1. State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan, China
2. College of Electrical and Information Engineering, Hunan University, Changsha, China
3. Hebei Key Laboratory of High-Speed Fly-wheel Energy Storage and Energy Saving Technology, Dunshi Magnetic Energy Technology Company Ltd., Shijiazhuang, China