1. College of Electrical Engineering, Sichuan University, Chengdu, China
2. Power China Sichuan Electronic Power Engineering Company Ltd, Chengdu, China
3. School of Electrical Engineering, Aalto University, Espoo, Finland
4. Department of Engineering, University of Hull, Hull, U.K.
5. School of Automation, Hangzhou Dianzi University, Hangzhou, China