Microgrids are considered one of the most promising solutions to integrate renewable distributed generation into the electric power system. During the last decade, the microgrid concept has been studied and developed and nowadays it is becoming a reality. Hence, in the coming years a transformation of the current electric power system to a multi-microgrid power system can be expected. In this direction, the study of multi-microgrids is currently being explored. Accordingly, this paper examines the possible multi-microgrid architectures to form a grid of microgrids. For this purpose, the microgrid as a single entity and its possible interactions with external grids is first defined. Then, the possible multi-microgrid architectures are defined in terms of layout, line technology and interface technology. Finally, a comparison between the different architectures is performed in terms of cost, scalability, protection, reliability, stability, communications and business models. This analysis is expected to be of great utility for grid planners and policy makers, who can select the most adequate architecture in function of their necessities.

This paper analyses, from a steady state point of view, the potential benefit of a Wind Power Plant (WPP) control strategy whose main objective is to maximise its total energy yield over its lifetime by taking into consideration that the wake effect within the WPP varies depending on the operation of each wind turbine. Unlike the conventional approach in which each wind turbine operation is optimised individually to maximise its own energy capture, the proposed control strategy aims to optimise the whole system by operating some wind turbines at sub-optimum points, so that the wake effect within the WPP is reduced and therefore the total power generation is maximised. The methodology used to assess the performance of both control approaches is presented and applied to two particular study cases. It contains a comprehensive wake model considering single, partial and multiple wake effects among turbines. The study also takes into account the Blade Element Momentum (BEM) theory to accurately compute both power and thrust coefficient of each wind turbine. The results suggest a good potential of the proposed concept, since an increase in the annual energy captured by the WPP from 1.86% up to 6.24% may be achieved (depending on the wind rose at the WPP location) by operating some specific wind turbines slightly away from their optimum point and reducing thus the wake effect. (C) 2015 Elsevier Ltd. All rights reserved.

The recent increase of intermittent power generation plants connected to the electric power grids may stress the operation of power systems. So, grid codes started considering these power plants should contribute to the grid support functions. Recently, a power ramp rate limitation is being included in several grid codes, which is a challenge for photovoltaic installations due to the lack of inertia. This paper presents a method to deal with the main grid code requirements considering a PV plant with an energy storage device, where a strict two-second time window ramp rate restriction is applied. A direct ramp rate control strategy is used, which includes a dynamic SOC control and battery support functionality for active power setpoint compliance. The control strategy is validated by simulations. (C) 2016 Elsevier Ltd. All rights reserved.

As a consequence of technological progress, wind power has emerged as one of the most promising renewable energy sources. Currently, the penetration level of wind energy in power systems has led to the modification of several aspects of power system behaviour including stability. Due to this large penetration, transmission system operators have established some special grid codes for wind farms connection. These grid codes require wind farms to provide ancillary services to the grid such as frequency regulation and reactive power regulation. In the near future, the capability of damping system oscillations will be required. For this reason, the influence of grid-connected wind farms on system oscillations is reviewed in this paper, focusing on the contribution or damping of power system oscillations, and on inner wind turbine oscillations. (c) 2012 Elsevier Ltd. All rights reserved.