1. Dept. of Engineering Science, Martin-Luther-University, Halle-Wittenberg, Germany. email: hans-michael.hanisch@iw.uni-halle.de
2. Dept. of Electrical Engineering, Institute for Automation Technology (IFAT), Otto-von-Guericke-University, Magdeburg, Germany. email: arndt.lueder@e-technik.uni-magdeburg.de