1. National Institute of Advanced Industrial Science and Technology, Onogawa, Tsukuba 305-8569, Japan
2. Fuji Electric Co., Ltd., Fuji, Hino 191-8502, Japan
3. Central Research Institute of Electric Power Industry, Nagasaka, Yokosuka 240-0196, Japan
4. Kyoto University, Kyotodaigaku-Katsura, Nishikyo 615-8510, Japan