1. College of Electrical and Information Engineering, Hunan University, Changsha 410082, China
2. School of Energy and Power Engineering, Changsha University of Science and Technology, Changsha 410114, China
3. State Grid Hunan Electric Power Corporation Limited Loudi Power Supply Company, Loudi 417000, China
4. Department of Electricity Supply Services, Changsha Electric Power Technical College, Changsha 410131, China