1. Faculty of Electric Power Engineering, Kunming University of Science and Technology, Kunming 650500, China
2. School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
3. Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK
4. School of Automation, China University of Geosciences, Wuhan 430074, China
5. Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
6. Warwick Manufacturing Group, The University of Warwick, Coventry CV4 7AL, UK