1. State Grid Shaanxi Electric Power Research Institute, Xian 710100, China
2. State Grid Shaanxi Electric Power Company Xixian New Area Power Supply Company, Xian 710016, China
3. School of Electrical Engineering and Automation, Wuhan University, Wuhan 430072, China
4. China Southern Power Grid Guangdong Guangzhou Power Supply Company, Guangzhou 510699, China