1. College of Electronic Information and Automation, Civil Aviation University of China, Tianjin 300300, China.
2. School of Electronics and Information Engineering, Dalian Jiaotong University, Dalian 116028, China.
3. The State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing 400044, China.
4. Traction Power State Key Laboratory, Southwest Jiaotong University, Chengdu 610031, China.