1. Power Science Research Institute of Yunnan Power Grid Co., Ltd., Kunming 650214, China
2. Qujing Power Supply Bureau of Yunnan Power Grid Co., Ltd., Qujing 655099, China
3. Electric Power Research Institute, China Southern Power Grid, Guangzhou 510623, China
4. School of Electrical Engineering and Automation, Wuhan University, Wuhan 430072, China