国家重点基础研究发展计划(973计划)资助项目(2009CB219701);国家自然科学基金资助项目(51277128);南方电网公司科技项目(K-ZD2012-006);supported by National Basic Research Program of China(973 Program)(No.2009CB219701);National Natural Science Foundation of China(No.51277128);China Southern Power Grid Science and Technology Projects(No.K-ZD2012-006)