1. School of Electrical Engineering Southwest Jiaotong University Chengdu Sichuan P.R. China
2. National Rail Transit Electrification and Automation Engineering Technique Research Center Southwest Jiaotong University Chengdu Sichuan 611756 P.R China
3. Yunnan Electrical Power Research Institute, Yunnan Kunming P.R. China
4. School of Information Science and TechnologySouthwest Jiaotong UniversityChengduSichuanP.R. China