1. School of Electrical Engineering, Beijing Jiaotong University, Beijing, China
2. School of Electrical Engineering, Hebei University of Technology, Tianjin, China
3. Department of Electrical and Computer Engineering, University of Connecticut, Storrs, CT, USA
4. College of Electrical Engineering, Sichuan University, Chengdu, China
5. Energy Innovation Center, Clemson University, North Charleston, SC, USA