1. School of Electrical Engineering and Electronic Information, Xihua University, Chengdu 610039, China
2. Key Laboratory of Fluid and Power Machinery, Ministry of Education, Xihua University, Chengdu 610039, China
3. College of Electrical Engineering, Sichuan University, Chengdu 610044, China
4. School of Electrical Engineering, Southwest Jiaotong University, Chengdu 611756, China