Abstract
This paper proposes technical solutions that can be implemented in variable speed permanent magnet synchronous generators driven wind turbine systems aiming to mitigate high voltage problems in low voltage MicroGrids by controlling the active power output. Due to the limited control capability of these systems, controlling the output power to prevent voltage rise will require the local accommodation of the generation surplus. For this purpose, additional control functionalities are developed to be integrated in the control systems of the power electronic based interfaces. Their performance is evaluated through numerical simulations performed in Matlab (R)/Simulink (R) environment and considering the detailed models of the power electronic converters. The results obtained demonstrate the effectiveness of the proposed control functionalities.

Abstract
Under normal operating conditions, a MicroGrid is interconnected with the medium voltage network; however, in order to deal with black start and islanded operation following a general blackout, an emergency operation mode must be envisaged. A sequence of actions and conditions to be checked during the restoration stage are identified and tested through numerical simulation. Voltage and frequency control approaches, inverter control modes, and the need of storage devices are addressed in this paper in order to ensure system stability, achieve robustness of operation, and not jeopardize power quality during service restoration in the low voltage area.

Abstract
Large deployment of Plug-in Hybrid Electric Vehicles (PHEVs) will put new challenges regarding the power systems operation. The MicroGrid (MG) concept can be exploited to support the progressive integration of PHEVs into the Low Voltage (LV) networks by developing smart charging strategies to manage the PHEVs batteries charging procedures in order to avoid reinforcements in the grid infrastructures. Assuming that a number of PHEVs owners allow managing the batteries charging when their cars are parked, this paper proposes an approach that aims to find suitable individual active power set-points corresponding to the hourly charging rate of each PHEV battery connected to the LV grid. The Evolutionary Particle Swarm Optimization (EPSO) tool is used to find these active power set points. This requires an additional software module to be housed in the MV/LV secondary substation level, called Optimal Power Set-points Calculator (OPSC). © 2011 IEEE.

Abstract
This paper presents a general overview about the system operation, management and control following a large scale integration of renewable energy sources, focusing in particular the wind generation, both onshore and offshore. Regarding the operation of distribution networks, the integration of renewable energy sources and other distributed generation systems requires the adoption of active control and management structures. These structures will contribute to extend intelligence from the transmission to the distribution networks, aiming to change the operation paradigm from passive towards the smart grids vision for European networks of energy. The MicroGrid concept plays a key role in this context and has been exploited in order to support the progressive integration of electric vehicles, trying to avoid grid reinforcements. © 2011 IEEE.

Abstract
Large deployment of MicroGrids will have a considerable impact on the future operation of the electrical networks and will greatly influence the power system dynamics mainly at the Medium Voltage (MV) level whenever the upstream system has been lost. In dynamic studies the whole power system cannot be represented in a detailed manner because the huge system dimension would require a very large computational effort Therefore dynamic equivalents for MicroGrids need to be derived. The proposed approach is based on system identification theory for developing dynamic equivalents for MicroGrids, which are able to retain the relevant dynamics with respect to the existing MV network.

Abstract
The continuous growth of wind energy integration on electrical networks has led many utilities to impose fault ride-through capability to wind farms. This means that wind turbines must remain connected to the system during severe fault occurrence. Regarding the existing wind farms equipped with fixed speed induction generators directly connected to the grid, fault ride-through capability is commonly assisted with dynamic compensation devices, such as DSTATCOM units. These power electronic devices are controlled for voltage regulation purposes and behave like a balanced three-phase voltage source converter since commonly used control techniques are based only on the positive sequence of both voltage and current measured at its connection point. These control techniques are suitable only when compensation devices are operated under balanced conditions and therefore its performance when facing unbalanced faults needs to be evaluated. This paper tackles with this subject and the results obtained through numerical simulations demonstrate that over voltages can arise on non faulty phases leading to the wind farm disconnection.