1. Key Laboratory of Advanced Technology of Materials Ministry of Education Superconductivity and New Energy R&D Center Southwest Jiaotong University Chengdu 610031 China
2. Nanjing Kangni Mechanical & Electrical Co., Ltd. Nanjing 210000 China
3. College of Physics and Energy Fujian Normal University Fuzhou 350117 China
4. College of Electrical Engineering Southwest Jiaotong University Chengdu 610031 China