1. Hainan Digital Grid Research Institute, China Southern Power Grid, No. 32, Haifu Road, Haikou 570204, P. R. China
2. Chengdu Software R&D Center, Postal Savings Bank of China, Chengdu 610094, P. R. China
3. School of Information and Safety Engineering, Zhongnan University of Economics and Law, No. 82, Nanhu Avenue, Wuhan 430073, P. R. China