1. Engineering Research Center of Intelligent Computin for Complex Energy Systems of Ministry of Education, North China Electric Power University, Baoding, Hebei, P.R. China + Department of Science and Technology Information, Zhejiang Electric Power Company Research Institute, Hangzhou, Zhejiang, P.R. China
2. Department of Mathematics and Physics, North China Electric Power University, Baoding, Hebei, P.R. China