1. School of Electrical Engineering and Automation; Jiangsu Normal University; Xuzhou, Jiangsu 221116 China
2. Nonlinear Dynamics Group, Department of Electrical Engineering; Yeungnam University; 214-1 Dae-Dong, Kyongsan 712-749 Korea
3. National Laboratory of Industrial Control Technology, Institute of Cyber-Systems and Control; Zhejiang University; Hangzhou Zhejiang 310027 China