1. Lanzhou Jiaotong University,School of Automation and Electrical Engineering,Lanzhou,China
2. Tibet Agricultural and Animal Husbandry University,School of Electrical Engineering,Nyingchi,China
3. Southwest Jiaotong University,School of Electrical Engineering,Chengdu,China
4. State Grid Tibet Electric Power Co. LTD,Electric Power Research Institute,Lasa,China