基金This work was supported by the National Natural Science Foundation of China (51507015, 61773402, 61540037, 71271215, 61233008, 51425701, 70921001, 51577014), the Natural Science Foundation of Hunan Province (2015JJ3008), the Key Laboratory of Renewable Energy Electric-Technology of Hunan Province (2014ZNDL002), and Hunan Province Science and Technology Program(2015NK3035).