1. School of Automation and Electrical Engineering, Lanzhou Jiaotong University, Lanzhou, China
2. Key Laboratory of Opto-technology and Intelligent Control, Ministry of Education, Lanzhou Jiaotong University, Lanzhou, China
3. Rail Transit Electrical Automation Engineering Laboratory of Gansu Province, Lanzhou Jiaotong University, Lanzhou, China
4. School of New Energy and Power Engineering, Lanzhou Jiaotong University, Lanzhou, China