Fault-Tolerant Control of Four-Wheel Independently Actuated Electric Vehicles with Active Steering Systems★★This work is partly supported by National Natural Science Foundation of China(Grant nos. 51205058, 51375086, 61403252), and Jiangsu Province Science Foundation for Youths, China(Grant no. BK20140634),the Foundation of Education Office of Guangxi Province of China (Grant no. KY2015YB101), the Fundamental Research Funds for the Central Universities and Jiangsu Postgraduate Innovation Programm (Grant no. KYLX-0102).