1. Department of Electronics and Information, Xi'an Polytechnic University, Xi'an, Shaanxi, China
2. Power Research Institute of State Grid Ningxia Electric Power Co., Ltd., Yinchuan, Ningxia, China
3. State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, Shaanxi, China
4. Electric Power Research Institute, China Southern Power Grid, Guangzhou, Guangdong, China
5. Department of Electrical Engineering and Computer Science, University of Tennessee, Knoxville, TN, USA