[1] Shandong Univ Sci & Technol, Qingdao 266590, Peoples R China
[2] Chinese Acad Sci, Inst Elect Engn, Key Lab High Dens Electromagnet Power & Syst, Beijing 100190, Peoples R China
[3] Inst Elect Engn & Adv Electromagnet Drive Technol, Qilu Zhongke, Shandong Key Lab Adv Electromagnet Convers Technol, Jinan 250013, Peoples R China
[4] Univ Chinese Acad Sci, Beijing 100049, Peoples R China
[5] Shandong Inst Ind Technol, Jinan 250102, Peoples R China