1. School of Mathematical Sciences, Guizhou Normal University, Guiyang, P. R. China
2. School of Electrical Engineering, Southeast University, Nanjing, P. R. China
3. College of Automation, Nanjing University of Posts and Telecommunications, Nanjing, P. R. China
4. School of Automation, Southeast University, Nanjing, P. R. China
5. Key Laboratory of Measurement and Control of CSE, Ministry of Education, Southeast University, Nanjing, P. R. China