1. Institute of Renewable Energy, Shenzhen Poweroak Newener Co., Ltd., Shenzhen 518116, China
2. Shenzhen International Graduate School, Tsinghua University, Shenzhen 518071, China
3. Department of Electrical Engineering, North China Electric Power University, Baoding 071000, China
4. School of Engineering, The University of Edinburgh, Edinburgh EH9 3FB, UK