1. Nanjing University of Science and Technology; Nanjing 210094 China
2. Guodian Science and Technology Research Institute; Chengdu 610041 China
3. Centre for Electric Power and Energy System, Department of Electrical Engineering; Technical University of Denmark; Kgs. Lyngby 2800 Denmark
4. State Grid Jiangsu Electric Power Research Institute; Nanjing 211103 China