1. State Key Laboratory of Power System Department of Electrical Engineering Tsinghua University Beijing, 100084 China
2. Department of Mechanical and Aerospace Engineering The Hong Kong University of Science and Technology Clear Water Bay Hong Kong SAR China
3. Electrical and Computer Engineering University of Connecticut 371 Fairfield Way Storrs CT 06269 USA
4. Department Electrical Electronic and Information Engineering University of Bologna Bologna 40136 Italy
5. Electrical and Computer Engineering Department Naval Postgraduate School, 1 University Circle Monterey, CA 93943 USA
6. State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of Technology Tianjin, 300131 China