State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China;
State Grid Suzhou Power Supply Company Suzhou 215000 Jiangsu Province China;
State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China;
State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China;
Electrical Engineering Division University of Cam-bridge Cambridge CB3 0FA UK;