1. School of Mechanical Engineering, Southwest Jiaotong University, Chengdu, China
2. Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Illinois, USA
3. Traction Power State Key Laboratory, Southwest Jiaotong University, Chengdu, China
4. National Engineering Research Center of Railway Vehicles, CRRC Changchun Railway Vehicle Co., Ltd., Changchun, China