1. Taiyuan University of Technology,Shanxi Key Lab. of Power System Operation and Control,Taiyuan,China
2. Harbin Institute of Technology,Department of Electrical Engineering,Harbin,China
3. Datong Power Supply Company, State Grid Shanxi Electric Power Company,Datong,China
4. Taiyuan University of Technology,School of Electrical and Power Engineering,Taiyuan,China