1. College of Power Engineering, Chongqing University, Chongqing 400030, P. R. China
2. Key Laboratory of Low-Grade Energy Utilization Technologies and Systems, Chongqing University, Ministry of Education, Chongqing 400030, P. R. China
3. College of Computer Science and Information Engineering, Chongqing Technology and Business University, Chongqing, 400067, China