1. School of Electric Power, South China University of Technology, Guangzhou, Guangdong 510640, China
2. Guangdong Province Engineering Research Center of High Efficient and Low Pollution Energy Conversion, Guangzhou, Guangdong 510640, China
3. AnHui Institute of Optics and Fine Mechanics, HeFei Institutes of Physical Sciences, Chinese Academy of Sciences, Hefei 230031, China