1. University of Kragujevac,Faculty of Technical Sciences Čačak,Department of Power Engineering,Čačak,Serbia
2. University of Priš tina in Kosovska Mitrovica,Faculty of Technical Sciences,Department of Power Engineering,Kosovska Mitrovica,Serbia
3. University of Niš,Faculty of Electronic Engineering Niš,Department of Theoretical Electrical Engineering,Niš,Serbia