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
A fully operational multiterminal dc (MTDC) grid will play a strategic role for mainland ac systems interconnection and to integrate offshore wind farms. The importance of such infrastructure requires its compliance with fault ride through (FRT) capability in case of mainland ac faults. In order to provide FRT capability in MTDC grids, communication-free advanced control functionalities exploiting a set of local control rules at the converter stations and wind turbines are identified. The proposed control functionalities are responsible for mitigating the dc voltage rise effect resulting from the reduction of active power injection into onshore ac systems during grid faults. The proposed strategies envision a fast control of the wind turbine active power output as a function of the dc grid voltage rise and constitute alternative options in order to avoid the use of classical solutions based on the installation of chopper resistors in the MTDC grid. The feasibility and robustness of the proposed strategies are demonstrated and discussed in the paper under different circumstances.

Abstract
Current electrical distribution systems are facing significant challenges due to the widespread deployment of Distributed Energy Resources (DER), particularly the integration of variable Renewable Energy Sources (RES). This requires a change in the paradigm of distribution grids from a purely passive perspective into fully active networks within the smart grid vision. This new paradigm involves new control and management architectures as well as advanced planning methods and operational tools for distribution systems exploiting a smart metering infrastructure. This infrastructure will enable leveraging data from smart meters and short-term forecasts of load demand and RES in order to manage the distribution system in a more efficient and cost-effective way, thus enabling large scale integration of RES. Future tests to be carried out in a new, state of the art laboratory environment will bring additional added-value to the validation of the proposed concepts and tools.

Abstract
The development of the Smart Grid (SG) concept is the pathway for assuring flexible, reliable and efficient distribution networks while integrating high shares of Distributed Energy Resources (DER): renewable energy based generation, distributed storage and controllable loads such as Electric Vehicles (EV). Within the SG paradigm, the Microgrid (MG) can be regarded as a highly flexible and controllable Low Voltage (LV) cell, which is able to decentralize the distribution management and control system while providing additional controllability and observability. A network of controllers interconnected by a communication system ensures the management and control of the LV microgrid, enabling both interconnected and autonomous operation modes. This new distribution operation philosophy is in line with the SG paradigm, since it improves the security and reliability of the system, being able to tackle the technical challenges resulting from the large scale integration of DER and provide the adequate framework to fully integrate SG new players such as the EV. By exploiting the MG operational flexibility and controllability, this chapter aims to provide an extended overview on MG self-healing capabilities, namely on its ability of operating autonomously from the main grid and perform local service restoration. The MG hierarchical management and control structure is revisited and adapted in order to exploit the flexibility of SG new players, like the EV and flexible loads and integrate smart metering infrastructures. The implementation of the MG architecture and communication infrastructure in a laboratorial facility is also presented and used to validate the MG self-healing capabilities. © 2014, Springer Science+Business Media Singapore.

Abstract
Microgrids are assumed to be established at the low voltage distribution level, where distributed energy sources, storage devices, controllable loads and electric vehicles are integrated in the system and need to be properly managed. The microgrid system is a flexible cell that can be operated connected to the main power network or autonomously, in a controlled and coordinated way. The use of storage devices in microgrids is related to the provision of some form of energy buffering during autonomous operating conditions, in order to balance load and generation. However, frequency variations and limited storage capacity might compromise microgrid autonomous operation. In order to improve microgrid resilience in the moments subsequent to islanding, this paper presents innovative functionalities to run online, which are able to manage microgrid storage considering the integration of electric vehicles and load responsiveness. The effectiveness of the proposed algorithms is validated through extensive numerical simulations.

Abstract
The concerns about global warming (greenhouse-gas emissions), scarcity of fossil fuels reserves, and primary energy independence of regions or countries have led to a dramatic increase of renewable energy sources (RES) penetration in electric power systems, mainly wind and solar power. This created new challenges associated with the variability and uncertainty of these sources. Handling these two characteristics is a key issue that includes technological, regulatory, and computational aspects. Advanced tools for handling RES maximize the resultant benefits and keep the reliability indices at the required level. Recent advances in forecasting and management algorithms provided means to manage RES. Forecasts of renewable generation for the next hours/days play a crucial role in the management tools and protocols of the system operator. These forecasts are used as input for setting reserve requirements and performing the unit commitment (UC) and economic dispatch (ED) processes. Probabilistic forecasts are being included in the management tools, enabling a move from deterministic to stochastic methods, which conduct to robust solutions. On the technological side, advances to increase mid-merit and base-load generation flexibility should be a priority. The use of storage devices to mitigate uncertainty and variability is particularly valuable for isolated power system, whereas in interconnected systems, economic criteria might be a barrier to invest in new storage facilities. The possibility of sending active and reactive control set points to RES power plants offers more flexibility. Furthermore, the emergence of the smart grid concept and the increasing share of controllable loads contribute with flexibility to increase the RES penetration levels. (C) 2013 John Wiley & Sons, Ltd.