Manuscript received August 09, 2009; revised February 18, 2010; accepted December 12, 2011. Date of publication February 03, 2012; date of current version July 18, 2012. This work was supported in part by the Department of Electrical Engineering of The Hong Kong Polytechnic University, the National Natural Science Foundation of China under Grant 71071025 and Grant 70601003, the Outstanding Youth Science Foundation of Hunan Province under Grant 10JJ1010, the Program for New Century Excellent Talents in University of China under Grant NCET-08-0676, the Open Innovation Platform Foundation of Hunan College under Grant 10K003, the National Outstanding Youth Science Foundation of China under Grant 70925006, and the Natural Science United Foundation of Hunan-Hengyang under Grant 10JJ8008. Paper no. TPWRS-00620-2009.
