Aspects of Grid Integration of Renewable Energy Sources in Weak Power Systems

In this paper some special aspects of grid integration of renewable energy systems (RES) and improving system behavior under weak grid conditions are analyzed. At first a principle to measure frequency dependent grid impedances by current injection is explained and field measurements are presented. Secondly, the economic efficiency of short time energy storage systems for wind turbines (WT) is under investigated. With these systems it is possible to provide additional active power to support the grid to maintain stable and it is shown that economical advantages for WT operators can be achieved. Finally the system response of an electric grid with RES at transient faults is presented and optimized. The key aspect is the reactive power exchange between different energy resources and the grid during grid faults. Results show that damping this power exchange is possible by modeling and adapting the synchronization algorithm.