1. North China Electric Power University,Department of Electrical Engineering,Baoding,China
2. Oita University,Division of Mechatronics,Oita,Japan
3. Saga University,Department of Electrical and Electronic Engineering,Saga,Japan
4. School of Electrical Engineering and Automation, Wuhan University,Wuhan,China
5. Oita University,Division of Electrical and Electronic Engineering,Oita,Japan