1. School of Advanced Technology, Xi'an Jiaotong-Liverpool University, Suzhou, China
2. College of Electrical Engineering, Zhejiang University, Hangzhou, China
3. School of Rail Transportation, Soochow University, Suzhou, China
4. Suzhou Vocational University, Suzhou, China
5. Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool, U.K.