Abstract
This paper addresses the provision of frequency control services with multi-terminal HVDC grids interconnecting several asynchronous AC control areas and integrating offshore wind farms. Regarding the operational performance of the multi-terminal HVDC grid, it is discussed and proposed a communication-free regulation scheme that allows these type of infrastructures to actively participate in primary frequency regulation services and provision of inertial emulation capabilities among the non-synchronous areas. Additionally, the proposed control scheme is extended such that offshore wind generators can also actively provide inertia and primary frequency control to the mainland AC grid. The main rational of the proposed control scheme relies of a cascading control mechanism based on the modulation of active power as a function of the frequency in the HVDC converter stations connected to mainland AC grids and on the control of the frequency in the HVDC converters associated to offshore wind farms. The DC grid voltage variations resulting from this principle is used as a natural communication channel to develop the control loops to be used in all the converter stations. The effectiveness of the proposed strategy is illustrated in the case of two non-synchronous areas linked by a multi-terminal HVDC system connecting two offshore wind farms.

Abstract
This study presents a methodology for siting and sizing static synchronous compensator (STATCOM) devices in the Portuguese transmission system in order to improve system security following severe grid faults. Security issues arise since the Portuguese transmission system incorporates significant levels of wind generation without fault ride through and reactive current injection capabilities during grid faults. As the transmission system operator (TSO) is responsible for assuring system security, the goal of the study is to take advantage of the proved STATCOM ability for injecting reactive current in order to mitigate the disconnection of large amounts of wind farms in case of severe grid faults. The proposed methodology was developed and tested in coordination with the Portuguese TSO and it is based on the formulation of an optimisation problem in order to minimise the installed STATCOM power while ensuring its compliance with the current grid code requirements, namely in what concerns to the system stability and security. Given the discrete and complex nature of the problem, a hybrid approach, combining both a heuristic method and an evolutionary particle swarm optimisation (EPSO) algorithm was developed. Results show the effectiveness of the proposed methodology as well as its robustness regarding the validity of the obtained solutions while facing the most severe operational scenarios.

Abstract

Abstract
In the decades to come spatial limitation poses a major challenge for islands, especially where tourism dominates and many heritage and natural conservation sites exist. Simultaneously, alternatives to lower energy import dependency are sought. Since onshore technologies are confronted by spatial limitation, the focus might shift towards integrating offshore technologies. Although most of those technologies lack market maturity, the benefit to be installed (far) off the coast is immense. Yet, it is a challenge to select the most appropriate technology for any given site location. Thereby, it is not pre-dominantly a matter of economic and environmental concerns, rather than an assessment of site conditions and resource characteristics. A set of indicators for, both, conditions and characteristics has been established that allows pre-selecting and comparing the suitability of various offshore technologies. Hence, energy planners will be able to select from the most appropriate technologies when planning for a sustainable future. © 2015 Taylor & Francis Group, London.

Abstract
Photovoltaic (PV) solar power capacity is growing in several countries, either concentrated in medium/large size solar parks or distributed by the medium and low voltage grid. Solar power forecasting is a key input for supporting grid management, participation in the electricity market and maintenance planning. This paper proposes a new forecasting system that is a hybrid of different models, such as electrical and statistical models, as well as different Numerical Weather Prediction (NWP) sources. The time horizon is 48 hours ahead. The proposed model was operationalized and tested in a real PV installation located in North Portugal with 16 kW.

Abstract
The current literature in wind power forecast is focused in generating accurate uncertainty forecasts and communicating this information to the end-user. Multi-temporal decision-making problems require information about the temporal trajectory of wind power for the next hours. Presently, this information is provided through a set of temporal trajectories (or scenarios). This paper aims at contributing with an alternative approach for communicating this information through simultaneous prediction intervals. These intervals include the temporal dependency of forecast errors since they provide information about the probability of having the observed wind power trajectory fully inside the quantiles forming the interval. First, a learning sample of temporal trajectories are generated with the Gaussian copula method and using the marginal prediction intervals. Then, two methods proposed in the literature are used to construct the simultaneous intervals. The quality of these intervals is evaluated for three real wind farms.