Abstract
It is now more than a decade since distributed generation (DG) began to excite major interest amongst electric power system planners and operators, energy policy makers and regulators as well as developers. This paper presents an overview of the key issues concerning the integration of distributed generation into electric power systems that are of most interest today. The main drivers behind the focus on DG integration, especially of the renewable type, in many countries around the world are discussed. A synopsis of the main challenges that must be overcome in the process is presented. Particular emphasis is placed on the need to move away from the fit and forget. approach of connecting DG to electric power systems to a policy of integrating DG into power system planning and operation through active management of distribution networks and application of other novel concepts. The paper also analyses the repercussions in transmission system operation and expansion that result from the connection of large amounts of DG of different energy conversion systems focusing on issues related with impacts in steady state operation, contingency analysis, protection coordination as well as dynamic behaviour analysis. A discussion on the possibility of provision of ancillary services by DG is also included. Some results from studies performed in the interconnected Portuguese transmission system are presented and discussed. Some of the opportunities that could be exploited in support of the integration and hence greater penetration of DG into electric power systems are also explored.

Abstract
This paper proposes a control scheme that allows doubly fed induction wind generators (DFIWG) to participate effectively in system frequency regulation. In this control approach, wind generators operate according to a deloaded optimum power extraction curve such that the active power provided by each wind turbine increases or decreases during system frequency changes. The control strategy defined at the wind generator to supply primary frequency regulation capability exploits a combination of control of the static converters and pitch control, adjusting the rotor speed and the active power according to the deloaded optimum power extraction curve. Results obtained in a small isolated system are presented to demonstrate the effectiveness of the approach.

Abstract
This paper presents an optimization strategy to be adopted at wind park control level. This approach transposes the classical formulations of a unit commitment and a generator dispatch problem to the turbines of a wind park, assuming that variable speed wind turbines are installed, and considering that wind speed forecasts are available. Wind speed forecasts, demands from grid operators or generation levels defined to comply with market strategies are the inputs of the problem. A small example is used to illustrate the proposed approach.

Abstract
In this paper the main parameters to assess the power quality of grid embedded wind farms are presented. International standards to assess and quantify the power quality of grid connected wind turbines exist for some years now, and are here extrapolated to wind farms. aggregates when possible being the correspondent methodologies identified in the document. Recently, the grid code requirements posed a novel challenge to this technologic area, particularly since they were issued with national or local objectives and without particular normalized global concerns. The form how the international standards are evolving in order to cope both with the power systems industry local requirements, but also with the global wind turbine manufacturers principles is addressed in the paper.

Abstract
In this paper the existing technical barriers that prevent the accomplishment of a very high wind generation penetration in a power system are presented. Since several countries and regions in Europe are already experiencing such high wind penetration or, as a minimum, planning their grids and operation strategies to cope with wind penetration from a high to a very high level, the solutions already identified for the most common constraints are also identified.

Abstract
This paper presents a formulation for an Optimal Power Flow problem that includes the DFIG wind generator reactive power characteristics in order to obtain set points that consider wind turbines loading capabilities. This approach can be adopted at the wind park control level to define the active and reactive set points following requests from the wind park dispatch centers.