Cost parameters for VSC HVDC transmission infrastructure have been gathered from an extensive collection of techno-economic sources. These cost parameter sets have been converted to a common format, based on a linear investment cost model depending on the branch length and the power rating of cable systems and converter stations. In addition, an average parameter set was determined as the arithmetic mean of the collected parameter sets, and included in the study. The uniform format allowed for a comparison of the parameter sets with each other, which revealed large differences between the cost parameter sets. The identified disparity between the parameter sets reflects a high level of uncertainty which can only in part be explained by a varying focus and modelling approach of their sources. This implies limitations regarding the validity of the parameters sets as well as of the results from grid expansion studies carried out on the basis of these parameter sets. Comprehensive cost reference data has been collected from realised and contracted VSC HVDC projects (back-to-back, interconnector, and offshore wind connection). The cost parameter sets have been evaluated against the reference project cost data. This evaluation has again shown large variations between the parameter sets. On average, the cost for back-to-back systems are slightly underestimated, interconnectors are overestimated, and offshore wind connections are heavily underestimated. To clearly state the validity and limitations of this comparison and evaluation, the applied methodology with its compromises and drawbacks is discussed in detail. Considering the interest in and momentum of offshore grid development, as well as the number of offshore grid investment and evaluation studies being conducted, both the availability of reliable cost reference data and the validity of investment model cost parameters need continuing attention

In this work a multi-objective model predictive control for reactive power management in transmission connected distribution grids with high share of wind power is presented. The proposed control utilizes reactive power capabilities of wind farms and tap-changer positions in order to improve distribution grid operation. Control signals namely tap-changer positions and reactive power set-points are smoothed over the forecast horizon. Further possible optimization objectives are power loss reduction, voltage profile smoothing and complying with reactive power exchange limits with the transmission grid. A mixed-integer non-linear optimal power flow problem (MINLP-OPF) is formulated incorporating grid operation limits. The performance is evaluated on a real German 110-kV distribution grid with 1.6 GW wind power for one year. With the proposed control, reactive power exchange within allowable limits is increased from 58.3% to 94.5%, compared to a reference operation where on ly tap-changer positions are utilized for loss reduction with a single time-step optimization

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In this publication, the authors present methodology and example results for the analysis of ancillary services of an offshore wind farm cluster and its electrical power system. Thereby the operation tool Wind Cluster Management System (WCMS) is used as simulation tool to evaluate certain planning scenarios. Emphasis is made on two topics: 1) the integration of high voltage direct current (HVDC) technology to the WCMS, 2) the ancillary service analysis. As examples, voltage source converter based HVDC (VSC-HVDC) and the provision of reserve respectively balancing power are discussed in detail. The analyzed study case considers the Kriegers Flak area while the associated power system connects wind farms to Sweden, Denmark and Germany.