Department of Automatic Control, Northwestern Polytechnical University, Xian 710072, Peoples Republic of China. shaowuzhang@hotmail.com|Department of Automatic Control, Northwestern Polytechnical University, Xian 710072, Peoples Republic of China. shaowuzhang@hotmail.com|Department of Automatic Control, Northwestern Polytechnical University, Xian 710072, Peoples Republic of China. shaowuzhang@hotmail.com|Department of Automatic Control, Northwestern Polytechnical University, Xian 710072, Peoples Republic of China. shaowuzhang@hotmail.com|Department of Automatic Control, Northwestern Polytechnical University, Xian 710072, Peoples Republic of China. shaowuzhang@hotmail.com