Abstract

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
Voltage imbalances are one of the most severe challenges in electrical networks, which negatively affect their loads and other connected equipment. This paper proposes a voltage support control strategy to mitigate the voltage imbalance in inverter-based low voltage distribution networks. The control scheme is derived taking in mind the following control objectives: a) to increase the positive sequence voltage as much as possible, b) to decrease the negative sequence voltage as much as possible, c) to inject the power generated by the primary source, and d) to minimize the output current of the inverter. The innovative contribution of the proposed solution is based on the design of a control algorithm that meets the aforementioned objectives without resorting to communications with other grid components. The theoretical results are experimentally validated by selected tests on a laboratory setup with X/R ratio close to one.

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.