1. Department of Electrical Engineering, Chungnam National University, 99, Dae-hak-ro, Yusung-gu, Daejeon 305-764, Republic of Korea
2. Department of Power System Engineering, Chonnam National University, 50 Daehak-ro, Yeosu 59626, South Korea
3. Department of Electrical, Electronic and Communication Engineering Education, Chungnam National University, Daejeon 305-764, South Korea