The widespread use of distributed generation (DG) relies on methods and techniques aimed at facilitating the network integration of DG. In this context a methodology for the evaluation of the quality and relative merits of these methods and techniques is missing. CIGRE Task Force C6.04.02, which is affiliated with CIGRE Study Committee C6, has addressed this problem by proposing a set of resource and network benchmarks. In the present paper, the benchmark for integrating DG in medium voltage distribution networks is described. The proposed benchmark is representative of a real network while it is also designed for ease of use. The application of the benchmark is described through several case studies that show the impact of DG on power flow and voltage profiles at the medium voltage level

The increase in the amount of generators based on renewable energy sources (RES) in the power system is leading to many changes in its operation. Since the RES depends on weather conditions, coordinating the operation of the entire power system has become a more complex issue. New challenges need to be faced in order to supply the electric energy to the customers at the appropriate quality level. In this paper the concept and architecture of a complex virtual power plant (VPP) will be introduced and discussed. The focus will be paid to the optimization of the structure of the VPP as well as to its optimal operation. The result of the optimization have been presented and discussed in the paper taking into account different operation scenarios.

The large dispersion of flexibility providing units among all voltage levels of the power system requires large, comprehensive grid models to assess the impact of flexibility usage during system operation. For this reason, aggregation methods are used to enable distributed concepts. This paper proposes a decentralized and hierarchical approach for the practical implementation of coordinated, vertical flexibility provision across multiple voltage levels, with the feasible operation region as an interface between adjacent grids. A top-down disaggregation process, based on a linear OPF model, is introduced in this paper. It is used during a flexibility provision request to distribute the requested operation point change to the underlying flexibility providing units. The objective function for this disaggregation process is chosen according to operational aspects. Both implemented methods for aggregation and disaggregation of flexibility consider grid constraints. The proposed concept is field tested during regular grid operation in a real distribution system. The results of the conducted studies show that accurate system operation in the more volatile distribution systems requires shorter time intervals compared to the transmission system. Good results with small control deviations were achieved by using time intervals of one minute for the MV and ten seconds for the LV level.

This paper uses a simulation to investigate the feasibility of applying low frequency AC (LFAC) transmission technology to connect large offshore wind farms to the onshore power system. Compared to the conventional AC transmission system with a power frequency of 50 or 60 Hz, the LFAC system can transfer more power through longer distance and with lower investment costs than the HVDC solution. Firstly, the characteristics of power cable operation at low frequency are discussed. Then a grid connection of an offshore wind farm based on a doubly fed induction generator (DFIG) through LFAC is studied. The simulation results show that there are no difficulties for the wind farm based DFIG when it operates at low frequency. Moreover, the reactive power control at the line side of DFIG can be applied to improve the operation of the cable.

In an effort to protect the environment despite the projected development of the electrical power system, the European community is focusing on a significant increase in the installed wind power capacity up to the level of 300 GW by the year 2030 throughout Europe. Most of the planned installations - about 150 GW - are going to be realized in the offshore sector, a large part of which will be located in the North Sea. Such development will lead to new challenges regarding integration of the bulk offshore wind power into the power systems and will require a comprehensive analysis concerning various aspects such as optimal planning and operation taking into account new concepts, as multi-terminal VSC HVDC. In this paper the establishment of a test system for analysis of the offshore DC grid behavior is proposed taking into account the recent structural and technological concepts on this field as well as the national plans. Hence, in the first step the configuration of the analyzed offshore grid was defined, which includes a mix of AC and DC system. Further, the assumptions for the system parameters will be discussed and the implementation of this test system into a power system simulator as well as some exemplary calculations will be shown.