1. Fuculty of Engineering, University of the Ryukyus, 1 Senbaru, Nishihara-cho 903-0213, Nakagami, Okinawa, Japan
2. Department of Electrical and Electronics Engineering, SASTRA Deemed University, Thanjavur 613401, Tamil Nadu, India
3. Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka-City 240-0196, Kanagawa, Japan
4. Fuji Elctric Co., Ltd., Tokyo 141-0032, Japan