1. College of Electrical Engineering, Chuzhou Polytechnic, Chuzhou 239000, China
2. Beijing Institute of Electro-machining Co., Ltd., Beijing Key Laboratory of Electro Discharge Machining Technology, Haidian District, Beijing 100191, China
3. Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Haidian District, Beijing 100084, China