Hakan Ergun

Transmission System Topology Optimization for Large-Scale Offshore Wind Integration

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.

Grid Impact of Voltage Control and Reactive Power Support by Wind Turbines Equipped With Direct-Drive Synchronous Machines

Summary form only given. 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 co-ordinated control of wind power plants in the area lowers the voltage reduction.

Building a new overlay grid for Europe

The strong growth and the expected further increase in renewable energy generation in Europe requires a fundamental upgrade of the transmission system. A potential option is to realize these upgrades at a higher voltage by constructing a new overlay grid or supergrid. Such a supergrid is likely to be built using VSC HVDC technology, especially when considering that a significant part will be offshore. The paper will first discuss how such a grid should be conceived. Aspects that will be covered are the potential topology of such a grid and the balance between mesh size and the connection to the AC system. It will be discussed how such a new overlay grid with multiple controllers interacts with the existing system. The second aspect that will be covered is the stepwise development of such a system. A new overlay grid will not be conceived in a single phase, but link by link. The differences between “green field” and “brown field” approach are highlighted and shown using an example.

Technology and Topology Optimization for Multizonal Transmission Systems

This paper presents a method to optimize equipment investments in multizonal transmission systems, considering spatial properties of the areas of focus. Together with a probabilistic technique for assessing nodal injection capability, the method in the paper completes the methodology of a long term transmission system planning tool. Transmission topology, line route and technology are optimized through iterative application of linear integer programming and Dijkstras shortest path algorithm. By optimizing the transmission route, the spatial properties of the area of focus are taken into account, which in turn can significantly influence the installation costs of transmission equipment. The optimization method considers both AC and DC technology and takes the N-1 security criterion into account.

Stepwise Investment Plan Optimization for Large Scale and Multi-Zonal Transmission System Expansion

This paper develops a long term transmission expansion optimization methodology taking the probabilistic nature of generation and demand, spatial aspects of transmission investments and different technologies into account. The developed methodology delivers a stepwise investment plan to achieve the optimal grid expansion for additional transmission capacity between different zones. In this paper, the optimization methodology is applied to the Spanish and French transmission systems for long term optimization of investments in interconnection capacity.

Identification of power injection capabilities for transmission system investment optimization

In this paper, method to identify strong nodes in a transmission grid is shown. The method can be used to identify transmission system investment needs and can serve as filter for transmission system investment optimization. Based on an optimal power flow calculation, the maximum power injection capability of buses is calculated. In this context AC OPF and DC OPF methods are compared in terms of accuracy, convergence and computational effort. To take uncertainties in generation and load into account, the Gaussian Component Combination Method (GCCM) is used, which is compared to Monte Carlo Simulation (MCS). The importance of considering security aspects while determining strong nodes is depicted using N-1 analysis. Additionally, the effect of power flow controlling devices on the maximum power injection capability of investigated grid nodes is shown, in particular with phase shifting transformers and HVDC links.

Long term investment optimization methodology for multi-zonal transmission expansion

This paper introduces a stepwise investment optimization methodology for transmission system expansion planning. The objective of the developed methodology is to determine transmission expansion plans to realize a desired interconnection capacity between multiple zones minimizing investment and operational costs. The methodology uses MILP optimization and a modified A* shortest path algorithm sequentially in order to determine the optimal investment time point, transmission topology, technology and routing. Spatial constraints and their effects on the installation cost are taken into account in the technology and route optimization. A possible application of the methodology is demonstrated on a stepwise investment plan for the North Sea region.

Optimization of transmission technology and routes for Pan-European electricity Highways considering spatial aspects

An algorithm to determine optimal transmission routes and to perform technology selection for transmission system expansion is developed and presented in this paper. The aim of the optimization is to minimize investment and installation costs of grid expansion, taking into account spatial properties. The optimization is performed by formulating possible expansion options around a weighted graph and using a modified A* shortest path algorithm to find the optimal solution. The algorithm delivers optimal locations routes and determines the best technology along the route. The algorithm is applied to possible future pan European electricity highways. The implications of different installation areas on transmission routes and total costs are discussed.

Transmission system topology optimization for large-scale offshore wind integration

Summary form only given. 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.

Grid impact of voltage control and reactive power support by wind turbines equipped with direct-drive synchronous machines

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.