Stability of Micro-Grids and Inverter-dominated Grids with High Share of Decentralised Sources

Mr. Oleg Osika was born on August 31, 1977, in Nowokusnetsk, in the Kemerovo Region, the south-western part of Siberia (Russia). He received the Bachelor degree of Engineering (B.Eng.) in the Electrical Engineering from the Faculty of Automatic and Electric Power Engineering, Tomsk Polytechnic Univesity, Tomsk, Russia, 1998. He gratuated from the University of Karlsruhe, Germany, where he received his Master of Science in 2002, specialization “Electric Power Systems”. The represented dissertation is a result of the scientific research activities at the Institute of Solar Energy Supply Technology (ISET) in Kassel, Germany. The areas of his research interests are: integration of the renewable energy sources into the electrical grids, investigation of the island grid’s stability, models for distributed energy sources.
The integration of the renewable energy sources and more efficient utilisation of primary energy sources due to local generation results in a large number of decentralised generators in the LV-Grid. For most microturbines, wind plants, fuel cells and photovoltaic cells electrical power is generated as a direct current (DC) and converted to an alternating current (AC) by means of inverters. These inverters, which can be represented as ideal voltage sources with grid forming functions, control the active and reactive power. So, inverters influence on the frequency and the voltage of the grid, consequently the stability depends on their behaviour.
This work assesses the expandability and the stability of decentralised inverter-dominated electric supply systems (MicroGrids) which can be operated either in grid-connected or in stand-alone mode. The combination of droop-controlled voltage source inverters of different sizes as well as inverters with rotating generators has been investigated. This work shows that each of these combinations can be operated stably with respective constraints. The “universal parameter set” has been obtained, which enables a stable operation of droop-controlled voltage source inverters in almost all relevant scenarios.