1. Xi'an University of Technology,Department of Power Grid Information and Control Engineering,Xi'an,P. R. China,710054
2. State Grid Linshu County Power Supply Company of Shandong Province,Linshu,P. R. China,276700
3. Energy and Electric Research Center, Jinan University,Zhuhai,P. R. China,519070
4. School of Electrical and Electronic Engineering, Nanyang Technological University,Singapore,639798