I would like to express my profound gratitude and sincere appreciation to my supervisor Dr. Tseng King Jet, associate professor of Electrical and Electronic Engineering School, for his constant and patient guidance, constructive suggestions, continuous encouragement and moral support during all phases of my Ph.D research program at Nanyang Technological University. His impressive knowledge, comprehensive technical skills and noble-minded human qualities have been a source of inspiration and a model for me to follow. I am thankful to Professor Wu Bin from Ryerson University (Canada), for his helpful guidance and suggestions at the beginning of this research work. I also thank to Professor Choi San Shing and Professor Lalit Goel for their concern which help me reach my goals at Power Division from School of Electrical and Electronics Engineering. Special acknowledgement should be given to Nanyang Technological University for providing me this opportunity to take my graduate study with financial support. I sincerely thank and highly value the support given by the laboratory staff of