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The connection of electronic power converters to the electrical network is increasing mainly due to\ud massive integration of renewable energy systems. However, the electrical dynamic performance of\ud these converters does not match the behavior of the network, which is mainly formed by generation\ud facilities based on big synchronous generation systems. Depending on the desired electrical operation\ud mode different control structures can be implemented in the converters in order to get adapted with the\ud grid conditions. However, changing between different control structures and operation is not an\ud optimal solution, as the resulting system results complex and is not highly robust. As an alternative,\ud this paper presents a new control technique for grid connected power converters based on the concept\ud of virtual admittance. The proposed control permits to emulate the electrical performance of\ud generation facilities based on classical synchronous generators with a power converter, with no need\ud of implementing different control structures, giving rise to a system that provides a friendly and robust\ud operation with the network.Peer ReviewedPostprint (published version

At the present time, distributed generation systems are required to disconnect from the main grid when there is an outage. In order to fulfill this requirement, photovoltaic (PV) power plants are equipped with anti-islanding algorithms, embedded in the converters controller, to avoid the island operation. However, the current trends in the development of the future electrical networks evidence that it is technically feasible and economically advantageous to keep feeding islanded systems under these situations, without cutting the power supply to the loads connected to the network. Nevertheless, commercial PV power converters are programmed as grid-feeding converters and they are unable to work in island mode if there is not an agent forming the grid. In order to overcome this problem, the synchronous power controller (SPC) is presented in this paper as a suitable alternative for controlling PV inverters. As will be further discussed, this controller permits PV plants to operate seamlessly in grid-connected and island mode, with no need of changing the control structure in either case. Moreover, the participation of SPC-based power converters integrating energy storage enables other grid-feeding systems to contribute to the grid operation in island conditions. The good results achieved with the SPC in different conditions will be shown in simulations, and also with experiments considering a real PV power plant combining SPC and commercial PV inverters.Index Terms-DC-AC power converters, distributed power generation, electric variables control, photovoltaic (PV) systems.

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Multi-terminal dc networks based on voltage source converters (VSC) are the latest trend in dc-systems; the interest in the area is being fueled by the increased feasibility of these systems for the large scale integration of remote offshore wind resources. Despite the active research effort in the field, at the moment, issues related to the operation and control of these networks, as well as sizing, are still uncertain. This paper intends to make a contribution in this field by analyzing the sizing of droop control for VSC together with the output capacitors. Analytical formulas are developed for estimating the voltage peaks during transients, and then it is shown how these values can be used to dimension the dc-bus capacitor of each VSC. Further on, an improved droop control strategy that attenuates the voltage oscillations during transients is proposed. The proposed methods are validated on the dc-grid benchmark proposed by the CIGRE B4 working group. Starting from the structure of the network and the power rating of the converters at each terminal, the output capacitors and the primary control layer are designed together in order to ensure acceptable voltage transients.(C) 2014 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author’s final draft