1. Department of Electrical Engineering Korea University Seoul 136‐713 Republic of Korea
2. Department of Electrical Engineering Seoul National University Seoul 151‐742 Republic of Korea
3. Department of Electrical Engineering Tongmyong University 428, Sinseon‐ro, Nam‐gu, Busan 48520 Korea
4. Power & Industrial System R&D Center, Hyosung Corporation Anyang‐Si 431‐080 Republic of Korea