1. State Key Lab of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China
2. School of Electrical Engineering, Shandong University, Jinan 250061, China
3. Sinomatech Wind Power Blade Co., Ltd, No.66 Xi Xiao Kou Rd., Beijing 100192, China
4. Department of Electronic and Electrical Engineering, The University of Strathclyde, Glasgow G1 1XQ, United Kingdom