1. School of Electrical Engineering; Wuhan University; Wuhan Hubei 430072 China
2. State Grid Hubei Electrical Power Company; Wuhan Hubei 430077 China
3. State Grid Hubei Electric Power Research Institute; Wuhan Hubei 430077 China
4. Yunnan Electric Power Test and Research Institute (Group) Co. Ltd.; Kunming Yunnan 650217 China