School of Electrical Engineering and Automation, Xuzhou Nor-mal University, Xuzhou 221116, P.R. China;
School of Electrical Engineering and Automation, Xuzhou Nor-mal University, Xuzhou 221116, P.R. China;
Institute of Au-tomation, Qufu Normal University, Qufu 273165, P.R. China;
School of Electrical Engineering and Automation, Xuzhou Nor-mal University, Xuzhou 221116, P.R. China;