1. State Power Investment Corporation Jiangsu Electric Power Co., Ltd., Nanjing 210008, China
2. Shanghai Power Equipment Research Institute Co., Ltd., Shanghai 200240, China
3. School of Electrical and Information Engineering, Zhengzhou University, Zhenzhou 450001, China
4. Key Laboratory of Control of Power Transmission and Conversion of Ministry of Education, Department of Electrical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China