's frequency domain's responses of active and reactive power flows, at the boundary of distribution-transmission interface substation.

Abstract
This paper addresses the stability analysis of a real island power system following the transformation occurring in the generation portfolio: from a 100 % synchronous-generation-based system (associated to a fleet of diesel generators) to a hybrid power system dominated by power electronics converters. The integration of a battery-wind-photovoltaic power plant in the island creates the necessary conditions for operating the system without synchronous units scenarios with a system dominated by power electronics - or, at least to minimize its use - scenarios with a reduced number of synchronous units in operation. The possibility of operating the system under these conditions is assured by grid-forming inverters connected to battery energy storage systems, that are responsible for performing frequency and voltage control tasks either in parallel with synchronous units or when synchronous units are disconnected. The resulting transient stability issues for the aforementioned operational scenarios are discussed and evaluated through dynamic simulations.

Abstract
The progressive decommissioning of large synchronous generators that should take place in face of increasing penetration ratios of Distributed Generation (DG) will demand additional control mechanisms for inertia provision and frequency and voltage regulation in the power system. The need to cope with increasing penetration ratios of DG in distribution grids, added to the necessity to integrate an expected massification of EV and distributed ESS, and to the necessity to enhance Power System resilience and controllability, makes the Smart-Transformer (ST) a suitable solution. In this paper it is demonstrated the feasibility of the ST to contribute to frequency control through the control of the resources available in the distribution AC/DC hybrid networks created from the ST. The feasibility of local droop controllers, acting on frequency and voltage magnitude of the AC/DC hybrid networks created from the ST, to achieve the aforementioned goal, is demonstrated through computational simulation.

Abstract
The decarbonization of the economy, for which the contribution of power systems is significant, is a growing trend in Europe and in the world. In order to achieve the Paris Agreement's ambitious environmental goals, a substantial increase in the contribution of renewable sources to the energy generation mix is required. This trend brings about relevant challenges as the integration of this type of sources increases, namely in terms of the distribution system operation. In this paper, the challenges foreseen for future power systems are identified and the most effective approaches to deal with them are reviewed. The strategies include the development of Smart Grid technologies (meters, sensors, and actuators) coupled with computational intelligence that act as new sources of data, as well as the connection of distributed energy resources to distribution grids, encompassing the deployment of distributed generation and storage systems and the dissemination of electric vehicles. The impact of these changes in the distribution system as a whole is evaluated from a technical and environmental perspective. In addition, a review of management and control architectures designed for distribution systems is conducted. This article is categorized under: Energy Infrastructure > Systems and Infrastructure Energy Infrastructure > Economics and Policy

Abstract
The large scale integration of electric vehicles and distributed energy resources on low voltage grids might cause serious problems related to, for instance, under/over voltages and line overloading. In order to cope with these problems, this paper presents a multi agent system (MAS) developed to dynamically schedule flexible loads on low voltage grids, preventing operation limit violations. Since different geographical positions of the loads in the grid will cause a different impact on the grid, load flow calculations are used to indicate operation limit violations. The application uses a decentralized algorithm which ensures similar chances of being scheduled to the customer loads using a priority scheme. A case study is carried out on a 70-bus feeder where electric vehicle loads are scheduled to prevent under voltages, showing the applicability of the approach.