1. State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology. School of Electronics and Information Engineering, Hebei University of Technology, 5340 Xiping Road, Tianjin 300401, P. R. China
2. School of Science and Engineering, The Chinese University of Hong Kong, No. 2001 Longxiang Boulevard, Longgang District, Shenzhen, Guangdong 518172, P. R. China