1. School of Electrical and Information Engineering Zhengzhou University Zhengzhou Henan 450001 China
2. National Maglev Transportation Engineering R&D Center Tongji University Shanghai 200092 China
3. Zhengzhou Runhua Intelligent Equipment Co., Ltd Zhengzhou Henan 450001 China
4. School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan Hubei 430074 China