1. Beihang University, School of Auto. Sci. and Electrical Eng., Beijing, China + North China University of Water Resources and Electric Power, School of Mech. Eng., Zhengzhou, China
2. Beihang University, School of Aeronautic Sci. and Eng., Beijing, China
3. Beihang University, School of Auto. Sci. and Electrical Eng., Beijing, China