1. College of Mechanical and Electrical Engineering; China JiLiang University; Hangzhou 310018 Zhejiang P. R. China
2. State Key Laboratory of Industrial Control Technology, Department of Control Science and Engineering; Zhejiang University; Hangzhou 310027 Zhejiang P. R. China
3. School of Automation and Electrical Engineering; Zhejiang University of Science and Technology; Hangzhou 310023 Zhejiang P. R. China