ZHANG Wanying,SHI Le ,ZHANG Jiefeng ,LIU Donghui,SHEN Hongzhe,HU Xuefeng
(1.College of Electrical and Information Engineering,Hunan University,Changsha 410082,China;2.Quzhou Power Supply Company of State Grid Zhejiang Electric Power Company,Quzhou 324000,China;3.Hengyang Power Supply Company of State Grid Hunan Electric Power Company,Hengyang 421000,China)