1. Ph.D. Candidate, College of Electric Engineering and Automation, Tianjin Univ., Tianjin 300072, China.
2. Professor, College of Electric Engineering and Automation, Tianjin Univ., Tianjin 300072, China.
3. Associate Professor, College of Electric Engineering and Automation, Tianjin Univ., Tianjin 300072, China (corresponding author).
4. Postdoctoral, School of Science, Yanshan Univ., Qinhuangdao, Hebei 066004, China.