1. School of Automation, Nanjing University of Science and Technology, Nanjing 210094, China.
2. School of Electrical Engineering, Korea University, Seoul 136-701, South Korea (e-mail: hironaka@korea.ac.kr)
3. School of Automation, Nanjing University of Science and Technology, Nanjing 210094, China (e-mail: xiangzr@njust.edu.cn)