A method to determine the optimal transmission system topology for multiple offshore wind farms is introduced using a rule-based generic algorithm. The methodology is implemented as a software tool determining the best economical and technically feasible offshore transmission solution. The optimization algorithm takes radial, ring shaped, and meshed transmission topologies into consideration. Besides the investments for the offshore grid also new connections or reinforcements in the existing onshore grid are proposed by the algorithm. The developed tool delivers a set of transmission system topologies ranked after their life cycle system costs with their corresponding transmission voltage and technology (HVAC or HVDC), the necessary transmission equipment, and its rating. The optimization results are based on publicly available data. The achieved results are compared with other studies and validated. The developed tool can be used in the planning phase as a guidance for offshore developers with investment decisions and for long-term offshore grid planning, e.g., towards an offshore supergrid.

This paper proposes voltage control and reactive power support with direct-drive synchronous machines in wind turbines during normal operation and transient events. The wind turbines are equipped with voltage and reactive power control for normal operation and undervoltage ride-through modes for voltage dips. The wind turbine contributions are evaluated both for theoretical test cases as well as for two specific locations in the Belgian grid. Simulations reveal that the preferred mode for voltage support during a voltage dip depends on the grid characteristics short-circuit power and X-R ratio. Additionally, the angle stability of both induction motor load and nearby synchronous generators can be improved by adding reactive power support by the wind turbines. From the Belgian case study, it is concluded that voltage control by wind power plants is preferred, especially in remote areas where the additional control becomes necessary to maintain operation in between voltage limits. In case of voltage dips, a coordinated control of wind power plants in the area lowers the voltage reduction.

The FlexPlan Horizon2020 project aims at establishing a new grid-planning methodology which considers the opportunity to introduce new storage and flexibility resources in electricity transmission and distribution grids as an alternative to building new grid elements, in accordance with the intentions of the Clean Energy for all Europeans regulatory package of the European Commission. FlexPlan creates a new innovative grid-planning tool whose ambition is to go beyond the state of the art of planning methodologies by including the following innovative features: assessment of the best planning strategy by analysing in one shot a high number of candidate expansion options provided by a pre-processor tool, simultaneous mid- and long-term planning assessment over three grid years (2030, 2040, 2050), incorporation of a full range of cost–benefit analysis criteria into the target function, integrated transmission distribution planning, embedded environmental analysis (air quality, carbon footprint, landscape constraints), probabilistic contingency methodologies in replacement of the traditional N-1 criterion, application of numerical decomposition techniques to reduce calculation efforts and analysis of variability of yearly renewable energy sources (RES) and load time series through a Monte Carlo process. Six regional cases covering nearly the whole European continent are developed in order to cast a view on grid planning in Europe till 2050. FlexPlan will end up formulating guidelines for regulators and planning offices of system operators by indicating to what extent system flexibility can contribute to reducing overall system costs (operational + investment) yet maintaining current system security levels and which regulatory provisions could foster such process. This paper provides a complete description of the modelling features of the planning tool and pre-processor and provides the first results of their application in small-scale scenarios.

This work develops a mathematical formulation to determine the combinatorial search space of the Offshore Wind Transmission Optimization Problem (OWTOP). The model accounts for Capital Expenditures (CAPEX), Corrective Maintenance (CM), losses and Expected Energy Not Transmitted (EENT) and determines the optimal radial transmission system topology to connect a number of Offshore Wind Power Plants (OWPPs) to the shore. The model also considers the stochastic nature of wind. In this context a greedy search algorithm is developed capable of finding the globally optimal solution for the location of offshore substations (OSSs), sizing of the transmission infrastructure and topological layout. Rather than a single optimal solution, the algorithm finds a solution space of feasible topologies, bounded from below by the optimal radial solution. The algorithm is applied to 4 test cases including one based on the Belgian North Sea area. It is shown to outperform a traditional Transmission Network Expansion Problem (TNEP) formulation both in computational speed and solution quality.