1. Institute of Precision Machinery and Smart Structure, Zhejiang Normal University, Jinhua, P. R. China
2. Key Laboratory of Urban Rail Transit Intelligent Operation and Maintenance Technology and Equipment of Zhejiang Province, Zhejiang Normal University, Jinhua, P. R. China
3. Department of Electrical and Computer Engineering, University of California-Riverside, Riverside, CA, USA
4. School of Electrical Engineering, Yanshan University, Qinhuangdao City, Hebei Province, China