1. Kocaeli Univ., Faculty of Technology, Electrical Engineering Dept., Umuttepe 41380, Izmit, Kocaeli, Turkey.
2. Univ. of Agder, Faculty of Engineering and Science, No. 4879, Grimstad, Norway; formerly, Univ. College London, School of Energy and Resources, Adelaide, SA 5000, Australia (corresponding author).